Search

A dispersion of phase-change materials is proposed as an experimental biphasic refrigerant. The phase-change material is water stabilized by a tri-dimensional network of polymer, obtained by using a polymerizing process. The particle contains 90 per cent of water and has the consistency of a viscoelastic solid above the phase-change temperature. The measured values of the physical properties of the biphasic refrigerant, that is, specific heat, latent heat, density and viscosity, are presented and discussed for the considered temperature range. A supercooling phenomena is observed if the size of the particles becomes lower than 1 mm. The degree of supercooling however does not exceed 3°C. The various advantages of this slurry are presented and the comparison with a common single-phase carrier fluid has proved how great its properties are as a secondary refrigerant. This material appears well adapted for a wide variety of schemes where the production involves low-temperature intervals, such as the refrigeration industry. Copyright © 2001 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Introduction: Central or peripheral vascular access devices have been in use for many decades. However, despite adequate care and maintenance, complete occlusion may occur, and its impact cannot be overlooked. A new procedure using a percussion technique has been published and referred as 'the POP technique'., Methods: A hydrodynamic bench was used permitting both the recording of the movement of the piston with a fast camera and the pressure variations in the polyurethane and silicone catheters while connected to 2- and 3-piece syringes., Results: The results are twofold. First the upward movement of the piston leads to the installation of a saturation vapour pressure in the body of the syringe. During this sequence, the clot is submitted to a force of aspiration. Then the release of the plunger leads to a pulse pressure whose dynamics and intensity are dependent of the types of syringes and catheters., Conclusions: The experiments bring to light the importance of practical features such as the orientation of the syringe and the nature of the polyurethane or silicone catheters. Then the analysis enables the definition of practical rules for safe practice of the POP technique. This study will impact clinicians as many may be tempted to use the technique in hope to resolve the occlusion safely, in a timely manner.

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 Re k ≈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., Competing Interests: The authors report no conflicts of interest in this work.

Introduction: To follow international guidelines and protect healthcare workers from needle stick injuries, manufacturers now provide safety non-coring needles., Methods: Numerical simulations show the potential efficacy of infusion and flushing flow in straight and curved side wall port chambers from a beveled non-coring needle (BNCN) or a bevel-free cannula (BFC)., Results: In straight and curved side wall port chambers, the stream of flow with a BNCN is determined by the direction of the bevel, whereas the outlet stream from a BFC leads to a cylindrical symmetric flow. This, along with the position of the BFC impacts the wall shear rate of the port chamber, and the hydraulic resistance within the chamber., Discussion: This last factor has never been the subject of extensive hydrodynamic study. Caregiver safety and patient comfort are paramount but physics show that the shape of the needle tip affects the hydrodynamics of the injected flow., Conclusions: The presence of a bevel at the needle tip is a key factor for ensuring efficient flushing of the port. The absence of a bevel may increase hydraulic resistance and deposits in the port chamber. Implantable port flushing protocols must take this notion into account if the patency of port chambers is to be maintained. The clinical impact of this study has yet to be determined.

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.

Now widely used, totally implantable venous access devices allow mid- and long-term, frequent, repeated, or continuous injection of therapeutic products by vascular, cavitary, or perineural access. The effective flushing of these devices is a key factor that ensures their long-lasting use. We present experimental results and a numerical simulation to demonstrate that the implementation of rounded edge wall cavities improves flushing efficiency. We use the same approaches to suggest that the deposit amount may be reduced by the use of rounded edge wall cavities.

