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Query: UMLS:C0851184 (thinning)
 11,252 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Blood viscosity varies during the course of artificial heart implants and is affected by pathological conditions. To gauge the potential effect of changing viscosity on valve performance, leakage rates were measured across a closed Medtronic-Hall valve with water, water/glycerol and fresh whole bovine blood for aortic and pulmonary pressure ranges. As might be expected from the low Reynolds numbers (< 140), losses across the valve were found to be primarily viscous. For the two Newtonian fluids, leakage was slightly less than linearly proportional to pressure. This is comparable with empirical data for orifice flow, which predicts three fifths power dependence on pressure. For blood, however, the greater than linear dependence on pressure found suggests that the pseudoplasticity (shear-thinning behavior) of blood is important. These data provide evidence that the viscous and non-Newtonian properties of blood must be taken into account in modelling prosthetic valve performance and may affect the test methods and flow regulation strategies for prosthetic blood pumps.
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PMID:Influence of viscosity and pressure on prosthetic valve regurgitation. 831 39

A preparational method was developed solving the problem of cross-sectional TEM preparation of thin films and layer systems deposited onto water-soluble substrates. The technique is based on the replacement of the sample onto steady substrate, followed by mechanical and ion beam thinning. Cross-sectional TEM micrographs of Ag and Ag/Ag2Se layers are shown presenting the efficiency of this novel technique.
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PMID:A novel method for the cross-sectional TEM preparation of thin films deposited onto water-soluble substrates. 835 85

The biocompatibility of hydrogel intracorneal lenses (ICLs) implanted in monkey eyes was evaluated for periods ranging up to five years. Seventy-three plus or minus powered ICLs made of Lidofilcon A (68% water) or Lidofilcon B (79% water) were implanted following lamellar dissection with a microkeratome. Ten sham surgical procedures were performed without ICL implantation as controls. Eyes were followed for up to five years by slitlamp biomicroscopy and specular microscopy. Light and transmission electron microscopic evaluations of enucleated eyes were performed at various intervals. Minimal tissue reaction was noted; both hydrogel materials appeared to be equally well tolerated. Failures usually occurred as a result of microkeratome problems encountered during surgery. Histopathological changes to the cornea included epithelial thinning anterior to the thickest portion of the ICL, fibroblastic activity along the ICL-stromal interface, and deposition of an amorphous extracellular material adjacent to the ICL. These observations did not appear to be clinically significant as the eyes were quiet by slitlamp examination. Removal of three ICLs eight to ten months prior to enucleation restored the normal histological characteristics of the cornea. The endothelial cell density of ICL-implanted eyes decreased by 4.3% (n = 17) six months after surgery but remained stable thereafter. The variation in endothelial cell area and percentage of hexagonal cells did not change over 50 months. The results appear to demonstrate that high water content synthetic ICLs can be well tolerated in the monkey cornea for up to five years.
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PMID:Assessment of the long-term corneal response to hydrogel intrastromal lenses implanted in monkey eyes for up to five years. 848 63

Evolutionary processes have adapted nektonic animals to interact efficiently with the water that surrounds them. Not all these adaptations serve the same purpose. This paper concentrates on reduction of drag due to friction in the boundary layer close to the body surface. Mucus, compliant skins, scales, riblets and roughness may influence the flow velocity gradient, the type of flow and the thickness of the boundary layer around animals, and may seriously affect their drag in a positive or negative way. The long-chain polymers found in mucus decrease the pressure gradient and considerably reduced drag due to friction. The effect is probably due to channelling of the flow particles in the direction of the main flow, resulting in a reduction of turbulence. Compliant surfaces could probably reduce drag by equalising and distributing pressure pulses. However, the existing evidence that drag reduction actually occurs is not convincing. There is no indication that instantaneous heating, reducing the viscosity in the boundary layer, is used by animals as a drag-reducing technique. Small longitudinal ridges on rows of scales on fish can reduce shear stress in the boundary by a maximum of 10% compared with the shear stress of a smooth surface. The mechanism is based on the impedance of cross flow under well-defined conditions. The effect has been visualized with the use of particle image velocimetry techniques. The function of the swords and spears of several fast, pelagic, predatory fish species is still enigmatic. The surface structure of the sword of a swordfish is shown to be both rough and porous. The height of the roughness elements on the tip of the sword is close to the critical value for the induction of a laminar-to-turbulent flow transition at moderate cruising speeds. A flow tank is described that is designed to visualize the effects of surface imperfections on flow in the boundary layer in direct comparison with a smooth flat wall. The flow in a 1 m long, 10 cm high and 1 cm wide channel is visualized by illuminating the particles in a thin laser light sheet. The first results show that a rough surface increases the shear stress in the boundary layer and makes it thinner. The function of the roughness on the sword of a swordfish is probably to reduce the total drag by generating premature turbulence and by boundary layer thinning, despite an increased friction over the surface of the sword. The function of the porous surface structures on the sword, and of the porous skins of sharks and of the castor oil fish, will probably be discovered soon using new particle image velocimetry techniques applied under strong magnification to visualize the local behaviour of the flow.
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PMID:Body surface adaptations to boundary-layer dynamics. 857 Dec 18

