Thermoregulatory effects of three different types of head cooling in humans during a mild hyperthermia.
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.
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Centre d'Etudes de Physiologie Appliquée, Centre National de la Recherche Scientifique, 21 rue Becquerel, F-67087 Strasbourg Cedex, France.
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D000328:Adult; D001831:Body Temperature; D001833:Body Temperature Regulation / Q000502:physiology*; D004432:Ear, Middle / Q000502:physiology; D004947:Esophagus / Q000502:physiology; D006257:Head / Q000502:physiology*; D006801:Humans; D006979:Hyperthermia, Induced / Q000379:methods; D008297:Male; D012016:Reference Values; D012143:Respiratory Physiological Phenomena; D012881:Skin Temperature