• Korea-Australia Rheology Journal
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• 제16권2호
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• pp.101-108
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• 2004

The hemodynamics behavior of the blood flow is influenced by the presence of the arterial stenosis. If the stenosis is present in an artery, normal blood flow is disturbed. In the present study, the characteristics of pulsatile flow in the blood vessel with stenosis are investigated by the finite volume method. For the validation of numerical model, the computation results are compared with the experimental ones of Ojha et al. in the case of 45％ stenosis with a trapezoidal profile. Comparisons between the measured and the computed velocity profiles are favorable to our solutions. Finally, the effects of stenosis severity and wall shear stress are discussed in the present computational analysis. It can be seen, where the non-dimensional peak velocity is displayed for all the stenosis models at a given severity of stenosis, that it is exponentially increased. Although the stenosis and the boundary conditions are all symmetric, the asymmetric flow can be detected in the more than 57％ stenosis. The instability by a three-dimensional symmetry-breaking leads to the asymmetric separation and the intense swirling motion downstream of the stenosis.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.10-12
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• 2008

Hemodynamic features of blood flow in the abdominal aorta aneurysm (AAA) are very important, because they are closely related with the rupture of aneurysm to death. It has been considered that the wall shear stress of blood flows influences the formation, growth, and rupture of AAA. On this account, it is important to understand the flow structure of blood in the aneurysm. In this study, the whole velocity field information inside a typical AAA was measured using an in vitro AAA model under the pulsatile flow condition. The vessel geometry was reconstructed based on the computerized tomography (CT) data of a patient. The AAA model was made by using a rapid prototyping (RP) method, based on the reconstructed vessel geometry. Velocity fields in the AAA model were measured at different pulsatile phases using a PIV (particle image velocimetry) system. As experimental results, a large-scale vortex is formed inside the AAA model and the vortices located near the AAA wall are supposed to increase the local pressure and wall shear stress. In this study, the AAA wall stress found to be was one of the most important governing parameters giving rise to the ruptured aneurysm.

• Transactions on Electrical and Electronic Materials
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• 제9권5호
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• pp.213-219
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• 2008

Pulse waves continuously change with respect to the characteristics and status of the cardiovascular system and in relation to the blood pressure (BP) and the pulse wave velocity (PWV). Monitoring the vascular condition by analyzing the variations in pulse waveforms has been used to diagnose vascular disorders and in drug treatment of arteriosclerosis and peripheral circulatory obstruction. In this paper, we investigated the vascular characteristic index with regard to the BP and classified by pulse wave signals. The pressure pulse wave and photoplethysmography (PPG) were measured simultaneously while subjects exercised, producing changes in the BP, to analyze the variation in the vascular characteristic index. We investigated the correlation between the BP and vascular characteristic index with regard to the classification methods of the pulse wave. The reflection index (RI) and vascular stiffness index were correlated with the diastolic BP, but no correlation was found between these parameters and the systolic BP. These results suggest the possibility of estimating BP through simple measurements of pulse waves.

• 대한기계학회논문집B
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• 제35권7호
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• pp.685-691
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• 2011

본 연구는 도플러 광 단층촬영법이 미세유동 및 미세구조를 동시에 측정하는 첨단 장비임을 보일뿐 아니라 기존의 도플러 광 단층촬영법의 한계를 극복한 새로운 방법을 제시하였다. 기존의 도플러 광단층촬영법은 샘플로 입사되는 광과 같은 방향의 속도성분만을 측정할 수 있다. 본 연구에서는 임의의 속도벡터의 세 성분을 동시에 측정할 수 있는 다관점 도플러 광 단층촬영법을 개발하였고 심전도 게이트를 사용하여 맥동혈류유동의 3 차원 공간 내에서 위상속도 벡터장을 측정하는 심전도 게이트 다관점 도플러 광 단층촬영법의 타당성 조사를 햄스터 모래주머니 모델을 사용하여 수행하였다. 이를 통해 측정 가능한 속도성분의 수를 증가할 뿐 아니라 프레임 레이트가 심박에 비해 상대적으로 느리기 때문에 발생하는 엘리아싱 문제를 해결하였다.

