Tunnel Closure Research Articles

Value of Intracardiac Echocardiography in the Interventional Closure of Patent Foramen Ovale with Adjacent Atrial Septal Defect

Objective. This study aimed to investigate the application value of intracardiac echocardiography (ICE) in transcatheter closure of a patent foramen ovale (PFO) combined with an adjacent atrial septal defect (ASD). Methods. This retrospective study included five patients with PFO combined with adjacent ASD who underwent transcatheter closure and were admitted to the Zhongshan Hospital of Fudan University from June to September 2023. General conditions, ultrasound and ICE findings, and operative data were recorded and followed up for 2–6 months. Results. Of the five patients, two and three had embolic stroke of undetermined source and migraine, respectively, aged 45.6 ± 12.0 years. All patients underwent successful transcatheter closure via the PFO tunnel under the guidance of ICE, without complications or new stroke, and showed significantly reduced migraine at the follow-up. Conclusion. In patients with PFO combined with adjacent ASD, closure of a PFO tunnel could be successfully achieved under ICE guidance; its clinical efficacy was accurate and worthy of promotion.

Numerical analysis of stress and deformation characteristics of compressed air energy storage chambers developed from a modified coal mine tunnel

The use of abandoned coal mine tunnels as underground compressed air energy storage (CAES) facilities has garnered significant attention given that it effectively repurposes unused underground space and enhances the efficiency of renewable energy utilization. However, existing coal mine tunnels, without optimization and retrofitting, may not meet the stability requirements of compressed air energy storage repositories. Sectional transformation is a retrofitting method with excellent optimization effects. In this study, numerical simulation based on Midas software was employed to create a three-dimensional model of straight-wall arched mine tunnels. The stress and displacement deformation of the tunnel sections were simulated under internal pressure of 10 MPa, and scenarios with no modification and circular-section backfilling were compared. The outcomes of the study are (1) For deeply buried soft rock mines, the existing structure without modification may not meet the stability requirements of compressed air storage facility due to low rock strength. (2) In the unmodified scenario, stress concentration effects and excessive floor tensile stress occur near the tunnel closure. (3) Backfilling straight-wall arched tunnels into circular shapes effectively reduces stress and displacement along the tunnel walls, preventing stress concentration near the tunnel closure. This study provides a retrofitting approach for repurposing abandoned mines into compressed air energy storage facilities, providing guidance for future projects facing complex geological conditions.

Sinus of Valsalva Aneurysm: Different Modes of Presentation and Techniques of Repair.

A sinus of valsalva aneurysm (SVA) is an asymmetrical dilatation of the aortic root located between the aortic valve anulus and the sino-tubular junction. Congenital weakness of the elastic lamina in the aortic media layer or trauma and infection as acquired events are the most principal causes of SVA. Presentation may be acute when rupture has occurred or SVA may be discovered fortuitously on echocardiography or CT scan when patients are examined because of unspecific chest pains, dyspnea or arrhythmias. Although endovascular treatment has been performed successfully in individual cases, surgical closure of the aneurysm aiming at preservation of the aortic valve whenever possible is the established procedure. This short report emphasizes the fact that individual treatment is required when SVA need to be operated, depending on the presentation, the location and the size of the finding. Surgery may consist of simple patch closure, bilateral tunnel closure (entry and exit) or more radical operation like Bentall in case the whole aortic root should be addressed. Overall results are excellent, independently of the clinical presentation (acute or elective) with a mortality approaching zero.

Flame self-interactions in MILD combustion of homogeneous and inhomogeneous mixtures

