William H. Corcoran

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The first heart sound of 29 normal, young males, recorded at the apex of the heart, was analysed for the power content as a function of frequency using the technique of the fast Fourier transform. The frequency spectra were seen to contain peaks in the low-frequency range (10–50 Hz) and the medium-frequency range (50–140 Hz). The average spectrum of the(More)
The fast Fourier transform (f.f.t.) is a powerful technique which facilitates analysis of signals in the frequency domain. This paper reviews some of the important features of the fast Fourier transform which are relevant to its increasing application to biomedical data. A distinction is made between the power spectrum of ergodic signals, computed from the(More)
Velocity measurements were made in vitro using laser Doppler anemometry (LDA) downstream from an lonescu-Shiley (IS) bioprosthetic aortic heart valve. Velocity measurements were made in both steady and pulsatile flow. A systematic, flow mapping approach to the measurement methodology showed that the IS valve generated a large jetlike flow constriction. The(More)
Thrombus formation and tissue overgrowth were observed in nine Björk-Shiley aortic prostheses recovered six months or longer after implantation. These pathologic findings may be attributed to the flow characteristics of the prosthesis. The open disc of the valve separates the flow into two unequal regions. Varying degrees of thrombus formation were observed(More)
Laser-Doppler anemometry is relatively new technique which is used for measuring velocity fields. It has major applications in the field ofin vitro biofluid mechanics. The laser-Doppler anemometers have many advantages compared with the traditional hot-wire or hot-film anemometers which are still mainly used in studies of biofluid mechanics. A laser-Doppler(More)
In this study,in vitro velocity measurements in the near vicinity of a Björk-Shiley aortic valve, one of the more commonly used aortic valve prostheses, were made using a laser-Doppler anemometer. The velocity measurements identified a zone of stagnation, about 20 mm wide, immediately downstream from the fully open disc. The measurements also showed that(More)
Anin vitro study was made of the sounds produced by a normal, Smeloffaortic-valve prosthesis and compared for the entire cardiac cycle with the same valve having a simulated overgrowth on the upstream struts. Time and amplitude information, power-density spectra, power-distribution functions, and three-dimensional power-frequency-time surfaces were(More)
A feasibility study was made to examine whether pressure measurements can be used to diagnose vascular obstructions in blood vessels. Distortion of a pressure wave due to an obstruction in an elastic tube was investigated theoretically and experimentally. Linear theory and the method of characteristics were employed in developing mathematical expressions(More)