Quantitative Changes in the Sleep EEG at Moderate Altitude (1630 m and 2590 m)

Abstract

BackgroundPrevious studies have observed an altitude-dependent increase in central apneas and a shift towards lighter sleep at altitudes >4000 m. Whether altitude-dependent changes in the sleep EEG are also prevalent at moderate altitudes of 1600 m and 2600 m remains largely unknown. Furthermore, the relationship between sleep EEG variables and central apneas and oxygen saturation are of great interest to understand the impact of hypoxia at moderate altitude on sleep.MethodsFourty-four healthy men (mean age 25.0±5.5 years) underwent polysomnographic recordings during a baseline night at 490 m and four consecutive nights at 1630 m and 2590 m (two nights each) in a randomized cross-over design.ResultsComparison of sleep EEG power density spectra of frontal (F3A2) and central (C3A2) derivations at altitudes compared to baseline revealed that slow-wave activity (SWA, 0.8–4.6 Hz) in non-REM sleep was reduced in an altitude-dependent manner (∼4% at 1630 m and 15% at 2590 m), while theta activity (4.6–8 Hz) was reduced only at the highest altitude (10% at 2590 m). In addition, spindle peak height and frequency showed a modest increase in the second night at 2590 m. SWA and theta activity were also reduced in REM sleep. Correlations between spectral power and central apnea/hypopnea index (AHI), oxygen desaturation index (ODI), and oxygen saturation revealed that distinct frequency bands were correlated with oxygen saturation (6.4–8 Hz and 13–14.4 Hz) and breathing variables (AHI, ODI; 0.8–4.6 Hz).ConclusionsThe correlation between SWA and AHI/ODI suggests that respiratory disturbances contribute to the reduction in SWA at altitude. Since SWA is a marker of sleep homeostasis, this might be indicative of an inability to efficiently dissipate sleep pressure.

Sleep respiratory disturbances and arousals at moderate altitude have overlapping electroencephalogram spectral signatures

“…Sleep EEG power density spectra [Fast Fourier Transform (FFT) routine, Hanning window, average of six 5‐s epochs; frequency resolution 0.2 Hz] were computed for each 30‐s epoch. EEG artefacts were identified semi‐automatically based on power in the 0.8–4.6 and 20–40 Hz frequency ranges (Buckelmüller et al ., ; Stadelmann et al ., ). Table indicates the number of epochs contributing to our analyses after artefact removal.…”

“…The ethical committee of the canton of Zurich (Switzerland) approved the study protocol and participants gave their written informed consent. The study was registered with Clinicaltrials.gov: ID#NCT01130948 (Latshang et al ., ; Stadelmann et al ., ; Stöwhas et al ., ).…”

“…Although central and obstructive apneas differ in origin, the cessation of breathing may affect sleep in a similar way. Indeed, similar to patients with obstructive sleep apnea syndrome (OSAS), we recently found decreases in slow wave activity (SWA; power in 0.8–4.6 Hz range) and theta activity (4.6–8 Hz) in healthy subjects sleeping at moderate altitude (Stadelmann et al ., ). SWA is a well‐established index of sleep depth and is necessary for restorative sleep—thus, a decrease in this measure may be indicative of reduced sleep quality (Achermann and Borbély, ).…”

“…SWA is a well‐established index of sleep depth and is necessary for restorative sleep—thus, a decrease in this measure may be indicative of reduced sleep quality (Achermann and Borbély, ). Interestingly, although central apneas occur more frequently with increasing altitude (Anholm et al ., ; Nussbaumer‐Ochsner et al ., ), we found only a moderate correlation between the central apnea/hypopnea index (AHI) and SWA (Stadelmann et al ., ). Therefore, the degree to which the central AHI, independent of other altitude‐related factors, contributes to the decline in SWA and its impact on other EEG frequencies remains unclear.…”

Electrophysiological measures of sleep pressure during wakefulness in the course of isolation at the Concordia Antarctica station and physical activity as a countermeasure

“…Since the oxygen concentration is at 13% instead of the usual 21%, the blood saturation in oxygen is lower, which increase the heart rate. Hypoxia has shown to impact cognitive performances and sleep quality (17; 18; 19; 20). Fortunately, the adaptation process to high altitude takes place within a few weeks and participants should be acclimated to their new environment for their first measurement (16; 21).…”