Chronic cough and the cough reflex in common lung diseases

Following the experience of asthma, characterised by the presence of bronchial hyper-responsiveness, the notion has been accepted that the chronic cough of disease occurs as a result of altered sensitivity of the afferent limb of the cough reflex. Methods for testing for the 'threshold' for eliciting the cough reflex have also been borrowed from asthma care. In the main aerosols are inhaled that contain the relevant stimulus.A number of factors influence the cough response to inhaled aerosols. The distribution of the inhaled aerosol is important as certain chemically sensitive receptors are distributed in different regions of the lungs. The larynx and central airways are important but so too are the peripheral airways. The degree of bronchodilatation is also important as airway narrowing can, itself, induce coughing in man.Asthma, oesophageal reflux and rhinitis patients experience increased coughing, that is associated with increased sensitivity to inhaled capsaicin. In syndromes of chronic obstructive pulmonary disease (COPD) and interstitial lung disease (ILD) increased sensitivity to coughing with capsaicin is common. This appears a specific effect of the pathogenic process of the disease. Modification of the disease process can lessen coughing and the sensitivity to capsaicin.