Abstract:
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 (Ø i ) for implantation and locking about a vessel.

Description:
TECHNICAL FIELD 
       [0001]    The field of the invention is that of medical devices that can be implanted by surgical route around a biological duct, in particular a vessel and more particularly a blood vessel such as the portal vein, in order to allow adjustment of the diameter of the duct and therefore of the flow rate of a fluid (blood) capable of circulating therein. 
         [0002]    These implantable medical devices are more precisely vascular rings that can be inflated and deflated using a fluid, so as to adjust their inner diameter and thus the inner diameter of the ducts/vessels around which they are intended to be implanted. 
         [0003]    The invention also relates to the manufacture of such vascular rings and concerns more specifically the moulds and methods for manufacturing the vascular rings involving said moulds. 
         [0004]    The invention also relates to the kit that can be implanted by surgical route and allow control of the inner diameter of a vessel and, as a result, the flow rate of a fluid circulating therein. 
       TECHNOLOGICAL BACKGROUND OF THE INVENTION 
       [0005]    It is known to implant medical devices constituted by inflating banding rings, around blood vessels of patients in order to restrict blood flow, for example on the pulmonary arteries. This is the subject of the patent application US2008/0097947A which discloses an annular banding device for the pulmonary artery, comprising an inflating banding ring intended to be put in place around the pulmonary artery of the patient, an inflation tube connecting the banding ring to an insufflating button. The banding ring is generally C-shaped and comprises an external thin rigid silicone layer and an internal thin silicone layer, forming an inflating balloon. The rigid silicone external layer or wall extends into the end zone corresponding to the opening of the “C” so as to form locking means making it possible to adapt the inflation bandage device to the diameter of the pulmonary artery. The ring also comprises holes for the passage of sutures allowing it to be fixed to the pulmonary artery of the patient. The inflation of this ring leads to the deformation of the thin flexible silicone inside wall in a centripetal direction, which causes a compression of the pulmonary artery and a reduction in its inner diameter. The inflation is carried out using a liquid which is injected using the insufflating button which can also be pulled to allow deflation of the ring. 
         [0006]    This type of inflatable vascular ring exists not only in cardiac surgery but also in hepatic surgery. Thus the PCT application WO2010/102661A describes an implant for controlling the blood flow inside a vessel, namely more precisely the portal vein. This control is particularly critical for the success of liver transplants and major hepatectomies. In fact, it is vital for the patient that blood flow in the portal vein just after the transplantation or hepatectomy is not excessive, at the risk of unacceptably damaging the hepatic graft. This phenomenon is known by the name of “Small For Size (SFS)” syndrome. This syndrome occurs in the case of a portal flow rate greater than 260 ml/min per 100 g of liver and/or a portal pressure greater than 20 mm Hg. It causes a lethal alteration of the liver. 
         [0007]    The perivascular adjustable implant according to WO2010/102661A comprises an inflatable balloon ( 3 ) of open annular shape, arranged inside a non-extendible band ( 4 ). The inflation balloon is connected to an injection chamber by an inflation tube. The non-extendible outer band is equipped with locking means ( 6 ) of the ring or vessel. The inflation and the deflation of the annular inner balloon makes it possible to restrict (inflation) or increase (deflation) the inner diameter of the vessel around which the implant is placed. This implant comprises, on the inside of the inflatable balloon, means for measuring the blood pressure inside the vessel.  FIGS. 2A to 2D  of WO2010/102661A show the change in shape of the inflatable balloon as it is inflated. It appears that the inner wall of the inflatable balloon changes from a circular shape ( FIG. 2A ) to a shape leaving a passage by growing, which is caused by a bulge in the inflation balloon. It is clear that such a compression of the portal vein is equivalent to crushing, causing a stenosis which leads to turbulences in the blood flow resulting in risks of thrombosis. 
         [0008]    This implant according to WO2010/102661A does not therefore allow satisfactory control of the flow rate and/or of the blood pressure inside the vessels, in particular the portal vein. This implant does not provide an effective solution to the problem of SFS syndrome, after a hepatectomy or a liver transplant. 
       OBJECTIVES OF THE INVENTION 
       [0009]    In this context, one of the objectives of the present invention is to provide a sophisticated device for control of the circulation flow rate of a fluid inside a biological duct, in particular of the blood in the portal vein, so as to regulate the flow rate or the blood pressure in the liver, in particular after a hepatectomy or a liver transplant and, as a result, to significantly improve the patient&#39;s chances of survival. 
