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Biomedical subjects

S Rush

Publications and source records attributed to S Rush.

At least 37 records · Page 2Linked to original sources
PubMed1980

Quantitative comparison of pre-mortem ECG's with those reconstructed from activation data of a revived heart.

The pioneering work of Durrer and associates has made available unique data showing activation isochrones in human hearts. To be certain that the complex experimental procedures do not seriously affect the activation sequence and also to validate accepted basic premises concerning the genesis of the electrocardiogram (ECG), it appears to be essential to show a reasonable correspondence between the subject's ECG before death and ECG's reconstructed from the activation data and heart-lead models. This paper reports the results of such a study. The comparison is evaluated in quantitative terms using several types of correlation coefficient. The significance of these is further evaluated through comparisons of similar coefficients from a random sample of normal records. The correlation coefficient considered to have the most general applicability gives a value of .80; only one subject from the random group showed a higher correspondence. A particular set of leads chosen to minimize the effects of inhomogeneities not accounted for in the modelling process, clearly selected the subject's records from all others with a correlation coefficient of .91 compared to .87, the highest from the random set. Considering the practical limitations on the accuracy of the models underlying these tests, the results are considered, with certain exceptions, to be supportive of the accuracy of the activation experiments and the assumption of a uniform double layer as the ECG source.

Electrocardiography↗
PubMed1978

Response of cultured myocardial cells to countershock-type electric field stimulation.

Myocardial cells isolated from 8-day chick embryos were grown in monolayer culture under conditions that produce "standard embryonic" and "adult-type" cells. These cells were subjected to electric field stimulation that had a waveshape and intensities similar to those used in clinical electric countershock procedures. Photocell mechanograms obtained before, during, and after stimulation were correlated with simultaneously measured transmembrane potentials to determine the relationship between membrane polarization and arrhythmia production that occured after the stimulus. The results of these experiments demonstrate that a predictable sequence of mechanical responses occurs after stimuli ranging in intensity from 6 to 200 V/cm. This sequence, which closely resembles that observed in vivo after similar stimulation intensities, consists of a single response (activation), tachyarrhythmia, relaxed arrest followed by transient tachyarrhythmia, arrest with contracture, and cellular fibrillation. This diverse pattern of arrhythmias is associated with a prolonged depolarization of the cell membrane which increases with the intensity of the applied stimulus. It is probable that this depolarization is caused by a transient electromechanical deformation of the cell membrane during the shock. These findings contribute to a better understanding of the causes of the arrhythmias that appear after clinical and experimental electric countershock procedures.

Animals↗
PubMed1978

Local potential gradients as a unifying measure for thresholds of stimulation, standstill, tachyarrhythmia and fibrillation appearing after strong capacitor discharges.

The pattern of arrhythmias following capacitor discharges of increasing amplitude, which have been observed by the authors in cultured myocardial cells from chick embryos, was compared to the arrhythmia patterns caused by similar discharges in experimental animals and humans, as reported in the literature. While the absolute voltages and currents causing each type of arrhythmia showed great variation, the scatter decreased considerably when the stimulus level was recalculated on the basis of peak current density in myocardial tissue, and was reduced further when the peak potential gradient at the cell level was used as the common basis of comparison. The similarity in the arrhythmia patterns and in the voltage gradients at which they occur indicates that the mechanism of these arrhythmias may be similar in cultured cells and intact animals and humans.

Action Potentials↗
PubMed1976

Current density in bilateral and unilateral ECT.

This paper describes a method of computer simulation which will enable the researcher to test, on the theoretical level, the effects of a wide variety of electrode placements, currents, tissue resistivities, and volumetric differences on the distribution of current within the brain. It is based on a nonhomogenous, threesphere model of the head and is capable of expansion to account for known inhomogenities within the brain. It should prove a useful research tool for a wide variety of purposes.

Computers↗