Regulation of Cardiac Output in Anesthetized Dogs During Induced Muscular Work

Abstract

The pathways (neural and humoral) mediating in the responsive agents which cause the increase in ventilation during exercise were studied in 9 pairs of cross-circulated dogs. The lower legs of one dog (the neural dog) were perfused exclusively by blood from another dog ( the humoral dog). It was found that during a steady state of induced exercise the O2 consumption of the humoral dog increases whereas that of the neural dog remains unchanged. The cardiac output increases in both dogs. The circulatory equivalent for O2 (cardiac output/02 consumption) increases in the neural dog and decreases in the humoral dog. The arteriovenous O2 difference decreases in the neural dog but increases in the humoral dog, and it increases more rapidly as a function of O2 consumption in the humoral dog than in the intact (non-cross-circulated) dog. It was concluded that both neural and humoral factors are involved in the regulation of cardiac output during exercise for 2 reasons: 1) the humoral dog demonstrates a situation analogous to that of peripheral circulatory failure because of lack of some "normal factors"; 2) the neural dog also shows an increase in cardiac output during exercise.