ARTIFICIAL ORGANS

From Big Medical Encyclopedia

ARTIFICIAL ORGANS — the technical devices intended for temporary or constant replacement for function of this or that internal human organ. The possibility of creation of the Deputy is connected both with progress of biology and medicine, and with achievements of physics, chemistry, mathematics, and also technical science.

Creation of the Deputy is caused also by the fact that transplantation will not be able to solve completely a problem of replacement of nonfunctioning vitals of the person since the number of donor organs, suitable for change, are much less than number of the patients needing this operation. Deputies not always completely replace function of natural body, especially when it possesses a number of difficult functions as, e.g., a liver, heart. More often Deputies replace not all body, but its most important part (e.g., the artificial valves of heart intended for providing the unidirectional blood flow, the electrocardiostimulators applied at disturbance of the carrying-out system of heart).

The deputy can be divided on not implanted into an organism and on partially and completely implanted (see. Implants ). An example of not implanted Deputy is eurysynusic in a wedge, practice artificial kidney (see) — the device for removal from blood of the patient of toxic metabolic products which collect at acute and hron, a renal failure. As an example of partially implanted Deputy applied only in an experiment can serve artificial heart (see) with the external drive. In this system the pump for pumping of blood is placed in a chest cavity, as a rule, within a pericardium; the pump is connected by system of hoses with the drive, most often a pneumatic, and managing complex of devices. Completely implanted Deputy is such device, all components to-rogo are placed in an organism. An example of it are electrocardiostimulators and artificial heart of such design where all nodes (pumps for blood, the drive, a control system of it, a source of power food) are implanted in an organism.

On time of functioning of the Deputy it is possible to divide into the devices supporting life activity of an organism only at their continuous operation (e.g., artificial heart), and the devices providing life activity of an organism at their discontinuous (discrete) connection (e.g., an artificial kidney).

In a problem of the Deputy the choice of materials of which the nodes of devices which are directly contacting to fabrics and fluid mediums of an organism are made is of great importance. All these materials shall be biologically inert, i.e. not causing inflammatory reaction of surrounding fabrics, not allocating from the surface of toxic chemicals etc. To materials of which make these or those details of various Deputies, besides, are shown as well the special requirements connected with need to carry out this or that selective function for what various selection polymeric semipermeable membranes are widely used. So, in the devices «artificial kidney» apply the membranes passing water, various salts and some other substances and blood, impenetrable for uniform elements — krupnomolekulyarny substances (proteins, lipids, polysaccharides etc.). In membrane oxygenators (see) apply the materials passing gases (O 2 and CO 2 ) and not passing blood.

Materials of which elements and nodes of the so-called physiological block of the Deputy are made shall be anti-thrombogenic, i.e. not cause a blood coagulation on their surface.

A number of materials and coverings (some types of polyurethane, avkotan, etc.) is created on which there is no formation of blood clots within several hours or days; at loss by these materials of anti-thrombogenic properties on operating time of the device it is necessary to enter heparin for reduction of coagulability of blood and prevention of a thrombogenesis into blood of the patient. However as the Deputy shall function within many hours or days, administration of heparin is undesirable since it leads to disturbance of coagulant system of blood. Absolutely anti-thrombogenic materials or coverings are not created yet, however two directions in the solution of this task are planned. The first of them is connected with «inoculation» on the surface of polymeric materials of heparin or geparinopodobny substances, with aiming at them of steady electric charges etc.; all these actions prevent fibrillation at contact with such materials. The second direction is connected with creation on the surface of polymer of a thin smooth vystilka from living cells. For this purpose on the surface of polymer thin, short fibers from synfils are pasted, e.g. At contact of a blood flow with such surfaces between fibers uniform elements and molecules of blood protein which form an autobiologichesky vystilka get stuck. Within 30 — 45 days this vystilka is transformed to the so-called pseudo-endothelium which is reliably protecting from developing of blood clots on its surface.

An important problem in creation of the Deputy is the engineering decision adequate to a goal. As a rule, during creation of the Deputy researchers aim at that the technical device as is possible more precisely performed function of a natural analog. Constructive decisions at the same time differ from very tectonics of appropriate authority markedly. So, designs of dialyzers of artificial kidneys do not even bear a faint resemblance to a structure of renal nephron. The same treats also models of oxygenators, the designs of the majority applied in a wedge, practice of artificial valves of heart etc. It is connected by hl. obr. with lack of materials from which the anatomic structure of natural body could produce the Deputy identical on the design, and also with a certain imperfection of modern technology.

