PubMed Health⌕ Search

Biomedical subjects

D D Streeter

Publications and source records attributed to D D Streeter.

9 recordsLinked to original sources
PubMed1983

Muscle pathway geometry in the heart wall.

Muscle fiber pathways in the heart wall are described. Procedures are introduced which permit data to be standardized from cadaver and animal hearts fixed at different points of the cardiac cycle or obtained in vivo from patients with different ejection fractions and heart masses. Design criteria are also developed here to construct a hypothetical standard left ventricle to compare the data from different hearts. The equations allow the nested set of toroidal fiber-shells to be depicted with typical muscle fiberpaths. With this formulation the heart wall and typical elements in it can be shown computergraphically as they move from the contracted state to the distended. Man-made fiber structures that simulate the fail-safe shockload absorbing features of the heart can now be designed and tested computergraphically by use of the mathematical procedures described here.

Animals↗
PubMed1981

Inhibition of growth rate of Escherichia coli induced by extremely low-frequency weak magnetic fields.

Cultures of Escherichia coli kept at 0 degree C in a phosphate buffer solution were exposed to a sinusoidal weak 60- or 600-Hz magnetic field of strength 2 X 10(-3) Tesla. A decrease of more than 40% in bacterial count was observed after a 60-h exposure to the magnetic field. Electron micrographs of exposed bacteria show ruptured cell walls, possibly due to the breaking away of flagella under the influence of the sinusoidally varying electromotive force.

Cell Membrane↗
PubMed1975

Myofilament flexibility: a possible role in Hill's model for cardiac and skeletal muscle.

The sarcomeric unit ("sark") is an elastic structure (cf. hard rubber). The sark stretch under load is the sum of the deflections of: (a) the naked thick filament, (b) the joined thick-thin filaments, (c) the naked thin filaments, (d) the parallel array of S1 moieties (bending deflection), (e) the parallel array of S2 rods, and (f) the Z-filaments. Hill's model can be revalidated at the molecular level, if the contractile element is identified as the instantaneous array of contract points between each S1 moiety and the thin filament, such that sark stretch accounts for series elasticity. A matrix array of variously activated and test-rig-damaged sarks can account for large quick-release compliances in cardiac muscles.

Animals↗
PubMed1975

Nonuniform subendocardial fiber orientation in the normal macaque left ventricle.

Fiber-angle changes in tangential planes through the heart wall are described in two macaque left ventricles at four equatorial and three near-apical sites. At each site, starting at a strongly negative angle at the epicardium, the fibers swing circumferentially short of midwall and continue their progressive climb to positive angles. Angles depart from the steady climb in the subendocardial region, and beyond the endocardium a wide scatter of fiber angles persist into the free trabeculae, the profuseness of which motivated this study. An interface is described histologically, coinciding with the fiber-angle deviations in the subendocardial sections, which divides the compact region of the wall from the trabeculated region. A dual function is postulated for the mural portion of the trabeculated region of the heart wall.

Animals↗
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↗