Measures of Arterial Stiffness: Standardization, Various Devices, and Measurement Conditions

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The University of Texas at Austin
Arterial stiffness, characterized by elevated pulse wave velocity (PWV), is a critical prognostic measure during the progression of arterial diseases that contribute to cardiovascular disease. The inability of the arterial wall to effectively buffer the pulsatile pressure results in disturbed blood flow and added stress on key end-organs including the heart, brain, and kidneys. The overall theme of this dissertation is centered around the utilization of PWV as a measure of arterial stiffness. A series of studies included in this dissertation aimed to better comprehend and improve the measurement of arterial stiffness via PWV. This dissertation is clinically important because it focuses on a critical issue in public health, measures for cardiovascular disease, which is the leading cause of death in most industrial countries. In the first study, we aimed to facilitate the comparison between different measures of arterial stiffness across different studies. We summarized and derived conversion equations for commonly used image-based measures of arterial stiffness to the standard measures of arterial stiffness carotid-femoral PWV. We gathered the conversion equations from the literature, created regression equations, and applied them to 49 healthy participants. Both equations produced local PWV values that were moderately and significantly associated with cfPWV. In the second study, PWV was assessed in 70 participants in varying body positions. Results showed that 10o upper body tilt-up was sufficient to increase PWV significantly from the reference fully supine position. For the last study, there was no significant difference between the recorded PWV when the participants wore different legwear. However, stiff fabric materials increased the measurement error to obtain cfPWV with tonometry. In conjunction, these findings highlight the importance of standardizing the measurement and the utilization of pulse wave velocity in both research and clinical settings to improve the assessment of arterial stiffness and, ultimately, cardiovascular health.
Cardiovascular disease continues to be the leading cause of death in the United States and many industrialized countries. During the COVID-19 pandemic, the presence of preexisting cardiovascular disease increased the relative risk of death 2.25- fold for individuals diagnosed with COVID-19. Arterial disease plays a significant role in the pathogenesis of cardiovascular disease, including coronary heart disease, cerebrovascular disease, high blood pressure, and peripheral artery disease. All of these diseases originate from arterial dysfunction. For over a century, blood pressure and other traditional risk factors for cardiovascular disease, such as obesity, smoking, and dyslipidemia, have been used to predict the risk of developing cardiac diseases. Arterial stiffness measures have emerged as additional valuable indicators in the development of cardiovascular, cerebrovascular, and kidney diseases. Moreover, arterial stiffness has predicted the development of high blood pressure in normotensive individuals. In several cohort studies, measures of arterial stiffness have not only proven to predict the risk of cardiovascular disease but also served as predictors of overall mortality. The physical proprieties of the healthy arterial wall aid cardiac functions by expanding and recoiling to dampen cardiac pulsations and blood pressure fluctuations. The stiffening of the arterial walls leads to various pathophysiological changes within the circulatory system. The stiffening of the arterial walls not only adds more afterload to the left ventricle causing hypertrophy and fibrosis but also causes damages in high-flow and low- resistance end-organs such as the kidneys, heart, and brain. Sedentary aging has been linked to increased arterial stiffness, which is particularly pronounced in clinical populations. A rise of 100 cm/s in pulse wave velocity (PWV), the standard reference measure of arterial stiffness, is associated with a ~15% increase in the risk of cardiovascular events. On the other hand, healthy aging, including the practice and the maintenance of regular exercise, attenuate this increase in arterial stiffness. Measuring arterial stiffness involves various techniques and devices. The commonly used technique is PWV, which determines the speed of pulse transmission from a proximal to a distal artery. PWV utilizes the two-point (segmental) method on the arterial tree, such as the carotid and femoral arteries which has become the reference standard non-invasive method for quantifying arterial stiffness. Alternatively, pulse detection using one-point (local) method (e.g., carotid artery compliance) is widely utilized in research laboratories, producing diverse outcomes and measures. When measuring arterial stiffness, several considerations and standardization come into play. The body position during measurement is an important factor that influence the stiffness measures, with some devices recommending the supine position while others suggest an upward tilt of the upper body. Additionally, different devices and methodologies employ various standardization methods and measurement unites, resulting in varying arterial stiffness values. Methodological differences between two-point and one-point methods, as well as discrepancies in the standardizations used for measuring stiffness, hinder the use of arterial stiffness measures. The body angle and the type of legwear used during measurements, have been identified in this dissertation as potential sources of measurement variability during PWV measurements. Therefore, this dissertation aimed to evaluate the associations between different arterial stiffness measures, and to identify possible sources of variability in different devices to facilitate the standardization methods during PWV measurements.
Pulse wave velocity, aging, cardiovascular diseases