Heart rate variability and electrocardiogram waveform as predictors of morbidity during hypothermia and rewarming in rats.

This study examined electrocardiogram (ECG) waveform, heart rate (HR), mean blood pressure (BP), and HR variability as potential autonomic signatures of hypothermia and rewarming. Adult male Sprague-Dawley rats had telemetry transmitters surgically implanted, and 2 weeks were allowed for recovery prior to induction of hypothermia. Rats were lightly anesthetized (sodium pentobarbital, 35 mg/kg i.p.) and placed in a coil of copper tubing through which temperature-controlled water was circulated. Animals were cooled to a core temperature (Tc) of 20 degrees C, maintained there for 30 min, and then rewarmed. Data (Tc, BP, HR from ECG, and 10-s strips of ECG waveforms) were collected every 5 min throughout hypothermia and rewarming. Both HR and BP declined after initial increases with the drop in HR starting at a higher Tc than the drop in BP (29.6 +/- 2.4 degrees C vs. 27.1 +/- 3.3 degrees C, p < 0.05). Animals that were not successfully rewarmed exhibited a significant (p < 0.05) increase in the normalized standard deviation of interbeat intervals (IBI) throughout cooling compared with animals that were successfully rewarmed. The T wave of the ECG increased in amplitude and area with decreasing Tc. T-wave amplitude and IBI variability show potential as predictors of survival in hypothermic victims.

Treatment of hyperthermia-induced extravasation with hypertonic saline (7.5%) in 6% dextran 70 (HSD) in Wistar/Furth rats.

This study determined the effectiveness of hypertonic saline (7.5%) in 6% Dextran 70 (HSD) in reducing hyperthermia-induced extravasation in Wistar/Furth (WF) rats and compared this extravasation with that previously reported in Sprague-Dawley (SD) rats. Wistar/Furth rats (male, n = 12/group, 300-325 g) were placed unrestrained in a chamber (41.5 degrees C) until a core temperature (Tc) of 42.6 degrees C was attained. Immediately following heat exposure, HSD or normal saline (4 mL/kg) was administered via jugular catheter, followed 15 min later by Evan's blue (Eb, 25 mg/kg) in normal saline. After another 15-min interval, animals were anesthetized, exsanguinated, tissues removed and washed in normal saline, and Eb was extracted with formamide. Another group of normothermic WF rats were also given Eb and had tissues harvested. Comparisons were made to extravasation in normothermic and hyperthermic SD rats. In hyperthermic SD rats, Eb content increased significantly in liver, kidney, and intestinal tissues. In hyperthermic WF rats compared to normothermic WF rats, Eb content of kidney and spleen was increased; however, Eb content of heart, skeletal muscle, and intestine was significantly decreased. HSD-treated WF rats had increased extravasation in intestinal tissue compared to that of saline-treated rats. However, HSD treatment resulted in significant decreases in wet weight/dry weight ratios of heart (4.34 +/- 0.10 versus 4.51 +/- 0.11) and skeletal muscle tissue (3.78 +/- 0.08 versus 3.91 +/- 0.08). Findings of this study indicate that HSD did not prevent the hyperthermia-induced extravasation of Eb in kidney and spleen; that the increase in plasma volume following HSD administration is most likely due to the movement of fluid into the vasculature from the skeletal muscle mass; and that the WF strain may have limited value for the study of extravasation.

Flunarizine pretreatment attenuates hyperthermia-induced extravasation in rats.

