NO790959L - END APPARATUS FOR HEMODIALYSIS SYSTEMS - Google Patents

Description

Venting device for a hemodialysis system.

The present invention generally relates to venting devices for removing soluble gases from heated water before it is fed to distribution devices in a hemodialysis system.

Hemodialysis systems have been in use in a number of ways

years for the treatment of kidney disorders and failing kidney capacity, and have proven to be very effective in that they provide artificial kidney functions for those people whose natural kidneys do not function fully satisfactorily. During operation of the hemodialysis system, the impure blood containing substances such as urea, creatinine, excess electrolytic salts and water will be removed from the body and passed through a dialyzer in an indirect mass transfer relationship with an aqueous dialysate solution. The dialyzer may be of various known types and may include a mass transfer unit, e.g. consisting of an expanded surface elastomeric membrane or in the form of a bundle of hollow fibers over which the waste substances are transferred by means of a concentration gradient (impurities in solution) or osmotic pressure (water) from the blood to the dialysate solution. From the dialyzer, the purified blood will be returned to the patient's body. The contaminated dialysate solution from the dialyzer is either discarded or recycled in a closed circuit from a dialysate solution source through the dialyzer to receive substances from the blood again.

The dialysate solution used in a normal hemodialysis treatment is an aqueous solution of various selected salts that provides the desired electrolytic balance with the blood in the dialyzer, thus preventing a loss of valuable blood components to the dialysate solution due to diffusion and osmosis. The aforementioned closed recirculation of the dialysate solution from such a source through the dialyzer has a limited mass transfer effect due to a progressively decreasing mass transfer concentration gradient as the dialysis treatment progresses. Consequently, distribution systems have been developed which ensure that the dialysate solution only passes through the dialyzer once, whereby a maximum mass transfer concentration gradient is obtained for the dialysis itself. Such distribution systems take in and mix water from a local source with a relatively small volume of a concentrate of the dialysate solution. Such systems usually use relatively small supply tanks for said concentrate,

and when such are connected to a water source by means of said distribution device, this enables a single passage of the dialysate solution through the dialyzer and from there to a normal drain, without the need for large liquid tanks.

During such dialysis treatments, it is often desirable to operate the system so that the pressure in the dialysate solution on one side of said mass transfer surface, e.g. a dialyzer membrane, is somewhat reduced in relation to the pressure in the blood on the other side of said membrane. Such a mode of operation means that there is a pressure difference across the membrane in the dialyzer, and this will facilitate the transfer of an excess of water from the patient's circulatory system to the dialysate flow itself due to an osmotic pressure. This removal of an excess of water, usually referred to as an ultrafiltration, provides a suitable means for removing water from the patient's body, a function that would otherwise be performed by the kidneys.

However, the application of a reduced pressure in the circuit where the dialysate solution flows, as described above, has certain specific operational disadvantages, as a reduction of the pressure of the dialysate solution from normal atmospheric pressure to a lower pressure, which can easily be accomplished by passing the dialysate solution through a current limiting device in said circuit can easily cause a release of soluble gases from the dialysate solution in the form of bubbles. A passage of a dialysate solution containing released gas bubbles through the circuit where the dialysate solution flows and the dialyser itself is highly detrimental to the functioning of the dialyser as well as to the effect of the dialysis treatment. In the dialyzer, the presence of gas bubbles near the mass transfer device between the dialysate solution and the blood will greatly weaken the mass transfer process and thereby reduce the speed and degree of removal of toxins from the blood to be treated, thereby generally weakening the dialysis treatment.

In addition to this, the gas bubbles can be transferred from the dialysate solution into the blood to be purified, and in this the gas bubbles can cause hemolysis and otherwise have a harmful effect on a number of blood components such as lipoproteins. Furthermore, the presence of gas bubbles in the dialysate solution will have a highly detrimental effect on a number of measuring mechanisms which are characteristically connected to the circuit through which the dialysate solution flows, and these measuring devices are inserted to ensure proper functioning of the dialysis system. E.g. such a typical dialysis flow circuit will usually use a measuring device for measuring the conductivity as well as various devices to ensure that the conductivity in the dialysate solution is in the right balance with the blood to be treated, because otherwise there would be a loss of valuable blood components to the dialysate solution due to a diffusion in the dialyzer. Such measure-

and control devices for the resolving power usually use electrodes that are reduced in the flow of dialysate solution. Gas bubbles present in the solution tend to

to accumulate on the surfaces of the electrodes, preventing an accurate measurement of the electrolytic conductivity. Similarly, temperature measuring devices will usually be placed in the flow of dialysate solution to ensure the appropriate temperature thereof, thereby preventing excessive heating or cooling of the blood due to a heat exchange with the dialysate solution in the dialyzer, as this can easily cause hemolysis of the blood. The temperature measurement and control devices usually use

small temperature probes that are placed in the flow of dialysate solution. Gas bubbles that are present in the solution that will flow past the temperature probes tend to accumulate on the surface of these, whereby false signals about the temperature of the solution are obtained.

The above-mentioned problems associated with the release of soluble gases from the dialysate solution are particularly a problem in such dialysis systems where the dialysate solution runs in an open circuit, i.e. only passes through the dialyzer once. As mentioned earlier, such a system will use a source of flowing water in combination with a distribution system. Water flowing into such a system will usually contain significant amounts of dissolved gases, this may be naturally dissolved oxygen or the water may have been "aerated" during its flow through ordinary water lines or leaky gaskets.

The problem with the release of dissolved gases in such systems is further exacerbated by the fact that the water used in the dialysate solution is often heated, which of course releases more dissolved gases. Said heating is carried out to prevent, as mentioned earlier, a too strong cooling of the blood due to heat exchange with the dialysate solution in the dialyser.

It is therefore a purpose of the present invention to provide effective venting devices to remove dissolved gases from the water before it is fed to distribution devices where the water and the dialysate concentrate are mixed in a predetermined ratio so that a suitable dialysate solution for hemodialysis is produced.

It is also a purpose of the present invention to provide such venting devices which are also compact and well suited for use in connection with a portable hemodialysis system.

Other purposes and advantages of the invention will be apparent from the following description. The present invention generally relates to venting devices for removing dissolved gases from heated water before this is fed to distribution devices for producing a suitable dialysate solution.

The invention thus provides an apparatus which provides a continuous flow of water at an elevated temperature to hemodialysis distribution devices where water and a dialysate concentrate are mixed in a predetermined ratio so that a suitable dialysate solution for hemodialysis is produced, and where said apparatus includes devices for supplying water as well as devices for heating the water to an elevated temperature.

The invention further relates to venting devices

to remove dissolved gases from the heated water before it is fed to the aforementioned distribution device. The venting devices include a first reservoir tank that receives the heated water from the heating devices, and where said first reservoir has venting devices that allow a release of the dissolved gases from the water that was heated, so that partially deaerated water is produced. Furthermore, a vacuum pump is provided together with a line that connects the first reservoir with the intake of the vacuum pump in order to

could lead the partially vented water from said first reservoir to the vacuum pump. Furthermore, adjustable current limiting devices are placed in the line in order to reduce

increase the pressure on the partially aerated water that is passed through the line, thereby further releasing gases from the water and forming a so-called low-pressure water, where the dissolved gases are dispersed. Furthermore, a line is provided which connects the outlet on the vacuum pump from which water is taken out at a higher pressure and where the freed gas bubbles are dispersed

done. Furthermore, another reservoir is connected to the other end of the latter line which can thereby receive the water with said higher pressure, and where said second reservoir also has

ventilation devices which enable a release of the dispersed gas bubbles from said water, so that a finally aerated water is produced. Furthermore, devices are provided for transferring the finally aerated water from the aforementioned others

reservoir for said distribution devices.

Figure 1 shows a schematic block diagram of a hemodialysis system of the type used in connection with the present invention. Figure 2 is a perspective drawing of a hemodialysis system of the type shown schematically in fig. 1. Figure 3 is a schematic diagram of a distribution system that can be used in the apparatus shown in fig. 1 and 2. Figure 4 is a plan view of a dialysate dissolution pump according to the present invention and which can

is used in the hemodialysis system shown in fig. 2.

Figure 5 shows a section through the dialysate solution pump in fig. 4 together with the connected drive devices. Figure 6 shows a diagram of the dialysate solution flow rate in ml/min. plotted as a function of the negative pressure of the dialysate solution in mm Hg, and which shows working curves for the dialysate solution pump in fig. 4 and 5

and a pump of a previously known type.

