Note: Descriptions are shown in the official language in which they were submitted.
~Z38831
This invention relates to a hollow fiber~type
artificial lung used in extracorporeal circulation to remove
carbon dioxide from blood and add oxygen to the blood. The
invention is applicable to an artificial lung having a blood
reservoir chamber and an artificial lung having a heat
exchanger.
This is a division of copending Canadian Patent
Application Serial No. 437,308, filed September 22, 1983.
Artificial lungs are broadly classified into those
of porous and membrane type. The membrane artificial lung,
such as of stacked membrane type, coil type or hollow fiber
type, is widely recognized as being superior to the
porous-type artificial lung in view of the fact that the blood
conveyed through the lung undergoes less hemolysis, albumin
degeneration, clotting and affixation, and as being extremely
close to the human lung in terms of its operating mechanism.
Nevertheless, because the membrane-type artificial lung
possesses a number of
1238831
disadvantages set forth hereinbelow, the artificial lung
of porous type is that used most widely in open-heart
surgery at the present time.
In order to obtain sufficient oxygenation with
the membrane-type artificial lung currently available, it
is required that the blood flow layer be reduced in thick-
ness. This means a narrow blood flow passage and, hence,
a large flow passage resistance. In consequence, it is
note possible to achieve perfusion of the blood within the
artificial lung by utilizing the head developed between
the patient and the lung.
Accordingly, as will be explained in more detail
below, a blood circuit using the membrane-type artificial
lung requires that a pump be disposed on the inlet or venous
side of the artificial lung. In a blood circuit, which will
be described in more detail below, the magnitude of the
pressure adjacent the outlet of the pump is greater than
the sum of the pressure loss at the blood feeding catheter
and the pressure loss of the artificial lung. The problem
that results is an increase in the internal pressure of the
circuit on the blood feeding side. A proposed solution to
this problem, disclosed in the specification of Japanese
Patent Application, Laid-Open No. 50-9299, is to pass the
blood on the outer side of the hollow fibers. However,
the proposed arrangement has not been put into practical
use due to difficulties in removing air bubbles appearing
in the blood in extracoporeal circuit. Further, there are
difficulties in priming and the like to put the proposed
artificial lung into practical use.
jb/
883~
The specification of the above-mentioned Japanese
publication discloses a theoretical arrangement for passing
oxygen gas on the outer side of hollow fibers, but the arrange-
ment does not maximize the gas exchange capability of the
hollow fibers. To obtain a practical system, not only must
the gas exchange capability be improved, but the other factors,
which will be described in more detail below, must be taken
into consideration.
The present invention provides a hollow fiber-type
artificial lung including an axially extending housing and a
hollow fiber bundle having a multiplicity of hollow fibers
accommodated within and along the axial direction of the housing,
the hollow fibers forming blood channels between outer wall
surfaces of neighboring ones thereof, and being arranged within
the housing in such a manner that neighboring blood channels
are brought into substantial communication. First and second
walls liquid-tightly support the hollow fibers at both end
portions thereof within the housing, and the first and second
walls, the inner wall of the housing and the outer wall surfaces
of the hollow fibers define a blood chamber. slood inlet
means is provided in a side wall of the housing in the vicinity
of the first wall and communicates with the blood chamber.
A blood reservoir chamber is provided in the vicinity of the
second wall and communicates with the blood chamber. Blood
outlet means communicates with the blood reservoir chamber and
gas inlet means is provided on an inner side of at least one
of the first and second walls and communicates with the hollow
interior of the hollow fibers. The inner wall of the housing
in the vicinity of the blood inlet means is flared outwardly
-- 3 --
mab/~^
^ ~ , ,.
~238831
relative to the inner surface of the housing at an intermediate
portion thereof, thereby forming an annular blood flow passage
between the outer periphery of the hollow fiber bundle and the
inner surface of the housing.
According to another aspect of the present invention
there is provided a hollow fiber-type artificial lung which
includes an axially extending housing with a hollow fiber bundle
having a multiplicity of hollow fibers accommodated within and
along the axial direction of the housing, the hollow fibers forming
blood channels between outer wall surfaces of neighboring ones
thereof and being arranged within the housing in such a manner that
neighboring blood channels are brought into substantial
communication. First and second walls liquid-tightly support the
hollow fibers at both end portions thereof within the housing, the
first and second walls, the inner wall of the housing and the outer
wall surfaces of the hollow fibers defining a blood chamber. slood
inlet means is provided in a side wall of the housing in the
vicinity of the first wall and has an opening communicating with
the blood chamber. Blood outlet means is provided in a side wall
of the housing in the vicinity of the second wall and has an
opening communicating with the blood chamber. The inner surface of
the housing at a portion communicting with the blood inlet means is
flared outwardly relative to the intermediate portion of the
housing, thereby forming an annular blood flow passage between the
outer periphery of the hollow fiber bundle and the inner surface of
the housing. A heat exchanger is provided integral with a blood
flow passage, which is formed by the blood chamber, at least at an
upstream, downstream or intermediate portion of the blood flow
passage. Gas inlet means is provided on an outer side of at least
one of the first and second walls.
-- 4 --
~238831
In a specific embodiment of the invention, the inner
surface of the housing in the vicinity of the blood inlet port
is flared outwardly relative to the inner surface of the
housing at the intermediate portion thereof, thereby forming
the first blood flow passage between the outer periphery of
the hollow fiber bundle and the inner surface of the housing,
the first blood flow passage being annular in shape. Similarly,
the inner surface of the housing in the vicinity of the blood
outlet port is flared outwardly relative to the inner surface
of the housing at the intermediate portion thereof, thereby
forming the second blood flow passage between the outer periphery
of the hollow fi.ber bundle and the inner surface of the housing,
the second blood flow passage also being annular in shape.
The flared inner surface of the housing in the
vicinity of the blood inlet means may be off centered with
respect to the hollow fiber bundle so as to increase the
mab/Jc
lZ38831
distance between the blood inlet means and the hollow
fiber bundle, thereby enlarging the flow area of the first
blood flow passage facing the blood inlet means. Likewise,
the flared inner surface OL the housing in the vicinit~ of
the blood outlet means is off centered with respect to the
hollow fiber bundle so as to increase the distance between
the blood outlet means and the hollow fiber bundle, thereby
enlarging the flow area of the second blood flow passage
facing the blood outlet means.
The gas venting portion may include a detachable
filter permeable to gas but impermeable to bacteria.
An object of the present invention, therefore, is
to provide a hollow fiber-type artificial lung which produces
a blood flow capable of improving gas exchange efficiency per
unit membrane area, which makes possible blood perfusion
utilizing the head developed between the patient and the
artificial lung, and which effectively removes are evolved
during priming and during use.
Another object of the present invention is to provide
a hollow fiber-type artificial lung which reduces the amount
of blood needed to fill the associated blood circuit, by
combining, into a substantially unitary body, a blood chamber
and a blood reservoir.
Still another object of the present invention is to
provide a hollow fiber-type artificial lung through which it
is possible to regulate the amount of extracorporeal circulation.
A further object of the present invention is to
provide a hollow fiber-type artificial lung which reduces
the amount of blood needed to fill the associated blood
jb/ - 6 -
1233~33~
circuit, by combining, into a substantially unitary body,
a blood chamber and a heat exchanger chamber.
The above and other objects, features and advantages
of the present invention will become more apparent from the
following description when taken in conjunction with the
accompanying drawings in which preferred embodiments of the
present invention are shown by way of illustrative example.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a diagram of a blood circuit to which
a prior-art membrane-type artificial lung is applied;
Fig. 2 is a diagram of a blood circuit to which
the hollow fiber-type artificial lung is applied;
Fig. 3 is a sectional view illustrating an embodiment
of a hollow fiber-type artificial lung;
Fig. 4 is a sectional view taken along line IV-IV
of Fig. 3;
Fig. 5, which appears on the same sheet of drawings
as Figs. 1 and 2, is a sectional view taken along line V-V
of Fig. 3;
Fig. 6 is a sectional view taken along line VI-VI
of Fig. 3;
Fig. 7 is a sectional view illustratirg a hollow
fiber-type artificial lung according to the prior art;
Fig. 8 is a sectional view showing the disposition
of the hollow fiber-type artificial lung during priming;
mab~C
lZ3~83~
- Fig. 9 is a diagram of a blood circuit in a case
where the present invention is applied to a hollow
fiber-type artificial lung having a blood reserv~ir
chamber;
S Fiq. 10 is a perspective view illustrating an
embodiment of a hollow fiber-type artificial lung
according to one application of the present invention;
Fig. 11 is a sectional view showing the hollow
fiber-type artificial lung of Fig. 10;
Fig. 12 is a sectional view taken along the line
XII-XII of Fig. 11;
Fig. 13 is a sectional view illustrating another
embodiment of the hollow fiber-type artificial lung shown
in Fig. 10;
Fig. 14 is a perspective view illustrating an
artificial lung, having a heat exchanger, according to an
application of the present invention;
Fig. 15 is a sectional view illustrating a first
embodiment of the artificial lung shown in Fig. 14;
Fig. 16 is a sectional view taken along line XVI-XVI
of Fig. 14;
F,ig. 17 is a perspective view illustrating an
artificial lung according to a second embodiment of the
artificial lung shown in Fig. 14;
Fig~ 18 is a perspective view illustrating an
artificial lung according to a third embodiment;
Fig. 19 is a perspective view illustrating an artificial
lung according to a fourth embodiment; and
Figure 20 is a perspective view illustrating an example
~,of a sle,nder tube having fins forming a heat exchanger.
