Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE
Plasmapheresis by
Reciprocatory Pulsatile Filtration
TECHNICAL FIELD
This invention pertains to a process and
an apparatus for plasmapheresis by reciprocatory
pulsatile filtration with microporous membranes.
BACKGROUND INFORMATION
Plasmapheresis is a process of separating
plasma from whole blood. The plasma-depleted blood
is comprised principally of cellular components,
e.g., red blood cells, white blood cells and plate-
lets. Plasma is comprised largely of water, but
also contains proteins and various other noncellular
compounds, both organic and inorganic.
Continuous plasmapheresis is the process of
continuously separating plasma from whole blood.
Plasmapheresis is currently used to obtain
plasma for various transfusion needs, e.g.,
preparation oE fresh-frozen plasma, for subsequent
fractionation to obtain specific proteins such as
serum albumin, to produce cell culture media, and for
disease therapies involving either the replacement of
plasma or removal of specific disease-contributing
factors from the plasma.
Plasmapheresis can be carried out by
centrifugation or by filtration. Generally, in known
filtration apparatus, whole blood is conducted in a
laminar flow path across one surface, iOe., the blood
side surface, of a microporous membrane. Useful
microporous membranes have pores which substantially
retain the cellular components of blood but allow
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plasma to pass through. Such pores are referred to
herein as cell-retaining pores. ~ypically,
cell-retaining pore diameters are 0.1 ~m to 1.O ~m.
In such known apparatus, as the blood flows
through the flow path, the cellular components tend
to migrate towards the center or axis of the path.
Ideally, plasma occupies the periphery of the path so
that it is predominantly plasma that contacts the
membrane. A pressure difference across the membrane
causes some of the plasma to pass through the pores
of the membrane while plasma-depleted blood continues
to flow to the end of the path. Ideally, the
filtrate is cell free; the plasma-depleted blood
collected at the end of the flow path is
lS concentrated, i.e., is depleted in plasma and
therefore has an increased hematocrit ~volume percent
of red blood cells).
After blood has been conducted across the
surface of a membrane at normal venous flow rates for
some time, the transmembrane flow of plasma becomes
impaired. This phenomenon is herein sometimes
referred to as membrane fouling or simply as
fouling. Known techniques for reducing fouling,
i.e., increasing the length of time for which the
process can be carried out without the occurrence of
significant impairment o plasma flow, include
varying the flow path size so as to optimize the wall
shear rate along the length of the flow path as
disclosed in UoS~ Patent 4,212~742, and recycling a
portion o the plasma-depleted blood to increase the
velocity of blood in the flow path; the latt~r
technique may result in less plasma-depletion.
Various filtration devices for
plasmapheresis are disclosed in the literature. U.S.
3,705,100 discloses a center-fed circular membrane
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having a spiral flow path. U.S. 4,212,742 discloses
a device having divergent flow channels. German
Patent 2,925,143 discloses a filtration apparatus
having parallel blood flow paths on one side of a
membrane and parallel plasma flow pa-ths, which are
perpendicular to the blood flow paths, on the
opposite surface of the membrane. U.K. Patent
Application 2,037,614, published July 16, 1980,
discloses a rectilinear double-membrane envelope in
which the membranes are sealed together a-t the ends
of the blood flow path. U.K. Patent Specification
1,555,389 discloses a circular, center-fed, double-
membrane envelope in which the membranes are sealed
around their peripheries. German Patent 2,653,875
discloses a circular, centre-fed double~membrane
device in which blood flows through slo-t-shaped
filter chambers.
It is an object of this invention to provide
a process and apparatus for plasmapheresis by
filtration. It is a further object to provide such
a process and apparatus whereby higly concentrated,
plasma-depleted blood can be continuously collected
without significant hemolysis and wi-th reduced
membrane fouling.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGo 1 is a cross-section of a
double-membrane filtration module which may be used
in the process of the invention, taken along line I-I
of FIG~ 2~
FIG. 2 is a perspective view of an
illustrative embodiment of the filtration module of
FIG. 1 having a loop and an oscillator to oscillate
blood in a blood flow path between inlet and outlet.
FIG. 3 is a perspective view of a module
having an end plate which has reciprocatory pulse
cavities.
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DISCLOSU~E OF THE INVENTION
For further comprehension of the invention
and of the objects and advantages thereof, reference
may be made to the following description and to the
appended claims in which various novel features of
the invention are more particularly set forth.
It has been found that the above objects
can be achieved by conducting blood over the surface
of a membrane in reciprocatory pulsatile flow. In
particular, the invention resides in a method for
continuously separating plasma from blood, which
method comprises:
(1) conducting blood in a forward direction
over a first surface, i.e., a blood side surface, of
each of one or more membranes having cell-retaining
pores, while maintaining a net positive transmembrane
pressure difference;
(2) terminating the forward conducting of
blood over the first surface of the membrane;
2Q (3) conducting the blood in the reverse
direction over said first surface, the volume of
blood flowed in the reverse direction being less than
the volume of blood flowed in the forward direction
in step (1);
(4) repeating steps (1)-(3) in sequence and
collecting plasma which passes through each membrane
from a second surface, i.e., a plasma side surface,
thereof and collecting plasma-depleted blood from
said first surface.
