CFD Challenge: Solutions Using the In-House Finite-Element-Based Solver NEWTETR

2012 ◽  
Author(s):  
Yiemeng Hoi ◽  
David A. Steinman
Keyword(s):  
Steady State ◽  
Pressure Measurements ◽  
Surface Geometry ◽  
Flow Rates ◽  
Pressure Drops ◽  
Or Groups ◽  
Giant Cerebral Aneurysm ◽  
Pulsatile Pressure ◽  
Nominal Surface

Briefly, this Challenge aims to test the sensitivity of steady and pulsatile pressure drops as predicted by different CFD solvers or groups, and ultimately against in vitro pressure measurements. The current study focuses on the Phase I of the Challenge. We simulated steady state and pulsatile pressure drops based on the nominal surface geometry and specific inlet flow rates on a giant cerebral aneurysm with proximal stenosis.

Acceleration of Dabigatran Elimination by Activated Charcoal Perfusion and Hemodialysis in a Pig Model.

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 2272-2272 ◽  
Author(s):  
Jessica Lange ◽  
Christian Thiel ◽  
Karolin Thiel ◽  
Wilfried Klingert ◽  
Kathrin Klingert ◽  
...  
Keyword(s):  
Steady State ◽  
Activated Charcoal ◽  
Plasma Levels ◽  
Binding Capacity ◽  
Flow Rates ◽  
Dialysate Flow ◽  
Maximum Binding Capacity ◽  
Set Up

Abstract Abstract 2272 Background and Aim: Dialysis based approaches can provide rapid removal of dabigatran in cases of emergency due to its low protein binding of ∼35%. However the in vitro properties of these filtration devices have not yet been characterized in detail. This study in the porcine system (both in vitro and in vivo) was performed to evaluate dabigatran elimination by hemodialysis and activated charcoal perfusion as compared to normal renal elimination. Methods: Porcine blood (5L) was supplemented with 1000 ng/mL dabigatran and circulated through an circuit of tubing allowing attached to an activated charcoal filter (Absorba 300 C, Gambro). Further supplementation of dabigatran allowed the determination of maximum binding capacity of the filter. A similar set up was used to also test dialysis (Polyflux 140H, Gambro) and determine the dependence of the flow rate on dabigatran removal. Dialysate flow rates were increased up to 500 ml/min. Anesthetized pigs (Domestic swine, female, ∼60 kg) were attached to an activated charcoal column or a High-Flux hemodialysis filter with a blood flow rate of 200 ml/min. Animals were given an initial i.v. infusion of dabigatran (7.5 mg in 15 min) and then reduced to 5 mg/hr to achieve steady state dabigatran over 1hr. Infusion was then stopped and elimination methods were applied over 4 hrs. An observation time of 1 hr followed. Dabigatran plasma levels were quantitated with diluted thrombin time. Preliminary settings/flow rates were obtained in vitro using 5L citrated porcine whole blood exposed to different AC or HD conditions. Results: Activated charcoal completely removed dabigatran within 1 hr from the 5L whole blood supplemented with 1000 ng/mL dabigatran, with a clearance rate of 100%. By repeatedly reapplying dabigatran, it was shown the active charcoal filter had a maximum binding capacity of ∼30 mg drug. Upon saturation there was no further clearance of dabigatran. Hemodialysis removed dabigatran with increasing clearance rates depending on dialysate flow rates (100 ml/min-35%, 200 ml/min-60%, 300 ml/min-65%) reaching a plateau of ∼65%. Further increases of dialysate flow to 500 ml/min had no further effect on drug clearance. Initial plasma levels of dabigatran ranged between 200–450 ng/mL after 60 min infusion in pigs. Exposure to activated charcoal or hemodialysis (dialysate flow 300 ml/min) resulted in 75–80% reduction in circulating dabigatran after 1 hr as compared to ∼25% reduction untreated controls after 1 hr. After 2 hrs dabigatran levels were below the detection limit using both elimination methods. Conclusions: Dabigatran can effectively be removed from the circulation in this in vivo porcine model using dialysis based approaches, which results in a restoration of blood coagulation. Active charcoal perfusion was fast and effectively removed dabigatran, but may be saturated if dabigatran plasma levels are too high (human body load for 150 mg dose in steady state is ∼14g). Stationary hemodialysis with sufficiently high dialysate flows achieves similar results in this model without saturation limitations; however, the set up for dialysis is much more specialized than the simpler approach of activated charcoal filtration. Disclosures: Formella: Boehringer Ingelheim: Employment. Clemens:Boehringer Ingelheim (Anticoagulant Therapy): Employment. van Ryn:Boehringer Ingelheim: Employment. Schenk:Boehringer Ingelheim: Research Funding.

