Thermoregulation during exercise under controlled hot ambient conditions is comparable in individuals with a history of exertional heat stroke, RYR1-related malignant hyperthermia, and healthy controls.

Abstract

Exertional heat stroke (EHS) and Malignant Hyperthermia (MH) are potentially life-threatening conditions with overlapping clinical characteristics. In this study, we compared the thermoregulatory response to exercise under increased environmental temperatures in individuals with a history of EHS (n = 15) or MH (n = 14) to healthy controls (n = 15). Groups were age- and sex-matched (31 male, 13 female, 42 ± 10 years). A 60-min exercise test was performed on a cycle ergometer at an ambient temperature of 30.3 ± 0.6°C and a relative humidity of 33.5 ± 4.7%. A stepwise incremental exercise protocol was used to reach a metabolic heat production of 6, 8 and 9 W/kg body mass. Gastrointestinal (T_gi) and skin (T_sk) temperature were monitored continuously, and partitional calorimetry was used to calculate dry (H_dry) and respiratory heat loss (H_resp). Whole-body sweat rate (WBSR) was assessed by measuring body mass. Exercise-induced increases in T_gi (1.4 ± 0.5°C) and T_sk (1.9 ± 0.8°C) were observed, but the magnitude of increase across groups was comparable (p_time*group = 0.80 and p = 0.57, respectively). H_dry was significantly lower in EHS participants (54 ± 4 W) compared to controls (65 ± 11 W, p = 0.023). No differences were observed in H_resp and WBSR. Our results suggest that individuals with MH or a history of EHS do not have an altered thermoregulatory response to exercise in the heat in a controlled setting. Further research is required to determine to what extent the complex accumulation of risk factors contributes to EHS susceptibility.