Pressure Mode Research Articles

A MINLP model for combination pressurization optimization of shale gas gathering system

The combination pressurization of the shale gas gathering system is one of the most common pressurization methods in the current engineering site, but it is mostly set by manual experience or simulation analysis, and thus the optimal pressurization scheme cannot be obtained. In order to optimize the pressurization mode of the shale gas gathering and transportation system, a mixed integer nonlinear programming model (MINLP) is established based on the existing pressurization mode of the shale gas field. The model takes the minimum total cost of the compressor unit as the objective function. Various constraints are also taken into account, such as pipe pressure, flowrate, compressor related, well and platform throttling, uniqueness for well and platform pressurization. Solving this optimization model can figure out the appropriate pressurization position, operating power, and compressor unit cost. An actual case for a shale gas block is applied to determine the combined pressurization scheme suitable for this production condition. The results show that the combination of more pressurization methods can meet the pressurization requirements under different production conditions. When both well and platform pressurization are considered, the optimized pressurization position is more concentrated, the number of compressors is reduced by two sets, and the total compressor cost is reduced by 99.28 × 104 Yuan, which reflects the advantages of combined pressurization in the pressurization of shale gas gathering and transportation systems.

The Effect of Multiple Coexisting Convective Modes in Determining Thermoacoustic Behavior of a Partially Premixed Swirl Flame

Abstract This study focuses on the effect of multiple heat release mode interactions on the amplitude of unsteady pressure oscillation for a partially premixed radial swirl burner, which uses methane as fuel. A range of operating conditions based on inlet airflow rate and global equivalence ratio is considered for this purpose. The pressure time series shows amplitude modulation at the dominant frequency for all the flow rates and equivalence ratios considered. Wavelet analysis based on continuous wavelet transform illustrates the presence of heat release rate fluctuations at multiple frequencies other than the dominant mode of pressure oscillation, with this more pronounced at low frequencies. Spectral proper orthogonal decomposition performed on time-resolved CH* chemiluminescence images reveal four dominant spatial modes of chemiluminescence, chosen based on the dominant wavelet coefficients for the same. The identified frequencies correspond to the duct-acoustic mode, helical mode (spectrally close to acoustic mode), low-frequency axisymmetric mode and low-frequency helical mode. The low-frequency helical mode (considered as the result of nonlinear interaction between acoustic and helical mode) and the low-frequency axisymmetric mode (considered to have independent existence) have similar spectral content. Amplitude modulation of unsteady pressure is found to be a result of the superposition of duct-acoustic mode and low-frequency axisymmetric mode, whereas reduction in overall pressure amplitude with the decrease in global equivalence ratio is seen to be a result of an increase in the dominance of low-frequency helical mode. The relative dominance of low-frequency helical mode over dominant pressure mode reduces the overall pressure amplitude.

Centrifugal Test and Instability Model Analysis of Excavation Surface Stability of a Shield Tunnel in a Clay Layer

In order to study the variation law of support pressure and instability mode of excavation face under different soil parameters, a complete set of centrifugal model seepage test device is independently developed. The results of centrifugal tests with different C/D (where C is the overburden thickness of the tunnel and D is the tunnel diameter), internal friction angles, and heights of water head show that with the increase of the retreating displacement S of the excavation surface, the support pressure P of the excavation surface can be divided into three stages: rapid decline (S < 1.5D%), slow rebound after reaching the limit support pressure Plim (1.5D% ≤ S ≤ 3D%), and gradually reaching the stable value (3D% < S). With the increase of C/D, the limit support pressure on the excavation face gradually increases and tends to be stable. For different soil properties, when C/D > 1.5, the limit support pressure on the excavation face tends to be stable. With the increase of internal friction angle, the limit support pressure decreases gradually, and its influence on support pressure can be ignored when φ > 40°. With the increase of height of water head Hw, the limit support pressure increases linearly. By establishing a numerical analysis model and analyzing the instability modes of soil under different C/D, internal friction angles, and cohesion, the instability mode of soil in front of the excavation face can have a great correlation with C/D of the soil and internal friction angle, while the influence of cohesion is minimal. With the increase of C/D, the soil changes from overall failure to local failure, the change of C/D mainly affects the height of soil arching effect and the width of the wedge below, while the internal friction angle mainly affects the width of the wedge and the instability angle of soil.

