-
[show abstract]
[hide abstract]
ABSTRACT: The effects of radiofrequency electromagnetic fields (RF-EMF) on the control of body energy balance in developing organisms have not been studied, despite the involvement of energy status in vital physiological functions. We examined the effects of chronic RF-EMF exposure (900 MHz, 1 V m(-1)) on the main functions involved in body energy homeostasis (feeding behaviour, sleep and thermoregulatory processes). Thirteen juvenile male Wistar rats were exposed to continuous RF-EMF for 5 weeks at 24 °C of air temperature (T (a)) and compared with 11 non-exposed animals. Hence, at the beginning of the 6th week of exposure, the functions were recorded at T (a) of 24 °C and then at 31 °C. We showed that the frequency of rapid eye movement sleep episodes was greater in the RF-EMF-exposed group, independently of T (a) (+42.1 % at 24 °C and +31.6 % at 31 °C). The other effects of RF-EMF exposure on several sleep parameters were dependent on T (a). At 31 °C, RF-EMF-exposed animals had a significantly lower subcutaneous tail temperature (-1.21 °C) than controls at all sleep stages; this suggested peripheral vasoconstriction, which was confirmed in an experiment with the vasodilatator prazosin. Exposure to RF-EMF also increased daytime food intake (+0.22 g h(-1)). Most of the observed effects of RF-EMF exposure were dependent on T (a). Exposure to RF-EMF appears to modify the functioning of vasomotor tone by acting peripherally through α-adrenoceptors. The elicited vasoconstriction may restrict body cooling, whereas energy intake increases. Our results show that RF-EMF exposure can induce energy-saving processes without strongly disturbing the overall sleep pattern.
Environmental Science and Pollution Research 11/2012; · 2.65 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In closed incubators, radiative heat loss (R) which is assessed from the mean radiant temperature (Tr) accounts for 40-60% of the neonate's total heat loss. In the absence of a benchmark method to calculate Tr--often considered to be the same as the air incubator temperature-errors could have a considerable impact on the thermal management of neonates. We compared Tr using two conventional methods (measurement with a black-globe thermometer and a radiative "view factor" approach) and two methods based on nude thermal manikins (a simple, schematic design from Wheldon and a multisegment, anthropometric device developed in our laboratory). By taking the Tr estimations for each method, we calculated metabolic heat production values by partitional calorimetry and then compared them with the values calculated from V(O2) and V(CO2) measured in 13 preterm neonates. Comparisons between the calculated and measured metabolic heat production values showed that the two conventional methods and Wheldon's manikin underestimated R, whereas when using the anthropomorphic thermal manikin, the simulated versus clinical difference was not statistically significant. In conclusion, there is a need for a safety standard for measuring TR in a closed incubator. This standard should also make available estimating equations for all avenues of the neonate's heat exchange considering the metabolic heat production and the modifying influence of the thermal insulation provided by the diaper and by the mattress. Although thermal manikins appear to be particularly appropriate for measuring Tr, the current lack of standardized procedures limits their widespread use.
Arbeitsphysiologie 12/2011; 112(8):2957-68. · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Given the liver's importance in controlling metabolic homeostasis in mammals, we sought to establish (i) whether the thermal status of this organ was involved in the link between sleep, thermoregulation and food intake and (ii) how the hypothalamic structures affect the functional interactions between processes involved in regulation of the body's energy balance. In 10 freely moving rats, the liver was heated artificially to and maintained at set-point temperatures of 39.5, 40.0 and 40.5 °C for 4 h. Each animal's feeding activity, cortical temperature and brown adipose tissue (T(BAT) ) temperature were measured continuously. Sleep organization and wakefulness were scored from electroencephalograms. Each animal served as its own control. Heating the liver induced a decrease in food intake and T(BAT) , corresponding to the development of a hypometabolic hypothermic status. The total amounts of wakefulness and rapid eye movement sleep fell, whereas the total amount of slow wave sleep increased accordingly. Our findings show that the liver is involved significantly in the body's thermodynamic equilibrium. The organ's thermal status can induce well-coordinated behavioural and autonomic adaptive responses involved in the control of food intake and in the maintenance of body homeothermia. Our study provides indirect evidence of the existence of hepatic thermosensors afferent to feeding and sleeping hypothalamic integrating centres that can be stimulated by physiological increases in liver temperature.
