Academic literature on the topic 'Colloid osmotic pressure'

Ten per cent low molecular weight hydroxyethyl starch is a plasma substitute only recently used as priming solution in an extracorporeal circuit, in contrast to human albumin and gelatin. To evaluate the effect of priming solutions on haemodynamics and colloid osmotic pressure, we studied 36 patients elected for cardiopulmonary bypass (CPB). They were randomly assigned to 2.5% hydroxyethyl starch, 3% gelatin or 4% human albumin priming solution. Total blood loss (perioperative + intensive care unit period) was higher in the gelatin group than in the albumin and hydroxyethyl starch groups. During CPB, the colloid osmotic pressure was best preserved in the gelatin group, although no excessively low colloid osmotic pressures were measured in the other two groups. Due to the extended half-life and the additional postoperative colloid administration, the hydroxyethyl starch group had a higher colloid osmotic pressure in the postoperative phase. We conclude that, next to human albumin, 2.5% hydroxyethyl starch is a safe CPB priming solution additive and is effective as plasma substitute. Its somewhat longer half-life requires adaptation of the routine protocol for transfusion of colloids and blood products.

Pulse reverse osmosis (1) is a new theory of fluid balance and exchange which suggests that the mean blood pressure and osmotic gradient control fluid balance and that the pulse controls fluid exchange. In vitro testing has confirmed some of the physico chemical principles underlying the theory (2). The hypothesis suggests a relationship between mean capillary blood pressure and osmotic gradient. Imbalance in this relationship can be related to the development of hypertension, hypotension, oedema and shock. In an attempt to test this concept mean blood pressures and colloid osmotic pressures were measured and compared in a group of 50 healthy human volunteers. The results suggest a curvilinear correlation between the mean blood pressure and the COP.

Nos quadros de sepse ocorre o aumento da permeabilidade vascular, translocação e perda de albumina para o espaço extravascular, resultando assim em hipoalbuminemia e redução da pressão coloidosmótica plasmática. Desta forma o objetivo deste estudo foi avaliar a relação da pressão coloidosmótica com a evolução clínica de 41 cadelas com sepse grave ou choque séptico decorrente de piometra que foram submetidas a ovariosalpingohisterectomia. Para tanto, os valores da pressão arterial sistólica, do débito urinário, do lactato, do déficit de base venoso e da pressão coloidosmótica foram avaliados a cada três horas ao longo do período de internação. O momento da mensuração da pressão coloidosmótica foi distinto entre os grupos, sendo grupo I (critério clínico) (n= 21) avaliado após o fim do tratamento e no grupo II (critério quantitativo) (n= 20), as amostras foram avaliadas imediatamente após a colheita. As variáveis clínicas utilizadas como guia a administração de coloide no grupo I não apresentaram correlação com os valores de pressão coloidosmótica baixo. A administração de coloide não apresentou impacto sobre os valores de albumina e pressão coloidosmótica, bem como não interferiu na perfusão tecidual. A pressão coloidosmótica apresentou uma correlação não significativa e inversamente proporcional com o SOFA. Desta forma, a partir dos resultados obtidos é possível concluir que os valores da pressão coloidosmótica não apresentaram correlação com os valores das variáveis de perfusão tecidual; o coloide não contribuiu para a melhora da perfusão tecidual e da manutenção da pressão coloidosmótica após a administração de grandes volumes de solução cristaloide.
Sepsis induces increased vascular permeability, translocation and albumin loss to extracellular space, resulting in hypoalbuminemia and lower plasma colloid osmotic pressure. This study correlate colloid osmotic pressure with the clinical progress of 41 female dogs presenting severe sepsis or sepsis shock due to pyometra, submitted to ovario-salpingo-hysterectomy. The parameters evaluated were: systolic arterial pressure, urinary debt, blood lactate, venous base excess and colloid osmotic pressure. Samples were collected every three hours during the inpatient period. Laboratorial analysis of colloid osmotic pressure was performed in different timings: group I (clinic criteria, n=21), samples analyzed only after the end of the treatment; and group II (quantitative criteria, n=20): samples analyzed immediately after collection. The parameters were a guide to evaluate the necessity of colloid administration. We found no correlation between the parameters evaluate and the values of colloid osmotic pressure. The administration of colloid presented a non-significant and inversely proportional correlation with SOFA. We concluded that colloid osmotic pressure is not directly correlated with tissue perfusion and colloid administration does not improve tissue perfusion or colloid osmotic pressure, even after the administration of substantial volumes of crystalloid solution.