Aeroelastic instability of an inverted cantilevered plate with cracks in axial subsonic airflow

This paper reports a mathematical modeling and theoretical instability analysis of an inverted cantilevered plate in the effect of both cracks and subsonic axial flow. The plate model is clamped at the trailing edge but free at the other and contains an arbitrary number of all-over part-through cracks. It focuses on an analysis methodology of such a plate aeroelastic instability problem and its convergent numerical solutions. We apply the Possio integral equation for fluids and the fracture mechanics for cracks’ modeling, respectively. We transfer the instability problem into a mathematical function approximation problem in the state-space formulation, avoiding the difficulty of solving the plate slope function directly because of the discontinuities caused by cracks. According to the Stone-Weierstrass theorem, the slope function of the cracked plate is expanded as a linear combination of polynomial functions, including the cracks’ effect. The numerical solution of the plate slope function is finally solved by the least square method. The numerical analysis shows that the critical flow speed significantly decreases as the crack flexible coefficient increases. The change of critical dynamic pressure and instability modes of the cracked plates has been theoretically analyzed and analytically expressed in terms of the crack parameters. The present modeling and analysis strategy has potential applications for investigations of other engineering problems, which can naturally exhibit plate-like systems with inverted configurations and discontinuity.

АНАЛІЗ ПРОБЛЕМ ЗАБЕЗПЕЧЕННЯ НАДІЙНОСТІ ТА ДОВГОВІЧНОСТІ ГІДРОТЕХНІЧНИХ СПОРУД ТРАНСПОРТНОГО БУДІВНИЦТВА З ДОРОЖНІХ ВОДОПРОПУСКНИХ ТРУБ В УМОВАХ ЕКСПЛУАТАЦІЇ

Abstract. Introduction. Failure to ensure the reliability and durability of hydraulic structures of transport construction of road culverts in operating conditions due to static and dynamic loads from vehicles and temperature and climatic influences, the destructive force of water flow, abrasive destruction, corrosion of metal. The reason for the lack of efficiency of design solutions of road culverts is the fundamental difference in the conditions of water flow through the road culvert, at the outlet of the pipe a two-dimensional flow is formed, and and, as a consequence, the destruction of the structure of the lower reaches, landslides, the destruction of the culvert as a whole. Problems. From the literature analysis it is established that road culverts are in difficult operating conditions, which causes their premature destruction. Goal. It consists in the analysis of problems of ensuring reliability and durability of hydraulic structures of transport construction from road corrugated metal culverts. Results. The analysis of problems of ensuring reliability and durability of hydraulic structures of transport construction from road culverts in operating conditions is carried out. Proposals for calculating the initial sections of the structure to ensure its reliability are given. Conclusions. To date, the issue of ensuring the reliability and durability of hydraulic structures of transport construction of road culverts is not fully studied - alternating changes in the modes of flooding of culverts, including the operation of road culverts in part in the pressure mode; change and influence of the roughness coefficient due to the presence of corrugations, their placement; the effect of metal corrosion on the durability of the structure; abrasive wear of corrugated walls. The question of the kinetics of the initial sections of the corrugated metal culvert is insufficiently studied. Key words: highways, culverts, hydraulic stru

