Figure 18

Factors that govern diffusion, where dn/dt = the rate of movement of molecules per unit time; D = Fick's diffusion coefficient;

A = area of the boundary through which molecules move; dc = concentration gradient; and dx = distance through which molecules move. Hemodialysis depends on the process of diffusion for removal of solutes. The amount of material removed depends on the magnitude of the concentration gradient, the distance the molecule travels, and the area through which diffusion takes place. For this reason those dialyzers that have a large surface area, thin membranes, and are designed to maximize the effect of concentration gradient (countercurrent design) are most efficient at removing solutes.

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