In creation and use of the Deputy the solution of a task of management of them is of great importance. It is especially important for the implanted bodies. So, artificial heart, is similar to natural, shall change very quickly the productivity depending on change of requirements of an organism in a blood-groove in each unit of time; change of its rate of volume flow shall be carried out with the broad range — 4 — 5 l/min (at rest) to 30 — 35 l/min (at considerable physical. loading). For creation of system of automatic control of artificial heart it is necessary to define the minimum quantity of the parameters bearing a maximum of information on adequacy of blood circulation in an organism, to develop an algorithm of automatic control of artificial heart and to create system, edges works by the principle of a feed-back, reacting to indications of sensors, changes pump delivery, pumping over blood. Hard work in this direction led to creation of the first such systems, in particular in the USSR, however their further improvement is necessary. For the purpose of use of systems of automatic control of artificial heart in completely implanted complexes not only their further completion, but also microminiaturization is necessary. The solution of this task is connected with progress of electronics and mechanics. Questions of management and for other Deputies — an artificial kidney, oxygenators (artificial lungs), etc. are important.

For the Deputies who are completely implanted into an organism, an important task is power supply of these systems. So, use different batteries, accumulators, isotope energy sources (plutonium-238) to electrocardiostimulators. Besides, in some designs use the principle of induction recharge of the organism of the accumulator implanted inside via the secondary coil implanted under skin of the patient. The task of power supply of the implanted artificial heart is even more difficult. For its decision use of isotope energy sources (plutonium-238), the energy which is marked out in the organism during exchange processes and also induction recharge of accumulators is supposed.

The broadest use in clinic, along with devices artificial circulation (see), received artificial kidney (see). With its help it is possible to support life of patients with hron, a renal failure within several years, and, besides, use of this device is in some cases a preliminary stage of operation of renal transplantation.

The wide spread occurance in a wedge, practice was received by also various oxygenators. However in the majority of industrial models of oxygenators gas exchange happens in direct contact of blood to gases that causes a considerable injury of its uniform elements, components of plasma and limits a possibility of safe use of such devices only several hours. All similar models are not implanted. Practically such oxygenators are suitable only for performance of operations on «open» heart. The researches conducted on creation of so-called membrane oxygenators in which the semipermeable plastic films dividing a flow of blood from a flow of gases are used allowed to begin use of such oxygenators in a wedge, practice both at operations with artificial circulation, and for auxiliary oxygenation at patients with acute respiratory insufficiency. There are observations of successful use of these oxygenators within several days. There are (still single) attempts in an experiment to implant tiny membrane oxygenators instead of a remote lung at an animal.

In the field of development of artificial heart it is perspective two directions were outlined: creation of the artificial heart capable to function several days, for providing in emergency situations of a reserve of time necessary for identification of a transplant, and creation of completely implanted artificial heart capable to function for a long time. All systems of artificial heart counted on work within several days are semi-implanted. The artificial heart counted on long-term use shall be completely implanted in an organism.

Devices which it would be possible to call an artificial liver it is not created yet, however there are already devices which are carrying out this or that function of a liver (removal of ammonia, bilirubin, etc.)? what improves a condition of patients with a liver failure and quite often promotes their recovery. Their use at treatment of a serious poisoning is especially effective.

Attempts of creation of artificial intestines and an artificial pancreas are in a stage of development. The artificial pancreas shall replace endogenous function of natural body, edges is broken at such widespread disease as a diabetes mellitus. The device consists of a tank for insulin, the micro pump working according to the set program or for the signals arriving from the sensor of glucose, a source of the power food (recharged from the outside the microaccumulator or the capsule with isotope), the block of electronic control. Such device is completely implanted into an organism. The first-ever similar operation in an experiment was executed in the USSR in Ying-those organ and tissue transplantations of M3 of the USSR. Except the implanted devices of this kind, is so-called parakorporalny (i.e. the skin located on a surface, napr, on a hand) the devices and devices located on nek-rum distance from the patient. However use of these Deputies is still possible only in an experiment.

Development of problems of creation of the Deputy, in particular creation of artificial heart, is a subject of intergovernmental agreements between the USSR and the USA.


Bibliography: Kiselyov Yu. M., etc. The power blocks used in the implanted artificial heart and systems of an artificial circulatory support, the Medical technician, No. 4, page 50, 1976, bibliogr.; P and with a p e in with to both y A. A. and d river. Artificial «membrane lung», in the same place, page 44, bibliogr.; Problems of artificial heart and an artificial circulatory support, under the editorship of B. V. Petrovsky and V. I. Shumakov, page 62, M., 1970; Shumakov V. I., etc. Experience of use of many-placed installation for a chronic hemodialysis, the Medical technician, No. 2, page 38, 1974; BevilacquaS. The nuclear artificial heart, Trans. Proc., v. 8, p. 63, 1976; L e f r a k E. A. a. o. Current status of prolonged extracorporeal membrane oxygenation for acute respiratory failure, Chest, v. 63, p. 773, 1973; Oster H. o. Survival for 18 days with a Jarvik type artificial heart, Surgery, v. 77, p. 113, 1975; S m i t h L. o. Power requirements for the A.E.C. artificial heart, Trans. Amer. Soc. artif. intern. Org., v. 21, p. 540, 1975.

V. N. Shumakov.

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