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Biomedical subjects

N Ohshima

Publications and source records attributed to N Ohshima.

At least 109 records · Page 6Linked to original sources
PubMed1979

Performance of baffled bubble blood oxygenators.

Bubble blood oxygenators equipped with baffles of various types in the oxygenating column were studied. The rate of hemolysis, the volumetric coefficient for oxygen absorption into blood, and the fractional gas holdup were found to be affected mainly by the superficial gas velocity. When compared with the conventional bubble blood oxygenator without baffles, the bubble oxygenators equipped with various types of baffles (i.e., horizontal perforated baffles, radial vertical baffles, and a concentric hollow cylinder with and without horizontal perforated baffles) showed less hemolysis, larger gas holdup and higher values of the coefficient for oxygen absorption. Values of the heat transfer coefficient on the surface of the cylindrical baffle, which is useful as a built-in heat exchanger, were several times greater than those for single-phase heat transfer in conventional blood heat exchangers.

Adsorption↗
PubMedDate not supplied

Flow injection determination of glucose, bile acid and ATP using immobilized enzyme reactor and chemiluminescent assay of NAD(P)H.

We have developed a chemiluminescent flow injection method for analysis of bile acid, glucose and ATP using the chemiluminescent assay of NADH using 1-methoxy-5-methylphenazinium methyl sulphate (1-MPMS)/isoluminol(IL)/microperoxidase (m-POD) system and immobilized enzyme reactors such as 3 alpha-hydroxysteroid dehydrogenase, glucose-dehydrogenase, hexokinase and glucose-6-phosphate dehydrogenase. The standard curves were obtained in the range of 5-100 pmol for bile acid, 0.5-5.0 nmol for glucose and 10(-7)-10(-5) mol/L for ATP. The coefficient of variation for each assay was not more than 4.1% for bile acid, 2.3% for glucose and 5.3% for ATP, respectively.

3-Hydroxysteroid Dehydrogenases↗
PubMedDate not supplied

Simulation of intraluminal gas transport processes in the microcirculation.

Intraluminal resistance to gas transport between the microcirculation and tissue was neglected for a half-century following the early work of Krogh. In recent years it has come to be understood that this neglect is seriously in error. This paper reviews the background for the long period of misdirection, and progress in placing the simulation of gas transport processes on a more accurate, quantitative basis.

Acid-Base Equilibrium↗
PubMedDate not supplied

Dynamics of platelet adhesion to artificial materials and cultured endothelial cells under shear flow.

To evaluate the dynamic features of platelet adhesion to biomedical materials, a new shear flow testing apparatus was constructed. A cone-plate rotational viscometer, equipped with a transparent cone and transparent bottom window, was mounted on the stage of an inverted microscope. Test materials (glass, silicone, polyvinyl chloride, Thermanox, and porcine endothelial cells cultured on glass coverslips) were placed on the bottom window. Real time microscopic images of platelets adherent to the test materials in a shear rate range between 3.6 and 360 1/s were observed and recorded with a videocassette recorder. Time course changes in the number of adherent platelets were analyzed on the basis of a convective diffusion model. With respect to effective diffusivity of platelets (De) and the surface reactivity constant (K), less significant differences were found among artificial materials. In the case of cultured endothelial cells, both De and K, which were evaluated for the first time in the present study, were two to four orders of magnitude lower than those obtained with artificial materials.

Animals↗
PubMedDate not supplied

Performance of a new hybrid artificial liver support system using hepatocytes entrapped within a hydrogel.

To develop a hybrid artificial liver support system (ALSS), the authors constructed a rotating-disk type ALSS using hepatocytes entrapped within a calcium alginate hydrogel. This module was designed in imitation of the gas-liquid contactor that uses the same principle. Forty disks with film-shaped hydrogel were mounted to a horizontal rotating axis and were kept in contact with blood. The concentration of hepatocytes in the gel varied from 1.9 X 10(9) to 1.7 X 10(10) cells/L gel. Entrapping hepatocytes within hydrogel kept the hepatocytes viable, and results of in vitro experiments showed ammonium metabolism and urea synthesis. The results of ex vivo perfusion experiments using cats with acute hepatic insufficiency indicated that this module had the ability to replace liver function in vivo.

Ammonia↗
PubMedDate not supplied

Improvement of metabolic performance of hepatocytes cultured in vitro in a packed-bed reactor for use as a bioartificial liver.