Purpose: The use of totally implantable venous access devices (TIVADs) certified as "high pressure resistant" or "power port" has begun to spread worldwide as a safe procedure for power contrast injection. Owing to the thermo-rheological properties of the contrast media, the primary aim of this work is to present an in vitro experimental impact study concerning the impact of the temperature level on flushing efficiency after contrast medium injection. Moreover, we report experimental data that confirms the role of needle bevel orientation. The secondary aim is to answer the following questions: Is there significant device contrast medium trapping after contrast medium injection? Is saline flushing efficient? And, finally, is it safe to inject contrast medium through an indwelled port catheter?, Results: The experimental results show that in addition to hydrodynamics, temperature is a key parameter for the efficiency of device flushing after contrast medium injection. It appears that this is the case when the cavity is incompletely rinsed after three calibrated flushing volumes of 10 mL saline solution, even by using the Huber needle bevel opposite to the port exit. This leads to a potentially important trapped volume of contrast medium in the port, and consequently to the possibility of subsequent salt precipitates and long term trisubstituted benzene nuclei delivery that might impair the solute properties, which may be further injected via the power port later on., Conclusion: We thus suggest, in TIVADS patients, the use of a temporary supplementary intravenous line rather than the port to perform contrast medium injections in daily radiology routine practice.

The use of totally implantable venous access devices developed as a medical device allowing mid- and long-term, frequent, repeated, or continuous injection of therapeutic products, by vascular, cavitary, or perineural access. The effective flushing of these devices is a central element to assure long-lasting use. Our experimental work demonstrates that directing the Huber point needle opening in the diametrically opposite direction of the implantable port exit channel increases the flushing efficiency. These results are consolidated by numerical computations, which support recommendations not only for their maintenance, but also for their use.

Purpose: To compare, under controlled conditions similar to practical situations, the efficacy of pulsed and continuous infusion for flushing IVADs. For both of them different flow rates, flushing volumes, and times were tested., Methods: The PU catheter lumens were filled with a mixture of fibronectin and bovine albumin to simulate physiologic protein depot. Flushing was performed with normal saline. An adapted pump controlled the flow rates. Efficacy was measured by the amount of albumin recovered from the lumen of the tested devices. Flow rate, volumes, and times tested were based upon values reported and/or measured in nursing practices. We compared: (A) single 10 mL bolus and 6 flushing times, (B) continuous infusion of 500 mL in 24 hours, (C) 10 successive boluses 1 mL flushed in 0.5 s each and 6 different time intervals between each bolus. Statistics were performed using the Mann and Whitney U test., Results: In group A, the maximum percentage of recovered protein (79.1% was achieved with the 10 mL bolus flushed in 2.5. In group B, 77% of protein was recovered at 24h. In group C: maximum efficacy (90 +/- 3%) was obtained when the time interval between 2 boluses was 0.4 s., Conclusions: We conclude that hydrodynamics has a determinant effect on the efficacy and that the adjunction of an intermittent component in the flow increases it. Flow type and the time interval between 2 boluses are the 2 critical variables.

The use of elastomeric diffusers (EDs) has grown together with the expansion of home care. In these devices, the fill volume of the drug reservoir and the flow rate are preset and cannot be modified. The elastomer, which makes up the reservoir walls, is what makes the infusate flow due to the pressure it exerts. The purpose of this work was to quantify, under standardized experimental conditions and following recommended conditions of use, the mechanical performances of the 2 commonly used elastomers (silicone and polyisoprene) and their impact on infusion flow rate consistency. Results show that they exhibit different mechanical performances which leads to concerns regarding the use of these devices for some intravenous (IV) therapies.

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.

Ibuprofen (IBU) loaded polyvinyl alcohol-based hydrogel beads (IBU-BB) were designed to alleviate side effects such as inflammation and pain following uterine artery embolization for the treatment of leiomyomata. The present in vitro and in vivo study examines whether IBU-BB provide a sustained-release of the drug. In vitro release studies of IBU from IBU-BB (10, 50, 100 mg/mL), IBU solution (PEDEA) and IBU powder were compared using the T apparatus and the beaker method. The pharmacokinetic profile of IBU release was examined in vivo, following sheep uterine artery embolization with 100 mg/mL IBU-BB or after intra-arterial injection of IBU solution. IBU-BB can deliver high concentrations of the drug over time. The in vitro release from IBU-BB was markedly slower compared to IBU solution. Increasing the concentration of loaded IBU from 10 to 100 mg/mL decreased the rate of release. IBU release from the T apparatus was slower than the release in the beaker. In vivo, the release of the drug was progressive, without the early peak observed with IBU solution. A high level of correlation was obtained between in vivo and in vitro (T apparatus) results. Theoretically, IBU-BB could sustainably release high concentrations of IBU at the site of the uterine fibroids, which makes it a promising approach for the control of post-embolization pain.

