• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.443-450
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• 1995

An analysis of the dynamics of a mechanical monoleaflet heart valve prosthesis in the closing phase is presented. Employing the moment equilibrium principles on the occluder motion and the squeeze film dynamics of the fluid between the occluder and the guiding strut at the instant of impact, the velocity of the occluder tip and the impact force were computed. The dynamics of fluid being squeezed between the occluder and the guiding struts is accounted for by Reynold's equation. The effect of the fluid being squeezed between the occluder and the guiding strut was to reduce the velocity of the occluder tip at the instant of valve closure as well as dampen the fluttering of the occluder before coming to rest in the fully closed position. The squeeze film fluid pressure changed rapidly from a high positive value to a relatively large negative value in less than 1 msec. The results of this study may be extended for the analysis of cavitation inception, mechanical stresses on the formed elements and valve components as well as to estimate the endurance limits of the prosthetic valves.

• Journal of Biomedical Engineering Research
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• v.12 no.3
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• pp.149-156
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• 1991

In this paper, fluttering behavior of mechanical bileaflet heart valve prosthesis was analyzed taking into consideration of the impact between valve plate and stopper Vibration system of the valve was modeled as a rotating system, and equations are induced by moment equilibrium equations. Lift force, drag force, gravity and buoyancy were considered as external forces acting on the valve plate/ The 4th order Runge-Kutta method was used to solve the equations. Valve plate does not come to the static equilibrium position at a stretch, but come to that position after under damping vibration. Damping ratio increases as the cardiac optput increases, and the mean damping ratio is in the range of 0.16~40.25. Fluttering frequency does not have any specific value, but varies as a function of time. It is in the range of 10~40Hz. Valve opening appears to be affected by the orientation of the of the valve relative to gravitational forces.

• Journal of Chest Surgery
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• v.32 no.11
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• pp.1031-1035
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• 1999

Background: ATS mechanical valve is a recently introduced pyrolytic carbon bileaflet prosthesis. This report is to evaluate the results of hemodynamic and anticoagulant therapy after ATS valve replacement. Material and Method: From May 1995 to October 1998, 53 patients received 65 ATS prosthesis; 38 Mitral(27-33 mm), 27 Aortic(19-25 mm). 2 CABGs and 5 Tricuspid annuloplasty were taken concomitantly. The follow up period was 769 patient-months(mean 16.2$\pm$10.0), varied from 1 month to 39 months with 92.5% follow up rate. All patients were evaluated with Doppler echocardiography, 7-14 days after operation. Result: NYHA functional class was improved significantly, from 2.6$\pm$0.8 preoperatively to 1.3$\pm$0.4 postoperatively. The average value of peak and mean transvalvular pressure gradients were 25.7$\pm$13.5 mmHg, 12.7$\pm$8.3 mmHg in aortic position. In the mitral position, the average values of peak and mean transvalvular pressure gradient and valve area were 5.9$\pm$2.5 mmHg, 3.1$\pm$0.8 mmHg and 2.9$\pm$0.5 $\textrm{cm}^2$, respectively. In the anticoagulant therapy, mean INR was 2.5$\pm$0.6 in mitral valve replacement and 1.9$\pm$0.5 in aortic valve replacement. There was no anticoagulant related complication. During that period, there were 3 hospital death(5.9%) and 1 late death(1.9%). Conclusion: The early clinical results of the ATS heart valve replacement is quite satisfactory, and low target INR reginmen is safe. And long term follow of hemodynamic characteristics is also necessary.

• Journal of Chest Surgery
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• v.30 no.3
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• pp.293-299
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• 1997

