Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
TITLE
Plasmapheresi~ by
Reciprocatory Pulsatile Fil~ration
TECHNICAL FIELD
This invention pertains to a process and
an apparatus for plasmapheresis by reciprvcatory
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 compxised largely of water, but
also contains proteins and various other noncellular
compounds~ both organic and inorganic.
Continuous plasmapheresis is the process of
~0 continuously separating plasma from whole bloodO
Plasmapheresis is currently used to obtain
plasma for various transfusion n~eds, e.g.,
preparation of fresh-fro~en plasma, for subsequent
fractionation to obtain specific proteins such as
serum albumin, to produce cell culture media, and or
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 ~urface, i.e., the blood
side surface, of a microporous me~brane. Useful
microporous membranes have pores which substantially
retain the cellular components of blood bu~ allow
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plasma to pass through. Such pores are referred to
herein as cell-reta1ning poresO Typically,
cell retaining pore diameters are 0.1 ~m to 1.0 ~.
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 occuples the periphery oP the path so
that it is predominantly pla~ma ~ha~ contacts the
membrane. A pressure difference across the membrane
10 causes some of the plasma to pass through ~he pores
of the ~embrane while plasma deplet~d blo~d contlnues
to 10w to the end of the pathO Ideally, ~he
filtrate is cell free; the plasma-depleted blood
collec~ed at the end of the flow pa~h i~
concentrated9 i.e. 9 is depleted in plasma and
therefore has an increased hematocrit ~volume percent
o~ red blood cells).
P,f ter blood has been conducted across the
surface o a membrane at normal venous flow ra~es or
20 some time, the transmembrane flow of plasma becomes
impaired. This phenomenon ls herein sometimes
referred to as membran~ fouling or simply as
fouling. Rnown ~echniques Çor reducing fouling,
i.e~, increasing ~he len~th of time for which the
process can be carried out withou~ the occurrence of
significant impairment of plasma flow, include
varying the flow path si2e so as to op~imize the wall
shear rate along the leng~h of the f low path as
disclosed in U.S. Patent 4,212,742, and recycling a
portion of the plasma-depleted blood ~o increase the
velocity of blood in ~he Çlow pa~h the latter
technique may result in less plasma-depletionO
Various fil~ra~ion devices for
plasmapheresis are di~closed in the litera~ure. U.S.
3,705,100 disclose~ a center-fed circular membrane
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having a spiral flow path. U~S. ~,212,7~2 ~iscloses
a device having divergent flow channels. German
Patent 2g925~143 discloses a filtration apparatus
having parallel blood flow paths on one side of a
membrane and parallel plasma flow paths, which are
perpendicular to the blood flow paths, on the
opposite surface of the membrane. U.~. Patent
Application 2,037,614, published July 16, 1980,
discloses a rectilinear double-membrane envelope in
which the membranes are sealed together at the ends
of the blood flow path~ U.K. Patent Specification
1,555,389 discloses a circular, center-fed, double-
mem~rane envelope in which the membranes are sealed
around their peripheries. German Patent 2,653,875
discloses a circular~ centre-fed doubl~-membrane
device in which blood flows through slot-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 with reduced
membrane fouling.
BRIEF DESCRIPTION OF THE DRAWINGS
_
FIG. 1 is a cross-section of a
double-membrane filtration module which may be used
in the process o 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.
DISCLOSURE OF THE INVENTION
For further comprehension of the invention
and of the objec~s and advantages thereo, reference
may be made to ~he following description and to the
appended claims in which v~rious novel features of
the invention are more particularly set forth,
It has been found that the above objects
can be ac~.ieved by conducting blood over the surface
of a membrane in reciprocatory pulsatile flow. In
10` 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 onP 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;
~3~ conducting the blood in the reverse
direction over ~aid first surface, the volume of
blood flowed in the reverse direction ~eing less than
the volume of blood flowed in the forward direction
in s~ep ~1);
~4) repeating steps (1)-(3) in sequence and
collecting plasma which pa~ses through each membrane
from a second surface, i,e., a plasma side surface,
thereof and collecting plasma-depleted blood from
said first surfaceO
The inv~ntion further resides in said
process wherein the transmembrane pressure difference
is reduced during periods of f1OWJ 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 conductin~ 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 reducing the
transmembrane pressure difference during periods of
flow, preferably, means for reducing said pressure
difference to below zero.
