U.S. patent application number 13/025306 was filed with the patent office on 2011-06-02 for blood treatment dialyzer/filter for permitting gas removal.
This patent application is currently assigned to NxStage Medical, Inc.. Invention is credited to James M. Brugger, Martin Stillig.
Application Number | 20110126714 13/025306 |
Document ID | / |
Family ID | 36319501 |
Filed Date | 2011-06-02 |
United States Patent
Application |
20110126714 |
Kind Code |
A1 |
Brugger; James M. ; et
al. |
June 2, 2011 |
BLOOD TREATMENT DIALYZER/FILTER FOR PERMITTING GAS REMOVAL
Abstract
A configuration of a blood microtubular filter/dialyzer used in
many kinds of renal replacement therapy systems can provide a
highly effective mechanism for removing air from the blood circuit
of such systems. Air is removed from an outlet header space of the
filter avoiding the need for a bubble trap or settling chamber such
as a drip chamber.
Inventors: |
Brugger; James M.;
(Newburyport, MA) ; Stillig; Martin; (Dransfeld,
DE) |
Assignee: |
NxStage Medical, Inc.
|
Family ID: |
36319501 |
Appl. No.: |
13/025306 |
Filed: |
February 11, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12432507 |
Apr 29, 2009 |
7901579 |
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13025306 |
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11163708 |
Oct 27, 2005 |
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12432507 |
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60622863 |
Oct 28, 2004 |
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Current U.S.
Class: |
96/219 ;
210/232 |
Current CPC
Class: |
B01D 19/0021 20130101;
B01D 61/20 20130101; B01D 65/00 20130101; B01D 61/30 20130101; B01D
63/02 20130101; B01D 2313/06 20130101; B01D 19/0042 20130101; A61M
1/3627 20130101; B01D 2313/18 20130101; B01D 63/00 20130101 |
Class at
Publication: |
96/219 ;
210/232 |
International
Class: |
B01D 63/02 20060101
B01D063/02; B01D 61/30 20060101 B01D061/30; B01D 19/00 20060101
B01D019/00 |
Claims
1-18. (canceled)
19. A system for removing gas from blood, the system comprising: a
blood processing device including a microtubular fiber filter
having a plurality of filter fibers with ends opening into an inlet
header space and an outlet header space, the inlet header space
including an inlet port and the outlet header space including an
outlet port and a gas release port, the outlet port and the gas
release port lying at opposite ends of the outlet header space, the
blood processing device being configured to allow blood entering
through the inlet port into the inlet header space to flow through
the plurality of filter fibers into the outlet header space and out
the outlet port, and further configured to allow gas to collect in
a portion of the inlet header space so as to be conveyed through a
subset of the plurality of filter fibers into the outlet header
space, the inlet and outlet header spaces having sizes and shapes
such that a shear rate of blood flow is sufficient to prevent
stagnant flow regions from arising in the inlet and outlet header
spaces; and a holder configured to support said blood processing
device in a position and orientation such that gas in the outlet
header space accumulates in a portion of the outlet header space
which is adjacent the gas release port, the gas release port being
configured to periodically release the accumulated gas.
20. The system of claim 19, wherein the filter has a longitudinal
housing with a longitudinal axis and is supported by the holder so
as to be at an angle with respect to the vertical.
21. The system of claim 19, further comprising a valve connected to
said gas release port and pre-connected and sterilized together
with said blood processing device, the valve being configured to
permit gas to egress from the outlet header space without
permitting blood to egress from the outlet header space.
22. The system of claim 19, further comprising a stopcock connected
to said gas release port and pre-connected and sterilized together
with said blood processing device.
23. The system of claim 19, further comprising a syringe connected
to said gas release port and pre-connected and sterilized together
with said blood processing device.
24. The system of claim 19, wherein the holder is configured to
orient said blood processing device such that said outlet port is
lower, with respect to a direction of gravity, than said gas
release port.
25. The system of claim 19, wherein the inlet and outlet header
spaces have a hydraulic shape to eliminate stagnant flow of
blood.
26. The system of claim 19, wherein the gas release port further
includes a microporous filter to prevent contamination from
entering the outlet header space.
27. The system of claim 19, wherein the portion of the inlet header
space where gas collects is connected to the portion of the outlet
header space where gas accumulates before release by said subset of
the filter fibers.
