Diffusion of water in clays on the microscopic scale: modeling and experiment.

Diffusion of water in montmorillonite clays at low hydration has been studied on the microscopic scale by two quasi-elastic neutron scattering techniques, neutron spin-echo (NSE) and time-of-flight (TOF), and by classical microscopic simulation. Experiment and simulation are compared both directly on the level of intermediate scattering functions, I(Q, t), and indirectly on the level of relaxation times after a model of atomic motion is applied. Regarding the dynamics of water in Na- and Cs-monohydrated montmorillonite samples, the simulation and NSE results show a very good agreement, both indicating diffusion coefficients of the order of (1-3) x 10(-10) m(2) s(-1). The TOF technique significantly underestimates water relaxation times (therefore overestimates water dynamics), by a factor of up to 3 and 7 in the two systems, respectively, primarily due to insufficiently long correlation times being probed. In the case of the Na-bihydrated system, the TOF results are in closer agreement with the other two techniques (the techniques differ by a factor of 2-3 at most), giving diffusion coefficients of (5-10) x 10(-10) m(2) s(-1). Attention has been also paid to the elastic incoherent structure factor, EISF(Q). Simulation has played a key role in understanding the various contributions to EISF(Q) in clay systems and in clearly distinguishing the signatures of "apparent" and true confinement. Indirectly, simulation highlights the difficulty in interpreting the EISF(Q) signal from powder clay samples used in experiments.

Study of individual Na-montmorillonite particles size, morphology, and apparent charge.

Size, morphology, and apparent charge of individual Na-montmorillonite particles of natural MX-80 sodium montmorillonite were investigated in the present study by the use of three coupling methods. In the first part of this work, natural and synthetic montmorillonite clays were studied with atomic force microscopy (AFM) and photo-correlation spectroscopy (PCS). Both techniques exhibit the presence of two clay populations with a high dispersion of the length distribution. Microscopic analysis of the system revealed that clay particles could be reasonably approximated at low concentrations to ellipsoidal tactoids about 1.2 nm high. Average dimensions of the first population were typically 320-400 nm long/250 nm wide and 200-250 nm long/120 nm wide for natural and synthetic clays, respectively. The second population exhibits smaller sizes: 65 and 50 nm long and 35 and 25 nm wide for natural and synthetic clays, respectively. The statistics obtained for natural clay were then verified by PCS experiments on sodium montmorillonite suspensions. Both techniques reveal an important length dispersion. However, the relative proportions of the two kinds of particles could not be established properly because of both lack of statistics and limitations of the employed techniques. In the following part, conductivity measurements were performed on dilute montmorillonite clay suspensions. Raw data were then interpreted with the sizes and morphological information gained in the first part of the present work. The apparent charge of the clay sheets was found to be 8% of the structural charge.

An analytical model for probing ion dynamics in clays with broadband dielectric spectroscopy.

A simple two-state model is proposed to explicitly derive the ionic contribution to the frequency-dependent dielectric permittivity of clay. This model is based on a separation of time scales and accounts for two possible solvation modes (inner/outer-sphere complexes) for ions in the interlayer spacing and a possible chemical exchange between both forms. The influence on the permittivity of thermodynamic (distribution constant K(d)) and dynamic (diffusion coefficient, chemical relaxation rate) parameters is discussed. In turn, this model is used to analyze experimental data obtained with Na-montmorillonite for two relative humidities. The values of the parameters extracted from these measurements, and their variation with water content, show that the proposed model is at least reasonable.

Extended lower limb venous ultrasound for the diagnosis of proximal and distal vein thrombosis in asymptomatic patients after total hip replacement.

