APD Alternans on a 1D Ring

Model has no memory and no strong electrotonic effects, with APD restitution slope > 1 for periods < 190 ms.

The applet simulates the propagation of an action potential on a ring (the edge at the right is the same as the edge at the left.

BUTTONS:

The Start button generates one action potential which is blocked on the right so that it only propagates to the left.
The Stop button then can stop the simulation at any time. The simulation can be resumed by using the Cont. button that replaces the Stop button when the simulation is stopped.
The simulation speed can be increased or decreased by clicking on the Faster or Slower buttons repeatedly until the desired speed is reached).
The Reset button brings the membrane potential of all the cells back to the rest state.
The Restart button reinitiates the original single pulse.

USE:

The period of the propagating action potential depends on the size of the ring, so that by changing the ring size the period is also changed. At the begining of the simulation the pulse (after a few rotations) will have a period of 232 ms (APD=112 ms, DI=120 ms) for the initial size of the ring (280 points).

Slowly decrease the ring size by clicking on the Smaller ring button (each click decreases the ring size by 5 points). Note that each time the size is changed small-magnitude transient alternans may be observed while the wave adjusts to the new period. However, once the period is smaller than 190 ms (220 points), sustained alterans will develop, because for periods in this range the slope of the APD restitution curve for this model is greater than one and there are no strong electrotonic or memory effects to suppress alternans.

The magnitude of the alternans increases as the period is decreased further. The minimum size for sustained alternans is 195 points (period = 179 ms), while for smaller rings conduction block occurs and the wave terminates.

Note that changing the ring size while the wave front is at the edges may terminate the reentry. To avoid this problem, change the ring size only when the wave front is not near the left and right boundaries.