Average Pressure Gradient Research Articles

Abstract TP407: Transvenous Pressure Monitoring Guides Endovascular Treatment of Vein of Galen Malformation

Background: Vein of Galen Malformation (VGM) is a complex vascular disorder with high morbidity and mortality. Mainstay management involves staged endovascular embolizations. Determining when to stop an embolization during any single intervention is challenging. If embolization is excessive, it precipitates thrombosis on the VGM, increase in cardiac post-load, and worsening on heart failure, as well as hemorrhages. Conversely, insufficient embolization may be futile. We report the use of transvenous pressure monitoring as an adjuvant for guiding the extent of embolization. Method: Arterial and venous accesses were obtained through the common femoral artery and vein, respectively. After diagnostic angiography, the best working projection was selected in early and late venous phases. A microcatheter was placed at the VG, and an intermediate 5 Fr. catheter was located at the persistent falcine sinus. The microcatheter was used for coil embolization, while the intermediate catheter provided support and was connected for continuous venous pressure monitoring. Continuous arterial pressure monitoring was obtained via an A-line and transduction of a glide catheter located in the carotid artery. Arterial and venous SBP were recorded. Result: Serial angiograms during treatment showed reduction of flow within the VGM. Concomitantly, there was an increase in the A-V-gradient over time (Figure 1). The difference between the A-V SBP went from 36 mmHg at the start of the case to 51 mmHg after the final coil. The average pressure gradient went from 38.3 mmHg in the first quarter to 43.5 mmHg in the last. Conclusion: The continuous assessment of transvenous pressure monitoring during embolization of VGM provides measurable changes that correlate with degree of flow. This quantifiable metric may be used as an adjunct to guide adequate reduction of flow during endovascular treatment of VGM.

Aortic valve neocuspidization in patients under 65years old.

We aimed to elucidate the surgical outcomes of aortic valve neocuspidization (AVNeo) in patients under 65years old. From December 2010 to February 2019, we performed AVNeo in a total of 168 patients. Of them, we evaluated 36 patients aged under 65years. Twenty-three patients had aortic regurgitation (AR) and 13 had aortic stenosis (AS). There were 20 patients who had isolated AVNeo, and the concomitant procedures were coronary artery bypass grafting in 5, mitral valve procedures in 4, ascending aorta replacement in 4, MAZE in 3, closure of atrial septum defect in 1, and tricuspid valve annuloplasty in 1. In the AS series, preoperative echocardiography revealed an average peak pressure gradient of 81 ± 33mmHg. In the AR series, preoperative echocardiography revealed 15 patients with severe AR and 8 patients with moderate-severe AR. There were no conversions to valve replacement. There were two in-hospital deaths owing to low output syndrome and sepsis in the emergent cases. In the AS series, postoperative echocardiography showed an average peak pressure gradient of 23 ± 15mmHg 1week post-procedure and 19 ± 9mmHg 26months post-procedure. In the AR series, postoperative echocardiography revealed no AR in 11, trivial in 9, and moderate in 1. Three patients underwent reoperation. The freedom from reoperation rates were 100% and 93% at 36 and 60months of follow-up, respectively. AVNeo in patients aged under 65years appears to be suitable considering its early and midterm outcomes. Verification and follow-up of its long-term outcomes and reliability are indispensable.

РЕЗУЛЬТАТЫ БИОПРОТЕЗИРОВАНИЯ СТВОРОК АОРТАЛЬНОГО КЛАПАНА У ПАЦИЕНТОВ СО СТЕНОЗОМ УСТЬЯ АОРТЫ ПРИ УЗКОМ ФИБРОЗНОМ КОЛЬЦЕ

Objective: To evaluate hemodynamic parameters after bioprosthetics of the aortic valve cusps, as well as complications arising in patients in the early and long-term period (6 months). Material and methods: 9 patients underwent bioprosthetics of the valves of the aortic valve with a narrow fibrous ring. The function of the cusps and left ventricle remodeling were evaluated on the 7-10th day and after 6 months. Results: Patients underwent echocardiographic examination before the intervention, in the early and long-term postoperative period. The analysis showed rather low values of pressure gradients on the aortic valve and rather large values of the effective and index area of the valve opening in patients after bioprosthetics of the aortic valve cusps. Conclusions: In the early postoperative period, prosthetics of the aortic valve leaflets with xenopericardium, according to an echocardiographic study, are associated with low average and peak pressure gradients on the aortic valve and a larger effective area and index effective area of the valve opening. The risk of the “patient-prosthesis mismatch” phenomenon with narrow fibrous rings is significantly lower with xenopericardial bioprosthetics than with standard prosthetics.

