No Evidence Of Systematic Changes In Brachial Artery FMD With Repeated Increases In Shear Stress
Bibliographic record
Abstract
To assess changes in endothelial function, multiple flow mediated dilation (FMD) tests must often be performed over a short period. In human FMD studies, an increase in brachial artery shear stress (SS) is typically achieved by releasing forearm occlusion (reactive hyperemia (RH)). RH results in a transient and uncontrolled SS stimulus. In contrast, using handgrip exercise (EX), it is possible to create similar sustained SS increases over repeated trials. PURPOSE: 1) To identify if there is a systematic change in FMD over 4 closely spaced trials when SS is increased via either RH or EX. 2) To assess the within-subjects variability of the SS stimulus and %FMD response. METHODS: Brachial artery diameter (BAD) and mean blood flow velocity (MBV) were assessed with echo and Doppler ultrasound respectively in 20 healthy subjects (10 males) (19-37yrs). Each subject performed 4 trials of 6 min handgrip EX at the contraction intensity required to achieve a shear rate (SR) ((SR) = MBV/BA; estimate of SS) of 65 s-1. On a separate visit, each subject experienced 4 trials of RH. RESULTS: Data are means ± SD. The average time between trials for RH and EX was similar (RH: 807s ± 203s, EX: 808± 140, p = 0.98). There was no difference in %FMD across 4 trials (t) for RH or EX (RH t1: 6.9 ± 3.5%, t2: 6.9 ± 2.3%, t3: 7.1 ± 3.5%, t4: 7.0 ± 2.8%, EX t1: 7.3±3.6%, t2: 7.0 ± 3.6%, 6.5 ± 3.5%, 6.8 ± 2.9%, p = 0.91). The SR area under the curve (AUC) to peak diameter was different between trials in RH (p = 0.01); however, RH peak SR was not different between trials (mean of 4 trials: 146.2 ± 5.8s-1, p = 0.12). The EX-induced SR (average over 6 min EX period) was similar across EX trials (SR = 64.5 ± 1.3s-1, p = 0.06). The within-subject trial-to-trial coefficient of variation (CV) of the SR stimulus was lower with EX vs. RH (EX CV: 4.6 ± 3.3 vs. RH shear AUC CV: 17.7 ± 7.5, RH peak SR CV: 11.6 ± 3.0, p<0.001). The within-subject trial-to-trial CV of RH %FMD was similar to that of EX %FMD (RH FMD CV: 28.9 ± 15.1, EX FMD CV: 25.1 ±13.4, p = 0.38). The within-subjects range in %FMD with EX vs. RH was also similar (%FMD range RH: 4.3 ± 2.5%, %FMD range EX: 3.7±2.1%, p = 0.34). CONCLUSION: There is no systematic change in the FMD response across 4 closely spaced trials using either RH or EX. EX significantly reduced within-subject SR stimulus variability, but not %FMD response variability vs. RH. Supported by NSERC and CFI.
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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 | 0.002 | 0.004 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 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 | 0.001 | 0.001 |
| 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".