Constant Low Flow Research Articles

Flow-controlled ventilation decreases mechanical power in postoperative ICU patients

BackgroundMechanical power (MP) is the energy delivered by the ventilator to the respiratory system and combines factors related to the development of ventilator-induced lung injury (VILI). Flow-controlled ventilation (FCV) is a new ventilation mode using a constant low flow during both inspiration and expiration, which is hypothesized to lower the MP and to improve ventilation homogeneity. Data demonstrating these effects are scarce, since previous studies comparing FCV with conventional controlled ventilation modes in ICU patients suffer from important methodological concerns.ObjectivesThis study aims to assess the difference in MP between FCV and pressure-controlled ventilation (PCV). Secondary aims were to explore the effect of FCV in terms of minute volume, ventilation distribution and homogeneity, and gas exchange.MethodsThis is a physiological study in post-cardiothoracic surgery patients requiring mechanical ventilation in the ICU. During PCV at baseline and 90 min of FCV, intratracheal pressure, airway flow and electrical impedance tomography (EIT) were measured continuously, and hemodynamics and venous and arterial blood gases were obtained repeatedly. Pressure–volume loops were constructed for the calculation of the MP.ResultsIn 10 patients, optimized FCV versus PCV resulted in a lower MP (7.7 vs. 11.0 J/min; p = 0.004). Although FCV did not increase overall ventilation homogeneity, it did lead to an improved ventilation of the dependent lung regions. A stable gas exchange at lower minute volumes was obtained.ConclusionsFCV resulted in a lower MP and improved ventilation of the dependent lung regions in post-cardiothoracic surgery patients on the ICU.Trial registration Clinicaltrials.gov identifier: NCT05644418. Registered 1 December 2022, retrospectively registered.

Continuous manufacturing of pharmaceutical products: A density-insensitive near infrared method for the in-line monitoring of continuous powder streams

Near infrared (NIR) spectroscopy is a valuable analytical technique for monitoring chemical composition of powder blends in continuous pharmaceutical processes. However, the variation in density captured by NIR during spectral collection of dynamic powder streams at different flow rates often reduces the performance and robustness of NIR models. To overcome this challenge, quantitative NIR measurements are commonly collected across all potential manufacturing conditions, including multiple flow rates to account for the physical variations. The utility of this approach is limited by the considerable quantity of resources required to run and analyze an extensive calibration design at variable flow rates in a continuous manufacturing (CM) process. It is hypothesized that the primary variation introduced to NIR spectra from changing flow rates is a change in the density of the powder from which NIR spectra are collected. In this work, powder stream density was used as an efficient surrogate for flow rate in developing a quantitative NIR method with enhanced robustness against process rate variation. A density design space of two process parameters was generated to determine the conditions required to encompass the apparent density and spectral variance from increases in process rate. This apparent density variance was included in calibration at a constant low flow rate to enable the development of a density-insensitive NIR quantitative model with limited consumption of materials. The density-insensitive NIR model demonstrated comparable prediction performance and flow rate robustness to a traditional NIR model including flow rate variation (“gold standard” model) when applied to monitoring drug content in continuous runs at varying flow rates. The proposed platform for the development of in-line density-insensitive NIR methods is expected to facilitate robust analytical model performance across variable continuous manufacturing production scales while improving the material efficiency over traditional robust modeling approaches for calibration development.

Evaluation of Baseflow Modeling with BlueM.Sim for Long-Term Hydrological Studies in the German Low Mountain Range of Hesse, Germany

