Flow patterns at the site of extracranial to intracranial end to side anastomosis. An experimental rheological study.

Abstract

Flow property measurements were performed in a plexiglass model of six various types of end-to-side anastomosis (as clinically shown in extracranial to intracranial arterial bypass surgery). Three anastomoses were made without, another three anastomoses with a ringshaped stenosis restricting the lumen to between 25 and 46% of the cross-section as it occurs clinically by formation of thrombi out of the striching canals. A rectangular type and two of 45 degree oblique types--one directed centrally and one directed peripherally--were tested. Pressure head losses at the site of anastomosis were measured under various circumstances of different anastomoses and different flow speeds along the proximal portion of the middle cerebral artery and the superficial temporal artery. Flow resistance values originated by the different types of anastomoses were expressed in terms of additional recipient vessel length. Differences between different types of anastomoses with and without stenosis were very small and under no circumstances exceeded the equivalent of lengthening the recipient vessel by 2 cm. Theoretically, the optimal type of anastomosis is the oblique and centrally directed version; the worst type is the rectangular form. Practically, however, such differences are not relevant. The explanation for such unexpectedly small differences can rheologically be given by considering the dominating role of blood viscosity under the given circumstances, other variables such as short stenosis and angling of flow playing a secondary role.