Design, analysis and construction of a simple pulse duplicator system

One of the most important human diseases that need to be considered in terms of development of the medical engineering devices is cardiovascular disease which is a significant cause of death globally recently. Valvular heart disease is normally treated by restoring or altering heart valves with an artificial one. But the new prosthetic valve designs necessitate testing for durability estimate and failure method. It is significant to simulate the circulation system by the building of a pulse duplicator system. This study is stated by clarifying the parameter and implementation steps of the pulse duplicator system in which the different researchers have utilized the system and tried to explain the design steps of using this system without going into the system design by steps or what are the main part of this system and how can be implemented, tested, and developed individually. In this design, a DC motor produces, through a hydraulic piston, a flow pulse to the left ventricle chamber model, which is linked with two interchangeable prosthetic heart valves. The computer is used to control and process data from volumetric flow rate and image. The findings show that the linear displacement, the velocity of the piston and the linear acceleration regularly become significant particularly and follows a sinusoidal wave shape during one cycle, when (crank length/connecting rod length) value is equal 0.2 or less. Several sets of measured flow rate readings were obtained by using flow meter sensor YF-S201, results after calibration showed the error rate falls within permissible limit

Comparison of heart valve flow dynamics assessment between echocardiography and pulse duplication

Published ThesisHeart valve surgery and valvular heart disease still pose a significant threat to patients worldwide. The aortic valve doesn't remain healthy and has largely been the focus of innovation and the development of replacement heart valves. Improving the ability of blood to flow througha prosthetic valve while minimizing the load on the heart is regarded as one of the performance objectives of prosthetic heart valves. In order to meet valvular performance objectives and to assess whether potential prosthetic heart valves meets hydrodynamic performance, testing simulated under in vivo flow conditions is necessary. Pulse duplication is widely accepted as a valid method to determine the performance of heart valves during their development. Few specialised centres exist to perform pulse duplication tests accurately and in accordance to the required ISO and FDA standards for cardiovascular implants. Real-time patient data of prosthetic heart valves is however not obtained with pulse duplication but with echocardiography. Modern day pulse duplicators come equipped with viewing chambers that can allow for echocardiographic measurements. Therefore, the aim of this study was to perform pulse duplication and echocardiography simultaneously on five different prosthetic heart valves using a commercial ViVitro pulse duplicator system. METHODS A hydrodynamic evaluation was performed on five prosthetic heart valves (i) Medtronic-Hall mechanical valve (tilting disc), (ii) Carbomedics mechanical valve (bileaflet), (iii) Glycar mechanical valve (Glycar), (iv) Edwards Perimount (tissue valve), (v) ViVitro reference (ViVitro) using pulse duplication and echocardiography. All the valves were inserted in the aortic position of the pulse duplicator and echocardiographic measurements was performed simultaneously. Each of the valves were tested at 5 different testing conditions by varying the stroke volume and beats per minute. The study concludes with a comparison between the pulse duplicator data and the echocardiography data acquired. RESULTS Pulse duplication: -The Glycar valve had the largest pressure drop across the valve at the lowest CO (3.6 L/min) of 17.15 mmHg, although it increased steadily at a slower rate than the other four valves. The Glycar and tissue valve had the highest EOA of 1.885 cm2 and 1.884 cm2 respectively at a peak CO of 9.6 L/min. The bi-leaflet valve had the highest EOA of 2.002 cm2 (CO 3.6 L/min), however the EOA deteriorated as the CO increased resulting in an EOA of 1.572 cm2 at a CO of 9.6L/min. The tissue valve had the largest RF for all testing conditions, ranging from 16.3% (CO 8.0 L/min) to 25.6% (4.9 L/min) where the bi-leaflet valve had the lowest (0.72% - 3.42%). Echocardiography: -The Glycar valve had the lowest overall pressure drop for all CO. The pulse duplicator pressure drop results were more consistent than three echocardiography results measured on the pulse duplicator. The bileaflet and Glycar valves EOA showed better consistency across the CO range than the ViVitro, tissue and tilting disk valves. The data showed that no definite correlation between all the valves exists between echocardiography and pulse duplication for EOA. However, a correlation for pressure drop between the pulse duplicator and echocardiographic data was demonstrated for both the tissue and bi-leaflet valve

A Newly Developed Tri-Leaflet Polymeric Heart Valve Prosthesis.