The invention further resides in said
process wherein the transmembrane pressure difference
is reduced during periods of flow, preferably to
below zero.
The invention also resides in apparatus for
carrying out the aforesaid steps. In particular, the
invention also resides in apparatus for separating
plasma from blood which apparatus comprises one or
more membranes having cell-retaining pores, means
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for conducting blood forward at a net positive
transmembrane pressure difference and reverse over a
first surface of each membrane, means for collecting
plasma which passes through each membrane from a
second surface, i.e., a plasma side surface, thereof
and means for collecting plasma-depleted blood from
said first surface. The invention also resides in
said apparatus comprising means for reducin~ the
transmembrane pressure difference during periods of
flow, preferably, means for reducing said pressure
difference to below zero.
Further, the inven-tion reside in the
membrane filter module which comprises:
first and second opposing module housing
plates having circular recesses within opposing
surfaces so as to form a blood flow region
between two plasma flow regions, there being a
central blood inlet port connected to the blood
flow region; a blood collection channel, around
the blood flow region, connect to a plasma-
depleted blood outlet port; and a plasma
collection channel around each plasma flow region
connected to a plasma outlet port;
a plasma-side support within each plasma
flow region; and
a pair of membranes, having cell-retaining
pores, between each plasma flow region and the
blood flow region, there being an elastomeric
seal between each membrane and each plate and a
blood flow path between the membranes.
The invention also resides in such a
filtration module in which blood side supports are
located between the membranes. Such module may have
means for imparting reciprocatory pulsatile flow to
blood in the flow path connected thereto.
By comprises is meant that the invention
includes the aforesaid steps and elements although it
is to be understood that other steps and elements are
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not excluded from the invention, e.g., recycling the
plasma-depleted blood, treating plasma during filtra-
tion, diluting the blood with a compatible Eluid and
measuring various biologically significant factors
and means therefor.
In the following description and examples of
the invention, the term "forward" is used to idicate
a direction generally away from the source of blood;
reverse indicates a direction generally towards the
source of blood. Transmembrane pressure difference
is determined by subtracting the pressure on the
plasma side, i.e., the second surface of the membrane,
from the pressure on the blood side, i.e., the first
surface of the membrane. It is to be understood that
the transmembrane pressure varies across the membrane
with the distance the blood has traveled from the
source. Thus, with regard to this invention, since
localized transmembrane pressure differences across
the membrane may be either positive or negative, only
the system transmembrane pressure differences are
reported, being referred to herein as net -trans-
membrane pressure differences. The -term "fouling"
is used to describe the impairment of plasma flow
-through a membrane.
In the invention, blood may be conducted in
a forward direction in a flow path over the first
surface of a membrane by any means which does not
cause significant damage to cellular components,
which does not cause significant discomfort or danger
to a donor or patient, which provides sufficient
forward flow rate and pressure to efficiently
fractionate blood in the manner and under the
conditions described below, and which allows the
forward flow to be periodically interrupted as
described below. Examples include various pumps such
as a rotary peristaltic pump, a piston or syringe
pump, and a plunger or hose pump; even manually
operated devices such as a flexible blood-containing
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chamber which can conduct blood forward when
compressed may be used.
The membrane is made of any blood-compatible
material, and has cell-retaining pores, i.e., pores
which substantially retain cellular components but
allow plasma to pass through; such pores are
typically about 0.1 to 1.0 ~m average diame~er. The
selection of a pore size may vary with the goal of a
particular treatment. Useful membranes are described
in some of the above-cited references relating to
plasmapheresis. The membrane may be of any suitable
~hape, e.g., tubular, such as hollow fibers or any
planar shape. When planar membranes are used,
membranes having low elongation, e.g., less than
about 65%, high modulus, e.g., at least about 10 kpsi
(70 MPa), and high tensile strength, e.g., at least
about 3000 psi (20 MPa), when tested wet in
accordance with standard procedures, are preferred,
because they are dimensionally stable. As exemplary
of membranes having these preferred properties are
mentioned the HT 450 polysulfone membrane
commercially ava;lable from Gelman Sciences, Inc. and
the polyester and polycar~onate membranes
commercially available from Nuclepore Corporation.
Of these, thin, e.g., less than about 1 mil (25 ~m),
preferably less than 0.5 mil (13 ~m), smooth
polycarbonate or polyester capillary pore membranes
are preferred because, in laboratory experiments,
such membranes were found, in general, to perform
better than the tortuous path membranes which were
tested. Under various conditions of practice,
however, any of the above-described or other types of
membranes may prove to be more or less advantageous.
It is to be understood that more than one membrane in
any arrangement may be used~ Conveniently, several
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membranes are stacked within an enclosed module so
that blood is fractionated by more than one membrane
simultaneously. A planar membrane is preferably
supported on the plasma side and more preferably
on both sides by, e.g., supports comprising plates
having grooves, pores or projections or fabric-like
materials. A preferred plasma side support comprises
a plurality of layers of a nonwoven polyester fabric.
