SE511932C2 - A method and catheter for detecting substances - Google Patents

Abstract

A catheter (1) to be inserted into and guided by a blood vessel, and a method for detecting substances in the coronary sinus. The catheter (1) comprises an elongate catheter body (2), having a distal end and a proximal end, and includes at least two channels (23, 24). A first and second channel (23, 24) for microdialysis solution are connected with each other so that microdialysis solution can flow from one channel to the other. An opening (25), in connection with which a microdialysis membrane (30) is arranged, is provided in the catheter body (2). A space (26) in the catheter body is formed by a part of the first channel in connection with said opening and forms a microdialysis chamber (26). The catheter is connectable to external means (10) for circulating and monitoring/analyzing the dialysis solution. In the method the concentration of at least one substance in a group, in a sample of a dialysis solution obtained by microdialysis of blood in the vascular system, e.g. in the coronary sinus, is measured and possibly compared with a reference concentration for the respective substance measured.

Description

15 20 25 30 35 511 932 the study of brain and skeletal muscle ”, Diabetologia, 1997, 40: pages 75-82, Springer-Verlag and PA Jansson, J Fowelin, U Smith and P Lönnroth, 1988,“ Characterization by microdialysis of intercellular glucose levels in subcutaneous tissue in Am J Physiol 255, E218-E220) as above and R Kanthan, A Shuaib, G Goplen and H Miyashita, “A humans”, and brain (Maggs et al, new method of in-vivo microdialysis of the human brain ", (1995) use of microdialysis in a clinical setting is, however, still Journal of Neuroscience Methods 60 151-155). Routine not established. Traditionally, microdialysis catheters are inserted into the tissue and after an equilibrium period, measurements of metabolic changes in the local the tissue is made.

US-A-4,694,832 discloses a dialysis probe which is primarily used inserted into biological tissues, eg brain tissue. In such use, the probe is placed in the tissue during surgery. It can also be inserted into a blood vessel or tissue in the same way as a cannula and is then provided with a pointed cutting edge.

Consequently, it is not suitable for insertion into and guided by a blood vessel. The design of the dialysis chamber also makes it unsuitable to be inserted and guided by a blood vessel because it is too fragile.

When patients with chest pain are admitted to cardiac intensive care units, they are routinely monitored with ECG and intermittently for peripheral venous plasma markers (AST, ALT, CK / CK-B, troponin-T and troponin-I), to detect damage to the heart. However, it is unsatisfactory that the metabolic changes are usually detected at a late stage of myocardial infarction and angina. These markers are monitored in peripheral venous plasma, and the response time is usually several hours. This delays active treatment and intervention against ongoing myocardial ischemia. Furthermore, a number of patients who undergo coronary artery bypass graft surgery with coronary artery bypass grafting or valve replacement have heart failure or other diseases, which increases the risk of surgery. Post- 23204seb; 1999-06-18 10 15 20 25 30 35 511932 such patients are surgically monitored hemodynamically in the intensive care unit, but suitable means for rapid detection of metabolic disorders in the heart are still lacking.

Continuous, rapid and selective detection of metabolic disorders of the heart in ischemia would greatly improve the chances of active intervention in the development of myocardial infarction with non-reversible damage to the heart in patients treated in cardiac intensive care units, as well as in patients undergoing cardiac surgery.

SUMMARY OF THE INVENTION It is an object of the invention to provide a method which can be used to obtain a safe and rapid response to the presence of certain substances in the blood in a blood vessel, which substances are related to metabolic changes in a heart.

It is also an object of the invention to provide an effective method which can be used for safe and rapid detection of substances in the vascular system which indicate reversible and non-reversible damage to the heart muscle.

These and other objects are achieved by the features of claims 1, 3 or 5.

The features of claims 1, 3 or 5 also provide a method that can be used for continuous monitoring.

The features of claims 1, 3 or 5 also provide a method for detecting substances, in a heart of a patient with myocardial ischemia, as one of a number of indications for the development of myocardial infarction and heart failure. 23204seb; 1999-06-18 10 15 20 25 30 35 511 952 The features of claims 1, 3 or 5 also provide a method for detecting metabolic changes, in a heart of a patient with myocardial ischemia, as one of a number of indications of development of myocardial infarction.

