The Effect of Inspired Hypoxia and Hyperoxia on Respiratory Sinus Arrhythmia Reactivity
Bibliographic record
Abstract
Respiratory sinus arrhythmia (RSA) is the normal fluctuation in heart rate (HR) in phase with the respiratory cycle, whereby HR increases during inspiration and decreases during expiration. The underlying mechanisms and potential utility remain elusive. RSA magnitude is thought to be affected by autonomic balance, whereby a dominant parasympathetic nervous system (NS) at rest facilitates RSA, and sympathetic NS activation attenuates its magnitude. Carotid body stimulation via acute hypoxia elicits sympathetic activation, whereas hyperoxia facilitates sympathetic withdrawal. In addition, RSA has been hypothesized to facilitate improvements in ventilation/perfusion (V/Q) matching, improving oxygenation when hypoxic. We hypothesized that (a) acute hypoxia and hyperoxia would increase and decrease the magnitude of RSA reactivity, respectively and (b) when hypoxic, those with larger RSA magnitude during deep breathing would have larger improvements in oxygen saturation (SpO 2 ). Healthy participants (n=13) were instrumented with a pneumotachometer and coached to breathe at three percentages (30, 40 and 50%) of their forced vital capacity (FVC) using visual cues while inspiring room air (21% F I O 2 ), hypoxia (13.5% F I O 2 ), hyperoxia (100% F I O 2 ). RSA was quantified via the peak‐valley approach, and RSA reactivity (RSA R ) was quantified via linear regression to calculate the slope of changes in RSA magnitude across all three FVC levels. RSA magnitude increased linearly with increases in inspired tidal volume in all three gases (R 2 >0.98). No significant differences were found in RSA R slopes between room air (0.32±0.2 ΔBPM/%FVC), hypoxia (0.33±0.26 ΔBPM/%FVC), and hyperoxia (0.34±0.26 ΔBPM/%FVC; P=0.97). There was also no correlation between RSA magnitude during deep breathing (50%FVC) and the associated improvements in SpO 2 in hypoxia (r=−0.11, P=0.72). Given that RSA R is not affected by oxygen availability, our data provides evidence that hypoxic stimulation of the carotid bodies elicits activation of both arms of the autonomic nervous system, maintaining autonomic balance and normal heart rate variability. In addition, RSA magnitude does not appear to bestow advantages on V/Q matching in the context of acute hypoxia. Support or Funding Information MRU Faculty of Science and Technology
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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 | 0.001 |
| 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".