• Journal of the Korean Society of Visualization
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• v.20 no.1
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• pp.52-63
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• 2022

Direct numerical simulation of blood flow in a stenosed, patient-specific carotid artery was conducted to explore the transient behavior of blood flow with special emphasis on the wall-shear stress distribution over the transition region. We assumed the blood as an incompressible Newtonian fluid, and the vessel was treated as a solid wall. The pulsatile boundary condition was applied at the inlet of the carotid. The Reynolds number is 884 based on the inlet diameter, and the maximum flow rate and the corresponding Womersley number is approximately 5.9. We found the transitional behavior during the acceleration and deceleration phases. In order to quantitatively examine the wall-shear stress distribution over the transition region, the probability density function of the wall-shear stress was computed. It showed that the negative wall-shear stress events frequently occur near peak systole. In addition, the oscillatory shear stress index was used to further analyze the relationship with the negative wall-shear stress appearing in the systolic phase.

• Structural Engineering and Mechanics
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• v.86 no.6
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• pp.751-764
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• 2023

In practical engineering such as aerial refueling pipes, the boundary of the fluid-conveying pipe is difficult to be completely immovable. Pipes under movable and immovable boundaries are controlled by different dominant nonlinear factors, where the boundary mobility will affect the nonlinear dynamic characteristics, which should be focused on for adopting different strategies for vibration suppression and control. The nonlinear dynamic instability characteristics of functionally graded fluid-conveying pipes lying on a viscoelastic foundation under movable and immovable boundary conditions are systematically studied for the first time. Nonlinear factors involving nonlinear inertia and nonlinear curvature for pipes with a movable boundary as well as tensile hardening and nonlinear curvature for pipes with an immovable boundary are comprehensively considered during the derivation of the governing equations of the principal parametric resonance. The stability boundary and amplitude-frequency bifurcation diagrams are obtained by employing the two-step perturbation- incremental harmonic balance method (TSP-IHBM). Results show that the movability of the boundary of the pipe has a great influence on the vibration amplitude, bifurcation topology, and the physical meanings of the stability boundary due to different dominant nonlinear factors. This research has guidance significance for nonlinear dynamic design of fluid-conveying pipe with avoiding in the instability regions.

• Journal of the Korean Society of Visualization
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• v.21 no.2
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• pp.14-23
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• 2023

The pressure difference across stenotic blood vessels is a commonly used clinical metric for diagnosing many cardiovascular diseases. At present, most clinical pressure measurements rely solely on invasive catheterization. In this study, we propose a novel method for non-invasive pressure estimation using the incompressible Navier-Stokes equations and a 3D multi-path integration approach. We verify spatio-temporal convergence on an in-silico dataset of a cylindrical straight pipe phantom with steady and pulsatile flow fields. We then evaluate the proposed method on an in vitro dataset of reconstructed control, pre-operative, and post-operative carotid artery cases acquired from 4D flow MRI. The performance of our method is compared to existing approaches based on the pressure Poisson equation and work-energy relative pressure. The results demonstrate the proposed method's high accuracy, robustness to spatio-temporal subsampling, and reduced sensitivity to noise, highlighting its great potential for non-invasive pressure estimation.

• Journal of the Korean Society of Visualization
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• v.22 no.1
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• pp.40-48
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• 2024

This study presents an in-vitro model designed to simulate mitral valve regurgitation, aiming to compare the quantification results between Proximal Isovelocity Surface Area(PISA) and 4D Flow MRI on both fixed and valve annulus tracking(VAT) views. The in-vitro model replicates the dynamic conditions of the mitral valve in a pulsatile environment, utilizing a piston pump set at 60 bpm. Through systematic experiments and analysis, the study evaluates the accuracy and effectiveness of PISA and 4D Flow MRI in assessing regurgitation severity, considering both fixed and valve annulus tracking. The displacement length measured in echo closely resembled that of optical measurements, making it advantageous for structural analysis. VAT-4D flow MRI exhibited the smallest deviation from actual flow rate values, establishing it as most accurate method for quantitative regurgitation assessment.