It is also an object of the present invention to provide a device which can be used to obtain a safe and rapid response to the presence of certain substances in the blood in a blood vessel and which is robust, easy to insert and has a simple construction.

It is also an object of the invention to provide an effective device which can be used for safe and rapid detection of substances in the coronary sinus, related to metabolic changes in the heart.

These and other objects are achieved with the features in the characterizing part of claim 7.

By arranging a microdialysis chamber, a device is obtained which can be used for measuring substances in blood without the need for blood samples to be taken.

By arranging a microdialysis chamber, a device is also obtained which has a short response time when it is used for measuring / monitoring substances in blood.

Due to the special design of the channels and the microdialysis chamber, a catheter is obtained which is easy to manufacture.

The features of claim 8 further provide a device that can quickly obtain a reliable reference value. 23204seb; 1999-06-18 10 15 20 25 30 35 511952 The features of claim 10 further provide a catheter that is simple to manufacture.

The features of claim 11 further provide that the insertion of the catheter is facilitated and that the catheter more easily remains in the correct position when properly positioned.

The features of claim 13 further provide that the catheter can be used to sample the coronary sinus and right atrium of an adult.

The features of claim 14 further provide a catheter having a stiffness suitable for use with the Selder technique in inserting the catheter.

The features of claim 15 further provide that a guide can be used to facilitate insertion of the catheter.

The features of claim 17 further provide that blood samples can be taken from the distal end of the catheter to ensure that the catheter is in the correct position.

The features of claim 18 further provide a catheter that is possible to place in a position where the patient's blood can easily pass and come into contact with the two microdialysis membranes.

The features of claim 19 further provide a catheter that is robust, simple in construction, cost effective and easy to manufacture.

The features of claim 21 further provide a catheter having a stiffness suitable for insertion using the Seldinger technique into the coronary sinus. 23204seb; 1999-06-18 10 15 20 25 30 35 511 932 The features of claim 22 further provide a catheter that is detectable by X-ray radiation, whereby the correct position of the catheter can be ensured by means of X-ray detection.

The features of claim 23 further provide a microdialysis catheter that has good uptake for a long time and is protected from thrombus formation.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partially broken away schematic view of a first embodiment of a catheter according to the invention.

Fig. 2 is a cross section taken at II-II in Fig. 1.

Fig. 3 is a cross-section taken at III-III in Fig. 1.

Fig. 4 is a longitudinal section taken at IV-IV in Fig. 2.

Fig. 5 is a partially broken away schematic view of a second embodiment of a catheter according to the invention.

Fig. 6 is a cross-section taken at VI-VI in Fig. 5.

Fig. 7 is a longitudinal section taken at VII-VII in Fig. 5.

DESCRIPTION OF PREFERRED EMBODIMENTS It should be noted that similar or corresponding parts have been designated by the same reference numerals in the drawings.

Figure 1 is a partially broken away schematic view of a first embodiment of a catheter 1 according to the invention. The catheter comprises an elongate catheter body 2 having a substantially cylindrical outer surface, a distal end 21 and a proximal end 23204seb: 1999-06-18 10 15 20 25 30 35 511932 22, between which it is preferably continuous except at the openings which will be explained below. The catheter body 2 is preferably made of X-ray-proof PVC or other suitable material, and its outer diameter is preferably in the range 5-7.5 Fr (~ 1.5-2.5 mm).

As shown in Figure 3, which shows a cross section taken at III-III in Figure 1, the catheter body 2 comprises a number of longitudinal channels. Two of the channels 23, 24 are arranged for circulation of dialysis fluid, and at their proximal ends they are connectable to a device 10 for circulation, monitoring or analysis, and preferably collection of dialysis fluid. The figure shows that the channels 23, 24 have the same inner diameters.

However, the channels may have different inner diameters and their cross-sections may have different shapes than those shown. In case they have different inner diameters, channel 24 preferably has the smaller one, and the dialysis fluid flows from the device 10 through channel 24 and back through channel 23.

