Note: Descriptions are shown in the official language in which they were submitted.
11~9ti7~
~ his invention relates to fil~er washing processes
and apparatus, ~nore particularly to processes and apparatus
for washing artificial kidneys.
The function of the normal, healthy kidney in the
animal body is to act as a filter for the blood circulating
through the body, to remove impurities therefrom and restore
correct blood composition balance. When the kidneys cease to
10 function, artificial kidneys can be employed in their place,
such an artificial kidney comprising a flexible dialysis
membrane used outside the body as a separate treatment
apparatus for blood dialysis or filtration purposes. Blood
from the body is circulated past one side of the membrane
and special dialysis fluid is circulated past the other side
of the membrane, so as to adjust and correct the blood
composition by osmosis, diffusion and ultrafiltration across
the membrane. A patient with deficient natural kidney
function normally makes periodic use of an artificial kidney
20 machine, in which his blood is circulated continuously
past such a dialysis membrane, a small volume at a time,
over a period of 4-8 hours for purification.
The kidney dialysis filters or artificial kidneys
as used in such artificial kidney machines are commercially
available in self-contained, cartridge form, ready for use
with the machine. The filters comprise a housing containing
a flexible dialysis membrane separating a blood side and a
dialysate side, with inlet and outlet connections for fluid
to both blood side and the dialysate side. Essentially,
30 however, such filters are single use, disposable items which
il39678
are discarded after one use on a single patient. Cleaning
of the filters for reuse ~as been con~ucted by hand, but it
is difficult to ensure a thorough enough cleaning, and is
very time consuming and unpleasant.
In any kidney dialysis filter washing process, it
is important to eliminate the risk of cross contamination,
which will arise if blooa particles washed out of one filter
become lodyed in the washing apparatus, so that they can be
washed into a different filter which is subsequently washed
10 using the apparatus, and hence contaminate the blood of the
patient who subsequently uses the second filter. If a filter
cartridge is washed manually, this problem does not arise.
However, any attempts to wash filters automatically and
successively whilst hooked up to a washing machine, are
likely to run this risk, if reversal of flow of liquids
through the filter housing is adopted.
It would be highly desirable to render kidney
dialysis filters reusable, by the same patient because of
the expense of them, and the frequency with which they need
20 to be used. One patient may need to use the artificial
kidney about 12 times per month, with a new filter unit
each time.
As noted above, manual washing of kidney dialysis
filters has been attempted, in the past, in which water
source connections are made to the filter hDusing, and water
is passed through the hDusing in contact with the filter
membrane in one direction for a period of time, and then the
29 directional flo~ of water is reversed, to assist in dislodging
113~678
blood particles which would otherwise remain attached to the
membrane. This is not however wholly satisfactory, because of
the manual techniques necessary, rendering the process time
consuming and difficult to conduct.
A proposal for a machine for cleaning artificial
kidneys ready for reuse was made by De Palma et al., and
published in "Transactions of the American Society of Artificial
Internal Organs", Volume XX, 1974, pages 584-588. It is under-
stood that a machine as described therein was in fact available
on the market at one time. However, it is an extremely expensive
machine, and hence is prohibitive for acquisition and use by
patients and even ~y many medical facilities. Moreover, it
involves the use of a disposable cartridge into which the kidney
is fitted for washing purposes, the cartridge being usable only
for cleaning the filters of a single patient, and then discarded.
This detracts from the economies otherwise obtainable by the reuse
of such artificial kidneys after cleaning.
It is an object of the present invention to provide
a novel process and apparatus for washing kidney dialysis filters
or artificial kidneys, to render them reuseable.
According to a first aspect of the invention, there is
provided a process of washing a flexible filter membrane within
a housing, said housing comprising a first compartment communi-
cating with the first side of the flexible membrane, a fluid inlet
communicating with the first compartment, a fluid outlet remote
from the fluid inlet and communicating with the first compartment
and a second compartment separated from said first compartment
by said flexible membrane, comprises the successive steps of:
29 connecting said fluid inlet of the housing to a washing
1~39~:;78
fluid feed hose, and connecting the fluid outlet to a fluid
outlet hose;
circulating washing liquid through the first compartment
of the housing in contact with the first side of the flexible
membrane by feeding washing liquid in through the fluid feed hose
and out through said fluid outlet hose;
closing the fluid outlet whilst continuing said feed
of washing liquid so as to increase fluid pressure within the
housing;
closing the fluid feed conduit to contain the increased
fluid pressure within the housing, whilst discontinuing the fluid
feed thereto;
opening the fluid inlet for a brief interval to cause
brief reversal of flow of washing fluid within the housing to
relieve the increased fluid pressure therein;
opening the fluid outlet and resuming the feed of
washing liquid through the fluid feed hose.
