Abstract:
A pressure actuated flow control valve for an infusion catheter permits gravity flow of a liquid through the catheter and into a patient while resisting back flow of blood from the patient and into the catheter. The valve has a hemispherical body with an outstanding circumferential flange and a normally closed, diametric slit. The slit is longer on the convex outer surface than on the concave inner surface. Dome thickness diminishes in the area adjacent the slit, reducing total apical deflection upon collapse of the slit toward the concave surface. An inner orthogonal rib biases the slit closed. Upon application of a predetermined pressure, the slit opens toward the concave surface to permit forward fluid flow. At lower pressures, the slit closes to check fluid flow. Greater reverse pressure is required to collapse the slit toward the concave surface to permit reverse fluid flow.

Description:
RELATED APPLICATION 
       [0001]    This is a continuation of application Ser. No. 10/304,833 filed Nov. 26, 2002, which is hereby incorporated by reference in its entirety herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention is broadly concerned with a control valve for a medical fluid infusion device. More particularly, it is concerned with a positive pressure actuated flow control valve that permits flow of a liquid from a reservoir, through a cannula and into a patient, while resisting reflux. 
         [0003]    Medical infusion therapy employs peripheral and central intravascular devices such as venous and arterial catheters as well as peripherally inserted central venous catheters to deliver fluids, blood products, and pharmaceuticals, including antibiotics and biologics as well as parenteral nutrition. Intravascular devices may also be coupled with pressure monitoring systems. 
         [0004]    Regardless of the location of the insertion site of the catheter or the placement of its terminus, intravascular devices, and central venous catheters (CVCs) in particular, are subject to retrograde blood flow into the catheter lumen whenever the pressure in the patient&#39;s vascular system exceeds resistance at the supply end of the catheter. This may occur, for example, when fluid pressure drops because a gravity supply source is empty, when an injection port is opened by removal of a syringe, or when a stopcock is opened. 
         [0005]    Retrograde blood flow is known to contribute to complications such as catheter-related septicemia, venous thrombosis, superior vena cava syndrome, pulmonary embolism and phlebitis. Thrombus formation may cause partial or complete occlusion of the catheter. Partial occlusion results in impaired sampling and fluid administration. Complete occlusion causes the catheter to lose patency, necessitating removal and replacement, so-called “unscheduled restarts”. 
         [0006]    Catheter reflux-induced thrombosis is not merely a mechanical complication, since it appears to be a major contributor to catheter related bloodstream infections associated with the use of long term catheters. Such infections are associated with increased morbidity and mortality as well as increased health care costs associated with extended hospitalization. 
         [0007]    Attempts have been made to develop improved intravascular devices in order to address the mechanical and infectious complications previously described. Peripherally inserted central venous catheters (PICCs) are known to reduce the incidence of thrombosis and phlebitis as well as commonly reported central catheter-related infections. However, PICC devices are not suitable for all applications, particularly where the solution to be administered has high osmolarity or may be a pH irritant. And patients with PICC infusion still experience thrombus formation and phlebitis at statistically significant levels. 
         [0008]    Guidewire assisted exchange has also been employed to achieve a lower rate of mechanical complications following insertion of replacement catheters. However, patients may experience bleeding, hydrothorax and subsequent catheter related infections. 
         [0009]    In-line filters have also been employed to reduce infusion-related phlebitis. However, they have not been found to prevent intravascular device-related infections. And use of such filters is not regarded as mechanically favorable, since solution filtration may be accomplished more efficiently prior to infusion and the filters themselves are subject to blockage. 
         [0010]    Impregnated catheters and needle-free devices have also been employed. Although they have not yet been thoroughly evaluated, antimicrobial coated or impregnated catheters appear to be more effective for central venous use than for peripheral use. There are concerns, however, that they may foster development of resistant bloodstream pathogens. Needle-free infusion systems also have not yet been fully studied, although one investigation has shown survival of skin flora in needleless infusion systems. 
