Analysis of time statistics of extreme variations of heart beat fluctuations

We analyzed heart beat fluctuations in terms of return times of extreme values of the RR increments. We considered 24 hours Holter ECG signals of 90 healthy individuals and 90 unhealthy ones suffering of congestive heart failure (chf). The increment time series RR corresponding to sleep and daily activity were studied separately. In both cases, our results pointed out strong differences in the median return times of the positive high thresholds between healthy and unhealthy people