Title:
SELF-ASPIRATING SYRINGE
United States Patent 3583399
Abstract:
A hypodermic syringe for medical, dental, or veterinary use employing cartridge ampuls of injectable fluid arranged to be automatically self-aspirating. A resilient membrane is deflected at the forward end of the ampul rearwardly of the ampul each time the syringe plunger is actuated, so that upon release of the plunger the membrane is automatically resiliently restored to its normal position thereby producing conditions of reduced pressure or aspiration within the ampul. The membrane is deflected on a stud positioned at the forward end of the ampul-receiving cavity in the syringe, or on a movable flanged tubular element on the ampul adjacent the membrane and projecting forwardly of the ampul.
US Patent References:
Syringe
Cressler - May 1929 - 1712070
Syringe
Brockway - March 1931 - 1798117
Hypodermic syringe and closure cap for containers
Goldberg - November 1935 - 2020828
Ampoule syringe
Smith - June 1941 - 2244969
Syringe casing and stoppered cylindrical ampoule for direct injection
Pontius - November 1953 - 2660168
Syringe
Cressler - May 1929 - 1712070
Syringe
Brockway - March 1931 - 1798117
Hypodermic syringe and closure cap for containers
Goldberg - November 1935 - 2020828
Ampoule syringe
Smith - June 1941 - 2244969
Syringe casing and stoppered cylindrical ampoule for direct injection
Pontius - November 1953 - 2660168
Application Number:
04/854054
Publication Date:
06/08/1971
Filing Date:
08/29/1969
View Patent Images:
Export Citation:
Assignee:
Astra Chemicals Ltd. (Middissauga, Ontario, CA)
Primary Class:
Other Classes:
604/900
International Classes:
A61M5/24; A61M5/31; A61M5/24; A61J1/06
Field of Search:
128/218R,218P,218D,218DP,221,272
US Patent References:
Primary Examiner:
Reich, Joseph S.
Claims:
I claim
1. A self-aspirating syringe for use with a plunger-type cartridge ampul of the type comprising a tubular body filled with injectable filled fluid having a rear end closed by a movable piston member and a forward end closed by a flexible resilient membrane, said syringe comprising: a body member having means providing a cavity to accommodate therewithin one of said cartridge ampules, and having axially disposed openings at the front and rear ends thereof; a plunger member extending through the opening at the rear end of said cavity and slidable with respect thereto, said plunger having a head at its forward end adapted to engage the said movable piston member to slide the same forwardly within said tubular body, and a manually engageable actuator at the rear end thereof for pressing said plunger forward; means for mounting an adapter within the opening at the front end of the syringe body member, said adapter being arranged to receive and secure a hypodermic needle in axial alignment with said tubular body with the rear end of the needle extending through said flexible membrane into said injectable solution; and stud means adjacent to the front end of said body, projecting rearwardly therewithin and adapted to be engaged by said membrane whereby upon movement forward by of said tubular body under the influence of said plunger said membrane is stretched rearwardly of said tubular body, and upon release of said influence said tubular body moves rearwards under the influence of said stretched membrane to create conditions of aspiration within said tubular body.
2. A self-aspirating syringe according to claim 1 wherein said plunger member is guided to slide within a bushing carried within said opening at the rear end of the body member, said bushing having a front end adapted to extend within the rear end of the tubular body of the cartridge ampul, said bushing extending rearwardly through said opening at the rear end of said body member and being axially slidable therein, and wherein resilient means engaging said bushing are adapted controllably to bias said bushing in a forward direction.
3. A self-aspirating syringe according to claim 2 wherein said bushing carries a flange at the rear of the syringe body member by means of which the bushing can be engaged and moved axially to urge said cartridge ampul forward; whereby said membrane is stretched inwardly of said tubular body and upon release of said bushing the tubular body moves rearwards under the influence of said stretched membrane to create conditions for aspiration within said tubular body.
4. A self-aspirating syringe according to claim 2 wherein said resilient means comprises a compression spring surrounding a length of the bushing between a flange at the forward end thereof and the rear end of said body member.
5. A self-aspirating syringe according to claim 2 wherein the plunger has a head at the forward end thereof and the forward end of the bushing is formed with an enlarged recess of a size to accommodate the head of said plunger.
