Abstract:
A phacoemulsification irrigation sleeve having a body configured to operatively connect to a phacoemulsification needle. The body has proximal and distal ends and defines a passageway for liquid. A first irrigation port is formed in the body between its proximal and distal ends. The body is slit to define a first flap configured to swing away from the first irrigation port in response to pressure of fluid flowing in the passageway to thereby reduce resistance of fluid flow through the first irrigation port. The first flap, when swung away from the first irrigation port, is oriented to direct fluid flowing through the first irrigation port in a direction from the proximal end of the body toward the distal end of the body.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 12/856,358, filed Aug. 13, 2010. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to surgical instruments and surgical techniques used in eye surgery and, more particularly, to the technique of phacoemulsification apparatus and methods for their use. 
         [0004]    2. Background Art 
         [0005]    A common ophthalmological surgical technique is the removal of a diseased or injured lens from the eye. Earlier techniques used for the removal of the lens typically required a substantial incision to be made in the capsular bag in which the lens is encased. Such incisions were often on the order of 12 mm in length. 
         [0006]    Later techniques focused on removing diseased lenses and inserting replacement artificial lenses through as small an incision as possible. For example, it is now a common technique to take an artificial intraocular lens (IOL), fold it and insert the folded lens through the incision, allowing the lens to unfold when it is properly positioned within the capsular bag. Similarly, efforts have been made to accomplish the removal of the diseased lens through an equally small incision. 
         [0007]    One such technique is known as phacoemulsification. A typical phacoemulsification tool includes a hollow needle to which electrical energy is applied to vibrate the needle at ultrasonic frequencies in order to fragment the diseased lens into small enough particles to be aspirated from the eye. Commonly, an infusion sleeve is mounted around the needle to supply irrigating liquids to the eye in order to aid in flushing and aspirating the lens particles and cortical material through an aspiration port formed in the hollow needle. 
         [0008]    It is extremely important to properly infuse liquid during such surgery. Maintaining a sufficient amount of liquid prevents collapse of certain tissues within the eye and attendant injury or damage to delicate eye structures. As an example, endothelial cells can easily be damaged during such a collapse and this damage is permanent because these cells do not regenerate. One of the benefits of using as small an incision as possible during such surgery is the minimization of leakage during and after surgery which aids in the prevention of such a collapse. 
         [0009]    One way to ensure infusion of a sufficient amount of liquid into the eye during an operation is to regulate the flow of irrigating liquid through the sleeve. For example, during phacoemulsification the aspiration port on the phaco needle can become occluded with lens fragments or particles. If the sleeve is of the type having an infusion port at its tip, surrounding the needle, it may also become occluded. When this happens, flow of irrigating liquid into the eye may decrease, meaning that not enough liquid flow may be available to help clear the occlusion. If the surgeon acts to increase liquid flow through the infusion sleeve, this can cause an increase in the Reynolds number of the infusion liquid to the point where the liquid flow becomes turbulent, which can in itself cause damage to the eye. 
         [0010]    Flow control may also be desirable, for sleeves having discharge ports that direct the liquid toward the needle tip may create a flow pattern that pushes lens or cortical material away from the aspiration port of the needle, prolonging the phaco procedure. 
         [0011]    Instruments using various types of infusing sleeves are well known and well-represented in the art and exemplify the attempts made by others to address the problem of maintaining an adequate flow of irrigating liquid without causing damage to the eye. 
         [0012]    U.S. Pat. No. 4,643,717 (Cook et al.) teaches and describes an aspiration fitting adapter formed as a sleeve concentric to the phaco needle and having a pair of bilaterally opposed discharge ports formed proximate the end of the sleeve to infuse irrigating liquid into the eye. 
         [0013]    U.S. Pat. No. 5,151,084 (Khek) teaches and describes an ultrasonic needle with an infusion sleeve that includes a baffle. The sleeve of Khek also fits concentrically about the needle and allows the needle to protrude a substantial distance therefrom while providing a pair of discharge ports bilaterally opposed to each other near the terminus of the sleeve. 
