BACKGROUND--Propranolol inhalation provocation tests are used to measure indirect airways responsiveness in the investigation of asthma. In this study the effects of repeated propranolol inhalation provocation tests within the same day on normal diurnal variation in the forced expiratory volume in one second (FEV1) and subsequent propranolol airways responsiveness were investigated. METHODS--Fifteen atopic asthmatic subjects were challenged with doubling concentrations of propranolol at 08.00 and 16.00 hours on the same study day and at 16.00 hours on a control day to exclude changes related to normal diurnal variation. RESULTS--Mean (SD) baseline FEV1 at 16.00 hours on the study day was 3.38 (0.23) 1, significantly lower than the value at 16.00 hours on the control day of 3.70 (0.24) 1 (p = 0.001). No differences were found between the geometric mean provocative concentration of propranolol causing a 20% fall in FEV1 (PC20) measured on the study day (08.00 hours, 9.3 mg/ml; 16.00 hours, 11.3 mg/ml) and on the control day (16.00 hours 9.3 mg/ml). CONCLUSIONS--The results suggest that propranolol provocation at 08.00 hours has a long lasting effect on FEV1, thereby counteracting the normal diurnal increase in diameter of the airways. This makes propranolol challenge tests less suitable for studying indirect airways responsiveness in the course of one day. Because the FEV1 does not return to control values, it is not possible to determine whether tachyphylaxis to repeated propranolol challenge with a time interval of up to eight hours occurs.
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