Abstract:
A medical instrument has a cannula and a seal disposed in the cannula. An expansion device serves for expanding an opening in the seal for guiding shafts of other instruments of greater diameter in a sealed manner through the expanded opening. The expansion device has an expansion cone with a plurality of slats mounted pivotably on an annular body at a first end thereof, a second end of the slats being connected to the seal in an area of the opening. The slats are connected at its first ends to the annular body via spherical heads engaged into corresponding openings in the annular body.

Description:
The present indention relates to a medical instrument, with a cannula through which shafts of other instruments having different shaft diameters can be guided, with a seal comprising an opening with a variable opening cross section through which the shafts having different shaft diameters can be guided sealingly, with an expansion device for expanding the opening of the seal, which expansion device has an expansion cone with a plurality of slats that are mounted pivotably on at annular body and form an expansion body that narrows from the proximal end to she distal end and that is connected to the seal in the area of the opening. 
     A medical instrument of this kind is known from EP 0 696 459 B1. 
     Said medical instrument is a trocar that is used in minimally invasive surgery. The trocar is introduced through a small opening, which can be formed by a small incision for example, through the abdominal wall into the abdominal cavity of the patient by means of a trocar mandrel. After removal of the trocar mandrel, shafts of other instruments used for the surgical intervention are then passed through this trocar. These instruments include, for example, gripping tools, coagulation instruments, endoscopes and the like. These have different diameters. 
     Since minimally invasive interventions of this kind are often performed during insufflation of the internal cavity in which the operation takes place, all the intervention points must be gas-tight. 
     In the aforementioned EP 0 696 459 B1, this purpose is served by an elastic conical seal that is arranged in the trocar and that narrows from the proximal end to the distal end. To permit uniform widening of the seal when an instrument is inserted into the trocar, the expansion cone is arranged in the proximal direction from this seal. An instrument inserted into the expansion cone expands the latter radially, which widens the opening in the seal. In addition to permitting easier widening of the seal, the expansion cone also prevents damage to the seal during insertion of sharp-edged instruments, because it can be made of a hard material. In this way, the seal is protected by the expansion cone. 
     To construct the expansion cone, the slats are mounted pivotably at a first end thereof on a ring, as a result of which the cortical body of the expansion cone is obtained and the slats can be pivoted radially. For this purpose, they have axial pins at one end, with which the slats have to be engaged pivotably in corresponding recesses in the annular body. 
     For this purpose, each slat therefore requires exactly shaped end pieces with axial pins. Correspondingly, the annular body must also have exactly shaped engagement means, in addition to which an exactly shaped cover has to be fitted onto the device in order to ensure that the slats do not fall off from the ring. The construction therefore requires a number of exactly produced individual parts with relatively complicated details. This is difficult, especially because of the small size of the components, in the millimeter range, and therefore makes construction complicated. The same also applies to the assembly work in which the very small axial pins have to be engaged in the corresponding recesses in the annular body. 
     It is therefore an object of the present invention to develop a medical instrument of this kind in such a way that the sealing system is of simpler construction and is less complicated to assemble and less expensive to produce. 
     SUMMARY OF THE INVENTION 
     According to the invention, the object is achieved, on the one hand, by the fact that the slats are connected to the annular body via film hinges. 
     The pivotable connection between slats and annular body by means of film hinges allows the expansion cone to be made as a single workplace by injection moulding. The work involved in producing the expansion cone is thus greatly reduced, since only a single part has to be manufactured and there is no need for individual parts to be assembled. This saves time and reduces costs. 
     According to the invention, the object is achieved, on the other hand, by the fact that the slats have spherical heads via which they can be engaged in corresponding openings in the annular body. 
     Although the expansion cone in this solution is composed of several parts, the provision of spherical heads, which have to be fitted into the corresponding openings of the annular body, represents a simple design measure. No particular attention has to be paid to fitting the spherical heads into the openings in the annular body, as a result of which the assembly is made simple. 
     In one embodiment, the spherical heads of the slats are held in the annular body by a cover ring. 
     The use of a cover ting presents the slats, mounted via their ball joints, from falling out of the annular body. It further supports the concept of simple construction, since the cover ring ensures a secure hold of the slats, mounted via their ball joints. 
     In another embodiment, the seal extends in the distal direction away from the distal end of the expansion core. 
     For it, the seal can be designed as a pot-seal, a bottom of said pot-seal is connected to said distal end of said expansion cone. 
