Note: Descriptions are shown in the official language in which they were submitted.
536
TW~N PACK HEMODIALYZER
This invention relates to an improved apparatus for
use in the cleansing of impurities from the blood by hemo-
dialysis.
The cleansing of cell waste and impurities from the
blood by the process of hemodialysis has been known and
routinely conducted for many years, with hemodialyzers,
commonly referred to as artificial kidneys, being used
successfully to treat patients suffering from kidney mal-
function or kidney disease. In recent years, efforts to
further develop and improve hemodialyzers have been
directed toward increasing the efficiency of the hemo-
dialyzer unit, improving the units from the standpoint of
providing for less stress on the patient and improved
safety in the use of the devices, lowering the expense
involved in hemodialysis treatment and making hemodial-
ysis treatment available to more of those in need of such
treatment.
The hemodialyzers presently being used in this
country fail to fully satisfy the needs of the vast num-
ber of kidney patients in several important respects.Hemodialyzer machines presently used are expensive and
hence require a large initial investment for the basic
machine and other associated equipment which is necessary
for the hemodialysis treatment. A blood pump is generally
required because of the flow resistance caused by the
large size of the present machines, which size often
makes a blood transfusion necessary because of the loss
of blood to the blood priming volume of the machines.
In-hospital treatment or the presence of trained medical
personnel is often necessary for hemodialysis treatment,
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as is the essential rebuilding of the hemodialyzer units
under sterile conditions following each hemodialyzer
treatment. Partially resulting from these mentioned
considerations, the cost of continuing hemodialysis
treatments is prohibitive to many patients in need of
such periodic treatment and the number of hemodialyzer
units available is severely limited in relation to the
vast number of those suffering from kidney disorders.
Hemodialyzers are presently being developed in
attempts to alleviate some of these problems. One
development effort has been directed toward de~ising a
small, pumpless, efficient and less expensive hemodialyzer
which can be made more widely available and which can make
hemodialysis treatment possible for more patients at 3
lower yearly cost. ThiS effort has resulted in the
development of a series of models of small pumpless hemo-
dialyzers which can meet some of the present needs of
kidney patients. The knowledge and advanced technology
obtained in the development of each of these hemodialyzer
models has enabled the development of the series of pro-
gressively more refined and efficient hemodialyzer models,
each replacing earlier models and successively offering
improvements to the more basic earlier model. The present
invention is an improved model in this series of hemodial-
yzers.
The present invention is an improved hemodialyzer
closely related to a series of models of hemodialyzers of
which the present inventor was a coinventor. Two earlier
model hemodialyzers, subject of U. S. patent 3,522,885 and
U. S. patent 3,56;,258, were small pumpless disposable
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units consisting of a series of parallel tubes arranged in a
stack within a rectangular shaped casing. The blood and the
dialysate fluid passed either within the tubes or across and
around the exterior of the tubes, with the hemodialyzer of
U. S. patent 3,565,258 providing for the passing of dialysate
fluid within the supported tubes while the blood flowed across
the dialyzer casing between and around the tubes. While this
latte~ model proved to be a satisfactory design and underwent
clinical testing, it remained desirable to improve the design
and increase the efficiency of the hemodialyzer.
An improved design over the dialyzer of U. S. pa-tent
3,565,258 became the subject of another hemodialyzer invented
by the present applicant, U. S. patent 3,778,369, which design
provided for at least one baffle extending from a side wall
of the casing across the width of each of the flattened tubes
such that the blood flowing through the dialyzer would flow
around the baffles and across the tubes a multiple number of
times. The baffles served to lengthen the flow path of the
blood passing through the hemodialyzer unit, thereby increasing
the amount of contact between the blood and the dialysate fluid
across -the semipermeable membrane. While this latter hemo-
dialyzer ~las proved to be satisfactory, improvements in the
design of hemodialyzers and increases in the efficiency of the
hemodialysis are never ending goals.
Therefore it is an object of the present invention to
provide a hemodialyzer which is small, can be operated without
the need of a blood pump and can be discarded after use.
It is also an object of the present invention to provide
a hemodialyzer which has improved efficiency of dialysis and
improved operation characteristics.
In accordance with the present invention, a hemodialyzer
is provided in which two completely independent stacks of parallel
flattened semipermeable membrane tubes are disposed within a
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casing. The two stacks are separated by a solid plate extending
from one wall of the casing across the width of the stack to a
point near to but not touching the opposite wall o the casing
so as to leave a gap between the plate and the opposite wall
and thereby divide the interior of the casing into two sections,
with each section containing one of the -two independent stacks.
