THE EFFECT OF THE SODIUM CHLORIDE INTAKE ON THE WORK PERFORMANCE OF MAN DURING EXPOSURE TO DRY HEAT AND EXPERIMENTAL HEAT EXHAUSTION

Abstract

The effects of 3 levels of NaCl intake (6, 15, and 30 gms. daily) were studied in 49 men in work and rest, during exposures of 2 to 8 days to hot dry air (120[degree]F.) under standardized conditions of diet and work. No advantage in working pulse rate, rectal temp. and rate of sweating or Crampton score (at rest) was shown for men on 30 as compared to 15 gs. NaCl daily. Men maintained on 6 gs. NaCl daily intake had higher pulse rates and rectal temps. in work and poorer Crampton scores than men on 15 gs. NaCl intake. The men on the 6 g. intake lost more than twice as much wt., drank less water and sweated less than the men on the 15 g. intake. Heat exhaustion, characterized by nausea, vomiting, tachycardia, hypotension, vertigo, dehydration and collapse occurred in 25% of the men on the 6 g. intake and in only 2.5% of the men on the 15 g. intake. Hypochloremia (as low as 89 M.E./liter) occurred often but heat cramps were not observed. The predominant role of NaCl (in heat) appears to be the stabilization of the cardiovascular system and the prevention of heat exhaustion. Hypochloremia is not the only factor in heat cramps.