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The measurement of breathing biomechanics, such as tidal volume, can be used to assess both the breathing performance and the respiratory health of individuals. State-of-the-art methods like spirometry or body plethysmography require a mouthpiece or facemask., which can be uncomfortable to the test person. As an alternative, we propose to use the change of the geometric shape of the subject’s torso while breathing. By acquiring 3D point clouds of the person with a real-time near-infrared (NIR) 3D scanner, we measure those changes in a comfortable, irritation-free, and contact-free manner. Accordingly, two continuously measuring structured light 3D sensors, using a GOBO-based aperiodic sinusoidal pattern projector at a wavelength of 850 nm, simultaneously capture the upper front and side torso of the subject at a frame rate of 200 Hz. Both 3D scanners are calibrated and operated in a sensor network fashion, yielding a unified data stream within a global coordinate system. This results in increased coverage and reduced occlusion of the patient’s body shape, enabling robust measurements even in the presence of loose clothing and varying body figure. We collected data from 16 healthy participants in an upright sitting position, wearing everyday clothing during the measurements. For reference, we simultaneously recorded spirometry readings. An algorithm (“OpTidal”) tracks the volume of the subject’s torso from the 3D data. Comparison whith the reference data shows high correlation and low mean error for the absolute tidal volume readings. As such, our method is a viable, safe, and accurate alternative to spirometry and plethysmography.
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