A quantitative study of the exchange microvasculature of muscles from the human foot and hand

In this study, transmission electron microscopy has been used to make a quantitative assessment of the exchange surface area of the microvessels of skeletal muscle from the human foot and hand. The numbers of capillaries per unit area of skeletal muscle were found to be similar in the foot (47.9 X 10(3) SEM +/- 7.5 X 10(3) cm-2) and the hand (49.3 X 10(3) SEM +/- 9.0 X 10(3) cm-2). However, the capillaries of the foot appeared significantly larger than those of the hand, having a mean diameter of 5.4 +/- 0.1 microns compared with 4.4 +/- 0.2 microns in the hand. Measurement of total capillary exchange surface area (SA) from low power (X 3000) electron micrographs of muscle samples from 11 subjects gave values of SA of 93.9 +/- 5.9 cm2/g tissue (n = 5) in the foot and 83.8 +/- 5.4 cm2/g tissue in the hand (n = 6). High power electron micrographs (X 21,600) of individual vessels showed the walls of the capillaries of the feet to be significantly thicker than those of the hand. The increase in wall thickness was mainly due to a 40% increase in the width of the basement membrane, which had a mean width of 221 +/- 16 nm in the hand and 312 +/- 34 nm in the foot.