Acceleration Plethysmography for Ambulatory Vascular Monitoring: A Pilot Study

As frequent monitoring of vascular ageing is gaining importance and the lack of a wearable sensing technology to track it through changes in vascular stiffness, we have developed a wearable accelerometric device. It could capture changes in vascular stiffness using our empirically derived markers from the amplitude features of acceleration plethysmogram (APG) at the carotid artery site. An in-vivo study on 12 subjects was conducted to (a) identify a few amplitude-based markers from the APG that exhibit significant change to physiologically induced hemodynamic perturbation; and (b) compare the magnitude of response of these APG-derived markers with that of carotid local stiffness metrics (β, Ep, and AC) measured using a clinically validated device, ARTSENS® Pen. The APG signals were reliable (SNR > 38 dB) and the amplitude features of APG were repeatable (CoV < 10 %). By examining all the APG-derived markers that showed statistically significant differences (p < 0.05) between pre and post-exercise measurements, it was found that the markers (ab)*(a-c) and (a*b) were having a high magnitude of response among others. The response (expressed as a percentage difference in mean values between pre and post-measurements) of the APG-derived markers, (a-b)*(a-c) and (a*b) were 42.41 % and 40.55 %, respectively, which were comparable to the response of carotid local stiffness metrics, β (32.34 %) and AC (41.83 %). The results suggest the potential of APG-derived markers, (a*b) and (a-b)*(a-c) for tracking stiffness changes, and the pilot study demonstrated the ability of the device to capture stiffness changes for ambulatory monitoring purposes.