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Plasma osmolality (A) and tear osmolarity (B) responses to progressive exercise-heat induced dehydration to 1%, 2% and 3% body mass loss, subsequent overnight fluid restriction (08:00 h) and rehydration (11:00 h) during fluid restriction (FR K ) and with fluid intake to offset fluid losses (FI J ). Values are
Source publication
Human hydration assessment is a key component for the prevention and proper treatment of heat-related fluid and electrolyte imbalances within military, sports and clinical medicine communities. Despite the availability of many different methods for assessing hydration status, the need for a valid method or technology that is simple, rapid, non-inva...
Context in source publication
Context 1
... volume and evaporation of tear fluid in the 3–5 min delay from collection to measurement (Tiffany, 2008). Until very recently, another obstacle to the general application of Tosm measurement was the need for an experienced investigator who could obtain the tear fluid without disturbing its basic composition: reflexive tearing can alter tear fluid composition (e.g. Tosm) (Nelson and Wright, 1986). Common tear collection techniques such as using glass capillary tubes or absorbing Schirmer papers are uncomfortable, time-consuming and technically demanding procedures that may irritate the ocular surface and initiate reflex tearing (Esmaeelpour et al., 2008). Very recently, a non-invasive tear collection and analyzing device has made it possible to measure Tosm on a very small sample of tear fluid (50 nL) (Benelli et al., 2010). The TearLab s osmolarity system utilizes a single-use test card mounted on a hand-held pen, which both collects the sample and initiates the measurement ( Fig. 3). The collection procedure is performed by resting the tip of the test card on the lower tear meniscus, which takes only a few seconds, is painless and requires little technical expertise; indeed, it is possible to perform the collection on oneself looking in a mirror. The pen is immediately docked onto the TearLab s platform where an output is generated within 10 s using the principle of electrical impedance. Using the TearLab s osmolarity system, one recent study showed that increases in plasma osmolality during exercise- evoked dehydration and subsequent overnight fluid restriction were reflected in increases in Tosm (Fig. 4) (Fortes et al., 2011). In addition, decreases in plasma osmolality during a fluid intake trial were also reflected in decreases in Tosm providing confidence that the changes in Tosm reflect changes in hydration and not an exercise artefact (Fortes et al., 2011). A large correlation was observed between Tosm and plasma osmolality ( r 1⁄4 0.72, P o 0.01), however the mechanism(s) for the observed association of Tosm and plasma osmolality remains to be elucidated (Fortes et al., 2011) (Fig. 2); for example, it remains a matter of contention whether tear fluid represents a direct filtrate from plasma (Ubels et al., 1994). Using Tosm as a hydration assessment tool may be especially appealing to clinicians because the procedure is less-invasive compared with plasma osmolality, requires little expertise to perform, and provides a rapid reading. Biological variation analysis also suggests that Tosm change values may be diagnostically useful for hydration assessment (Fortes et al., 2011). It remains to be seen how Tosm responds to isotonic- hypovolaemia or if it can be applied successfully in an outdoor sports medicine setting where sunlight, wind, movement convection, sweat (in the eyes) and other factors may complicate Tosm ...
Citations
... A number of authors have emphasised the need for a simple, rapid, and non-invasive test to diagnose systemic dehydration, particularly in the elderly [117,[167][168][169][170]. The purpose of this report has been to suggest that measurement of the BTO, if its credentials are confirmed, could satisfy the role of a screening test for water-loss dehydration, in that, a positive result could lead to effective rehydration. ...
... There are many situations in which environmental conditions and physical exercise lead to or threaten to cause dehydration. The test described here could find a place in the community at large, in the study of body hydration in sports medicine, [170] and in field conditions in both sports medicine [169,171], and military environments [168]. ...
