Plasma volume and endocrine responses to water immersion with intermittent positive-pressure breathing in men

The effect of intermittent positive-pressure breathing (PB), induced by expiring against a resistance of 12.5 mm Hg, on plasma volume and endocrine responses to standing water immersion, was studied in seven male subjects, 28-49 years of age. The men were immersed to the neck (35 +/- 0.5 degrees C) for 90 min with PB from 30 to 60 min. Compared to control values, the hematocrit and hemoglobin concentration decreased (p less than 0.001) during immersion while plasma osmolality was unchanged, indicating an isotonic increase in plasma volume (hemodilution) which peaked after 75 min at +15.5% of the preimmersion plasma volume. This hemodilution was not significantly affected by PB. Plasma renin activity and vasopressin and aldosterone concentrations decreased progressively throughout immersion (p less than 0.001) and were unaffected by PB. The magnitude of these hormonal decreases was accentuated by preexisting, presyncopal symptoms in four subjects. It is concluded that intermittent PB as 12.5 mm Hg failed to compensate for the negative-pressure breathing of standing subjects immersed in water to the neck.     

Renal, endocrine, and cardiovascular responses during head-out water immersion in legless men.

BACKGROUND: The hydrostatic pressure gradient during head-out water immersion (HOI) causes a blood shift from the legs into the thoracic cavity to stretch the receptors in the cardiac atria and results in a diuresis in hydrated subjects. The present study was conducted to examine whether the HOI-induced diuresis and related circulatory and hormonal changes were attenuated in the subjects who had no legs (legless men). METHODS: Two legless men served as the subjects. They lost both legs 15 and 17 yr ago by accidents and were otherwise healthy. Six normal males participated as controls. The experimental protocol was consisted of a 1-h control, a 3-h HOI (water temperature, 34.5 degrees C) and a 1-h recovery. RESULTS: Average urine flow (0.6 ml x min(-1)), urinary excretion of sodium (90 microeq x min(-1)), and osmolal clearance (1.4 ml x min(-1)) of the legless subjects increased in the first h of immersion to 0.7 ml x min(-1), 139 microeq x min(-1), and 1.8 ml x min(-1), respectively. These values remained elevated during HOI, however, the magnitude of the increase was smaller compared with the control subjects. Plasma arginine vasopressin was significantly (p < 0.05) decreased from 1.0+/-0.4 microU x 100 ml(-1) to 0.4+/-0.2 microU x 100 ml(-1) during HOI in the normal subjects, but was not in the legless subjects (from 0.5 at control period to 0.4 microU x 100 ml(-1) during HOI). A concurrent reduction of aldosterone and plasma renin activity was observed with an increase in atrial natriuretic peptide during HOI in both subject groups, however, the magnitude of the changes was smaller in the legless subjects compared with the control subjects. Similarly, the average increase in cardiac output during HOI in the legless subjects (by 17%) was less compared with the control subjects (by 31%). CONCLUSION: The magnitude of renal, endocrine, and cardiovascular changes in response to HOI in the legless subjects were less than in control subjects, but the responses were qualitatively similar. Accordingly, we suggest that the cephalad blood expansion during immersion is not only due to translocation of blood from the legs but also the abdominal region.     

Cooling hyperthermic firefighters by immersing forearms and hands in 10 degrees C and 20 degrees C water

