Apparatus for widening a stenosis in a body cavity

An apparatus for widening a stenosis in a body cavity, such as an artery, in the bile duct, in the ureter, etc. is proposed, which in view of a problem-free, reliable and permanent widening of a stenosis is characterized by a memory alloy part having a cylindrical jacket-shaped outer contour, said part radially widening at a transition temperature, which is above ambient temperature, but below body temperature, whilst maintaining a cylindrical outer contour and at a temperature below the transition temperature the diameter is smaller than that of the vessel.

FIELD OF THE INVENTION 
The invention relates to an apparatus for widening or expanding a stenosis 
in a body cavity, such as in an artery, in the bile duct, in the ureter, 
etc. 
BACKGROUND ART 
An occlusion in an elongated body cavity such as in a vessel, especially in 
an artery, is generally initially widened, in that deposition material, 
such as plaque is removed by cutting and sucking out or the like. However, 
this cannot take place up to the tissue material, because at that point an 
injury risk exists. If merely a narrowing and not a complete occlusion has 
formed, i.e. a stenosis or a certain through-flow area has been created in 
the aforementioned manner in the previous complete occlusion, a radial 
widening of the stenosis is desired. This is carried out not only in blood 
vessels, but also in other body passages or tubes, such as in the ureter, 
bile duct, etc. 
For this purpose hitherto use has been made of a balloon catheter with a 
double internal diameter, which brings about an instantaneous radial 
widening, which is to remain after the catheter has been removed. 
Permanent widening of such a stenosis is also known. Thus, it has been 
proposed to axially fix a widening part to such a balloon catheter, insert 
it with the latter and by widening the balloon catheter to plastically 
deform the same in such a way that the radial dimensions of the widening 
part are increased, it is forced into the wall of the stenosis and after 
the removal of air from the catheter the latter can be removed, whereas 
the widening part remains in situ in the plastically deformed state. As 
such a part, e.g. a sleeve in the form of a "helical" envelope has been 
provided. 
A significant disadvantage of the last-mentioned process is that the sleeve 
can be introduced into the stenosis located on the outer circumference of 
a catheter. Firstly the axial fixing is complicated and can either not be 
reliably achieved, so that a part can be left behind on advancing the 
catheter, or a subsequent release of the part from the catheter is 
difficult. In addition, damage can result from a widening part externally 
mounted on a catheter. Finally a widening by the balloon catheter in the 
case of such a part must lead to a radial extension, which significantly 
exceeds the ultimately desired radial extension, because such parts, like 
conventional biocompatible materials, to the extent that they have an 
adequate strength to keep open a stenosis, have a considerable elastic 
deformation range, before a permanent plastic deformation occurs to the 
desired radius. This more particularly applies to a "helically" shaped 
part of the aforementioned type. 
DISCLOSURE OF THE INVENTION 
The problem of the invention is therefore to provide an apparatus for 
widening a stenosis, which allows a simple, problem-free, reliable 
widening of a stenosis in a short time, while avoiding the aforementioned 
disadvantages. 
According to the invention this problem is solved by an apparatus for 
widening a stenosis in a body cavity, such as in an artery, the bile duct, 
the ureter, etc., which is characterized by a shape memory alloy with a 
cylindrical jacket-like outer contour, said part radially widening, while 
maintaining a cylindrical contour, at a transition temperature, which is 
above the ambient temperature, but below the body temperature, and at a 
temperature below the transition temperature the diameter is smaller than 
that of the vessel. 
The invention proposes a widening part made from a memory alloy, which 
assumes a shape above a certain transition temperature, which is below the 
body temperature, which corresponds to the desired widening of the body 
cavity According to a preferred development the memory alloy is a 
nickel-titanium alloy. However, it is also possible to use Cu-Zn-Al or 
Cu-Al-Ni alloys. Such alloys are known under the names Nitinol, Biometal 
(Toki, Japan), Memotal. 