         [0014]    U.S. Pat. No. 6,117,151 (Ulrich et al.) teaches and describes an eye incision temperature protection sleeve fitted concentrically about a needle and having a single discharge port through which irrigating liquid is passed. 
         [0015]    U.S. Pat. No. 6,605,054 (Rockley) teaches and describes a multiple bypass port phaco tip having multiple aspiration ports and a single discharge port to infuse liquid into the eye. 
         [0016]    U.S. Pat. No. 5,879,356 (Geuder) teaches and describes a surgical instrument for crushing crystalline eye lenses by means of ultrasound and for removing lens debris by suction which demonstrates the use of a sleeve positioned concentric to the needle and having a pair of discharge ports formed thereon. 
         [0017]    A series of patents issued to Richard J. Mackool illustrates further variations of irrigating sleeves. Mackool forms the sleeve with a somewhat flattened cross-section configuration intended to more closely approximate the shape of the incision through which the sleeve is inserted into the eye. This cross-section can be seen at FIG. 3 of U.S. Pat. No. 5,084,009. 
         [0018]    U.S. Pat. No. 5,084,009 (Mackool) teaches and describes a liquid infusion sleeve for use during eye surgery with the sleeve having a flattened cross-section and having a pair of infusion ports formed on the forward portion of the flattened section. 
         [0019]    U.S. Pat. No. 5,286,256 (Mackool) teaches and describes a liquid infusion sleeve having a free-floating rigid sleeve surrounding a needle which is intended to prevent the outer flexible sleeve from collapsing onto the needle. 
         [0020]    U.S. Pat. No. 5,354,265 (Mackool) teaches and describes a liquid infusion sleeve showing yet another construction intended to keep the outer flexible infusion sleeve from collapsing onto the vibrating needle. 
         [0021]    U.S. Pat. No. 5,505,693 (Mackool) teaches and describes a method and apparatus for reducing friction and heat generation by an ultrasonic device during surgery incorporating a needle support to prevent collapse of the outer flexible sleeve. 
         [0022]    The Mackool patents are characterized by a pair of discharge ports formed at the distal end of the sleeve through which irrigating liquid is passed into the eye during the operation. 
         [0023]    U.S. Pat. No. 5,645,530 (Boukhny) teaches and describes a phaco emulsification sleeve, one variation of which has a bellows portion attached to a discharge port ring which directs an annular flow of liquid around the needle and into the eye. The use of the bellows is intended to allow the sleeve to absorb spikes in liquid pressure during the operation. 
         [0024]    U.S. Pat. No. 5,634,912 (Injev) teaches and describes an infusion sleeve having a rotating tip to allow the phaco needle to be repositioned during surgery. The top also has a single discharge port for infusing liquid during surgery. 
         [0025]    Published U.S. Patent Application 2003/0004455 (Kadziauskas) teaches and describes a bi-manual phaco needle using separate emulsification and aspiration needles inserted into the eye simultaneously during surgery. 
         [0026]    U.S. Pat. No. 6,007,555 (Devine) teaches and describes an ultrasonic needle for surgical emulsification and details the tendency of some ultrasonic phaco needles to force lens fragments away from the needle&#39;s aspiration port. 
         [0027]    U.S. Pat. Nos. 6,299,591; 6,159,175; 5,743,871; 5,741,226; and 5,725,495 (Banko) all teach and describe a phacoemulsification handpiece, sleeve and tip, with the sleeve having permanently fixed exterior and/or internal baffles thereon to direct the flow of irrigation fluid away from the needle&#39;s aspiration port. The external baffles effectively increase the diameter of the sleeve while the internal baffles are relatively difficult or expensive to manufacture as compared to an extruded sleeve. 
