Seven young male volunteers were subjected to passive body warming in a climatic chamber (air temperature, 28°C; relative humidity, 40%) . Passive body warming was induced by placing the subjects in a box-shaped body warming unit enclosing all but the subject's head. While raising body core temperatures, tympanic (T
ty) and esophageal (T
es) temperatures, forehead skin blood flow (
Qsk), forehead sweating rate (
msw) and blood flow through the angular oculi-ophthalmic vein (
Qov) were continuously monitored. At the start of body warming, T
tywas 36.74±0.14°C which was slightly higher than T
es. During body warmng, T
tyand T
esrose almost linearly, but the rate of rise in T
eswas higher than that of T
ty. Q
skand m
swincreased linearly until T
tyreached about 37.24±0.08°C and 37.47±0.07°C and then levelled off. Mean skin temperature reached about 37°C and maintained. In some subjects,
Qskand msw reached complete plateau levels even when temperatures were still rising.
Qovwas increased to a great extent after the levelling-off of the heat loss responses occurred. When this occurred, the rate of increase in T
tywas suppressed to a slight extent. These results indicate that further rise of brain temperature would not affect the heat loss responses, once the levelling-off occurs in the hyperthermia. We, thus, suggest that the fall in brain temperature by the selective brain cooling would not suppress the heat loss responses as far as skin temperature is high and brain temperature is within the range of temperature at which the heat loss responses remain at their maximum levels.
View full abstract