Variation in mental performance under different levels of heat stress-induced dehydration was recorded in 11 subjects heat acclimatized to the tropicals. Dehydration was induced by a combination of water restriction and exercise in heat. The psychological functions--arithmetic ability, short-term memory, and visuomotor tracking--were assessed in a thermoneutral room after the subjects recovered fully from the effects of exercise in heat, as reflected by their oral temperature and heart rate. The results indicated significant deterioration in mental functions at 2% or more body dehydration levels.

The effect of primary dehydration of various levels (1, 2 and 3% body-weight deficits) on mental functions of different complexities were studied in eight heatacclimatized subjects drawn from tropical regions of India. These subjects were also studied after a bout of exercise in heat under two conditions viz., Hot Dry (45°C DB, 30% rh), and Hot Humid (39°C DB, 60% rh) at 34OC WBGT. No significant change in routine mental work was seen either under dehydration per se of any level or after subsequent exercise under heat when compared with the normal state. On the other hand, at 2 and 3% levels of primary dehydration a further reduction was noted in all the functions though it was not significant. Inter-variations in Hot Huniid and Hot D r y conditions were not significant ex&pt for more pronounced reductions in the concentration component in Hot Hdmid conditions.

No abstract

Twenty five subjects acclimatised to heat artificially were exposed to "basic effective temperatures" (BET) of 25.0 degrees, 29.6 degrees, 32.2 degrees, 33.3 degrees and 35.0 degrees C BET under conditions of both humid and dry heat. The object of the investigation was to ascertain the nature of effects of varying degrees of heat stress on mental alertness, associative learning, reasoning ability and dual-performance efficiency. A further aim was to determine the temperature levels at which impairment of psychological functions was severe enough to be of practical concern. The duration of each exposure was four hours, during which subjects performed physical exercise followed by rest every 30 min. It was found that all the psychological functions tested were adversely affected under extreme heat, and that a significant drop in various psychological functions was seen at effective temperatures of 32.2 degrees C and 33.3 degrees C in hot-humid and hot-dry conditions respectively. It is concluded that at the same effective temperatures the magnitude of the overall effect on psychological functions under humid conditions is relatively greater than that under dry conditions.

No abstract