Respiratory symptoms and peripheral airway dysfunction are common in smokers with normal spirometry. Symptoms of chronic bronchitis related to conductive airway abnormalities, while wheeze was related to spirometry and IOS. The clinical significance of abnormalities in peripheral airway function in smokers remains undetermined.

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.

BackgroundExpiratory flow limitation (EFL) is seen in some patients presenting with a COPD exacerbation; however, it is unclear how EFL relates to the clinical features of the exacerbation. We hypothesized that EFL when present contributes to symptoms and duration of recovery during a COPD exacerbation. Our aim was to compare changes in EFL with symptoms in subjects with and without flow-limited breathing admitted for a COPD exacerbation.Subjects and methodsA total of 29 subjects with COPD were recruited within 48 hours of admission to West China Hospital for an acute exacerbation. Daily measurements of post-bronchodilator spirometry, resistance, and reactance using the forced oscillation technique and symptom (Borg) scores until discharge were made. Flow-limited breathing was defined as the difference between inspiratory and expiratory respiratory system reactance (EFL index) greater than 2.8 cmH2O·s·L−1. The physiological predictors of symptoms during recovery were determined by mixed-effect analysis.ResultsNine subjects (31%) had flow-limited breathing on admission despite similar spirometry compared to subjects without flow-limited breathing. Spirometry and resistance measures did not change between enrolment and discharge. EFL index values improved in subjects with flow-limited breathing on admission, with resolution in four patients. In subjects with flow-limited breathing on admission, symptoms were related to inspiratory resistance and EFL index values. In subjects without flow-limited breathing, symptoms related to forced expiratory volume in 1 second/forced vital capacity. In the whole cohort, EFL index values at admission was related to duration of stay (Rs=0.4, P=0.03).ConclusionThe presence of flow-limited breathing as well as abnormal respiratory system mechanics contribute independently to symptoms during COPD exacerbations.

The forced oscillation technique (FOT) is an emerging clinical lung function test, with commercial devices becoming increasingly available. However comparability across existing devices has not been established. We evaluated in vivo and in vitro measurements made using three commercial devices against a custom-built device (WIMR): Resmon Pro Diary (Restech srl, Italy), tremoFlo C-100 (Thorasys Medical Systems, Canada), Jaeger Masterscope CT IOS (CareFusion, Hoechberg, Germany). Respiratory system resistance Rrs and reactance Xrs at 5 Hz were examined in twelve healthy subjects (mean age 33 ± 11 years, 7 males), and in two test standards of known resistance and reactance. Subjects performed three measurements during tidal breathing on the four devices in random order. Total, inspiratory and expiratory Rrs and Xrs were calculated and compared using one-way repeated measures ANOVA and Bonferroni post-hoc tests. Rrs did not differ between devices, with <10% deviation from predicted, except for the IOS device. With Xrs, similar values were seen between the WIMR and Resmon devices and between the tremoFlo and IOS devices. No differences were observed using test standards; deviation from theoretical value was <2% for resistance and <5% for reactance. The WIMR, tremoFlo and Resmon Pro but not IOS devices measure similar Rrs, whereas there was more disparity across devices in the estimation of Xrs parameters. The discrepancy between in vivo and in vitro measurements suggest that FOT validation procedures need to take into account the breathing pattern, either using biological controls or a breathing model.