Systemic dehydration due to inadequate water intake or excessive water loss, is common in the elderly and results in a high morbidity and significant mortality. Diagnosis is often overlooked and there is a need for a simple, bedside diagnostic test in at-risk populations. Body hydration is highly regulated with plasma osmolality (pOsm) being tightly controlled over a wide range of physiological conditions. By contrast, normal tear osmolarity (tOsm) is more variable since the tear film is exposed to evaporation from the open eye. While plasma hyperosmolality is a diagnostic feature of systemic dehydration, tear hyperosmolality, with other clinical features, is diagnostic of dry eye. Studies in young adults subjected to exercise and water-deprivation, have shown that tOsm may provide an index of pOsm, with the inference that it may provide a simple measure to diagnose systemic dehydration. However, since the prevalence of both dry eye and systemic dehydration increases with age, the finding of a raised tOsm in the elderly could imply the presence of either condition. This diagnostic difficulty can be overcome by measuring tear osmolality after a period of evaporative suppression (e.g., a 45 min period of lid closure) which drives tOsm osmolality down to a basal level, close to that of the pOsm. The arguments supporting the use of this basal tear osmolarity (BTO) in the diagnosis of systemic dehydration are reviewed here. Further studies are needed to confirm that the BTO can act as a surrogate for pOsm in both normally hydrated subjects and in patients with systemic dehydration and to determine the minimum period of lid closure required for a simple, “point-of-care” test.
... A recent method of estimating hydration status involves assessing fluid of the eye. Tear osmolality has emerged as a strong candidate for hydration assessment [67,68]. Indeed, tear osmolality closely correlates with P OSM with the relationship being stronger than USG [20]. ...
... Indeed, tear osmolality closely correlates with P OSM with the relationship being stronger than USG [20]. However, literature has reported a large variability of tear osmolality potentially due to evaporation and differences in collection techniques [20,67]. Recently, a non-invasive tear collection and analysing device has provided a potential solution for the disparate collection techniques [67]. ...
... However, literature has reported a large variability of tear osmolality potentially due to evaporation and differences in collection techniques [20,67]. Recently, a non-invasive tear collection and analysing device has provided a potential solution for the disparate collection techniques [67]. However, a recent study using the non-invasive tear collection and analysing device found that while tear osmolality did change following exercise-induced fluid loss, it did not correlate to other laboratory hydration measures including plasma osmolality and urine specific gravity [69]. ...
Background
Despite a substantial body of research, no clear best practice guidelines exist for the assessment of hydration in athletes. Body water is stored in and shifted between different sites throughout the body complicating hydration assessment. This review seeks to highlight the unique strengths and limitations of various hydration assessment methods described in the literature as well as providing best practice guidelines.
Main body
There is a plethora of methods that range in validity and reliability, including complicated and invasive methods (i.e. neutron activation analysis and stable isotope dilution), to moderately invasive blood, urine and salivary variables, progressing to non-invasive metrics such as tear osmolality, body mass, bioimpedance analysis, and sensation of thirst. Any single assessment of hydration status is problematic. Instead, the recommended approach is to use a combination, which have complementary strengths, which increase accuracy and validity. If methods such as salivary variables, urine colour, vital signs and sensation of thirst are utilised in isolation, great care must be taken due to their lack of sensitivity, reliability and/or accuracy. Detailed assessments such as neutron activation and stable isotope dilution analysis are highly accurate but expensive, with significant time delays due to data analysis providing little potential for immediate action. While alternative variables such as hormonal and electrolyte concentration, bioimpedance and tear osmolality require further research to determine their validity and reliability before inclusion into any test battery.
Conclusion
To improve best practice additional comprehensive research is required to further the scientific understanding of evaluating hydration status.
... Tosm can replace plasma and urine osmolarity as a standard form of measuring hydration. Many authors have linked plasma osmolality with Tosm (Fortes et al., 2011;Sollanek et al., 2012;Ungaro et al., 2015;Vera et al., 2017). However, previous studies have provided mixed results regarding the correlation between Tosm and plasma osmolality. ...
