• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 춘계학술대회
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• pp.111-115
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• 1997

The objective of present study is to obtain information about stenosis effects on the blood flow in the coronary artery bifurcation. The three dimensional steady of blood in the coronary artery bifurcation with stenosis and without stenosis are simulated using the finite volume method. Apparent viscosity of blood is represented as a function of shear rate by the Carreau models. Velocities vectors and wall shear stresses along the branch tubes with stenosis are compared with those of without stenosis for steady flows. Flow phenomena in the stenosed branch tubes are discussed extensively.

• 한국산학기술학회논문지
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• 제18권3호
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• pp.545-550
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• 2017

대동맥이나 협착된 경동맥에서는 심장수축기에 간헐적으로 난류현상이 발생하고 있으며, 혈액의 점성특성으로 인해 기존 난류모델로는 정확한 해석이 어려운 실정이다. 혈류는 점탄성 유체의 성질을 가지고 있어 유체의 전단 변형률 증가에 따라 점도가 감소하는 점탄성 유체이며, 이러한 점탄성 유체는 난류 유동시 저항 감소 현상이 발생한다. 기존의 난류해석 모델들은 점성변화가 없는 뉴턴 유체에 적합한 모델들이 대부분이기 때문에, 점탄성 유체의 저항 감소 현상을 고려한 비뉴턴 유체 해석에 적합한 난류 모델개발이 필요하다. 본 논문은 난류 모델 가운데 수렴성이 좋고 해석시간이 짧은 표준 $k-{\varepsilon}$ 모델을 기반으로 저항 완충 함수를 이용하여 비뉴턴 유체의 저항감소 현상을 해석할 수 있는 수정된 난류모델을 제시하였으며, 이를 기존 난류모델들과 비교하여 제시된 난류 모델을 검증하였다. 새로 제시된 수정된 난류모델은 벽함수 및 점성저층을 고려하지 않았기 때문에 해석시간이 대폭적으로 감소하였으며, 적은 격자수를 이용하여 효율적으로 비뉴턴 유체의 난류 현상을 해석할 수 있기 때문에 향후 혈류해석 및 점탄성유체 해석에 적용할 예정이다.

• 대한기계학회논문집A
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• 제29권12권
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• pp.1615-1620
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• 2005

We present a novel flow-rate independent cell counter using a fixed control volume between double electrical sensing zones. The previous device based on the single electrical cell sensing in a given flow-rate requires an accurate fluid volume measurement or precision flow rate control. The present cell counter, however, offers the flow-rate independent method for the cell concentration measurement with counting cells in a fixed control volume of $22.9{\pm}0.98{\mu}{\ell}$. In the experimental study, using the RBC (Red Blood Cell), we have compared the measured RBC concentrations from the fabricated devices with those from Hemacytometer. The previous and present devices show the maximum errors of $20.3\%\;and\;16.1\%$, which are in the measurement error range of Hemacytometer (about $20\%$). The present device also shows the flow-rate independent performance at the constant flow-rates ($5{\mu}{\ell}/min$ and $10{\mu}{\ell}/min$) and the varying flow-rate (4, 2, and $4{\mu}{\ell}/min$). Therefore, we demonstrate that the present cell counter is a simple and automated method for the cell concentration measurement without requiring an accurate fluid measurement and precision flow-rate control.

• International Journal of Fluid Machinery and Systems
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• 제3권2호
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• pp.102-112
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• 2010

Artificial heart pumps have attracted the attention of researchers around the world as an alternative to the organ used in cardiac transplantation. Conventional centrifugal pumps are no longer considered suitable for long-term application because of the possibility of occurrence of blood leakage and thrombus formation around the shaft seal. To overcome this problem posed by the shaft seal in conventional centrifugal pumps, the magnetically suspended centrifugal pump has been developed; this is a sealless rotor pump, which can provide contact-free rotation of the impeller without leading to material wear. In Europe, clinical trials of this pump have been successfully performed, and these pumps are commercially available. One of the aims of our study is to numerically examine the internal flow and the effect of leakage flow through the gap between the impeller and the pump casing on the performance of the pump. The results show that the pressure head increases compared with the pump without a gap for all flow rates because of the leakage of the fluid through the gap. It was observed that the leakage flow rate in the pump is sufficiently large; further, no stagnant fluid or dead flow regions were observed in the pump. Therefore, the present pump can efficiently enhance the washout effect.

