- On 25 Jan 2005 at 16:51:02, "Jose Cortinas" (jose.cortinas.-at-.luc.ac.be) sent the message

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The following message was posted to: PharmPK

Dear All,

Not so long ago I posted a message asking for help, Now I am posting it

again. In case someone can help me I will really appreciate it.

I have a question related to PK modeling.

I am recently working with PK models. Now I am studying the

"ELIMINATION OF PHOSPHATE DURING HEMODIALYSIS". I found an article by

Spalding,Chamney and Farrington (2002). They did something similar and

they propose 3 models based on 2, 3 and 4 compartments. In their

article they present the differential equations. The three models are

bellow:

Model A: Passive diffusion

dCi=(Ci-Ce)Kie

dt Vi

dCe=(Ci-Ce)Kie - CeKd - CeQu

dt Ve

dVe=Qu

dt

Model B: Passive Diffusion + regulated intracellular phosphate

They assumed that from the third compartment the flux (F3) is:

F3 = (Ci - Ciset) G3

Ciset: desired set point

Thus the differential equation for the extracellular compartment needs

to be modified and it is

dCe=(Ci-Ce)Kie - CeKd - CeQu + F3

dt Ve

Model C: Passive Diffusion + regulated intracellular + immediate action

Consider an aditional mechanism that is invoked when phosphate falls

bellow a critical level

If Ci < Cicrit AND F4 off, then F4 on

If Cicrit < Ci < Cihighlimit AND F4 on, then F4 off

My question is the following. I would like to use this model, but I

would like to have the solutions for this equation for the 3 models, if

someone can help me I will appreciate it very much.

Thanks in advance,

Jose Cortinas Abrahantes

jose.cortinas.-at-.luc.ac.be

[You may be able to derive the equations using Laplace transforms, see

http://www.boomer.org/c/p3/c02/c0208.html and

http://www.boomer.org/c/p3/c07/c0701.html - db]

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