Membrane potential in multi-ionic mixtures.

The membrane potential arising through charged porous membranes separating electrolyte mixtures at identical hydrostatic pressures but different concentrations was investigated theoretically by means of the steric, electric, and dielectric exclusion (SEDE) model. Transport phenomena were described through the Nernst-Planck formalism, while ion partitioning at the membrane/solution interfaces was accounted for by means of modified Donnan equations including steric and dielectric effects. The high concentration limit of the membrane potential depends on the mixture composition and the pore size as well. A specific feature of membrane potential in multi-ionic systems is the dependence at high concentration on the effective dielectric constant of the solution confined inside pores. Indeed, the effective dielectric constant inside pores does not affect the high concentration limit of the membrane potential in the case of single salt solutions. The low concentration limit of the membrane potential is independent of the mixture composition, the effective dielectric constant inside pores, and the pore radius, but it is ruled by counterions with the highest charge number. The membrane potential measured at high salt concentration with single salt solutions and electrolyte mixtures could be used to determine the pore size and the effective dielectric constant inside pores, respectively. This may constitute an alternative way for membrane characterization with the advantage of avoiding the need for additional rejection rate measurements.

Characterization of charge properties of an ultrafiltration membrane modified by surface grafting of poly(allylamine) hydrochloride.

A polyethersulfone ultrafiltration membrane was functionalized by a cationic polyelectrolyte, the poly(allylamine) hydrochloride (PAH). The influence of the time of adsorption of PAH on the membrane charge properties was studied. Several characterization techniques were used to investigate the membrane modification. Tangential and transmembrane streaming potential measurements were conducted to characterize the outer and inner surfaces of the membrane, respectively. Both techniques indicated that the surface modification of the membrane was efficient. The charge of the outer surface was reversed (from negative values for the unmodified membrane to positive values for the modified membrane) and the charge of the inner surface was neutralized after adsorption of the cationic polyelectrolyte onto the pore walls. The modification of both the outer surface of the membrane and the pore walls was also put in evidence with membrane potential measurements. It was found that the charge of the PAH-modified membrane is affected by the time of immersion in PAH solution. Experimental data seem to show a fast modification of the membrane for the first 15 min; nevertheless, the modification was more pronounced after 24 h of PAH adsorption. Diffusion experiments carried out with unmodified and modified membranes for four salts (KCl, NaCl, MgCl, and CaCl(2)) showed a decrease in the salt permeability after functionalization of the membrane. The permeability decrease was greater for 2:1 salts than for 1:1 salts. This decrease was explained by electrostatic interactions.

Evaluation of the steric, electric, and dielectric exclusion model on the basis of salt rejection rate and membrane potential measurements.

The current work focuses on the application of the steric, electric, and dielectric exclusion (SEDE) model to the study of both the ion rejection rate and the membrane potential of a nanofiltration polyamide membrane. The aim of this study was to evaluate the performance of the SEDE model and to compare it with steric/electric exclusion theory. Experiments were conducted with CaCl(2) solutions at various concentrations. The SEDE model is a four-parameter model because the effective pore size (r(p)), the effective thickness-to-porosity ratio (Delta x/A(k)), the effective volume charge density of the membrane (X), and the dielectric constant of the solution inside the pores (epsilon(p)) have to be known to predict the rejection rate and the membrane potential. The first parameter was estimated from membrane potential measurements performed at high salt concentrations and the second from water permeability. In the case of single salt solutions, experimental rejection rates and membrane potentials can be described by a number of couples of values (X,epsilon(p)) because both electric and dielectric exclusion contribute to reject ions. A set of couples (X,epsilon(p)) were first estimated by fitting membrane potentials. One of the couples was found to provide a good description of experimental rejection rates as well. Results showed that the polyamide membrane is negatively charged in CaCl(2) solutions at natural pH and that the membrane charge increases with the salt concentration. A decrease in the effective dielectric constant inside the pores with respect to its bulk value was found. This is indirect evidence that dielectric exclusion plays a major role in the transport phenomena of the studied NF membrane. The standard steric/electric theory was also used to fit experimental rejection rates and membrane potentials, the effective volume charge density being the single adjustable parameter in this case. Unlike the SEDE model, the steric/electric exclusion theory was unable to account simultaneously for both rejection rate and membrane potential data by using a unique choice for X and epsilon(p). This highlights the global coherence of the SEDE model and the nonappropriateness of the description of transport in NF membranes by the classical steric/electric exclusion theory.

