ARTIFICIAL CIRCULATORY SUPPORT (synonym parallel blood circulation, auxiliary perfusion) — various methods of the temporary help to the weakened myocardium with recovery of the broken hemodynamics in an organism based on use of special mechanical devices.
The principle B. to. provides impact on a hemodynamics for the purpose of decrease in the metabolic cost of a myocardium connected with implementation of delivery function of heart. Along with this V. to. increases an organ, and in particular coronary, blood stream, improves microcirculation) fabrics.
External cardiac performance and level of the power processes interfaced to it depend generally on the size of aortal resistance and volume of the blood which is pumped over by heart. This dependence is reflected by a formula of work of ventricles of heart [Uiggers (S. of Wiggers), 1957]:
where Q — a stroke output of a ventricle of heart; R — average pressure in an aorta or average pulmonary pressure; m — the mass of blood which is thrown out for one reduction by a ventricle of heart; V \average speed of a blood-groove; W — external work.
External cardiac performance can be reduced doubly: by pressure decrease in vessels (methods of counterpulsation or an antipulsation are based on this principle) or by reduction of the volume of blood which is pumped over by heart (methods of a bypass — shunting — ventricles of heart are based on it).
The method of a counter pulsation offered by Harken (D. Harken, 1958), assumes aspirating of blood in the special valveless pump with the general entrance and an exit for blood from a peripheral artery in a phase of a systole with the subsequent forcing of the same portion of blood in an arterial bed in a phase of a diastole. It reaches decrease in external cardiac performance on overcoming aortal resistance to cordial emission due to reduction of final diastolic pressure in an aorta; at the same time inflow of blood to coronary arteries increases.
There are several kinds of a method of counterpulsation differing in features of synchronization of operation of the pump with phases of a cardial cycle [D. Watkins, 1965], way and the place of connection of the pump to arterial system [A. Kantrowitz et al., 1967; V. I. Shumakov et al., 1968, 1970], design features of the used pump [the intra aortal pump barrel offered by Mulopulos (1961) and further improved for a clinical use].
One of modifications of a method of counterpulsation is so-called outside counterpulsation [J. Osborn, 1962] with use of hermetic tanks, in to-rye place the lower extremities or all body of the patient. The cycling increase and pressure decline in these tanks synchronized with action of the heart of the patient allows to gain the same hemodynamic effect, as at other methods of counterpulsation.
Shunting of ventricles (partial or full) also combines group of methods. At the same time blood is aspirated from an auricle or a ventricle of heart and forced in an aorta or in one of peripheral arteries by the special pumps having separate entrances and exits for blood.
The main complexity at these methods — need of a fence of a large amount of blood since at the small volumes (less than 60 — 80% of the general minute emission) the efficiency of shunting determined by decrease in oxygen consumption by a myocardium is insignificant. During the aspirating over 80% of cordial emission are noted decrease in external cardiac performance twice and sharp reduction of oxygen consumption by a myocardium of a left ventricle of heart.
To this group of methods B. to. veno-arterial perfusion belongs (a partial cardiopulmonary bypass — S. S. Bryukhonenko, 1926; B. V. Petrovsky et al., 1970) with its versions: without oxygenation of blood, with artificial oxygenation.
In a wedge, practice veno-arterial perfusion with oxygenation of blood is carried out both in the option synchronized with action of the heart, and in not synchronized, considerably inferior by efficiency to the first.
The general for these methods B. to. simplicity of connection of the executive mechanism (the pump counterpulsator, the pump barrel, AIK), short duration of use and comparative simplicity of the equipment is that allows to apply them at seriously ill patients.
The method B. is more difficult to., connected using artificial ventricles of heart. This method is intensively developed as in experimental, and clinical aspects. Century to. by means of artificial ventricles of heart it is interconnected with a problem of the creation implanted artificial heart (see).
The analysis of opportunities of various methods of an artificial circulatory support confirms the considerable decrease in external cardiac performance and a metabolic cost of a myocardium connected with implementation of delivery function, essential increase in volume of a coronary blood-groove, improvement of metabolism of a myocardium, gradual increase of a stroke output of heart and normalization of hemodynamic indicators. Efficiency of methods B. to., reducing external cardiac performance by reduction of aortal resistance to cordial emission, it is directly proportional to amount of the blood aspirated in the pump. This circumstance defines the greatest efficiency of the method providing connection of the executive pump counterpulsator directly to the site of an aorta located close to heart (the central counterpulsation). At connection of the pump with a peripheral artery efficiency of a method significantly decreases. As the amount of the blood aspirated in the pump has direct dependence on the volume of cordial emission, efficiency of these methods sharply decreases at decrease in volume of cordial emission and comes down practically to zero at an asystolia and fibrillation of ventricles of heart.