At a distance from its distal end, the catheter body 2 has an opening 25, which is best seen in Figures 1 and 2. The shape of the opening 25 in the outer surface of the catheter body 2 may, for example, be circular, oval or substantially rectangular. The length of the opening 25 in the longitudinal direction is preferably 10-30 mm. The opening in the catheter body 2 can be formed by removing a part of its wall by cutting off a piece of the catheter body 2 in the wall area of channel 23, thereby opening a section of channel 23, and thus forming a space or chamber 26. As will be explained further below, the chamber 26 is provided with a wall formed by a microdialysis membrane 30, to provide a microdialysis chamber 26. Preferably, the channel 23 is enlarged in this section by removing the wall portion as shown in the figures. Part or all of the circumference of said region may be cut away to further enlarge the chamber 26 and thus enlarge the dialysis surface. 23204Seb; 1999-06-18 10 15 20 25 30 35 In figure 4, which shows a longitudinal section taken at IV-IV in figure 2 it is shown that the channels 23 and 24 are connected through a channel or opening 27 between the chamber 26 and the channel 24 so that dialysis fluid can flow between the channels. The channel or opening 27 is preferably arranged to connect a distal part of the chamber 26 and the channel 24, but other locations could also be possible. Preferably, the channels 23 and 24 are plugged or closed between the channel 27 and the distal end of the catheter body 2 by means of a plug or seal 28, 29 to prevent dialysis fluid from entering the channels 23, 24 beyond the channel 27. Furthermore, the channels 23 and 24 are plugged or sealed at the distal end 21 of the catheter body 2.

In an area around the opening 25, the catheter body 2 is provided with a microdialysis membrane 30 which has a sleeve-like shape and which surrounds a part of the catheter body 2. In Figure 1, the microdialysis membrane 30 is partially broken so that the opening 25 and the chamber 26 can be seen. The microdialysis membrane 30 can be slid onto the catheter body 2 over the distal end 21. At its edge regions 301, 302, the microdialysis membrane 30 is further connected or secured with an adhesive or adhesive, or with other suitable means to the catheter body 2 to prevent any liquid from entering. or out between the microdialysis membrane 30 and the catheter body 2 from or to the outside.

Possibly, the catheter body 2 may be provided with an annular recess for receiving the microdialysis membrane 30 in said region surrounding the opening 25.

Depending on the substance to be detected during the microdialysis, a microdialysis membrane of cuprophan, polycarbonate or PES (molecular limit between 200 kD) can be used. To prevent the initiation of coagulation when it comes in contact with blood, the surface of the microdialysis membrane 30 can be heparinized. 23204seb; 1999-06-18 10 15 20 25 30 35 9 511932 To facilitate insertion of the catheter into a particular blood vessel, a channel 50 for receiving a guide wire 51 may be provided in the catheter body 2. The distal end of the catheter body 2 is closed or closed except at an opening 52. This opening 52 forms a continuation of the inner surface of the channel 50 for the conductor. The conductor 51 is used during insertion of the catheter to increase the stiffness of the catheter 1 and to enable the catheter 1 to be bent into a desired curve shape to facilitate its insertion. After insertion of the catheter, the conductor 51 is removed and a blood sample can be taken at the proximal end of the catheter 1 through the opening 52 and the channel 50 for the conductor.

To prevent the conductor from coming out through the opening 52, the conductor 51 is provided with a stop 53.

The catheter body 2 can advantageously be manufactured from an extruded continuous profile body. The profile body is cut to a desired length and the channels, in addition to the channel for the conductor, are sealed or plugged at their distal ends. Furthermore, microdialysis chambers are formed by cutting, the channel 27 between the channels 23, 24 (the microdialysis chamber 26 and the channel 24) is formed and the idle ends of the channels are sealed or plugged. The catheter body is then provided with a microdialysis membrane and connections or connection tubes at the proximal end.

The distal end of the catheter can be preformed into a desired curve shape so that by rotating the catheter about its longitudinal axis the catheter can be manipulated to the desired position.