Reasons for performing study: Adverse effects on renal health and haemostasis have been documented in human patients administered hydroxyethyl starches (HESs). Gelatins could provide useful substitutes should similar adverse effects be identified in horses. Objectives: To compare the effects of a 4% modified fluid gelatin (MFG) with a 6% (130/0.4) HES on haemodilution, colloid osmotic pressure (COP), haemostasis and renal parameters in healthy ponies. Study Design: Randomised crossover experiment. Methods: Three treatments (A=10 ml/kg bwt HES, B=10 ml/kg bwt MFG and C=20 ml/kg bwt MFG) were administered to 6 healthy ponies with a 1-week washout period. Haematocrit, platelet count, total serum protein, COP, thromboelastography (TEG), prothrombin time (PT), activated partial thromboplastin time (aPTT) and fibrinogen were measured at baseline and at multiple time points up to 24 h post-infusion. Serum creatinine, urine specific gravity (USG), urine protein: creatinine ratio (UPC), urine gamma glutamyltransferase:creatinine ratio (UGC) and urine sediment examination (USE) were performed before and 24 h after each treatment, as well as one week after the final treatment. Results: All treatments resulted in significant haemodilution and increases in COP, with treatment C having a significantly greater effect on haematocrit than other treatments. The platelet count decreased with all treatments and was significantly lower following treatment C compared with treatment B. No clinically relevant differences were observed in any of the TEG parameters within or between treatments. No significant differences in PT, aPTT or fibrinogen were observed between treatments. Serum creatinine, UPC and UGC did not change significantly between pre- and post-study measurements. USG and USE remained within normal limits. Conclusions: MFG could be considered as an alternative to HES for volume expansion and oncotic support. Neither MFG nor HES were associated with clinically significant adverse effects on haemostasis or renal parameters.
Dissertation (MSc)--University of Pretoria, 2015.
tm2016
Companion Animal Clinical Studies
MSc
Unrestricted

A hemostasia é um evento biológico passível de ser avaliado e estudado, assim como seus distúrbios. Há situações durante a anestesia que podem cursar com alterações hemostáticas culminando com aumento do sangramento ou até mesmo hemorragias graves. Os tempos de coagulação têm recebido especial atenção tendo-se em vista os diferentes contratempos hemostáticos que pode ocorrer durante o procedimento anestésico-cirúrgico. Sendo assim, nesse estudo buscou-se estabelecer os valores padrões para tempo de protrombina (TP) e de tromboplastina parcial ativada (TTPA) para cães submetidos a diferentes procedimentos cirúrgicos. Foram estudados 50 cães hígidos para padronização dos valores de TTPA e TP utilizando aparelho automático. Os valores de TTPA estavam dentro dos valores de normalidade da literatura (6,9 a 17,6 segundos) e valores de TP discretamente maiores (de 6,65 a 12,8 segundos). Foram estudadas 20 cadelas classificadas como ASA I e 18 cães ASA II e III. Nestes animais observaram-se aumentos significativos de valores de TTPA (de 12,04 para 14,29 segundos em ASA I, com P<0,0378; e de 13,4 para 15,11 segundos nos cães ASA II e III, P<0,0067) e de TP (de 8,36 para 9,7 segundos em ASA I, P<0,0323; e de 8,32 para 9,34 segundos nos caes ASA II e III, P< 0,0084) entre os momentos pré e pós-anestésicos Estes aumentos acompanham quedas da pressão coloidosmótica, indicando que o processo de anestesia, cirurgia e fluidoterapia causam hemodiluição, e conseqüente aumento nos tempo de coagulação.
Hemostasis is a biological event that could be evaluated and studied, just like yours disturbs. There are situations in to anesthetic procedures that could curse with hemostatics disturbs causing bleeding increase or even critical blood loss. The blood clotting times have been received special attention because different hemostatic setbacks that could occur during the anesthetic and surgical procedures. This way, this study look for establish the values for reference to protrombine time (PT) and to activated partial tromboplastin time (APTT) for dogs. Were studied 50 healthy dogs to standardize the values of PT and APTT utilizing an automatic instrument. The APTT values was in agreement with the literature values (6,9 to 17, 6 seconds), and the PT values was discret increased when compared with literature (from 6,65 to 12,8 seconds). Was studied 20 bitches classifieds as ASA I and 18 dogs classifieds as ASA II and III. In this animals observed significant increase values of APTT (from 12,04 to 14,29 seconds in the ASA I, P<0,0378; and from 13,4 to 15,11 seconds in the dogs ASA II and III, P<0,0067) and of PT (from 8,36 to 9,7 seconds in ASA I, P<0,0323; and from 8,32 to 9,34 seconds in the ASA II and III dogs) between the pre and post anesthetic moments. These increases attendance decease in the colloid osmotic pressure, indicating that the anesthetic, surgical and fluid therapy procedures can cause hemodilution, and consequent increase in the blood clotting times.

