Partial Pressure Gradient Research Articles

An Arteriovenous Bioreactor Perfusion System for Physiological In Vitro Culture of Complex Vascularized Tissue Constructs

Background: The generation and perfusion of complex vascularized tissues in vitro requires sophisticated perfusion techniques. For multiscale arteriovenous networks, not only the arterial, but also the venous, biomechanical and biochemical conditions that physiologically exist in the human body must be accurately emulated. For this, we here present a modular arteriovenous perfusion system for the in vitro culture of a multi-scale bioartificial vascular network. Methods: The custom-built perfusion system consisted of two circuits: in the arterial circuit, physiological arterial biomechanical and biochemical conditions were simulated using a modular set-up with a pulsatile peristaltic pump, compliance chambers, and resistors. In the venous circuit, venous conditions were emulated accordingly. In the center of the system, a bioartificial multi-scale vascularized fibrin-based tissue was perfused by both circuits simultaneously under biomimetic arteriovenous conditions. Culture conditions were monitored continuously using a multi-sensor monitoring system. Results: The physiological arterial and venous pressure- and flow-curves, as well as the microvascular arteriovenous oxygen partial pressure gradient, were accurately emulated in the perfusion system. The multi-sensor monitoring system facilitated live monitoring of the respective parameters and data-logging. In a proof-of-concept experiment, vascularized three-dimensional fibrin tissues showed sustained cell viability and homogenous microvessel formation after culture in the perfusion system. Conclusions: The arteriovenous perfusion system facilitated the in vitro culture of a multiscale vascularized tissue under physiological pressure-, flow-, and oxygen-gradient conditions. With that, it presents a promising technique for the in vitro generation and culture of complex large-scale vascularized tissues.

Comprehensive theoretical study on ionic transport numbers of triple ionic-electronic conducting oxides determined by the electromotive force method

Triple ionic-electronic conducting (TIEC) oxides, as an emerging class of materials with complex conduction properties, are used in diverse electrochemical energy devices. Accurately determining the transport numbers (tx) of TIEC oxides is significant. In this study, we theoretically evaluate the reliability of the electromotive force (EMF) method in determining tx of TIEC oxides and address the issue that tx obtained by the EMF method is an apparent value (txapp). Initially, based on a precise defect distribution model, it reveals the non-uniform distributions of transport numbers within the TIEC membrane. Subsequently, through a comprehensive multiple-factor analysis, it discloses that compared with temperature and thermodynamic parameters of defect reactions, the gradient of gas partial pressure in concentration cells is the primary influencing factor affecting txapp. Notably, under conditions of relatively small gradients of gas partial pressure, txapp can be approximated as the average value of tx at both sides of the membrane. Motivated by these findings, we propose a new EMF method, which can determine the accurate tx of materials at a specific gas composition, rather than an apparent one. Overall, the finding of this study furnishes valuable insights into determining transport numbers of TIEC oxides.

The Role of Ocean Mesoscale Variability in Air‐Sea CO2 Exchange: A Global Perspective

AbstractOcean mesoscale flows significantly influence nutrient distribution and biological productivity, yet the scarcity of eddy‐permitting observational data sets and climate modeling hinders understanding their role in carbon sequestration. Using an eddy‐resolving global simulation, this study investigates the significance of ocean mesoscales in air‐sea carbon dioxide (CO2) exchange. Results show over 30% of CO2 flux variance in energetic regions attributed to flows with horizontal scales smaller than 2°. Mesoscale flows can drive a cumulative CO2 flux that is either a net carbon sink or source depending on region, with magnitudes on the order of 105 tonnes of carbon per year. Variations in this mesoscale‐related CO2 flux are correlated with local relative vorticity and the background gradient of ocean partial pressure of CO2. This analysis underscores the importance of considering ocean mesoscales in monitoring carbon flux, highlighting the need to explore the influence of increasing eddy activity on carbon uptake in a changing climate.