In order to provide adequate control over the movements of the catheter, it is necessary that its structure be somewhat rigid.

However, the catheter must not be so rigid that the insertion of the catheter through the blood vessels is prevented, in order for it to be able to reach the exact position where the microdialysis process is to be performed. In addition, it is necessary that the catheter is not so 23204seb; 1999-06-18 10 15 20 25 30 35 511 932 10 rigid that it causes damage to the blood vessels through which it paSSeIaI.

While it is important that the catheter is not so rigid that it causes damage to blood vessels, it is also important that there is sufficient rigidity in the catheter to operate torsional control, ie. the ability to transmit a torsional force along the length of the catheter. Sufficient rotational control enables controllable maneuverability of the catheter by applying a rotating force, at the proximal end of the catheter, which is transmitted along the catheter to its distal end.

The preform is also beneficial in that it helps the catheter stay in the correct position when properly positioned.

Figure 5 shows a second embodiment of a catheter according to the invention. This catheter comprises a first microdialysis chamber 26 with associated channels 23, 24, a first opening 25 and a first microdialysis membrane 30, as described in connection with the first embodiment according to Figure 1. At a center distance of approximately 100-120 mm from the first the opening 25 in the catheter body 2, in the direction of the proximal end 22, a second opening 45 is arranged in the catheter body 2, located on the opposite side relative to the first opening 25. As shown in Figures 5 and 7, a second microdialysis chamber 46 with associated second microdialysis membranes 31 and channels 43, 44 arranged in connection with the second opening 45, in the same way as in the first embodiment.

The channels 43, 44 are connected by means of a channel 47, preferably at the distal end of the second microdialysis chamber, and the channels 43, 44 are preferably sealed or plugged 48, 49 to prevent dialysis fluid from entering the parts of the channels between the channel 47 and the distal end of the catheter body 2, in the same way as in the first embodiment. 232045613; 1999-06-18 10 15 20 25 30 511 932 11 The two channels 43, 44 are connected at their proximal ends to the same device 10 for circulation, monitoring or analysis and preferably collection of the dialysis fluid, as the two channels 23, 24 or to separate device.

Figure 6 is a cross-section taken at VI-VI in Figure 5, showing a possible placement of the two channels 23, 24, the two channels 43, 44, the conductor 51 and the channel 50 of the conductor inside the catheter body 2.

In use, the catheter body is inserted with the aid of the guide into a patient's blood vessel, eg the jugular vein or the subclavian vein with Seldingerteknik. The catheter is then guided into the vein and advanced into the right atrium of the patient's heart and positioned in, for example, the coronary sinus, so that the first microdialysis chamber will be located in the coronary sinus. By preforming the catheter into an optimal curve shape and / or by bending the guide, the achievement of the correct position is facilitated. The correct position is confirmed by blood sampling through the opening 52 and the conduit 50 and measurement of oxygen saturation, or alternatively by X-ray or ultrasound detection. When using the catheter with two microdialysis chambers, the distance between the two chambers is chosen so that the other chamber will then be located in the right atrium so that microdialysis can be performed in both the coronary sinus and the right atrium. The distance is about 100-120 mm for an adult. In the case of two microdialysis chambers, it is important that the openings in the catheter body are located on substantially diametrically opposite sides of the catheter body 2, so that it is possible to place the catheter in a position where the patient's blood can easily pass and contact both microdialysis membranes. To be able to use Seldinger technology, the catheter must have a suitable flexibility. This is accomplished by selecting the thickness of its parts with respect to 23204seb; 1999-06-18 10 15 20 25 30 35 511932 12 the properties of each material. However, this is general knowledge for a person skilled in the art.

Alternatively, the catheter 1 can be tunneled through the patient's skin and placed directly in the coronary sinus during a heart operation.

The insertion opening is closed with a suture to allow removal of the catheter through the skin during postoperative monitoring.