So far, research with the hydrological model BlueM.Sim has been focused on reservoir management and integrated river basin modeling. BlueM.Sim is part of the official toolset for estimating immissions into rivers in Hesse (Germany) via long-term continuous modeling. Dynamic runoff modeling from rural catchments is permitted within the Hessian guidelines, but in practice, a constant flow or low flow is used. However, due to increasing water stress in the region caused by climate change, the dynamic modeling of runoff from rural catchments will become necessary. Therefore, dynamic baseflow modeling with BlueM.Sim is of the greatest importance. This study evaluated baseflow modeling with BlueM.Sim in a representative hard-rock aquifer in the German Low Mountain range. Two model setups (Factor Approach (FA): CN method + monthly baseflow; Soil Moisture Approach (SMA): physical soil moisture simulation) were calibrated (validated) for a 9-year (5-year) period. The FA achieved an NSE of 0.62 (0.44) and an LnNSE of 0.64 (0.60) for the calibration and validation periods. The selection of a solution for the successful validation of the FA was challenging and required a selection that overestimated baseflow in the calibration period. This is due to the major disadvantage of the FA, namely, that baseflow can only vary according to an estimated yearly pattern of monthly baseflow factors. However, the data requirements are low, and the estimation of monthly baseflow factors is simple and could potentially be regionalized for Hesse, leading to a better representation of baseflow than in current practice. The SMA achieved better results with an NSE of 0.78 (0.75) and an LnNSE of 0.72 (0.78). The data requirements and model setup are extensive and require the estimation of many parameters, which are limitations to its application in practice. Furthermore, a literature review has shown that a single linear reservoir, as in BlueM.Sim, is not optimal for modeling baseflow in hard-rock aquifers. However, for detailed climate change impact studies in the region with BlueM.Sim, the SMA should be preferred over the FA. It is expected that BlueM.Sim would benefit from implementing a more suitable model structure for baseflow in hard-rock aquifers, resulting in improved water balance and water quality outcomes.

Assessment of ecological state of serially impounded Himalayan River using diatoms-based matrices: Identification of critical stretches for management

The ecological state of the serially impounded Himalayan river Bhagirathi is assessed using benthic diatom-based matrices. Six stations (S1-S6) located in stretches receiving constant low flow (S2, S4,S5) and regulated flow regimes (S3, S6) along the continuum were sampled for the diatom community at monthly intervals from October 2016 to September 2017. The samples were processed and identified according to standard literature. The van Dam ecologic values revealed identical prevailing condition based on their percent abundance, reflecting the existing state of riverine ecosystem. Compared to S1 (located upstream in natural flow) the percent share of the dominant category tolerant-N-autotroph for nitrogen-uptake; polyoxybiontic (100% O2 saturation) for oxygen requirement; and β-mesosprobe (BOD 2–4 mg l−1) for saprobity valuesshow decline in the modified stretches except for S6 and being serious at S3 followed by S2, S4 and S5. On the contrary, obligatory-N-heterotrophs (taxa needing continuously elevated organically bounded nitrogen), low to moderate oxygen saturation (30–70%), and α-meso-poly saprobous (biological oxygen demand 8–12 mg l−1) appeared in these modified stretches. The eutrophic (high level of nutrients) and hypereutrophic (nutrient rich water characterised by algal blooms) catagories occurred at S2, S3 and S4, reflecting enhanced organic load, which is further demonstrated by water quality indices. Some tolerant taxa (Nitzschia palea, Nitzschia paleacae) contributed a considerable share in the flow modified stretches and hence are considered taxa of concern for future studies as they are rarely reported from Himalayan rivers. The anomalies in ecological state confirm deterioration and hence the sections along the modified stations are called critical stretches, S3 followed by S2 and S4 being the most stressed and recommended for proper management. The study also affirms the applicability of diatom-based matrices for Hydroelectric project (HEP) impact assessment in the Himalayan rivers.

Experimental investigation of plugging and fracturing mechanisms in unconsolidated sand reservoirs under injection of water containing suspended fine particles

