Abstract:
A system and method of accurately pumping a fluid using tubing of variable inner diameter and material is disclosed. The disclosed pump comprises a pumping mechanism configured to compress and release a portion of a flexible tube to cause fluid to flow along the flexible tube, a gauging apparatus, and a vacuum apparatus. The gauging apparatus is configured to determine the inner diameter of the flexible tube, which value is used in calibrating the pumping rate of the pump. The vacuum apparatus is configured to reduce the ambient pressure in a volume surrounding the portion of the flexible tube, thereby causing the flexible tube to fully expand to its original outside diameter when the flexible tube is released by the pumping mechanism.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    The present disclosure generally relates to systems and methods of pumping intravenous (IV) fluids, and, in particular, relates to IV pumps adapted to use tubing having an unknown diameter and/or insufficient recovery of the uncompressed shape. 
         [0003]    2. Description of the Related Art 
         [0004]    Infusion pumps have become commonplace within the healthcare world as a way to precisely administer intravenous (IV) fluids. Use of a pump in place of a simple roller clamp with an elevated fluid container to control the flow of the IV fluid allows more accurate and consistent control of the rate of delivery of the fluid to a patient. 
         [0005]    The assembly of drip chamber, tubing, valves, fittings, and Luer fittings that connect the fluid container to the patient may be referred to as an “IV set.” IV sets designed for use with IV pumps may have a pumping segment or chamber incorporated into the set, wherein the pumping segment fits into a compartment in the IV pump, as shown in  FIG. 1 . In use, medical fluid passes from the IV fluid container  14  through the tubing of IV set  18  to a infusion needle inserted in the arm of patient  10 . The IV set  18  passes through a pumping module  20  of IV pump  12  that contains actuators (not shown) that act upon the pumping segment under the control of control unit  16  to force the medical fluid to flow to the patient  10  at a specified rate. 
         [0006]    One of the factors that affect the accuracy of the pumping rate of a peristaltic IV pump is the inside diameter of the tubing of the IV set. A second factor is the material of the tubing, wherein the tubing must fully recover its uncompressed shape between compressions so that the tube refills to the maximum volume. Precision IV sets having tubing made from a highly resilient material and with precise control of the inside diameter may be both expensive and, in some areas, difficult to obtain. There is, therefore, a desire for IV pumps to be able to use “generic” tubing, i.e. tubing that does not have precision control of the inner and/or outer diameter or may be made of a material that takes a compression “set” and does not fully return to the uncompressed shape. 
       SUMMARY 
       [0007]    In order to provide an accurate rate of delivery of fluid using a peristaltic pump while using generic tubing, it is advantageous to provide a system that automatically measures the tubing as well as fully expanding the tubing between compression strokes. The system and method disclosed herein provide at least some of these advantages. 
         [0008]    A pump is disclosed that comprises a pumping mechanism configured to compress and release a portion of a flexible tube to cause fluid to flow along the flexible tube, a gauging apparatus, and a vacuum apparatus. The gauging apparatus is configured to determine the inner diameter of the flexible tube, thereby calibrating the pumping rate of the pump. The vacuum apparatus is configured to reduce the ambient pressure in a volume surrounding the portion of the flexible tube, thereby causing the flexible tube to fully expand when released by the pumping mechanism. 
         [0009]    A pump is disclosed that comprises a pumping mechanism configured to compress and release a portion of a flexible tube to cause fluid to flow along the flexible tube, and a vacuum apparatus that is configured to reduce the ambient pressure in a volume surrounding the portion of the flexible tube, thereby causing the flexible tube to fully expand when released by the pumping mechanism. 
         [0010]    A pump is disclosed that comprises a pumping mechanism configured to compress and release a portion of a flexible tube to cause fluid to flow along the flexible tube, and a gauging apparatus configured to determine an inner diameter of the flexible tube, thereby calibrating the pumping rate of the pump. 
