3. Dual-channel 24hour oesophageal pH monitoring will be undertaken using a digitrapper (Medtronic, Sweden)and dual antimony tipped probe (Synectics, Sweden). Following calibration of the probes the distal antimony tip is positioned 5cm above the upper border of the lower oesophageal sphincter and the proximal probe 15 cm above the distal probe in the upper oesophagus.The patient will be instructed in using the three event buttons on the digitrapper recording start and finish time of meals, upright versus supine positioning and reflux episodes. The subject will be provided with a detailed 24hr 'Activity Diary' to record all meals (including percutaneous gastrostomy feeds), positions and activities including usual chest physiotherapy and physical exercise.The recorded pH information is downloaded into a computer program for analysis. The following indices will be measured in the distal and proximal oesophagus: