Pulsatile flow studies of a porcine bioprosthetic aortic valve in vitro: PIV measurements and shear-induced blood damage

Hemolysis performance analysis and a novel estimation model of roller pump system

OBJECTIVE

Hemolysis performance is a crucial criterion for roller pumps utilized in life supporting system. In this study, the factor of hemolysis for roller pumps was selected as the target, and an estimation formulation was built to evaluate its hemolysis.

METHODS

Several models were proposed and then simulated with the assistant of Computational fluid dynamics (CFD) framework. The hemolysis performance was calculated using the power law model based on CFD and the estimation model in accordance with geometry parameters proposed in this study. The results of the in vitro experiments were compared with the simulation results. Power law model with the lowest error was utilized in following analysis.

RESULTS

As indicated by the simulation result, the rotary speed most significantly affected the hemolysis performance of roller blood pumps, followed by roller number and diameter of tube. The index of hemolysis (IH) for roller blood pumps at a rotary speed of 20-100 rpm ranged from 8.73E-7 to 8.07E-5. The relative error of the estimation model (4.93%) was lower than of the power law model (6.78%).

CONCLUSION

The IH led by pumps shows a significant, nonlinear relationship with the rotary speed. The design of multiple rollers design is harmful for hemolysis performance and larger diameter of tube exhibits decreased hemolysis at constant flow rate. An estimation formula was proposed with lower relative error for roller pump with the same shell set, which exhibited reduced computation and elevated convenience. And it can be utilized in hemolysis estimation of roller pumps potentially.

A novel model for hemolysis estimation in rotating impeller blood pumps considering red blood cell aging

For blood pumps with a rotating vane-structure, hemolysis values are estimated using a stress-based power-law model. It has been reported that this method does not consider the red blood cell (RBC) membrane's shear resistance, leading to inaccurate estimation of the hemolysis value. The focus of this study was to propose a novel hemolysis model which can more accurately predict the hemolysis value when designing the axial flow blood pump. The movement behavior of a single RBC in the shear flow field was simulated at the mesoscale. The critical value of shear stress for physiological injury of RBCs was determined. According to the critical value, the equivalent treatment of RBC aging was studied. A novel hemolysis model was established considering the RBC's aging and the hemolysis' initial value. The model's validity was verified under the experimental conditions of shear stress loading and the conditions of the shear flow field of the blood pump. The results showed that compared with other hemolysis models for estimating the hemolysis value of blood pumps, the novel hemolysis model proposed in this paper could effectively reduce the estimation error of the hemolysis value and provide a reference for the optimal design of rotary vane blood pumps.

Long-term durability of a new surgical aortic valve: A 1 billion cycle in vitro study

Background

This study assessed the long-term hemodynamic functional performance of the new Inspiris Resilia aortic valve after accelerated wear testing (AWT).

Methods

Three 21-mm and 23-mm Inspiris valves were used for the AWT procedure. After 1 billion cycles (equivalent to 25 years), the valves' hemodynamic performance was compared with that of the corresponding zero-cycled condition. Next, 1 AWT cycled valve of each valve size was selected at random for particle image velocimetry (PIV) and leaflet kinematic tests, and the data were compared with data for an uncycled Inspiris Resilia aortic valve of the same size. PIV was used to quantitatively evaluate flow fields downstream of the valve. Valves were tested according to International Standards Organization 5840-2:2015 protocols.

Results

The 21-mm and 23-mm valves met the International Organization for Standardization (ISO) durability performance requirements to 1 billion cycles. The mean effective orifice areas for the 21-mm and 23-mm zero-cycled and 1 billion–cycled valves were 1.89 ± 0.02 cm² and 1.94 ± 0.01 cm², respectively (P < .05) and 2.3 ± 0.13 cm² and 2.40 ± 0.11 cm², respectively (P < .05). Flow characterization of the control valves and the study valves demonstrated similar flow characteristics. The velocity and shear stress fields were also similar in the control and study valves.

Conclusions

The Inspiris Resilia aortic valve demonstrated very good durability and hemodynamic performance after an equivalent of 25 years of simulated in vitro accelerated wear. The study valves exceeded 1 billion cycles of simulated wear, 5 times longer than the standard requirement for a tissue valve as stipulated in ISO 5840-2:2015.

In Vitro Assessment of Right Ventricular Outflow Tract Anatomy and Valve Orientation Effects on Bioprosthetic Pulmonary Valve Hemodynamics

PURPOSE

The congenital heart defect Tetralogy of Fallot (ToF) affects 1 in 2500 newborns annually in the US and typically requires surgical repair of the right ventricular outflow tract (RVOT) early in life, with variations in surgical technique leading to large disparities in RVOT anatomy among patients. Subsequently, often in adolescence or early adulthood, patients usually require surgical placement of a xenograft or allograft pulmonary valve prosthesis. Valve longevity is highly variable for reasons that remain poorly understood.

METHODS

This work aims to assess the performance of bioprosthetic pulmonary valves in vitro using two 3D printed geometries: an idealized case based on healthy subjects aged 11 to 13 years and a diseased case with a 150% dilation in vessel diameter downstream of the valve. Each geometry was studied with two valve orientations: one with a valve leaflet opening posterior, which is the native pulmonary valve position, and one with a valve leaflet opening anterior.

RESULTS

Full three-dimensional, three-component, phase-averaged velocity fields were obtained in the physiological models using 4D flow MRI. Flow features, particularly vortex formation and reversed flow regions, differed significantly between the RVOT geometries and valve orientations. Pronounced asymmetry in streamwise velocity was present in all cases, while the diseased geometry produced additional asymmetry in radial flows. Quantitative integral metrics demonstrated increased secondary flow strength and recirculation in the rotated orientation for the diseased geometry.

CONCLUSIONS

The compound effects of geometry and orientation on bioprosthetic valve hemodynamics illustrated in this study could have a crucial impact on long-term valve performance.

Evolution of Thin-Liquid Films Surrounding Bubbles in Microfluidics and Their Impact on the Pressure Drop and Fluid Movement

The evolution of thin-liquid films in a microchannel is one of the most critical and intricate phenomena to understand two-phase movement, evaporation, micromixing, heat transfer, chemical synthesis, biological processes, and efficient energy devices. In this paper, we demonstrate experimentally the effect of a liquid film on the removal of an initially dry and lodged bubble in laser-etched poly(methyl methacrylate) microfluidic networks and discuss the evolution of the liquid film in accordance with the bubble superficial velocity and the effect of liquid properties and branch angle on the evolution of the liquid film and the pressure drop. During the removal of a dry bubble, four stages have been observed in the bubble velocity profile and they directly relate to the evolution of the liquid film. The correlation of maximum bubble velocity has been derived as a function of bubble length, fluid viscosity, surface tension, geometry of the cross-sectional area, and dimensions of the microchannel and agrees with the experimental results. The bubble moving distance required for the full deposition of a continuous and stable thin-liquid film is affected by the liquid viscosity and network branch angle. The liquid with a higher viscosity will increase the pressure drop for removing dry bubbles from microfluidic networks, while this effect will be hampered by increasing the microfluidic network complexity. The deposition of the thin-liquid film surrounding bubbles significantly decreases the pressure drop required to remove bubbles from microfluidics. Compared with deionized water, the glycerol solution is prone to acting as the lubricating liquid due to its strong H-bond interaction with the channel wall and the reduction in interfacial energy of the gas-water interface.

