Gérard Guiffant

Investigation of heat transfer in a polymeric phase change material for low level heat storage

A new material for low level heat storage has been elaborated. It is a stable mixture of water with a water soluble polymerised and cross-linked monomer such as polyacrylamid. Quantitative results regarding the thermophysical properties of the material are presented. These parameters are used in a theoretical approach describing the progression of a phase change front in a slab of finite thickness, and the computed results are found to be in good agreement with the experimental data for the considered duration of freezing and thawing in samples.

A new experimental method for the evaluation of the release profiles of drug-loaded microbeads designed for embolisation

Abstract The development of a galenical form must take into account the drugs physico-chemical properties as well as the external conditions that govern its performances. In the case of loaded microbeads designed for embolisation, the drug-release kinetics strongly depends on the local hydrodynamic conditions. Currently the apparatuses recommended by the European Pharmacopoeia allow the measurement in vitro of these kinetics; but the measured kinetics are very different from those met in the in vivo embolisation procedures. A new methodology is presented for evaluating the controlled release of a drug from ion exchange resins for embolisation. Experimental and numerical data are reported on the release kinetics of two closely related galenical formulations (DEAE Trisacryl LS and QAE Trisacryl LS).

AN EXPERIMENTAL AND THEORETICAL STUDY OF MASS TRANSFER FROM LOADED EMBOLISATION MICROBEADS: POSSIBLE OPTIMISATION

The development of loaded galenical formulations requires specific tests leading to a sharp discrimination of kinetics release. We have presented an experimental protocol where particular hydrodynamic conditions are implemented, permitting the drug to be transported by a controlled diffusive-convective process, after chemical liberation from the microbeads. This study shows that the procedure leads to satisfactory results regarding the characterization of closely related galenical formulations. A two dimensional phenomenological approach leads to the promising possibility of optimizing the procedure.

Forced convection heat transfer in a slurry of phase change material in an agitated tank

The heat transfer during the crystallisation in a slurry of a stable mixture of water with a water-soluble polymerised and cross-linked monomer, suspended in oil is investigated. Some experimental data are presented which emphasize that such a suspension of millimetric particles of a phase change material allows both a high capacity of heat storage and limited super cooling phenomena. A phenomenological description of the crystallisation process is proposed which permits to predict the duration of the plateau of crystallisation as a function of the weight fraction and the temperature of the cold spring. The results compare very well with the experimental data thus giving a new impulse to the design of new complex fluids for both storage and heat transport.

Pulsative flushing as a strategy to prevent bacterial colonization of vascular access devices

Central venous device infections are associated with increased physical and psychological morbidity, mortality, length of stay, and costs. The aim of this study was to prove the efficacy of pulsatile flushing to prevent the bacterial colonization of vascular access devices. One hundred and forty four tests using 576 polyurethane short venous access catheters were performed. Four catheters per test were polluted with a fibronectin-serum albumin solution. Three were filled with a Staphylococcus aureus broth; one served as negative control. One contaminated catheter was not flushed (positive control), and two were flushed (10 mL.sec−1) with normal saline solution, either by ten successive boluses of 1 mL each or by one bolus of 10 mL. Each catheter was cultivated. The S. aureus quantity observed after continuous flushing was significantly higher than that observed after pulsative flushing (P<0.001). Unflushed catheters were 20.71 and 6.42 times more polluted than catheters flushed with the pulsative method or the continuous method, respectively. Pulsative flushing was at least twice as effective as continuous flushing in reducing the S. aureus count. Pulsative flushing is more effective than continuous flushing in reducing the endoluminal contamination. Pulsative flushing is a simple, effective, and inexpensive technique to reduce catheter bacterial colonization.

An embolic gelling solution based on acrylic copolymers in ethanol for the treatment of arteriovenous malformations

We report the preparation of an embolic agent based on specific association of an acrylic copolymer with dedicated particles formulated in ethanol. The copolymers were synthesized by radical polymerization of tertiobutylacrylamide (tBA) and 2-hydroxypropyl methacrylate (HPMA). Influences of the monomers composition, molecular weight and copolymer concentration have been evaluated on an in vitro model. Introduction of tBA units improves significantly the occlusion properties but these properties are similar whatever the molecular weight of the copolymer. As observed by viscosity studies, it seems necessary to work with a relatively high polymer concentration (C > Ce) to form a cohesive embolus. Addition of solid particles composed by a crosslinked polymer of 2-hydroxyethyl methacrylate (HEMA) and N-trishydroxymethyl methacrylamide (TRIS) in the acrylic copolymer solution has allowed to obtain an embole having an enhanced cohesion and giving a more compact structure. An in vivo evaluation has been performed by injection of this embolic agent in intercostal arteries and renal artery of sheep. There was no fragmentation of the plug during and after injection and a complete arterial occlusion by a cohesive embole. The pathological examination confirmed that there was a complete arterial occlusion by the plug and that the dedicated particles were as expected embedded in the precipitate acrylic copolymer.

