ArticlesDifferences between asthma exacerbations and poor asthma control
Introduction
Viral infections are the most common cause of asthma exacerbations in adults and children,1, 2 and contribute substantially to asthma-related absenteeism and admission to hospital. There has been much discussion about possible mechanisms for viral exacerbations of asthma;3, 4, 5 most attention has focused on inflammatory effects, but there is some evidence for abnormal β2-adrenoceptor function with viral infections.6, 7 Patients commonly report that inhaled β2-agonists “stop working” during a respiratory infection. This phenomenon has received little attention, despite the fact that it is frequently the trigger for presentation to a physician or emergency department;8, 9 there are no published reports about bronchodilator reversibility during viral infections in asthma.
Increased variability of peak expiratory flow (PEF) is characteristic of asthma, and decreases with inhaled corticosteroid treatment.10 Published guidelines on asthma management recommend calculation of diurnal variability of PEF, usually as daily amplitude percent mean:
for the assessment of asthma severity.11, 12, 13 Diurnal variability has also been used for prediction of impending exacerbations,14 and British Thoracic Society guidelines recommend that patients admitted to hospital for an asthma exacerbation should not be discharged until diurnal variability falls to 25%.11
These international guidelines do not make any distinction between the PEF patterns found during periods of poor asthma control and during asthma exacerbations. We tested the hypothesis that asthma exacerbations that occurred against a background of well-controlled asthma had different PEF characteristics from those seen during a period of poor asthma control. We examined PEF variation from electronic spirometric records for patients who had poorly controlled asthma before they were given inhaled corticosteroid treatment. Three periods were compared: poor asthma control (before treatment), during stable asthma before exacerbations, and during asthma exacerbations.
Section snippets
Study design
All patients had poorly controlled asthma (based on symptom frequency, night waking, and bronchodilator use) for at least 3 months before the start of monitoring, but without recent exacerbation. They completed a run-in period of 7–28 days, then received inhaled budesonide by Turbuhaler (Astra Draco AB, Lund, Sweden) twice daily for 18 months, with clinic visits every 8 weeks. Lung function was measured with a pressure differential heated pneumotach (Jaeger Masterscope version 4·17, Erich
Results
Baseline characteristics of the 26 patients who experienced at least one exacerbation are listed in table 1. All patients were skin-prick-test positive to house dust mite. Clinical characteristics and PEF indices (table 2) confirm poor asthma control during the run-in period. With inhaled budesonide treatment, average morning PEF improved from 63% to 90% predicted (mean time to plateau of PEF 10·0 [SD 5·3] weeks), and diurnal variability (amplitude % mean) fell from 21·3% to 5·3%, with good
Discussion
We have shown that patients who achieved good control of asthma with inhaled corticosteroids were still vulnerable to asthma exacerbations, usually in association with clinical respiratory infections. During these exacerbations, there was a linear decline and then a linear recovery in consecutive PEF values, with no significant increase in diurnal variability. This pattern was strikingly different from that seen during the initial period of poor asthma control, when PEF charts were
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