EP0959817A1

EP0959817A1 - Heart valve activation system and activated heart valve

Info

Publication number: EP0959817A1
Application number: EP97906229A
Authority: EP
Inventors: Alain Carpentier; Vincent Garitey; Michel Hassler
Original assignee: INDUSTRIELLE DE COMBUSTIBLE NUCLEAIRE -SICN Ste
Current assignee: INDUSTRIELLE DE COMBUSTIBLE NUCLEAIRE -SICN Ste
Priority date: 1996-02-20
Filing date: 1997-02-20
Publication date: 1999-12-01
Also published as: AU2098797A; CN1213955A; HUP9901124A3; US5961550A; NO983703D0; BR9707591A; CA2246645A1; IL125727A0; FR2744909A1; FR2744909B1; WO1997030658A1; AU734016B2; KR19990087088A; HUP9901124A2; US5814100A; JP2000504613A; NO983703L

Abstract

A heart valve activation system including a seat (1) and at least one pivotable flap (2a, 2b) mounted thereon. The system includes at least one movable magnetic member (4) consisting of said flap (2a, 2b) and optionally at least one stationary magnetic member (3) secured to the seat (1). Said magnetic members (3, 4) generate a force that is exerted on said flap (2a, 2b) as it is opened and/or closed.

Description

ACTIVATION SYSTEM OF A HEART VALVE AND ACTIVATED HEART VALVE

The present invention relates to a system for activating a heart valve as well as an activated heart valve.

Artificial heart valves, also called valvular, mitral or aortic prostheses, generally consist of one or two movable valves mounted on a seat by means of one or more joints, said seat being also sutured on the patient's natural pathways.

In the working cycle of the valves, the opening and closing phases of the valves have very short durations compared to those which correspond to the blood flow or the obturation, however these opening and closing phases, and the precise moment when they intervene in the cardiac cycle largely determine the quality of the valve.

The opening and closing mechanisms of a traditional artificial valve are as follows.

When an artificial valve is closed, and the pressure difference on either side of the valve orifice is reversed, the pressure force which kept the valves closed changes direction and tends to open them. This force and therefore the pressure difference which generates it must reach a level sufficient to initiate the opening of the valve (s) and at the same time initialize the blood flow through the prosthesis. The closing of an open mechanical valve allowing the blood flow to pass takes place as follows. The pressure difference on either side of the valve orifice reverses and increases, then eventually produces an inversion of the blood flow, this reflux then closes the valve by driving its valves. In summary, a traditional mechanical valve operates with a delay time compared to pressure fluctuations since it must establish a significant pressure difference before a movement is initiated. In addition, the opening and closing mechanisms Traditional artificial valve closure are identical, whether implanted in the aortic or mitral position, which is not the case with natural valves.

The opening and closing mechanisms of natural valves are described below.

The natural aortic valve opens simultaneously with the reversal of the ventriculo-aortic pressure difference, because being without inertia, it opens under a zero pressure difference unlike a mechanical valve prosthesis. It closes gradually, but quickly and without reflux, at the end of systole under the action of local pressure differences on the sheets which are the equivalent of the valves. These local pressure differences precede the global inversion of the pressure difference between the aorta and the ventricle, an inversion necessary for the initialization of a reflux. This is why the natural aortic valve closes without reflux when the aortic pressure becomes higher than the ventricular pressure while it is the reflux which closes a mechanical valve prosthesis.

The natural mitral valve opens actively under the effect of the tension of cords attached on the one hand to the edges of its leaves and on the other hand to the internal walls of the ventricle. It is the dilation of the ventricle during diastole that simultaneously causes the fall in ventricular pressure (and therefore the inversion of the difference in atrioventricular pressure) and the opening of the mitral valve by traction on its ropes. The opening of the natural mitral valve is therefore strictly synchronous with the inversion of atrioventricular pressure, whereas a mechanical valve prosthesis requires the intervention of a pressure difference to open, and therefore opens in delay. The closure of the sheets of the natural mitral valve is done by the simultaneous competition of several events: the ropes that hold the sheets relax, the sheets gradually close under the action of local pressure differences (preceding the global reversal of the pressure difference between the atrium and the ventricle), and the mitral valve orifice narrows (which brings the leaflets together). So like the aortic valve, the valve / 30658 *

mitral valve closes without reflux, as opposed to an artificial valve whose valve (s) are driven throughout their closure by reflux.

