Effect of post-hypoxic acclimatization on extremity temperature during exposure to acute cold stress in man.

Twelve male volunteers aged 20-28 yr, who were physically fit for high altitude duties were studied. Recordings of oral temperature, mean skin temperature, extremity temperature, O2 consumption and heart rate were taken in a thermoneutral room (26 degrees +/- 2 degrees C) and cold room (6 degrees-8 degrees C) initially; after 4 wk stay at 3353 m (502 mm Hg); again after 4 wk at 4115 m (455 mm Hg); and finally after return to Delhi (740 mm Hg). The oral temperature, mean skin temperature, oxygen consumption and heart rate did not show any significant difference from their initial sea level values recorded in the thermoneutral room or the cold room. It may be concluded that our subjects did not exhibit any degree cold acclimatization when retested at sea level. A significant elevation (P less than 0.001) of extremity temperature observed during retest in cold might be due to some degree of vasodilatation through relaxation of constrictor tone that might have taken place during exposure to hypoxia at high altitude.

Physiological and metabolic responses to work in heat with graded hypohydration in tropical subjects.

Studies were conducted on 25 healthy male volunteers aged 20-25 years drawn randomly from the tropical regions of India. The subjects initially underwent an 8 day heat acclimatization schedule with 2 hours moderate work in a climatic chamber at 45 degrees C DB and 30% RH. These heat acclimatized subjects were then hypohydrated to varying levels of body weight deficits, i.e. 1.3 +/- 0.03, 2.3 +/- 0.04 and 3.3 +/- 0.04%, by a combination of water restriction and moderate exercise inside the hot chamber. After 2 hours rest in a thermoneutral room (25 +/- 1 degree C) the hypohydrated subjects were tested on a bicycle ergometer at a fixed submaximal work rate (40 W, 40 min) in a hot dry condition (45 degrees C DB, 30% RH, 34 degrees C WBGT). Significant increases in exercise heart rate and oral temperature were observed in hypohydrated subjects as compared to euhydration. Sweat rate increased with 1% and 2% hypohydration as compared to euhydration, but a significant decrease was observed with 3% hypohydration. Na+ & K+ concentrations in arm sweat increased with increase in the level of hypohydration. Oxygen consumption increased significantly only when hypohydration was about 2% or more. It appears that the increased physiological strain observed in tropical subjects working in heat with graded hypohydration is not solely due to reduced sweat rates.