Experiments on carotid artery flow increase as a result of contralateral carotid occlusion

Summary

No infallible preoperative method exists to predict accurately a patient's tolerance to unilateral carotid artery ligation. It has recently been hypothesized that the magnitude of increase in contralateral carotid artery flow resulting from trial compression of the ipsilateral common carotid artery might be of value in determining the result of permanent ligation. The purpose of this study is to evaluate three factors which might influence the contralateral flow increase: the carotid sinus reflex, the vertebro-basilar artery circulation, and the degree of anastomotic crossover in the anterior part of the circle of Willis.

The effects of these three factors were studied in the following situations: (1) Before and after ablation of the ipsilateral carotid sinus in eight dogs (by cutting the ninth and tenth cranial nerves); (2) Before and after ligation of both vertebral arteries in three dogs: (3) Before and after separation of the anterior circle of Willis by clipping an anterior cerebral artery in two monkeys.Results: (1) Carotid sinus denervation had no effect in three dogs, diminished the increase by an average of 25% in three dogs, and enhanced the increase by an average of 50% in two dogs: (2) Bilateral vertebral artery ligation enhanced the increase in all three dogs by an average of 66%; (3) Separation of the anterior circle of Willis caused a diminution of the increase in both monkeys by an average of 66%; (4) There was no relationship between the degree of contralateral flow increase and 1. systemic blood pressure, 2. contralateral flow prior to occlusion, or 3. ipsilateral flow prior to occlusion.Conclusions: (1) In the experimental situation, the carotid sinus reflex is not consistently responsible for the contralateral carotid flow increase; (2) The observations on the vertebral artery occlusion and monkey studies lend support to the concept that if a contiguous vascular bed is removed from access to carotid blood, the flow through the system will decrease, and vice versa. The data are placed into clinical perspective.