This invention concerns a pump for delivering a fluid, preferably a micro fluid, comprising an outflow connector, wherein the flow rate of the fluid delivered by the pump depends on the position of a needle in the outflow connector. The needle may be connected to an infusion catheter the fluid being a drug or medication, or a dialysis probe, the fluid being a perfusion fluid.

Micro fluid systems are used for several purposes, among others for monitoring concentrations of substances like glucose, hormones and enzymes in body tissue. The system is often equipped with a probe consisting of a semi-permeable membrane in connection with a fluid supply outlet. The membrane is inserted in touch with the tissue and the other side is in con- nection with a perfusion fluid, which is supplied via the fluid supply. The perfusion fluid collects the substances in the tissue diffusion across the membrane. The enriched perfusion fluid is removed via the outlet for further analysing purposes.

Since the carrier fluid has to stay a certain amount of time within the probe to allow significant transfer of species from the body fluid into the perfusion fluid, the perfusion fluid flow is very slow. Typical flow rates are in the range of a few μl/min, which are realized by flow restrictions being arranged in the fluid channels. When connecting an analysis system to the sensing probe, the flow channel from the carrier fluid reservoir of the analysis-system to the probe and the probe volume itself have to be completely filled before monitoring of species concentration can be performed. This time period for priming the system can be of considerable length, perhaps even hours.

It is therefore an object of the invention to provide a pump with considerably reduced priming time.

This is achieved by equipping the pump with at least two parallel flow communications having different flow restrictions, and means to direct the fluid through the chosen one of the flow communications. Before the sys- tern is set into operation, the system is flushed by directing fluid through the flow communication having the smallest of the flow restrictions, preferably being significantly smaller, ensuring that the time period for the priming is considerably reduced to minutes or perhaps even seconds. When the system is primed and set into operation, the fluid is directed through the second flow communication having a large flow restriction.

A typical method of regulating the flow resistance of micro fluid communicating means is to insert flow restrictors. Flow restrictors are often realised in the form of small pieces of glass capillary tubes, which have the quality that the flow rate has a well-defined relation to the length and the inner diameter of the capillary tube and the pressure drop across it. For a given pressure drop, the flow rate will thus be determined by selecting a capillary tube of the right length and inner diameter.

The pump is equipped with connecting means for connecting it to an outlet part, e.g. an infusion catheter or a micro dialysis probe, where the connecting means of the pump is equipped with the directing means for switching between the individual fluid communications.

In a preferred embodiment the direction of the fluid is achieved by changing the relative position of the outflow connecter of the pump to the inflow connecter of the outlet part.

In a preferred embodiment of the inflow connector the outlet part is a nee- die having an internal flow channel and an opening close to the needle tip.

To connect the outlet part to the pump, the needle is pierced into the out-

flow connector of the pump, the flow rate depending on how deep the needle is pierced into the outflow connector.

In a preferred embodiment the outflow connector comprises a row of 5 chambers each in flow communication with the fluid reservoir through a separate flow restriction, all chambers thus having different flow rates.

In a preferred embodiment the chambers are divided by check valves, or more specifically duck bill valves, placed in a row with small spaces be- o tween them, the flow rate then depending upon the chamber in whose opening the needle is positioned.

In short, the invention concerns a pump system comprising:

- a pressurized fluid reservoir, 5 - an outlet connector

- at least one fluid communicating means connecting said pressurized fluid reservoir to said outflow connector,

characterized in that, o the outflow connector and an inflow connector are adapted to connect in fluid communication in at least a first position and a second position, the flow rate of the first position being different from that of the second position.

5 The invention and other and further features of this invention will be apparent to those skilled in the art from the following detailed description of the annexed drawings which show some embodiments of the invention.

Fig. 1 is a schematic representation of the invention, when the inflow con- o nector of the outlet part is not connected to the outflow connector of the pump.

Fig. 2 shows the invention when the inflow connector of the outlet part is connected to the outflow connector of the pump in a first position, representing a first flow rate.

