P227 Cross-sectional assessment of small airways tests in identifying early disease in alpha-1 antitrypsin deficiency

Abstract

Rationale Alpha-1 Antitrypsin Deficiency (AATD) is a rare genetic disease that can lead to the COPD, particularly in severe deficiency (PiZZ). COPD is currently defined by an FEV1/FVC ratio below 70%, at which point significant disease can already be well established. We have previously shown that a baseline Maximal Mid-Expiratory Flow (MMEF) less than 80% predicted in patients with a normal FEV1/FVC ratio can identify AATD patients with worse health status and a faster subsequent FEV1 decline (Stockley et al. ERJ 2017;49(3).pii:1602055). We sought to determine if other small airways tests could identify a similar at risk population. Methods 88 never- or ex-smoking PiZZ subjects were studied (57 without COPD and 31 with GOLD Stage I mild COPD) with routine lung function tests (spirometry, lung volumes and gas transfer) and tests of small airway function (lung clearance index (LCI), impulse oscillometry (R5 and R5-R20), and specific resistance (sRaw) and specific conductance (sGaw) by plethysmography). Additional spirometric parameters were also investigated (MMEF and the area under the expiratory flow-volume curve standardised for FVC (AEx/FVC)). Scatter plots of each ‘small airways’ parameter versus FEV1/FVC were visually analysed and, where appropriate, analysed by Spearman’s rank correlation. The data were also grouped into non-COPD and mild COPD and compared using a Mann-Whitney U test. Results Oscillometry and sGaw did not correlate with FEV1/FVC and were not different between the non-COPD and COPD cohorts. There were weak but significant correlations between FEV1/FVC and LCI (r2=0.163, p Conclusions Cross-sectionally, LCI, impulse oscillometry and plethysmography do not appear to be useful markers of early disease in AATD. MMEF and AEx may be more useful but will need to be assessed longitudinally for their ability to detect change in lung physiology that reflects long term progression.