A network thermodynamic model of kidney perfusion

A network thermodynamic model has been devised to describe the coupled movement of water and a permeable additive within a kidney during perfusion. Both flows are governed by a combination of the individual osmotic potential and pressure differences between compartments of the kidney, the viscoelastic behavior of the tissue, and the momentum transferred between the two flows. Other solutes, which are typically added to the perfusate, are also included in the model. The bond graph technique was applied in conjunction with the ENPORT7 simulation package to develop a series of models illustrating the behavior of the system under typical conditions of perfusion with cryoprotective agents. These results include: (1) A series of subcomponent bond graph model are presented which illustrate the fundamental mass transfer processes involved. (2) A full kidney model was assembled from these sub component models. Results of this model were compared to experimental results presented by Pegg (1993) using 60 minute 2M step perfusions with DMSO, glycerol, and sucrose. The results used in this comparison were kidney weight, vascular resistance, and compartment volumes. (3) Families of curves were generated by varying each of the significant parameters over a range that was broad enough to encompass the uncertainty in that parameter. The results of this sensitivity analysis were used to describe the dynamics of the system. (4) The full kidney model was used to simulate the realistic perfusion protocols published by Pegg & Wusteman (1977). Simulation and experimental results were statistically compared for both kidney weight and vascular resistance. An additional mechanism is proposed to improve the prediction of changes in vascular resistance. This involved including the effects of endothelial cell swelling on the radius of the capillary lumen. (5) Finally, a series of design optimization recommendations are proposed based upon the effects of modifying critical input variables on kidney weight and vascular resistance. These recommendations are outlined in Chapter Seven.