Note: Descriptions are shown in the official language in which they were submitted.
104Z3S9
BACKGROU~D OF THE I~VE~TIO~
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The present invention is directed to the filtration
of blood. In medical, hospital and surgical treatments
today there are a number of instances when blood is fil-
tered, e.g. during blood transfusions, dialysis treatments,
and in the extracorporeal blood circuits used during some
surgical procedures.
The filters used in the filtration of blood must
meet stringent requirements. The blood filter must be
sterile and hence should be readily sterilizable. The
filter must be efficient and remove the unwanted materials
from the blood without removing the desired materials
or having any detrimental effect on the desirable materials
in the blood. The filter must be constructed to prevent
gas bubbles in the blood flowing to the patient. The fil-
ter must not contain any foreign material that might be
~ released intc the blood being filtered.
- In view of the problems involved in cleaning and
sterilizing reusable filters, disposable filters have
- 20 gained considerable acceptance in the filtration of blood.
The disposable blood filters generally comprise a number
of parts, such as the housing, the core for holding the
-~ media, and the filter media or cartridge itself. These
parts must be assembled and sealed or secured together
to form a filter unit and the unit cleaned, flushed, and
sterilized prior to being placed into use. After a single
use, the filter is discarded. This means the filter cannot
be exp2nsive yet must meet critical specifications.
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SUMMARY OF THE rNvENTIo~
We have discovered an improved unit for filtering
blood. Our new blood filter may be readily flushed and
made medically clean prior to its final assembly. our
new unit is easily assembled and positively sterilized
- by steam, gas or radiation sterilization. Also, our new
filter does not damage the blood being filtered and has
excellent gas bubble elimination characteristics. our
new filter has reduced blocking characteristics and
improved flow characteristics.
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`~ In accordance with the present invention, our new
unit for filtering blood comprises an assembly fQr sup-
porting a filter cart~idge, a filter cartridge and a
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~ housing for the assembly and cartridge. The housing and
.
~- the assembly are fixedly securable to each other so as to
be leak-proof. In a preferred embodiment, the housing
~~ threads on to the assembly as will hereinafter be des-
cribed.
~.,
- The assembly for supporting the filter cartridge com-
-- 20 prises a permeable cylindrical core. A top cap is attached
-~` to one end of the core to seal this end of the core along
~- with filter media positioned about the periphery of the
--` core. On the other end of the core, there is a bottom
member which extends outwardly from the core for supporting
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. the media. The construction is such as to leave the cen-
ter of the core open to act as the outlet for the filtered
blood. The outer edge of the bottom member may be pro-
vided with threads for attaching the aQsembly to the housing.
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The filter media extends between the top cap and bottom
member about the circumference of the core. The core
and media are in contact only at a minimum of intermittently
spaced-apart areas with the areas of contact spaced longi-
tudinally and circumferentially about the core. In one
embodiment of our new filter unit, the distance between the
media and the core is greatest adjacent the bottom member
and the distance between the media and the core is the least
adjacent the top cap.
In a preferred embodiment of our unit for filtering
blood, the housing has a tapered cylindrical form. The
housing is smaller in diameter at its upper portion and
larger in diameter at its lower portion. The distance
between the media and inside wall of the housing is
smallest adjacent the bottom member with the distance
between media and inside wall of the housing the largest
~- adjacent the top cap.
The housing has a blood inlet and a vent in its
`~ uppermost portion to allow air to escape.
~ 20 The filter media used may be in the form of a con-
, .,
voluted cartridge. In this pleated configuration, the
pleats run the length of the cartridge. We have dis-
covered when using such a pleated cartridge, it is pre-
ferred that the pleats have a greater density at the top
of the filter than at the bottom of the filter, i.e.
the pleats are closer together at the top of the filter
than at the bottom of the filter. It is believed that
this configuration aids in allowing the material being
removed from the blood to easily settle to the bottom of
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the filter and not get caught in the pleats and block off
portions of the filter.
