Endovascular stents are commonly used to manage arterial diseases such as Aortic Abdominal Aneurysm (AAA), aortic dissection and coarctation. The radial force the stent applies to the vessel must be large enough to resist stent migration, but not so large that the mechanical stimulus initiates adverse vessel remodeling. We employed two approaches to characterize the radial force of Gianturco stents: first, by applying an external pressure to the stent and, second, by measuring the force exerted by the stent when deployed. From the second approach, we determined the force exerted at various area reductions that correspond to clinically relevant diameter oversizings. In this study, stent stiffness was determined from the force-area reduction curves. Comparing similar stents of various diameters revealed that smaller diameter stent had greater radial force and stiffness than larger diameter stents. Comparing similar stents of various lengths revealed that stents with longer lengths (and greater number of wires) has greater force and stiffness. Overlapping two stents increased the force and stiffness to values greater than the sum of those parameters for the individual stents. These data may have important clinical implications for understanding the effect of oversized and overlapped stents on vessel mechanics.

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The intravenous fluid of choice for acute blood volume replacement remains controversial. We focus here on the two hydroxyethyl (HES) available in Canada: HES 130/0.40 (Voluven®) and HES 260/0.45 (Pentaspan®). Although information regarding their pharmacokinetic and risk/benefit profiles are available, how the infusion of these fluids could affect blood viscosity and vascular endothelial function in humans is largely unknown. Dynamic viscosity was measured at 21°C and 37°C through capillary viscometry. The HES solutions were driven through a closed flow loop at room temperature (21°C). Viscosity at 21°C was 7.62 centipoise (cP) for HES 260/0.45 and 2.73 cP for HES 130/0.40 decreasing to 4.23 cP for HES 260/0.45 and 1.72 cP for HES 130/0.40 at 37°C. Analysis of viscous behaviour through pipe flow found that HES 260/0.45 displayed marginal variations in viscosity suggesting Newtonian behaviour across our range of Re measured. HES 130/0.40 displayed an appreciable increase in viscosity at higher Re suggesting the presence of shear thickening behaviour. Human aortic endothelial cells (HAEC) and human microvascular endothelial cells (HMVEC) were exposed to the HES solutions and saline to identify chemical effects on vascular endothelium. Western blot quantification showed that E-selectin was the leukocyte adhesion receptor that was most strongly affected, and this was not dose dependent. Interestingly, HAEC and HMVEC had different responses to HES treatment, suggesting that different vascular tissues may have different outcomes to HES infusion. Protein expression in HMVEC decreased when exposed to both HES solutions.

Introduction: There are two hydroxyl-ethyl starches (HES) available for volume expansion in Canada: HES 260/0.45 and HES 130/0.4. While information regarding their pharmacokinetic(1) and risk/benefit profiles is available(2), there is no published data on their respective viscosities. Methods: The viscosity for each HES was determined at concentrations of 1.0, 0. 75, 0.5, 0.25 and 0.125 the original. For each concentration the viscosity was evaluated at temperatures of 21, 25, 30 and 37 degrees Celsius. Three measurements were made for each concentration and temperature. Serial dilutions were with normal saline. The use of an incubator assured a constant temperature throughout the course of a measurement. Saline and tap water were used as controls. The viscosity was measured using a capillary viscometer, with all measurements taking greater than 100 seconds. Results: There is a non-linear relationship between the HES concentration and viscosity (Fig. 1). This effect was greatest for the 10% HES and was attenuated by increased temperature. At concentrations of less than 5%, the HES viscosity is 2/3 to 1/3 that of whole blood. The kinematic viscosity (viscosity / density) demonstrated a similar relationship. Discussion: The non-linear relationship between concentration and viscosity suggests the development of large molecular complexes at the lower temperatures. In spite of the published differences in their mean molecular weights, at body temperature and clinically relevant concentrations (1-5%), the differences between the two HES solutions are minimal. Whether these small differences translate into clinically important differences in plasma viscosity and shear stress is unknown. References: (1) Jungheinrich C, Neff TA. Pharmacokinetics of hydroxyethyl starch. [Review] [64 refs]. Clinical Pharmacokinetics 44(7):681-99, 2005. (2) Boldt J. Do plasma substitutes have additional properties beyond correcting volume deficits?[see comment]. [Review] [96 refs]. Shock 25(2):103-16, 2006 Feb.

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