Gastro-oesophageal reflux (GORD) and its extraoesophageal manifestations present with a variety of symptoms in both adult and paediatric populations. In children the effects of refluxate above the upper oesophageal sphincter (UES) has been implicated as a contributory factor in the underlying pathological processes of a number of conditions including apnoea, asthma, chronic cough, subglottic stenosis, chronic rhinosinusitis and otitis media. The absence of typical symptoms in addition to the inability to obtain a formal symptom history from a young paediatric population contributes to the difficulty in establishing a diagnosis. At present there are no studies or data directly measuring extraoesophageal reflux and its correlation to oesophageal pH monitoring in children.

The use of twenty-four hour oesophageal pH monitoring is regarded as the established technique for diagnosis of GORD, however this technique has been less reliable for detecting extra-oesophageal reflux. The investigators intend to use the Dx-pH Measurement system, a sensitive and minimally invasive transnasal device, to assess the feasibility and validate its use in a paediatric population.

Gastro-oesophageal reflux (GORD) and its extraoesophageal manifestations present with a variety of symptoms in both adult and paediatric populations. In children the effects of refluxate above the upper oesophageal sphincter (UES) has been implicated as a contributory factor in the underlying pathological processes of a number of conditions including apnoea, asthma, chronic cough, subglottic stenosis, chronic rhinosinusitis and otitis media.

The absence of typical symptoms in addition to the inability to obtain a formal symptom history from a young paediatric population contributes to the difficulty in establishing a diagnosis.

At present there are no studies or data directly measuring extraoesophageal reflux and its correlation to oesophageal pH monitoring in children. As a result there is no baseline data for a paediatric population and subsequently no measureable definition of a significant extraoesophageal reflux event. There is a poor correlation between reflux events measured with an oesophageal probe and extra-oesophageal symptoms of reflux. Studies have demonstrated that 51% of patients without pharyngeal reflux had abnormal distal oesophageal pH studies.

This is secondary to both technical concerns regarding the ability of such probes in detecting aerosolized and vapour forms of reflux in the pharynx and due to the inadequacy of the definition of a significant reflux event above the upper oesophageal sphincter. Moving cephaled (upwards) within the upper aerodigestive tract will result in shorter, higher pH events that may not be recognised using traditional oesophageal analysis, which define a pH<4 as defining a significant oesophageal reflux event.

The use of twenty-four hour oesophageal pH monitoring is regarded as the established technique for diagnosis of GORD, however this technique has been less reliable for detecting extra-oesophageal reflux.

The Dx-pH Measurement system (Dx-pH; Respiratory Technology Corp., San Diego, CA) is a sensitive and minimally invasive transnasal device for detection of aerosolized extra-oesophageal acid reflux in the posterior oropharynx.

The investigators intend to use the Dx-pH measurement system and the Peptest salivary pepsin assay (RBiomed, UK) in children already undergoing oesophageal pH studies. The investigators aim to assess the feasibility of these systems in a paediatric population,to provide baseline data and to validate its use in measuring extra-oesophageal reflux events in children. These results will be correlated against symptom questionnaire scores and the results of the 24 hour oesophageal pH study results.

The investigators' results will guide further interventional studies in this area, with the eventual aim of improving diagnosis and guided treatment for the extra-oesophageal manifestations of GORD

Inclusion Criteria:

• All children between the age of 1 year old and 16 years old consecutively referred for outpatient 24 hour oesophageal pH / impedance monitoring will be invited to participate in the study. This is regardless of the underlying diagnosis, aetiology and manifestation of symptoms.

Exclusion Criteria:

• Children under the age of 1 year old. Children under 1 year old will be excluded due to the technical difficulty of placing both the pH / impedance monitoring probe and the Dx-pH probe into the same nostril. Firstly, this is due to the size restriction of placing 2 probes into one nostril. Secondly, the non-pathologic high incidence of regurgitation and positing in below the age of 1 will make data difficult to interpret.
• Children with an nasogastric feeding tube in situ will be excluded. Firstly due to the difficulty in placing and securing the nasogastric, oesophageal pH and Dx-pH probe (3 tubes / probes) through the nostrils, with resultant bilateral nasal obstruction. Secondly, the nasogastric tube causes increased iatrogenic reflux within the pharynx, making data more difficult to interpret and creating artificial reflux events.
• Children with cleft palate prior to surgical repair will be excluded as the Dx-pH probe will be difficult to locate in the oropharynx and may displace into the oral cavity.
• Children requiring pH monitoring as inpatients during an acute medical admission. Children will be excluded from the study if their condition has necessitated an acute hospital admission, therefore participation in the study will not affect other ongoing investigations, treatment or their acute condition.