Pumps – Expansible chamber type – Elongated flexible chamber wall progressively deformed
Reexamination Certificate
1998-10-12
2001-05-22
Thorpe, Timothy S. (Department: 3746)
Pumps
Expansible chamber type
Elongated flexible chamber wall progressively deformed
C417S053000, C604S153000
Reexamination Certificate
active
06234773
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a linear peristaltic pump for providing adjustable volumetric flow through a flexible, fluid-filled tubing, such as with infusion, of intravenous solutions through a flexible IV tubing. Particularly, the invention relates to a pump having plurality of pumping elements or plungers which operate sequentially and repeatedly along a portion of the flexible fluid carrying tubing to squeeze the fluid therealong with a “milking” type of action. Fluid is forced through the tubing from the entry end to the output end in the direction of the sequential actuation of the pumping elements. The volumetric flow rate is adjusted by changing the rate of sequential and repeated squeezing.
BACKGROUND OF THE INVENTION
Traditionally intravenous infusion has been accomplished using gravity flow systems or drip regulated systems. Modern advances for regulating intravenous infusion have included various types of volumetric pumping systems. In situations where a patient is already established with a gravity-fed or drip-type IV, it often becomes helpful to convert the same system into one with a pump-controlled volumetric flow. For example, an emergency IV can be established in the field by paramedics, and upon arrival at a hospital, a doctor may need to administer medication at a precisely controlled flow rate. The same IV tubing system can then be conveniently adapted for controlled volumetric flow pumping through the use of various types of peristaltic pumps which engage the exterior of the established IV tubing. The typical IV tubing is made of a medical grade polyvinyl chloride (PVC) which has thin walls and is both flexible and resilient. Other more expensive tubing has been proposed to reduce collapsing, but at a cost of about ten times as much as PVC tubing. Alternatively, a combination of types of tubing has been proposed, such as silicon tubing spliced along a length which will be subjected to peristaltic pumping action. Such combination systems can also have a cost significantly greater than PVC (about five to eight times as much), because of the materials, splicing and additional sterilization required. Pumps which act upon the outside of the tubing walls to pump fluid within the tubing at a controlled rate permit the medical practitioners to avoid disturbing existing catheters or needles already established into the patient.
Thus, various types of modern pumps have been used for pumping fluid through an IV tubing, including pumps with a rotating arm, with rollers affixed at both ends of the arm. The rollers are positioned adjacent a curved IV holding channel to engage and roll along a section of tubing placed into the holding channel, thereby advancing a column of liquid there through. As the arm rotates, the rollers alternately engage the tubing, one behind the other, and successive columns of liquid are moved through the tubing. Rotation of the arm continues and repeats the pumping action.
Another type of pump is one which is referred to as a single-plunger peristaltic pump. This type of pump has an entry valve which compresses the tubing shut at an upstream point. A single elongated plunger then squeezes a predetermined length of the tubing along a linear section ahead of the closed entry valve. An outlet valve then compresses the tubing downstream from the elongated plunger after the liquid in the linear section is squeezed out and moved toward the patient. With the outlet valve closed, the entry valve is opened and the elongated plunger is retracted to allow fluid to move back into the linear section between the entry valve and the outlet valve. The entry valve is then closed, and the outlet valve is opened so that compression of the single, elongated plunger can pump more fluid through the tubing.
Another type of pump, which is referred to here as a linear peristaltic pump, uses a series of pumping elements which each engage and sequentially compress a plurality of small segments along an engaged portion of the IV tubing. Each pumping element in sequence at its maximum stroke acts as a seal valve to prevent unwanted reverse flow. Separate inlet and outlet valves are not required in such a linear peristaltic pump. The sequence repeats, and the pumping element reciprocating strokes are typically timed to repeat the milking cycle without interruption. The rate of flow is controlled by changing the rate of reciprocation while the magnitude of the stroke is constant.
With each of the various types of peristaltic pumps described above, the IV tubing is repeatedly collapsed to force the fluid out of the tubing in one direction and then released to allow fluid to reenter from the other direction. After a period of use, the PVC tubing material becomes progressively flattened and permanently deformed such that the walls become creased and the interior volume of the tubing changes over the normal time period of operation. Tubing subject to permanent deformation reduces the pumping efficiency and reduces the accuracy of the pump. To the extent that attempts at reshaping may cause additional crease lines, the risk of premature cracking, tearing or rupture may also be increased, particularly at crease lines. Thus, the tubing must be changed frequently and must be carefully monitored to avoid lost efficiency, inadequate flow, inaccurate and improper volumetric flow or other failure of the system.
SUMMARY OF THE INVENTION
The present invention provides advantages of a linear peristaltic pump and overcomes many of the difficulties which arrive with other types of peristaltic pumps. The use of a linear peristaltic pump with a plurality of sequentially actuated elements does not require separate entry and outlet valves as with the single plunger type of peristaltic pump. The present invention further provides reshaping fingers, which engage a flexible fluid-filled tubing, such as an IV tubing, adjacent to each pumping element contact point, thereby continuously returning the tubing to a constant internal volume and thus maintaining a constant flow rate during operation at a given speed. The time of operation before the tubing becomes permanently deformed is increased. A plurality of pairs of interdigitated reshaping fingers are used and are sequentially actuated transverse to the actuation direction of the pumping elements along the engaged length of the tubing. The interdigitated positioning of the reshaping fingers with the pumping elements advantageously facilitates reshaping of the tubing immediately adjacent each of the compression elements so that reshaping of the tubing is effectively accomplished. Further, the present invention provides pairs of opposed reshaping fingers, each having concave jaws which the shape of a cylindrical arc matching the outside diameter of the flexible tubing. The unique arc shape of the jaws, and particularly a substantial arc of more than about 90°, is made possible by the interdigitation of the fingers with the pumping elements so that reshaping does not interfere with the pumping elements. The result is to round the tubing to its original dimensions without adding additional stress or fatigue and without causing additional potential rupture corners.
According to another aspect of the present invention, a pressure sensor is provided upstream from the pump engagement portion at which the flexible tubing is acted upon by reciprocating pumping elements. A second sensor is provided downstream from the pumping elements and a valve mechanism is provided for closing the flexible tubing downstream from the second pressure sensor. During operation, the tubing will be closed at at least one of the pumping element at any given time so that the upstream pressure can be measured separate from the downstream and the downstream pressure likewise can be measured separate from the upstream pressure. At initialization of the pump, the downstream and upstream sensors are calibrated by closing the downstream valve and disengaging the flexible tubing from compression by the pumping elements. The disengagement is advantag
Copp Harry C.
Hill Roger J.
Lindemann Gary
Monti, Jr. James H.
Oliver Joseph A.
B-Braun Medical, Inc.
Haynes and Boone LLP
Montgomery John W.
Solak Timothy P
Thorpe Timothy S.
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