Abstract:
Catheter for inserting into a hollow organ, in particular a blood vessel, wherein at least one tube- or balloon-like flexural element ( 12, 12   a   , . . . , 12   l ) which can be filled with a filling medium is provided inside the catheter, which flexural element is flexible in the non-pressurized state and stiffens as a result of pressure buildup internally and assumes a predetermined curved shape.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to the German application No. 10 2004 003 166.5, filed Jan. 21, 2004 which is incorporated by reference herein in its entirety. 
     FIELD OF INVENTION 
     The invention relates to a catheter for inserting into a hollow organ, in particular a blood vessel. 
     BACKGROUND OF INVENTION 
     Flexible catheters which are advanced through arteries or veins are used for intravascular or intracardial treatment. At the tip or side of said catheters functional mechanisms are provided, for example to stimulate or cauterize tissue or to conduct electrical signals. In order to be able to deliver the catheter to the correct positions in the cardiac or vascular system, the catheters have to be moved and guided by the physician. Such guidance has to be precise, fast and highly flexible, in particular because the vascular system is a convoluted system that contains a number of bends. Most of the time during treatment is taken up by the navigation of the catheter. Catheters of this kind are conventionally steered solely by manipulating the end that projects out of the patient. By rotating, pushing forward and retracting the catheter, said actions being observed through X-ray monitoring, in combination with a curvature in the tip of the catheter, the catheter tip is caused to take the desired route, which the rest of the catheter then follows. A catheter of this kind moved by the user has to be relatively stiff so that movements can be reliably continued also when negotiating bends. This runs counter to safety requirements, however, since a stiff catheter is more likely to cause injuries. 
     SUMMARY OF INVENTION 
     A known guidance method is the use of pull wires that allow the end of the catheter to be moved. The disadvantage thereof is firstly the complexity of the catheter and secondly the limited angle of curvature that can be set. A further known technique is magnetic navigation. This type of catheter has at its end, which is designed to be extremely flexible, a tip comprising magnetic material. By applying an external homogeneous magnetic field through the patient it is possible for the catheter tip and thus the whole of the end of the catheter to be aligned along the lines of the magnetic field. By also advancing the catheter it is possible to navigate through complex vascular systems. However, the above method requires a substantial outlay in terms of technology, equipment and cost, and furthermore the size of the area that can be navigated is limited due to the dimensions of the magnetic field. 
     The invention addresses the problem of providing a catheter that allows simple navigation. 
     To solve the above problem there is provided according to the invention a catheter of the type cited at the beginning, inside of which there is provided at least one tube- or balloon-like flexural element which can be filled with a filling medium, which is flexible in a non-pressurized state and which stiffens due to the buildup of pressure inside it and assumes a predetermined curved shape. 
     Using the flexural element usefully provided on the catheter tip side, a curvature of the catheter can be achieved in a simple manner when required. Said curvature allows the catheter to adapt to the subsequent course of the blood vessel and to be threaded in a simple manner into a branch of a blood vessel, for example. For this purpose, the flexural element, which is flexible in a non-pressurized state, has simply to be filled with the filling medium in order to build up the pressure. As a result of the increasing pressure the flexural element increasingly stiffens and assumes a predetermined curved shape. According to the filling level, any intermediate shape ranging from completely flexible to completely stiff can be set, there being various degrees of rigidity. Depending on the embodiment of the flexural element, any desired angles of curvature can therefore be set in the stiffened state. 
     It is useful if a plurality of individually controllable flexural elements are provided so that, according to the position of the catheter and the required curvature, a required flexural element can be activated and the catheter or, as the case may be, the catheter tip, which in this catheter is sufficiently flexible and so designed to avoid a risk of injury when the catheter is advanced, can flex in the right direction. 
