Syringes

Details Syringes Syringes

1990-05-17

1991-11-19

Yasko, John D.

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

604218, A61M 500

Patent

active

050662805

DESCRIPTION:

BRIEF SUMMARY
This invention relates to syringes and in particular to so-called disposable syringes, which are used in general medical practice as an effective way of preventing cross-infection. However, due to shortages of these products, and possibly ignorance, there is a tendency, particularly in the Third World, to use the syringe maybe five or six times before throwing it away. Drug users also commonly share syringes, which are used many times, because they do not have access to a regular supply.
It is an object of this invention to provide a disposable syringe which is effective in operation, can be used in a conventional manner, is cheap to produce and will deter attempts to reuse the syringe.
According to the invention there is provided a syringe comprising a barrel housing both a piston and a plunger for moving the piston to enable a liquid to be drawn in to and ejected from a portion of the barrel, the piston and plunger being interconnected by a decoupling linkage such that the plunger is operatively disconnected from the piston after the plunger has been retracted and subsequently depressed.
In the preferred arrangement the piston and the plunger are interconnected by a coupling member. In this case the coupling member may be interconnected to both the piston and the plunger by a decoupling linkage. Ideally the piston or the coupling member carries a flange which interacts with latches on the inner wall of the barrel so as to be able to pass the latches before disconnection of the or each decoupling linkage but is unable to pass the latches upon attempted withdrawal of the plunger after such disconnection. The latches may, for example, be in the form of inwardly projecting serrated ribs on inwardly sprung-loaded arms. Preferably, the flange will incorporate keyways which can ride up the latches whilst the flange is in one rotational attitude, the latches abutting the flange when the flange is in alternative rotational attitudes. In this case the or each decoupling linkage will ideally be effective to cause rotation of the part carrying the flange upon application of reciprocation movements to the plunger. It will be understood that any connection means which fulfils this function is applicable. For example, the or each decoupling linkage may be threadedly engaged and the piston may be interconnected with the barrel of the syringe so that it is caused to rotate during axial movement, the threaded engagement being such that on a second retraction of the plunger the piston and plunger become disengaged.
In the preferred embodiment the or each decoupling linkage includes a camway on one part for receiving a cam follower on the other part, the camway being shaped such that movement of the plunger causes relative movement between the cam follower and the camway, whereby the cam follower is removed from the camway on a second retraction of the plunger.
The cam followers may, for example, be diametrically opposed pins, locating in a ring having the camway formed on an inner surface. These pins may, with advantage be positioned at the ends of fingers which are flexible but biased in the axial position of the piston, so that the pins will be biased to follow the camways in one direction only. Additionally the pins may carry projecting webs which resist movement of the pins in the other direction through the camway.
If desired the parts of the or each decoupling linkage defining the camway and the cam follower respectively may be biased apart by a spring or other biasing means.
The plunger and piston may be keyed together for rotational movement but separable on retraction after disconnection of the decoupling linkage. The syringe may include one or more cover plates for preventing access to the decoupling linkage after operative disconnection of the piston and plunger. Where the plunger can be full withdrawn from the syringe it may be hollow so that it can be used as a needle cover to prevent infection spreading, due to accidental scratches during subsequent handling.
The mechanism employed in the syringes of this inv

REFERENCES:
patent: 4699614 (1987-10-01), Glazier
patent: 4908020 (1990-03-01), Pettersen

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