Neurovascular Coupling is Not Attenuated During Reflex‐Mediated Sympathetic Activation via Lower Body Negative Pressure in Humans
Bibliographic record
Abstract
Introduction Cerebral blood flow is tightly coupled with local neuronal activation and metabolism (i.e., neurovascular coupling; NVC). Attenuated NVC has been identified in several chronic diseases, including hypertension, but the underlying mechanism(s) remains unknown. Raised peripheral sympathetic vasoconstrictor activity can play a malevolent role in the pathology of hypertension and might also contribute to the blunted NVC as cerebral arteries are autonomic innervated. However, the role of sympathetic nervous system in the regulation of cerebral blood flow remains controversial. Given this, the purpose of the current study was to test the hypothesis that reflex‐mediated sympathetic activation via lower body negative pressure (LBNP) blunts NVC in humans. Methods NVC was assessed using a visual stimulation protocol (5 cycles of 30 s eyes closed and 30 s of reading) in 10 young and healthy participants (3 women; aged 25 ± 3 years). In a randomized and counterbalanced order, NVC assessments were made under control conditions and during graded sympathetic activation via LBNP at −20 mmHg and −40 mmHg. Posterior (PCA) and middle cerebral artery (MCA) mean blood velocity (v mean ) were determined (transcranial Doppler ultrasound). Vertebral artery blood flow (VA flow ) was measured using duplex Doppler ultrasound and vessel wall tracking software. Mean arterial pressure (finger photoplethysmography), stroke volume (Modelflow), heart rate (electrocardiogram) and the partial pressure of end‐tidal carbon dioxide (P et CO 2 ; capnograph) were obtained. Data are presented as mean ± SD. Results LBNP to −20 mmHg and −40 mmHg evoked an anticipated reduction in stroke volume and increase in heart rate, while mean arterial pressure was unchanged. Prior to visual stimulation, PCAv mean and MCAv mean were not different between control, −20 LBNP and −40 LBNP conditions ( P >0.05), while VA flow was reduced at −40 mmHg ( P =0.02 vs . control). Under control conditions, the NVC test evoked a robust increase in PCAv mean (Δ22 ± 4%), a modest increase in MCAv mean (Δ10 ± 3%), and a moderate rise in VA flow (Δ14 ± 5%). The magnitude of these responses was unaffected by LBNP at both −20 mmHg and −40mmHg (PCAv mean Δ23 ± 4% and Δ23 ± 4%; MCAv mean Δ10 ± 1% and Δ11 ± 4%; VA flow Δ15 ± 3% and Δ16 ± 6%; P >0.05). P et CO 2 decreased at −20 mmHg (37.0 ± 3.1 mmHg) and −40 mmHg (36.3 ± 3.1 mmHg) LBNP trials compared to control (40.2 ± 3.7mmHg; P =0.004). Conclusion In summary, these findings indicate that reflex‐mediated sympathetic activation via LBNP does not blunt the NVC response in healthy humans. Support or Funding Information Funding received from Coordination for the Improvement of Higher Education Personnel (Finance Code 001) (MS), the University of Auckland (JPF, JFRP) and the Health Research Council of New Zealand (JPF, JFRP).
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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) | 0.002 | 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".