Clinical application of nasal nitric oxide measurement.

Nitric oxide is present in high concentration in the upper respiratory tract. The main source of this gaseous molecule is the paranasal sinus epithelium. The physiological role of this mediator is to contribute to local host defense, modulate ciliary motility and serve as an aerocrine mediator in helping to maintain adequate ventilationperfusion matching in the lung. Abnormal values of nasal NO (nNO) have been reported in different pathological conditions of the respiratory tract. Reduced nNO values have been recorded in subjects with acute and chronic sinusitis, cystic fibrosis and nasal polyps. Particularly low concentrations have been described in children with primary ciliary dyskinesia, so nNO measurement has been proposed as a reliable screening test for this chronic lung disease.