Biomedical Engineering Reference
In-Depth Information
common IBI is clearly not the arithmetic average of the IBI values for each of the
cells. Fluctuations of IBI still occur during the coupling period with differences of up
to 34 ms for IBI values of the two cells even for cycles, which are associated in time
as part of the entrainment process. The activation delay (lower panel) shows
significant fluctuations from 24 to 64 ms with an average value of 43 ms.
Fig. 3.
Interbeat interval for the two rabbit SAN cells of Fig. 2 (
upper panel
;
filled circles
and
open squares
, respectively) and the delay in activation between the two cells (
lower panel
;
filled triangles
) for a coupling conductance
G
c
= 0.2 nS (indicated by a
horizontal arrow
).
From Verheijck et al. [20].
3 Interactions Among a Spontaneously Pacing Cell Model and an
Atrial Cell Model
For the simulations shown in Fig. 1, we used two isopotential spontaneously active
membrane regions coupled by a resistance
R
c
. For the simulations of Fig. 4 we used
an SA NODE region with the same Irisawa-Noma [10] model as for Fig. 1, and for
the ATRIAL region we used the model of Beeler and Reuter [2] with the only
modification being a reduction in the magnitude of the conductance for the slow
inward current to 20% of the standard model to produce an action potential duration
of ~100 ms to correspond with the atrial action potential duration [14]. It would have
been more appropriate to also decrease the
I
K1
of the Beeler-Reuter model to match
the input resistance of atrial cells (see section E) so these simulations somewhat
overestimate the effects of electrical load of the surrounding cells on the function of
the SAN region. These results [14] illustrate the three possibilities of such a coupled
system. Each symbol plotted represents a simulation of 2 s, with the simulation results
being either (a) failure of the SA region to pace (NOT PACE,
solid circle
), (b) pacing
of the SA region without activation of the atrial region (PACE BUT NOT