6. A self-aspirating syringe according to claim 1 wherein said stud means comprises a central rearwardly projecting stud integral with said adapter.
7. A self-aspirating syringe according to claim 1 wherein said stud means comprises a collar on said hypodermic needle arranged to seat against the rear face of the adapter when the needle is secured therein.
8. A plunger-type cartridge ampul for use in a hypodermic syringe comprising a generally tubular container having a rear end sealed by a piston which is movable axially of the container, and a front end sealed by a resilient membrane, the cartridge having a central forwardly projecting element at the forward end thereof which in use is operative to transmit to the membrane a deflection rearwardly of the front end of the container.
9. A plunger-type cartridge ampul according to claim 8 wherein said membrane is secured to the front end of the container by an annular collar which has a radial inwardly-projecting flange which overlies the peripheral area of said membrane, said element comprising a short tubular member extending forwardly from the membrane and having a radial outwardly extending flange retained between the membrane and the collar flange.
10. A self-aspirating syringe comprising a generally tubular body having a cavity and an open rear end and a plunger-type cartridge ampul received in said syringe body and comprising a tubular body filled with injectable fluid and having a rear end closed by a movable piston member and a forward end closed by a flexible resilient membrane, the syringe having an axially disposed plunger extending through the opening in the rear end thereof and into the cavity and being axially movable said plunger having a forward end having a head operative to engage the piston member of the ampul to slide the same forwardly within said tubular body, an actuating member at the rear end of the plunger for manual actuation thereof, the syringe having a forward end formed with an axial opening in which is received means mounting a hypodermic needle in axial alignment with the tubular body of the ampul, said needle having a rear end piercing said membrane and extending into said ampul, and abutment means positioned between the forward end of the syringe body and the resilient membrane and engaging said membrane, said abutment means being operative, upon forward movement of said ampul in said cavity under the influence of said plunger, to stretch said membrane rearwardly of said tubular body, whereby upon release of said influence said stretched membrane is operative to move said tubular body rearwardly to create conditions of aspiration within said ampul.
1. A self-aspirating syringe for use with a plunger-type cartridge ampul of the type comprising a tubular body filled with injectable filled fluid having a rear end closed by a movable piston member and a forward end closed by a flexible resilient membrane, said syringe comprising: a body member having means providing a cavity to accommodate therewithin one of said cartridge ampules, and having axially disposed openings at the front and rear ends thereof; a plunger member extending through the opening at the rear end of said cavity and slidable with respect thereto, said plunger having a head at its forward end adapted to engage the said movable piston member to slide the same forwardly within said tubular body, and a manually engageable actuator at the rear end thereof for pressing said plunger forward; means for mounting an adapter within the opening at the front end of the syringe body member, said adapter being arranged to receive and secure a hypodermic needle in axial alignment with said tubular body with the rear end of the needle extending through said flexible membrane into said injectable solution; and stud means adjacent to the front end of said body, projecting rearwardly therewithin and adapted to be engaged by said membrane whereby upon movement forward by of said tubular body under the influence of said plunger said membrane is stretched rearwardly of said tubular body, and upon release of said influence said tubular body moves rearwards under the influence of said stretched membrane to create conditions of aspiration within said tubular body.
2. A self-aspirating syringe according to claim 1 wherein said plunger member is guided to slide within a bushing carried within said opening at the rear end of the body member, said bushing having a front end adapted to extend within the rear end of the tubular body of the cartridge ampul, said bushing extending rearwardly through said opening at the rear end of said body member and being axially slidable therein, and wherein resilient means engaging said bushing are adapted controllably to bias said bushing in a forward direction.
3. A self-aspirating syringe according to claim 2 wherein said bushing carries a flange at the rear of the syringe body member by means of which the bushing can be engaged and moved axially to urge said cartridge ampul forward; whereby said membrane is stretched inwardly of said tubular body and upon release of said bushing the tubular body moves rearwards under the influence of said stretched membrane to create conditions for aspiration within said tubular body.
4. A self-aspirating syringe according to claim 2 wherein said resilient means comprises a compression spring surrounding a length of the bushing between a flange at the forward end thereof and the rear end of said body member.
