Reduction In Pressure Gradient Research Articles

Safety and Efficacy of Portal Vein Recanalization with Creation of Intrahepatic Portosystemic Shunt (PVR-TIPS) to Treat Chronic Portal Vein Thrombosis in Non-cirrhotic Patients.

This study assesses the efficacy and safety of Portal Vein Recanalization with Intrahepatic Portosystemic Shunt (PVR-TIPS) in non-cirrhotic patients with chronic portal vein occlusion (CPVO), cavernomatous transformation, and symptomatic portal hypertension (PH) and/or portal vein thrombotic progression. Medical records of 21 non-cirrhotic patients with CPVO and portal cavernoma undergoing PVR-TIPS were analyzed. Hemodynamic (intraprocedural reduction in portosystemic pressure gradient), clinical (data on gastrointestinal bleeding, abdominal pain, ascites, and presence of esophageal varices from imaging exams) and technical success (PVR-TIPS) assessed efficacy. Safety was determined through complications classified according to the CIRSE Classification System. PVR-TIPS was successfully performed in all patients, resulting in a significant reduction in portal pressure gradient by 10mmHg (21.475 ± 9.7mmHg - 11.454 ± 5,4mmHg, p < 0.001), alleviating portal hypertension symptoms without thrombotic progression. Clinical success included resolution or reduction of ascites (p = 0.016), gastroesophageal varices (p = 0.004), abdominal pain (p = 0.0021), and cessation of gastrointestinal bleeding (p = 0.021). Complications occurred in 33% of patients, including six grade III events (1 perioperative liver bleeding, 5 delayed stent occlusions) and one grade VI event resulting in death (4.8%). Primary patency rate was 76% (21.3months, range:0.2-82), secondary patency 100% (4months, range:3.8-40.8). Survival at follow-up was 90.4%, with one unrelated death. One patient underwent liver transplantation, three became eligible post-recanalization. PVR-TIPS proves effective and safe in reducing portal pressure gradient, thereby alleviating PH symptoms without evidence of portal thrombosis progression in non-cirrhotic patients with CPVO and portal cavernoma. It expands therapeutic options, including liver transplantation.

End-procedural adherence to recommended hemodynamic targets does not improve the outcome of elective TIPS in patients with cirrhosis.

In clinical practice, the reduction of portocaval pressure gradient (PCPG) following TIPS does not always meet the recommendation of current guidance. We evaluated the impact of different degrees of PCPG reduction, measured at the end of an elective TIPS, on ascites control, recurrence of portal hypertension-related bleeding (PHRB), and survival. Patients with cirrhosis receiving TIPS for refractory ascites (RA) or for the secondary prophylaxis of PHRB were consecutively enrolled. Reduction in PCPG was defined as inadequate hemodynamic response (IHR) in patients not achieving a PCPG <12mmHg for both secondary prophylaxis of PHRB and RA, or a reduction of at least 50% only for PHRB. Four hundred fifteen patients were analyzed. An adequate hemodynamic response (AHR) was achieved in 66%. Fifty percent of patients received an under-dilated (≤7mm) endoprosthesis. No significant differences between patients with IHR and AHR were observed in rebleeding rate and ascites control, while overt HE was higher in AHR. Regardless of TIPS indication, survival was not significantly different between IHR and AHR, while advanced age and liver function before TIPS were significantly associated with a higher cumulative incidence of liver-related death. Notably, in patients with RA the cumulative incidence of liver-related mortality was higher when AHR was defined as a post-TIPS PCPG <12mmHg or a reduction ≥50%. AHR measured at the end of an elective TIPS may not be essential to define the eventual outcome, while a marked drop in PCPG could negatively affect the prognosis of patients with RA.

Identification of optimal portal pressure decrease to control ascites while minimizing hepatic encephalopathy after TIPS: A multicenter study.

