Non-Contact Monitoring of Inhalation-Exhalation (I:E) Ratio in Non-Ventilated Subjects

Abstract

The inhalation-exhalation (I:E) ratio, known to be an indicator of respiratory disease, is the ratio between the inhalation phase and exhalation phase of each breath. Here, we report on results from a non-contact monitoring method for the determination of the I:E ratio. This employs a depth sensing camera system that requires no sensors to be physically attached to the patient. A range of I:E ratios from 0.3 to 1.0 over a range of respiratory rates from 4 to 40 breaths/min were generated by healthy volunteers, producing a total of 3,882 separate breaths for analysis. Depth information was acquired using an Intel D415 RealSense camera placed at 1.1 m from the subjects' torso. This data was processed in real-time to extract depth changes within the subjects' torso region corresponding to respiratory activity. This was further converted into a respiratory signal from which the I:E ratio was determined (I:Edepth). I:Edepth was compared to spirometer data (I:Espiro). A Bland Altman analysis produced a mean bias of -0.004, with limits of agreement [-0.234, 0.227]. A linear regression analysis produced a line of best fit given by I:Edepth = 1.004 × I:Espiro - 0.006, with 95% confidence intervals for the slope [0.988, 1.019] and intercept [-0.017, 0.004]. We have demonstrated the viability of a non-contact monitoring method for determining the I:E ratio on healthy subjects breathing without mechanical support. This measure may be useful in monitoring the deterioration in respiratory status and/or response to therapy within the patient population.