OBJECTIVE: To assess the performance of extended lower limb venous ultrasound (US) for the diagnosis of asymptomatic deep vein thrombosis (DVT) and to estimate a 3-month DVT incidence on repeated US after total hip replacement. DESIGN: Diagnostic performance study and prospective cohort study. MATERIALS AND METHODS: US was compared to phlebography in 70 consecutive patients and interobserver agreement was assessed in the last 48 patients at day 8. US was repeated in these 48 patients at day 13 and day 90. RESULTS: Phlebography demonstrated a DVT in 18/70 (26%) patients, with five proximal and 13 distal and US in 23/70 (33%) patients, with eight proximal and 15 distal. Sensitivity and specificity of US with 95% CI were 94% (73-100) and 89% (76-96), respectively. Sensitivity in isolated distal vein thrombosis was 92% (67-99). The Kappa coefficient for agreement between observers was 0.84 (0.66-1.00). Follow-up showed a DVT in 15/48 (31%) patients on day 8, in 20/48 patients (42%) on day 13. DVT recurred in two patients during follow-up. CONCLUSIONS: The incidence of asymptomatic DVT is still significant despite prophylaxis but most DVTs remain distal and occur in the first 2 weeks. Extended US could replace phlebography for systematic screening in clinical trials using surrogate endpoints in view of its high accuracy and reliability.

Clinical outcome and cost of hospital vs home treatment of proximal deep vein thrombosis with a low-molecular-weight heparin: the Vascular Midi-Pyrenees study.

BACKGROUND: Low-molecular-weight heparins have been shown to be effective and safe in the treatment of deep vein thrombosis. To our knowledge, there have been no direct comparisons of such treatment on an outpatient vs an inpatient basis. OBJECTIVE: To conduct a randomized, comparative, multicenter trial to evaluate the clinical outcomes and treatment costs of deep vein thrombosis in the outpatient and inpatient settings. METHODS: Two hundred one patients presenting with proximal deep vein thrombosis, without known risk factors for pulmonary embolism or hemorrhagic complications, were randomized to receive a low-molecular-weight heparin at the registered dose followed by an oral anticoagulant for up to 6 months, either in the hospital for the first 10 days followed by treatment at home (n=102) or at home from the outset (n=99). The primary clinical outcome was the incidence of venous thromboembolism recurrence, pulmonary embolism, or major bleeding. The economic analysis was performed from the point of view of the health insurance company. Total costs of the 2 management strategies were calculated to compare the cost consequences during the first 10 days. RESULTS: No differences in clinical outcome were detectable between the 2 groups. There was no increase in the rates of primary efficacy outcome in the patients treated at home vs in the hospital (3.0% vs 3.9%), while a cost reduction of 56% was demonstrated for outpatient management. CONCLUSION: For patients with proximal deep vein thrombosis and no symptoms of pulmonary embolism or increased risk of major bleeding, home treatment using a low-molecular-weight heparin is an effective, safe, and cost-saving strategy.

[Treatment of deep venous thrombosis at home: evolution from ideas to medical practice]. / Traitement des thromboses veineuses profondes à domicile: de l'évolution des idées á la pratique médicale.

The diagnosis of Deep Venous Thrombosis (DVT) by duplex ultrasound is absolutely possible out of specialized centers. Low Molecular Weight Heparins (LMWH) allow to obtain a greater efficacy and safety compared to Unfractionated Heparin (UFH). The control of LMWH is very reduced. Two studies have just been published on the topic of treatment of DVT at home. The group of patients treated at home with LMWH is not presenting more complications than the group of patients initially treated at the hospital with UFH. Nevertheless, these studies concern a very selective population of patients. Our center has been proceeding to a study for 4 years (1993-1997) in comparing the treatment at home of proximal DVT by LMWH then oral anticoagulant, to the initial treatment (10 days) in hospital by also using LMWH then oral anticoagulant. The first results show that there is no difference between both groups in terms of end-points: death, extension or recurrence of the thrombus, pulmonary embolism, bleeding. Therefore, the treatment of some type of proximal DVT is possible at home. Nevertheless, it is necessary to be very cautions as the population studied so far is a selected one. Etiologies of DVT are a constant obsessive fear. DVT or pulmonary embolism represents a real general disease which is going to progress along life. The intervention of a specialized center is always necessary. It is a work in team which must get the upper hand compared to an isolated medical action.

Characterization of vanadyl sulfate effect on vascular contraction: roles of calcium and tyrosine phosphorylation.

