A Piezoelectric Actuated Airwave Oscillometry Device

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 in adults and children that, over the last decade, has gained a place as an alternative to conventional spirometry used in research studies and clinical practice. OS applies low amplitude pressure oscillations during normal breathing and, unlike spirometry, it doesn’t require challenging respiratory maneuvers enabling its use in over a wider range of ages, patient physical conditions and treatment settings.

The present article describes the design and construction of an OS device. Current technology for measuring impedance using oscillatory pressure and flow is bulky using a loudspeaker and devices are substantially more expensive than spirometers, which significantly slows the adoption of this technology despite its clinical advantages. The device we develop here is innovative in that it uses an inexpensive lightweight beam bending piezoelectric based actuator system potentially greatly reducing cost, and simplifying the mechanical requirements. The device applies 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 signal to noise ratios of the pressure and flow signals were satisfactory, achieving greater than 30dB even when employed on test loads up to a resistance of 15 cmH2O/l/s. This device can be implemented as a clinical diagnostic device or for home use in monitoring applications or included within the breathing circuit during mechanical ventilation.