Apparatus for preventing the entry of air into an artificial organ

Air or gas is prevented from entering into the exchange zone of an artificial organ such as an artificial kidney, dialyzer, or hemofilter. For this purpose a separating path is arranged in parallel with the artificial organ or with the exchange zone or other operative portion of the artificial organ between the liquid inflow and outflow conduits. This parallel path is provided with a high flow resistance for the liquid and with a low flow resistance for the air. Such differential flow resistance may, for example, be accomplished by apertures, gas permeable materials, and eddy chambers. The gas separating path is incorporated as an integral part of the artificial organ or as an integral part of the liquid inflow and outflow conduits. According to several embodiments, an enlargement is provided in the separating path or conduit in which the liquid may "rise and dwell" to enhance air separation before the liquid flows into the operative portion of the artificial organ.

BACKGROUND OF THE INVENTION 
The present invention relates to an apparatus for preventing air from 
entering into the operative portion of an artificial organ such as an 
artificial kidney, a dialyzer, a hemofilter, or an artificial liver, for 
example including a hemoperfusion cartridge. 
During a dialysis treatment, air frequently enters the dialyzer space 
containing the dialysate because in the most frequent type of operation a 
reduced pressure is present in the space containing the dialysate. As a 
result, air may be drawn into such space through possible leaks or because 
the dialysate solution has not been degassed sufficiently. 
Thus, if air enters into the dialysate containing space of the dialyzer 
larger air bubbles are often produced which can be removed only very 
slowly by dissolving the air into the degassed dialysate. Such air bubbles 
cover the operative surface portions of the artificial organ membrane. The 
efficiency of the diffusion exchange between the blood flowing on one side 
of the membrane and the dialysate flowing on the other side of the 
membrane is correspondingly impaired or diminished by such air bubbles. 
Similar considerations apply when air enters into the space of the dialyzer 
on the side through which the blood flows similarly covering respective 
membrane surface areas. Another disadvantage is that air on the blood flow 
side increases the danger of clotting. An air bubble in the blood flow 
channel, for example, between the supporting grids or in a hollow fiber 
reduces the flow speed of the blood. 
Similar difficulties may occur in a hemofilter where no dialysate is used. 
Rather, a fraction of the blood is caused to pass under pressure through 
the hemofilter membrane for separating a blood fraction by filtration. 
PRIOR ART STATEMENT 
The closest prior art references of which applicants are aware are the 
patents cited by the Examiner during prosecution of the parent 
application. The references are of record in the parent application and 
the more relevant ones are identified as follows: 
______________________________________ 
U.S. In- 
Pat. No. 
Title ventor Date 
______________________________________ 
4,137,160 
DEVICE FOR SEATING Ebling 1979 
LOW DENSITY MATERIAL et al 
SUCH AS GAS BUBBLES 
FROM A LIQUID, AND THE 
USE THEREOF FOR A DIAL- 
YSIS DELIVERY SYSTEM 
4,162,974 
DEAERING AND RECIRCULA- 
Pernic 1979 
TION SYSTEMS FOR DIAL- 
YSIS MACHINES 
3,626,670 
FLUID CIRCULATION AP- 
Pecker 1971 
ATUS INCLUDING DEAERATION 
AND NEGATIVE PRESSURE 
CONTROL 
3,827,561 
DEAERATOR FOR DIALYSIS Serfass 1974 
SYSTEM et al 
3,920,556 
HEMODIALYSIS SYSTEM Bow- 1975 
man 
3,878,095 
DIALYSIS APATUS Frazier 1975 
et al 
______________________________________ 
These patents and publications describe a variety of dialysis type machines 
with devices for separating air and gas from liquids used in the machines. 
In each case, however, the air trap or degassing apparatus constitutes a 
distinct and separate device or appliance not incorporated into the 
dialysis structure. Each device is generally of relatively large size and 
complexity in the order of magnitude of the dialysis machine itself. 