28. The system of claim 19, wherein the holder is configured to
hold the blood processing device so that the inlet port and the
outlet port are oriented below the gas release port.
29. The system of claim 19, wherein the holder is fixedly
attachable to a blood treatment machine.
30. The system of claim 19, wherein the blood processing device is
one of a blood dialyzer and a hemofilter processing element.
31. The system of claim 19, wherein the gas release port is further
configured to permit adding or removing biocompatible non-blood
fluid.
32. The system of claim 19, wherein the portion of the inlet header
space where gas collects is opposite the inlet port.
33. A system for processing blood, the system comprising: a blood
processing element including filter media, the filter media being
configured to convey blood and air from an inlet header chamber
into an outlet header chamber through the filter media, the blood
processing element including the outlet header chamber at a
position where blood and air exit said filter media, said outlet
header chamber having at least one outlet; and a holder configured
to support said processing element in a preferred position and
orientation, wherein the preferred position and orientation is such
that air can accumulate in said outlet header chamber in a position
remote from said outlet, wherein the holder includes a flexible
holding portion configured to accept the blood processing element
only in the preferred position and orientation.
34. A holding device for holding a blood filtering element in a
preferred orientation relative to a blood processing machine, the
holding device comprising: a flexible holding portion to receive
the blood filtering element in a predetermined orientation; an
attachment portion to detachably attach the flexible holding
portion to the blood processing machine, the blood processing
machine including a fluid circuit, wherein when the attachment
portion is attached to the blood processing machine, the blood
filtering element is positioned in a preferred orientation relative
to the blood processing machine, and wherein the preferred
orientation is such that gas accumulates in a specific portion of
the blood filtering element.
35. The holding device of claim 34, wherein the blood filtering
element is connected to the fluid circuit before the attachment
portion is attached to the blood processing machine.
36. The holding device of claim 34, wherein the fluid circuit
includes a cartridge enclosed between two separate parts of the
blood treatment machine, and the holding device is configured to be
detachably attached to the cartridge so that the preferred
orientation of the blood filtering element relative to the blood
processing machine is determined by the attachment of the holding
device to the cartridge.
37. The holding device of claim 34, wherein the holding device is
integral with the blood processing machine.
38. The holding device of claim 34, wherein, the blood filtering
element includes a microtubular fiber filter having a plurality of
filter fibers with ends opening into an inlet header space and an
outlet header space, the inlet header space including an inlet port
and the outlet header space including an outlet port and a gas
release port, the outlet port and the gas release port lying at
opposite ends of the outlet header space, the blood filtering
element being configured to allow blood entering through the inlet
port into the inlet header space to flow through the plurality of
filter fibers into the outlet header space and out the outlet port,
and further configured to allow gas to collect in a portion of the
inlet header space so as to be conveyed through a subset of the
plurality of filter fibers into the outlet header space, the inlet
and outlet header spaces having sizes and shapes such that a shear
rate of blood flow is sufficient to prevent stagnant flow regions
from arising in the inlet and outlet header spaces, and the
preferred orientation is such that gas accumulates in a portion of
the outlet header space adjacent the gas release port.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/163708, filed Oct. 27, 2005, now pending,
which claims the benefit of U.S. Provisional Application Ser. No.
60/622,863, filed Oct. 28, 2004, both of which are incorporated by
reference herein in their entireties.
BACKGROUND
[0002] One of the problems with fluid circuits in blood treatment
systems is entrained air (bubbles) in treatment fluids, infusate,
or blood. Treatment systems normally have air detectors to prevent
air from being injected into a patient, either because a venous
line carrying blood back to the patient contains air or because an
infusate line, such as the replacement fluid line of a
hemofiltration system, contains air. It is desirable for the air
detectors to be made sufficiently sensitive to prevent the rare
instances of long trains of air bubbles being injected into a
patient. But sensitivity high enough to prevent long thin trains of
bubbles may be high enough to alarm very small amounts of air which
pose no risk. In other words, sensitive air detectors alarm on a
lot of fall positives if they protect against all possible
risks.
[0003] A prior art approach has been to remove as much air from a
protected fluid circuit as possible. Putting air traps in fluid
circuits, particularly blood lines, has drawbacks. Air-settling
chambers necessarily involve stagnant flow, which creates a risk of
fowling clots (e.g., for blood) or sedimentation or other
concentration of entrained material (e.g. medication).