Further, the invention 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 r~gion
~ 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-
d~pleted blood outlet port; and a plasma
collection channel around each plasma flow region
connected ko 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 invent;on 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 10w 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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no~ excluded from the invention, e~gD~ recycling ~he
plasma-deple~ed blood, treating plasma during filtra-
tion, diluting the blood with a compatible fluid and
measuring various biologically ~ignificant fac~ors
and means thereforu
In the following description and examples of
the inven~ion, the term ~forward~ is used to idicate
a direction generally away from the source of blood;
reverse indicates a direction ger.erally towards the
source of bloodO 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 eith~r 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 ~he 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 variou~ pumps such
as a rotary peristaltic pump, a piston or syr~nge
pump, and a plunger or hose pump; even manually
operated devices such as a flexible blood-containing
chamber which can conduct blood forward when
compr e s s ed may be u ~ ed .
The m~mbrane ls made of any ~ )d~compatible
ma~erial, and has cell-retairling pores, i.20 ~ pores
5 which substantially retain cellular component~ but
allow plasma to pass through ~uch pores are
typically abou~ 0-1 ~o ~ . O ~n average di ~neter O The
selection of a pore size may vary with the goal of a
part:icular treatment. IJseful membranes are described
in so~e of the above-ci~ed referenc~s relating ko
plasmapheres 1 s . The membrane may be of any 5Ui ~able
shape , e .g ., tubular , such as hollcw fibers or any
planar sha~e. When planar membranes are used,
membranes having low elongation , e .g ., less than
15 about 65%, h~gh modulus, e.g., at least about 10 kp~i
(70 MPa), and high ~ensile strength, e.g., at lea~
about 3000 psi (20 MPa), when tested wet in
accordance with standard procedure~, are pref~rred,
because they are dimen~ionally stable. As exemplary
of membranes having these preferxed properties are
mentioned the ~T 450 polysulfone membrane
commercially available from Gelman Sciences, Inc~ and
the palyester and polyc rbonate membranes
commer~ially available from Nuclepore Corpora~ionO
Of these, thin ; e .g ., less than about 1 mil (25 ~m),
preferably les~ ~han 0. 5 mil (13 ~m), smoo~ch
polycarbonate or polyes~er capillary pore membranes
are preferred because, in laboratory experiment-~,
such membranes were found, in general, to perform
30 better than the tortuou~ pa'ch membranes which were
tested. Under various conditions of practice,
however, any of the above-descrlbed or other types of
membranes may prove to be more or le3s advantageous.
I is to be unders~ood that more than one membrane in
35 any arrangement may be used. Convenierltly, several
membranes are stacked withln 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 projec~ions 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 i5
conducted in a forward direction in one or more flow
paths~ A flow path is the spac~ through which the
blood flows on the first surface of the membrane.
lS 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 ~G.76
mm). Preferably, said depth is also at least about
4 mils tO.10 mm) but, preferably no more than about
10 mils ( Or 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 ne~ positive trans-
membrane pressure difference. The flow velocitytypically varies during each period o fo~ward flow7
The preferred average orward flow rate from the
source to the membrane is about S0 to 60 ~l-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
positive transmembrane pressure difference.
Typieally, positive transmern~rane pressure difference
is generated primarily by resis~ance ~o for~ard flow~
but it can also be generated in other ways~ e.g., by
decreasing pressure on the plasma on ~he second
surface.
It has been found that the amount of
transmembrane pressure differenee 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 074 to 0O~ ~m. 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 diame~er is smaller or
largerr hi~her 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 mem~rane with a positive transmembrane
pressure difference is continued for some time, the
membrane becomes progressively fouledv i.e., the flow
of plasma through the membrane becomes increasingly
impaired. The 1 ngth of time for which blood can
be so conducted is beli~ved to depend upon several
factors such as, e.g., flow velocity, hematocrit,
pore size, transmembrane pressure difference, and the
individual characteristics of the blood being treated.
The frequency and volume of the reciprocatory pulses
are selected to maximize the flow of plasma through
~he membrane w thout causing extensive blood trauma.
In planar blood flow paths having a height of about
4 to 10 mils (100 to 254 ~m), a useful frequency and
volume are about 20 to 140 pulsations per minute,
preferably 40 to 80 pulsations per minute, and 0.5
to ~ mL per pulsation, perferably about 3 mL~ By
pulsations per minute, also referred to herein as
cycles per minute, is meant the number of tim~s per
minute the blood is conducted throught a cycle, a
cycle consisting of one forward 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
treatmen~, but conveniently may be selected and fixed
~or an entire treatment.
