Oscillometry and expiratory flow limitation in COPD and α-1-antitrypsin deficiency (AATD)

<bold>Introduction:</bold> Oscillometry (IOS) provides information about the mechanical properties of the lungs at tidal breathing. The measurements show moderate correlation with expiratory flow limitation. We hypothesise that this may be related to the underlying mechanism of airflow limitation. <bold>Aims:</bold> To examine the relation between oscillometry airflow obstruction and the extent of emphysema in subjects with AATD (mainly emphysema) and individuals with COPD (bronchial disease ± emphysema). <bold>Methods:</bold> We studied 12 subjects with COPD and 14 with AATD. Spirometry and IOS were performed after bronchodilation. Extent of emphysema was assessed by computed tomography (expressed as percentage of low attenuation volume (LAV)). Data were analysed by group comparisons and by multiple regression using IOS variables (resistance (R5) and reactance (X5) at 5 Hz and resonant frequency (f_res), all expressed as %predicted) as dependent variables and LAV and diagnosis (AATD/COPD) as predictors. <bold>Results:</bold> FEV1 was lower in COPD than in AATD (90±32 vs 53±17 %pred, p<0.001), whereas LAV did not differ significantly (17±11 vs 15±9 %). X5 showed linear relation to LAV (Figure), but with considerable offset between groups. Diagnosis was a significant predictor for X5. Findings were similar for f_res, whereas diagnosis was not a significant predictor for R5. <fig><object-id>erj;64/suppl_68/PA3458/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig> <bold>Conclusions:</bold> For a given degree of emphysema, reactance is more abnormal in COPD than in AATD.