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Thirst Sensations and AVP Responses at Rest and during Exercise-Cold Exposure
Abstract
The purpose of this study was to 1) determine the effect of hypohydration (HYPO) on thirst sensations during moderate exercise in the cold and 2) determine a possible mechanism for a cold-induced decline in thirst.
In the first phase of the study, eight males walked on four occasions, in T-shirts, shorts, and shoes, at 50% VO2max, for 60 min in either a 4 degrees C (cold) or 27 degrees C (temperate) environment in a state of HYPO or euhydration (EU). In the second phase, nine males in states of EU or HYPO randomly performed four trials consisting of 30 min standing at 27 degrees C, followed by 30 min of standing and 30 min of treadmill exercise at 50% of VO2max, in either 4 degrees C or 27 degrees C air.
In phase 1, thirst sensations were lower throughout 60 min of exercise (P < 0.05) in both HYPO and EU conditions during the cold trials. In phase 2, despite elevated plasma osmolality (P < 0.05), perception of thirst and plasma arginine vasopressin [AVP] similarly decreased (P < 0.05) after 30-min standing rest and 30-min exercise in the HYPO-cold trial, compared with the HYPO-temperate, EU-cold, and EU-temperate trials.
When either euhydrated or hypohydrated, cold exposure attenuated thirst by up to 40% at rest and during moderate-intensity exercise. The attenuated thirst when hypohydrated during cold exposure was associated with lower plasma [AVP] despite an elevated plasma osmolality. This decline in thirst and AVP in the cold may be the result of peripheral vasoconstriction, mediating an increase in central blood volume and stimulation of central volume receptors.
... 8,9 a major cause of dehydration during sporting activities is an imbalance between sweating and fluid intake. The sweating rate in training and competition was reported to be 0.3-2.6 l/h; however, it differed depending on individ-sations at rest and during moderate exercise 16 cause insufficient fluid intake and prepractice dehydration. However, no study has investigated the prepractice hydration status and changes in hydration status during training in fencing in a cool environment. ...
... d=1. 16). ...
... 15 additionally, it was reported that perceived thirst sensations at rest and during moderate exercise were lower in cool environments than in temperate environments. 16 Therefore, these results suggest that athletes might be susceptible to insufficient fluid intake in cool environments, and fencing athletes have a higher risk of severe dehydration before training. ...
Background:
Fencing is suggested as one of the most dangerous sporting events in terms of dehydration because of the uniform and gear covering the entire body. We aimed to elucidate the change in hydration status before and after training in elite fencing athletes in winter along with the assessment of sex and fencing style differences.
Methods:
Twenty-seven elite fencing athletes (14 males and 13 females) belonging to the Japanese National Team participated in this clinical survey. Dehydration status before and after winter training was assessed using body mass change, fluid intake, urine osmolarity, urine specific gravity (USG), and sodium, potassium, chlorine, and creatinine levels.
Results:
More than half of the participants (59.3%) drank water and tea during training. The change rate of body mass (males vs. females, 1.61 ± 0.82% vs. 0.45 ± 0.68%, p < 0.01; foil vs. epee, 2.25 ± 0.45% vs. 1.16 ± 0.72%, p < 0.05) and sweating rate (males vs. females, 938 ± 251 g/h vs. 506 ± 92 g/h, p < 0.01; foil vs. epee, 1136 ± 156 g/h vs. 796 ± 207 g/h, p < 0.05) during training showed significant differences between sexes and fencing styles. Of all participants, 66.7% were dehydrated (USG ≥ 1.020), and 37.0% were seriously dehydrated (USG ≥ 1.030) before training.
Conclusions:
Fencing athletes may be susceptible to severe dehydration before training, even in winter. Additionally, males and foil fencers appear to be at a greater risk than females and epee fencers of developing dehydration during exercise.
... Seven of the trials used one-group crossover or beforeafter designs (Burrell, Palmer, & Baylis, 1992;Figaro & Mack, 1997;Maresh et al., 2004;O'Neill, Duggan, & Davies, 1997;E. M. Phillips, Butler, & Baylis, 1994;Thompson, Selby, & Baylis, 1991;Wazna-Wesly, Meranda, Carey, & Shenker, 1995), while two groups of volunteers participated in each of the remaining seven crossover studies (Davies, O'Neill, McLean, Catania, & Bennett, 1995;Farrell et al., 2008;Kenefick, Hazzard, Mahood, & Castellani, 2004;Merry, Ainslie, Walker, & Cotter, 2008;P. A. Phillips et al., 1993;Stachenfeld, DiPietro, Nadel, & Mack, 1997;Takamata et al., 1999). ...
... In the majority of the remaining studies, thirst was activated by a variety of methods to produce approximately 2-4% losses in body weight to raise pOsm levels (Figaro & Mack, 1997;Kenefick et al., 2004;Maresh et al., 2004;Merry et al., 2008). In the remaining study, an unspecified amount of weight loss was achieved after 6 consecutive days of exercise cycles in 36°C conditions (Takamata et al.,1999). ...
... In Maresh et al.'s (2004) study, subjects underwent 4 days of treadmill exercises. Kenefick et al.(2004) induced thirst by first imposing a period of dehydration followed by controlled rehydration. After this subjects rated their thirst then exercised or stood still in cold (4°C) or temperate (27°C) conditions while blood samples were drawn. ...
Thirst, as a symptom, has long been considered the most prevalent clinical complaint patients voice in healthcare settings. Yet, rarely have researchers examined thirst by its correlation with physiologic factors. This review was undertaken to examine the relationships between thirst ratings and factors mediating its primary physiologic correlates: plasma osmolality (pOsm) and arginine vasopressin peptide (AVP). A literature search was undertaken to identify clinical studies in human subjects that investigated the relationship of thirst to specific physiologic thirst-related correlates and associated thirst mediators. Thirst was induced in 17 selected clinical studies by hyperosmolar infusion, through water deprivation or exercise weight-loss regimens. Positive linear relationships between the subjects' thirst ratings and rising serum pOsm levels confirmed the presence of intact osmotic thirst drives. However, there were significant variations in normal compensatory rises in AVP levels that followed the rises in plasma osmolality after the subjects were exposed to cold, physical pre-conditioning and water immersion tests. Notably, older adults in the studies reported diminished thirst ratings. Weak correlations suggest that angiotensin II may play only a minor role in thirst mediation. Atrial natriuretic hormone's inhibitory effect on thirst was inconsistent. Findings indicated that older adults are at higher risk for profound dehydration due to sensory deficits along with failure to correct volume losses. The thirst trials results support the close correlation between serum pOsm values and patients' thirst ratings, with the exception of the older adult.
... In resting dogs exposure to cold temperatures has been reported to result in an increase in the osmotic threshold for the stimulation of thirst due to an increase in central blood volume (Sobocinska and Kozlowski 1987). Recently, we reported (KeneWck et al. 2004a) a decrease (up to 40%) in arginine vasopressin release and thirst sensations in eu-and dehydrated men (¡4% body mass), both at rest and during exercise, when exposed to 4°C air. Similar to Sobocinska and Kozlowski (1987), we hypothesized that R. W. KeneWck (&) · S. N. Cheuvront · J. W. Castellani Thermal and Mountain Medicine Division, US Army Research Institute of Environmental Medicine, Kansas Street, Natick, MA 01760, USA e-mail: Robert.KeneWck@us.army.mil A. St Pierre · N. A. Riel Department of Kinesiology, University of New Hampshire, Durham, NH 03824, USA this thirst response to cold exposure in humans was likely due to an increase in central volume, secondary to coldinduced peripheral vasoconstriction. ...
... Previous work from our laboratory showed up to a 40% decrease in thirst during rest and exercise when subjects were exposed to cold (4°C) air even when made hyperosmotic by dehydration (KeneWck et al. 2004a ). We hypothesized that cold exposure caused an upward shift in the osmotically induced threshold for thirst stimulation, secondary to an increase in central blood volume induced by peripheral vasoconstriction. ...
... The results of this study suggest that at rest, cold exposure elevates the osmotic threshold to stimulate thirst to »304 mOsm kg ¡1 of H 2 O due to an increase in central volume which is greater than the reported osmotic threshold for thirst stimulation (»290 mOsm kg ¡1 of H 2 O) (Phillips et al. 1985). Previously we observed a blunting of thirst along with a decrease in plasma arginine vasopressin in subjects who were hyperosmotic and hypovolemic upon exposure to cold (4°C) (KeneWck et al. 2004a). In the present study, cold exposure again resulted in an attenuation of thirst. ...
The effects of elevating plasma osmolality (P
osm) on thirst ratings was studied in eight dehydrated males during exposure to 4°C. On two occasions, subjects were dehydrated (DH; 3–4% body mass) via 90 min exercise-heat exposure and overnight fluid restriction (day 1). On a third occasion, subjects were exposed to heat but were given fluid (EU). On day 2, subjects consumed NaCl (NaCl; 0.1 g NaCl kg−1 body mass in 500 ml H2O; DH only) or Placebo (P; 500 ml H2O; DH and EU). Subjects stood for 30 min at 24°C and for 45 min at 4°C (75 min post-dose). P
osm was elevated (P < 0.05) 30 and 75 min after NaCl administration in DH + NaCl versus DH + P and EU + P treatments. Thirst ratings remained elevated (P < 0.05) in the DH + NaCl treatment 30 min after dosing and 45 min at 4°C versus DH + P and EU + P. Attenuation of thirst when dehydrated in the cold can be over-ridden by increasing P
osm.
... 8 Penelitian dari Kenefick menjelaskan bahwa ketika individu berada dalam keadaan terhidrasi atau dehidrasi, namun persepsi rasa haus tak terasa hampir 40% dalam dingin dibandingkan dengan suhu lingkungan kerja yang normal. 9,10 Penelitian pada pekerja hutan menunjukkan konsumsi cairan kurang dari yang seharusnya. 11 Penelitian yang telah dilakukan di Afrika Selatan pada pekerja saat suhu lingkungan dingin menunjukan bahwa 63% pekerjanya mengalami dehidrasi. ...
... Tindakan ini, disebut vasokonstriksi perifer,dan menggerakan darah ke inti tubuh, adanya peningkatan volume darah sentral membuat otak tidak mendeteksi penurunan volume darah maka asupan cairan lebih tidak dianggap perlu, bahkan ketika cairan dibutuhkan 23 dan merangsang reseptor volume sentral untuk menghambat pelepasan AVP (Arginin Vasopresin Plasma) dan menyebabkan penurunan rasa haus serta ginjal mendapatkan sinyal untuk tidak menghemat cairan sehingga meningkatkan output urin. 9 Selain respon haus tertahan, perilaku kurang minum subjek dapat dikarenakan subjek malas untuk pergi ke kamar mandi. Pada penelitian ini sebanyak 50% subjek memiliki frekuensi buang air kecil yang sering. ...
Latar Belakang: Pekerja indoor yang telah terpapar suhu dingin dalam waktu yang lama berpotensi mengalami dehidrasi karena ketidakcukupan asupan air akibat kurangnya kepekaan rasa haus serta pengeluaran air melalui urine dan sebagian lainnya melalui kulit dan pernapasan. Namun belum banyak penelitian yang melaporkan hal tersebut. Tujuan penelitian ini untuk menganalisis hubungan konsumsi cairan dengan status hidrasi pada pekerja di lingkungan dingin.Metode: Penelitian Observasional dengan desain cross sectional, bertempat di PT Kompas Gramedia Semarang dengan jumlah sampel 34 subjek yang dipilih dengan simple random sampling. Data yang dikumpulkan meliputi karakteristik subjek, suhu lingkungan kerja, konsumsi cairan, gejala dehidrasi, dan status hidrasi. Konsumsi cairan diukur dengan menggunakan recall selama 1x24 jam dan status hidrasi diketahui dengan pemeriksaan berat jenis urin. Gejala dehidrasi diukur dengan kuesioner.Hasil: Pada penelitian ini ditemukan sebanyak 44.1% pekerja mengonsumsi cairan kurang dari 2500 ml/hari dan 55.9 % mengonsumsi cairan 2500-4000 ml/hari (rerata total konsumsi cairan 2538.30 ± 456.01 ml dan kebutuhan cairan 2500-4000 ml). Sebanyak 67.6 % pekerja yang memiliki status hidrasi baik. Sisanya ditemukan mengalami dehidrasi ringan 32.4 %. Terdapat hubungan signifikan antara konsumsi cairan dengan status hidrasi pada pekerja di suhu lingkungan dingin ( p = 0,001).Simpulan: Terdapat hubungan konsumsi cairan dengan status hidrasi pada pekerja di lingkungan dingin.
... The results of the studies examine sodium values without liquid supplements and subjected to dehydration have opposite results to the findings. Thus, Kenefick et al. 2004(Fahlström et al. 2006) got athletes exercised for 90 minutes and ensured that two to four percent body weight would be lost. Then, the subjects' blood hematocrit parameters were evaluated and it was observed that blood and sodium (Na) levels decreased. ...
... Twerenbold et al. (2003) in their study researched running exercises and various sodium-containing beverage supplements given. In the obtained conclusions and according to the results obtained in restricted fluid section while in the values of blood sodium (Na), a significant decrease was observed; in the liquid supplement parts a statistical significance was not found (Kenefick et al. 2004). In another study by Morgan et al. 2004(Weschler 2006) eight male subjects were studied while cycling for 2 hours and fluid restriction was applied to the subjects during this time. ...
