Abstract:
A blood flow reversal valve useful in hemodialysis having rotational detent features enabling audible and tactile feedback to a clinician and alignment features such as visible indicators associated with the blood lines on either side of the valve to confirm normal or reverse flow.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/616,794, filed Oct. 7, 2004 and entitled “Blood Flow Reversal Device for Hemodialysis,” which is incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     This invention relates to blood flow reversal valves and related systems and methods. 
     BACKGROUND 
     Many modern medical procedures use tubing sets of varying complexity to withdraw fluid from a patient, or to administer fluid to a patient, or to do both. One example of such a procedure is hemodialysis. In hemodialysis, the patient&#39;s blood is cleansed by drawing it out of the patient through a blood access site, typically via a catheter, and passing it through an artificial kidney (often called a “dialyzer”). The artificial kidney includes a semi-permeable membrane which removes impurities and toxins by a process of diffusion. The purified blood is then returned to the patient. An extracorporeal circuit including a pump and hemodialysis tubing set is typically used to transport the blood between the blood access site and the artificial kidney. 
     Many of the tubing sets used in medical procedures involving extracorporeal treatment of fluid, such as hemodialysis, are configured so that fluid can flow through the system in a desired direction during the medical procedure. A pumping device can be used to control the fluid flow rate in the system. In hemodialysis, for example, a peristaltic pump is typically used to draw blood from the patient and move the blood through the tubing set during the treatment procedure. During hemodialysis, blood is initially drawn from the patient&#39;s blood access (e.g., a vein or an artery, but more typically an arteriovenous graft or fistula) and flows through a series of connected tubing segments to the artificial kidney for cleansing. After passing through the artificial kidney, the blood then flows through other tubing segments that return the blood to the patient. Thus there is generally a continuous circuit of blood flowing from the patient, through the artificial kidney, and then back to the patient during treatment. 
     During hemodialysis, blood is generally drawn from an upstream position in the blood access and then returned to a downstream position in the blood access. However, it has been found to be advantageous, for limited time periods, to reverse the direction that blood is received from and returned to the patient during hemodialysis. When the blood flow is reversed, blood is initially drawn from a downstream position in the blood access. The blood then flows through tubing segments to the artificial kidney for treatment before it is returned to the upstream position in the blood access. Typically this procedure is carried out by trained clinical personnel, e.g., dialysis clinicians. When the blood flow is reversed, any of various parameters, such as blood access flow rate, can be measured or derived from measurements. The data can provide useful information about the patient&#39;s condition and the effectiveness of the treatment. For example, practitioners can use information gathered during periods of reversed blood flow to evaluate the condition of the blood access, to get advanced warning on other health problems, such as access restrictions, and to prescribe preventive measures, such as blood access revision or replacements, which are generally needed after a few years of continuous dialysis. 
     Anything which makes the blood reversal maneuver faster and more secure would be generally helpful to clinicians in mastering and flawlessly carrying out this important procedure. 
     SUMMARY 
     In one aspect of the invention, a blood flow reversal valve for extracorporeal blood lines includes a first valve portion defining first and second ports extending therethrough and a second valve portion defining first and second ports extending therethrough. The valve portions are rotatably secured to one another, and configured to be rotated into a first position in which the first ports are aligned with one another and the second ports are aligned with one another. The valve portions are constructed to produce an audible click upon being rotated into the first position. 
     In another aspect of the invention, a blood flow reversal valve for extracorporeal blood lines includes a first valve portion defining first and second ports extending therethrough and a second valve portion defining first and second ports extending therethrough. The valve portions are rotatably secured to one another, and configured to be rotated into a first position in which the first ports are aligned with one another and the second ports are aligned with one another. The valve portions are constructed to provide tactile feedback to a clinician when the clinician manually rotates the valve portions into the first position. 
     In a further aspect of the invention, a blood flow reversal valve for extracorporeal blood lines includes a first valve portion defining first and second ports extending therethrough and a second valve portion defining first and second ports extending therethrough. The first and second valve portions are rotatable relative to one another between a first engaged position and a second engaged position. Each of the first and second valve portions includes at least one alignment feature. The alignment features are arranged to align with one another when the valve portions are in one of the engaged positions. 
     Embodiments may include one or more of the following features. 
     In some embodiments, the second valve portion includes a detent mechanism, and the first valve portion includes a projection configured to engage the detent when the valve portions are in the first position. 
     In certain embodiments, the detent mechanism includes two raised members that are circumferentially spaced from one another, and the projection is adapted to fit securely between the raised members when the valve portions are in the first position. 
     In some embodiments, one of the raised members includes a stop configured to prevent the first and second valve portions from being rotated relative to one another beyond a predetermined position. 
     In certain embodiments, the raised members extend from a side surface of the second valve portion. 
     In some embodiments, the projection extends from an inner surface of the first valve portion. 
     In certain embodiments, the projection is configured to snap into engagement with the detent mechanism when the first and second valve portions are rotated into the first position. 
     In some embodiments, the snapping of the projection into engagement with the detent mechanism produces the audible click. 
     In certain embodiments, the valve portions are constructed to provide tactile feedback to a clinician when the clinician manually rotates the valve portions into the first position. 
     In some embodiments, the valve portions are constructed to be substantially rotationally fixed relative to one another in the first position. 
     In certain embodiments, the first and second valve portions are configured to be rotated into a second position in which the first port of the first valve portion is aligned with the second port of the second valve portion and the second port of the first valve portion is aligned with the first port of the second valve portion. 
     In some embodiments, the second valve portion includes first and second detent mechanisms that are circumferentially spaced from one another by approximately 180 degrees. 
     In certain embodiments, the first valve portion includes a projection configured to engage the first detent mechanism when the valve portions are in the first position and configured to engage the second detent mechanism when the valve portions are in the second position. 
     In some embodiments, the valve portions are constructed to be substantially rotationally fixed relative to one another in the first and second positions. 
     In certain embodiments, the first and second valve portions are substantially disk-shaped, and coaxially rotatably connected to each other. 
     In some embodiments, the first and second valve portions are rotatable to a third position in which none of the ports are aligned with one another. 
     In certain embodiments, in the third position, blood is substantially prevented from passing from the first valve portion to the second valve portion. 
     In some embodiments, each of the valve portions includes an alignment feature, and the alignment features are arranged to align with one another when the valve portions are in the first position. 
     In certain embodiments, the first and second valve portions include blood line connectors configured to fluidly connect blood lines to the first and second valve portions, and the alignment features are disposed on the blood line connectors. 
