Sensores termo-resistivos e ultrassônicos na medição de fluxo respiratório com a técnica de oscilações forçadas.

Abstract

The forced oscillations technique is a non invasive method to investigate lung mechanics. It is used to determine the impedance of the respiratory system that is derived from the pressure and flow signals recorded at the mouth of the patient. In the conventional setup these signals are induced starting from sinusoidal pressure signals imposed by means of a loudspeaker, and the flow transducer is a pneumotachometer. This equipment measures the pressure difference between two points on a tube with an inner mechanical resistance element consisting of a bundle of capillary tubes or a wire mash screen. The pneumotachometer tendency is to become clogged with mucous and condensations during prolonged use, due to the particles expelled by the patient in the respiratory process. This increases the effective resistance of the flow head and leads to errors. In order to find alternative methods for the measurement of the respiratory flow with the forced oscillations technique, other kinds of sensor are used, such as platinum wire termoresistive sensors and ultrasonic sensors. Experimental results of the respiratory flow measured with these sensors are showed and compared with the results obtained by a pneumotachometer.