The skin blood flow response in wound healing

Although vasodilation is conventionally held to be the predominant microvascular response to a wound, there has been no previous attempt to actually quantitate skin blood flow within and in the neighborhood of wounds. In particular, there has been no differentiation between sites with primarily nutritive (NUTR) blood flow and those with considerable arteriovenous (AV) perfusion. We used our previously described model of cutaneous blood flow in the rat to study the blood flow response to wounding. We measured skin blood flow at the centers and at the undisturbed perimeters of wounds placed at the back, a NUTR site, and at the paw, an AV site, in 11 Wistar Kyoto rats. Measurements were performed at baseline, and then at 3 hr, 24 hr, 72 hr, and 7 days postwounding. At 3 hr, flow at the center of the back wound had increased to 11.3 +/- 1.4 ml/min/100 g from a baseline of 2.1 +/- 0.1 ml/min/100 g and remained elevated at 7 days (8.3 ml/min/100 g). Flow at the perimeter of the back wound rose as well, but not as high as at wound center, to twice the baseline level (4.1 ml/min/ 100 g at Day 7). Flow values at control sites on the back did not increase from baseline. Flow at the center of the paw wound rose from 7.2 +/- 0.5 ml/min/100 g at baseline to 15.6 +/- 4.3 ml/min/100 g at Day 3 but then fell back to 6.9 +/- 0.9 ml/min/100 g at Day 7. There was only a very small increase in the basal temperature wound response at the paw perimeter. Blood flow at all wound sites showed a response to heat. At the back, heating to 44 degrees stimulated an 80% increase in blood flow at baseline. This degree of increase was maintained at both the center and the perimeter of the back wound. In contrast, although there was also a thermal response at the paw wound center, it was of much lower magnitude than the nonwounded baseline response. As a result, the heat-stimulated flow value actually fell over the 7 days to approximately half of the baseline level. At the paw wound periphery, there was an initial fall in the heat stimulated response, but it then recovered to the baseline level and remained stable over the 7 days. Thus, the skin blood flow response seen at the paw wound challenges the conventional concept of vasodilation as the expected wound blood flow response. The mechanisms of blood flow response in the healing wound may be more complex than the simple inflammatory vasodilation conventionally postulated.