3.    GENTEX Reference

3.1.   Overview

3.1.1.   Model structure

GENTEX, represented diagrammatically by Fig. 3.1.1, models the transport and exchange of three reference tracers that are not permeant to the tissue cells, and five permeant chemical species (tracer and nontracer) in an organ. It is comprised of discrete submodels that reflect the organ structure or the parts of the experimental apparatus that affect tracer concentrations and residues in the organ. These submodels represent nonexchanging vessels (such as tubes, arteries, arterioles, venules, and veins, modeled with vascular operators) and exchanging vessels (capillary-tissue units modeled by blood-tissue exchange, BTEX, operators).

For each tracer or nontracer substance, there is one inlet tube, one artery, one vein, and one outlet tube. There may be a maximum of twenty flow pathways each consisting of an arteriole, a blood-tissue exchange unit, and a venule. Each pathway has its own flow rate and receives a specific fraction of the total mass of the tracers and nontracer substances.

3.1.2.   GENTEX, XSIM and the parameters

GENTEX runs under XSIM. In this manual, when a description of a parameter is given, it will be given as in the following example:

Input parameters (i.e., those for which the user must enter a value) are shown in normal type, while output parameters (i.e., those into which GENTEX writes values) are shown in italics. For example:

The first parameter is named "Fb", and it contains the total blood flow. The user must enter the value of this parameter. The second parameter is named "Cout_v". It contains the concentration of the vascular reference tracer at the outlet of the organ; the value of this parameter is set by GENTEX when a simulation is run.

The names shown are those that appear in the popup window after double clicking on a parameter button or field.

The XSIM convention for inputs and outputs is that input parameters are shown with a lighter field background, and the outputs are displayed on a shaded background, as shown in Fig. 3.1.2.

3.1.3.   Using the GENTEX reference

In addition to this overview, the GENTEX Reference Guide is divided into five parts. Input Functions ( Section 3.2) deals with the several ways of getting the driving function, or functions, for the model. Heterogeneity ( Section 3.3) deals with specifying heterogeneity of flow, PS, and consumption. Vascular and BTEX Operators ( Section 3.4) deals with setting values for the transport and exchange parameters for the vessel operators. These sections are all concerned with specifying the inputs to GENTEX. The final section, Displaying Results ( Section 3.5), deals with the outputs from the model.

Each of these sections begins with a table that lists the model parameters that apply to the topic being discussed. This is followed by subsections that deal with the various aspects of the topic. The sections conclude with a listing and discussion of pertinent error messages and some tips on correcting error conditions.