Efficiency of methods B. to., based on decrease in external cardiac performance by reduction of volume of the blood which is pumped over by it, also increases with increase in volume of the blood coming to an organism through different types of shunting.
In this group of methods bigger efficiency the method of synchronous veno-arterial perfusion with artificial oxygenation of blood has.
Being same highly effective at a left ventricular failure, as well as a method of bypass shunting of a left ventricle of heart, it is much less traumatic and makes positive impact on the right departments of heart, reducing external work and a metabolic cost of a myocardium. Efficiency of veno-arterial perfusion does not depend on inflow of blood to the left departments of heart that allows to use it for maintenance of adequate blood circulation in an organism at an asystolia and fibrillation of ventricles of heart.
The next ways of clinical use of V. are possible to.: at an acute heart failure owing to a myocardial infarction, massive blood loss, intoxication, after heart operations with use of extracorporal blood circulation; at treatment hron, coronary insufficiency with a heavy anginous syndrome; as a preventive action during the performance of traumatic operations at patients with the accompanying disturbances from cardiovascular system; after heart transplantation for maintenance of its function.
The clinical use was found by methods B. to. (counterpulsation the intra aortal pump barrel and veno-arterial perfusion with oxygenation of blood) at patients with the complicated myocardial infarction. A number of authors accumulated experience of use of V. to. at cardiogenic shock, after heart operations, during the performance of coronary angiography in the acute period of a myocardial infarction [D. Bregman et al., 1972; V. I. Shumakov, V. E. Tolpekin, 1973]. At the same time it is established that in most cases it is necessary to combine V. to. with methods of surgical revascularization of a myocardium.
V.'s use to. in parallel with cardiac performance of the patient during quite long time it has to be obligatory synchronously. For this purpose use special electronic devices — the cardiosynchronizers giving the chance to carry out work of the device B. to. in an antiphase with cordial activity.
The most important part of system of V. to. the executive mechanisms representing special blood pumps are. Several their modifications are offered: diaphragm (B. V. Petrovsky et al.; M. De Becky et al.), meshotchaty [Akutsu (T. Akutsu) et al.; W.Burns et al.], roller (Akutsu), piston [J. Horton et al.], rotor etc. They are put in action by means of special hydraulic or pneumatic pressure drives. Degree of traumatization of uniform elements of blood depends on a design of the pump and the mode of its work. Pumps of meshotchaty type are less traumatic. Also selection of the artificial valves (ball, petal, tear-shaped, etc.) providing the unidirectional pulsing blood flow is important.
Materials for production of pumps shall be biologically inert, rather strong and not cause a thrombogenesis at contact with blood.
One of the essential reasons limiting broad use of methods B. to., providing intermediate oxygenation) blood, high degree of traumatization of uniform elements of blood in the existing types is oxygenators (see).
Bibliography: Bryukhonenko S. S. the Device for artificial circulation hematothermal, Ekspery, biol, and medical, t. 11, No. 26, page 296, 1928; Sh at m and-kov V. I., etc. Experimental studying of various methods of vsshzhoga-telny blood circulation and a possibility of their use in clinic, in book: Reconstructive hir., under the editorship of B. V. Petrovsky, century 2, page 17, M., 1971; AcutsuT., Mirkowitch V. Topaz S. Application of mechanical ventricular assistance, Trans. Amer. Soc. artif. intern. Org., v. 10, p. 162, 1964; Bregman D. Goetz R. H. A new concept in circulatory assistance the dual-chambered intraaortic balloon, Mount Sinai J. Med., y. 39, p. 123, 1972; De Bakey M. B. Left ventricular bypass pump for cardiac assistance, Amer. J. Cardiol., v. 27, p. 3, 1971; Dennis C. o. Clinical use of cannula for left heart bypass without thoracotomy, Ann. Surg., v. 156, p. 623, 1962; Kantrowitz A. o. Clinical experience with cardiac assistance by means of intraaortic phase-shift balloon pumping, Trans. Amer. Soc. artif. intern. Org., v. 14, p. 344, 1968; Z war t H. H. a. lake of Transarterial closed-chest left ventricular bypass, ibid., v. 15, p. 386, 1969.
V. I. Shumakov.