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. 2023 Dec 14;5(4):793-805.
doi: 10.3390/clockssleep5040051.

Methods for REM Sleep Density Analysis: A Scoping Review

Tamires Tiemi Kishi  1 , Monica Levy Andersen  1   2 , Ygor Matos Luciano  1 , Viviane Akemi Kakazu  1 , Sergio Tufik  1   2 , Gabriel Natan Pires  1   2
Affiliations

Methods for REM Sleep Density Analysis: A Scoping Review

Tamires Tiemi Kishi et al. Clocks Sleep. .

Abstract

Rapid eye movements (REM) sleep density is the parameter proposed to explain the variability in the amount of eye movements during REM sleep. Alterations in REM sleep density have been proposed as a screening criterion for individuals with depression and other mental health conditions, but its accuracy has not been properly evaluated. The lack of consensus and the variability of the methods used to score it reduces the external validity of the results, hindering an adequate analysis of its diagnostic accuracy and clinical applicability. This scoping review aimed to identify and quantify the methods used to score REM sleep density, describing their main characteristics. A literature search was conducted in PubMed, Scopus, PsycInfo, and Web of Science. Only studies with objective measures for REM sleep density analysis in individuals with depression were considered eligible. The final sample comprised 57 articles, covering 64 analyses of REM sleep density. The relative frequency methods were the predominant measurement parameter for analyzing REM sleep density across studies. The most frequently adopted REM estimation unit was the number of REM events followed by mini-epochs containing REM. The most common unit of measurement were frequency/time measures. The results demonstrate that there is no consistency in the methods used to calculate REM sleep density in the literature, and a high percentage of studies do not describe their methods in sufficient detail. The most used method was the number of REM episodes per minute of REM sleep, but its use is neither unanimous nor consensual. The methodological inconsistencies and omissions among studies limit the replicability, comparability, and clinical applicability of REM sleep density. Future guidelines should discuss and include a specific methodology for the scoring of REM sleep density, so it can be consensually implemented in clinical services and research.

Keywords: REM sleep density; depression; polysomnography; sleep.

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Conflict of interest statement

G.N.P. is a shareholder at SleepUp©. The other authors have no conflict of interests to disclose.

Figures

Figure 1
Figure 1
Terminology used to define the methods of REM sleep density analyses. This example details a relative time method, in which the number of REM events is divided by the total REM sleep time. Absolute measurement methods (time or duration) have no denominator. Acronyms: REM: rapid eye movements. N: frequency/number of events. Min: minutes.
Figure 2
Figure 2
Scoping review flowchart.
Figure 3
Figure 3
Measurement parameters used for the analysis of REM sleep density. Acronyms: ND: Not disclosed.
Figure 4
Figure 4
Variables related to the calculation of REM sleep density. (A) REM estimation unit. It disclosed the exact way by which REM was estimated. (B) Denominator. It refers to the variables used to correct for the amount of REM, being applicable only to relative measurement parameters. (C) Unit of measurement. It refers to the resulting unit of measurement of REM sleep density. Acronyms: IRIs: interrapid eye movements interval. Min: minutes. N: frequency/number of events. ND: not disclosed. REM: rapid eye movements. S: seconds.
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