The aim of the study is to investigate the differences in blood electrolyte values for football players in the case of consumption of water and sports drinks during contests and regular training. One group was given 1000 ml (4x250ml) of sports drinks starting 20 minutes before the training match and during the whole exercise, and the other subject groups Were given water to consume at the same time and rate. The level of significance was set at 0.05. In the exercises lasting up to 90 minutes no effect of water and sports drinks were found on electrolyte levels. It was concluded that replacement between sports drinks and water consumption reflect similar results and depending on the type that athletes are accustomed to, both type of fluids can be used during exercise.
... In a previous human experiment, it was shown that shortterm cold exposure (1 h) attenuated thirst and lowered vasopressin concentration despite a condition of underhydration and elevated plasma osmolality. 26 Other experimental evidence suggest that low outdoor temperature decreases thirst. 27 Whereas the underlying mechanism may be central volume expansion mimicking volume expansion, which in turn affects vasopressin secretion and thirst, 22 oral cooling also increases the thirst quenching effect of fluids. ...
Background:
Whereas outdoor temperature is linked to both mortality and hydration status, the hormone vasopressin, measured through the surrogate copeptin, is a marker of cardiometabolic risk and hydration. We recently showed that copeptin has a seasonal pattern with higher plasma concentration in winter. Here, we aimed to investigate the association between outdoor temperature and copeptin.
Methods:
Copeptin was analysed in fasting plasma from five cohorts in Malmö, Sweden (n = 26,753, 49.7% men, age 18-86 years). We utilized a multivariable adjusted non-linear spline model with four knots to investigate the association between short-term temperature (24 h mean apparent) and log copeptin z-score.
Findings:
We found a distinct non-linear association between temperature and log copeptin z-score, with both moderately low and high temperatures linked to higher copeptin concentration (p < 0.0001). Between 0 °C and nadir at the 75th temperature percentile (corresponding to 14.3 °C), log copeptin decreased 0.13 z-scores (95% CI 0.096; 0.16), which also inversely corresponded to the increase in z-score log copeptin between the nadir and 21.3 °C.
Interpretation:
The J-shaped association between short-term temperature and copeptin resembles the J-shaped association between temperature and mortality. Whereas the untangling of temperature from other seasonal effects on hydration warrants further study, moderately increased water intake constitutes a feasible intervention to lower vasopressin and might mitigate adverse health effects of both moderately cold and hot outdoor temperatures.
Funding:
Swedish Research Council, Å Wiberg, M Stephen, A Påhlsson, Crafoord and Swedish Heart-Lung Foundations, Swedish Society for Medical Research and Swedish Society of Medicine.
... The association between cold exposure and AKI can be explained by the following biological mechanisms. Cold exposure may increase urinary voiding and respiratory water losses and decrease fluid intake, leading to dehydration (Kenefick et al., 2004;Lim et al., 2015). Dehydration, in turn, may increase the risk of AKI by imposing ischemic damage caused by reduced renal flow and renal vein thrombosis (Kim et al., 2018a;Lim et al., 2015;Suga et al., 2001). ...
Background:
Emerging evidence supports an association between heat exposure and acute kidney injury (AKI). However, there is a paucity of studies on the association between cold exposure and AKI.
Objective:
We aimed to investigate the associations of cold exposure with hospital admission and mortality due to AKI and to explore whether these associations were influenced by age and sex.
Methods:
Information on daily counts of hospital admission and mortality due to AKI in 16 regions of Korea during the cold seasons (2010-2019) was obtained from the National Health Insurance Service (a single national insurer providing universal health coverage) and Statistics Korea. Daily mean temperature and relative humidity were calculated from hourly data obtained from 94 monitoring systems operated by the Korean Meteorological Administration. Associations of low temperatures (<10th percentile of daily mean temperature) and cold spells (≥2 consecutive days with <5th percentile of daily mean temperature) up to 21 days with AKI were estimated using quasi-Poisson regression models adjusted for potential confounders (e.g., relative humidity and air pollutants) with distributed lag models and univariate meta-regression models.
Results:
Low temperatures were associated with hospital admission due to AKI [relative risk (RR) = 1.12, 95 % confidence interval (CI): 1.09, 1.16]. Cold spells were associated with hospital admission (RR = 1.87, 95 % CI: 1.46, 2.39) and mortality due to AKI (RR = 4.84, 95 % CI: 1.30, 17.98). These associations were stronger among individuals aged ≥65 years than among those aged <65 years.
Conclusion:
Our results underscore the need for the general population, particularly the elderly, physicians, and other healthcare providers to be more vigilant to cold exposure, given the risk of AKI. Government agencies need to develop specific strategies for the prevention and early detection of cold exposure-related AKI.
... Adequate fluid intake is critical in hot and humid environments to avoid heat-related injuries and early fatigue, which can hinder occupational performance while also posing a risk to overall health. Moreover, cold environments might reduce thirst [81]; thus, fluid intake may be reduced. This is even more problematic in high-altitude environments because hypoxia-induced increases in ventilation and diuresis can exacerbate fluid imbalance and likely are coupled with poor thirst sensation. ...
This position stand aims to provide an evidence-based summary of the energy and nutritional demands of tactical athletes to promote optimal health and performance while keeping in mind the unique challenges faced due to work schedules, job demands, and austere environments. After a critical analysis of the literature, the following nutritional guidelines represent the position of the International Society of Sports Nutrition (ISSN).
GENERAL RECOMMENDATIONS Nutritional considerations should include the provision and timing of adequate calories, macronutrients, and fluid to meet daily needs as well as strategic nutritional supplementation to improve physical, cognitive, and occupational performance outcomes; reduce risk of injury, obesity, and cardiometabolic disease; reduce the potential for a fatal mistake; and promote occupational readiness.
MILITARY RECOMMENDATIONS Energy demands should be met by utilizing the Military Dietary Reference Intakes (MDRIs) established and codified in Army Regulation 40-25. Although research is somewhat limited, military personnel may also benefit from caffeine, creatine monohydrate, essential amino acids, protein, omega-3-fatty acids, beta-alanine, and L-tyrosine supplementation, especially during high-stress conditions.
FIRST RESPONDER RECOMMENDATIONS Specific energy needs are unknown and may vary depending on occupation-specific tasks. It is likely the general caloric intake and macronutrient guidelines for recreational athletes or the Acceptable Macronutrient Distribution Ranges for the general healthy adult population may benefit first responders. Strategies such as implementing wellness policies, setting up supportive food environments, encouraging healthier food systems, and using community resources to offer evidence-based nutrition classes are inexpensive and potentially meaningful ways to improve physical activity and diet habits. The following provides a more detailed overview of the literature and recommendations for these populations.
... The study done in Taiwan found that low room temperature was protective for the prevalence of thirst, similarly our study showed that low room temperature < 20 °C was a protective factor for the prevalence of thirst in comparison with room temperature ≥ 20 °C [3]. This could be due to a diminished thirst response in cold weather, which occurs when human blood vessels constrict to prevent blood from flowing easily to the extremities when the environment is cold pulling more blood to its core, the body can conserve heat [24]. ...
... The study done in Taiwan found that low room temperature was protective for the prevalence of thirst, similarly our study showed that low room temperature < 20 °C was a protective factor for the prevalence of thirst in comparison with room temperature ≥ 20 °C [3]. This could be due to a diminished thirst response in cold weather, which occurs when human blood vessels constrict to prevent blood from flowing easily to the extremities when the environment is cold pulling more blood to its core, the body can conserve heat [24]. ...
Abstract Introduction Thirst is a powerfully distressing sensation that occurs most frequently in the immediate postoperative period. Postoperative thirst is prevalent, the moderate-to-severe type is estimated to affect 53.2–69.8% of patients and causes significant patient discomfort. Objective The objective of this study was to assess the prevalence, and factors associated with postoperative thirst among surgical patients in PACU at the University of Gondar Comprehensive Specialized Hospital from April 20 to June 27, 2021. Methods An institution-based cross-sectional study was conducted at the University of Gondar Comprehensive Specialized Hospital. A total of 424 participants were included in the study. Statistical analysis had performed using SPSS 26.00 version statistical software. Binary logistic regression analysis was performed to identify the association between the prevalence of postoperative thirst and independent variables and only variables with p-value
... The study done in Taiwan found that low room temperature was protective for the prevalence of thirst, similarly our study showed that low room temperature < 20 °C was a protective factor for the prevalence of thirst in comparison with room temperature ≥ 20 °C [3]. This could be due to a diminished thirst response in cold weather, which occurs when human blood vessels constrict to prevent blood from flowing easily to the extremities when the environment is cold pulling more blood to its core, the body can conserve heat [24]. ...
... Notably, a decline of plasma vasopressin has also been reported during cold exposure in the context of normal hydration. 48 As copeptin levels have also been associated with additional metabolic effects including lipid oxidation hyperinsulinaemia, metabolic syndrome and future type 2 diabetes, the observed changes in copeptin in our study might encompass additional physiologic processes besides haemodynamic control. 49,50 Finally, the observed changes in circulating insulin C-peptide levels upon cold exposure is in line with existing literature linking insulin's requirement for cold-induced thermogenesis, presumably due to alterations in insulin sensitivity following cold exposure. ...
This discovery study investigated in healthy subjects whether a short-term cold exposure may alter circulating microRNAs and metabolic parameters and if co-expression networks between these factors could be identified. This open randomized crossover (cold vs no cold exposure) study with blind end- point evaluation was conducted at 1 center with 10 healthy adult male volunteers. Wearing a cooling vest perfused at 14°C for 2 h reduced the local skin temperature without triggering shivering, increased norepinephrine and blood pressure while decreasing copeptin, C-peptide and heart rate. Circulating microRNAs measured before and after wearing the cooling vest twice (4 time points) identified 196 mature microRNAs with excellent reproducibility over 72 h. Significant correlations of microRNA expression with copeptin, norepinephrine and C-peptide were found. A co-expression-based microRNA-microRNA network, as well as microRNA pairs displaying differential correlation as a function of temperature were also detected. This study demonstrates that circulating miRNAs are differentially expressed and coregulated upon cold exposure in humans, supporting their use as predictive and dynamic biomarkers of cardio-metabolic disorders.
... À1 H _ prod , followed by the 6MWT. Skin temperature (T sk ), HR and T re were recorded every 5 min and TS, 35 thermal comfort (TC), 36 thirst sensation (ThS) 37 and rating of perceived exertion (RPE) 38 were recorded every 10 min. Whole body sweat rate (WBSR) was estimated from a before and after nude body mass measurement. ...
Objectives:
The elderly are the most at-risk population for heat-related illness and mortality during the periods of hot weather. However, evidence-based elderly-specific cooling strategies to prevent heat-illness are limited. The aim of this investigation was to quantify the elderly's physiological and perceptual responses to cooling through cold water ingestion (COLD) or an L-menthol mouth rinse (MENT) during simulated activities of daily living in UK summer climatic conditions.
Study design:
Randomised, controlled repeated measures research design.
Methods:
A total of ten participants (men n = 7, women n = 3: age; 69 ± 3 yrs, height; 168 ± 10 cm, body mass; 68.88 ± 13.72 kg) completed one preliminary and three experimental trials; control (CON), COLD and MENT. Experimental trials consisted of 40 min rest followed by 30 min of cycling exercise at 6 metabolic equivalents and a 6-min walk test (6MWT), within a 35 °C, 50% relative humidity environment. Experimental interventions (every 10 min); cold water (4 °C) ingestion (total of 1.5L) or menthol (5 ml mouth swill for 5 s, menthol concentration of 0.01%).
Results:
Peak rectal temperature (Tre) was significantly (P < 0.05) lower in COLD compared with CON (-0.34 ± 0.16 °C) and MENT (-0.36 ± 0.20 °C). End exercise heart rate (HR) decreased in COLD compared with CON (-7 ± 9 b min-1) and MENT (-6 ± 7 b min-1). There was no difference in end exercise thermal sensation (TS) (CON; 6.1 ± 0.4, COLD; 6.0 ± 0.4, MENT; 6.4 ± 0.6) or thermal comfort (TC) (CON; 4 ± 1, COLD; 4 ± 1, MENT; 4 ± 1) between trials. The participants walked significantly further during the COLD 6MWT compared with CON (40 m ± 40 m) and MENT (40 m ± 30 m). There was reduced physiological strain in the COLD 6MWT compared with CON (Tre; -0.21 ± 0.24 °C, HR; -7 ± 8 b min-1) and MENT (Tre; -0.23 ± 0.24 °C, HR; -4 ± 7 b min-1).
Conclusion:
The elderly have reduced physiological strain (Tre and HR) during activities of daily living and a 6MWT in hot UK climatic conditions, when they drink cold water. Furthermore, the elderly's perception (TS and TC) of the hot environment did not differ from CON at the end of exercise with COLD or MENT interventions. Menthol provided neither perceptual benefit to exercise in the heat nor functional gain. The TS data indicate that elderly may be at increased risk of heat illness, due to not feeling hot and uncomfortable enough to implement physiological strain reducing strategies such as cold-water ingestion.
