A pilot study to evaluate Australian predictive equations for the impulse oscillometry system

Impulse oscillometry (IOS) measures respiratory function during normal breathing by transmitting mixed frequency rectangular pressure impulses down the airways and measuring the resultant pressure and flow relationships, which describe the mechanical parameters of the lungs. Respiratory impedance and its components, airways resistance and reactance, at a range of frequencies from 0.1 to 150 Hz are calculated by computer analysis. The IOS software generates predictive normal values for each of the parameters measured, including total airway resistance (R5), proximal airway resistance (R20) and peripheral capacitive reactance (X5). However, these values are based on German data and no other Caucasian data or Australian normative data exist.

This was a cross-sectional study of over 100 community dwelling adults, with about 10 men and 10 women per 10-year cohort. Inclusion criteria were age between 25 and 74 years and apparently good respiratory health. Exclusion criteria were smoking, asthma and acute or chronic respiratory disease. IOS and spirometry were performed on all participants.

Australian predictive normal equations were generated and compared with current published equations. The IOS parameters were correlated with the spirometric data. Results were analysed by gender, age, height and weight, and compared with the predicted normal values for each parameter provided by the German manufacturer of the IOS instrument.

A preliminary set of Australian predictive equations have been produced for the IOS. These have been compared with international equations. IOS has potential applications in a range of respiratory diseases and in population screening for occupational health assessment.