EP0671894A1

EP0671894A1 - Gas injector

Info

Publication number: EP0671894A1
Application number: EP94902669A
Authority: EP
Inventors: Wolfgang Kloess; Martin Dr. ZWAAN
Original assignee: Daum Kloess Wolfgang GmbH
Current assignee: Daum GmbH
Priority date: 1992-12-04
Filing date: 1993-12-03
Publication date: 1995-09-20
Also published as: DE9216558U1; WO1994013204A1

Abstract

A gas injector for introducing a gas into a liquid-filled vessel system has a carbon dioxide bottle (1) as pressure source connected to the inlets of proportional valves (8, 11). The carbon dioxide may be introduced into the blood vessel (26) through the proportional valve (8) and the catheter (23) with an adjustable volume flow. In addition, the blood vessel may be blocked by means of the balloon (24) which is inflatable through the proportional valve (8) and the lumen (23a) of the catheter (23).

Description

Gas injector

The invention relates to a device for introducing gaseous media into a liquid-filled vessel system, with a pressure source for the gaseous medium, a metering valve for adjusting the gas flow, a gas outlet which can be connected to the vessel system and a sensor arranged between the metering valve and gas outlet for detecting the pressure, mass flow or Volume flow of the gaseous medium, a control variable for the metering valve being able to be derived from the output signal of the sensor.

Such a gas injector is used, for example, in angiography. Angiography is the X-ray imaging of blood vessels with the aid of a contrast agent introduced into the bloodstream. In principle, positive contrast agents which increase the radiation absorption and negative contrast agents which reduce the radiation absorption are known in radiology to improve the recognizability of anatomical structures. In angiography, iodine-containing liquids are usually used as positive contrast agents. However, a considerable part (approx. 13% for ionic and 3% for non-ionic contrast agents) of the angiographed patients has allergic reactions to contrast agents, which can lead to serious and even fatal incidents.

It is also known to use carbon dioxide as a gaseous negative contrast medium in angiography. CC puts little strain on the organism, as it physically dissolves very quickly in blood and is exhaled in one breath via the lungs. The C0 _? must under defined and reproducible conditions are introduced into the bloodstream. Injection with too little pressure leads to the blood not being completely displaced in the vascular section to be angiographed, but rather only a gas / blood mixture being formed (so-called "bubbles"). The remaining blood residues can be misinterpreted as a stenosis in Angiogra m. Injecting CC under too high pressure can cause vascular injury.

In a gas injector of the type mentioned at the beginning of DE-B 3802 128, a servo valve with a downstream metering resistor is used to regulate the gas flow. A servo valve is a directional valve usually constructed as a longitudinal slide or rotary slide valve. Exemplary embodiments are described in the journal "Oil hydraulics and pneumatics" 35 (1991), pp. 43-47. Such servo valves, which can be adjusted by an electric motor, have a relatively complicated structure and also require a signal feedback of the travel path covered, i.e. A separate position transducer, which generates a corresponding signal, is required to determine the current control state of the servo valve. Servo valves also require relatively high working pressures, the desired low gas pressures corresponding to the pressure prevailing in the blood vessel cannot be given off directly, so that a downstream throttling resistance is required which has to be changed every time after use of this known injector for hygienic reasons.

The invention has for its object to provide a device of the type mentioned, which does not have the disadvantages mentioned or to a lesser extent and which is simple and inexpensive to manufacture.

The invention solves this problem in that the metering valve is designed as a proportional valve.

A proportional valve in the sense of the invention is any poppet valve whose opening cross-section is proportional to the (usually electrical) manipulated variable and in which no signal feedback of the valve path is required to determine the current actuating state of the valve, since the respective actuating state (opening cross-section) of the Proportional valve can be derived directly from the supplied (electrical) manipulated variable. Such a proportional valve is considerably less expensive than the servo valve used in the prior art. In addition, it has been found that a proportional valve can release the gaseous medium directly with the relatively low excess pressure required for introduction into a blood vessel; an additional metering or throttling resistance as in DE-B 38 02 128 is not necessary. With the gas injector according to the invention, small gas volume flows (about 5-40 ml / s, depending on the vessel size) can also be metered precisely and flutter-free against the pulsating blood pressure.