5. A self-aspirating syringe according to claim 2 wherein the plunger has a head at the forward end thereof and the forward end of the bushing is formed with an enlarged recess of a size to accommodate the head of said plunger.
6. A self-aspirating syringe according to claim 1 wherein said stud means comprises a central rearwardly projecting stud integral with said adapter.
7. A self-aspirating syringe according to claim 1 wherein said stud means comprises a collar on said hypodermic needle arranged to seat against the rear face of the adapter when the needle is secured therein.
8. A plunger-type cartridge ampul for use in a hypodermic syringe comprising a generally tubular container having a rear end sealed by a piston which is movable axially of the container, and a front end sealed by a resilient membrane, the cartridge having a central forwardly projecting element at the forward end thereof which in use is operative to transmit to the membrane a deflection rearwardly of the front end of the container.
9. A plunger-type cartridge ampul according to claim 8 wherein said membrane is secured to the front end of the container by an annular collar which has a radial inwardly-projecting flange which overlies the peripheral area of said membrane, said element comprising a short tubular member extending forwardly from the membrane and having a radial outwardly extending flange retained between the membrane and the collar flange.
10. A self-aspirating syringe comprising a generally tubular body having a cavity and an open rear end and a plunger-type cartridge ampul received in said syringe body and comprising a tubular body filled with injectable fluid and having a rear end closed by a movable piston member and a forward end closed by a flexible resilient membrane, the syringe having an axially disposed plunger extending through the opening in the rear end thereof and into the cavity and being axially movable said plunger having a forward end having a head operative to engage the piston member of the ampul to slide the same forwardly within said tubular body, an actuating member at the rear end of the plunger for manual actuation thereof, the syringe having a forward end formed with an axial opening in which is received means mounting a hypodermic needle in axial alignment with the tubular body of the ampul, said needle having a rear end piercing said membrane and extending into said ampul, and abutment means positioned between the forward end of the syringe body and the resilient membrane and engaging said membrane, said abutment means being operative, upon forward movement of said ampul in said cavity under the influence of said plunger, to stretch said membrane rearwardly of said tubular body, whereby upon release of said influence said stretched membrane is operative to move said tubular body rearwardly to create conditions of aspiration within said ampul.
Description:
BACKGROUND OF THE INVENTION
This invention relates to improvements in hypodermic syringes and in particular to a new or improved self-aspirating syringe. "Aspiration" is the procedure whereby an operator in making an injection determines whether or not the needle is in a proper position for injecting to prevent inadvertent deposition of injection solution directly into a blood vessel which could cause untoward patient reaction. After the needle has been inserted in the area to be injected, the syringe is manipulated to create a reduced pressure within the fluid to be injected whereby if the needle is uncorrectly positioned, blood from the area to be injected is drawn back through the hypodermic needle into the syringe where it can be observed by the operator.
DESCRIPTION OF THE PRIOR ART
In the medical, dental and veterinary fields cartridge ampuls of injectable fluid are now commonly used in hypodermic syringes. Such ampuls usually comprise a cylindrical container of glass or clear plastics material, the forward end of which is sealed by a rubber membrane and the rear end of which is sealed by a rubber piston which is slidable within the body of the container. In use such cartridge ampuls are positioned within the barrel of a syringe so that the membrane is pierced by the rear end of the needle and the rubber piston is advanced by a thumb-operated plunger to inject the fluid. Where such a syringe is required to be capable of aspiration, it has generally been found necessary to form the syringe plunger with a pointed tip having barbs or flukes so that when the plunger is pressed forward to engage the piston of the ampul, the barbs or flukes bite into the material of the piston so that the piston can be drawn rearward slightly by the plunger to create conditions of aspiration within the ampul.
