Beat to beat analysis of mechanical heart valves by means of return map

Three mechanical heart valves (two bileaflet prostheses and a tilting one) were investigated in a basic hardware setup in order to evaluate with a hydrophone their opening and closing action in time and in amplitude of each beat. The recorded signal was then segmented into the series of cycles xi(t) having a temporal duration equal to the working period imposed on the valve. Two return maps were defined, in order to evaluate the degree of dispersion of the resulting scatter plot: (i) the amplitude map xi(t) versus xi+1(t); (ii) the delay map for the closure of the valve within each beat versus the successive ones. To evaluate the results obtained, two indices were proposed based on both the degree of dispersion and the deviation of the regression line of the resulting scatter plot with respect to the bisector of the map plane. The tilting disc valve showed a lower degree of dispersion, both in the amplitude signal and in the closure time delays, with respect to the other two bileaflet heart valves. The methodology proposed here could be regarded as an alternative non-invasive tool to investigate the dynamic behaviour of prosthetic heart valves, especially in the case of their suspected failure.     

Advances in prosthetic heart valves: fluid mechanics of aortic valve designs

The in vitro hemodynamic characteristics of a variety of mechanical and tissue heart valve designs used during the past two decades were investigated in the aortic position under pulsatile flow conditions. The following valve designs were studied: Starr-Edwards ball and cage (model 1260), Bj?rk-Shiley tilting disc (convexo-concave model), Medtronic-Hall tilting disc, St. Jude Medical bileaflet, Carpentier-Edwards porcine and pericardial (models 2625, 2650 and 2900), Hancock porcine (models 250 and 410) and Ionescu-Shiley standard pericardial. The Starr-Edward ball and cage, Bj?rk-Shiley tilting disc, Carpentier-Edwards porcine (model 2625) and Ionescu-Shiley standard pericardial valves were designed prior to 1975, while the Medtronic-Hall tilting disc, St. Jude Medical bileaflet, Hancock porcine (model 250), Hancock II porcine (model 410), Carpentier-Edwards porcine (model 2650) and Carpentier-Edwards pericardial (model 2900) valves were designed after 1975. The pressure drop results indicated that the valves designed prior to 1975 had performance indices of 0.30 to 0.45, whereas the valves designed after 1975 had performance indices of 0.40 to 0.70. The regurgitant volumes were higher for the mechanical designs (5.0 to 11.0 cm3/beat) compared to the tissue bioprostheses (1.0 to 5.0 cm3/beat). Two-dimensional laser Doppler anemometry studies indicated that the valves designed after 1975 tended to create more centralized flow fields, with reduced levels of turbulent shear stresses. However, none of the current valve designs is ideal: they all create areas of stasis and/or regions of low velocity reverse flow; and regions of elevated turbulent shear stresses that are capable of causing sub-lethal and/or lethal damage to the formed elements of blood.     

A 44-year experience of prosthetic heart valve implantation at Niigata University Hospital

Based on a single hospital experience of heart valve implantation from 1965 to 2009, the superiority of prosthetic heart valves including Starr-Edwards caged ball valves, Omniscience aortic tilting disc valves, and St. Jude Medical bileaflet valves are reviewed. This review discusses the prominent antithrombogenicity of the Starr-Edwards model 1200 aortic prosthesis under selected conditions, the relatively rarely thrombosed (despite its decreased opening angle) Omniscience aortic valve, the long-term outcomes 10 as well as 30 years after St. Jude Medical valve replacement, and finally the latest results on the significance of patient-aortic prosthesis mismatch in relation to myocardial hypertrophy. The findings described here should be considered in further investigations of cardiac valve prostheses.     