In another context (pressure control of a known volume), US-A-5 094260 describes a so-called "proportional valve", which, however, is actually not a proportional valve in the sense of the present invention, but rather a conventional servo valve, which means an actuator is set. Its operating principle corresponds to the valve used in DE-B 3802 128. A particularly serious disadvantage of these servo valves, particularly in medical technology, is that such electromotive operated valves remain open in the last set position in the event of a power failure, while the proportional valve used according to the invention closes automatically in the event of a power failure. So it offers a much higher inherent security.

It should also be noted that the injection of CO "creates only a relatively low negative contrast with the normal blood filling of the vessel. So-called digital subtraction angiography (DSA) is used to make the vessels clearly visible despite this small difference in contrast. In this method, a so-called mask image (the vessel in the normal state filled with blood) and a filling image (the vessel with the gas filling) are recorded. The images are digitized and subtracted from each other to enhance contrast.

The control loop containing the sensor and the proportional valve is expediently designed to regulate the gas volume flow. It has been shown that the gas volume flow is the essential parameter influencing the quality of the angiogram, so that the controllability and Reproducibility of this parameter is particularly important. The sensor arranged between the proportional valve and the gas outlet can be designed directly for measuring the volume flow or mass flow. As a rule, however, this sensor is a pressure sensor, which then measures the pressure prevailing at the outlet of the proportional valve. The pressure at the proportional valve on the inlet side is the known outlet pressure of the pressure source. The pressure drop via the proportional valve, the opening cross section of which is known in each case, can then be used to calculate and regulate the gas volume flow resulting on the output side of the proportional valve. In this way, the primary pressure prevailing on the outlet side of the pressure source is also monitored without an additional pressure sensor being required. If a certain gas pressure at the outlet side of the proportional valve is no longer reached with a certain opening cross section of the proportional valve, this indicates a pressure drop in the pressure source, for example an empty gas bottle. The injector can then switch off automatically and trigger an alarm signal.

When introducing the gas into the vascular system, it is important that the gas be released at the desired pressure and volume flow at the connection point between the gas outlet and the vascular system. However, since the pressure and volume flow at the outlet of the proportional valve are measured and since gas is a compressible medium, the pressure and volume flow at the outlet of the proportional valve do not have to be identical to the pressure and volume flow at the connection point gas outlet / vascular system. It is therefore expedient that the control loop for regulating the gas volume flow can be subjected to correction factors corresponding to the compressibility of the gas used and the flow resistance of the gas outlet used. These correction factors can be taken, for example, from a database and fed to the control loop as a control variable. This ensures that the gas is actually released into the vascular system at the desired pressure and volume flow.

A temperature control device for the gaseous medium is advantageously provided. It can be designed, for example, as a temperature control chamber upstream of the proportional valve with electrical heating devices. In addition or instead, the proportional valve itself can also be provided with heating elements to heat the gaseous medium or to prevent the heated medium from cooling. In this way, the medium can be warmed to body temperature (37 ° C.) before being introduced into the blood vessel system, so that the vascular spasms (spastic occlusion of the blood vessel) that otherwise occur when liquid or gaseous media are injected into blood vessels are avoided. To monitor the gas temperature, temperature sensors can be provided in the temperature control chamber and / or between the proportional valve and the gas outlet. The cooling of the gas by pipe flows can be neglected given the small diameters and lengths of the gas outlets used.

The device according to the invention expediently has an adjustable maximum narrow limit for the gas introduced into the vascular system. This limitation prevents the body from being fed carelessly with an impermissibly high amount of carbon dioxide.

