Small and large airways' reactions to inhaled capsaicin in patients with chronic idiopathic cough, or asthma and in healthy control subjects

Aims: Cough is a common medical problem, and when it persists for more than 8 weeks it is arbitrarily defined as chronic. While spirometry assesses the large airways, impulse oscillometry system (IOS) measures peripheral airway function. The present study investigated whether provocation with inhaled capsaicin affects the large and small airways in patients with chronic idiopathic cough (CIC) or asthma and in healthy controls. Materials and methods: Twenty-one patients with CIC, 18 patients with asthma, and 22 healthy controls were subjected to a provocation with capsaicin, and lung function was assessed by IOS and spirometry. Results: At baseline, before the capsaicin provocation, the CIC group had significantly increased airway resistance compared to the controls. After capsaicin provocation, the CIC group exhibited a significant increase in total airway resistance. The asthma group showed a small but significant reduction in spirometry, increased airway resistance, and reactance after capsaicin provocation. Capsaicin inhalation affected neither the spirometry nor the IOS of the healthy controls. Conclusions: The present study demonstrates that inhaled capsaicin induces changes in lung function, both in patients with CIC and in patients with asthma, when IOS, which measures changes also in the peripheral airways, is used. IOS appears to be a more sensitive tool than spirometry for the detection of airway impairment in airway provocation studies. In patients with CIC, higher peripheral resistance at baseline may have clinical significance.