Effect of expiratory loadings on changes in oesophageal pH during coughing evoked by maximal lung emptying

<bold>Background:</bold> Deflation cough (DC), i. e. the expulsive efforts evoked by maximal lung emptying, is inhibited by antacid drug administration. The observation that DC is reduced when patients expire through the nose rather than the mouth led us to speculate that an increased expiratory load might inhibit DC. <bold>Aims:</bold> To investigate i) the real time changes in oesophageal pH along with the DC; ii) the effects of expiratory loadings on DC frequency. <bold>Methods:</bold> Six chronic coughers (2 females, mean age 50±5 yr) who exhibited DC were studied. Real-time oesophageal pH recordings were obtained by an oesophageal catheter. Patients breathed through a two-way valve and a pneumotachograph to acquire flow and volume for DC detection. Increasing expiratory loadings (2-5 cmH2O) were obtained connecting the expiratory valve limb to a water tank. Each patient produced unloaded and loaded full expirations during which DC and the ongoing pH changes were recorded. <bold>Results:</bold> Maximal lung emptying induced DC which was accompanied by a fall in oesophageal pH corresponding to 1.7±0.34 pH units; in most cases, the pH drop shortly preceded (0.48±0.03 sec) the appearance of DC. Increasing expiratory loadings caused proportional reductions (P<0.01) of DC frequency up to complete inhibition of the phenomenon with 5 cm H2O. No significant pH change occurred with a 5 cmH2O load. <bold>Conclusions:</bold> Deflation cough is frequently preceded by oesophageal acidification, suggesting a causative relationship between the phenomena. The mechanism(s) by which expiratory loading inhibits DC and oesophageal acidification remains to be understood.