Intra and inter‐day reproducibility of the functional sympatholysis protocol during rhythmic handgrip exercise in healthy humans
Bibliographic record
Abstract
Introduction The effects of increased sympathetic activity on vasoconstriction are blunted in active skeletal muscle during exercise. This mechanism, termed functional sympatholysis (FSY), plays a vital role in the maintenance of blood perfusion and oxygen delivery to meet the metabolic demands of active skeletal muscle. In humans, FSY can be determined experimentally by applying low‐levels of lower‐body negative pressure (LBNP) to unload the cardiopulmonary baroreceptors and induce a reflex sympathoexcitation at rest and simultaneously during rhythmic handgrip exercise. In young healthy individuals, LBNP causes a pronounced vasoconstrictor response at rest, but not during exercise in the working forearm. Although this paradigm has been used extensively to assess the FSY in humans, to date, no studies have examined the reproducibility of this protocol. Therefore, the aim of the present study is to assess the within‐visit and between‐visit reproducibility of the FSY protocol in healthy adults. Methods Twenty‐three (12 females) young, healthy adults (26 ± 4 years; 73 ± 13 kg [mean ± SD]) participated in the study. Forearm blood flow (Doppler ultrasound) and beat‐to‐beat BP (finger photoplethysmography) were measured continuously at rest and during 6‐min of rhythmic handgrip exercise at 30% of maximum voluntary contraction. LBNP at ‐20 mmHg was applied for 2 min at rest and from the 3 rd to the 5 th min of handgrip. Participants performed two visits separated by ≥48h where two FSY bouts were completed. Forearm vascular conductance (FVC) was calculated as FBF/Mean blood pressure. The FSY index (FSYi) was calculated using the following formula: FSYi = (∆%handgrip ‐ ∆%rest)/100. Intraclass correlation coefficients (ICC; two‐way mixed effects, average measures, and absolute agreement) were used as a primary reproducibility measure (ICC values >0.75 are considered very good). Results At rest, LBNP induced a decrease in forearm blood flow (Visit 1 trial 1: ∆‐43±16%; Visit 1 trial 2: ∆‐38±10%; Visit 2: ∆‐39±14%) while these responses were attenuated during LBNP+handgrip (Visit 1 trial 1: ∆‐7±7%; Visit 1 trial 2: ∆‐5±8%; Visit 2: ∆‐4±7%). Each of these responses was similar across the trials (all P≥ 0.17). The FSYi calculated based on the forearm blood flow responses demonstrated excellent intra (ICC=0.93 [95% CI: 0.82‐0.97]; P <0.001) and inter‐day (ICC=0.94 [95% CI: 0.85‐0.97]; P <0.001) reproducibility. Similarly, FVC responses demonstrated very good intra (ICC=0.81 [95% CI: 0.55‐0.92]; P <0.001) and inter‐day (ICC=0.86 [95% CI: 0.65‐0.95]; P <0.001) reproducibility. Conclusion This is the first study to demonstrate that Doppler ultrasound‐derived assessments of FSY using LBNP and forearm handgrip exercise possess high intra‐ and inter‐day reproducibility in young, healthy adults.
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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 | 0.003 | 0.005 |
| 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 | 0.001 | 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".