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MII–EM is a new technique using two complementary methods of EFT: (i) esophageal manometry (EM) provides information about intraluminal pressures generated during swallowing, and (ii) MII assesses bolus movement during swallowing. Although it does not provide the anatomic details offered by radiographic barium swallow, MII has the advantage of not requiring radiation exposure in evaluating bolus movement. Furthermore, bolus transit and pressures are obtained during a single test procedure, and thus on the same swallows.

Figure 9.4 HRiM recording. Impedance data is shown as a color‐contour mode (purple) overlaying the pressure topography plots of HRM. This example shows two normal swallows with complete bolus transit (i.e. no residual bolus color between swallows).

The indications for combined MII–EM are the same as for EM: evaluation of dysphagia, non‐cardiac chest pain, and gastroesophageal reflux disease (GERD), including preoperative evaluation before antireflux surgery or endoscopic antireflux procedures.

Initial studies on normal subjects indicated that MII could detect the presence of small volumes of swallowed liquid (i.e. 1 mL) and confirmed known pharmacologic effects of cholinergic medications on esophageal peristalsis and bolus movement [3].

There are catheters that enable combined impedance and manometry (both conventional and high resolution) measurements. These catheters incorporate a varying number of pressure transducers as well as multiple impedance measuring segments; an example of a combined MII–EM catheter is shown in Figure 9.5. Dedicated software programs are available for editing and analysis. Generally, these software programs facilitate the production of reports with details on manometric (contraction amplitude, duration and velocity, lower [LES] and upper esophageal sphincter [UES] characteristics), as well as impedance (bolus presence time, total and segmental bolus transit times) parameters. The clinical applications of combined impedance–manometry are described in greater detail in Chapter 11.