... This action called peripheral vasoconstriction, and moves blood to the body's core, an increase in central blood volume makes the brain not detect a decrease in blood volume so more fluid intake is not considered necessary, even when fluid is needed 7,8 . This activity stimulates central volume receptors to stimulate the release of AVP (Arginine Vasopressin Plasma) and causes a decrease in thirst and the kidneys get a signal to conserve fluids thereby decreasing urine output 9 . ...
... In addition, such cold and dry air conditions may blunt thirst mechanisms while simultaneously augmenting airway water losses, both contributing to dehydration processes. [41][42][43][44][45][46] CA and RE USG values indicated that hydration status was less severe in these groups compared to SF, although improvements in their hydration strategies would still be preferable given that the majority of the values were above the 1.010 threshold indicating suboptimal hydration status. The USG outcomes of SF and RE in the present study are similar to those reported in the cross-sectional study by Blacker et al., 23 with only 12% of the officer cadet subjects being classified as euhydrated over a 5-day period based on urine osmolality assessment. ...
Introduction
Malnutrition, suboptimal hydration, and inadequate body composition can have negative consequences on soldiers’ performance and health. A recent consensus statement concerning “soldiers’ physical performance” points to the scarcity of data in specific military populations. Therefore, the aim of the present study was to assess and compare dietary intake, hydration status, and body composition of three military groups during their specific military training.
Materials and Methods
Eighty-five soldiers (ie, 21 in a qualification course to join the Special Forces [SF], 22 Infantrymen [Chasseurs Ardennais, CA], and 42 Recruits [REs]) participated in this 3- to 4-day study. Body mass was assessed before and after each study period. All soldiers self-reported their dietary intakes, from which energy and macronutrient intakes were calculated. In addition, their morning urine samples were collected daily to assess urine specific gravity (USG) as a measure of hydration status. Fat mass was estimated at the end of the study using bioelectrical impedance analysis.
Results
All groups lost significant amounts of body mass (ie, mean losses ranging between 1.3 and 1.7 kg). Macronutrient intakes were not fully met in respect to the recommendations. Most notably, REs’ fat intake was high (ie, 42.3 [±1.6] energy percent [E%]), while their carbohydrate intake was low (ie, 44.5 [±2.1] E%). Furthermore, saturated fat intakes were high among all groups (ie, group means ranging between 13.6 and 21.4 E%). USG values indicated suboptimal hydration status was prevalent in all groups. Most noteworthy, for SF, only 5.4% of the USG values indicated optimal hydration. The average fat mass (%) for SF, CA, and RE was 11.2 (±3.1), 18.8 (±5.1), and 19.4 (±5.0), respectively.
Conclusion
The present study showed that military men are not always adequately fed nor hydrated. These issues should be resolved by creating nutritional packages, and individual dietary and hydration strategies, all in function of military planning and weather conditions.
... Therefore, non-alcohol drink (NAD) intake is commonly recommended for prevention of heat stroke in hot seasons because dehydration, which is one of the important causes of heat stroke, is commonly believed to occur in summer. However, disruption of hydration status does not necessarily occur in hot summer [15] and dehydration in winter should not be neglected because the body's thirst response is decreased in cold temperatures [16] and cold-induced diuresis [17]. Accordingly, the occurrence of ischemic stroke has been reported to rise with decreasing temperature [18] and its incidence does not vary significantly with season [19,20]. ...
The present study sought to clarify if being conscious of water intake (CWI) is associated with sufficient non-alcohol drink (NAD) intake. We used data of healthy participants without diabetes, aged 40–74 years, in the Kobe Orthopedic and Biomedical Epidemiologic (KOBE) study. The association between being CWI and NAD intake was evaluated by multivariate linear regression analyses after adjusting for age, sex, surveyed months (seasons), alcohol drinking, health-awareness life habits, socioeconomic factors, serum osmolarity, estimated daily salt intake, and reasons for NAD intake. Among 988 (698 women and 290 men) participants eligible for the present analyses, 644 participants (65.2%) were CWI and 344 participants (34.8%) were not CWI (non-CWI). The most popular reason for being CWI was to avoid heat stroke in summer and to prevent ischemic cerebral stroke in winter. The CWI group took more NAD, especially decaffeinated beverages, than the non-CWI group (1846.7 ± 675.1 mL/day vs. 1478.0 ± 636.3 ml/day, p < 0.001). There was a significant association between being CWI and NAD intake in multivariate linear regression analyses ever after adjusting for the relevant variables (β = 318.1, p < 0.001). These findings demonstrated CWI, regardless of the reasons and the seasons, was associated with high NAD intake in Japanese healthy population.
... Therefore, persons older than represented in this analysis may benefit from planning their fluid intake during exercise. Alterations in the hormonal control of fluid regulation occurs during cold exposure [45] or the heat acclimatization process [46]. Under these circumstances, it may be optimal to use PD. ...
... In contrast, increases in appetite and energy intake have been demonstrated in cold environments (both with and without strenuous physical activity) [12,21,23]. Both dehydration and hypohydration are also concerns in the cold due to exercise-induced respiratory water losses, sweating and decreased thirst sensations [24][25][26]. Overall, it is well established that maintaining adequate nutritional and hydration status is integral to individual operational readiness [2]. Additionally, research also indicates that there might be altered requirements for micronutrients under temperature extremes as a result of environmental stress impacting intestinal absorption and/or increased utilization of some of these nutrients [16,27]. ...
Background:
Dietary Reference Intakes are used to guide the energy intake of the Canadian Armed Forces (CAF) field rations provided to military personnel deployed for training or operations. However, the high energy expenditures likely to occur under harsh environmental/metabolically challenging deployment conditions may not be adequately considered. This study examined the Ad libitum energy and nutrient intakes of CAF personnel (n = 18) consuming field rations in a resting thermoneutral environment and during a day of standardized strenuous infantry activities at varying environmental temperatures.
Methods:
Dietary intake was assessed using a measured food intake/food waste method during the experimental treatment and for 6 h after treatment. Four treatments were administered in a randomized counterbalanced design: exercise (as standardized infantry activities) in the heat (30 °C), exercise in the cold (- 10 °C), exercise in temperate thermoneutral (21 °C) air temperatures and a resting (sedentary) trial (21 °C).
Results:
The average Ad libitum consumption of field rations was 70% of the provided total energy (2776 ± 99 kcal/8 h) during all treatments. Even with an acute challenge of increased energy expenditure and temperature stress in the simulated field conditions, participants' energy intakes (1985 ± 747 kcal/8 h) under hot, cold and temperate treatments did not differ from energy intake during the sedentary condition (1920 ± 640 kcal/8 h). Participants' energy intakes (1009 ± 527 kcal/6 h) did not increase during the 6 h posttreatment period when the stresses of the strenuous physical activities and the harsh environmental temperatures had subsided.
Conclusion:
These results should be considered when planning the provision of field rations for CAF personnel expected to be engaged in strenuous physical activities with prolonged exposure to temperature extremes.
... Habit of Water Intake before the Onset of CI Although dehydration is thought to mainly occur in summer, dehydration in winter should not be neglected, because the body's thirst response is decreased in cold temperatures [19] and cold-induced diuresis [20]. Accordingly, the occurrence of ischemic stroke has been reported to rise with decreasing temperature [21] and its incidence does not vary significantly with season [22]. ...
Background:
While water intake is frequently recommended to prevent cerebral infarction (CI), only few studies have been published on this topic.
Objectives:
This study retrospectively estimated the daily non-alcohol drink (NAD) intake in CI patients before CI onset and compared it with NAD in healthy subjects.
Methods:
We performed a cross-sectional study on CI patients in 3 hospitals and healthy subjects in the Kobe Orthopedic and Biomedical Epidemiologic (KOBE) study. Data from 1,287 subjects (274 CI patients and 1,013 healthy subjects) were used for the analyses. By dividing the CI patients into "increased", "unchanged", and "decreased" groups according to their current NAD intake, we compared the NAD intake between these 3 groups and healthy subjects by analyses of covariance and the post hoc test, adjusting for sex, age, surveyed month, body mass index, alcohol drinking history, and smoking history. Under the assumption that the NAD intake in the "unchanged" group was equal to the NAD intake before CI onset, the OR of less NAD intake for CI adjusting for the relevant variables in the "unchanged" group and the healthy subjects was calculated; the cut-off point was chosen using Youden's index.
Results:
The mean age (mean ± SD) of the participants was 62.8 ± 9.3 years. One hundred and fifty-one patients (36 women) were included in the "increased" group; 105 (30 women), in the "unchanged" group; 18 (2 women), in the "decreased" group; and 1,013 (706 women), in the "healthy" group. The mean NAD intake was 1,702.5 ± 670.2 mL in the "increased" group, 1,494.2 ± 611.2 mL in the "unchanged" group, 1,268.0 ± 596.1 mL in the "decreased" group, and 1,720.6 ± 686.0 mL in the "healthy" group. After adjusting for the relevant variables, a significant difference in NAD intake between the groups was observed (F = 6.1, p < 0.001), and a post hoc test demonstrated significant differences (p < 0.05) in NAD intake between the "healthy" and "unchanged" groups, and between the "increased" and "unchanged" groups. The OR of less NAD intake (<1,570 mL/day, chosen using Youden's index) for CI was 2.48 (95% CI 1.52-4.07).
Conclusion:
This study showed that daily NAD intake before CI onset in CI patients was less than that in healthy persons, indicating that sufficient intake of NAD may be protective for CI.
... Therefore, persons older than represented in this analysis may benefit from planning their fluid intake during exercise. Alterations in the hormonal control of fluid regulation occurs during cold exposure [45] or the heat acclimatization process [46]. Under these circumstances, it may be optimal to use PD. ...
Background
Debate continues on how athletes should hydrate during exercise. Several studies have recently been published comparing the effect of ad libitum (ALD) and programmed drinking (PD) on endurance performance (EP).
Objective
This work examined whether one drinking strategy offers an EP advantage over the other.
Design
Systematic review and meta-analysis of crossover controlled trials.
Data Sources
PubMed and SPORTDiscus database searches.
Eligibility Criteria for Selecting Studies
Key criteria were (1) experiments performed under controlled settings; (2) exercise lasting ≥ 1 h; (3) exercise initiated in an euhydrated state; (4) fluid intake during PD > ALD; (5) fluid composition matched for electrolytes; and (6) carbohydrate intake varied by > 25% between conditions when the exercise was 1 h and matched for exercise > 1 h.
Results
Seven publications, producing eight effect estimates, including cycling and running exercises and representing 82 subjects, were included. Mean (± standard deviation) ambient temperature, exercise intensity and duration of the experiments were 28 ± 6 °C, 81 ± 12% of maximal heart rate and 96 ± 25 min, respectively. Mean rate of fluid consumption for the PD and ALD conditions was 1073 ± 247 mL/h and 505 ± 156 mL/h, respectively. Mean change in body mass for the PD and ALD conditions was − 1.0 ± 0.5% and − 2.1 ± 0.7%, respectively. Compared with PD, ALD improved EP by 0.98 ± 0.44% (95% confidence interval 0.11–1.84%). The greater EP conferred by ALD is likely trivial.
Conclusions
Despite ALD being associated with an hourly rate of fluid consumption half as much as PD, and resulting in a dehydration level considered sufficient to impair EP, both strategies were found to similarly impact 1–2 h cycling or running performances conducted at moderate to high intensity and under temperate to warm ambient conditions.
... Maintaining body fluid balance in cool climate could be an equally great challenge as in temperate or warm environments because of the changed thirst sensation. Kenefick et al. [38] reported that when either euhydrated or hypohydrated, thirst at rest and during moderate-intensity exercise was attenuated by up to 40% in cool compared to temperate environments in young men. The findings of Maughan et al. [7] who compared sweat losses and fluid intake in football players training in temperate (25 °C, relative humidity 60%) and cool (5 °C, relative humidity 81%) environments, corroborate the involvement of attenuated thirst sensation in developing acute training-induced dehydration in cold. ...
Background and Objectives: Only a few studies have reported the pre-practice hydration status in soccer players (SPs) who train in a cool climate. The primary purpose of this study was to examine the hydration status of male semiprofessional SPs immediately before their regular training session in winter. The secondary purpose was to compare the urinary indices of the hydration status of Estonian and Latvian SPs. Materials and Methods: Pre-training urine samples were collected from 40 Estonian (age 22.1 ± 3.4 years, soccer training experience 13.7 ± 3.9 years) and 41 Latvian (age 20.8 ± 3.4 years, soccer training experience 13.3 ± 3.0 years) SPs and analyzed for urine specific gravity (USG). The average outdoor temperature during the sample collection period (January–March) was between −5.1 °C and 0.2 °C (Estonia) and −1.9 °C and −5.0 °C (Latvia). Results: The average pre-training USG of Estonian and Latvian SPs did not differ (P = 0.464). Pooling the data of Estonian and Latvian SPs yielded a mean USG value of 1.021 ± 0.007. Hypohydration (defined as a USG ≥ 1.020) was evident altogether in fifty SPs (61.7%) and one of them had a USG value greater than 1.030. Conclusions: Estonian and Latvian SPs do not differ in respect of USG and the prevalence of pre-training hypohydration is high in this athletic cohort. These findings suggest that SPs as well as their coaches, athletic trainers, and sports physicians should be better educated to recognize the importance of maintaining euhydration during the daily training routine in wintertime and to apply appropriate measures to avoid hypohydration.