     The choice of this structural arrangement has the advantage, on the one hand, that joining together the expansion cone and the seal is simple, since both components are connected to each other via easily accessible outer races. On the other hand, the resulting arrangement of the seal facilitates the removal of tissue samples, since it in this way has a funnel-like shape that narrows from the pedal end to the proximal end. If, for example, such a sample is taken hold of by a gripping tool and is then guided through the trocar sleeve in the proximal direction, it finally reaches the seating system. There, by virtue of the gradually decreasing diameter of the seal it is guided to the proximal narrow opening of the seal and, if appropriate, also adapted in shape. This avoids an undesirable situation in which the sample, during its removal, becomes caught because of an abrupt change in diameter. 
     In another embodiment of the invention, the seal surrounds the expansion cone. 
     For it, the seal can be designed as a pot-seal wherein said expansion cone is arranged within said pot-seal, and a distal end of said expansion cone is connected to said opening in a bottom of said pot-seal. 
     This embodiment leads to a compact sealing system. By virtue of its small size, the latter is compatible with many known trocar systems. Since it can be preassembled and easily handled by virtue of this compact structure, it can also be easily fitted into the trocar systems. 
     In another embodiment of the invention, the distal end of the slats of the expansion cone is connected with a form fit to a socket at the edge of the opening in the seal. 
     This connection of the distal end of the slats to the socket at the edge of the opening of the seat prevents the slats from slipping during expansion of the seal. This counteracts the possibility of the slats coming loose from the edge and ensures uniform expansion. Moreover, the connection has the effect that, after the removal of a shaft from the trocar, the slats move back to the starting position again together with the sealing opening, on account of the restoring force of the expanded elastic seal. 
     In one embodiment of the invention, the distal end of the slats of the expansion cone is adhesively bonded to the seal. 
     Adhesive bonding between the slats and the opening of the seal ensures a non-releasable and secure contact between the components. Undesired separation of the components is thereby avoided, such that the slats are at all times arranged on the opening of the seal. The adhesive bonding is conceivable as a single measure, but also in combination with the form-fit connection. 
     In another embodiment of the invention, the seal is arranged together with the expansion cone in a casing structure. 
     The use of a casing structure confers increased stability on the system composed of expansion cone and seal. The assembly composed of the expansion cone, made of stiff material, and of the seal, made of elastic material, forms a structure that is relatively unstable in the lateral direction. This is particularly so to the configuration in which the expansion cone and the seal extend diametrically away from each other starting from their point of connection to each other. An instrument inserted whir a lateral offset or obliquely into the expansion cone would cause a lateral shift or lateral displacement of the assembly. The casing structure counteracts this, but provides a certain degree of flexibility. 
     In another embodiment of the in vendors, the casing structure is composed of a double ball joint, which is preferably composed of a seal holder, a middle part with ball sections, and a proximal ball socket. 
     The embodiment of the casing structure as a double ball joint that is movable to a certain degree allows the expansion cone, and fire seal connected to the latter, to execute certain tilting or shifting movements. This is useful particularly for instruments whose shafts have a small diameter. In the case of instruments with thin shafts, they may become offset from the central passage through the opening of the seal. Moreover, particularly in the case of thin flexible shafts, a curved extent of the shaft through, the trocar may arise. Both of these situations nave the effect that the seal does not come uniformly into contact with the shaft about the whole circumference of the latter. The result of this is undesired loss of leaktightness. 
     By virtue of the casing structure in the form of a double ball joint, the sealing system is able to move such that the shaft once again extends centrally through the opening of the seal. In this way, the desired leaktightness of the trocar system is maintained. 
     In another embodiment of the invention, the casing structure is composed of a flexible casing tube. 
     The use of a flexible casing tube also permits very good adaptation of the seal to the offset of an inserted instrument, since such a flexible tube likewise permits a mobility of the sealing system. Adapting the seal to the offset or oblique course of the shad through the opening of the seal likewise ensures the leaktightness of the trocar system. 
     In another embodiment of the invention, the flexible casing tube is composed of a substantially parallel series of ring elements, wherein two adjacent ring elements are preferably connected to each other at two radially opposite sites, and, furthermore, the sites connecting a ring element to the distally adjacent ring element are in each case always offset by 90° with respect to the connecting sites to the proximally adjacent ring element. 
