WO2009049823A1

WO2009049823A1 - Catheter and methods of operating and manufacturing the same

Info

Publication number: WO2009049823A1
Application number: PCT/EP2008/008546
Authority: WO
Inventors: Werner Regittnig
Original assignee: Werner Regittnig
Priority date: 2007-10-16
Filing date: 2008-10-09
Publication date: 2009-04-23

Abstract

A catheter, the catheter comprising a first tubular member having a first lumen and a first perforation, and a second tubular member having a second lumen and a second perforation, wherein the second lumen is adapted to receive the first tubular member so that a channel is formed between the first tubular member and the second tubular member and so that a part of an outer surface of the first tubular member contacts a part of an inner surface of the second tubular member, wherein the first tubular member and the second tubular member are arranged to form a first fluidic path from the first lumen through the first perforation, to a body under investigation, and wherein the first tubular member and the second tubular member are arranged to form a second fluidic path from the body under investigation, through the second perforation, and to the channel.

Description

Catheter and methods of operating and manufacturing the same

The invention relates to a catheter.

The invention further relates to a method of operating a catheter. Moreover, the invention relates to a method of manufacturing a catheter.

There are numerous instances in the treatment and diagnosis of illnesses where repetitive samplings of body fluids need to be made, or in which repetitive introductions of medication or therapeutic fluid must be made to interior regions of the body. An example is the repetitive sampling of blood by fingersticking to measure glucose, and the repetitive insulin injection by hypodermic needles into the subcutaneous adipose tissue, such as in the current standard treatment of diabetes. To reduce inconvenience and pain associated with repetitive needle penetrations, various instruments have been devised that, once inserted or implanted into an internal region of the body, give access to this body region over an extended period of time.

Depending on the kind of instrument applied, this continuous access can be used for introducing therapeutic fluids to, and/or withdrawing body fluids from, an interior region of the body. An example is the continuous subcutaneous infusion of insulin (CSII) in diabetic patients by means of a transcutaneous cannula connected to an external infusion pump. For example, US 5,257,980, US 5,522,803, US 6,572,586, US 6,840,922, and US 6,302,866 describe flexible, transcutaneous cannulae, which are introduced into the subcutaneous tissue with the help of a metal needle ("over the needle insertion", "over the needle type catheter"). After the removal of the metal needle, the transcutaneous cannula may then dwell for an extended period of time in the tissue (for instance 2 to 3 days). Transcuatenous indwelling cannulae of this type may only be used for delivery of substances to the tissue. Removal of substances from the tissue, for example glucose for the purpose of determining the tissue glucose concentration, is not possible using this type of indwelling catheter. An example of an indwelling catheter which is suitable both for the delivery and for the removal of substances would be a catheter which operates according to the principle of microperfusion. Schaupp et al., Am. J. Physiol. 276: E401-408, 1999 discloses a microperfusion catheter. US 6,706,009 and US 6,936,026 each disclose a micro perfusion device and method for obtaining at least one constituent of a body fluid. The at least one constituent is obtained using a subcutaneously- positioned perfusion catheter into which perfusate is introduced by a supply channel and an insertion needle. The perfusate absorbs the at least one constituent as it flows out of the perfusion catheter and through a discharge channel.

It is an object of the invention to provide a powerful catheter system.

In order to achieve the object defined above, a catheter, a method of operating a catheter, and a method of manufacturing a catheter according to the independent claims are provided.

According to an exemplary embodiment of the invention, a catheter is provided, the catheter comprising a first tubular member having a first lumen and a first perforation, and a second tubular member having a second lumen and a second perforation, wherein the second lumen is adapted to receive the first tubular member so that a channel is formed between the first tubular member and the second tubular member and so that a part of an outer surface of the first tubular member contacts a part of an inner surface of the second tubular member, wherein the first tubular member and the second tubular member are arranged (relative to one another) to form a first fluidic path from the first lumen through the first perforation, into a body under investigation, and wherein the first tubular member and the second tubular member are arranged (relative to one another) to form a second fluidic path from the body under investigation, through the second perforation, and to the channel.

According to another exemplary embodiment of the invention, a method of operating a catheter comprising a first tubular member having a first lumen and a first perforation and a second tubular member having a second lumen and a second perforation is provided, wherein the second lumen receives the first tubular member so that a channel is formed between the first tubular member and the second tubular member and so that a part of an outer surface of the first tubular member contacts a part of an inner surface of the second tubular member, wherein the method comprises guiding a perfusion fluid along a first fluidic path from the first lumen through the first perforation, to a body under investigation, and guiding a sample fluid produced by an at least partial (particularly a complete) equilibration between the perfusion fluid and a body fluid along a second fluidic path from the body under investigation, through the second perforation, and to the channel.

According to still another exemplary embodiment of the invention, a method of manufacturing a catheter is provided, the method comprising the steps of providing a first tubular member having a first lumen, forming a first perforation in the first tubular member, providing a second tubular member having a second lumen, forming a second perforation in the second tubular member, accommodating the first tubular member in the second lumen so that a channel is formed between the first tubular member and the second tubular member and so that a part of an outer surface of the first tubular member contacts a part of an inner surface of the second tubular member, arranging the first - A -

tubular member and the second tubular member to form a first fluidic path from the first lumen through the first perforation, to an environment (such as surrounding tissue of a human or animal body in which the catheter is inserted), and arranging the first tubular member and the second tubular member to form a second fluidic path from the environment, through the second perforation, and to the channel.

According to yet another exemplary embodiment of the invention, a catheter is provided, the catheter comprising a first tubular member, a second tubular member having a lumen and a perforation, wherein the lumen is adapted to receive the first tubular member so that a channel is formed between the first tubular member and the second tubular member and so that a part of an outer surface of the first tubular member contacts a part of an inner surface of the second tubular member, wherein the first tubular member and the second tubular member are arranged to form a fluidic path between the body under investigation, the perforation, and the channel, the catheter further comprising a bidirectional fluid transport unit coupled to the channel and adapted for selectively transporting a fluid through the channel, through the perforation and into the body under investigation, or from the body under investigation, through the perforation and into the channel.

According to still another exemplary embodiment of the invention, a method of operating a catheter comprising a first tubular member and a second tubular member having a lumen and a perforation is provided, wherein the lumen receives the first tubular member so that a channel is formed between the first tubular member and the second tubular member and so that a part of an outer surface of the first tubular member contacts a part of an inner surface of the second tubular member, wherein the method comprises the steps of guiding a perfusion fluid along the channel to a body under investigation, and guiding a sample fluid produced by an at least partial equilibration between the perfusion fluid and a body fluid along a fluidic path from the body under investigation, through the perforation, and to the channel.

In the context of this application, the term "catheter" may particularly denote a small flexible tube for withdrawing fluids from and/or introducing fluids into a cavity of a physiological body, that is to say to drain fluid from and/or infusion fluid into the body.

The term "tubular member" may particularly denote an oblong hollow structure having any desired geometry and having a lumen (i.e. a cavity or a passageway, capable of receiving and conducting a fluid) of any desired shape, such as a lumen having a cylindrical, oval, or polygonal cross-section.

The term "perforation" may denote any hole, bore, passageway, opening, etc. formed in a tubular member, for instance a hole formed in a lateral wall thereof or an outlet formed in an end face thereof. This term may particularly cover holes having microscopic dimensions, for instance larger than 10 μm or 100 μm. Such perforations may define a fluid outlet portion out of a fluidic passageway. A perforation may comprise one hole or a plurality of holes.

The term "fluidic path" may particularly denote a consecutive fluidic structure of one or more individual sections which are in fluid communication to one another so as to allow a fluid to flow along the corresponding fluidic path.

The term "body under investigation" may particularly denote any human being, any animal, and any plant (any organism). It may be a living body so that living tissue may be investigated.

The term "physiological parameter" may particularly denote any parameter which is related to the physiology of a living organism, for instance the metabolism, etc. Such a physiological parameter may include the concentration of an exogenous or endogenous marker, a protein concentration, etc. The physiological parameter to be measured may preferably be a glucose concentration in the body (particularly a tissue glucose concentration in the body), but may alternatively or additionally also be a lactate concentration in the body, an oxygen concentration in the body, an ion concentration (such as hydrogen-ion concentration, i.e., pH) in the body, a cholesterol concentration in the body, a quantity of bacteria in the body, a quantity of viruses in the body, or a medication concentration in the body. In this way, the measurement of such a physiological parameter or another physiological parameter may provide information about a current state of the body and thus be used as a meaningful decision criterion as to whether and to what extent a physiologically active substance is to be supplied to the body locally or systemically.

The term "fluid" may include any substance in this context which at least partially contains components in the liquid phase. Of course, solid and/or gaseous components may also be contained or dissolved in such a fluid and may even make up the predominant component of the fluid.

A part of the body penetrated by the catheter may be particularly subcutaneous tissue, an organ, a vein, an artery, and a blood vessel. An intravenous application of the device is possible. Also applications in the skin are possible, for instance by cutaneous ultrafiltration or

(micro)perfusion. The fluid which is removable from the body may be tissue liquid. Alternatively or additionally, the fluid may, however, also be blood, lymph, spinal fluid, urine, or other tissue.

The term "perfusion fluid" may particularly denote any carrier liquid in which a physiologically active substance may be optionally included, dissolved or diluted so as to obtain a solution of a physiologically active substance in a desired concentration. It is common practice to provide physiologically active substances, like insulin, in a liquid perfusate solution in which the physiologically active substances is contained. Particularly, the skilled person knows many examples for perfusion fluids which are appropriate for containing insulin or other physiologically active substances. A perfusion fluid may also comprise or consist of a neutral solution, a rinse fluid, or a cleaning fluid.

The term "physiologically active substance" may particularly denote any substance which may have an effect on the physiology of a living organism, for instance a medication, a drug, etc. The physiologically active substance may be a medication, particularly a glucose-regulating medication such as insulin, insulin analogues, glucagon, catecholamines, Cortisol, or growth hormone. In this way, the supply of the physiologically active substance to the body may selectively and effectively influence the glucose level in the body or in specific parts of the body (for instance, tissue, blood). However, the physiologically active substance may also be any other arbitrary substance (such as aldosterone, bicarbonate, oxygen, phosphate) which has a functional influence on the body or organism. This particularly also includes any type of medicine, vitamin, carrier substances (such as artificial oxygen carriers), etc.

