by way of illustrating and providing a more complete appreciation of the present invention and many of the attendant advantages thereof , the following detailed description is given concerning the novel implantable body fluid control device and uses thereof . referring now in more detail to the drawings , in which like numerals refer to like parts throughout several views , fig1 - 4 show a body fluid flow control device according to the present invention . the body fluid flow control device comprises a first engaging element 102 and a second engaging element 104 . when the first engaging element 102 is coupled with the second engaging element 104 , an inner diameter is formed which is suited for fitting around a host body canal , i . e ., any tube or vessel v within the human or animal body , such as the urethra . the body fluid flow control device also comprises a locking mechanism 106 for locking the first and second engaging elements 102 and 104 together . the locking mechanism 106 may be of any suitable form . in the illustrated embodiment , locking mechanism 106 is in the form of locking pins 108 located on the first engaging element 102 and locking holes 110 located on the second engaging element 104 . in the illustrated embodiment , two locking holes 110 are provided on each side of engaging element 104 . each locking pin 108 is capable of being attached to either of the locking holes 110 . the inner diameter formed between parts 102 and 104 may thus be adjusted for use with different sized vessels . it should be understood that any other equivalent locking mechanism can be used for this purpose . alternative locking mechanisms contemplated by the present invention include , but are not limited to , the use of a strap and snap pins or interconnecting molding on the first and second engaging elements 102 and 104 . the body fluid flow control device of the present invention preferably further includes a piston - like or plunging member 112 located within the inner diameter formed by the coupling of the first and second engaging elements 102 and 104 such that the plunging member 112 may apply pressure against a body canal or vessel , such as a urethra . as can be seen most clearly from fig2 and 15 , plunging member 112 may have a curved profile such that only outer edges of the plunging member contact the vessel surface in use . this substantially reduces the likelihood of necrosis of the tissue of the vessel because it allows pressure to be placed on the vessel over a smaller area than would be possible with a flat plunging member . the curved profile of plunging member 112 may be provided on a removable plunger head , so that a surgeon may select an appropriately sized plunger head for the size of the vessel . it should be appreciated that the fluid flow control device may take other forms than that illustrated . for example , instead of a plunging member provided in two engagement members , one of the engagement members could be moveable with respect to the other to compress the vessel in order to restrict fluid flow therein . alternatively , a fluid flow control device in the form of an artificial external annular sphincter or other means for compressing the vessel may be applied to the vessel . apertures 113 may be provided in first engaging element 102 . the apertures 113 permit tissue growth therethrough from and to the surface of the vessel in order to anchor the body fluid control device onto the vessel . further apertures ( not shown ) may be provided to allow dissolvable sutures to be used to secure the engaging element to the vessel on a temporary basis , until the engaging element is completely anchored in place by the tissue growth . alternatively , the material of the engaging element may be such as to allow suturing therethrough , or the engaging element may be otherwise attached to the vessel . it has been found that tissue growth is achieved within a few weeks of implantation of the device into a host body and so it may also be possible to implant the device without any form of attachment to the vessel , and to simply let the tissue growth firmly attach the device to the vessel over time . all components of the device are made from biologically inert and compatible materials . for example , the fluid flow control device may be made of polypropylene , silicone , titanium , stainless steel and / or teflon . an actuating member is utilized by the body fluid flow control device of the present invention to bias the plunging member 112 to apply pressure against the body vessel when the body fluid flow control device is in the closed position , and to pull the plunging member 112 away from the vessel to open the device . the actuating member may comprise a cable 114 covered by a protective sleeve or sheath 116 , the cable 114 having a first end 118 and a second end 120 . cable 114 is preferably a braided stainless steel cable , although any suitable material may be used . protective sleeve 116 is preferably made from a bio - compatible material having non - stick properties to discourage tissue growth thereon . a suitable material is teflon . the cable 114 may be slidably moveable within sleeve 116 , or cable 114 and sleeve 116 may be slidably moveable together . the first end 118 of the cable 114 runs slidably through an aperture ( not shown ) in the second engaging