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Airway responsiveness and peak flow variability in the diagnosis of asthma for epidemiological studies

¹ Division of Respiratory Medicine, Clinical Sciences Building, City Hospital, University of Nottingham, UK. ² Channing Laboratory, Dept of Medicine, Brigham and Women's Hospital, Boston, USA

CORRESPONDENCE: S.A. Lewis, Division of Respiratory Medicine, Clinical Sciences Building, City Hospital, Hucknall Road, Nottingham, NG5 1PB, UK. Fax: 44 1158404771

Keywords: asthma epidemiology, bronchial reactivity, peak flow variability

Received: February 2, 2001
Accepted June 14, 2001

This study was funded by the UK National Asthma Campaign and the British Lung Foundation. S. Lewis was funded by the Medical Research Council.

Airway responsiveness and variability in peak expiratory flow (PEF) are widely used as objective diagnostic measures of asthma, but it is not clear how these variables should be calculated or adjusted to obtain the highest diagnostic validity for physician-diagnosed asthma in the community.

Data from a community-based sample of 1,513 adults has been used. Airway responsiveness to methacholine and 7-day PEF data were obtained in 1991, asthma and respiratory symptoms were diagnosed by questionnaires in 1991 and 1999. Airway responsiveness was expressed as the provocative dose causing a 20% fall in forced expiratory volume in one second (PD₂₀), two-point and least-squares regression slopes. PEF variability was expressed as daily amplitude, weekly standard deviation and mean of the two lowest readings. Continuous measures were adjusted for measures of baseline airway calibre by linear regression.

Measures of airway responsiveness had greater sensitivity for specificity for self-reported diagnosed asthma than expressions of PEF variability, before and after adjustment for airway calibre. Diagnostic validity was substantially better in adults aged <50 yrs; PD₂₀ provided the best sensitivity for specificity (61% for 95% at 8.3 µmol). In those aged 50 yrs, no measure was closely related to diagnosed asthma.

In younger age groups, provocative dose causing a 20% fall in forced expiratory volume in one second provides a valuable objective measure of asthma for epidemiological studies, but is unable to distinguish between asthma and chronic obstructive pulmonary disease in older people.