Hypoxia Differentially Affects Healthy Men and Women During a Daytime Nap With a Dose-Response Relationship: a Randomized, Cross-Over Pilot Study

Alain Riveros-Rivera; Thomas Penzel; Hanns-Christian Gunga; Oliver Opatz; Friedemann Paul; Lars Klug; Michael Boschmann; Anja Mähler

doi:10.3389/fphys.2022.899636

Hypoxia Differentially Affects Healthy Men and Women During a Daytime Nap With a Dose-Response Relationship: a Randomized, Cross-Over Pilot Study

Front Physiol. 2022 May 24:13:899636. doi: 10.3389/fphys.2022.899636. eCollection 2022.

Authors

Alain Riveros-Rivera^{1

2}, Thomas Penzel³, Hanns-Christian Gunga¹, Oliver Opatz¹, Friedemann Paul^{4

5

6}, Lars Klug^{4

5

6}, Michael Boschmann^{4

5

6}, Anja Mähler^{4

5

6

7}

Affiliations

¹ Center for Space Medicine and Extreme Environments Berlin, Institute of Physiology, Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, Berlin, Germany.
² Department of Physiological Sciences, Faculty of Medicine, Pontificia Universidad Javeriana, Bogotá, Colombia.
³ Interdisciplinary Center of Sleep Medicine, Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, Berlin, Germany.
⁴ Experimental and Clinical Research Center, A Cooperation Between the Max-Delbrück Center for Molecular Medicine in the Helmholtz Association and Charité Universitätsmedizin Berlin, Berlin, Germany.
⁵ Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Experimental and Clinical Research Center, Berlin, Germany.
⁶ Max Delbrück Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin, Germany.
⁷ DZHK (German Centre for Cardiovascular Research), Partner Site Berlin, Berlin, Germany.

Abstract

Context: The use of daytime napping as a countermeasure in sleep disturbances has been recommended but its physiological evaluation at high altitude is limited. Objective: To evaluate the neuroendocrine response to hypoxic stress during a daytime nap and its cognitive impact. Design, Subject, and Setting: Randomized, single-blind, three period cross-over pilot study conducted with 15 healthy lowlander subjects (8 women) with a mean (SD) age of 29(6) years (Clinicaltrials identifier: NCT04146857, https://clinicaltrials.gov/ct2/show/NCT04146857?cond=napping&draw=3&rank=12). Interventions: Volunteers underwent a polysomnography, hematological and cognitive evaluation around a 90 min midday nap, being allocated to a randomized sequence of three conditions: normobaric normoxia (NN), normobaric hypoxia at FiO₂ 14.7% (NH15) and 12.5% (NH13), with a washout period of 1 week between conditions. Results: Primary outcome was the interbeat period measured by the RR interval with electrocardiogram. Compared to normobaric normoxia, RR during napping was shortened by 57 and 206 ms under NH15 and NH13 conditions, respectively (p < 0.001). Sympathetic predominance was evident by heart rate variability analysis and increased epinephrine levels. Concomitantly, there were significant changes in endocrine parameters such as erythropoietin (∼6 UI/L) and cortisol (∼100 nmol/L) (NH13 vs. NN, p < 0.001). Cognitive evaluation revealed changes in the color-word Stroop test. Additionally, although sleep efficiency was preserved, polysomnography showed lesser deep sleep and REM sleep, and periodic breathing, predominantly in men. Conclusion: Although napping in simulated altitude does not appear to significantly affect cognitive performance, sex-dependent changes in cardiac autonomic modulation and respiratory pattern should be considered before napping is prescribed as a countermeasure.

Keywords: autonomic nervous system; high altitude (low air pressure); hypoxia; napping; physiological stress; sleep.

Associated data

ClinicalTrials.gov/NCT04146857