Wave-packets in a reacting, imperfectly-expanded supersonic jet

The present work focuses on the large coherent structures of a turbulent, reacting and imperfectly-expanded supersonic jet. These have been extracted from a Large Eddy Simulation (LES) including chemical reactions by Spectral Proper Orthogonal Decomposition (SPOD). While SPOD is now a standard tool for non-reactive flows, very few studies have dealt with reactive jets. The article shows that the pressure and axial velocity fields exhibit coherent wave-packets with a well-defined wavelength and amplitude envelope. The shock/recompression cells have a strong effect on the amplitude of the wave-packet, but a weak effect on the wavelength. The temperature field exhibits a lower self-coherence and exhibits small scale structures upstream, generated within the mixing layer, and an irregular pattern of larger structures downstream in agreement with Prasad and Morris (2020) [65]. A high-energy coherent structure has been observed at a Strouhal number of St=0.4 (normalized by the jet diameter and the jet exit velocity), which appears to result from a mutual reinforcement between the main shear layer instability and the vortex shedding from the normal shock. An attempt is made to model the wave-packets using the parabolized stability equations (PSE) about the mean flow, ignoring the chemical reactions. The PSE solution fails to model the temperature fluctuations, but shows rather good agreement with the leading SPOD modes of pressure and axial velocity downstream. This reveals that the flame impacts the pressure and velocity wave-packets in a weak manner: the coherent structures in the pressure and velocity field are generated by hydrodynamic convective instability, without being significantly altered by the reactive nature of the flow.

Analytical Study of Different Modes of Continuous Positive Airway Pressure (CPAP) in Management of Respiratory Distress Syndrome (RDS) Preterm Neonates

Analytical Study of Different Modes of Continuous Positive Airway Pressure (CPAP) in Management of Respiratory Distress Syndrome (RDS) Preterm Neonates

Co-firing of coal and biomass under pressurized oxy-fuel combustion mode: Experimental test in a 10 kWth fluidized bed

• Pressurized oxy-fuel combustion of coal/biomass in a fluidized bed is successful. • Stable, pressurized, oxy-fuel combustion mode using coal/biomass can be realized. • Increased pressure leads to higher combustion efficiency and CO 2 enrichment. • Increased pressure has the advantages of reducing CO, NO x , and SO 2 emissions. • Increased pressure makes the fly ash particles finer with surface more cracked. Pressurized oxy-fuel combustion (POFC) of solid fuels in fluidized beds possess the potential for CO 2 capture at low cost. However, the practical experience of oxy-coal combustion in pressurized fluidized beds (PFB) is still very limited, and there is a lack of attempts on the co-firing of coal and other fuels. In this study, the co-firing of coal and biomass in a POFC mode at a 10 kW th PFB was tested. The dynamic behaviors of the start-up process and combustion mode switching were investigated. The effects of key operating parameters, including combustion pressure ( P ), biomass blending ratio ( M b ), and excess oxygen coefficient ( α ), on the temperature distributions, CO 2 enrichment and conversion, pollutant emissions (CO, NO X , SO 2 ), and solid residues were methodically studied. The results show that the stable, pressurized, and oxy-fuel combustion mode with coal and biomass mixtures as fuels can be successfully realized in a fluidized bed. Increasing P and M b not only conduces to better temperature distribution, more CO 2 enrichment in flue gas, and higher combustion efficiency but also has the advantage of reducing NO x and SO 2 emissions by over 30%. In the oxy-fuel PFB, the positive effect of α on the combustion performance is more significant than that under atmospheric conditions. As P increases, the fly ash surface is more cracked, and the particle size distribution of fly ash decreases, while the bottom slag surface is smoother. Besides, the increase in P results in a decreased specific surface area and cumulative pore volume but an increased average pore diameter in fly ash.

Seismic signature of electron degeneracy in the core of red giants: Hints for mass transfer between close red-giant companions

The detection of mixed modes in red giants with space missions COROT and Kepler has revealed their deep internal structure. These modes allow us to characterize the pattern of pressure modes (through the measurement of their asymptotic frequency separation Δν) and the pattern of gravity modes (through the determination of their asymptotic period spacing ΔΠ1). It has been shown that red giant branch (RGB) stars regroup on a well-defined sequence in the Δν − ΔΠ1 plane. Our first goal is to theoretically explain the features of this sequence and understand how it can be used to probe the interiors of red giants. Using a grid of red giant models computed with MESA, we demonstrate that red giants join the Δν − ΔΠ1 sequence whenever electron degeneracy becomes strong in the core. We argue that this can be used to estimate the central densities of these stars, and potentially to measure the amount of core overshooting during the main sequence part of the evolution. We also investigate a puzzling subsample of red giants that are located below the RGB sequence, in contradiction with stellar evolution models. After checking the measurements of the asymptotic period spacing for these stars, we show that they are mainly intermediate-mass red giants. This is doubly peculiar because these stars should have nondegenerate cores and they are expected to be located well above the RGB sequence. We show that these peculiarities are well accounted for if these stars result from the interaction between two low-mass (M ≲ 2 M⊙) close companions during the red giant branch phase. If the secondary component has already developed a degenerate core before mass transfer begins, it becomes an intermediate-mass giant with a degenerate core. The secondary star is then located below the degenerate sequence, which is in agreement with the observations.

