Stoner Lee, McCully Kevin K
Department of Kinesiology, University of Georgia, Ramsey Center, Athens, GA 30602, USA.
J Clin Ultrasound. 2012 Jul-Aug;40(6):341-51. doi: 10.1002/jcu.21900. Epub 2012 Mar 11.
To determine whether peak and time-integrated shear rates independently predict flow-mediated dilation (FMD).
Eleven physically active (25 ± 5 years old) male subjects were tested. FMD was defined as the shear rate-diameter relationship. Hierarchical linear modeling was used to estimate brachial artery diameter change with repeated measures of shear rate nested within each subject. Two models were tested: 1) FMD was induced using ischemia-induced hyperemia (2, 4, 6, and 10 minutes); and 2) FMD was induced following transient (ischemia) and steady-state (forearm heating and handgrip exercise) increases in shear rate. For both models we determined whether peak, in addition to time-integrated shear rates, explained a significant portion of variation for diameter change.
Model 1: Time integrated shear rates explained most of the variation for diameter change. However, peak shear rate explained an additional significant portion of variation. Model 2: The transient condition resulted in significantly (p = 0.012) smaller diameter change per shear rate change than the steady-state condition. However, when specifying peak shear rate as a covariate, the difference between conditions became nonsignificant (p = 0.138).
Peak and time-integrated shear rates independently predict FMD. Future studies using the FMD test should consider both parameters.
确定峰值剪切率和时间积分剪切率是否能独立预测血流介导的血管舒张（FMD）。
对11名身体活跃的（25±5岁）男性受试者进行测试。FMD定义为剪切率与直径的关系。采用分层线性模型，通过对每个受试者重复测量嵌套的剪切率来估计肱动脉直径变化。测试了两个模型：1）使用缺血诱导的充血（2、4、6和10分钟）诱导FMD；2）在剪切率短暂（缺血）和稳态（前臂加热和握力运动）增加后诱导FMD。对于这两个模型，我们确定除了时间积分剪切率外，峰值剪切率是否能解释直径变化的很大一部分变异。
模型1：时间积分剪切率解释了直径变化的大部分变异。然而，峰值剪切率额外解释了很大一部分变异。模型2：与稳态条件相比，短暂条件下每次剪切率变化导致的直径变化显著更小（p = 0.012）。然而，当将峰值剪切率指定为协变量时，条件之间的差异变得不显著（p = 0.138）。
峰值剪切率和时间积分剪切率能独立预测FMD。未来使用FMD测试的研究应考虑这两个参数。