... Costill et al. [31] and Sejersted et al. [32] observed a significant increase in the amount of blood potassium (K) due to muscle potassium (K) exchange in the event of body fluid loss based on training. Kenefik et al. [33], Ebert et al. [34] and Rivera et al. [35] observed an increase in blood potassium (K) levels in blood parameter results after exercise and heat acclimatization. Noakes et al. [36] studied 2135 athletes in their study and examined blood Hematocrit values there. ...
... Individuals reduce the amount of fluid they consume, resulting in voluntary dehydration. Additional confounding factors for fluid intake in the cold include cold-induced diuresis and an increase in insensible sweat and respiratory fluid loss [15,16]. ...
Abstract Background Despite exercising in cool environments, ice hockey players exhibit several dehydration risk factors. Individualized fluid plans (IFPs) are designed to mitigate dehydration by matching an individual’s sweat loss in order to optimize physiological systems and performance. Methods A randomized control trial was used to examine IFP versus ad libitum fluid ingestion on hydration in 11 male minor professional ice hockey players (mean age = 24.4 ± 2.6 years, height = 183.0 ± 4.6 cm, weight = 92.9 ± 7.8 kg). Following baseline measures over 2 practices, participants were randomly assigned to either control (CON) or intervention (INT) for 10 additional practices. CON participants were provided water and/or carbohydrate electrolyte beverage to drink ad libitum. INT participants were instructed to consume water and an electrolyte-enhanced carbohydrate electrolyte beverage to match sweat and sodium losses. Urine specific gravity, urine color, and percent body mass change characterized hydration status. Total fluid consumed during practice was assessed. Results INT consumed significantly more fluid than CON (1180.8 ± 579.0 ml vs. 788.6 ± 399.7 ml, p = 0.002). However, CON participants replaced only 25.4 ± 12.9% of their fluid needs and INT 35.8 ± 17.5%. Mean percent body mass loss was not significantly different between groups and overall indicated minimal dehydration (
... Insufficient fluid intake for athletes training in cold and moderate temperatures can be explained by reduced thirst sensation [16]. For example, the fluid intake volume among elite football players in a cold environment (5°C) was much smaller than the sweat loses [17]. ...
Background and Study Aim. The impact of natural alternation of seasons on hydration status in athletes is not known, but it is a factor influencing efficiency of the training. The aim of our investigation was to compare pre- and post- training body hydration status, a body mass (BM) changes and sweating rate in male rugby seven players in early spring and summer.
Material and Methods. Twenty four male rugby seven players participated: 13 players in March (air temperature: +4°C, humidity 65%), 13- in June (air temperature: +19°C, humidity 70%). The pre- and post-training urine samples were collected. Players with urine specific gravity (USG) ≤1.020 were “euhydrated”, with USG 1.021-1.030 “hypohydrated”, with USG >1.030 “seriously hypohydrated”. Sweating intensity was calculated from the BM changes, consumed water mass, urine volume and the duration of training.
Results. The mean pre-training USG in cool environment was in norm: 1.019±0.008, but in warm conditions exceeded the boundary of norm: 1.021±0.005. The mean USG after training indicated similar hypohydration in spring and summer. The mean BM did not significantly decreased after training in cool and warm environment. Decrease of the BM >2% was observed in two athletes and for 1.5-2 % in six players
only in cool conditions.
Conclusion. Fluid consumption in cool conditions was insufficient in preventing the body hydration status worsening and a decrease in BM for more than 1.5-2% in some players. The fluid consumption in warm environment better allows prevent the body hypohydration and keep the BM decrease below 1.5%.
Key words: rugby seven • sweating intensity • urine specific gravity
... Acute exposure to cold causes peripheral vasoconstriction, shivering, and increased metabolic heat production (Castellani et al., 2006), as well as attenuation of thirst (Kenefick et al., 2004). Acute cold stress also reduces plasma volume and increases urine flow rate (Castellani et al., 2006). ...
Thermoregulation is a vital function of the autonomic nervous system in response to cold and heat stress. Thermoregulatory physiology sustains health by keeping body core temperature within a degree or two of 37 °C, which enables normal cellular function. Heat production and dissipation are dependent on a coordinated set of autonomic responses. The clinical detection of thermoregulatory impairment provides important diagnostic and localizing information in the evaluation of disorders that impair thermoregulatory pathways, including autonomic neuropathies and ganglionopathies. Failure of neural thermoregulatory mechanisms or exposure to extreme or sustained temperatures that overwhelm the body's thermoregulatory capacity can also result in potentially life-threatening departures from normothermia. Hypothermia, defined as a core temperature of < 35.0 °C, may present with shivering, respiratory depression, cardiac dysrhythmias, impaired mental function, mydriasis, hypotension, and muscle dysfunction, which can progress to cardiac arrest or coma. Management includes warming measures, hydration, and cardiovascular support. Deaths from hypothermia are twice as frequent as deaths from hyperthermia. Hyperthermia, defined as a core temperature of > 40.5 °C, may present with sweating, flushing, tachycardia, fatigue, lightheadedness, headache, and paresthesia, progressing to weakness, muscle cramps, oliguria, nausea, agitation, hypotension, syncope, confusion, delirium, seizures, and coma. Mental status changes and core temperature distinguish potentially fatal heat stroke from heat exhaustion. Management requires the immediate reduction of core temperature. Ice water immersion has been shown to be superior to alternative cooling measures. Avoidance of thermal risk and early recognition of cold or heat stress are the cornerstones of preventive therapy.
... However, the chlorine values of other subjects decreased significantly. Kenefick and Hazzard (2004) conducted a research on the athletes who exercised for 90 minutes. The exercises caused the athletes to lose 2.4 percent of their weight. ...
The purpose of this study was to investigate the effects of sports drinks (isotonic) and water consumptions of the elite wrestlers during the exercise. Eighteen-trained elite wrestlers participated in this study. The subjects were divided into two groups according to their bodyweight and were also given either water or isotonic sports drink. Water and sports drinks get rid of the dehydration during the trainings (P>0.05). Blood samples were taken before and after the exercises,and were analyzed for Sodium (Na), Potassium (K) and Chlorine (Cl). Body temperatures of subjects were measured as ºC. Post exercise sodium values of the two experimental groups were lower than the pre-exercise values (P<0.05) and there were nosignificant differences between sodium values of these two groups. Water could be replaced with sports drinks for shorter activities as compared to the sports drinks. Thus, water is very helpful for athletes when water is consumed before and during the exercise.
... Osmolality was also related to an increase in vasopressin, suggesting a possible association between vasopressin and thirst. Kene fl ick et al. assessed the response of thirst during 1 h of walking at 50% of maximum on a treadmill in temperate (27°C) or cold (4°C) environments ( 150 ) . In the cold environment the sensation of thirst was reduced by 40% and associated with lower levels of vasopressin, even though plasma osmolality was increased. ...
In response to exercise, there are numerous alterations in fluid and electrolyte homeostasis. These perturbations occur immediately upon initiation of exercise and can persist for hours or even days after completion of exercise. The endocrine system plays an important role in the regulation of fluid and electrolyte homeostasis that must occur with exercise. Dysregulation of the endocrine system may limit exercise activity and, in some incidences, result in debilitating morbidities or death. This chapter emphasizes responses to exercise and reviews the importance and factors involved in the maintenance of fluid and electrolyte balance. Previous reviews will be used to address the basics of effected systems; however, emphasis is placed on new data and the current discussions about performance of work and exercise.
... If skin temperatures fall significantly, thirst is less noticeable in cold compared to hot weather. 93 In addition, individuals may voluntarily not drink fluid in an effort to decrease the need to urinate brought on by CID. Given the fluid loss brought on by CID, attenuation of thirst when exposed to cold, and voluntarily not ingesting fluid, dehydration can result. ...
... Thermal comfort and thermal sensation were reported on 1-4 and 1-7 scales, respectively (Gagge et al., 1967). Thirst sensation was reported on a 1-9 scale (Kenefick et al., 2004). ...
Using intravenous infusion, we separated the physiologic consequences of 3% body mass dehydration from the conscious awareness of fluid replacement on time trial (TT) performance in the heat. Eleven trained cyclists performed 90 min of steady-state (50% V ˙ O 2 peak ) cycling followed by a self-paced 20-km TT in a hot-dry (35 °C, 10% relative humidity, wind speed 3.0 m/s) environment while euhydrated-not thirsty (EU-NT), euhydrated-thirsty (EU-T), dehydrated-not thirsty (DH-NT), or dehydrated-thirsty (DH-T). Thirst was manipulated by providing (NT) or withholding (T) ad libitum 35 °C water oral rinse. Distinct hydration states existed, with 0.4 ± 0.5% dehydration following the 20-km TT (EU) compared with 3.2 ± 0.6% in DH (P < 0.001). Greater perceived thirst existed in T (7 ± 2 on a 1-9 scale) than NT (4 ± 2, P < 0.001) after the TT. No significant differences in power output existed during the TT between hydration (EU 202.9 ± 36.5 W vs DH 207.0 ± 35.9 W, P = 0.362) and thirst conditions (NT 203.3 ± 35.6 W vs T 206.6 ± 36.8 W, P = 0.548), nor were there differences in completion time (P = 0.832) or pacing profile (P = 0.690). Within the range of up to 3% body mass loss, neither the physiologic effects from lowered hydration status nor the perception of thirst, separately or combined, affected sustained submaximal exercise performance in the heat for a healthy and fit population.
© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.
... Critically, in both of these studies individuals exercised in the heat and for prolonged periods at a low intensity resulting in high core and skin temperatures. Given that cooling the skin has been shown to reduce thirst sensation [ 16 ] , it may be that thirst amplifi es the impact skin and core temperature have on RPE rather than being a primary driver. ...
This study examined the effect of exercise-induced dehydration by ~4% body mass loss on 5-km cycling time trial (TT) performance and neuromuscular drive, independent of hyperthermia. 7 active males were dehydrated on 2 occasions, separated by 7 d. Participants remained dehydrated (DEH, -3.8±0.5%) or were rehydrated (REH, 0.2±0.6%) over 2 h before completing the TT at 18-25 °C, 20-30% relative humidity. Neuromuscular function was determined before dehydration and immediately prior the TT. The TT started at the same core temperature (DEH, 37.3±0.3°C; REH, 37.0±0.2 °C (P>0.05). Neither TT performance (DEH, 7.31±1.5 min; REH, 7.10±1.3 min (P>0.05)) or % voluntary activation were affected by dehydration (DEH, 88.7±6.4%; REH, 90.6±6.1% (P>0.05)). Quadriceps peak torque was significantly elevated in both trials prior to the TT (P<0.05), while a 19% increase in the rate of potentiated peak twitch torque development (P<0.05) was observed in the DEH trial only. All other neuromuscular measures were similar between trials. Short duration TT performance and neuromuscular function are not reduced by dehydration, independent of hyperthermia.
... Although comprehensive, the time-consuming nature of the TSS may have prompted investigators to adopt a 9-point categorical rating scale with integer descriptors ranging from "not thirsty at all" to "very, very thirsty. " 26,[40][41][42] Further simplification of a Thirst Likert scale collapsed ratings into three categories: no thirst, mild thirst, or moderate/severe thirst. 43 Although there is an increasing reliance upon VAS as a robust psychometric instrument, 44 the preferred instrument (categorical versus VAS) in terms of sensitivity and validity to assess thirst is not clear, particularly with regard to the population to be studied (e.g., elderly persons, children). ...
Water is an essential nutrient for all persons; thus, maintaining a chronic state of optimal hydration is recognized to provide health benefits. Fluid balance is maintained via thirst, a feedback-controlled variable, regulated acutely by central and peripheral mechanisms. However, voluntary drinking is also a behavior influenced by numerous social and psychological cues. Therefore, whether thirst-guided drinking maintains optimal hydration status is a multifactorial issue. Thirst perception is typically assessed by subjective ratings using either categorical or visual analog scales; however, which instrument yields greater sensitivity to change in hydration status has not been examined. Ratings of thirst perception do not always yield predictable patterns of voluntary drinking following dehydration; therefore, perceived thirst and ad libitum drinking are not equivalent measures of human thirst. The recommendation drink to thirst is frequently given to healthy individuals during daily life. However, factors and conditions (e.g., age, disease) that influence thirst should be recognized and probed further. (C) 2012 International Life Sciences Institute
... The decision to standardize participants’ fluid intake was also based partially on the variability of fluid intake observed during the CCS and from inadequate fluid intake reported in previous studies [9,14]. A leading cause of insufficient fluid intake for athletes training and competing in cold temperatures is reduced thirst, which is restored in warm conditions [24]. Examination of elite football players training in cool (5°C) temperatures revealed athletes consumed far less fluid than was lost from sweating [15]. ...
Background
Olympic class sailing poses physiological challenges similar to other endurance sports such as cycling or running, with sport specific challenges of limited access to nutrition and hydration during competition. As changes in hydration status can impair sports performance, examining fluid consumption patterns and fluid/electrolyte requirements of Olympic class sailors is necessary to develop specific recommendations for these elite athletes. The purpose of this study was to examine if Olympic class sailors could maintain hydration status with self-regulated fluid consumption in cold conditions and the effect of fixed fluid intake on hydration status in warm conditions.