Previous work has established that there is an increase in endothelial permeability in hyperthermic rats. This work assessed the potential of the calcium channel blocker (E)-1-bis(4-fluorophenyl)methyl-4-(3-phenyl-2-propenyl)piperazine dihydrochloride (flunarizine) as a pretreatment to ameliorate this extravasation. Five groups of male rats (n=12 rats per group, 400-500 g) were given 0, 0.3, 1, 2, or 3 mg/kg flunarizine (FL0, FL0.3, FL1, FL2, and FL3, respectively) by gavage 30 min prior to induction of hyperthermia. Hyperthermia was achieved by placing unrestrained animals in their own cages in a chamber maintained at 41.5 degrees C until a core temperature (Tc) of 42.6 degrees C was attained. Then, 25 mg/kg of Evans blue in saline was administered via a jugular cannula. After 15 min the animals were anesthetized, exsanguinated, tissues removed and washed in saline, and Evans blue extracted with formamide. As the dose of flunarizine was increased, there was a significant (P<0.05) reduction of Evans blue recovered from the liver, kidney, lung, spleen, and intestinal tissue. Endurance time in the heat to reach a Tc of 42.6 degrees C increased significantly from 194+/-39 min (mean+/-SD) with FL0 to 275+/-33 min with FL1, but decreased again with FL2 (206+/-42) and FL3 (199+/-60). Thus, flunarizine pretreatment attenuated hyperthermia-induced extravasation, and 1 mg/kg flunarizine markedly increased the tolerance time to heat exposure.

Flow cytometric method using fluorescent microspheres to measure reticuloendothelial function or particulate translocation.

The reticuloendothelial system (RES) influences the outcome of vascular shock and environmental stress. We describe a procedure that employs flow cytometry and 1 microm fluorescent microspheres (FM) to study RES function. FM (2 x 10(10) beads/kg) were administered via a jugular cannula in Sprague-Dawley rats. After 15 min, blood and tissues were collected and digested in 15% KOH. Phycoerythrin 1 microm beads were added to each sample as an internal standard and analyzed by flow cytometry. FM were preferentially cleared by the spleen, liver and lung. Clearance was confirmed by fluorescent photomicroscopy. Addition of the internal standard to determine accurately aspiration volume enhanced precision. This procedure offers advantages over other RES clearance methods including bacterial, radioactive or carbon clearance assays. Moreover, this method could enhance accuracy, reproducibility and speed of data collection in particulate transport studies that are based on manual microscopic scanning and FM counting.

Effects of almitrine bismesylate in a microswine model of hypoxemic hypothermia.

We have developed an anesthetized microswine model of hypoxemic hypothermia and rewarming for testing prophylaxes and treatments. The respiratory stimulant almitrine bismesylate (ALM) was considered as a potential field expedient therapy for hypoxemic hypothermia. Preliminary experiments demonstrated that five consecutive 100 micrograms.kg-1 ALM intravenous (i.v.) doses given to normothermic microswine 3-4 min apart increased minute ventilation from an average of 3.4 L.min-1 to 4.5 L.min-1 (n = 2). However, when either a single i.v. ALM dose of 150 micrograms.kg-1 (n = 1) or three consecutive 100 micrograms.kg-1 i.v. doses given 15 min apart (n = 1) to hypoxemic hypothermic microswine with a mean esophageal temperature (Tes) = 28.8 degrees C, and a mean arterial O2 partial pressure (PaO2) = 49 mmHg, the hypoxemia was potentiated (mean PaO2 = 32 mmHg) and respiratory arrest ensued. Other experiments using continuous ALM i.v. infusion (1.0 microgram.kg-1.min-1) in hypoxemic hypothermic microswine (n = 6, Tes = 30.6 +/- 0.5, PaO2 = 55.4 +/- 12.9) did not demonstrate significant (p < or = 0.05) cardiorespiratory differences (ventilation, heart rate, blood pressure, blood gases) when compared to hypoxemic hypothermic controls (n = 6, Tes = 30.7 +/- 0.5, PaO2 = 53.3 +/- 13.6). These results suggest that high dose i.v. bolus administration of ALM is not indicated as a potential field expedient therapy for hypoxemic hypothermia, while further work is required to assess the potential efficacy of other continuous low dose i.v. infusion regimens.

A miniswine model of acute exertional heat exhaustion.

