PubMed · 10262521
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R R Tyson, B M Derrick. 1983. Vascular prostheses today.. https://pubmed.ncbi.nlm.nih.gov/10262521/
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Fractures in Björk-Shiley convexoconcave (BScc) heart valves have raised questions about the feasibility of early diagnosis of technical defects by means of acoustic assessment. Three laboratory tests were conducted. To establish acoustic fingerprints, 66 valves with a defect, such as single-leg fracture (SLF) or single-leg separation (SLS), or without a defect were connected with a contact sensor and excited by dropping a small metal ball onto the outlet strut. In the second test, we simulated the valve sound propagation within the thorax. In the third test, intact, SLF, and SLS valves were placed in a mock heart immersed in a large water tank. We observed a resonance frequency corresponding with valve size and presence of defects. The second test showed that both the chest wall and the lungs created numerous reflections. This led to a substantial overlap of the original pulse frequencies and the frequencies measured. The third test confirmed that submersion of the chest in water can significantly reduce chest wall reflections. Reliable noninvasive assessment of BScc valve clicks for the presence of defects of the outlet strut is hampered by complex sound propagation within the thorax and variability of valve excitation. Acoustic fingerprints to diagnose mechanical defects should be integrated in valve design.
The Lenz effect on the motion of metal containing moving parts of artificial heart valves has not been considered to date. In this paper the basic theory is outlined and a simple model applied to estimate worst-case forces on such valves. The results indicate a potential for forces over 100 times greater than for the more widely recognized ferromagnetic interation. Resistive pressure effects comparable to cardiac pressure differences may occur for such valves in the mitral position even at fields as low as 1.5 T. The effect will increase linearly with field strength. Additional monitoring and perhaps even exclusion of such patients may be prudent, even at 1.5 T.
The need for prosthetic heart valves was long recognized but seemed an impossible dream before 1952 when Dr Charles Hufnagel clinically introduced a ball valve that he placed into the descending thoracic aorta for treatment of aortic valvular insufficiency. Fulfillment of that dream became a reality with the advent of extracorporeal circulation in the early 1950s. Development of prosthetic heart valves involved the search for biologically compatible materials and hemologically tolerant designs. Success could not be achieved without the union of these two factors. As there was no satisfactory mechanism to scientifically achieve this goal, trial and error was the method of choice. The development of prosthetic heart valves became the purview of the cardiovascular surgeon who often collaborated with engineers. To distinguish one valve from another each prosthesis often became identified with the surgeon developer. The development of bioprostheses occurred later in the development of artificial heart valves and constitutes a separate subject not covered in this presentation.