Estimation of instantaneous blood flow through a rigid, coronary artery stenosis in anaesthetised domestic swine

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Abstract
This study tested the hypothesis that instantaneous coronary flow rate (Q) through a severe rigid coronary artery stenosis of known dimensions can be reliably estimated by measuring the instantaneous pressure gradient (ΔP) across the stenosis. A non-linear model for stenosis ΔP was employed (Δ P=RQ+SQ2, where R and S are constants describing stenosis geometry). Flow rate was determined by solving for the positive root of the quadratic equation, Q=(−R+√R2+4S (ΔP))/2S. Four open chest, anaesthetised, domestic swine were studied. A 7.0 mm long rigid stenosis (82% reduction in vessel diameter) was placed in the left anterior descending (LAD) coronary artery. Pressure distal to the stenosis was obtained with a fluid filled catheter (ID=1.4 mm) the distal end of which was secured within and open to the distal end of the stenosis. Aortic pressure corrected for phase delay in the time domain was taken as pressure proximal to the stenosis. An electromagnetic (EMF) flow probe positioned just proximal to the stenosis measured instantaneous flow. All pressure wave forms and the EMF flow signal were digitised on line and transmitted to a computer for analysis. Simultaneous computed and EMF flows for an average cardiac cycle were obtained in each animal: 1) at control; 2) after 10 min of adenosine infusion into the distal LAD; and 3) at a second control period. Computed and measured flow signals were compared on a point by point basis (5 ms resolution). The correlation coefficient (r) was 0.94±0.04 (mean±1SD) for the entire cycle (P3·s−1) correlated well (r=0.95, P<0.001), with mean flow rate measured (0.53±0.22). Computed mean diastolic flow rate (0.64±0.15) also correlated well (r=0.79, P<0.002) with measured mean diastolic flow rate (0.69±0.21). Thus, instantaneous coronary blood flow through a severe, rigid stenosis of known dimensions can be reliably estimated from instantaneous measurement of stenosis pressure gradient and a non-linear, quadratic model of stenosis pressure-flow relations.