The Feasibility of Measuring Lung Hyperinflation With a Smart Shirt: An in Vitro Study

Home monitoring of patients with chronic obstructive pulmonary disease can increase quality of life and decrease health care costs. Despite the existence of an important relationship between lung hyperinflation (LH) and patient outcomes, LH is often ignored in home monitoring as it difficult to assess at home. A smart shirt containing respiratory inductance plethysmography (RIP, which measures thoracic and abdominal cross-sectional area changes) is a promising tool for home monitoring of LH. This study investigates the feasibility of a smart shirt to monitor LH. We aimed to describe the relationship between temperature and the output, and between the circumference and output of the smart shirt and to correct for temperature dependency. To do so, the smart shirt was applied to a custom-made torso model. Ambient temperature was increased and decreased in 15 tests, while maintaining a constant torso circumference to derive a temperature correction. Additionally, sensor output was monitored with varying circumference. The results revealed a linear relation between temperature and RIP output. Nine of the twelve shirts showed a linear output to changes in circumference. A median temperature drift of -34.7 mL/°C was observed and corrected to a minimum drift of -0.5 mL/°C. In conclusion, RIP is a promising method for measuring LH in home monitoring. Patients will not be falsely diagnosed with LH due to temperature changes. Sensor output can easily be corrected for temperature. Furthermore, the relationship between circumference and output is linear, confirming the ease of implementing the calibration procedure for obtaining lung volumes.