SUMMARY OF THE INVENTION
According to the present invention there is provided a self-aspirating syringe adapted for use with a plunger-type cartridge ampul of the type comprising a tubular body filled with injectable fluid closed at one end by a movable piston member and at the other end by a flexible membrane, said syringe comprising: a body member having a cavity adapted to accommodate therewithin one of said cartridge ampuls, and having axially disposed openings at the front and rear ends thereof; a plunger member extending through the opening at the rear end of said cavity and slidable with respect thereto, said plunger having a head at its forward end adapted to engage the said movable piston member to slide the same forwardly within said tubular body, and a thumb piece or palm rest at the rear end thereof for pressing said plunger forward; a adapter within the opening at the front end of the syringe body member arranged to receive and secure hypodermic needle in axial alignment with said tubular body with the rear end of the needle extending through said flexible membrane into said injectable solution; and stud means at the front end of said cavity projecting rearwardly thereof and adapted to engate said membrane whereby upon movement forward of said tubular body under the influence of said plunger, said membrane is stretched rearwardly of said tubular body, and upon release of said influence said tubular body moves rearwards under the influence of said stretched membrane to create conditions of aspiration within said tubular body.
With this arrangement, conditions of aspiration are created within the ampul each time the plunger is released.
Preferably the plunger is guided within a bushing in the opening in the rear end of the body member, the bushing itself being movable axially of the opening and being resilient urged in a forwards direction to engage the rear end of the cartridge ampul. Preferably, the rear end of the bushing carries a flange to the rear of the syringe body whereby the bushing can be manually engaged and moved axially to cause aspiration of the syringe without movement of the plunger. The stud means may comprise a central rearwardly projecting stud integral with the adapter or alternatively may comprise a collar on the hypodermic needle itself arranged to seat against the rear face of the adapter when the needle is secured therein.
From another aspect, the invention provides a plunger-type cartridge ampul comprising a generally tubular container having a rear end sealed by a piston which is movable axially of the container, and a front end sealed by a resilient membrane associated with which is a central forwardly projecting element which is capable of transmitting to the membrane a deflection inwards of the front end of the container. The forwardly projecting element associated with the membrane performs the same function as the stud means referred to above in the aspiration of the syringe.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will further be described with reference to the accompanying drawings wherein:
FIG. 1 is a perspective view of a plunger-type cartridge ampul;
FIG. 2 is a longitudinal sectional view of a self-aspirating hypodermic syringe according to the invention;
FIG. 3 and 4 are fragmentary sectional views to a larger scale illustrating details of the operation of the syringe of FIG. 2;
FIG. 5 is a fragmentary sectional view showing a modified syringe; and
FIG. 6 is a fragmentary longitudinal sectional view of a modified cartridge ampul according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a cartridge ampul 10 of known kind which comprises a container defined by generally cylindrical glass wall sealed at one end by a rubber piston 11 and at the other end by a rubber membrane 12. The injectable fluid is sealed in the container between the piston 11 and membrane 12. The membrane is secured against the end of the container by an annular sheet metal collar 13, one end of which is spun or crimped into a depression 14 in the surface of the container and the other end of which carries an inwardly projecting radial flange 15 which overlies the peripheral area of the membrane and presses it against the end of the container.
The syringe generally indicated at 16 in FIG. 2, comprises a cylindrical barrel 17 defining a cavity 18 to receive a cartridge ampul 10. As is common practice, the barrel 17 is formed with a large axially extending aperture (not shown) in its wall to permit insertion and removal of the ampul. The forward end of the barrel is secured to a fitting 19 formed with a central axially directed screw-threaded opening 20. An adapter 21 in threaded engagement with the opening 20 is formed with a central stud 22 which projects rearwardly into the cavity 18. The front end of the adapter 21 is formed with a spigot 23 which is in threaded engagement with a hub 24 which carries an axially extending hypodermic needle 25. The needle 25 extends rearwardly from the hub through an axial bore 26 in the adapter and in the stud 22 and extends into the cavity 18 beyond the stud 22.
The rear end of the barrel 17 is received in a fitting 27 which carries a pair of laterally extending finger grips 28. A sleeve 29 in threaded engagement with the fitting 27 carries at its rear end a gland 30 having a radial flange 31. The gland 30 extends forwardly within the sleeve 29 and its inner surface forms a smooth cylindrical continuation of the inner surface of the barrel 17. A bushing 32, which extends through an axial hole in the gland 30, has a flanged head 33 which is guided for reciprocating movement by the cylindrical inner surface of the gland. The rear end of the bushing 32 carries a radially extending flange 34 secured thereto by a retaining clip 35. The bushing is surrounded within the gland 30 by a compression spring 36 acting between the flanged head 33 and the end wall of the gland 30 and urging the bushing in a forward direction.