     In some embodiments, the alignment features include bands adapted to be secured to the blood line connectors. 
     In certain embodiments, the blood flow reversal valve includes a gasket configured to be compressed between the first and second valve portions. 
     In some embodiments, the gasket is securable to one of the valve portions. 
     In certain embodiments, the tactile feedback includes increased rotational resistance. 
     In some embodiments, the valve is configured to produce increased rotational resistance over a span of about 15° to about 30°. 
     In certain embodiments, the tactile feedback includes an abrupt stop in rotation of the first and second valve portions relative to one another. 
     In some embodiments, the first valve portion includes a detent mechanism, and the second valve portion includes a projection configured to engage the detent mechanism when the valve portions are in the first position. 
     In certain embodiments, the detent mechanism includes a raised member constructed to provide rotational resistance to the valve portions. 
     In some embodiments, the raised member is configured to deflect the projection when the valve portions are rotated into the first position. 
     In certain embodiments, the alignment features include visual indicators. 
     In some embodiments, each of the valve portions includes first and second alignment features, and the first alignment features are dissimilar to the second alignment features. 
     In certain embodiments, the first alignment features are aligned with one another in the first position. 
     In some embodiments, the first alignment feature of the first valve portion is aligned with the second alignment feature of the second valve portion when the valve portions are in the second position. 
     In certain embodiments, the first and second valve portions include blood line connectors extending from outer surfaces of the valve portions, and the alignment features include visual indicators disposed on the blood line connectors. 
     In some embodiments, the alignment features include colored bands. 
     Embodiments may include one or more of the following advantages. 
     In some embodiments, the first and second valve portions are constructed to produce an audible click and/or tactile feedback when they are rotated relative to one another into a first position (e.g., a standard flow position) and/or a second position (e.g., a reversed flow position). The audible click and/or the tactile feedback can help to inform the clinician when the valve portions have been moved into the first position and/or the second position. 
     In certain embodiments, the blood line connectors include alignment features (e.g., visual indicators, such as colored bands). The alignment features can, for example, help to inform the clinician whether the valve is in the first position, the second position, or an intermediate position in between the first and second positions. 
     In some embodiments, the valve portions are configured to become rotationally fixed relative to one another when the valve is in the first and/or the second position. This rotationally fixed arrangement can help to prevent unintentional rotation of the valve portions relative to one another during treatment. 
     Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of a blood flow reversal valve. 
         FIG. 2  is an axially exploded side view of the blood flow reversal valve of  FIG. 1 , showing its internal gasket as well as its top and bottom valve bodies. 
         FIG. 3  is an axially exploded, perspective view of the blood flow reversal valve of  FIG. 1 , with portions cut away. 
         FIG. 4  is a side view of the top valve body of the blood flow reversal valve of  FIGS. 1-3 . 
         FIG. 5  is a top, perspective view of the top valve body of  FIG. 4 . 
         FIG. 6  is a bottom view of the top valve body of  FIG. 4 . 
         FIG. 7  is a bottom, perspective view of the top valve body of  FIG. 4 . 
         FIG. 8  is an enlarged detail view of the region  8  in  FIG. 7 . 
         FIG. 9  is a top view of the top valve body of  FIG. 4 . 
         FIG. 10  is a side view of the bottom valve body of the blood flow reversal valve of  FIGS. 1-3 . 
         FIG. 11  is a bottom, perspective view of the bottom valve body of  FIG. 10 . 
         FIG. 12  is a top view of the bottom valve body of  FIG. 10 . 
         FIG. 13  is a top, perspective view of the bottom valve body  FIG. 10 . 
         FIG. 14  is a bottom view of the bottom valve body of  FIG. 10 . 
         FIGS. 15A and 15B  are, respectively top and bottom, perspective views of the gasket inside the blood flow reversal valve of  FIGS. 1-3 . 
         FIG. 16  is a cross-sectional view taken along line  16 - 16  in  FIG. 1 . 
         FIGS. 17A-17D  are top, schematic views illustrating the operation of the blood flow reversal valve of  FIG. 1 , showing respective phases of relative rotation between the top and bottom valve bodies, features of the top valve body being shown in phantom. 
         FIG. 18  is a schematic diagram of the blood flow reversal valve of  FIG. 1  connected to an extracorporeal blood line for hemodialysis in an embodiment of a blood treatment system. 
         FIGS. 19A and 19B  are similar schematic diagrams illustrating how the blood treatment system of  FIG. 18  can be used to accomplish blood flow reversal in a hemodialysis patient, showing the valve of  FIG. 1  in its normal and reversed orientation, respectively. 
     
    
    
     Like reference numerals in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-3 , a blood flow reversal valve  100  includes a generally cylindrical top valve body  102 , a generally cylindrical bottom valve body  104 , and a generally disk-shaped gasket  114  situated between top valve body  102  and bottom valve body  104 . Top valve body  102  includes two fluid passages  106  and  108  extending therethrough, and bottom valve body  104  includes two fluid passages  110  and  112  extending therethrough. Gasket  114  similarly includes two ports  118  and  120  extending therethrough. Passages  106 ,  118  and  110  are normally aligned, as are passages  108 ,  120  and  112  as shown in  FIG. 2 . Gasket  114 , as described below, can be secured to bottom valve body  104  so that ports  118  and  120  of gasket  114  remain aligned with fluid passages  110  and  112  of bottom valve body  104 , respectively, during use. Top valve body  102  and bottom valve body  104  are generally injection molded components preferably made of a biocompatible high-impact thermoplastic materials. Gasket  114  is generally a compression molded component made of silicone-like material as described in more detail below. 
     Top valve body  102  and bottom valve body  104  are coaxially rotatably secured to one another. Top valve body  102  and bottom valve body  104  can, for example, be rotated relative to one another into a first position in which fluid passage  106  is aligned with fluid passage  110  and fluid passage  108  is aligned with fluid passage  112 , as shown in  FIGS. 1 and 2 . Top valve body  102  and bottom valve body  104  can also be rotated, preferably up to 180 degrees into other relative positions. In particular, top valve body  102  and bottom valve body  104  can be rotated relative to one another into an alternative, second position in which the alignment is reversed so that fluid passage  106  is aligned with fluid passage  112  and fluid passage  108  is aligned with fluid passage  110 . 
     Blood flow reversal valve  100  is constructed to produce an audible click and tactile feedback when rotated into the first and second positions, which correspond to normal and reverse flow. Valve  100 , as described below, also includes alignment features (e.g., visual indicators) that can help the clinician determine the rotational position of top valve body  102  and bottom valve body  104  relative to one another during use. The audible click, the tactile feedback, and the alignment features of valve  100  can, for example, help the clinician determine whether valve  100  is arranged in the first position, in the second position, or in an intermediate position between the first and second positions. 
