David O. Cooney

Analyses of mass transfer in hemodialyzers for laminar blood flow and homogeneous dialysate

Abstract Theoretical analyses of mass transfer in hemodialyzers which contain flowing blood and dialysate streams separated by a semi-permeable membrane are presented. Semi-infinite parallel-plate and cylindrical tube geometries are considered. Solutions are obtained in terms of well-known functions, a method which avoids difficulties associated with computing the higher eigenvalues encountered in previous analyses. Applications of the mathematical model to systems used in clinical practice are discussed.

An improved theoretical model for hollow-fiber enzyme reactors

Abstract An analysis of hollow-fiber enzyme reactors is presented, for first-order kinetics, which leads to explicit expressions for the concentration fields on both the enzyme and substrate sides. These expressions are easily evaluated numerically. Results are presented which show that the substrate-side profiles of bulk concentration versus axial distance can be expressed as functions of a single parameter (an overall mass transfer resistance). Limiting forms of the equations and of system behavior which arise for very low and very high values of the Thiele modulus (corresponding to the reaction-controlled and diffusion-controlled limits) are discussed in some detail. The method of analysis presented is shown to be applicable to other “conjugated boundary value” problems of a similar nature.

A “Superactive” Charcoal for Antidotal Use in Poisonings

Amoco Grade PX-21 powdered activated charcoal was found to adsorb nearly three times as much sodium salicylate from simulated gastric fluid than did another charcoal (Norit A), which is representative of the best of all other charcoals heretofore available. This indicates the potential superior effectiveness of the Amoco charcoal as an oral antidote in poisonings.

Mass transfer between capillary blood and tissues

The Krogh cylinder type of model for capillary-tissue mass transfer is solved analytically as a conjugated boundary value problem. The analysis avoids recourse to the use of arbitrary interphase mass transfer coefficients. For O2, CO2 and glucose, the model was solved to obtain axial, interfacial, and radial concentration profiles in both the blood and tissue phases, for various conditions, e.g. zero and first order metabolic consumption rates. Both plug and parabolic blood velocity profiles were considered. Blood phase flow rates and diffusivities were varied, as were the magnitudes of the zero order metabolic rate constants and the relative degree of solute binding to hemoglobin. Little computation is required to obtain numerical results from the solutions presented. The results indicate which factors are most important in determining the shapes and magnitudes of concentration profiles in such systems.

Mass transfer in parallel-plate dialyzers—A conjugated boundary value problem

Abstract Mass transfer in semi-infinite parallel-plate dialysers has been analyzed by solving the convective diffusion equations for the two fluids (blood and dialysate) for arbitrary interfacial concentration distributions, and linking the two solutions via a continuity-of-flux boundary condition at the membrane surfaces. This yields expressions for the true interfacial concentration distributions which, when substituted for the arbitrary distributions, produces complete solutions for the concentration fields in both fluid phases. This model was applied to typical parallel-plate Kiil hemodialyzers. A parametric study was performed to determine which variables influence hemodialyzer performance most strongly. Our computed results provide substantial information about mass transfer in such systems without introducing empirical constants, which are not known a prior.

“Superactive” Charcoal Adsorbs Drugs as Fast as Standard Antidotal Charcoal

Experimental data on the uptake of two test drugs by powdered Amoco PX-21 and Norit A activated charcoals in stirred-batch tests indicate that the rate of uptake by the Amoco charcoal is equal to, or higher than, the uptake rate by Norit A. In contrast to the conjecture of Medema [1], the superactive Amoco charcoal is not kinetically inferior to Norit A. The superactive charcoal remains highly recommended for antidotal uses.

Rates of Heparin Adsorption in Hemoperfusion Devices

In vitro studies have shown that the rates of adsorption of heparin from saline in commercially available hemoperfusion devices at 100 to 200 ml/min flow rates are intrinsically quite low. Thus the potential for significant heparin removal from blood (and thus a rise in the possibility of clotting problems) in clinical applications seems remote.

Multicomponent sorption operations: Bed shrinking and swelling in an ion-exclusion case

Abstract The effects of the resin particle shrinking and swelling which occur during sorption operations involving beds of ion exchange resins are elucidated for two multicomponent processes—the elution of a bed uniformly presaturated with a two-solute feed, and the ion exclusion separation of a finite slug of a two-solute feed. The investigation was performed via the numerical integration of finite-difference forms of the relevant equations. Several unique phenomena (shifting of concentration profiles, concentrating effects in certain zones) are seen to arise which would not be revealed by classical “static bed” descriptions. This study indicates that shrinking and swelling effects must be taken into account if an accurate theoretical description of such operations is desired.

Heparin Adsorption on Activated Charcoal

By vitro studies have shown that sodium heparin adsorbs significantly at pH 7.4 conditions onto a typical activated charcoal. These results imply that enhanced heparin removal from blood should be anticipated in hemoperfusion systems that utilize uncoated charcoals.