[0004] Another prior art problem is stagnant flow in the headers of
microtubular filter used for most dialyzers and hemofilters. This
is a particular problem in the venous header where flow from many
microtubules coalesces into a single slow moving flow.
[0005] The inventive embodiments provide various other features and
advantages in addition to or in lieu of those discussed above and
below. Many of these features and advantages are apparent from the
description below with reference to the following drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a cross-section view of a filter usable in a
variety of different types of blood treatment systems oriented to
trap air in one or two header portions of the filter.
[0007] FIGS. 2A through 2C illustrate holders for use with the
filter device embodiment described herein, including a particular
example of application to a blood treatment device such as that of
FIG. 1.
[0008] FIG. 2D illustrates an example of a holder feature to
restrict orientations of a filter ensure that the filter is
oriented with respect to the force of gravity.
[0009] FIG. 3 illustrates a filter similar to that of FIG. 1 but
with a header port for removing air and/or disrupting or cleaning
clots.
[0010] FIG. 4A illustrates an assembly for use with the port of
FIG. 3 for removing air and/or disrupting or cleaning clots.
[0011] FIG. 4B illustrates a drip-chamber (or bubble trap)
embodiment similar to the embodiment of FIG. 4A.
[0012] FIG. 5 illustrates a header cap with a hydrophobic membrane
for automatically venting air.
[0013] FIGS. 6A through 9B illustrate a method for manufacturing a
filter having a two-piece header caps that allow the use of a
cylinder for a majority of the filter.
[0014] FIGS. 10A, 10B, and 11 illustrate the filter whose
manufacture is described with respect to FIGS. 6A through 9B.
[0015] FIG. 12 shows an alternative configuration for connecting a
dialysate manifold with a tubular body of the a filter according to
an embodiment of the invention.
[0016] FIG. 13 illustrates a single element header component that
uses a simple tube for the dialysate portion.
DETAILED DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a cross-section view of a filter usable in a
variety of different types of blood treatment systems oriented to
trap air in one or two header portions of the filter. A filter 100,
which may be a dialyzer, hemofilter, hemodiafilter, or any other
compatible blood treatment has a bundle of tubular media 132
connecting an arterial 160 and venous 155 head space which is
isolated from a filtrate space 130. Blood flows through ports 122
and 124 in header caps 110 and 136 as indicated by arrows 118 and
112 into and out of the arterial 160 and venous 155 head spaces,
respectively. A cylindrical filter body 128 encloses the filtrate
space 130 and contains filtrate (e.g., dialyzer) ports 126 and 120.
Arterial and venous headers 142 and 134 isolate the filtrate space
130 from the respective arterial 160 and venous 155 head
spaces.
[0018] The orientation of the filter 100 with respect to the pull
of gravity is shown with the understanding that gravity is assumed
to pull down with respect to the profile orientation of the drawing
page. If any air is entrained in the blood, it may settle in
pockets 151 and 153 in the arterial 160 and venous 155 head spaces
as indicated by air/liquid interfaces 152 and 150. The flow of
blood through the arterial 160 and venous 155 head spaces is
extremely slow due to the very small cross-sectional areas of the
filter fibers in the bundle 132. As a result, the arterial 160 and
venous 155 head spaces are an idea place for air to settle out.
With the indicated orientation, with blood outlet 124 pointing down
and away from the pocket 151. Since the blood moves at a very slow
rate in the arterial 160 and venous 155 head spaces, there is
little risk of reentrainment and air settles out very
effectively.
[0019] Air trapped in pocket 153 may travel through filter fibers
in bundle 132 up to venous head space 155 and accumulate in pocket
151. Since the pocket 153 is located near the top of the arterial
head space 160, air will tend to travel up a few of the fibers
closest to the top and collect in the pocket 151 without mixing in
with blood. This keeps the vast majority of fibers filled with
blood.
