Related Experiment Videos
Understanding the coronary circulation through studies at the microvascular level
M L Marcus1, W M Chilian, H Kanatsuka
1Department of Internal Medicine, University of Iowa, Iowa City 52242.
Insights
Coronary vascular resistance is complex, with significant control in larger vessels. Physiological and pharmacological stimuli alter this distribution, impacting coronary microcirculation and macromolecule exchange.
Area of Science:
- Cardiovascular Physiology
- Microcirculation Research
Background:
- Coronary vascular resistance is traditionally divided into large vessels, small resistance vessels, and veins.
- Epicardial microcirculation studies suggest more precise resistance control in specific vascular segments.
Purpose of the Study:
- To investigate the distribution of coronary vascular resistance.
- To examine how physiological and pharmacological stimuli alter vascular resistance.
- To understand macromolecule exchange in the coronary microcirculation.
Main Methods:
- Measurements of coronary pressure in various arterial sizes.
- Stroboscopic illumination of the epicardial microcirculation.
- Studies of macromolecule exchange using fluorescent-labeled dextrans.
Main Results:
- Under normal conditions, 45-50% of total coronary vascular resistance is in vessels >100 microns.
- Vascular resistance distribution is altered non-uniformly by physiological and pharmacological stimuli.
- A small pore size (35-50 A) in coronary microvessels was identified, affected by myocardial ischemia.
Conclusions:
- Coronary vascular resistance control is highly complex.
- Mechanisms underlying heterogeneous responses in coronary microcirculation require further investigation.
Abstract:
Studies of the coronary circulation have divided vascular resistances into three large components: large vessels, small resistance vessels, and veins. Studies of the epicardial microcirculation in the beating heart using stroboscopic illumination have suggested that resistance is more precisely controlled in different segments of the circulation. Measurements of coronary pressure in different sized arteries and arterioles have indicated that under normal conditions, 45-50% of total coronary vascular resistance resides in vessels larger than 100 microns. This distribution of vascular resistance can be altered in a nonuniform manner by a variety of physiological (autoregulation, increases in myocardial oxygen consumption, sympathetic stimulation) and pharmacological stimuli (norepinephrine, papaverine, dipyridamole, serotonin, vasopressin, nitroglycerin, adenosine, and endothelin). Studies of exchange of macromolecules in the microcirculation using fluorescent-labeled dextrans have also identified the size of the small pore (35-50 A) in coronary microvessels that can be altered by myocardial ischemia. Studies of the coronary microcirculation have demonstrated that the control of vascular resistance is extremely complex, and mechanisms responsible for these heterogeneous responses need further examination.