Comparison of cumulative and non-cumulative techniques to measure dose-response curves for beta agonists in patients with asthma.

It has been suggested that the use of a cumulative technique to obtain bronchodilator dose-response curves will cause a greater response than a non-cumulative technique, because sequential doses of drug will penetrate further into the lung. To test this hypothesis we have compared cumulative and non-cumulative dose-response curves for inhaled isoprenaline in 10 subjects with stable asthma, measuring FEV1, forced vital capacity (FVC), and peak expiratory flow rate (PEFR). With both techniques there was an increased response with increasing doses of isoprenaline for all the dose-response curves except for the non-cumulative PEFR response, which reached a plateau with the 20 micrograms dose. The area under the dose-response curve for FEV1 was significantly greater after cumulative administration of isoprenaline than with the non-cumulative technique. The increase in FVC and PEFR tended to be greater with the cumulative technique but the differences were not significant. This study confirms that the airway response to an inhaled beta agonist may be greater when a cumulative inhalation technique is used.