Head and neck cooling by air, water, or air plus water in hyperthermia.

The effects of air, water, and air plus water head cooling on thermoregulatory responses and human operator performance were studied in nonacclimatized, heat-exposed men. Forty chamber exposures (46 degrees C, 30 mm Hg water vapor pressure) were conducted under noncooled and the aforementioned subconditions of head cooling. Five subjects, exposed for 80 min, were monitored for mean skin and rectal temperatures, heart rate, sweat loss, and compensatory tracking performance. A modified Air Force helmet shell provided facial air ventilation (24 degrees C) at 8 cfm. Eight interconnected neoprene modules fastened beneath a helmet linear provided water cooling (20 degrees C at 0.9 l/min). Tracking performances was unchanged across conditions. Elevation of rectal temperature and heart rate, sweat loss, and Physiological Index of Strain were significantly reduced by each condition of head cooling. Air is as effective as water as a cooling agent. Air ventilation acts synergistically with water cooling in reducing physiological strain. Relative merits of each approach to head cooling, in an operational context, are discussed.     

Computer simulation for postmortem cooling processes in the outer ear

INTRODUCTION: A simulation using a computer model was undertaken to investigate postmortem cooling patterns in the outer ear. METHODS: Cooling patterns were analyzed using a 3-dimensional head model built from brain CT images of a volunteer. The simulation was verified with a case subject under constant environmental conditions to obtain an appropriate heat transmission coefficient. RESULTS: The cooling pattern of the head model agreed with that of the case subject when the heat transmission coefficient was 6W/m(2) degrees C, and it could be approximated to a single exponential curve. DISCUSSION: This is the first simulative study to show the postmortem cooling pattern of the head of an adult human. Our head model will prove useful to predict the cooling patterns of not only the outer ear but also of the entirety of the head.     

Effect of wearing an ice cooling jacket on repeat sprint performance in warm/humid conditions

OBJECTIVE: To examine the effect of cooling the skin with an ice jacket before and between exercise bouts (to simulate quarter and half time breaks) on prolonged repeat sprint exercise performance in warm/humid conditions. METHODS: After an initial familiarisation session, seven trained male hockey players performed two testing sessions (seven days apart), comprising an 80 minute intermittent, repeat sprint cycling exercise protocol inside a climate chamber set at 30 degrees C and 60% relative humidity. On one occasion a skin cooling procedure was implemented (in random counterbalanced order), with subjects wearing an ice cooling jacket both before (for five minutes) and in the recovery periods (2 x 5 min and 1 x 10 min) during the test. Measures of performance (work done and power output on each sprint), heart rates, blood lactate concentrations, core (rectal) and skin temperatures, sweat loss, perceived exertion, and ratings of thirst, thermal discomfort, and fatigue were obtained in both trials. RESULTS: In the cooling condition, chest (torso) skin temperature, thermal discomfort, and rating of thirst were all significantly lower (p<0.05), but no significant difference (p>0.05) was observed between conditions for measures of work done, power output, heart rate, blood lactate concentration, core or mean skin temperature, perceived exertion, sweat loss, or ratings of fatigue. However, high effect sizes indicated trends to lowered lactate concentrations, sweat loss, and mean skin temperatures in the cooling condition. CONCLUSIONS: The intermittent use of an ice cooling jacket, both before and during a repeat sprint cycling protocol in warm/humid conditions, did not improve physical performance, although the perception of thermal load was reduced. Longer periods of cooling both before and during exercise (to lower mean skin temperature by a greater degree than observed here) may be necessary to produce such a change.     

