• 한국전산유체공학회지
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• 제13권3호
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• pp.44-50
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• 2008

The present study is carried out in order to investigate the effect of the periodic acceleration in the stenosed and bifurcated blood vessels. The blood flow and wall shear stress are changed under body movement or acceleration variation. Numerical studies are performed for various periodic acceleration phase angles, bifurcation angles and section area ratios of inlet and outlet. It is found that blood flow and wall shear stress are changed about ${\pm}20%$ and ${\pm}24%$ as acceleration phase angle variation with the same periodic frequency. also wall shear stress and blood flow rate are decreased as bifurcation angle increased.

• Journal of Chest Surgery
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• 제39권5호
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• pp.354-358
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• 2006

배경: 체외순환에 사용되는 박동성 펌프는 비박동성 펌프에 비해 조직관류가 좋지만 혈구손상이 많다고 알려져 왔다. 관상동맥우회술 시 박동성 펌프인 $T-PLS^{TM}$(이중 박동성 인공심폐기)와 비박동성 펌프인 $Bio-pump^{TM}$의 임상결과를 비교하여 $T-PLS^{TM}$의 안전성 및 장단점을 알아보고자 하였다. 대상 및 방법: 2003년 4월부터 2005년 6월까지 관상동맥우회술을 시행 받은 40명을 대상으로 하였다. $T-PLS^{TM}$을 이용하여 관상동맥 우회술을 시행 받은 환자는 20명이었고 $Bio-pump^{TM}$을 이용하여 관상동맥우회술을 시행 받은 환자는 20명이었다. 수술은 모든 환자에서 심폐체외순환하에서 박동하여 시행하였다. 수술 전 위험인자와 수술 중 상태, 술 후 결과를 비교하였다. 결과: 두 군 간 연령, 남녀비, 당뇨, 고혈압, 흡연력 및 폐쇄성 폐질환, 심근경색, 신부전 등 술 전 위험요소는 차이가 없었다. 수술시간, 심폐기 사용시간, 사용한 우회도관 및 문합한 관상동맥분지는 두 군에서 차이가 없었다. 수술 중 수축기 동맥압, 이완기 동맥압, 평균동맥압은 두 군 간 차이는 없었지만 맥박압은 $T-PLS^{TM}$군에서 높게 측정되었다$(46{\pm}15\;mmHg\;in\;T-PLS^{TM}\;vs\;35{\pm}13\;mmHg\;in\;Bio-pump^{TM},\;p<0.05)$. 수술 중 소변량은 $T-PLS^{TM}$군에서 높은 경향이 있었지만 통계적 의미는 없었다$(9.7{\pm}3.9\;in\;T-PLS^{TM}\;versus\;8.9{\pm}3.6\;in\;Bio-pump^{TM},\;p=0.20)$. 수술 후 평균 호흡기 사용시간, 24시간 실혈량은 두 군간 차이는 없었다. 수술 후 유리혈장색소는 $T-PLS^{TM}$군에서 유의하게 낮게 측정되었다$(24.5{\pm}21.7\;mg/dL\;in\;T-PLS^{TM}\;vs\;46.8{\pm}23.0\;in\;Bio-pump^{TM},\;p<0.05)$. 수술 후 심근경색, 부정맥, 신부전, 뇌혈관질환 이환율은 두 군에서 차이가 없었다. 수술 후 사망은 $T-PLS^{TM}$군에서 1예(5%) 발생하였으나 통계적 유의성은 없었다. 결론: 박동성 혈류펌프인 $T-PLS^{TM}$를 이용하여 심폐기하 관상동맥 우회술을 시행하였다. 수술 중 기계오류에 의한 사고는 없었고 수술 후 임상경과가 $Bio-pump^{TM}$를 이용하여 수술한 경우와 차이가 없었다. 또한 박동성 혈류의 문제점이었던 혈구손상은 감소하였다. 저자들은 본 연구를 통해 $T-PLS^{TM}$의 안정성을 확인하였다.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1992년도 춘계학술대회
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• pp.92-97
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• 1992

The pulsatile nature of blood flow makes artefacts in 2D Fourier transform image. Spatial presaturation is known to be effective in eliminating flow artefacts when the spin echo acquisition is employed. However. this method requires additional RF pulse and spoiling gradient for presaturation. In this paper a new flow saturation technique which does not require additional saturation-RF and gradient is proposed. The proposed technique is equivalent to the existing saturation technique but the elimination of the flow component is achieved by a pair of tailored $90^{\circ}-180^{\circ}$ RF pulses in tile spin echo sequence. By use of two tailored RF pulses with opposite phase polarity, a linear phase gradient is generated for those moving materials and consequently all the spins of moving materials become dephased thereby no signal is observable. Computer simulations and experimental results obtained using both a phantom and a human volunteer with a 2.0 T whole body system are also presented.

• 한국가시화정보학회지
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• 제3권1호
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• pp.26-35
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• 2005

The combination of ultrasound echo images with digital particle image velocimetry (DPIV) method has resulted in a two-dimensional, two-component velocity field measurement technique appropriate for opaque flow conditions including blood flow in clinical applications. Advanced PIV processing algorithms including an iterative scheme and window of offsetting were used to increase spatial resolution. The optimum concentration of the ultrasound contrast agent used for seeding was explored. Velocity validation tests in fully developed laminar pipe flow and pulsatile flow showed good agreement with both optical PIV measurements and the known analytic solution. These studies indicate that echo PIV is a promising technique for the non-invasive measurement of velocity profiles and shear stress.

