WO2009127624A2

WO2009127624A2 - Blood treatment apparatus

Info

Publication number: WO2009127624A2
Application number: PCT/EP2009/054406
Authority: WO
Inventors: Lennart JÖNSSON; Olof Jansson; Mattias Holmer; Jan Sternby; Anders Nilsson; Per Hansson
Original assignee: Gambro Lundia Ab
Priority date: 2008-04-15
Filing date: 2009-04-14
Publication date: 2009-10-22
Also published as: CA2721248A1; US20110024353A1; US8580110B2; EP2268337A2; US9446181B2; US20140061132A1; WO2009127624A3; AU2009237690B2; EP2268337B1; CA2721248C; AU2009237690A1

Abstract

A proposed blood treatment apparatus includes : a blood treatment unit (8), a pair of fluid pumps (14, 15) and a pair of blood pumps (1a, 1b). The blood treatment unit (8) is configured to receive untreated blood and fresh blood treatment fluid, and emit treated blood and used blood treatment fluid. The fluid pumps (14, 15) are configured to pass blood treatment fluid through the blood treatment unit (8). The blood pumps (1a, 1b) are configured to extract untreated blood from a blood source (S), pass extracted blood through the blood treatment unit (8) and deliver treated blood to a target vessel (T). Additionally, the fluid pumps (14, 15) are configured to control the operation of the blood pumps (1a, 1b) via the blood treatment fluid. Moreover, a flow control means (16a) is configured to control a trans- membrane flow between the blood side (8B) and the a fluid side (8F) of the blood treatment unit (8). Hence, for instance ultrafiltration can be adjusted to a desired level in a very straightforward manner.

Description

Blood Treatment Apparatus

THE BACKGROUND OF THE INVENTION AND PRIOR ART The present i nvention relates generally to extracorporeal blood treatment. More particularly the i nvention relates to a blood treatment apparatus according to the preamble of claim 1 and a method according to the preamble of claim 1 5. The invention likewise pertains to a computer program accordi ng to claim 21 and computer readable medium according to claim 22.

A conventional single-needle blood treatment apparatus, for i nstance a hemodialysis system or a hemodiafiltration system, contains a dialysis fluid circuit and a blood circuit with one or two blood pumps. For patient security reasons, single-needle dialysis is advantageous in a self care setting. Namely, here, there is no risk for dislodgement of a venous needle and thereby loss of blood being pumped out uni ntentionally via an arterial needle. Additionally, fewer needle punctures to the patient blood access are required relative to dual-needle treatment. Generally, the si ngle-needle system is also well suited for long lasting treatments, such as nocturnal treatments. Moreover, si ngle- needle dialysis may be used when the patient blood access is defective.

The prior art includes a range of examples of solutions for sing- le-needle blood treatment, as well as pump means adapted to such implementations. For example, US 4,552,552 describes a dialysis pumping system for a single-needle dialysis apparatus with a dialyzer having blood and dialysate circuits, and wherein the blood inlets and outlets are joined by intake and outtake Ii- nes with at least one blood connection. The intake line has a dri- ving pump and pump valves placed upstream and downstream of the blood pump. The blood pump unit has a generally stiff housing with a diaphragm therein walling off the space in the housing into a first chamber for blood and a second chamber for driving fluid that is joined up with the driving pump. A respective high and low pressure limiting valve means prevent pressure levels outside a given interval by venting the working chamber whenever the pressure falls outside predetermined threshold values. US 6,645, 1 66 reveals a blood treatment device and disposable kit for a blood treatment device, e.g. a dialysis machine, which permits both si ngle- and dual-needle operation. Here, a blood treatment unit has an inlet connected to a feed line and an outlet connected to a return line. The feed line has two parallel line branches, where a positive displacement pump is connected to a first line branch, and a negative displacement pump is connected to a second line branch. Moreover, a connection line is provided to produce a fluid connection between the outlet of the blood treatment unit and one of the two pumps. For single-need- Ie operation, the feed and return lines are brought together and connected to a common needle.

US 6,899,693 discloses a compact pulsating pumpi ng unit including means suitable to draw blood from an intake connector in order to send it to an outlet connector. Said means are contai- ned in an enclosure provided with valves connected to the inlet and the outlet. An elastic membrane here separates the enclosure into two domes. This allows a working fluid to act on one side of the membrane, such that the membrane acts on blood located on the opposite side. The membrane thereby controls the operation of an inlet valve and an outlet valve, such that blood is moved into respective out from a pumping chamber.

Although the above solutions may have specific beneficial characteristics, they fail to provide an overall optimal fluid flow in a blood treatment apparatus. For example attaini ng a desired level of ultrafiltration is complicated. Moreover, operating the apparatus requires pressure measurements on the blood side. Hence, the design of the apparatus is compelled to be relatively intricate, and handling the apparatus becomes impractical . This, in turn, renders the apparatus unsuitable for a self care setting. I n this respect, the present invention is also advantageous because it requires relatively few interfaces between the apparatus and the disposable units thereof. Furthermore, blood pressure measurements on the blood side are problematic due to the potential risk of infection and contamination of the blood via the pressure measuring means. Specifically, in a self care setting, the patient risks to be stricken with infections caused by his/her own blood residuals from earlier treatments, whereas in a hospital environment i nfectious substances may be transferred from one patient to another.

SUMMARY OF TH E INVENTION

The object of the present invention is therefore to alleviate the above problems and provide an efficient and yet uncomplicated blood treatment sol ution, which is well adapted for home/self treatment environment.

Accordi ng to the invention, the object is achieved by the apparatus as i nitially described, wherein the fluid pumps are configured to control the operation of the blood pumps via the blood treatment fluid. The apparatus is further configured to operate according to a cyclic process of which during a first phase the untreated blood is extracted from the blood source, and during a second phase the treated blood is delivered to the target vessel .

In the apparatus according to the invention the flow of untreated blood extracted from the blood source (access flow) is equivalent to a difference between the second fluid flow of used blood treatment fluid ejected from the apparatus and the first fluid flow of fresh blood treatment fluid drawn from the fluid reservoir. Likewise, in the apparatus according to the invention the flow of treated blood to the target vessel is equivalent to a difference between the first fluid flow of fresh blood treatment fluid drawn from the fl uid reservoir and the second fluid flow of used blood treatment fluid ejected from the apparatus.

Moreover, the apparatus includes a flow control means configured to control a trans-membrane flow between the blood side and the fluid side of the blood treatment unit.

The proposed blood treatment apparatus is advantageous be- cause it renders adjustment of for example the ultrafiltration level a straightforward task.

Accordi ng to an embodiment of the invention, each of the blood pumps i ncludes a pumpi ng chamber. A flexible member separates the pumpi ng chamber into a first accumulation contai ner and a second accumulation container. The flexible member is movable withi n the pumping chamber so as to vary a volume relationship between the first and second accumulation contai ners. The second accumulation container is configured to receive an amount of working fluid to act on the flexible member and thus pump blood to and from the first accumulation container. Moreover, the fluid pumps and the blood pumps are arranged such that the blood treatment fluid constitutes the working fluid for the blood pumps.

Accordi ng to one embodiment of the invention, the flow control means incl udes a first flow restrictor that is configured to cause a first pressure drop during operation of the apparatus. The first flow restrictor is arranged in series with the blood treatment unit in a conduit system configured to pass blood through the blood treatment unit. Optionally, the apparatus likewise includes a second flow restrictor. This flow restrictor is arranged in series with the blood treatment unit in a conduit system configured to pass blood treatment fluid through the blood treatment unit.

During operation of the apparatus, the second flow restrictor is configured to cause a second pressure drop. It is further preferable if, during operation of the apparatus, a pressure drop on the blood side of the blood treatment unit and the second flow restrictor is equal to the pressure drop on the fluid side of the blood treatment unit and the first flow restrictor. Thus the respective pressure drop may be set such that an appropriate flow is achieved on the respective side of the blood treatment unit, i .e. such that a trans-membrane flow is attained.

The flow restriction is also configured to provide for synchronized operation of the blood pumps, i .e. the flexible members of the first and second blood pumps reach their respective end positions simultaneously. In operation, when the blood pumps have reached their respective end positions, the fluid pumps may be operated to adjust the trans-membrane flow, i .e. to supply or withdraw fluid from the blood.