     Valve  100 , as described in more detail below, can be used as a component of the extracorporeal circuit of a blood treatment system (e.g., a hemodialysis system). During treatment, the route of blood flowing through fluid passages  106  and  108  of top valve body  102  can be switched by changing the position of top valve body  102  and bottom valve body  104  relative to one another. The direction in which blood enters and exits valve top valve body  102  can be reversed by rotating valve  100  from the first position in which fluid passage  106  is aligned with fluid passage  110  and fluid passage  108  is aligned with fluid passage  112  to the second position in which passage  106  is aligned with passage  112  and passage  108  is aligned with passage  110 . Reversal of the blood flow can, for example, help the clinician take measurements to determine the flow rate of blood through the blood access. 
     Referring to  FIGS. 4 and 5 , top valve body  102  is a generally cap-shaped device that includes a disk-shaped plate  116  and a cylindrical side wall  128  extending integrally from plate  116 . Multiple circumferentially spaced connectors  133  extend inwardly from side wall  128  and connect side wall  128  to plate  116 . Tubular blood line connectors  136  and  138  extend integrally from the outer surface  140  of plate  116  of top valve body  102 . Plate  116  and blood line connectors  136  and  138  together form fluid passages  106  and  108 , which extend from the outer end surfaces of blood line connectors  136  and  138  to an inner surface  124  ( FIG. 6 ) of top valve body  102 . Fluid passages  106  and  108  fluidly connect the exterior of top valve body  102  to the interior of top valve body  102 . As a result, during use, blood can pass from the exterior of top valve body  102  to the interior of top valve body  102 , and vice versa. 
     Side wall  128  generally extends around the circumference of plate  116 . Side wall  128  and inner surface  124  form a cavity in which a seat portion of bottom valve body  104  can be secured when valve  100  is assembled, as described below. 
     As shown in  FIG. 5 , multiple outer apertures  145  are circumferentially spaced about the perimeter of top valve body  102  between connectors  133 . Multiple center apertures  147  are circumferentially spaced about the perimeter of center pin  122 . An exterior surface  130  of side wall  128  includes multiple grooves or depressions  132 . Grooves  132  can provide improved grip for the clinician to rotate top valve body  102  relative to bottom valve body  104  during use. Other gripping mechanisms, such as ribs, knurls, and/or tabs, can alternatively or additionally be used to enhance the manual rotatability of top valve body  102 . 
     As shown in  FIG. 6 , fluid passages  106  and  108  are circumferentially spaced by about 180° and are positioned equidistant from the center of top valve body  102 . Fluid passages  106  and  108  typically have a diameter of about 3.0 millimeters to about 3.8 millimeters. However, fluid passages can have larger or smaller diameters. Fluid passages  106  and  108  can, for example, have diameters ranging from about 1.5 millimeters to about 6.35 millimeters. In some embodiments, the diameters of fluid passages  106  and  108  gradually increase toward the distal end surfaces of blood line connectors  136  and  138 . This gradual increase in diameter can help to prevent bubbles from developing in the blood as the blood enters and/or exits blood line connectors  136  and  138 . 
     Referring to  FIG. 7 , multiple resilient retaining members (e.g., resilient wedges)  135  extend inwardly (e.g., toward the center of top valve body  102 ) from side wall  128 . Retaining members  135  are circumferentially spaced around side wall  128 . As shown in  FIG. 8 , retaining members  135  include engagement surfaces  137  that extend substantially perpendicular to side wall  128 , and guide surfaces  139  that extend at an acute angle relative to side wall  128 . Retaining members  135 , as described below, help to secure the seat portion of bottom valve body  104  within the cavity of top valve body  102 . 
     Referring again to  FIGS. 6 and 7 , center pin  122  extends from the center of inner surface  124  of top valve body  102 . Center pin  122  extends approximately along the rotational axis of top valve body  102 . Multiple resilient fingers  126  are spaced about the circumference of center pin  122  at its free end. Resilient fingers  126  can be elastically deformed inwardly (e.g., toward the center of center pin  122 ) when an inward compressive force is applied to center pin  122 . Like retaining members  135 , center pin  122  cooperates with surfaces of bottom valve body  104  to secure top valve body  102  and bottom valve body  104  together. 
     As shown best in  FIGS. 6 and 7 , a resilient projection  134 , designed to interact with cam-like surfaces on the bottom valve body during rotation, protrudes from inner surface  124  of top valve body  102  at a location that is spaced inwardly from side wall  128  and circumferentially about half way between the location of the two passages  106  and  108  situated between two of the resilient retaining members  135 . Resilient projection  134  is constructed to elastically deform outwardly (e.g., toward side wall  128 ) when an outward force that exceeds a predetermined limit is applied to it, and is designed to snap back into its original position upon removal of the outward force. Resilient projection  134 , as shown in  FIG. 7 , is substantially wedge-shaped and has generally flat circumferential end surfaces. Resilient projection  134  can cooperate with one or more structural features of bottom valve body  104  to prevent top valve body  102  and bottom valve body  104  from rotating relative to one another beyond a predetermined position. The inner surface of resilient projection  134  generally extends at an acute angle relative to side wall  128 . 
     Annular channels  125  and  127  are formed in inner surface  124  as shown in  FIGS. 6 and 7 . Channel  125  extends generally around the perimeter of plate  116 , and channel  127  extends around the perimeter of center pin  122 . These channels can be configured to receive raised annular edges or rims of gasket  114  when valve  100  is assembled, which insures a fluid tight seal between top valve body  102  and gasket  114  during use. Annular rims  129  and  131  extend from inner surface  124  around fluid passages  106  and  108 , respectively. Annular rims  129  and  131  also help to promote a fluid-tight seal between top valve body  102  and gasket  114  while top valve body  102  is being rotated relative to bottom valve body  104  and gasket  114  and while top valve body  102  is stationary relative to bottom valve body  104  and gasket  114 . 
