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Constant Flow (constant + flow)

Distribution by Scientific Domains

Medical Sciences	60%
Life Sciences	20%

Terms modified by Constant Flow

constant flow rate

Selected Abstracts

Temporal Dynamics of River Biofilm in Constant Flows: A Case Study in a Riverside Laboratory Flume

INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 2 2010
Stéphanie Boulêtreau
Abstract A 15-week experiment was performed in a riverside laboratory flume (with diverted river water) to check variations of river biofilm structure (biomass, algal and bacterial compositions) and function (community gross primary production GPP and respiration) under constant flow while water quality went through natural temporal variations. One major suspended matter pulse coinciding with one river flood was recorded after 10 weeks of experiment. Epilithic biofilm first exhibited a 10-week typical pattern of biomass accrual reaching 33 g ash-free dry matter (AFDM) m,2 and 487 mg chlorophyll- a m,2 and then, experienced a shift to dominance of loss processes (loss of 60% AFDM and 80% chlorophyll- a) coinciding with the main suspended matter pulse. Algal diversity remained low and constant during the experiment: Fragilaria capucina and Encyonema minutum always contribute over 80% of cell counts. DGGE banding patterns discriminated between two groups that corresponded to samples before and after biomass loss, indicating major changes in the bacterial community composition. GPP/R remained high during the experiment, suggesting that photoautotrophic metabolism prevailed and detachment was not autogenic (i.e., due to algal senescence or driven by heterotrophic processes within the biofilm). Observational results suggested that silt deposition into the biofilm matrix could have triggered biomass loss. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

A laboratory method for measuring the isotropic character of soil swelling

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2000
J. -C.
Summary Although the swelling of clays has been thoroughly studied, the mechanism by which this occurs in clay soils is not so fully understood. We have developed a technique to study the swelling and three-dimensional deformation of a soil sample during wetting by adapting a triaxial apparatus. This equipment applies a controlled, confined and isotropic pressure to the periphery of the samples. A constant flow of solution is injected into the base of the sample while the lateral and axial deformations are simultaneously controlled. The development of the interstitial pressure, positive or negative, is measured. When the soil is thoroughly wetted, the equipment measures the saturated hydraulic conductivity. The swelling of the soil is not necessarily isotropic, and practically all the possibilities of lateral, isotropic and vertical swelling can be encountered. Furthermore, the swelling can be preceded by significant lateral shrinkage, caused by fissures. The results show the importance of confinement pressure when measuring the swelling of the samples. The adaptation of a triaxial apparatus to the study of the permeability and swelling of soils appears to be promising as it also allows the geometric development of the samples to be traced as well as the changes in the chemical composition of the percolating solutions. [source]

Development of an Improved Technique for the Perfusion of the Isolated Caudal Lobe of Sheep Liver

EXPERIMENTAL PHYSIOLOGY, Issue 5 2000
A. M. Ali
The study was designed to develop an improved technique for perfusing the isolated caudal lobe of sheep liver. Twenty caudal lobes were perfused for 3-4 h, in a non-recirculating mode, with Krebs-Henseleit bicarbonate buffer. The perfusion system was designed to give a constant flow. The hepatic viability and functional normality of the perfused lobe were assessed by measuring the perfusion flow rate, pH, K+ efflux, O2 uptake, substrate uptake, gluconeogenesis from propionate and amino acids, and ureagenesis from ammonia and amino acids. Liver tissue was sampled for histological examination, as well as for the determination of liver glycogen and wet: dry weight ratio. The perfusion flow rate and pH were both stable throughout the perfusion. The potassium concentration in the effluent perfusate did not increase during the perfusion, suggesting that there was no loss of viability or hypoxia. The perfused lobe extracted more than 50% of the O2 supply. The rate of oxygen consumption was comparable to the rate reported in vivo. The initial glycogen content was reduced by about 40% after 4 h perfusion. The wet: dry weight ratio was 3.6, consistent with the absence of tissue oedema. Urea production was stimulated when NH4Cl (0.3 mM) was added to the medium but there was no significant increase in urea release when alanine (0.15 mM), glutamine (0.2 mM) or lysine (0.2 mM) was added. Urea production, however, increased by about 171% when a physiological mixture of amino acids was added. Propionate (0.5 mM), alanine and glutamine stimulated glucose production but not lysine or the complete amino acid mixture. Glutamine release was lower than that reported in the rat liver. Changing the direction of flow also revealed an apparent difference between livers from sheep and rats in their metabolism of ammonia. The improved technique offers a simple practical and inexpensive approach to many problems in ruminant physiology and nutritional biochemistry. [source]

