Methodological and Measurement Concerns of Local Pulse Wave Velocity Assessment

Abstract

Local pulse wave velocity (local PWV) provides localized information on the stiffness of a particular segment of the heterogeneous arterial bed. As a screening tool for a host of cardiovascular events and hypertension, high accuracies may not be required for the local PWV measures. However, such high accuracies are required when the yielded local PWV measures are directly used for calculations of other biomechanical and physiological parameters. There are several techniques for measuring local PWV and each possesses its own methodological challenges and considerations for ensuring accuracy. This work focuses on the salient methodological and measurement concerns of the transit time-based local PWV evaluation techniques while pinpointing the ones that are equally applicable to the other approaches. To demonstrate these concerns, we have used our extensively validated image-free ultrasound technology – ARTSENS®, for the measurement of local PWV. We have conducted an in-vivo study on 20 subjects to investigate and comment on various hardware and software aspects that affect the measurement accuracy. Firstly, non-invasive sensing modalities that capture blood pulse waveforms uncorrupted by the influence of intervening tissue layers may be chosen. Inter-channel delay should be carefully quantified and eliminated as the transit time measures for an arterial segment smaller than 50 mm, are of the orders less than 20 ms. The presented study results demonstrate that the blood pulse waveforms should be sampled at high rates, to ensure adequate temporal resolution for performing transit time measurements of such small orders. Further, it was observed that the specifications of the bandpass filters used to process the blood pulse signals effect the accuracy of the measurements. The higher cut-off frequency of the band pass filter used is suggested to be in the range of 10 – 16 Hz and the filter order to be greater than 2 to achieve an RMSE smaller than 0.5 m/s.