     In this case the flexural elements can be arranged in such a way that the predetermined directions of deformation are aligned to different directions. The multiple flexural elements thus all curve in a different direction, with the result that a high degree of flexibility is achieved with respect to the catheter tip deformation. According to a first invention alternative the flexural elements can be arranged sequentially essentially in the center of the catheter relative to the longitudinal axis of the catheter. In other words the flexural elements, which are dimensioned to be relatively short in this case, are arranged one after the other in series. Furthermore it is also possible that at least some of the flexural elements are disposed in a distributed arrangement about the longitudinal axis of the catheter. In this case, therefore, the flexural elements are staggered radially outward; they are disposed in a distributed arrangement around the internal catheter cavity in which, for example, signal lines or similar are run. In this way a fully variable tip deformation can be set in particular for different preferred directions of flexure. 
     A development of the inventive idea provides that a plurality of flexural elements are arranged at a common longitudinal position relative to the longitudinal axis of the catheter, that is to say that relative to the length of the catheter they are disposed staggered radially outward at one point or in a segment-like arrangement at a plurality of points. Alternatively it is possible to dispose said elements in a distributed arrangement over a part of the length of the catheter, in other words to provide any number of flexural elements over a specific length of the catheter in a distributed and staggered arrangement with respect to one another in order to achieve an adequate flexural capability relative to said longitudinal section at a plurality of different locations. The length along which the flexural elements are disposed in the aforementioned arrangements can be selected at random and usually depends on the purpose for which the catheter is used and the possibility of integrating the flexural elements. 
     A flexural element itself is usefully made from a non-elastic material. In order to achieve the defined shape in the filled state, the walls thereof are non-symmetrical in design, that is to say the lengths of the side walls are different, with the result that a curved shape is produced in the filled state. Usefully, polyurethane or polytetrafluoroethylene is utilized for this purpose, in other words materials that are non-elastic, thereby avoiding any stretching of the material that would result in an approximation to a spherical shape. 
     A fluid can be used as the filling medium; possible fluids include, for example, water or a saline solution or another, preferably biocompatible, fluid. Alternatively, a gaseous filling medium such as air or oxygen or also a different, preferably biocompatible, gas can be used. 
     Since, as described above, the simple means of navigation is based on the situation-dependent activation of the flexural element or elements, a development of the inventive idea for simple and fast setup of the catheter, in other words when it is needed and is to be used, provides that it has a central connection device for a feed device for the filling medium, at which connection device the or all lines for the filling medium leading to the flexural element or elements converge. Thus, a defined connection point for all fluid or gas feed lines is provided, usefully in the form of a simple plug-in connection to which a corresponding counterpart can be connected as part of a feed device. 
     All in all, the catheter according to the invention allows easy navigation without a large outlay in terms of external equipment. All that is required is a feed device which simultaneously handles control functions in order to activate the flexural elements. In particular with a distribution of a plurality of flexural elements over a specific length of the catheter, control of the catheter curvature is also advantageously possible not only at the end of the catheter, but quasi segmentally or approximately randomly at different points of the catheter. It is also conceivable to be able to vary the flexibility or stiffness of the catheter over the entire length along which the flexural elements are distributed, or only over a part thereof. For it is of course possible to put a plurality of flexural elements, of a segment for example, under pressure simultaneously so that their forces cancel one another out and the catheter does not deform but stiffens in sections. It is therefore possible to stiffen the catheter over the entire length along which the flexural elements are distributed, or only over a section thereof. In this way it is possible to minimize the risk of injury, where this is necessary because of the anatomical conditions, as well as to optimize the controllability and “pushability”, where this is possible from the point of view of risk of injury. The controllable curvature at any point of the catheter over the range of the flexural elements also results in the curvatures along the vascular structures exerting no deformation force from the catheter on the vascular walls, since of course there is also the possibility of producing corresponding vascular curvatures on the catheter side, even if the catheter tip has already long since passed this section. The shape of the catheter thus adapts itself as far as possible to the actual shape of the blood vessel, and the vascular walls are not too greatly irritated and deformed via the catheter. This reduces the risk of injury during interventions. 