When the catheter 1 is positioned in a blood vessel to be monitored, the proximal ends of the two channels 23, 24 and possibly the two channels 43, 44 are connected to the external device 10. This device comprises a container for dialysis fluid, container for collecting microdialysis fluid which has passed a microdialysis chamber 26, 46 and pumps for circulation of the microdialysis fluid through respective pairs of channels 23, 24 and 43, 44. Furthermore, it comprises devices or apparatus for monitoring or analyzing the microdialysis fluid which has passed a microdialysis chamber. For example, the concentration of substances that have passed from the blood in the vein through a microdialysis membrane 30, 31 to the microdialysis fluid in the microdialysis chamber 24, 46 by microdialysis and transported to the monitoring or analyzing apparatus can be measured. Such substances may be metabolic markers such as AST, ALT, CK / CK-B, troponin-T and troponin-I or substances such as lactate, pyruvate, glucose, glycerol, urea, aspartate, glutamate, myoglobin, hypoxanthines or peptides.

In the embodiment with two microdialysis chambers 26, 46, the concentration of the monitored substances can be measured in, for example, both the coronary sinus and the right atrium. The measurement from the right atrium is then used as a reference value in detecting changes in the coronary sinus. The values thus obtained with either of the two embodiments of the catheter can be used for 23204seb; 1999-06-18 10 15 20 25 30 35 13 511 952 detection of metabolic changes in the heart of a patient with myocardial ischemia, as one of a number of indications of the development of myocardial infarction. Other indications are obtained from ECG monitoring and monitoring of hemodynamic changes, arrhythmias and changes in blood pressure. By using the catheter and the method according to the invention, a rapid response to metabolic changes in a heart is achieved. The response time is approximately 15-20 minutes, which should be compared with several hours, which is the response time for the methods used today.

Since the substance (s) to be detected and / or measured is produced in the heart, its concentration (s) is highest in the heart. Therefore, in order to obtain the safest and fastest answer, it is preferable that the sample for the measurements be taken in the heart, preferably in the coronary sinus. Some of the substances to be detected and / or measured have a very short lifespan in the blood because they are absorbed and metabolised, for example by the red blood cells (erythrocytes). It is therefore very advantageous to isolate these substances from the blood through the microdialysis process. In the microdialysis fluid, they will remain constant (ie non-metabolized), which is beneficial for the measurements, especially when they can be isolated already in the heart. Although it is preferred that the samples to be analyzed be obtained by microdialysis of blood in the coronary sinus, they may also be obtained by microdialysis of blood in other parts of the blood vessel system, for example in an artery. Particularly advantageously, the concentration of the substance (s), eg glutamate, can be measured in samples taken by microdialysis in the pulmonary artery. Furthermore, the blood from the heart muscle will mix and thin in the blood flow, leading to a lower concentration of the substances to be measured. The metabolism and absorption in the blood of some of the substances also causes a decreased concentration at a distance from the heart. Some of the substances 23204seb; 1999-06-18 10 15 20 25 30 35 511 932 14 have a long lifespan, ie they are not metabolised in the blood or tissue and can very advantageously also be measured in the venous system. Although the response is not as fast and the concentrations are lower compared to measurements from the coronary sinus, a satisfactory and reliable result can be obtained in most cases.

The substances that can be obtained, monitored and / or measured (eg its concentration (s) in an artery are the same as in the coronary sinus, ie at least one of the substances in a group consisting of both metabolic markers such as AST, ALT CK / CK B, troponin-T and troponin-I, and substances such as lactate, pyruvate, glucose, glycerol, urea, amino acids, myoglobin, purines and peptides As in the case of samples obtained from the coronary sinus, the substances can be monitored continuously when the microdialysis process is continuous, also when samples are obtained from other parts of the blood vessel system.