Figure 7 shows a section of one. roller design that can be used in the pump shown in fig. 4 and 5• Figure 8 is another section through another roller design which can also be used in the pump in fig. 4 and 5 • Fig. 1 shows a schematic block diagram of a hemodialysis system of the type that can be used in connection with the present invention. In this system, the patient 118 is connected by a closed blood flow circuit formed by the blood flow tube segments 119 and 121 with the dialyzer device 112 which can be of any suitable type, e.g. of the type with parallel plates or with hollow fiber bundles. Blood with impurities is removed from the patient using an arterial fistula, cannula or other tube (not shown) and transferred via tube segment 119 to the peristaltic blood pump 120 which is placed in front of the dialyzer 112. With the help of the blood pump 112, the blood with impurities will be peristaltically pumped through the circuit described above.The blood pump 120

can be of e.g. the type described in US patent

Application No. 720,672 filed Sep. 7, 1976 by J.T. Hutchison. The speed of the peristaltic blood pump can be suitably regulated by means of a motor speed control device which is connected to the pump, so that the desired and necessary flow rate of blood through the blood circuit is achieved, e.g. about. 200 ml/min.

After pumping the blood with impurities through the peristaltic blood pump 120, the blood is passed via line or tube 119 through the dialyzer 112 in an indirect mass transfer dialysis relationship with the lyolysis solution supplied to the dialyzer in line or tube 109. As mentioned earlier, the dialyzer device can conveniently be of the type where you have parallel flow through a hollow fiber bundle, where the blood to be purified is led inside the hollow fibers in countercurrent with the dialysate solution that flows around the fiber bundle along the outer surfaces of the individual hollow fibers. The purified blood is returned from the dialyzer device to the patient via tube or hose 121. The blood return line has an air leak detector 122 which can indicate the presence of any gas bubbles in the blood that is returned to the patient. The detector device 122 can suitably be connected to some other visual display device or light alarm device so that the patient can be made aware of the presence of gas bubbles in the blood stream that is returned to him, and in addition the detector device can be operatively connected to closing devices (not shown ) which functions so that the return blood in line 121 is closed when air is detected in the blood, so that any gas in the blood is prevented from being returned to the patient's body.

As shown in fig. 1, the hemodialysis system is separated into three individual parts, each surrounded by a dashed line and representing a discrete module of the entire hemodialysis system. Part "C" in fig. 1 represents the hemodialysis module for the entire hemodialysis system. Parts "A" and "B" represent alternative sources of dialysate solution for hemodialysis module "C". Part "A" represents a module where recirculation is used, and this includes a dialysate solution container or

-tank 123 equipped with supply and return lines 124 and 125 respectively. As shown in the drawing, the intake and return lines in this module will be connected to the current system indicated in module "C" by means of the devices 100 and 101. In this way, a closed dialysate solution flow circuit is formed where the dialysate solution from the container 123 is passed via line 124 into line 102 for further flow through the dialyzer 112. Dialysate solution enriched in impurities from the blood is taken out from hemodialysis module "C" in line 117 which, via connecting devices 100, leads the blood over into line 125 for the removal of the solution to the container 123. Alternatively, you can have a module "B" which can be connected to module "C", whereby you get an open single flow circuit of dialysate solution. Distribution module "B" includes a distribution system 12.6 which receives a continuous flow of water in line 129 from suitable

devices. In distribution system 126, water from line 129 and a dialysate concentrate supplied to the system from line 128 that comes from a dialysate concentrate container 127 will be mixed in a predetermined ratio so that a dialysate solution for hemodialysis is produced, and this is transferred to module "C" via line 130 Line 130 is suitably connected to line 102 in said module "C" by means of connection devices 101. In this single-circuit system, outlet 117 on the dialyzer can be suitably connected to a waste system of one or another arrangement. By providing separate delivery arrangements for dialysate solution, whether open or closed circuit, the apparatus is much easier to use for different users, especially if the respective modules "A", "B" and "C" are designed so that they can be easily carried, as module "B" can be used where suitable water source devices exist, while the part where recirculation is used can be used otherwise.

Whether you use supply module "A" or "B",

then the voltage of the circuit connected to hemodialysis module "C" will be the same. Dialysate solution that is fed in via line 102 is fed to heating devices 103 where the solution is heated, if desired, to approx. 37°C. Such heating is carried out to give the solution a suitable temperature so as to prevent excessive heating or cooling of the blood during the heat exchange with the dialysate solution and to prevent hemolysis. Hot dialysate solution flows from the heating devices 10 3 to the temperature meter 104.

In said temperature meter 104, the temperature of the dialysate solution is measured, while devices are provided to transfer the temperature of the dialysate solution into a transmittable signal. This temperature signal is transmitted by means of suitable transmission devices to a temperature control circuit, which compares the temperature signal with a fixed value and develops a resulting control signal which is transmitted by means of suitable signal transmission devices to heating device 103 so that the necessary heating is obtained to maintain the previously set value. In this way, the heating rate of the dialysate solution by means of said heating devices will be adjusted in relation to the temperature measured in meter 104, as follows. that you have a predetermined temperature of the dialysate solution at all times.

In addition to the control function that one has

in meter 104, the signals can also be used to display the temperature visually on a screen, or linked to an audio alarm system if the temperature exceeds certain limits.

From temperature meter 104, the solution will be led to meter 105 where the conductivity of the blood is measured. In said meter 105, devices are provided for measuring the electrolyte conductivity in the dialysate solution together with devices for converting the measured value of the conductivity into a transferable signal. With the help of other devices, this can be transferred to a suitable visual screen where the measured conductivity can be indicated. Such an examination of the conductivity is desirable to ensure that the dialysate solution has the appropriate level with regard to salinity and other electrolyte properties, so that vital components of the blood are not lost to the dialysate solution by ion diffusion over the mass transfer surfaces in the dialyser.

From the conductivity meter 105, the dialysate solution will be passed through a negative pressure regulator/flow control device 106. This device has options for adjusting the negative pressure and measuring it. As stated earlier, negative pressure is used on the dialysate solution side during the mass transfer in the dialyzer to produce water removal from the blood by ultrafiltration. The negative pressure on the dialysate solution can be adjusted in device 106, e.g. by means of an elliptical flow valve or a needle valve which regulates said negative pressure and regulates the flow of dialysate solution through the circuit.

Placed after said negative pressure regulator device 106 are measuring devices 107 for said pressure. This measuring device can suitably include a gauge for a negative pressure which is connected to a visual screen where the pressure can be read directly. This negative pressure meter can also be operated together with said negative pressure adjustment device 106, whereby the negative pressure on the dialysate solution can be kept at a predetermined level.

The dialysate solution taken from the pressure gauge 107 is led in line 108 to line 109 and from this through the dialyzer itself 112. In this, the dialysate solution is led in indirect mass transfer conditions with blood containing impurities that flows through the dialyzer from the blood flow circuit consisting of blood in lines 119 and 121 As a result of the mass transfer in said dialyzer, impurities from the blood will be transferred to the dialysate solution which is then carried away in line 113. From this, the dialysate solution will be led in line 114 to the blood leak detector 115. This detector contains a device for detecting any blood in the dialysate solution, as well as devices to transfer any blood leakage into a transmissible signal. The signal can possibly be transmitted using suitable devices to a visual screen or an audio alarm system. This blood-stained vector is provided to ensure that only a direct mass transfer occurs, i.e. a transfer by diffusion and osmosis across the dialyzer's transfer parts, i.e. that no direct leakage occurs between the respective fluids in the dialyzer.

After passing through the blood leak detector 115, the dialysate solution is pumped by means of the peristaltic pump 116, which functions so that the dialysate solution is passed through the current circuit, and the resulting pumped dialysate solution is taken out from module "C" in line 117.

In the circuit described above, a side branch 110 is provided where regulating devices 111 are provided. The purpose of this arrangement is possibly to be able to divert the dialysate solution from line 108 into line 114 so that part of the solution bypasses the dialyzer 112. The regulating devices 111 is arranged and constructed so that the dialysate solution is diverted through line 110 and bypasses the dialyzer 112 only when the dialysate solution is not suitable for dialysis. To achieve this, the regulator devices 111 will usually be connected to one or more of the temperature meters 104, the conductivity meter 105, the pressure meter 107 and the blood leak detector 115, so that the dialysate solution is diverted when it has one or more properties that exceed permissible limits or when blood leakage is detected in the detector 115.

Fig. 2 shows a perspective sketch of a compact: portable hemodialysis system of the type shown in fig. 1. Corresponding system elements have the same numbering in fig. 1 and 2.

