Abstract:
In one aspect, an extended range fluid flow resistor includes a housing having an inlet and an outlet and defining a fluid passageway therebetween A plunger is slidably received within the fluid passageway and an actuator is rotatably coupled to the housing and the plunger, such that rotation of the actuator causes sliding movement of the plunger within the fluid passageway The plunger has a sealing region and a variable flow region axially adjacent the sealing region Fluid flow through the fluid passageway is prevented when the sealing region is aligned with the inlet and fluid flow through the fluid passageway is permitted when the variable flow region is aligned with the inlet The variable flow region includes a helical groove extending from a first end of the variable flow region adjacent the sealing region and away from the sealing region to a second end of the vanable flow region.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority benefit under 35 U.S.C. §119(e) of U.S. provisional patent application No. 61/138,690 filed Dec. 18, 2008. The aforementioned application is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to flow control systems and, more particularly, to a flow resistor assembly for a fluid flow control system, such as a flow control system for an intravenous (IV) infusion pump. While the flow resistor assembly herein may be adapted for use with all manner of flow control systems, it may advantageously be used in connection with feedback control infusion pumps, such as those disclosed in International Application No. PCT/US2007/002039 filed Jan. 23, 2007, International Application No. PCT/US2007/004945 filed Feb. 27, 2007, and International Application No. PCT/US2007/005095 filed Feb. 27, 2007, which are commonly owned herewith. Each of the aforementioned patent applications is incorporated herein by reference in its entirety. 
         [0003]    Conventional flow resistors do not offer a stable and adjustable resistance over the required flow rate range for IV therapy. Conventional resistors, such as needle valves, generally use mechanical, face-to-face collisions as the means to shut off the infusion pump and, as a result, have difficulty controlling low flow rates. 
         [0004]    An ideal embodiment of a flow resistor would be one with continuous flow, wide flow rate range, wide range of viscosity compatibility, wide range of density compatibility, wide range of biocompatibility, suitability for long term use, low cost, simplicity, intuitive operation, automated information exchange, safety, and reliability. 
         [0005]    The present disclosure contemplates a new and improved fluid flow resistor that operates over a wide range of fluid flow rates for fluids of varying viscosities and densities. 
       SUMMARY 
       [0006]    In one aspect, the present disclosure provides an extended range fluid flow resistor for a fluid flow control system comprising an outer housing, an adjustment cap and a movable plunger. The outer housing comprises an interior passageway with an axially extending channel and a fluid inlet and outlet. The movable plunger comprises a screw interface region, a variable spiral region, a sealing region, and an interior fluid pathway. The adjustment cap comprises a body, a screw interface region, a distal seal and one or more interior protrusions. The adjustment cap is rotatably coupled to the outer housing enabling the cap to be rotated about the housing. The movable plunger is moveably secured within the interior passageway of the outer housing and includes a screw interface, which interacts with the screw interface of the adjustment cap. As the adjustment cap is rotated, the movable plunger translates linearly through the interior passageway of the outer housing. As the movable plunger translates through the interior passageway, a portion of a variable spiral flow path, located in the variable spiral region, interacts with the fluid inlet and enables fluid to travel through the fluid flow resistor and out the fluid outlet at the desired fluid flow rate. The spiral flow path contains a channel with a variable width and/or depth over its path creating a wide range of fluid flow rates. In exemplary, non-limiting embodiments, the fluid flow resistor can provide flow rates from 0.1 mL/hr to 6,000 mL/hr. 
         [0007]    In another aspect, a method for controlling the fluid flow rate using an extended range fluid flow resistor is provided. Infusion data is input, e.g., via an electronic control board, and instructions based on the input data are output to control a resistor adjustment motor. The position of an inline flow object is monitored as IV fluid travels from the fluid inlet through the flow resistor and out via the fluid outlet. The position of the inline flow object varies as a function of the flow rate and the position of the flow object may be monitored optically, e.g., using an LED array or other light source and an optical detector. By monitoring the position of the inline flow object, the extended range flow resistor is adjusted with the adjustment motor until a target flow rate is achieved. 
         [0008]    In yet another aspect, a flow control system employing the extended range flow resistor herein is provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention. 
           [0010]      FIG. 1  is a top view of an exemplary extended range fluid flow resistor. 
           [0011]      FIG. 2  is a side view of the exemplary extended range fluid flow resistor appearing in  FIG. 1 . 
           [0012]      FIG. 3  is a cross-sectional view taken along the lines  3 - 3  appearing in  FIG. 2 . 
           [0013]      FIG. 4  is a side view of an exemplary spiral fluid flow resistor assembly. 
           [0014]      FIG. 5  is an isometric view illustrating an exemplary adjustment cap. 