The bushing is preferably of a low friction material such as nylon and is formed with a central bore within which is slidably received a plunger 37. The forward end of the plunger carries a head 38 adapted to engage the rubber piston of an ampul 10. The plunger 37 may be pressed forward by means of a thumb plate 39 carried on the rear end thereof. In the retracted position of the plunger 37, the head 38 is received in a recess 40 in the forward end of the flanged head of the bushing 32.
To load a cartridge ampul into the syringe 16, the plunger 37 is withdrawn rearwardly and the ampul is inserted through the aperture in the barrel 17, plunger end first. The plunger is thereafter released and the bushing 32 is advanced under the force of the compression spring 36 until the flanged head thereof engages the end of the cylindrical wall of the ampul. This movement forces the ampul 10 forward so that the membrane 12 of the ampul is pierced by the rear end of the hypodermic needle 25. In this position the end of the stud 22 at the forward end of the cavity 18 rests against the membrane 12 but the strength of the spring 36 is chosen such that this engagement does not cause any appreciable deflection of the membrane.
Subsequent forward pressure applied to the thumb plate 39 forces the ampul 10 forwards until the flange 15 of the collar 13 engages the end face of the adapter 21 as shown in FIG. 3. In reaching this position, the membrane 12 is deflected by the stud 22 as shown in the Figure. Forward pressure applied to the thumb plate 39 will now cause the piston 11 to be advanced within the ampul 10 so that the fluid from the ampul is ejected through the needle 25. Upon release of the thumb plate 39, the syringe is automatically aspirated by the resilient action of the membrane 12 which restores to its normal position as indicated in FIG. 4 thus causing conditions of reduced pressure within the ampul 10. Aspiration can also be effected by pressing forward and releasing the flange 34 of the bushing 32 as indicated by the arrows in FIG. 2. The piston 11 is adapted to engage the internal wall of the ampul 10 with sufficient friction to enable the head 38 to cause the membrane 12 to be flexed as shown in FIGS. 3 and 4, and also to permit the ejection of the contents of the ampul when and as desired.
An alternative arrangement is shown in FIG. 5 wherein an adapter 21a, also constitutes a hub to secure a hypodermic needle 25a in the forward end of the syringe. In this case the stud means is formed not on the adapter but as a collar 41 on the needle 25a itself. As shown, the collar 41 is positioned to the rear of the adapter 21a and performs a function similar to that of the stud 22 in the embodiment of FIGS. 2 to 4.
Alternatively, the stud means instead of being associated with the syringe or with the needle can be formed as an integral part of the ampul. Thus, as shown in FIG. 6, an ampul 10b, generally similar to the one illustrated in FIG. 1, has an aspirating element 42 positioned between the collar 13b and the membrane 12b. The element 42 comprises an outwardly extending radial flange 43 positioned between the radial flange 15b of the collar 13b and the membrane 12b and a forwardly extending tubular portion 44 extending from the front end of the ampul. It will be apparent that the ampul 10b, when fitted in a syringe 16 of the type shown in FIG. 2, the adapter of which does not have the stud 22, will perform the same aspirating function as the stud 22 or as the collar 41 in the embodiment shown in FIG. 5.
This invention relates to improvements in hypodermic syringes and in particular to a new or improved self-aspirating syringe. "Aspiration" is the procedure whereby an operator in making an injection determines whether or not the needle is in a proper position for injecting to prevent inadvertent deposition of injection solution directly into a blood vessel which could cause untoward patient reaction. After the needle has been inserted in the area to be injected, the syringe is manipulated to create a reduced pressure within the fluid to be injected whereby if the needle is uncorrectly positioned, blood from the area to be injected is drawn back through the hypodermic needle into the syringe where it can be observed by the operator.
