Note: Descriptions are shown in the official language in which they were submitted.
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BackQround of the Invention
The filtration of blood is a delicate and critical
operation. Blood filtration requires that the debris, such
as clots and various types of agglomerates, be removed with-
out removing desirable red cells or other desirable portions
S of the blood and without degradation of the blood.
Whole blood comprises plasma, red cells, white cells
and platelets. The red cells have diameters of from about 8
to 10 microns and the white blood cells have diameters of from ~:
about 12 to 20 microns. Whole blood, after storage for a
relatively short period of time, and blood which is passing
through an extracorporeal circuit, such as is used in open -~
heart surgery, or through a dialysis operation will tent to
degrade and build debris in the blood. This debris must be
filteret from the blood before the blood is returned or given -~
lS to a patient. The debris may comprise blood clots or various
types of aggregates of the platelet type or the leucocyte type
and may include agglomeration of protein precipitatesand other
undesirable debris. In filtering this blood, the ultimate is
to remove all of the undesirable debris while not removing any
of the desirable red blood cells or white blood cells or t~e
platelets. Hence, media used in the filtration of blood must
meet certain requirements. It must have no harmful effects on
the blood or degrade the blood. The media should be stable
during filtration, that is its pore size distribution range
should not be altered. Very often some media will start to
plug and after limitèd use will remove some of the desirable
red and white blood cells from the blood. The media should
have as much open area as possible to make the most efficient
use of the media area and make the filter small and easily
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Summarv of the Pre~ent Invention
We have discovered an improved blood filter media.
Our improved media haq a nominal pore size rating of 20 microns.
Our improved media is stable during use and retain~ this pore
size rating even after considerable quantities of blood have
been filtered. Our improved filter media has minimal deleter-
ious effect~ on the blood being filtered. Unexpectedly, our
new blood filter media has a very narrow distribution range and
while it removes all of the undesirable debris from the blood
it does not remove the desirable red blood cells and white
blood cells in the blood.
In accordance with a broad a~pect of the present in-
vention, there is provided a unit for filtering blood having
:; the improvement comprising an uncalendered, unbonded, woven
m~DIVhl
fabric filter mcdialhaving a nominal pore 8i ze rating of 20
microns, a pore size distribution range of from 17 microns to
23 microns, and woven with monofilament yarns having a yarn
h1ED UM
diameter of from 30 microns to 36 microna. The ~ is woven
in a two-up and two-down twill weave, whereby the media is
stable and retains its nominal pore size rating and pore size
distribution range during use.
Brief DescriDtion of the Drawinas
The invention will be further described in conjunc-
tion with the accompanying drawings wherein: ;
FIGURE 1 is a plan view of the improved filter mediaof the present invention, and
~ IGURE 2 is a cros~-sectional view of a blood filter
unit incorporating the media of the present invention.
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- Detailed DescriPtion of the Drawings
Referring to the drawings, in Figure 1, there is
shown the improved blood filter ~edia ~O of t~ç present invention. -
The metia is woven with nylon monofilament yarns 11 ant these -~
yarns are used in both the warp ant the filling directions.
The media is woven in a regular, even-sided, two up and two
down twill weave. Though nylon monofilament yarns are preferret,
the metia may also be woven ~ith polyester monofilament yarns
or other monofilament yarns which will not dograte or have a
teleterious effect on the blood. It i5 important that mono-
fila ent yarns be used as it is believed that such yarns, being -
smoother and with less rough areas such as are present in multi-
fila ent or spun yarns, have a longer life ant have 105s
deleterious effects on the bloot. The size of the monofilaments
should be as small as possible. The smaller the dia eter of
lS oach yarn, the more opon area in the filter while still msin-
taining a desired pore size. Sizes of from about 30 microns
in diamot~r to 36 microns in diameter have been found suitable
in accordance with the present invention.
The metia shoult not be calenderet or the yarns bontod
or held together at thoir cross-over points. This is important
as it appears that calondoring or bonting tends to tisrupt the
pore size rating ant distribution range and, surprisingly, does
not have any improvet effect on the stability of the two up ant
two town twill weave. By stability, it is meant that its
initially rated pore size is maintained throughout its expectet
life. The improvet bloot filter metia has a nominal pore size
rating of 20 microns. If its rating is less than 20 microns, it
will remove tesirable portions such as white ant red bloot colls
from the bloot being filtered. If its pore size rating is
greater than 20 microns, it will not remove all of the untesirable
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debris. The media should have a particle distribution range
of from 17 microns to 23 microns. This is a narrow distribu-
tion range; however, it is important to the present invention.
A witer tistribution range will either remove too many impor-
S tant portions of the blood or not remove sufficient debris or,
in some instances, may have both harmful effects. Furthermore,
the witer distribution ranges to not maintain that distribution -~
ran8e turing extended uses ant hence are unsatisfactory.
The two up and two down twill weave using substantially - -
the same size yarns in the warp and fill direction produces a
fabric having very uniform openings which is essential to the
present invention. The fact that our fabric media is not cal- ~ -
endered or heat set allows us to insure the maintenance of this
opening in a blood filter unit.
It has been theorized that the above-described twill
weave combinet with the lack of calendering protuces some dopth
to the fabric media or tepth to the openings or pores in the
fabric. This slight dopth to the pore helps in preventing
slightly largor particles than the size of the opening from
changing shape and squeozing through an opening or pore.
In Pigure 2, there is shown one embotiment of a blood
filter unit 15 that utilizes the bloot filter media of tho
prosent invention. The unit comprises a housing 16 and a filtor
cartridgo 17 disposed within the housing. At the top of tho
housing is an inlet opening 18 for the incoming bloo~ and an air
vent l9 to allow air to escape from the filter unit. The filter
cartridge is cylintrical in shape. The outside walls of the
cylinder are formed by the filter media 20 of the present in-
vention. The media may be flat or fluted in its cylindrical
form. The insite surface of the metia is supportet by an open
mesh-like cylinter 21. The upper end of the media is sealed
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by a cap 22. The lower end of the media is sealed into the
bottom portion of the housing. In the center of the bottom
portion of the housing and positioned adjacent the center
of the filter cartridge is the blood outlet opening 23.
In operation, the blood flows in the path as shown
by the arrows in the drawing. The blood enters through the
inlet I8 and from outside the filter cartridge into the
center of the cartridge and out the outlet 23.
Though a cylindrical blood filter unit has been ;
shown, the unit may be of any desired shape and the metia
may take any configuration as desired.
Having thus described the presen~ invention, it shoult
be understood that many variations and modifications may be made --
without teparting from the scope of the invention itsolf; the
lS invention is only limitod by the scope of the clains appented
hereto.
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