         [0011]    There have also been attempts to develop methods of using conventional intravascular devices in order to prevent catheter-related thrombus formation and to maintain catheter patency. Turbulent positive pressure flushing with anticoagulant heparin solution, use of thrombolytic agents such as urokinase, streptokinase and t-Pa, and prophylactic warfarin administration have all been employed. 
         [0012]    However, some in vitro studies have suggested that heparin flush solutions may serve to enhance growth of Coagulase-negative staphylococci (CoNS). The United States Public Health Service, Centers for Disease Control and Prevention (CDC) has cited CoNS as “the primary pathogen causing catheter-related infections”. It has recommended clinical trials to evaluate the practice of flushing with anticoagulant solutions to prevent catheter-related infections. The CDC has also cited an association between use of low dose heparin and thrombocytopenia and thromboembolic and hemorrhagic complications. 
         [0013]    All of the preventive methods that are currently available appear to contribute in some manner to general health care delivery problems, such as delay, increased requirements for nursing care, pharmaceutical and supply costs, increased patient risk and discomfort. 
         [0014]    Accordingly, there is a need for an improved intravascular device that will resist retrograde blood flow and thereby reduce rates of thrombus formation, catheter-related blood stream infection, and unscheduled restarts and thereby extend catheter indwelling times. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention is directed to a pressure actuated flow control valve for an infusion catheter which permits gravity flow of a liquid through the catheter and into a patient while resisting back flow of blood from the patient and into the catheter. The valve includes a hemispherical dome-shaped body having concave inner and convex outer surfaces. A normally closed, slit communicates between the surfaces. The slit is configured so that it is longer on the convex outer surface than on the concave inner surface. The cross-sectional thickness of the dome diminishes in the area adjacent the slit, reducing total apical deflection upon collapse of the slit toward the concave surface. The dome inner surface includes an orthogonal rib that biases the wall of the dome adjacent the slit to a closed position. Upon application of a predetermined pressure, the slit opens toward the convex surface for facilitating fluid flow in the intended direction. At lower pressures, the slit resumes a closed position to check fluid flow. Relatively greater reverse pressure is required to collapse the slit toward the concave surface to permit reverse fluid flow. The valve includes an outstanding circumferential flange for engagement within a housing. 
         [0016]    Objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0017]      FIG. 1  is a combination diagrammatic and perspective, partially exploded view of a flow control valve assembly in accordance with the invention, installed in a medical fluid infusion system. 
           [0018]      FIG. 2  is an enlarged sectional view taken along line  2 - 2  of  FIG. 1  and shows details of the housing construction. 
           [0019]      FIG. 3  is a front perspective view of the valve depicted in  FIG. 1 . 
           [0020]      FIG. 4  is an enlarged bottom plan view of the valve depicted in  FIG. 1 . 
           [0021]      FIG. 5  is an enlarged top plan view of the valve depicted in  FIG. 1 , showing the rib in phantom. 
           [0022]      FIG. 6  is a further enlarged sectional view taken along line  6 - 6  of  FIG. 4  and shows details of the valve slit. 
           [0023]      FIG. 7  is a still further enlarged sectional view taken along line  7 - 7  of  FIG. 4  and shows details of the rib. 
           [0024]      FIG. 8  is a fragmentary sectional view similar to the view shown in  FIG. 2  at a reduced scale, showing the valve in an open, forward fluid flow enabling position. 
           [0025]      FIG. 9  is similar to the view depicted in  FIG. 8 , showing the valve in a collapsed, reverse fluid flow enabling position. 
           [0026]      FIG. 10  is an enlarged sectional view of a valve assembly incorporating an alternate threaded Luer housing. 
           [0027]      FIG. 11  is an enlarged bottom plan view of an alternate valve having a cylindrical rib configuration. 
