Thermoregulatory responses of circum-pubertal children.

Passive temperature lability of nine circum-pubertal children [11.4 (1.2) years] was compared to that of nine young adult males [26.6 (5.2) years]. Each subject completed a 20-min period of exercise, followed immediately by post-exercise immersion in water at 28 degrees C. The aim of the exercise protocol was to induce a steady rate of sweating (Esw) while the postexercise immersion period induced cooling of the core region (tympanic temperature: Tty). The Tty values (relative to rest, delta Tty) at which sweating abated and at which shivering commenced were defined as the thresholds for the cessation of sweating and onset of shivering, respectively. While there was no significant difference between the delta Tty sweating thresholds, the onset of shivering, as reflected in the oxygen uptake (VO2) response, occurred at significantly higher (P < 0.05) delta Tty values in the children [mean (SD): - 0.07 (0.07) degrees C] than in the adults [ -0.22 (0.10) degrees C]. The slope of the Esw/delta Tty relationship was found to be significantly lower in the children (z = -5.64; P < 0.05), while the slopes of the VO2/delta Tty relationship were not significantly different (z = -0.84; P > 0.05). Skin blood perfusion was measured at the forehead (SkBP), and the slope of the SkBP/delta Tty relationship across the null-zone was significantly less in the children than in the adults (z = -2.13; P < 0.05) with the greatest reduction in perfusion occurring prior to the offset of sweating in the children. The subjective ratings of thermal comfort indicated that the children were more sensitive to changes in core temperature than the adults. It is concluded that maturation plays an important role in modifying thermoregulatory responses to deviations in core temperature. These results suggest that there may be differences in thermoregulatory "strategies" which are maturationally related.