Methods
In our cold condition study (CCS), 11 elite Olympic class sailors were provided ad libitum access to three different drinks. Crystal Light (control, C); Gatorade (experimental control, G); and customized sailing-specific Infinit (experimental, IN) (1.0:0.22 CHO:PRO), were provided on three separate training days in cold 7.1°C [4.2 – 11.3]. Our warm condition study (WCS) examined the effect of fixed fluid intake (11.5 mL.kg.-1.h-1) of C, G and heat-specific experimental Infinit (INW)(1.0:0.074 CHO:PRO) on the hydration status of eight elite Olympic Laser class sailors in 19.5°C [17.0 - 23.3]. Both studies used a completely random design.
Results
In CCS, participants consumed 802 ± 91, 924 ± 137 and 707 ± 152 mL of fluid in each group respectively. This did not change urine specific gravity, but did lead to a main effect for time for body mass (p < 0.001), blood sodium, potassium and chloride with all groups lower post-training (p < 0.05). In WCS, fixed fluid intake increased participant’s body mass post-training in all groups (p < 0.01) and decreased urine specific gravity post-training (p < 0.01). There was a main effect for time for blood sodium, potassium and chloride concentration, with lower values observed post-training (p < 0.05). C blood sodium concentrations were lower than the INW group post-training (p = 0.031) with a trend towards significance in the G group (p = 0.069).
Conclusion
Ad libitum fluid consumption in cold conditions was insufficient in preventing a decrease in body mass and blood electrolyte concentration post-training. However, when a fixed volume of 11.5 mL.kg.-1.h-1 was consumed during warm condition training, hydration status was maintained by preventing changes in body mass and urine specific gravity.
... It is a well-established fact that the thirst mechanism is blunted with exercise. 37 Therefore, in order to prevent complications secondary to dehydration, diabetic athletes should monitor and consume adequate fluid before, during, and after exercise. 24 Adequate hydration helps prevent a rise in ''core'' body temperature and reduces heat-induced stress of the cardiovascular system. ...
The unique demands of exercise and competition can predispose diabetic athletes to harmful complications. A basic understanding of glucose metabolism during exercise, nutritional adequacy, blood glucose control, medications, and management of on-field complications is important for medical personnel who care for diabetic athletes on a daily basis. Diabetic athletes are best managed by "individualized" preventive and treatment algorithms that should be developed by a team of medical professionals including the athletic trainer, sports nutritionist, and physician.
... [20][21][22] Athletes should be encouraged to hydrate even if they are not thirsty, as evidence suggests the normal thirst mechanism is blunted with cold exposure. 23 Evidence Category: C 6. Develop event and practice guidelines that include recommendations for managing athletes participating in cold, windy, and wet conditions. 24,25 The influence of air temperature and wind speed conditions should be taken into account by using wind-chill guidelines. ...
To present recommendations for the prevention, recognition, and treatment of environmental cold injuries.
Individuals engaged in sport-related or work-related physical activity in cold, wet, or windy conditions are at risk for environmental cold injuries. An understanding of the physiology and pathophysiology, risk management, recognition, and immediate care of environmental cold injuries is an essential skill for certified athletic trainers and other health care providers working with individuals at risk.
These recommendations are intended to provide certified athletic trainers and others participating in athletic health care with the specific knowledge and problem-solving skills needed to address environmental cold injuries. Each recommendation has been graded (A, B, or C) according to the Strength of Recommendation Taxonomy criterion scale.
... Hypohydration often occurs during cold exposure through combined effects of reduced fluid intake and increased fluid losses (11). Cold exposure is associated with blunted thirst, both during rest and exercise, and even when subjects are hypohydrated (15). Active individuals may also increase fluid losses through sweating despite cold temperatures, and cold-induced diuresis (CID) can occur cold and may amount to 1-3% of body mass (8). ...
Hypohydration occurs during cold-air exposure (CAE) through combined effects of reduced fluid intake and increased fluid losses. Because hypohydration is associated with reduced physical performance, strategies for maintaining hydration during CAE are important. Glycerol ingestion (GI) can induce hyperhydration in hot and temperate environments, resulting in greater fluid retention compared with water (WI) alone, but it is not effective during cold-water immersion. Water immersion induces a greater natriuresis and diuresis than cold exposure; therefore, whether GI might be effective for hyperhydration during CAE remains unknown. This study examined physiological responses, i.e., thermoregulatory, cardiovascular, renal, vascular fluid, and fluid-regulating hormonal responses, to GI in seven men during 4 h CAE (15 degrees C, 30% relative humidity). Subjects completed three separate, double-blind, and counterbalanced trials including WI (37 ml water/l total body water), GI (37 ml water/l total body water plus 1.5 g glycerol/l total body water), and no fluid. Fluids were ingested 30 min before CAE. Thermoregulatory responses to cold were similar during each trial. Urine flow rates were higher (P = 0.0001) with WI (peak 11.8 ml/min, SD 1.9) than GI (5.0 ml/min, SD 1.8), and fluid retention was greater (P = 0.0001) with GI (34%, SD 7) than WI (18%, SD 5) at the end of CAE. Differences in urine flow rate and fluid retention were the result of a greater free water clearance with WI. These data indicate glycerol can be an effective hyperhydrating agent during CAE.
Background
Thirst is a sensation normally aroused by a lack of water and associated with a desire to drink more fluid.
Aim
The aims of this brief review are twofold: (a) to summarize the thirst mechanism in how it is initiated and diminished, and (b) to describe techniques to assess human thirst accurately in a variety of situations.
Discussion
Thirst is maintained via a feedback-controlled mechanism, regulated by central and peripheral factors, as well as social and psychological cues. Most studies of thirst have focused on the initiation of water intake and the neural mechanisms responsible for this vital behavior. Less attention has been paid to the stimuli and mechanisms that terminate a bout of drinking and limit fluid ingestion, such as oropharyngeal and gastric signals, coupled with osmotic sensations. Thirst perception is typically assessed by subjective ratings using a variety of questionnaires, rankings, or visual analog scales. However, the appropriate perceptual tool may not always be used for the correct assessment of thirst perception.
Conclusions
In considering the many factors involved in thirst arousal and inhibition, similar questions need to be considered for the correct assessment of this ingestive behavior.
In response to exercise, there are numerous alterations in body fluid and electrolyte homeostasis. These perturbations occur immediately upon initiation of exercise and can persist for hours or even days after completion of exercise. The endocrine system plays an important role in the regulation of fluid and electrolyte homeostasis that must occur with exercise. Dysregulation of the endocrine system may limit exercise activity and, in some incidences, result in debilitating morbidities or death. This chapter emphasizes responses to exercise and reviews the importance and factors involved in the maintenance of fluid and electrolyte balance. Previous reviews will be used to address the basics of effected systems; however, emphasis is placed on new data and the current discussions about performance of work and exercise.
A large body size and mass are advantages in rugby. The desire to gain weight can bring players to become overweight or obese. This can worsen their thermoregulation and health risks. The aim was to evaluate anthropometric characteristics and to determine the effect of additional body fat percentage on sweat loss during play-match in male rugby players. Nineteen qualified male rugby players were tested during play-match. The age, height, body mass, body mass index (BMI) and body fat percent of participants were: 29 ± 6 years, 183 ± 7 cm, 96.86 ± 12.88 kg, 29.07 ± 3.90 kg/m ² , 20.52 ± 5.64%, respectively. The skin fold thickness measurement was used to assess body fat percent. Body mass loss was detected by weighting. The mean BMI was 26.18 ± 2.37 (kg/m ² ) and the body fat 15.87 ± 3.97% in backs. Forwards were significantly heavier and had BMI 31.18 ± 3.44 (kg/m ² )( p = 0.002) and the body fat 23.91 ± 4.02% ( p < 0.001). The mean body mass decrease in the play-match was 1.83 ± 0.84%. The mean sweating intensity was 2.24 ± 1.07 l/h, but individual varied among players in very wide range (1.12–6.16 l/h). Relationships between the body fat percentage and sweating intensity was not determined ( p > 0.05). Recommendation is to increase the volume of regular strength training, to correct the diet and liquid consumption.
alışmanın amacı, yüzücülerdeki antrenman sonrası sıvı kaybına bağlı ağırlık değişiminin kandaki, sodyum (Na +), potayum (K +) ve klor (Cl-) düzeylerine etkisini ortaya koymaktır. Çalışmaya Ankara İli'nde aktif olarak yüzme sporuyla uğraşan 31 gönüllü (9 kadın, 22 erkek) yüzücü katılmıştır. Katılımcıların yaşları 13-16 yıl arasında (erkeklerde 14.40±1.44 yıl, kadınlarda 14.33±1 yıl), boy uzunlukları 166.00±6.61 cm (erkeklerde 166.66±6.61 cm ve kadınlarda 160.95±4.82 cm), spor yaşları 6.41±1.31 yıl olarak ölçülmüştür. Havuz ısısı 23°C, nemlilik %97 olarak ayarlanmıştır. Katılımcıların antrenman öncesi ve sonrası vücut ağırlıkları (kadınlarda AÖ: 48.96±5.79kg, AS: 47.33±5.51kg; erkeklerde AÖ: 59.30±5.89 kg, AS: 57.43±5.79 kg), kan sodyum (Na +) (kadınlarda AÖ: 142.77±1.64 mmol/L, AS: 140.88±2.14 kg; erkeklerde AÖ: 143.40±1.91 mmol/L, AS:141.66±2.10 mmol/L), kan potasyum (K +) (kadınlarda AÖ: 4.77±0.21 mmol/L, AS: 4.87±0.21 mmol/L; erkeklerde AÖ: 4.71±0.2 mmol/L, AS: 4.80±0.17 mmol/L), kan klor (Cl-) (kadınlarda AÖ: 108.0±1.22 mmol/L, AS: 106.22±1.09 mmol/L, erkeklerde AÖ: 105.72±2.31 mmol/L, AS: 103.90±2.61 mmol/L) olarak ölçülmüştür. Daha sonra elde edilen veriler SPSS 15.0 programı kullanılarak ilişkileri incelenmiştir. Sonuç olarak yüzücülerde uzun süreli ve yoğun interval antrenman programı ile kandaki Na + ve Cl-iyonlarında azalma ve K + iyonlarında ise artışın anlamlı seviyede olduğu gözlemlenmiştir (p<0.05). Kaybedilen sıvı ve elektrolitlerin yerine konması sporcunun, sağlığı ve performansının korunması için son derece önemlidir. Vücut sıvılarının azalması ile performansta düşme, termoregülasyonda bozulma, sıcağı tolera edememe gibi çeşitli fizyolojik durumlar ortaya çıkmaktadır. Bu durumlardan korunmak ve düzeltmek için sporcuların gün içerisinde düzenli olarak belirli aralıklarla sıvı tüketmeye özen göstermesi kendilerine özel bir sıvı alım planı oluşturmaları gerekmektedir. Abstract The aim of the study to identify the level of changes in blood sodium (Na +), potassium (K +) and chlorine (Cl-) due to dehydration after training in swimmers. 31 swimmers (9 female, 22 male) which are training in Ankara City participated in this study. The ages of the subjects vary between ages 13-16, (in male 14.40±1.44 years and in female 14.33±1 years), their height vary between 166.00±6.61 cm (in male 166.66±6.61 cm and in female 160.95±4.82 cm) and their total training time is 6.41±1.31 years. The pool temperature is fixed to 23°C and the humidity to 97%. The before and after training analyses of the subjects yielded the following results, body weight (BW) (in female BT:48.
This literature survey is based on publications listed in the databases Embase and Medline between 1.1.2004 and 31.12.2004 and matching with one of the following 8 keywords: “thermography”, “thermology“, “thermometry”, “temperature measurement”, “skin temperature”, “core temperature”, “warming” or “ cooling”. This has resulted in 2478 references, which is far the highest number of references since this annual literature survey was first published.
Thermal imaging was the main subject of 219 papers. Therapeutic hypothermia for patients in a critical state of health was the most discussed temperature related treatment. A high number of publications was related to physics and chemistry.
Special Operations Forces (SOF) training, combat, and contingency operations are unique and demanding. Performance nutrition within the Department of Defense has emphasized that nutrition is relative to factors related to the desired outcome, which includes successful performance of mentally and physically demanding operations and missions of tactical and strategic importance, as well as nonoperational assignments. Discussed are operational, nonoperational, and patient categories that require different nutrition strategies to facilitate category-specific performance outcomes. Also presented are 10 major guidelines for a SOF comprehensive performance nutrition program, practical nutrition recommendations for Special Operators and medical providers, as well as resources for dietary supplement evaluation. Foundational health concepts, medical treatment, and task-specific performance factors should be considered when developing and systematically implementing a comprehensive SOF performance nutrition program. When tailored to organizational requirements, SOF unit- and culture-specific nutrition education and services can optimize individual Special Operator performance, overall unit readiness, and ultimately, mission success.
2015.
Background.
