**1.1 Why is it important to monitor breathing activity with wearable devices?**

The development of wearable devices to monitor breathing activity allows giving rise to various medical care services. For example, considering people with asthma or chronic obstructive pulmonary disease, the environmental conditions directly affect their breathing, and a wearable device is able to continually measure air quality and pulmonary function [7]. The device could trigger alarm functions for drug uptake, contact a general practitioner for an appointment, or call emergency services [8].

The measurement of air quality is important, as pollutant exposure can lead to acute asthma attacks [7]. This happens usually after days under exposure. If a system detects pollutant exposure, it can warn the person and help to prevent attacks [7, 9].

Other applications of wearable devices include sleep monitoring for apnea detection [3], speaking detection as an indicator of social interaction [10], respiratory impedance [8], etc. The detection and tracking of respiratory movement for imageguided chest and abdomen radiotherapy, for compensation of movement during treatment, are additional uses of wearable devices [11]. Moreover, researchers have studied ways to develop smart fabrics, which are comfortable and nonintrusive, for different applications such as healthcare, sports, and military scenarios [5].
