Mechanism for dynamic changes in stenotic severity.

The mechanism responsible for rapid changes in stenotic severity or resistance due to alterations in perfusion pressure and distal resistance is addressed by this study. An in vitro, eccentric arterial stenosis model was created using 15 canine carotid arteries cannulated with silicone plugs containing special pressure-transducing catheters designed to measure pressure directly, within the stenosis. The vessels were perfused at perfusion pressures of 150, 100, and 75 mmHg and at two levels of distal resistance while perfusion pressure, distal pressure, stenotic pressure, and flow were recorded. Orthogonal arteriograms were performed. Stenotic resistance was calculated as (perfusion pressure--distal pressure)/flow. All variables changed significantly (P less than 0.05) with decreases in perfusion pressure. Stenotic resistance always increased (P less than 0.02) as perfusion pressure or distal resistance decreased. These dynamic changes in stenotic resistance occurred at stenotic pressures well above the atmospheric, extraluminal pressure. Arteriographic data demonstrated decreasing stenotic luminal area with decreasing stenotic pressure. These results confirm the assertion that rapid changes in stenotic resistance are related to changes in stenotic luminal area and are not due to extrinsic forces. The principles of the Starling resistor are, therefore, not applicable to dynamic arterial stenoses. This information is immediately relevant to clinical situations in which complaint, severe stenosis results in ischemia.