• Journal of Chest Surgery
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• v.19 no.1
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• pp.92-100
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• 1986

Results of reoperation for tissue valve failure were presented with review of current knowledge. Through January 1986, 19 patients required reoperation: 18 had undergone mitral, 2 aortic, and 1 tricuspid valve. Primary tissue failure was the main cause of tissue valve failure: it occurred in 18 valves [15 mitral, 2 aortic, and 1 tricuspid] at a mean postoperative interval of 54-25 months [range 29-120]. During the same period, 2 patients required reoperation for prosthetic valve endocarditis, 1 for paravalvular leakage. The types of valves failed were 12 lonescu-Shiley valves, 5 Hancock valves, and 1 Carpentier-Edwards valve. All 6 patients younger than 15 years of age at first operation had been implanted with lonescu-Shiley valves and failed after a mean interval of 35 months. In contrast, 11 patients older than 15 years had been implanted with 5 Hancock, 6 lonescu-Shiley, and 1 Carpentier-Edwards valve initially, and eventually failed after mean intervals of 81, 53, 47 months each other. The kinds of valves used at reoperation were 8 lonescu-Shiley, 4 Bjork-Shiley, and 6 St. Jude Medical valves for primary tissue failure cases and 3 lonescu-Shiley valves for the other 3 cases. Overall mortality at reoperation was 10%: 5.6% for primary tissue failure, 50% for prosthetic valve endocarditis. In 15 cases [all mitral] primary tissue failure were caused by calcification associated with or without leaflet destruction or fibrous ingrowth, and in 2 cases [all aortic] caused by cusp perforation and tearing without any evidence of calcification. In conclusion: 1 primary tissue failure is the main cause of reoperation in patients with tissue valve failure; 2. the majority of the failed valves is in mitral position; 3. leaflet calcification is the leading pathology of primary tissue failure; 4, reoperation for tissue valve failure may be a major concern, although the mortality is low; 5. the limited durability of tissue valve suggests its use be restricted to selected cases.

• Journal of Chest Surgery
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• v.24 no.11
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• pp.1074-1080
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• 1991

A total and consecutive 62 patients between 13 and 58 years of age receiving biological prosthetic heart valves at the Korea University Hospital from January 1978 through October 1983 were analyzed. Out of 71 valves replaced, 64 were Carpentier-Edwards valves, 4 were Ionescu-Shiley valves, 2 were Angell-Shiley valves, 1 was Hancock valve. Early mortality within 30 days after operation was noted in 4 cases[6.4%]. There were no cases of valve-related early death. The 58 early survivors were followed-up for a total 387 patient-year over a period of 3 years to 12 years[Mean$\pm$S.D: 6.37$\pm$2.51 years] at the follow-up end of April 1991. During follow-up, seven patients died and late mortality rate was 12%. There were two major late complications: the one is thromboembolism[1.6% /patient-year], the other is primary tissue failure[2.76% /patient-year]. Ten patients underwent re-replacement of 13 tissue valves because of primary tissue failure[nine Carpentier-Edwards, two Ionescu-Shiley, two Angell-Shiley]. There was operative mortality. The probabilities of freedom from primary tissue failure were 95.4% and 75.3% at 5 and 10 years after operation respectively, The actuarial survival rates were 86.2% and 81.8% at 5 and 10 years after initial surgery respectively.

• Journal of Drive and Control
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• v.16 no.4
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• pp.38-47
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• 2019

In this paper, a real-time simulation model of an excavator using Amesim was proposed, considered the operation of functional valves with the main control valve (MCV). The hydraulic system models including the pump and MCV have been developed. The kinematic and dynamic models of the manipulator have also been developed, to confirm the behavior of the excavator. The MCV model includes various functional valves such as the regenerative valves, holding valves, swing and boom priority valves, and regen-cut valves so that simulations similar to real excavators can be performed. Additionally, to obtain the real-time calculation performance, the parts with no major influence on the dynamic behavior were simplified, high frequency factors were removed, and parameters were optimized. The models were compared with each other through the numerical analysis with variable time-step and fixed time-step, and the results were verified by comparison with the results of the actual vehicle tests.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.11
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• pp.109-112
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• 1997

