METHOD AND APPARATUS FOR TESTING THE INTEGRITY OF A CAPILLARY DIALYST

Description

[0001] The invention relates to a method for testing the integrity of a liquid capillary filter, in particular a capillary dialyzer, which is constructed from a plurality of capillaries enclosed by a membrane, comprising the steps of: flowing a liquid through the inside or outside of the capillaries, subjecting the respective corresponding outside or inside of the capillaries to a gas, wherein the gas has a higher pressure than the liquid, and determining an amount of the gas which penetrates into the liquid through leaks in the membrane.

[0002] Furthermore, the invention relates to a system for testing the integrity of a liquid capillary filter, in particular of a capillary dialyzer, which is constructed from a plurality of capillaries enclosed by a membrane, comprising: a flushing system which is configured to conduct a liquid through the interior or exterior of the capillaries of a capillary dialyzer to be tested, a gas pressure system which is configured to subject the respective corresponding exterior or interior of the capillaries of the liquid capillary filter to be tested, in particular of the capillary dialyzer, to a gas, wherein the pressure of the gas is higher than the pressure of the liquid, and a measuring device for determining an amount of gas penetrating into the liquid through leaks in the membrane during a predetermined or predeterminable reference period.

[0003] Methods and systems for carrying out integrity tests are known from the prior art, for example from US 6 324 898 B1, DE 42 15 585 A1 and JP 2001 099775 A.

[0004] Capillary dialyzers are used in medicine to filter contaminants from the blood of patients with impaired kidney function. To do this, the contaminant-laden blood is brought into contact with a dialysis fluid via a semipermeable membrane. The dialysis fluid contains a vanishingly low concentration of the contaminants to be removed, such as urea, so that the contaminants diffuse through the membrane into the dialysis fluid due to a concentration gradient or enter the dialysis fluid due to convective effects. At the same time, the membrane is at least partially impermeable to other blood components such as blood plasma or particulate matter. This process is called dialysis.

[0005] Other liquid capillary filters are also frequently used in medical technology, for example, to treat raw water for dialysis. Such filters can also be used in other water treatment applications.

[0006] A large membrane surface area is particularly necessary for effective blood purification. For this purpose, conventional capillary dialyzers have a large number of capillaries, for example, approximately 10,000. The capillary walls are formed by a semipermeable membrane. The capillaries are arranged as a loose bundle in a tube-like volume.

[0007] During dialysis, the patient's blood is pumped through the capillaries, while the dialysis fluid flows through the tube-like volume. The flow directions of blood and dialysis fluid are preferably opposite, so the dialyzer operates on the countercurrent principle.

[0008] Capillary dialyzers are typically provided as sterile, single-use products and are subjected to a sterilization process after manufacture. Steam sterilization is often used for this. Other liquid capillary filters are also frequently sterilized with steam.

[0009] Because capillaries have very thin walls, leaks in individual capillaries can occur during the manufacture of a liquid capillary filter or capillary dialyzer. Leaks can also occur due to various other types of damage. Such leaks can, on the one hand, allow blood to leak from the capillaries into the dialysis fluid during dialysis, and, on the other hand, allow dialysis fluid to penetrate into the blood. Both are undesirable, and the penetration of dialysis fluid into the patient's blood in large quantities can be particularly physiologically problematic.

[0010] To detect leaks, liquid capillary filters, especially capillary dialyzers, are subjected to a test. Since leaks can also occur during sterilization, the test is usually performed immediately after sterilization.

[0011] In a common test procedure for capillary dialyzers, a test fluid, usually water, is passed through the capillaries while a gas is simultaneously introduced into the volume surrounding the capillaries. The gas is under a higher pressure than the fluid, allowing it to penetrate the capillaries through any leaks.

[0012] The gas in the liquid forms small bubbles, which are flushed out of the capillaries by the liquid flow. To detect the bubbles, the liquid flow is then passed through a sight glass, which is monitored by a camera.

[0013] However, this method makes quantitative determination of the amount of gas entering difficult, as each individual bubble must be assessed as it flows past, and the shape of the bubbles cannot be fully captured. Furthermore, the sight glass must be monitored over a longer period of time to achieve sufficient sensitivity. Furthermore, if the inspection is performed on an intermittent conveyor with multiple stops, the observation must be interrupted, and individual bubbles can easily be overlooked.