Flame self-interaction (FSI) events in Moderate or Intense Low-Oxygen Dilution (MILD) combustion of homogeneous and inhomogeneous mixtures of methane and oxidiser have been analysed using three-dimensional Direct Numerical Simulations (DNS). The simulations have been conducted at the same global equivalence ratio (⟨ϕ⟩=0.8\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle \\phi \\rangle = 0.8$$\\end{document}) for different levels of O2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm {O_2}$$\\end{document} concentration (dilution) and initial turbulence intensities. It has been reported that both homogeneous and inhomogeneous mixture MILD combustion cases exhibit significant occurrences of FSI events, with the peak frequency of FSI events occurring towards the burned gas side in all cases. Moreover, the frequency of FSI events increases with increasing dilution level and turbulence intensity, but the presence of mixture inhomogeneity leads to a reduction in total FSI events. In all cases, the cylindrical FSI topologies (i.e. tunnel formation and tunnel closure) were found to have a higher likelihood of occurrence compared to spherical FSI topologies (i.e. unburned and burned gas pockets). The geometries of FSI topologies were also analysed using the mean and Gaussian curvatures. It has been shown that the inward propagating spherical FSI topologies (i.e. unburned gas pockets) are associated with negative mean curvature, while outward propagating spherical FSI topologies (i.e. burned gas pockets) are associated with positive mean curvature. Moreover, tunnel formation (tunnel closure) FSI topologies predominantly exhibit either elliptic geometries with positive (negative) mean curvature or hyperbolic saddle geometries with negative (positive) mean curvature. It has been shown for the first time in MILD combustion that the mean values of kinematic restoration and dissipation terms in the transport equation of the magnitude of the reaction progress variable conditional upon the reaction progress variable tend to cancel each other in the vicinity of the critical points associated with cylindrical topologies. Thus, the singular contributions in these terms, which are obtained from analytical descriptions in the vicinity of tunnel formation and tunnel closure topologies, do not affect the balance equation of the magnitude of the gradient of the reaction progress variable. Consequently, there is no need for a separate model treatment for singularities in modelling approaches based on the magnitude of the gradient of the reaction progress variable. The FSI events in the reaction dominated and propagating flame regions of MILD combustion have also been analysed for the first time. It has been found that more FSI events occur in the reaction dominated region, particularly towards the burned gas side. However, the majority of spherical FSI topologies are found in the propagating flame region. The findings from this study indicate that turbulence intensity, dilution level and mixture inhomogeneity effects need to be considered in any attempt to extend flame surface-based modelling approaches to MILD combustion.

Propagation and topology in turbulent premixed flames

The mechanism of propagation close to flame–flame interaction events is analysed using direct numerical simulation of a turbulent premixed methane–air flame. Four canonical local topologies arising from flame–flame interaction are identified in the vicinity of critical points. These correspond to reactant pocket, tunnel closure, tunnel formation and product pocket. The two spherical topologies (reactant and product pockets) are found to propagate consistently with no change in direction. Reactant pockets tend to propagate in the direction normal to the flame while product pockets tend to diffuse in the counter–normal direction. In contrast, both cylindrical topologies (tunnel closure and formation) may propagate either normally or counter–normally. It is shown that the direction of propagation for these topologies is strongly linked to principal curvatures of the flame surface. In such cases, the direction of propagation may reverse as the topology evolves and the principal curvatures change over time. Thus the conditioning on topology allows for more accurate estimation of displacement speed which is central to modelling turbulent flame speed.

Comprehensive Application of Borehole Fine Detection Methods: A Case Study in Shantou Bay Subsea Tunnel

Water inrush disaster is one of the most severe problems during the construction of sea tunnels, primarily due to faults, karst, and weathered zones. Once a water inrush disaster occurs, it can lead to construction delays, traffic disruptions, and major economic losses, as well as potential consequences such as seawater intrusion, casualties, project suspension, and tunnel closure. Thus, advanced geological prediction is indispensable. During the construction of the Shantou Bay subsea tunnel, a sudden water inrush accident occurred in the sea–land transition section. To prevent such incidents and ensure safety, an integrated approach was employed. Firstly, the cross‐hole resistivity method was used to predict water content in front of the tunnel, as it is highly sensitive to water. Subsequently, borehole ground‐penetrating radar was applied to finely characterize the geological structure. By combining these two methods, the size, scale, location, water content, and spatial distribution of water‐bearing structures in front of the tunnel were identified. With the above measures, the Shantou Bay subsea tunnel passed through the detection section successfully. Herein, we present a case study and offer a valuable reference for similar projects concerning subsea tunnel construction.

