Direct measurement of coronary collateral blood flow in conscious dogs by an electromagnetic flowmeter.

The development of collateral circulation has been indirectly monitored by determining peripheral coronary pressure and Xe clearance. In the present experiments, the development of collateral blood flow following gradual (three dogs) and rapid (three dogs) complete occlusion of the central circumflex branch, during partial central occlusion, and in parallel with a rise in peripheral coronary pressure was directly demonstrated by finding phasic coronary flow patterns in distal branches of the circumflex coronary artery. Collateral blood flow patterns were not consistently observed until a flow of 4-6 ml/ min developed. In five dogs branch flow before central occlusion averaged 20 ml/min, but peak collateral blood flow after occlusion averaged 11.6 ml/min (range 7 to 17 ml/min). To circumvent central occlusion collateral blood flow must enter the circumflex bed retrograde; we proved this fact by finding collateral blood flow patterns that were mirror images of normal antegrade patterns and flow values that were negative with respect to mechanical reference zeros. Unexpectedly, collateral blood flow was antegrade in some branches indicating a redistribution of retrograde collateral blood flow within the circumflex bed. In a terminal open-chest experiment, there was indirect evidence of alternate collateral blood flow opposing measured collateral blood flow; this finding could explain some of the small reactive hyperemias observed after the release of a temporary occlusion of a distal branch. In summary, phasic collateral blood flow patterns in distal epicardial branches that developed rapidly in response to occlusion of the central circumflex branch and in conjunction with a rise in peripheral coronary pressure were demonstrated, and reversal from antegrade to retrograde collateral blood flow was documented.