S and full research articles published in SLEEP, the official journal of the APSS. Sleep and sleep disorder scientific findings.

Lowlanders commonly report a poor sleep quality during the first few nights after arriving at high altitude. Polysomnographic studies reveal that reductions in slow wave sleep are the most consistent altitude-induced changes in sleep structure identified by visual scoring. Quantitative spectral analyses of the sleep electroencephalogram have confirmed an altitude-related reduction in the low-frequency power (0.8-4.6 Hz). Although some studies suggest an increase in arousals from sleep at high altitude, this is not a consistent finding. Whether sleep instability at high altitude is triggered by periodic breathing or vice versa is still uncertain. Overnight changes in slow wave-derived encephalographic measures of neuronal synchronization in healthy subjects were less pronounced at moderately high (2,590 m) compared with low altitude (490 m), and this was associated with a decline in sleep-related memory consolidation. Correspondingly, exacerbation of breathing and sleep disturbances experienced by lowlanders with obstructive sleep apnea during a stay at 2,590 m was associated with poor performance in driving simulator tests. These findings suggest that altitude-related alterations in sleep may adversely affect daytime performance. Despite recent advances in our understanding of sleep at altitude, further research is required to better establish the role of gender and age in alterations of sleep at different altitudes, to determine the influence of acclimatization and of altitude-related illness, and to uncover the characteristics of sleep in highlanders that may serve as a study paradigm of sleep in patients exposed to chronic hypoxia due to cardiorespiratory disease.

Rationale: Quantitative data on ventilation during acclimatization at very high altitude are scant. Therefore, we monitored nocturnal ventilation and oxygen saturation in mountaineers ascending Mt. Muztagh Ata (7,546 m). Objectives: To investigate whether periodic breathing persists during prolonged stay at very high altitude. Methods: A total of 34 mountaineers (median age, 46 yr; 7 women) climbed from 3,750 m within 19–20 days to the summit at 7,546 m. During ascent, repeated nocturnal recordings of calibrated respiratory inductive plethysmography, pulse oximetry, and scores of acute mountain sickness were obtained. Measurements and Main Results: Nocturnal oxygen saturation decreased, whereas minute ventilation and the number of periodic breathing cycles increased with increasing altitude. At the highest camp (6,850 m), median nocturnal oxygen saturation, minute ventilation, and the number of periodic breathing cycles were 64%, 11.3 L/min, and 132.3 cycles/h. Repeated recordings within 5–8 days at 4,497 m and 5,533 m, respectively, revealed increased oxygen saturation, but no decrease in periodic breathing. The number of periodic breathing cycles was positively correlated with days of acclimatization, even when controlled for altitude, oxygen saturation, and other potential confounders, whereas symptoms of acute mountain sickness had no independent effect on periodic breathing. Conclusions: Our field study provides novel data on nocturnal oxygen saturation, breathing patterns, and ventilation at very high altitude. It demonstrates that periodic breathing increases during acclimatization over 2 weeks at altitudes greater than 3,730 m, despite improved oxygen saturation consistent with a progressive increase in loop gain of the respiratory control system. Clinical trial registered with www.clinicaltrials.gov (NCT00514826).

Background The Epworth Sleepiness Scale (ESS) is a widely used tool for assessing sleepiness in patients with obstructive sleep apnoea (OSA). We aimed to estimate the minimal important difference (MID) in patients with OSA. Methods We used individual data from three randomised controlled trials (RCTs) in patients with OSA where the preintervention to postintervention change in ESS was used as a primary outcome. We used anchor-based linear regression and responder analysis approaches to estimate the MID. For anchors, we used the change in domains of the Functional Outcomes of Sleep Questionnaire and 36-Item Short Form Health Survey. We also used the distribution-based approaches Cohen’s effect size, SE of measurement and empirical rule effect size to support the anchor-based estimates. The final MID was determined by triangulating all estimates to a single MID. Findings A total of 639 patients with OSA were included in our analyses across the three RCTs with a median (IQR) baseline ESS score of 10 (6–13). The median (IQR) ESS change score overall was −2 (−5 to 1). The anchor-based estimates of the MID were between −1.74 and −4.21 points and estimates from the responder analysis were between −1 and −3 points. Distribution-based estimates were smaller, ranging from −1.46 to −2.36. Interpretation We propose an MID for the ESS of 2 points in patients with OSA with a disease severity from mild to severe. This estimate provides the means to plan trials and interpret the clinical relevance of changes in ESS. Trial registration number Provent, NCT01332175; autoCPAP trial, NCT00280800; MOSAIC,ISRCTN (3416388).

Research from JAMA — Effect of Acetazolamide and AutoCPAP Therapy on Breathing Disturbances Among Patients With Obstructive Sleep Apnea Syndrome Who Travel to Altitude — A Randomized Controlled Trial

S and full research articles published in SLEEP, the official journal of the APSS. Sleep and sleep disorder scientific findings.