The effects of oral slow-release terbutaline on the circadian variation in spirometry and arterial blood gas levels in patients with chronic airflow obstruction.

The circadian variation of spirometry and blood gases was studied in eight male, normoxemic, patients with chronic air flow obstruction and complaints of early morning dyspnea. The patients were selected for a high amplitude in circadian variation of PEFR. They were treated for eight days with placebo and slow-release terbutaline tablets (5 mg at 8 am and 10 mg at 8 pm). Thereafter, arterial blood gas levels were measured at four-hour intervals over 24 hours. Just after blood sampling, FEV1 measurements were performed. The results on placebo therapy were compared with results in eight healthy volunteers matched for age, sex, and smoking habits. The circadian rhythms of FEV1, PaO2, and SaO2 in these patients showed a higher amplitude than in normal subjects. The decrease of FEV1 in the patient group at 8 am coincided with the decrease in PaO2 and SaO2. In normal subjects no significant nocturnal fall in FEV1, PaO2, or SaO2 occurred. Administration of slow-release terbutaline tablets for eight days, providing comparable diurnal and nocturnal serum levels, prevented the nocturnal decrease of FEV1, PaO2, and SaO2. The increase of the FEV1 at all hours of observation showed a significant correlation with the increase of the PaO2.