Structural basis of RNA-induced autoregulation of the DExH-type RNA helicase maleless

RNA unwinding by DExH-type helicases underlies most RNA metabolism and function. It remains unresolved if and how the basic unwinding reaction of helicases is regulated by auxiliary domains. We explored the interplay between the RecA and auxiliary domains of the RNA helicase maleless (MLE) from Drosophila using structural and functional studies. We discovered that MLE exists in a dsRNA-bound open conformation and that the auxiliary dsRBD2 domain aligns the substrate RNA with the accessible helicase tunnel. In an ATP-dependent manner, dsRBD2 associates with the helicase module, leading to tunnel closure around ssRNA. Furthermore, our structures provide a rationale for blunt-ended dsRNA unwinding and 3'-5' translocation by MLE. Structure-based MLE mutations confirm the functional relevance of our model for RNA unwinding. Our findings contribute to our understanding of the fundamental mechanics of auxiliary domains in DExH helicase MLE, which serves as a model for its human ortholog and potential therapeutic target, DHX9/RHA.

Epidermal inclusion cyst after uneventful small incision cataract surgery: A diagnostic dilemma

Conjunctival cysts are not so uncommon after surgical procedures. They are usually benign in nature and are filled with serous material and mucous. They may be congenital or acquired in origin. Acquired cysts are mostly seen after ocular surgery and trauma. Hereby, we report two cases of conjunctival inclusion cysts following uneventful manual small incision cataract surgery in two elderly females. Both cases were treated by cyst excision and suturing of the scleral tunnel with interrupted sutures was done. An unstable scleral wound may be a contributory factor in the formation of cysts. Hence, we conclude that closure of the scleral tunnel with overlying tenon and conjunctival apposition is a critical step in controlling such complications of cataract surgery.

Prospective randomized controlled trial comparing the effect of Monocryl versus nylon sutures on patient- and observer-assessed outcomes following carpal tunnel surgery.

Controversy remains regarding the optimal technique and suture type for wound closure after carpal tunnel surgery. Adult patients undergoing open carpal tunnel release were prospectively randomized to receive either interrupted, buried Monocryl sutures or traditional nylon horizontal mattress sutures for their wound closures. At the 2-week and 6-week postoperative visits, Patient and Observer Scar Assessment Scale questionnaires were completed. At 2 weeks, patients and observers had a significantly better opinion of incisions closed with Monocryl. By 6 weeks, neither patients nor observers found a difference between suture types in any category. Scars of wounds closed with Monocryl did not change appreciably in appearance between 2 and 6 weeks. However, patients and observers noted significant improvement in scar appearance in the nylon group over time. Monocryl suture represents an effective method for carpal tunnel closure that leads to improved patient- and observer-reported outcome scores in the early postoperative period compared with nylon.Level of evidence: II.

Flame Self-interaction and Flow Topology in Turbulent Homogeneous Mixture n-Heptane MILD Combustion

Moderate or Intense Low-oxygen Dilution (MILD) combustion has potential to achieve both high energy efficiency and ultra-low emissions. This analysis adopts the critical point theory to characterise the Flame-Self Interaction (FSI) events and flow topologies in turbulent, homogeneous mixture, n-Heptane MILD combustion using Direct Numerical Simulations (DNS) with reduced chemical mechanism. The local flame geometry has also been categorised using the mean and Gauss curvatures. It was found that the Tunnel Formation (TF) and Tunnel Closure (TC) topologies are the most probable FSI events at all values of the reaction progress variable c, while the Unburned Pocket (UP) and Burned Pocket (BP) topologies were mostly present towards the unburned and burned mixtures of the flame, respectively. Moreover, increasing the turbulence intensity did not result in any significant changes in the distribution of FSI events. Investigation of the flow topology distribution showed that the features associated with non-zero dilatation rate did not exist in the MILD cases considered. This is a consequence of the negligible thermal expansion effect due to the small temperature rise in MILD combustion cases. Increasing the dilution factor caused a reduction in the frequency of FSI events for all c levels. The distributions of flame self-interaction events in homogeneous mixture MILD combustion have been found to be significantly different from previously reported distributions for conventional turbulent premixed combustion.