     In addition to the catheter the invention also relates to a catheter device, comprising a catheter of the above-described kind, as well as a feed device for the filling medium which can be coupled to the catheter. This is usefully embodied for separate activation of the plurality of flexural elements provided on the catheter side. In order to perform a precise activation, the feed device must know the assignment of the individual feed lines to the respective flexural element and of course the latter&#39;s position on the catheter side. For this purpose means for identifying the feed lines converging at the connection device on the catheter side are usefully provided at the catheter and/or the feed device. Said identifying means can be a type of plug-in coding, for example, or any other signaling means which allows a unique assignment of the respective line to the flexural element. For only then can it be guaranteed that the feed device activates the right flexural element for the desired curvature locally and with regard to the direction of curvature. 
     The feed device itself can be embodied for automatic activation of the required flexural element or elements as a function of at least one item of information relating to the desired direction of curvature of the catheter. Said information can be provided for example by the physician who is continuing, as before, to control the movement of the catheter with the aid of X-ray monitoring. If he or she sees that the tip must be curved in one direction or the other, he/she can supply this information to the feed device, which subsequently performs the automatic activation. For this purpose an input device for this information can usefully be provided, which input device, according to a particularly advantageous embodiment of the invention, comprises a monitor on which it is possible to display a three-dimensional image of the blood vessel and the catheter, in which displayed image the user can define the direction of curvature by means of a marker or suchlike, for example a cursor. In other words, the physician is presented with a preferably three-dimensional display of a blood vessel tree along with the catheter, which display can be produced in any manner, via parallel X-ray monitoring or using other sets of image data that were obtained from previous investigations (for example magnetic resonance tomography or computer tomography) and which incorporate the catheter image as captured via the X-ray monitoring. The physician now has the ability to navigate in the displayed image, for example via the monitor cursor, and to define a desired direction of curvature. According to the information supplied, the feed device is then able to perform the corresponding activation in order to achieve the desired curvature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages, features and details of the invention will become apparent from the exemplary embodiments described below and by reference to the drawings, in which: 
         FIG. 1  shows a schematic diagram illustrating the principle of a catheter device according to the invention, 
         FIG. 2  shows a schematic diagram depicting a flexural element in the non-pressurized state, 
         FIG. 3  shows a schematic diagram of the flexural element from  FIG. 2  in the filled state, 
         FIG. 4  shows a schematic diagram of the catheter tip with non-pressurized flexural element and filled flexural element, 
         FIG. 5  shows a schematic diagram of the catheter tip having two flexural elements acting in opposite directions, 
         FIG. 6  shows a cross-sectional view through a catheter having a plurality of flexural elements staggered radially outward and disposed in a distributed arrangement, 
         FIG. 7  shows a schematic diagram of a catheter having a plurality of segmentally arranged flexural elements, 
         FIG. 8  shows a schematic diagram of a catheter having a plurality of flexural elements disposed in a staggered arrangement over the length of the catheter, 
         FIG. 9  shows a schematic diagram of a catheter course obtained by activation of different flexural elements, and 
         FIG. 10  shows a schematic diagram of a connection device of the catheter. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
       FIG. 1  shows a catheter device  1  according to the invention comprising a catheter  2 , at the free end of which (i.e. the end that is not to be inserted into the patient) there is provided a connection device  3  which is coupled to a connection device  4  that forms part of a feed device  5  for a liquid or gaseous filling medium. By means of said feed device  5 , a liquid or gaseous filling medium can be supplied to the individual flexural elements which are integrated into the catheter and which are hereinafter described in further detail. The feed device  5  is coupled to an input device  6  comprising a monitor  7 , a keyboard  8  and a mouse  9 . By means of said device, the operator, referring to an image displayed on the monitor  7 , said image being supplied for example by an X-ray image taken in parallel by an X-ray device  10  during the invasive procedure, or where appropriate using an image data set  11 , obtained for example by magnetic resonance tomography or computer tomography, can specify the direction in which the catheter is to be bent. 
