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Abstract Functional luminal imaging probe (FLIP) is used to measure cross-sectional area (CSA) and pressure at sphincters. It consists of a catheter surrounded by a fluid filled cylindrical bag, closed on both ends. Plotting the pressure-CSA hysteresis of a sphincter during a contraction cycle, which is available through FLIP testing, offers information on its functionality, and can provide diagnostic insights. However, limited work has been done to explain the mechanics of these pressure-CSA loops. This work presents a consolidated picture of pressure-CSA loops of different sphincters. Clinical data reveal that although sphincters have a similar purpose (controlling the flow of liquids and solids by opening and closing), two different pressure-CSA loop patterns emerge: negative slope loop (NSL) and positive slope loop (PSL). We show that the loop type is the result of an interplay between (or lack thereof) two mechanical modes: (i) neurogenic mediated relaxation of the sphincter muscle or pulling applied by external forces, and (ii) muscle contraction proximal to the sphincter which causes mechanical distention. We conclude that sphincters which only function through mechanism (i) exhibition NSL whereas sphincters which open as a result of both (i) and (ii) display a PSL. This work provides a fundamental mechanical understanding of human sphincters. This can be used to identify normal and abnormal phenotypes for the different sphincters and help in creating physiomarkers based on work calculation. 

The esophagogastric junction (EGJ) is located at the distal end of the esophagus and acts as a valve allowing swallowed food to enter the stomach and preventing acid reflux. Irregular weakening or stiffening of the EGJ muscles results in changes to its opening and closing patterns which can progress into esophageal disorders. Therefore, understanding the physics of the opening and closing cycle of the EGJ can provide mechanistic insights into its function and can help identify the underlying conditions that cause its dysfunction. Using clinical functional lumen imaging probe (FLIP) data, we plotted the pressure-cross-sectional area loops at the EGJ location and distinguished two major loop types—a pressure dominant loop and a tone dominant loop. In this study, we aimed to identify the key characteristics that define each loop type and determine what causes the inversion from one loop to another. To do so, the clinical observations are reproduced using 1D simulations of flow inside a FLIP device located in the esophagus, and the work done by the EGJ wall over time is calculated. This work is decomposed into active and passive components, which reveal the competing mechanisms that dictate the loop type. These mechanisms are esophageal stiffness, fluid viscosity, and the EGJ relaxation pattern. 

A FLIP device gives cross-sectional area along the length of the esophagus and one pressure measurement, both as a function of time. Deducing mechanical properties of the esophagus including wall material properties, contraction strength, and wall relaxation from these data are a challenging inverse problem. Knowing mechanical properties can change how clinical decisions are made because of its potential for in-vivo mechanistic insights. To obtain such information, we conducted a parametric study to identify peristaltic regimes by using a 1D model of peristaltic flow through an elastic tube closed on both ends and also applied it to interpret clinical data. The results gave insightful information about the effect of tube stiffness, fluid/bolus density and contraction strength on the resulting esophagus shape through quantitive representations of the peristaltic regimes. Our analysis also revealed the mechanics of the opening of the contraction area as a function of bolus flow resistance. Lastly, we concluded that peristaltic driven flow displays three modes of peristaltic geometries, but all physiologically relevant flows fall into two peristaltic regimes characterized by a tight contraction. 

We used in silico models to investigate the impact of the dimensions of myotomy, contraction pattern, the tone of the esophagogastric junction (EGJ), and musculature at the myotomy site on esophageal wall stresses potentially leading to the formation of a blown-out myotomy (BOM). We performed three sets of simulations with an in silico esophagus model, wherein the myotomy-influenced region was modeled as an elliptical section devoid of muscle fibers. These sets investigated the effects of the dimensions of myotomy, differing esophageal contraction types, and differing esophagogastric junction (EGJ) tone and wall stiffness at the myotomy affected region on esophageal wall stresses potentially leading to BOM. Longer myotomy was found to be accompanied by a higher bolus volume accumulated at the myotomy site. With respect to esophageal contractions, deformation at the myotomy site was greatest with propagated peristalsis, followed by combined peristalsis and spasm, and pan-esophageal pressurization. Stronger EGJ tone with respect to the wall stiffness at the myotomy site was found to aid in increasing deformation at the myotomy site. In addition, we found that an esophagus with a shorter myotomy performed better at emptying the bolus than that with a longer myotomy. Shorter myotomies decrease the chance of BOM formation. Propagated peristalsis with EGJ outflow obstruction has the highest chance of BOM formation. We also found that abnormal residual EGJ tone may be a co-factor in the development of BOM, whereas remnant muscle fibers at myotomy site reduce the risk of BOM formation. NEW & NOTEWORTHY Blown-out myotomy (BOM) is a complication observed after myotomy, which is performed to treat achalasia. In silico simulations were performed to identify the factors leading to BOM formation. We found that a short myotomy that is not transmural and has some structural architecture intact reduces the risk of BOM formation. In addition, we found that high esophagogastric junction tone due to fundoplication is found to increase the risk of BOM formation. 