. ;, , ' '
123~831
As shown in Figure 1, a blood circuit using the
membrane-type artificial lung requires that a pump 2 be
disposed on the inlet or venous side of the artificial lung,
indicated a numeral 1. Numeral 3 denotes a blood reservoir,
and 4 a heat exchanger. With the blood circuit shown in
Figure 1, however, the magnitude of the pressure adjacent
the outlet of the pump 2 is greater than the sum of the
pressure loss at the blood feeding catheter and the pressure
loss of the artificial lung.
As indicated above, to obtain a practical system,
not only must the gas exchange capability be improved, but
a number of other factors must be taken into account. More
specifically, through us of the blood reservoir 3 shown in
Fig. 1, the extracorporeally circulating blood is temporarily
stored so that any air bubbles entrained within the blood may
be removed. The reservoir 3 is also necessary for the purpose
of maintaining a certain degree of blood flow in the event
that the blood extracted from a vein is deficient because of
a bend in the associated tubing, or if there is leakage of
blood from the system. However, since the blood reservoir 3
is provided in the blood circuit independently of the artifi-
cial lung 1 in the conventional membrane-type artificial lung
systme, the circuit is structurally complex and much time and
effort are involvea in setting up the circuit and in extract-
ing bubbles during priming. Furthermore, because of the
extensive priming and the large amount of blood required
to fill the conventional system, it is required
b/ _ g _
1238831
that a preliminary transfusion of blood be made into the
priming liquid, with which the artificial lung is filled
in advance, in order to mitigate dilution of the blood
within the patient's body. In particular, the allowable
amount of blood available for filling an artificial lung
for surgery involving infants and children is small
because of low body weight. Therefore, when the
membrane-type artificial lung, which reguires a large
quantity of blood to fill the entire circuit, is used in
surgical operations on infants or children, a problem
arises in that the total amount of blood available is
small.
The heat exchanger 4 in the blood circuit of Fig. 1
is needed for lowering blood temperature during a low
lS body temperature process, and for heating the blood or
for keeping the blood warm. However, since the heat
exchanger 4, as well as the blood reservoir 3, is
provided in the blood circuit independently of the
artificial lung 1 in the conventional membrane-type
artificial lung system, the circuit becomes even more
complex structurally and greater time and effort are
required for circuit set up and bubble extraction during
priming. Also, as mentioned above, the extensive priming
and the large amount of blood required to fill the
conventional system require that a preliminary
transfusion be made in the priming liquid, with which the
artificial lung is filled in advance, to counter dilution
-- 10 --
lZ3~3~331
of the blood within the patient's body. Because of the
small amount of blood available for filling an artificial
lung in surgery directed to infants and children, there is
demand for an arrangement capable of greatly diminishing the
amount of blood needed to fill the overall blood circuit.
Reference will now be had to Figs. 2 through 5
to describe the artificial lung of the present invention in
detail. Fig. 2 is a diagram of a blood circuit to which
the hollow fiber-type artificial lung of the present invention
is applied, Fig. 3 is a sectional view illustrating an
embodiment of a hollow fiber-type artificial lung according
to the present invention, Fig. 4 is a sectional view taken
along line IV-IV of Fig. 3, Fig. S is a sectional view taken
jb/ - lOa -
-' 1238831
along line V-V of Fig. 3, and Fig. 6 is a sectional view taken
along line VI-VI of Fig. 3.
As shown in Fig. 2, a blood circuit is applied has
an artificial lung 11, a blood reservoir 12, a pump 13 and
a heat exchanger 14 through which blood is passed in the order
mentioned.
As illustrated in Figs. 3 through 6, the artificial
lung 11 includes a tubular housing 15 accommodating a bundle
17 of hollow fibers 16. The ends of the hollow fibers 16
are retained liquid tightly within the housing 15 via walls
18,19. A header 20 is attached to one end portion of the
housing 15, and a header 21 to the other end thereof. The
inner side of the header 20 and the wall 18 define a gas inlet
chamber 22 communicating with the space within each of the
hollow fibers 16. The inner side of the header 21 and the
wall 19 define a gas outlet chamber 24 similarly communicating
with the space within each of the hollow fibers. The header
21 is formed to include a gas outlet port 25, and the header
20 is formed to include a gas inlet port 23. Thus, a gas
such as oxygen or air supplied from the gas inlet port 23
is capable of being passed through the interior of the hollow
fibers 16. It should be noted that the header 21, and hence
the gas outlet chamber 24 and gas outlet port 25, is not
particularly essential, for an arrangement can be adopted
--wherein the gas exiting from the hollow fibers l6 is released
directly into the atmosphere.
h /~ ^
123t~fl3~
-12-
The walls 18, 19, the inner surface of the housing
15, and the outer peripheral surface of the hollow fibers
16 define a blood chamber 26. Formed at the respective
ends of the housing 15 in the side thereof are a blood
inlet port 27 and a blood outlet port 28, each of which
communicates with the blood chamber 26. More
specifically, the outer walls of adjacent hollow fibers
16 define channels through which the entrant blood may
flow, and neighboring channels communicate with one
another owing to the clustered hollow fiber bundle. In
consequence, the streams of blood flowing through these
channels interfere with one another, causing the blood to
flow in a turbulent manner. This makes it possible to
achieve a turbulent blood flow at the periphery of the
lS hollow fibers 16 within the blood chamber 26.
The inner surface of the housing 15 at the portion
where the blood inlet port 27 is provided is flared
outwardly relative to the inner surface of the housing at
the intermediate portion thereof, thereby forming an
annular blood flow passage 29 between the outer periphery
of the hollow fiber bundle 17 and the inner surface of
the housing at the flared end, as shown in Fig. 5. This
makes it possible for the entrant blood to be distributed
to each of the hollow fibers 16 smoothly from the entire
outer periphery of the bundle 17 facing the blood flow
passage 29. Further, as shown in Fig. 5, the flared
inner surface of the housing lS is off centered with
~23~3i
-13-
respect to the hollow fiber bundle 17 so as to increase
the distance between the blood inlet port 27 and the
bundle, thereby enlarging the flow area of that part of
the blood flow passage 29 facing the blood inlet port 27.
Thus, the flow passage area of the blood flow passage 29
gradually diminishes with an increase in distance from
the blood inlet port 27, so that the blood from the blood
flow passage 29 is distributed in a uniform amount
circumferentially of the hollow fiber bundle 17. This
makes it possible for the flow rate of the blood
traveling axially of the housing 15 within the blood
chamber 26 to be uniformalized in relation to the
circumferential direction of the hollow fiber bundle 17.
The inner surface of the housing 15 at the portion
where the blood outlet port 28 is provided is flared
outwardly relative to the inner surface of the housing at
the intermediate portion thereof, thereby forming an
annular blood flow passage 30 between the outer periphery
of the hollow fiber bundle 17 and the inner surface of
the housing at this flared end, as shown in Fig. 6. The
blood enveloping each of the hollow fibers 16 will
therefore flow from the entire outer periphery of the
bundle 17, which is facing the blood flow passage 30,
into the abovementioned blood channels, and will proceed
toward the blood outlet port 28 while mixing of the blood
flowing through a plurality of the channels takes place.
