Thermodynamics of water confined in porous calcium-silicate-hydrates.

Water within pores of cementitious materials plays a crucial role in the damage processes of cement pastes, particularly in the binding material comprising calcium-silicate-hydrates (C-S-H). Here, we employed Grand Canonical Monte Carlo simulations to investigate the properties of water confined at ambient temperature within and between C-S-H nanoparticles or "grains" as a function of the relative humidity (%RH). We address the effect of water on the cohesion of cement pastes by computing fluid internal pressures within and between grains as a function of %RH and intergranular separation distance, from 1 to 10 Å. We found that, within a C-S-H grain and between C-S-H grains, pores are completely filled with water for %RH larger than 20%. While the cohesion of the cement paste is mainly driven by the calcium ions in the C-S-H, water facilitates a disjoining behavior inside a C-S-H grain. Between C-S-H grains, confined water diminishes or enhances the cohesion of the material depending on the intergranular distance. At very low %RH, the loss of water increases the cohesion within a C-S-H grain and reduces the cohesion between C-S-H grains. These findings provide insights into the behavior of C-S-H in dry or high-temperature environments, with a loss of cohesion between C-S-H grains due to the loss of water content. Such quantification provides the necessary baseline to understand cement paste damaging upon extreme thermal, mechanical, and salt-rich environments.

Molecular simulation of water confined in nanoporous silica.

This paper reports on a molecular simulation study of the thermodynamics, structure and dynamics of water confined at ambient temperature in hydroxylated silica nanopores of a width H = 10 and 20 Å. The adsorption isotherms for water in these nanopores resemble those observed for experimental samples; the adsorbed amount increases continuously in the multilayer adsorption regime until a jump occurs due to capillary condensation of the fluid within the pore. Strong layering of water in the vicinity of the silica surfaces is observed as marked density oscillations are observed up to 8 Å from the surface in the density profiles for confined water. Our results indicate that water molecules within the first adsorbed layer tend to adopt a H-down orientation with respect to the silica substrate. For all pore sizes and adsorbed amounts, the self-diffusivity of confined water is lower than the bulk, due to the hydrophilic interaction between the water molecules and the hydroxylated silica surface. Our results also suggest that the self-diffusivity of confined water is sensitive to the adsorbed amount.

[Intestinal perforations in percutaneous surgery of the kidney]. / Les perforations digestives dans la chirurgie percutanée du rein.

Using 9 personal surveys and 11 cases found in the literature, the authors analyse the etiologies of this iatrogenic accident, the often secondary modalities of the diagnosis and the benign nature of the fistula which usually heals spontaneously.

[Preserved saphenous grafts in hemodialysis. 20 years' experience]. / Greffons saphènes conservés en hémodialyse. Vingt ans d'expérience.

From 1972 to 1992, 790 vascular conduits were implanted as vascular access in hemodialysis patients, of whom 402 were "longs" (length above 15 cm), with 168 PTFE grafts and 234 homosaphenous preserved vein grafts matching 136 manufactured and 98 self-prepared grafts. Functional period of time as 10 years has been obtained with the two materials, and up to twelve years with one manufactured graft. Among complications were observed 12% serious infection with PTFE graft compared to 2% with homosaphenous graft; aneurysm on 9% of PTFE grafts and 11% of saphenous graft, stenosis on vein graft anastomosis in 65% of the PTFE cases and 85% of the saphenous cases. There were 12% complications specific to PTFE grafts. Finally, homosaphenous vein is a material of choice in hemodialysis vascular access, mainly with the manufactured grafts.

[The Carboclip, a new, atraumatic vascular access for hemodialysis]. / Le Carboclip, un nouvel accès vasculaire atraumatique pour hémodialyse.

The Carboclip is a no-needle vascular access device made of an inverted Titanium body. The horizontal bar of 6 mm inner diameter is connected with artery and vein via a vascular graft. The vertical body houses an elastic plug in which is inserted a double canula diving in the blood stream for extracorporeal blood circulation (EBC). The body is wrapped by a flange made of microporous biocarbon in which the subcutaneous fibroblast will growth, forming an antimicrobial barrier and fixing the port to the skin. We report our experience on 30 devices implanted in 30 sheep with 26 extracorporeal circulation simulating hemodialysis. The results demonstrate good tightness of the plug as well at rest as during EBC procedure, sufficient blood flow rate of about 400 ml/min, and benefits of the microporous carbon flange.

Expanded polytetrafluoroethylene prostheses as secondary blood access sites for hemodialysis: pathological findings in 29 excised grafts.

The popularity of expanded polytetrafluoroethylene (PTFE) arteriovenous fistulas for hemodialysis access is increasing. The low infection rate, low thrombogenicity and low body reactivity make it an important blood access for patients on routine hemodialysis. The authors examined 29 PTFE graft fistulas surgically excised from patients on hemodialysis for one or more of the following complications: infection 7, 2 with associated hemorrhage; thrombosis 9; aneurysm 11, 3 with associated thrombosis; stenosis 5, 3 with associated thrombosis; hemorrhage 4 and arterial steal 2. The explanted prostheses were reinforced Gore-tex in 20, Gore-tex thin wall in 1, Impra I in 4, Impra II in 3 and Vitagraft in 1. It was also noted that the implants failed in the short term mainly because of infection, in the medium term mainly because of thrombosis and stenosis, and in the long term usually because of aneurysm.

