Alveolar Nitric Oxide in Chronic Obstructive Pulmonary Disease-A Two-Year Follow-Up.

Chronic obstructive pulmonary disease (COPD) affects the airways and gas exchange areas. Nitric oxide (NO) production from the airways is presented as F E NO 50 and from the gas exchange areas as alveolar NO (C A NO). We aimed to evaluate, over two years, the consistency of the C A NO estimations in subjects with COPD. A total of 110 subjects (45 men) who completed the study were included from primary and secondary care settings. C A NO was estimated using the two-compartment model. C A NO increased slightly during the two-year follow-up ( p = 0.01), but F E NO 50 remained unchanged ( p = 0.24). Among the subjects with a low C A NO (<1 ppb) at inclusion, only 2% remained at a low level. For those at a high level (>2 ppb), 29% remained so. The modified Medical Research Council dyspnoea scale (mMRC) score increased at least one point in 29% of the subjects, and those subjects also increased in C A NO from 0.9 (0.5, 2.1) ppb to 1.8 (1.1, 2.3) ppb, p = 0.015. We conclude that alveolar NO increased slightly over two years, together with a small decline in lung function. The increase in C A NO was found especially in those whose levels of dyspnoea increased over time.