Influence of prior hyperventilation duration on respiratory chemosensitivity and cerebrovascular reactivity during modified hyperoxic rebreathing
Bibliographic record
Abstract
NEW FINDINGS: What is the central question of this study? We characterized and compared the cardiorespiratory and cerebrovascular responses to the 'Duffin' modified hyperoxic CO2 rebreathing test by randomly altering the prior hyperventilation duration. What is the main finding and its importance? Our main finding was that prior hyperventilation duration (1, 3 or 5 min) had no effect on cardiorespiratory and cerebrovascular responses to the hyperoxic rebreathing test, within individuals. These findings suggest that the standard 5 min prior hyperventilation duration used to clear body CO2 stores is unnecessary and can reasonably be shortened to 1 min, reducing protocol times and improving participant comfort. The 'Duffin' modified hyperoxic rebreathing test allows investigators to characterize and quantify the ventilatory and cerebrovascular responses to CO2 across a large physiological range, allowing quantification of basal ventilation and the ventilatory recruitment threshold (VRT). Although the standard protocol includes 5 min of prior hyperventilation to clear body CO2 stores, there is no experimental evidence that a full 5 min is required. We hypothesized that there would be no within-individual differences in the cardiorespiratory or cerebrovascular responses to rebreathing with shortened hyperventilation duration prior to hyperoxic rebreathing. Using a rebreathing apparatus, transcranial Doppler ultrasound and beat-to-beat blood pressure monitoring, we tested 19 participants in the supine position using three randomly assigned hyperoxic rebreathing tests with 1, 3 or 5 min of prior hyperventilation. We measured VRT (in Torr CO2 ), time to VRT (in seconds), central respiratory chemoreflex (breathing frequency, tidal volume and minute ventilation), cerebrovascular (middle and posterior cerebral artery velocity) and cardiovascular (heart rate and mean arterial pressure) responses to CO2 during hyperoxic rebreathing. Using linear regression and repeated-measures ANOVAs, we found no differences in any of the cardiorespiratory or cerebrovascular response magnitudes between trials (P > 0.05). The only difference observed was in the time to VRT (in seconds), whereby 1 min prior hyperventilation duration was shorter (135.4 ± 19.7 s) than with 3 or 5 min prior hyperventilation (176.3 ± 15.1 and 187.2 ± 11.6 s, respectively; P < 0.001). Our findings indicate that 5 min of prior hyperventilation is unnecessary during modified rebreathing when using it to quantify respiratory or cerebrovascular responses and can be reasonably shortened to 1 min, reducing protocol times and improving participant comfort.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".