The Hydrodynamic performance of the trileaflet polymer prosthetic valves depends on the design of the leaflet and the physical properties of the leaflet membrane. In order to study the effect of leaflet membrane elasticity on the hemodynamic performance of trileaflet prosthetic valve, leaflet membranes are manufactured using two different polymers - Biospan and Tecoflex SG-93A. The hemodynamic performance parameters are measured under steady and physiological pulsatile flow, and compared with monoleaflet polymer valve(floating valve) and bileaflet mechanical valve(St. Jude Medical valve). Well designed trileaflet valve shows the lowest mean pressure drop among the tested valves. The trileaflet valves with Biospan membrane show lower pressure drop and back low comparing to those with Tecoflex membrane. More elastic membrane may provide wide opening area during systole and close membrane ree edge contact during diastole. Durability of trileaflet valves are also tested in vitro. Trileaflet valves with non-uniform membrane thickness ail within 17 days because of stress concentration. Trileaflet polymer valves with uniform membrane thickness perform well over 55 days without failure.

• Proceedings of the KOSOMBE Conference
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• v.1998 no.11
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• pp.227-228
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• 1998

Lumbrokinase, potent fibrinolytic enzyme purified from earthworm, was immobilized onto polyurethane valves using photoreaction, photoreactive polyallyl-amino as a photoreactive linker. For evaluation of blood compatibility, lumbrokinase immobilized polymer valves were assembled into the total artificial heart (TAH). This TAH was implanted to 60kg healthy lamb for 1-3 days with the cardiac output 5 L/min. In the control lamb, the valves were untreated, in ore other, only valves on the right were treated, and in the remaining animal, only those on the left. To facilitate the thrombus formation, low doses of heparin were administered. For evaluation of the immobilized lumbrokinase, thrombus formation, proteolytic and fibrinolytic activity was measured. This data shows that lumbrokinase-treated polyurethane valves lead to decreased thrombus formation in vivo, and that their biocompatibility is therefore higher than that of untreated valves.

• Journal of Chest Surgery
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• v.26 no.1
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• pp.24-31
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• 1993

The long term clinical results following valve replacement with Hancock and Carpentier-Edwards bioprostheses were compared between tow valve models and between tow groups totaling 249 patients who were discharged after valve replacement from 1976 to 1986. The two groups of patients were treated with nonrandomized fashion. Follow-up was 87% complete. Cummulative duration of follow-up was 1909 patient-years, with maximum follow-up duration of 15 years. The actuarial survival for 122 patients with Hancock valves was 95.2%[\ulcornerstandard deviation] and 84.4% after 5 and 10 years of follow-up, respectively. Comparable figures for 127 patients undergoing valve replacement with Carpentier-Edwards valves were 87.3% and 76.4%, respectively[p=NS]. The probability of freedom from structural valve deterioration after 5 and 10 years of follow-up was 97.2% and 60.6%, respectively, with Hancock valves and 97.2% and 55.7%, respectively, with Carpentier-Edwards valves[p=NS]. Considering all 249 patients, multivariate [Cox model] regression revealed that ejection fraction was only significant predictor of structural valve deterioration. The probability of freedom from thromboembolism after 5 and 10 years of follow-up was 91.3% and 86.4%, respectively, with Hancock valves and 94.2% and 82.5%, respectively, with Carpentier-Edwards valves[p=NS]. Hence more strict control of anticoagulation should be done on patients with left atrial factors. In summary, there were no significant differences in actuarial survival rate and major valve related complications between tow valve models. These results suggests that its use should be confined to older patients or patients with a contraindication of anticoagulation.

