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.