Physical analysis of the Björk-Shiley prosthetic valve sound

The closing sound of an implanted Björk-Shiley heart valve prosthesis can be heard clearly in the proximity of the patient. A clinical interrogation of 35 patients showed that 16 (46%) were disturbed by the clicking noise and 10 (29%) reported disturbance of those nearby. A silent prosthesis would be preferred by 15 (43%) patients, eight (23%) declined such a valve for reasons of their own security, and 12 (34%) patients were undecided. The frequency spectrum of the metallic closing sound and its loudness were measured by noninvasive techniques in 20 patients. In the aortic as well as in the mitral position, a high peak of the sound pressure level was registered at 9.8 kHz. In 20 patients the average value of the sound pressure level was 35 dbA measured at a distance of 10 cm from the patient's chest. In vitro studies demonstrated a high peak of the sound pressure level at 9.5 kHz for the Björk-Shiley valve when recorded in free air and at 7 kHz in a standardized valve chamber of a mock circulatory system filled with blood or water. A decrease of the sound pressure level could be achieved by a textile wrap around the chest which damps frequencies around 10 kHz. This protects those nearby but not the patient, who hears the clicking mainly through internal conduction. This unpleasant valve noise can be eliminated only during construction of a new prosthesis provided that such "minor" side effects are measured and taken into consideration.