Accordi ng to another embodiment of the i nvention, the apparatus i ncludes a control unit configured to control the fl uid pumps to be operated i n such a manner that a base flow is constituted. The base flow is constituted by a flow of blood treatment fl uid passing through the blood treatment unit during both the first and second phases of the cyclic process, i .e. the base flow is not passed through the blood pumps. I n an alternative embodiment of the i nvention the base flow in the first phase of the cyclic process is different from the base flow in the second phase of the cyclic process. The base flow is independent of the flow of untreated blood extracted from the blood source. The base flow is also independent of the flow of treated blood delivered to the target vessel . The base flow may be used together with one or more flow control means to control the blood pumps to operate in a synchronized manner by securing the same flow of blood treatment fl uid to and from the first and the second accumulation contai ner, respectively. A synchronized operation of the blood pumps ensures that undesired transients i n the trans-membrane flow are avoided. Accordi ng to still another embodiment of the invention, the base flow may be adjusted during the treatment. A feedback signal received by the control unit includes a blood pressure measurement. The blood pressure measurement is used to control the blood treatment fl uid pumps to provide a base flow permitting synchronized operation of the blood pumps. More specifically the feed back signal gives input on when the flexible member i n the blood pump reaches its end position by identifying a blood pressure peak. The blood pressure may be measured on a conduit configured to pass fresh blood treatment fluid. Alternatively the blood pressure may be measured by means of a blood pressure meter on a conduit configured to pass blood. The magnitude of the base flow may be chosen such that the flow on the blood treatment fluid side of the blood treatment unit and on the blood side of the blood treatment unit is more or less equal . I n yet another embodiment of the invention the base flow is chosen such that there is a significant difference between the blood treatment fluid flow and the blood flow. Accordi ng to yet another embodiment of the invention, the flow control means incl udes a pair of auxiliary fluid pumps arranged in a conduit system configured to pass blood treatment fluid through the blood treatment unit. Each of the auxiliary fluid pumps is configured to influence a flow of blood treatment fluid that is passed through the blood treatment unit. Specifically, it is preferable if a first auxiliary fluid pump is arranged in an outlet conduit downstream of the blood treatment unit, and the first auxiliary fluid pump is configured to withdraw fluid from the blood being passed through the blood treatment unit. Analogously, a second auxiliary fluid pump is optionally arranged in an inlet conduit upstream of the blood treatment unit. The second auxiliary fluid pump is configured to supply fluid to the blood bei ng passed through the blood treatment unit. Consequently, in operation the pair of auxiliary fluid pumps may be used to control the trans-membrane flow. Since the flow of blood treatment fluid to the blood pumps is controlled by the fluid pumps, synchronized operation of the blood pumps may be provided for without any base flow.

Accordi ng to a further embodiment of the invention, the flow control means i ncludes first and second adj ustable flow rest- rictors and first and second fluid valve means. The first adjustable flow restrictor is arranged in a first blood-treatment- fluid conduit upstream of the blood treatment unit. The first blood-treatment-fluid conduit is parallel to a conduit in which a first fluid pump of said fl uid pumps is arranged. Analogously, the second adj ustable flow restrictor is arranged in a second blood- treatment-fl uid conduit downstream of the blood treatment unit, and the second blood-treatment-fluid conduit is parallel to a conduit in which the second fluid pump of said fluid pumps is arranged. I n this context, parallel means that the second blood- treatment-fl uid conduit and the conduit in which the second fluid pump is arranged constitute two branches that originate from a common point. Furtheron, the first fluid valve means is arranged upstream the fist adj ustable flow restrictor and the first fl uid pump in the inlet conduit configured to receive fresh blood treatment fl uid into the apparatus. The second fl uid valve means is arranged downstream the second adjustable flow restrictor and the second fluid pump i n an outlet conduit configured to discharge used blood treatment fluid from the apparatus. By adjusting, during operation, the first and second adj ustable flow restrictors and by opening and closing the first and the third fluid valve means alternatingly in the first and second phase respectively of the cyclic process, a desired trans-membrane flow may be attained. Accordi ng to a further embodiment of the invention, the flow control means incl udes four fluid valve means, which are controllable in response to a respective valve control signal , e.g. originating from the control unit. A first fluid valve means is arranged on an inlet conduit configured to receive fresh blood treatment fluid into the apparatus. Downstream of the first fluid valve means the i nlet conduit is further connected to the first fluid pump via a first fluid conduit. Downstream of the first fluid valve means the i nlet conduit is also further connected to the blood treatment unit via a second fluid conduit means. A third fluid valve means is arranged on the second fluid conduit means between the first fluid valve means and the blood treatment unit. A second fluid valve means is arranged on an outlet conduit configured to discharge used blood treatment fluid from the apparatus. The second fluid valve means is arranged downstream of the blood treatment unit, and is also connected to the second fl uid pump. A fourth fl uid valve means is arranged on a conduit between the blood treatment unit and the second fluid valve means. By opening and closing, during operation, the first and the third fl uid valve means alternatingly i n the first and second phase respectively of the cyclic process, and openi ng and closing the second and fourth fl uid valve means intermittently, a desired trans-membrane flow may be attained.

Accordi ng to another aspect of the i nvention the object is achieved by the method described initially, wherein the method i nvol- ves: controlling the blood pumps to operate by passing blood treatment fluid through the fl uid pumps, controlling the apparatus according to a cyclic process of which untreated blood is extracted from the blood source during a first phase and treated blood is delivered to the target vessel duri ng a second phase, and controlling a trans-membrane flow between the blood side and the fluid side of the blood treatment unit through the medium of a flow control means. The advantages of this method, as well as the embodiments thereof, are apparent from the discussion above with reference to the proposed apparatus. Accordi ng to a further aspect of the invention the object is achieved by a computer program, which is directly loadable into the memory of a computer, and i ncludes software adapted to control the method proposed above when said program is run on a computer. Accordi ng to another aspect of the i nvention the object is achieved by a computer readable medium, having a program recorded thereon, where the program is to control a computer to perform the method proposed above when the program is loaded into the computer.

Clearly, the invention is applicable to dual-needle implementations. However, the proposed solution is especially advantageous for blood treatment in the form of single-needle hemodialysis or hemodiafiltration. The solution is particularly suitable for self care treatment, daily/nocturnal dialysis and intensive care. Further advantages, beneficial features and applications of the present invention will be apparent from the following description and the dependent claims.

BRI EF DESCRI PTION OF TH E DRAWINGS The present invention is now to be explained more closely by means of embodiments, which are disclosed as examples, and with reference to the attached drawi ngs.

Figures 1 a-b show block diagrams over a blood treatment apparatus according to a first embodiment of the inven- tion duri ng a first and a second phase respectively of a cyclic treatment process;

Figure 2 shows a pair of graphs which elucidate a relationship between a set of pressure drops according to the first embodiment of the i nvention illustrated i n Figures 1 a and 1 b;

Figures 3a-b show block diagrams over a blood treatment apparatus according to a second embodiment of the invention duri ng a first and a second phase respectively of the proposed cyclic treatment process; Figures 4a-b show block diagrams over a blood treatment apparatus according to a third embodiment of the invention duri ng a first and a second phase respectively of the proposed cyclic treatment process;

Figures 5a-b show block diagrams over a blood treatment apparatus according to a fourth embodiment of the i nvention duri ng a first and a second phase respectively of the proposed cyclic treatment process;

Figures 6a-b show block diagrams illustrati ng the measurement of a trans-membrane flow between the blood side and the a fluid side of the blood treatment unit in the fourth embodiment of the i nvention; Figure 7 shows graphs exemplifying how a flow of input fresh blood treatment fl uid and a flow of output used blood treatment fluid may vary over time according to one embodi ment of the invention;

Figure 8 shows a graph illustrating how a trans-membrane flow between a blood side and a fluid side of the blood treatment unit may vary over time according to one embodiment of the i nvention;

Figure 9 shows a graph exemplifying a pump-chamber blood volume as a function of time according to one embodiment of the i nvention; and

Figure 1 0 illustrates, by means of a flow diagram, a general method of operating a blood treatment apparatus accordi ng to the invention.

DESCRI PTION OF EMBODIMENTS OF TH E I NVENTION We refer initially to Figure 1 a, which shows a block diagram over a blood treatment apparatus (e.g. a dialysis apparatus) according to a first embodiment of the i nvention duri ng a first phase of a proposed cyclic blood treatment process.

