Skeletal muscle blood flow in exercising dogs.

We have recently described the skeletal muscle blood flow response to maximal exercise in the foxhound as well as the skeletal muscle blood flow response to various levels of submaximal and maximal exercise in the mongrel dog using the radioactive microsphere technique. Results from these studies demonstrated that blood flow increased progressively up to VO2max in the gracilis, semitendinosus, and semimembranosus muscles of the dog; however, blood flow to the gastrocnemius leveled off during submaximal exercise. These studies have also shown that the magnitude of the blood flow response to maximal exercise in the different muscles examined is extremely varied and that some muscle blood flows exceeded 300 ml.100 g-1.min-1. Whether or not these high blood flows were the consequence of microsphere streaming effects was evaluated, and results from both studies suggest that these effects were minimal. Also, the high muscle blood flows appeared to be reasonable with respect to the maximal cardiac outputs generated by the dogs in both studies. Based on the data presented we conclude that the radioactive microsphere technique appears to be a reliable technique for measuring muscle blood flow in the exercising dog. Moreover, the skeletal muscle blood flow response to exercise in the dog is variable and highly dependent on the individual muscle(s) studied.