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Inter- and intraindividual variability of the pupillary unrest index

Inter- und intraindividuelle Variabilität des Pupillenunruheindex

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Abstract

Objective

The recording of slow pupillary oscillations in complete darkness is a promising approach for objective evaluation of daytime sleepiness at the physiological level. The aim of the present study was to analyze the magnitude of between- and within-subject variation of the pupillary unrest index (PUI) in a sample of healthy individuals.

Materials and methods

The present data were collected within the framework of a mobile phone study on possible effects of radiofrequency electromagnetic fields (RF-EMF) on the central nervous system. Pupillary behavior was monitored in 30 young healthy male volunteers (age 18–30 years) on ten non-consecutive experimental days at 11:00 a.m. and 04:00 p.m., using infrared video pupillography (compact integrated pupillograph, CIP). Since RF-EMF had no impact on the PUI, data were pooled for the present analysis.

Results

Mixed-model analyses of variance (ANOVAs) showed that the PUI was subject to higher interindividual variation as compared to intraindividual variation at both times of measurement. This resulted in intraclass correlation coefficients pointing to a substantial stability of these interindividual differences. A comparison of the PUI results with currently used cutoff values revealed that more than 50% of recordings from young, healthy, non-sleep-disturbed males showed values beyond the “normal” range.

Conclusion

The significant interindividual variability implies that the PUI is not only a state marker. Evaluations of such measurements should therefore consider the PUI as a possible trait marker to ensure comparability and correct interpretation.

Zusammenfassung

Zielsetzung

Die Registrierung von langsamen Pupillenbewegungen in kompletter Dunkelheit ist ein vielversprechendes Verfahren zur objektiven Bewertung von Tagesschläfrigkeit auf der physiologischen Ebene. Ziel der vorliegenden Untersuchung war die Analyse von inter- und intraindividueller Variabilität des Pupillenunruheindex (PUI) anhand einer Gruppe gesunder Personen.

Methodik

Die Daten wurden im Rahmen einer Mobilfunkstudie erhoben, in der ein möglicher Einfluss von elektromagnetischen Feldern auf das zentrale Nervensystem untersucht wurde. An 30 gesunden jungen Männern im Alter von 18 bis 30 Jahren wurde das Pupillenverhalten an zehn nicht aufeinander folgenden Terminen jeweils am Vormittag (11:00 Uhr) und am Nachmittag (16:00 Uhr) mittels der Infrarot-Video-Pupillographie (Compact Integrated Pupillograph, CIP) aufgezeichnet. Da in dieser Studie kein Expositionseffekt durch elektromagnetische Felder auf den PUI beobachtet werden konnte, wurden die Daten für die vorliegende Untersuchung zusammengefasst.

Ergebnisse

Die Mixed-Model-Varianzanalysen ergaben, dass dem PUI sowohl am Vor- als auch am Nachmittag eine höhere interindividuelle Variabilität im Vergleich zur intraindividuellen Variabilität zugrunde lag. Daraus konnten Intraklassen-Korrelationskoeffizienten berechnet werden, die auf eine beträchtliche Stabilität dieser interindividuellen Unterschiede hindeuteten. Bei Orientierung an den aktuell gültigen Grenzwerten sind die Ergebnisse von gesunden, nicht schlafgestörten jungen Erwachsenen in mehr als 50 % der Fälle als nicht „normal“ einzustufen.

Schlussfolgerung

Die signifikante interindividuelle Variabilität spricht dafür, dass der PUI nicht nur ein State-Merkmal darstellt. Bei Bewertungen dieser Ergebnisse sollte daher der PUI als mögliches Trait-Merkmal mit berücksichtigt werden, um eine Vergleichbarkeit und korrekte Interpretation sicherzustellen.

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Authors and Affiliations

  1. Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Competence Centre of Sleep Medicine, Charitéplatz 1, 10117, Berlin, Germany

    Torsten Eggert, Cornelia Sauter, Hans Dorn, Anita Peter, Marie-Luise Hansen & Heidi Danker-Hopfe

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  1. Torsten Eggert
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  2. Cornelia Sauter
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  3. Hans Dorn
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  4. Anita Peter
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Correspondence to Torsten Eggert.

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Conflict of interest

T. Eggert, C. Sauter, H. Dorn, A. Peter, M.-L. Hansen and H. Danker-Hopfe declare that they have no competing interests.

This human study was conducted in accordance with the Declaration of Helsinki and was approved by the ethics committee of the Charite – University Medicine, Berlin. Each participant gave his written informed consent and was compensated for contribution.

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Eggert, T., Sauter, C., Dorn, H. et al. Inter- and intraindividual variability of the pupillary unrest index. Somnologie 21, 187–192 (2017). https://doi.org/10.1007/s11818-017-0128-2

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