Mean Capillary Pressure Research Articles

Calculation of IFT in porous media in the presence of different gas and normal alkanes using the modified EoS

Gas injection can increase oil recovery because the gas–oil interfacial tension is less than the water–oil interfacial tension (IFT) and tends to zero in the miscibility state. However, little information has been provided on the gas–oil movement and penetration mechanisms in the fracture system at the porosity scale. The IFT of oil and gas in the porous medium changes and can control oil recovery. In this study, the IFT and the minimum miscibility pressure (MMP) are calculated using the cubic Peng-Robinson equation of state that has been modified using the mean pore radius and capillary pressure. The calculated IFT and MMP change with the pore radius and capillary pressure. To investigate the effect of a porous medium on the IFT during the injection of CH4, CO2, and N2 in the presence of n-alkanes and for validation, measured experimental values in references have been used. According to the results of this paper, changes in IFT vary in terms of pressure in the presence of different gases and, the proposed model has good accuracy for measuring the IFT and the MMP during the injection of hydrocarbon gases and CO2. In addition, as the average radius of the pores gets smaller, the interfacial tension tends to lower values. This effect is different with increasing the mean size of interstice in two different intervals. In the first interval, i.e. the Rp from 10 to 5000 nm, the IFT changes from 3 to 10.78 mN/m and in the second interval, i.e. the Rp from 5000 nm to infinity, the IFT changes from 10.78 to 10.85 mN/m. In other words, increasing the diameter of the porous medium to a certain threshold (i.e. 5000 nm) increases the IFT. As a rule, changes in IFT affected by exposure to a porous medium affect the values of the MMP. In general, IFT decreases in very fine porous media, causing miscibility at lower pressures.

Recruitment Microcirculatory - Mitochondrial through a permissive systemic perfusion pressure combats microcirculatory - mitochondrial distress syndrome. Cases report

Systemic Perfusion Pressure, SPP disorders cause ischemia of the affected microcirculation with critical mitochondrial damage, manifested by a hypercarbia pCO2 AV > 6 mm Hg. Thus, pCO2 has become an alarm signal, used as a marker of ischemia in terminal states with the generation of microcirculatory-mitochondrial distress syndrome, MMDS, and the installation of multiorgan organs dysfunction syndrome, MODS. Definition of SPP (~ 70 mm Hg), there is a difference between mean arterial pressure, MAP (90 mm Hg), and capillary resistance pressure, CRP (20 mm Hg) [1]. According to Maria Vasilieva's study [2,3], a tear can be a diagnostic test for various diseases. CRP in the practice of the doctor on duty can be compared with intraocular pressure, by the Kalmakov method, except for oculist glaucoma, consultation of which is essential for examining the fundus in these patients. Permissive optimization of perfusion pressure through Microcirculatory - Mitochondrial recruitment, MMR reduces the AV gap < 6 mm Hg, thus reducing MMDS. Mitochondria promote energy homeostasis by improving the functions of biosystems and pauses the expansion of MODS. Maintaining permissive SPP in critically terminal states in daily emergency clinical practice contributed to their survival [1-5]. Thus, the decisive success of Multi-organ Supportive Therapy (MOST) in Extracorporeal Life Support Organizations (ELSO) has perfusion pressure.

Pore-scale processes in tertiary low salinity waterflooding in a carbonate rock: Micro-dispersions, water film growth, and wettability change

HypothesisThe wettability change from oil-wet towards more water-wet conditions by injecting diluted brine can improve oil recovery from reservoir rocks, known as low salinity waterflooding. We investigated the underlying pore-scale mechanisms of this process to determine if improved recovery was associated with a change in local contact angle, and if additional displacement was facilitated by the formation of micro-dispersions of water in oil and water film swelling. ExperimentsX-ray imaging and high-pressure and temperature flow apparatus were used to investigate and compare high and low salinity waterflooding in a carbonate rock sample. The sample was placed in contact with crude oil to obtain an initial wetting state found in hydrocarbon reservoirs. High salinity brine was then injected at increasing flow rates followed by low salinity brine injection using the same procedure. FindingsDevelopment of water micro-droplets within the oil phase and detachment of oil layers from the rock surface were observed after low salinity waterflooding. During high salinity waterflooding, contact angles showed insignificant changes from the initial value of 115°, while the mean curvature and local capillary pressure values remained negative, consistent with oil-wet conditions. However, with low salinity, the decrease in contact angle to 102° and the shift in the mean curvature and capillary pressure to positive values indicate a wettability change. Overall, our analysis captured the in situ mechanisms and processes associated with the low salinity effect and ultimate increase in oil recovery.