Further, as shown in Fig. 6, the flared inner surface of
383~
-14-
the housing 15 at the blood outlet end thereof is off
centered with respect to the hollow fiber bundle 17 so as
to increase the distance between the blood outlet port 28
and the bundle, thereby enlarging the flow area of that
part of the blood flow passage 30 facing the blood outlet
port 28. Thus, the flow passage area of the blood flow
passage 30 gradually diminishes with an increase in
distance from the blood outlet port 28, so that the
amount of blood introduced to the blood flow passage 30
is uniformalized circumferentially of the hollow fiber
bundle 17. This ma~es it possible for the flow rate of
the blood traveling axially of the housing 15 within the
blood chamber 26 to be uniformalized in relation to the
circumferential direction of the hollow fiber bundle 17.
The housing 15 is shaped such that its inner diameter
has a minimum value at the mid portion of the housing
axially thereof and a gradually larger value as the ends
of the housing are approached. Thus, the housing 15
narrows or tapers towards it center from both ends to
constrict the outer periphery of the hollow fiber bundle
17 at the central portion thereof in the axial direction.
Owing to the constriction of the fiber bundle 17 produced
by the tapered shape of the housing 15, a uniform flow of
blood through a transverse cross section of the fiber
bundle 17 is obtalned, and the flow speed varies along
the axis of the bundle to promote a turbulent flow
condition. This makes it possible to improve gas
123~383:1
-15-
exchange efficiency. It will be appreciated from Figs. 3
and 4 that the centrally tapered inner wall of the
housing 15 and the inner walls of the housing defining
the blood flow passages 29, 30 form a continuous inner
wall surface flaring outwardly from the central portion
of the housing. This configuration assures that air,
which is to be purged from the housing 15 during priming,
will travel along the inner wall surface of the housing
and exit from a gas venting port 31, described later,
without residing in the blood chamber 26. Alternatively,
the inner wall of the housing 15 may be flared linearly
from, say, the end having the blood inlet port 27 to the
end having the blood outlet port 28.
A conventional artificial lung llA, shown in Fig. 7,
lS has portions Pl, P2 projecting discontinuously in the
direction of blood flow, these portions being located on
the inner surface of a housing 15A defining a blood
chamber 26A. With such an arrangement, the air to be
vented during priming is entrapped by the projecting
portions Pl, P2, so that complete discharge of the air
from the blood chamber 26A does not take place.
Each of the hollow fibers 16 consists of a
microporous membrane. More specifically, each hollow
fiber comprises a porous polyolefin resin such as
polypropylene or polyethylene, with polypropylene being
preferred. In this case, the hollow fibers 16 have a
multiplicity of small pores or holes interconnecting the
383:~
inside and outside of the fiber wall. The hollow fiber
has an inner diameter of about 100 to 1,000~, a wall
thickness of about 10 to 500 and preferably 10 to 50~,
and a porosity in the range of amout 20 to 80 percent.
With hollow fibers 16 of this kind, membrane resistance
to gas flow may be reduced and an excellent gas exchange
performance obtained because the gas flow occurs as a
volume flow. It should be noted that the hollow fibers
16 need not necessarily consist of a microporous
membrane. For example, use can be made of a silicone
membrane that permits travel of a gas by dissolution or
diffusion.
The packing rate of the housing 15 having hollow
fibers of the foregoing type is as specified by the
following formula:
packing rate~)
=total cross-sectional area of fibers x 100
housing cross-sectional area
More specifically,
packing rate P(~) = (lr)2~n/(la)27Lx 100
where r represents the outer diameter of the hollow
fibers, _ the number of hollow fibers enclosed within the
housing, and a the inner diameter of the housing. The
preferred packing rate at the end portions of the
housing, namely at the portions of maximum diameter, is
20 to 50%. The preferred packing rate at the centrally
constricted portion of the housing is from 1.2 to 4 times
~Z3~31
-17-
the packing rate at the housing end portions. If the
packing rate at the housing end portions is less than
20%, there is little surface contact with the outer wall
of the hollow fibers and the blood flow is too linear.
The result is an unsatisfactory gas exchange performance.
If the packin~ rate at the housing end portions is
greater than 50~, on the other hand, the flow of blood is
impeded, giving rise to an excessive pressure loss. In a
case where the centrally constricted portion is provided,
it is necessary to increase the packing density at the
constricted P~rtion by at least 1.2 times. A figure
below 1.2 tim~S will make it difficult for the blood to
flow in the d~sired turbulent manner, while a packing
ratio greater than four times end portion packing ratio,
or in excess of 80%, will give rise to an undesirable
pressure loss
The hollow fiber-type artificial lung most preferred
has 40,000 hollow fibers, each having an outer diameter
of 250 um, enclosed within a housing the inner diameter
whereof is 80.0 mm at the end portions and 64.0 mm at the
constricted Portion thereof. The packing rate is 39.1%
at the end portions and 61.0% at the constricted portion.
The walls 18, 19 are formed by a centrifugal
injection proceS5 in the following manner. First, a
multiplicity of the hollow fibers 16, which are longer
than the housing 15, are prepared, both open ends of the
fibers are plugged with a highly viscous resin, and the
~23~3831
-18-
fibers are then placed side by side within the housing
15. Thereafter, with both ends of the hollow fibers
completely covered, a polymeric potting agent is poured
in from both ends of the housing 15 while the housing is
S being rotated about a center of rotation decided by the
longitudinal direction of the housing, under a condition
in which the central axis of the housing is situated in
the direction of the radius of rotation. After the
poured resin has hardened, the outer faces of the resin
are cut off by means of a sharp blade to expose both open
ends of the hollow fibers 16. This completes the
formation of the walls 18, 19. As will be understood
from Figs. 3 and 4, the sides of the walls 18, 19 facing
the blood chamber 26 define cylindrical concavities.
lS The housing 15 is provided with a gas venting port 31
communicating with the blood chamber 26, the port being
situated higher than the blood outlet port 28 when the
artificial lung is in use. The gas venting port 31 is
fitted with a detachable filter 32 permeable to air but
not to bacteria. The filter 32 is removed during priming
and reattached after priming and serves to prevent
bacterial contamination of the artificial lung 11 during
the venting of air evolved when the artificial lung is
used.
During priming, the gas venting port 31 allows air to
escape from the interior of the blood circuit and
artificial lung 11, which air is displaced by a filling
123~331
--19--
liquid such as a physiologic saline. Following the
removal of air, the port 31 is plugged to form a hermetic
seal.
The gas venting port 31 and blood outlet port 28 are
provided at positions symmetrical with respect to the
axis of the housing 15. During priming, as shown in Fig.
8, the central axis of the artificial lung 11 is tilted
in a plane which contains both the gas venting port 31
and blood outlet port 28, whereby the gas venting port 31
is placed higher than the blood outlet port 28 to assure
and facilitate the discharge of air. The gas venting port
31 is located in the side wall of the housing lS at a
point adjacent the concave surface of the wall 18, as
best shown in Fig. 4, so as to communicate with the
uppermost part of the blood chamber 26. This makes
possible the complete discharge of air during priming, as
well as the complete discharge of air which occurs when
the artificial lung is used, as when air that remains in
the blood circuit connecting joints flows into the
artificial lung during use. It should be noted that the
gas venting port may be so provided as to penetrate the
center of the wall 18.
The operation of the artificial lung shown in Figs. 3
through 6 will now be described. The artificial lung is
for use in, e.g., open-heart surgery, and is installed in
a blood circulating circuit of the kind shown in Fig. 2.
Ordinarily, blood is extracted at a flow rate of 4 l/min.
~Z3~f33~
-20-
First, prior to introducing blood into the artificial
lung 11, physiologic saline mixed with heparin is
introduced from the blood inlet port 27 to exclude all
air from the blood chamber 26 within the artificial lung
11. During this process, a tube communicating with the
blood reservoir will be connected to the gas venting port
31, from which the filter 32 has been removed, and the
blood outlet port 28 is either connected to a tube in the
same manner as the gas venting port 31, or otherwise
sealed by means of a cap or the like. Following the
complete purging of the air from the interior of the
artificial lung 11, the filter 32 is fitted into the gas
venting port 31 which is then sealed by means of a cap,
not shown. Blood is introduced from the patient into the
lS artificial lung 11 from the blood inlet port 27 at a
predetermined head (on the order of 1 m). The entrant
blood impinges upon the outer walls of the hollow fibers
16 near the blood inlet port 27 and flows into the
annular blood flow passage 29 defined within the
artificial lung. Owing to the force of gravity and the
1 m head, the blood rises within the blood chamber 26.
