PT - JOURNAL ARTICLE AU - K D Dawkins AU - M F Muers TI - Diurnal variation in airflow obstruction in chronic bronchitis. AID - 10.1136/thx.36.8.618 DP - 1981 Aug 01 TA - Thorax PG - 618--621 VI - 36 IP - 8 4099 - http://thorax.bmj.com/content/36/8/618.short 4100 - http://thorax.bmj.com/content/36/8/618.full SO - Thorax1981 Aug 01; 36 AB - Twelve patients fulfilling strict criteria for chronic obstructive bronchitis recorded serial peak expiratory flow rates (PEFR) five times daily for a two-week period. Despite a 9.2% improvement in forced expiratory volume in one second (FEV1) with ipratropium bromide, and an 11.3% improvement with ipratropium bromide plus salbutamol, the inherent diurnal variation in PEFR while on no medication was greater than the improvement caused by either bronchodilator. In the group as a whole, the difference between the highest and the lowest daily PEFR over the two weeks was 24% of the mean daily value. Using cosinor analysis, 10 of the 12 patients showed a significant rhythm in PEFR with a computed mean amplitude between highest and lowest readings of 8.6% of the mean daily value. This is no greater than that found in normal subjects, but is considerably less than the variation in PEFR in patients with bronchial asthma.