Electromagnetic Biosensing of Tidal Volume

Continuous monitoring of tidal volume (TV) is crucial for predicting lung disease and for the assessment of lung conditions such as asthma. Current monitoring methods, including spirometry, can be obtrusive, uncomfortable, and immobilize the patient. Wireless wearable technology can monitor respiratory activity while providing comfort and mobility but require regular battery replacement, which presents an environmental hazard as well as a barrier for compliance and adoption of the technology. In this paper, we propose to harvest and sense TV simultaneously with an electromagnetic (EM) generator, which can be later realized into a zero-net energy biasensor. An off-the-shelf dc brushed motor was modified into a chest belt, tested on both a mechanical chest and on 20 human subjects and successfully detected chest circumference change and TV while harvesting 7-70 mu W from human subjects. On the mechanical chest, chest circumference change was detected with a mean absolute error of 0.54 +/- 0.36 mm. For human subjects, TV was detected with a mean difference of 1.4 +/- 179.6 mL (sitting), -8.4 +/- 184.9 mL (standing), and -21.1 +/- 188.6 mL. (walking). This paper shows that it can be possible to measure TV with an EM sensor on the chest, while simultaneously harvesting energy to supplement the sensor's power requirements.