Evaluation of the role of skin temperature in the response of cutaneous capillary blood flow to indirect heat.

The purpose of this study was to test the hypothesis that the rise in cutaneous capillary blood flow that occurs while heating a remote region of the body; i.e., indirect heating, is mediated by an increase in local heat flux secondary to the opening of larger vessels; e.g. AVAs. Twelve unanesthetized rats were placed in a chamber and exposed to a 35 degree C environment while their tail remained unheated. Measurements of regional skin blood flow in the tail were obtained by a laser Doppler flowmeter (LDF) while measurements of blood cell velocity in individual capillaries (CBV) within the subepidermal vascular plexus were made by videodensitometry before and during body heating under two procedures: A control procedure in which skin temperature of the tail (TS) was allowed to increase as LDF increased, then under an experimental procedure during which TS was "clamped" at 25 degree C during body heating. During the control procedure TS increased from 24.5 to 33.2 degrees C while LDF increased by 404% and CBV increased by 89%. During the experimental heating procedure in which TS was clamped, respective increments in LDF and CBV were 414% and 72%. Respective changes in LDF and CBV between the control and experimental procedures were not significantly different. These results argue against local heat flux as a major mechanism for an increase in cutaneous capillary blood flow during indirect heating.