Patent Publication Number: US-9402987-B2

Title: Devices and methods for occluding a flexible tube

Description:
RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 12/714,056, filed Feb. 26, 2010 and entitled Devices and Methods for Occluding a Flexible Tube, now U.S. Pat. No. 8,950,728, issued, Feb. 10, 2015 which claims priority to U.S. Provisional Patent Application Ser. No. 61/158,174, filed Mar. 6, 2009, and entitled Device and Method for Occluding a Flexible Tube, which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to devices and methods for occluding or constricting the lumen of a segment of flexible tubing by compressing the wall of the tubing. In an exemplary application, it relates to the partial or complete occlusion of flexible tubing in fluid communication with the blood vessel of a patient. 
     BACKGROUND 
     Systems that use flexible tubes to transfer fluids from one location to another frequently take advantage of the compressibility of the tubes to adjust, restrict or stop fluid flow within them. This is particularly useful in medical applications in which biological or therapeutic fluids are transferred between a source or destination and a patient by means of an electro-mechanical instrument. In hemodialysis, for example, blood is pumped from a patient&#39;s body through a dialyzer to remove wastes and excess fluid from the blood. Blood is removed from the patient, pumped through the dialyzer, and then returned back to the patient in a closed-loop system. External blood loss can occur if the intravenous (IV) needle (e.g. a fistula needle) returning the treated blood is removed or dislodged from the patient&#39;s body and the blood pump is not stopped in a timely manner. Generally, a dislodgement of an arterial needle or catheter (in which blood is being drawn to the machine from the patient) can be readily detected by the machine&#39;s air-in-line detectors. It is much more difficult, however, to detect dislodgement of a venous needle or catheter. This risk is heightened when a patient is asleep or otherwise unaware that tension applied to the intravenous line has resulted in dislodgement of the IV needle. Current dialysis systems cannot readily detect when an indwelling venous IV needle delivering blood from the dialysis machine to the patient has become dislodged from the patient&#39;s body. However, such machines can detect an increase in the back-pressure on the pump discharge line, typically from an occlusion or kink in the blood tubing downstream of the pump, which can trigger an alarm and pump shutdown. A device that can compress the flexible tubing transporting fluid to the patient can provide the necessary increase in intraluminal pressure, or possibly even provide complete occlusion, that can prevent excessive fluid loss from a dislodged catheter. The problem is how a threatened intravascular catheter dislodgement can be made to trigger such an occluding device. 
     It is therefore an object of this invention to provide a device to occlude any flexible tubing carrying a fluid, in which the device can be triggered by the application of a pulling or traction force on a segment of the flexible tubing, the pulling force being sufficient to cause movement of the tubing (if there is slack in the tubing) or elastic stretching of the tubing (if there is no slack in the tubing). In medical applications, such as, for example hemodialysis applications, either the blood tubing connected to the dialyzer or the tubing connected to the intravascular catheter or needle can serve as such a segment of flexible tubing. When a predetermined threshold amount of pulling force occurs along a segment of the tubing between the blood pump and the IV needle, a portion of that segment of tubing will either move or stretch in an amount sufficient to trigger an attached occluding device. The threshold tension required to trigger the device can be set to be less than the force that could cause dislodgement of an indwelling needle or catheter assembly that has been taped to a person&#39;s arm or other part of the body. Since dialysis machines are generally programmed to detect an occlusion on the pump discharge tubing, the invention can be easily integrated into an existing dialysis system by locating the occluder on the tubing between the blood pump and the IV needle, thus reducing the risk of accidental exsanguination. 
     SUMMARY 
     The present invention is directed to a device and method for occluding or constricting the lumen of a segment of a flexible tube. In some applications, such a device will help prevent accidental blood loss by occluding flexible tubing coupled to an intravenous catheter or needle. The occlusion can be partial or complete. In either case, the increase in flow resistance or change in intraluminal pressure can be detected by appropriate sensors in the fluid line, resulting in the generation of a pump controller alarm and a pump shutdown signal. A device having features of the present invention comprises generally an occluder assembly having an actuator constructed and positioned to cause one or more occluding elements to act on the walls of the flexible tube. The actuator functions when a predetermined threshold amount of pulling force along the length of a segment of the tube causes a portion of the segment of tube to move or to stretch slightly. Certain embodiments of the present invention provide a device and method for constricting the lumen of a segment of flexible tube a portion of which is moved or stretched in response to a pulling force being applied to the tube. 
     In an embodiment, the device includes a grip for holding a segment of a flexible tube, at least one occluder under an elastic force urging the occluder to compress a flexible tube held by the grip, and at least one occluder stop connected to or comprising the grip to engage and block the occluder from moving under influence of the elastic force. Movement of the grip in response to a pulling force on a segment of flexible tube being held by the grip can disengage the occluder stop from the occluder, releasing the occluder to compress the tube. 
     The device can also include a frame for holding a segment of flexible tubing, the frame having a first end and a second end, the first end connected to or comprising the grip, wherein the occluder is movably connected to the frame near the second end of the frame. 
     The device can also include an arm having an occluding end and a connecting end, the connecting end being slidably connected to the frame near the second end. The occluding end can have a surface for engaging the occluder stop and an occluding element adapted to compress a segment of flexible tube held by the grip, such that movement of the grip away from the occluder causes disengagement of the occluder stop from the occluding end of the occluder. 
     The occluder can also be pivotally mounted near the second end of the frame to a base unit, the base unit being slidably mounted to the frame, so that disengagement of the occluder stop from the occluder causes movement of the frame away from the base unit. 
     The base unit can have a first end and a second end, the occluder being mounted to the base unit near the first end of the base unit; and a second grip can be attached to the second end of the base unit. 
     The device can also have an actuator that is slidably mounted to the frame between the base unit and the first end of the frame, the actuator contacting the arm of the occluder and urging the occluding element toward a tube on the frame as the actuator slides toward the first end of the frame. 
     An actuator spring can be mounted between the actuator and the base unit, the actuator spring urging the actuator to move away from the base unit and toward the first end of the frame, the actuator then being able to actuate the occluder upon disengagement of the occluder from the occluder stop. 
     The actuator arm can have a jog feature is included on the actuator arm against which the actuator can be positioned when the occluder is in contact with the occluder stop. 
     The frame can further comprise a triggering spring compressible by the base unit, wherein the occluder can be actuated upon the application of a pulling force on a tube being held by the grip, the pulling force being sufficient to compress the triggering spring and cause movement of the frame away from the base unit. 
     The base unit can further comprise a dowel disposed in a slot near the second end of the frame, wherein movement of the dowel within the slot causes contact between the dowel and the triggering spring. 
     The grip can have a channel in which a segment of flexible tubing can be positioned, the surface of the channel having raised features such as ridges, ribs, cross hatches, or scales; and a second latch can be hingedly mounted on the second grip, the second latch being closeable over the channel. 
     In a further embodiment, the device can have a mounting pad for mounting the base unit, frame and occluder to a surface such as a person&#39;s body, the mounting pad connectable to the base unit and having one or more extensions to which tape or adhesive can be applied to secure the mounting pad to the surface. 
     The mounting pad can be pivotably connectable to the base unit, allowing the base unit, frame and occluder to rotate in a plane that is generally parallel to the surface on which the mounting pad is mounted. 
     The mounting pad can be slidably connectable to the base unit. The mounting pad can also be attachable to a member, the member slidably connected to the base unit through a slot of the base unit, and disposed within a recess of the frame, wherein a pulling force on a segment of tubing held by the second grip causes the member to contact a wall of the recess, urging the frame to move away from the base unit and the occluder stop to disengage from the occluder. 
     The frame can include a post, the post being capable of contacting a pair of cams on the mounting pad, wherein rotation of the frame in a first direction can cause contact between the post and a first cam, and rotation of the frame in a second direction can cause contact between the post and a second cam, and either contact creating a force to urge the frame to move away from the base unit and the occluder stop to disengage from the occluder. 
     In another embodiment, the device can comprise two or more occluders, and the at least one occluder stop comprises two or more occluder stops. In some embodiments, the pulling force on the tube comprises stretching of at least a segment of the tube. 
     Another aspect of the present invention includes an occluder having an elastic force actuating member (e.g. torsion spring, leaf spring, elastic band). The elastic member remains in a compressed or tensioned position until a threshold force triggers the elastic member to move the occluder from a first position to a second position causing fluid flow within the flexible tubing to be restricted. 
     In another embodiment of the present invention, the occluder includes a tapered housing having two openings where a flexible tube may enter and exit the housing. The housing also encloses a cylindrical body which may engage the tube. The housing is tapered allowing the body to pinch the tube against an interior wall as the tube moves toward the tapered end of the housing. 
     In another embodiment of the present invention, a single coil of flexible tubing is enclosed by a cylindrical housing having a first opening and a second opening along a circumferential edge. The tube enters the housing at the first opening and exits the housing at the second opening. The tube occludes itself by kinking when the flexible tube is exposed to a predetermined threshold force between the first and second openings of the housing. 
     In another embodiment of the present invention, the flexible tube is releasably attached to the occluder at a first location and restrained between two cylindrical bodies rotatably connected to the occluder. As the tubes move from a first position to a second position, the bodies rotate towards each other and apply a generally equal and opposite pinching force on the tube capable of occluding the tube. 
     In another embodiment of the present invention, a single coil of flexible tubing is enclosed by a cylindrical housing. An occluding edge is located along an interior loop of the enclosed coil whereby the tube is occluded along the edge when a predetermined threshold force is applied along the tube. 
     In another embodiment of the present invention, the device includes a first body having a pair of support arms pivotably attached to the body. The flexible tube is demountable attached to the support arms. A second body having an occluding edge perpendicular to the tube is pivotably attached to a hinge on the first body. A spring abuts the first and second body in order to provide the necessary force to occlude the tube when a threshold tensional force acts on the tube. The force moves the support arms into a second position, whereby the spring-loaded body occluded the tube along the occluding edge. 
     In another embodiment of the present invention, the device includes a body having a pair of support arms pivotably attached to the body. A flexible tube to be occluded is releasably attached to the support arms. A plunger is slideably attached to the body and a spring is compressed between the body and plunger. A notch near the distal end of the plunger temporarily engages one of the support arms. The plunger is triggered into a second position when the support arms rotate away from each other. The spring then provides a compressive force necessary to occlude the flexible tube. 
     In another embodiment of the invention, the device includes a first body and a second body pivotably attached at a central hinge. An occluding tab engages a flexible tube releasably attached to the first body by a pair of clips. A spring provides a compressive force necessary to rotate the occluding tab about the central hinge to occlude the flexible tube. The bodies are held in a first position by locking engagement of a retaining tab mounted on the bottom surface of the second body near the spring. The restraining tab extends away from the second body and lockingly engages the first body at a flexible arm. A rod extends outwardly and away from the flexible arm where a clip is attached to the distal end of the rod. The tube is releasably attached to the clip. A predetermined threshold amount a force along the flexible tube moves the flexible arm from a first position to a second position thus disengaging the restraining tab from the flexible arm, activating the spring, and occluding the flexible tube through the occluding tab. 
     In another embodiment of the invention, the device includes a housing which positions the flexible tubing into an s-shaped configuration without any restriction of flow within the tube. As one end of the tube is pulled by a predetermined force outwardly and away from the housing, the tube in the housing is occluded. 
     In another embodiment of the invention, the device includes a tab slideably attached to a first body. A flexible tube is releasably attached to the tab and the first body. As a predetermined force pulls on the flexible tube, the tab slides outwardly and away from the first body, thus triggers a second body to occlude the tube. An occluding edge, located along a bottom surface of the second body, normally rests on the tab but occludes the tube when the tube moves from a first position to a second position. 
     In additional embodiments of the invention, the device includes a cylindrical tube having a tapered first end and a tapered second end. The first end is inserted into a first valve wherein the tube creates an open flow path through the first valve. The second end is inserted into a second valve wherein the tube creates an open flow path through the second valve. The first and second valves are located in a female and male coupling respectively. A compression spring is also housed within the couplings while engaged. When the couplings are brought into locking engagement the spring is compressed and the tapered ends of the tube penetrate the first and second valves to create a continuous flow path between a first and second flexible tube. A predetermined threshold amount of tension acting on the distal end of a least one of the tubes disengages couplings allowing the compression spring to expand and separate the couplings from locking engagement with each other. As the spring expands the tube is withdrawn from both the first and second valves, whereby any flow between the flexible tubes is blocked. 
     In some methods of the invention, the method can include the steps of: providing an occluder having a force actuating element; mounting the occluder to the flexible tube having a first end and a second end; applying a tensional force along a central axis of the flexible tube between the first end and the second end wherein the flexible tube moves relative to the occluder; and occluding the flexible tube using the force actuating element in combination with the occluder. 
     A typical method for occluding a flexible tube as embodied in this invention generally comprises the steps of: providing an occluding device having an occluding member; coupling the device to a flexible tube to be occluded; applying a predetermined threshold amount of tension to one end of the tubing; triggering the occluding member to occlude the tube. 
     Another method for occluding a flexible tube as embodied in this invention generally comprises the steps of: providing a device having an elastic actuating member and an occluding member; coupling the device to a flexible tube to be occluded; applying a predetermined threshold amount of tension to the tubing; triggering the elastic actuating member; occluding the tube with the occluding member. 
     Another method includes arming an occluding device, the occluding device comprising a grip for holding a segment of the tube, an occluder under an elastic force urging the occluder to compress the flexible tube held by the grip, and an occluder stop connected to the grip to block the occluder from moving under influence of the elastic force, the method comprising: moving the occluder to engage the occluder with the occluder stop, positioning the tube next to the occluder, and securing a segment of the tube to the grip. 