Effect of parathyroid hormone on bicarbonate absorption by proximal tubules in vitro

1979 ◽  
Vol 236 (4) ◽  
pp. F387-F391 ◽  
Author(s):  
Y. Iino ◽  
M. B. Burg
Keyword(s):  
Steady State ◽  
Parathyroid Hormone ◽  
Proximal Tubules ◽  
Renal Tubules ◽  
Bicarbonate Concentration ◽  
Flow Rates ◽  
Straight Tubules ◽  
Convoluted Tubules ◽  
Tubule Fluid

The effect of parathyroid hormone on bicarbonate absorption was tested in rabbit proximal renal tubules perfused in vitro. In proximal straight tubules 0.05 U/ml of parathyroid hormone caused a large and reversible increase in the steady-state bicarbonate concentration in tubule fluid. Further, the rates of bicarbonate and fluid absorption (measured at faster flow rates) were inhibited approximately 50% by the hormone. We conclude that parathyroid hormone directly inhibits fluid and bicarbonate absorption by proximal straight tubules, causing an increase in the bicarbonate concentration in the tubule fluid, and we suggest that this action of the hormone contributes to the increase in renal bicarbonate excretion that is generally caused by the hormone. In proximal convoluted tubules, parathyroid hormone was previously demonstrated by other investigators to inhibit fluid and bicarbonate absorption approximately proportionally, so that there was little or no change in the bicarbonate concentration in tubule fluid. In agreement we found in the present studies that 0.05 U/ml of the hormone did not affect the steady-state bicarbonate concentration in proximal convoluted tubule fluid and that 5 U/ml caused only an equivocal increase in tubule fluid bicarbonate concentration.

Pressure Distributions in a Single and Two Versions of a Double Volute of a Centrifugal Pump

1992 ◽  
Author(s):  
W. de Ojeda ◽  
R. D. Flack ◽  
S. M. Miner
Keyword(s):  
Centrifugal Pump ◽  
Leading Edge ◽  
Pressure Measurements ◽  
Flow Rates ◽  
Pressure Drops ◽  
Pressure Distributions ◽  
Single Discharge ◽  
Repeated Pattern ◽  
Specific Speed

Pressure measurements were recorded around the impeller and along the casing wall of a centrifugal pump, 0.60 (1583 US units) specific speed, assembled with a single volute/single discharge, and two versions of a double volute/single discharge. The latter comprised a splitter positioned in the second half of the discharge (i) midway between the impeller and casing, and (ii) along a spiral symmetric to the first–half casing section. The objective of such double volute casings is to reduce forces on the impeller and thus provide longer lives. Flow rates tested ranged from 20% to 105% of design. A repeated pattern consisted of pressure increasing from the first cutwater to the splitter leading edge at which the pressure drops and thereafter increases to the discharge. This pattern was noted at all flow rates with the symmetric volute geometry and only at flow rates higher than 60% for the centered splitter. By integration of the pressures static forces were found. Time averaged static forces ranged from 6.2 N at design to 33.0 N at 20% flow for the single volute. Both double volute configurations showed considerable thrust reduction throughout but for a few exceptions. Reductions ranged from 26% at 30% flow to 62% at 90% flow for the center splitter, and from 52% reduction at 20% flow to 72% at 80% flow for the symmetric splitter. For comparison of performance of the different configurations, at flow rates above 85% of design the head was 8% and 9% less for the double volutes than for the single volutes. At flows below 40% of design the head was 3% and 4% higher for the double volutes than for the single volute.

Intercept Method—A Novel Technique To Correct Steady-State Relative Permeability Data for Capillary End Effects

2015 ◽  
Vol 19 (02) ◽  
pp. 316-330 ◽  
Author(s):  
Robin Gupta ◽  
Daniel R. Maloney
Keyword(s):  
Steady State ◽  
Relative Permeability ◽  
Data Interpretation ◽  
End Effect ◽  
Fractional Flow ◽  
End Effects ◽  
Flow Rates ◽  
Pressure Drops ◽  
State Tests ◽  
State Measurement

Summary In laboratory measurements of relative permeability, capillary discontinuities at sample ends give rise to capillary end effects (CEEs). End effects affect fluid flow and retention. If end-effect artifacts are not minimized by test design and data interpretation, relative permeability results may be significantly erroneous. This is a well-known issue in unsteady-state tests, but even steady-state relative permeability results are influenced by end-effect artifacts. This work describes the intercept method, a novel modified steady-state approach in which corrections for end-effect artifacts are applied as data are measured. The intercept method requires running a steady-state relative permeability test with several different flow rates for each fractional flow. Obtaining multiple (three or four) sets of rates (Q), pressure drops (ΔP), and saturation data allows for assessment of CEE artifacts. With Darcy flow, a plot of pressure drop vs. total flow rate is typically linear. A nonzero intercept or offset is an end-effect artifact. To correct for the effect, the offset is subtracted from measured pressure drops. Corrected pressure drops are used in permeability calculations. The set of saturations from measurements at the target fractional flow is used to calculate a corrected final saturation. Because corrections for end effects are made during the test rather than after the test is complete, any discrepancies can be resolved by additional measurements before moving on to the next fractional flow. Rates are then adjusted to yield the next target fractional-flow condition, and the same protocol is repeated for each subsequent steady-state measurement. The method is validated by theory and is easy to apply.