Progressive plugging of the medium due to filter cake formation is considered as a major challenge during Produced Water Re-Injection (PWRI), leading decreased well injectivity during production. Field operations have shown that injectivity can be at least partially restored by fracturing the clogged medium when injecting in the frac-regime. An experimental investigation is performed to explore the effect of the injection of a suspension on the plugging and fracturing processes in an unconsolidated sand formation. The tests are performed by injecting water containing fine particles at a constant low flow rate to first clog a sand specimen (phase 1), then by increasing the flow rate until fracturing (phase 2). Experimental results exhibit a continuous increase of the injection pressure (decrease of injectivity) during phase 1 due to the formation of filter cake build-up caused by the deposition of injected solid particles. During phase 2 when the flow rate is increased, pressure drops are observed and attributed to the formation of fractures, resulting in the increase of the overall permeability of the medium. This is confirmed by post-mortem analysis of the specimens using X-ray Computed Tomography. Small radial fractures (“pseudo-cracks”) induced around the injection point are visible. They appear as localized zones of higher porosity. The effect of the confining pressure and of the suspended particles concentration on the clogging and fracturing of the medium is investigated. It is shown that the clogging process strongly depends on the concentration of particles in the injected fluid. A lower quantity of injected particles is needed to induce the same level of permeability impairment when a lower concentration is used. No significant effect of particle concentration is observed on the fracturing pressure. As with pure water injection, the fracturing pressure is proportional to the imposed confining stress. Moreover, it is observed that the clogged specimen requires a higher injection pressure to reach the frac-regime as compared to an injection scenario with pure water and no filter cake formation and that permeability recovery could be higher.

A novel technique for assessment of post-extubation airway obstruction can successfully replace the conventional cuff leak test: a pilot study

BackgroundPost-extubation airway obstruction is an important complication of tracheal intubation. The cuff leak test is traditionally used to estimate the risk of this complication. However, the cuff leak test parameters are not constant and may depend on the respiratory system and ventilator settings. Furthermore, deflating the cuff also be a risk factor for patient-ventilator asynchrony and ventilator-associated pneumonia.Instead of using the cuff leak test, we measured the pressure of the leak to the upper airway through the gap between the tube and glottis with a constant low flow from the lumen above the cuff without deflating the cuff and called it "pressure above the cuff."The purpose of this study was to investigate whether pressure above the cuff can be used as an alternative to the cuff leak volume.MethodsThis prospective observational study was conducted at Kumamoto University Hospital after obtaining approval from the institutional review board. The pressure above the cuff was measured using an endotracheal tube with an evacuation lumen above the cuff and an automated cuff pressure modulation device. We pumped 0.16 L per minute of air and measured the steady-state pressure using an automated cuff pressure modulation device. Then, the cuff leak test was performed, and the cuff leak volume was recorded. The cuff leak volume was defined as the difference between the expiratory tidal volume with the cuff inflated and deflated. The relationship between the pressure above the cuff and cuff leak volume was evaluated. The patient-ventilator asynchrony during each measurement was also examined.ResultsThe pressure above the cuff was measured, and the cuff leak volume was assessed 27 times. The pressure above the cuff was significantly correlated with the cuff leak volume (r = -0.76, p < 0.001). Patient-ventilator asynchrony was detected in 37% of measurements during the cuff leak test, but not during the pressure above the cuff test.ConclusionsThis study suggests that pressure above the cuff measurement may be a less complicated alternative to the conventional cuff leak test for evaluation of the risk of post-extubation airway obstruction.Trial registrationUniversity Hospital Medical Information Network Clinical Trials Registry (UMIN000039987; March 30, 2020). https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000044604

Floods on Alluvial Fans: Implications for Reworking Rates, Morphology and Fan Hazards

AbstractFlood events are the agents of change on alluvial fans. However, most alluvial fan experiments have used constant flows to model fans and the channels upon them. Here, we present results from a series of alluvial fan experiments with different patterns of flow variation (i.e., different hydrograph shapes). We conducted experiments with (a) constant flow, (b) alternating high and low flows, (c) a moderate flood peak that decayed slowly, alternating with a constant low flow, and (d) a high flood peak that decayed rapidly, alternating with a constant low flow. We found that different hydrographs generated fans with different slopes, even though all experiments had the same mean flow and sediment supply. In addition, higher peak flows led to increased lateral migration rates and increased erosion and deposition. These results challenge the notion that a single representative flow can be used to approximate the geomorphic effects of a range of flows in a natural stream. Moreover, our findings indicate that hydrograph shape can govern the geomorphic impact of a flood event. This means that altered basin hydrology (for instance, through land cover change) likely exerts an important impact on geomorphic change and natural hazards on alluvial fans.