     In an additional embodiment, the occluding device can further comprise a frame for holding a segment of flexible tubing and having a first end connected to or comprising the grip and a second end, a base unit slidably mounted to the frame near the second end, an actuator slidably mounted to the frame between the base unit and the first end, and an actuator spring mounted between the actuator and the base unit, wherein the occluder comprises an arm that makes contact with the actuator and has an occluding end and a connecting end, the occluding end having a surface for engaging the occluder stop and the connecting end pivotably mounted to the base unit, wherein movement of the actuator toward the first end of the frame causes the occluder to pivot toward the segment of tube, the method of engaging the occluder with the occluder stop further comprising: moving the actuator toward the base unit while compressing the actuator spring, moving the occluder stop toward the occluding end of the occluder, and pivoting the occluder to engage the occluding end of the occluder with the occluder stop. 
     In another embodiment, a method of constricting the lumen of a flexible tube includes using an occluding device comprising a grip for holding a segment of the tube, an occluder under an elastic force urging the occluder to compress the tube, and an occluder stop connected to the grip to block the occluder from moving under influence of the elastic force, the method comprising: securing a segment of tube to the grip, positioning the tube next to the occluder, applying a pulling force on the tube near the grip, disengaging the occluder stop from the occluder, and releasing the occluder to compress the tube. The device can further comprise a frame for holding a segment of the tube and having a first end and a second end, the first end connected to or comprising the grip, wherein the occluder comprises an arm having an occluding end and a connecting end, the connecting end being slidably connected to the frame near the second end, and the occluding end having a surface for engaging the occluder stop and an occluding element for compressing the tube, and wherein applying a pulling force on the tube near the grip further comprises the method of increasing the distance between the grip and the occluder. The device can further comprise a base unit slidably mounted to the frame near the second end, an actuator slidably mounted to the frame between the base unit and the first end, and an actuator spring mounted between the actuator and the base unit, the occluder arm making contact with the actuator and the connecting end of the occluder being pivotably mounted to the base unit, wherein releasing the occluder further comprises the method of releasing the actuator to move toward the first end under influence of the actuator spring, and allowing the actuator to slide along the occluder arm, causing the occluder arm to pivot toward the tube. 
     Still another method for occluding a flexible tube as embodied in this invention generally comprises the steps of: providing a normally-closed valve at each end of two tubes to be hydraulically connected; establishing fluid communication between the two tubes by inserting a hollow cylinder into the body of each valve; compressing a spring between the two valves; restraining the cylinder using a male and female coupling; applying a predetermined threshold axial force along at least one of the tubes; disengaging the male and female couplings; urging the coupling apart using the spring; and closing both valves. 
     Another aspect of the present invention provides a method for occluding a flexible tube. The method includes the steps of: providing a normally-closed valve at each end of two tubes to be hydraulically connected; establishing fluid communication between the two tubes by inserting a hollow cylinder into the body of each valve; compressing a spring between the two valves; restraining the cylinder using a male and female coupling; applying a predetermined axial force along at least one of the tubes; disengaging the male and female couplings; urging the coupling apart using the spring; and closing both valves thereby preventing further fluid flow from either end resulting in an occlusion alarm on the dialysis machine and preventing blood egress from the patient. A further aspect of the present invention is a method whereby if the axial force exerted along at least one of the tubes is great enough, the device will completely separate between the two valves after the valves have closed thereby removing the axial force from further acting on the tubing connected to the IV needle and assuring that it will not be accidentally removed. 
     Yet another aspect of the present invention provides a method for stopping a blood pump when a force is applied to an IV tube during dialysis treatment. The method includes the steps of: providing an occluder releasably attached to the IV tube having a first and second end, the first end hydraulically connected to a discharge of the blood pump, the second end hydraulically attached to an IV needle, wherein the IV needle is connected to a patient receiving dialysis treatment; applying a tensional force along the IV tube between the first end and the second end; occluding the IV tube; triggering an occlusion alarm; and stopping the blood pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description and accompanying drawings: 
         FIG. 1  is a schematic view of an extracorporeal blood circuit that embodies features of the invention; 
         FIG. 2  is a perspective view of an embodiment of the invention in an occluded position with a segment of flexible tube latched within the device; 
         FIG. 3  is a perspective view of an embodiment of the invention in an unoccluded position with a segment of flexible tube removed from the device; 
         FIG. 4  is a plan view of the embodiment of  FIG. 3  in an occluded position with a segment of flexible tube mounted in the device; 
         FIG. 5  is a plan view of the embodiment of  FIG. 3  in an unoccluded and armed position with a segment of flexible tube mounted in the device; 
         FIG. 6  is a plan view of the embodiment of  FIG. 3  in an unoccluded position with the actuator in a fully retracted position with a segment of flexible tube mounted in the device; 
         FIG. 7  is a bottom perspective view of the embodiment of  FIG. 2  with the actuator fully extended; 
         FIG. 8  is a top section perspective view of the embodiment of  FIG. 2  showing the occluders in an occluding position; 
         FIGS. 9 a  and 9 b    are perspective and plan view, respectively, of a triggering spring used in the embodiment of  FIG. 8 ; 
         FIGS. 9 c  and 9 d    are plan views of triggering springs used in the embodiment of  FIG. 8  and having different thicknesses and spring rates; 
         FIG. 10  is a top section perspective view of the embodiment of  FIG. 8  showing the occluders in a non-occluding armed position; 
         FIG. 11  is a top perspective view of the frame of the embodiment of  FIG. 8 ; 
         FIG. 12  is a perspective view of the embodiment of  FIG. 2  shown attached to a mounting pad; 
         FIG. 13  is a perspective view of the mounting pad shown in  FIG. 12 ; 
         FIG. 14  is a bottom perspective view of the embodiment of  FIG. 2  showing the female component of a snap fastener by which the device attaches to the mounting pad; 
         FIG. 15  is a perspective view of the snap fastener mount by which the female component of the snap fastener is mounted to the device; 
         FIG. 16  is a bottom perspective view of the frame of the embodiment of  FIG. 7  showing the positioning of the snap fastener mount; 
         FIG. 17  is a bottom perspective view of the base unit mounted on the frame of the embodiment of  FIG. 7  showing the snap fastener mount protruding through the base unit slot; 
         FIG. 18  is a bottom perspective view of the base unit mounted on the frame of the embodiment of  FIG. 7  showing the snap fastener mount in a forward position in the base unit slot, and disposed to trigger the device upon application of a pulling force on the rear tubing grip. 
         FIG. 19  is a top view of another embodiment of the invention with a flexible tube attached; 
         FIG. 19 a    is a cross-sectional view of the embodiment shown in  FIG. 19  taken through  FIG. 19  along the line 1-1; 
         FIG. 19 b    is a cross-sectional view of the embodiment shown in  FIG. 19  taken through  FIG. 19  along the line 2-2; 
         FIG. 20  is a top view of an embodiment of the invention with a flexible tube attached and a cover removed for clarity; 
         FIG. 21  is a top view of the embodiment shown in  FIG. 20  with a flexible tube attached and shown in an occluded position; 
         FIG. 22  is a top view of an embodiment of the invention with a flexible tube attached; 
         FIG. 23  is a top view of the embodiment shown in  FIG. 22  with a flexible tube attached and shown in an occluded position; 
         FIG. 24  is side view of the embodiment shown in  FIG. 22  taken along line 1-1 of  FIG. 22 ; 
         FIG. 25  is a top view of an embodiment of the invention with a flexible tube attached; 
         FIG. 25 a    is a cross-sectional view of the embodiment taken along the line 1-1 of  FIG. 25 ; 
         FIG. 26  is a side view of a trigger of the embodiment shown in  FIG. 25  with a flexible tube attached; 
         FIG. 26 a    is a cross-sectional view of the trigger taken through  FIG. 26  along the line 2-2; 
         FIG. 27  is a top view of the embodiment shown in  FIG. 25  with a flexible tube attached and shown in an occluded position; 
         FIG. 28  is a perspective view of an embodiment of the invention with a flexible tube attached and a top surface of the embodiment not shown for clarity; 
         FIG. 29  is a plan view of the embodiment shown in  FIG. 28  with a flexible tube shown in both an occluded and unoccluded position; 
         FIG. 30  is a perspective view of an embodiment of the invention with a flexible tube attached; 
         FIG. 31  is a top view of the embodiment shown in  FIG. 30  with a flexible tube in an unoccluded position; 
         FIG. 32  is a top view of the embodiment shown in  FIG. 30  with a flexible tube in an occluded position; 
         FIG. 33  is a perspective view of an embodiment of the invention with a flexible tube attached; 
         FIG. 34  is a top view of the embodiment shown in  FIG. 33  with a flexible tube in an unoccluded position; 
         FIG. 35  is a top view of the embodiment shown in  FIG. 33  with a flexible tube in an occluded position; 
         FIG. 36  is a perspective view of an embodiment of the invention with a flexible tube attached; 
         FIG. 37  is a top view of the embodiment shown in  FIG. 36  with a flexible tube in an unoccluded position; 
         FIG. 38  is a top view of the embodiment shown in  FIG. 36  with a flexible tube in an occluded position; 
         FIG. 39  is a perspective view of an embodiment of the invention with a flexible tube attached; 
         FIG. 40  is a top view of the embodiment shown in  FIG. 39  with a flexible tube attached in an unoccluded position; 
         FIG. 41  is a top view of the embodiment shown in  FIG. 39  with a flexible tube attached in an occluded position; 
         FIG. 42  is a perspective view of an embodiment of the invention with a flexible tube attached; 
         FIG. 43  is a cross-sectional view of the embodiment shown in  FIG. 42  with a flexible tube attached in an occluded position; 
         FIG. 44  is a front view of the embodiment shown in  FIG. 42  with a flexible tube attached in an unoccluded position; 
         FIG. 45  is a perspective view of an embodiment of the invention with a flexible tube attached; 
         FIG. 46  is a cross-sectional view of the embodiment shown in  FIG. 45  with a flexible tube attached in both an unoccluded position and occluded position; 
         FIG. 47  is a perspective view of an embodiment of the invention with a flexible tube attached; 
         FIG. 48  is an exploded side view of the embodiment shown in  FIG. 47  with a flexible tube attached; 
         FIG. 49  is a top view of the first body of the embodiment shown in  FIG. 47  as taken along line 1-1 of  FIG. 48 . 
         FIG. 50  is a bottom view of the second body of the embodiment shown in  FIG. 47  as taken along line 2-2 of  FIG. 48 ; 
         FIG. 51  is a side view of the embodiment along the line 3-3 of  FIG. 48  with a flexible tube attached shown in an unoccluded position. 
         FIG. 52  is a side view of the embodiment along line 3-3 of  FIG. 48  with a flexible tube attached shown in an occluded position. 
         FIG. 53  is a perspective view of an embodiment of the invention with a flexible tube attached; 
         FIG. 54  is a top view of a base and trigger of the embodiment shown in  FIG. 53  with a flexible tube attached; 
         FIG. 55  is a cross-sectional view of the embodiment shown in  FIG. 53  in the unoccluded position ( FIG. 55 a   , top figure) and occluded position ( FIG. 55 b   , bottom figure) taken along the line 1-1 of  FIG. 54 ; 
         FIG. 56  is a bottom view of the cover of the embodiment shown in  FIG. 53 ; 
         FIG. 57  is a side view of the trigger of the embodiment shown in  FIG. 53 ; 
         FIG. 58  is a top view of an embodiment of the invention with a flexible tube attached and shown in an unoccluded and occluded position; 
         FIG. 59  is a cross-sectional view of the embodiment shown in  FIG. 58  taken along the line 1-1 of  FIG. 58  with a flexible tube in the occluded position; 
         FIG. 60  is an exploded perspective view of an embodiment of the invention with a flexible tube attached; 
         FIG. 61  is a cross-sectional view of the embodiment shown in  FIG. 60  taken along the centerline with a flexible tube attached; 
         FIG. 62  is a cross-section view of an embodiment of the invention in an unoccluded position taken along the centerline with a flexible tube attached; 
         FIG. 63  is a cross-section view of the embodiment in  FIG. 62  in a partially occluded position taken along the centerline with a flexible tube attached; 
         FIG. 64  is a cross-section view of the embodiment of  FIG. 62  in an occluded position taken along the centerline with a flexible tube attached; 
         FIG. 65  is a side view of an embodiment of the invention in an unoccluded position with a flexible tube attached; 
         FIG. 66  is a perspective view of the embodiment of  FIG. 65  in an occluded position; 
         FIG. 67  is a side view of the embodiment of  FIG. 65  in an occluded position with a flexible tube attached; 
         FIG. 68  is a side view of the embodiment of  FIG. 65  in an unoccluded/compressed position with a flexible tube attached; 
         FIG. 69  is a side view of an embodiment of the invention in an unoccluded position with a flexible tube attached; 
         FIG. 70  is a cross-sectional view of the embodiment shown in  FIG. 69  taken along the line A-A; 
         FIG. 71  is a perspective view of the embodiment shown in  FIG. 69  in an unoccluded position with a flexible tube attached; 
         FIG. 72  is a side view of the embodiment shown in  FIG. 69  in an occluded position with a flexible tube attached; 
         FIG. 73  is a cross-sectional view of the embodiment shown in  FIG. 72  taken along the line A-A; 
         FIG. 74  is a perspective view of the embodiment shown in  FIG. 69  in an occluded position with a flexible tube attached; 
         FIG. 75  is a front view of the embodiment shown in  FIG. 69  in an unoccluded position with a flexible tube attached; 
         FIG. 76  is a rear view of the embodiment shown in  FIG. 69  in an unoccluded position with a flexible tube attached; 
         FIG. 77  is a cross-sectional view of an embodiment shown in  FIG. 79  taken along the line A-A; 
         FIG. 78  is a perspective view of the embodiment shown in  FIGS. 77 and 79  in an unoccluded position; 
         FIG. 79  is a top view of the embodiment shown in  FIG. 78  in an unoccluded position with a flexible tube attached; 
         FIG. 80  is a side view of the embodiment shown in  FIG. 78  in an unoccluded position with a flexible tube attached; 
         FIG. 81  is a side view of the embodiment shown in  FIG. 83  taken along the line A-A; 
         FIG. 82  is a perspective view of the embodiment shown in  FIGS. 81 and 83  in an occluded position; 
         FIG. 83  is a top view of the embodiment shown in  FIG. 82  in an occluded position with a flexible tube attached; 
         FIG. 84  is a side view of the embodiment shown in  FIG. 82  in an occluded position with a flexible tube attached. 
