Characterization of basket-forceps-type micro-flow-sensor for breathing measurements in small airway

We previously proposed a basket-forceps-type flow sensor, in which a flexible thermal flow sensor is mounted onto basket forceps to fix the flow sensor onto the inside surface of the airway. The basket-forceps-type flow sensor has an asymmetrical structure to prevent reciprocating airflow; thus, we investigated the characteristics of the basket-forceps-type flow sensor under both expired- and inspired-airflow conditions in this study. The thermal flow sensor was fabricated on a flexible polyimide film and mounted onto a guide tube of a basket-forceps. Two heaters and their electrical wiring patterns were designed to produce symmetric heat distribution over the heaters. The effects of the basket structure and guide tube on flow-rate measurement were experimentally evaluated, and it was confirmed that they did not affect sensor output. Conversely, sensor output decreased with the increase in tube diameter due to the reduction in the average flow velocity with the diameter increase. Thus, we carried out a procedure to construct a calibration curve under an arbitrary tube diameter. Finally, we applied the basket-forceps-type flow sensor in an animal experiment in which it successfully detected the breathing properties in the airway of a rat.