DESCRIPTION OF THE PRIOR ART
In the medical, dental and veterinary fields cartridge ampuls of injectable fluid are now commonly used in hypodermic syringes. Such ampuls usually comprise a cylindrical container of glass or clear plastics material, the forward end of which is sealed by a rubber membrane and the rear end of which is sealed by a rubber piston which is slidable within the body of the container. In use such cartridge ampuls are positioned within the barrel of a syringe so that the membrane is pierced by the rear end of the needle and the rubber piston is advanced by a thumb-operated plunger to inject the fluid. Where such a syringe is required to be capable of aspiration, it has generally been found necessary to form the syringe plunger with a pointed tip having barbs or flukes so that when the plunger is pressed forward to engage the piston of the ampul, the barbs or flukes bite into the material of the piston so that the piston can be drawn rearward slightly by the plunger to create conditions of aspiration within the ampul.
SUMMARY OF THE INVENTION
According to the present invention there is provided a self-aspirating syringe adapted for use with a plunger-type cartridge ampul of the type comprising a tubular body filled with injectable fluid closed at one end by a movable piston member and at the other end by a flexible membrane, said syringe comprising: a body member having a cavity adapted to accommodate therewithin one of said cartridge ampuls, and having axially disposed openings at the front and rear ends thereof; a plunger member extending through the opening at the rear end of said cavity and slidable with respect thereto, said plunger having a head at its forward end adapted to engage the said movable piston member to slide the same forwardly within said tubular body, and a thumb piece or palm rest at the rear end thereof for pressing said plunger forward; a adapter within the opening at the front end of the syringe body member arranged to receive and secure hypodermic needle in axial alignment with said tubular body with the rear end of the needle extending through said flexible membrane into said injectable solution; and stud means at the front end of said cavity projecting rearwardly thereof and adapted to engate said membrane whereby upon movement forward of said tubular body under the influence of said plunger, said membrane is stretched rearwardly of said tubular body, and upon release of said influence said tubular body moves rearwards under the influence of said stretched membrane to create conditions of aspiration within said tubular body.
With this arrangement, conditions of aspiration are created within the ampul each time the plunger is released.
Preferably the plunger is guided within a bushing in the opening in the rear end of the body member, the bushing itself being movable axially of the opening and being resilient urged in a forwards direction to engage the rear end of the cartridge ampul. Preferably, the rear end of the bushing carries a flange to the rear of the syringe body whereby the bushing can be manually engaged and moved axially to cause aspiration of the syringe without movement of the plunger. The stud means may comprise a central rearwardly projecting stud integral with the adapter or alternatively may comprise a collar on the hypodermic needle itself arranged to seat against the rear face of the adapter when the needle is secured therein.
From another aspect, the invention provides a plunger-type cartridge ampul comprising a generally tubular container having a rear end sealed by a piston which is movable axially of the container, and a front end sealed by a resilient membrane associated with which is a central forwardly projecting element which is capable of transmitting to the membrane a deflection inwards of the front end of the container. The forwardly projecting element associated with the membrane performs the same function as the stud means referred to above in the aspiration of the syringe.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will further be described with reference to the accompanying drawings wherein:
FIG. 1 is a perspective view of a plunger-type cartridge ampul;
FIG. 2 is a longitudinal sectional view of a self-aspirating hypodermic syringe according to the invention;
FIG. 3 and 4 are fragmentary sectional views to a larger scale illustrating details of the operation of the syringe of FIG. 2;
FIG. 5 is a fragmentary sectional view showing a modified syringe; and
FIG. 6 is a fragmentary longitudinal sectional view of a modified cartridge ampul according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a cartridge ampul 10 of known kind which comprises a container defined by generally cylindrical glass wall sealed at one end by a rubber piston 11 and at the other end by a rubber membrane 12. The injectable fluid is sealed in the container between the piston 11 and membrane 12. The membrane is secured against the end of the container by an annular sheet metal collar 13, one end of which is spun or crimped into a depression 14 in the surface of the container and the other end of which carries an inwardly projecting radial flange 15 which overlies the peripheral area of the membrane and presses it against the end of the container.
The syringe generally indicated at 16 in FIG. 2, comprises a cylindrical barrel 17 defining a cavity 18 to receive a cartridge ampul 10. As is common practice, the barrel 17 is formed with a large axially extending aperture (not shown) in its wall to permit insertion and removal of the ampul. The forward end of the barrel is secured to a fitting 19 formed with a central axially directed screw-threaded opening 20. An adapter 21 in threaded engagement with the opening 20 is formed with a central stud 22 which projects rearwardly into the cavity 18. The front end of the adapter 21 is formed with a spigot 23 which is in threaded engagement with a hub 24 which carries an axially extending hypodermic needle 25. The needle 25 extends rearwardly from the hub through an axial bore 26 in the adapter and in the stud 22 and extends into the cavity 18 beyond the stud 22.