[Stripped veins for secondary vascular access in hemodialysis. Pathologic study of the grafts after surgical excision]. / Veines de stripping comme abord vasculaire secondaire pour l'hémodialyse. Etude pathologique de greffons après exérèse chirurgicale.

The suitability of stripping vein homografts as AV fistulae for intermittent hemodialysis has been evaluated. Microscopic investigation of stored veins indicated the superiority of cryopreservation over refrigeration. A systematic study of 12 venous homograft fistulae surgically excised from hemodialysis patients revealed that the homograft walls are the sites of both connective tissue proliferation and of mural degeneration. It was also noted that the implants failed in the short term (less than 1 yr) mainly due to stenosis, in the medium term (1 yr-3 yrs) mainly due to aneurysmal dilatation and for a variety of reasons beyond 3 years. It was concluded that when suitably selected, handled and stored, stripping vein homografts are a viable alternative to treated human umbilical or bovine heterografts as blood access fistulae if no autograft is available.

[Progressive complications associated with the use of a bovine heterograft for vascular access]. / Complications évolutives associées à l'utilisation d'une hétérogreffe bovine comme abord vasculaire.

Three bovine carotid heterografts, used for vascular access, were analysed after removal following the development of aneurysms in two cases and thrombosis in one. The first prosthesis was implanted in a 17-year-old man who suffered from myasthenia gravis and was undergoing plasmapheresis. It became notably dilated several months after implantation, and resection was necessary 14 months after insertion. The second graft was placed in a 31-year-old woman being treated for a severe chronic potassium insufficiency. It was removed 16 months after insertion because of thrombosis. The third bovine carotid heterograft was inserted in a 48-year-old patient on long-term hemodialysis and was removed 3.5 months later because of aneurysmal dilatation adjacent to the arterial anastomosis. These evolutionary and degenerative changes associated with the bovine carotid heterograft illustrate the limitations of this material as an interpositional limb for arteriovenous fistulas in angioaccess therapy. Small weaknesses have sometimes been noted in the microstructure of the graft material studied before implantation.

[Results of a serological survey made in France (Vendeé region) in domestic ducks]. / Resultats d'une enquete serologique effectuee en France (vendee) Chez le canard a rotir.

The sera of domestic ducks were examined for antibodies to several infectious agents of palmipeds during the winter of 1982 in the abattoirs in la Vendée, an important region of duck production in the West of France. The performance of each batch and their antecedents was also studied. In Barbary ducks and crossbred ducks (from male wild ducks and female domestic ducks), antibodies were found to the virus of egg drop syndrome 16 (EDS 76), to Newcastle disease virus (NDV), to duck hepatitis virus and to chlamydia psittici. In Nantais ducks (resulting from a cross between Khaki Campbell and Pekin ducks), antibodies were detected against EDS 76 virus, duck hepatitis virus and chlamydia. The frequency and levels of antibodies varied between types or strains of ducks. About 50% of the Barbary ducks had high levels of antibodies to EDS 76 virus, whereas 70 to 80% of crossbred and Nantais ducks had these antibodies but at very low levels. Virtually 100% of Barbary ducks had high levels of antibodies against Derzsy's disease virus whereas only 10% of the batches of crossbred ducks had antibodies at varying levels. The proportion of batches with antibodies against NDV was higher in crossbred ducks (25%) than in Barbary ducks (2%) and the titres were low. Antibodies to duck hepatitis virus, when present, were of a high titre irrespective of type or strain of duck. Infection by chlamydia was suspected in 3% of lots of Barbary ducks, in 33% of lots of crossbred ducks, and in 3.7% of lots of Nantais ducks. These findings are discussed and considered in relation to breeding history and performance of the flocks. The EDS 76 virus could in certain circumstances cause weight loss in male Barbary ducks. These epidemiological observations need to be confirmed experimentally.

Renoureteral bypass in obstructions and losses of substance of the initial ureter.

When the renal pelvis and the proximal ureter are destroyed, surgical repair is always difficult. In case of a loss of substance of the upper ureter, it is possible to replace the obstructed (or destroyed) segment and to preserve the healthy iliopelvic ureter. The 'renoureteric bypass' consists of the insertion of an intermediate segment between the lower calyx of the kidney and the lumboiliac ureter. A prosthesis or an intestinal loop may be used to restore the continuity of the urinary tract. The results obtained in dogs being excellent, the technique was applied successfully in man in 2 cases.

["Suspended" segmental replacement of the ureter using the ileum. Experimental results at five years (author's transl)]. / Le remplacement segmentaire "suspendu" de l'uretère par l'iléon. Résultats expérimentaux à 5 ans.

Segmental replacement of the ureter using an intestinal segment has given good long term experimental results. Preservation of the pelvic ureter has two advantages:--The use of a short intestinal loop, which decreases the secretion of mucus, stagnation and electrolyte reabsorption;--preservation of the normal uretero-vesical junction, thereby avoiding reflux. At the beginning of this experimental study, it was feared that the pelvic ureter would become obstructed by mucus and that the insufficiently contractile and atonic ileal loop would dilate, forming a "pool" of stagnant urine. In fact, no such complications were seen.