The sections communicate only along the gap between -the plate and
the casing wall. The hemodialyzer has associa-ted therewith means
for passing dialysate fluid through the casing within the tubes,
with that means including a dialysate inlet at one end of the
casing and a dialysate outlet at the opposite end of the casing.
The hemodialyzer has associated therewith means for passing
blood through the casing around and between the tubes such that
the blood flows across and between the tubes in a first of the
two independent stacks of tubes and subsequently acxoss and
between the tubes in a second of the two independent stacks of
tubes, with that means including a blood inle-t near the same
end of the casing as the dialysate outlet and a blood ou-tlet
near the same end of the casing as -the dialysate inlct.
~ The bloocl and dialysate fluid are separa-ted by and make
contact across the semipermeable membrane across which active
dialysis takes place.
The blood flow through this hemodialyzer design can generally
be described as across and between the tubes in a first of ~hc
two independent stacks of tubes and subsequently across and
between the tubes in a second of the two independent stacks.
The dialysate fluid passes through the dialyzer within the tubes
of both of the two independent stacks with the volume of dialy-
sate which passes through the tubes of one of the two independent
stacks not passing through the tubes of the other stack.
A better understanding of the features of the present in-
vention and the inherent advantages can be obtained from a
D reading of the following description of the invention wi-th
reference to the drawings, in which:
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Fig. 1 is a perspective view of a hemodialyzer cons-
tructed in accordance with the preferred embodiment of
the present invention which has an end removed to expose
the interior structure of the hemodialyzer.
Fig. 2 is an end view of a hemodialyzer constructed
in accordance with the preferred embodiment of the
present invention with the end partially broken away to
e~pose the interior structure of the hemodialyzer.
Fig. 3 is a vertical section of the end of the hemo-
dialyzer taken along the line 3--3 of Fig. 2.
Fig. 4 is a horizontal section taken along the line
4--4 of Fig. 2.
Fig. S is a vertical section of an alternative
embodiment of the present invention, appearing with Fig. 1.
While the invention is here described in connection
with a preferred embodiment, it will be understood that
is not intended to limit the invention to only that
specific embodiment, but it is intended to cover all
alternatives, modifications and equivalents as may be
included within the spirit and scope of the invention as
defined by the appended claims.
The construction and operation of the present inven-
tion can best be understood by referring first to Fig. 1
wherein there is shown a hemodialyzer unit in accordance
with a preferred embodiment of the present invention with
the end thereof removed to expose the interior structure.
The hemodialyzer in accordance with the present invention
includes a casing indicated generally at 11. A plurality
of flattened semipermeable membrane tubes, such as tubes
13, are arranged in parallel and form two independent
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stacks indicated generally a~ 15 and 17. The two stacks
15 and 17 of the parallel flattened semipermeable mem-
brane tubes 13 are disposed separately within the casing
11. As illustrated in Fig. 1, it is preferred that
these two stacks be arranged one on the other.
Means are provided for passing dialysate fluid
through the hemodialyzer and the casing within the tubes
13. While any of various means well known and fully
understood by those skilled in the art can be used for
passing the dialysate fluid through the hemodialyzer, one
such possible means will be described below. It should
be appreciated, however, that the means described herein
are only one possibility of many available in the art
which would be readily adaptable for use with the present
hemodialyzer. Referring to Fig. 3 where the example
of a means for passing the dialysate fluid through the
hemodialyzer can most easily be visualized, there is
shown on one end of the casing 11 a dialysate inlet 19.
Referring momentarily to Fig. 4, there is shown on the
opposite end of the casing 11 a dialysate outlet 21 con-
structed in the identical manner to the dialysate inlet
19. Consequently the description will be limited to the
dialysate inlet 19, it being understood that the struc-
ture of the dialysate outlet 21 is identical to that of
the inlet 19.
Referring again to Fig. 3, it can be appreciated
that the dialysate inlet 19 is adapted to be connected to
tubing appropriate for the carrying of dialysate fluid
from an appropriate reservoir by a pump to the hemo-
dialyzer. Dialysate inlet 19 therefore is shown as an
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approximately tubular structure. The dialysate inlet 19opens to a dialysate inlet plenum 23 which communicates
with the interior of the semipermeable membrane tubes
through the openings at their ends. The dialysate inlet
plenum 23 serves to distribute the dialysate fluid to all
the tubes in both of the stacks of tubes 15 and 17. As
indicated by the arrows in Fig. 3, dialysate fluid would
enter the inlet 19, distribute through the dialysate
inlet plenum 23 and pass therefrom to the interiors of
the semipermeable membrane tubes 13, the dialysate fluid
flowing through all the tubes in both stacks lS and 17.