The apparatus incl udes a blood treatment unit 8 (typically repre- sented by a dialyzer), first and second fluid pumps 1 4 and 1 5 respectively and first and second blood pumps 1 a and 1 b res- pectively. First and second blood valve means 3 and 4 respectively are also incl uded, which are controlled to be open and closed in an alternati ng fashion, such that the first blood valve means 3 is open when the second blood valve means 4 is clo- sed, and vice versa.

The blood treatment unit 8 has a blood side 8B and a fluid side 8F that are separated by means of a semi-permeable membrane structure. For example, this structure may be represented by a large number of hollow fibers whose walls constitute a respec- tive semi-permeable membrane and which fibers are configured to transport blood . The structure is also configured to allow blood treatment fl uid to be passed outside said fibers when blood is transported there through. Naturally, the opposite situation is equally well applicable, i .e. that blood treatment fluid is passed through the fibers and blood is passed outside thereof. In any case, blood treatment (e.g. dialysis) takes place over each fiber's semi-permeable membrane. Hence, the blood treatment unit 8 is configured to receive untreated blood and fresh blood treatment fluid, and emit treated blood and used blood treatment fluid.

The fluid pumps 1 4 and 1 5 are configured to pass blood treatment fluid through the blood treatment unit 8. The blood pumps 1 a and 1 b are configured to extract untreated blood from a blood source S (e.g. a bag containing blood to be treated, or a patient), pass extracted blood through the blood treatment unit 8 and deliver treated blood to a target vessel T (e.g. a bag for cleaned blood, or a patient). Specifically, the apparatus is controlled to operate according to a cyclic process of which during a first phase untreated blood is extracted from the blood source S, and during a second phase treated blood is delivered to the target vessel T. According to the invention, the fluid pumps 1 4 and 1 5 are also configured to control the operation of the blood pumps 1 a and 1 b via the blood treatment fluid. The apparatus has a flow control means configured to control a trans-membrane flow between the blood side 8B and the fluid side 8F of the blood treatment unit 8. I n the first embodiment of the invention illustrated in Figures 1 a and 1 b, a first flow restrictor Rb represents one component of the flow control means. The first flow restrictor Rb is arranged downstream of a treated-blood outlet from the blood treatment unit 8 and upstream of the second blood pump 1 b, which in turn, is configured to deliver the treated blood to the target vessel T. During operation of the blood treatment apparatus, the fluid side 8F is associated with a fluid pressure drop and the blood side 8B is associated with a blood pressure drop. During operation of the apparatus, the first flow restrictor Rb is configured to cause a first pressure drop over the first flow restrictor Rb. As will be explained below, this is advantageous with respect to the proposed control of the trans-membrane flow between blood side 8B and the fluid side 8F. In an alternative embodiment of the invention a second flow restrictor Rf is arranged upstream of the fluid side of the blood treatment unit 8F. A further alternative embodiment of the invention comprises a first as well as a second flow restrictor Rb, Rf. The second flow restrictor will be described further below. Accordi ng to one embodiment of the invention, each of the blood pumps 1 a and 1 b includes a pumpi ng chamber. A flexible member 9a and 9a' (e.g. in the form of a soft/elastic membrane) separates this pumping chamber i nto a first accumulation container 9b and 9b' respectively, and a second accumulation contai- ner 9c and 9c' respectively. The flexible member 9a and 9a' is movable within its pumping chamber so as to vary a vol ume relationship between the first and second accumulation containers 9b, 9b' and 9c, 9c' respectively. Furthermore, each second accumulation container 9c and 9c' is configured to receive an amount of working fl uid to act on the flexible member 9a and 9a' respectively, and thus pump blood through the first accumulation container 9b and 9b' respectively. Accordi ng to the invention, the fluid pumps 1 4 and 1 5 respectively and the blood pump 1 a and 1 b are arranged relative to one another, such that the blood treatment fl uid constitutes the working fluid for the blood pumps 1 a and 1 b. Hence, the fluid pumps 1 4 and 1 5 control the operation of the blood pumps 1 a and 1 b via the blood treatment fluid.

During a first phase of the cyclic blood treatment process (Figure 1 a), the second fluid pump 1 5 is configured to extract/suck fresh blood treatment fluid from the second accumulation container 9c of the first blood pump 1 a and draw this blood treatment fl uid through the fluid side 8F of the blood treatment unit 8. The operation of the second fl uid pump 1 5 also causes used blood treatment fl uid to be extracted/sucked from the second accumulation container 9c' of the second blood pump 1 b. After passing the second fluid pump 1 5, this blood treatment fl uid is discharged from the apparatus, e.g. i nto the drain or a waste compartment 1 2b. The first fluid pump 1 4 is configured to draw blood treatment fluid (e.g. dialysis fluid) from a fluid source, such as a reservoir compartment 1 2a i n a second phase of the cyclic blood treatment process (Figure 1 b). Optionally, during the first phase of the cyclic blood treatment process illustrated in Figure 1 a, the first fluid pump 1 4 draws a relatively small flow of blood treatment fluid (also referred to as base flow which will be further described below), and pumps this fl uid directly to a drai n or waste compartment 1 2b via a fluid side 8F of the blood treatment unit 8 (and optionally via a second flow restrictor Rf, which will be described below). Here, the operation of the first and second fluid pumps 1 4 and 1 5 causes a trans-membrane flow from the fluid side 8F to the blood side 8B of the blood treatment unit 8. .

The above-mentioned first blood valve means 3 is configured to control the extraction of untreated blood from the blood source S via a first needle connector 31 and a first needle N 1 . Analogously, the above-mentioned second blood valve means 4 is configured to control the delivery of treated blood to the target vessel T via a second needle connector 32 and a second needle N2. Of course, in a single-needle implementation the first and second blood valve means 3 and 4 are instead both connected to one needle, which is attached to a patient's blood system.

In any case, duri ng the first (or blood extraction) phase of the cyclic blood treatment process illustrated in Figure 1 a, the first blood valve means 3 is open and the second blood valve means 4 is closed. As a result, when the second fluid pump 1 5 pulls the fresh blood treatment fluid out from the second accumulation container 9c of the first blood pump 1 a, untreated blood is extracted from the blood source and fed i nto the first accumulation container 9b of the first blood pump 1 a. I ncomi ng blood also continues i nto the blood side 8B of the blood treatment unit 8. Moreover, since the second fluid pump 1 5 also draws used blood treatment fluid out from the second accumulation con- tainer 9c' of the second blood pump 1 b, the blood located on the blood side 8B of the blood treatment unit 8 is further pulled into the first accumulation container 9b' of the second blood pump 1 b. Hence, blood passes through the blood treatment unit 8, and as a result, this blood is treated by the blood treatment fluid passing through the fl uid side 8F of the blood treatment unit 8.

Figure 1 b illustrates the second (or blood delivery) phase of the cyclic blood treatment process. I n this phase, the first blood valve means 3 is closed while the second blood valve means 4 is open. The blood valve means 3 and 4 are controlled via a respective control signal C₁ and C₂ generated by a control unit 20, which will be discussed in more detail below. In any case, in contrast to the first phase, during the second phase the first fl uid pump 1 4 draws a relatively large flow of fresh blood treatment fluid from the reservoir compartment 1 2a. The thus extracted blood treatment fluid continues i nto the second accumulation contai ner 9c of the first blood pump 1 a. The entry of fresh blood treatment fl uid into the second accumulation container 9c of the first blood pump 1 a, i n turn, causes untreated blood located in the first accumulation container 9b of the first blood pump 1 a to be pushed through the blood side 8B of the blood treatment unit 8.

Moreover, the operation of the first fluid pump 1 4 causes fresh blood treatment fluid to be extracted/sucked from the reservoir compartment 1 2a. This blood treatment fluid conti nues directly into the fluid side 8F of the blood treatment unit 8 (possibly via the above-mentioned flow restrictor Rf). After passing the blood treatment unit 8, the blood treatment fl uid continues into the second accumulation container 9c' of the second blood pump 1 b. This, in turn, causes blood located in the first accumulation container 9b' of the second blood pump 1 b to be ejected into the target vessel via the blood valve means 4, the second needle connector 32 and the second needle N2.

