Effect of skin sympathetic response to local or systemic cold exposure on thermoregulatory functions in humans

We studied how sympathetic response to cold exposure determines thermoregulatory function. Three female and seven male volunteers (age, 23.2±1.9 years) were exposed to abrupt local cooling and gradual systemic cooling with recording of microneurographic skin sympathetic nerve activity (SSNA), skin temperatures (Ts), tympanic temperature (Tty), skin blood flow measured by laser Doppler flowmetry, and sweating rate measured with a ventilated capsule. Local cooling induced an abrupt vasoconstrictor SSNA increase and Tty rise. There was a significant positive correlation between the increase in the vasoconstrictor SSNA and the change rate of Tty. Systemic cooling at 0.2°C/min enhanced SSNA but gradually decreased Tty, and a significant negative correlation was observed between them. A 10-min delay separated the SSNA rise from the subsequent Tty rise following local cooling. A delay of less than 1 min preceded the SSNA increase after the Tty fall induced by systemic cooling. These findings suggested that subjects with a good SSNA response to cold stress can maintain core temperature, but 10 min is necessary to raise the core temperature by reducing heat loss from the skin surface. In contrast, vasoconstrictor SSNA responds linearly to a fall in core temperature with a delay of less than 1 min.