BLOOD VOLUME CHANGES IN MEN EXPOSED TO HOT ENVIRONMENTAL CONDITIONS FOR A FEW HOURS

Abstract

The plasma and blood vols. of human subjects were studied by means of dye T 1824 in comfortable (28.6[degree] C dry bulb and 19.7[degree] C wet bulb), hot (dry bulb 37.2[degree] C to 44.7 C; wet bulb 20.1[degree] C to 27.5[degree] C) environments. Exposure to hot environments lasted from 1-4 hrs. In 6 expts. there was an increase in circulating plasma vol., red cell mass, and gs. of total circulating proteins, all of which would be expected on the assumption that the new fluids were contributed by blood from the body reservoirs. In 4 expts. there was a decrease in circulating plasma vol. and variable changes in red cell mass. These changes were attributed to water lost by evaporation from the blood plasma. In 14 expts. there were no significant changes in circulating plasma vol., serum proteins or blood counts. The lack of change was attributed to a summation of the 2 factors described above, which tend to neutralize each other. Considerable quantities of water can be requisitioned from the tissues and evaporated from blood plasma without affecting the circulating blood vol. In steady states, the increase in pulse rate correlates well with rises in rectal temps. If the plasma vol. increases, the rise in pulse rate per degree rise in rectal temp, is less than in those subjects whose plasma vol. remains unchanged or decreases.