[0014] It is therefore an object of the invention to provide an improved method and an improved system for testing the integrity of a liquid capillary filter, in particular a capillary dialyzer.

[0015] This object is achieved according to a first aspect of the invention by a method for testing the integrity of a liquid capillary filter, in particular a capillary dialyzer, which is constructed from a plurality of capillaries enclosed by a membrane, comprising the steps of: flowing a liquid through the inside of the capillaries and subjecting the outside of the capillaries to a gas, or flowing a liquid through the outside of the capillaries and subjecting the inside of the capillaries to a gas, wherein the gas has a higher pressure than the liquid, and determining an amount of the gas which penetrates into the liquid through leaks in the membrane, which is further developed in that the liquid is passed through a bubble trap after flowing through the capillaries,and that a volume of gas accumulating in the bubble trap during a given or predeterminable reference period is determined.

[0016] The individual gas bubbles entering or exiting the capillaries are collected in the bubble trap, forming a largely uniform gas volume. This gas volume can be easily determined, allowing an accurate quantitative determination of the amount of gas entering even without long-term observation.

[0017] It is thus possible to apply the gas to the outside of the capillaries or the inside, with the complementary side then being applied with the liquid.

[0018] The liquid capillary filter is preferably a capillary dialyzer. The membranes of these dialyzers have a particularly thin wall thickness of 10 to 50 µm, preferably 15 to 35 µm, making them particularly susceptible to leaks. Furthermore, the requirements for leak-free performance are particularly stringent for dialyzers due to the demands placed on patient safety. At the same time, it has been shown that the escaping gas bubbles are particularly fine and thus difficult to visually detect as individual bubbles. The method according to the invention is therefore particularly advantageous for capillary dialyzers.

[0019] Particularly for capillary dialyzers containing membranes with the selective surface in the membrane lumen, it is preferable to apply gas to the outside and liquid to the inside. This ensures particularly gentle treatment of the membrane lumen during the leak test.

[0020] In an advantageous development of a method according to the invention, an initial value of the gas volume can be determined at the beginning of the reference period, a final value of the gas volume can be determined at the end of the reference period, and the amount of gas that has penetrated into the capillaries in the reference period can be determined from the difference between the initial value and the final value.

[0021] Water is the preferred liquid. Using water as the test fluid can prevent any solvent mixtures from being generated as waste from the process. Furthermore, residual amounts of water can remain in a filter, especially in a dialyzer, after the test without adversely affecting the patient's health.

[0022] In a particularly advantageous implementation of a method according to the invention, a line system comprising the bubble trap and the liquid capillary filter, in particular the capillary dialyzer, can be exposed to water vapor before the start of the test.

[0023] The piping system can be exposed to steam to sterilize the liquid capillary filter, especially the capillary dialyzer, as well as the temporarily connected piping sections. The steam fills the bubble trap, displacing any gas contained therein from a previous test procedure. As the steam cools and condenses, the steam volume in the bubble trap collapses, allowing it to be almost completely filled with water without the need for a valve.

[0024] In a preferred implementation of a method according to the invention, the gas volume accumulated in the bubble trap can be determined optically. For this purpose, the bubble trap can have a transparent section, and the position of a liquid surface in the transparent section can be evaluated to determine the gas volume accumulated in the bubble trap. Optical methods have proven to be particularly robust, i.e., less susceptible to interference, and simple.

[0025] The position of the liquid surface in the transparent section can be easily determined after optical detection using image processing.

[0026] In an advantageous embodiment of a method according to the invention, at least one first camera image of the transparent section can be recorded at the beginning of the reference period and the initial position of the liquid surface can be determined by means of an image evaluation method, at least one second camera image of the transparent section can be recorded at the end of the reference period and the final position of the liquid surface can be determined by means of an image evaluation method, and the accumulated gas volume can be determined from the initial position of the liquid surface and the final position of the liquid surface.

[0027] The first and second camera images can preferably be captured using a transmitted-light process. Transmitted-light processes can be implemented with minimal equipment and space requirements in a compact production facility.