Journal of Sleep Research 10/2011; 21(2):204-11. · 3.16 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Maternal smoking during pregnancy is associated with adverse perinatal outcomes. In view of concerns about underreporting, benzo[a]pyrene (B[a]P)-DNA adducts could be used to provide information about long-term in utero exposure to smoking but have not previously been used with samples from neonates. This study aimed to verify whether B[a]P-DNA adducts could accurately assess tobacco smoke exposure during fetal life. The objectives were to correlate B[a]P-DNA adduct levels with active maternal and passive smoking and to determine the sensitivity and specificity of smoking and nonsmoking status by comparing neonatal B[a]P-DNA adduct levels with those of maternal self-reports.
B[a]P-DNA adducts in neonatal buccal cell samples were determined by a competitive immunoassay. Three groups of neonates were constituted according to maternal self-reported smoking status during pregnancy: nonsmokers (n=25; control group), <10 cigarettes per day (n=18; S- group), or >10 cigarettes per day (n=21; S+ group).
The mean B[a]P-DNA adduct level rose significantly when comparing the controls with the S- and S+ groups. Maternal active smoking had the strongest effect on B[a]P-DNA adduct levels in neonates. A cross analysis between B[a]P-DNA adduct levels and maternal self-reported levels revealed high sensitivity and specificity.
This preliminary study suggests that B[a]P-DNA adducts are reliable biomarkers for the screening of long-term in utero exposure to smoking and are accurate when compared with maternal self-reported levels of active smoking. Detection of B[a]P-DNA adducts in neonates could provide a useful, noninvasive tool in clinical risk assessment studies but would benefit from further confirmation with another validated biomarker.
Therapeutic drug monitoring 06/2011; 33(3):329-35. · 2.43 Impact Factor
-
Handbook of Clinical Neurology 01/2011; 98:215-27.
-
[show abstract]
[hide abstract]
ABSTRACT: Wrapping low-birth-weight neonates in a plastic bag prevents body heat loss. A bonnet can also be used, since large amounts of heat can be lost from the head region, but may provide too much thermal insulation, thus increasing the risk of overheating. We assessed the time required to reach warning body temperature (t38 degrees C), heat stroke (t40 degrees C), or extreme value (t43 degrees C) in a mathematical model that involved calculating various local body heat losses. Simulated heat exchanges were based on body surface temperature distribution measured in preterm neonates exposed to 33 degrees C air temperature (relative air humidity: 35%; air velocity: <0.1 m/s) and covered (torso and limbs) or not with a transparent plastic bag. We also compared metabolic heat production with body heat losses when a bonnet (2 or 3.5 mm thick) covered 10%, 40%, or 100% of the head. Wrapping neonates in a bag (combined or not with a bonnet) does not induce a critical situation as long as metabolic heat production does not increase. When endogenous heat production rises, t38 degrees C ranged between 75 and 287, t40 degrees C between 185 and 549, and t43 degrees C between 287 and 702 min. When this increase was accompanied by a fall in skin temperature, overheating risk was accentuated (37<or=t38 degrees C<or=45; 99<or=t40 degrees C<or=117; 169<or=t43 degrees C<or=194 min). Thus plastic bag and bonnet may result in hyperthermia but only when metabolic heat production rises while skin temperature falls (impeding body heat losses), as can sometimes happen with fever.
Journal of Applied Physiology 03/2010; 108(6):1674-81. · 3.75 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We aimed to assess the involvement of peripheral chemoreceptor tonic activity in the ventilatory pattern during sleep in preterm neonates exposed in utero to maternal smoking.