The rear end of the barrel 17 is received in a fitting 27 which carries a pair of laterally extending finger grips 28. A sleeve 29 in threaded engagement with the fitting 27 carries at its rear end a gland 30 having a radial flange 31. The gland 30 extends forwardly within the sleeve 29 and its inner surface forms a smooth cylindrical continuation of the inner surface of the barrel 17. A bushing 32, which extends through an axial hole in the gland 30, has a flanged head 33 which is guided for reciprocating movement by the cylindrical inner surface of the gland. The rear end of the bushing 32 carries a radially extending flange 34 secured thereto by a retaining clip 35. The bushing is surrounded within the gland 30 by a compression spring 36 acting between the flanged head 33 and the end wall of the gland 30 and urging the bushing in a forward direction.
The bushing is preferably of a low friction material such as nylon and is formed with a central bore within which is slidably received a plunger 37. The forward end of the plunger carries a head 38 adapted to engage the rubber piston of an ampul 10. The plunger 37 may be pressed forward by means of a thumb plate 39 carried on the rear end thereof. In the retracted position of the plunger 37, the head 38 is received in a recess 40 in the forward end of the flanged head of the bushing 32.
To load a cartridge ampul into the syringe 16, the plunger 37 is withdrawn rearwardly and the ampul is inserted through the aperture in the barrel 17, plunger end first. The plunger is thereafter released and the bushing 32 is advanced under the force of the compression spring 36 until the flanged head thereof engages the end of the cylindrical wall of the ampul. This movement forces the ampul 10 forward so that the membrane 12 of the ampul is pierced by the rear end of the hypodermic needle 25. In this position the end of the stud 22 at the forward end of the cavity 18 rests against the membrane 12 but the strength of the spring 36 is chosen such that this engagement does not cause any appreciable deflection of the membrane.
Subsequent forward pressure applied to the thumb plate 39 forces the ampul 10 forwards until the flange 15 of the collar 13 engages the end face of the adapter 21 as shown in FIG. 3. In reaching this position, the membrane 12 is deflected by the stud 22 as shown in the Figure. Forward pressure applied to the thumb plate 39 will now cause the piston 11 to be advanced within the ampul 10 so that the fluid from the ampul is ejected through the needle 25. Upon release of the thumb plate 39, the syringe is automatically aspirated by the resilient action of the membrane 12 which restores to its normal position as indicated in FIG. 4 thus causing conditions of reduced pressure within the ampul 10. Aspiration can also be effected by pressing forward and releasing the flange 34 of the bushing 32 as indicated by the arrows in FIG. 2. The piston 11 is adapted to engage the internal wall of the ampul 10 with sufficient friction to enable the head 38 to cause the membrane 12 to be flexed as shown in FIGS. 3 and 4, and also to permit the ejection of the contents of the ampul when and as desired.
An alternative arrangement is shown in FIG. 5 wherein an adapter 21a, also constitutes a hub to secure a hypodermic needle 25a in the forward end of the syringe. In this case the stud means is formed not on the adapter but as a collar 41 on the needle 25a itself. As shown, the collar 41 is positioned to the rear of the adapter 21a and performs a function similar to that of the stud 22 in the embodiment of FIGS. 2 to 4.
Alternatively, the stud means instead of being associated with the syringe or with the needle can be formed as an integral part of the ampul. Thus, as shown in FIG. 6, an ampul 10b, generally similar to the one illustrated in FIG. 1, has an aspirating element 42 positioned between the collar 13b and the membrane 12b. The element 42 comprises an outwardly extending radial flange 43 positioned between the radial flange 15b of the collar 13b and the membrane 12b and a forwardly extending tubular portion 44 extending from the front end of the ampul. It will be apparent that the ampul 10b, when fitted in a syringe 16 of the type shown in FIG. 2, the adapter of which does not have the stud 22, will perform the same aspirating function as the stud 22 or as the collar 41 in the embodiment shown in FIG. 5.