Discrimination between Healthy and Sick Cardiac Autonomic Nervous System   by Detrended Heart Rate Variability Analysis
  Multiresolution Wavelet Transform and Detrended Fluctuation Analysis have been recently proven as excellent methods in the analysis of Heart Rate Variability, and in distinguishing between healthy subjects and patients with various dysfunctions of the cardiac nervous system. We argue that it is possible to obtain a distinction between healthy subjects/patients of at least similar quality by, first, detrending the time-series of RR-intervals by subtracting a running average based on a local window with a length of around 32 data points, and then, calculating the standard deviation of the detrended time-series. The results presented here indicate that the analysis can be based on very short time-series of RR-data (7-8 minutes), which is a considerable improvement relative to 24-hours Holter recordings. 
Y. Ashkenazy, M. Lewkowicz, J. Levitan, S. Havlin, K. Saermark, H.   Moelgaard and P.E. Bloch Thomsen