Pre-training hydration status is considered a factor influencing efficacy of training. Research
literature does not contain data regarding the potential impact of natural alternation of seasons on pre-training
hydration status in athletes. The purpose of this study was to assess and compare pre-training hydration status in
well-trained male soccer (football) players in moderate temperate autumn and cold winter
.
Methods.
Research participants were
57 male soccer players from two Latvian First League teams, who were
studied prior to their ordinary training session. Participants provided a midstream urine sample for analysis of urine
specific gravity (USG), and their body mass (kg), body fat percentage and total body water percentage were measured.
Results.
Pre-training hydration status did not differ in moderate temperature autumn (mean USG 1.020 ± 0.010;
mean total body water 64.2 ± 2.9%) in cold winter (mean USG 1.020 ± 0.008; mean total body water 64.8 ± 2.7%;
for both parameters
p
> .05). Prevalence of hypohydration and serious hypohydration (defined as USG 1.021 – 1.030
and USG > 1.030, respectively) was similar in moderate temperate autumn (47.4%) and cold winter (60%), (χ
2
=
1.50;
p
> .05). Significant correlation between the within-subject USG values measured in moderate temperate and
cold environment was observed (
r
= .60,
p
= .009).
Conclusion.
In well-trained soccer players pre-training hydration status does not differ in moderate temperature
autumn and cold winter. Individual-related factors such as nutritional behaviour (including pattern of voluntary fluid
intake) may have stronger impact on hydration status than environment-related factors like natural alternation of
seasons.
Exercising in cold environments results in water losses, yet examination of resultant voluntary water intake has focused on warm conditions. The purpose of the study was to assess voluntary water intake during and following exercise in a cold compared with a warm environment. Ten healthy males (22 ± 2 years, 67.8 ± 7.0 kg, 1.77 ± 0.06 m, VO2peak 60.5 ± 8.9 ml·kg-1·min-1) completed two trials (7-8 days). In each trial subjects sat for 30 min before cycling at 70% VO2peak (162 ± 27W) for 60 min in 25.0 ± 0.1 °C, 50.8 ± 1.5% relative humidity (RH; warm) or 0.4 ± 1.0 °C, 68.8 ± 7.5% RH (cold). Subjects then sat for 120 min at 22.2 ± 1.2 °C, 50.5 ± 8.0% RH. Ad libitum drinking was allowed during the exercise and recovery periods. Urine volume, body mass, serum osmolality, and sensations of thirst were measured at baseline, postexercise and after 60 and 120 min of the recovery period. Sweat loss was greater in the warm trial (0.96 ± 0.18 l v 0.48 ± 0.15 l; p < .0001) but body mass losses over the trials were similar (1.15 ± 0.34% (cold) v 1.03 ± 0.26% (warm)). More water was consumed throughout the duration of the warm trial (0.81 ± 0.42 l v 0.50 ± 0.49 l; p = .001). Cumulative urine output was greater in the cold trial (0.81 ± 0.46 v 0.54 ± 0.31 l; p = .036). Postexercise serum osmolality was higher compared with baseline in the cold (292 ± 2 v 287 ± 3 mOsm.kg-1, p < .0001) and warm trials (288 ± 5 v 285 ± 4 mOsm·kg-1; p = .048). Thirst sensations were similar between trials (p > .05). Ad libitum water intake adjusted so that similar body mass losses occurred in both trials. In the cold there appeared to a blunted thirst response.
The purpose of this study was to identify the effects of superficial cooling on thermoregulatory responses while exercising in a hot, humid environment while wearing an American football uniform. Nine male and female subjects wore a superficial cooling garment while in a cooling (CS) experimental condition or a no cooling (NCS) control condition during an exercise task consisting of: warm-up (WU), exercise (EX), and recovery (R). The exercise task simulated an American football conditioning session with subjects wearing a full American football uniform and performing anaerobic and aerobic exercises in a hot, humid environment. Subjects were allowed to drink water ad libitum during rest breaks. During the WU, EX and R periods, core body temperature (Tc) was measured to assess the effect of the cooling garment. Neither baseline resting (pre-warm-up) Tc nor post- warm-up Tc were significantly different between trials. We found no significant differences in exercise Tc between conditions. Time to return to baseline Tc revealed no significant differences between the experimental and control conditions. We found that the volume of fluid consumed was 34% less in the experimental (711.1 +188.0 mL) condition compared to the control (1077.8 +204.8 mL) condition. Our findings indicate the cooling garment was not effective in blunting the rise in Tc during warm up, attenuating a rise in Tc during intermittent exercise, nor in increasing a return to baseline Tc during a resting recovery period in a hot, humid environment while wearing an American football uniform.
The 1910-1913 Terra Nova Expedition to the Antarctic, led by Captain Robert Falcon Scott, was a venture of science and discovery. It is also a well-known story of heroism and tragedy since his quest to reach the South Pole and conduct research en route, while successful was also fateful. Although Scott and his four companions hauled their sledges to the Pole, they died on their return journey either directly or indirectly from the extreme physiological stresses they experienced. One hundred years on, our understanding of such stresses caused by Antarctic extremes and how the body reacts to severe exercise, malnutrition, hypothermia, high altitude, and sleep deprivation has greatly advanced. On the centenary of Scott's expedition to the bottom of the Earth, there is still controversy surrounding whether the deaths of those five men could have, or should have, been avoided. This paper reviews present-day knowledge related to the physiology of sustained man-hauling in Antarctica and contrasts this with the comparative ignorance about these issues around the turn of the 20th century. It closes by considering whether, with modern understanding about the effects of such a scenario on the human condition, Scott could have prepared and managed his team differently and so survived the epic 1,600-mile journey. The conclusion is that by carrying rations with a different composition of macromolecules, enabling greater calorific intake at similar overall weight, Scott might have secured the lives of some of the party, and it is also possible that enhanced levels of vitamin C in his rations, albeit difficult to achieve in 1911, could have significantly improved their survival chances. Nevertheless, even with today's knowledge, a repeat attempt at his expedition would by no means be bound to succeed.
Children and adults employ different thermoregulatory strategies, particularly in dealing with heat stress. Children rely more on 'dry' heat exchange, while evaporative heat loss is adults' foremost heat-dissipation venue. Several anatomical, physiological, and psychological factors can affect differential risk of thermal injury in the child vs. the adult athlete, in some situations. Children have greater surface-area- to-mass ratio, lower sweating rate, higher peripheral blood flow in the heat, and a greater extent of vasoconstriction in the cold. They can acclimatise to a similar extent but do so at a lower rate than adults. Differences in perceived exertion and thermal strain, cumulative experience, cognitive development, and decision-making capacity may negatively affect the young athlete's behaviour under competitive and other situations, possibly subjecting him/her to sub-par performance or to greater risk of thermal injury. However, except for very limited environmental conditions, children in general, and young athletes in particular, are physiologically as capable as adults to handle environmental challenges.
Exercise-associated hyponatremia (EAH) is hyponatremia that occurs <or= 24 hours after prolonged physical activity. It is a potentially serious complication of marathons, triathlons, and ultradistance events, and can occur in hot and cold environments. Clear evidence indicates that EAH is a dilutional hyponatremia caused by excessive fluid consumption and the inappropriate release of arginine vasopressin. Cerebral and pulmonary edema can cause serious signs and symptoms, including altered mental status, respiratory distress, seizures, coma, and death. Rapid diagnosis and urgent treatment with hypertonic saline is necessary to prevent severe complications or death. Prevention is based on educating athletes to avoid excessive drinking before, during, and after exercise.
The purpose of this study was to evaluate how interval (INT) and continuous (CONT) exercise alter body temperatures and manual dexterity in the cold (5 degrees C). Fourteen young men underwent two trials consisting of a 90-min period of acute cold exposure (ACE), 30 min of exercise (INT or CONT), and a 60-min recovery period (REC). Participants donned approximately 1 clo but the hands remained bare for the entire protocol so that a steep decline in dexterity performance occurred prior to the initiation of exercise. INT and CONT were isoenergetic, reflecting 50 +/- 1% of each individual's VO(2) peak. Rectal (Tre) and skin temperatures were monitored continuously and dexterity testing was conducted at ten time points throughout each 3-h trial. In addition, oxygen consumption (VO(2)) and torso hemodynamics were assessed via indirect calorimetry and impedance cardiography (ICG), respectively. As expected, finger temperature and dexterity declined during ACE, relative to baseline. Both modes of exercise increased finger temperature and dexterity, relative to ACE. However, CONT was more effective than INT at increasing finger temperature on the dominant hand, which was associated with better dexterity scores during REC. Tre was not different between trials but a significant increase in stroke volume was found following CONT. Perhaps elevated stroke volume during post-exercise REC plays a role in finger rewarming and dexterity performance. Further mechanistic studies are needed to confirm the role of cardiovascular function in the enhancement of manual performance in the cold.
Cardiovascular-related mortality peaks during cold winter months, particularly in older adults. Acute physiological responses, such as increases in blood pressure, in response to cold exposure may contribute to these associations. To determine whether the blood pressure-raising effect (pressor response) of non-internal body temperature-reducing cold stress is greater with age, we measured physiological responses to 20 min of superficial skin cooling, via water-perfused suit, in 12 younger [25 +/- 1 (SE) yr old] and 12 older (65 +/- 2 yr old) adults. We found that superficial skin cooling elicited an increase in blood pressure from resting levels (pressor response; P < 0.05) in younger and older adults. However, the magnitude of this pressor response (systolic and mean blood pressure) was more than twofold higher in older adults (P < 0.05 vs. younger adults). The magnitude of the pressor response was similar at peripheral (brachial) and central (estimated in the aorta) measurement sites. Regression analysis revealed that aortic pulse wave velocity, a measure of central arterial stiffness obtained before cooling, was the best predictor of the increased pressor response to superficial skin cooling in older adults, explaining approximately 63% of its variability. These results indicate that there is a greater pressor response to non-internal body temperature-reducing cold stress with age in humans that may be mediated by increased levels of central arterial stiffness.
The relationship among changes in thirst sensations, blood variables, and differential fluid intake in hypohydrated humans was examined. Seven subjects were hypohydrated by 0%, 3%, 5%, and 7% of their body weight on four separate trials which were systematically randomized between subjects. Hypohydration levels were achieved with a regimen of restricted food and fluid intake and moderate heat-exercise stress. Statistically significant linear and quadratic trends were found for the intensity of several sensations with progressive hypohydration levels. In general, plasma osmolality and renin activity increased and plasma volume decreased with increasing hypohydration levels. During a one hour period of ad lib drinking, all subjects consumed insufficient fluid to rehydrate back to baseline body weights. Using regression analyses, fluid intake was predicted by the magnitude of subjective and physiological indices of hypohydration. Results demonstrate that both hypovolemia and plasma osmolality contribute significantly to fluid intake in hypohydrated humans. The results also indicate that thirst sensations make a substantial contribution to differential fluid intake in humans.
Hypertonic saline was infused into 11 volunteers to osmotically stimulate vasopressin secretion. A strong positive correlation between plasma arginine vasopressin (PAVP) and plasma osmolality (Pos) was obtained, defined by the function PAVP=0.63 (Pos-284), r=+0.80, P<0.001. The sensitivity of vasopressin secretion to osmotic stimulation was represented by the slope of the expression and the theoretical threshold of vasopressin release by the abscissal intercept. Plasma osmolality at the onset of thirst was 298.5±1.1 mmol/kg. Application of hypertonic saline infusion to 10 polyuric patients clearly separated those with normal osmoregulation of vasopressin secretion from those with cranial diabetes insipidus.
This study examined the effects of hypohydration on thermoregulation during cold exposure. In addition, the independent influences of hypohydration-associated hypertonicity and hypovolemia were investigated. Nine male volunteers were monitored for 30 min at 25 degrees C, then for 120 min at 7 degrees C, under three counterbalanced conditions: euhydration (Eu), hypertonic hypohydration (HH), and isotonic hypohydration (IH). Hypohydration was achieved 12 h before cold exposure by inducing sweating (HH) or by ingestion of furosemide (IH). Body weight decrease (4.1 +/- 0.2%) caused by hypohydration was similar for HH and IH, but differences (P < 0.05) were found between HH and IH in plasma osmolality (292 +/- 1 vs. 284 +/- 1 mosmol/kgH2O) and plasma volume reduction (-8 +/- 2 vs. -18 +/- 3%). Heat debt (349 +/- 14 among) did not differ (P > 0.05) among trials. Mean skin temperature decreased throughout cold exposure during Eu but plateaued after 90 min during HH and IH. Forearm-finger temperature gradient tended (P = 0.06) to be greater during Eu (10.0 +/- 0.7 degrees C) than during HH or IH (8.9 +/- 0.7 degrees C). This suggests weaker vasoconstrictor tone during hypohydration than during Eu. Final mean skin temperature was higher for HH than for Eu or IH (23.5 +/- 0.3, 22.6 +/- 0.4, and 22.9 +/- 0.3 degrees C, respectively), and insulation was lower on HH than on IH (0.13 +/- 0.01 vs. 0.15 +/- 0.01 degree C.W-1.m-2, respectively), but not with Eu (0.14 +/- 0.01 degree C.W-1.m-2). This provides some evidence that hypertonicity impairs the vasoconstrictor response to cold. Although mild hypohydration did not affect body heat balance during 2-h whole body exposure to moderate cold, hypohydration-associated hypertonicity may have subtle effects on vasoconstriction that could become important during a more severe cold exposure.
