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Biomedical subjects

A Kamiya

Publications and source records attributed to A Kamiya.

At least 181 records · Page 10Linked to original sources
PubMed1988

Roles of fluid shear stress in physiological regulation of vascular structure and function.

The effects of fluid shear stress on the function and structure of the vascular system are outlined, based on the findings obtained in our laboratory or of our colleagues. First, it is pointed out that the adaptive response of the vascular wall to flow changes which we observed in the canine carotid artery shunted with the jugular vein altering the internal diameter to keep the wall shear stress constant, can attain the optimum vascular branching structure as predicted in the minimum work model by Murray. Electronmicroscopic studies of similarly shunted arteries revealing various morphological changes in the endothelial cells have suggested that the shear stress initially affects the endothelium. The in vitro experiments using cultured endothelial cells as well have exhibited that the mitotic activity of the cells significantly increases by applying fluid shear stress. From these findings, it is concluded that the adaptive response of the endothelium to the fluid shear stress is an inherent and key process locally regulating the vascular system to be in the most functional state.

Animals↗
PubMed1988

A disk-type apparatus for applying fluid shear stress on cultured endothelial cell.

To study the effect of fluid shear stress on cultured endothelial cells, we have developed an apparatus for the stress creation, which consists of a stainless steel disk driven by an electric DC motor and a stage to place a culture dish and to adjust the distance between the disk and the dish. When the disk is rotated, a concentric fluid movement occurs in the culture medium in the dish and exerts the shear stress on the endothelial cells cultured on the bottom of the dish. A theoretical analyses concerning the induced concentric flow velocity predicted that when the angular velocity of the disk rotation (omega) is slow enough to maintain a Reynolds' number of the order of 10, the exerted wall shear stress tau w on the endothelial cell monolayer is given for a constant as tau w = mu r omega/d where mu is the viscosity of the medium, d the distance from the plate to the monolayer and r the radial distance from the center of the dish. When omega is varied in a sinusoidal mode tau w also becomes sinusoidal, thus allowing to apply a pulsatile stress. In vitro experiments carried out to examine the validity of the theoretical results, using a suspension of polystyrene as a tracer with the ordinary culture medium and 99% ethanol, revealed excellent agreement of the measured velocity profiles with the predicted ones. The results demonstrated that the present apparatus can create both the steady and pulsatile wall shear stress on the culture cell layer as expected, unless Reynolds' number greatly exceeds the level of 10.

Cells, Cultured↗
PubMed1987

Noninvasive measurement of arterial blood pressure and elastic properties using photoelectric plethysmography technique.

The objective of this paper is to review our developed method for measuring noninvasively the arterial blood pressure as well as the mechanical properties of the vascular system in a thin portion of the biological segment such as human fingers or small animal extremities like rat tails and rabbit forelegs. This measurement is based on a principle called the 'volume-oscillometric method'. During the gradual change in cuff pressure, the amplitude of consecutive arterial volume pulsations associated with pulse pressure shows change characteristically due to the nonlinearity of arterial pressure-volume(P-V) relation. Arterial pressure can be accurately determined by detecting this characteristic change in the amplitude, while the arterial elastic properties such as P-V relationship and volume elastic modulus can be noninvasively obtained as a function of arterial transmural pressure, provided that the arterial volume changes are quantitatively determined during this pressure measurement. The validity and accuracy of this pressure and elasticity measurement with photoelectric plethysmography technique for detecting arterial volume changes are clearly demonstrated on the in vitro and in vivo experiments. Considering the simplicity and practicability of this measurement using the photoelectric plethysmography, we present a new portable instrument for the long-term ambulatory monitoring of indirect arterial pressure and a handy fully-automatic instrument for the noninvasive measurement of arterial elastic properties, and a few examples obtained by each instrument are also described.

Animals↗
PubMed1987

The effect of fluid shear stress on the migration and proliferation of cultured endothelial cells.

We have examined the effect of shear stress on the regenerative response of cultured vascular endothelial cells by using a fluid shear apparatus designed in our laboratory. The shear stress was created on the endothelial cell layer of a fetal calf and grown confluently in a culture dish by whirling the medium, with a rotating disk placed on the fluid surface. The effect of the shear load (0.3-1.7 dyn/cm2) over 24 hr was evaluated by counting the number of regenerated cells in a denuded area that had been created by mechanically removing some cells before rotating the medium. The cell number observed in the denuded area after the exposure to shear stress was about twice as great as that of the static control. The difference was statistically significant (P less than 0.01 to P less than 0.05). Cell migration and proliferation occurred more prominently in the downstream portion of the flow than in the upstream part. The cell number in the downstream portions correlated significantly with the intensity of the applied shear stress (P less than 0.05). These results indicate that shear stress can stimulate the migration and proliferation of endothelial cells.

Animals↗
PubMed1987

Study of the behaviour of mutagens in wastewater and emission gas from a municipal incinerator evaluated by means of the Ames assay.

We have investigated the mutagenic activity of extracts from the wastewater of sewage treatment plants in municipal waste incinerators and evaluated the relative contribution of various routes of emission from the incinerator to the total output of mutagens. The mutagenicity of wastewater extracts from a complete combustion incinerator was 10% of that from an incomplete combustion unit. About 90% of all the mutagens produced in a municipal incinerator are discharged into the atmosphere as emission gases, and 10% are disposed of in the wastewater treatment plants. Most of the mutagens in wastewater treatment plants are not decomposed by normal aeration times, but are removed by adsorption onto suspended solids.

