Characteristics of an optimized catheter-type thermal flow sensor for measuring reciprocating airflows in bronchial pathways

Abstract

We optimized a catheter-type thermal flow sensor to measure the reciprocating airflows in bronchial pathways. The electrical wiring in the outer tube was extracted to keep the symmetry of the temperature distribution on the heaters. First, a flexible sensor was fabricated on polyimide film with photolithography, and then the enameled wires were bonded to the contact pads on the film with anisotropic conductive film. The film sensor was finally assembled with a catheter configuration that had a diameter of 1.8 mm by applying a heat shrinkable tube. We experimentally confirmed that the sensor outputs under both forward and reverse flow conditions had the same output characteristics when a design with symmetrical heating elements was applied. The sensor outputs we obtained at a reciprocating flow frequency ranging from 1 to 3 Hz almost coincided, and they also fit that obtained under unidirectional airflow conditions. Finally, the aspirated- and inspired-air characteristics in the air passages of small laboratory animals (rats and mice) were measured. Due to our development of a flexible method of electrical wiring, we could try a new approach to intubation measurements in which the sensor was inserted into the air passage from the mouth with a fiberscope, and we confirmed that the sensor we developed was able to directly measure the breathing characteristics in air passages. Implanted measurements were also attempted in this study.