Cerebrovascular Responses During Voluntary Breath Holding are Larger than Rebreathing
Bibliographic record
Abstract
Both voluntary breath‐holding and rebreathing of expired air elicit changes in respiratory gas chemostimuli (CO 2 and O 2 ) at the metabolic rate. These chemostimuli elicit increases in cerebral blood flow (CBF), proportional to the magnitude of concomitant increases in CO 2 and reductions in O 2 . These chemostimuli also activate the sympathetic nervous system, which increases systemic blood pressure. Although blood pressure responses appear small during rebreathing, evidence from obstructive sleep apnea (OSA) patients suggests higher mean blood pressure during sleep in those with worse OSA. We aimed to assess how superimposed changes in blood gases and increases in blood pressure affect the CBF responses during breath holding vs. rebreathing. We recruited 23 healthy participants (12 females) and instrumented them with a finometer (for beat‐by‐beat mean arterial blood pressure; MAP), transcranial Doppler ultrasound (middle and posterior cerebral artery velocity; MCAv, PCAv) and a pneumotachometer with gas sampling via a dual gas analyzer to assess the pressure of end‐tidal (P ET )CO 2 and O 2 . Participants carried out two protocols in randomized order: (a) a maximal, voluntary end‐inspiratory breath hold (BH) and (b) a rebreathing (RB) test. A breath‐by‐breath stimulus index (SI) was calculated as P ET CO 2 /P ET O 2 during rebreathing, whereas the end‐tidal gas values used to calculate SI were interpolated during breath holding from initial and break point values. During both BH and RB, cerebrovascular reactivity (CVR) was calculated as the MCAv or PCAv/SI. MAP reactivity (MAPR) was calculated as the slope of the MAP/SI response. Cerebrovascular conductance (CVC; MCA or PCA/MAP) reactivity (CVCR) was calculated as the slope of the MCA CVC or PCA CVC /SI responses. We found that (a) CVR was larger during BH vs. RB (MCA: 167.5±102.0 vs. 38.8±20.5 cm/s/SI, P<0.0001, n=23; PCA: 76.3±40.1 vs. 26.0±11.0 cm/s/SI, P<0.0001, n=19), (b) MAPR during BH was significantly higher than during RB (134.0±102.7 vs. 31.0±12.6 mmHg/SI, P=0.0001, n=23). and (c) CVCR during BH vs. RB (MCA: 0.75±0.69 vs. 0.16±0.15 cm/s/mmHg/SI, P<0.001, n=22; PCA: 0.26±0.29 vs. 0.12±0.09 cm/s/SI, cm/s/mmHg/SI, P=0.03, n=19). Our data demonstrate that breath holding elicited ~4‐fold increases in MAP, translating to a larger anterior and posterior CVR compared to rebreathing. These findings suggest that the sympathetic responses during voluntary breath holding were larger than those during rebreathing across similar chemostimuli, potentially due to the differential sympathetic effects of struggling against a closed glottis during breath holding. This is the first evidence that voluntary apnea has larger effects on brain blood flow beyond that elicited by blood gas stimuli alone. Our data may have implications for understanding stroke risk in clinical populations with obstructive sleep apnea, whereby patients experience intermittent breath holds throughout the night, with associated spikes in arterial blood pressure.
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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 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".