Turbulence Characteristics Downstream of Bileaflet Aortic Valve Prostheses

Abstract

This study was focused on a series of in vitro tests on the turbulent flow characteristics of three bileaflet aortic valves: St. Jude Medical (SJM), CarboMedics (CM), and Edwards Tekna (modified Duromedics, DM). The flow fields of the valves were measured in a pulsatile flow model with a laser-Doppler anemometer (LDA) at the aortic sinus area downstream of the valves. The heart rate was set at 70 beats per minute, the cardiac output was maintained at 5 liters per minute, and the aortic pressure wave forms were kept within the physiological range. Cycle-resolved analysis was applied to obtain turbulence data, including mean velocity, Reynolds stresses, autocorrelation coefficients, energy spectral density functions, and turbulence scales. The Reynolds shear stresses of all three valves induced only minor damage to red blood cells, but directly damaged the platelets, increasing the possibility of thrombosis. The smallest turbulence length scale, which offers a more reliable estimate of the effects of turbulence on blood cell damage, was three times the size of red blood cells and five times the size of platelets. This suggests that there is more direct interaction with the blood cells, thus causing more damage.

Effect of Eddy Length Scale on Mechanical Loading of Blood Cells in Turbulent Flow

“…According to these results, the peak membrane tension induced by the Kolmogorov eddy is nearly independent of the eddy length scale. Figure 9 shows the corresponding results for microscale eddies with velocity scales determined from the turbulent energy spectrum of Liu et al 21 .…”

“…8,14,21,33 However, the Reynolds stress is an averaged momentum flux which contains no information about the size of flow structures in turbulence, and therefore cannot fully characterize the mechanical environment of individual cells. It has been shown that the Reynolds stress is an inaccurate indicator of true viscous stresses in turbulent flow of a homogeneous fluid, 13,17 and of flowinduced stress on blood cells suspended in turbulent flow.…”

“…It has been shown that the Reynolds stress is an inaccurate indicator of true viscous stresses in turbulent flow of a homogeneous fluid, 13,17 and of flowinduced stress on blood cells suspended in turbulent flow. 30 Quinlan and Dooley 30 calculated the approximate contribution to the flow-induced stress on blood cells from eddies across a spectrum of length scales, based on measurements by Liu et al 21 of flow downstream of a MHV.…”

Erratum to: Quantitative Assessment of Turbulence and Flow Eccentricity in an Aortic Coarctation: Impact of Virtual Interventions

“…Additionally, it has also been argued that the possible error induced by the SGS model would be less pronounced at peak flow conditions due to the more developed turbulence field. 35 By only simulating steady LES the computational cost could be reduced substantially compared to a pulsatile counterpart, where as much as 20 cardiac cycles have been proven necessary to obtain sufficient phase average results (see Online Resource). In a combined framework, accuracy and speed should be enhanced in order to approach clinical practice.…”

High-Resolution Measurement of the Unsteady Velocity Field to Evaluate Blood Damage Induced by a Mechanical Heart Valve

“…Geometry and dynamics of artificial occluders promote abnormal features such as jets, separation, and vortex shedding, which can subject cell trajectories to prolonged or intermittent exposure to large shearing forces 5,6 . It has been suggested that flow structures in these fields are effective at scales down to tens of µm 7,8 or mathematical models 15,[19][20][21][22] . Since cellular response to stress is dependent on history, such models must be integrated over the Lagrangian trajectory of a cell through the flow field of a given device in order to predict flow-induced blood damage.…”