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 (1 st -5 th 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 1 st -5 th order arterioles. Metarteriole (i.e., 5 th 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 1 st -4 th order arterioles. Conclusion-Metarteriolesare not only necessary, but sufficient to explain the origin of the biphasic flow response in skin blood flow.

Increasing acclimation period improves the reproducibility of short-heating local thermal hyperemia

“…Metarterioles are the origin of the biphasic flow response in skin blood flow during heating (Widmer, et al, 2008). Skin heating may result in the dilatation of metarterioles to passively increase skin blood flow.…”

Are the precapillary sphincters and metarterioles universal components of the microcirculation? An historical review

“…However, the metarterioles and precapillary sphincters were topics of later physiological research on the microcirculation of various tissues and organs including the skeletal muscles [31–39], skin [40, 41], subcutaneous adipose tissue [42], gastric mucosa [43], liver [44] and heart [45]. In these studies the metarterioles and precapillary sphincters obviously differed from the original concepts by Zweifach.…”

“…In these studies the metarterioles and precapillary sphincters obviously differed from the original concepts by Zweifach. In these studies, the metarterioles were conceived in a restricted sense as representing the smallest and last order of arterioles [41, 45], and they were fundamentally different from the thoroughfare channels connecting arterioles and venules as originally proposed by Zweifach [11, 13, 17] and accepted in modern physiology textbooks [1, 2, 10, 15, 16, 18–23]. Furthermore, in these studies the precapillary sphincters were not substantially demonstrated at specific portions of the microcirculation, but the change in vascular resistance was interpreted as effected by “precapillary sphincter tone” or “precapillary sphincter activity” [34–39, 43], or the last segments of the arterial tree before capillaries were merely designated as the precapillary sphincters without showing any specific localization of smooth muscle cells [31–33, 40, 42, 44].…”

Optical coherence tomography in the assessment of acute changes in cutaneous vascular diameter induced by heat stress

“…However, structural and functional changes in the cutaneous vasculature often manifest at a resolution between these two different scales. For example, the response to a heating challenge is multifaceted, involving dilation of individual vessels at a scale of tens of microns, the recruitment of previously non-perfused vessels and increased flow across the local vascular network, apparent over a field of view of several millimetres (32,40). It is also important to note that glabrous (hairless) and non-glabrous (hairy) skin are viewed as distinct areas in terms of vascular structure and physiological control.…”