Impact of left heart disease risk factors on risk stratification and treatment response in pulmonary arterial hypertension

Abstract Background Contemporary registries have documented a change in the epidemiology of PAH patients displaying increasing co-morbidities associated with left heart disease (LHD). These patients are often excluded from randomized clinical trials. It is unclear whether the presence of LHD comorbidities may adversely impact the accuracy of risk stratification and response to PAH therapy. Method Data was extracted from the Pulmonary Hypertension Society of Australia and New Zealand registry for incident patients with a diagnosis with idiopathic/heritable/toxin-induced (I/H/D)-PAH and connective tissue disease (CTD) associated PAH from 2011 - 2020. Patients without available medication and follow up data were excluded. We used the AMBITION trial exclusion criteria to define the subpopulation with LHD risk factors and haemodynamic phenotype (PAH-rLHD). Results 489 patients (I/H/D-PAH=251, CTD-PAH=238) were included in our analysis, with 103 (21.0%) fulfilling the definition of PAH-rLHD (34 had ≥3 risk factors for left heart disease (rLHD-hypertension, diabetes, obesity or ischaemic heart disease) and 76 had borderline haemodynamics (mean capillary wedge pressure 13–15 with pulmonary vascular resistance <500 dynes sec/cm5) including 7 who met both criteria). Compared to classical PAH, patients with PAH-rLHD were older at diagnosis (66±13 vs 58±19, p<0.001), had lower pulmonary vascular resistance (PVR: 393±266 vs 708±391, p=0.031) but worse exercise capacity (6MWD: 286±130m vs 327±136m, p=0.005). PAH-rLHD were more likely to be started on initial monotherapy, compared with “classical” PAH (73% vs 56%, p=0.002). In the monotherapy groups, endothelin receptor antagonists (ERA) were used in 73% PAH-rLHD, compared with 66% in classical PAH group. Both groups exhibited similar response to both mono- and combination therapy with commensurate improvements in WHO functional class (mean change 0.3±0.6 vs 0.3±0.8, p=0.443) and 6-minute walk distance (mean change 44±82 vs 48±101, p=0.723). There was no difference in survival between classical PAH and PAH-rLHD (log rank, p=0.29). The REVEAL 2.0 risk score effectively discriminated risk in both populations at baseline and first follow up (classical PAH: baseline C statistic 0.750, follow up 0.774 and PAH-rLHD: baseline C statistic 0.756, follow up 0.791). Conclusion Despite lower PVR at diagnosis, PAH-rLHD patients and “classical” PAH demonstrate similar response to first-line therapy with similar long term survival. The REVEAL 2.0 risk score can be effectively applied to the subpopulation of PAH-rLHD in real life clinical practice. Funding Acknowledgement Type of funding sources: None.

Predictors of death and heart transplantation in biopsy-proven myocarditis: a machine-learning approach