As shown in fig. 2, hemodialysis module "C" is placed in a suitcase-like box. This consists of an upper and lower part which are hinged together, and when__the device is not in use, the upper and lower part are held together by means of a suitable locking arrangement (not shown). When the device is closed, it will be very compact, and can e.g. measure 50 cm in length, 30 cm in width and 15 cm in height. In practice, the case itself will be made of a lightweight material such as aluminium, so that the weight of the device is kept sufficiently low for it to be easily carried, e.g. in the order of 10 kg.

The device itself-- is designed so that it can be operated using normal 120/220 volt alternating current, which is supplied to the device by means of wire l80 which is fed into the lower part of the device. In this lower part, the energy required to drive the various measuring instruments and light signal systems will be taken out with the help of a direct current source which is placed just below the top plate on the lower part.

As shown, the apparatus is placed on a box 193. The distribution system 126 is placed on a higher shelf, and the dialysate concentrate container is placed on the floor next to the box 193. Together with the hemodialysis system, there are recirculation devices for the dialysate solution, and this includes a container 123 as well as supply and return lines 124 and 125 respectively. The container 123 is placed on a small rolling device 170 so that it can be easily carried or transported.

The blood flow circuit in fig. 2 consists of the wire segments 119, 172, 176, 173 and 121 which can be of a common type, e.g. made from transparent polyvinyl chloride, polyurethane or a silicone elastomer. Impure blood is taken from the patient, e.g. by means of an arterio-venous fistula and is led via line 119 to the peristaltic blood pump 120, which can be of the type that e.g. is described in US Patent Application No. 720,672 filed September 7, 1976 and submitted by J.T. Hutchison. Peristaltically pumped blood from the blood pump 120 is led via line 172 to the artery drop chamber 177 - The pressure in this chamber is measured by means of a transfer line 178 which connects the chamber 177 with measuring devices 179 - From said chamber the blood is led in line 176 through the dialyzer 112. This can be suitable of the type where you have parallel hollow fibers and can e.g. have 1.5 m 2 surface area for membrane mass transfer. In the dialyzer, impurities in the blood such as urea, uric acid and creatine will diffuse from the blood through the membrane and into the dialysate solution. Water removal from the blood is performed by means of ultrafiltration, which is produced by applying up to a negative pressure of 350 mm Hg on the dialysate solution side of the membrane, and up to a total pressure difference between the two sides of 500 mm Hg. Typically, from 1 to 2 liters of water will be removed during the dialysis treatment.

From the dialyzer 112 which is suitably placed

on the side of the apparatus by means of a hoop and a rod, the purified blood will flow in line 173 to the vein drop chamber which has devices 122 for detecting air leaks, and these devices serve to be able to detect the possible presence of gas bubbles in the flowing blood through the venous drip chamber. There is a transfer line 174 from the venous drip chamber to the venous pressure gauge 175 which consequently measures the pressure in the venous drip chamber. From said chamber, the purified blood will be returned to the patient in line 121.

The dialysate solution flow circuit shown in FIG. 2 can be either an open circuit (ie, a single pass for the flow) or a closed circuit, either using the portion recycle container 123 or the distribution system 126 as a source of the dialysate solution. In fig. 2, the system 126 is shown operatively connected to hemodialysis module "C", so that in this case this is adapted to an open circuit, i.e. a single passage of the dialysate solution.

In this arrangement, the dialysate solution circuit will

consist of the wires 130, 109, 114 and 117, which can also be made of commonly known material, e.g. polyvinyl chloride, polyurethane or silicone rubber.

The distribution system 126 for this type of review of the dialysate solution is described in more detail below, and is provided in a small closed device. The system is designed so that it can be operated on normal 120/220 volt alternating current, which is supplied to the system by means of wire 194 which is fed into the device at the back. Water is supplied to the system through line 129 which can be connected to common known water supply devices, e.g.

a normal spring or similar. Dialysis concentrate is supplied to the system from container 127 and flows from this through line 128 to system 126 to be mixed in a predetermined ratio with water from line 194 so that dialysate solution for hemodialysis is produced. The dialysate solution is taken out from the system 126 in line 130. From line 130, the solution is passed through a series of measuring and control devices as previously described in connection with fig. 1, and is connected to a removable dialysate solution manifold 171. This can suitably be constructed as, e.g. is described in US Patent Application No. 720,673 filed September 7, 1976 by J.T. Hutchison. After the dialysate solution has been passed through a series of measuring and control devices connected to the dialysate manifold 171, the solution is passed through line 109 to the dialyzer 112 for mass transfer of impurities from the blood to the solution.

The used solution is withdrawn from the dialyzer 112 in line 114 and fed to the peristaltic dialysate solution pump 116 which is described in more detail below. From pump 116, the solution is led out of the system through line 117. As mentioned earlier, line 117 can suitably be connected with a drain or other devices to receive the impure dialysate solution.

If one has a closed circuit for the dialysate solution and uses a recirculation, then solution is fed from container 123 through line 124 and fed into the dialysate manifold 171 instead of through the previously described line 130 which was in connection with system 126. For the return of solution to container 123, line 117 can be connected by means of suitable devices (not shown I to return line 125 which goes down into container 123. In this way, the solution from container 123 will be taken out again via line 124 and thus flows through the dialysate solution current circuit connected to the hemodialysis system "C" in the same way as described earlier in connection with the system 126, but this time so that the used dialysate solution is returned via lines 117 and 125 to the container 123.

On the upper part of the apparatus, a series of control lights 190 are provided which indicate the state of the system at any given time. The top light—in the series—is green and will illuminate when all components of the system are operating within acceptable limits. The lowest light in the series is switched on when the dialysate solution bypasses the dialyzer itself as described earlier in connection with fig. 1, because one or more of the measured properties of the solution lie outside the permitted limits. The remaining lights are warning lights that are switched on when one of the measured properties of the dialysate solution is outside the permitted limits. Light is provided for temperature, conductivity, vein pressure which is measured by pressure gauge 175, arterial pressure which is measured by pressure gauge 179, the dialysate solution's negative pressure, blood leakage into the dialysate solution and air leakage or the presence of gas bubbles in the blood stream. The measuring devices in the system are also connected in such a way that an audio alarm system 189 is simultaneously switched on when one or more of the measured parameters goes outside the permitted limits.

Also located on the upper panel is a row of switches 188. The top switch is an audible alarm override switch, which when the corresponding panel button is pressed, will turn off the alarm devices 189. The next switch is an alarm override switch, which when pressed will turn off the of the blood leak and air leak alarms. The next switch is suitably illuminated to indicate normal operation of the system. The bottom switch has two positions that regulate a temperature for heating the dialysate solution. The two positions on this switch correspond to a solution temperature of 36.8°C and 38°C, which regulates the heating rate for the dialysate solution by means of heating devices that are placed in the dialysate manifold. These devices regulate the temperature of the solution to the given level. Under normal operating conditions, you will have the switch in a position corresponding to 36.8°C, if the temperature in the room falls below normal room temperature, you will set the switch at 38°C to maintain blood that is carried in indirect heat exchange conditions with the dialysate solution in the dialyzer at a suitable normal body temperature.

Located next to the audible alarm 189 and the safety control switches 188 on the panel on the upper part of the apparatus are dials 191 and 192. The upper dial 191 provides a continuous measurement of the venous pressure as measured by pressure gauge 175. The lower dial 192 is connected to the respective "control devices for temperature, conductivity, negative pressure and arterial pressure, and the particular parameter desired to be controlled can be selected by means of switch l8l which is located on the top panel of the lower part of the apparatus. The series 18.1 are each individually individual switches where

can select each of the aforementioned parameters, so that by pressing an appropriate button connected to switch l8l, transmission of a signal from the measuring devices connected to this specific parameter is started, whereby the measured value is instantly transferred to a disc or screen . 192.

Located directly above the switches 181 is a group of four switches 182. These switches include, among other things, a switch to turn on the dialysate solution pump 116, a switch to adjust the set limits for the measured parameters, which can be used to avoid setting both the sound and light alarms during heating and start-up of the system, a switch which, when pressed, indicates the given points for the various measured and regulated operating parameters for normal dialysis operation, as well as a switch which deactivates the various measuring and control devices , like for example. can be used when cleaning the system.

Placed above the aforementioned switches is a blood pump speed control device 183 which is connected to a variable motor speed control device which, by means of drive devices, is connected to the blood pump part 120 for rotation of this, e.g. with speeds varying from 50 to 400 rpm. Furthermore, there is a fuse 187, a conductivity meter calibration unit 184 which is used to adjust the conductivity reading on the numeric display 192 to calibrate the conductivity measurement system with respect to a reference data of known electrolyte conductivity,

a voltage meter 185 which indicates the voltage entering the system through line 180, as well as calibration devices 186 for the blood leak detector, and this can be used to adjust the level at which the detector begins to detect a presence of blood in the dialysate solution flowing through the part""

of the circuit that is after the dialyzer 112.