Ebling et al. employ a circumferentially swirling liquid chamber while 
Serfass et al describe a variety of complex arrangements for separate 
degassing apparatuses. Pernic provides a ball valve deairing tank. Many of 
the air traps such as those of Pecker and Serfass et al., Frazier et al. 
and Pernic employ an air space above the liquid to provide a liquid air 
interface which the present invention avoids. Bowman shows yet another 
separate degassing appliance. These references do not teach nor suggest 
incorporating the air trap and degassing capability directly into the 
internal structure of an artificial organ as contemplated by the present 
invention. 
Most importantly, none of the above references suggests or teaches the 
advantage of obviating separate air traps for artificial organs thereby 
avoiding sterilization for reuse. The prior art devices are too elaborate 
and expensive for one time use. The present invention, on the other hand 
incorporates air separating means into the very structure of the 
artificial organ substantially without additional expense. 
Moreover, none of the references discloses nor suggests the aspect of the 
present invention where the input and output conduits of the artificial 
organ are integrated across a common gas permeable or restrictive barrier 
wall so that the liquid input flow is degassed, discharging air directly 
into the outflow. Nor do any of these references propose to form a conduit 
wall itself of a differentially permeable or restrictive material for 
separating air from liquid as it flows in the conduit and discharging gas 
into the environment through the conduit wall. And finally, none of these 
references describes in the context of the foregoing variations of the 
invention the use of an enlargement in the conduit flow path or auxiliary 
flow path into which the liquid may rise and "dwell" before proceeding 
along the liquid flow path. The dwell time afforded by such enlargement of 
the conduit or flow path facilitates separation and removal of air before 
the liquid flows on to the artificial organ. 
OBJECTS OF THE INVENTION 
In view of the above it is the aim of the invention to achieve the 
following objects singly or in combination: 
to provide artificial organs with a separate flow path which enables gas 
and air to bypass the artificial organ, to be removed prior to reaching 
the artificial organ, or to bypass the exchange zone or other operative 
portion within the artificial organ; 
to arrange a parallel flow path having a differential flow resistance for 
different media for bypassing an artificial organ such as a dialyzer or a 
hemofilter or the like or the operative portions of such organ, whereby 
air may flow through the parallel path to a substantially larger extent 
than liquid; 
to make the volume of the bypass as small as possible; 
to assure a laminar, smooth flow in the parallel bypass, especially when 
used on the blood side of a dialyzer membrane to avoid blood clotting; and 
to provide air separating auxiliary flow path means incorporated as an 
integral portion of an artificial organ or as an integral portion of the 
liquid inflow and outflow conduits for the organ. 
SUMMARY OF THE INVENTION 
According to the invention an apparatus is provided for keeping air away 
from the active portion of an artificial organ by defining an auxiliary 
flow path extending in parallel with the organ or its operative portions 
between the liquid inflow conduits and the liquid outflow conduits. The 
parallel path affords a high flow resistance for the liquid and a low flow 
resistance relative to air or gas. Thus, air passes preferentially through 
the bypass, rather than the liquid. The difference in viscosity of the two 
media facilitates this differential response to air and liquid. However, 
the arrangement of apertures and/or eddy chambers increases the difference 
in flow resistances. Such apertures and/or eddy chambers exhibit a flow 
resistance which is non-linear relative to the viscosity. Thus, during 
normal operation when there is no gas or air present, the quantity of 
liquid flowing through the bypass is small and hence negligible relative 
to the entire dialysis flow. On the other hand, when air is present, the 
suitably arranged auxiliary flow path will guide the air that has entered 
into the system exclusively through this parallel bypass avoiding the 
functional region of the organ. 
The parallel or bypass should, especially in the area which determines the 
flow resistances, have a relatively small volume in order to avoid the 
necessity of displacing liquid in the bypass before air can flow through 
the bypass in larger volume. The bypass may include apertures and/or eddy 
chambers, especially on the side where the dialysate flows and there is no 
risk of blood clotting. However, on the blood side care must be taken in 
the bypass that the tendency of the blood to coagulate is counteracted by 
a respective laminar, short flow path in the parallel connection. 
