Cough-inducing capsaicin challenge test in a healthy population

Objective: Cough-inducing agents are used to study the cough reflex in both pharmacological and physiological research. Clinical use of cough challeng e testing as a tool in diagnostic algorithms has been limited by the lack o f 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 th e test. Material and methods: Ninety-two healthy subjects were enrolled and given a capsaicin challenge test using concentrations from 0.49 to 500 mg. The con centrations of capsaicin that triggered two and five coughs, C-2 and C-5 re spectively, were recorded. The test was repeated three days later in a sub- sample of 30 subjects. Results: No subject showed clinical or functional signs of bronchoconstrict ion. The mean values obtained for the study population were log C-2: 1.5 +/ -0.69 mM. and log C-5: 2.1 +/-0.4 muM. The geometric means were 31.6 and 13 4.8 muM for C-2 and C-5, respectively. No significant differences were foun d for sex or smoking; however age was significantly related to log C-5 (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 C-2 and C-5 respectively. Conclusion: The capsaicin challenge test was safe and easy to administer, g ave reproducible results and allowed us to obtain reference values for a he althy population in our community.