The effect of pre-exercise cooling on high intensity running performance in the heat

The purpose of this study was to determine the effect of pre-exercise cooling on high intensity, moderate duration running performance and thermoregulatory responses in a hot environment (38 degrees C, 40 %RH). On separate days, 11 male subjects completed two treadmill runs to exhaustion at 100% of maximal aerobic power with (CL) and without (CT) pre-exercise cooling. Cooling consisted of 20 min of standing rest in a 22 degrees C environment with fan cooling (4.0 m x sec -1) and water spraying (50 ml x min -1) applied to both anterior and posterior body surfaces. Core temperature (T(c)) was determined with an esophageal T(es) probe, and skin temperatures (T(sk)) were measured using surface thermistors positioned at four sites. Finger prick blood samples were taken before and after exercise for the determination of blood lactate. Heart rates and ratings of thermal sensations and comfort were also recorded. Time to exhaustion was significantly shorter in the CL condition (368.9 +/- 56.2) compared to the CT condition (398.8 +/- 55.5 sec). Peak T(es) (37.51 +/- 0.57 vs. 38.56 +/- 0.30 degrees C for CL and CT, respectively), T(sk) (34.18 +/- 1.22 vs. 36.15 +/- 0.70 degrees C for CL and CT, respectively), rates of heat gain (0.20 +/- 0.05 vs. 0.28 +/- 0.05 degrees C x min -1 for CL and CT, respectively), and net heat storage (238.4 +/- 109.6 vs. 531.9 +/- 78.3 kJ for CL and CT, respectively) were all lower in the CL compared to CT throughout the treadmill runs. There were no differences in lactate accumulation between the two conditions. Based on these data, it can be concluded that pre-exercise cooling influences thermoregulatory responses during high intensity, moderate duration exercise; however, performance is impaired compared to a control trial in which no cooling procedures were employed.     

Efficiency of liquid cooling garments: prediction and manikin measurement

INTRODUCTION: We studied the efficiency of liquid cooling garments (LCG) and their relationship to the insulation of outer clothing, perfusate inlet temperatures, and environmental conditions by both theoretical analysis and thermal manikin (TM) testing. METHODS: An equation to estimate LCG cooling efficiency was developed on the basis of energy balance. Cooling efficiency is a function of the thermal resistance between the TM skin and perfusate in the LCG, the thermal resistance between the environment and the perfusate, and TM skin, ambient, and perfusate temperatures. Three ensembles, a cooling vest (CV) only, CV plus a battle dress uniform (CVB), and CVB plus a battle dress overgarment (CVO), were tested on a sweating TM in dry and wet conditions. The TM surface temperature was maintained at 33 degrees C and the environment was 30 degrees C and 50% RH. The LCG heat removal from the TM was calculated using the power inputs to the TM with and without perfusate flow. RESULTS: The cooling efficiency was increased from approximately 0.45 for CV to approximately 0.70 for CVO in dry experiments and from approximately 0.53 for CV to 0.78 for CVO in wet experiments. CONCLUSION: With additional outer clothing layers, higher thermal resistances increased the rate of heat removal from the TM surface, and decreased heat gain from the ambient environment, thus increasing efficiency. The perfusate inlet temperature had minimal influence on the efficiency. The equations developed can predict cooling efficiency and heat removal rates under a wider range of environmental conditions.     

Comparative cold responses of men and women to external and internal cold stimuli

Experiments were conducted comparing the relative contribution of internal and external cold stimuli in the initiation of horripilation (cutis anserina or "goose flesh") in men and women. Five men and five women were compared. Subjects wore a water perfused vest which covered the entire thorax and allowed torso skin temperature to be maintained at either 34 degrees C, 30 degrees C, 26 degrees C, or 22 degrees C in four separate experiments. After stabilization, the subject's legs were immersed in water maintained at 16 degrees C for 20 min. After removing their legs from the water, subjects then pedalled a stationary bicycle ergometer at minimum resistance to facilitate the return of cooled venous blood to the thoracic core. Horripilation was episodic in both men and women but related significantly to torso skin temperature in men and percent body fat in women over the range of torso skin temperatures tested. There was no significant association between horripilation episodes and either the stabilization, immersion, or minimal exercise phase of the experiment. Core body temperature, as measured by rectal and esophageal thermistors, decreased significantly in men from 37.0 degrees C and 36.6 degrees C at 34 degrees C torso skin temperatures, but remained unchanged in women. The results suggest that skin cooling initiates horripilation whose occurrence and pattern are affected by different combinations of morphological or physiological variables in men and women.     