     Top valve body  102  also includes alignment features, which can help the clinician to operate valve  100  in accordance with the methods described herein, and, in addition, serve as an aid in assembling the valve. Referring to  FIG. 9 , for example, outer surface  140  of top valve body  102  includes a letter  141  and an arrow  143 . Letter  141  and/or arrow  143  can be raised relative to outer surface  140 . As a result, letter  141  and arrow  143  can provide the clinician with tactile reference points as well as visual reference points during use. Letter  141  and arrow  143  is preferably integrally molded but can be formed on top valve body  102  using any of various techniques, such as molding, printing, pressing, and/or stamping. Letter  141  and arrow  143  can help the clinician to position top valve body  102  as desired relative to bottom valve body  104  during use. Letter  141  can, for example, help the clinician to initially align top valve body  102  and bottom valve body  104  during assembly, and arrow  143  can help indicate to the clinician the direction in which top valve body  102  can be rotated relative to bottom valve body  104  in order to move valve  100  from the first position to the second position. 
     Top valve body  102  is preferably formed of biocompatible injection molded acrylic-based multipolymer compound (e.g., a biocompatible high impact MMA/styrene/acrylonitrile terpolymer or similar injection moldable thermoplastic compound). However, in some embodiments, one or more other materials and/or manufacturing techniques can be used. In certain embodiments, top valve body  102  and bottom valve body  104  may be formed of one or more biocompatible thermoplastic or thermoset materials. In some embodiments, top valve body  102  may include one or more relatively rigid materials. In certain embodiments, top valve body  102  may include one or more relatively resilient materials. Top valve body  102  can, for example, include acrylic-based multipolymers, polycarbonate, polysulfone, or blends of these types of materials. 
     Referring to  FIGS. 10 and 11 , bottom valve body  104 , like top valve body  102 , is a substantially disk-shaped device. Bottom valve body  104  includes a tapered seat  149 , which has a slightly smaller diameter than the cavity formed by side wall  128  and inner surface  124  of top valve body  102 . Consequently, seat  149  can be inserted into the cavity formed by top valve body  102 . Generally, when seat  149  is inserted into the cavity of top valve body  102 , as shown in  FIG. 1 , for example, sufficient space remains between a side surface  152  of seat  149  and side wall  128  of top valve body  102  ( FIGS. 4-7 ) to allow top valve body  102  and bottom valve body  104  to rotate relative to one another. For example, a clearance of about 0.127 millimeter can exist between seat  149  and side wall  128 . 
     Tubular blood line connectors  164  and  166  extend from an outer surface  144  of bottom valve body  104 . Blood line connectors  164  and  166  include base portions  168  and  170 , respectively, which have a larger outer diameter than the remainder of the blood line connectors. Base portions  168  and  170  can provide blood line connectors  164  and  166  with increased mechanical strength, which can help to prevent shearing of the blood line connectors  164  and  166  as the clinician rotates bottom valve body  104  relative to top valve body  102 . Blood line connectors  164  and  166 , together with seat  149 , form fluid passages  110  and  112 , which fluidly connect the interior of bottom valve body  104  to the exterior of bottom valve body  104 . Fluid passages  110  and  112  are circumferentially spaced by about 180° and are positioned equidistant from the center of bottom valve body  104 . Fluid passages  110  and  112  of bottom valve body  104  and fluid passages  106  and  108  of top valve body  102  preferably have substantially similar dimensions (e.g., substantially similar diameters). The similar dimensions of the fluid passages help to prevent turbulent blood flow as blood passes through valve  100 , from top valve body  102  to bottom valve body  104  and vice versa. This can help to prevent blood conditions, such as hemolysis, from occurring during use of valve  100 . 
     As shown in  FIG. 10 , flange  153  extends circumferentially around an outer edge of seat  149 . Flange  153  includes an outer surface  155  and a tapered surface  158 . When top valve body  102  and bottom valve body  104  are assembled, retaining members  135  (e.g., engagement surfaces  137  of retaining members  135 ) ( FIG. 8 ) engage outer surface  155  of flange  153  to trap the bottom valve body as it snaps in place and thus prevent top valve body  102  and valve  104  from being separated from one another. 
     Referring to  FIGS. 12 and 13 , a cylindrical passage  162  extends through the center of seat  149 . Passage  162  has a diameter that is slightly less than (e.g., about 0.51 millimeter to about 0.61 millimeter less than) the diameter of center pin  122  of top valve body  102  ( FIGS. 6 and 7 ). Passage  162  can be configured to receive center pin  122  of top valve body  102  when valve  100  is assembled to help secure top and bottom valve bodies  102  and  104  together. 
     Still referring to  FIGS. 12 and 13 , the inner surface of bottom valve body  104  includes a recessed region  157 . Recessed region  157  is sized and shaped to receive gasket  114 . Tubular members  159  and  161  extend from the surface of recessed region  157  around fluid passages  110  and  112 . A tubular member  163  similarly extends from the surface of recessed region  157  around the perimeter of passage  162 . Multiple annular channels  165 ,  167 ,  169 , and  171  are formed in the surface of recessed region  157 . Annular channel  165  extends around the circumference of recessed region  157 . Annular channels  167 ,  169 , and  171  extend around the perimeters of tubular members  159 ,  161 , and  163 , respectively. Annular channels  165 ,  167 ,  169 , and  171  are sized and shaped to receive raised features (e.g., raised ridges)  173 ,  175 ,  177 , and  179 , respectively, of gasket  114  ( FIG. 15A ) when valve  100  is assembled. The mating relationship between the channels of valve body  104  and the raised features of gasket  114  insure a relatively fluid tight seal between those components. 
     A semi-circular ridge  180  extends from tapered side surface  152  of seat  149  and is integrally attached to stops  182  and  184  at its circumferential ends. Stops  182  and  184  are raised members that extend outwardly from side surface  152 . End surfaces  186  and  188  of stops  182  and  184 , respectively, can, for example, extend at an angle that is substantially perpendicular to side surface  152 . Semi-circular ridge  180  reinforces stops  182  and  184 . Thus, semi-circular ridge  180  can help to prevent stops  182  and  184  from being deformed when a rotational force is applied to stops  182  and  184 . 
     Two locking features (e.g., raised bars)  148  and  150  also extend from side surface  152  of seat  149 . Locking features  148  and  150  can, for example, extend about 0.4 millimeter to about 0.5 millimeter outwardly from side surface  152 . Locking features  148  and  150  are generally circumferentially spaced from stops  182  and  184 , respectively, by a distance that is slightly greater than or equal to the circumferential length of projection  134  ( FIGS. 6 and 7 ). Locking features  148  and  150  can, for example, be circumferentially spaced apart from stops  182  and  184 , respectively, by about 10 degrees to about 15 degrees (e.g., about 12.5 degrees to about 13.5 degrees). Locking features  148  and  150  can be circumferentially spaced from stops  182  and  184 , respectively, by about 2.0 millimeters to about 5.0 millimeters (e.g., about 3.63 millimeters to about 3.70 millimeters). Stops  182  and  184  can extend outwardly from side surface  152  by about 2.0 millimeter or more (e.g., about 3.0 millimeters or more, 4.0 millimeters or more) and/or about 5.0 millimeters or less (e.g., about 4.0 millimeters or less, about 3.0 millimeters or less). 