The martensitic reaction or transformation bringing about the shape change 
takes place by modifying the temperature. Whereas the transition 
temperature can be within wide limits, provided that it is below the body 
temperature, according to a preferred development the transition 
temperature is 20.degree. C. This temperature is sufficiently below the 
temperature bringing about a reliable widening of the memory alloy part in 
its high temperature state. However, simultaneously the temperature is 
sufficiently high that a part taken by the surgeon at ambient temperature, 
which is therefore in its low temperature state with small radial 
dimensions, only radially widens after a certain time, which is adequate 
for inserting the part into the body up to the stenosis. 
Various developments and constructions of such apparatuses are possible. 
Thus, the memory alloy part can comprise a bent, flat sheet metal part or 
can be a wire part. 
In the first case, according to a preferred development the sheet metal 
part has a spiral shape at a temperature below the transition temperature 
and widens to a cylinder jacket on passing above the transition 
temperature. This construction has the advantage that there is no axial 
shortening of the widening part. The latter occurs in a preferred 
development, which is characterized in that the memory alloy metal is a 
cylinder jacket provided with elongated slots and web regions left between 
them, in which the parallel directed, adjacent elongated slots are 
reciprocately displaced in their extension direction and, accompanied by 
the formation of diamond-shaped gaps between the webs, the part is 
radially made erect on increasing the temperature to above the transition 
temperature. This construction can be relatively simply obtained, in that 
a metal sheet with the desired dimensions is punched as expanded metal, 
then cylindrically bent and welded together at the longitudinal edges 
parallel to the slots. The shortening of the part in the case of a radial 
widening can be taken into account from the outset by having a greater 
length. 
The latter also applies for another preferred development, in which the 
part is made from a metal braid or gauze and is constructed as a cylinder 
jacket, or the memory alloy part is made from a multiply helically guided 
wire. 
A particularly preferred development of the inventive apparatus is 
characterized in that the metallic material is constructed in meander-like 
manner in the axial direction and the individual meanders are bent in an 
almost circular manner. If the meanders have axial outward bends, then 
according to a preferred further development the outward bends of a 
meander arm are connected to an adjacent meander arm. Joining can in 
particular take place by soldering. If all the outward bends are not 
firmly joined to the adjacent meander arms in the typical manner and 
instead only part of them are joined, then according to another preferred 
development, the joining forces of the joints are greater than the 
"weighing" forces of the meander bends. Thus, the inventive apparatus, 
which can also be referred to as an endoprosthesis or stent, in the areas 
in which the meanders are not axially firmly joined together by joints, 
such as soldered joints, can be expanded or compressed and therefore 
position-adapted, without the joints (soldered joints) at other points 
fracturing or breaking. 
The joining points must also be constructed as clearly defined breaking 
points if a stent constructed in the above-described manner is to be 
subsequently removed, so that on pulling at one end of the wire forming 
the stent the joining points break open, the wire stretches and therefore 
in easy manner the stent can be removed. The removal of a stent in the 
above-described construction, but also in a circular knitted construction 
or with a helically shaped stent, is facilitated if at least one end of 
the wire forming the apparatus a ball is provided. It is then possible to 
apply hollow forceps to the ball and consequently the stent can be 
stretched. According to another preferred construction it has a 
substantially axially parallel extending connecting web from which extend 
laterally circularly bent ribs, which extend on either side of the 
connecting web and are in the axial direction in each case alternately 
offset to one another. It is alternatively possible to provide in the case 
of such stents that the ribs extend under an angle of 90.degree. to the 
connecting web or the ribs extend under an angle not equal to 90.degree., 
preferably an angle of 50.degree. to 70.degree. to the connecting web. 
While the outer contour of the stents is generally cylindrical 
jacket-shaped, in certain individual cases conical or biconical outer 
contours are preferred. 
According to another preferred development the metal of the thus far 
described catheter is embedded in tissue-compatible plastics or preferably 
silicone, so that despite the gaps between areas of the memory metal a 
closed jacket area is created. Thus, in the case of malignant tumours, it 
is ensured that cells do not grow into the interior of the stent. 
The stent according to the invention can be used in numerous different 
fields and for numerous different purposes, e.g. in the urethra, ureter, 
neck of the bladder, deducti bilipheri, in blood vessels, such as arteries 
and veins, in the esophagus and trachea, as well as in the intestinal 
region, particularly in the intestinum rectum. 