         FIG. 85  is a partial cutaway view of an embodiment of the invention in an unoccluded position with a flexible tube attached. 
         FIG. 86  is a partial cutaway view of the embodiment of  FIG. 85 , with the actuator assembly separated from the occluder. 
         FIG. 87  is a partial cutaway view of the embodiment of  FIG. 85  in an occluded position with a flexible tube attached. 
         FIG. 88  is a perspective view of an embodiment of the invention in an unoccluded position with a flexible tube attached. 
         FIG. 89  is a top view of the embodiment of  FIG. 88  in an unoccluded position with a flexible tube attached. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , a typical hemodialysis system includes an extracorporeal blood circuit  5  connected to a patient  10 . The extracorporeal circuit  5  generally includes two sections of flexible intravenous (“IV”) tubing  20  configured for hemodialysis treatment (commonly referred to as arterial and venous blood sets). In a two-needle arrangement, blood is withdrawn from the patient through an arterial access catheter or needle  12  and returned through a venous access catheter or needle  14 , each of which may have an attached or connected length of extension tubing that is typically of smaller diameter than the blood sets of the extracorporeal circuit. Each access catheter/needle also typically terminates in a female luer locking connector. Blood from the arterial catheter/needle is transferred via a blood pump  30  to a dialyzer  40  mostly continuously during a given therapy session at anywhere between 200 and 800 ml/min. Dialysate, a clean solution, is pumped to the inlet  42  of the dialyzer  40  where it flows in a counter-current direction to the blood and exits the dialyzer at the outlet  44 . Heparin, an anticoagulant, is typically added to the extracorporeal blood circuit  5  at an injection site  32  upstream of the dialyzer  40 . The treated blood leaves the dialyzer  40  and is pumped through the venous blood set before the blood is returned to the patient  10  through a venous catheter/needle  14  with or without extension tubing. In some embodiments, the occluding device  50  that is the subject of this invention may either be located on the venous or arterial blood set, or along the extension tubing between the venous or arterial blood set and the venous or arterial catheter/needle by incorporating male and female locking luer connectors on the ends of tubing segments and the connecting end of the venous catheter/needle assembly. It may be preferable to place the occluding device  50  over a segment of intervening extension tubing because it is typically of smaller diameter and therefore more easily occluded. In any case, the occluding device  50  is preferably located sufficiently close to the venous fistula needle  14  such that any force tending to dislodge the needle from the patient&#39;s arm will also be applied to the occluding device  50 , triggering its actuation before a dislodged needle can cause significant blood loss. 
     Certain elements of the circuit may communicate with a dialysis control system  70 . The control system  70  may receive pressure signals from a number of pressure sensors, and most particularly form pressure sensor  60  on the venous return line of extracorporeal circuit  5 . The control system  70  may also receive signals from a number of air-in-line sensors, and most particularly from air-in-line sensor  62  on the arterial side of extracorporeal circuit  5 . Detection by sensor  62  of any air in the arterial line can result in an alarm-level signal being sent to controller  70 , which can then send a stop command to blood pump  30 , and signal an audible and/or visual alarm to the patient  10  or a health care provider. Detection by sensor  60  of intraluminal pressure above or below a predetermined operating pressure range can trigger control system  70  to issue an alarm signifying partial or complete occlusion of the venous tubing in circuit  5 , resulting, for example in a stop command  80  being sent to blood pump  30 . Pressure in the extracorporeal blood circuit  5  can be affected by an obstruction or flow restriction within the blood tubing  20  of the extracorporeal circuit (an “occlusion”). Typically occlusions in the blood sets or needle sets downstream from blood pump  30  are caused by kinking or bending of flexible tube  20 , reducing the cross-sectional area of the tube enough to restrict the flow of blood through tube  20  and creating excessive back pressure in the upstream blood circuit, and detectable, for example, by pressure sensor  60 . If an occlusion occurs upstream of blood pump  30 , an additional pressure sensor in the arterial line may detect a pressure below the predetermined operating range. In either case, an occlusion alarm can be triggered in the control system  70 , sending, for example, a stop command  80  to blood pump  30 . 
     The presence of occluding device  50  for compressing or occluding a flexible tube  20  can cause a similar stop command  80  if there is a threatened dislodgement of catheter/needle  14  from the patient&#39;s body  10 . Triggering of the device  50  will raise intraluminal pressure in the venous tubing  20  sufficiently to send an alarm-level signal to controller  70  via pressure sensor  60 . The predetermined operating pressure range can be programmed independently for pressure sensor  60 , as well as any other pressure sensors in the system. 
     In an additional embodiment, and as part of a redundant or failsafe safety system, the occluding device  50  may also include a mechanical, electrical or magnetic switch or sensor capable of sending an occlusion signal  82  to control system  70  upon actuation of the occluding device  50 , the control system then transmitting a stop command  80  to blood pump  30 . The occlusion signal  82  may be transmitted to control system  70  wirelessly or by conventional means such as a signal wire. 
     In an embodiment, the occluder assembly is a tubing tension-activated clamp that is capable of applying an occluding force on the wall of a flexible tubing, restricting the flow of fluid within the tubing and increasing its intraluminal pressure, in response to a pulling force being applied to the tubing on either end of the device. The occluder assembly is triggered whenever a pulling force is applied to a length of the flexible tubing that would be sufficient to risk dislodgment of an intravascular needle connected to the flexible tubing and secured to the patient by standard means such as taping. The invention takes advantage of the fact that tension on a length of tubing can cause a certain degree of stretching of the tubing before it causes an attached intravascular catheter to dislodge, assuming that a section of the tubing or catheter is secured to a person&#39;s body by tape. Alternatively, tension on a length of tubing can cause a length of that tubing to move if a sufficient amount of slack exists in a segment of the tubing located in an occluder assembly. In this example, the occluder assembly is relatively flatter in one dimension than an orthogonal dimension, allowing it to rest reasonably securely and comfortably on a patient&#39;s arm or other part of the body. Preferably, the occluder assembly allows the user to easily load a length of tubing into the assembly and reset or rearm the assembly using one hand. 
       FIG. 2  illustrates an occluder assembly  100  in which a segment of flexible tubing  20  attached to access needle  14  is mounted. In this embodiment, the occluder assembly  100  includes one or more occluders  110  having occluding elements  111  at the distal end of occluders  110 , the occluders  110  being pivotally connected at their proximal ends  112  to a base unit  120 . The one or more occluders  110  can be forced together (or forced toward a stationary member in the case of a single occluder), directing occluding elements  111  toward the enclosed tubing  20  by the actuator  130  as it advances distally toward the distal end of the one or more occluders  110 . The clamping action of the one or more occluders  110  is not unlike the clamping action that a collet exerts on an internally disposed object when a collet socket is advanced over the collet. In this example, the flexible tubing  20  is colleted within one or more occluders  110  as an enclosing actuator  130  advances distally along the outer surface of the one or more occluders  110 . (Note that pairs or a plurality of components of the occluder assembly  100  will be described below, assuming the presence of two or more occluders. Although two or more occluders may be a preferred embodiment, the description should not be interpreted to exclude the possibility of having single components as appropriate if only one occluder is contemplated for the invention.) 
     The actuator  130  is driven distally by actuator springs  140 , and in so doing forces the distal ends of occluders  110  toward each other (or toward a stationary member in the case of a single occluder). Frame  150  includes occluder stops  151  that support the distal ends of occluders  110  in an open or ‘armed’ position, preventing actuator springs  140  from moving actuator  130  distally along occluders  110 . Upon application of a pulling force on flexible tubing  20 , frame  150  is distracted from base unit  120 . The distraction is sufficient to move the distal ends of occluders  110  off the occluder stops  151 , thereby allowing the occluders  110  to move toward each other and the actuator  130  to advance distally under the force of actuator springs  140 . Any stretching force applied to tubing  20  is translated into a distracting force between base unit  120  and frame  150  because the tubing  20  is gripped securely at each end of occluder assembly  100 . In this case, the spring force needed to drive the actuator  130  along occluders  110  can be divided among two or more springs in order to minimize the diameter or thickness of the individual springs, allowing the assembly  100  as a whole to have a flatter profile in one plane. 
       FIG. 3  is a perspective view of an exemplary dual-spring occluder assembly  100 . A c-shaped actuator  130  has two actuator segments  130   a  and  130   b , each of which is driven by a separate actuator spring  140  (more clearly shown in  FIGS. 4 and 5 ). The two actuator springs  140  are on one end partially housed in—or otherwise attached to—base unit  120 , and on the other end partially housed in—or otherwise attached to—actuator segments  130   a  and  130   b  of actuator  130 . Actuator  130  is guided by frame  150  of occluding assembly  100 , frame  150  in this case also incorporating or attached to front tubing grip  152 . A rear tubing grip  160  can be connected or attached to base unit  120 , in this example by means of dowels or spindles  161 . In the example shown, occluders  110  interact with actuator segments  130   a  and  130   b  of actuator  130  to apply a pinching force against the sides of tubing segment  20 . The proximal ends  112  of occluders  110  are secured and pivot about occluder dowels or spindles  113  mounted in base unit  120 . In other embodiments, a single occluding arm may be present, the opposing member acting merely as a stationary guide for the opposing actuator segment of the actuator. Tubing segment  20  can be placed between occluders  110  and the two actuator segments  130   a  and  130   b  of actuator  130 . Base unit  120  is also c-shaped to accommodate the placement of tubing segment  20  in the center of occluding assembly  100 . 
     Occluding assembly  100  can be triggered to occlude tubing segment  20  when a pre-determined threshold amount of tension is applied to the flexible tubing  20 , causing the tubing to stretch slightly (or at least causing a slackened tubing segment to straighten), pull frame  150  slightly away from base unit  120 , and disengage the distal ends of occluders  110  from the occluder stops  151 . Once the ends of occluders  110  clear contact with occluder stops  151 , the actuator spring  140  provides a force against actuator  130  that is sufficient to overcome frictional resistance between actuator segments  130   a  and  130   b  and occluders  110 , and advance actuator  130  along the outer surfaces of occluders  110 , imparting a pincer or clamping force between occluding elements  111 . As shown in  FIG. 4 , a longitudinally directed actuator spring  140  provides a force causing movement of actuator  130  along occluders  110  imparts an orthogonal force against the side walls of tubing  20 , occluding or constricting its lumen. The occluding force of the occluders  110  is maintained by the force of the actuator springs  140  acting on actuator  130 . 
     Front  152  and rear  160  tubing grips can comprise channels that can secure tubing segment  20  within occluder assembly  100 . In an additional embodiment, a front latch  153  and rear latch  163  are pivotally connected to front  152  and rear  160  tubing grips, respectively, and can swing and snap open and closed over grips  152  and  160 , and the enclosed tubing using one finger or a finger and thumb of a single hand. The latches  153  and  163  can have handles that facilitate manipulating the latches with a fingertip. The latches  153  and  163  preferably allow a user to mount a tubing segment onto occluder assembly  100  with one hand while it is resting on the user&#39;s body. The surfaces of the channels of grips  152  and  160  can preferably have tube gripping features such as ridges, ribs, cross hatches, scales or other raised surface features (including, for example, transversely aligned sawtooth ridges), or even non-raised adhesive or elastomeric surfaces, or otherwise clinging surfaces that can help to hold tubing  20  in position. These surfaces or features can provide sufficient frictional resistance to the adjacent tubing wall to prevent movement of the tubing with respect to the grips  152  and  160 , particularly once the respective sections of the tubing segment  20  are securely enclosed by latches  153  and  163 . In one embodiment, the surface features are capable of gripping the bare flexible tubing segments themselves. In another embodiment, the surface features are shaped to capture the profile of the flexible tube overlying the barb  21  and  22  of a coupling to which the tubing segment  20  is attached. 
     As shown in  FIG. 5 , when occluder assembly  100  is in an armed state, occluders  110  are kept apart from each other and tubing segment  20  by occluder stops  151  acting on the ends  114  of occluders  110 . The distance between occluders  110  can be sufficient to prevent actuator  130  from moving distally under the force of compressed actuator springs  140 . Tension on a segment of tubing  20  outside of the occluder assembly  100  sufficient to overcome the frictional resistance between occluder stops  151  and occluder ends  114  will cause disengagement of occluders  110  from occluder stops  151 . The composition, shape and area of the mating surfaces can be varied empirically until the desired triggering tension for the flexible tubing is obtained. The triggering tension of the tubing can be determined by measuring the tubing tension required to dislodge an attached needle that has been properly taped to a person&#39;s body, and setting the triggering tension to a value safely below this needle dislodgement tension. For example, the occluder assembly  100  can be constructed to trigger upon application of approximately 0.6-1 lb of tension on a segment of the tubing  20 . In some embodiments, the triggering tension may be lower than 0.6 lbs. In most circumstances, it will be prudent for the device  100  to actuate below a tension of about 1 lb., in order to accommodate situations in which an IV catheter has been taped to a person&#39;s body in a relatively cursory manner. 
