Forced oscillation technique and impulse oscillometry

Abstract

Conventional methods of lung function testing provide measurements obtained during specific respiratory actions of the subject. In contrast, the forced oscillation technique (FOT) determines breathing mechanics by superimposing small external pressure signals on the spontaneous breathing of the subject. FOT is indicated as a diagnostic method to obtain reliable differentiated tidal breathing analysis. Because FOT is performed without closure of a valve connected to the mouthpiece, and without maximal or forced respiratory manoeuvres, it is unlikely that FOT itself will alter airways smooth muscle tone. FOT utilises the external applied pressure signals and their resultant flows to determine lung mechanical parameters. These pressure–flow relationships are largely distinct from the natural pattern of individual respiratory flows, so that measured FOT results are, for the most part, independent of the underlying respiratory pattern. Therefore, oscillometry minimises demands on the patient and requires only passive cooperation of the subject: maintenance of an airtight seal of the lips around a mouthpiece and breathing normally through the measuring system with a nose-clip occluding the nares. Potential applications of oscillometry include paediatric, adult and geriatric populations, comprising diagnostic clinical testing, monitoring of therapeutic regimens, and epidemiological evaluations, independent of severity of lung disease. Oscillometry is also applicable to veterinary medicine. The last two main sections Relevance of oscillometry in clinical practice and Oscillometry in the clinical pulmonary laboratory emphasise clinical aspects of application and interpretation of FOT rather than methodological details and technological solutions, which are discussed in the two sections that follow immediately below. Clinical application of FOT does not require mastery of the mathematical infrastructure of the technical methodology, and readers interested in the clinical use of FOT may find it more useful to begin with these clinical sections and refer subsequently to methodological and technological details.