Relationship between changes in diurnal variation of expiratory flows, lung volumes and respiratory symptoms after acute asthma.

We looked at the comparative recovery of asthma symptoms and changes in airflow obstruction after an acute exacerbation of asthma in 26 asthmatics, aged 18-69 years (mean = 43). In the 4 weeks following the acute episode, they recorded their respiratory symptoms and twice-daily peak expiratory flow rates (PEFR). In 14 subjects, lung volumes were also measured on days 1, 7 and 30. Mean initial FVC and FEV1 [+/- SEM (% predicted)] were 2.30 +/- 0.16 (61%) and 1.18 +/- 0.08 (39%). The rate of improvement of airflow obstruction initially paralleled that of asthma symptoms in subjects with mild or with a recent onset of asthma. On the first study day, diurnal variation of PEFR was minimal, increased rapidly during the first week of treatment and stabilized thereafter. Mean daily delta PEFR was significantly higher in the first than at the fourth week (P = 0.005). Recovery of asthma symptoms was associated with an overall reduction in FRC and RV but there was no significant correlation between FRC or RV and dyspnea score or PEFR. Perception of airflow obstruction was generally lower, improvement of symptoms slower and of smaller amplitude in those with long-standing asthma. In conclusion, during recovery from acute asthma: (1) diurnal variation of PEFR is initially minimal, increases rapidly after beginning steroids and stabilize in the two following weeks; (2) in patients with more than mild or long-standing asthma, and magnitude and range of perception of asthma symptoms is reduced and correlates less with PEFR; and (3) no significant correlation could be found between FRC or RV and dyspnea score or PEFR.