     The connecting sites between the ring elements, arranged in a circle shape and alternately offset by 90°, permit a flexibility of the casing lobe in ah lateral directions since, as a result of the connecting sites being arranged radially opposite one another, the connected ring elements have a tilt axis. By means of this, they can be tilted towards one another, born the mutually parallel arrangement, at sites lying circumferentially between the connecting sites. Within the overall arrangement of the ring elements, the 90° offset from one pair to the next pair of ring elements ensures that tilting is possible in two mutually perpendicular directions. That is to say, the casing structure thus formed cars be moved, at its free proximal end in two independent directions and, therefore, in the plane defined by these directions, in addition to the good mobility, and the associated ability to compensate for ah offset of a strait in the trocar, the connecting sites offset by 90° to each other at the same time provide good axial stability since, in the event of loading, the acting forces are distributed uniformly. 
     A further advantage of using, ring elements is that they are fairly uncomplicated structural components, which simplifies production. 
     In one embodiment of the invention the connections are flexible webs. 
     The advantage of this embodiment is that the narrow and therefore flexible webs are arranged directly on the respective elements without multi-part hinges. In this way, the flexible casing tube thereby formed can be produced as a single workpiece, e.g. from plastic, by an injection moulding technique. Since this does away with subsequent assembling of the ring elements, production is very quick and straightforward. 
     In one embodiment of the invention, the connections are tilting joints. 
     By constructing the flexible casing tube born individual ring elements and connecting these by means of tilting joints, the length of the flexible casing tube can be varied. In the design of a sealing system, this length can therefore be adapted to the length of the expansion, cone and to the length of the seal. With one type of ring element, it is therefore possible to construct casing tubes of different lengths, which means that this embodiment affords great variability. 
     In one embodiment of the invention, the ring elements are higher at the sites of a tilting-joint socket than at those of a tilting-joint insert. 
     The site of the tilting-joint socket in the ring element must have a certain height in order to be able to receive the complete tilting-joint insert. This height is lower at the other parts of the ring element. In this way, the area in which the ring elements can be tilted relative to one another is enlarged, since the distance between the ring elements is greater at the sites lying circumferentially between the tilting joints. In this way, the greatest possible angle of inclination is achieved, which increases the flexibility of the casing tube. As a result, the sealing system can better adapt to any offset of a shaft in the opening of the seal. 
     In another embodiment of the invention, the flexible casing structure widens conically from the proximal end to the distal end. 
     By means of this widening, the casing structure is adapted to the difference in cross section between the annular body of the expansion cone and the in most cases greater cross section of the distal end of the seal. This ensures, on the one hand, a good hold on the distal end of the seal and the trocar housing on which the latter is arranged and, on the other hand, on the expansion cone. This leads to the desired stability. 
     In another embodiment of the invention, the expansion cone is composed of eight to twelve slats, preferably ten slats. 
     The use of eight to twelve slats, preferably ten slats, permits uniform widening of the opening of the seal, since the number of slats used is such that the gaps arising during widening are as small as possible and, in addition, the distance between two slats in the expanded state is small. Thus, even in the expanded state, a uniform and round shape is still formed by the slats at the opening of the seal. This in particular enhances the leaktightness at the opening of the seal during and after the insertion of a shaft. Moreover, however, these slats also have sufficient stability, since they still have a sufficiently great width. They are therefore not damaged or destroyed by insertion of especially sharp-edged instruments, thereby also providing protection of the seal. 
     In another embodiment of the invention, the individual slats narrow from the proximal end to the distal end. 
     In the unexpended state of the expansion cone, the latter should have a surface that is as far as possible closed in order to ensure tied, upon insertion of a shaft, there are no free spares through which the shaft can reach the seal and thus possibly damage the latter. Since a conical structure is present, the circumference at the annular body is much greater than at the level of the opening of the seal. In the case of slats which constantly have the same width along their extent, and in which a closed surface is intended to be present even at the annular body, this has the effect that the slats overlap at the distal end of the expansion cone. This in turn can lead to the slats becoming jammed and thus impeding the function of the expansion cone. 
     By contrast, the narrowing of the slats means that, in the unexpanded state, there can be no undesired overlapping or jamming of the individual slats. This guarantees the unimpaired functioning of the expansion cone and, despite the continuously decreasing width, an unexpended expansion cone with an almost closed inner surface. 
