Note: Descriptions are shown in the official language in which they were submitted.
CA 02610650 2007-11-21
FLUID FLOW LIMITING DEVICE
CROSS REFERENCE TO RELATED APPLICATIONS
Not Applicable.
STATEMENTS REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable.
BACKGROUND OF THE INVENTION
Shunt systems for directing body fluid from one region to another are known
in the medical field. One application for such a fluid shunt system is in the
treatment
of hydrocephalus in order to direct cerebrospinal fluid away from the brain
and into
the venous system or to another region of the body. In this application, a
shunt is
implanted on the patient's skull, under the scalp, and is coupled to a brain
ventricle
catheter which is adapted for insertion into the brain and to a distal
catheter which is
adapted for insertion into the drainage region, such as the peritoneal cavity,
the atrium
or other drainage site.
Generally, fluid shunt systems include a valve mechanism for controlling, or
regulating the fluid flow rate. Illustrative valve mechanisms operate to
permit fluid
flow only once the fluid pressure reaches a certain level and may permit
adjustment
of the pressure level at which fluid flow commences.
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CA 02610650 2007-11-21
One such adjustable valve, described in U.S. Patent No. 4,551,128 (Hakim et
al.), includes a flexible diaphragm and plate positioned to divide a housing
into inlet
and outlet chambers which communicate through an aperture in the plate. A
valve
element is biased against the aperture to close the aperture until the fluid
pressure in
the inlet chamber exceeds a preselected "popping pressure." The popping
pressure
is adjustable by adjusting an external screw of the valve. However, due to the
elastomeric properties of the diaphragm material, maintenance of the implanted
valve
may be required. Further, flow rate adjustment of the Hakim et al. device
after
implantation may require a surgical procedure.
Another adjustable valve mechanism, described in U.S. Patent No. 4,781,673
(Watanabe), includes two parallel fluid flow passages, with each passage
including a
flow rate regulator and an on-off valve. Fluid flow through the passages is
manually
controlled by palpably actuating the on-off valves through the scalp. Although
the
Watanabe device permits flow rate control palpably through the scalp and thus,
without surgical intervention, patient and/or physician attention to the valve
settings
is required.
Effective fluid flow rate control is particularly important since overdrainage
of
cerebrospinal fluid can result in dangerous conditions, including subdural
hematoma.
Overdrainage tends to occur when a patient moves from a horizontal position to
a
sitting or standing position, due to a siphon effect in the shunt system. In
order to
reduce the risk of overdrainage, some shunt systems include additional
devices,
sometimes referred to as anti-siphon devices, for preventing overdrainage.
Some such
devices use weights, which move in response to the patient changing position,
to
open or close the fluid flow path. One system, described in U.S. Patent No.
5,368,556 (Lecuyer), includes spherical weights which provide additional
compressive
force against a valve spring to help maintain the valve in a closed position
when the
patient is sitting or standing. However, noise associated with the use of such
weights
may be objectionable.
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SUMMARY OF THE INVENTION
The invention relates to a fluid flow limiting device for use with a shunt
system. The device includes an inlet for receiving fluid from a first region
of a
patient's body into the device, an outlet for directing the fluid from the
device, and
two fluid passages, or flow paths. A primary fluid passage directs fluid from
the inlet
to the outlet substantially directly in response to the flow rate being less
than a
predetermined level. A secondary fluid passage directs fluid from the inlet to
the
outlet in response to the flow rate being greater than the predetermined
level.
Preferably, the secondary passage is tortuous so as to present a higher
resistance to
fluid flow than the primary passage. A detector is operable to close the
primary
passage when the flow rate reaches the predetermined level in order to force
the fluid
to pass through the secondary passage. As soon as the flow rate decreases
below the
predetermined level, the primary passage opens automatically.
With this arrangement, when the fluid flow rate is less than a predetermined
level characteristic of overdrainage, most of the fluid flows through the
substantially
direct primary passage since the secondary passage presents a higher
resistance.