The valves of artificial valves therefore have a certain inertia and both their opening and their closing require an energy expenditure taken from the energy of the blood flows. It is clear that this energy which is produced by the heart, then communicated to the blood flows, will have to be all the more important that the loss of traπsvalvulaire load is great and that the blood reflux, through the valve, at closing, is important. The additional cardiac effort thus generated is penalizing for the patient, particularly in the case of mitral valves where the flow rates and therefore the energies of the already weak blood flows naturally are even more so in the presence of cardiac pathologies. If we want to reduce the transvalvular pressure drop, we can give the valves a maximum opening capacity by large amplitudes of movement, but this then causes an increase in reflux during the necessarily elongated closing phase. Conversely, by wanting to reduce the reflux by reducing the opening and closing stroke of the valves, the transvalvular pressure drop is increased.

At high heart rate, some valve prostheses see the ratio of the refluxing volume to the volume of the flow increasing in a prohibitive way (because the duration of the reflux necessary for the closing of the valves tends to occupy an important place in the cycle). In the case of valve prostheses with several valves, one of the valves may not open, which causes thrombosis. This can happen, in particular, when the patient has a pathological low flow cardiac regime and / or adopts a substantially horizontal position. Furthermore, the blood flows at the cardiac orifices are not necessarily symmetrical, conventional valve prostheses can therefore have an asymmetrical operation. However, such a mode of operation can be detrimental to the integrity of the valve prosthesis due to the poor distribution of stresses which it then undergoes.

In addition, in traditional artificial valves, the valves pass directly from a fully open position to a closed position, which requires large and sudden movements of the valves, sometimes causing rupture or premature wear of the valve as well as the appearance of noise and cavitation.

All these drawbacks linked to the very nature of all existing mechanical valve prostheses largely explain the complications encountered in patients with a valve prosthesis: excessive pressure drop, and thromboembolic accidents. The latter are particularly frequent in the mitral position when the natural mitral valve with active opening is replaced by a valve prosthesis with passive opening. Indeed, fitted with two valves, the prosthesis can open asymmetrically, particularly when the patient is at low flow rate, a condition in which the risk of thrombosis is increased.

The invention aims to solve the above problems or at least to mitigate them satisfactorily. This object is achieved according to the invention by means of an activation system for a heart valve comprising a seat and at least one pivoting valve mounted on the seat, characterized in that it comprises at least one mobile magnetic element, formed by said valve and possibly at least one fixed magnetic element, integral with the seat, said magnetic elements creating a force which is exerted on said valve during its opening and / or closing movements.

According to a particular embodiment, said mobile magnetic element produces a first magnetic field and said fixed magnetic element produces a second magnetic field. Preferably, the first and second magnetic fields are determined in such a way that their mutual influence creates, when the blood pressure is identical on both sides of the valve, an equilibrium position, towards which the valve is recalled at all moment by said force which varies according to the position of said valve so 7/30658 5 PCI7FR97 / 00312

to minimize blood reflux without increasing the loss of transvalvular load.

This equilibrium position preferably corresponds to an intermediate opening position of the valve. According to an advantageous characteristic, the variations of said force, as a function of the position of the valve, are independent on either side of the equilibrium position.

According to another characteristic, said force produces a magnetic torque exerted on the valve, the maximum value of which is between 10 ^~ 3 _e t lO '^ Nm This torque is less than the blood pressure forces exerted on the valve in its full opening and closing positions.

According to other advantageous characteristics, the first and second magnetic fields are determined so that the valve pivots in the seat with the minimum of friction.

Preferably, the equilibrium position is located between the full opening and closing positions.

Furthermore, the mutual influence of the first and second magnetic fields produces repulsive magnetic forces between the mobile magnetic element and the fixed magnetic element.

These repulsive magnetic forces have an intensity of at most 10-1 N.

According to a first embodiment, said fixed magnetic element is integrated into the thickness of the seat, for example, in the vicinity of a joint. This arrangement avoids contact with blood. In parallel, said movable magnetic element is integrated into the thickness of the valve and sealed so that also avoids contact with the blood. These provisions make it possible to make the activation system of the invention biocompatible and above all hemocompatible.