     As shown in  FIG. 14 , an outer surface  185  of bottom valve body  104  includes an annular depression  187  extending around passage  162 . Annular depression  187  provides a flanged surface that can be engaged by resilient fingers  126  of center pin  122  ( FIG. 7 ) when valve  100  is assembled. The engagement of resilient fingers  126  with the flanged portion of outer surface  185  can help to secure top valve body  102  and bottom valve body  104  to one another. Outer surface  185  also includes a letter  189  and an arrow  190 . Letter  189  and arrow  190  are similar to those discussed above with respect to top valve body  102 . Letter  189  and arrow  190  can help the to initially align top valve body  102  and bottom valve body  104  during assembly and can help indicate to the clinician the direction in which bottom valve body  104  can be rotated relative to top valve body  102  in order to move valve  100  from the first, standard flow position to the second, reverse flow position. Letter  189  and arrow  190  can also be used together with letter  141  and arrow  143  on top valve body  102  to determine the rotational position of bottom valve body  104  relative to top valve body  102  (e.g., to determine whether valve  100  is in the first position, the second position, or an intermediate position between the first and second positions). 
     Bottom valve body  104 , like top valve body  102 , is generally formed of an injection molded thermoplastic, preferably an acrylic-based multipolymer (e.g., a biocompatible high impact MMA/styrene/acrylonitrile terpolymer or similar injection moldable thermoplastic compound). Bottom valve body  104 , however, can alternatively or additionally be formed using any of the various other materials and/or techniques described above with respect to top valve body  102 . 
     Referring to  FIGS. 15A and 15B , gasket  114  includes fluid ports  118  and  120  and a central aperture  121 . Ports  118  and  120  are circumferentially spaced by approximately 180° and are spaced equidistant from the center of gasket  114 . Gasket  114  is generally sized and shaped to fit within recessed region  157  of bottom valve body  104  ( FIGS. 12 and 13 ). A bottom side of gasket  114 , as shown in  FIG. 15A , includes multiple protruding ridges  173 ,  175 ,  177 , and  179 . Protruding ridge  173  extends around the perimeter of gasket  114 . Ridges  175  and  177  extend around ports  118  and  120 , and ridge  179  extends around central aperture  121 . Gasket  114  can be secured within recessed region  157  of bottom valve body  104  such that ports  118  and  120  of gasket  114  are aligned with fluid passages  110  and  112 , respectively, of bottom valve body  104 . When positioned within recessed region  157  of bottom valve body  104 , tubular members  159  and  161  of bottom valve body  104  extend at least partially through ports  118  and  120 , and tubular member  163  of bottom valve body  104  extends at least partially through central aperture  121 . Similarly, ridges  173 ,  175 ,  177 , and  179  of gasket  114  extend into channels  165 ,  167 ,  169 , and  171 , respectively, formed in the inner surface of bottom valve body  104 . As a result, gasket  114  can be substantially prevented from rotating relative to bottom valve body  104  during use. The interaction between the ridges of gasket  114  and the channels of bottom valve body  104  can also help to promote a fluid-tight seal between gasket  114  and bottom valve body  104 . 
     As shown in  FIG. 15B , an opposite side of gasket  114  also includes a protruding annular rim  181  extending about its perimeter and a raised annular surface  183  extending around aperture  121 . When valve  100  is assembled, rim  181  and raised surface  183  of gasket  114  extend into channels  125  and  127 , respectively, of top valve body  102  ( FIGS. 6 and 7 ). The interaction of rim  181  with channel  125  and of raised surface  183  with channel  127  helps to promote a fluid-tight seal between gasket  114  and top valve body  102 . Rim  181  and raised surface  183  can slide within channels  125  and  127 , respectively, when top valve body  102  and bottom valve body  104  are rotated relative to one another. 
     Gasket  114  is generally more compliant than top valve body  102  and bottom valve body  104 . In certain embodiments, gasket  114  has a thickness that is slightly greater than the distance between the inner surfaces of top valve body  102  and bottom valve body  104  when they are secured to one another. As a result, gasket  114  can be compressed between top valve body  102  and bottom valve body  104  when valve  100  is assembled, which can help to ensure a fluid tight seal of valve  100 . 
     Gasket  114  is generally formed of polyisoprene using compression molding techniques. However, other materials and/or techniques can be used to form gasket  114 . In certain embodiments, gasket  114  includes one or more biocompatible materials. In some embodiments, gasket  114  includes one or more relatively compliant materials. Gasket  114  can, for example, include one or more materials that have a durometer of about 30 Shore D to about 40 Shore D (e.g., about 30 Shore D). In certain embodiments, gasket  114  includes one or more thermoplastic elastomers. In some embodiments, gasket  114  includes latex, silicone, krayton, or blends of these types of materials. 
     To assemble valve  100 , gasket  114  can first be positioned in bottom valve body  104 , as described above, and then top valve body  102  and bottom valve body  104  can be snap fitted together. Seat  149  of bottom valve body  104  and gasket  114  can, for example, be inserted into the cavity of top valve body  102 . While inserting seat  149  into the cavity of top valve body  102 , blood line connectors  136  and  138  of top valve body  102  can be circumferentially spaced apart from blood lines  164  and  166  bottom valve body  104  by approximately 90 degrees. This spacing can help to insure that projection  134  of cover  102  ( FIG. 7 ) is positioned within the space between locking features  148  and  150  of bottom valve body  104  ( FIG. 12 ). 
     As shown in  FIG. 16 , when top valve body  102  and bottom valve body  104  are pressed together, retaining members  135  (e.g., engagement surfaces  137  of retaining members  135 ), which extend inwardly from side wall  128  of top valve body  102 , engage flange  153  (e.g., outer surface  155  of flange  153 ), which extends around the perimeter of bottom valve body  104 . As top valve body  102  and bottom valve body  104  are pressed together, guide surfaces  139  of retaining members  135  slide against tapered surface  158  of flange  153 , causing retaining members  135  to deflect outward. As seat  149  of bottom valve body  104  becomes seated within the cavity of top valve body  102 , engagement surfaces  137  of retaining members  135  snap into engagement with outer surface  155  of flange  153 . The engagement of retaining members  135  and the outer surface of bottom valve body  104  provides a compressive force about the outer circumference of valve  100 , which can help to secure top valve body  102  and  104  together and can help to promote a fluid tight seal between top valve body  102  and bottom valve body  104  by compressing gasket  114  between top valve body  102  and bottom valve body  104 . 
