Abstract
Summary. Using laser Doppler techniques in nine healthy volunteers, we contrasted the effect of increasing local skin temperature at the elbow, a skin site with nutritive microvasculature, and the finger pulp, with predominantly arteriovenous anastomic (AVA) perfusion). We also assessed flow at the finger dorsum, with contributions of both types of microvasculature. In parallel with the laser Doppler studies, we determined the effect of increasing temperature on the red cell deformability of our subjects, using the new technique of Cell Transit Time Analysis (CTTA). Thermal stimulation produced very large increases in skin blood flow at all three sites tested. However, the magnitude and the pattern of increase were different at the three sites. At the finger pulp, there was a linear approximately threefold increase in flow as temperature increased from the basal level to 44°C. At the elbow, basal flow was considerably lower than at the finger pulp and increased very slowly until skin temperature reached 38°C. From that point, flow increased sharply, reaching tenfold the basal level at 44°C. The thermally induced increase at the finger dorsum was intermediate between the other two sites, with a pattern resembling the elbow more than the finger pulp. These differences among the sites were attributable to substantially different patterns of change in the two components of flow, microvasvular volume and velocity. At the finger pulp, there was very little increase in microvascular volume with increasing temperature. The curve was practically flat from basal temperature to 44°C. In contrast, there was a linear increase in red blood cell velocity of about 300%. At the elbow, both microvascular volume and red blood cell velocity exhibited a parallel curvilinear pattern of equivalent increase, on the order of 300% for each. There was only a small increase in both parameters until the temperature reached 38°, at which point there was a sharp increase in both. At the finger dorsum, the situation was intermediate, again resembling the elbow more than the finger pulp. Cell Transit Time Analysis revealed a progressive decrease in red cell transit time (TT), from 3.28 ms at 28°C to 2.48 m at 44°C, an overall change of 24%. The decrease in TT was accompanied by an increase in transit frequency, measured as counts s‐1 (C s‐1), from 3.1 to 5.3, an overall change of 71%. The changes in both TT and C/S were essentially linear. Our present findings demonstrate that cutaneous AVA beds differ significantly from nutritive capillary beds in the mechanisms of thermally induced flow change. The 24% observed increase in red cell transit time on CTTA would suggest only a small potential rheological contribution to increased red blood cell velocity. However, the increase in counts s‐1 of about 70% suggests that improved red cell entry into capillaries is a factor in the thermally induced increase in microvascular volume.