After the forward conducting of blood is
terminated, blood is conducted in the reverse direc-
tion in each flow pathO 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 ne~ 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 ~he membrane
can be at pressure which is positive but lower than
the upstream blood pressure and lower than the plasma
side pressure. Other means will beeome apparent
hereinafter. It is to be understood that said
reduction need not occur simultaneously over the
entire membrane, e.g., at any given inRtant, there
may be areas on the membranQ with high transmembrane
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pressure difference and o~her areas with low
transmembrane pressure difference and, at any given
point on the membrane, the ~ransmembrane pressure
difference may continuously fluctuate. Preferably,
the transme~brane pressure difference i5 reduced to
below zero, e.g., about -.1 to -3.0 p5i ( -- . 7 to -20.7
kPa), and, more preferably, to about -0.8 to -1.0 psi
(-5.3 to -6O9 kPa). Preferably, a large amount of
plasma backflow through the membrane is avoided.
The dura~ion of the reverse flow of blood is
selected to main~ain substantially unimpaired flow of
plasma ~hrough the membrane as well as to increase
the distance which the blood travels across the mem-
brane~ A wide ran~e 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 tha~
the frequency of the reciprocatory pulsations be
low, but at least twenty, in the early stages cf a
treatment and then be gradually raised to a desirable
requency. 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 bloQd, plasma-depleted blood and/or plasma lines.
Pressure accum~lators, nr ~urye chamber~, may also be
useful. Some Yuch useful mean~ are disclosed ln the
ollowing examples, which are illus~rative only, of
S treatm~nts in accordanse wi~h ~he Invention. ~ther
means will be obvious to persons skilled in the art.
Referring ~o FIG. 1, a ~ ra~ion module,
which may be u~ed wi~h reciproca~ory pulsa~ile flow
and may have means for yeneratlng reciproca~ory
pulsa~ions connected theretop comprises ~wo circular
opposing mo~ule housing plates lA, lB which are
prepared from a blood compa~ible material. A
circular blood flow region 2 is recessed within an
opposing surface of one or both plates. Further
reces3ed within each plate is a plasma flow region
3A, 3B. Typically, though not necessarily, the
plasma flow region ~s of smaller diameter than the
blood flow region.
The dep h of the plasma flow region is
typically about 5 ts 20 mils ~127 to 508 ~m)~ The
surface of the plasma flow region may be smooth or
grooved to enhance radial flow of plasma. ~n the
plasma flow region, or connected thereto, may be
means f or treating the plasma f or the removal of
25 disease-contributing factors.
One or both plates lA, lB have plasma outlet
ports 4A, ~B 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.
30 There may be one or more of such ports in ei~her or
both plates. The ports and channel may be located at
any position but preferably, as herein illust:rated~
are located near the periphery of each plasma flow
reg~ on.
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Near the center of plate LA is ~lood ~nlet
port 5, the walls 6 of which extend through plasma
flow region 3A ~o the blood flow region 20 Around
tne periphery of blood flow region 2 is a
plasma-depleted blood collection channel 7, This
channel connec~s to one or more plasma-depleted blood
outlet ports 8.
Within each plasma flow region is a plasma
side membr3n~ suppor~ 9~f 9B which may be, e.g.~ a
plate having ~rooves, pores or pro~ections nr
fabric-like materials. hs illustrated, the plasma
cide suppor~s are comprised of layer~ of fabric-like
material~, such as layers of a nonwoven polyester
fabric. The preferred support is three layers of
4 mil (102 ~m) thick ~ollytex, made by calendering
Du Pont Reema~ spunbonded polyes~er, because it
provides adequate support while allowin~ tran~verse
and radial flow o~ plasma. The support 9A which fits
in plasma flow region 3A is provided with an ap~rture
which its around wall 6 of bl~od inlet port 5.
Within each blood flow region is a membrane
lOA, lOB. Membrane lOA which fits in blood flow
region 2 in plate lA is provided with an aperture
which lies approxima~ely in regis~ry with bl~od inlet
port 5.
