Abstract:
The apparatus relates to a membrane based pressure sensor placed on an aspiration tube to determine a more accurate vacuum pump pressure within the aspiration tube, and to the connectors and connector assemblies for use with the pressure sensor.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to vacuum sensors and to apparatus for use in medical procedures that involve aspiration of tissues, fluids and the like. 
       BACKGROUND OF THE INVENTION 
       [0002]    Many medical procedures require the aspiration of tissues and/or fluids. These procedures generally use an apparatus including a pump for generating a negative pressure for providing aspiration. Phacoemulsification and phacoemulsification machines are an example of these procedures and apparatus. 
         [0003]    For the purpose of discussing the background to the invention, there now follows a review of phacoemulsification and machines used in this procedure as an example of a type of application to which the invention may be put. It will be understood that the invention may also be applicable to other medical procedures and apparatus that require or provide for aspiration of tissues and/or fluids, especially those procedures wherein tissue architecture is to be retained after aspiration of tissue and/or fluid, such as phacoemulsification. 
         [0004]    Phacoemulsification machines are used in eye surgery to remove cataract-affected eye lenses. A typical prior art peristaltic pump-based phacoemulsification machine comprises a probe which includes an irrigation sleeve surrounding a hollow phacoemulsification needle. The needle projects from an end of the irrigation sleeve and is vibrated at ultrasound frequencies by ultrasound crystals which reside inside the probe and which are connected to a driver which is operable to cause the ultrasound crystals to vibrate. The sleeve of the probe is connected to an elevated and inverted bottle of irrigation fluid by an irrigation tube, while the needle is connected to the input port of a peristaltic pump by a length of aspiration tubing. 
         [0005]    The peristaltic pump comprises a rotor on which is mounted a plurality of rotatable rollers. A portion of a length of compliant pump tubing which is connected to the aspiration tubing extends partially around the circumference of the rotor and is located between the rotor and an arcuate wall such that the rollers which are in contact with the pump tube pinch the tube between themselves and the arcuate wall. As the rotor rotates about its axis, each of the rollers progress along the length of the arcuate wall so that the pinches in the tubing also progress along the wall. The direction of rotation of the rotor is such that fluid is drawn through the pump tube from the aspiration tube connected thereto and is expelled from an output port of the pump and into a waste collection bag. 
         [0006]    The typical prior art peristaltic pump-based phacoemulsification machine also comprises a vacuum sensor for sensing the vacuum which is produced inside the aspiration and pump tubes through the operation of the peristaltic pump. 
         [0007]    A vent valve is normally connected to the aspiration tubing near the pump, and is normally operated to connect the interior of the aspiration and pump tubes to atmospheric pressure by venting to a fluid or air source. An example of a suitable fluid source is the output of the pump. The vent valve may be deployed at any time to neutralize any residual vacuum in the aspiration and pump tubes. 
         [0008]    The operation of the peristaltic pump is normally controlled by a pedal such that depression of the pedal by the foot of the machine operator (who is usually a surgeon) causes the rotor of the pump to commence rotating at a speed which is proportional to the amount by which the pedal is depressed. The pump will normally commence operating once the pedal has been depressed to a third of its total travel. The pump will normally cease operating once the pedal is released. 
