Physiology of the Cough Reflex: Sensory and Mechanical Features

Cough is one of the most important airway defensive mechanisms. Reflex cough shares similar features with the corresponding voluntary or behavioral motor acts. It is triggered by nociceptive stimulation of cough-related vagal afferents arising from rapidly adapting receptors and from C-fiber endings located in the larynx and tracheobronchial tree. Rapidly adapting receptors of the upper airways probably comprise a subgroup of “cough receptors” specifically sensitive to punctate mechanical stimuli and acid. The central terminus of cough-related afferents is the nucleus tractus solitarii, where also bronchopulmonary sympathetic afferents terminate. Cough can be considered a modified respiratory act that involves upper airway and chest wall muscles, and displays three or four phases. The role of respiratory muscles during normal breathing and coughing is described and the mechanical characteristics of each cough phase and related expiratory flow are illustrated.