The Wright peak expiratory flow meter was introduced in 1959¹ and provided a portable piece of equipment for assessing some aspects of lung function in the ambulatory care setting. The original device has been supplanted by the mini Wright peak flow meter (and a range of other devices) which have become relatively cheap but are reasonably reliable for home monitoring.²

So, with an available device for measuring peak expiratory flow (PEF), what is its role in the 21st century? PEF reflects a range of physiological characteristics of the lungs, airways, and neuromuscular characteristics of individuals. These include lung elastic recoil, large airway calibre, lung volume, effort, and neuromuscular integrity.³ The reflection of airway calibre makes the PEF meter suitable for measuring variation in PEF over time to provide support for:

• confirmation of the diagnosis of asthma;

• diagnosis of occupational asthma;

• monitoring variation in PEF over time;

• identification of asthma control;

• use in self-management of asthma by patients via written action plans based on changes in PEF.

We must note that the PEF is not the same as the forced expiratory volume in 1 second (FEV₁)—either in repeatability or in the interpretation of what it is measuring—and they cannot necessarily be interchanged.⁴ An earlier trend to suggest regular PEF monitoring for many asthmatics has been modified as issues of balancing adherence versus need versus usefulness have been recognised. Regular PEF monitoring in asthma does remain relevant in particular situations such as monitoring of poor perceivers of symptoms.⁵

The report by Reddel et al⁶ in this issue of Thorax highlights a further advance in the evidence for the use of PEF monitoring. The identification of best PEF provides a target for individual asthma patients and treating health professionals to enable the development of action plans and for the assessment of asthma control. The finding by Reddel et al⁶ that, on average, the best PEF can be determined using high dose inhaled corticosteroids for 3 weeks from an unstable asthma state with twice daily PEF measurements therefore provides helpful information for the treating doctor. It is noteworthy that the time frame moves out to approximately 8 weeks if a single daily morning measurement of PEF is done—possibly a reflection of the number of measurements, but the time for drug effect cannot be dismissed.

Can we translate these data to our usual practice? The answer has to be a cautious yes because of (a) the use of electronic spirometers in the study and (b) the involvement of the patients in a clinical trial. Neither of these conditions is available to the usual asthma patients. However, the concept of an average of 3 weeks of inhaled budesonide (1600 μg) or its equivalent to achieve best PEF with twice daily readings provides a sound basis for the therapeutic trial which may become more important in the diagnosis as well as the management of asthma. Daily morning PEF monitoring in the study by Reddel et al⁶ showed that an average of 8 weeks of high dose inhaled corticosteroid treatment study is needed to obtain the best PEF across a population of at least moderate and even severe asthma. We can therefore take away two messages from this study. The first is that, in reliable morning PEF data, a period of 8 weeks of high dose inhaled corticosteroids results in identification of the best PEF function for individuals on average. The second message is that, on average, 8 weeks of treatment with up to 1600 µg budesonide daily or its equivalent is a reasonable therapeutic trial for diagnosis or identifying best function in symptomatic patients. This is an important concept because the therapeutic trial over a period of time to confirm a diagnosis of asthma is likely to become more important, given the recognised reduced usefulness of a single bronchodilator response in either predicting future management or in diagnosis.⁷

Other data have supported an 8 week time frame for maximising the major airway effects of inhaled corticosteroids.^8,9 Providing we are not absolute in our application of average data, the study by Reddel et al can be usefully applied in day to day clinical practice and provides a guide to an appropriate level of inhaled corticosteroid for a treatment trial. The study has not necessarily identified the lowest dose, but the time frame of 8 weeks for daily morning PEF measurements and the dose equivalent of 1600 μg inhaled budesonide seems to provide a reasonable baseline for clinical practice. It is possible that a lower dose of inhaled corticosteroids may be effective in a therapeutic trial, and this needs to be tested despite a recent meta-analysis.¹⁰ The combination of an inhaled corticosteroid with a long acting β agonist is likely to have a place in the future therapeutic trial.

A further question to be answered for treatment trials is whether the PEF (maximum) before and at the completion of a treatment trial is compared or whether it is the change in PEF variation. In children, questions have been raised about PEF monitoring missing important changes.¹¹ We therefore must remember that much of our evidence base relates to averages, and in the clinical setting we should individualise our assessments and management. The diagnosis of asthma remains a clinical diagnosis.