Generally, the valve is made in the mass with a hemocompatible material allowing the incorporation of magnets without modification of their magnetic characteristics. According to another embodiment, the system comprises a mobile magnetic element and two or three fixed magnetic elements, for each articulation of the valve. Preferably, the fixed magnetic elements are then arranged in a ring around an axis of articulation of the valve.

According to yet another embodiment, said magnetic elements are so-called permanent rare earth magnets, based on Samarium and Cobalt, or based on Neodymium, Iron and Boron.

Another object of the invention is a heart valve equipped with the activation system described above.

A particular embodiment of such a valve consists in machining a valve made in the mass of a hemocompatible titanium alloy to form a housing, placing the movable magnetic element in this housing, closing this housing with a cover of the same titanium alloy, and finally hermetically weld this cover to the valve.

Of course, an alternative may consist in producing the valve in any material, then in completely coating said valve with a hemocompatible material. A first variant embodiment of the valve of the invention consists in providing it with two valves activated by the only reciprocal influence of the mobile magnetic elements of each valve.

A second variant consists in producing at least one of the two valves or one of the two seats with a ferromagnetic material, so as to form at least one mobile or fixed magnetic element which does not produce a magnetic field but which is under influence of the magnetic field (s) produced by other mobile or fixed magnetic elements.

Another variant consists in providing only movable magnetic elements on the valve; the seat then comprising no magnetic element.

Yet another variant consists in providing for the presence of interactive mobile magnetic elements and the presence on the seat fixed magnetic elements that are inactive, or whose influence is negligible.

The s ^y stem Activation of the invention allows, thanks to the intermediate open position of the valve, resulting in pressure equilibrium on either side of the valve, an active valve opening, especially in the mitral position, guaranteeing a symmetrical opening of all the valves, even in the event of very low blood flow, and reducing the reflux on closing. Guaranteed opening of all valves reduces the risk of thrombus formation. The valves fitted with these activation systems are controlled by variations in blood pressure, and not by the flow rates as is the case with passive valves, that is to say not activated according to the principle of the invention. Because the flow is itself generated by the pressure variations, it is possible to have anticipated opening and closing phases with respect to the operating sequences of the artificial and traditional valves that are not activated. As a result, the valves of the activated valves appear to be without inertia for the blood flows which thus conserve all their acquired energy. The activation system of the invention also makes it possible to improve the efficiency of the valves by reducing blood reflux. Indeed, the magnetic assistance causes the anticipated closure of the valve even though the rate of blood reflux is still almost zero. The jets which occur at the time of closing when it is carried out in the presence of a significant reflux speed (as is the case with the valves not activated) generally involve risks of cavitation and hemolysis which are therefore limited by the use of the invention.

It is recognized that the transient phases of blood flow are accompanied by sudden changes in pressure causing opening or closing. The anticipation of the opening and closing movements with respect to the flow reversals at the level of the valve orifice therefore allows the valve to perform its movement under low loads, unlike passive valves including valves, especially at the end of the race, support high loads. In addition, the stroke portion of the valve being effected under a high pressure difference is shorter than with the valves not activated, which limits shock and therefore wear. This same anticipation balances the movements of the valves because they are identical magnetic couples which initiate the movements of the valves. Consequently, the movements of the valves being symmetrical, the distribution of the stresses is symmetrical, which is favorable to the good fatigue strength of the active valve prosthesis. The opening and closing movements have a first phase which takes place under the impulse of magnetic forces and a second phase which is under the influence of hydraulic forces. Thus, the automatic return of the valves to the intermediate equilibrium opening position also makes it possible to break down the movements and reduce the speeds at the end of opening and closing, which eliminates violent shocks on the seat, thereby reducing the risks of rupture, noise, cavitation and hemolysis.

The activation system of the invention allows a greater opening of the valve to reduce the transvalvular pressure loss and this without increasing the reflux thanks to the anticipation of the movement at closing.