           [0015]      FIG. 6  is a functional block diagram of a flow resistor assembly and control circuit operable to embody an exemplary embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    Referring to the drawings, wherein like reference numerals are used to indicate like or analogous components throughout the several views, and with particular reference to  FIGS. 1-3 , there appears an extended range fluid flow resistor  10  in accordance with an exemplary embodiment of the present disclosure. The fluid flow resistor assembly  10  includes a fixed outer housing  20 , an adjustment cap  40 , and a movable plunger  60 . 
         [0017]    The fixed outer housing  20  contains a fluid inlet  22  and a fluid outlet  24 . The fluid inlet  22  is fluidically coupled to a fluid source (not shown), e.g., an IV fluid source coupled to the inlet  22  via a fluid inlet tube. The fluid outlet  24  may be fluidically coupled to the vasculature of a patient, e.g., via an IV catheter or cannula (not shown), as generally known in the art. The outer housing  20  is coupled at a rotational interface to the adjustment cap  40  to enable the adjustment cap  40  to rotate about the fixed outer housing  20 . The outer housing  20  also contains an interior passageway  26  slidably receiving the movable plunger  60 . 
         [0018]    Referring now to  FIG. 4  and with continued reference to  FIGS. 1-3 , the movable plunger  60  of the flow resistor assembly  10  is located within the passageway  26  of the outer housing  20 . The movable plunger  60  includes a screw interface region  62  having a helical groove  66 , a variable spiral region  70 , a sealing region  80  including a proximal seal  82  and a distal seal  84  defining a fluid containing section therebetween, and an interior fluid pathway  64 . The adjustment cap  40  includes a body  42 , an internal helical protrusion  44 , and a distal seal  46 . One or more protrusions  48  extend inwardly from the body  42  to connect the cap  40  to the housing  20 . 
         [0019]    The movable plunger  60  rotatably engages the adjustment cap  40  at the screw interface region  62 . The screw interface region  62  consists of the external helical thread  66  on the plunger  60  and the complimentary internal helical thread  44  in the adjustment cap  40 . In the depicted embodiment, the external thread  66  is a groove and the internal thread  44  is a complimentary protrusion. In alternative embodiments, the external thread  66  could be a helical protrusion and the internal thread  44  could be a helical groove. The internal helical thread  44  is configured to allow fluid to flow there past, as described below. 
         [0020]    In the illustrated embodiment, the internal helical thread  44  rotatably engages the external helical thread  66 . Rotation of the cap  40  causes the plunger  60  to be selectively advanced or retracted linearly with respect to the cap  40 , depending on the direction of rotation. The linear translation of plunger  60  along the axis of outer housing  20  enables control of the fluid flow rate. When the desired fluid flow rate has been reached, the mechanical stability of the adjustment cap  40  and the plunger  60  enables the adjustment cap  40  to stay in the selected position without requiring additional energy to maintain that position. 
         [0021]    The pitch of the screw interface region  62  between the plunger  60  and the cap  40  can be selected to achieve a desired correspondence between the degree of rotation by the cap  40  and the distance moved by the plunger  60  as the cap  40  is rotated between its fully closed position and its fully open position. As the plunger  60  moves from a closed position to an open position, the flow resistance decreases and the flow rate increases. Likewise, as the plunger  60  moves from an open position toward the closed position, the flow resistance increases and the flow rate decreases. Fluid flow is stopped when the plunger  60  is moved to the fully closed position. 
         [0022]    In a preferred embodiment, the adjustment cap  40  will have 300 degrees of rotation to move the plunger  42  through its entire path from the closed position to the fully open position. When the degree of rotation is less than 360 degrees (e.g., as determined by the helical twist of the screw interface region  62 ), mechanical stops (not shown) can be inserted between the adjustment cap  40  and the plunger  60 , thereby preventing any additional rotation of the cap  40  and in turn preventing a mechanical collision of the plunger  60  and the cap  40 . In addition, when the degree of rotation of the adjustment cap  40  is set below one rotation, the resistor valve (not shown) can be mechanically keyed to a control mechanism (not shown), to prevent the loading or unloading of the resistor valve from the control mechanism in any position other than the closed position. This ensures that the resistor valve is always in the “off” position when removed from the flow control system and prevents any free flowing condition from occurring. 
