Reference ranges for interrupter resistance technique: the Asthma UK Initiative.

Measuring interrupter resistance (R(int)) is an increasingly popular lung function technique and especially suitable for preschool children because it is simple, quick and requires only passive cooperation. A European Respiratory Society (ERS)/American Thoracic Society (ATS) Task Force recently published empirical recommendations related to procedures, limitations and interpretation of the technique. However, for valid interpretation, high-quality reference equations are required and these have been lacking. The aim of the present study was to collate R(int) data from healthy children in order to produce more robust reference equations. A further aim was to examine the influence of methodological differences on predicted R(int) values. R(int) data from healthy children were collected from published and unpublished sources. Reference equations for expiratory and inspiratory R(int) were developed using the LMS (lambda, mu, sigma) method. Data from 1,090 children (51% males) aged 3-13 yrs were collated to construct sex-specific reference equations for expiratory R(int) and data from 629 children (51% males) were collated for inspiratory R(int). Height was the best independent predictor of both expiratory and inspiratory R(int). Differences between centres were clinically irrelevant, and differences between ethnic groups could not be examined. The availability of a large and generalisable sample and the use of modern statistical techniques enabled the development of more appropriate reference equations for R(int) in young children.