Regulation of Coronary Blood Flow

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Abstract
Recent contributions in the field are evaluated to indicate how they substantiate or modify current views of the regulation of coronary blood flow under physiological conditions. The 2 major physical factors discussed, perfusion pressure and extravascular pressure, probably exert only a slight effect on coronary blood flow. It appears that autoregulation does occur in the heart to the same extent as in the intestine probably as a result of the release of vasoactive metabolites secondary to tissue hypoxia. Adenosine may be the regulating metabolite in cardiac muscle. Neural control of coronary blood flow is still not completely resolved. Studies with vagus nerve stimulation have failed to obtain any effect which could not be accounted for by concomitant reduction in blood pressure and/or heart rate. The vasomotor effect of the sympathetic nerves is predominantly vasoconstrictor and probably is due to release of nor-epinephrine at the termination of the postganglionic fibers. At present, the existence of local intracoronary reflexes is in doubt. Direct evidence in support of the myogenic theory that vascular smooth muscle responds to transmural pressure changes is difficult to obtain.