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Biomedical subjects

A C Barnard

Publications and source records attributed to A C Barnard.

17 recordsLinked to original sources
PubMed1979

Performance of conventional orthogonal and multiple-dipole electrocardiograms in estimating left ventricular muscle mass.

For estimating left ventricular mass (LVM), ECG criteria for left ventricular hypertrophy (LVH) were selected from conventional 12-lead ECGs, orthogonal three-lead ECGs, and multiple-dipole ECGs (MDECG). The three cardiograms were recorded in 139 patients for whom the degree of LVH was independently determined from biplane ventriculograms. Tested ECG criteria included Sokolow-Lyon measurements for the 12-lead ECG; for the orthogonal ECG, maximal QRS magnitude in the horizontal plane, R duration in the z-lead and Jxyz (spatial magnitude of point J); and for the 126 leads of the MDECG, the dipole activity (DA) of the septum and the free left ventricular wall. Correlation coefficients between LVM and the 12-lead ECG, three-lead ECG and MDECG were 0.61, 0.78 and 0.89, respectively, with corresponding errors of estimated LVM of 103, 82 and 60 g. More complex recording and analytic methods clearly led to increased accuracy in LVM estimates. However, the large error of estimate may limit practical applicability of such correlations. For classification of subjects into normal and above-normal categories, a likelihood ratio was also used and led to a maximum performance index of 86% with MDECG measurements.

Electrocardiography↗
PubMed1977

A study of the human heart as a multiple dipole source. IV. Left ventricular hypertrophy in the presence of right bundle branch block.

This report concerns the task of electrocardiographic (ECG) diagnosis and quantitation of left ventricular hypertrophy (LVH) in patients with right bundle branch block (RBBB). In 36 patients with RBBB the left ventricular mass (LVM) of each patient was independently known from quantitative biplane angiography. Two ECG techniques, standard 12-lead ECG and multiple dipole electrocardiography (MDECG), were evaluated. In diagnosing LVH, the best performance of the several standard ECG criteria was sensitivity = 29%, specificity = 100%, and that of the MDECG was sensitivity = 94%, specificity = 96%. In quantitating LVH, the standard ECG gave a correlation with LVM of r = 46% and a standard error of estimate of 98 g. The corresponding figures for the MDECG were r = 81% and the root mean square prediction error = 64 g. These results confirm other studies showing that the conventional ECG is of only marginal value in the task of diagnosing LVH in the presence of RBBB. In contrast, the MDECG performs well both in this task and that of quantitating LVH. The results provide further support of the accuracy of the model of the cardiac electrical generator and volume conductor used in the MDECG method.

Adolescent↗
PubMed1976

Comparison of Frank's and McFee's lead systems using multivariate statistics.

Two widely used orthogonal corrected 3-lead system - the Frank and the McFee systems - were studied in order to evaluate whether a significant difference in diagnostic performance could be observed; in the case of a positive answer, we would be able to advocate one system instead of the other. No such overall difference was noticed. Although +/- 17% discrepancies were found on the individual classification level (a patient correctly classified with system A and missed with system B and conversely), the practical implication is negligible since each system is responsible for +/- half of these discrepancies. Multivariate analysis, as already largely proved by Pipberger's group, drastically ameliorates the diagnostic results. Special caution has been given to the number of selected discriminators in order to enhance repeatability of the results; the reproducibility, using the approach developed by Cornfield, was found excellent. Some particular features as to the choice and location of the best discriminators were found somewhat puzzling by the autors but no deterministic explanation could be offered: the selection of the variables, indeed, rested on statistical bases and not on the (sometimes fragmentary) knowledge of what is going on in the heart and how these events relate to surface waveform patterns.

Adult↗
PubMed1967

The application of electromagnetic theory to electrocardiology. I. Derivation of the integral equations.

One of the fundamental problems of theoretical electrocardiology is to determine the potential distribution on the surface of the torso due to the time-varying dipolar heart source. In this paper we present a rigorous derivation of the integro-differential equations for the potential, containing, for the first time, the effects of the time dependence of the source and the dielectric properties of the medium. These equations provide a general and rigorous basis from which to attack the problem numerically on a computer and permit the use of a detailed model of the thorax as a multiple region volume of different dielectric and conducting properties.

Biophysical Phenomena↗
PubMed1967

The application of electromagnetic theory to electrocardiology. II. Numerical solution of the integral equations.

In an earlier paper exact integral equations were derived for the surface potentials resulting from sources within an irregularly shaped inhomogeneous body. These exact equations cannot usually be solved. In this paper a discrete analogue is constructed which is not straightforward to solve, but which can be treated by careful mathematical methods. In particular a deflation procedure greatly facilitates the iterative solution of the problem and overcomes the divergence encountered by other authors. Numerical solutions obtained for simple geometries are compared to the exact analytic solutions available in such cases. The necessary convergence of the solutions of the discrete analog towards the solution of the continuous problem is shown to occur only if the coefficients of the discrete analogue are carefully evaluated. Calculations are then presented for realistic thoracic geometries, typical results being presented as surface potential maps. Finally the important effect of the internal regional inhomogeneities, particularly a realistic cardiac blood mass, is demonstrated by obtaining vector loops with and without these effects.

Biophysical Phenomena↗
PubMed1966

A theory of fluid flow in compliant tubes.

Starting with the Navier-Stokes equations, a system of equations is obtained to describe quasi-one-dimensional behavior of fluid in a compliant tube. The nonlinear terms which cannot be shown to be small in the original equations are retained, and the resulting equations are nonlinear. A functional pressure-area relationship is postulated and the final set of equations are quasi-linear and hyperbolic, with two independent and two dependent variables. A method of numerical solution of the set of equations is indicated, and the application to cases of interest is discussed.

Biophysical Phenomena↗
PubMed1966

Numerical hydrodynamic calculations of catheter characteristics.

The theory of fluid flow in compliant tubes developed in a previous paper is applied to a catheter, and the results of various calculations are compared with experiment. When a parabola is used for the unknown velocity profile, the calculated gains are too high. Agreement is slightly improved by using more reasonable profiles. It is shown that there exists a functional relationship between the parameter gamma and the nondimensional parameter alpha(10) which gives reasonable agreements with all the experimental data considered. The theory of Womersley is applied to the catheter, and the calculated gains are larger than those observed experimentally. A form for the frictional force suggested by Lambossy is used in some further calculations.

Biophysical Phenomena↗
PubMed1966

Peaking of the pressure pulse in fluid-filled tubes of spatially varying compliance.

Calculations are made for a fluid-filled tube with characteristics approximately those found physiologically. The pressure variation, diameter, and compliance at the input end are as measured by Lawton for the abdominal aorta of a dog. After a 30 cm-long input section of constant k (=dp/dA), the tube is taken to stiffen by approximately the amount measured by Patel et al., i.e., k increases by a factor of 5 over the next 40 cm. The cross-section remains constant. Pressure and velocity wave forms are calculated at 8 stations spaced at 10-cm intervals down the tube. The pressure pulse leading edge is found to become steeper in the stiffening section. The peak height of the pressure pulse is found to increase by about 50% and the velocity pulse to decrease by about 30% as the disturbance propagates over a distance of 70 cm. These values agree qualitatively with the experimental physiological values given by McDonald. Most of the pressure peaking takes place upstream of the stiffening section.

Animals↗