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.

Oscillometry is increasingly adopted in respiratory clinics, however many recommendations regarding measurement settings and quality control remain subjective. The aim of this study was to investigate the optimal number of measurements and acceptable within-session coefficient of variation (CoV) in health, asthma and COPD.Fifteen healthy, 15 asthma and 15 COPD adult participants were recruited. Eight consecutive 30 s measurements were made using an oscillometry device (tremoFlo C-100, Thorays Thoracic Medical Systems Inc., Canada) from which resistance at 5 Hz (Rrs5) was examined. The effect of progressively including a greater number of measurements on Rrs5 and its within-session coefficient of variation (CoV) was investigated. Data was analysed using one-way repeated measures ANOVA with Bonferroni post-hoc test.The CoV(Rrs5) of the first 3 measurements was 6.7±4.7%, 9.7±5.7%, and 12.6±11.2% in healthy, asthma and COPD participants, respectively. Both mean Rrs5 and CoV(Rrs5) were not statistically different when progressively including 4–8 measurements. Selecting the 3 closest Rrs5 values over an increasing number of measurements progressively decreased the CoV(Rrs5). In order for ≥95% of participants to fall within a target CoV(Rrs5) of 10%, ≥4, 5 and 6 measurements were needed in health, asthma, and COPD, respectively.Within-session variability of oscillometry is increased in disease. Furthermore, the higher number of measurements required to achieve a set target for asthma and COPD patients may not be practical in a clinical setting. Provided technical acceptability of measurements is established, i.e. by removing artefacts and outliers, then a CoV of 10% is a marker of quality in most patients, but we suggest higher CoVs upto 15–20% should still be reportable.