[0020] FIGS. 2A through 2C illustrate holder variations for the
filter embodiments of the present patent disclosure. The variations
are intended to illustrate examples and not intended to be
comprehensive or limiting. In FIG. 2A, a holder 175 of a blood
treatment machine orients a filter such as that of FIG. 1 and those
of the further filter embodiments described below. The holder 175
may be attached at a base thereof (not shown separately) to a blood
treatment machine 172 which may contain actuators, sensors, and
control elements as well as a fluid circuit, here illustrated as a
cartridge 180 enclosed between two parts 171 and 172 of the blood
treatment machine 172. A filter 100 that is preconnected to the
fluid circuit can easily be mounted in such an apparatus. The
holder 175 may be articulating to allow for some movement or change
of orientation of the filter 100 and is preferably a
spring-tensioned clamp that allows for one-handed insertion of a
filter 100. In an alternative embodiment, the holder 175 may be
attached to the 180 cartridge such that its orientation is obtained
when the cartridge 180 is positioned with respect to the blood
treatment machine 170. In FIG. 2B, a holder 194 is integrated into
a disposable unit 190 (such as the fluid circuit cartridge of FIG.
2A). For example, the holder 194 may be made of wire which is
connected to a plastic panel support 191 of the disposable unit.
Examples of such disposable units are disclosed in U.S. Pat. No.
6,955,655 for "Hemofiltration system" and U.S. Pat. No. 6,579,253
for "Fluid processing systems and methods using extracorporeal
fluid flow panels oriented within a cartridge," each of which is
hereby incorporated by reference as if full set forth in its
entirety herein and U.S. patent application Ser. No. 10/650,935
published as US 2004-0069709, which is incorporated by reference
above. The holder 194 supports a filter 192 such that when the
disposable unit 190 is mounted, in a treatment device such as 170,
the filter 192 is held at an angle as shown. Another alternative
arrangement shown in FIG. 2C is to provide a separate support 178
that is attached, or attachable, to a support 176.
[0021] FIG. 2D illustrates an example of a holder feature to
restrict orientations of a filter ensure that the filter is
oriented with respect to the force of gravity. The view is a
sectional view. In the example, the filter 166 has tabs 162 and 164
that prevent the filter 166 from being received fully within a
flexible trough 168 which functions as a holder. This may be
confirmed by inspection. The flexible trough 168 allows the filter
166 body to fit into it fully in only one orientation, the holder
providing an urging force that keeps the filter 166 in place when
inserted. Note that the example illustrated in FIG. 2D is only one
of many devices that may be used to restrict the orientation of the
filter when attached to a holder and is not intended to be limiting
of the scope of any of the inventions described in the present
disclosure.
[0022] FIG. 3 illustrates a filter similar to that of FIG. 1 but
with a header cap 210 having an integrated header port 200 for
removing air and/or disrupting or cleaning clots. Tubing 265 may be
connected to the port and provided with a clamp 260. The clamp 260
may be released, at intervals, by an operator, to vent air from the
air pocket 251 and re-engaged to prevent blood loss. The clamp 260
may be a normally-closed type clamp with a strong spring so that it
reclamps tubing 265 when released. The tubing 265 may be capped
with a microporous filter end cap 253 to prevent any contamination
re-entering the blood in the venous head space 155. The entire
assembly that includes the filter 100, tubing 265, and microporous
filter end cap 253 may be fused, sealed, and sterilized as a unit.
In addition the same may be fused, sealed and sterilized as a unit
with an entire treatment circuit, combining it with the circuit
described in U.S. patent application Ser. No. 10/650,935 published
as US 2004-0069709, which is hereby incorporated by reference as if
full set forth in its entirety herein. With this combination, the
entire circuit may be isolated from contamination.
[0023] FIG. 4A illustrates an assembly 350 for use with the port of
FIG. 3 for removing air and/or disrupting or cleaning clots. The
port 200 has a tube 310 connecting the venous head space 155 with a
multi-way valve (e.g., a stopcock as shown) 312. The multi-way
valve 312 is further connected to a syringe 320 and tubing 375
connecting a supply of blood normal saline 375, heparin, drug, or
other medicament (such as from a tube 360 and bag 365) such as
anticoagulants, drugs, etc. The multi-way valve allows the syringe
to be connected, in a first position, to draw saline from the
source of saline 375 and, in a second position, to draw air from
the venous head space 155. In the second position, saline may be
pushed into the head space 155 to clear clots or for prophylaxis by
injecting medicament, for example, an anticoagulant such as
heparin. In an illustrative usage method, the multi-way valve 312
is set in the second position and air is drawn from the head space
155. Then it is set in the first position and saline is drawn into
the syringe 320. Then the multi-way valve 312 is set in the second
position again and saline (or saline and heparin) is injected into
the venous head space 155. The apparatus including the multi-way
valve 312, syringe 320, tubing 310, 375, 360 and clamp 260 may be
pre-attached to the filter 100 and presterilized as a unit.