With the introduction of new cardiac prosthesis, it behooves surgeons and cardiologists to monitor its performance carefully. ATS (Advancing The Standard) prosthetic valve has been used first in Guro hospital in Korea, since August 1994. Between August 1994 and July 1995, 21 patients received 28 ATS prosthesis(9 aortic, 19 mitral).19mi1ra1 valves were implanted through the "Extended Transseptal Approach" 10 were ma e and 11 were female, ranging from 20 to 54 years of age(Mean age : 37 years). The follow up period 126 patient-months(mean 6.1 months), varied from 1 month to 12 months. NYHA functional class was improved significantly, from $2.9\pm0.7$ preoperatively to $1.4\pm0.5$ postoperatively. Ejection fraction was also improved from $55.5\pm6.1%$ preoperatively to 59.8 $\pm7.4%$ postoperatively. Lactic dehydrogenase(LDH) was used as an indicator of hemolysis. The value of LDH changed from 483.3 $\pm$ 162 lUlL preoperatively to $527\pm274$ lUff postoperatively with no clinical significailce. Valve related complications, such as thromboembolism, valve thrombosis, anticoagulant related hemorrhage and prosthetic valve endocarditis did not develop except one anticoagulant related intracranial hemorrhage. There were no mortalities. This experience encourages us to continue using the ATS prosthetic valve, and this study will help those patients who need to have their heart valves replaced. replaced.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.11
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• pp.2090-2097
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• 1992

In this paper, fluttering behavior of mechanical monloleaflet heart valve prosthesis was analyzed taking into consideration of the impact between the valve occluder and the stopper. The motion of valve occluder was modeled as a rotating system, and equations were derived by employing the moment equilibrium conditions. Lift force, drag force, gravity and buoyancy were considered as external forces acting on the valve occluder. The 4th order Runge-Kutta method was used to solve the equations. The results demonstrated that the occluder reaches steady eguilibrium position only after damped vibration. The mean damping ratio is in the range of 0.197-0.301. Fluttering frequency does not have any specific value, but varies as a function of time. It is in the range of 11-84Hz. Valve opening appears to be affected by the orientation of the valve relative to gravitational forces.

• Journal of Chest Surgery
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• v.16 no.1
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• pp.91-96
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• 1983

A study was carried out to observe the clinical progress and results after modified Blalock-Taussing shunts on II patients with cyanotic complex heart diseases unsuitable for corrective surgery. The operation was performed by interposing a vascular prosthesis [PTEE] between the left subclavian artery and the left pulmonary artery. Vascular prostheses larger than the diameter of left subclavian artery were selected. The results were as follows: 1. The postoperative courses in 10 patients were uneventful without any complications. One patient died of low cardiac output syndrome immediate postoperatively. 2. The average value of RBC count before operations was 751.2291.68 [xl00]/cubic mm. It was decreased to 588.11 90.45 [xl 0,000]/cubic mm. After the operation. 3. The average value of Hemoglobin before operations was 20.07 3.01 mg/dl. The value was decreased to 15.361.68mg/dl after the operation. 4. The value of Hematocrit before operations was 62.878.89%. The value was decreased to 49.6 5.84% 5. Patency after the shunt operations using PTFE was good for maximal 16 months follow-up period. 6. The physiological impairment like anoxic spells, degree of cyanosis and other clinical symptoms were markedly improved after the shunt operations. Although a longer follow-up seems to be necessary to assess the validity of these shunts, the early results were encouraging.

• The Journal of Korean Physical Therapy
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• v.11 no.2
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• pp.43-50
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• 1999

The purpose of this study was to evaluate the change of the energy consumption when loading to leg of the 60persons who don't have past history of cardiopulmonary and neuromuscular disease, To evaluate the change or energy consumption, heart rate was measured in sitting position for 5minute, during walking for 3minute at for 4.8km on treadmill, and during resting state after walking with 1Kg loading to right ankle, and the other 1Kg loading was added to left ankle and then heart rates were measured in the The results were as follow; 1. PCI value without loading to Ankle were significantly increased compared to 1Kg, and 2Kg. (p<0.05) 2. Female Subjects showed mon increased PCI value in without leading and 2Kg loading compared to male subjects. ( p<0.05) 3. When 1Kg ana 2Ka loading to ankle significantly differences were showed between them. (p<0.05) 4. In the case of 1Kg and 2Kg loading, the difference among age groups was observed and the significant difference among PCI, PCI 1kg, PCI 2kg was showed in the only group that is less than 30 years old. 5. In every PCI condition the difference among height groups was observed and the significant difference among PCI conditions was showed in the only group that is less than 165cm. 6. The difference among weight groups in each PCI condition was not observed, but the significant differences among PCI conditions was showed in every group except the group that h from 60kg to 69kg. These results showed that energy consumption was increased according to loading on the ankle during Sate so weight of orthosis or prosthesis met be considered when choosing them and during gait training with these ones.