           [0028]      FIG. 12  is an enlarged sectional view taken along line  12 - 12  of  FIG. 11  and shows details of the valve slit. 
           [0029]      FIG. 13  is an enlarged bottom plan view of a second alternate valve having a cruciform rib configuration. 
           [0030]      FIG. 14  is an enlarged sectional view taken along line  14 - 14  of  FIG. 13  and showing details of the rib. 
       
    
    
       [0031]    The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
         [0033]    Certain terminology will be used in the following description for convenience in reference only and will not be limiting. For example, the words “distally” and “proximally” will refer to directions respectively toward and away from a patient. 
         [0034]    Referring now to the drawings, a pressure actuated flow control valve assembly in accordance with the invention is generally indicated by the reference numeral  10  and is depicted in  FIGS. 1 and 2 .  FIG. 1  illustrates exemplary use of the valve assembly  10  installed in-line between an intravascular device  12  such as an intravenous (IV) fluid delivery catheter set and an intravascular fluid source  14 , such as an IV fluid reservoir. Those skilled in the art will appreciate that the pressure actuated valve assembly  10  can also be used in conjunction with a variety of other medical fluid delivery devices, such as an arterial catheter and associated chemotherapy fluid reservoir and/or pressure monitoring device, or a gastrostomy tube set having a corresponding fluid reservoir. 
         [0035]    The intravascular device  12  includes an elongate, flexible catheter  16  having an outer surface and an inner surface defining a lumen or fluid passageway  18 . A distal end of the catheter  16  is adapted for insertion into a vein of a patient. The outer surface of the proximal end of the catheter  16  is overmolded by a compression strain relief cuff  20  and is coupled with a Y-connector  22 , which serves as a manifold for coupling a pair of connector tubes  24  in fluidic communication with the single catheter  16 . Each connector tube  24  has an outer surface and an inner surface defining a lumen  26 , and proximal and distal end portions  28  and  30  respectively. The proximal end portions  28  are each overmolded by a compression strain relief cuff  32 . The Y-connector  22  receives the distal end portions  30 . While  FIG. 1  depicts an intravascular device  12  having two connector tubes  24 , it is foreseen that any operable number of such tubes may be employed, including a single tube. In addition, while  FIG. 1  depicts only the distal end of the catheter  16  as indwelling, the entire intravascular device  12  may be constructed for indwelling installation and use. 
         [0036]    As more fully described herein, each connector tube proximal end portion  28  is coupled with a valve assembly  10 , which in turn is coupled with a connector  34 . The connector  34  has a generally cylindrical overall shape and is hollow and open at one end to receive the valve assembly  10 . The connector  34  includes a threaded interior surface  36  and an exterior surface  38  that is swaged or flanged to facilitate gripping. One end of the connector  34  is axially apertured to permit coupling with a supply tube  40  having an outer surface and an inner surface defining a fluid passageway or lumen  42 . The outer surface of the supply tube  40  adjacent the connector  34  is equipped with a molded fitment  44  to accommodate tubing attachment. The proximal end of the supply tube  40  is coupled with the fluid reservoir  14  so that the lumen  42  is in fluidic communication with the reservoir  14 . 
         [0037]    Although not shown in  FIG. 1 , the connector  34  may also be equipped with a stopcock or a plurality of infusion ports with plugs for receiving a syringe and/or needle. A pump may be installed in line with the supply tube  40 , which may also be equipped with clamps (neither is shown). 
         [0038]    The catheter  16 , connector tubes  24  and supply tube  40  are flexible and pliant to facilitate placement, usage, and to minimize both mechanical insult to the blood vessels and patient discomfort during long-term use. They may be constructed of any suitable medical grade material, such as, for example, polyethylene, polyvinyl chloride, Teflon, silicone elastomer or polyurethane or mixtures thereof. The material may be coated or impregnated with an antimicrobial or antiseptic composition to reduce bacterial adherence and biofilm formation. The catheter  16  may also be constructed of a radiopaque material in order to facilitate imaging for locating any breaks and/or separated sections. 
