THE PRESSURE-FLOW RELATION IN THE CANINE CORONARY-ARTERY - COMBINED EFFECTS OF CRITICAL STENOSIS AND INTRACORONARY THROMBOSIS

Objective: To characterise the effect of coronary intra-arterial throm bosis upon the downstream vascular bed. Background: The vascular respo nse downstream from a coronary intra-arterial thrombus has not previou sly been characterised. We postulated that downstream vasoconstriction might result from the presence of endothelial damage with consequent growth of platelet-rich thrombus. Methods: We measured the pressure gr adient and flow across, and the pressure/flow ratio distal to, a canin e left circumflex artery stenosis with and without endothelial damage causing intracoronary thrombosis. We also observed the effects of tran sient complete occlusions. Results: At occlusion, the pressure gradien t was maximal; relief of occlusion caused a rapid increase flow and di stal pressure with a rapid decrease in stenosis pressure gradient and resistance. Subsequently there was a period of stable stenosis resista nce with pressure gradient and flow declining; distal pressure therefo re increased at this time. Finally in the thrombus group only, stenosi s resistance increased again towards re-occlusion. During occlusion, d istal pressure averaged 49 +/- 18 mmHg in the presence of thrombus vs. 22 +/- 4 mmHg in its absence (P < 0.001). Following release of occlus ion, the flow increased faster than distal pressure, so that the ratio (distal pressure/flow) fell rapidly. Subsequently, distal pressure co ntinued to increase after flow had reached a peak and begun to decline , suggesting vasoconstriction. In the presence of thrombus, the distal pressure/flow ratio was higher than in the absence of thrombus, both at maximal vasodilatation (P < 0.005) and at maximum vasoconstriction (P < 0.025). Conclusions: During cyclic flow variations the stenosis r esistance changes are exactly as expected from thrombus growth and emb olisation. The distal pressure/flow ratio showed a time-dependent incr ease which appeared greater when conditions favoured intracoronary thr ombosis.