Cardiovascular Stress Response Laboratory, School of Kinesiology and Health Studies, Queen's University, Kingston, ON K7L 3N6, Canada.
Eur J Appl Physiol. 2013 Jul;113(7):1849-58. doi: 10.1007/s00421-013-2612-0. Epub 2013 Feb 24.
Endothelial function is essential for vasoprotection and regulation of vascular tone. Using handgrip exercise (HGEX) to increase blood flow-associated shear stress is an increasingly popular method for assessing brachial artery endothelial function via flow-mediated dilation (FMD). However, different exercise duty cycles [ratio of handgrip relaxation: contraction (seconds)] produce different patterns of brachial artery shear stress with distinct antegrade/retrograde magnitudes. To determine the impact of HGEX duty cycle on brachial artery %FMD, three distinct duty cycles were employed while maintaining a uniform mean shear stress. Brachial artery diameter and mean blood velocity were assessed via echo and Doppler ultrasound in 16 healthy male subjects. Shear stress was estimated as shear rate (SR = blood velocity/brachial artery diameter) and the target mean SR during HGEX was 75 s(-1). Subjects performed three 6-min HGEX trials on each of 2 days (like trials averaged). In each trial, subjects performed one of the three randomly ordered HGEX duty cycles (1:1, 3:1, 5:1). %FMD was calculated from baseline to the end of HGEX and (subset N = 10) during each minute of HGEX. Data are mean ± SD. As intended, mean SR was uniform across duty cycles (6 min HGEX average: 72.9 ± 4.9s(-1), 72.6 ± 3.6s(-1), 72.8 ± 3.5 s(-1), p = 0.835), despite differences in antegrade/retrograde SR (p < 0.001). End-exercise %FMD (4.0 ± 1.3 %, 4.1 ± 2.2 %, 4.2 ± 1.4 %, p = 0.860) and %FMD during exercise (p = 0.939) were not different between duty cycles. These data indicate that the endothelium responds to the mean shear stress and is not specifically sensitive to the contraction/relaxation or retrograde shear stress created by a range of HGEX protocols.
内皮功能对于血管保护和血管张力调节至关重要。使用握力运动（HGEX）来增加与血流相关的切变应力是一种越来越受欢迎的评估肱动脉内皮功能的方法，通过血流介导的扩张（FMD）。然而，不同的运动负荷周期[握力放松与收缩的时间比（秒）]会产生不同的肱动脉切变应力模式，具有不同的前向/后向幅度。为了确定 HGEX 负荷周期对肱动脉 %FMD 的影响，在保持均匀的平均切应力的情况下，采用了三种不同的负荷周期。通过回声和多普勒超声评估 16 名健康男性受试者的肱动脉直径和平均血流速度。切应力估计为切变率（SR = 血流速度/肱动脉直径），HGEX 期间的目标平均 SR 为 75 s(-1)。受试者在两天内（相似试验平均）进行了三次 6 分钟的 HGEX 试验。在每次试验中，受试者随机进行三种 HGEX 负荷周期之一（1:1、3:1、5:1）。%FMD 从基线计算到 HGEX 结束，并在 HGEX 的每一分钟（子集 N = 10）计算。数据为平均值±标准差。如预期的那样，平均 SR 在负荷周期之间是均匀的（6 分钟 HGEX 平均：72.9 ± 4.9 s(-1)、72.6 ± 3.6 s(-1)、72.8 ± 3.5 s(-1)，p = 0.835），尽管前向/后向 SR 存在差异（p < 0.001）。运动结束时的 %FMD（4.0 ± 1.3%、4.1 ± 2.2%、4.2 ± 1.4%，p = 0.860）和运动期间的 %FMD（p = 0.939）在负荷周期之间没有差异。这些数据表明，内皮对平均切应力有反应，而不是对一系列 HGEX 方案产生的收缩/松弛或后向切应力特别敏感。