Optionally, during the second phase of the cyclic blood treatment process, the second fluid pump 1 5 is also operated to some extent. This causes a fraction (a base flow) of the used blood treatment fluid to exit directly from the blood treatment unit 8 (i .e. without being temporarily stored in any of the blood pumps 1 a, 1 b). The operation of the first and second fluid pumps 1 4 and 1 5 duri ng the second phase causes a trans-membrane flow from blood side 8B to the fluid side 8F of the blood treatment unit 8. Thus, by controlling first and second fluid pumps 1 4 and 1 5 an amount of fluid drawn from the blood passing through the blood treatment unit 8 may be adjusted.

The first and the second fl uid pumps 1 4, 1 5 may, as mentioned above, be operated in such a manner that a base flow is constituted. The base flow is constituted by a flow of blood treatment fluid passing through the blood treatment unit 8 during both the first and second phases of the cyclic process, i .e. the base flow is not passed through the blood pumps 1 a, 1 b. The base flow is independent of the flow of untreated blood extracted from the blood source, S. The base flow may be used together with one or more flow control means to control the blood pumps 1 a, 1 b to operate in a synchronized manner by securing the same flow of blood treatment fl uid to and from the first and the second accumulation container 9c, 9c', respectively. Furtheron, the base flow may be used together with one or more flow control means to control the transmembrane flow. As mentioned above the blood treatment apparatus may comprise a first flow restrictor Rb. The embodiment shown i n Figure 1 a and 1 b also comprises a second flow restrictor Rf which is arranged in series with the blood treatment unit 8 in a conduit system configured to pass blood treatment fluid through the blood treatment unit 8. As mentioned above, during operation of the apparatus, the first flow restrictor Rb is configured to cause a first pressure drop and the second flow restrictor Rf is configured to cause a second pressure drop. The pressure drops over the first and second flow restrictors Rb and Rf are desirable because it facilitates creation of an appropriate trans-membrane flow. The pressure drops over the first and second flow restrictors Rb and Rf are also desirable because it facilitates synchronization of the blood pumps 1 a and 1 b, i .e. that the flexible members 9a and 9a' are allowed to reach their respective end positions simultaneously.

Optionally, first and second motoric signals m l and m2 from the control unit 20 control the operation of the fl uid pumps 1 4 and 1 5 respectively.

Moreover, first and second pressure parameters are optionally measured via a first pressure sensor signal Sp₁ registered on a conduit configured to pass fresh blood treatment fluid from the fluid container 1 2a into the apparatus, and a second pressure sensor signal S_P2 registered on a conduit configured to discharge used blood treatment fluid from the apparatus. For reasons of simplicity, we here assume that a pressure measuring unit is included in a control unit 20. I n any case, the pressure measuring unit does not come into contact with the blood. I nstead, the blood pressure is measured via the blood treatment fluid, which due to the contact with the flexible members 9a and 9a' respectively has a pressure level equal to that of the blood. Specifically, the first pressure parameter represents a first pressure level of the untreated blood extracted from the blood source S, and the second pressure parameter represents a se- cond pressure level of the treated blood being delivered to the target vessel T.

It is further advantageous if the control unit 20, i n response to the pressure sensor signals Sp₁ and S_P2 (expressi ng the first and second pressure parameters) , is configured to control the first and second blood valve means 3 and 4, such that the proposed cyclic process is effected. Of course, this control also involves controlling the fluid pumps 1 4 and 1 5 via the motoric signals m l and m2 respectively. Specifically, during the first phase (the blood extraction phase), the control unit 20 is confi- gured to generate a first control signal C₁ such that the first blood valve means 3 is opened, a second control signal C₂ such that the second blood valve means 4 is closed. The control unit 20 further produces motoric signals m l and m2 such that the fluid pumps 1 4 and 1 5 are operated as desired. Then, during the second phase (the blood delivery phase), the control unit 20 is configured to generate the first control signal C₁ such that the first blood valve means 3 is closed, the second control signal C₂ such that the second blood valve means 4 is opened, and motoric signals m l and m2 such that the fl uid pumps 1 4 and 1 5 are operated as desired. The control unit 20 uses the first and second pressure parameters to determine appropriate transitions between the first and second phases, and thus control the valve means 3, 4 and the fluid pump 1 4 and 1 5 as described above. Optionally, the control unit 20, in turn, incl udes, or is associated with; a memory means 21 storing computer software for controlling the control unit 20 to effect the above-described procedure.

In a start up phase (i .e. prior to initiating the above-mentioned cyclic process) the fl uid circuit may be filled (or more precisely filled, such that superfluous fluid rinses the circuit) with fresh blood treatment fluid (e.g. dialysis fluid) from the fluid contai ner 1 2a. The filling of the fluid causes any air in the dialysis fluid circuit to be pushed into the waste compartment 1 2b (or drain) where it is vented. Correspondi ngly, the first needle N 1 may be connected to a saline solution (or other appropriate fluid) to fill and rinse, and thus eliminate any gas bubbles in the blood circuit. This process of filling and rinsi ng the apparatus is normally referred to as priming.

Figure 2 shows an example of a first pressure P_8B along the blood treatment unit 8 on the blood side 8B as a function of a length L along the blood treatment unit 8. Figure 2 also exemplifies of a second pressure P_8F along the blood treatment unit 8 on the fluid side 8F as a function of a length L along the blood treatment unit 8. I n this example, we assume that the blood treatment unit 8 has length L = L_Bτu- A difference pressure ΔP is defined as the difference between the first and the second pressure points P1 and P2. I n Figure 2, the first pressure drop over the first flow restrictor Rf is designated ΔP_Rf, and the second pressure drop over the second flow restrictor Rb is designated ΔP_Rb.

A trans-membrane pressure drop TMP between the blood side 8B and the fluid side 8F of the blood treatment unit 8 is given by the expression:

ΔP + Δ/> ₁ TMP = Rb ΔP - AP Rf ΔP_sfc + ΔP_s/

In other words, by adequate selection of a combination of blood treatment fluid flows in the first and second phases of the cyclic process and the first and second pressure drops ΔP_Rf and ΔP_Rb respectively (i .e. choosing the characteristics of the first and se- cond flow restrictors Rf and Rb), a desired trans-membrane flow can be attained and thereby ultrafiltration.

Figures 3a and 3b show block diagrams over a blood treatment apparatus according to a second embodiment of the i nvention during a first and a second phase respectively of the proposed cyclic treatment process. I n Figures 3a and 3b all units and components havi ng reference signs, which also occur i n Figures 1 a and 1 b designate the same units and components as those described above with reference to Figures 1 a and 1 b.

The second embodiment differs from the first embodiment of the invention i n that the fluid pumps 1 4 and 1 5 are i ncluded in the respective fluid paths which connect the blood pumps 1 a and 1 b to the blood treatment unit 8. I n the second embodiment, the first fluid pump 1 4 is arranged i n a conduit between the second blood pump 1 b and an inlet configured to receive fresh blood treatment fluid into the blood treatment unit 8. Analogously, the second fluid pump 1 5 is arranged in a conduit between the first blood pump 1 a and an outlet configured to emit used blood treatment fluid from blood treatment unit 8. The fist and the second fluid pumps 1 4, 1 5 may be controlled to supply and withdraw the same flow to and from the first and the second secondary accumulation containers 9c, 9c'. Furthermore, the flow control means includes first and second auxiliary fluid pumps 1 6a and 1 6b instead of the first and second flow restrictors Rb and Rf. In this embodiment of the invention, the first auxiliary fluid pump 1 6a is located in an outlet conduit downstream of the blood treatment unit 8. The second auxiliary pump 1 6b is located in an i nlet conduit upstream of the blood treatment unit 8. The auxiliary fluid pumps 1 6a and 1 6b are configured to infl uence a flow of blood treatment fluid through the blood treatment unit 8. More specifically the auxiliary fluid pumps 1 6a, 1 6b may be adapted to the flows generated by the fluid pumps 1 4, 1 5 and thereby control of the trans-membrane flow during the cyclic process. Thus the blood treatment fluid through the blood treatment unit, the blood flow and the transmembrane flow may be adjusted independently. I n one embodiment of the i nvention, during the first phase of the proposed cyclic process, the first auxiliary fluid pump 1 6a is adapted to control the trans-membrane flow while the second auxiliary pump 1 6b is idle and, and during the second phase of the proposed cyclic process the second auxiliary fluid pump 1 6b is adapted to control the trans-membrane flow while the first auxiliary pump 1 6a is idle. This is illustrated in Figures 3a and 3b, where the auxiliary fluid pump 1 6a is controlled to operate via a motoric signal m3, and the second auxiliary fluid pump 1 6b is controlled to operate via a motoric signal m4 from the control unit 20. The operation of the auxiliary fluid pumps 1 6a and 1 6b causes more or less blood treatment fluid to be ejected into the waste compartment 1 2b than what is stored in the accumulation contai ners 9c and 9c' of the first and second blood pumps 1 a and 1 b respectively. This fluid may originate from the source 1 2a via the second auxiliary pump 1 6b, or from the blood side, as a trans-membrane flow, or both. Hence the flow of blood treatment fluid through the blood treatment unit 8 can be more or less than what is controlled by the fluid pumps 1 4 and 1 5. The task of auxiliary fluid pumps 1 6a and 1 6b is hence to augment the flow through the blood treatment unit 8, as well as to control the trans-membrane flow.

