[Sputum viscosity and respiratory tract obstruction in chronic unspecific airway diseases]

The relationship between the physico-chemical characteristics of sputum and pulmonary function tests was investigated in patients with chronic nonspecific airway diseases. 141 sputum specimens were categorized on the basis of neutrophil content as slightly inflammatory (mucoid), inflammatory (mucopurulent) and highly inflammatory. "Apparent" viscosity, fucose and N-acetylneuraminic acid content were determined. Forced vital capacity, forced expiratory volume in one second and maximal voluntary ventilation measurements were performed simultaneously for each patient. "Apparent" viscosity and fucose content did not differ among the sputum categories; N-acetylneuraminic acid was slightly increased in the inflammatory sputa. There was a statistically significant inverse correlation between "apparent" viscosity, forced expiratory volume and maximal voluntary ventilation. In contrast, "apparent" viscosity did not correlate with forced vital capacity. As for the bronchial glycoprotein components, fucose correlated directly with "apparent" viscosity, whereas N-acetylneuraminic acid did not. "Apparent" viscosity was approximately the same in all sputum categories; it did not depend on the sputum neutrophil frequency except in the case of the slightly inflammatory, mucoid sputa in which "apparent" viscosity correlated indirectly with the sputum neutrophil frequency. These results show that physicochemical characteristics of sputum or bronchial secretions may play an important role in obstruction of the airways in patients with chronic nonspecific airway diseases. In the case of low inflammation of the bronchi, bronchial glycoproteins produced in the hypertrophied tracheobronchial glands and goblet cells are mainly responsible for increased "apparent" viscosity. With increasing inflammation of the bronchi, factors other than bronchial glycoproteins appear to determine this flow property.