  Objective: Arterial stiffness is an important marker to predict cardio
vascular events. Common measurement techniques to determine the condition of
the aorta are limited to the acquisition of the arterial pulse wave at the
extremities. The goal of this work is to enable non-invasive measurements of
the aortic pulse wave velocity, instead. An additional aim is to extract
further information, related to the conditions of the aorta, from the pulse
wave signal instead of only its velocity. Methods: After discussing the
problems of common pulse wave analysis procedures, an approach to determine the
frequency response of the aorta is presented. Therefore, the aorta is modelled
as an electrical equivalent circuit. To determine the specific numeric values
of this system, a measurement approach is presented, which is based on
non-invasive bioimpedance plethysmography measurements above the aortic arch
and at the inguinal region. The conversion of the measurement results to the
system parameters is realized by a digital algorithm, which is proposed in this
work as well. To evaluate the approach, a study on three subjects is performed.
Results: The measurement results demonstrate that the proposed approach yields
realistic frequency responses. For better approximation of the aortic system
function, more complex models are recommended to investigate in the future.
Since this study is limited to three subjects without a ground truth, further
measurements will be necessary. Significance: The proposed approach could solve
problems of current methods to determine the condition of the aorta. Its
application is non-invasive, harmless and easy to execute.
