Continuous Observations of Cardiac Output with Electromagnetic Flowmeter during Cardiovascular Reflexes.

By measuring blood flow in the ascending aorta with an electromagnetic flowmeter, continuous observations of cardiac output were performed in the dog during various cardiovascular reflexes. Attempts were made to analyze how changes in cardiac output and peripheral resistance contributed to each reflex. The depressor reflex to sinus nerve stimulation was attributable to three separate processes which might occur in the following order: an early decrease in cardiac output with bradycardia due to vagal impulses, a decrease of peripheral resistance, and a late decrease in cardiac output. The pressor reflex to strong stimulation of a mixed nerve was usually induced by an increase of both peripheral resistance and cardiac output. On the other hand, the pressor response to occlusion of the bilateral common carotid arteries was evoked by an increase of peripheral resistance alone. It is concluded that cardiac output and peripheral resistance, two major blood pressure determining factors, may be changed separately in cardiovascular reflexes.