Afterload dependence of cardiac contraction parameters.
In rabbits the afterload dependence of baroreflex inotropy was studied, based on the contraction parameters CI = (dP/dt/P)max and a systolic time interval RP. These were estimated 1. for stepwise aortic coarctation and 2. for aortic nerve stimulation under pressure clamp conditions. CI is enhanced by aortic pressure elevation whereas RP is shortened. Aortic nerve stimulation caused higher CI and RP effects at free-running pressure than under pressure clamp conditions. The RP effects are always smaller. For clamping at low holding pressures the CI effects are higher and vice versa, whereas the RP effects are nearly independent of pressure. These results show that baroreflex inotropy, generally, is influenced by concomitant afterload changes, but the CI parameter and its inotropic effect is more afterload-dependent than RP.
Julius Bernstein Institute of Physiology, Martin Luther University, Halle, GDR.
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D000818:Animals; D001017:Aortic Coarctation / Q000503:physiopathology; D004558:Electric Stimulation; D004562:Electrocardiography; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D009200:Myocardial Contraction; D011311:Pressoreceptors / Q000502:physiology; D011817:Rabbits