Van Brackle Charles H, Harris Ryan A, Hallow K Melissa
College of Engineering, University of Georgia, Athens, Georgia.
Georgia Prevention Institute, Department of Pediatrics, Augusta University, Augusta, Georgia; and.
J Appl Physiol (1985). 2017 May 1;122(5):1292-1303. doi: 10.1152/japplphysiol.00734.2016. Epub 2016 Dec 15.
The brachial artery flow-mediated dilation (FMD) test is the most widely utilized method to evaluate endothelial function noninvasively in humans by calculating the percent change in diameter (FMD%). However, the underutilized velocity and diameter time course data, coupled with confounding influences in shear exposure, noise, and upward bias, make the FMD test less desirable. In this study, we developed an exposure-response, model-based approach that not only quantifies FMD based on the rich velocity and diameter data, it overcomes previously acknowledged challenges. FMD data were obtained from 15 apparently healthy participants, each exposed to four different cuff occlusion durations. The velocity response following cuff release was described by an exponential model with two parameters defining peak velocity and rate of decay. Shear exposure derived from velocity was used to drive the diameter response model, which consists of additive constriction and dilation terms. Three parameters describing distinct aspects of the vascular response to shear (magnitude of the initial constriction response, and magnitude and time constant of the dilation response) were estimated for both the individuals and population. These parameters are independent of shear exposure. Thus this approach produces identifiable and physiologically meaningful parameters that may provide additional information for comparing differences between experimental groups or over time, and provides a means to completely account for shear exposure. While flow-mediated dilation (FMD) is a valuable tool for evaluating endothelial function, analytical challenges include confounding influences of shear exposure, upward bias, and underutilization of rich time course data collected during FMD testing. We have developed an exposure-response, model-based approach that quantifies endothelial function based on the velocity and diameter data and fully accounts for shear exposure. It produces physiologically meaningful parameters that may provide useful information for comparing differences between experimental groups or over time.
肱动脉血流介导的血管舒张（FMD）试验是通过计算直径变化百分比（FMD%）来无创评估人体内皮功能的最广泛使用的方法。然而，未充分利用的速度和直径随时间变化的数据，再加上剪切暴露、噪声和向上偏差等混杂影响，使得FMD试验不太理想。在本研究中，我们开发了一种基于暴露-反应模型的方法，该方法不仅基于丰富的速度和直径数据对FMD进行量化，还克服了先前公认的挑战。FMD数据来自15名表面健康的参与者，每人暴露于四种不同的袖带阻断持续时间。袖带松开后的速度反应由一个指数模型描述，该模型有两个参数定义峰值速度和衰减率。从速度导出的剪切暴露用于驱动直径反应模型，该模型由相加的收缩和舒张项组成。针对个体和总体，估计了描述血管对剪切反应不同方面的三个参数（初始收缩反应的幅度、舒张反应的幅度和时间常数）。这些参数与剪切暴露无关。因此，这种方法产生了可识别且具有生理意义的参数，这些参数可能为比较实验组之间或随时间的差异提供额外信息，并提供一种完全考虑剪切暴露的方法。虽然血流介导的血管舒张（FMD）是评估内皮功能的一种有价值的工具，但分析挑战包括剪切暴露的混杂影响、向上偏差以及FMD测试期间收集的丰富时间进程数据未得到充分利用。我们开发了一种基于暴露-反应模型的方法，该方法基于速度和直径数据量化内皮功能，并充分考虑剪切暴露。它产生具有生理意义的参数，这些参数可能为比较实验组之间或随时间的差异提供有用信息。