         [0028]    U.S. Pat. No. 7,601,135 (Akahoshi) teaches and describes a multi-port infusion sleeve with ports formed on the curved portion of the sleeve proximate the end thereof. 
         [0029]    U.S. Pat. No. 7,601,136 (Akahoshi) teaches and describes an infusion sleeve with ports formed on the curved portion of the sleeve proximate the end thereof. 
         [0030]    The need exists for an improved infusion sleeve which allows for a greater volume of liquid to be infused into the eye while avoiding the problems described in the prior art with respect to pushing lens and cortical material away from the aspiration port or damaging delicate eye tissue impacted by such direct flow due to increased pressure, turbulence and the like. 
         [0031]    The need also exists for such improved infusion sleeves to incorporate a flow-directing expedient that does not extend above the surface of the sleeve during insertion and removal of the phaco needle through the incision. 
         [0032]    The need also exists for such improved infusion sleeves to be simple in construction, efficient in operation and economical to manufacture. 
       SUMMARY OF THE INVENTION 
       [0033]    In one form, the invention is directed to a phacoemulsification irrigation sleeve having a body configured to operatively connect to a phacoemulsification needle. The body has proximal and distal ends and defines a passageway for liquid. A first irrigation port is provided on the body between the proximal and distal ends of the body through which fluid in the passageway can flow. The body is slit to define a first flap. The first flap is configured to swing away from the first irrigation port in response to pressure of fluid flowing in the passageway, to thereby reduce resistance of fluid flow through the first irrigation port. The first flap is configured so that the first flap, when swinging away from the first irrigation port, is oriented to direct fluid flowing through the first irrigation port in a direction from the proximal end of the body toward the distal end of the body. 
         [0034]    In one form, the body is slit so that a living hinge is formed that allows the first flap to swing towards and away from the first irrigation port. 
         [0035]    In one form, the body is slit to define a “U” shape that opens towards the proximal end of the body. 
         [0036]    In one form, the body is slit to define a horseshoe shape that opens towards the proximal end of the body. 
         [0037]    In one form, the first flap has one of a square, rectangular, and triangular shape. 
         [0038]    In one form, the phacoemulsification sleeve further includes at least a second irrigation port and at least a second flap substantially the same as the first irrigation port and first flap, respectively. 
         [0039]    In one form, the phacoemulsification irrigation sleeve is provided in combination with a phacoemulsification needle. 
         [0040]    In one form, the phacoemulsification needle has a hub. A section of the body surrounds the hub with the sleeve operatively connected to the phacoemulsification needle. 
         [0041]    In one form, the phacoemulsification needle extends through the body to past the distal end of the body and terminates at an aspiration port. 
         [0042]    In one form, the first flap is configured to be placed in a closed position wherein the first flap blocks the first irrigation port. 
         [0043]    In one form, the invention is directed to a method of performing phacoemulsification. The method includes the steps of: obtaining the phacoemulsification irrigation sleeve and phacoemulsification needle as described above; and directing infusion liquid into the passageway and into the first irrigation port to thereby cause the first flap to: a) swing away from the first irrigation port; and b) direct the fluid flowing through the first irrigation port in the direction from the proximal end of the body toward the distal end of the body. 
         [0044]    In one form, the step of causing the first flap to swing away from the first irrigation port involves causing the first flap to swing from a closed position wherein the first flap blocks the first irrigation port. 
         [0045]    In one form, the method of performing phacoemulsification further includes the step of passing cortical and lens material into the phacoemulsification needle. 
         [0046]    In one form, the phacoemulsification needle extends through the body to past the distal end of the body and terminates at an aspiration port. The step of passing cortical and lens material into the phacoemulsification needle involves passing cortical and lens material into the aspiration port. 