An abnormal gene expression of the ,-adrenergic system contributes to the pathogenesis of cardiomyopathy in cirrhotic rats,

HEPATOLOGY, Issue 6 2008
Giulio Ceolotto
Decreased cardiac contractility and ,-adrenergic responsiveness have been observed in cirrhotic cardiomyopathy, but their molecular mechanisms remain unclear. To study ,-adrenergic,stimulated contractility and ,-adrenergic gene expression patterns, 20 Wistar Kyoto rats were treated with carbon tetrachloride to induce cirrhosis and 20 rats were used as controls. Left ventricular contractility was recorded in electrically driven isolated hearts perfused at constant flow with isoproterenol (10,10 to 10,6 M). A cardiac gene expression profile was obtained using a microarray for the myocyte adrenergic pathway. The cardiac contractility maximal response to isoproterenol was significantly reduced in cirrhotic rats in comparison to control rats, whereas the half-maximal effective concentration was not different. In cirrhotic rats, cardiac gene expression analysis showed a significant overexpression of G protein alpha,inhibiting subunit 2 (G,i2), cyclic nucleotide phosphodiesterase (PDE2a), regulator of G-protein signaling 2 (RGS2), and down-expression of adenylate cyclase (Adcy3). These results indicate that overexpression of G,i2, PDE2a, and RGS2 down-regulates the ,-adrenergic signaling pathway, thus contributing to the pathogenesis of cirrhotic cardiomyopathy. (HEPATOLOGY 2008;48:1913-1923.) [source]

Temporal Dynamics of River Biofilm in Constant Flows: A Case Study in a Riverside Laboratory Flume

Ranolazine Attenuates Palmitoyl- l -carnitine-induced Mechanical and Metabolic Derangement in the Isolated, Perfused Rat Heart

JOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 6 2000
KAZUYASU MARUYAMA
The effect of ranolazine, a novel anti-ischaemic drug that stimulates the activity of pyruvate dehydrogenase, on palmitoyl- l -carnitine-induced mechanical dysfunction and metabolic derangement in isolated perfused rat hearts has been studied and compared with the effect of dichloroacetate, an activator of pyruvate dehydrogenase. Rat hearts paced electrically were perfused aerobically at constant flow by the Langendorff technique. Palmitoyl- l -carnitine (4 ,m) increased left ventricular end-diastolic pressure and reduced left ventricular developed pressure (i.e. induced mechanical dysfunction); it also reduced tissue levels of adenosine triphosphate and increased tissue levels of adenosine monophosphate (i.e. induced metabolic derangement). These functional and metabolic alterations induced by palmitoyl- l -carnitine were attenuated by ranolazine (5, 10, and 20 ,m) in a concentration-dependent manner. In contrast, dichloroacetate (1 and 10 mm) did not attenuate palmitoyl- l -carnitine-induced mechanical and metabolic derangement. In the normal (palmitoyl- l -carnitine-untreated) heart, however, ranolazine did not modify mechanical function and energy metabolism. These results suggest that ranolazine attenuates palmitoyl- l -carnitine-induced mechanical and metabolic derangement in the rat heart, and that the beneficial action of ranolazine is not because of the energy-sparing effect or activation of pyruvate dehydrogenase. [source]

