Circulation during exercise in normal dogs and dogs with cardiac valvular lesions

¹ Department of Physiology, Harvard Medical School, Boston, Massachusetts

Cardiac outputs, venous pressure gradients, and femoral A-V O₂ differences have been measured at rest and during graded exercise in normal dogs, in dogs with mild valvular lesions, and in dogs with severe failure. In the normal animals a correlation was observed between the rise in cardiac output and the increase in venous gradient, with femoral A-V O₂ difference increasing to approximately 14 vol %. In the dogs with mild valvular damage, resting output was not significantly reduced, with a normal venous gradient. Peak output was only one-half to two-thirds of normal, with a similar reduction in venous pressure gradient; femoral A-V O₂ difference increased more rapidly than normal, and was significantly higher than normal at exhaustion. The dogs in failure had low outputs and gradients at rest, and were unable to increase them significantly in the mild exercise they were able to perform. Femoral A-V O₂ difference at rest was as large as that measured in the normal dog at exhaustion. In both the normal dogs, and those with mild valvular damage, the increments in heart rate during exercise correlated closely with the rise in peripheral venous pressure.