Caractériser les dispersions colloïdales en fonction de leur concentration en colloïdes en un minimum de temps constitue le cœur du sujet de cette thèse. Pour y parvenir, des mesures de la pression osmotique des dispersions, c’est-à-dire de leur résistance à la compression, peuvent être réalisées à différentes concentrations et pour diverses conditions expérimentales (salinité, pH etc.). L’utilisation classique de sacs de dialyse permet de telles mesures, mais, inconvénients majeurs, ces expériences dites « de compression osmotique » nécessitent des semaines d’équilibrage et ne peuvent pas être suivies in-situ. Le but de ces travaux consiste donc à mettre en œuvre des expériences de compression osmotique à haut débit, permettant également d’observer in-situ le système colloïdal à l’étude.Pour se faire, l’échelle microfluidique (10-100 µm) apparaît comme pertinente. A la suite du prototypage ultra-rapide de dispositifs fabriqués en PEG-diacrylate, l’enjeu est d’y intégrer des membranes nanoporeuses par photopolymérisation in-situ d’un hydrogel de PEGDA. La puce microfluidique ainsi transformée en un « micro-osmomètre à membrane », mesures de la pression osmotique des dispersions et observations in-situ à tout instant de l’expérience et en tout point du système sont alors possibles, à l’aide d’un simple microscope optique.Grâce à cette technologie, l’équation d’état d’une dispersion colloïdale, c’est-à-dire l’évolution de sa pression osmotique en fonction de sa concentration, mais également nombre d’informations sur l’état physico-chimique des particules ou encore sur leur organisation structurale pendant la compression peuvent être obtenues, en seulement quelques heures, ouvrant ainsi la voie à un criblage rapide de divers fluides complexes
Characterizing colloidal dispersions according to their concentration in colloids in a minimum of time is the heart of this thesis project. To reach this goal, measurements of the osmotic pressure of the dispersions, i.e. their resistance to concentration, can be carried out at different concentrations and for various experimental conditions (pH, salts concentration etc.). The common use of dialysis sacks allows such measurements, but with major drawbacks: these so-called "osmotic compression" experiments require weeks to reach the equilibrium and they cannot be in-situ monitored. Therefore, the aim of this work is to implement high throughput osmotic compression experiments, which also allow in-situ observations of the studied colloidal system.To do so, the microfluidic scale seems to be particularly smart. Following the ultra-fast prototyping of PEG-diacrylate-based devices, the issue is to integrate nanoporous membranes inside the channels by photopolymerization of a PEGDA-based hydrogel. The microfluidic chip is then turned into a “membrane micro-osmometer”. Thus, measurements of the osmotic pressure of the dispersions and in-situ observations whenever during the experiment and wherever in the system are then possible, using a simple optical microscope.Thanks to this technology, the equation of state of a colloidal dispersion, i.e. the evolution of its osmotic pressure as a function of its concentration, but also a great deal of information on the physico-chemical state of the particles or on their structural organization during the compression can be obtained, in just a few hours, paving the way to high throughput screening of complex fluids