Storm‐Driven pCO2 Feedback Weakens the Response of Air‐Sea CO2 Fluxes in the Sub‐Antarctic Southern Ocean

AbstractThe sub‐seasonal CO2 flux (FCO2) variability across the Southern Ocean is poorly understood due to sparse observations at the required temporal and spatial scales. Twinned surface and profiling gliders experiments were used to investigate how storms influence FCO2 through the air‐sea gradient in partial pressure of CO2 (ΔpCO2) in the sub‐Antarctic zone. Winter‐spring storms caused ΔpCO2 to weaken (by 22–37 μatm) due to mixing/entrainment and weaker stratification. This weakening in ΔpCO2 was in phase with the increase in wind stress resulting in a reduction of the storm‐driven CO2 uptake by 6%–27%. During summer, stronger stratification explained the weaker sensitivity of ΔpCO2 to storms, instead temperature changes dominated the ΔpCO2 variability. These results highlight the importance of observing synoptic‐scale variability in ΔpCO2, the absence of which may propagate significant biases to the mean annual FCO2 estimates from large‐scale observing programmes and reconstructions.

Enhancement of carbon sink in the main marginal sea ice zone by cold season Arctic cyclones

The Arctic Ocean, as a significant carbon sink, is attracting increased attention within the scientific community. This study focused on the main marginal sea ice zone, which has been the most sensitive to environmental changes in recent decades. Using data from reanalysis, models, and on-site observations, the changes in air–sea CO2 flux (FCO2) were analyzed during the influence of Arctic cyclones (ACs) in 2021–2022. Results indicated that the passage of ACs tended to increase the average carbon sink in the main marginal ice zone, with a more pronounced effect during the cold season. During ACs, the average FCO2 could reach −6.95 mmolC m−2 d−1. This was mainly associated with the stronger and more concentrated distribution of ACs where there was lower pCO2 (air–sea gradient of CO2 partial pressure) in the cold season. Additionally, the change in FCO2 during ACs was primarily affected by the sea surface wind and sea-ice concentration in the cold season, while it was influenced by a variety of environmental factors in the warm season, including the sea surface wind, sea-ice concentration, and ecological factors.

Distribution and transformation characteristics of water vapor field in the fissured rock mass and its ecological significance

Opencast mining has produced a large number of high and steep rock slopes, leading to serious safety and environmental challenges. Extreme water scarcity conditions severely impede the survival and development of natural and artificial vegetation when carrying out ecological restoration work. The water vapor field within rocks is a significant but often neglected component of the terrestrial hydrologic cycle and can provide a hidden but critical source of water for plants. However, there is a lack of understanding of the distribution characteristics of the water vapor field within rocks and the pattern of liquid water formation as well as whether it is quantitatively significant and ecologically relevant. This study conducted monitoring experiments on the water vapor field of fissured rock mass and studied the distribution and transformation characteristics of water vapor field in the fissured rock mass and its ecological significance. The results showed temperature and absolute humidity gradually decreased with horizontal depth in spring and summer, and the opposite in autumn and winter. Relative humidity increased rapidly and stabilized with horizontal depth in the spring and summer, and increased rapidly in the autumn and winter, before decreasing slightly. The driving force of water vapor migration is the water vapor partial pressure gradient. In spring and summer, water vapor migrated from air along the fissures to the deep part of the rock mass, while the opposite was true in autumn and winter. While the water vapor migrated through the fissured rock mass, water vapor saturation zones would be produced locally, where potential condensate is generated. The fissure network functioned as a sustained system of water supply pipelines, and the plant roots that grew into the fissures could absorb the condensate, continuously supplying the growth and development of the rock slope plants. This study provides a comprehensive understanding of the rock water vapor field and its effects on ecosystems in arid and semi-arid areas, which can guide the restoration of ecosystems on rock slopes.

Multiplying Oxygen Permeability of a Ruddlesden-Popper Oxide by Orientation Control via Magnets.

Ruddlesden-Popper-type oxides exhibit remarkable chemical stability in comparison to perovskite oxides. However, they display lower oxygen permeability. We present an approach to overcome this trade-off by leveraging the anisotropic properties of Nd2 NiO4+δ . Its (a,b)-plane, having oxygen diffusion coefficient and surface exchange coefficient several orders of magnitude higher than its c-axis, can be aligned perpendicular to the gradient of oxygen partial pressure by a magnetic field (0.81 T). A stable and high oxygen flux of 1.40 mL min-1 cm-2 was achieved for at least 120 h at 1223 K by a textured asymmetric disk membrane with 1.0 mm thickness under the pure CO2 sweeping. Its excellent operational stability was also verified even at 1023 K in pure CO2 . These findings highlight the significant enhancement in oxygen permeation membrane performance achievable by adjusting the grain orientation. Consequently, Nd2 NiO4+δ emerges as a promising candidate for industrial applications in air separation, syngas production, and CO2 capture under harsh conditions.

