Airway responses to repeated exercises detected by krypton-81m in asthmatic children.

A repeated exercise program was used to test 7 asthmatic children for changes in ventilation. These changes were examined by continuously inhaled Krypton-81m and compared in subjects with positive and negative refractoriness, as defined by forced expiratory volume in 1 second (FEV,). Three of the seven patients showed significant refractoriness (% reduction in FEV1 >50%). After the first exercise, they showed one or two ventilation defects which improved after the second exercise. The patient with incomplete refractoriness showed similar results. On the contrary, subjects without refractoriness showed several ventilation defects which fluctuated after the second or third exercise program. One defected area improved after the second exercise session, but deteriorated after the third; and another area deteriorated after the second exercise and improved after the third. It was concluded that approximately half of the patients were refractory in view of FEV1, but that they were all refractory in view of regional ventilation Kr-81m images.