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BACKGROUND OF THE INVENTION
The present invention relates to devices for dispensing fluids at a slow
rate for a sustained period of time, and in one important aspect to such
devices used for dispensing medicinal fluids into a patient's body.
The art is replete with various devices adapted for dispensing medicinal
fluids at a slow sustained rate, U.S. Pat. Nos. 2,295,849; 2,602,446;
2,605,765; 3,279,653; 3,398,860; 3,468,308; 3,469,578; 3,486,539;
3,895,631 and 3,951,147 being illustrative examples.
While the fluid dispensing devices described in these patents may with
varying facility be able to dispense fluids into patients, most are more
complex than may be desired, many require activation or regulation by a
person attaching them which if improperly done can result in the wrong
dispensing rate, and most do not provide the level of protection against
inadvertent improper operation of the device or tampering with the device
by the patient or another that may be desired.
SUMMARY OF THE INVENTION
The present invention provides a device for dispensing fluid at a slow
uniform rate over a sustained period of time which has a simple,
inexpensive structure, is easy to use, requires no regulation or
adjustment by the persons using the device, and which is well-safeguarded
against tampering with or inadvertent improper operation of the device.
The dispensing device comprises a metering assembly adapted to be coupled
to a conventional syringe, which metering assembly includes a length of
capillary tubing through which the fluid must pass into a length of
flexible hose which delivers the fluid to a patient, and means for
applying a uniform force to the plunger to provide fluid flow through the
capillary tube at a slow, steady rate over a long period of time (e.g., in
the range of 1 to 40 milliliters per hour).
The rate of flow Q in cc/sec through the capillary tube can be estimated
from Poiseuille's Law expressed in the equation:
Q=(Pr.sup.4)/81n
where P is the pressure drop through the tube in dynes/cm.sup.2, r is the
internal radius of the tube in cm, 1 is the length of the tube in cm, and
n is the liquid viscosity in poise.
By solving this equation it can be found that capillary tubes of a
reasonable length suitable for restricting flow to rates in the range
indicated under the influence of pressures of the range of pressures
easily developed in a syringe (e.g., about 69,000 to 2,068,400
dynes/cm.sup.2) can have bores in the range of about 0.0025 to 0.023 cm.
With current technology it is difficult to produce capillary tubing in
this size range with bore diameters which deviate less than about 10% from
a nominal diameter, however. Since the rate of flow through a tube is
proportional to the forth power of its diameter, such a deviation could
cause a variation of about -34% to +46% in flow rate, which would be
unacceptable for most medical uses. By only using long lengths of
capillary tubing, however, (i.e., capillary tubes over 2 centimeter in
length) much less variation in flow rates is found between different
lengths of capillary tubing than is suggested above; perhaps because
diameter variations tend to cancel each other along the length of the
capillary tubes. With capillary tubing of polytetrafluoroethylene sold
under the trade designation "Teflon" (which is preferred) having a nominal
inside diameter in the range of 0.0025 to 0.023 cm, it has been found that
lengths of the capillary tubing in excess of 2 cm. Normally produce flow
rate variations of less than 10%, which is acceptable for medical use of
the device described herein.
Metering assemblies having capillary tubes of different nominal diameters
which afford different rates of fluid flow (which rates, for example, may
be indicated by color coding of the metering devices) can be used
interchangeably in the device, it being contemplated that the inexpensive
metering devices and the hoses attached thereto could be disposed of after
use to insure sanitation for medical or other uses.
To afford initial purging of air from the hose attached to the metering
assembly with fluid from the syringe, the metering assembly includes parts
moveable between a metering position at which fluid flowing through the
metering assembly must pass through the capillary tubing, and a purging
position at which fluid propelled by manual operation of the syringe can
bypass the capillary tube and flow rapidly through the metering assembly
to purge the hose.
The device, however, insures that the metering assembly is in its metering
position when inserted in the dispensing device to preclude operation of
the device with the metering assembly in its purge position. Support means
on the device (which both supports the metering assembly and a syringe
coupled thereto and is included as part of a frame for the device) is
specially adapted so that it will engage and support the metering assembly
only when it is in its metering position.
Also the device includes manually operated activating means which allows
the syringe and the metering assembly attached thereto to be easily
inserted in or removed from the device, and which secures the syringe and
metering assembly in the device so they may not be tampered with when the
spring means is engaged with the syringe.
The activating means includes a cover which is manually moveable between
open and closed positions and is coupled to the spring means to move it to
a disengaged position when the cover is opened so that a metering assembly
coupled to a syringe may be inserted in the support means; and to move the
spring means to an engaged position at which the spring means will apply a
uniform force against the plunger of the syringe to cause fluid to flow
through the metering assembly into the hose when the cover is moved to its
closed position at which the cover encloses the syringe and spring means.