The utilization of membrane treatment for the production of potable water has become more prevalent in today's industry. As drinking water regulations become more stringent this trend is expected to continue. Widespread use is also a result of membrane treatment being the best available treatment in many cases. While membrane treatment is a proven technology that can produce a consistently superior product to conventional treatment methods, membrane fouling and concentrate disposal are issues that drive up the cost of membrane treatment and can effectively eliminate it from consideration as a treatment alternative. This research focused on membrane fouling. A series of filtration experiments were conducted on various membranes to investigate the physical and chemical factors that influence fouling. The effects of both organic and colloidal fouling were explored by conducting research on various commercial membranes and experimental membranes by Saehan Industries, Inc. (Saehan). Saehan's membranes were in various stages of development in their process of creating a more fouling resistant membrane (FRM). Various hydrodynamic and chemical conditions were used to characterize the evolution of the Saehan commercial products to the experimental FRMs. The developmental stage of the membrane tested included analysis of the various trade secret coating techniques termed single, double, and special. A proprietary post-treatment process was also utilized in combination with each of the coating techniques. The developmental membranes were also compared to commercially available FRMs. The existing FRMs showed better fouling resistance than Saehan's commercially available products in high organic surficial groundwater testing. Synthetic colloidal water testing demonstrated the superior performance of the FRMs, but was not acute enough to differentiate the fouling performance within the group of FRMs or Saehan products. Average roughness decreased slightly as coating technique progressed from single to double to special. Post-treatment increased roughness in single coated membranes and reduced the roughness in double and special coated membranes. The relative charge differences in the developmental membranes were exhibited among non post-treated membranes. Post-treatment membranes did not demonstrate relative surface charge differences consistent with the manufacturer. Initial mass transfer coefficient, determined by clean water testing, increased as coating moved from single to double to special. Clean water testing showed increased initial mass transfer coefficient for membranes with post-treatment. Single coated membranes showed the best salt rejection capability among non post-treated membranes. Post-treatment increased selectivity for all membrane coating techniques. The coating effect on fouling potential had an inverse relationship between single coated versus double and special coated membranes. The post-treatment increased fouling resistance for the single coated membranes, but decreased fouling resistance of double and special coated membranes. The SN7 membranes showed the best performance of the developmental membranes.
M.S.Env.E.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Environmental Engineering

