Reflex vascular responses to independent changes in left ventricular end-diastolic and peak systolic pressures and inotropic state in anaesthetised dogs

1. Ventricular mechanoreceptors are known to exist and can when stimulated induce reflex vasodilatation, but the nature of the effective stimuli and t he physiological role of the reflex remain to be established. 2. Dogs were anaesthetised with chloralose and a cardiopulmonary bypass est ablished. Ventricular pressures were separated from those in the aortic roo t and coronary arteries by a balloon inflated in the ventricular outflow tr act. Ventricular filling was controlled by adjusting the rate of inflow of blood through an apical cannula and peak pressure by regulating the outflow pressure from the same cannula. Carotid and aortic pressures were also con trolled and vascular resistance was assessed from changes in perfusion pres sure (constant flow conditions) to the descending abdominal aorta. 3. Increased coronary or carotid sinus pressure induced a significant vasod ilatation. Changes in ventricular peak systolic pressure, without associate d changes in end-diastolic pressure, had no significant effect on vascular resistance. In contrast, changes in end-diastolic pressure did induce vasod ilatation that, although small, was proportional to the magnitude of the en d-diastolic pressure change. 4. Changes in ventricular inotropic state induced by dobutamine infusion or by stimulation of efferent cardiac sympathetic nerves did not induce signi ficant responses. Furthermore, the combined effects of reduced ventricular filling and increased inotropic state were also ineffective in inducing res ponses. 5. We conclude that, to induce reflex responses, the only effective stimulu s to ventricular mechanoreceptors was an increase in filling. Compared with other mechanoreflexes, however, responses to ventricular distension were s mall and seem unlikely to be of importance except perhaps during abnormal v entricular distension.