Fumihiko Kajiya

Analysis of flow characteristics in poststenotic regions of the human coronary artery during bypass graft surgery.

Poststenotic blood flow velocities were evaluated in nine patients with 75% to 99% stenosis of the left anterior descending coronary artery (LAD) during coronary artery bypass graft surgery. We used the 20 MHz 80-channel pulsed Doppler velocimeter developed in our laboratory. An operator placed a specially designed probe on the native LAD with his fingers. Before induction of extracorporeal circulation, LAD blood velocities were measured at several locations distal to the stenosis. The poststenotic flow velocities were rich in systolic flow component with reduced diastolic component. The velocity configuration in the poststenotic portions was characterized by the presence of reverse flow velocities and/or irregularity of the velocity pattern near the vessel wall, indicating the existence of flow separation and recirculation in the regions. The broadening of the velocity spectrum observed at central axial regions suggested the occurrence of flow disturbances. After grafting, the velocity waveform in the LAD beyond a vein bypass graft changed to a diastolic-predominant pattern with a relatively small systolic component. A transient bypass graft occlusion caused a marked reduction in diastolic flow velocity. The systolic-to-diastolic velocity ratio increased from 0.27 +/- 0.07 to 1.50 +/- 0.50 (p less than .01) by the graft occlusion.

Comparison of blood-flow velocity waveforms in different coronary artery bypass grafts. Sequential saphenous vein grafts and internal mammary artery grafts.

Characteristics of blood-flow velocities were investigated at different sites in two types of coronary artery bypass grafts, sequential saphenous vein grafts (SSVG) and internal mammary artery grafts (IMAG). The latter appear to have the longest life span. The patency rate of the side-to-side anastomosis of the SSVG is better than that of the end-to-side anastomosis. The SSVG was anastomosed to the major diagonal branch by side-to-side anastomosis and to the left anterior descending coronary artery (LAD) by end-to-side anastomosis in 13 patients who had 75-100% and 75-90% stenoses in the LAD and major diagonal branch, respectively. IMAG anastomoses were performed to the LAD in 10 patients with 75-100% stenoses of the artery. The blood-flow velocities were measured by the 20-MHz, eighty-channel ultrasound pulsed Doppler method during surgery. In six patients in the SSVG group, we investigated the configuration of velocity profiles at the region just proximal to the side-to-side anastomosis and at the bridge portion between the side-to-side and end-to-side anastomosis. In the other seven patients, we measured the blood-flow velocity at several centimeters proximal to the side-to-side anastomosis and compared it with that in the IMAG. At the region just proximal to the side-to-side anastomosis, the velocity profile skewed toward the anastomosis side wall in all patients, and the flow velocity near the wall opposite to the side-to-side anastomosis was reversed in five of six patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of the characteristics of the flow velocity waveforms in left atrial small arteries and veins in the dog.

To clarify the characteristics of the phasic blood velocity pattern in small arteries and veins on the left atrial surface, we used our newly developed fiber-optic laser Doppler velocimeter. We intended particularly to examine the Influence of atrial contraction and relaxation on velocity waveforms to obtain some insight into the nature of the mechanical force acting on the atrial intramyocardial vascular beds. In 14 anesthetized open-chest dogs, the left atrial appendage was gently displaced to expose small branches of the artery and vein. Vessels with an outer diameter of about 150-500 μm were chosen for the measurements because their walls are transparent to laser light. The fiber tip (velocity sensor) was fixed on the vessel surface with a drop of cyanoacrylate when good-quality Doppler signals were consistently observed. Additional experiments with three dogs were performed to observe the blood velocities in the atrial artery and vein during arrhythmia. The blood velocity waveform in the artery was similar to the pattern of aortic pressure during ventricular ejection (peak velocity, 18.8 ± 7.8 cm/sec) but was characterized by a pronounced dip during atrial contraction. The temporal coincidence between the dip formation and atrial contraction was confirmed during atrial flutter with an atrioventricular block. After isoproterenol administration (2 μg i.v.), the acceleration rate of the forward flow velocity increased by 176% (p <0.05), and reverse flow appeared during atrial contraction in five cases out of eight (p =0.013). The blood flow velocity in atrial small veins, on the other hand, was predominant during atrial contraction (peak velocity, 15.6 ± 5.8 cm/sec). Isoproterenol increased the acceleration rate of this forward flow velocity by 121% (p <0.01). Nitroglycerin did not change the blood velocity waveform significantly in atrial arteries or in veins. The phase opposition between arterial inflow into and venous outflow from the atrial myocardium indicates that a large portion of the coronary inflow to the atrial myocardium may be stored due to the presence of atrial myocardial vascular capacitance. We conclude that atrial myocardial contraction impedes atrial inflow and promotes venous outflow from atrial capacitance vessels.