         [0009]    The pedal which is used to control the operation of the peristaltic pump is normally also used to, control the vibration of the phacoemulsification needle and the flow of irrigation fluid from the irrigation bottle through the irrigation tube and the sleeve of the probe. When the pedal is initially depressed, a control valve in the irrigation tube is opened so that irrigation fluid is permitted to flow from the bottle through the irrigation tube and from the sleeve. Once the pedal is depressed to two thirds of its total travel, the ultrasound crystals in the probe commence vibrating which causes the needle to vibrate. In addition to stopping the pump as mentioned previously, release of the pedal causes the ultrasound crystals to stop vibrating and closes the irrigation control valve. Releasing the pedal may also deploy the vent valve to vent the aspiration and pump tubes to atmospheric pressure, or a small pump reversal can neutralise any vacuum, stored in the aspiration tube. 
         [0010]    In use, the tip of the phacoemulsification needle is inserted into the anterior chamber of a patient&#39;s eye by an eye surgeon such that the tip is positioned adjacent the cataract-affected lens of the eye which is to be removed by the phacoemulsification machine to make way for an artificial replacement lens. The surgeon then depresses the pedal of the machine to a third of its total travel so that irrigation fluid flows from the irrigation bottle and into the anterior chamber of the eye from the irrigation sleeve. Further depression of the pedal by the surgeon causes the peristaltic pump to commence operating. Once the surgeon depresses the pedal to two thirds or more, the ultrasound crystals commence vibrating which causes the needle to vibrate at ultrasound frequencies. The vibration of the needle breaks up the natural cataract-affected lens and small particles of the lens are aspirated through the hollow needle and into the aspiration tube as a result of the vacuum produced in the aspiration tube by the operation of the peristaltic pump. The particles then flow through the pump tube from the aspiration tube and into the waste collection bag for disposal. The object of the surgery is to leave the thin outer capsule of the lens behind to form a home for the artificial plastic lens which is inserted into the eye to replace the cataract-affected lens. Irrigation fluid from the irrigation bottle flows into the anterior chamber of the eye from the sleeve of the probe so as to maintain volume and pressure in the chamber and to prevent the chamber from collapsing while the peristaltic pump is operating. 
         [0011]    The vacuum sensor of the machine is used to continuously monitor the vacuum inside the aspiration tube at a location therein which is adjacent the input port of the peristaltic pump. If the sensor senses that the vacuum inside the aspiration tube has reached a predetermined maximum allowable level, such as 300 to 500 mmHg vacuum, the peristaltic pump automatically stops operating. Any level from 0 mmHg to 500 mmHg vacuum can be set by the surgeon on the machine. In the peristaltic pump phaco machine, vacuums of 150 to 500 mmHg are usually only generated when the tip of the needle is occluded by particles of the cataract or other tissue. In general, the vacuum would not rise above 150 mmHg without a degree of occlusion, as only modest vacuums of 0 to 100 mmHg are required in the un-occluded state to support the typically used 20 to 60 ml/minute fluid flow rates through the aspiration tube. 
         [0012]    A post-occlusion surge will appear in the aspiration tube and eye if, after the vacuum in the aspiration tube has reached the pre-determined maximum level and the peristaltic pump has stopped, the occlusion in the tip of the needle suddenly breaks free. The post-occlusion surge is a result of the pump tube, vacuum sensor, and the aspiration tube, which are normally fabricated from compliant materials, being compressed by atmospheric pressure just prior to the surge occurring so that they store potential energy. When the occlusion breaks free, the pump tube, vacuum sensor, aspiration tube, and other compliant components connected