A PCA-Based Method to Select the Number and the Body Location of Piezoresistive Sensors in a Wearable System for Respiratory Monitoring

This work aims at selecting the number and the body location of piezoresistive sensors to instrument wearable systems for respiratory rate (RR) estimation. We tested a novel method based on Principal Component Analysis on 10 healthy male subjects, who were asked to perform six trials on a treadmill (at rest, during walking and low speed running). We monitored RR using both a smart garment composed of six piezoresistive sensors and a flowmeter, used as reference signal. On the basis of the results, we propose the following guidelines: i) breathing assessment at rest requires one sensor, placed on the lower thorax; ii) low speed walking assessment requires three sensors, placed on upper thorax, lower thorax and abdomen; iii) high speed walking and running assessment requires a four-sensor configuration (one sensor placed on the upper thorax, one on the lower thorax and two on the abdomen); iv) an effective assessment can be performed at all speeds using the above-mentioned four-sensor configuration, denoted as General Purpose Configuration.