Referring again momentarily to Fig. 4, it can be appreci-
ated that after the dialysate fluid flows along the
length of the tubes 13 it will exit from the tubes at
the ends opening to a similar dialysate outlet plenum 25
located at the opposite end of the casing ll and communi-
catng with dialysate outlet 21 from which the dialysate
fluid will exit from the hemodialyzer.
It is, o course, essential that there be no inter-
mingling of the fluids in the hemodialyzer casing.
Therefore the dialysate fluid must flow through the
hemodialyzer casing only within the tubes while the blood
flows through the hemodialyzer casing only around and
outside of the tubes. Any such intermingling of the
dialysate fluid and the blood is prevented by a barrier
27 located at the ends of the tubes near the dialysate -
inlet plenum 23. This barrier 27 sealingly separates
the dialysate inlet plenum from the interior portions of
the dialysate casing through which the blood flows. The
ends of the tubes 13 project through the barrier 27 and
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open to the dialysate inlet plenum 23, thus permitting
the flow of dialysate fluid from the plenum through the
tubes. A similar barrier 29 is located at the opposite
end of the casing 11 and sealingly separates the interior
of the dialysate casing from the dialysate outlet plenum
25. The position and relation of the two barriers can
best be seen from Fig. 4. While the barrier can be any
sort of a structure which will seal the ends of the tubes
and separate the plenum from the interior of the dialy-
sate casing, it has been found that a layer of epoxyembedding the ends of the tubes 13 works particularly
well and enables construction of a dialyzer in accordance
with the present invention through uncomplicated straight-
forward technigues. Such a barrier has been constructed
and used in accordance with the dialyzers subject of the
previous U. S. patents discussed above.
Means are also provided for passing blood through
the dialyzer casing around and between the tubes 13.
While many of the well-known prior art techniques for
introducing blood into a dialyzer casing and removing
blood therefrom can be adapted for use with the hemo-
dialyzer in accordance with the present invention, one
such example which can readily be employed with the
present invention can best be appreciated by first
referring to Fig. ~ where there is shown near one end of
the hemodialyzer casing 11 a blood inlet 31. While the
inlet can be located near either end of the casing 11, it
is preferred that the inlet 31 be located on the same end
of the casing as the dialysate outlet 21. The blood
outlet 33 will correspondingly be located on the opposite
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end of the casing 11, such end being the same end of the
casing 11 as the dialysate inlet 19.
This arrangement is preferred, as the blood entering
the dialyzer throu~h inlet 31 contains the highest con-
centrations of impurities. ~he blood containing the high
concentration of impurities then undergoes active dialysis
exchange across the semipermeable membrane near the dialy-
sate outlet 21 where the dialysate will have already
removed a portion of impurities from the blood, thereby
providing the dialysate with a higher degree of impurities
than the dialysate contains at the dialysate inlet 19.
Near the blood outlet 33 the blood will have undergone
dialysis in flowing through the dialyzer from the inlet
31 and the concentration of impurities in the blood will
have been reduced. The dialysate entering the hemo-
dialyzer through the inlet 19 will, of cour~e7 contain no
impurities. This dialysate with no impurities then
undergoes active hemodialysis across the membrane with
the blood near the blood outlet 33, which blood having
already undergone dialysis in its passage through the
dialyzer will have a reduced concentration of impurities.
A high differential of impurity concentration in the blood
as opposed to in the dialysate is thereby maintained
throughout the hemodialyzer unit. If the blood and
dialysate were introduced on the same end of the dialyzer
unit, the concentration of impurities in the dialysate
near the outlet would be fairly high for having undergone
dialysis with the blood as it passes through the hemo-
dialyzer, while the concentration of impurities in the
blood will have been reduced through dialysis as it
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passes through the hemodialyzer. Consequently, the con-
centrations in the blood and dialysate near the outlet
would have tended to equalize, reducing the concentration
differential, and reducing the efficiency of dialysis at
the latter portion of the flow path. Therefore it is
preferred that the blood inlet be located on the end of
the hemodialyzer casing adjacent the dialysate outlet.