The rheological characteristics of bovine amniotic fluid have been studied at different shear rates. The viscosity of bovine amniotic fluid at 20 degrees C was found to increase with time at a constant low shear rate during the measurement. Additionally, the viscosity was observed to decrease with increasing shear rate, indicating that a shear thinning behaviour of the fluid was occurring. The log-log plot of shear stress versus shear rate yielded a straight line consistent with non-Newtonian behaviour of the fluid and characteristic of pseudoplastic liquids. The data of shear stress versus shear rate could be represented by a power law model. The treatment of amniotic fluid with cetylpyridinium chloride (CPC) resulted in the precipitation of a mixture of components, including complex sulphated polysaccharides and extracellular proteoglycans, with the viscosity of the resulting liquid similar to that of water at 20 degrees C. In addition, the viscosity of the CPC-pretreated fluid did not increase with time at constant shear rate and remained constant with the increase in shear rate. The apparent increase in viscosity with time and the shear thinning behaviour of the amniotic fluid can thus be attributed to pseudoplastic liquid behaviour associated with the presence of structurally complex polysaccharides and extracellular proteoglycans. The implications of this fluid viscosity behaviour are discussed in terms of their impact on the operation of packed or expanded (fluidized) chromatographic bed systems when amniotic fluid biofeedstocks are used as a source of commercially important proteins.
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PMID:Investigations into the rheological characteristics of bovine amniotic fluid. 862 81

The purpose of this study was to determine if air thinning three dentin adhesives would affect bond strength to dentin. Ninety human molars were mounted in acrylic and the occlusal surfaces ground to expose a flat dentin surface. Thirty teeth were randomly assigned to one of the following dentin bonding agent/composite combinations: A) Universal Bond 3/TPH (Caulk), B) All-Bond 2/Bis-Fil-P (Bisco), and C) Scotchbond Multi-Purpose/Z-100 (3m). The primers were applied following the manufacturers' instructions. The adhesives were applied by two methods. A thin layer of adhesive was applied with a brush to 15 specimens in each group and light cured. Adhesive was brushed on to the remaining 15 teeth in the group, air thinned for 3 seconds, and then polymerized. The appropriate composite was applied in 2 mm increments and light cured utilizing a 5 mm-in-diameter split Teflon mold. Following 3 months of water storage, all groups were shear tested to failure on an Instron Universal Testing Machine. Bond strength was significantly higher in all groups when the dentin bonding agent was painted on without being air thinned. Scotchbond Multi-Purpose had significantly higher bond strength than All-Bond 2, which had significantly higher bond strength than Universal Bond 3.
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PMID:The effect of air thinning on dentin adhesive bond strength. 870 Jul 80

This study evaluated the effect a food simulating solution, 75% v/v ethanol/water, and an artificial saliva, Moi-Stir, have on the microstructure and on the diametral tensile strength (DTS) of three dentine bonding agents (Tenure, Scotchbond Multi-Purpose and Optibond). The microstructure was examined by using a scanning electron microscope (SEM). The DTS data were analysed using ANOVA and the Tukey LSD test. The microstructural observations were compared with changes in DTS. The SEM observation revealed deterioration of all bonding agents due to conditioning in the solutions for 30 days. The different solutions appeared to cause different reactions in the bonding agents. However, these effects may be exaggerated due to the presence of an air-inhibited surface layer. Those conditioned in Moi-Stir showed swelling. The presence of filler particles in the Optibond bonding agent appears to decrease the deterioration resulting from soaking. Materials conditioned in ethanol exhibited both dissolution and thinning. Diametral samples of each bonding material were tested after being conditioned in the above-mentioned solutions for 1, 7, 14 and 30 days. Conditioning significantly decreased the DTS of all bonding agents, except Optibond in Moi-Stir. Filled Optibond maintained its DTS longer than did the two unfilled bonding agents. The decrease in DTS of all the ethanol-conditioned groups is a function of the square root of time (P < 0.001) and conforms to Fick's laws of diffusion. The filled Optibond showed a lower ethanol diffusivity (0.5 x 10(-5) cm2 s-1) than the other two unfilled bonding agent systems (average 1.2 x 10(-5) cm2 s-1) (P < 0.05). The high ethanol diffusivities were thought to be due to the presence of HEMA, a hydrophilic resin, in the bonding agent. These results also suggest that solution uptake occurred through the resin matrix. Filler particles may therefore play an important role in weathering resistance of these materials to oral environment solutions. The physical appearance and strength of dentine bonding agents are significantly altered by exposure to oral environment solutions.
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PMID:Effects of food/oral simulating fluids on microstructure and strength of dentine bonding agents. 873 49