Assessment of Pressure Drop Flowrate Relationship of Axillobifemoral Bypass Grafts

1991 ◽  
Vol 205 (4) ◽  
pp. 243-249 ◽  
Author(s):  
T V How ◽  
S Al-Shukri
Keyword(s):  
Pressure Drop ◽  
In Vitro Study ◽  
Side Branch ◽  
Lower Limbs ◽  
Bypass Grafts ◽  
Pressure Drops ◽  
Pulsatile Pressure ◽  
Axillobifemoral Bypass

An in vitro study was conducted to measure the pressure distributions in knitted polyester axillobifemoral bypass grafts under steady and pulsatile flow of a Newtonian fluid. The relationship between pressure drop and flowrate was determined across the outflow branches of two types of axillobifemoral grafts. Pressure losses were greater across the 90° side branch of the T-type graft than in the Y-type graft at all Reynolds numbers studied. Mean pulsatile pressure drops in the T graft were greater than those measured in steady flow at the same Reynolds number. Estimates of the likely in vivo pressure drops are made under resting and exercise flow conditions. It is suggested that the Y graft is less likely to have a significant effect on blood supply to the lower limbs, even at high blood flowrates.

Experimental and Theoretical Analysis of Transient Response of Plate Heat Exchangers in Presence of Nonuniform Flow Distribution

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
N. Srihari ◽  
Sarit K. Das
Keyword(s):  
Steady State ◽  
Heat Exchangers ◽  
Sudden Change ◽  
Temperature Response ◽  
Flow Distribution ◽  
Transient Temperature ◽  
Nonuniform Flow ◽  
Flow Rates ◽  
Plate Heat ◽  
Flow Maldistribution

Transient analysis helps us to predict the behavior of heat exchangers subjected to various operational disturbances due to sudden change in temperature or flow rates of the working fluids. The present experimental analysis deals with the effect of flow distribution on the transient temperature response for U-type and Z-type plate heat exchangers. The experiments have been carried out with uniform and nonuniform flow distributions for various flow rates. The temperature responses are analyzed for various transient characteristics, such as initial delay and time constant. It is also possible to observe the steady state characteristics after the responses reach asymptotic values. The experimental observations indicate that the Z-type flow configuration is more strongly affected by flow maldistribution compared to the U-type in both transient and steady state regimes. The comparison of the experimental results with numerical solution indicates that it is necessary to treat the flow maldistribution separately from axial thermal dispersion during modeling of plate heat exchanger dynamics.

scholarly journals Pharmacokinetics and dialytic clearance of apixaban during in vitro continuous renal replacement therapy

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
Lauren Andrews ◽  
Scott Benken ◽  
Xing Tan ◽  
Eric Wenzler
Keyword(s):  
Renal Replacement Therapy ◽  
Linear Regression ◽  
Protein Binding ◽  
Continuous Renal Replacement Therapy ◽  
Replacement Therapy ◽  
Flow Rate ◽  
Systemic Exposure ◽  
Flow Rates ◽  
Filter Type

Abstract Background To evaluate the transmembrane clearance (CLTM) of apixaban during modeled in vitro continuous renal replacement therapy (CRRT), assess protein binding and circuit adsorption, and provide initial dosing recommendations. Methods Apixaban was added to the CRRT circuit and serial pre-filter bovine blood samples were collected along with post-filter blood and effluent samples. All experiments were performed in duplicate using continuous veno-venous hemofiltration (CVVH) and hemodialysis (CVVHD) modes, with varying filter types, flow rates, and point of CVVH replacement fluid dilution. Concentrations of apixaban and urea were quantified via liquid chromatography-tandem mass spectrometry. Plasma pharmacokinetic parameters for apixaban were estimated via noncompartmental analysis. CLTM was calculated via the estimated area under the curve (AUC) and by the product of the sieving/saturation coefficient (SC/SA) and flow rate. Two and three-way analysis of variance (ANOVA) models were built to assess the effects of mode, filter type, flow rate, and point of dilution on CLTM by each method. Optimal doses were suggested by matching the AUC observed in vitro to the systemic exposure demonstrated in Phase 2/3 studies of apixaban. Linear regression was utilized to provide dosing estimations for flow rates from 0.5–5 L/h. Results Mean adsorption to the HF1400 and M150 filters differed significantly at 38 and 13%, respectively, while mean (± standard deviation, SD) percent protein binding was 70.81 ± 0.01%. Effect of CVVH point of dilution did not differ across filter types, although CLTM was consistently significantly higher during CRRT with the HF1400 filter compared to the M150. The three-way ANOVA demonstrated improved fit when CLTM values calculated by AUC were used (adjusted R2 0.87 vs. 0.52), and therefore, these values were used to generate optimal dosing recommendations. Linear regression revealed significant effects of filter type and flow rate on CLTM by AUC, suggesting doses of 2.5–7.5 mg twice daily (BID) may be needed for flow rates ranging from 0.5–5 L/h, respectively. Conclusion For CRRT flow rates most commonly employed in clinical practice, the standard labeled 5 mg BID dose of apixaban is predicted to achieve target systemic exposure thresholds. The safety and efficacy of these proposed dosing regimens warrants further investigation in clinical studies.

