Measurement of Response to Isoprenaline in Asthmatic Children*

Spirometry has made possible the objective assessment of drugs used in the treatment of asthma. Many studies have been carried out to measure the bronchodilator effect of sympathomimetic amines in adults, but few studies on children have been reported. Lukas (1951) studied 6 asthmatic children between the ages of 11 and 16 years during their symptom-free period, and showed that pulmonary function could be improved by the administration of adrenaline hydrochloride subcutaneously or adrenaline by nebulizer. In a study of 30 symptom-free asthmatic children (6-16 years), Kraepelien (1958) measured the lung volume changes before and after bronchodilators, and found that there was a significant lowering of the residual volume (RV), and functional residual capacity (FRC) after these drugs. Pain and Read (1963) measured the vital capacity (VC) and forced expiratory volume in 1 second (FEV1.0), before and after 1 % iso-prenaline inhalations in 4 symptomatic asthmatic children (10-13 years). Byrepeatingthesemeasure-ments daily, they found that the greatest response to therapy was obtained early in an episode of asthma. The response to bronchodilators may be under-estimated, unless the correct timing for the post-bronchodilator tests is chosen. A study was there-fore undertaken to measure the response to a bronchodilator in relation to time. Materials and Methods Isoprenaline hydrochloride (U.S.P.) was chosen, as it is one of the most active sympathomimetic amines in relaxing the smooth muscle of the bronchial tree when given by inhalation, and acts almost exclusively on the f-receptors of the post-ganglionic adrenergic nerve endings (Goodman and Gilman, 1965). Two aspects were studied: first, the response to an inhalation was measured at timed intervals to discover when the maxi-mum effect occurred; and second, repeated inhalation