Clinically-significant portal hypertension (CSPH) in liver cirrhosis patients can lead to refractory ascites. A transjugular-intrahepatic-portosystemic shunt (TIPS) treats CSPH but may cause overt hepatic encephalopathy (oHE). Our aim was to determine the optimal reduction of the portal pressure gradient (PPG) via TIPS to control ascites without raising oHE risk. This multicenter study screened 1509 patients from three European centers (Hannover, Vienna, Hamburg) undergoing TIPS-implantation between 2000-2023. Patients with TIPS-indications other than refractory ascites/hepatic hydrothorax, vascular-liver-disease, hepatocellular-carcinoma or insufficient PPG data were excluded. PPG was measured before and after TIPS insertion. Outcome data was assessed up to one year after TIPS-insertion. Analyses were conducted utilizing a modern machine leaning model, namely a competing-risk (CR) random survival forest (RSF), partial-dependence-plots (PDP) and CR-analyses with liver transplantation/death as competitors. The cohort was divided into a 60% derivation and 40% validation cohort. Overall, 729 patients (median MELD: 13 (IQR 10-16), 66% male, 23% oHE before TIPS) were analyzed. The derivation cohort comprised 438 and validation cohort 291 patients. The optimal PPG reduction, determined by maximally selected Grays-statistic and PDP of the RSF, was 60-80%. In this range, patients showed significantly fewer hepatic decompensations due to ascites (HDA) (sHR: 0.7 [0.52-0.96]) with similar oHE incidences (sHR: 0.92 [0.67-1.27]). The PPG range was confirmed in the validation cohort (HDA: sHR: 0.66 [0.46-0.96]; oHE: sHR: 0.89 [0.61-1.32]). A targeted PPG reduction of 60-80% showed significantly reduced HDA without increased oHE risk. Therefore, PPG reduction within this range could be a valid reduction target.

Fully Covered Stent-TIPS for Advanced HCC Patients with Portal Vein Tumor Thrombus-Related Severe Symptomatic Portal Hypertension.

Portal vein tumor thrombus (PVTT)-related severe symptomatic portal hypertension (SPH) leads to a poor prognosis in patients with advanced hepatocellular carcinoma (HCC). Traditional transjugular intrahepatic portosystemic shunt (TIPS) using covered plus bare stent can effectively relieve SPH, however, the bare segment is susceptible to obstruction due to PVTT invasion. This study aimed to evaluate the safety and efficacy of fully covered stent-TIPS (FCS-TIPS) for treatment of PVTT-related SPH in advanced HCC patients. This retrospective study enrolled 25 patients with advanced HCC who underwent FCS-TIPS for PVTT-related severe SPH from June 2018 to January 2024. The evaluated outcomes included overall survival (OS), technical success rate, reduction in portal venous pressure gradient (PPG), stent patency rate, SPH control rate, liver function and complications. The technical success rate was 100% without perioperative deaths or severe procedure-related adverse events. The average PPG decreased by 13.4±4.6mmHg. The overall symptom control rate of SPH was 96.0%. Variceal bleeding, ascites/hydrothorax, and enteropathy control rates were 100%, 95.0%, and 100%, respectively. Liver function showed mild improvement one month after TIPS. One patient (4.0%) experienced overt hepatic encephalopathy (OHE) and three (12.0%) patients developed shunt dysfunction during the follow-up period. None of the patients experienced shunt-induced extrahepatic metastasis. The median OS was 6.0 months and the cumulative survival rates at 3, 6, 12 months were 80.0%, 52.0% and 21.3%. FCS-TIPS is safe and effective for treating PVTT-related severe SPH and can serve as a bridging therapy for advanced HCC.

Comparison of Carvedilol and Propranolol in Reducing the Portal Vein Pressure: A Systematic Review and Meta-analysis.

