Do inotropic stimulation or postural changes affect stroke volume in conscious dogs at a constant heart rate?
In conscious dogs at a constant heart rate, stroke volume is significantly altered by changes in posture (affecting end-diastolic dimensions) rather than by inotropic stimulation.
Some factors affecting stroke volume were investigated in conscious dogs in which left ventricular outflow was measured with an electromagnetic flowmeter. Stimulation of the heart at constant heart rate, by intracoronary injections of calcium gluconate and isopropylnorepinephrine, or postectopic potentiation failed to produce any increase in stroke volume. By contrast, alterations of posture at constant heart rate with the presumed associated changes in end diastolic dimensions, produced large changes in stroke volume. This resulted from a change in late systolic flow.
Noble et al. (Fri,) studied this question.