Sodium Nitroglycerin and Hypercapnic Stimuli Reduce Cerebral Vascular Bed Compliance in Humans
Bibliographic record
Abstract
Human cerebral arteries dilate to various stimuli and this change in contractile state is often quantified as a steady‐state change in vascular resistance. In oscillatory blood flow, compliance of the vascular bed also contributes to the regulation of cerebral perfusion. However, very little is known about the impact of cerebral dilation on cerebral vascular bed compliance. Therefore, the present study examined the impact of cerebral vasodilatory stimuli on cerebrovascular compliance in humans. Fifteen young, healthy adults (27 ± 5 years, 7 females) participated in the present study. Participants completed a sodium nitroglycerin (SNG) protocol involving a 2‐minute baseline period, administration of one 0.4 mg sublingual spray of SNG, followed by 10 minutes of data collection. Following the completion of the SNG protocol, participants rested for at least 5 minutes after which the hypercapnia protocol was completed. Following a 2‐minute baseline period, participants breathed a low percentage (5‐6%) carbon dioxide (CO 2 )gas mixture for 4 minutes followed by a 3‐minute recovery period breathing room air. Throughout the experimental protocols, blood pressure (BP) waveforms (finger photoplethysmography; Finapres Medical Systems) and middle cerebral artery blood velocity (BV) waveforms (transcranial Doppler ultrasound; Multigon Industries) were collected in the supine position. Five individual BP and corresponding BV waveforms were extracted during each protocol's baseline period, at each minute of SNG and CO 2 , and during the last minute of the CO 2 recovery period. The waveforms were input into a modified Windkessel model and an index of cerebrovascular compliance (Ci) was calculated. During the SNG protocol, Ci was 5.0e ‐4 ± 2.3e ‐4 cm·s ‐1 ·mmHg ‐1 at baseline and decreased significantly by minute 7 of SNG administration ( P = 0.01, d = 1.07). Overall, Ci decreased by 29% to its nadir, 3.6e ‐4 ± 1.2e ‐4 cm·s ‐1 ·mmHg ‐1 , at minute 10 of the protocol ( P = 0.01, d = 0.98). During the hypercapniaprotocol, Ci was 4.4e ‐4 ± 2.0e ‐4 cm·s ‐1 ·mmHg ‐1 at baseline and decreased significantly by minute 1 of breathing CO 2 ( P = 0.003, d = 1.04). Overall, Ci was reduced by 30% to its lowest value of 3.1e ‐4 ± 1.4e ‐4 cm·s ‐1 ·mmHg ‐1 by minute 4 of hypercapnia ( P < 0.001, d = 1.56). However, following 3 minutes of recovery, Ci increased to 4.2e ‐4 ± 1.5e ‐4 cm·s ‐1 ·mmHg ‐1 , which was not different from baseline values ( P = 0.86). BP remained unchanged during the SNG protocol (BSL: 87 ± 8 mmHg, Min 10: 89 ± 8 mmHg; P = 0.99), while it increased by 5 mmHg during the hypercapnia protocol (BSL: 86 ± 10 mmHg, Min 4: 91 ± 10 mmHg; P < 0.001, d = 1.44). However, no significant relationship was observed between the change in BP and the change in Ci with hypercapnia (r = ‐0.09, P = 0.75). Both vasodilatory stimuli reduced Ci by approximately 30% from supine baseline values. The attenuation of Ci likely relates to the predominance of collagen fibers in supporting wall tension during vessel distension.
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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".