• Journal of Chest Surgery
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• v.20 no.2
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• pp.223-229
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• 1987

Doppler echocardiography provides valuable information regarding prosthetic heart valve function rather than structure. There are three methods of expressing the severity of mitral valve obstruction: the transvalvular pressure gradient, effective valve area, and pressure half-time. Of these, the transvalvular pressure gradient [~p] can be determined by the measurement of maximum transvalvular blood flow velocity [V] according to the modified Bernoulli`s equation [gp=4V*]. Eleven patients, who underwent mitral valve replacement with Duromedics mechanical prostheses, and 17 normal persons were investigated. There were significantly higher calculated pressure gradients in prosthetic than normal mitral valves [9.*10*2.22mmHg-vs-3.26*0.99mmHg:p<0,01], and there was a inverse relationship between pressure gradient and prosthetic valve size [11.17*0.%mmHg in size 27mm and 29mm -v- 7.38*1.12mmHg in size 31mm and 33mm; r=0.85, p<0.01] The noninvasive Doppler technique should be useful in the diagnosis of prosthetic valve obstruction.

• Journal of Chest Surgery
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• v.33 no.2
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• pp.146-150
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• 2000

background: The prognosis after an aortic valve replacment can be affected significantly by the transprosthetic pressure gradient which is determined mainly by the size of the patients body and the prosthesis used. We analyzed the hemodynamic feature of two relatively new prosthese the ATS and the evensized Medtronic-Hall(M-H) valves by measuring the transprosthetic pressure gradient in the cases where small sizes (23mm or smaller) were used. Material and method: There were 94 patients who received whom aortic valve replacement with prosthesis smaller than 23 mm from October 1994 to June 1998. In these patients the transprosthetic pressure gradient clalculated from the pressure half time during postoperative Dopper echocardiographic examination was compared between the prostheses of different sizes. The body surface area of each patient was also taken into consideration. result: The mean pressure gradient and body surface area in each group were 21.7$\pm$10.2 mmHg and 1.52$\pm$0.14m2 in ATS 19mm 11.4$\pm$6.5 mmHg and 1,57$\pm$0.20m2 in M-H 20mm 15.2$\pm$6.3 mmHg and 1.54$\pm$0.13m2 in ATS 21mm 9.3$\pm$2.5 mmHg and 1.63 $\pm$0.14m2 in M-H 22 mm and 12.9$\pm$5.3 mmHg and 1.69$\pm$0.13m2 in ATS 23mm. Conclusion: The 19mm ATS prosthesis showed significant trasprosthetic pressure gradient which is similar to the values previously reported with other bileaflet prosthesesm Close follow-up was needed in terms of exercise capacity and change in left ventiricular geometry. In patients with small aortic valve annulus the 20mm M-H valve is recomendable as an alternative to 19mm bileaflet valves because it has less pressure gradient with similar outer diameter.

• Journal of Chest Surgery
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• v.20 no.3
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• pp.458-472
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• 1987

A heart supplies bloods of about 15, 000 liters to each human organ in a day. A normal function of heart valves is necessary to this act of heart. The disease of heart valve develops to a narrowness of a closure, resulting in an abnormal circulation of bloods. In an attempt to eliminate the affliction of heart valves, the operation method to repair with artificial heart valves has been developed and saved numerous patients over past 30 years. This replacement operation has been performed since early 1960`s in Korea, but all the artificial heart valves used are imported from abroad with very high costs until recent years. The artificial heart valve using pyrolytic carbon has been developed at KAIST, which was proved to be stable in the mechanical performance and durability. Therefore, the in viva performance of this valve was examined through animal tests. The artificial heart valves used in this study are tilting disc type valves, in which the disc were made of graphite coated with pyrolytic carbon and the cages were made of titanium. In viva testings of these valves were performed in 12 dogs, in which right ventriculo-pulmonary arterial [Croup I] or inter-aortic [Croup IV] valved conduit was implanted using polytetrafluoroethylene conduits containing KAIST valve and aortic valve [Group II] or pulmonary valve [Croup III] was replaced by a KAIST valve with a 21mm or 19mm tissue annulus diameter. In group I and II, pre-and post-operative transvalvular pressure gradient was measured and compared with other prosthetic valves. During post operative period laboratory examination was performed including hemoglobin, hematocrit, red cell count, white cell, lactic acid dehydrogenase and platelet. The eight surviving dogs were sacrificed and autopsy was performed at 2, 6, and 8 weeks. KAIST valve has low transvalvular gradient and relatively high orifice area. Average ventriculo-aortic peak systolic transvalvular gradient was 14 mmHg in 21 mm valve and 19 mmHg in 19 mm valve. The valve has slight intravascular hemolysis effect. Thrombogenic effect of low polishing quality and eddy currents around small orifice is high. The valve has vulnerability of disc movement. These animal tests suggest that the improvement of the heart valve design, surface polishing state and prescription methods.

