Feasibility Study of Arterial Stiffness Monitoring based on Reflected Wave Transit Time using Carotid Acceleration Plethysmogram

The paper describes a non-invasive method using an accelerometric system with a patch probe for arterial stiffness monitoring based on the estimation of the reflected wave transit time (RWTT). The study aims to validate the designed accelerometric system based on RWTT by comparison with currently used ultrasound-based imaging techniques. The proposed system consists of an accelerometric probe with a MEMS acceleration sensor fabricated on a flexible PCB for continuous monitoring of surface acceleration plethysmogram (APG) from the carotid arterial site. An analog front-end circuitry was designed for the reliable acquisition of APG signal and its pre-processing. The acquired APG signal was then processed in real-time, and carotid RWTT was displayed in a beat-by-beat way. Also, an additional hardware module, referred to as the hydrostatic pressure sensing unit, was designed for automated correction of the hydrostatic pressure gradient in the carotid blood pressure (BP). The in-vivo validation experiments on 16 healthy subjects aged between 22-37 years in sitting position confirm that the RWTT values can be reliably estimated from the high fidelity carotid APG signals. The mean values of measured carotid RWTT were in the range of 0.24 s - 0.33 s (beat-by-beat variation = 6 % - 15 %). These accelerometric derived RWTT values were then compared with reference ultrasound-based carotid arterial stiffness measures, such as relative distension, distensibility coefficient (DC), and pulse wave velocity (PWV). Accelerometric RWTT evaluations showed a significant correlation with relative distension (R = 0.7), DC (R = 0.65), and carotid PWV (R = 0.68) assessments. Therefore, the prototype accelerometric system is a promising method for long-term continuous monitoring of location-specific arterial stiffness.