The magnetic activation of the valve has particularly important effects especially in the phases of the cardiac cycle where the hydraulic forces are weak, that is to say between the diastole and the systole and conversely between the systole and the diastole. The intensities of the torques and the magnetic forces at play can remain low while being effective. They are therefore not likely to disturb the hydraulic functioning of the valve during the diastolic and systolic phases. Thus, the values of these couples are not likely to cause any increase in the transvalvular pressure drop, when the valve is open, any more than an increase in the transvalvular leakage flow rate when the valve is closed.

The invention will be better understood on reading the description which follows, accompanied by the drawings in which: - Figures la to the represent schematic sectional views of the heart during the different phases of the cardiac cycle;

- Figures 2a and 2b are graphs respectively representing the pressure variations and the ventricular volume variations during the cardiac cycle for the left heart;

- Figures 3a, 3b, 3c are respectively perspective views, in cross section and in top view of a valve equipped with an embodiment of the activation system of the invention, in the closed position; - Figures 4a, 4b, 4c are perspective views respectively, in cross section and in top view of the valve of Figures 3a, 3b, 3c in the intermediate equilibrium position;

- Figures 5a, 5b, 5c are respectively perspective views, in cross section and in top view of the valve of Figures 3a, 3b and 3c in the fully open position;

- Figures 6, 7 and 8 show some of the various magnetic configurations possible for the activation system of the invention;

FIGS. 9, 10 and 11 show the graphs of variations of the magnetic return torque corresponding, respectively, to the magnetic configurations of FIGS. 6, 7 and 8.

Figures la to le represent the different phases of the cardiac cycle. Blood behaves like all fluids, it always flows from a high pressure area to a low pressure area, thereby generating a flow. The heart contraction puts the blood under pressure and the valves direct the flow of blood thus generated. The pressure and flow variations which appear during the cardiac cycle are shown, for the left heart, in FIGS. 2a and 2b. The behavior of the right heart is qualitatively identical to that of the left heart. The systole corresponds to the period of ventricular contraction (figures le and ld), while the diastole corresponds to that of the relaxation (figures la and lb). The following description will make it possible to locate in the cardiac cycle the opening and closing movements of the aortic and mitral valves previously described.

During the start of the diastole (Figure la) the left atrium A is released and the left ventricle B begins to dilate. This expansion leads to an early opening of the mitral valve VI by traction on the ropes. As the pressure in the atrium becomes greater than that of the ventricle, blood passes from atrium A into ventricle B. Meanwhile, the aortic valve V2 is closed because the pressure in aorta C is higher than in the ventricle B. But the aortic pressure drops slowly while the ventricular pressure rises slightly. At the end of the diastole (figure lb), the atrium A contracts so as to inject an additional volume of blood into the ventricle B. Then, the systole phase begins and the ventricle B begins to contract by compressing the blood it contains. The ventricular pressure therefore increases very suddenly, almost immediately exceeding the atrial pressure, which causes the closure of the valve VI, facilitated by the equally abrupt release of the tension on the strings (FIG. 1a and point f in FIG. 2a). . Blood reflux to atrium A is no longer possible. In addition, because for a short time the aortic pressure still exceeds the ventricular pressure, the aortic valve V2 remains closed. Then the ventricular pressure exceeds the aortic pressure, the valve V2 opens and the ventricular ejection occurs (Figure 1d and point 0 in Figure 2a). As blood flows into aorta C, the aortic pressure increases but the ventricle B does not empty completely and the maximum aortic pressure is reached before the ejection is completed. The flow of blood from ventricle B during the terminal phase of systole is low and less than the flow of blood from the aorta. At the same time, the atrial pressure also increases slowly over the duration of the ejection. Then ventricle B relaxes and the ventricular pressure drops below the aortic pressure, which causes the aortic valve V2 to close (point f, Figure 2a). However, the decreasing ventricular pressure is still greater than the atrial pressure, so that the atrioventricular valve VI remains closed (Figure le). When the left ventricle begins to dilate, simultaneously with the inversion of the ventriculo-atrial pressure, the valve VI opens (point 0 ', FIG. 2a) and the filling of the ventricle begins again as described previously in relation to the start of the diastole (figure la).