Acute cold stress is a consistent stimulus to ACTH secretion in rats yet inhibits arginine vasopressin (AVP) in both rats and humans. We have studied the interrelationships of AVP, corticotrophin-releasing factor, and atrial natriuretic factor (ANF) in the hypothalamo-pituitary-adrenal response to acute cold stress in normal humans. Six healthy male volunteers deprived of food and fluid for 6 h, and minimally clothed, were studied in the early afternoon. After a 30-min period at 22 C, subjects were exposed to cold stress (4 C for 30 min), followed by a 30-min equilibration period at 22 C. By the end of the period of cold exposure there was a fall in plasma volume of 7.8 +/- 1.4% (mean +/- SEM), a significant increase in both systolic blood pressure (P = 0.0001) and in plasma norepinephrine level (P = 0.0001), but no change in plasma epinephrine or in plasma ANF. Plasma AVP levels fell significantly (P less than 0.01) to reach a nadir at 5-10 min after cold exposure before returning to baseline levels. A significant fall in plasma cortisol levels occurred during the first 15 min of the baseline period and remained stable thereafter. No significant changes in plasma corticotrophin-releasing factor or ACTH occurred. These results suggest that cold inhibition of AVP release, presumably via afferent baroreceptor pathways, may act to reduce the response of the corticotrophs to a potentially noxious stimulus. Inhibition of AVP and/or ACTH during acute cold exposure are not dependent upon an increase in plasma ANF.
The Metabolic responses (VO2 and lactic acid accumulation) of six nationally ranked marathon runners were examined during submaximal and maximal treadmill running. At all running speeds the runners were confronted with a 242 m/min head wind to partially account for the actual air resistance experienced during competitive running. Based on the metabolic laboratory data and mean competitive running speeds, marathon performances were evaluated. The average Max VO2 for the 6 runners was 4.54 l/min (71.4 ml/kg-min). During a marathon race that requires about 2400 Kcal it was estimated that the runners utilized 75% of their aerobic capacities with little lactic acid accumulation.
(C)1969The American College of Sports Medicine
In two experiments a total of 12 men were subjected to 5 days of starvation under survival conditions in the winter subarctic. They wore flying clothing rated at 3.5 clo. The caloric cost, as calculated from oxygen consumption, was 2,300 kcal/m ² for the first day and 2,000 kcal/m ² for subsequent days at ambient temperatures of -30 C. At -10 C the cost of subsequent days fell to 1,500 kcal/m ² . The subjects lost 8% of body weight but regained 5% body weight after 5 days refeeding on a barely maintenance diet. One-third of the original (8%) weight loss was due to an isotonic contraction of extracellular fluid. Changes in heart rate, pulse pressure, and hematocrit consistent with this fluid contraction were observed. Although the water intake did not exceed the 5-day urine volume (5 liters), the subjects did not experience thirst until after return to the warm.
Note:(With the Technical Assistance of William P. Esser and Kermitt R. Skrettingland)
caloric cost; cold exposure; electrolyte balance in starvation; fasting; fluid balance in starvation; IMP, integrating motor pneumotachograph; fat carbohydrate and protein catabolism in cold exposure and starvation; cold diuresis; sodium, potassium and acid-base balance in acute starvation
Submitted on June 3, 1963
The concept that secretion of the antidiuretic hormone, arginine vasopressin, is regulated by the osmolality of body water originated with the pioneering studies of Verney over 25 years ago [1]. In a classical series of experiments, this investigator showed that the injection of hypertonic saline into the carotid artery of conscious, hydrated dogs resulted in a prompt and reversible fall in urine output that was indistinguishable from that produced by the i.v. injection of small amounts of pituitary extract. On the basis of this and other indirect evidence, Verney concluded that the release of vasopressin from the neurohypophysis was controlled by an intracranial osmoreceptor that was extremely sensitive to changes in the blood concentration of sodium and certain other solutes.
Efforts to confirm and extend these observations were limited for many years by the lack of a suitable method for measuring vasopressin directly at the low concentrations normally present in body fluids. Recently, however, several laboratories have succeeded in developing sensitive and specific radioimmunoassay methods that permit the hormone to be measured at physiologic concentrations with greater ease and precision [2,3]. As reviewed in the following pages, these new assay methods now have made it possible to begin to characterize osmoregulatory function in a more concrete and comprehensive way and also to use such information to analyze systematically certain clinical disorders of salt and water balance.
5 men trained 4 h/day for 43 days with increasing work loads on bicycle ergometers. Maximum oxygen consumption (VO 2max) and lactate turn points (VO 2 at which lactate production increases exponentially) were assessed before, during and after training. Following training the subjects were acclimatized to heat. A 4-h work test (stepping at 35 W) was done in a cool (18-22°C) environment before training began, at intervals during training, and after acclimatization. The test was also repeated in a hot environment (33.8°C db, 32.4°C wb) before and after training and acclimatization. During each test, mean skin temperature (Tsk), rectal temperature (Tre), body weights, VO 2, and blood samples were obtained. Training had little effect on thermoregulation during cool tests but did modify thermoregulatory mechanisms early in heat exposure. Work tests done in a cool environment were accompanied by hemoconcentration before and hemodilution after 3 wk of training. Protein dynamics and improvement in muscle metabolism appeared to contribute to the shift from hemoconcentration to hemodilution. Training stabilized plasma volume during a heat exposure but acclimatization afforded further protection against heat stress because of increased hemodilution and sensitivity of the sweat mechanism.
Acute cold stress is a consistent stimulus to ACTH secretion in rats yet inhibits arginine vasopressin (AVP) in both rats and humans. We have studied the interrelationships of AVP, corticotrophin-releasing factor, and atrial natriuretic factor (ANF) in the hypothalamo-pituitary-adrenal response to acute cold stress in normal humans. Six healthy male volunteers deprived of food and fluid for 6 h, and minimally clothed, were studied in the early afternoon. After a 30-min period at 22 C, subjects were exposed to cold stress (4 C for 30 min), followed by a 30-min equilibration period at 22 C. By the end of the period of cold exposure there was a fall in plasma volume of 7.8 +/- 1.4% (mean +/- SEM), a significant increase in both systolic blood pressure (P = 0.0001) and in plasma norepinephrine level (P = 0.0001), but no change in plasma epinephrine or in plasma ANF. Plasma AVP levels fell significantly (P less than 0.01) to reach a nadir at 5-10 min after cold exposure before returning to baseline levels. A significant fall in plasma cortisol levels occurred during the first 15 min of the baseline period and remained stable thereafter. No significant changes in plasma corticotrophin-releasing factor or ACTH occurred. These results suggest that cold inhibition of AVP release, presumably via afferent baroreceptor pathways, may act to reduce the response of the corticotrophs to a potentially noxious stimulus. Inhibition of AVP and/or ACTH during acute cold exposure are not dependent upon an increase in plasma ANF.
The mechanism for reduced voluntary water intake during water immersion was studied in eight men (19-25 yr of age) immersed to the neck while sitting for 3 h at 34.5 degrees C or in air at 28 degrees C when euhydrated (Eu-H2O and Eu-air, respectively) and hypohydrated (Hypo-H2O and Hypo-air) by 3.6% body weight loss. Thirst sensations (degree of thirst, mouth dryness and taste, drinking desirability, and stomach fullness) were similar at the beginning of Hypo-air and Hypo-H2O test periods. Initial drinking of tap water (15 degrees C) was 216 +/- 30 ml/7 min (P less than 0.05) with Hypo-air, decreased to 108 +/- 28 ml/7 min (P less than 0.05) with Hypo-H2O, and was 10-50 ml/10-30 min thereafter. Intake was less than 10 ml/10-30 min in Eu-air, and there was no drinking in Eu-H2O. Within the first 10 min of immersion, compared with Hypo-air findings, the significant reduction in drinking in the Hypo-H2O experiment was associated with unchanged plasma Na+, plasma osmolality, heart rates, and mean arterial pressures; the different responses were increased cardiac output, plasma volume, and atrial natriuretic peptides and decreased plasma renin activity and arginine vasopressin. Thus the extracellular pathway, as opposed to the osmotic pathway, appears to be the major mechanism for immersion-induced suppression of drinking.
To examine the influence of an increase in central blood volume with head-out water immersion (WI) on fluid-regulating hormones during exercise, 10 healthy men underwent upright leg cycle exercise on land and with WI. Venous plasma renin activity and plasma venous concentrations of atrial natriuretic peptide, plasma aldosterone, and arginine vasopressin were determined at exercise intensities corresponding to approximately 40, 60, 80, and 100% peak oxygen consumption (VO2) and at minutes 1 and 5 of seated rest recovery within each environment. Peak VO2 did not differ on land and with WI. Atrial natriuretic peptide concentration was higher (P less than 0.05) and plasma renin activity was lower (P less than 0.05) in water than on land at 40% peak VO2 through minute 5 of recovery. Plasma aldosterone and arginine vasopressin concentrations were lower (P less than 0.05) in water at peak exercise and at minutes 1 and 5 of recovery. Osmolality and plasma sodium and potassium concentrations during exercise were similar in water and on land. The results indicate that WI alters the circulating levels of several hormones involved in fluid and electrolyte regulation during exercise. These hormonal alterations can best be explained by stimulation of low-pressure baroreceptors and atrial stretch due to increased central blood volume with head-out WI.
The effect of an imposed drinking discipline versus ad libitum drinking was studied on 21 healthy, well-trained volunteers, during a continuous 4.5-h march at an altitude of 1,700 m and an ambient temperature of 0 degree C, SD 1. Group I (n = 13) was instructed to drink 250 ml of warmed, artificially sweetened fluid every 30 min, whereas group II (n = 8) drank plain water ad libitum. The median fluid intake in group I was significantly higher than in group II (P less than 0.0002). Serum urea and osmolality decreased during the march in group I (P less than 0.05; P less than 0.002, respectively) with no significant change in group II. In both groups, a similar increase in haemoglobin concentration concomitant with a reduction in calculated blood and plasma volume was observed after exercise and did not correlate with the state of hydration. Total urine volume, creatinine clearance, urea clearance and potassium excretion were significantly higher and urinary osmolality was lower in group I than in group II (P less than 0.05). These results reflect a state of extreme "voluntary dehydration" in the control group when no fluid intake was obligatory. Thus, during exercise in the cold, under conditions similar to those in this study, a fluid intake of 150 ml.h-1 should be maintained in order to keep a urinary flow of about 1 ml.kg-1.h-1 and to achieve a good state of hydration.
The act of drinking ameliorates thirst and inhibits the secretion of vasopressin before changes in extracellular fluid volume or osmolality in both animals and man. We evaluated whether this reflex inhibition of vasopressin secretion might be due to the presence of oropharyngeal receptors in humans. After dehydration, normal subjects (n = 4) were allowed to suck on ice chips for 30 min. Despite the absence of changes in plasma sodium (Na+) or osmolality, the mean plasma vasopressin level decreased promptly within 10 min from 2.8 to 1.8 pg/mL, and it remained low for 30 min after ice ingestion. When the dehydration protocol was repeated with the subjects receiving 100 mL water (25 C) for 30 min rather than ice chips, plasma vasopressin levels did not change. These data demonstrate that activation of cold-sensitive oropharyngeal receptors results in inhibition of vasopressin secretion independently of osmotic or gastric factors. In a second study 0.2 mL/kg X min 3% NaCl was administered for 90 min as a second stimulus to vasopressin secretion, and ice chips were given during the last 30 min of infusion. Plasma vasopressin levels increased steadily to 3.3 +/- 0.5 (+/- SEM) pg/mL by 45 min, and despite ice ingestion increased further to 4.6 +/- 0.8 pg/mL by 90 min. Consequently, hypertonicity appears to be a stronger stimulus to vasopressin release, since the suppressive effect of stimulation of oropharyngeal receptors with ice was not evident during the NaCl infusion. Finally, no changes in vasopressin levels were found in subjects holding concentrated NaCl solutions in their mouths for 30 min, indicating that the oropharyngeal receptors are not responsive to local changes in osmolality. The presence of such cold-sensitive oropharyngeal receptors may explain the desire of severely dehydrated patients, e.g. patients with diabetes insipidus, for cold liquids.
Body temperature, urine output, osmotic and free water clearances, plasma osmolality, sodium and potassium concentrations, blood lactate level, osmotic thirst and central blood volume were measured in dogs exposed to cold (+1 to -8 degrees C) for 1-3 hours and compared to those obtained under control conditions at ambient temperatures (18-20 degrees C). In some additional experiments osmotic thirst threshold and arterial blood pressure during intravenous infusion of norepinephrine were also examined. Exposure to low ambient temperature caused an increase in the osmotic thirst threshold and rise in central blood volume. Transient increase in the urine output and free water clearance accompanied by a decrease in the urine osmolality were also observed. No changes were found in rectal temperature, plasma osmolality and plasma sodium concentration. Infusion of norepinephrine elevated the osmotic thirst threshold in a dose-dependent manner. It is concluded that the cold-induced suppression of osmotic thirst may result from the increased central blood volume. A possible involvement of the sympathetic nervous system in the thirst inhibition in low ambient temperature is also considered.
