It has been shown to have an accuracy of 97% compared with fluoroscopy.23 Impedance uses the changes in electrical conductivity

associated with the passage of a bolus to map bolus transit and clearance (Fig. 4). Recent developments have enabled the data to be depicted as a topographical plot as with manometric data. Impedance monitoring is used in combination with manometry in the evaluation of non-obstructive dysphagia (NOD). The value of impedance lies with it being a complementary, rather than competing, tool to manometry by providing information on the functional outcome of motility; namely flow or transit. Thus, impedance allows for inferences to be made about the relationship between abnormalities of motility seen on manometry Tyrosine Kinase Inhibitor Library with abnormalities in bolus transit seen on impedance. The use of viscous boluses also provides Deforolimus clinical trial a more physiological assessment of motility than the more conventional liquid boluses used in manometry. In a multi-centre study on 40 patients with NOD, impedance monitoring was shown to identify abnormalities of transit in 35% of patients with NOD who had apparently normal manometric assessment.24 Conversely, manometric abnormalities do not always translate to abnormal bolus transit.24,25 Bolus transit was normal in up to 15% of patients with manometric diagnosis of ineffective esophageal motility

and one third of patients with diffuse esophageal spasm.24 Impedance, however, is of limited use in patients with achalasia, presumably due to esophageal retention.26 More recently, combined impedance-manometry has also been used to assess oropharyngeal transit and risk of aspiration,27 either as an alternative or adjunct to radiology. Using fluoroscopy as the gold standard, a number of important pressure-flow variables were identified from the combined impedance-manometry assessment which, in turn, was used in an automated analytic program to evaluate the swallow risk index. This approach has been

shown to positively predict pharyngeal dysfunction and risk of aspiration.27 The functional lumen imaging probe is a largely experimental tool not yet in routine clinical use. The technique uses impedance planimetry, which measures Methisazone impedance inside a saline-filled cylindrical balloon, thus allowing calculation of the cross-sectional area of the balloon.8,28,29 This tool has been used to evaluate the opening and pressure across the gastroesophageal junction, and may prove to be useful in assessing patients with achalasia before and after treatment.8 More recently, impedance planimetry has been further modified to measure the axial (or longitudinal) force in the esophagus, rather than the cross-sectional area, which offers additional information regarding the longitudinal propulsive force exerted on a bolus, in addition to horizontal force measured by manometry.