Fig. 3 is a schematic block diagram of a distribution system 126 that can be used in conjunction with the system shown in Fig. 1 and 2. Water from a suitable source such as ordinary tap water is introduced into the system 126 through line 129. Before the water is supplied to the system it may be subjected to filtration, deionization or reverse osmosis to remove unwanted constituents from the water (these devices are not shown). Suitable devices for carrying out the aforementioned water treatment steps are well known and form no part of the present invention.

Water flowing into the system 126 through line 129 is first passed through a pressure shut-off valve 150 which is adapted to shut off the flow of water through line 129 if the water pressure exceeds a predetermined upper limit or drops below a predetermined lower limit. This valve is of the usual type, and suitable upper and lower limits can e.g. be 7 and 1.3 kg/cm 2 respectively. These limits are used to avoid possible damage to the system due to either too high or too low water pressure.

From valve 150, the water will pass through a flow control valve 151 which functions so that it maintains a constant flow of water in line 129. This control unit can e.g. be such that it maintains a constant pressure difference across a control valve. In this regulatory mechanism, e.g. an internal diaphragm-actuated control valve is placed so that it is affected by the pressure in the inflowing liquid on one side and on the other by the pressure of the liquid and any spring devices. In this way, variations either in the pressure on the upper or lower side of the valve will disturb the balancing forces on the diaphragm, whereby the control valve will open or close as needed so that a fixed pressure difference is maintained across the control valve. During operation, the control valve will be set so that it supplies a water quantity of between 500 and 600 ml of water per minute in line 129. A suitable current-regulating unit for this purpose is e.g. Brooks Model Series 8800 manufactured by Brooks InstrumentaDivision

of Emerson Electric Company, Hatfield, Pennsylvania.

The water in line 129 is then led to the heating element 152, where the temperature is raised to approx. 32.5°C. The heating element can be of any appropriate type for this purpose.

As mentioned earlier, the dialysate solution that is passed through the dialyzer must have fairly close to normal body temperature of 37°C

to avoid too much heating or cooling of the blood due to a heat transfer in the dialyzer. Consequently, the water in line 129 must be heated to a level which approaches, but is somewhat lower than, the temperature which is ultimately desirable for the dialysate solution which is formed by mixing water and dialysate concentrate. In this way, the dialysate solution that is carried out of the distribution system will only require a small degree of additional heating in dialysis module "C" in fig. 1 and 2.

For this reason, one can reduce the size of the heating devices used in module "C" to heat the dialysate solution. In order to make efficient use of the heating element 152, this can conveniently be a heat exchanger where the water in line 129 is led in indirect heat exchange conditions with used dialysate solution from the dialyzer which is led through line 117, whereby heat is recovered from the used dialysate solution. Such a heat exchanger arrangement will reduce to a minimum the energy required to raise the temperature of the inflowing water to the desired temperature, whereby a relatively small heating device can be used in the distribution system.

The water supplied to the distribution system in line 129 will usually contain entrained and dissolved gases, this may be the result of aeration and introduction of gas in leaks in the water supply pipes and in various connections. As the temperature of the water in line 129 rises quite significantly, e.g. from 2 to 32.5°C, then any gases that were dissolved in the water introduced through line 129 will be released from the water leaving the heating element 152, which is due to the fact that the solubility of gases in liquids usually decreases as a function of the temperature.

As a result, the heated water leaving the heating element 152 will contain a significant component of released gases.

Generally, the presence of gases in the dialysate solution that is fed to the dialyzer will _significantly_ weaken the safety and efficiency of the hemodialysis treatment. Consequently, the distribution system 126 will be provided with venting devices to remove soluble gases from the heated waste water before it is carried on. From the heat exchanger 152, the dissolved water containing liberated gases will be transferred into line 129 in an amount of e.g. 550 ml/min., a temperature of from 30 - 35°C and a pressure of 1.5 - 7 kg/cm<2> and is then fed to the first storage tank 153. This tank has a volume of from 150 - .400 ml and a cylindrical vessel with a diameter of 5 cm and a height of approx. 17.5 cm. The tank 153 is equipped with venting devices such as valve 154 where released gases from the heated water can be released, whereby a partially deaerated water is formed. In addition to serving as a venting valve for released gases, can overhead valve 154 also function as an overflow to keep the liquid level in the tank below? a predetermined level. For this purpose, e.g. valve 154 be located approx. 13 cm above the bottom of the tank. In connection with its function as an overflow, the valve 154 can be equipped with a non-return valve (not shown) to prevent the backflow of water into the first tank 153-

During operation, flow control device 151 will be set so that it provides a water flow that is from 10-20% above that required in the dialysate solution flow circuit. Thus, flow control valve 151 can be adjusted so that the water flow in line 129 is set to 550 ml/min., so that the excess of liquid is up to 40 ml/min. and this can flow out via valve 154. The purpose of providing a small excess of heated water to the first tank 153 is to ensure that there is always sufficient water in this tank during operation. Without supplying an excess, the flow of heated water to the first tank would have to correspond to the water flow in the dialysate dissolution circuit, and this would be difficult to achieve in practice. By providing an overflow to keep the liquid level in the first reservoir below a predetermined level, and by adding a 10-20% excess of water to the tank, then

this excess will enable a corresponding 10-20% variation in the flow rate of the dialysate solution which is carried around the dialysate solution circuit by means of the pump devices. In this way, variations in the flow of the dialysate solution from the pump in said circuit can be adjusted by ensuring that a full supply tank for dialysate solution is always ensured. Nevertheless, in certain embodiments of the present invention, it will be possible to tolerate variations in the flow rate of dialysate solution in the hemodialysis system, so that an excess of liquid to tank 153 and the use of an overflow 154 is not necessary.

Partially vented water from tank 153 is led out of this through line 155. This line has adjustable current limiting devices 156 to possibly reduce the pressure on the partially vented water that flows through the line, thereby further releasing gas and to form low-pressure water where the released the gas is dispersed. Suitable current limiting devices for this purpose are a Neutrol needle valve, 3 mm in size, EPL 10B manufactured by DeUitrol Corporation, Bellwood, Illinois.

These devices are adjusted so that you get a significant pressure drop in the liquid, e.g. to 600-750 mm Hg as the liquid comes out of said limiting devices, which enables a water flow in line 155 of from 600-750 ml/min. The purpose of said devices 156 is to reduce the pressure

in the liquid that flows in line 155 is to partially put the liquid under vacuum and thereby release further quantities of soluble gases. After the limiting devices 156 is a vacuum adjusting device 157 which can suitably include a conventional vacuum valve. Such measuring devices mean that the pressure on the water from said devices can be easily determined, so that any adjustments can be made in devices 156 so that the pressure in the liquid is kept at

a predetermined level.

The end of line 156 is attached to the intake of a vacuum pump 152. As the term is used here, a vacuum pump is understood to mean a positive displacement pump that is adapted so that it can operate from a vacuum, i.e. that it can receive liquid at pressures that are under normal atmospheric pressure, and pump the liquid further at higher pressure. Pump 158

is preferably of a type that is magnetically coupled and thus leak-proof and also does not pollute the water it pumps. A suitable pump is the Model 12-50-316 pump manufactured by Micropump, Incorporated, Concord, California. As mentioned

will pump 158 operate in partial vacuum and pump 600-750 ml of water per minute by pressing e.g. 7^0 mm Hg negative pressure in the liquid fed into the pump's inlet side. From an inlet pressure of 600-750 mm Hg, the liquid in pump 158 will be put under a pressure corresponding to approx. normal atmospheric pressure. A line 159 is attached to the outlet end of vacuum pump 158 for carrying on the water where the released gas is dispersed. A new reservoir tank 160 is attached to the other end of line 159 for receiving this water. This tank is also equipped with ventilation devices for extracting the released gas, whereby total aerated water is produced. The ventilation devices can suitably include a ventilation pipe 167 from the reservoir, and a manually closable valve 168 can be placed in this.

Tank 160 can be of the same size as tank 153 so that the second tank will also be a cylindrical vessel approx. 5 cm in diameter and approx. 17.5 cm in height. Although first tank 153 and tank 160 may be provided as separate tanks,

then they can also be placed concentrically where a smaller second reservoir tank is placed inside a first reservoir tank. Such a concentric location will mean that the distribution system 126 can be made relatively small and compact. From said second tank 106, the aerated water will be transferred through line 162 b/li to distribution devices.

