EndoVizX 's Background
Principles of Endoflip Testing:
High resolution manometry (HRM) has been in use for 15 years, it measures pressures inside the lumen of the esophagus using small diameter (3 - 4.5mm) catheters that has up to 36 or more sensors at closely spaced locations along the length of the catheter. The technique mostly measures active muscle contraction under isometric conditions, i.e., when the lumen of the esophagus collapses to the diameter of probe. The HRM is important in measuring the tonic contraction and relaxation of the upper and lower esophageal sphincters and phasic contractions of the esophagus during peristalsis. The principle by which endoflip testing measures esophageal motility is quite different from the HRM. The endoflip probe consists of 18 metal electrodes located inside a 16 cm long distensible balloon. Using principles of Ohm’s law, endoflip probe measures the cross sectional area/diameter of the balloon at 16 different locations along the length of the balloon. There is one pressure sensor located inside the balloon at its distal end to measure the intra-balloon pressure. The CSA measurements at each location can be displayed as topographical or color plots (heat map). The endoflip catheter is placed through the mouth while the subject is partially sedated, with 2-3 electrode inside the stomach and the remainder in the lower esophageal sphincter and distal esophagus. The endoflip bag is inflated with saline of known concentration (provided by the manufacturer) in the increments of 10 ml, starting at 20ml to 70ml. At each distension volume, recordings are made for 30-60 seconds, thus the entire recording can be accomplished in > 10 minutes.
Endoflip Testing for Esophageal Motility Disorders4
Endoflip testing is a recent addition to the list of tests available in the diagnose of symptoms pertaining to the esophagus, i.e., dysphagia, chest pain, heartburn and gastroesophageal reflux. Upper GI series (barium swallow or esophagogram) using X ray fluoroscopy and upper endoscopy (EGD) are the first line diagnostic testing of above symptoms and when normal esophageal manometry (high resolution manometry, HRM) is done routinely to diagnose entities such as, achalasia esophagus, diffuse esophageal spasm, nutcracker esophagus (jackhammer esophagus), hypotensive/ineffective esophageal motility disorders. Endoflip testing, the new kid on the block, is able to diagnose majority of the esophageal motor disorders with almost similar sensitivity and specificity as HRM and may replace high resolution manometry. The advantage of endoflip testing, also referred to as panometry, is that it can be done under conscious sedation (making it patient friendly) and at the time of upper endoscopy (making it more efficient, one hospital visit as compared to two visits, one for EGD and the other for manometry). Placement of the HRM catheter (usually through the nose) can be quite uncomfortable for the patient. Endoflip testing is also important for the surgeons in the operation theaters, e.g., to assess the adequacy of esophageal myotomy in patients with achalasia esophagus and assess the degree of tightness of fundoplication (Nissen Fundoplication) during antireflux surgery. It is not surprising therefore that the endoflip testing has gained wide acceptance very quickly, more than 170 centers in the USA are using this type of testing.
Endoflip testing for Anal Sphincter Assessment
Studies shows that the endoflip testing is quite useful to assess the anal sphincter strength. One of the parameters measured by endoflip testing, i.e., distensibility index is significantly higher in patients with anal incontinence compared to normal subjects. A unique advantage of the endoflip testing in the anal sphincter testing is that it allows anal sphincter loop analysis. The latter is a measurement of the length – tension function of the sphincter muscle. Similar to cardiac muscle, anal sphincter muscles generate more tension when stretched. Above is an extremely useful information because based on the length-tension measurements, it may be possible to develop novel surgical/device therapies to adjust the anal sphincter muscle length using minimally invasive procedure/device in the future. Endoflip probe can also be used for novel physical/exercise therapy to improve the strength of the anal sphincter muscles. Based on the work done to date,the following parameters/measurements are displayed on the screen during the testing; 1) 16 balloon diameters/CSA along the length of the balloon, 2) one pressure measurement and 3) volume of the saline injected. Distensibility index is calculated as the CSA divided by the pressure at each location in the esophagus. Sequential changes in the CSA of the balloon along its entire length in an antegrade (repetitive antigrade contraction RACs) or retrograde (repetitive retrograde contractions RRCs) can also be visualized and is important in the diagnosis of esophageal motility disorders. In the current format, it is only possible to observe distensibility index (DI), RACs and RRCs while the testing is being done. Based on the distensibility index (normal > 2.8) and directionality of the repetitive esophageal contractions one can make diagnosis of currently known esophageal motor disorders (based on HRM) with fair precision. Given the efficiency (can be done at the time of EGD) and patient friendliness (can be done under sedation), endoflip testing, even though currently touted as complimentary to the HRM has the potential to replace it for the esophageal motor and sensory function testing, and possible anorectal motility disorders.
References
1. Carlson DA. Functional lumen imaging probe: The FLIP side of esophageal disease. Curr Opin Gastroenterol 2016;32:310-8.2. Carlson DA, Kou W, Lin Z, et al. Normal Values of Esophageal Distensibility and Distension-Induced Contractility Measured by Functional Luminal Imaging Probe Panometry. Clin Gastroenterol Hepatol 2019;17:674-681 e1.
3. Gregersen H. Analysis of Functional Luminal Imaging Probe Data. Clin Gastroenterol Hepatol 2017;15:1313-1314.
4. Abrahao L, Jr., Bhargava V, Babaei A, et al. Swallow induces a peristaltic wave of distension that marches in front of the peristaltic wave of contraction. Neurogastroenterol Motil 2011;23:201-7, e110.
5. Carlson DA, Kahrilas PJ, Lin Z, et al. Evaluation of Esophageal Motility Utilizing the Functional Lumen Imaging Probe. Am J Gastroenterol 2016;111:1726-1735.
6. Donnan EN, Pandolfino JE. Applying the Functional Luminal Imaging Probe to Esophageal Disorders. Curr Gastroenterol Rep 2020;22:10.
7. Gourcerol G, Granier S, Bridoux V, et al. Do endoflip assessments of anal sphincter distensibility provide more information on patients with fecal incontinence than high-resolution anal manometry? Neurogastroenterol Motil 2016;28:399-409.
8. Zifan A, Sun C, Gourcerol G, et al. Endoflip vs high-definition manometry in the assessment of fecal incontinence: A data-driven unsupervised comparison. Neurogastroenterol Motil 2018;30:e13462.
9. Zifan A, Mittal RK, Kunkel DC, et al. Loop analysis of the anal sphincter complex in fecal incontinent patients using functional luminal imaging probe. Am J Physiol Gastrointest Liver Physiol 2020;318:G66-G76.
10. Zifan A, Song HJ, Youn YH, et al. Topographical plots of esophageal distension and contraction: effects of posture on esophageal peristalsis and bolus transport. Am J Physiol Gastrointest Liver Physiol 2019;316:G519-G526.
11. Mittal RK, Liu J, Puckett JL, et al. Sensory and motor function of the esophagus: lessons from ultrasound imaging. Gastroenterology 2005;128:487-97. 12. Park S, Zifan A, Kumar D, et al. Genesis of Esophageal Pressurization and Bolus Flow Patterns in Patients With Achalasia Esophagus. Gastroenterology 2018;155:327-336.