Multiplying Oxygen Permeability of a Ruddlesden‐Popper Oxide by Orientation Control via Magnets

AbstractRuddlesden‐Popper‐type oxides exhibit remarkable chemical stability in comparison to perovskite oxides. However, they display lower oxygen permeability. We present an approach to overcome this trade‐off by leveraging the anisotropic properties of Nd2NiO4+δ. Its (a,b)‐plane, having oxygen diffusion coefficient and surface exchange coefficient several orders of magnitude higher than its c‐axis, can be aligned perpendicular to the gradient of oxygen partial pressure by a magnetic field (0.81 T). A stable and high oxygen flux of 1.40 mL min−1 cm−2 was achieved for at least 120 h at 1223 K by a textured asymmetric disk membrane with 1.0 mm thickness under the pure CO2 sweeping. Its excellent operational stability was also verified even at 1023 K in pure CO2. These findings highlight the significant enhancement in oxygen permeation membrane performance achievable by adjusting the grain orientation. Consequently, Nd2NiO4+δ emerges as a promising candidate for industrial applications in air separation, syngas production, and CO2 capture under harsh conditions.

Impaired O2 unloading from stored blood results in diffusion-limited O2 release at tissues: evidence from human kidneys

AbstractThe volume of oxygen drawn from systemic capillaries down a partial pressure gradient is determined by the oxygen content of red blood cells (RBCs) and their oxygen-unloading kinetics, although the latter is assumed to be rapid and, therefore, not a meaningful factor. Under this paradigm, oxygen transfer to tissues is perfusion-limited. Consequently, clinical treatments to optimize oxygen delivery aim at improving blood flow and arterial oxygen content, rather than RBC oxygen handling. Although the oxygen-carrying capacity of blood is increased with transfusion, studies have shown that stored blood undergoes kinetic attrition of oxygen release, which may compromise overall oxygen delivery to tissues by causing transport to become diffusion-limited. We sought evidence for diffusion-limited oxygen release in viable human kidneys, normothermically perfused with stored blood. In a cohort of kidneys that went on to be transplanted, renal respiration correlated inversely with the time-constant of oxygen unloading from RBCs used for perfusion. Furthermore, the renal respiratory rate did not correlate with arterial O2 delivery unless this factored the rate of oxygen-release from RBCs, as expected from diffusion-limited transport. To test for a rescue effect, perfusion of kidneys deemed unsuitable for transplantation was alternated between stored and rejuvenated RBCs of the same donation. This experiment controlled oxygen-unloading, without intervening ischemia, holding all non-RBC parameters constant. Rejuvenated oxygen-unloading kinetics improved the kidney’s oxygen diffusion capacity and increased cortical oxygen partial pressure by 60%. Thus, oxygen delivery to tissues can become diffusion-limited during perfusion with stored blood, which has implications in scenarios, such as ex vivo organ perfusion, major hemorrhage, and pediatric transfusion. This trial was registered at www.clinicaltrials.gov as #ISRCTN13292277.

Study on Mechanism of Preparing Spherical Aluminum Powder by Evaporative Condensation

The nucleation of aluminum vapor in phase transition and its condensation were studied at 15 pa. The impacts of the condensing conditions, including the aluminum partial pressure, temperature, and condensation zone temperature gradient, on aluminum vapor nucleation and condensation, were discussed from the point of view of atom collision. Aluminum powder and beads were produced under different conditions and characterized by scanning electron microscopy (SEM) and the proportion of fine powder. The rate of evaporation increases with increasing temperature and evaporation surface area. The condensation position at which the aluminum vapor becomes solid is further away from the evaporation surface area, with the temperature of the heating source increasing. It can benefit to the condensation and crystallization of aluminum vapor by appropriately increasing the condensing zone’s crucible diameter and temperature gradient.