In order to improve the removal of dissolved gases in the above devices, a line l6l is provided which connects tank 150 with tank l6Q, and through which part of the vented water can be recycled from the second tank to the first tank. Such a recirculation line is not an essential feature of the venting system, but it is desirable to use it in practice to improve the removal of soluble gases in the venting system. As mentioned earlier, the water flow in line 155 can be from 600-750 ml/min., and this will consequently also be the water flow in line 159, while through line l6l you can recycle from 20-50% of the water supplied to tank l60. The flow of deaerated water which is thus taken out from another reservoir tank, can e.g. be of the order of 510 ml/min. If one uses a recirculation line l6l, the flow rate of water in line 159 will be greater than that required for the withdrawal of vented water through line 162, as the water flow through line l6l always goes from the main reservoir tank l60 to the first tank 153-As mentioned previously approx. 20-50% of the water fed into tank l60 will be recycled to tank 153, and the water will then be recycled through the entire system again so that a new aeration can take place before the water returns to tank l60.

Both tank 153 and tank l6o are vented to the atmosphere, but tank l60 is equipped with a closable valve, e.g. a manually closable valve 168 which is placed in vent pipe 167. Provision of a closable valve is highly desirable as this enables a draining of the first and second tanks when the distribution system is out of operation. A withdrawal is carried out by emptying tank l60 and then tank 153.

To carry out this tapping, the manually closable valve 168 in line 167 will be closed, after which the water in line 129 will be shut off together with vacuum pump 158, while maintaining the pumping devices for dialysate solution in the circuit for this solution. When this pump is in operation, the liquid content of tank 160 will be taken out through line 162. When the second tank is emptied, the liquid in the first tank will be drawn over to the second tank via line l6l due to the pressure difference that occurs between the tanks .

Via line 162, the aerated water from tank 160 will be led into the mixing valve 163. In this, the aerated water will be mixed with dialysate concentrate in a predetermined ratio so that a suitable dialysate solution for hemodialysis is formed. Dialysate concentrate is supplied to the mixing valve from dialysate tank 127, from which the concentrate is removed through line 12 8 by means of pump 164 which leads the concentrate to. valve 163. After the water and dialysate concentrate have been mixed in valve 163, the dialysate solution will be fed via line 165 into the conductivity meter 166. The conductivity meter 166 can be connected to a visual reading screen that indicates the conductivity of the dialysate solution, so that the patient or the user of the system can easily can read variations in the conductivity and accordingly adjust the speed of pump 164 so as to change the ratio between water and dialysate concentrate that is mixed, so that the value for electrolytic conductivity in the dialysate solution reaches the desired value. Alternatively, the conductivity meter 166 can be connected to dialysate concentrate pump 164 , for example by means of a feedback circuit which functions so that it adjusts the speed of pump 164 in relation to deviations in the desired electrolytic conductivity so that this is maintained at a predetermined value. The mixing ratio between vented water and dialysate concentrate in mixing valve 163 can suitable is put on e t volumetric ratio of approx. 34:1, which corresponds to a quantity of water in line 162 of 510 ml per minute, and a quantity of dialysate concentrate in line 128 of 15 ml/min., so that 525 ml/min is formed. of dialysate solution in line 165 and this will have a temperature of from 30-35°C and a pressure of approx. atmospheric. From the conductivity meter 166, the dialysate solution is led out of the distribution system via line 130 and transferred into the hemodialysis module as previously described.

An advantage of the distribution system described above,

is that it provides dialysate solution for a hemodialysis system under essentially the same conditions with respect to pressure, temperature and conductivity as any dialysate solution that may have been supplied to the hemodialysis system from a disposable container. The fact that the dialysate solution essentially has the same properties regardless of how it is produced means that the hemodialysis module can quickly and easily go from one source to another without having to make changes to the device or its operating conditions.

Fig. 4 is a section through a peristaltic pump of the type used in a system as shown in fig.g. 2, and the drawing shows the dimensional characteristics of the pump. As shown

pump 116 is placed in a small rectangular box. 2Q0.

As shown, pump 116 includes a pump head 201. This has a raised cylindrical spindle portion 203 which is adapted to fit on a rotatable shaft which is connected to a drive motor which drives the pump itself. In this way, the pump head 201 will be able to rotate around a fixed axis. Four peripherally placed rollers 202a-d are suitably attached to the pump head 201.'

The part of the dialysate solution circuit which is connected to the pump includes pipe segments 114 and 117 which are passed through the wall of the box 200 and are fixed in suitable couplings 204 and 205 respectively. The couplings 204 and 205 include flanged female couplings 206 and 207 respectively. For attachment to the specified female connectors, there are male connectors 208 and 209. The latter are held in position by means of inwardly directed flanges 210 and 211 that go around the flanged parts of the respective female connectors 206 and 207, so that the male connectors can be easily disconnected from the female connectors by pressing

the protruding parts of the male couplings, thereby freeing the inwardly aligned flange parts. The male couplings are provided with tapered ends 212 and 213 which are attached to the respective ends of a flexible and elastic tube section 214 through which the dialysate solution is pumped. The attachment devices described above enable the end segments to be attached to said flexible and elastic pipe section 214 so that the pipe lies in tension around the pump head and is simultaneously touched and pressed by at least two of the circumferentially positioned rollers, these being mounted so that a longitudinal movement of the compression points along the tube during rotation of the pump head, whereby the dialysate solution is pushed through the tube.

The dialysate solution pump shown in fig.

4 represents a great improvement in that essentially a constant flow of dialysate solution is provided in the circuit despite variations in the negative pressure that occurs in the dialysate solution due to varying requirements with regard to ultrafiltration of water from the patient's blood. As a result of this, the dialysis effect will significantly

degree be improved, and the pump maintains a steady flow of dialysate solution even at high negative pressure differences,

so that the dialysis treatment can be carried out within a relative

short period of time even at high negative pressure levels.

The present peristaltic dialysate solution pump consists of four rollers placed on a base part,

and each of the aforementioned rollers has a maximum diameter D as shown in fig. 4 of between 6 and 18 mm and circumferentially placed at an angle of 90° in relation to the other' rollers and with a radial distance P between the axes of the rollers and the fixed axis of the pump head varying from 12.5 - 37.5 mm. The improvement also requires a flexible, elastic tube pump section with a length measured from the two points where it is attached varying from 17 - 27.5 cm, a wall thickness from 1.25 - 3 mm and an internal diameter from 4.5 - 9 mm, as well as drive devices which are connected to the pump head so that it can be rotated at a speed varying from 150-400 rpm.

Although peristaltic pumps have previously been used to pump dialysate solution in hemodialysis system solution circuits, by means of previously known methods it has not been possible to achieve an essentially uniform flow from the pump under varying conditions with regard to the negative pressure of the dialysate solution. The pump of the present invention represents a significant improvement over the peristaltic pump described in US Patent Application No. 720,672, filed September 7, 1976 by J.T. Hutchisson, which will be shown in detail in what follows.

The peristaltic pump mentioned in the previously mentioned US patent application is suitable for pumping dialysate solution in a hemodialysis system, and consists of three rollers placed on a rotatable pump head, and each roller has a diameter of from 6-18 mm and they are circumferentially positioned at an angle of 120° in relation to the other rollers, and the radial distance between the axis of the rollers and the fixed axis of the rotatable pump head varies from 12.5 - 30 cm. The previously known pump uses a flexible, elastic pipe pump section with a length measured as the length of the pipe between its two attached points varying from 15 - 17 cm, a wall thickness from 0.6 - 2.5 mm and an internal diameter from 4.5 - 6 mm , and where driving devices are connected to the rotatable pump head so that it can rotate at a speed varying from 200-600 rpm.

Although the pump according to the present invention is structurally somewhat similar to the pump from US patent application no. 720,672, the pump according to the present invention stands out due to several structural differences, which means that you get a significant improvement with regard to the flow rate of dialysate solution regardless to variation in the negative pressure that may occur in the dialysate solution. Mentioned significant differences in the present peristaltic pump compared to the pump from US Patent Application No. 720,672 include providing a greater number of rollers, and the rollers have a convex surface profile compared to the flat profile found in the rollers of the previously known pump , as well as providing a longer flexible and elastic tube pump section.

In order to be able to fully understand the advantages achieved with the help of the present peristaltic pump, it is first necessary to look at the effects a variation in the negative pressure in the dialysate solution has on the flow rate of the dialysate solution as this manifests itself when using the aforementioned previously known pump. In this pump, a flexible, elastic tube with dialysate solution in tension is placed around a peristaltic pump head and said tube section is simultaneously touched and pressed together by at least two circumferentially positioned rollers. The rollers are mounted so that there is a longitudinal movement of the compression points along the tube when the pump head rotates, whereby the dialysate solution is pushed forward through the tube. At the contact points between the rollers and the pipes, the rollers will compress the pipe and change its cross-section in relation to the normal circular cross-section. The degree of reduction in the cross-sectional area of the tube at the point of compression with the roller is usually characterized as the degree of closure of the flexible, elastic tube.