When the fluid flow rate reaches the predetermined level, the fluid is forced
to flow
through the secondary passage which serves effectively to reduce the flow rate
through
the device and prevent overdrainage. Further, the device advantageously
prevents
overdrainage in response to the increased fluid flow rates without the need
for manual
intervention and with a rigid structure that is not susceptible to occlusion
by the
application of normal external forces. The fluid flow limiting device is
suitable for
use as a separate device in series with a valve component of the shunt system,
or it
can be readily incorporated into a drainage system along with the valve
component.
In one embodiment, the overdrainage protection device includes a housing
defining the inlet, a body disposed at least partially within the housing and
having a
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body channel terminating at the outlet, a detector disposed between the inlet
and the
body channel and a flow reducing element. The detector includes a detector
channel
in substantial axial alignment with the body channel to form the primary
passage and
the flow reducing element is disposed between the body and the housing to form
the
secondary passage. In one embodiment, the flow reducing element includes a
helical
passageway. Many other passageway configurations may also be used.
One illustrative detector includes a detector seat having an aperture and a
closure element that is moveable between a first position in spaced relation
with the
detector seat in which the primary passage is open and a second position
abutting the
detector seat to block the aperture and close the primary passage. Preferably,
the
closure element is biased into spaced relation with the detector seat in order
to expose
the aperture and open the primary passage. In one embodiment, a first bias
element
urges the closure element away from the detector seat to maintain the primary
passage
in an open position. The force of the first bias element is at least partially
opposed
by a counterbias element which urges the closure element back towards the
detector
seat. The force of the first bias element preferably exceeds that of the
counterbias
element so that, in normal operation, without an excessive rate of fluid flow,
the
primary passage is open.
The invention also provides a method for limiting fluid flow through a device
having an inlet, an outlet, a primary flow path between the inlet and the
outlet and a
secondary flow path between the inlet and the outlet. The method includes the
steps
of directing the fluid through the primary passage of the device in response
to the fluid
flow rate being less than a predetermined level and directing the fluid
through a
secondary passage in response to the fluid flow rate reaching or exceeding the
predetermined level. The primary passage is closed, such as with the use of a
detector, when the fluid flow rate reaches the predetermined level in order to
force the
fluid to pass through the secondary passage. In one embodiment, the step of
directing
the fluid through the secondary passage includes directing the fluid through a
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passageway of a desired configuration, as may be provided by the threads of a
screw
element. The secondary passage can include multiple adjacent helical
passageways.
BRIEF DESCRIPTION OF THE DRARTINGS
Figure 1 illustrates placement of a fluid flow limiting device of the
invention
relative to a fluid shunt system disposed in a patient.
Figure 1A illustrates an alternate placement of a fluid flow limiting device
of
the invention relative to a fluid shunt system disposed in a patient.
Figure 2 is an isometric view of a fluid flow limiting device in accordance
with
the invention.
Figure 3 is a cross-sectional isometric view of the fluid flow limiting device
of
Figure 2 taken along line 3-3 of Figure 2.
Figure 4 is an isometric view of the body of the fluid flow limiting device of
Figure 2.
Figure 5 illustrates a flat spring for use with the fluid flow limiting device
of
Figure 2.
Figure 6 illustrates an alternate flat spring for use with the fluid flow
limiting
device of Figure 2.
Figure 7 is a view of the screw element of the fluid flow limiting device of
Figure 2.
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Figure 7A shows the screw element of Figure 7 rotated by 180 degrees.
Figure 8 is a cross-sectional view of an alternate embodiment of a fluid flow
limiting device in accordance with the invention.
Figure 9 is an enlarged cross-sectional view of the detector of the fluid flow
limiting device of Figure 8.
Figure 10 is a cross-sectional view of a further alternate embodiment of a
fluid
flow limiting device in accordance with the invention.
Figure 10A is a cross-sectional view of a slightly modified version of the
fluid
flow limiting device of Figure 10.
