Coronary Blood Flow Velocities in Humans Evaluated During Cardiac Surgery Using a 20 MHz 80+1 Channel Ultrasound Pulsed Doppler Velocimeter

Abstract

We have developed an 80 + 1 channel high resolution pulsed Doppler velocimeter for measuring in detail the blood flow velocities in relatively small human vessels (1-5 mm in diameter). Real time velocity measurements were performed at 80 sample points using a multigated zero-cross method. The Doppler signal in the desired channel was subjected to real time Fourier analysis. This facilitated analyzing in detail the blood flow velocity profile across vessel, as well as the velocity distribution in a sample volume. The sampling volume was pi X 0.5(2) X 0.2 mm3 and the maximum depth was 1.5 cm. When the incidence angle was selected as 60 degrees, the velocity resolution and maximum velocity were 1.5 and 1.9 m/sec, respectively. Blood flow velocities were measured in the coronary artery and in the aorto-coronary bypass graft in patients during cardiac surgery. The blood flow velocities in the normal coronary artery had a predominantly diastolic pattern which is characteristic of coronary artery flow. Comparing with the systolic forward velocities in the left coronary artery, those of the right coronary artery were more prominent. The velocity wave forms in the graft and in the coronary artery distal to the insertion of the graft had a predominantly diastolic pattern when there was sufficient coronary blood flow through the graft. In contrast, during the occlusion of the graft, the blood velocity wave form in the distal coronary artery became predominantly systolic, indicating insufficient myocardial inflow before the bypass graft. Intravenous dipyridamole administration increased the bypass flow by 50% in a patient who had 100% occlusion before the bypass operation. This indicates that the coronary reserve can still be preserved in some cases of total coronary occlusion. With an intra-aortic balloon pumping (IABP) assist (2:1), the velocity wave form in the graft had predominantly diastolic in both IABP-on and -off beats. However, diastolic augmentation and systolic reduction of the velocity wave form were clearly observed in beats with IABP-on. The velocity wave forms in the anterior descending coronary artery in a patient with aortic regurgitation showed a predominantly systolic pattern with a broad velocity spectrum. After aortic valve replacement, the blood velocity pattern became predominantly diastolic, indicating improvement of the coronary perfusion into the myocardium. In conclusion, our velocimeter proved effective for evaluating coronary blood flow velocities in patients during cardiac surgery.