35 Coughing


Coughing is a voluntary or reflex action in which deep inspiration is followed by forced expiration against a closed glottis. This requires strong contraction of the respiratory muscles and the larynx. The sudden opening of the glottis releases air in an explosive manner. Its passage through the vocal folds creates the characteristic sound. It may be followed by a terminal retch.

It is stimulated by irritation of the pharynx, larynx, trachea, extrapulmonary bronchi and rarely by other intrathoracic structures. The reflex is mediated by the medulla oblongata. Afferent input is supplied by the glossopharyngeal nerve (CN IX) innervating the pharynx and the vagus (CN X) which contains sensory input from the pharynx, larynx and thoracic structures. The motor arc is governed by the intercostal muscles (T1–12), the diaphragm (phrenic nerve, C5–7) and the larynx (CN X).

A weak cough, termed ‘bovine cough’ in human neurology, results from a failure to build up sufficient intrathoracic pressure due to a vagal lesion (recurrent laryngeal nerve) or generalized weakness.

A goose-honking sound is associated with tracheal collapse.

The Valsalva manoeuvre is forceful exhalation against the resistance of a closed mouth and nose, as occurs during vomiting, straining to defecate, and coughing with the subsequent release of resistance and exhalation. This gives rise to autonomically mediated cardiovascular reflexes with changes in heart rate and blood pressure and is the basis for ‘cough syncope’. Cough syncope may result from the increased intrathoracic pressure blocking venous return to the heart or strong vagal stimulation inducing vasodilation and bradycardia (vasovagal syncope).


Dogs presenting with laryngeal paralysis usually have a gradual onset of respiratory stridor, cyanosis and decreasing exercise tolerance; there may be worsening of signs in hot weather as the dog will be attempting to shift more air through the larynx to thermoregulate. Syncope is sometimes seen with light as well as vigorous exercise and animals may present in severe respiratory distress. It is only with careful questioning that a more chronic history becomes apparent. A change in bark will have been apparent in some cases.

There may also be a history of coughing, sometimes with lethargy and pyrexia. There may be a low level of irritation due to small amounts of saliva and food entering the trachea, or if more severe aspiration occurs, aspiration pneumonia may result. This has previously been thought to occur because the vocal folds are not guarding the rima glottidis as effectively as normal; however it may also be due to reduced function of pharyngeal nerves and muscles caused by the generalized neuropathy. Owners may notice this as increased coughing during eating or drinking, or if the animal struggles or is slower to eat.

Megaoesophagus is sometimes reported with this condition, and so a history of regurgitation should be ruled out. If this is diagnosed, concurrent aspiration pneumonia should always be considered and the prognosis is more guarded.

The generalized neuropathy may also lead to pelvic limb weakness. This is usually mild and may be misdiagnosed as osteoarthritis as the animals are large breed and quite old. Owners sometimes report scuffing of the nails as the dog walks on hard surfaces, or stumbling on tight turns. Weakness on rising is very common. More severely affected dogs may be unable to rise and progression of this aspect of the disease is sometimes a cause for the animal to be euthanized.

Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Coughing

Full access? Get Clinical Tree

Get Clinical Tree app for offline access