Role of the parasympathetic cholinergic system in normal and obstructed airways.

The cholinergic motor component of the parasympathetic nervous system supplies several structures which may be important in determining the resistance of normal and diseased airways. Lower airway smooth muscle. Here the nervous control is predominantly cholinergic and vagal, as shown by nerve and field stimulation experiments, and by inhibition of contraction by atropine. The cholinergic motor system can be driven reflexly, and most bronchoconstrictor reflexes have been established as vagal and cholinergic. The importance of other innervations, adrenergic and non-adrenergic, non-cholinergic, has not been established. Mucus secretion. As for smooth muscle, this has multiple innervation but, at least in health, the dominant control is vagal and cholinergic, and blocked by atropine. The importance of mucus secretion in causing airway obstruction has yet to be quantified. Sub-mucosal tissues. The effect of cholinergic nerves on the airway vasculature, and on associated structures such as mast cells, is a possibility requiring study. The larynx. Several recent studies have shown that laryngeal constriction occurs in lower airways disease, and must contribute to the changes in total airway resistance. This constriction would be cholinergic but atropine-resistant. The nose. Cholinergic parasympathetic nerves cause nasal congestion and secretion, and therefore changes in nasal airflow resistance. This is a potentially important factor in changing the balance between nasal and oral breathing and thus affecting the conditioning of inspired air.