As this proceeds, an exchange is effected between the
carbon dioxide contained in the blood and oxygen, which
enters from the gas inlet port 23 through the hollow
fibers 16. The oxygenated blood flows out of the blood
outlet port 28 through the blood flow passage 30, is held
in the reservoir 12 (Fig. 2) and then, under the
-" 123~831
influence of the blood feeding pump 13, is heated or cooled
by the heat exchanger 14 before being fed back into the patient.
Any air that appears in the artificial lung 11 during
the feeding of the blood, which air is primarily the result
of residual air from the tube connections of the blood circuit,
flows in from the blood inlet port 27 together with the entering
blood, rises within the blood chamber 26 and collects in the
concave portion of the wall 18 at the upper end of the blood
flow path 30. The collected air is released to the outside
through the filter 32 by removing the cap from the gas venting
port 31. At such time the artificial lung 11 preferably is
tilted, as shown in Fig. 8, to bring the gas venting port
31 to a position higher than that of the blood outlet port
2~.
The actions and effects of the artificial lung 11
shown in Figs. 3 through 6 and in Fig. 8 will now be set forth.
The above-described fiber-type artificial lung 11
is also described and is claimed in above-identified copending
Canadian Patent Application 437,308.
An embodiment of the hollow fiber-type artificial
lung of the present invention as shown in Figs. 3 through
6 will now be described.
In this embodiment, the artificial lung is equipped
with a blood reservoir chamber. Specifically, the hollow
fiber-type artificial lung comprises an axially extended
housing, a hollow fiber bundle having a multiplicity of hollow
fibers accommodated within and along the axial direction of
the housing, the hollow fibers forming blood
- 21 -
mab/l~
lZ3883~
channels between outer wall surfaces of neighboring ones
thereof, and being arranged within the housing in such a
manner that neighboring blood channels are brought into
communication, first and second walls liquid~tightly
supporting the hollow fibers at both end portions thereof
within the housing, the first and second walls, the inner
wall of the housing and the outer wall surfaces of the
hollow fibers defining a blood chamber, a blood inlet
port provided in a side wall of the housing in the
vicinity of the first wall and communicating with the
blood chamber, a blood reservoir chamber provided in the
vicinity of the second wall and communicating with the
blood chamber, a blood outlet port communcating with the
blood reservoir chamber, and a gas inlet port provided on
lS an outer side of at least one of the first and second
walls and communicating with the hollow interior of the
hollow fibers.
The artificial lung includes a gas venting port
communicating the blood reservoir chamber with the
atmosphere.
The blood reservoir chamber has an outer wall comprising
a rigid material, a side surface of the outer wall having
graduations. The blood reservoir chamber is so adapted
that, when blood is introduced from the blood inlet port
so as to rise within the blood chamber, the blood will
flow downwardly into the blood reservoir chamber from the
blood chamber and will be collected within the blood
- 22 -
~23~383~
reservoir chamber.
The inner surface of the housing in the vicinity of
the blood inlet port is flared outwardly relative to the
inner surface of the housing at the intermediate portion
S thereof, thereby forming an annular blood flow passage
between the outer periphery of the hollow fiber bundle
and the inner surface of the housing. The flared inner
surface of the housing in the vicinity of the blood inlet
port is off centered with respect to the hollow fiber
bundle so as to increase the distance between the blood
inlet port and the hollow fiber bundle, thereby enlarging
the flow area of the blood flow passage facing the blood
inlet port.
The housing comprises an inner cylinder defining the
blood chamber, and an outer cylinder surrounding a
portion of the inner cylinder for defining the blood
reservoir chamber between itself and the inner cylinder,
the first wall being retained in the inner cylinder, the
second wall being retained in the outer cylinder.
Alternatively, the first and second walls may both be
retained in the inner cylinder.
The hollow fibers are made of a microporous membrane.
The gas venting port has a filter permeable to gas but
impermeable to bacteria.
Reference will now be had to Figs. 9 through 12 to
describe the artificial lung in detail. Fig. 9 is a
diagram of a blood circuit to which the hollow fiber-type
- 23 -
123~31
artificial lung is applied, Fig. 10 is a perspective
view the embodiment of the hollow fiber-type artificial
lung according to one application of the present
invention, Fig. 11 is a sectional view showing the hollow
fiber-type artificial lung of Fig. 10, and Fig. 12 is a
sectional view taken along the line XII-XII of Fig. 11.
As shown in Fig. 9, a blood circuit to which the
present invention is applied has an artificial lung 111,
a pump 112 and a heat exchanger 113 through which blood
is passed in the order mentioned.
As illustrated in Figs. 10 through 12, the artificial
lung 111 includes a housing 114 the hollow interior
whereof accommodates a bundle 116 of hollow fibers 115.
The hollow fibers 115, similar to the hollow fibers 16
described earlier, are made of a microporous membrane,
silicone membrane or the like. Reference should be had
to the earlier description for further details. Also, as
described above with reference to Figs. 3 through 6, the
hollow fibers 115 are accommodated within the housing 114
in such a manner that entrant blood will flow
therethrough in a turbulent manner. The housing 114
comprises an internal cylinder 117 which receives the
hollow fiber bundle 116 substantially in its entirety,
and an outer cylinder 118 receiving the upper portion of
the inner cylinder 117 substantially coaxially. The
inner and outer cylinders 117, 118 are formed from a
rigid material such as acryl-styrene copolymer,
- 2 4 -
~238831
polycarbonate or polystyrene. The upper edge portion of
the inner cylinder 117 and a wall 120 define an annular,
continuous and circumferentially extending communication
passage 121. Further, the inner cylinder 117 and the
outer cylinder 118 define a blood reservoir chamber 131,
which is communicated with a blood chamber 128 via the
passage 121. A blood outlet port 132 communicating with
the blood reservoir 131 is formed on the outer cylinder
118 at the lowermost position thereof. Here the side of
the outer cylinder 118 is provided with engraved
graduations 133 for indicating an amount of blood which
will collect within the reservoir chamber, as described
later
The volume of the blood reservoir chamber 131 is such
that a certain degree of blood flow will be maintained in
the event that the blood extracted from a vein is
deficient because of a bend in the associated tubing, or
if there is leakage of blood from the system.
Specifically, the blood reservoir chamber 131 is designed
to have a volume such that the upper level of the
collected blood will not rise to a position higher than
the upper edge of the inner cylinder 117, even if the
amount of blood collected is enough for half of the
extracorporeal blood circulation rate ~ml/min) planned
for safety. When blood flows into the inner cylinder 117
from a blood inlet port 129 and rises within the blood
chamber 128, the blood from the blood chamber 128
- 2 5 -
. .
123~331
eventually overflows from the upper edge of the inner
cylinder 117 and collects within the blood reservoir
chamber 131. sy designing it so that the blood reservoir
chamber 131 has the above-described volume, the blood
which collects within the blood reservoir chamber does
not exert any pressure upon the blood rising in the blood
chamber 128.
The outer cylinder 118 is provided at its upper
portion with a gas vent 134 capable of communicating the
blood reservoir chamber 131 with the outside air. The
gas vent 134 is fitted with a filter which is permeable
to air but impermeable to bacteria, thereby preventing
bacterial contamination of the artificial lung 111 during
use.
With the artificial lung 111 shown in Figs. 10
through 12, the hollow interior of each hollow fiber 115
serves as gas flow passage, while the blood chamber 128
is formed at the outer periphery of the hollow fibers
115. As a result, the entrant blood is subjected to gas
exchange in the blood chamber 128 while the blood flows
in a turbulent manner, and the membrane area contacting
the blood is increased by an amount corresponding to the
difference between the inner and outer diameters of the
hollow fibers 115. Thus, the oxygenation capability per
membrane area is raised so that it is possible to reduce
the membrane area required to obtain a given oxygenation
capability.
- 26
1238~331
Further, since the blood flow paths forming the blood
chamber 128 are not narrowed, there is little resistance
to the flow of blood within the blood chamber 128. This
makes it possible to achieve perfusion of the blood
within the artificial lung 111 by virtue of the head
developed between the patient and the artificial lung
111, as shown in the blood circuit of Fig. 9.
Accordingly, the internal circuit pressure on the blood
feeding side is solely the pressure of the blood feeding
catheter portion, thereby eliminating the possiblity of
accelerated hemolysis and damage to the blood circuit
connections. In addition, owing to the unnarrowed blood
flow paths in the blood chamber 128, the extraction of
bubbles during priming can be carried out quickly and
easily.