The gas outlet is generally designed as a catheter that can be inserted into the vascular system. The connection point already mentioned above between the gas outlet and the vascular system is then the catheter tip from which the gas is released into the area of the vascular system to be angiographed. Since carbon dioxide has a low viscosity, even small blood vessels can be angiographed using appropriately thin catheters.

In an advantageous embodiment of the invention, an additional switching valve is arranged between the proportional valve and the gas outlet. In this context, "between" means that the switching valve is arranged in the flow direction of the gas between the proportional valve and the gas outlet. The term “between” is also to be understood in this sense in the remaining claims. “Switching valve” is to be understood as a valve that can be switched back and forth between the two states “closed” and “open”. Such an additional switching valve makes it possible to pneumatically separate the gas outlet from the rest of the injector. On the one hand, the device can be immediately separated from the vascular system in the event of malfunctions, on the other hand it can be prevented, for example, that blood rises back into the injector when the catheter is inserted and contaminates it. An additional pressure sensor is advantageously provided between the switching valve and the gas outlet. After inserting the catheter, this sensor measures the blood pressure in the vascular system. Thus, even when the switching valve is still closed, the pressure against which the gas must be introduced into the vascular system is already known. Even before the switching valve is opened, the pressure prevailing at the proportional valve on the output side can therefore be adjusted accordingly, so that on the one hand no blood flows back into the injector when the switching valve is opened and on the other hand no carbon dioxide with excessive pressure is released into the vascular system . This additional pressure sensor thus serves to measure the back pressure prevailing in the vascular system and to adjust the injection parameters accordingly before the start of the injection process.

A filter can also be arranged between the switching valve and the gas outlet. Such a filter is expediently designed as a microfilter with a mesh structure of about 0.2 μm pore size. On the one hand, it serves as a very fine filter for the gas to be introduced into the vascular system and, on the other hand, as a reservoir with hydrophobic properties (impermeable to blood) which, for example in the event of malfunctions of the device, initially collects blood flowing back before it can enter the injector. It is possible here to use microfilters that are commonly used in anesthesia machines and that are changed after each use.

The filter can also be provided with a hydrophobic membrane as a gas-liquid barrier. In this way, it is prevented that liquid (blood) flows from the patient into the gas channels of the injector. The mutual contamination of both the patient and the device according to the invention is prevented.

A check valve and / or a liquid detector can additionally be arranged between the switching valve and the gas outlet as additional safeguards against the backlash of blood into the injector. The check valve prevents backflow from occurring at all. The liquid detector triggers an alarm when liquid flows back to it, closes the switching valve and shuts down the injector. A foot switch can be provided to trigger the gas injection, so that the operating doctor has his hands free for other activities.

Advantageously, all parts of the device according to the invention that come into contact with the gaseous medium are heat and chemical resistant. They can then be sterilized by heating to temperatures around 65 ° C. and / or fumigation, for example with ethylene oxide or formaldehyde.

Another method for examining blood vessels is angioscopy. In this method, an angioscope (endoscope) with a camera or comparable optical device is inserted at the tip into the blood vessel to be examined. The section of the vessel to be angioscoped must be rinsed free with an optically transparent medium. In the prior art, this is usually done with a physiological salt solution. This liquid must be applied via a catheter at a relatively high pressure so that the blood is completely washed away and the corresponding section of the vessel is visible to the angioscope. This leads to turbulence in the interior of the vessel, which in turn can damage the inner walls of the vessel. Since large amounts of irrigation fluid (between 120 - 1100 ml / min) must also be injected, the heart may become overloaded. It has therefore already been proposed to use CO2 as a rinsing medium for angioscopy. However, this is particularly problematic if smaller blood vessels in the vicinity of larger vessels located downstream are to be angioscoped. Due to the venturi effect of these larger vessels, the applied C0 _? immediately aspirated without a clear view in the vessel to be examined at least for a limited period of time.