In the process of the invention, use is made of the
elasticity of the dialysis membrane itself, within the housing,
and of the fluid outlet hose, to arrange for brief intermittent
reversal of flow of the washing fluid. This causes back and
forth motion and resultant scrubbing action of the washing
liquid, to ensure dislodgement of blood particles left from
the previous use of the filter. The reversal of flow occurs
after building up excess pressure in the housing with the washing
1139~78
fluid, by subsequently opening a drain branch of the fluid
inlet hose. However, this opening of the drain branch, and
consequent reversal of flow, is so brief that the washing
fluid does not reverse into the fluid inlet hose of the washing
apparatus. As a consequence, therefore, no dislodged blood
particles can be washed into the fluid inlet hose of the
washing apparatus, to be deposited in the next filter washed
on the same apparatus, so that risk of cross contamination of
the filters is avoided.
According to another aspect of the invention, there
is provided an apparatus for washing a flexible filter membrane
within a housing, said housing haviny a first compartment in
contact with one side of the membrane, a second compartment in
contact with the other side of the membrane, and having a fluid
inlet and a fluid outlet for said first compartment, said inlet
and said outlet communicating with the first compartment at
locations remote from each other, said apparatus comprising:
a fluid inlet hose adapted to communicate with said
fluid inlet;
a washing fluid inlet branch communicating with the
fluid inlet hose;
first valve means in said washing fluid inlet branch
adapted to open and close fluid communication therethrough;
a drain branch communicating with the fluid inlet
30 hose;
78
second valve mc(~lls in said ~rain ~ranch adapted to
open and close fluid communication theret])rouyh;
a fluid outlet conduit hose havlng a resiliently
expandable and contractable section adapted to communicate
with said outlet;
third valve means in said fluid outlet hose
adapted to open and close fluid communication therethrough;
operating means for opening and closing the first,
second and third valve means;
timing means controlling said operating means and
arranged to actuate said operating means for,opening and
',closing the first, second and third valve means in a pre-
determined se~uence and for predetermined time intervals.
In the apparatus according to the invention, the
operating means for opening and closing the first, sëcond
and third valve means is suitably a series of electrical
controls, such as solenoids, operable to open or close the
valves when energized. These are suitably electrically
connected to an electronic timing device, which is preset
20 to open and close the valves automatically in the desired
sequence and according to the prearranged time intervals.
Both the blood side and the dialysate side may be
washed by a process or by use of an apparatus according to
the invention, if desired~ Thus the apparatus may also
include a similar set of fluid inlet' tubes or hoses with
valved inlet and drain branches, and a valved fluid outlet
tube, with a valYe'operating means, for washing the 'dialysate
side, as well as those previously described for washing the
113!~678
blood side. The ~aslling of the dialysate side is, however,
less critical, since the dialysate solution does not ten'd
to clog the mem~rane, which is the proble~n with blood
particles on the other side of the membrane.
It is most convenient to include a washing fluid
inlet branch, with valve, and a valved drain branch in the
fluid outlet hose for flexibility in operation. Also,
further valved inlet branches can be provided if desired,
in the inlet hoses connectable to the blood side and the
10 dialysate side of the filter, for introducing sterilizing
or preservative solution into the filter. Whilst the
predominant amount of cleaning of the filter takes place with
water, it is of advantage to be able to wash the membrane
and other parts of the structure with a water compatible
blood solvent also, such as hydrogen peroxide. Storage
of artificial kidneys in a sterile condition, e.g. filled
with sterilizing liquid, is also desirable. The preferred
form of the present invention thus includes means for washing
the artificial kidney with liquid blood solvent, and means
20 for filling the artificial kidney with sterilizing liquid.