РЕЗУЛЬТАТЫ ИМПЛАНТАЦИИ ПРОТЕЗОВ БЫСТРОГО РАЗВЕРТЫВАНИЯ PERCEVAL У ПАЦИЕНТОВ СО СТЕНОЗОМ УСТЬЯ АОРТЫ ПРИ УЗКОМ ФИБРОЗНОМ КОЛЬЦЕ

Objective: To evaluate hemodynamic parameters after implantation of Perceval prostheses of quick deployment, as well as various complications that arose in patients in the early and long-term postoperative period (6 months).Material and methods: We performed 20 implantations of Perceval prostheses of quick deployment in a narrow fibrous ring. The function of the prosthesis was evaluated in the postoperative period on the 7-10th day and after 6 months. The patients underwent echocardiographic examination before the intervention, in the early and long-term postoperative period.Results: The analysis of the results of echocardiography showed rather low values of pressure gradients on the aortic valve and rather large values of the effective and indexed area of the valve opening in patients after implantation of Perceval prostheses.Conclusions: According to the results of echocardiographic study, implantation of Perceval prostheses is associated with low average and peak pressure gradients on the aortic valve and the effective area and indexed effective area of the valve opening.

Sitting posture recognition by body pressure distribution and airbag regulation strategy based on seat comfort evaluation

Unbalanced body pressure distribution caused by poor sitting posture is a significant factor causing lumbar disease. Research on the dynamic adjustment strategy for comfort sitting posture is of great significance to the prevention and improvement of lumbar disease. In this study, based on the pressure sensor array, the body pressure distribution in different sitting postures are obtained, including: back bow, waist bow, body slip, body right leaning, standard sitting position, and body left leaning. The recognition of the human body posture was achieved using the support vector machine algorithm and the accuracy rate reach to 83.33%. Furthermore, the evaluation indicators for sitting comfort of the human body are proposed using the maximum pressure, average pressure, maximum pressure gradient, average pressure gradient and asymmetry coefficient, the accuracy of the above indicators were verified using semantic differential subjective evaluation method. Experimental results show that there is a strong positive correlation between objective indicators and seat comfort. In addition, the dynamic adjustment strategy using airbag base on seat comfort evaluation is studied.

Numerical calculation of relative phase permeabilities for two-phase flow in the channel

Two-phase flow through a channel is considered for different viscosity ratios, surface tension (σ) and types of displacement (drainage or imbibition). The simulation is based on the numerical solution of the incompressible Navier–Stokes equations. Numerical calculation results of the relative phase permeability are compared for different mesh sizes. For calculation of relative phase permeability there is a problem with calculation of the average pressure gradient. Following approaches for calculation of average pressure gradient had been chosen: velocity weighted average of the pressure gradient and velocity weighted average of the viscous force. The approach of velocity weighted average of the viscous force gives more accurate results than the approach of velocity weighted average of the pressure gradient. Fingering instability was observed depending on the viscosity ratio and surface tension. All numerical calculations are performed using OpenFOAM finite volume library.

Noninvasive determination of the fetal cardiac interatrial pressure gradients by Doppler ultrasonography: preliminary results

Objective In 2000, Johnson et al. measured the atrial pressures puncturing the atria invasively in 19 fetuses that will be terminated. In this study, it is aimed to define the fetal cardiac interatrial pressure gradient noninvasively. The pressure gradients were calculated using the ductus venosus (DV) and pulmonary vein (PV) blood flow velocities and Bernoulli equation for flowing fluids. Methods “S,” “a,” and the time-averaged maximum velocities in both veins of 246 fetuses were used in the simplified Bernoulli equation; Δp =4 (). Additionally, the umbilical vein maximum velocity is measured in order to calculate ducto-umbilical pressure gradient. Results The average interatrial pressure gradient was biggest in the ventricular systole and the least gradient was in the atrial systole of a cardiac cycle. The pressure gradient changes throughout the second and the third trimester have four periods with two increases and two decreases. Conclusions The interatrial and ducto-umbilical pressure gradients can be measured noninvasively in order to follow the hemodynamic of the fetal circulatory system.