thereto, expand and rapidly draw fluid into the aspiration tube. This causes a sudden rush of fluid from the anterior chamber of the eye into the needle and the aspiration tube. This sudden rush of fluid can cause the anterior chamber of the eye to collapse and cause eye tissue to rush toward the tip of the needle. Eye tissue such as the lens capsule, corneal endothelium (important fragile cells on the inner surface of the cornea), or iris may be engaged by the needle at the time of the surge so that the surge causes significant damage to the tissue. The probability of the post-occlusion surge collapsing the anterior chamber of the eye increases if there is fluid leakage from the anterior chamber around the instruments, probe, and manipulators which are received by the anterior chamber. 
         [0013]    The vent valve is used for venting purposes and is generally closed when the pump is operating. The vent valve may be opened to vent the aspiration tube when the pedal is released so that the vacuum in the aspiration tube is neutralized. The vent valve is not deployed in existing phaco machines during a post occlusion surge. This is because the surge peaks around 0.2 seconds after it begins and the vent valve electromechanical delay is too long to be of any use, unless special provisions are made to deploy it. 
         [0014]    The peak flow rate of fluid from the eye, and peak pressure loss in the eye during a post-occlusion surge are proportional to the vacuum inside the compliant structures of the phacoemulsification machine just prior to the occlusion in the needle breaking free. The magnitude of the post occlusion surge is also increased by the resistance to fluid flow and the inertia of the fluid in the irrigation pathway. In addition the surge amplitude is influenced by the compliance of the individual&#39;s eye. More compliant eyes experience lower amplitude surges, all other things being equal. 
         [0015]    Manufacturers of phacoemulsification machines have attempted to reduce the post-occlusion surge by reducing the compliance of the compliant components by using non-compliant aspiration tubing and by improving the flow of irrigation fluid from the sleeve of the probe into the eye. 
         [0016]    Before a phacoemulsification machine is used to operate on an eye, the irrigation tube, aspiration tube, and at least parts of the vacuum sensor of the machine must be sterilised or replaced with sterile components. This is because, during surgery, fluid is able to flow between the eye and part of the interior of the vacuum sensor together as well as the lumen of the irrigation and aspiration tubes. 
         [0017]    It has become the standard practice of phacoemulsification machine manufacturers to sell kits to the users of their machines which contain lengths of sterilised irrigation and aspiration tubing connected to a sterile single use vacuum sensor cartridge. The vacuum sensor cartridges typically comprise a membrane permanently fixed in a housing with a metal member glued to the membrane so that the membrane can be mechanically attached to a force transducer of the machine without un-sterilising the interior of the irrigation and aspiration tubes or the interior of the vacuum sensor cartridge which communicates with the interior of those tubes. A single kit containing a single vacuum sensor cartridge and lengths of irrigation and aspiration tube connected thereto is relatively expensive and typically costs between seventy and one hundred and twenty Australian dollars. The kits are meant to be disposed of after they are used in an operation as it is not possible to reliably re-sterilise them. 
         [0018]    There is a need for new apparatus and components for use in procedures involving aspiration of tissues and fluids, such as phacoemulsification. 
       SUMMARY OF THE INVENTION 
       [0019]    In one embodiment there is provided an assembly for connection to an aspiration tube to monitor pressure in an aspiration tube, the assembly comprising: 
         [0000]    a pressure sensor assembly including a pressure sensor and a coupling device;
 
