Relationship Between Gastro-Oesophageal Reflux and Airway Diseases: The Airway Reflux Paradigm
Pacheco-Galván A, Hart SP, Morice AH. Arch Bronconeumol. 2011.
Our understanding of the relationship between gastroesophageal reflux and respiratory disease has recently undergone important changes. The previous paradigm of airway reflux as synonymous with the classic gastro-oesophageal reflux disease (GORD) causing heartburn has been overturned. Numerous epidemiological studies have shown a highly significant association of the acid, liquid, and gaseous reflux of GORD with conditions such as laryngeal diseases, chronic rhinosinusitis, treatment resistant asthma, COPD and even idiopathic pulmonary fibrosis. However, it has become clear from studies on cough hypersensitivity syndrome that much reflux of importance in the airways has been missed, since it is either nonor weakly acid and gaseous in composition. The evidence for such a relationship relies on the clinical history pointing to symptom associations with known precipitants of reflux. The tools for the diagnosis of extra-oesophageal reflux, in contrast to the oesophageal reflux of GORD, lack sensitivity and reproducibility. The original methods for measuring pharyngeal pH were not quite right due to technical problems, such as the drying out of the catheter and the accumulation of mucus and food. The Dx-pH measuring system (Dx-pH; Restech Corporation, San Diego, CA) is a highly sensitive and minimally-invasive device for detecting acid reflux in the posterior pharynx. This sensor detects aerosolised or liquid acid, resists drying out and its electrical continuity is not impeded by the contact of liquids or tissues. Ayazi S et al. have shown the characteristics of mean pH in the oropharynx of healthy subjects using the Dx-pH catheter. The pharyngeal pH score (RYAN) for abnormal pH (limit of 5.5 for standing and 5.0 in supine position) has been calculated in a way similar to the DeMeester oesophageal score. Furthermore, an alternative scoring system has been developed based on the changes in pH. Wiener et al. compared traditional 24-hour pharyngo-oesophageal monitoring with Dx-pH monitoring in 15 patients with extra-oesophageal symptoms. All the events measured with the Dx-pH method were preceded by and associated with falls in distal oesophageal pH in a progressive anterograde manner. However, oropharyngeal studies with the Dx-pH catheter showed a growing pH gradient from the distal oesophagus to the oropharynx. The oropharynx usually presents a mildly acidic pH, rarely with a pH less than 4. This could help explain why the previous attempts at distinguishing normal subjects from the subgroup of patients with atypical symptoms using quantitative cut-values of pH < 4 have not been reliable.