The invention also contemplates providing an air separating auxiliary flow 
path for artificial organs where such bypass is incorporated as an 
integral, internal portion of the artificial organ, or as an integral part 
of the liquid inflow and/or outflow conduits associated with the 
artificial organ. 
According to one form of the invention the auxiliary flow path means 
provides a liquid flow path in series with the artificial organ liquid 
inflow and outflow conduits and a gas or air flow path in parallel with 
such conduits delivering air and gas directly from the liquid inflow to 
the liquid outflow. An advantage of this arrangement is that the lower 
pressure at the liquid stream outflow draws gas or air through the air 
flow path from the liquid inflow. In other forms of the invention the gas 
or air flow path vents directly to the environment. In the various 
embodiments, an enlargement is provided in the liquid conduit or auxiliary 
flow path at the air separation side into which the liquid rises. The 
dwell time afforded by the enlargement enhances air separation. The air 
escapes upward while the liquid flows downward from the enlargement on its 
way to the artificial organ.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE 
OF THE INVENTION 
FIG. 1 shows an example embodiment of a hollow fiber dialyzer equipped with 
a gas bypass according to the invention. The hollow fibers 1 are arranged 
around a core 2 which defines a central volume air trap 2'. The core 2 is 
mounted in a housing 3 and the blood flows through the hollow fibers 1. 
The hollow fibers 1 are held and sealed together at their ends by a 
curable, hardening material, for example polyurethane resin. Part of the 
cured resin is cut off in a direction perpendicular to the longitudinal 
axis of the dialyzer so that along the cut surface 5 the fiber ends are 
open. The outer surfaces, however, are sealed together at the ends toward 
the space 6 through which the dialysate flows. The housing 3, bundle of 
fibers 1, and interstices 6 form an annular configuration exchange zone 
surrounding the coaxial core 2 and central space 2'. 
Each end of the dialyzer is equipped with a flange 7 forming a blood 
distribution space in operative contact with the open end surface area 5 
of the hollow fibers 1. The blood enters through an inlet 9 into the upper 
distribution space 8 and thus into the hollow fibers 1 through which the 
blood flows downwardly into the lower distribution space 8'. The blood is 
withdrawn from the lower distribution space 8' through an outlet member 
10. 
The dialysate is introduced into the dialysate space 6 in the housing and 
between the hollow fibers 1 through an inlet member 11 which is sealed off 
from the blood distribution space 8' and leads upward through a pipe 
section 12 into the space 2' of the hollow core 2. The path 13 of the 
dialysate then turns downward through holes 14 in the bottom of the hollow 
core 2 into the interstices 6 between fibers 1 where the dialysate 
envelopes the outer surface of the hollow fibers. The dialysate continues 
its flow through hole 15 in a pipe section 16 also sealed off from the 
upper distribution space 8 and connected to an outlet 17 for the 
dialysate. Such dialyzers are further described, for example, in U.S. Pat. 
No. 4,141,835 assigned to the assignee of the present invention. 
According to the invention the upper end wall 18' of the hollow core 2 is 
provided with an aperture 18 which constitutes a relatively high flow 
resistance to the dialysate whereby the parallel flow 19 of dialysate is 
negligibly small relative to the main dialysate flow 13. 
In operation, if air enters through the inlet 11 with the dialysate, it 
will immediately rise inside the hollow core 2. The small volume of 
dialysate inside the aperture 18 is quickly displaced by the air whereby 
the latter can pass through the aperture 18 directly into the pipe section 
16 and thus into the outlet 17 without contacting the fibers 1. The 
aperture 18 constitutes a small flow resistance for the air whereby a 
large airflow may pass along the parallel path 19. 
In a practical embodiment according to the invention the aperture has a 
diameter of 0.8 mm. The proportion of dialysate flow along the path 19 
measured for this example was about 5% of the entire dialysate flow. 
Simultaneously it was possible to prevent any air in single quantitites in 
amounts up to 150 milli-liters from passing into contact with the hollow 
fibers 1 by passing the air through the path 19 and through the aperture 
18. 