• Journal of Chest Surgery
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• v.31 no.8
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• pp.781-786
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• 1998

Materials and methods: Between 1984 to 1994, 136 patients underwent primary and isolated aortic valve replacement with 79 Carbomedics and 57 St. Jude prostheses. Results: Age ranged from 16 to 67 year(mean : 44.5${\pm}$12.7 years). Statistically significant differences in preoperative clinical characteristics between two groups were not found. There was one early death in the St. Jude group and none in the Carbomedics group. Early prosthetic valve-related complications including death were not significantly different between the two groups(p value= 0.572). One hundred thirty five early survivors were followed for a total of 354.2 patient-years(mean=31.5${\pm}$16 months). In the CarboMedics group, actuarial survial rate at 5 years was 97.1${\pm}$1.9%, and in the St. Jude group, it was 95.9${\pm}$2.8%. In the CarboMedics group, actuarial free rate from all valve-related events at 5 years was 92.1${\pm}$3.1%, and in St. Jude group, it was 89.8${\pm}$5.0%. Conclusion: We conclude that early and late results after performing isolated aortic valve replacement with CarboMedics and St. Jude valve are not significantlly different.

• Journal of Chest Surgery
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• v.38 no.11 s.256
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• pp.746-760
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• 2005

Background: Following the implantation of heart valve prostheses, it is important to maintain therapeutic INR to reduce the risk of thromboembolism. The objectives of this study were to determine the causes of nontherapeutic INRs, and to identify the factors associated with nonadherences to warfarin therapy in Korean outpatients with prosthetic heart valves managed by a pharmacist-run anticoagulation service (ACS). Material and Method: A retrospective chart review was completed for all patients enrolled in the ACS at Seoul National University Hospital from March, 1997b to September, 2000. The data on 868 patients (5,304 visits) who were at least 6 months post-valve replacement were included. All possible causes of nontherapeutic INRs were documented for each patient visit. The association of covariates to noncompliance was investigated by univariate analysis. Result: The reasons for nontherapeutic INRs were identified as follows: inadequate dosage adjustment $(21\%)$, nonadherences to dosing regimen $(13\%)$, drug/herbal interactions $(12\%)$, changes in diet $(7\%)$, and indeterminate cause $(42\%)$. Younger age, shorter duration of ACS and longer duration of warfarin therapy were associated with nonadherence. Conclusion: In this study, nonadherence and interactions between diet and medications were found to be important factors influencing nontherapeutic INRs. Longer duration of enrollment in the ACS affected the adherence to warfarin therapy Positively whereas younger age and longer duration of warfarin therapy affected negatively.

• Journal of Chest Surgery
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• v.38 no.11 s.256
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• pp.761-772
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• 2005

Background: Following the implantation of heart valve prostheses, it is important to maintain therapeutic INR to reduce the risk of thromboembolism. The objective of this study was to suggest a practical dosing guideline for Korean outpatients with prosthetic heart valves managed by a pharmacist-run anticoagulation service (ACS). Material and Method: A retrospective chart review was completed for all patients enrolled in the ACS at Seoul National University Hospital from March, 1997 to September, 2000. Patients who were at least 6 months post-valve replacement and had nontherapeutic INR value (less than 2.0 or greater than 3.0) were included. The data on 688 patients (1,782 visits) requiring dosing adjustment without any known drug or food interaction with warfarin were analyzed. The amount of adjusted dose and INR changes based on the INR at the time of the event were calculated. Aortic valve replacements (AVR) patients and mitral or double valve replacement (MVR/DVR) patients were evaluated separately. Result: Two methods for the warfarin dosage adjustment were suggested: Guideline I (mg-based total weekly dose (TWD) adjustment), Guideline II (percentage-based TWD adjustment). The effectiveness of Guideline 1 was superior to Guideline II overall in patients with both AVR and MVR/DVR. Conclusion: The guideline suggested in this study could be useful when the dosage adjustment of wafarin is necessary in outpatients with mechanical heart valves.