ARTIFICIAL HEART — the device for full replacement by this or that time of pumping function of heart; is in process of development.
First model I. page it was created by the Soviet scientific V. Demikhov in 1937 and it is applied in an experiment on dogs, the Crimea ventricles of heart were removed. It consisted of two coupled pumps of membrane type put in action by the electric motor located out of a chest cavity. By means of this device it was possible to support blood circulation in an organism of a dog within two and a half hours. However wide-ranging studies on this problem began only in the late fifties.
In 1966 under the leadership of B. V. Petrovsky in All-Union research in-those clinical and experimental surgery the USSR's first laboratory I was created. page. Problem of creation And. the page develops in two directions. One of them — creation And. page with the external drive. Practical value of works in this direction is caused first of all by need to have for the emergency resuscitation situations the ready to use model of heart capable of a short span (from several hours to several days) to provide the blood stream necessary for life activity of an organism, from the moment of the sudden termination of activity of sore heart * until selection of a cordial transplant. Besides, creation And. the page with the external drive allows to make in experimental conditions a research of materials for production of model of the implanted artificial heart, to study the modes of its work, and also influence of the device on an organism in general and on separate bodies and systems. The second, immeasurably more difficult direction — creation and use completely implanted And. the page intended for long-term providing an organism with adequate blood circulation.
Models of such devices I. villages during the use in an experiment allow to carry out also tests of various materials, systems of automatic control. Search of special sources and converters of energy is conducted.
From 70th the Soviet scientists-physicians in the commonwealth with engineers created more than 20 models I. page.
Two models meet performance and medicobiological specification as a result of long-run tests at hydrodynamic stands. One of them — model of «meshotchaty type» (fig. 1) — is made of ftorsilikonovy rubber. Topographical researches of heart of the person and requirements imposed to «the heart pump» are the basis for this model. These requirements provide: use of the materials capable to maintain long cyclic loadings and to interfere with a thrombogenesis; creation of the designs excluding formation of hold-up spots, areas of the increased speeds of shift and local tension; data to a minimum of the area of cyclically adjoining surfaces on which size the injury of uniform elements of blood in many respects depends.
An outside wall of cameras of ventricles rigid or semifixed, and internal — soft and elastic. On an entrance and escaping of an internal bag there are valves. At air delivery or liquid between walls of such ventricle the internal bag contracts and there is a squeezing of blood from it»
At pressure decrease between bags there is a raspravleniye of an internal bag; pressure in it becomes less, than pressure in front of in the gate, the valve opens and there is a filling of a ventricle with blood.
Modern model I. the page has the ventricles providing the pulsing blood flow. This model has small weight, corresponds to the average size of heart of the person, is convenient for implantation. The device is highly sensitive to a venous inflow and has ability to increase number of pulse cycles to 140 — 150 in 1 min. that allows to reach the minute volume of the pumped-over blood to 14 — 15 l.
Other model I. the page (fig. 2) has «diaphragm type» of a design in the rigid case. Active auricles reduce pressure of the pulsing blood flow in a venous bed thanks to what hemolysis decreases.
Systolic emission of blood in this model I. the page and the subsequent filling of ventricles result from a postural change of a diaphragm under pressure upon its surface of gas or liquid from the drive. The unidirectional blood flow in artificial ventricles is provided entrance and output by valves.
Designs of valves for And. pages are extremely various. Everything them can be divided on petal and valve type. Petal valves happen one - two - three - and even four petal. Valves of valve type have locking elements in the form of a disk, a cone or a hemisphere. In some models I. pages with the external drive are applied natural (fresh or tinned) valves of heart of animals (calfs or pigs) which fix on special frameworks. The surface of a rigid structure of the case is used for drawing a conducting layer which serves as a facing of the condenser of the capacity sensor of volume of blood; the second facing of the condenser is blood on limit of the section blood — a diaphragm.
As drives for And. pages are quite widely used electromechanical devices. In various designs And. they differ in page from each other; the simplest electromechanical drive consists of electric motors of a direct current. The drives located outside connect to cameras of executive mechanisms by means of plastic hoses for leading of gas or liquid to pumps.
Diameter of highways through which there passes gas depends on what gas is used in system. E.g., at use of air diameter of the highway shall be not less than 6 — 7 mm. When it is necessary to bring the electric power, use the wires covered with biologically inert plastic.
In one of models as an energy source the radio isotope ampoule with plutonium-238 placed in the thermal accumulator is used. As the engine serves the two-piston thermal car with the independent drive on each ventricle And. page. The blood pump is at the same time both the heat exchanger, and primary sensor for system of regulation. Gross weight of model is less than 2 kg, volume apprx. 1,8 l.
Along with technical issues on creation And. page great difficulties are presented by a problem of research of materials for production of nodes I. page. The following requirements are imposed to them: high durability, lack of «fatigue», ability to keep the physical. - chemical properties in a human body to possess biol, inertness.
During the designing And. pages are used stainless steel, titanium alloys, polymeric materials (ftoroplasta, polyolefins), various compounds of organosilicic rubbers (silicones), polyurethane, poliefirsilikonuretana, pyrocarbons, materials with tromborezistentny coverings on the basis of hydrophilic gels, polyelectrolytic complexes with negative surface-bound charge, etc. Designs from polymeric materials even during the long work allow to reduce danger of thrombosis. However, despite it, the problem of prevention of thrombosis which is observed both in cardial cavities, and in connecting highways and intraorganic blood vessels remains urgent. In this regard researches of pathogenetic mechanisms of a thrombogenesis in the conditions of contact of blood with the big area of polymer surface, the extensive operational injury caused by a kardiektomiya, features of artificial circulation and an injury of uniform elements of blood are conducted. At the same time considerable emission in blood of fabric and blood thromboplastin which creates a hypercoagulative background and promotes activation of thrombogenic properties of blood is noted.
