A new view of a stationarity of the RR series for sinusal variability analysis.

The influence of ANS in sinusal variability is studied through analysis of RR series, and particularly RR interval variations during time. Different kinds of RR series signal analysis are applied to clinical situations found in cardiology. However, some of the RR series may be stationary as well as non-stationary. Statistical tests applied to the RR series will establish determinism and stationarity of these signals. The aim of this article is to characterize the statistical behaviour pattern of RR series in order to identify precautions that should be observed when time-frequency transform techniques are used in sinusal clinical investigations. Eight kinds of RR series concerning sinusal variability were submitted to the statistical tests. The results showed the uncertain character of the RR series and their non-stationarity. This result is consequently a warning against using several techniques of time-frequency transform for sinusal variability analysis. Some of the techniques studied are adapted to non-stationary signals under some conditions.