Kidney machines

While it would be difficult to enumerate all of the efforts in the area of implants where plastics are involved, some of the significant ones are (1) the implanted pacemaker, (2) the surgical prosthesis devices to replace lost limbs, (3) the use of plastic tubing to support damaged blood vessels, and (4) the work with the portable artificial kidney. The kidney application illustrates an area where more than the mechanical characteristics of the plastics are used. The kidney machine consists of large areas of a semi-permeable membrane, a cellulosic material in some machines, where the kidney toxins are removed from the body fluids by dialysis based on the semi-permeable characteristics of the plastic membrane. A number of other plastics are continually under study for use in this area, but the basic unit is a device to circulate the body fluid through the dialysis device to separate toxic substances from the blood. The mechanical aspects of the problem are minor but do involve supports for the large amount of membrane required. 

Another indirect electrochemical heahng method involves the artificial kidney machine, with electrochemical regeneration of the dialysis solution. The common kidney machine is a dialyzer in which blood of the patient (who suffers from kiduey insufficiency) and a dialysis solution are pumped arouud iu two differeut loops, aud carbamide (urea), creatinine, and other metabolites are transferred by dialysis into the dialysis solution. For complete extraction of the metabolites, each hemodialysis session requires almost 200 L of this solution to be pumped through, so hemodialysis cau only be performed in a hospital setting. In machines equipped with electrochemical regeueratiou, the dialysis solutiou is ruu iu a closed loop, iucludiug au electrolyzer in which the carbamide is oxidized to nitrogen and carbon dioxide. The solution volume needed in this loop is rather small, so that portable kidney machines could become a reality. 

Heparin is clearly an extraordinarily complex substance with many highly polar groups, and its mode of action as an anticoagulant is not clear. At present, because of increases in the use of artificial kidney machines, heparin is in rather short supply. 

Perhaps the most important medical use of dialysis is in artificial kidney machines, where hemodialysis is used to cleanse the blood of patients whose kidneys have malfunctioned. Blood is diverted from the body and pumped through a cellophane dialysis tube suspended in a solution formulated to contain many of the same components as blood plasma. These substances—glucose, NaCl, NaHC03, and KC1—have the same concentrations in the dialysis solution as they do in blood, so that they have no net passage through the cellophane membrane. 

Reversed-phase liquid chromatography has been used by Veening and co-workers (K22, S18) to monitor dialysate, serum, and urine from patients on artificial kidney machines. They report that RPLC is a reliable method for monitoring blood composition during dialysis. 

Victims of kidney disease rely upon artificial kidney machines to remove waste products from their blood. Such machines use a process called dialysis, which is similar to osmosis. The difference is that the dialyzing membrane permits not just water, but also salts and other small molecules dissolved in the blood to pass through. These move out into a surrounding tank of distilled water. The red blood cells are too large to pass through the dialyzing membrane, so they return to the patient s body. 

Several other reactors for immobilized heparinase have been designed (53,54). The initial reactor (47) caused no more blood damage than conventionally used extracorporeal devices such as the artificial kidney machine (54a). By controlling the mode of immobilized enzyme bead suspension, all blood damage can be essentially eliminated (54). The FDA... 

Some information must remain empirical and will never become a generally accepted first principle. After all, there can only be a small number of fundamental principles (according to the presiding conceptual framework of science). Empirical information is useful nonetheless, especially in the designs of utilitarian devices to be used with living systems. Designs of artificial kidney machines, bioreactors, automobiles, hospital ventilators, and even light bulbs are based on empirical information that serves to produce better products. 

In osmosis a semipermeable membrane prevents transfer of all solute particles. A similar phenomenon called dialysis occurs at the walls of most plant and animal cells. However, in this case the membrane allows transfer of both solvent molecules and small solute molecules and ions. One of the most important applications of dialysis is the use of artificial kidney machines to purify the blood. The blood is passed through a cellophane tube, which acts as the semipermeable membrane. The tube is immersed in a dialyzing solution (see Fig. 17.17). This washing solution contains the same concentrations of ions and small molecules as blood but has none of the waste products normally removed by the kidneys. The resulting dialysis of waste products cleanses the blood. 

A semipermeable membrane can be used to separate ions from colloidal particles because the ions can pass through the membrane but the colloidal particles cannot. This type of separation is known as dialysis and is used to purify blood in artificial kidney machines. Our kidneys normally remove waste products from blood. In a kidney machine, blood is circulated through a dialyzing tube immersed in a washing solution. The solution contains the same concentrations and kinds of ions as blood but no waste products. Dissolved wastes therefore dialyze out of the blood, but the large colloidal particles such as proteins do not. 

A life-saving application of dialysis has been the development of artificial kidneys. The blood of a patient suffering from partial kidney failure is passed through the artificial kidney machine for several hours, during which time the soluble waste products are removed by dialysis. 

In fermentation processes, nutrients, sugars, oxygen, and so on, diffuse to the microorganisms and waste products and at times enzymes diffuse away. In the artificial kidney machine various waste products diffuse through the blood solution to a membrane and then through the membrane to an aqueous solution. 

The Scribner shunt, a U-shaped Teflon tube, is the creation of Chicago-born Belding Scribner. The shunt, inserted between an artery and vein in a patient s forearm, could be opened and connected to the artificial kidney machine during dialysis. Teflon was relatively new to the biomedical community at the time, and its nonstick properties made it less likely to clot. Before Scribner s shunt, a patient could receive only a few dialysis treatments before doctors would run out of places to connect the machine to the patient. The shunt was first used on March 9, 1960, on Clyde Shields, who was dialyzed repeatedly for eleven years. Another patient was dialyzed for thirty-six years, undergoing 5,700 cycles of hemodialysis, before his death. In 1962, Scribner and American physician James Haviland developed the first free-standing dialysis center in the world, the three-bed Seattle Ar-tihcial Kidney Center. 

Semipermeable membranes can also be used to separate ions from colloidal particles, because the ions can pass ttirough the membrane but the colloid particles cannot. This type of separation is known as dialysis and is used to purify blood in artificial kidney machines. Our kidneys remove the waste products of... 

In addition to the well-known uses to which cellulose film is put, there are some other more diverse applications, eg cellulose film flakes are used in oil well drilling for blocking cracks in porous strata in the shredded form, cellulose is widely used as a cushioning material in the packing of fragile goods and in the uncoated form as the membrane in artificial kidney machine dialysers. It is as a consequence of the vast range of end uses to which it may be put that a healthy future for cellulose film is ensured. 

Dialysis involves diffusion of solutes and fluids (e.g., water) through a semipermeable membrane separating out larger molecules and solid particles. Hie membranes employed are generally similar to the reverse osmosis or the nano-/ ultrafiltration type. Historically, dialysis has heen employed for various laboratory separations and commercially employed for NaOH or dilute sulfuric add recovery. The primary com-merdal application involves hemodialysis employed in artifidal kidney machines. Initially, cellulose and cellulose acetate membranes were employed, but polysulfone and poly (ether sulfone) are now in use with biocompatibiUty being a key membrane requirement. 

An artificial kidney machine cleaning the blood of patients with impaired kidney func-... 

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