When using the gas injector for angioscopy, it is provided according to the invention to solve this problem that the catheter has at least two lumens and that a lumen is connected to an inflatable balloon that surrounds the outer circumference of the catheter. By inflating the balloon, the blood vessel upstream of the section to be examined can be blocked, thus preventing blood from flowing in again. The injected C0 _? is not immediately replaced by the flowing blood that clear view in the blood vessel is maintained longer. An advantageous material for the balloon is latex.

The balloon should be inflated with a pressure which is sufficient to largely block the undesirable flow of blood, but which is also not so great that damage to the inner walls of the vessel occurs. It is therefore expedient if the catheter lumen connected to the balloon is connected to the pressure source for the gaseous medium via a second proportional valve. In this way, the balloon can be inflated with a predetermined, defined pressure. Advantageously, a pressure sensor is also arranged between the second proportional valve and the balloon, so that it can be reliably determined whether the balloon pressure required to block the blood vessel has been reached.

In order to achieve the greatest possible reproducibility of the angioscopic recordings, it is advantageous if the balloon can first be inflated with a predetermined gas pressure and then the gas introduction into the vascular system can be triggered with an adjustable time delay.

In the previously described embodiments of the invention, which are used for angioscopy, the angioscope is introduced into the vessel through the same catheter lumen through which the CO 2 is also introduced into the vessel. This is possible because modern angioscopes have an outer diameter of only 0.5 mm. The narrowing of the cross-section of this catheter lumen through the angioscope can, however, lead to the pressure drop across this catheter lumen increasing in a manner which is hardly calculable. In addition, the angioscope at the catheter outlet can be made to flutter by the gas flow or pressed against the vessel wall, so that no satisfactory angioscopic images are produced. It is therefore advantageous if the catheter has a separate, additional lumen for inserting an angioscope (endoscope). According to the invention, a catheter for use as a gas outlet of a device described above has at least three lumens. The gas flow through the angioscope then no longer occurs. In such a catheter, the lumen for inflating the balloon and the lumen for introducing the carbon dioxide into the vascular system have a diameter of approximately 0.4 mm, the lumen for inserting the angioscope has a diameter of approximately 1 mm. Advantageous materials for such a catheter are PVC, polyurethane or polyethylene.

An embodiment of the invention is explained below with reference to the drawing. In it show:

Figure 1 is a schematic representation of the gas injector.

2 shows a proportional valve in longitudinal section;

Fig. 3 shows schematically a Vierlu igen catheter;

4 shows the catheter from FIG. 3 in cross section;

5 is an exploded view of the microfilter used behind the outlet of the switching valve.

