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Biomedical subjects

R L Lux

Publications and source records attributed to R L Lux.

95 records · Page 6Linked to original sources
PubMed1976

Experimental evidence for regional cardiac influence in body surface isopotential maps of dogs.

Isopotential mpas based on 192-200 body surface electrocardiograms were obtained for 20 dogs during multiple patterns of ventricular activation. The purposes of the study were to determine whether the cardiac location of events responsible for surface potentials had a recognizable influence on surface potential patterns and to examine the influence of electrical events occurring simultaneously in multiple cardiac regions. Substantially different effects of electrical activity in various cardiac regions on body surface potentials were evidenced by the body surface location of potential maxima and minima and by patterns of isopotential lines during early portions of ventricular excitation initiated at different ventricular sites. Simultaneous stimulation at some sites gave surface potential distributions with multiple extrema. These were demonstrated to be due to effects of the different cardiac regions, because addition of potentials due to stimulation of the individual sites duplicated those associated with simultaneous stimulation of the same sites. It was also shown that body surface locations of maxima and minima are not related in the same manner to the cardiac location of the responsible events when these events are present in single and multiple regions. Slopes of potentials due to events in single cardiac regions were shown to combine with slopes produced by events in other regions to yield maxima or minima at new body surface locations. Results of the study support the possibility of regional cardiac examination by electrocardiography but suggest that this will require quantitative descriptions of the details of potential patterns in addition to the location of potential peaks.

Animals↗
PubMedDate not supplied

Three-dimensional activation mapping in ventricular muscle: interpolation and approximation of activation times.

Interpolation plays an important role in analyzing or visualizing any scalar field because it provides a means to estimate field values between measured sites. A specific example is the measurement of the electrical activity of the heart, either on its surface or within the muscle, a technique known as cardiac mapping, which is widely used in research. While three-dimensional measurement of cardiac fields by means of multielectrode needles is relatively common, the interpolation methods used to analyze these measurements have rarely been studied systematically. The present study addressed this need by applying three trivariate techniques to cardiac mapping and evaluating their accuracy in estimating activation times at unmeasured locations. The techniques were tetrahedron-based linear interpolation, Hardy's interpolation, and least-square quadratic approximation. The test conditions included activation times from both high-resolution simulations and measurements from canine experiments. All three techniques performed satisfactorily at measurement spacing < or = 2 mm. At the larger interelectrode spacings typical in cardiac mapping (1 cm), Hardy's interpolation proved superior both in terms of statistical measures and qualitative reconstruction of field details. This paper provides extensive comparisons among the methods and descriptions of expected errors for each method at a variety of sampling intervals and conditions.

Animals↗
PubMedDate not supplied

A novel interpolation method for electric potential fields in the heart during excitation.

In mapping the electrical activity of the heart, interpolation of electric potentials plays two important roles. First, it permits the estimation of potentials in regions that could not be sampled or where signal quality was poor, and second, it supports the construction of isopotential lines and surfaces for visualization. The difficulty in developing robust interpolation techniques for cardiac applications lies in the abrupt change in potential in the vicinity of the activation wave front. Despite the resulting nonlinearities in spatial potential distributions, simple linear interpolation methods are the current standard and the resulting errors due to aliasing can be large if electrode spacing does not lie on the order of 0.5-2 mm--the thickness of the activation wave front. We have developed a novel interpolation method that is based on two observations specific to the spread of excitation in the heart: (1) that propagation velocity changes smoothly within a region large enough to contain several measurement electrodes and (2) that electrogram morphology varies very little in the neighborhood of each sample point except for a time shift in the potential wave forms. The resulting interpolation scheme breaks the interpolation of one highly nonlinear variable--extracellular potential--into two separate interpolations of variables with much less drastic spatial variation--activation time and electrogram morphology. We have applied this method to potentials originally recorded at 1.5 mm spacing and then subsampled at a range of densities for testing of the interpolation. The results based both on reconstruction of isopotential contour maps and statistical comparison showed significant improvement of this novel approach over standard linear techniques. The applications of the new method include improved determination of electrophysiological parameters such as spatial gradients of potential and the path of cardiac activation and recovery, estimation of electrograms at desired locations, and visualization of electric potential distributions.

Algorithms↗
PubMedDate not supplied

A field-compatible method for interpolating biopotentials.

Mapping of bioelectric potentials over a given surface (e.g., the torso surface, the scalp) often requires interpolation of potentials into regions of missing data. Existing interpolation methods introduce significant errors when interpolating into large regions of high potential gradients, due mostly to their incompatibility with the properties of the three-dimensional (3D) potential field. In this paper, an interpolation method, inverse-forward (IF) interpolation, was developed to be consistent with Laplace's equation that governs the 3D field in the volume conductor bounded by the mapped surface. This method is evaluated in an experimental heart-torso preparation in the context of electrocardiographic body surface potential mapping. Results demonstrate that IF interpolation is able to recreate major potential features such as a potential minimum and high potential gradients within a large region of missing data. Other commonly used interpolation methods failed to reconstruct major potential features or preserve high potential gradients. An example of IF interpolation with patient data is provided to illustrate its applicability in the actual clinical setting. Application of IF interpolation in the context of noninvasive reconstruction of epicardial potentials (the "inverse problem") is also examined.

Action Potentials↗