From the location at which the blood first
contacts the membrane, which may or may not be near a
point on an edge or end of the membrane, blood is
conducted in a forward direction in one or more flow
paths. A flow path is the space through which the
blood flows on the first surface of the membrane.
For example, in a preferred embodiment, the membrane
is planar and circular, the location at which the
blood contacts the membrane is near the center
thereof, and the flow path extends radially, ending
near the periphery of the membrane. It is apparent
that when the membrane is tubular and blood is
conducted within the tube, the membrane may alone
define the flow path. Typically the depth of blood
in each flow path is less than about 30 mils (0.76
mm). Preferably, said depth is also at least about
4 mils (0.10 mm) but, preferably no more -than about
10 mils (0~25 mm).
The rate at which blood is conducted over
the first surface of the membrane is at least as high
as may be needed to provide a net positive trans-
membrane pressure difference. The flow velocitytypically varies during each period of forward flow.
The preEerred average forward flow rate from the
source to the membrane is about 50 to 60 ml-min~l
when the source of blood is a vein of a normal human
donor although the process may be carried out at
higher or lower flow rates.
Plasma is driven through the cell-retaining
pores in the membrane at a practical rate by a
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positive transmembrane pressure difference.
Typically, positive transmembrane pressure difference
is generated primarily by resistance to forward flow,
but it can also be generated in other ways, e.g., by
decreasing pressure on the plasma on the second
surface.
It has been found that the amount of
transmembrane pressure difference that can be with-
stood by blood without hemolysis is largely a function
of cell-retaining pore size. For most purposes, the
preferred pore diameter is about 0.4 to 0.5_um. In
this range, a positive transmembrane pressure differ-
ence of up to about 4 psi (28 kPa) is desirable
although up to about 1.5 psi (10 kPa) is believed to
be preferred. When the pore diameter is smaller or
larger, higher or lower transmembrane pressure dif-
ferences, respectively, are acceptable. It is to be
understood that the pressure on the blood side and the
plasma side surfaces, and the transmembrane pressure
difference, may vary during the course of a treatment
and in different regions of the flow path~
After the conducting of blood over the first
surface of the membrane with a positive transmembrane
pressure difference is continued for some time, the
membrane becomes progressively fouled, i.e., the flow
of plasma through the membrane becomes increasingly
impaired. The length of time for which blood can
be so conducted is believed to depend upon several
factors such as, e.g., flow velocity, hematocrit,
pore size, transmembrane pressure difference, and the
individual characteris-tics of the blood being treated.
The frequency and volume of the reciprocatory pulses
are selected to maximize the flow of plasma through
the membrane without causing extensive blood trauma.
In planar blood flow paths having a height of about
4 to 10 mils (100 to 254 um), a useful frequency and
volume are about 20 to 140 pulsations per minute,
preferably 40 to 80 pulsations per minute, and 0.5
20s
to 4 mL per pulsation, perferably about 3 mL. By
pulsations per minute, also referred to herein as
cycles per minute, is meant the number of tlmes per
minute the blood is conducted throught a cycle, a
cycle consisting of one ~orward movement and one
reverse (backward) movement of blood across the
membrane. Said parameters should be selected to
provide a mean linear velocity up to about 400
mm-sec~l, preferably, up to about 250 mm-sec~l.
These parameteres may be adjusted during a particular
treatment, but conveniently may be selected and fixed
for an entire treatment.
After the forward conducting of blood is
terminated, blood is conducted in the reverse direc-
tion in each flow path. The termination of forwardflow and the conducting of blood in the reverse
direction need not occur simulataneously over the
entire membrane. Because blood is conducted in for-
ward and reverse direction with a net forward flow
during the procedure, the blood flow is referred to
as reciprocatory pulsatile flow.
In a preferred embodiment, the transmembrane
pressure difference is reduced when conducting blood
in either direction. The preferred method is by
using a pulse pump connected to the module blood
inlet and outlet. The pulse pump suction produces a
negative pressure at peak flow rate over the portion
of the filtration membrane from which pulse blood is
being drawn for that portion of the pulse cycle.
Another method is to increase plasma side pressure so
that the blood in the downstream area of the membrane
can be at pressure which is positive but lower than
the upstream blood pressure and lcwer than the plasma
side pressure. Other means will become apparent
hereinafter. It is to be understood that said
reduction need not occur simultaneously over the
entire membrane, e.g., at any given instant, there
may be areas on the membrane with high transmembrane
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pressure difference and other areas wi-th low
transmembrane pressure difference and, at any given
point on the membrane, the transmembrane pressure
difference may continuously fluctuate. Preferably,
the transmembrane pressure difference is reduced to
below zero, e.g., about -.1 to -3.0 psi (-.7 to -20.7
kPa), and, more preferably, to about -0.8 to -1.0 psi
(-5.3 to -6.9 kPa)~ Preferably, a large amount of
plasma backflow through the membrane is avoided.
