Pure compartment modeling

Pure compartment modeling is based on the schematiza-tion of the body under study by a system of interconnected... 

The simplest practicable approach considers the membrane as a continuous, nonporous phase in which water of hydration is dissolved.In such a scenario, which is based on concentrated solution theory, the sole thermodynamic variable for specifying the local state of the membrane is the water activity the relevant mechanism of water back-transport is diffusion in an activity gradient. However, pure diffusion models provide an incomplete description of the membrane response to changing external operation conditions, as explained in Section 6.6.2. They cannot predict the net water flux across a saturated membrane that results from applying a difference in total gas pressures between cathodic and anodic gas compartments. 

FIGURE 3.6 Compartmental analysis for different terms of volume of distribution. (Adapted from Kwon, Y., Handbook of Essential Pharmacokinetics, Pharmacodynamics and Drug Metabolism for Industrial Scientists, Kluwer Academic/Plenum Publishers, New York, 2001. With permission.) (a) Schematic diagram of two-compartment model for compound disposition. Compound is administrated and eliminated from central compartment (compartment 1) and distributes between central compartment and peripheral compartment (compartment 2). Vj and V2 are the apparent volumes of the central and peripheral compartments, respectively. kI0 is the elimination rate constant, and k12 and k21 are the intercompartmental distribution rate constants, (b) Concentration versus time profiles of plasma (—) and peripheral tissue (—) for two-compartmental disposition after IV bolus injection. C0 is the extrapolated concentration at time zero, used for estimation of V, The time of distributional equilibrium is fss. Ydss is a volume distribution value at fss only. Vj, is the volume of distribution value at and after postdistribution equilibrium, which is influenced by relative rates of distribution and elimination, (c) Time-dependent volume of distribution for the corresponding two-compart-mental disposition. Vt is the starting distribution space and has the smallest value. Volume of distribution increases to Vdss at t,s. Volume of distribution further increases with time to Vp at and after postdistribution equilibrium. Vp is influenced by relative rates of distribution and elimination and is not a pure term for volume of distribution. 

Of course, it is quite clear from section 4.1 that a pure statistical model is an oversimplification that will adversely affect the accuracy of prediction despite its attractive ease of implementation. Therefore, mixed models are also used that take at least some regional information into consideration and can be seen as statistical models split into compartments. Within the compartments solely statistical features are considered, but promoter organization is somewhat reflected by the arrangement of the compartments which represent different promoter regions. 

Some models of the uptake and distribution of slow-acting drugs do not exphcitly use a heart or, for that matter, a circulation. These fall under the category of purely compartmental models. In these models, the heart and circulation are subsumed into an assumption that each compartment m the model is uniformly mixed. 

As a byproduct of work on cough CPR (Section 18.3.1.3 and Section 18.3.1.10), Rosborough found that using ventilation to increase intrathoracic pressure with simultaneous compression of the abdominal compartment maintained carotid artery flows similar to flows from standard CPR in dog experiments [36]. This model, based on a pure thoracic pump concept, has not been demonstrated to improve outcome in humans, and has been associated with pulmonary complications attributed to high airway pressures. 

Consider an idealized cylinder model containing two compartments separated by a membrane permeable only to the solvent (Figure 3C.la) Each compartment has a sliding piston. One compartment contains only solvent the other, solvent plus solute. When no outside force acts on the system, solvent will tend to migrate from the compartment containing pure solvent into the solution compartment. As the solvent compartment becomes depleted, the resulting... 

The literature in this field is replete with a wide variety of model systems using for example cellulose, or silica, or amylopectin as solid supports, extruded mixtures of polyunsaturated fatty acids and esters with pure proteins, in the presence of humectants (to control moisture content) such as glycerol, or dextran as water-binding agent. Studies with such model systems are inherently problematic, because they do not simulate real foods where oxidation is naturally inhibited by the separation of lipids from catalysts in different cellular compartments. There is a serious lack of knowledge on the interactions of oxidized lipids and proteins in complex foods. 

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