The invention offers stiff and highly flexible, particularly axially 
bendable stents, the latter more particularly applying for those having a 
wire guided in meandering manner.

BEST MODE FOR CARRYING OUT THE INVENTION 
FIG. 1 shows a first embodiment of an inventive apparatus for widening a 
stenosis in an elongated body cavities, such as in an artery the bile 
duct, the ureter, etc. and which is hereinafter referred to as a stent. In 
its low temperature state the stent of FIG. 1 has a spiral shape and which 
on passing above a transition temperature in its high temperature state 
widens to an almost cylindrical jacket-shape as illustrated to the right. 
The stents according to the invention are made from a shape memory metal, 
particularly from nickel-titanium alloys, but also Cu-Zn-Al or Cu-Al-Ni 
alloys. Memory alloys are known under the names Nitinol, Bimetal or 
Memotal. The manufacture of the stent according to FIG. 1 takes place in 
that in its high temperature form, i.e. the cylindrical jacket-shape of 
FIG. 1, the stent is bent and then undergoes a heat treatment. After 
cooling to below the transition temperature the stent is permanently 
brought into its spiral low temperature form. If it is again heated to 
above the transition temperature, which is in the range 30.degree. to 
35.degree. C. and preferably at 35.degree. C., then it "remembers" its 
cylindrical jacket-shaped high temperature form and reassumes the latter. 
FIG. 2 shows another stent in the form of an expanded metal. In the case of 
the latter into a sheet metal part are punched in successively aligned and 
juxtaposed manner a plurality of slots and adjacent, juxtaposed slots are 
in each case so reciprocately longitudinally displaced, that the two upper 
and lower regions of a slot overlap with the near end region of adjacent 
slots. If the sheet metal is expanded transversely to the extension 
direction of the slots, then it can be stretched, the slots widening to 
diamonds as illustrated to the right. Such a sheet metal piece is given a 
cylindrical jacket shape and is interconnected, such as by welding or 
soldering by its longitudinal sides parallel to the slots. It is brought 
into its widened form showing the diamonds and as is represented to the 
right in FIG. 2 and is then correspondingly subject to the high 
temperature treatment and subsequently at low temperature is again 
permanently deformed in the stretched form (to the left of FIG. 2). On 
heating to above the transition temperature this stent also remembers its 
widened high temperature form. In the case of radial widening the stent of 
FIG. 2 and also those of FIGS. 3 and 4 shorten, unlike in the case of the 
stent of FIG. 1. However, this shortening can be taken into account by 
choosing a corresponding length. The width of the webs is extremely small 
and is preferably approximately 0.2 mm. 
FIG. 3 shows a metal braid or gauze stent, which also has a cylindrical 
jacket-shaped outer contour. The temperature and shape treatment once 
again takes place in the above-described manner, so that on increasing the 
temperature to above the transition temperature the stent widens from its 
small diameter, stretched state into a radially widened high temperature 
state illustrated. The same applies with respect to the further helical 
design of a metal wire stent with shape memory and here again the 
corresponding heat treatment is carried out. 
FIG. 5 shows the mesh pattern of an inventive, circular knitted stent. It 
has conventional knitted meshes formed from a weft thread 11, the meshes 
having a leg 12, a head 13 at the upper binding point and a base 14 at the 
lower binding point around which the head is placed. 
According to a preferred development a ball 16 is fixed to the end of the 
wire filament 11. If an inserted stent is to be removed for some reason, 
then action can take place on the ball 16 by means of hollow forceps so as 
to pull the same and the mesh pattern of the stent is loosened and the 
latter can be removed from the body cavity in which it was positioned. 
Such a removal by stretching the wire filament forming the stent is also 
possible in the case of the constructions according to FIGS. 6 and 7. 
These stents comprise a meandering, longitudinally wound wire (i.e. the 
meanders extend transversely to the longitudinal direction). The meanders 
are bent in circular manner, so that the remote webs of adjacent meanders 
are bent towards one another. Such a stent has the important advantage 
that its length can be changed without significantly influencing the 
cross-section. Compared with its normal longitudinal extension the stent 
can be compressed or stretched and is held in the resulting position by 
the frictional forces between it and the surrounding vessel walls. 
