Using a 30-second Transient Hypercapnic Douglas Bag Technique to Assess the Impact of Sex on Internal Carotid Artery Shear-mediated Vasodilation
Bibliographic record
Abstract
Hypercapnia has been demonstrated to cause vasodilation in the extracranial internal carotid artery (ICA). Studies using transient end-tidal forcing have demonstrated that cerebral hypercapnic vasodilation is mediated by endothelial shear stress. Previous techniques have used a Douglas bag to provoke a prolonged steady-state hypercapnic vasodilation have not demonstrated an endothelial-mediated technique. Objective: This study aimed to integrate these methodologies, creating an affordable and safe transient Douglas bag hypercapnic endothelial function test. We hypothesized that a transient hypercapnic Douglas bag approach would elicit shear-mediated vasodilation. Results: Sixteen young healthy adults (female = 7) completed a 30-second transient hypercapnic (9% Fi CO 2 ) paced-breathing (7.5 breaths per minute) protocol which using a 100 L Douglas bag. ICA blood flow was measured using a vascular duplex ultrasound. Peak ICA diameter (0.52±0.05 cm) was observed 75.22±12.33 seconds after the onset of CO 2 (p <0.0001). ICA velocity, flow, and shear rate increased throughout the transient CO 2 test (51.55 ±11.70 cm*sec-1; 547.67±126.61 mL*min-1; 443.65±138.25 s-1) and at the time of peak dilation (47.54±11.91 cm*sec-1; 588.41±122.58 mL*min-1; 412.90±132.27 s-1) compared to during rest and paced room-air breathing (p<0.005; p<0.001; p<0.0001). Pooled analysis (males and females) demonstrated a strong positive (r = 0.60) correlation between peak diameter and shear-rate area under the curve (SR AUC). After stratifying by sex, it was shown that there is a greater positive correlation (p <0.05) between SR AUC and percent dilation in females (r = 0.73) compared to males (r = 0.42). When accounting for the effect of baseline ICA diameter on the amount of shear-mediated dilation occurring from transient hypercapnia, only the males were found to have a significant, strong negative (r=-0.79, p=0.01) correlation between baseline ICA diameter and shear. The results demonstrate that the transient hypercapnic Douglas bag technique provides an economically friendly option for assessing shear-mediated vasodilation. Dr. Kurt Smith is funded through a National Sciences and Engineering Research Council (NSERC) of Canada RGPIN-2020-06269 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
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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 | 0.000 |
| 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 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".