Influence of near-wall PIV data on recirculation hemodynamics in a patient-specific moderate stenosis: Experimental-numerical comparison

BACKGROUND

Recirculation zones within the blood vessels are known to influence the initiation and progression of atherosclerotic lesions. Quantification of recirculation parameters with accuracy remains subjective due to uncertainties in measurement of velocity and derived wall shear stress (WSS).

OBJECTIVE

The primary aim is to determine recirculation height and length from PIV experiments while validating with two different numerical methods: finite-element (FE) and -volume (FV). Secondary aim is to analyze how FE and FV compare within themselves.

METHODS

PIV measurements were performed to obtain velocity profiles at eight cross sections downstream of stenosis at flow rate of 200 ml/min. WSS was obtained by linear/quadratic interpolation of experimental velocity measurements close to wall.

RESULTS

Recirculation length obtained from PIV technique was 1.47 cm and was within 2.2% of previously reported in-vitro measurements. Derived recirculation length from PIV agreed within 6.8% and 8.2% of the FE and FV calculations, respectively. For lower shear rate, linear interpolation with five data points results in least error. For higher shear rate either higher order (quadratic) interpolation with five data points or lower order (linear) with lesser (three) data points leads to better results.

CONCLUSION

Accuracy of the recirculation parameters is dependent on number of near wall PIV data points and the type of interpolation algorithm used.

In vitro Implementation of Photopolymerizable Hydrogels as a Potential Treatment of Intracranial Aneurysms

Intracranial aneurysms are increasingly being treated with endovascular therapy, namely coil embolization. Despite being minimally invasive, partial occlusion and recurrence are more frequent compared to open surgical clipping. Therefore, an alternative treatment is needed, ideally combining minimal invasiveness and long-term efficiency. Herein, we propose such an alternative treatment based on an injectable, radiopaque and photopolymerizable polyethylene glycol dimethacrylate hydrogel. The rheological measurements demonstrated a viscosity of 4.86 ± 1.70 mPa.s, which was significantly lower than contrast agent currently used in endovascular treatment (p = 0.42), allowing the hydrogel to be injected through 430 μm inner diameter microcatheters. Photorheology revealed fast hydrogel solidification in 8 min due to the use of a new visible photoinitiator. The addition of an iodinated contrast agent in the precursor contributed to the visibility of the precursor injection under fluoroscopy. Using a customized light-conducting microcatheter and illumination module, the hydrogel was implanted in an in vitro silicone aneurysm model. Specifically, in situ fast and controllable injection and photopolymerization of the developed hydrogel is shown to be feasible in this work. Finally, the precursor and the polymerized hydrogel exhibit no toxicity for the endothelial cells. Photopolymerizable hydrogels are expected to be promising candidates for future intracranial aneurysm treatments.

Ghost Cells for Mechanical Circulatory Support In Vitro Testing: A Novel Large Volume Production

The aim of this work is to establish a large volume batch production system to produce sufficient volumes of ghost cells to facilitate hemolysis testing of mechanical circulatory support devices. A volume of more than 405 mL with a hematocrit of at least 28% is required to perform in vitro hemolysis testing of mechanical circulatory support devices according to international standards. The established ghost cell production method performed at the institute is limited to 3.1 mL of concentrated cells, that is, cells with 100% hematocrit, due to predominantly manual process steps. Through semi-automation of the existing method by using the large volume batch production system, productivity is increased 60-fold to 188 mL while almost doubling process efficiency to 23.5%. Time-consuming manual work such as pipetting is now supported by sensor-based process engineering. With the help of the large volume batch production system, the objective of producing large quantities of ghost cells is successfully achieved. Thus, this work lays the foundation for spatially resolved hemolysis evaluation of mechanical circulatory support devices in combination with the small-scale fluorescent hemolysis detection method.

Does transcatheter aortic valve alignment matter?

Objective

This study investigates the effect of transcatheter aortic valve (TAV) angular alignment on the postprocedure haemodynamics. TAV implantation has emerged as an effective alternative to surgery when treating valve dysfunction. However, the benefit of avoiding surgery is paid back by the inability to remove the native diseased leaflets and accurately position the device in relation to the aortic root, and the literature has shown the root anatomy and substitute position can play an essential role on valve function.

Methods

A commercial TAV was placed in a silicone mock aortic root in vitro, including mock native leaflets, and either aligned commissure-to-commissure or in maximum misalignment. Haemodynamic performance data at various stroke volumes were measured, and Particle Image Velocimetry analysis was performed at a typical stroke volume for rest conditions. The two configurations were also studied without mock native leaflets, for comparison with previous in vitro studies.

Results

Haemodynamic performance data were similar for all configurations. However, imaging analysis indicated that valve misalignment resulted in the central jet flow not extending to the root wall in the native commissures’ vicinity, replaced by a low shear flow, and a reduction of upper sinus flow of 40%, increasing flow stagnation in the sinus.

Conclusions

TAV misalignment did not result in a significant change in valve hydrodynamic performance, but determined some change in the fluid flow patterns, which may promote pathological scenarios, such as increased thrombogenicity of blood flow within the sinuses of Valsalva, and plaque formation around the lumen of the sinotubular junction.

Validation of pressure drop assessment using 4D flow MRI-based turbulence production in various shapes of aortic stenoses

PURPOSE

To validate pressure drop measurements using 4D flow MRI-based turbulence production in various shapes of stenotic stenoses.

METHODS

In vitro flow phantoms with seven different 3D-printed aortic valve geometries were constructed and scanned with 4D flow MRI with six-directional flow encoding (ICOSA6). The pressure drop through the valve was non-invasively predicted based on the simplified Bernoulli, the extended Bernoulli, the turbulence production, and the shear-scaling methods. Linear regression and agreement of the predictions with invasively measured pressure drop were analyzed.

