Elsevier

The Lancet

Volume 353, Issue 9150, 30 January 1999, Pages 364-369
The Lancet

Articles
Differences between asthma exacerbations and poor asthma control

https://doi.org/10.1016/S0140-6736(98)06128-5Get rights and content

Summary

Background

Increased variation in peak expiratory flow (PEF) is characteristic of poorly controlled asthma, and measurement of diurnal variability of PEF has been recommended for assessment of asthma severity, including during exacerbations. We aimed to test whether asthma exacerbations had the same PEF characteristics as poor asthma control.

Methods

Electronic PEF records from 43 patients with initially poorly controlled asthma were examined for all exacerbations that occurred after PEF reached a plateau with inhaled corticosteroid treatment. Diurnal variability of PEF was compared during exacerbations, run-in (poor asthma control), and the period of stable asthma before each exacerbation.

Findings

Diurnal variability was 21·3% during poor asthma control and improved to 5·3% (stable asthma) with inhaled corticosteroid treatment. 40 exacerbations occurred in 26 patients over 2–16 months; 38 (95%) of exacerbations were associated with symptoms of clinical respiratory infection. During exacerbations, consecutive PEF values fell linearly over several days then improved linearly. However, diurnal variability during exacerbations (7·7%) was not significantly higher than during stable asthma (5·4%, p=0·1). PEF data were consistent with impaired response to inhaled β2-agonist during exacerbations but not during poorly controlled asthma.

Interpretation

Asthmatics remain vulnerable to exacerbations during clinical respiratory infections, even after asthma is brought under control. Calculation of diurnal variability may fail to detect important changes in lung function. PEF variation is strikingly different during exacerbations compared with poor asthma control, suggesting differences in β2-adrenoceptor function between these conditions.

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:

maximum PEFminimum PEFmean PEF(%)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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