• Journal of Biomedical Engineering Research
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• v.19 no.3
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• pp.291-296
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• 1998

A new mechanical heart valve prosthesis has been designed appling systematic design methodology. The function of the heart valve was defined, and search for design variation has been carried out according to the functional structure, Optimal model among the various variations was determined in view of the design specificationn. Proto type valve was fabricated and test has been carried out using a mock circulation system. It has been observed that the pressure profile, cardiac output and behavior characteristics are generally satisfactory.

• Journal of Biomedical Engineering Research
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• v.21 no.5
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• pp.505-512
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• 2000

기계식 인공심장판막을 통한 혈액의 유동과 이 유동에 관련된 판첨의 거동특성을 수치해석기법을 이용하여 연구하였다. 혈액은 맥동류, 층류, 비압축성 유동으로 가정하였으며 유체-고체의 상호작용을 고려하기 위하여 혈액의 유동방정식과 고체의 운동방정식이 동시에 계산되었다. 심실과 대동맥에서의 압력파형을 경계조건으로 사용하였다. 연구의 결과로서 혈액유동과 판첨의 거동이 예측되었으며, 판막을 통한 3개의 제트가 발견되었으며 vortex가 판첨의 끝단에서 발생하여 하부로 흘러가는 것이 관찰되었다. 판첨의 닫힘 거동은 열림 거동에 비하여 2배정도 빠르게 진행되었으며 sinus에서 2개의 큰 vortex가 관찰되었다. 유체-고체 상호작용을 고려하는 본 연구방법은 향후 판막의 연구와 개발에 매우 유용할 것으로 판단된다.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.3 s.168
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• pp.154-161
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• 2005

In this study, the leaflet motion of a mechanical heart valve and the characteristics of two-dimensional transient blood flow in an elastic blood vessel have been numerically investigated by using fluid-structure interaction method. Here, blood has been assumed as a Newtonian, incompressible fluid. Pressure profiles have been used as boundary conditions at the ventricle and the aorta. As a result, closing motion of the leaflet is faster than opening one. While opening angles of leaflet grow up, vortex is detected at the sinus and backward of the leaflets. When the leaflet is fully closed, vortex is detected at the ventricle and at that moment maximum displacement of the elastic blood vessel is observed in the vicinity of the sinus region. Maximum displacement is caused in association with the blood flow that is oriented toward the elastic blood vessel.

• 순환기질환의공학회:학술대회논문집
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• 2001.11a
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• pp.43-44
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• 2001

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.504-512
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• 2002

Bileaflet mechanical valves have the complications such as hemolytic and thromboembolic events, leaflet damage, and leaflet break. These complications are related with the fluid velocity and shear stress characteristics of mechanical heart valves. This fact makes clear the importance of determining the fluid velocity and shear stress characteristics of mechanical heart valves, and requires a detailed understanding of these system properties and further substantial research. The first aim of current study is to introduce fluid-structure interaction method for calculation of unsteady and three-dimensional blood flow through bileaflet valve and leaflet behavior interacted with its flow, and to overcome the shortness of previous studies, where the leaflet motion has been ignored or simplified, by using FSI method. To accomplish this goal, a finite volume computational fluid dynamics code and a finite element structure dynamics code have been used concurrently to solve the flow and structure equations, respectively, to investigate the interaction between the blood flow and leaflet. Physiologic ventricular and aortic pressure waveforms were prescribed as flow boundary conditions. The interaction of aortic flow and valve motion were computed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.11a
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• pp.185-186
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• 2008

• Journal of Chest Surgery
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• v.42 no.2
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• pp.193-200
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• 2009

