Validity of wearable breath monitoring system using stretchable strain sensors in walking

Abstract

Chronic obstructive pulmonary disease (COPD) patients often have shortened inspiration phase and experience breathlessness even during light exercise The respiratory rate that reflects breathlessness during exercise is usually measured by a flow sensor with a face mask Since many COPD patients use oxygen therapy with a nasal cannula and face mask that sometimes inhibit breathing, a less invasive wearable sensor for monitoring respiratory rate is required This study investigated the characteristics of a new wearable respiratory sensor and its performance was compared with that of a standard flow sensor. Twenty-four healthy volunteers wore wearable stretch sensors (STRs) while performing a treadmill walking test protocol that included standing and sitting, an incremental walking with and without a stick on treadmill (belt speed was increased from 2 to 6 km/h) Two STRs were symmetrically attached to a band placed around the participant's trunk Participants wore two sets of the STR bands at the 4th rib level and 10th rib level Each respiratory cycle including respiration phase was determined by the stretching and shortening cycle of the STR signal Based on the respiratory cycle, the number of breaths was counted every 1 min We compared breath counts by the STR and flow sensor using Bland–Altman plot. Breath counts ranged from 8 to 45 bpm throughout the test protocol STR signals showed positive correlation with flow signals ( P < 0.05) In more than 90% of testing periods, the difference in breath counts between the STR and flow sensor was less than 10% The limit of the agreement between breath count differences was less than 3 bpm in all movement conditions. The wearable respiratory monitoring system showed high accuracy and precision for breath counts even while the participants were walking The results suggest high potential of the system for clinical applications.