The pumping effect of a peristaltic pump is a function of the degree of closure in the pipe and the liquid volume that is in the pipe between two adjacent compression points. This liquid volume is again a function of the local cross-sectional area of the pipe along its length between the two adjacent compression points, and this is again dependent on the degree of closure and the length of the pipe between the adjacent compression points. The local cross-sectional area of the pipe segment between adjacent rollers depends on the degree of closure at the compression points themselves, as the compression of the rollers tends to flatten the tube3 and this flattening of the tube also takes place at a certain distance from the rollers themselves. The pumping effect of the peristaltic pump is even more directly affected by the degree of closure in the tube section due to the fact that if there is a less than total closure of the tube, this enables a back-flow of liquid from the part of the tube that lies beyond the rollers to the part of the pipe that lies in front of the rollers, and this happens through the unclosed cross-sectional area in the pipe at the point of compression. For this reason, the previously mentioned pump has used a relatively short piece of pipe in order to obtain a relatively high tensile stress on the piece of pipe that is around the pump head, whereby a total closure of the pipe is achieved at the contact points between the pipe and the rollers. Such a total closure of the pipe at the compression points between the pipe and the rollers has been used to obtain maximum pumping power and to prevent a backflow of liquid from the pipe parts located after the pump to the pipe parts located in front of the pump, thereby achieving an essentially positive forward displacement of liquid through the pump.

Despite this total closure of the tube at the contact points between the rollers and the tube in the previously known pump, which should give a high pumping effect, it has been found that the liquid flow of dialysate solution provided by this previously known pump drops drastically with increasing negative pressure. Such a dependence between the flow rate and the negative pressure represents serious operating disadvantages for the aforementioned previously known pump, when this was used to pump dialysate solution in a hemodialysis system, because it is generally desirable to be able to vary the level of the negative pressure, in the dialysate solution that is pumped through the dialyzer partly from patient to patient, and for a given patient from time to time. The purpose of being able to vary the negative pressure on the dialysate solution is to adjust the pressure-driving force to obtain a varying mass transfer of water from the blood through the dialyzer's transfer surface to the dialysate solution, so that one ensures an essentially complete removal of water from the blood during dialysis treatment. The previously described pump responded to an increasing negative pressure with a drastic drop in the amount of dialysate solution pumped through the pump. This resulting reduction in the flow rate of the dialysate solution in the actual circuit of the hemodialysis system weakens the overall effect of the treatment and requires a significant increase in the treatment time to obtain the desired removal of impurities from the blood being treated.

The reason why you get the above-described drastic reduction in the flow rate of the dialysate solution when the negative pressure increases on it is connected, ironically enough, with the fact that you completely close the tube at the compression points, which was actually used to increase the pump effect. As mentioned above, the pipe itself in the pump is placed in tensile stress around the rollers, and this results, as mentioned above, in a flattening of the pipe's cross-sectional area not only at the contact point itself, but also at a certain distance from this to both sides. The degree of this flattening along the pipe is a function of the degree of closure and how strongly the pipe is flattened, and the effect of this flattening is greatest when the pipe is completely closed at the contact point between the pipe and the roller. IN

such a fully closed pump system, an increasing negative pressure on the liquid inside the pipe will cause an increasing

pressure difference between the pressure inside the pipe and the atmospheric pressure acting on the pipe's outer surface. This pressure difference tends to compress the pipe relative to the configuration it would otherwise have

was any such pressure difference. The pipe in a totally closed pump system is particularly susceptible to further compression due to the fact that a significant part of the pipe in the pump is already flattened to a rather large extent due to the fact that the pipe is completely closed at the contact points as mentioned above. In other words, the deformation of the pipe due to a negative pressure difference will be greater in a pipe section that is already somewhat

added in relation to a pipe having a normal circular cross-section. This compression of the tube between adjacent rollers will substantially reduce the liquid volume found in such tube segments, so that the amount of dialysate solution that is pushed through the tube with the help of the pump is correspondingly reduced. This is the main reason why you get a drastic reduction in the flow of the dialysate solution in previously known pumps, when the negative pressure on the dialysate solution is increased.

Viewed against the background of the above-mentioned disadvantages, one would assume that by using a relatively thick-walled pipe, the problems mentioned above could be avoided when the negative pressure increases, as a pipe with a thicker wall would be less susceptible to deformation due to pressure differences. Now, however, it is the case that a relatively thick-walled pipe is not suitable for use in such pumping systems, because it becomes correspondingly difficult to obtain a sufficient closure to enable efficient pumping. It is of course understood that there must be at least a partial closure of the tube at the points of contact between the tube and the rollers, because otherwise the pump system would not function at all and push the dialysate solution through the tube. The previously known pump has also used a principle that the pipe has been completely closed at the contact points between the rollers and the pipe, and this would be correspondingly more difficult if the wall thickness were to be increased. For practical reasons, previously known pumps have therefore not been able to use a wall thickness that has exceeded 2.5 mm.

In relation to the previously described peristaltic pump, a pump according to the present invention will provide a significant improvement by obtaining an essentially constant flow rate of the dialysate solution despite an increase in its negative pressure.

In relation to the above-described previously known pump, the pump according to the present invention includes four rollers placed on a pump head compared to three rollers in the previously known pump. The provision of a further roll will reduce the length of the pipe segments between adjacent rolls, so that the pipe segments between the rolls will be correspondingly "stiffer", and will have a higher resistance to deformation, like this. that the said pipe segments are to a lesser extent pressed together due to negative pressure differences than was the case with the previously known pump.

Furthermore, rollers of the type used in the present pump have a convex surface profile which is adapted for only partial closure of the tube at the points of contact between the tube and the rollers. By the rollers having this configuration, a total closure of the tube at the contact points is avoided and this results in a smaller flattening of the tube segments between adjacent rollers, making them less susceptible to deformation due to negative pressure differences. The convex the surface profile of the rollers tends to localize the deformation of the tube to a small area close to the point of compression with the roller, in contrast to previously known systems which had a -flat roller and a total closure at the very point of contact between the rollers and the tube, which resul- resulted in a significant flattening of the pipe segment at a considerable distance from the contact point itself.

Furthermore, the pump according to the present invention uses a longer piece of pipe inside the pump than was used in the aforementioned previously known pump. This will also cause the tensile stress on the pipe inside the pump to change. Generally, the shorter the piece of pipe inside the pump, the higher the tensile stress will be on the pipe, and the longer the pipe, the lower the tensile stress will be.

The previously known pump used relatively short pipe-pump segments, and this produced a relatively high tensile stress which was necessary to facilitate a total closure of the pipe at the contact points with the rollers. In contrast to this, the pump according to the present invention uses a relatively longer pipe pump segment, which gives a relatively lower tensile stress so that you only get a partial closure of the pipe at the contact points with the rollers.

Increasing the pipe length inside the pump does this

that a lower rotation speed can be used on the pump diode,

which gives a longer life for the pipe part in the pump itself by reducing the degree of contact between the pipe and the rollers, besides achieving quieter operation. To achieve the scheme

with a lower rotation speed while at the same time having to take into account the size and weight of the portable hemodialysis system, the distance between the fixed axis of the pump head and the axis of the rollers was increased as far as practically possible, whereby it was possible to obtain the necessary pipe length.

As described above, the tube in the present pump is only partially closed at the contact points between the tube and the rollers. Such a partial closure of the tube enables a constant flow rate of the dialysate solution despite increasing negative pressure on the dialysate solution being pumped. When the negative pressure on the dialysate solution increases, there will be an increasing pressure difference between the pressure on the outer surface of the tube and the pressure inside the tube, and this will to some extent deform the parts of the tube that lie between the rollers and reduce the volume of these tube segments, which which also occurs in the previously described pump system described above. In the present system, however, a deformation of the pipe also occurs at the contact points between the rollers, which results in an increasing closure of the pipe at these points. This increasing degree of closure reduces the degree of backflow of liquid, thereby increasing the pumping power. This beneficial effect of increasing closure at higher negative pressure levels has been found to fully compensate for the reduction of the volume of the pipe segments between the rollers due to said increasing negative pressure, so that these two countervailing effects are essentially balanced, thereby obtaining an essentially constant flow rate of dialysate solution from the pump despite the negative pressure increasing in the dialysate solution.

