Near Valve Flows and Potential Blood Damage During Closure of a Bileaflet Mechanical Heart Valve

Abstract

Blood damage and thrombosis are major complications that are commonly seen in patients with implanted mechanical heart valves. For this in vitro study, we isolated the closing phase of a bileaflet mechanical heart valve to study near valve fluid velocities and stresses. By manipulating the valve housing, we gained optical access to a previously inaccessible region of the flow. Laser Doppler velocimetry and particle image velocimetry were used to characterize the flow regime and help to identify the key design characteristics responsible for high shear and rotational flow. Impact of the closing mechanical leaflet with its rigid housing produced the highest fluid stresses observed during the cardiac cycle. Mean velocities as high as 2.4 m/s were observed at the initial valve impact. The velocities measured at the leaflet tip resulted in sustained shear rates in the range of 1500-3500 s À1 , with peak values on the order of 11,000-23,000 s À1. Using velocity maps, we identified regurgitation zones near the valve tip and through the central orifice of the valve. Entrained flow from the transvalvular jets and flow shed off the leaflet tip during closure combined to generate a dominant vortex posterior to both leaflets after each valve closing cycle. The strength of the peripheral vortex peaked within 2 ms of the initial impact of the leaflet with the housing and rapidly dissipated thereafter, whereas the vortex near the central orifice continued to grow during the rebound phase of the valve. Rebound of the leaflets played a secondary role in sustaining closure-induced vortices.

Surgical Aortic Valve Replacement: Are We Able to Improve Hemodynamic Outcome?

“…This is particularly important when considering mechanical valves. Our study demonstrated superior optimization potential when using mechanical valves, but it did not show the increased blood damage potential during leaflet closure reported by other studies (35,36). This limited scope of modeling would thus artificially favor mechanical valves over biological ones.…”

Simulation of Mechanical Heart Valve Dysfunction and the Non-Newtonian Blood Model Approach

“…When the blood flow passes through the MHV, it will generate a high-pressure drop, resulting in recirculation and stagnation [ 67 – 70 ]. The increase of shear stress will lead to blood damage (hemolysis) and platelet activation.…”

“…Although the shear rate is generally high in large arteries, some cardiovascular disease induces blood flow disturbance and generates stagnant and recirculation regions, significantly reducing the shear rate [ 133 ]. When the blood flows through the MHV, the recirculation, stagnation, vortex structures, and flow separation are obvious, which enhance the probability of occurrence of low shear rates and require the use of the non-Newtonian models [ 21 , 26 , 35 , 67 – 70 ]. In dysfunction MHV simulation, the blood flow behind the dysfunction leaflet has more significant recirculation flow and stagnation.…”

Blood Damage Through a Bileaflet Mechanical Heart Valve: A Quantitative Computational Study Using a Multiscale Suspension Flow Solver

“…These complications are thought to be due to nonphysiologic shear stress levels imposed on blood elements by complex flows through BMHVs [6][7][8]. Thrombus formation in the valves may lead to dislodged emboli that can cause stroke and death [9][10][11], Various experimental studies have been performed on flow through prosthetic heart valves to study the complex flow dynamics [12][13][14][15][16], though experimental studies are often limited to lower spatiotemporal resolution and obstructed viewpoints. Blood damage experiments are also possible, in which human blood can be run through valves and assays are performed to assess blood damage potential [17][18][19], but only give bulk blood damage results.…”