Materials characterization of explanted mechanical heart valves and comparison to patients' clinical data

In the present study, twelve explanted mechanical heart valves (MHVs)with pyrolitic carbon tilting disc and 14 bileaflet MHVs were analyzed to investigate the effects of material properties on valve performance and patients' general health conditions. Optical and scanning electron microscopy was used to investigate material imperfections, wear patterns or damages to housing and occluder components. All analyzed tilting disc valves exhibited wear effects, particularly due to abrasion and impact to both disc and housing. Wear of pyrolitic carbon disc and housing did not influence their in vivo performance. In the bileaflet MHVs, breakaway of the pyrolitic carbon coating sometimes caused malfunctioning and required surgical retrieval of the valve. In all cases, occurrence of clinical symptoms was more likely when wear effects were located in critical areas. The study supports a correlation between the properties of the MHVs material and patients' symptoms.     

Hydrodynamics of a Newly China-Made Jiuling Bileaflet Heart Valve Prostheses

INTRODUCTION　　 Implantation of heart valve substitute has become the standard treatment forend-stage valvular heart disease since the1 960 s.There are two different types ofmechanical heart valve in widespread use at present,the tilting disc valve and t…     

Mechanism for cavitation of monoleaflet and bileaflet valves in an artificial heart

It is possible that mechanical heart valves mounted in an artificial heart close much faster than those used for clinical valve replacement, resulting in the formation of cavitation bubbles. In this study, the mechanism for mechanical heart cavitation was investigated using the Medtronic Hall monoleaflet valve and the Sorin Bicarbon bileaflet valve mounted at the mitral position in an electrohydraulic total artificial heart. The valve-closing velocity was measured with a charge-coupled device (CCD) laser displacement sensor, and images of mechanical heart valve cavitation were recorded using a high-speed video camera. The valve-closing velocity of the Sorin Bicarbon bileaflet valve was lower than that of the Medtronic Hall monoleaflet valve. Most of the cavitation bubbles generated by the monoleaflet valve were observed near the valve stop; with the Sorin Bicarbon bileaflet valve, cavitation bubbles were concentrated along the leaflet tip. The cavitation density increased as the valve-closing velocity and the valve stop area increased. These results strongly indicate that squeeze flow holds the key to cavitation in the mechanical heart valve. From the perspective of squeeze flow, bileaflet valves with a low valve-closing velocity and a small valve stop area may cause less blood cell damage than monoleaflet valves.     

In Vitro Study of Influence of Mimic Cardiac Rate on Hydrodynamics of the Different Mechanical Cardiac Valve Prostheses

To assess the influence of mimic cardiac rate on hydrodynamics of the different mechanical prosthetic cardiac valves. Methods. US-made CarboMedics bileaflet valve and China-made Jiuling bileaflet valve and C-L tilting disc valve have been tested in a pulsatile flow simulator in the aortic position. The testing condition was set at the mimic cardiac rate of 55 beats/min,75 beats/min,100beats/min and a constant mimic cardiac output of 4L/min. The mean pressure differences (△P),leakage volumes (LEV) and closing volumes(CLV) across each valve,and the effective orifice areas(EOA) have been analyzed. Results.Within the range of physiology,the AP,LEV and CLV were falling as the increasing of mimic cardiac rate,and the extent of variance was larger. The EOA was increasing with the increase of the mimic cardiac rate. It is a different response as the altering of the cardiac rate for the different type of the mechanical prosthetic cardiac valves.Conclusions.The change of the mimic cardiac rate can affect the hydrodynamics of the mechanical prosthetic cardiac valves. The hydrodynamics of the bileaflet valve prosthesis is better than the tilting disc valve.     

Effects of leaflet geometry on the flow field in three bileaflet valves when installed in a pneumatic ventricular assist device

Our group is currently developing a pneumatic ventricular assist device (PVAD). In this study, in order to select the optimal bileaflet valve for our PVAD, three kinds of bileaflet valve were installed and the flow was visualized downstream of the outlet valve using the particle image velocimetry (PIV) method. To carry out flow visualization inside the blood pump and near the valve, we designed a model pump that had the same configuration as our PVAD. The three bileaflet valves tested were a 21-mm ATS valve, a 21-mm St. Jude valve, and a 21-mm Sorin Bicarbon valve. The mechanical heart valves were mounted at the aortic position of the model pump and the flow was visualized by using the PIV method. The maximum flow velocity was measured at three distances (0, 10, and 30 mm) from the valve plane. The maximum flow velocity of the Sorin Bicarbon valve was less than that of the other two valves; however, it decreased slightly with increasing distance it the X-Y plane in all three valves. Although different bileaflet valves are very similar in design, the geometry of the leaflet is an important factor when selecting a mechanical heart valve for use in an artificial heart.     