     As seat  149  is inserted into the cavity of top valve body  102 , center pin  122  of top valve body  102  penetrates cylindrical passage  162  of bottom valve body  104 . An inward force is applied to center pin  122  by seat  149  of bottom valve body  104  as center pin  122  passes through cylindrical passage  162 . This inward force deflects resilient fingers  126  of center pin  122  inwardly until the end region of center pin  122  has passed through cylindrical passage  162 . After the end region of center pin  122  has passed through cylindrical passage  162 , resilient fingers  126  expand outwardly to their original shape. Consequently, as shown in  FIG. 16 , resilient fingers  126  engage the flanged region of the outer surface of bottom valve body  104  formed by annular depression  187 . This engagement can create a compressive force in the center region of valve  100 , which can help to prevent top valve body  102  and bottom valve body  104  from becoming detached from one another. The compressive force can further help to ensure a fluid tight seal in the center region of valve  100  by compressing gasket  114  between top valve body  102  and bottom valve body  104 . 
     By providing engagement around both the perimeter and at the central region of valve  100 , the compressive forces acting on gasket  114  can be distributed more evenly across gasket  114 . 
     When valve  100  is assembled, top valve body  102  and bottom valve body  104  can be rotated between first and second positions, which are circumferentially spaced by approximately 180°. To rotate top valve body  102  and bottom valve body  104  relative to one another, the clinician can grasp side wall  128  of top valve body  102  and rotate top valve body  102  while holding bottom valve body  104  in a fixed position (e.g., by grasping blood line connectors  164  and  166  of bottom valve body  104 ). Alternatively or additionally, the clinician can grasp the blood line connectors of both top valve body  102  and bottom valve body  104  to rotate top valve body  102  and bottom valve body  104  relative to one another. 
     Referring to  FIG. 17A , after initial assembly of valve  100 , projection  134  is positioned in an intermediate position between locking features  148  and  150  (e.g., between the first and second positions). The clinician can rotate top valve body  102  and bottom valve body  104  relative to one another in the clockwise direction in order to reposition valve  100  from this intermediate position to the first position. When projection  134  is positioned between locking features  148  and  150 , top valve body  102  and bottom valve body  104  can rotate relatively freely relative to one another (e.g., with little resistance). A clearance of about 0.13 millimeter and 0.18 millimeter generally exists between projection  134  and side wall  152  of bottom valve body  104  when projection  134  is positioned in the zone between locking features  148  and  150 . Consequently, projection  134  provides substantially no rotational resistance within this zone. 
     As shown in  FIG. 17B , as top valve body  102  and bottom valve body  104  are rotated toward the first position, projection  134  contacts locking feature  148 . The clinician generally feels a tactile sensation (e.g., increased rotational resistance) when projection  134  contacts locking feature  148 . 
     Referring to  FIG. 17C , as the clinician continues to rotate top valve body  102  and bottom valve body  104  relative to one another, locking feature  148  deflects projection  134  outward as projection  134  slides along and rides over locking feature  148 . As projection  134  slides over locking feature  148 , the rotational resistance encountered by the clinician is at an increased level as compared to the level of resistance encountered when projection  134  is positioned in the low-resistance zone between locking features  148  and  150 . The zone of increased resistance (e.g., the zone in which projection  134  rides over locking feature  148 ) can span about 15° to about 30° (e.g., about 22.5° to about 23.5°, about 23°). This increased resistance indicates to the clinician that projection  134  is in contact with locking feature  148 . The increased resistance can, therefore, serve as tactile feedback to inform the clinician that top valve body  102  and bottom valve body  104  are adjacent and approaching the first position. 
     As shown in  FIG. 17D , continued rotational force applied by the clinician can cause projection  134  to slide completely over locking feature  148  into the detent region formed between locking feature  148  and stop  182 , where it becomes “trapped”. Consequently, valve  100  becomes rotationally locked or fixed in the first position in which fluid passages  106  and  110  are aligned with one another and fluid passages  108  and  112  are aligned with one another. When rotated into the detent region between locking feature  148  and stop  182  (e.g., when rotated into the first position), projection  134  snaps inward as it slides off the locking feature  148 , producing an audible click. For example, abrupt contact between projection  134  and side wall  152  of bottom valve body  104  can produce the audible click. Alternatively or additionally, the audible click can be produced by contact made between projection  134  and stop  182  as projection  134  is forcibly rotated into stop  182 . The audible click produced by top valve body  102  and bottom valve body  104  as the projection  134  seats, serves to indicate to the clinician that valve  100  has been successfully rotated completely into the first position. The contact between projection  134  and side wall  152  and/or the contact between projection  134  and stop  182 , can cause energy to be transmitted to the clinician (e.g., to the hand of the clinician) through top valve body  102  and/or bottom valve body  104 . Consequently, in addition to the audible click, the clinician can experience a tactile sensation that can serve as an indication that top valve body  102  and bottom valve body  104  have reached the first position. 
     When valve  100  is in the first position, as shown in  FIG. 17D , projection  134  abuts end surface  186  of stop  182 . Consequently, top valve body  102  is prevented from rotating any further in the clockwise direction (as viewed from the top of top valve body  102 ). At its other end, projection  134  abuts locking feature  148 . Locking feature  148  is constructed to retain projection  134  in the detent formed between locking feature  148  and stop  182  such that top valve body  102  and bottom valve body  104  are held in a substantially rotationally fixed position relative to one another. Projection  134  can, for example, be fixed between stop  182  and locking feature  148  until sufficient rotational force is applied to top valve body  102  and/or bottom valve body  104  to cause projection  134  to slide back over locking feature  148  toward the second position (e.g., toward locking feature  150  and stop  184 ). 
     In order to release top valve body  102  and bottom valve body  104  from the first position, the clinician can, by using sufficient force, rotate top valve body  102  in the counter clockwise direction (as viewed from the top of top valve body  102 ) relative to bottom valve body  104  such that projection  134  is rotated into and back over locking feature  148 . The clinician can continue to rotate top valve body  102  and bottom valve body  104  relative to one another until reaching the second position in which projection  134  is seated in between locking feature  150  and stop  184 . Rotation of valve  100  into the second position can produce an audible click and tactile feedback in the same manner as discussed above with respect to the first position. 