     The functional principle is based on the fact that there are integrated in the catheter one flexural element or a plurality of flexural elements which, when pressure builds up inside the catheter, can be directed into a particular shape.  FIG. 2  shows a schematic diagram illustrating a flexural element  12  which is tube-like in design. Said element consists of a non-elastic plastic material, for example PUR or PTFE, but any other plastic can be used. The flexural element  12  has a shorter wall segment  13  on one side, while a longer wall segment  14  is provided on the opposite side; in other words, the walls are non-symmetrical overall. If filling medium, for example water, saline solution or air or oxygen, is now supplied via the feed line  15 , then the pressure builds up inside, resulting in the flexural element  12  attempting to achieve a maximum volume in a minimum surface area. Since the walls are non-elastic, no stretching can occur. The wall  14  stretches such that the flexural element  12  assumes the curved shape shown in  FIG. 3 , in which it is sufficiently stiff as a result of the pressure inside the catheter. The diagram shows how a curvature that is created by the geometrical shape of the flexural element  12  can be set in this way. In the example shown, the angle of curvature α is drawn. If such a flexural element is now integrated into the catheter  2 , as shown schematically in  FIG. 4 , a defined deformation of the catheter can be achieved. In the non-pressurized state the flexural element  12  is flexible, that is to say it has not been stiffened and the shape thereof is determined by the shape of the catheter or catheter sheath. The catheter sheath consists, for example, of a slightly elastic plastic material and possesses sufficient stiffness or rigidity to allow manipulation of the catheter. As the diagram shows, the shape of the catheter  2  changes when the flexural element  12  is subjected to pressure, as indicated by the dashed lines in  FIG. 4 . As shown in  FIG. 4 , the catheter curves upward, essentially describing a curvature of 90°, caused by the defined alteration in shape of the flexural element  12 . If pressure on the flexural element  12  is released again, said element becomes flexible again and collapses, as it were, possibly with the assistance of the resetting force of the slightly elastic catheter sheath. 
       FIG. 5  shows the catheter  2 , in which are integrated two flexural elements  12   a ,  12   b  which are essentially identical in design, both therefore having a short and a longer wall side. Depending on which flexural element is filled, the direction of curvature changes since the said two elements exhibit different preferred directions of curvature. If the flexural element  12   a  is filled, then the catheter tip curves upward, as shown in  FIG. 4 , and the flexible, non-pressurized flexural element  12   b  automatically follows the same curvature. Conversely, if the flexural element  12   b  is filled, the catheter tip curves downward because of the preferred direction of said element, as shown in  FIG. 5 , and here the non-pressurized flexural element  12   a  assumes the same change in shape. The respective radius or angle of curvature α that can be achieved depends on the ratio of the material length of the wall sections which are opposite each other and are of different lengths. According to the embodiment and dimensions thereof, the angle of curvature can consequently be varied, as can also, of course, the position of the point of flexure, that is, depending on where the wall section that is “long” in terms of the material used is provided relative to the length of the flexural element. 
       FIG. 6  shows a cross-sectional view of a catheter  2  around whose central aperture  16 , in which, for example, a further working catheter is guided or signal or control lines etc. are routed, six flexural elements  12   a ,  12   b ,  12   c ,  12   d ,  12   e  and  12   f  are arranged, radially staggered outward and, in the example shown, symmetrically distributed. Each of the flexural elements  12   a - f  can be controlled independently via a separate feed line (not shown in any further detail). The positioning, alignment and design of the flexural elements in the above arrangement is such that each flexural element has its own preferred direction of curvature, said preferred direction of curvature being oriented in a different direction in each case. Said preferred directions of curvature are represented by the respective arrows in the flexural elements. The arrow indicates how the respective flexural element—as shown for example in FIGS.  4  and  5 —starts off from the more or less straight catheter shape and then bends in the direction of the arrow. If a plurality of flexural elements are therefore integrated into the catheter and the directions of deformation of the individual flexural elements are aligned as shown in  FIG. 6 , then a different direction of flexure can be achieved by increasing the pressure in each separate flexural element. Combinations are also possible of course; in other words, pressure can be applied to two adjacent flexural elements such that the resulting direction of flexure is the direction that lies between the individual main element-related directions. It is also conceivable of course for pressure to be applied to all the flexural elements so that the individual effects thereof are cancelled out, but the catheter itself stiffens considerably in the zone where the flexural elements are provided. 