nhile the blood inlet 31 and outlet 33 can be any of
a variety of structures which are adaptable or permit
connection to blood-carrying tubing, a particular inlet
and outlet which are readily adaptable and found to be
highly useful in the present apparatus are those blood
inlet and blood outlet ports described in the applicantls
previous U. S. patent 3,778, 369 These previously des-
cribed blood ports are tapered so as to provide advan-
tageous distribution of the blood across the entire stack
of tubes. The structure and advantages obtained thereby
are fully described in the mentioned U. S. patent and the
advantages obtained thereby are also provided when these
particular blood ports are employed in the apparatus of
the present invention. The preferred use of these
tapered slit blood ports is indicated by the tapered
blood inlet 31 and the tapered blood outlet 33 as illus-
trated in Fig. 2.
Referring again to Fig. 1, it can be appreciated that
the b~ood inlet leads to a blood inlet plenum indicated
at 35 which serves to distribute the blood along the
height and length of the first stack of tubes 15.
Following distribution of the blood through the blood
3~ inlet plenum 35, the blood can 10~ across the surfaces
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of the semipermeable membrane tubes 13 between and around
the tubes of the first stack 15 and subsequently across
and around the semipermeable membrane tubes of the second
stack 17 to the blood outlet plenum 37 which serves to
collect the blood. The blood then flows from the outlet
plenum 37 through the blood outlet.
In accordance with the hemodialyzer of the present
invention, the blood passes through the casing around and
between the tubes in a manner such that the blood passes
in succession through each of the two independent stacks.
The essential features and the clearest explanation of
the blood flow can best be understood by referring to
Fig. 5 wherein there is shown another embodiment of the
present invention. In Fig. 5, identical numerals will be
used to identify the similar components of the hemo-
dialyzer unit although in this particular embodiment these
components may be arranged somewhat differently. Accor-
dingly, it can be appreciated that flattened semiper-
meable membrane tubes 13 are arranged in parallel to form
a stack, and two independent stacks, a first stack 15 and
a second stack 17 independent of the first, are disposed
within the hemodiaiyzer casing indicated generally at 11.
In this particular embodiment, it can be seen that the
first stack 15 and the second stack 17 are arranged side
by side in the casing 11. Blood flow through the hemo-
dialyzer in accordance with this embodiment can be
represented by the small arrows and can be seen to be
from the blood inlet 31 to a blood inlet plenum 35 along
the length of one side of the casing 11 wherein the blood
distributes along the length and height of the first
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stack of tubes 15. Blood flow is then around and between
the tubes 13 in the first stack 15 and in succession
around and between the tubes 13 in the second stack 17 to
the blood outlet plenum 37 which serves to collect the
blood and permit its exit from the hemodialyzer casing
through the blood outlet 33. Blood flow can generally be
described as from the blood inlet plenum 35, through the
first stack of tubes 15, across the small gap 39 (some-
what exaggerated in the drawing) and in succession
through the second stack of tubes 17 to the blood outlet
plenum 37.
In conducting hemodialysis, blood is normally main-
tained at a slight positive pressure compared to the
dialysate fluid in order that excess water can be driven
across the semipermeable membrane from the blood. As a
result of this blood pressure, the casing 11 of the
embodiment illustrated in Fig. 5 tends to bulge where the
blood passes across the gap or intermediate plenum 39
from the one stack of tubes to the other. The bulge at
the top of the casing at point 41, illustrated by the
dotted line and arrow in Fig. 5, and bulge in the bottom
of the casing at point 43, similarly illustrated by the
dotted line of the casing and small arrow, causes a path
to open between the stack of tubes and the top surface or
bottom surface of the casing. Blood flow then tends to be
along the top and bottom surfaces of the dialyzer casing
rather ~han through the interior of the two stacks 15 and
17. Dialysis across the semipermeable membrane tubes 13
is therefore reduced due to the preferential blood flow
path along the top and bottom surface of the casing.
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Therefore a preferred embodiment which offers other
advantages over and above the embodiment of Fig. 5 is one
in which the two independent stacks of parallel semiper-
meable membrane tubes are arranged one on the other.
Such a preferred embodiment is illustrated in Figs. 1-4.