Recently, it has been reported that tear osmolarity (Tosm) is correlated with plasma osmolarity and will increase during exertion. We aimed to assess whether inhaling oxygen-enriched air between exercises could significantly change the Tosm value. Thirty men aged 24.9 years were included in the study. A cycloergometer was used to perform the exercise protocol. We recorded the participants’ Tosm (mOsm/L), heart rate (HR, beats/minute), oxygen saturation, and blood pressure values. After the first exhaustive exercise (T1), participants inhaled oxygen in the experimental group and a placebo in the control group. After the second exercise (T2), another set of measurements was obtained. The Tosm value before exercise was 297.4 ± 1.21 and 296.53 ± 1.11 mOsm/L (p = 0.61718) and the HR was 72.6 ± 2.59 and 73 ± 2.59 beats/minute (p = 0.39949) in the study and the control group, respectively. At T1, Tosm was 303.67 ± 1.25 and 302.2 ± 1.25 mOsm/L (p = 0.41286) and the HR reached 178.04 ± 2.60 and 176.4 ± 2.60 beats/minute (p = 0.65832), respectively. At T2, Tosm in the study group reached 305.73 ± 0.86 mOsm/L (correlation with the use of oxygen: r = −0.3818), and in the control group, it was 308.4 ± 0.86 mOsm/L (p = 0.0373), while the HR reached 172.20 ± 2.53 beats/minute in the study group and 178.2 ± 2.53 beats/minute in the control group (p = 0.057). It was concluded that inhaling oxygen before and after exercise could increase the rate of recovery after exhaustive exercise.
... Although the patient's history and physical examination may indicate the appearance of dehydration (symptoms and signs), it is obvious that medical staff should not only rely on these clinical data, but also have to integrate biochemical parameters to enable the diagnosis (Table 2) [33,58,59]. Plasma osmolarity ≥300 mOsm/kg, plasma sodium, urine specific gravity, tear, and saliva osmolality have all been shown to be suitable to diagnose dehydration [58,65,66]. For an optimal diagnostic strategy, you need at least calculate or measure BUN, glucose, creatinine, sodium, bicarbonate, and osmolality [32]. ...
Swallowing difficulties, also called dysphagia, can have various causes and may occur at many points in the swallowing process. The treatment and rehabilitation of dysphagia represent a major interdisciplinary and multiprofessional challenge. In dysphagic patients, dehydration is frequent and often accelerated as a result of limited fluid intake. This condition results from loss of water from the intracellular space, disturbing the normal levels of electrolytes and fluid interfering with metabolic processes and body functions. Dehydration is associated with increased morbidity and mortality rates. Dysphagic patients at risk of dehydration thus require close monitoring of their hydration state, and existing imbalances should be addressed quickly. This review gives an overview on dehydration, as well as its pathophysiology, risk factors, and clinical signs/symptoms in general. Available management strategies of dehydration are presented for oral, enteral, and parenteral fluid replacement.
... Previously, a larger amount of tears were required to be collected to measure Tosm, and the process of collection might have led to reflex lacrimation; moreover, the long time needed for this procedure might have been a source of large variability. Currently, it is possible to conduct Tosm measurements within a minute using a TearLab (Sollanek et al., 2012). In their study, Vera et al. (2017) demonstrated that physical exertion led to the rise in Tosm in untrained patients 5 min after strenuous exercise compared to the trained group. ...
... We indicated that the changes in Tosm were different in men and women, in response to physical exercise and that changes in Tosm were partially attributed to alterations in the blinking rate. Previous studies have shown some correlation between hydration status and IOP, as well as Tosm and tear breakup time (Vera et al., 2017;Sollanek et al., 2012). Moreover, some authors have found a positive correlation between body fat and the occurrence of DED (Ho et al., 2017). ...
Physical exertion leads to the rise in tear osmolarity. However, previous studies have been conducted mostly on males and did not consider sex differences and the possible alteration in blinking during physical exercise. Sixteen women and 18 men aged 25.09 ± 1.70 were divided into equal groups with eyes open and shut. Participants performed 8-min medium-intensity exercise and 5-min intense exercise on a cycloergometer. Tear osmolarity (in mOsm/L) was evaluated before ( T0), after medium-intensity (T1) and intense exercise (T2). The blinking rate was assessed in a group with eyes open. Tear brake up time was measured in T0 and T1. With tear osmolarity measuring 305.72 ± 1.22 and 313.56 ± 1.90 for men and women, respectively, we observed significant differences in T1. In T2, tear osmolarity in men was 303.3 ± 1.28 vs. 310.87 ± 1.36 in women. The blinking rate decreased from 14.24 ± 2.54/min in T0 to 9.41 ± 2.83/min in T1. There was a statistically significant change in tear osmolarity in both groups, that is, in the group with eyes shut from 300.53 ± 1.37 in T0 to 308.06 ± 1.55 in T1 to 304.88 ± 1.54 in T2. In the group with eyes open, tear osmolarity increased from 300.29 ± 1.37 in T0 to 310.76 ± 1.55 in T1 and then dropped to 308.88 ± 1.54 in T2. Tear brake up time measured in T0 was 14.7 ± 1.43 vs. 13.53 ±1.48 in the open eyes condition. Due to physical exercise, short-term changes in tear osmolarity are partially caused by altered blinking. Sex differences in tear osmolarity in response to exertion may confirm the relationship between total body water and tear osmolarity.
