Abstract:
A pressure monitoring system allows for more accurate and reliable measurement of the pressure inside of a tube in a pump. The pressure monitoring system prevents movement of the tubing or a change in size of the tubing due to external forces applied to the pump, eliminating inaccuracies due to handling of the pump during use.

Description:
PRIORITY 
       [0001]    The present application claims the benefit of U.S. Provisional Application Ser. No. 61/388,977, filed Oct. 1, 2010 which is herein incorporated by reference in its entirety. 
     
    
     THE FIELD OF THE INVENTION 
       [0002]    The present invention relates to pressure monitoring systems in pumps. More specifically, the present invention relates to a pressure monitoring system for medical pumps such as feeding pumps and infusion pumps which allows for more accurate pressure measurement in a fluid delivery tube while utilizing inexpensive components. The pressure monitoring system isolates the pressure measurement from environmental effects such as movement of the pump or, more importantly, external forces applied to the pump such as a user grasping the pump. 
       BACKGROUND 
       [0003]    Medical pumps such as peristaltic pumps are commonly used to deliver fluids. In medical applications, peristaltic pumps and fluid delivery systems are used to deliver medication, nutrition, and other fluids to a patient. In these applications, it is important to monitor the pressure inside of the delivery tubing. Typically, pressure is measured and monitored before and after the pumping motor. This allows the pump to determine if a blockage is present in the tubing or if the pressure in the tubing is outside of a safe working range. Measuring the pressure may also enable the pump to more accurately determine the rate of fluid delivery. 
         [0004]    It has been difficult to accurately measure the pressure in the delivery tubing. For medical applications, a disposable tubing set is loaded into the pump and used for a relatively short period of time. This requires that the pressure monitoring system does not interfere with the loading and unloading of the tubing. Existing pressure monitoring systems have experienced inaccuracies due to the inconsistent loading or placement of the tubing or due to external forces which are applied to the pump such as when a user grabs or moves the pump. 
         [0005]    There is a need for a pressure monitoring system for fluid delivery pumps which more accurately measures the fluid pressure inside of the tubing. There is a need for such a system which overcomes inconsistencies in tubing placement, and which is not affected by environmental conditions such as movement or forces applied to the pump. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an object of the present invention to provide an improved pressure monitoring system. 
         [0007]    According to one aspect of the invention, a pressure monitoring system is provided which allows the infusion tubing to be easily loaded and unloaded from the pump. The tubing is simply placed in a channel in the pump and the door is closed. No additional latch mechanisms are necessary. 
         [0008]    According to another aspect of the invention, a pressure monitoring system is provided where the pressure readings are isolated from external forces acting on the pump, and acting on the pump door in particular. The pressure monitoring system thus provides a more consistent and reliable measurement of the pressure within the tubing. 
         [0009]    These and other aspects of the present invention are realized in a pressure monitoring system as shown and described in the following figures and related description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Various embodiments of the present invention are shown and described in reference to the numbered drawings wherein: 
           [0011]      FIG. 1  shows a perspective view of a fluid delivery pump according to the present invention; 
           [0012]      FIG. 2  shows a perspective view of the pump of  FIG. 1 ; 
           [0013]      FIG. 3  shows a partial cross-sectional view of the pump of  FIG. 1 ; 
           [0014]      FIG. 4  shows a partial cross-sectional view of the pump of  FIG. 1 ; and 
           [0015]      FIGS. 5 through 7  show partial cross-sectional views of the pressure monitoring channel of pump of  FIG. 1 . 
       
    
    
       [0016]    It will be appreciated that the drawings are illustrative and not limiting of the scope of the invention which is defined by the appended claims. The embodiments shown accomplish various aspects and objects of the invention. It is appreciated that it is not possible to clearly show each element and aspect of the invention in a single figure, and as such, multiple figures are presented to separately illustrate the various details of the invention in greater clarity. Similarly, not every embodiment need accomplish all advantages of the present invention. 
       DETAILED DESCRIPTION 
       [0017]    The invention and accompanying drawings will now be discussed in reference to the numerals provided therein so as to enable one skilled in the art to practice the present invention. The drawings and descriptions are exemplary of various aspects of the invention and are not intended to narrow the scope of the appended claims. 
         [0018]    Turning now to  FIG. 1 , a perspective view of a pump  10  is shown. The present application applies to many types of pumps such as nutrition delivery and feeding pumps and I.V. or medication delivery pumps. For simplicity, the application simply refers to pumps or infusion pumps to indicate these types of pumps. The pump  10  is typically used for delivery of medical fluids, such as delivering medicine or nutritional solutions. Many of the controls or features of the pump  10  are known in medical peristaltic pumps, and are not discussed herein for clarity in discussing the invention. The pump  10  includes a door  14  which is closed after mounting an infusion cassette into the pump. The door  14  is used to ensure proper loading of the infusion cassette. 
