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Biomedical subjects

S Guido

Publications and source records attributed to S Guido.

9 recordsLinked to original sources
PubMed1999

Experimental Determination of Drop Shape in Slow Steady Shear Flow.

Theoretical predictions for the 3D shape of a Newtonian drop immersed in a Newtonian fluid under slow flow have been available for a long time (C.E. Chaffey and H. Brenner, J. Colloid Interface Sci. 24, 258 (1967); J.M. Rallison, J. Fluid Mech. 98, 625 (1980)). The predictions contain four scalar coefficients, given in terms of the viscosity ratio of the component fluids. In this work, experimental values of such coefficients were measured for the case of two Newtonian fluids in simple shear flow. The experiments were carried out in a parallel plate apparatus, equipped with video-enhanced microscopy, and the measurements were performed by image analysis techniques. The results were also compared to theoretical calculations and provide the first complete assessment of shape predictions for the case of Newtonian fluids. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Measurement of Interfacial Tension by Drop Retraction Analysis.

The retraction of a deformed drop back to the spherical, equilibrium shape at rest has been the subject of several studies in the literature with the aim of measuring the interfacial tension between the drop and the continuous phase. In this work, the retraction of a drop deformed under the action of a shear flow was analyzed by using the theoretical approach proposed by Rallison in the limit of small deformations. A single exponential decay was then obtained for the time evolution of the deformation parameter in the course of retraction. By fitting such expression to the experimental data the interfacial tension can be determined. Experiments of drop retraction were performed by using a parallel plate apparatus. The experimental trend of the deformation parameter during retraction was well represented by a single exponential decay and the calculated interfacial tension was in good agreement with values reported in the literature for the system investigated. A detailed comparison of the proposed analysis of drop retraction with other methods available in the literature is also presented. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Home hospital program: a pilot study.

OBJECTIVE: To evaluate the basic safety and feasibility of hospital care at home (Home Hospital (HH)) for treating acutely ill older persons requiring hospitalization. DESIGN: Prospective case series SETTINGS AND PARTICIPANTS: Community-dwelling persons aged 65 and older requiring acute hospital admission for community-acquired pneumonia, chronic heart failure, chronic obstructive airways disease, or cellulitis. RESULTS: Seventeen subjects were treated in HH. One hundred twenty-two could not be enrolled because they presented for admission at times when HH was not operational. Six patients refused to enroll in HH. Subjects treated in HH had comparable clinical outcomes to those treated in the acute hospital and were highly satisfied with HH. Charges for HH care were 60% of those for the acute hospital care. CONCLUSIONS: In this pilot study, HH was safe, feasible, highly satisfactory, and cost-effective for certain acutely ill older persons who required acute hospitalization.

Acute Disease↗
PubMed1993

A methodology for the systematic and quantitative study of cell contact guidance in oriented collagen gels. Correlation of fibroblast orientation and gel birefringence.

Despite the likely role of contact guidance in every physiological process involving cell migration, its study in a three-dimensional tissue-equivalent environment has been precluded, heretofore, by inherent difficulties in systematically preparing well-defined contact guidance fields and quantifying the resultant contact guidance. Here, we describe a novel use of a magnetic field to orient collagen fibrils during fibrillogenesis, entrapping cells dispersed in the collagen solution. Using computer-controlled staging and image analysis, we show from automated birefringence measurements of the resultant slab of cell-populated gel contained in a specially designed observation chamber that the fibril orientation is biased along the long axis of the chamber uniformly throughout the chamber. Further, we show that the degree of fibril orientation, and consequently the elicited contact guidance, can be controlled by independently varying the magnetic field strength or temperature during fibrillogenesis. We characterize the contact guidance response to the imposed contact guidance field by measuring cell orientation relative to the axis of fibril orientation from still images obtained in time-lapse via automated image analysis. We present the first quantitative correlation of contact guidance (based on cell orientation) with collagen fibril orientation (based on birefringence) for human foreskin fibroblasts cultured in a collagen gel, by using gels of varying orientation resulting from different magnetic field strengths and temperatures during fibrillogenesis, and by using sufficiently low cell concentrations and early observation times.

Birefringence↗
PubMed1992

Effect of chemically different calcium antagonists on lipid profile in rats fed on a high fat diet.

Different classes of calcium antagonists, viz. verapamil (diphenylalkylamine), diltiazem (benzothiazepine), nifedipine, felodipine and nimodipine (dihydropyridines), were examined for their effects on lipid profile in rats. Clofibrate was the reference standard. Clofibrate significantly prevented the rise of serum triglycerides and total cholesterol produced by high fat diet and raised antiatherogenic index to 1.6 times than that of high fat diet controls. Of the calcium antagonists studied, felodipine was most effective in preventing the rise of serum triglycerides and total cholesterol in high fat diet fed rats. Felodipine's antiatherogenic index was very high (886%)--much more than that of clofibrate (303%). Diltiazem and nimodipine which also significantly prevented the rise in triglycerides and total cholesterol produced by high fat diet had a moderately beneficial antiatherogenic index similar to that of clofibrate. Though verapamil and nifedipine slightly increased the triglyceride levels, total cholesterol levels were reduced only by verapamil and not by nifedipine. Despite this both these drugs moderately raised antiatherogenic index similar to clofibrate.

Animals↗
PubMedDate not supplied

Biased cell migration of fibroblasts exhibiting contact guidance in oriented collagen gels.

We present here the first quantitative correlation for cell contact guidance in an oriented fibrillar network in terms of biased cell migration. The correlation is between the anisotropic cell diffusion parameter, DA = Dx/Dy, and the collagen gel birefringence, delta n, a measure of axially biased collagen fibril orientation in the x-direction. The cell diffusion coefficients, Dx and Dy, measure the dispersal of cells in the directions coincident with and normal to the axis of fibril orientation, respectively. Three essential methodological components are involved: (i) exploiting the orienting effect of a magnetic field on collagen fibrils during fibrillogenesis to systematically prepare uniform axially oriented collagen gels; (ii) using a microscope/image analysis workstation with precise, computer-controlled rotating and translating stages to automate birefringence measurement and, along with rapid "coarse optical sectioning" via digital image processing, to enable 3-D cell tracking of many cells in multiple samples simultaneously; and (iii) employing a rigorous statistical analysis of the cell tracks to estimate the magnitude and precision of the direction-dependent cell diffusion coefficients, Dx and Dy, that define DA. We find that this measure of biased migration in contact guidance (DA) increases with increasing collagen fibril orientation (delta n) due mainly to a rapid enhancement of migration along the axis of fibril orientation at low levels of fibril orientation, and to a continued suppression of migration normal to the axis of fibril orientation at high levels of fibril orientation.

Anisotropy↗