In a particularly preferred embodiment, the washing process
according to the invention includes a sequence of steps,
carried out automatically, in which the used filter is
washed on both sides by water in a steady, or static flow
condition, and then thP blood side is washed with pressurizing
and brief reversal of flow, as previously described, i~e.
dynamic washing, whilst thP dialysate side'is drained. In a
subsequent step, the dialysate side is filled and pressurized
Z9 with hydrogen peroxide'solution wh~lst the blood side is
il39~7R
drained. Subsequently both sides are flushed with water,
rinsed and filled with formalin as sterilizing solution, to
complete the washing operation.
A specific preferred embodiment of the invention is illustrated
in the accompanying drawings, in which:
FIGURE 1 is a perspective, exterior view of a portion
of an apparatus for washing an artificial kidney, in accordance
with the present invention;
FIGURE 2 is a diagrammatic view of parts of the
artificial kidney or dialysis filter washing apparatus according
to the invention, with a dialysis filter cartridge diagrammatically
illustrated in place;
FIGURE 3 is a diagrammatic sectional view of the valve
box used in the apparatus of Fig. 1 and Fig. 2, showing the
valve and conduit arrangements;
FIGURE 4 is a block diagram of the electrical control
arrangements of an apparatus according to the invention;
FIGURE 5 is a graphical representation of the pressure
variations within the blood compartment during operation of a
2a part of the washing process.
With reference to Fig. 1, an artificial kidney or
dialysis filter washing apparatus according to the present
invention comprises an electrical control box 10, provided with
manually operable controls 12 on the front panel thereof, and a
valve box 14 mounted below the control box 10. Protruding from the
valve box 14 are four flexible outlet hoses 16, 18, 20, 22, for
connection to a filter unit housing for washing purposes in accord-
ance with the invention. Reagent storage vessels 24, 26 are
29 provided at a convenient location, for supply of sterilizing and
cleaning liquids namely formalin and hydrogen peroxide respectively,
1139~78
to the valve box. At its rea~ face, not shown, the valve box 14
is provided with four inlet hoses, two of wl-ich 28, 3~.
connect respectively to the foLmalin vessel 24 and the
hydrogen peroxide vessel 26, one of the others of which
connects to a source of clean water, and the other of which
is connected to a drain.
Fig. 2 shows diagrammatically a kidney dialysis
filter cartridge or artificial kidney 32 which has a blood
side 34 and dialysate side 36, separated by a flexible
10 membrane 38. The blood side 34 has an inlet 4a and an
outlet 42, at opposite ends thereof. The dialysate side
36 has an inlet 46 and an outl.et 44. When in use.by a
patient, the artificial kidney has the patient's blood
continuously flowing through inlet 40 and outlet 42 to
pass through the blood side 34, and a suitable dialysate
solution flowing through inlet 46 and outlet 44 to pàss
through the dialysate side 36. The composition of the
patient's blood is corrected by dialysis, across the membrane
38 separating the two compartments. After use, it is extremely
20 important that the blood side 34 be carefully cleaned, to
remove all traces of the patient's blood, before the artificial
kidney 32 is reused on the same patient. It is less
important, but nevertheless desirable, to clean the dialysate
side 36 between uses. In addition, the whole artificial
kidney should be sterilized and stored in clean, sterile
condition between uses.
To ensure the necessary cleaning, according to the
present invention, the artificial kidney 32 is connected up
29 to the apparatus of Fig. 1, as shown diagra~matically in
1139tj78
Fig. 2. The flexible outlet hose 16, which. i5 of resilient,
flexi~le tubingr is connected to t~e inlet 40 of the blood
side 34 and similarly outlet hose 22 is connected to the
outlet 42 of the blood side 34. Outlet hose 18 from the
valve box 14 is connected to the outlet 44 of the dialysate
side 36, and ou~let hose 20 from the valve box 14 is
connected to the inlet 46 of the dialysate side. The various
resilient flexible hoses 16, 18r 20, 22 in effect constitute
branched hoses as shown diagrammatically in Fig. 2 and more
10 precisely in Fig. 3I the various branche~ being valved and
connected to various liquid sources and drain arrangements,
to provide ~or a washing process according to the invention.