According to an exemplary embodiment of the invention, a catheter is provided which allows to be manufactured by simply mounting two tubular members in a manner that one surrounds the other (so that the two members are in close contact to one another in one portion and form a channel in between in another portion), wherein perforations in these tubular members define a fluidic path for infusing a fluid into a surrounding environment of the catheter such as a body of a human or animal patient. For instance after an at least partial equilibration between such a fluid and a body fluid, a withdrawal or backflow of such a sample fluid from the body under investigation back into the catheter for analysis may be enabled as well. By taking this measure, it is possible to supply a sample fluid which may optionally include a medication such as insulin into a body and to simultaneously measure a physiological parameter such as a glucose level in the body fluid. The supply of the physiologically active substance may be regulated in dependence of the measured value of the physiological parameter, thereby simulating an artificial pancreas in the context of insulin as a medication and glucose as a parameter to be monitored/adjusted. By arranging the tubular members to surround one another so that a part of an outer surface of the first tubular member contacts a part of an inner surface of the second tubular member, a section of the catheter may be provided at which the tubular members are connected to one another (for instance are fixed to one another). This allows for a stable and robust configuration, which may simultaneously serve as a sealing.

Exemplary embodiments of the invention may provide a (micro)perfusion catheter which is designed in a small and robust manner, has a high exchange efficiency and is usable in a simple and convenient manner by a physician or a patient. Furthermore, exemplary embodiments of the invention may provide designs which are appropriate for mass production with low manufacture costs and can therefore also be used for the therapy of widespread diseases such as diabetes.

Exemplary embodiments of the invention may be formed based on a modification of conventional transcutaneous infusion catheters (see for instance US 5,522,893, US 6,572,586, US 6,840,922, US 6,302,866). Such concepts may be modified in such a manner that not only a delivery into tissue or other physiologic regions but also a withdrawal of substances from the tissue or other physiologic regions is made possible. According to another exemplary aspect of the invention, two tubular members may be arranged to surround one another to define a fluidic channel therebetween in a first section, and to define a contacting/sealing portion in a second section. A single fluidic path between channel, perforation in the outer tubular member and surrounding environment may first be operated in a first flow direction by pumping perfusion fluid (for instance in a range between O.lμl and 10μl_; more particularly of lμl), using a bidirectional pump, into the channel. After an appropriate equilibration time (for instance 30 seconds), the pump may be switched off and the perfusion fluid may equilibrate with the body fluid through the perforation. Subsequently, the bidirectional pump may be reversed regarding its pumping direction to pump the equilibrated fluid through the channel to a connected equipment for further analysis of this fluid. The present inventors have recognized that such an embodiment may work properly with low effort (see also Fig. ID and Fig. 2E). Such an embodiment may be combined with any of the other embodiments described herein. Such embodiments may or may not include a lumen and a perforation also in the first tubular member. However, in the above described operation mode, such an inner lumen may be deactivated (or closed). Such an embodiment may allow the use of a single (bidirectional) pump, and may allow to reduce the dead space to a very small volume.

Next, further exemplary embodiments of the catheters will be explained. However, these embodiments also apply to the method of manufacturing a catheter and for the methods of operating a catheter. The first tubular member and the second tubular member (which may be shaped essentially as hollow cylinders) may be arranged (for instance concentrically) so that the first fluidic path may be formed from the first lumen through/via the first perforation, through/via the channel, and through/via the second perforation into a body under investigation. Such a fluidic path may be defined by a pump pumping along a corresponding direction and may allow perfusion fluid to flow essentially within the catheter so as to allow for a sufficiently weak interaction with the surrounding body fluid. Furthermore, such a geometry allows for a proper control of the fluidic path. The catheter may comprise an insertion needle adapted to be received in the first lumen of the first tubular member and adapted to be detachable/removable from the first lumen after insertion of the catheter into the body under investigation. In such an embodiment, in addition to the two tubular members, a rigid (i.e. essentially non-flexible), for instance metallic, needle may be provided which significantly simplifies insertion of the catheter into the body. By removing the needle after insertion into the body while maintaining the remainder of the catheter in the body, the remaining structure formed by the two tubular members which may be free of metallic components may have a flexible character so as to allow for a convenient wear of the remaining portion of the catheter by a patient.

Alternatively, a hollow needle may be provided as the first tubular member and may be adapted to be received in the second lumen of the second tubular member. In such an embodiment, the hollow needle may be used for insertion of the catheter system and may also be adapted to guide a perfusion fluid along its inner lumen. Thus, such an embodiment may allow for immediate catheter operation after insertion into the tissue. The first tubular member and/or the second tubular member may be a cannula, particularly a flexible cannula. In this context, the term "flexible" may particularly denote a cannula made of a material which is sufficiently soft to essentially follow a motion of a body part of the human patient, so that a motion of a human patient does not result in a catheter maintaining its position in a rigid manner, thereby not harming the body or involving the danger of an injury. In this context, a sufficiently flexible cannula may allow to follow body motions to improve the convenience in use. For example, such a flexible cannula may be made of a plastic material. The first perforation may comprise one or more holes in the first tubular member. In other words, it is possible that the first perforation consists of exactly one hole. According to another exemplary embodiment, the first perforation comprises a plurality of holes, for instance 2, 3, 4, 5, 6, 7, 8, 9, 10 or more holes. Particularly, the one or more holes related to the first perforation may be formed in an end face and/or in a lateral wall of the first tubular member. For example, when the first tubular member is a needle, an end portion/a tip portion of the needle being tapered for proper insertion into a body under investigation may simultaneously serve as a hole. However, additionally or alternatively, a lateral sidewall of the first tubular member may be provided with one bore or several bores to form this first perforation.

Accordingly, the second perforation may comprise one or more holes in the second tubular member. The larger the number of holes are provided in the second tubular member, the better is the exchange between the surrounding body fluid and the perfusion fluid within the catheter. For example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more holes may be formed in the lateral wall of the second tubular member. The adjustment of number, position and dimensions of the holes may allow to tune the degree of interaction between body fluid and perfusion fluid.

Each of the one or more holes of the first perforation and/or of the second perforation may have a dimension of at least 0.1 mm, particularly of at least 0.2 mm, more particularly of at least 0.4 mm. Therefore, microscopic holes (and not only pores in a porous or sintered structure) may be formed in a wall to allow a sufficiently proper interaction between body fluid and perfusion fluid.

The one or more holes of the first perforation may be aligned with the one or more holes of the second perforation. This may simplify the fluidic communication between the different fluidic channels and may also simplify the manufacture of the catheter, since the production of the holes can be performed in a common milling, drilling or laser treatment procedure when the tubular members are provided the one within the other. Alternatively, the one or more holes of the first perforation may be disaligned/displaced/staggered or angularly offset with respect to one another with the one or more holes of the second perforation. This may strengthen the mechanical stability of the device.

The catheter may be adapted so that a perfusion fluid may be supplyable along the first fluidic path. In other words, the perfusion fluid may be pumped through the first lumen (for instance by a pump such as a peristaltic pump), optionally through further fluidic components such as the first perforation, the second perforation and the channel, or directly from the first lumen into the body fluid.

Furthermore, the catheter may be adapted so that a body fluid is supplyable along the second fluidic path. This may be achieved by providing a pump such as a peristaltic pump sucking body fluid through the second perforation and the channel back into the catheter. According to one embodiment, it may be possible to use only the second fluidic path in combination with a bidirectional pump, not the first fluidic path (which may be closed in such a configuration). In such an embodiment, perfusion fluid may be pumped into the channel for subsequent equilibration with surrounding body fluid. After at least partial equilibration (during equilibration, the pump may be switched off), the pumping direction may be reversed so that the fluid is removed from the channel with a flowing direction opposite to a direction along which the perfusion fluid is introduced in the channel.

The pump for pumping the perfusion fluid into the body under investigation and the pump for sucking the body fluid into the catheter may be realized as two different pumps, or as one common bidirectional pump which may be operated in different modes (such as a pumping mode and a sucking mode). The second tubular member may have a first section (for instance a front section in insertion direction of the catheter) and a second section (for instance a back section in insertion direction of the catheter), wherein an inner diameter of the second lumen in the first section may differ from (for instance may be smaller than) an inner diameter of the second lumen in the second section. By such a geometry, particularly when providing the second lumen in a stepped manner at a border between the first section and the second section, two advantageous effects may be achieved simultaneously. Firstly, in a narrow portion close to an end part, a stable and sealing contact between the two tubular members may be achieved. Friction may support such a sealing and fastening feature. Secondly, in a portion remote from the end part of the catheter, the second tubular member may have a wider opening for receiving the first tubular member, so that a sufficiently large fluidic channel can be formed used for pumping back the mixture of body fluid and optionally perfusion fluid which has been inserted into the body under investigation beforehand.

Also the first tubular member may have a first section (for instance a front section in insertion direction of the catheter) and a second section (for instance a back section in insertion direction of the catheter), wherein an inner diameter of the first lumen in the first section may differ from (for instance may be smaller than) an inner diameter of the first lumen in the second section. By such a geometry, particularly when providing the first lumen in a stepped manner at a border between the first section and the second section, an advantageous effect may be achieved. Namely, in a narrow portion close to an end part, a stable and sealing contact between the first tubular member and an insertion needle may be achieved. Friction may support such a sealing and fastening feature. The second tubular member may have a length which is smaller than a length of the first tubular member. The second tubular member may have a width which is larger than a width of the first tubular member. Thus, one long thin tubular member may be combined with a shorter and thicker tubular member, allowing to obtain a tip-like configuration in a body penetration section when the first tubular member is inserted within the second tubular member. This may simplify introduction of the catheter into a physiological body.

At least one of the group consisting of the first tubular member and the second tubular member may have a tapering outer end portion. Two such tapering outer end portions of the first tubular member and the second tubular member (and optionally a third one from an insertion needle) may allow to further refine the tip-like configuration of the catheter, thereby avoiding the fracturing, or peeling back of the first and second tubular members when inserted into a body tissue. The tapering portions of the different components may be adjusted to one another so that an essentially smooth transition from a thicker part to a thinner part is achievable.

