• Journal of Mechanical Science and Technology
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• v.20 no.8
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• pp.1118-1124
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• 2006

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 mono leaflet 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 mono leaflet 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.

• Molecules and Cells
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• v.37 no.4
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• pp.330-336
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• 2014

Thymosin beta4 (TB4) has multiple functions in cellular response in processes as diverse as embryonic organ development and the pathogeneses of disease, especially those associated with cardiac coronary vessels. However, the specific roles played by TB4 during heart valve development in vertebrates are largely unknown. Here, we identified a novel function of TB4 in endothelial-mesenchymal transformation (EMT) in cardiac valve endocardial cushions in zebrafish. The expressions of thymosin family members in developing zebrafish embryos were determined by whole mount in situ hybridization. Of the thymosin family members only zTB4 was expressed in the developing heart region. Cardiac valve development at 48 h post fertilization was defected in zebrafish TB4 (zTB4) morpholino-injected embryos (morphants). In zTB4 morphants, abnormal linear heart tube development was observed. The expressions of bone morphogenetic protein (BMP) 4, notch1b, and hyaluronic acid synthase (HAS) 2 genes were also markedly reduced in atrio-ventricular canal (AVC). Endocardial cells in the AVC region were stained with anti-Zn5 antibody reactive against Dm-grasp (an EMT marker) to observe EMT in developing cardiac valves in zTB4 morphants. EMT marker expression in valve endothelial cells was confirmed after transfection with TB4 siRNA in the presence of transforming growth factor ${\beta}$ ($TGF{\beta}$) by RT-PCR and immunofluorescent assay. Zn5-positive endocardial AVC cells were not observed in zTB4 morphants, and knockdown of TB4 suppressed TGF-${\beta}$-induced EMT in ovine valve endothelial cells. Taken together, our results demonstrate that TB4 plays a pivotal role in cardiac valve formation by increasing EMT.

• Journal of Mechanical Science and Technology
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• v.19 no.9
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• pp.1761-1772
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• 2005

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.

• Journal of Biomedical Engineering Research
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• v.2 no.2
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• pp.89-102
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• 1981

The recirculating flows which occur in the prosthetic heart valve have been known to cause several diseases in the human body. And the recent studies show that the shear stress at the wall of the artery is also very important factor in the formation of thrombus. And many studies knave been devoted in obtaining more information about the blood flow through the prosthetic heart valve. In this Paper, the steady axisymmetric flow through the Disc-Type Heart Valve is studied by using the numerical method. The geometry of the Disc-Type Heart Valve is simplified, and the flow is assumed to be steady axisymmetric flow. The vorticity transport equation derived from the Wavier-Stoke's equation is used as the governing equation, and the explicit finite difference method is used to obtain the steady state solution. The results for several Reynolds numbers show that the recirculating flow becomes large as the Remolds number increases. Furthermore, it can be shown that the magnitudes of the vorticity and the stresses are also increased with the Reynolds number, but there is only a little change in their configurations of distribution and in their positions of maximum values.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.131-134
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• 1999

This paper considers the acoustical characteristics of the mechanical valve employed in the Korean type Artificial Heart. $Bj\"{o}rk-Shiley$ tilting disc valve was chosen for the study and acoustic measurements were performed for the artificial heart operated in a mock circulation system as well as implanted to an animal as a Bi Ventricular Assist Device (BVAD). In the mock system, three different conditions of the valve were examined which were normal, damaged (torn off), pseudothrombus attached. Microphone measurements for the BVAD were carried out at a regular time interval for 5 days after the implantation operation. Of the recorded acoustic emissions from the artificial heart, click sounds mainly originated from the valves were further analyzed using Multiple Signal Classification (MUSIC) for estimating their spectral properties. It was shown that the spectral peaks below 4 kHz and the optimal order number for MUSIC, equivalent to the number of the spectral component, might be the key parameters which were highly correlated to the physiological states of the valve like the mechanical damage of the valve or the formation of thrombus on the valves.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.703-704
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• 2002

The two major problems related to the blood flow in a floating type polymer valve are thrombus formation and hemolysis. It is well known that the shear stress in the fluid and flow separation around the valve are blamed for such disastrous phenomena. In this viewpoint, through study of the flow field around the valve is imperative to improve design of the valve. The aim of this study is to investigate the fluid flow around a floating type polymer valve. The numerical method employed in this study is the finite element software called ADINA. Incompressible viscous flow is assumed for blood using the assumption of Newtonian fluid. In this study, two prominent features of the axisymmetric flow around the floating type polymer valve are observed: jet-like flows observed near the gap between the conduit and the valve, and recirculating flow downstream of the valve. We also provided a detailed description of shear stress field according to the variation of flow conditions. The shear stress in fluid has its maximum value near the gap between the valve and the conduit.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.5
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• pp.629-639
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• 2002

In-vitro flow characteristics downstream of a polyurethane artificial heart valve and a Bjork-Shiley Monostrut mechanical valve have been comparatively investigated in pulsatile flow using particle image velocimetry (PIV). With a triggering system and a time-delayed circuit the velocity distributions on the two perpendicular measurement planes downstream of the valves are evaluated at any given instant in conjunction with the opening behaviors of valve leaflets during a cardiac cycle. The regions of stasis and high shear stress can be found simultaneously by examining the entire view of the instantaneous velocity and Reynolds shear stress fields. It is known that high shear stress regions exist at the interface between strong axial jet flows along the wall and vortical flows in the central area distal to the valves. In addition. there are large stagnation or recirculation regions in the vicinity of the valve leaflet, where thrombus formation can be induced by accumulation of blood elements damaged in the high shear stress zones. A correlation between the unsteady flow patterns downstream of the valve and the corresponding opening postures of the polyurethane valve membrane gives useful data necessary for improved design of the frame structure and leaflet geometry of the polyurethane valve.

