Differences in the Stability of the Heart Interbeat Rate During Wake and Sleep Periods

The Allan (ADEV) and Hadamard (HDEV) deviations are mathematical tools developed in the field of time and frequency metrology to define quantitatively the frequency instabilities of an oscillator; which consist of any unwanted departure from its nominal frequency value over a specified time interval. We use both deviations to analyze the stability of the heart interbeat rate for healthy subjects and patients with congestive heart failure (CHF) during wake and sleep periods. We find that the ADEV and HDEV profiles for the subjects in the CHF group exhibit remarkably different trends between wake and sleep periods, namely, larger dispersion between the results for each member of the group while the results for the healthy subjects show some uniformity across the members of the group. Moreover, we observe that the stability for both groups degrades for low scales during the sleep phase, being more significant for the CHF group. Both ADEV and HDEV statistics reveal that healthy data can be described by more uniform deviation values along several scales, particularly for the wake period, whereas CHF data shows important variations.