Nongrafted Skin Area Best Predicts Exercise Core Temperature Responses in Burned Humans

Abstract

Grafted skin impairs heat dissipation, but it is unknown to what extent this impacts body temperature during exercise in the heat. PURPOSE We examined core body temperature responses during exercise in the heat in a group of individuals with a large range of grafts covering their body surface area (BSA; 0-75%). METHODS Forty-three individuals (19 females) were stratified into groups based upon BSA grafted: Control (0% grafted, n=9), 17-40% (n=19), and >40% (n=15). Subjects exercised at a fixed rate of metabolic heat production (339 ± 70 W; 4.3 ± 0.8 W/kg) in an environmental chamber set at 40°C, 30% RH for 90 min or until exhaustion (n=8). Whole-body sweat rate and core temperatures were measured. RESULTS Whole body sweat rates were similar between groups (Control: 14.7±3.4 ml/min, 17-40%: 12.6±4.0 ml/min, and >40%: 11.7±4.4 ml/min, P>0.05), but the increase in core temperature at the end of exercise in the >40% BSA grafted group (1.6±0.5°C) was greater than the 17-40% (1.2±0.3°C) and Control (0.9±0.2°C) groups (P<0.05). Absolute BSA of non-grafted skin (expressed in m2) was the strongest independent predictor of the core temperature increase (r2=0.41). When re-grouping all subjects, individuals with the lowest BSA of non-grafted skin (<1.0 m2) had greater increases in core temperature (1.6±0.5°C) than those with >1.5 m2 non-grafted skin (1.0±0.3°C, P<0.05). CONCLUSIONS These data imply that individuals with grafted skin have greater increases in core temperature when exercising in the heat and that the magnitude of this increase is best explained by the amount of non-grafted skin available for heat dissipation.

Post Junctional Sudomotor and Cutaneous Vascular Responses in Noninjured Skin Following Heat Acclimation in Burn Survivors

“…This is the first study to examine whether such responses are due, in part, to improvements in post-junctional sweating and cutaneous vascular responses from non-injured, non-donor skin in burn survivors. Interestingly, the increase in core temperature during exercise, and therefore the stimulus for adaptation to heat acclimation, was greater in burn survivors relative to healthy uninjured subjects 7,32 . Given this, it was reasonable to hypothesize that the heat acclimation regimen would provide a sufficient stimulus for post-junctional adaptations in the healthy non-injured/non-donor skin of burn survivors.…”

“…Logically, this is suggestive of an increased sweat output per active gland in burn survivors. In burn survivors, the reliance on fewer active sweat glands in non-injured skin prior to heat acclimation may be a contributing factor predisposing these individuals to impaired heat dissipation and thermal intolerance 5-7 , although such a maladaptation would pale in comparison to the reduced amount of skin available for sweating 14 . Following heat acclimation, the increased number of active sweat glands in non-injured skin may help improve thermal tolerance on the basis that a greater number of active skin glands may result in a larger wetted area of the skin and therefore a larger surface area able to participate in evaporative cooling.…”

“…This protocol and informed consent were approved by the Institutional Review Boards at the University of Texas Southwestern Medical Center at Dallas and Texas Health Presbyterian Hospital of Dallas. The present data were collected simultaneously with data previously published that addressed unique hypotheses 7,32 .…”

“…Subjects visited the laboratory on two separate occasions, both before and after a 7 day heat acclimation regimen as described previously in detail 7,32 . Briefly the heat acclimation regimen involved 7 days of exercise in a 39.6 ± 1.1°C temperature, 31 ± 3% relative humidity environment.…”

“…Burn survivors display evidence of heat intolerance 3 and an elevated risk of hyperthermia and thus related illnesses 4 . This is evident by a greater increase in internal body temperature during exercise in a hot environment in burn survivors with grafted skin relative to unburned individuals 5-7 . Split thickness grafting is commonly used to treat areas of burned skin.…”