Differences in spectral composition between monostrut Bjork-Shiley and Carbomedics valves implanted in the aortic position.

The paper investigates the differences in spectral composition between monostrut Bjork-Shiley and Carbomedics valves implanted in the aortic position using a modified overdetermined forward-backward Prony's method. Spectral composition of the closing sounds produced by these two valves are compared in terms of the e number of spectral components and their relative energy. Results show that, for both valves, the major spectral components are concentrated below 2 kHz. In the case of the Carbomedics valve, it is found that 97% of the total energy lies below 120 Hz where the sensitivity of the human auditory system is poor. This is one of the main reasons why the Carbomedics valve is acoustically quieter than a monostrut Bjork-Shiley valve when in operation. In addition, a clear difference monostrut and Carbomedics valves has also been found in the 400 Hz-2 kHz sub-band. A distinct difference between normal and malfunctioning cases of each prostheses has been found in the frequency components beyond 400 Hz. In the malfunctioning cases the frequency components in that region move to the lower regions of the spectrum and a large part of the energy is concentrated between 250 and 400 Hz.