Surface topologies and self interactions in reactive and nonreactive Richtmyer–Meshkov instability

The reactive Richtmyer–Meshkov instability (RMI) exhibits strong wrinkling of a reactive flame front after an interaction with a shock wave. High levels of deformation and wrinkling can cause the flame surface to intersect with itself, leading to the events of flame self interactions (FSI). As FSI can have a significant influence on the development and topology of the flame surface, it should be considered an important factor affecting the burning characteristics of the flame. The topological structure and statistics of FSI are analyzed using data from high-fidelity simulations of a planar shock wave interacting with a statistically planar hydrogen/air flame for stoichiometric, lean and nonreactive gas mixtures. FSI events are detected by searching for critical points in the field of the reaction progress variable c and divided into the following topological categories: burned gas mixture pocket (BP), unburned gas mixture pocket (UP), tunnel formation (TF) and tunnel closure (TC). It is found that reactivity and flame thickness are decisive factors, influencing the frequency and topological distribution of the detected FSI events. While in early RMI-stages the FSI is found to be mainly dependent on the flame thickness, later stages are heavily influenced by the reactivity, as high reactivity quickly burns out emerging wrinkled structures (in the stoichiometric case) leading to massively reduced levels of FSI. The findings are further supported by the results from the nonreactive case, which at later stages of the RMI closely resembles the less reactive lean case. Analysis of the topology distribution over time and conditioned over c, reveals further differences between the lean and stoichiometric case, as the strong wrinkling and mixing encountered with the lean case facilitates the build up of many pocket-type and tunnel-type interactions throughout the wrinkled flame front. For the stoichiometric case, mainly tunnel-type and unburned pocket topologies are found in the narrow flame funnels extending into the burned gas.

Off-label Use of ADO II® in the Closure of Various Congenital Heart Defects

Devices may be used for special purposes different than their production purpose. For instance, Amplatzer Ductal Occluder is actually designed for duct closure and its usage for closing defects other than ductus is named as off-label. The aim of this study is to emphasize off-label use of device: not only for PDA and VSD but also for other various defects. This study is designed retrospectively, performed by the evaluation catheterization records of patients in whom ADO II and ADO II-AS devices were used in Erciyes University Medical Faculty Children Hospital, Pediatric Cardiology Department between 2011 and 2018. Patients’ demographic criteria: age, weight at the time of procedure was gathered. The diagnosis, size of device, follow-up period and complications were also noted. From April 2011 to March 2018, a total of 121 patients underwent transcatheter closure by ADO II and 66 patients by ADO II AS. The number of PDA closure with ADO II was 48; with ADO II AS were 62. Rest of the procedures were all off-label. Types of off-label procedures performed were: VSD closure, residual mitral cleft closure, Aorta-Right atrium tunnel closure, pulmonary arteriovenous fistula occlusion, aorta-pulmonary window closure, and occlusion of the artery feeding accessory lobe in scimitar syndrome, Gerbode defect occlusion. Up to our knowledge; this study includes the largest pediatric case series with various different congenital heart defects which were closed with ADO-II. Also our ADO-II occluded VSD case series is one of the largest series in the literature with almost 6 years’ follow-up. We believe in that ADO-II device may be an alternative in percutaneous closure of various rare heart defects. It is used successfully for non-ductal defects with low complication and high compliance rates.

Successful percutaneous closure of a recurrent aorto-left ventricular tunnel with an Amplatzer Vascular Plug II.

Aorto-left ventricular tunnel is an extremely rare CHD clinically impressing as aortic regurgitation. This is usually corrected surgically, sometimes by percutaneous catheter intervention. Recurrent aorto-left ventricular tunnel has been reported occasionally. Reports of percutaneous closure of such recurrent aorto-left ventricular tunnels are rare. We hereby describe successful closure of a recurrent aorto-left ventricular tunnel with an Amplatzer Vascular Plug II.

Prozesse der Versinterung – Kenntnisstand und aktuelle Herausforderungen

AbstractScale formation in water drainage systems occurs in diverse forms. In tunnel drainage systems in particular, calcium carbonate deposition can significantly impair water discharge, resulting in costly maintenance work and tunnel closures. This review paper presents and discusses the state of knowledge as well as the current challenges regarding scale formation in tunnel drainage systems in terms of typification, parameters controlling formation, such as hydrochemistry, interfacial phenomena, microbial activity, and countermeasures, such as appropriate adaptation of construction materials, drainage design, inhibitor use and cleaning. Detailed knowledge of the case‐specific scale formation environment and the scaling capacities of the waters provides the basis for the tailored development and evaluation of suitable strategies for successfully reducing maintenance efforts and tunnel closure. For this purpose, time‐ and site‐resolved monitoring of the composition of the solid phases, waters and the tunnel atmosphere during the implementation of the construction project and during the operation of the tunnel is paramount.