Ephedrine in the cat lung vasculature

ACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 8 2003
A. M. Fields
Background:, Ephedrine is one of the most commonly used non-catecholamine sympathomimetic agents. It is used in operating rooms and critical care settings worldwide. While it has many side effects, its ability to rapidly raise blood pressure makes it an ideal agent to maintain homeostasis as well as in emergency situations. While its effects are known to be mediated by an ,-mediated mechanism, the exact , subtype is unknown. In addition, no studies using ephedrine have been performed in the pulmonary vascular bed of the cat. Methods:, The effects of phentolamine, a non-selective ,-receptor blocker, and prazosin, an ,1 -selective antagonist, were investigated on pulmonary arterial responses to ephedrine, phenylepherine, norepinephrine, and U-46619. Lobar arterial perfusion pressure was continuously monitored, electronically averaged, and recorded with constant flow in the isolated left lower lobe vascular bed of the cat. Results:, Phentolamine and prazosin significantly reduced vasoconstrictor pulmonary perfusion pressure increases induced by ephedrine. Conclusion:, Ephedrine has significant vasopressor activity in the pulmonary vascular bed of the cat meditated predominantly by ,1 adrenergic receptor activation. [source]

Single-breath exhaled nitric oxide in preschool children facilitated by a servo-controlled device maintaining constant flow,

PEDIATRIC PULMONOLOGY, Issue 6 2004
Philip E. Silkoff MD
Abstract Fractional concentration of exhaled nitric oxide (FENO), an index of airway inflammation, is optimally measured in adults and school-age children using a single-breath online (SBOL) exhalation at constant flow. However, preschool-aged (<6 years old) children have difficulty exhaling at constant flow, and alternative methods are needed. We employed a servo-controlled variable resistance device (servo device) that controls expiratory flow while allowing the child to vary expiratory pressure. To validate this device, 8 children (aged 6,12 years) performed SBOL exhalations with and without the servo device at expired flow rates between 20,50 ml/sec. We then studied 32 young children aged 24,71 months with the servo device alone at exhalation flows of 30, 40, and 50 ml/sec. Test difficulty (TD) with each method was rated by questioning the older children, or as observed by the physician obtaining the data in the younger children (0,=,no difficulty, 1,=,mild difficulty, 2,=,moderate difficulty, and 3,=,unable to perform test). In the older children, SBOL exhalations with and without the servo device demonstrated equivalent flow-dependence of FENO values. Test difficulty was low (0.125,0.625) at all flow rates, with excellent agreement between the two methods (P,<,0.001). Twenty-eight young children (<6 years old) were able to complete measurements at all three flow rates evaluated. The 4 subjects who were not able to successfully complete all the measurements were between 2,3 years old (mean 2.75,±,SD). Exhaled NO (mean,±,SD; ppb) was 8.8 (±6.2), 10.6 (±6.7), and 13.2 (±8.8) ppb at flows of 50 ml/sec, 40 ml/sec, and 30 ml/sec, respectively. Mean values of SD scores were 1.00, 1.14, and 1.43 at flows of 50, 40, and 30 ml/sec, respectively (P,=,NS). In conclusion, exhaled NO measurement by the SBOL method was facilitated in preschool children by the use of a servo-controlled variable resistance device. This device may allow these measurements to be applied to aid in the diagnosis and treatment of asthma in the preschool child, where spirometry is generally impossible. Pediatr Pulmonol. 2004; 37:554,558. © 2004 Wiley-Liss, Inc. [source]

Study of the Cathode Potential in a Sputtering Discharge by Pulsing the Reactive Gas: Case of a W Target in an Ar-O2 Atmosphere

PLASMA PROCESSES AND POLYMERS, Issue 1 2007
Nuno M.G. Parreira
Abstract The process we used was d.c. magnetron sputtering, and we studied both the conventional process, using a constant flow of oxygen, and the process in which we pulsed the reactive gas. Square regulation signal with different pulsing periods (T) and oxygen injection time (ton) was used in the reactive gas pulsing (RGP), while the partial argon pressure was kept constant for all depositions. The oxygen flow rate during the injection time was sufficient to switch the process to compound sputtering mode, while the oxygen flow was stopped in the rest of period to allow cleaning of target. Sputtering experiments have shown that the instability phenomena, typical of the reactive sputtering process and known as the "hysteresis effect", are relatively weak due to the small reactivity of tungsten. The influence of the pulsing period and of the oxygen injection time on the deposition parameters is discussed in relation to the poisoning effect. It has been shown that d.c. magnetron sputtering with the oxygen pulsing is a suitable method to prepare tungsten oxide films. This process is very stable, leads to multilayered W-O coatings, and the deposition rates are slightly lower than those of obtained during the conventional process. [source]