Abstract Background Risk stratification for death and heart transplantation (HTx) in myocarditis is complex. A random forest (RF) is a tree-based machine learning technique (MLT) which is being increasingly used for clinical data analysis; it allows the detection of complex relationships between the outcome of interest and the covariates, overcoming the limits of traditional statistical analysis (i.e. regression approaches). Purpose To assess the potential role of clinical and diagnostic features at presentation as predictors of death and HTx in biopsy (Bx)-proven myocarditis using RF. Methods From January 1993 to August 2019, we consecutively enrolled 357 patients with Bx-proven myocarditis (65% male, median age 39 years, interquartile range (IQR) 26–51). An RF approach for survival data was used. Variables included in the analysis were: histology type by Bx, NYHA, type of presentation (infarct-like, arrhythmia, heart failure), viral genome detection on Bx, serum antiheart (AHA), antiintercalated disk (AIDA), anticardiac endothelial cells (AECA), antinuclear (ANA) autoantibodies, immunosuppressive therapy, cardiac catheterisation (left ventricular enddiastolic volume (LVEDV), mean capillary wedge pressure, right and left ventricular enddiastolic pressure) and 2-D echocardiographic measures (LVEDV, left ventricular ejection fraction (LVEF) at presentation and at follow-up, right ventricular fractional area change (FAC%), right ventricular diastolic area). Results The median follow-up time was of 1352 days (IQR 423.25–2535.75). At the end of follow-up, 42 patients were dead or transplanted. The 1-year, 5-year, and 10-year survival probabilities were of 0.928, 0.854, and 0.817, respectively. The most relevant predictors of death or HTx identified by the RF algorithm (according to the variable importance measure) were histological type, NYHA, clinical presentation, LVEF, and FAC%. Among the circulating auto-antibodies AECA were found to be the most important. Histological type was the strongest predictor of death/HT (100% relative importance, (RI)), giant cell myocarditis having a lower survival probability compared to other types. The next stronger predictors were advanced (III-IV) NYHA and heart failure presentation with lower survival probabilities (90% and 84% RI respectively). AECA-positive patients had lower survival probability compared to AECA negative ones (20% RI). The RF algorithm revealed an excellent predictive performance in the correct identification of all alive patients, with only 5 dead patients being misclassified (balanced accuracy 94%). Conclusions Autoimmune features, i.e Giant cell myocarditis and AECA, as well as severity of heart failure and of left ventricular disfunction at presentation were the strongest predictors of dismal prognosis. Our RF approach provides a new automated powerful tool for accurate risk stratification for death/HTx in Bx-proven myocarditis. Funding Acknowledgement Type of funding source: Public Institution(s). Main funding source(s): Budget Integrato per la Ricerca dei Dipartimenti (BIRD, year 2019), Padova University, Padova, Italy (project Title: Myocarditis: genetic background, predictors of dismal prognosis and of response to immunosuppressive therapy.)

Hemodynamic variables in piglets anesthetized with isoflurane or propofol, kept under spontaneous ventilation and FIO2 of 0.5

ABSTRACT This study aimed to evaluate comparatively the effects of propofol or isoflurane on hemodynamic variables in piglets that received inspired oxygen fraction (FIO2) of 0.5 under spontaneous ventilation. Therefore, sixteen piglets weighing 16±1.1kg, were randomly divided into two groups: GI (Isoflurane and FIO2 of 0.5) and GP (Propofol and FIO2 of 0.5). Heart rate (HR), systolic, diastolic and mean arterial pressure (SAP, DAP and MAP), central venous pressure (CVP), cardiac output (CO), mean pulmonary arterial pressure (mPAP) and mean capillary pulmonary pressure (mCPP) were assessed 40 minutes after anesthetic induction (T0), followed by 15 minutes intervals (from T15 to T60). The variables cardiac index (CI), stroke volume (SV), stroke index (SI), total peripheral resistance (TPR), total peripheral resistance index (TPRI), pulmonary vascular resistance (PVR), and pulmonary vascular resistance index (PVRI) were calculated. SAP and TPRI were significantly different between groups at T30 and T60 (P< 0.05) with higher GP values being recorded. There were no differences in the other variables, however, GP presented mean closer to normality on most of the analyzed variables. Therefore, we conclude that total intravenous anesthesia with propofol presented greater stability of the hemodynamic variables evaluated.

Pulmonary Microcirculation in Experimental Model of Pulmonary Thromboembolism under Conditions of α-Adrenoceptor Blockade

Changes in the pulmonary microcirculation in isolated perfused rabbit lungs during modeling of pulmonary thromboembolism were studied in control animals and against the background of α-adrenoceptors blockade with phentolamine. Intravenous injection of emboli to control animals was followed by an increase in pressure in the pulmonary artery, mean capillary hydrostatic pressure, capillary filtration coefficient, pulmonary vascular resistance, as well as precapillary and postcapillary resistances. Against the background of α-adrenoceptor blockade, the increase in most parameters was less pronounced than in control animals, while capillary filtration coefficient increased more drastically. Thus, adrenergic mechanisms are involved in the constrictor reactions of both arterial and venous pulmonary vessels under conditions of pulmonary thromboembolism.

Reference equations for pulmonary diffusing capacity of carbon monoxide and nitric oxide in adult Caucasians.

