Medical syringe abstract
A medical syringe has a tubular body extending along an axis and
having a front end and a rear end, a plunger axially slidable in
the body and carrying a stem projecting axially rearward out of
the body from the plunger, and a free piston slidable in the body
forward of the plunger and subdividing the body forward of the plunger
into a front compartment at the front body end and a rear compartment
between the plunger and the piston. The body is formed with a bypass
passage forward of the piston in a starting position so the front
compartment can hold a soluble medicament and the rear compartment
can hold its solvent. Structure at the rear body end forms a radially
inwardly open angularly limited cutout and at least two axially
spaced, angularly offset, and radially outwardly projecting stop
bumps on the stem are axially displaceable through the cutout in
respective angularly offset positions of the stem. The stop bumps
are axially engageable against the structure except when the stem
is in the respective angular position. An elastically deformable
brake element engaged between the body and the stem for axially
slowing axial forward advance of the stem.
Medical syringe claims
We claim:
1. A medical syringe comprising: a tubular syringe body extending
along an axis and having a front end and a rear end; a plunger axially
slidable in the body; a stem projecting axially rearward out of
the body from the plunger; a free piston slidable in the body forward
of the plunger and subdividing the body forward of the plunger into
a front compartment at the front body end and a rear compartment
between the plunger and the piston, the body being formed with a
bypass passage; structure at the rear body end forming a radially
inwardly open angularly limited cutout; at least two axially spaced,
angularly offset, and radially outwardly projecting stop bumps on
the stem axially displaceable through the cutout in respective angularly
offset positions of the stem, the stop bumps being axially engageable
against the structure except when the stem is in the respective
angular position; and means including an elastically deformable
brake element engaged between the body and the stem for axially
slowing axial forward advance of the stem.
2. The medical syringe defined in claim 1 wherein the stop bumps
are provided in pairs with the bumps of each pair diametrically
opposite each other but axially level with each other, the structure
being formed with two such cutouts diametrically opposite each other.
3. The medical syringe defined in claim 1 wherein the stop bumps
are offset by about 90.degree. to each other relative to the axis.
4. The medical syringe defined in claim 1 wherein the stop bumps
include a frontmost stop bump that is in axial engagement with the
structure when the plunger is axially forwardly engaged with the
piston.
5. The medical syringe defined in claim 1 wherein the stop bumps
are axially uniformly spaced along the stem.
6. The medical syringe defined in claim 1 wherein the brake element
is a forwardly directed flexible lip.
7. The medical syringe defined in claim 1 wherein the bumps have
angled front flanks and rear flanks extending in planes generally
perpendicular to the axis.
8. The medical syringe defined in claim 1 wherein the stem is formed
with an axially extending row of bumps engageable with the brake
element.
9. The medical syringe defined in claim 8 wherein the bumps are
of sawtooth shape with an angled front flank and a perpendicular
rear flank and the element is a flexible lip extending radially
inward and axially forward from the body rear end.
10. The medical syringe defined in claim 1 wherein the cutout has
generally radially extending end flanks.
Medical syringe description
FIELD OF THE INVENTION
The present invention relates to a medical syringe. More particularly
this invention concerns such a syringe which is prefilled with a
liquid and powder and which is set up for mixing the liquid and
powder immediately before use.
BACKGROUND OF THE INVENTION
A standard syringe has a tubular body with a front end adapted
to receive a needle or cannula and a rear end formed with radially
projecting finger braces. A plunger is axially displaceable in the
body and has a rod projecting axially rearwardly from the rear end
so that, when the plunger is advanced, liquid is expressed through
the needle mounted on the front end.
In prefilled syringes a piston is provided in the body forward
of the plunger and subdivides the body in a starting position into
a front compartment that is typically filled with a freeze-dried
medicament powder and a rear compartment that is filled with a solvent,
typically distilled water. Immediately forward of the piston in
the starting position is a bypass normally formed as an inwardly
open and axially extending groove. Thus when the plunger is advanced,
the liquid in the rear compartment moves the piston forward until
the rear end of the bypass groove is exposed in the rear compartment.
Further advance of the plunger forces the liquid in the rear compartment
past the piston into the front compartment where it mixes with the
medicament therein. When the plunger comes to rest on the rear face
of the piston and all of the liquid in the rear compartment has
been driven through the bypass into the front compartment, further
advance of the plunger pushes the piston forward and expresses the
mixed liquid and medicament from the front end of the syringe body.