         [0011]    A method of accurately pumping fluid using a flexible tube of unknown inner diameter is disclosed, wherein the method comprises the step of placing a flexible tube in a pump such that a portion of the flexible tube is coupled to a pumping mechanism, wherein the pumping mechanism is configured to manipulate the portion of the flexible tube to cause fluid to flow along the flexible tube. The pump automatically measures an outside diameter of the flexible tube, and then compresses the flexible tube until an inner wall of the internal channel makes contact with the inner wall on an opposite side of the internal channel and measures a residual thickness of the compressed flexible tube. From these measurements, the pump calculates the inner diameter of the flexible tube by subtracting the residual thickness from the outer diameter and automatically adjusting the operating parameters of the pumping mechanism to pump fluid at a specific rate. 
         [0012]    A method of accurately pumping fluid using a flexible tube of unknown inner diameter is disclosed, wherein the method comprises the step of placing a flexible tube in a pump such that a portion of the flexible tube is coupled to a pumping mechanism, wherein the pumping mechanism is configured to manipulate the portion of the flexible tube to cause fluid to flow along the flexible tube. The pump then forms a sealed vacuum enclosure around the pumping mechanism and the portion of the flexible tubing and reduces the pressure within the vacuum enclosure. The pump then activates the pumping mechanism to manipulate the portion of the flexible tube. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The accompanying drawings, which are included to provide further understanding and are incorporated in and constitute a part of this specification, illustrate disclosed embodiments and together with the description serve to explain the principles of the disclosed embodiments. In the drawings: 
           [0014]      FIG. 1  depicts a patient receiving medical fluid through an IV set using an IV pump. 
           [0015]      FIG. 2  depicts the construction of an IV set according to the prior art. 
           [0016]      FIG. 3A  depicts the construction of a peristaltic pumping mechanism according to the prior art. 
           [0017]      FIG. 3B  depicts the operation of the peristaltic pumping mechanism of  FIG. 3A . 
           [0018]      FIG. 4  depicts a vacuum apparatus that provides a vacuum around the pumping mechanism constructed according to certain aspects of the present disclosure. 
           [0019]      FIG. 5  depicts a portion of a flexible tube that is used with the disclosed IV pump according to certain aspects of the present disclosure. 
           [0020]      FIGS. 6A-6B  illustrate the function of a vacuum in expanding a flexible tube according to certain aspects of the present disclosure. 
           [0021]      FIGS. 7A-7B  depict close-up cross-sections of pressure sensors according to certain aspects of the present disclosure. 
           [0022]      FIG. 8  depicts the vacuum enclosure of  FIG. 4  in the closed position according to certain aspects of the present disclosure. 
           [0023]      FIG. 9  depicts an exemplary split seal according to certain aspects of the present disclosure. 
           [0024]      FIG. 10A  illustrates details of construction of the split seal of  FIG. 1  according to certain aspects of the present disclosure. 
           [0025]      FIG. 10B  illustrates details of operation of the split seal of  FIG. 1  according to certain aspects of the present disclosure. 
           [0026]      FIGS. 11A-11B  depict an exemplary gauging apparatus according to certain aspects of the present disclosure. 
           [0027]      FIG. 11C  depicts another embodiment of a gauging apparatus according to certain aspects of the present disclosure. 
           [0028]      FIG. 12  depicts another embodiment of a gauging apparatus according to certain aspects of the present disclosure. 
           [0029]      FIG. 13  depicts another embodiment of a gauging device according to certain aspects of the present disclosure. 
           [0030]      FIG. 14  is a block diagram of an exemplary IV pump with a vacuum apparatus and a gauging apparatus according to certain aspects of the present disclosure. 
           [0031]      FIG. 15  is a flow chart illustrating an exemplary method of pumping a fluid according to certain aspects of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    The disclosed methods and system provide a pumping system that is able to accurately pump fluid using a flexible tube that may have unknown inner and/or outer diameters or may be made of a material that does not have the resilience to fully recover its uncompressed shape between compressions or may take a compression set after some period of use. 