• Journal of Chest Surgery
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• v.23 no.3
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• pp.438-451
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• 1990

Pneumatic total artificial heart[TAH] has been clinically applied for the purpose of permanent or temporary use followed by cardiac transplantation in the patients with end stage heart diseases. In spite of the good durability of the pneumatic TAH, thrombus formation, bleeding and infection resulted in death. The Tomasu heart, which is a type of pneumatic TAH, was used in this study. This model is a modified Jarvik heart and consists of atrial cuffs, outflow vascular grafts and thin-layer seamless diaphragm type of ventricles. Cardiac outputs of the left artificial heart were measured by Donovan`s mock circulation under variable conditions of driving parameters, and an experimental artificial heart implantation was performed in 4 calves to observe the changes of hemodynamic parameters in early postoperative period and hematologic and bio-chemical changes in a long-term survival case. In the mock circulation test, cardiac output of the heart was increased with the increase of the left atrial pressure and left driving pressure. Maximum cardiac output was obtained at the heart rate of 120 to 130/min and percent systole of 40 to 45Zo under the condition of a constant left driving pressure of 180mmHg and left atrial pressure of 10mmHg. During the first 24 hours of TAH pumping, driving pressure ranged from 178$\pm$5mmHg to 187$\pm$8mmHg for the left heart and from 58$\pm$6mmHg to 78$\pm$28mmHg for the right heart. The Mean arterial pressure significantly increased between 2 and 8 hours after the start of pumping. The survival time ranged from 27 hours to 46 days. The causes of death were respiratory failure in 2 cases, mechanical valve failure in one, and left ventricular outflow obstruction due to thrombus in a 46-day survival case. This study demonstrated that Tomasu artificial heart operated effectively during the first 24 hours of artificial heart pumping, but thrombus formation around the valve holding area was the main problem in long-term survival case.

• Journal of the Institute of Convergence Signal Processing
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• v.14 no.1
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• pp.1-5
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• 2013

The two major problems related to the blood flow in replaced prosthetic heart valve are thrombus formation and hemolysis. Reliability of prosthetic valve is very important because its failure means the death of patient. There are many factors affecting the valvular failures and their representatives are mechanical failure and thrombosis, so early noninvasive detection is essentially required. The purpose of this study is to detect the various thromboses formation by using acoustic signal acquisition and its spectral analysis on the frequency domain. We made the thrombosis models using Polydimethylsiloxane (PDMS) and they are thrombosis model on the disc, around the sewing ring and fibrous tissue growth across the orifice of valve. Using microphone and amplifier, we measured the acoustic signal from the prosthetic valve, which is attached to the pulsatile mock circulation system. A/D converter sampled the acoustic signal and the spectral analysis is the main algorithm for obtaining spectrum. Then the spectrum of normal and 5 different kinds of abnormal valve were obtained. Each spectrum waveform shows a primary and secondary peak. The secondary peak changes according to the thrombus model. To quantitatively distinguish the frequency peak of the normal valve from that of the thrombosed valves, analysis using a neural network was employed. Acoustic measurement has been used as a noninvasive diagnostic tool and is thought to be a good method for detecting possible mechanical failure or thrombus.

• Journal of Chest Surgery
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• v.18 no.3
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• pp.446-455
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• 1985

A total and consecutive 156 patients have undergone cardiac valve surgery including 13 closed mitral commissurotomy, 13 open mitral commissurotomy, one mitral annuloplasty, 75 mitral valve replacement, one aortic annuloplasty, 24 aortic valve replacement, 3 tricuspid valve replacement, 25 double valve replacement and one triple valve replacement. 155 prosthetic valves were replaced in a period between September 1976 and August 1985. There were 68 males and 88 females with age range from 8 to 69 yrs [mean 36.5 yr]. Out of replaced valves, 61 was tissue valve including 54 Carpentier-Edwards, and 4 was mechanical valves including 74 St. Jude Medical, and the position replaced was 101 valves for mitral, 46 for aortic and 8 for tricuspid. Single valve replacement in 102 cases, double valve replacement in 25 cases [17 for AVR+MVR, and 8 for MVR+TVR], and only one case was noted in the triple valve replacement. Early mortality within 30 days after operation was noted in 11 cases [7%]; 7 after MVR, 2 after DVR, and each one after open mitral commissurotomy and mitral annuloplasty. Cause of death was valve thrombus, cerebral air embolism, low output syndrome, uncontrollable arrhythmia, parapneumonic sepsis, acute cardiac tamponade and left atrial rupture. 7 late deaths were noted during the follow-up period from 1 to 104 months [average 48 month]; three due to valve and left atrial thrombus formation, two due to CVA from overdose of warfarin, and each one due to congestive heart failure and chronic constrictive pericarditis, Anticoagulants after prosthetic valve replacement were maintained with warfarin, dipyridamole and aspirin to the level of around 50% of normal prothrombin time in 79 cases, and Ticlopidine with aspirin in 47 cases to compare the result of each group. There were 11 major thromboembolic episodes including 3 deaths in the warfarin group. Two cases of CVA due to overdose of warfarin was noted in the warfarin group. In the ticlopidine group, there was only one left atrial thrombus confirmed at the time of autopsy. Among the survived 138 cases, nearly all cases[136 cases] were included in NYHA functional class I and II during the follow-up period. In conclusion, surgical treatment of the cardiac valve disease in 156 clinical cases revealed excellent result with acceptable operative risk and late mortality. Prevention of thrombus formation with anti-platelet aggregator Ticlopidine has better result than warfarin group presently with no specific side effect such as bleeding or gastrointestinal trouble.