Allen C. Eberhardt Charles E. Chassaing
Structural Acoust., Inc., 5801 Lease Ln., Raleigh, NC 27613
A replacement prosthetic heart valve functions in a corrosive environment in which it cannot readily be inspected or repaired. It must cycle repeatedly, at a rate of 40 million cycles per year, over a service life that may extend many years. The opening and closing sounds of Bjoerk--Shiley convexo-concave prosthetic heart valves are brief transients that are being studied for detection of incipient valve failure. The sounds are produced by the impact of the occluder disk with the metallic struts that retain it within an orifice ring. These sounds have been recorded in vivo for two distinct conditions or classes, valves that are intact, and valves that exhibit an in-service failure of one of two legs of a strut which is critical to the function of the valve. The small size and rapid motion of the valve occluder disk produce a broadband acoustic transient that exhibits subtle changes as a valve strut proceeds toward failure. Features are detected, and a nonlinear expansion is used to develop a set of coefficients from the time and frequency domains to separate the two conditions. The recorded in vivo data are used as the training set. The coefficients are then applied to in vivo recordings as a method of detection of a progressive failure of the valve. Results of the expansion and of a parallel approach using neural nets are shown to be most effective for patients with normal heart rhythm.