Evaluation of Arterial Diameter by Mathematical Transformation of APG for Ambulatory Stiffness

Non-invasive, continuous measurement of arterial stiffness indices has established utility in cardiovascular risk stratification. This study aims to develop a subject-specific model of soft tissue sandwich from the common carotid artery wall to the skin surface layer using acceleration plethysmograph (APG) waveforms. It was then used to estimate the lumen arterial diameter waveform using APG for stiffness evaluation. The carotid APG waveforms were collected using the developed accelerometer probe and its associated measurement system. The relationship between carotid diameter and APG from the neck was evaluated via mathematical models using system identification in MATLAB. The performance of the developed model for non-invasive assessment of carotid diameter and stiffness indices was validated on 15 subjects.The developed model was implemented in real-time and continuously evaluated carotid diameter using APG from the neck. An RMSE of less than 0.14 mm was observed between the constructed carotid diameter waveform (using APG) when compared with an actual diameter measured using the ultrasound-based system. The study results demonstrated the feasibility of a subject-specific skin-tissue model with APG waveforms for arterial diameter measurement and estimation of the vessel stiffness.