As mentioned earlier, the hollow fibers 115 consist
of a microporous membrane. If water vapor contained
within the blood should penetrate into the hollow fibers
115 through the membranous walls thereof, the water vapor
will not form dew within the apparatus owing to the
temperature, on the order of 37C, of the blood flowing
by the outer periphery of the hollow fibers 115. Thus,
there will be no decline in the effective membrane area
of the hollow fibers 115 and, hence, no reduction in gas
exchange performance.
Since the artificial lung 111 is provided with the
internal blood reservoir chamber 131 communicating with
- 2 7 -
123~3831
the blood chamber 128, the blood circuit takes on the
simple arrangement shown in Fig. 9, the circuit can be
set up quickly in a simple manner, and the extraction of
bubbles during priming can proceed rapidly without
obstruction. In addition, the blood circuit in which the
artificial lung 111 is used requires little priming and
only a small amount of blood for filling, and a
preliminary transfusion is unnecessary. In particular,
the artificial lung 111 may be used to perform open-heart
surgery, without a transfusion, even iD the case of
infants or children for which the allowable blood filling
quantity is low.
Fig. 13 is a sectional view illustrating a hollow
fiber-type artificial lung 141 according to another
embodiment of the present invention. The artificial lung
141 includes a housing 142 comprising an inner cylinder
143 and an outer cylinder 144. The inner cylinder 143
accommodates a bundle 146 of a multiplicity of hollow
fibers 145. The ends of the hollow fibers 145 are
retained liquid tightly within the inner cylinder 143 via
walls 147, 148 retained in the upper and lower ends of
the inner cylinder 143, respectively. A header 149 is
attached to one end portion of the inner cylinder 143,
and a header 150 to the other end portion thereof. The
25 inner side of the header 150 and the wall 148 define a
gas inlet chamber 151 communicating with the space within
each of the hollow fibers 145. The inner side of the
2~
~238~31
header 149 and the wall 147 define a gas outlet chamber
153 similarl~ communicating with the space within each of
the hollow fibers. The header 149 is formed to include a
gas outlet port 154, and the header 150 is formed to
include a gas inlet port 152. Thus, a gas such as oxygen
or air supplied from the gas inlet port 152 is capable of
being passed through the interior of the hollow fibers
145.
The walls 147, 148, the inner surface of the inner
cylinder 143, and the outer surface of the hollow fibers
145 define a blood chamber 155. The lower end of the
inner cylinder 143 is formed to include a blood inlet
port 156 in the side thereof, as well as a blood flow
passage 157 similar to the blood flow passage 29 in the
artificial lung 11 of Figs. 3 and 4. Thus, blood
supplied from the blood inlet port 156 is passed over the
periphery of the hollow fibers 145 in the blood chamber
155 in a turbulent state so that a gas exchange may take
place.
In the artificial lung 141 of Fig. 13, the outer
cylinder 144 is fitted on the inner cylinder 143 from the
upper part thereof and encircles the upper end portion of
the inner cylinder 143 and the header 150. A blood
reservoir chamber 158 is formed between the inner
25 cylinder 143 and the outer cylinder 145. The side wall
of that portion of the inner cylinder 143 inside the
outer cylinder 144 is provided with a plurality of
- 29
1238~33~
circumferentially spaced windows or communication
passages 159 for communicating the interior of the blood
chamber 155 with the interior of the blood reservoir
chamber 158. A blood outlet port 160 communicating with
the blood reservoir chamber 158 is formed on the outer
cylinder 144 at the lowermost position thereof. The
outer cylinder 144 is provided at its upper portion with
a gas vent 162, having a filter 161, for communicating
the blood reservoir chamber 158 with the outside air.
The volume of the blood reservoir chamber 158 is such
that the upper level of blood, which collects within the
chamber, will remain below the communication passages 159
at all times. As with the artificial lung 111 of Figs.
10 through 12, the arrangement is such that blood
overflows into the blood reservoir chamber 158 from the
blood chamber 155. - In this case, however, the blood
flows out of the communcation passages 159.
Thus, as with the artificial lung 111, the artificial
lung 141 of the present embodiment improves the gas
exchange performance per unit membrane area of the hollow
fibers 145, makes it possible to achieve perfusion of the
blood by virtue of the head developed between the patient
and the artificial lung 141, and reduces the quantity of
blood needed to fill the blood circuit in which the
artificial lung is used. In addition, since the inner
cylinder 143 retains the pair of walls 147, 148 and
accommodates the bundle 146 of hollow fibers 145, and
- 30 -
~238831
since the outer cylinder 144 is fitted on the inner
cylinder 143 from the top part thereof, the overall
artificial lung is simplified in construction and easy to
manufacture.
The operation of the artificial lung 111 illustrated
in Figs. 10 through 12 will now be described.
First, prior to introducing blood into the artificial
lung 111, physiologic saline mixed with heparin is
introduced from the blood inlet port 129 to excl~de air
from the blood chamber 128 within the artificial lung.
In this process, a tube communicating with a heat
exchanger is connected to the blood outlet port 132 and
the gas venting port 134 is sealed. Or, conversely, the
tube is connected to the gas venting port 134 (from which
the detachable filter 135 is removed), and the blood
outlet port 132 is sealed. Alternatively, the tube is
bifurcated and connected to both ports 132, 134.
Following the complete purging of the air from the
interior of the blood chamber, the filter, if it has been
removed, is fitted into the gas venting port. slood
taken from the patient at a predetermined head (on the
order of 1 m) is mixed with heparin and then introduced
into the artificial lung 111 from the blood inlet port
129. Ordinarily, the blood is introduced at a rate of 4
l/min. The entrant blood impinges upon the outer walls
of the hollow fibers 116 near the blood inlet port 129
and flows into the blood flow passage 130 defined within
- 31 -
123~ 31
the artificial lung. Owing to the force of gravity andthe 1 m head, the blood rises within the blood chamber
128. As this proceeds, an exchange is effected be'cween
the carbon dioxide contained in the blood and oxygen,
which en~ers from the gas inlet port 125 through the
hollow fibers 116. The oxygenated blood overflows from
the upper edge of the inner cylinder 117 and is collected
in the blood reservoir chamber 131. The gas venting port
134 is open to the air through the filter 135. The
amount of blood which exits from the artificial lung is
regulated by a change in the amount of blood collected
within the blood reservoir chamber. The blood that flows
from the blood outlet port 132 is returned to the patient
by the blood feeding pump 112 (Fig. 9) following heating
or cooling to a suitable temperature by means of the heat
exchanger 113.
Any air that appears in the artificial lung 111
during the feeding of the blood, which air is primarily
the result of residual air from the tube connections of
the blood circuit, flows in from the blood inlet port 127
together with the entering blood, rises within the blood
chamber 126, passes through the blood reservoir chamber
131 and is released to the outside through the filter 135
in the gas venting port 134.
The actions and effects of the foregoing artificial
lung will now be set forth.
As described, the hollow fiber-type artificial lung,
123~a331
having the blood reservoir chamber, comprises a housing,
a hollow fiber bundle having of a multiplicity of hollow
fibers for gas exchange accommodated within the housing,
first and second walls liquid-tightly supporting the
S hollow fibers at both end portions thereof within the
housing, the first and second walls, the inner wall of
the housing and the outer wall surfaces of the hollow
fibers defining a blood chamber, a blood inlet port
provided in a side wall of the housing in the vicinity of
the first wall and communicating with the blood chamber,
a blood reservoir chamber provided in the vicinity of the
second wall and communicating with the blood chamber, a
blood outlet port communcating with the blood reservoir
chamber, and a gas inlet port provided on an outer side
of at least one of the first and second walls and
communicating with the hollow interior of the hollow
fibers. Owing to such construction, gas exchange takes
place while the blood is flowing in a turbulent state,
making it possible to improve the gas exchange
performance per unit membrane area. In addition, the
blood flow resistance interiorly of the blood chamber is
reduced to a small value, so that perfusion of the blood
may achieved owing to the head developed between the
patient and the artificial lung. Furthermore, the amount
of blood needed to fill the blood circuit is small
because the blood chamber and blood reservoir chamber are
substantially united.
~ 33 ~
~238831
Since the artificial lung is provided with the blood
reservoir chamber, it is possible to regulate the amount
of blood during extracorporeal circulation. Since the
outer wall of the blood reservoir chamber consists of a
rigid material and is provided with graduations
indicating the volume of collected blood, one may readily
grasp the amount of blood being extracorporeally
circulated. Further, the blood reservoir chamber is so
adapted that, when blood is introduced from the blood
inlet port so as to rise within the blood chamber, the
blood will flow downwardly into the blood reservoir
chamber from the blood chamber and will be collected
within the blood reservoir chamber. Therefore, the
collected blood will not exert significant pressure upon
the blood moving within the blood chamber.
