Thermoregulatory responses to combined moderate heat stress and hypoxia

The aim of this study was to examine the cutaneous vascular and sudomotor responses to combined moderate passive heat stress and normobaric hypoxia.

Thirteen healthy young males, dressed in a water-perfused suit, underwent passive heating (Δcore temperature ~0.7°C) twice (Normoxia; 20.9% O₂ and Hypoxia; 13% O₂ ). Chest and forearm skin blood flow (SkBF; laser-Doppler flux) and sweat rate (SR; capacitance hygrometry), core (intestinal pill), and skin temperatures, were recorded.

Hypoxia reduced baseline oxygen saturation (98±1 vs 89±6%, P<.001) and elevated chest (P=.03) and forearm SkBF (P=.03), and HR (64±9 vs 69±8 beats.min^-1 , P<.01). During heating, mean body temperature (T¯BODY) thresholds for SkBF (P=.41) and SR (P=.28) elevations were not different between trials. The SkBF: T¯BODY linear sensitivity during the initial phase of heating was lower at the chest (P=.035) but not different at the forearm (P=.17) during hypoxia. With increasing levels of heating chest SkBF was not different (P=.55) but forearm SkBF was lower (P<.01) during hypoxia. Chest (P=.85) and forearm (P=.79) SR: T¯BODY linear sensitivities were not different between trials.

While sudomotor responses and the initiation of cutaneous blood flow elevations are unaffected, hypoxia differentially effects regional SkBF responses during moderate passive heating.