According to a preferred development arms 19 of the meanders 20 have 
outward bends 21, which extend up to the adjacent meander arm, e.g. 19a. 
At least part of the outward bend 21 can be connected to the in each case 
adjacent meander arm 19a by a soldered joint 22. As a function of the 
intended use all the outward bends can be connected to adjacent meander 
arms. In this case the length of the stent is limited. Only part of the 
outward bends may be connected, no soldered joints being provided on 
certain of them and as a result the length can be changed to a limited 
extent. Finally, stents can be constructed in such a way that no outward 
bends are firmly connected to adjacent meander arms. The outward bends 
cause a certain resilience in the radial or angular direction of the 
stent. 
The stents according to FIGS. 6 and 7 once again have the balls 16 at the 
filament ends, so as to be able to remove the stent by stretching the 
filament forming the same. If there are soldered joints 22, then their 
fastening force is much less than the tensile strength of the filament. 
However, it must exceed the bending force of the wire in the vicinity of 
the webs 17,18 of the meanders. 
As in the case of other stent constructions according to the invention, the 
construction described above can have a cylindrical outer contour in 
accordance with FIG. 6. However, like other of the stents shown, it can be 
conical or biconical, as shown in FIG. 7 and in this case the larger 
diameter is on the end faces of the stent. 
The inventive stent according to FIGS. 6 and 7 has very considerable 
flexibility, which is greater than that in the case of FIG. 5. The stent 
according to FIGS. 6 and 7 is almost completely bendable. The inventive 
metal stents can be embedded in compatible plastics or preferably 
silicone, which assumes the same contour as the actual stent. This makes 
it possible to ensure that in the vicinity of a thus designed stent a 
malignant tumour cannot migrate through the same. 
The above-described stent formed by a meandering configuration can be used 
in many different ways and for many different purposes. With particular 
advantage such a stent can be used as a urethral stent in the vicinity of 
the prostate for widening the urethral area there when the prostate is 
enlarged. As a result of its flexibility, it adapts particularly well to 
the configuration of the male urethra. As a result of its longitudinal 
variability its length can be modified in such a way that its rear or 
outer end does not come to rest in the vicinity of the external sphincter, 
so that the stent does not impair this function. Particularly in the case 
of such a use the above-described stent extraction possibility by 
stretching the wire filament forming it and pulling out proves 
particularly advantageous. 
Another preferred construction of an inventive stent is shown in FIG. 8 and 
FIG. 9 shows a modification in the wound-up state. Such a stent could be 
referred to as a "skeleton stent". It substantially has an axially 
parallel extending ridge, or a connecting web 31 and from it extend on 
either side ribs 32,33 at a right angle (FIG. 8) or under an angle 
differing from a right angle (FIG. 9), preferably in the range 50.degree. 
to 70.degree.. The ribs 32,33 extending to either side are in each case 
alternately displaced in the longitudinal direction of the ridge 31, so 
that the circularly bent ribs 33, which extend to one side in each case 
engage in the gap between two ribs, which extend to the other side and 
vice versa. 
The length of the ribs 32,33 and the diameter of the stent in the low and 
high temperature position can be chosen in such a way that in the low 
temperature position there is an overlap of the material walls of the 
stent, as would otherwise be the case under identical conditions, if the 
ribs 32,33 extending on either side of the ridge 31 were arranged at the 
same height of the latter. The stent shown in FIGS. 8 and 9 also has a 
very considerable flexibility and longitudinal bendability. In addition, 
the ribs 32,33 can be so closely juxtaposed, that from the surrounding 
tissue of a cavity held by the stent liquid can enter and be removed from 
the interior of the stent. However, tissue cannot penetrate the interior 
and lead to a narrowing. In the construction according to FIG. 9 a 
somewhat greater rigidity is obtained than in the case of FIG. 8. 
FIG. 10 shows a blank for a further stent. From a sheet metal part are 
punched elongated holes and Juxtaposed elongated holes are alternately 
reciprocately displaced and can consequently give in the end regions 
elongated holes with a shorter length than the other elongated holes.