     In other embodiments of the invention, the slats, the annular body and the casing structure are made of hard plastic. 
     In the present case, the use of hard plastic for the slats, the annular body and the casing structure represents a good compromise, since this provides sufficient stability, e.g. during insertion of sharp-edged instruments, but still permits simple production, for example by injection moulding. 
     In another embodiment of the invention, the seal is made of an elastic material. 
     The use of an elastic material, for the seal permits suitable widening of the opening of the seal by the expansion cone during insertion of the shaft of an instrument and, at the same time, permits optimal sealing of the shaft of such an instrument, by virtue of the tight contact between elastic material and shaft. This is achieved in particular by the fact that the expanded opening of the seal is pressed against the circumference of the inserted shaft by virtue of the restoring force of the elastic material. 
     It will be appreciated that the aforementioned features and those still to be explained below can be used not only in the respectively cited combination but also in other combinations or singly, without departing from the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described and explained in more detail below on the basis of a number of selected illustrative embodiments and with reference to the attached drawings, in which; 
         FIG. 1  shows a perspective side view of a medical instrument with a flexible sealing system, 
         FIG. 2  shows a cross section along the line II-II in  FIG. 1 , 
         FIG. 3  shows a sealing system of the medical instrument, viewed from the proximal direction, 
         FIG. 4  shows a perspective view of a flexible casing tube of the sealing system, 
         FIG. 5  shows a cross section along the line V-V in  FIG. 3 , 
         FIG. 6  shows a perspective view of an expansion cone, 
         FIG. 7  shows a perspective view of a seal, 
         FIG. 8  shows a sectional view of a sealing system in which the seal surrounds the expansion cone, 
         FIG. 9  shows a perspective view of a flexible casing tube with tilting joints, 
         FIG. 10  shows a sectional view of a sealing system with a double ball bearing as a casing structure, 
         FIG. 10   a  shows a seating system as in  FIG. 10 , but with the casing structure deflected, 
         FIG. 11  shows a perspective exploded view of the double ball bearing from  FIG. 10 , 
         FIG. 12  shows a perspective view of an expansion cone with slats that comprise a spherical head, 
         FIG. 13  shows a perspective view of an individual slat comprising a spherical head, 
         FIG. 14  shows a sectional view of the sealing system with double ball bearing and an applied shaft, 
         FIG. 14   a  shows a sectional view of the sealing system with double bad bearing, with the shaft inserted. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A medical instrument shown in the figures is designated in its entirety by reference number  10 . 
     The medical instrument  10  shown is a trocar and has at its distal end a trocar sleeve  11 , formed here by a cannula  12 , at its centre a trocar housing  27  and, arranged at the proximal end of the latter, a sealing system  18 .  FIG. 1  also shows a valve  17 , which is arranged on the trocar housing  27  and which can serve, for example, as an admission line for gases. These axe used to perform insufflation of the operating site, in order thereby to obtain better access to the organs, vessels, tissues or the like, on which the operation is to be performed. In order to avoid undesired escape of the gases through the trocar in the proximal direction, a self-closing obturator  29  is arranged in the distal direction from the sealing system  18  ( FIG. 2 ). It closes the proximal opening as soon as there is no shaft inserted into the medical instrument  10 . 
     As can be seen from  FIGS. 1 ,  2  and  5 , the scaling system  18  comprises a seal  14 . The seal  14  is designed as a pot-seal. The pot-seal has a peripheral edge designed as a sealing edge. An opening  16  is provided in the bottom area of the pot-seal. The sealing edge  37  of the lade is fastened by a fastening ring  36  to a seal holder  28 , with which the sealing system  18  is mounted on the trocar housing  27 . The seal  14  extends in the proximal direction away from the seal holder  28  and in so doing narrows. At its proximal end, the seal  14  has a socket  30  that surrounds this opening  16  ( FIGS. 5 and 7 ). An expansion cone  20  is secured on the socket  30  and extends in the proximal direction away from the seal  14  ( FIG. 5 ). 
     As can be seen from  FIGS. 5 and 6 , this expansion cone  20  is composed of an annular body  24  on which slats  22 , oriented in the distal direction, are mounted pivotably by means of film binges  34  in a ring shape. At the distal end, these slats  22  have codpieces  32  that are connected with a form fit to the socket  30  of the seal  14 . The expansion cone  20  acquires its corneal shape as a result of the difference in cross section between the annular body  24  and the socket  30 . The slats  22  narrow front the proximal end to the distal end in such a way as to provide a uniform and almost closed inner surface of the expansion cone  20  in the unexpanded state. 