The first tubular member may be fixedly connected with the second tubular member. For example, the first tubular member may be adhered, welded, clamped, etc. to the second tubular member so as to permanently fix the two tubular members to one another. It is also possible to integrally form the first tubular member and the second tubular member as a single piece, for instance by moulding and/or casting. This may allow to obtain a proper sealing regarding the channel. Furthermore, this allows to provide an integrally formed product which is easy to use and is not prone to abuse by a user.

A support member (see Fig. 13 to Fig. 15) may be provided which may be adapted for receiving an arrangement of the first tubular member and the second tubular member. Such a support member may comprise two or more components which may be connectable to one another, for instance with a snap-on or Luer-lock connection. Within a cavity formed in the support member, a portion of the tubular members or the insertion needle may be accommodated so as to provide a fluidic coupling/communication between the tubular members, the insertion needle and fluid reservoirs or fluid evaluation units such as a sensor.

Furthermore, an annular sealing may be arranged in the channel, particularly between the first and the second tubular member. Such an annular sealing which may be a rubber ring may allow with simple measures to regulate fluidic paths within the communicative connection in an interior of the catheter. For example, such an annular sealing may contribute to redirect a fluid flow in an interior and an exterior of the catheter in a controlled manner.

The catheter may comprise a fluid reservoir for containing a perfusion fluid arranged in fluid communication with the first lumen. Such a perfusion fluid may include a physiologically active substance, particularly a glucose regulating substance. For example, insulin, glucagon, aldosterone or bi-carbonate may be used as an infusion fluid which may have the physiological effect of manipulating the glucose concentration in a surrounding body. This may allow to use the device in the context of an artificial pancreas.

A first fluid transport unit may be provided and adapted for transporting the perfusion fluid from the fluid reservoir through the first lumen and along the first fluidic path. Such a first fluid transport unit may be a pump, for instance a peristaltic pump. Beyond this, a second fluid transport unit may be provided which may be adapted for transporting a sample fluid produced by/obtained from an at least partial equilibration between the perfusion fluid and the body fluid along the second fluidic path. Such a second fluid transport unit may be a second pump, for example a second peristaltic pump. Alternatively, a single bidirectional pump may be used via which fluid may be pumped into the channel, and out of the channel (in such an operation mode, the first lumen and the first perforation may be dispensable).

The first fluid transport unit and the second fluid transport unit may be provided as separate (for instance unidirectional) sucking or pumping pumps. Alternatively, the first fluid transport unit and the second fluid transport unit may be realized as a common fluid transport unit, for example a bidirectional pump.

A sensor may be provided for sensing a value of a physiological parameter based on an analysis of the sample fluid. Thus, such a sensor may detect the value of the physiological parameter, for example a glucose level.

The catheter may further comprise a control unit adapted for controlling the first fluid transport unit and the second fluid transport unit for transporting the perfusion fluid from the fluid reservoir into the body under investigation and for subsequently transporting the sample fluid and the body fluid from the body under investigation into the channel. Such a control unit or regulating unit may coordinate the function of the various components of the catheter. It may be adapted to determine the amount of the physiologically active substance to be delivered to the body under investigation based on the value of the physiological parameter sensed by the sensor. Therefore, a fully automatic regulation system may be provided which detects the present value of a parameter and which supplies a correspondingly determined amount of physiologically active substance so as to adjust the detected value to a desired value.

For example, the sensor may be adapted for determining at least one of the group consisting of a glucose concentration, a lactate concentration, an oxygen concentration, an ion concentration, a cholesterol concentration, an amount of bacteria, an amount of a virus, a drug concentration and a medication concentration.

For example, the catheter may be adapted for determining the value of the physiological parameter of the body fluid of the group consisting of interstitial fluid, blood, lymph, cerebrospinal fluid, urine and tissue.

A calibration unit may be provided in the catheter for determining a mixture degree indicative of a mixture ratio between the perfusate and the body fluid. For instance, a conductivity measurement may be a proper indicator whether the mixture between body fluid and perfusion fluid has been sufficient for a meaningful subsequent sensor analysis. The amount of the physiologically active substance (for instance insulin) to be supplied to the body may be dosed quantitatively on the basis of the value of the physiological parameter which has been sensed by the sensor (for instance the glucose level). A mixture degree determined by the calibration may be taken as a basis for the control unit to decide whether a physiologically active substance shall be supplied to the body, and in which concentration or dose.

The control unit may be adapted to accept or reject to determine the amount of the physiologically active substance based on the mixture degree determined by the calibration unit. For instance, when the mixture degree is too small, the control unit may reject to use a sensor parameter for adjusting an amount of the physiologically active substance. If the mixture degree is sufficiently large, for instance exceeds a predetermined threshold value, the measurement may be accepted and the insulin dose may be selected in accordance with the sensor result. By taking this measure, the reliability of the system may be increased.

Due to a possible (back-)flow of the perfusate between the tissue and the catheter surface, the environment around the catheter can be "diluted". This dilution or equilibration or mixture degree may be measured using a marker, and the measurement of the physiological parameter may be corrected accordingly. It is also possible to stop or interrupt the perfusate infusion, to wait until an essentially completely equilibration has occurred, and to measure the physiological parameter then. The information with regard to the time at which the equilibration is essentially finished can be obtained from the marker sensor. Sucking back the perfusion fluid into the catheter can be performed for accelerating an equilibration procedure.

The catheter may be adapted to extract the mixture of the perfusion fluid and the body fluid from the body under investigation. In other words, the pump may be brought in a pumping direction in which the mixture is pumped back from the body into the catheter, for analysis.

Particularly, the extracted mixture of the perfusion fluid and the body fluid from the body under investigation may be brought in functional contact with one or more sensors, each of the sensors being indicative of the present value of the physiological parameter and/or marker. The sensor may be adapted for determining the physiological parameter and/or marker continuously over time or intermittently over time. For the purpose of a intermittent determination, a reception may be provided in the catheter into which a (for instance single-use) test unit may be inserted. For example, a glucose measuring strip may be inserted into the reception of the catheter via a human user. This may allow for an easy and simple measurement of the glucose level with a perfusion fluid which simultaneously may comprise the necessary insulin. The sensor may be adapted for at least one of the group consisting of an optical detection, an electrical detection and a chemical detection.

An optical detection unit may determine information concerning the physiological parameter and/or marker as a consequence of a modification of at least one optical property of a sensor after being brought in contact with the body fluid sample. For instance, the colour, the reflectivity, the absorption or a fluorescence property of such a sensor may be altered in a characteristic manner in dependence of the value of the physiological parameter.

Alternatively, the detection may be performed in an electrical manner, for instance using an effect like a modification of an ohmic resistance, a conductivity, a capacity, a magnetic parameter or the like of the sensor.

A chemical detection may be based on the fact that a test unit, after being brought in contact with the body fluid sample, may have modified chemical or biochemical characteristics, for instance a modified pH value, a modified concentration of a chemical substance, or the like. The control unit may be a microprocessor. Such a microprocessor may be a central processing unit (CPU). It may be manufactured as an integrated circuit (for instance monolithically integrated in a semiconductor substrate) and can be manufactured, for instance, in silicon technology. Such a microprocessor may have computational resources and may, for instance, have access to a memory device (for instance an EEPROM) for storing data. Such a control unit may further control the entire or a part of the functionality of the catheter and may receive control commands from a user interface.

The second lumen may be adapted to receive the first tubular member so that the part of the outer surface of the first tubular member sealingly contacts the part of the inner surface of the second tubular member. In other words, in a portion of the catheter in which the tubular members do not cooperatively form the channel, then may be mechanically coupled directly to one another (so that an outer diameter of the inner tubular member equals or essentially equals an inner diameter of the outer tubular member) to thereby form a dead end of the channel at which no fluid can pass between the tubular members. Thus, the arrangement of the tubular members may be such that they form a closed end and an open end, the latter serving as a fluid outlet and the former forming a sealed connection end.

The second lumen may be adapted to receive the first tubular member so that the part of the outer surface of the first tubular member fastens the part of the inner surface of the second tubular member. Such a fastening may be permanently (for instance by adhering the first tubular member and the second tubular member by glue), or may be non-permanently/detachably (for instance by a form-locking connection or a friction-locking connection). The second lumen may be adapted to receive the first tubular member so that the part of the outer surface of the first tubular member which contacts the part of the inner surface of the second tubular member is located at a distal end of the catheter. This distal end may be the end at which the catheter is adapted to be inserted into the body under investigation. In contrast to this, the proximal end may be the end to which, via the channel, the fluid may be sucked off for further analysis. Thus, the proximal end may be directed towards a physician operating the catheter.

The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to these examples of embodiment.

The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

Fig. IA to Fig. 16E show catheters and catheter arrangements according to exemplary embodiments of the invention.

The illustration in the drawing is schematically. In different drawings, similar or identical elements are provided with the same reference signs.

In the following, referring to Fig. IA to Fig. ID, a catheter 100 according to an exemplary embodiment of the invention will be explained. The catheter 100, as illustrated in Fig. IA, comprises a first tubular member 101 realized as an insertion needle having a first lumen 102 and a first perforation realized as a hole 103 in a lateral wall of the insertion needle 101 and by a hole 104 in an end face of the insertion needle 101. Beyond this, a second tubular member 105 is provided which has a second lumen 106 forming a channel 107 and a reception for the insertion needle 101. A second perforation of the second tubular member 105 is realized by a number of holes 108 formed in a sidewall of the second tubular member 105. Thus, the second lumen 106 is adapted to receive the first tubular member 101 so that the channel 107 is formed between the first tubular member 101 and the second tubular member 105. However, in a front section of the catheter 100 in insertion direction, the second lumen 106 is adapted to receive the first tubular member 101 with a direct frictional contact, thereby providing a sealing and fastening function and also allowing an "over the needle type" insertion of the catheter 100.