In the present invention, the pipe inside the pump must be both pliable and elastic, so that the pipe, even with continuous and varying tensile stress and compression, does not have a tendency to get fatigue breaks or cracks and so that the pipe quickly regains its undeformed shape and dimension after the roller has passed. It has been found in the present invention that it is possible to produce satisfactory pipe pieces using silicon elastomers and in particular, silicon elastomers with from 40-60 durometer.

The rollers placed on the rotatable pump head have a generally convex surface profile and a maximum diameter of between 6 and 18 mm.. At a diameter below 6 mm it becomes increasingly difficult to achieve only a partial closure of the pipe segment, which is essentially according to the present invention.

If the roller diameter exceeds 18 mm, the pipe will be too long; partially closed by contact between the rollers and the pipe, thereby lowering the immediate volumetric pumping capacity and consequently the pumping power.

The present invention requires a radial distance measured between a given roller axis and the fixed rotatable axis of the pump head from 12.5 - 37 mm. The reason for these limits is given in relation to the roller diameters stated above. If the radial distance is less than 12.5 mm,

then the rotation speed had to be increased too strongly in order to maintain a sufficient flow rate of the dialysate solution. If the radial distance is below 12.5 mm, then an excessively large length of the pipe would also be partially closed, whereby one would undesirably lower the pump's volumetric capacity and consequently the pump's effect. If, on the other hand, the radial distance is greater than 37 mm, then the length of the pipe sections between adjacent rolls would tend to be too long in relation to the size of the rolls contacting the pipes, so that these longer lengths of pipe are more exposed for deformation due to the pressure differences mentioned earlier.

The flexible, elastic tube pump section according to the present invention must have a length measured as the length of the tube between the two end points in the pump varying from 17 to 27.5 cm, a wall thickness of from 1.25 - 3 mm and an internal diameter of from 4.5- 9 mm. If the length of the pipe inside the pump, i.e. the measured length of the pipe between the connections 208 and 209 as shown in fig. 4, goes below 17 cm, so you reach a point where the pump head itself has to rotate at such a high speed that this would shorten the life of the pipe, and it would be difficult to stretch the pipe around the rotatable pump head with sufficiently low tension so that you only got a partial closure of the tube at the points of contact with the rollers. If the pipe length goes beyond 33 cm, then this will tend to be too long in relation to the pump head itself, and it will be correspondingly difficult to get sufficient tension on the pipe when it is to be stretched around the rollers so that you get sufficient closure of the pipe by the contact points with the rollers. A wall thickness of at least 1.25 mm is necessary to ensure a leak-proof pipe, as this is subjected to continuous and rapid changes in tension and relaxation, which tends to weaken fatigue fracture in pipes whose wall thickness is less. If the wall thickness increases beyond 3 mm, the pipe will be too stiff to achieve satisfactory compression of the rollers. If the inner diameter of the pipe is below 4.5 mm, then too large a part of the pipe's volume will be partially closed due to the rollers, and this will lead to a corresponding reduction of the pumping power. If, on the other hand, the inner diameter of the tube is greater than 6 mm, then the tube will tend to be too strongly deformed at high negative pressures in the dialysate solution, and this in turn will adversely affect the pump effect at such values.

The peristaltic dialysate pump according to the present invention includes drive devices connected to the rotatable pump head so that it can rotate at a speed varying from 150 - 400 rpm. These limits are set because of the requirements placed on the flow of dialysate solution in the hemodialysis system. To achieve a suitably high dialyzing effect, the flow of dialysate solution in the system must be of the order of 450 -

550 ml/min. The rotation speed of the pump will be a function of the radial distance measured between a given roller axis and the fixed axis of the pump head. The reason for this is that the liquid volume in the pipe segments between adjacent rollers is a function of this radial distance, so that when the radial distance decreases, the rotation speed of the pump must be increased to keep the flow rate of the dialysate solution in the circuit at a desired level. In the aforesaid variation range of said radial distance, i.e. from 12.5 - 37.5 mm, the rotation speed of the pump to maintain a sufficient flow of dialysate solution in the system will progressively decrease from 400 rpm. at a radial distance of 12.5 mm to approx. 150 rpm. at a radial distance of

37.5 mm.

In practice, the pipe length inside the pump according to the present invention will have a length of 17.5 -'25 cm, and the ratio between wall thickness to internal diameter of the pipe is in the range from 0.35 - 0.40 to avoid too strong load on the drive devices on the pump, while providing a pipe section with sufficient resistance to deformation with increasing negative pressure on the dialysate solution.

As shown in fig. 5, the pump head is placed in a box 200 with a supply line 114 for dialysate solution which ends in the coupling 204 described above which consists of a flanged part 206. The rotatable pump head includes a piece 201 positioned for rotation about a fixed axis and a number of circumferentially placed rollers 202a to 202c placed on said rotatable piece for independent rotation about their respective axes which are parallel to said fixed axis. The rotatable piece 201 includes a peripheral horizontal part 220 on which the roller is placed, e.g. using suitable screws or bolts. The rollers are held in position by means of a plate 221 to which the rollers can also be suitably attached with screws or bolts or the like, which will allow an independent rotation of the rollers around their own axes. The rollers 202a and 202c each have a convex surface profile so that only a partial closure of the tube is obtained at the contact points between the tube and the rollers. The rollers have outward facing flange parts 222 and 223 to keep the pipe in place on the roller during operation.

The rotatable piece 201 in the pump head has a spindle part 203 which is placed on an axis 224 of an electric motor 225 to which electric power is supplied by means of the wires 226 and 227.

Fig. 6 is a diagram showing the relationship between the flow rate of the dialysate solution (as pump capacity in ml/min., in relation to the negative pressure in mm Hg for a dialysate solution pump according to US Patent Application No. 720,672 (curve A] and a pump according to present invention (curve B). Curve A was constructed according to the practice described in the aforementioned US patent application and the pump had three rollers, each with a diameter of 12.5 .em and where the radial distance between the rollers, axis and the fixed rotatable axis was 18.5 mm. The length of pipe inside said former pump was 16.2 cm, the pipe having an inner diameter of 4.7 mm and an outer diameter of 758 mm. The drive devices were connected to the rotatable pump head which was rotated at a speed of 400 rpm.

Curve B was constructed according to the present invention with a pump with four rollers, each of which had a convex surface profile with a maximum diameter of 9.2 mm and with a radial distance between the axis of the rollers and the fixed axis of 20.1 mm. The length of the pipe inside the pump was 21.7 cm, the pipe had a wall thickness of 2.35 mm and an internal diameter of 6 mm. The pump head was rotated at a speed of 200 rpm.

As shown in fig. 6, the pump according to the present invention (curve B) gave a relatively constant flow rate of the dialysate solution, varying from 490 to 570 ml/min. ■ over a variation of the negative pressure from 0 to 350 mm Hg. In contrast, the previously known pump (curve A) gave a drastic reduction of the pump's capacity from approx. 560 ml/min., at 0 mm Hg negative pressure,

down to approx. 150 ml/min. at a negative pressure of 300 mm Hg. As mentioned earlier, a total closure of the pipe at the contact points with the rollers, together with the distance between the rollers and the pipe dimensions in the previously known pumping system, will mean that the pipe segments between adjacent rollers will be strongly flattened when the negative pressure increases, and this causes the pumping capacity to drop drastically with increasing negative pressure as shown in fig. 6. In contrast to this, the flow rate of dialysate solution from a pump according to the present invention will lie within a relatively narrow range of variation regardless of how the negative pressure varies as shown by curve B. As shown on curve B, there is a slight lowering of the flow rate at approx. 60 mm Hg negative pressure, after which the mari gets a slow increase in the flow rate to approx. 200 mm Hg negative pressure and then Again a certain. decrease in the flow rate when the negative pressure increases

beyond 200 mm Hg. These variations can be explained based on the degree of closure and the degree of pipe deformation within these negative pressure areas. From 0 to 6'0 mm Hg negative pressure, an increasing negative pressure will result in a slight deformation of the tube segments between the rollers so that the flow of dialysate solution through the pump drops somewhat within this range of variation. When the negative pressure increases beyond 60 mm Hg, this will cause an increasing degree of closure of the pipe at the contact points at the rollers,

and this results in an increase in the pump effect which cancels out the negative effect mentioned earlier so that you slowly get an increasing flow of dialysate solution as the value of the negative pressure approaches approx. 200 mm Hg. When the negative pressure increases beyond this, the effect of a decreasing liquid volume in the pipe sections between the rollers will tend to increase in relation to the improvement you get with the help of increasing pumping power, so that the curve again decreases somewhat. Despite large variations above the negative pressure, curve B shows only a 7.5% variation from an average flow rate of 530 ml/min. within an area where the negative pressure thus varies from 0 to 350 mm Hg. In contrast, the previously known pump shows a drastic drop of approx. 73% in terms of dialysate solution flow when the negative pressure varies from 0 to 300 mm Hg. The curves in fig. 6 clearly shows which improvement is achieved by means of the present pump in relation to the previously known pump.

