Heterogeneity of capillary density of skin over the dorsum of the foot and toes of healthy subjects.

The spatial pattern of capillaries is one of many factors important for the optimisation of oxygen and nutrient delivery in a specified region of tissue. One area of particular interest to the vascular specialist is the skin of the dorsum of the foot and toes, as these are especially prone to ulceration in patients with arterial disease. The aim of this study was therefore to establish the extent of capillary density (CD) heterogeneity in the normal skin of the dorsum of the foot and toes, since any great non-uniformity might produce regions of low perfusion, which may become vulnerable to ulceration. Using white-light (native) videomicroscopy at a magnification of x 40 in 15 healthy subjects (mean age 72 years), the dorsum of the foot and toes was systematically mapped by determining the CD at each of 25 sites on the dorsum of the foot, and at 2 sites on the distal phalanx of each toe. Off-line analysis of videoprints was then undertaken to determine CD at each site, according to a fixed protocol of measurement and data analysis. The mean value and spatial coefficient of variation of CD was then calculated for each foot. There was striking spatial heterogeneity of CD in the dorsum of the foot, some areas having low numbers of capillaries and other areas in the same foot having higher capillary numbers. This spatial heterogeneity of CD was observed in all the feet studied, and the mean coefficient of variability was 22.3%. The toes had a significantly higher mean CD (47.7/mm2) than the dorsum of the foot (33.5/mm2, p < 0.001). The finding of a significant spatial heterogeneity of CD in the foot of normal subjects has important implications in relation to function, methodology of CD measurement and the possibility that regional 'rarefaction' of CD may contribute to the pathogenesis of skin ulceration in arterial disease.