Yasuo Ogasawara

Evaluation of Coronary Blood Flow by Fiber-Optic Laser Doppler Velocimeter

Our laser Doppler velocimeter (LDV) with an optical fiber is a powerful tool for the measurement of both coronary artery and vein flow velocities because of its excellent accessibility to the coronary vessels of a moving heart. In this paper, we briefly describe the optical arrangement of the LDV and then introduce some results of measurements of the blood velocity patterns of epicardial large coronary vessels, and epicardial small arteries and veins obtained by two different routes of access of fiber probe. We also touch upon the dual-core-fiber system which is probably promising as a Doppler catheter for clinical use

Functional Characteristics of Intramyocardial Capacitance Vessels and Their Effects on Coronary Arterial Inflow and Venous Outflow

The intramyocardial capacitance vessels have two functional components, unstressed volume and ordinary capacitance. The estimated value of unstressed volume was about 5% of the left ventricular mass, and the time constant in relation to ordinary capacitance was about 1 s, although both are pressure-dependent. The coronary venous outflow was closely related to the total displaceable blood volume stored in the intramyocardial capacitance vessels, i.e., the more intramyocardial blood volume, the more coronary venous outflow. On the other hand, the diastolic coronary arterial inflow was decreased when the blood volume in the intramyocardial vessels increased above the unstressed volume. This may be important as a mechanical control of the coronary circulation system.

Coronary Venous Flow

It is well known that coronary arterial flow is predominantly diastolic, whereas coronary venous flow is predominantly systolic. Since coronary venous flow is squeezed out from the myocardial vascular bed by direct and indirect extravascular compressive forces of the myocardium, the coronary venous system is therefore very unique and offers a suitable model to investigate the relationship between cardiac contraction and coronary blood flow. Moreover, the intramyocardial coronary venous system has a negative feedback control system against arterial inflow into the myocardium; that is the increase of intramyocardial venous blood volume decreases arterial inflow and this decrement enhances arterial inflow. Therefore, analysis of coronary venous outflow in relation to the mechanical control of coronary arterial inflow is also important. We overviewed the phasic blood flow patterns of proximal and distal coronary vessels of the left ventricle, right ventricle, and left atrium.

Blood Velocity Profiles Along Poststenotic Coronary Artery and Stenotic Intramyocardial Flow

To evaluate the effect of coronary stenosis on coronary flow, we evaluated: (1) the blood velocity profiles across the vessel at portions distal to stenosis, (2) the velocity waveform in the septal artery during left main coronary artery stenosis with or without vasodilators, and (3) transmural flow distribution with low perfusion pressure as in stenosis before and after intracoronary nitroglycerin. The experiments were performed in 29 dogs using our 80-channel 20 MHz ultrasound velocimeter. The poststenotic velocity configuration was characterized by a narrow region of high velocity with diastolic reverse flows near the wall which may dissipate energy. Septal artery blood flow velocity which reflected myocardial inflow showed a diastolic-predominant waveform always accompanied by a systolic retrograde blood velocity component. Coronary artery stenosis enhanced the systolic retrograde flow with a decrease in diastolic flow, reducing myocardial inflow. The systolic retrograde flow was augmented further by coronary vasodilation (intracoronary adenosine or nitroglycerin) and did not improve myocardial inflow (or decreased it). Intracoronary nitroglycerin increased epimyocardial flow, but did not increase endomyocardial flow. In conclusion, an augmented retrograde flow which is increased by vasodilators plays an important role in disturbing myocardial inflow during coronary artery stenosis. This could be called a “coronary slosh phenomenon”. Thus, increased systolic retrograde flow and the decreased diastolic flow are closely related in reducing myocardial flow, especially subendocardial flow.

Characteristics and Possible Cause of Instantaneous Velocity Waveforms in Small Coronary Arteries and Veins

Instantaneous blood flow velocities were measured in coronary arteries and veins of both the left and right ventricles and the left atrium by our laser Doppler velocimeter (LDV) with an optical fiber. The phase opposition of velocity waveforms between coronary arteries and veins was observed consistently in all coronary arteries and veins if the velocity waveform reflected an intramyocardial velocity waveform by minimizing the effect of capacitance of large epicardial vessels. The systolic component of the velocity waveform in the right coronary artery was slightly larger than that in the left coronary artery. A sharp decrease in atrial arterial flow was observed during atrial contraction and atrial vein flow was systolic predominant. The nature of force of myocardial contraction may be closely related to myocardial contractility, as the velocity waveforms are similar despite large differences in cavity pressure.

A Study of Coronary Circulation by Laser Doppler Velocimetry

Our laser Doppler velocimeter (LDV) with an optical fiber is a powerful tool for the measurement of both coronary artery and vein flow velocities because of its excellent accessibility to coronary vessels of the beating heart. We designed four different accesses of a fiber probe to measure blood velocities, depending upon the objectives of the measurements, i. e., epicardial large coronary vessels, the epicardial small artery and vein, the intramyocardial artery and vein, and a laser catheter. The blood flow velocities showed a diastolic-predominant pattern in the coronary artery and a systolic-predominant pattern in the coronary vein. The phase opposition between arterial and venous flows was more remarkable in intramyocardial vessels, i. e., the systolic reverse flow in the artery showed a reciprocal relation to the systolic forward flow in the vein. In veins, suction of blood from superficial veins to a deeper portion may occur during diastole. The laser Doppler catheter was found to be useful for monitoring coronary vein flows in the coronary sinus and the great cardiac vein. We found that the four different routes of access of optical fiber probe are useful for the evaluation of coronary flows.