Peripheral chemoreceptor activity was measured at thermoneutrality in neonates (postmenstrual age: 36.1 +/- 1.2 weeks) born to nonsmoking (n = 21) or smoking (n = 16) mothers by performing a 30-second hyperoxic test during active and quiet sleep. Blood oxygen saturation, baseline ventilatory parameters, and central apnea were monitored.
Prenatal smoking exposure did not modify baseline ventilation. It was interesting to note that prenatal smoking exposure decreased the peripheral chemoreceptor tonic activity during active sleep and increased the response time during quiet sleep. These changes could explain the increase in the time spent in apnea (both with and without blood oxygen desaturation) and in the mean duration of apneic episodes with desaturation found in neonates exposed to smoking in utero. The involvement of a change in the chemoreceptor function is supported by the fact that the peripheral chemoreceptor tonic activity was negatively correlated with the mean duration of apneic episodes with desaturation in the control group only.
To our knowledge, this is the first study to reveal that prenatal smoking exposure does not directly modify baseline ventilatory parameters in the neonate but has a negative impact on peripheral chemoreceptor tonic activity. These alterations may increase the risk of sleep respiratory disorders, especially via apnea with desaturation.
PEDIATRICS 02/2010; 125(3):e592-9. · 4.47 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In utero exposure to smoking is known to adversely affect brain regions involved in behavioral state organization and could therefore interact with the neurophysiological development of neonates.
The present study investigated the effects of prenatal smoking exposure on sleep patterns in the preterm neonate.
Overnight sleep patterns were polysomnographically assessed at thermoneutrality. Sleep continuity and structure were scored for the respective frequencies, durations and percentages of active, quiet, and indeterminate sleep and wakefulness after sleep onset. The number and duration of body movements were also analyzed.
The neonatal intensive care unit at Amiens University Medical Center (France).
Healthy preterm neonates (postconceptional age: 33.9 +/- 6.0 weeks) were enrolled according to whether their mothers had not smoked at all during pregnancy (control group, n=19), smoked less during pregnancy (low-smoking group, Slow, n=10), or smoked more (heavy-smoking group, Sheavy n=10) than 10 cigarettes per day throughout pregnancy.
Neonates born to heavy-smoking mothers had a significantly lower mean birth weight than controls (-21%) and displayed disrupted sleep structure and continuity: they slept less overall (with a higher proportion of active sleep and a lower proportion of quiet sleep) and had more wakefulness after sleep onset. Compared with controls, neonates from both smoking groups displayed more body movements and, as a result, more disturbed sleep.
High prenatal smoking exposure modifies sleep patterns in preterm neonates by disrupting sleep organization and increasing nocturnal body movements. These findings raise the question of the repercussions of these sleep disturbances (at what is a critical stage in brain development) on the child's physiological and neurobehavioral outcomes.
Sleep 01/2009; 31(12):1683-9. · 5.05 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Apneic episodes are frequent in the preterm neonate and particularly in active sleep (AS), when functional residual capacity (FRC) can be decreased. Furthermore, FRC may be inversely correlated with the speed of blood-O(2)-desaturation. We evaluated the potential involvement of FRC in the mechanisms responsible for blood-O(2)-desaturation during short central apneic events (>3 s) in "late-preterm" infants and analyzed the specific influence of sleep state. Apneic events were scored in 29 neonates (postmenstrual age: 36.1 +/- 1.2 wk) during AS and quiet sleep (QS). FRC was measured during well-established periods of regular breathing. Apneas with blood-O(2)-desaturation (drop in SpO(2) >5% from the baseline, lowest SpO(2) during apnea: 91.4 +/- 1.8%) were more frequent in AS than in QS, whereas no difference was seen for apneas without desaturation. The magnitude of the FRC did not depend on the sleep state. In AS only, there was a negative relationship between FRC and the proportion of apneas with desaturation. Even in late preterm infants who do not experience long-lasting apnea, blood-O(2)-desaturation during short apneic events is related (in AS but not QS) to a low baseline FRC. Sleep stage differences argue for a major role of AS-related mechanisms in the occurrence of these apneas.