METHOD: We examined the thermoregulatory and hemodynamic responses of 12 miniswine (31 +/- 3.9 kg) during 25-30 min of treadmill exercise (5.4 km.h-1, 5% grade) under cool (10 degrees C), moderate (20 degrees C) and warm (30 degrees C) ambient temperature (Ta) conditions. RESULTS: Within 15-20 min of exercise at Ta = 30 degrees C, the miniswine demonstrated significant hyperventilation, hypersalivation, and unsteady gait. Exercise-heat endurance time (T) at Ta = 30 degrees C decreased by 35% and 40% in comparison to T at Ta = 20 degrees C and 10 degrees C, respectively. This resulted from a significant rise in heat strain (S)-defined as the rate of change in rectal temperature. Averaged throughout exercise, S increased from 0.04 +/- 0.01 degree C.min-1 and 0.05 +/- 0.02 degree C.min-1 at Ta = 10 degrees C and 20 degrees C, respectively, to 0.10 +/- 0.03 degree C.min-1 at Ta = 30 degrees C. Due to the comparatively large storage capacity of the porcine spleen relative to humans, splenectomized miniswine were used. This permitted calculation of percentage changes in plasma volume (% delta PVc) from hematocrit (HCT) and hemoglobin (HGB) without the confounding effects of splenic red cells released into the circulation during exercise. Independent of Ta, pre-exercise PVc decreased 3%-5% (p < or = 0.05) within the first 10 min of exercise, but increased 5%-9% (p < or = 0.05) by 10 min post-exercise. CONCLUSION: We conclude that the poor thermoregulatory ability of miniswine manifested in insignificant sweating and restricted evaporative cooling, may make them an appropriate model for acute exertional heat exhaustion in humans working in hot, humid conditions and/or wearing impermeable protective clothing. Further, evaluation of plasma volume changes from HCT and HGB in a miniswine model should consider the merit of a splenectomized design.

Splenic effects on hemodynamics induced by hypothermia and rewarming in miniature swine.

Central arterial hemodynamic changes were assessed during cooling, hypothermia, and rewarming in splenectomized (SPX, n = 4) and unsplenectomized (SP, n = 4) 8-10 month old male Yucatan miniature swine (34.0 +/- 1.4 kg). Under isoflurane anesthesia, and using circulating-water blankets, pigs were cooled to and then maintained for 2 h at a rectal temperature (Tre) of 27 +/- 1 degrees C; hypothermia was followed by rewarming to normothermia (37 +/- 1 degrees C). There were significantly (p < or = 0.05) greater changes in central arterial hematocrit and hemoglobin (delta HCT and delta HGB) from respective precooling baseline levels in the SP group during hypothermia and early rewarming (SP: delta HCTmax = 9-10%RBC, and delta HGBmax = 3.0-3.5 g/dl vs. SPX: delta HCTmax = 3-4%RBC, and delta HGBmax = 1.5-1.8 g/dl). By the end of rewarming, splenic resequestration and extravascular fluid shifts resulted in these values returning to baseline. In addition, cardiovascular instability was seen in the SPX group compared to the SP animals as evidenced by significant tachycardia and hypotension during rewarming. We have concluded from these studies that hypothermia causes significant hemoconcentration, and that splenic contraction is the major cause of this hemoconcentration during hypothermia and initial rewarming in miniature swine. A splenectomized design should be considered for swine studies that purport to pattern human pathophysiology, especially for modelling rewarming shock.

Chronic implantation of nonocclusive catheters and flow probes in the splanchnic and hindlimb vasculature of the rabbit.

