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KMID : 1034320100010010020
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Sleep Medicine Research
2010 Volume.1 No. 1 p.20 ~ p.25
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Preserved Sleep Quality under Simulated Altitude as Assessed by Electroencephalography Power and the Electrocardiogram-Derived Sleep Spectrogram
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Yun Chang-Ho
Mietus Joseph E
Lee Chien-I
Thomas Robert J
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Abstract
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Background and Objective Simulated altitude as a model for hypoxia has shown inconsistent results in terms of impaired cognition. We hypothesized that preserved periods of stable sleep even under hypoxia could explain stable cognitive function. Delta spectral power on electroencephalography during stable sleep as well as high frequency coupling on the electrocardiogram-based spectrogram was adopted as measures of sleep quality.
Methods: Eleven healthy, non-smoking subjects (7 men, 27 ± 1.5 years) were exposed to 9 hours of continuous hypoxia for 13 consecutive nights. Polysomnography was done at baseline and during 3 time points, at night 3, 7, and 14. In each study, delta spectral power was obtained during stable N2 and N3 sleep. Stable sleep was defined when there was no significant fragmentation in electroencephalography and fluctuation in electromyography and cardiorespiratory signals. The time threshold was 2 or 5 continuous minutes for N2 and 2 minutes for N3. The amount of high frequency coupling for the sleep period on the electrocardiogram-based spectrogram was computed. Randomized block ANOVA was used with electroencephalography delta power and high frequency coupling as dependent variables with post hoc Tukey test.
Results: Delta spectral power during stable sleep was not significantly different across the entire hypoxic exposures (p = 0.98 for N2; p= 0.32 for N3). High frequency coupling was different between pre-exposure and mid-exposure (night 7; 52.5 ± 23.6% vs. 39.0 ± 16.7%, p= 0.02) but returned to the baseline level at the post-exposure (night 14; 45.4 ± 18.2%, p = 0.39).
Conclusions: Both preservation of the proportion of stable sleep and unchanged delta power during these periods may help explain maintained cognition in conditions of chronic nocturnal hypoxic exposures.
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KEYWORD
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Sleep, Hypoxia, Electroencephalography, Electrocardiography, Cognition
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