Time factor in the measurement of response to bronchodilators

Abstract

The measurement of response to bronchodilators by recording the change in forced expiratory volume in 1 second (F.E.V._1·0) can underestimate response unless the correct time for postbronchodilator tests is chosen. In 18 patients given isoprenaline, the time of peak response varied, but a 30-minute testing time gave the closest approximation to peak response. In order to test whether repeated doses would increase the response, inhalations of isoprenaline were given at 30-minute intervals, the F.E.V._1·0 being measured after each dose. There was a further response after successive doses until a plateau was reached, usually after the third dose. The maximum response obtained was often considerably greater than the response after the first administration of isoprenaline, the average increase in F.E.V._1·0 being 600 ml. after the first dose and 840 ml. after repeated doses. A similar response was obtained in four patients using orciprenaline spray administered with a metered aerosol, the dose being repeated at hourly intervals. Four patients were given repeated inhalations of isoprenaline until the response reached a plateau, and then 250 mg. of aminophylline was injected intravenously. None of these patients showed any further improvement with aminophylline. The significance of these findings is discussed.