RESULTS

All pressure drop predictions using 4D Flow MRI were linearly correlated to the true pressure drop but resulted in different regression slopes. The regression slope and 95% limits of agreement for the simplified Bernoulli method were 1.35 and 11.99 ± 21.72 mm Hg. The regression slope and 95% limits of agreement for the extended Bernoulli method were 1.02 and 0.74 ± 8.48 mm Hg. The regression slope and 95% limits of agreement for the turbulence production method were 0.89 and 0.96 ± 8.01 mm Hg. The shear-scaling method presented good correlation with an invasively measured pressure drop, but the regression slope varied between 0.36 and 1.00 depending on the shear-scaling coefficient.

CONCLUSION

The pressure drop assessment based on the turbulence production method agrees well with the extended Bernoulli method and invasively measured pressure drop in various shapes of the aortic valve. Turbulence-based pressure drop estimation can, as a complement to the conventional Bernoulli method, play a role in the assessment of valve diseases.

Rapid Deployment Aortic Valves Deliver Superior Hemodynamic Performance In Vitro

OBJECTIVE

Clinical studies have demonstrated excellent hemodynamic performance of rapid deployment aortic valves; however, few studies have directly compared the performance of these valves with conventional bioprosthetic valves. Thus, the hemodynamic function of the EDWARDS INTUITY valve (rapid deployment valve) was compared with the Edwards Magna Ease valve in vitro (Edwards Lifesciences Corp, Irvine, CA USA).

METHODS

Elastomeric material was used to create an aortic root model that included a left ventricular outflow tract and aortic annulus. The model was based on reconstructions from 3-dimensional multislice computed tomography images in patients with aortic stenosis; the aortic root was scaled to a 21-mm effective annulus diameter. EDWARDS INTUITY valves (21-mm diameter) were deployed by stent frame expansion within the aortic root; Edwards Magna Ease valves (21-mm diameter) were sutured to the annulus. The left ventricular outflow tract area index (left ventricular outflow tract area/baseline area) and ellipticity or noncircularity as indexed by Dmax/Dmin were measured under a video microscope after valve placement. Hemodynamic data were collected under pulsatile flow with saline (70 beats per minute, 5 L/min, 100 mm Hg aortic pressure).

RESULTS

Compared with the Edwards Magna Ease valve (n = 4), the EDWARDS INTUITY valve (n = 4) had a greater effective orifice area (1.56 ± 0.01 vs 1.85 ± 0.06 cm, P < 0.001) and a lower transvalvular pressure gradient (23.4 ± 0.51 vs 16.8 ± 1.3 mm Hg, P < 0.001). Multiple regression analysis showed that 93% of the variation in the effective orifice area and transvalvular pressure gradient was due to variation in the left ventricular outflow tract area index and ellipticity index.

CONCLUSIONS

A clinically relevant aortic root model was developed to evaluate aortic valve performance. The superior performance of the EDWARDS INTUITY valve seemed to be related to both a greater inflow area and a more circular left ventricular outflow tract.

The Fluid Dynamical Performance of the Carpentier-Edwards PERIMOUNT Magna Ease Prosthesis

The aim of the present in vitro study was the evaluation of the fluid dynamical performance of the Carpentier-Edwards PERIMOUNT Magna Ease depending on the prosthetic size (21, 23, and 25 mm) and the cardiac output (3.6–6.4 L/min). A self-constructed flow channel in combination with particle image velocimetry (PIV) enabled precise results with high reproducibility, focus on maximal and local peek velocities, strain, and velocity gradients. These flow parameters allow insights into the generation of forces that act on blood cells and the aortic wall. The results showed that the 21 and 23 mm valves have a quite similar performance. Maximal velocities were 3.03 ± 0.1 and 2.87 ± 0.13 m/s; maximal strain E_xx, 913.81 ± 173.25 and 896.15 ± 88.16 1/s; maximal velocity gradient E_yx, 1203.14 ± 221.84 1/s and 1200.81 ± 61.83 1/s. The 25 mm size revealed significantly lower values: maximal velocity, 2.47 ± 0.15 m/s; maximal strain E_xx, 592.98 ± 155.80 1/s; maximal velocity gradient E_yx, 823.71 ± 38.64 1/s. In summary, the 25 mm Magna Ease was able to create a wider, more homogenous flow with lower peak velocities especially for higher flow rates. Despite the wider flow, the velocity values close to the aortic walls did not exceed the level of the smaller valves.

Time Dependent Non-Newtonian Numerical Study of the Flow Field in a Realistic Model of Aortic Arch

A three-dimensional time dependent numerical simulation was performed in a geometric model of aortic arch complete with a realistic aortic root and major branches originating from the arch, for a peak Reynolds number set at 2200 and Womersley number set at 20.4. The computational fluid dynamic analysis was aimed to provide spatial and temporal distribution of the shear stress all along the entire model together with the velocity patterns, related both to the non planar geometry of the aortic system here considered and to the pulsatility imposed on the numerical model to simulate physiologic conditions. A non-Newtonian evolving fluid was considered to account for the actual rheological nature of blood; a comparison on the incidence of wall shear stress, implementing a Newtonian fluid, was also made as reference.

The spatial shear stress pattern, within the cardiac cycle, was shown to have higher values in correspondence to the inner wall of the aortic arch and the sites where the major vessels originated from the arch itself. The velocity patterns, on transversal sections of the aorta, resulted in highly skewed morphology. The resulting complex fluid dynamics, established in the aortic arch and in its branches, can be related to the possible endothelium response to mechanical stimuli, induced by wall shear stress, in the promotion of inflammatory events.

Proposal for a Quantitative Description of Blood Spiral Flow in Medical Devices

The association between specific blood flow patterns and blood behaviour through medical devices suggests that a Lagrangian study may be a useful instrument for the evaluation of the thrombogenic and/or hemolytic potential of certain devices' geometries and biomaterials. In this study a description of blood particle trajectories in terms of their spiral contents is proposed; such a mathematical description for blood spiral flow, computed along several pathlines, is tested for a quantitative determination of the spiralled motion of blood flow into two three-dimensional numerical models, having different design characteristics, of venous cannula inserted in a vessel. As the influence of vortical flow conditions have been observed to have both beneficial and detrimental influence on blood behaviour in terms of blood-device interaction, of the degradation of its components, and of the efficiency of mass-exchange (in red cells oxygenation and plasma filtration, for example), the herein proposed method for the description of spiral laminar motion may be a helpful instrument to build up a tool to investigate, for example, the existence of correlations between level of spiral flow and geometry (as in the present investigated test case), rather than the effects of blood-surface contact. The results obtained in this test case investigation, confirm the effectiveness of the proposed function for a quantitative analysis of spiral flow in medical devices.