Figure 11 is a cross-sectional view of another alternate embodiment of a fluid
flow limiting device in accordance with the invention.
Figure 12 is a graph illustrating the effect of use of a fluid flow limiting
device
according to the present invention.
DETAII.ED DFSCRIPTION OF THE INVENTION
The fluid flow limiting device of the present invention, which is described in
detail below, is suitable for implanting into a patient to limit the flow of a
body fluid
from a first region to a second region. The illustrated devices limit the flow
of
cerebrospinal fluid from the brain of a patient to a drainage system or
region, such as
the peritoneal region. However, it will be appreciated by those of ordinary
skill in
the art that the concepts and techniques described herein are suitable for use
in other
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applications in which it is desired to limit the flow of a fluid from one
region of a
patient to another.
In general, the fluid flow limiting device includes an inlet for receiving
fluid
from the brain into the device and an outlet for directing fluid from the
device to the
drainage region (e.g., peritoneal cavity, atrium). The device is intended for
use with
a shunt system including a valve for controlling flow rate and various
placements of
the fluid flow limiting device relative to the shunt system are possible.
Referring to Figure 1, the fluid flow limiting device 11 may be disposed in an
entourage 15 of the shunt system, along with the valve 12. A first end of the
entourage 15 is adapted for coupling to the patient's brain via an inlet tube
17 and a
second end of the entourage is adapted for coupling to the drainage site via
an outlet
tube 19. Referring to Figure 1A, the fluid flow limiting device 13 may
alternatively
be disposed in line with the entourage 15, between a first outlet tube 21 and
a second
outlet tube 23, as shown.
Referring to Figures 2 and 3, a fluid flow limiting device 10 according to the
invention is shown. The device 10 is intended for placement in an entourage,
like
device 11 of Figure 1. To this end, device 10 includes an inlet 18 in the form
of an
aperture disposed in the entourage and an outlet 20 in the form of a connector
70
suitable for coupling to a drainage catheter (i.e., outlet tube 19 in Figure
1).
The device 10 includes a housing 14 defining the inlet 18 at the proximal end
of the device. A device body 16 defines the outlet 20 at the distal end of the
device
through which the fluid is directed from the device. At least a portion of the
device
body 16 is disposed in the housing 14, as shown. The components of the device
10,
including the housing 14 and body 16, are fabricated with any suitable
biocompatible
material. Examples of such preferred materials include polyethersulfone (PES),
polysulfone (PS), polyurethane, polyethylene and polypropylene.
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Referring to Figure 4, the device body 16 includes the outlet connector 70, a
plurality of external screw threads, or helical vanes 48 and a longitudinal
channel,
referred to as the body channel 28 which extends along a direct path from a
proximal
end of the body to the distal end. A flange 72 separates the outlet connector
70 from
the threads 48, as shown.
A detector 30 (Figure 3), referred to alternatively as a valve element, is
disposed within the housing 14 in substantial axial alignment with the body
channel
28. The detector 30 includes a detector channel 24 extending from an aperture
22 of
the inlet 18 to the body channel 28, a detector seat 104 having an aperture
106 and
a closure element 110. The closure element 110 is moveable between a first
position
away from and in spaced relation to the detector seat 104 to expose the
aperture and
open the channel 24 and a second position in abutment with the detector seat
104 to
block the aperture 106 and close the channel 24. The detector 30 preferably
has a
bias element 114 that urges the closure element 110 away from the detector
seat 104
to maintain channe124 in an open position. The force of bias element 114 is at
least
partially opposed by counterbias element 112 which urges the closure element
back
towards detector seat 104. The force of bias element 114 preferably exceeds
that of
counterbias element 112 so that, in normal operation, without an excessive
rate of
fluid flow, channel 24 is open.
