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BACKGROUND OF THE INVENTION
This invention relates to an artificial kidney device and in particular an
artificial kidney device for automatically maintaining an ultrafiltration
pressure substantially constant.
By "an ultrafiltration pressure" is meant a difference between internal and
external pressures applied to a dialysis membrane consisting of a
semipermeable membrane which is provided within a dialyzer.
A variety of artificial kidney devices, for example, a coil-type one,
kiil-type one or one utilizing hollow fibers has been known up to this
date. These artificial kidney devices are adapted to send blood from the
artery of a human being through a suitable means to a dialyzer where urea,
nitrogen, sodium, potassium, water content etc., included in blood are
separated through a semipermeable membrane. The blood passed through the
dialyzer is returned to the vein of the human being. With the dialyzer,
the water content should be eliminated, in an amount far greater than that
of the other components, through the semipermeable membrane. In addition
to osmotic pressure, therefore, an additional pressure is generally
required for the dialysis operation. One method is to apply
ultrafiltration pressure to a dialyzer in an attempt to eliminate more
water content. Taking the strength etc. of the semipermeable membrane into
consideration, the ultrafiltration pressure is generally desired to be
maintained at a level of 200 mm Hg. If the ultrafiltration pressure is too
high, there is a fear that blood will flow out due to a breakage of the
semipermeable membrane. If, on the other hand, it is too low, a dialyzing
effect is lowered, and water content is not sufficiently eliminated from
blood. For the purpose of maintaining the ultrafiltration pressure at
suitable level, a method employed in the prior art is to mount a
pinch-cock at a midway of a tube extending from a dialyzer into a vein of
a human being. An ultrafiltration pressure of, for example, 200 mm Hg can
be provided by restricting the flow passage of the tube by means of the
pinch-cock.
However, a very delicate operation of the pinch-cock is required in
adjusting the ultrafiltration pressure. Any slight operation of the
pinch-cock causes a greater change in the resistance of blood. To make the
ultrafiltration pressure at a prescribed level, therefore, the adjustment
of the pinch-cock is conducted gradually, i.e., by repeating the
adjustment several times. It will take more than 2 minutes for
ultrafiltration pressure to settle down to a prescribed level after one
adjustment has been made. For this reason, more than 10 minutes will be
required in adjusting the ultrafiltration pressure to a desired level. If
no due care should be exercised during adjustment, there is a chance that
blood will flow out due to a breakage of the dialysis membrane.
The ultrafiltration pressure is related not only to the extent to which the
pinch-cock is closed but also to the operation of transporting means of
blood from the artery of a human being into a dialyzer, for example,
rotations of a pump. If, therefore, the pump is changed in the number of
rotations to increase a flow of blood, the above-mentioned delicate
adjustment will be required on each occasion.
SUMMARY OF THE INVENTION
It is accordingly the object of this invention to provide an artificial
kidney device equipped with a pressure adjusting means capable of
automatically maintaining an ultrafiltration pressure of a dialyzer at all
times substantially constant irrespective of the variations of blood
pressure or a change in the number of rotations of a pump and capable of
being manufactured at lower cost without involving any complicated
structure.
With an artificial kidney device according to this invention, a
double-walled tube is mounted midway of a tube provided for transporting,
into a vein of a human being, blood passed through a dialyzer for
separating specified components from blood. The double-walled tube
consists of a flexible inner tube communicating with said
blood-transporting tube and a non-flexible outer tube surrounding the
inner tube to define a closed chamber therebetween. The inner tube is
automatically collapsed or inflated, in response to a change in an
internal pressure prevalent within a dialyzer, due to a difference between
an internal pressure of the inner tube and an internal pressure within the
closed chamber, whereby an ultrafiltration pressure is automatically
maintained substantially constant.
BRIEF DESCRIPTION OF THE DRAWING
This invention will be further described, by way of example, by reference
to the accompanying drawings.