According to a broad aspect of the present invention,
there is provided a unit for filtering blood. The unit com-
prises an assembly for supporting a filter cartridge and a
housing for the assembly and the cartridge. The housing has
a tapered cylindrical form with the smaller diameter end of
the housing having an inlet for the blood to be filtered and
an air vent. The housing and the assembly are fixedly secur-
able to each other. The assembly for supporting a filter
cartridge-comprises a permeable cylindrical core, a top cap
attached to one end of the core to seal that end, a bottom
member attached to the opposite end of the core and extending
outwardly from the periphery of the core leaving the center of
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the core oper, to act as the filter outlet, and a filter cart-
ridge comprising filter media extending between the top cap
ana the bottom member and about the circumference of the core.
The media is sealed to the top cap and the bottom member. The
core and the media being in contact only at discrete, inter-
' 20 mittent areas spaced longitudinally and circumferentially aboutthe core and the distance between the housing and the filter
media being uniformly increased from the bottom member to the
top cap and the area of the internal opening of the filter
media being steadily increased from the top cap to the bottom
member, whereby the uniformity of filter media utilization is
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increased.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be further described in
conjunction with the accompanying drawings wherein:
Figure 1 is a cross-sectional view of a blood filter
unit in accordance with the present invention, and
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Figure 2 is a cross-sectional view taken along line
2-2 of Figure 1.
DETAILED DESCRIPTIO~ OF
THE PRESENT INVENTIO~
Referring to the drawings in Figures l and 2, there
is shown a blood filter unit 10 comprising the assembly
for supporting a filter cartridge 11, the cartridge 12,
and the housing 13. The assembly 11 comprises a core 14
which is cylindrical in shape and is permeable. The
core comprises a number of longitudinal struts 15 held
in spaced-apart relationship by a plurality of annular
rings 16.
It is preferred that the core be conical in shape
for ease of manufacture and ease of assembly of the filter
unit.
The filter media is in the form of a cartridge 12
which has a convoluted configuration and encircles the
entire periphery of the core. The media contacts the
core only at those portions of the flutes which contact
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the outwardly extending rings so that contact between
core and media is only at intermittently spaced-apart
areas which are spaced longitudinally and circumferen-
tially about the core. The contact between solid por-
tions of the core and filter media is kept to a minimum
to reduce blockage of the filter area. By using ver-
tical pleats in the media and horizontal annular rings
as the only contacting supporting structure, it is insured
that contact between core and media is kept to a minimum
and only at discrete, intermittently spaced-apart areas.
This construction reduces harmful effects on blood caused
by obstructions in the flowing blood stream as these ob-
structions have been reduced to a minimum.
Covering the top of the core and the filter media
is the top cap 18. The media is sealed to the top cap
by a hot melt adhesive 19. Attached to the bottom of
the core is the bottom member 20 which extends outwardly
from the periphery of the core. This construction leaves
the center of the core 21 open to form the outlet 22 for
the filter. The media is sealed in the bottom member
by hot melt adhesive 23. The outer edge of the bottom
member is threaded 24 and carries a suitable gasket 25
so that the botto~member may be securely attached to
the filter housing 13 and a tight, leak-proof seal pro-
duced at the gasket.
The above described construction allows the entire
assembly and cartridge to be flushed and medically cleaned
before it is inserted in the housing, sealed and sterilized.
The assembly and cartridge may be flushed from both directions
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1042359
to insure that any foreign particles or impurities that
might be present are removed and eliminate the possibility
of foreign material being present in this portion of the
filter when it is placed in use.
In use, the blood being filtered flows from the
outside of the filter media, through the media, through
the core and out the center outlet of the core. It
may be theorized that the space between the media and
the core and the minor contact between the two reduces
the deleterious effects on blood. The smaller the area
of filter media that is blocked by the core, the less
the pressure drop during the filtering operation. Also
the above described configuration of the space between
the media and the core aids in eliminating entrapment
of gas in the filtered blood.
