Biomedical subjects

Masao Doi

Publications and source records attributed to Masao Doi.

26 records · Page 2Linked to original sources

PubMed2004

Stenting at the flow-limiting segment in tracheobronchial stenosis due to lung cancer.

Airway stenting at the wave-speed flow-limiting segment (the choke point) is assessed. We determined prospectively the precise location of the choke point using the flow-volume curve, endobronchial ultrasonography, ultrathin bronchoscopy, and three-dimensional computed tomography scan before and after stenting in 64 patients with extrincic compression due to lung cancer. We noted distinct flow-volume curve patterns specific to the type of stenosis. The tracheal stenosis group indicated fixed narrowing patterns with an expiratory plateau, bronchial stenosis group dynamic collapse patterns with an expiratory flow deterioration (choking), carinal stenosis group combined fixed and dynamic patterns, and extensive stenosis group complex patterns containing elements of all the former. After stenting, almost full-function patterns with significant improvement in PEF were observed in all groups (p < 0.01, p < 0.05, p < 0.001, p < 0.01, respectively). In patients with extensive stenosis, implantation of additional stents was required when the choke points were observed to have migrated to the areas of malacia with cartilage destruction by the tumor. Secondary stenting at migrated choke points resulted in a significant improvement in PEF over the initial stenting (p < 0.01). Stenting at the choke point improved expiratory flow limitation by increasing the cross-sectional area, supporting the weakened airway wall and relieving dyspnea.

Adult↗

PubMed2004

Theory of one-dimensional swelling dynamics of polymer gels under mechanical constraint.

Recently, the swelling kinetics of thin-plate gels with rectangular surfaces under mechanical constraint was experimentally investigated [J. Chem. Phys. 114, 5012 (2001)]]. In this system, the top and bottom surfaces of gels were chemically clamped on the glass plates, and the gels could swell and shrink only along the thickness direction when the osmotic pressure of the solvent is changed. Here, we analyze this process using the linearized stress-diffusion coupling model of gels based on the two fluids model. The result is somewhat unusual in that the time evolution of the thickness is described by a single exponential even though the swelling is governed by the diffusion of solvent. This result and that the characteristic relaxation time depends on the lengths of the rectangular surfaces and not on the thickness of gels agree well with the experiment.

Journal Article↗

PubMed2004

Molecular dynamics simulation study on the phase behavior of the Gay-Berne model with a terminal dipole and a flexible tail.

To study the effect of the alkyl tail and the terminal dipole on the stability of the liquid crystalline phase of mesogens, we have carried out molecular dynamics simulations for 1CB(4-methyl-4'-cyanobiphenyl) and 5CB(4-n-pentyl-4'-cyanobiphenyl) by using a coarse-grained model. In the coarse-grained model, a 5CB molecule is divided into the rigid part of 1CB moiety, which is represented by an ellipsoid, and the remaining flexible part which is represented by a chain of united atoms. The nonbonded potential between coarse-grained segments is represented by the generalized Gay-Berne (GB) potential and the potential parameters are determined by directly comparing the GB potential with the atomistic potentials averaged over the rotation of the mesogen around its axis. In addition, a dipole moment is placed at one end of the ellipsoid opposite to the flexible tail. The ordered state obtained in the polar 5CB model was assigned as the nematic phase, and the experimental static and dynamical properties were reproduced well by using this coarse-grained model. Both the dipole-dipole interactions and the thermal fluctuation of the flexible tail increase the positional disorder in the director direction, and stabilize the nematic phase. Thus, the nematic phase in the polar 5CB is induced by a cooperative effect of the flexible tail and the terminal dipole. It is noted that a local bilayer structure with head-to-head association is formed in the nematic phase, as experimentally observed by x-ray diffraction measurements.

Journal Article↗

PubMed2004

Low-titer cold agglutinin disease with systemic sclerosis.

A 60-year-old woman with systemic sclerosis (SSc) was admitted because of severe anemia and Raynaud's phenomenon. Her anemia was associated with a low serum haptoglobin level and positive results of direct Coomb's tests, which indicated the presence of autoimmune hemolysis. Other laboratory investigations revealed positive anti-nuclear antibodies, anti-topoisomerase antibody, cold agglutinins, as well as low serum levels of IgM, C3, C4 and CH50. Bone marrow aspiration showed discrete hyperplasia of the erythropoietic system. She was diagnosed as low-titer cold agglutinin disease rousing secondarily to SSc. The anemia was alleviated with the oral administration of prednisolone. This case emphasized, in terms of pathogenesis, the close association between systemic rheumatic diseases and hematological abnormalities evoked by autoimmunity.

