Capillary density of skeletal muscle in Andean dogs.

High capillary density and small muscle fiber diameters were found in the sternothyroid muscle of dogs native to 4350 m. The number of capillaries per square millimeter was three times greater while the diameter was less than half of those obtained in the same muscle of normoxic dogs. These findings suggest that tissular adaptative mechanisms are important in the process of acclimatization to hypoxia, contributing to the maintenance of adequate levels of PO2 in the tissue in the presence of hypoxemia.