In the illustrative embodiment, the detector seat 104 includes a substantially
circular aperture 106 and the closure element 110 is a substantially spherical
ball. The
counterbias element 112 and bias element 114 can be any suitable material or
structure
able to direct a force of a predetermined magnitude in one direction. In one
embodiment, counterbias element 112 is a spring element, such as a coil spring
and
the bias element 114 is a flat spring. A fixation ring 118 positioned under
the detector
seat 104 maintains the flat spring 114 in contact with the detector seat 104.
Suitable
materials for fabricating the ball 110 and seat 104 include synthetic ruby
(aluminum
oxide), suitable materials for fabricating the detector components are the
same as
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described above for the housing 14 and body 16 and suitable materials for
fabricating
the bias elements 112 and 114 include stainless steel (ASTM 300 Series, 316,
308,
304 and preferably, 316L).
The counterbias and bias elements 112 and 114 are designed to bias the closure
element 110 relative to the detector seat 104 in order to provide a desired
fluid flow
rate through the channel 24. It will be appreciated by those of ordinary skill
in the
art that both the particular design of the springs, as well as their
dimensions (e.g.,
thickness) and the material from which they are made, determine the relative
"stiffness" of the springs and the resulting bias on the closure element 110.
Flow rate
can be controlled, at least in part, by altering the structure and/or design
of elements
112, 114 or changing the relative position of the parts 118, 114 and 104 in
the
detector body 30.
Referring also to Figures 5 and 6, two illustrative flat springs for use in
providing the bias element 114 are shown. The flat spring 116 of Figure 5
includes
an exterior ring 130 and an interior ring 132 attached to the exterior ring by
a
connection member 136. A finger 134 is cantilevered inwardly from the interior
ring
132 at a location opposite to the connection member 134, as shown. In
assembly, the
exterior ring 130 is pressed by the fixation ring 118 against the detector
seat 104 and
the interior ring 132 and the finger 134 are in contact with the closure
element 110
so as to bias the closure element 110 away from the seat 104. The design of
the
spring 116 advantageously avoids impeding the flow of fluid through the
detector
channel 24.
The flat spring 122 of Figure 6 includes a spiral member 140 attached to an
exterior ring 144, as shown. In assembly, the exterior ring 144 is pressed
against the
detector seat 104 by the fixation ring 118 and the spiral member 140 contacts
the
closure element 110 so as to bias the closure element 110 away from the
detector seat
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104. The design of the flat spring 122 of Figure 6 provides reduced stiffness
for the
same thickness of material, as compared to the spring 116 of Figure 5.
A first, or primary fluid flow path, or passage 26 (Figure 3) in fluid
communication with the inlet 18 and the outlet 20 includes the detector
channel 24 and
the substantially axially aligned body channel 28. In normal operation,
without an
excessive rate of fluid flow, fluid flows directly from the inlet 18 to the
outlet 20
through the primary passage 26.
A flow reducing element 46 (Figure 3) is disposed between the housing 14 and
the body 16 to form a secondary fluid passage 40 between the inlet 18 and the
outlet
through which fluid is directed in response to the fluid flow rate reaching
and/or
exceeding the predetermined level, as will be described. Preferably, the
secondary
passage 40 can be characterized as a tortuous path and presents a higher
resistance to
15 fluid flow than does the primary passage 26. More particularly, the
secondary
passage 40 is tortuous in the sense that it includes twists, bends, turns,
obstructions,
or some combination thereof, and a combination of the length and design of the
secondary passage results in a reduced fluid flow rate as compared to fluid
flow
through the primary passage 26. Shear and other forces create drag on the
fluid as
20 it passes through the secondary passage 40, reducing the flow rate.
In the illustrative embodiment, the flow reducing element 46 is in the form of
a screw element 46 disposed concentrically between the body threads 48 and the
housing 14, as shown. The screw element 46 has an inner surface 68 and a
plurality
of exterior helical vanes, or threads 50. In assembly, the screw threads 50
abut,the
inner surface 64 of the housing 14 in a fluid tight seal to form a first
channel 60 of
the secondary passage 40. Further, the body threads 48 abut the inner surface
68 of
the screw element 46 in a fluid tight seal to form a second channel 62 of the
secondary
passage 40.
