Browsing by Author "Murphey, Carey Richard"

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    A model of normal and depressed conduction in cardiac strands
    (1988) Murphey, Carey Richard; Clark, John W., Jr.
    Mathematical modeling of the electrical activity of a single cardiac cell and of strands of cardiac cells are problems of fundamental interest in the area of electrophysiology. New and increasingly comprehensive data on the electrophysiological behavior of single, isolated cardiac myocytes have facilitated the development of more 'complete' models and are used here for the development of mathematical characterizations of cells exhibiting 'normal' electrophysiologic behavior as well as those exhibiting 'depressed' activity. Simulation and parameter estimation techniques are utilized to investigate model-generated single cell electrical behavior and to adjust this behavior to best fit observed responses. Suitably 'identified' models may be used in further simulations of electrical activity in linear strands of resistively coupled cardiac cells. It is hoped that together with advances in experimental methods, these methods for analysis and adjustment of model behavior will provide new and meaningful insight into the mechanisms of cardiac electrical activity.
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    Mathematical models of atrial and ventricular myocytes from the rabbit heart
    (1991) Murphey, Carey Richard; Clark, John W., Jr.
    Mathematical models of rabbit atrial and ventricular myocytes that are based on quantitative voltage clamp data from emzymatically isolated cardiac myocytes have been developed. These models are capable of accurately simulating the transmembrane ionic currents recorded in response to a step change in membrane potential (whole-cell voltage clamp response), the nonpropagated membrane action potential (MAP), and the frequency-dependent action potential waveshape changes occurring in response to variations in rate of stimulation. Rectangular pulse, ramp and action potential voltage-clamp measurements of the transmembrane ionic currents have allowed us to model a number of processes thought to be important during repolarization. These computations provide important biophysical insights into the electrophysiological activity of atrial and ventricular cells and their associated intra- and extracellular ionic concentration changes. The present model also has useful predictive capabilities. We have used the model to: (1) estimate the intracellular $Ca\sp{2+}$ transient in these myocytes and to compare the relative occupancy of the $Ca\sp{2+}$ binding sites in the contractile proteins with known cellular mechanical activity, and (2) predict the response of the atrial cell to potassium current blockade via $BaCl\sb2$ to the bathing medium.