An IMU-Based Wearable System for Respiratory Rate Estimation in Static and Dynamic Conditions

Integration of a body sensor network of wearable devices for cardio-respiratory monitoring

Wearable devices represent a non-invasive tool to monitor cardio-respiratory parameters. This paper presents a telemedicine platform constituted of four wireless units. Three wearable inertial measurement units monitor the respiratory-related excursions of the thorax and of the abdomen with respect to a reference unit (positioned on the lower back), through which respiratory rate and normalized tidal volume are extracted. The fourth unit is a reflectance wrist-worn pulse oximeter. To validate the system, 20 healthy volunteers (12 men) participated in a protocol designed to induce desaturation conditions and subsequent changes in the respiratory pattern by means of rebreathing. The results were evaluated against two different gold standards (SenTec for pulse oximetry and Cardiopulmonary Exercise Testing machine for all units) with Bland-Altman analyses. The resulting biases for the oxygen saturation comparison between the device to be validated and the SenTec and CPET systems are -0.90% and -2.68% respectively, with agreement intervals equal to [-6.37, 4.57] and [-9.00, 3.63]. Regarding the respiratory rate comparison with respect to the CPET system, the bias is -0.01 bpm with a [-11.36, 11.35] agreement interval.Clinical Relevance-This paper provides a validation of an integrated non-invasive wearable system for cardio-respiratory monitoring to be used outside of clinical settings and during the daily life of patients.