February 2, 2026Open Access

Effects of nocturnal periodic breathing on sympathetic nerve activity and ventilatory control at high altitude: a randomised, crossover study

Q: What does this research mean for the field?

Nocturnal periodic breathing does not contribute to increased sympathetic nerve activity or ventilation during 3 days of high altitude exposure. Novelty: ClaimNovelty.CONFIRMATORY. Consensus alignment: ConsensusAlignment.NEUTRAL.

Key Result

Nocturnal periodic breathing did not contribute to increased sympathetic nerve activity or ventilation during 3 days of high altitude exposure.

Key Points

This study aims to determine the effect of nocturnal periodic breathing on sympathetic nerve activity and ventilation during high altitude exposure.
Randomised, placebo-controlled, crossover design.
Twelve healthy men completed two 3-day sojourns in hypobaric hypoxia.
Nocturnal periodic breathing was inhibited during one sojourn using increased inspiratory CO2 fraction.
Ventilation and plasma catecholamines were measured; muscle sympathetic nerve activity (MSNA) was assessed before and after each sojourn.
Increases in MSNA burst frequency and incidence were not significantly different between the inhibited (nPB−) and unaltered (nPB+) conditions.
Catecholamine concentrations were similar across sojourns, indicating consistent sympathetic response.
Ventilation parameters were generally equivalent, with only a slight increase in tidal volume during the nPB+ condition.

Structured PICO

Does inhibiting nocturnal periodic breathing reduce sympathetic nerve activity and hyperventilation in healthy men exposed to high altitude?

Population

12 healthy men

Intervention

Inhibition of nocturnal periodic breathing (nPB) by increasing inspiratory CO2 fraction during the nights of a 3-day sojourn in hypobaric hypoxia equivalent to 4000 m altitude

Comparator

Placebo (no nPB inhibition) during a 3-day sojourn in hypobaric hypoxia equivalent to 4000 m altitude

Outcome

Muscle sympathetic nerve activity (MSNA) burst frequency and incidence, plasma catecholamines, and ventilatory variablessurrogate

Inhibiting nocturnal periodic breathing does not contribute to the sympathoexcitation and hyperventilation associated with 3 days of exposure to high altitude in healthy men.

Main Result

Absolute Event Rate: 0% vs 0%

Abstract

During acute exposure to the hypoxia of high altitude, activation of the peripheral chemoreflex increases sympathetic nerve activity (SNA) and pulmonary ventilation. If exposure extends over several days, SNA and ventilation further increase and we investigated whether nocturnal periodic breathing (nPB) – a form of sleep‐disordered breathing that is common at high altitude – contributes to these further increases. In a randomised, placebo‐controlled, crossover protocol, twelve healthy men completed two 3‐day sojourns in hypobaric hypoxia equivalent to 4000 m altitude. nPB was inhibited by increasing inspiratory CO₂ fraction during the nights of one (nPB−), but not the other sojourn (nPB+). Ventilation and plasma catecholamines were measured daily, while muscle SNA (MSNA) was assessed before and at the end of sojourns, without and with peripheral chemoreflex inhibition (transient hyperoxia). The hypoxia‐induced increases in MSNA burst frequency (nPB−, +104%; nPB+, +94%; P = 0. 789) and incidence (nPB−, +47%; nPB+, +50%; P = 0. 791) were not different between sojourns. Catecholamine concentrations throughout the sojourns were also similar (sojourn: P ≥ 0. 271, time × sojourn: P ≥ 0. 495). Ventilatory variables were not different between sojourns (sojourn: all P ≥ 0. 090, time×sojourn: all P ≥ 0. 062) except for a slightly greater tidal volume throughout nPB+ (sojourn: P = 0. 047, time × sojourn: PP = 0. 482). Chemoreflex inhibition induced similar reductions in ventilation during both sojourns (all P ≥ 0. 151) and larger reductions in MSNA burst frequency (nPB−: −7. 3 ± 2. 7 bursts min^−1, nPB+: −4. 4 ± 5. 1 bursts min^−1, P = 0. 037) and incidence after the nPB− (−0. 9 ± 5. 7 bursts (100 heart beats (HB) ) ^−1) than after the nPB+ sojourn (+2. 4 ± 7. 3 bursts (100 HB) ^−1, P = 0. 046). We thus conclude that nPB does not contribute to the sympathoexcitation and hyperventilation associated with 3 days of exposure to high altitude. imageKey points Prolonged exposure to high altitude leads to progressive increases in sympathetic nerve activity and pulmonary ventilation. Nocturnal periodic breathing (nPB), a form of sleep‐disordered breathing that is common at high altitude, may contribute to these progressive increases in sympathetic nerve activity and ventilation. In this randomised, placebo‐controlled, crossover study, twelve healthy men completed two 3‐day sojourns in hypobaric hypoxia where nPB was either inhibited or not. The hypoxia‐induced increases in sympathetic nerve activity and ventilation were not different between the two sojourns. We conclude that nPB does not contribute to the sympathoexcitation and hyperventilation associated with 3 days of exposure to high altitude.

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