CA 02610650 2007-11-21
Referring also to Figures 7 and 7A, two views of the screw element 46 are
shown. The screw 46 has a flange 52 at a proximal end and a pair of slots 56,
58.
A first one of the slots 56 is disposed at the proximal end of the screw
element and
extends longitudinally slightly beyond the flange 52, as is apparent from
Figure 7.
The second slot 58 is disposed at the distal end of the screw 46, as shown.
Slot 56
provides fluid communication between the inlet 18 and the channel 60 and slot
58
provides fluid communication between the channel 60 and the channel 62, as
will be
described. Thus, in the illustrative embodiment, the inlet 18 includes the
screw slot
56 in fluid communication with the secondary passage 40 and the detector
aperture 22
in fluid communication with the primary passage 26. In the illustrative
embodiment,
the threads 48 and 50 have a pitch of between approximately 1 to 40 and,
preferably
approximately 30 .
In assembly, the screw element 46 is positioned within the housing 14, with
the
screw flange 52 adjacent to the proximal end of the housing 14. The body 16 is
inserted into the screw 46, with the body flange 72 adjacent to the distal end
of the
screw element 46 and the housing 14, as shown. The detector 30 is sized and
shaped
to fit within the screw element 46, in substantial axial alignment with the
body 16.
Ledges 54 on the inner surface 68 of the screw element 46 maintain alignment
of the
detector 30 and the body 16.
In operation, the springs 112 and 114 are provided with a stiffness suitable
to
bias the closure ball 110 into spaced relation with the detector seat 104 when
the fluid
flow rate through the detector 30 is less than a predetermined level, such as
between
approximately 25 to 100 ml/hour, and, more preferably, between approximately
30
to 60 mllhour. It will be appreciated by those of ordinary skill in the art
that flow
rate is a function of the fluid pressure and velocity and thus, the
predetermined fluid
flow rate corresponds to a predetermined fluid pressure and velocity. With the
valve
in the open position, fluid enters the inlet aperture 22 and travels through
the
30 primary passage 26. Note that some fluid will also enter the secondary
passage 40
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through the slot 56. However, since the secondary passage 40 presents a higher
resistance to fluid flow than the primary passage 26, most of the fluid will
flow
through the primary passage 26. More particularly, in the primary passage 26
the
fluid travels directly through the detector channel 24 and the body channe128
to the
outlet 20.
Once the flow rate of fluid entering the inlet aperture 22 reaches the
predetermined level, the pressure on the closure element 110 exceeds the
biasing force
exerted by bias element 114. Preferably, the detector 30 is oriented so that,
as the
patient moves to a sitting or standing position, gravity acts in the same
direction as the
counterbias element 112, further forcing the ball 110 towards the seat 104.
Under
these conditions, the ball 110 is pushed into abutment with the detector seat
104,
blocldng the aperture 106 and closing the fluid channel 24 through the
detector 30.
With the detector cha.nne124 and primary passage 26 effectively blocked, the
fluid is forced to flow through the inlet slot 56 and into the secondary
passage 40.
More particularly, the fluid flows along the channel 60 in a substantially
helical
pattern between the screw threads 50 and the housing 14. Once the fluid
reaches the
distal end of the channel 60, the fluid enters the channel 62 via the screw
slot 58
(Figure 7A) and travels between the body threads 48 and the inner surface 54
of the
screw element 46. At the end of channe162, the fluid enters the primary
passage 26
at an intermediate location 76, between the detector 30 and the body channel
24. That
is, the body 16 is spaced from the detector 30 by a slot 74 through which the
fluid
enters the body channel 28 where it is directed to the outlet 20. Thus, in the
device
10, fluid flow through the secondary passage 40 can be characterized as
axially bi-
directional since fluid travels along the device axis directed by screw
threads 50 in a
first direction and then by body threads 48 in a second direction.