The membr2nes lOA, 10~ 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
sufEicient flexibility to avoid rupture of tbe
membranes during use. Th~ ar~as 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 when thin
polycarbonate or polyester mem~ranes which have low
break elongation, l.e., le~s than about 40~r are
employed in fllter modules in which, ~s herein
S illustrated, the membranes are not rigldly ~upported
a~ross a large part of their surface area~, it ig
advantageous ~o employ an elastameric seaI be~ween
the membrane3 and supports. Use of an elastomerlc
~eal provides sufficient flexibility ~o avoid rupture
10 of the membranes during use. When such membrane~ ar~
employed, ~he seal preferably has a break elon~ation
of at least about 100%. The optimal break elongation
will depend on several factors which ~ e obviou~
to persor~s skilled in the art, including the
thickness of the seal. An elastcmer~c ~eal which has
been found to perform well wi~h such membranes is an
adhesive having a break elongation of about 400% and
applied in a layer about 3 mils ~76 ~o) ~hick9
When the module is assembled, the
corres~onding flow reqions of each plate are
ad;acent. The plates are held together by any
~uitable means, e.g., clamp~, bolts and adhesives.
An O-ring 12 can be used to seal the plates. The
region between ~he membranes is the blood flow pa~h.
The to~al effec~ive surface area of the membranes,
i.e~, the sum o~ the areas on both membranes through
whic~ plasma can flow, is about .02 to .06 m~.
Blood side supports 13 are located between
the membranes. Blood side supports, though not
necessary~ have been found to be advantageous when
nonrigid plasma side supports, such as layers of
~ollytex, which may tend to buckle durin3 use, are
employed. Various suitable supports are described in
the literature. The illustrated and preferred
suppor~s comprise a plurality of smooth pillars,
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e.9., substantlally c1rcular, do'cs of cured adhe~ive
o~ the type used to adhere the membranes to 'che
plates. These have sufficient sof tness ~o avoid
breakage of the membranes during use.
FIG. 2 is an illustration of an embodiment
of the inventiorl in whlch the filtration module of
FIG. 1 ls used. The loop for generating
r~ciprocatory pulsatlons as illu~trated herein is ~he
inverl~ion of one other than ~he inventor herein.
la Blood is conducted from the source ~co ~he blood 10w
path v~ a blood inlet port 5 in module housing plate
lA. Plasma which passes through the membranes exi ~s
~rom 1:he module through a plasma ou~clet port ~A, and
a second plasma outlet port ~ n4t shown .
15 Plasma-deple~ed blood from the end o the blood flow
path exits from 'che module through plasma-deple~ed
blood outle~ port 8. In addition, blood flow is
pulsed in reciprocatory fashion by a peristaltic
oscillator 15, which ~s connected to cen~ral and
2û peripheral porJcs 16 and 17 through loop 18, which
per~pheral ports are connected to areas near an end
of the flow- path, directly, or indirec~ly via a blood
collection channel, not shown, The loop is
preferably short so that blood in the loop is
25 f requently mixed and exchanged wi~h blood in the flow
path . q`here pref erably ~s li ttle or no exchange of
blood across the oscillator. Any suitable type o
pump may be used to cause the reciproca~ory
pulsations. Such p~nps axe described in the
3û literature and in the ~3xamples below; a peristaltic
pump is preferred. Preferably, though not
necessarily, the oscillator is connected ~o the ~lood
flow path via one centrally located port and two
peripherally lc~ated ports, a~ shown, s:~r to the blood
35 inlet and plasma-depleted blood outlet lines at a
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loca~ion close to the moduleO The duratlon and
frequency of oscillations can be regulated by
ad~usting ~che oscillator. The forward and reverse
strokes are typically of equal volume.
FIG. 3 illustrates a module having an end
plate, 1.~. 9 module housing plate, which has
reciproca~ory pulse cavi~ies integral therewi~h, The
end plate i8 ~he 3 nverltion o~ one o~her than tlle
inventor hereln.
Blood is c:onducted into the module v~a an
inlet, not shown, in end plate 19B and is condus::ted
~hrough a matched port 20 in end pla~e 19~lo From
port ~0 in end pla~e l~A, ~he blood is con~ucted
through ~hallow channel 21, O, 2 inch IS. l mm) wide x
O. 06 inch (1. 5 ~n) deep, into inlet reciproca'cory
pulse cavity 22 which has a volume o~ abou~ 3 mL and
is about 2 inches ( S0. 8 mm) in diameter x 0~, 06 inch
(1. S mm) deep O Cavi ty 22 is employed in ~he
generat~on o~ recipl:ocatory pul~atlon~ as described
below. From cavity 22, the blood i~ conducted
through shallow channel 23t 0.5 inch (127 nm~ wide x
0013 incb (3.3 mm) deep, to blood flow path inle'c 24
whi~:h is about 0.38 inch (9. 7 mm) in diameterO The
blood is conducted throu~h port 24 into a blood flow
region between 'c~ membrane~ as described above.