The aim of this study was to determine reference equations for the combined measurement of diffusing capacity of the lung for carbon monoxide (CO) and nitric oxide (NO) (DLCONO). In addition, we wanted to appeal for consensus regarding methodology of the measurement including calculation of diffusing capacity of the alveolo-capillary membrane (Dm) and pulmonary capillary volume (Vc).DLCONO was measured in 282 healthy individuals aged 18-97 years using the single-breath technique and a breath-hold time of 5 s (true apnoea period). The following values were used: 1) specific conductance of nitric oxide (θNO)=4.5 mLNO·mLblood-1·min-1·mmHg-1; 2) ratio of diffusing capacity of the membrane for NO and CO (DmNO/DmCO)=1.97; and 3) 1/red cell CO conductance (1/θCO)=(1.30+0.0041·mean capillary oxygen pressure)·(14.6/Hb concentration in g·dL-1).Reference equations were established for the outcomes of DLCONO, including DLCO and DLNO and the calculated values Dm and Vc Independent variables were age, sex, height and age squared.By providing new reference equations and by appealing for consensus regarding the methodology, we hope to provide a basis for future studies and clinical use of this novel and interesting method.

Similarity Analysis of Instability Phenomenon in Porous Media with Mean Capillary Pressure

Similarity Analysis of Instability Phenomenon in Porous Media with Mean Capillary Pressure

Minimized Capillary End Effect During CO2 Displacement in 2‐D Micromodel by Manipulating Capillary Pressure at the Outlet Boundary in Lattice Boltzmann Method

AbstractWe propose a new outflow boundary condition to minimize the capillary end effect for a pore‐scale displacement simulation. The Rothman‐Keller lattice Boltzmann method with multi‐relaxation time is implemented to manipulate a nonflat wall and inflow‐outflow boundaries with physically acceptable fluid properties in 2‐D microfluidic chip domain. Introducing a mean capillary pressure acting at ‐water interface to the nonwetting fluid at the outlet effectively prevents injection pressure from suddenly dropping upon breakthrough such that the continuous invasion and the increase of saturation are allowed. This phenomenon becomes most pronounced at capillary number of logCa = −5.5, while capillary fingering and massive displacement of prevail at low and high capillary numbers, respectively. Simulations with different domain length in homogeneous and heterogeneous domains reveal that capillary pressure and saturation near the inlet are reproducible compared with those with a proposed boundary condition. The residual saturation uniquely follows the increasing tendency with increasing capillary number, corroborated by experimental evidences. The determination of the mean capillary pressure and its sensitivity are also discussed. The proposed boundary condition is commonly applicable to other pore‐scale simulations to accurately capture the spatial distribution of nonwetting fluid and corresponding displacement ratio.

手指における平均毛細管圧,前後毛細管抵抗比の無侵襲的推定法(杏林大学学位論文要旨ならびに審査要旨)

手指における平均毛細管圧,前後毛細管抵抗比の無侵襲的推定法(杏林大学学位論文要旨ならびに審査要旨)

The Feasibility of Tracheal Oxygen Supplementation during Flexible Bronchoscopy

Background: Hypoxemia is a frequent adverse event occurring during flexible bronchoscopy and is usually prevented by close monitoring and, if needed, oxygen supplementation by nasal cannula. Objective: We aim to demonstrate that tracheal oxygen supplementation during flexible bronchoscopy is a feasible, safe and effective method to restore oxygen saturation levels after oxygen desaturation. Methods: In a first phase, we compare oxygen supplementation by the tracheal or nasal route in a single blinded cross-over design in healthy volunteers. In a second phase, we study patients referred for diagnostic flexible bronchoscopy, who desaturate despite oxygen supplementation by nasal cannula, in order to assess the ability to correct hypoxemia through tracheal oxygen supplementation. Results: In the first phase, the mean capillary partial pressure of oxygen was 181 mm Hg when oxygen at a flow rate of 4 liters/min was administered by the tracheal route, compared to 125 mm Hg by the nasal route (p < 0.001). The capillary partial pressure of carbon dioxide was not significantly different. During 950 bronchoscopic procedures in the second phase of the trial, 30 patients desaturated below 90% despite oxygen supplementation by nasal cannula. In 22 out of these 30 patients, switching to the tracheal route resulted in a correction of the saturation within 120 s. In the remaining 8 patients, saturation levels were corrected after increasing the oxygen flow rate to 4 liters/min. After restoring saturation levels, the bronchoscopy could be completed in 25 of 30 patients. Conclusions: Tracheal oxygen supplementation is safe, feasible and an effective way to restore oxygen saturation levels during flexible bronchoscopy.