The duration of the reverse flow of blood is
selected to maintain substantially unimpaired flow of
plasma through the membrane as well as to increase
the distance which the blood travels across the mem-
brane. A wide range of reverse flow durations are
useful. The volume of blood flowed in the reverse
direction is less than the volume of blood flowed
forward.
It is to be understood that reverse flows
of blood may begin in some regions of the flow paths
prior to cessation of the forward flow of blood in
other, or even in the same, regions, i.e., forward
and reverse flows may overlap. It is preferred that
the frequency of the reciprocatory pulsations be
low, but at leas-t twenty, in the early stages of a
treatment and then be gradually raised to a desirable
frequency. It may be necessary to adjust the
apparatus during a procedure to maintain desirable
pressures and flows.
The blood which approaches the ends of each
flow path is plasma-depleted blood. It is collected
and conducted away from the membrane by any suitable
means, as is the plasma which flows through the
membrane.
The reciprocatory pulsations and
transmembrane pressure difference reductions, as is
apparent from the above discussion, can be carried
out in numerous ways. Typically, the means include a
plurality of coordinated pumps and valves positioned
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on blood, plasma-depleted blood and/or plasma lines.
Pressure accumulators, or surge chambers, may also be
useful~ Some such useful means are disclosed in the
following examples, which are illustrative only, of
treatments in accordance with the invention. Other
means will be obvious to persons skilled in the art.
Referring to FIG. 1, a filtration module,
which may be used with reciprocatory pulsatile flow
and may have means for generating reciprocatory
pulsations connected thereto, comprises two circular
opposing module housing plates lA, lB which are
prepared from a blood-compatible material. A
circular blood flow region 2 is recessed within an
opposing surface of one or both plates. Further
recessed within each plate is a plasma flow region
3A, 3B. Typically, though not necessarily, the
plasma flow region is of smaller diameter than the
blood flow region.
The depth of the plasma flow region is
typically about 5 to 20 mils (127 to 508 ~m)O The
surface of the plasma flow region may be smooth or
grooved to enhance radial flow of plasma. In the
plasma flow region, or connected thereto, may be
means for treating the plasma for the removal of
disease-contributing factors.
One or both plates lA, lB have plas~a outlet
ports 4A, 4B connected to the plasma flow regions 3A,
3B via a plasma collection channel around the plasma
flow regions, e.g., about 3 mm deep and 1.5 mm wide.
There may be one or more of such ports in either or
both plates. The ports and channel may be located at
any position but preferably, as herein illustrated,
are located near the periphery of each plasma flow
region.
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Near the center of plate lA is blood inle~
port 5, the walls 6 of which extend through plasma
flow region 3A to the blood flow region 2. Around
the periphery of blood flow ~egion 2 is a
plasma-depleted blood collection channel 7. This
channel connects to one or more plasma-depleted blood
outlet ports 8.
Within each plasma flow region is a plasma
side membrane support 9A, 9B which may be, e.g., a
plate having grooves, pores or projections or
fabric-like materials. As illustrated, the plasma
side supports are comprised of layers of fabric-like
materials, such as layers of a nonwoven polyester
fabric. The preferred support is three layers of
4 mil (102 ~m) thick Hollytex, made by calendering
Du Pont Reemay~ spunbonded polyester, because it
provides adequate support while allowing transverse
and radial flow of plasma. The support 9A which fits
in plasma flow region 3A is provided with an aperture
which fits around wall 6 of blood inlet port 5.
Within each blood flow region is a membrane
lOA, lOB. M,embrane lOA which fits in blood flow
region 2 in plate lA is provided with an aperture
which lies approximately in registry with blood inlet
port 5.
The membranes lOA, lOB are adhered to the
plates near the peripheral edges of the membranes
and, in the case of the membrane lOA, near the edge
of the aperture in the membrane which is in registry
with blood inlet port 5, with an elastomeric
adhesive. Use of an elastomeric seal provides
sufficient flexibility to avoid rupture of the
membranes during use. The areas of membranes lOA,
lOB which are adhered to plates lA, lB are identified
in FIG. 1 by the number 11.
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It has been found that ~hen thin
polycarbonate or polyester membranes which have low
break elonga~ion, i.e., less than about 40~, are
employed in filter modules in which, as herein
S illustrated, the membranes are not rigidly supported
across a large part of their surface areas, it is
advantageous to employ an elastomeric seal between
the membranes and supports. Use of an elastomeric
seal provides sufficient flexibility to avoid rupture
of the membranes during use. When such membranes are
employed, the seal preerably has a break elongation
of at least about 100%. The optimal break elongation
will dep~end on several factors which will be obvious
to persons skilled in the art, including the
thickness of the seal. An elastomeric seal which has
been found to perform well with such membranes is an
adhesive having a break elongation of about 400% and
applied in a layer abou~ 3 mils (76 ~m) thick.
When the module is assembled, the
corresponding flow regions of each plate are
adjacent. The plates are held together by any
suitable means, e.g., clamps, bolts and adhesivesO
An O-ring 12 can be used to seal the plates. The
region between the membranes is the blood flow path.