       FIG. 18  illustrates an exemplary blood treatment system (e.g., a hemodialysis system)  200  that includes valve  100 . Bottom valve body  104  of valve  100  is fluidly connected to a pump  202  via an outlet blood line  206 . Bottom valve body  104  is fluidly connected to a blood treatment device (e.g., a dialyzer)  204  via an inlet blood line  208 . Pump  202  is fluidly connected to blood treatment device  204  via a connection tube  210 . On the opposite side of valve  100 , arterial and venous blood lines  212  and  214  are fluidly connected to top valve body  102 . At their opposite ends, arterial and venous blood lines  212  and  214  can be connected to a patient during treatment, as discussed below. 
     Outlet and inlet blood lines  206  and  208  can be secured to blood line connectors  164  and  166 , respectively, of top valve body  102  by applying a solvent, such as cyclohexanone, to blood line connectors  164  and  166  and then sliding blood lines  206  and  208  over blood line connectors  164  and  166 . Arterial and venous blood lines  212  and  214  can be connected to blood line connectors  136  and  138  of bottom valve body  104  using a similar technique. As an alternative to or in addition to applying a solvent to the blood line connectors, any of various other techniques can be used to secure the blood lines to the blood line connectors. For example, the blood lines can be thermally bonded and/or adhesively attached to the blood line connectors. 
     Blue bands  216  and  220  are secured to blood lines  208  and  214 , respectively, and to blood line connectors  112  and  108 , respectively. Red bands  218  and  222  are secured to blood lines  206  and  212 , respectively, and to blood line connectors  110  and  106 , respectively. The colored bands can be secured to the blood lines and the blood line connectors using any of various techniques. In some embodiments, the bands include a shoulder that has a diameter that is slightly greater than the outer diameter of its respective blood line connector and slightly less than the outer diameter of its respective blood line. In such embodiments, prior to securing the blood line to the blood line connector, the colored band can be slid over the blood line connector. The blood line can then be slid over the connector so that the colored band is compressed between the blood lien and the outer surface of the valve body. After the blood line is secured to the blood line connector, the colored band can be held in place between the blood line and the valve body. 
     When blue bands  216  and  220  are aligned with one another and red bands  218  and  222  are aligned with one another, as shown in  FIG. 18 , this indicates to the clinician that valve  100  is in the first position (e.g., the normal flow position). When blue band  216  is aligned with red band  222  and blue band  220  is aligned with red band  218 , this indicates to the clinician that valve  100  is in the second position (e.g., the reversed flow position). If none of the bands are aligned with one another, this indicates to the clinician that valve  100  is in an intermediate position between the first and second positions. 
     While the bands have been described as being red and blue, any of various other colors can alternatively or additionally be used. Moreover, any of various other types of visual indicators can alternatively or additionally be displayed on the bands to help the clinician to identify the rotational position of valve  100 . Examples of visual indicators include colors, letters, numbers, characters, patterns, etc. 
     When clear blood lines are used, the blood line connectors may themselves be colored. The coloring of the blood line connectors is generally visible through the clear tubes, providing a similar visual aid for determining the rotational position of valve  100 . The blood line connectors can, for example, be colored using any of various coloring techniques, such as painting. Alternatively or additionally, the blood line connectors can be molded from one or more colored materials (e.g., colored plastics). 
     As described above, valve  100  also includes other types of alignment features. Top valve body  102  and bottom valve body  104  of valve  100 , for example, include letters  141  and  189  and arrows  143  and  190 . The letters and arrows, like the colored bands, can help the clinician to determine in what position valve  100  is disposed. For example, alignment of the letters and the arrows can indicate that valve  100  is in the first position (e.g., the standard flow position), and misalignment of the letters and arrows can indicate that valve  100  is in the second position or in an intermediate position between the first and second positions. 
       FIGS. 19A and 19B  illustrate an exemplary method of using blood treatment system  200  to perform hemodialysis. Referring to  FIG. 19A , arterial and venous blood lines  212  and  214  are connected to an artery and vein, respectively, of a subject. Any of various known methods can be used to connect arterial and venous blood lines  212  and  214  to the subject. For example, blood lines  212  and  214  can be fluidly connected to a fistula, graft or shunt implanted within a subject, which connects a vein of the subject to an artery of the subject. To begin treatment, valve  100  is configured in the first position, in which arterial blood line  212  is aligned with outlet blood line  206  and venous blood line  214  is aligned with inlet blood line  208 . When in this position, as discussed above, blue bands  216  and  220  are aligned with one another and red bands  218  and  222  are aligned with one another to inform the clinician that valve  100  is in the first position. Pump  202  is then activated, causing blood to be drawn from the artery of the subject through arterial blood line  212  and outlet blood line  206  to pump  202 . The blood is then forced through connection line  210  to blood treatment device  204 , the blood is treated. After exiting blood treatment device  204 , the blood continues through inlet blood line  208  and venous line  214  to the subject. The blood re-enters the vein of the subject via venous line  214 . The blood is generally pumped through system  100  at a flow rate of approximately 300 ml/min. However, other flow rates are possible. Pump  202  can, for example, be configured to pump the blood at a rate of about 50 ml/min to about 600 ml/min. 
     As discussed above, it may be desirable at certain times during hemodialysis to reverse the flow of blood. Certain parameters can, for example, be measured in the standard flow and reversed flow configurations and compared to one another in order to determine the blood access flow rate. Examples of methods of determining blood access flow rates are described, for example, in U.S. Pat. Nos. 5,830,365 and 6,648,845, which are incorporated by reference herein. 
     In order to reverse the blood flow during the treatment, pump  202  is briefly stopped. The clinician then rotates top valve body  102  and bottom valve body  104  relative to one another until valve  100  reaches the reversed flow position (e.g., the second position) at which time an audible click and tactile feedback are produced along with visible confirmation from the aligned connectors. In the second position, blue band  216  is aligned with red band  222  and blue band  220  is aligned with red band  218 , as shown in  FIG. 19B . Thus, arterial blood line  212  is aligned with inlet blood line  208 , and venous blood line  214  is aligned with outlet blood line  206 . Pump  202  is then restarted, causing blood to be drawn from the vein of the subject and drawn through venous blood line  214  and outlet blood line  206  to pump  202 . The blood is then passed through blood treatment device  204  to inlet blood line  208 . The blood then passes through valve  100  to arterial blood line  221 . The blood re-enters the artery of the subject via arterial blood line  212 . During reversed flow, pump  202  pumps blood at a rate of about 300 ml/min. However, other flow rates are possible. Pump  202  can, for example, be configured to pump the blood at a rate of about 50 ml/min to about 600 ml/min during periods of reversed blood flow. 
