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 fo r the optimisation of oxygen and nutrient delivery in a specified regi on of tissue. One area of particular interest to the vascular speciali st is the skin of the dorsum of the foot and toes, as these are especi ally 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 t oes, since any great non-uniformity might produce regions of low perfu sion, which may become vulnerable to ulceration. Using white-light (na tive) videomicroscopy at a magnification of x 40 in 15 healthy subject s (mean age 72 years), the dorsum of the foot and toes was systematica lly 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 a nalysis of videoprints was then undertaken to determine CD at each sit e, according to a fixed protocol of measurement and data analysis. The mean value and spatial coefficent of variation of CD was then calcula ted for each foot. There was striking spatial heterogeneity of CD in t he dorsum of the foot, some areas having low numbers of capillaries an d other areas in the same foot having higher capillary numbers. This s patial heterogeneity of CD was observed in all the feet studied, and t he mean coefficient of variability was 22.3%. The toes had a significa ntly higher mean CD (47.7/mm(2)) than the dorsum of the foot (33.5/mm( 2), p < 0.001). The finding of a significant spatial heterogeneity of CD in the foot of normal subjects has important implications in relati on to function, methodology of CD measurement and the possibility that regional 'rarefaction' of CD may contribute to the pathogenesis of sk in ulceration in arterial disease.