         [0010]    The present invention also aims to provide a perivascular ring with an inner diameter that can be adjusted by inflation/deflation and is intended to be implanted and closed around a vessel in order to control the inner diameter of this vessel and thus the flow rate and/or the pressure of a fluid circulating in this vessel, this ring having to satisfy at least one of the objectives set out below: 
         [0011]    i to have a behaviour and change in shape for adjustment of the diameter of the vessel, which leads to no crushing of the latter and therefore no stenosis accompanied by secondary effects that are harmful to the patient. 
         [0012]    ii to allow reliable control of the flow rate and/or pressure of the fluid, in particular of the blood, circulating in the duct around which it is implanted. 
         [0013]    iii to be simple to put in place and lock around the biological duct/vessel the flow rate and/or of the internal pressure of which is to be controlled. 
         [0014]    iv to be comfortable and have no harmful effect on the health of the patient. 
         [0015]    v to be biocompatible. 
         [0016]    vi to be secure and reliable, in particular untearable. 
         [0017]    vii to offer optimum locking around the biological duct, for example the vessel, the flow rate and/or the pressure of which is to be controlled. 
         [0018]    viii to be capable of industrial mass production according to stringent standards and at the best cost. 
         [0019]    viii to be radio-opaque at least in part. 
         [0020]    ix to be easily implantable, in a stable, non-aggressive and effective manner in terms of control of the flow rate. 
         [0021]    The present invention also aims to provide a method and a mould for obtaining the ring which is viable and simple to implement on an industrial scale. 
         [0022]    The present invention also aims to provide a kit that can be implanted by surgical route, for controlling the flow rate and/or pressure inside a vessel, comprising a perivascular ring meeting the above objectives as defined in the present disclosure, an inflation/deflation module and optionally a suture for closing the ring, this suture being selected to break in the event of overpressure in the ring. 
     
    
     
       BRIEF DESCRIPTION OF THE INVENTION 
         [0023]    These objectives, among others, are achieved by the present invention which relates to a ring with an adjustable inner diameter Ø i , intended to be implanted and closed around a biological duct, preferably a vessel, in order to control the diameter of this duct and thus the flow rate and/or pressure of a fluid circulating in the duct, this ring comprising:
   an outer belt with a diameter that is substantially constant in the closed position;   an inner chamber that can be inflated and deflated in the closed position, so as to vary its inner diameter Ø i ;   a flexible inflation/deflation tube, one end of which is connected to the inner chamber and the other end of which is intended to be connected to inflation means;
 
the outer belt and the inner chamber forming open collars, at least one of which, preferably that forming the outer belt, is equipped with means for closing the ring around the duct; characterized in that the inner chamber, at rest and in the closed position, has an inner diameter Ø ir  corresponding to the smallest reduced diameter required when in use, for controlling the diameter of the duct.
   
 
           [0027]    The duct is advantageously a blood vessel, such as for example the portal vein. 
           [0028]    The ring according to the invention is a remarkable development of the known implantable perivascular rings intended for controlling the blood flow rate, in particular the portal flow rate and/or pressure. 
           [0029]    Due to its original structure, this ring proposes a novel type of non-traumatic pneumatic or hydraulic modulation of the flow rate or pressure of the fluid, for example the blood, circulating in the duct, for example a vessel. 
           [0030]    This constitutes significant progress towards successful hepatectomies and liver transplants, by offering the practitioner an effective means of combating SFS syndrome. 
           [0031]    This ring is moreover secure, reliable, of a reasonable cost and capable of being produced on an industrial scale in compliance with the required quality and productivity standards. 
           [0032]    The invention also relates to a mould and a method for obtaining this ring, as well as a kit that can be implanted by surgical route, for controlling the flow rate or blood pressure, comprising this ring and an inflation/deflation module intended to be connected to the proximal end of the inflation/deflation tube, in order to allow the in situ injection of an inflation/deflation fluid into the inner chamber or the in situ extraction of an inflation/deflation fluid out of the inner chamber. 
         Definitions 
         [0033]    In the present disclosure, each singular and each plural interchangeably refers to a plural or a singular. 
           [0034]    The definitions which are given below by way of examples, are intended to facilitate the interpretation of the present disclosure. 
           [0035]    “duct” and “vessel” interchangeably refer to a channel in which a biological fluid circulates, for example blood or lymph. 
           [0036]    “closed position” of the ring means that the two ends of the ring are fixed to each other, so that the ring defines a cylinder. 
