The stretch conductance in each fibroblast was held at 20 nS until a positive threshold crossing in the reference cell occurred. This simulation of atrial diastolic stretch was repeated during four consecutive cardiac cycles, before the initial protocol was reinstated. This sequence was chosen in order to model temporarily increased venous return to the heart as observed, for example, during changes in posture. Cardiac activity was simulated for a total of 5 s.Results of this computation are shown in Figure 1. The membrane potentials calculated for the central SA node cell, a peripheral SA node cell close to the SA node/atrial border and an atrial cell are plotted over the time of simulation.Under these conditions, cell-to-cell coupling of 10 nS within the SA node was more than sufficient to assure frequency ent trainment in the node. Consistent with this, the background oscillation period (the interval between two consecutive beats) in the absence of diastolic stretch was stable and on average 332.5±0.58 ms (mean ± SD) during the four cycles preceding the intervention. In the presence of diastolic stretch, the spontaneous depolarization rate of the pacemaker int creased.
Figure 1 Response of sinoatrial (SA) node/atrial cell network model to diastolic stretch of mechanosensitive cardiac fibroblasts in the pacemaker region. Diastolic stretch was simulated during four consecutive diastoles, as indicated by bars. Responses of the central SA node cell (trigger cell, top); a peripheral SA node cell (middle); and an atrial cell (bottom) are illustrated. Note different scales for membrane potentials
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