An EndoFLIP is a diagnostic procedure that measures how well your esophagus or other parts of your digestive tract stretch and contract. It uses a thin catheter with a small balloon on the tip, inserted through your mouth during a standard upper endoscopy while you’re sedated. The balloon inflates with a conductive fluid, and sensors along its length measure the size, shape, and pressure of the surrounding tissue in real time, producing a three-dimensional map of the area being tested. The entire process adds roughly 10 to 15 minutes to a standard endoscopy.
How the Technology Works
The name stands for “functional lumen imaging probe,” and the underlying technology is called impedance planimetry. The catheter is about 240 mm long with a 3 mm outer diameter. Inside the balloon sit 16 paired electrodes and a pressure sensor. When the balloon is filled with conductive fluid, the electrodes emit a small electrical current and measure the voltage at each point along the balloon. Using those voltage readings and basic physics (Ohm’s law), the system calculates the diameter and cross-sectional area of the space the balloon occupies at multiple points simultaneously.
At the same time, the pressure sensor records how much force the surrounding tissue exerts on the balloon at each stage of inflation. The system then combines these measurements into a single key number: the distensibility index. This index represents how easily a sphincter or section of the digestive tract opens in response to pressure. A higher number means the tissue stretches more readily; a lower number means it’s stiff or tight. In healthy adults, the distensibility index at the junction between the esophagus and stomach is above 2.8 mm²/mmHg, with a typical median around 5.8.
Conditions It Helps Diagnose
EndoFLIP is used to evaluate several esophageal and gastrointestinal conditions where the core problem involves tissue that’s too tight, too loose, or not contracting properly.
Achalasia
This is one of the strongest applications. Achalasia is a condition where the lower esophageal sphincter fails to relax properly, making it difficult for food to pass into the stomach. EndoFLIP can identify a poorly relaxing sphincter and distinguish between the three subtypes of achalasia based on how the esophageal body contracts (or doesn’t) in response to the balloon’s stretch. It’s particularly useful for patients whose symptoms strongly suggest achalasia but whose results on standard testing fall into a gray zone.
Difficulty Swallowing Without a Visible Blockage
When someone has persistent trouble swallowing and an endoscopy shows no tumor, stricture, or other structural cause, EndoFLIP can reveal problems that aren’t visible to the eye. The balloon can detect abnormal wall stiffness or disordered contractions in the esophageal body that explain the symptom. It’s increasingly used during a patient’s first endoscopy to get motility information right away, rather than scheduling a separate test later.
Eosinophilic Esophagitis
In eosinophilic esophagitis (EoE), chronic inflammation gradually remodels the esophageal wall, making it stiffer and narrower. This remodeling can be invisible on a standard endoscopy, especially early on. EndoFLIP detects reduced compliance of the esophageal wall before it becomes severe enough to cause visible narrowing, helping guide treatment decisions and track whether the tissue is improving over time.
Gastroparesis
EndoFLIP isn’t limited to the esophagus. It can also be placed across the pylorus, the muscular valve between the stomach and small intestine. In a study of 44 gastroparesis patients, smaller pyloric diameter and reduced distensibility correlated with worse vomiting and delayed stomach emptying. These measurements help doctors determine whether the pylorus itself is contributing to the problem and predict whether treatments aimed at loosening it are likely to help.
GERD and Anti-Reflux Surgery
For gastroesophageal reflux disease, EndoFLIP is used primarily in the surgical setting. Before or during anti-reflux procedures like fundoplication, the balloon can measure how loose or tight the esophageal junction is, helping surgeons calibrate their repair. The goal is a junction that’s tight enough to prevent reflux but open enough to allow comfortable swallowing afterward.
How It Compares to Manometry
The traditional gold standard for measuring esophageal function is high-resolution manometry, which involves threading a thin pressure-sensing catheter through your nose and down into your esophagus while you’re fully awake. You then swallow water or food while the sensors record how your esophagus contracts. It provides detailed information, but many patients find the nasal insertion uncomfortable and anxiety-provoking, and some can’t tolerate the test at all.
EndoFLIP offers a different type of information. Rather than measuring the force of your swallowing contractions, it measures how easily your esophagus and its sphincters stretch, and whether normal contraction patterns appear in response to that stretch. Because it’s done during an endoscopy under sedation, there’s no nasal catheter and no discomfort during the test itself. For some patients, this means their motility evaluation can happen during an endoscopy they were already going to have, rather than requiring a separate office visit for manometry. The two tests provide complementary data, and in many cases EndoFLIP is used alongside manometry rather than replacing it entirely.
What the Procedure Feels Like
You won’t feel the EndoFLIP itself. The catheter is placed through your mouth and into position while you’re under sedation for your endoscopy. The balloon inflates in controlled steps, and the measurements are captured automatically at each volume. There’s no separate preparation beyond what you’d already do for a standard upper endoscopy: fasting beforehand, arranging a driver, and following your doctor’s instructions about medications.
Afterward, you’ll go to a recovery area until the sedation wears off. You’ll need someone to drive you home. Most people resume normal activities the next day. The procedure carries a very low complication rate. In a series of 60 pediatric cases (which involve the same equipment used in adults), the adverse event rate was 3.3%, and both events were related to anesthesia rather than the balloon itself.
What the Results Tell You
Your doctor will look at several measurements. The distensibility index at the esophageal junction is the headline number for most esophageal evaluations. Values above 2.8 mm²/mmHg are normal. Values well below that threshold suggest a junction that isn’t opening adequately, pointing toward achalasia or similar conditions. Values that are abnormally high may indicate a lax junction contributing to reflux.
Beyond that single number, the system generates a real-time topographic image of the balloon’s shape as it inflates. This image reveals contraction patterns in the esophageal body. In a healthy esophagus, you’ll see repetitive, coordinated contractions moving in the right direction (toward the stomach). In achalasia or other motility disorders, these contractions may be absent, disorganized, or moving backward. For the esophageal body itself, a normal diameter under stretch (called the distensibility plateau) is above 18 mm. Values below that suggest the wall is stiffer than it should be, which is a hallmark of conditions like eosinophilic esophagitis.
These results help your doctor choose between treatments, assess how well a previous treatment worked, or confirm a diagnosis that other tests left uncertain. For surgical patients, the measurements can be taken during the procedure itself, giving the surgeon real-time feedback on whether the repair is calibrated correctly.