Non-Contact Vital Sign Monitoring in the Clinic

Current monitoring systems available to track changes in the vital signs of patients (such as heart rate, respiratory rate or peripheral oxygen saturation) require contact with the subject. Most patients requiring regular monitoring find the probes difficult to wear over prolonged periods of time. Research in non-contact vital sign monitoring has recently expanded through the use of off-the-shelf video cameras; nevertheless, most of the current work in video-based non-contact vital sign monitoring has so far been performed over short time periods (typically up to a couple of minutes), under tightly controlled conditions with relatively still and healthy volunteer subjects. Using an off-the-shelf camera, we have been able to compute estimates of heart rate and respiratory rate, and also detect changes in peripheral oxygen saturation in a real hospital scenario, without interfering with regular patient care. Videos were recorded for 369.1 hours from 40 patients undergoing haemodialysis treatment in the Renal Unit of the Churchill Hospital in Oxford, UK. The mean absolute error between the heart rate estimates from the camera and the average from two reference pulse oximeters (positioned at the finger and earlobe respectively) was 2.8 beats per minute for over 65% of the time, which was comparable to the error between the two reference pulse oximeters. The mean absolute error between the respiratory rate estimates from the camera and the reference values (computed from the Electrocardiogram and a thoracic expansion sensor - chest belt) was 2.1 breaths per minute for over 69% of the time for which the reference signals were valid. By calibrating the camera data with the reference pulse oximeters, changes in peripheral oxygen saturation could also be tracked during time periods with minimal patient motion.