FIGS. 2a and 2b respectively represent the variations in pressure and ventricular volume during the different phases described above and with reference to FIGS. 1a to 1c as mentioned at the bottom of FIG. 2b. It appears quite clearly in the study of the cardiac cycle that the natural valves are synchronized with the relative pressures prevailing in the atrium, the ventricle and / or the aorta and not with the flow rates. These valves therefore have anticipated opening and closing modes with respect to variations in flow rates. In addition, the opening of the mitral valve is facilitated by ventricular dilation which is accompanied by traction on the tendon cord.

The activation system of the invention aims to operate the artificial valves, according to opening and closing modes which are very close to those of natural valves.

The valve shown in Figures 3a, 3b and 3c and following is an artificial valve equipped with the activation system of the invention.

This valve comprises a seat 1, at least one valve and preferably here two valves 2a, 2b identical, mounted on the seat 1 symmetrically, with respect to the diametrical axis XX '. Each of the valves 2a, 2b pivots about an axis YY ', parallel and close to the axis XX' by means of two symmetrical articulations, arranged on either side of each valve.

A joint is, for example, made up of a transverse finger 10 integral with the internal lateral flank of the seat 1 and intended to engage with freedom of relative rotation inside a cylindrical cavity 20 formed in the thickness of the edge lateral of the valve 2a, 2b or in an added boss 21. In the embodiment of the valve shown, the two valves 2a, 2b come into the closed position (Figures 3a to 3c), abutted against each other by their respective inner edge 22a, 22b oriented along the axis XX '. For this purpose, the inner edges 22a, 22b are chamfered so that in the closed position, the valves 2a, 2b make between them an angle of 2β between 90 ° and 180 °. The open position is here fixed at α = 85 ° (see Figure 9), relative to the base plane S of the seat 1.

The actual activation system comprises, by articulation, on the one hand, at least one and in the embodiment shown, three fixed magnetic elements 3, integral with the seat 1 and at least one mobile magnetic element 4 here carried by the valve 2a, 2b. The magnetic elements 3,4 are adapted and intended to create a force which is exerted on the valve 2a, 2b during its opening and / or closing movements.

In the embodiment shown in the figures, the fixed magnetic elements 3 and mobile 4 respectively produce a first and a second magnetic field whose specific characteristics are possibly different. These magnetic elements 3, 4 are preferably permanent magnets called rare earths (for example based on Samarium and Cobalt or based on Neodymium of Iron and Boron) with strong magnetizations and coercivities and therefore with great magnetic stability.

The fixed magnetic elements 3, which are compact and can be integrated into the thickness of the outer flank of the seat 1 and are therefore not likely to come into contact with the blood. The fixed magnetic elements 3 can be arranged in a crown as illustrated in particular in FIG. 3b, but they can have any other arrangement favorable for obtaining the desired magnetic fields. The first and second magnetic fields are determined so as to produce repulsive magnetic forces between the mobile element 4 and the fixed element 3. These forces have an intensity between 0 and 10 ^_ lN. These repulsive forces allow both the control of the pivoting of the valve 2a, 2b and the centering of said valve in the seat, this which in particular ensures a minimum of friction. The mobile magnetic element 4 is integrated into the thickness of the valve 2a, 2b.

In the embodiment shown cut away in the figure

3a, the movable magnetic element 4 is fixed integrally in a housing 24 formed laterally in the boss 21. The housing 24 is itself sealed in a sealed manner by a welded cover (not shown) thereby enclosing the element 4.

The valves 2a, 2b are, at least as far as the bosses 21, preferably made of a hemocompatible titanium alloy. This metal also has the advantage of being light, resistant and allowing both the machining of the housings 24 and the welding of the cover. It also allows, because of its solidity, the production of thinner valves than those existing in traditional materials (for example pyrocarbon), and thus makes it possible to free up a larger passage surface, and therefore to reduce the pressure drop transvalvular. However, the activation system is compatible with any other hemocompatible material (ceramics, metal alloys, pyrolytic carbon ...).