The total effective surface area of the membranes,
i.e/, the sum of the areas on both membranes through
which plasma can flow, is about .02 to .06 m2.
Blood side supports 13 are located between
the membranes. Blood side supports, though not
necessary, have been found to be advantageous whPn
nonrigid plasma side supports, such as layers of
Hollytex, which may tend ~o buckle during use, are
employed. Various suitable supports are described in
the literature. The illustrated and preferred
supports comprise a plurality of smooth pillars,
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e.g., substa~tially circular, dots of cured adhesive
of the type used to adhere the membranes to the
plates. These have sufficient softness to avoid
breakage of the membranes during use.
FIG. 2 is an illustration of an embodiment
of ~he invention in which the filtration module of
FIG. 1 is used. The loop for generating
reciprocatory pulsations as illustrated herein is the
invention of one other than the inventor herein.
Blood is conducted from the source to the blood flow
path via blood inlet port 5 in module housing plate
lA. Plasma which passes through the membranes exits
from the module through a plasma outlet port 4A, and
a second plasma outlet port, not shown.
Plasma-depleted blood from the end o~ the blood flow
path exits from the module through plasma-depleted
blood outlet port 8. In addition, blood flow is
pulsed in reciprocatory fashion by a peristaltic
oscillator 15, which is connected to central and
peripheral ports 16 and 17 through loop 18, which
peripheral ports are connected to areas near an end
of the flow path, directly, or indirectly via a blood
collection channel, no~ shown. The loop is
preferably short so that blood in the loop is
fre~uently mixed and exchanged with blood in the flow
path. There preferably is little or no exchange of
blood across the oscillator. Any suitable type of
pump may be used to cause the reciprocatory
pulsations. Such pumps are described in the
literature and in the Examples below; a peristaltic
pump is preEerred. Preferably, though not
necessarily, the oscillator is connected to the blood
flow path via one centrally located port and two
peripherally located ports, as shown, or to the blood
inlet and plasma-depleted blood outlet lines at a
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- location close to the module. The duration and
frequency of oscillations can be regulated by
adjusting the oscill~or. The forward and reverse
strokes are typically of equal volume.
FIG. 3 illustrates a module having an end
plate, i.e.~ module housing plate, which has
reciprocatory pulse cavities integral therewith. The
end plate is the invention of one other than the
inventor herein.
Blo~d is conducted into the module via an
inlet, not shown, in end plate l9B and is conducted
through a matched port 20 in end plate 19A. From
port 20 in end plate l9A, the blood is conducted
through shallow channel 21, 0.2 inch (5.1 mm) wide x
Q.06 inch (1.5 mm) deep, into inlet reciprocatory
pulse cavity 2~ which has a volume of about 3 mL and
is about 2 inches (50.8 mm) in diameter x 0.06 inch
(1.5 mm) deep. Cavity 22 is employed in the
generation of reciprocatory pulsations as described
below. From cavity 22, the blood is conducted
through shallow channel 23, 0.5 inch (127 mm) wide x
0.13 inch (3.3 mm) deep, to blood flow path inlet 24
which is about 0.38 inch (9.7 mm) in fli~meter. The
blood is conducted through port 24 into a blood flow
region between two membranes as described above.
Plasma-depleted blood is conducted through flow path
outlets 25 and through branch channels 26 to outlet
reciprocatory pulse cavity 27 in end plate l9A. The
branch channels from the four outle~s 25, which are
equidistant from each other, begin as four channels
each about .250 inch (6.4 mm) wide x .060 inch ~1.5
mm) deep and merge into two channels each about .500
inch (12.7 mm) wide x .060 inch (l.S mm) deep. The
branch channels are of equal length and cross-section
so as to produce substantially e~ual pressure
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conditions during use. Cavity 27 is also employed in
the generation of reciprocatory pulsations as
described below. From cavity 27~ the plasma-depleted
blood is conducted through shallow channel 28, .200
inch (5.1 mm) wide x .060 inch (1.5 mm) deep, and
through plasma depleted blood outlet 29 which extends
through a matched port in end plate l9B.
Plasma which pa~ses through the membranes
flows radially in a plasma flow path and through a
plasma collection channel, as described above, to an
outlet port, not shown, in end plate l9B.
The entire module is enclosed by envelope 30
which is comprised of two sheets of a flexible blood
impermeable material, such as poly(vinyl chloride),
the sheets being joined together at seal 31 aroun~
the perimeter of the stack. The envelope thus
provides a unitary flexible enclosure for the
module. The three apertures in end plate l9B mate
with tube connectors in envelope 30.
Envelope 30 covers and seals the various
channels, cavities and apertures in end plate l9A and
forms a flexible diaphragm over each cavity 22, 27.
A perimeter lip~ not shown, around each cavity and
channel in end plate 19A aids in sealing.
Reciprocatory pulsations are generated by alternately
compressing the diaphragm over each cavity 22, 27
such as by the use of reciprocating plungers.