In the artificial lung, the inner surface of the
housing where the blood inlet port is provided is flared
outwardly relative to the inner surface of the housing at
the intermediate portion thereof, thereby forming an
annular blood flow passage between the outer periphery of
the hollow fiber bundle and the inner surface of the
housing. This makes it possible for the entrant blood to
be distributed to each of the hollow fibers smoothly from
the entire outer periphery of the bundle facing the blood
flow passage.
The flared inner surface of the housing in the
vicinity of the blood inlet port is off centered with
- 34 -
~23~3~
respect to the hollow fiber bundle so as to increase the
distance between the blood inlet port and the hollow
fiber bundle, thereby enlarging the flow area of the
blood flow passage facing the blood inlet port. As a
result, the blood from the blood flow passage is
distributed in a uniform amount circumferentially of the
hollow fiber bundle, making it possible for the flow rate
of the blood traveling axially of the housing within the
blood chamber to be uniformalized in relation to the
circumferential direction of the hollow fiber bundle.
The housing of the artificial lung comprises an inner
cylinder defining the blood chamber, and an outer
cylinder surrounding a portion of the inner cylinder for
defining the blood reservoir chamber between itself and
the inner cylinder, the first wall being retained in the
inner cylinder, the second wall being retained in the
outer cylinder. The result is a comparatively simple
construction. Alternatively, the first and second walls
may both be retained in the inner cylinder. This affords
an even simpler construction and facilitates the
manufacture of the artificial lung.
The hollow fibers are made of a microporous membrane
to reduce the resistance of the membrane to traveling
gases, and to enhance the gas exchange performance.
Further, the gas venting port has a filter permeable to
gas but impermeable to bacteria. This prevents bacterial
contamination of the artificial lung during use.
- 35 ~
123~831
In another embodiment of the present invention, the
holIow fiber-type artificial lung is equipped with a heat
exchanger mechanism. Specifically, the artificial lung
comprises an axially extended housing, a hollow fiber
bundle having a multiplicity of hollow fibers
accommodated within and along the axial direction of the
housing, ~he hollow fibers forming blood channels between
outer wall surfaces of neighboring ones thereof, and
being arranged within the housing in such a manner that
neighboring blood channels are brought into substantial
communication, first and second walls liquid-tightly
supporting the hollow fibers at both end portions thereof
within the housing, the first and second walls, the inner
wall of the housing and the outer wall surfaces of the
hollow fibers defining a blood chamber, a blood inlet
means provided in a side wall of the housing in the
vicinity of the first wall and having an opening
communicating with the blood chamber, a heat exchanger
provided integral with a blood flow passage, which is
formed by the blood chamber, at least at an upstream,
down stream or intermediate portion of said blood flow
passage, and gas inlet means provided on an outer side of
at least one of the first and second walls.
The housing has a blood outlet port, the blood
Z5 reservoir being provided on the blood outlet means side.
~he housing has the heat exchanger which is provided in
the blood chamber on the blood outlet means side. The
- 36 -
lZ3~3~31
heat exchanger is provided within the blood reservoir.
The housing has a blood inlet means, the heat
exchanger being provided on the side of the blood inlet
means.
The heat exchanger comprises a bundle of a
multiplicity of slender tubes supported at both ends by a
pair of walls. The ends of the tubes are open, so that
the hollow interiors of the tubes define blood flow
passages. The heat exchanger is so adapted that a heat
transfer medium may be passed along the periphery of the
tubes. Alternatively, the heat exchanger comprises a
tubular body through the hollow interior of which a heat
transfer medium may be passed.
The blood reservoir has a gas vent communicating with
lS the atmosphere, and an outer wall comprising a rigid
material.
The hollow fibers are made of microporous membrane.
The housing comprises an inner cylinder accommodating
the hollow fibers, and an outer cylinder surrounding a
portion of the inner cylinder for defining the blood
reservoir between itself and the inner cylinder. The
first wall supporting the hollow fibers is retained in
the inner cylinder, and the second wall supporting the
hollow fibers is retained in the outer cylinder.
Alternatively, both walls supporting the hollow fibers
are retained in the inner cylinder.
The inner surface of the housing at a portion
communicating with the blood inlet means is flared
1;~3fi~3~
outwardly relative to the intermediate portion of the
housing, thereby forming an annular blood flow passage
between the outer periphery of the hollow fiber bundle
and the inner surface of the housing. The flared inner
surface of the housing in the vicinity of the blood inlet
means is off centered with respect to the hollow fiber
bundle so as to increase the distance between the blood
inlet port and the hollow fiber bundle, thereby enlarging
the flow area of the blood flow passage facing the blood
inlet means.
The artificial lung will now be described with
reference to Figs. 14 through 16.
As shown in Fig. 9, the artificial lung, designated
at numeral 250, is installed in a blood circuit together
with a pump 211. Blood introduced from the patient's
vein passes through these components in the order
mentioned.
As illustrated in Figs. 14 through 16, the artificial
lung 250 includes a housing ~51 comprising an inner
cylinder 252 and an outer cylinder 253 consisting of a
rigid material such as acryl-styrene copolymer,
polycarbonate or polystyrene. A bundle 255 of a
multiplicity of hollow fibers 254 are accommodated within
the inner cylinder 252. The ends of the hollow fibers
254 are retained liquid tightly within the inner cylinder
252 via walls 256, 257 retained in the upper and lower
ends of the inner cylinder 252, respectively. A header
- 38 -
lZ3~31
258 is attached to one end portion of the inner cylinder
252, and a header 259 to the other end portion thereof.
The inner side of the header 258 and the wall 256 define
a gas inlet chamber 258A communicating with the space
within each of the hollow fibers 254. The inner side of
the header 259 and the wall 257 define a gas outlet
chamber 259A similarly communicating with the space
within each of the hollow fibers. The header 259 is
formed to include a gas outlet port 261, and the header
258 is formed to include a gas inlet port 260. Thus, a
gas such as oxygen or air supplied from the gas inlet
port 260 is capable of being passed through the interior
of the hollow fibers 254. It should be noted that the
header 259, and hence the gas outlet chamber 259A and gas
outlet port 261, is not particularly essential, for an
arrangement can be adopted wherein the gas exiting from
the hollow fibers 254 is released directly into the
atmosphere.
The housing 251, the outer surface of the hollow
fibers 254, and the walls 256, 257 define a blood chamber
262. The inner cylinder 252 is formed to include a blood
inlet port 263 in the vicinity of the wall 257, the port
communicating with the blood chamber 262. As described
above with reference to Figs. 3 through 6, the hollow
fibers 254 are accommodated within the housing 251 in
such a manner that entrant blood will Elow therethrough
in a turbulent manner.
~ 3
1:~3~831
The inner surface of the inner cylinder 252, which
forms the housing 251, is flared outwardly in the
vicinity of the blood inlet port 263 relative to the
inner surface of the inner cylinder 252 at the
intermediate portion thereof, thereby forming an annular
blood flow passage 263A between the hollow fiber bundle
255 and the inner surface of the inner tube, as shown in
Fig. 16. This makes it possible for the entrant blood to
be distributed to each of the hollow fibers 254 s~oothly
from the entire outer periphery of the hollow fiber
bundle 255 facing the blood flow passage 263A. The
flared inner surface of the inner cylinder 252 in the
vicinity of the blood inlet port 262 is off centered with
respect to the hollow fiber bundle 255 so as to increase
the distance between the blood inlet port 262 and the
hollow fiber bundle, thereby enlarging the flow area of
the blood flow passage 263A facing the blood inlet port
262. Thus, the flow passage area of the blood flow
passage 263A gradually diminishes with an increase in
distance from the blood inlet port 263, so that the blood
from the blood flow passage 263A is distributed in a
uniform amount circumferentially of the hollow fiber
bundle 255. This makes it possible for the flow rate of
the blood rising in the blood chamber 262 to be
uniformalized in relation to the circumferential
direction of the hollow fiber bundle 255.
