Effects of heat exposure on the thermoregulatory responses of young children

The purpose of this study was to determine whether young children's thermoregulation during heat exposure varies with age and body size. A total of 34 young children (aged 6 months-8 years)-18 boys and 16 girl-s-participated in the study. They were divided into five groups according to age (<1 year, 1 year, 2-3 years, 4-5 years, and 8 years). The participants sat for 30 min in a 27 degrees C, 50% rh room, then moved to a 35 degrees C, 70% rh room and remained seated for at least 30 min. They then returned to the first 27 degrees C room and remained stationary for 30 min. Rectal temperature (Tre) and skin temperature (Tsk) were continuously recorded, and the amount of whole-body sweat rate (SR) was measured. Local SR of the back and upper arm were collected with filter paper to calculate local sweating volume, and Na + concentration was measured later. The smaller the age, the signifi-cantly greater the increase in Tre. There was no significant difference in the amount of whole-body SR and the increase in Tsk during the heating among the five groups. Furthermore, there was no significant difference in whole-body SR per increase in Tre during heating between the five groups, but a significant difference was found in back local SR per increase in Tre with age. Difference in local SR between upper arm and back was observed at age 2 years and above, and difference in Na+ concentrations in sweat was observed at age 8 years. The devel-opment of thermoregulatory responses with growth was observed. The results indicate that the thermoregulatory response is disadvantaged by immature mechanisms and small body size in younger children.