• Journal of Chest Surgery
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• v.21 no.4
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• pp.727-733
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• 1988

Two cases of the discrete membranous subaortic stenosis were experienced at the Department of Thoracic & Cardiovascular Surgery, National Medical Center, Seoul, Korea. Case I was 31 years old male with a history of aortic valve replacement[Ionescu-Shiley, 19mm] at the other hospital in 1980. Heart failure was noticed 6 years later. On cardiac catheterization, pressure gradient between left ventricle 4 aorta was 104 mmHg, but subvalvular aortic stenosis was not detected by preoperative 2-D echo <% left ventriculogram. Above case revealed stenoinsufficiency of the prosthetic valve. Under the diagnosis of the prosthetic valve failure, re-do aortic valve replacement[Bjork-Shiley, 23 mm] was done. During operation, the discrete membranous subaortic stenosis was incidentally found, and it was completely resected. So we thought that above discrete membranous subaortic stenosis was not detected at first operation, and it was progressed during 6 years, and accelerated the degeneration of the prosthetic valve. Case II was 20 years old female. Her complaints were exertional dyspnea, angina, syncope, which were aggravated since 5 years ago. 2-D echo <% left ventriculogram revealed the discrete membranous subaortic stenosis. Pressure gradient was 20 mmHg, but her symptoms were serious. Associated cardiac anomaly was the persistent left superior vena cava without connection with right superior vena cava. Complete excision of the membranous tissue was done. Post-operative pressure gradient between left ventricle & aorta was absent, and her complaints were nearly subsided. Both cases were type I according to the Newfeld classification of the discrete subvalvular aortic stenosis, and complete excision of the membranous tissue was done without myotomy or mymectomy. And short-term follow-up results[Case I:2 years, Case II: 1 ~ years] were good except soft systolic murmur[grade II/VI] at the aortic area in both cases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.238-244
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• 2002

A 5-valve(intake 3-valve) engine has been developed to increase engine performance. These engines have a high power caused by the decrease of inertia mass of an intake valve and the increase of intake effective area. In this study, in-cylinder flow patterns were visualized with laser sheet method and velocity profiles at near intake valves were inspected by using a two-color PIV. In addition, steady flow tests were performed to quantify tumble ratio of flow-fields generated by a tumble control valve(TCV). Experimental results of steady flow test show that the cure of tumble ratio in intake 3-valve engine farmed as a S shape with valve lift changes. This tendency is different from the one in intake 2-valve engine. Using laser sheet method and two color PIV method, we can find that the intake flow through upper valve increases and the velocity gradient also slightly increases as valve lift increases. From this study, the in-cylinder flow characteristics around intake valves were made clearly.

• Journal of Chest Surgery
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• v.12 no.4
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• pp.350-354
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• 1979

The incidence of congenital aortic valvular stenosis has been known rare, and approximately 3-6% of congenital heart diseases. Recently, we experienced 1 case of congenital aortic valvular stenosis, and which was corrected surgically under extracorporeal circulation successfully. A 11 years old male pt. was admitted to N.M.C. because of dyspnea, dizziness, chest pain and episode of syncope. An auscultation, harsh systolic murmur [Gr. IV/VI] was noted at aortic area and also palpable strong thrill. ECG showed LVH c strain pattern and suspicious LVH finding in simple chest P-A film. In Lt. cardiac catheterization, abrupt pressure change [110mmHg] between LV & Aorta was noted across the aortic valve. And aortic insufficiency was absent, well visualized both coronary arteries and suspicious bicuspid aortic valve in aortography. Valve form was bicuspid, large one was noncoronary cusp and another cusp was Rt. & Lt. coronary cusp which was interpositioned rudimentary commissure. Central aortic orifice was about 5ram in diameter. Valvulotomy was done along the fusioned commissure between noncoronary cusp and Rt. & Lt.coronary cusp, and then short incision was added between Rt. coronary cusp & Lt. coronary cusp. Immediate postoperative course smooth but unknown cardiac arrest was noted in POD second day. Complete recovery was done without sequelae by resuscitation. After operation, clinical symptoms were subsided but systolic murmur [Gr. II/VI] was audible at aortic area, diastolic murmur was absent. ECG showed still remained LVH but much decreased R wave voltage in Lt. precordial leads. Simple chest P-A showed no interval changes compared to preop film. Control Lt. heart catheterization revealed still remained pressure gradient [40ramrig] between LV & Aorta. But much decreased pressure gradient compared to preop pressure gradient [110mmHg].