Time-Resolved PIV Technique for High Temporal Resolution Measurement of Mechanical Prosthetic Aortic Valve Fluid Dynamics

Prosthetic heart valves (PHVs) have been used to replace diseased native valves for more than five decades. Among these, mechanical PHVs are the most frequently implanted. Unfortunately, these devices still do not achieve ideal behavior and lead to many complications, many of which are related to fluid mechanics. The fluid dynamics of mechanical PHVs are particularly complex and the fine-scale characteristics of such flows call for very accurate experimental techniques. Adequate temporal resolution can be reached by applying time-resolved PIV, a high-resolution dynamic technique which is able to capture detailed chronological changes in the velocity field. The aim of this experimental study is to investigate the evolution of the flow field in a detailed time domain of a commercial bileaflet PHV in a mock-loop mimicking unsteady conditions, by means of time-resolved 2D Particle Image Velocimetry (PIV). The investigated flow field corresponded to the region immediately downstream of the valve plane. Spatial resolution as in “standard” PIV analysis of prosthetic valve fluid dynamics was used. The combination of a Nd:YLF high-repetition-rate double-cavity laser with a high frame rate CMOS camera allowed a detailed, highly temporally resolved acquisition (up to 10000 fps depending on the resolution) of the flow downstream of the PHV. Features that were observed include the non-homogeneity and unsteadiness of the phenomenon and the presence of large-scale vortices within the field, especially in the wake of the valve leaflets. Furthermore, we observed that highly temporally cycle-resolved analysis allowed the different behaviors exhibited by the bileaflet valve at closure to be captured in different acquired cardiac cycles.

By accurately capturing hemodynamically relevant time scales of motion, time-resolved PIV characterization can realistically be expected to help designers in improving PHV performance and in furnishing comprehensive validation with experimental data on fluid dynamics numeric modelling.

Hydrodynamic Assessment of Aortic Valves Prepared from Porcine Small Intestinal Submucosa

Infants and children born with severe cardiac valve lesions have no effective long term treatment options since currently available tissue or mechanical prosthetic valves have sizing limitations and no avenue to accommodate the growth of the pediatric patient. Tissue engineered heart valves (TEHVs) which could provide for growth, self-repair, infection resistance, and long-term replacement could be an ideal solution. Porcine small intestinal submucosa (PSIS) has recently emerged as a potentially attractive bioscaffold for TEHVs. PSIS may possess the ability to recruit endogenous cardiovascular cells, leading to phenotypically-matched replacement tissue when the scaffold has completely degraded. Our group has successfully implanted custom-made PSIS valves in 4 infants with critical valve defects in whom standard bioprosthetic or mechanical valves were not an option. Short term clinical follow-up has been promising. However, no hydrodynamic data has been reported to date on these valves. The purpose of this study was to assess the functional effectiveness of tri-leaflet PSIS bioscaffolds in the aortic position compared to standard tri-leaflet porcine bioprosthetic valves. Hydrodynamic evaluation of acute PSIS function was conducted using a left heart simulator in our laboratory. Our results demonstrated similar flow and pressure profiles (p > 0.05) between the PSIS valves and the control valves. However, forward flow energy losses were found to be significantly greater (p < 0.05) in the PSIS valves compared to the controls possibly as a result of stiffer material properties of PSIS relative to glutaraldehyde-fixed porcine valve tissue. Our findings suggest that optimization of valve dimensions and shape may be important in accelerating de novo valve tissue growth and avoidance of long-term complications associated with higher energy losses (e.g. left ventricular hypertrophy). Furthermore, long term animal and clinical studies will be needed in order to conclusively address somatic growth potential of PSIS valves.

Physiological vortices in the sinuses of Valsalva: An in vitro approach for bio-prosthetic valves

PURPOSE

The physiological flow dynamics within the Valsalva sinuses, in terms of global and local parameters, are still not fully understood. This study attempts to identify the physiological conditions as closely as possible, and to give an explanation of the different and sometime contradictory results in literature.

METHODS

An in vitro approach was implemented for testing porcine bio-prosthetic valves operating within different aortic root configurations. All tests were performed on a pulse duplicator, under physiological pressure and flow conditions. The fluid dynamics established in the various cases were analysed by means of 2D Particle Image Velocimetry, and related with the achieved hydrodynamic performance.

RESULTS

Each configuration is associated with substantially different flow dynamics, which significantly affects the valve performance. The configuration most closely replicating healthy native anatomy was characterised by the best hemodynamic performance, and any mismatch in size and position between the valve and the root produced substantial modification of the fluid dynamics downstream of the valve, hindering the hydrodynamic performance of the system. The worst conditions were observed for a configuration characterised by the total absence of the Valsalva sinuses.

CONCLUSION

This study provides an explanation for the different vortical structures described in the literature downstream of bioprosthetic valves, enlightening the experimental complications in valve testing. Most importantly, the results clearly identify the fluid mechanisms promoted by the Valsalva sinuses to enhance the ejection and closing phases, and this study exposes the importance of an optimal integration of the valve and root, to operate as a single system.

Flow-Induced Damage to Blood Cells in Aortic Valve Stenosis

Valvular hemolysis and thrombosis are common complications associated with stenotic heart valves. This study aims to determine the extent to which hemodynamics induce such traumatic events. The viscous shear stress downstream of a severely calcified bioprosthetic valve was evaluated via in vitro 2D particle image velocimetry measurements. The blood cell membrane response to the measured stresses was then quantified using 3D immersed-boundary computational simulations. The shear stress level at the boundary layer of the jet flow formed downstream of the valve orifice was observed to reach a maximum of 1000-1700 dyn/cm(2), which was beyond the threshold values reported for platelet activation (100-1000 dyn/cm(2)) and within the range of thresholds reported for red blood cell (RBC) damage (1000-2000 dyn/cm(2)). Computational simulations demonstrated that the resultant tensions at the RBC membrane surface were unlikely to cause instant rupture, but likely to lead to membrane plastic failure. The resultant tensions at the platelet surface were also calculated and the potential damage was discussed. It was concluded that although shear-induced thrombotic trauma is very likely in stenotic heart valves, instant hemolysis is unlikely and the shear-induced damage to RBCs is mostly subhemolytic.

Duration of Systole and Diastole for Hydrodynamic Testing of Prosthetic Heart Valves: Comparison Between ISO 5840 Standards and in vivo Studies

Objective

To complement the ISO 5840 standards concerning the duration of left ventricular systole and diastole as a function of changes in heart rates according to in vivo studies from the physiologic literature review.

Methods

The systolic and diastolic durations from three in vivo studies were compared with the durations of systole proposed by the ISO 5840:2010 and ISO 5840-2:2015 for hydrodynamic performance assessment of prosthetic heart valves.