The flow configuration achieved by the example embodiment of FIG. 1 also 
facilitates bypass of air or gas around the exchange zone defined by 
fibers 1 and interstices 6. Dialysate liquid rises upward through liquid 
inlet 11 and channel or conduit 12 into the elongate central chamber or 
volume 2' which functions as an eddy chamber, air or gas trap, and 
provides dwell time for enhancing separation. The dialysate liquid, from 
which the air and gas is to be separated in the volume 2', exits, however, 
in a downward direction through the bottom openings 14. The dialysate 
liquid enters into the volume 2' in an upwardly directed current thereby 
imparting an upward flow tendency to the entrained air and gases. The 
liquid has some dwell time, however short in the chamber 2', before the 
liquid exits into the exchange zone through the holes 14 in the base of 
chamber 2' while air and gas continue to rise. The gas exits through 
aperture 18 and enters into the dialysate fluid downstream of the exchange 
zone. The auxiliary path of the present invention through the chamber 2' 
thus provides a true parallel bypass for entrained air and gases. The 
lower pressure in the liquid flow at outlet 17 facilitates the reentry of 
the separated air or gas coming from the eddy chamber volume 2', back into 
the used up dialysate. 
A similar structure may be provided for removing air from blood. 
Preferably, the bypass for gas removal from blood is arranged separately 
so that the flow passages for the inflowing blood and for the outflowing 
blood may be arranged close to each other. However, the gas separator may 
also be incorporated in the dialyzer itself. 
A feature and advantage of the example dialyzer of FIG. 1 is that the 
auxiliary flow path and air bypass 19 is defined by the normal internal 
structures of the artificial organ as described, for example, in U.S. Pat. 
No. 4,141,835. The air separating path is thus incorporated into the 
internal spaces of the device and forms an integral part of the artificial 
organ. Thus, the air separating flow path utilizes the central coaxial 
space 2' defined by hollow core wall 2, part of the existing structures 
and internal spaces of the artificial organ. 
Furthermore, the auxiliary flow path elements define a liquid flow path 
through inlet 12 and through the holes 14 which is in series with the 
intersticeal spaces 6 upstream of the exchange zone. The air or gas flow 
path 19 is connected in parallel with space 6 through inlet 12, and flow 
impedance 18 and outlet 17. 
FIG. 2 shows an example embodiment of a gas separator not forming an 
integral component of the artificial organ. The embodiment of FIG. 2 is 
particularly useful for degassing the blood, and comprises a coupling 
member 20 for the blood hose members. The coupling member 20 includes two 
flow channels 26 and 27. The blood which is supposed to enter into the 
dialyzer, for example, through the inlet 9 in FIG. 1, enters the coupling 
member 20 through an inlet member 21 and into the space 26 whence it flows 
through the outlet 22 into the dialyzer. The blood exiting from the outlet 
10 of the dialyzer in FIG. 1 enters into the inlet 23 and into the space 
27. The blood leaves the space 27 through the outlet 24. The two spaces 26 
and 27 are integrated into the liquid flow inlet and outlet conduits 
providing a common wall 30 between them. The inflow and outflow conduits 
leading to and from the artificial organ are interconnected or coupled 
across common wall 30, for example, by a small aperture 25 which permits 
air or gas exchange by a flow of air from the domed space 26 into the 
space 27 without any substantial flow resistance. However, only a small 
quantity of blood may pass through the aperture 25 which constitutes a 
large flow resistance to the incoming blood or rather to the blood flow in 
the blood supply conduit connected to the inlet 21. Hence air in the blood 
conduit has a chance to pass directly into the blood discharge conduit or 
space 27. The domed space 26 constitutes an eddy chamber air trap 
affording dwell time for the liquid during which separation is enhanced. 
If the device of FIG. 1 is combined with that of FIG. 2 gas may be removed 
from blood that is being dialyzedas well as from the dialysate. 
