Mechanism for cavitation phenomenon in mechanical heart valves

Recently, cavitation on the surface of mechanical heart valve has been studied as a cause of fractures occurring in implanted Mechanical Heart Valves (MHVs). It has been conceived that the MHVs mounted in an artificial heart close much faster than in vivo sue, resulting in cavitation bubbles formation. In this study, six different kinds of monoleaflet and bileaflet valves were mounted in the mitral position in an Electro-Hydraulic Total Artificial Heart (EHTAH), and we investigated the mechanisms for MHV cavitation. The valve closing velocity and a high speed video camera were employed to investigate the mechanism for MHV cavitation. The closing velocity of the bileaflet valves was slower than that of the monoleaflet valves. Cavitation bubbles were concentrated on the edge of the valve stop and along the leaflet tip. It was established that squeeze flow holds the key to MHV cavitation in our study. Cavitation intensity increased with an increase in the valve closing velocity and the valve stop area. With regard to squeeze flow, the bileaflet valve with slow valve-closing velocity and small valve stop areas is better able to prevent blood cell damage than the monoleaflet valves.     

A new method for quantitative evaluation of perceived sounds from mechanical heart valve prostheses

Closing clicks from mechanical heart valve prostheses are transmitted to the patient's inner ear mainly in two different ways: as acoustically transmitted sound waves, and as vibrations transmitted through bones and vessels. The purpose of this study was to develop a method for quantifying what patients perceive as sound from their mechanical heart valve prostheses via these two routes. In this study, 34 patients with implanted mechanical bileaflet aortic and mitral valves (St Jude Medical and On-X) were included. Measurements were performed in a specially designed sound insulated chamber equipped with microphones, accelerometers, preamplifiers and a loudspeaker. The closing sounds measured with an accelerometer on the patient's chest were delayed 400 ms, amplified and played back to the patient through the loudspeaker. The patient adjusted the feedback sound to the same level as the 'real-time' clicks he or she perceived directly from his or her valve. In this way the feedback sound energy includes both the air- and the bone-transmitted energies. Sound pressure levels (SPLs) were quantified both in dB(A) and in the loudness unit sone according to ISO 532B (the Zwicker method). The mean air-transmitted SPL measured close to the patient's ear was 23 +/- 4 dB(A). The mean air- and bone-transmitted sounds and vibrations were perceived by the patients as an SPL of 34 +/- 5 dB(A). There was no statistically significant difference in the perceived sound from the two investigated bileaflet valves, and no difference between aortic and mitral valves. The study showed that the presented feedback method is capable of quantifying the perceived sounds and vibrations from mechanical heart valves, if the patient's hearing is not too impaired. Patients with implanted mechanical heart valve prostheses seem to perceive the sound from their valve two to three times higher than nearby persons, because of the additional bone-transmitted vibrations.     

Numerical analysis for the structural strength comparison of St. Jude Medical and Edwards MIRA bileaflet mechanical heart valve prostheses

This paper presents a numerical analysis for the structural strength comparison of the St. Jude Medical bileaflet mechanical heart valve prosthesis with flat leaflet and the Edwards MIRA bileaflet mechanical heart valve prosthesis with curved leaflet. Computer aided engineering systems are used in the analysis. The blood fluid pressure is applied to both flat and curved leaflets of the bileaflet mechanical heart valve prostheses for the rigid body dynamic analysis to confirm the almost same dynamic characteristics of both flat and curved leaflet motions. Thereafter, using the same blood fluid pressure and dynamic characteristics of leaflet motions, structural mechanic analyses for both flat and curved leaflets of the mechanical heart valve prostheses are carried out to show quite different stress and deformation results, respectively. Conclusively, from the viewpoint of stress, it is revealed that the St. Jude Medical bileaflet mechanical heart valve prosthesis is structurally stronger and better than the Edwards MIRA bileaflet mechanical heart valve prosthesis. Computer aided engineering systems used in this comparative structural analysis are ADAMS for the rigid body dynamic analysis, and NISA for the structural mechanic analysis.     

Analysis of blood flow interacted with leaflets in MHV in view of fluid-structure interaction

Interaction of blood flow and leaflet behavior in a bileaflet mechanical heart valve was investigated using computational analysis. Blood flows of a Newtonian fluid and a non-Newtonian fluid with Carreau model were modeled as pulsatile, laminar, and incompressible. A finite volume computational fluid dynamics code and a finite element structure dynamics code were used concurrently to solve the flow and structure equations, respectively, where the two equations were strongly coupled. Physiologic ventricular and aortic pressure waveforms were used as flow boundary conditions. Flow fields, leaflet behaviors, and shear stresses with time were obtained for Newtonian and non-Newtonian fluid cases. At the fully opened phase three jets through the leaflets were found and large vortices were present in the sinus area. At the very final stage of the closing phase, the angular velocity of the leaflet was enormously large. Large shear stress was found on leaflet tips and in the orifice region between two leaflets at the final stage of closing phase. This method using fluid-structure interaction turned out to be a useful tool to analyze the different designs of existing and future bileaflet valves.     