INTRODUCTION: Firefighters experience significant heat stress while working with heavy gear in a hot, humid environment. This study compared the cooling effectiveness of immersing the forearms and hands in 10 and 20 degrees C water. METHODS: Six men (33 +/- 10 yr; 180 +/- 4 cm; 78 +/- 9 kg; 19 +/- 5% body fat) wore firefighter 'turn-out gear' (heavy clothing and breathing apparatus weighing 27 kg) in a protocol including three 20-min exercise bouts (step test, 78 W, 40 degrees C air, 40% RH) each followed by a 20-min rest/cooling (21 degrees C air); i.e., 60 min of exercise, 60 min of cooling. Turn-out gear was removed during rest/cooling periods and subjects either rested (Control), immersed their hands in 10 or 20 degrees C water (H-10, H-20), or immersed their hands and forearms in 10 or 20 degrees C water (HF-10, HF-20). RESULTS: In 20 degrees C water, hand immersion did not reduce core temperature compared with Control; however, including forearm immersion decreased core temperature below Control values after both the second and final exercise periods (p < 0.001). In 10 degrees C water, adding forearm with hand immersion produced a lower core temperature (0.8 degrees C above baseline) than all other conditions (1.1 to 1.4 degrees C above baseline) after the final exercise period (p < 0.001). Sweat loss during Control (1458 g) was greater than all active cooling protocols (1146 g) (p < 0.001), which were not different from each other. DISCUSSION: Hand and forearm immersion in cool water is simple, reduces heat strain, and may increase work performance in a hot, humid environment. With 20 degrees C water, forearms should be immersed with the hands to be effective. At lower water temperatures, forearm and/or hand immersion will be effective, although forearm immersion will decrease core temperature further.     

Effect of acclimation on changes in water and electrolyte homeostasis in soldiers during exertional heat stress

BACKGROUND/AIM: Exertional heat stress is a common problem in military services. The aim of this study was to exemine changes in body water and serum concentrations of some electrolites in soldiers during exertional heat stress (EHST), as well as effects of 10-day passive or active acclimation in a climatic chamber. METHODS: Forty male soldiers with high aerobic capacity, performed EHST either in cool (20 degrees C, 16 degrees C WBGT-wet bulb globe temperature), or hot (40 degrees C, 25 degrees C WBGT) environment, unacclimatized, or after 10 days of passive or active acclimation. The subjects were allowed to drink tap water ad libitum during EHST. Mean skin (Tsk) and tympanic (Tty) temperatures and heart rates (HR) measured physiological strain, while sweat rate (SwR), and serum concentrations of sodium, potassium and osmolality measured changes in water and electrolite status. Blood samples were collected before and immediately after the EHST. RESULTS: Exertional heat stress in hot conditions induced physiological heat stress (increase in Tty, HR, and SwR), with significant decrease in serum sodium concentration (140.6 +/- 1.52 before vs. 138.5 +/- 1.0 mmol/l after EHST, p < 0.01) and osmolality (280.7 +/- 3.8 vs. 277.5 +/- 2.6 mOsm/kg, p < 0.05) in the unacclimatized group. The acclimated soldiers suffered no such effects of exertional heat stress, despite almost the same degree of heat strain, measured by Tty, HR and SwR. CONCLUSION: In the trained soldiers, 10-day passive or active acclimation in a climatic chamber can prevent disturbances in water and electrolitic balance, i.e. decrease in serum sodium concentrations and osmolality induced by exertional heat stress.     

Exercise thermoregulation in men after 6 hours of immersion

Rectal (Tre) and mean skin (Tsk) temperature, skin heat conductance (Ksk), heart rate, and total body sweat rate were measured in 6 men (20-35 years) during 70 min of supine leg exercise (Ta = 23.5 degrees C, rh = 40%) at 50% of their peak O2 uptake (VO2 peak); these data were taken after a 6-h control (C) period in air and after immersion to the neck (NI) in water (34.5 degrees C) for 6 h after overnight food and fluid restriction. After NI mean (+/- S.E.) water balance was -1,285 +/- 104 ml for the 6 h and plasma volume (delta Hb and Hct) decreased by 5.2%. End exercise heart rates after C (141 +/- 3 b X min-1) increased to 148 +/- 3 b X min-1 (p less than 0.05) after NI while Vo2 were both 2.2 L X min-1 Tre increased by 0.5 C degrees (p less than 0.05) between the end of NI and the start of exercise. During exercise following C and NI, delta Tre were +1.0 degrees C and +0.9 degrees C (NS), Ksk were 44 +/- 2 and 43 +/- 1 kcal X m-2 X hr-1 X degrees C-1 (NS), while sweat rates increased from 248 +/- 19 to 366 +/- 52 g X h-1 (p less than 0.05), respectively. Both the total integrated Tre and Tsk curves after NI were higher (p less than 0.05) than for C. These results suggest that, compared with control responses, the equilibrium level of core temperature during submaximal exercise is regulated at a higher level after immersion.     

