Collateral influence on pressure-flow characteristics of coronary circulation

The purpose of this study was to determine the role of the coronary collateral circulation on the shape of the coronary pressure-flow (P-F) relationship and its effects on the pressure at zero flow (PZF) or pressure intercept. We investigated the P-F characteristics of the coronary circulation under two conditions. 1) To minimize the influence of collaterals, we measured coronary flow by timed collections of coronary sinus outflow in 15 dog hearts, as perfusion pressure to all vessels was varied; 2) to maximize the effect of collaterals, we measured circumflex artery flow in six dog hearts, as perfusion pressure to only the circumflex coronary artery was varied and the pressure in the remaining vessels was maintained constant. We used an isolated heart preparation in which ventricular chamber and venous outflow pressures equalled atmospheric pressure and the vessels were maximally dilated with adenosine. In the first condition, the P-F relationship was curvilinear with a PZF of 0 mmHg; in the second condition, the P-F relationship was curvilinear with a PZF of 16 +/- 2 mmHg, and flow was retrograde at pressures below PZF. We conclude that in both conditions the curvilinearity of the coronary P-F relationship was the result of nonlinear elastic properties of blood vessels, not requiring the "waterfall" concept to be invoked, and that in the second condition the influence of collateral vessels produced the positive pressure intercept.