For example, it has been recognized that the patient's subjective symptoms, and physician's subjective assessment correlate poorly with pulmonary function, and that declines in pulmonary function may predate acute exacerbations of asthma. Poor perceptions of severity of symptoms by either the physician or patient may lead to delays in treatment. Peak expiratory flow rates provide a simple, quantitative measure of airflow obstruction which can be performed in the home, school, workplace or office for a quick measure of lung functions. Declines in PEFR may prompt changes in asthma management. Monitoring PEFR for 2 or more weeks can help establish patterns of variability and a diagnosis of asthma.
Daily monitoring can also identify environmental triggers and guide decisions for therapy.
Ideally, patients measure their PEFR twice daily and record the values along with any concurrent symptoms in a symptom diary. In addition to establishing the diagnosis, the data can be used to assess the patient's disease severity for use in developing an individualized Asthma Action Plan, particularly in patients with moderate to severe persistent asthma, where exacerbations are most prevalent. The patient's personal best PEFR serves as a baseline measurement that other measurements are compared to. The personal best is typically recorded in the early afternoon when therapy has stabilized the patient's symptoms. After the personal best is established, the PEFR should be measured upon awakening, before the use of a bronchodilator.