The influence of ethnicity on thermosensitivity during cold water immersion

PURPOSE: This investigation evaluated the influence of ethnicity, Caucasian (CAU) vs. African American (AA), on thermosensitivity and metabolic heat production (HP) during cold water immersion (20 degrees C) in 15 CAU (22.7 +/- 2.7 yr) vs. 7 AA (21.7 +/- 2.7 yr) males. METHODS: Following a 20-min baseline period (BASE), subjects were immersed in 20 degrees C water until esophageal temperature (Tes) reached 36.5 degrees C or for a maximum pre-occlusion (Pre-OCC) time of 40 min. Arm and thigh cuffs were then inflated to 180 and 220 mm Hg, respectively, for 10 min (OCC). Following release of the inflated cuffs (Post-OCC), the slope of the relationship between the decrease in Tes and the increase in HP was used to define thermosensitivity (beta). RESULTS: ANOVA revealed no significant difference in thermosensitivity between CAU and AA (CAU = 3.56 +/- 1.54 vs. AA = 2.43 +/- 1.58 W.kg(-1). degrees C(-1)). No significant differences (p > 0.05) were found for Tsk (CAU = 24.2 +/- 1.1 vs. AA = 25.1 +/- 1.1 degrees C) or HP (p > 0.05; CAU = 2.5 +/- 0.8 vs. AA = 36.5 +/- 1.8 W.kg(-1)). However, a significant (p < 0.05) main effect for ethnicity for Tes was observed (CAU = 36.7 +/- 1.8 vs. AA = 36.5 +/- 1.8 degrees C). CONCLUSION: These data suggest, despite a differential response in Tes between AA and CAU groups, the beta of HP during cold water immersion is similar between CAU and AA. Therefore, these data demonstrate that when faced with a cold challenge, there is a similar response in HP between CAU and AA that is accompanied by a differential response in Tes.     

Finger and toe temperatures on exposure to cold water and cold air

INTRODUCTION: Subjects with a weak cold-induced vasodilatation response (CIVD) to experimental cold-water immersion of the fingers in a laboratory setting have been shown to have a higher risk for local cold injuries when exposed to cold in real life. Most of the cold injuries in real life, however, occur in the foot in cold air rather than in the hand in cold water. Therefore, an experiment was conducted to investigate the within-subject relation between CIVD in the fingers and toes exposed to cold water and cold air. METHODS: In 4 experimental sessions, 11 healthy male subjects immersed their toes and fingers in 5 degrees C water and exposed the fingers and toes to -18 degrees C cold air for 30 min. The pad temperature of the middle three digits was measured. RESULTS: CIVD in water was more pronounced in the fingers (onset time 5.1 +/- 1.8 min; amplitude 5.0 +/- 2.1 degrees C) than in the toes (onset time 10.6 +/- 6.0 min; amplitude 3.0 +/- 1.0 degrees C). Out of 22 skin temperature responses to cold air, 13 were not identifiable as CIVD. The mean skin temperatures for fingers and toes during the last 20 min of cold exposure were 25.6 +/- 7.1 degrees C and 20.9 +/- 6.8 degrees C, respectively, for air and 9.3 +/- 1.9 degrees C and 7.1 +/- 1.3 degrees C for water immersion. There was a strong relation between the mean temperature of the fingers during cold-water immersion and toes during cold air exposure (r = 0.83, P < 0.01), showing that a weak CIVD response in the hand is related to a weak response in the foot. DISCUSSION: We conclude that the cold-water finger immersion test is related to the temperature response in the toes and may thus continue to serve as a valid indicator for the risk of local cold injuries.     