The first tubular member 101 and the second tubular member 105 are arranged relative to one another to form a first fluidic path from the first lumen 102 through the hole 103, the channel 107 and the holes 108 into a human body under investigation in which the catheter 100 is inserted, or which surrounds the catheter 100. Beyond this, the first tubular member 101 and the second tubular member 105 are arranged to form a second fluidic path from the body under investigation through the second perforation holes 108 and into the channel 107. A portion of the first fluidic path is indicated by arrows 109, whereas a portion of the second fluidic path is indicated by arrows 110.

The insertion needle 101 facilitates insertion of the catheter 100 into a human body. The insertion needle 101 is a metallic needle, whereas the second tubular member 105 is made from plastics. As indicated by arrows 109, a perfusion fluid which may also comprise insulin may be pumped into the physiological body via the first fluidic path. An at least partial equilibration between a body fluid such as an interstitial fluid and the perfusion fluid may be obtained outside of the catheter 100 after a waiting time of, for instance, several seconds to several minutes. However, due to the hydrodynamic properties of the system 100, particularly a sucking force sucking back fluid through the channel 107, a mixture of perfusion fluid and interstitial fluid may be sucked back via the second fluidic path into the catheter 100 for further analysis which may be carried out for instance by a sensor (not shown in Fig. 1).

As can be taken from Fig. IA, the second tubular member 105 has a first section arranged on a left-hand side of a step 111 and comprises a second section arranged on a right-hand side of the step 111. As can be taken from Fig. IA, the second tubular member 105 has a larger inner diameter in the first section than the second section. By such a stepping geometry, the formation of the channel 107 and the simultaneous frictional fastening of the insertion needle 101 in a sealing manner with regard to the second tubular member 105 is enabled. A length of the insertion needle 101 is larger than a length of the second tubular member 105. Furthermore, both the insertion needle 101 as well as the second tubular member 105 have a tapering outer end portion, indicated by reference numerals 112 and 113, respectively. This pointed or spiry geometry facilitates insertion of the catheter 100 into a living body without a fracturing, or peeling back of the second tubular member. Fig. IB illustrates a first cross-sectional view 140 of the catheter 100 along a line B-B indicated in Fig. IA.

Fig. 1C illustrates a second cross-sectional view 160 along a line C-C indicated in Fig. IA.

After insertion of the catheter 100, the cavity 107 formed between an outer wall of the insertion needle 101 and the perforated cannula wall 105 is perfused using an isotonic solution. The isotonic solution may be guided via the inner lumen 102 of the insertion needle 101 and the lateral hole 103 into the cavity 107 (see Fig. IA, wherein the fluid can in general also flow in the opposite direction). In the presence of concentration differences between substances dissolved in the perfusion fluid and in the interstitial fluid, a diffusion driven transport of substances through the perforated cannula wall 105 is enabled. Depending on the kind of the concentration difference, substances can be brought from the interstitial fluid via the perforated cannula wall 105 into the perfusion fluid, or in opposite direction substances of the perfusion fluid may be transported via the perforated cannula wall 105 into the tissue.

Four rows of holes 108 are formed in the cannula wall 105. In order to increase the mechanical robustness, the hole rows are bored displaced or misaligned relative to one another. An advantage of the embodiment of Fig. 1 is the immediate readiness for operation after inserting the catheter 100 into the tissue.

For manufacturing the catheter 100, a PTFE

(Polytetrafluoroethylene) cannula 105 of Disetronic Medical Systems AG (Akku-Chek Tender Link, 24 G cannula) and a needle 101 with a lateral hole 103 of Becton Dickinson (BD Insyte Autogard Winged, 24 G) may be used. Into the 24 G cannula 105, three rows of holes 108 may be formed which are angularly displaced by 120°. The rows of holes 108 may be bored using a high precision milling device. The holes 108 have a diameter of 0.2 mm. However, it is also possible to use a laser for precisely boring such holes 108 with dimensions in the range of, for instance, 0.1 mm to 0.4 mm. The manufacture of a lateral needle hole 103 of Becton Dickinson is disclosed as such in US 7,002,098.

It may be advantageous that the front end of the cannula reliably surrounds the needle (cone with press fit), and that a cavity 107 is present along the cannula 105 and the needle 101. These conditions are fulfilled with conventional transcutaneous and intravenous infusion catheters ("over the needle insertion catheters"). US 4,588,398, US 6,248,196 and US 5,957,893 disclose the manufacture of such cannula- needle configurations. Fig. ID shows an operation mode of the catheter 100 in which only the second fluidic path is used, whereas the first fluidic path remains inactive. Thus, in such an operation mode, it is also possible to omit the components forming the first fluidic path, for instance to omit hole 103, opening 104, etc. In such an operation mode, 1 μl of a perfusion fluid is pumped into the channel 107. As indicated schematically by bidirectional arrows 130, an exchange/interaction between the perfusion fluid and surrounding body fluid is then enabled via the perforation holes 108. In this operation mode, the bidirectional pump may be switched off for, for example, 30 seconds. After this, the sample fluid formed by a mixture of the perfusion fluid and surrounding body fluid may be pumped out of the catheter 100 by the bidirectional pump which now pumps the fluid through the channel 107 in a direction from right to left, according to Fig. ID. A bidirectional arrow 135 illustrates schematically that the fluid pumping direction through the channel 107 can be reversed. In the following, referring to Fig. 2A to Fig. 2E a catheter 200 according to another exemplary embodiment of the invention will be explained.

As can be taken from Fig. 2A, the catheter 200 differs from the catheter 100 in that an additional plastic cannula 201 is provided between the insertion needle 101 and the cannula 105. The further cannula 201 has a tapering end section 202, an interior step 203 and further lateral perforation holes 204.

As can be taken from Fig. 2B, after insertion of the catheter 200 into a human body, the insertion needle 101 can be removed from the catheter 200 and from the body so that only the flexible plastic cannulae 105, 201 remain within the body which increases the convenience of wear of the catheter 200. Further, as can be taken from Fig. 2B, an inner lumen 210 is formed by retracting the insertion needle 101 after the insertion procedure. The lumen 210 performs a similar function as the first lumen 102 of the embodiment of Fig. 1.

Fig. 2C shows a first cross-sectional view 240 of the catheter 200 taken along a line C-C indicated in Fig. 2B.

Furthermore, Fig. 2D shows a second cross-sectional view 260 of the catheter 200 taken along a line D-D indicated in Fig. 2B. In the embodiment of Fig. 2A to Fig. 2D, a second plastic cannula

201 is placed between the injection needle 101 and the perforated cannula 105. This additional plastic cannula 201 comprises one or several perforations 204 in the cannula wall (see Fig. 2A). After insertion of the catheter 200, the insertion needle 101 is removed (see Fig. 2B), and then the cavity 107 between the inner perforated plastic cannula 201 and the outer perforated cannula 105 is perfused with an isotonic solution. The isotonic solution is guided via the inner lumen 210 of the inner plastic cannula 201 and the cannula wall perforation holes 204 into the cavity 107 (see Fig. 2B). In the presence of a concentration gradient between the substances dissolved in the perfusion fluid and in the interstitial fluid, a diffusion driven transport of substances through the perforated cannula wall 105 occurs. Depending on a direction of the concentration gradient, substances of the interstitial fluid may be transported via the perforated cannula wall 105 into the perfusion fluid or, in the opposite direction, perfusion fluid substances may be introduced via the perforated cannula wall 105 into the tissue.

In this embodiment, four rows of holes 108 are formed in the outer cannula wall 105, and two holes are formed in the wall of the inner cannula 201. An advantage of the embodiment of Fig. 2 is a high wear comfort, since only flexible plastic material remains within the tissue after removal of the insertion needle 101.

For example, the embodiment of Fig. 2 may be manufactured using a 26 G polyurethane cannula 201, an insertion needle 101 (BD Vasculon Plus, 26 G) and a 24 G polyurethane cannula 105 (BD Insyte Autogard Winged, 24 G), of Becton Dickinson. In the 24 G cannula 105, rows of holes 108 which are disaligned by certain angles are bored using a high precision milling device. The holes can have a diameter of 0.2 mm. In the 26 G cannula 201, holes 204 having a diameter of 0.3 mm have been bored. Subsequently, the 26 G cannula 201 can be inserted together with the insertion needle 101 into the 24 G cannula 105, as illustrated in Fig. 2.

Fig. 2E shows an operation mode of the catheter 200 in which only the second fluidic path is used, whereas the first fluidic path remains inactive. Thus, in such an operation mode, it is also possible to omit the components forming the first fluidic path, for instance to omit hole 204. In such an operation mode, 1 μl of a perfusion fluid is pumped into the channel 107. As indicated schematically by bidirectional arrows 130, an exchange/interaction between the perfusion fluid and surrounding body fluid is then enabled via the perforation holes 108. In this operation mode, the bidirectional pump may be switched off for, for example, 30 seconds. After this, the sample fluid formed by a mixture of the perfusion fluid and surrounding body fluid may be pumped out of the catheter 200 by the bidirectional pump which now pumps the fluid through the channel 107 in a direction from right to left, according to Fig. 2E. A bidirectional arrow 135 illustrates schematically that the fluid pumping direction through the channel 107 can be reversed.

In the following, referring to Fig. 3A to 3C, a catheter 300 according to another exemplary embodiment of the invention will be explained.

The embodiment of Fig. 3 differs from the embodiment of Fig. 1 particularly in that the insertion needle 101 only has a hole 104 at an end face, and only very few perforation holes 108 are formed in the cannula 105. In the present embodiment, four holes 108 are formed in the cannula wall 105.

Fig. 3A shows the catheter 300 in a plan view, and Fig. 3B shows a first cross-sectional view 340 thereof taken along a line B-B shown in Fig. 3A. Fig. 3C shows a second cross-sectional view 360 taken along a line C-C of Fig. 3A. In the embodiment of Fig. 3A to Fig. 3C, the plastic cannula 105 of the catheter 300 is provided with several perforation holes 108 close to the tip. After insertion of the catheter 300 into a body, an isotonic solution may be supplied via the cavity 102 to a tip portion of the catheter 300. Since the hydraulic conductivity at the border between catheter 300 and tissue may be higher than in the tissue, a back flux indicated with reference numeral 305 is generated at the tip 104 of the insertion needle 101, so that the isotonic fluid flows back in a space or gap between an outer surface of the catheter 300 and the tissue (so- called back flux principle). Via the perforations 108 in the cannula wall 105, this back flowing fluid can be guided back into the channel 107 between the cannula 105 and the needle 101, and can be guided out of the device 300 (for instance using a suction pump, see arrows 110 in Fig. 3A).

