혈류의 유동이 혈관-인조혈관 접속부 혈관 내막 세포증식에 미치는 영향

이계한 대한의용생체공학회 1994 의공학회지 Vol.15 No.2

Wall shear rate or stress is believed to be a major hemodynamic variable influencing atherosclerosis and artery-graft anastomic intimal hyperplasia. The purpose of this study is to verify the effects of radial wall motion, artery-graft compliance and diameter mismatch, and impedance phase angle on the wall shear rate distribution near an end-to-end artery-graft anastomosis model. The results show that radial wall motion of the elastic artery model lowers the mean wall shear rates under pulsatile flow condition by 15 to 20 % comparing to those under steady flow condition at the same mean flow rate. Impedance phase angle seems to have small effects on the mean and amplitude of the wall shear rate distribution. In order to study the effects of compliance and diameter mismatch on the wall shear rates, two models are studied-Model I has 6% and Model I has 6% and Model II has 11% smaller graft diameter. Divergent geometry caused by diameter mismatch near the distal sites reduces the mean wall shear rates significantly, and this low shear region is believed to be prone to intimal hyperplasia.

스텐트 삽입에 의한 방추형 동맥류 내부 유동의 변화

이계한,서남현 대한의용생체공학회 2001 의공학회지 Vol.22 No.6

스텐트를 이용한 동맥류 색전술은 방추형 동맥류 등 목이 넓은 광경동맥류의 치료에 최근 사용되고 있다. 동맥류 내부의 혈류유동은 혈전의 형성 및 동맥류 폐색에 중요한 역할을 하므로 스텐트의 삽입으로 인한 동맥류 내부 혈류 유동의 변화를 고찰하기 위하여 광색성 염료를 이용한 유동가시화 방법을 사용하였다. 제작된 방추형 동맥류 모델에 대해 맥동 유동시 동맥류 벽 다섯 위치에서 유동장의 정성적 관탈 및 벽 전단변형률의 측정이 수행되었다. 스텐트의 삽입은 동맥류 내부의 유동을 감소시켰으며 동맥류 내부의 느린 와류유동이 감속후기가지 지속되었다. 또한 스텐트가 삽입된 모델은 스텐트가 없는 모델에 비하여 벽 전단변형률이 감소하였으며. OSI는 증가하였다 이러한 혈류유동의 변화는 혈전의 형성 및 내막거식증대가 일어나기 쉬운 혈류역학적 환경을 제공한다. 따라서 스텐트의 삽입으로 인한 동맥류 내부의 혈류 유동은 혈전의 형성 및 동맥류 폐색을 촉진하도록 변화함을 알 수 있었다.. Endovascular embolization technique using a steno is currently used to treat the wide neck aneurysm. Since intraaneurysmal flow characteristics affect thrombus formation and embolisation process. flow visualization technique incorporating photochromic dye was used to elucidate hemodynamic changes by stenting Inside the fusiform aneurysm models. Qualitative observation of flow field and measurement of wall shear rates were Performed at five aneurysm wall locations under pulsatile flow. Intraaneurysmal flow motion was reduced and sluggish vortical motion was maintained during late deceleration phase by stenting. Also wall shear rates were reduced and OSI's were increased in the stented model. These flow characteristics Provide hemodynamic environment favorable for thrombus formation and intimal hyperplasia. The results of this study show hemodynamic changes by stenting Promote thrombus formation and aneurysm embolisation.

