Smart Textile Based on Piezoresistive Sensing Elements for Respiratory Monitoring

Wearable systems are gaining large interest in applications related to the monitoring of physiological parameters. Piezoresistive strain sensors are a valid option to develop wearables for several medical applications. Among them, respiratory monitoring can be performed by recording chest movements. The aim of this paper is threefold: 1) the experimental assessment of elastic piezoresistive textile; 2) the influence of length and width on piezoresistive response; and 3) the use of these elements to develop a smart textile (ST) for respiratory monitoring. The ST consists of six piezoresistive elements. The static calibration and the hysteresis analysis were carried out to assess the characteristics of the piezoresistive elements. The feasibility assessment of the ST for respiratory monitoring was performed on four healthy volunteers under two conditions (i.e., quiet breathing and tachypnea). Respiratory frequency values were estimated by the ST and compared with the ones gathered by means of a reference system (i.e., a motion capture system). Length and width influence both the sensitivity and hysteresis of the piezoresistive element. Regarding the ST performance, good agreement with data provided by the reference system was found. Indeed, results obtained by considering the output of single sensing elements and their sum were promising: the difference between the average respiratory frequency was always lower than 1% and 4% during quiet breathing and tachypnea, respectively. The proposed ST seems to be suitable for respiratory frequency monitoring in a wide range of values, where unobtrusiveness is of great value.