Thus inlet hose or conduit 16 to the.blood side
34 has an inlet branch 48 closable by means- of a solenoid
operated valve 50, and a drain branch 52 closable by means of
a solenoid operated valve 54. A third branch 56 with a
solenoid operated valve 58, for provision of formalin, also
communicates with hose 16. The outlet hose 22 from the blood
side 34 has a drain branch 60 closable by a solenoid
20 operated valve 62, and a fluid inl.et branch 64 closable by
a solenoid operated valve 66 therein.
The washing steps of the invention will now be
described with reference to Fig. 2. In practice, in this
specific preferred embodiment, these are steps in a longer
sequence of operations also involving the washing of the
dialysate side 36. However, the essential process steps
according to the invention are as follows. Inlet branch 48
is connected, via valve box 14, to a wash water supply
hose 68 fed into th~ back of the valve box 14. Drain
30 branch 52 is connected, via valve box 14, to a drain hose
-- 10 --
i139~78
70 fed into the back of th~ valve box 14. Fluid inlet
branch 64 and drain ~ranch 60 of the outlet hose 22 of the
blood side 34 are similarly connected ~y a valve box 14 to
the water supply hose 68 and the drain hose 70 respectively.
With valve 50 and valve 62 in the open position, whilst
valves 58, 54 and 66 remain closed, wash water is
continuously circulated through blood side 34, in through
branch 48 and inlet hose 16, and out through outlet hose 22
and drain branch 60. After thus flushing for a period of
10 time, e.g. 15 minutes, valve 62 in the outlet drain branch
60 is closed whilst introduction of water continues. This
causes fluid pressure in the blood side 34 of the cartridge
to build up, with consequent resilient expansion of the
hoses 16, 22, and the membrane 38. About 1 second later,
the valve 50 is closed to cut off the water supply and
contain the pressure within the cartridge 32 and the hoses.
Next, about 1/2 second later, valve 54 in the drain branch
52 of the inlet conduit 16 is opened briefly, for about 1
second. This causes a brief reversal of the direction of
20 flow of water within the blood side 34 of the cartridge 32,
as the hoses 16, 22 and the membrane 38 relax. This reversal
of flow results in a desirable scrubbing effect to complete
the cleaning and dislodgement of contaminating particles
from the membrane and elsewhere in the blood side of the
cartridge. However, the reversal of flow is for such a
brief duration that no contaminated washing water re-enters
the washin~ apparatus tubes such as tube 16, where
contaminating particles might become deposited to cross-
29 contaminate water flowing therethroug~ into another filter
78
~eing washed in a subsequent operation in the apparatusaccording to the invention.
The above dynamic washing procedure applied to the
blood side 34 of the cartridge 32 constitutes, in the
specific preferred embodiment o~ the invention, a step in
an overall washing sequence for the cartridge 32, for
washing both blood side 34 and the dialysate side 36, in
a preset, automatic, sequential process in a single apparatus.
Thus the dialysate side outlet 44 is connected to flexible
10 outlet hose 18 from the valve box 14, which hose constitutes
a branched outlet hose for the dialysate side 36. Inlet
branch 72, provided with solenoid operated valve 74,
connects via valve box 14 with water supply hose 68. Drain
branch 76, provided with solenoid operated valve 78, connects
via valve box 14 with drain hose 70. A third branch 80
constitutes a formalin supply branch, and is provided with
a solenoid operated valve 82 and connected by valve box 14
with the formalin supply hose 28. The dialysate side inlet
is connected to the flexible inlet hose 20 from the valve
20 box 14, which hose constitutes a branched hose or conduit for
the dialysate side, having three branches therein. Inlet
branch 84 with solenoid operated valve 86, connects via valve
box 14 with water supply hose 68. Drain branch 88 with
solenoid operated valve 90 connects via valve box 14 with
drain hose 70. Peroxide supply branch 94 with solenoid
operated valve 96 connects via valve box 14 with hydrogen
peroxide supply hose 30. As sho~n in Fig. 3, the water supply
hose in the valve box 14 is provided with pressure regulator
29 valves ~8, 100, and the valYe box outlet hoses 16, 18, 20, 22
- 12 -
113~78
are provided with respective pressure meters 102, 104, 106
and 108 to report pressure flows etc. therethrough, for
control purposes'.
