Abstract:
An infusion pump for continuously conveying a fluid includes an inlet, an outlet, a first piston movably supported in a first chamber connected to the inlet, a second piston movably supported in a second chamber connected to the outlet, and a connecting channel connecting the first chamber to the second chamber. At least one control element, in a first position, connects the inlet to the first chamber and, in a second position, connects the first chamber to the second chamber. A controller acts upon the first piston, the second piston, and the control element so that, when the control element is set in the first position, the first chamber is filled while the second chamber is drained, and when in the second position, the first chamber is drained and the second chamber is filled, wherein a constant discharge at the outlet is maintained at a predefined flow rate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application represents a National Stage application of PCT/DE2010/0014368 entitled “Continuously Conveying Infusion Pump” filed Dec. 10, 2010, pending. 
     BACKGROUND OF THE INVENTION 
     The invention relates to an infusion fusion pump for continually conveying a fluid, comprising an inlet, an outlet, a first piston movably supported in a first chamber, and a second piston movably supported in a second chamber. The invention relates in particular to an infusion pump, using which very small amounts of a drug can be applied precisely and with a constantly uniform flow or conveying rate. 
     EP 045 8114 B1 already discloses an infusion pump where using four valves two cylinders in each case equipped with a piston can alternately be filled with a drug from a reservoir and the drug can be drained by discharging the drug to the patient. Switching over the drug supply from a drained to a filled cylinder can achieve an approximately continuous conveying of drugs with relatively simple means. 
     A disadvantage of this infusion pump however is that due to the valve clearance an additional volume is created in the valve when the valve is opened, there being a reduced conveying of the drug. On the other hand, this reduced volume is displaced again when the valve is closed, resulting in increased conveying. 
     Over longer periods, the drug delivery corresponds to the therapy plan established by the physician. Under certain circumstances however, only a temporally brief under or oversupply of the patient with the drug conveyed by the infusion pump can—as a function of the drug—lead to the desired therapeutic success not being achieved. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the invention to provide an infusion pump, using which even very small amounts of liquid, preferably in the microliter range, can conveyed with a high degree of precision and continuously. 
     The continuously conveying infusion pump according to the invention ensures, as a result of the arrangement of the first chamber designated as conveying chamber and the second chamber designated as equalisation chamber together with volume-neutral valves, that the drug release is only dependent on the control of the actuators of the previously mentioned elements and is thus continuous at each desired conveying rate, the control cycles being identical. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail with reference to an exemplary embodiment of particularly preferred design, in which: 
         FIG. 1  shows a schematic sectional view through a particularly preferred exemplary embodiment of the inventive infusion pump, 
         FIG. 2  shows a schematic sectional view of the infusion pump from  FIG. 1  in a first switching state, and 
         FIG. 3A  shows a schematic sectional view of the infusion pump from  FIG. 1  in a second switching state. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a schematic sectional view through a particularly preferred exemplary embodiment of the infusion pump according to the invention. The infusion pump  10  exhibits an inlet  20  for introducing a fluid, for example a drug, from a reservoir (not shown) into the infusion pump  10 , and an outlet  30  that passes on the fluid from the infusion pump  10  to the patient. The inlet  20  and the outlet  30  of the infusion pump are arranged, preferably aligned, at mutually opposite sides of the infusion pump  10 . 
     The infusion pump  10  exhibits a first chamber  50  with a first piston  40  and a second chamber  70  adjacent preferably parallel, subsequent in the flow direction, with a second piston  60 , the first chamber  50  and the first piston  40  also been designated as conveying chamber  50  or equalisation piston  60 , and the second piston  60  also being designated as equalisation chamber  70  and equalisation piston  60 . The first chamber  50  is connected to the inlet  20  (or an intake channel) whereas the second chamber  70  is connected to the outlet  30  (or an exhaust channel). The chambers  50 ,  70  are mutually connected by a connecting channel  80 , the connecting channel  80  preferably being arranged such that it is aligned to the outlet  30 . In a particularly preferred manner the inlet  20 , the connecting channel  80  and the outlet  30  are arranged such that they are aligned. 
