Sleep-related periodic breathing does not acclimatize to chronic hypobaric hypoxia: a 1-year study at high altitude in Antarctica.

Abstract

At altitudes above 2,500 m, ventilation in healthy subjects commonly shows periodic breathing: an oscillatory behavior with alternating periods of hyperventilation followed by central apneas or hypopneas (1–3). Although an increase in altitude is correlated with an increase in the occurrence of periodic breathing (1, 4), the magnitude, the time course, and the altitude of occurrence differ markedly between studies. Some studies found an increase in periodic breathing over time at different altitudes, despite an improvement of SpO2 (oxygen saturation as measured by pulse oximetry), and they found no relationship with acute mountain sickness (AMS) (1, 5). Other studies, however, found a decrease (6, 7) or no changes (3) in the amount of periodic breathing over time. All of these studies were performed at different altitudes and ascending rates. Furthermore, in these studies the time spent in hypobaric hypoxia was short, from several days to up to 4 weeks. We aimed to observe the occurrence of periodic breathing over a longer time period, beyond the period of adaptation (8, 9). This study was conducted within the framework of the European Space Agency’s Life Science campaign at the Antarctic base Concordia, located at an equivalent altitude of 3,800 m above sea level. Living conditions within the station are comparable to European standards of living, with the inhabitants conducting research and maintaining the base. Because of the confinement conditions, day–night cycles at the station are imposed by daily routines rather than daylight, which is absent for 3 months during the polar winter. Participants remained at the station an average of 13 months. This study was approved by the Ethics Committee of the Free University of Brussels (Brussels, Belgium). Some of the results of this study have been previously reported in the form of conference abstracts (10, 11). Thirteen members of the 14 all-male crew of one winter campaign participated in the experiment (n = 13; age = 396 9.8 yr; body mass index [BMI] = 24.2 6 2.2; 3 smokers). None of the subjects reported a history of significant medical conditions. On arrival at the station, participants’ acclimatization progress was monitored weekly through physical examination, SpO2, and self-report assessment of AMS through the Lake Louise AMS questionnaire. During the campaign, nocturnal breathing patterns were recorded on eight occasions approximately every 6 weeks via portable polysomnography. All recordings were analyzed by the same professional sleep technician in accordance with the American Academy of Sleep Medicine criteria (12). Data from every two cycles were pooled to represent four major sessions mapping seasonal variations. The evolution of parameters over time was assessed by parametric repeated measures analysis of variance (ANOVA). For nonnormally distributed data, nonparametric equivalent statistical tests were used (Friedman ANOVA). The stability of interindividual differences was quantified by means of the intraclass correlation coefficient (ICC) and estimates were interpreted on the basis of published benchmark ranges (13). Of the 13 participants, 11 participated until the end of the study. A summary of results can be seen in Table 1. Symptoms of AMS were below clinical significance within the first 3 weeks on arrival (median AMS score after 3 wk was 1 [range, 0–1.5]). As a result of periodic breathing, the average number of apneic/ hypopneic events per sleeping hour (AHI) during the entire campaign was above the level clinically considered as severe (AHI = 65.4 6 29.1). Statistically, there was no effect of time on the evolution of AHI [F(3,30) = 0.500, P = 0.685, hp = 0.048] (see Figure 1A), but we found “substantive” stable interindividual differences (ICC = 0.770) (see Figure 1B). In contrast, there was a significant effect of time on SpO2 [F(3,33) = 4.706, P = 0.008, hp = 0.300], characterized by a linear increase over time [F(1,11) = 17.359, P = 0.002, hp = 0.612] (see Figure 1A). There was no significant correlation between AHI and SpO2 (all P values. 0.25). In addition, interindividual differences in SpO2 remained

DOI: 10.1164/rccm.201403-0598LE

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@article{Tellez2014SleeprelatedPB, title={Sleep-related periodic breathing does not acclimatize to chronic hypobaric hypoxia: a 1-year study at high altitude in Antarctica.}, author={Helio Fernandez Tellez and Olivier Mairesse and Eoin Macdonald-Nethercott and Xavier Neyt and R. Meeusen and Nathalie Pattyn}, journal={American journal of respiratory and critical care medicine}, year={2014}, volume={190 1}, pages={114-6} }