     Over time and use, and depending on the type of material used for the occluders  110  and frame  150 , the frictional resistance between occluder ends  114  and occluder stops  151  may change, leading to a change in the threshold tubing tension force at which the occluder assembly  100  will trigger. In addition or optionally, as shown in  FIG. 6 , actuator rests  115  may be incorporated on occluders  110  to contact the leading edges of actuator segments  130   a  and  130   b  of actuator  130  when in an armed position. The actuator rests  115  in an embodiment comprise jog features on the outer aspect of the occluders  110 , forming a mating relationship with the leading edge of the actuators  130 , relieving some of the colleting forces acting on the occluders  110 . Preferably, the angle of incline of the actuator rests  115  with respect to the surface of occluders  110  is sufficiently close to vertical to direct most of the compressed spring force of actuator springs  140  longitudinally along the length of occluders  110 . In this manner, the amount of clamping or colleting force acting on the distal ends  114  of occluders  110  against the occluder stops  151  is decreased, reducing frictional resistance between occluder ends  114  and occluder stops  151  upon actuation of the device  100 , and creating a more predictable release force when it is activated. Preferably, actuator rests  115  have an angle of incline several degrees from vertical in order not to inhibit actuator  130  from being released under the force of the compressed actuator springs  140  upon disengagement of occluder ends  114  from occluder stops  151 . 
     Once the tubing segment  20  is no longer under a distracting force, occluding assembly  100  can be re-armed after it has been released by simply grasping actuator  130  and retracting it toward base unit  120 , compressing actuator springs  140 . As shown in  FIG. 6 , arming occluding assembly  100  involves having a user grip the leading sides of actuator segments  130   a  and  130   b  that preferably are shaped as finger rests, grasping, for example, with the index and middle fingers respectively, and pulling actuator  130  in a rearward direction toward base unit  120 , which is being grasped by the thumb. Alternatively, the base unit segments  120   a  and  120   b  (shown in  FIG. 6 ) can be grasped by the index and middle fingers, respectively, and the actuator can be grasped by the thumb to effectuate re-arming. By placing the thumb of the user&#39;s hand on a trailing side of base unit  120 , or on a leading side of actuator  130 , it is possible to arm the device using one hand. Upon doing so, as shown in  FIG. 7 , the trailing edge  131  of the bottom of actuator  130  can engage a frame post  155  formed from or attached to frame  150 , and pull frame  150  proximally, forcing occluder stops  151  against the distal ends  114  of occluders  110 , spreading occluders  110  apart and seating the distal ends  114  of occluders  110  onto occluder stops  151 . In an embodiment, the trailing edge  131  of the bottom of actuator  130  optionally can comprise a slot  132  within which frame post  155  can travel, as shown in  FIG. 7 . In some embodiments, the slotted trailing edge  131  of the bottom of actuator  130  can help to align actuator occluders  110  with occluder stops  151  during re-arming of the device  100 . In other embodiments, actuator slot  132  is long enough to allow a force on the trailing side of frame post  155  to move frame  150  forward relative to base unit  120  to trigger occluder assembly  100 . As shown in  FIG. 4 , the leading edges  116  of occluder ends  114  can be angled to correspond to the angle of the trailing edges  154  of occluder stops  151  in order to facilitate having the occluder stops  151  slide past occluder ends  114 . Once occluders  110  have been loaded onto occluder stops  151 , release of actuator  130  by the user allows it to move forward under spring  140  force until reaching actuator rests  115  of occluders  110 . The combination of contact with actuator rests  115  and occluder end  114  contact with occluder stops  151  places the device  100  in an armed state. Preferably, the spring rates of actuator springs  140  are moderated to allow persons of modest strength or frail constitutions to re-arm the device  100  using one hand. For example, the re-arming force required to compress actuator springs  140  and arm the device  100  can be kept at between about 4.5-5.0 lbs. Preferably, to accommodate users with a wide variety of medical conditions or infirmities, the maximum re-arming force is kept below about 6 lbs. Generally, for most medical intravenous tubing in current use, the spring rates of occluder springs  140  that this guideline permits are still sufficient to fully occlude a flexible tubing containing fluid under at least about 800 mm Hg of intraluminal pressure. In other medical or non-medical applications, the amount of intraluminal pressure under which the occluding device will still operate successfully may be higher. If so, then the occluder springs may need to be replaced by springs having higher spring rates. Furthermore, if the stiffness or resiliency of the flexible tubing being used varies from the tubing covered by the described embodiments of device  100 , the occluder springs may need to be replaced by springs having higher or lower spring rates. 
     The distracting force on tubing segment  20  needed to trigger release of occluders  110  can be adjusted by altering the frictional surface characteristics of occluder ends  114 , for example, or by altering the surface area with which they contact occluder stops  151 , or of their incline angle with occluder stops  151 . In addition, the contacting surfaces between occluder stops  151  and occluder ends  114  can have different mating relationships (e.g., tooth-and-groove profile), depending on the degree of distracting force desired to activate the occluding assembly  100 . 
     Preferably, the tension-activated occluding assembly  100  should trigger within a relatively narrow range of applied tension on the flexible tubing  20  to which it is attached. Furthermore, the triggering characteristics of the occluding assembly  100  should preferably not vary over time and after repeated use. Factors such as variations in manufacturing processes, required tolerances between moving parts, and wear of contacting surfaces from repeated use can be mitigated by additional enhancements of the occluding assembly  100  described above. 
       FIG. 8  is a cutaway view of another embodiment of occluding assembly  100  incorporating a triggering spring  170  that can assist in keeping occluding assembly  100  in an armed state until a distracting force is applied that is sufficient to slide trigger dowels or spindles  161  across slots  157  and compress triggering spring  170 , allowing movement of frame  150  away from base unit  120  (or vice versa) under the force of actuator springs  140 . As shown in  FIG. 10 , note that occluder dowels or spindles  113  are mounted in base unit  120  and can slide along slots  158  of frame  150  along with trigger dowels or spindles  161 , allowing for translational or longitudinal movement of occluders  110  (along with base unit  120 ) relative to frame  150 . 
     A circular triggering spring  170  is illustrated in this embodiment, but any other type of spring could be used to achieve the same result, i.e., providing a spring-based trigger mechanism that does not depend on friction between moving parts to cause the occluding assembly  100  to release. For example, occluder stops  151  could include spring-loaded protrusions positioned to keep occluders with appropriately shaped ends in an armed position. The spring-loaded protrusions would be compressible by a pre-determined threshold tension force on tubing  20 , allowing the occluder ends to slip off the occluder stops and trigger the device. Triggering spring  170  can be placed within its recess  156 , and can be held in position by positioning rear tubing grip  160  over the spring  170  and recess  156 . With this type of installation, one can readily adjust the triggering force by disassembling the rear tubing grip  160  from the base unit  120 , and substituting a triggering spring having a different spring rate. This can be accomplished, for example, by varying the thickness of the ring of triggering spring  170 , as shown in  FIG. 9 .  FIGS. 9 a  and 9 b    show a triggering spring having the lowest of three exemplary spring rates in perspective and top views, respectively.  FIGS. 9 c  and 9 d    show triggering springs having progressively increasing spring rates, respectively. In a typical application using current medical-grade tubing, triggering spring  170  should be compressible by trigger dowels or spindles  161  in response to a pulling force on the tubing  20  of about 0.6-1 lb. In some embodiment, the pulling force range that can cause compression of triggering spring  170  can be in the range of about 0.5 to 2 lbs. The triggering force can be adjusted up or down for other medical or non-medical uses by substituting a triggering spring  170  having a different spring rate. The triggering spring characteristics can also be changed if the flexible tubing in use has different elastic or tensile properties from those covered by the embodiments of device  100  described herein. 
     Use of a triggering spring as the principal means of triggering the device reduces reliance on the frictional resistance between occluder stops  151  and occluder ends  114  for an accurate and precise response to a triggering force. By having the triggering force depend mostly on compression of the triggering spring, the device  100  is able to trigger in response to a tension force on tubing  20  in a more reliable or consistent manner over many cycles of device use. In the illustrated example, trigger dowels or spindles  161  compress triggering spring  170  as frame  150  slides back and forth within the track formed by base unit  120 .  FIG. 8  shows the positions of trigger dowels or spindles  161  relative to triggering spring  170  and frame  150  when occluders are in a released or occluding position.  FIG. 10  shows the positions of trigger dowels or spindles  161  relative to triggering spring  170  and frame  150  when occluders  110  are in an armed position. Movement from an armed position to a released (occluding) position requires trigger dowels or spindles  161  to move along slots  157 , transiently compressing triggering spring  170  in the process. In an embodiment, trigger dowels or spindles  161  may also serve to attach rear tubing grip  160  to base unit  120 , as shown, for example, in  FIG. 3  and  FIG. 12 . In different embodiments, the rear tubing grip  160  can be a detachable or permanently affixed component of the occluder assembly  100 . The rear tubing grip  160  can include a channel in which a segment of tubing  20  is placed and secured. As with front tubing grip  152 , the channel of rear tubing grip  160  can have surface features that promote gripping of the enclosed segment of tubing  20 , particularly when latch  163  has been secured over the channel of tubing grip  160 . In this embodiment, frame  150  includes a triggering spring recess  156  to accommodate secure placement and proper function of triggering spring  170 . Frame  150  also has slots  157  to accommodate movement of frame  150  relative to base unit  120 . These features are more clearly shown in  FIG. 11 , which shows the top side of frame  150  in isolation. Slots  157  allow frame  150  to move relative to trigger dowels or spindles  161  mounted in base unit  120 , while slots  158  allow frame  150  to move relative to occluder dowels or spindles  113  mounted in base unit  120 . Also shown in this embodiment are actuator stops  159 , which prevent actuator  130  from overshooting its fully triggered position. 
     In another embodiment, occluder assembly  100  can be mounted onto a mounting pad  180 , which in turn can be affixed to any surface, including a patient&#39;s arm or other body part. Preferably, mounting pad  180  is shaped so that portions of it can be readily taped onto a person&#39;s arm, for example, using only one hand.  FIG. 13  shows one such example, in which mounting pad  180  includes one or more extensions or wings  181  across which strips of tape may be placed when affixing mounting pad  180  onto a person&#39;s arm. In this case, one need only apply a strip of tape onto one of the extensions  181 , lift the mounting pad  180  by the tape-extension combination, and place it on a suitable surface, pressing the two ends of the strip of tape onto the receiving surface. Following this, additional strips of tape can be placed on the remaining extensions or wings  181  to secure mounting pad  180  to the recipient surface. The mounting pad may also be a disposable pad with pre-applied adhesive or VELCRO material covering the undersurface of the mounting pad, which allows the mounting pad to be securely mounted to the user&#39;s skin. In other embodiments, the structural components of the mounting pad that interact with the occluder assembly  100  may be connected or attached to a strap that can be worn around a user&#39;s arm or wrist. 
     In an embodiment, mounting pad  180  attaches to the bottom of occluder assembly  100  by means of a snap fastener, the male component  182  of which is seen in  FIG. 13 . The snap fastener comprises a male component and female component, either of which can be attached to the center of mounting pad  180 . In this example, the male component  182  is attached to mounting pad  180 . Using a snap fastener allows the attached occluder assembly  100  to rotate about an axis formed by the male component  182  (or alternatively a snap fastener female component). The occluder assembly  100  advantageously can also be attached to and removed from mounting pad  180  using one hand. The female component  183  of the snap fastener is shown in  FIG. 14 . In this example, it is screwed to the bottom of occluder assembly  100  adjacent the bottom side of base unit  120 . A Teflon washer  184  or other relatively frictionless spacer can be inserted between female component  183  and the adjacent surface of base unit  120 . In an embodiment, the female component  183  is connected rigidly to base unit  120 . Thus, any pulling force on tubing  20  on the front end of occluder assembly  100  (i.e. next to front tubing grip  152 ) will be resisted through the base unit by both the portion of the tubing  20  that is taped onto the user&#39;s body, and by the mounting pad  180 , which is also secured to the user&#39;s body. 
     In another embodiment, the mounting pad  180  is loosely connected to occluder assembly  100  via a mounting body that can move back and forth a short distance in a slot within base unit  120 . If the mounting body is made to contact a trailing edge of frame  150  before contacting the front edge of the base unit  120  slot, then occluder assembly  100  can be made to trigger with a pulling force being applied to tubing  20  at the back end of occluder assembly  100  (i.e. next to rear tubing grip  160 ), in addition to the front end of occluder assembly  100 . Rather than attaching directly to base unit  120 , for example, female component  183  can be connected to a snap fastener mount  185 , shown in  FIG. 7 . Snap fastener mount  185  protrudes through, and can move back and forth within base unit slot  121 . Snap fastener mount  185  is shown in isolation in  FIG. 15 . The base  186  of snap fastener mount  185  is sized to fit loosely within frame slot  159  on the bottom side of frame  150 , as shown in  FIG. 16 . Snap fastener mount  185  can thus move back and forth within slot  159 . Snap fastener mount  185  is held within occluder assembly  100  by base unit  120 , as shown in  FIG. 17 . The mounting feature of snap fastener mount  185  protrudes through base unit slot  121 . Thus, snap fastener mount  185  (and therefore its subsequently attached mounting pad  180 ) can move relative to both frame  150  and base unit  120 . Once snap fastener mount  185  has reached the end of aft travel (i.e. toward rear tubing grip  160 ) with respect to base unit slot  121  (as shown in  FIG. 17 ), it can travel further aft with respect frame slot  159 , taking base unit  120  along with it. This extra travel can occur when a pulling force is applied to tubing  20  near the front tubing grip  152 . The extra aft travel allowed by frame slot  159  is enough for trigger dowels or spindles  161  to travel in slots  157 . If the tension force on tubing  20  has reached the threshold level specified to deploy occluders  110 , trigger dowels or spindles will be able to compress triggering spring  170 , and the device  100  will trigger. 