Abstract Balloon dilation catheters are often used to quantify the physiological state of peristaltic activity in tubular organs and comment on their ability to propel fluid which is important for healthy human function. To fully understand this system's behavior, we analyzed the effect of a solitary peristaltic wave on a fluid-filled elastic tube with closed ends. A reduced order model that predicts the resulting tube wall deformations, flow velocities, and pressure variations is presented. This simplified model is compared with detailed fluid–structure three-dimensional (3D) immersed boundary (IB) simulations of peristaltic pumping in tube walls made of hyperelastic material. The major dynamics observed in the 3D simulations were also displayed by our one-dimensional (1D) model under laminar flow conditions. Using the 1D model, several pumping regimes were investigated and presented in the form of a regime map that summarizes the system's response for a range of physiological conditions. Finally, the amount of work done during a peristaltic event in this configuration was defined and quantified. The variation of elastic energy and work done during pumping was found to have a unique signature for each regime. An extension of the 1D model is applied to enhance patient data collected by the device and find the work done for a typical esophageal peristaltic wave. This detailed characterization of the system's behavior aids in better interpreting the clinical data obtained from dilation catheters. Additionally, the pumping capacity of the esophagus can be quantified for comparative studies between disease groups. 

In this study, we quantify the work done by the esophagus to open the esophagogastric junction (EGJ) and create a passage for bolus flow into the stomach. Work done on the EGJ was computed using functional lumen imaging probe (FLIP) panometry. Eighty-five individuals underwent FLIP panometry with a 16-cm catheter during sedated endoscopy including asymptomatic controls ( n = 14), 45 patients with achalasia ( n = 15 each, three subtypes), those with gastroesophageal reflux disease (GERD; n = 13), those with eosinophilic esophagitis (EoE; n = 8), and those with systemic sclerosis (SSc; n = 5). Luminal cross-sectional area (CSA) and pressure were measured by the FLIP catheter positioned across the EGJ. Work done on the EGJ (EGJW) was computed (millijoules, mJ) at 40-mL distension. Additionally, a separate method was developed to estimate the “work required” to fully open the EGJ (EGJROW) when it did not open during the procedure. EGJW for controls had a median [interquartile range (IQR)] value of 75 (56–141) mJ. All achalasia subtypes showed low EGJW compared with controls ( P < 0.001). Subjects with GERD and EoE had EGJW 54.1 (6.9–96.3) and 65.9 (10.8–102.3) mJ, similar to controls ( P < 0.08 and P < 0.4, respectively). The scleroderma group showed low values of EGJW, 12 mJ ( P < 0.001). For patients with achalasia, EGJROW was the greatest and had a value of 210.4 (115.2–375.4) mJ. Disease groups with minimal or absent EGJ opening showed low values of EGJW. For patients with achalasia, EGJROW significantly exceeded EGJW values of all other groups, highlighting its unique pathophysiology. Balancing the relationship between EGJW and EGJROW is potentially useful for calibrating achalasia treatments and evaluating treatment response. NEW & NOTEWORTHY Changes in pressure and diameter occur at the EGJ during esophageal emptying. Similar changes can be observed during FLIP panometry. Data from healthy and diseased individuals were used to estimate the mechanical work done on the EGJ during distension-induced relaxation or, in instances of failed opening, work required to open the EGJ. Quantifying these parameters is potentially valuable to calibrate treatments and gauge treatment efficacy for subjects with disorders of EGJ function, especially achalasia. 

The goal of this study was to conceptualize and compute measures of “mechanical work” done by the esophagus using data generated during functional lumen imaging probe (FLIP) panometry and compare work done during secondary peristalsis among patients and controls. Eighty-five individuals were evaluated with a 16-cm FLIP during sedated endoscopy, including asymptomatic controls ( n = 14) and those with achalasia subtypes I, II, and III ( n = 15, each); gastroesophageal reflux disease (GERD; n = 13); eosinophilic esophagitis (EoE; n = 9); and systemic sclerosis (SSc; n = 5). The FLIP catheter was positioned to have its distal segment straddling the esophagogastric junction (EGJ) during stepwise distension. Two metrics of work were assessed: “active work” (during bag volumes ≤ 40 mL where contractility generates substantial changes in lumen area) and “work capacity” (for bag volumes ≥ 60 mL when contractility cannot substantially alter the lumen area). Controls showed median [interquartile range (IQR)] of 7.3 (3.6–9.2) mJ of active work and 268.6 (225.2–332.3) mJ of work capacity. Patients with all achalasia subtypes, GERD, and SSc showed lower active work done than controls ( P ≤ 0.003). Patients with achalasia subtypes I and II, GERD, and SSc had lower work capacity compared with controls ( P < 0.001, 0.004, 0.04, and 0.001, respectively). Work capacity was similar between controls and patients with achalasia type III and EoE. Mechanical work of the esophagus differs between healthy controls and patient groups with achalasia, EoE, SSc, and GERD. Further studies are needed to fully explore the utility of this approach, but these work metrics would be valuable for device design (artificial esophagus), to measure the efficacy of peristalsis, to gauge the physiological state of the esophagus, and to comment on its pumping effectiveness. NEW & NOTEWORTHY Functional lumen imaging probe (FLIP) panometry assesses esophageal response to distension and provides a simultaneous assessment of pressure and dimension during contractility. This enables an objective assessment of “mechanical work” done by the esophagus. Eighty-five individuals were evaluated, and two work metrics were computed for each subject. Controls showed greater values of work compared with individuals with achalasia, gastroesophageal reflux disease (GERD), and systemic sclerosis (SSc). These values can quantify the mechanical behavior of the distal esophagus and assist in the estimation of muscular integrity.