Biomedical subjects

Ichiro Taga

Publications and source records attributed to Ichiro Taga.

5 recordsLinked to original sources

PubMed2006

In vitro evaluation of a newly developed implantable artificial lung.

A prototype of an implantable artificial lung without a pump (Prototype II) has been tested. A commercially available membrane oxygenator, MENOX AL6000alpha (Dainippon Ink and Chemicals, Inc., Tokyo, Japan), was used as a basic model. The packing density of the hollow fiber was decreased in order to achieve low resistance through the blood pathway. The configuration of its housing was also re-designed using computational fluid dynamics (CFD). The first prototype, known as Prototype I, was already tested in a 15 kg pig, which showed excellent gas exchange with normal hemodynamics. A second prototype, Prototype II, has a larger membrane surface area than Prototype I. The device was evaluated for resistance through the blood path and gas transfer rate in an in vitro setting by the single pass method using fresh bovine blood. The resistance through the blood path of Prototype II was 2.7+- 0.7 mmHg/(L/min) at Q = 5L/min. The oxygen (O2) transfer rate was 178 +- 5.3 ml/min at Q = 5 L/min, V/Q = 3, and the carbon dioxide (CO2) transfer rate was 149 +- 28 ml/min at Q = 5 L/min, V/Q = 2 (Q: blood flow rate, V: sweep oxygen flow rate through the artificial lung). For the purpose of implantation, this prototype showed sufficiently low resistance in the pulmonary circulation with reasonable gas exchange.

Artificial Organs↗

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↗