Phase-Contrast MRI Detection of Ventricular Shunt CSF Flow: Proof of Principle.

The evaluation of a suspected malfunction of a ventricular shunt is a common procedure in neurosurgery. The evaluation relies on either the interpretation of the ventricular width using cranial imaging or invasive techniques. Several attempts have been made to measure the flow velocity of cerebrospinal fluid (CSF) utilizing different phase-contrast magnet resonance imaging (PC MRI) techniques. In the present study, we evaluated 3 T (Tesla) MRI scanners for their effectiveness in determining of flow in the parenchymal portion of ventricular shunt systems with adjustable valves containing magnets. At first, an MRI phantom was used to measure the phase-contrasts at different constant low flow rates. The next step was to measure the CSF flow in patients treated with ventricular shunts without suspected malfunction of the shunt under observation. The measurements of the phantom showed a linear correlation between the CSF flow and corresponding phase values. Despite many artifacts resulting from the magnetic valves, the ventricular catheter within the parenchymal portion of shunt was not superimposed by artifacts at each PC MRI plane and clearly distinguishable in 9 of 12 patients. Three patients suffering from obstructive hydrocephalus showed a clear flow signal. CSF flow detected within the parenchymal portion of the shunt by PC MRI may reliably provide information about the functional status of a ventricular shunt. Even in patients whose hydrocephalus was treated with magnetic adjustable valves, the CSF flow was detectable using PC MRI sequences at 3 T field strength.

Development of High Pressure and Constant Low Flow Test System for Hydraulic Support Safety Valve

The existing test equipment for safety valve with low-flow start and overflow closure characteristics of hydraulic support cannot provide the test conditions stipulated in relevant standards, which affects the accuracy of test results. Aiming at the shortage of the existing test equipment, a test system of high pressure and low flow rate of safety valve with hydraulic support is designed, and a technical solution of using straight line driver to push the plunger cylinder to realize high pressure and low flow rate of liquid supply is put forward. The simulation software AMESim was used to construct the virtual prototype of the test system, and the simulation analysis was carried out to determine the main parameters and the influencing rules of the rigidity of the liquid supply velocity. Based on the simulation study, prototype trial production, flow calibration and field experiment were completed. The experimental results showed that the instantaneous output flow fluctuation of the test system was within the range of ±10% of the rated value of 40ml/min, and the output flow fluctuation range was reduced by 25% compared with the existing way.

Derecruitment volume assessment derived from pressure-impedance curves with electrical impedance tomography in experimental acute lung injury.

ObjectiveTo investigate the accuracy of derecruitment volume (VDER) assessed by pressure–impedance (P-I) curves derived from electrical impedance tomography (EIT).MethodsSix pigs with acute lung injury received decremental positive end-expiratory pressure (PEEP) from 15 to 0 in steps of 5 cmH2O. At the end of each PEEP level, the pressure–volume (P-V) curves were plotted using the low constant flow method and release maneuvers to calculate the VDER between the PEEP of setting levels and 0 cmH2O (VDER-PV). The VDER derived from P-I curves that were recorded simultaneously using EIT was the difference in impedance at the same pressure multiplied by the ratio of tidal volume and corresponding tidal impedance (VDER-PI). The regional P-I curves obtained by EIT were used to estimate VDER in the dependent and nondependent lung.ResultsThe global lung VDER-PV and VDER-PI showed close correlations (r = 0.948, P<0.001); the mean difference was 48 mL with limits of agreement of −133 to 229 mL. Lung derecruitment extended into the whole process of decremental PEEP levels but was unevenly distributed in different lung regions.ConclusionsP-I curves derived from EIT can assess VDER and provide a promising method to estimate regional lung derecruitment at the bedside.

