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Capsaicin cough sensitivity increases during upper respiratory infection
F O'Connell1, V E Thomas, J M Studham
1Department of Clinical Pharmacology, Royal Postgraduate Medical School, London, U.K.
Respiratory Medicine
|May 1, 1996
Summary
Upper respiratory infections (URIs) may cause cough by increasing the sensitivity of airway nerves. This study found heightened capsaicin sensitivity during URIs, particularly in dry cough cases, without affecting airway responsiveness.
Area of Science:
- Respiratory Medicine
- Neuroscience
- Immunology
Background:
- The mechanisms underlying cough during upper respiratory infections (URIs) remain unclear.
- Capsaicin-sensitive afferent airway nerves are implicated in cough reflex sensitivity.
Purpose of the Study:
- To investigate the role of altered capsaicin-sensitive airway nerve sensitivity in URI-associated cough.
- To assess changes in cough reflex sensitivity and airway responsiveness during URI.
Main Methods:
- A prospective study involving 103 healthy volunteers.
- Baseline, URI, and recovery challenge testing with capsaicin and methacholine.
- Measurement of log concentration of capsaicin required to elicit two (C2) and five (C5) coughs.
- Assessment of FEV1 and methacholine-induced airway responsiveness (PC15).
Main Results:
- Log C2 and C5 values were significantly lower during URI compared to recovery and baseline, indicating increased cough reflex sensitivity.
- Increased capsaicin sensitivity correlated with cough severity in subjects with dry cough.
- FEV1 and methacholine responsiveness remained unchanged during URI.
- Control subjects without URI showed no changes in capsaicin sensitivity.
Conclusions:
- URI can lead to cough due to increased sensitivity of capsaicin-sensitive afferent airway nerves.
- This heightened sensitivity occurs without significant changes in airway caliber or responsiveness.
- The findings suggest a specific neural mechanism contributing to URI-induced cough, particularly dry cough.