Changes in plasma volume and protein content during exposures of working men to various temperatures before and after acclimitization to heat: separation of the roles of cutaneous and skeletal muscle circulation

Abstract

SUMMARY1. Ten male subjects were trained in stair stepping for 2 weeks. Group A (six subjects) was thereupon sequentially exposed for 45 min to dry bulb temperatures of 20, 40 and 300 C, a vapour pressure of 10-11 mm Hg and a wind speed of 1 m/sec in a climate tunnel. While temperature changes were being effected the subjects rested in an antechamber. Group B (four subjects) was exposed to a sequence of 40, 20 and 300 C. Work rate was the same for all subjects, i.e. 216 kg m/min (-to an oxygen consumption of 0 9 1./min). Duplicate experiments were run on both groups of subjects before and after acclimatization to heat.2. Throughout, periodic samples of venous blood, water and protein movement into or out of the extravascular compartment was assessed during exercise periods wherein blood flow was increased to exercising muscles (Group A, 20°C) or to both exercising muscles and skin (Group B, 400 C; Groups A and B, 300 C.) 3. Mild exercise in a cool environment before and after acclimatization to heat was accompanied by expansion of the vascular volume and an increase in the amount of circulating protein.4. Mild exercise in a warm environment for 45 min was accompanied by haemoconcentration and loss of protein from the vascular volume before subjects were heat acclimatized. The results were reversed following heat acclimatization; i.e. exposure of Group B to 400 C and of Groups A and B to 300 C was accompanied by haemodilution and addition to (or maintenance of) plasma protein concentration.5. Effects of heat acclimatization on exposure of Group A to 400 C were also noted.6. The effects of heat acclimatization were ascribed to: (a) a change in permeability of cutaneous capillaries to large molecules, (b) an increased availability of translocatable protein within cutaneous interstitial spaces, and (c) a combination of both a and b. 7. Further, the results supported a previous suggestion that addition or loss of water and protein from the vascular volume is dependent on the ratio of cutaneous to muscle blood flow.

Body fluids and temperature responses of heat‐exposed women before and after ovulation with and without rehydration

“…Each subject behaved similarly in that the increase in To during post-ovulatory dehydration was much less than pre-ovulatory increments in To, Indeed, two subjects showed an ability to reduce their body temperatures even as weight loss was continuing. The intercepts of all the regression equations (b, (Adolph & Associates, 1947;Bass & Henschel, 1956;Senay & Christensen, 1965;Senay, 1972). The reason for this lack of plasma volume expansion in these female subjects is not directly revealed by the experimental results.…”

“…The reason for this lack of plasma volume expansion in these female subjects is not directly revealed by the experimental results. However, from events occurring during the rehydration experiments and early in dehydration experiments, the differences between male and female may directly involve the cutaneous vascular bed (Senay, 1972). In resting males, heat-induced haemodilution appears to depend upon dilatation of the cutaneous vascular bed (Senay & Christensen, 1965;Senay, 1972).…”

Challenges to Temperature Regulation When Working in Hot Environments

“…The substrate for this elevated sweat secretion is provided via an expansion of the plasma volume, which occurs in association with an elevated, and a superior maintenance of the osmotic potential of the blood 29,67) . An expanded plasma volume is better able to withstand fluid loss via sweating.…”

Seasonal Difference in Responses of Body Fluids to Heat Stress

“…Sweat, secreted to regulate body temperature, becomes a threat to homeostasis of the body fluid, and many reports have been published on changes of body fluids caused by sweating (GLICKMAN et al, 1941;LADELL, 1949;ITOH, 1953;CHRISTENSEN, 1965, 1968;SENAY, , 1970SENAY, , 1972. According to the review by BASS and HENSCHEL (1956), an acute heat stress elicits responses which, in the absence of dehydration, result in increased plasma and blood volumes with little change in their compositions , although the behaviors of extracellular and interstitial fluids are still controversial.…”