Calculation of the Cross Section Active Area for a Polymeric Spiral Wound Reverse Osmosis Membrane

Cross flow filtration is the typical way that water is filtered in membrane technology; that means that feed solution passes tangencially over the membrane and rejected components are washed away of the membrane by the rejected stream. In such a way, that minimal solids building up and at constant low flow resistance are achieved. In this paper, a calulation method regarding to the value of cross-section active area for a polymeric spiral wound reverse osmosis (RO) membrane is presented, in order to obtain the value of the cross-flow velocity of the system. This velocity is needed to improve the knowledge fouling mechanisms and it is not easy to know without obtaining the cross section area. To determine cross-section area of a RO polymeric spiral wound membrane a series of calculations were performed to obtain the initial values of some parameters. The mathematical calculation was also achieved with the Roll Length program. Based on the results obtained, it was concluded that only 65.36% of the total cross-section of the membrane is useful to cross flow and it was possible to determine the active cross-section of filtration with a value of 1,915.4 mm2, for the membrane studied. This methodology allows the calculation for any RO spiral membrane.

Tidal modulated flow and sediment flux through Wax Lake Delta distributary channels: Implications for delta development

Abstract. In this study, a Delft3D model of the Wax Lake Delta was developed to simulate flow and sediment flux through delta distributary channels. The model was calibrated for tidal constituents as well as velocity and sediment concentration across channel transects. The calibrated model was then used to simulate full spring–neap tidal cycles under constant low flow upstream boundary conditions, with grain size variation in suspended load represented using two sediment fractions. Flow and sediment flux results through distributary channel cross-sections were examined for spatial and temporal variability with the goal of characterizing the role of tides in sediment reworking and delta development. The Wax Lake Delta has prograded through channel extension, river mouth bar deposition, and channel bifurcation. Here we show that tidal modulation of currents influences suspended sand transport, and spatial acceleration through distributary channels at low tides is sufficient to suspend sand in distal reaches during lower flows. The basinward-increasing transport capacity in distributary channels indicates that erosive channel extension could be an important process, even during non-flood events.

Adventitial vessel growth and progenitor cells activation in an ex vivo culture system mimicking human saphenous vein wall strain after coronary artery bypass grafting.

Saphenous vein graft disease is a timely problem in coronary artery bypass grafting. Indeed, after exposure of the vein to arterial blood flow, a progressive modification in the wall begins, due to proliferation of smooth muscle cells in the intima. As a consequence, the graft progressively occludes and this leads to recurrent ischemia. In the present study we employed a novel ex vivo culture system to assess the biological effects of arterial-like pressure on the human saphenous vein structure and physiology, and to compare the results to those achieved in the presence of a constant low pressure and flow mimicking the physiologic vein perfusion. While under both conditions we found an activation of Matrix Metallo-Proteases 2/9 and of microRNAs-21/146a/221, a specific effect of the arterial-like pressure was observed. This consisted in a marked geometrical remodeling, in the suppression of Tissue Inhibitor of Metallo-Protease-1, in the enhanced expression of TGF-β1 and BMP-2 mRNAs and, finally, in the upregulation of microRNAs-138/200b/200c. In addition, the veins exposed to arterial-like pressure showed an increase in the density of the adventitial vasa vasorum and of cells co-expressing NG2, CD44 and SM22α markers in the adventitia. Cells with nuclear expression of Sox-10, a transcription factor characterizing multipotent vascular stem cells, were finally found in adventitial vessels. Our findings suggest, for the first time, a role of arterial-like wall strain in the activation of pro-pathologic pathways resulting in adventitial vessels growth, activation of vasa vasorum cells, and upregulation of specific gene products associated to vascular remodeling and inflammation.

Provocative diskography: safety and predictive value in the outcome of spinal fusion or pain intervention for chronic low-back pain.