• Archives of Obesity and Metabolism
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• v.3 no.1
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• pp.43-48
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• 2024

Idiopathic intracranial hypertension (IIH) is characterized by increased intracranial pressure without detectable causes. Its main symptoms include headache, vision problems, and pulsatile tinnitus. Obesity is a major risk factor for IIH; therefore, weight reduction is required to ameliorate these symptoms in patients with obesity and IIH. We present four cases of obesity-related IIH whose symptoms improved through weight reduction. In three patients, the dose of IIH medications, such as acetazolamide, decreased. Based on these cases, we report that weight reduction contributes to the improvement of symptoms in patients with IIH as the main part of treatment. Further clinical research is necessary to evaluate the effects of weight reduction on IIH treatment in Korean patients.

• Journal of radiological science and technology
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• v.30 no.3
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• pp.205-212
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• 2007

To evaluate the feasibility and efficacy of a pulsatile aortic aneurysm phantoms for in-vitro study. The phantoms consisted of a pulsating motor part(heart part) and an aortic aneurysm part, which mimicked true physiologic conditions. The heart part was created from a high-pressured water pump and a pulsatile flow solenoid valve for the simulation of aortic flow. The aortic aneurysm part was manufactured from paper clay, which was placed inside a acrylic plastic square box, where liquid silicone was poured. After the silicone was formed, the clay was removed, and a silicone tube was used to connect the heart and aneurysm part. We measured the change in pressure as related to the opening time(pulse rate, Kruskal-Wallis method) and pressure before and after the stent-graft implantation(n = 5, Wilcoxon's signed ranks test). The changes in blood pressures according to pulse rate were all statistically significant(p<0.05). The systolic/diastolic pressures at the proximal aorta, the aortic aneurysm, and the distal aorta of the model were $157.80{\pm}1.92/130.20{\pm}1.92$, $159.40{\pm}1.14/134.00{\pm}2.92$, and $147.20{\pm}1.480/129.60{\pm}2.70\;mmHg$, respectively, when the pulse rate was 0.5 beat/second. The pressures changed to $161.40{\pm}1.34/90.20{\pm}1.64$, $175.00{\pm}1.58/93.00{\pm}1.58$, and $176.80{\pm}1.48/90.80{\pm}1.92\;mmHg$, respectively, when the pulse rate was 1.0 beat/second, and $159.40{\pm}1.82/127.20{\pm}1.48$, $166.60{\pm}1.67/138.00{\pm}1.87$, and $161.00{\pm}1.22/135.40{\pm}1.67\;mmHg$, respectively, when it was 1.5 beat/second. When pulse rate was set at 1.0 beat/second, the pressures were $143.60{\pm}1.67/90.20{\pm}1.64$, $147.20{\pm}1.92/84.60{\pm}1.82$, and $137.40{\pm}1.52/88.80{\pm}1.64\;mmHg$ after stent-graft implantation. The changes of pressure before and after stent-graft implantation were statistically significant(p<0.05) except the diastolic pressures at the proximal(p =1.00) and distal aorta(p=0.157). The aortic aneurysm phantoms seems to be useful for the evaluation of the efficacy of stent-graft before animal or clinical studies because of its easy reproducibility and ability to display a wide range of pressures.