The potential of polymeric heart valves (PHV) prostheses is to combine the hemodynamic performances of biological valves with the durability of mechanical valves. The aim of this work is to design and develop a new tri-leaflet prosthetic heart valve (HV) made from styrenic block copolymers. A computational finite element model was implemented to optimize the thickness of the leaflets, to improve PHV mechanical and hydrodynamic performances. Based on the model outcomes, 8 prototypes of the designed valve were produced and tested in vitro under continuous and pulsatile flow conditions, as prescribed by ISO 5840 Standard. A specially designed pulse duplicator allowed testing the PHVs at different flow rates and frequency conditions. All the PHVs met the requirements specified in ISO 5840 Standard in terms of both regurgitation and effective orifice area (EOA), demonstrating their potential as HV prostheses.This work was funded by the British Heart Foundation (New Horizons NH/11/4/29059).This is the final published version. It first appeared at http://www.worldscientific.com/doi/abs/10.1142/S0219519415400096?src=recsys

Degradation of engineered polyurethane heart valves in a mechanically demanding environment with variable mixing of polyester and polycarbonate soft segments

Valvular heart disease (VHD) is a major source of morbidity and mortality leading to approximately 290,000 valve replacement surgeries worldwide each year. Current replacement prosthetics include mechanical and bioprosthetic heart valves, which are burdened by chronic anticoagulation therapy and tissue degeneration, respectively, as well as an inability to grow and remodel. Tissue engineered heart valves (TEHVs) have been proposed to overcome these limitations by providing a scaffold that is designed to be gradually replaced by autologous functional tissue. As such, TEHVs should degrade at a rate matching new tissue formation to achieve proper function and avoid structural failure. Biodegradable polyurethane elastomers are suitable candidates for TEHVs and offer tunable degradability based on soft segment chemistry. Polyester soft segments in poly(ester urethane)urea (PEUU) generate faster degradation than polycarbonate soft segments in poly(carbonate urethane)urea (PCUU). These biodegradable polyurethanes can be electrospun into fully assembled, fibrous TEHVs. The objectives of this study were to evaluate the in vitro degradation profile of three polyurethane soft segment mixing strategies and the effects of a mechanically demanding environment on the degradation rate. Equal ratios of faster-degrading polyester and slower-degrading polycarbonate segments were mixed into polyurethanes using three strategies: 1) soft segment mixing during synthesis to form poly(ester carbonate urethane)urea, 2) physical blending of PEUU and PCUU polymers during solvation to form a single solution, and 3) electrospinning from two independent streams of PEUU and PCUU solutions. These mixing strategies varied the chemical composition of the polymer chains and electrospun fibers between groups. Electrospun TEHVs from each mixing strategy were subjected to accelerated degradation in a pulse duplicator with enzymatic solution for two weeks. Relative degradation rates were quantified based on scaffold mass and thickness loss, macro- and microscopic structural changes, and viscosity reduction. Additionally, biaxial mechanical compliance was monitored throughout degradation and initial scaffold blood compatibility was assessed. Soft segment mixed TEHVs had the most degradation while co-spun TEHVs degraded very little. Additionally, mechanical strength was maintained for each mixing strategy throughout degradation. Findings of this study are instrumental in efficiently designing TEHVs where tunable degradation is critical to match the in vivo tissue formation rate

Development of a Tubular Biological Tissue-Engineered Heart Valve with Growth Potential

University of Minnesota Ph.D. dissertation. May 2016. Major: Biomedical Engineering. Advisor: Robert Tranquillo. 1 computer file (PDF); xi, 158 pages.This thesis investigates tissue-engineered cardiovascular devices for pediatric patients and their function and growth potential in preclinical testing. Specifically, engineered tissue tubes were fabricated by entrapping dermal fibroblasts in a fibrin gel and allowing them to replace it with circumferentially-aligned extracellular matrix. Following in vitro culture, the engineered tubes possessed physiological strength and were decellularized to increase their shelf-life and reduce their immunogenicity. An allogeneic tubular heart valve was fabricated by inserting one engineered tube inside of another and attaching them together using degradable sutures. Extensive hemodynamic testing was performed in order to optimize and verify valve design. The growth potential and in vivo function of a single engineered tube (as a pulmonary artery replacement) and pulmonary heart valve were evaluated in a growing lamb model. We observed extensive host cell invasion and growth of the valve root/single tube, but to a lesser degree in the leaflets, which resulted in diminished valve function. A modified animal model is proposed and proof-of-concept studies were performed in order to address this shortcoming