In this embodiment of the invention the first and the second auxiliary pumps 1 6a, 1 6b may be operated such that the above described base flow is constituted. However, the base flow is not needed for synchronization of the blood pumps. The magnitude of the base flow is chosen such that the flow on the blood treatment fluid side 8F of the blood treatment unit 8 and on the blood fluid side 8B of the blood treatment unit 8 is more or less equal . Alternatively, the base flow is chosen such that there is a significant difference between the blood treatment fluid flow and the blood flow, e.g. the blood treatment fl uid flow is 500 ml/min and the blood flow is 300 ml/min

In an alternative embodiment of the blood treatment apparatus shown in Figure 3a and 3b the first fluid pump 1 4 is arranged upstream the second auxiliary pump 1 6b and the second fluid pump 1 5 is arranged downstream the first auxiliary pump 1 6a i n order to lessen any transients in the trans-membrane flow. I n a further alternative embodiment the first and the second fluid pumps 1 4, 1 5 are both arranged upstream the second auxiliary pump 1 6b or downstream the first auxiliary pump 1 6a in order to lessen any transients in the trans-membrane flow.

Figures 4a and 4b show block diagrams over a blood treatment apparatus according to a third embodiment of the i nvention during a first and a second phase respectively of the proposed cyclic treatment process. I n Figures 4a and 4b all units and components havi ng reference signs, which also occur i n Figures 1 a, 1 b, 3a and 3b designate the same units and components as those described above with reference to Figures 1 a, 1 b, 3a and 3b.

The third embodiment differs from the second embodiment of the invention in that the flow control means i nstead of one or more auxiliary fluid pumps, includes first and second adjustable flow restrictors Rf 1 and Rf2 respectively. The first adjustable flow restrictor Rf 1 is controllable in response to a first restriction control signal r1 from the control unit 20, and the second adjustable flow restrictor Rf2 is controllable in response to a second restriction control signal r2 from the control unit 20.

The first adjustable flow restrictor Rf 1 is arranged i n a first blood-treatment-fluid conduit upstream of the blood treatment unit 8. The first blood-treatment-fl uid conduit is parallel to a con- duit in which a first fl uid pump 1 4 is arranged. I .e. both the first adjustable flow restrictor Rf 1 and the first fluid pump 1 4 are connected to a conduit configured to receive incoming fresh blood treatment fluid, however the first fluid pump 1 4 is further connected to the second blood pump 1 b whereas the first ad- justable flow restrictor Rf 1 is further connected to the blood treatment unit 8.

The second adjustable flow restrictor Rf2 is arranged in a second blood-treatment-fluid conduit downstream of the blood treatment unit 8. The second blood-treatment-fl uid conduit is parallel to a conduit in which the second fluid pump 1 5 of said fluid pumps is arranged. In other words, both the second adjustable flow restrictor Rf2 and the second fluid pump 1 5 are con- nected to a conduit configured to eject used blood treatment fluid from the apparatus, however the second fluid pump 1 5 is further connected to the first blood pump 1 a whereas the second adjustable flow restrictor Rf2 is further connected to the blood treatment unit 8. The third embodiment further differs from the second embodiment of the invention in that the flow control means instead of the auxiliary pumps 1 6a, 1 6b includes a first and second valve means V_{1 1} and V₂₁ , where each valve means is controllable in response to a respective valve control signal V_{1 1} and V₂₁ from the control unit 20.

The first fluid valve means V_{1 1} is controllable in response to a first valve control signal V_{1 1}. The first fluid valve means V_{1 1} is arranged on an inlet conduit configured to receive fresh blood treatment fluid into the apparatus. Downstream of the first fluid valve means V_{1 1} the inlet conduit is further connected to the first fluid pump 1 4 via a first fl uid conduit. Downstream the first fluid valve means V_{1 1} the i nlet conduit is also further connected to the blood treatment unit 8 via a second fluid conduit means and the first adj ustable flow restrictor Rf 1 . The second fluid valve means V₂₁ , is controllable in response to a second valve control signal v₂₁. The second fluid valve means V₂₁ is arranged on an outlet conduit configured to discharge used blood treatment fluid from the apparatus. Specifically, the second fl uid valve means V₂₁ is arranged downstream of the blood treatment unit 8 via the second adjustable flow restrictor Rf2. Further the second valve means V₂₁ is connected to the second fluid pump 1 5.

By controlling the first and the second valve means V_{1 1} and V₂₁ , to alternati ngly open and close during the respective first and second phase of the cyclic process and controlling the adjustable flow restrictors Rf 1 and Rf2 to appropriate val ues in the first and second phases of the cyclic process, the trans- membrane flow between the blood side 8B and the fl uid side 8F of the blood treatment unit 8 may be controlled in a manner equivalent to that described above.

Figures 5a and 5b show block diagrams over a blood treatment apparatus according to a fourth embodiment of the invention during a first and a second phase respectively of the proposed cyclic treatment process. I n Figures 5a and 5b all units and components havi ng reference signs, which also occur i n Figures 1 a, 1 b, 3a, 3b, 4a and 4b designate the same units and components as those described above with reference to Figures 1 a, 1 b, 3a, 3b, 4a and 4b.

The fourth embodiment differs from the third embodiment of the invention i n that the flow control means, i nstead of the adjustable flow restrictors, includes a third and a fourth valve means V₁₂ and V₂₂, where each valve means is controllable in response to a respective valve control signal V₁₂ and V₂₂ from the control unit 20.

The third fluid valve means V₁₂, which is controllable in response to a second valve control signal v₁₂, is arranged on the second fl uid conduit between the first fluid valve means V_{1 1} and the blood treatment unit 8.

The fourth fl uid valve means V₂₂, which is controllable in response to the fourth valve control signal V₂₂, is arranged on a conduit between the blood treatment unit 8 and the second fluid valve means V₂₁. Specifically, accordi ng to one embodiment of the invention, the control unit 20 is configured to control the fluid valve means V_{1 1} , V₁₂, V₂₁ and V₂₂ as follows. Duri ng the first phase (i .e. when blood is being extracted from the blood source S), the control unit 20 controls the first fluid valve means V_{1 1} to a closed position; the third fluid valve means V₁₂ to an open position; and the second valve means V₂₁ to an open position. Moreover, the control unit 20 controls the fourth fluid valve means V₂₂ in an intermittent manner, between an open and a closed position, such that a desired trans-membrane flow is attained. This is illustrated in Figure 5a.

Figure 5b illustrates the second phase (i .e. when blood is being delivered to the target vessel T). During this phase, the control unit 20 controls the first fl uid valve means V_{1 1} to an open position; the third fluid valve means V₁₂ in an intermittent manner, between an open and a closed position, such that a desired trans-membrane flow is attained ; the second valve means V₂₁ to a closed position; and control the fourth fluid valve means V₂₂ to an open position.

In order to keep track of the fl uid balance between the untreated and the treated blood (e.g. represented by blood extracted from a patient and blood returned to the patient) it is important to measure the trans-membrane flow in each phase of the cyclic process. For example such measurements may be made based on signals registered via first and second flow measurement sensors 33 and 34 respectively (see Figures 6a and 6b).