Plasma-deple~e~l blood i~ conducted thrvugh flow path
outlets 25 and through branch channels 26 to outlet
reciproca~ory pulse cavi~y 27 in end plate 19~. The
brancb channels from the four outlet3 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 ~wo channels each about . 500
inch (12. 7 mm) wide x . 060 inch (1. 5 nun) deep. The
branch channel3 are of e~ual leng~h and cross-sectlor
so as to produce substantially egual pressure
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conditions during use. Cavity 27 i8 also employed in
the qeneration of reciprocatory pul~ations as
described below~ From cavity 27, ~he plasma-depleted
blood is conduc~ced ~hrough shallow channel 28, .200
S inch (5,.1 nun) wide x ~060 inch (1.5 mm) deep, and
through plasma depleted bloo~ ou~let 29 which extends
through a matched por~c in end plate 19B.
!~lasma which passes through 'cAe membranes
flows radially in a plasma flow path and through a
10 plasma collection channel, as described above~ to an
outlet port, no~ shown, in end plate l9B.
The en~i re modu~e is enclosed by enYelope 30
wbich is comprised of two shee~s of a flexibl~ blood
impermeable material , such as poly (vinyl chloride),
15 ~he shee~s being joined toge~her at seal 31 arouns~
the perimet~r of the s~ack. The envelope thus
provides a unitary flexible enclosure-for the
module, The three apert ures irl end plate l9B mate
with tube connectors in envelope 30.
13nvelope 30 coYers and seals the various
channels; cavi~ies and apertures in end plate 19~ and
forms a flexible diaphragm over each cavity 22, 27.
A perimeter lip, no~ shown, around each cavity and
channel in end plate l9A aids in sealing.
Reciproca~ory pulsations are generated by alternately
compressing the diaphraglll over each cavity 22, 27
such as by the use of reciprocating plunger~.
All of the above illustrated modules must be
clamped using pressure which i-~ at least sufficient
to offset internal pre~sure. In the examples, below,
a series of C-clamps around the perimeter of each
module was employed.
EXAIIPLES
In all of the following examples, which are
35 illustrative of single pa~s treatmen~s to separate
~;26~
plasma f rom blood in accord~nce s~ith the lnvention,
compatibility-matched human blood coll~cted in ei~her
ACD or hepa~in wa~ used. The hematocrit of the
blood, which was maintained at 37C during treatment,
5 was 37~38%.
In all Examples, planar circular supported
membranes were encased in membrane filter modules
made from Du Pont Luf~te~ acrylic resin~ The
membrane filter modules each compr ised two circular
10 discs between which were placed one or ~cwo supported
membranes. Blood was fed to an inl~t port a~ ~he
center of ~he module and conducted rad~ally therefrom
across the surface of each membrane. Plasma-deple~:ed
blood and plasma were collected by méans of
15 p~ripheral channels, cut into ~he discs, which led to
outlet ports.
The membranes were polycarbonate capillary
pore membranes, available from Nuclepore Corporatlon,
having average c~ Æetaining pore diameters of about
20 0.4 ~Im and about 10% pore area and were about 10 ~Jm
thick .
Three materials were alternatively used in
~he con~truction of membrane supports. One of these
was ~ollyte~c and two were high density polyethylene.
25 ~ollytex is a nonwoven polyester fabric produced from
layers of Du Pont Reemay~) spunbonded polyester by a
calendering procedure. ~he Hollytex material was
used in layers 10 mils (254 llm) or 4 mils tlO2 ~
~hick. The polyethylene materials were porous plates
30 about 6. 3 mils ~160. 0 lJm) thick; one had pores which
were about 70 llm and ~he other, about 120 ~m, in
diameter. Radial chamlels in the disc below the
polyethylene plate allowed or lateral flow of plasma
Prior to each 'creatment, the module was
35 purged of air by flushing with saline. The ~ollytex
18
.
