Respiratory sensors piezoresistive sensor

Figure 10.1 Respiratory-monitoring shirt with integrated piezoresistive sensors. Data are acquired and wirelessly transmitted using a Shimmer device.

Most respiratory sensors are based on the pneumography and measure the changes of chest or abdomen circumference. As the circumference increases or decreases, the electrical property of the textile sensor changes, and this change could be interpreted into inhalation and exhalation activities of the wearer. The most common methods include respiratory inductive plethysmography (RIP), piezoresistive sensors, and piezoelectric sensors (Merritt et al., 2009). 

Respiratory rate is measured by techniques based on either measuring thoracic expansion or based on measuring changes in skin impedance. For the former technique, most systems use strain gauges made from piezoresistive material combined with textile structures. Hertleer et al. reported a fabric sensor made of SS yam knitted in spandex belt [18]. For the latter technique, noninvasive skin electrodes are placed on the thorax, and the variation of the electrical impedance can be detected during respiration cycles. 

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