Acute changes in bronchoconstriction influences exhaled nitric oxide level

In previous studies the exhaled nitric oxide (NO) level of asthma patients was investigated only in association with bronchial inflammation, and wheth er the degree of bronchoconstriction itself influences the exhaled NO level has never been investigated. We therefore evaluated the effect of inhalati on of a bronchoconstrictor (methacholine) or a bronchodilator (salbutamol) on the exhaled NO level of healthy volunteers and asthma patients. The exha led NO level of the healthy volunteers decreased after methacholine inhalat ion. The exhaled NO level of patients with mild or moderate persistent asth ma, who had no asthma attacks on the day of measurement, increased after sa lbutamol inhalation, and the exhaled NO level of asthma patients during ast hma attacks increased after salbutamol inhalation followed by intravenous d rip infusion of aminophylline. It is suspected that large amounts of NO are trapped in the lung distal to the constricted airway, contributing little to the exhaled NO level at the mouth. However, we expect that the trapped N O is exhaled at a larger fraction after the dilatation of the constricted s mall airway, thereby increasing the exhaled NO level at the mouth, in concl usion, the results of this study suggest that acute changes in bronchoconst riction themselves influence the exhaled NO level independently of the chan ge in NO synthase activity associated with airway inflammation.