Page 104 - ExtendSim User Guide
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Areas of Application
Drug Ingestion
There really can be too much of a good thing. For some drugs, such as blood thinners, it is important that the patient get enough of a dose to cause the desired outcome, but not so much as could be harmful. One method is to monitor the concentration of the drug in the patient's bloodstream to determine if it is at effective, but safe, level. Many factors influence drug absorption - the amount ingested, the rate of absorption, the patient's diet, and so forth - and simulation is the best method to explore the effect of those factors.
☞ The Drug Ingestion model is located in the folder \Examples\Continuous\Standard Block Mod- els. This model uses blocks from the Value and Plotter libraries.
Model assumptions
• Constant blocks specify the dosage amount (1500 mg) and frequency (3 doses/day) • The stomach’s volume is 500ml and the absorption percentage is 0.693
• Blood volume is 5,000ml and the metabolic constant 0.0433
• Themodelrunsfor96hours;deltatimeis0.25
Model details
The Drug Ingestion model illustrates the bloodstream concentration for a periodi- cally ingested drug. The drug is taken at even inter- vals and is absorbed into the bloodstream based on the amount of the drug ingested, the specific rate of absorption for the drug, and the metabolism, stomach volume, and blood volume of the person involved.
Hierarchy compartmental-
izes the Drug Ingestion
model into submodels rep-
resenting the stomach,
intestines, and blood stream. (To see the contents of these hierarchical blocks, double-click their icons or use the Navigator in Model mode to drill down to the underlying layers.) In the Stomach hierarchical block, the drug is introduced with a Pulse block that generates a periodic pulse based on the value from the Constant block that outputs the number of doses per day. This is then multiplied by the drug dosage and placed in a Holding Tank block representing the amount of drug in the stomach.
In the Absorption section, an Equation block calculates the absorption rate by dividing the amount of drug in the stomach by the stomach volume, subtracting the concentration of the drug in the bloodstream, and multiplying that by the absorption constant and the stomach vol- ume constant. The absorption rate is then used to reduce the amount of the drug in the stomach and increase the amount of the drug in the bloodstream (represented by the Holding Tank in the hierarchical block named Bloodstream). The concentration of the drug in the bloodstream is then calculated by dividing the amount of the drug in the bloodstream by the blood volume.
Drug Ingestion model

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