Impact of Burn Injury Size on Critical Environmental Limits during Exercise in the Heat in Young and Middle-Aged...

Burn injuries impair sweating and evaporative heat loss. This project 1) investigated the extent to which the size of a burn injury alters the critical relative humidity (RH crit ) for heat balance during exercise-heat stress among burn survivors with injuries spanning ~20% ( n = 9), ~40% ( n = 6), and ~60% ( n = 9) total body surface area (TBSA), and 2) compared RH crit values between burn survivors and 10 noninjured individuals with simulated burns of 20%, 40%, and 60% TBSA.

Participants cycled (heat production: 192 ± 17 W·m -2 ) in 40°C and 24% relative humidity for 30 min, after which relative humidity increased 3% every 5 min until an upward inflection in esophageal temperature.

RH crit averaged 41.3 ± 6.6% and 30.2 ± 3.8% in burn survivors with 20% and 40% injuries, respectively, and averaged 40.7 ± 5.3%, 38.2 ± 4.8%, and 31.73 ± 4.3% in noninjured individuals with 0%, 20%, and 40% TBSA-simulated burn injuries, respectively. There was a significantly higher probability of achieving RH crit sooner (i.e., at a lower relative humidity) with larger actual and simulated injuries up to 40% TBSA ( P < 0.001). Notably, esophageal temperature never reached a stable plateau, and thus RH crit could not be determined, in half of the participants with 40% TBSA actual and simulated injuries, likely reflecting the influence of burn size plus other factors that influence thermolytic capacity. No participants exhibited an RH crit with a 60% TBSA injury (actual or simulated), indicating that 60% TBSA injuries are too large to permit heat balance at even the lower relative humidity tested.

Higher %TBSA injuries lead to lower RH crit values, with no difference between simulated and actual burn injuries.