Thomas RJ, Bianchi MT, Yun CH, Wood C, Shin C. Multicomponent analysis of sleep using electrocortical, respiratory, autonomic and hemodynamic signals reveals distinct features of stable and unstable NREM and REM sleep. Front Physiol 2020. DOI: 10.3389/fphys.2020.592978
A fundamental electrophysiological signature of NREM sleep is the < 1 Hz cortical slow oscillation (SO) and the associated defining “UP” and “DOWN” neuronal states, which is seen in virtually every cortical cell when recorded intracellularly. The slow oscillation can be recorded at subcortical and brainstem levels, and likely influences neural activity. Generally, the SO is enriched during stage N3, but is also presented during stage N2. How does the SO relate to downstream autonomic effects of sleep state? The hypothesis tested in this study is if (1) SO have distinct and different kinetics during cardiopulmonary coupling (CPC) calculated NREM-Stable Sleep (NREMs)and NREM-Unstable sleep (NREMus), (2) if blood pressure dipping occurs during NREMs, regardless of conventional sleep stage, (3) if REM sleep demonstrated stable and unstable pattern.
The association of blood pressure dipping exclusively during NREMs is important as NREMs is in turn associated with a continuous mode of expression of the NREM SO. It is important to use multi-physiology approach to identify sleep states and to evaluated effects of sleep that just rely on EEG-based sleep stages exclusively.
Non-rapid eye movement sleep is conventionally scored in grades of increasing depth, N1 to N3, based on electroencephalographic (EEG) features. This classification has limitations including ignoring other sleep state signals, not incorporating the < 1Hz slow oscillations and that increasing age rapidly “degrades” sleep quality based on the percentage of N3, even in health individuals. By measuring beat-to-beat blood pressure and computing electrocardiogram-derived cardiopulmonary coupling (CPC), this analysis documents that NREM sleep has strong bimodal characteristics, presenting in one of two forms with non-overlapping integrated electrocortical, autonomic, hemodynamic and respiratory features. REM sleep also exhibits bimodality when considering sleep apnea patterns in relation to REM stage.