a connector for providing pressure communication between an aspiration tube and the coupling device of the pressure sensor assembly; and
 
a membrane interposed between the pressure sensor assembly and the coupling device which is adapted to flex as a consequence of changes in pressure in the aspiration tube, said flexure being communicated to the pressure sensor via the coupling device, the membrane forming an impermeable barrier between the interior of the aspiration tube and the pressure sensor.
 
         [0020]    In another embodiment there is provided an apparatus for sensing pressure in an aspiration tube including:
       a pressure sensor for sensing pressure;   a connecting member having:
           a first connection arrangement to connect the connecting member to the pressure sensor;   a second connection arrangement to enable the connecting member to be connected to an aspiration tube coupling;   a passage extending from an opening in the first connection arrangement to an opening in the second connection arrangement, to bring the sensor into communication with an aspiration tube coupling;   membrane mounting means formed around the opening in the second connection arrangement;
 
wherein the membrane mounting means is configured to locate a membrane against the second connection arrangement when the connecting member is connected to an aspiration tube coupling.
   
               
 
         [0027]    In another embodiment there is provided a connector for connecting an aspiration tube to a pressure sensor to enable the pressure sensor to monitor the pressure in an aspiration tube including:
       a connector body having a recess,   a first connection arrangement to enable the connector to be connected to an aspiration tube;   a second connection arrangement to enable the connector to be connected to a pressure sensor;   a flow passage between the recess and the first connector arrangement;   membrane mounting means in or adjacent the recess;
 
wherein when mounted to a pressure sensor, a membrane mounted by the mounting means within or adjacent the recess forms an impervious barrier between the flow passage and the pressure sensor and flexure of the membrane within the recess is adapted to communicate pressure variance in the flow passage to the pressure sensor.
       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1 . A cross section of a disassembled connector assembly according to an embodiment of the invention. 
           [0034]      FIG. 2 . A cross section of an assembled connector assembly according to an embodiment of the invention showing engagement of membrane mounting means on first and second connecting members with a membrane. 
           [0035]      FIG. 3 . A cross section of an apparatus according to an embodiment of the invention wherein the membrane mounting means includes a recess on the first end of the first connecting member of the apparatus. 
           [0036]      FIG. 4 . A cross section of a connector according to an embodiment of the invention showing membrane means located on a second connecting member. 
           [0037]      FIG. 5 . A 3D view of a connector according to a further embodiment of the invention showing a bayonet style attachment for attachment of the connector to an apparatus according to the invention and a membrane pre-tensioner. 
           [0038]      FIG. 6A . A 3D view of a membrane for use with an assembly according to the invention. 
           [0039]      FIG. 6B . A 3D view of a membrane according to  FIG. 6A , further comprising a pre-tensioner for pre-tensioning the membrane. 
           [0040]      FIG. 6C . A 3D view of a membrane having mounting means. 
           [0041]      FIG. 6D  A 3D view of a membrane according to  FIG. 6C , further comprising a pre-tension for pretensioning the membrane. 
           [0042]      FIG. 7 . A plan view of a membrane according to  FIG. 6B . 
           [0043]      FIG. 8 . A plan view depicting use of the assembly according to the invention in a phacoemulisification machine having a peristaltic pump mechanism. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0044]    In one embodiment there is provided an assembly for connection to an aspiration tube to monitor pressure in an aspiration tube, the assembly comprising: 
         [0000]    a pressure sensor assembly including a pressure sensor and a coupling device;
 
a connector for providing pressure communication between an aspiration tube to the coupling device of the pressure sensor assembly; and
 
a membrane interposed between the pressure sensor assembly and the coupling device which is adapted to flex as a consequence of changes in pressure in the aspiration tube, said flexure being communicated to the pressure sensor via the coupling device, the membrane forming an impermeable barrier between the interior of the aspiration tube and the pressure sensor.
 
         [0045]    In one embodiment the coupling device includes a body having a generally planar end face, and a pressure communication passage extending through the body to an inlet in said end face, the membrane forming a seal with said end face around said inlet. 
         [0046]    The end face may have an annular membrane sealing formation formed therein which will seal with the membrane, and which will cause said membrane to seat against said end face when the aspiration tube is at atmospheric pressure. 
         [0047]    The connector may include a recess and the membrane may be mounted to the connector to form a seal around the recess, with a pressure communication passage extending from the recess through the connector so that, in use, the aspiration tube is in pressure communication with the recess, and changes of pressure in the aspiration tube causes flexure of the membrane. 
         [0048]    The membrane may have one or more annular ribs and/or grooves formed therein adapted to engage with one or more corresponding annular formations in the coupling device to ensure proper operative location and/or sealing of the membrane with the coupling device. 
         [0049]    The connector may be a single use disposable item having a substantially contaminant free internal passage, and the membrane forms a barrier against the ingress of contaminants into said passage. 
         [0050]    In another embodiment there is provided an apparatus for sensing pressure in an aspiration tube including:
       a pressure sensor for sensing pressure;   a connecting member having:
           a first connection arrangement to connect the connecting member to the pressure sensor;   a second connection arrangement to enable the connecting member to be connected to an aspiration tube coupling;   a passage extending from an opening in the first connection arrangement to an opening in the second connection arrangement, to bring the sensor into communication with an aspiration tube coupling;   membrane mounting means formed around the opening in the second connection arrangement;
 
wherein the membrane mounting means is configured to locate a membrane against the second connection arrangement when the connecting member is connected to an aspiration tube coupling.
   