Cold water recovery reduces anaerobic performance

This study investigated the effects of cold water immersion on recovery from anaerobic cycling. Seventeen (13 male, 4 female) active subjects underwent a crossover, randomised design involving two testing sessions 2 - 6 d apart. Testing involved two 30-s maximal cycling efforts separated by a one-hour recovery period of 10-min cycling warm-down followed by either passive rest or 15-min cold water immersion (13 - 14 degrees C) with passive rest. Peak power, total work and postexercise blood lactate were significantly reduced following cold water immersion compared to the first exercise test and the control condition. These variables did not differ significantly between the control tests. Peak exercise heart rate was significantly lower after cold water immersion compared to the control. Time to peak power, rating of perceived exertion, and blood pH were not affected by cold water immersion compared to the control. Core temperature rose significantly (0.3 degrees C) during ice bath immersion but a similar increase also occurred in the control condition. Therefore, cold water immersion caused a significant decrease in sprint cycling performance with one-hour recovery between tests.     

Physiological and thermal responses of males with varying body compositions during immersion in moderately cold water.

The effect of body composition on the thermal and metabolic responses of 24 male volunteers (20 to 35 years) was examined during 90 min of moderately cold (18, 22, or 26 degrees C) water immersion to the first thoracic vertebrae. Body composition was determined via underwater densitometry. Subjects were divided with respect to body fat (high fat (HF) = 18-22%, n = 12; Low fat (LF) = 8-12%, n = 12) and randomly assigned to one of three water temperatures. Rectal temperature (degree C) after 90 min of immersion did not differ in LF and HF at 18 degrees C (35.9 vs. 36.2), 22 degrees C (36.0 vs. 36.0), and 26 degrees C (36.0 vs. 36.3). Oxygen uptake (VO2, ml-kg-1.min-1) was greater in LF than in HF in all water temperatures. Oxygen uptake at 90 min was greater for LF than HF in 18 degrees C (11.48 vs. 9.19), 22 degrees C (9.79 vs. 4.70), and 26 degrees C (6.21 vs. 5.44). Mean skin temperature in LF and HF approached water temperature within the first 5 min. Despite the thermal strain of cold water immersion, the LF subjects were able to maintain a similar Tre compared to the HF due to a significantly greater shivering thermogenesis.     

The influence of gender and menstrual phase on thermosensitivity during cold water immersion

BACKGROUND: This investigation evaluated the influence of gender and phase of menstrual cycle [follicular (FOL: days 2-6) and luteal (LUT: days 19-24) phases] on thermosensitivity and metabolic heat production (HP) during cold water immersion (20 degrees C) in 10 females (22.4 +/- 2.8 yr) and 16 males (22.4 +/- 2.9 yr). METHODS: Following a 20-min baseline period (BASE), subjects were immersed until esophageal temperature (Tes) reached 36.5 degrees C or for a maximum pre-occlusion (Pre-OCC) time of 40 min. An arm and thigh cuff were then inflated to 180 and 220 mmHg, respectively, for 10 min (OCC). Following release of the inflated cuffs (Post-OCC), the slope (beta) of the relationship between the decrease in Tes and the increase in HP was used to quantify thermosensitivity. RESULTS: ANOVA revealed no significant difference in thermosensitivity between phases of the menstrual cycle or between men and women (FOL = -2.76, LUT = -3.05, Males = -3.24 W x kg(-1) x degrees C(-1)). A significant (p < 0.05) main effect for gender for HP, and a significant (p < 0.05) main effect for menstrual phase for mean skin temperature (Tsk) were observed. CONCLUSIONS: These data suggest, despite gender differences in HP, that the thermosensitivity of HP during cold water immersion is similar between males and females and is not influenced by menstrual cycle phase. Therefore, these data indicate that when faced with a cold challenge, women respond similarly to men in both phases of their menstrual cycle.     

