No abstract

No abstract

The resistivity of tissues of the thorax of dogs has been measured in situ under nearly normal conditions. Additional data have been obtained from humans. Approximate values of tissue resistivity found are 160 ohm-cm for blood, 2,000 ohm-cm for lung, 2,500 ohm-cm for fat, 700 ohm-cm for liver, 250 and 550 ohm-cm (anisotropic) for heart muscle and 150 and 2,500 ohm-cm (anisotropic) for skeletal muscle. Reasons for the differences between these and previously reported values have been found, and in some cases, verified experimentally. Predictions of whole trunk resistivity based on anatomical data and these measurements are within 8% of actual trunk measurements.

Experimental studies have shown that cardiac fibroblasts are electrically inexcitable, but can contribute to electrophysiology of myocardium in various manners. The aim of this computational study was to give insights in the electrophysiological role of fibroblasts and their interaction with myocytes. We developed a mathematical model of fibroblasts based on data from whole-cell patch clamp and polymerase chain reaction (PCR) studies. The fibroblast model was applied together with models of ventricular myocytes to assess effects of heterogeneous intercellular electrical coupling. We investigated the modulation of action potentials of a single myocyte varying the number of coupled fibroblasts and intercellular resistance. Coupling to fibroblasts had only a minor impact on the myocyte's resting and peak transmembrane voltage, but led to significant changes of action potential duration and upstroke velocity. We examined the impact of fibroblasts on conduction in one-dimensional strands of myocytes. Coupled fibroblasts reduced conduction and upstroke velocity. We studied electrical bridging between ventricular myocytes via fibroblast insets for various coupling resistors. The simulations showed significant conduction delays up to 20.3 ms. In summary, the simulations support strongly the hypothesis that coupling of fibroblasts to myocytes modulates electrophysiology of cardiac cells and tissues.