               
 
         [0057]    The membrane mounting means may be an annular recess that is formed around the opening in the second connection arrangement. The recess may have a generally rectangular cross section. The diameter of the recess may be from 15 to 50 mm, preferably 20 to 25 mm. 
         [0058]    The second connection arrangement may include a connection means for detachably connecting the connecting member to an aspiration tube coupling. The connection means may be a screw thread such as a male screw thread. 
         [0059]    Alternatively, the connection means may be a lug for engaging with a slot on an aspiration tube coupling. 
         [0060]    In some embodiments, the connecting member can be detached from the pressure sensor. 
         [0061]    The connecting member may further include a sleeve or cuff for supporting the attachment of the connecting member to the pressure sensor. 
         [0062]    In another embodiment there is provided a connector for connecting an aspiration tube to a pressure sensor to enable the pressure sensor to monitor the pressure in an aspiration tube including:
       a connector body having a recess,   a first connection arrangement to enable the connector to be connected to an aspiration tube;   a second connection arrangement to enable the connector to be connected to a pressure sensor;   a flow passage between the recess and the first connector arrangement;   membrane mounting means in or adjacent the recess;
 
wherein when mounted to a pressure sensor, a membrane mounted by the mounting means within or adjacent the recess forms an impervious barrier between the flow passage and the pressure sensor and flexure of the membrane within the recess is adapted to communicate pressure variance in the flow passage to the pressure sensor.
       
