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Ventilation inhomogeneity in ₁-antitrypsin-deficient emphysema

Lung Function Laboratory, Dept of Pulmonology, Leiden University Medical Centre, Leiden, The Netherlands.

CORRESPONDENCE: L. Fregonese, Dept of Pulmonology (C3-P), Leiden University Medical Centre, P.O. Box 9600, 2300 RC Leiden, The Netherlands. Fax: 31 715266927. E-mail: l.fregonese{at}lumc.nl

Keywords: ₁-Antitrypsin deficiency, cigarette smoking, diffusion capacity, emphysema, single-breath nitrogen wash-out test, small airways

Received: October 19, 2005
Accepted March 12, 2006

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 ₁-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 ₁-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.