Pore Pressure Prediction in Onshore West Niger Delta Using Inverted Seismic Velocity and Derived Velocity (Vp) - Vertical Effective Stress (VES) Coefficients

In this study, pore pressure has been predicted using seismic data and derived compressional wave velocity (V p ) - Vertical Effective Stress (VES) coefficients. Post Stack Time Migration (PSTM), angle stack gathers, seismic horizons, checkshot, wireline logs, drilling and pressure data from six wells in the Onshore West Niger Delta, Nigeria were analysed and interpreted. Using generated velocity and density crossplots, the active overpressure generating mechanisms for the studied area were deduced. The V p -VES coefficients were modelled using the direct pressure data and the overburden profile computed from density log. Post stack seismic inversion was performed to improve the seismic resolution as well as derive acoustic impedance using well velocities and stacking velocities from velocity analysis of the 3-D seismic data. The derived V p -VES coefficients were used to transform the seismic acoustic impedance velocity into seismic pore pressure volume. Pore pressure profiles were accordingly extracted along well paths so as to test the accuracy of the model. Interpreted density-velocity crossplots revealed a decrease in velocity at constant density of 2.4 g/cc, an indication that unloading mechanisms contribute to overpressure in the field. The Bowers’ V p -VES coefficients of 7.43 and 0.77 were determined for A and B parameters respectively. Based on the results obtained, the top of overpressure occurred at a depth of 3750 ft and 3800 ft in UMO-001 and UMO-002 wells respectively with a corresponding average pore pressure gradient of 0.47 psi/ft for both wells, indicating that the wells are mildly overpressured. Onsets of unloading were observed in UMO-001 and UMO-002 wells at depths of 6250 ft and 6800 ft with pore pressure gradients of 0.51 psi/ft and 0.60 psi/ft respectively. The Derived Seismic Pore Pressure (DSPP) matched the measured pressure value (kick) of 5300 psi at a depth of 7450 ft and this validated and further increased confidence on the values of the V p -VES coefficients derived. These results show that the derived seismic acoustic impedance volume, vertical effective stress and overburden model produce high resolution seismic pore pressure cube in both time and space. The derived models when applied especially, with seismic acoustic impedance volume can be used to plan and drill future wells with great successes in the studied area. Keywords: pore pressure, vertical effective stress, seismic velocity, acoustic impedance DOI : 10.7176/JEES/9-10-07 Publication date :October 31 st 2019

Modeling of the Instantaneous Transvalvular Pressure Gradient in Aortic Stenosis.

The simplified and modified Bernoulli equations break down in estimating the true pressure gradient across the stenotic aortic valve due to their over simplifying assumptions of steady and inviscid conditions as well as the fundamental nature in which aortic valves are different than idealized orifices. Nevertheless, despite having newer models based on time-dependent momentum balance across an orifice, the simplified and modified Bernoulli continue to be the clinical standard because to date, they remain the only models clinically implementable. The objective of this study is to (1) illustrate the fundamental considerations necessary to accurately model the time-dependent instantaneous pressure gradient across a fixed orifice and (2) propose empirical corrections when applying orifice based models to severely stenotic aortic valves. We introduce a general model to predict the time-dependent instantaneous pressure gradient across an orifice that explicitly model the Reynolds number dependence of both the steady and unsteady terms. The accuracy of this general model is assessed with respect to previous models through pulse duplicator experiments on a round orifice model as well as an explanted stenotic surgical aortic valve both with geometric areas of 0.6cm2 (less than 1cm2 which is the threshold for stenosis determination) over cardiac outputs of 3 and 5L/min and heart rates of 60, 90 and 120bpm. The model and the raw experimental data corresponding to the orifice showed good agreement over a wide range of cardiac outputs and heart rates (R2 exceeding 0.91). The derived average and peak transvalvular pressure gradients also demonstrated good agreement with no significant differences between the respective peaks (p > 0.09). The new model proposed holds promise with its physical and closed form representation of pressure drop, however accurate modeling of the time-variability of the valve area is necessary for the model to be applied on stenotic valves.