In a complete sequence of operations according
to this specific embodiment of the present invention,
twelve distinct steps are involved. In the zero, reset,
step all the drain valves 54, 62, 78 and 90 are set to the
open position so that both sides of the'cartridge 32 are
effectively emptied of fluids. In the first operational
10 step, water is flushed steadily and continuously through
both the blood side 34, using inlet branch 48 and drain
branch 60, and through the dialysate side 36, using inlet
branch 84 and drain branch 76, so that there is static water
flow on both sides of membrane 38, but in opposite directions.
In the second operational step, dynamic flow in the blood
side 34 is conducted, as previously described, with the
pressurizing and brief reversal of fluid flow caused by
resilient contraction of the hoses and membrane. Dur-ing this
dynamic flow in the blood side, water supply to the dialysate
20 side is discontinued and the drain valves 78, 90 thereto are
opened. The third operational step has the drain valves
54, 62 to the blood side 34 open, so as essentially to empty
it, whilst the drain valve 78, 90, water inlet valves 74, 86,
and formalin supply valve 82 to the dialysate side 36 are
closed and peroxide supply valve 96 thereto is opened, thus
- filling the'dialysate side with hydrogen peroxide solution.
Operational step four comprises a continuation of step three
to build up pressure of hydrogen peroxide in the dialysate
29 side,' closing of all valves to the dialysate'side 36 to
li39~i78
maintain hydroyen peroxide pressure therein~ with the b]ood
side draining out. rhis causes pene~ration of the membrane
with hydrogen peroxiae for efficient cleaning thereof.
~ ow, in operational step five, the first
operational step is repeated, with water flow through both
the blood siae and the dialysate side, in reverse directions.
Operational step six is similarly a repeat of the second
operational step, with a dynamic washing of the blood side
in accordance with the invention, with draining of the
10 dialysate side. Next, in operational step seven, the blood
side is drained and then filled with formalin, for
sterilizing purposes. Operational step eight involves the
discharge of a small amount of formalin through the drain
branch 52 and valve 54 of the bl-ood side 32 for sterilization
of this branch. In operational step nine, the dialysate side
is filled with formalin for sterilization, and in operational
step ten, a small amount of the formalin is drained through
drain conduit 76 of the dialysate side, so as to sterilize
it. Then in operational step eleven, both sides are
20 maintained full of formalin and all valves are closed. The
cartridge 32 can now be removed from the machine, stored
full of formalin, and the machine returned to the reset,
zero position ready for use with another cartridge.
~ ccordin~ to another aspect of the invention, the
variation of pressure with time in the blood side of the
artificial kidney is used to determine the extent of obstruc-
tion of the blood compartment. For this purpose, a pressure
sensitive switch 120 (Fig. 3~ is included in fluid inlet
29 branch 64 of the outlet hose 22 from the blood compartment 34.
- 14 -
'3~78
The switch is connected to a timing circuit in an alarm module
of the machine controls, described below.
Fig. 5 of the accompanying drawings illustrates the
variations in pressure with time in the blood compartment during
the above described se~uence of operations. In the first
operational step, in which water is flushed through blood side
34, the pressure in the blood side 34 remains steady, as
represented by segment AB of the curve of Fig. 5. When the
valve 62 in outlet drain branch 60 is closed, with continued
water feed, the pressure increases, as represented by segment BC
of the curve of Fig. 5. When valve 50 is closed to cut off
water supply, the blood side is held under increased but steady
pressure, as represented by segment CD of Fig. 5. When valve 54
is opened to cause the reversal of flow, the pressure in the
blood side 34 drops, and represented by segment DE. This
segment DE is used to determine extent of obstruction of the
unit. It has been found that this rate of pressure drop is
influenc0d by the degree of obstruction, the greater the
obstruction the slower the pressure drop.
In practice, therefore, pressure switch 120 is set to
close when the pressure sensed in the convert exceeds the
pressure value at the mid-point of segment DE of the curve of
Fig. 5.
The time interval between the opening of the drain
valve 54 (point E on the curve of Fig. 5) and the closing of the
switch 120 is measured. If this time interval exceeds a pre-
determined value, an alarm is activated, indicating obstruction,
to allow the washing cycle to be stopped.
