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The aim of this study was to look at changes in peak expiratory flow rates (PEFR) prior to emergency department visits for decompensated chronic obstructive pulmonary disease (COPD). It was designed as a prospective, double-blind study at the Albuquerque Veterans Affairs Medical Center. Twelve patients with an irreversible component of airflow obstruction on pulmonary function tests were assessed. At entry, all subjects were instructed in the use of a mini-Wright peak flow meter with electronic data storage. They then entered a 6-month monitoring phase in which they recorded PEFR twice daily, before and after bronchodilators. The meter displays were disabled so that the patients and their physicians were blinded to all values. Medical care was provided in the customary manner. Patients were considered to have respiratory decompensation if they required treatment for airflow obstruction in the Emergency Department (ED) and no other causes of dyspnea could be identified. Simple linear regression was used to model changes in PEFR over time. The 12 subjects had 22 episodes of respiratory decompensation during 1741 patient-days of observation. Two episodes could not be analysed because of missing values. Ten episodes in seven subjects were characterized by a significant linear decline in at least one peak flow parameter prior to presentation. The mean rates of change for the four daily parameters varied from 0.22% to 0.27% predicted per day (or 1.19 to 1.44 1 min-1 day-1). The average decrement in these parameters ranged from 30.0 to 33.8 1 min-1 (or 18.6%-25.9% of their baseline values). No temporal trends were found for the 10 episodes occurring in the other five subjects. We concluded that respiratory decompensation is characterized by a gradual decline in PEFR in about half of cases. Future studies should be done to elucidate the mechanisms of respiratory distress in the other cases.