 
         [0068]    The membrane mounting means may be an annular rib that is located adjacent the recess. The rib may have a generally triangular cross section. 
         [0069]    The second connection arrangement may include connection means for detachably connecting the connector to a pressure sensor. The connection means may be a screw thread, such as a female screw thread. 
         [0070]    The connector may further include a membrane being configured to flex in the recess in response to a pressure conditions created therein. The membrane may further include a tensioning means for tensioning the membrane. The membrane may be integrally formed with the connector body. 
         [0071]    The membrane may be made from silicone rubber with a hardness over the range of 10 to 60 durometers, with about 10 to 30 durometers hardness preferred. The membrane can also be moulded and contain areas of different thickness which can help give the membrane properties for assisting with sealing. 
         [0072]    The connector may further include an aspiration tube attached to the first connection arrangement. 
         [0073]    In order that the invention may be more fully understood and put into practice, a various embodiments thereof will now be described with reference to the accompanying illustrations. 
         [0074]      FIG. 1  depicts a connection assembly  10  for connecting an aspiration tube to an input of a vacuum sensor  11  of an apparatus for sensing a vacuum in an aspiration tube. A phacoemulsification machine is an example of such an apparatus. 
         [0075]    The connection assembly  10  includes a first connecting member  12 , and a second connecting member  13 . A membrane,  14 , is also depicted although in certain embodiments it will be understood that the assembly may be manufactured and sold without the membrane, the membrane being sold separately. 
         [0076]    Second connecting member  13  is depicted as having attachment means being a screw cap that includes an end wall  15  (also referred to herein as a “first end”) and a continuous side wall  16  extending from the perimeter of the end wall  15 . 
         [0077]    As discussed herein, other forms of attachment means are contemplated, including a bayonet style attachment means that is based on the principle of a lug interlocking with a slot. 
         [0078]    A hollow spigot  17  extends perpendicularly from the centre of the end wall  15  in a direction which is opposite to the direction in which the side wall  16  extends from the end wall  15 . Spigot  17  includes a passage  18  extending there through, and is designed to be received in the end of an aspiration tube such that the connecting member  13  is thereby connected to the aspiration tube. When the connecting member  13  is connected to the aspiration tube a seal is formed between the aspiration tube and the spigot  17 , and air or fluid may flow between the aspiration tube and the connecting member  13  through the passage  18  in the spigot  17 . This effectively brings the “recess” or “depression” described herein into communication with pressure in an aspiration tube. 
         [0079]    Spigot  17  may alternatively be offset with respect to the axis of the depression also described herein as a “recess”  19 . The spigot  17  may then be orientated uppermost to avoid any trapped air in the depression  19 . Moreover, there may be more than one spigot  17 . 
         [0080]    End wall  15  includes a conical-shaped depression  19  and a sealing means in the form of a continuous circular rib  20  which are both concentric with the passage  18 . Rib  20  encircles the depression  19  and has a triangular profile which is about 1.2 mm wide at its base. The sides of the rib  20  taper toward each other from the base such that the sides are about perpendicular with respect to each other. 
         [0081]    Side wall  16  includes attachment means in the form of a helical thread  21  which extends along an inner surface of the side wall  16  so as to form a female screw thread. Membrane  14  may be an inexpensive and resilient silicone rubber disc having a 1 inch diameter, a thickness of 0.8 mm, and a relatively low mass. The diameter of the membrane  14  is such that the membrane  14  is able to be received by the passage defined by the side wall  16  and is able to cover the rib  20  and the depression  19 . 
         [0082]    Both the connecting member  13  and the membrane  14  may be reused and may be reliably sterilised using an autoclave. Alternatively the member  13  and membrane  14  may be disposable. 
         [0083]    The second connecting member  13  may be detachably secured to the first connecting member  12 . As depicted, the first connecting member  12  includes a cylindrical portion  30 , a flange portion  31 , a projecting portion  32 , and a spigot portion  33 . 
         [0084]    Attachment means are depicted in the form of a helical thread  34  that extends around the circumference of the first end of the first connecting member  12  that is depicted as cylindrical portion  30  so as to form a male screw thread. The diameter of the cylindrical portion  30  is such that the female threaded portion of the second connecting member  13  can be screwed on to the male threaded portion of the cylindrical portion  30  to thereby secure the connecting members  12 ,  13  together. 