Pediatric Research 05/2008; 64(2):171-6. · 2.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The incidence of apnea in neonates depends on a number of factors, including sleep state and thermoregulation.
To assess the role of thermal drive (body heat loss [BHL]) in the mechanisms underlying short episodes of central apnea during active and quiet sleep in neonates.
Twenty-two neonates (postconceptional age: 36.3 +/- 0.9 weeks) were exposed at thermoneutral (incubator temperature: 32.5 degrees C), warm (34.2 degrees C), and cool (30.4 degrees C) conditions during 3 consecutive morning naps. Oxygen consumption (VO2), skin and rectal temperatures, and central apnea were scored during active sleep and quiet sleep. The thermal drive was expressed as BHL calculated using indirect partitional calorimetry.
As expected, apnea occurred more frequently in active sleep than in quiet sleep (P < 0.001). The frequency of apnea in active sleep was higher in the warm condition (P < 0.05). In contrast, apnea episodes were less frequent (P < 0.05) and shorter (P < 0.05) for cool exposure, during which VO2 and rectal temperature increased. The frequency (P < 0.001, r2 = 0.31), mean (P < 0.05, r2 = 0.06), and maximum (P < 0.001, r2 = 0.19) durations of apnea were correlated with the BHL: the greater the BHL (body cooling), the less frequent and the shorter the apnea episodes. In contrast, no relationship between apnea and mean skin or rectal temperature was observed.
Apneic events were more closely related to BHL than to body temperatures. In cool exposure, the decreases in the duration and frequency of apneic episodes suggest that these events depend on the metabolic drive (which is proportional to energy expenditure).
Sleep 04/2008; 31(4):549-56. · 5.05 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present here a new, dedicated mechanical device for monitoring quick-release movements of the wrist. The ergometer was designed to easily assess musculotendinous properties during wrist flexion. Maximal voluntary contractions (MVC) and quick-release (QR) movements during wrist flexion were performed on 14 subjects. A validation of the ergometer, using a test-retest methodology, was performed to assess its reliability and sensitivity. The device has been technically and biomechanically validated in a range of situations, including inertia measurement (mean inertia was found 0.0119+/-0.0012 N m s(2) rad(-1)) and appearance of the unloading reflex. Our results indicate that the device provides highly reliable, sensitive evaluation of wrist muscle stiffness (intraclass correlation coefficient for inertia, maximal voluntary contraction and stiffness index were 0.873, 0.994 and 0.930, respectively). Its portability facilitates measurement of the influence of repetitive, occupational activity on the musculotendinous complex of the wrist flexors.
Journal of Electromyography and Kinesiology 03/2008; 18(1):160-8. · 1.97 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The aim of the present study was to validate the measurement of metabolic heat production using partitional calorimetry (PC) in preterm neonates exposed to a near-thermoneutral environment in an incubator. In order to reduce experimental uncertainty (due to the different variables involved in the calculation of body heat exchanges between the infant and the environment), the mean radiant temperature and the heat transfer coefficients for convection, radiation and evaporation were measured using a multisegment, anthropometric thermal mannequin which represents a small-for-gestational-age neonate (body surface area: 0.150 m2; simulated birth weight: 1500 g). The metabolic heat production calculated by PC was compared with the results of indirect respiratory calorimetry, which is rarely done in clinical setting since this method interferes with the neonate's environment and requires a high degree of technical preparedness. The oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured in 20 preterm neonates exposed to thermoneutral (32.3 degrees C) and to slightly cool environments (30.2 degrees C). The mean skin temperature was measured by infrared thermography. The measurements were made during well-established periods of active and quiet sleep. Metabolic heat production was assessed by weighting each value of VO2 and VCO2 by the duration of the sleep stages. Our results showed that there was no significant difference between the two methods in terms of their estimation of metabolic activity at thermoneutrality (mean overall difference: 0.34 kJ h(-1) kg(-1)) and in the cool environment (0.26 kJ h(-1) kg(-1)). We observed significant interneonate variability. Partitional calorimetry enabled the prediction of body growth with a daily error of less than 5.3 g (2.38 kJ h(-1) kg(-1)) for all the neonates at thermoneutrality and for 85% of the subjects (3.03 kJ h(-1) kg(-1)) in the cool environment. Despite this limitation, we demonstrate here that PC provides reliable information for calculating the energy expenditure of individual preterm neonates on the basis of standard environmental input variables. We suggest that the technique can be advantageously used to assess the energy expenditure and normal growth of these infants.