         [0047]    In one form, the method of performing phacoemulsification further includes the step of stopping the infusion of liquid into the passageway, and thereby causing the first flap to swing back towards the first irrigation port to block the first irrigation port. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0048]    These and further aspects of the present invention will become apparent upon consideration of the accompanying drawing figures in which: 
           [0049]      FIG. 1  is a first prior art illustration of a prior art irrigation sleeve; 
           [0050]      FIG. 2  is a second illustration of a prior art irrigation sleeve; 
           [0051]      FIG. 3  is a third illustration of a prior art irrigation sleeve; 
           [0052]      FIG. 4  is an end view of a prior art irrigation sleeve having two circular and bilaterally opposed discharge ports; 
           [0053]      FIG. 5  is a lateral view of a portion of the sleeve shown in  FIG. 4 ; 
           [0054]      FIG. 6  is a top view of a portion of the sleeve shown in  FIG. 4 ; 
           [0055]      FIG. 7  is a detail view of a prior art sleeve showing interior and exterior baffles; 
           [0056]      FIG. 8  is a lateral view of a sleeve embodying the present invention and having flaps that swing to control fluid flow through ports; 
           [0057]      FIG. 9  is a top view of the sleeve of  FIG. 8 ; 
           [0058]      FIG. 10  is a view of the sleeve of  FIG. 9  with infusing liquid passing therethrough; 
           [0059]      FIG. 11  is a lateral view of a sleeve embodying an embodiment of the present invention; 
           [0060]      FIG. 12  is a lateral view of the sleeve of  FIG. 11  showing the discharge port distended to allow increased liquid flow; 
           [0061]      FIG. 13  is a schematic representation of a modified form of sleeve, according to the present invention, in combination with a needle to which the sleeve is operatively connected, and having flaps with the general configuration as shown in  FIGS. 8-10 , but swinging in a different manner; 
           [0062]      FIG. 14  is a schematic representation of a sleeve as in  FIG. 13  and identifying a slit used to form one of the flaps; 
           [0063]      FIG. 15  is a view as in  FIG. 14  wherein the depicted slit forms a flap having a configuration different from that in  FIGS. 13 and 14 ; 
           [0064]      FIG. 16  is a view as in  FIGS. 14 and 15  and schematically identifying slits that swing in the manner in  FIGS. 8-10  but having a different configuration; and 
           [0065]      FIG. 17  is a view of a sleeve as in  FIGS. 8-10  with a modified form of slit and as shown schematically in  FIGS. 13-15 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0066]    Referring now to  FIG. 1 , the numeral  10  indicates generally a partial sectional view of a prior art phacoemulsification hand piece having a needle  12  defining a hollow internal chamber  14  through which irrigation liquid and emulsified particles of a lens are aspirated from the capsular bag. As seen in  FIG. 1 , an irrigating sleeve  16  is mounted to hand piece  10 , from which needle  12  protrudes. Sleeve  16  communications with an irrigation liquid supply  17  within handpiece  10  and provides irrigating liquid to the capsular bag through an annular channel  18  formed between needle  12  and sleeve  16 . 
         [0067]    Referring now to  FIG. 2 , an enlarged partial sectional view of a second prior art phacoemulsification apparatus is shown having a sleeve  20  surrounding a hollow needle  22  and defining therebetween an annular channel  24  as a conduit for irrigating liquid. 
         [0068]    Both  FIG. 1  and  FIG. 2  show a prior art apparatus with the flow of irrigating liquid directed annularly about the periphery of the hollow phaco needle. 
         [0069]    Referring now to  FIG. 3 , a partial sectional view of a second embodiment of the apparatus of  FIG. 2  is shown where the infusion sleeve  26  tapers to form an opening  28  through which needle  30  extends. A pair of infusion ports  32 ,  34  is formed in the angled side walls of sleeve  26  to form a pathway for infusing liquid. 
         [0070]    The embodiments shown in  FIGS. 2 and 3  are taken from U.S. Pat. No. 5,084,009 and, as discussed above, it appears that ports  32 ,  34  are formed along the flattened portion of sleeve  26  and are the only infusion ports present. 