         [0085]    Sealing means are depicted in the form of a continuous circular groove  35  that extends along an end of the cylindrical portion  30  of the connecting member  12  and is coaxial with the cylindrical portion  30 . Groove  35  may have a constant rectangular profile of about 0.2 mm deep and about 0.8 mm wide. The diameter of the circle formed by the groove  35  is such that when the connecting member  13  is secured to the connecting member  12 , the pack of the rib  20  is aligned with the centre of the groove  35  of the complete length of the rib  20  and groove  35 . 
         [0086]    In use, the projecting portion  32  and the spigot portion  33  of the first connecting member  12  extend through an opening  36  in a panel  37  of the apparatus such that the flange portion  31  rests against an exterior surface of the panel  37 . The connecting member  12  is secured to the panel  37  by a plurality of screws  38 . Each screw  38  extends through a respective washer  39  and a respective opening  40  in the panel  37 . A threaded portion  41  of each screw  38  is screwed into a respective threaded hole  42  which extends into the flange portion  31  of the connecting member  12 . The screws  38  are tightened so that the connecting member  12  is firmly secured to the panel  37 . 
         [0087]    A passage  43  extends through the first connecting member  12  from an opening at the first end  30  such that the passage  43  passes through the cylindrical, flange, projecting, and spigot portions  30  to  33  of the connecting member  12 . Passage  43  may have a diameter of about 0.5 mm and may be about 15 to 30 mm long. 
         [0088]    In use, the spigot portion  33  of the connecting member  12  is received by a complementary opening  50  in a projecting portion  51  of the vacuum sensor  11 . Passage  43  is aligned with a passage  52  which extends through the projecting portion  51 . In this depiction, a “chamber” is formed by the connection of passage  43  with passage  52 . 
         [0089]    Although not forming part of the assembly, the vacuum sensor  11  is a commercially available standard vacuum sensor device that employs a semi-rigid silicon diaphragm  53  operating on a piezo-resistive principle to sense variations of pressure in the passage  52 . Terminals  54 ,  55  are used to connect the sensor  11  to a suitable electrical power supply. Sensor  11  produces a voltage output across output terminals  56 ,  57  which is proportional to the pressure or vacuum sensed in the passages  52  and  43  by the diaphragm  53 . Sensor  11  has a relatively good high frequency response. 
         [0090]    A sleeve  60  assists in securing the projecting portion  32  of the connecting member  12  to the projecting portion  51  of the sensor  11 . Also, the sleeve  60  assists in forming a seal where the sensor  11  joints the connecting member  12 . 
         [0091]    Before commencing a medical procedure, the surgeon, theatre nurse, or other appropriate person who is “gloved up” and sterile, ensures that the second connecting member  13  and membrane  14  are sterile and then places the membrane  14  into the passage of the second connecting member  13  which is formed by the side wall  16  such that the depression  19  and rib  20  of the connecting member  13  are covered by the membrane  14 . The connecting member  13  is then detachably secured to the connecting member  12  by screwing the threaded portion  21  of the sidewall  16  tightly on to the threaded portion  34  of the cylindrical portion  30  of the connecting member  12 . A sterile aspiration tube is then connected to the connecting member  13  such that the spigot  17  is received by an end of the aspiration tube. 
         [0092]    Where the apparatus is a phacoemulsification membrane, the other end of the aspiration tube is connected to the probe of the phacoemulsification machine so that fluid is able to flow into the aspiration tube from the needle of the probe. A sterile irrigation tube is also connected to the probe and to an irrigation bottle so that irrigation fluid is able to flow from the sleeve of the probe. 
         [0093]    After a procedure is completed, the second connecting member  13  is then unscrewed and removed from the first connecting member  12 , and the aspiration and irrigation tubes are disconnected from the probe. The aspiration tube is also disconnected from the connecting member  13 , and the irrigation tube is also disconnected from the irrigation bottle. The aspiration and irrigation tubes are then preferably disposed of as it is not possible to reliably re-sterilise them. Both the stainless steel connecting member  13  and the membrane  14  may be sterilised as it is possible to reliably sterilise both components. Alternatively, the membrane  14  may be removed from the connecting member  13  and disposed of as it is relatively inexpensive to replace (i.e. twenty Australian cents), and only the connecting member  13  re-sterilised so that it can be safely reused in another operation. 
         [0094]    When the sterile membrane  14  is placed in the sterile second connecting member  13 , and the connecting member  13  is secured to the first connecting member  12 , the membrane  14  forms a seat between the connecting members  12  and  13  which prevents the un-sterilised connecting member  12  and sensor  11  from contaminating side A of the membrane and the internal portions of the connecting member  13  including the depression  19  and the passage  18  in the spigot  17  which are located on side A of the membrane  14 . Once side B of the membrane  14  contacts the un-sterilised connecting member  12 , that side of the membrane  14  then becomes un-sterile. Further the sensor is prevented from contamination by fluids and tissues drawn into the aspiration tube. Thus membrane  14  functions as a barrier. 
