The congenital bicuspid aortic valve (BAV) is associated with increased leaflet calcification, ascending aortic dilatation, aortic stenosis (AS) and regurgitation (AR). Although underlying genetic factors have been primarily implicated for these complications, the altered mechanical environment of BAVs could potentially accelerate these pathologies. The objective of the current study is to characterize BAV hemodynamics in an in vitro system. Two BAV models of varying stenosis and jet eccentricity and a trileaflet AV (TAV) were constructed from excised porcine AVs. Particle Image Velocimetry (PIV) experiments were conducted at physiological flow and pressure conditions to characterize fluid velocity fields in the aorta and sinus regions, and ensemble averaged Reynolds shear stress and 2D turbulent kinetic energy were calculated for all models. The dynamics of the BAV and TAV models matched the characteristics of these valves which are observed clinically. The eccentric and stenotic BAV showed the strongest systolic jet (V = 4.2 m/s), which impinged on the aortic wall on the non-fused leaflet side, causing a strong vortex in the non-fused leaflet sinus. The magnitudes of TKE and Reynolds stresses in both BAV models were almost twice as large as comparable values for TAV, and these maximum values were primarily concentrated around the central jet through the valve orifice. The in vitro model described here enables detailed characterization of BAV flow characteristics, which is currently challenging in clinical practice. This model can prove to be useful in studying the effects of altered BAV geometry on fluid dynamics in the valve and ascending aorta. These altered flows can be potentially linked to increased calcific responses from the valve endothelium in stenotic and eccentric BAVs, independent of concomitant genetic factors.

Batch mixing of viscous fluids with helical‐ribbon agitators in 2.4 liter and 13 liter vessels has been studied for agitator speeds up to 200 RPM. Seven different agitators of different dimensions were employed in this work. Mixing times were measured using a decoloration technique and circulation times were determined by the tracer bead method. In addition, velocity profiles were obtained from streak photographs using selective illumination of the vessel and PVC powder as tracer particles. It was found that the mixing times of Newtonian fluids, which agreed with previously published data, were considerably (3 to 7 times) shorter than those of the viscoelastic fluids. The mixing time was strongly affected by the fluids' elasticity; increasing as the fluid elasticity increased. The velocity profiles were qualitatively similar for all the fluids but showed decreased axial circulation and increased circumferential flow as fluid elasticity increased. However, mixing is not only a function of the axial circulation (impeller pumping rate) but also is a function of the perturbations superimposed on the main flow. A simple, first approximation model based on the impeller geometry and flow patterns is proposed to correlate the circulation capacity and mixing time data for the various geometries studied.

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Aortic valve (AV) stenosis, if untreated, leads to heart failure. From a mechanics standpoint, heart failure can be interpreted as the failure of the heart to generate sufficient power to overcome energy losses in the circulation. Thus, energy efficiency-based measures for evaluating AV performance and disease severity have the advantage of being a direct measure of the contribution of the AV hydrodynamic characteristics toward heart failure. We present a new method for computing the rate of energy dissipation as a function of systolic time, by modifying the Navier-Stokes momentum equation. This method preserves the dynamic term of the Navier-Stokes momentum equation, and allows the investigation of the trend of the rate of energy dissipation over time. This method is applied to a series of in vitro experiments, where a trimmed porcine valve is exposed to various conditions: varying stroke volumes (50 ml to 90 ml) at the fixed heart rate; varying heart rates (60-80 beats/min) at fixed stroke volume; and varying stenosis levels (normal, mild stenosis, moderate stenosis). The results are: (1) energy dissipation waveform has a distinctive pattern of being skewed toward late systole, due to flow instabilities during deceleration phases; (2) increasing heart rate and stroke volume increases energy dissipation, but the normalized shape of the energy dissipation waveform is preserved across heart rates and stroke volumes; (3) increasing stenosis level increases energy dissipation, and also alters the normalized shape of the energy dissipation waveform. Since stenosis produces a signature energy dissipation waveform shape, dynamic energy dissipation analysis can potentially be extended into a clinical tool for AV evaluation.