Immersion of distal arms and legs in warm water (AVA rewarming) effectively rewarms mildly hypothermic humans

INTRODUCTION: Active rewarming of hypothermic victims for field use, and where transport to medical facilities is impossible, might be the only way to restore deep body temperature. In active rewarming in warm water, there has been a controversy concerning whether arms and legs should be immersed in the water or left out. Further, it has been suggested in the Royal Danish Navy treatment regime, that immersion of hands, forearms, feet, and lower legs alone might accomplish rapid rates of rewarming (AVA rewarming). METHODS: On three occasions, six subjects (one female) were cooled in 8 degrees C water, to an esophageal temperature of 34.3+/-0.8 (+/-SD) degrees C. After cooling the subjects were warmed by shivering heat production alone, or by immersing the distal extremities (hands, forearms, feet and lower legs) in either 42 degrees C or 45 degrees C water. RESULTS: The post cooling afterdrop in esophageal temperature was decreased by both 42 degrees C and 45 degrees C water immersion (0.4+/-0.2 degrees C) compared with the shivering alone procedure (0.6+/-0.4 degrees C; p < 0.05). The subsequent rate of rewarming was significantly greater with 45 degrees C water immersion (9.9+/-3.2 degrees C x h(-1)) than both 42 degrees C water immersion (6.1+/-1.2 degrees C x h(-1)) and shivering alone (3.4+/-1.5 degrees C x h(-1); p < 0.05). CONCLUSION: The extremity rewarming procedure was experienced by the subjects as the most comfortable as the rapid rise in deep body temperature shortened the period of shivering. During the extremity rewarming procedures the rectal temperature lagged considerably behind the esophageal and aural canal (via indwelling thermocouple) temperatures. Thus large gradients may still exist between body compartments even though the heart is warmed.     

The influence of regional insulation on the initial responses to cold immersion

Twelve healthy male subjects performed three 10-min head-out immersions in water at 10 degrees C. The responses of the subjects to immersion were recorded under three conditions: a) Control condition (CC)--torso and limbs exposed; b) Torso protected/limbs exposed condition (TPC); and c) Limbs protected/torso exposed condition (LPC). Results showed that the LPC significantly reduced the heart rate (p less than 0.01), minute ventilation (p less than 0.05), and respiratory frequency (p less than 0.05) during the first minute of immersion compared to the CC. Subjects also found the LPC the most comfortable. The TPC significantly reduced minute ventilation (p less than 0.01) and respiratory frequency (p less than 0.01) on immersion compared to the CC, but did not significantly lower the heart rate response. A comparison of the LPC and TPC revealed no significant difference in minute ventilation and respiratory frequency recorded on immersion. The LPC however, produced significantly lower heart rates on immersion (p less than 0.05) than the TPC. It was concluded that the limbs may be more important than the torso for the initiation of cardiac response to cold water immersion.     

Protection provided against the initial responses to cold immersion by a partial coverage wet suit

The protection provided against the initial responses to cold water immersion by a partial coverage wet suit was assessed. Eighteen subjects performed three 2-min immersions into water at 5 degrees C. During each immersion, the subjects wore either: a) cotton overall, b) trunk and arms "wet" immersion suit, or c) "dry" immersion suit. Results showed that the dry suit provided significantly (p less than 0.05) greater protection against the initial cardiac and ventilatory responses to immersion than either the wet suit or cotton overall assemblies. The responses recorded in the wet suit were similar to, and in some cases did not differ from, the cotton overall. We conclude that immersion suit design and tests should consider all of the responses associated with accidental cold water immersion and not just those resulting in a fall in core temperature.     

Regional heat loss in resting man during immersion in 25.2 degrees C water.