         [0039]    The strain relief cuffs  20  and  32  and fitment  44  are constructed of an elastomeric medical grade synthetic resin material. The connector  34  may be constructed of a medical grade rigid or semirigid synthetic resinous material suitable for supporting an operable threaded connection, such as, for example, polyvinyl chloride or polycarbonate. 
         [0040]    As best shown in  FIGS. 1 and 2 , the valve assembly  10  broadly includes a housing  46  supporting a valve member  48 . The housing  46  has an elongate, stepped external configuration surrounding an internal fluid passageway or lumen  50 . The lumen  50  has an enlarged diameter adjacent the proximal end to form a hemispherical cavity  52  sized for receiving the dome-shaped valve  48 . The housing  46  includes a hub portion  54 , which is shown positioned for installation in a proximal orientation and a body portion  56  shown in a distal orientation. The housing  46  is formed of a suitable medical grade synthetic resin, such as for example, a polycarbonate. 
         [0041]    The body  56  includes a tapered nipple  58  sized for reception within the lumen  26  of a connector tube  24 . The nipple  58  includes a plurality of spaced, radially expanded annular barbs  60 . While  FIG. 1  depicts two barbs  60  evenly spaced along the nipple  58 , it is foreseen that any number of barbs  60  may be included with any suitable degree of radial expansion and in any spaced configuration. 
         [0042]    The proximal end of the nipple  58  is radially expanded to form a midportion or barrel  62 , having a pair of opposed axial flanges or finger tabs  64  to facilitate manual rotation of the valve assembly  10 . The barrel  62  is radially expanded at the proximal end to form an annular seat  66  for receiving the hub  54 . The seat  66  includes a series of concentric steps  68  perpendicular to the axis of the lumen  50 , each step  68  presenting a concentric side wall  70 , which is coaxial with the lumen  50 . The proximal step  68  serves as a valve seat  72 . The surface of the valve seat  72  includes a raised annular ring or stake  74 , having an angular or pointed, proximal surface adapted for gripping engagement of a valve  48 . 
         [0043]    The hub  54  has a hollow, stepped cylindrical configuration, including a distal skirt portion  76  and a proximal neck  78  with a central lumen  80 . The inner surface of the skirt includes a series of concentric steps  82 , each including a concentric side wall  84  for mating engagement with respective corresponding steps  68  and side walls  72  of the body portion  56 . The proximal step serves as a valve seat  86 . The surface of the valve seat  86  includes a raised annular ring  88 , for gripping engagement of a valve  48 . One of the steps  82  subtends an angle of less than 90 to form an energy director  90 . The neck  78  includes a series of female Luer lock threads,  92  designed for mating engagement with corresponding standard male IV Luer threads in the connector  34 . Alternately, a conventional threaded or bayonet-type fitting may be substituted in the neck  78  and connector  34  for the Luer fittings shown and described. 
         [0044]    As best shown in  FIGS. 3-9 , the valve member  48  includes a dome portion  94  coupled with an outstanding radial flange or lip portion  96 . It is also foreseen that the flange  96  may be of lesser radial extent or omitted entirely. The valve  48  has outer and inner surfaces  98  and  100  respectively and includes a circumferential slit  102  centered on the dome  94 . The slit  102  extends across the fluid flow path for providing fluid communication through the valve  48  when it is in an open position. As best shown in  FIGS. 3 and 5 , the slit  102  is bisected by a central axis C, is coplanar with a slit axis S, and is crossed by a rib axis R perpendicular to axis S. As shown in  FIG. 6 , the slit  102  has outer and inner margins  104  and  106  and a pair of ends  108  and  110 . Because the outer margin  104  is longer than the inner margin  106 , the ends  108  and  110  subtend an angle. 
