Page 17, O2 Uptake, Exercise & Cor. Circ., Dr. D. Penney
Coronary Circulation (continued..):
Metabolic activity of the cardiomyocytes acts to control blood flow through mechanisms which may involve messenger substances and/or direct physical action of blood flow/pressure on vascular smooth muscle. As in other organs, the larger veins serve the role of capacitance vessels in holding the largest fraction of myocardial blood volume, but do not significantly influence coronary flow or resistance under normal conditions. Collateral channels are also present, which while initially less than 20 um in diameter, dilate dramatically up to 200 um in response to demand over days to months.
Each of the three coronary arteries, LAD, CIRC, and RCA carry approximately 100 ml of blood per min at rest, each to about 100 g of myocardium. Thus each vessel has a blood flow rate of approximately 1 ml per g per min, a rule-of-thumb easily remembered. With one exception, all of the coronary tree is supplied from these three vessels. About 2% of coronary flow, that reaching the inner 1 mm of the endocardium, is supplied from the ventricular lumen. This route is the main supply for Purkinje fibers and for chordae tendineae attachment sites. A small fraction of coronary venous flow drains directly into the ventricular lumina (e.g. Thebesian circulation).
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