Capsaicin Inhalation Test in Man

Stimulation of TRP receptors on sensory nerves is likely involved in chemically induced airway symptoms. A subgroup of patients has been identified with nonallergic, nonasthmatic symptoms from the upper and lower airway that are induced by environmental stimuli normally regarded as nontoxic. These patients have substantially increased cough response to inhaled capsaicin, known to initiate cough via TRPV1 receptors on airway sensory nerves. Hence, the condition has been termed sensory hyperreactivity (SHR). As a diagnostic tool of SHR, a standardized capsaicin inhalation cough test was developed. However, the capsaicin inhalation test can also be positive in other conditions which must be excluded before a diagnosis of SHR can be made. The capsaicin inhalation protocol described here could also be applied to testing TRP channels blockers as antitussive agents.