Note: Descriptions are shown in the official language in which they were submitted.
DESCRIPTION
Two-leaflet ~osthetic heart valve
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The present invention relates to valve prostheses or,
in short, to heart valves which are fitted as
replacements for natural valves should the latter be
malformed. The invention concerns, in particular,
heart valves of the type comprising two leaflets which
are arranged to open when a pressure difference is
established in a certain direction and to close again
the moment the pressure difference is reversed.
These prosthetic valves are generally constituted by a
base ring of rigid material which houses a ring of
material which can be sutured to the heart tissue in
its generally recessed outer surface. A structure with
one or more leaflets linked in some way to the base
ring and arranged to oscillate from a position in which
the passage created in the base ring is open and a
position in which it is closed regulates the blood flow
in one-direction.
The characteristics of such prosthetic heart valves
vary with the form of the leaflets and of the base ring
and with the criteria of operation of the assembly;
these criteria determine the means provided for causing
the oscillation of the leaflets, means which generally
involve both the bodies of the leaflets and that of the
base ring.
There are various requirements, both mechanical and
biological, which a prosthetic heart valve must
satisfy.
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Of these requirements the following may be considered
fundamental:
speed of response and speed of closure of the
leaflets to avoid backflow;
absence of highly curved surfaces, both in the
leaflets and in the base ring, to avoid turbulence and
haemolysis of the blood as well stagnation thereof; and
structural profiles which do not project too far
axially to avoid harmful contact with the walls of the
heart.
Other requirements concern the materials used in the
prosthetic valve, and amongst these the criterion of
compatibility of the materials with the biological
masses, and in particular with the blood, holds first
place.
The evolution of heart valve models with time has
satisfied the aforesaid requirements by successive
approximations. Changes have been made from ball
valves to disc valves, to cuspidate leaves; more
recently, there has been a proposal of valves with two
leaflets hinged in some way to the base ring with their
opening and closing travel arrested in some way.
In spite of continual progress, there are still many
problems which have not been resolved satisfactorily.
that is, there are still difficult points, essentially
two in number: the way in which the leaflets are
pivoted in the base ring and the structures for
stopping the openin~ and closing of the leaflets.
In some models the leaflets pivot about pins fixed to
the base ring; in other models the pins are carried b~
the leaflets and held in suitable cavities formed in
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the base ring.
These pin solutions, however, have revealed quite
serious deficiencies due to the stagnation of blood in the
cavities and to the relatively complex structure of the hinge
region.
The arrest of the closing and opening of the
leaflets is generally achieved by structures with steps,
corners or projecting edges: these parts have also been found
unsatisfactory as sites which are prone to turbulence and
lo haemolysis.
The prosthetic heart valve which is the subject of
the present invention prevents these and other problems, has
an extremely simple and compact structure reduced to the
essential elements without the addition of projecting parts,
and is safe, prompt and quick in operation.
The present invention has the further advantage that
it does not give rise to regions where the blood may stagnate
and that it does not have possible haemolysis and turbulence
points.
A further characteristic of the heart valve of the
present invention is that it is absolutely biocompatible,
since the materials are covered with a thin/ dense,
homogeneous film of carbon in the turbostratic state which is
that state which has the greatest degree of biocompatibility.
The main subject of the present invention is a
prosthetic heart valve for reducing the formation of thrombi
comprising: (a) a base ring adapted to house a suture ring in
its exterior for suturing to the heart tissue, wherein the
base ring includes an inner surface with walls forming two
diametrically opposed recesses which communicate with the
exterior, and wherein the recesses include: (i) an upper
portion having a substantially flat surface with an opening
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therebetween; (ii) a lower portion separated into two
spherical bottom surfaces by a separator body wherein the
separator body extends from the lower portion of the recess
and the separator body comprises a wedge shape to provide an
opposing recess portion on each side of the separator body;
and (b) two leaflets having an open position and a closed
position for regulating the flow of blood i.n one direction
wherein each of the leaflets has a pair of tongues with one
tongue on each side of each leaflet positioned in a recess
portion of each of the opposing recesses, and wherein the
tongues of the leaflets have continuously changing point
contact with the walls of the opposing recesses when the
leaflets move between the open position and the closed
position for preventing the formation of thrombi as the blood
flows from and through the recesses.