• 대한의용생체공학회:의공학회지
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• 제19권2호
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• pp.143-152
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• 1998

In this paper, we present the performances of a Doppler system using single channel RF(Radio Frequency) sampling. This technique consists of undersampling the ultrasonic blood backscattered RF signal on a single channel. Conventional undersampling method in Doppler imaging system have to use a minimum of two identical parallel demodulation channels to reconstruct the multigate analytic Doppler signal. However, this system suffers from hardware complexity and problem of unbalance(gain and phase) between the channels. In order to reduce these problems, we have realized a multigate pulsed Doppler system using undersampling on a single channel, It requires sampling frequency at $4f_o$(where $f_o$ is the center frequency of the transducer) and 12bits A/D converter. The proposed " single-Channel RF Sampling" method aims to decrease the required sampling frequency proportionally to $4f_o$/(2k+1). To show the influence of the factor k on the measurements, we have compared the velocity profiles obtained in vitro and in vivo for different intersequence delays time (k=0 to 10). We have used a 4MHz center frequency transducer and a Phantom Doppler system with a laminar stationary flow. The axial and volumetric velocity profiles in the vessel have been computed according to factor k and have been compared. The influence of the angle between the ultrasonic beam and the flow axis direction, and the fluid viscosity on the velocity profiles obtained for different values of k factor is presented. For experiment in vivo on the carotid, we have used a data acquisition system with a sampling frequency of 20MHz and a dynamic range of 12bits. We have compared the axial velocity profiles in systole and diastole phase obtained for single channel RF sampling factor.ng factor.

• Journal of Korean Neurosurgical Society
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• 제54권3호
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• pp.159-163
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• 2013

Objective : Cerebral hyperperfusion syndrome (CHS) is a serious complication after carotid endarterectomy (CEA). However, the prevalence of CHS has decreased as techniques have improved. This study evaluates the role of strict blood pressure (BP) control for the prevention of CHS. Methods : All 18 patients who received CEA from February 2009 through November 2012 were retrospectively reviewed. All patients were routinely managed in an intensive care unit by a same protocol. The cerebral perfusion state was evaluated on the basis of the regional cerebral blood flow (rCBF) study by perfusion computed tomography (pCT) and mean velocity by transcranial doppler (TCD). BP was strictly controlled (<140/90 mm Hg) for 7 days. When either post-CEA hyperperfusion (>100% increase in the rCBF by pCT or in the mean velocity by TCD compared with preoperative values) or CHS was detected, BP was maintained below 120/80 mm Hg. Results : TCD and pCT data on the patients were analyzed. Ipsilateral rCBF was significantly increased after CEA in the pCT (p=0.049). Post-CEA hyperperfusion was observed in 3 patients (18.7%) in the pCT and 2 patients (12.5%) in the TCD study. No patients developed clinical CHS for one month after CEA. Furthermore, no patients developed additional neurological deficits related to postoperative cerebrovascular complications. Conclusion : Intensive care with strict BP control (<140/90 mm Hg) achieved a low prevalence of post-CEA hyperperfusion and prevented CHS. This study suggests that intensive care with strict BP control can prevent the prevalence of post-CEA CHS.

• 대한한의학회지
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• 제30권1호
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• pp.95-108
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• 2009

Objectives: Uwhangchungsim-won (DC) has been used in various medical fields such as stroke, hypertension, atherosclerosis, autonomic imbalance and mental instability, etc. The aim of this study was to evaluate the effect of UC on cerebral hemodynamics and estimate the appropriate dose of UC. Methods: We studied changes of hyperventilation-induced cerebrovascular reactivity and mean blood flow velocity of middle cerebral arteries (MCA) using transcranial Doppler. We observed the changes of mean blood pressure, pulse rate and expiratory CO2 using S/5 Compact Anesthesia Monitor from 10 healthy young volunteers who were administered UC twice a day in the 1 st section and then once a day in the 2nd section. Results: Mean blood pressure tended to decrease at 1 hour and pulse rate tended to decrease at 2 hours after second administration. After 2 hours, mean blood pressure rose to state before administration, but pulse rate maintained from 2 hours to 4 hours. The changes were not statistically significant. Cerebral blood flow velocity in middle cerebral artery was not statistically significant after second administration. Cerebrovascular reactivity increased from 2 hours to 4 hours after second administration. Conclusions: This study provides that administration of UC twice a day is more effective on hyperventilation-induced cerebrovascular reactivity than administration of UC once a day.