element 104 and is attached to the plunging member 112 . a collar 122 is provided around the sleeve 116 where it passes through the aperture in the second engaging element 104 , in order that any tissue growth on and around second engaging element 104 does not interfere with the movement of sleeve 116 through the aperture , if the sleeve 116 is designed to move with cable 114 . if cable 114 is slidably moveable within sleeve 116 , collar 122 prevents tissue ingress into the end of sleeve 116 . fig5 - 9 illustrate a control box for the fluid flow control device that is connected to end 120 of cable 114 . the control box comprises a housing 202 , a motor 204 having a worm gear 206 , a spring 208 and bellows 210 to provide a seal around sleeve 116 . the housing 202 may be made of polypropylene or any other suitable biologically inert material . batteries 212 are also provided , which should preferably be suitable for implantation in the body , such as batteries manufactured by wilson greatbatch ltd , of clarence , n . y ., usa . an operating mechanism ( not shown ) may be provided in the control box , or may be implanted separately in the host body in an easily accessible place . the arrangement of the control box and cable 114 allows the control box to be implanted in the body separately from the fluid flow control device . for example , the control box may be implanted close to the patient &# 39 ; s skin in their abdomen , with the cable 114 and sleeve 116 extending from the control box 202 to the fluid flow control device that is implanted around the urethra or other body vessel . cable 114 is attached at end 120 to a nut 216 which is located in the interior of a slidably moveable casing 214 in housing 202 . spring 208 is also located within casing 214 , which has a threaded aperture 218 to allow worm gear 206 to pass into the interior of casing 214 . spring 208 is interposed between the motor 204 and cable 114 in order to provide a coupling for selectively transmitting axial movement from the motor 204 to the cable 114 and hence to the body vessel v , the operation of which is described with reference to fig7 to 9 below . in the illustrated embodiment , the motor 204 acts on casing 214 to move spring 208 and cable 114 by means of the nut 216 . however , any suitable compressible member may be used in the casing 214 to cushion the vessel from the action of the motor , for example , a resiliently deformable material may be used , or a compressible fluid such as a gas could be used if casing 214 was suitably sealed . alternatively , a spring or other compressible member may be connected directly to or inserted in cable 114 . such an arrangement would preferably use a compressible member that was stiff enough so that pushing and pulling motions were still imparted to the cable 114 on operation of the motor . the slidable casing 214 and worm gear 206 allow axial movement to be imparted to cable 114 by motor 204 , but it should be appreciated that any suitable axial actuation of cable 114 may be used . for example , the motor 204 may have an axially moveable actuator , or suitable gearing could be provided to act on a toothed rack or other axially moveable element . alternatively , the cable could have a flexible end that may be wound around an axle in housing 202 . the sleeve 116 containing cable 114 should be sealed to housing 202 to prevent ingress of body fluids from damaging the motor and other components of the control box . any suitable seal may be used , but it should be noted that where sleeve 116 is designed to be slidably moveable , it is not possible to seal tightly around sleeve 116 , as the sleeve needs to be axially moveable in order to impart movement to plunging member 112 . one method of sealing sleeve 116 to housing 202 is to use a bellows mechanism . a suitable bellows mechanism 210 is illustrated in fig7 - 9 . bellows 210 is designed so that as sleeve 116 moves axially , bellows 210 expands or collapses in on itself so that fluid that seeps into housing 202 around sleeve 116 is captured by bellows 210 , and can be forced back out of the housing 202 when the device is moved to a closed position . the sleeve 116 may be sealed to bellows 210 and housing 202 by means of a threaded bolt 220 , and a nut 222 . bolt 220 is passed through an aperture in housing 202 with its head 224 in the interior of the housing . sleeve 116 passes through and is a close fit with a central bore 226 in bolt 220 . bellows mechanism 210 is generally tubular and is sealed to the underside of head 224 of bolt 220 by an o - ring seal 228 . as the nut 222 is tightened on bolt 220 , compression of the o - ring seal 228 causes a tight seal to prevent ingress of fluid into housing 202 around the exterior of bolt 220 . bellows 210 extends around the head 224 of bolt 220 and is sealed to sleeve 116 in the interior of housing 202 by a tightly wound spring 230 . the spring 230 may be placed onto the bellows 210 before the sleeve 116 is forced through the bellows 210 and spring 230 in order to obtain the tightest seal possible . other methods of sealing bellows 210 to sleeve 116 include cable clamps , c - clips , adhesive , etc . a reinforcing ring 234 is provided on one surface of bellows 210 , to ensure that the bellows 210 collapses correctly as the sleeve 116 is moved axially . the reinforcing