Medical Physics 02/2008; 35(1):89-100. · 2.83 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Chemoreception is frequently involved in the processes underlying apnea in premature infants. Apnea could result from a decrease in carotid body effectiveness. However, increased carotid body activity could also initiate apnea through hypocapnia following hyperventilation when the receptors are stimulated. The aim of this study was to analyze the relationship between carotid body effectiveness and short apneic episodes in older preterm neonates. Carotid body effectiveness was assessed at thermoneutrality in 36 premature neonates (2.07 +/- 0.26 kg) by performing a 30-s hyperoxic test during sleep, the oxygen inhalation involving a ventilation decrease. Blood O(2) saturation (Sp(o2)) and ventilatory parameters were monitored before and during the hyperoxic test. Short episodes of apnea (frequency and mean duration) were recorded during the morning's 3-h interfeeding interval. Pretest Sp(o2) was not related to any of the measured respiratory parameters. A higher frequency of short apneic episodes was linked to a greater ventilation decrease in response to the hyperoxic test (rho = -0.32; p = 0.01). Increased carotid body response is correlated with greater apneic episodes frequency, even in the absence of concomitant oxygen desaturation. Fetal or early postnatal hypoxemia could have increased peripheral chemoreceptor activity, which could initiate a "overshoot/undershoot" situation, which in turn could induce a critical P(o2)/P(co2) combination and apnea.
Pediatric Research 12/2007; 62(5):591-6. · 2.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We assessed the relationship between a high-fat (HF) diet and central apnea during rapid eye movement and non-rapid eye movement sleep stages by recording ventilatory parameters in 28 non-obese rats in which insulin resistance had been induced by an HF diet. We also studied whether metformin (an anti-hyperglycemic drug frequently used to treat insulin resistance) could reverse sleep apnea or prevent its occurrence in this experimental paradigm.
Rats were fed with a standard diet (10 rats), an HF diet (8 rats), or an HF diet concomitantly with metformin treatment (10 rats). Each animal was instrumented for electroencephalographic and electromyographic recording. After 3 weeks, ventilatory parameters during sleep were recorded with a body plethysmograph. All rats were treated with metformin for 1 week, after which time the ventilatory measurements were measured again.
Our results showed that the three groups of animals did not differ in terms of body growth over the entire experimental period. The HF diet did not modify sleep structure or minute ventilation in the different sleep stages. A great increase (+266 +/- 48%) in central apnea frequency was observed in insulin-resistant rats. This was explained by an increase in both post-sigh (+195 +/- 35%) and spontaneous apnea (+437 +/- 65%) in the different sleep stages. These increases were suppressed by metformin treatment.
Insulin resistance induced by the HF diet could be the promoter of sleep apnea in non-obese rats. Metformin is an efficient curative and preventive treatment for sleep apnea, suggesting that insulin resistance modifies the ventilatory drive independently of obesity.
