the following description of a preferred embodiment of the ring according to the invention , will highlight other remarkable features . this detailed description is given with reference to the attached figures in which : fig1 a & amp ; 1b represent perspective views of the ring according to the invention , deflated and in the closed and open positions respectively . fig2 a , 2b & amp ; 2c represent top views of the ring according to the invention , at rest and respectively in closed ( 2 a ) and open positions according to a preferred embodiment ( fig2 c ) and according to an embodiment variant ( fig2 c ), ready to be positioned around the duct . fig3 is a longitudinal cross - sectional view along the cutting plane iii - iii of fig2 a , 2b or 2c . fig4 a & amp ; 4b are front views of the ring shown in fig2 a & amp ; 2b or 2c respectively . fig4 c is a longitudinal cross - sectional view along the cutting plane iv - iv of fig3 , fig5 a and 5 b are top views of another embodiment of the ring with closing means capable of being separated from one another , after the ring is implanted and closed around a biological duct , by over - inflation of the inner chamber , lips of closing means being joined to one another by a tongue attached to one of the lips and friction fitted in a through hole of the other lip , fig5 c is a top view of another embodiment of the ring with closing means capable of being separated from one another , after the ring is implanted and closed around a biological duct , by over - inflation of the inner chamber , lips of closing means being joined to one another by a tongue attached to one of the lips and snap fitted in a through hole of the other lip . as shown in the attached figures the ring ( 1 ) according to the invention is a ring that can be inflated and deflated so as to vary its inner diameter ( ø i ) so as to be able to compress and release the segment of biological duct for example of blood vessel such as the portal vein , around which said ring ( 1 ) is intended to be implanted and closed for controlling the flow circulating in the duct / vessel ( 2 ) represented by dot - and - dash lines in the figures . an outer belt ( 3 ); an inner chamber ( 4 ) that can be inflated and deflated ; a flexible inflation / deflation tube ( 5 ). the outer belt ( 3 ) has a substantially constant inner diameter and outer diameter . this outer belt ( 3 ) is similar to an open collar ( fig1 b , 2b , 2c & amp ; 4b ) the 2 free ends of which have closing means ( 7 ) comprising two outer lips ( 3 1 , 3 2 ) extending in the centrifugal direction and having faces ( 3 3 , 3 4 ) opposite one another in the open collar ( fig1 b , 2b , 2c & amp ; 4b ) and in contact with one another in the closed collar ( fig1 a , 2a & amp ; 4a ). as shown in fig2 a , 2b , 2c and 3 . these lips ( 3 1 , 3 2 ) each comprise at least one , in the case in point one , perforation ( 3 5 ), allowing the passage of at least one suture ( not shown in the drawings ) preferably resorbable , in order to ensure the closing ( fig1 a , 2a & amp ; 4a ) of the ring ( 1 ) after implantation around the vessel ( 2 ) the flow rate of which is to be regulated . this suture completes the closing means ( 7 ). advantageously , this suture is selected in order to break in the event of overpressure of the inner chamber ( 4 ) of the ring ( 1 ). this arrangement is a safety feature for preventing a stenosis of the duct , which could have irreversible consequences for the patient . this arrangement also allows the surgeon to open the ring ( 1 ) by over - inflation , before proceeding to remove this ring ( 1 ). this outer belt ( 3 ) is made of a semi - rigid material of hardness d1 and selected from the group of biocompatible elastomers , comprising or , even better , constituted by silicone elastomers or analogues . the inner chamber ( 4 ) is an inflatable and deflatable balloon having , at rest and in the closed position ( fig2 a ), a diameter ( ø ir ), which corresponds to the minimum diameter value (+/− 10 %) desired for use , namely a diameter which restricts the diameter dc of the duct around which it is positioned as soon as it is put in place . in the case of the human portal vein , the normal diameter or maximum value d vpn before reduction is , for example , comprised between 10 mm and 20 mm . the ring put in place and locked around the portal vein has an inner diameter ø ir , which determines a reduction of the portal flow rate preferably by at the most 50 %. under the effect of the inflation , the inner chamber ( 4 ) increases in volume in a centripetal direction , which reduces its inner diameter ø 1 . the deflation produces a reduction in the volume of the inner chamber ( 4 ), in centrifugal direction , in order to compress or release respectively the vessel ( 2 ) of a patient ( e . g portal vein ), around which the ring ( 1 ) is put in place and closed using the means ( 7 ). in the preferred embodiment shown in fig2 b , the open collar constituted by the outer belt ( 3 ) has an opening extending along a narrow channel delimited by the parallel faces 3 3 and 3 4 