Reference Index Page 5

Artificial Kidneys

Basic Components of an Artificial Kidney

1) Blood Compartment
2) Dialysate Compartment
3) Semipermeable membrane separating (1) and (2)
4) Membrane support structure

Geometries of Dialyzers

    There are two types of geometry of artificial kidneys. The geometry refers to the cross sectional area which is in contact with the blood, semipermeable membrane, and dialysate. The first geometry is rectangular. An example of these dialyzers are the parallel plate design. The second geometry is circular. An example of these dialyzers are hollow-fiber design.

Coil Kidneys

    This artificial kidney was the first to be mass produced. Its design was fairly simple and with that came lots of problems. It had a cellulose coil wrapped around a wire mesh drum. The filtration rate was unpredictable.

Parallel Plate Dialyzers

    This type of artificial kidney is called the parallel plate dialyzer for an obvious reason. Instead of the classic drum rotating system, this dialyzer uses several parallel plates with ridges and grooves in them. The dialysate flows along the grooves or ridges. A semipermeable membrane rests between the grooves and the blood flow. With these dialyzers, resistance to blood flow is low. The diagram below illustrates one type of parallel plate dialyzers, the disc hemofilter.

    Some advantages to the use of this dialyzer are its low resistance to blood flow. Because of this fact, there is not as much need for the use of an anti-blood clotting solution. Another advantage of this dialyzer is that its filtration rate is controllable and predictable. The next advantage of this dialyzer is the amount of blood contained within the dialyzer is relatively low. The less blood that is out of the body at one point in time, the better the dialyzer. The final advantage of the parallel plate dialyzer is that it is inexpensive.

Hollow-Fiber Artificial Kidneys

    This type of artificial kidney is the most common type used. This artificial kidney makes use of countercurrent flow (Fig 2). Countercurrent flow is where the blood is flowing in one direction and the dialysate is flowing in the opposite direction. Countercurrent flow is less efficient, but seems to be more gentle. Because it is more gentle, it is used on pediatric patients and some first time dialysis patients. The hollow-fiber dialyzer comes in many different sizes. It looks like a cylinder filled with thousands of tiny hollow-fibers(Fig 3). Blood flows into one end of the dialyzer and through these thousands of tiny hollow-fibers. Dialysate, at the same time, is pumped into the cylinder and across the tiny hollow-fibers. This method keeps fresh dialysate circulating constantly.

Fig 2

Fig 3