Neural and Humoral Control of the Airways

This chapter presents a brief overview of the neural humoral control of airway nerves. Airway nerves and circulating hormones regulate the caliber of the airways and have an influence on airway smooth muscle tone, airway blood flow, and mucus secretion. They may also influence the inflammatory process and play an integral role in host defense. Several neural mechanisms are involved in the regulation of airway caliber and abnormalities in neural control may contribute to airway narrowing in disease. There is a close interrelationship between inflammation and neural responses in the airways, since inflammatory mediators may influence the release of neurotransmitters via activation of sensory nerves leading to reflex effects and via stimulation of pre-junctional receptors that influence the release of neurotransmitters. Airway afferent nerves may become sensitized in inflammatory airway diseases, resulting in increased symptoms, such as cough and chest tightness. Cough is a prominent symptom of asthma and COPD, and there is evidence that cough sensitivity is increased. This may be due to senitization of afferent nerves in the airways as a result of inflammatory mediators produced during asthma and COPD. Humoral mechanisms play a more important role in the regulation of airway tone in diseased states of the airways such as asthma and possibly in other disorders such as COPD, cor pulmonale, congestive cardiac failure, respiratory failure, and thyroid disease.