ring 234 may be a thickened area in the wall of the bellows 210 , or may be a separate ring that is attached to the bellows , by gluing or any other suitable means . instead , or in addition to , the reinforcing ring 234 , the bellows may be pleated or folded in order to ensure correct folding when the fluid flow control device is moved to the closed position . it should be noted that bellows 210 can be of any suitable shape , provided that a seal is made at the housing and around the sleeve , and that bellows allows movement of the sleeve into and out of the housing . for example , bellows 210 may be a simple tubular shape , with ends of the tube being sealed to the housing and sleeve . alternatively , bellows 210 may be of a frusto - conical shape , or a more complicated shape such as a bell - shape or could be folded or pleated . the seal to the housing could be close to the aperture in the housing through which the seal extends , as illustrated , either inside the housing or outside the housing . alternatively , the seal could be made to the wall of the housing , around or behind the bolt 220 . it is possible to seal the sleeve 116 and the housing 202 without using a bellows mechanism , but it has been found that energy losses are created as movement of the sleeve 116 creates friction against the seal . this can cut the battery life of the motor by up to ⅓ . for example , a flexible annular ring may be sealed between the sleeve 116 and the housing 202 , the annular ring stretching as the sleeve is axially moved . alternatively , a series of seals may be provided along sleeve 116 , each seal preventing some fluid ingress to housing 202 . control circuitry ( not shown in fig7 - 9 ) is provided , which operates the motor on receipt of a signal from an operating mechanism . any of the several well - known control devices can be used to control the operation of the body fluid flow control devices of the present invention by a user so long as the objectives of the present invention are not defeated . suitable operating mechanisms include radio - control devices , or a magnetic devices that can be sensed by the control circuitry . with a magnetic device , the user may be provided with a separate magnet that they carry with them , and which they position adjacent the skin over the implanted switch when they wish to operate the device . the magnet may be of any suitable shape , and may be shaped for example like a pen or credit card so that its purpose is not immediately apparent to other people . the magnet should have a weak magnetic field so that it must be placed close to the switch in order to operate the device , in order to prevent accidental operation of the device if the magnet is carried in a pocket . alternatively , a touch sensor , infrared , voice or sound activation may be used , or a manually operated switch may be implanted under the skin of the patient . a remotely operated operating mechanism is preferred because the device can be operated without irritation to the skin , as would happen with a manually operated trigger . in the preferred embodiment , a manual override switch may be provided in addition to the remotely operated triggering mechanism . the manual override switch is designed to be used temporarily if the control box fails and the user is not close to a physician &# 39 ; s office or hospital to have the control box changed . the manual override switch may be provided in the control box , and may be sealed from the interior of the control box until the first activation of the switch , for example by a membrane seal . such a use of the manual override switch may eventually allow fluid ingress into the control box , which may then need to be replaced . alternatively , no manual override switch may be provided , which would mean that the user would have to use incontinence pads until the control box could be replaced . the control circuitry controls operation of the motor , and may detect the position of the plunging member , for example , via the position of the casing or via the drag exerted on the motor . preferably , the control circuitry also monitors the level of charge in the battery . the control circuitry can be used to initiate opening or prevent closing of the fluid flow control device if a problem such as low battery or a defective motor is detected , so that the device can be caused to remain in the open position . for example , once the device has been opened , an abutment ( not shown ) may be caused to contact the casing 214 to prevent any further movement thereof . the motor may also be shut off . the device may still be operable by a manual override , as the spring 208 can be compressed and allowed to expand within casing 214 to allow movement of the cable 114 to open and close the device . the control box 202 may also contain components that allow a physician to interrogate the control circuitry by a remote telemetry system without accessing the box itself . such components may be interrogated and / or controlled by radio waves or other interactive signals transmitted and received by the telemetry system , or any other suitable mechanism . this allows the physician to check the charge in the batteries , any internal sensors , to alter the tension in the cable 114 , and to make other suitable adjustments . a pressure sensor may be provided