[A high troponin value: about a favourable evolution case]. / Valeur élevée de troponine: à propos d'un cas d'évolution favorable.

Cardiac troponin I (TnIC) is a sensitive and specific marker for myocardial injuries. A part from its diagnosis character, troponin is a major element for mid term prognosis with regard to occurred cardiovascular events. We are reporting the case of a 56-year-old man admitted to hospital for an inaugural myocardial infarction with positive evolution despite a very high level of troponin (1200 ng/ml) in post re-vascularisation. The context of moderate risk factors and the early re-vascularisation probably contributed to a favourable evolution of the patient. A very high troponin value seems to be more in favour of an effective re-perfusion rather than a mid term prognosis factor in this case.

Contribution of convection, diffusion and migration to electrolyte transport through nanofiltration membranes.

Transport mechanisms through nanofiltration membranes are investigated in terms of contribution of convection, diffusion and migration to electrolyte transport. A Donnan steric pore model, based on the application of the extended Nernst-Planck equation and the assumption of a Donnan equilibrium at both membrane-solution interfaces, is used. The study is focused on the transport of symmetrical electrolytes (with symmetric or asymmetric diffusion coefficients). The influence of effective membrane charge density, permeate volume flux, pore radius and effective membrane thickness to porosity ratio on the contribution of the different transport mechanisms is investigated. Convection appears to be the dominant mechanism involved in electrolyte transport at low membrane charge and/or high permeate volume flux and effective membrane thickness to porosity ratio. Transport is mainly governed by diffusion when the membrane is strongly charged, particularly at low permeate volume flux and effective membrane thickness to porosity ratio. Electromigration is likely to be the dominant mechanism involved in electrolyte transport only if the diffusion coefficient of coions is greater than that of counterions.

Evaluation of the "DSPM" model on a titania membrane: measurements of charged and uncharged solute retention, electrokinetic charge, pore size, and water permeability.

The DSPM (Donnan steric partitioning pore model) was evaluated in the case of a titania membrane with "nanofiltration properties" by measuring the electrokinetic charge, pore size, and water permeability of the membrane, along with charged and uncharged solute retention. The zeta potential values (zeta) were determined from measurements of the electrophoretic mobility (EM) of titania powder forming the filtering layer of the membrane. Zeta potential values were converted into membrane volume charge (X) by assuming two limiting cases: a constant surface charge (sigma(s)(cst)) and a constant surface potential (psi(s)(cst)). The mean pore radius and thickness/porosity ratio of the membrane were determined by permporometry and from water permeability measurements, respectively. Retention measurements were carried out as a function of the permeate volume flux for both neutral solutes (polyethylene glycol PEG of different size) and salts (KCl, MgSO4, K2SO4, and MgCl2) at various pH values. Ionic retentions showed minimum values near the IEP of the membrane. Retention data were analyzed using the DSPM. Very good agreement was found between the pore radius calculated by the model and that determined by permporometry. X values calculated from fitting retention data using the DSPM were also in satisfactorily agreement with X values calculated from EM measurements assuming a constant surface potential for a large pH range. Furthermore, the DSPM leads to X values (X(DSPM)) between those calculated from EM (X(EM)) using the two limiting bounds. In other words, X(DSPM) was higher than X(EM) assuming psi(s)(cst) at pH values far from the isoelectric point (IEP) and lower than X(EM) assuming sigma(s)(cst). These results show that the DSPM is in qualitative agreement with the charge regulation theory (increase of the pore surface potential and decrease of the pore surface charge density with decreasing the pore size). On the other hand, the thickness/porosity ratio of the membrane calculated from solute retention data differed significantly from that determined from water permeability measurements. Moreover, a single value of Deltax/Ak could not be determined from PEG and salt retention data. This means that the Deltax/Ak parameter loses its physical meaning and includes physical phenomena which are not taken into account by the DSPM. Nevertheless, the model satisfactorily predicted the limiting retention, as this is not influenced by the Deltax/Ak parameter.

Electrokinetic characterization of porous plugs from streaming potential coupled with electrical resistance measurements.

The zeta potential of mixed nickel-iron oxide particles is evaluated by a new laboratory instrument. This latter allows the measurement of streaming potential together with the electrical resistance of porous plugs. The conductivity of electrolyte inside plug (pore conductivity) is deduced from electrical resistance measurements and is used together with streaming potential to evaluate the zeta potential by accounting for the surface conduction phenomenon. It is shown that neglecting the surface conduction phenomenon leads to a substantial underestimation of the zeta potential. The coupled measurements of streaming potential and plug electrical resistance yield zeta potential values that are in very good agreement with those obtained by electrophoresis. The densification of the porous plug with increasing pressure increments is put in evidence by the decrease in measured streaming potentials. Electrical resistance measurements make it possible to account for the increase in surface conductivity resulting from the more compacted structure of the plug. By doing so, the calculated zeta potential is found to be virtually independent of the pressure difference involved in streaming potential experiments, whereas the negligence of surface conduction phenomenon leads to a decrease in the apparent zeta potential with increasing pressure level.