Also included are means for releasably latching the cover in its closed
position at which an edge portion of the cover will engage the metering
assembly in the support means. Thus access to the syringe or removal of
the metering assembly from the support means are precluded unless the
cover is opened, which opening of the cover will disengage the spring
means from the syringe and stop operation of the dispensing device.
BRIEF DESCRIPTION OF THE DRAWING
The device will further be described with reference to the accompanying
drawings wherein like numerals refer to like parts through the several
views and wherein:
FIG. 1 is a horizontal sectional view of a fluid dispensing device
according to the present invention having inserted therein a syringe from
which fluid is to be dispensed;
FIG. 2 is a sectional view taken approximately along line 2--2 of FIG. 1;
FIG. 3 is an enlarged sectional view taken approximately along line 3--3 of
FIG. 2;
FIG. 4 is an enlarged end view of the fluid dispensing device of FIG. 1;
FIG. 5 is a sectional view taken approximately along line 5--5 of FIG. 4
except that a cover for the fluid dispensing device is open, and a
metering device included in the device and the syringe are not inserted in
the device;
FIGS. 6 and 7 are enlarged fragmentary sectional views of the novel
metering assembly included in the fluid dispensing device of FIG. 1 shown
coupled to the syringe and shown respectively with parts of the metering
assembly in a purging and a metering position; and
FIG. 8 is a sectional view taken approximately along line 8--8 of FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawing, there is illustrated a fluid dispensing
device according to the present invention generally designated by the
reference numeral 10.
The fluid dispensing device 10 is adapted to dispense fluid at a slow,
steady rate over a prolonged period of time from a conventional syringe 12
of the type including an elongate housing 14 with an outlet tube 16 at one
end, and a plunger 18 adapted to expel fluid within the syringe 12 through
the outlet tube 16.
Briefly the device 10 includes a metering assembly 20 coupled between the
syringe 12 and a length of flexible hose 22 (which hose 22 is shown
coupled to a needle 23 via a leur-lock fitting 21 at its end opposite the
metering assembly 20 to facilitate injecting the fluid into a patient's
veins or tissues, but which hose 22 alternatively could be open-ended to
facilitate insertion of the hose 22 into a patient's digestive or
breathing passages or have attached thereto any shape of head via the luer
lock fitting portion on the hose 22 or otherwise to facilitate
distributing fluids to a patient's body), which metering assembly 20
includes a capillary tube 25 (FIG. 7) through which the fluid must flow to
restrict flow of fluid from the syringe 12; a support frame 24 comprising
spaced fork-like members 26 and 28 for supporting the metering assembly 20
and the syringe 12; and spring means 30 for applying uniform force against
the plunger 18 of the syringe 12 to press it towards the fork-like members
26 and 28 and cause fluid within the syringe 12 to flow through the
metering assembly 20 and hose 22.
The syringe 12 which the dispensing device 10 is adapted to receive is of a
conventional type comprising the housing 14 which includes a tubular wall
34 having an open end 35, and an end wall 36 at its end opposite the open
end 35 from which projects the outlet tube 16 which defines an outlet
opening for the housing 14; the plunger 18 which has one end portion
positioned within and sealing against the inner surface of the tubular
wall 34 and an opposite end portion projecting from the open end 35 of the
tubular wall 34; and fluid within the tubular wall 34 between the end wall
36 and the plunger 18.
The metering assembly 20 includes means for bypassing the capillary tube 25
so that prior to use of the device 10, air can be purged from the metering
assembly 20 and hose 22 by manual operation of the syringe 12.
As is best seen in FIGS. 6 and 7, the metering assembly 20 includes a first
part 38 having first and second ends 39 and 40 and a through opening
between the ends 39 and 40 having a portion adjacent its first end 39
adapted to frictionally receive the outlet tube 16 on the syringe 12 to
attach the syringe 12 and metering assembly 20 together. A sintered metal
filter 41 is fixed to the first part 38 within its through opening and
adjacent its first end 39, and a cup-like seal 42 is fixed to the first
part 38 within its through opening adjacent and opening toward its second
end 40. The seal 42 provides a transverse wall 44 in the through opening
defining inlet and outlet chambers 45 and 46 within said first part 38 on
opposite sides of the transverse wall 44. The transverse wall 44 has a
plurality of through orifices 48 (FIG. 8) communicating through the
tranverse wall 44 between the chambers 45 and 46. One end portion of the
capillary tube 25 is fixed in and extends through the transverse wall 44
and communicates with the inlet chamber 45, whereas the other end portion
is unsupported and extends through the metering assembly 20 and into the
hose 22 attached thereto. The metering assembly 20 also includes a second
part 50 which has a through opening and has an annular portion 52 sealably
and movably mounted within the first part 38 for movement relative to the
first part 38 between a purging position of the parts 38 and 50 at which
the annular portion 52 is spaced from the orifices 48 so that fluid can
flow between the chambers 45 and 46 through the orifices 48 (FIG. 6), and
a metering position with the annular portion 52 of the second part 50
seated in the cup-like seal 42 and blocking the orifices 48 (FIG. 7) so
that fluid in the inlet chamber 45 can pass the transverse wall 44 only
through the capillary tube 25. Thus prior to insertion of the metering
assembly 20 and attached syringe 12 into the frame 24, the parts of the
metering assembly 20 may be positioned in their purging position to afford
rapid manual purging of fluid through the metering assembly 20, hose 22,
and needle 23 by manual operation of the syringe 12.
