EFFECTS OF HCL-PEPSIN LARYNGEAL INSTILLATIONS ON UPPER AIRWAY PATENCY-MAINTAINING MECHANISMS

Gastroesophageal reflux has been indicated as an etiopathological fact or in disorders of the upper airway. Upper airway collapsing pressure stimulates pressure-responsive laryngeal receptors that reflexly incre ase the activity of upper airway abductor muscles. We studied, in anes thetized dogs, the effects of repeated laryngeal instillations of HCl- pepsin (KCl-P; pH = 2) on the response of laryngeal afferent endings a nd the posterior cricoarytenoid muscle (PCA) to negative pressure. The effect of negative pressure on receptor discharge or PCA activity was evaluated by comparing their response to upper airway (UAO) and trach eal occlusions (TO). It is only during UAO, but not during TO, that th e larynx is subjected to negative transmural pressure. HCl-P instillat ion decreased the rate of discharge during UAO of the IO laryngeal rec eptors studied from 56.4 +/- 10.9 (SE) to 38.2 +/- 9.2 impulses/s (P < 0.05). With UAO, the peak PCA moving time average, normalized by divi ding it by the peak values of esophageal pressure, decreased after six HCl-P trials from 4.29 +/- 0.31 to 2.23 +/- 0.18 (n = 6; P < 0.05). T he responses to TO of either receptors or PCA remained unaltered. We c onclude that exposure of the laryngeal mucosa to HCl-P solutions, as i t may occur with gastroesophageal reflux, impairs the patency-maintain ing mechanisms provided by laryngeal sensory feedback. Inflammatory an d necrotic alterations of the laryngeal mucosa are likely responsible for these effects.