Chemoreceptor control of the airways.

The peripheral chemoreceptors act reflexly not only on respiration, but also on many motor systems in the respiratory tract. They cause a reflex bronchoconstriction, although this may be modified or even reversed by secondary dilator reflexes such as that from pulmonary stretch receptors. They promote a reflex secretion of mucus from submucosal glands in the trachea, and possibly other parts of the airways. They cause systemic reflex vasoconstriction both in nose (with reduction in airflow resistance) and trachea, and probably in the bronchi. There is also a reflex pulmonary vasoconstriction, although the strength of this has not been determined. The larynx dilates during peripheral chemoreceptor stimulation, as does the oropharynx. All these changes affect airway calibre, most components increasing it but some having the opposite effect. In turn these airway responses will affect lung ventilation and blood-gas tensions. The whole respiratory tract seems to be an important target organ for reflexes from the peripheral chemoreceptors.