Are nocturnal breathing, sleep, and cognitive performance impaired at moderate altitude (1,630-2,590 m)?

Abstract

Study objectives: Newcomers at high altitude (> 3,000 m) experience periodic breathing, sleep disturbances, and impaired cognitive performance. Whether similar adverse effects occur at lower elevations is uncertain, although numerous lowlanders travel to moderate altitude for professional or recreational activities. We evaluated the hypothesis that nocturnal breathing, sleep, and cognitive performance of lowlanders are impaired at moderate altitude.

Design: Randomized crossover trial.

Setting: University hospital at 490 m, Swiss mountain villages at 1,630 m and 2,590 m.

Participants: Fifty-one healthy men, median (quartiles) age 24 y (20-28 y), living below 800 m.

Interventions: Studies at Zurich (490 m) and during 4 consecutive days at 1,630 m and 2,590 m, respectively, 2 days each. The order of altitude exposure was randomized. Polysomnography, psychomotor vigilance tests (PVT), the number back test, several other tests of cognitive performance, and questionnaires were evaluated.

Measurements and results: The median (quartiles) apnea-hypopnea index at 490 m was 4.6/h (2.3; 7.9), values at 1,630 and 2,590 m, day 1 and 2, respectively, were 7.0/h (4.1; 12.6), 5.4/h (3.5; 10.5), 13.1/h (6.7; 32.1), and 8.0/h (4.4; 23.1); corresponding values of mean nocturnal oxygen saturation were 96% (95; 96), 94% (93; 95), 94% (93; 95), 90% (89; 91), 91% (90; 92), P < 0.05 versus 490 m, all instances. Slow wave sleep on the first night at 2,590 m was 21% (18; 25) versus 24% (20; 27) at 490 m (P < 0.05). Psychomotor vigilance and various other measures of cognitive performance did not change significantly.

Conclusions: Healthy men acutely exposed during 4 days to hypoxemia at 1,630 m and 2,590 m reveal a considerable amount of periodic breathing and sleep disturbances. However, no significant effects on psychomotor reaction speed or cognitive performance were observed.

Clinical trials registration: Clinicaltrials.gov: NCT01130948.

Keywords: Altitude; healthy; hypoxia; sleep apnea; vigilance.

Figures

Figure 1

Patient flow according to the four different altitude exposure sequences A through D.

Figure 2

The mean nocturnal oxygen saturation (A), psychomotor vigilance test response speed (B), apnea-hypopnea index (C), and slow wave sleep (D, nonrapid eye movement sleep stages 3 and 4 in % of total sleep time) at the different altitudes. Horizontal lines, boxes, and whiskers represent the median, quartiles, and the 10th and 90th percentiles, respectively; individual values beyond this range are displayed by an x. † indicates P < 0.05 versus 490 m, †† indicates P < 0.05 versus 490 m and 1,630 m, respectively.