Aim: 

Nasal diseases are common causes of chronic cough. Accordingly to the idea of cough plasticity we designed the studies to address the effect of stimulation of nasal afferents on experimentally induced cough in laboratory animals and human volunteers.

Methods: 

SurveyA) Intranasal challenges with capsaicin (50mM) and histamine (16mM) were performed in anaesthetized cats (n = 13) and guinea-pigs (n = 15) and in 15 conscious guinea-pigs. Coughing was provoked after these challenges by mechanical stimulation of the larynx and tracheobronchial region in anaesthetized animals and by inhalation of 0.3M of citric acid aerosol in awake animals placed in bodyplethysmograph. Parameters of cough reflex were evaluated from either interpleural or esophageal pressures in anesthetized animals and from pneumotachographic traces in conscious guinea-pigs during cough expulsions. SurveyB) Healthy volunteers (32) and patients with allergic rhinitis (20), mean age 27.1 yr, 26M/26F, nonsmokers, with normal FVC/FEV1, without acute respiratory infection in past four weeks, were randomly challenged with intranasal capsaicin (750mM, 25ml) and histamine (4mg/ml 25 ml) versus saline. Nasal symptom score, cough sensitivity to inhaled capsaicin and number of coughs during provocation were determined.

Results: 

Intranasal stimulation with capsaicin and histamine increases the cough response in anaesthetized and conscious animals. Nasal stimulation enhances the cough response in healthy humans and this facilitation of the cough response is exaggerated extremely in allergic subjects.

Conclusion: 

We speculate that facilitation of the cough response could be the consequence of increased afferent inputs from the nose into the brainstem thus stimulating synaptic activity of cough pattern generator.