A phenomenological description of the progression of a freezing front in a slab. Application to a new heat storage material

Abstract The restatement of a new material for the heat storage gave the opportunity to develop a phenomenological model, based on a heat balance approach, for the description of the progression of a freezing front in a slab. The method applies when the sample is submitted to initial and final temperatures different from the transition temperature. The theoretical results are in very good agreement with the experimental data.

Diagnosis of azygos catheter misplacement

mislead to an anteroposterior catheterization of the azygos ostium (Fig. 2). Mechanical and anatomical factors favoring azygos catheter tip misplacement include a high flexibility (silicone vs. polyurethane), small diameter (4/5F vs. 6/7F) of indwelling catheter, the azygos arch position, and large vein diameter. Coughing or vomiting as well as power catheter injection might create catheter whiplash and subsequent secondary displacement (3). Anatomical variants of the azygos system include rare agenesis of the azygos vein, congenital interruption of the inferior vena cava (IVC), different opening levels into SVC, mostly at T3 level (T2-T5), and diameters (mean 8.6 mm; range, 4-16 mm), azygos lobe (1%) (Fig. 1A) and various numbers of venous valves (1 to 4) (4). Usually azygos catheter misplacement is asymptomatic clinically. However, some particular issues have been reported in the literature. They include a life-threatening azygo-tracheal fistula (5), “idiopathic” aneurysms, thrombosis cases with subsequent pulmonary embolism likely due to side-walling catheter tip motions. Interestingly, we never observed any primary azygos catheter misplacement when routing from the right side, as the right innominate vein does not face the azygos arch opening. To prevent and/or diagnose azygos vein catheter misplacement we recommend the following:

Mechanical characteristics of plastic base Ports and impact on flushing efficacy

Background Three types of totally implantable venous access devices, Ports, are currently in use: titanium, plastic (polyoxymethylene, POM), and mixed (titanium base with a POM shell). Physics theory suggests that the interaction between a non-coring needle (NCN, made of stainless steel) and a plastic base would lead to the stronger material (steel) altering the more malleable material (plastic). Objectives To investigate whether needle impacts can alter a plastic base’s surface, thus potentially reducing flushing efficacy. Study design and methods A Port made of POM was punctured 200 times with a 19-gauge NCN. Following the existing guidelines, the needle tip pricked the base with each puncture. The Port’s base was then examined using a two-dimensional optical instrument, and a bi-dimensional numerical simulation using COMSOL® was performed to investigate potential surface irregularities and their impact on fluid flow. Results Each needle impact created a hole (mean depth, 0.12 mm) with a small bump beside it (mean height, 0.02 mm) the Reynolds number Rek≈10. A numerical simulation of the one hole/bump set showed that the flushing efficacy was 60% that of flushing along a flat surface. Discussion In clinical practice, the number of times a Port is punctured depends on patient and treatment characteristics, but each needle impact on the plastic base may increase the risk of decreased flushing effectiveness. Therefore, the more a plastic Port is accessed, the greater the risk of microorganisms, blood products, and medication accumulation. Conclusions Multiple needle impacts created an irregular surface on the Port’s base, which decreased flushing efficacy. Clinical investigation is needed to determine whether plastic base Ports are associated with an increased risk of Port infection and occlusion compared to titanium base Ports.

Paramètres rhéologiques et risques de thrombose veineuse : impact du rapport des diamètres cathéter sur veine

La thrombose est un risque important lors du catheterisme vasculaire et particulierement veineux, peripherique ou central. Les diametres respectifs du catheter insere et de la veine catheterisee et leur rapport sont-ils facilitateurs de thrombose ? Dans une approche rheologique, nous decrivons les modifications physiques des conditions d’ecoulement sanguin veineux, leurs implications dans le transport et le depot de proteines et d’elements figures du sang provoquees par l’introduction d’un catheter. Ce travail conduit a l’idee selon laquelle un intervalle de valeurs du rapport des diametres catheter sur veine offrirait des conditions de risques thrombogeniques reduits. Il en resulte evidemment la necessite de mesures echographiques, de tout reseau veineux, prealable a toute pose de catheter peripherique ou central.