Arterial path selection to measure pulse wave velocity as a surrogate marker of blood pressure

The velocity of the propagating arterial pulse wave (pulse wave velocity, PWV) has been proposed as an unobtrusive and possibly continuous surrogate measure of systolic blood pressure (SBP). PWV is derived from the arrival time of the blood pulse at a peripheral arterial location, most often the finger. Reported performances were not yet accurate enough for clinical application but good enough as an unobtrusive surrogate in other settings. However, the finger PPG is not an ideal location in the home setting as it obstructs hand movement and can suffer from peripheral vasomotion and orthostatic pressure changes. In this paper we examine the viability of other pulse arrival locations for the measurement of PWV. PWV was derived to the finger (most common location), wrist (less obtrusive location), ear (more proximal) and ankle (more distal). Correlation analysis for PWV from each location with SBP was performed and the calibration procedure was studied. Wrist PWV accuracy is found to be comparable to finger PWV in terms of correlation and estimation error with SBP. The ear PWV, being a theoretically favorable location, is shown to have a larger inter-subject variance in the calibration procedure compared to other locations. Ankle PWV shows stable calibration parameters across subjects but Bland-Altmann analysis reveals unusual error trends. In conclusion, while results indicate that all sensor locations are usable to some extent, there are still some distinct properties associated with each sensor location that should be taken into account when designing an SBP algorithm based on PWV.