The effect of short-term descent to low altitude in healthy residents at moderate altitude — a randomized crossover trial

We examined the effect of a short-term descent to low altitude on sleep-disordered breathing (SDB) in healthy moderate altitude residents. Forty-four healthy participants (50% females), median age 47 years, living > 1000 m (median (IQR) altitude of 1230 m (1130; 1560)), were included. Polysomnographies were carried out for two consecutive nights at the participants’ home elevations and for two nights at the sleep laboratory in Chur (590 m), Switzerland, after a 2-week washout period, in accordance with a randomized crossover design. The primary outcome was time spent under 90% oxygen saturation (T90). Important secondary outcomes were nocturnal oxygen saturation (SpO 2 ), apnea–hypopnea index (AHI), and oxygen desaturation index (ODI). Additional outcomes were sleep stage-related parameters. The trial has been registered at clinicaltrials.gov (NCT05826808). Mean ± SE T90 was 1 ± 2 min at 590 m and 5 ± 2 min at > 1000 m (mean difference of 4 min, 95% CI of 1 to 7, p = 0.005). At 590 m, the total AHI was 9.2 ± 1.6/h (2.3% with AHI > 30/h), ODI 6.0 ± 1.4/h, and SpO 2 95.2 ± 0.2%. At > 1000 m, the total AHI was 14.2 ± 1.6/h (13.6% with AHI > 30/h, p = 0.025 vs. 590 m), ODI 10.0 ± 1.4/h, and SpO 2 93.8 ± 0.2% ( p < 0.001 all comparisons versus 590 m). Mean slow wave sleep on the second night at 590 m was 10.0 ± 1% and 8.0 ± 1% at > 1000 m ( p = 0.001). In males, descent to low altitude showed a more significant effect on T90 (mean difference of 7 min, 95% CI of 1 to 12, p = 0.024) and REM sleep stage (mean difference of 4%TST, 95% CI of 1 to 7, p = 0.011) compared to females. A short-term, low-altitude stay of healthy moderate altitude residents leads to a reduction in nocturnal hypoxemia and SDB, especially in males. These findings suggest that sleep-disordered breathing assessments at lower-than-living altitude might underestimate the severity of SDB in patients permanently living at moderate altitudes. Study rationale: Several million people worldwide permanently live at moderate altitude. Due to the vast variety in heights worldwide, the altitude of the closest sleep laboratory might vary and be at a lower altitude, which may lead to underestimated results. Study impact: To our knowledge, the current study is the first to investigate the effect of a short-term descent to low altitude on sleep-disordered breathing (SDB) in healthy moderate altitude residents. In this paper, we show that a short-term, low-altitude stay leads to a reduction in nocturnal hypoxemia and less sleep-associated breathing disorders, especially in males. Moreover, the proportion of severe SDB is underestimated at lower-than-living sleep laboratory assessments.