Temperature-compensated catheter flow sensor and its application to breathing measurement in a mouse

A catheter flow sensor with temperature compensation was developed to measure breathing characteristics in small bronchi. Grooves were introduced between flow and temperature sensors for thermal isolation. Grooves with a depth of 7.5 μm were fabricated by applying oxygen plasma, and an infrared thermography was used to evaluate the effect of the thermal isolation. A heater was successfully thermally isolated, and heat was not transferred to the temperature sensor. The relationship between flow rate and sensor output was evaluated. The temperature dependency on the sensor output was successfully reduced less than 1.5% by adding a temperature compensation function. Finally, a catheter flow sensor was inserted into the air passage of a mouse by using an adapter, and the air flow passing through the tube was directly measured. By adding the temperature compensation function, the volumes of the expired and inspired air closely matched.