• 한국자기학회지
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• 제26권4호
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• pp.142-148
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• 2016

자기공명영상에서 위상대조(phase contrast; PC) 기법으로 혈류 속도와 혈류량을 정량적으로 측정하기 위해 VENC(150 cm/s)에서 숙임각의 변화에 따른 혈류 속도와 혈류량을 측정하였다. 1.5T MRI로 지원자 17명(여: 8, 남: 9, 평균연령 $57.9{\pm}15.4$)을 대상으로 non-breath holding 기법을 적용하여 상행대동맥에서 VENC(150 cm/s)로 숙임각을 $20^{\circ}$, $30^{\circ}$, $40^{\circ}$ 변화하여 측정하였다. 혈류는 average velocity, peak velocity, net forward volume, net forward volume/body surface area를 획득하였다. 상행대동맥에서 AV(average velocity)의 평균값은 숙임각 $20^{\circ}$(9.87 cm/s), $30^{\circ}$(9.6 cm/s), $40^{\circ}$(10.05 cm/s)로 측정되었다. 숙임각을 $20^{\circ}$, $30^{\circ}$, $40^{\circ}$에서 peak velocity, average velocity, net forward volume, net forward volume/body surface area는 통계적인 유의한 차이가 없었다(p > .05). 혈류속도와 혈류량 측정은 매개변수를 조정하여 적용하면 심장혈관 질환의 진단 및 치료에 중요한 정보가 되는 혈류량을 정확히 계산하고, 혈류량 측정에 관한 연구에 도움을 줄 수 있다.

• 대한의용생체공학회:의공학회지
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• 제21권5호
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• pp.449-455
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• 2000

순간적으로 승모판에서 혈류가 역류하는 영역을 측정하기 위해서, PISA 방법이 자주 이용되고 있다. 이 방법은 물질보존법칙에 근거하여, 구멍을 통과하는 유체량을 isotach 표면적과 이에 대응하는 속도의 곱으로 구하는 것이다. 이러한 PISA 방법에서 사용되는 유동모델은 반구모델과 비반구모델의 형태인데, 이는 isotach 표면적이 반구이거나 비반구임을 가정하여 계산된 것이다. 이러한 isotach 모델링에서는 isotach의 높이와 폭의 결정이 유체량을 추정하는데 아주 중요한 변수가 된다. 본 연구에서는 in-vitro 칼라 도플러 영상으로부터 PISA 영역을 추정을 위하여 영역기반을 근간으로 하는 비반구모델에 대한 표면적 추정방법을 제안하였다. 이 방법의 타당성을 알아보기 위해 180개의 칼라 도플러 영상에 대해 isotach의 높이와 폭을 추정한 결과, 기존의 에지기반방법이 19개 영상에서 에러를 가지는 반면, 제안한 방법에서는 에러영상이 없음을 알 수 있었다.

• 대한의용생체공학회:의공학회지
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• 제25권6호
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• pp.489-496
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• 2004

혈액이 케뉼라를 통과할 때 생리적인 범위를 벋어나는 기계적인 하중이나 전단응력을 받게 되며, 그 결과로 용혈의 발생기전이 되는 ADP(Adenosine Diphospate)를 증가 시키게 된다. 저자는 수치해석적인 방법을 이용하여 사이드 홀을 가진 케뉼라의 3차원 유동을 해석하였다. 연구의 대상이 되는 케뉼라는 환자의 대퇴정맥에 삽입되어 혈액을 배출하는 배액 케뉼라이다. 이러한 배액 케뉼라는 배출 성능을 높이기 위해 일반적으로 사이드 홀을 장착한다. 4개, 12개, 20개인 사이드 홀을 가진 케뉼라에 대하여 경우에 대하여, 각각 엇갈림 배열, 직렬 배열. 변형된 직렬배열을 적용하여, 총 9가지 서로 다른 모델을 시뮬레이션 해보았으며 이것을 사이드 홀이 없는 케뉼라와 더불어 비교하였다. 유량, 벽면전단응력(Wail Shear Stress. WSS), 전단율(Shear Rate. SR) 값을 구하여 분석하므로 사이드 홀의 영향을 알아보았다. 연구를 통하여 사이드 홀의 개수와 배열이 모두 혈류 역학적인 변수들에 영향을 주는 것을 확인하였다. 유량이 사이드 홀의 개수에 비례하지 않는 것을 확인 하였고 사이드 홀의 개수가 많을 수로 평균 전단율을 줄이는 것을 확인 하였다.

