Extent of myocardial flow from luminal collateral circulation

In dogs the transport of radioactive microspheres directly from the ventricular chambers into the myocardium to determine the extent of luminal collateral flow was studied. Microspheres of 9 and 15 μm diameters were injected into the inferior cava to measure right ventricular luminal myocardial flow under normal hemodynamic conditions and during right ventricular hypertension, hypoxemia, and right ventricular hypertension with hypoxemia. Total luminal flow to the right ventricular free wall was insignificant, less than 0.3 ml/min^-1. In left ventricular studies radioactive microspheres were injected into the left atrium when the left coronary artery was perfused with microsphere free blood. Flow determinations were made during normal coronary perfusion pressure, reduced coronary perfusion pressure, and reduced coronary perfusion pressure with perfusion of hypoxemic blood. Total luminal flow to the left ventricular free wall was insignificant, less than 0.15 ml/min^-1. Therefore, essentially no flow of significance enters either the right or left ventricular myocardium through luminal vessels. These data demonstrate that luminal flow does not contribute to myocardial perfusion even under the abnormal conditions of hypoxemia and decreased coronary perfusion pressure.