... An innovative method to assess hydration status in the field may lie in the measurement of tear osmolarity (T osm ) (Fortes et al., 2011;Sollanek et al., 2012). Various methods have been trialled to capture and analyse tear fluid, primarily for the diagnosis of dry eye disease. ...
... The acinar cells of the lacrimal gland secrete tear fluid that is primarily isotonic and a filtrate reflective of plasma; it is on this basis that T osm may reflect P osm under varying states of hyper-or hypovolemia. When hypohydration occurs there is an increase in P osm and a possible concomitant reduction in tear secretion from the lacrimal gland (Sollanek et al., 2012). Both of these factors have the potential to influence T osm and therefore provide insight into an individual's or groups hydration status. ...
... Whilst T osm displays all of these qualities it has only been tested in a laboratory setting. In the field, tear fluid is exposed to a range of variables including sunlight, wind, sweat, evaporation and dust, all of which have the potential to interact with the tear film and interfere with the association between plasma and tear fluid (Sollanek et al., 2012). Furthermore, it is not always possible in the field to implement a control period prior to hydration assessment which then requires the use of spot collections. ...
This investigation (i) examined changes in tear osmolarity in response to fluid loss that occurs with exercise in a field setting, and (ii) compared tear osmolarity with common field and laboratory hydration measures. Sixty-three participants [age 27.8 ± 8.4 years, body mass 72.15 ± 10.61 kg] completed a self-paced 10 km run outside on a predetermined course. Body mass, tear fluid, venous blood and urine samples were collected immediately before and after exercise. Significant (p < 0.001) reductions in body mass (1.71 ± 0.44%) and increases in tear osmolarity (8 ± 15 mOsm.L⁻¹), plasma osmolality (7 ± 8 mOsm.kg⁻¹), and urine specific gravity (0.0014 ± 0.0042 g.mL⁻¹; p = 0.008) were observed following exercise. Pre- to post-exercise change in tear osmolarity was not significantly correlated (all p > 0.05) with plasma osmolality (rs = 0.24), urine osmolality (rs = 0.14), urine specific gravity (rs = 0.13) or relative body mass loss (r = 0.20). Tear osmolarity is responsive to exercise-induced fluid loss but does not correlate with the changes observed using other common measures of hydration status in the field setting. Practitioners shouldn’t directly compare or replace other common hydration measures with tear osmolarity in the field.
Abbreviations: BML: Body Mass Loss; CV: Coefficient of Variation; Posm: Plasma osmolality; SD: Standard Deviation; Tosm: Tear Osmolarity; Uosm: Urine Osmolality; USG: Urine Specific Gravity; WBGT: Wet bulb globe thermometer
... Recently the eye has been identified (Sollanek et al., 2012;Sherwin et al., 2015) as having the potential to provide a valid hydration assessment in field settings, where the use of invasive procedures is limited. The relationship between ocular fluids (tear and aqueous humor), blood pressure and plasma osmolality has provided a case for tear fluid osmolarity (Fortes et al., 2011), tear break-up time (Sweeney et al., 2013), and intraocular pressure (IOP) (Hunt et al., 2012) as potential non-invasive measures of hydration status. ...
... This study is the first to experimentally evaluate the efficacy and sensitivity of using IOP to assess hydration status following intermittent exercise in the heat, with and without fluid restriction. Assessing thermal hypohydration using ocular fluids has recently gained interest in sports medicine literature (Fortes et al., 2011;Hunt et al., 2012;Sollanek et al., 2012;Sherwin et al., 2015) and IOP, in particular, may be appealing to sports medicine practitioners, clinicians, and researchers because the procedure is non-invasive, causes minimal discomfort, requires minimal training to perform accurately, and provides a reading within seconds. The novel findings of this investigation were: ...