     The pistons  40 ,  60  are movably supported in the first chamber  50 , designated as conveying chamber, or the second chamber  70 , designated as equalisation chamber, the intermediate space between the pistons  40 ,  60  and the inside wall of the chambers  50 ,  70  being, if necessary, sealed with suitable means. The piston pumps that are formed by the pistons  40 ,  60  in the chambers  50 ,  70  are actuated by means of suitable actuators (not illustrated). 
     According to the invention, a control element  90  is provided that is preferably designed as a two-way cock, the sleeve of the cock  90  being preferably formed by the housing of the infusion pump  10 . The plug of the cock  90  is sealingly supported in the sleeve. The plug can also be designed as part of a three-way cock, so that for exerting the function of the control element  90 , only a small rotation of the three-way cock through a few angular degrees is necessary. 
     That is to say, the control element  90  is designed such that in a first position of the control elements  90  the inlet  20  is connected to the first chamber  50  in a communicating manner, whereas the communication between the first chamber  50  and the second chamber  70  is blocked by the control element  90 . In this position, the first chamber  50  can be filled from the reservoir by a downwards movement of the first piston  40 , and the second chamber  70  can pass on its content by means of an upwards movement of the second piston  60  to the patient through the outlet  30  in a continually conveying manner (see  FIG. 2 ). 
     In a second position, for example rotated through 180°, of the two-way cock  90  (or its plug  90 ), the communication between the inlet  20  and the first chamber  50  is blocked by the plug  90 , however a communication between the first chamber  50  and the second chamber  70  being produced via the connecting channel  80 . The upwards movement of the first piston  40  conducts the fluid, that has been displaced from the first chamber  50 , into the second chamber  70  that is filled during a simultaneous downwards movement of the second piston  60  (see  FIG. 3 ). 
     As an alternative, the control element can also be provided by two valves (not shown) instead of the cock  90 , a first valve being arranged between the inlet and the first chamber and second valve being arranged between the first chamber and the second chamber. In the process, the valves are switched alternately, so that the two valves assume the function of the cock shown above. 
     As a further preferred design of the alternative it can be envisaged that the first valve is designed as a non-return valve and the second valve as a valve that is actuated by an actuator. Again as a particularly preferred alternative for this design, the first valve can be designed as a non-return valve and the second valve as a siphon that preferably does not open until a differential pressure of &gt;100 hPa. 
     Here the movements of the two pistons  40 ,  60  are coordinated by a control system (not shown) such that the differential volume that is produced by draining the first chamber  50  and filling the second chamber  70  and is ejected corresponds to that volume that is required for continually conveying the desired medication. The continuity of the conveying action ensures that the drug is always infused under pressure into the tissue, as is demanded for example by the “Convection Enhanced Delivery” (CED) method. 
     In the exemplary embodiment, the connected unit is designed as a piston  100  to be connected for pressure measurement purposes. The piston  100  is seated on a suitable force sensor (not shown), for example a cantilevered beam. From the force with which this piston  100  is held in its position, the pressure in the equalisation chamber  70  that is connected to the outflow channel  30  can be determined taking into account the piston surface. As an alternative, instead of the previously mentioned movably supported third piston  100  it is also possible to use an inflatable/deflatable membrane for pressure measurement purposes. The pressure measurement is necessary for example to detect an occlusion, it is being provided in the case of a pressure rise above a predetermined value that an alarm is emitted. 
     Finally, there is also provided an area  110 ,  120  for connecting to the infusion pump a detector for bubble detection in the fluid. Bubble detection can for example be provided by means of ultrasound measurement at a frequency in the MHz range or by optical measurement utilising the different indices of refraction of liquid and gas. To this end, a receiving chamber  110  for the sound or light transmitter and a receiving chamber  120  for the sound or light receiver are integrated into the pump carrier of the infusion pump  10 . In the exemplary embodiment, the outlet  30  exhibits a rectangular cross-section for avoiding unwanted reflections or refractions of light or sound at boundary surfaces that are not even. 
