<P> Longterm complications of hemodialysis include hemodialysis - associated amyloidosis, neuropathy and various forms of heart disease . Increasing the frequency and length of treatments have been shown to improve fluid overload and enlargement of the heart that is commonly seen in such patients . Due to these complications, the prevalence of complementary and alternative medicine use is high among patients undergoing hemodialysis . </P> <P> Folate deficiency can occur in some patients having hemodialysis . </P> <P> The principle of hemodialysis is the same as other methods of dialysis; it involves diffusion of solutes across a semipermeable membrane . Hemodialysis utilizes counter current flow, where the dialysate is flowing in the opposite direction to blood flow in the extracorporeal circuit . Counter-current flow maintains the concentration gradient across the membrane at a maximum and increases the efficiency of the dialysis . </P> <P> Fluid removal (ultrafiltration) is achieved by altering the hydrostatic pressure of the dialysate compartment, causing free water and some dissolved solutes to move across the membrane along a created pressure gradient . </P>

Why do the blood and dialysis flow in opposite direction
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