Current hydration assessments involve biological fluids that are either compromised in dehydrated individuals or require laboratory equipment, making timely results unfeasible. The eye has been proposed as a potential site to provide a field-based hydration measure. The present study evaluated the efficacy and sensitivity of intraocular pressure (IOP) to assess hydration status. Twelve healthy males undertook two 150 min walking trials in 40°C 20% relative humidity. One trial matched fluid intake to body mass loss (control, CON) and the other had fluid restricted (dehydrated, DEH). IOP (rebound tonometry) and hydration status (nude body mass and serum osmolality) were determined every 30 min. Body mass and serum osmolality were significantly (p < 0.05) different between trials at all-time points following baseline. Body mass losses reached 2.5 ± 0.2% and serum osmolality 299 ± 5 mOsmol.kg−1 in DEH. A significant trial by time interaction was observed for IOP (p = 0.042), indicating that over the duration of the trials IOP declined to a greater extent in the DEH compared with the CON trial. Compared with baseline measurements IOP was reduced during DEH (150 min: −2.7 ± 1.9 mm Hg; p < 0.05) but remained stable in CON (150 min: −0.3 ± 2.4 mm Hg). However, using an IOP value of 13.2 mm Hg to predict a 2% body mass loss resulted in only 57% of the data being correctly classified (sensitivity 55% and specificity 57%). The use of ΔIOP (−2.4 mm Hg) marginally improved the predictive ability with 77% of the data correctly classified (sensitivity: 55%; specificity: 81%). The present study provides evidence that the large inter-individual variability in baseline IOP and in the IOP response to progressive dehydration, prevents the use of IOP as an acute single assessment marker of hydration status.
... When left chronically untreated, moderate-to-severe dehydration increases the risk of urinary tract infection, chronic kidney disease [4,5 & ,6], and also increases medical costs, morbidity, and mortality [7]. Unfortunately, despite numerous investigations [8 && ], the methods of dehydration assessment have not been refined to the point that a single reference standard has been identified for clinical decision-making [9]; this magnifies the difficulty of diagnosing dehydration in clinical practice [9][10][11][12]. This article provides recommendations to improve clinical decision-making based on the strengths and weaknesses of commonly used hydration biomarkers and clinical assessment methods. ...
... Blood osmolality has been proposed as a suitable index of dehydration (typically defined as >300 mmol/kg) [9,12]; however, this is not universally accepted [13,17 & ]. Evidence supporting blood osmolality as a hydration index typically comes from studies that incorporate a sweat-loss model of hypertonic hypovolemia in young, fit, and healthy individuals. ...
Purpose of review:
The purpose of the review is to provide recommendations to improve clinical decision-making based on the strengths and weaknesses of commonly used hydration biomarkers and clinical assessment methods.
Recent findings:
There is widespread consensus regarding treatment, but not the diagnosis of dehydration. Even though it is generally accepted that a proper clinical diagnosis of dehydration can only be made biochemically rather than relying upon clinical signs and symptoms, no gold standard biochemical hydration index exists. Other than clinical biomarkers in blood (i.e., osmolality and blood urea nitrogen/creatinine) and in urine (i.e., osmolality and specific gravity), blood pressure assessment and clinical symptoms in the eye (i.e., tear production and palpitating pressure) and the mouth (i.e., thirst and mucous wetness) can provide important information for diagnosing dehydration.
Summary:
We conclude that clinical observations based on a combination of history, physical examination, laboratory values, and clinician experience remain the best approach to the diagnosis of dehydration.
... This occurs following excessive sweating (following exercise, fever or high environmental temperatures), insufficient oral hydration or osmotic diuresis secondary to glycosuria or mannitol. 7,8 In these circumstances, serum osmolality will usually exceed 300 mmol/kg and serum sodium will usually exceed 145 mmol/L. 6 In the elderly, the aetiology of dehydration is generally multifactorial: reduced patient access to fluid, lower intake of fluids, decreased sensation of thirst and hormonal resistance within the reninangiotensin-aldosterone system (RAAS), each play a role. ...
