On the Measurement of Tidal Volume with Wearable Devices

In the field of wearable devices, respiratory monitoring is relatively less developed than other consolidated approaches like cardiac and activity monitoring. Specifically, several devices offer the possibility to monitor the respiratory rate, i.e., the number of breaths per minute, in static conditions. However, obtaining the same signal in dynamic conditions is challenging because of movement artifacts. Furthermore, there are only a few devices available that allow us to monitor the tidal volume, i.e., the volume of air that moves into and out of the lungs with each breath. As tidal volume is needed to directly compute minute ventilation, which is the product between respiratory rate and tidal volume, most devices on the market cannot compute this parameter. For this reason, models of minute ventilation based on measured heart or pulse rate, respiratory rate, and other individual characteristics such as age, body mass index or estimated forced vital capacity are used. This work presents the most common strategies to estimate minute ventilation together with the challenges and opportunities of measuring tidal volume with wearables.