[0024] Note that besides using the multi-way valve and bag 365 to
draw air from the header of a filter and inject medicaments into
the filter header, the same devices may be used in connection with
an air trap or drip chamber. Referring to FIG. 4B, a drip chamber
393 (which could also be a bubble trap or other similar device in
which air may accumulate and possibly be vented), has an inlet 391
and an outlet 394. A connection 392 to the top of the drip chamber
393 may be connected to the line 310 shown in FIG. 4A and used in
the manner described for removing air and/or injecting
medicaments.
[0025] FIG. 5 illustrates a header cap 210 with cover 280 sealed to
and covering the header port 200. The cover includes a hydrophobic
membrane 285 that allows air in the head space 155 to vent
automatically while preventing any contamination from entering.
[0026] Referring to FIGS. 6A and 6B, a method for manufacturing a
filter design that incorporates features of the foregoing examples
begins with the insertion of a filter fiber bundle 420 into a
cylindrical tube 405 which fauns part of a housing (discussed with
reference to FIG. 11). The tube 405 is a straight tube with no
other structural features, in the present example. As such, the
tube 405 may be a thin walled structure allowing material to be
saved. In addition, it may be made of a material that is not
necessarily injection moldable, as filter housings generally are. A
preferred material is glycol-modified polyethylene terephthalate, a
copolyester (PETG) which may be a clear amorphous thermoplastic
with high stiffness, hardness, and toughness as well as good impact
strength. Other advantages of using a tube for the main part of the
housing will become clear from the further description below. Note
that in the drawing only one end of the tube is shown in the
present and following figures, but a complementary operation may be
performed at an opposite end of the tube 405 such that a
mirror-image structure is obtained.
[0027] The filter fiber membrane bundle 420 may be inserted such
that the fibers 415 extend beyond the end 407 of the tube 405 as
indicated at 445. Referring now to FIGS. 7A and 7 B, the resulting
combination 430 of tube 405 and filter fibers 420 may be inserted
in a dialysis cap 435. Note that the term "dialysis cap" is for
convenience is not intended to limit the scope of the invention to
the manufacture of a dialyzer. The outer surface of the tube 405
lies adjacent an inner annular surface 440 of the dialysis cap and
a 450 bond is formed by thermal welding or sealing using adhesive,
solvent, or filling type bonding agent such as urethane to form a
completed structure 480. A symmetrical structure is formed at the
opposite end so that both ends of the tube 405 have a dialysate cap
435.
[0028] Referring now to FIGS. 8A and 8B, potting caps (not shown)
are placed over the ends of the structure 480 and the ends of the
fiber bundle are potted as according methods that are known in the
art of manufacturing filters. A preferred method of potting is
described in U.S. Pat. No. 6,872,346 for a "Method and apparatus
for manufacturing filters," which is hereby incorporated by
reference as if fully set forth in its entirety herein. The result
of potting is the creation of a sealed end of potting material
indicated at 440 which, after hardening, is cut along a planar
surface indicated at 460. The cut 460 is done in such a way that
the end of the filter fibers 420 are open at the surface 465
forming. A portion of the dialysate cap 435 may be trimmed off in
the process of cutting 460, as illustrated, although it will be
apparent to those skilled in the art that this is not essential and
instead, the fibers 420 could extend beyond the end of the
dialysate cap 435 before potting such that the fibers 420 can be
opened by cutting without cutting the dialysis cap 435. The
completed end portion is shown in FIG. 8B, and as discussed, a
symmetrical end portion may be completed at the opposite end (not
shown here).
