The differential effect of gastroesophageal reflux disease on mechanostimulation and chemostimulation of the laryngopharynx

Objectives: Laryngo-hypopharyngeal sensitivity (LPS) as measured by thresholds to mechano-stimulation and chemostimulation is important in the prevention of pulmonary aspiration. The presence of gastroesophageal reflux disease (GERD) increases thresholds to mechanostimulation. However, the effect of GERD on thresholds to chemostimulation remains unknown. The aim of this study was to compare laryngo-hypopharyngeal thresholds to chemostimulation in subjects with GERD with those of healthy subjects and to determine the relationship between thresholds to mechanostimulation and chemostimulation. Methods: Forty-eight patients with GERD and 18 control subjects without GERD underwent LPS testing using the Fiberoptic Endoscopic Evaluation of Swallowing with Sensory Testing technique. All 48 patients and 10 of the control subjects also underwent threshold testing for chemostimulation via hypopharyngeal infusions of normal saline and 0.1 N hydrochloric acid performed in a randomized, blinded manner. Thresholds to mechanical stimulation, as measured by the lowest air pressure level required to elicit the laryngeal adductor reflex (LAR), were determined before and after laryngo-hypopharyngeal infusions. Thresholds to chemical stimulation were measured by determining the infusion volume of acid or saline required to trigger an airway protection response. Results: The mean LAR threshold of the patient group was significantly higher compared with that of control subjects (9.5 mm Hg vs 3.9 mm Hg, P<.01). Compared with control subjects, significantly less acid (0.13 mL vs 0.21 mL, P<.01) was required to trigger airway protective responses in GERD subjects. There is a strong negative correlation between the volume of acid infused and the LAR thresholds in the control subjects (r = -0.69, P<.05). Conclusions: Compared with the control subjects, subjects with GERD have significantly increased thresholds to mechanical stimulation, suggesting reduced mechanosensitivity, but significantly reduced thresholds to chemical stimulation, suggesting heightened chemosensitivity. There is an inverse relationship between mechanosensitivity and chemosensitivity. This relationship may be integral in maintaining airway protection. Trial registry: Australian New Zealand Clinical Trials Registry (ANZCTR); Trial number: ACTRN12610000449033; URL:www.ANZCTR.org.au