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With this arrangement, when the fluid flow rate reaches a level characteristic
of overdrainage, the lower resistance path from the inlet 18 to the outlet 20
via the
primary passage 26 is blocked by the detector 30 and the fluid is forced to
flow
through the tortuous secondary passage 40. In this way, the flow rate of fluid
flowing
between the inlet 18 and the outlet 20 is effectively reduced and overdrainage
is
prevented. Once the fluid flow decreases below the predetermined level, the
force of
the bias element 114 exceeds that of the counterbias element 112, thereby
causing the
primary passage 26 to automatically open.
It will be appreciated by those of ordinary skill in the art that the
particular
structure and arrangement of the device 10 is illustrative only and may be
varied
without departing from the spirit of the invention. For example, the
substantially
helical, axially bi-directional secondary passage 40 of the device 10 may be
modified
in order to tailor the desired fluid flow rate reduction. As examples, the
number and
size of the threads defining the channels 60, 62 of the secondary passage may
be
modified. Also, the pitch of the threads 48, 50 may be modified and/or the
slot 56
leading to the secondary passage 40 may be modified in size and/or number.
Further,
structures other than helical vanes, or threads may be provided in the
secondary
passage 40 and/or the threads may be alternated with one or more regions
without
threads in order to introduce a desired fluid flow rate reduction.
Additionally, fluid
flow schemes other than axially bi-directional may be implemented to provide
either
the primary and/or secondary passages. For example, the secondary passage may
comprise only the channe160, with the fluid entering the body channe124 at the
distal
end of channel 60 (i.e., rather than entering channel 62.) Such an
arrangement, as
shown in the embodiments of Figures 8 and 10, may be characterized as axially
uni-
directional. As a further alternative, a circumferentially bi-directional
fluid flow
scheme may be implemented in which the fluid flows at least partially around
the
circumference of the device in a first direction then axially, and then at
least partially
around the circumference of the device in a second, opposite direction.
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Referring to Figure 8, an alternate embodiment of a fluid flow limiting device
200 includes a housing 202, a body 204, a detector 208 and a flow reducing
element
in the form of a screw element 206, each of which is substantially identical
to
respective elements 14, 16 and 46 of the device 10 of Figures 2 and 3. Thus,
device
200 includes a primary passage 236 formed by a channel 230 (Figure 9) through
the
detector 208 and a substantially axially aligned channel through the body 204
and a
secondary passage 240 formed by the screw element 206 and body 204.
The device 200 differs from the device 10 of Figures 2 and 3 in that the
device
200 is separate from the shunt system valve and is suitable for placement as
illustrated
in Figure 1A. To this end, the device 200 includes an inlet connector 210
adapted for
mating with a brain ventricle catheter 21 (Figure 1A) and an outlet connector
215
adapted for mating with the drainage catheter 23 (Figure 1A). Further, the
secondary
passage 240 can be characterized as axially uni--directional. Device 200
further
includes a slightly modified detector 208 in order to accommodate the inlet
connector
210.
Referring also to the expanded view of the detector 208 in Figure 9, the
detector 208 includes a housing 216 in which a seat 220, a spherical ball 222,
a coil
spring 226 and a flat spring 228 are positioned, each of which is
substantially identical
to respective components 104, 110, 112 and 114 of the device 10 of Figures 2
and 3.
The housing 216 includes a neck 224 which is tapered to mate with the inlet
connector 210 so that, in assembly, a channe1230 through the detector 208 is
aligned
with the input connector 210. The detector 208 includes an aperture 214 which
permits fluid to flow from the inlet connector 210 into the secondary passage
240. A
guide 232 is positioned to maintain a.xial alignment of the spring 226 and the
ball 222
and a fixation ring 234 maintains the flat spring 228 pressed against the
detector seat
220.
