✓ Preliminary experiments with glass model bifurcation aneurysms demonstrated that turbulent flow pattern occurs in the sac of an aneurysm at a low flow rate (critical Reynolds number, 400 ± 10 S.E.M.). A prediction that flow is turbulent in the sac of human intracranial saccular aneurysms was confirmed in a clinical study. Bruits, indicative of turbulence, were recorded with a phonocatheter from the sacs of 10 out of 17 intracranial aneurysms exposed at surgery where the mean arterial pressures were above 50 mm Hg. The amplitude of the bruits varied with the pressure. All of the patients in whom no bruit was found had profound Arfonad hypotension at the time of recording.
Turbulence causes vibration in the wall of a vessel. This vibration produces and accelerates degenerative changes in vascular tissue by a process similar to the structural fatigue of metals by vibration. The author proposes that the turbulent blood flow within an aneurysm contributes to the degeneration of the elastica, and the production of the atheromatous changes, characteristically seen in its wall. This weakens the wall causing continuing enlargement and eventual rupture.