The respective magnetic fields of the fixed 3 and mobile 4 elements are determined in such a way that their reciprocal influence can ensure control of the movements of the valve. In particular, when the blood pressure is identical on either side of the valve, an equilibrium position E of the valves 2a, 2b is created. The valves are returned to this stable equilibrium position E at any time by a force which produces a magnetic torque varying as a function of the angular position of said valves. The laws and graphs of the variations of the magnetic return torque are determined so as to minimize the blood reflux without increasing the transvalvular pressure drop. Furthermore, these graphs, represented in FIG. 9 (in relation to the embodiment described), are independent on either side of the equilibrium position E. The maximum torque is between 10-3 _e t lO - Nm The equilibrium position E is shown in Figures 4a, 4b and 4c. It corresponds to zero magnetic torque and offers an intermediate opening of the valves, here halfway between the positions closing angles (Figures 3a to 3c) and full opening (Figures 5a to 5c). This intermediate opening generally corresponds to an angle of 2β between the valves 2a, 2b between 60 ° and 140 °, the positions of the valves being at all times symmetrical with respect to the diametrical plane D passing through the axis XX '. The equilibrium position E of the valves corresponds, here, to an angle α of 55 °, relative to the base plane S of the seat 1 (see FIG. 9).

In FIGS. 5a, 5b and 5c, the valve is shown with the valves 2a, 2b in the fully open position. In this position, the two valves 2a, 2b are oriented in planes parallel both to each other and to the diametral plane D.

In the closed position (Figure 3a) and in the fully open position (Figure 5a), the movable magnetic element 4 carried by the valve 2a, 2b, is arranged exactly parallel and opposite one 3 extreme fixed magnetic elements.

In the half-opening position corresponding to equilibrium, the mobile magnetic element 4 is oriented opposite but perpendicular to the fixed magnetic element 3 in between.

The first and second magnetic fields produced respectively by the mobile magnetic element 4 and by the magnetic elements 3 depend, of course, on the respective geometry and the relative positions of said elements 3, 4 as well as their magnetization directions.

Figures 6, 7 and 8 show only some of the various magnetic configurations of the activation system of the invention. Other configurations are possible allowing, as here, to obtain variations of the booster torque which minimize blood reflux without increasing the transvalvular pressure drop.

The magnetic configuration with three fixed magnets 3 and a movable magnet 4, by valve corresponding to the embodiment of Figures 3a, 4a and 5a, is shown in Figure 6, in the equilibrium position E.

Generally, the magnetization vector is always directed towards the magnetic North of the magnet considered. In the configuration shown, the magnetization vectors N of the fixed magnets 31, 32, 33 are oriented positively along the axis of articulation YY ', that is to say from Y to Y'.

The magnetization vector N * of the mobile magnet 4 is also oriented parallel to the axis of articulation but in the opposite direction, that is to say from Y ′ to Y.

The intensity of the magnetic field produced by the intermediate fixed magnet 32 (and therefore the value of its vector N) is less than that of the other fixed magnets 31 and 33. As the pivoting of the valve 2a does not change the orientation of the magnetic field produced by the mobile magnet 4 (the magnetization vector N 'remaining, in this pivoting, oriented along X'X), a torque is therefore automatically created tending to align the mobile magnet 4 with the fixed intermediate magnet 32, recalling the valve 2a towards the equilibrium position E. FIG. 9 represents the graphs of variation of the magnetic torque as a function of the angle α of the valve relative to the base plane S of the seat 1 (see FIG. 3b, 4b , 5b). The fully open position corresponds to an angle α of 85 °, the equilibrium position E to an angle α of 55 ° and the closed position to an angle α of 25 °. The magnetic return torque, applied from the closed position to the magnetic equilibrium position E, gives the valve an impulse to open it when the pressure difference on either side of the valve is zero, and guides it to 'at its magnetic equilibrium position E. Thus, even if the flow rate is very low, the valves open symmetrically, during the downstream flow phase, at least at 55 °, so as to offer the blood an area of significant passage, which guarantees a minimum pressure drop. The rest of the opening path (from 55 ° to full opening) is done without significant loss of energy for the flow, because the magnetic forces are very weak compared to the hydraulic forces.

The return torque, applied from the fully open position to the magnetic equilibrium position E, makes it possible to initiate the movement, then to guide the valve to its magnetic equilibrium position, at the moment when the transvalvular pressure difference reverses. From this last position, the movement of the valve towards its closed position is very brief, because the valve offers a large bearing surface for the fluid, which minimizes the reflux. The valve then remains closed, ensuring a seal of the same level as a passive valve of the same profile, until the start of the next cycle.

