Search

The influence of the filling condition of the unstressed volume (UV) of intramyocardial vessels on the diastolic coronary arterial pressure-flow relationship was analyzed. UV is defined as the blood volume at zero transmural pressure. In seven anesthetized, paced dogs with induced heart block, coronary artery inflow was occluded so that blood in the UV was displaced into the coronary vein by myocardial contraction. After pacing was turned off, coronary perfusion pressure was increased stepwise to seven target pressures (20-90 mmHg). After reperfusion, left anterior descending coronary arterial (LAD) flow reached an initial quasi-steady level, but great cardiac venous (GCV) flow was absent (UV-unfilled phase). With reappearance of the GCV flow (UV-filled phase), LAD flow decreased to a final steady level. Pressure-flow relationships during both phases were linear (r = 0.97-0.99). The inverse of the slope of the pressure-flow relationship during the UV-filled phase, 0.69 +/- 0.08 mmHg.min.ml-1, was significantly higher than that during the UV-unfilled phase, 0.55 +/- 0.06 mmHg.min.ml-1 (P less than 0.01), although the zero-flow pressure intercepts were similar (18.9 +/- 1.8 mmHg for UV filled vs. 19.9 +/- 2.2 for UV unfilled). These results indicate that diastolic coronary arterial inflow is impeded by a blood volume within intramyocardial vessels that exceeds the UV.

Digital radiography (100 pixels/mm2) combined with the technique of 3H-labeled desmethylimipramine deposition was employed to visualize regional blood flow distributions in rabbit left ventricular myocardium. A fluctuated pattern of myocardial flow and its dependence on arterial oxygen tension (PaO2) was evaluated with the coefficient of variation (CV) computed at each step of coarse-graining; flow images were revisualized by increasing pixel area (PA) step by step from 0.01 to 1 mm2. The CV values decreased with hypoxia at all resolution levels, suggesting that there is a vascular regulatory mechanism for making myocardial perfusion uniform in response to decreased PaO2. In both perfusion states, Cl/decreased with increasing PA. The relationship between CV and PA fitted the noninteger power law function, implying an apparent fractality of CV.

Direct and continuous observation of subendocardial (deep myocardial) microcirculation provides essential information on coronary circulation, since cardiac contraction affects subendocardial vessels most vigorously. To achieve this aim, we developed a portable needle-probe video-microscope with a charge-coupled-device (CCD) camera to visualize the subendocardial microcirculation. Images of the subendocardial microcirculation of a porcine beating heart were successfully observed in all cases. The vascular compression by cardiac contraction decreased the diameter of subendocardial arterioles and venules by about 20%.

To clarify the characteristics and possible causes of phasic blood velocity patterns in pressure overload hypertrophy, we measured blood flow velocities in the left anterior descending coronary arteries in 16 patients with left ventricular hypertrophy secondary to systemic hypertension. These measurements were made with a 20MHz Doppler catheter. All patients had normal coronary arteriograms. The blood flow velocity patterns were characterized by the decrease in the rise of early diastolic inflow velocity. Prolongation in the time from the onset of diastole to peak velocity (TDPV) correlated with the degree of left ventricular hypertrophy. TDPV was prolonged in proportion to the increase in the peak left ventricular systolic pressure and left ventricular ejection fraction. The flow reserve calculated from the ratio of the diastolic mean velocity after the intracoronary injection of papaverine to the resting flow showed a trend toward the decrease proportional to the prolongation in TDPV due to an increase of wall thickness. In conclusion, preceding systolic vascular compression and systolic vascular strain can be factors causing early diastolic inflow disturbance in left ventricular hypertrophy secondary to hypertension. The decrease of coronary reserve may partially be attributable to the decrease in the rise of early diastolic inflow 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.