' ~ :
19
~upport3 were fir~t solvent-exchanged in isopropanol,
soaked in saline and then placed wet ~.n the membrane
filter module. The membrarle filter module was
submerged in saline, 37C, during treatment to
5 prevent air leakage. Removing air from and
maintaining air out of the apparat~s is important.
The transmembrane pressure dif~erence was
measured by means of pressure straln gauge
transducers and moni tored near the center and/or near
10 ~he peripher~ of the module and was recorded 7 usually
at 5 to lû min. intervalsO The plasma side of the
apparatus was vented, except where noted, and was
assumed to be a~ atmospheric pressure.
~emolysis was determined by visual
observation of sample8 of plasma periodically
collected during each treatment.
The opera~ing conditions and results o~ each
example are tabulated af ter a general descr iption of
the apparatus used therein. Elapsed time is in
20 minutes and indicates the times during each treatment
when measurements were taken. Peak and low pressures
are in psig (kPa) and were measurPd near the
indical~ed location~. Blood flow rate is thé rate of
flow of whole blood ~rom the sou~ce to the module in
25 mL per min, Plasma flow rate is the flow rate of
collected plasma in n~ per min. The hematocrit
(~Ict . ) of plasma-depleted blood which was collected
was calculated. Flux is mL of plasma collected per
min. per cm2 of membrane filter.
30 EXAMPL~ lo This example illus~rates plasmapheres 1
by reciprocatory pulsatile filtration using two
membranes in a membrane filter module such that blood
is filtered by both membrane~ simultaneously.
Two layers of Hollytex w~ re placed b~tween
35 two membranes 80 ~hat blood ~lowed across the fir~t
19
.. . . .
~ . ', ', ' . ', : ,
:
surfaces of both ~embranes wlthln recessed flow
regions cut ~nto the inside surfaces of ~h~ ~isc and
plasma which pa~sed through the membrane3 flowed
radially through the ~upport between the membranes.
5 The blood flow paths were abou~ 8 mil~ (203~2 ~m3 in
dep~h and had a combined surface area of ~bout .05
m2. Plasma-deple~ed blood from the ends of ~he
flow paths was conducted fur~her through outle~ ports
and collection tubing ~o a collection vess~l~
Blood was conducted forward and reverse by
~wo pumps which were similar ~o ~he hose pump
deæcribed in ~OXo Specifica~on 2,020,735, published
November 21, 1979, except that the ou~le~ valves were
removed, and which were positioned between the blood
ba~ and the membrane filter module. Each pump
comprised an inle~ valve and a 4~ (10~2 ~m) plunger.
Th~ inlet valves were closed while the plungers were
rising and were par~ially closed while ~he plungers
w~re withdrawing so tha~ blood was ~onducted from the
directions of the blood bag and of the membrane
fil~er module as ~he plungers were withdrawing. The
plunger~ never completely occluded the tubing. Each
pump di~placed about 3.2 mL during each forward pulse.
Blood pa~sed fro~ the blood bag through a
single tubing which was divided into two lines. ~ach
line passed through one of the pumps and was rejoined
into a single line.
Blood wa~ also conducted ~n the reverse
direction by pressure which accumulated in a surge
chambe~ 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 p~i ~2.3 kPa) check v~lve prevented
back~low of blood to the blood bag. ~ control valve
on the plasma-depleted blood collection line was
ad~usted during the trea~men~ to control blood side
pressures and transmembrane pressure difference.
Th~ oondi'cions and results of this example
are in Table 1.
s
lû
..
..
22
S X ~ ~ ~
:~ o ~ o o o C:~ o o o o
~ ........... ~
I ~ ~.a u~ ~D ~1 ~` O O ~ O
~ ~ o
m
~ 0 U~
~ , n ~ ~0 ~ o
a~ ~ ~ _ _ .~
~ ~ ., O O O
~ o CD
~ ~ ~ ~ O ~ ~ ~o
~ m JJ -J~ T ~
~ o a~
~1 ~ ~ I I I I ~ I I I
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~ ~ ô ~ ~ û~ U~
e~ o . . . . . .
2Q ~ ~ ;~ ~
g~ ~ ~ O ~ ~ ~ O S`
~ a ¦ --1 N C~ J ~`i t`i ~ ~ U~ ~
;i~l~ ~ o 0 o
~ Q~
3~ H ~ ~ ~ ~ ~ ~ 0
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~ u~ ~ ~ a~ ~ l~ ~` ~
~ ~ ~ ~; 0 ~ o ~ ~ o u~ uO
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o U~ o o U~ o U~
O u~, O O
.
