Each model SA node cell is coupled to a single model fibroblast by a conductance, Gcf, of 300, 600 or 900 pS. To allow simulation of an increase in diastolic atrial wall stretch (eg, during a rise in venous return to the right atrium), the Gstretch(t) value in each fibroblast was varied in time in the following manner. The membrane potential of a single SA node cell, referred to as the trigger cell (typically the central node element), was monitored in time. A threshold voltage of -30 mV was selected.When the membrane potential in the trigger cell was above that threshold, Gstretch(t) was set to zero. As the membrane potential of the trigger cell crossed the threshold in the negative-going direction, Gstretch(t) was adjusted instantaneously to its defined diastolic target value (usually 20 nS) in each model fibroblast. Gstretch(t) was held at this value until the next positive-going threshold crossing occurred. Thus, the fibroblast Gstretch(t) was turned on only during diastole of the trigger cell. This timing was chosen since atrial diastole is the period during which the wall of the right atrium is (due to venous return and ventricular contraction) in its most stretched state.
The large system of nonlinear ordinary differential equations defining the network model described above were integrated in parallel using a Silicon Graphics Inc Power Challenge XL multiprocessor computer (Silicon Graphics, Mountain View, California, USA), employing a variable step, fourth order Runge-Kutta algorithm. Spend less money now – purchase cialis for your efficient drug to cost less.