To analyze the origin of the coronary artery inflow and the coronary vein outflow, we measured the intramyocardial artery flow and the epicardial small vein flow by means of a laser Doppler velocimeter with an optical fiber. The functional characteristics of the intramyocardial capacitance vessels were investigated by analyzing the responses of coronary vein flow after stepwise changes in coronary artery pressure during long diastole. Then the effect of the intramyocardial capacitance vessels on coronary artery inflow and vein outflow was evaluated. Intramyocardial artery flow was found to be almost exclusively diastolic with frequent systolic reverse flow, whereas peripheral coronary vein flow was almost systolic exclusively. The intramyocardial capacitance vessels have two functional components, unstressed volume and ordinary capacitance. When the unstressed volume was saturated, the intramyocardial displacable blood volume impeded the coronary artery inflow, but promoted vein outflow.

To elucidate the role of the haemorheological properties of the perfusate in the coronary circulation, the diastolic pressure-flow relation was studied in nine open chest heart blocked dogs with minimal vasomotor tone when blood with various packed cell volumes (12-67%) was used as perfusate. An electrical analogue model with proximal resistance R1, capacitance C, distal resistance R2, and the zero flow pressure intercept Pint was derived from the observation of the pressure-flow relation to support the data analysis. The diastolic pressure decay was then determined after the perfusion line had been clamped to calculate stop flow coronary artery pressure (Psf). The stop flow coronary artery pressure decreased in relation to packed cell volume (r = 0.45, p less than 0.01), and the value for the lowest packed cell volume (10-29%) was slightly higher than the great cardiac vein pressure (about 3 mmHg). The zero flow pressure intercept of the steady state pressure-flow relation showed a close correlation with the stop flow coronary artery pressure (r = 0.87, p less than 0.001). The value of R1 + R2, which reflects the inverse of the steady state pressure-flow slope, decreased simultaneously with the packed cell volume (r = 0.62, p less than 0.001). The resistance ratio R2/(R1 + R2) by our model prediction decreased in relation to packed cell volume (r = 0.5, p less than 0.001). The values of stop flow coronary artery pressure, zero flow pressure intercept, and R1 + R2 for the highest packed cell volume (50-69%) were 17.8(1.1) mmHg, 25.1(1.3) mmHg, and 0.48(0.05) mmHg.ml-1.min.100 g-1 respectively, whereas those for the lowest packed cell volume (10-29%) were 13.4(0.8) mmHg, 19.7(1.0) mmHg, and 0.24(0.02) mmHg.ml-1.min.100 g-1. The pressure difference between the stop flow coronary artery pressure and the zero flow pressure intercept may be due to the non-linearity in the pressure-flow relation at a low perfusion pressure. The left ventricular end diastolic pressure and great cardiac vein pressure did not change in relation to the packed cell volume of the coronary perfusate. Thus it is concluded that packed cell volume is one factor determining the high zero flow pressure.

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 microns 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 micrograms i.v.), the acceleration rate of the forward flow velocity increased by 176% (p less than 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 less than 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.

To evaluate local blood flow velocities accurately at many sampling points in small vessels, especially in human coronary arteries, we have developed an 80 channel 20 MHz pulsed Doppler velocimeter. Doppler signals from 80 channels are detected by a zero-cross method and a signal from an optional channel is analyzed by a fast-Fourier transform method, both in real time. Basic experiments using a model and animals have demonstrated the accuracy and utility of our method of measurement of blood flow velocity for both nondisturbed and disturbed flow. Velocity waveforms in a native coronary artery beyond a vein bypass graft insertion were measured during cardiac surgery. They showed a diastolic-predominant pattern with a small systolic component. During transient graft occlusion, the waveforms changed to a systolic-predominant pattern in a patient with severe stenosis and to a to-and-fro pattern in a patient with total occlusion. In a patient with severe aortic regurgitation, the coronary arterial velocity waveforms exhibited a systolic-predominant pattern with a broad velocity spectrum. After aortic valve replacement, however, a diastolic-predominant pattern with a narrow spectrum was observed.

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.