         [0071]      FIGS. 4-6  demonstrate a prior art phaco infusion sleeve. For purposes of clarity, only the tip portion of each such sleeve will be shown, it being understood that the sleeve is fitted coaxial to a phaco needle which extends outward from the sleeve. 
         [0072]      FIG. 4  is an end view of a known prior art infusion sleeve  36  having an outer sleeve wall  38 , a central passage  40  to accommodate the phaco needle, and a pair of diametrically opposed infusion ports  42 ,  42   a.  This is the present arrangement on a currently available infusion sleeve. 
         [0073]      FIG. 5  is a lateral side view of the sleeve tip shown in  FIG. 4 , demonstrating that the infusion ports  42 ,  42   a  are circular in shape.  FIG. 6  is a top view of the tip of  FIG. 4 , again demonstrating the diametrically opposed positions of infusion ports  42 ,  42   a  are positioned on taper  44 . 
         [0074]    Referring to  FIG. 7 , detail of a prior art phaco sleeve is shown, corresponding to FIG. 3G of U.S. Pat. No. 6,299,591. Using the numerals in the original drawing, a phaco sleeve is shown having an irrigation port  17  through which irrigating liquid passes. Also seen in  FIG. 7  are baffles  19 , shown formed on both the interior and exterior of the sleeve. According to the patentee, baffles  19  redirect the flow of irrigating liquid in the direction of the arrow which, in this case, is a direction away from the aspiration port formed at the distal end of the phaco needle (not shown in this illustration). It is apparent that the exterior baffle  19  effectively increases the diameter of the sleeve and must be compressed, bent, or otherwise distended to fit through a typical incision made for phaco purposes. 
         [0075]    Referring now to  FIGS. 8-10 , the numeral  46  identifies a portion of a phaco sleeve having a body  48  and a tip portion  50  which tapers to a distal end  52 . The body  48  has a proximal end  53  spaced from the distal end  52 . Sleeve  46  is of the type having a central passageway CP for aspiration liquid flow which extends to end  52 . A section S of the body  48  is shaped and dimensioned to fit around the periphery of a hollow phaco needle  64  and allow the end of the needle to extend past the end  52  as seen in  FIG. 10  with the sleeve  46  operatively connected to the needle  64 . 
         [0076]    In the embodiment shown in  FIGS. 8-10 , a portion of sleeve  46  is cut to form a generally U-shaped or horseshoe-shaped slit  54  to form a flap  56 . Slit  54  terminates at slit end points  58 ,  60  which, in this embodiment, are intermediate flap  56  and end  52 . 
         [0077]    Referring now to  FIG. 9 , sleeve  46  is shown in a top view, showing the formation of a second flap  62 , formed in the same fashion as flap  56 . Although flaps  56  and  62  are shown formed to be diametrically opposed to each other on sleeve  46 , it should be understood that different numbers of flaps can be formed on sleeve  46  to create or modify flow patterns as desired. In like fashion, the size and positioning of flaps such as  56  can also be changed to create different flow patterns. 
         [0078]    Referring now to  FIG. 10 , the operation of sleeve  46  can now be described. In  FIG. 10 , sleeve  46  is seen mounted concentrically to the needle  64  which, as is typical, terminates in an aspiration port  66  through which lens and cortical material are passed. Sleeve  46  fits sufficiently liquid-tightly to needle  64  to force irrigating liquid passing through sleeve  46  at flaps  56 ,  62  to force flaps  56 ,  62 , initially in their closed positions of  FIGS. 8 and 9 , to swing outward and away from sleeve body  48 , opening infusion ports  68 ,  70  and directing liquid passing therethrough to flow in directions A and B which, in this embodiment, are in a direction away from aspiration port  66  (i.e., in a direction from the distal end  52  toward the proximal end  53 ). 