There is still no clear definition of diskogenic low-back pain and no consensus on a generally agreed test, such as provocative diskography (PD), to diagnose painful disk degeneration, and probably more importantly, to predict the outcome of therapy intended to reduce pain that is presumed to be diskogenic in nature. Nevertheless, PD is the most specific procedure to diagnose diskogenic low-back pain. Its accuracy, however, is rather low or at best unknown. Although rare, the most prevalent complication, postdiskography diskitis, can be devastating for the individual patient, so all measures, like strict sterile conditions and antibiotic prophylaxis, should be taken to avoid this complication. It is advised to perform the procedure in a pressure-controlled way with a constant low flow, and optionally computed tomography imaging. PD should not be performed in morphologically normal disks. A standardized execution of the test should be established in order to perform high-quality studies to determine its accuracy to lead to meaningful interventions, and find best practices for diagnosis and treatment of diskogenic back pain. Possibly, PD may have detrimental effects on the disk, causing early degeneration, although it is unknown whether this will be related to clinical symptoms. Especially with these possible adverse side effects in mind, the risk–benefit ratio with the lack of clear benefits from treatments provided, and possible complications of disk puncture, the rationale for PD is questionable, which should be stressed to patients in the process of shared decision making. Diskography as a stand-alone test is not recommended in clinical decision making for patients with chronic low-back pain.

Syringe-assisted point-of-care micropumping utilizing the gas permeability of polydimethylsiloxane

By utilizing the high gas permeability of polydimethylsiloxane (PDMS), a simple syringe-assisted pumping method was introduced. A dead-end microfluidic channel was partially surrounded by an embedded microchamber, with a thin PDMS wall isolating the dead-end channel and the embedded microchamber. A syringe was connected with the microchamber port by a short tube, and the syringe plunger was manually pulled out to generate low pressure inside the microchamber. When sample liquid was loaded in the inlet port, air trapped in the dead-end channel would diffuse into the surrounding microchamber through the PDMS wall, creating an instantaneous pumping of the liquid inside the dead-end channel. By only pulling the syringe manually, a constant low flow with a rate ranging from 0.089 to 4 nl/s was realized as functions of two key parameters: the PDMS wall thickness and the overlap area between the dead-end channel and the surrounded microchamber. This method enabled point-of-care pumping without pre-evacuating the PDMS devices in a bulky vacuum chamber.

Controlled growth of SiNPs by plasma synthesis

Abstract Quantum confined silicon nanoparticles (SiNPs) may allow for the fabrication of an all silicon multiple junction photovoltaic cell, or novel photovoltaic cells that surpasses the single junction limitations. One method of growing SiNPs is by PECVD where the plasma is confined to a quartz tube. To further understand this technique, computational fluid dynamic calculation were coupled with experimental growths, which allows for the development of a phase diagram based around the reactor pressure, and gas flow. SiNP size and crystallinity were evaluated using a combination of Raman scattering, X-ray diffraction, and transmission electron microscopy (TEM), these results were used to further the develop the phase diagram. For residence times less than 1 ms, SiNPs were produced a band gap of >1.6 eV, but very low crystallinity. By maintaining a constant low gas flow (100 sccm) and increasing reactor pressure, crystallinity and size of the SiNPs were improved and increased, respectively. For SiNPs grown with a constant residence time (~2 ms), we observe a reduction in the crystallinity with increased gas flow. Closer inspection by TEM showed a significant amount of a-Si with the SiNPs. Using this growth technique we can reliably grow SiNPs with diameters from 3 nm to 8 nm, relating to a photoluminescence peak position from 1.6 eV to 1.3 eV. This range is ideal for the development of an all silicon tandem photovoltaic cell.

Anisokinetic Shrouded Nozzle System for Constant Low-Flow Rate Aerosol Sampling from Turbulent Duct Flow

An anisokinetic shrouded nozzle system was designed for sampling particles at a constant low flow rate from a ventilation duct to an aerodynamic particle sizer (APS). Shrouded anisokinetic nozzles are a means for sampling from a moving airstream with higher particle transmission than with unshrouded isokinetic nozzles. This shrouded nozzle sampling system was evaluated in an experimental ventilation duct system. Aspiration and transport efficiency measurements were made for five particle sizes in the range 1–13 μm at each of three duct air speeds in the range 2.2–8.8 m/s. Under these conditions, the shrouded nozzle system showed improved performance compared to buttonhook isokinetic nozzles, especially for larger particles and higher air speeds. Measured transmission efficiencies through the shrouded nozzle sampling system were generally higher and more reliably predictable than those through buttonhook isokinetic nozzles. Model predictions of transport and aspiration efficiencies of the shrouded nozzle s...

