Musical murmurs in human cerebral arteries after subarachnoid hemorrhage.

A transcranial ultrasonic method for the recording of murmurs from cerebral vessels is described. Using the new approach the authors have observed musical murmurs of pure tone quality in 15 patients with increased flow velocities in the cerebral arteries after spontaneous subarachnoid hemorrhage (SAH). The frequency range of the pure tones was from 140 to 820 Hz, corresponding to flow velocities between 73 and 215 cm/sec. The musical murmurs occurred as a transitional state between silent flow and the well known phenomenon of bruit. They were observed between the 4th and the 20th day after SAH. The most likely cause of the musical murmur is a periodic shedding of vortices in the cerebral arteries, commonly referred to as "a von Kármán vortex street." Clinically the presence of musical murmurs indicated that pathologically increased blood velocities were present in the artery under investigation. This probably reflected the degree of spasm.