FIG. 1 is a schematic general view showing an artificial kidney device
according to this invention;
FIG. 2 is a schematic view showing the major part of this invention;
FIG. 3 is an enlarged, perspective view showing a pressure adjusting means
comprised of a double-walled tube;
FIGS. 4 and 5 are longitudinal cross-sectional views respectively showing
widely open and collapsed states of the pressure adjusting means of FIG.
3;
FIGS. 6 and 7 are cross-sectional views showing the pressure adjusting
means of FIG. 3, each corresponding to FIG. 4 and FIG. 5;
FIGS. 8 and 9 are cross-sectional views showing modified forms of an inner
tube of the double-walled tube of FIG. 3; and
FIG. 10 is a graph showing a comparison in ultrafiltration pressure holding
characteristic between the artificial kidney device according to this
invention and the prior art artificial kidney device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a schematic diagram showing an artificial kidney device according
to this invention which is provided with a coil type dialyzer. A tube 1 is
connected at one end to the artery of a human being and at the other end
to the dialyzer 2. Midway of the tube 1 is connected a pump 3 for sending
blood to the dialyzer 2 at a predetermined flow rate. The dialyzer 2 is a
known coil-type one formed by winding one or a plurality of semipermeable
membranes, into a coil 4 with a mesh interposed therebetween and
submerging the coil into a dialysis solution within a container 5. The
dialysis solution is one having a specified concentration which is
prepared by mixing at a mixer 7 and at a suitable ratio, water and an
undiluted solution containing, for example, sodium chloride etc. The
dialysis solution from the mixer 7 is sequentially forwarded to and
discharged from an outlet 8 while it is contacted with a dialysis
membrane. On the other hand, blood is passed through the dialyzer 2, where
unnecessary components are separated, and flows through a tube 9 into the
vein of the human being. Midway of the tube 9, a drip tube 11 connected to
a manometer 10 and a double-walled tube 12 are provided in communication
with the tube 9. An air pump 13 and air reservoir 14 communicate with the
double-walled tube. FIGS. 2 to 9 show the detail of the double-walled tube
and its modifications. As shown in FIG. 2 the blood passed through the
dialyzer 2 is sent through the tube 9 to the drip tube 11. Since the
manometer 10 is connected to the drip tube 11, a pressure prevailing
within the drip tube 11, or consequently an ultrafiltration pressure
prevailing at the dialyzer 2, is indicated at the manometer 10. 15 denotes
a mesh. The drip tube 11 etc. are conventionally known and may be suitably
selected by those skilled in the art.
The blood passed through the drip tube flows into the double-walled tube
12. The double-walled tube 12 has an inner tube 16 as shown in FIGS. 3 to
7 and an outer tube 17. The inner tube 16 is made of, for example,
non-rigid polyvinyl chloride and has such a relatively thin wall that it
can be easily collapsed. As shown in FIGS. 4 and 6, the inner tube 16 is
formed by superposing one over the other two sheets of non-rigid polyvinyl
chloride wider than the diameter of the tube 9 and sealing them at the
side edge portions. The outer tube 17 is formed to have such a rigidity
that it is not deformed under the maximum pressure to be applied in use.
It is made of, for example, a rigid polyvinyl chloride and has a form
substantially elliptical in cross section. The inner and outer tubes 16
and 17 of the double-walled tube 12 are hermetically heat sealed at each
end to define a closed chamber 18 between the inner and outer tubes 16 and
17. The tube 19 opened at one end into the closed chamber 18 and at the
other end detachably connected to an air reservoir 20. The air reservoir
is made, for example, of acrylic acid resin and has a cylindrical shape. A
manometer 21 is connected to the air reservoir 20, indicating an air
pressure within the air reservoir 20. A manually operated air pump 23
consisting of a rubber bulb is connected through a tube 22 to the air
reservoir 20 and adopted to adjust the air pressure prevailing within the
closed chamber 18. 24 denotes a valve for releasing the air confined
within the air reservoir 20. 25 denotes a valve for controlling a flow of
the air reservoir 20.
