Reference equations for specific airway resistance in children: the Asthma UK initiative

Plethysmographic specific airway resistance (sRaw) is a useful research method for discriminating lung disease in young children. Its use in clinical management has, however, been limited by lack of consensus regarding equipment, methodology and reference data. The aim of our study was to collate reference data from healthy children (3–10 yrs), document methodological differences, explore the impact of these differences and construct reference equations from the collated dataset. Centres were approached to contribute sRaw data as part of the Asthma UK initiative. A random selection of pressure–flow plots were assessed for quality and site visits elucidated data collection and analysis protocols. Five centres contributed 2,872 measurements. Marked variation in methodology and analysis excluded two centres. sRaw over-read sheets were developed for quality control. Reference equations and recommendations for recording and reporting both specific effective and total airway resistance (sReff and sRtot, respectively) were developed for White European children from 1,908 measurements made under similar conditions. Reference sRaw data collected from a single centre may be misleading, as methodological differences exist between centres. These preliminary reference equations can only be applied under similar measurement conditions. Given the potential clinical usefulness of sRaw, particularly with respect to sReff, methodological guidelines need to be established and used in prospective data collection.