Effects of nocturnal periodic breathing on sympathetic nerve activity and ventilatory control at high altitude: a randomised, crossover study
Bibliographic record
Abstract
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. image Key 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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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.004 | 0.003 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.004 | 0.002 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.002 | 0.002 |
| Insufficient payload (model declined to judge) | 0.005 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".