Flow probes and nonocclusive catheters were simultaneously implanted in the splanchnic and hindlimb vasculature to measure regional blood flows and arteriovenous differences of individual organs in the conscious rabbit. Pulsed Doppler flow probes were constructed by modifying the technique of Haywood et al., and nonocclusive catheters were designed and constructed from Silastic tubing (0.6- or 0.9-mm OD) and surgical velour. Laparotomy was performed on rabbits under anesthesia, and the renal, mesenteric, iliac, or hepatic artery and portal vein were isolated and instrumented with a flow probe. A nonocclusive catheter was then inserted into the respective vein. Instrumentation of the hepatic system required probes on the hepatic artery and portal vein, and nonocclusive catheters were placed into hepatic and portal veins. One week later, rabbits were reanesthetized and nonocclusive catheters were inserted into the cranial vena cava via the jugular vein and abdominal aorta to the level of the celiac axis. Probes and catheters were evaluated daily up to 30 days. Implants remained functional for an average of 3 weeks, permitting chronic measurement of velocity and blood variables in individual tissue beds of the conscious rabbit.

Effects of exercise modality on patterns of ventilation and respiratory timing.

Ventilatory patterns and respiratory timing were measured in 14 subjects during cycling (CYC) and treadmill exercise (TM) at similar leg frequencies (fLEG) to determine if mode of exercise affects patterns of ventilation and respiratory timing. Measurements of breathing frequency (fR), tidal volume (VT), expired ventilation (VE), and inspiratory (TI) and expiratory (TE) time were obtained at fLEG of 50, 70, and 90 rev.min-1 (rpm) for CYC and at similar incremental fLEG (strides.min-1; spm) during TM achieved by increasing belt speed at 0% grade. CYC exercise intensity was approximately 50% VO2,max at all fLEG, whereas VO2 increased progressively with TM. fR increased significantly (P < 0.001) with increasing fLEG of TM (20.5 +/- 4.6, 25.4 +/- 5.8, and 36.3 +/- 7.6 breaths.min-1; mean +/- SD), but during CYC fR changed significantly (P < 0.05) only between fLEG of 70 and 90 rpm (25.0 +/- 5.9 vs 28.5 +/- 6.9 breaths.min-1). Both average breath TI and TE obtained by grouping into incremental ranges of fR decreased significantly (P < 0.05) with increasing fR up to 36 breaths.min-1 and the relationships of TI and TE to fR, TI to TE, and central inspiratory drive (VT/TI) to VE were the same for CYC and TM. Group average fR and fLEG were synchronized during TM, but individual subjects did not exhibit a high degree of entrainment. This study shows respiratory timing patterns to be independent of mode of exercise over the range of fR observed when describing patterns by grouping into incremental ranges of fR.

Fluid-electrolyte losses in uniforms during prolonged exercise at 30 degrees C.

The effects of several uniform configurations on fluid and electrolyte losses in a hot environment (30 degrees C db, 18 degrees C wb) were studied in 15 healthy males, during 6 h of intermittent treadmill exercise (1.56 m.s-1, 0% grade, 50 min.h-1, 28 km total distance). The uniforms were: the temperate battle dress uniform (BDU), two variants (C and F) of full military oriented protective posture (MOPP IV), and MOPP IV with no mask or hood (M). Sweat rate, urine volume, electrolyte losses (Na+, Cl-, K+, Mg++, Ca++) in sweat and urine, rectal temperature, mean skin temperature, heart rate, and temperature/humidity inside uniforms were measured. Observations indicated that both MOPP IV configurations (C and F) resulted in significantly greater (p. less than 0.05) fluid losses and physiological strain than BDU and M. However, there were no between-uniform differences in the total loss of any electrolyte. Total body fluid losses (kg.6h-1) and electrolyte losses in sweat (mEq.6h-1) were consistently greater than in urine. It was concluded that 6 h of exercise in uniforms at 30 degrees C can result in losses of Na+ and Ca++ which exceed the normal daily intake of these electrolytes. Supplementation of fluid, Na+, and Ca++ appears to be warranted when scenarios require 6 h or more of uniformed exposure to heat.

Incidence of hypohydration when consuming carbohydrate-electrolyte solutions during field training.