The portal vein pressure higher than 10mm Hg in patients with hepatic cirrhosis is more likely to have serious complications and poor prognosis. Nonselective receptor blockers (NSBBs) can reduce the portal vein pressure; however, the efficacy and safety of different NSBBs in reducing portal vein pressure were unconsistent. A systematic review and meta-analysis was conducted to evaluate the efficacy and safety of carvedilol versus propranolol in reducing portal vein pressure in this study. We assessed Randomized controlled trials (RCTs) through PubMed, Web of science, Embase, and Cochrane library up to January 2024. Data from eligible studies were pooled in fixed-effect or random-effect meta-analysis models, using RevMan software. Two researchers screened articles, extracted data, and assessed the study quality independently according to the PRISMA guidelines. The primary outcomes were the reduction of hepatic venous pressure gradient (HVPG), the hemodynamic response rate, and the incidence of adverse events. Secondary outcomes were mean artery pressure (MAP) and heart rate (HR). A total of 7 RCTs, including 351 patients, were included in our meta-analysis. The results indicated that the magnitude of reduction in HVPG was greater in carvedilol compared with propranolol (MD: 1.08; 95% CI: 0.61 to 1.54; I2=0%, P<0.00001) in short-term follow-up. Carvedilol's hemodynamic response rate was higher than that of propranolol (OR: 0.44; 95% CI: 0.27 to 0.72; I2=0%, P = 0.001). Our meta-analysis indicated that compared with propranolol, carvedilol was better in lowering portal hypertensive and had higher response rate in patients with hepatic cirrhosis. There was no obvious difference in safety between the 2 medications.

The sedimentology and multi-stage evolution of a Pleistocene esker on soft substratum, a case from North Central Poland

Eskers are one of the meltwater landforms that enable the reconstruction of the nature of subglacial drainage systems. Therefore, they play a significant role in the study of palaeo ice sheets. While the spatial distribution of subglacial tunnels and their geometry resulting from the geomorphological features of eskers are relatively well known, the course and time of sedimentation processes taking place inside the subglacial conduits are understood only to a certain extent, especially in the case of eskers developed on soft substrata. The paper presents an example of an esker that developed on a soft substratum from Central-North Poland, which was formed in several stages. In the initial stage, meltwater drainage took place through a channel that dissected the substratum (N-channel). Its development was associated with intense flow under pressure, but the sediments filling the channel were already deposited under atmospheric pressure when the flow used only part of the available space of the conduit. The high frequency of large-scale, cross-stratified lithofacies indicates significant flow depth and sediment deposition under a lower flow regime. The succession filling the channel resembles the sediments of a low-sinuosity open river systems with varied channel morphology, however, it also contains deposits like the point bar succession. Later, the R-channel developed, dominated by deposition from supercritical flows, probably of a much smaller depth. The sediments were deposited from a traction carpet or a highly turbulent suspension. The massive structure of many lithofacies indicates that flow overload was common. The transformation of the system from N-channel to R-channel was probably related to the decrease in the slope of the ice sheet surface during ablation, which resulted in a reduction of the potential hydraulic pressure gradient. The final stage of esker sedimentation was associated with deposition in an open channel, which indicates the passive nature of the marginal part of the ice sheet.

Clinical assessment of patient outcomes post percutaneous pulmonary valve implantation: Insights from a single tertiary centre

Background: Percutaneous pulmonary valve implantation (PPVI) has emerged as a promising treatment for congenital right ventricular outflow tract (RVOT) dysfunction and restoring conduit graft viability. Methods: This is a single-centre retrospective study of 41 patients (18 men, 23 women; mean age 26.1±10.2 years) who underwent PPVI between December 2007 and November 2014 and were evaluated for right ventricular pressures and exercise tolerance. Results: PPVI significantly reduced mean baseline RVOT gradients across different pathologies: stenosis (45 vs 18.4 mmHg), regurgitation (19.2 vs 7.6 mmHg), and mixed disease (32.5 vs 12 mmHg). Furthermore, mean right ventricular (RV) systolic pressures decreased from 61.6±2.3 to 41.9±2 mmHg (p&lt;0.001), while RV diastolic pressures decreased by about 60% from 14.3±1.1 to 8.6±1.4 mmHg (p&lt;0.001). Echocardiography revealed significant improvements in pulmonary and tricuspid valve velocities (p for trend&lt;0.01). Additionally, there was a consistent reduction in the main pulmonary artery maximum pressure gradient measured pre-procedure. No significant changes were observed in PR, QRS, or QTc interval duration on follow-up electrocardiograms. Similarly, no changes were noted in cardiopulmonary exercise test performance during follow-up. Conclusion: The study highlights the effectiveness of PPVI using Medtronic Melody and Edwards SAPIEN valves in patients with various pulmonary diseases. Immediate improvements in right ventricular pressures and functional outcomes suggest that PPVI is a valuable treatment option for individuals with RVOT dysfunction. Multi-centre collaborations are crucial for further elucidating the long-term effects of PPVI on cardiac function, exercise tolerance, and quality of life in RVOT dysfunction.