Air Pollutants↗
PubMed1987

Polyamine oxidase from water hyacinth: purification and properties.

Polyamine oxidase was purified to homogeneity from leaves of water hyacinth by the criterion of sodium dodecyl sulfate gel electrophoresis (SDS disc PAGE). The enzyme showed a high specificity for spermidine and spermine (K(m) values 28 micromolar and 20 micromolar, respectively). The optimal pH of the enzyme for both spermidine and spermine was 6.5. The molecular weight of the enzyme estimated by Sephadex G-200 gel filtration was 87,000, while SDS disc PAGE gave a single band at the molecular weight of 60,000. Octamethylenediamine and quinacrine were strong inhibitors of the enzyme, but p-chloromercuribenzoate was without effect. A prosthetic group in the enzyme was identified as flavin adenine dinucleotide.

Journal Article↗
PubMed1987

A compact centrifugal blood pump for extracorporeal circulation: design and performance.

A new compact centrifugal blood pump driven by a miniature DC servomotor has been designed for use for short-term extra corporeal and cardiac-assisted circulation. The impeller of the pump was connected directly to the motor by using a simple-gear coupling. The shaft for the impeller was sealed from blood by both a V-ring and a seal bearing. Either pulsatile or nonpusatile flow was produced by controlling the current supply to the motor. The pump characteristics and the degree of hemolysis were evaluated with regard to the configuration of the impeller with a 38-mm outer diameter in vitro tests; the impeller having the blade angles at the inlet of 20 deg and at the outlet of 50 deg was the most appropriate as a blood pump. The performance in an operation, hemolysis and thrombus formation in the pump were assessed by a left ventricular bypass experiment in dogs. It was suggested by this study that this prototype pump appears promising for use not only in animal experiments but also in clinical application.

Animals↗
PubMed1986

Step response analyses of the cardiovascular system and their application to the measurement of systemic and pulmonary vein compliances.

A theoretical analysis of the step response in the closed cardiovascular system induced by a sudden shift of the right cardiac output curve predicted that if the relations of the right heart output (COr) and the total systemic capillary flow (CFs) to the systemic venous pressure (Psv) are linear, then the time course of Psv change will become monoexponential with a time constant T given by T = Csv/(Gr + Gs), where Csv is the systemic vein compliance and Gr and Gs are the conductances of the transient COr-Psv and CFs-Psv relationships. A similar prediction was obtained for the time constant T of the pulmonary vein pressure (Ppv) response to the step change in the left cardiac output (COl) curve, pulmonary vein compliance (Cpv) and the conductances of the COl curve, and the pulmonary capillary flow (CFp) curve against Ppv. The actual Psv or Ppv changes following sudden alteration of the COr or COl curve by inflation and deflation of the balloon in the right or left atrium revealed monoexponential time courses. Semilogarithmic plots of the transient vein pressure changes yielded correlation coefficients of -0.995 +/- 0.006 (means +/- SD) in 11 curves for Psv and 0.977 +/- 0.017 in 16 curves for Ppv (P less than 0.01). The assumed linearity of dynamic COr and COl curves was confirmed by beat by beat COr-Psv and COl-Ppv relationships during the step responses, except for the first few beats immediately after the balloon maneuver. The linearity of the dynamic CFs curve was examined by measuring CFs with a double-step balloon maneuver so as to cause rapid equilibrium between COr and CFs at varied moments of the transient process. The correlation coefficient between CFs and Psv thus obtained was 0.98 +/- 0.04 (P less than 0.01). A similar linearity of the dynamic CFp-Ppv relationship was suggested from their steady-state curves. The values of Csv calculated from the experimental data were 1.70 +/- 0.12 ml/mmHg/kg body wt in 11 curves and those of Cpv were 0.13 +/- 0.03 ml/mmHg/kg in 15 curves. These results are mostly consistent with those previously reported.

Animals↗
PubMed1985

Cytoplasmic microfilaments in endothelial cells of flow loaded canine carotid arteries.

To observe cytoplasmic microfilaments in the endothelial cells of flow-loaded arteries, an arteriovenous shunt was constructed between the common carotid artery and the external jugular vein in 26 dogs. After measuring the flow rates of the arteries, the endothelial layer was examined ultrastructurally with a transmission electron microscope at three different times: 1 week (acute experiments), 2-4 weeks (subacute experiments), and 4-7 months (chronic experiments). Six-to seven-nanometer microfilaments were found forming bundles, which usually ran longitudinally along the long axis of the vessel. In the acute experiments, the bundles increased in the endothelial cells of the flow-loaded arteries. They showed incomplete striation and were mostly located close to the basal cell membrane. In the subacute experiments, they showed an increase with the development of cross-striation. The half-desmosomal structure of the basal cell membrane had developed a close connection to the bundles. In the chronic experiments, the bundles were especially conspicuous around the intercellular junction. Tennanometer microfilaments increased in the endothelial cells of the flow-loaded artery in the subacute and chronic experiments. We consider that the bundles of 6- to 7-nm microfilaments might be structures developed to combat wall shear stress corresponding to actin filament stress fibers.

Actin Cytoskeleton↗