With regard to the housing 251, the outer cylinder
- 40 -
~3~31
2S3 surrounds the upper end portion of the inner cylinder
252, so that a blood reservoir tank 264 communicating
with the blood chamber 262 is defined between the inner
and outer cylinders. The side wall of that portion of
the inner cylinder 252 inside the outer cylinder 253 is
provided with a plurality of circumferentially spaced
windows or communication passages 265 for communicating
the interior of the inner cylinder 252 with the interior
of the reservoir chamber 264. The upper portion'of the
outer cylinder 253 is formed to include a gas vent 266
having a filter 266A permeable to air but impermeable to
bacteria. This prevents bacterial contamination of the
artificial lung 250 during use and maintains the interior
of the reservoir 264 at atmospheric pressure at all
times. The side surface of the r,eservoir tank 264 is is
provided with engraved graduations to indicate the amount
of blood collected within the reservoir.
The volume of the reservoir tank 264 is such that a
certain degree of blood flow will be maintained in the
event that the blood extracted from a vein is deficient
because of a bend in the associated tubing, or if there
is leakage of blood from the system. Specifically, the
reservoir tank 264 is designed to have a volume such that
the upper level of the collected blood will not rise to a
position higher than the lower edge of the communication
passages 265, even if the amount of blood collected is
enough for half of the extracorporeal blood circulation
- 41 -
~23883~
rate (ml/min) planned for safety. When blood flows into
the inner cylinder 252 from the blood inlet port 263 and
rises within the blood chamber 262, the blood eventually
overflows from the lower edge of the communication
passages 265 and collects within the blood reservoir tank
264. sy designing it so that the blood reservoir 264 has
the above-described volume, the blood which collects
within the blood reservoir does not exert any pressure
upon the blood rising in the blood chamber 262.
A blood outlet port 268 communicates with the
interior of the blood reservoir tank 264 through a heat
exchanger tank 267, the latter accommodating a heat
exchanger 269. The heat exchanger 269 is supported at
both ends by respective walls 270, 271 located within the
heat exchanger tank 267, and has a bundle of slender
tubes 272 whose upper ends open into the reservoir 264
and whose lower ends open into the blood outlet port 268.
The hollow interior of each slender tube 272 serves as a
blood flow passage, while the outer walls of the slender
tubes 272 and the inner sides of the walls 270, 271
define a flow passage for a heat transfer medium.
Connecting with the heat transfer medium flow passage are
a inlet and outlet ports 273A, 273B, respectively, for
heating and cooling water. The slender tubes 272
comprise stainless steel or aluminum tubes having a high
heat transfer coefficient. The heat exchanger tank 267
of the artificial lung 250 makes it possible to raise or
- 42 -
1238~3~
lower blood temperature, or to keep the blood warm.
The hollow fibers 254 are made of a microporous
membrane, as described earlier with regard to the hollow
fibers 16. It should be noted that the hollow fibers 254
need not necessarily consist of a microporous membrane.
For example, use can be made of a silicone membrane that
permits travel of a gas by dissolution or diffusion.
The walls 256, 257 are formed by a centrifugal
injection process in the same manner as the walls 18, 19
described earlier. The process need not be discussed
again here.
Since the artificial lung 250 of Figs. 14 through 16
incorporates the blood chamber 262, the blood reservoir
264 and heat exchanger tank 267, the blood circuit takes
lS on the simple arrangement shown in Fig. 9, which is
similar to the arrangement in which the porous-type
artificial lung is used. In addition, the circuit can be
set up quic~ly in a simple manner, and the extraction of
bubbles during priming can proceed rapidly without
obstruction. Furthermore, the blood circuit in which the
artificial lung 250 is used requires little priming and
only a small amount of blood for filling. There is also
little need to carry out a preliminary transfusion into
the priming liquid, such as physiologic saline, with
which the artificial lung 250 is filled. In particular,
the artificial lung 250 is effective even for infants or
children for which the allowable blood filling quantity
- 43 -
1238#3
is low.
In the artificial lung shown in Figs. 14 through 16,
both of the walls 256, 257 supporting the upper and lower
ends of the hollow fibers 254 are retained within the
inner cylinder 252. However, an arrangement is possible
wherein the wall supporting the upper ends of the hollow
fibers is retained in the outer cylinder.
Fig. 17 is a perspective view illustrating an
artificial lung 280, which is an another example of the
artificial lung 251 shown in Figs. 14 through 16.
The artificial lung 280 has a housing 281 comprising
an inner cylinder 282 and an outer cylinder 283. A
bundle 285 of a multiplicity of hollow fibers 284 are
accommodated within the inner cylinder 282. The ends of
the hollow fibers 284 are retained liquid tightly within
the inner cylinder 282 via walls 286, 287 retained in the
upper and lower ends of the inner cylinder 282,
respectively. A header 288 is attached to one end
portion of the inner cylinder 282, and a header 289 to
the other end portion thereof. The inner side of the
header 288 and the wall 286 define a gas inlet chamber
similar to that formed in the artificial lung 250. The
inner side of the header 289 and the wall 287 define a
gas outlet chamber similar to that formed in the
25 artificial lung 250. The header 289 is formed to include
a yas outlet port 291, and the header 288 is formed to
include a gas inlet port 290. The inner wall of the
- 44 -
~Z3~3~331
housing 281, the outer wall of the hollow fibers 284, and
the walls 286, 287 define a blood chamber 292. The lower
end of the inner cylinder 282 is formed to include a
blood inlet port 293. Thus, a gas such as oxygen or air
supplied from the gas inlet port 290 can be passed
through the interior of the hollow fibers 284, while
blood supplied from the blood inlet port 293 is passed in
a turbulent state along the periphery of the hollow
fibers 284 within the blood chamber 292, allowing a gas
exchange to take place.
Further, in the artificial lung 280, a blood
reservoir 294 is formed, as a portion of the blood
chamber 292, between the inner cylinder 282 and outer
cylinder 283. The side wall of that portion of the inner
cylinder 282 inside the outer cylinder 283 is provided
with a plurality of circumferentially spaced windows or
communication passages 295 for communicating the blood
chamber 292 inside the inner cylinder 282 with the
interior of the blood reservoir 294. The outer cylinder
283 is provided at its upper portion with a gas vent 296
communicating with the reservoir 294. The lower portion
of the outer cylinder 283 is formed to include a blood
outlet port 294A communicating with the reservoir 294.
Thus, the blood reservoir 294 is adapted to collect blood
which has undergone a gas exchange, similar to the blood
reservoir 264 of the artificial lung 250.
The blood reservoir 294 of the artificial lung 280
- 45 -
~23~83~
accommodates a heat exchanger 29a so that it may also
function as a heat exchanger tank 297. The heat
exchanger 298 comprises a bundle of slender tubes 301
supported at both ends by respective walls 299, 300
located within the heat exchanger tank 297. The ends of
the slender tubes 301 open externally of the blood
reservoir 294 on the outer sides of the walls 299, 300,
the hollow interior of each tube serving as a flow
passage for a heat transfer medium. Inlet and outlet
ports 302A, 302B for cooling and heating water are
connected to the flow passages for the heat transfer
medium. Thus, the heat exchanger tank 297 serves to
heat, cool or maintain the temperature of blood following
the gas exchange.
Thus, as with the artificial lung 250, the artificial
lung 280 improves the gas exchange performance per unit
membrane area of the hollow fibers 284, makes it possible
to achieve perfusion of the blood by virtue of the head
developed between the patient and the artificial lung
280, and reduces the quantity of blood needed to fill the
blood circuit in which the artificial lung is used. This
is because of the blood reservoir 294 and heat exchanger
tank 297, which communicates with the blood chamber 292.
Fig. 18 is a perspective view showing another example
of the artificial lung 250.
In Fig. 18, the artificial lung, designated at
numeral 310, is substantially the same as the artificial
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lung 280. Portions that have the same function as those
of the artificial lung 280 are designated by like
reference characters and are not described again. The
artificial lung 310 differs from the artificial lung 280
in that the interior of the heat exchanger tank 297 is
provided with a different heat exchanger 311. In this
case, the heat exchanger 311 comprises a coil-shaped
tubular body 312, which is equipped with inlet and outlet
ports 313A, 313s for heating and cooling water. `
As with the artificial lung 250, the artificial lung
310 improves the gas exchange performance per unit
membrane area of the hollow fibers 284, makes it possible
to achieve perfusion of the blood by virtue of the head
developed between the patient and the artificial lung
310, and reduces the quantity of blood needed to fill the
blood circuit in which the artificial lung is used,
thanks to the blood reservoir 294 and heat exchanger tank
297, which form part of the blood chamber 292.
