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Biomedical subjects

E C Eckstein

Publications and source records attributed to E C Eckstein.

At least 37 records · Page 2Linked to original sources
PubMed1982

Rheophoresis--a broader concept of platelet dispersivity.

Interactions among red cells and platelets in flowing blood result in significant dispersive motions of the platelets, which are commonly modelled by an effective diffusion coefficient. This paper examines an additional platelet flux, termed rheophoresis, to model platelet motions due to the gradient of hematocrit. Rheophoretic effects occur near walls because geometric exclusion and fluid mechanical repulsion of red cells create a hematocrit gradient there. Models using rheophoretic flux show that platelet concentration near walls is elevated; such models provide a consistent interpretation of available experimental data. Estimates show the coefficients for traditional effective diffusivity and the rheophoretic diffusivity have similar magnitudes. The effects of rheophoresis on axial development of platelet concentration profiles and on surface deposition are discussed.

Blood Flow Velocity↗
PubMed1981

Pressurized polymerization for reaction casting of poly(2-hydroxyethyl methacrylate).

Homopolymers of the hydrogel poly(2-hydroxyethyl methacrylate) are produced with no observable bubbles trapped in the lattice by performing the free radical initiated polymerization reaction under pressure (700 kPa). Implantable hydrogel structures of intricate and exact geometry, such as nipples for ureteral anastomoses in the prosthetic urinary bladder, can be made using this technique.

Animals↗
PubMed1981

The effect of hemofiltration on fiber platelet concentration.

Experimental methods and apparatus were developed to measure platelet concentration in an ultrafiltering hollow fiber with blood and ultrafiltrative flow rates that are characteristic of current hemofiltration practice. Values are presented for the adjusted local platelet concentration, which allows for the expected increase due to loss of ultrafiltrate volume. Platelet concentrations in fiber samples are of interest since ultra-filtration can create platelet polarization in a fashion similar to the concentration polarization that occurs for proteins. For many combinations of inlet flow rate, ultrafiltrative flow rate, and fiber dimension, there are significant elevations in adjusted fiber platelet concentration. The adjusted platelet concentrations of the outflow samples are nominally equal to those of the feed (reservoir) samples; thus, reaction and adhesion of platelets is not a significant source of fiber concentration. Experiments with fibers of different diameters indicate that, as expected in concentration polarization, the excess platelets are located near the wall. Data for the fiber platelet concentration depend in a complex fashion upon the inlet wall shear rate and ultrafiltrative velocity. For certain fixed ultrafiltrative velocities, a maximum fiber platelet concentration occurs at an intermediate inlet wall shear rate. The data are qualitatively explained by an extension of a published model involving diffusive, ultrafiltrative, and wall-induced fluxes of red cells and platelets.

Artificial Organs↗
PubMedDate not supplied

The interaction of urea with the generic class of poly(2-hydroxyethyl methacrylate) hydrogels.

Work reported here shows that, contrary to reports in the literature, hydrogels made from pure poly(2-hydroxyethyl methacrylate), pHEMA, at crosslinker content greater than 0.15 mol % do not swell above the usual equilibrium values of 39-42% water content in aqueous urea solution. However, hydrogels containing small (impurity) amounts of methacrylic acid (MAA) do swell dramatically (approximately 90%) in dilute urea solution, but not directly due to the urea. The urea decomposes to produce ammonium ions, thus raising the pH of the solution. Ionization of MAA occurs above pH 6, causing electrostatic interactions within the gel. The grossly swollen state of these gels represents an internal equilibrium among forces due to rubber elasticity, polymer-polymer/solvent affinity, and electrostatic interactions.

Aluminum Hydroxide↗
PubMedDate not supplied

Near wall concentration profiles of 1.0 and 2.5 microns beads during flow of blood suspensions.

A freeze-capture method was used to determine the concentration profiles of latex beads in the flow of blood suspensions at a wall shear rate of 400 s-1 in hollow fibers of 200 microns i.d. Bead diameters of 1.0 and 2.5 microns and suspension hematocrits from 15 to 80% were used. All profiles exhibited an excess of beads in the 20 microns closest to the wall and a uniform central concentration. Near-wall excesses greater than 2.5 times the central concentration occurred with suspensions having 2.5 microns beads when the hematocrit was 15-40%. Although large near-wall excesses sometimes occurred for the small beads and higher hematocrits, the usual event was a small near-wall excess. A Mann-Whitney-Wilcoxan test showed that the group of data for 2.5 microns beads in suspensions with hematocrits ranging from 15 to 40% was significantly different from all other data (p less than 0.0002). As the 2.5 microns beads approximate the average platelet, these data suggest that blood flows with physiologic hematocrits are associated with larger near-wall excesses of platelets than blood flows with elevated hematocrits.

Blood Physiological Phenomena↗
PubMedDate not supplied

The dynamics of platelet thrombus formation rate, thrombus retention time, and rate of embolization on a control and heparin bonded polyurethane angio-catheter.

The dynamics of platelet deposition and embolization from control and heparin bonded polyurethane catheters (CPC and HBPC) was evaluated with In-111 labeled autologous platelets (IN-PLT) and a computerized gamma camera (CGC). Ten non-heparinized dogs (18-25 kg) were catheterized in both femoral arteries with 10 cm of CPC and HBPC (5 Fr., Cordis) 24 hr after injection of 300-420 microCi of In-PLT, and imaged for 3 hr with the computerized gamma camera. The regional platelet deposition curves (RPDC) indicated multiple peaks and valleys; the curves were analyzed for early rate of thrombus formation (upswing), thrombus retention time (full width at half maxima of the RPDC-peak), and rate of embolization (downswing) on both catheters. The four parameters (mean +/- SD) of thrombosis on catheters and integral of the radioactivity time curve for the 3 hr duration of imaging were calculated from normalized counts/sec. The rate of thrombus formation and rate of embolization are higher for the control than HBPC, suggesting that heparin-bonding decreases the early rate of thrombosis and embolization. The thrombus adhesivity and retention time appear shorter for the control catheter, indicating that the control thrombogenic catheter forms multiple thrombi and emboli than HBPC. The integral appears larger for the control catheter than HBPC. In vivo (dynamic) studies, in vitro studies, and critical analyses of the radioactivity time curve were essential for complete evaluation of thrombogenicity of catheters and other cardiovascular prostheses.

Animals↗
PubMedDate not supplied

Concentration profiles of 1 and 2.5 microns beads during blood flow. Hematocrit effects.

Freeze-capture techniques were used to obtain concentration profiles of 1.0 and 2.5 microns latex beads in suspension flows with hematocrits from 15 to 60%. Profiles with near-wall concentrations more than twice the central concentration occurred for 2.5 microns beads in this range of hematocrits, but the near-wall excess appeared wider and shorter in 60% suspensions. For suspensions with 1.0 microns beads, the nature of the profile was dependent upon hematocrit. In all cases, at least a small near-wall excess was observed. For hematocrits of 40 and 60%, profiles for 1.0 microns beads were sometimes similar to those for 2.5 microns beads. For the 60% hematocrit and small beads, however, the excess was less than twice the central concentration in two of five trials. These findings are discussed in the context of previous experiments.

Hematocrit↗