         [0079]    In the closed position for the flaps  56 ,  62 , the flaps  56 ,  62  fully block the infusion ports  68 ,  70 . In effect, as seen in  FIG. 8 , the portion of sleeve  46  extending between slit end points  58 ,  60  forms a living hinge  72  which allows flap  56  to swing away from body  48  responsive to the pressure of the flow of liquid passing through sleeve  46 . It is expected that as flow increases, flaps  56 ,  62  will swing farther away from body  48 , thus reducing the resistance to flow through irrigation ports  68 ,  70 . Reduction of fluid flow pressure allows the flaps  56 ,  62  to move towards the ports  68 ,  70 , which eventually close, at least when there is no fluid flow. 
         [0080]    The effect on phacoemulsification created by flaps  56 ,  72  is seen in  FIG. 10  where, when liquid is aspirated through needle port  66 , particle  74  is drawn toward aspiration port  66  without being impeded or repulsed by the flow of irrigating liquid into the eye. 
         [0081]    While the embodiment shown in  FIGS. 8-10  is intended to direct liquid flow away from aspiration port  66  in one preferred manner, it should be readily understood that the manner in which slit  54  is cut can change the flow direction. 
         [0082]    In  FIGS. 13 and 14 , a modified form of sleeve, corresponding to the sleeve  46 , is shown schematically at  46 ′, with other corresponding parts identified with the same number together with a “′” designation. The sleeve  46 ′ has a body  48 ′ with proximal and distal ends  53 ′,  52 ′, respectively. Flaps  56 ′,  62 ′ are formed in the sleeve  46 ′ by slitting the body  48 ′. Exemplary flap  56 ′ is formed by a slit  54 ′ that terminates at slit end points  58 ′,  60 ′. Slit  54 ′ is cut to place end points  58 ′,  60 ′ toward the proximal end  53 ′ of the body  48 ′ of sleeve  46 ′, whereby the flap  56 ′ would open in a fashion generally oppositely to the manner shown for the flap  56  in  FIG. 10 . As a result, the flap  56 ′ is oriented to direct irrigating liquid in a forward direction, generally oppositely to that indicated by the arrow A in  FIG. 10 , toward aspiration port  66 , should such a flow pattern be deemed useful. This is in a direction from the proximal body end  53 ′ toward the distal body end  52 ′. 
         [0083]    With the flap  56 ′ U-shaped or horseshoe-shaped, the “U” or “U” shape of the horseshoe opens toward the proximal end  53 ′. 
         [0084]    A section S′ on the proximal end of the tubular body  48 ′ is configured to surround the hub H on the phacoemulsification needle  64  and for connection to a phacoemulsification handpiece HP. 
         [0085]    Different flow patterns can also be achieved if flap  56  is formed in a different geometrical shape, such as a square, rectangle, triangle or the like. These different shapes for the exemplary flap  56 ′ for the sleeve embodiment shown in  FIGS. 13 and 14  are encompassed by the generic showing of the sleeve  46 ″ in  FIG. 15  with elements  48 ″,  52 ″,  53 ″,  54 ″,  58 ″,  60 ″ corresponding to like-numbered elements in  FIGS. 13 and 14  but distinguished by a “″” designation. 
         [0086]      FIG. 16  is intended to generically encompass a sleeve  46 ′″ with the multiple different slit configurations that produce different flap shapes that open in the same manner as the flaps  56 ,  62  in  FIGS. 8-10  open. The elements  48 ′″,  52 ′″,  54 ′″,  58 ′″,  60 ′″ correspond to like-numbered elements in  FIGS. 8-10  and  13 - 15  but are distinguished by a “′″” designation. 
         [0087]    Referring now to  FIG. 11 , a phaco sleeve  76  is shown having a tip  78  terminating at an open sleeve end  80 . A curved or tapered shoulder  82  extends from end  80 . The depiction of sleeve  76  is for illustrative purposes, understanding that such sleeves are available in a number of different sizes and configurations. 
