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Biomedical subjects

D J Patel

Publications and source records attributed to D J Patel.

At least 289 records · Page 16Linked to original sources
PubMed1972

Nonlinear anisotropic elastic properties of the canine aorta.

A nonlinear theory of large elastic deformations of the aortic tissue has been developed. The wall tissue has been considered to be incompressible and curvilinearly orthotropic. The strain energy density function for the tissue is expressed as a polynomial in the circumferential and longitudinal Green-St. Venant strains. Limiting application to states of strains wherein the geometric axes are the principal axes and truncating the energy expression to include terms with highest degrees 2, 3, and 4, three expressions with 3, 7, and 12 constitutive constants are obtained. Results of application of these expressions to data from three series of in vitro and in vivo experiments involving 31 dogs have been presented. Whereas all the three expressions are found to be applicable to various degrees, the third-degree expression for the strain energy density function with seven constitutive constants is particularly recommended for general use.

Animals↗
PubMed1972

Proton nuclear magnetic resonance studies of ribonuclease A in H 2 O.

A resonance (designated a) due to an exchangeable proton titrates (pK(a) = 6.1) between 11.5 and 13 ppm in the nuclear magnetic resonance spectrum of RNase A-0.2 M NaCl in H(2)O at 20 degrees . Comparison with models has permitted assignment to a ring-nitrogen proton of histidine in slow exchange with solvent H(2)O. The pH and temperature-dependent line-width changes of resonance a are analyzed in terms of an exchange between histidine and protonated histidine, without the necessity to invoke any exchange processes associated with protein conformational changes. Several other resonances due to exchangeable protons are observed between 10 and 15 ppm in the nuclear magnetic resonance spectrum of RNase A in H(2)O.

Histidine↗
PubMed1970

Stress distribution in the canine left ventricle during diastole and systole.

A model is proposed for stress analysis of the left ventricular wall (LV wall) based on the realistic assumption that the myocardium is essentially composed of fiber elements which carry only axial tension and vary in orientation through the wall. Stress analysis based on such a model requires an extensive study of muscle fiber orientation and curvature through the myocardium. Accordingly, the principal curvatures were studied at a local site near the equator in ten dog hearts rapidly fixed in situ at end diastole and end systole; the fiber orientation for these hearts had already been established in a previous study. The principal radii of curvature were (a) measured by fitting templates to the endocardial and epicardial wall surfaces in the circumferential and longitudinal directions and (b) computed from measured lengths of semiaxes of ellipsoids of revolution representing the LV wall ("ellipsoid" data). The wall was regarded as a tethered set of nested shells, each having a unique fiber orientation. Results indicate the following. (a) Fiber curvature, k, is maximum at midwall at end systole; this peak shifts towards endocardium at end diastole. (b) The pressure or radial stress through the wall decreases more rapidly near the endocardium than near the epicardium at end diastole and at end systole when a constant tension is assumed for each fiber through the wall. (c) At end diastole the curve for the circumferential stress vs. wall thickness is convex with a maximum at midwall. In the longitudinal direction the stress distribution curve is concave with a minimum at midwall. Similar distributions are obtained at end systole when a constant tension is assumed for each fiber through the wall. (d) The curvature and stress distributions obtained by direct measurements at a selected local site agree well with those computed from "ellipsoid" data.

Animals↗
PubMed1970

Spin delocalization in retinals.

A 220-MHz proton nuclear magnetic resonance study of the binding of Ni(II) and Co(II) acetylacetonates to retinyl-N-methyl Schiff's bases is presented. The study has yielded the magnitude and sign of spin densities at the carbon atoms in the pi system of the 9-cis, 13-cis, and all trans isomers. From a comparison of the experimental results with molecular orbital calculations, a mechanism for transfer of spin from the metal to the retinyl Schiff's base and its subsequent delocalization down the polyene chain is provided.

Chemical Phenomena↗
PubMed1970

Proton nuclear magnetic resonance studies of myoglobin in H2O.

Exchangeable hydrogens in proteins can be identified by comparison of nuclear magnetic resonance spectra obtained in H(2)O and in D(2)O. In oxymyoglobin and myoglobin we have been able to observe resonances of the NH protons of the two tryptophans, as well as one resonance from arginine and one from histidine in the range -10 to -15 ppm downfield from 3-(trimethylsilyl)propanesulfonic acid (sodium salt). These resonances have been identified by chemical modifications coupled with considerations of crystallographic structure and the dependence of the resonances on the species (sperm whale, porpoise, horse) from which the myglobin was obtained and on spin, pH, and temperature.

Animals↗