인공판막 후부 공동부가 판막의 수력학적 성능에 미치는 영향

이계한,서종천 대한의용생체공학회 1998 의공학회지 Vol.19 No.3

판막 후부의 공동부는 판막의 닫힘 거동과 판막 주위의 혈류 유동장을 변화시켜 인공 판막의 수력학적 성능에 영향을 미칠 수 있다. 계식 이엽 판막(SJMV), 폴리머 단엽 판막(MLPV), 폴리머 삼엽 판막(FTPV)을 판막 후부에 공동부가 있는 시험부와 공동부가 없는 직관형 시험부에 설치하여 모의 순환 장치에서 판막의 수력학적 성능을 평가하였다. 판막의 누수량은 공동부가 있는 시험부에서 약간 작았고, 수축기 평균 압력강하는 크게 나타났으나 통계적으로는 큰 차이가 없었다. 따라서 판막 후부의 공동부는 판막의 수력학적 성능에 큰 영향을 나타내지 않았다. 유량 파형의 해석 결과 판막 후부 공동부는 MLPV에서는 판막의 닫힘에 큰 영향을 주지 않았으나, SJMV에서는 판막의 닫힘이 일찍 시작하게 하였고 이 영향은 FTPV에서 더욱 크게 나타났다. FTPV는 공동부가 있는 시험부에서 역류 최대 유량이 감소하였으므로 판막 후두에 공동부는 판막의 급격한 닫힘에 의한 역류 제트의 발생을 감소시키리라 기대된다. The sinus distal to the prosthetic heart valve influences the valve closure behavior and velocity field near the valve, therefore affects the hydrodynamic performance of the prosthetic heart valve. In order to study the effects of valve distal geometry on the hydrodynamic performance of the prosthetic valves, mechanical bileaflet valve(SJMV), monoleaflet polymer valve(MLPV) and trileaflet polymer valve(FTPV) are inserted in the test sections which have the straight and the sinus shape distal to the valve. Leakage volumes and systolic mean pressure drops are measured in the pulsatile mock circulation flow loop. Leakage volumes are slightly less and systolic mean pressure drops are higher in the sinus test section comparing to those in the straight test section, but the differences are statistically insignificant. Flow waveforms are analyzed in order to predict the valve closure behavior. The distal sinus does not affect the closure of the MLPV, but early valve closure of SJMV is observed in the sinus test section. This effect is more significant in FTPV, and the reverse flow peak of FTPV is reduced in the sinus test section. Therefore the sinus distal to the valve can reduce the reverse flow jet caused by sudden valve closure.

입자영상유속계를 이용한 인공판막 후부의 유동장 측정 ( Measurement of Velocity Fields distal to the Prosthetic Heart Valves using Particle Image Velocitimeter )

이계한,서종천 대한기계학회 1998 대한기계학회 춘추학술대회 Vol.- No.-

Nonpoint Source Pollutants Removal by Multi-Species Riparian Forest Buffers

이계한 한국산림과학회 2004 한국산림과학회지 Vol.93 No.4

Riparian forest buffers reduce the transport of materials in surface runoff from uplands to streams. A series of field-plot studies was conducted to evaluate the ability of an established multi-species riparian forest buffer to remove sediment, nitrogen, and phosphorus from cropland runoff. The first rainfall and runoff simulation was to compare the effectiveness of 6m and 3m wide buffers of switchgrass(Panicum virgatum) and cool-season filter strips consisting of bromegrass(Bromus inermis), timothy(Phleum pratense) and fescue(Festuca spp.). Differences between 6m and 3m buffers were significant(P<0.05) for sediment and nutrient removal. Switchgrass buffers removed significantly more total-N, NO3-N, total-P and PO4-P than cool-season grass buffers(P<0.05). The second rainfall simulation study was to compare treatment plots with a 4.1 by 22.1m bare cropland source area paired with either no buffer, a 7.1m wide switchgrass buffer, or a 16.3m wide switchgrass/woody buffer located at the lower end of each plot. The switchgrass buffer removed 70% of the incoming sediment, while the switchgrass/woody plant buffer removed over 94%. The switchgrass buffer was effective in trapping sediment and sediment-bound nutrients. An additional buffer width with high infiltration capacity provided by the deep-rooted woody plant zone was effective in trapping soluble nutrients.

탄성을 가진 확장형 인조혈관 문합부 내부 유동 특성에 관한 연구 ( A Study on the Flow Characteristics in Elastic Divergent Graft Anastomosis Model )

