Functional significance of collateral blood flow in working skeletal muscle of the dog.

The semitendinosus muscle of the dog is supplied by two separate arteries and drained by two corresponding veins. In the muscles used in this study no blood entering via the distal artery was found to leave via the proximal vein during perfusion through both arteries (orthograde perfusion). Therefore, collateral flow (CF) could be determined as proximal venous outflow during occlusion of the proximal artery. During orthograde perfusion total blood flow averaged 12 ml x min-1 x 100 g-1 at rest and 58.4 ml x min-1 x 100 g-1 during exercise. CF was found to average 6.2 ml x min-1 x 100 g-1 at rest and increased to 9.2 ml x min-1 x 100 g-1 during exercise. CF was sufficient to cover the metabolic demand of resting muscle. During exercise the O2-uptake (VO2) of the distal muscle portion was increased 13.4 fold in comparison to a 3.1 fold increase in the proximal muscle portion. The average contractile power decreased by 46%. Additional infusion of adenosine into the distal artery resulted in an increase of CF to 11.4 ml x min-1 x 100 g-1 and of orthograde flow to 71 ml x min-1 x 100 g-1. The average contractile power of the muscle increased by 13%. Both orthograde flow and CF were found to decrease with increasing muscle load. But this decrease was significantly more pronounced in the case of CF especially at a lower range of loads. It is concluded that after acute occlusion of orthograde flow, CF is limited by the number, the size and the dilatory capacity of precapillary network vessels. Furthermore, CF is influenced considerably by changes of extravascular support.