The jugular venous‐to‐arterial PCO2${P_{{\mathrm{C}}{{\mathrm{O}}_{\mathrm{2}}}}}$ difference during rebreathing and end‐tidal forcing: Relationship with cerebral perfusion
Bibliographic record
Abstract
Abstract We examined two assumptions of the modified rebreathing technique for the assessment of the ventilatory central chemoreflex (CCR) and cerebrovascular CO 2 reactivity (CVR), hypothesizing: (1) that rebreathing abolishes the gradient between the partial pressures of arterial and brain tissue CO 2 [measured via the surrogate jugular venous and arterial difference ( P jv‐a CO 2 )] and (2) rebreathing eliminates the capacity of CVR to influence the P jv‐a CO 2 difference, and thus affect CCR sensitivity. We also evaluated these variables during two separate dynamic end‐tidal forcing (ETF) protocols (termed: ETF‐1 and ETF‐2), another method of assessing CCR sensitivity and CVR. Healthy participants were included in the rebreathing ( n = 9), ETF‐1 ( n = 11) and ETF‐2 ( n = 10) protocols and underwent radial artery and internal jugular vein (advanced to jugular bulb) catheterization to collect blood samples. Transcranial Doppler ultrasound was used to measure middle cerebral artery blood velocity (MCAv). The P jv‐a CO 2 difference was not abolished during rebreathing (6.2 ± 2.6 mmHg; P < 0.001), ETF‐1 (9.3 ± 1.5 mmHg; P < 0.001) or ETF‐2 (8.6 ± 1.4 mmHg; P < 0.001). The P jv‐a CO 2 difference did not change during the rebreathing protocol (−0.1 ± 1.2 mmHg; P = 0.83), but was reduced during the ETF‐1 (−3.9 ± 1.1 mmHg; P < 0.001) and ETF‐2 (−3.4 ± 1.2 mmHg; P = 0.001) protocols. Overall, increases in MCAv were associated with reductions in the P jv‐a CO 2 difference during ETF (−0.095 ± 0.089 mmHg cm −1 s −1 ; P = 0.001) but not during rebreathing (−0.028 ± 0.045 mmHg · cm −1 · s −1 ; P = 0.067). These findings suggest that, although the P jv‐a CO 2 is not abolished during any chemoreflex assessment technique, hyperoxic hypercapnic rebreathing is probably more appropriate to assess CCR sensitivity independent of cerebrovascular reactivity to CO 2 . image Key points Modified rebreathing is a technique used to assess the ventilatory central chemoreflex and is based on the premise that the rebreathing method eliminates the difference between arterial and brain tissue . Therefore, rebreathing is assumed to isolate the ventilatory response to central chemoreflex stimulation from the influence of cerebral blood flow. We assessed these assumptions by measuring arterial and jugular venous bulb and middle cerebral artery blood velocity during modified rebreathing and compared these data against data from another test of the ventilatory central chemoreflex using hypercapnic dynamic end‐tidal forcing. The difference between arterial and jugular venous bulb remained present during both rebreathing and end‐tidal forcing tests, whereas middle cerebral artery blood velocity was associated with the difference during end‐tidal forcing but not rebreathing. These findings offer substantiating evidence that clarifies and refines the assumptions of modified rebreathing tests, enhancing interpretation of future findings.
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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 | 0.002 |
| 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 | 0.001 |
| 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".