Role of the pericardium in the regulation of myocardial blood flow and its distribution in the normal and acutely failing left ventricle of the dog

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Abstract
The effects of the pericardium on the amount and distribution of left ventricular myocardial blood flow were studied. In 10 normal dogs, transfusion of blood from a donor dog resulted in modest increases in coronary flow and ventricular diameter that were greater with an open than a closed pericardium. The ratio of subendocardial to subepicardial flow remained normal with or without the pericardium, at low and high diastolic ventricular pressure, and before and after pharmacological vasodilatation with chromonar. In 18 dogs, cardiac failure was induced by constant infusion of the metabolic inhibitor, phenformin. Modest ventricular dilatation occurred if the pericardium was open. A progressive rise in myocardial blood flow developed in those with the pericardium open (1.06 rising to 3.02 ml·g−1·min−1). A lesser increase (0.62 to 1.75 ml·g−1·min−1) was seen in dogs with the pericardium closed; they selectively increased subendocardial flow, producing an average subendocardial to subepicardial flow ratio of 2.25. Pharmacological vasodilatation then resulted in uniform transmural flow. The pericardium can influence myocardial flow indirectly by influencing myocardial metabolic demand, when the heart is stressed. It may have a beneficial role in preventing the increased oxygen and coronary flow requirements produced by ventricular dilatation.