| Popis: |
The phasic red cell velocity pattern and the phasic change in diameters in the epimyocardial microvessels were investigated in the beating canine left ventricle. We also studied the effects of nitroglycerin and dilazep, an adenosine potentiator, on the red cell velocity curves in epimyocardial microvessels and on the diameters of arterioles. Using a floating objective system and high-speed cinematography, we measured red cell velocities in arterioles, capillaries, and venules, and also microvascular diameters in the epimyocardium of left ventricle in open-chest anesthetized dogs. In arterioles and capillaries, peak red cell velocity occurred in mid-systole, followed by a decrease during diastole. In venules, red cell velocity reached its peak in late systole, followed by a gradual decline during diastole. An abrupt decline in red cell velocity and a momentary cessation or reverse flow were observed in these microvessels during the pre-ejection period. The internal diameter of small venules was significantly increased in late systole, while there was no significant change in the diameter of arterioles throughout the entire cardiac cycle. There was no significant change in the red cell velocity pattern in epimyocardial micro-vessels after administration of nitroglycerin. Nitroglycerin also failed to dilate the epimyocardial small arterioles. After administration of dilazep, red cell velocity curves in the epimyocardial microvessels were shifted upward throughout the entire cardiac cycle, with a significant increase in the total area under the velocity curves accompanied by significant dilation of small arterioles. These results suggest that the characteristics of velocity waveform in coronary microvessels in epimyocardium are quite different to those of endomyocardium in the beating left ventricle. Furthermore, using an intravital microscope system, we directly demonstrated that nitroglycerin has little effect on small arterioles and capillary flow, and that dilazep has a potent dilative effect on small arterioles and markedly increases capillary flow in the epimyocardium. |