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Referring to Figure 10, a further alternative fluid flow limiting device 250
is
shown. Like the above-described devices 10 and 200, the device 250 includes a
housing 252, a body 254, a detector 256 and a flow reducing element in the
form of
a screw element 258. This embodiment differs from that of Figure 8 in that the
length
of the screw element 258 is increased. Increasing the length of the screw
element 258
illustrates one way to increase the extent to which the flow rate is reduced
when the
fluid flows through the secondary passage defined by the screw element 258.
Referring also to Figure 10A, in which like numbers refer to like elements, a
further alternate embodiment 270 differs from device 250 of Figure 10 only in
that the
inlet 272 and outlet 274 are in the form of apertures. That is, flow limiting
device
270 does not include inlet and/or outlet connectors as shown in Figures 8 and
10. The
device 270 illustrates a further alternative scheme for placement relative to
a fluid
shunt system. Specifically, the device 270 is suitable for placement within a
catheter
tube 275, as shown.
Referring to Figure 11, an alternate fluid flow limiting device 300 includes a
housing 304, a device body 308, a detector 310 and a flow reducing element in
the
form of a screw element 314. The overall operation of device 300 is similar to
device
10 described above in conjunction with Figures 2 and 3. More particularly, the
device
300 has a primary passage 322 between the inlet 328 and the outlet 332 which
is
formed by a channel 324 through the detector 310 and an axially aligned body
channel
326. Further, a secondary passage 330 includes a first channel formed by screw
threads 334 and a second channel formed by body threads 336 and thus, provides
an
axially bi-directional fluid flow path.
The device 300 differs from the device 10 (Figures 2 and 3) in several ways.
First, the housing 304 of the device 300 is integral with the outlet connector
318,
whereas, in the device 10, the outlet connector 70 is integral with the device
body 16
and the housing 14 is a separate component. Further, the device 300 includes
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CA 02610650 2007-11-21
aperture 340 between the detector 310 and the secondary passage 330, through
which
fluid enters the secondary passage. This arrangement is contrasted to the
screw slot
56 (Figure 3) through which fluid enters the secondary passage 40 of the
device 10
and advantageously causes all of the fluid flow through the device 300 to be
directed
toward the closure element 342 of the detector 310.
Other differences between the fluid flow limiting device 300 and the device 10
are attributable to the design of the detector 310. Unlike the detector
30.(Figure 3),
the detector 310 does not include side portions which abut ledges 76 of the
screw
element 46 (Figure 3) in assembly. Rather, in assembly, the detector 310 is
seated
within the body 308 and is prevented from moving further into the body by a
combination of an interference fit with interior walls of the body 308 and
ledges 320
of the body. Elimination of the side portions of the detector adjacent to
screw element
ledges 76 (Figure 3) provides the device 300 with a smaller diameter than the
device
10 and the body ledges 320 further permit the elimination of the fixation ring
118
(Figure 3).
Finally, the device 300 permits use of an advantageous calibration technique
by
which a bias element 344 and a counterbias element 346 of the detector 310 are
calibrated. In particular, during manufacture, a calibrating fluid, such as
nitrogen is
directed through the device from the inlet 328 to the outlet 332 while the
detector 310 is
pushed into the device body 308, toward the outlet, until a desired fluid flow
reading is
obtained.
Referring also to Figure 12, a graph illustrates the effect of use of a fluid
flow
limiting device according to the invention. As is apparent, when the distance
between
the device and the region to which the fluid is directed (i.e., the distal
extremity)
exceeds approximately twenty-five centimeters, the fluid flow rate decreases
significantly, thereby preventing overdrainage.
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The foregoing description of the Ulustrative embodiments of the invention is
presented to indicate the range of constructions to which the invention
applies.
Variations in the physical architecture and dimensions of the invention will
be apparent
to those having ordinary skill in the art based upon the disclosure herein,
and such
variations are considered to be within the scope of the invention in which
patent rights
are asserted, as set forth in the claims appended hereto. All publications and
references cited herein are expressly incorporated herein by reference in
their entirety.
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