Generally, the distance of backflow along the outer surface of an infusion cannula is mainly determined by cannula diameter, volumetric infusion rate, and tissue mechanics (see Morrison, PF, Chen, MY, Chadwick, RS, Lonser RR, and Oldfield, EH "Focal delivery during direct infusion to brain: role of flow rate, catheter diameter, and tissue mechanics", Am J Physiol 277:R1218-R1229, 1999). Thus, to easily guide the perfusion fluid through the catheter 300, the distance between the entrance location of the perfusion fluid (i.e., catheter tip 104) and the sucking position of the interstitial fluid (i.e., perforation holes 108) should be similar or less than the maximal backflow distance obtained with a given catheter diameter, perfusion flow rate, and tissue type. As a result of the direct contact or proper coupling between the fluid and the tissue (convection), a high exchange efficiency of the substances (relative to the dimension of the exchange area) may be obtained with the embodiment of Fig. 3.

In order to manufacture the catheter shown in Fig. 3, a PTFE cannula 105 with a needle 101 of Disetronic Medical Systems AG (Akku- Chek Tender Link, 24 G) may be used. In the 24 G cannula 105, holes 108 may be bored using a high precision milling machine at a front end. The holes 108 have a diameter of 0.3 mm in the present embodiment. In the following, referring to Fig. 4A to Fig. 4D, a catheter 400 according to another exemplary embodiment of the invention will be explained.

The embodiment of Fig. 4 differs from the embodiment in Fig. 2 particularly in that the additional cannula 201 is free of perforation holes along a lateral wall surface. However, a perforation hole 401 is formed in a front portion of the cannula 201 so that a liquid can leave the lumen 210 through this front end perforation 401 and may enter into a human body.

Fig. 4A shows the catheter 400 before removal of the insertion needle 101 from the lumen 210. Fig. 4B shows the catheter 400 after removal of the insertion needle 101 from the lumen 210.

Fig. 4C shows a first cross-sectional view 440 taken along a line C- C indicated in Fig. 4B, and Fig. 4D shows a second cross-sectional view 460 taken along a line D-D indicated in Fig. 4B. In the embodiment of Fig. 4, the additional plastic cannula 201 is placed between the insertion needle 101 and the perforated cannula 105 (see Fig. 4A). In the present embodiment four holes 108 are bored in the cannula wall 105. After insertion of the catheter 400, the insertion needle 101 is removed (see Fig. 4B), and subsequently an isotonic solution can be pumped via the interior lumen 210 of the inner plastic cannula 201 to the catheter tip 401. There, a back flux may be generated (see Fig. 4B), so that the fluid flows back in a space or gap between an outer catheter 400 surface and the surrounding tissue. By means of holes 108 in the outer cannula wall 105, the fluid may be guided back into the channel 107 between the outer cannula 105 and the inner cannula 201, and can then be guided off (see Fig. 4B).

Apart from the significantly higher exchange efficiency of the substances (relative to the size of dimension of the exchange surface) as compared to conventional systems, the embodiment of Fig. 4 may have the further advantage of a proper wear comfort, since after inserting the catheter 400 into the body and removal of the insertion needle 101, only flexible plastic materials 105, 201 remain in the tissue.

The embodiment of Fig. 4 can be manufactured using a 26 G polyurethane cannula 201, an insertion needle 101 (BD Vasculon Plus, 26 G) and a 24 G polyurethane cannula 105 (BD Insyte Autogard Winged 24 G) of Becton Dickinson. In the outer 24 G cannula 105, holes 108 may be bored using a high precision milling device. The holes 108 have a diameter of 0.2 mm. Subsequently, the 26 G cannula 201 may be inserted, for instance slid, into the 24 G cannula 105, as shown in Fig. 4. In the following, referring to Fig. 5A to Fig. 5D, a catheter 500 according to another exemplary embodiment of the invention will be explained.

The catheter 500 shown in a plan view in Fig. 5A is similar to the catheter 300 shown in Fig. 3, however the hole 103 is provided in a front portion of the insertion needle 101 which is not covered by the tubular member 105. In contrast to this, in Fig. 3, the hole 103 is provided in a central portion of the insertion needle 101 which is covered by the tubular member 105 adjacent to the channel 107. Four holes 108 are provided in the cannula wall 105, and one hole 103 is provided close to the needle tip 104.

Fig. 5B shows a first cross-section 530 along a line B-B indicated in Fig. 5A. A second cross-sectional view 550 shown in Fig. 5C shows a cross-section along a line C-C indicated in Fig. 5A. Furthermore, a third cross-sectional view 570 shown in Fig. 5D shows a cross-section along the line D-D indicated in Fig. 5A.

The catheter 500 shown in Fig. 5 is a modification of the catheter configuration of Fig. 3. In contrast to Fig. 3, the insertion needle 101 of the catheter 500 comprises an additional lateral opening 103 in the portion of the tip 104 (see Fig. 5A). By taking this measure, the distance between the entrance location of the perfusion fluid and the sucking position of the interstitial fluid in the region of the cannula tip can be varied in a better manner so that the variability of the amount of the sucked fluid can be reduced.

For manufacturing the catheter 500, a PTFE cannula 105 of Disetronic Medical Systems AG (Akku-Chek Tender Link, 24 G cannula) and a needle 101 (having a lateral hole 103) of Becton Dickinson (BD Insyte Autogard Winged 24 G) may be used. In the 24 G cannula 105, holes 108 may be provided at the front end using a high precision milling machine. The holes 108 can have a diameter of 0.3 mm. In the following, referring to Fig. 6A to Fig. 6D, a catheter 600 according to another exemplary embodiment of the invention will be explained.

The cannula 600 is similar to the cannula 400 shown in Fig. 4, as can be taken from a plan view shown in Fig. 6A. A main difference is the provision of holes 601 in an exposed portion of the cannula 201 so that a direct fluidic communication between the cannula 201 and a surrounding tissue fluid is obtained.

Fig. 6B shows the catheter 600 in an operation mode in which the insertion needle 101 has been removed. Furthermore, Fig. 6C shows a first cross-sectional view 630 of the catheter taken along a line C-C indicated in Fig. 6B. Fig. 6D shows a second cross-sectional view 650 of the catheter 600 taken along a line D- D indicated in Fig. 6A.

The catheter 600 is a modification of the catheter 400 of Fig. 4. In the wall of the inner cannula 201, additional holes 601 are formed in a region close to the cannula tip 401 (see Fig. 6B). By taking this measure, the distance between the introduction position of the perfusion fluid and the sucking position of the tissue fluid can be varied in a proper manner, so that the variability in the amount of the sucked fluid can be kept small. In this scenario, four holes 108 are formed in the outer cannula wall 105, and two holes 601 are formed in the wall of the inner cannula 201.

To manufacture the catheter 600, a 26 G polyurethane cannula 201, an insertion needle 101 (BD Vasculon Plus, 26 G) and a 24 G polyurethane cannula 105 (BD Insyte Autogard Winged, 24 G) of Becton Dickinson may be used. In the outer 24 G cannula 105, holes 108 are formed in the front end of the cannula 105 and two holes are formed in the inner 26 G cannula 201. The holes 108, 601 may have a diameter of 0.2 mm. Subsequently, the 26 G cannula 201 loaded with the insertion needle 101 can be inserted into the 24 G cannula 105, and can be positioned as shown in Fig. 6.

In the following, referring to Fig. 7 A to Fig. 7D, a catheter 700 according to another exemplary embodiment of the invention will be explained. The catheter 700 shown in a plan view in Fig. 7A differs from the catheter 100 particularly in that additionally an annular sealing ring 701 is provided which is positioned in the channel 107, that is to say is clamped between the plastic cannula 105 and the insertion needle 101. In other words, the annular sealing ring 701 which may be made of a rubber material prevents a direct fluid communication of portions of the outer lumen 106 on the left-hand side of the annular sealing ring 701 and on the right-hand side of the annular sealing ring 701 to provide a sealing function.

Fig. 7B shows a first cross-sectional view 720 of the catheter 700 along a line B-B of Fig. 7A. Fig. 7C illustrates a second cross-sectional view 740 of the catheter 700 along the line C-C of Fig. 7A. Fig. 7D shows a third cross-sectional view 760 along a line D-D of Fig. 7A.

Within the catheter 700, an isolating ring 701 is arranged between the plastic cannula 105 and the insertion needle 101. Furthermore, a lateral opening 103 is provided at the insertion needle 101. The plastic cannula 105 of the infusion catheter 700 is provided with two axially spaced rows of perforation holes 108, wherein the isolation ring 701 is fixedly positioned between these two rows of perforation holes 108 (see Fig. 7A). In this embodiment, two perforation rows 108 with each four holes in the cannula wall 105 are provided by drilling.

After insertion of the catheter 700 into tissue, an isotonic fluid may be guided via the lumen 101, the lateral hole 103 and the front cannula wall perforation holes 108 to an outer surface of the cannula 105. The fluid flowing in the space or gap between the surface of the cannula 105 and the tissue may then be guided back into the cannula 105 via the perforation holes 108 to enter the channel 107 between cannula 105 and insertion needle 101 (see Fig. 7A).

Due to the proper communication between the fluid and the tissue, the catheter 700 may allow to obtain a high exchange efficiency of the substances (relative to the dimension of the exchange surface).

Furthermore, by modifying or adjusting the width and/or the position of the isolating ring 700 between the perforation rows 108 (see Fig. 7A), the exchange surface of the catheter 700 can be adjusted in accordance with specific requirements of an application. By taking this measure, also the amount of the sucked fluid can be controlled particularly well.