Carbohydrate-electrolyte solutions (CE1, CE2) were evaluated for their ability to reduce the incidence of hypohydration during field training in hot weather (max Tamb = 88 degrees-100 degrees F). Hydration status was monitored twice daily in Army reservists who consumed ad libitum CE1, or CE2, or water, or a flavored water placebo. The water group had the highest percentage incidence of urine specific gravity greater than or equal to 1.030 (22%), whereas CE2 and flavored water placebo groups had the lowest (6% and 8%, respectively). Average total fluid intake was greatest in CE2 and lowest in CE1. CE2 and flavored water placebo were more effective than CE1 and water in reducing the overall incidence of hypohydration during this field exercise.

Prediction of the exercise-heat tolerance of soldiers wearing protective overgarments.

The purpose of this investigation was to see whether subject characteristics and physiologic measurements predicted exercise-heat tolerance (EHT) and voluntary tolerance time in young soldiers. A total of 18 unacclimatized males attempted six 50-min periods of treadmill walking (4.0 km.h-1, 0% grade, 33 degrees C db, 20% rh) while wearing protective overgarments. Two post hoc groups of soldiers were defined: high EHT (H) and low EHT (L), having mean (+/- S.E.) tolerance times of 360 +/- 0 and 222 +/- 12 min, respectively. Significant (p less than 0.05) H vs. L differences were observed in pretrial body mass, percent fat, and mass-to-surface area ratio (M/SA), as well as 170 min HR, Tsk and heat storage. The first three of these factors indicated that preexercise anthropomorphic characteristics may be used to distinguish H from L. The HR and Tsk differences were interpreted to mean that L experienced greater cardiovascular strain in protective overgarments because of a higher Tsk, which resulted in increased pooling of blood in cutaneous vessels, decreased cardiac filling pressure, and increased fatigue. Because HR variables were the strongest correlates of exercise tolerance time (r2 = 0.60 for HR at 170 min, r2 = 0.83 for time to reach HR of 160 beats.min-1) a novel HR monitoring technique was proposed which uses a wrist-mounted cardiotachometer to predict tolerance time.

Patterns of human drinking: effects of exercise, water temperature, and food consumption.

The effects of exercise, water temperature, and food consumption on patterns of ad libitum drinking were studied in 33 men during 6 consecutive cycles of 30 min walking (4.8 km.h-1, 5% grade) and 30 min rest in a climatic chamber (40 degrees C, 40% relative humidity). On two nonconsecutive days, subjects consumed 15 degrees C (cool) water during one trial and 40 degrees C (warm) water during the other. We previously reported that two groups of drinkers can be identified during work in the heat by the criterion of body weight (BW) loss during the trial. Thus, avid drinkers (D) drank sufficiently such that they lost less than 2% of their initial BW when consuming cool water and libitum, while reluctant drinkers (RD) lost more than 2% of their BW. When warm water was provided, fluid consumption was reduced by 29% and 54% in D and RD, respectively and BW deficits were comparably increased. Intake of cool water elicited cyclic drinking patterns with higher rates during walking than during rest periods in both D and RD, whereas consumption of warm water produced this cyclic pattern only after food ingestion during the third rest. Food consumption stimulated fluid intake and reduced BW losses in both trials. Compared to pre-prandial (hours 1-2.5) rates, average post-lunch drinking rates during the last 3 h increased 14% in D and 19% in RD when consuming cool water, and by 46% and 74%, respectively, with warm water. While food consumption has been encouraged to replace electrolytes lost in sweat when working in hot climates, our results indicate that food ingestion also enhances fluid consumption.

Plasma renin activity and aldosterone: correlations with moderate hypohydration.