Halbach阵列磁弹簧减压阀特性研究

为改善传统减压阀中机械弹簧应力松弛和疲劳断裂等问题,提出一种基于Halbach阵列磁弹簧的直动式减压阀。利用Maxwell对Halbach阵列磁弹簧进行磁力仿真,设计出满足减压阀性能要求且铁磁耗材较低的Halbach阵列。利用AMESim软件仿真分析静态压力-流量特性与动态阶跃响应特性对Halbach阵列磁弹簧减压阀与机械弹簧直动式减压阀的影响规律。结果表明：相较于同规格机械弹簧直动式减压阀,Halbach阵列磁弹簧减压阀压力-流量曲线更平缓,即入口流量相同的情况下,磁弹簧减压阀压力损失更小,稳压精度更高;当进出口压差为2.5 MPa时,响应速度接近,当进出口压差提升至4.5 MPa时,Halbach阵列磁弹簧减压阀压力脉冲较小,即超调量较小,响应速度略有提高。     

The effects of the tilt angle of a bileaflet mechanical heart valve on blood flow and leaflet motion

Diseased heart valves can be replaced with bileaflet mechanical heart valves (BMHVs), which may be affected by complications such as hemolysis, platelet activation and device failure. These complications are closely related to the characteristics of blood flow through mechanical valves and leaflet dynamics, and can become worse with tilted implantation of BMHVs. This study simulated the interactions of blood flow and leaflet motion for BMHVs implanted at different tilt angles. A fluid-structure interaction (FSI) method was employed to solve the problems of blood flow and leaflet motion interactively. A validation of the present numerical methods was performed against data produced in a previous work, indicating that the method presented in this study is reliable. Our results reveal detailed blood flow and leaflet motion in an aorta caused by the systole and diastole of the ventricle. As the tilt angle increased, the degree of asymmetry of blood flow and the time delay in the motions of the two different leaflets also increased, which may cause worsening of complications.     

A structural analysis on the leaflet motion induced by the blood flow for design of a bileaflet mechanical heart valve prosthesis

This paper presents a structural analysis on the rigid and deformed motion of the leaflet induced by the blood flow required in the design of a bileaflet mechanical heart valve (MHV) prosthesis. In the study on the design and the mechanical characteristics of a bileaflet mechanical heart valve, the fluid mechanics analysis on the blood flow passing through leaflets, the kinetodynamics analysis on the rigid body motion of the leaflet induced by the pulsatile blood flow, and the structural mechanics analysis on the deformed motion of the leaflet are required sequentially and simultaneously. Fluid forces computed in the previous hemodynamics analysis on the blood flow are used in the kinetodynamics analysis on the rigid body motion of the leaflet. Thereafter, the structural mechanics analysis on the deformed motion of the leaflet follows to predict the structural strength variation of the leaflet as the leaflet thickness changes. Analysis results show that structural deformations and stresses increase as the fluid pressure increases and the leaflet thickness decreases. Analysis results also show that the leaflet becomes structurally weaker and weaker as the leaflet thickness becomes smaller than 0.6 mm.     

热力管网大型蝶阀故障的试验研究

通过对某厂热力管网典型蝶阀的变形及应力的实验检测及力学理论分析,探讨了蝶阀在管网中的受载状况,对该管网上大量蝶阀故障原因进行了研究分析,提出了具体的改进建议。     

Nanocomposite biomaterial mimicking aortic heart valve leaflet mechanical behaviour

The main problem with polymeric heart valves (which are already biocompatible) is that they usually fail in the long term owing to tearing and calcification of the leaflets under high dynamic tensile bending stress and oxidative reactions with blood. To overcome this shortcoming, it is hypothesized that synthetic valve leaflets which mimic native valve leaflet structure fabricated from fibre-reinforced composite material will optimize leaflet stresses and decrease tears and perforations. The objective of this study is to develop a PVA-BC (polyvinyl alcohol-bacterial cellulose)-based hydrogel that mimics not only the non-linear mechanical properties displayed by porcine heart valves, but also their anisotropic behaviour. By applying a controlled strain to the PVA samples, while undergoing low-temperature thermal cycling, it was possible to create oriented mechanical properties in PVA hydrogels. The oriented stress-strain properties of porcine aortic valves were matched simultaneously by a PVA hydrogel (15 per cent PVA, 0.5 BC cycle 4, 75 per cent initial tensile strain). This novel technique allows the control of anisotropy to PVA hydrogel, and gives a broad range of control of its mechanical properties, for specific medical device applications.     

