Tidal volume and breathing frequency responses to poikilocapnic and isocapnic hypoxia in humans
Bibliographic record
Abstract
The acute response to hypoxia in humans has been reported to arise predominately from increases in tidal volume (V T ) with negligible changes in breathing frequency (f B ). The effect of arterial CO 2 on this response has not been described. We examined the ventilatory contributions of V T and f B to the hypoxic response under both poikilocapnic (PH) and isocapnic (IH) conditions in 10 normal adults (26 ± 4 yrs, mean ± SD). During IH, PETCO 2 was held constant at 37 ± 2.0 Torr (1 Torr above resting values) while PETO 2 was reduced stepwise to 45 Torr using the technique of dynamic end‐tidal gas forcing. During PH, PETO 2 was reduced stepwise to 45 Torr while PETCO 2 was uncontrolled (i.e. zero inspired CO 2 ). Hypoxia was maintained for 20 minutes, and tests were separated by 1 hour. Peak ventilation (V E ), was significantly higher during IH (49.8 ± 14.3 L·min −1 ) compared to PH (24.1 ± 7.7 L·min −1 , P < 0.001). During IH, peak V E was mediated by increases in both V T (1.0 ± 0.4 to 2.2 ± 0.5 L, P < 0.001) and f B (14.7 ± 4.6 to 19.2 ± 4.5 breaths·min −1 , P < 0.05), while during PH peak V E was mediated by increased V T (0.8 ± 0.2 to 1.5 ± 0.4 L, P < 0.01) with no change observed in f B . At the termination of both IH and PH, a significant frequency undershoot was observed (20 ± 23 %, P < 0.05 and 22 ± 22 %, P < 0.01 respectively), previously documented only in animals. These data demonstrate a role of arterial CO 2 in the development of a f B response to hypoxia, though whether this is due to CO 2 per se or the magnitude of peak V E remains unknown. We have also documented a significant post hypoxic frequency decline not previously reported in humans occurring during both conditions. This study was approved by the local Ethics board and supported by AHFMR, HSFA and CIHR.
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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".