The mechanism of cough

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Sensing something is wrong…

Both the upper and lower airways are lined by slow-reacting and fast reacting receptors which can respond to a number of different types of stimuli ranging from dust to irritant gases as well as excess mucus. Once the receptors are triggered, a signal is sent via the vagus nerve, setting up a reflex with the signal being transmitted to your brainstem and consciousness making you aware that you need to clear these noxious particles or gases.

Preparing for the cough…

The cough centre situated in the medulla in a matter of milliseconds, makes your consciousness aware of the fact that you need to cough as well as sending impulse back down to the diaphragm and intercostal rib muscles, preparing them for the cough action.

The first action is that the diaphragm ‘drops’ to suck air into the chest filling the thoracic cavity. The second action following the diaphragm movement is the glottis or ‘voice box’ closes to prevent any air from leaving the chest.

Finally the actual cough…

Thereafter the cough centre triggers the diaphragm and intercostal muscles to contract, making the thoracic cavity smaller and building up pressure inside the chest… then the closed glottis opens allowing the high pressure air to suddenly escape from the chest through the airways hopefully taking with it any irritating particles, foreign bodies or phlegm which triggered the entire reflex to start with. Air leaving the chest can reach speeds of up to 200 km/h and even faster in the event of a sneeze! 

Compiled February 2011 by Dr. Greg Symons [MB. ChB, DipPEC, FCP (SA), Cert. Pulm. (SA)], Consultant Pulmonologist, Division of Pulmonology, Department of Medicine, Groote Schuur Hospital & Clinical Researcher, UCT Lung Institute (Pty) Ltd www.lunginstitute.co.zain George Street, Mowbray. Contact the UCT Lung Institute on ph 021 406 6850.

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