     The connection between the slats  22  and the seal  14 , wherein the codpieces  32  are fitted in the socket  30 , means that when a shaft is inserted, the slats  22  are initially forced radially outwards, as a result of which the opening  16  of the seal  14  is at the same rime expanded, but without being expanded directly by the shaft. 
     The assembly of the seal  14  and of die expansion, cone  20  is enclosed by a casing structure designed as a casing tube  26 . For this purpose, the casing tube  26  is connected at the distal end to the seal holder  20  and at the proximal end to the annular body  24  ( FIG. 3 ). The casing tube  26  is composed of individual ring elements  38 , which are interconnected via webs  40  lying radially opposite each other ( FIG. 4 ). To obtain a flexibility of the casing tube, the latter is made of a sufficiently elastic material, to ensure a flexibility of the webs  40 , and the webs  40  are in each case also offset by 90° from one to the next pair of ring elements. 
     An additional cap (not shown here) having a continuous outer surface can also be arranged around the casing tube  26 . In this way, the penetrable casing tube  26  is closed off, such that no contaminants can make their way into and settle within the space between the casing tube  26  and the expansion cone  20  and seal  14 . 
     In contrast to the previously described variant in which the expansion cone  20  extends in the proximal direction away from the proximal end of the seal  14 , the pot-seal  66  in the illustrative embodiment in  FIG. 8  is arranged such that it narrows from the proximal end to the distal end and in so doing surrounds the expansion cone  20 . For this purpose, it is secured by a fastening ring  68  to a trocar housing  64 , on which the annular body  24  of the expansion cone  20  is also secured at the proximal end. The distal end of the seal  66  forms an opening  70  surrounded by a socket  72 . Analogously to the previously described illustrative embodiment, the end pieces  32  of the slats  22  are arranged with a form fit in the socket  72 . 
     Another illustrative embodiment of a flexible casing tube is shown in  FIG. 9 . In contrast to the casing tube  26  shown in  FIG. 4 , which can be produced as a single part by means of an injection moulding technique, for example,  FIG. 9  shows a casing tube  73  composed of separate ring elements  74 . These ring elements  74  have two different sides. Whereas one side has two tilting-joint sockets  80 , the other side has two tilting-joint inserts  78 . The tilting-joint inserts  78  and the tilting-joint sockets  80 , respectively, are arranged radially opposite each other. The tilting-joint socket  80  and the tilting-joint insert  78  on one ring element  74  are arranged in a circle and offset by 90° to each other. 
     As is shown in  FIG. 9 , several ring elements  74  are interconnected by connection of the tilting-joint inserts  78  of one ring to the tilting-joint sockets  80  of another ring. In this way, the casing tube  73  is formed which, with its connections between the tilting-joint inserts  78  and tilting-joint sockets  80 , resembles the webs  40  between the ring elements  38  of the casing tube  26  ( FIG. 4  and  FIG. 9 ). The tilting-joint insert  78  and the tilting-joint socket  80  thus form a tilting joint  76 , which is responsible for the flexibility of the casing tube  73 . 
     To obtain the greatest possible range of mobility, the ring element  74  is higher at the tilting-joint sockets  80  than at the sites of the tilting-joint insert  78  ( FIG. 9 ). The ring element  74  can thus be pivoted further about the axis formed by the radially opposite tilting joints  76 . A first ring element  74  can thus be pivoted, at the site of the tilting-joint socket  80 , to a second ring element  74 ′ further than if the latter at the site of the tilting-joint insert  78 ′ were to have the same height as at the site of the tilting joint  76 . 
     Another illustrative embodiment of a casing structure is shown in  FIG. 10 . 
     This casing structure is a double ball joint  41  and is composed of a seal holder  50 , a middle part  52  and a ball socket  54 . The seal holder  50  has a spherical recess  56  into which the middle part  52  is fitted. For this purpose, the middle part  52  in turn has two ball inserts  60  and  62 . 
     The ball insert  60  is arranged in the spherical recess  56  and is movable in the latter. The ball socket  54 , with a spherical recess  58 , is arranged, movably on the proximal end of the ball insert  62  ( FIGS. 10 and 11 ). 