A fractional model of fluid flow through porous media with mean capillary pressure

In this paper, we discuss a fractional model arising in flow of two incompatible liquids through homogenous porous media with mean capillary pressure. The solution is derived by the application of the Sumudu transform and the Fourier sine transform. The results are received in compact and graceful forms in terms of the generalized Mittag-Leffler function, which are suitable for numerical computation. The mathematical formulation leads to generalized fractional derivative which has been solved by using a numerical technique by employing the iterative process with the help of appropriate boundary conditions. This problem has great importance in petroleum technology.

Anisotropy of Unsaturated Layered Soils: Impact of Layer Composition and Domain Size

Soils commonly exhibit hydraulic anisotropy under field conditions due to layering. Previous studies on saturation-dependent anisotropy were mostly focused on the impact of saturation degree, bulk density, and soil texture. In this study, the impact of layer composition and domain size on the anisotropy of unsaturated soils was investigated. We applied the same capillary pressure at top and bottom of the layered domain to simulate a mean unit hydraulic gradient condition and determined the anisotropy factor by the ratio of fluxes in the directions parallel and perpendicular to the layering. The anisotropy factors were then examined in relation to the layer composition, domain size, and mean capillary pressure for both two- and three-layer formations. In addition, the performance of the conveniently used conceptual anisotropy based on the harmonic and arithmetic mean hydraulic conductivities was also investigated for comparison. The maximum anisotropy is reached when the more permeable layer thickness is <50% in the two-layer formation. Both two-layer and three-layer formations exhibit a nonmonotonic anisotropic behavior in relation to the mean capillary pressure head. In the three-layer formations, anisotropy always exists because the minimum anisotropy factor is larger than one. In the dry range, the anisotropy of layered formations decreases significantly with increasing domain size. The anisotropy behavior of layered formations that is influenced by layer composition and domain size should be appropriately quantified, as the commonly used approach based on the harmonic and arithmetic mean of hydraulic conductivities may introduce large errors.

Right ventriculo-arterial coupling in repaired Fallot patients with pulmonary valve regurgitation before and after pulmonary valve implantation: a CMR study

Background Right ventricular-pulmonary arterial coupling plays an important role in the occurrence of right ventricular failure. Ventricular-arterial coupling is defined as Ea/ Emax. Ea is the effective arterial elastance and an index of the post-load, and includes vascular resistances, vessel compliance, vascular impedance, systolic and diastolic time intervals. Ea = (arterial end-systolic pressure/stroke volume), where arterial end-systolic pressure = (mean pulmonary arterial pressure wedge capillary pressure). The role of wedge capillary pressure can be considered negligible in subjects with normal pulmonary artery pressure and normal left ventricular (LV) function. Therefore, the formula can be simplified to Ea = (mean pulmonary arterial pressure/stroke volume). Emax is the maximal systolic ventricular elastance. This is a loadindependent index. It occurs at the end of the systole and is given by the formula Emax = [end-systolic pressure/(end-systolic volume volume (theorical) at zero load)]. Volume at zero load can be considered negligible, and end-systolic pressure can be approximated by mean pulmonary arterial pressure. Therefore Emax = (mean pulmonary artery pressure/end-systolic volume). Consequently, Ea/Emax = [(mean pulmonary artery pressure/ stroke volume)/(end-systolic volume/mean pulmonary artery pressure)] and results in Ea/Emax = (end-systolic volume/stroke volume). Optimal ventricular-arterial coupling is when Ea/Emax=1. Objective of this study is to evaluate by CMR the right ventricular-arterial coupling before and after surgical or transcatheter pulmonary valve implantation (PVI) in subjects who underwent surgery for tetralogy of Fallot (ToF) and have pulmonary valve (PV) regurgitation and/ or stenosis.

A mathematical model of the growth of uterine myomas.