         [0045]    As illustrated in  FIGS. 6 and 7 , the outer surface  98  of the valve dome  94  has the symmetrical configuration of a hemisphere. It is also foreseen that the dome  94  may be configured as a spherical cap or chordal segment (the region of a sphere that lies above a chordal plane that does not pass through the center of the sphere) which may be either greater or less than one-half of a sphere. The valve dome  94  need not be strictly hemispherical or partially spherical; however it is preferred that it be at least dome-like or cap-like. The outer and inner surfaces  98  and  100  of the valve dome  94  are not perfectly concentric. The inner surface  100  of the valve dome  94  is depicted as having a generally hemispherical configuration, with a slightly increased curvature as it approaches the axis C. As a result, the dome  94  has a variable wall thickness, which diminishes as it approaches an apex region of the dome  94  at the axis C. 
         [0046]    The inner surface  100  of the valve dome  94  is shown in FIGS.  4  and  6 - 7  and in  FIG. 5  in phantom to include an elongate rib  112 . The rib  112  extends generally circumferentially inwardly in the direction of axis R, perpendicular to and centered on the slit  102 , and serves to bias the slit  102  to the closed position depicted in  FIG. 3 . The rib  112  is of approximately rectangular overall configuration, including a pair of spaced, parallel side surfaces or sides  114  and a pair of ends  116  convergent with the inner surface  100  of the valve dome  94 . 
         [0047]    As shown in  FIGS. 6 and 7 , the rib  112  has a depth  118  which diminishes as the ends  116  are approached. The rib  112  may be constructed so that the depth  118  also diminishes as the sides  114  are approached. The rib  112  is bisected by the slit  102  at a center portion  120  of the rib. Thus, the wall thickness of the dome thins as it approaches the geometric center of the slit  102 , and is reinforced at the center along axis R by the depth of the rib  112 . It is foreseen that, rather than bisecting the rib  112 , the slit  102  may intersect the rib  112  eccentrically or asymmetrically, or that the slit  102  may be coextensive with the rib  112 . It is also foreseen that the ends of the rib  116  could be truncated (not shown) so that the depth  118  does not diminish as the ends  116  are approached, or that the ends  116  could be constructed so that the depth  118  increases as the ends are approached. 
         [0048]      FIGS. 11 and 12  depict a valve  122  having an alternate rib construction. The structure of the valve  122  is substantially identical to that previously described, and the numbering and description of like elements and axes is hereby adopted and will not be reiterated. The valve  122  includes a circumferential slit  124  centered on the dome  94 . The inner surface  100  of the dome  94  includes a rib  126  having an approximately hemi-cylindrical overall configuration, including a curvate surface  128  and a pair of ends  130  convergent with the inner surface  100  of the valve dome  94 . As previously described, the rib depth diminishes as the ends  130  are approached. 
         [0049]      FIGS. 13 and 14  depict a valve  132  having a second alternate rib construction. The structure of the valve  132  is also substantially identical to that previously described, and the numbering and description of like elements and axes is also adopted and will not be reiterated. The valve  132  includes a circumferential slit  134 , also centered on the dome  94 . The inner surface  100  of the valve dome  94  includes a rib  136  having an approximately X-shaped or cruciform overall configuration. The rib  136  has a first leg  138  and a second leg  140 , each of approximately rectangular overall configuration. Each of the legs  138  and  140  include a pair of sides  142  and  144 , and a pair of ends  146  and  148  respectively. The first leg  138  is coextensive with the slit  134 , whereas the second leg  140  is orthogonal to the slit  134 . The leg ends  146  and  148  are convergent with the inner surface  100  of the valve dome  94 . As previously described, the rib depth diminishes as the ends  146  and  148  are approached. Those skilled in the art will appreciate that, in addition to the rib configurations previously described, the rib may be of oblong, elliptical, quadrilateral, star-shaped, curvate, compound curvate, circular, curvilinear or any other suitable configuration. 