The medicament takes some time to dissolve so it is known to provide
screwthreads between at least a portion of the plunger rod and the
syringe body. Thus during at least the initial stages of advance
of the plunger, the rod must be screwed into the syringe body ensuring
slow and deliberate advance that gives the medicament time to mix
and dissolve in the liquid being pumped through the bypass into
the front compartment.
The problem with this system is that it takes two hands to manipulate
the syringe for the mixing operation, one holding the syringe body
and the other rotating the plunger. Furthermore the screwthreads
make the syringe more expensive to manufacture and more difficult
to assemble, unnecessarily increasing the cost of this mass-produced
throw-away item.
Another difficulty with the known medical syringes is that it is
frequently necessary, for instance when treating hives or dosing
anesthetic, to inject carefully metered quantities of the medicament.
This is typically done by providing a scale on the side of the syringe.
The user must therefore be in a position to see the scale, something
that is frequently impossible when an injection is actually being
given, and even so it is difficult to accurately gauge the tiny
plunger movements necessary to dispense the small quantities that
often are needed.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an
improved medical syringe.
Another object is the provision of such an improved medical syringe
which overcomes the above-given disadvantages, that is which makes
it easy to accurately dispense small quantities of medicament.
A further object is to provide a mixer-type syringe which is of
simple construction but which ensures slow and controlled mixing
of the liquid and solid phases of the mixed medicament.
SUMMARY OF THE INVENTION
A medical syringe has according to the invention a tubular body
extending along an axis and having a front end and a rear end, a
plunger axially slidable in the body and carrying a stem projecting
axially rearward out of the body from the plunger, and a free piston
slidable in the body forward of the plunger and subdividing the
body forward of the plunger into a front compartment at the front
body end and a rear compartment between the plunger and the piston.
The body is formed with a bypass passage forward of the piston in
a starting position so the front compartment can hold a soluble
medicament and the rear compartment can hold its solvent. Structure
at the rear body end forms a radially inwardly open angularly limited
cutout and at least two axially spaced, angularly offset, and radially
outwardly projecting stop bumps on the stem are axially displaceable
through the cutout in respective angularly offset positions of the
stem. The stop bumps are axially engageable against the structure
except when the stem is in the respective angular position. An elastically
deformable brake element engaged between the body and the stem for
axially slowing axial forward advance of the stem.
Thus with this system the brake element will prevent the plunger
from advancing too rapidly, so that the solvent in the rear compartment
will be pumped at a slow uniform rate around the piston through
the bypass to the front compartment. The stop bumps stop advance
of the piston and plunger, requiring the user to twist the piston
stem to align those stop bumps striking the body rear end with the
cutouts for further advance. Thus once the syringe has been fitted
with a needle, cleared of air, stuck into a vein, and tested, the
user can simply push down on the stem until the next set of stop
bumps arrests its further advance, automatically dispensing a metered
dose of the mixed medicament. A further dose can be administered
once the stem is angularly indexed, and so on until the syringe
is empty. The rearmost set of stop bumps includes at least one extra
bump so that they define a frontmost end position for the piston
and plunger.
The stop bumps according to the invention are provided in pairs
with the bumps of each pair diametrically opposite each other but
axially level with each other. The structure is formed with two
such cutouts diametrically opposite each other. Normally each pair
is offset by 900 to the preceding and following pairs.
They are spaced apart by a distance that is exactly that necessary
to express a predetermined dose from the syringe. In fact the prefilled
syringes can be provided with stems having differently spaced bumps,
each such stem having an identifying color so that a user will know
what the standard dose for a given syringe is according to its stem
color. The doses can therefore be administered without looking.
The stop bumps include a frontmost stop bump that is in axial engagement
with the structure when the plunger is axially forwardly engaged
with the piston. Thus the user will know exactly when the rear compartment
has been emptied and will not further advance the stem and waste
the often valuable medicament.
The stop bumps are axially uniformly spaced along the stem and
have generally radially extending end flanks. The brake element
is a forwardly directed flexible lip. The cutouts can be rectangular,
seen axially, or formed as sectors.
The bumps can also have angled front flanks and rear flanks extending
in planes generally perpendicular to the axis, like sawteeth. The
stem is formed with an axially extending row of bumps engageable
with the brake element. These bumps also are of sawtooth shape with
an angled front flank and a perpendicular rear flank and the element
is a flexible lip extending radially inward and axially forward
from the body rear end.