Personalized tourniquet pressure may be a better choice than uniform tourniquet pressure during total knee arthroplasty: A PRISMA-compliant systematic review and meta-analysis of randomized-controlled trials.

Background:Pneumatic tourniquets are widely used in total knee arthroplasty (TKA). Some surgeons prefer a uniform tourniquet inflation pressure (UTIP) for all patients; others use personalized tourniquet inflation pressures (PTIP) based on systolic blood pressure and limb occlusion pressure. However, no consensus exists regarding the optimal mode of inflation pressure during TKA. This review aimed to appraise if personalized tourniquet inflation pressures are better than uniform tourniquet inflation.Methods:The databases (Web of Science, Embase, PubMed, Cochrane Controlled Trials Register, Cochrane Library, Highwire, CBM, CNKI, VIP, Wanfang) were searched on March 2021 to systematically identify and screen the literature for randomized controlled trials involving PTIP and UTIP during total knee arthroplasty.Results:Thirteen randomized controlled trials, involving 1204 TKAs (1201 patients) were included in the systematic review. The meta-analysis identified a trend toward less visual analogue scale (VAS) score at rest with PTIP group at 1 day (P = .002), 2 to 3 days (P = .01), and less VAS score at activity 1 day (P < .0001), 2 to 3 days after the operation (P < .00001), and discharge (P < .0001). No significant difference was found between the groups in terms of VAS score at rest when discharge (P = 1.0). We also found no significant difference in terms of intraoperative blood loss (P = .48), total blood loss (P = .15), lower limb vein thrombosis (P = .42), and thigh bullae (P = .17). However, in the PTIP group, we found a significant higher hospital for special surgery (HSS) score (P = .007), broader knee Range of motion (P = .02), less rate of thigh ecchymosis (P = .00001), and shorter thigh circumference at 1 day (P = .006), 2 to 3 days (P = .0005), and discharge (P = .02).Conclusion:PTIP provides a similar bloodless surgical field compared with the conventional UTIP. Furthermore, PTIP provides less pain intensity, thigh circumference, rate of thigh ecchymosis, higher hospital for special surgery, and better initial recovery of knee flexion in total knee arthroplasty. Therefore, we recommend using a PTIP method during TKA. More adequately powered and better-designed randomized controlled trials studies with long-term follow-up are required to produce evidence-based guidelines regarding the PTIP method.

Effects of filtration modes on fouling characteristic and microbial community of bio-cake in a membrane bioreactor

This study investigated the effects of filtration modes, i.e., constant transmembrane pressure (TMP) and constant flux mode, on nutrient removal, fouling characteristic and microbial community in a membrane bioreactor. The results showed that filtration mode had minor effects on membrane rejection of COD and nutrients. Membrane fouling rate was higher in constant flux mode than in constant TMP mode. Significantly higher polysaccharide and protein concentrations were found for membrane bio-cake operated under constant flux mode. Fourier transform infrared spectroscopy revealed a significant difference in chemical compositions of SMP and EPS in bio-cake between two filtration modes. Furthermore, constant flux mode had higher portion of α-helix (70.35%) and β-sheet (67.53%), which is related to aggregation and biofilm formation of bacterial cells, in amide I band than those of constant TMP mode (45.67% and 43.44%, respectively). This was corroborated by the fact that thicker bio-cake layer was formed on membrane surface operated under constant flux mode. In addition, excitation-emission matrix fluorescence spectroscopy showed that the fluorescence intensity related to protein-like and humic acid-like substances in constant flux mode were higher than that in constant TMP mode, suggesting their important roles in accelerating membrane fouling. Finally, the microbial communities of bio-cake in constant TMP mode differed significantly from those in constant flux mode. Overall, the results indicated that different contents, characteristics and microbial communities of membrane foulants led to distinct fouling rates between filtration modes.

