Search PubMed⌕ Search

Biomedical subjects

R S Chadwick

Publications and source records attributed to R S Chadwick.

22 records · Page 2Linked to original sources
PubMed1985

Pulse-wave propagation in an artery with leakage into small side branches.

Linear pulse propagation theory is applied to a network of elastic tubes. The network is specialized to one having a main branch with many low-admittance side branches. Continuum approximations and an asymptotic analysis of side-branch network input admittance reduce the original network to a tapered leaky tube. The outflow law is equivalent to distributed Windkessels. The conductance and time constant of the Windkessels are related to the geometry of the side-branch networks. Viscous effects are included in the theory. Asymptotic methods are used to determine the dispersion relation and waveform amplitude in the frequency domain. Periodic pressure and flow waveforms are computed using Fourier synthesis.

Animals↗
PubMed1982

Mechanics of the left ventricle.

A theory is presented for the mechanics of the left ventricle. A linear continuum description of the myocardium is developed, which incorporates anisotropic elastic effects due to the fiber direction field. The relation between fiber tension and fiber strain contains a time-dependent activation function that drives the ventricle around its cycle. The theory is applied to a simplified geometry consisting of a thick-walled finite cylinder in which fibers spiral on helical paths and terminate on planar end surfaces. The helix pitch angle varies continuously through the wall. The ventricular cycle is analyzed by specifying the pressures at which the aortic and mitral valves open and close. Key quantities are tabulated which permit a simple determination of the properties of the model under changes of wall thickness, fiber angles, muscle parameters, preload, afterload, etc. It is shown how the active muscle parameters can be inferred from a measurement of the end systolic pressure-volume line.

Animals↗
PubMed1980

Modes and waves in a cochlear model.

A simplified model hydroelastic system having many features in common with the cochlea is studied theoretically and experimentally. The system consists of a slender rigid tube filled with a viscous incompressible fluid. The tube is divided lengthwise into two chambers (scala vestibuli, scala tympani) by an interior surface, part of which is rigid and part elastic. The elastic portion is an isotropic plate having variable width and is clamped on its edges. The system is driven by a sinusoidal imput at the stapes end. The mechanical model is 24 times life size and dynamical similarity is maintained. Wave patterns in the plate are measured using time-averaged and stroboscopic holographic interferometry. At low frequency (corresponding to less than 500 cycles/s in the cochlea) the response can be adequately predicted by a one dimensional theory. The waves are a combination of traveling and standing waves. The traveling component is solely a dissipative effect. Discrete resonances are readily observed in the low frequency range.

Cochlea↗