In light of recently recognized independent clinical values of longitudinal wall motion ux(t) at the common carotid artery (CCA) and the struggle on appropriate arterial indices for interpreting ux(t), this paper hypothesizes a mechanistic model of ux(t) and explores clear implications of the antegrade amplitude ux0-ante and retrograde amplitude ux0-retro of ux(t) in systole to the cardiovascular (CV) system. By examining findings on ux(t) and other relevant findings through the lens of the engineering essence of ux(t), a mechanistic model of ux(t) is hypothesized: the left ventricle (LV) base rotation is the excitation source for initiating the longitudinal elastic wave propagating along the arterial tree; wall shear stress at an artery serves as a local external source for supplying energy to the longitudinal elastic wave; and longitudinal elasticity at the arterial wall dictates the wave propagation velocity. Integrating the mechanistic model with findings on ux(t) gives rise to interpretation of ux0-ante and ux0-retro for their clear implications: longitudinal elasticity Exx at the common carotid artery (CCA) is estimated from ux0-ante, and ux0-retro is an inverse indicator of the maximum base rotation of the LV and a positive indicator of longitudinal elasticity at the ascending aorta (AA). For the first time, this model reveals the mechanisms underlying those statistical-based findings on ux(t).

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