Results

Based on the in vivo studies analyzed, the systolic durations proposed by the ISO 5840 standard seemed consistent for 45 and 120 beats per minute (bpm), and showed diverse results for the 70 bpm condition.

Conclusion

Information on the realistic validation of the operation of left ventricular models for different heart rates were obtained.

Experimental investigations on the fluid-mechanics of an electrospun heart valve by means of particle image velocimetry

End-stage failing heart valves are currently replaced by mechanical or biological prostheses. Both types positively contribute to restore the physiological function of native valves, but a number of drawbacks limits the expected performances. In order to improve the outcome, tissue engineering can offer an alternative approach to design and fabricate innovative heart valves capable to support the requested function and to promote the formation of a novel, viable and correctly operating physiological structure. This potential result is particularly critical if referred to the aortic valve, being the one mainly exposed to structural and functional degeneration. In this regard, the here proposed study presents the fabrication and in vitro characterization of a bioresorbable electrospun heart valve prosthesis using the particle image velocimetry technique either in physiological and pathological fluid dynamic conditions. The scaffold was designed to reproduce the aortic valve geometry, also mimicking the fibrous structure of the natural extracellular matrix. To evaluate its performances for possible implantation, the flow fields downstream the valve were accurately investigated and compared. The experimental results showed a correct functionality of the device, supported by the formation of vortex structures at the edge of the three cusps, with Reynolds stress values below the threshold for the risk of hemolysis (which can be comprised in the range 400-4000N/m(2) depending on the exposure period), and a good structural resistance to the mechanical loads generated by the driving pressure difference.

Effect of Arched Leaflets and Stent Profile on the Hemodynamics of Tri-Leaflet Flexible Polymeric Heart Valves

Polymeric heart valves (PHV) can be engineered to serve as alternatives for existing prosthetic valves due to higher durability and hemodynamics similar to bioprosthetic valves. The purpose of this study is to evaluate the effect of geometry on PHVs coaptation and hemodynamic performance. The two geometric factors considered are stent profile and leaflet arch length, which were varied across six valve configurations. Three models were created with height to diameter ratio of 0.6, 0.7, and 0.88. The other three models were designed by altering arch height to stent diameter ratio, to be 0, 0.081, and 0.116. Particle image velocimetry experiments were conducted on each PHV to characterize velocity, vorticity, turbulent characteristics, effective orifice area, and regurgitant fraction. This study revealed that the presence of arches as well as higher stent profile reduced regurgitant flow down to 5%, while peak systole downstream velocity reduced to 58% and Reynolds Shear Stress values reduced 40%. Further, earlier reattachment of the forward flow jet was observed in PHVs with leaflet arches. These findings indicate that although both geometric factors help diminish the commissural gap during diastole, leaflet arches induce a larger jet opening, yielding to earlier flow reattachment and lower energy dissipation.

In Vitro 2D PIV Measurements and Related Aperture Areas of Tricuspid Bioprosthetic Mitral Valves at the beginning of Diastole

Purpose

Besides ventricular parameters, the design and angular orientation of a prosthetic heart valve induce a specific flow field. The aim of this study was to know the inflow characteristics of a left ventricular model (LVM), investigating the behavior of tricuspid bioprosthetic mitral valves in terms of velocity profiles and related valve aperture areas at the beginning of diastole, under different conditions.

Methods

3 heart rates (HRs) were established in the LVM and each mitral bioprosthesis (27 and 31 mm diameter) was installed in 2 orientations, rotated by 180°. For each experimental setup, 2-dimensional particle image velocimetry (2D PIV) measurements and simultaneous mitral valve (MV) area detection were obtained from 50 samples.

Results

The results from the velocity profiles immediately downstream of mitral bioprostheses showed the influence of valve orientation for moderate HRs, although for a similar magnitude of mean velocity vectors. The geometries of MV open areas for each HR were similar regardless of valve orientation, except for the 27-mm valve at 90 beats per minute (bpm), and for the 31-mm valve at 60 bpm. Moreover, for each HR, similar percentages of valve open area were obtained regardless of MV nominal diameters.

Conclusions

In conclusion, the experimental setup for the 2D PIV measurements synchronized with the MV area detection was a useful tool for knowing the inflow characteristics of the LVM.

Long-Term Durability of Carpentier-Edwards Magna Ease Valve: A One Billion Cycle In Vitro Study

BACKGROUND

Durability and hemodynamic performance are top considerations in selecting a valve for valve replacement surgery. This study was conducted in order to evaluate the long-term mechanical durability and hydrodynamic performance of the Carpentier-Edwards PERIMOUNT Magna Ease Bioprostheses, through 1 billion cycles (equivalent to 25 years).

METHODS

In vitro valve hydrodynamic performance, durability, and quantitative flow visualization were conducted in accordance with ISO 5840:2005 heart valve standard. The study valves were subjected to accelerated valve cycling to an equivalent of 25 years of wear. Hydrodynamic evaluations at intervals of 100 million cycles (2.5 years) were performed on the study valves. New uncycled Magna Ease valves were used as hydrodynamic controls in this study. A quantitative assessment of the fluid motion downstream of the control and study valves was performed using particle image velocimetry. The results between the test and control valves were compared to assess valve performance after an equivalent of 25 years of wear.

RESULTS

All study valves met the ISO 5840 requirements for effective orifice area, 1.81 ± 0.06 cm(2) and 2.06 ± 0.17 cm(2), and regurgitant fraction, 1.11% ± 0.87% and 2.5% ± 2.34%, for the 21 mm and 23 mm study valves, respectively. The flow characterization of the control valves and the billion-cycle valves demonstrated that the valves exhibited similar flow characteristics. The velocity and shear stress fields were similar between the control and study valves.

CONCLUSIONS

The Magna Ease valves demonstrated excellent durability and hydrodynamic performance after an equivalent of 25 years of simulated in vitro wear. All study valves successfully endured 1 billion cycles of simulated wear, 5 times longer than the standard requirement for a tissue valve as stipulated in ISO 5840.

Blood damage through a bileaflet mechanical heart valve: a quantitative computational study using a multiscale suspension flow solver

Bileaflet mechanical heart valves (BMHVs) are among the most popular prostheses to replace defective native valves. However, complex flow phenomena caused by the prosthesis are thought to induce serious thromboembolic complications. This study aims at employing a novel multiscale numerical method that models realistic sized suspended platelets for assessing blood damage potential in flow through BMHVs. A previously validated lattice-Boltzmann method (LBM) is used to simulate pulsatile flow through a 23 mm St. Jude Medical (SJM) Regent™ valve in the aortic position at very high spatiotemporal resolution with the presence of thousands of suspended platelets. Platelet damage is modeled for both the systolic and diastolic phases of the cardiac cycle. No platelets exceed activation thresholds for any of the simulations. Platelet damage is determined to be particularly high for suspended elements trapped in recirculation zones, which suggests a shift of focus in blood damage studies away from instantaneous flow fields and toward high flow mixing regions. In the diastolic phase, leakage flow through the b-datum gap is shown to cause highest damage to platelets. This multiscale numerical method may be used as a generic solver for evaluating blood damage in other cardiovascular flows and devices.

