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Airway smooth muscle cells from severe asthma patients with FAO respond to β 2 -agonists and corticosteroids in vitro , and at a level similar to mild asthmatics. Intrinsic dysfunction of these signalling pathways is unlikely to contribute to FAO. https://bit.ly/3muvNsW., Competing Interests: Conflict of interest: S. Rutting has nothing to disclose. Conflict of interest: D. Xenaki has nothing to disclose. Conflict of interest: K.D. Reddy has nothing to disclose. Conflict of interest: M. Baraket has nothing to disclose. Conflict of interest: D.G. Chapman has nothing to disclose. Conflict of interest: G.G. King reports grants, personal fees and nonfinancial support from AstraZeneca, Boehringer Ingelheim, Chiesi, GlaxoSmithKline, Menarini, MundiPharma and Novartis; and unrestricted research grants from the NHMRC, Boehringer Ingelheim, CycloPharma, GlaxoSmithKline, Menarini, MundiPharma, philanthropic individuals and societies; and nonfinancial and other support from Restech, Italy, during the conduct of the study. Conflict of interest: B.G. Oliver has nothing to disclose. Conflict of interest: K.O. Tonga reports a Lung Foundation Australia Ludwig Engel grant-in-aid during the conduct of the study., (Copyright ©The authors 2021.)

Higher body mass index (BMI) is associated with less severe airway obstruction in older asthma patients with fixed airflow obstruction. This is potentially mediated through BMI-related mechanisms that increase lung stiffness ( i.e. reduce lung compliance). https://bit.ly/3jBwCNy., Competing Interests: Conflict of interest: S. Rutting has nothing to disclose. Conflict of interest: D.G. Chapman has nothing to disclose. Conflict of interest: T. Badal has nothing to disclose. Conflict of interest: F. Sanai has nothing to disclose. Conflict of interest: S.C. Zimmermann reports nonfinancial support for travel and accommodation for educational respiratory symposia attendance from GlaxoSmithKline, Boehringer Ingelheim, Menarini, AstraZeneca and Novartis, outside the submitted work. Conflict of interest: C. Thamrin has nothing to disclose. Conflict of interest: G.G. King reports unrestricted research grants to support research projects, fees for consultancy services (which include lectures and advisory board services) and conference attendance support from AstraZeneca, Boehringer Ingelheim, GlaxoSmithKline, Novartis, Menarini and MundiPharma, and research grants from the National Health & Medical Research Council, professional societies, The University of Sydney, and philanthropic individuals and societies, outside the submitted work. Conflict of interest: K.O. Tonga has nothing to disclose., (Copyright ©ERS 2021.)

Functional residual capacity (FRC) accuracy is essential for deriving multiple-breath nitrogen washout (MBNW) indices, and is the basis for device validation. Few studies have compared existing MBNW devices. We evaluated in vitro and in vivo FRC using two commercial MBNW devices, the Exhalyzer D (EM) and the EasyOne Pro LAB (ndd), and an in-house device (Woolcock in-house device, WIMR). FRC measurements were performed using a novel syringe-based lung model and in adults (20 healthy and nine with asthma), followed by plethysmography (FRC pleth ). The data were analysed using device-specific software. Following the results seen with ndd, we also compared its standard clinical software (ndd v.2.00) with a recent upgrade (ndd v.2.01). WIMR and EM fulfilled formal in vitro FRC validation recommendations (>95% of FRC within 5% of known volume). Ndd v.2.00 underestimated in vitro FRC by >20%. Reanalysis using ndd v.2.01 reduced this to 11%, with 36% of measurements ≤5%. In vivo differences from FRC pleth (mean±sd) were 4.4±13.1%, 3.3±11.8%, -20.6±11% (p<0.0001) and -10.5±10.9% (p=0.005) using WIMR, EM, ndd v.2.00 and ndd v.2.01, respectively. Direct device comparison highlighted important differences in measurement accuracy. FRC discrepancies between devices were larger in vivo , compared to in vitro results; however, the pattern of difference was similar. These results represent progress in ongoing standardisation efforts., Competing Interests: Conflict of interest: Disclosures can be found alongside this article at openres.ersjournals.com