     Furthermore, the device  100  can trigger if a pulling force is applied to tubing  20  next to rear tubing grip  160 . In this case, aft tension on tubing grip  160  (i.e. between needle  21  and tubing grip  160 ) and attached base unit  120  with respect to snap fastener mount  185  (which is immobilized when attached to mounting pad  180 ) causes the leading edge of snap fastener mount base  186  to contact the trailing edge of frame slot  159 . This position is shown relative to frame slot  159  in  FIG. 16 , and with respect to base unit slot  121  in  FIG. 18 . If the tubing tension reaches the threshold force specified to trigger occluder assembly  100 , then snap fastener mount  185  can push frame  150  forward, with the trigger dowels or spindles  161  overcoming and compressing triggering spring  170  to trigger occluder assembly  100 . Thus in this embodiment, occluder assembly  100 , appropriately immobilized on a user&#39;s body, can be triggered by a pulling force acting either on front tubing grip  152  or rear tubing grip  160 . 
     In another embodiment, the occluder assembly  100  can trigger if an off-axis pulling force is applied to tubing  20 , causing occluder assembly  100  to tend to rotate on its mounting pad  180 . An off-axis pulling force can occur, for example, if the segment of tubing  20  external to occluder assembly  100  is pulled at an angle with respect to the segment of tubing  20  that is secured within occluder assembly  100 . Frame post  155  (seen, e.g. in  FIG. 14 ) can be made tall enough to extend beyond the bottom surface of actuator  130  and the female component  183  of the snap fastener. In an embodiment, the length of actuator slot  132  allows for enough forward travel of frame  150  to advance trigger dowels or spindles  161  against triggering spring  170  (as shown in  FIG. 10 ) and trigger occluder assembly  100 . Referring to  FIG. 13 , when frame post  155  is positioned in a trough  187  of mounting pad  180 , the occluder assembly  100  can rotate clockwise or counterclockwise until frame post makes contact with cam elements  188   a  or  188   b . An off-axis tension on tubing  20  causing occluder assembly  100  to rotate about the axis of its mounting pad attachment point (which, for example, can be a snap fastener assembly previously described) will trigger occluder assembly  100  as soon as sufficient force is applied by frame post  155  against cam elements  188   a  or  188   b , causing frame post  155  to move forward in actuator slot  132 . 
     In a further embodiment, the threshold off-axis tension force on tubing  20  required to trigger occluder assembly  100  can be adjusted to approximately match the on-axis threshold tension force (i.e. when the segment of tubing  20  external to occluder assembly  100  is in line with the segment situated within occluder assembly  100 ). In this case, spring arms  189   a  and  189   b  on mounting pad  180  (shown in  FIG. 13 ) are positioned to enclose the proximal narrower portion  122  of base unit  120 , as shown in  FIG. 12 . The spring arms  189   a  and  189   b  can be constructed to have spring rates that will restrain rotation of occluder assembly  100  until an off-axis tension force on tubing  20  reaches a level equivalent to the on-axis tension force at which a triggering event is desired. Thus, it is possible to prevent premature triggering of occluder assembly  100  through contact of frame post  155  with cam elements  188   a  or  188   b  upon application of an off-axis tension on tubing  20 . 
     Spring arms  189   a  and  189   b  can be constructed of a number of materials, including metals or plastics with tensile properties. In an embodiment, both the mounting pad  180  and spring arms  189   a  and  189   b  can be constructed from popypropylene, such as, for example, EXXON ESCORENE™ 9074). The materials from which the frame  150 , actuator  130 , base unit  120 , occluders  110 , grips  152  and  160 , and latches  153  and  163  preferably may be constructed include any suitable metals or plastics with the requisite hardness to resist wearing due to contact among moving parts. In an embodiment, these components can be constructed from 6061-T6 Aluminum which has been hard-coat anodized. Preferably, actuator springs  140 , triggering spring  170  and trigger dowels or spindles  161  are constructed from stainless steel or other similarly hardened material in order to resist wear and to maintain consistent functional relationships. To assist the user in mounting occluder assembly  100  onto mounting pad  180  in the proper orientation with respect to mounting pad  180 , an icon  191  can be painted or inscribed onto any suitable surfaces of corresponding ends of both occluder assembly  100  and mounting pad  180 . In an embodiment, a matching icon  191  is inscribed on the top surface of rear latch  163  and the rear support surface  190  of mounting pad  180 . 
     As shown in  FIG. 19 , another embodiment  200  of a device for occluding a flexible tube generally comprises a tapered planar body  201  having a first peripheral edge  202  and second peripheral edge  204  where the first peripheral edge is generally longer than the second peripheral edge  204 . A housing  208  is attached to a top surface of the body  201 . A cover to the housing is removed for clarity. The general plan dimensions of the housing  208  follow the general shape of the body  201 . A first opening  210  and a second opening  212  in the housing are sized to accept the tube  20 . The tube  20  having a first end  20   a  and a second end  20   b  is temporarily attached to the body  201  at a clip  206  located near the first peripheral edge  202  of the body. A cylinder or cylindroid body  220  is slideably contained within the housing and is adjacent to the tube  20  which extends from the first opening  210  to the second opening  212 . Operationally, this embodiment of the device can occlude a flexible tube in response to a threshold force F acting on the tube. The threshold force F acts on the second end of the tube, thus moving the tube outwardly and away from the second opening  212 . The resulting movement of the tube  20  within the housing  208  rotates the cylinder  220  to a second position  220   a , thus deforming the tube  20  into an occluded position  22  against an interior wall  209  of the housing. 
       FIG. 19 a    is a cross-sectional view of the embodiment shown in  FIG. 19  taken through  FIG. 19  along the line 1-1. The cylinder  220  and tube  20  are contained within the housing  208 . The cylinder  220  includes a first surface  224 , a second surface  226 , and a peripheral edge  222 . A plurality of ridges  228  can be located along the peripheral edge  222  and may be oriented generally perpendicularly to the first  224  and second  226  surfaces. Ridges  228  become adjacent to tube  20  and engage tube  20  within the housing  208 , whereby longitudinal movement of tube  20  within housing  208  translates into rotational movement of cylinder  220 . The interior surfaces of housing  208  can be generally smooth to allow tube  20  to slideably move within housing  208 . Additionally, the first surface  224  and second surface  226  can be generally smooth to allow cylinder  220  to move slideably and/or rotationally in housing  208 . 
       FIG. 19 b    is a cross-sectional view of the embodiment shown in  FIG. 19  taken through  FIG. 19  along the line 2-2. Tube  20  is secured to body  201  by means of clip  206 . Other means may be used to restrain the tube to body  201  as long as enough pulling force can be applied to the second end  20   b  of tube  20  to cause cylinder  220  to rotate and to compress the wall of tube  20 . Additional mounting means of the tube to the body  201  may include a permanent connection between tube  20  and body  201 , or a disengageable connection, allowing for reuse of the occluding device. 
     As shown in  FIG. 20 , another embodiment  300  of a device for occluding a flexible tube generally comprises a first support arm  310  and a second support arm  312 . The arms being disposed between a first planar body  302  and a second planar body (the second planar body is essentially a cover; not shown for clarity). The planar bodies are generally parallel to each other. A tube  20  is positioned between the planar bodies and the support arms  310  and  312 . The first planar body  302  has a first peripheral edge  304  and second peripheral edge  306 . Clips  308 ,  309  are located on the first planar body  302  near the first peripheral edge  304  to hold tube  20  in place. The second planar body (not shown) does not extend over the tube clips in order to assist in removing the tube from the first planar body. The support arms  310  and  312  are pivotably connected to the planar bodies by means of hinges or pivot points  314  and  316  respectively. In an embodiment, the hinges can generally be located near the midpoints of the support arms. Occluding member  318  and  320  are attached to support arms  310  and  312  respectively. The occluding members  318  and  320  extend towards each other and engage the outer surface of tube  20 . Trigger arms  326  and  328  are pivotally mounted on the distal ends of support arms  310  and  312  respectively. Each trigger arm  326  and  328  can be semicircular or c-shaped, and in an opposed configuration can surround the adjacent section of tubing  20 , the inside edges of the arms lightly in contact with the sides of the tubing. The opposing legs of the trigger arms  326  and  328  are in contact when they are generally perpendicular to the longitudinal axis of the tubing  20 . When the distal ends of the trigger arms engage each other and tube  20 , occluding arms  318  and  320  do not occlude the tube  20 . In a first position  21 , the tube  20  is provided with an amount of slack for strain relief between clips  308 / 309  and occluding members  318 / 320 . While tube  20  is in the first position  21 , the trigger arms  326  and  328  are generally perpendicular to the longitudinal axis of the tube  20  and the tube  20  remains unoccluded. 
     As shown in  FIG. 20 , a first spring  334  provides a compressive force against a first contact surface  330  of the first support arm  310 . Similarly, a second spring  336  provides a similar force against a second contact surface  332  of the second support arm  312 . The springs  334  and  336  are attached to the first planar body by spring clips  338  and  340  respectively. The springs are generally the same size and provide the same amount of force to each arm. The springs are shown as leaf springs, but may be any type of elastic element (such as, e.g., coil springs) capable of providing the force necessary to occlude tube  20 . While trigger arms  326  and  328  are generally perpendicular to the axis of tube  20  and in contact with one another, springs  334  and  336 , are prevented from occluding the tube. However, when the trigger arms are rotated to a second position (as shown in  FIG. 21 ) the springs  334  and  336  provide the force necessary to occlude the tube  20  by pinching the tube between the pair of occluding members  318  and  320 . 
     As shown in  FIG. 21 , the embodiment  300  is shown in an occluded position. When a predetermined threshold force F acts on the second end  20   b , the slack  21  in tube  20  is removed and the tube generally moves towards the second peripheral edge  306 . Since triggering arms  326  and  328  engage the tube, a longitudinal movement of tube  20  acts to rotate arms  326  and  328 . The rotation of the triggering arms leads to the rotation of the support arms  310  and  312 ; and under the force of springs  324  and  326 , occluding members  318  and  320  apply an occlusive force against the sides of tube  20 . 
     As shown in  FIG. 22 , another embodiment  400  of a device for occluding a flexible tube generally comprises two bodies  402  and  404  pivotally connected by a central hinge  410 . A first clip  406  is mounted to body  402  and second clip  408  is mounted to body  404  to hold the tube  20  in a first position  21  between the clips. Strain relief is provided when the tube  20  is in the first position  21  in order for the tube to properly occlude as shown in  FIG. 23 . A spring  420  is rotatably connected to the hinge  410  where it is compressed between the clips  406  and  408  and held in compression by a tongue  430  and groove  432  shown in  FIG. 24 . The bodies are held in the first position by the tongue and groove connection as shown in  FIGS. 22 and 24  until a predetermined force F is applied to a first end  20   a  and a second end  20   b  of the tube. The force F results in a rotational force about the hinge  410 . When the rotational force overcomes the resistance of the tongue  430  and groove  432  connection, the spring decompresses and moves the tube into a second position  22  as shown in  FIG. 23 . 
     As shown in  FIG. 25 , another embodiment  500  of a device for occluding a flexible tube generally comprises a hollow cylindrical body  502  having a first circular edge  504  and a second circular edge  505  located at opposite ends of the body. Semicircular arms  506  and  508  are connected to and extend away from the second peripheral edge  505 . An elastic actuating member  520  is located at the distal ends of the arms  506  and  508  and is capable of deflecting the distal ends of the arms toward each other. Actuating member  520  may alternatively be any element that exerts a spring-like force to compress the distal ends of arms  506  and  508  toward each other, such as, for example, a metallic spring clip. The arms  506  and  508  are capable of bending towards each other resulting in the occlusion of the tube  20  and then returning to their original position. A first occluding member  510  and a second occluding member  512  are attached to the first arm  506  and the second arm  508  respectively. The occluding members  510  and  512  are rigid and capable of occluding the tube  20  when the elastic actuating member  520  deflects the arms  506  and  508  towards each other. Tube  20  can be secured to the cylindrical body near the first circular edge  504  by a clamp  514  disposed within the cylindrical body  502 . Clamp  514  holds the tube  20  securely to the body. Preferably, tube  20  is generally centered along the longitudinal axis of the embodiment  500 . A curved bracket  550  can be secured to tube  20  near the distal ends of arms  506  and  508 . A tapered head  552  of curved bracket  550  can slideably engage the inside surface of first arm  506  and second arm  508  so as to resist the elastic actuating member  520  from occluding the tube  20 . In an unoccluded position  21 , the tube is provided with a predetermined amount of strain relief while the tapered head  552  is positioned between the distal ends of first arm  506  and second arm  508 . 
