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Individual stability of sleep spindle characteristics in healthy young males

Individuelle Stabilität von Schlafspindelparametern bei gesunden jungen Männern

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Abstract

Objective

The purpose of the present analysis was to quantify the magnitude of intersubject and intrasubject variation of sleep spindle characteristics in a sample of healthy young males.

Materials and methods

A total of 32 volunteers (age range 20–30 years) participated in a crossover study aimed at investigating possible effects of Terrestrial Trunked Radio (TETRA) signals on cognitive performance and human brain activity during sleep and waking. Sleep was polysomnographically assessed on nine identically organized study nights per individual. The inter- and intraindividual variability of automatically detected stage 2 non-rapid eye movement (NREM) sleep spindle (11–16 Hz) characteristics (number, density, duration, frequency, amplitude) derived from C3-A2 was determined. Stability of individual differences and the underlying variations were quantified using intraclass correlation (ICC) and coefficients of variation (CV), respectively. Note that there was no significant exposure effect on the considered sleep spindle characteristics.

Results

All sleep spindle variables showed an ICC coefficient higher than 0.8, indicating almost perfect stability of interindividual differences. Interindividual variability differed strongly between the considered spindle parameters (CV range: 2–53 %). Intraindividual variability was for all parameters less pronounced (mean CV range: 1–24 %), but their ratios underline the high degree of individuality of each of the investigated parameters.

Conclusion

The present analysis confirms the strong individual night-to-night stability of sleep spindle characteristics reported by previous studies. The results provide further evidence for treating sleep spindles as a possible trait, an issue which should be considered in studies relying on a parallel-group design. These data can also be used as reference values.

Zusammenfassung

Zielsetzung

Ziel dieser Studie war es, das inter- und intraindividuelle Ausmaß der Variation von Schlafspindelparametern anhand einer Gruppe gesunder, junger Männer zu bestimmen.

Material und Methoden

32 Versuchspersonen (Altersspanne: 20–30 Jahre) nahmen an einer Cross-over-Studie teil, in der untersucht wurde, ob elektromagnetische Felder des Behördenfunks TETRA (Terrestrial Trunked Radio) einen Einfluss auf kognitive Leistungen sowie auf die Gehirnaktivität im Wachzustand und im Schlaf haben. Von jedem Teilnehmer wurde der Schlaf in neun identisch organisierten Nachtschlafuntersuchungen polysomnographisch erfasst. Anschließend wurde die inter- und intraindividuelle Variabilität von automatisch detektierten Schlafspindelparametern (Anzahl, Dichte, Dauer, Frequenz, Amplitude) für die Elektrodenposition C3-A2 bestimmt. Die Stabilität individueller Unterschiede wurde mittels Intraklassen-Korrelation (ICC) berechnet und für die Quantifizierung der zugrunde liegenden Varianzen wurden Variationskoeffizienten (CV) verwendet. Die Exposition hatte keinen signifikanten Einfluss auf die hier berücksichtigten Schlafspindelparameter.

Ergebnisse

Die ICC-Koeffizienten ergaben für alle fünf untersuchten Schlafspindelparameter einen Wert größer 0,8, was einer fast perfekten Stabilität in den individuellen Unterschieden entspricht. Das Ausmaß der interindividuellen Variabilität zwischen den einzelnen Schlafspindelparametern wies große Unterschiede auf (CV-Spanne: 2–53 %). Die intraindividuelle Variabilität war bei allen Schlafspindelparametern geringer ausgeprägt (mittlere CV-Spanne: 1–24 %), das Verhältnis der Variabilitäten unterstreicht allerdings die hohe Individualität der untersuchten Parameter.

Schlussfolgerungen

Die hier präsentierten Ergebnisse bestätigen die Beobachtungen aus früheren Studien, in denen eine deutliche Nacht-zu-Nacht-Stabilität von Schlafspindelparametern gezeigt werden konnte. Die Ergebnisse liefern dementsprechend weitere Hinweise dafür, Schlafspindeln als mögliches „Trait“-Merkmal anzusehen, was in Studien, die einem Parallelgruppendesign folgen, berücksichtigt werden sollte. Zusätzlich können diese Daten auch als Normwerte herangezogen werden.

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Acknowledgements

The study was funded (grant number: FM 8846) by the Federal Agency for Public Safety Digital Radio (BDBOS), commissioned by the German Federal Office for Radiation Protection (BfS). The authors would like to thank all participants and PD Dr. Blanka Pophof from the BfS for her competent expert consultation.

Compliance with ethical guidelines

Conflict of interest. H. Danker-Hopfe was shareholder and chairman of the supervisory board of the SIESTA Schlafanalyse GmbH until May 2013. T. Eggert, C. Sauter, H. Dorn, A. Peter, ML. Hansen, and A. Marasanov state that there are no conflicts of interest.

All studies on humans described in the present manuscript were carried out with the approval of the responsible ethics committee and in accordance with national law and the Helsinki Declaration of 1975 (in its current, revised form). Informed consent was obtained from all patients included in studies.

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Authors and Affiliations

  1. Competence Centre of Sleep Medicine, Charité—University Medicine, Campus Benjamin Franklin, Hindenburgdamm 30, 12203, Berlin, Germany

    T. Eggert, C. Sauter, H. Dorn, A. Peter, M.-L. Hansen, A. Marasanov & H. Danker-Hopfe

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  1. T. Eggert
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  2. C. Sauter
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  3. H. Dorn
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  4. A. Peter
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Correspondence to T. Eggert.

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Eggert, T., Sauter, C., Dorn, H. et al. Individual stability of sleep spindle characteristics in healthy young males. Somnologie 19, 38–45 (2015). https://doi.org/10.1007/s11818-015-0697-x

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