This example of magnetic assistance corresponds well to the functional requirements of a mitral valve prosthesis.

It appears in FIG. 9, that the graph of the closing torque of the valve for α between 55 ° and 85 °, is different from the graph of the opening torque for α between 55 ° and 25 °. Indeed, the symmetry of the graphs, on both sides of the equilibrium position E, exists only for α between 35 ° and 75 °. Beyond that, the curves differ, by the very fact that the laws governing the variations of the torque, for opening and closing, are independent of each other. FIG. 7 represents a magnetic configuration with two fixed magnets 31, 32 and a movable magnet 4.

The magnetization vectors N, fixed magnets 31, 32, are oriented along the axis of articulation Y'Y, that is to say, in the direction of Y 'towards Y, contrary to the configuration of the figure 6. The magnetization vector N ', of the mobile magnet 4, is oriented along the longitudinal axis AA' of the valve 2a, which makes an angle α with the base plane S of the seat 1 and towards the free end edge of the said valve. When the valve 2a approaches its fully open position, the movable magnet 4 is pushed back by the fixed magnet 32, which creates a return torque towards the equilibrium position E, shown in FIG. 7 where the valve makes an angle α of 35 ^* with the base plane S.

The same phenomenon occurs when the valve 2a approaches its closed position by interaction of the mobile magnet 4 with the fixed magnet 31. The magnetic return torque, applied from the closed position to the position of magnetic equilibrium, guarantees a minimum opening of the valve at 35 ° during the downstream blood flow phase.

The return torque, applied from the fully open position to the magnetic equilibrium position E, makes it possible to initiate and then to guide the valve to this position when the transvalvular pressure difference reverses. From this latter position, the movement of the valve to its closed position is almost instantaneous, because the valve offers a large bearing surface for the fluid, and there remains only an angular travel of 10 ° to travel. The magnetic return torque towards the magnetic equilibrium position still exists when the valve forms an angle of 90 ° with the base plane S of the seat, the profile of the valve can therefore allow the valves to be opened at 90 °, so to minimize the loss of transvalvular load in the event of high flow, without having to fear an increase in reflux.

This example of magnetic assistance corresponds well to the functional requirements of an aortic valve prosthesis.

FIG. 10 represents the graph of the variations of the return torque as a function of the angular position of the valve for the magnetic configuration represented in FIG. 7.

The equilibrium position E is at α = 35 ° relative to the plane S and therefore does not correspond, here, to a half-opening. It is clear from this graph that there is no symmetry in the law of variation of the magnetic torque on either side of the equilibrium position E. This variation does not therefore necessarily obey the same rules for the opening phase and for the closing phase, but it must in no case present abrupt changes in slope.

FIG. 8 represents a magnetic configuration with a fixed magnet 3 and a movable magnet 4. The magnetization vector N of the fixed magnet 3 is oriented in a direction d, while the magnetization vector N 'of the movable magnet 4 is oriented according to the normal on the upper surface of the valve 2a. Consequently, the mobile magnet 4 tends to move, so that its magnetization vector N ′ is parallel to the magnetization vector N of the fixed magnet 3, but in an opposite direction, so as to loop the field lines magnetic. This amounts to putting the fixed 3 and mobile 4 magnets facing each other. This phenomenon creates a magnetic torque for returning the valve 2a to an equilibrium position E, materialized by the plane BB 'of FIG. 8. Here, the valve is in its magnetic equilibrium position E, when it forms an angle 45 ° with 30658

the basic plan S of the seat. The magnetic return torque, applied from the closed position to the magnetic equilibrium position, guarantees a minimum opening of the valve at 45 ° during the downstream blood flow phase. The return torque, applied from the fully open position to the magnetic equilibrium position, makes it possible to guide the valve to this position, at the moment when the transvalvular pressure difference reverses, and thus minimize reflux.

This example of magnetic assistance may also be suitable for the functional requirements of an aortic or mitral valve prosthesis, but will constitute a less optimal solution, because it is less specific.

