The Effect of Acute Hypocapnia and Respiratory Alkalosis on Neurovascular Coupling Magnitude
Bibliographic record
Abstract
The brain requires well‐regulated cerebrovascular perfusion to match local metabolic demand. Regional coupling of perfusion to metabolic rate is termed neurovascular coupling (NVC). NVC remains stable during blood gas perturbations upon ascent and acclimatization to altitude, where individuals are exposed to antagonistic effects of hypoxia (vasodilation) and hypocapnia (vasoconstriction), where acid‐base variables are likely well‐compensated. Few studies have addressed the effects of acute hypocapnia and respiratory alkalosis independently. The aim of this study was to assess the specific effects of acute steady‐state hypocapnia on NVC magnitude in a laboratory setting. We recruited 10 healthy participants and instrumented the posterior cerebral artery (PCA) with a transcranial Doppler ultrasound. NVC was elicited using a standardized strobe light stimulus (6 Hz; 5×30sec on/off), and both peak and mean absolute responses from baseline (BL) were quantified. Participants were coached to hyperventilate to reach steady‐state hypocapnic steps of Δ‐5 and Δ‐10 Torr end‐tidal (P ET )CO 2 from baseline levels. P ET CO 2 levels were significantly decreased from 36.7±4.2 (BL) to 31.0±5.1 and 25.9±5.4 Torr (P<0.05), with estimated arterial pH(a) values of 7.43±0.05 (BL), 7.47±0.08 (Δ‐5) and 7.59±0.11 (Δ‐10), respectively (P<0.05). There was a significant reduction in NVC magnitude from BL (10.2±2.5 cm/s) during controlled hypocapnia at both Δ‐5 (8.3±2.6 cm/s) and Δ‐10 (8.1±2.7 cm/s) in peak PCA velocity (PCAv) (P<0.05), but no significant decrease in mean PCAv (P>0.05). Our study demonstrates that acute respiratory alkalosis attenuates peak NVC magnitude with a floor effect at Δ‐5 Torr P ET CO 2 (~7.47 pHa), without further attenuation at Δ‐10 (~7.59 pHa). This is one of few studies demonstrating a change in NVC with acute blood gas challenges. However, the effect is small and only observed in peak PCAv responses, with no differences between mild and more severe respiratory alkalosis. Support or Funding Information MRU Faculty of Science and Technology, University College Cork, University of Calgary
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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 | 0.001 |
| 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".