Anemia, Hemolytic, Autoimmune↗

PubMed2003

Molecular modelling of entanglement.

The modelling of molecular entanglement in polymeric materials is an old problem, and has evolved gradually over the last 60 years, with two key approaches: the network model of Green & Tobolsky, and the tube model of Edwards and de Gennes. We will show that these models can be merged together in a straightforward manner. The resulting model, called the dual slip-link model, can be handled by computer simulation, and it can predict the linear and nonlinear rheological behaviours of linear and star polymers with arbitrary molecular weight distribution.

Models, Molecular↗

PubMed2003

Sarcoidosis with multiple organ involvement emerging as Löfgren's syndrome.

A 52-year-old woman was admitted because of high-grade remittent fever, erythema nodosum, and arthritis which had been lasting two months. Antibiotics did not improve her condition. A chest CT scan examination revealed bilateral hilar and mediastinal adenopathy and multiple nodular opacities in the bilateral lungs. The wedge biopsy of the right lower lobe using video-assisted thoracoscopy presented the histological findings of sarcoidosis. Finally, this case fulfilled the criteria of Löfgren's syndrome. Due to the uncovered cardiac involvement, the systemic glucocorticoid therapy had to be initiated. This case suggests that atypical forms of sarcoidosis should be kept in mind as well, when facing cases with unknown fever.

Arthritis↗

PubMed2003

On the communication pathways between the central pacemaker and peripheral oscillators.

Circadian rhythms are regulated by clocks located in specific structures of the CNS, such as the suprachiasmatic nucleus (SCN) in mammals, and by peripheral oscillators present in various other tissues. The expression of essential clock genes oscillates both in the SCN and in peripheral pacemakers. Peripheral tissues in the fly and in the fish are directly photoreceptive. In particular, we have established the Z3 embryonic zebrafish cell line that recapitulates the dynamic light-dependent regulation of the vertebrate clock in vitro. In mammals the synchronization to daily light cycles involves neural connections from a subset of light-sensitive receptor-containing retinal ganglion cells. Humoral and/or hormonal signals originating from the SCN are thought to provide timing cues to peripheral clocks. However, alternative routes exist, as some peripheral clocks in mammals can be specifically entrained in a SCN-independent manner by restricted feeding regimes. Thus, not all peripheral tissues are equal in circadian rhythmicity. Testis, for example, displays no intrinsic circadian rhythmicity and the molecular mechanisms of clock gene activation in male germ cells appear to differ from other tissues. The study of the connecting routes that link the SCN to peripheral tissues is likely to reveal signalling pathways of fundamental physiological significance.

Animals↗

PubMed2002

Light-dependent changes in the chick pineal temperature and the expression of cHsp90 alpha gene: a potential contribution of in vivo temperature change to the photic-entrainment of the chick pineal circadian clock.

The circadian clock is entrained to the diurnal alteration of environmental conditions such as light and temperature, but the molecular mechanism underlying the entrainment is not fully understood. In the present study, we employed a differential display-based screening for a set of genes that are induced by light in the chick pineal gland, a structure of the central clock entrainable to both light and temperature changes. We found that the level of the mRNA encoding chicken heat shock protein 90 alpha (cHSP90 alpha) was rapidly elevated in the pineal gland within a 5-min exposure of chicks to light. Furthermore, the pineal cHsp90 alpha mRNA was expressed rhythmically under both 12-hr light/12-hr dark (LD) cycles and constant dark (DD) conditions. The total amount of the pineal cHSP90 alpha protein was, however, kept at nearly constant levels under LD cycles, and immunohistochemical analyses of the pineal cHSP90 alpha showed invariable localization at the cytoplasm throughout the day. In vivo measurement of the chick pineal temperature demonstrated its light-dependent and time-of-day-dependent change, and the profile was very similar to that of the pineal cHSP90 alpha mRNA level. These observations suggest that the in vivo temperature change regulates the expression of temperature-responsive genes including cHSP 90 alpha in the pineal gland. The temperature change may induce a phase-shift of the pineal clock, thereby facilitating its efficient entrainment to environmental LD cycles.

Animals↗