The value of blood flow velocity and pressure gradient in differentiating patients with different types of heart failure.

Patients with different types of heart failure (HF) exhibit varying rates of blood flow through cardiac chambers and pressure gradients across the aortic valve, attributed to differing degrees of myocardial contractility. Assessment of these dynamics offers insights into early HF diagnosis. This study aimed to analyze left ventricular outflow tract (LVOT) blood flow parameters, specifically peak blood flow velocity and pressure gradient derived from four-dimensional flow cardiovascular magnetic resonance (4D flow CMR), and to evaluate 4D flow CMR's utility in distinguishing HF types. This prospective cross-sectional study recruited 115 HF patients from January 2019 to May 2022 at the General Hospital of Ningxia Medical University, classified by the New York Heart Association Cardiac Function Classification of Heart Failure as class II-IV, alongside a control group (n=30). Participants underwent cardiovascular magnetic resonance (CMR), including 4D flow. HF patients were categorized into heart failure with reduced ejection fraction (HFrEF, n=55), heart failure with mildly reduced ejection fraction (HFmrEF, n=30), and heart failure with preserved ejection fraction (HFpEF, n=30), based on ejection fraction. The cardiac functional parameters and aortic valve flow indices were measured using Circle Cardiovascular Imaging. LVOT 4D flow data were obtained 3 mm below the junction of the aortic valve leaflets, assessing peak velocities above and below the valve. Differences in cardiac function and blood flow parameters between groups were analyzed using one-way analysis of variance (ANOVA). The accuracy of these parameters in identifying subgroups was assessed using the receiver operating characteristic (ROC) curve. Analysis of conventional cardiac function parameters revealed that left ventricular ejection fraction (LVEF) was significantly lower in the HFrEF and HFmrEF groups compared to the HFpEF and control groups (P<0.01). Additionally, end-diastolic volume and end-systolic volume were significantly higher in the HFrEF and HFmrEF groups than in the HFpEF and control groups (P<0.01). However, there were no significant differences in cardiac function parameters between the HFpEF and control groups (P>0.05). Significant differences were observed in aortic valve peak pressure gradients (Supra-APGmax) among the four study groups (5.01±1.09 vs. 6.23±2.94 vs. 7.63±1.81 vs. 8.89±2.97 mmHg, P<0.05). Aortic valve peak velocities in the HFrEF group differed significantly from the HFpEF and control groups (111.31±12.05 cm/s vs. 137.2±16 vs. 147.15±24.55 cm/s, P<0.001). The ROC curve for the pressure gradient below the aortic valve had an area under the curve (AUC) of 0.728 [95% confidence interval (CI): 0.591-0.864, P=0.002], with an optimal threshold of 4.72 mmHg (sensitivity: 0.8, specificity: 0.7, Youden index: 0.5). HF patients exhibit reduced pressure gradients across the aortic valve during systole, indicative of altered intracardiac blood flow dynamics. Combining aortic valve velocities and pressure gradients can aid in distinguishing different types of HF, including HFpEF patients.

Transjugular intrahepatic portosystemic shunting in patients over 60 years with cirrhosis and comorbidities when liver transplantation is reasonably denied

Aim. To determine the potential of TIPS that provides effective portal decompression for longevity and quality of life of patients over 60 years with cirrhosis and concomitant pathology when liver transplantation is reasonably denied.Materials and methods. The study included 27 patients aged over 60 with comorbidities, who underwent TIPS in 2016–2023 due to life-threatening manifestations of complicated portal hypertension of cirrhotic origin.Results. TIPS provided effective portal decompression in all 27 patients, confirmed by a 55.4 ± 5.2% reduction in portal pressure gradient. No hospital and 6-week mortality was recorded. 2 deaths (7.4%) were registered within one year after shunt surgery.Conclusion. In addition to lessening the risk of life-threatening complications, reduction of portal hypertension in liver cirrhosis provides favorable conditions for therapy of concomitant diseases, limited by concerns regarding hepatic decompensation. Due to the achieved stabilization of comorbidities, the denial to include the patient in the waiting list for liver transplantation can be reconsidered.

