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Redistribution of coronary microvascular resistance produced by dipyridamole
W M Chilian1, S M Layne, E C Klausner
1Department of Medical Physiology, College of Medicine, Texas A&M University, College Station 77843.
Insights
Dipyridamole significantly reduces coronary vascular resistance by dilating microvessels. This study quantifies resistance changes in coronary arteries, microvessels, and veins during vasodilation, highlighting microvessels as key contributors.
Area of Science:
- Cardiovascular Physiology
- Pharmacology
Background:
- Coronary vascular resistance regulation is crucial for myocardial blood flow.
- Understanding how vasodilators like dipyridamole affect different coronary vessel segments is important.
Purpose of the Study:
- To assess the redistribution of coronary microvascular resistance during dipyridamole-induced vasodilation.
- To quantify resistance changes in coronary arteries, microvessels, and veins.
Main Methods:
- Measurements of microvascular diameter and pressure in anesthetized cats using a computer-controlled system.
- Calculation of vascular resistance from pressure gradients and myocardial perfusion using radioactive microspheres.
Main Results:
- Dipyridamole increased coronary blood flow significantly.
- Coronary artery resistance decreased from 25% to 42% of total resistance; microvessel resistance decreased from 68% to 27%.
- Venous resistance remained largely unaffected by dipyridamole.
Conclusions:
- Dipyridamole markedly reduces coronary vascular resistance.
- The major component of this resistance reduction is attributed to the dilation of coronary microvessels.
Abstract:
This study assessed the redistribution of coronary microvascular resistance during vasodilation produced by dipyridamole. Measurements of microvascular diameter and pressure in the beating left ventricle of anesthetized cats were accomplished by means of a computer-controlled system that enabled measurements in the beating heart. Resistances of coronary arteries, microvessels, and veins were calculated from the quotients of the pressure gradient across each vascular compartment and myocardial perfusion (radioactive microspheres). Administration of dipyridamole increased coronary blood flow from 1.80 +/- 0.09 to 6.42 +/- 0.31 ml.min-1. g-1 (P less than 0.05). During control conditions, 25 +/- 8% of total resistance occurred in coronary arteries (proximal to 170 microns), 68 +/- 8% of total resistance was in coronary microvessels (between arterioles less than 170 microns in diameter and venules less than 150 microns in diameter), and 7 +/- 7% of resistance resided in veins (distal to 150 microns). There was a significant redistribution (P less than 0.05) of resistance in all vessel classes after dipyridamole: coronary arteries constituted 42 +/- 6%, microvessels contained 27 +/- 5%, and veins had 31 +/- 8% of total coronary resistance. During control conditions, vascular resistance in coronary arteries and microvessels was 17 +/- 4 and 45 +/- 6 mmHg.min.g.ml-1, respectively. During vasodilation, resistance was significantly reduced (P less than 0.05) in both the arterial and microvessel segments to 6 +/- 2 and 4 +/- 2 mmHg.min.g.ml-1, respectively. Venous resistance was not significantly affected during dipyridamole-induced vasodilation. In conclusion, there was a marked reduction of coronary vascular resistance in response to dipyridamole, with the major component accounted for by dilation of microvessels.(ABSTRACT TRUNCATED AT 250 WORDS)