دانلود رایگان مقاله فقدان سازش تمامیت الیاف الاستیک تابع شریان کاروتید مشترک

Abstract

Competent elastic fibers endow central arteries with the compliance and resilience that are fundamental to their primary mechanical function in vertebrates. That is, by enabling elastic energy to be storedin the arterial wall during systole and then to be used to work on the blood during diastole, elastic fibers decrease ventricular workload and augment blood flow in pulsatile systems. Indeed, because elastic fibers are formed during development and stretched during somatic growth, their continual tendency to recoil contributes to the undulation of the stiffer collagen fibers, which facilitates further the overall compliance of the wall under physiologic pressures while allowing the collagen tolimit over-distension during acute increases in blood pressure. In this paper, we use consistent methods of measurement and quantification to compare the biaxial material stiffness, structural stiffness, and energy storage capacity of murine common carotid arteries having graded degrees of elastic fiber integrity e normal, elastin-deficient, fibrillin-1 deficient, fibulin- 5 null, and elastase-treated. The finding that the intrinsic material stiffness tends to be maintained nearly constant suggests that intramural cells seek to maintain a favorable micromechanical environment in which to function. Nevertheless, a loss of elastic energy storage capability due to the loss of elastic fiber integrity severely compromises the primary function of these central arteries.

Discussion

The human common carotid artery becomes progressively less distensible with increasing age,37 which appears to increase the risk of neurovascular-related conditions, including stroke.38 Distensibility and similarly pulse wave velocity, which reflect underlying structural stiffness, are convenient to measure and correlate with current or future clinical presentation, but they do not capture well the fundamental function of a central artery - storage and use of elastic energy. To glean increased insight, we measured pressureediameter and axial forceelength behaviors of murine common carotid arteries in vitro, which yielded information sufficient for quantifying stored energy as well as for computing common metrics of structural behavior (pulse wave velocity) and intrinsic material behavior (biaxial stressestrain relations and material stiffness). Despite being beyond the scope of the current study, combining information on biaxial mechanical properties gleaned in vitro with non-invasive assessments of distensibility in vivo should allow one to estimate the energy stored by the arterial wall under physiologic conditions while accounting for contributions of other factors that remain hard to quantify (e.g., effects of surrounding perivascular tissue on pressure-induced distention). We suggest, therefore, that a mechanistic understanding of the biomechanical factors underlying common prognostic indexes of cardiovascular function can only be achieved by accounting for the evolving multiaxial material properties of the arterial wall, whether during normal aging, hypertension, or progressive disease conditions.