Influence of air velocity and heat acclimation on human skin wettedness and sweating efficiency

Abstract

Before and after heat acclimation, four male resting subjects were exposed to humid heat that caused levels of skin wettedness ranging from 50 to 100%. The physical experimental conditions were chosen so that the same skin wettedness was attained with modification of only the ambient water vapor pressure, at two wind speeds (0.6 and 0.9 m . s-1). The esophageal temperature (Tes), mean skin temperature (Tsk), sweating rate (msw), and dripping sweat rate (mdr) were recorded; the amounts of local drippage in the same thermal conditions before and after acclimation were also determined. The relationship between the evaporative efficiency of sweating (eta sw) and the skin wettedness (w) is reported, as is the influence of the subject's acclimation to humid heat on adjustments of skin wettedness. The effects of the air velocity on the coefficient of evaporation and on sweating efficiency are discussed. Beneficial increases in evaporation were achievable by increasing skin wettedness only when there was a consistent drippage, which differed from one body area to another and from one subject to another. The relation of drift in body temperature to skin wettedness changed with the acclimation of the subjects.

Thermoregulatory Efficiency is Increased after Heat Acclimation in Tropical Natives

“…This finding is corroborated by some (Candas et al, 1979b, Rowell et al, 1967 but not by others. (Patterson et al, 2004;Mitchell et al, 1976;Kenney et al, 1990).…”

“…Increased Ṁ sw is partly responsible for the higher w sk and E sw also observed, (Mitchell et al, 1976;Candas et al, 1979b); however, as shown by others (Mitchell et al, 1976), Ṁ sw was also related to an increase in the nonevaporated sweat. Belding and Hatch (1955) have stated that nonevaporated sweat should not be considered physiologically inefficient, because oversweating is necessary to satisfy the w sk requirements, which, in turn, has been found to be responsible for the higher E sw (Berglund and Gonzalez, 1977).…”

“…However, despite the increase in nonevaporated sweat, we did not find a reduction in h sw . Differently, Candas et al (1979b) described an augmented drippage of around 30% to 65% of the sweat produced being wasted while Mitchell et al (1976) found a 200% increase in sweat drippage, which led to lower h sw . These differences might be related to the higher evaporative capacity of the environment employed in the present study.…”

“…Belding and Hatch (1955) have stated that nonevaporated sweat should not be considered physiologically inefficient, because oversweating is necessary to satisfy the w sk requirements, which, in turn, has been found to be responsible for the higher E sw (Berglund and Gonzalez, 1977). Candas et al (1979b) suggested, therefore, that the role of HA is to develop the required w sk for sweat evaporation. However, despite the increase in nonevaporated sweat, we did not find a reduction in h sw .…”

Should electric fans be used during a heat wave?

“…additional air flow does not improve the evaporative efficiency of sweat ( sw )). Seminal work by Candas (1979aCandas ( , 1979b and others (Givoni, 1963;Kerslake, 1963) demonstrated that as E req approaches E max , an exponential reduction in  sw occurs, that is, progressively more sweat drips off the body and does not contribute to evaporative heat loss from the skin. With electric fan use, the additional air flow increases the evaporative heat transfer coefficient (h e ), and subsequently increases E max.…”