Segmented post-column analyte addition; a concept for continuous response control of liquid chromatography/mass spectrometry peaks affected by signal suppression/enhancement

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2005
Anton Kaufmann
A novel technique, "segmented post-column analyte addition", is proposed to visualize and compensate signal suppression/enhancement effects in electrospray ionization tandem mass spectrometry (ESI-MS/MS). Instead of delivering a constant flow of analyte solution between the liquid chromatography (LC) column exit and the ESI interface into the eluent resulting from LC separation of analyte-free matrix in order to determine retention time widows in which suppression/enhancement is unimportant (King et al., J. Am. Soc. Mass Spectrom. 2000; 11: 942), segmented packets of analyte-containing solvent and analyte-free solvent were infused into an LC eluent resulting from separation of an analyte-containing sample. The obtained, superimposed, periodic spikes are much narrower than the analyte peak eluting from the column. The height of the spikes is affected by signal suppression phenomena to the same extent as the analyte signal, and hence variations of the spike height can be used to correct the peak area of analyte peaks affected by signal suppression/enhancement. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Development of a Disposable Magnetically Levitated Centrifugal Blood Pump (MedTech Dispo) Intended for Bridge-to-Bridge Applications,Two-Week In Vivo Evaluation

ARTIFICIAL ORGANS, Issue 9 2010
Eiki Nagaoka
Abstract Last year, we reported in vitro pump performance, low hemolytic characteristics, and initial in vivo evaluation of a disposable, magnetically levitated centrifugal blood pump, MedTech Dispo. As the first phase of the two-stage in vivo studies, in this study we have carried out a 2-week in vivo evaluation in calves. Male Holstein calves with body weight of 62.4,92.2 kg were used. Under general anesthesia, a left heart bypass with a MedTech Dispo pump was instituted between the left atrium and the descending aorta via left thoracotomy. Blood-contacting surface of the pump was coated with a 2-methacryloyloxyethyl phosphorylcholine polymer. Post-operatively, with activated clotting time controlled at 180,220 s using heparin and bypass flow rate maintained at 50 mL/kg/min, plasma-free hemoglobin (Hb), coagulation, and major organ functions were analyzed for evaluation of biocompatibility. The animals were electively sacrificed at the completion of the 2-week study to evaluate presence of thrombus inside the pump, together with an examination of major organs. To date, we have done 13 MedTech Dispo implantations, of which three went successfully for a 2-week duration. In these three cases, the pump produced a fairly constant flow of 50 mL/Kg/min. Neurological disorders and any symptoms of thromboembolism were not seen. Levels of plasma-free Hb were maintained very low. Major organ functions remained within normal ranges. Autopsy results revealed no thrombus formation inside the pump. In the last six cases, calves suffered from severe pneumonia and they were excluded from the analysis. The MedTech Dispo pump demonstrated sufficient pump performance and biocompatibility to meet requirements for 1-week circulatory support. The second phase (2-month in vivo study) is under way to prove the safety and efficacy of MedTech Dispo for 1-month applications. [source]

