Thermal responses to cold wind of thermoneutral and cooled subjects

Abstract

The effects of initial thermal state on thermoregulatory responses to cold (−10°C) in a 0.2 (still air), 1.0, and 5.0 m · s⁻¹ wind speed were studied. Eight young male subjects were first preconditioned in thermoneutral (+20°C, TN) or cool (−5°C, CO) environment for 60 min. After preconditioning the subjects were exposed to wind at −10°C in a standing position, facing the wind, for 30 min. Precooling decreased mean skin temperature (T¯ _sk) by 4.0 (SEM 0.1)°C (P < 0.001) and increased heat flux by 57 (SEM 2) W · m⁻² (P < 0.001) in comparison to TN. Cooling rate of T¯ _sk was faster (P < 0.001) in TN than in CO at every wind speed. Even so, T¯ _sk ended up at a lower level in CO (P < 0.001–0.01) than in TN at every wind speed. Local skin temperatures of hand, finger, foot and toe were significantly lower in CO than in TN at the end of all exposures to wind. Heat flux from the skin was 8% higher (NS) in TN at 5.0 m · s⁻¹ wind speed in comparison to CO. A 5.0 m · s⁻¹ wind speed increased oxygen consumption significantly (P < 0.001) in both CO and TN in comparison to still air. At 5.0 m · s⁻¹ wind speed the general thermal sensation was the same (cold) in both TN and CO, despite the higher T¯ _sk in TN. In conclusion, T¯ _sk decreased more rapidly in TN, probably due to rapid skin vasoconstriction and redistribution of circulation to the central body. Probably for the same reason, dry heat loss from the skin was at nearly the same level in both TN and CO. Although the initial thermal state did not affect the amount of heat loss, it significantly affected the peripheral temperatures and thermal sensations and should therefore be taken into consideration in the prediction of thermophysiological responses to wind.