Cardiac output by dye dilution using a left carotid loop in conscious rats

By a modified dye dilution method using a simple dichromatic densitometer, cardiac output (CO) in conscious rats was determined. Under anesthesia, a carotid loop was made in the left carotid artery with a polyethylene tube (PE50) and exteriorized. A sensor of the densitometer was set at the center of the carotid loop. Indocyanine green dye solution was injected into the right atrium via the jugular vein. CO was calculated from the dye dilution curve obtained. In the conscious state (6 hours after ether anesthesia),CO in normotensive, spontaneously and DOC/saline hypertensive rats was determined without affecting blood pressure and heart rate. However, CO in the pentobarbital or urethane anesthetized rats was decreased with other hemodynamic changes. The validity of this method was confirmed with a hydraulic model system and in anesthetized open-chest cats using an electromagnetic flowmetry. From these studies, it was concluded that the modifed dye dilution method for measuring CO in conscious rats was reliable and useful for hemodynamic studies in hypertensive rats.