• Journal of Biomedical Engineering Research
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• v.45 no.3
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• pp.128-137
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• 2024

It is necessary to develop a pulsatile Extracorporeal Membrane Oxygenator (p-ECMO) with counter-pulsation control(CPC), which ejects blood during the diastolic phase of the heart rather than the systolic phase, due to the known issues with conventional ECMO causing fatal complications such as ventricular dilation and pulmonary edema. A promising method to simultaneously detect the pulsations of the heart and p-ECMO is to analyze blood pressure waveforms using deep neural network technology(DNN). However, the accurate detection of cardiac rhythms by DNNs is challenging due to various noises such as pulsations from p-ECMO, reflected waves in the vessels, and other dynamic noises. This study aims to evaluate the accuracy of DNNs developed for CPC in p-ECMO, using human-like blood pressure waveforms reproduced in an in-vitro experiment. Especially, an experimental setup that reproduces reflected waves commonly observed in actual patients was developed, and the impact of these waves on DNN judgments was assessed using a multiple DNN (m-DNN) that provides accurate determinations along with a separate index for heartbeat recognition ability. In the experimental setup inducing reflected waves, it was observed that the shape of the blood pressure waveform became increasingly complex, which coincided with an increase in harmonic components, as evident from the Fast Fourier Transform results of the blood pressure wave. It was observed that the recognition score (RS) of DNNs decreased in blood pressure waveforms with significant harmonic components, separate from the frequency components caused by the heart and p-ECMO. This study demonstrated that each DNN trained on blood pressure waveforms without reflected waves showed low RS when faced with waveforms containing reflected waves. However, the accuracy of the final results from the m-DNN remained high even in the presence of reflected waves.

• Korea-Australia Rheology Journal
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• v.21 no.3
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• pp.161-173
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• 2009

This study analyzes especially drag and lift models recently developed for fluid-solid, fluid-fluid or liquid-liquid two-phase flows to understand their applicability on the computational fluid dynamics, CFD modeling of pulsatile blood flow. Virtual mass effect and the effect of red blood cells, RBCs aggregation on CFD modeling of blood flow are also shortly reviewed to recognize future tendencies in this field. Recent studies on two-phase flows are found as very useful to develop more powerful drag-lift models that reflect the effects of blood cell's shape, deformation, concentration, and aggregation.

• Membrane and Water Treatment
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• v.1 no.4
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• pp.253-271
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• 2010

A theoretical study for the flux enhancement by pulsation of transmembrane pressure is presented for osmotic pressure controlled ultrafiltration under laminar flow regime. The transient velocity profile is solved analytically using Green's function method. Time dependent convective diffusive equation is solved to quantify the membrane surface concentration and the permeate flux, numerically. The effects of the amplitude and frequency of pulsation on flux, surface concentration and observed retention are studied.

• The Journal of Korean Medicine
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• v.23 no.3
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• pp.1-10
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• 2002

Objective: There exist gender differences in pulsatile contour waveform. Women have a greater age-related increase in left ventricular mass than do men and more likely to experience symptomatic heart failure after infarction. SDPTG (the second derivative of photoplethysmogram waveform) is a noninvasive method for evaluating the pulse wave and is correlated with age and other risk factors for atherosclerosis. We studied the effect of gender on SDPTG and made clear why the gender differences appear. Methods: To study the effects of effect factors, including height and blood pressure, on SDPTG in the fourth decade, data on height, weight, PTD (pulse transit distance), blood pressure, serum lipid levels, and SDPTG were collected in 115 laboratory healthy men and women. SDPTG is derived from double-differential processing of fingertip photoplethysmography and consists of a, b, c, and d waves in systole and an e wave in diastole; SDPTG aging index (AI) was calculated as (b-c-d-e)/a. Results: There were significant gender-related differences of SDPTG AI, height, and blood pressure. Age, height, and mean blood pressure were respectively and significantly correlated with SDPTG AI. SDPTG is dependent upon age, height, and blood pressure. Restricting analysis to SDPTG AI, age, height, and mean blood pressure, yielded that there were gender-related differences in SDPTG AI (P<0.05) which were derived from those of height (F<0.001, df=l, P=0.994). Conclusions: These new data may help to explain previous findings about age-related differences in pulsatile contour waveforms and why gender differences of SDPTG appear. The results of this study suggest that SDPTG AI, used for evaluation of biological vascular aging, should be calibrated by height as well as age and blood pressure.

• International Journal of Vascular Biomedical Engineering
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• v.3 no.2
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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.