on the plunger 112 to monitor the pressure between the plunger 112 and the vessel v when the plunger is in the closed position . the pressure sensor may also be interrogated by the telemetry system , which can then be used to alter the settings for the control device . for example , the number of turns that the motor 204 causes worm gear 206 to make on each operation of the device may be altered in order to set the correct distance of travel of the cable 114 , and hence plunger 112 for any particular patient so as to alleviate any excess pressure exerted on the vessel v . in addition , the telemetry system may include control commands to cause the motor to open and close the body fluid flow control device , either as an override system to the normal operating means , or in addition to the normal operating means in order to test the device in situ . if the control box causes the device to fail or remain in the open position if a problem is detected , this will simply mean that the patient will return to the condition that they were in before implantation of the device , in other words , in a condition of incontinence . if the device failed in the closed position , the patient would need to be catheterized . however , a manual override system would allow the patient to operate the system manually for a considerable period of time or until medical aid was obtainable . actuation of the device is described with reference to fig7 to 9 . in the open position shown in fig7 , the motor 204 has operated the worm gear 206 to draw casing 214 towards the motor 204 . this pulls nut 216 along with the casing 214 , and thus acts on cable 114 to pull the plunging member 112 away from the vessel v . bellows 210 is also at its fully extended position . in order to close the fluid control device , the motor 204 is activated to turn worm gear 206 in the opposite direction to that used to open the device . as worm gear 206 is operated , casing 214 is moved away from the motor 204 , spring 208 pushing on nut 216 to bias plunging member 112 against the vessel v , as shown in fig8 . as the motor 204 is operated further , the vessel v prevents plunger 112 moving , and prevents movement of cable 114 and hence nut 216 , due to the increased force needed to move cable 114 against the vessel v when the vessel v is already closed . nut 216 presses against spring 208 , causing compression of the spring 208 , as shown in fig9 . it can thus be seen that any further movement of worm gear 206 by motor 204 does not result in compression and injury of the vessel v , but the further compression of spring 208 . in this way , axial movement of casing 214 may be selectively transmitted to cable 114 . this protects the vessel v against failure of the device by continuous running of the motor 204 , as the vessel cannot be further compressed due to the interplay between the vessel v and the spring 208 . an alternative embodiment of the control box is illustrated in fig1 and 11 . the control box comprises a housing 902 , a motor 904 having a worm gear 906 , a spring 908 and bellows 910 . batteries 912 are also provided , along with control circuitry ( not shown ). the spring 908 is located in a slidable spring casing 914 . an operating mechanism ( not shown ) may be provided in the control box , or may be implanted separately in the host body in an easily accessible place . the spring , worm gear and motor arrangement are as described for fig5 - 9 , and will not be further described . housing 902 is preferably formed in two pieces , a main body 916 and an end lid 918 . end lid 918 includes a lip 920 that fits inside an end 922 of main body 916 . a groove 924 is provided around lip 920 , in order to receive an o - ring 926 . end lid 918 is also sonically welded to main body 916 in order to provide a good seal . a groove 928 is provided around the exterior of end 922 of main body 916 , in order to allow for ease of removal of lid 918 with a suitable tool when necessary . an interior housing 930 extends along the length of housing 902 , to one side thereof , in order to separate the motor 904 , worm gear 906 , slidable casing 914 , bellows 910 and other moveable parts from the batteries 912 . interior housing 930 has a flange 932 at an end 934 remote from end 922 of main body 916 , with an o - ring groove 936 provided in flange 932 . a set screw 938 is also provided in interior housing 930 , in order to lock motor 904 . electrical contacts 940 extend to motor 904 from end lid 918 . an internally directed collar 942 having an internal thread extends around flange 932 within housing 902 , and interior housing 930 is secured into housing 902 by means of an externally threaded nut 944 which is screwed into place to hold flange 932 in position . nut 944 may have pin holes 946 to allow for tightening thereof . an externally directed collar 948 having an internal thread is also provided in housing 902 , in order to allow the cable 114 to pass into interior housing 930 . sleeve 116 has an end 950 which is attached to a hollow connector 952 having a first end 954 and a second end 956 . at end 954 , connector 952 has backwardly - directed teeth 958 around the circumference thereof which attach to the inside of sleeve 116 adjacent to end 950 , and act to prevent sleeve 116 from being pulled loose . the second end 956 of connector 952 