Catheter type of flow sensor for trans-bronchial measurement forlung functions

We propose a novel catheter type of flow sensor as a tool for trans-bronchial measurement. An on-wall in-tube thermal flow sensor is mounted on the inside of a tube, and it is used as a diagnostic tool in a bronchoscope. The external diameter of the tube is less than a few mm, and therefore, it can evaluate the flow characteristics in the bronchiole. The relationship between the input power of the sensor and the flow rate obeyed King´s equation. The sensor output dependence on ambient temperature was also studied, and the curve obtained at 39.2degC was used as the calibration curve in animal experiments. The sensor characteristics under reciprocating flow were studied by using a ventilator, and we confirmed that the sensor was able to measure the reciprocating flow at of 2.0 Hz. Finally, we successfully measured the inspired and expired air characteristics in rats in vivo.