MEDizzy - You are riding the bus home after a busy clinic one day. A

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Cardinal Manifestations and Presentation of Diseases 2

You are riding the bus home after a busy clinic one day. A man sits next you and, ignoring the easily seen signs, begins to smoke a cigarette. You feel a “tickle in your throat” and then proceed to cough. All of the following statements regarding the cough are true EXCEPT:

ExplanationAlthough common in everyday life, the cough refex is really quite intricate. First, some sensory input must trigger it. Spontaneous cough is triggered by stimulation of sensory nerve endings that are thought to be primarily rapidly adapting receptors and C fbers. Both chemical (e.g., capsaicin) and mechanical (e.g., particulates in air pollution) stimuli may initiate the cough refex. Aferent nerve endings richly innervate the pharynx, larynx, and airways to the level of the terminal bronchioles and extend into the lung parenchyma. In some patients, they may also be located in the external auditory meatus (the auricular branch of the vagus nerve, or the Arnold nerve). To initiate the cough, the vocal cords adduct, leading to transient upper-airway occlusion. Expiratory muscles contract, generating positive intrathoracic pressures as high as 300 mmHg. With sudden release of the laryngeal contraction, rapid expiratory fows are generated, exceeding the normal “envelope” of maximal expiratory fow seen on the fow-volume curve Bronchial smooth muscle contraction, together with dynamic compression of airways, narrows airway lumens and maximizes the velocity of exhalation. The kinetic energy available to dislodge mucus from the inside of airway walls is directly proportional to the square of the velocity of expiratory airfow.