Introducció. Un determinat percentatge dels pacients intervinguts de cirurgia cardíaca presenten durant el període postoperatori una síndrome de vasoplejia (Síndrome clínica de Resposta Inflamatòria Sistèmica- SIRSc), arribant fins i tot a desenvolupar alguns d'ells un quadre de xoc distributiu (SIRSc-Greu). Canvis en els valors de la pressió coloidosmótica plasmàtica podrien jugar un paper important en el desenvolupament d'aquestes entitats. L'objectiu general d'aquest estudi és analitzar la relació entre els valors de pressió coloidosmótica plasmàtica i l'aparició de SIRSc i SIRSc-Greu en pacients sotmesos a una cirurgia cardíaca. Material i mètodes. Es va efectuar un estudi prospectiu en 214 pacients consecutius intervinguts de cirurgia cardíaca en el nostre centre durant el període de juny a desembre de 2018. Es va efectuar un seguiment dels valors de pressió coloidosmótica plasmàtica durant els tres primers dies de el període postoperatori utilitzant les fórmules proposades per Landis-Pappenheimer, Nematbakhsh-Moradi i l'Índex de Briones. Es va analitzar la relació existent entre els nivells de pressió coloidosmótica plasmàtica i l'aparició de la síndrome de vasoplejia postoperatòria (SIRSc), i el quadre de xoc distributiu (SIRSc-Greu). Resultats. En el postoperatori immediat dels pacients tractats amb una cirurgia cardíaca es va produir una reducció significativa dels valors de pressió coloidosmótica, que es van mantenir disminuïts de forma estable al llarg dels tres primers dies de període postoperatori. Un 77,5% dels pacients avaluats van desenvolupar una síndrome de vasoplejia postoperatòria (SIRSc) durant els tres primers dies del postoperatori, sense que aparegués una relació significativa entre els valors de la pressió coloidosmótica i el quadre de SIRSc. El percentatge de pacients que van presentar un xoc distributiu (SIRSc-Greu) al llarg de el període postoperatori va ser de l'12,1%. Vam poder apreciar una relació significativa entre els valors de pressió coloidosmótica plasmàtica i el risc d'aparició de SIRSc-Greu. Els pacients amb uns valors de pressió coloidosmótica inferiors als 18,5 mmHg van comptar amb un risc significativament superior de patir un SIRSc-Greu. El percentatge de SIRSc-Greu en els pacients amb valors de pressió coloidosmótica plasmàtica superiors a 18,5 mmHg durant el primer dia postoperatori (n = 155, 72,4%) va ser de l'5,2%, mentre que en els pacients amb uns valors inferiors a 18,5 mmHg (n = 69, 27,6%) aquest va ser de l'27,6%. Es va poder apreciar una relació significativa entre el diagnòstic de SIRSc-Greu i l'aparició de complicacions postoperatòries, un increment en la durada de l'ingrés a la Unitat de Cures Intensives post-Cirurgia Cardíaca, així com un increment en la durada de el període d'ingrés hospitalari . Els pacients que van presentar valors de pressió coloidosmótica plasmàtica inferiors a 18,5 mmHg durant el període postoperatori immediat van tenir un risc 4,5 vegades superior de patir l'aparició de complicacions postoperatòries. Conclusions. En els pacients intervinguts de cirurgia cardíaca es va produir un descens significatiu en els valors de pressió coloidosmótica plasmàtica en les primeres 72 h de l'postoperatori. Hi ha una relació significativa entre nivells de pressió coloidosmótica plasmàtica inferiors a 18,5 mmHg al llarg d'aquest i l'aparició d'un xoc distributiu i de complicacions postoperatòries.
Introducción. Un determinado porcentaje de pacientes intervenidos de cirugía cardíaca presentan durante el periodo postoperatorio un síndrome de vasoplejia (Síndrome clínico de Respuesta Inflamatoria Sistémica- SIRSc), llegando incluso a desarrollar algunos de ellos un cuadro de shock distributivo (SIRSc-Grave). Cambios en los valores de la presión coloidosmótica plasmática podrían jugar un papel importante en el desarrollo de estas entidades. El objetivo general del presente estudio es analizar la relación entre los valores de presión coloidosmótica plasmática y la aparición de SIRSc y SIRSc-Grave en pacientes tratados con una cirugía cardíaca. Material y métodos. Se efectuó un estudio prospectivo en 214 pacientes consecutivos intervenidos de cirugía cardíaca en nuestro centro durante el periodo de junio a diciembre de 2018. Se efectuó una monitorización de los valores de presión coloidosmótica plasmática durante los tres primeros días del periodo postoperatorio utilizando las fórmulas propuestas por Landis-Pappenheimer, Nematbakhsh-Moradi y el Índice de Briones. Se analizó la relación existente entre los niveles de presión coloidosmótica plasmática y la aparición del síndrome de vasoplejia postoperatoria (SIRSc), y el cuadro de shock distributivo (SIRSc-Grave). Resultados. En el postoperatorio inmediato de los pacientes tratados con una cirugía cardíaca se produjo una reducción significativa de los valores de presión coloidosmótica, que se mantuvieron disminuidos de forma estable a lo largo de los tres primeros días de periodo postoperatorio. Un 77,5% de los pacientes