Effectiveness of an air-cooled vest using selected air temperature and humidity combinations

We evaluated the effectiveness of an air-cooled vest in reducing thermal strain of subjects exercising in the heat (49 degrees C dry bulb (db), 20 degrees C dew point (dp] in chemical protective clothing. Four male subjects attempted 300-min heat exposures at two metabolic rates (175 and 315 W) with six cooling combinations--control (no vest) and five different db and dp combinations. Air supplied to the vest at 15 scfm ranged from 20-27 degrees C db, 7-18 degrees C dp; theoretical cooling capacities were 498-687 W. Without the vest, endurance times were 118 min (175 W) and 73 min (315 W). Endurance times with the vest were 300 min (175 W) and 242-300 min (315 W). The five cooling combinations were similarly effective in reducing thermal strain and extending endurance time, although there was a trend for the vest to be more effective when supplied with air at the lower dry bulb temperature. At 175 W, subjects maintained a constant body temperature; at 315 W, the vest's ability to extend endurance is limited to about 5 hours.     

Preliminary results: Effect of whole-body cooling in patients with myasthenia gravis

INTRODUCTION: Local muscle cooling has been shown to reduce symptoms in some neuromuscular diseases. PURPOSE: To determine whether lowering body temperature using a cooling vest would result in improvement in muscle strength, subjective perceptions of weakness and fatigue, and pulmonary function in patients with generalized myasthenia gravis (MG). METHODS: Patients (five female, one male) with generalized MG, aged 29-58 yr, were studied when mean body temperature was lowered (34.9 +/- 0.62 degrees C) using a cooling vest (CT) and at normal body temperature (35.8 +/- 0.58 degrees C) (NT). Isokinetic and isometric muscle strength and isokinetic endurance were measured using upper body muscle groups. The myasthenic muscle score (MMS) was performed to assess muscle impairment specific to MG patients. Pulmonary function measurements included forced vital capacity (FVC), maximal inspiratory pressure (MIP), and maximal expiratory pressure (MEP). The fatigue impact scale (FIS) was used to track subjective perceptions of fatigue. Core body and skin temperatures were measured throughout each NT and CT trial. RESULTS: Mean body temperature (0.65(core) + 0.35(skin)) was reduced significantly following 30-45 min of cooling (NT = 35.76 +/- 0.58, CT = 34.96 +/- 0.62 degrees C). The MMS and MIP increased significantly (NT = 91.9 vs CT = 96.3; and NT = 69.3 vs CT = 79.5 cm/H2O) with cooling. Although all other variables were not statistically different between temperature conditions, individual results for grip strength of the right hand, fatigue ratio for wrist extensors and shoulder internal and external rotators, FVC, and MEP showed improvement for the majority of the subjects. CONCLUSION: Cooling in patients with MG shows promise to decrease symptoms of weakness and fatigue, thus allowing increased muscle strength and endurance in some patients.     

Life jacket design affects dorsal head and chest exposure, core cooling, and cognition in 10 degrees C water

PURPOSE: Personal floatation devices (PFDs) differ in whether they maintain the head out of the water or allow the dorsum of the head to be immersed. Partial head submersion may hasten systemic cooling, incapacitation, and death in cold water. METHODS: Six healthy male volunteers (mean age = 26.8 yr; height = 184 cm; weight = 81 kg; body fat = 20%) were immersed in 10 degrees C water for 65 min, or until core temperature = 34 degrees C, under three conditions: PFD#1 maintained the head and upper chest out of the water; PFD#2 allowed the dorsal head and whole body to be immersed; and an insulated drysuit (control) allowed the dorsal head to be immersed. Mental performance tests included: logic reasoning test; Stroop word-color test; digit symbol coding; backward digit span; and paced auditory serial addition test (PASAT). RESULTS: Core cooling was significantly faster for PFD#2 (2.8 +/- 1.6 degrees C x h(-1)) than for PFD#1 (1.5 +/- 0.7 degrees C x h(-1)) or for the drysuit (0.4 +/- 0.2 degrees C x h(-1)). Although no statistically significant effects on cognitive performance were noted for the individual PFDs and drysuit, when analyzed as a group, four of the tests of cognitive performance (Stroop word-color, digit symbol coding, backward digit span, and PASAT) showed significant correlations between decreasing core temperature to 34 degrees C and diminished cognitive performance. CONCLUSIONS: Performance in more complicated mental tasks was adversely affected as core temperature decreased to 34 degrees C. The PFD that kept the head and upper chest out of the water preserved body heat and mental performance better than the PFD that produced horizontal flotation.     

