COUGH RESPONSIVENESS IN NEUROGENIC DYSPHAGIA

Objectives-In neurogenic dysphagia a good cough is important for airwa y protection. If triggering of cough, or its effectiveness, is impaire d this might result in an increased aspiration risk. Capsaicin, an age nt which induces cough through sensory nerve stimulation, was used to test cough sensitivity in groups of patients with and without neurogen ic dysphagia. Methods-On the basis of swallowing speed (ml/s) in a val idated water test 28 alert neurological inpatients (16 women, aged 22- 71 years) were classified into 13 with abnormal and 15 with normal swa llowing (median swallowing speed 23% and 99%, median volume/swallow 43 % and 106% of that predicted for age and sex respectively: p<0.001). C apsaicin nebulised on air in saline was inhaled via a low resistance v alve using a mouthpiece and noseclip. Up to seven incremental concentr ations of capsaicin ranging from 0.07-20.0 x 10(-4) mol/l were each in haled for up to a minute. A pneumotachograph connected to the expirato ry limb gave a paper recording of expiratory air flow. Coughs were rec orded as high flow expirations of short duration. Capsaicin concentrat ions at first cough (threshold) were recorded; concentrations at frequ encies of 10 and 20 coughs/minute were interpolated fk om the dose-rep onse curve. Results-Cough threshold tended to be lower in those with a bnormal swallowing (non-significant): the (log) concentration of capsa icin producing 10 or 20 coughs/ minute also tended to be lower (p=0.12 and 0.07 respectively) in those with abnormal swallowing. Conclusion- Contrary to expectation, these results suggest that cough responsivene ss is enhanced in alert patients with neurogenic dysphagia even after allowing for diagnostic category, the possible presence of a bulbar up per motor neuron lesion, or voluntary respiratory capacity. It is conc luded that these patients with neurogenic dysphagia do not have a redu ced sensitivity of cough triggering.