EFFECTS OF ANTERIOR COMMUNICATING ARTERY DIAMETER ON CEREBRAL HEMODYNAMICS IN INTERNAL CAROTID-ARTERY DISEASE - A MODEL STUDY

Background Collateral circulatory pathways are considered the primary determinant of cerebral hemodynamics in patients with obstructive lesi ons of the internal carotid arteries (ICaAs). However, the hemodynamic effects of the diameter of the anterior communicating artery (ACoA) h ave never been assessed quantitatively in humans. Methods and Results Two different mathematical models were used to simulate changes affect ing blood pressures and flows in cerebral arteries as a function of AC oA diameter and ICaA stenoses or occlusions. Small changes in ACoA dia meter were found to have marked hemodynamic effects when they occurred within the range of 0.4 to 1.6 mm, a situation observed in 80% of the cases. Outside this range, changes in ACoA diameter had no effect. Si mulated pressure drops through a stenotic ICaA were consistent with th ose observed. They were found to depend on the degrees of the stenoses in both ICaAs and on ACoA diameter according to a simple equation. Pr essure reserve in the middle and Interior cerebral arteries decreased to below the lower limit of autoregulation, despite a normal mean arte rial blood pressure, when the arteries were distal to a unique 70% ICa A stenosis associated with a small-diameter ACoA or to a 50% ICaA sten osis associated with a contralateral ICaA occlusion and a large-diamet er ACoA. Above these thresholds, the circle of Willis allowed for an a lmost complete global cerebral blood flow compensation that involved a ll the afferent and communicating vessels. Conclusions ACoA diameter s trongly modulates the effects of ICaA lesions on cerebral hemodynamics . Some proposals for endarterectomy indications can be derived from ou r study.