• Development and Reproduction
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• v.7 no.1
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• pp.35-40
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• 2003

Gonadotropin releasing hormone(GnRH), which is secreted from the hypothalamus, has a pivotal role in the reproduction of mammals. Golden hamsters are seasonal breeding mammal and their sexual activity is determined by photoperiod(length of light per day). Long photoperiod(LP, $\leq$ 12.5 hours of light) maintains the reproductive activity and short photoperiod(SP, $\leq$ 12 hours of light) suppresses it. In order to investigate in detail, the sexual activity was individually examined in SP-housed male golden hamsters received a vector at three different concentrations which contains rat GnRH cDNA. The gonadal regression was significantly(P<0.05) accelerated by the highest concentrations of the vector at 8 and 10 weeks after the treatment in comparison to the other groups. In the light of pulsatile release of GnRH in maintaining reproductive activity, the vector containing GnRH cDNA might secrete the GnRH in a constant high level. These results suggest that the GnRH-containing vector might desensitize the anterior pituitary, leading to acceleration or testicular regression.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1472-1477
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• 2005

Recently, the performance development of the exhaust system of a car is very important. The most important part of parts that constructing the exhaust system of a car is a muffler. The muffler reducing the exhaust noise from the engine influence on the engine performance directly. The inner parts of the muffler construct with the baffle and perforated pipes and so on. In the recent study, the study to design the semi-active muffler sensing the exhaust gas pressure controlling the back pressure variably with a EVV progress activity. So that the inner parts of the muffler show the complicated turbulent flow phenomena because of pulsatile flow from the engine and the structural properties and so on. The qualitative and quantitative analysis about the turbulent flow phenomena of the inner parts of the muffler is required gradually. In this study, to analysis the flow field of the inner parts of the muffler, analysis results with the PIV measurement to be able to analysis the variable change of the time and the space. Therefore, try to show the design variables to need to design the inner parts of a muffler of a car.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.6
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• pp.1257-1264
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• 2019

The traditional cuff-based method for BP(Blood Pressure) measurement is not suitable for continuous real-time BP measurement techniques. For this reason, the previous studies estimated various blood pressures by fusion with the electrocardiography (ECG) and photoplethysmogram (PPG) sensor signals. However, conventional techniques based on PPG bio-sensing measurement face many challenging issues such as noisy supply fluctuation, small pulsation, and drifting non-pulsatile. This paper proposed a novel BP estimation methods using PPG and ECG sensors, which can be derived from the relationship between PPG and ECG using PTT(Pulse Transit Time) and PWV(Pulse Wave Velocity). Unlike conventional height ratio features, which are extracted on the basis of the peaks in the PPG and ECG waveform. The proposed method can be reliably obtained even if there are missing peaks among the sensed PPG signal. The increased reliability comes from periodical estimation of the peak-to-peak interval time using ECG and PPG. After 250,000 times trials of the blood pressure measurement, the proposed estimation technique was verified with the accuracy of ±28.5% error, compared to a commercialized BP device.

• International Journal of Vascular Biomedical Engineering
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• v.1 no.1
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• pp.32-40
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• 2003

Axillo-bifemoral (Ax-Fem) bypass are now well accepted for bilateral iliac artery occlusion as the second best option. This extra-anatomical (unnatural) bypasses, however, have various hemodynamic liabilities affecting the patency. Hemodynamic conditions of each different type of Ax-Fem bypass were assessed with computer simulation model to determine the hemodynamically more sound type. Simulation models of five different types of Ax-Fem bypass were constructed. Our investigation based on the computer simulation models have shown distinct differences between two most popular Lazy-S type and Inverted-C type on the distribution of flow volume, shear stress and recirculation zone, etc., though both types have shown similar clinical results. Lazy-S type has shown better hemodyanmic status than inverted-C type. The theoretical advantage of "Lazy-S" type has never been adequately proved for its superiority clinically over the inverted-C type. Inverted-C type is now in more favor with clinically better results in spite of many hemodynamic liabilities including retrograde flow to the branching graft. The improvement of over-all long-term patency rate of various extra-anatomical bypasses is still warranted through proper correction of the hemodynamic liability. Even though clinical outcome of the extra-anatomical bypass has been equal regardless of the type of crossover femoral graft configuration, there are distinct differences on the hemodynamic characteristics among various types of configuration. Further hemodynamic study in the pulsatile flow status is warranted to correct hemodynamic defects with proper modification of various hemodynamic factors of each model.