         [0033]    In the following detailed description, numerous specific details are set forth to provide a full understanding of the present disclosure. It will be apparent, however, to one ordinarily skilled in the art that embodiments of the present disclosure may be practiced without some of the specific details. In other instances, well-known structures and techniques have not been shown in detail so as not to obscure the disclosure. 
         [0034]    The methods and systems disclosed herein are presented in terms of administration of a medical fluid as an infusion by a nurse in a healthcare environment. It will be apparent to one of ordinary skill in the art that the same methods and systems, however, may be used in other areas of fluid handling and pumping. Nothing in this disclosure should be interpreted, unless specifically stated as such, to limit the application of any method or system disclosed herein to a healthcare environment. 
         [0035]      FIG. 1  depicts a patient  10  receiving medical fluid through an IV set  18  using an IV pump  12 . The fluid is provided, in this example, in a flexible container  14  that is commonly hung above the pump  12  to provide a positive pressure at the pump inlet. The IV pump  12  shown herein has a control unit  16  and an attached pumping module  20 . The IV set  18  connects the fluid container  14  to the patient  10 , and passes through the pumping module  20 . The flow rate of the medical fluid is volumetrically controlled by the positive displacement pumping action of pumping module  20  under the control of control unit  16 . 
         [0036]      FIG. 2  depicts the construction of a IV set  18  according to the prior art. This IV set  18  is set up for use with a peristaltic pump and the pumping segment that fits into the peristaltic pump is the length of tubing and fitting indicated by bracket  8 . A special material such as silicone rubber or a highly plasticized polyvinyl chloride (PVC) is commonly used to form this segment. These materials are used to provide high dimensional stability and resilience to restore to their undeformed shape when not contacted by the positive displacement mechanism and thus ensure accuracy from set to set and over the duration of use of a single set. A length of flexible tube  4  is attached to each end of the pumping segment  8 . A container spike  2  is attached to the other end of one length of flexible tube  4 , wherein a container spike  2  is a standard IV fitting configured to attach to a IV container  14  and puncture a seal that is part of the connection fitting on the IV container  14 . An alternate connection is a needleless Luer fitting or other type of fluid connector adapted for connection to a fluid source. At the other end of the other length of flexible tube  4 , in this example, is a needleless Luer connector  6  that is suitable for connection to an infusion needle, such as shown in  FIG. 1 . In certain embodiments, other types of connectors and devices are attached in place of Luer connector  6 . Also shown is a clamp  9  that, when closed completely, blocks flow through the flexible tube  4  to which the clamp  9  is attached. This is frequently used to prevent flow and spillage while setting up or removing a IV set  18  from a pump. In certain embodiments, other types of fitting and connectors are added to create a multitude of other configurations of IV sets, depending on the application and type of treatment. 
         [0037]      FIG. 3A  depicts the construction of a peristaltic pumping mechanism  22  according to the prior art. A series of cams  23  are arranged along a shaft  27  such that the orientation of the cams are incrementally displaced between adjacent cams. Each cam  23  has an associated cam follower  24  that moves “up” and “down”, in the orientation of  FIG. 3A , as the cam  23  rotates. A portion of a flexible tube  4  is placed over platen  25  and under the cam followers  24 . The spacing of the cam followers  24  and the platen  25  is selected such that the cam follower  24  fully compresses the flexible tube  4  when the cam follower  24  is in the fully extended or “down” position. 
         [0038]      FIG. 3B  schematically depicts the operation of the peristaltic pumping mechanism  22  of  FIG. 3A . As the shaft  27  of  FIG. 3A  rotates, each cam follower  24  moves up and down, in the orientation of  FIG. 3B , as controlled by the associated cam  23 . It can be seen in  FIG. 3B  that a volume  26  is formed within the internal channel  5  of tube  4  by the two cam followers  24  that are fully extended, or “down”, thereby pinching the tube  4  together. The incrementally offset orientations of cams  23  causes a wave-like motion to ripple through the cam followers  24 , which causes the volume  26  to move along the length of flexible tube  4 . As each of the cam followers  24  retracts into the “up” position, the flexible tube  4  recovers and expands. The materials of typical precision IV sets are commonly selected to have a high resilience such that the tube  4  fully and repeatably expands to the maximum cross-section during this recovery, ensuring accurate volumes  26  as they are formed and carried along the pumping mechanism  22 . If a flexible tube  4  does not fully recover its undeformed shape, the volume  26  is reduced and the pumping accuracy is also reduced. As materials that have the necessary level of resilience to fully recover between compressions tend to be more expensive than other materials, IV sets made from this resilient material will tend to be higher in cost than they would be if made from non-resilient materials. Chemical plasticizers are added to some tubing materials to increase their resilience, however there is a recognized clinical concern around the potential for some of these chemicals to reach the patient. 