Surface pressure spectrum variation with Mach number on a CD airfoil

The surface pressure spectrum characteristics are studied on a Controlled Diffusion airfoil at varying Mach numbers and a fixed Reynolds number. Compressible large eddy simulation datasets have been used for this analysis. The study focusses on the noise generation mechanism and the source locations responsible for it. A mid-high frequency hump is observed for the higher Mach number cases in the pressure spectrum and the amplitude of this observed hump increases with Mach number. To investigate the cause of this hump, different hydrodynamic and acoustic pressure modes traveling at specific speeds are obtained by a wavenumber–frequency decomposition. The acoustic component originating from the separation bubble region near the leading edge is found to be responsible for the hump in the pressure spectrum. The interaction of hydrodynamic and acoustic waves also plays a significant role in the appearance of the hump in the spectrum. There is also an increase in the amplitude of the high frequency region in the acoustic spectrum as we go towards the trailing edge for higher Mach number which can be attributed to an increase in turbulent fluctuation amplitude in the leading edge region. Furthermore, stability analysis has been performed on one-dimensional mean boundary-layer profiles. The higher reverse velocity in the separation bubble with increasing Mach number seems to be causing higher growth rates of instabilities, ultimately resulting in the significant surface spectrum variations. The directivity in the farfield also confirms a significant contribution of the hump in the spectrum in the overall sound pressure level.

Detection of Gravity Modes in RR Lyrae Stars

Abstract We report the detection of gravity modes in RR Lyrae stars. Thanks to Photometer AntarctIca eXtinction (PAIX), the first Antarctic polar photometer. Unprecedented and uninterrupted UBVRI time-series photometric ground-based data are collected during 150 days from the highest plateau of Antarctica. PAIX light-curve analyses reveal an even richer power spectrum with mixed modes in RR Lyrae stars. The nonlinear nature of several dominant peaks, showing lower and higher frequencies, occurs around the dominant fundamental radial pressure mode. These lower frequencies and harmonics linearly interact with the dominant fundamental radial pressure mode and its second and third overtone pressure modes, as well. Half-integer frequencies are also detected, likewise side-peak structures, demonstrating that HH Puppis is a bona-fide Blazhko star. Fourier correlations are used to derive underlying physical characteristics for HH Puppis. The most striking finding is the direct detection of gravity waves. We interpret the excitation mechanism of gravity waves in RR Lyrae stars by the penetrative convection-driving mechanism. We demonstrate that RR Lyrae stars’ pulsation is excited by several distinct mechanisms, and hence RR Lyrae stars are simultaneously g-mode and p-mode pulsators. Our discoveries make RR Lyrae stars very challenging stellar objects, and provide their potential to undergo at the same time g and p modes toward an advancement of the theory of stellar evolution and a better understanding of the universe.

Gravitational wave asteroseismology on cooling neutron stars

We examine the gravitational wave frequencies from neutron stars during thermal evolution, adopting the relativistic Cowling approximation. We particularly focus on the neutron star models, in which the direct Urca (rapid cooling process) does not work, without the superfluidity and superconductivity. For such models, the cooling curve hardly depends on the equation of state (EOS) as well as the mass of neutron star, while we show that the gravitational wave frequencies strongly depend on the both properties. Then, we find that the frequencies of the fundamental and the 1st pressure mode multiplied with the stellar mass are well expressed as a function of the stellar compactness almost independently of the EOS. We also find that the frequency of the 1st gravity mode in later phase of the thermal evolution is strongly correlated with the stellar compactness. In addition, we derive the empirical formula estimating the threshold mass for the onset of the direct Urca inside the neutron star as a function of the nuclear saturation parameter. This formula will give us a constraint on the neutron star properties, if it would be observationally found that the direct Urca occurs (or does not work) inside the neutron star.

