THE EFFECT OF INCREASING TEMPERATURE ON SKIN BLOOD-FLOW AND RED-CELL DEFORMABILITY

Using laser Doppler techniques in nine healthy volunteers, we contrast ed the effect of increasing local skin temperature at the elbow, a ski n site with nutritive microvasculature, and the finger pulp, with pred ominantly arteriovenous anastomic (AVA) perfusion). We also assessed f low at the finger dorsum, with contributions of both types of microvas culature. In parallel with the laser Doppler studies, we determined th e effect of increasing temperature on the red cell deformability of ou r subjects, using the new technique of Cell Transit Time Analysis (CTT A). Thermal stimulation produced very large increases in skin blood fl ow at all three sites tested. However, the magnitude and the pattern o f increase were different at the three sites. At the finger pulp, ther e was a linear approximately threefold increase in flow as temperature increased from the basal level to 44-degrees-C. At the elbow, basal f low was considerably lower than at the finger pulp and increased very slowly until skin temperature reached 38-degrees-C. From that point, f low increased sharply, reaching tenfold the basal level at 44-degrees- C. The thermally induced increase at the finger dorsum was intermediat e between the other two sites, with a pattern resembling the elbow mor e than the finger pulp. These differences among the sites were attribu table to substantially different patterns of change in the two compone nts of flow, microvasvular volume and velocity. At the finger pulp, th ere was very little increase in microvascular volume with increasing t emperature. The curve was practically flat from basal temperature to 4 4-degrees-C. In contrast, there was a linear increase in red blood cel l velocity of about 300%. At the elbow, both microvascular volume and red blood cell velocity exhibited a parallel curvilinear pattern of eq uivalent increase, on the order of 300% for each. There was only a sma ll increase in both parameters until the temperature reached 38-degree s, at which point there was a sharp increase in both. At the finger do rsum, the situation was intermediate, again resembling the elbow more than the finger pulp. Cell Transit Time Analysis revealed a progressiv e decrease in red cell transit time (TT), from 3.28 ms at 28-degrees-C to 2.48 m at 44-degrees-C, an overall change of 24%. The decrease in Tr was accompanied by an increase in transit frequency, measured as co unts s-1 (C s-1), from 3.1 to 5.3, an overall change of 71%. The chang es in both TT and C/S were essentially linear. Our present findings de monstrate 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% sugge sts that improved red cell entry into capillaries is a factor in the t hermally induced increase in microvascular volume.