Evaluation of three commercial microclimate cooling systems

Three commercially available microclimate cooling systems were evaluated for their ability to reduce heat stress in men exercising in a hot environment while wearing high insulative, low permeability clothing. Five male volunteers performed three 180-min experiments (three repeats of 10 min rest, 50 min walking at 440 watts) in an environment of 38 degrees C dry bulb (Tdb), 12 degrees C dew point (Tdp). The cooling systems were: 1) ILC Dover Model 19 Coolvest (ILC), mean inlet temperature 5.0 degrees C; 2) LSSI Coolhead (LSSI), mean inlet temperature 14.5 degrees C; and 3) Thermacor Cooling Vest (THERM), mean inlet temperature 28.3 degrees C. Endurance time (ET), heart rate (HR), rectal temperature (Tre), mean skin temperature (Tsk), sweating rate (SR), rated perceived exertion (RPE), and thermal sensation (TS) were measured. A computer model prediction of ET with no cooling was 101 min. ET was greater (p less than 0.01) with ILC (178 min) than THERM (131 min) which was greater (p less than 0.01) than LSSI (83 min). The subjects self terminated on all LSSI tests because of headaches. Statistical analyses were performed on data collected at 60 min to have values on all subjects. There were no differences in HR, Tre, SR, or TS values among the cooling vests. The subjects' Tsk was lower (p less than 0.05) for the LSSI than THERM; and RPE values were higher (p less than 0.05) for LSSI than the other two vests. These data suggest an improved physiological response to exercise heat stress with all three commercial systems with the greatest benefit in performance time provided by the ILC cooling system.     

Individual thermal profiles as a basis for comfort improvement in space and other environments

BACKGROUND: The development of individualized countermeasures to address problems in thermoregulation is of considerable importance for humans in space and other extreme environments. A methodology is presented for evaluating minimal/maximal heat flux from the total human body and specific body zones, and for assessing individual differences in the efficiency of heat exchange from these body areas. The goal is to apply this information to the design of individualized protective equipment. METHODS: A multi-compartment conductive plastic tubing liquid cooling/warming garment (LCWG) was developed. Inlet water temperatures of 8-45 degrees C were imposed sequentially to specific body areas while the remainder of the garment was maintained at 33 degrees C. RESULTS: There were significant differences in heat exchange level among body zones in both the 8 degrees and 45 degrees C temperature conditions (p < 0.001). The greatest amount of heat was absorbed/released by the following areas: thighs (8 degrees C: -2.12 +/- 0.14 kcal min(-1); 45 degrees C: +1.58 +/- 0.23); torso (8 degrees C: -2.12 +/- 0.13 kcal min(-1); 45 degrees C: +1.31 +/- 0.27); calves (8 degrees C: -1.59 +/- 0.26 kcal min(-1); 45 degrees C: +1.53 +/- 0.24); and forearms (8 degrees C: -1.67 +/- 0.29 kcal x min(-1); 45 degrees C: +1.45 +/- 0.20). These are primarily zones with relatively large muscle mass and adipose tissue. Calculation of absorption/release heat rates standardized per unit tube length and flow rate instead of zonal surface area covered showed that there was significantly greater heat transfer in the head, hands, and feet (p < 0.001). The areas in which there was considerable between-subject variability in rates of heat transfer and thus most informative for individual profile design were the torso, thighs, shoulders, and calves or forearms. CONCLUSIONS: The methodology developed is sensitive to individual differences in the process of heat exchange and variations in different body areas, depending on their size and tissue mass content. The design of individual thermal profiles is feasible for better comfort of astronauts on long-duration missions and personnel in other extreme environments.     