[0028] According to a preferred embodiment, the illumination can be effected by means of a fluorescent film which is illuminated with excitation light of a first wavelength and which, in response to the illumination with excitation light, emits fluorescent light of a second wavelength, wherein the second wavelength is greater than the first wavelength, and the camera images can be recorded through a filter which is opaque to light of the first wavelength.

[0029] With appropriate lighting, disruptive reflections on the surfaces of the transparent section are minimized, while at the same time the camera and light source can be positioned on the same side of the transparent section. This further reduces the space required for the measuring device.

[0030] A flow system comprising the bubble trap and the capillary dialyzer can be arranged on a synchronously operated conveyor, which is moved by at least one conveyor position during the reference period.

[0031] The object is achieved according to a further aspect of the invention by a system for testing the integrity of a liquid capillary filter, in particular a capillary dialyzer, which is constructed from a plurality of capillaries enclosed by a membrane, comprising a flushing system which is configured to conduct a liquid through the interior of the capillaries of a liquid capillary filter to be tested and a gas pressure system which is configured to apply a gas to the exterior of the capillaries of the liquid capillary filter to be tested, or a flushing system which is configured to conduct a liquid through the exterior of the capillaries of a filter to be tested and a gas pressure system which is configured to apply a gas to the interior of the capillaries of the filter to be tested, wherein the pressure of the gas is in each case higher than the pressure of the liquid,and a measuring device for determining a quantity of gas penetrating into the liquid through leaks in the membrane during a predetermined or predeterminable reference period, which is further developed in that the flushing system comprises a bubble trap arranged downstream of the liquid capillary filter, and in that the measuring system is configured to determine a volume of gas accumulating in the bubble trap during a predetermined or predeterminable reference period.

[0032] It is thus possible to apply the gas to the outside of the capillaries or the inside, with the complementary side then being applied with the liquid.

[0033] The liquid capillary filter is preferably a capillary dialyzer. The membranes of these dialyzers have a particularly thin wall thickness of 10 to 50 µm, preferably 15 to 35 µm, making them particularly susceptible to leaks. Furthermore, the leak-free requirements for dialyzers are particularly stringent.

[0034] Especially in the case of capillary dialyzers containing membranes with the selective surface in the lumen of the membrane, it is preferable to expose the outside with gas and the inside with liquid. This makes it possible to ensure particularly gentle treatment of the lumen of the membrane during the leak test.

[0035] In an advantageous embodiment of a system according to the invention, the measuring device can be configured to determine an initial value of the gas volume at the beginning of the reference period, to determine a final value of the gas volume at the end of the reference period, and to determine the amount of gas that has penetrated into the capillaries during the reference period from the difference between the initial value and the final value.

[0036] In a particular embodiment, the bubble trap has a trap section in the flow channel of the test liquid, so that the flow velocity of the test liquid is reduced at least briefly, for example, for 100 ms to 10 seconds. This allows bubbles to be released particularly effectively from the test liquid and fed to the volume detection system. The bubbles are preferably guided through an upper wall of the trap section to a sight glass. The upper wall is preferably conical.

[0037] According to a further embodiment of a system according to the invention, the measuring device can be configured to optically determine the gas volume accumulating in the bubble trap. For this purpose, the bubble trap can have a transparent section, and the measuring device can be configured to evaluate the position of a liquid surface in the transparent section to determine the gas volume accumulated in the bubble trap.

[0038] In a preferred embodiment of a system according to the invention, the measuring device can comprise at least one camera and an image evaluation system. The measuring device can comprise at least one fluorescent film and at least one source of excitation light.

[0039] As an alternative to optical detection, an alternative level detection can also be provided, for example using an ultrasonic level sensor.

[0040] In a further embodiment of the invention, the system can be part of a synchronously driven conveyor system comprising a plurality of conveyor elements, wherein each conveyor element is provided for receiving at least one liquid capillary filter, in particular a capillary dialyzer, and wherein each conveyor element comprises a bubble trap for each liquid capillary filter to be received, which bubble trap is movable along the conveyor system together with the liquid capillary filter.

[0041] The measuring device can comprise a first camera, which is arranged stationary adjacent to a conveying path of the conveyor system. The measuring device can further comprise a second camera, which is arranged stationary adjacent to the conveying path of the conveyor system. The first and / or the second camera can preferably be arranged adjacent to a stop position of the conveyor system.

