EVIDENCE FOR BLUNTED SYMPATHETIC NEURAL VASOCONSTRICTION IN EXERCISING HUMAN MUSCLES
Bibliographic record
Abstract
The need for local exercising muscle perfusion to meet metabolic demand may be opposed by the need for sympathetic restraint of muscle perfusion to regulate blood pressure. Thus, understanding the nature of the interaction(s) between local vasodilator influences and sympathetic neural vasoconstrictor influences in muscle is fundamental for understanding vascular control and blood pressure regulation in exercise. PURPOSE Data are presented from a recent study designed to test the hypothesis that local factors in exercising muscle blunt vessel responsiveness to sympathetic vasoconstriction in humans. METHODS Selective infusion of three doses of tyramine into the brachial artery (n = 8) were used to evoke endogenous release of norepinephrine at rest and during moderate (MEx) and heavy (HEx) rhythmic handgrip exercise. In separate experiments, tyramine was administered during two doses of adenosine infusion (n = 7) and two doses of sodium nitroprusside infusion (n = 8). Vasoconstrictor effectiveness across conditions was assessed as the percentage reduction in forearm vascular resistance (%rFVC), calculated from invasive blood pressure and non-invasive Doppler ultrasound blood flow measurements at the brachial artery. RESULTS All values mean ± SE. Tyramine evoked a similar dose-dependent vasoconstriction at rest in all three groups, with the highest dose resulting in a 42–46% reduction in FVC. This vasoconstriction was blunted with increasing exercise intensity (e.g. tyramine high dose %rFVC; rest −43 ± 3.7%, MEx −27.5 ± 2.3%, HEx −16.7 ± 3.6% P < 0.05). In contrast, tyramine infusion during vasodilator-induced elevations in forearm blood flow resulted in a greater percentage reduction in FVC vs. rest. CONCLUSIONS These observations support the concept of exercise intensity-dependent functional sympatholysis. A schema of cardiovascular control is presented in which functional sympatholysis permits appropriate blood pressure control while minimizing the potentially deleterious effects of sympathetic restraint of muscle perfusion in active muscle. Supported by NIH Grant #HL46493;NSERC Canada
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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) | 0.002 | 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".