Respiration is one of the important vital signs of human in daily life. Respiratory signals including the information of rates, patterns, and phase are highly related to condition of respiratory organs and activity of exercise. Monitoring respiration rates helps us to find a risk of respiratory disorders such as sleep apnea, asthma, and chronic obstructive pulmonary disease.1 Conventional respiratory monitoring system, such as transthoracic impedance plethysmography, mainly records respiration of subjects at rest because motion of a target person can affect the observation of respiration. Therefore, wearable respiration sensors using various sensing mechanisms have been intensively studied.2
In this study, for monitoring human respiratory condition during exercise, we develop a portable respiration sensor with a humidity-sensitive nanoparticle film. We adopt surface-oxidized silicon-based nanoparticle (silicon nanocrystal, silica nanoparticle) thin films as a humidity-sensitive film.2,3 The thin films are solution-processed on flexible polyimide films by using the colloidal nanoparticle solution. Interdigitated electrodes on the polyimide films have 100 μm spacing. Fabricated devices work as a respiration sensor which detects water vapor in exhaled air. Response of the respiration sensor is fast enough to fully monitor human respiration condition up to 1.7 Hz. Patterns and phase of respiration can be analyzed by using the signal of the sensor. We also demonstrate a portable sensor using a portable data logger and a humidity-sensitive film for monitoring human respiration during running. This sensor can track and assess respiratory information during exercise easily.
1 Y. Khan, A.E. Ostfeld, C.M. Lochner, A. Pierre, and A.C. Arias, Adv. Mater. 28, 4373 (2016).
2 S. Kano, Y. Dobashi, and M. Fujii, IEEE Sensors Lett. 2, 24 (2018).
3 S. Kano, K. Kim, and M. Fujii, ACS Sensors 2, 828 (2017).