Of course, it is also possible, still according to the invention, to obtain the graphs of variations of FIGS. 9, 10 and 11 with configurations different from those represented in FIGS. 6, 7 and 8, or other configurations, by choosing geometries and / or relative positions, and / or particular magnetizations of the fixed 3 and mobile 4 magnets.

Furthermore, it is also conceivable to create a reciprocal influence between the activation system of the valve 2a and the activation system of the valve 2b.

According to this embodiment, the activation system operates under the sole influence of mobile magnetic elements. In this case, the fixed magnetic elements of the seat are then non-existent or inactive or else produce a negligible influence compared to that produced by the mobile magnetic elements.

Claims

1. Activation system for heart valve comprising a seat (1) and at least one pivoting valve (2a, 2b) mounted on the seat (1) characterized in that it comprises at least one mobile magnetic element (4), formed by said valve (2a, 2b) and possibly at least one fixed magnetic element (3), integral with the seat (1); said magnetic elements (3, 4) creating a force which is exerted on said valve (2a, 2b) during its opening and / or closing movements.

2. System according to claim 1, characterized in that said mobile magnetic element (4) produces a first magnetic field and said fixed magnetic element (3) produces a second magnetic field.

3. System according to claim 2, characterized in that the first and second magnetic fields are determined in such a way that their reciprocal influence creates, when the blood pressure is identical on either side of the valve, a position of equilibrium (E), to which the valve (2a, 2b) is recalled at any time by said force which varies according to the position of said valve so as to minimize blood reflux without increasing the transvalvular pressure drop.

4. System according to claim 3, characterized in that said equilibrium position (E) corresponds to an intermediate opening position of the valve (2a, 2b).

5. System according to claim 3 or 4, characterized in that the variations of said force, depending on the position of the valve (2a, 2b), are independent on either side of the equilibrium position (E) .

6. System according to one of the preceding claims, characterized in that said force produces a magnetic torque exerted on the valve (2a, 2b), whose maximum value is between 10 ~ 3 and lO- ^ N.m.

7. System according to one of claims 2 to 6, characterized in that the first and second magnetic fields are determined from so that the valve (2a, 2b) pivots in the seat with the minimum of friction.

8. System according to one of claims 3 to 7, characterized in that the equilibrium position (E) is located between the full opening and closing positions.

9. System according to one of claims 2 to 8, characterized in that the reciprocal influence of the first and second magnetic fields produces repulsive magnetic forces between the mobile magnetic element (4) and the fixed magnetic element (3) .

10. System according to claim 9, characterized in that said repulsive magnetic forces have an intensity of at most 10-1 N,

11. System according to one of the preceding claims, characterized in that said fixed magnetic element (3) is integrated into the thickness of the seat (1).

12. System according to one of the preceding claims, characterized in that said mobile magnetic element (4) is integrated in a sealed manner in the thickness of said valve.

13. System according to one of the preceding claims, characterized in that it comprises three fixed magnetic elements (3).

14. System according to one of claims 1 to 12, characterized in that it comprises two fixed magnetic elements (3).

15. System according to claim 14, characterized in that the two fixed magnetic elements (3) are placed on the seat (1) so as to respectively define the opening and closing positions of the valve (2a, 2b).

16. System according to one of claims 13 to 15, characterized in that the fixed magnetic elements (3) are arranged in a ring around an axis of articulation (YY ') of the valve (2a, 2b).

17. System according to one of the preceding claims, characterized in that at least one of said magnetic elements (3, 4) is a permanent magnet.

18. System according to one of the preceding claims, characterized in that at least one of said magnetic elements (3, 4) is a permanent magnet called rare earth based on Samarium and Cobalt or based on Neodymium, Iron and Boron.

19. System according to one of the preceding claims, characterized in that the valve (2a, 2b) is made in the mass or coated with a hemocompatible material allowing the incorporation of magnets without modification of their magnetic characteristics.

20. Heart valve comprising an activation system according to one of the preceding claims.

21. Valve according to claim 20, characterized in that it comprises two valves (2a, 2b) activated by the only reciprocal influence of the mobile magnetic elements (4) of each valve (2a, 2b).

22. Valve according to claim 20 or 21, characterized in that the valve (2a, 2b) is made in the mass of a hemocompatible Titanium alloy.