Carotid chemoreceptor control of muscle sympathetic nerve activity in hypobaric hypoxia
Bibliographic record
Abstract
New Findings What is the central question of this study? High‐altitude hypoxia increases muscle sympathetic nerve activity (MSNA), but whether intravenous infusion of dopamine, to blunt the responsiveness of the carotid chemoreceptors, reduces MSNA at high altitude is not known. What is the main finding and its importance? Muscle sympathetic nerve activity was elevated after 15–17 days of high‐altitude hypoxia (3454 m) compared with values at ‘sea level’ (432 m). However, intravenous dopamine infusion to blunt the responsiveness of the carotid chemoreceptors did not significantly decrease MSNA either at sea level or at high altitude, suggesting that high‐altitude sympathoexcitation arises via a different mechanism. High‐altitude hypoxia causes pronounced sympathoexcitation, but the underlying mechanisms remain unclear. We tested the hypothesis that i.v. infusion of dopamine to attenuate carotid chemoreceptor responsiveness would reduce muscle sympathetic nerve activity (MSNA) at high altitude. Nine healthy individuals [mean (SD); 26 (4) years of age] were studied at ‘sea level’ (SL; Zurich) and at high altitude (ALT; 3454 m; 15–17 days after arrival), both while breathing the ambient air and during an acute incremental hypoxia test (eight 3 min stages; partial pressure of end‐tidal O2 90–45 mmHg). Intravenous infusions of dopamine (3 μg kg−1 min−1) and placebo (saline) were administered on both study days, according to a single‐blind randomized cross‐over design. Sojourn to high altitude decreased the partial pressure of end‐tidal O2 (to ∼60 mmHg) and increased minute ventilation [ ; mean ± SEM, SL versus ALT: saline, 8.6 ± 0.5 versus 11.3 ± 0.6 l min−1; dopamine, 8.2 ± 0.5 versus 10.6 ± 0.8 l min−1; P < 0.05] and MSNA burst frequency by ∼80% [SL versus ALT: saline, 16 ± 3 versus 28 ± 4 bursts min−1; dopamine, 16 ± 4 versus 31 ± 4 bursts min−1; P < 0.05) when breathing the ambient air, but were not different with dopamine. Increases in MSNA burst frequency and during the acute incremental hypoxia test were greater at ALT than SL (P < 0.05). Dopamine did not affect the magnitude of the MSNA burst frequency response to acute incremental hypoxia at either SL or ALT. However, was lower with dopamine than saline administration throughout the acute incremental hypoxia test at ALT. These data indicate that i.v. infusion of low‐dose dopamine to blunt the responsiveness of the carotid chemoreceptors does not significantly decrease MSNA at high altitude.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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".