• The KSFM Journal of Fluid Machinery
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• v.7 no.3 s.24
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• pp.14-22
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• 2004

Bileaflet mechanical valves have the complications such as hemolysis and thromboembolism, leaflet damage, and leaflet break. These complications are related with the fluid velocity and shear stress characteristics of mechanical heart valves. The first aim of the current study is to introduce fluid-structure interaction method for calculation of unsteady and three-dimensional blood flow through bileaflet valve and leaflet behavior interacted with its flow, and to overcome the shortness of the previous studies, where the leaflet motion has been ignored or simplified, by using FSI method. A finite volume computational fluid dynamics code and a finite element structure dynamics code have been used concurrently to solve the flow and structure equations, respectively, to investigate the interaction between the blood flow and leaflet. As a result, it is observed that the leaflet is closing very slowly at the first stage of processing but it goes too fast at the last stage. And the results noted that the low pressure is formed behind leaflet to make the cavitation because of closing velocity three times faster than opening velocity. Also it is observed some fluttering phenomenon when the leaflet is completely opened. And the rebounce phenomenon due to the sudden pressure change of before and after the leaflet just before closing completely. The some of time-delay is presented between the inversion point of ventricle and aorta pressure and closing point of leaflet. The shear stress is bigger and the time of exposure is longer when the flow rate is maximum. So it is concluded that the distribution of shear stress at complete opening stage has big effect on the blood damage, and that the low-pressure region appeared behind leaflet at complete closing stage has also effect on the blood damage.

• Journal of Chest Surgery
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• v.40 no.7 s.276
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• pp.512-516
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• 2007

A mechanical circulatory support system is a life-saving option for treating acute severe respiratory failure or cardiac failure. There are currently a few types of assist devices and the Twin-Pulse Life Support (T-PLS) system is a kind of pulsatile pump. We report here on three patients with severe life threatening cardiopulmonary dysfunction who had the T-PLS system used as an assist device. The indications for applying the T-PLS system were continuing respiratory or cardiac failure in spite of maximal ventilatory and inotropic support. There were two patients with acute respiratory failure due to infection and one patient with cardiac failure due to acute myocarditis. One respiratory failure patient and one cardiac failure patient survived after applying the T-PLS system for 3 days and 5 days, respectively. The T-PLS system is useful as an assist device and it should be considered before multi-organ failure occurs.

• Journal of the Korean Institute of Intelligent Systems
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• v.22 no.4
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• pp.500-506
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• 2012

A method to model left ventricular assist device (LVAD) and detect suction occurrence for safe LVAD operation is presented. An axial flow blood pump as a LVAD has been used to assist patient with heart problems. While an axial flow blood pump, a kind of a non-pulsatile pump, has relative advantages of small size and efficiency compared to pulsatile devices, it has a difficulty in determining a safe pump operating condition. It can show different pump operating statuses such as a normal status and a suction status whether suction occurs in left ventricle or not. A fuzzy subtractive clustering method is used to determine a model of the axial flow blood pump with this pump operating characteristic and the developed pump model can provide blood flow estimates before and after suction occurrence in left ventricle. Also, a fuzzy subtractive clustering method is utilized to develop a suction detection model which can identify whether suction occurs in left ventricle or not.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.5
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• pp.629-639
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• 2002

In-vitro flow characteristics downstream of a polyurethane artificial heart valve and a Bjork-Shiley Monostrut mechanical valve have been comparatively investigated in pulsatile flow using particle image velocimetry (PIV). With a triggering system and a time-delayed circuit the velocity distributions on the two perpendicular measurement planes downstream of the valves are evaluated at any given instant in conjunction with the opening behaviors of valve leaflets during a cardiac cycle. The regions of stasis and high shear stress can be found simultaneously by examining the entire view of the instantaneous velocity and Reynolds shear stress fields. It is known that high shear stress regions exist at the interface between strong axial jet flows along the wall and vortical flows in the central area distal to the valves. In addition. there are large stagnation or recirculation regions in the vicinity of the valve leaflet, where thrombus formation can be induced by accumulation of blood elements damaged in the high shear stress zones. A correlation between the unsteady flow patterns downstream of the valve and the corresponding opening postures of the polyurethane valve membrane gives useful data necessary for improved design of the frame structure and leaflet geometry of the polyurethane valve.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.606-611
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• 2007

Pulsation is an inherent phenomenon in reciprocating compressors. It interacts with piping to cause vibrations and performance problems. Indiscriminately connecting to a compressor can be dangerous and cost money in the form of broken equipment and piping, poor performance, inaccurate metering, unwanted vibration, and sometimes noise. Piping connected to a compressor can materially affect the performance and response. To minimize these detrimental effects, reciprocating compressor system should be equipped by pulsation suppression system. This study discusses pressure pulsation phenomena occurred in a reciprocating compressor system. An experiment applied air compressor unit, as pulsating pressure generator, has been done. The compressor was connected sequentially to a snubber model and pressure tank. Sensor probes were placed on the inlet and outlet pipes of snubber. Compressor was driven by a motor controlled by a frequency regulator. The experiment was conducted by adjusting the regulator at 40Hz. General information about an internal gas flow can be achieved by numerical analysis approach. Information of the velocity, pressure and turbulence kinetic energy distribution are presented in this paper. Based on this result, the design improvement might be done.