Instability of non-REM sleep in older women evaluated by sleep-stage transition and envelope analyses

Insung Park; Chihiro Kokudo; Jaehoon Seol; Asuka Ishihara; Simeng Zhang; Akiko Uchizawa; Haruka Osumi; Ryusuke Miyamoto; Kazumasa Horie; Chihiro Suzuki; Yoko Suzuki; Tomohiro Okura; Javier Diaz; Kaspar E Vogt; Kumpei Tokuyama

doi:10.3389/fnagi.2022.1050648

Instability of non-REM sleep in older women evaluated by sleep-stage transition and envelope analyses

Front Aging Neurosci. 2022 Dec 6:14:1050648. doi: 10.3389/fnagi.2022.1050648. eCollection 2022.

Authors

Insung Park¹, Chihiro Kokudo^{1

2}, Jaehoon Seol^{1

3

4}, Asuka Ishihara¹, Simeng Zhang¹, Akiko Uchizawa², Haruka Osumi², Ryusuke Miyamoto⁵, Kazumasa Horie⁵, Chihiro Suzuki¹, Yoko Suzuki¹, Tomohiro Okura^{1

3

6}, Javier Diaz¹, Kaspar E Vogt¹, Kumpei Tokuyama¹

Affiliations

¹ International Institute for Integrative Sleep Medicine (WPI-IIIS), University of Tsukuba, Tsukuba, Japan.
² Graduate School of Comprehensive Human Science, University of Tsukuba, Tsukuba, Japan.
³ Faculty of Health and Sports Sciences, University of Tsukuba, Tsukuba, Japan.
⁴ Japan Society for the Promotion of Science, Tokyo, Japan.
⁵ Center for Computational Sciences, University of Tsukuba, Tsukuba, Japan.
⁶ R&D Center for Tailor-Made QOL, University of Tsukuba, Tsukuba, Japan.

Abstract

Study objective: Traditionally, age-related deterioration of sleep architecture in older individuals has been evaluated by visual scoring of polysomnographic (PSG) recordings with regard to total sleep time and latencies. In the present study, we additionally compared the non-REM sleep (NREM) stage and delta, theta, alpha, and sigma wave stability between young and older subjects to extract features that may explain age-related changes in sleep.

Methods: Polysomnographic recordings were performed in 11 healthy older (72.6 ± 2.4 years) and 9 healthy young (23.3 ± 1.1 years) females. In addition to total sleep time, the sleep stage, delta power amplitude, and delta, theta, alpha, and sigma wave stability were evaluated by sleep stage transition analysis and a novel computational method based on a coefficient of variation of the envelope (CVE) analysis, respectively.

Results: In older subjects, total sleep time and slow-wave sleep (SWS) time were shorter whereas wake after sleep onset was longer. The number of SWS episodes was similar between age groups, however, sleep stage transition analysis revealed that SWS was less stable in older individuals. NREM sleep stages in descending order of delta power were: SWS, N2, and N1, and delta power during NREM sleep in older subjects was lower than in young subjects. The CVE of the delta-band is an index of delta wave stability and showed significant differences between age groups. When separately analyzed for each NREM stage, different CVE clusters in NREM were clearly observed between young and older subjects. A lower delta CVE and amplitude were also observed in older subjects compared with young subjects in N2 and SWS. Additionally, lower CVE values in the theta, alpha and sigma bands were also characteristic of older participants.

Conclusion: The present study shows a decrease of SWS stability in older subjects together with a decrease in delta wave amplitude. Interestingly, the decrease in SWS stability coincided with an increase in short-term delta, theta, sigma, and alpha power stability revealed by lower CVE. Loss of electroencephalograms (EEG) variability might be a useful marker of brain age.

Keywords: K-complexes; SWS; delta power; envelope analysis; older; sleep transition.