Impulse oscillometry as a rule-out method for emphysema

Abstract

Background: Body plethysmography (BP) is the standard pulmonary function test (PFT) for diagnosing pulmonary emphysema, but not all patients can cooperate to this procedure. An alternative PFT, impulse oscillometry (IOS), has never been investigated in emphysema.

Aims and objectives: We investigate the ability of IOS to discriminate between the presence and absence of emphysema.

Methods: One hundred patients from the pulmonary outpatient clinic in Vejle, Denmark, were consecutively included in this cross-sectional study. A clinical assessment including disease history, a BP, and an IOS was performed in all patients. A computed tomography scan was performed in 88 of these 100 patients, and emphysema was present on the scan in 20 patients. The ability of BP and IOS in discriminating between emphysema or not was evaluated with two multivariate logistic regression models: BP (FEV1 %-predicted, FVC %-predicted, TLC %-predicted, RV %-predicted, DLCOc %-predicted) and IOS (R5Hz %-predicted, R5-20Hz, X5Hz, Fres, Ax).

Results: BP: AUC 0.933 (95% CI: 0.837 – 1.00), Positive predictive value (PPV)=61.5%, Negative predictive value (NPV)=95.1%. IOS: AUC=0.878 (95% CI: 0.794 – 0.962), PPV=57.1%, NPV=92.5%. We found no significant difference between the AUC of the two models (P=0.24).

Conclusions: BP showed a higher AUC than IOS for discriminating between emphysema or not, but the difference was not significant. IOS showed excellent diagnostic precision. IOS is both quick and easy to perform, and it may be used when BP is impossible and as a reliable rule-out method for emphysema.