Emerging Trends in Heart Valve Engineering: Part IV. Computational Modeling and Experimental Studies

In this final portion of an extensive review of heart valve engineering, we focus on the computational methods and experimental studies related to heart valves. The discussion begins with a thorough review of computational modeling and the governing equations of fluid and structural interaction. We then move onto multiscale and disease specific modeling. Finally, advanced methods related to in vitro testing of the heart valves are reviewed. This section of the review series is intended to illustrate application of computational methods and experimental studies and their interrelation for studying heart valves.

The Influence of the Aortic Root Geometry on Flow Characteristics of a Prosthetic Heart Valve

In this paper, performance of aortic heart valve prosthesis in different geometries of the aortic root is investigated experimentally. The objective of this investigation is to establish a set of parameters, which are associated with abnormal flow patterns due to the flow through a prosthetic heart valve implanted in the patients that had certain types of valve diseases prior to the valve replacement. Specific valve diseases were classified into two clinical categories and were correlated with the corresponding changes in aortic root geometry while keeping the aortic base diameter fixed. These categories correspond to aortic valve stenosis and aortic valve insufficiency. The control case that corresponds to the aortic root of a patient without valve disease was used as a reference. Experiments were performed at test conditions corresponding to 70 beats/min, 5.5 L/min target cardiac output, and a mean aortic pressure of 100 mmHg. By varying the aortic root geometry, while keeping the diameter of the orifice constant, it was possible to investigate corresponding changes in the levels of Reynolds shear stress and establish the possibility of platelet activation and, as a result of that, the formation of blood clots.

Shear-Induced Hemolysis: Species Differences

The nonphysiological mechanical shear stress in blood-contacting medical devices is one major factor to device-induced blood damage. Animal blood is often used to test device-induced blood damage potential of these devices due to its easy accessibility and low cost. However, the differences in shear-induced blood damage between animals and human have not been well characterized. The purpose of this study was to investigate shear-induced hemolysis of human and three commonly used preclinical evaluation animal species (ovine, porcine, and bovine) under shear conditions encountered in blood-contacting medical devices. Shear-induced hemolysis experiments were conducted using two single-pass blood-shearing devices. Driven by an externally pressurized reservoir, blood single-passes through a small annular gap in the shearing devices where the blood was exposed to a uniform high shear stress. Shear-induced hemolysis at different conditions of exposure time (0.04 to 1.5 s) and shear stress (25 to 320 Pa) was quantified for ovine, porcine, bovine, and human blood, respectively. Within these ranges of shear stress and exposure time, shear-induced hemolysis was less than 2% for the four species. The results showed that the ovine blood was more susceptible to shear-induced injury than the bovine, porcine, and human blood. The response of the porcine and bovine blood to shear was similar to the human blood. The dependence of hemolysis on shear stress level and exposure time was found to fit well the power law functional form for the four species. The coefficients of the power law models for the ovine, porcine, bovine, and human blood were derived.

Steady flow hemodynamic and energy loss measurements in normal and simulated calcified tricuspid and bicuspid aortic valves

The bicuspid aortic valve (BAV), which forms with two leaflets instead of three as in the normal tricuspid aortic valve (TAV), is associated with a spectrum of secondary valvulopathies and aortopathies potentially triggered by hemodynamic abnormalities. While studies have demonstrated an intrinsic degree of stenosis and the existence of a skewed orifice jet in the BAV, the impact of those abnormalities on BAV hemodynamic performance and energy loss has not been examined. This steady-flow study presents the comparative in vitro assessment of the flow field and energy loss in a TAV and type-I BAV under normal and simulated calcified states. Particle-image velocimetry (PIV) measurements were performed to quantify velocity, vorticity, viscous, and Reynolds shear stress fields in normal and simulated calcified porcine TAV and BAV models at six flow rates spanning the systolic phase. The BAV model was created by suturing the two coronary leaflets of a porcine TAV. Calcification was simulated via deposition of glue beads in the base of the leaflets. Valvular performance was characterized in terms of geometric orifice area (GOA), pressure drop, effective orifice area (EOA), energy loss (EL), and energy loss index (ELI). The BAV generated an elliptical orifice and a jet skewed toward the noncoronary leaflet. In contrast, the TAV featured a circular orifice and a jet aligned along the valve long axis. While the BAV exhibited an intrinsic degree of stenosis (18% increase in maximum jet velocity and 7% decrease in EOA relative to the TAV at the maximum flow rate), it generated only a 3% increase in EL and its average ELI (2.10 cm2/m2) remained above the clinical threshold characterizing severe aortic stenosis. The presence of simulated calcific lesions normalized the alignment of the BAV jet and resulted in the loss of jet axisymmetry in the TAV. It also amplified the degree of stenosis in the TAV and BAV, as indicated by the 342% and 404% increase in EL, 70% and 51% reduction in ELI and 48% and 51% decrease in EOA, respectively, relative to the nontreated valve models at the maximum flow rate. This study indicates the ability of the BAV to function as a TAV despite its intrinsic degree of stenosis and suggests the weak dependence of pressure drop on orifice area in calcified valves.

Comparison of hinge microflow fields of bileaflet mechanical heart valves implanted in different sinus shape and downstream geometry

The characterization of the bileaflet mechanical heart valves (BMHVs) hinge microflow fields is a crucial step in heart valve engineering. Earlier in vitro studies of BMHV hinge flow at the aorta position in idealized straight pipes have shown that the aortic sinus shapes and sizes may have a direct impact on hinge microflow fields. In this paper, we used a numerical study to look at how different aortic sinus shapes, the downstream aortic arch geometry, and the location of the hinge recess can influence the flow fields in the hinge regions. Two geometric models for sinus were investigated: a simplified axisymmetric sinus and an idealized three-sinus aortic root model, with two different downstream geometries: a straight pipe and a simplified curved aortic arch. The flow fields of a 29-mm St Jude Medical BMHV with its four hinges were investigated. The simulations were performed throughout the entire cardiac cycle. At peak systole, recirculating flows were observed in curved downsteam aortic arch unlike in straight downstream pipe. Highly complex three-dimensional leakage flow through the hinge gap was observed in the simulation results during early diastole with the highest velocity at 4.7 m/s, whose intensity decreased toward late diastole. Also, elevated wall shear stresses were observed in the ventricular regions of the hinge recess with the highest recorded at 1.65 kPa. Different flow patterns were observed between the hinge regions in straight pipe and curved aortic arch models. We compared the four hinge regions at peak systole in an aortic arch downstream model and found that each individual hinge did not vary much in terms of the leakage flow rate through the valves.