Uterine myomas or fibroids are common, benign smooth muscle tumours that can grow to 10cm or more in diameter and are routinely removed surgically. They are typically slow- growing, well-vascularised, spherical tumours that, on a macro-scale, are a structurally uniform, hard elastic material. We present a multi-phase mathematical model of a fully vascularised myoma growing within a surrounding elastic tissue. Adopting a continuum approach, the model assumes the conservation of mass and momentum of four phases, namely cells/collagen, extracellular fluid, arterial and venous phases. The cell/collagen phase is treated as a poro-elastic material, based on a linear stress-strain relationship, and Darcy's law is applied to describe flow in the extracellular fluid and the two vascular phases. The supply of extracellular fluid is dependent on the capillary flow rate and mean capillary pressure expressed in terms of the arterial and venous pressures. Cell growth and division is limited to the myoma domain and dependent on the local stress in the material. The resulting model consists of a system of nonlinear partial differential equations with two moving boundaries. Numerical solutions of the model successfully reproduce qualitatively the clinically observed three-phase "fast-slow-fast" growth profile that is typical for myomas. The results suggest that this growth profile requires stress-induced resistance to growth by the surrounding tissue and a switch-like cell growth response to stress. Analysis of large-time solutions reveal that while there is a functioning vasculature throughout the myoma, exponential growth results, otherwise power-law growth is predicted. An extensive survey of the effect of parameters on model solutions is also presented, and in particular, the enhanced growth caused by factors such as oestrogen is predicted by the model.

Prevalence of iron deficiency in pulmonary hypertension and comparison according etiology

Background and objectives: Although iron is a pivotal player in several critical enzymes, limited data is available on the prevalence of iron deficiency in pulmonary hypertension (PH). We sought to assess the prevalence of iron deficiency in a population with PH. Methods: We performed a clinical, hemodynamic and echocardiographic characterization of all PH patients currently being followed in PH clinic between 2008 and 2012. We have assessed the prevalence of iron deficiency in this population by the evaluation of ferritin and transferrin saturation at baseline, nadir values and latest assessment on outpatient clinic. We also compared the different groups of PH. A total of 114 patients (68.4% female, mean age 44±18.3 years) were included. Results: Most patients were from group 1 PH (40.6%) whereas chronic thromboembolic PH comprised 23.8% patients, followed by congenital heart disease-associated PH in 22,8% (18.3% with Eisenmenger's Syndrome). At baseline, most patients were in NYHA 3 (44%) and NYHA 4 (28.4%). Mean brain natriuretic peptide was 355 pg/mL, mean pulmonary artery pressure was 51 mmHg, mean capillary wedge pressure was 9 mmHg and cardiac output was 3.0 L/min. Approximately one-third of patients were receiving warfarin and 14% patients required continuous oxygen. We have found that all the three groups showed transferrin saturation values lower than the reference values. The difference between the groups was statistically significant (DADOS p=0,009). The lowest values were found in group 1, with a mean value of 12%. Serial ferritin values were normal or elevated and no difference between groups was found. After follow-up, there was a favorable outcome when assessing the final transferrin saturation with respect to the minimum value (p<0,0001). Conclusion: The prevalence of iron deficiency is significantly high in PH, particularly in groups 1 and 2. However, there is a good response to treatment.

In vitro hemodynamic model of the arm arteriovenous circulation to study hemodynamics of native arteriovenous fistula and the distal revascularization and interval ligation procedure