As is illustrated in Fig. 1, it is preferred that
the stacks 15 and 17 be arranged one on the other. As
can be seen from Fig. 1 blood flow is then from the blood
inlet plenum 35 across the stack of tubes 15 to the
intermediate plenum 39, downward in the intermediate
plenum 39 to the level of the stack of tubes 17, and in
succession across the stack of tubes 17 to the outlet
plenum 37. The flow of blood in the intermediate plenum
39 exerts a pressure on the side 45 of the casing 11 in
a manner similar to that described in connection with the
embodiment of Fig. 5. However, any tendency for ~his
side of the casing to bulge will not hinder the normal
blood flow path. Blood flow must still be across the
stack 15 to the intermediate plenum 39 and the bulging of
the side 45 o the casing 11 merely enlarges the inter-
mediate plenum 3g rather than creating a preferential
blood flow path which will avoid the semipermeable mem-
brane tube surfaces. The blood must still flow across
the tubes of stack 17 from the intermediate plenum 39 to
the outlet plenum 37.
The two stacks of tubes 15 and 17, although being
one on the other, are separate and independent stacks,
the two stacks being separated such that the blood must
pass in succession through each of the two independent
stacks. Such separation and blood flow can ~e
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accomplished by means such as, for example, a solid plate
47 disposed between the two stacks. The two stacks 15
and 17 are then separated by solid plate 47 which extends
from one wall 49 of the casing. The solid plate 47
extends from the wall 49 of the casing, such wall forming
a side of the casing the same as that on which the blood
inlet and blood outlet lie, across the width of the
stacks 15 and 17 to a point near to but not touching the
opposite wall 45 of the casing so as to leave a gap for
the intermediate plenum 39 between the edge of the plate
47 and the opposite wall 45. The interior of the casing
11 is thereby divided by the plate 47 into two sections,
each section containing one of the two independent stacks
15 or 17. It can then be appreciated that the two sec-
tions containing the stacks 15 and 17 communicate only
along the gap or intermediate plenum 39 between the plate
47 and the casing wall 45. 8100d flow then must be
across the stack of tubes 15 from the blood inlet plenum
35 to the intermediate plenum 39 and back across the
second stack of tubes 17 to the blood outlet plenum 37.
Such blood flow can perhaps be most clearly understood by
considering the blood flow as following the small arrows
illustrated in Fig. 2.
As was mentioned previously, the blood flowing
through the dialyzer is at a slightly higher pressure
than the dialysate in order to drive excess water from
the blood to the dialysate fluid. As a consequence, it
is preferred that support members be inserted within the
tubes to hold the interior walls of the tubes apart and
provide a flow path for the dialysate fluid. The blood
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will force the membrane down onto the support member
to open a flow path for the blood while the support mem-
ber will retain a flow path for the dialysate fluid.
While many types of support members can be used, a
nonwoven plastic mesh support has been found to be par-
ticularly useful. While such support members are well
known in the art, a full description of the support
members and their function can be obtained from a
reading of two previous U. S. Patents, No. 3,788,482 and
No. 3,565,258.
~ everal significant advantages are offered by a
hemodialyzer in accordance with the present invention.
In addition to the advantage offered by the preferred
embodiment as mentioned above, other advantages over
previous dialyzer designs can be seen from the following
considerations. In comparison with a hemodialyzer con-
taining only a single stack of tubes, for a volume flow
of blood through the dialyzer unit per unit time
remaining ~he same, the path length in the dialyzer of
the present invention is increasad. Correspondingly,
the blood velocity must be increased, which increase in
velocity helps prevent the buildup of fibrin on the semi-
permeable membrane surface. The buildup of fibrin is
undesirable for several reasons, among which are the
buildup of fibrin on the semipermeable membrane surface
will reduce the dialysis efficiency of the membrane and,
perhaps more importantly, the buildup of fibrin on the
semipermeable membrane surface can lead to the formation
of a blood clot which would prove highly dangerous to the
3~ patient undergoing hemodialysis treatment. With the
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increase in path length for the blood flowing through the
hemodialyzer unit in accordance with the present inven-
tion, the blood also will pass across two independent
stacks of tubes, thereby coming in contact with dialysate
fluid across the semipermeable membrane tubes over a path
length double that of a single stack unit. The increase
in contact of the blood with dialysate fluid across the
semipermeable membrane will, of course, increase the
efficiency of dialysis occurring in the hemodialyzer
unit.
While the invention has been described in conjunc-
tion with specific embodiments and a preferred embodiment
thereof, many alternatives, modifications and variations
as well as other advantages will be evident to those
skilled in the art in light of the foregoing description.
Accordingly, it should be unde}stood that the invention
is not intended to be limited to the details given herein
but it is intended to embrace all such alternatives,
modifications and variations as fall within the spirit
and scope of the appended claims.
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