     As shown in  FIG. 27 , once a threshold force F is applied to a first end  20   a  of tube  20 , the tapered head  552  is urged outwardly and away from the distal ends of the first arm  506  and second arm  508  by the elastic actuating member  520 , resulting in the occluding members  510  and  512  deforming the tube into a second position  22  where flow is obstructed. At that time, the strain relief provided in the unoccluded position  21  is generally removed from the tube and the arms  506  and  508  deflect an angle α whereby the tube  20  is deformed into a second position  22 . 
       FIG. 25 a    shows a cross-sectional view of the embodiment taken along the line 1-1 of  FIG. 25 . The first occluding member  510  and second occluding member  512  are adjacent to opposite sides of the tube shown in the unoccluded state. The elastic actuating element  520  provides a compressive force to the first arm  506  and second arm  508 . 
       FIG. 26  shows a side view of a trigger of the embodiment shown in  FIG. 25  with a flexible tube attached therein. The bracket  550  is comprised of a curved support section  551  attached to a tapered cylindrical head  552 . Curved tabs  554 - 557 , extend outwardly from the support section  551  and are configured to keep the tube in contact with the support section. The inside perimeter of the tapered head  552  is generally in full contact with the outside perimeter of the tube. The head  552  tapers away from the curved support section  551  so that it is urged away from the first arm  506  and second arm  508  when a threshold force F is applied to the first end  20   a  of the tube in the direction indicated. Additionally,  FIG. 26 a    is a cross-sectional view of the trigger taken through the line 2-2 of  FIG. 26 . 
     As shown in  FIG. 28 , another embodiment  600  of a device for occluding a flexible tube generally comprises a cylindrical housing  610  having a top surface (not shown for clarity), bottom surface  630 , and a curved peripheral edge  620 . A single loop of tube  20  having a first end  20   a  and second end  20   b  is fully enclosed within the housing  610 . 
       FIG. 29  shows the tube in a first position  21  and second position  22 . The tube enters the housing  610  through a first opening  640  along the curved peripheral edge  620  and exits in a similar manner through a second opening  642 . While in the first position  21 , the tube is unoccluded and flow within the tube is unobstructed. However when a threshold force, F, is applied to either the first end  20   a  or second end  20   b  of the tube, the tube is deformed, or kinks, within the housing to a second position  22 , and fluid flow within the tube is restricted. 
     As shown in  FIG. 30 , and in top view in  FIG. 31 , another embodiment  700  of a device for occluding a flexible tube generally comprises a first arm  710  and second arm  712  pivotally connected by a hinge  714 . A flexible tube  20  is secured to the second arm  712  by a clip  726  and is disposed between the length of the two arms. A first pair of trigger arms  722   a  and  722   b  is located on the first arm  710  on opposite sides of the tube  20 . Similarly, a second pair of trigger arms  724   a  and  724   b  is located on the second arm  712 . The distal end of the first trigger arm  722   a  and  722   b  engage a notch on the distal end of the second trigger arm  724   a  and  724   b . The notch resists the compressive force of an elastic actuating element  720  located around the arms  710  and  712 . A pair of rods  728   a  and  728   b  extend outwardly and away from trigger arms  722   a  and  722   b  respectively. The distal ends of the rods are each connected to a tube clamp  730 . The tube clamp  730  is securely fastened to the flexible tube  20  near the first end  20   a  of the tube to minimize any slippage between the tube  20  and the clamp  730 . Strain relief  21  is provided between the tube clamp  730  and clip  726 . Such relief allows axial movement of tube  20  between clamp  730  and clip  726  without pulling on the clip  726 . 
     As shown in  FIG. 32 , movement of the clamp  730  away from the trigger arms is translated along the rods  728   a  and  728   b  resulting in deflection of the first trigger arms  722   a  and  722   b  away from the second trigger arms  724   a  and  724   b . Once the distal ends of the first trigger arms  722   a  and  722   b  move beyond the notch on the second trigger arms  724   a  and  724   b , the elastic actuating element  720  rotates the first arm  710  about the hinge  714  an angle α. This rotation brings the occluding members  716  and  718  closer together thus pinching a section  22  of tube as shown in  FIG. 32 . 
     As shown in  FIG. 33 , another embodiment  800  of a device for occluding a flexible tube  20  generally comprises a first arm  820  and second arm  822  pivotably connected by hinges  860  and  862 . A tube  20  having a first end  20   a  and second end  20   b  is releasably attached to clips  870  and  872 . The tube  20  is disposed between the first and second arms and between the first hinge  860  and second hinge  862 . An elastic force actuator  845  is stretched over a first support member  840  and second support member  842 , the support members  840  and  842  are attached to the first arm  820  and second arm  822  respectively. The support members keep the elastic actuator  845  from slipping when the arms  820  and  822  are pivoted about the hinges  860  and  862  as shown in  FIG. 35 . A plurality of ribs  890  can be positioned along the outer surface of the arms  820  and  822  as gripping surfaces in order to assist in rotating the arms about hinges  860  when the device is returned to an unoccluded position. 
     As shown in  FIG. 34 , while in a first position  21 , the arms  820  and  822  are generally parallel to each other and the elastic actuator  845  generates approximately zero moment about the hinges. However, when the arms  820  and  822  are rotated towards each other, the elastic actuator  845  generates a moment about the hinges. An occluding member  850  is located at the distal end of the first arm  820  located opposite the trigger arm  830 . The occluding member  850  is generally perpendicular to the tube  20  so as to occlude the tube  20  when a threshold force F is applied to the first end  20   a  as shown in  FIG. 35 . Supporting the tube  20  near the occluding edge is a pair of clips  870  and  872 . The clips allow the tube  20  to be releasably attached to the second arm  822 . A tapered head  880  is attached to the tube near the first end  20   a . The tapered head  880  is generally cylindrical in shape and slideably engaged to the distal ends of the trigger arms  830  and  832 . While in the first position  21 , the narrowest part of the tapered head  880  is located between the trigger arms  830  and  832 . 
     As shown in  FIG. 35 , when a threshold force F is applied to the first end  20   a , the tapered head  880  moves outwardly and away from the trigger arms  830  and  832  resulting in the arms being urged open. As the trigger arms  830  and  832  separate, the occluding edge  850  occludes the tube  20  near the second end  20   b . After the embodiment of the device has been triggered and the tube  20  is in the second position  22 , and may be returned to the first position  21  by sliding the tapered head  880  so that the narrowest portion of the tapered head  880  is positioned between the trigger arms  830  and  832 . By sliding the tapered head  880  towards the trigger arms a predetermined amount of strain relief  21  will be created in the tube  20  between the tapered head  880  and the pair of clips  870  and  872 . The strain relief is required so that a force F can slide the tapered head  880  a certain distance without excessive straining on the tube  20 . 
     As shown in  FIG. 36 , another embodiment  900  of a device for occluding a flexible tube  20  generally comprises a base  910  having a pair of eccentric or cam-shaped bodies  920  and  922  rotatably mounted on one side of the base  910 . In the exemplary embodiment, the bodies  920 ,  922  have an eccentric peripheral edge with a gripping means capable of frictionally engaging an adjacent tube  20 . The gripping means may be a plurality of ridges and grooves oriented perpendicular to planar surface of the base. The flexible tube  20  is disposed between the bodies  920  and  922  and releasably attached to the opposite side of the base with a clip  930 . The tube  20  may be releasably attached by any means so long as it resists the tube  20  from sliding in the clip and does not occlude the tube while restrained. The bodies  920 ,  922  are shaped so that the gripping means engages the adjacent tube  20  but does not create an occlusion condition while the tube  20  in is a first position  21  as shown in  FIGS. 36 and 37 . 
     As shown in  FIG. 38 , when a force F is applied to a first end  20   a  the tube  20  moves outwardly and away from the base  910  but is restrained by the clip  930 . While moving, the tube  20  then engages the gripping means and rotates the eccentric bodies towards each other. The eccentric members rotate in a cam fashion, thereby deforming the tube  20  into a second occluded position  22 . The tube  20  may be returned into the unoccluded first position  21  if first end  20   a  is moved towards clip  930  so that bodies  920  and  922  rotate away from each other to a predetermined position which allows the flow in the tube  20  to be unrestricted. 
     As shown in  FIGS. 39, 40 and 41 , another embodiment  1000  of a device for occluding a flexible tube  20  generally comprises a cylindrical housing  1010  having a sloped internal surface for supporting a single loop of a tube  20  (this embodiment is essentially a refinement of embodiment  600  found in  FIG. 28 ). The single loop of tube is fully enclosed within the housing  1010 . The tube  20  enters the housing  1010  at a first opening  1014 , forms a single unoccluded loop along the sloped internal surface and exits the housing  1010  at a second opening  1016 . A cover  1012  is attached to the housing  1010  by means of two flexible tabs  1018 . An occluding edge  1022  extends from the sloped internal surface to the cover  1012 . A flexible arm  1020  having a pointed tab  1021  extends from the sloped surface to a predetermined position below the cover  1012 . The tab  1021  does not engage the tube  20  while the tube  20  is in an unoccluded position as shown in  FIGS. 39 and 40 . 
     As shown in  FIG. 41 , when a threshold force F is applied to the first end  20   a  of the tube, a portion of the tube moves outwardly and away from the first opening  1014 . The arm  1020  is configured to deflect away from the tube  20  so that the tab  1021  may engage and hold the tube  20  in an occluded position  22 . The tube  20  is bent around the occluding edge  1022  and held in position  22  until the arm  1020  is deflected so the tube  20  may return to its unoccluded position as shown in  FIGS. 39 and 40 . The sloped surface provides a means for supporting and shaping the tube  20  so that when a force F is applied, the tube  20  is able to deflect about the occluding edge without moving relative to the second opening  1016 . 
     As shown in  FIG. 42 , another embodiment  1100  of a device for occluding a flexible tube  20  generally comprises a base  1110  pivotally connected to an occluding member  1114  having an edge  1118  for occluding a tube  20 . A spring  1116  is compressed between the base  1110  and occluding member  1114 , whereby the occluding member  1114  is urged to rotate about a central hinge  1120 . The tube  20  having a first end  20   a  and second end  20   b  is secured to a first arm  1111  by a clip  1113   a  and a second arm  1112  also by a clip  1113   b . The arms  1111  and  1112  are generally symmetrical to each other and are able to rotate away from the base  1110 . In an unoccluded position, as shown in  FIGS. 42 and 44 , the front edge of the occluding member  1114  is supported by the top surfaces of members  1112  and  1111  while they are positioned relatively close together with just a small gap between them. 
     As shown in  FIG. 43 , when a threshold force F pulls on the first and second ends of the tube the arms  1111  and  1112  rotate apart from each other and away from the base  1110 . Once the arms rotate away from each other, the gap between them increases and the occluding member  1114  no longer rests on the arms, and is urged by the spring  1116  to occlude the tube  20 . By compressing the spring  1116  and resting the occluding member  1114  on the arms  1111  and  1112  in their original positions, the tube  20  will return to its unoccluded position. 
     As shown in  FIGS. 45 and 46 , another embodiment  1200  of a device for occluding a flexible tube generally comprises a first body  1202  having a generally planar surface; a second body  1206  pivotably attached to the first body  1202 ; a plunger  1220  slideably attached to the first body  1202 ; and compression spring  1230  positioned between the plunger and the first body. A first channel  1204  having two curved sidewalls for positioning a tube  20  therebetween is located at one end of the first body  1202 , while a curved member  1210  is attached to the opposite end of the first body  1202 . Additionally, a plunger  1220  is slideably mounted on the first body  1202  where the compression spring  1230  provides the force necessary to move the plunger  1220  into the first channel  1204  and occlude the tube located therein. 
     As shown in  FIGS. 45 and 46 , in a first position, the spring  1230  is compressed against the curved member  1210  and the plunger  1220 . It is restrained by a tab  1224  extending from the plunger  1220  where it engages the sidewall of a second channel  1208 . A threshold force F acting on a first end  20   a  and second end  20   b  of the tube  20  urges a second channel  1208  to rotate away from a first channel  1204 . The plunger  1220  is held in place by the tab  1224  until a second member  1206  moves away from a first member  1202  thus releasing the plunger  1220  by means of the compression spring  1230  into the first channel  1204  and deforming the tube  20  into a second position  22  as shown in  FIG. 46 . The tube  20  is releasably attached within the first and second channels  1204 ,  1208  by means of clips  1210  located near the entrance of each channel. The tube  20  is slightly bent curved within the channels to allow free movement of the tube  20  between the clips when the force F acts on the first and second ends  20   a ,  20   b  of the tube  20 . The tube  20  may be unoccluded by compressing the spring  1230  and engaging the tab  1224  with the second member in order to hold the spring in compression. 
     As shown in  FIG. 47 , another embodiment  1300  of a device for occluding a flexible tube  20  generally comprises a first body  1302  having an arm  1306  extending rearward from the first body; a second body  1304  pivotably attached the first body by means of a hinge (not shown), the second body having an occluding edge  1312 ; a rod  1308  is attached to the distal end of the arm  1306  and extends outwardly and away from the arm; a clamp  1309  is affixed to the distal end of the arm configured to be releasably connected to a first end  20   a  of a tube  20 . A pair of clips  1310  extend from the first body  1302  and securely hold the tube  20  against the first body  1302 . The clips  1310  are separated by a predetermined distance to allow the occluding edge  1312  to pass between them without touching the clips  1310 . An extension  1314  projects outwardly and away from the second body  1304 . It is received between the first body  1302  and arm  1306  so that a tab  1316  engages the arm and holds the spring  1330  in compression. While the spring  1330  is in compression, the occluding edge does not occlude the tube  20 . However, when a threshold force F is applied to the first end  20   a  of the tube  20  it moves the clamp  1309 , the rod  1308  and the arm  1306  away from the first body  1302 . The outward movement of the arm  1306  triggers the spring to decompress since the tab  1316  no longer engages the arm  1306  as shown in  FIG. 52 . The expansion of the spring  1330  moves the occluding edge into the tube  20 , thus occluding the tube  20 . 