         [0039]      FIG. 4  depicts a vacuum apparatus  30  that provides a vacuum around the pumping mechanism  22  constructed according to certain aspects of this disclosure. The IV pump  12  includes a pumping mechanism  22  that is configured to manipulate a portion of flexible tube  4  to cause fluid to flow along the flexible tube  4 . In the example of  FIG. 4 , the portion of flexible tube  4  is a straight segment across a multi-element pumping mechanism  22 . In other embodiments using other types of peristaltic pumping mechanisms  32 , such as a roller on a rotating arm, the portion of flexible tube  4  may be circular or follow another non-straight path. 
         [0040]    The vacuum apparatus  30  comprises a fixed panel  40  and a movable panel  42  that are, in this example, hingedly connected (not shown connected in  FIG. 4 ) and have perimeter seals  36 A and  36 B configured to seal to each other when the movable panel  42  is moved into contact with the fixed panel  40 . There are two split seals  34  located at positions along the perimeter seals  36 A,  36 B, wherein each split seal  34  has a split seal segment  34 A that is coupled to the fixed panel  40  and a split seal segment  34 B that is coupled to the movable panel  42 . The split seal segments  34 A and  34 B are in contact with each other when the movable panel  42  is in contact with fixed panel  40  and form a seal around flexible tube  4 . The combination of the perimeter seals  36 A,  36 B and the split seals  34  provide an airtight seal between the fixed panel  40  and a movable panel  42  such that a vacuum can be created within the vacuum enclosure  38 . The split seal  34  is discussed in more detail with respect to FIGS.  8  and  9 A- 9 B. The split seal may be formed as a contiguous portion of a membrane covering the pumping fingers and thus assuring no leakage of air via the pumping finger mechanism. The IV pump  12  also includes, in this example, two pressure sensors  40 A and  40 B upstream and downstream of the pumping mechanism  22  that are used to detect problems such as occlusions in the flexible tube  4  and depletion of the source of the fluid. 
         [0041]      FIG. 5  depicts a portion of a flexible tube  4  that is used with the disclosed IV pump  12  according to certain aspects of this disclosure. Flexible tube  4  is, in this example, circular in cross-section with an outside diameter  50  and has an internal channel  5  with an internal wall  46 , wherein the internal channel  5  has an inner diameter  48 . 
         [0042]      FIGS. 6A-6B  illustrate the function of a vacuum in expanding a flexible tube  4  according to certain aspects of this disclosure. The internal channel  5  of the flexible tube  4  has a pressure that, for the purpose of this example, is considered to be ambient pressure. In some embodiments, this pressure may be lower if the fluid source  14  is below the pump  12 , thereby creating a negative pressure head within the tubing at the elevation of the IV pump  12 . In current IV pumps, this would result in some collapse of the tubing  4 . In the vacuum enclosure  38  that surrounds the flexible tube  4 , a reduced pressure has been created, wherein the reduced pressure is below the pressure inside internal channel  5 . In  FIG. 5A , the flexible tube  4  is partially compressed and the internal channel  5  has a cross-section area  52 . The difference between the pressure within the internal channel  5  and the reduced pressure outside of the flexible tube  4  create a uniform force on the internal wall  46  that tends to force the flexible tube  4  to expand to maximize the area of the cross-section of the internal channel, as shown in  FIG. 5B , wherein internal channel  5  has a cross-section area  54  that is larger than area  52  of the partially flattened flexible tube  4  of  FIG. 5A . Cross-section area  54  is maximized when the flexible tube  4  assumes a circular profile, which is considered to be the natural circular geometric configuration of flexible tube  4 . 
