G. Norris Melville

Tracheobronchial function in health and disease: effect of mucolytic substances

The effect of mucolytic and expectorant substances on ciliary beat frequency, mucus transport velocity and mucus production, was investigated in normal and bronchitic rats. The results showed that: (i) N-acetylcysteine and S-carboxymethylcysteine were mildly cilioexcitatory at low and ciliodepressive at higher concentrations in both normal and bronchitic rats. A similar pattern was seen in mucus transport velocity. (ii) Bisolvon enhanced all aspects of mucociliary activity in both groups of animals. Sobrepin was less effective than Bisolvon and more effective than Tachoquilin. (iii) Geleomyrtol, Ozothin and prostaglandin E1 were all cilioexcitatory in rats with bronchitis. Mucus transport velocity was similarly stimulated by both Geleomyrtol and Ozothin. (iv) Ammonium chloride and potassium iodide enhanced mucociliary activity in normal and bronchitic rats. (v) All substances stimulated mucus production, however, the most potent was prostaglandin E1. The mechanisms for increased mucociliary activity involve inter alia the probable cleaving of disulfide bridges, decreased mucosal swelling, altered rheological characteristics and stimulation of adenylate cyclase.

Comparative Observations of Mucus Transport Velocity in Health and Disease

The present study evaluated mucus transport velocity (MTV) in different areas of the tracheobronchial tree in vitro in normal, acute and chronic bronchitic animals. The average MTV in normal animals ranged from 11.5 mm/min in the trachea to 0.64 mm/min in the pre-terminal bronchus. Chronic bronchitic animals showed mucus hypersecretion, areas of ciliary abnormality and mucus stagnation. The mean transport velocities ranged from 21.2 mm/min in the trachea to 4.1 mm/min in the pre-terminal bronchus. In the acutely ill animals, MTV ranged from 2.5 mm/min in the trachea to zero below the upper lobar bronchus. It is postulated that the higher than normal values in chronic bronchitis are due to altered mucus rheology, increased peristalsis and linear acceleration; whereas those in acute bronchitis were attributed to an early phase of viral or bacterial infection.