Role of aortic and carotid sinus baroreceptors on Valsalva-like vasoconstrictor and heart rate reflexes in the conscious rabbit.

Graded 30 s manoeuvers were used to elicit cardiovascular responses in conscious instrumented rabbits by applying pressures from 2.5 to 20 mm Hg (Valsalva Pressure, VP) to the animal's respiratory valve and to a sphygmomanometer cuff wrapped around its thorax and abdomen. In normal rabbits the Valsalva-like manoeuvers elicited VP-related rises in total peripheral resistance (TPR), heart rate and in right atrial pressure (RAP), VP-related fall in cardiac output (CO) and no change in mean arterial pressure (MAP). The rises in TPR and heart rate and the maintenance of MAP were reflexly mediated, whilst the CO and RAP changes were largely a mechanical consequence of the manoeuver as assessed from the responses after autonomic effector blockade. In rabbits with selective section of the carotid sinus nerves the reflex responses were little altered from normal, but after selective section of the aortic nerves there was significant attenuation of the TPR response, indicating that the input from the aortic baroreceptors was more important for this response than that from the carotid receptors. After combined denervation of the aortic and carotid baroreceptor zones (but with the vagi intact) the reflex TPR and heart rate changes were completely abolished, with the responses the same as after autonomic effector block. The results indicate that the arterial baroreceptor zones make a major contribution to the reflex cardiovascular responses to the Valsalva manoeuver in the rabbit and that any reflex effects of cardiopulmonary baroreceptor stimulation are only expressed in the presence of an intact arterial baroreceptor input.