Coronary Flow Velocity Waveforms in Aortic Stenosis and the Effects of Valve Replacement

In 6 patients with pure aortic stenosis, the flow velocity waveforms in the left anterior descending coronary artery were studied using an 80-channel 20-MHz pulsed Doppler velocimeter before and immediately after aortic valve replacement. All patients showed normal coronary arteriograms. The left anterior descending coronary artery flow velocity waveform in aortic stenosis was characterized by a reverse flow in the first half of systole and a slowly increasing diastolic inflow. After aortic valve replacement, the reverse flow in the first half of systole disappeared in all patients, but an end-systolic reverse flow was discerned in 5 of 6 patients. The increasing rate of the diastolic inflow was augmented in all patients. After aortic valve replacement, the time from onset of diastole to the diastolic peak velocity was shortened from 176.8 +/- 28.8 to 90.5 +/- 18.8 ms (p less than 0.01), and the diastolic peak velocity increased from 90.5 +/- 28.0 to 122.5 +/- 17.2 cm/s (p less than 0.05). Blood pressure and heart rate, however, did not change significantly before and after valve replacement. These changes in the left coronary artery velocity waveforms after valve replacement suggest the beneficial effects of removal of aortic stenosis on human coronary artery inflow.

An optical-fiber laser Doppler velocimeter and its application to measurements of coronary blood flow velocities

In this paper we describe a laser Doppler velocimeter (LDV) with an optical fiber that measures blood flow velocities accurately in a small sample volume. The principle, optical arrangement, spatial and the temporal resolutions and accuracy for blood flow measurements are delineated, followed by a report of the results of measurements of coronary artery and vein blood flow velocities in dogs. Finally, we touch upon some recent progress made in the LDV with an optical fiber pickup.

Dual-fiber laser doppler velocimeter and its application to the measurements of coronary blood velocity

To obtain a smaller sample volume and a suitable sample position for the measurement of blood velocity, we fabricated a laser Doppler velocimeter (LDV) with a dual-fiber pickup. The two fibers (clad: 62.5 micron and core: 50 micron) were placed side by side. An He-Ne laser was introduced into the blood through one fiber and the backscattered light was collected by the other fiber. The Doppler signal was analyzed by a spectrum analyzer. The spectrum of the Doppler shift frequency showed a sharp peaked pattern for both forward and reverse flows and exhibited an excellent correlation with the known blood velocity. The blood velocity in the poststenotic portion of canine coronary artery was successfully measured by the dual-fiber LDV. These results indicate that the dual-fiber LDV is useful for measuring blood velocity accurately with a small sample volume even in disturbed flow fields.

Evaluation of Blood Flow Velocity Waveforms in Intramyocardial Artery and Vein by Laser Doppler Velocimeter with an Optical Fiber

It is well established that the part of the left ventricle at greatest risk to ischemia is the subendocardium. Both in myocardial infarction in humans and experimental myocardial infarction in dogs, the subendocardial muscle shows the most extensive necrosis and the subepicardium is spared. Thus, it is important to evaluate phasic blood flow in deeper intramyocardial layers. Measurements, however, have been restricted in the region of epimyocardium because of the methodological limitations [1–3].

Intraoperative Evaluation of Blood Velocity Waveforms in Different Coronary Artery Bypass Graft

We investigated the characteristics of blood velocities in different types of coronary bypass grafts, i.e., the saphenous vein graft (SVG; 6 cases) vs the internal mammary artery graft (IMAG; 6 cases) and for different positioning of the sequential saphenous vein bypass graft (SSVG), i.e., the side-to-side anastomosis (SSA) vs the end-to-side anastomosis (ESA), the life span of which are known to be different. The blood velocities were measured by the dual mode (zerocross and FFT), multichannel, high frequency ultrasound Doppler method during bypass graft surgery. Comparing the blood velocities in the SVG with those in the IMAG (longer life span), the velocity profile was much more parabolic and the velocity spectrum was narrower in the IMAG. Regarding the velocities in the SSVG (the SSA has longer life span), the skew of the velocity profile and the reverse flow at the position just proximal to the SSA were always recognized near the probe-side wall (the opposite side of the SSA), indicating the existence of flow separation and recirculation in this region. The direction of skew changed between the SSA and the ESA in almost all cases. These patterns of blood flow seem to be a contributory factor in determining the fate of the graft.

Flow Characteristics in Poststenotic Regions of the Human Coronary Artery Assessed by 20-MHz 80-Channel Pulsed Doppler Velocimetry

A detailed assessment of flow dynamics in coronary stenosis is essential for better understanding of the pathophysiology of the obstructive coronary artery disease. However, measurements of phasic blood flow velocity and velocity distribution in a native human coronary artery have been hampered by methodological limitations. The ultrasound pulsed Doppler method is useful for measuring local blood flow velocity in vessels noninvasively. However, a conventional single-channel pulsed Doppler velocimeter with low carrier frequencies cannot obtain detailed blood velocity profiles of small vessels like the coronary artery. Recently, we have developed an 80-channel 20-MHz pulsed Doppler velocimeter [1-3], which detects Doppler signals from 80 channels by a zero-cross method and analyzes Doppler signals from one optional channel by a fast Fourier transform method, both in real time.