         [0043]      FIGS. 7A-7B  depict close-up cross-sections of pressure sensors  40 A,  40 B according to certain aspects of the present disclosure. The pressure sensors  40 A,  40 B are really ‘force sensors’ which measure the sum of tube wall force and fluid force. The design of the force sensors may take further advantage of the presence of the vacuum. Conventionally there must be sufficient wall force present to maintain the wall of the tube  4  in contact with the sensors  40 A,  40 B. This is needed when the sensor  40 A,  40 B must detect negative pressures as when the pump  12  is higher than the patient  10  or in the intake pathway to detect an occlusion between the container  14  and the pump  12 . With the vacuum design, there need not be ANY wall force present and yet the tube will still attempt to expand and thus can be trapped between the sensor  30 A,  40 B and the opposite wall  25  as shown in  FIGS. 7A and 7B .  FIG. 7A  shows a sensor  40 A that senses the deflection of a flexible element  43 A to measure the force.  FIG. 7B  uses a moving element  43 B mounted on a spring  43 C and measures the displacement of the moving element  43 B, which correlates with the force. By reducing the need for wall force, a preferred tube  4  design may be chosen with either a thin wall or a highly elastic wall, similar to a fire hose. With this tube  4 , the accuracy of the sensors  40 A,  40 B is increased due to less uncertainty in the magnitude of the wall force which typically changes over time as tubes  4  visco-elastically deform. Note also that the sensors  40 A,  40 B must measure the gauge vacuum pressure, i.e. below ambient atmosphere, in order to accurately convert the sensed force to a pressure. 
         [0044]      FIG. 8  depicts the vacuum apparatus  30  of  FIG. 4  in the closed position according to certain aspects of this disclosure. Movable panel  42  has been rotated from its open position as shown in  FIG. 4  to be in contact with fixed panel  40 . Vacuum enclosure  38  has been formed around pumping mechanism  22  by cooperation of perimeter seals  36 A,  36 B and split seals  34 A,  34 B surrounding the flexible tube  4  at the points where flexible tube  4  crosses the perimeter seal  36 A,  36 B. 
         [0045]    In the cutaway depiction of movable panel  42 , an exemplary vacuum mechanism  60  can be seen. Vacuum mechanism  60  reduces the air pressure within the vacuum enclosure  38 , in this example, by deforming a flexible panel formed within the fixed panel  40 , wherein the deformation expands the volume of the vacuum enclosure  38 . This expansion is indicated by the arrows  60 A. As the amount of air within the vacuum enclosure  38  is fixed, expansion of the volume of the vacuum enclosure  38  causes a reduction in the air pressure within the vacuum enclosure  38 . In certain embodiments, the deformable panel of vacuum mechanism  60  is actuated mechanically as the movable panel  42  is rotated against fixed panel  40 . In certain embodiments, the deformable panel of vacuum mechanism  60  is actuated by a manual lever (not shown). In certain embodiments, the deformable panel of vacuum mechanism  60  is actuated by a solenoid or motor (not shown). In other embodiments, the pressure of the air within the vacuum enclosure  38  is reduced by withdrawing air from the vacuum enclosure  38  using an air pump (not shown). In certain embodiments, a check valve (not shown) is positioned such that air can be drawn through the check valve by a cyclic pumping mechanism (not shown). 