Transesophageal echocardiography during endovascular aortic valve replacement (TAVI)

Objective: to evaluate the effectiveness of endovascular aortic valve replacement (TAVI) according to transesophageal echocardiography. Materials and methods: 29 TAVI operations were performed in patients with aortic valve stenosis (AV) with Lotus Valve system (Boston Scientific, USA) and CoreValve (Medtronic, USA). All patients underwent intraoperative Chpehokg on devices sh50 (Philips, the Netherlands), ACUSON SC2000 (Siemens, Germany) transesophageal sensors X7-2t, Z6Ms, at the following stages of operation: 1 - after intubation of the patient; 2 - the main stage of operation: when placing the conductor in the cavity of the left ventricle, after balloon valvuloplasty, when positioning and implantation of the prosthesis; 3 - the end of the operation. TEE at the beginning and end of the operation was conducted according to the accepted Protocol. Results: all patients had pronounced AV stenosis, peak and average pressure gradients on AV were 90.0±27.0 and 51.5±16.5 mm Hg. respectively. Intraoperative TEE in 3D mode and creating a model of the aortic root, the calculated linear dimensions of the aortic root, which coincided with the data of CT. One patient was diagnosed with worsening of the degree of mitral stenosis to expressed in the formulation of the CoreValve system, and also recorded one episode of severe pericardial effusion after placing the conductor in the cavity of the left ventricle. In all patients, hemodynamic parameters and function of prostheses after surgery were within normal limits, with an average pressure gradient on the AK prosthesis was 5.9±2.8 mm Hg. Conclusion: Tee is a basic method in the assessment of valvular structures of the heart, is of great importance for the timely diagnosis of complications during surgery endovascular aortic valve replacement, and research in 3D and 4D modes can replace the expensive research.

Endovascular Stenting in a Transgender Patient With Idiopathic Intracranial Hypertension

Endovascular Stenting in a Transgender Patient With Idiopathic Intracranial Hypertension

Computational Fluid Dynamics Flow Simulations in Discrete Element Method-Resolved Packed Beds

This paper presents computational simulations of flows in packed beds and compares the computational pressure-drop results with those given by the Ergun correlation. The computational methodology used in this work follows the combined discrete element method (DEM) and computational fluid dynamics (CFD) technique. DEM is used to predict the locations and packing structure of the particles in the bed, while CFD is used to predict the flow field in the void space surrounding the packed particles. The computational results obtained for irregular packed beds show that the local packing-structure parameters have significant effects not only on the local velocity and pressure fields but also on macroscopic quantities, such as the average pressure gradient along the length of the packed column. The computational results also show that classical correlations based on averaged values, such as the Ergun correlation, have poor predictive accuracy for macroscopic variations along a packed column, and this is mainly because such correlations do not account for local packing-structure parameters. The computational results confirm the existence of sections with linear variation of macroscopic parameters along the length of the packed column, and this leads to the conclusion that accurate results from DEM-CFD methods on shortened columns can be extrapolated to full-length columns. Moreover, it was found that unlike regularly packed beds, the predicted pressure for randomly packed beds experiences an apparent strong recovery near the downstream end of the packed bed, and then experiences a strong dip down to the plateau leading to the exit pressure.

Numerical Simulation Study on Seepage Theory of a Multi-Section Fractured Horizontal Well in Shale Gas Reservoirs Based on Multi-Scale Flow Mechanisms