Redirection of biological heat from head to hands to support finger comfort in the cold

INTRODUCTION: Maintaining hand comfort in the cold while sustaining optimal performance is still a challenge. There has been little research on the efficacy of transporting biological heat from the head to the hands to stabilize finger comfort, although there are notable temperature differences between these two areas in the cold. METHOD: A tubing bypass between the head and the hands was designed as an independent component in a liquid cooling/warming garment (LCWG). Seven subjects (four men, three women) were studied, comparing finger temperature (Tfing) change in two conditions: LCWG with additional bypass; and LCWG without bypass. The protocol consisted of three stages: 1) comfort stabilization, LCWG inlet water temperature 33 degrees C, water in loop in bypass condition 23 degrees C; 2) body cooling, LCWG inlet water temperature 20 degrees C; and 3) rewarming, LCWG inlet water temperature 45 degrees C. RESULTS: The time to reach the 25 degrees C Tfing discomfort criterion was significantly longer in the bypass condition (p < 0.01); Tfing was significantly higher at the same time point when Tfing of 25 degrees C was reached in the control condition (p < 0.01). CONCLUSION: The incorporation of a bypass transferring biological heat from a high to a low skin temperature area has potential to improve local finger comfort and thus increase the time personnel can work in cold environments.     

Heat stress on helicopter pilots during ground standby.

We attempted to use measurements of ambient thermal conditions to characterize and then predict thermal conditions in the cockpit before takeoff and during an hour standby period in Bell 206 and Bell 212 helicopters with a crew of two and with the cockpit doors opened. Dry bulb, wet bulb, and globe temperatures were measured on 28 separate summer days. The wet bulb globe temperature index (WBGT) was used to estimate heat stress. Ambient WBGT at time 0 ranged from 13 degrees C to 31 degrees C. There was a 2.9 +/- 3.7 degree difference in WBGT between ambient and cockpit conditions at time 0 which increased to 7.2 +/- 3.5 degrees after 1 h. Because of the cooling effect of opening the helicopter cockpit doors, the cockpit WBGT actually decreased over the standby period when cockpit WBGT values were 30 degrees C or more at time 0. Thus, there was an inverse correlation between cockpit WBGT at time 0 and the change in cockpit WBGT over the 1-h period (r = -0.767, p less than 0.001). The mean WBGT in the cockpit over the 1-h standby period was positively correlated with the ambient WBGT at time 0 (r = 0.783, p less than 0.001). We conclude that the greenhouse effect results in a cockpit WBGT which is significantly higher than ambient conditions. Subsequent changes in cockpit WBGT depend on the balance between heat transfer from the pilot's bodies to the cockpit and the loss of heat after the doors of the helicopters are opened. Ambient thermal conditions can be used to predict heat stress during the ground standby period.     

Heat strain attenuation while wearing NBC clothing: dry-ice vest compared to water spray

BACKGROUND: While wearing impermeable nuclear, biological, and chemical (NBC) clothing, reduction of thermal stress is of primary importance. We compared the effect between two cooling methods on the attenuation of heat strain. METHODS: There were six male subjects who were divided into two groups of three and exposed on two consecutive days to 125 min of exercise in a high heat load (40 degrees C, 40% RH) wearing NBC clothing. They were cooled by one of two different cooling methods: an active cooling vest (CV) based on the sublimation of dry ice, or tap water spraying (TP). RESULTS: After 2 h, rectal temperature (Tre) was significantly higher for the CV compared with the TP (38.1 +/- 0.04 degrees C vs. 37.7 +/- 0.10 degrees C, respectively). Skin temperature (Tsk) was significantly higher for the CV compared with the TP (36.60 +/- 0.54 degrees C vs. 34.90 +/- 0.35 degrees C, respectively). In the second hour, heart rate (HR) was significantly higher for CV compared with TP (118 +/- 13 bpm vs. 104 +/- 64 bpm, respectively). Heat storage was significantly higher after the first and second hours for the CV compared with the TP. The physiological strain index (PSI) was higher for CV compared with TP in the second hour. Sweat rate (msw) was significantly higher for CV compared with TP (560 +/- 45 g x h(-1) vs. 409 +/- 84 g x h(-1), respectively). Subjective thermal comfort was not significantly different. CONCLUSIONS: TP was more effective than the CV in reducing heat strain under the conditions used in the study. Until a significant breakthrough in reducing heat strain while wearing NBC clothing in field conditions can be found, TP appears to be an effective and recommended cooling method.     