An explanation will now be made as to how an ultrafiltration pressure is
automatically controlled in the so constructed artificial kidney.
Blood from the artery of a human being is sent to the dialyzer 2 while
being gradually increased in amount by changing the number of rotations of
the pump 3. The air pump 23 is repeatedly squeezed by the hand of an
operator so that a pressure prevailing within the dialysis coil of the
dialyzer 2 comes to, for example, 200 mm Hg. When the manometer 10
connected to the drip tube 11 indicates just 200 mm Hg, the squeezing
operation of the pump 23 is stopped and the valve 25 is closed. Since, at
this time, the weight of blood occupied from the drip tube 11 down to the
double-walled tube 12 is applied, air pressures within the closed chamber
18 and air reservoir 20 are increased by that extent and maintained at
levels somewhat higher than 200 mm Hg.
The establishment of the ultrafiltration pressure may be conveniently
conducted preliminarily setting a pressure within the closed chamber 18 by
watching the manometer 21 at a value little higher than that of the
ultrafiltration pressure. But the manometer 21 may be omitted.
When the pressure within the dialysis coil 4 is maintained to 200 mm Hg,
blood is sent toward the vein side in a manner that the double-walled tube
12 is inflated to suitable extent shown, for example, in FIGS. 4 and 6.
When, however, the pressure within the dialysis coil 4 comes to below 200
mm Hg, the inner tube 16 of the double-walled tube 12 is collapsed as
shown in FIGS. 5 and 7 with its cross-sectional opening being narrowed,
since the internal pressure of the inner tube 16 is smaller than the
external pressure of the inner tube 16. In this case, the inner tube 16 is
closed in a direction indicated by arrows in FIG. 5, because the inner
tube 16 tends to be more easily collapsed in a vertical i.e., than in a
horizontal direction. As the inner tube 16 is so collapsed, the blood
passed through the dialysis coil is restricted, causing the
ultrafiltration pressure i.e., the pressure prevailing within the dialysis
coil 4 to be increased. As a result, the ultrafiltration pressure is
automatically adjusted to 200 mm Hg. When, on the other hand, the pressure
within the dialysis coil 4 exceeds 200 mm Hg, the internal pressure of the
inner tube 16 exceeds the external pressure of the inner tube 16, causing
the inner tube 16 to be again inflated as shown in FIG. 4. As a result,
blood flow rate is increased and the pressure prevailing within the
dialysis coil is dropped and automatically adjusted to 200 mm Hg. In this
way, the ultrafiltration pressure i.e. the pressure within the dialysis
coil is automatically maintained to 200 mm Hg. This automatic adjustment
is effected within several seconds to scores of seconds. Though a volume
within the closed chamber 18 is somewhat changed due to the collapse or
inflation of the inner tube 16, this change is absorbed by a relatively
great amount of air confined within the air reservoir 20. Consequently,
the change of pressure within the closed chamber 18 due to the collapse or
inflation of the inner tube 16 can be disregarded. The change of pressure
within the inner tube 16 due to the collapse or inflation of the inner
tube 16 is decreased as the volume of the air reservoir 20 is increased.
From this viewpoint the greater the volume of the air reservoir 20, the
better. There is, however, a fear that if by any chance the inner tube 16
should be ruptured, a greater amount of air flows into the blood vessel of
the human being. If, on the other hand, the volume of the air reservoir 20
is too small, the change of pressure within the closed chamber 18 due to
the collapse or inflation of the inner tube 16 can not be disregarded.
Taking into consideration the safety of the inner tube 16 against rupture
as well as the necessity to absorb the change of pressure resulting from
the inflation or constriction of the inner tube 16, it is preferred that
the volume of the air reservoir be of the order of about 70 ml. If the
closed chamber 18 is designed to have an ample volume, the air reservoir
can be omitted. In this case, however, the cost of the double-walled tube
is raised.