The catheter 700 can be manufactured based on a PTFE cannula 105 of Disetronic Medical Systems AG (Akku-Chek Tender Link, 24 G cannula), and a needle 101 (with a lateral hole 103) of Becton Dickinson (BD Insyte Autogard Winged, 24 G). In the 24 G cannula 105, two rows of holes 108 may be manufactured axially displaced by, for instance, 3 mm. Between the two rows of holes 108 and between cannula 105 and insertion needle 101, a 2 mm broad 26 G ring 701 (cut with an appropriate size from a 26 G BD Vasculon Plus cannula) can be attached to the channel 107. In the following, referring to Fig. 8A to Fig. 8E, a catheter 800 according to another exemplary embodiment of the invention will be explained.

The catheter 800 which is shown in a plan view in Fig. 8A differs from the catheter 200 particularly in that an annular sealing ring 701 is arranged between the inner plastic cannula 201 and the outer plastic cannula 105, that is to say within the channel 107. The ring 701 is inserted between two rows of holes 108.

Fig. 8B shows the catheter 800 in an operation state in which the insertion needle 101 has been removed from the catheter 800. Fig. 8C shows a first cross-sectional view 820 along a line C-C of Rg. 8B.

Fig. 8D shows a second cross-sectional view 840 along a line D-D of Fig. 8B.

A third cross-sectional view 860 shown in Fig. 8E shows a cross- sectional view taken along a line E-E of Fig. 8B.

The plastic cannula 201 is inserted between the insertion needle 101 and the perforated cannula 105, and the sealing ring 701 is placed between the two plastic cannulae 105, 201 (see Fig. 8A). The additional plastic cannula 201 comprises some perforations 204 in the cannula wall (see Fig. 8A), so that after insertion of the catheter 800 in the body and the removal of the insertion needle 101, an isotonic liquid may be guided via the lumen 210 in the inner plastic cannula 201, the perforations 204, 108 of the inner and outer cannula walls 201, 105 to the outer surface of the cannula 105. The liquid flowing between the outer surface of the cannula 105 and the tissue is then guided back via the perforations 108 in the cannula 105 into the channel 107 between the outer cannula 105 and the inner cannula 201.

Fig. 8C to Fig. 8E show cross-sectional views of the catheter 800. In this embodiment, two perforation rows each having four holes 108 are provided in the outer cannula wall 105, and two holes 204 are provided in the wall of the inner cannula 201.

Due to the direct contact between the guided fluid and the tissue a high exchange efficiency of the substances can be obtained with the catheter 800. Furthermore, by adjusting the width of the isolating ring 701 between the perforation rows 108, 108, the flow variability of the sucked liquid can be controlled and can be kept sufficiently small, if desired. Furthermore, this catheter 800 shown in Fig. 8 has the advantage of an increased comfort of wear, since after the injection, essentially only flexible plastic material remains in the tissue. In order to manufacture the catheter 800, a 26 G polyurethane cannula 201, an insertion needle 101 (BD Vasculon Plus, 26 G) as well as a 24 G polyurethane cannula 105 (BD Insyte Autogard Winged, 24 G) of Becton Dickinson may be used. In the 24 G cannula 105, two rows of holes 108 axially displaced by 3 mm can be bored. The holes 108 may have a diameter of 0.2 mm. In the 26 G cannula 201, the holes 204 with a diameter of 0.3 mm can be bored. Subsequently, a ring 701 having a width of 2 mm (which may be cut in a proper size from a 26 G BD Vasculon Plus cannula and can be radially widened, if desired) can be attached to the 26 G cannula 201, and can be slid into the 24 G cannula 105.

In the following, referring to Fig. 9 to Fig. 12, catheters according to further exemplary embodiments will be explained in which the exchange principle of diffusion (microperfusion realizations) and convection (back flux) may be advantageously combined. In the following, referring to Fig. 9A to Fig. 9D, a catheter 900 according to another exemplary embodiment of the invention will be explained.

The catheter 900 shown in a plan view in Fig. 9A differs from the catheter 100 particularly in that an annular sealing ring 701 is provided between the needle 101 and the cannula 105.

Fig. 9B shows a first cross-sectional view 920 along a line B-B of Fig. 9A. A second cross-sectional view 940 along a line C-C of Fig. 9A is shown in Fig. 9C. A third cross-sectional view 960 along a line D-D shown in Fig. 9A is shown in Fig. 9D. An isolating ring 701 is arranged between the plastic cannula 105 and the insertion needle 101. A lateral opening 103 is provided at the insertion needle 101, and the plastic cannula 105 of the infusion catheter 900 is provided several perforation rows each having several radially displaced perforation holes 108 (see Fig. 9A). After the insertion of the catheter 900 into a destination, an isotonic fluid may be injected via the lumen 102, the lateral hole 103 into the cavity 106 between the needle wall 101 and the perforated cannula wall 105. The fluid may leave the catheter 900 through the cannula wall perforations 108 towards an outer cannula surface. The fluid flowing in the space between the cannula surface and the tissue can then be guided via the cannula wall perforations 108 into the cavity 107 between the cannula 105 and the insertion needle 101 (see Fig. 9A). This flow back into the catheter 900 can be promoted by a sucking force of a correspondingly controlled pump (not shown). As can be taken from the cross-sectional views 920, 940, 960 of the catheter 900, four radially displaced perforation holes 108 of each perforation row are bored into the cannula wall 105.

An advantage of the catheter 900 may be a high exchange efficiency of the substances (diffusion and convection) and the immediate readiness for use after insertion into the body. The catheter 900 may be manufactured based on a PTFE cannula 105 of Disetronic Medical Systems AG (Akku-Chek Tender Link, 24 G cannula), and a needle 101 (with a lateral hole 103) of Becton Dickinson (BD Insyte Autogard Winged, 24 G) may be used. The holes 108 may have a diameter of 0.2 mm. Between the cannula 105 and the insertion needle 101, a 2 mm broad 26 G ring 701 (appropriately cut from a 26 G BD Vasculon Plus cannula) is attached.

In the following, referring to Fig. 1OA to Fig. 1OE, a catheter 1000 according to another exemplary embodiment of the invention will be explained.

The catheter 1000 differs from the catheter 200 particularly in that an annular ring 701 is provided additionally.

Fig. 1OA shows the catheter 1000 in a configuration in which the insertion needle 101 is still part of the catheter 1000. Fig. 1OB shows the catheter 1000 after the insertion needle 101 has been removed. Fig. 1OC shows a first cross-section 1020 along a line C-C of Fig. 1OB. Fig. 1OD shows a second cross-section 1040 along a line D-D of Fig. 1OB. Fig. 1OE shows a third cross-section 1060 along a line E-E of Fig. 1OB.

The plastic cannula 201 is inserted between the needle 101 and the cannula 105 provided with holes 108 (see Fig. 10A). The additional plastic cannula 201 comprises a few perforations 204 in the cannula wall 201 (see Fig. 10A). After insertion of the catheter 1000 into the body and after the subsequent removal of the needle 101, an isotonic fluid can be pumped via the lumen 210 of the inner plastic cannula 201 and the cannula wall perforations 204 into the cavity 106 between the inner and the outer cannula walls 201, 105, and further through the holes 108 towards the outer surface of the catheter 1000. The liquid flowing in the space between the catheter surface and the tissue is then guided back via the cannula wall perforations 108 into the cavity 107 between the inner and the outer cannula wall 201, 105 and sucked off (see Fig. 10B).

In this embodiment, four radially displaced perforation holes 108 are provided by each perforation row in the outer cannula wall 105, and two holes 204 are provided in the inner cannula wall 201.

An advantage of the catheter 1000 is the high exchange efficiency of the substances (diffusion and convection), and a high comfort during wear, since only flexible plastic materials need to remain in the tissue after insertion and removal of the needle 101.

To manufacture the catheter 1000, a 26 G polyurethane cannula 201 and an insertion needle 101 (BD Vasculon Plus 26 G) as well as a 24 G polyurethane cannula 105 (BD Insyte Autogard Winged, 24 G) of

Becton Dickinson may be used. In the 24 G cannula 105, holes 108 are bored which may have a diameter of 0.2 mm. In the 26 G cannula 201, holes 204 with a diameter of 0.3 mm may be bored. Subsequently, a 2 mm broad ring 701 (cut from a 26 G BD Vasculon Plus cannula and slightly widened in a radial manner) can be attached to the 26 G cannula 201 and may be slid in the 24 G cannula 105.

In the following, referring to Fig. HA to Fig. HD, a catheter 1100 according to another exemplary embodiment of the invention will be explained. The catheter 1100 shown in a plan view in Fig. HA differs from the catheter 900 particularly in that the (360°) annular sealing ring 101 is replaced by a first annular segment sealing 1101 (180°) provided at a back end portion of the catheter 1100 and by a second annular segment sealing 1102 (180°) provided in a front portion of the catheter 1100. The first annular segment sealing 1101 is tilted by 180° around a main axis of the catheter 1100 relative to the second annular segment sealing 1102. Bands 1103, 1104 connect the first annular segment sealing 1101 with the second annular segment sealing 1102.

Fig. HB shows a first cross-sectional view 1120 of the catheter 1100 along a line B-B of Fig. HA. A second cross-sectional view 1140 shown in Fig. HC relates to a line C-C of Fig. HA. A third cross- sectional view 1160 shown in Fig. HD relates to a line D-D of Fig. HA.

The catheter HOO is a modification of the catheter configuration 900. The sealing ring 701 shown there is substituted by two axially spaced half rings HOl, 1102 which are connected by the two bands 1103, 1104. By taking this measure, an exchange surface is increased and a decrease of the hydraulic conductivity may be prevented.

As can be taken from the cross-sectional views of Fig. HB to Fig. HD, six radially displaced perforation holes are inserted into the cannula wall 105 per perforation row.

To manufacture the catheter 1100, a PTFE cannula 105 of Disetronic Medical Systems AG (Akku-Chek Tender Link, 24 G cannula) and a needle 101 (with a lateral hole 103) of Becton Dickinson (BD Insyte Autogard Winged, 24 G) may be used. The holes 108 have a diameter of 0.2 mm. Between the cannula 105 and the needle 101, the isolation ring configuration 1101 o 1104 is attached (which may be manufactured by appropriately cutting a 26 G BD Vasculon Plus cannula).