Quantitative 1H MRS to determine cerebral metabolite patterns and MRI to determine CSF flow were applied to 12 patients with ventricular dilation-Group A, cortical atrophy (N = 5); or Group B, hydrocephalus (N = 7)- and in 9 normal controls. While mean brain water (Group A = 80% +/- 6; Group B = 86% +/- 5; normal = 85% +/- 4) did not differ between the two groups of patients and controls, 1H MRS distinguished those patients with cortical atrophy (Group A) (N-acetylaspartate/ creatine (NAA/Cr) = 0.69 +/- 0.17, versus normal = 1.06 +/- 0.16; P < 0.002; [NAA] = 5.9 +/- 1.3 mmoles/kg, versus normal 8.0 +/- 1.4; P < 0.02) from those with hydrocephalus (Group B) (NAA/Cr = 1.16 +/- 0.11; [NAA] = 9.2 +/- 1.2; P > 0.13 and P > 0.07). Lactate levels were elevated in 3/5 patients with cortical atrophy, but in 0/7 of those with hydrocephalus. Mean absolute concentrations (mmoles/kg) of the five major cerebral osmolytes were 41 +/- 4 (Group A), 43 +/- 6 (Group B), and 42 +/- 4 (normal), so that despite massive brain deformation, constant osmolality was maintained. 1H MRS may directly benefit surgical planning in hydrocephalus infants by clearly identifying those with cortical atrophy who do not require CSF diversion. Thinning of the cortical mantle in hydrocephalus may result from osmotically driven reduction in individual cell volumes, (shrinkage), rather than brain-compression.
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PMID:Differentiation between cortical atrophy and hydrocephalus using 1H MRS. 905 30

Oral administration of an ammonia solution (0.01%) or a sodium taurocholate solution (TCA solution, 5 mM) as drinking water for 4 weeks or 13 weeks, respectively, resulted in gastric mucosal thinning and decreased parietal cell numbers. Oral administration of TCA solution also caused cell infiltration in the lamina propria of the mucosa and mucosal fibrosis. When lafutidine (3, 10 mg/kg) was administered orally once daily for one week after the withdrawal of ammonia or TCA solution, the recovery of the mucosal thickness in the fundic gland area and the parietal cell number were significantly accelerated, and the recovery of mucosal thickness in the pyloric gland area also tended to be accelerated. Lafutidine at 10 mg/kg for 1 week had no influence on normal mucosal thickness and parietal cell numbers. At the doses that produce equal or greater acid antisecretory effect than lafutidine, oral administration of cimetidine (30 mg/kg) and famotidine (1 mg/kg) had no effect on either of these atrophy indexes. These results demonstrate that lafutidine, unlike cimetidine and famotidine, can accelerate the healing of mucosal injuries in ammonia- and TCA-induced chronic gastritis models.
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PMID:[Effect of a novel antiulcer drug, lafutidine, on experimental chronic gastritis in rats]. 906 97

Manganese chloride (Mn) was dissolved in the drinking water (0, 2, or 10 mg/ml) of dams and their litters from conception until postnatal day (PND) 30. Parturition was uneventful in the Mn-exposed rats and no physical abnormalities were observed. The rats exposed to 10 mg/ml Mn showed a 2.5-fold increase in cortical Mn levels. Their weight gain was attenuated from PND 9-24 and they were hyperactive at PND 17. Neither the 2 nor the 10 mg/ml Mn-exposed groups differed from the controls on the elevated plus apparatus or on the Morris water maze and the radial arm maze. Brain monoamine levels and choline acetyltransferase activity were affected. Tyrosine hydroxylase immunohistochemistry showed that dopamine cells of the substantia nigra were intact. Glial fibrillary acidic protein immunoreactivity was not increased in cortex, caudate, and hippocampus. However, both the low- and high-dose Mn-exposed groups showing thinning of the cerebral cortex. This could have resulted from perinatal malnutrition or from a direct effect of Mn on cortical development.
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PMID:Perinatal manganese exposure: behavioral, neurochemical, and histopathological effects in the rat. 908 7


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