Fig. 19 is a perspective view showing another example
of the artificial lung 250. The artificial lung,
designated at 320, has a housing 321 comprising an inner
cylinder 322 and an outer cylinder 323. A bundle 325 of
a multiplicity of hollow fibers 324 are accommodated
within the inner cylinder 322. The ends of the hollow
fibers 324 are retained liquid tightly within the inner
cylinder 322 via walls 326, 327 retained in the upper and
lower ends of the inner cylinder 322, respectively. A
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header 328 is attached to one end portion of the inner
cylinder 322, and a header 329 to the other end portion
thereof. The inner side of the header 328 and the wall
327 define a gas inlet chamber similar to that formed in
the artificial lung 250. The inner side of the header
329 and the wall 326 define a gas outlet chamber similar
to that formed in the artificial lung 250. The header
329 is formed to include a gas outlet port 331, and the
header 328 is formed to include a gas inlet port 330.
The inner wall of the housing 321, the outer wall of the
hollow fibers 324, and the walls 326, 327 define a blood
chamber 332. A blood inlet port 333 is connected to the
lower end of the inner cylinder 322 through a
communication portion 333A. Thus, a gas such as oxygen
lS or air supplied from the gas inlet port 330 can be passed
through the interior of the hollow fibers 324, while
blood supplied from the blood inlet port 333 is passed in
a turbulent state along the periphery of the hollow
fibers 324 within the blood chamber 332, allowing a gas
exchange to take place.
Further, in the artificial lung 320, a blood
reservoir 334, which communicates with the blood chamber
332, is formed between the inner cylinder 322 and outer
cylinder 323, which form the housing 321. The side wall
of that portion of the inner cylinder 322 inside the
outer cylinder 323 is provided with a plurality of
circumferentially spaced windows or communication
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~23~3~
passages 335 for communicating the blood chamber 323
inside the inner cylinder 322 with the interior of the
blood reservoir 334. The outer cylinder 323 is provided
at its upper portion with a gas vent 336 communicating
with the interior of the reservoir 334. The lower
portion of the outer cylinder 323 is formed to include a
blood outlet port 334A communicating with the reservoir
334. Thus, the blood reservoir 334 is adapted to
collect blood which has undergone a gas exchange,
similar to the blood reservoir 264 of the artificial lung
250.
In the housing 321, there is defined between
the blood inlet port 333 and the communication passage
333A a heat exchanger tank 336' constituting part of the
blood chamber 332 and accommodating a heat exchanger 335.
'l'he heat exchanger 335 is supported at both ends by a pair
of walls 337, 338 located within the heat exchanger tank
336', and comprises a bundle of slender tubes 339 opening
at one end into the blood inlet port 333 and at the other
end into the communication passage 333A. The hollow
interior of each slender tube 339 serves as a blood flow
yassage, while the walls 337, 338 and the ou-ter walls of
the slender tubes 339 form a flow passage for a heat
transfer medium. Inlet and outlet ports 340A, 340s for
cooling and heating water are connected to the flow
passage for the heat transfer medium.
Thus, as with the artificial lung 250, the artificial
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jrc~
123~3831
lunq 320 improves the gas exchange performance per unit
membrane area of the hollow fibers 324, makes it possible
to achieve perfusion of the blood by virtue of the head
developed between the patient and the artificial lung
320, and reduces the quantity of blood needed to fill the
blood circuit in which the artificial lung is used,
thanks to the blood reservoir 324 and heat exchanger tank
336, which form part of the the blood chamber 332.
It is preferred that the heat exchanger of Fig. 19 be
provided on the side of blood outflow port, as in Fig.
14, or within the blood reservoir, as in Figs. 17 and 18.
The reason is that disposing the heat exchanger at a
point preceding the oxygenation apparatus will reduce the
momentum of the blood provided by the head, thereby
lS having a deleterious effect upon head-induced perfusion.
However, if a hollow heat exchanger is used as shown in
Fig. 19, loss of momentum is minimal and satisfactory
results can be obtained. There will be little influence
from external temperature and, hence, a higher heat
exchange efficiency if the heat exchanger is provided
within the blood reservoir or on the side of the blood
outlet port.
A slender tube 342 having fins 341, as shown in Fig.
20, may be employed as the tubes forming the heat
exchanger in the above embodiment.
Further, the annular blood flow passage 263A in the
artificial lung 250 ~Fig. 16) may be selected as the
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blood chamber for receiving the heat exchanger.
The actions and effects of the foregoing artificial
lung will now be set forth.
As described, the hollow fiber-type artificial lung,
having the heat exchanger, comprises an axially extended
housing, a hollow fiber bundle having of a multiplicity
of hollow fibers accommodated within and along the axial
direction of the housing, the hollow fibers forming blood
channels between outer wall surfaces of neighboring ones
thereof, and being arranged within the housing in such a
manner that neighboring blood channels are brought into
substantial communication, first and second walls
liquid-tightly supporting the hollow fibers at both end
portions thereof within the housing, the first and second
walls, the inner wall of the housing and the outer wall
surfaces of the hollow fibers defining a blood chamber, a
blood reservoir provided integral with the blood chamber
and having its interior communicated with the blood
chamber, and a heat exchanger provided integral with a
blood flow passage, which is formed by the blood chamber,
at least at an upstream, downstream or intermediate
portion of the blood flow passage. Owing to such
construction, gas exchange takes place while the blood is
flowing in a turbulent state, making it possible to
improve the gas exchange performance per unit membrane
area. In addition, the blood flow resistance interiorly
of the blood chamber is reduced to a small value, so that
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~23~#31
perfusion of the blood may achieved owing to the head
developed between the patient and the artificial lung.
Furthermore, the amount of blood needed to fill the blood
circuit is small owing to provision of the heat exchanger
S interiorly of the blood chamber.
Since the blood reservoir is provided integral with
the blood chamber and communicates with the blood
chamber, the blood circuit is reduced in length so that
less blood is needed to fill the circuit. By placing the
heat exchanger within the blood reservoir on the side of
the blood outlet port, the above-described effects are
enhanced and there is no loss of blood momentum provided
by the head.
Further, the heat exchanger comprises a bundle of a
multiplicity of slender tubes supported at both ends,
which ends are open, the hollow interiors of the tubes
define blood flow passages, and the heat exchanger is so
adapted that a heat transfer medium may be passed along
the periphery of the tubes. As a result, the blood flows
through the tubes in the axial direction and meets little
resistance, so there is but little loss in the blood
momentum provided by the head. Operability is enhanced
as well.
Since the blood reservoir has a gas vent
communicating with the atmosphere, the interior of the
blood reservoir is held at atmospheric pressure at all
times. The outer wall of the blood reservoir consists
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of a rigid material, and is provided with graduations so
that a change in the amount of extracorporeally
circulating blood can be verified with ease.
The hollow fibers are made of microporous membrane.
This diminishes membrane resistance to gas travèl so that
the gas exchange performance can be enhanced.
The housing comprises an inner cylinder accommodating
the hollow fibers, and an outer cylinder surrounding a
portion of the inner cylinder for defining the biood
reservoir betweèn itself and the inner cylinder. The
first wall supporting the hollow fibers is retained in
the inner cylinder, and the second wall supporting the
hollow fibers is retained in the outer cylinder. This
results in a comparatively simple construction.
Alternatively, both the first and second walls supporting
the hollow fibers may be retained in the inner cylinder
to further simplify construction and facilitate
manufacture.
The inner surface of the housing at a portion
communicating with the blood inlet port is flared
outwardly relative to the intermediate portion of the
housing, thereby forming an annular blood flow passage
between the outer periphery of the hollow fiber bundle
and the inner surface of the housing. This makes it
possible for the entrant blood to be distributed to each
of the hollow fibers smoothly from the entire outer
periphery of the bundle facing the blood flow passage.
~238831
The flared inner surface of the housing in the
vicinity of the blood inlet port is off centered with
respect to the hollow fiber bundle so as to increase the
distance between the blood inlet port and the hollow
fiber bundle, thereby enlarging the flow area of the
blood flow passage facing the blood inlet port. As a
result, the blood from the blood flow passage is
distributed in a uniform amount circumferentially of the
hollow fiber bundle, making it possible for the flow rate
of the blood traveling axially of the housing within the
blood chamber to be uniformalized in relation to the
circumferential direction of the hollow fiber bundle.
As many apparently widely different embodiments of
the present invention can be made without departing from
the spirit and scope thereof, it is to be understood that
the invention is not limited to the specific embodiments
thereof except as defined in the appended claims.
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