Characterization of a double probe for local pulse wave velocity assessment

Local pulse-wave velocity (PWV) is an accurate indicator of the degree of arteriosclerosis (stiffness) in an artery, providing a direct characterization of the properties of its wall. Devices currently available for local PWV measurement are mainly based on ultrasound systems and have not yet been generalized to clinical practice since they require high technical expertise and most of them are limited in precision, due to the lack of reliable signal processing methods. The present work describes a new type of probe, based on a double-headed piezoelectric (PZ) sensor. The principle of PWV measurement involves determination of the pulse transit time between the signals acquired simultaneously by both PZs, placed 23 mm apart. The double probe (DP) characterization is accomplished in three main studies, carried out in a dedicated test bench system, capable of reproducing a range of clinically relevant properties of the cardiovascular system. The first study refers to determination of the impulse response (IR) for each PZ sensor, whereas the second one explores the existence of crosstalk between both transducers. In the last one, DP time resolution is inferred from a set of three different algorithms based on (a) the maximum of cross-correlation function, (b) the maximum amplitude detection and (c) the zero-crossing point identification. These values were compared with those obtained by the reference method, which consists of the simultaneous acquisition of pressure waves by means of two pressure sensors. The new probe demonstrates good performance on the test bench system and results show that the signals do not exhibit crosstalk. A good agreement was also verified between the PWV obtained from the DP signals (19.55 +/- 2.02 ms(-1)) and the PWV determined using the reference method (19.26 +/- 0.04 ms(-1)). Although additional studies are still required, this probe seems to be a valid alternative to local PWV stand-alone devices.