A packed-bed reactor using reticulated polyvinyl formal (PVF) resin as a support material is a useful configuration to achieve high density culture of hepatocytes for use as a bioartificial liver. The authors investigated the effects of oxygen concentrations of the culture medium on the metabolic performance of hepatocytes cultured in the reactor. A packed-bed reactor loaded with 250 PVF resin cubes (2 x 2 x 2 mm) was used. Hepatocytes obtained from male Wistar rats were inoculated into the reactor. Culture medium was perfused from the reservoir into the reactor through an oxygenator using a roller pump. Concentration of the dissolved oxygen in the medium was controlled by changing the gas mixture ratio supplied to the oxygenator. Hepatocytes cultured in the packed-bed reactor (cell density: 8.6 x 10(6) cells/cm3 PVF) under conditions of high dissolved oxygen concentrations ranging from 260 to 460 micromol/L showed 30% higher ammonium metabolic activity and 85% higher albumin secretion activity compared with those from the monolayer culture in the earlier culture stage (up to 2 days). However, low oxygen concentrations in the medium (<100 micromol/L) impaired activities of cultured hepatocytes.

Animals↗
PubMedDate not supplied

Effects of shear stress on metabolic function of the co-culture system of hepatocyte/nonparenchymal cells for a bioartificial liver.

To improve the culture conditions of hepatocytes for use as a bioartificial liver, the effects of shear flow on the co-culture system of hepatocytes/nonparenchymal cells (NPC) were investigated. A flow chamber with a collagen coated rectangular glass plate, where hepatocytes (5 x 10(4) cell/cm2) and NPC (2 x 10(5) cell/cm2) were seeded, was used to attain a shear stress of 4.7 dyne/cm2. Concentrations of ammonia and urea in the medium were measured daily during the 2 week experiment. The metabolic activity of hepatocytes in the homotypic culture were lower than those of the co-culture, especially when the cultivation time exceeded 1 week. In addition, the applied shear flow promoted activity of the co-culture system. An enhancement in the rates of ammonium removal and urea synthesis was obtained in the perfusion systems. Morphologic observation revealed that aggregates of hepatocytes formed abundantly in the perfusion system and hepatocytes developed a cuboid shape. This suggested that perfusion affected the function and morphology of hepatocytes in the co-culture system. Shear flow could induce cell-cell interactions and secretion of extracellular matrix through the activation of NPC.

Animals↗
PubMedDate not supplied

Long-term culture of fetal liver cells using a three-dimensional porous polymer substrate.

To develop a bioartificial liver, long-term culture of fetal liver cells over a month's time was performed under three different culture conditions, i.e., stationary cultures and shaken-flask cultures, both by using a substratum made of porous polyvinyl formal (PVF) resin and conventional monolayer dish cultures as controls. Time course changes in cell numbers and albumin secretion were evaluated in cultures using Williams' E medium (WE) or minimum essential medium alpha (aMEM) supplemented with serum and hormones. In the WE medium, the numbers of fetal liver cells in all culture conditions gradually decreased with time, and albumin secretion rates rapidly decreased. In the stationary cultures using PVF, however, a significant increase in albumin secretion was observed after two weeks of culture. When cells were cultured in aMEM, the fetal liver cells exhibited sufficient proliferation in stationary and monolayer cultures, although albumin secretion rates per single cell were lower than those in WE. On the basis of these results, another series of culture experiments were performed, in which aMEM was used for the first 10 days to encourage cell proliferation, and the medium was changed to WE afterward. In these cultures, albumin secretion rates in the stationary cultures dramatically increased after the medium exchanges and were maintained at these high levels throughout the remaining culture period.

Animals↗
PubMedDate not supplied

New type of matrix support for bone marrow cell cultures: in vitro culture and in vivo transplantation experiments.

A new type of bone marrow cell culture system was developed by using a highly porous substrate matrix, i.e., porous polyvinyl formal (PVF) resin. Murine bone marrow (BM) cells were cultured without the use of exogenous growth factors in a three-dimensional matrix support made of collagen coated porous PVF resin. To examine the optimal conditions for highest stromal cell density, short-term and long-term in vitro culture experiments using PVF were performed. In the short-term culture experiments, it was found that cubes of PVF (10 x 10 x 2 mm and 130 microm in pore size) coated with type I collagen with a seeding density of 2x10(7) BM cells offered the most appropriate culture conditions. In the long-term cultures, BM cells in PVF maintained their viability for up to 6 weeks. In another series of re-inoculation experiments, freshly isolated BM cells were inoculated onto the already developed stromal layer. In this study, a higher cell density of the stromal layer was obtained in the PVF culture compared with those in the control dish culture. Based upon the results of in vitro experiments, in vivo transplantation studies were also performed. Histologic examinations of the subcutaneously transplanted PVF with stroma revealed host derived hematopoiesis inside the PVF matrix. Moreover, survival of approximately 15% of the transplanted BM cells that were cultured in PVF were confirmed in X-ray irradiated recipients. From these results, it is suggested that PVF resin is a promising three-dimensional substrate for BM cell culture and that it can maintain hematopoietic stem cells or progenitor cells after transplantation.

