On the relation between capsaicin sensitivity and responsiveness to CO2: detection sensitivity and event-related brain potentials

Objective  Sensory hyperreactivity (SHR) with predominantly airway symptoms is a subgroup of chemical intolerance to various environmental substances with pungent/odorous properties. The hallmark of SHR is sensitivity to capsaicin inhalation, resulting in extensive coughing likely to be mediated by a C-fiber hyperreactivity of the airway sensory neurons. However, it is not clear whether capsaicin sensitivity implies a greater sensitivity to chemosomatosensory substances in general. Therefore, the present study tested the hypothesis of an association between capsaicin cough sensitivity and sensitivity to CO₂ with respect to detection sensitivity and electrophysiological brain response. Methods  A correlational study was employed to investigate the relation between capsaicin cough sensitivity and detection thresholds and chemosomatosensory event-related potentials (ERPs) for CO₂ presented in the nasal cavity in 35 persons varying in capsaicin cough sensitivity. Results  Number of coughs were found to correlate negatively with CO₂ threshold and tended to correlate negatively also with N1 and P2 latencies of the chemosomatosensory ERP for CO₂. No tendencies of correlations were found between number of coughs and latencies for olfactory and auditory ERPs, recorded for comparison, but, unexpectedly, were found between number of coughs and auditory N1 amplitude. Conclusions  The results imply that capsaicin cough sensitivity, such as in SHR, is related to higher detection sensitivity, and tends to be related to faster cortical processing of other chemosomatosensory substances, at least of CO₂.