Deterministic Chaos

Control of Chaos

Here are results reported by Ditto, Spano, and coworkers.
Atrial Fibrillation, or AFib, is the most common cardiac arrhythmia requiring treatment. It occurs in over 5% of the population over 65 and increases the risk of stroke and death.
These experiments were performed on 25 patients at Emory University.
(1) For each patient, AFib was induced and an unstable fixed point determined from the return map of the interbeat intervals.
(2) A learning phase determined how the fixed point changed as the stimulus was varied.
(3) Then the method of contol was applied to keep the interbeat interval near this fixed point.
This method worked in 3/4 of the patients, though in about half of these, the control was more short-lived.
Pictured on the right are histograms of the distribution of the return map before (upper graph) and after (lower graph) control was implemented.
The strong central spike in the middle of the lower graph demonstrates the effectiveness of the control method. Note the change of vertical scale between the two graphs.

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