         [0046]      FIG. 9  depicts an exemplary split seal  34  according to certain aspects of this disclosure. The split seal, in this example, is formed from 3 partial o-rings  62 A,  62 B, and  62 C. Partial o-rings  62 A and  62 C are a part of a split seal segment such as the split seal segment  34 A of  FIG. 4 , while partial o-ring  62 B is a part of a matching split seal segment similar to split seal segment  34 B. In the embodiment of  FIG. 8 , partial o-ring  62 A is positioned between partial o-rings  62 A and  62 C and in contact with both partial o-rings  62 A and  62 C in lateral areas  64 , forming a bore  68  through the complete split seal  34 . Bore  68  has an inner diameter  70  that is, in this example, slightly smaller than the outer diameter  50  of flexible tube  4 . In certain embodiments, the seals are sufficiently adaptable to accommodate a range of tubing diameters, for example 0.12-0.17 inches outer diameter (OD). The partial o-rings  62 A- 62 C are formed, in this example, from a soft elastomer that deforms around the flexible tube  4  to form a continuous seal around the outside of flexible tube  4 . In certain embodiments, the partial o-rings  62  are configured such that pairs of opposing partial o-rings  62 , e.g. partial o-rings  62 A and  62 B, are aligned and sized such that they contact each other on cut surfaces  66 . In certain other embodiments, the partial o-rings  62  have a rectangular cross-section that provides a larger contact area to each other and to flexible tube  4  compared to a circular cross-section. In certain other embodiments, the split seal segments  34 A and  34 B comprise more or fewer partial o-rings than shown in  FIG. 9 . In certain other embodiments, an additional fitting (not shown) is placed around the flexible tube, conceptually similar to the ferrules used to seal rigid metal tubing to plumbing fittings, at the time of placement of the flexible tube  4  in IV pump  12  to provide improved sealing. 
         [0047]      FIG. 10A  illustrates details of construction of the split seal  34  of  FIG. 1  according to certain aspects of this disclosure. Split seal segment  34 A, in this embodiment, comprises two partial o-rings  62  and split seal segment  34 B comprises three partial o-rings  64 . The partial o-rings  62  are configured such that they interlock when split seal segments  34 A and  34 B are brought together. 
         [0048]      FIG. 10B  illustrates details of operation of the split seal  34  of  FIG. 1  according to certain aspects of this disclosure. Split seal segments  34 A and  34 B have been brought together around a flexible tube  4 . It can be seen that there is a continuous seal is formed around the flexible tube  4  by the partial o-rings  62 . 
         [0049]      FIGS. 11A-11B  depict an exemplary gauging apparatus  80  according to certain aspects of this disclosure. Flexible tube  4  is, in this example, positioned against the fixed panel  40 . The gauging apparatus  80  comprises a tip  82  mounted on a shaft  88 , wherein the shaft  88  includes a force sensor  84 . The tip  82  is moved forward, i.e. toward the flexible tube  4 , by the action of actuator  86 . In certain embodiments, shaft  88  is threaded and constrained from rotating, and actuator  86  comprises a rotating nut (not shown) that causes the shaft  88  to move axially as the rotating nut turns. In  FIG. 11A , the tip  82  is moved forward until the tip  82  contacts the flexible tube  4 . The distance between the tip  82  and the fixed panel  40  is the outer diameter  50  of flexible tube  4 . This measurement of the gauging apparatus  80  can be calibrated by touching tip  82  directly to the fixed panel  40  when the flexible tube  4  is not present. In certain embodiments, tip  82  comprises a detector (not shown) that senses contact between the tip  82  and flexible tube  4 . In certain embodiments, this measurement is taken only after the pressure around flexible tube  4  has been reduced to fully expand the flexible tube  4 . 
         [0050]    The vacuum created around the tube  4  by the vacuum apparatus  30  of  FIG. 4  works cooperatively with the gauging apparatus  80  of  FIG. 11A . The vacuum encourages the tube  4  to assume a circular profile, as the internal pressure within tube  4  seeks to reach the most expanded configuration. This enhances the reliability of a single diameter measurement to be representative of the true fully expanded diameter of tube  4 . 
