The effect of hypoxemia on muscle sympathetic nerve activity and cardiovascular function: a systematic review and meta-analysis
Bibliographic record
Abstract
We conducted a systematic review and meta-analysis to determine the effect of acute poikilocapnic, high-altitude, and acute isocapnia hypoxemia on muscle sympathetic nerve activity (MSNA) and cardiovascular function. A comprehensive search across electronic databases was performed until June 2021. All observational designs were included: population (healthy individuals); exposures (MSNA during hypoxemia); comparators (hypoxemia severity and duration); outcomes (MSNA; heart rate, HR; and mean arterial pressure, MAP). Sixty-one studies were included in the meta-analysis. MSNA burst frequency increased by a greater extent during high-altitude hypoxemia [ P < 0.001; mean difference (MD), +22.5 bursts/min; confidence interval (CI) = −19.20 to 25.84] compared with acute poikilocapnic hypoxemia ( P < 0.001; MD, +5.63 bursts/min; CI = −4.09 to 7.17) and isocapnic hypoxemia ( P < 0.001; MD, +4.72 bursts/min; CI = −3.37 to 6.07). MSNA burst amplitude was only elevated during acute isocapnic hypoxemia ( P = 0.03; standard MD, +0.46 au; CI = −0.03 to 0.90), and MSNA burst incidence was only elevated during high-altitude hypoxemia [ P < 0.001; MD, 33.05 bursts/100 heartbeats; CI = −28.59 to 37.51]. Meta-regression analysis indicated a strong relationship between MSNA burst frequency and hypoxemia severity for acute isocapnic studies ( P < 0.001) but not acute poikilocapnia ( P = 0.098). HR increased by the same extent across each type of hypoxemia [ P < 0.001; MD +13.81 heartbeats/min; 95% CI = 12.59–15.03]. MAP increased during high-altitude hypoxemia ( P < 0.001; MD, +5.06 mmHg; CI = 3.14–6.99), and acute isocapnic hypoxemia ( P < 0.001; MD, +1.91 mmHg; CI = 0.84–2.97), but not during acute poikilocapnic hypoxemia ( P = 0.95). Both hypoxemia type and severity influenced sympathetic nerve and cardiovascular function. These data are important for the better understanding of healthy human adaptation to hypoxemia.
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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 | 0.010 | 0.023 |
| Meta-epidemiology (narrow) | 0.003 | 0.002 |
| Meta-epidemiology (broad) | 0.017 | 0.032 |
| Bibliometrics | 0.005 | 0.006 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.003 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.002 | 0.002 |
| Insufficient payload (model declined to judge) | 0.003 | 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".