Microvascular Dimensions and Blood Flow in Skeletal Muscle

In cats anesthetized with chloralose the lengths and diameters of the different vascular segments in the tenuissimus muscle were measured in the vital microscope. The flow characteristics, including red cell velocity, were registered. Fixed and stained muscle specimens were analyzed histologically as well as Indian ink‐perfused muscles treated according to the method of Spalteholz. The average muscle fibre diameter was 44 μm. 62% of the muscle fibres were red (48% B‐fibres, diameter 41 μm and 14% C‐fibres, diameter 26 μm) and the remaining 38% were white (A‐fibres, diameter 55 μm). The average muscle fibre was surrounded by 3.6 capillaries. The capillaries were 1015 ± 16.3 (S.E.) μm long and 5.3 ± 0.0(3) (S.E.) μm in internal diameter. The calculated capillary surface area was 0.9 m 2 /100 cm 3 of muscle tissue. Average red cell velocity in the capillaries was found to be 0.5 mm/s, but there was a wide variation with time and between different capillaries. Neither “spontaneous” changes in internal diameters of the microvessels nor a distinct precapillary sphincter activity could be observed. Arterio‐venous anastomoses within the muscle tissue were rare exceptions.