2~
23
No hemolysis was observed during ~he flrs~
39.5 minu~es. Hemolysis was o~served during the
period when the frequency of pulsations was lncreased
to 100 as a resul~, it i5 believed, o ~he hlgh
5 frequency and the high p~ak transmembrane pressure
difference. After the pump speed and pressure were
reduced, the pl~sma began to clear, i nd~catin~ that
hemoly~is had cea~ed or was lessening.
EX~MPLE 2. This example illustrates plasmapheresi~
10 by reciprocatory pulsatile filtration as per the
1 nvention using a single membrane .
The membrane was support~d by a polyethylene
plate tl20 ~Im pores~. The ~low path surfac:e area was
about .013 m~. The depth of the flow path was
15 about 5 mils ~152 ~Jm) from the cen~er ~chereof to a
point along its radius abouJc 3.25~ (8. 3 cm)
therefrom, from which poin~, the dep~b ~apered ~o
abou~ 9 mils (229 llm) at the end of the flo~ pa~ch.
The peripheral edge of ~he membrane was pre~sed
20 between the discs. Blood flowed radially across the
first ~urface of the membrane while plasma which
passed through the membrane pas~ed through the pores
in 'che polyethylene plate and flowed radially in a
pla~ma ~low region cut into the inside surface of ~he
25 plasma-side disc.
Reciprocatory pulsa~cili ty and reductions in
transmembrane pressure difference were provide~ by a
peristaltic rotary pump which was modified by removal
of all but one of the rollers therein. The circular
30 path of the roller was about 5. 38" (13. 65 cm) of
which th~ roller occlud0d the tubing for about 5,25H
(13.34 cm); the tubing was .13" (.32 cn~) rD ~ilicon
tubing. There~ore, the d~splacement of ~he pump~
which was set at 60 rpm, was about lol mL~
.
,
24
A check valve and plasma-depleted blood
contrQl valve were used~
~ he peak plasma side pressure remained at
about 1.0 psi (6.9 kPa) at the center and periphery
5 of ~he module; the low plasma side pressure was about
0 to 0.3 psi (0 to 2.1 kPa) at the center and
per iphery.
~ o hemolysis was observed. The conditions
and results of this example are in Table 2.
24
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2 ~
o o C~ o ~ o
.. . . . .
J ei~ O ~
v C~i ~rt C:) U') 1~)
~ ~ ~ ~ ~ ~ U~
~ ~ co ~
15 .L~ 0
~ ~P ~9 0 ~ U~
:1 ~3
~_ m ~ o O
20 ~ ~
_ ,~, _ _~ _
~a Q~
~ ~ u~
25 " ~ I _~ ^ ô
U~
~E~
. .
,
., . ~ .
26
EX~MæL~ 3. This example illus~rates that
rec1procatory pulsa~ile flow during plasmapheresis
can result in an improved eate 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 enti re ~low path depth
was about 6 mils (152 ~m) in depth and the porous
plate had pores which were about 70 ~m in diameterO
Initially, bl~od was conducted forward by a
pressure infuser cuff wrapped around ~he blood bag.
A 0.5~ ~1.3 cm~ ID control valve posit~oned between
the bag and the module was opened and closed at
various intervals (reported in seconds) ~o generate
15 pulsatile flow. Af~er some time, the infuser cuff
was removed and the rotary pUMp descr ibed above in
Example 2 was utilized. Then the ro~cary pump was
. disconnected and the infuser cuff system was restored.
The conditions and resul~s of this example
20 are in Table 3.
26
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: .
xu~ ~ o` `o ~ ~ ~ u~
o g
~D O1~ a ~ o o a`
O ~ D
i~ p w ~ ~ ~ ~ ~Po
~ ~, ? ,~, 7 ~ ~ ~
~ ~
~ H~ P 3D U7 ~ N
2 3 ~~ `' ~ N
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a~
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2 5 ~ N
~2 ~ ~ ~ ~o ~ ~ ~ ~
~ o 3 ~ æ ~ æ ~
~- ~
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,,
~8
- Hemoly~is was observed to result when
pulsations were generated by the infuser cuff~valve
system but not when reciproca~ory pulsations were
generated by the rotary pump.
