Interaction of compliant coronary stenoses in series in a canine model

Resistance and flow across compliant coronary stenoses may be altered by changes in intraluminal pressure. The effects of a distal circumflex coronary stenosis on a proximal compliant circumflex stenosis were evaluated in 17 open-chest dogs. In ten dogs, both stenoses were produced with external snares. As the distal stenosis was tightened, a point was reached at which flow through the circumflex coronary artery paradoxically increased (8 +/- 1 to 11 +/- 1 ml/min; p less than 0.001). At the point of flow increase, there was an increase in intraluminal pressure between the stenoses (35 +/- 4 to 61 +/- 5 mmHg; p less than 0.001), and a decrease in pressure gradient (69 +/- 5 to 43 +/- 4 mmHg; p less than 0.001) and resistance (10.5 +/- 2.7 to 4.7 +/- 0.8 units; p less than 0.025) across the proximal stenosis. A similar increase in circumflex blood flow was found in dogs in which the proximal compliant stenosis was produced with an intraluminal balloon. In six additional dogs in which the proximal stenosis was produced with fixed noncompliant plastic tubing, tightening the distal snare did not result in an increase in circumflex blood flow. Thus, the increase in flow occurred only when the proximal stenosis was compliant. Increasing the severity of the distal stenosis caused an increase in intraluminal pressure in the area of the proximal stenosis and may have passively distended the compliant proximal stenosis decreasing its severity. Therefore, in the presence of compliant coronary stenoses in series, increasing severity of the distal stenosis may cause a paradoxical increase in flow through the stenotic artery.