The gas injector has a carbon dioxide bottle 1 as a pressure source, which is connected via a pressure reducing valve 2 and a microfilter 3 to a manually operated emergency shutdown valve 4. By actuating this valve 4, the pressure source 1 is separated from the gas injector in emergencies. An electrically operated input valve 5 then follows, with which the pressure source can also be separated from the gas injector. In emergency situations recognized by the automatic control of the gas injector, this input valve 5 serves as an emergency shutdown valve. The pressure prevailing on the outlet side of the inlet valve 5 is monitored by a pressure sensor 5a, and pressure switches and sensors 6 are also provided for limit pressure detection of the permissible minimum and maximum pressures, which can be, for example, 3 or 5 bar. On the output side of the input valve 5, the temperature control chamber 7 is connected with an electrical heating device in which the gas is heated to the desired temperature, generally the body temperature of 37 ° C. This temperature is monitored by means of the temperature sensor 7a. The proportional valves 8 and 11 are connected in parallel on the output side of this temperature control chamber 7. Each of these proportional valves 8, 11 has a pressure sensor 8a, 11a on the output side, which detects the respective output pressure of the proportional valve and converts it into an electrical signal, which is then used again as Controlled variable for controlling the proportional valve is fed back. The proportional valves 8, 11 are actuated electromagnetically and are explained in more detail below. They are heated by means of the electric heating elements 8b, 11b in order to prevent the gas heated in the temperature control chamber 7 from cooling. The temperature of the gas on the outlet side of the proportional valve 8 is monitored by means of the temperature sensor 10. The pressure sensor 12 monitors the pressure on the output side of the proportional valve 11; in addition, for safety reasons, a limit pressure switch 18 is provided, which emits an alarm signal when a permissible maximum pressure (for example between 1 and 3 bar) is overwritten. The pressure on the output side of the proportional valve 8 is monitored by a pressure sensor 9, and in addition a limit pressure switch 13 is also provided, which emits an alarm signal when a permissible maximum pressure is exceeded. On the output side of the proportional valves 8, 11 there are electromagnetically actuated switching valves 14, 19, each of which is assigned a pressure sensor 16, 20 which, in the closed state of these switching valves 14, 19, measures the pressure present on the output side thereof. An additional vent valve 15, designed as a 3/2-way valve, is provided behind the switching valve 14, by means of which the inflated balloon 24 can be vented. A temperature sensor 17 for monitoring the gas temperature is provided downstream of the switching valve 19. Microfilters 21, 22 connect to the output side of the vent valve 15 and the switching valve 19, the structure of which is explained in more detail below. The outlet of the switching valve 19 feeds the lumen 23b of a catheter 23 via this microfilter 22. This lumen 23b is open at the catheter tip 25 and serves to introduce C0 ₂ into the blood vessel 26. The switching valve 14 is on the outlet side via the vent valve 15 and the microfilter 21 is connected to the lumen 23a of the catheter 23, via which the balloon 24 can be inflated. A control unit 27 is provided for monitoring all functions of the gas injector and for controlling the valves. For safety reasons, this control unit 27 has a microprocessor control with double redundancy.

The structure of the microfilters 21, 22 is explained in more detail in FIG. 5. O-rings 56, 53 are inserted into the filter housing 57 and the screw cover 52, respectively. A steel grid 54 also serves as the actual filter elements a mesh size of 5 μm and a hydrophobic membrane 55 with a pore size of 0.2 μm. This filter disk or membrane 55 is hydrophobic and does not allow liquids such as blood to penetrate. It therefore represents a gas-liquid barrier. The microfilters are connected to the gas line system via Luer lock connections 58, 59.

The structure of the proportional valves 8, 11 is explained in more detail in FIG. 2. The valve housing 31 has a pressure inlet 28, a pressure outlet 29 and a vent outlet 30. In the idle state of the valve, the connection between the pressure inlet 28 and the outlet 29 is blocked by the main piston 32, which is pressed against the valve seat 34 in a sealing manner by a spring 33. The magnetic device 35, which is only schematically indicated in the drawing, actuates the control piston 37 via a piston rod 36, which, in the idle state, rests sealingly on an axial surface of the main piston 32. Main piston 32 and control piston 37 are designed as essentially cylindrical hollow bodies. The control piston 37 has openings on its axial surface facing the magnetic device 35, which connect its interior to the ventilation opening 30. When the magnetic device 35 exerts a force on the control piston 37 in the direction of arrow A in FIG. 2, which exceeds the holding force of the spring 33, the control piston 37 moves in the direction of this arrow A and thereby lifts the main piston 32 from its valve seat 34. The pressure inlet 28 is now connected to the annular space 38 and thus also to the pressure outlet 29. The opening cross section of the valve depends on the force which the magnetic device 35 exerts on the control piston 37 and is proportional to the current flow through the magnetic device 35. The current flowing through the magnetic device 35 is therefore a direct measure of the opening cross section of the valve Valve; In contrast to servo valves, a separate position transducer for determining the control status of the valve is not required.