[A case report of Cardiobacterium hominis endocarditis]. / Endocardite a Cardiobacterium hominis.

We here report a case of endocarditis due to Cardiobacterium hominis in a 53-year-old patient, who presented with large vegetations on the mitral valve. Good cooperation between clinicians and microbiologists and an efficient automated blood culture system were the decisive factors in establishing the diagnosis. Early and appropriate treatment prevented the septic embolisms often observed in this pathology.

Determining the Zeta Potential of Porous Membranes Using Electrolyte Conductivity inside Pores.

The zeta potential is an important and reliable indicator of the surface charge of membranes, and knowledge of it is essential for the design and operation of membrane processes. The zeta potential cannot be measured directly, but must be deduced from experiments by means of a model. The possibility of determining the zeta potential of porous membranes from measurements of the electrolyte conductivity inside pores (lambda(pore)) is investigated in the case of a ceramic microfiltration membrane. To this end, experimental measurements of the electrical resistance in pores are performed with the membrane filled with KCl solutions of various pHs and concentrations. lambda(pore) is deduced from these experiments. The farther the pH is from the isoelectric point and/or the lower the salt concentration is, the higher the ratio of the electrolyte conductivity inside pores to the bulk conductivity is, due to a more important contribution of the surface conduction. Zeta potentials are calculated from lambda(pore) values by means of a space charge model and compared to those calculated from streaming potential measurements. It is found that the isoelectric points are very close and that zeta potential values for both methods are in quite good agreement. The differences observed in zeta potentials could be due to the fact that the space charge model does not consider the surface conductivity in the inner part of the double layer. Measurements of the electrolyte conductivity within the membrane pores are proved to be a well-adapted procedure for the determination of the zeta potential in situations where the contribution of the surface conduction is significant, i.e., for small and charged pores. Copyright 2001 Academic Press.

[Hepatitis C epidemiology at a general hospital center. Management and natural history as a function of the manner of identification]. / Epidémiologie de l'hépatite C dans un centre hospitalier général. Prise en charge et histoire naturelle en fonction du mode de découverte.

OBJECTIVES: To study the epidemiological characteristics of patients with chronic hepatitis C virus followed in a primary referral hospital and the clinical influence of "systematic screening" defined as the screening of patients without symptoms and with known risk factors of hepatitis C (past transfusion, past or present intravenous drug use, haemodialysis) on the natural history and treatment of chronic hepatitis C virus. METHODS: The files of 311 consecutive patients who screened positive for anti-hepatitis C virus and were seen at the primary referral hospital, Creil, from January 1992 to February 1996, were analyzed. RESULTS: Patients who underwent "systematic screening" were younger with a shorter duration of infection. They were more often intravenous drug addicts and had lower alanine aminotransferase activity and Knodell scores than patients who underwent screening during "a diagnostic procedure", because of symptoms and/or abnormal liver biochemistry. Increased age at contamination and alcohol consumption of more than 40 g per day was associated with an increased risk of cirrhosis while patients who underwent "systematic screening" had a lower risk of cirrhosis and higher survival rate. Interferon therapy was attempted less often in anti-hepatitis C virus positive patients from "systematic screening" programs. CONCLUSIONS: Anti-hepatitis C virus positive patients from "systematic screening" programs had a benign disease and were rarely treated with interferon compared to anti-hepatitis C virus positive patients diagnosed during a "diagnostic procedure".

Electrokinetic Phenomena in Homogeneous Cylindrical Pores.

The electrokinetic phenomena occurring in homogeneous cylindrical pores containing symmetric electrolytes are studied. The local relations for flow in the pores (Nernst-Planck and Navier-Stokes equations) are developed. The analysis includes a numerical solution of the nonlinear Poisson-Boltzmann equation. The integral expressions of the phenomenological coefficients coupling the solvent flow and the electrical current with the hydrostatic pressure and the electrical potential gradients are established and calculated numerically. The mobilities of anions and cations are individually specified and the electroviscous effects as well as the surface conductance are taken into account. Streaming potentials obtained from numerical calculations are compared with results given by classical relations in a range of zeta potentials and electrokinetic radii that may commonly occur in experimental investigation of micro- and ultrafiltration membranes. In this work, it is shown that classical approximated relations can give rise to very misleading conclusions and that the determination of the true zeta potential requires a full analysis (including numerical calculations) of the basic relations for flow and potential distribution in charged pores. Copyright 1999 Academic Press.