Next, referring to Fig. 12A to Fig. 12E, a catheter 1200 according to another exemplary embodiment of the invention will be explained. The catheter 1200 can be obtained by substituting the sealing ring

701 of the catheter 1000 by two actually displaced half rings 1101, 1102 connected by two bands 1103, 1104, in a similar manner as described above referring to Fig. 10.

Fig. 12A shows the catheter 1200 before removal of an insertion needle 101, Fig. 12B shows the catheter 1200 after removal of the insertion needle 101, Fig. 12C shows a first cross-sectional view 1220 along a line C-C of Fig. 12B, Fig. 12D shows a second cross-sectional view 1240 along a line D-D of Fig. 12B, and Fig. 12E shows a cross- sectional view 1260 along a line E-E of Fig. 12B. The catheter 1200 is a modification of the catheter 1000. The isolating ring 701 of the catheter 1000 is substituted by two actually spaced half rings 1101, 1102 which are connected by two bands 1103, 1104. Thus, an increased exchange surface with a high hydraulic conductivity may be obtained. As can be taken from the cross-sectional views in Fig. 12C to Fig. 12E, six radially distributed holes 108 in each perforation row are bored in the cannula wall.

In order to manufacture the catheter 1200, a 26 G polyurethane cannula 201 and a needle 101 (BD Vasculon Plus 26 G) as well as a 24 G polyurethane cannula 105 (BD Insyte Autogard Winged, 24 G) of Becton Dickinson has been used. In the 24 G cannula 105, radially displaced holes 108 are bored. The holes 108 may have a diameter of 0.2 mm. In the 26 G cannula 201, holes 204 with a diameter of 0.3 mm may be bored. Between the cannula walls, the isolation ring structure 1101 to 1104 (for instance cut from a 26 G BD Vasculon Plus cannula) may be attached. Fig. 13 to Fig. 16 show support structures for the above described cannulae/needle configurations. These support structures allow, apart from the fastening of the cannulae and the needle, also a high comfort contacting of tubes for supplying and guiding off various liquids. For realizing such supports, embodiments of the invention build up on conventional supports (such as disclosed for instance in US 5,522,803, US 6,572,586, US 6,840,922, US 6,302,866, US 4,369,781, US 4,452,473, US 4,607,868) which have been modified in such a manner that not only the contacting of the supply line, but also the contacting of the withdrawal line can be made possible.

In the following, referring to Fig. 13A to Fig. 13D, a support 1300 (which may be part of a catheter configuration) according to an exemplary embodiment of the invention will be explained.

Fig. 13A shows a first plan view of a support structure 1300 which can be used for fastening the cannula and needle configurations described above, particularly the configurations of Fig. 1, 3, 5, 7, 9 and 11.

Fig. 13B shows a second plan view of the support structure 1300. Fig. 13C shows a first cross-sectional view of the support structure along a line D-D of Fig. 13A. Fig. 13D shows a second cross-sectional view of the support structure 1300 according to a line C-C of Fig. 13B.

The support member 1300 shown in Fig. 13A comprises a first member 1301 and a second member 1302 which are connected or connectable to one another by a snap-on connection. The support structure 1300 is a further development of the support structure disclosed in US 5,522,803.

In the second member 1302, the needle 101 as well as an additional suck off tube 1310 are included (for instance adhered). In the first member 1301, a sleeve and sleeve support 1320, a septum 1305 and a back end of the cannula 105 are accommodated. The suck off tube 1310 and the needle 101 penetrate into the septum 1305. The tip of the suck off tube 1310 extends into the sleeve 1320 at one end of which the cannula 105 is slid on, and at the other end of which the septum 1305 is attached (see Fig. 13C, Fig. 13D). In operation, a perfusion fluid is supplied via the lumen 101, and tissue fluid is guided off via the cavity 107 between needle wall 101 and cannula wall 105 and through the suck off tube 1310 (see Fig. 13D).

In the following, referring to Fig. 14A to 14G, a support structure 1400 according to another exemplary embodiment of the invention will be explained.

The support structure 1400 allows for fastening the cannula and needle configurations described above, particularly the configurations of the catheters shown in Fig. 2, 4, 6, 8, 10 and 12.

The support structure 1400 is a modification of the support structures disclosed in US 5,522,803 and US 6,572,586.

Fig. 14A shows a first plan view and Fig. 14B shows a second plan view of the support structure 1400 in a first operation mode. Fig. 14C shows a cross-sectional view of the support structure 1400 in the first operation mode along a line C-C of Fig. 14B. Fig. 14D shows a cross- sectional view of the support structure 1400 in the first operation mode along a line D-D of Fig. 14A.

Fig. 14E shows a first plan view and Fig. 14F shows a second plan view of the support structure 1400 in a second operation mode. Fig. 14G shows a cross-sectional view of the support structure 1400 in the second operation mode along a line G-G of Fig. 14E.

The support structure 1400 comprises a first member 1301 and two replaceable second members 1302', 1401.

For inserting the catheter components into the support structure 1400, the second member 1302' with the needle 101 anchored therein is clipped onto the first member 1301 using a snap-on connection mechanism, see Fig. 14A to Fig. 14D.

After this inserting procedure, the second member 1302' with the needle 101 anchored therein is replaced and substituted by the second member 1401 with a suck off tube 1402 and with a supply tube 1403, see Fig. 14E to Fig. 14G.

The first member 1301 comprises a first septum 1430 and a first sleeve 1431. The first member 1301 further comprises a second septum

1432 and a second sleeve 1433. At one end of the second sleeve 1433, the outer cannula 105 is slid on. In the first operation mode, the needle 101 penetrates through the second septum 1430 and penetrates through the first septum 1432 arranged in the first member 1301. In the second operation mode, a tip of the supply tube 1403 penetrates through the second septum 1430 arranged in the first member 1301. At one end of the first sleeve 1431, the inner cannula 201 is slid on. In operation, the perfusion fluid is supplied via the supply tube 1403, the sleeves 1431,

1433 and the inner cannula 201. The tissue fluid is sucked off via the cavity 107 between the inner cannula wall 201 and the outer cannula wall 105 and is further guided to the suck off tube 1402 (see Fig. 14G).

In the following, referring to Fig. 15A to 15F, a support structure 1500 according to another exemplary embodiment of the invention will be explained.

The support structure 1500 allows for fastening the cannula and needle configurations described above, particularly the configurations of the catheters shown in Fig. 2, 4, 6, 8, 10 and 12. The support structure 1500 is a modification of the support structures disclosed in US 6,302,866 and US 5,968,011.

Fig. 15A shows a first plan view and Fig. 15B shows a second plan view of the support structure 1500 in a first operation mode. Fig. 15C shows a cross-sectional view of the support structure 1500 in the first operation mode along a line C-C of Fig. 15B. Fig. 15D shows a first plan view and Fig. 15E shows a second plan view of the support structure 1500 in a second operation mode. Fig.

15F shows a cross-sectional view of the support structure 1500 in the second operation mode along a line F-F of Fig. 15E. The support structure 1500 comprises a first member 1501 and two replaceable second members 1502, 1550.

For inserting the catheter components into the support structure

1500, the second member 1550 with the needle 101 anchored therein is clipped onto the first member 1501 using a snap-on connection mechanism, see Fig. 15A to Fig. 15C.

After this inserting procedure, the second member 1550 with the needle 101 anchored therein is replaced and substituted by the second member 1502 with a suck off tube 1402 and with a supply tube 1403, see Fig. 15D to Fig. 15F. In contrast to the support structure 1400 described referring to

Fig. 14, the support structure 1500 described referring to Fig. 15 comprises a possibility to position the cannulae 105, 201 and the needle

101 perpendicular, which allows vertical insertion of the cannula (see Fig.

15A to 15C). The second member 1502 comprises two sleeves 1540, 1541, a spacer tube 1542, four septa 1543 to 1546. In the second member 1502, the needle 101 is provided in a slidable manner.

After insertion of the cannulae 105, 201 in the body, the needle

101 is pushed out of the first member 1501. The second member 1502 is clipped on the first member 1501 comprising the suck off tube 1402 and the supply tube 1401.

A tip of the suck off tube 1402 penetrates through the septum

1546 provided in the first member 1501 and extends into a channel which is in fluid communication with the inner cannula 201 (see Fig. 15F). A tip of the supply tube 1403 penetrates through the septum 1545 provided in the first member 1501 and extends into a second channel which is in fluid communication with the lumen between the inner and the outer cannula walls 105, 201. In operation, the perfusion fluid is guided via the supply tube 1403 and the inner cannula 201, and the tissue fluid is guided via the cavity 107 between the inner and the outer cannula walls 105, 201 and the suck off tube 1402 to an exterior position (see Fig. 15F).

In the following, referring to Fig. 16A to 16E, a support structure 1600 according to another exemplary embodiment of the invention will be explained.

The support structure 1600 allows for fastening the cannula and needle configurations described above, particularly the configurations of the catheters shown in Fig. 2, 4, 6, 8, 10 and 12. The support structure 1600 is a modification of the support structures disclosed in US 4,369,781, US 4,452,473, and US 4,607,868.

Fig. 16A to Fig. 16C show the Luer lock support configuration for insertion the catheter, and Fig. 16D to Fig. 16E show the Luer lock support configuration for perfusion. A sleeve 1641 and an end of the outer cannula 105 slid on the sleeve 1641 are arranged (for instance in a fluid sealing manner, for example by casting) at the right hand side end of a Luer lock female part 1601. In a conic inner bore of the Luer lock female part 1601, a conic Luer lock male part 1642 and a septum 1643 are provided. The female Luer lock connector 1601 has a inner Luer tapered bore which receives the Luer tapered male connector part 1642 and the septum 1643. The Luer tapered male connector part 1642 comprises a lateral groove 1665 and a concentric bore, in which a sleeve 1640 is inserted with a slid on end of the inner cannula 201. At the left end of the female Luer lock connector 1601, a Luer guide projection 1663 is screwed on a Luer closure ring 1662 in such a manner that a connection tube 1661 is fastened to the left end of the female Luer lock connector 1601, and simultaneously the septum 1643 and the male Luer lock connector 1642 can be pressed into the conic inner bore of the female Luer lock connector 1601 in a fluid sealed manner. The proximal end of the female Luer lock connector 1601 is provided with a outwardly extending Luer lock lug or tab 1663 which is threaded into threads of the Luer locking ring 1662.

