Noninvasive assessment of age-related arterial changes using the carotid stress-strain relationship in vivo: A pilot study

The feasibility of noninvasively measuring regional carotid artery stiffness by way of the stress-strain relationship was recently demonstrated in young normal adults in vivo. In this paper, similar methods were used to assess the stress-strain curve and derive the Young´s moduli in young and older subjects to evaluate the sensitivity of this approach in assessing age-related wall changes. Two types of recordings were performed on the common carotid arteries of 3 young (23-24 years) and 2 older (37 and 43 years) subjects: (a) RF signals acquired at 505-642 Hz, and (b) the pulse pressure signal using applanation tonometry. Subsequently, (a) arterial strain was calculated from the diameter waveform obtained using the radial displacements estimated by a 1D cross-correlation technique on the RF signals, and (b) arterial stress was estimated using the pressure (tonometry) signal, the diameter, and the wall thickness measured on the B-mode. The strain and stress signals were combined to produce the stress-strain curve. Using bilinear curve fitting, the Young´s modulus of the elastin-collagen fibers (E₂), as well as the moduli for elastin (E₁) and collagen (E₃), separately, were estimated, under the assumption of a linear elastic two-parallel spring model. E₁ and E₂ were significantly larger in the older subjects, indicating stiffer tissues probably due to reduced elastin, which is in agreement with the related literature. No differences in E₃ were noted between young and older subjects. The method holds promise for characterizing age-related arterial changes and can provide useful insight into the complex phenomena involved in arterial biomechanics.