evaluados desarrollaron un síndrome de vasoplejia postoperatoria (SIRSc) durante los tres primeros días del postoperatorio, sin que apareciera una relación significativa entre los valores de la presión coloidosmótica y el cuadro de SIRSc. El porcentaje de pacientes que presentaron un shock distributivo (SIRSc-Grave) a lo largo del periodo postoperatorio fue del 12,1%. Pudimos apreciar una relación significativa entre los valores de presión coloidosmótica plasmática y el riesgo de aparición de SIRSc-Grave. Los pacientes con unos valores de presión coloidosmótica inferiores a los 18,5 mmHg contaron con un riesgo significativamente superior de sufrir un SIRSc-Grave. El porcentaje de SIRSc- Grave en los pacientes con valores de presión coloidosmótica plasmática superiores a 18,5 mmHg durante el primer día postoperatorio (n=155, 72,4%) fue del 5,2%, en tanto que en los pacientes con unos valores inferiores a 18,5 mmHg (n=69, 27,6%) éste fue del 27,6%. Se pudo apreciar una relación significativa entre el diagnóstico de SIRSc-Grave y la aparición de complicaciones postoperatorias, un incremento en la duración del ingreso en la Unidad de Cuidados Intensivos post-Cirugía Cardíaca, así como un incremento en la duración del periodo de ingreso hospitalario. Los pacientes que presentaron valores de presión coloidosmótica plasmática inferiores a 18,5 mmHg durante el periodo postoperatorio inmediato tuvieron un riesgo 4,5 veces superior de sufrir la aparición de complicaciones postoperatorias.Conclusiones. En los pacientes intervenidos de cirugía cardíaca se produjo un descenso significativo en los valores de presión coloidosmótica plasmática en las primeras 72h del postoperatorio. Existe una relación significativa entre niveles de presión coloidosmótica plasmática inferiores a 18,5 mmHg a lo largo de este y la aparición de un shock distributivo y de complicaciones postoperatorias.
Introduction. During the postoperative period, a certain percentage of patients undergoing cardiac surgery have vasoplegia syndrome (Clinical Systemic Inflammatory Response Syndrome- SIRSc), some of them even developing a distributional shock chart (Severe-SIRSc. Changes in plasma colloid osmotic pressure values could play an important role in the development of these entities. The general objective of this study is to analyze the relationship between plasma colloid osmotic pressure values and the appearance of SIRSc and Severe-SIRSc in patients treated with cardiac surgery. Material and methods. A prospective study was carried out in 214 consecutive patients undergoing cardiac surgery in our center during the period from June to December 2018. Monitoring of plasma colloid osmotic pressure values was carried out during the first three days of the postoperative period using the formulas proposed by Landis-Pappenheimer, Nematbakhsh-Moradi and the Briones Index. The relationship between the levels of plasma colloid osmotic pressure and the appearance of postoperative vasoplegia syndrome (SIRSc), and the distributional shock chart (Severe-SIRSc) was analyzed. Results. In the immediate postoperative period of the patients treated with cardiac surgery, there was a significant reduction in the colloid osmotic pressure values, which remained stable in the first three days of the postoperative period. 77.5% of the evaluated patients developed a postoperative vasoplegia syndrome (SIRSc) during the first three postoperative days, without showing a significant relationship between the colloid osmotic pressure values and the SIRSc chart. The percentage of patients who presented a distributional shock (Severe- SIRSc) throughout the postoperative period was 12.1%. We were able to appreciate a significant relationship between plasma colloid osmotic pressure values and the risk of developing Severe- SIRSc. Patients with colloid osmotic pressure values less than 18.5 mmHg had a significantly higher risk of suffering a Severe-SIRSc. The percentage of Severe-SIRSc in patients with plasma colloid osmotic pressure values greater than 18.5 mmHg during the first postoperative day (n = 155, 72.4%) was 5.2%, whereas in patients with values below 18.5 mmHg (n = 69, 27.6%) this was 27.6%. A significant relationship between the diagnosis of Severe-SIRSc and the appearance of postoperative complications, an increase in the duration of the Intensive Care Unit stay after Cardiac Surgery, as well as an increase in the duration of the hospital stay, could be seen. Patients who presented plasma colloid osmotic pressure values below 18.5 mmHg during the immediate postoperative period had a 4.5 times higher risk of developing postoperative complications. Conclusions. In patients undergoing cardiac surgery, there was a significant decrease in plasma colloid osmotic pressure values in the first 72 hours postoperatively. There is a significant relationship between plasma colloid osmotic pressure levels below 18.5 mmHg throughout this and the appearance of distributional shock and postoperative complications.