         [0051]    In  FIG. 11B , the gauging apparatus  80  is configured to measure the wall thickness of the flexible tube  4 . The tip  82  has been moved forward until the flexible tube  4  is collapsed and the distance  90  between tip  82  and fixed panel  40  is twice the thickness of the wall of flexible tube  4 . In certain embodiments, the distance  90  at which the internal surfaces  46  of flexible tube  4  touch can be sensed by the force sensor  84  as the force will begin to increase as a much higher rate after the walls come into contact. The inner diameter  48  can therefore be calculated by subtracting the measurement  90  from the measured OD  50  as shown: 
         [0000]      ID=OD−(2×wall)  (1)
 
         [0052]      FIG. 11C  depicts another embodiment of a gauging apparatus  81  according to certain aspects of the present disclosure. In this embodiment, the tip  82  is attached to a force sensor (not visible in  FIG. 11C ) inside one of the cam followers  24 A. The cam follower can be moved in the same manner as the actuator  86  of  FIG. 11A , moving the cam follower  24 A forward until the tip  82 A touches the tube  4 . 
         [0053]      FIG. 12  depicts another embodiment of a gauging apparatus  92  according to certain aspects of this disclosure. This embodiment employs two gauges  80  to measure the outside diameter  50  in two perpendicular directions to compensate for any out-of-round condition of flexible tube  4 . When the tips of both probes are both advanced until the tips touch the flexible tube  4 , similar to the situation shown in  FIG. 11A , then the two measurements will compensate for the flexible tube  4  not being truly round as is assumed in the measurement configuration of  FIG. 11A . The system of  FIG. 11  is more accurate but more complex than the system of  FIG. 11A . 
         [0054]      FIG. 13  depicts another embodiment of a gauging device  92  according to certain aspects of this disclosure. In this embodiment, an array of light-emitting devices  94  is positioned on one side of flexible tube  4  while an array of light-detecting devices  98  is positioned on the opposite side of flexible tube  4  and parallel to the light-emitting array  94 . In this embodiment, a single light emitting device  94 A is activated and projects a beam  96 . Some of the light-detecting devices  98  will detect the beam  96  while flexible tube  4  blocks the beam from reaching others of the light-detecting devices  98 . Other light emitting devices  94  will be individually activated until the beam  96  reaches light-detecting devices  98  on both sides of flexible tube  4 , whereupon the diameter of flexible tube  4  is calculated using knowledge of the geometry of the gauging device  92  and the positions of the light-emitting device and the light-detecting devices that are receiving the beam  96 . 
         [0055]      FIG. 14  is a block diagram of an exemplary IV pump  12  with a vacuum apparatus  30  and a gauging apparatus  80  according to certain aspects of this disclosure. An IV set  18  is coupled between a source of medical fluid  14  and a patient  10  with a portion of the flexible tube  4  of IV set  18  passing through pumping mechanism  22 . Vacuum enclosure  38  encompasses pumping mechanism  22 . A vacuum source  120  is connected to the vacuum enclosure  38 . In this example, a gauging apparatus  80  is contained within the vacuum enclosure  38  and coupled to the flexible tube  4  such that the gauging apparatus  80  measures, in this example, the OD  50  and compressed thickness  90  of the flexible tube  4 . In certain embodiments, the gauging apparatus  80  is outside the vacuum enclosure  38 . The vacuum apparatus  30  also includes pressure sensors  40 A,  40 B and an air-in-line sensor  41  that are located within the vacuum enclosure  38 . The IV pump  12  comprises a processor  105  that is coupled to a memory  110  and to the gauging apparatus  80  through a network  115 , wherein the processor  105  retrieves executable instructions that are stored in the memory  110 , receives signals from the gauging apparatus  80 , and calculates the ID of the flexible tube  4 . In certain other embodiments, the processor  105 , memory  110 , and gauging apparatus  80  are interconnected by any of a variety of methods known to those of ordinary skill in the art, such as a RS-232 serial communication link and a direct parallel bus link. 
