Surface compartment model, effects

To study the effects of electrochemical properties on passive ion transport processes, we developed a model that focuses on ionic processes at membrane and channel surfaces (14). The surface compartment model (SCM) is based on a Helmholtz electrical double layer, where the enhanced concentration of counterions and the depletion of co-ions at charged surfaces is described by straight line gradients. Treatment of the electrical double layer as a compartment greatly simplifies the calculation of ion transport. 

Rituximab is a monoclonal antibody to the CD20 receptor expressed on the surface of B lymphocytes the presence of the antibody is determined during flow cytometry of the tumor cells. Cell death results from antibody-dependent cellular cytotoxicity. The pharmacokinetics of rituximab are best described by a two-compartment model, with a terminal half-life of 76 hours after the first infusion and a terminal half-life of 205 hours after the fourth dose.36 Rituximab has shown clinical activity in the treatment of B-cell lymphomas that are CD20+. Side effects include hypersensitivity reactions, hypotension, fevers, chills, rash, headache, and mild nausea and vomiting. 

Equations 46 have been directly derived from the full model in [19]. On the other hand, they are almost identical with the relations obtained from the so-called two-compartment model (the only difference is that the numerical coefficient is a little bit lower). The two-compartment model was first developed for sensors with receptors placed on small spheres [23]. In [24-26] it was adapted for the SPR flow cell and in [ 18] it was approved and verified by comparison of munerical results with those obtained from the full model. The two-compartment model approximates the analyte distribution in the vicinity of the receptors by considering two distinct regions. The first is a thin layer around the active receptor zone of effective thickness fiiayer> and the second is the remaining volume with the analyte concentration equal to the injected one, i.e., a. While the analyte concentration in the bulk is constant (within a given compartment), analyte transport to the inner compartment is controlled by diffusion. The actual analyte concentration at the sensor surface is then given by the difference between the diffusion flow and the consump-tion/production of the analyte via interaction with receptors. For the simple pseudo first-order interaction model we obtain ... 

Figure 8.4 Origin of the electro-osmotic flow in a capillary filled with an electrolyte. Model of the double layer. If the inner wall has not been treated (polyanionic layer of a silica or glass capillary) then a pumping effect arises from the anodic to the cathodic compartment this is the electro-osmotic flow which is reliant upon the potential which exists on the inner surface of the wall. If the wall is coated with a non polar film (e.g. octadecyl) then this flow no longer exists. The electro-osmotic flow is proportional to the thickness of the double cationic layer attached to the wall. It is reduced if the concentration of the buffer electrolyte increases. Ugos pH dependant between pH 7 and 8 can increase by as much as 35 per cent.

Additional respiratory control models have recently been reported by Milhom and Reynolds (42) and Duflin (49), Milhoms model is similar to his previous model except that a peripheral sensor compartment is added, and the central H+ sensor is located beneath the surface of the medulla. The depth of the central sensor was adjusted (effectively adjusting the diffusional time lag) to provide close agreement between computed and experimental ventilatory responses to C02 inhalation. When the model is applied to CSF perfusion, good agreement is reported. 

An ideal pharmacokinetic model of the percutaneous absorption process should be capable of describing not only the time course of penetration through skin and Into blood (or receptor fluid In a diffusion cell), but also the time course of disappearance from the skin surface and accumulation (reservoir effect) of penetrant within the skin membrane. Neither Pick s Plrst Law of Diffusion nor a simple kinetic model considering skin as a rate limiting membrane only Is satisfactory, since neither can account for an accumulation of penetrant within skin. To resolve this dilemma, we have analyzed the In vitro time course of absorption of radiolabeled benzoic acid (a rapid penetrant) and paraquat (a poor penetrant) through hairless mouse skin using a linear three compartment kinetic model (Figure 5). The three compartments correspond to the skin surface (where the Initial dose Is deposited), the skin Itself (considered as a separate compartment), and the receptor fluid In the diffusion cell. The Initial amount deposited on the skin surface Is symbolized by XIO, and K12 and K23 are first order rate constants. 

The effects of the torso volume conductor on the electrocardiographic potential distribution were examined utilizing an eccentric spheres model. The effects of the blood cavity, lung region, and the surface muscle layer are described. The importance of interactions between the various torso compartments in determining the potential distribution is demonstrated. 

The parameter kg-out must account for diffusion/dispersion and advection losses at the lower boundary of a soil compartment. Advection with water that infiltrates through the soil is typically a unidirectional process, which removes chemicals with the effective velocity obtained in Equation 8.11. However, dispersion and diffusion processes such as molecular diffusion and bioturbation move chemicals both up and down within the soil, making it difficult to define a net loss factor applicable to the bulk soil. However, with a single well mixed compartment receiving chemical input at is surface, we can assume that the net diffusion is in the downward direction and proportional to the concentration gradient in the penetration depth z. In this case the parameter kg-out is obtained from a simple model for mass loss at the lower boundary of the soil compartment ... 

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