Effect of ambient temperature rise on the core temperature change in humans

Abstract

Vasoconstrictive Skin Sympathetic Nerve Activity (SSNA) plays an important role in human thermoregulation by controlling heat loss from the skin via constricting or dilating cutaneous vessels with major interindividual differences. It was sought to clarify how this variance influences changes in tympanic temperature (core temperature) in the warming process of ambient temperature. Subjects were 15 healthy volunteers who gave informed consent. They reclined on a bed wearing a T-shirt and short pants while their vasoconstrictive SSNA was recorded microneurographically from the peroneal nerve simultaneously with skin temperature, tympanic temperature, and effector response (sweat rate and skin potential, and skin blood flow by laser Doppler flowmetry). Analyzable data were obtained from 12 subjects. The ambient temperature rise from 15 C to 25 C (0.5 C/min) induced significant vasoconstrictor suppression from 15.2 +/- 2.4 to 7.4 +/- 4.0 bursts/min (p less than 0.01) with a decrease in tympanic temperature from 36.55 +/- 0.07 to 36.35 +/- 0.07 C (p less than 0.05). The suppression rate of vasoconstrictor SSNA has significant correlations with the decreasing rate of tympanic temperature (p less than 0.0072) and the magnitude of that decrease (p less then 0.0002). A cross-correlogram between vasoconstrictor SSNA and tympanic temperature showed a peak at 12 min (r = 0.52). It was concluded that the human thermoregulatory function was largely dependent on the suppression capability of vasoconstrictor, and that such suppression exerted its greatest influence on the core temperature drop with a 12-min delay.