Thermoregulatory Response to Exercise After Exertional Heat Stroke

Abstract

Background: After one episode of exertional heat stroke (EHS), risk factors must be identified to determine the potential for subsequent episodes. One of these risk factors, core body temperature (T_co) kinetics during strenuous exercise, may be a surrogate marker suggestive of impaired thermoregulation. This study aimed to determine the kinetics of increases in T_co among military subjects who had a history of EHS.

Methods: Forty subjects (38 males, mean age 28.4 ± 4.9 years, mean body mass index 24.9 ± 2.4) who had a history of EHS ran 8 km in full combat gear with continuous monitoring of T_co and heart rate. The run was a qualifying event for military service. T_co was assessed using an ingestible sensor (Cortemp HQ Inc., Palmetto, Florida). Maximum oxygen uptake (VO_2max) was measured on the day before the run.

Findings: The mean performance time for the run was 44.6 ± 6.6 minutes achieved under mild climatic conditions. No neurological impairment was observed. The mean maximum T_co was 39.9 ± 0.5°C. On the basis of T_co during the last 10 minutes of running, two T_co profiles were identified: increased T_co (T_co increase > 0.5°C) and plateaued T_co. Neither profile depended on initial, mid-run, or maximal T_co, VO_2max, speed running, body surface area or body fat mass.

Discussion: Subjects who had a history of EHS exhibited different T_co profiles at the end of an 8-km run. Laboratory studies will be necessary to identify the mechanisms underlying these profiles; future longitudinal studies can determine whether a T_co increase >0.5°C during the last 10 minutes is a risk factor for EHS recurrence.