Effect of distal coronary pressure on rigid and compliant coronary stenoses

The effects of changes in distal coronary pressure on the hemodynamics of rigid and compliant coronary stenoses were studied in anesthetized open-chest dogs. In dogs with severe compliant circumflex stenoses produced with an external snare, pressure distal to the stenosis was lowered by closing a catheter connecting the carotid artery to the distal circumflex artery and was raised by reopening the catheter. Lowering mean distal circumflex pressure from 57 +/- 14 to 18 +/- 3 (SE) mmHg (P less than 0.01) increased stenotic resistance (2.1 +/- 0.7 to 14.1 +/- 7.8 units, P less than 0.01) and decreased circumflex flow (19 +/- 6 to 6 +/- 4 ml/min, P less than 0.01). Raising distal pressure (18 +/- 3 to 49 +/- 15 mmHg, P less than 0.05) decreased stenotic resistance (14.1 +/- 7.8 to 3.7 +/- 0.9 units, P less than 0.05) and increased circumflex flow (6 +/- 4 to 13 +/- 3 ml/min, P less than 0.05). In dogs with rigid stenoses produced with plastic tubing, a fall in distal pressure significantly increased flow without a change in stenotic resistance. Therefore, changes in resistance and flow through compliant coronary stenoses occur in response to changes in distal pressure. These hemodynamic changes are consistent with passive collapse and distension of the stenotic segment.