Hemodynamic effects of endurance training on canine left ventricle

To investigate the effects of endurance training on myocardial performance seven beagle dogs (exercise group, EG) were trained by treadmill running for 6-7 wk. Before and after experimental period the EG and control group (CG, n = 7) underwent a standard submaximal exercise test (SMT), and hemodynamic status was checked during anesthesia by catheterization technique exposing the animals to different loadings: pacing, volume loading, and isoproterenol infusion. The increase of heart rate during SMT was about 30 beats/min less in the EG than in the CG. A highly linear relationship between stroke work and end-diastolic volume was observed within the groups (for EG r = 0.953, for CG r = 0.846), but the slope of the regression line obtained for EG appeared to be significantly (P less than 0.001) greater. In EG isoproterenol induced increases in end-diastolic (27%), end-systolic (37%), and stroke volumes (19%), but, on the contrary, decreases of these volumes in CG (19, 15, and 22%, respectively); ejection fraction remained unchanged for both EG and CG. Ventricular stroke work was significantly greater in EG. Systemic vascular resistance decreased in EG in every loading test. The results indicate an improved pump performance, which is related not only to the heterometric autoregulatory adjustments, but also to extracardial adaptations.