Power Density Spectra of the Velocity Waveforms in Artificial Heart Valves
To find the possible frequencies induced by the vibration of the flexible membrane of the Jellyfish valve, power density spectra of the the valvular velocity waveforms were carried out.
Most of the spectral energy was contained in frequencies lower than 11 Hz and all spectra exhibited pronounced peaks which implied wave motions in the preferred frequency range.
Two distinct peak frequencies, 1.2 and 2.4 Hz, were observed downstream of the Jellyfish valve which qualified as the frequencies of fundamental harmony of the waveform velocity and one of its sub harmonics.
Effect of oscillation on elevating turbulent shear stresses through the jellyfish and St. Vincent valves has also been investigated. Laser Doppler Anemometry (LDA) was employed to determine the velocity and shear stress distributions at various locations downstream of the valves. Comparison between two valves revealed that at 0.5D downstream of the valves the magnitude of shear stresses in the Jellyfish valve were much higher than those of the St. Vincent valve at cardiac outputs of 4, 5.5 and 7 l/min.
The cause of high shear stresses in close proximity to the Jellyfish valve could be attributed to the oscillation of the membrane which in turn generated a wake downstream of the valve (in the core of valve chamber) and produced a wide region of disturbance further downstream. This resulted in further pressure drag and consequently, higher pressure drops across the valve and higher shear stresses downstream of the valve.
KeywordsPower density spectra Heart valves shear stresses oscillation LDA technique
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