Tunnel support practice in small hydropower tunnels in the Himalayas through observational approach

With the high mountains, steep terrain and fast flowing river, the Himalayan region has a great opportunity and potential for hydropower development. In Nepal, many hydropower projects have been constructed and many are under construction among which majority of the project are small to medium scale project. For such project, medium size tunnel provides an economic and safe route for water convergence. Squeezing and collapse have been observed in most of the hydropower tunnels, which have resulted in support failure, as the tunnel passes through weak rock mass under high in-situ stress during construction. Due to insufficient tunnel closure measurements, field-based observation has been conducted to study the installed support at different tunnels in the Himalayas. The observational approach is used for analysis and recommendations have been made for designing a stable and safe support system for tunnels. Through an analysis of a case study from Nepal, comparison has been made on the design and practiced support systems, and description of supports used in various case histories from Nepal have been provided.

Anterior cruciate ligament graft healing by peptide-based vascular endothelial growth factor and bone morphogenetic protein recruitment

<h2>ABSTRACT</h2><h3>Introduction</h3> The frequency of adverse outcomes after revision ACLR emphasizes the importance of the primary reconstruction regarding intra-articular graft healing and tunnel osteointegration. <h3>Objectives</h3> The objective was to generate a functionalized suture based on peptide attachments that spatially recruits VEGFs and BMPs for graft healing. It was hypothesized that the suture would capture cytokines with favorable graft-bone integration in an ACLR rabbit model. <h3>Methods</h3> Suture functionalization with established peptides was tested by immunofluorescence (IF) for recombinant VEGFA and BMP2. Three rabbit groups (<i>n</i> = 12/group) underwent ACLR using either a dual functionalized, plain suture (DF vs suture groups) or no suture (tendon group). Outcomes were assessed by μCT, molecular analysis, histology, and biomechanics at 4 to 12 weeks postoperatively. <h3>Results</h3> Adequate functionalization was verified by IF for both growth factors. In vivo, the bone mineral density trended towards an increase at 4 weeks in the DF group (<i>P</i> > .194) but not at 12 weeks. Healing was better in the mid-section bone tunnel areas of the tendon group at 12 weeks compared to the suture (<i>P</i> = .026), or DF group (<i>P</i> = .011). Molecular analysis was inconclusive. Accumulation of growth factors was not evident by immunohistochemistry. Biomechanics showed no intergroup difference. <h3>Conclusions</h3> The study established the development of a suture capable of capturing BMP2 and VEGFA by a peptide-binding strategy. This technology did not show superior tissue response or changes in biological parameters of ingrowth in vivo but seems to be interfering with bone tunnel closure at 12 weeks. The current model and technology should be further optimized.

Stochastic event simulation model for quantitative prediction of road tunnel downtime

Given the importance of road tunnels in a transportation network, it is essential to quantitatively assess and predict tunnel functionality loss due to disruptive events. In this study, a stochastic event simulation model was developed to evaluate the resilience of tunnel infrastructure, quantified using a functionality metric as a function of loss in traffic capacity and its duration. The model consists of individual modules to account for disruptive events that cause tunnel closures. In this paper, the mechanism and probabilistic models used for each simulation module are presented. A simulation for Eisenhower tunnel, Colorado, was conducted using the proposed method as a validation case study. The results showed that the proposed model could simulate realistic tunnel operation status. While the validation was made for a specific tunnel, the model was designed to be applied to the resilience analysis of any road tunnel with defined design and operation parameters.