Obesity 07/2007; 15(6):1409-18. · 4.28 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Objective: We assessed the relationship between a high-fat (HF) diet and central apnea during rapid eye movement and non-rapid eye movement sleep stages by recording ventilatory parameters in 28 non-obese rats in which insulin resistance had been induced by an HF diet. We also studied whether metformin (an anti-hyperglycemic drug frequently used to treat insulin resistance) could reverse sleep apnea or prevent its occurrence in this experimental paradigm.Research Methods and Procedures: Rats were fed with a standard diet (10 rats), an HF diet (8 rats), or an HF diet concomitantly with metformin treatment (10 rats). Each animal was instrumented for electroencephalographic and electromyographic recording. After 3 weeks, ventilatory parameters during sleep were recorded with a body plethysmograph. All rats were treated with metformin for 1 week, after which time the ventilatory measurements were measured again.Results: Our results showed that the three groups of animals did not differ in terms of body growth over the entire experimental period. The HF diet did not modify sleep structure or minute ventilation in the different sleep stages. A great increase (+266 48%
) in central apnea frequency was observed in insulin-resistant rats. This was explained by an increase in both post-sigh (+195 35%
) and spontaneous apnea (+437 65%
) in the different sleep stages. These increases were suppressed by metformin treatment.Discussion: Insulin resistance induced by the HF diet could be the promoter of sleep apnea in non-obese rats. Metformin is an efficient curative and preventive treatment for sleep apnea, suggesting that insulin resistance modifies the ventilatory drive independently of obesity.Keywords: respiratory, sleep disorders, insulin resistance, high-fat diet
Obesity 05/2007; 15(6):1409-1418. · 4.28 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Arousal from sleep can be a protective response to life-threatening stimuli. Hence, faults within state-switching processes may lead to fatal events. To investigate the role of the nervous system during cardiac failure triggered by phasic, vagally mediated stimulation, we analysed autonomic and behavioural reactions in 50 premature neonates during quiet sleep (QS) -- a sleep state characterized by a preponderance of tonic, parasympathetic activity. Bradycardia was induced with a standardized ocular compression test. Neither awakening nor behavioural escape reactions were observed during or after an episode of bradycardia. Eighty-six per cent of the provoked bradycardic episodes induced central apnoea. During QS, the neonates' respiratory response and arousability were found to be time-dependent: when the test was performed early in the QS episode, apnoea was more frequent (94%), and no sleep state change occurred. When ocular compression was performed in the later part of the QS episode, a transition towards active sleep was observed, together with significantly fewer episodes of apnoea (64%). These results indicate that a progressive decrease in the respiratory system's responsiveness to phasic, parasympathetic stimulation occurs during QS, whereas arousability increases. Our study suggests that newborns could be more vulnerable to potentially fatal events during the initial portion of a QS episode.
Journal of Sleep Research 07/2006; 15(2):167-73. · 3.16 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We investigated the effects of diabetes on the spontaneous motor activities (SMA) of streptozotocin-treated rats fed a high-fat diet (HFD), a new nonobese model of type 2 diabetes. The daily changes in the duration of SMA were assessed via infrared cells, which detected all movements of rats that had been fed for 3 weeks with a standard or HFD and then injected with vehicle or 50 mg/kg of streptozotocin. Five to six days after streptozotocin injection, the daily body weight and the levels of duration of SMA of the diabetic rats were depressed, manifest by a substantial decline in the frequency of occurrence of nocturnal SMA episodes. The dramatic depression of daily duration of SMA levels observed in the rats given a HFD and treated with streptozotocin appears to be related solely to the diabetic state and not to body weight and/or HFD consumption, since the HFD (and/or related metabolic effects) remained ineffective in altering this feature in rats that grow normally. By thoroughly separating the prediabetic and the diabetic phases, we have been able to more readily explore the deleterious effects of the stages of both of these phases on changes in daily SMA levels.