~XAMPLE 4. In ~his example, modules su~s~an~ially as
illustrated in FIGS. 1 and 2 were employ~d. The
membranPs were 7 inches (178 mm) ~n diameter, and
provided a total membrane surface area of about
. 05 m . The membranes were adhered to circular
plates, made from Du Pont Lucite~) acrylic resin, with
Gener~ lectr ic RTV 102 silic:on adhesive which had a
break elongation of 400%, a tensile strength of
350 psi (204 MPa), and a Shore A hardness of 30. The
adhe~ive was applied by hand in a layer about 3 mils
15 (76 ym) thick.
The same adhesive was used to form blood
side suppor~s by placing dots of the adhesive,
between the membranes in two concentric circles. The
blood flow path between the membranes was abou~ 8
mils (.20 mm) deep~ The adhesive suppor~s were cured
on the blood side surface of one membrane at 60C
oYernight prior to assembly of the module. The
plates were held together with clamps, without
0-rings~
The blood was condu~ted forward by a 3-arm
rotary peris~altic pump. A .33 psi (2.3 x 103 Pa)
check valve was located between th is pusnp and the
blood reservoir.
Reciprocatory pulsations and pressure
fluctuations were provided by a modified per istaltic
pump, positioned on a l~op, i.e., a length of tubing~
which extended from two peripherally located por~s
and one centrally located por t .. The pump was
modified so ~hat a single roller, in constan~ contact
with ~he tubing, oscillated in about a 50 mm s~roke
2g
%~
29
- at about ~0 cycles-min 1, thereby displacing about
1.6 mL per s~roke. A micrometer control Yalve was
placed on the plasma-depleted blood ou~let line and
was adjusted during the treatment.
Re~ults and conditions of this treatmen~ are
summarized in Table 4. No hemolysis was observed.
29
'
.
3~
,~
o o o o o o
o
_î
C
u~
,~ ~ r ~ 0
~J ~ ~
~ i I
~ u~
~q ~ U~
~1~ ~ ~1 7 ,~
~ o ~
P~ ~ _l ~ o o ~ In
: e a) ~ _I ~ ~ ~ c~
D ~ _ _ _ _ _
~ ~ ~ ~` ~ ~D ~
~ u~oo~a
. ,.~ ~ ~ ~ ~a ~
~
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~æ~
~3 ^o u~ u~ o o u~
~, ~ C
- '~ '., '
.
EXAMPLE 5. 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 ~his treatment are
summarized in Table 5O No hemolysis was observed.
.
:
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~ o o o o c:~
~ . . ~ ~ .
v ~
~ ~ ~ ~ ~ c~ ~
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~ '~c ~ ~ t~ o ~
10 ~ ~ ~
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1~ ~ a~
U~ ~ ~ ~ ~ o ~ o~
~ ~ ~ ,', ~
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20 ~ x ~- s~ o ~ u~ cr
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33
EXAMPLE 6. The apparatus used in ~his ex~mple was
subs~antially identical to 'chat described in
Example 5 . The stroke leng~ch of the osci llating pump
was varied during ~che treatmen~. The oscillator was
5 turned off for a three minu~ce interval so ~hatt
during this period, blood was being conduc~ed Eorward
only. The inlet hematocr it was 37% .
~ esults and conditlons of this ~creatment are
summarized in Table 6n Slight hemolysis was briefly
lG observed when the s~roke leng~h was changed from four
inches (101 mm) to three inches ( 76 mm) and again
when the oscillator was ~urned on after the one
minute in~erval of constant flow.
3~
~ I o o o o ~ o o
a) ~ I ~ o 1~ U~ a) ~ o
1 0 â~
~1 c~
~ ~ v
~ ~1 1 ~ )~o
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3~ ~ 1` a) u~ ~ ~
~ '` ~
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C~ ~ o o
~ ~
- . . . ~ .
.
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- ' , ' . ' '
~2~
BEST MODE
The ~est mode for carrying out the invention
is illustrated generally by Examples ~ and 5.
UTILITY
The process and appara~us of the invention
have several useful applications including the
treatment o certain disease states by plasma
exchange or plasma therapy, the collection of plasma
for various tr~nsfusion needs, for further
fractionation to isolate specific serum proteins, and
~or the production of cell culture media. The
invention is particularly useful ~or continuous
plasmapheres is,
This application is a division of copending
Canadian Patent Application Serial No. 407,621, filed
~982 July 20.
~0
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,