In order to explore the mechanism of action of vanadyl sulfate (VOSO4), previously described as an antidiabetic and antihypertensive agent, we have investigated the role of calcium and tyrosine phosphorylation in the contractile responses of rat aorta or skinned rabbit mesenteric artery rings. VOSO4 induced a concentration-dependent contraction of aorta (pD2 = 3.2), which was potentiated by endothelium removal (pD2 = 4.2). After a first exposure to VOSO4, no change in responsiveness was observed even though high vanadium concentrations had accumulated in the aortic tissue (approximately 4 x 10(-3) M). VOSO4 induced, in calcium-free medium, a significant response that, relative to contractions measured in Krebs-Henseleit buffer, was higher (36%) than norepinephrine (16%)-, arginine-vasopressin (8%)- or KCI (5%)-induced responses. 8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8), an intracellular calcium release inhibitor, did not modify VOSO4-induced response either in the presence or in the absence of ambient calcium. On skinned preparations, VOSO4 antagonized Ca++-induced contraction. The tyrosine kinase inhibitors tyrphostin 23 (T23) and tyrphostin 47 (T47) potentiated by 4- and 14-fold, respectively, the activity of VOSO4, in contrast to the lack of effect of T47 on pervanadate-induced contraction. When phosphotyrosine content was revealed by Western blotting, VOSO4 had no effect alone, but in the presence of T47, it dramatically increased the phosphotyrosine content. This result contrasts again with PV-induced tyrosine phosphorylation, which was blocked by T47. These data suggest that the signaling events involved in vascular effects of VOSO4, although they depend little on calcium mobilization, are related to tyrosine phosphorylation, likewise through a pathway different from that of pervanadate.

Vanadyl sulphate differently influences insulin response to glucose in isolated pancreas of normal rats after in vivo or in vitro exposure.

The effect of the antidiabetic agent vanadyl sulphate (VOSO4) on the endocrine pancreas function of normal rats was studied using the isolated pancreas preparation. A short-term (8 days) i.p. treatment (15 mg/kg per day) resulted in attenuation of high glucose-stimulated insulin release, at day 9 but also at days 19, i.e., after full recovery of appetite and weight, while blood and pancreas vanadium concentrations were still elevated. Six months of oral VOSO4 treatment (0.75 mg/ml in drinking water) resulted in elevated vanadium concentrations while glucose-stimulated insulin release was attenuated as compared to pair-fed animals. Conversely, when directly perfused in pancreas, VOSO4 potentiated glucose-stimulated insulin release. These apparently opposite effects may be related to the ability of VOSO4 to exert both peripheral insulinomimetic effects-leading to chronic reduction in insulin demand-, and a direct pancreatic insulinotropic activity.

Long-term correction of STZ-diabetic rats after short-term i.p. VOSO4 treatment: persistence of insulin secreting capacities assessed by isolated pancreas studies.

We have previously shown that 3 week oral VOSO4 treatment of streptozotocin (STZ, 60 mg/kg)-induced diabetic rats was able to correct diabetes for 13 weeks after treatment withdrawal. In the present study, we investigated whether a short-term (8 days) i.p. VOSO4 treatment was similarly able to reverse the diabetic state. Insulin secretory capacities were assessed at distance of treatment using the isolated pancreas preparation. Seven treatment-groups were performed: high dose VOSO4-treated diabetics (HVD, 1.3 mM/kg/8 days), food-restricted diabetics (FRD, food adjusted to HVD levels), low dose VOSO4-treated diabetes (LVD, 0.06 mM/kg/day), insulin-treated diabetics (ID, dose adjusted to normalize glycaemia) and VOSO4 (0.06 mM/kg/day) + insulin (dose adjusted to normalize glycaemia in the presence of vanadium)-treated diabetics (IVD), in addition to the corresponding untreated non-diabetic controls (C) and diabetics (D). Our results indicate that long-term correction of diabetes (a) can be obtained after an 8 day treatment using i.p. VOSO4 in diabetic animals retaining some degree of pancreatic function, (b) is not obtained with insulin treatment or food restriction although the association of VOSO4 and insulin was found beneficial, (c) can be prolonged in some individuals for at least 4 months, i.e. in conditions such that tissue vanadium concentrations had returned to values close to pre-treatment levels, (d) is associated with improved and in some cases normalized insulin secretion from isolated pancreas. The protective or corrective role of VOSO4 on diabetes-related pancreatic alterations, as well as the potential of the VOSO4-insulin association should be further studied in view of the possible use of vanadium derivatives in the treatment of diabetes.