These and other characteristics of the present
invention will become clearer from the following description
of a preferred embodiment thereof taken in combination with
the appended drawings, in which:
Figure 1 is a perspective view of the prosthetic
valve unit of the present invention with the leaflets both in
the open and in the closed positions;
Figure 2 is a partially-sectioned schematic plan
view of the base ring of the valve indicated 1 in Figure 1;
Figure 3 is a diametral section of the base ring of
the valve, taken on the line III-III of Figure 2;
Figure 4 is a diametral section of the base ring of
the valve, taken on the line IV-IV of E'igure 2;
Figure 5 is a plan view of the valve of Figure 1
with the leaflets in the closed position;
Figure 6 is a diametral section of the valve with
the leaflets in the closed position, taken on the line
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VI-VI of Figure 5;
Figure 7 is a diametral section of the valve with the
leaflets in the closed position, taken on the line
VII-VII of Figure 5,
Figure 8 is a plan view of the valve of Figure 1, with
the leaflets in the open position;
Figure 9 is a diametral section of the valve with the
leaflets in the open position r taken on the line IX-IX
of Figure 8;
Figure 10 is a diametral section of the valve with the
leaflets in the open position, taken on the line X-X
of Figure 8.
The body of the heart valve which will now be described
has elements which are identical and elements which are
mirror imaged. For simplicity of description, these
elements have been labelled with the same reference
numerals. Different numerals, however, have been
provided where any ambiguity could arise.
With reference to Figure 1, a substantiall~ cylindrical
base ring, indicated 1, has a recess 2 in its outer
surface which can house a suture ring (not shown in the
drawing) of relatively soft material, generally of
textile fibre, which can be sutured to the heart
tissue.
The inner surface 3 of the ring 1 is cylindrical except
for two diametrally-opposite portions in which the
cylidnrical surface is replaced by two parallel flat
surfaces 4 which cause corresponding thickenings of the
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body of the ring 1~ Within each of these thicker parts
is a recess 5 with curved surfaces divided into two
mirror-imaged sectors by a separator body 6 whose
function will be seen below.
Each recess 5 extends upwardly into a chimney-like
aperture 7 which puts the xecess into communication
with the exterior.
Two leaflets, indicated ~ and 9, are shown both in the
open position (8a, 9a) and in the closed position (8c,
9c) of the valve.
With reference to Figure 2, in this the base ring 1 of
the valve is shown in plan in two different ways: above
the line III-III is a view from above, below the line
is a section of the ring in a horizontal plane passing
through the top of the separator bodies 6 (Figure 1).
The inner aperture of the base ring 1 (Figure ~) is
constituted by two circumferential arcs 3 connected by
two chords 4; the curved recesses 5 are, to a first
approximation, spherical segments; in their central
parts are the separator bodies 6.
Reference 10 indicates the line at which two faces 11
of the separator body 5 meet.
Reference 12 indicates the lines at which the faces 11
of the separator body meet the part-spherical bottom
surfaces of the recesses 5.
The said recess is seen from the front in Figure 3
whic~ shows the section taken on the line III-III of
Figure 2, and in vertical section in Figure 4 which
4a)
shows a section taken on the line IV-IV of Eigure 2.
It is constituted by two lower spherical segment-shaped
parts 13 (Figure 3) separated by the separator body 6,
and by a roof 14 (Figures 3 and 4) which constitutes a
pseudo-flat. The lines at which the two segments meet
are indicated 15.
It should be noted that, for simplicity and clarity of
graphical representation, the meeting of the flat or
curved surfaces is represented by lines in all the
drawings illustrating the present invention; in
reali-ty, these are connection zones, since all the
changes from one surface to another are rounded.
Each of the separator bodies 6 in the recesses 5 is
essentially half a spherical nail whose curved sides
are the meeting lines 12 (Figure 2); the
triangle-section which delimits the half-nail is the
vertical face 4 (Figure 2, 3); the corners are the line
(Figures 2, 4) and the line 16 (Figure 3) which
delimit the face on the flat surface 4.
The chimney-like aperture 7 is formed in correspondence
with the curved recesses 5 centrally thereof (Figures
3, 4) and a slightly raised part 17 may be provided on
the base ring 1 in correspondence therewith.
With reference to Figure 5, this shows the leaflets 8
and 9 in plan, in the closed position. Each of these
is circumscribed by: an outer edge 18 which is
essentially an elliptical arc which follows the inner
surface of the base ring l; two straight portions 19
which follow the flat surfaces 4 of the ring; the
curved outlines of two tongues 20; and, finally, by the
inner edge 21, which is essentially elliptical in
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shape.
Each leaflet has its own plane of symmetry, shown by
the line VI-VI in Figure 5.
The profile of each tongue 20 is divided into two
curved parts, the first, indicated 22, is a
circumferential arc with a raclius of curvature which is
less than or equal to the radius of curvature of the
spherical bottom surface of the recess 5, the second,
indicated 23, is a segment of an ellipse and is formed
by an extension of the internal edge 21 of the leaflet.