Fig. 7 shows a roller type that is well suited to the present invention. The rollers have a contact surface 300 against which the pipe lies during operation of the pump as shown in fig. 4. The contact surface 300 has a convex surface profile which provides a partial closure of the pipe when it is in contact with the roller. As used here, "generally convex surface profile" is understood to mean that the surface contour of the contact surface taken along a radial plane that passes through the axis of rotation generally has a convex shape, i.e., that. the diameter of the roller is larger in the middle than at each end. The roller has a maximum diameter D measured in a plane far perpendicular to the roller's rotation

St

sion axis, from 6 to 18 mm, e.g. 9.1 mm. The height E of the roller for the aforementioned maximum diameter D of the roller is approx. 14.8 mm. As shown, the rollers have flanged end segments 301 and 302 which serve to hold the pipe in place in contact with the roller's contact surface 300. The roller is equipped with an axis 303 which passes through a central passage in the roller. The axis 303 consists of flattened end parts 304 and 305 which hold the roller in place on the longitudinal rotatable axis.

In this way, the rollers can be mounted on the rotatable pump head for independent rotation around their own axes which are parallel to the fixed rotatable axis, e.g. by mechanically attaching the flattened end parts 305 to the axis of the pump head itself. In practice, the rollers can be made of any suitable construction material, but it has been shown in practice that polymeric materials are highly preferred due to their low surface friction so that minimal wear is obtained on the pipe in contact with the rollers.

Fig. 8 shows an alternative design of a roller that can be used in the present invention. This roller has a contact surface 306 with a convex surface profile. The roller consists of flanged end parts 307 and 308 to hold the pipe in place in contact with the roller during operation. Axis 309 extends through a central hollow in the roller and includes end members 310 and 311 to hold the roller in place on the rotatable axis. The roller has a maximum diameter of 6 to 18 mm. The roller in fig. 8 differs from that shown in fig. 7 in that the former has a contact surface formed by means of a bilinear tapering convex surface profile, while the latter has a smoother convex surface profile. Both rollers have a convex surface profile so that you only get a partial closure of the pipe upon contact with the rollers.

Although preferred embodiments of the invention

have been described in detail, then it is obvious that other embodiments and variations can be included without thereby abandoning the intention of the invention as this appears from the subsequent claims.

Claims (9)

1. Apparatus for providing a continuous flow of water with an elevated temperature to hemodialysis distribution devices where said water and a dialysate concentrate are mixed in a predetermined ratio so that a dialysis water solution is formed for hemodialysis, and where said device includes devices for supplying water as well as devices. to heat said water from said devices to said elevated temperature, and where venting devices are provided to remove dissolved gases from the heated water before it is fed to said distribution device, characterized in that the venting devices consist of: (a) a first reservoir which receives heated water from said heating devices, and where devices are provided to remove the gas which has been released from said water during said heating, so that a partially deaerated water is produced; (b) a vacuum pump; (c) a line connecting said first reservoir with the intake of said vacuum pump for supplying said partially deaerated water from said first reservoir to said vacuum pump; (d) adjustable current limiting devices placed in said line to thereby reduce the pressure on the partially deaerated water that is passed through said line in order to thereby further release gases from said water, whereby a water with a lower pressure is formed in which the released is dispersed gas; (e) a pipe which is attached to the outlet of said vacuum pump so that water can be taken from it at a higher pressure where the released gas is dispersed; (f) another reservoir connected to the other end of said pipe (e) so that the water at higher pressure can be brought to this reservoir, and where devices are provided so that the released gas can be removed from said water at higher pressure , whereby a finally deaerated water is produced; and (g) devices for transferring said finally vented water from said second reservoir to said distribution device. 2. Apparatus according to claim 1., characterized in that said devices for heating the water, said venting devices and said distribution devices are placed in a single closed container which can thus act as a supply module for dialysate solution. 3. Hemodialysis system, characterized by including an apparatus according to claim 1, and where said distribution device is connected to devices for transferring dialysate solution to a dialyzer and where devices are provided for removing used dialysate solution from said dialyzer, and where said transfer device and said outlet device form a through-flow circuit for dialysate solution, and where this is connected together with a simple peristaltic pump so that the dialysate solution is pumped through said flow-through circuit. 4. Hemodialysis system according to claim 3, characterized in that said peristaltic pump is mounted for operation in a single closed dialysis module. 5. Hemodialysis system according to claim 4, characterized in that part of said flow-through circuit for dialysate solution is placed in said closed dialysis module, and where said flow-through circuit is removably connected to said distribution devices, and where the latter is mounted for operation in a single closed container as a supply module for dialysate solution. 6. Apparatus according to claim 1, characterized by further including an overflow to keep the liquid level in said first reservoir below a predetermined level, as well as a line that connects said first reservoir with said second reservoir so that part of the finally vented can be recycled water from said second reservoir to said first reservoir in order to thereby improve the removal of dissolved gases by means of said venting device? 7. Apparatus according to claim 1, characterized in that the volume of each of said first and second reservoirs is from 150 to 400. ml. 8. Hemodialysis system according to claim 3, characterized in that said devices for heating water to said elevated temperature include "devices for bringing said water into an indirect heat exchange relationship with said used dialysate solution which is taken out from said dialyser, in order to recover the heat" in the used the dialysate solution. 9. Hemodialysis apparatus for treating blood to remove impurities from it and where the apparatus includes dialyzer devices through which the impure blood and a dialysate solution are passed in an indirect mass transfer ratio to thereby transfer said impurities from said blood to said dialysate solution, means for conveying the impure blood from a patient to said dialyzer means as well as means for returning purified blood to said patient, whereby a blood flow circuit is formed which includes a flexible, elastic tube pump section through which the blood is pumped, peristaltic blood pump devices which have a rotatable pump head which includes a part which can be rotated around a fixed axis and where on this part there is a series of circumferentially positioned rollers mounted for independent rotation around their respective axes, and where these are parallel to said fixed axis, further there are devices for attaching the end segments to the flexible , the elastic blood pump section so that the tube is in tension around said blood pump head and at the same time is contacted and fastened together by at least two of said circumferentially placed rollers, and where said rollers are mounted for longitudinal movement of the contact points along the tube during rotation of said blood pump head, whereby blood is pressed through said pipe; devices for transferring a dialysate solution to said dialyser as well as devices for removing used dialysate solution from the same dialyser, whereby a through-flow circuit for dialysate solution is formed which includes, among other things, a flexible, elastic tube pump section through which the dialysate solution is pumped, as well as peristaltic pump devices for said dialysate solution and where said pump consists of a rotatable pump head which includes a part which can rotate around a fixed axis and on which there are a number of circumferentially positioned rollers which can independently rotate around their respective axes which are parallel to said fixed axis, devices for attach the end pieces to said flexible, elastic pipe pump section so that said pipe is in tensile stress around said pump head, and where the pipe is simultaneously contacted and pressed together by at least two of the said circumferentially placed rollers, and where these rollers are mounted so that a longitudinal movement occurs a v the contact points along the tube during the rotation of said pump head, whereby the dialysate solution is pushed through said tube, characterized in that (1) the part of the through-flow circuit for the dialysate solution that is in front of the dialyzer is connected to: (a) devices for heating said dialysate solution, (b) devices for measuring the temperature of said dialysate solution, and where these devices are placed after said heating devices in addition to the fact that devices are provided to adjust the heating rate of said dialysate solution in relation to the signals you get from said temperature gauge so that you keep the temperature of the solution at a predetermined level; and. (c) means for measuring the electrolytic conductivity of said dialysate solution; (2) devices are provided to detect a blood leak in said flow-through circuit for dialysate solution, and where said detection devices are placed after said dialyzer in said flow-through circuit; (3) . said peristaltic blood pump devices, said peristaltic pump devices for dialysate solution, said heating device for said dialysate solution, said temperature gauge for the dialysate solution as well as devices for adjusting the heating of said solution, as well as said devices for measuring the electrolytic conductivity of said dialysate solution as well as said devices for detecting any blood leaks, are placed for operation in a single closed container as a dialysis module, and (41 in that a part of said flow-through circuit for dialysate solution is placed in said closed dialysis module and where this flow-through circuit is removably connected to distribution devices located in a supply module for dialysate solution according to claim 2, characterized in that said dialysis module can be connected together with said supply module for dialysate solution."""