All of the above illustrated modules must be
clamped using pressure which is at least sufficient
to offset internal pressure. In the examples, below,
a series of C-clamps around the perimeter of each
module was employed.
EXAMPLES
In all of the following examples, which are
illustrative of single pass treatments to separate
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plasma from blood in accordance with the invention,
compatibility-matched human blood collected in either
ACD or heparin was used. The hematocrit of the
blood, which was maintained at 37C during treatment,
was 37-38%.
In all Examples, planar circular supported
membranes were encased in membrane filter modules
made from Du Pont Lucite~ acrylic resin. The
membrane fil~er modules each comprised two circular
discs between which were placed one or two supported
membranes. Blood was fed to an inlet port at the
center of the module and conducted radially therefrom
across the surface of each membrane. Plasma-depleted
blood and plasma were collected by means of
peripheral channels, cut into the discs, which led to
outlet ports.
The membranes were polycarbonate capillary
pore membranes, available from Nuclepore Corporation,
having average cell-retaining pore diameters of about
0.4 ~m and about 10% pore area and were about 10 ~m
thick.
Three materials were alternatively used in
the construction of membrane supports. One of these
was HolLytex and two were high density polyethylene.
Hollytex is a nonwoven polyester fabric produced from
layers o Du Pont Reema~ spunbonded polyester by a
calendering procedure. The Hollytex material was
used in layers 10 mils (254 ~m) or 4 mils (102 ~m)
thick. The polyethylene materials were porous plates
about 6~3 mils (160.0 ~m) thick; one had pores which
were about 70 ~m and the other, about 120 ~m, in
diameter. Radial channels in the dis~ below the
polyethylene plate allowed for lateral flow of plasma
Prior to each treatment, the module was
purged of air by flushing with saline. The Hollytex
lg 1~205
supports were first solvent-exchanged in isopropanol,
soaked in saline and then placed wet in the membrane
filter module. The membrane filter module was
submerged in saline, 37C, during treatment to
prevent air leakage. Removing air from and
maintaining air out of the apparatus is important.
The transmembrane pressure difference was
measured by means of pressure strain gauge
transducers and monitored near the center and/or near
the periphery of the module and was recorded, usually
at 5 to 10 min. intervals. The plasma side of the
apparatus was vented, excep~ where noted, and was
assumed to be at atmospheric pressure.
Hemolysis was determined by visual
observation of samples of plasma periodically
collected during each treatment.
The operating conditions and results of each
example are tabulated after a general description of
the apparatus used therein. Elapsed time is in
minutes and indicates the times during each treatment
when measurements were taken. Peak and low pressures
are in psig (kPa) and were measured near the
indicated locations. Blood flow rate is the rate of
flow of whole blood from the source to the module in
mL per min. Plasma flow rate is the flow rate of
collected plasma in mh per min. The hematocrit
(Hct.) of plasma-depleted blood which was collected
was calculated. Flux is mL of plasma collected per
min. per rm of membrane filter.
EXAMPLE 1. This example illustrates plasmapheresis
by reciprocatory pulsatile filtra~ion using two
membranes in a membrane filter module such that blood
is filtered by both membranes simultaneously.
Two layers of Hollytex were placed between
two membranes so that blood flowed across the first
19
surfaces of both membranes within recessed flow
regions cut into the inside surEaces of the discs and
plasma which passed through the membranes flowed
radially through the support between the membranes.
The blood flow paths were about 8 mils (203~2 ~m) in
depth and had a combined surface area of about .05
m . Plasma-depleted blood from the ends vf the
flow paths was conducted further through outlet ports
and collection tubing to a collection vessel.
Blood was conducted forward and reverse by
two pumps which were similar to the hose pump
described in U.K. Specification 2,020,735, published
November 21, 1979, except that the outlet valves were
removed, and which were positioned between the blood
bag and the membrane filter module. Each pump
comprised an inlet valve and a 4" (10.2 cm) plunger.
The inlet valves were closed while the plungers were
rising and were partially closed while the plungers
were withdrawing so that blood was conducted from the
directions of the blood bag and of the membrane
filter module as the plungers were withdrawing. The
plungers never completely occluded the tubing. Each
pump displaced about 3.2 mL during each forward pulse.
81Ood passed from the blood bag through a
single tubing which was divided into two lines. Each
line passed through one of the pumps and was rejoined
into a single line.
Blood was also conducted in the reverse
direction by pressure which accumulated in a surge
chamber of about 50 mL which was connected by tubing
to the blood flow path at two locations near the end
of the flow path.
A .33 psi (2.3 kPa) check valve prevented
backflow of blood to the blood bag. A control valve
on the plasma-deple~ed blood collection line was
~0
~ 2 ~.
21
adjusted during the treatment to control blood side
pressures and transmembrane pressure difference.
The conditions and results of this example
are in Table 1.
