Pulmonary pharmacology
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Pulmonary pharmacology · Oct 1996
The role of capsaicin-sensitive C-fibre afferent nerves in the cough reflex.
While airway rapidly adapting receptors can mediate the cough reflex, much evidence suggests that bronchial C-fibre receptors are also involved in guinea-pigs and man. In man local and systemic C-fibre stimulants have a potent tussive action, which is blocked by low doses of local anaesthetics which leave the reflex bronchoconstriction intact. ⋯ Thus there may be subpopulations of airway C-fibres responsible for the different reflexes such as apnoea, cough and bronchoconstriction. The evidence for the role of C-fibre receptors in cough is described and discussed.
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Both human and animal studies show that irritation of airway mucosa elicits a variety of reflex responses such as coughing, apnoea, and laryngeal closure. Most of the information concerning these reflex responses were obtained in anesthetized conditions with little applicability to awake conditions. Various aspects of cough and other reflexes on irritation of the airway mucosa are discussed. ⋯ An increase in depth of anesthesia abolishes expiratory efforts such as coughing and the expiration reflex whereas the apnoeic reflex and laryngeal closure reflex are resistant to the depressant effect of anesthesia. Also, the respiratory reflex responses to airway irritation varied, depending on the site of stimulation: both laryngeal and tracheal stimulation cause vigorous respiratory responses whereas bronchial stimulation causes little or no respiratory responses. These results indicate not only that the types and magnitude of reflex responses is greatly modified by the central nervous state but also that the site of stimulation is crucial for determining the pattern of respiratory responses elicited by airway stimulation in humans.