脉动流下机械心脏瓣膜瓣阀开启状态的评价

背景：体外机械型人工心脏瓣膜(机械瓣)性能的评价涉及心输出量、反流量、有效瓣口面积、跨瓣压差,以及应力场、流场和成穴现象等。 目的：对3种机械瓣的瓣阀开启状态进行可视性观察和评价。 方法：用脉动流模拟循环装置系统,维持系统整个状态不变,在模拟心搏出量4 L/min、模拟心率75次/min和收缩时间占其循环周期46.2%的条件下,分别将久灵双叶瓣、Carbomedics双叶瓣和C-L侧倾碟瓣置于主动脉瓣位,将高速摄像机置于模拟循环装置动脉腔的正上方,观察10个连续模拟心动周期中瓣阀开启状态。利用自编图像处理软件包,捕获瓣阀开启角度最大的1幅图像,作为计算该只瓣膜在1个心动周期中最大开放面积和开启角度的基准。 结果与结论：脉动流下,25 mm CarboMedics瓣、25 mm和23 mm久灵双叶瓣在开放到最大位时,可见瓣阀抖动现象,27 mm C-L侧倾碟瓣未见瓣阀抖动。用不同的计算方法测量上述瓣膜的瓣口面积显示,由厂家提供的瓣口实际面积最大,用Green公式计算的瓣膜开放面积次之,用Gorin公式计算的有效瓣口面积最小。根据三角形定理计算的瓣阀开放角度,久灵双叶瓣和CarboMedics瓣的两个瓣阀的开放角度不一致,并均小于瓣膜固有的开放角度;C-L侧倾碟瓣的开放角度也未达其固有的开放角度。提示机械型人工心脏瓣膜双叶瓣的瓣阀开放不同步,瓣阀有抖动现象;瓣阀在脉动周期中呈不完全性开启。     

Wavelet analysis of valve closing sound detects malfunction of bileaflet mechanical valve

Several studies have reported the asynchronous closure of normal bileaflet valves (NBVs), resulting in a split in its closing sound; however, the clinical significance of this split has never been studied in malfunctioning bileaflet valves (MBVs). The study comprised 218 valves in 184 patients, including normal monoleaflet valves (n = 10), NBVs (n = 198), and MBVs (n = 10). Valve function was confirmed by cinefluoroscopy prior to analysis of the valve sound by the Morlet continuous wavelet transform (CWT). The split interval (SI) for each heartbeat was measured, and the coefficient of variation (CV) of its mean (valve SI) was calculated as a parameter for the fluctuation of the SI. The CWT of monoleaflet valves showed a single spike, whereas NBVs exhibited a clear split. There was no significant difference in valve SI between the aortic and mitral positions; however, the mean of the CV was significantly greater in the mitral position (n = 90, 0.507 ± 0.254) than in aortic position (n = 108, 0.353 ± 0.228, P = 0.000045). The split was not found in six (aortic; three, mitral; three) of ten patients with MBVs. The other four patients had a distinct split, but the CV was significantly lower for MBVs (0.138 ± 0.105) than for NBVs (0.343 ± 0.221, P = 0.042). Receiver-operating characteristics analysis demonstrated the cutoff line of the CV to be 0.112 for detecting malfunctioning aortic valves with the highest accuracy of 86.1%. This new system using the Morlet CWT can detect MBVs. It will be a useful modality for screening the function of bileaflet valves.     