Adult male test subjects (n = 16) were assigned to one of three clothing configurations (Army fatigues, fatigues with impermeable chemical protective garments, and fatigues with protective garments plus protective masks) prior to exercise (level treadmill, 1.11 m/s, 50 min/h, 6 h) in a moderate (wet bulb globe temperature, WBGT = 23 degrees C) environment with ad lib water consumption. When protective masks were worn, two through-mask drinking systems were evaluated: the current gravity-fed system for fluid delivery and a new system utilizing a small hydraulic pump (Fist-Flex). Antecubital blood samples were taken prior to the start of and subsequent to the completion of exercise and analyzed for fluid-electrolyte regulatory hormones. During all trials with chemical protective garments, plasma renin activity (PRA) and aldosterone levels (PA) were significantly (p less than 0.05) elevated following the exercise protocol while neither was affected during exercise in fatigues only. Individual hypohydration levels during all trials ranged from low (0.84%) to moderate (4.04%). Levels of PRA were closely correlated (r = 0.635, t = 4.35, p less than 0.001) with hypohydration as measured by percentage of body weight lost during the 6 h trial. Likewise, PA was also correlated (r = 0.47, t = 2.81, p less than 0.01) with body weight loss. We concluded from this study that PRA and PA responses were exacerbated in moderate environments by the additional heat stress, sweat rate, and dehydration caused by the impermeable garments. Further, the logistical difficulty inherent in delivering fluid through the chemical protective mask reduced voluntary consumption, increased hypohydration, and elicited the greatest elevations in PRA and PA.(ABSTRACT TRUNCATED AT 250 WORDS)

Variability in intake and dehydration in young men during a simulated desert walk.

Voluntary dehydration was examined in young unacclimatized men walking under simulated desert conditions. Thirty-three subjects (20-33 years) walked on a treadmill (4.82 km.h-1, 5% grade) for 30 min.h-1 for 6 h in a hot environment (40 degrees C db/26 degrees C wb, 4.02 km.h-1 windspeed). Cool (15 degrees C) water was provided ad libitum in canteens. Because thirst is stimulated and drinking should occur at about 2% body weight loss as body water, we used this criterion to identify two groups of individuals. Individuals who maintained body weight (BW) loss at less than 2% (0.44-1.88%) were defined as avid drinkers (D, n = 20) and those who exceeded the 2% BW loss (2.07-3.51%) despite the continual availability of cool (15 degrees C) water were called reluctant drinkers (RD, n = 13). RD consumed 31% less water (2.05 +/- 0.14 L) than D (2.98 +/- 0.12 L), and this resulted in a significantly greater BW loss in RD (2.65 +/- 0.11%) than D (1.16 +/- 0.11%). However, the only statistically significant differences in plasma indices of dehydration were the higher final plasma Na+ and protein levels in RD. Rectal temperature was higher in the RD, whereas final heart rates were unaffected. In the current study, about 40% of the young adult male subjects were reluctant to drink, and thus voluntarily dehydrated even when given cool water ad libitum during intermittent exercise in the heat. The reduced intake of these reluctant drinkers may be critical in predisposing them to increased risk of dehydration and heat injury.

Effects of water temperature and flavoring on voluntary dehydration in men.

Effects of water temperature and flavoring on fluid consumption and body weight losses were studied in fourteen unacclimatized men (21-33 years) during 6 hr of treadmill exercise (4.8 km.hr-1, 5% grade for 30 min.hr-1) in a hot environment. Subjects consumed each of four beverages (15 degrees C water, 40 degrees C water, 15 degrees C flavored water, and 40 degrees C flavored water) on four nonconsecutive days. We identified two groups of individuals by body weight (BW) loss during the cool water trial: drinkers (D) who lost less than 2% initial BW (0.80 +/- 0.15%) and reluctant drinkers (RD) who lost more than 2% (2.53 +/- 0.12%). Although sweat losses were not different between the two groups, D consumed 31% more cool water than RD and experienced 68% less BW loss. Compared to the warm water trial, 6 hr consumption of cool water was significantly increased in both D (59%) and RD (141%) and BW loss was dramatically reduced in both groups. Flavoring significantly enhanced warm water consumption and reduced BW loss in RD only. Reduced consumption of warm water increased rectal temperature, heart rate and plasma osmolality in both groups. The results of this study indicate that either flavoring or cooling warm water will enhance fluid intake and reduce body weight deficits in men reluctant to drink.