The Law and Mechanism of the Sample Size Effect of Imbibition Oil Recovery of Tight Sedimentary Tuff.

Imbibition is an important mechanism to improve the recovery factor (RF) of a tight oil reservoir. Accurately evaluating the oil production capacity of tight oil reservoirs by imbibition is of great significance for the formulation of oilfield production plans and productivity prediction. However, there is currently no unified regulation on the selection of rock sample size in tight oil reservoir imbibition evaluation experiments, resulting in great differences in reservoir imbibition oil production capacity obtained from rock samples of different sizes, which brings great challenges to the efficient development of tight oil reservoirs. To clarify the law and mechanism of the rock sample size effect of tight core imbibition oil recovery, this paper takes the newly discovered tight sedimentary tuff (TST) oil reservoir as an example. First, several representative real cores were collected. Then, their wettability and pore structure characteristics were analyzed. Finally, physical simulation experiments of imbibition under different rock sample sizes were conducted. The results show that the TST has very favorable imbibition conditions, which are manifested in the following: (i) the wettability is weakly hydrophilic to hydrophilic; (ii) the mineral composition is tuffaceous minerals, calcite, and quartz, without clay minerals; (iii) micro-nanoscale pores are developed; and (iv) the pore throats are evenly distributed. In the imbibition experiments of rock samples of different sizes, the oil production characteristics of the core surface, the variation form of imbibition rate, pore production characteristics, and the influence mode of imbibition pressure on imbibition do not have the sample size effect. However, the RF of the spontaneous imbibition has an obvious sample size effect, and there is a good exponential function relationship between the imbibition RF and the specific surface area (SSA) of cores. The fundamental reason why the rock sample size effect of the TST imbibition oil recovery is relatively stable and has strong regularity is that its pore structure and wettability are relatively homogeneous and stable. The change of rock sample size does not have a great impact on the distribution of the core pore structure and wettability, resulting in no significant change in its imbibition power, resistance, and distance. Therefore, the main factor determining the imbibition RF of rock samples with different sizes is their SSA. The research results of this work can provide an important theoretical basis for understanding the law and mechanism of TST imbibition oil recovery and unifying the imbibition experimental results of small-sized rock samples.

APAP, BPAP, CPAP, and New Modes of Positive Airway Pressure Therapy.

Positive airway pressure (PAP) is the primary treatment of sleep-disordered breathing including obstructive sleep apnea, central sleep apnea, and sleep-related hypoventilation. Just as clinicians use pharmacological mechanism of action and pharmacokinetic data to optimize medication therapy for an individual, understanding how PAP works and choosing the right mode and device are critical to optimizing therapy in an individual patient. The first section of this chapter will describe the technology inside PAP devices that is essential for understanding the algorithms used to control the airflow and pressure. The second section will review how different comfort settings including ramp and expiratory pressure relief and modes of PAP therapy including continuous positive airway pressure (CPAP), autotitrating CPAP, bilevel positive airway pressure, adaptive servoventilation, and volume-assured pressure support control the airflow and pressure. Proprietary algorithms from several different manufacturers are described. This chapter derives its descriptions of algorithms from multiple sources including literature review, manufacture publications and websites, patents, and peer-reviewed device comparisons and from personal communication with manufacturer representatives. Clinical considerations related to the technological aspects of the different algorithms and features will be reviewed.

適応的空力弾性制御モデルの構築と風洞実験による検証 ---圧力制御と翼端変位推定---

GLA (= Gust Load Alleviation) control is an important active safety technology, especially for light-weight flexible wing aircraft with high aspect ratio wings. This paper proposes an adaptive aero-servo-elastic model for control design, including an aerodynamic load distribution estimator using in-flight partial pressure sensing. The GLA control law obtained based on the proposed model consists of pressure control and mode estimation. In general, aero-servo-elastic models require an wing structure dynamics and an aerodynamic model around the wing. However, it is difficult to construct a generic model in advance for complex unsteady aerodynamic phenomena where turbulence and vibration of flexible wings interact. In this case, the optimality and the reliability of a model-based GLA control is significantly reduced. To minimize the uncertainty of the model for unsteady aerodynamics, this method proposes the use of an autoregressive model with time-varying coefficients, which are updated in real-time based on in-flight pressure sensing. The feasibility of the proposed GLA scheme is demonstrated in terms of both pressure control and wing tip displacement estimation through wind tunnel experiments.