A numerical analysis on the curved bileaflet mechanical heart valve (mhv): leaflet motion and blood flow in an elastic blood vessel

In blood flow passing through the mechanical heart valve (MHV) and elastic blood vessel, hemolysis and platelet activation causing thrombus formation can be seen owing to the shear stress in the blood. Also, fracture and deformation of leaflets can be observed depending on the shape and material properties of the leaflets which is opened and closed in a cycle. Hence, comprehensive study is needed on the hemodynamics which is associated with the motion of leaflet and elastic blood vessel in terms of fluid-structure interaction. In this paper, a numerical analysis has been performed for a three-dimensional pulsatile blood flow associated with the elastic blood vessel and curved bileaflet for multiple cycles in light of fluid-structure interaction. From this analysis fluttering phenomenon and rebound of the leaflet have been observed and recirculation and regurgitation have been found in the flow fields of the blood. Also, the pressure distribution and the radial displacement of the elastic blood vessel have been obtained. The motion of the leaflet and flow fields of the blood have shown similar tendency compared with the previous experiments carried out in other studies. The present study can contribute to the design methodology for the curved bileaflet mechanical heart valve. Furthermore, the proposed fluid-structure interaction method will be effectively used in various fields where the interaction between fluid flow and structure are involved.     

A comparative study of the shear stress induced in the leakage backflow produced by four types of heart valve prostheses

The clinical selection of a prosthetic heart valve requires the consideration of many factors. These include the pressure drop across the prosthesis, the amount of leakage backflow when the valve is closed as well as the associated shear stress within this flow for a particular valve design. Major emphasis has been placed upon the documentation of the pressure drop across prosthetic valves. Consideration of the shear stress induced in the leakage backflow associated with prosthetic valves, however, has received less attention. The purpose of this investigation, therefore, is to determine theoretically the extent of this particular shear stress for four types of currently used mechanical prosthetic cardiac valves. All valves have the same tissue annulus diameter of 27 mm. The leakage backflow is relatively small compared to the main forward flow through the orifice. However, it is important from the haemolysis point of view. The effect of the shear stress on the suspected occurrence of haemolysis is analysed by two theoretical approaches: (a) the laminar flow approach, and (b) the entry flow approach, and then compared with the findings of previous investigators dealing with the critical shear stresses which may damage the red blood cells. It was found that both approaches give practically equal shear stresses under the same pressure differential for all valves investigated. Some haemolysis is expected to occur but it is generally compensated by bone marrow hyperfunction, since that type of shear stress is sustained for only a short duration of time.     

整体开启阀与悬臂梁阀压电泵性能研究

设计了两种形式的被动截止薄膜阀一整体开启阀与悬臂梁阀,对两种形式阀的过流特性进行了理论分析,并应用两种形式的阀体制成了双腔串联压电泵的样机.对样机的实验测试表明,整体开启阀压电泵的自吸能力和输出流量都要好于悬臂梁阀压电泵.在200V交流电压驱动下,前者的最大自吸高度和输出流量分别为430 mm水柱和972 ml/min,而后者为410 mm水柱和480 ml/min.     

永磁弹簧单向阀的设计与特性研究

针对目前单向阀中因机械螺旋弹簧存在疲劳、断裂等导致其性能降低, 压力和流量损失增大等问题, 利用磁性材料“同性相斥、异性相吸”的原理, 提出斥力、引力两种永磁弹簧单向阀结构。利用ANSYS的Fluent模块对其进行流场仿真分析。在实验室条件下进行相同开启压力流量和压差-流量特性试验。结果表明:新型永磁弹簧单向阀结构合理, 斥力永磁弹簧单向阀开启压力最小, 反应最灵敏;引力永磁弹簧单向阀压力损失最小。两种永磁弹簧单向阀性能比机械弹簧单向阀优越。     

配合间隙对溢流阀稳态液动力的影响

针对稳态液动力影响电液比例溢流阀调压精度的问题,建立了内流式滑阀液动力数学模型,基于CFD仿真平台,构建了考虑配合间隙的滑阀模型,并搭建了试验平台以验证模型的正确性,研究了不同配合间隙对滑阀稳态液动力的影响。结果表明：考虑配合间隙的滑阀模型与试验测试结果有很好的一致性;溢流阀在工作过程中,阀口开度与配合间隙非常接近,随着压力升高,阀口开度变小,射流角接近20°;随着配合间隙增大,阀口开度变小,射流角变大;配合间隙在一定范围内,液动力随着间隙增大而增大,当达到临界值后,配合间隙对液动力的影响变小。     

Condition monitoring of engine timing system by using wavelet packet decomposition of a acoustic signal

