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Phasic blood flow velocity pattern in epimyocardial microvessels in the beating canine left ventricle
Insights
This study quantifies coronary blood flow in the beating left ventricle, revealing distinct microcirculatory patterns and flow dynamics in epimyocardial vessels during the cardiac cycle.
Area of Science:
- Cardiovascular Physiology
- Microcirculation Research
- Coronary Blood Flow Dynamics
Background:
- Understanding coronary blood flow is crucial for diagnosing and treating heart conditions.
- Previous research has focused on larger coronary arteries, with less known about subepimyocardial microcirculation.
- Phasic flow patterns in the beating heart's microvasculature remain incompletely characterized.
Purpose of the Study:
- To quantify phasic epimyocardial microcirculatory coronary blood flow velocity patterns in the beating left ventricle.
- To investigate microvascular diameter changes throughout the cardiac cycle.
- To compare subepimyocardial microvascular flow patterns with those in larger coronary arteries.
Main Methods:
- Utilized a novel floating objective and high-speed cinematography in open-chest anesthetized dogs.
- Measured red blood cell velocities and microvascular diameters in arterioles, capillaries, and venules.
- Maintained a heart rate of 140 beats/min via atrial pacing.
Main Results:
- Peak red blood cell velocity occurred in midsystole (arterioles, capillaries) and late systole (venules).
- Flow cessation or reversal was observed in microvessels during the pre-ejection period.
- Arteriolar diameter remained constant, while venule diameter increased in late systole.
- A significant portion of blood flow occurred during the ejection phase (40-51%).
- Dilazep treatment increased velocity and arteriolar dilation, indicating improved microcirculation.
Conclusions:
- Subepimyocardial microvascular blood flow patterns differ significantly from larger coronary arteries.
- Phasic flow dynamics are complex within the beating left ventricle's microvasculature.
- These findings provide insights into transmural differences in coronary blood flow and potential therapeutic targets.
Abstract:
We quantitated phasic epimyocardial microcirculatory coronary blood flow velocity patterns in the beating left ventricle. Using a newly developed floating objective and high-speed cinematography, red cell velocities in small arterioles, capillaries, and small venules and microvascular diameters in the superficial layer of the epimyocardium of beating left ventricle were determined throughout the entire cardiac cycle in open-chest anesthetized dogs. Heart rate was maintained at 140 beats/min by means of left atrial pacing. Peak red cell velocity was observed in midsystole in small arterioles and capillaries, and in late systole in small venules. Abrupt decline in red cell velocity and, in many cases, a momentary cessation or reverse of flow, was observed in these microvessels during the pre-ejection period. The internal diameter of small venule was increased in late systole, while that of small arteriole remained almost constant during the cardiac cycle. Furthermore, in these epimyocardial microvessels, a higher percentage of the total area under the velocity curve occurred during the ejection phase; 51% in small arterioles, 43% in capillaries, and 40% in small venules. These findings indicate that the phasic blood flow pattern is markedly different in the subepimyocardial microvessels from that in the large epicardial artery and the septal artery. During vasodilation following dilazep (50 micrograms/kg, i.v.), an adenosine potentiator, red cell velocity increased throughout the entire cardiac cycle in epimyocardial microvessels with significant increases in the total area under the velocity curves accompanied by significant dilation of the arterioles. The present data will provide information useful in predicting or simulating transmural differences in the phasic blood flow pattern.