Means are provided in the device for insuring that the parts 38 and 50 of
the metering assembly 20 are in their metering position when the metering
assembly 20 is inserted in the dispensing device 10, thereby precluding
operation of the dispensing device 10 with the metering assembly 20 in its
purge position. Each of the parts 38 and 50 has a distal end portion 54
which is smaller in cross sectional area than its portion adjacent the
other part 38 or 50. The slots in the fork like members 26 and 28 are
sized so that they will only receive the distal end portions 54 of the
parts 38 and 50. Also the pairs of fork-like members 26 and 28 are spaced
sufficiently close that the distal end portions 54 will be separated by
too great a distance and will not align with the fork like members 26 and
28 unless the parts 38 and 50 of the metering assembly are in their
telescoped together metering position, thus precluding operation of the
device 10 with the parts 38 and 50 of the metering assembly 20 in their
extended purging position.
Also the device 10 includes activating means manually operated by movement
of a cover 53 coupled to the spring means 30 for allowing the syringe 12
and attached metering assembly to be easily inserted in or removed from
the device 10 by moving the spring means 30 to a disengaged position
relative to the syringe 12 when the cover 53 is opened, and by moving the
spring means 30 to an engaged position against the plunger 18 of the
syringe 12 when the cover 53 is closed, and means for securing the syringe
12 and metering assembly 20 in the device 10 when the cover 53 is closed
so that they may not be tampered with when the spring means is applying a
uniform force to expel fluid from the syringe 12.
The frame 24 includes an elongate bar-like base portion 55 at one end of
which is fixed a support member 56 including the spaced fork-like numbers
26 and 28 which are disposed so that they will position the syringe 12
attached to the metering assembly 20 received in the fork-like members 26
and 28 over and parallel to the base portion 55. The bar-like base portion
55 has upstanding opposed generally L-shaped rails 58 along its edges
between which a hollow block 60 is mounted for movement longitudinally of
the base portion 55 via four rollers 62 projecting from the edges of the
block 60 adjacent the base portion 55. A plate-like slide 64 is also
mounted between the rails 58 for sliding movement longitudinally of the
base portion 55 between the block 60 and the member 56. A spring 66 of the
type having the registered tradename "Neg'ator" has a portion 68 coiled
about a hub 69 rotatably mounted within the block 60 on a shaft 70, and a
straight end portion 71 extending from the block 60 to the slide 64 where
it is attached by a rivet 72. The "Neg'ator" spring 66 provides a
constant force attempting to wrap the entire length of the spring 66 onto
its coiled portion 68, and thus provides a constant force biasing the
block 60 toward the slide 64.
The cover 53 is a rectangular box-like member of rigid transparent plastic
material (preferably polysulfone) having an open side disposed adjacent
the base portion 55 and having opposite outwardly projecting trunnions 74
on its end opposite the support member 56 which are pivotably mounted
between the rails 58 and two pins 76 spaced along each of the rails 58 to
afford pivotal movement of the cover 53 from an open position spaced from
the base member 55, block 60 and syringe 12 (FIG. 5); and a closed
position adjacent the base member 55 enclosing the block 60 and the
syringe 12, therebetween, and with an edge portion 78 of the cover 53
against the metering assembly 22 received in the fork-like members 26 and
28 to preclude their removal (FIG. 2), at which closed position the cover
53 will be retained by releasable latch means later to be explained.
