Doppler Cardiac Output and Left Ventricular Performance after Cardiac Surgery: Pulsed Doppler Ascending Aorta and Pulmonary Blood Flows and Left Ventricular Function Using Implanted Microprobes

Abstract

We have developed novel implantable Doppler microprobes to monitor beat-by-beat stroke volume and cardiac output (CO) after cardiac surgery. In 11 adults undergoing either coronary artery bypass grafting (n = 6) or valve replacement (n = 5), Doppler microprobes were implanted on the ascending aorta or the main pulmonary artery to measure aortic blood flow (ABF) or pulmonary artery blood flow (PBF). The diameters of both vessels were determined before surgery using two-dimensional echocardiography. Stroke volume was obtained from velocity tracings measured by a 4-MHz zero-crossing pulsed Doppler flowmeter. Simultaneous measurements of Doppler and thermodilution CO (TDCO) were compared. We found the following: ABF = 1.03 TDCO - 0.22 L/min (r = 0.89); while PBF = 0.69 TDCO - 1.24 L/min (r = 0.75). Furthermore, peak flow velocity and maximum acceleration of blood in the ascending aorta were measured after inotropic stimulation with dobutamine; both values increased significantly from control values (25.2 +/- 6.1 percent and 44.6 +/- 8.6 percent, respectively, at 7.5 micrograms/kg/min). We conclude that implanted aortic Doppler microprobes provide a sensitive and reliable method to measure aortic blood flow velocity after surgery and then allow monitoring of stroke volume and CO and analysis of left ventricular function after cardiac surgery.