Diurnal Variability of Peak Expiratory Flow

Diurnal variation in peak expiratory flow (PEF_var) has been suggested as a surrogate for bronchial hyperreactivity, and may be a useful tool in the management of bronchial asthma. Several indices have been postulated to measure PEF_var; however, the number of daily measurements and the timing of recordings are not clearly established. Although several investigators have defined ranges for PEF_var in healthy individuals, clear cutoff values that differentiate asthmatics from others are not available. Despite this shortcoming, PEF_var is an important measurement in screening and diagnosis of asthma in population-based studies, as well as for assessing disease severity and prognosis. Treatment of asthma with either inhaled corticosteroids or bronchodilators may influence the magnitude of PEF_var in a complex fashion. Therefore, PEF_var should only be interpreted in conjunction with other clinical and laboratory information.