Static lung volumes and diffusion capacity in adults 30 years after being diagnosed with asthma

BACKGROUND: Long-term follow-up studies of adults with well-characterized asthma are sparse. We aimed to explore static lung volumes and diffusion capacity after 30 + years with asthma. METHODS: A total of 125 adults with an objectively verified diagnosis of asthma between 1974–1990 at a Danish respiratory outpatient clinic completed a follow-up visit 2017–19. All participants (age range 44–88 years) completed a comprehensive workup and were, based on these assessments, classified as having either active asthma or being in complete remission. The examination program included measurements of static lung volumes and diffusion capacity. RESULTS: Participants with active asthma were hyperinflated (residual volume/total lung capacity ratio 0.43, 95% CI 0.41—0.45) (RV/TLC ratio) compared with those in remission (RV/TLC ratio 0.38, 95% CI 0.36—0.41) (p < 0.03). A tendency towards higher diffusion capacity per liter lung volume was seen in participants with active asthma (KCO 100% predicted, 95% CI 97—104) compared with those in remission (KCO 94% pred., 95% CI 89—99) (P = 0.10). Longer asthma duration was associated with a higher KCO 0.47% pred./year (95% CI 0.14—0.80), adjusted for age and smoking. Patients on GINA step 4 and 5 treatment were more hyperinflated ([Formula: see text] RV 14% pred., 95% CI 3—27) and had higher airway resistance (mean 53% pred., 95% CI 9—97) than participants on lower GINA steps. Patients with uncontrolled disease had substantially higher airway resistance (72% pred. 95% CI 20—124) than well-controlled patients. CONCLUSION: Thirty years after a confirmed diagnosis of asthma, those continuing to have active asthma and those having severe asthma, have higher diffusion capacity and more hyperinflation than patients in remission.