         [0023]    The variable spiral region  70  provides a spiral flow path  72  for the fluid as it enters the fluid inlet  22 . The spiral flow path  72  is a helical channel, which has an increasing cross-sectioned area along its length, e.g., which is tapered in terms of width and/or depth and, preferably, has a tapering width and depth. In a closed position, the variable spiral region  70  is not exposed to the fluid inlet  22 , thereby preventing fluid flow through the interior of the plunger  60 . However, as the cap  40  is rotated, the movable plunger  60  is moved linearly along the interior axis of the housing  20  and exposes a differing portion of the spiral flow path  72  to the fluid entering via the fluid inlet  22 . The distal end (relative to the spiral interface region  62 ) of the spiral region  70  contains the portion of the spiral flow path  72  with the smallest width and/or depth enabling the flow resistor  10  to control relatively low fluid flow rates. The proximal end (left end in the orientation depicted in  FIG. 4 ) of the spiral region  70  contains the portion of the spiral flow path  72  with the largest width and/or depth enabling the flow resistor assembly  10  to control relatively high fluid flow rates. 
         [0024]    In the depicted preferred embodiment, the channel  72  gradually increases in width and depth from the smallest size to the largest size as it travels from the distal end to the proximal end of the spiral region  70 , providing the wide range of fluid flow rates necessary for IV therapy. In the preferred embodiment, the resistor assembly  10  can operate at flow rates varying over five orders of magnitude, e.g., from about 0.1 mL/hr to about 6,000 mL/hr. In the preferred embodiment, the relationship between flow resistance and plunger translation is fundamentally logarithmic. However, it will be recognized that the profile of the spiral flow path  72  can be tailored to achieve virtually any monotonic profile of flow resistance versus plunger translation, providing an infinite number of possible flow rate ranges. 
         [0025]    When the fluid resistor assembly  10  is in an open position, the IV fluid enters the resistor assembly  10  via the fluid inlet  22 . The fluid then travels through the open or exposed portion of the channel  72  into the interior space defined between the interior diameter of the cap  40  and the outer diameter of the plunger  60 . The fluid travels around the plunger  60  and into an inlet end  65  of the interior pathway  64  of the plunger  60 . The interior diameter of the cap  40  and the outer diameter of the plunger  60  are such that a sufficient clearance is provided to allow fluid to pass from the inlet  22  to the plunger inlet end  65 . The fluid passes out the outlet end  67  of the plunger  60  into the passageway  26  and exits the resistor outlet  24 . 
         [0026]    In the depicted embodiment, the fluid passes from the resistor outlet  24  into an integral flow sensor portion  69  including a flow object  120  whose position in an interior flow passageway  125  varies as a function of flow rate. The flow sensor  69  includes a light source  122  and an optical position detector  124  for optically detecting the position of the flow object  120 . 
         [0027]    In the depicted embodiment, as best seen in  FIG. 3 , the flow object  120  is a cylinder having a generally “H” shaped cross-sectional shape although, other configurations are contemplated, including without limitation a ball-shaped flow object. A spring, such as a coil spring  123  or other resilient spring member is seated within the interior passageway  125  of the flow sensor portion  69 . The spring  123  urges the flow object  120  in a direction opposite to the direction of fluid flow, with the position of the flow object  120  varying as a function of the flow rate, with higher flow rates causing greater displacement of the flow object against the urging of the spring  123 . The interior passageway  125  of the flow sensor portion  69  is generally conical or tapered, opening toward the outlet end  110 . In this manner, the annular gap between the flow object  120  and the passageway  125  increases as the flow rate increases. In the depicted preferred embodiment, a spring seat  127  is provided to engage the flow object  120  at very high flow rates, thereby providing an upper limit to the range of axial movement of the flow object  120  within the flow passageway  125 . 
         [0028]    In alternative embodiments, the flow resistor and flow sensor portions may be separately formed and fluidically coupled. The flow sensor may be of the type described in International Application No. PCT/US2007/002039 filed Jan. 23, 2007, which has entered the National Stage in the U.S. as Ser. No. 12/280,869 filed Aug. 27, 2008, International Application No. PCT/US2007/004945 filed Feb. 27, 2007, which entered the National Stage in the U.S. as Ser. No. 12/280,894 filed Aug. 27, 2008, and International Application No. PCT/US2007/005095 filed Feb. 27, 2007, which entered the National Stage in the U.S. as Ser. No. 12/280,894 filed Aug. 27, 2008, each of which is incorporated herein by reference in its entirety. The IV fluid exiting the flow sensor  69  then travels through the outlet  110  to an outlet tube coupled to a patient or subject. 
         [0029]    When the flow resistor assembly  10  needs to be turned off, the cap  40  can be turned to the off position either manually or electronically under programmed control (e.g., by using a touch screen or other user interface of an electronic control center, not shown, to stop the infusion). The off position is achieved when no portion of the spiral flow path  72  is exposed to the IV fluid at the fluid inlet  22 . Since the spiral region  70  contains a region with no fluid flow channel, the disclosed flow resistor  10  does not require mechanical collision to turn off the fluid flow. Rather, the flow resistor  10  contains an off zone or range. Therefore, the flow resistor assembly  10  can be turned off without a mechanical face-to-face collision, such as is required when using needle valves. Thus, the off zone provides a region or range of positions where no fluid can flow through the flow resistor assembly  10  and where a mechanical stop is not required to reach the off condition. 