BRIEF DESCRIPTION OF THE DRAWING
The above and other objects, features, and advantages will become
more readily apparent from the following description, reference
being made to the accompanying drawing in which:
FIGS. 1a to 1f are axial sections through a syringe at succeeding
steps of use;
FIGS. 2a, 2b, and 2c are sections taken along respective lines
IIa--IIa, IIb--IIb, and IIc--IIc of respective FIGS. 1a, 1b, and
1c;
FIGS. 3a to 3e are axial sections through another syringe according
to the invention as it expresses succeeding doses of mixed medicament;
and
FIG. 4 is a section taken along line IV--IV of FIG. 3a.
SPECIFIC DESCRIPTION
As seen in the drawing, a syringe has a basically tubular glass
or plastic body 1 centered on an axis A and slidably receiving a
plunger 2. A rod or stem 3 projects axially rearward from the plunger
2 through a hole 5 in a finger-brace end cap 4. A free piston 6
subdivides the tube 1 forward of the plunger 2 into a front compartment
7 that is to start with filled with a soluble medicament, normally
in powder form, and a rear compartment 8 that to start with is filled
with a liquid solvent for the medicament. A radially inwardly open
and axially extending bypass groove 9 is formed in the tube 1 forward
of the piston 6 in the FIG. 1a starting position. Initially the
front end of the tube 1 is covered by a cap 14 which is replaced
for use by a needle or cannula 15.
According to the invention the rod 3 is formed with two diametrically
opposite and axially extending rows of radially outwardly projecting
and axially uniformly spaced brake lugs 10. Each lug 10 is axially
level with a diametrically opposite such lug 10 and each lug 10
has a rear flank extending perpendicular to the axis A and a front
flank inclined at about 45.degree. to the axis A, giving them a
right-triangular or sawtooth shape. Seen from the end (FIGS. 2a-2c)
each lug 10 is basically rectangular.
The end cap 4 on the rear end of the tube 1 is formed with diametrically
opposite inwardly open cutouts 11 each extending over 90.degree.
and of a radial depth slightly greater than the radial height of
the lugs 11. In addition each cutout 11 is provided with a respective
radially inwardly and axially forwardly extending brake lip or tab
12 that forms with the lugs 10 a ratchet-type brake.
Thus as the plunger 2 is moved from the starting position of FIG.
1a to that of FIG. 1b, the liquid in the back compartment 8 will
be forced through the bypass 9 to mix with the powder in the front
compartment 7. As this is happening according to the invention the
lugs 10 will ratchet on the tabs 12 to slow advance of the plunger
2 and thereby ensure that the liquid from the compartment 8 is pumped
slowly into the front compartment 7 giving the medicament time
to dissolve.
The rod 3 is formed rearward of the brake lugs 10 with two diametrically
oppositely extending stop bumps 13a that are offset by 90.degree.
to the rows of lugs 10 and rearward therefrom by four more such
bumps 13b angularly equispaced about the axis A. The position of
the two front stop bumps 13a is such that they abut the rear surface
of the end cap 4 when the plunger 2 bottoms on the rear face of
the piston 6 as shown in FIG. 1c. To advance the plunger 2 and piston
6 further, it is necessary to rotate the stem 3 through 90.degree.
so that the bumps 13a can pass through the cutouts 11. The bottoming
of the front stops 13a on the finger brace 4 can be sensed by the
user who will then know that the mixing operation is over and that
he or she can proceed to clearing air from the syringe and actually
using it. Thereafter as shown in FIG. 1d, further advance of the
plunger 2 will expel the mixture from the front compartment 7 and
retraction as shown in FIG. 1e will allow blood to be drawn back
to insure that the stick is good.
In the system of FIGS. 3a-3f the stem 3 is formed with several
intermediate pairs of stop bumps 13c, with each succeeding pair
offset angularly from the pair preceding it and the pair following
it. Thus each intermediate bump 13c is associated with a diametrically
opposite such bump 13c that is axially level with it, and the pairs
of bumps 13a, 13b, and 13c, are axially uniformly spaced. The spacing
between adjacent stop-bump pairs is equal to a predetermined axial
displacement of the plunger 2 which in turn expresses a predetermined
volume of liquid from the tube 1. Thus the user can only advance
the plunger 2 a certain distance before he or she must rotate the
stem 3 through 90.degree. to be able to advance it again through
a similar distance, expressing an accurate dose of the medicament
with each stepping of the piston 2. The result is extremely accurate
dosing that can be done entirely by feel. |