Bio-Medico-Mechanical Behavior of Natural Artery Blood Vessel Under Constant and Variable Internal Pulsatile Pressure Flow Test In Vitro

1986 ◽  
Vol 108 (4) ◽  
pp. 295-300 ◽  
Author(s):  
A. T. Yokobori ◽  
T. Maeyama ◽  
T. Ohkuma ◽  
T. Yokobori ◽  
H. Ohuchi ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Blood Vessel ◽  
Mechanical Behavior ◽  
Arterial System ◽  
Pressure Amplitude ◽  
Constant Amplitude ◽  
Pressure Flow ◽  
Fluctuating Pressure ◽  
Pulsatile Pressure

Studies have been carried out on the bio-medico-mechanical behavior in vitro of natural blood vessel (dogs) under constant and variable internal pulsatile pressure flow. The apparatus designed by us well simulated the arterial system. The studies were made for the case of pressure amplitude kept as constant, of the two-step-multi-duplicated pulsatile pressure and of the fluctuating pressure. For the case of the fluctuating pressure, the strength of the artery becomes considerably lower than those under constant amplitude and two-step-multi-duplicated pulsatile pressure. SEM observations of the inner walls of the artery shows that collagen fibers are more elongated under fluctuating pulsatile pressure flow. In conclusion, in order to avoid the mechanical deterioration of the artery strength, it is useful to keep the pulsatile blood pressure at constant amplitude. Even for the case of the blood pressure fluctuation, it is necessary to manage to keep the blood pressure as near a regular wave as possible, the total number of repeated pulse being equal.

Transport of L-proline and alpha-methyl-D-glucoside by chicken proximal cecum during development

1991 ◽  
Vol 260 (3) ◽  
pp. G457-G463 ◽  
Author(s):  
M. Moreto ◽  
C. Amat ◽  
A. Puchal ◽  
R. K. Buddington ◽  
J. M. Planas
Keyword(s):  
Surface Area ◽  
Transport Systems ◽  
Independent System ◽  
Passive Components ◽  
Sugar Absorption ◽  
Carrier Mediated Transport ◽  
Lower Capacity ◽  
Nominal Surface ◽  
Passive Influx

We examined the characteristics of amino acid and sugar absorption by the proximal cecum (PC) of chickens during posthatch development. Rates of absorption of L-proline (Pro) and alpha-methyl-D-glucoside (MG) were measured at 2 days, 5 wk, and 13 wk after hatch with an in vitro everted-sleeve method. For each age, pieces of PC and midjejunum were incubated in solutions containing 0.1-50 mM Pro or MG, and the active and passive components of Pro and MG absorption were determined. Five conclusions may be stated. 1) There are two carrier-mediated transport systems for Pro in the PC: a higher capacity Na(+)-dependent system (Vmax between 1.6 and 3.2 nmol.mg-1.min-1), and a lower capacity Na(+)-independent system (Vmax 0.3-0.8 nmol.mg-1.min-1). 2) Whereas both Pro transport systems are present in the PC at 5 and 13 wk, only the Na(+)-dependent system was found at 2 days. Although rates of transport per milligram tissue by the Na(+)-dependent system fell during development, when rates were normalized to nominal surface area, Vmax was significantly higher in the 5-wk-old group than in the other groups. 3) MG transport is by a Na(+)-dependent system. Vmax values (nmol.mg-1.min-1) were 0.32 (2 days), less than 0.43 (5 wk), and = 0.55 (13 wk). These differences were not affected by normalization to surface area. 4) Because at physiological concentrations passive influx of Pro and MG would be negligible, absorption of amino acids and sugars by the PC would be dependent on the presence of carrier-mediated systems.(ABSTRACT TRUNCATED AT 250 WORDS)

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