Aimed at the multi-scale fractures for stimulated reservoir volume (SRV)-fractured horizontal wells in shale gas reservoirs, a mathematical model of unsteady seepage is established, which considers the characteristics of a dual media of matrix and natural fractures as well as flow in the large-scale hydraulic fractures, based on a discrete-fracture model. Multi-scale flow mechanisms, such as gas desorption, the Klinkenberg effect, and gas diffusion are taken into consideration. A three-dimensional numerical model based on the finite volume method is established, which includes the construction of spatial discretization, calculation of average pressure gradient, and variable at interface, etc. Some related processing techniques, such as boundedness processing upstream and downstream of grid flow, was used to limit non-physical oscillation at large-scale hydraulic fracture interfaces. The sequential solution is performed to solve the pressure equations of matrix, natural, and large-scale hydraulic fractures. The production dynamics and pressure distribution of a multi-section fractured horizontal well in a shale gas reservoir are calculated. Results indicate that, with the increase of the Langmuir volume, the average formation pressure decreases at a slow rate. Simultaneously, the initial gas production and the contribution ratio of the desorbed gas increase. With the decrease of the pore size of the matrix, gas diffusion and the Klinkenberg effect have a greater impact on shale gas production. By changing the fracture half-length and the number of fractured sections, we observe that the production process can not only pursue the long fractures or increase the number of fractured sections, but also should optimize the parameters such as the perforation position, cluster spacing, and fracturing sequence. The stimulated reservoir volume can effectively control the shale reservoir.

Early and mid-term results of isolated aortic valve neocuspidization in patients with aortic stenosis.

This study aimed to elucidate the surgical outcome of aortic valve neocuspidization (AVNeo) in patients with aortic stenosis (AS). From December 2010 to June 2017, we performed AVNeo for aortic valve pathologies in 144 patients. Of them, we evaluated 57 patients with AS who underwent AVNeo. Their mean age was 77.5 ± 8.8years. Fifty-five patients had AS from degenerative changes, 1 from pericardium endocarditis, and 1 from prosthetic valve endocarditis. Forty patients had a tricuspid aortic valve, 1 had a unicuspid valve, 14 had a bicuspid valve, 1 had a quadricuspid valve, and 1 had postoperative aortic valve replacement (AVR). Preoperative echocardiography revealed an average peak pressure gradient of 89 ± 32.9mmHg and a mean pressure gradient of 52 ± 18.8mmHg. The surgical procedure complies with the 3 cuspid suturing to the aortic annulus with the glutaraldehyde-treated pericardium. There were no conversions to AVR. There were 2 noncardiac-related deaths owing to liver failure and sepsis. Postoperative echocardiography showed an average peak pressure gradient of 22 ± 10.7mmHg 1week after the procedure and 19.2 ± 9.7mmHg 20months after the procedure. Two patients underwent reoperation owing to infective endocarditis and recurrent aortic regurgitation. The mean follow-up period was 30.4 ± 20.8months. The freedom from reoperation rates was 98.1 and 95.3% at 12 and 81months of follow-up, respectively. AVNeo is suitable for patients with AS considering its early and mid-term outcomes. Verification of long-term outcomes and reliability is necessary.

On the Significance of Systolic Flow Waveform on Aortic Valve Energy Loss.

This study aims to quantitatively and qualitatively assess energy dissipation in the aortic valve as a function of systolic aortic flow waveform representing pathologies where flow time-to-peak is delayed. A bioprosthetic valve was tested in the aortic position of a left-heart simulator under physiological pressure and flow conditions. The flow loop piston pump was programmed to generate three different flow waveforms each with a different peak time annotated as early peak (EP) with a rapid acceleration, mid peak (MP) and late peak (LP) with a rapid deceleration. Energy dissipation was calculated from flow and pressure measurements while sinus vorticity dynamics were evaluated using time-resolved planar particle image velocimetry. Average pressure gradients during systole are found 30.2 ± 0.19, 30.7 ± 0.25 and 32.9 ± 0.29mmHg and average dissipation over systole is found 0.95 ± 0.026, 1.05 ± 0.034 and 1.25 ± 0.043W for EP, MP and LP respectively. As systole's acceleration phase is slower, sinus vortices are more likely to form, necessitating more energy exchange from shear layers inducing more viscous dissipation. EP found in healthy individuals is superior in terms of reducing energy dissipation and increasing aortic valve efficiency. In the context of possible left ventricular dysfunction and aortic stenosis, this means that delayed time-to-peak in the aortic flow waveform seen is not compensatory.

Transverse venous stenting for the treatment of idiopathic intracranial hypertension, or pseudotumor cerebri.

