O. Shido et al., Core temperature and sweating onset in humans acclimated to heat given at a fixed daily time, AM J P-REG, 45(4), 1999, pp. R1095-R1101
Citations number
30
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physiology
Journal title
AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY
The thermoregulatory functions of rats acclimated to heat given daily at a
fixed time are altered, especially during the period in which they were pre
viously exposed to heat. In this study, we investigated the existence of si
milar phenomena in humans. Volunteers were exposed to an ambient temperatur
e (T-a) of 46 degrees C and a relative humidity of 20% for 4 h (1400-1800)
for 9-10 consecutive days. In the first experiment, the rectal temperatures
(T-re) of six subjects were measured over 24 h at a T-a of 27 degrees C wi
th and without heat acclimation. Heat acclimation significantly lowered T-r
e only between 1400 and 1800. In the second experiment, six subjects rested
in a chair at a T-a of 28 degrees C and a relative humidity of 40% with bo
th legs immersed in warm water (42 degrees C) for 30 min. The T-re and swea
ting rates at the forearm and chest were measured. Measurements were made i
n the morning (0900-1100) and afternoon (1500-1700) on the same day before
and after heat acclimation. Heat acclimation shortened the sweating latency
and decreased the threshold T-re for sweating. However, these changes were
significant only in the afternoon. The results suggest that repeated heat
exposure in humans, limited to a fixed time daily, alters the core temperat
ure level and thermoregulatory function, especially during the period in wh
ich the subjects had previously been exposed to heat.