         [0030]    The sealing region  80  of the plunger  60  includes a proximal seal  82  and a distal seal  84 . The proximal seal  82  and distal seal  84  are each of the same diameter and when a consistent diameter is coupled with the interior fluid pathway  64 , the resistor assembly  10  can be reset to any desired flow rate without causing a pumping effect. Since there is no pumping effect, the fluid is prevented from being pumped into or out of the patient when the resistor is rapidly turned on or shut off, thereby maintaining the desired flow rate. The sealing region  80  also contains one or more anti-rotate protrusions  86 , each of which rides in a corresponding, aligned axially extending channel  28  as the plunger  60  translates linearly along the interior axis of the housing  20 , thus preventing rotation of the plunger  60  relative to the outer housing  20  as the cap  40  is rotated. 
         [0031]    Referring now to  FIG. 5 , there is shown an exemplary adjustment cap  40  including a cap body  42 , an internal helical thread  44  (see  FIG. 3 ), a distal seal  46 , and one or more protrusions  48 . The interior of the cap body  42  contains the internal helical thread  44 , which engages the external helical thread  66  of the plunger  60  enabling the rotational adjustment of the plunger  60 . The distal seal  46  provides a fluidic seal between the outer housing  20  and the adjustment cap  40 , thereby preventing IV fluid from leaking therebetween. The one or more protrusions  48  secure the cap  40  to the outer housing  20 . An O-ring  90  sits between the cap  40  and the outer housing  20  to provide an additional seal for preventing IV fluid from leaking from the flow resistor assembly  10 . 
         [0032]    Referring now to  FIG. 6 , there is outlined a preferred exemplary system  100  for controlling the fluid flow resistor  10  within a sensor based fluid control system. An electronic control board  104  and its software may control the operation of the flow resistor  10  and monitor the conditions within which the flow resistor  10  is operating. An operator, such as a healthcare provider or patient, can either manually input the desired infusion information or input the infusion information using an alternative input means, such as a bar code reader. After the infusion data is input, it is desirable to confirm the infusion data before the infusion can begin. Once the infusion information is confirmed, the electronic control board  104  will determine the proper setting for the flow resistor  10  based on the flow rate and, optionally, other parameters such as fluid viscosity, temperature, and others. 
         [0033]    After confirmation of the desired infusion information, the electronic control board  104  will drive operation of the fluid flow resistor  10  under programmed control by sending signals from the electronic control board  104  to a resistor adjustment motor  106 , such as a servo motor or the like, coupled to the cap  40 . The adjustment motor  106  provides the necessary power to turn the adjustment cap  40  on the flow resistor  10  to control fluid flow in accordance with the input infusion information. The input information may be, for example, a target flow rate, a target volume, a target time for completion of an infusion, and so forth. During infusion of the IV fluid into the patient, the electronic control board  104  can adjust the settings of the flow resistor  10  and the driving pressure to fine-tune the flow rate in accordance with the input infusion information. It will be recognized that the adjustment of the flow resistor  10  herein need not be the sole variable controlling flow rate. For example, a flow control system embodying the flow resistor  10  herein may have additional variables for controlling fluid flow rate, such as an inflatable bladder or other means for varying the fluid driving pressure. 
         [0034]    The position of the flow object  120  can be monitored optically to determine the actual flow rate of the IV fluid as it passes out of the flow resistor  10  to the patient. The flow object  120  may be monitored, for example, by an optical sensor, which includes a light source  122  such as an LED array and an optical detector  124 , which may be a photosensor array, such as a charged-coupled device (CCD) array or the like. The light source  122  and optical detector  124  are preferably disposed on opposite sides of a flow chamber containing the flow object  120 , although other configurations are contemplated, such as an optical detector positioned to sense light emitted by the light source  122  and reflected by the flow object  120 . The pattern of light is sensed by the detector  124  to determine the position of flow object  120  within the flow sensor. The position information, in turn, is used to determine an actual fluid flow rate. The flow rate information can be sent to the electronic control board to control fluid flow in accordance with the infusion information. The electronic control module  104  may also be programmed to shut off flow in response to a detected alarm condition such as occlusion, detected an air bubble, etc. 
         [0035]    The fluid flow resistor assembly  10  of the present disclosure can be used in conjunction with various flow control systems and optical flow sensors, including those described in the aforementioned International application Nos. PCT/US2007/002039, PCT/US2007/004945, and PCT/US2007/005095. 
         [0036]    The invention has been described with reference to the preferred embodiments. Modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.