Thermoregulatory effects of three different types of head cooling in humans during a mild hyperthermia

Abstract

Seven healthy young men participated in six trials with three different types of local cooling [cool air breathing (CAB), face skin cooling (FaC), and combined cooling (CoC)] in a warm environment for 90 min while either resting (operative temperature: T(0) = 40 degrees C, dew point temperature: T(dp) = 15 degrees C, air velocity: v(a) = 0.3 m x s(-1)) or exercising on a cycle ergometer with an external work load of 90 W (T(0) = 36 degrees C, T(dp) = 15 degrees C, v(a) = 0.3 m x s(-1)). Cool air (10 degrees C) arrived at the entry point of the hood and/or the mask at a ventilation rate of 12 m x s(-1). Oesophageal temperature was not affected by any kind of cooling, while tympanic temperature was decreased at rest by both FaC and CoC [respectively -0.15 (0.06) and -0.09 (0.03) degrees C, P </= 0.05]. Mean skin temperature was decreased by FaC and CoC at rest [respectively -0.31 (0.07) and -0.27 (0.09) degrees C, P </= 0. 05] and during exercise [respectively -0.64 (0.15) and -1.04 (0.22) degrees C, P </= 0.01]. CAB had no effect on skin temperatures. CoC and FaC reduced head skin temperature during both rest and work (P < 0.001) with no effect on the skin temperature of the rest of the body, except under CoC with exercise (P < 0.05). CAB did not influence local sweating. FaC, however, decreased the more profuse sweat rates (P </= 0.05) at rest, while CoC decreased all sweating rates at rest (P </= 0.05) and only the back, head and leg sweating rates during exercise (P </= 0.05). These results suggest that head skin cooling causes a reduction in heat strain, while CAB does not. This beneficial influence does not, however, appear to be the result of selective brain cooling. Tympanic temperature seems to be a good index of the core thermal inputs to the hypothalamic regulatory system, since variations in that parameter were associated with similarly directed variations in the sweating outputs.

Local body cooling to improve sleep quality and thermal comfort in a hot environment

“…47,48 In the waking state, cooling the head has previously been shown to be effective in reducing thermal stress. 33,35 However, in this study, local cooling of the head (neck) alone was not enough to maintain efficient sleep (Table 4), although it reduced thermal sensation, increased thermal comfort slightly (Table 3), and increased subjective sleep quality ( Figure 3) and duration of Stage N3 sleep (Table 4). Studies of waking people have previously found that thermal sensation is based on area summation.…”

“…Local cooling was applied to the head (together with the neck) and upper back because cooling of these parts has been shown to be effective in improving the thermal comfort of subjects who were awake. [30][31][32][33][34][35] The lower body sections were not cooled as people are most comfortable with warm feet 32 and warm feet have been shown to promote the rapid onset of sleep. 39 Wyndham observed that the daytime temperature for comfort (26.6°C) was higher than the nighttime comfort temperature (24.7°C) in the hot humid tropics of Australia when air-conditioning…”

Spatial differences in sensible and latent heat losses under a bicycle helmet

“…This causes high temperatures and sweat production on the head (Rasch et al 1991). Research has shown that, on whole body scale, the amount of sweat production diVers from body part to body part (Kuno 1956;Johnson et al 1997;Machado-Moreira et al 2008a, b;Havenith et al 2008) and that the distribution of the total amount of latent heat losses changes with changing eVort level and environmental conditions (Desruelle and Candas 2000).…”

The effects of two kinds of mask (with or without exhaust valve) on clothing microclimates inside the mask in participants wearing protective clothing for spraying pesticides

“…There are some studies that investigate the effects of wearing a respirator (James et al 1984; Morgan and Raven 1985;Nielsen et al 1987aNielsen et al , 1987bWhite et al 1989White et al , 1991Jette´et al 1992;Flaherty et al 1995;Alston et al1997;Desruelle and Candas 2000), but there are no reports on the thermophysiological responses in participants wearing masks while spraying pesticides in warm environments.…”