[0042] The conveyor system can be a circular conveyor.

[0043] The invention is explained in more detail below with reference to some exemplary figures, wherein the embodiments shown in the figures are intended only to provide a better understanding of the invention without limiting it.

[0044] They show: Fig. 1 : a capillary dialyzer as an example of a liquid capillary filter in a simplified sectional view, Fig. 2 : a capillary with a leak, Fig. 3 : a measuring device with bubble trap, Fig. 4 : a circular conveyor.

[0045] In Figure 1 A capillary dialyzer 1 is shown in a simplified sectional view. The capillary dialyzer 1 consists of an approximately cylindrical housing 2, which is divided into three chambers 5, 6, and 7 by sealing inserts 3 and 4. In a departure from the exemplary embodiment, a liquid capillary filter can also be provided instead of a capillary dialyzer.

[0046] The end chambers 5, 7 each have a connecting piece 10, 11. The middle chamber 6 has two connecting pieces 12, 13, each located near the sealing inserts 3, 4. The connecting pieces 10, 11, 12, 13 can be Luer-Lock connectors, for example.

[0047] Capillaries 15 run from the chamber 5 through the sealing inserts 3, 4 and the middle chamber 6 into the chamber 7. The representation of the capillaries 15 in the Figure 1 is greatly simplified. A capillary dialyzer usually has Figure 1The four capillaries shown may contain up to 18,000 capillaries, which are generally not fully extended. The wall thickness of the capillaries 15 can be approximately 10–50 µm, in particular 15–35 µm, and the inner diameter of the capillaries 15 can be approximately 180–300 µm. The walls of the capillaries 15 consist of a biocompatible semipermeable membrane. The membrane preferably comprises a polysulfone material modified with polyvinylpyrrolidone (PVP).

[0048] If the filter is used for the treatment of raw water, the membrane is also preferably hydrophilic, so that good wettability is ensured, especially with water.

[0049] During dialysis, blood is pumped along the arrows 16, 17 through the connection piece 10 into the chamber 5 and then flows through the interior of the capillaries 15 into the chamber 7. From there, the blood is released again through the connection piece 11 and returned to the patient.

[0050] At the same time, dialysis fluid is directed along arrows 18, 19 through the connecting piece 13 into the central chamber 6, where it flows against the direction of blood flow along the capillaries 15 before being released again through the connecting piece 12. Toxic substances such as urea diffuse from the blood through the membrane of the capillaries 15 into the dialysis fluid. This purifies the blood.

[0051] For the effective and safe function of the capillary dialyzer 1, it is necessary that the flow paths for blood and dialysis fluid are sufficiently sealed from each other. Leaks can allow uncontrolled transfer of dialysis fluid into the blood, and conversely, a loss of blood into the dialysis fluid, which is physiologically undesirable.

[0052] Some possible sources of leaks are mechanical defects in the membrane shells that may occur during the extrusion of the capillaries 15, insufficient sealing between the sealing inserts 3, 4 and the capillaries 15 or the housing 2, or broken capillaries 15. Such defects may occur during the manufacture of the capillary membranes, the capillary dialyzer 1, or during subsequent sterilization.

[0053] Sterilization of the capillary dialyzer 1 is necessary because it comes into contact with the patient's blood during dialysis. A common sterilization method is steam sterilization, in which hot steam is passed through the capillary dialyzer 1. The steam flows through both the blood flow path and the dialysis fluid flow path, heating all surfaces in the capillary dialyzer, for example, to over 124°C, and killing any pathogens present.

[0054] To exclude capillary dialyzers with leaks from use, the capillary dialyzers are subjected to a leak test after sterilization. The test principle is described in Figure 2 shown.

[0055] For this purpose, a test liquid, usually water, is passed through the capillaries 15 in the direction of arrow 20, while at the same time a test gas, e.g. air, is introduced into the chamber 6. In deviation from the exemplary embodiment, it can also be provided that the test liquid is introduced into the chamber 6, while the test gas is passed into the capillaries 15. In this case, the test gas is under a higher pressure than the test liquid, which is indicated by the arrow 21. If the capillary dialyzer 1 now has a leak 22, the test gas can penetrate through this leak 22 into the test liquid and form bubbles 25 there. These bubbles are flushed out of the capillary 15 with the test liquid and can then be detected.