Hyperbolic–parabolic normal form and local classical solutions for cross-diffusion systems with incomplete diffusion

We investigate degenerate cross-diffusion equations, with a rank-deficient diffusion-matrix, modelling multispecies population dynamics driven by partial pressure gradients. These equations have recently been found to arise in a mean-field limit of interacting stochastic particle systems. To date, their analysis in multiple space dimensions has been confined to the purely convective case with equal mobility coefficients. In this article, we introduce a normal form for an entropic class of such equations which reveals their structure of a symmetric hyperbolic–parabolic system. Due to the state-dependence of the range and kernel of the singular diffusive matrix, our way of rewriting the equations is different from that classically used for symmetric second-order systems with a nullspace invariance property. By means of this change of variables, we solve the Cauchy problem for short times and positive initial data in for

Diffusion Barriers Minimizing the Strength Degradation of Reactive Air Brazed Ba0.5Sr0.5Co0.8Fe0.2O3-δ Membranes during Aging.

The separation of oxygen from air by means of inorganic ceramic membranes requires gas-tight ceramic-metal joints that enable reliable permeation operation in the oxygen partial pressure gradient at 850 °C. Reactive air brazing is a promising method to solve this challenge. However, reactive air brazed BSCF membranes suffer from a significant strength degradation that is caused by unhindered diffusion from the metal component during aging. In this study, we investigated how diffusion layers applied on the austenitic steel AISI 314 influence the bending strength of BSCF-Ag3CuO-AISI314 joints after aging. Three different approaches were compared as diffusion barriers: (1) aluminizing via pack cementation, (2) spray coating with NiCoCrAlReY, and (3) spray coating with NiCoCrAlReY and an additional 7YSZ top layer. Coated steel components were brazed to bending bars and aged for 1000 h at 850 °C in air prior to four-point bending and subsequent macroscopic as well microscopic analyses. In particular, coating with NiCoCrAlReY showed low-defect microstructures. The characteristic joint strength was raised from 17 MPa to 35 MPa after 1000 h aging at 850 °C. In addition, the dominant delamination fracture between the steel and the mixed oxide layer, observed in the reference series with uncoated steel, could be replaced by mixed and ceramic fractures of higher strength. The effect of residual joint stresses on the crack formation and path is analyzed and discussed. Chromium poisoning could no longer be detected in the BSCF, and interdiffusion through the braze was effectively reduced. Since the strength degradation of reactive air brazed joints is mainly caused by the metallic joining partner, the findings on the effect of the diffusion barriers in BSCF joints might be transferred to numerous other joining systems.

Multi-scale simulation of the fracture behavior of non-stoichiometric gadolinia-doped ceria solid electrolytes under the coupled mechanical and electrochemical field

Solid oxide fuel cell (SOFC) works in a complex working environment, which is affected by many factors such as temperature, load and electrochemical reaction. When there are cracks in the material, the multi-field coupling effect will cause the electrolyte performance degradation, even failure and damage. In this paper, the coupling effects of mechanical and electrochemical field on mechanical behavior of gadolinia-doped ceria (GDC) electrolyte are investigated by using the Atom-to-Continuum (AtC) multi-scale method combining molecular dynamics (MD) and finite element method (FEM). Based on the electrochemomechanical coupling theory, we derive the defect diffusion equation of the finite element form. The non-stoichiometry of the cracked GDC electrolyte is calculated, and it is found that the stress concentration at the crack tip will induce non-stoichiometric effects, causing further concentration of oxygen vacancy defects at the crack tip. Subsequently, the effect of electrochemomechanical coupling effect on the fracture toughness of GDC electrolyte is studied by using the AtC multi-scale method. At 800°C under oxygen partial pressure logPO2=−22, this multi-field coupling effect reduces the fracture toughness of 10GDC and 20GDC by 16.13% and 23.33%, and this effect is more apparent with the increase of oxygen partial pressure gradient and external load.