이계한,이상만 대한기계학회 1997 대한기계학회 춘추학술대회 Vol.- No.-

코일 위치에 따른 측방 동맥류 내부 혈류 유동의 변화

이계한,송계웅,변홍식 대한의용생체공학회 2002 의공학회지 Vol.23 No.5

Aneurysm embolisation method using coils have been widely used. Micro coils are introduced via a small catheter, and are packed inside of aneurysm sac, which induces intraaneurysmal flow stagnation and thrombus formation. When partial blocking of an aneurysm is inevitable, the location of coils is important since it changes the flow patterns inside the aneurysm, which affect the embolisation process. We measured the flow field inside the partially blocked lateral aneurysm models in vitro, and tried to suggest the effective locations of coils for aneurysm embolisation. Velocity fields are measured using a particle image velocitimeter for different coil locations- proximal neck, distal neck, proximal dome and distal dome. Flow into the aneurysm sac was significantly reduced in the distally blocked models, and coils at distal neck blocked inflow more effectively comparing to those at distal dome. This study suggests that distal neck should be the most effective location for aneurysm embolisation. 코일을 이용한 동맥류 색전술은 동맥류 내부에 코일을 삽입하여 혈류 유동의 정체를 유도하여 혈전을 형성시키므로 동맥류를 폐색하는 방법이다. 코일을 이용하여 동맥류를 부분 폐색할 경우 동맥류의 폐색 위치에 따라 동맥류 내부의 유동 특성이 변하며, 이는 동맥류 내부의 현전 형성에 영향을 미칠 수 있다. 본 연구에서는 내경 동맥에서 발생한 측방 동맥류에 코일로 인한 부분 폐색이 발생할 경우, 부분 폐색 위치 및 내경 동맥의 곡률 반경의 변화에 따른 동맥류 내부 혈류 유동의 변화를 생체외 모델 실험을 이용하여 측정하여, 효율적인 동맥류 폐색 위치를 제시하고자한다. 내경동맥에서 발생한 측방 동맥류 내부에 코일을 동맥류 천정 근위부, 천정 원위부, 목 근위부 및 목 원위부에 각각 삽입하여 폐색 위치가 다른 모델을 제작하여, 입자영상속도계를 이용하여 속도장을 측정하였다. 동맥류 주머니의 원위부 폐색은 근위부 폐색에 비해 동맥류 내부고의 유입되는 유동이 적었으므로 동맥류 원위부 폐색이 혈전의 형성 및 동맥류 색전에 효율적임을 나타냈다. 동맥류 목 원위부 폐색은 천정 원위부 폐색에 비해 동맥류 내부로 혈류 유입을 효율적으로 차단하였으므로, 목 원위부 폐색이 동맥류 색전에 가장 효율적인 위치임을 알 수 있었다.

벽 탄성도가 확장관(인조혈관) 벽 전단변형률에 미치는 영향

이계한,이상만,Rhee, Kye-Han,Lee, Sang-Man 대한기계학회 1999 大韓機械學會論文集A Vol.23 No.6

Shear stress acting on the arterial wall by blood flow is an important hemodynamic factor influencing blocking of blood vessel by thickening of an arterial wall. In order to study the effects of wall elasticity on the wall shear rate distribution in an artery-divergent graft anastomosis, a rigid and a elastic model are manufactured. These models are placed in a pulsatile flow loop, which can generate the desired flow waveform. Flow visualization method using a photochromic dye is used to measure the wall shear rate distribution. The accuracy of measuring technique is verified by comparing the measured wall shear rate in the straight portion of a model with the theoretical solution. Measured wall shear rates depend on the wall elasticity and flow waveform. The mean and maximum shear rate in the elastic model are lower than those in rigid model, and the decreases are more significant near the end of a divergent tube. The reduction of mean and maximum of wall shear rate in an elastic model are up to 17 percent.

Soil Respiration and Microbial Biomass in Sycamore(Platanus occidentalis L.) Plantations Treated with Irrigation and Nitrogen Fertilization

이계한 한국산림과학회 2003 한국산림과학회지 Vol.92 No.5

입자영상속도계를 이용한 기저동맥류 내부 유동 측정

이계한,오지순 명지대학교 산업기술연구소 2001 産業技術硏究所論文集 Vol.20 No.-

Among the various factors influencing the formation of cerebral aneurysm, blood flow is believed to be one of the important factors. In order to study the blood flow characteristics in the basilar tip aneurysm, a three dimensional aneurysm model is constructed based on the CT image data of a patient. The flow fields in the aneurysm are measured using particl image velocitimeter(PIV) in the mock circulation loop which can generate physiological flow waveform. Blood jet impingement is observed near the apex of aneurysm, and high shear stresses are distributed near the neck of aneurysm. Therefore we suspect that blood jet impingement may affect on the aneurysm formation and high shear stresses near the neck of aneurysm may influence the growth of aneurysm.