Distribution of coronary collateral blood flow at different levels of collateral growth in conscious ponies

Coronary collateral growth was stimulated in chronically instrumented conscious ponies by a previously validated intermittent coronary occlusion method. Changes in regional myocardial function (sonomicrometry) and reactive hyperemia (Doppler method) were used to monitor collateral growth and to program measurements of regional myocardial blood flow (microsphere method). A serial analysis of the transmural and lateral distributions of collateral blood flow was performed at the native and three superimposed levels of collateral growth. Results in nine animals undergoing an average of 553 +/- 188 brief coronary occlusions over 68 +/- 18 days demonstrated that as collateral conductance increased, the perfusion field within the ischemic region increased from the epicardium to the endocardium but not from the lateral edges to the center of the ischemic region. The findings are consistent with an analog model consisting of interarterial collaterals whose collective resistance is in series with arteriolar resistance of the recipient artery. No special protection of deeper myocardial layers by a subendocardial plexus or intramural collaterals was noted. Instead, the findings suggest that coronary extravascular compressive forces play a more important role than the transmural location of collaterals in determining the volume and spatial distribution of collateral blood flow during collateral growth in the pony.