           [0037]    The “at rest” state of the ring means that the pressures inside and outside the inner chamber of the ring are balanced at the ambient atmospheric pressure. When the ring is positioned and closed around the duct, at rest, it is at least partially inflated so that it restricts the diameter of the duct, compresses it and reduces it. 
           [0038]    The distal end of the flexible tube is its free end situated outside the body of the patient in whom the implant is put in place, i.e. the free end intended to be connected to the inflation/deflation means. 
           [0039]    The proximal end of the flexible tube is the end opposite to its distal end, i.e. the end connected to the ring according to the invention. 
           [0040]    By hardness D1, D2, is meant the Shore A hardness of the material(s) constituting the ring. 
           [0041]    By the smallest reduced diameter required when in use for controlling the diameter of the duct is meant the inner diameter of the inner chamber at rest, i.e. partially inflated, for which the diameter of the duct Dc, on which the ring is intended to be positioned, is restricted and reduced to a minimal value Dcr with respect to the normal diameter Dcn (or maximum diameter) that the duct would have in a “normal state” without this ring around it. For each duct to be enclosed, the Dcr value that the duct must reach once the ring is positioned around it is determined. For example, if the duct is the portal vein, the smallest reduced diameter required when in use for controlling the diameter of the portal vein is the inner diameter Ø ir  of the inner chamber with which the diameter of the portal vein is restricted by 55%, preferably 50% with respect to the natural, normal diameter Dcn of the portal vein with no restriction. It must obviously be borne in mind that the diameter Dc of the duct can also be reduced if necessary, once the ring is positioned around it, by inflation of the inner chamber of the ring or increased by deflation of the inner chamber. By “normal state”, is meant the state of the duct with no restriction and in which the biological fluid circulates at a non-pathological, normal, average biological flow rate. In the normal state, the biological duct has a normal diameter Dcn, which depends on the biological species, sex and age of the individual. 
         Preferred Features and Advantages of the Invention 
         [0042]    The fact that the inner chamber, at rest and in the closed position, has an inner diameter Ø ir  corresponding to the smallest reduced diameter required when in use for controlling the diameter of the duct, makes it possible to define a shape of the inner chamber, with no invagination, bulge or fold, in which the ring reduces, to a certain level, the diameter of the duct, and therefore the flow rate and/or pressure of the fluid circulating in the duct. 
           [0043]    The smallest reduced diameter required for use can be defined by the level of reduction (e.g. expressed as a percentage of reduction) of the diameter of the duct around which the ring is intended to be implanted and locked. According to the invention, this percentage of reduction corresponds to the requirements for use. In particular, as regards the modulation of the flow rate and/or blood pressure, such as in the portal vein, it is provided, according to a remarkable feature of the invention, that the ring has a Ø ir  selected in order to reduce by at the most 55%, preferably by at the most 50%, the diameter of the vessel around which the ring is intended to be arranged and locked. Thus, when the ring according to the invention is positioned and closed around the portal vein, at rest and therefore already partially inflated, the ring restricts the diameter of the vein. It reduces this diameter by at the most 55%, preferably 50%. Depending on the requirement and desired treatment of the patient, it is then possible either to further inflate the ring and thus further reduce the diameter of the inner chamber and as a result the diameter of the vein, or to deflate the ring and increase the diameter of the inner chamber and as a consequence the diameter of the vein around which it is positioned. 
           [0044]    The percentage reduction is adapted depending on the ducts around which the ring is intended to be put in place and also depending on the aim of the operation and of the positioning of such a ring. Thus, in the case of SFS, it is desirable to reduce the diameter of the portal vein by 55% or even 50%. As a general rule, a human portal vein has a diameter of 15 mm (±5 mm). The ring positioned and closed around the portal vein, in a rest position, i.e. inflated (but not to its maximum) must reduce the diameter to 6.75 mm (±2.25 mm) for a 55% reduction of the diameter of the portal vein. 
           [0045]    When the vessel is a vein (flexible wall), the diameter of the vessel is that for which the flow rate of the circulating fluid corresponds to the normal average biological flow rate. 
           [0046]    In practice, during a hepatectomy or a liver transplant, the surgeon puts the open ring according to the invention in place around the portal vein, upstream of the liver, and closes this ring by firmly fixing its ends to each other. The portal vein is thus restricted so that its diameter is reduced by at the most 55%, preferably by at the most 50%. The portal diameter considered is, for example, that corresponding to the normal average portal flow rate in humans, namely 700 ml (+/−200 ml) per minute, i.e. approximately 50 ml/min per 100 g of liver, in a healthy individual; or also approximately 260 ml/min per 100 g of liver, in a patient having undergone a major hepatectomy (80% of the liver removed). This flow rate value of approximately 260 ml/min per 100 g of liver corresponds to the maximal value, below which the patient is exposed to SFS syndrome. 