Surrounding the filter cartridge is the housing 13.
The bottom open end of the housing is threaded so it
may be joined to the bottom member of the assembly. The
housing is cylindrical in shape and in a preferred embodi-
ment of the present invention, the side walls:of thehousing are tapered as shown in Figure 1, to improve the
flow characteristics of the filter and aid in the evacuation
of gas or air entrapped by the filter. At the top of the
filter is an inlet 26 for the incoming blood. The inlet
is shown substantially in the center of the top portion
of housing though it could be off-set or moved to the side
of the housing as desired. Also at the uppermost point
of the filter, there is a vent 27 to allow air to escape
from the filter as it is being filled and to allow any
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gases removed from the blood to continue to escape
during filtration.
In use, the blood enters the top center inlet 26
and flows down over the top cap 18 down along the side
walls of the housing to fill up the housing forcing the
air to escape through the top vent 27. The blood flows
through the filter media to the space between the
core and the media and the filtered blood passes through
~ the permeable core and out the center bottom outlet 22.
; 10 This flow is shown by the arrows in Figure 1.
A preferred spacing between the inside walls of the
housing and the media is shown in Figure 1. The spacing
~-` (A) is greater at the upper portion of the media than the
spacing (B) at the bottom of the media. This configura-
tion improves the ease with which gas is allowed to
escape from the housing and aids in degassifying the blood
being filtered. This configuration also improves the
fluid flow characteristics of the blood and reduces
turbulence or undesirable agitation of the blood which
may be harmful.
Also the configuration eliminates secondary flow
zones within the filter, that is zones where blood might
sit and not move for periods of time. The configuration
allows for the continual movement of blood throughout
the filter. A quiet zone in the filter may cause sedi-
mentation and be harmful and disrupt or reduce the fil-
- tering efficiency of the unit. Also, this configuration
unexpectedly eliminates the problem of "unloading" of the
filter media. In many blood filter units, there is a
~)4Z359
problem with the media starting to become blocked.
This blocking will increase the pressure drop across
the media. If conditions are right, at certain times,
the filter will unload or pass portions of the material
which may be damaging to the patient. Unexpectedly, the
relative shape of the inside housing wall to the upstream
filtering surface of the media as has been described
and as showntin Figure 1 greatly reduces this problem
of "unloading".
The filter housing and support assembly may be
made from various plastic or metal materials provided
the material is inert to the action of blood. The
material may be opaque, translucent or transparent as
desired. Suitable materials are polyolefins, such as
polypropylene, polyethylene, the butadiene-styrene
polymers, polycarbonates, and similar materials.
With the two-piece assembly as described each piece
may be thoroughly and completely flushed to make it medi-
cally clean and remove any foreign particles that might
remain in the parts as a result of their manufacture or
their handling prior to being assembled. The pieces
after being thoroughly cleaned and flushed are assembled
as described and the unit sterilized by gas sterilization
or radiation sterilization.
The media used in our improved filter is either depth
type media such as the synthetic fiber felts, synthetic
foams and the like, or sieve type media such as woven
polyester fabrics, woven nylon fabrics and the like. The
specific media used will be determined by the type of
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104~Z3S9
operation in which the filter unit will be used.
In a specific embodiment, the filter media is in
a pleated configuration with the pleats running the length
of the media. As may be seen in the drawings, the number
of pleats used in the cartridge 12 are uniform, however,
the distance between pleats is greater at the bottom
end cap 20 than at the top cap 18. This means the spacing
between pleats is tapered with adjacent pleats diverging
from each other from the top cap to the bottom cap.
Filtered material which may be caught between pleats
at the top portion will readily settle to the bottom of
the filter and reduce the propensity for the media to
become blocked.
Having thus described the invention, it should be
understood that many variations and modifications may be
made to the invention without departing from the inven-
tion itself. The invention is only limited by the scope
of the claims appended hereto.
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