Five male subjects having a wide range of relative body fat, 9.2-20.2%, were studied during total body immersion in water at 25.2 degrees C. The regional surface area of each subject was calculated from anthropometric data utilizing a segmental geometric model. Skin temperatures (Tsk) and regional skin heat loss were measured prior to and during 30 min immersion at 13 sites. During immersion, mean Tsk was 25.9 degrees C and remained significantly higher than the water temperature. A measurable temperature gradient for heat flow was observed from all body segments. Segimental temperature in water ranged from 26.7-25.4 degrees C, being warmest at the neck and coolest at the foot. Heat the flow per regional area was highest in the neck, 187 W/m2, and least at the foot, 12 W/m2. Heat flow from each body region was dependent on regional Tsk. Skinfold thickness was a minor factor in altering regional heat flow in the foot, hand, lower arm, upper arm, thigh, and calf; in the torso, neck, and head regions it was of major importance in detering heat loss.     

Simulated parachute descent in the cold: thermal responses and manual performance

BACKGROUND: Ejection from a fighter aircraft can expose the pilot to extreme cold and windy conditions. Knowledge of the effects of such conditions on thermal responses and performance of the pilot is scarce. HYPOTHESIS: It is expected that the temperature of bare skin and fingers may decrease to the level where health and/or performance are hampered. METHODS: Seven fighter pilots performed a simulated parachute descent (SPD) at ambient temperature (Ta) of -35 degrees C and wind velocity of 10 m x s(-1). The 8-min SPD was followed by a 60-min cold exposure (CE) at Ta of -20 degrees C. Flight garments with or without immersion suit were used. During SPD the subjects performed basic survival tasks. Rectal and skin temperatures were measured and manual performance was tested. RESULTS: Thermal responses did not significantly differ between the clothing ensembles. Mean skin temperature was 28 degrees C and 27 degrees C at the end of SPD and CE, respectively. The cheek temperature was 9 degrees C (range 3.2-13.8 degrees C) at the end of SPD. Finger skin temperature was 7 degrees C and 9 degrees C at the end of SPD and CE, respectively. The subjects could perform the defined tasks during SPD while manual performance was slightly impaired during CE. CONCLUSIONS: Subjects could tolerate the 8-min SPD and the following CE in the studied conditions without a loss of vital performance in basic survival actions. However, the risk of frostbite on the uncovered skin area as well as numbness of the fingers may jeopardize pilots' health and performance during parachuting.     

Effect of longitudinal physical training and water immersion on orthostatic tolerance in men

To test the hypothesis that moderately intense physical training has no effect on orthostasis, orthostatic and fluid-electrolyte-endocrine responses to 60 degrees head-up tilt were compared before and after 6 h of water immersion (34.5 +/- 0.1 degrees C) up to the neck following 6 months of exercise training. During the tilt test the five male subjects (27-42 years) each wore a lower-body positive-pressure suit (MAST-111A antishock trousers). The tilt procedure consisted of a 40-min supine control period (suit deflated), followed by a maximum 90-min tilt period (suit inflated to 50 +/- 5 mm Hg for 30 min, then deflated for 60 min or until presyncope). The mean +/- S.E. pretraining cycle ergometer peak VO2 was 3.20 +/- 0.14 L.min-1 (39 +/- 2 ml.min-1.kg-1), 3.36 +/- 0.27 L.min-1 (42 +/- 4 ml.min-1.kg-1) after 3 months (N.S.), and increased by 18% to 3.78 +/- 0.36 L.min-1 (48 +/- 5 ml.min-1.kg-1, +22%, p less than 0.05) posttraining. During pretraining, water immersion tilt tolerance decreased from 74 +/- 16 min before to 34 +/- 9 min (delta = 40 min, p less than 0.05) after immersion. During posttraining, water immersion tilt tolerance decreased similarly from 74 +/- 16 min preimmersion to 44 +/- 13 min (delta = 30 min, p less than 0.05) postimmersion (74 vs. 74 min, N.S.; 34 vs. 44 min, N.S.).(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of water immersion on postural and visual orientation.

