No Thermoregulatory Impairment in Skin Graft Donor Sites during Exercise-Heat Stress

Abstract

The US Army's Standards of Medical Fitness, AR 40-501, state that "Prior burn injury (to include donor sites) involving a total body surface area of 40% or more does not meet the standard." Inclusion of donor sites (sites harvested for skin grafts) in this standard implies that thermoregulatory function is impaired within donor sites during exercise-heat stress; however, supporting evidence is currently lacking.

Purpose: To test the hypothesis that well-healed donor and noninjured sites demonstrate similar elevations in skin blood flow and sweating during exercise-induced hyperthermia.

Methods: Twenty burn survivors (>1 yr postinjury; four females) cycled for 60 min in a 39.7°C ± 0.3°C and 21.1% ± 3.3% relative humidity environment at approximately 50% of maximal aerobic capacity. Core and mean skin temperatures were recorded throughout exercise. Skin blood flow (laser-Doppler imaging) was measured at baseline and after exercise within donor (LDFDON) and adjacent noninjured control (LDFCON) sites. At 45 min of exercise, local sweat rates (Technical Absorbents) were measured within the same donor (LSRDON) and noninjured (LSRCON) areas.

Results: After 60 min of exercise, core and skin temperatures reached 38.2°C ± 0.4°C and 35.5°C ± 1.2°C, respectively. The increase in skin blood flow from baseline to end-exercise (LDFDON, 91.6 ± 44.5 AU; LDFCON, 106.0 ± 61.6 AU; P = 0.17) and local sweat rates (LSRDON, 0.46 ± 0.26 mg·cm·min; LSRCON, 0.53 ± 0.25 mg·cm·min; P = 0.14) were not different between donor and noninjured control sites.

Conclusions: Well-healed donor sites retain the ability to increase skin blood flow and sweating during exercise heat stress, providing evidence against the inclusion of donor sites when determining whether a burn injury meets the Army's Standards of Medical Fitness.

FIGURE 1—

Comparison of the elevation in skin blood flow within non-injured (LDF_CON) and donor (LDF_DON) skin sites from baseline to the end of a 60-min bout of exercise in the heat. Individual (n=19; small closed circles with participant number) and mean (± SD; large open circle) skin blood flow values are expressed as laser-Doppler flux in arbitrary perfusion units (AU).

FIGURE 2—

Comparison of local sweat rates within non-injured (LSR_CON) and donor (LSR_DON) skin sites during minutes 45 to 50 of exercise in the heat. Individual (n=16; small closed circles with participant number) and mean (± SD; large open circle) local sweat rate values are shown.