22 ~ /S
x ~ c~ o o ~ o 'ol
i~
. ~ I 1~ 0 0 ~ O
O ~ ~ ~ er ~r
CD ~ U~ ~ O~ ~ ~ O
~ ~ ~ ~ x
,~ o~
P~
~ o ~ ~_ _
~ J ~ a:l N O ~1 ~ `I O CO
,~ ~i
~ ~ -- ~ ~
15 ~ ~ ~ ~- O ~` '9
m v I I ~
o a~ Ln er ~ ~ ~ _1 CO ~r
_I ~ ~ ~i ~ ~1 ~ _I I I I
ô cô
~ ~ ~3
~ ~ ~ o u~ n ~ ~ o 1
~, ml~ ~. o. ~. o. ~r, ? ~
1~ ~1 ~ ~ ~ cn o
2 5 ~3 ~ ~ ~, ~ ~ ~ ~ u. ~
u~ ~ ~ ~ ~ r-- I~
~3 3 a.? ~D oo a~ O el~ ~ CD O u~ U~
ra ~ ~ o
m ~ ~; ~ ~ ,, ~
~Q _
" ~ ~ O O O O u~ ~ ~ O O O
Q ~ ~ o O ~
~ ~ ~ ~ _I
~ O u~ O O u~ ~ O ul
~ ~D O er 1~ ~
1~5~205
No hemolysis was observed during the first
39.5 minutes. Hemolysis was observed during the
period when the frequency of pulsations was increased
to 100 as a result, it is believed, of the high
5 frequency and the high peak transmembrane pressure
difference. After the pump speed and pressure were
reduced, the plasma began to clear, indicating that
hemolysis had ceased or was lessening.
EXAMPLE 2. This example illustrates plasmapheresis
10 by reciprocatory pulsatile filtration as per the
invention using a single membrane.
Tbe membrane was supported by a polyethylene
plate [120 ~m pores). The flow path surface area was
about .013 m2. The depth of the flow path was
about 6 mils (152 ~m) from the center thereof to a
point along its radius about 3.25" (8.3 cm)
therefrom, from which point, the depth tapered to
about 9 mils (229 ~m) at the end of the flow path.
The peripheral edge of the membrane was pressed
~o bPtween the discs. ~lood flowed radially across the
first surface of the membrane while plasma which
passed through the membrane passed through the pores
in the polyethylene plate and flowed radially in a
plasma flow region cut into the inside surface of the
plasma-side disc.
Reciprocatory pulsatili~y and reductions in
transmembrane pressure difference were provided by a
peristaltic rotary pump which was modified by removal
of all but one of the rollers therein. The circular
path of the roller was about 5.38" (13.65 sm) of
which the roller occluded the tubing for about 5.25"
~13.34 cm); the tubing was .13" (~32 cm) ID silicon
tubing. Therefore, the displacement of the pump,
which was set at 60 rpm, was about 1.1 mL.
Z~S
24
A check valve and plasma-depleted blood
control valve were used.
The peak plasma side pressure remained at
about 1.0 psi (6.9 kPa) at the center and periphery
5 of the module; the low plasma side pressure was about
0 to 0.3 psi ~0 to 2.1 kPa) at the center and
periphery.
No hemolysis was observed. The conditions
and results of this example are in Table 2.
24
-t~2~5
~ 1 In o C~ N ~ ~
101 ~ c~ ~ o u~ ~
o In ~ ~ '
a) N ei' ~D ~i ~
~ r ~ O ~ o
~ _ ,_ _ ~
~ er ~D ~ ~ ~D
m ~ ~ ~ ~ ~ c~
~ _ _ _
2 S ~ ~ N N N N ~1
1~') ~ N ~ a~ r
H tY) ~
~ E~
2~)5
26
EXAMPLE 3. This example illustrates that
reciprocatory pulsatile flow during plasmapheresis
can result in an improved rate of plasma separation
per unit area of membrane as compared to pulsatile
5 flow without reciprocatory pulsations.
The membrane filter module was the same as
in Example 2 except that the entire flow path depth
was about 6 mils (152 ~m) in depth and the porous
plate had pores which were about 70 ~m in diameter.
Initially, blood was conducted forward by a
pressure infuser cuff wrapped around the blood bay.
A 0.5" (1.3 cm) ID control valve positioned between
the bag and ~he module was opened and closed at
various intervals (reported in seconds) to generate
15 pulsatile flow. After some time, the infuser cuff
was removed and the rotary pump described above in
Example 2 was utilized. Then the rotary pump was
disconnected and the infuser cuff system was restored.
The conditions and results of this example
are in Table 3.