If the pressure outlet 29 is to be vented, the magnet device 35 pulls the control piston 37 in the opposite direction to the arrow A in FIG. 2 to such an extent that it lifts off the axial surface of the main piston 32 and thus the pressure outlet 29 with its inner cavity and thus also connects to the vent outlet 30. The function of the injector is described below using the example of a gas injection with a previous balloon blockage of the blood vessel. The following injection parameters are entered into the control unit 27 or are already stored in it:

1. Compressibility of the gas

2. Catheter type (volume, flow resistance, number of lumens, catheter with or without balloon)

3. Duration and start of the balloon blockade (before, during or after a gas injection)

4. Gas pressure with which the balloon is to be inflated

5. maximum gas volume to be injected

6. Desired gas volume flow

The catheter 23 is inserted into the blood vessel to be examined. Its two lumens 23a and 23b are connected to the corresponding connections of the injector. It must be ensured that the entire gas-carrying system no longer contains any foreign gases other than carbon dioxide, since otherwise air boluses could occur. For example, the catheter 23 can be rinsed with physiological saline for this purpose. Instead, an automatic flushing of the entire dead spaces of the gas injector, which can still contain ambient air, can be provided with C0 ₂ .

The control unit 27 now opens the input valve 5. At the inputs of the proportional 1 valves 8 and 11 there is now carbon dioxide with a defined pressure determined by the setting of the pressure reducing valve 2 (generally 4 bar). The outlet pressure of the proportional valve 8 is now set so that it corresponds to the desired filling pressure of the balloon 24. It is monitored by the pressure sensor 8a. The output pressure of the proportional valve 11 (monitored by the pressure sensor 11a) is set such that it is somewhat higher than the blood pressure in the blood vessel 26 measured by the pressure sensor 20. The amount by which it is set higher than this blood pressure is determined on the one hand by the pressure drop taking place in the catheter and on the other hand by the desired volume flow with which the CO _{2 is} to be injected into the blood vessel 26. The switching valve 14 is now opened and connects the output of the Proportional valve 8 with the lumen 23a of the catheter 23 and thus with the balloon 24. This balloon is now inflated with the desired pressure and blocks the blood vessel 26. After the desired balloon pressure has been reached, the switching valve 14 can be closed again, the pressure transducer 16 then monitors the balloon pressure. After an adjustable time delay has elapsed, the switching valve 19 opens and connects the outlet of the proportional valve 11 to the lumen 23b of the catheter 23. C0 _? can now flow into the blood vessel 26 from the catheter tip 25. The volume flow of the inflowing carbon dioxide is regulated if necessary by adjusting the proportional valve 11 and kept constant over the desired period of time. The gas volume flow at the outlet 25 of the catheter 23 is calculated from the following parameters:

1. Inlet pressure at the proportional valve 11 (the known outlet pressure of the pressure reducing valve 2)

2. Output pressure at the proportional valve 11 (measured by the pressure transducer 11a)

3. Opening cross section of the proportional valve 11 (proportional to the current through the magnetic device 35)

4. Flow resistance and pressure drop across the lumen 23b of the catheter 23 (taken from a database in the control unit 27)

After completion of the injection, the balloon 24 can be vented again via the corresponding vent outlet of the additional switching valve 15. The gas injection is ended by closing the switching valve 19. During the entire injection process, the gas is heated in the temperature chamber 7 and by means of the heating elements 8b, 11b provided in the proportional valves 8, 11, the monitoring or regulation of the desired temperature is carried out by means of the thermal sensors 7a, 10, 17. The In addition to the pressure sensors 8a, 11a, pressure sensors 9, 12 monitor the pressure prevailing on the output side at the proportional valves 8, 11 and thus offer increased security against malfunctions.