         [0088]    A lateral infusion port  84  is shown on sleeve  76  as described generally above. The depiction of port  84  is illustrative only, recognizing the number of varied sizes and shapes of such ports known in the prior art. At point  86  of port  84 &#39;s perimeter, a slit  88  is formed extending laterally along and through sleeve  86 , beginning at and communication with port  84 . In other words, port  84  is an opening extending through sleeve  76 , and slit  88  likewise extends through sleeve  76  and connects with port  84 . 
         [0089]      FIG. 11  represents sleeve  76  in a first state under normal flow conditions with no occlusions of either the sleeve or the needle&#39;s aspiration port. Under such circumstances, slit  88  remains closed or undistended and little or no infusion liquid passes therethrough. 
         [0090]    Referring now to  FIG. 12 , port  84  is shown as it would appear when occlusion is taking place and with the sleeve  48  in a second state. Slit edges  90 ,  92  have been pushed or folded outward by the force of the infusion liquid flow, forming flaps  94 ,  96 . In this illustration, flap  94  comprises a generally triangular flap defined by slit edge  90 , contiguous port rim segment  98  and “fold line”  100 . Similarly, flap  96  is defined by slit edge  92 , contiguous port rim portion  102  and “fold line”  104 . 
         [0091]    It should be apparent that the shape and size of flaps  94 ,  96  will vary with the shape and size of port  84  and the length of slit  88 . All of these parameters can be selected to result in a sleeve port that will allow a determinable change in flow characteristics to meet the demands of a particular sleeve configuration or phaco needle apparatus. In any such configuration the distension or “folding out” of flaps  94 ,  96  creates a larger cross-section available for infusion liquid flow when occlusion or other changes in flow occur. When the flow returns to normal, flaps  94 ,  96  return to their “closed” position and port  84  returns to its original configuration and size. 
         [0092]    A section S″ on the proximal end of the tubular body is configured to surround the hub H on the phacoemulsification needle  64  and for connection to the phacoemulsification handpiece HP. 
         [0093]    One specific form of the flap  56 ′, depicted schematically in  FIGS. 13 and 14 , is shown in  FIG. 17  on a portion of the body  48 ′ of the sleeve  46 ′. The flap  56 ′ is formed by the slit  54 ′ that has an overall “U” shape opening toward the proximal end  53 ′ of the body  48 ′. The “U” shape of the slit  54 ′ is defined by a curved base portion B and spaced legs L 1 , L 2  that project from the base portion B towards the proximal body end  53 ′. 
         [0094]    The legs L 1 , L 2  have the same shape and are curved to cooperatively approximate a portion of an oval shape, with a major axis extending parallel to the length of the sleeve  46 ′, that terminates at points A and B. From points A and B, the slit  54 ′ projects in straight lines SL 1 , SL 2  to the end points  58 ′,  60 ′, respectively. The straight lines SL 1 , SL 2  diverge where they project from the points A, B. 
         [0095]    With this slit configuration, depending upon the nature of the body material and fluid pressure: a) the entire length of the flap  56 ′ between the base B and end points  58 ′,  60 ′ may swing about a first live hinge LH 1 , defined between the spaced end points  58 ′,  60 ′; b) the length of the flap  56 ′ between the base B and points A, B may swing about a second live hinge LH 2 , defined between the points A, B; or c) the flap  56 ′ may swing in stages—initially about the second live hinge LH 2  and subsequently about the first live hinge LH 1 . 
         [0096]    The flaps  56 ′,  62 ′ may have the same or a different configuration. The flaps  56 ′,  62 ′ may be at diametrically opposite locations or spaced in a different circumferential relationship. Use of one flap  56 ′,  62 ′ or more than two flaps  56 ′,  62 ′ are contemplated. 
         [0097]    The foregoing disclosure of specific embodiments is intended to be illustrative of the broad concepts comprehended by the invention.