FIG. 10 is a graph showing the result of measurement made as to the effect,
on the ultrafiltration pressure, of a change in the flow of blood from the
artery of a human being. For comparison, measurement was also made of the
case where a conventional pinch-cock is used. A curve a appearing in the
graph of FIG. 10 shows a change in the ultrafiltration pressure of the
artificial kidney device according to this invention as obtained when a
flow of blood is changed in a range of 50 cc/minute to 330 cc/minute by
changing the number of rotations of the pump 3, wherein the
ultrafiltration pressure is at first set at 180 mm Hg when the flow of
blood is 150 ml/minute. On the other hand, a curve b appearing in the
graph of FIG. 10 shows the change of ultrafiltration pressure when a flow
of blood is changed by changing the number of rotations of the pump 3,
wherein the ultrafiltration pressure is at first set at 180 mm Hg when the
flow of blood is 150 ml/minute and that the conventional pinch-cock is
used. From the curve a it will be seen that according to this invention
the ultrafiltration pressure is maintained substantially constant, even if
the flow rate of blood is widely changed. In the case of the curve b, on
the other hand, it will be easily understood that a slight change in the
flow rate of blood will cause a large or great change in the
ultrafiltration pressure. The ultrafiltration pressure is, therefore, very
unstable.
According to this invention, once a predetermined pressure is applied to
the closed chamber 18 of the double-walled tube 12, the ultrafiltration
pressure is maintained substantially constant even in the event of any
change in the number of rotations of the pump 3. This obviates the
necessity of making a troublesome and time-consuming adjustment.
Furthermore, there is less chance that a dialysis membrane will be
ruptured due to a pressure prevalent within the dialysis coil being
excessively raised under no due care or attention. In the operation of the
prior art artificial kidney device wherein a pinch-cock is employed as
described above, it is necessary for the attendant to pay, at all times,
due care or attention to the ultrafiltration pressure. According to this
invention, only an occasional check on the ultrafiltration pressure is
required. Consequently, a fatigue on the part of the attendant can be
prominently alleviated. Where a medical treatment is effected at night, a
safety as well as a labor-saving is required. This invention will prove
advantageous even in such cases.
According to this invention the ultrafiltration pressure can be maintained
substantially constant by a combination, with a pressure applying
mechanism, of the double-walled tube 12 consisting of the inner tube 16
and the outer tube 17. This makes the device simple in construction and
low in manufacturing cost. After use, the double-walled tube can be
detached from the pressure mechanism for disposal.
Though with the above-mentioned embodiment the inner tube 16 of the
double-walled tube 12 is formed by heat sealing the pair of sheets at
their side edge portions, it may take a variety of forms if it is easily
collapsible. For example, it may take a form 26 elliptical in cross
section as shown in FIG. 8 or a flattened tubular form 27 as shown in FIG.
9, or it may be formed by folding back a sheet upon itself and sealing the
opposite free side edge portions thereof. As a material for the inner tube
15, use is made of, in addition to the above-mentioned polyvinyl chloride,
the other flexible synthetic resins, rubbers or flexible air-impermeable
sheets. It is, however, required that these materials can be easily
deformed in response to a difference between the internal and external
pressures of the inner tube 16 and that they are harmless to blood or a
human being. For the outer tube 17, any material may be used as far as it
is not deformed under any available pressure applied to the closed chamber
18. However, a rigid thermoplastic synthetic resin is considered
preferable from the standpoint of the easiness in manufacture etc.
Though with the above-mentioned embodiment the air pressure is applied to
the closed chamber, any fluid pressure may be applied to the closed
chamber. Use of water, however, assures a safety against the possible
rupture of the inner tube 16.
The artificial kidney device according to this invention may be applied not
only to the above-mentioned coil type dialyzer, but also to all
dialyzers-including one using hollow fibers-which are adapted to effect
dialysis utilizing an ultrafiltration pressure.
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