Cardiovascular response to static exercise in the conscious cat

A chronic, unanesthetized cat preparation was used as an experimental model for the study of cardiovascular response to static exercise. Seven cats were operantly conditioned to hold a bar with their right forelimb against increasing resistance for 15 seconds. The exercise regimen lasted from 3 to 6 months. The cats were instrumented with a left ventricular pressure transducer and a left atrial catheter. With exercise, heart rate (HR, + 10%), left ventricular systolic pressure (LVSP, +16%), and maximal rate pressure development (LV dp/dt, +15%) increased significantly. The rise in HR began prior to the onset of exercise and reached peak in less than 5 seconds and then decreased to pre-exercise levels, although LVSP and LV dp/dt remained elevated during exercise. The magnitude of the LVSP response (range 23 to 31 mmHg) was constant after 2 weeks of training even though the exercise intensity was increased 200 g to 700 g. After 3 months of training, the cats were exercised at the intensity first observed to induce a significant LVSP response. Peak HR, LVSP, and LV dp/dt were significantly reduced. Selective autonomic blockade with propranolol, atropine, and combined atropine-propranolol was utilized to elucidate the role of the autonomic nervous system in the cardiovascular responses that occur during voluntary static exercise. The increased HR in response to exercise was mediated primarily by the parasympathetic nervous system, whereas the increases in LV max dp/dt were mediated by the sympathetic nervous system.