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.171-176
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• 2008

Active suspension controls stiffness and damping between unsprung mass and sprung mass in order to increase the ride quality. However, to increase the riding quality, the handling quality should be decreased and the rattle space should be increased. So, active suspension should cope with these conflict conditions. Therefore its actuating devices have to produce sufficient actuating force and have sufficiently short response time. In this paper, the dynamic characteristics of 1/4 car model with an active suspension is studied according to hydraulic design variables. The active suspension consists of a hydraulic servo valve and a hydraulic cylinder. It shows better performance when it has more powerful and faster actuator.

• Journal of Chest Surgery
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• v.48 no.5
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• pp.328-334
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• 2015

Background: There have been a number of studies on mitral valve replacement and repeated percutaneous mitral balloon valvotomy for mitral valve restenosis after percutaneous mitral balloon valvotomy. However, studies on mitral valve repair for these patients are rare. In this study, we analyzed postoperative outcomes of mitral valve repair for mitral valve restenosis after percutaneous mitral balloon valvotomy. Methods: In this study, we assessed 15 patients (mean age, $47.7{\pm}9.7years$; 11 female and 4 male) who underwent mitral valve repair between August 2008 and March 2013 for symptomatic mitral valve restenosis after percutaneous mitral balloon valvotomy. The mean interval between the initial percutaneous mitral balloon valvotomy and the mitral valve repair was $13.5{\pm}7years$. The mean preoperative Wilkins score was $9.4{\pm}2.6$. Results: The mean mitral valve area obtained using planimetry increased from $1.16{\pm}0.16cm^2$ to $1.62{\pm}0.34cm^2$ (p=0.0001). The mean pressure half time obtained using Doppler ultrasound decreased from $202.4{\pm}58.6ms$ to $152{\pm}50.2ms$ (p=0.0001). The mean pressure gradient obtained using Doppler ultrasound decreased from $9.4{\pm}4.0mmHg$ to $5.8{\pm}1.5mmHg$ (p=0.0021). There were no early or late deaths. Thromboembolic events or infective endocarditis did not occur. Reoperations such as mitral valve repair or mitral valve replacement were not performed during the follow-up period ($39{\pm}16months$). The 5-year event-free survival was 56.16% (95% confidence interval, 47.467-64.866). Conclusion: On the basis of these results, we could not conclude that mitral valve repair could be an alternative for patients with mitral valve restenosis after percutaneous balloon mitral valvotomy. However, some patients presented with results similar to those of mitral valve replacement. Further studies including more patients with long-term follow-up are necessary to determine the possibility of this application of mitral valve repair.

• Journal of Chest Surgery
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• v.29 no.7
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• pp.780-784
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• 1996

The localized form of subaortic stenosis shows a spectrum of pathological lesions varing from dis- crete membrane to a thickened flbromuscular collar. Aortic valve is commonly involved late in the pro- cess resulting in regurgitation. Because of the likelihood o the progressive obstruction and aortic regurgitation, early elective oper- ation should be considered for the patient with subaortic stenosis. We experienced a case of localized fibromuscular subaortic stenosis associated with aortic regurgi- tation. Excision of the fibromuscular ridge and septal myectomy-myotomy relieved the subaortic seen- osis. Regurgitant aortic valve was repaired by peeling away the Hbrotic tissue on the cusps and subcommissural annuloplasty at the each commissural area. On postoperative echocardiographic examination, the systolic pressure gradient between left ventricle and aorta decreased markedly and the aortic regurgitation was not detected at all.

• 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.