Another test which can be conducted with the present
invention is the determination of the integrity or porosity of
:,~
il;~9~7~3
.
the filter. For this purpose, the dialysate compartment 36 is
pressurized, by feeding water thereto whilst maintaining the
drain valves closed. The blood compartment 34 is then sealed by
closing the drain valves. Due to the porosity of the filter
membrane 38, the pressure will cause water to flow from the
dialysate compartment 36, through the membrane 38 into the blood
compartment 34, with consequent equalization of the pressure
across the membrane. The rate at which the pressure increases
in blood compartment 34 can be used to determine the porosity of
the filter - an excessively clogged filter will give excessively
slow pressure increase.
Pressure sensitive switch 120 is thus used, pre-set to
close when a predetermined pressure in blood compartment 34 is
reached and exceeded, and a time recording means namely a timing
circuit is used to measure the time interval from the sealing of
the blood compartment 34 to the closing of the switch 120.
Excessive time delays will operate an alarm, to indicate a
clogged filter which can then be eliminated. Insufficient time
intervals will operate an alarm to indicate a leaking or
ruptured membrane.
Similar pressure switches 122, 124 and 126 are included
in outlet hoses 16, 18, 20 respectively, connected to the alarm
system. The switches are pre-set to determine the abnormal loss
of fluid pressure during a washing cycle, and to trigger the
alarm if this occurs.
The control and operation of the apparatus according to
the preferred embodiment of the invention is suitable by
standard electrical components arranged to open and close the
solenoid operated valves according to a predetermined sequence
and for predetermined intervals of time. Such components and
arrangements thereof are within the skill
- 16 -
7~3
of the art, being generally similar to those previously employed
for other automatic washing machines, although set for different
sequences and combinations of operations, of course. Detailed
description of the individual components and their function is
not necessary herein. By way of example, a suitable arrangement
is illustrated diagrammatically in Fig. 4, and comprises a cycle
timer 110, a program module 112 and a drive module 114. The
cycle timer 110 is fed by a clock signal, and includes a binary
step counter, a multiplexer, a demultiplexer and ten electronic
timers, one for each of the operational steps, omitting the
zero, reset step and the final, formalin filled storage steps
which are not timed. As indicated diagrammatically in Fig. 4,
the cycle timer thus feeds twelve different signals 116, in
sequence to the program module 112, for the sequential operation
by the program madule of each of the twelve operational steps.
The program module 112 receives these command signals 116 from
the cycle timer and, by means of a diode matrix sends
appropriate energizing signals 118, one for each solqnoid
operated valve in the valve box 14, to the driver module 114.
The driver module includes solenoid drivers for operating each
of the eleven solenoid operated valves 50, 54, 58, 66, 62, 74,
78, 82, 86, 90, 96, controlling the branches of the branched
hoses connecting to the filter unit 32 being washed, to open and
close these valves as necessary to perform the above described
operations in the desired sequence. An alarm module is
provided, incorporating the time recording means for pressure
variations and electrically connected to the pressure sensing
switches 120, 122, 124, 126 and to the driver module to
interrupt the washing operation upon
-- 17 -
1139~i7~
closing of any of the switches, and to give visible and audible
alarm also.
It will be noted that the electrical control box 10
containing the cycle timer and program module has ten manually
operable controls 12 readily accessible on its front face.
These are adapted to set the time intervals for which each of
the operating steps 1-lO will extend. These intervals can thus
be varied readily and simply, to obtain the optimum washing
cycle. A reset control is also suitably provided to stop the
apparatus in mid-cycle if required.
The materials from which the various components are
made should be chosen with regard to the requirement to avoid
unnecessary contamination of the washing fluids, etc. Tubing
of polyethylene, nylon or the like has been found suitable.
For conduits 16, 22 which are required to exhibit elasticity,
thin wall polyethylene tubing of outer diameter of about 1/2
inch is preferred.
In some circumstances, it is preferred to have the
controls 12 inaccessible on the inside of the box 10, and preset
to the desired washing cycle. This is particularly so when a
patient is to be provided with such a machine in his own home,
to operate himself. Then it is desirable to have the controls
preset, to be altered only by qualified personnel.
The process and apparatus of the invention is adapted
to wash cartridges containing of a wide variety of filter mem-
branes. A whole variety of such artificial kidneys are available
on the market, having membranes of widely differing shapes, sizes
and configurations - fluted, planar, convoluted etc. The
29 configuration of the membrane is not critical in the present
invention.
- 18 -