         [0056]      FIG. 15  is a flow chart illustrating an exemplary method of pumping a fluid according to certain aspects of this disclosure. Starting in step  105 , the user connects a flexible tube  4  to a source of fluid  14  and places a portion of the flexible tube  4  within a pump  12  that comprises a pumping mechanism  22  that is configured to manipulate the portion of the flexible tube  4  to pump the fluid. In step  110 , the user closes the vacuum enclosure  38  of the pump  12  around the pumping mechanism  22  and reduces the air pressure within the vacuum enclosure  38 . The pump  12  also comprises a gauging apparatus  80  that measures, in this example, the OD  50  and the compressed thickness  90  of the flexible tube  4  in step  115  and, in step  120 , a processor  105  that coupled to the gauging apparatus  80  takes the signals from the gauging apparatus and calculates the ID  48  of the flexible tube  4 . The processor  105  then configures the pump  12  in step  125  to accurately pump fluid with this particular flexible tube  4  having an ID  48 . The user starts the pump in step  130  and continues to operate the pump in step  135 . This continues until the pumping is complete, whereupon the decision block  140  branches along the “YES” path to the end. If the pumping is not complete, the decision block  140  branches along the “NO” path back to step  135  and continues to pump fluid. 
         [0057]    In summary, systems and methods of accurately pumping fluids using peristaltic pumps and flexible tubes of unknown inner diameter and material are disclosed. By creating an enclosure having a reduced air pressure around the flexible tube, the tube is urged to fully expand between compression cycles of the peristaltic pumping mechanism by the pressure differential between the fluid inside the flexible tube and reduced pressure outside the flexible tube. By automatically gauging the outside diameter and the wall thickness of the flexible tube, the inside diameter of the tube can be calculated, enabling the pump to be calibrated to accurately pump with the particular tubing in use. Together, these systems and methods enable IV pumps that comprise theses system and methods to accurately deliver IV fluids using “generic” tubing, i.e. tubing where the ID is not precisely controlled to a specific value and the tubing material may not be sufficiently resilient to return to the fully expanded shape on its own. 
         [0058]    These same methods and systems may be applied to other types of pumps and devices besides peristaltic pumps applying compression to lengths of the tubing that have been used as examples herein. For example, an IV pump that manipulates a hemispherical pumping chamber formed in a cassette that is part of an IV set may employ the vacuum apparatus to fully expand the pumping chamber or employ the gauging apparatus to measure the actual height of the pumping chamber. Similarly, other types of devices such as a flow meter may be improved by utilization of the gauging apparatus as knowledge of the precise inner diameter of the tubing through which the fluid is flowing. 
         [0059]    The previous description is provided to enable a person of ordinary skill in the art to practice the various aspects described herein. While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the terms “a set” and “some” refer to one or more. Pronouns in the masculine (e.g., his) include the feminine and neuter gender (e.g., her and its) and vice versa. Headings and subheadings, if any, are used for convenience only and do not limit the invention. 
         [0060]    It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Some of the steps may be performed simultaneously. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented. 
         [0061]    Terms such as “top,” “bottom,” “front,” “rear” and the like as used in this disclosure should be understood as referring to an arbitrary frame of reference, rather than to the ordinary gravitational frame of reference. Thus, a top surface, a bottom surface, a front surface, and a rear surface may extend upwardly, downwardly, diagonally, or horizontally in a gravitational frame of reference. 
         [0062]    A phrase such as an “aspect” does not imply that such aspect is essential to the subject technology or that such aspect applies to all configurations of the subject technology. A disclosure relating to an aspect may apply to all configurations, or one or more configurations. A phrase such as an aspect may refer to one or more aspects and vice versa. A phrase such as an “embodiment” does not imply that such embodiment is essential to the subject technology or that such embodiment applies to all configurations of the subject technology. A disclosure relating to an embodiment may apply to all embodiments, or one or more embodiments. A phrase such an embodiment may refer to one or more embodiments and vice versa. 
         [0063]    The word “exemplary” is used herein to mean “serving as an example or illustration.” Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. 
         [0064]    All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.” Furthermore, to the extent that the term “include,” “have,” or the like is used in the description or the claims, such term is intended to be inclusive in a manner similar to the term “comprise” as “comprise” is interpreted when employed as a transitional word in a claim.