Functional lumen imaging probe: The FLIP side of esophageal disease

Abstract

Purpose of review: The aim of this review is to summarize use of the functional lumen imaging probe (FLIP) for the evaluation and management of esophageal diseases.

Recent findings: The FLIP utilizes high-resolution impedance planimetry to evaluate the functional geometry and cross-sectional area/pressure relationship (i.e. distensibility) of the esophageal sphincters and body. Recent studies have reported the potential utility of FLIP to evaluate esophageal diseases, such as achalasia, gastroesophageal reflux disease, and eosinophilic esophagitis.

Summary: Esophageal distensibility measures provided by the FLIP will add to our understanding of the contribution of esophageal mechanical properties to esophageal symptoms and function. Application of the FLIP in clinical practice complements the diagnostic evaluation of esophageal function and may also be a valuable tool to help direct and target clinical management of esophageal diseases.

Figure 1. The functional lumen imaging probe (FLIP)

Schematics (left) and real-time images (right) representing typical position of the two primary FLIP device sizes: A, left panel) An 8-cm cylindrical, measurement segment with impedance planimetry channels spaced at 5-mm intervals within a 10-cm length balloon (EF-325) and B, left panel) A 16-cm cylindrical, measurement segment with 1-cm channel spacing housed within an 18-cm length balloon (EF-322). The EGJ can be identified on the real time imaging by the waist in the hour-glass formation. A, right panel). An example of a patient with achalasia studied intra-operatively during a POEM using the 8-cm measurement length device. The EGJ distensibility index (EGJ-DI, the median narrowest CSA divided by median intra-balloon pressure) measured at a 40-ml fill volume was 0.9 mm²/mmHg. D_est=estimated luminal diameter at each impedance planimetry channel. B, right panel). An example of a patient with GERD studied during endoscopy using the 16-cm measurement length device. The EGJ-DI measured at a 60-ml fill volume was 8.0 mm²/mmHg. Figure used with permission from the Esophageal Center at Northwestern.

Figure 2. Distensibility plateau

Real-time images from the maximum-achieved fill volume of A) an asymptomatic volunteer and patients with EoE and B) a focal stricture (identified with a white arrow) and C) diffuse narrow-caliber esophagus. D). The distensibility plateau was developed to represent the luminal CSA (or diameter) at which the pressure increases at a fixed luminal opening. Thus, the distensibility plateau is determined as the peak of the best-fit line generated from plotted data points of the narrowest esophageal body diameter and intra-balloon pressure for each distension volume during step-wise volumetric distension. The displayed distensibility plateaus are A) 22-mm, B) 14.6 mm, and C) 12.1 mm. Figure used with permission from the Esophageal Center at Northwestern.

Figure 3. FLIP Topography

Color-coded diameters (topography) generated by interpolation of data from the 16 impedance planimetry channels at 1-cm spacing (top), along with intra-balloon pressure (bottom) and distension volume (bottom) over a portion of a distension protocol in an asymptomatic, healthy volunteer. Repetitive, antegrade contraction (RACs) can be appreciated in the topographic plot. Figure used with permission from the Esophageal Center at Northwestern.