Airway response to deep inspiration: Role of nitric oxide

Deep inspirations (DI) have been shown to have both bronchoprotective and bronchodilator effects in healthy subjects. The bronchodilator effects of a DI appear to be impaired in asthmatics compared with healthy subjects. This study investigated the role of nitric oxide (NO) in the bronchodilator role of a DI. In five anaesthetised and ventilated dogs, high-resolution computed tomography was used to measure the changes in airway size after a small (25 cmH₂O) and large (45 cmH₂O) DI before and after administering N^G-nitro-L-arginine methyl ester to block NO synthesis. The depth of the inspiratory manoeuvre during a deep inspiration determined the subsequent qualitative behaviour of the airway response. Inflation to relatively high pressure resulted in airway dilation, whereas one to lower pressure leads to airway constriction. When N^G-nitro-L-arginine methyl ester was administered, both a large and a small deep inspiration resulted in subsequent airway constriction. These results support the idea that nitric oxide may be a potential bronchoprotective agent in the airways.