           [0047]    The practitioner can choose, as a function of the clinical data at their disposal, to further reduce or to increase the portal diameter by inflation or deflation of the inner chamber, in order to fix the portal flow rate at a value that is desirable for the patient, by gradually bringing this value back to normal, whilst taking the patient&#39;s state of health into account. 
           [0048]    This procedure could be applied to other medical or non-medical species, for which the positioning of a perivascular ring is prescribed in order to reduce and then optionally increase the intravascular flow rate. 
           [0000]    The diameter of the biological duct may be reduced using the ring according to the invention, until the duct is obstructed (clamping of the duct). 
           [0049]    According to a preferred embodiment of the invention, the ring is a means intended to be put in place and locked around the portal vein of a patient, upstream of the liver, in order to reduce, by at the most 55%, preferably by at the most 50%, the diameter D vp  of the portal vein, down to a minimal value D vpr  and in order to then allow the modulation of D vp  between D vpr  and its normal diameter D vpn  (or maximum diameter) in which the ring does not reduce D vp , said modulation consisting of deflating the ring in order to increase Ø i  and therefore D vp  from D vpr  to D vpn , so as to reduce the portal pressure downstream of the ring and maintain the intrahepatic pressure at a value less than or equal to 20 mm Hg, preferably at 15 mmHg and thus treat/limit SFS (Small For Size) syndrome, suitable for hepatectomies and liver transplants. 
           [0050]    The invention therefore relates, in particular, to a means for treating Small For Size syndrome suitable for hepatectomies and liver transplants, characterized in that it comprises the ring as defined in the present disclosure. 
           [0051]    The invention also relates to a method for the treatment of Small For Size syndrome suitable for hepatectomies and liver transplants characterized in that it essentially consists of:
       putting in place and locking around the portal vein of a patient, upstream of the liver, a perivascular ring as defined in the present disclosure, in order to reduce by at the most 55%, preferably by at the most 50%, the diameter D vp  of the portal vein down to a minimal value D vpr ;   modulating D vp  between D vpr  and its normal diameter D vpn  (or maximum diameter) in which the ring does not reduce D vp ; said modulation consisting of deflating the ring in order to increase Ø i  and therefore D vp  from D vpr  to D vpn , so as to reduce the portal pressure downstream of the ring and maintain the intrahepatic pressure at a value less than or equal to 20 mm Hg, preferably at 15 mmHg;   gradually bringing D vp  back to its value D vpn  over a sufficient period of time so that the intra-hepatic pressure stabilizes at a value less than or equal to 20 mm Hg, preferably at 15 mmHg;   then unlocking the ring and removing it.       
 
           [0056]    According to a preferred feature of the invention, the inner chamber has no invagination at rest and in the closed position of the ring, and the inner edge of the inner chamber that is intended to be in contact with the duct has a substantially circular, flat shape, with no invagination, fold or bulge. It conforms to the outer wall of the duct on which it is positioned whilst restricting the diameter of the duct. 
           [0057]    Preferably, Ø i  decreases by inflation and increases by deflation. 
           [0058]    The fact that the inner chamber of the ring is inflated at rest in the closed position around the duct and, moreover, that its inner diameter Ø i , decreases by inflation and increases by deflation, makes it possible to safely and reliably control the flow rate and/or the internal pressure of a fluid circulating in the biological duct/vessel around which the ring is put in place in the closed position, limiting the associated risks of stenosis and thrombosis. 
           [0059]    According to a notable feature of the invention, the ring is characterized in that the inner chamber forms no invagination (nor fold), nor bulge and has a “substantially” circular inner shape, in the closed position of the ring, when this inner chamber is inflated. By “substantially” circular is meant, within the meaning of the present disclosure, a closed plane curve, the points of which are at the same distance from the centre with a tolerance of plus or minus 20%, preferably 10%, of Ø i . 
           [0060]    As indicated above, the ring according to the invention is an open collar which can be defined by at least one of the following features:
       (i) the inner chamber forms, at rest and in the non-closed position of the ring, an open collar on an angular sector less than or equal to, in ° and in increasing order of preference, 5; 4; 3; 2; 1;   (ii) the outer belt forms, at rest and in the non-closed position of the ring, an open collar over an angular sector less than or equal to, in ° and in increasing order of preference, 10; 8; 6; 4; 2.       