The development of a transcatheter mitral valve

Transcatheter heart valve replacements avoid the main risks associated with conventional open heart surgery and so is the preferred replacement technique for high-risk patients with aortic stenosis. Due to technical challenges, adaptation for the mitral position is still in early stages of research. The aim of this project was to develop the novel UCL transcatheter mitral valve (TMV) based on a prior conceptual design. The UCL TMV is designed to treat mitral regurgitation (MR) and is based on the UCL transcatheter aortic valve (TAV) which is retrievable, repositionable and has enhanced anchoring and sealing. The UCL TMV leaflets, which ensure unidirectional blood flow, are novel because they mimic native mitral valve morphology by having two leaflets, being D-shaped and conical. Their optimal design criterion and two key design parameters were identified using a failure mode and effects analysis and numerical simulations were used to select a design with acceptable stress levels and maximum coaptation area. The optimal leaflets were prototyped as a surgical valve to evaluate their performance against available commercial device designs and were then incorporated in TMV prototypes, and assessed for hydrodynamic performance, both of which exceeded international standard requirements. Durability assessment of the TMV is ongoing and very encouraging; currently withstanding > 80 million cardiac cycles. In conclusion, the results presented and ongoing durability assessments for the UCL TMV indicate it could be a new and effective treatment option for severe MR in high-risk patients whom are declined surgical interventions

Fabrication and In Vitro Characterization of a Tissue Engineered PCL-PLLA Heart Valve.

Heart valve diseases are among the leading causes of cardiac failure around the globe. Nearly 90,000 heart valve replacements occur in the USA annually. Currently, available options for heart valve replacement include bioprosthetic and mechanical valves, both of which have severe limitations. Bioprosthetic valves can last for only 10-20 years while patients with mechanical valves always require blood-thinning medications throughout the remainder of the patient's life. Tissue engineering has emerged as a promising solution for the development of a viable, biocompatible and durable heart valve; however, a human implantable tissue engineered heart valve is yet to be achieved. In this study, a tri-leaflet heart valve structure is developed using electrospun polycaprolactone (PCL) and poly L-lactic acid (PLLA) scaffolds, and a set of in vitro testing protocol has been developed for routine manufacturing of tissue engineered heart valves. Stress-strain curves were obtained for mechanical characterization of different valves. The performances of the developed valves were hemodynamically tested using a pulse duplicator, and an echocardiography machine. Results confirmed the superiority of the PCL-PLLA heart valve compared to pure PCL or pure PLLA. The developed in vitro test protocol involving pulse duplicator and echocardiography tests have enormous potential for routine application in tissue engineering of heart valves

Possible Early Generation of Physiological Helical Flow Could Benefit the Triflo Trileaflet Heart Valve Prosthesis Compared to Bileaflet Valves

Background—Physiological helical flow in the ascending aorta has been well documented in the last two decades, accompanied by discussions on possible physiological benefits of such axial swirl. Recent 4D-MRI studies on healthy volunteers have found indications of early generation of helical flow, early in the systole and close to the valve plane. Objectives—Firstly, the aim of the study is to investigate the hypothesis of premature swirl existence in the ventricular outflow tract leading to helical flow in the valve plane, and second to investigate the possible impact of two different mechanical valve designs on the preservation of this early helical flow and its subsequent hemodynamic consequences. Methods—We use a pulse duplicator with an aortic arch and High-Speed Particle Image Velocimetry to document the flow evolution in the systolic cycle. The pulse-duplicator is modified with a swirl-generating insert to generate early helical flow in the valve plane. Special focus is paid to the interaction of such helical flow with different designs of mechanical prosthetic heart valves, comparing a classical bileaflet mechanical heart valve, the St. Jude Medical Regent valve (SJM Regent BMHV), with the Triflo trileaflet mechanical heart valve T2B version (Triflo TMHV). Results—When the swirl-generator is inserted, a vortex is generated in the core flow, demonstrating early helical flow in the valve plane, similar to the observations reported in the recent 4D-MRI study taken for comparison. For the Triflo trileaflet valve, the early helical flow is not obstructed in the central orifice, similar as in the case of the natural valve. Conservation of angular momentum leads to radial expansion of the core flow and flattening of the axial flow profile downstream in the arch. Furthermore, the early helical flow helps to overcome separation at the outer and inner curvature. In contrast, the two parallel leaflets for the bileaflet valve impose a flow straightener effect, annihilating the angular momentum, which has a negative impact on kinetic energy of the flow. Conclusion—The results imply better hemodynamics for the Triflo trileaflet valve based on hydrodynamic arguments under the discussed hypothesis. In addition, it makes the Triflo valve a better candidate for valve replacements in patients with a pathological generation of nonaxial velocity in the ventricle outflow tract