Journal
PHYSIOLOGICAL MEASUREMENT
Volume 35, Issue 5, Pages 807-831Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0967-3334/35/5/807
Keywords
non-contact monitoring; PPG; video; auto-regressive models; vital signs; dialysis
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Funding
- Oxford Centre of Excellence in Medical Engineering - Wellcome Trust
- EPSRC [WT88877/Z/09/Z]
- NIHR Biomedical Research Centre Programme, Oxford
- RCUK Digital Economy Programme [EP/G036861/1]
- Engineering and Physical Sciences Research Council [1104460] Funding Source: researchfish
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Remote sensing of the reflectance photoplethysmogram using a video camera typically positioned 1 m away from the patient's face is a promising method for monitoring the vital signs of patients without attaching any electrodes or sensors to them. Most of the papers in the literature on non-contact vital sign monitoring report results on human volunteers in controlled environments. We have been able to obtain estimates of heart rate and respiratory rate and preliminary results on changes in oxygen saturation from double-monitored patients undergoing haemodialysis in the Oxford Kidney Unit. To achieve this, we have devised a novelmethod of cancelling out aliased frequency components caused by artificial light flicker, using auto-regressive (AR) modelling and pole cancellation. Secondly, we have been able to construct accurate maps of the spatial distribution of heart rate and respiratory rate information from the coefficients of the AR model. In stable sections with minimal patient motion, the mean absolute error between the camera-derived estimate of heart rate and the reference value from a pulse oximeter is similar to the mean absolute error between two pulse oximeter measurements at different sites (finger and earlobe). The activities of daily living affect the respiratory rate, but the cameraderived estimates of this parameter are at least as accurate as those derived from a thoracic expansion sensor (chest belt). During a period of obstructive sleep apnoea, we tracked changes in oxygen saturation using the ratio of normalized reflectance changes in two colour channels (red and blue), but this required calibration against the reference data from a pulse oximeter.
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