Figures 6a and 6b show block diagrams, which illustrate how the trans-membrane flow between the blood side 8B and the a fluid side 8F of the blood treatment unit 8 is measured. In Figures 6a and 6b all units and components having reference signs, which also occur i n Figures 1 a, 1 b, 3a, 3b, 4a, 4b, 5a and 5b designate the same units and components as those described above with reference to Figures 1 a, 1 b, 3a, 3b, 4a, 4b, 5a and 5b. Here, we have chosen to describe the trans-membrane flow measurement referri ng to the fourth embodiment of the invention. Nevertheless, the same pri nciple is equally well applicable to any one of the above-described first, second, or third embodiments of the i nvention, wherei n the first measurement sensor 33 is arranged in proximity to the inlet configured to receive fresh blood treatment fluid into the apparatus, and the second flow measurement sensor 34 is arranged in proximity to the outlet configured to eject used blood treatment fluid from the ap- paratus.

The proposed flow measurement during each phase i nvolves (a) registering a first amount A₁ of blood treatment fluid fed i nto the apparatus, and (b) registering a second amount A₂ of fluid ejected from the apparatus. The first flow measurement sensor 33 is configured to deliver the first amount A₁ to the control unit 20, and the second flow measurement sensor 34 is configured to deliver the second amount A₂ to the control unit 20. Based on these parameters, the control unit 20 is configured to determi ne an average trans-membrane flow as the difference between the first and second amounts A₁ and A₂ divided by the duration of the phase i n question.

To enable measurement of the first and second amounts A₁ and A₂ as well as a total amount of blood treatment fl uid fed i nto the apparatus, the third embodiment of the invention shown i n Figu- res 6a and 6b includes a set of additional fluid valve means V₃₁ , V₃₂, V₃₃, and V₃₄. For reasons of clarity, the figures 6a and 6b do not show control lines to these means V₃₁ , V₃₂, V₃₃ and V₃₄, or to the valve means V₁₂, V₂₁ or V₂₂. However, analogous to the control signal V_{1 1} in respect of the first fluid valve means V_{1 1} , each of these fluid valve means is controllable via a respective control signal transferred from the control unit 20.

During the first phase illustrated in Figure 6a (i .e. when blood is being extracted from the blood source S), the control unit 20 is configured to control a first additional fluid valve means V₃₁ to an open position; control a second additional fluid valve means V₃₂ to a closed position; control a third additional fl uid valve means V₃₂ to a closed position; and control a fourth additional fluid valve means V₃₄ to an open position. The fluid valve means V_{1 1} , V₁₂, V₂₁ and V₂₂ are controlled as described above with re- ference to Figure 5a.

During the second phase illustrated in Figure 6b (i .e. when blood is being delivered to the target vessel T), the control unit 20 is configured to control the first additional fluid valve means V₃₁ to a closed position; control the second additional fluid valve means V₃₂ to an open position; control the third additional fluid valve means V₃₃ to an open position ; and control the fourth additional fluid valve means V₃₄ to a closed position. The fluid valve means V_{1 1} , V₁₂, V₂₁ and V₂₂ are controlled as described above with reference to Figure 5b.

Optionally, the control unit 20 is likewise configured to determine a respective amount of blood treatment fluid fed into the second accumulation contai ner 9c' of the second blood pump 1 b during the second phase of the cyclic process and delivered out of the second accumulation contai ner 9c of the first blood pump 1 a during the first phase of the cyclic process , as well as a total amount of fluid fed i nto and taken out of the blood treatment apparatus.

Figure 7 shows a first graph Q₁₄ exemplifying how a flow of input fresh blood treatment fl uid may vary over time t. Figure 7 also shows a second graph Q₁₅ exemplifying how a flow of output used blood treatment fl uid may vary over time t. The duration of one phase of the cyclic process is denoted T_ph in Figure 7. Moreover, Figure 7 illustrates an access flow F_A as a difference between the flow of input fresh blood treatment fl uid and the flow of output used blood treatment fluid. The access flow F_A represents a flow of blood extracted from the blood source S. Figure 7 also shows a base flow level F_B (dashed line), which represents a minimum flow level . As can be seen, i n this ex- ample base flow level F_B is approximately 20 ml/min.

Accordi ng to one embodiment of the invention, the control unit 20 is configured to control the first fluid pump 1 4 to draw fresh blood treatment fluid from the fluid reservoir 1 2a, control the second fl uid pump 1 5 to eject used blood treatment fluid from the apparatus, such that the access flow F_A attains a desired level .

Accordi ng to another embodiment of the invention, the control unit 20 is configured to control the fluid pumps 1 4 and 1 5 to be operated during the first and second phases of the cyclic blood treatment process in such a manner that the flows Q₁₄, Q₁₅ of blood treatment fluid passing through the blood treatment unit 8 is equal to or exceeds the base flow level F_B during the first phase as well as the second phase of this process. I n a further alternative embodiment of the invention the auxiliary pumps 1 6a, 1 6b are operated such that the blood treatment fluid passing through the blood treatment unit 8 is equal to or exceeds the base flow level F_B duri ng the first phase as well as the second phase of this process.

Figure 8 shows a graph, which illustrates an example of the trans-membrane flow Q_{U F} between the blood side 8B and the fluid side 8F of the blood treatment unit 8 as a function of time t.

Here, the first phase of the cyclic process i ncludes an extraction period E duri ng which an increasi ng amount of blood runs i nto the first accumulation containers 9b and 9b' respectively of the first and second blood pumps 1 a and 1 b, and an extended extraction period E_ext duri ng which the flexible membranes 9a and 9a' are (essentially) positioned in their respective first end posi- tions, and thus no more blood may enter the first accumulation containers 9b and 9b'. As a result, fluid is drawn from the blood during this period E_ΘXt. Analogously, the second phase of the cyclic process includes a delivery period D during which an increasing amount of blood treatment fluid runs into the second accumulation containers 9c and 9c' respectively of the first and second blood pumps 1 a and 1 b, and an extended delivery period D_6Xt during which the flexible membranes 9a and 9a' are (essentially) positioned i n their respective second end positions, and thus no more blood treatment fluid may enter the second accumulation contai ners 9c and 9c'. As a result, during this period D_6Xt, fl uid is transferred to the blood over the semi-permeable membrane. Hence, by adj usti ng the extended delivery periods D_6Xt, an accumulated trans-membrane flow between the blood side 8B and the fl uid side 8F of the blood treatment unit 8 can be controlled.

Figure 9 shows a graph illustrating the amount of blood stored in one of the blood pumps 1 a or 1 b as a function of time t corresponding to the trans-membrane flow Q_{U F} of Figure 8. As is appa- rent, the first accumulation container 9b or 9b' has a vol ume of 50 ml , and an interval t_end-_E during which the chamber 9b or 9b' is completely filled with blood is somewhat shorter than an interval t_end-_D duri ng which the chamber 9b or 9b' is completely empty (i .e. when the second accumulation contai ner 9c or 9c' is completely filled with blood treatment fluid).

To sum up, we will now describe the proposed method of operating a blood treatment apparatus with reference to the flow diagram of Figure 1 0. Here, we presume that the blood treatment apparatus incl udes: a blood treatment unit configured to receive untreated blood and fresh blood treatment fluid, and emit treated blood and used blood treatment fluid. Moreover, it is assumed that the blood passes on a blood side of a semi-permeable membrane structure and that the blood treatment fluid passes on a fluid side of said structure. A pair of fluid pumps are configured to pass blood treatment fluid through the blood treatment unit and a pair of blood pumps are configured to extract untreated blood from a blood source, pass extracted blood through the blood treatment unit and deliver treated blood to a target vessel .

A first step 1 01 0 opens a first valve means, and in parallel there with a second step 1 01 5 closes a second valve means. Here, the first valve means controls an input of untreated blood from a blood source, and the second valve means controls an output of treated blood to a target vessel . Thereafter, a step 1 020 controls first and second fluid pumps to eject blood treatment fl uid, which currently is located in the blood pumps. A first fraction of the blood treatment fluid stored in the second accumulation container of the first blood pump is fresh and passes the blood treatment unit before being ejected from the apparatus, and a second fraction of the blood treatment fluid stored in the second accumulation container of the second blood pump has already passed the blood treatment unit (i .e. is used). As a result of the blood treatment fluid ejection, untreated blood from the blood source is extracted. A first fraction of this blood is stored untreated i n the first accumulation container of the first blood pump, and a second fraction of this blood is stored after havi ng passed the blood treatment unit (i .e. as treated) in the first accumulation contai ner of the second blood pump. In parallel with step 1 020, a step 1 025 controls a trans-membrane fl uid flow between the blood side and the a fluid side of the blood treatment unit. This may involve any one of the above- described strategies, for instance exclusively controlling the first and second fluid pumps (cf. the first embodiment of the inven- tion).