1. The relationship between thirst perception and plasma osmolality was studied during hypertonic and physiological saline infusion in ten healthy volunteers.
2. Thirst perception was quantified using a linear visual analogue scale which volunteers marked at intervals during the infusion periods.
3. Infusion of hypertonic saline caused a steady rise in plasma osmolality together with a progressive linear increase in thirst perception and also plasma arginine vasopressin. No significant changes in thirst, plasma osmolality or plasma arginine vasopressin occurred during infusion of physiological saline.
4. Linear regression analysis of the results defined the functions. Thirst (cm) = 0.3 (plasma osmolality −281) (r = + 0.92, P < 0.001) and plasma arginine vasopressin (pmol/l) = 0.4 (plasma osmolality −285) (r = + 0.96, P < 0.001). The osmolar threshold for thirst onset thus defined (281 mosmol/kg) was much lower than in previous studies and similar to the theoretical osmolar threshold for vasopressin release (285 mosmol/kg).
5. We conclude that thirst perception rises in a progressive fashion throughout a wide range of plasma osmolality and that the osmolar threshold for thirst onset is similar to the theoretical osmolar threshold for vasopressin release.
6. The results are compatible with the concept of either a single osmoreceptor subserving both thirst and vasopressin release, or two osmoreceptors sharing similar functional characteristics.
Thirst is a subjective sensation. Therefore to investigate further the nature, intensity, and specificity of osmotic thirst, we studied the effects of double-blind infusions of hypertonic (0.45 M) and isotonic (0.15 M) saline on subjective ratings and sensations of thirst, water intake, plasma vasopressin, and body fluids in seven healthy volunteer young men. Only the hypertonic saline significantly increased plasma sodium concentration, plasma osmolality, plasma vasopressin concentration, and visual analog ratings of thirst sensations. Both infusions expanded blood volume, which was greater with the hypertonic saline infusion. Neither solution significantly altered mean arterial blood pressure nor plasma angiotensin levels. Throughout a 60-min drinking period after the infusions, water intake was always significantly greater after the hypertonic saline than after the isotonic saline. The subjects described the thirst sensations as mainly due to a dry unpleasant tasting mouth, which was promptly relieved by drinking. Visual analog rating changes confirmed the subjective reports. Finally, the effects on thirst and vasopressin secretion were observed at plasma sodium concentration and osmolality changes that are well within the physiological range.
During the French 1980 Mount Pabil (7,102 m) Expedition, a study was made of four altitude-acclimatised climbers (age 36.5±3.6 years; 50.5±3.1 ml · kg−1). Intake of various nutrients, body weight, skinfold thicknesses as indices of body composition, and water and nitrogen balances, were recorded before, and during high altitude exposure, and again after the return to low altitude.
There was a significant (35–57%) reduction in total caloric intake at high altitude. Body weight decreased progressively, mainly due to a reduction in body fat. The subjects apparently remained in water balance, while the nitrogen balance was always negative during high altitude exposure.
The significant nutritional alterations were mainly observed above 6,000 m. They are discussed with respect to changes in feeding patterns and in hormonal status of the climbers accompanying hypoxia and other stressors proper to high altitude.
Exposure of rats to air at 5 C for 1-12 days is accompanied by a relative dehydration in spite of the continued presence of water. Dehydration during exposure to cold was manifested by: 1) a reduction in the ratio of water/food ingested; 2) an increase in the ratio of urine excreted/water ingested; 3) an increased evaporative water loss; 4) an increased serum osmolality and chloride concentration; and 5) a striking thirst and ingestion of water after transfer from cold to air at 26 C. Drinking began within 15 min and lasted approximately 1 h. Thermogenic drinking persisted for at least 120 days of exposure to cold. It was not thwarted by preventing access to water for either 1 or 2 h after transfer to warm air, but either intragastric or intraperitoneal administration of a water load equal to 3% of body weight inhibited water intake after transfer. These characteristics of thermogenic drinking are similar to those observed after 24 h of dehydration at 26 C; they also suggest that the cold-exposed rat is dehydrated relative to controls. These results suggest that osmoreceptors may play a role in the induction of thermogenic drinking. However, angiotensin II receptors may also play a role. Thermogenic drinking was inhibited by a beta 2-adrenergic, but not a beta 1-adrenergic, antagonist as well as by captopril, an inhibitor of the conversion of angiotensin I to angiotensin II. Further, plasma renin activity increased fourfold within 15 min after removal from cold. This suggests that an additional component involved in thermogenic drinking is the angiotensin II receptor. The extent to which thermogenic drinking is mediated by each pathway is unknown and will require additional studies.
Osmoregulation was studied in 13 mountaineers who had experienced long-term exposure to high altitude on Mt Everest. Serum osmolality rose from 290± 1 mOsm/kg to 295 ±2 mOsm/kg at 5,400 m and finally to 302 ±4 mOsm/kg at 6,300 m after a mean of 26.5 days above 5,400 m. Despite this degree of osmoconcentration, plasma arginine-vasopressin concentration remained unchanged: 1.1± 0.1 μU/mL at sea level, 0.8 ± 0.1 μU/mL at 5,400 m, and 0.9±0.1 μU/mL at 6,300 m. Urinary vasopressin excretion was also similar at all three altitudes. We conclude that prolonged exposure to high altitude may result in persistent impairment of osmoregulation, caused in part by an inappropriate arginine-vasopressin response to hyperosmolality.
(JAMA 1984;252:524-526)
This paper describes a modification of the standard oxygen-dilution technique for determining residual lung volume, whereby rapid responding oxygen and carbon dioxide analyzers are used to determine the point of nitrogen equilibration, and a five-liter rebreathing bag is substituted for the standard spirometer. This simplified method reduced the total test time to five min or less for duplicate determinations, and eliminated the need for a nitrogen analyzer and a spirometer. This method was found to be both reliable (r = 0.99) and valid (r = 0.92), with a standard error of prediction of 125 ml, and a mean difference of only eight ml, when compared with the established oxygen-dilution technique on a sample of 76 healthy men and women, 19 to 55 years of age. In a subsample of 13 subjects, residual volume was also determined with the nitrogen washout technique, which correlated r = 0.89 and r = 0.91 with the established and modified oxygen-dilution techniques respectively. The use of assumed values for the initial and final alveolar concentrations of nitrogen did not appear to significantly influence the final results.
The purpose of the present study was to investigate the possible role of vasopressin (ADH) in the control of thirst. With this aim spontaneous water intake (WI) was examined in conscious dogs after 1) electric stimulation in the basal forebrain causing release of ADH, 2) injection of 0.03, 0.05, 0.10, 0.15, 0.30, and 3.00 mU of ADH into the third cerebral ventricle (3rd V), 3) injection of 0.3, 3.0, and 30 mU of ADH into the lateral cerebral ventricle (LV) and injection of 5.0 and 10.0 mU of ADH into the carotid artery (CA). Stimulation through 10 of 16 electrodes located in various structures of the limbic system caused a significant increase in blood ADH, decrease of urine output, increase in renal free-water reabsorption, nonstimulus-bound drinking, positive water balance, and decrease in plasma osmolality (Posmol). Injection of ADH to the 3rd V caused a significant increase in WI. The maximum WI was observed after injection of 0.10-0.15 mU of ADH. Elevation of WI caused a significant decrease in Posmol 1 h after injection of ADH to the 3rd V. Insignificant increases or no changes in WI were observed when ADH was injected into the LV and CA, respectively. The results suggest that ADH may exert central dipsogenic effects.
James S. Skinner and Thomas M. McLellan begin this section with a discussion of the transition from aerobic to anaerobic metabolism. Discrepancies are identified in activities being defined as anaerobic and the relative importance and meaning of lactate concentration in the blood. Skinner and McLellan propose a hypothetical model to more accurately explain anaerobic activities. The second article, by Frank Katch and Victor Katch, contains a review of sources of error in body composition assessment by laboratory and field methods. Katch and Katch describe problems occurring in the use of hydrostatic weighing, residual air volume, skinfolds, and circumferences. In addition, the importance of statistical considerations is stressed, with an emphasis on the proper use of multiple regression techniques in conducting studies of the measurement of body composition.
The purpose was to determine whether extracellular volume or osmolality was the major contributing factor for reduction of thirst in air and head-out water immersion in hypohydrated subjects. Eight males (19-25 yr) were subjected to thermoneutral immersion and thermoneutral air under two hydration conditions without further drinking: euhydration in water (Eu-H2O) and euhydration in air, and hypohydration in water (Hypo-H2O) and hypohydration in air (3.7% wt loss after exercise in heat). The increased thirst sensation with Hypo-H2O decreased (P < 0.05) within 10 min of immersion and continued thereafter. Mean plasma osmolality (288 +/- 1 mosmol/kgH2O) and sodium (140 +/- 1 meq/l) remained elevated, and plasma volume increased by 4.2 +/- 1.0% (P < 0.05) throughout Hypo-H2O. A sustained increase (P < 0.05) in stroke volume accompanied the prompt and sustained decrease in plasma renin activity and sustained increase (P < 0.05) in plasma atrial natriuretic peptide during Eu-H2O and Hypo-H2O. Plasma vasopressin decreased from 5.3 +/- 0.7 to 2.9 +/- 0.5 pg/ml (P < 0.05) during Hypo-H2O but was unchanged in Eu-H2O. These findings suggest a sustained stimulation of the atrial baroreceptors and reduction of a dipsogenic stimulus without major alterations of extracellular osmolality in Hypo-H2O. Thus it appears that vascular volume-induced stimuli of cardiopulmonary baroreceptors play a more important role than extracellular osmolality in reducing thirst sensations during immersion in hypohydrated subjects.
Athletes and researchers could benefit from a simple and universally accepted technique to determine whether humans are well-hydrated, euhydrated, or hypohydrated. Two laboratory studies (A, B) and one field study (C) were conducted to determine if urine color (Ucol) indicates hydration status accurately and to clarify the interchangeability of Ucol, urine osmolality (Uosm), and urine specific gravity (Usg) in research. Ucol, Uosm, and Usg were not significantly correlated with plasma osmolality, plasma sodium, or hematocrit. This suggested that these hematologic measurements are not as sensitive to mild hypohydration (between days) as the selected urinary indices are. When the data from A, B, and C were combined, Ucol was strongly correlated with Usg and Uosm. It was concluded that (a) Ucol may be used in athletic/industrial settings or field studies, where close estimates of Usg or Uosm are acceptable, but should not be utilized in laboratories where greater precision and accuracy are required, and (b) Uosm and Usg may be used interchangeably to determine hydration status.
On the basis of an analysis of the skin temperature data on three resting human subjects from 112 experiments, a simple weighting system for computing the mean skin temperature from observations on four areas of the body, namely, chest, arms, thighs, and legs, has been proposed. The proposed system of weighting yields mean skin temperature values identical with the elaborate Hardy-Dubois weighting formula. The value of the medial thigh temperature as an index of the mean skin temperature has also been investigated and discussed.
skin temperature measurement
Submitted on May 20, 1963
It has been postulated that alterations in the intravascular distribution of blood affect antidiuretic hormone (ADH) secretion in man. The studies reported here were designed to alter blood distribution by thermal and by positional change to test this thesis.HUMAN BLOOD ADH LEVELS HAVE BEEN SHOWN TO VARY WITH POSITION: a mean value of 0.4 +/- 0.6 (SD) muU/ml was obtained while the subject was supine, a value of 1.4 +/- 0.7 muU/ml while sitting, and 3.1 +/- 1.5 muU/ml while standing. In 79 control subjects, sitting comfortably for 30 min in a normal environment, a blood ADH level of 1.65 +/- 0.63 muU/ml was found. It is suggested that subjects assume this position during experiments in which blood is drawn for measurement of ADH levels.In eight seated subjects the ADH level rose from 1.6 +/- 0.4 to 5.2 +/- 0.8 muU/ml after a 2 hr exposure at 50 degrees C and fell to 1.0 +/- 0.26 muU/ml within 15 min at 26 degrees C.Six subjects with a mean ADH level of 2.2 +/- 0.58 muU/ml sat quietly in the cold (13 degrees C) for 1 hr, and the ADH level fell to 1.2 +/- 0.36 muU/ml. After 15 min at 26 degrees C, the level rose to 3.1 +/- 0.78 muU/ml. The serum sodium and osmolal concentrations remained constant during all studies.Water, sodium, and total solute excretion decreased during exposure to the heat, whereas the urine to plasma (U/P) osmolal ratio increased. During cold exposure, water, sodium, and total solute excretion increased, and there was a decrease in the U/P osmolal ratio.These data are interpreted as indicating that changes in activity of intrathoracic stretch receptors, in response to redistribution of blood, alter ADH secretion independently of changes in serum osmolality. The rapidity of change of blood ADH concentration indicates a great sensitivity and a prime functional role for the "volume receptors" in the regulation of ADH secretion.
Influence of cold stress on human fluid balance In: Nutrient Requirements for Work in Cold and High Altitudes
- M N Sawka
FREUND, B. J., and M. N. SAWKA. Influence of cold stress on human
fluid balance. In: Nutrient Requirements for Work in Cold and
High Altitudes, B. M. Marriott (Ed.). Washington, DC: National
Academy of Sciences, 1995, pp. 161–180.