Validation protocol of analytical hemostasis systems: measurement of anti-Xa activity of low-molecular-weight heparins.

A standard validation protocol adapted to the chromogenic assay of anti-Xa activity of low-molecular-weight heparins was used in a multicenter study to assess its suitability for comparing and evaluating analytical hemostasis systems. The protocol included: familiarization with the system (repeatability); assessment of limits of linearity, detection limits, and cross-contamination; and validation (reproducibility and accuracy of measurements of treated patients' plasmas). We calibrated the systems with the same range of lyophilized plasmas daily and evaluated repeatability and reproducibility by using a single batch of lyophilized plasmas at three anti-Xa activities. The two automated systems tested [SB 300 (Gilford) and ACL (IL)] and the two semiautomated systems [ST 888 (D. Stago) and Chromotimer (Behring)] gave similar mean values. Dispersion of results was lower with the automated systems than with the semiautomated ones, especially at low anti-Xa activities, a tendency that also was observed for reproducibility. Because each analytical system gave linear results for activities as great as 1000 IU/L, suitable sample dilution is advisable for higher anti-Xa activities. Accuracy was greater in the automated systems. We conclude that this protocol is feasible and is applicable to validation of other analytical hemostasis instruments, in particular the latest generation of fully automated instruments.

[Detection of multivessel lesions after myocardial infarction. Improvement of the predictive value of early exercise stress test by discriminant analysis]. / Détection des lésions multitronculaires après infarctus du myocarde. Amélioration de la valeur prédictive de l'épreuve d'effort précoce à l'aide d'une analyse discriminante.

The aim of this study was to assess, by a discriminant analysis, the different parameters of exercise stress testing associated with multivessel disease after uncomplicated myocardial infarction and to determine whether their combination improved the diagnostic value of ST depression alone, the usual diagnostic criterion. One hundred and seventeen out of 240 consecutive pts admitted for acute myocardial infarction between october 1992 and may 1994 underwent early exercise stress testing and coronary angiography 8.5 +/- 3 days and 13 +/- 8 days respectively after infarction. The population was divided into two groups: a "study" group (pts recruited between october 1992 and october 1993) for whom a diagnostic equation had been established based on a discriminant analysis, and "a control" group (pts recruited between november 1993 and may 1994) allowing validation of the diagnostic equation. Of the 9 clinical and 14 exercise stress test variables, only 3 remained statistically significant after discriminant analysis in this study group: the number of METS achieved (p < 0.0005), maximal ST depression in V5 (p < 0.005) and maximal heart rate (p < 0.01). Using these three parameters, a discriminating equation was established in the study group and then validated in the control group. Using this equation, the percentage of pts correctly identified as having multivessel disease was 75% in the study group and 79% in the control group, whereas ST depression, the most commonly used criterion, only classified 68% of the study group and 60% of the control group correctly. This study confirmed the good tolerance of early maximal exercise stress testing after uncomplicated myo-cardial infarction. The combination of three easily discernable parameters improved the diagnostic performance of the stress test in identifying multivessel disease after myocardial infarction.

[Nodular regenerative hyperplasia associated with primary antiphospholipid syndrome]. / Hyperplasie nodulaire régénérative associée à un syndrome primaire des antiphospholipides.

Nodular regenerative hyperplasia of the liver is characterized by diffuse nodularity of the hepatic parenchyma without fibrotic septa. It may be related to venous or arterial obstruction in the portal tract. We report a case of primary antiphospholipid syndrome associated with nodular regenerative hyperplasia in a 45-year old woman. The patient had an ischemic stroke, associated with an acute arterial ischemia of the left leg. She had high titers of serum anticardiolipin antibodies. Nodular regenerative hyperplasia of the liver was histologically confirmed and was associated with anicteric cholestasis. This case provides additional evidence that a thrombotic mechanism may play a role in the pathogenesis of nodular regenerative hyperplasia of the liver.

Validity in nulliparas of increased beta-human chorionic gonadotrophin at mid-term for predicting pregnancy-induced hypertension complicated with proteinuria and intrauterine growth retardation.

