Converting FENO by different flows to standard flow FENO

Abstract

In clinical practice, assessment of expiratory nitric oxide (FENO) may reveal eosinophilic airway inflammation in asthmatic and other pulmonary diseases. Currently, measuring of FENO is standardized to exhaled flow level of 50 ml s−1, since the expiratory flow rate affects the FENO results. To enable the comparison of FENO measured with different expiratory flows, we firstly aimed to establish a conversion model to estimate FENO at the standard flow level, and secondly, validate it in five external populations. FENO measurements were obtained from 30 volunteers (mixed adult population) at the following multiple expiratory flow rates: 50, 30, 100 and 300 ml s−1, after different mouthwash settings, and a conversion model was developed. We tested the conversion model in five populations: healthy adults, healthy children, and patients with COPD, asthma and alveolitis. FENO conversions in the mixed adult population, in healthy adults and in children, showed the lowest deviation between estimated FENO from 100 ml s−1 and measured FENO at 50 mL s−1: −0·28 ppb, −0·44 ppb and 0·27 ppb, respectively. In patients with COPD, asthma and alveolitis, the deviation was −1·16 ppb, −1·68 ppb and 1·47 ppb, respectively. We proposed a valid model to convert FENO in healthy or mixed populations, as well as in subjects with obstructive pulmonary diseases and found it suitable for converting FENO measured with different expiratory flows to the standard flow in large epidemiological data, but not on individual level. In conclusion, a model to convert FENO from different flows to the standard flow was established and validated.