Multi-stimulus semiconductor Cu(i)–I-pyrimidine coordination polymer with thermo- and mechanochromic sensing

The 1D-[Cu(aClpym)I]n coordination polymer behaves as an intelligent material with response to different stimuli since its emission is altered with temperature and with varying modes of pressure, making it a potential multi-response material.

Efficacy of high-flow nasal cannula therapy in bedridden patients.

A growing number of studies have demonstrated the efficacy of high-flow nasal cannula therapy (HFNC) for treating children with acute respiratory distress. However, it remains unknown whether HFNC is effective in bedridden patients with acute respiratory distress. We retrospectively reviewed the medical records of bedridden patients with acute respiratory distress who were treated with HFNC using a home ventilator in continuous positive airway pressure mode at our center between March 2014 and August 2016. We assessed heart rate, respiratory rate, oxygen saturation measured using a pulse oximeter, the partial pressure of venous carbon dioxide, or the transcutaneous partial pressure of carbon dioxide, and symptoms of respiratory distress before and after the initiation of HFNC. During the 2-year-study period, 25 patients were treated with HFNC. The patients' mean heart rate, respiratory rate, oxygen saturation measured using a pulse oximeter, and pressure of venous carbon dioxide/the transcutaneous partial pressure of carbon dioxide values improved significantly (P < 0.05). Symptoms of respiratory distress were considerably ameliorated at 1-3 h after the HFNC initiation, except in two patients. In these two patients, the HFNC was replaced with non-invasive positive pressure ventilation. Non-invasive positive pressure was also required at 16 to 168 h after the initiation of HFNC in five of the 28 episodes in which the patient was initially responsive to HFNC, as the patients' respiratory symptoms gradually deteriorated. Performing HFNC with a home ventilator in continuous positive airway pressure mode is effective at treating bedridden patients with acute respiratory distress. However, it is essential that the HFNC can be switched to non-invasive positive pressure if needed.

Renal and Cerebral Hypoxia and Inflammation During Cardiopulmonary Bypass.

Cardiac surgery-associated acute kidney injury and brain injury remain common despite ongoing efforts to improve both the equipment and procedures deployed during cardiopulmonary bypass (CPB). The pathophysiology of injury of the kidney and brain during CPB is not completely understood. Nevertheless, renal (particularly in the medulla) and cerebral hypoxia and inflammation likely play critical roles. Multiple practical factors, including depth and mode of anesthesia, hemodilution, pump flow, and arterial pressure can influence oxygenation of the brain and kidney during CPB. Critically, these factors may have differential effects on these two vital organs. Systemic inflammatory pathways are activated during CPB through activation of the complement system, coagulation pathways, leukocytes, and the release of inflammatory cytokines. Local inflammation in the brain and kidney may be aggravated by ischemia (and thus hypoxia) and reperfusion (and thus oxidative stress) and activation of resident and infiltrating inflammatory cells. Various strategies, including manipulating perfusion conditions and administration of pharmacotherapies, could potentially be deployed to avoid or attenuate hypoxia and inflammation during CPB. Regarding manipulating perfusion conditions, based on experimental and clinical data, increasing standard pump flow and arterial pressure during CPB appears to offer the best hope to avoid hypoxia and injury, at least in the kidney. Pharmacological approaches, including use of anti-inflammatory agents such as dexmedetomidine and erythropoietin, have shown promise in preclinical models but have not been adequately tested in human trials. However, evidence for beneficial effects of corticosteroids on renal and neurological outcomes is lacking. © 2021 American Physiological Society. Compr Physiol 11:1-36, 2021.