Abstract
Wearable physiological monitors are becoming increasingly commonplace in the consumer domain, but in literature there exists no substantive studies of their performance when measuring the physiology of ambulatory patients. In this paper, we investigate the reliability of the heartrate sensor in an exemplar “wearable" wrist-worn monitoring system (the Microsoft Band 2); our experiments quantify the propagation of error from (i) the photoplethysmogram (PPG) acquired by pulse oximetry, to (ii) estimation of heart rate (HR), and (iii) subsequent calculation of heart rate variability (HRV) features. Our experiments confirm that motion artefacts account for the majority of this error, and show that the unreliable portions of heart rate data can be removed, using the accelerometer sensor from the wearable device. Our experiments further show that acquired signals contain noise with substantial energy in the high-frequency band, and that this contributes to subsequent variability in standard HRV features often used in clinical practice. We finally show that the conventional use of long-duration windows of data is not needed to perform accurate estimation of time-domain HRV features.