Cold and heat strain during cold-weather field training with nuclear, biological, and chemical protective clothing

The objective of this study was to quantify the thermal strain of soldiers wearing nuclear, biological, and chemical protective clothing during short-term field training in cold conditions. Eleven male subjects performed marching exercises at moderate and heavy activity levels for 60 minutes. Rectal temperature (Tre), skin temperatures, and heart rate were monitored. Ambient temperature (Ta) varied from -33 to 0 degrees C. Tre was affected by changes in metabolism, rather than in Ta. Tre increased above 38 degrees during heavy exercise even at -33 degrees C. The mean skin temperature decreased to tolerance level (25 degrees C) at Ta below -25 degrees C with moderate exercise. Finger temperature decreased below 15 degrees C (performance degradation) at Ta of -15 degrees C or cooler. The present results from the field confirm the previous results based on laboratory studies and show that risk of both heat and cold strain is evident, with cooling of extremities being most critical, while wearing nuclear, biological, and chemical protective clothing during cold-weather training.     

Heat stress reduction of helicopter crew wearing a ventilated vest

BACKGROUND: Helicopter pilots are often exposed to periods of high heat strain, especially when wearing survival suits. Therefore, a prototype of a ventilated vest was evaluated on its capability to reduce the heat strain of helicopter pilots during a 2-h simulated flight. HYPOTHESIS: It was hypothesized that the ventilated vest would reduce pilot heat stress. METHODS: Five male and one female helicopter pilots flew for 2 h in a simulator in three different conditions; 15 degrees C wet bulb globe temperature (WBGT) without ventilation, 32 degrees C WBGT without ventilation, and 32 degrees C WBGT with a ventilated vest. RESULTS: Wearing the ventilated vest significantly reduced the increase in rectal temperature and increased thermal comfort. This made it possible for all subjects to complete the 2-h session. CONCLUSION: With the ventilated vest the subjects experienced less heat stress, thereby allowing all subjects to successfully complete the experiment, though two of the six pilots could not complete the 2-h flying task in the hot condition without cooling due to heat-related problems.     

Reflective inserts to reduce heat strain in body armor: tests with and without irradiance

BACKGROUND: This study evaluated adding reflective thermal inserts (RTI) to reduce the physiological strain during exercise-heat stress with a radiant load. RTI were used with a U.S. Army desert battle dress uniform, body armor, and helmet. METHODS: Four male volunteers attempted four trials (10 min rest followed by 100 min walking at 1.56 m x s(-1)). All trials were at 40.0 degrees C dry bulb (Tdb), 12.4 degrees C dew point (Tdp), 20% RH, and 1.0 m x s(-1) wind speed. On 2 d, there was supplementary irradiance (+1) with globe temperature (Tbg) = 56.5 degrees C and on 2 d there was no supplementary irradiance (-I) with Tbg approximately Tdb. Trial conditions were: 1) RTI and armor with supplementary irradiance (RA+I); 2) plain armor with supplementary irradiance (PA+I); 3) RTI and armor with no supplementary irradiance (RA-I); and 4) plain armor with no supplementary irradiance (PA-I). RESULTS: Endurance times were not significantly different among trials. With one exception, armor and helmet interior and exterior surface temperatures were not significantly different between either RA+I and PA+I or RA-I and PA-I. Temperature on the inside of the helmet in RA+I (47.1 +/- 1.4 degrees C) was significantly lower than in PA+I (49.5 +/- 2.6 degrees C). There were no differences for any physiological measure (core temperature, heart rate, mean weighted skin temperature, forehead skin temperature, sweating rate, evaporative cooling, rate of heat storage) between either RA+I and PA+L or RA-I and PA-I. CONCLUSIONS: Results showed no evidence that wearing RTI with body armor and helmet reduces physiological strain during exercise-heat stress with either high or low irradiance.     

