Time-varying analysis of the heart rate variability during REM and non REM sleep stages

Spectral decomposition of the heart rate variability during whole night recordings was obtained, in order to assess the characteristic fluctuations in the heart rate and their spectral parameters during REM and NREM sleep stages. A time-varying autoregressive model was used in the analysis since it allows both real time and transitory episodes evaluation of spectral parameters of the heart rate variability and consequently an analysis of the autonomic nervous system behavior. Three whole nights records coming from three healthy subjects were used in the study. The results obtained during the study are in accordance with the previous ones in literature: an increment in LF power and in LF/HF ratio and a decrement in HF power when REM values are compared with NREM sleep stage. The pole of the autoregressive model in the HF range helps to separate the REM and NREM sleep epochs. When NREM is evaluated, the pole tends to be very close at unitary circle, while in REM this pole goes far from the unitary circle and its phase becomes less stable.