Biomedical subjects

Yasuhiro Fukui

Publications and source records attributed to Yasuhiro Fukui.

13 recordsLinked to original sources

PubMed2002

A functionally graded titanium/hydroxyapatite film obtained by sputtering.

A functionally graded film of titanium/hydroxyapatite (HA) was prepared on a titanium substrate using a radio frequency magnetron sputtering. The ratio of titanium to HA was controlled by moving the target shutter. The film was composed of five layers, with overall film thickness of 1 microm. The HA was concentrated close to the surface, while the titanium concentration increased with proximity to the substrate. The bonding strength between the film and the substrate was 15.2 MPa in a pull-out test and the critical load from a scratch test was 58.85 mN. The corresponding values of a pure HA sputtered film were 8.0 MPa and 38.47 mN, respectively. The bonding strength of a pure HA plasma spray coating was 10.4 MPa in the pull-out test. The graded film and the pure HA film were sputter-coated to a thickness of 1 microm on titanium columns (10 mm in length and 4 mm in diameter). These columns were implanted in diaphyses of the femora of six adult dogs and a push-out test was carried out after 2, 4, and 12 weeks. After 12 weeks, the push-out strengths of the graded film, the pure HA film and the non-coated columns were 3.7, 3.5, and 1.0 MPa.

Journal Article↗

PubMed2002

An investigation of blood damage induced by static pressure during shear-rate conditions.

Many investigators have studied the effect of a mechanical force (shear rate, pressure, or temperature) on hemolysis. However, there exists no investigation of a relationship between the interactions of mechanical forces and hemolysis. The purpose of this study is to investigate the interactions of mechanical forces on hemolysis. We performed in vitro tests by using bovine blood, applying shear rate (0, 500, 1,000, and 1,500 s-1), positive pressure (0, 200, 400, and 600 mm Hg), and temperature (21, 28, and 35 degrees C) simultaneously. In all temperatures at the shear rate of 1,500 s-1, there are statistically significant differences in the hemolysis rate between 0 and 600 mm Hg (p < 0.05). However, to investigate the effect of temperature on hemolysis, shear stress was calculated at each blood temperature. There were no statistically significant differences among them. The results suggested that erythrocyte trauma caused by pressure related to the level of shear rate. It was found that the causes of hemolysis included the shear rate as well as shear rate and pressure.

Erythrocytes↗

PubMed2002

Flow rate and pressure head estimation in a centrifugal blood pump.

Considering a miniaturization of percutaneous cardiopulmonary support (PCPS) system, we have developed a pump system that can estimate flow rate and pressure head in the circuit. A commercially available centrifugal blood pump (C1E3, Kyocera Co., Ltd., Kyoto, Japan) with an exclusive motor driver was used in the experiment. In this system, the motor revolutions per minute and torque were used to derive an estimation equation. Taking into consideration fluid viscosity, the accuracy of the estimation was increased. Bovine blood was used to evaluate the system in vitro. The average maximum difference between the estimated flow rate and the measured flow rate was 0.56 L/min (for 98% accuracy). The average difference between the estimated pressure head and the measured pressure head was 30.7 mm Hg (for 94.2% accuracy). Because of the stability of the estimations, we believe this system has the possibility of use for real-time monitoring and miniaturization of PCPS system.

Animals↗

PubMed2002

A dynamic action potential model analysis of shock-induced aftereffects in ventricular muscle by reversible breakdown of cell membrane.

To elucidate the subcellular mechanism underlying the aftereffects of high-intensity dc shocks, a small pore, which mimics reversible breakdown of the cell membrane (electroporation), was incorporated into the phase-2 Luo-Rudy (L-R) model of ventricular action potentials. The pore size was set to occupy 0.15%-4.25% of the total cell membrane during the 10-ms shock. The pore was assumed to decrease after the shock exponentially with a time constant of 100-1,400 ms to simulate resealing process. In normal myocytes, the pore formation results in a delay of repolarization of the shocked action potential, which is followed by prolonged depolarization and oscillation of membrane potential like early afterdepolarization (EAD). Time- and voltage-dependent changes in the delayed rectifier K+ currents (IKr, IKs) in combination with those of L-type Ca2+ current (ICa,(L)) and ion flux through the pore (I(pore)) are responsible for the potential changes. Spontaneous excitation from the oscillation depends on activation of ICa,(L). In myocytes overloaded with Na+ and Ca2+ secondary to 90% inhibition of Na+-K+ pump, the pore formation results in a delay of repolarization of the shocked action potential, which is followed by slower cyclic depolarization in response to spontaneous release of Ca2+ from the sarcoplasmic reticulum (SR). This delayed afterdepolarization-type oscillation is abolished by complete block of Ca2+ release from the SR. These findings suggest that high-intensity electric field application will cause arrhythmogenic responses through a transient rupture of sarcolemma with different subcellular events in ventricular cells under normal and pathological conditions.