The possible relation of ventilation ear tubes with nocturnal noise-induced discoordination of the stress response axis – Anatomical and physiological considerations

Nocturnal noise above 30 dB Leq can impact the hypothalamus–pituitaryadrenal axis and discoordinate cortisol circadian rhythms, affecting, among others, blood pressure, sleep architecture, and behavior. A physiologic middle ear-based model suggested in this article may attenuate noise during sleep, especially at low frequencies. As a significant part of gas exchange occurs viadiffusion, caused by the partial pressure gradient of gases between the middle ear cleft and submucosa capillaries, physiologically expected hypoventilation during sleep may account for hypercapnia and CO2 accumulation in the middle ear due to its rapid diffusion rate and the Eustachian tube’s relative dysfunction during sleep. Pressure on the tympanic membrane can render it less compliant, thus attenuating low-frequency noise. However, this model does not function with a perforated tympanic membrane, as in the case of children having ventilation tubes (VT) placed for otitis media with effusion. Thus, we hypothesize that children treated with VT present with cortisol circadian rhythm discoordination. We propose the evaluation of morning urine or salivary samples and arterial pressure levels along with questionnaires concerning behavioral parameters in children with VT and their comparison with the corresponding measurements of a referral population, weighted for age, endocrinology history, medications, and household noise levels. The findings mayunderline the need to reconsider therapeutic options for otitis media with effusion in selected cases by relying on more physiologically-oriented therapeutical approaches, like the endoscopic balloon Eustachian tube dilatation.

Hollow fiber nanoporous membrane contactors for evaporative heat exchange and desalination

The paper reports the performance of nanoporous polypropylene membrane contactors in water evaporative transfer processes, depending on membrane packing density, flow, and temperature conditions. The membrane evaporator's heat and mass transfer efficiency were evaluated in a wide range of partial pressure gradients and gas phase Reynolds numbers. A protocol for simple evaluation of evaporative heat flux to the heat exchange flux is introduced to reveal the efficiency of mass-to-heat transfer. It has been shown the evaporation efficiency significantly depends on gas flow conditions, increasing at Re ∼ 30 and exceeding 4.6 kg × m-2×h−1 (3.0 kW × m-2×h−1) at the temperature of inlet water of 60 °C. It is achieved by inducing convective flows in the gas phase, which enable the rise of effective heat transfer coefficient for membrane evaporator ∼250 W × m-2×K−1. The attained efficiency is confirmed to originate from heat extraction from the gaseous phase and the evaporation of water from the external surface of fibers. While exhibiting maximal heat flux the regime requires liquid phase penetration through the pores, leading to degradation of the membrane performance in desalination applications. To avoid penetration of ions thin (∼300 nm) graphene oxide coating was deposited onto the internal surface of the nanoporous evaporator, enabling to avoid liquid penetration through the pores and salts crystallization at the external surface, while exhibiting slightly lower performance of the membrane.

Multifactor theoretical study on ionic transport numbers of mixed oxygen ionic-electronic conducting oxides determined by the electromotive force method

The electromotive force (EMF) method is widely applied to measure the ionic transport numbers (ti) of mixed oxygen-ionic and electronic conducting oxides. However, the results determined by the EMF method are the average/apparent ti (tiapp), subjected to a given gradient of oxygen partial pressure (PO2), rather than ti at a specific PO2, making it challenging to reveal the accurate properties of materials. In this study, to clarify the impact of this issue, a precise defect distribution model of Gd doped CeO2 (GDC), considering defect equilibrium and local charge neutrality, is built. A multifactor theoretical analysis is conducted to compare tiapp and ti of the membrane at different sides. The modeling results reveal that a thick membrane is recommended for avoiding the influence of membrane thickness on tiapp. When there is a large difference of PO2 between two sides of the GDC membrane (PO2highPO2PO2lowPO2>1025), tiapp is inclined to ti at the side of high PO2. Only when both sides of the GDC membrane are reducing atmosphere, tiapp of the modified EMF method is approximately the average of ti at both sides. The findings of this study are instructive for the rational application of EMF methods.

Selective serotonin reuptake inhibitors and inflammatory bowel disease; Beneficial or malpractice.