OBJECTIVE Idiopathic intracranial hypertension (IIH) is a commonly occurring disease, particularly among young women of child-bearing age. The underlying pathophysiology for this disease has remained largely unclear; however, the recent literature suggests that focal outflow obstruction of the transverse sinus may be the cause. The purpose of this study was to report one group's early experience with transverse venous sinus stenting in the treatment of IIH and assess its effectiveness. METHODS The authors performed a retrospective chart review to identify patients who had undergone stenting of an outflow-obstructed transverse venous sinus for the treatment of IIH at Gates Vascular Institute between January 2015 and November 2017. Patient demographic data of interest included age, sex, BMI, and history of smoking, hypertension, obstructive sleep apnea, hormonal contraceptive use, and acetazolamide therapy. Each patient's presenting signs and symptoms and whether those symptoms improved with treatment were reviewed. The average opening lumbar puncture (LP) pressure preprocedure, average pressure gradient across the obstructed segment prior to stenting, treatment failure rate (need for shunt placement), and mean follow-up period were calculated. RESULTS Of the 18 patients who had undergone transverse venous stenting for IIH, 16 (88.9%) were women. The mean age of all the patients was 38.3 years (median 38 years). Mean BMI was 34.2 kg/m2 (median 33.9 kg/m2). Presenting symptoms were headache (16 patients [88.9%]), visual disturbances (13 patients [72.2%]), papilledema (8 patients [44.4%]), tinnitus (3 patients [16.7%]), and auditory bruit (3 patients [16.7%]). The mean opening LP pressure pre-procedure was 35.6 cm H2O (median 32 cm H2O). The mean pressure gradient measured proximally and distally to the area of focal obstruction within the transverse sinus was 16.5 cm H2O (median 15 cm H2O). Postprocedurally, 14 patients (77.8%) continued to have headaches; 6 (33.3%) continued to have visual disturbances. No patients continued to have auditory bruit (0%) or papilledema (0%). One patient (5.6%) had new-onset tinnitus postprocedure. Overall improvement of symptoms was noted in 16 patients (88.9%) postprocedure, with 1 patient (5.6%) requiring shunt placement and 2 other patients (11.1%) requiring postprocedural LP to monitor intracranial pressure to determine candidacy for further surgical interventions to treat residual symptoms. The mean duration of follow-up was 194.2 days. CONCLUSIONS Transverse sinus stenting is a rapidly developing technique that has shown good effectiveness and safety in the literature. Authors of the present study found that stenting a flow-obstructed transverse sinus in patients with IIH was a safe and effective way to treat the condition.

Impact of membrane orientation on the energy efficiency of dual stage pressure retarded osmosis

The performance of Dual Stage Pressure Retarded Osmosis (DSPRO) was analyzed using a developed computer model. DSPRO process was evaluated on Pressure Retarded Osmosis (PRO) and Forward Osmosis (FO) operating modes for different sodium chloride (NaCl) draw and feed concentrations. Simulation results revealed that the total power generation in the DSPRO process operating on the PRO mode was 2.5–5 times more than that operating on the FO mode. For DSPRO operating on the PRO mode, the higher power generation was in the case of 2 M NaCl-fresh and 32% the contribution of the second stage to the total power generation in the DSPRO. To the contrast, he total power generated in the DSPRO operating on the FO mode was in the following order 5M-0.6M > 5M-0.7M > 2M-0.01 > 2M-0.6 M. Interestingly, single stage process operating on the FO mode performed better than DSPRO process due to the severe concentration polarization effects. The results also showed that power density of the DSPRO reached a maximum amount at a hydraulic pressure less than the average osmotic pressure gradient, Δπ/2, due to the variation of optimum operating pressure of each stage. Moreover, results showed that the effective specific energy in the PRO process was lower than the maximum specific energy. However, the effective specific energy of the DSPRO was larger than that of the single stage PRO due to the rejuvenation of the salinity gradient, emphasizing the high potential of the DSPRO process for power generation.