An in vitro evaluation of the impact of eccentric deployment on transcatheter aortic valve hemodynamics

Patients with aortic stenosis present with calcium deposits on the native aortic valve, which can result in non-concentric expansion of Transcatheter Aortic Valve Replacement (TAVR) stents. The objective of this study is to evaluate whether eccentric deployment of TAVRs lead to turbulent blood flow and blood cell damage. Particle Image Velocimetry was used to quantitatively characterize fluid velocity fields, shear stress and turbulent kinetic energy downstream of TAVRs deployed in circular and eccentric orifices representative of deployed TAVRs in vivo. Effective orifice area (EOA) and mean transvalvular pressure gradient (TVG) values did not differ substantially in circular and eccentric deployed valves, with only a minor decrease in EOA observed in the eccentric valve (2.0 cm(2) for circular, 1.9 cm(2) for eccentric). Eccentric deployed TAVR lead to asymmetric systolic jet formation, with increased shear stresses (circular = 97 N/m(2) vs. eccentric = 119 N/m(2)) and regions of turbulence intensity (circular = 180 N/m(2) vs. eccentric = 230 N/m(2)) downstream that was not present in the circular deployed TAVR. The results of this study indicate that eccentric deployment of TAVRs can lead to altered flow characteristics and may potentially increase the hemolytic potential of the valve, which were not captured through hemodynamic evaluation alone.

Numerical estimation of hemolysis from the point of view of signal and system

The power-law based models for predicting shear-induced hemolysis are widely used in the optimization design of blood-contacting devices. However, this category of models has fallen short of accuracy when compared with the results of the in vitro experiments. The aim of this study is to develop an alternative model from the point of view of signal and system. Under the action of constant shear stress, the released hemoglobin was regarded as the output of system, and the system function that characterized the resistance to hemolysis was derived from the power-law equation. Two state variables were introduced to adequately capture the history of the system. The proposed model takes into account another known empirical formula, the threshold equation, by setting a nonzero initial condition of the blood. By comparing the estimated results with the published experimental data, it showed that the accuracy of the proposed model was notably improved. Furthermore, the analysis in frequency domain indicated that the damage contribution of the time-varying shear stress decreased with the increase of frequency. As the frequency domain analysis is important in many fields, it may play a role in the estimation of hemolysis in the future.

Innovative technologies for the assessment of cardiovascular medical devices: state-of-the-art techniques for artificial heart valve testing

Prosthetic heart valves (PHVs) are engineered devices used for replacing diseased natural cardiac valves. This article presents several investigational techniques for the evaluation of the performance of these clinical devices, whose implantation is not completely free of drawbacks. The state-of-the-art in the technological approach for PHV testing is addressed. As the fluid dynamics of PHVs are particularly complex, the main focus will be on experimental velocimetric techniques and computational analysis. A methodology for the analysis of the valve's signature, in terms of its characteristic sound in the opening and closing phases, is also presented. The aforementioned techniques are necessary to guarantee an operational life of the implanted device as free as possible from clinical complications. It can be realistically expected that this characterization will help designers in improving PHV performance.

Purely phase-encoded MRI of turbulent flow through a dysfunctional bileaflet mechanical heart valve

OBJECT

We have used a purely phase-encoded magnetic resonance imaging (MRI) technique, single-point ramped imaging with T1 enhancement (SPRITE), to investigate the steady, turbulent flow dynamics through a bileaflet mechanical heart valve (BMHV).

MATERIALS AND METHODS

We have measured in vitro the turbulent diffusivity and velocity downstream of the valve in two configurations (fully opened and partially opened), which mimic normal and dysfunctional operation. Our constant-time implementation of the MRI measurement is unusually robust to fast turbulent flows, and to artefacts caused by the pyrolytic carbon construction of the valve.

RESULTS

Turbulent diffusivity downstream of the normally functioning valve peaks at 1.05 × 10(-6)m(2)/s, while the turbulent diffusivity is higher downstream of the dysfunctional valve (peaking at 3.15 × 10(-6) m(2)/s) and is accompanied by a high-velocity fluid jet and re-circulating flow. The fluid jet is not along the centreline of the valve, as might be anticipated in conventional Doppler echocardiography measurements.

CONCLUSION

The nature of motion-sensitized SPRITE makes it unusually capable in turbulent flows and near to boundaries between different magnetic susceptibilities. These qualities have allowed us to compare the three-dimensional flow fields through normal and dysfunctional BMHVs.

Moving domain computational fluid dynamics to interface with an embryonic model of cardiac morphogenesis

Peristaltic contraction of the embryonic heart tube produces time- and spatial-varying wall shear stress (WSS) and pressure gradients (∇P) across the atrioventricular (AV) canal. Zebrafish (Danio rerio) are a genetically tractable system to investigate cardiac morphogenesis. The use of Tg(fli1a:EGFP) (y1) transgenic embryos allowed for delineation and two-dimensional reconstruction of the endocardium. This time-varying wall motion was then prescribed in a two-dimensional moving domain computational fluid dynamics (CFD) model, providing new insights into spatial and temporal variations in WSS and ∇P during cardiac development. The CFD simulations were validated with particle image velocimetry (PIV) across the atrioventricular (AV) canal, revealing an increase in both velocities and heart rates, but a decrease in the duration of atrial systole from early to later stages. At 20-30 hours post fertilization (hpf), simulation results revealed bidirectional WSS across the AV canal in the heart tube in response to peristaltic motion of the wall. At 40-50 hpf, the tube structure undergoes cardiac looping, accompanied by a nearly 3-fold increase in WSS magnitude. At 110-120 hpf, distinct AV valve, atrium, ventricle, and bulbus arteriosus form, accompanied by incremental increases in both WSS magnitude and ∇P, but a decrease in bi-directional flow. Laminar flow develops across the AV canal at 20-30 hpf, and persists at 110-120 hpf. Reynolds numbers at the AV canal increase from 0.07±0.03 at 20-30 hpf to 0.23±0.07 at 110-120 hpf (p< 0.05, n=6), whereas Womersley numbers remain relatively unchanged from 0.11 to 0.13. Our moving domain simulations highlights hemodynamic changes in relation to cardiac morphogenesis; thereby, providing a 2-D quantitative approach to complement imaging analysis.

