Handgrip exercise and reactive hyperemia produced no systematic change in flow-mediated dilation across 4 closely spaced trials (p=0.91), though exercise reduced shear rate stimulus variability.
Does handgrip exercise compared to reactive hyperemia reduce variability in flow-mediated dilation over repeated trials in healthy subjects?
Repeated closely spaced FMD trials using either reactive hyperemia or handgrip exercise do not cause systematic changes in FMD response, validating the use of repeated measures in endothelial function studies.
p-value: p=0.91
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.
Jazuli et al. (Sat,) conducted a other in Healthy (n=20). Handgrip exercise vs. Reactive hyperemia was evaluated on Systematic change in %FMD across 4 closely spaced trials (p=0.91). Handgrip exercise and reactive hyperemia produced no systematic change in flow-mediated dilation across 4 closely spaced trials (p=0.91), though exercise reduced shear rate stimulus variability.