Action Potentials↗

PubMed2002

Discrimination of walking patterns using wavelet-based fractal analysis.

In this paper, we attempted to classify the acceleration signals for walking along a corridor and on stairs by using the wavelet-based fractal analysis method. In addition, the wavelet-based fractal analysis method was used to evaluate the gait of elderly subjects and patients with Parkinson's disease. The triaxial acceleration signals were measured close to the center of gravity of the body while the subject walked along a corridor and up and down stairs continuously. Signal measurements were recorded from 10 healthy young subjects and 11 elderly subjects. For comparison, two patients with Parkinson's disease participated in the level walking. The acceleration signal in each direction was decomposed to seven detailed signals at different wavelet scales by using the discrete wavelet transform. The variances of detailed signals at scales 7 to 1 were calculated. The fractal dimension of the acceleration signal was then estimated from the slope of the variance progression. The fractal dimensions were significantly different among the three types of walking for individual subjects (p < 0.01) and showed a high reproducibility. Our results suggest that the fractal dimensions are effective for classifying the walking types. Moreover, the fractal dimensions were significantly higher for the elderly subjects than for the young subjects (p < 0.01). For the patients with Parkinson's disease, the fractal dimensions tended to be higher than those of healthy subjects. These results suggest that the acceleration signals change into a more complex pattern with aging and with Parkinson's disease, and the fractal dimension can be used to evaluate the gait of elderly subjects and patients with Parkinson's disease.

Acceleration↗

PubMedDate not supplied

Immobilization and clustering of structurally defined oligosaccharides for sugar chips: an improved method for surface plasmon resonance analysis of protein-carbohydrate interactions.

Oligosaccharides are increasingly being recognized as important partners in receptor-ligand binding and cellular signaling. Surface plasmon resonance (SPR) is a very powerful tool for the real-time study of the specific interactions between biological molecules. We report here an advanced method for the immobilization of oligosaccharides in clustered structures for SPR and their application to the analysis of heparin-protein interactions. Reductive amination reactions and linker molecules were designed and optimized. Using mono-, tri-, or tetravalent linker compounds, we incorporated synthetic structurally defined disaccharide units of heparin and immobilized them as ligands for SPR. Their binding to an important hemostatic protein, von Willebrand factor (vWf), and its known heparin-binding domain was quantitatively analyzed. These multivalent ligand conjugates exhibited reproducible binding behavior, with consistency of the surface conditions of the SPR chip. This novel technique for oligosaccharide immobilization in SPR studies is accurate, specific, and easily applicable to both synthetic and naturally derived oligosaccharides.

Animals↗

PubMedDate not supplied

Newly developed ventricular assist device with linear oscillatory actuator.

The goal of this study was to develop a new direct electromagnetic left ventricular assist device (DEM-LVAD) with a linear oscillatory actuator (LOA). The DEM-LVAD is a pulsatile pump with a pusher plate. The pusher plate is driven directly by the mover of the LOA. The LOA provides reciprocating motion without using any movement converter such as a roller screw or a hydraulic system. It consists of a stator with a single winding excitation coil and a mover with two permanent magnets. The simple structure of the LOA is based on fewer parts to bring about high reliability and smaller size. The mover moves back and forth when forward and backward electric current is supplied to the excitation coil. The pump housings have been designed using three-dimensional computer aided design software and fabricated with the aid of computer aided manufacturing technology. Monostrut valves (Bjork-Shiley #21) were used for the prototype. The DEM-LVAD dimension is 96 mm in diameter and 50 mm thick with a mass of 0.62 kg and a volume of 280 ml. An in vitro test (afterload 100 mm Hg; preload 10 mm Hg; input power 10 W) demonstrated more than 6 L/minute maximum output and 15% maximum efficiency at 130 beats per minute (bpm). Dynamic stroke volume ranged between 40 and 60 ml. The feasibility of the DEM-LVAD was confirmed.

Biophysical Phenomena↗

PubMedDate not supplied

Investigating the functionality of diamond-like carbon films on an artificial heart diaphragm.