Variation in systemic hydration status, namely chronic systemic hypohydration or dehydration, can influence the development of several chronic non-ophthalmic diseases. Owing to the eye's high water content and unique system of fluid regulation, we hypothesised that hydration status may affect the eye in health and disease states. Therefore, we performed a systematic review of the current evidence implicating changes in hydration and their association with ocular physiology and morphological characteristics. We also reviewed relevant clinical correlations of changes in hydration and major common eye diseases. Our findings suggest systemic hydration status broadly affects a variety of ocular pathophysiologic processes and disease states. For example, dehydration may be associated with development of dry eye syndrome, cataract, refractive changes and retinal vascular disease. On the other hand, excessive hydration is associated with some ocular diseases. Tear fluid osmolarity may be an effective marker of systemic hydration status. Recent studies implicate chronic renin-angiotensin-aldosterone system activation in the pathogenesis of diabetic retinopathy and glaucoma but also suggest its antagonism may be a useful therapeutic target. Our findings indicate that assessment of hydration status may be an important consideration in the management of patients with chronic eye diseases and undergoing eye surgery. Further research investigating the role of acute and chronic changes in hydration in individuals with and without ocular disease is warranted.
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... A novel approach to measure changes in hydration status is through the use of human tears, specifically the measurement of tear fluid osmolarity (T osm ) (Fortes et al. 2011;Sollanek et al. 2012). Lacrimal gland fluid, consisting of water, electrolytes, protein, and mucin (Dartt 2009), is secreted into the tear film and represents an ultra-filtrate of the plasma (Mircheff 1989). ...
... Lacrimal gland fluid, consisting of water, electrolytes, protein, and mucin (Dartt 2009), is secreted into the tear film and represents an ultra-filtrate of the plasma (Mircheff 1989). T osm is reportedly isotonic with the plasma (Rolando and Zierhut 2001); therefore, it has been hypothesized that a progressive increase in P osm during exercise/heat-induced dehydration would be reflected in T osm (Sollanek et al. 2012). Traditionally, tear collection techniques such as glass capillary tubes and Schirmer paper were cumbersome, invasive, and required expertise (Esmaeelpour et al. 2008;Posa et al. 2013). ...
... The exact mechanism for the association of changes in T osm with changes in hydration status is unclear, but others have proposed potential mechanisms (see Sollanek et al. 2012 for review). Dehydration may decrease tear flow rate from the lacrimal gland, which in turn has been associated with increases in T osm , possibly due to the increased time for ductal water re-absorption. ...
To determine if tear fluid osmolarity (Tosm) can track changes in hydration status during exercise and post-exercise rehydration.
Nineteen male athletes (18-37 years, 74.6 ± 7.9 kg) completed two randomized, counterbalanced trials; cycling (~95 min) with water intake to replace fluid losses or water restriction to progressively dehydrate to 3 % body mass loss (BML). After exercise, subjects drank water to maintain body mass (water intake trials) or progressively rehydrate to pre-exercise body mass (water restriction trials) over a 90-min recovery period. Plasma osmolality (Posm) and Tosm measurements (mean of right and left eyes) were taken pre-exercise, during rest periods between exercise bouts corresponding to 1, 2, and 3 % BML, and rehydration at 2, 1, and 0 % BML.
During exercise mean (± SD) Tosm was significantly higher in water restriction vs. water intake trials at 1 % BML (299 ± 9 vs. 293 ± 9 mmol/L), 2 % BML (301 ± 9 vs. 294 ± 9 mmol/L), and 3 % BML (302 ± 9 vs. 292 ± 8 mmol/L). Mean Tosm progressively decreased during post-exercise rehydration and was not different between trials at 1 % BML (291 ± 8 vs. 290 ± 7 mmol/L) and 0 % BML (288 ± 7 vs. 289 ± 8 mmol/L). Mean Tosm tracked changes in hydration status similar to that of mean Posm; however, the individual responses in Tosm to water restriction and water intake was considerably more variable than that of Posm.
Tosm is a valid indicator of changes in hydration status when looking at the group mean; however, large differences among subjects in the Tosm response to hydration changes limit its validity for individual recommendations.