         [0019]      FIG. 2  shows a perspective view of the pump  10  with the door  14  removed. An infusion cassette  18  is mounted in the pump. The infusion cassette  18  includes a cassette body  22 , an inflow tubing  26 , an outflow tubing  30  and a pump tubing  34 . The pump tubing  34  is typically flexible silicone tubing. The cassette body  22  provides connectors to attach the inflow tubing  26  to the first end of the pump tubing  34  and the outflow tubing to the second end of the pump tubing. The pump tubing thus forms a loop which is stretched around the pump rotor  38 . It will be appreciated, however, that the pressure monitoring system of the present invention may also be used in other pumps such as linear peristaltic pumps. 
         [0020]    The cassette  18  is typically loaded into the pump  10  by placing the loop of pump tubing  34  over the pump rotor  38 , stretching the pump tubing, and placing the cassette body  22  into a nesting area  42 . The pump includes pressure monitoring channels  46 . The pressure monitoring channels  46  receive the pump tubing  34  to monitor the pressure therein. It is typically desired to monitor the pressure inside the tubing both upstream and downstream from the pump rotor  38 . This allows the pump  10  to more accurately determine the fluid delivery rate and allows the pump to determine if a blockage or overpressure situation has occurred. 
         [0021]      FIG. 3  shows a partial cross-sectional view of the pump  10  taken through the pressure monitoring channels  46 . For clarity, not all structures are shown. The pump tubing  34  is loaded into the pressure monitoring channels  46 . The pump door  14  is shown open. Pressure sensors  50  are located in the bottom of the channels  46 . Piezoelectric crystals are typically used for the sensors  50 , but other types of pressure sensors could be used. Variances in the pressure within the pump tubing  34  change the amount of force applied to the pressure sensors, providing a signal which may be used to calculate the pressure inside of the tubing  34 . The sidewalls  54  of the pressure monitoring channels  46  may contact the tubing  34  in order to constrain the tubing. In this case the sidewalls  54  would be slightly narrower than the outer diameter of the tubing to limit the movement or expansion of the tubing and to slightly compress the tubing. Alternatively, the sidewalls  54  may be spaced apart from the tubing slightly to allow the tubing to more freely press against the pressure sensors  50 . 
         [0022]    The pump door  14  has pedestals  58  formed thereon which are formed in alignment with the pressure monitoring channels  46 . The pedestals  58  extend downwardly from the inside of the door  14 . The bottoms of pedestals  58  have a tubing contacting surface  62  and channel contacting surfaces  66 . When the door  14  is closed, the tubing contacting surface  62  contacts the top of the tubing  34  and compresses the tubing slightly, pressing the tubing against the pressure sensor  50 . When the door  14  is closed, the channel contacting surfaces  66  contact the top of the channels  46  and rest against the channel, preventing the pedestals  58  from moving towards the tubing  34  and further compressing the tubing. The door  14  is pivotably attached to the pump  10  via a hinge  70  and is secured close with a latch or catch  74 . 
         [0023]      FIG. 4  shows the pump door  14  in the closed position. When the pump door  14  is closed, the projections  58  are pushed down against the tubing  34  and the pressure monitoring channels  46 . The projections  58  are made slightly taller than the available distance between the closed pump door  14  and the channels  46 , causing interference when closing the pump door. Thus, the projections  58  contact the pressure monitoring channels  46  before the pump door  14  is completely closed and the pump door is bent as shown in order to close the latch  74  and secure the pump door in a closed position. The bend in the door  14  is exaggerated to illustrate the bending of the door. In use, a slight interference and a slight bend in the door  14  is sufficient to ensure that the projections  58  are always disposed in contact with the channels  46 . The portion of the pump door  14  adjacent the projections  58  is bowed outwardly relative to the rest of the pump door. This bending of the door biases the projections  58  against the pressure monitoring channels  46  and maintains contact and pressure therebetween. The contact and applied pressure between the channel contacting surfaces  66  of the projections  58  and the pressure monitoring channels  46  prevents the projections  58  from moving relative to the channels  46  when the pump is in use, moved, or grasped by a user, preventing erroneous changes in the pressure reading. Thus, the tubing  34  is held in a consistent position and is consistently held against the pressure sensor  50  with a small amount of preload. This allows for more reliable pressure monitoring. 
         [0024]      FIG. 5  shows an enlarged view of a single projection  58  and pressure monitoring channel  46  with the pump door  14  in the closed position. The channel contacting surfaces  66  are biased towards and pressed against upper surfaces  78  of the pressure monitoring channel  46 . Thus, the contact between the channel contacting surfaces  66  and upper channel surfaces  78  prevents the projection  58  from moving further towards the tubing  34  and further compressing the tubing if a person grabs the pump  10 . The tubing contacting surface  62  presses against the tubing  34  and compresses the tubing slightly. In this configuration, the tubing  34  is contacted on four sides by the projection  58 , channel side walls  54 , and pressure sensor  50 . As discussed above, the channel side walls  54  may be slightly wider than the tubing such that the tubing contacts the projection  58  and pressure sensor  50 . Because the tubing  34  is loaded consistently, more accurate and consistent pressure readings are obtained. If the tubing  34  is constrained on all sides, expansive force due to pressure within the tube may be more fully directed towards the pressure sensor  50 . If the tubing  34  is not contacted by the side walls  54 , the tubing may more easily seat against the pressure sensor  50  and eliminate friction with the side walls as a source of error. 
