Different Impacts of Normobaric/Hypobaric Hypoxia on Physiological and Subjective Responses at a Cold Environment

Abstract

Impacts of normobaric/hypobaric hypoxia on physiological and subjective responses were examined in resting eight healthy young males at a low environmental temperature of 17 °C. They were exposed to the sea level maintained at 27 °C as baseline and then to the three experimental conditions which were combination of barometric (Pe) and partial oxygen (O2) pressures; normobaric hypoxia (NH, Pe= 760 mmHg and O2= 87 mmHg), hypobaric hypoxia (HH, Pe= 418 mmHg and O2= 87 mmHg), and normobaric normoxia (Control, Pe= 760 mmHg and O2= 159 mmHg). Temperatures of rectum (Tre) and 10 sites of skin surface (Tsk), oxygen consumption were measured. Finger-tapping test was performed to assess manual performance. Thermal sensation and subjective shivering activity were also evaluated. A significant difference in the Tre was not seen during exposure to the aimed test condition. On the other hand, a significant difference in the Tsk was observed, the Tsks in both the HH (28.5 ± 0.6 °C) and the NH (27.8 ± 0.5 °C) indicated higher value than that in the Control (27.2 ± 0.7 °C). Despite of larger temperature differences between the Tsk and the environment in the HH and the NH, the heat loss from the body in the HH (87 ± 23 W/m2) was significantly smaller than that in the NH (105 ± 19 W/m2). This is because the convective thermal resistance from the body increases with the decreasing atmospheric pressure so that the convective thermal resistance in the HH was larger than that in the NH. As the consequence, decline in the manual performance was suppressed in the HH and voted score of the subjective shivering was also statistically higher in the HH than in the NH, even though the O2 in air was identically kept at the low level in both the HH and the NH.