         [0050]    The valve dome  94 , lip  96  and ribs  112 ,  126  and  136  are of unitary construction and are formed of a resilient medical grade elastomeric material such as a silicone elastomer. The characteristics of the material used to construct the valve  48  and housing  46 , the dimensions of the valve dome  94 , flange  96 , ribs  112 ,  126  and  136  and slit  102 ,  124  or  134  the wall thickness of the valve  48  as well as the magnitude of thinning of the wall as it approaches the top of the dome  94  and location of the slit  102 ,  124  or  134  (whether centered on the dome or eccentric) are variables which collectively determine both the magnitude and difference between individual pressure differentials P.sub. 1  and P.sub. 2  under which the slit  102 ,  124  or  134  flexes in forward and reverse fluid-enabling manner. 
         [0051]    The valve assembly  10  may be constructed by aligning the valve member  48  or  122  or  132  on the body portion  56  of the housing  46  so that the outer surface  98  of the valve flange  96  engages the body valve seat  72  and projecting stake  74 , and is received within cavity  52 . 
         [0052]    The hub  54  is installed over the body  56  with the body and hub steps  68  and  82  in mating engagement and the hub valve seat  86  and projecting ring  88  overlying the valve flange  96 . The hub  54  and body  56  are then subject to ultrasonic welding under pressure to form a hermetic seal. The energy director  90  serves to direct the ultrasonic melt, so that the surfaces of the mated steps  68  and  82  fuse and the valve flange  96  is captured between the stake  74  and the ring  88  in a generally S-shaped cross sectional configuration as depicted in  FIG. 2 . In this manner, the valve  48  or  122  or  132  is secured in place against dislodgement by fluid pressure or force exerted by any object which might be inserted into the housing lumen  50 . Alternatively, the hub  54  and body  56  may be secured together by an adhesive composition, by a strictly mechanical junction, or by other arrangements. 
         [0053]    The valve assembly may be installed in an intravascular device  12  by grasping the housing  47  and using the finger tabs  64  to rotatingly introduce the nipple  58  into the lumen  26  at the proximal end portion  28  of a connector tube  24  until all of the barbs  60  are received within the lumen  26 . The barbs  60  serve to frictionally engage the inner surface of the connector tube lumen  26  in a force fit. It is foreseen that, where a single IV line is to be employed, a connector tube  24  may be unnecessary so that the housing  46  may be introduced directly into the catheter lumen  18  at the proximal end of a catheter  16 . A connector  34  is aligned over the neck  78  and rotated until the threaded interior surface  36  tightly engages the threads  92  of the neck  78 . More than one valve assembly  10  may be installed in-line in an intravascular device  12 . 
         [0054]    In use, the catheter  16  is inserted into a blood vessel of a patient, so that the catheter lumen  18  is in fluidic communication with the patient&#39;s blood. If the catheter  16  is to be centrally placed, it is then threaded into a large central vein where it may remain indwelling for a prolonged period of time. 
         [0055]    An intravascular fluid source or reservoir  14  is coupled with the supply tube  40  so that the supply tube lumen  42  is in fluidic communication with the reservoir. Gravity fluid flow is initiated from the fluid source  14  by any conventional means, such as by opening a stopcock or removing a clamp. Fluid flow may also be initiated by actuating a pump. Fluid from the reservoir  14  travels in a flow path through the supply tube  40  into the housing lumen  50  and through the valve  48  or  122  or  132  until it contacts the inner surface  100  of the dome. 
         [0056]    As shown in  FIG. 8 , when the forward fluid flow exerts or exceeds a predetermined fluid pressure differential P.sub. 1  or cracking pressure against the dome inner surface  100 , the slit  102  flexes distally to an open, forward flow-enabling position. In valves  122  and  132 , similar pressure conditions cause similar flexion of the respective slits  124  and  134 . The axial thinning of the dome  94 , the shorter length of the slit inner margin  106  with respect to the slit outer margin  104 , and the angle subtended by the ends of the slit  108  and  110  all cooperate to facilitate flexing of the slit  102  or  124  or  134  at a relatively low pressure differential, such as is provided by the force of gravity on an elevated fluid reservoir. 