         [0025]      FIG. 6  shows an alternate configuration where the tubing contacting surface  62  and the channel contacting surfaces  66  are at or near the same height, or in the same plane. In this configuration, the pressure monitoring channel  46  is made slightly shallower so that the tubing  34  protrudes slightly from the channel  46  before the pump door  14  is closed, causing the tubing contacting surface  62  to press the tubing  34  downwardly when the door  14  is closed. As discussed above, the door  14  is slightly bent when fully closed to bias the projection  58  towards the channel  46  and maintain pressure between the channel contacting surfaces  66  and upper surfaces of the channel  46 . 
         [0026]      FIG. 7  shows an alternate configuration where the pressure sensor  50  is separated from the tubing  34 . A rigid intermediate connecting member  82  is placed therebetween to transfer force between the tubing  34  and the pressure sensor  50 . The connecting member  82  is coupled to the pump  10  by a flexible membrane  86 , allowing the connecting member to move relative to the pump body and transfer force from the tubing to the pressure sensor  50 . The membrane  86  seals around the connecting member  82  and isolates the pressure sensor  50  from the exterior of the pump, making the pump easier to clean and less likely to become damaged due to liquid spills around the pump. The pressure sensor configuration of  FIG. 7  functions with the projection  58  as discussed above. 
         [0027]    The pressure sensor configuration shown is advantageous in allowing for more consistent pressure measurements. The tube  34  is held against the pressure sensor  50  with a consistent amount of preload by the projection  58 . The projection  58  is held against the channel with a consistent amount of preload by the slightly bent door  14 , but is prevented from moving further towards the channel  46  and tube  34  by the channel contacting surfaces  66 . In this manner, the tube  34  is held in a consistent position where it is unaffected by external influences such as movement of the pump or pressure placed on the pump door. Thus, the pressure sensing is more accurate where the pump is used in an ambulatory (carried with the person) application, where the pump is moved about with a hospital bed, or where a person must move the pump around. 
         [0028]    It will be appreciated that various aspects of the invention may be combined together. Thus, for example, in accordance with principles of the present invention, a pressure monitoring system for a pump may include: a pump having a pressure monitoring channel; a tubing disposed in the pressure monitoring channel; a pressure sensor disposed in communication with the tubing to monitor the pressure in the tubing; a pump door; and a projection disposed on the inside of the pump door, the projection engaging the tubing and the pressure monitoring channel when the pump door is closed, and wherein closing the door causes a portion of the door adjacent the projection to bend outwardly and thereby bias the projection towards the pressure monitoring channel. The pressure monitoring system may also include the projection having a channel contacting surface which contacts the channel when the door is closed to thereby prevent further movement of the projection towards the channel; the channel contacting surface contacting an upper surface adjacent the channel; and/or the projection having a tubing contacting surface on the bottom thereof, the tubing contacting surface contacting the tubing and compressing the tubing when the door is closed; or combinations thereof. 
         [0029]    In accordance with one aspect of the invention, a pressure monitoring system may include: a pump having a channel therein for receiving a flexible tubing; a tubing disposed in the channel; a pressure sensor disposed in communication with the tubing; a pump door; a projection on the pump door; and wherein, when the pump door is closed: the projection is moved adjacent the channel; the projection compresses the tubing into the channel; the projection contacts a pump surface to stop movement of the projection towards the tubing; and the projection is biased towards the tubing. The pressure monitoring system may further include a portion of the door adjacent the projection being bent outwardly when the door is closed to thereby bias the projection towards the tubing; the projection having a tubing contacting surface for contacting the surface and a channel contacting surface which contacts the channel to thereby stop movement of the projection towards the tubing; the projection having first and second channel contacting surfaces, and the first channel contacting surface contacting a first side of the channel and the second channel contacting surface contacting a second side of the channel opposite the first side; and/or channel contacting surface contacting a surface adjacent the top of the channel; or combinations thereof. 
         [0030]    In according with an aspect of the invention, a pressure monitoring system may include a channel; a flexible tube disposed in the channel, the flexible tube being expandable due to pressure; a pressure sensor disposed in communication with the tube; a projection disposed in contact with the channel and in contact with the tube to hold the tube in the channel. The pressure monitoring system may also include: the projection having a channel contacting surface which contacts the channel to prevent movement of the projection towards the channel; the projection having a tube contacting surface which holds the tube in the channel; the tube contacting surface pressing the tube against the pressure sensor; the tube contacting surface extending into the channel; the channel being part of a pump; the projection being formed as part of a pump door; the projection having an interference fit between the pump door and the channel, causing the pump door to bend when the pump door is closed; the projection being biased towards the channel; and/or a channel contacting surface and preventing movement of the projection towards the channel; or combinations thereof. 
         [0031]    There is thus disclosed an improved pressure monitoring system. It will be appreciated that numerous changes may be made to the present invention without departing from the scope of the claims.