3 and 4 show a four-lumen catheter for use as a gas outlet for an injector according to the invention. At its device end, this catheter has four connections 39-42, which are connected to the respective lumens. The connection 39 is above the lumen or Channel 49 (diameter 0.33 mm) in connection with the latex balloon 44 arranged near the patient end of the catheter. This latex balloon can thus be inflated by introducing gas into the connection 39. Connection 40 is used to insert the angioscope and is connected to the angioscopy channel 48 (diameter 1 mm). Connection 41 is connected to an additional working channel 50 (diameter 0.66 mm), which is used for aspiration or as an instrument channel. Connection 42 is connected to the gas channel 51 (diameter 0.33 mm) through which the carbon dioxide is introduced into the vessel. The channels 48, 50 and 51 are open towards the end of the catheter on the patient side, which is indicated in FIG. 3 by the reference symbols 45, 46 and 47. The channel integrator or channel separator 43 brings together the four connections 39-42 and connects them to the respective lumens of the catheter. The embodiment of the catheter shown has a length of 1.3 m and an outer diameter of 2.1 mm. The latex balloon 44 is dimensioned so that it can block vessels up to a maximum inside diameter of 25mm.

Claims

1. Device for introducing gaseous media into a liquid-filled vessel system (26), with a pressure source (1) for the gaseous medium, a metering valve (11) for adjusting the gas flow, a gas outlet (25) that can be connected to the vessel system (26) and a sensor (11a) arranged between the metering valve and gas outlet for detecting the pressure, volume flow or mass flow of the gaseous medium, a control variable for the metering valve (11) being able to be derived from the output signal of the sensor (11a), thereby characterized in that the metering valve (11) is designed as a proportional valve.

2. Device according to claim 1, characterized in that the control loop containing the sensor (11a) and the proportional valve (11) is designed to regulate the gas volume flow.

3. Apparatus according to claim 2, characterized in that the Regel¬ loop can be acted upon with correction factors corresponding to the compressibility of the gas used and the flow resistance and / or volume of the gas outlet used.

4. Device according to one of claims 1 to 3, characterized in that a temperature control device is provided for the gaseous medium.

5. The device according to claim 4, characterized in that the proportional valve (11) is provided with a heating device (11b) for heating the gaseous medium.

6. Device according to one of claims 1 to 5, characterized in that a maximum quantity limit for the gas introduced into the vascular system (26) is adjustable.

7. Device according to one of claims 1 to 6, characterized in that the gas outlet is designed as a catheter (23) which can be inserted into the vascular system (26).

8. Device according to one of claims 1 to 7, characterized in that an additional switching valve (19) is arranged between the proportional valve (11) and gas outlet (25).

9. The device according to claim 8, characterized in that an additional pressure sensor (20) is arranged between the switching valve (19) and gas outlet (25).

10. Apparatus according to claim 8 or 9, characterized in that a filter (22) is arranged between the switching valve (19) and gas outlet (25).

11. The device according to claim 10, characterized in that the filter (22) is equipped with a hydrophobic membrane (55) as a gas-liquid barrier.

12. Device according to one of claims 8 to 11, characterized in that a check valve is arranged between the switching valve (19) and gas outlet (25).

13. Device according to one of claims 8 to 12, characterized in that a liquid detector is arranged between the switching valve (19) and gas outlet (25).

14. Device according to one of claims 1 to 13, characterized in that a foot switch is provided for triggering the gas inlet.

15. The device according to one of claims 1 to 14, characterized in that all parts coming into contact with the gaseous medium are heat and chemical resistant.

16. The device according to one of claims 7 to 15, characterized in that the catheter (23) is at least two-lumen and that a lumen (23a) is connected to a balloon (24) which surrounds the outer circumference of the catheter (23) in a ring.

17. The apparatus according to claim 16, characterized in that the catheter lumen (23a) connected to the balloon (24) can be connected to the pressure source (1) for the gaseous medium via a second proportional valve (8).

18. The apparatus of claim 16 or 17, characterized in that the balloon (24) is inflatable with a predetermined gas pressure and then the gas introduction can be triggered with an adjustable time delay.

19. Device according to one of claims 16 to 18, characterized gekennzeich¬ net that the catheter has an additional lumen for inserting an endoscope (angioscope).

20. Catheter for use as a gas outlet of a device for introducing a gaseous medium into a liquid-filled vascular system, in particular for use as a gas outlet of a device according to one of claims 1 to 19, characterized in that it is at least three-lumen.