The use of patterned heating in controlling pressure losses within sloping channels

The effectiveness of utilizing heating patterns as a drag-reduction tool in sloping channels is analysed. The usefulness of heating is judged by determining the pressure gradient required to maintain the same flow rate as in the isothermal case. The key to reducing pressure loss is the formation of separation bubbles, although these bubbles are washed away at relatively large Reynolds numbers. The bubbles reduce the direct contact between the stream and the side walls, thereby reducing the friction experienced by the flow. Moreover, the fluid inside the bubbles tends to rotate, a motion provoked by longitudinal temperature gradients. This rotation also seems to reduce the resistance. On the other hand, the existence of the bubbles tends to obstruct the stream, increasing the flow resistance. In general, channels oriented close to horizontal experience a relatively small pressure loss, but this loss grows markedly as the channel inclines towards the vertical. When modest heating is applied, the pressure loss is approximately proportional to the square of the associated Rayleigh number. It is also shown that if the heating wavelength is too short or too long, the heating loses its effectiveness. In certain circumstances, it turns out that the theoretical pressure-gradient reduction achieved by judicious heating is so large that it exceeds the pressure gradient required to drive the flow in the isothermal problem. The conclusion is that in these instances, a pressure gradient of the opposite sign must be applied to prevent flow acceleration.

Least-squares pressure recovery in reduced order methods for incompressible flows

In this work, we introduce a method to recover the reduced pressure for Reduced Order Models (ROMs) of incompressible flows. The pressure is obtained as the least-squares minimum of the residual of the reduced velocity with respect to a dual norm. We prove that this procedure provides a unique solution whenever the full-order pair of velocity-pressure spaces is inf-sup stable. We also prove that the proposed method is equivalent to solving the reduced mixed problem with reduced velocity basis enriched with the supremizers of the reduced pressure gradients. Optimal error estimates for the reduced pressure are obtained for general incompressible flow equations and specifically, for the transient Navier-Stokes equations. We also perform some numerical tests for the flow past a cylinder and the lid-driven cavity flow which confirm the theoretical expectations, and show an improved convergence with respect to other pressure recovery methods.

Immediate and short-term outcomes of percutaneous balloon mitral commissurotomy for severe mitral stenosis at a Resource Limited Setting, Addis Ababa, Ethiopia

BackgroundRheumatic heart disease is a common cause of mitral stenosis (MS) in developing nations. Percutaneous mitral balloon commissurotomy (PMBC) is the treatment of choice for patients with MS with favorable anatomy. ObjectiveThis study aimed to assess immediate and short-term outcomes of percutaneous balloon mitral commissurotomy for symptomatic patients with rheumatic severe mitral stenosis. MethodsThe clinical records of patients who underwent Percutaneous Mitral Balloon Commissurotomy (PBMC) at Saint Paul Hospital Millennium Medical College, Cardiac Center were reviewed. A retrospective observational study was conducted from February 01, 2018, to August 30, 2021. All eligible patients who underwent Percutaneous Mitral Balloon Commissurotomy during the study period at the cardiac center were included in this study. Ninety-one patients were enrolled in the study after excluding repeat procedures, those with incomplete data, and lost medical records. Data were collected through chart reviews using a structured questionnaire by trained physicians, with daily supervision by the investigators. Data analysis was performed using SPSS version 25. Associations were checked using a paired t-test and Fisher's Exact Test, with statistical significance set at a p-value of <0.05. ResultPercutaneous mitral balloon commissurotomy was successful in 91.2 % of patients. Following the procedure, there was a significant increase in the mean mitral valve area from 0.799 cm2 to 1.674 cm2 and a reduction in the trans-mitral mean pressure gradient from 20 mmHg to 7.71 mmHg (P < 0.001). Atrial fibrillation and a high Wilkins score were identified as correlates of non-successful PMBC. A Wilkin's score of ≤8 and a post-procedure mitral valve area > 1.5 cm2 were associated with New York Heart Association functional class improvement three months after the procedure. ConclusionIn this study, percutaneous mitral balloon Commissurotomy (PMBC) demonstrated an excellent success rate. The majority of patients exhibited significant improvement in the New York Heart Association (NYHA) functional class.

