Vascular resistance changes distal to progressive arterial stenosis: a critical re-evaluation of the concept of vasodilator reserve.

Previous studies have shown that with progressive arterial stenosis, resting blood flow does not start to diminish until 85-95% luminal area stenosis is reached. However, during hyperemic states, peak flow starts to diminish at only 40-60% stenosis. An autoregulatory mechanism has been postulated, whereby peripheral arterioles undergo compensatory vasodilatation, thereby maintaining resting flow. During hyperemia, some vasodilator reserve is presumably already used up, resulting in flow dropoff at an earlier stage. We measured flow and pressure and calculated peripheral vascular resistance (Rp) distal to progressive iliac artery stenoses in five dogs. Contrast injections proximal to the stenoses allowed precise angiographic quantitation of the lesions and provided reproducible hyperemic stimuli. Flow-stenosis relationships proved similar to those discussed above, but Rp distal to the lesions failed to show progressive decrease as stenosis increased. Thus, compensatory peripheral vasodilatation does not occur during most phases of progressive arterial stenosis. The contours of resting and hyperemic flow-stenosis curves are not related to the concept of vasodilator reserve but instead are readily explained by basic hydrodynamic principles.