The objective of the present study was to investigate whether increased beta-human chorionic gonadotrophin (beta HCG) plasma concentrations in an unselected population of nulliparas could predict the occurrence of complicated pregnancy-induced hypertension (PIH). The design was that of a prospective population study. It was conducted at the obstetric departments of Amiens University Hospital and Creil General Hospital on 434 consecutive nulliparas with singleton pregnancies after natural fertilization who accepted the systematic offer of trisomy 21 screening but for whom this disorder was finally estimated. Measurement of plasma concentration of beta HCG (ELISA method) was carried out between 14 and 20 weeks (mean: 17 weeks) of amenorrhea, and measurement of blood pressure and proteinuria (> 300 mg/24 h or Albustix +2) during the first, second and third term and 2-3 months after the delivery, as well as measurement of birth weight for determination of small for gestational age (SGA) babies, 37 women developed PIH, 10 without other complication, 16 with proteinuria (5 of which with SGA babies) and 11 with SGA babies. Furthermore 2 patients presented abruptio placentae without PIH. 395 women did not develop PIH including 389 normotensive women and 6 chronic hypertensive patients without superimposed toxemia. Only 1 was diabetic. None had chronic renal disease. Mean (+/- SD) levels of beta HCG were higher in PIH than in controls: 46,805 +/- 19,068 versus 23,479 +/- 13,463 IU. A pathologic threshold was chosen as the mean for the whole population + 1 SD: 25,613 + 15,479 = 41,082 IU. Elevated levels (above this value) were significantly associated with isolated PIH or PIH complicated with proteinuria and/or with SGA babies. The positive predictive value of this criterion was respectively 11, 15 and 12% for each of these complications. The relative risk (and 95% confidence limit) of women with elevated beta HCG for each of these complications was 20 (6-79), 11 (4-43) and 22 (7-93). Elevated plasma beta HCG found around 17 weeks of amenorrhea predicts PIH complicated with either proteinuria or SGA babies with a positive predictive value comparable to that of the best and earliest test proposed up to now to select nulliparas at high risk of preeclampsia, namely the abnormalities of the Doppler waveforms of the uterine arteries. Since this test is simpler to perform, it represents the most convenient method to screen a population of nulliparas for evaluation of the benefits of low-dose aspirin.

[Hypertension and pregnancy. Diagnosis, physiopathology and treatment]. / Hypertension et grossesse. Diagnostic, physiopathologie et traitement.

This review on hypertension in pregnancy focuses mainly on the pathophysiology and prevention of pregnancy induced hypertension which, when associated with proteinuria, is usually called preeclampsia. Rather than a genuine hypertensive disease, preeclampsia is mainly a systemic endothelial disease causing activation of platelets and diffuse ischemic disorders whose most obvious clinical manifestations involve the kidney (hence the proteinuria, edema and hyperuricemia), the liver (hence the hemolytic elevated liver enzymes and low platelets, or HELLP syndrome), and the brain (hence eclamptic convulsions). Hypertension is explained by increased vascular reactivity rather than by an imbalance between vasoconstrictive and vasodilating circulating hormones. This increased reactivity is due to endothelial dysfunction with imbalance between prostacyclin and thromboxane A2 and possibly dysfunction of NO and endothelin synthesis. The aggressive substances for endothelium are thought to be of placentar origin and the cause of their release is explained by placentar ischemia related to a defect of trophoblastic invasion of the spiral arteries. The etiology of this latter defect is unknown but involves immunologic mechanisms with genetic predisposition. The only effective treatment for PIH is extraction of the baby with the whole placenta. The decision for extraction is often a very delicate obstetric problem. Antihypertensive drugs are mainly indicated in severe hypertension (> 160-100 mm Hg), with the aim of preventing cerebral hemorrhage in the mother, but have not been shown to improve fetal morbidity or mortality. Eclamptic seizures can be prevented and treated more effectively with magnesium sulfate than with diazepam or phenytoin. Prevention of preeclampsia remains the main challenge. Whereas antihypertensive drugs are ineffective, calcium supplementation and low dose aspirin have proven effective but mainly in selected populations with a relatively high incidence of preeclampsia (> 8-10%). In multiparas the selection of such a high risk population is relatively easy when at least 2 (or 1?) previous pregnancies were complicated with early preeclampsia and/or intrauterine growth retardation. In nulliparas the selection of the high-risk population is still a subject of research. The 2 most promising criteria are abnormal Doppler velocimetry of the uterine arteries at around 20 weeks of amenorrhea, and abnormally high plasma levels of beta HCG at 17 weeks of amenorrhea.