Coral farming: effects of light, water motion and artificial foods

Improved coral cultivation will facilitate the reduction of wild harvesting, reef restoration, preservation of biodiversity, and the use of corals as model experimental organisms. In this study, we examine species-specific responses in growth and survival of corals from the effects of light, water motion and artificial (i.e. non-living aquarium trade) food supplements. Three species representing distinct, diverse and abundant coral genera were chosen (Montipora capitata(Mc), Porites compressa (Pc) and Pocillopora damicornis (Pd)) for three experiments to examine: (1) the interaction of water flow and light on growth and survival of Mc and Pc; (2) the effects of artificial foods on Mc, Pc and Pd; and (3) the effects of increasing dosage of artificial foods in an open system on Mc and Pc. Pc thrived at the highest light levels with low flow, while Mc exhibited bleaching and reduced growth in the same conditions and grew best in shaded treatments. High constant flow (~11 cm s-1) resulted in slightly less overall growth than low constant flow (~4 cm s-1). Some artificial foods resulted in a significant increase in growth in Mc and Pd, but not in Pc. These combined results suggest that Mc may be more heterotrophic than Pc. This study illustrates that each species has unique requirements for optimal growth conditions that can be determined by relatively simple and low cost experiments, but that ideal conditions for one species might not be generalized to others.

Anaesthetic gas monitoring comparison between two side-stream monitors

End-tidal gas monitoring has become standard of care during inhaled general anaesthesia. We studied the performance of a new side stream gas monitor the ISA multi-gas monitor. The performance was studied at constant low flow of calibration gas and end-tidal anaesthetic measure was studied during routine day case anaesthesia. Pair wise readings of end-tidal halogenated anaesthetic concentration were recorded during low flow anaesthesia. Performance was found to be high; all calibration gas measures were within 0.1 vol% deviation. During routine anaesthesia mean bias was -0.036 vol% and 93 out of 97 pair-wise readings were within the agreement limits as compared to the reference Datex instrument.

Heterogeneities in magma chambers: Insights from the behavior of major and minor elements during mixing experiments with natural alkaline melts

We present new electron microprobe and Sr-isotope analytical results from mixing experiments using natural volcanic samples. In order to constrain the dynamics of such mixing events, we applied a Taylor–Couette flow, simulating forced convection under very low Reynolds numbers, in a time series ranging from 1 h up to 1 week. The end-member melts derive from samples of the Campanian Ignimbrite (CI), in Italy. The CI is thought to represent a layered reservoir formed in 3 stages: 1) a resident phono-trachytic magma reservoir (end-member A); replenished by 2) a less evolved trachybasaltic–trachytic magma (end-member B of trachytic composition); 3) short-term pre-eruptive mixing in the shallow chamber between a new trachytic and the phono-trachytic resident magmas. Our experiments are motivated by this hypothesis. The two end-members are stirred together, under constant low flow velocity (0.5 rotations per minute). This initially generates single convection cells, which cause progressive homogenization of some major components. This is the case after 1, 4 and 9 h. After 16 h the 87Sr/ 86Sr-isotopic system is homogenized and the starting compositions are fully mixed. Then separate convection cells and compositional layering for major and minor elements emerged. Based on microprobe measurements of quenched melts (glass) from the 16-hour, 25-hour and 1-week long experiments, we confirm the separation of layers having different densities. This phenomenon is locally complicated by the production of micro-volumes of unmixed melts. Our results support the effectiveness of the interplay between convection and diffusion, enhanced by a double-diffusive–convection-driven differentiation for moderately high-silica magmas under high (near- liquidus) temperatures, attesting that differentiation initiates in the liquidus before the onset of fractional crystallization.