[Cough-inducing capsaicin challenge test in a healthy population]

Cough-inducing agents are used to study the cough reflex in both pharmacological and physiological research. Clinical use of cough challenge testing as a tool in diagnostic algorithms has been limited by the lack of either uniform methodology or reference values for healthy subjects. The objective of this study was to determine the cough threshold for capsaicin in a sample of healthy subjects, while also evaluating the influence of age, sex and smoking. We also assessed the reliability and repeatability of the test.

Ninety-two healthy subjects were enrolled and given a capsaicin challenge test using concentrations from 0.49 to 500mg. The concentrations of capsaicin that triggered two and five coughs, C2 and C5 respectively, were recorded. The test was repeated three days later in a sub-sample of 30 subjects.

No subject showed clinical or functional signs of bronchoconstriction. The mean values obtained for the study population were log C2:1.5 +/- 0.69 mM. and log C5: 2.1 +/- 0.4 microM. The geometric means were 31.6 and 134.8 microM for C2 and C5, respectively. No significant differences were found for sex or smoking; however age was significantly related to log C5 (r: -0.27, p < 0.05). Repeatability of the capsaicin test was high, with intra-class correlation coefficients and 95% confidence intervals of 0.75 (0.53-0.87) and 0.88 (0.76-0.97)for C2 and C5, respectively.

The capsaicin challenge test was safe and easy to administer,gave reproducible results and allowed us to obtain reference values for a healthy population in our community.