The origin of the biphasic flow response to local heat in skin.
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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 mum, 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 degrees C for 10 min then increased to 37 degrees 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.
