Effect of viral upper respiratory tract infection on the urge-to-cough sensation

Background: Recently, interest has emerged in the sensation of irritation that precedes the motor act of coughing; this phenomenon has been termed the urge-to-cough (UTC). Although one previous study has demonstrated a transient enhancement of cough reflex sensitivity during acute upper respiratory tract infection (URI), the effect of URI on UTC has not previously been investigated. Methods: Employing standard cough challenge methodology, we measured cough reflex sensitivity in 24 otherwise healthy adult nonsmokers during URI and again after recovery (4-8 weeks later) by determining C₂ and C ₅, the concentrations of capsaicin inducing 2 or more and 5 or more coughs, respectively. In addition, we determined the capsaicin concentration at which the UTC sensation first occurred, without an associated motor cough, and termed it C_u. Furthermore, we determined the difference between concentrations of capsaicin inducing the first motor event of cough (C ₁) and C_u, and have termed it C_Δ. Results: During URI, cough reflex sensitivity as measured by C₁ (p = 0.033) and C₅ (p = 0.001), as well as the urge-to-cough threshold, C_u (p = 0.046), were significantly enhanced compared to the post-recovery state. The degree of change in cough reflex sensitivity (C ₅) was significantly greater than that of the urge-to-cough threshold, C_u (p = 0.044). Conclusion: Our results demonstrate that the UTC sensation is transiently enhanced during URI. We also confirm the results of the lone previous study that demonstrated transient enhancement of cough reflex sensitivity during URI. The UTC threshold may represent an additional relevant end point to measure in future studies evaluating potential antitussive agents.