Ventilation inhomogeneity in α1-antitrypsin-deficient emphysema

Abstract

The slope of phase III of the single-breath nitrogen wash-out test (sbN2-test) measures ventilation inhomogeneity and, in smokers, is strongly associated with small airways pathology. The present authors aimed to study ventilation inhomogeneity in emphysema related to type Z α1-antitrypsin (AAT) and to assess its relationship with indices of parenchymal damage and airways obstruction. A total of 18 subjects, consisting of ex-smokers with type Z AAT and emphysema (confirmed by computed tomography scan), were studied in a cross-sectional design. Post-bronchodilation flow-volume curves and gas transfer parameters were measured; sbN2-test curves were obtained and the slope of phase III was determined. The mean value of the slope (4.6±1.3% N2·L-1) was higher than reference values +2SD; it was significantly correlated with the transfer factor of the lung for carbon monoxide (R=-0.75) and the transfer coefficient of the lung for carbon monoxide (R=-0.58), but not with airways obstruction. There was no correlation between phase III slope values and cumulative smoking. In patients with type Z α1-antitrypsin emphysema, the increased ventilation inhomogeneity predominantly reflects parenchymal abnormalities, demonstrating that measurement of airways obstruction is not sufficient to characterise the disease. Determination of the sensitivity of the single-breath nitrogen wash-out test slope in detecting disease progression may give complementary information to spirometry. Copyright © ERS Journals Ltd 2006.