Subsequently, a step 1 030 checks whether or not the flexible members of the first and second blood pumps have reached their respective end positions. As described above, this conclusion is optionally drawn based on pressure measurements on the fluid side of the apparatus. If in step 1 030 it is found that the blood pumps' flexible members have not yet reached their end positions, the procedure loops back to steps 1 01 0 and 1 020. Otherwise, case steps 1 040 and 1 045 follow.

Step 1 040 closes the first valve means, and in parallel there with step 1 045 opens the second valve means.

Thereafter, a step 1 050 controls the first and second fluid pumps to draw blood treatment fluid into the first and second blood pumps. A first fraction of this fluid goes directly to the se- cond accumulation container of the first blood pump, and a second fraction of this fluid passes through the blood treatment unit before entering the second accumulation contai ner of the second blood pump. As a result of the entry of blood treatment fluid, treated blood is delivered to the target vessel . A first fraction of this blood in the first accumulation container of the first blood pump passes the blood treatment unit where it is treated , and a second fraction of this blood located in the first accumulation contai ner of the second blood pump has already passed the blood treatment unit and goes directly to the target vessel .

In parallel with step 1 050, a step 1 055 controls a trans-membrane fluid flow between the blood side and the fluid side of the blood treatment unit. Again, this may involve any one of the above-described strategies. Then, a step 1 060 checks whether or not the flexible members of the first and second blood pumps have reached their respective end positions. If this is found to be the case a step 1 065 follows, and otherwise the procedure loops back to steps 1 050 and 1 055. Step 1 065 checks whether or not a desired trans-membrane fluid transport has been accomplished between the blood side and the fluid side of the blood treatment unit. If this is found to be the case, the procedure loops back to steps 1 01 0 and 1 01 5, and otherwise the procedure loops back to steps 1 050 and 1 055. The procedure iterates as described above until the treatment is finalized.

All of the steps, as well as any sub-sequence of steps, described with reference to Figure 1 0, above may be controlled by means of a programmed computer apparatus. Moreover, al- though the embodiments of the invention described above with reference to the drawings comprise computer apparatus and processes performed in computer apparatus, the i nvention thus also extends to computer programs, particularly computer pro- grams on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the procedure according to the invention. The program may either be a part of an operating system, or be a separate application. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a Flash memory, a ROM (Read Only Memory), for example a DVD (Digital Video/Versatile Disk), a CD (Compact Disc), an EPROM (Erasable Programmable Read-Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or a magnetic recording medium, for example a floppy disc or hard disc. Further, the car- rier may be a transmissible carrier such as an electrical or optical signal which may be conveyed via electrical or optical cable or by radio or by other means. When the program is embodied in a signal which may be conveyed directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant procedures.

In this specification, the wording that: "a fluid pump is arranged in a conduit" shall be understood to also encompass arrangements wherein the pump is configured to operate on a fluid passing through the conduit by other means than having the pump actually included in the conduit, such as hose pumps manipulating the exterior of a fluid conduit. In this specification is exemplified that the first accumulation container 9b or 9b' has a volume of 50 ml. However, the volume may be smaller or larger, e.g. in the range of 25-75 ml.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any suggestion that the referenced prior art forms part of the common general knowledge in Australia, or in any other country.

The term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components. However, the term does not preclude the presence or addition of one or more additional features, integers, steps or components or groups thereof.

The invention is not restricted to the described embodiments in the figures, but may be varied freely within the scope of the claims.

Claims

1 . A blood treatment apparatus, comprising : a blood treatment unit (8) configured to receive untreated blood and fresh blood treatment fluid, and emit treated blood and used blood treatment fluid, the blood being passed on a blood side (8B) of a semi-permeable membrane structure and the blood treatment fluid being passed on a fluid side (8F) of said structure, a pair of fluid pumps (1 4, 1 5) configured to pass blood treatment fluid through the blood treatment unit (8), and a pair of blood pumps (1 a, 1 b) configured to extract untreated blood from a blood source (S), pass extracted blood through the blood treatment unit (8) and deliver treated blood to a target vessel (T), characterized in that the fluid pumps (1 4, 1 5) are configured to control the operation of the blood pumps (1 a, 1 b) via the blood treatment fluid, the apparatus is configured to operate according to a cyclic process of which during a first phase the untreated blood is extracted from the blood source (S), and during a second phase the treated blood is delivered to the target vessel (T), and the apparatus comprises a flow control means (Rb, Rf; 1 6a, 1 6b; Rf 1 , Rf2; V_{1 1} , V₁₂, V₂₁ , V₂₂) configured to control a transmembrane flow between the blood side (8B) and the fluid side (8F) of the blood treatment unit (8).

2. The blood treatment apparatus according to claim 1 , wherein during operation of the apparatus the fluid side (8F) of the blood treatment unit (8) is associated with a fluid pressure drop and the blood side (8B) of the blood treatment unit (8) is associated with a blood pressure drop, and the flow control means comprises a first flow restrictor (Rb) arranged downstream of a blood outlet from the blood treatment unit (8) and upstream of a blood pump (1 b) of said blood pumps configured to deliver the treated blood to the target vessel (T), the first flow restrictor (Rb) being configured to cause a first pressure drop (ΔP_Rb) during operation of the apparatus.

3. The blood treatment apparatus according to claim 1 , comprising a second flow restrictor (Rf) arranged i n series with the blood treatment unit (8) in a conduit system configured to pass blood treatment fluid through the blood treatment unit (8) the second flow restrictor (Rf) being configured to cause a second pressure drop (ΔP_Rf) during operation of the apparatus.

4. The blood treatment apparatus according to claim 2 or 3, wherein is comprised a first and a second flow restictor (Rb, Rf) where, during operation of the apparatus a sum of the first pressure drop (ΔP_Rb) and the blood pressure drop over the blood side (8B) of the blood treatment unit (8) is approximately equal to a sum of the second pressure drop (ΔP_Rf) and the fluid pressure drop over the fluid side (8F) of the blood treatment unit (8).

5. The blood treatment apparatus according to claim 4, whe- rein the first and second pressure drops (ΔP_Rb, ΔP_Rf) over the first and second flow restrictors (Rb; Rf) have such magnitudes that a desired trans-membrane pressure drop (TMP) between the blood side (8B) and the fluid side (8F) of the blood treatment unit (8) is attai ned.

6. The blood treatment apparatus according to claim 1 , wherein the flow control means comprises a pair of auxiliary fluid pumps (1 6a; 1 6b) arranged i n a conduit system configured to pass blood treatment fluid through the blood treatment unit (8), each of the auxiliary fluid pumps (1 6a; 1 6b) being configured to influence a flow of blood treatment fluid being passed through the blood treatment unit (8).

7. The blood treatment apparatus according to claim 6, wherein a first auxiliary fluid pump (1 6a) is arranged in an outlet conduit downstream of the blood treatment unit (8), and the first auxiliary fluid pump (1 6a) is configured to withdraw fluid from the blood being passed through the blood treatment unit (8).

8. The blood treatment apparatus according to claim 7, comprising a control unit (20) configured to control the auxiliary pumps (1 6a, 1 6b) to be operated to pass a base flow through the blood treatment unit (8) during both the first and second phases of the cyclic process of a certain base flow level (F_B).

9. The blood treatment apparatus according to any one of claims, 2-4 comprising a control unit (20) configured to control the fluid pumps (1 4, 1 5) to be operated during the first and second phases in such a manner that a flow (Q₁₄, Q₁₅) of blood treatment fluid passing through the blood treatment unit (8) is equal to or exceeds a base flow level (F_B) during both the first and second phases.

