The testing measures the pressures at the lower oesophageal sphincter and your acid levels over a 24 hour period.
You will usually be off medication for a few days before and during the test.
The initial test takes about 20 minutes. A thin tube is passed through the nose and down the oesophagus via the back of the throat. This will measure pressure changes as you swallow small amounts of water, about a teaspoonful at a time, fed to you by the nurse running the test.
The tube is then removed and replaced by a wire with a sensor to measure acidity.
Pictured above: the pH probe
The wire protruding from the nose is connected to a recording device about the size of a personal CD player that is worn on a belt around the waist.
The recorder has three buttons. One is pressed to signal when you start and stop eating, one is pressed to signal when you lie down or stand up and the third is the "event" button to be pressed whenever you experience acid reflux.
The next day, the device will be removed and a print out of the data recorded will show your levels of acid during the 24 hours use.
The Bravo capsule essentially does the same job. Using an endoscope, it is attached to the wall of the lower oesophagus and transmits the data to the recorder using a radio signal rather than requiring the wire protruding from the nose. It is usually used over a 48 hour period. The recorder is returned to the hospital while the capsule breaks free and passes out through the digestive system within a few days.
From the data collected, these factors are recorded: the percentage of time your stomach pH is less than 4 (ie high acid), the percentage of time pH is less than 4 when you're upright, the amount of time your pH is less than 4 when you are lying down, the number of reflux episodes experienced, the number of episodes greater than 5 minutes and the length of time of the longest reflux incident. From these data a Composite pH score is calculated known as the DeMeester score. Anything greater than 14.72 indicates reflux problems.