In this study, the authors used diamond-like carbon film to coat the ellipsoidal diaphragm (polyurethane elastomer) of artificial hearts. The purpose of such coatings is to prevent the penetration of hydraulic silicone oil and blood through the diaphragm. To attach diamond-like carbon film uniformly on the diaphragm, the authors developed a special electrode. In estimating the uniformity of the diamond-like carbon film, the thickness was measured using a scanning electron microscope, and the characteristics of the diamond-like carbon film was investigated using infrared spectroscopy, Ar-laser Raman spectrophotometer, and x-ray photoelectron spectrometer. Also, to estimate the penetration of silicone oil through the diaphragm, in vitro testing was operated by alternating the pressure of silicone oil for 20 days. The authors were able to successfully attach uniform deposition of diamond-like carbon film on the ellipsoidal diaphragm. In this in vitro test, diamond-like carbon film was proven to have good stability. The amount of silicone oil penetration was improved by one-third using the diamond-like carbon film coating compared with an uncoated diaphragm. It is expected that through the use of the diamond-like carbon film, the dynamic compatibility of an artificial heart diaphragm will increase.

Carbon↗

PubMedDate not supplied

Arterial sound based noninvasive malrotation detection of rotary LVAD.

A number of advanced cardiovascular assist devices have been developed recently with the capability to prolong the life expectancy of patients with cardiac disease. To allow long-term use, it is necessary to assemble these devices using as few accessories as possible; however, a sensor for mechanical disorder detection is typically included to ensure mechanical reliability. Although a rotary left ventricular assist device (LVAD) has a simple mechanism, a malrotation caused by thrombogenesis can occur at any time. This situation could cause fatal damage to the cardiovascular circulation of the patient. In this study, we propose a simple, noninvasive method based on Korotkoff sounds, which would be able to detect the pressure-flow state during circulation supported by a rotary LVAD. Korotkoff sounds provide a means to noninvasively measure blood pressure in auscultation. We have found that the sounds are directly influenced by the pressure-flow state. We measured the arterial sound generated by an occluded brachial artery, as well as the Korotkoff sound generated during rotary LVAD circulation. To verify the effectiveness of the system, a circulatory simulator, rather than a human subject, was used. The arterial sound of several abnormal pressure-flow conditions was investigated. The simulator consists of a pulsatile blood pump, a compliance chamber, flow valves, a venous reservoir, and a rotary LVAD. Abnormal pressure-flow states are generated by simply changing the rotational speed of the rotary LVAD. We established the relationship between an abnormal pressure-flow state and the characteristics of the arterial sound, thus demonstrating that a malrotation of the rotary LVAD can be detected by the change of the arterial sound.

Aorta↗

PubMedDate not supplied

Design and development of an artificial implantable lung using multiobjective genetic algorithm: evaluation of gas exchange performance.

In this study, we constructed an automatic optimization system applying the multiobjective genetic algorithm (MOGA) and developed an artificial implantable lung possessing antithrombogenicity and high gas exchange performance based upon fluid dynamics. This system consists of a three dimenstional CAD system, computational fluid dynamics software, and the multiobjective optimization tool modeFRONTIER (ESTECO CO., Trieste, Italy). The objectives were to minimize the volume of the region having a flow rate of less than 0.5 mm/s by assuming that thrombus formation occurs at this limit (ObjTF) and to minimize the standard deviation of the flow rate in the hollow fiber to obtain high gas exchange performance (ObjGEP). In optimization 1, the arc heights (six variables) and the distance between cross-sections (two variables) were used as design variables in the inflow and outflow portions. In optimization 2, the edges (two variables) of the inflow and outflow portions were optimized in the resulting designs from optimization 1. The optimum designs were manufactured using the rapid prototyping system and were examined by evaluating gas exchange performance (ObjGEP) in vitro. Gas exchange performance increased as the improvement ratio of ObjGEP became higher. For the optimum design (improvement ratio of 74.8% for ObjGEP), O2 transfer increased by an average of 18.4%, and CO2 transfer increased by an average of 40.5% when compared with the original design. The results suggest that this system was not only effective for reducing the time, cost, and labor of developing artificial organs but was also useful as a design and development support system for high performance artificial organs for transplantation.

Algorithms↗

PubMedDate not supplied

New method for the detection of thrombus formation in cardiovascular devices: optical sensor evaluation in a flow chamber model.