of the outer lips 3 1 & amp ; 3 2 . in the embodiment variant shown in fig2 c , the open collar constituted by the outer belt ( 3 ) has an opening extending over an angular sector α 3 equal to approximately 10 ° in this example . in this variant , the inner chamber ( 4 ) is an open collar the ends of which delimit an opening extending over an angular sector α 4 equal to approximately 5 °. as shown by the figures , in particular fig3 , this inner chamber ( 4 ) is annular and comprises , in the example shown in the drawings ( fig3 ), an outer wall ( 4 1 ) in contact with and / or firmly fixed to the outer belt ( 3 ) and a curved inner wall ( 4 2 ), the outer wall ( 4 1 ) and the inner wall ( 4 2 ) being connected to one another by lateral faces that are substantially straight in the example selected , but which could be curved and are denoted by the reference numbers ( 4 3 , 4 4 ). the inner chamber ( 4 ) could be toroid - shaped according to a variant . the inner wall ( 4 2 ) forms the inner edge of this inner chamber ( 4 ). this inner edge ( 4 2 ) has a circular shape , when the ring is at rest ( neither inflated : no internal overpressure , nor deflated : no internal low pressure ) in the closed position ( fig1 a , 2a & amp ; 4a ), and not arranged around a duct . according to the invention , this circular shape of the inner edge ( 4 2 ), and , more generally , of the inner chamber ( 4 ) is maintained once the ring is arranged around a duct ( e . g vein ) and during the inflation and deflation operations . this means that the inner chamber ( 4 ) forms no invagination , fold or bulge , either in the rest state , in the inflated state , or in the deflated state . the shape of the inner edge ( 4 2 ) and , more generally , of the inner chamber ( 4 ), remains “ substantially ” flat and circular , once the ring is arranged around a duct ( e . g . vein ), from the inflated rest state to a further inflated state and a deflated state corresponding to the requirements of use . in the case of adjustment of the human portal flow rate , these inflated and deflated states are included , for example , within the following inner diameter ø i limits ( in mm and in increasing order of preference ): [ 5 - 25 ]; [ 6 - 24 ]; [ 7 - 20 ]. as shown in fig2 a , 2b , 2c , 3 , 4c , a radio - opaque band ( 4 ′) is inserted between the inner chamber ( 4 ) and the outer belt ( 3 ), in the outer wall ( 4 2 ). the inner chamber ( 4 ) is , for example , made of a flexible material of hardness d2 and selected from the group of biocompatible flexible elastomers comprising or , even better , constituted by silicone elastomers or analogues . according to a preferred feature of the invention , the hardness d1 of the outer belt ( 3 ) is greater than the hardness d2 of the inner chamber ( 4 ). for example , d1 is comprised between 60 and 100 , preferably 70 - 90 , for example of the order of 80 shore a . according to another preferred feature of the invention , the hardness d2 of the inner belt ( 4 ) is comprised between 5 and 40 , preferably 10 and 30 , and even more preferably of the order of 20 shore a . the flexible inflation / deflation tube ( 5 ) is connected by its proximal end ( 5 p ) to the inside of the inner chamber ( 4 ) and by its distal end ( 5 d ) to inflation means not shown in fig3 . the inflation / deflation tube ( 5 ) is diametrically opposite the opening of the ring ( 1 ) as can be seen in fig1 a , 1b , 2a , 2b , 2c , 3 and 4c . the outer belt ( 3 ) has an end piece ( 6 ) which extends towards the outside and which receives the proximal end ( 5 p ) of the inflation tube ( 5 ). this inflation tube ( 5 ) can be equipped with a plastic non - return valve . the inflation tube ( 5 ) can be made of the same material as the inner chamber ( 4 ), for example , with a hardness d3 comprised between d1 and d2 , e . g . of the order of 60 shore a . the inflation / deflation means ( not shown in the drawings ) are constituted for example by a syringe , preferably a screw syringe making it possible to make precise inflation / deflation adjustments by injection / tapping of the inflation / deflation fluid . the ring ( 1 ) according to the invention can be put in place around the vessel ( 2 ) by the standard surgical route ( laparotomy ) or by the coelioscopic route . the closing of the ring ( 1 ) is carried out by suture with resorbable sutures , though the perforation ( 3 5 ) of the inner chamber ( 3 )— closing means ( 7 )—. the ring ( 1 ) thus positioned has a reduced inner diameter ( ø ir ) which restricts the vessel ( 2 ) to the smallest reduced diameter required for use ( dvpr ) and thus limits the flow rate or pressure , for example blood , to a given level dependent on ø ir . the practitioner then proceeds to adjust the flow rate and / or pressure , by inflation / deflation . in the case of hepatectomy or liver transplant , this adjustment aims to maintain an intrahepatic pressure less than or equal to 20 mm hg , preferably 15 mm hg . ø i is gradually increased by deflation . d vp and with it the flow rate and / or the blood pressure in the portal vein