Experimental modeling of arteriovenous hemodialysis fistula (AVF) hemodynamics is challenging. Mathematical modeling struggles to accurately represent the capillary bed and venous circulation. In vivo animal models are expensive and labor intensive. We hypothesized that an in vitro, physiologic model of the extremity arteriovenous circulation with provisions for AVF and distal revascularization and interval ligation (DRIL) configurations could be created as a platform for hemodynamic modeling and testing. An anatomic, upper extremity arteriovenous model was constructed of tubing focusing on the circulation from the subclavian artery to subclavian vein. Tubing material, length, diameter, and wall thickness were selected to match vessel compliance and morphology. All branch points were constructed at physiologic angles. The venous system and capillary bed were modeled using tubing and one-way valves and compliance chambers. A glycerin/water solution was created to match blood viscosity. The system was connected to a heart simulator. Pressure waveforms and flows were recorded at multiple sites along the model for the native circulation, brachiocephalic AVF configuration, and the AVF with DR without and with IL (DR no IL and DRIL). A preset mean cardiac output of 4.2 L/min from the heart simulator yielded a subclavian artery pressure of 125/55 mm Hg and a brachial artery pressure of 121/54 mm Hg with physiologic arterial waveforms. Mean capillary bed perfusion pressure was 41 mm Hg, and mean venous pressure in the distal brachial vein was 17 mm Hg with physiologic waveforms. AVF configuration resulted in a 15% decrease in distal pressure and a 65% decrease in distal flow to the hand. DR no IL had no change in distal pressure with a 27% increase in distal flow. DRIL resulted in a 3% increase in distal pressure and a 15% increase in distal flow to the hand above that of DR no IL. Flow through the DR bypass decreased from 329 mL/min to 55 mL/min with the addition of IL. Flow through the AVF for both DR no IL and DRIL was preserved. Through the construction and validation of an in vitro, pulsatile arteriovenous model, the intricate hemodynamics of AVF and treatments for ischemic steal can be studied. DR with or without IL improved distal blood flow in addition to preserving AVF flow. IL decreased the blood flow through the DR bypass itself. The findings of the AVF as a pressure sink and the relative role of IL with DR bypass has allowed this model to provide hemodynamic insight difficult or impossible to obtain in animal or human models. Further study of these phenomena with this model should allow for more effective AVF placement and maturation while personalizing treatment for associated ischemic steal. The complications of arteriovenous fistula (AVF)-associated steal with its concurrent surgical treatments have been clinically described but have relatively little published, concrete hemodynamic data. A further understanding of the underlying hemodynamics is necessary to prevent the occurrence of steal and improve treatment when it occurs. Specific objectives are to study the blood flow through an AVF with varying anatomic and physiologic parameters, determine what factors contribute to the development of arterial steal distal to an AVF, and create optimal interventions to treat arterial steal from an AVF when it occurs. The long-term goal is creation of AVF tailored to patient-specific parameters, resulting in higher rates of functional fistulas with decreases in fistula-related complications. The ability to study fluid dynamics using a unique, in vitro, upper extremity pulsatile arteriovenous circulation simulator creates the ideal platform for this work.

A new statistical approach to pore/throat size distribution of porous media using capillary pressure distribution concept

This paper proposes a method of an indirect representation of pore/throat size distribution (PSD) of porous media using capillary pressure curves by introducing two important concepts; Capillary Pressure Distribution (CPD) and Pressure Duration.First, the drainage Pc- Sw trend was modeled using a Shifted Power equation involving three regression parameters. The CPD curves were then obtained using the capillary pressure curves for five desired Pressure Durations (Pressure Duration is defined as a specific pressure range (ΔPi) based on which the vertical axis (Pc axis) in capillary pressure curve is divided into equal ranges of capillary pressure). This duration can be of various sizes depending on the application.A diagram including five curves (for five durations) of distribution (or percent of drainage) vs. Pressure Duration were then plotted, each having a peak point, representing the average mean capillary pressure (Pcm.av) of the porous medium under study which is a measure of degree of homogeneity of the medium. Finally, it was shown that the CPD curve, indirectly, accounts for size distribution of the medium; hence, no need to calculate the PSD curve. Of course, simply, using CPD curve, the PSD curve as well as the average mean throat size (if drainage process) or pore size (if imbibition process) of the medium can be obtained using the general capillary pressure equation.

Effect of acute postural variation on diabetic macular oedema

This study aimed to study the pathophysiology of diabetic macular oedema (DMO) by analysis of concomitant changes in macular volume (MV), mean arterial blood pressure (MABP), intraocular pressure (IOP), and retinal artery and vein diameters in response to acute postural changes in patients with DMO and healthy subjects. Thirteen patients with DMO (13 eyes) and five healthy subjects (five eyes) were examined after resting in a chair for 15 mins using optical coherence tomography to measure MV and fundus photography to assess retinal vessel diameters. The patients then lay down for 60 mins, during which they were examined repeatedly before they were reseated and examined again. Intraocular pressure was measured using pulse-air tonometry, arterial blood pressure by sphygomanometry and fluid columns using rulers and a spirit level. In healthy subjects, retinal artery (p = 0.02) and vein (p = 0.001) diameters decreased when subjects lay down, whereas MV remained stable. In patients with DMO, no orthostatic variation in retinal vessel diameters could be demonstrated, whereas MV had increased by 2.4 +/- 0.6% (mean +/- standard error of the mean; p = 0.006) 50 mins after assuming a recumbent position. In both healthy subjects and DMO patients, MABP decreased and IOP increased in a recumbent position, with no significant difference between the groups. The increase in MV that occurs in DMO when changing from a seated to a recumbent position is associated with a failure of retinal artery contraction, a response seen in healthy subjects that appears to counter-regulate the increase in ocular perfusion pressure caused by assuming a recumbent position.