Assessment of perceived mechanical heart valve sound level in patients

Background and aim of the study: When mechanical heart valves close, they g enerate an impulse that is transmitted to the patient's inner ear by two ro utes: (i) As acoustically transmitted sound waves; and (ii) as vibrations t ransmitted through bones and vessels. The aim of this study was to quantita te what patients perceive as sound from their mechanical heart valve prosth eses - including both air-transmitted sound waves and bone-transmitted vibr ations. Methods: Thirty-four patients with implanted mechanical bileaflet aortic an d mitral valves (St. Jude Medical and On-X) were included in the study. Mea surements were performed in a specially designed sound-insulated chamber eq uipped with microphones, accelerometers, preamplifiers and a loudspeaker. T he closing sounds measured by an accelerometer on the patient's chest were delayed 400 ms, amplified and played back to the patient through the loudsp eaker. The patient adjusted the feedback sound to the same level as the 're al-time' clicks they perceived directly from their valve. In this way the f eedback sound energy includes both the air- and bone-transmitted energies. Sound pressure levels (SPL) were quantitated in both dB(A) and in loudness units (sones) according to ISO 532B (Zwicker method). Results: The mean air-transmitted SPL measured close to the patient's ear w as 23 +/- 4 dB(A). The total air-and bone-transmitted sounds and vibrations were perceived by the patients as a SPL of 34 +/- 5 dB(A). There was no st atistically significant difference in perceived sound from the two bileafle t valves investigated, and no difference between aortic and mitral valves. Conclusions: The study showed that the presented feedback method is capable of quantitating the perceived sounds and vibrations from mechanical heart valves, if the patient's hearing is not too impaired. Patients with implant ed mechanical heart valve prostheses seem to perceive the sound from their valve two to four times higher than nearby persons, because of the addition al bone-transmitted vibrations.