Effects of vasoconstriction and distal dilation on carotid stenoses in the dog

Traditionally, arterial stenoses have been assumed to be inflexible, static obstructive lesions that could not acutely change their configuration or cross-sectional area. However, recent clinical and experimental observations have shown that coronary arterial stenoses can respond to vasoconstriction and intraluminal pressure changes. This experimental study evaluated whether similar dynamic changes could occur in a carotid artery stenosis. The effects of dilation distal to a circumferential snare were examined in 6 mongrel dogs. To eliminate collateral flow, the distal carotid artery was occluded and blood flow diverted through a 16 or 20 gauge needle. With no stenosis, distal dilation increased flow from 29.0 +/- 2.0 to 90.1 +/- 3.8 ml/min, (p less than 0.01). With moderate stenosis, the flow increase (25.5 +/- 1.3 to 56.4 +/- 3.7 ml/min, p less than 0.01 following dilation was attenuated. With severe stenosis, flow paradoxically decreased (20.4 +/- 1.0 to 11.4 +/- 1.0 ml/min, (p less than 0.01). This flow decrease was associated with a large stenotic resistance increase (2.13 +/- 0.51 to 18.93 +/- 5.58 mm Hg/ml . min-1, (p less than 0.01). In eight additional experiments, an in vitro preparation was used to examine the effects of vasoconstriction on stenotic severity. Vasoconstriction, induced by ergonovine, methoxamine, angiotensin, or vasopressin, resulted in a significant flow decrease and stenotic resistance increase. Thus, both vasoconstriction and intraluminal pressure were shown to affect stenotic severity, and thereby influence blood flow. These data illustrate hemodynamic factors which may be important in patients with severe carotid artery stenosis.