 
           [0063]    In the preferred embodiment, the open collar has no angular sector but a narrow channel, the ends to be joined in order to close the ring being parallel when the ring is in open position at rest. 
           [0064]    In one possible version of the invention, the flexible inflation tube comprises at least one non-return valve. 
           [0065]    According to an interesting feature of the invention aimed at improving the reliability of the locking of the ring around the biological duct/vessel, the ring is characterized in that the outer belt is equipped with closing means comprising two outer lips extending in the centrifugal direction and capable of being joined to one another in a diametral plane, in reversible manner, in order to close the ring around the duct, preferably using (a) suture(s), preferably resorbable, threaded through at least one perforation made in these outer lips. 
           [0066]    In order to allow it to be visible to X-rays, it may be useful, according to the invention, for the ring to comprise at least one radio-opaque part, for example a radio-opaque insert. 
           [0067]    The ring according to the invention can be also characterized by manufacturing features. Thus, this ring can advantageously be obtained by moulding using a mould. The latter has features which make it possible to indirectly define the ring according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0068]    The following description of a preferred embodiment of the ring according to the invention, will highlight other remarkable features. 
         [0069]    This detailed description is given with reference to the attached figures in which: 
         [0070]      FIGS. 1A &amp; 1B  represent perspective views of the ring according to the invention, deflated and in the closed and open positions respectively. 
         [0071]      FIGS. 2A, 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 ( FIG. 2C ) and according to an embodiment variant ( FIG. 2C ), ready to be positioned around the duct. 
         [0072]      FIG. 3  is a longitudinal cross-sectional view along the cutting plane III-III of  FIG. 2A, 2B or 2C . 
         [0073]      FIGS. 4A &amp; 4B  are front views of the ring shown in  FIGS. 2A &amp; 2B or 2C  respectively. 
         [0074]      FIG. 4C  is a longitudinal cross-sectional view along the cutting plane IV-IV of  FIG. 3 , 
         [0075]      FIGS. 5 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, 
         [0076]      FIGS. 5 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. 
         [0077]    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. 
         [0078]    The ring ( 1 ) comprises:
       an outer belt ( 3 );   an inner chamber ( 4 ) that can be inflated and deflated;   a flexible inflation/deflation tube ( 5 ).       
 
         [0082]    The outer belt ( 3 ) has a substantially constant inner diameter and outer diameter. This outer belt ( 3 ) is similar to an open collar ( FIGS. 1B, 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 ( FIGS. 1B, 2B, 2C &amp; 4B ) and in contact with one another in the closed collar ( FIGS. 1A, 2A &amp; 4A ). As shown in  FIGS. 2A, 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 ( FIGS. 1A, 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 ). 
         [0000]    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. 
         [0083]    The inner chamber ( 4 ) is an inflatable and deflatable balloon having, at rest and in the closed position ( FIG. 2A ), 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%. 
         [0000]    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 ). 
         [0084]    In the preferred embodiment shown in  FIG. 2B , 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 . 
         [0085]    In the embodiment variant shown in  FIG. 2C , 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°. 
         [0086]    As shown by the figures, in particular  FIG. 3 , this inner chamber ( 4 ) is annular and comprises, in the example shown in the drawings ( FIG. 3 ), 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. 
         [0087]    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 ( FIGS. 1A, 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]. 
         [0088]    As shown in  FIGS. 2A, 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 ). 
         [0089]    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. 
         [0090]    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. 
         [0091]    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. 
         [0092]    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  FIG. 3 . The inflation/deflation tube ( 5 ) is diametrically opposite the opening of the ring ( 1 ) as can be seen in  FIGS. 1A, 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. 
         [0000]    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. 
         [0093]    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. 
         [0094]    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 . 
         [0000]    This significantly limits the risks of SFS syndrome for the patient. 
         [0095]    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. 
         [0096]      FIGS. 5A, 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. 
         [0097]    In the embodiment illustrated on  FIGS. 5A 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. 
         [0098]    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 ′. 
         [0099]    The tongue and the through hole could have any other suitable cross section, preferably complementary to one another. 
         [0100]    The embodiment illustrated on  FIG. 5C  differs from that of  FIGS. 5A 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. 
         [0101]    As in the embodiment of  FIGS. 5A and 5B , the tongue  8 ′ may comprise a grasping portion adjacent the fitting portion opposite the second lip  3   2 . 
         [0102]    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.