PubMed · 15151136
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Ivan Oransky. 2004-05-08. Obituary. Harold Kletschka.. https://doi.org/10.1016/s0140-6736(04)16173-4
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In the 1994 Replacement Heart Valve Guidance of the U.S. Food and Drug Administration (FDA), in-vitro testing is required to evaluate the potential for cavitation damage of a mechanical heart valve (MHV). To fulfill this requirement, the stroboscopic high-speed imaging method is commonly used to visualize cavitation bubbles at the instant of valve closure. The procedure is expensive; it is also limited because not every cavitation event is detected, thus leaving the possibility of missing the whole cavitation process. As an alternative, some researchers have suggested an acoustic cavitation-detection method, based on the observation that cavitation noise has a broadband spectrum. In practice, however, it is difficult to differentiate between cavitation noise and the valve closing sound, which may also contain high-frequency components. In the present study, the frequency characteristics of the closing sound in air of a Björk-Shiley Convexo-Concave (BSCC) valve are investigated. The occluder closing speed is used as a control parameter, which is measured via a laser sweeping technique. It is found that for the BSCC valve tested, the distribution of the sound energy over its frequency domain changes at different valve closing speeds, but the cut-off frequency remains unchanged at 123.32 +/- 6.12 kHz. The resonant frequencies of the occluder are also identified from the valve closing sound.
Based on the development of an impeller total artificial heart (TAH) (1987) and a permanent maglev (magnetic levitation) impeller pump (2002), as well as a patented magnetic bearing and magnetic spring (1996), a novel permanent maglev impeller TAH has been developed. The device consists of a rotor and a stator. The rotor is driven radially. Two impellers with different dimensions are fixed at both the ends of the rotor. The levitation of the rotor is achieved by using two permanent magnetic bearings, which have double function: radial bearing and axial spring. As the rotor rotates at a periodic changing speed, two pumps deliver the pulsatile flow synchronously. The volume balance between the two pumps is realized due to self-modulation property of the impeller pumps, without need for detection and control. Because the hemo-dynamic force acting on the left impeller is larger than that on the right impeller, and this force during systole is larger than that during diastole, the rotor reciprocates axially once a cycle. This is beneficial to prevent the thrombosis in the pump. Furthermore, a small flow via the gap between stator and rotor from left pump into right pump comes to a full washout in the motor and the pumps. Therefore, it seems neither mechanical wear nor thrombosis could occur. The previously developed prototype impeller TAH had demonstrated that it could operate in animal experiments indefinitely, if the bearing would not fail to work. Expectantly, this novel permanent magnetic levitation impeller TAH with simplicity, implantability, pulsatility, compatibility and durability has satisfied the most requirements on blood pumps and will have more extensive applications in experiments and clinics.