[0056] For the qualitative and quantitative detection of the bubbles 25, the test liquid is passed through a bubble trap 30 after passing through the capillary dialyzer 1. This is Figure 3shown.

[0057] The bubble trap 30 consists of a flow chamber 31 into which the test fluid flows through an inlet 32. Adjacent to the inlet 32, the flow chamber has an ascending section 33, which is defined by a separating body 34. Above the separating body 34, the ascending section 33 transitions into a trap section 35. Adjacent to the trap section 35 is a descending section 36, which transitions into an outlet 37.

[0058] The trap section 35 is designed so that the flow velocity of the test fluid is temporarily reduced. The bubbles 25 detach from the flow of test fluid and are guided through a conical upper wall of the trap section 35 to a sight glass 40.

[0059] In the sight glass 40, the bubbles 25 collect to form a coherent gas volume 41. Between the gas volume 41 and the test liquid, an interface 42 is formed, which is used for the optical measurement of the gas volume 41.

[0060] The flow paths of the test liquid and the bubbles 25 are indicated in the figure by arrows 44, 45.

[0061] To measure the gas volume 41, the sight glass 40 is observed by a camera 50, and the position of the interface 42 is determined by an image processing unit 51 on one or more consecutively recorded images of the camera.

[0062] To suppress reflections, the optical measurement of the gas volume 41 is carried out using a transmitted light method. However, since Figure 3Although there is little space on the rear side of the sight glass 40 shown on the left due to its design, the camera 50 and a light source 53 must nevertheless be arranged on the same side of the sight glass 40. The light source 53 is arranged such that it does not obscure the view of the camera 50 onto the sight glass 40. For this purpose, the light source 40 can be arranged slightly offset vertically or horizontally, or the light source 40 can be designed as a ring light arranged around the viewing direction of the camera 40.

[0063] To still be able to work with transmitted light, a fluorescent film 55 is arranged behind the viewing glass 40. The light source 53 emits excitation light of a first wavelength, for example, in the blue spectral range, which is partially reflected by the viewing glass 40 toward the camera 50. However, a large portion of the excitation light falls on the fluorescent film 55, where it is converted into fluorescent light of a second wavelength, for example, in the orange spectral range. The fluorescent light is emitted toward the viewing glass 40 and the camera 50.

[0064] A color filter 56 is arranged in front of the lens of camera 50. This filter is opaque to the short-wave excitation light and transparent to the fluorescent light. Consequently, the excitation light reflected by the viewing glass 40 does not reach the camera 50, and the recorded image is free of interfering reflections. In a correspondingly recorded image, the interface 42 can be easily located and its position determined using well-known image analysis methods. From the position of the interface 42, the gas volume 41 can, in turn, be easily determined.

[0065] A corresponding fluorescent film can be purchased from Keyence Corporation, for example, under the product name "CA-DWC30".

[0066] The sterilization and testing of capillary dialyzers takes place on a time-controlled conveyor, for example a circular conveyor. Such a circular conveyor 60 is Figure 4shown schematically. The circular conveyor 60 comprises a plurality of individual receptacles 61, 62, each for one or more capillary dialyzers 1. Each of the receptacles 61, 62 comprises a bubble trap 30 for each capillary dialyzer 1 to be accommodated, of which the viewing glasses 40 and the fluorescent foils 55 are visible here.

[0067] The capillary dialyzers are inserted into the receptacles 61, 62 in a loading station 63. The circular conveyor 60 moves one position at a time at specified intervals so that the next of the receptacles 61, 62 in the loading station 63 can be loaded with a capillary dialyzer.

[0068] The receptacles 61, 62 are moved step by step along the circular conveyor 60 and, among other things, pass through a preparation section I and a sterilization section II, in which hot steam is passed through the capillary dialyzer and the piping system of the receptacles 61, 62 to sterilize them. The steam penetrates into the sight glass 40, so that this too is completely filled with steam and sterilized.

[0069] In test section III, the section of the capillary dialyzer that forms the blood flow path is flushed with sterile-filtered water. This causes the vapor in the sight glass 40 to collapse, completely filling it with water. At the same time, the section of the capillary dialyzer that forms the dialysis fluid flow path is flushed with sterile-filtered air to expel the water vapor. Optionally, flushing with sterile-filtered water can also be performed before flushing with sterile-filtered air.