IBD, a chronic inflammatory disease, has been manifested as a growing health problem. No Crohn’s and Colitis councils have officially ratified anti-depressants as a routine regimen for IBD patients. However, some physicians empirically prescribe them to rectify functional bowel consequences such as pain and alleviate psychiatric comorbidities. On the other side, SSRIs’ prescription is accompanied by adverse effects such as sleep disturbances. Prolonged intermittent hypoxia throughout sleep disturbance such as sleep apnea provokes periodic reductions in the partial oxygen pressure gradient in the gut lumen. It promotes gut microbiota to dysbiosis, which induces intestinal inflammation. This phenomenon and evidence representing the higher amount of serotonin associated with Crohn’s disease challenged our previous knowledge. Can SSRIs worsen the IBD course? Evidence answered the question with the claim on anti-inflammatory properties (central and peripheral) of SSRIs and illuminated the other substantial elements (compared to serotonin elevation) responsible for IBD pathogenesis. However, later clinical evidence was not all in favor of the benefits of SSRIs. Hence, in this review, the molecular mechanisms and clinical evidence are scrutinized and integrated to clarify the interfering molecular mechanism justifying both supporting and disproving clinical evidence. Biphasic dose-dependent serotonin behavior accompanying SSRI shifting function when used up for the long-term can be assumed as the parameters leading to IBD patients’ adverse outcomes. Despite more research being needed to elucidate the effect of SSRI consumption in IBD patients, periodic prescriptions of SSRIs at monthly intervals can be recommended.

This Month in Anesthesiology

This Month in Anesthesiology

Gas Phase Diffusion Does Not Limit Lung Volatile Anesthetic Uptake Rate.

Inefficiency of lung gas exchange during general anesthesia is reflected in alveolar (end-tidal) to arterial (end-tidal-arterial) partial pressure gradients for inhaled gases, resulting in an increase in alveolar deadspace. Ventilation-perfusion mismatch is the main contributor to this, but it is unclear what contribution arises from diffusion limitation in the gas phase down the respiratory tree (longitudinal stratification) or at the alveolar-capillary barrier, especially for gases of high molecular weight such as volatile anesthetics. The contribution of longitudinal stratification was examined by comparison of end-tidal-arterial partial pressure gradients for two inhaled gases with similar blood solubility but different molecular weights: desflurane and nitrous oxide, administered together at 2 to 3% and 10 to 15% inspired concentration (FiG), respectively, in 17 anesthetized ventilated patients undergoing cardiac surgery before cardiopulmonary bypass. Simultaneous measurements were done of tidal gas concentrations, of arterial and mixed venous blood partial pressures by headspace equilibration, and of gas uptake rate calculated using the direct Fick method using thermodilution cardiac output measurement. Adjustment for differences between the two gases in FiG and in lung uptake rate (VG) was made on mass balance principles. A 20% larger end-tidal-arterial partial pressure gradient relative to inspired concentration (PetG - PaG)/FiG for desflurane than for N2O was hypothesized as physiologically significant. Mean (SD) measured (PetG - PaG)/FiG for desflurane was significantly smaller than that for N2O (0.86 [0.37] vs. 1.65 [0.58] mmHg; P < 0.0001), as was alveolar deadspace for desflurane. After adjustment for the different VG of the two gases, the adjusted (PetG - PaG)/FiG for desflurane remained less than the 20% threshold above that for N2O (1.62 [0.61] vs. 1.98 [0.69] mmHg; P = 0.028). No evidence was found in measured end-tidal to arterial partial pressure gradients and alveolar deadspace to support a clinically significant additional diffusion limitation to lung uptake of desflurane relative to nitrous oxide.

Influence of sublimation surface on mass transport in AlN crystal growth by physical vapor transport process

A series of numerical experiments were performed to investigate the influence of the sublimation surface on mass transport during the aluminum nitride (AlN) growth process. The distribution of Al partial pressure is strongly affected by the cover of the sublimation interface. The morphology of the growth interface can be controlled by the cover of the sublimation interface to achieve the growth of a specific crystal shape. Based on the same temperature field, the influence of sublimation interface cover on the growth rate indicates that temperature and temperature gradient are not the main limiting factors of the growth rate and further verifies that Al partial pressure gradient is the rate-limiting step. Under the growth system and specific growth conditions, a smooth growth interface can be obtained by using [0, 2/6] sublimation interface cover, so as to realize the rapid growth of high quality AlN crystals.