Cardiac muscle ischemia, ie the quantitative lack of oxygenated blood delivered to the heart muscle tissue caused by local blockage of the arterial flow, is a serious condition that ultimately leads to permanent irreversible damage to heart muscle cells (myocardial infarction). Myocardial infarction accounts for 25023 deaths in 1992 in Sweden, as mentioned above. The development of myocardial infarction is strongly dependent on the duration of the ischemia. Thus, a total blockage of the arterial blood flow to a specific area (risk area) begins to cause irreversible damage within 10-15 minutes, and after 60 minutes 80-90% of the risk area is covered by a heart attack. It is therefore of great importance that metabolic changes and substances that indicate ischemia are detected so that appropriate intervention to restore blood flow can be performed before permanent damage develops. These interventions include dilating a blocked vessel, dissolving thrombi, or performing acute coronary bypass surgery. 23204seb; 1999-06-18 l0 15 20 25 30 35 511952 15 The detection of cardiac muscle ischemia today is mainly dependent on changes in the electrocardiogram (ECG), however, with an approximate sensitivity and specificity of only 70%. Other agents by which myocardial infarction can be detected include analysis of enzymes and other substances in venous blood, which are released by irreversible damage to heart muscle cells. The disadvantages of these analyzes are that the time taken by the analysis itself, often several hours, and the time delay (3-6 hours) between the irreversible heart muscle damage and the appearance of the special markers. Ischemia in a heart causes an immediate shift in metabolism from aerobic to anaerobic, which is reflected, for example, by a rapid transient production of lactate instead of consumption. This production of lactate and certain substances related to ischemia such as glutamate, aspartate, taurine, hypoxanthine and adenosine is released into the bloodstream, with a maximum concentration in venous blood in the heart, ie that which is enclosed in the coronary sinus and the Thebes veins, whereby the substances further spreads rapidly into the main bloodstream pumped by the heart. The half-lives of the substances are also short, depending on the metabolic consumption of the blood itself and peripheral tissue, and thus a detection of these substances is possible only in the pulmonary artery and possibly in systemic arteries but not in central venous blood.

Microdialysis has been used to monitor the intercellular space in various body organs for local metabolic changes, as mentioned above. The present invention relates to a method for the continuous detection of transient or more prolonged production or release of substances from the heart which are related to metabolic changes in a heart and a specially designed microdialysis catheter intended for use in the method. The method has the advantage over the traditional metabolic analysis of markers related to cardiac muscle ischemia, that it is not limited to the analysis of 23204seb; 1999-06-18 10 15 511 952 16 substances with a long service life (eg half-life which is hours-days), and does not require blood sampling, whereby continuous analysis with a short analysis time is possible. The method can indicate ischemic changes in a heart at an early stage before the development of extensive permanent heart muscle damage, so it will be very useful in guiding an intervention. A disadvantage of conventional blood sampling is that it is limited to momentary situations. With a continuous technique according to the invention it is possible to follow the development of metabolic changes, whereby a serious condition can be detected. Although the invention has been described in connection with a number of preferred embodiments, it is to be understood that various modifications may still be made without departing from the spirit and scope of the invention as defined in the appended claims. For example, the dimensions may vary depending on the particular use. 23204seb; 1999-06-18

Claims (1)