     After the desired period of reversed blood flow is completed, pump  202  is again stopped and valve  100  is rotated back into the first position. Pump is then restarted, and the blood treatment is resumed. 
     Pump  202  can be any of various pumping devices capable of forcing blood through system  200 . Examples of such pumping devices include peristaltic pumps, such as those available from Sarns, Inc. (Ann Arbor, Mich.). 
     Blood treatment device  204  can include any of various dialyzers. Examples of dialyzers include Fresenius Optiflux® series dialyzers. 
     Blood lines  206 ,  208 ,  210 ,  212 , and  214  can be any of various types of blood lines. In some embodiments, the blood lines are formed of one or more compliant materials. Examples of materials from which the blood lines can be formed include polyvinylchloride (PVC), Di(2-ethylhexyl) phthalate (DEHP), polyolifins, etc. 
     While various embodiments have been described above, other embodiments are possible. 
     As an example, while the embodiments of valve  100  above describe projection  134  of top valve body  102  snapping into the detent formed between locking features  148  and stop  182  and between locking feature  150  and stop  184  to produce an audible click and tactile feedback, other techniques can alternatively or additionally be used to produce the audible click and/or tactile feedback. In some embodiments, for example, top valve body  102  can be equipped with a spring loaded ball and bottom valve body  104  can include a detent sized and shaped to receive the ball. In such embodiments, the rotational resistance provided can be a function of the size of the ball relative to the detent and the spring force applied to the ball by the spring. 
     As another example, while in the embodiments described above valve  100  was configured to be fixed in two positions (the first and second positions), valve  100  can alternatively be configured to be fixed in three or more positions. For example, two additional circumferentially spaced locking features can be located between locking features  148  and  150  so that valve  100  can be fixed in a third position that is intermediate to the first and second positions. Valve  100  can be arranged such that the ports of top valve body  102  are not aligned with the ports of bottom valve body  104  when valve is in the third position. Consequently, the flow of blood through valve  100  can be substantially prevented in the third position. 
     As an additional example, while each of top valve body  102  and bottom valve body  104  has been described as including two fluid passages or ports, top valve body  102  and bottom valve body  104  can include three or more ports. The ports can, for example, be circumferentially spaced by equal distances and positioned equidistant from the center such that any of the various ports can be aligned with one another by rotating top valve body  102  and bottom valve body  104 . 
     As a further example, while embodiments of top valve body  102  have been described in which projection  134  extends from the inner surface of top valve body  102 , projection  134  can alternatively or additionally be positioned at other locations within top valve body  102 . For example, projection  134  can extend from side wall  128  of top valve body  102 . Moreover, while the embodiments described above relate to top valve body  102 , which includes projection  134 , and bottom valve body  104 , which includes stops  182  and  184  and locking features  148  and  150 , top valve body  102  can alternatively or additionally include a stop and locking features, and bottom valve body  104  can alternatively or additionally include a resilient projection configured to be seated between the locking features and stops. 
     As another example, while gasket  114  has been described as being secured to bottom valve body  104  using protruding features that mate with recessed features of bottom valve body  104 , other techniques can be used. Examples of other securing techniques include thermal bonding, adhesive bonding, and mechanical fasteners. 
     As an additional example, while gasket  114  has been described as being secured to bottom valve body  104 , gasket can alternatively be secured to top valve body  102 . 
     As a further example, while valve  100  has been described as including gasket  114  between top valve body  102  and bottom valve body  104 , in other embodiments, valve  100  need not include a gasket. In such embodiments, top valve body  102  and bottom valve body  104  can be configured and designed to mate with one another to form a substantially fluid tight seal. 
     As another example, while the embodiments above describe top valve body  102  as including center pin  122 , which fits into cylindrical passage  162  of bottom valve body  104  to secure top valve body  102  and bottom valve body  104  to one another, other techniques can alternatively or additionally be used to secure top valve body  102  and bottom valve body  104  together. In certain embodiments, for example, top valve body  102  and bottom valve body  104  are snap fitted together only from their outer circumferences using retaining members  135 . In some embodiments, other types of securing devices or mechanisms can be used. For example, other types of mechanical fasteners can be used to secure the top valve body and bottom valve body together. 
     As a further example, while embodiments of valve  100  have been described in which valve  100  is configured to produce an audible click and tactile feedback when rotated into the first and second positions, and in which valve  100  further includes alignment features to help the clinician identify the position in which valve  100  is disposed, other configurations are possible. Valve  100  can, for example, include only one or two of the above-noted features. 
     As an additional example, while resilient fingers  126  of center pin  122  have been described as deflecting inward as center pin  122  is inserted through central aperture  162 , the surfaces of bottom valve body  104  that form aperture  162  can alternatively or additionally be configured to deflect outward in response to center pin  122  being inserted through aperture  162 . 
     As a further example, while fingers  126  of center pin  122  have been described as being resilient, in certain embodiments fingers  126  are relatively rigid. In such embodiments, fingers  126  can outwardly deflect the surfaces of bottom valve body  104  that define aperture  162  as center pin  122  is inserted through aperture  162 . Alternatively or additionally, fingers  126  can core through a portion of the surface of bottom valve body  104  that forms aperture  162  as center pin  122  is inserted through aperture  162 . Ridged portions of fingers  126  can, for example, both stretch and core the surfaces defining aperture  162  of bottom valve body  104  as top valve body  102  and bottom valve body  104  are pressed together. The coring that takes place generally causes about 0.25 millimeter or less of material to be removed from portions of bottom valve body  104  that define aperture  162 . The removed material is pushed toward the outer surface of bottom valve body  104  as the ridged portions of center pin  122  are forced through aperture  162 . The removed material creates circumferentially spaced apart lands around aperture  126 . After the ridged portions of fingers  126  have cleared aperture  126 , aperture  126  closes back toward its original dimensions. Consequently, shoulder regions of fingers  126  sit atop the lands to prevent top valve body  102  and bottom valve body  104  from being separated from one another. Top valve body  102  can also be rotated such that the shoulder regions of fingers  126  are rotated along and rest on shelf portions of bottom valve body  104  that have not experienced coring. Thus, top valve body  102  and bottom valve body  104  can be prevented from becoming separated from one another along their entire range of rotation relative to one another. 
     As another example, while valve  100  has been described as a component for a hemodialysis systems, valve  100  can alternatively or additionally be used with other types of blood treatment systems where flow reversal is desired. Examples of other types of blood treatment systems include plasma phersis, autotransfusion devices, and hemoabsorptive devices. 
     Other embodiments are in the claims.