Sleep stage related heart rate variability distinguishes between insomnia and normal sleep

Introduction:

In insomnia disorder a mismatch between subjective perception of poor sleep and quite normal objective sleep EEG results is a common finding. The aim of this study was to evaluate the capability of sleep stage related heart rate variability (HRV), a correlate of autonomous nervous system activity, to objectify insomnia.

Methods:

Forty-seven adults (age: 39.7 ± 12.5 years, 51.1% females) suffering from primary insomnia according to DSM-IV criteria were compared to a control group of 23 adults (age: 37.6 ± 12.3 years, 60.9% females) with no sleep complaints. Sleep was objectively assessed with polysomnography. HRV was assessed in artefact-free 5-min ECG segments of pure sleep stages. Sleep EEG variables and sleep stage related HRV frequency domain measures, like power of high frequency (HF), low frequency (LF) and very low frequency (VLF) band, were compared between patients and controls.

Results:

Insomnia and normal sleep did not differ in regard to any of the common measures of objective sleep continuity and sleep architecture except for a lower amount of REM-sleep (%) in insomnia (p < 0.05; Hedges g = 0.57 [M]). In the insomnia group, absolute HRV frequency power over all frequency bands was suppressed in REM sleep and in NREM sleep. Furthermore, in the first available REM sleep ECG segments relative HF-power was decreased (p < 0.05, g = 0.85 [L]) and relative VLF-power was increased (p < 0.01, g = 0.80 [L]).

Conclusion:

Our results are in line with the hypothesis of hyperarousal in insomnia. Sleep stage related HRV analysis and specifically HRV in early REM-sleep deliver more sensitive biomarkers for insomnia than common sleep EEG variables.