A change in the technical condition of mechanical components of internal combustion engines may not be detected by on-board diagnostic systems installed in vehicles. In similar cases, measurements and analyses of vibroacoustic signals being recorded prove useful. Since there are certain limitations to vibration measurements, including those related to the vibration transmission and the engine’s high temperature at measurement points, the authors of this paper have proposed that measurements and analyses of acoustic signals should be applied for the sake of assessment of the internal combustion engine technical condition. However, such an assessment requires new acoustic signal processing methods to be developed, and so this subject has been elaborated in the paper. The article provides a discussion on the option of applying a wavelet packet decomposition while filtering the internal combustion engine’s acoustic signal in order to diagnose an excessive valve clearance. The authors prepared an algorithm enabling selection of the chosen details and approximation of the wavelet analysis to low-frequency components, which constitute the noise, as well as high-frequency components comprising information on the possible enlarged engine valve clearance. Next, based on the selected high-frequency acoustic signal components, a method for automatic detection of enlarged clearance valves was developed, assuming that energy participations of the acoustic signal being emitted were to be determined while opening and closing individual valves. Under the study discussed, identification tests were conducted using two 4-cylinder internal combustion engines featuring valves of different clearances to consequently confirm the efficiency of the algorithm developed for the acoustic signal filtration and automatic detection of enlarged clearance valves.     

基于应力均匀化的超纯水隔膜阀隔膜优化

超纯水隔膜阀具有结构简单、耐化学腐蚀、低离子析出等优点,多用于半导体行业,隔膜的疲劳破损是影响隔膜阀寿命和设备可靠性的关键性能指标。通过COMSOL模拟了隔膜启闭过程中的应力变化情况,并详细分析了隔膜工作时的受力特点。结果表明:隔膜启闭过程中受到的应力与阀口开度成线性关系,且阀口开度最大时出现峰值;对于小流量、低流速的超纯水隔膜阀,隔膜失效的主要因素是隔膜启闭过程中机械拉伸引起的疲劳损坏;优化后的隔膜在工作时的应力趋于均匀化,对进一步提高其工作寿命具有良好的工程指导意义。     

高压气动压力流量复合控制数字阀压力特性研究

气体的可压缩特性使得压力和流量可以通过同一个阀门进行控制,为此提出了一种高压气动压力和流量复合控制数字阀,该阀包括八个二级开关阀,通过控制器和压力传感器构成压力闭环反馈控制,二级阀阀口采用临界流喷嘴结构以减少压损。在介绍阀门结构和工作原理的基础上,对二级开关阀阀口面积的编码方案进行了研究,并利用仿真软件AMESim建立了系统模型。仿真结果表明,该复合控制阀能够实现快速准确且稳定的压力输出,气源压力为20 MPa的情况下,输出压力的范围为1~19 MPa,稳态偏差在±01 MPa 以内,具有较好的压力控制特性。     

Biomechanical assessment of surgical repair of the mitral valve

Repair of the mitral valve is defined (loosely) as a procedure that alters the valve structure, without replacement, enabling the natural valve itself to continue to perform under the physical conditions to which it is exposed. As the mitral valve is driven by flow and pressure, it should be feasible to analyse and assess its function, failure and repair as a mechanical system. This article reviews the current state of mechanical evaluation of surgical repairs of the failed mitral valve of the heart. This review describes the anatomy and physiology of the mitral valve, followed by the failure of the mitral valve from a mechanical point of view. The surgical methods used to repair failed valves are introduced, while the use of engineering analysis to aid understanding of mitral valve repair is also reviewed. Finally, a section on recommendations for development and future uses of engineering techniques to surgical repair are presented.     

基于小波包与关联维数的阀片故障诊断

结合了小波包降噪和关联维数对某往复压缩机阀片故障做了定量识别。实测阀片在正常和磨损两种工况下的振动信号,用小波包对信号进行降噪处理后,用改进的关联维数算法分别计算两个信号的关联维数。实例表明:小波包降噪能明显地滤除噪声,阀片在正常和磨损两种工况下的关联维数明显不同,关联维数可作为阀片故障特征的定量提取。     

Numerical analysis of 3-D flow through LNG marine control valves for their advanced design

A numerical analysis of three dimensional incompressible turbulent flows through high pressure drop control valves was carried out by using a CFD-ACE code to develop anti-cavitation control valve used in LNG marine system. For this, numerical simulation was performed on several models of control valve that have different orifice diameters of anti-trim and the size of valve discharge. In this study, flow characteristics of control valves with complex flow fields including pressure drop, cavitation effect and variation of flow coefficient as well as correlation of discharge coefficient were investigated and analyzed. Comparing with conventional control valves, newly designed valves by using the CFD analysis showed an improved flow pattern with reduced cavitation and an anticipated performance characteristic. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.