Background and objective: Fixed airflow obstruction (FAO) in asthma occurs despite optimal inhaled treatment and no smoking history, and remains a significant problem, particularly with increasing age and duration of asthma. Increased lung compliance and loss of lung elastic recoil has been observed in older people with asthma, but their link to FAO has not been established. We determined the relationship between abnormal lung elasticity and airflow obstruction in asthma. Methods: Non-smoking asthmatic subjects aged >40 years, treated with 2 months of high-dose inhaled corticosteroid/long-acting beta-agonist (ICS/LABA), had FAO measured by spirometry, and respiratory system resistance at 5 Hz (Rrs 5 ) and respiratory system reactance at 5 Hz (Xrs 5 ) measured by forced oscillation technique. Lung compliance (K) and elastic recoil (B/A) were calculated from pressure-volume curves measured by an oesophageal balloon. Linear correlations between K and B/A, and forced expiratory volume in 1 s/forced vital capacity (FEV 1 /FVC), Rrs 5 and Xrs 5 were assessed. Results: Eighteen subjects (11 males; mean AE SD age: 64 AE 8 years, asthma duration: 39 AE 22 years) had moderate FAO measured by spirometry ((mean AE SD zscore) post-bronchodilator FEV 1 : −2.2 AE 0.5, FVC: −0.7 AE 1.0, FEV 1 /FVC: −2.6 AE 0.7) and by increased Rrs 5 (median (IQR) z-score) 2.7 (1.9 to 3.2) and decreased Xrs 5 : −4.1(−2.4 to −7.3). Lung compliance (K) was increased in 9 of 18 subjects and lung elastic recoil (B/A) reduced in 5 of 18 subjects. FEV 1 /FVC correlated negatively with K (r s = −0.60, P = 0.008) and Rrs 5 correlated negatively with B/A (r s = −0.52, P = 0.026), independent of age. Xrs 5 did not correlate with lung elasticity indices. Conclusion: Increased lung compliance and loss of elastic recoil relate to airflow obstruction in older nonsmoking asthmatic subjects, independent of ageing. Thus, structural lung tissue changes may contribute to persistent, steroid-resistant airflow obstruction.Clinical trial registration: ACTRN126150000985583 at anzctr.org.au (UTN: U1111-1156-2795) SUMMARY AT A GLANCEWe measured lung elastic recoil, spirometry and the forced oscillation technique in older non-smoking asthmatic subjects with fixed airflow obstruction (FAO). In addition to airway remodelling, FAO can be attributed to reduced lung elastic recoil. Identification of the mechanisms leading to loss of lung elasticity may offer new targets for intervention.

We are currently limited in our abilities to diagnose, monitor disease status and manage chronic airway disease like asthma and chronic obstructive pulmonary disease (COPD). Conventional lung function measures often poorly reflect patient symptoms or are insensitive to changes, particularly in the small airways where disease may originate or manifest. Novel pulmonary function tests are becoming available which help us better characterise and understand chronic airway disease, and their translation and adoption from the research arena would potentially enable individualised patient care.In this article, we aim to describe two emerging lung function tests yielding novel pulmonary function indices, the forced oscillation technique (FOT) and multiple breath nitrogen washout (MBNW). With a particular focus on asthma and COPD, this article demonstrates how chronic airway disease mechanisms have been dismantled with the use of the FOT and MBNW. We describe their ability to assess detailed pulmonary mechanics for diagnostic and management purposes including response to bronchodilation and other treatments, relationship with symptoms, evaluation of acute exacerbations and recovery, and telemonitoring. The current limitations of both tests, as well as open questions/directions for further research, are also discussed.