The Origin of the Biphasic Flow Response to Local Heat in Skin

Abstract

Objective: Although it is well established that the application of local heat causes a biphasic increase in skin blood flow, the responsible microvessels have not been identified. Methods: A bifurcating network of arterioles (1st–5th orders, 60–15 μm, n = 10 per group) of the intact, unanesthetized, translucent bat wing were visualized on a transparent heat plate via intravital microscopy. Similar to previous bat wing studies, plate temperature was set at 25°C for 10 min then increased to 37°C for 20 min. Vessel diameter and red blood cell velocity were recorded and used to calculate resistance and blood flow. Results: The average flow response in arterioles was biphasic (p = 0.02) and proportional to the temporal decrease in total resistance calculated from 1st–5th order arterioles. Metarteriole (i.e., 5th order arteriole) resistance had the greatest impact on total resistance (−67.0 ± 20.7%) and exhibited a biphasic trend that was opposed by temporal changes in resistance of 1st–4th order arterioles. Conclusion: Metarterioles are not only necessary but sufficient to explain the origin of the biphasic flow response in skin blood flow.