Physiological responses during work in hot humid environments.

Studies have been conducted on 6 young healthy Indians in simulated comfortable, hot humid and very hot humid conditions to evaluate the physiological reactions during work. Physiological responses like exercise oxygen consumption (VO2), pulmonary ventilation (VE) and heart rate (HR) were noted during sub-maximal fixed work rates of 400, 500 and 600 kgM/min. In addition, duration of continuous work at these three rates of work, in the three simulated environments was also noted. Physiological responses i.e. VO2, VE and HR were noted every 15 minutes of work. Besides these responses, rectal temperature (Tr), mean skin temperature (Ts) and mean sweat rate were also noted during the continuous work. Results indicated a significantly higher oxygen cost (VO2) during 400 kgM/min of work in hot and very hot humid environments whereas, in the higher rates of work, the changes were not significant. The cardiac frequency showed a significantly higher rise during different grades of activities in hot and very hot environments except in the highest work rate in hotter environments, possibly due to attainment of maximum heart rate. The duration of continuous physical efforts in various grades of activities decreased significantly (P less than 0.001) in hot humid environments than in the comfortable temperature. During the progression of the work, the mean skin temperature decreased in comfortable temperature but increased in hot humid environments. The mean rectal temperature, increased during work in hot humid environment, and the rate of rise was much faster in higher work rates attaining the target temperature much earlier. The rate of sweating increased significantly as the heat load of the body increased. In hot humid environments, work performance decreased due to early attainment of maximum heart rate, reduction in VO2 max, disproportionate rise in rectal temperature, narrowing of the difference between the core and the skin temperature and attainment of maximum sweating rate.