Usefulness and early detection of acute exacerbation by peak expiratory flow rate in the management of asthma

Abstract

The monitoring of peak expiratory flow (PEF) and maintenance of a symptom diary have been proposed as means to monitor asthma severity. This study assessed via longitudinal analysis, the usefulness and limitation of daily PEF monitoring (amplitude percent mean) as an index for asthma severity, and the usefulness of recording daily intake of beta-agonists as a measure of symptom severity. Nine subjects with moderate to severe asthma were treated with inhaled beclomethasone dipropionate (BDP). Sustained-release theophylline and oral corticosteroids supplemented inhaled BDP according to both individual symptom prevalence and PEF measurements. The patients kept records four times daily of their PEF and asthmatic symptoms (cough, sputum and number of attacks), from the beginning to the end of treatment. They also recorded the daily frequency of beta-agonist inhalation (as needed for symptomatic relief). Minimum daily PEF (expressed as percent best) correlated significantly with symptom scores: cough (r = -0.69), sputum (r = -0.69) and attack (r = -0.69). Minimum PEF correlated strongly with the daily frequency of beta agonist inhalation (r = 0.76). Each symptom score and the daily frequency of beta-agonist inhalation was zero when the minimum PEF was approximately 80%. We evaluated the correlation between minimum PEF and daily PEF variability in all data (r = -0.72): for a minimum PEF > or = 20% (r = -0.72), a minimum PEF > or = 30% (r = -0.77), a minimum PEF > or = 40% (r = -0.82) and a minimum PEF > or = 50% (r = -0.80). We determined the correlation between minimum PEFs of > or = 35 to 45% in 1% increments and daily PEF variability in relation to the severity of asthma. With a minimum PEF > or = 40%, the strongest correlation was demonstrated between minimum PEF and daily PEF variability. Daily PEF variability was a reliable indicator for the management of asthma when the PEF > or = 40%. When the minimum PEF was 80%, daily PEF variability was approximately 10%. When the minimum PEF was 40%, daily PEF variability was 46%, and the daily frequency of beta-agonist inhalation was 2.6. We concluded that, 1) The target values of minimum PEF and daily PEF variability are 80% and 10% respectively in the treatment of asthmatic patients, 2) The daily frequency of beta-agonist inhalation is recommended as an indicator for the severity of asthmatic symptoms, and 3) Daily PEF variability in combination with the daily frequency of beta-agonist inhalation is very useful in the management and early detection of acute asthma.