Measurement of Respiratory Flow with Ultrasonic Sensor Using the Technique of Forced Oscillations

With the evolution of electronics and measurement processes, today there are many systems capable to accomplish the measurement of the respiratory aerial flow. For the air flow measurement several methods can be used, such as the differential pressure method using a pneumotachometer and several measurement methods using anemometers. In this work, it is intended to design and to develop a system capable to measure the respiratory flow using the technique of forced oscillations, using an ultrasonic anemometer. A study of uncertainties propagation for two ultrasonic methods (time difference and phase difference) is also carried out in order to determine which is the best for the determination of the air speed and consequently of the respiratory flow. Experimental results obtained with the proposed method are compared with those obtained from a pneumotachometer, which is normally employed for this application