Variability of lung function predicts loss of asthma control following withdrawal of inhaled corticosteroid treatment
- 1Division of Respiratory Medicine, Department of Paediatrics, Inselspital and University of Bern, Switzerland
- 2Dunedin School of Medicine, University of Otago, New Zealand
- 3Department of Biomedical Engineering, Boston University, USA
- Correspondence to Dr Cindy Thamrin, Division of Paediatric Respiratory Medicine, University Children's Hospital of Bern, Inselspital, 3010 Bern, Switzerland;
Contributors CT designed and performed the analysis and wrote the manuscript. DRT and SL conceived the original study and contributed to this manuscript. BS and UF contributed to study design, interpretation and drafting of the manuscript.
- Received 19 October 2009
- Accepted 5 March 2010
Background One aspect of a multidimensional approach to understanding asthma as a complex dynamic disease is to study how lung function varies with time. Variability measures of lung function have been shown to predict response to β2-agonist treatment. An investigation was conducted to determine whether mean, coefficient of variation (CV) or autocorrelation, a measure of short-term memory, of peak expiratory flow (PEF) could predict loss of asthma control following withdrawal of regular inhaled corticosteroid (ICS) treatment, using data from a previous study.
Methods 87 adult patients with mild to moderate asthma who had been taking ICS at a constant dose for at least 6 months were monitored for 2–4 weeks. ICS was then withdrawn and monitoring continued until loss of control occurred as per predefined criteria. Twice-daily PEF was recorded during monitoring. Associations between loss of control and mean, CV and autocorrelation of morning PEF within 2 weeks pre- and post-ICS withdrawal were assessed using Cox regression analysis. Predictive utility was assessed using receiver operator characteristics.
Results 53 out of 87 patients had sufficient PEF data over the required analysis period. The mean (389 vs 370 l/min, p<0.0001) and CV (4.5% vs 5.6%, p=0.007) but not autocorrelation of PEF changed significantly from prewithdrawal to postwithdrawal in subjects who subsequently lost control, and were unaltered in those who did not. These changes were related to time to loss of control. CV was the most consistent predictor, with similar sensitivity and sensitivity to exhaled nitric oxide.
Conclusion A simple, easy to obtain variability measure of daily lung function such as the CV may predict loss of asthma control within the first 2 weeks of ICS withdrawal.
- coefficient of variation
- lung function tests
- peak expiratory flow rate
- respiratory measurement
Funding Thoracic Society of Australia and New Zealand/Allen Hanburys Respiratory Research Fellowship to CT.
Competing interests None.
Ethics approval This study was conducted with the approval of the University of Otago Ethics Committee.
Provenance and peer review Not commissioned; externally peer reviewed.