Technic for Measuring Cardiac Output Directly by Cannulation of the Pulmonary Artery

Cardiac output has been measured directly in the experimental animal by inserting flow meters into the aorta( 1 , 2 ), or into the venae cavae( 3 , 4 ). Such procedures, however, do not determine total cardiac output, since they fail to measure coronary flow. By measuring aortic plus coronary flow simultaneously, the total output of the heart can be obtained, but this requires the added operation of cannulating both coronary arteries successfully. Since these difficulties could be avoided if the pulmonary artery were cannulated and flow through it measured, a technic to do this in the dog has been devised and is presented here.

Under anesthesia and artificial respiration, the left side of the chest is opened (ribs 3 to 6 removed) and the pulmonary artery exposed. The artery is dissected free from its origin out onto the right and left branches about ¾ of an inch. After heparinization (10 mg per kilo), the right branch is ligated at its origin, cannulated peripherally, and cut free from the bifurcation (Fig. 1). A continuous vessel, long enough for cannulation, is now formed by the pulmonary artery and its left branch. This structure may be cannulated without bleeding by one of 2 procedures.

In the technic which has been most often successful, a shunt around the pulmonary artery is provided during cannulation. To do this, a pump, primed with compatible, donor blood, is connected between the right atrial appendage and the previously cannulated peripheral end of the right pulmonary artery (see dashed lines in Fig. 1). When ligature D is tightened just above the pulmonic valves, the main pulmonary artery and left branch can be cannulated, while the circulation is maintained via the pump-shunt system. The rotameter assembly unit is then attached to the cannula.