26
05
27
X ~ ~ o ~ ~ ~ ~ ~
~i 8 ~ '' o o 8 o
~D O ~ ~ o o C~
~1 ~ 1` o co ~ r~
~1
~ ~ $ ~ ~ ~ ~o 1, o u~
0 ~I
_
~ In ~ _ _ _ _ _
~ _ _ _ _ _ _ _ _
m
~r ~ ~
' ~ ~ I ~ ô ~
~ In :n cs~ ~ ~ ~ ,i
., r ~ ~ ~ ~ ~ ~ ~ ~ ~
~ 8 ~ OD
P~ r~r~: ~
~ H
o
~ o ~
~ ~ o
o o~ ~ o
~ 3 ~ a 8 ~ ~ 8 5
,~
2~)5
28
Hemolysis was observed to result when
pulsations were generated by the infuser cuff/valve
system but not when reciprocatory pulsations were
generated by the rotary pumpO
5 EXAMPLE 4O In this example, modules substantially as
illustrated in FTGS. 1 and 2 were employed. The
membranes were 7 inches (178 mm) in diameter, and
provided a total membrane surface area of about
O05 m . The membranes were adhered to circular
plates, made from Du Pont Lucite~ acrylic resin, with
General Electric RTV 102 silicon adhesive which had a
break elongation of 400%, a tensile strength of
350 psi ~2.4 MPa), and a Shore A hardness of 30. The
adhesive was applied by hand in a layer about 3 mils
(76 ~m) thick.
The same adhesive was used to form blood
side supports by placing dots of the adhesive,
between the membranes in two concentric circles. The
blood flow path between the membranes was about 8
mils (.20 mm) deep. The adhesive supports were cured
on the blood side surface of one membrane at 60C
overnight prior to assembly of the module. The
plates were held together with clamps, without
0-rings.
The blood was conducted forward by a 3-arm
rotary peristaltic pump. A .33 psi (2.3 x 103 Pa)
check valve was located between this pump and the
blood reservoir.
Reciprocatory pulsations and pressure
fluctuations were provided by a modified peristaltic
pump, positioned on a loop, i.e., a length of tubing,
which extended from two peripherally located ports
and one centrally located port. The pump was
modified so that a single roller, in constant contact
with the tubing, oscillated in about a 50 mm stroke
28
29 ~ J2~)~
at about 40 cycles-min 1, thereby displacing about
1.6 mL per stroke. A micrometer control valve was
placed on the plasma-depleted blood outlet line and
was adjusted during the treatment.
Results and conditions of this treatment are
summarized in Table 4. No hemolysis was observed.
29
3L2~;2().5
~ ~ I Ln ,1 ~ ,I cn ~
,Bæl ~ O
~,
,~ ~o o~ co oo o~ co
~ ~, ~
,, ,, I CO .
~ ~ ~ -- U. -- 'I
G 1 81 H .~
ti~ ~r ~ O o~ u~
2 0 ~ x
_I ~ ~ ~
a~
~ L~ ~ O O ~`
2 5 H _I C~l ~ t'~ ~ ~')
H ;~ ~ r-- ~--1 1~ ~r ~ ~1
3 0 ~ o ~ u~ o o u~
31 ~ 2~5
EXAMPLE S. The apparatus used in this example was
identical to that described above in Example 4 except
that the module was smaller, the membranes being
about 6 inches (152 mm) in diameter and providing a
5 total membrane surface area of about .04 m .
Results and conditions of this treatment are
summarized in Table 5. No hemolysis was observed.
~L2~205
32
x ~ o el~
,1 ~ r'1
~ o O O o O
~ J
/3
~t
~ ~: ~ O oo
~ ~ cn
10 ,~ u~
~ ~, Lî
LO O-- ~i fY- ~
;~
~ ~ r-~
~1 ~ ,
2 0 1
00 î~
m .....
I ~ o,
o ~
~ ~ ~ ~ ~ ~r
~
I .
_,
m ~ ~,
3 0 ~ ~ O O Ln O n
33 ~ ~5~
EXAMPLE 6. The apparatus used in this example was
substantially identical to that described in
Example 5. The stroke length of the oscillating pump
was varied during the treatment. The oscillator was
turned off for a three minute interval so that,
during this period, blood was being conducted forward
only. The inlet hematocrit was 37%.
Results and conditions of this treatment are
summarized in Table 6. Slight hemolysis was briefly
observed when the stroke length was changed from four
inches (101 mm) to three inches (76 mm) and again
when the oscillator was turned on after the one
minute interval of constant flow.
34 ~ S
o u~ ~
o o o o o o o
I` o r- ~D CO ~ O
8 u~
,,
~r CD 1` ~ ~
~ ~ r _, ,, _, ..... ..
_ _ ~ _ u~
V ~ ~ C`~ ~ ~ ~ ~,
O ~ ~ ~1 er ~ 1`
8 ~
~ ~1 v u~
s ~ 1 1 ~
~D i~
h ~ ¦ 0 ei~ --1 _ N
=i
m
_____~
Q) ~
N Ln a~ O Ll~ ~ N
,_, f~ ~ ~ ~r
~ L~ ~ ~ c~ er 1-
~ .~ ,i t~ ~ ~) ~ N ei~
m ~ ~,
~ ~ s
~ o r~ ~ ~1
~1 In o o o o o
34
35 ~ V5
BEST MO E
The best mode for carrying out the invention
is illustrated generally by Examples 4 and 5.
UTILITY
The process and apparatus of the invention
have several useful applications including the
treatment of certain disease states by plasma
exchange or plasma therapy, the collection of plasma
for various transfusion needs, for further
fractionation to isolate specific serum proteins, and
for ~he production of cell culture media. The
invention is particularly useful for continuous
plasmapheresis.
2~