     In summary, the method sequence of the infusion pump that is controlled by the control system is described once more: 
     The plug  90  closes the connecting channel  80  and has connected the conveying chamber  50  via the inlet  20  to the liquid supply (not shown). In this state, the equalisation piston  60  is forced inwards (i.e. upwards in the drawing plane) at the velocity that is necessary to continually convey the desired amount of liquid through the outlet  30 . At the same time, the conveying piston  50  is pulled outwards (i.e. downwards in the drawing plane) at the maximum intended velocity. At the same time the conveying chamber  50  is filled with the fluid, e.g. a drug, from the liquid supply. Due to the closed connecting channel  80 , these liquid streams are independent from each other. After, the supply chamber  50  is filled, the conveying piston  40  is no longer moved. After this the plug  90  in the exemplary embodiment is rotated through 180° until the inlet  20  is closed and the connecting channel  90  is open, while the equalisation piston  60  continues to be pushed inwards at a constant velocity. These procedures ensure that the outflow velocity of the fluid in the outlet  30  is not changed. 
     Then the conveying piston  40  is pushed inwards (i.e. upwards in the drawing plane) such that a larger amount of liquid is ejected from the conveying chamber  50  than is necessary for the constant conveying through the outlet  30 . At the same time, the equalisation piston  60  is pulled outwards (i.e. downwards in the drawing plane) at the that velocity and thus the volume of the equalisation chamber  70  is increased, a fluid leaving the connecting channel  80  being taken up in the equalisation chamber  70  as a result. This takes place to the extent that is necessary to keep the outflow velocity of the liquid constant at the outlet  30 . 
     After the conveying chamber  70  is drained, the conveying piston  40  is no longer moved and the equalisation piston  60  is again forced inwards (i.e. upwards in the drawing plane) at that velocity that is requisite to further maintain the constant outflow velocity of the fluid in the outlet  30 . In the process, the fluid collected in the equalisation chamber  70  during the draining of the conveying chamber  40  is ejected. 
     Now the plug  90  is again rotated through 180° until the connecting channel  80  is closed and the conveying chamber  50  is connected to the inlet  20 . Thereafter, the conveying piston  40  is again pulled outwards (i.e. downwards in the drawing plane) at the maximum intended velocity and the conveying chamber  50  is filled again and another control cycle sets in as described above. The continued ejection of liquid in the outlet  30  can in this way be maintained until the liquid supply to which the inlet is connected is exhausted. 
     As a result of the property of the inventive, continuously conveying infusion pump  10 , that due to the construction in the exemplary embodiment at no time a situation can arise, where the free flow (uncontrolled drug flow on account of the pressure difference between the liquid supply and the patient access) is possible, additional measures in the case of a pressure difference as a result of gravity, temperature fluctuations or other influences can be dispensed with. 
     It is possible at any time to change the outflow velocity of the liquid between the minimum and maximum intended limits by correspondingly controlling the actuators. These limits are a function of the design of the pump  10 , such as for example the performance of the selected actuators and dimensions of the pump that determine the size of the chambers  50 ,  70  and the diameters of the pistons  40 ,  60 . 
     Finally, the invention also facilitates a design of the infusion pump  10  as a disposable product in a sterile embodiment. That is, the simple construction of the inventive infusion pump  10  facilitates the manufacture in the shape of an injection-moulded part, this facilitating cost-effective production and making it possible to use the infusion pump  10  as a disposable product. 
     Among others, the pump also complies with the requirement for supplying the drug directly into the brain tissue according to the “Convection Enhanced Delivery” (CED) method that exhibits great advantages compared to the non-continuous delivery of the drug.