Besides, the big role in the processes happening on border blood — polymer, is played by the electrokinetic phenomena. They are connected with the fact that uniform elements and blood proteins are loaded negatively. Not changed internal cover of heart and vessels also bears a negative charge. Pushing away of elements of blood from the same loaded vascular wall — your ny factor interfering a thrombogenesis. Existence of positive or zero potential on the surface of polymeric material, apparently, one of the reasons contributing to a thrombogenesis.
Laymen (D. Lyman, 1972), Adati (M. of Adachi, 1973) noted feature of synthetics like velor with not dissect loop or with very short fibers at their use as plastic material in a heart surgery — ability to detain uniform elements of blood. At treatment by blood of such surface in loops of velor or between fibers settle uniform elements and blood proteins and in 40 — 45 days forms very smooth and thin biol, a vystilka, on a microscopic structure extremely similar to an endothelium. Duration of term of formation of a protective vystilka on the surface of synthetics considerably limits possibilities of use of such way of prevention of a thrombogenesis in And. page since the possibility of formation of blood clots on the surface of the used polymeric materials during this time is not excluded.
The important place in development And. pages occupy hydrodynamic researches. Their main goal — improvement of geometry of cavities, an exception of hold-up spots, vortex turbulent flows, flows with big gradients of speeds.
Not less complex challenge — creation of automatic control of work And. the page providing a blood stream according to requirements of an organism. It is known that heart of the person and animals changes the dynamics with very broad range. So, at the person at rest it is equal to 5,5 — 6,5 l in 1 min. and at considerable physical. to loading increases several times.
In model I. the control system is based by page of «diaphragm type» on information from the capacity sensor of volume of an auricle. The control system is developed, in a cut as the sensor of information the remaining part of live heart — its auricles and a sinus node serving as the multiparametrical sensor in a control system is used. For formation of frequency of reductions of ventricles use R-volnovy an electric pacemaker and the converter of duration of a systole.
Implantation And. page did not receive a wedge, uses. Ready models I. the village, its separate nodes (e.g., valves and drives) before they begin to be studied in an experiment on animals, are explored at various stands (fig. 3). These stands — hydraulic model of cardiovascular system, of course, with a set of assumptions and simplifications. Liquid, edges circulates at the stand, on the viscosity approaches viscosity of blood. As a rule, include flowmeters and some other devices in a contour of bench installations, napr, the camera for measurement of size of a reversed current of liquid via entrance and output valves at various duties And. page. The sensors of pressure entered into various departments And. pages, allow to define fluctuations of pressure in it, pressure differences on valves and some other parameters. At special stands study also turbulence of the fluid flows passing through And. page and its valves, rate of decay of blood etc.
The models I tested at stands. pages are implanted to animals (to dogs, pigs, sheep, but is more often to calfs weighing 70 — 110 kg). The choice, e.g., of calfs is caused by the fact that uniform elements of their blood on physical. are closest to properties to human. Besides, the sizes of heart of a calf of the specified weight are approximately equal to dimensions of heart of the adult.
Operation of implantation And. the page in an experiment is carried out under an endotracheal anesthesia in conditions artificial circulation (see) or under a hypothermia (see. Hypothermia artificial ).
After switching off of heart of an animal from blood circulation it is deleted, leaving the right and left auricles. The aorta and a pulmonary trunk are crossed at the level polulun ny valves. Then make implantation And. page by means of cannulas or vascular seams connecting the corresponding cameras. During the use of cannulas of an auricle, an aorta and a pulmonary artery And. pages connect to auricles and large vessels of an animal. More perfect is the technique of implantation And. page by means of vascular seams. Technology of this operation essentially does not differ from the standard equipment orthotopical heart transplantations (see). After connection I. the page with an organism air from his all cavities is forced out fiziol, solution; only after removal even of the smallest air traps Y. page it is possible to include. As soon as work And. by page it was stabilized, the thorax is sewn up.
Life expectancy of experimental animals with And. the page averages 3 — 5 days. In separate experiments it approaches 1 month.
During the work And. pages develop various changes in lungs, a liver, kidneys, etc. bodies. These changes can be both functional, and morphological.
See also Artificial organs .
Bibliography: Problems of artificial heart and artificial circulatory support, under the editorship of B. V. Petrovsky and V. I. Shumakov, M., 1970; Shumakov V. I., etc. Model of artificial heart for intrapericardiac implantation, the Medical technician, No. 5, page 5, 1970, bibliogr.; A k u t s u T. Artificial heart, Total replacement and partial-support, Amsterdam, 1975; Kennedy J. H. a. o. Progress toward an orthotopic cardiac prosthesis, Biomater, med. Devices artif. Org., v. 1, p. 3, 1973; Lyman D. J., Hill D. W. a. S t i r k R. K. The interaction of tissue cells with polymer surfaces, Trans. Amer. Soc. artif. intern. Org., v. 18, p. 19, 1972, bibliogr.
V. I. Shumakov.