Ce travail de thèse porte sur le développement technologique d’outils miniaturiséspour l’exploration de diagrammes de phase de fluides complexes (dispersions colloïdales,solutions de polymères ou tensioactifs, etc). Les outils élaborés permettent dedéterminer des diagrammes de phase par une approche continue à l’aide de la microfluidique.Ils sont basés sur deux types de procédés membranaires différents : la pervaporation(mécanisme d’évaporation de solvant) et la dialyse (mécanisme d’échangesosmotiques). En s’appuyant sur le processus de pervaporation, il a été montré théoriquementet expérimentalement qu’il existe une géométrie pour laquelle le séchageconfiné est homogène. Il est donc possible de construire des diagrammes de phase demélanges à plusieurs composants de l’échelle moléculaire aux colloïdes. Une étudeconsacrée à la compréhension de la complexité du séchage des nanoparticules de silicecommerciales dans un canal microfluidique de type microévaporateur a été miseen place. La cinétique de concentration des particules est décrite jusqu’à la formationd’un état dense ainsi que les divers phénomènes liés au séchage comme l’existenced’une transition de phase dans un système colloïdal, l’apparition de fractures ou la délaminationdu matériau dense. Un nouvel outil microfluidique intégrant une membranede type dialyse offre la possibilité de contrôler les échanges osmotiques à l’échelle dunanolitre. Le protocole de fabrication ainsi que le dimensionnement de la géométriesont présentés. Grâce à cet outil, il est possible de mesurer des pressions osmotiquesde dispersions colloïdales
This work deals with the technological development of miniaturized tools for theexploration of the phase diagram of complex fluids (colloidal dispersions, solutions ofpolymers or surfactants, etc). The microfluidic tools we elaborated make it possibleto determine phase diagrams of a series of formulations of complex fluids by consumingonly minute amounts of samples. These devices exploit two types of membraneprocesses to concentrate the chemical species : pervaporation (solvent evaporationthrough a dense membrane) and dialysis (osmotic exchanges through a membrane).Concerning the case of pervaporation, we demonstrated theoretically and experimentallythat a specific microfluidic design exists for which concentration fields of chemicalspecies remain spatially homogeneous along the kinetic path followed withinthe phase diagram. Then, it enables to obtain phase diagrams of multi-componentsmixtures from molecular compounds up to colloids, at the nanolitre scale. We reporta study concerning the understanding of the drying process of commercial silica nanoparticlesusing a dedicated microfluidic experiment involving pervaporation. Wepresent the kinetics of the concentration of the particles within the channel up to theformation of a dense colloidal packed bed which invades the channel at a controlledrate. We developed an original microfluidic tool integrating a dialysis membranewhich makes it possible to control osmotic exchanges at the nanoliter scale. We reportthe protocol of microfabrication of this chip and its specific geometry.We presentpreliminary results showing that this tool can be used to measure osmotic pressures ofcolloidal suspensions

