Evaluation of a temperate-environment test of heat tolerance in prior heatstroke patients and controls

Summary

It has been reported that scores from a temperate-environment step test describe the heat-tolerance status of prior heatstroke patients (HP). This investigation evaluated the ability of this temperate-environment heat-tolerance test (HTT) to indicate altered heart rate (HR) and rectal temperature (T _re )responses of HP, after 7 days of heat acclimation. On day 1, ten male HP (61 ± 7 days post-heatstroke) and five control subjects (C) bench-stepped (0.30 m high, 27 steps · min⁻¹) for 15 min (25.8° C dry bulb, 16.2° C wet bulb). On days 2–8, subjects underwent heat acclimation (40.1° C dry bulb, 23.8°C wet bulb; treadmill, 90 min · day⁻¹). Heat acclimation resulted in significant decreases in final HR (152±5 vs 130±3 beats·min⁻¹ P<0.025) and finalT _re (38.62±0.11 vs 38.13±0.07°C,p < 0.01) in HP. One HP but no C was defined heat intolerant, exhibiting inability to adapt to daily exercise in the heat. On day 9, HP repeated HTT, exactly as performed on day 1; mean group HTT scores did not change (day 1=39±6; day 9=48±6,P>0.05). All physical characteristics and physiological responses of HP (days 1, 2, 7, 9) were statistically similar (P>0.05) to those of C. In contrast to heat-acclimation data, HTT scores (score ≤30) indicated that four HP were heat intolerant on day 1 and two HP were heat intolerant on day 9. It was concluded that HTT was not a substitute for lengthier tests of heat tolerance conducted in hot environments, because HTT scores (at 25.8°C did not reflect HR andT _re responses (at 40.1° C) in 33% of heat-acclimated (e.g., heat-tolerant) HP. In addition, HTT scores did not validly discriminate between heat tolerant and heat-intolerant HP.