The gas separating unit 20 according to the example embodiment of FIG. 2 
contrasts with the example of FIG. 1 in providing an air bypass directly 
from the inflowing conduit to the outflowing conduit around the entire 
artificial organ outside of the organ. This is accomplished, however, by a 
combination or integration of the inflow and outflow conduits across a 
common wall and by a device which itself becomes an integral part of the 
conduits. The inlet channel is below the common wall 30 while the outlet 
channel is above so that gas and air may rise through the differentially 
or selectively permeable area 25. The inflow channel 21/22 is preferably 
formed in a domed upward bend or configuration with an eddy space or 
widening 26 at the turn to facilitate separation of air from the blood. 
Gas separating unit 20 may also be used to degas the dialysate either alone 
or in combination with the arrangement of FIG. 1. A connection for 
dialysate degassing is shown in FIG. 2a. Inflow conduit 32 is coupled 
between the outlet 22 of the separator 20 and the inlet 33 of the dialyzer 
34 while outflow conduit 35 is coupled between the inlet port 23 of the 
separator 20 and outlet 36 of dialyzer 34. 
FIG. 3 illustrates an embodiment of the invention in which a liquid conduit 
28, for example for blood, is provided with a so-called "air-window" 29 
made of a hydrophobic filter material which passes air but prevents blood 
from passing through the "air window" or filter 29. Thus, air may be 
directly eliminated to the environment. In this example embodiment the 
operative air separating bypass filter 29 is incorporated as an integral 
portion of the conduit wall itself. In the preferred arrangement the 
conduit also acts as an air trap when the filter 29 is arranged as a domed 
portion of the conduit 28 as shown in FIG. 3a. The enlargement 31 into 
which the blood or other liquid rises introduces a "dwell time" which 
enhances air separation. Thus, any air that might have possibly entered 
into the blood conduits may be removed again. 
The arrangement of FIG. 3 may also be realized in many different ways. For 
example, the filter 29 may for a porous hose section whereby the conduit 
28 functions as a filter or window along an entire section of its length. 
Further, the filter 29 may form part of a chamber, having for example a 
larger diameter than the hose 28 itself and so forth. In these embodiments 
in which the filter 29 is a hydrophobic porous filter care will be taken, 
to keep the size of the pores small enough so that air or gas may exit 
outwardly through the filter while simultaneously functioning as a sterile 
filter. In other words, the pores must be small enough to prevent the 
entry of germs into the blood stream. Thus, the pores will normally be 
smaller than 45 microns. 
Yet another example embodiment for separating entrained air from flowing 
liquid is shown in FIG. 4. This air trap device 40 is coupled or 
integrated into the inflowing conduit and may be used alone or in 
combination with the devices described above. The separator device 
comprises an elongated gas trap or chamber 41 with vertical orientation in 
the operative position. The chamber introduces residence time for the 
liquid between inlet and outlet during which separation occurs. The inlet 
channel or conduit 42 delivers liquid in an upward direction into the 
chamber 41. An outlet channel 43 extends into the gas trap chamber from 
above with an opening 44 near the bottom 45 of the chamber. The outflow 
pipe or channel 43 is offset relative to the portion of the inflow channel 
to permit entrained air and gas to rise in the chamber 41. The opening 44 
at the base of the trap 40 substantially restricts entry of liquid into 
the outflow channel to liquid at the base of the air trap. A portion 48 of 
the upper wall 46 of the trap is formed of a filter or gas permeable 
material having a high flow inpedance for liquids and a low gas flow 
impedance. Portion 48 may comprise, for example, a hydrophobic filter. 
Gases entrained in liquid delivered through inflow conduit 42 with an 
upward impetus, rise unimpeded toward the top of the gas trap and escape 
through permeable wall portion 48 while liquid is constrained to flow out 
the opening 44 and channel 43. 
The above described examples made reference to dialyzers. However, the 
invention may equally be realized in connection with a hemofilter or a 
hemoperfusion cartridge as well as any other artificial organs and 
extra-corporal circulatory systems such as that of an artificial heart or 
of an oxygenator and so forth. 
