Patterns of variation in airflow obstruction and risk of death in clinically stable asthma.

In an attempt to identify patterns of variation in airflow obstruction and to detect patients with marked bronchial lability, a factor reported to be associated with an increased risk of sudden asthma death, we obtained serial peak expiratory flow rate (PEFR) recordings from out-patients with chronic, clinically stable, asthma (N = 27) for one week. Similar recordings were obtained for comparison from out-patients with chronic obstructive pulmonary disease (COPD) (N = 14) and from healthy controls (N = 14). Analysis of the recordings disclosed patterns of PEFR variation for 20 asthmatics but not for COPD patients or healthy subjects. Ten asthmatics were classified as "brittle" asthmatics (BA), nine as morning dippers (MD) and one as a gradually deteriorating (GD) asthmatic. Patients were considered at risk when their diurnal fall (DF) in PEFR was greater than 50% on at least one occasion during the survey. This was the case for seven BA, three MD and one GD patient. Diurnal falls in PEFR of this magnitude were not observed among asthmatics without a discernible pattern of variation of airflow obstruction or COPD patients. A relationship was found between the amplitude of PEFR fluctuations and the frequency of significant DF in PEFR (greater than 25%) during half or more days of the survey. A significant fraction of out-patients with chronic, clinically stable asthma may present patterns of variation in airflow obstruction and diurnal falls in PEFR of a magnitude such as has been associated with sudden asthma death.