Effect of the mechanical prosthetic mono- and bileaflet heart valve orientation on the flow field inside the simulated ventricle

Two groups of typical contemporary mechanical heart valves, the Advancing the Standard (ATS) and the Carbomedics (CM) valve (of bileaflet design) and the Bjork-Shiley (BS) mono and Bicer-Val (BV) valves (of tilting-disc design), were tested in the mitral position under the pulsatile-flow condition. This study extends a previous report studying the effect of orientation of the St. Jude Medical (SJM) valve, representing bilcaflet valve design, and the Meditronic-Hall (MH) valve, representing mono-leaflet valve design. The test program utilized a flow visualization technique to map the velocity field inside the simulated ventricle. The study was carried out using a sophisticated cardiac simulator in conjunction with a high-speed video system (200 frames·s⁻¹). The continuous monitoring of velocity-vector time histories revealed useful details about the complex flow and helped establish the locations and times of the peak parameter values. Comparison of the velocity profiles at corresponding flow phases reveals the effects of the differences in valve design and orientation. Based on precise examination of the data, the following general conclusions can be made: pulsatile flow creates three distinct flow phases consisting of accelerating, peak, and decelerating flow; the bileaflet CM and ATS valves in the antianatomical orientation generally create a single, large circulatory flow; the ATS valve scems to offer smoother flow patterns, similar to the SJM valve; and the monoleaflet BV valve and the BS monostrut valve seem to affect the flow characteristics more dramatically, with the posterior orientation exhibiting simple and stable circulatory flow.     

Near velocity field downstream prosthetic valves in aortic position.

Using a cardiovascular simulator to duplicate in vitro the flow conditions through valves in aortic position, bidimensional velocity maps very near the valve are reconstructed, from an ultrasonic 8 Mhz doppler system, in an elastic model of the ascending aortic arch. Three mechanical heart valves representative of the different types of commercial models (a tilting disc, a ball in cage and a two-leaflet valve) and a new bileaflet prototype were investigated. From examination of the velocity field, it is possible to define the main characteristics of the valve wake and to observe the development of negative velocities associated with regurgitant flows. From a comparison with tests in rigid tubes, the role played by the arch elasticity is analysed.     

A three-dimensional analysis of flow in the pivot regions of an ATS bileaflet valve

Bileaflet heart valves are currently the most commonly implanted type of mechanical prosthetic valve, because of their low transvalvular pressure drop, centralised flow and durability. However, in common with all mechanical heart valves, implanted bileaflet valves show an inherent tendency for blood clot formation at the valve site. Fluid dynamical phenomena associated with blood clotting are elevated blood shear stresses and regions of persistent blood recirculation, particularly when both occur together. Using three-dimensional CFD modelling, combined with enlarged scale experimental modelling, we investigated the blood flow through the ATS bileaflet valve during forward flow, with particular attention to the leaflet pivot regions. Recirculating regions were found both within and downstream of the valve housing ring. Qualitative assessment of the entire cardiac cycle suggested that recirculating blood within the housing ring will be washed away whilst the valve is closed, but as with all bileaflet valve designs recirculating blood downstream of the valve may have a residence time much longer than one cardiac cycle.     

Numerical comparison of the closing dynamics of a new trileaflet and a bileaflet mechanical aortic heart valve

The closing velocity of the leaflets of mechanical heart valves is excessively rapid and can cause the cavitation phenomenon. Cavitation bubbles collapse and produce high pressure which then damages red blood cells and platelets. The closure mechanism of the trileaflet valve uses the vortices in the aortic sinus to help close the leaflets, which differs from that of the monoleaflet or bileaflet mechanical heart valves which mainly depends on the reverse flow. We used the commercial software program Fluent to run numerical simulations of the St. Jude Medical bileaflet valve and a new trileaflet mechanical heart valve. The results of these numerical simulations were validated with flow field experiments. The closing velocity of the trileaflet valve was clearly slower than that of the St. Jude Medical bileaflet valve, which would effectively reduce the occurrence of cavitation. The findings of this study are expected to advance the development of the trileaflet valve.     

