Inotropic responses of the left ventricle to changes in aortic arch pressure in anaesthetized dogs.

1. Inotropic changes in the left ventricle in chloralose anaesthetized dogs were determined in response to changes in non-pulsatile pressure perfusing the vascularly isolated aortic arch.2. Inotropic responses were assessed by measuring the maximum rate of change of left ventricular pressure (dP/dt max) in preparations in which heart rate, mean ascending aortic pressure and brachiocephalic (i.e. carotid sinus and cerebral) perfusion pressure were held constant.3. dP/dt max increased (average +43%) when aortic pressure was reduced from a level above that which produced maximum depression of the myocardium to a level below which no further responses could be obtained; responses occurred as aortic arch pressure was changed between 250 and 90 mm Hg.5. In the same preparations changes in the brachiocephalic artery perfusion pressure with aortic arch pressure held constant resulted in similar inotropic responses.6. It is suggested that aortic arch baroreceptors may be of importance in the control of the inotropic state of the heart.