PIEZOELECTRIC MULTILAYER BENDING ACTUATED OSCILLOMETRY PROTOTYPE

Abstract

Oscillometry (OS), also known as the forced oscillation technique (FOT) is used to measure lung mechanics and can be used to assess airflow obstruction in diseases such as asthma and chronic obstructive pulmonary disease. OS is primarily used in research, but increasingly has found a place in clinical practice. OS applies low amplitude pressure oscillations during normal breathing and it doesn’t require challenging respiratory manoeuvres. Most OS technology is bulky using a loudspeaker, although one uses electromagnetic actuators enabling a smaller accurate device. However, all devices are expensive and together these features significantly slow adoption. To advance the technique and help solve this issue, this thesis presents an innovative method that uses an inexpensive, lightweight beam bending piezoelectric based actuator system potentially greatly reducing costs, and simplifying the mechanical requirements. Two different versions of the system were developed; a single-actuator and a multi-actuator prototype. The compact and lightweight single actuator device is presented as the most compelling approach. It applies a single frequency oscillatory pressure at 6 Hz or 19 Hz by moving a mesh-disk of known resistance within a chamber through which the patient also breathes. The prototype measures airflow resistance of test loads (TL) consistently and the signal to noise ratios of the pressure and flow signals were satisfactory compare to a similar FOT available in the market. The similar but larger multi actuator device, developed with the goal of applying FOT with composite frequency oscillations, was able to produce oscillations over a range of frequencies, but exhibited too low signal to noise ratio, due to too great a leak in the gap around the mesh disk. With improvements in design this method could also potentially measure respiratory impedance. This thesis gave proof of concept and demonstrated the feasibility of using piezoelectric beam bending actuators for the application of the FOT. The single frequency device has the highest potential to be implemented as a clinical diagnostic device, for home use in monitoring applications or included within the breathing circuit during mechanical ventilation. The device has the potential to have an impact in the respiratory market.