Monitoring respiratory rates with a wearable system using a stretchable strain sensor during moderate exercise

Respiratory rate, a sensitive indicator of respiratory status, is rarely measured during the field walking test. Our objective was to develop and validate a non-invasive, wearable monitoring system using stretchable strain sensors and an accompanying algorithm capable of providing real-time measurements of respiration during exercise. Twenty-four healthy volunteers wore stretchable sensors during a walking test protocol that included standing, sitting, walking, and walking with a stick. Sensors were placed on the ribcage and abdomen. The Bland-Altman method was used to assess the accuracy and precision of breath counts; total respiration time and inspiration time ratio were determined by custom algorithms and compared with measurements obtained with the standard flow sensor. The output signal from the stretchable sensor was highly synchronized with flow signals. The limits of agreement were within 3 breaths/min throughout the test protocol. Differences between sensors for total respiration time and inspiration time ratio were less than 14% and 26%, respectively. The agreement was maintained regardless of respiratory rate or volume. The wearable respiratory monitoring system yielded accurate and precise breath counts and total duration of respiratory cycle during moderate exercise in healthy young individuals, suggesting that it might be useful in clinical practice.