has an external thread 960 , as well as a groove 962 suitable for receiving an o - ring 964 . thread 960 is screwed into the internal thread provided within collar 948 on housing 902 . cable 114 extends into housing 902 through connector 952 , and is attached at its end 120 to a link member 966 which extends into casing 914 and terminates in nut 216 . the connection between cable 114 and link member 966 is shown enlarged in fig1 . the cable end 120 is fitted into a connector piece 968 that has a tapered end 970 and a groove 972 for receiving a sealing ring . link member 966 has an opening 974 for receiving connector piece 968 , opening 974 having an internal shoulder 976 . a metal o - ring 978 is received by shoulder 976 and is held in place by a ring retainer 980 . connector piece 968 is pushed into opening 974 until the metal o - ring 978 seats in groove 972 to form a seal between connector piece 968 and link member 966 . bellows 910 are attached to housing 902 by means of nut 944 screwed into inwardly directed collar 942 . bellows 910 has an end flange 982 , which extends adjacent to flange 932 of interior housing 930 , and has an integral o - ring 984 to seal in o - ring groove 936 of flange 932 so that bellows 910 is tightly sealed to housing 902 by interior housing 930 . bellows 910 is also attached to cable link member 966 by means of a cable link 986 , and has a pleated conical shape above flange 982 so that it may fold easily when compressed . it should be noted that in the embodiment of fig1 , the bellows 910 is not attached to the sleeve 116 , as the sleeve 116 is not axially moveable . instead , cable 114 is axially moveable within sleeve 116 . in this embodiment , bellows 910 may not be necessary , as a good seal may be provided between connector 952 and control box 902 . however , it is advantageous to provide an additional seal , for example using bellows 910 , to prevent fluid ingress into control box 902 . the operation of the control box of fig1 is the same as for the control box of fig5 to 9 , and will not be further described . a further alternative embodiment of a seal for the sleeve and an actuator for the cable is illustrated in fig1 . in the illustrated embodiment , control box 1200 is completely sealed so that no fluid ingress into the box can take place . a hollow cylindrical bore 1202 that is sealed at one end 1204 is formed in control box 1200 . bore 1202 has internal threads 1206 provided adjacent an outer surface of control box 1200 . an end of sleeve 116 is attached to a hollow connector 1208 , connector 1208 having an end 1210 and an end 1212 . end 1210 of connector 1208 is dimensioned to pass into the end of sleeve 116 , connector 1208 having outwardly and rearwardly directed teeth 1214 at end 1210 to engage the interior of sleeve 116 , thereby securing connector 1208 to sleeve 116 . end 1212 of connector 1208 is dimensioned to be slightly larger in diameter than sleeve 116 , and has external threads 1216 . connector 1208 may be screwed into bore 1202 of control box 1200 by means of threads 1216 and 1206 . end 120 of cable 114 is located in bore 1202 , and is provided with a collar 1218 . an annular magnet 1220 is supported by collar 1218 around end 120 of cable 114 . cable 114 is axially moveable within sleeve 116 , and therefore a bellows seal is not necessary around sleeve 116 . in addition , as sleeve 116 is not moveable , tissue growth around the sleeve cannot affect the operation of the device . a motor 1222 has a threaded worm gear 1224 engaged with a casing 1226 through a screw - threaded aperture 1228 located in the bottom of the casing . casing 1226 extends around bore 1202 , and an annular magnet 1230 is supported around the interior of an upper edge of casing 1226 . magnet 1230 is aligned with magnet 1220 located on end 120 of cable 114 . in order to actuate cable 114 to open and close the fluid flow control device , the motor 1222 operates the worm gear 1224 , which moves casing 1226 along the exterior of bore 1202 . magnet 1230 acts through the plastic material comprising bore 1202 , and causes magnet 1220 to track its movement . this in turn causes cable 114 to be axially moved , operating the fluid flow control device . if the motor 1222 continues operating the worm gear 1224 towards the cable 114 when the body vessel has already been closed , the attraction of magnet 1220 for magnet 1230 is not enough to cause the cable 114 to be moved further , due to resistance from the vessel walls , thus preventing potential damage to the vessel . thus , axial movement of casing 1226 is selectively transmitted to cable 114 . in addition , the casing 1226 will come to rest against bore 1202 or an interior surface of control box 1200 , preventing the magnets from getting too far out of alignment . it should be appreciated that a magnetic link between the motor and cable may be achieved in many ways other than that illustrated in fig1 . for example , the magnets need not be annular , but could be placed to one side of the cable . in addition , the magnets need not operate by mutual attractions , but could work by repelling each other to close the vessel , with a spring action or other means operating to open the vessel once the motor - driven magnet was pulled back towards the motor . with a repelling action , magnets could be placed directly on