         [0057]    The slit  102  or  124  or  134  remains in an open position to permit the flow of fluid in a forward direction as long as the pressure differential P.sub. 1  is maintained against the dome inner surface  100 . When the fluid supply in the fluid reservoir  14  is exhausted, the pressure differential against the dome inner surface  100  falls below the cracking pressure P.sub. 1 , and the rib  112 , or  122  or  128  serves to bias the slit  102  or  124  or  134  back into a closed, flow-blocking position, depicted in  FIG. 7 . The rib  112 , or  122  or  128  also biases the closed slit margins  104  and  106  into sealing alignment, so that there is no overlap which might permit leakage through the valve. The pressure differential P.sub. 1  is preselected by design so that the slit  102  or  124  or  134  closes while a fluid head remains in the supply tube  40 , so that air does not enter the valve  48  or  122  or  132 . 
         [0058]    At times, it may be necessary to permit reverse fluid flow, for example to withdraw a blood sample. In such instances, a syringe may be inserted into the hub  54  and the plunger withdrawn to create a negative pressure. As shown in  FIG. 9 , when a predetermined fluid pressure differential P.sub. 2 , or collapsing pressure, is exerted or exceeded against the dome outer surface  98 , the slit  102  or  124  or  134  flexes proximally to an open, reverse flow-enabling position. Flexing of the slit is accompanied by proximal collapse of a portion of the dome  94 . Because of the axial thinning of the dome  94  in the region of the slit once the pressure differential P.sub. 2  is reached, only a limited portion of the dome flexes proximally, and the entire dome  94  does not invert into the hub lumen  80 . In this manner, the volume of fluid displace back in to the housing lumen  50  is minimized when the pressure falls below P.sub. 2  and the rib  112  or  122  or  128  biases the slit  102  or  124  or  134  back into a closed, fluid flow blocking position depicted in  FIG. 7 . Advantageously, the combination of the hemispherical shape of the dome  94 , the angular ends of the slit  102 , the anterior thinning of the dome  94  in the region of the slit  102  or  124  or  134 , and the rib  112  or  122  or  128  combine to provide a valve  48  having a relatively low cracking pressure P.sub. 1 , a relatively high reflux pressure P.sub. 2  and minimal fluid displacement following reverse fluid flow. This combination of features permits forward fluid flow by gravity from a reservoir and into a patient, while inhibiting thrombus promoting fluid backflow and minimizing reflux volume. 
         [0059]    The structure of a an alternate valve assembly housing is illustrated in  FIG. 10  and is generally indicated by the reference numeral  150 . The housing  150  has an elongate, generally cylindrical external configuration surrounding a fluid passageway or lumen  152 , which widens proximally for receiving the dome-shaped valve member  48  previously described. The housing  150  includes a hub portion  154  and a body portion  156 . 
         [0060]    The distal portion of the body  156  is configured as a standard Luer connector, including a standard Luer taper  158  and standard male luer lock threaded overmantle  160  or internally threaded collar. The proximal portion of the body  156  and distal portion of the hub  154  are matingly stepped as previously described with respect to the body  56  and hub  54 . The proximal portion of the hub  154  is configured with a truncated, Luer threaded top  162 . 
         [0061]    In use, the male Luer body  156  may be rotatingly coupled with any standard female Luer connection, while the female Luer hub  154  may be coupled with any standard male Luer connection in order to install the valve assembly housing  150  in-line between an intravascular fluid source and an indwelling catheter  16 . The operation of the valve member  48  within the housing  150  is substantially the same as previously described with respect to the valve member  48  within the housing  46 . 
         [0062]    It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.