Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Patent
1996-08-29
1999-09-28
DeMille, Danton D.
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
604218, 604211, A61M 3700, A61M 5315, A61M 5145
Patent
active
059578890
DESCRIPTION:
BRIEF SUMMARY
The invention relates to displacement systems for controlled infusion of a liquid from a cartridge of the kind comprising a tubular vessel, which is at a rear end closed by a piston which may be forced by a piston rod into the tube to press out the liquid through an outlet arranged at a front end of the tube.
Designated as pumps such displacement systems are used for therapeutic infusion of medicine, e.g insulin for diabetics to whom the natural production of insulin is simulated in this way.
A commonly used pump structure comprises a housing with a cavity accommodating an infusion syringe cartridge having a piston and a piston rod by which the piston may be forced into the cartridge to press out the medicament in the cartridge through an outlet at the end of the cartridge opposite the piston. Such infusion pumps, which are based on the technique known from syringes by which the dosage can be adjusted with very close accuracy, has many advantages. They are simple in their construction and a precise indication of the medicine left in the cartridge may currently be obtained by monitoring the position of the piston in the cartridge, and in the same way the amount infused can be very precise controlled by controlling the distance of movement of the piston in the cartridge.
A heavy drawback by the pumps of the cartridge and piston type is the fact that at least one of the dimensions of the pump have to be at least more than two times the overall stroke of the piston in the cartridge as the cartridge has to be at least a little longer than this stroke and as space must be reserved for the piston rod behind the cartridge when the piston in a new cartridge is in its rearmost position. Thereby a limit is set for the extent of the miniaturization which is aimed at to make it as comfortable as possible to carry the pump during the activities of a day.
Consequently it is an object of the invention to provide a displacement system of the cartridge/piston type wherein this drawback is avoided.
This is obtained by a displacement system of the kind mentioned in the ingress of this specification and which system is according to the invention characterized in that the piston rod is provided as a flexible incompressible construction and at a position behind the rear end of the cartridge is deflected away from the axis of the cartridge.
The deflection of the piston rod away from the axis of the cartridge may be obtained by a piston rod guide being provided behind the rear end of the cartridge. The piston rod guide governs the deflection of the piston rod so that this rod will only be deflected in the way determined by the guide.
Preferably the piston rod is deflected 180.degree. so that it forms two parallel straight portions extending from the piston rod guide.
To ensure that the necessary deflecting forces on the piston rod are exerted by the guide alone so that the straight portions projecting from the guide are parallel without any need for deflecting forces on these projecting portion, the piston rod guide has a guide track having an upper curved part and a lover linear part at each end of the curved part and having a length in the direction of the projecting parallel portions, which length taken from the ends of the guide track from which these portions projects to the centre of the piston rod at the top of the curved part is equal to or larger than the distance between the axes of the projecting parallel portions.
It is also important that the piston rod is abutting the curved guiding surface all the way so that the spring effect of the piston rod does not cause any slack in the guiding as such a slack may result in an imprecise dose. This continuous abutment is obtained by elaborating the curved part of the guide in accordance with the shape which the curved part of the piston rod will spontaneously adopt when its end portions are kept parallel.
The piston rod may be made flexible in several ways. By being a flexible band stiffened by having an arcuate cross section the piston rod has one preferred mode of deflection
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Ejlersen Henning Munk
Heger Anders
Klitmose Lars Peter
Ljunggreen Henrik
M.o slashed.ller-Jensen Jens
DeMille Danton D.
Novo Nordisk A S
Zelson Esq. Steve T.
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