Effect of viral upper respiratory tract infection on cough reflex sensitivity

Abstract

Acute viral upper respiratory tract infection (URI; common cold) is among the most common medical conditions affecting man, with cough being a typical feature of the associated syndrome. Studies employing capsaicin inhalation challenge to measure cough reflex sensitivity have demonstrated a transient tussive hyperresponsiveness induced by URI that reverts to normal by 4-8 weeks post infection. Mechanisms proposed to explain the induction of cough by URI include a number of infection-associated airway effects, such as enhanced release of cytokines, neurotransmitters, and leukotrienes; increased neural receptor levels; reduced activity of neutral endopeptidases; transient modulation of afferent neural activity; mucus hypersecretion; and, possibly, effects on cholinergic motor pathways. Recent studies evaluating urge-to-cough (UTC), the sensation of irritation preceding the motor act of coughing, have demonstrated that URI induces a transient enhancement of UTC analogous to the effect observed on cough reflex sensitivity. The recently introduced concept of the Cough Hypersensitivity Syndrome may provide an explanation for the commonly observed clinical phenomenon of acute viral URI triggering what will develop into chronic, refractory cough in a subgroup of patients.

Keywords: Cough; capsaicin; common cold; viral infection; virus.

Figures

Figure 1

Typical dose-response curve observed during capsaicin inhalation challenge. In this subject, C2, the concentration of capsaicin inducing two or more coughs, is 7.8 µM; C5, the concentration of capsaicin inducing five or more coughs, is 31.25 µM.

Figure 2

Mean values for log C5 (open circles) and log Cu (solid circles) during viral upper respiratory tract infection (URI) and after recovery (4-8 weeks after URI). Error bars indicate ±SEM. Values were significantly lower (i.e., sensitivity enhanced) during URI. *P=0.046; **P=0.001. C5 was affected to a greater degree by URI than was Cu (P=0.044). [from Reference (8), with permission].

Figure 3

Mean log C5 values for subjects (n=42) measured on consecutive days during the first 8 days of acute viral upper respiratory tract infection (URI-1 and URI-2), and 4-8 weeks after URI (recovery). Error bars indicate ±SEM.