     This device forms the casing structure for an arrangement of expansion cone  20  and seal  42  comparable to the sealing system  18  from  FIG. 5 . Here, a sealing edge  48  of the seal  42  is secured on the seal holder  50 . At the proximal end, the seal  42  has a socket  46  in which the endpieces  34  of the slats  22  are arranged with a form fit. Moreover, at the proximal end, the seal  42  has an opening  44  and, between the opening  44  and the surrounding socket  46 , a sealing lip  45 . 
     The proximal end of the ball socket  54  is connected to the annular body  24  of the expansion cone  20 . 
     If a force is applied, to the sealing system in the direction of the arrow  63 , for example by the oblique offset of a shaft of smaller cross section, the expansion cone  20  moves along with the shaft in a movable casing body of this hind ( FIG. 10   a ). By means of the movement of the expansion cone  20  in the direction of the arrow  63 , the ball socket  54  connected directly thereto is also similarly moved. This is made possible by the ball socket  54  being arranged, pivotably on the middle part  52 . The latter in turn also moves to a certain extent, since if is arranged pivotably on the seal holder  50 . 
     During such a movement of the expansion cone  20 , the connection between the slats  22  and the socket  46  ensures a corresponding deformation of the seal  48 . The result of this is that the shaft, despite the offset, has a central position in the opening  44  of the seal  48  and does not became wedged in the opening  44  and does not cause any loss of leaktightness. By means of the double hall joint  41 , the sealing system thus adapts to any offset of a shaft in the medical instrument. 
     The same also applies to the flexible casing tubes  26  ( FIGS. 1-5 ) and  73  ( FIG. 9 ). 
     Another illustrative embodiment of slats is shown in  FIG. 13 . A slat  84  shown there has an endpiece  89  at the second distal end and a spherical head  86  at the first proximal end. 
     This spherical head  86  serves for movable connection of the slat  84  to an annular body  82 . For this purpose, the annular body  82  has openings  88  into which dm spherical heads  86  can be inserted. It is conceivable for the slats to be inserted in the mariner of a catch mechanism and also a simple engagement mechanism. For the latter alternative at least, a covet ring (not shown here) would also be required, to prevent the slats  84  from falling out of the annular body  82  ( FIG. 12 ). 
     In this way, an expansion cone  81  is obtained similar to the expansion cone  20  with the film hinges  34  in the previously mentioned illustrative embodiment. Similarly to the latter, the slats  84  also narrow from the proximal end to the distal end. 
     The way in which the above-described scaling systems function is now shown, in  FIGS. 14 and 14   a , taking the example of the sealing system with the double ball joint  41  from  FIG. 10 . 
     A shaft  90  is inserted from the proximal direction through the annular body  24  into the sealing system ( FIG. 14 ). This shaft  90  abuts with its distal end against the slats  22  of the expansion cone  20 . As it continues to move in the direction indicated by the arrow  92 , it is guided in the direction of the opening  44  by the slats  22 . 
     Since the distal end of the shaft  90  tapers to a point, its diameter at the level of the opening  44  increases as it continues to move in the direction indicated by the arrow  92 . This has the result that the endpieces  34  of the slats  22  are forced further outwards. This is indicated by the arrows  96 . On account of the form-fit connection between the endpieces  34  and the socket  46 , the seal  42  is therefore also widened at its opening  44  in the direction indicated by the arrows  96 . The widening of the opening  44  by the shaft  90  is thus effected by way of the slats  22 . 
     By virtue of the sealing lip  45  surrounding the opening  44 , and of the continuous pressure directed counter to the expansion and provided by the restoring force of the elastic material of the seal  42 , the entire system is permanently sealed off during the insertion of the shaft  90 , as is shown in  FIG. 14 . 
     The state of maximum widening shown in  FIG. 14   a  is reversible in this example by movement of the shaft  90  in the direction indicated by the arrow  94 . 
     By virtue of the restoring force of the elastic material of the seal  42 , the latter, as has already been mentioned, exerts a constant pressure on the shaft  90  at the opening  44 . When the diameter of the shaft  90  decreases at the level of the opening  44  during the movement in the proximal direction, the diameter of the opening  44  also decreases. This is indicated by the arrows  98 . Moreover, because of their connection to the seal  42  via the socket  46 , the slats  22  are also pressed against the shaft  90 . The slats  22  and the seal  42  thus once again reach their starting position, as can be seen in  FIG. 10 .