THE RELATIONSHIP OF LASER-DOPPLER SKIN BLOOD-FLOW MEASUREMENTS TO THECUTANEOUS MICROVASCULAR ANATOMY

The hairless plantar paw surface of the rat shows high skin blood flow with a substantial response to thermal stimulation. This contrasts wi th hair-covered areas such as the back, where there is much lower basa l flow and thermal response. These properties are similar to the diffe rences seen in humans between skin sites which have a high density of arterioles and venules (AV areas) and sites with predominantly nutriti ve (NUTR) capillary perfusion. However, there has been no previous stu dy of the microvascular anatomy of rodent skin. We used NIH Image, a q uantitative imaging program, to count the capillaries, arterioles, and venules in the skin of the plantar paw surface and the back of 14 Wis tar-Kyoto rats. We also used laser-Doppler techniques to determine ski n blood flow at these sites. We found significantly more vessels per u nit area at the paw. There were twice as many capillaries in the paw ( 19.6 +/- 2.4 per mm(2)) compared to the back (9 +/- 1.5 per mm(2)) (P < 0.001). Similarly, there were three times as many venules (11.8 +/- 1.2 per mm(2) vs 3.48 +/- 0.45 per mm(2); P < 0.001). The largest diff erence was in the number of arterioles (7.76 +/- 0.74 per mm(2) vs 0.7 9 +/- 0.13 per mm(2) at the back; P < 0.001). The greater microvascula r density at the paw was reflected in a threefold higher basal blood f low (6.6 +/- 0.44 ml/min/100 g) compared to that in the back (1.99 +/- 0.07 ml/min/100 g) (P < 0.001). Microvascular volume at the back was 0.14 +/- 0.01 x 10(6) RBC/ml in the basal state compared to 0.31 +/- 0 .01 x 10(6) RBC/ml at the paw. Thus, the increased number of vessels a t the paw resulted in a twofold increase in microvascular volume. The plantar paw surface has considerably more vessels than the back. As mi ght be expected, there is a higher proportion of arterioles and venule s compared to capillaries at the paw than at the back. Thus, the plant ar paw surface is an AV site compared to the back, which is a NUTR sit e. Although our prior studies have largely assumed that we could use t he paw and back as contrast sites comparable to AV and NUTR sites in h umans, we have now for the first time conclusively established this fa ct. The increased microvascular density at the paw results in higher s kin blood flow at this site. (C) 1998 Academic Press.