Parallel links 80 are pivotably mounted at their ends between the cover 53
and the slide 64, and are sized and disposed so that moving the cover 53
to its open position (FIG. 5) will move the slide 64 and block 60 to a
position sufficiently spaced from the fork-like members 26 and 28 that the
metering assembly 20 and attached syringe 12 may be inserted in or removed
therefrom; and that moving the cover 53 to its closed position (FIG. 2)
will move the slide 64 adjacent the support member 56 so that when the
syringe 12 and attached metering assembly 20 are supported from the
fork-like members 26 and 28 the block 60 will engage the plunger 18 on the
syringe 12 during such movement with the end of the plunger received in a
centering pocket 81 in the adjacent face of the block 60. Such engagement
will cause the slide 64 to separate from the block 60 in opposition to the
spring 66 so that while the cover 53 is closed the spring 53 will apply a
constant force against the plunger 18. Also while the cover 53 is closed,
the edge portion 78 rests transversely against the metering assembly 20
and precludes its removal from between the fork-like members 26 and 28.
The means for releasably latching the cover 53 in its closed position
comprises transverse mating hook-like lips 84 and 86, one of which lips 84
is a part of the cover 54 adjacent its edge portion 78, and the other of
which lips is a part of the fork-like member 26 adjacent its distal end;
the spring 66; and a spacing between the pins 76 that allows limited
longitudinal movement of the cover 53 relative to the base portion 55 of
the frame 24. When the cover 53 is being moved to its closed position and
after the block 60 engages the plunger 18 of the syringe 12, the force
applied by the spring 66 between the separated block 60 and slide 64 via
the links 80 will press the trunnions 74 on the cover 53 against the pins
76 oppposite the support member 56. As the cover 53 approaches its closed
position cam surfaces on the lips 84 and 86 engage to move the center
portion of the cover 53 toward the support member 56 and allow the
hook-like lips 84 and 86 to pass each other, whereupon the spring 66 again
moves the center portion of the cover 53 away from the support member 56
to engage the lips 84 and 86 as the cover 53 reaches its fully closed
position. Opening the cover 53 then requires sliding its center portion
longitudinally toward the support member 56 to disengage the lips 84 and
86 before the cover can be pivoted to its open position, which opening
operation is not apparent from a casual inspection of the closed cover 53
and could deter unauthorized deactivation of the device 10.
As an example of the use of the liquid dispensing device 10, a person first
fills the syringe 12 with a fluid to be dispensed. Next he moves the parts
38 and 50 of the metering assembly 20 to their extended purging position
(FIG. 6), attaches the metering assembly 20 to the syringe 12, and
manually activates the syringe 12 so that fluid flows rapidly through the
orifices 48 in the metering assembly 20 and purges air from the metering
assembly 20 and hose 22. Next the user telescopes the parts 38 and 50 of
the metering assembly 20 together to their metering position to block the
orifices 48 so that fluid can flow through the metering assembly only via
the capillary tube 25, and presses the metering assembly between the
fork-like members 26 and 28 with the syringe 12 projecting over the base
portion 55. The user then couples the part of the fitting 21 on the hose
22 with the part on the needle 23 or a cannula (not shown) which he has
previously inserted in a patient's vein or tissues, and moves the cover 53
toward its closed position so that the cover 53 via the links 80, slide
64, and spring 66 moves the block 60 into engagement with the plunger 18
on the syringe 12, after which the slide 64 is separated from the block 60
so that the spring 66 will apply a force against the plunger 18. Further
movement of the cover 53 to its closed position will cause the lips 84 and
86 on the cover 53 and fork-like members 26 to cam past each other
whereupon the spring 66 will maintain the lips 84 and 86 in engagement to
latch the cover 53 closed. In this condition, the "Neg'ator" spring 66
will continue to apply a uniform force to cause fluid to flow at a slow
uniform rate from the syringe 12 through the capillary tube 25, hose 22
and needle 23 or cannula into the patient. During this time the device 10
can be positioned in any attitude or carried on the patient to afford
ambulation without affecting the fluid dispensing rate. Also tampering
with the syringe 12 or metering device 20 while the fluid is being
dispensed is precluded since the syringe 12 is enclosed by the cover 53,
and the metering device 20 is locked between the fork-like members 26 and
28 by the edge portion 78 of the cover, and anyone attempting to gain
access to either the syringe 12 or metering device 20 will have to open
the cover 53, thereby deactivating the device 10.
The present invention and its use have been explained with respect to one
general type of medical use. The device may, however, be used in ways
other than that indicated both for medical or other uses. For example, one
or more of the devices 10 may be used to dispense fluids into a standard
intravenous administration set. Also, the fluid dispensing device 10 may
be used in industrial applications such as to introduce chemicals such as
a catalyst into fluids moving through a continuous process, or for other
uses where a small continuous supply of fluids is needed. Thus the scope
of the invention should not be limited by either the structure or use of
the embodiment described herein, but should be determined only by the
scope of the dependent claims.
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