• 한국자기학회지
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• 제27권3호
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• pp.92-97
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• 2017

펄스자기장을 인체에 자극했을 때 몸 안에 있는 이온성 전해물질에 의해 유도전류가 발생하며, 최근에는 이를 활용하여 자기장 치료기술이 새롭게 연구 개발되고 있다. 본 연구에서는 강한 펄스자기장을 자극했을 때, 여러 층으로 응집되어 붙어있는 적혈구 연전형성의 변화를 동역학적으로 조사 분석하였다. 적혈구의 연전형성은 여러 가지 원인에 의해 발생하는데 물리학적으로 보면 적혈구 중심에 있는 $Fe^{+3}$ 이온에 의한 전기장 발생과 혈액 내에 녹아있는 음이온의 상호작용이 원인으로 고려된다. 본 연구에서 사용된 펄스자기장의 세기와 시간은 0.27 Tesla, 0.102 msec이고 펄스 반복시간은 1초이다. 인체에 가한 펄스자기장의 자극시간은 5분에서 10분, 15분, 20분까지 증가시켰고, 이에 따라 적혈구의 연전상태 변화를 동영상으로 조사하였다. 펄스자기장을 10분 동안 가했을 때 적혈구의 연전상태는 매우 호전되어 대체로 개별로 분리되었으며 slide glass 위에서 이동속도 역시 가장 활발하게 움직여서 $8{\times}10^{-4}m/sec$로 증가하였다. 그러나 20분까지 자기장 자극을 증가시키면 오히려 적혈구의 연전상태가 증가하고 활동성이 떨어지는 것을 확인하였다. 이에 대한 해석은 좀 더 체계적인 연구와 분석이 필요해 보인다.

• 동의생리병리학회지
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• 제23권6호
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• pp.1513-1520
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• 2009

The purpose of this study was to compare cerebral blood flow between hyperlipidemic patient group and normal healthy aldult group using transcranial doppler ultrasonography(TCD). I investigated cerebral blood flow of 63 hyperlipidemic patients and 42 healthy adults. To evaluate the cerebral blood flow, I measured the systolic peak velocity(Vs) and mean flow velocity(Vm) of the milddle cerebral artery(MCA), anterior cerebral artery(ACA), posterior cerebral artery(PCA), basilar artery(BA), internal carotid artery(ICA) in the two groups using TCD. In normal healthy adults, subjects showed a decerease in Vs and Vm with advancing in age. There was a significant difference in the Vm of ICA. There was no significant differences in the Vm of ACA and ICA. In normal healthy adults, females showed high velocities of all examined vessel. There was a significant difference in the Vs of ICA. There was a significant differences in the Vm of MCA and ICA. Normal healthy adults higher than hyperlipidemic patients in the Vs of MCA, ACA, PCA. There was no significant difference in the Vs of all exmined vessels. Hyperlipidemic patientsincrease higher than normal healthy adults in the Vm of ACA. There was a significant difference in the Vs of BA. In the patients aged under 50's, normal healthy adults higher than hyperlipidemic patients in the Vs and Vm except BA. But there was no significant difference in all exmined vessels. In the patients aged over 50's, hyperlipidemic patients higher than normal healthy adults in all examined vessel expect PCA. There was a significant difference in the Vs of BA and ICA. And hyperlipidemic patients higher than that normal healthy adults in all exmined vessels. There was a significant difference in BA and ICA. In this study, visible differences in blood flow between hyperlipidemic patient group and normal healthy aldult group were shown. However, these results do not come up to the previous values that were reported and known worldwide.

• 동의신경정신과학회지
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• 제18권1호
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• pp.143-151
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• 2007

Objective : This study was performed to evaluate the effects of Hap-Kok(LI4) and Jok-Sam-Lee(ST36) acupuncture on blood flow in In-Young(ST9). Method : Monitoring of TCD was examined in each 25's healthy men and wemen in 20s before and after acupucture on both(right and left) Hap-kok(LI4) and was done on both(right and left) Jok-Sam-Lee(ST36) by different group with same condition. Mean velocity and Pulsatility index analyzed from TCD at both In-Young(ST9). Both group was acupuctured for 15-20 minutes laying at bed. Results : The results showed a significant($p{\le}0.05:$ Paired T-test) decrease in mean velocity and increase in pulsatility index at both group. Conclusion : These results suggest that acupuncture could have a specific effect on blood flow called In-Young acupoint.