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Association between Hypoxia, Sleep, and the Circadian System during Long-Haul Flights. A Commentary [Letter]

Authors Coste O, Touitou Y

Received 9 July 2022

Accepted for publication 15 July 2022

Published 22 July 2022 Volume 2022:14 Pages 1311—1312


Checked for plagiarism Yes

Editor who approved publication: Prof. Dr. Ahmed BaHammam

Olivier Coste,1 Yvan Touitou2

1Hôpital Instruction des Armées, Pathologie du Sommeil, Lyon, France; 2Unité Chronobiologie, Fondation Rothschild, Paris, 75019, France

Correspondence: Yvan Touitou, Email [email protected]

View the original paper by Dr Elmenhorst and colleagues

Dear editor

We would like to comment on the paper by Elmenhorst et al1 regarding the quality of a short nocturnal sleep episode in double aircrews on commercial ultra-long-haul flights.

The study’s goal was to assess the effects of mild hypobaric hypoxia at a simulated 8000 ft altitude. The authors discovered that hypoxia had a significant impact on sleep with an increase in N2 sleep and a rise in heart rate, the effects were reversible once the hypoxia was corrected with enriched O2 air inhalation.

A study limitation is the absence of any daytime hypoxic exposure during the waking period preceding the actual study when the objective was to study ultra-long-haul flights when hypoxia is present. Hypoxia can occur during the waking period of a long-distance flight; unfortunately, the authors did not plan for or discuss this though data do exist in the literature.

Indeed, we documented on a circadian basis the effects of 8-hr mild hypobaric hypoxia simulating a flight in a pressurized cabin. Following this hypoxic exposure, we discovered a phase delay in the core body temperature rhythm, and changes in melatonin and cortisol circadian rhythms which could explain, at least in part, subjective complaints of poor recovery sleep quality.2–4 Last, the effects of hypoxia on sleep architecture as measured by polysomnography allowed to show an increase in sleep onset latency and sleep fragmentation, and a reduction in the total sleep period, during the two nights following the hypoxic exposure.5

These findings complement and shed light on potential mechanisms for the effects of hypoxia on sleep, although the experimental design of the studies differs. To make a realistic inventory of aircrews’ sleep quality on long and ultra-long-haul flights, we believe it is necessary to factor in hypoxia’s alteration of the circadian time structure.


The authors declare no conflicts of interest in this communication.


1. Elmenhorst EM, Rooney D, Benderoth S, Wittkowski M, Wenzel J, Aeschbach D. Sleep-induced hypoxia under flight conditions: implications and countermeasures for long-haul flight crews and passengers. Nature Sci Sleep. 2022;14:193–205. doi:10.2147/NSS.S339196

2. Coste O, Beaumont M, Van Beers P, Batejat D, Charbuy H, Touitou Y. Hypoxic depression of melatonin secretion after simulated long lasting flights in man. J Pineal Res. 2004;37:1–10. doi:10.1111/j.1600-079X.2004.00128.x

3. Coste O, Beaumont M, Van Beers P, Batejat D, Touitou Y. Prolonged mild hypoxia modifies human circadian core body temperature and may be associated with sleep disturbances. Chronobiol Int. 2004;21:419–433. doi:10.1081/CBI-120038611

4. Coste O, Van Beers P, Bogdan A, Charbuy H, Touitou Y. Hypoxic alterations of cortisol circadian rhythm in man after simulation of a long duration flight. Steroids. 2005;70:803–810. doi:10.1016/j.steroids.2005.05.003

5. Coste O, Van Beers P, Touitou Y. Hypoxia-induced changes in recovery sleep, core body temperature, urinary 6-sulfatoxymelatonin and free cortisol after a simulated long-duration flight. J Sleep Res. 2009;18:454–465. doi:10.1111/j.1365-2869.2009.00744.x

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