therefore also increase ( s ) gradually , until d vp , reaches d vpn ( normal diameter or maximum diameter of the portal vein ). the time taken for this rise of d vpr to d vpn is that which is necessary for hepatic parenchyma in order to recover a capacity to contain the intrahepatic pressure below 20 mm hg , preferably below 15 mm hg , for the pressure and / or the flow rate downstream of the ring , corresponding to a portal diameter equal to d vpn . the ring according to the invention , once closed by a suture or sutures , preferably bioresorbable , can be reopened by over - inflation of the inner chamber , which causes the suture or sutures to break . after opening the ring ( 1 ), the practitioner can also take advantage of the over - inflation of the ring ( 1 ), in order to keep the free ends of the ring ( 1 ) apart from each other and thus facilitate its extraction . this has the advantage of avoiding further anaesthesia and its associated risks . fig5 a , 5b and 5c show embodiments of the ring according to the invention wherein the lips of the closing means are capable of being separated from one another , after the ring is implanted and closed around a biological duct , by over - inflation of the inner chamber . in the embodiment illustrated on fig5 a and 5b , the closing means comprise one perforation 3 5 ′ arranged on the face 3 3 , forming a contact surface , of a first 3 1 of the lips and one protrusion 8 protruding from the face 3 4 , forming a contact surface , of a second 3 2 of the lips . in particular , the perforation 3 5 ′ is a through hole , for example of circular cross - section , formed in the first lip 3 1 and the protrusion 8 is a tongue extending from the contact surface 3 4 of the second lip 3 2 . as previously mentioned , the first 3 1 and second 3 2 lips are formed of deformable material , and especially elastomeric material , such as silicone . the tongue is made in one piece with the second lip 3 2 so as to be elastically deformable . the tongue is for example cylindrical of circular cross - section and has a length measured perpendicularly to the second lip 3 , from which it extends . the tongue comprise a fitting portion 8 a attached to the contact surface face 3 4 of the second lip 3 2 and sized , in terms of diameter and length , to be retained in the through hole of the first lip 3 1 by friction fitting . the friction fitting resulting from the combination of sizes and material is selected to be released in the event of overpressure in the ring . the tongue is also provided with an extension adjacent the fitting portion 8 a opposite the second lip 3 2 . the extension has a conical shape with a diameter reducing from the base adjacent the fitting portion 8 a to a tip . the extension provides an extra - length able to pass through the perforation 3 5 ′ and thereby forms a grasping portion 8 b enabling the used to grasp the tongue so as to pull the fitting portion 8 a within the perforation 3 5 ′. the tongue and the through hole could have any other suitable cross section , preferably complementary to one another . the embodiment illustrated on fig5 c differs from that of fig5 a and 5b in that the tongue 8 ′ comprises an enlarged portion 8 a ′ sized to rest on a surface of the first lip 3 1 opposite the contact face of the first lip 3 1 when the ring is closed , thereby providing a snap - fitting . the enlarged portion has a transverse dimension greater than that of the through hole and , in particular , a transverse dimension that is 5 % to 20 % greater than that of the through hole . in the illustrated embodiment , the fitting portion of the tongue 8 ′ attached to the contact surface of the second lip 3 2 is narrower that the through hole of the first lip 3 1 . the fitting portion may then be arranged within in the through hole without contacting walls of the through hole . however , the fitting portion could be otherwise configured so as to provide a friction fitting with the through hole . as in the embodiment of fig5 a and 5b , the tongue 8 ′ may comprise a grasping portion adjacent the fitting portion opposite the second lip 3 2 . the invention is not limited to the disclosed tongues and through holes . the closing means could comprise any other kind of protrusion and perforation configured so that the protrusion is retained in the perforation by fitting such as force fitting , friction fitting , snap fitting and others , the fitting being selected to be released in the event of overpressure in the ring .
the invention relates to a perivascular ring having an inner diameter adjustable by inflation / deflation and adapted to be implanted and closed about a vessel for controlling the inner diameter of said vessel and thus the flow and / or pressure of a fluid flowing in said vessel . the ring of the invention is capable of regulating blood flow to the liver , in particular after an hepatectomy or hepatic transplant , and to substantially improve the survival chances of the patient . the ring according the invention has an adjustable inner diameter for implantation and locking about a vessel .