We proposed a new method of detecting the onset of thrombus formation based upon the backscattered light intensity changes caused by the alteration of blood flow behavior in the cardiopulmonary devices. In an optical senor based upon the First Order Scattering theory, the relationship between the backscattered light intensity and hematocrit exhibited a monotonically decaying curve for the hematocrit level greater than 45%. To distinguish the effect either by thrombus formation or erythrocyte aggregation on the back-scattered light intensity with a flow chamber connected to a rabbit arterial-venous bypass model, we generated an oscillatory flow using a roller pump and analyzed the results using a Fast Fourier Transform (FFT) method. Our hypothesis was that the nonclotting blood flow would yield an unchanged fundamental spectral power density of the oscillation frequency generated by a roller pump, whereas the thrombus formation would attenuate its power. We measured the back-scattered light intensity in the flow chamber of high shear region and low shear region (n = 5). The blood flow rate was 40 ml/min with the roller pump. The activated clotting time and the hematocrit level were adjusted to 170 +/- 10 s with heparin and 35 +/- 5% with a phosphate buffered sulfate solution, respectively. As a result, the backscattered light intensity from the low shear rate region gradually diminished with time (p < 0.05; 0-5 minutes vs. more than 10-15 minutes), whereas that from the high shear rate region remained fairly constant. The experimental finding supported the hypothesis that the decrease of the backscattered light intensity and diminished spectral power density were caused by the aggregation or clotting erythrocytes. In conclusion, we found that the measurement of the average backscattered light intensity level together with FFT analysis of the backscattered light from the flowing blood is a valuable approach in detecting the onset of thrombus formation.

Animals↗

PubMedDate not supplied

Development of an implantable oxygenator with cross-flow pump.

Thrombogenicity, a problem with long-term artificial lungs, is caused by blood-biomaterial interactions and is made worse by nonuniform flow, which also causes decreased gas exchange. To overcome these obstacles, we changed the inlet and added a uniform flow pump to our previous oxygenator design. Conventional membrane oxygenators have a (1/2)-inch port for the inlet of blood. These port structures make it difficult for the blood to flow uniformly in the oxygenator. In addition, the complex blood flow patterns that occur in the oxygenator, including turbulence and stagnation, lead to thrombogenicity. A cross-flow pump (CFP) can result in uniform blood flow to the inlet side of an oxygenator. In this study, we evaluated the usefulness of an integrated oxygenator with a fiber bundle porosity of 0.6 and a membrane surface area of 1.3 m2. The inlet part of the oxygenator is improved and better fits the outlet of the CFP. Each of the three models of the improved oxygenator has a different inlet taper angle. The computational fluid dynamics analysis showed that, compared with the original design, uniform flow of the integrated oxygenator improved by 88.8% at the hollow fiber membrane. With the integrated oxygenator, O2 transfer increased by an average of 20.8%, and CO2 transfer increased by an average of 35.5%. The results of our experiments suggest that the CFP, which produces a wide, uniform flow to the oxygenator, is effective in attaining high gas exchange performance.

Blood Flow Velocity↗

PubMedDate not supplied

Flow vectorial analysis in an artificial implantable lung.

An artificial implantable lung would be a useful device to support patients awaiting lung transplantation. A suitable device must offer low resistance and adequate gas exchange, be impermeable to plasma, and nonthrombogenic. Although plasma permeability is an intrinsic quality of the materials, the other requirements are largely a function of device geometry, particularly as it relates to fluid dynamics. Using a CAD system and the requirements of a membrane surface area of 1.5 m2 and an inlet outlet port distance of 12 cm, we designed 10 models that varied in their other dimensions. Computational fluid dynamic (CFD) software was applied to the models to determine which minimized regions of low flow velocity. A prototype built to these specifications was used in an in vivo ovine experiment to verify the CFD predictions. The prototype was placed in parallel to the native pulmonary circulation (pulmonary artery to left atrium) for 120 minutes while the activated coagulation times were kept between 110 and 120 seconds and device flow was maintained between 1.5 and 2.5 L/min. Examination of the prototype confirmed a correlation between predicted areas of low flow and thrombus formation. Although nearly identical low flow velocity conditions exist at both the inlet and outlet ports, thrombus formation occurs only near the outlet port. This finding agrees with detailed vectorial analysis, which predicts a more complex flow pattern near the outlet port. Although near the inlet port flow vectors are nearly parallel, near the outlet port flow vectors collide. This area of flow collision corresponds to the area of thrombus formation in vivo. The addition of microflow vectorial analysis to flow velocity predictions allows for improved accuracy in predicting regions at risk of thrombosis in an artificial implantable lung.

Animals↗