• 대한기계학회논문집B
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• 제29권1호
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• pp.63-70
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• 2005

The main objective of the present study is to predict characteristics of three dimensional pulstitile flow by location of stenosis in blood vessel with the second order bifurcation. The present study simulates the incompressible non-Newtonian laminar blood flows using a Fluent V. 6.0. The Carreau model is employed as the constitutive equation for blood. The numerical simulation carried out at five cases without and with symmetry or asymmetry stenosis. It is found that the no stenosis and stenosis before first bifurcation do not have influence on flow at second bifurcated blood vessel. However, the stenosis after first biburcation has effect on flow at second bifurcated blood vessel.

• 대한기계학회논문집A
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• 제30권12호
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• pp.1588-1595
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• 2006

The stabilities of a pinned-pinned straight pipe conveying fluid are investigated by complexification-averaging method. The flow is assumed to vary harmonically about a constant mean velocity. Instability conditions of a governing equation are analytically obtained about parametric primary, secondary and combination resonances. The resulted stability conditions show that instabilities exist when the frequency of flow fluctuation is close to one and two times the natural frequency or to the sum of any two natural frequencies. In case that the fluctuated flow frequency is close to the difference of two natural frequencies, instabilities does not exist.

• International Journal of Vascular Biomedical Engineering
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• 제3권2호
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• pp.1-9
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• 2005

Flow-induced dilation of blood vessel is the result of a series of bioreaction in vascular endothelial cells(VEC). Shear stress change by blood flow in human artery or vein is sensed by the mechanoreceptor and responsible for such a chain reaction. The inositol(1,4,5)-triphophate($IP_3$) is produced in the first stage to elevate permeability of the intercellular membrane to calcium ions by which the cytosolic calcium concentration is consequently increased. This intracellular calcium transient triggers synthesis of EDRF and prostacyclin. The mathematical model of this VEC calcium dynamics is reproduced from the literature. We then use the Computational Fluid Dynamics(CFD) technique to investigate the blood stream dictating the VEC calcium dynamics. The pulsatile blood flow in a stenosed blood vessel is considered here as a part of study on thrombogenesis. We calculate the pulsating shear stress (thus its temporal change) distributed over the stenosed artery that is implemented to the VEC calcium dynamics model. It has been found that the pulsatile shear stress induces larger intracellular $Ca^{2+}$ transient plus much higher amount of EDRF and prostacyclin release in comparison with the steady shear stress case. It is concluded that pulsatility of the physiological shear stress is important to keep the vasodilation function in the stenosed part of the blood vessel.

• Journal of Chest Surgery
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• 제54권2호
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• pp.81-87
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• 2021

Background: Artificial grafts such as polyethylene terephthalate (Dacron) and expanded polytetrafluoroethylene (ePTFE) are used for various cardiovascular surgical procedures. The compliance properties of prosthetic grafts could affect hemodynamic energy, which can be measured using the energy-equivalent pressure (EEP) and surplus hemodynamic energy (SHE). We investigated changes in the hemodynamic energy of prosthetic grafts. Methods: In a simulation test, the changes in EEP for these grafts were estimated using COMSOL MULTIPHYSICS. The Young modulus, Poisson ratio, and density were used to analyze the grafts' material properties, and pre- and post-graft EEP values were obtained by computing the product of the pressure and velocity. In an in vivo study, Dacron and ePTFE grafts were anastomosed in an end-to-side fashion on the descending thoracic aorta of swine. The pulsatile pump flow was fixed at 2 L/min. Real-time flow and pressure were measured at the distal part of each graft, while clamping the other graft and the descending thoracic aorta. EEP and SHE were calculated and compared. Results: In the simulation test, the mean arterial pressure decreased by 39% for all simulations. EEP decreased by 42% for both grafts, and by around 55% for the native blood vessels after grafting. The in vivo test showed no significant difference between both grafts in terms of EEP and SHE. Conclusion: The post-graft hemodynamic energy was not different between the Dacron and ePTFE grafts. Artificial grafts are less compliant than native blood vessels; however, they can deliver pulsatile blood flow and hemodynamic energy without any significant energy loss.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 추계 학술대회논문집
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• pp.203-206
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• 2004

In this study, 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 terms of fluid-structure interaction. Here, blood has been assumed as a Newtonian, incompressible fluid. Pressure profiles have been used as boundary conditions at the ventricle and the aorta. From this analysis, the motion of the leaflet has been observed with fluttering phenomenon and rebound, and the flow fields of blood have been obtained with recirculation and regurgitation. The results can contribute to the development of design methodology for the curved bileaflet mechanical heart valve.

• International Journal of Precision Engineering and Manufacturing
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• 제4권4호
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• pp.5-12
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• 2003

This paper discusses about the thickness effects on the structural durability of a bileaflet mechanical heart valve (MHV). In the study on the design and the mechanical characteristics of a bileaflet mechanical heart valve, the fluid mechanics analysis on the blood flow passing through leaflets, the kinetodynamics analysis on the rigid body motion of the leaflet induced by the pulsatile blood flow, and the structural mechanics analysis for the deformed leaflet are required sequentially and simultaneously. Fluid forces computed in the fluid mechanics analysis on the blood flow are used in the kinetodynamics analysis for the leaflet motion. Thereafter, the structural mechanics analysis for the deformed leaflet follows to predict the structural strength variation of the leaflet as the leaflet thickness changes. Analysis results show that structural deformations and stresses increase as the fluid pressure increases and the leaflet thickness decreases. Analysis results also show that the leaflet becomes structurally weaker and weaker as the leaflet becomes thinner and thinner.