ОПРЕДЕЛЕНИЕ ДАВЛЕНИЯ ГИДРОРАЗРЫВА ПЛАСТА ПРИ БУРЕНИИ СКВАЖИН НА ШЕЛЬФЕ

The purpose of the article is to focus on the breakdown pressure of the well bore when drilling offshore for oil and gas. It is much lower than the one when drilling on shore and can vary significantly. Domestic articles on this topic are little to choose. One of the reasons of this situation is that drilling on the already explored offshore deposits is not performed now as the oil prices are low, and drilling from the floating drilling rigs is too expensive. Moreover, severe ice conditions and imperfection of drilling equipment for offshore drilling hinder the development of drilling works in the Northern and Eastern seas. We should also note the lack of experience of Russian drillers in the development of offshore oil and gas fields. Methods. The study uses a refined analytical calculation of the breakdown pressure of the well bore and its gradient. Results. To determine the breakdown pressure it is proposed to allow for the shelf depth and rotary table elevation above the average level of the shelf surface. The depth of the shelf is often not taken into account allegedly because of its small depths. But the described factor is not the only one that causes a short-term increase in the hydrostatic pressure. It could also be caused by daily tides, swabbing under RIH/POOH operations and etc. All together they can cause the loss of circulation. Besides, the article presents the average overburden and formation pressure gradients in tabular variants instead of graphical ones in order to facilitate the calculations. Conclusions. Analytical determination of the fracture pressure when drilling offshore wells (water holes) is an important task as it gives the real values of the fracture pressure. This can help to prevent the loss of circulation.

Comparison of phase-contrast MR and flow simulations for the study of CSF dynamics in the cervical spine.

Background Investigators use phase-contrast magnetic resonance (PC-MR) and computational fluid dynamics (CFD) to assess cerebrospinal fluid dynamics. We compared qualitative and quantitative results from the two methods. Methods Four volunteers were imaged with a heavily T2-weighted volume gradient echo scan of the brain and cervical spine at 3T and with PC-MR. Velocities were calculated from PC-MR for each phase in the cardiac cycle. Mean pressure gradients in the PC-MR acquisition through the cardiac cycle were calculated with the Navier-Stokes equations. Volumetric MR images of the brain and upper spine were segmented and converted to meshes. Models of the subarachnoid space were created from volume images with the Vascular Modeling Toolkit. CFD simulations were performed with a previously verified flow solver. The flow patterns, velocities and pressures were compared in PC-MR and CFD flow images. Results PC-MR images consistently revealed more inhomogeneous flow patterns than CFD, especially in the anterolateral subarachnoid space where spinal nerve roots are located. On average, peak systolic and diastolic velocities in PC-MR exceeded those in CFD by 31% and 41%, respectively. On average, systolic and diastolic pressure gradients calculated from PC-MR exceeded those of CFD by 11% and 39%, respectively. Conclusions PC-MR shows local flow disturbances that are not evident in typical CFD. The velocities and pressure gradients calculated from PC-MR are systematically larger than those calculated from CFD.

Medium-Term Outcomes After Implantation of Expanded Polytetrafluoroethylene Valved Conduit

Pulmonary valve replacement is becoming the most frequent congenital heart surgery performed on adolescents and young adults. Numerous surgical options are available, including autologous pericardium, mechanical valves, allografts, and bioprosthetic valves. Each option has limitations with durability and freedom from reintervention for stenosis or insufficiency, particularly in the pediatric population. The purpose of this study was to analyze our uniquely designed, expanded polytetrafluoroethylene (ePTFE) valved conduit (VC) for right ventricular outflow tract reconstruction. Beginning in 2012, ePTFE VC were implanted in 26 patients with a median age of 9.8 years (range, 1.0 to 15.9). Bicuspid VC were used in the first 3 patients, and tricuspid VC were used in 23 patients. The ePTFE VC is fashioned from commercially available ePTFE tube graft (16 mm in 1 patient, 20 mm in 7 patients, 24 mm in 18 patients) and 0.1 mm thick ePTFE membrane for the leaflet material. Valve function was assessed by echocardiogram after the implantation. There were no postoperative hospital deaths. Mean follow-up was 2.6 years (range, 4 months to 4.7 years), and there have been no reoperations for the ePTFE VC. There was one reintervention for stenosis at the distal anastomosis. Pulmonary insufficiency was mild or less in 24 patients (92%). The average peak instantaneous pressure gradient between the right ventricle and the pulmonary artery was 22.4 ± 15.1 mm Hg at latest follow-up. Compared with historical data for other pulmonary valve replacement options, our ePTFE VC shows superior medium-term performance, with less reintervention or significant valve dysfunction.