       FIG. 48  is a side view of the embodiment  1300  with the first body  1302  and second body  1304  separated for clarity. Pins  1320  are located on each side of the occluding edge  1312  and are received by the hinges  1321  located on the first body. Spring  1330  is located between the two bodies and held in position by a pair of spring receivers  1331  shown in  FIGS. 49 and 50 . 
       FIG. 49  is a top view of the first body  1302  with tube  20  taken along line 1-1 of  FIG. 48 . The clips  1310  hold the tube  20  in place while a force F (not shown) acts on the first end  20   a  of the tube  20 .  FIG. 50  is a section view of the underside of the second body  1304  taken along line 2-2 of  FIG. 48 .  FIG. 51  is a side view of the embodiment  1300  taken along line 3-3 of  FIG. 49  in an unoccluded state showing the spring  1330  in a fully compressed position. The tab  1316  holds the spring  1330  in compression until a force F acts upon the rod  1308  and then the tab  1316  releases the second body  1304  thus rotating the occluding edge  1312  into the tube  20 .  FIG. 52  is a section view of the embodiment  1300  taken along line 3-3 of  FIG. 49  in an occluded state showing a force F acting on the rod  1308 . The embodiment  1300  may be returned to the unoccluded state by removing the force F and reengaging the tab  1316  and the arm  1306 . 
     As shown in  FIGS. 53 and 54 , another embodiment  1400  of a device for occluding a flexible tube  20  generally comprises a base  1402  having a trigger  1406  slideably mounted along the longitudinal axis of the base  1402 . A tube  20  is releasably coupled to the trigger  1406  along the longitudinal axis of the base  1402 . The tube  20  is additionally coupled to the base  1402  at one of a pair of clips  1418  positioned on opposite sides of the base  1402 . The clips secure the tube  20  to the base  1402  so that it does not move when the trigger is activated. A cover  1404  is pivotably attached to the base  1402  by means of a pair of hinges  1416  centrally located on opposite sides of the base  1402 . 
     As shown in  FIG. 55 , an occluding edge  1412  rests upon the trigger  1406  when the trigger  1406  is fully inserted into the base  1402 . However, when the trigger  1406  is moved outwardly and away from the base  1402  a distance D due to a threshold force F acting on a first end  20   a  of the tube, the occluding edge is urged onto the tube  20  by a spring  1420  with a compressive force sufficient to fully occlude the tube  20 . 
     As shown in  FIG. 56 , the underside of the cover  1404  comprises an occluding edge  1412 , a pair of tabs  1414  and a spring retainer  1422 . The occluding edge  1412  is perpendicular to the longitudinal axis of the base  1402 . The pair of tabs extends from the base and rotatably engage the pair of hinges  1416  on the base. The spring retainer  1422  is positioned on the opposite side of the tabs as the occluding edge and is configured to accept the spring  1420 . 
     As shown in  FIG. 57 , the trigger  1406  includes a channel  1410  which is slideably received by a pair of ridges on the base (not shown). Additionally, the top edge  1408  of the trigger is positioned so that the occluding member  1412  is not in contact with the tube  20  while the tube  20  is fully inserted into the base  1402 . 
     As shown in  FIG. 58 , another embodiment  1500  of a device for occluding a flexible tube  20  generally comprises a curved hollow body having a first entrance  1502  and a second entrance  1504 . The body has a first curved end  1510  and a second curved end  1512  which define the shape of the tube within the housing. A first section of tube  21  may freely move towards the first entrance  1502  when a first end  20   a  of the tube is moved outwardly and away from the first entrance  1502 . When a threshold force F acts on the first end  20   a  and the tube  20  is deformed into a second position  22 , whereby the tube  20  is fully occluded. A second end  20   b  is positioned by means of a clip  1506  extending outwardly and away from the second curved end  1512 . Additionally, the tube  20  is frictionally held in place by the first curved end  1510  so that any force which acts on the second end  20   b  is resisted by the clip  1506  and the friction generated between the tube  20  and the first curved end  1510 . 
       FIG. 59  is a cross-sectional view of the embodiment  1500  taken along section line 1-1 of  FIG. 58 . A removable cover  1514  having a slot  1508  comprises one side of the embodiment for ease of access to the tube  20 . 
     As shown in  FIG. 60 , another embodiment  1600  of a device for occluding a flexible tube  20  generally comprises a male coupling  1602  and a female coupling  1604 . A first tube  20   a  may be secured to the male coupling  1602 , while a second tube  20   b  may be secured to the female coupling  1604 . A first valve  1606  having a watertight slit extending completely through is normally closed and positioned within the distal end of the male coupling  1602 . A second valve  1608 , also having a watertight slit, is normally closed and positioned inside the distal end of the female coupling  1604 . The slits are configured to accept a hollow cylinder  1610 , whereby a watertight seal is created between the exterior of the hollow cylinder  1610  and the interior of the slits when the cylinder  1610  is fully inserted into the slit. The male coupling  1602  is configured to lockingly engage the female coupling  1604 . A tongue and groove assembly as shown in  FIGS. 60 and 61  is just one means to lockingly engage the coupling. When the male and female coupling  1602 ,  1604  are fully engaged and locked, an internal spring  1612  is held in compression between the two couplings. Once coupled, the hollow cylinder  1610  creates a flow path through the first valve and second valve so that the first tube  20   a  and second tube  20   b  are in fluid communication with each other. When the hollow cylinder  1610  is removed from the slits, the valves are closed, and the distal ends of each tube  20  are sealed. Unlike the previously described embodiments, when this invention is triggered, the two halves,  1602  and  1604 , completely separate. This terminates fluid flow and prevents further force from acting on the needle site. 
     As shown in  FIG. 61 , the spring  1612  is held in compression between the male and female couplings  1602 ,  1604  by a tongue and groove assembly at the distal ends of each coupling. The spring  1612  will urge the couplings apart from each other once the locking force between the tongue and groove assemblies is overcome by a threshold force F acting outwardly and away from the first and second tubes. The spring  1612  may be encapsulated in a tearable biocompatible material  1614  (i.e. a polyolefin) or its equivalent, whereby the spring  1612  does not come into direct contact with the fluid within the hollow cylinder  1610 . 
     As shown in  FIGS. 62, 63 and 64 , another embodiment  1700  of a device for occluding a flexible tube generally comprises a female coupling  1702  and male coupling  1704  lockingly engaged to create a fluid connection between a first tube  20   a  and a second tube  20   b .  FIGS. 62, 63 and 64  show a cross-sectional view of the embodiment  1700  in different occluded positions. The female coupling  1702  generally comprises a first cylindrical body  1708  and second cylindrical body  1712  adapted to retain a one-way valve  1705  which is normally closed. A peripheral groove  1720  and a first gasket  1722  are located on the outer circumference of the second body. Both the groove  1720  and gasket  1722  are adapted to engage the male coupling  1704  and create a seal with the female coupling. The male coupling  1704  comprises a one-way valve  1705  and a hollow tapered body  1706 , the body being capable of opening the one-way valves. A spring  1714  is compressed between the hollow tapered body  1706  and a third cylindrical body  1710 . As the two couplings are brought together several sequential events occur within the embodiment: First, the hollow tapered body begins to engage the concave portions of the one-way valves  1705  as shown in  FIG. 63 . Then, the hollow tapered body compresses the spring  1714  against the third cylindrical body until the gasket  1724  has fully mated with the groove  1720 . Finally, once mated, the hollow tapered body fully extends through the one way valves  1705 , thus creating an unrestricted flow path for any fluid inside tubes  20   a  and  20   b . An additional fluid seal is provided by the first gasket and the inside diameter of the third cylindrical body. 
     The patient and male coupling  1704  may be connected by means of a trigger wire  1718 . The wire creates a separating force between the female coupling  1702  and male coupling  1704  when the threshold force F acts on the female coupling  1702  as shown in  FIG. 63 . 
     As shown in  FIG. 62 , during normal flow conditions, the trigger wire  1718  is slack and the male and female couplings  1704 ,  1702  are fully engaged. However, as shown in  FIGS. 63 and 64 , when a threshold force F acts on the female coupling  1702  through the first tube  20   a , the couplings begin to separate from each other resulting in a cascade of events: First, the trigger wire  1718  becomes taught and a force F′ is equally and oppositely applied to the male coupling  1704  though bracket  1716 . Second, the groove  1720  and gasket  1724  disengage from each other. Next, the spring  1714  urges the couplings apart resulting in the withdrawal of the tapered body  1706  from both the one-way vales, thus ensuring that flow between tubes  20   a  and  20   b  is terminated. To unocclude the tubes, the force F must be removed from the tube  20   a , and the couplings must be brought back into locking engagement as shown in  FIG. 62 . 
     As shown in  FIGS. 65 and 66 , another embodiment  1800  of a device for occluding a flexible tube generally comprises two one-way valve couplings  1814   a,b  (e.g. duckbill valves) located on either end of an interior channel  1806  lockingly engaged with two male couplings  1812   a,b  to create a fluid connection between a first tube  20   a  and a second tube  20   b . Each coupling has a corresponding male/female portion of a duckbill valve disposed therein. In  FIGS. 65 and 66 , a portion of the housing is depicted as transparent so that connection between the duckbill valves  1814   a ,  1814   b  can be seen. Locking engagement is facilitated by a pair of latching arms  1802   a,b  attached to a base  1810   a,b  of each male valve coupling  1812   a,b . Inner and outer rings  1808   a,b  (respectively) extend radially from the interior channel  1806  to engage with a detent  1818  on each latching arm  1802   a,b.    
     A bellows  1816  may surround the interior channel  1806  and engage with each base  1810   a,b . The bellows  1816  defines an interior cavity of sufficient volume to allow the device to operate in multiple positions without unintended disengagement of the latching arms  1802   a ,  1802   b  from the rings  1808   a,b . The bellows  1816  accommodates multiple positions by compressing and decompressing as the distance varies between each base  1810   a,b . In various embodiments, as shown in  FIG. 68  (detail omitted), the bellows  1816  may incorporate a spring  1820  to reduce the force required to disengage the latching arms  1802   a ,  1802   b  from the rings  1808   a,b . The spring  1820  may be fully encapsulated within the bellows  1816  such that fluid flowing through the interior channel  1806  essentially runs through a central longitudinal axis of the spring  1820  in the first position. 
     In the preferred embodiment, there is one inner ring  1808   a  and two outer rings  1808   b  to facilitate multiple positions in which fluid flow may be permitted or terminated. In a first position, as shown in  FIG. 65 , the detent  1818  on each pair of latching arms  1802   a ,  1802   b  is engaged with the inner ring  1808   a . The latching arms  1802   a ,  1802   b  are opposite each other to accommodate simultaneous attachment to the inner ring  1808   a . As a result of this configuration, the male valve couplings  1812   a,b  are engaged with the female valve couplings  1814   a,b  such that fluid can freely flow through the interior channel  1806  via penetrated duckbill valves. Each base  1810   a,b  can provide an additional fluid seal with the use of o-rings (not shown). 
     In a second position, as shown in  FIG. 67 , one pair of latching arms  1804  is disengaged from the inner ring  1808   a  which disengages the corresponding duckbill valve portions. As a result, one duckbill valve is unpenetrated and fluid is prevented from flowing through the interior channel  1806 . In a third position, as shown in  FIG. 66 , each pair of latching arms  1802   a ,  1802   b  is disengaged from the inner ring  1808   a  but remain engaged with the outer ring  1808   b . As a result, fluid flow into the interior channel  1806  is terminated as both duckbill valves are in an unpenetrated state. Positions two and three may be the result of a force acting on one or both ends of the tube  20 . Additionally, a force triggering disengagement of latching arms  1802 ,  1804  from their respective rings may allow the spring  1820  to further urge the housing sections  1812   a,b  in opposite directions, thereby transitioning the device  1800  out of the first position. If a substantial force acts on one or both ends of the tubing  20 , the device may completely separate, terminating fluid flow indefinitely. 
     As shown in  FIGS. 69-76 , another embodiment  1900  of a device for occluding a flexible tube generally comprises a movable housing  1904  capable of sliding over a pair of arms  1906   a,b  and occluding the tube  20 . As shown in  FIG. 69  and  FIG. 70 , a spring  1908  disposed between the fixed housing  1902  and movable housing  1904  has a potential energy that tends to urge the movable housing  1904  away from the fixed housing  1902  but for the trigger  1914 , which holds the device in an unoccluded state. The trigger  1914 , best viewed in  FIGS. 70, 71 and 75 , interacts with the movable housing  1904  on both sides of the arms  1906   a,b . The trigger  1914  is essentially part of a flexible coupling  1912  attached to the fixed housing  1902  at one end and the tube  20  at the other end. This flexible configuration allows the trigger  1914  to move inwardly in response to pulling or stretching force exerted on the tube  20 , thereby disengaging the trigger  1914  from movable housing  1904  and releasing the potential energy in the spring  1908 . 
     In the unoccluded state, the arms  1906   a,b  generally diverge from the longitudinal axis of the tube  20 . Thus, occluding members  1910   a,b , located at the distal ends of the arms  1906   a,b , are held away from the tube  20  such that fluid may freely flow through the device  1900 . In a occluded state, as shown in  FIGS. 73 and 74 , the occluding members  1910   a,b  pinch and terminate flow within the tube  20  as potential energy from the spring  1908  is released and the sliding action of the movable housing  1904  forces the arms  1906   a,b  together. The device may be returned to an unoccluded state by forcing the housing sections  1902 ,  1904  together such that the trigger  1914  is reset. 