the ends of the cable and an axially movable actuator driven by the motor . an alternative embodiment of a magnetic coupling for selectively transmitting axial movement to the cable is illustrated in fig1 and 14 . these figures illustrate a control box 1300 that is completely sealed . a bore 1302 having a blind end 1304 is provided in the control box 1300 for receiving the end 120 of cable 114 . a connector 1306 is used to connect sleeve 116 to bore 1302 . the connector 1306 has a first end 1308 with rearwardly directed teeth 1310 , a central shoulder 1312 and a second end 1314 having external screw threads 1316 . end 1308 of connector 1306 is pushed into the end of sleeve 116 , the teeth 1310 acting on the inner surface of the sleeve . end 1314 of connector 1306 is connected to control box 1300 by means of an o - ring seal 1318 and an internally threaded nut 1320 which is threaded onto threads 1316 . nut 1320 is welded at 1322 to the control box 1300 to form a tight seal . the cable 114 extends into bore 1302 . a cylindrical magnet 1324 is attached to end 120 of cable 114 by a collar 1326 which is deformed onto the magnet 1324 and cable end 120 for a tight fit . the control box 1300 includes a motor 1328 , a worm gear 1330 and batteries 1332 as described for the fig1 embodiment . a casing 1334 having an annular magnet arrangement 1336 is threaded onto worm gear 1330 , and operates in the same manner as in the fig1 embodiment so will not be further described . control circuitry including ic &# 39 ; s 1338 and other standard components 1340 including resistors and capacitors are also shown . fig1 illustrates an embodiment of a connector joining first end 118 of cable 114 to the body fluid control device . connector 1500 has a first end 1502 having outwardly directed teeth 1504 which grip into the inner surface of sleeve 116 . a second end 1506 of connector 1500 has a collar with inwardly directed threads 1508 which are threaded onto outwardly directed threads 1510 on a collar 1512 attached to the body fluid flow control device . an o - ring 1514 forms a tight seal to the collar 1512 . fig1 also illustrates plunger 112 in detail . plunger 112 includes a perforated metal bracket 1516 attached to a metal collar 1518 . the main body of plunger 112 is formed of silicon that is molded onto the perforated bracket 1516 , the silicon extending through the perforations in the bracket to form a tight fit between plunger 112 , bracket 1516 and collar 1518 . metal collar 1518 may be simply crimped onto end 118 of cable 118 . fig1 illustrates a further alternative method of connecting cable 114 and sleeve 116 to the body fluid flow control device . in the embodiment of fig1 , the fluid flow control device has a collar 1600 with internal threads 1602 . a connector 1604 is used to connect sleeve 116 to collar 1600 . connector 1604 has external threads 1606 , a central collar 1608 and outwardly directed teeth 1610 . it should be noted that connector 1604 may be the same as connector 1306 illustrated in fig1 . this allows for economies in manufacture , as only one type of connector need be provided for both ends of the sleeve 116 . a metal collar 1612 is used to connect the plunger ( not shown in fig1 ) to end 118 of cable 114 . an o - ring 1614 may seal between collar 1612 and connector 1604 . it will be understood that various embodiments of the present invention have been disclosed by way of example and that other modifications and alterations may occur to those skilled in the art without departing from the scope and spirit of the appended claims . thus , the invention described herein extends to all such modifications and variations as will be apparent to the reader skilled in the art , and also extends to combinations and subcombinations of the features of this description and the accompanying figures . although preferred embodiments of the present invention have been illustrated in the accompanying figures . and described in the foregoing detailed description , it will be understood that the present invention is not limited the embodiments disclosed , but is capable of numerous rearrangements , modifications and substitutions without departing from the spirit of the present invention as set forth and defined by the following claims , such as for example those embodiments described in non - provisional u . s . patent application ser . no . 09 / 048 , 823 , filed mar . 26 , 1998 , which is incorporated hereinto in its entirety by reference .
an implantable apparatus and a method for controlling fluid flow within a host body , for example for use as an incontinence device . a constricting member is provided for reducing fluid flow within a body canal when in a closed position , and for allowing fluid flow within the body canal when in an open position . in addition , there is a control mechanism for controlling movement of the constricting member between said open and closed positions . a link member links the constricting member and the control mechanism such that the constricting member and the control mechanism are implantable in different parts of the host body . a coupling for selectively transmitting axial movement to the link member may be provided between the link member and the control mechanism so that the constricting member cannot apply a damaging amount of force to the body canal .