Bandpass Speaker Box to Perform Forced Oscillation Technique Using the Wavetube Method

Abstract

Respiratory impedance provides us a consider-able amount of information about respiratory diseases and is an important tool in medical diagnosis. One useful technique for determining the respiratory impedance is the Forced Oscil-lation Technique (FOT), consisting in applying a known flow or volume signal in the study component and measuring its resulting pressure. Our interest is in the wavetube method, which consists of using a loudspeaker to generate the oscillato-ry known signal. This speaker is attached to a rigid circular tube, which is then connected to the element that we want to calculate the impedance. To perform this calculation, there are pressure signals, which are acquired with pressure transduc-ers. In this article we focus on developing a bandpass speaker box for the realization of the oscillations for the wavetube method. Based on an absence in studies about the pressure generator for the wavetube method, we compared the bandpass box with a vented box. We conducted a computer simulation of the amplitude response of each box and then collect experimental data of pressure signals generated from each speaker to perform the comparison between the ampli-tude responses generated by each box. We concluded that the use of a bandpass speaker is an interesting alternative for the realization of the FOT. However, the use of a vented speaker box is not totally invalid, as predicted by the computer simula-tions.