Background: In asthma treatment, doses of inhaled corticosteroids are often adapted to symptoms and need for bronchodilators. However, in cross-sectional studies in emergency room settings, lung function and respiratory symptoms are not always concordant. Available longitudinal data are based on written peak flow diaries, which are unreliable. Using home spirometry, we studied prospectively whether mild respiratory symptoms, prompting reliever therapy are accompanied by a clinically relevant drop in lung function in children with asthma.
Methods: For 8 weeks, children with asthma scored symptoms and measured peak expiratory flow (PEF) and forced expiratory volume in 1 sec (FEV1) on a home spirometer twice daily. Additional measurements were recorded when respiratory symptoms prompted them to use bronchodilators.
Results: The mean difference between symptom free days and at times of symptoms was 6.6% of personal best for PEF (95% CI: 3.2–10.0; p = 0.0004) and 6.0% of predicted for FEV1 (95% CI: 3.0–9.0; p = 0.0004). There was complete overlap in PEF and FEV1 distributions between symptom free days and at times of symptoms.
Conclusions: Although statistically significant, the degree of airway narrowing at times of respiratory symptoms, prompting the use of reliever therapy, is highly variable between patients, limiting the usefulness of home spirometry to monitor childhood asthma.