Impulse oscillometry: an alternative modality to the conventional pulmonary function test to categorise obstructive pulmonary disorders.

Impulse oscillometry (IOS) was introduced as an alternative modality to the conventional pulmonary function test (cPFT) to test lung mechanics. The objective of this study is to assess the use of IOS as an alternative, or in conjunction with cPFT, to categorise an obstructive respiratory disorder as chronic obstructive pulmonary disease (COPD) or asthma. Patients referred to the PFT laboratory, with different diagnoses of obstructive airways disorders, completed a standardised respiratory questionnaire prior to testing. All recruited subjects completed both modalities of PFT. A total of 146 patients were included. The overall mean age was 51+/-18.4 SD. The majority were non-smokers (68.7%). A standardised diagnosis of asthma was found for 51 subjects, while COPD was diagnosed in 36 subjects and 59 subjects were categorised as normal. The sensitivity of IOS in relation to asthma was 31.3% and 19.6% for cPFT. Among cases of COPD, the cPFT had better sensitivity (47.4%) than IOS (38.95%). The specificity was comparable for IOS and cPFT in relation to asthma and COPD. IOS had better sensitivity (45.8%) in detecting normal subjects than cPFT (28.8%), while specificity was comparable (80.5% and 86.2%, respectively). IOS may replace cPFT where the latter cannot be carried out due to feasibility or lack of cooperation. It can, however, discriminate between diseased and non-diseased subjects.