Respiratory rate monitoring with cellulose optical fiber

Cellulose as a material brings new opportunities to optical fiber (OF) sensors. It will not change exist-ing OFs use in telecommunication or in current sensor applications. Cellulose can offer novel charac-teristics to OF sensors since it is modifiable, biodegradable, biocompatible, renewable, and recyclable material. Especially glass OFs are inert and perhaps the only challenge is the brittleness of the material itself. Polymer OFs can offer higher flexibility than glass. Unlike glass and polymers, cellulose material is hygroscopic, having fast repeatable wetting and drying in water and moisture. OFs have been used for respiratory rate monitoring both with polymer and glass fibers. Optical respiratory rate mon-itoring is needed for example, in magnetic resonance imaging (MRI) to avoid electrical interference]. We have also shown carboxymethyl cellulose (CMC) based OF breathing sensor with loop and reflection type sensor.
Here we show regenerated cellulose (RC) OF for respiratory rate monitoring. CMC fiber can be disin-tegrated (dissolved) in long term wetting, but RC fiber keeps a good mechanical performance in wet state and during breathing. We prepared a face mask with a 5 cm long RC fiber loop with 3 dB/cm at-tenuation. We demonstrate a wireless measurement setup with battery operated 650 nm laser light source and a photodetector with Bluetooth connection to Android mobile phone application. Breathing was monitored during light sport activities with indoor cycling and rowing. Slow in-door cycling has the same respiratory rate after 5 min cycling as the rest state 16 breaths/min. Heavier indoor rowing increased respiratory rate to 24 breaths/min after 10 min steady rowing. Corresponding heart rates with Garmin’s sensor were 80 bpm and 97 bpm with cycling and rowing, respectively.