Intrinsic vasomotricity and adrenergic effects in a model of isolated rabbit eye

ACTA OPHTHALMOLOGICA, Issue 4 2009
Esmeralda Delgado
Abstract. Purpose:, We aimed to investigate the responsiveness of the ocular arteries to adrenergic drugs in a model of perfused isolated rabbit eye. Methods:, Rabbit external ophthalmic arteries (n = 15) in a head-mounted preparation were cannulated and the retinal and uveal vasculature perfused at a constant flow with warmed tyrode. The three-way polypropylene catheter was further connected to a pressure transducer and intraluminal pressure was taken as a measure of vascular resistance. Effects of intra-arterial injections of phenylephrine (group A, n = 5), prazosin (group B, n = 5) and phentolamine (group C, n = 5) on the recorded pressure were obtained. Student's paired- t test and one-way analysis of variance were used for statistical analysis (p < 0.05). Results:, Intrinsic vasomotricity was observed in all preparations prior to any drug administration. Phenylephrine produced an increase in total vascular resistance. Intrinsic vasomotricity became more evident, showing a lower frequency but higher amplitude of oscillations. Evoked vasomotor responses with phenylephrine (250 ,g/ml) were inhibited by intra-arterial administration of the selective ,1 -adrenergic antagonist, prazosin (0.5 mg/ml), as well as the non-selective ,-adrenergic antagonist phentolamine (6 mg/ml). Conclusions:, Rabbit external ophthalmic arteries showed spontaneous contractions under constant perfusion. Phenylephrine elicited a vasoconstrictor response that was inhibited by adrenergic antagonists. In addition, the intrinsic vasomotricity was enhanced by phenylephrine and blocked by adrenergic antagonists. These results show that under in vitro perfusion the territory presents similar responses to adrenergic drugs to those observed in in vivo models and also provides evidence of myogenic autoregulatory properties in the rabbit ophthalmic artery and/or choroid. [source]

NG -NITRO- l -ARGININE METHYL ESTER POTENTIATES ANAPHYLACTIC VENOCONSTRICTION IN RAT PERFUSED LIVERS

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 11 2006
Toshishige Shibamoto
SUMMARY 1The effects of the nitric oxide (NO) synthase inhibitor NG -nitro- l -arginine methyl ester (l -NAME) on anaphylaxis-induced venoconstriction were examined in rat isolated livers perfused with blood-free solutions in order to clarify the role of NO in anaphylactic venoconstriction. 2Rats were sensitized with ovalbumin (1 mg) and, 2 weeks later, livers were excised and perfused portally in a recirculating manner at a constant flow with Krebs',Henseleit solution. The antigen (ovalbumin; 0.1 mg) was injected into the reservoir 10 min after pretreatment with l-NAME (100 mmol/L) or d -NAME (100 mmol/L) and changes in portal vein pressure (Ppv), hepatic vein pressure (Phv) and perfusate flow were monitored. In addition, concentrations of the stable metabolites of NO ( and ) were determined in the perfusate using an HPLC,Griess system. 3The antigen caused hepatic venoconstriction, as evidenced by an increase in Ppv from a mean (SEM) baseline value of 7.7 ± 0.1 cmH2O to a peak of 21.4 ± 1.1 cmH2O at 3 min in d -NAME-pretreated livers. Pretreatment with l-NAME augmented anaphylactic venoconstriction, as reflected by a higher Ppv (27.4 ± 0.8 cmH2O) after antigen than observed following d -NAME pretreatment. The addition of l -arginine, a precursor for the synthesis of NO, reversed the augmentation of anaphylactic venoconstricion by l -NAME. This suggests that hepatic anaphylaxis increased the production of NO, which consequently attenuated anaphylactic venoconstriction. However, perfusate NOx levels did not increase significantly after antigen in livers pretreated with either l -NAME or d -NAME. 4In conclusion, l -NAME potentiates rat anaphylactic hepatic venoconstriction, suggesting that NO contributes to the attenuation of the venoconstriction. However, this functional evidence was not accompanied by corresponding changes in perfusate NOx concentrations. [source]

Mouse isolated perfused heart: Characteristics and cautions

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 11 2003
Fiona J Sutherland
Summary 1.,Owing to the considerable potential for manipulating the murine genome and, as a consequence, the increasing availability of genetically modified models of cardiovascular diseases, the mouse is fast becoming a cornerstone of animal research. However, progress in the use of various murine preparations is hampered by the lack of facilities and skills for the adequate physiological assessment of genetically modified mice. 2.,We have attempted to address this problem by refining and characterizing a mouse isolated heart preparation that was originally developed for use with larger hearts. 3.,We used the isolated buffer-perfused Langendorff preparation (perfused at constant flow or constant pressure) to characterize: (i) the frequency,response characteristics; (ii) heart isolation conditions; (iii) perfusion chamber conditions; (iv) temperature,function relationships; (v) stability over extended periods of perfusion; (vi) perfusate calcium,function relationships; (vii) pressure,volume relationships; (viii) pressure,rate relationships; and (ix) flow,function relationships. [source]