Inverse hydraulic and transport model of groundwater recovery experiment using mixed-dimensional concept

Understanding evolution of groundwater hydraulic and chemical conditions is important for safety assessment of radioactive waste disposal. Perturbations to groundwater can occur due to the construction and operation of the underground facility. The initial perturbations and their recovery after the tunnel closure were observed in the Groundwater REcovery Experiment in Tunnel (GREET) in Mizunami, Japan, at 500-m depth in granite. In a 100-m-long tunnel, 50 m was isolated by building a plug. Aside from other measurement and exploration data, groundwater pressures and chemical composition were monitored in boreholes with 24 packer sections. This work used numerical modelling to better understand and be able to predict the observed water flow and solute transport phenomena. The model covered 100-m scale around the tunnel and was divided into a continuum far-field domain and a near-field domain with deterministic discrete fractures and matrix blocks. A mixed-hybrid finite element solution was used with independent degrees of freedom for 3D and 2D elements. Modelling started with a blind prediction followed by a calibration (inverse model) for drainage and flooding experiment phases. The inverse hydraulic model fitted the more/less communicating sections and estimated transmissivity and conductivity parameters that are consistent for the two phases. The model sensitivity on transport parameters was insufficient for the inverse model, which can use only simplified measured evolution to avoid noisy data.

The archaeal triphosphate tunnel metalloenzyme SaTTM defines structural determinants for the diverse activities in the CYTH protein family

CYTH proteins make up a large superfamily that is conserved in all three domains of life. These enzymes have a triphosphate tunnel metalloenzyme (TTM) fold, which typically results in phosphatase functions, e.g., RNA triphosphatase, inorganic polyphosphatase, or thiamine triphosphatase. Some CYTH orthologs cyclize nucleotide triphosphates to 3′,5′-cyclic nucleotides. So far, archaeal CYTH proteins have been annotated as adenylyl cyclases, although experimental evidence to support these annotations is lacking. To address this gap, we characterized a CYTH ortholog, SaTTM, from the crenarchaeote Sulfolobus acidocaldarius. Our in silico studies derived ten major subclasses within the CYTH family implying a close relationship between these archaeal CYTH enzymes and class IV adenylyl cyclases. However, initial biochemical characterization reveals inability of SaTTM to produce any cyclic nucleotides. Instead, our structural and functional analyses show a classical TTM behavior, i.e., triphosphatase activity, where pyrophosphate causes product inhibition. The Ca2+-inhibited Michaelis complex indicates a two-metal-ion reaction mechanism analogous to other TTMs. Cocrystal structures of SaTTM further reveal conformational dynamics in SaTTM that suggest feedback inhibition in TTMs due to tunnel closure in the product state. These structural insights combined with further sequence similarity network–based in silico analyses provide a firm molecular basis for distinguishing CYTH orthologs with phosphatase activities from class IV adenylyl cyclases.

Gastric Peroral Endoscopic Myotomy: A Specific Learning Curve.

Gastric peroral endoscopic pyloromyotomy (G-POEM) is a novel option for patients with gastroparesis. It involves submucosal tunneling across the pylorus, followed by pyloromyotomy, and subsequent closure of the endoscopic tunnel. The aim of this study was to determine the learning curve for G-POEM. Consecutive patients undergoing G-POEM by a single operator were included from a prospective registry over 2 years. Demographics, procedure info, postprocedure follow-up data, and adverse events were collected. Nonlinear regression and cumulative sum control chart analyses were conducted for the learning curve. Clinical outcomes were improvement in Gastroparesis Cardinal Symptom Index score and gastric emptying scintigraphy. Thirty-six patients were included (16.7% M, mean age 46 y). The majority had idiopathic gastroparesis (n=16, 44%), with the remaining having diabetes (n=5, 17%), postsurgical (n=10, 28%), or other (n=4, 11%). Technical success was achieved in 35 of 36 (97%). There was a significant reduction in the total Gastroparesis Cardinal Symptom Index score (2.09 units, P<0.00001) and a significant reduction in postoperative gastric emptying scintigraphy (82.44 mins, P<0.00001). Mean follow-up was 15 months (SD, 1.05). Median procedure time was 60.5 minutes (range, 35 to 136). Cumulative sum control chart shows 60-minute procedure was achieved at the 18th procedure. Procedure durations further reduced with consequent procedures with the last 3 being 45 minutes, thus demonstrating continued improvement with ongoing experience (nonlinear regression P<0.0001). Endoscopists experienced in G-POEM are expected to achieve a reduction in procedure time over successive cases, with efficiency reached at 60.5 minutes and a learning rate of 18 cases with continuing improvement.