Stability of the BSCC heart valve outlet strut resonant frequency under changing physiological conditions and observation times

Abstract

Acoustic monitoring techniques have been developed to determine the state of BSCC (Bjork-Shiley Convexo-Concave) artificial heart valves. The signal processing is based primarily on time-windowed Fourier analysis that extracts the resonant frequency of the intact outlet strut (IOS). The absence of the resonant waveform is an indicator that the outlet strut has one of its legs separated from the valve's flange, a condition called SLS (single leg separation) that may lead to the separation of the remaining leg from the valve's flange, resulting in escape of the disc. Due to a low signal to noise ratio, the IOS waveform is usually not detectable unless an ensemble-averaged, time-windowed spectrum is computed using several hundred heartbeat signals. This technique works effectively only if the IOS frequency remains stable over the data recording time interval. Research that establishes the stability of the IOS resonant frequency is described. Three independent experimental procedures that generated the data used in the analysis were (1) strain gauge measurements of BSCC valves tested in artificial heart simulators; (2) acoustic and strain gauge data from valves implanted in sheep; and (3) acoustic data acquired from BSCC valve patients whose valve states (Intact or SLS) were confirmed following valve explanation. Another important observation from the sheep experiment is that both during exercise and rest conditions, the IOS frequency remained constant whereas the disc tonals showed significant variations. This feature of the IOS may be used to distinguish its resonant frequency from interfering disc tonals. >