[0070] While passing through the rinsing section, the images 61, 62 reach a first measuring position, where a first camera 50' and first light sources 53' are arranged. The first camera 50' captures one or more images of the sight glass 40 at the first measuring position and forwards them to an image evaluation unit 51. The image evaluation unit 51 determines the position of the interface 42 in the first measuring position and stores it together with an identifier for the individual image 61, 62.

[0071] Towards the end of the rinsing section, the receptacles 61, 62 move to a second measuring position, at which a second camera 50" and second light sources 53" are provided. The second camera 50" takes one or more images of the sight glass 40 at the second measuring position and also forwards them to the image evaluation unit 51. The image evaluation unit 51 determines the position of the interface 42 in the second measuring position.

[0072] From the change in the position of the interface 42 between the first measuring position and the second measuring position, the image evaluation unit 51 or a downstream controller determines the amount of air that has penetrated into the capillaries 15 of the capillary dialyzer 1 during transport from the first measuring position to the second measuring position. If the cycle rate of the circular conveyor 60 is known and constant, this amount of air can be used directly as a criterion for the tightness of the capillary dialyzer 1. If the cycle rate is unknown, a first time stamp can be saved together with the measurement result at the first measuring position, and a second time stamp can be saved together with the measurement result at the second measuring position. The throughput time of the capillary dialyzer can then be determined from the difference between the two time stamps and taken into account in the assessment.

[0073] If the amount of air that has penetrated or the leak rate exceeds a specified limit, the corresponding capillary dialyzer must be assessed as leaking and excluded from further use.

[0074] After passing through the rinsing section, the water is pressed out of the capillary dialyzer and it is removed from the circular conveyor in an unloading station 65 so that another capillary dialyzer can be inserted into the corresponding receptacle 61, 62.

[0075] The loading station 63 and the unloading station 65 can, as in Figure 4 shown, be combined into one station.

[0076] The representation of the rotary runner 60 in Figure 4is again greatly simplified. The rotary table 60 can have a significantly higher number of receptacles 61, 62 in order to provide a sufficient throughput of capillary dialyzers 1. Between the test section III and the unloading station 65, a drying section can be provided, which is not shown here. The relative lengths of the individual sections are shown in Figure 4 Not necessarily drawn to scale. For clarity, the lines and valves required for the known functions of the rotary table are not shown.

Claims

1. Method for checking the integrity of a hollow-fibre fluid filter (1), in particular a hollow-fibre dialyzer, which is constructed from a plurality of hollow fibres (15) enclosed by a membrane, with the steps of: - perfusing the inside of the hollow fibres (15) with a fluid and - supplying the outside of the hollow fibres (15) with a gas, or - perfusing the outside of the hollow fibres (15) with a fluid and - supplying the inside of the hollow fibres (15) with a gas, wherein in each case the gas has a higher pressure than the fluid, and - determining a quantity of the gas which penetrates into the fluid through holes in the membrane, characterized in that, - after flowing through the hollow-fibre fluid filter (1), the fluid is channelled through a bubble trap (30), and in that - a gas volume (41) collecting in the bubble trap (30) during a predefined or predefinable reference period is determined.

2. Method according to claim 1, characterized in that - an initial value of the gas volume (41) is determined at the start of the reference period, - a final value of the gas volume (41) is determined at the end of the reference period, and - in that the quantity of gas that has penetrated into the fluid in the reference period is determined from the difference between the initial value and the final value.

3. Method according to claim 1 or 2, characterized in that water is used as fluid.

4. Method according to one of claims 1 to 3, characterized in that a line system comprising the bubble trap (30) and the hollow-fibre fluid filter (1) is supplied with steam before the start of the check.

5. Method according to one of claims 1 to 4, characterized in that the determination of the volume of gas collected in the bubble trap (30) is effected visually.

6. Method according to claim 5, characterized in that the bubble trap (30) has a transparent section (40), and in that, for the determination of the volume of gas (41) collected in the bubble trap (30), the location of a fluid surface (42) in the transparent section (40) is assessed.