The leaflets 8 and 9 have straight profiles in the
front-to-back direction, as can be seen from Figure 6
which is a section in a plane perpendicular to the basP
ring l, taken on the diameter VI-VI of Figure 5. Each
of these leaflets is essentially a curved surface
generated by a straight line segment, supported at the
inner edge 21 and at the outer edge 18 and displaced
parallel to itself from the end of one tongue 20 to the
end of the diametrally opposite tongue.
The edge 21 of each leaflet is a flat face at an angle
alpha to the outer surface of the leaflet, this angle
being equal to the angle between the surface of the
leaflet itself and the generatrix of the internal
cylindrical surface 3 of the ring, obviously with the
leaflets in the closed position.
A section of the valve taken on the line VII-VII of
Figure 5 is shown in Figure 7. From this, both the
shape of the leaflet and its tongues 20, and the
positioning of the tongues within the curved recesses
5, can be seen more clearly.
0
The closed position of the leaflets can be seen from a
combination of the three Figures 5, 6 and 7. The inner
edges 21 mate throughout their entire thicknesses along
the diameter of the aperture of the base ring 1, that
is, between the chimney-like aper-tures 7. The tongues
20 of each leaflet are inserted in the upper parts of
the recesses 5, that is, in the parts which are
delimited at the top by the roofs 14, without, however,
touching their bottoin surfaces. The straight portions
19 follow the flat surfaces 4 of the base ring 1 and
the outer edges 18 of the leaflets bear against the
inner surface 3 of the base ring 1.
The positions of the leaflets 8 and 9 when the valve
is open can be seen in Figures 8, 9 and 10. In this
case, the tongues 20 are inserted in the lower sectors
13 (Figures 9 and 10) of the corresponding curved
recess 5. The circumferential arcuate parts 22 of the
tongues 20 bear against the faces 11 (Figure 8) of the
separator body 6, whilst the point at which the
straight portion 19 of the leaflet (Figures 9 and 10)
and the curved part 22 of the tongue 20 meet bears on
the connection between the bottom surface of the curved
recess 5 and the flat surface 4 of the base ring 1.
The aperture of the base ring 1 is divided into three
regions: a central region 24 (Figure 8) between the
open leaflets, and two lateral regions 25 between the
outer surfaces of the leaflets and the base ring 1.
The three parts are hydraulically equivalent so as not
to cause differences between the flow of blood in the
central region 24 and in the lateral regions 25. This
equality of flow in the three regions is the best
condition for reducing turbulence.
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The kinematics of the valve in operation are as
follows.
When, with the valve closed, that is, with the leaflets
in the position shown in Figures 5, 6 and 7, there is a
positive pressure difference in the direction of the
arrow of Figure 9; this presses on the upper surfaces
of the leaflets 8 and 9 thrusting them downwards.
There is thus both a simultaneous pivoting of the
leaflets which brings them int:o the position of Figures
8, 9 and 10, and a translational movement of the
leaflets themselves in the direction of the blood flow.
More precisely, each tongue 20 (Figure 6) slips down
into the sector 13 of the recess 5 from its upper
position in the recess in which it bears against the
roof 14. The simultaneous pivoting and sliding of the
leaflets 8, 9 obviously also cause pivoting of the
tongues 20 which had been bearing against the faces 11
(Figure 8) of the separator body 6.
The pivoting of the leaflets is arrested by the
separator body 6 and the sliding of the leaflets in the
direction of the flow is arrested by the abutment of
the circumferential-arc portions 22 of the tongues 20
against the bases of the spherical sectors 13 of the
recesses 5. In this position parts of the straight
portions 19 of the leaflets lie against the flat
surfaces 4 (Figure 9) of the base ring 1.
When the pressure difference starts to reverse, the
leaflets 8 and 9 are urged to pivot and to move
upwardly and the operations seen for opening are
repeated in reverse order for closing.
The closure is stopped by three actions:
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- 11
the inner edges 21 of the leaflets mate with each
other over their entire thicknesses; the outer edges 18
of the leaflets contact the inner wall 3 of the ring 1;
the tongues 20 of the leaflets contact the roofs 14 of
the curved recesses 5.
The two degrees of freedom in the movement of the
leaflets which make the rotary-translatory movement
possible also enables the recesses 5 to be washed. In
fact, both during the phase in which the leaflets move
from the closed position into the open position, and in
the open phase, the blood flow also passes through the
curved recesses 5 and through the chimney-like
apertures 7, thus washing the insides of the recesses.
This washing drastically reduces the danger of
stagnation and the formation of clots or fibrous
deposits.
The described embodiment of the present invention may
be modified and varied without thereby departing from
the scope of the invention.
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