Determination of coronary collateral flow by a load line analysis.

We have examined the feasibility of determining coronary collateral blood flow in an open-chest dog by a "load line" type of analysis as is often employed to analyze transistors and vacuum tubes. The load line equation states that collateral flow is given by the quantity: [Formula: see text] where PcP is peripheral coronary pressure, AOP is aortic pressure, Qret is retrograde flow, and K is a constant. The validity of this equation was critically tested in a series of dog experiments in which the collateral vessels were found to approximate a linear resistance, the source pressure for the collaterals (K in the equation) was found to be 0.8 of aortic pressure, and the retrograde flow with zero back pressure was found to account for all of the collateral flow. Finally, we found that estimates from the equation correlated well with direct microsphere measurements of collateral flow. All of these findings support the use of the proposed technique which determines collateral flow by three easily measured laboratory parameters.