Validation of a modified one-step rebreathing technique for measuring exercise cardiac output.

A modification of the Farhi one-step rebreathing technique (1) is described for determining submaximal exercise cardiac output (Q). Factors critical in the estimation of Q are initial rebreathing bag volume and constant bag volume during the maneuver. By substituting a high flow rate analyzer (500 ml.min-1) for the recommended low flow rate mass spectrometer (60 ml.min-1), adding a recirculation circuit from the outlet of the analyzer to an inlet at the base of the rebreathing bag, and reducing the length of sample tubing to the analyzer, we were able to recirculate the subject's expired gas and achieve no loss of bag volume. No statistically significant differences in estimate of cardiac output were noted between the mass spectrometer and LB-2 analyzer with recirculation circuit during submaximal cycling. Heart rate and oxygen uptake were highly correlated with cardiac output and agreed well with the literature, irrespective of the CO2 analyzer system used. A unique feature of our method is that the subject's tidal volume is measured prior to the maneuver and then used as the initial rebreathing bag volume. Varying the bag volume by +/- 0.2 L from the tidal volume had no significant effect on the estimate of cardiac output during exercise. Now quick, reliable, and noninvasive measurements of cardiac output are feasible in subjects--not only in the laboratory but also in the field where a mass spectrometer is not readily portable.

Heat intolerance, heat exhaustion monitored: a case report.

A 32-year-old male (Mr. A.), monitored during an 8-d heat acclimation (HA) investigation, unexpectedly exhibited heat intolerance and heat exhaustion. Thirteen other males completed HA without indications of either heat intolerance or heat exhaustion. Because Mr. A. responded normally to HA on days 1-4, the intervention of an unknown host factor on days 5-8 was suggested. Mr. A.'s heat exhaustion episode (day 8) was apparently forewarned by loss of body weight and increased delta HR, delta Tsk (days 5-8) and delta Tre (days 7-8) during daily 90-min trials. His symptoms indicated classical salt depletion heat exhaustion, but the calculated salt deficit (less than 0.1 g NaCl.kg-1 body weight) was mild. Post-heat exhaustion serum enzyme levels were either normal (ALT, AST) or acutely elevated (CPK). Blood beta-endorphin and cortisol levels were six times and two times greater than control values, respectively. This case report is unique because clinical/physiological measurements and blood analyses were performed before, during, and after heat intolerance and heat exhaustion.

Urinary and hematologic indexes of hypohydration.

As part of a large-scale field feeding system test we were able to collect and study hundreds of aliquots of overnight urine samples obtained immediately prior to a fasting blood sample on days 1, 20, and 44 of the field test. The large number of experimental samples (greater than 650) and concomitant collection of blood and urine aliquots along with data on body weights gave us the opportunity to assess and quantitate the sensitivity of commonly used criteria of hypohydration. Urine aliquots for all test days were initially categorized by specific gravity (SG) greater than or equal to 1.03 (n = 124) or less than 1.03 (n = 540). Creatinine levels were elevated (P less than 0.001) in the concentrated urine samples, but a decreased trend in sodium-to-potassium ratios in these samples failed to achieve statistical significance (P greater than 0.05). However, when individuals with high SG urine were subclassified by a criterion of weight loss greater than 3% from original body weight, then creatinine concentrations were elevated (P = 0.05), whereas sodium-to-potassium ratios were decreased (P = 0.05) when subjects also with high SG but weight loss less than 3% were compared. Because of the moderate altitude (2,000 m) of the field site and the time of sojourn (44 days), there occurred a slight, but significant (P less than 0.001), erythropoietic response. Hematocrit and serum osmolality were not significantly different when examined by the criteria of high or low SG urine and weight loss greater than or less than 3% original body weight.(ABSTRACT TRUNCATED AT 250 WORDS)