Bileaflet Aortic Valve Prosthesis Pivot Geometry Influences Platelet Secretion and Anionic Phospholipid Exposure

The clinical histories of the Medtronic Parallel (MP) and St. Jude Medical (SJM) Standard valves suggest pivot geometry influences the thrombogenic characteristics of bileaflet prostheses. This work studied the effects of various pivot geometries on markers of platelet damage in a controlled, in vitro apparatus. The Medtronic Parallel valve, two St. Jude Medical valves, and two demonstration prostheses were used to study the effects of bileaflet pivot design, gap width, and size on platelet secretion and anionic phospholipid expression during leakage flow. A centrifugal pump was used to drive blood through a circuit containing a bileaflet prosthesis. Samples were taken at set time intervals after the start of the pump. These samples were analyzed by cell counting, flow cytometry, and enzyme-linked immunosorbant assay. No significant differences were observed in platelet secretion or anionic phospholipid expression between experiments with the SJM 27 Standard regular leaker, the SJM 20 regular leaker, and the MP 27 valves. Significant differences in platelet secretion and anionic phospholipid expression were observed between a SJM 27 Standard regular leaker and a SJM 27 high leaker valve. These studies suggest that leakage gap width within bileaflet valve pivots has a significant effect on platelet damage initiated by leakage flow. © 2001 Biomedical Engineering Society. PAC01: 8719Uv, 8719Tt, 8380Lz, 8768+z     

The closing behavior of mechanical aortic heart valve prostheses

Mechanical artificial heart valves rely on reverse flow to close their leaflets. This mechanism creates regurgitation and water hammer effects that may form cavitations, damage blood cells, and cause thromboembolism. This study analyzes closing mechanisms of monoleaflet (Medtronic Hall 27), bileaflet (Carbo-Medics 27; St. Jude Medical 27; Duromedics 29), and trileaflet valves in a circulatory mock loop, including an aortic root with three sinuses. Downstream flow field velocity was measured via digital particle image velocimetry (DPIV). A high speed camera (PIVCAM 10-30 CCD video camera) tracked leaflet movement at 1000 frames/s. All valves open in 40-50 msec, but monoleaflet and bileaflet valves close in much less time (< 35 msec) than the trileaflet valve (>75 msec). During acceleration phase of systole, the monoleaflet forms a major and minor flow, the bileaflet has three jet flows, and the trileaflet produces a single central flow like physiologic valves. In deceleration phase, the aortic sinus vortices hinder monoleaflet and bileaflet valve closure until reverse flows and high negative transvalvular pressure push the leaflets rapidly for a hard closure. Conversely, the vortices help close the trileaflet valve more softly, probably causing less damage, lessening back flow, and providing a washing effect that may prevent thrombosis formation.     

Termination Kinetics of Dibutyl Itaconate Free‐Radical Polymerization Studied via the SP–PLP–ESR Technique

Summary: The termination kinetics of dibutyl itaconate (DBI) bulk polymerization was studied via SP–PLP–ESR single pulse–pulsed laser polymerization with time‐resolved detection of free‐radical concentration by electron‐spin resonance, at temperatures between 0 and 60 °C. As is characteristic of PLP experiments, termination rate coefficients, k_t(i,i), are measured for radicals of (almost) identical chain length (CL) i. CL‐averaged 〈k_t〉, for chain lengths up to 200 monomer units, and also kequation/tex2gif-stack-1.gif referring to termination of very small‐size radicals are directly deduced from measured DBI radical concentration vs time traces. At 45 °C, 〈k_t〉 is (3.4 ± 0.6) · 10⁵ L · mol^?1 · s^?1 and kequation/tex2gif-stack-2.gif is (7.2 ± 1.0) · 10⁵ L · mol^?1 · s^?1. Both rate coefficients are independent of monomer conversion up to the highest experimental conversion of 18%. The associated activation energies are E_A(〈k_t〉) = 23.0 ± 3.2 kJ · mol^?1 and E_A(kequation/tex2gif-stack-3.gif) = 27.6 ± 2.8 kJ · mol^?1, respectively. “Model‐dependent” and “model‐free” analyses of radical concentration vs time profiles indicate a pronounced CL dependence of k_t(i,i) for DBI radicals of moderate size, 5 < i < 50. The lowering of k_t(i,i) with CL corresponds to an exponent α close to 0.5 in a power‐law expression k_t(i,i) = kequation/tex2gif-stack-4.gif · i^?a. At higher chain lengths, the variation of k_t(i,i) with CL becomes weaker and may be represented by an α value of 0.16 or even below. These results are consistent with models according to which α varies to a larger extent at low CL and to a smaller extent at high CL with the crossover region between the two ranges being located somewhere around i = 100.