Animals↗
PubMedDate not supplied

Effect of shear stress on platelet adhesion to expanded polytetrafluoroethylene, a silicone sheet, and an endothelial cell monolayer.

We visualized in real-time platelets adhering to the surface of three representative biomaterials, by using an apparatus consisting of a modified cone and plate rheometer combined with an upright epifluorescence microscope under two shear flows (0.1 and 5.0 dyne/cm2). The materials were expanded polytetrafluoroethylene (ePTFE), silicone sheet, and a monolayer of bovine endothelial cells (ECs) formed on glass, all of which are opaque materials used for artificial blood vessels and medical devices. According to quantitative analysis, the monolayer of ECs formed on glass had better blood compatibility than did either the ePTFE or the silicone sheet under shear flow conditions. Under a shear flow condition of 0.1 dyne/cm2, platelet adhesion was silicone sheet > ePTFE. In contrast, under a shear flow condition of 5.0 dyne/cm2, ePTFE > silicone sheet. These results indicate that the intensity of shear stress could modify the order of hemocompatibility of the materials. Therefore, direct observation of platelet adhesion under shear flow conditions is indispensable for testing and screening biomaterials and for providing a precise quantitative evaluation of platelet adhesion.

Animals↗
PubMedDate not supplied

Blood flow and leukocyte adhesiveness are reduced in the microcirculation of a peritoneal disseminated colon carcinoma.

Dynamic behavior of leukocytes in the microcirculation of solid tumor tissue was visualized using a fluorescent labeling technique combined with the use of a real-time confocal laser-scanning microscope (CLSM) system. Colon tumor cells (RCN-9) were inoculated into the peritoneal cavity of male Fischer 344 rats. Tumor-free rats were similarly injected with physiological saline (intraperitoneally). Ten days after tumor inoculation, the mesentery was exteriorized and subjected to vital microscopic observation under the CLSM system. Leukocytes were labeled with rhodamine 6G (100 microg kg(-1), intravenously), and their behavior within the microvessels (10-30 microm in diameter) was analyzed both in the solid tumor tissues and the normal mesentery. Wall shear rate was calculated from the measured values of vessel diameter and erythrocyte flow velocity. In tumor microvasculature of tumor-bearing rats, the centerline erythrocyte velocity (0.73 +/- 0.58 mm s(-1), mean +/- standard deviation) and wall shear rate (210 +/- 151 s(-1)) were significantly lower than those of the tumor-free rats (1.27 +/- 0.83 mm s(-1), 344 +/- 236 s(-1), respectively). Despite such reduced flow conditions, flux of the rolling leukocytes as well as density of the adhered leukocytes both decreased significantly in tumor microvasculature as compared with normal controls. The methods developed in this work show promise in improving our understanding of tumor biology and pathophysiology.

Adhesiveness↗
PubMedDate not supplied

Platelet thrombi produced on cultured endothelial cells by the dye/light method.

Platelet adhesion and aggregation were induced on cultured endothelial cells using the fluorescent dye/light method. A cone-and-plate apparatus was newly developed to observe interactions between platelets and cultured endothelial cells under a shear flow condition. The platelet deposition grew on the light-irradiated area of the cells. Degree of endothelial cell injury induced by the dye/light reaction seemed to depend on the dye concentration. Application of either aspirin or indomethacin significantly inhibited the growth of platelet aggregation, but was not effective for the platelet adhesion to endothelial cells. The platelet thrombi were formed on endothelial cells without their denudation. It was found by transmission electron microscopy that platelets directly adhered to endothelial cells which were not seriously damaged. This thrombus model is expected to be applicable to some physiological and pharmacological studies investigating platelet-endothelial cell interaction and mechanism of platelet thrombus formation in blood vessels.

Animals↗