Experimental and Theoretical Studies of Nano-Silica Solutions in Narrow Flow Paths Applied to Sealing Cement Cracks

Summary A cement crack is a typical cause of oil and gas well failure. Cracks weaken cement, reducing zonal isolation and fluid leakage. Nanoparticle (NP) gels are being tested for fracture treatment. When crushed into cracks, the flow behavior of NP problem solutions should be predicted. The potential efficacy of utilizing NP gels as a remedial measure for fractures is currently under investigation. It would be advantageous to determine if the flow behavior of solutions for NP problems can be anticipated when they are compressed into crevices. This study aimed to analyze the behavior of nano-silica solutions as they flow through ducts with rectangular cross-sections and varying crack dimensions. The introduction of NP solutions into the core leads to a decrease in pressure, which suggests that the nano-silica has been effectively transported through the crack. As the size of the fracture decreases, there is a corresponding increase in pressure drops, while the flow rate experiences a concurrent increase. This study presents responses of a pressure gradient to fluid concentration for a range of fracture widths, heights, and flow rates. The prediction of laminar flow in ducts is based on the linear correlation between the flow rate and the pressure gradient. Furthermore, the reduced pressure gradient indicates enhanced fluid flow within the fracture because of the amplified slot width. The fluid flow model proposed by Guo et al. (2022) was utilized to conduct a comparative analysis with the experimental data. Compared with test data, the model differs by roughly 90%. The technical cause of the flow model-observed data discrepancies is unknown. The flow model did not account for friction between NPs-NPs and NPs-walls in rough ducts. An empirical correlation has been found that quantifies the ratio as a function of nonsilica solution flow rate, cross-sectional geometry parameters, and nano-silica concentration. The correlation was calculated using nonlinear regression. The empirical relation and actual ratio have a significant correlation, as shown by R2 = 0.8965. In practice, Guo et al.’s (2022) hydraulic model’s pressure drops should be multiplied by the empirical correlation’s ratio to reduce errors.

Propagation Characteristics of Initial Compression Wave Induced by 400 km/h High-Speed Trains Passing through Very Long Tunnels

When high-speed trains enter tunnels, an initial compression wave is generated. As the compression wave propagates at the local speed of sound to the tunnel exit, it radiates into the surrounding environment, forming micro-pressure waves (MPWs). MPWs create sonic booms, resulting in significant environmental issues. The magnitude of the micro-pressure waves is directly proportional to the pressure gradient of the compression wave at the tunnel exit. The nonlinear effects of the initial compression wave during propagation lead to a significant increase in pressure gradient. Therefore, the propagation characteristics of the initial compression wave during the tunnel are the crucial factor affecting the amplitude of MPWs. Based on the one-dimensional compressible unsteady non-isentropic flow model and the improved generalized Riemann variable characteristic method, this paper researched the propagation and evolution characteristics of an initial compression wave generated when 400 km/h high-speed trains enter tunnels with three portal shapes: (no tunnel entrance hood (no hood), an oblique, enlarged tunnel entrance hood (type A), an enlarged equal-section non-uniform opening hole tunnel entrance hood (type B)). The results show that when the initial compression wave propagates inside very long tunnels, the pressure gradient of the compression wave exhibits a trend of initially increasing and then decreasing with the increase in propagation distance. When the pressure gradient of the compression wave reaches its maximum value, the corresponding propagation distance is the steepening critical distance. For no tunnel entrance hoods, type A tunnel entrance hoods, and type B tunnel entrance hoods, the steepening critical distances are 5 km, 6 km, and 16 km, respectively. The steepening critical distance shortens with increasing train speed. Steady friction and unsteady friction effects mainly affect the pressure amplitude and pressure gradient during compression wave propagation, respectively. At lower ambient temperatures, the nonlinear effects in compression wave propagation are significantly enhanced. The mitigation effects of type A tunnel entrance hoods and type B tunnel entrance hoods on pressure gradient reduction are mainly concentrated within 4 km and 12 km, respectively. It is necessary to determine the optimal matching relationship between the tunnel entrance hood and tunnel length based on the characteristics of compression wave propagation to ensure their mitigating performance is maximized.