[0029] Referring now to FIGS. 9A through 11, the two ends 600 A and
600 B of a single tube structure are indicated. Respective blood
caps 505 and 605 are fitted to the ends 600 A and 600 B of the
structure 480. Each blood cap has a respective blood port 510, 610
and one of the blood caps has a secondary port 611 which will be
recognized from the discussion of embodiments such as shown and
discussed with respect to FIGS. 3 through 5. The blood caps 505 and
605 have respective header spaces 545, 645 that are preferably
hydraulically shaped to ensure that no, or a minimal number of,
dead (stagnant flow of blood) spaces arise when in use. In the
embodiment shown, a rim 515 fits into an annular recess 470 (or rim
615 into annular recess 471). Prior to fitting the blood caps 505
and 605, a bead 605, 606, 607, 608 of adhesive or sealing material
may be applied or injected in the annular recesses 470 and 471 to
form a bond between the structure 480 and the respective blood caps
505 and 605. The bonding may be done by thermal, friction, solvent
welding, compression bonding, or other technique. Dialysate ports
30 and 531 in the dialysate caps 435 and 425, respectively, allow
dialysate to flow into and out of the space occupied by bundle 420
and in contact with the external surfaces of the filter bundle 420.
For a hemofilter or other kinds of filters, such as sterile
filters, reverse osmosis filters, ultrafilters, etc.; only one
"dialysate" port would be required. Blood ports 510 and 610 in
blood caps 505 and 605, respectively, supply blood into, and be
recovered from, the header spaces 545 and 645, respectively. Air
can be removed from air removal/access (secondary) port 611. As
explained above, removal/access port 611 can also be used for
injection of anticoagulants, drugs, or other medicaments.
[0030] As best seen in FIGS. 10A and 10B, a small gap 685, 686 is
provided between the end 407 (FIGS. 6A, 7A, 8 A) of the tube 405
(FIGS. 6A, 6B) and the surface of the potting 440 to allow
dialysate to flow into the space occupied by the filter bundle 420.
The dialysate (or filtrate, depending on the application) is
distributed by an annular dialysate manifold space 626, 626.
Referring momentarily to FIG. 12, it is noted that instead of
providing for the gap 685, 686 in the manner described, the fiber
bundle may be extended all the way to the end 407 of the tube 405
and openings 705 can be provided to perform the function of the
openings 685, 686. The same features provide for extraction of
filtrate or dialysate or other fluid depending on the application.
FIG. 11 shows a complete filter unit. One of the benefits of the
design is that it makes it possible to confine the capital expense
associated with injection molding to the dialysate and blood header
reducing first costs in new filter designs. In addition, the design
allows the tubular portion to be lengthened and shorted without
requiring major design and manufacturing changes. Note that
although injection molding is not contemplated to be a requirement
for the practice of the invention or all its embodiments, it is a
preferred means for achieving the high precision and economies of
scale for articles of manufacture such as dialyzers, filters, and
hemofilters, as well as other applications of the disclosed
embodiments.
[0031] Referring to FIG. 13, the benefit of using a tube for the
filtrate/dialysate portion of the filter can be obtained by using a
single-element header cap rather than separate "dialysate" and
"blood" caps. In the example shown, a one-piece cap 725 has an
annular dialysate manifold 740 that is sealed by O-rings 747
against the surface of a tube 760. A blood header space 732 is in
communication with a blood port 730 and the dialysate manifold 740
is in communication with a dialysate port 735. Slits 750
(configured such as illustrated in FIG. 11) allow fluid
communication between the dialysate manifold 740 and the external
surfaces of the fiber bundle 733. A potting plug 745, in addition
to performing its normal function, serves to reinforce the
cylindrical structure of the tube 760 against the pressure of the
O-ring 747 seals. In this embodiment, a tube is permitted to be
used with a single-element cap 725 structure providing many of the
benefits of the inventions discussed above.
[0032] A tension band 757 may be used to ensure a good seal and
provide a final shape to the one-piece cap 725 if made of a
somewhat compliant resin to allow it to be removed from an
injection mold despite the recess defined by the dialysate manifold
740. Alternatively, the one-piece cap 725 may have a discontinuous
dialysate manifold that allows it to be created without requiring
the cap to yield, the cap could be machined rather than molded, or
the cap could be made of two molded pieces that are assembled into
a single cap. Many variations are possible.
[0033] It will be understood that while the invention has been
described above in conjunction with a few exemplary embodiments,
the description and examples are intended to illustrate and not
limit the scope of the invention. That which is described herein
with respect to the exemplary embodiments can be applied to the
measurement of many different formation characteristics. Thus, the
scope of the invention should only be limited by the following
claims.
* * * * *