Noninvasive assessment of arterial stiffness by pulse wave analysis

Pulse wave evaluation is an effective method for arteriosclerosis screening. The pulse wave comprises two displacement components, the incident wave ε(i)(t) and the reflected wave ε(r)(t). Because the amplitude of the reflected wave changes markedly with arterial stiffness, analysis of this wave is useful for evaluation of such stiffness. In this paper, a noninvasive method for extracting the reflected component from a pulse wave is proposed. First, the pulse wave ε(i)(t) + ε(r)(t) and blood flow velocity u(i)(t) - u(r)(t) were measured at the common carotid artery. A new approach is used to estimate the displacement wave ε(i)(t) -ε(r)(t), in which a transform of the conservation of mass, an elastic tube model, and a Voigt model for a viscoelastic body are applied to blood flow velocity data. Twice the amplitude of the reflected wave [TARW; 2ε(r)(t)] was obtained by subtracting the amplitude of the calculated displacement wave from that of the observed pulse wave. This method was applied to subjects aged from their 20s to 60s to evaluate differences in the reflected component. The results indicate moderate correlation between age and TARW (R(2) = 0.65). To evaluate the validity of this method for screening arterial stiffness, we compared TARW with existing diagnostic indices pulse wave velocity (PWV) and cardio-ankle vascular index (CAVI). TARW was moderately correlated with PWV (R(2) = 0.48) and CAVI (R(2) = 0.71). Therefore, this new method has potential for diagnosing arterial stiffness.