Effect of symmetry-breaking on the MHD edge stability limit of tokamak plasmas

We demonstrate for the first time that symmetry-breaking in tokamak plasmas reduces the window of stable edge operational space, leading to a lower achievable edge pressure gradient. Predictive simulations with the linear magnetohydrodynamic stability code CASTOR3D show a reduction of the critical pressure gradient by up to 30%, in agreement with experimental observations. The analysis has been extended to experimental plasmas considering, for the first time, ion diamagnetic drift effects in realistic non-axisymmetric (3D) tokamak geometry. The 3D geometry in plasmas with edge localised modes (ELMs) increases the growth rate of edge instabilities compared to the axisymmetric case. Further reducing the edge pressure gradient eliminates the instabilities corresponding to an experiment with suppressed ELMs, reproducing the empirically observed threshold for ELM suppression. Our findings highlight the importance of predictions of the ELM occurrence in full 3D geometry for future tokamak devices with intentionally and unintentionally broken axisymmetry.

Alleviation of SWBLI over the payload of a launch vehicle by change of nose shape

Wind tunnel tests on a typical heavy-lift launch vehicle configuration featuring a core vehicle flanked by two strap-on boosters showed very high levels of unsteady pressures over the payload region at transonic Mach numbers when the nose had a cone-cylinder shape. This was due to very high levels of Shock Wave Boundary Layer Interactions (SWBLI) associated with the conical shape, which caused alternating flow featuring the formation of a unsteady λ-shock system over the payload region and a pair of counter-rotating vortices. The phenomenon was found to strongly depend on the proximity of the noses of the strap-on boosters to the boat tail downstream of the payload region. When the conical nose was replaced by an ogive-shaped nose, significant reduction in SWBLI occurred, with dramatic reduction of shock oscillations, pressure fluctuations, replacement of alternating flow by steady flow and disappearance of the vortex-pair. Time-averaged pressure fluctuations indicate reduction in pressure gradients due to a more gradual expansion of flow over the ogive nose compared to conical nose, an observation also supported by CFD simulations. The alleviation of SWBLI with ogive nose was so effective that the presence or absence of strap-on boosters had practically no effect on pressure fluctuations over the payload region. Unlike the conical shape, the ogive nose cone shape seems to meet both the shape and pressure parameter-criteria of NASA to ensure buffet-free environment.

Analysis of Unsteady Flow Characteristics Near the Cutwater by Cutting Impeller Hub in a High-Speed Centrifugal Pump

Centrifugal pumps are essential fluid transfer devices in marine engineering. As the two most critical components of a centrifugal pump, the dynamic–static interference between the volute and the impeller makes the flow near the cutwater highly unstable, with significant and erratic pressure pulsation, which seriously affects the stability of the operation. The impeller can be improved by cutting the hub, which helps stabilize the flow and reduce pressure pulsation near the cutwater, thus minimizing hydraulic loss. In this study, four different cutting angles were applied to the impeller hub. Computations are conducted using large eddy simulation to analyze the flow and pressure pulsation near the cutwater. Compared to the prototype pump, the modified impeller exhibits a significant reduction in pressure gradient near the blade outlet close to the cutwater. The modified impeller also shows a more uniform flow and lower amplitude of pressure pulsation. Furthermore, under various flow conditions, the centrifugal pump with the modified impeller exhibits lower hydraulic loss compared to the prototype pump, indicating that this method effectively suppresses hydraulic loss.

20-year follow-up of rheumatic mitral stenosis patients after percutaneous mitral commissurotomy: invasive transmitral gradient differential as a predictor of events.