BACKGROUND: The subjective visual vertical (SVV) and the subjective horizontal body position (SHP) perceptually dissociate and may therefore be based on a differential participation of graviceptive references. This study focuses primarily on the effects that are caused by an alteration of somatosensory information on the skin surface induced by water immersion. We expect the SHP to be selectively affected during water immersion while the SVV remains unchanged. METHODS: Four diving subjects took part in the experiments. An underwater apparatus (UWA) allowed for a determination of the SHP and the SVV during water immersion. On land, the adjustments of the SHP and SVV were made in a tilt chair apparatus (TCA). RESULTS: Three of four subjects show a significant head-upward shift between 7 degrees and 20.3 degrees of the SHP when tested under water (p < 0.02). The adjustments of the SVV were compared within corresponding physical roll inclinations and did not differ with the exception of one subject who showed a significant change of the SVV toward the physical vertical. CONCLUSIONS: The SHP and SVV perceptually dissociate on land and, as we determined for the first time, also under water. Water immersion leads to an increased roll tilt perception as measured by the SHP. However, a systematic influence on SVV could not be observed under water thus supporting the assumption that the SVV and SHP depend on gravitoreceptive information that is selectively altered during water immersion.     

Plasma TSH, T3, T4 and cortisol responses to swimming at varying water temperatures.

The acute effect of 30-min swimming at a moderate speed, at three water temperatures (20, 26 and 32 degrees C) on plasma thyroid stimulating hormone (TSH), free thyroxine (F.T4), triiodothyronine (T3) and cortisol concentrations was studied in 15 élite male swimmers. Blood was sampled before and immediately after the events. The heart rate, which was continuously monitored during exercise, had the highest response at 32 degrees C and the lowest at 20 degrees C. Blood lactate concentrations were found to be similar after the three tests. Plasma TSH and F.T4 were found to be significantly increased (by 90.4% and 45.7% respectively) after swimming at 20 degrees C, decreased at 32 degrees C (by 22.3% and 10.1% respectively) and unchanged at 26 degrees C. Exercise at these three water temperatures did not significantly affect T3. Finally, plasma cortisol was found to be increased after swimming at 32 degrees C (by 82.8%) and 26 degrees C (by 46.9%), but decreased at 20 degrees C (by 6.1%).     

Hypothermia during sports swimming in water below 11 degrees C

OBJECTIVES: To assess precautions needed to avoid dangerous hypothermia in endurance sports swims in water below 11 degrees C, using rectal temperature, anthropometric measurements, and voluntary swim times during a six day marathon relay swim. METHODS: The time in the water and the decrease in rectal temperature were measured during the longest of three to five relay swims by each of eight experienced swimmers in 9.4-11.0 degrees C water. Height, weight, and four skinfold thicknesses were measured. RESULTS: Swimmers with less subcutaneous fat terminated their swims after significantly less time in the water than those with thicker skinfold thickness, even though their rectal temperatures were not significantly lower. The lowest rectal temperature recorded was 34.3 degrees C. CONCLUSIONS: Subjective sensation in these experienced swimmers gave reliable guidance on safe durations for swims, and all voluntarily left the water with rectal temperatures that present no threat to people able to rewarm in safe surroundings. Endurance swims in highly competitive conditions or water below 9 degrees C may require continuous temperature monitoring for safety.     

Patterns of skin temperature and surface heat flow in man during and after cold water immersion

The region of the lateral thorax, previously identified as an area of high heat transfer during cold water immersion, was investigated using heat flow discs and thermography to determine values of local heat flow and surface temperature before, during and after immersion. The effect of different positions of the arms on local heat flow from the torso was also investigated. No large site-to-site variation in local heat flow was detected for immersion in water temperatures in the range 18.7-24 degrees C. When the arms were positioned close to the torso, there was a decrease in local heat flow and an increase in local surface temperatures. Thermographic examinations revealed local regions of elevated temperature after the arms were briefly held against the body in the post-immersion stage. In this circumstance, erroneous results can follow from the assumption that an elevated surface temperature always constitutes a signal of increased regional heat flow.