In vitro and in vivo investigations on the effects of low-density lipoprotein concentration polarization and haemodynamics on atherosclerotic localization in rabbit and zebrafish

Atherosclerosis (AS) commonly occurs in the regions of the arterial tree with haemodynamic peculiarities, including local flow field disturbances, and formation of swirling flow and vortices. The aim of our study was to confirm low-density lipoprotein (LDL) concentration polarization in the vascular system in vitro and in vivo, and investigate the effects of LDL concentration polarization and flow field alterations on atherosclerotic localization. Red fluorescent LDL was injected into optically transparent Flk1: GFP zebrafish embryos, and the LDL distribution in the vascular lumen was investigated in vivo using laser scanning confocal microscopy. LDL concentration at the vascular luminal surface was found to be higher than that in the bulk. The flow field conditions in blood vessel segments were simulated and measured, and obvious flow field disturbances were found in the regions of vascular geometry change. The LDL concentration at the luminal surface of bifurcation was significantly higher than that in the straight segment, possibly owing to the atherogenic effect of disturbed flow. Additionally, a stenosis model of rabbit carotid arteries was generated. Atherosclerotic plaques were found to have occurred in the stenosis group and were more severe in the stenosis group on a high-fat diet. Our findings provide the first ever definite proof that LDL concentration polarization occurs in the vascular system in vivo. Both lipoprotein concentration polarization and flow field changes are involved in the infiltration/accumulation of atherogenic lipids within the location of arterial luminal surface and promote the development of AS.

The quantification of hemodynamic parameters downstream of a Gianturco Zenith stent wire using newtonian and non-newtonian analog fluids in a pulsatile flow environment

Although deployed in the vasculature to expand vessel diameter and improve blood flow, protruding stent struts can create complex flow environments associated with flow separation and oscillating shear gradients. Given the association between magnitude and direction of wall shear stress (WSS) and endothelial phenotype expression, accurate representation of stent-induced flow patterns is critical if we are to predict sites susceptible to intimal hyperplasia. Despite the number of stents approved for clinical use, quantification on the alteration of hemodynamic flow parameters associated with the Gianturco Z-stent is limited in the literature. In using experimental and computational models to quantify strut-induced flow, the majority of past work has assumed blood or representative analogs to behave as Newtonian fluids. However, recent studies have challenged the validity of this assumption. We present here the experimental quantification of flow through a Gianturco Z-stent wire in representative Newtonian and non-Newtonian blood analog environments using particle image velocimetry (PIV). Fluid analogs were circulated through a closed flow loop at physiologically appropriate flow rates whereupon PIV snapshots were acquired downstream of the wire housed in an acrylic tube with a diameter characteristic of the carotid artery. Hemodynamic parameters including WSS, oscillatory shear index (OSI), and Reynolds shear stresses (RSS) were measured. Our findings show that the introduction of the stent wire altered downstream hemodynamic parameters through a reduction in WSS and increases in OSI and RSS from nonstented flow. The Newtonian analog solution of glycerol and water underestimated WSS while increasing the spatial coverage of flow reversal and oscillatory shear compared to a non-Newtonian fluid of glycerol, water, and xanthan gum. Peak RSS were increased with the Newtonian fluid, although peak values were similar upon a doubling of flow rate. The introduction of the stent wire promoted the development of flow patterns that are susceptible to intimal hyperplasia using both Newtonian and non-Newtonian analogs, although the magnitude of sites affected downstream was appreciably related to the rheological behavior of the analog. While the assumption of linear viscous behavior is often appropriate in quantifying flow in the largest arteries of the vasculature, the results presented here suggest this assumption overestimates sites susceptible to hyperplasia and restenosis in flow characterized by low and oscillatory shear.

Evaluation of Eulerian and Lagrangian models for hemolysis estimation

Hemolysis caused by flow-induced mechanical damage to red blood cells is still a problem in medical devices such as ventricular assist devices (VADs), artificial lungs, and mechanical heart valves. A number of different models have been proposed by different research groups for calculating the hemolysis, and of these, the power law-based models (HI(%)=Ct(α)τ(β)) have proved the most popular because of their ease of use and applicability to a wide range of devices. However, within this power law category of models there are a number of different implementations. The aim of this work was to evaluate different power law-based models by calculating hemolysis in a specifically designed shearing device and a clinical VAD, and comparing the estimated results with experimental measurements of the hemolysis in these two devices. Both the Eulerian scalar transport and all the Lagrangian models had fairly large percentage of errors compared with the experiments (minimum Eulerian 91% and minimum Lagrangian 57%) showing they could not accurately predict the magnitude of the hemolysis. However, the Eulerian approach had large correlation coefficients (>0.99) showing that this method can predict relative hemolysis, which would be useful in comparative analysis, for example, for ranking different devices or for design optimization studies.

Design, construction, and evaluation of a dynamic MR compatible cardiac left ventricle model

PURPOSE

Development of magnetic resonance (MR) sequences is important to answer clinical questions and to overcome current limitations. To meet the challenges of cardiac MR, dynamic and reproducible testing conditions are required. We aimed at developing a dynamic MR-compatible cardiac left ventricle model that imitates myocardial tissue properties and simulates dynamic motion.

METHODS

A dynamic left ventricle silicone model was designed to match myocardial T(1) and T(2) relaxation times. Silicone mixtures were explored to replicate T(2) values of myocardial edema. A controllable piston pump was constructed to produce pulsatile flow paradigms. They were validated against flow sensors and MR data, including SSFP-based and phase-contrast-based sequences. A dedicated software interface was developed for the control.

RESULTS

Model dimensions represented cardiac left ventricle dimensions of healthy men. The range of end diastolic volumes was 85-175 ml, depending on the driven stroke volume. Stroke volume quantification for flow paradigms of 30∕60∕90∕120 ml resulted in 29.2∕57.6∕88.8∕118.4 ml by MR volumetry, 29.6∕59.9∕89.4∕119.0 ml by phase contrast measurements, and 29.9∕60.4∕91.1∕120.9 ml by flow meter revealing consistency. The system accurately replicated physiological and pathophysiological flow paradigms. The silicon model exhibited T(1) of 1002 ± 8 ms, T(2) of 58 ± 1 ms. Signal intensities (a.u.) of the ventricle model were 128 ± 23 for FGRE (vs 138 ± 17 in vivo) and 1156 ± 37 for b-SSFP (vs 991 ± 96 in vivo). T(2) of 75 ± 2 ms was achieved for the myocardial pathology.

CONCLUSIONS

We developed a controllable left ventricle model resembling MR signal characteristics of human myocardium, including pathological conditions, and allowing for the replication of contraction and flow paradigms.