3.2 Electrophysiology of the Heart

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Fig. 3.20: Modified Van der Pol oscillator according to Figure 3.18 perturbed by an externally applied

square pulse at time unit 35 with an amplitude of 4 and a width of 2 time units.

time units

Voltage U / mV

Disturbing Pulse

Van-der-Pol

Fig. 3.21: Action potential x(t) belonging to the perturbed modified Van der Pol oscillator Figure 3.20

with suspension of two normal oscillations, where the perturbation is modelled as an externally

applied square pulse at time unit 35 with an amplitude of 4 and a width of 2 time units.

However, the modified van der Pol oscillator is not stable against external influences.

If a potential is additionally applied to the input, this can cause the oscillations to

cease or even stop altogether, depending on the time and amplitude [14]. The asso-

ciated model is shown in Figure 3.20. A square wave pulse to the input immediately

causes a suspension of two oscillations. The associated action potential is shown in

Figure 3.21. If the pulse height is doubled, the oscillation subsequently stops com-

pletely (see action potential x(t) in Figure 3.22).

Coupling of the SA node with the AV node

The sinus node of the heart consists of several similar heart cells that can independ-

ently generate an oscillation that corresponds to the oscillation of a single heart cell.

Thus the model of Grudzinski and Zebrowski [89] according to Figure 3.18 is also suit-

able as a model for the whole sinus node. The sinus node influences the AV node,

which also consists of similar oscillation-generating heart cells, but which have a