Conversion‐dependence of 〈k_t〉 and kequation/tex2gif-stack-5.gif from laser‐induced photopolymerization of DBI.     

Phonocardiogram spectral analysis simulator of mitral valve prostheses.

Spectral analysis of sounds produced in vitro by mitral valve prostheses placed in a specially designed flow simulator has been carried out using a short-time Fourier representation of the recorded signal. Time variations of power spectra are displayed as a three-dimensional plot. Sounds produced by three types of valves, namely ball and cage, tilting disk and porcine valves, were analysed. Each valve type produced a characteristic spectrogram, and, for a given valve, spectrograms were reproducible to within a margin of 5 dB. The simulator may be used to detect structural deficiencies and functional abnormalities of prosthetic heart valves. In addition to quantifying the noise level of mechanical valves, the system may be used for quality control purposes to identify faulty valves.     

Echocardiographic characteristics of transprosthetic blood peak velocity in the Sorin Bicarbon bileaflet prosthetic heart valve

The Bicarbon prosthetic heart valve with two curved leaflets is designed so that the blood flows through the three orifices are parallel jets of equal size. This study was conducted to confirm that the Bicarbon valve functions clinically as designed. Forty-three patients underwent valve replacement with the Bicarbon valve. Forty-eight Bicarbon valves were implanted: 25 valves in the mitral position and 23 in the aortic position. Peak blood flow velocity through the three prosthetic orifices was measured postoperatively by Doppler echocardiography. The three flow jets through the prosthesis were parallel. The velocity through the lateral orifice was 2.33±0.38 m/min, and the velocity through the central orifice was 2.14±0.43 m/min at the aortic position (P>0.05). The velocity through the lateral orifice was 1.72±0.06 m/min at the mitral position, and that through the central orifice was 1.73±0.06 m/min (P>0.05). Serum lactic acid dehydrogenase values were also lower than those of patients or whom another bileaflet prosthesis had been implanted. The results confirm that the Bicarbon prosthetic heart valve performs clinically as designed, producing three parallel blood flow jets with equal flow velocity.     

Mechanisms of mechanical heart valve cavitation in an electrohydraulic total artificial heart

Until now, we have estimated cavitation for mechanical heart valves (MHV) mounted in an electrohydraulic total artificial heart (EHTAH) with tap water as a working fluid. However, tap water at room temperature is not a proper substitute for blood at 37 degrees C. We therefore investigated MHV cavitation using a glycerin solution that was identical in viscosity and vapor pressure to blood at body temperature. In this study, six different kinds of monoleaflet and bileaflet valves were mounted in the mitral position in an EHTAH, and we investigated the mechanisms for MHV cavitation. The valve closing velocity, pressure drop measurements, and a high-speed video camera were used to investigate the mechanism for MHV cavitation and to select the best MHV for our EHTAH. 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 Bj?rk-Shiley valve, because it is associated with slow squeeze flow, and the bileaflet valve with low valve closing velocity and small valve stop areas are better able to prevent blood cell damage than the monoleaflet valves.