     With regard to the arrangement of the flexural elements that are staggered radially outward, different embodiments are possible.  FIG. 7  shows a catheter  2  in which the flexural elements  12  are disposed in a quasi-segmental arrangement. The figure shows four segments I, II, III, IV in which a plurality of flexural elements  12  are arranged in each case. Based on  FIG. 6 , six flexural elements distributed in a symmetrical arrangement are contained in each segment (for reasons of presentation only three are shown in  FIG. 7 ). This permits on the one hand a corresponding catheter flexure to be performed segment by segment, and on other hand a segment-by-segment catheter stiffening to be achieved. 
     A different type of arrangement of the flexural elements  12  is shown in  FIG. 8 . In this case, the flexural elements  12  are staggered radially outward as shown in  FIG. 6 , but they also overlap one another, in other words a kind of spiral-shaped arrangement of the flexural elements is chosen. Since here, too, each flexural element can be activated independently (for the sake of clarity the individual feed lines are not shown in greater detail; the same applies to  FIG. 7 ), a locally defined curvature can also be achieved here. 
       FIG. 9  is a diagram showing in schematic form an example of the deformation of a catheter  2  that is achievable by separate activation of individual flexural elements. A plurality of individual flexural elements  12  are distributed along the length of part of the catheter. Said elements can either be distributed in segments, as shown in  FIG. 7 , or staggered in a spiral arrangement, as shown in  FIG. 8 . A total of six different flexural points A, B, C, D, E and F are shown in  FIG. 9 . In order to achieve flexure at the flexural point A, the flexural element  12   g  is activated and the adjacent, in particular opposite flexural elements  12  remain non-pressurized and therefore flexible. In order to achieve flexure at the flexural point B, the flexural element  12   h  is activated, and in order to achieve flexure at the flexural point C, the flexural element  12   i  is activated. A similar procedure is followed in order to achieve flexure at the flexural point D, and here the flexural element  12   j  is activated by the feed device. In order to achieve flexure at the flexural point E, the flexural element  12   k  is activated, and finally in order to achieve flexure at the flexural point F, the flexural element  12   l  is activated. As the diagram shows, the fact that each of said flexural elements has a defined preferred direction of curvature and assumes said curvature when in a pressurized state results in the whole of the catheter in the respective area assuming the corresponding curvature and consequently producing the highly convoluted shape shown in  FIG. 9 . 
     The flexural elements can be of any length and to allow sufficient flexure relative to the diameter of the catheter, they should be at least 1 cm or more in length. The diameter thereof varies according to the type and diameter of the catheter and the type of arrangement of the flexural elements and the number thereof. It should be at least 1 mm or more in length. 
     Finally,  FIG. 10  shows a schematic representation of the connection device  3  of the catheter  2 . As can be seen, a plurality of feed lines  15 , each of which leads to a specific flexural element  12 , converge in the connection device  3 . Different codings or suchlike are provided at the connection device  3  to indicate which feed line  15  leads to which flexural element. This can take the form, for example, of a plug-in coding, that is to say the two connection devices  3  and  4  can only be coupled to each other in a quite specific manner, so that the respective feed line  15  is then identified on the basis of a defined positional assignment. Alternatively it is also conceivable that other information means such as transponders or the like permit the identification. 
     All in all, the catheter or, as the case may be, the catheter device according to the invention permits easy navigation, since the physician can perform a desired catheter flexure or tip deformation as required based on the anatomical conditions in the blood vessel under investigation. By this means it is also possible, when a plurality of segments are activated, to achieve a specific catheter shape and “freeze” it, in other words the catheter can be, as it were, “braced out” in the blood vessel. If the catheter is a guidance catheter in which a working catheter is guided for example for a biopsy or suchlike, no dislocation of the catheter can occur on account of the “bracing out” if, for example, a wall or suchlike has to be penetrated by means of the working catheter or if the catheter runs up against such a wall.