Elevated carotid body tonic activity contributes to ventilatory acclimatization and de‐acclimatization to high altitude at rest and during exercise
Bibliographic record
Abstract
Abstract Exposure to hypoxia is associated with increased ventilation, which escalates with continued exposure. Carotid chemoreceptors play a critical role in ventilatory acclimatization to prolonged hypoxia in animals. However, the contribution of carotid chemoreceptor tonic activity to ventilatory acclimatization in humans has not been directly demonstrated. We assessed carotid chemoreceptor tonic activity in lowlanders following acclimatization to high altitude and during de‐acclimatization. Fourteen healthy participants (7 male, 27 ± 4 years) were assessed at 340 m, following 13 days at high altitude (3800 m), and 3 days post‐descent to 1200 m. Carotid chemoreceptor tonic activity was indexed by the two‐breath nadir in minute ventilation () during 1 min of hyperoxia (100% inspired O2), at rest and during cycling exercise, matched for relative intensity [∼50% maximal oxygen consumption ()] and absolute intensity (∼90 W). Resting increased from sea level (12.9 ± 2.3 l/min) to 3800 m (16.8 ± 3.6 l/min, P < 0.001) and 3‐days post‐descent (18.2 ± 3.5 l/min, P < 0.001), with no difference between high altitude and post‐descent (P = 0.366). The hyperoxic nadir in ventilation was greater than sea level at 3800 m (+153%; P = 0.070, Cohen's d = 1.3) and 3‐days post‐descent (+74%; P = 0.048), with no significant difference between 3800 m and post‐descent (P = 0.326). During 50% exercise, the hyperoxic ventilation nadir was also greater than sea level at 3800 m (+225%; P = 0.007) and 3 days post‐descent (+183%; P = 0.004). The degree of ventilatory acclimatization was associated with the change in the hyperoxic nadir in ventilation (as an index of carotid chemoreceptor tonic activity; r2 = 0.60, P = 0.014). In conclusion, carotid chemoreceptor tonic activity is elevated and associated with acclimatization to high altitude, and this persists 3 days post‐descent. image Key points Ascent to high altitude is associated with adjustments in ventilation (i.e. ventilatory acclimatization). Heightened carotid chemoreceptor activity plays a critical role in ventilatory acclimatization to prolonged hypoxia in animals; However, there have been no studies in humans directly assessing the contribution of carotid body tonic activity in ventilatory acclimatization during rest and exercise. We aimed to elucidate the changes in carotid chemoreceptor tonic activity in the process of ventilatory acclimatization and de‐acclimatization during rest and exercise conditions. Ventilation at rest and during exercise increased at high altitude during acclimatization, and this corresponded with increased inhibition of ventilation with hyperoxia. Increased ventilation persisted at 3 days following descent from high altitude, along with the persistence of elevated carotid body tonic activity. We conclude that elevated carotid body tonic activity plays a major role in ventilatory acclimatization to, and de‐acclimatization from, high altitude, and this persists during exercise.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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".