• 대한임상전기생리학회지
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• 제8권2호
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• pp.19-24
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• 2010

Purpose : This study aims to examine the influences of galvanic vestibular stimulation on autonomic reaction of normal adults. Methods : Participants in this research totaled 28 (14 men and 14 women). Galvanic vestibular stimulation was conducted with a binaural electrode configuration for 60 sec. Galvanic vestibular stimulation measurements were conducted with the subjects in a prone position. Measured items included skin conductance, blood flow, pulse rate, and respiratory rate. Measurements were repeated for a total of five times, before application, during application, after application, 5 minutes after application and 10 minutes after application. Results : Skin conductance reaction showed statistically significant differences in changes depending on time after galvanic vestibular stimulation and there were statistically differences in changes of blood flow, pulse rate and respiratory rate after galvanic vestibular stimulation. Conclusion : Blood flow, pulse rate and respiratory rate of autonomic reactions were not influenced by galvanic vestibular stimulation, but skin conductance reaction was influenced by it and it was found that it was reduced during and after stimulation rather than before stimulation. Consequently, it was considered that galvanic vestibular stimulation affected the autonomic reaction.

• 대한한의학회지
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• 제18권1호
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• pp.299-315
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• 1997

The present experiments were designed to investigate the effects of Samsaengyeum. water extracts on the Cardiovascular System in the Experimental Animals. Thus, the changes of blood pressure and heart rate were measured after oral administration. Measurement of Mortality rate was observed for measuring the effect of Samsaengyeum water extract Samsaengyeum water extract against pulmonary thromboembolism induced by collagen the mixture(0.1me/10g, 2mg/kg B.W) plus serotonin(5mg/kg B.W) in mouse. The effect of Samsaengyeiim water extract was examined by observing the change of collagen-induced platelet aggregation, coagulation activity, ex vivo and in vitro fibrinolytic activity of euglobulin fraction in rats. The results were summarized as followings. 1. Samsaengyeum dropped the blood pressure in spontaneous hypertensive rat. 2. The drug increased the auricular blood flow in rabbit. 3. The drug relaxed the artery contraction by pretreated norepinephrine in rat. 4. The drug inhibited the death rate of mouse which was led to thromboembolism by serotonin and collagen. 5. The drug inhibited the platelet aggregation in rat. 6. The drug prolonged the prothrombin time and activated partial thromboplastin time on the test of plasma coagulation factor activity in rat, but was not valuable. 7. The drug reduced the fibrinogen lyses time and increased the lyses area of rat. 8. Samsaengyeum reduced fibrinogen lyses time of rat in vitro assay. According to the above mentioned results, Samsaengyeum increased the blood flow and dropped the blood pressure by the dilation of blood vessel. And the drug inhibited the platelet aggregation.

• Journal of Oral Medicine and Pain
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• 제40권1호
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• pp.10-16
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• 2015

Purpose: Pilocarpine has the effects on improvement of salivary flow and subjective symptoms for xerostomic patients. Because of unwanted side effects following its systemic administration, topical pilocarpine has been paid attention as an alternative. This study aimed to investigate effects of pilocarpine solution as mouthwash on salivary flow and adverse effects compared to systemic administration of 5 mg pilocarpine tablet in healthy subjects. Methods: The study was a double blind, placebo-controlled, crossover clinical trial. Five milligrams pilocarpine tablets, 4 mL of 2% pilocarpine solution and placebo solution were given to 12 healthy volunteers (6 males and 6 females) in a predetermined order with wash-out period of at least two days and unstimulated whole saliva was collected before and after administration of each drug. Blood pressure and pulse rate was also measured and subjective effect and potential side effects were evaluated by a self-administrated questionnaire. Results: Systemic (5 mg tablet) and topical (2% solution) use of pilocarpine significantly increased salivary flow rate in healthy subjects compared to placebo (p<0.001). In both the pilocarpine solution and tablet groups, salivary flow rates at 120 minutes after administration remained increased. Subjective effect on salivation was the largest in the pilocarpine tablet group, followed by the pilocarpine solution group (p<0.05). There was no significant difference in blood pressure and pulse rate after administration of all three drugs. Fewer side effects reported in the pilocarpine solution group than in the tablet group. Conclusions: Two percents pilocarpine solution as mouthwash increases salivary flow rate, definitely superior to placebo solution and comparable to pilocarpine tablet, with fewer side effects in healthy subjects. It indicates a possibility of pilocarpine solution as a useful alternative of pilocarpine tablets for the xerostomic patients with systemic diseases.