From the above description of FIG. 1 it will be appreciated that the 
invention takes advantage of the space in the hollow core of a dialyzer 
which as such is known. The provision of the aperture 18 is rather 
expedient and economical and hardly increases the production cost of these 
dialyzers while at the same time greatly improving their efficiency by 
providing the air bypass through this hollow space 2'. However, the 
invention is not limited to a dialyzer having a hollow space core. A 
parallel bypass, such as 19, may be provided in any type of dialyzer and 
in such position that it bypasses the membrane arrangement as long as the 
bypass comprises at a suitable location a flow resistance which is larger 
for one medium than for the other. In an alternative embodiment the 
dialysate may pass through a coupling member as shown in FIG. 2. In any 
event, the invention may be realized in many and various modifications 
without departing from the basic teaching. 
As mentioned, the blood stream or flow passage itself may be provided with 
a gas separator directly in the dialyzer structure. Thus, for example, the 
inlet 9 in FIG. 1 could be provided with a filter 29 as shown in FIG. 3. 
Instead of using in a separate structure a coupling member 20, it would be 
possible to connect the two blood conduits to each other, for example, by 
means of an adhesive to interconnect the blood conduits by one or more 
apertures as shown at 25 in FIG. 2. A filter of the type shown in FIG. 3 
at 29 could also be used instead of the aperture 25 either in conjunction 
with a chamber 26 or without such a chamber. The use of a hydrophobic 
filter 29 has the advantage that a passage of liquid through the filter 
may be maintained substantially at zero by keeping the pore sizes 
sufficiently small as mentioned above. Porous TEFLON or polyethylene have 
been found to be suitable for realizing a filter such as shown at 29 in 
FIG. 3. Such filter may be connected in series with the artificial organ. 
In the light of the above disclosure it will be appreciated that the 
invention may be realized as a bypass to the dialysate flow path and/or as 
a bypass to the blood flow path and various means may be used to provide 
said flow resistance in the form of a channel, an aperture, or in the form 
of an eddy chamber, or even in the form of a hydrophobic filter whereby 
these elements may be arranged to provide a bypassing connection from the 
inflow to the outflow or directly to the environment. 
Furthermore, the elements of the invention may be used alone or in various 
combinations as shown in the example of FIG. 5. FIG. 5 illustrates the 
upper portion of a hollow fiber dialyzer of the kind described with 
reference to FIG. 1. Corresponding elements are identified by the same 
reference numerals as in FIG. 1. In addition to the auxiliary air 
separating flow path 19 provided for degassing the dialysate flow, the 
example embodiment of FIG. 5 incorporates two separating means which may 
be used alone or in combination for deaerating the blood. 
The first air separating and removal element 50 is incorporated as an 
integral portion of the upper wall of inlet conduit 9 where blood enters 
the distribution space 8 over the face 5 of the annular bundle of open 
ended fibers 1. Thus, air separating element 50 is of the type shown in 
FIG. 3 and preferably would be located at a bend in the conduit as shown 
in FIG. 3a. Element 50 may be formed by hydrophobic filter material. 
The second air separating and removing element 52 is formed over the ring 
chamber blood distribution space 8 at the top of the dialyzer, where it is 
incorporated as an integral part of the end housing cover or flange 7. The 
flange cover 7 in combination with the end face 5 of the open ended, 
annular fiber bundle defines the ring chamber space 8 in which blood is 
distributed. According to the invention this housing cover or flange 7 is 
curved or tapered over the space 8 with a line or region of greatest 
height over the face of the fiber bundle. The air separating element 52 is 
formed by selectively gas permeable material such as hydrophobic filter 
material incorporated into the housing end cover or flange 7 in this 
region of greatest height over the fiber bundle. By this arrangement an 
air trap is formed over the ring chamber blood distribution space 8 for 
selective removal and venting of air to the environment through the 
separating element 52. It can be appreciated that the dialyzer of this 
embodiment of the invention is normally operated with the longitudinal 
axis vertically oriented. 
Although the invention has been described with reference to specific 
example embodiments, it will be appreciated, that it is intended to cover 
all modifications and equivalents within the scope of the appended claims.