Mechanical Factors Associated With the Development of Intimal and Medial Thickening in Vein Grafts Subjected to Arterial Pressure

Abstract

Arteries exposed to sustained hypertension undergo a moderate degree of intimal thickening and a marked amount of medial thickening. Autogenous veins that are used as bypass grafts undergo similar histological changes. In this study autogenous vein grafts were used as an indirect model of arteries exposed to sustained hypertension. It was hypothesized that it is not pressure per se but rather mechanical changes brought about by exposure to increased pressures that act as a stimulus inducing histological changes. Exposure to arterial pressure increases the following nine mechanical factors: deformation in the circumferential, longitudinal, and radial directions; stresses in each of these three directions; pulsatile deformations and pulsatile stresses; and flow velocity. All of these mechanical changes occur simultaneously. Accordingly, a three-step algorithm was devised to separate each of the nine mechanical factors and correlate them with histological changes. Three sequential experimental studies were performed in 38 dogs following the algorithm. These experiments demonstrated that intimal thickening was best correlated with low flow velocity, a correlate of low shear stress, whereas medial thickening was best correlated with deformation in the circumferential direction.

Carotid Intimal-Medial Thickness and Stiffness Are Not Affected by Hypercholesterolemia in Uncomplicated Essential Hypertension

“…Data from our study suggest that when IMT is measured in areas free of discrete atherosclerotic lesions, common carotid wall thickness in hypertensive patients is not strongly affected by mild to moderate hypercholesterolemia. Moreover, our results are in accordance with experimental studies 45 that suggest that intimal-medial thick- ening is mainly related to increased deformational arterial stresses due to blood pressure elevation, whereas hypercholesterolemia may be more influential in the genesis of discrete atherosclerotic plaques by focal deposition of lipids in the subintimal layers of the arterial wall. This concept is in agreement with observations that normotensive hypercholesterolemic children had mean wall thicknesses similar to those of normocholesterolemic controls, whereas the maximum IMT was significantly higher in the hypercholesterolemic group.…”

Attenuated Age-Related Carotid Arterial Remodeling in Adults with a High Level of Cardiorespiratory Fitness

“…Agerelated arterial remodeling is primarily an adaptive response of the arterial wall to progressive elevations in chronic arterial BP 30) . The results of animal and human studies indicated that an increase in distending pressure is a major stimulus for hypertrophy of smooth muscle cells and the synthesis of extracellular matrix in the arterial wall [31][32][33][34] . Repeated intense cyclic stress may cause fracture of the load-bearing elastin fibers and thus dilation of the lumen 11) .…”

Effects of muscle contraction timing during resistance training on vascular function

“…Thus, differences in the timing of muscular contraction affected arterial stiffness. Acute intermittent elevations in arterial blood pressure during resistance exercise decrease elastin and increase collagen, 25 which regulate the elasticity of the artery. The changes in blood pressure during resistance exercise are related to the lifting (CON) and lowering (ECC) of the load.…”