1 0. The blood treatment apparatus according to any of the preceeding claims, wherein a first fluid pump (1 4) of said fluid pumps is configured to draw fresh blood treatment fluid from a fluid reservoir (1 2a) and a second fluid pump (1 5) of said fl uid pumps is configured to eject used blood treatment fluid from the apparatus, and a control unit (20) is configured to control said fluid pumps (1 4, 1 5) to be operated such that an access flow (F_A) of untreated blood extracted from the blood source (S) is equivalent to a difference flow between a first fluid flow (Q₁₄) of fresh blood treatment fluid drawn from the fluid reservoir (1 2a) and a second fluid flow

(Q₁₅) of used blood treatment fluid ejected from the ap- paratus, and control said fluid pumps (1 4, 1 5) to be operated such that a flow of treated blood to the target vessel (T) is equivalent to a difference between the second fluid flow (Q₁₅) of used blood treatment fluid ejected from the apparatus and the first fluid flow (Q₁₄) of fresh blood treatment fluid drawn from the fl uid reservoir (1 2a).

1 1 . The blood treatment apparatus according to claim 1 , wherein the flow control means comprises: a first fluid valve means (V_{1 1}) controllable in response to a first valve control signal (V₁₁), the first fluid valve means (V₁₁) being arranged on an inlet conduit configured to receive fresh blood treatment fluid into the apparatus, the first fluid valve means (V₁₁) is further connected to the first fluid pump (14) and via a first adjustable flow restrictor (Rf 1) to the blood treatment unit (8), and a second fluid valve means (V₂₁) controllable in response to a second valve control signal (v₂₁), the second fluid valve means (V₂₁) being arranged on an outlet conduit configured to discharge used blood treatment fluid from the apparatus, the second fluid valve means (V₂₁) is connected to the blood treatment unit (8) via a second adjustable flow restrictor (Rf2) and to the second fluid pump (15).

12. The blood treatment apparatus according to claim 1 , wherein the flow control means comprises:a first fluid valve means (V₁₁) controllable in response to a first valve control signal (V₁₁), the first fluid valve means (V₁₁) being arranged on an inlet conduit configured to receive fresh blood treatment fluid into the apparatus, the first fluid valve means (V₁₁) is further connected to the first fluid pump (14) and via a third fluid valve means (V₁₂) to the blood treatment unit (8), the third valve means (V₁₂) being controllable in response to a third valve control signal (v₁₂), and a second fluid valve means (V₂₁) controllable in response to a second valve control signal (v₂₁), the second fluid valve means (V₂₁) being arranged on an outlet conduit configured to discharge used blood treatment fluid from the apparatus, the second fluid valve means (V₂₁) is connected to the blood treat- ment unit (8) via a fourth fluid valve means (V₂₂) and to the second fluid pump (15), the fourth valve means (V₂₂) being controllable in response to a fourth valve control signal (v₂₂).

13. The blood treatment apparatus according to claim 12, comprising a control unit (20) configured to: during the first phase, control the first fluid valve means (V_{1 1}) to a closed position; control the third fluid valve means (V₁₂) to an open position; control the second valve means (V₂₁) to an open position; and control the fourth fluid valve means (V₂₂) in an intermittent manner, between an open and a closed position, such that a desired trans-membrane flow is attained ; and during the second phase, control the first fluid valve means (V_{1 1}) to an open position; control the third fluid valve means (V₁₂) in an intermittent manner, between an open and a closed position, such that a desired trans-membrane flow is attained ; control the second valve means (V₂₁) to a closed position ; and control the fourth fl uid valve means (V₂₂) to an open position.

1 4. The blood treatment apparatus according to any one of the precedi ng claims, wherein each of the blood pumps (1 a, 1 b) comprises a pumpi ng chamber and a flexible member (9a, 9a') separating the pumpi ng chamber into a first accumulation contai ner (9b, 9b') and a second accumulation container (9c, 9c'), the flexible member (9a, 9a') is movable within the pumping chamber so as to vary a volume relationship between the first and second accumulation containers (9b, 9b' ; 9c, 9c'), the second accumulation container (9c, 9c') is configured to receive an amount of working fluid to act on the flexible member (9a, 9a') and thus pump blood from the first accumulation container (9b, 9b'), and the fluid pumps (1 4, 1 5) and the blood pump (1 a, 1 b) are arranged such that the blood treatment fl uid constitutes the working fluid for the blood pumps (1 a, 1 b).

1 5. A method of treating blood i n a blood treatment apparatus includi ng : a blood treatment unit (8) configured to receive un- treated blood and fresh blood treatment fluid, and emit treated blood and used blood treatment fluid, the blood being passed on a blood side (8B) of a semi-permeable membrane structure and the of blood treatment fluid being passed on a fluid side (8F) of said structure; a pair of fluid pumps (1 4, 1 5) configured to pass blood treatment fluid through the blood treatment unit (8) ; and a pair of blood pumps (1 a, 1 b) configured to extract untreated blood from a blood source (S), pass extracted blood through the blood treatment unit (8) and deliver treated blood to a target vessel (T), the method characterized by controlling the blood pumps (1 a, 1 b) to operate by passi ng blood treatment fluid through the fl uid pumps (1 4, 1 5), controlling the apparatus according to a cyclic process wherein duri ng a first phase the untreated blood is extracted from the blood source (S) and duri ng a second phase the trea- ted blood is delivered to the target vessel (T), and controlling a trans-membrane flow between the blood side (8B) and the a fluid side (8F) of the blood treatment unit (8) through the medium of a flow control means (Rb, Rf; 1 6a; 1 6b; Rf1 , Rf 2; V_{1 1} , V₁₂, V₂₁ , V₂₂).

1 6. The method according to claim 1 5, wherein the fluid side (8F) of the blood treatment unit (8) is associated with a fluid pressure drop or the blood side (8B) of the blood treatment unit (8) is associated with a blood pressure drop, and the method comprising : restricting a flow of treated blood (Rb) downstream of the blood treatment unit (8) and upstream of a blood pump (1 b) of said blood pumps configured to deliver the treated blood to the target vessel (T) thus causing a first pressure drop (ΔP_Rb), or restricting a flow of blood treatment fluid in series with the blood treatment unit (8) in a conduit system configured to pass blood treatment fluid through the blood treatment unit (8) thus causing a second pressure drop (ΔP_Rf), and controlling the trans-membrane flow by means of the fluid pumps (1 4, 1 5) and at least one of the first and the second pressure drops (ΔP_Rb,ΔP_Rf).

1 7. The method according to claim 1 5, comprising controlling the trans-membrane flow by controlling a pair of auxiliary fluid pumps (1 6a; 1 6b) arranged i n a conduit system configured to pass blood treatment fluid through the blood treatment unit (8) .

1 8. The method according to claim 1 5, comprising : restricting a flow of blood-treatment fluid in a conduit segment located upstream of the blood treatment unit (8) and being parallel to a conduit in which a first fluid pump (1 4) of said fluid pumps is arranged, and restricting a flow of blood-treatment-fluid in a conduit segment located downstream of the blood treatment unit (8) and being parallel to a conduit in which the second fluid pump (1 5) of said fluid pumps is arranged.

1 9. The method according to any one of the claims 1 5 to 1 8, comprising controlling the fluid pumps (1 4, 1 5) to operate during the first and second phases in such a manner that a flow (Q₁₄, Q₁₅) of blood treatment fluid passing through the blood treatment unit (8) exceeds a base flow level (F_B) duri ng both the first and second phases.

20. The method according to any one of the claims 1 5 to 1 9, comprising : controlling a first fluid pump (1 4) of said fluid pumps to draw fresh blood treatment fluid from a fluid reservoir (12a), controlling a second fluid pump (1 5) of said fluid pumps to eject used blood treatment fluid from the apparatus, controlling said fluid pumps (1 4, 1 5) to operate such that an access flow (F_A) of untreated blood extracted from the blood source (S) is equivalent to a difference flow between a first fluid flow (Q₁₄) of fresh blood treatment fluid drawn from the fluid reservoir (1 2a) and a second fluid flow (Q₁₅) of used blood treatment fluid ejected from the apparatus, and controlling said fluid pumps (1 4, 15) to operate such that a flow of treated blood to the target vessel (T) is equivalent to a dif- ference between the second fluid flow (Q₁₅) of used blood treatment fluid ejected from the apparatus and the first fluid flow (Q₁₄) of fresh blood treatment fluid drawn from the fluid reservoir (12a).

21 . A computer program loadable into the memory (21 ) of a computer, comprising software for controlling the steps of any of the claims 14 to 20 when said program is run on the computer.

22. A computer readable medium (21 ), having a program recorded thereon, where the program is to make a computer control the steps of any of the claims 14 to 20 when the program is loaded into the computer.