Shivering heat production and core cooling during head-in and head-out immersion in 17 degrees C water

INTRODUCTION: Many cold-water scenarios cause the head to be partially or fully immersed (e.g., ship wreck survival, scuba diving, cold-water adventure swim racing, cold-water drowning, etc.). However, the specific effects of head cold exposure are minimally understood. This study isolated the effect of whole-head submersion in cold water on surface heat loss and body core cooling when the protective shivering mechanism was intact. METHODS: Eight healthy men were studied in 17 degrees C water under four conditions: the body was either insulated or exposed, with the head either out of the water or completely submersed under the water within each insulated/exposed subcondition. RESULTS: Submersion of the head (7% of the body surface area) in the body-exposed condition increased total heat loss by 11% (P < 0.05). After 45 min, head-submersion increased core cooling by 343% in the body-insulated subcondition (head-out: 0.13 +/- 0.2 degree C, head-in: 0.47 +/- 0.3 degree C; P < 0.05) and by 56% in the body-exposed subcondition (head-out: 0.40 +/- 0.3 degree C and head-in: 0.73 +/- 0.6 degree C; P < 0.05). DISCUSSION: In both body-exposed and body-insulated subconditions, head submersion increased the rate of core cooling disproportionally more than the relative increase in total heat loss. This exaggerated core-cooling effect is consistent with a head cooling induced reduction of the thermal core, which could be stimulated by cooling of thermosensitive and/or trigeminal receptors in the scalp, neck, and face. These cooling effects of head submersion are not prevented by shivering heat production.     

Responses of children with cerebral palsy to arm-crank exercise in the heat

PURPOSE: In response to passive heating, adults with hemispheric brain infarction demonstrate lower skin temperatures (Tsk) and higher sweating rates (SR) on the affected side. It is unknown whether children with similar conditions demonstrate a similar response and whether this response is advantageous to defending body temperature during exercise in the heat. The purpose of this study was to determine whether children with spastic cerebral palsy (CP) demonstrate less thermal strain than healthy peers during short (10 min each) bouts of arm cranking, a mode of exercise where metabolic rate can be matched between the two groups. METHODS: Eleven young people (8.3-18.3 yr) with spastic CP and 11 individually matched (body size, age, and maturity) healthy controls (CON) performed 3 x 10-min arm-cranking bouts (40 rpm) in 35 degrees C, 50% RH. Body mass, metabolic and heart rate (HR) responses, and body temperatures were periodically measured. Individuals within each CP-CON pair worked at the same intensity (0.55 +/- 0.18 W.kg-1 body mass). Data were analyzed using a repeated measures ANOVA (alpha = 0.05). RESULTS: Subjects with CP showed no difference from CON in metabolic and HR responses, or SR (as inferred from body mass changes corrected for fluid intake and output). There were also no differences between the groups in the rectal temperature change from room temperature (21-23 degrees C). The increase in Tsk from room temperature, however, was slightly (0.6 degrees C) but significantly lower (P < 0.0001; 95% CI = 0.5-0.7 degrees C) in the subjects with CP compared with CON. CONCLUSION: Subjects with CP demonstrate thermal strain responses similar to CON during upper-body exercise at relatively low intensities for short duration in a warm climate.     

Effect of a practical neck cooling device on core temperature during exercise

Previous studies have documented the effectiveness of combined head and neck cooling in reducing thermal stress during exercise. However, these studies investigated low intensity exercise and devices that are not practical for use on a widespread basis during recreational exercise. In the present study, we investigated the effect of a commercially available, practical neck cooling device on core temperature during strenuous exercise. In a randomized cross-over fashion, 10 male endurance athletes (age 29 +/- 2 yr) performed a 45-min submaximal run (Borg rating of perceived exertion approximately 15) at a constant speed, with and without neck cooling. Runs were conducted on an indoor track, where the ambient temperature was maintained at approximately 21 degrees C dry bulb and approximately 17 degrees C wet bulb. Exercise heart rates and subjective perception of effort were not significantly modified by neck cooling. In contrast, rectal temperature rises (by 0.21 degrees C or 9.5%, P less than 0.02) and sweat rates (by 92 ml.h-1 or 6.4%, P less than 0.02) were reduced by neck cooling. Our study therefore concludes that this practical neck cooling device is capable of inducing reductions in thermal stress during strenuous exercise that, although numerically small, are in a direction of potential benefit.