Physiology & Behavior 05/2006; 87(4):765-72. · 2.87 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To assess the various heat exchanges with the environment a multisegment, anthropometric, thermal mannequin representing a neonate with a birth weight of 900 g has been designed. The mannequin simulates not only dry heat loss (radiative+conductive+convective body heat exchanges) but also the evaporative skin water loss which can be encountered in low-birth-weight neonates. The model was placed in the supine or prone position in a closed incubator (air temperature, 33 C; relative air humidity, 50%; air velocity below 0.1 m s(-1)). Experiments were performed with the mannequin either naked or wrapped in a flexible, plastic bag (with the head exposed) used to prevent excessive body water loss at delivery and during the following hours About 30% of the model's total surface was wetted with water. Our results demonstrated that body position does not modify dry and evaporative heat losses, whatever the experimental conditions. The plastic bag acts rapidly and reduces total heat loss by 30% to 34%, primarily through a reduction in evaporative water loss (between 5.4 and 6.7 g kg(-1) h(-1)). When the bag is present, the uncovered surface of the head accounts for about 50% of the total heat loss. This simple and inexpensive solution can be used to prevent thermal stress and dehydration in very small premature neonates.
Medical Physics 04/2006; 33(3):637-44. · 2.83 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In human adults, experimental assessment of the evaporative heat loss coefficient (h(e)) requires a fully wetted skin surface area implying exposure to severe heat stress. For ethical reasons, this type of experimental situation is impossible to perform on neonates. The aim of the present study was to assess h(e) values in clinical situations for the body as a whole and for the different body segments, in particular, in natural and forced convection and using an anthropomorphic, sweating, thermal mannequin to represent a very small premature neonate (body mass 900 g). Skin hydration (i.e., simulated sweating) was performed by two electronic pumping systems, providing a steady adjustable flow of water to the mannequin surface. Experiments were carried out in a closed-incubator heated to air temperatures of 33 degrees C and 36 degrees C, with air velocities (Va) ranging from 0.01 to 0.7 m s(-1), and with four levels of air relative humidity (40, 50, 60, and 80%). For the body as a whole, h(e)=7 W m(-2) mb(-1) in natural convection, whereas in forced convection h(e) was 11.7, 12.4, and 14.1 W m(-2) mb(-1) for air velocities of 0.2, 0.4, and 0.7 m s(-1), respectively. As far as local h(e) is concerned, our results showed that the relative values of regional water loss in forced convection differ greatly from those observed under still air conditions. Thus, increasing air velocity enhances the heterogeneity in regional skin cooling, which may contribute to the neonate's thermal discomfort.
Medical Physics 04/2005; 32(3):752-8. · 2.83 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This study assessed the relative efficiency of different warming devices (surgical sheets covering the body and a tubegauze on the head, forced-air warming, warming mattress) commonly used to prevent body hypothermia during neonatal surgery. Dry heat losses were measured from a thermal manikin, which simulated a low-birth-weight neonate of 1,800 g. The manikin's surface temperatures (35.8 degrees C) corresponded to those of neonates nursed in closed incubators. Experiments were performed in a climatic chamber at an ambient temperature of 30 degrees C, as commonly found in operating theatres. The supine manikin was naked or covered with operative sheets with a 5x5 cm aperture over the abdomen. Its head could be covered by a tube-gauze. Additional warming was provided by conduction through a warming mattress (surface temperature, 39 degrees C) and/or by convection (Bair Hugger, forced-air temperature 38 degrees C). Covering the manikin with surgical sheets decreased the dry heat loss by 10.4 W. Additional forced-air warming was more efficient than the warming mattress to reduce the total dry heat loss (6.8 W vs 2.1 W). Heat losses were reduced by 7.9 W when combining the warming mattress and Bair Hugger. The heat loss from the head of the covered manikin was reduced from 4.5 W to 3.9 W when the head was covered with the tubegauze. Our data indicate that forced-air warming is more effective than conductive warming in preventing neonatal hypothermia during abdominal operations.
Arbeitsphysiologie 10/2004; 92(6):694-7. · 2.15 Impact Factor