         [0095]    As the vacuum inside the aspiration tube may be very large (e.g. over 500 mmHg) during a phacoemulsification procedure and other procedures involving aspiration of tissues and fluids, there needs to be a “full” vacuum (in some cases reliable to at least one atmosphere or 760 mmHg) between the peripheral portions of the membrane  14  which contact and form a seal with the second connecting member  13  and the first connecting member  12  between passages  18  and  43  in order to ensure that a leak does not form between the membrane  14  and the connecting member  13 , or the membrane  14  and the connecting member  12  when there is such a large vacuum in the aspiration tube. The seal formed by the membrane  14  between the connecting members  12 ,  13  is strong enough to be able to withstand large vacuums in the aspiration tube without a leak forming between the membrane  14  and either of the connecting members  12 ,  13 . In certain embodiment, the seal between the membrane  14  and the connecting members  12 ,  13  is formed by the tip  70  (see  FIG. 2 ) of the rib  20  (see  FIG. 1 ) compressing the membrane  14  against the flat floor  71  of the groove  35 , and by the edges  72  of the groove  35  compressing the membrane  14  against the flat sides  73  of the rib  20  as depicted in  FIG. 2 . The seal between the membrane  14  and connecting members  12 ,  13  is able to be formed by hand-tightening the connecting members  12 ,  13 . Completion of the tightening of the connecting members  12 ,  13  is obvious to feel as the space between the connecting members  12 ,  13  reaches the thickness of the membrane  14  and the relative rotation, of the connecting members  12 ,  13  appears to stop abruptly. The tip  70  of the rib  20  is not sharp enough to cut the membrane  14  while the connecting members  12 ,  13  are being tightened. 
         [0096]    The threads on the connecting members  12  and  13  may be replaced if desired with a bayonet style fitting to allow the members  12 ,  13  to be tightened together by hand in a quarter turn or less. Connecting member  13  and membrane  14  could also be in the form of a single disposable unit if needed. 
         [0097]    The geometry of the sealing means  20  and  35  as depicted in an embodiment of the invention shown in  FIG. 2  are such that there is negligible displacement of the material of the membrane  14  radially toward the centre of the membrane  14  when the connecting members  12 ,  13  are tightened together by hand. This is advantageous as otherwise “pseudo vacuum” can be produced when the connecting members  12 ,  13  are tightened to such an extent that the membrane  14  is radially compressed to cause microscopic bowing of the membrane  14  toward the connecting member  13  and a reduction of pressure in the passage  43  of the connecting member  12 . If an excessive pseudo vacuum were present, appropriate electronics or software would be required to offset or zero out the pseudo vacuum. No such electronics or software is required when the connection assembly is used, as the pseudo vacuum is very small. 
         [0098]    In order to minimise the compliance of the combination of the connection assembly  10  and sensor  11  so that it does not aggravate post-occlusion surges, the volume of passage  43  is made as small as possible so as to minimise the amount of air which can be held in the passage  43  between the membrane  14  and the vacuum sensor  11 . In addition the range of travel of the membrane  14  is kept as small as possible so that a “full” vacuum in the aspiration tube which is connected to the connecting member  13  does not result in the membrane  14  “bottoming out” in the depression  19 . Due to the small amount of air which can be stored in the passage  43  and the sensor  11 , the compliance of the assembly  10  is kept very low. 
         [0099]    In certain embodiments, the presence of the membrane  14  results in the recovered signal from the sensor  11  being attenuated by approximately 5 to 10%. This signal loss can be compensated for by suitably amplifying the signal output by the sensor  11  using an electronic amplifier. The amplified signal can then be processed in the apparatus. 
         [0100]    The low mass of the membrane  14  combined with the good high frequency response of the vacuum sensor  11  assist the sensor  11  in responding to very rapid changes in vacuum compared to other sensors which have much more mechanical inertia. This enables an apparatus such as a phacoemulsification machine to detect rapid changes in vacuum. 
         [0101]    The sensor  11  in combination with the assembly  10  is able to operate over a broad range of 0 mgHg to 600 mmHg, even though in practice a range of 0 mmHg to 500 mmHg is required. Moreover, the combination of the sensor  11  and assembly  10  has a wide dynamic range as it is able to resolve small changes in vacuum levels such as, for example, from 0 mmHg to 10 mmHg, or 0 mmHg to 500 mmHg. In addition, the assembly  10  and sensor  11  combination has excellent linearity so that the signal which is output by the sensor  11  does not need to be linearised using compensating algorithms or other linearising techniques. The connection assembly  10  and sensor  11  combination is relatively simple and inexpensive so that it can be incorporated into an apparatus such as a phacoemulsification machine at a relatively low cost and can make the machine more affordable to use.