Effects of total body core cooling on heat production of conscious goats.

Experiments were performed to investigate the effect of general body core cooling on heat production at various air temperatures between +1 degree C and +56 degrees C in conscious goats. An intravascular heat exchanger (IVHE) was used to alter body core temperature independently of air temperature. Heat loss via the IVHE caused a fall in body core temperature, the extent of which depended on the rate of extraction and air temperature. Irrespective of air temperature the decrease in body core temperature resulted in shivering and an increase in heat production, which eventually balanced the heat loss. During steady state conditions the extra heat production was approximately equal to that lost via the IVHE. The threshold body core temperature at which heat production increased in response to central cooling did not significantly alter with air temperature. However, the slopes of the curves describing this response were smaller at higher than at lower air temperatures, which indicated that central thermosensitivity decreased with increasing air temperature. Irrespective of air temperature the threshold temperatures for shivering were higher and the slopes of the curves were steeper than those previously found with combined cooling of the hypothalamus and spinal cord in the same species which indicated the existence of central thermosensors outside the above two mentioned areas.