Percutaneous mitral valve commissurotomy (PMC) is a viable alternative to mitral valve (MV) surgery in the treatment of patients with rheumatic mitral stenosis (RMS). In this single-center retrospective study of consecutive patients with RMS submitted to PMC from 1991 to 2008, we analyzed clinical, echocardiographic, and hemodynamic data and events during follow-up (FUP) until December 2021. Major adverse cardiovascular events (MACE) were a combined endpoint of all-cause death, cardiovascular hospitalization, and MV re-intervention. A total of 124 patients were enrolled: 108 (87.1%) were female, with a mean age at PMC of 46 [standard deviation (SD) 11] years. PMC was successful in 91.1%, with a mean reduction in invasive transmitral pressure gradient (TMPG) of 8 (SD 7) mmHg at PMC time. During the mean FUP of 20 (SD 6) years, 51 (41.1%) patients had MV re-intervention (86.3% surgery and 13.7% redo-PMC), 37 (29.8%) were hospitalized, and 30 (24.2%) died. Approximately 75% of patients remained MACE-free after 10 years, and this percentage decreased to around 40% after 20 years; at this time mark, about 8 in 10 patients were alive. A reduction of <5 mmHg in TMPG at PMC time was associated with a 2.7-fold greater rate of MACE compared to a reduction of ≥5 mmHg, independent of MV regurgitation after PMC and moderate disease of other valves (adjusted hazard ratio 2,7; 95% confidence interval 1.395-5.298, p=0.003). In this cohort with favorable long-term results after PMC, a reduction of <5 mmHg in TMPG at PMC time was associated with MACE during FUP. More studies are needed to validate this independent predictor.

Liver cirrhosis and antibiotic therapy but not TIPS application leads to a shift of the intestinal bacterial communities: A controlled, prospective study.

The gut-liver axis is discussed to play an important role in hepatic cirrhosis. Decompensated liver cirrhosis is associated with portal hypertension, which can lead to a variety of complications. Transjugular intrahepatic portosystemic shunt (TIPS) is an established treatment option for the complications of portal hypertension. In this study we focused on the effect of TIPS on intestinal microbial composition in cirrhotic patients. Thirty patients with liver cirrhosis were compared to 18 healthy adults. Seventeen patients with cirrhosis and portal hypertension received a TIPS. Clinical characteristics, including age, sex, and liver function measured with a Child-Pugh score and model for end-stage liver disease score, were obtained. Intestinal microbial composition was assessed via 16S rRNA gene amplicon sequencing from stool probes before and after TIPS. TIPS led to a reduction of hepatic venous pressure gradient. However, TIPS did not cause a shift in the intestinal bacterial communities. Independent from the application of TIPS, antibiotic therapy was associated with a significant difference in the intestinal bacterial microbiota and also a reduced α-diversity. In addition, a significant difference was observed in the intestinal bacterial composition between patients with liver cirrhosis and healthy controls. The presence of liver cirrhosis and the use of antibiotic therapy, but not the application of TIPS, were associated with a significant shift of the intestinal bacterial communities, showing a high impact on the microbiota of patients with liver cirrhosis.

Acute Effect in Mechanical Efficiency by Pressure-Volume Loop Analysis after Transcatheter Aortic Valve Implantation.

This study aimed to evaluate the immediate effect of transcatheter aortic valve implantation (TAVI) on mechanical efficiency. A total of 46 patients (25 females) with an average age of 83 ± 6.4 years underwent TAVI using the CoreValve system. During the same hospitalization, we conducted a comprehensive comparison of the patients before and after TAVI without inotropic support using echocardiography. The parameters encompassed left ventricular (LV) geometry, valvular load, global LV afterload and ventricular hemodynamics. The analysis using pressure-volume loops enabled the determination of load-independent contractility (Ees) and afterload, in addition to assessing potential energy, stroke work, and mechanical efficiency. The immediate effect was an augmented aortic valve area accompanied by a reduction in the transvalvular pressure gradient. We observed reductions in left ventricular end-systolic volume and end-diastolic volume, and also reductions in global afterload and end-systolic meridional wall stress. The Ea index decreased, while the Ees index remained relatively stable. We noted increases in stroke volume and systemic arterial compliance, indicating more efficient blood transfer from the ventricle to aorta. These changes contributed to the normalization of ventricular-arterial coupling. In terms of mechanical work of the chamber, we observed significant decreases in potential energy, stroke work, and pressure-volume area. There was an increase in the mechanical efficiency of the chamber. The TAVI procedure immediately reduced global afterload and improved diastolic compliance of the chamber, resulting in enhanced ventricular function and mechanical efficiency.