Fig. 3 shows the invention when the inflow connector of the outlet part is connected to the outflow connector of the pump in a second position, representing a second flow rate.

Fig. 4 is a altemativ embodiment of the invention, where the inflow con- o nector is equipped with two channel sections comprisimg seperate flow restrictors.

Fig. 1 illustrates the basic embodiment of the preferred design of the invention. The pump system 1 comprises a fluid reservoir 2 containing the 5 fluid 3 to be infused into a body, through a probe or the like. Fluid communicating means 4, 5 connects the fluid reservoir to the outflow connector 6 of the pump. The fluid communicating means comprise flow restrictions 7, 8. The outflow connector 6 comprise two sections, or chambers, 9, 10, the two chambers being separated by the valve 11 , and chamber 10 further o being separated from the surroundings by the valve 12.

In a preferred embodiment of the invention the valves 11 , 12 are duck bill valves, positioned in such a way that fluid is denied communication from chamber 9 to chamber 10, and from chamber 10 to the surroundings. 5

In the preferred embodiment the flow restriction 8 is larger than the flow restriction 7. One consequence of this set-up is that the pressure inside chamber 9 is larger than inside chamber 10, thus helping to keep the valve 11 closed, restricting, or preferably denying a flow from chamber 10 to o chamber 9. In the same way, as the pressure inside chamber 10 is larger than the surrounding pressure, the valve 12 is effectively closed.

The inflow connector 20 of the preferred embodiment of the invention is a needle with an internal flow channel 22 connected to the outflow part, the outflow part not shown in the figures. At the tip of the needle is an opening 21 into the internal flow channel 22.

5

Figs. 2 and 3 illustrate the operation of the pump system 1 of the invention. In Fig. 2 the needle 20 is inserted into the outflow connector 6, so that the opening 21 in the needle tip is positioned inside chamber 9. This may be referred to as a first position of the needle 20. This first position en- o sures a first flow rate of the fluid through the internal channel 22 of the needle. The needle 20 in Fig. 3 is positioned in the second position having the opening inside chamber 10, the needle 20 being clear of valve 11 , the valve thus being closed. This position ensures a second flow rate of the fluid through the internal channel 22 of the needle 5

When the flow restriction 7 is different from the flow restriction 8, then the first flow rate will be different from the second flow rate, and if, as illustrated in Figs. 1-3, the flow restriction 8 is much larger than the flow restriction 7, the second flow rate going through the flow restriction 8 will be o much smaller than the first flow rate going through the flow restriction 7.

The connectors 6 and 20 may preferably be equipped with male and female screwing threads, to make a stable and leak tight connection when they are connected for operation. 5

The connectors may preferably be equipped with fixation positions for each of the individual chambers, keeping the needle fixed with the opening 21 of the needle 20 in fluid communication with only one of the fluid communications 4, 5, the needle possibly only being movable by overcoming o some small resisting force.

The fluid reservoir 2 may preferably be an elastomeric bladder, a bellows, or some other reservoir operating in the way where a restoring energy is stored as it is filled with the fluid, thus, when some access to the external of the reservoir is opened, the stored restoring energy compresses the in- 5 ternal volume of the reservoir squeezing the fluid out into the fluid communications 4, 5

The fluid reservoir 2 may preferably be equipped with some access port 30 as seen in Fig. 1 , for filling the reservoir with the fluid. The access port o may be a septum, a check valve or any other thinkable means to give a one-way fluid access to the internal of the reservoir.

Fig. 4 shows an alternative embodiment of the invention, where the inflow connector 40 is equipped with two channel sections 41 , 45, merging to a 5 single flow channel 43, and each having a separate opening 44, 42 to the surroundings. The outflow connector 46 now only comprises a single communication chamber 47 being in fluid communication with the reservoir 48, and two 'blind' chambers 49, 50. Now, each of the two channel sections 41 , 45 comprise a separate flow restriction 51 , 52, so the flow rate will de- o pend on which of the openings 44, 45 is positioned in the communication chamber 47, the other being positioned in one of the 'blind' chambers 49, 50.