A method for detecting at least one substance that indicates metabolic changes in a heart, characterized in that the concentration of at least one substance in a group consisting of both metabolic markers such as AST, ALT, CK / CK-B, troponin-T and troponin-I and substances such as lactate, pyruvate, glucose, glycerol, urea, amino acids, myoglobin, purines and peptides, in a sample of dialysis fluid obtained by microdialysis of blood in the blood vessel system, preferably in an artery measured and possibly compared with a reference concentration for each substance being measured. Method for detecting substances in a heart, characterized in that the concentration of at least one substance in a group consisting of both metabolic markers such as AST, ALT, CK / CK-B, troponin-T and troponin-I, and substances such as lactate , pyruvate, glucose, glycerol, urea, aspartate, glutamate, myoglobin, hypoxanthines and peptides in a sample of dialysis fluid obtained by microdialysis of blood in the coronary sinus are measured and possibly compared with a reference concentration for each substance measured. A method according to claim 2, wherein the reference concentration is obtained by measuring the concentration of said at least one substance in a second sample of dialysis fluid obtained by microdialysis in the right atrium. Method for detecting metabolic changes in a heart, characterized in that the concentration of at least one substance in a group consisting of both of metabolic markers such as AST, ALT, CK / CK-B, troponin-T and troponin-I, and substances such as lactate, pyruvate, glucose, glycerol, urea, aspartate, glutamate, myoglobin, hypoxanthines and peptides in a sample of dialysis fluid obtained by microdialysis of blood in the coronary sinus are measured and possibly compared with a reference concentration for each substance being measured. A method according to claim 4, wherein the reference concentration is obtained by measuring the concentration of said at least one substance in a second sample of dialysis fluid obtained by microdialysis in the right atrium. A method according to any one of claims 1-5, wherein the concentration of the substance (s) to be detected is measured continuously in a sample of dialysis fluid obtained by continuous microdialysis of blood. A catheter for insertion into and guided by a blood vessel and for use in a method according to any one of claims 1-6, comprising an elongate catheter body having a distal end, a proximal end and an outer substantially cylindrical surface defining a wall structure enclosing at least two channels, characterized in that said at least two channels comprise a first and a second channel for microdialysis fluid, each channel having a proximal and a distal end, the first and second channels being connected to each other at a first distance from the distal end of the catheter body so that microdialysis fluid can flow from one channel to the other, 23204seb; An opening, in connection with which a microdialysis membrane is arranged, is arranged in the catheter body at a second distance from its distal end, a space in the catheter body formed by a part of the first the channel adjacent to said opening forms a microdialysis chamber having at least a portion of the microdialysis membrane as part of its walls, the proximal end of each of said first and second channels being connectable to an external device for circulating and monitoring / analyzing the dialysis fluid. A catheter according to claim 7, wherein a third and a fourth channel for microdialysis fluid are arranged in the catheter body, each channel having a proximal and a distal end, the third and fourth channels being connected to each other at a third distance from the distal end of the catheter body so that microdialysis fluid can flow from one of the third and fourth channels to the second, a second opening, adjacent to which a second microdialysis membrane is arranged, is arranged in the catheter body at a fourth distance from its distal end, a second space in the catheter body formed by a part of a third channel adjacent to said second opening forms a second microdialysis chamber, which has at least a part of the second microdialysis membrane as part of its walls, the proximal end of each of said third and fourth channels being connectable to an external device for circulation and monitoring / analysis of the dialysis fluid. 23204seb: 1999-06-18 10 15 20 25 30 10. 11. 12. 13. 14. 15. 16. 17. 511 932 A catheter according to claim 7 or 8, wherein each microdialysis membrane covers the respective opening. A catheter according to any one of claims 7-9, wherein each microdialysis membrane has a sleeve-like shape. A catheter according to any one of claims 7-10, wherein the catheter is preformed into a desired curve shape. A catheter according to any one of claims 7-11, wherein each dialysis membrane is glued, adhered, connected or attached by other suitable means to the catheter body at areas near their respective edges, said edges being located on opposite sides of respective openings. A catheter according to any one of claims 8-12, wherein the fourth distance is approximately 100-120 mm longer than the second distance. A catheter according to any one of claims 7-13, wherein the catheter has a flexibility which enables it to be inserted into and guided in a blood vessel, for example according to Selderderknik. A catheter according to any one of claims 7-14, wherein a channel for receiving a conductor is formed in the catheter body. A catheter according to any one of claims 7-15, wherein the catheter body is closed at its distal end. A catheter according to claim 15, wherein 23204seb; 1999-06-18 10 15 20 25 18. 19. 20. 21. 22. 23. (> 7 21 511 M2 the catheter body is closed at its distal end except at an opening which is a continuation of the channel for the conductor. A catheter according to any one of claims 7-17, wherein the openings in the catheter body are located on substantially diametrically opposite sides of the catheter body. A catheter according to any one of claims 7-18, wherein the catheter body is formed by extrusion. A catheter according to any one of claims 7-19, wherein each An catheter according to any one of claims 7-20, wherein the catheter has a flexibility which enables it to be inserted into and guided into the coronary sinus, for example by Seldinger technology. A catheter according to any one of the claims A catheter body according to any one of claims 7-22, wherein the microdialysis membrane (n) is heparinized (de) 7201, wherein the catheter body is X-ray sealed.