One of the major problems in the use of catheters is their thrombogenicity since the embolization of clots near the central nervous system or the coronary arteries can cause permanent damage. Catheter thrombogenicity was evaluated in humans during angiographic procedures by their tendency to become occluded. Characterization of catheters was achieved using roughness measurements, FTIR with ATR, DSC and ESCA. The catheters were 5 commercially available catheters, made mainly of polyethylene, Pebax or polyamide sterilized and ready for clinical use. Thirty-one patients due to have an angiographic procedure and with normal blood and hemodynamic parameters were included in the study. The 50 cm catheter test sample was inserted through an introducer into the femoral artery at the beginning of an angiographic procedure. The outcoming blood flow rate (BFR) was continuously monitored by a special computerized device for 15 min or until the total amount of blood reached 30 ml. The angiographic procedure was then normally resumed. DSC and FTIR showed results consistent with the expected composition of catheters. ESCA results showed very high Si/C ratios and could not be explained in all instances. Occlusion of the catheters occurred in 44% of the cases and the average time to obtain occlusion was 8.5 min (3-15 min). Values of the decrease rate of BFR in ml/min2 allowed separation of the catheters into 3 groups of low, medium and high thrombogenicity. However, occlusion occurred at least one time for each type of catheter. Blood volume and BFR curves vs. time allowed the determination of 3 main types of thrombotic behavior: type I shows no significant reduction of BFR; type II shows a progressive decrease in flow rate; type III is much less frequent and shows an abrupt decrease of BFR either quickly followed by a compensatory increase and resuming of a steady flow or by abrupt occlusion. In type II curves the pattern of occlusion follows a classical diffusion model because the Peclet number is greater than 1 and then the classical Higbie solution for diffusion could be used. The most thrombogenic material was the smoothest. There was no correlation between surface chemical composition and thrombogenicity. However, catheters that were based on PE appeared less thrombogenic than PA catheters in this study.

A new theoretical approach was used to study the nonlinear response of a microvascular segment subjected to a pressure step at one end. The method is suitable for both large and small deformations of the vessel wall in the case of an elastic response of the segment. It is shown that the use of this simulation permits an indirect determination of the compliance of the vessel. The procedure is applied in two cases of major interest: first the in-vivo study of the intermittent blood flow in the microcirculation, and second, the analysis of experiments using micropipettes. The resulting values of the compliance agree with other values found in the previous studies. The theoretical method is particularly adapted to nonlinear equations.

This study presents the effects of red blood cell (RBC) hyperaggregation on the blood flow and pressure in the rat mesentery and cremaster network. We exclusively studied in situ non-vasodilated organs, in order to maintain the physiological regulation mechanisms. Dextran 500 was injected at different concentrations to increase RBC aggregation. The aggregation rate was measured on very small blood samples with an erythroaggregameter (SEFAM) which evaluated the disaggregating shear stress (tau D) needed to break the RBC aggregates. Microscopic observations and laser Doppler velocimetry were used to quantify the flow rate. The plasmatic dextran concentration (C) increase had different correlated effects: for example, tau D increased from 3 dynes cm-2 (for the control sample) to 14 dynes cm-2 (for C = 75 microM L-1); the flow rate was reduced threefold and very large aggregates were observed in the venules; the arteriolar pressure increased while venular pressure decreased. In order to differentiate the effects of RBC hyperaggregation from those of plasma hyperviscosity (due to dextran 500) on microcirculatory blood flow, we injected an RBC antiaggregating drug (troxerutine) (50 or 100 mg kg-1 i.v.). The consequences were a high reduction for (tau D) (from 14 dynes cm(-2)-9 dynes cm-2), smaller aggregates and higher blood flow in the venules. No effect of troxerutine was observed on plasma viscosity (plasma control: 1.9 cP with or without troxerutine; plasma with dextran at C = 75 microM L-1: 2.45 cP with or without troxerutine). The results strongly suggest that RBC aggregation has a significant influence on blood flow rate in the microcirculatory network.