Benchtop Characterization of Wearable Respiratory Monitors for Assessing Feasibility of Measuring Lung Volume

Objective: This study characterizes three commercially available wearable respiratory monitors (WRMs): (1) Hexoskin Smart Garment, (2) Smartex WWS, and (3) Equivital EQ02 LifeMonitor, each with a unique chest motion sensor technology: respiratory inductance plethysmography, piezoresistor, and strain gauge, respectively. WRMs comprise of a body garment with embedded sensors that measure ambulatory chest motion in real-time. Once calibrated, chest motion waveforms from WRMs can be converted to lung volume waveform, which is then used to derive respiratory topography. The aim of this study is to assess and compare these WRMs in terms of: (i) their response signal to chest motion linearity, which is necessary for successful calibration, and (ii) their ability to measure breath-hold, which is a parameter of interest for lung deposition modeling. Methods: A benchtop test setup was built to simulate chest motion in a controlled way to facilitate comparison across the three devices. A staircase square-wave chest motion profile was used to simultaneously assess both signal linearity and ability to measure breath-hold. The respiratory response from the sensors was compared to the simulated chest motion. Results: The Hexoskin showed the best performance in both metrics, whereas the Equivital had the worst performance in both. The Smartex showed moderate ability to measure breath-hold but poor signal linearity. Conclusion: Of the three WRMs tested, the Hexoskin appears to be the best choice for ambulatory lung volume measurement. Significance: This study demonstrates the feasibility of adapting current technology to observe respiratory behavior valuable in many research domains, including tobacco research.