Studies of functional site of origin of native coronary collaterals.

Studies were performed to determine the pressure at the origin of the native coronary collaterals (Pstem) and thus assess the contribution of collaterals arising from proximal conduit coronary vessels vs. those arising from distal microvessels. Nine isolated blood-perfused dog hearts were studied. Aortic pressure was maintained at 80 mmHg. Collateral flow to the circumflex perfusion field was measured (radioactive microspheres) repeatedly before and after successive 25-micron nonradioactive microsphere embolization of the circumflex vasculature. After each microembolization, collateral flow decreased and peripheral coronary pressure (PCP) increased. After all embolizations collateral flow decreased from an initial value of 17 +/- 4 to 2 +/- 0.4 ml X min-1 X 100 g-1 and PCP increased from an initial value of 15 +/- 3 to 65 +/- 3 mmHg. The relationship between decreasing collateral flow and increasing PCP was linear with a pressure intercept of 74 +/- 3 mmHg. This pressure intercept predicts the PCP that would be observed if microembolization produced complete cessation of collateral flow. Accordingly, this pressure intercept allowed an accurate estimate of Pstem. This estimate of Pstem was similar to left anterior descending pressure (75 +/- 2 mmHg). These studies show that Pstem may be accurately estimated by measuring pressure in a nonoccluded large epicardial vessel. The contribution of microvascular anastomoses to total collateral flow is likely small.