• The KSFM Journal of Fluid Machinery
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• v.10 no.5
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• pp.20-26
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• 2007

Some gate valves are susceptible to pressure locking and thermal binding which prevent the safety function. The safety related gate valves susceptible to pressure locking and thermal binding shall be identified and taken preventive actions to ensure the safety function. The identification of the gate valves susceptible to pressure locking and thermal binding needs the evaluation of system design, valve and piping arrangement, test requirements, and operating conditions. Application of preventive methods should consider the system safety function, applicability, effectiveness, interface with system design, and cost. The selection procedure of valves susceptible to pressure locking and thermal binding can be effectively used in industry including nuclear power plants. In order to prevent the pressure locking, the hole can be drilled through the one disc of upstream side or down stream and the external equalizing line can be installed from bonnet to downstream or upstream. The double disc parallel seat valve type can be used instead of flexible wedge gate valve to prevent the thermal binding. The identification of gate valves susceptible to pressure locking and thermal binding, and preventive actions will meet the regulatory requirements and enhance the availability and safety of plants.

• Journal of Chest Surgery
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• v.56 no.6
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• pp.435-444
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• 2023

Background: Edwards Intuity is recognized as a relatively contraindicated bioprosthesis for bicuspid aortic valve disease. This study compared the early echocardiographic and clinical outcomes of rapid-deployment aortic valve replacement for bicuspid versus tricuspid aortic valves. Methods: Of 278 patients who underwent rapid-deployment aortic valve replacement using Intuity at Seoul National University Hospital, 252 patients were enrolled after excluding those with pure aortic regurgitation, prosthetic valve failure, endocarditis, and quadricuspid valves. The bicuspid and tricuspid groups included 147 and 105 patients, respectively. Early outcomes and the incidence of paravalvular leak were compared between the groups. A subgroup analysis compared the outcomes for type 0 versus type 1 or 2 bicuspid valves. Results: The bicuspid group had more male and younger patients. Comorbidities, including diabetes mellitus, hypertension, chronic kidney disease, and coronary artery disease, were less prevalent in the bicuspid group. Early echocardiographic evaluations demonstrated that the incidence of ≥mild paravalvular leak did not differ significantly between the groups (5.5% vs. 1.0% in the bicuspid vs. tricuspid groups, p=0.09), and the early clinical outcomes were also comparable between the groups. In the subgroup analysis between type 0 and type 1 or 2 bicuspid valves, the incidence of mild or greater paravalvular leak (2.4% vs. 6.7% in type 0 vs. type 1 or 2, p=0.34) and clinical outcomes were comparable. Conclusion: Rapid-deployment aortic valve replacement for bicuspid aortic valves demonstrated comparable early echocardiographic and clinical outcomes to those for tricuspid aortic valves, and the outcomes were also satisfactory for type 0 bicuspid aortic valves.

• The KSFM Journal of Fluid Machinery
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• v.15 no.4
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• pp.12-18
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• 2012

This study was performed to found out the deviations for clamp-on type ultrasonic flowmeter installed in downstream of valves. It was selected three types of two-path flowmeter mainly used for K-water as test. Experiment carried out to confirmed characteristics of deviation depending on the sensor location, straight pipe length and maker for 1-path, 2-path and 4-path combined 2-path flowmeter. It was selected two kinds of valves with 100 % and 50 % opening, butterfly valves and gate valves, for flow disturbance factor. Finally, we suggested number of sensors by maker, straight pipe length and installed location of sensors satisfying the tolerance depending on the experiment results.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.6 no.2
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• pp.41-46
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• 2007

Butterfly valves are commonly used as control valves in applications where the pressure drops required of the valves relatively low. As the shutoff valve (on/off service) or throttling valves (for flow or pressure control), the higher order and the better precision of butterfly valves are required. The it's more and more essential to know the flow characteristic around the valve. Due to the fast progress of the flow visualization and numerical technique, it becomes possible to observe the flows around a valve and to estimate the performance of a valve. Researching these results did not gave only access to understand the process of the valve flows at different valve opening angles, but also was made to determine the accuracy of the employed method. Furthermore, the results of the three-dimensional analysis can be used in the design of butterfly valve in the industry.