This study is the next evolutionary step from the classic pH probe. Impedance testing is an ambulatory study that allows a clinician to quantify the amount of acid and non-acid reflux a patient is experiencing. This accomplished by measuring the electrical resistance generated between ports on a probe. When the resistance is high, the distance between ports is occupied by gas, when it is low it is occupied by liquid. Standard pH-metry is not able to detect non-acid reflux. An additional advantage is that it can measure the extent of reflux, that is the distance up the esophagus that refluxate will travel. When conducting the test, the probe is placed in the nose. The probe is connected to a unit, and the patient is allowed to go home, or to the hospital floor. Measurement takes place over 24 hours.