A constitutive modeling interpretation of the relationship among carotid artery stiffness, blood pressure, and age in hypertensive subjects

Abstract

Aging has a profound influence on arterial wall structure and function. We have previously reported the relationship among pulse wave velocity, age, and blood pressure in hypertensive subjects. In the present study, we aimed for a quantitative interpretation of the observed changes in wall behavior with age using a constitutive modeling approach. We implemented a model of arterial wall biomechanics and fitted this to the group-averaged pressure-area (P-A) relationship of the "young" subgroup of our study population. Using this model as our take-off point, we assessed which parameters had to be changed to let the model describe the "old" subgroup's P-A relationship. We allowed elastin stiffness and collagen recruitment parameters to vary and adjusted residual stress parameters according to published age-related changes. We required wall stress to be homogeneously distributed over the arterial wall and assumed wall stress normalization with age by keeping average "old" wall stress at the "young" level. Additionally, we required axial force to remain constant over the cardiac cycle. Our simulations showed an age-related shift in pressure-load bearing from elastin to collagen, caused by a decrease in elastin stiffness and a considerable increase in collagen recruitment. Correspondingly, simulated diameter and wall thickness increased by about 20 and 17%, respectively. The latter compared well with a measured thickness increase of 21%. We conclude that the physiologically realistic changes in constitutive properties we found under physiological constraints with respect to wall stress could well explain the influence of aging in the stiffness-pressure-age pattern observed.

Determination of the Material Parameters in the Holzapfel-Gasser-Ogden Constitutive Model for Simulation of Age-Dependent Material Nonlinear Behavior for Aortic Wall Tissue under Uniaxial Tension

“…According to the literature, aging has a significant effect on the structure and function of the arterial wall [31,32]. They studied the evolution of structural components for the human thoracic aorta from the strain energy function considering the composition of the soft tissue, and the axial stretch and residual strain in the biomechanical analysis were considered in order to examine the variation of the collagen fiber.…”

“…In this study, the increase of stretch and the decrease of stress and Young's modulus in the aortic tissue were investigated with the progress of age from the literature [17,31,32]. Moreover, the numerical simulations considering the variation rate of the material constants based on the age were conducted.…”

Heart Rate Dependency of Large Artery Stiffness

“…Our BP correction method using mathematical modeling incorporates the nonlinear relationship between BP and cfPWV, and it is based on an assumed exponential P-A relationship. 23 However, the exact exponential nature of this relationship can be debated, as other descriptives 47 as well as P-A relationship based on the actual wall constituents [48][49][50] have also been proposed. Nevertheless, the exponential relationship provides an acceptable compromise between accuracy and practical use.…”

Head orientation should be considered in ultrasound studies on carotid artery distensibility

“…Previously, we have used pressure and diameter measurements (i.e. the pressure-diameter relation) to quantify age-related changes in mechanical properties of the collagen-elastin matrix in the carotid artery wall [9]. These matrix properties were estimated by means of fitting a biomechanical model to the measurements.…”