     As shown in  FIGS. 77-84 , another embodiment  2000  of a device for occluding a flexible tube generally comprises a first channel  2014  and a second channel  2016  slideably coupled and capable of linearly disengaging in response to a force on the tube  20 . As shown in  FIG. 77 , a first housing  2002  defines a first channel  2014  to accept one end of a flexible tube  20   a . The first channel  2014  directs fluid into a second channel  2016 , within a second housing  2004 , via a sealable interface  2012 . The sealable interface  2012  may be an elastic material, such as medical grade silicone, to prevent fluid from seeping though the device  2000  in sliding and disengaged positions. In the preferred embodiment, the sealable interface  2012  is embedded in the first housing  2002 , however, in other various embodiments, both housing sections may incorporate a sealable interface. Housing sections  2002 ,  2004  are slideably joined via two hooked portions  2006   a,b  protruding from the second housing  2004 . A spring  2010 , located between housing sections  2002 ,  2004  provides the force necessary to disengage the channels  2014 ,  2016  in response to a force applied to either end of the tube  20 . 
     In an unoccluded position, as shown in  FIGS. 77-80 , fluid may flow through the device  2000  as the channels  2014 ,  2016  are aligned. The compressed spring  2010  is designed using a cam-over-center methodology such that it applies a force on the housing sections  2002 ,  2004  which essentially holds the device  2000  together. In the event that either of the housing sections  2002 ,  2004  begin to slideably disengage, i.e., an axially applied force on the tube  20 , the curved nature of the spring  2010  allows it to rotate and decompress. As the spring  2010  decompresses the housing sections  2002 ,  2004  are urged farther apart, forcing the device  2000  into an occluded position. 
     In the occluded position, as shown in  FIGS. 81-84 , the spring  2010  remains partially decompressed such that a constant force acting on the housing sections  2002 ,  2004  holds the channels  2014 ,  2016  in misalignment. The channels  2014 ,  2016  are occluded as the sealable interface  2012  prevents fluid from leaking out of the device  2000 . Arms  2008  attached to the first housing  2002  may provide a means of returning the device  2000  to the unoccluded position, allowing the spring  2010  to be repositioned to an over-center compressed state. 
     In another aspect, the invention comprises an occluder assembly that surrounds a section of flexible tubing, and that derives its occluding force from a spring-loaded actuator, the spring acting longitudinally in line with the flexible tubing. A pre-determined threshold amount of tension (generated by a pulling force estimated to threaten the risk of dislodgement of an intravenous catheter) applied to the section of tubing causes a specified amount of stretching (if there is no slack) or movement (if there is slack) of the tubing, which in turn causes a releasing member to trigger the spring-loaded actuator. The actuator can then interact with an occluder to convert the longitudinal spring force into a transverse occluding force against the tubing, occluding or constricting its lumen. The assembly can include a releasing member, an occluder, an actuator, a spring and a spring housing. At least a part of the releasing member is attached to the tubing, so that stretching or movement of the tubing results in translational movement of the releasing member longitudinally along the section of tubing. Movement of the releasing member triggers release of the spring-loaded actuator. The releasing member can be in direct contact with the actuator or a spring retention element in order to trigger release of the actuator, or it can act indirectly through contact with the occluder, which in turn can be in contact with the actuator or a spring retention element. Once released, the actuator, under the force of the compressed spring, can travel longitudinally along the flexible tubing and press the occluder against the flexible tubing, occluding or constricting its lumen. 
     In an embodiment, the occluder can serve as an intermediary structure between the releasing member and the actuator. For example, when the assembly is in an armed state, the releasing member is engaged with the occluder to immobilize it. In addition, another portion of the occluder can hold the actuator in an armed position, the actuator being under the force a compressed spring within a spring housing. The releasing member can respond to a pre-determined threshold amount of pulling force on the tubing by moving longitudinally along with the affected segment of tubing and disengaging from the occluder, which in turn can release the actuator to press the occluder against the tubing under the force of the actuator spring. 
       FIG. 85  shows a partial cutaway view of an embodiment of the invention incorporating a longitudinally acting spring-loaded actuator. In the embodiment shown in  FIGS. 85-87 , the occluder assembly  3000  is positioned along a length of flexible tubing  20 . The tubing section can either be incorporated into an otherwise standard vascular catheter (e.g., a hemodialysis or central venous catheter), or can be connectable on both ends to any other flexible tubing via a coupling (e.g., such as a Luer lock coupling). In the illustrated embodiment, a Luer lock coupling  3050  is shown at one end of the assembly, capped by cap  3060 . An occluder  3002  is positioned so that an arm  3010  of occluder  3002  includes occluding element  3006 . A first section  3032  of releaser  3030  is attached to a first section  20   a  of flexible tubing  20 . A second section of releaser  3030  includes a contact element  3034  for contacting a corresponding contact element  3014  of occluder  3002 . In the illustrated embodiment, releaser contact element  3034  is frictionally wedged with occluder contact element  3014 , keeping arm  3010  of occluder  3002  slightly raised and relatively immobile, preventing deflection of occluder  3002  toward tubing  20 . 
     At least a portion of occluder  3002  is attached to a second section  20   b  of flexible tubing  20 . In the illustrated embodiment in  FIG. 85 , for example, a section  3022  of occluder  3002  is attached (e.g., by adhesive, ultrasonic welding, or other means) to the second section  20   b  of tubing  20 . An actuator assembly  3070  (see  FIG. 86 ) can be mounted over an elongate section  3026  of occluder  3002 . In the illustrated embodiment, actuator assembly  3070  includes actuator  3072 , spring housing  3074 , and spring  3076 . At least a portion of actuator assembly  3070  (such as, for example the spring housing  3074 ) can be permanently fixed to a second section  20   b  of tubing  20  or to section  3022  of occluder  3002 ; or it can be releasably mounted to section  3022  of occluder  3002  (allowing for potential re-use of actuator assembly  3070 ). In an armed position, actuator  3072  is slideably mounted on spring housing  3074 , compressing spring  3076  situated within spring housing  3074 . A stop  3018  formed on the outer side of occluder  3002  makes contact with a leading edge  3078  of actuator  3072 . 
     In the armed state, contact between releaser contact element  3034  and occluder contact element  3014  positions occluder arm  3010  away from tubing  20 , and positions occluder stop  3018  against leading edge  3078  of actuator  3072 . In this armed position, occluder stop  3018  prevents actuator  3072  from being released by compressed spring  3076 . 
     When sufficient pulling force is applied longitudinally to tubing  20 , either from the first end  20   a  or the second end  20   b , a longitudinal force tending to separate releaser  3030  from occluder  3002  is generated. Once a pre-determined threshold traction force is reached, the resistance to separation of releaser contact element  3034  from occluder contact element  3014  is overcome, and occluder arm  3010  is free to move inwardly toward tubing  20 . Upon movement of occluder arm  3010  occluder stop  3018  disengages from leading edge  3078  of actuator  3072 , releasing actuator  3072  to slide longitudinally along occluder arm  3010 , as shown in  FIG. 87 . Under the longitudinal force provided by spring  3076 , actuator  3072  slides along occluder arm  3010 , pressing occluder element  3006  against the side wall of tubing  20 , thereby occluding or constricting its lumen. 
     In the illustrated embodiment, the amount of traction force needed to cause release of actuator  3072  can be changed by altering the holding characteristics between releaser contact element  3034  and occluder contact element  3014 . The two contact elements  3034  and  3014  are wedge shaped, and their holding characteristics can be varied by changing the smoothness and composition of the mating surfaces, as well as the angle at which the surfaces wedge together. In addition, altering the lengths of engagement between the contact elements can also vary the holding characteristics, and thus the threshold amount of pulling force that must be applied to the tubing to trigger release of the device and occlusion of the tubing. More generally, contact elements whose interaction is designed to trigger a spring-loaded actuator can take many forms. Another non-limiting embodiment of contact elements can include, for example, a tooth and groove arrangement, in which the shape of the tooth element or the shape and depth of the groove element can be varied to alter the holding characteristics of the elements, and thus the force required to separate them. In other embodiments, it is also possible that the contact elements could be constructed to trigger an actuator by making contact with one another (rather than separating) upon the pulling of an attached flexible tubing segment. 
     Although the embodiment shown in  FIGS. 85-87  is equipped with two opposing occluder arms  3010  and  3012  and occluder elements  3006  and  3008 , a similar occluding mechanism can be applied to a single occluder arm or three or more occluder arms positioned around the circumference of tubing  20 . With any of these embodiments, the longitudinal force applied by the spring can be converted to an approximately transverse force acting on the flexible tubing by an actuator such as actuator  3072  interacting with an occluder such as occluder  3002 . In this example, the actuator is driven by the spring so that the inside surface of the actuator slides along the surface of one or a plurality of occluders, compressing them against the tubing. 
     The occluder assembly  3000  illustrated in  FIGS. 85-87  can be re-armed after the pulling force on tubing  20  has been relieved. Finger holds  3080  and  3082  can be grasped by two fingers with the thumb positioned behind the base  3084  of spring housing  3074 , and actuator  3072  can then be retracted back to its armed position, as shown in  FIG. 85 . With tubing  20  in a relaxed state, the releaser contact element  3034  can return to a wedged relationship with occluder contact element  3014 , allowing occluder stop  3018  to once again hold actuator  3072  in its armed position. 
     Should the elasticity of tubing  20  be insufficient to cause a suitable re-engagement of the releaser contact element with its opposing contact element, actuator  3072  can be designed to pull the releaser contact element into proper re-engagement, as the actuator itself is being pulled by the user into an armed position. An example of this is shown in  FIG. 86 , in which a section of releaser  3030  can include a jog feature  3036  that can be captured by the trailing edge  3088  of actuator slide guide  3086 , as it is retracted to an armed position. Retracting releaser  3030  a distance equal to gap  3090  provides the correct distance required to fully re-engage releaser contact element  3034  with occluder contact element  3014 . 
     In another embodiment, as shown in  FIGS. 88 and 89 , an embodiment  4000  of a device for occluding a flexible tube generally comprises a first body  4002  frictionally connected to a second body  4004  by a spring-loaded clip  4006 . A flexible tube  20  having a first end  20   a  and a second end  20   b  is secured to each body by a plurality of clamps  4010 . When the two bodies are separated by a predetermined threshold force F (not shown) acting axially on either the first end or second end of the tube  20  so as to cause the bent section of tubing  20  to straighten, the spring-load clip  4006  occludes the tube  20  secured by the second body. More specifically, the spring-loaded clip  4006  lockingly engages a cylindrical hub  4012  located on the first body  4002 . The clip  4006  generates enough compressive force to hold the bodies  4002  and  4004  together with a frictional force that is less than the predetermined force F acts on the flexible tube  20 . The clip  4006  slides off the hub  4012  and triggers the occlusion when the two bodies are pulled apart from each other by the predetermined force F. 
     In other embodiments, a visual or auditory alarm can be included in the occluder assembly. Actuator motion during release can serve to trigger an electrical switch of a battery-operated alarm attached to or included on the occluder assembly. For example, a Hall sensor or mechanical switch can be used to detect release of the actuator, which can then activate a piezo buzzer or light emitting diode (“LED”) light attached to the unit. The local alarm could be useful in extracorporeal blood flow systems such as hemodialysis or hemoperfusion systems, for example. The auditory or visual alarm could serve to alert the user of the tubing occlusion before a pressure sensor in a hemodialysis apparatus would trigger a shut-down of the hemodialysis pump. In the case of a pulling force that does not lead to dislodgement of the intravenous catheter, the user would thus have the opportunity to relieve tension on the flexible tubing and re-arm the occluder assembly before treatment (i.e. blood pumping) is automatically interrupted. An LED light can also be used to indicate to the user that the device is properly armed. 
     In yet other embodiments, the occluding assemblies described above, (such as, e.g., those utilizing a longitudinally acting spring force) can have two channels situated side-by-side to accommodate both an arterial and a venous line when these lines are used separately in an extracorporeal blood flow circuit. Each line can have a dedicated occluding member that can pinch each line against a common wall or septum separating the two lines in the device. Both occluding members can be pressed against their respective lines by the same actuator, as described above for occluding assemblies  100  and  3000 . Thus any potential dislodgement of an intravenous catheter associated with one of the lines will automatically trigger occlusion of both lines, helping to avoid the risk of air being drawn into the patient&#39;s circulation via the remaining intact intravenous catheter. 
     The invention described herein need not be limited to flexible tubing used for intravenous infusion. It can also be applied, for example to medical tubing used in non-IV applications, such as tubes leading to the peritoneal cavity, the stomach, the bladder, or any other hollow organ. In addition, the invention can also be applied in circumstances in which it is desirable to stop the flow of a fluid into any dependent container once the container accumulates a specified amount of fluid and reaches a threshold weight. Furthermore, the invention can be applied to circumstances—whether medical or non-medical—in which it is desirable to stop the flow of fluid in a flexible tube if excessive tension is applied to the tubing. It can also be appreciated that a flexible tube having tensile properties can contract upon release of a distracting force. Thus, the invention described herein can also be constructed to trigger from a non-occlusive to an occlusive state, or conversely from an occlusive to a non-occlusive state, if a flexible tube held under longitudinal tension is released and allowed to relax back into its pre-tension length. A change in length in either direction can be exploited to cause the occluding device to release.