Background: The long-term administration of oral anticoagulant to the patients with a mechanical heart valve prosthesis is mandatory. However, the appropriate intensity of oral anticoagulant therapy to prevent thromboembolic or hemorrhagic complications is still controversial. We tried to apply low intensity anticoagulant therapy for which the International Normalized Ratios ranged between 1.5 and 2.5, and we analyzed the anticoagulation-related long term outcomes. Material and Method: From January 1992 to December 2002, 144 patients who underwent a single cardiac valve replacement were included in the study, and their ages ranged from 15 to 72 years (mean age: $47.4{\pm}15.1$): there were 49 aortic valve replacements (AVR) and 95 mitral valve replacements (AVR). The patients were followed up monthly or bi-monthly at the outpatient clinic with clinical examinations and measuring the prothrombin time to adjust the International Normalized Ratios (INRs) within the low-intensity target range between 1.5 and 2.5. Result: The follow-up period was 835.3 patient-years (mean: $5.9{\pm}3.5$) and the INRs of 7,706 measurements were available for evaluation. The mean INRs of the aortic and the mitral valve replacement groups were significantly different (p<0.01). All the patients' INRs were within the target range in 61.9% of the measurements. The mean INRs $(2.16{\pm}0.23)$ of the patients with atrial fibrillation, which was found in 30.3% of the patients, were definitely higher than those $(2.03{\pm}0.27)$ measured in the patients with regular rhythm (p<0.01). Thromboembolic episodes occurred in 9 patients with an incidence of 1.08%/patient-year. Major bleeding occurred in 2 patients (MVR) with an incidence of 0.24%/patient-year. The patients who displayed better compliance showed a lower incidence of complications (p=0.000). Conclusion: The anticoagulation therapy with a low-intensity target range after MVR or AVR seems to be effective and feasible, and increasing the patients’ compliance should be done for achieving more effective anticoagulation therapy.

• Journal of Biomedical Engineering Research
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• v.23 no.4
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• pp.309-315
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• 2002

Since the discovery, in the 1980s, of erosion-pit-induced fractures in implanted mechanical heart valves. cavitation on the surface of mechanical heart valves has been widely studied as a possible cause of pitting. Several factors, including peak dp/dt of the ventricular pressure. maximum closing velocity of the leaflet, and squeeze flow. have been studied as indices of the cavitation threshold. In the present study. cavitation erosion on the surface of a mechanical valve was examined by focusing on squeeze flow and the water hammer phenomenon during the closing period of the valve. In this study, we measures pressure wave forms near a valve and closing velocities of a disk, which were placed in a holder with and without compliance. In case of all holders, pressure drop of below vapor pressure expect at near the surface disk. It was also found that the closing velocity of the disk increased and that cavitation erosion was enhanced too. These results suggest that disk closing velocity during the closing phase has signifiant effects on pitting erosion.

• The KSFM Journal of Fluid Machinery
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• v.7 no.3 s.24
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• pp.14-22
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• 2004

Bileaflet mechanical valves have the complications such as hemolysis and thromboembolism, leaflet damage, and leaflet break. These complications are related with the fluid velocity and shear stress characteristics of mechanical heart valves. The first aim of the current study is to introduce fluid-structure interaction method for calculation of unsteady and three-dimensional blood flow through bileaflet valve and leaflet behavior interacted with its flow, and to overcome the shortness of the previous studies, where the leaflet motion has been ignored or simplified, by using FSI method. A finite volume computational fluid dynamics code and a finite element structure dynamics code have been used concurrently to solve the flow and structure equations, respectively, to investigate the interaction between the blood flow and leaflet. As a result, it is observed that the leaflet is closing very slowly at the first stage of processing but it goes too fast at the last stage. And the results noted that the low pressure is formed behind leaflet to make the cavitation because of closing velocity three times faster than opening velocity. Also it is observed some fluttering phenomenon when the leaflet is completely opened. And the rebounce phenomenon due to the sudden pressure change of before and after the leaflet just before closing completely. The some of time-delay is presented between the inversion point of ventricle and aorta pressure and closing point of leaflet. The shear stress is bigger and the time of exposure is longer when the flow rate is maximum. So it is concluded that the distribution of shear stress at complete opening stage has big effect on the blood damage, and that the low-pressure region appeared behind leaflet at complete closing stage has also effect on the blood damage.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.643-646
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• 2001

This paper investigates the structural analysis and design of mechanical heart valve through the numerical analysis methodology. In a numerical analysis methodology application to the thickness minimization structural design of mechanical heart valve, structural analysis is performed for the blood flow through a bileaflet mechanical heart valve. The structural static analysis is carried out to confirm the thickness minimization structural condition (minimum thickness shape of leaflet).