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

Abstract

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 (SpO₂), 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 SpO₂ 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 SpO₂ 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. 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.