7. Method according to claim 6, characterized in that - at least one first camera image of the transparent section (40) is captured at the start of the reference period and the initial location of the fluid surface (42) is determined by means of an image evaluation method, - at least one second camera image of the transparent section (40) is captured at the end of the reference period and the final location of the fluid surface (42) is determined by means of an image evaluation method, and in that - the volume of gas (41) collected is determined from the initial location of the fluid surface (42) and the final location of the fluid surface (42).

8. Method according to claim 7, characterized in that the first and the second camera image are captured using a transmitted light method.

9. Method according to claim 8, characterized in that the illumination is effected by means of a fluorescent film (55), which is illuminated with excitation light of a first wavelength, and which, in response to the illumination with excitation light, emits fluorescent light of a second wavelength, wherein the second wavelength is greater than the first wavelength, and wherein the camera images are captured through a filter (56) that is not transparent for light of the first wavelength.

10. Method according to one of claims 2 to 9, characterized in that a flow system comprising the bubble trap (30) and the hollow-fibre fluid filter (1) is arranged on a conveyor (60) operated in a pulsed manner, which is moved on at least one conveying position during the reference period.

11. Equipment for checking the integrity of a hollow-fibre fluid filter (1), in particular a hollow-fibre dialyzer, which is constructed from a plurality of hollow fibres (15) enclosed by a membrane, comprising: - a flushing system which is set up to channel a fluid through the interior of the hollow fibres (15) of a hollow-fibre fluid filter (1) to be checked and - a gas pressure system which is set up to supply the exterior of the hollow fibres (15) of the hollow-fibre fluid filter (1) to be checked with a gas, or - a flushing system which is set up to channel a fluid through the exterior of the hollow fibres (15) of a hollow-fibre fluid filter (1) to be checked and - a gas pressure system which is set up to supply the interior of the hollow fibres (15) of the hollow-fibre fluid filter (1) to be checked with a gas, wherein in each case the pressure of the gas is higher than the pressure of the fluid, and - a measuring device for the determination of a quantity of gas (41) penetrating into the fluid through holes in the membrane during a predefined or predefinable reference period, characterized in that - the flushing system comprises a bubble trap (30) arranged downstream of the hollow-fibre fluid filter (1), and - in that the measuring device is set up to determine a volume of gas (41) collecting in the bubble trap (30) during a predefined or predefinable reference period.

12. Equipment according to claim 11, characterized in that the measuring device is set up - to determine an initial value of the gas volume (41) at the start of the reference period, - to determine a final value of the gas volume (41) at the end of the reference period, and - to determine the quantity of gas that has penetrated into the hollow fibres (15) in the reference period from the difference between the initial value and the final value.

13. Equipment according to claim 11 or 12, characterized in that the measuring device is set up to determine the volume of gas (41) collecting in the bubble trap (30) visually.

14. Equipment according to claim 13, characterized in that the bubble trap (30) has a transparent section (40), and in that, for the determination of the volume of gas (41) collected in the bubble trap (30), the measuring device is set up to assess the location of a fluid surface (42) in the transparent section (40).

15. Equipment according to claim 14, characterized in that the measuring device comprises at least one camera (50) and an image evaluation system (51).

16. Equipment according to claim 15, characterized in that the measuring device comprises at least one fluorescent film (55) and at least one source (53) for excitation light.

17. Equipment according to one of claims 11 to 16, characterized in that the equipment is a component of a conveying system (60) driven in a pulsed manner, which [comprises] several conveying elements (61, 62), wherein each conveying element (61, 62) is provided for receiving at least one hollow-fibre fluid filter (1), and wherein each conveying element (61, 62) comprises, for each hollow-fibre fluid filter (1) to be received, a bubble trap (31) which is movable along the conveying system (60) together with the hollow-fibre fluid filter (1).

18. Equipment according to claim 15 or 16, characterized in that the measuring device comprises a first camera (50') which is arranged stationary adjacent to a conveying path of the conveying system (60).

19. Equipment according to claim 18, characterized in that the measuring device comprises a second camera (50") which is arranged stationary adjacent to the conveying path of the conveying system (60).

20. Equipment according to claim 18 or 19, characterized in that the first and / or the second camera (50', 50") are arranged adjacent to a stopping position of the conveying system (60).

21. Equipment according to one of claims 17 to 20, characterized in that the conveying system is a circular conveyor (60).