After insertion of the catheter, the insertion tube 101 with an insertion tube support 1650 is removed from the lumen of the inner cannula 201, and the suck and feed tube 1402, 1403 penetrates through the septum 1643 of the female Luer lock connector 1601, so that the tips of the suck and feed tube 1402, 1403 respective extend into the grooved 1665 and the sleeve 1640 of the male Luer lock connector 1642 (see Fig. 16D, Fig. 16E). At the left hand side of the connection tube 1661 a further Luer guide projection 1664 is arranged on which a further Luer closure ring 1666 for fastening the suck and feed tube 1402, 1403 can be screwed on.

It should be noted that the term "comprising" does not exclude other elements or steps and the "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined.

It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims

C l a i m s

1. A catheter, the catheter comprising a first tubular member having a first lumen and a first perforation; a second tubular member having a second lumen and a second perforation; wherein the second lumen is adapted to receive the first tubular member so that a channel is formed between the first tubular member and the second tubular member and so that a part of an outer surface of the first tubular member contacts a part of an inner surface of the second tubular member; wherein the first tubular member and the second tubular member are arranged to form a first fluidic path from the first lumen through the first perforation, to a body under investigation; wherein the first tubular member and the second tubular member are arranged to form a second fluidic path from the body under investigation, through the second perforation, and to the channel.

2. The catheter of claim 1, wherein the first tubular member and the second tubular member are arranged so that the first fluidic path is formed from the first lumen through the first perforation, through the channel, and through the second perforation to a body under investigation.

3. The catheter of claim 1 or 2, comprising an insertion needle adapted to be received in the first lumen of the first tubular member and adapted to be removable from the first lumen after insertion of the catheter into the body under investigation.

4. The catheter of claim 1 or 2, wherein the first tubular member is a hollow insertion needle.

5. The catheter of claim 3 or 4, wherein the insertion needle is a rigid needle, particularly a metallic needle.

6. The catheter of any one of claims 1 to 5, wherein at least one of the group consisting of the first tubular member and the second tubular member is a cannula, particularly a flexible cannula.

7. The catheter of any one of claims 1 to 6, wherein the first perforation comprises one or more holes in the first tubular member.

8. The catheter of claim 7, wherein the one or more holes are formed in an end face and/or in a lateral wall of the first tubular member.

9. The catheter of any one of claims 1 to 8, wherein the second perforation comprises one or more holes in the second tubular member.

10. The catheter of claim 9, wherein the one or more holes are formed in a lateral wall of the second tubular member.

11. The catheter of any one of claims 7 to 10, wherein each of the one or more holes has a dimension of at least

0.1 mm, particularly of at least 0.2 mm, more particularly of at least 0.4 mm.

12. The catheter of any one of claims 7 to 11, wherein the one or more holes of the first perforation are aligned with the one or more holes of the second perforation.

13. The catheter of any one of claims 1 to 12, adapted to guide a perfusion fluid along the first fluidic path.

14. The catheter of any one of claims 1 to 13, adapted to guide a body fluid along the second fluidic path.

15. The catheter of any one of claims 1 to 14, wherein the second tubular member has a first section and a second section, wherein an inner diameter of the second lumen in the first section differs from an inner diameter of the second lumen in the second section.

16. The catheter of claim 15, wherein the second lumen is stepped at a border between the first section and the second section.

17. The catheter of any one of claims 1 to 16, wherein the first tubular member has a first section and a second section, wherein an inner diameter of the first lumen in the first section differs from an inner diameter of the first lumen in the second section.

18. The catheter of claim 17, wherein the first lumen is stepped at a border between the first section and the second section.

19. The catheter of any one of claims 1 to 18, wherein the second tubular member has a length which is smaller than a length of the first tubular member.

20. The catheter of any one of claims 1 to 19, wherein at least one of the group consisting of the first tubular member and the second tubular member has a tapering outer end portion.

21. The catheter of any one of claims 1 to 20, wherein the first tubular member is fixedly connected to the second tubular member.

22. The catheter of any one of claims 1 to 21, comprising a support member adapted for receiving an arrangement of the first tubular member and the second tubular member.

23. The catheter of any one of claims 1 to 22, comprising at least one annular sealing or at least one annular segment sealing arranged in the channel.

24. The catheter of any one of claims 1 to 23, comprising a fluid reservoir for containing a perfusion fluid arranged in fluid communication with the first lumen.

25. The catheter of claim 24, wherein the fluid reservoir contains the perfusion fluid including a physiologically active substance, particularly a glucose regulating substance, more particularly at least one of the group consisting of insulin, glucagon, aldosterone and bi-carbonate as the infusion fluid.

26. The catheter of claim 24 or 25, comprising a first fluid transport unit adapted for transporting the perfusion fluid from the fluid reservoir through the first lumen and along the first fluidic path.

27. The catheter of claim 26, comprising a second fluid transport unit adapted for transporting a sample fluid produced by an at least partial equilibration between the perfusion fluid and a body fluid along the second fluidic path.

28. The catheter of claim 27, comprising a sensor for sensing a value of a physiological parameter based on an analysis of the sample fluid.

29. The catheter of claim 27 or 28, comprising a control unit adapted for controlling the first fluid transport unit and the second fluid transport unit for transporting the perfusion fluid from the fluid reservoir into the body under investigation and for subsequently transporting the sample fluid and the sample fluid from the body under investigation into the channel.

30. The catheter of claim 29, wherein the control unit is adapted to determine an amount of the physiologically active substance to be delivered to the body under investigation based on the value of the physiological parameter sensed by the sensor.

31. The catheter of any one of claims 28 to 30, wherein the sensor is adapted for determining at least one of the physiological parameters selected from the group consisting of a glucose concentration, a lactate concentration, an oxygen concentration, an ion concentration, a cholesterol concentration, an amount of bacteria, an amount of virus, a drug concentration and a medicament concentration.

32. The catheter of any one of claims 28 to 31, wherein the sensor is adapted for determining the value of the physiological parameter of the sample fluid comprising at least one of the group consisting of interstitial fluid, blood, lymph, cerebrospinal fluid, urine and tissue.

33. The catheter of any one of claims 1 to 32, adapted as a perfusion catheter.

34. The catheter of any one of claims 1 to 33, wherein the second lumen is adapted to receive the first tubular member so that the part of the outer surface of the first tubular member sealingly contacts the part of the inner surface of the second tubular member.

35. The catheter of any one of claims 1 to 34, wherein the second lumen is adapted to receive the first tubular member so that the part of the outer surface of the first tubular member fastens the part of the inner surface of the second tubular member.

36. The catheter of any one of claims 1 to 35, wherein the second lumen is adapted to receive the first tubular member so that the part of the outer surface of the first tubular member fastens the part of the inner surface of the second tubular member by one of the group consisting of a form-locking manner, a friction-locking manner, and an adhering manner.

37. The catheter of any one of claims 1 to 36, wherein the second lumen is adapted to receive the first tubular member so that the part of the outer surface of the first tubular member which contacts the part of the inner surface of the second tubular member is located at a distal end of the catheter.

38. The catheter of any one of claims 1 to 37, wherein the first tubular member is integrally formed with the second tubular member.

39. A method of operating a catheter comprising a first tubular member having a first lumen and a first perforation and a second tubular member having a second lumen and a second perforation, wherein the second lumen receives the first tubular member so that a channel is formed between the first tubular member and the second tubular member and so that a part of an outer surface of the first tubular member contacts a part of an inner surface of the second tubular member, wherein the method comprises guiding a perfusion fluid along a first fluidic path from the first lumen through the first perforation, to a body under investigation; guiding a sample fluid produced by an at least partial equilibration between the perfusion fluid and a body fluid along a second fluidic path from the body under investigation, through the second perforation, and to the channel.

40. The method of claim 39, comprising inserting an insertion needle in the first lumen of the first tubular member or in the second lumen of the second tubular member; and removing the insertion needle from the first lumen or from the second lumen after insertion of the catheter into the body under investigation.

41. A method of manufacturing a catheter, the method comprising providing a first tubular member having a first lumen forming a first perforation in the first tubular member; providing a second tubular member having a second lumen; forming a second perforation in the second tubular member; accommodating the first tubular member in the second lumen so that a channel is formed between the first tubular member and the second tubular member and so that a part of an outer surface of the first tubular member contacts a part of an inner surface of the second tubular member; arranging the first tubular member and the second tubular member to form a first fluidic path from the first lumen through the first perforation, to an environment surrounding the catheter; arranging the first tubular member and the second tubular member to form a second fluidic path from the environment surrounding the catheter, through the second perforation, and to the channel.

42. The method of claim 41, wherein at least one of the group consisting of the first perforation and the second perforation is formed by one of the group consisting of milling, drilling and a laser treatment.

43. A catheter, the catheter comprising a first tubular member; a second tubular member having a lumen and a perforation; wherein the lumen is adapted to receive the first tubular member so that a channel is formed between the first tubular member and the second tubular member and so that a part of an outer surface of the first tubular member contacts a part of an inner surface of the second tubular member; wherein the first tubular member and the second tubular member are arranged to form a fluidic path between the body under investigation, the perforation, and the channel; further comprising a bidirectional fluid transport unit coupled to the channel and adapted for selectively transporting a fluid through the channel, through the perforation and into the body under investigation, or from the body under investigation, through the perforation and into the channel.

44. A method of operating a catheter comprising a first tubular member and a second tubular member having a lumen and a perforation, wherein the lumen receives the first tubular member so that a channel is formed between the first tubular member and the second tubular member and so that a part of an outer surface of the first tubular member contacts a part of an inner surface of the second tubular member, wherein the method comprises guiding a perfusion fluid along the channel to a body under investigation; guiding a sample fluid produced by an at least partial equilibration between the perfusion fluid and a body fluid along a fluidic path from the body under investigation, through the perforation, and to the channel.