The mechanism by which loss of serum proteins into the urine causes expansion of extracellular fluid volume and oedema has become clearer. A key initiating abnormality is avid sodium retention by the kidney, leading to increased whole-body sodium and increased extracellular fluid volume. This appears to be driven primarily by overactivation of the amiloride-sensitive epithelial sodium channel (ENaC) in the collecting duct, activated proteolytically through abnormal filtration of plasminogen, and its activation to plasmin in the nephron. Conventional explanations for nephrotic oedema focused on low colloid osmotic pressure as a consequence of loss of serum proteins, leading to egress of extracellular fluid from the intravascular compartment. It was hypothesized that this led to underfilling of the circulation and a drive to sodium retention. While low osmotic pressure may play a part in the clinical picture of nephrotic syndrome, a variety of observations suggest that underfilling is not a common feature except in the most severe nephrotic syndrome. Furthermore the gradient in colloid osmotic pressure between serum and interstitium tends to be preserved in nephrotic syndrome. The distribution of excess extracellular fluid is markedly different in patients with nephrotic syndrome from that seen in patients who have reduced glomerular filtration rate as the cause of sodium retention. This is not fully understood but hypotheses centre on capillary permeability and colloid osmotic pressure effects.

Peripheral oedema is a palpable swelling caused by increased interstitial fluid in soft tissues, and can be due to local or systemic disease. Fluid distribution between capillaries and the interstitium is governed by Starling forces. The lymphatic system returns excess fluid and protein from the extracellular, interstitial space to the bloodstream. Thus, interstitial oedema may arise from factors that increase capillary pressure or permeability, factors that reduce plasma colloid osmotic pressure, factors that impede lymphatic drainage, or a combination of these causes. This topic addresses the diagnosis of peripheral oedema.

Severe capillary leak is an important factor in the pathogenesis of organ dysfunction following inflammatory syndromes such as sepsis-induced acute lung injury and acute respiratory distress syndrome (ARDS). Various interventions, such as a conservative fluid strategy, albumin, and diuretics are designed to maintain an adequate intravascular colloid osmotic pressure, reduce capillary leak and reduce extravascular water. Of these, only a conservative, rather than liberal fluid strategy is currently recommended. Preclinical studies in ARDS and sepsis suggest that preventing microvascular leak may represent a viable therapeutic approach to prevent or ameliorate organ dysfunction. The challenge is to now go further with carefully designed clinical trials.

The formation of pulmonary oedema depends on the balance between capillary hydrostatic pressure, interstitial tissue pressure, plasma colloid osmotic pressure, endothelial permeability, and lymphatic function. The efficiency of lymphatic drainage of interstitial fluid (which can increase >10-fold) is critical in determining the onset and extent of hydrostatic oedema....

The study aimed to investigate haematocrit variation as acute phase reactants rise in myocardial infarction.Serial measurements of haematocrit were undertaken in a cohort (N = 60) of patients over periods ranging from 6 to 28 days. Concurrent measurements of plasma fibrinogen were made by the method of Clauss. Patients with clinical or radiological evidence of heart failure were excluded as were patients with history or evidence of bleeding for any cause.Results showed a small initial transient rise in haematocrit above baseline of 3% within the first 12 hours post-infarction, followed by a mean decrease below baseline of the order of −16%. The decrease was maintained at the time of discharge from hospital (mean 9.5 days) at a level of −11%. In the single case where serial haematocrits were measured up to 28 days, haematocrit was still reduced by −12%. The maximum individual percentage decrease measured in any patient exceeded −30% and occurred at 3 days post-infarct. The decrease parallelled the rise in plasma fibrinogen but apart from the early post−infarct period, the correlation was poor because of the rise in other acute phase reactants subsequently.A postulated mechanism for the fall in haematocrit is that it reflects haemodilution. This is in part a physiological compensatory mechanism for the increasein colloid osmotic pressure that is attendant on the increase in acute phase reactants due to myocardial tissue destruction. The blood loss due to serial diagnostic phlebotomies cannot explain the magnitude of the decrease.

Reverse osmosis and nanofiltration membranes remove colloids, macromolecules, salts, bacteria and even some viruses from water. In crossflow filtration, contaminated water is driven parallel to the membrane, and clean permeate passes through. A large pressure gradient exists across the membrane, with permeate flow rates two to three orders of magnitude smaller than that of the crossflow. Membrane filtration is hindered by two mechanisms, concentration polarization and caking. During filtration, the concentration of rejected particles increases near the membrane surface, forming a concentration polarization layer. Both diffusive and convective transport drive particles back into the bulk flow. However, the increase of the apparent viscosity in the concentration polarization layer hinders diffusion of particles back into the bulk and results in a small reduction in permeate flux. Depending on the number and type of particles present in the contaminated water, the concentration polarization will either reach a quasi-steady state or particles will begin to deposit onto the membrane. In the later case, a cake layer eventually forms on the membrane, significantly reducing the permeate flux. Contradictive theories suggest that the cake layer is either a porous solid or a very viscous (yield stress) fluid. New and refined models that shed light on these theories are presented.