Device for measuring pressure in an extracorporeal blood circuit

Abstract

The invention relates to a dialysis device configured to carry out a method for referencing at least one pressure sensor or force sensor (PA, PBE, PV) designed to measure the conduit internal pressure in a conduit (1) filled with a fluid, wherein the at least one pressure sensor or force sensor (PA, PBE, PV) is located in an extracorporeal circuit and integrated into or inserted in a clamping device (3), the method comprising the steps of: referencing the pressure signal or force signal emitted by the at least one pressure sensor or force sensor (PA, PBE, PV) using a force reference signal or pressure reference signal measured by a force reference sensor or pressure reference sensor (PHOP, PDA, PDE) not designed as a clamping device (3); and using at least one dialysis fluid side force reference sensor or pressure reference sensor (PDA, PDE) which is a force reference sensor or pressure reference sensor in a dialysis fluid circuit and which is designed to detect the conduit internal pressure in the dialysis fluid circuit in order to reference the at least one pressure sensor or force sensor (PA, PBE, PV) arranged in the extracorporeal circuit. The invention also relates to a device designed to use at least one dialysis fluid side force reference sensor or pressure reference sensor (PDA; PDE) which is a force reference sensor or pressure reference sensor in the dialysis fluid circuit and which is designed to detect the conduit internal pressure in the dialysis fluid circuit in order to reference the at least one pressure sensor or force sensor (PA, PBE, PV) arranged in the extracorporeal circuit.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a method and to a device for calibrating pressure measurements and / or force sensor measurements for determining the internal pressure of a conduit in an extracorporeal circuit, whereby the measurements determined by the pressure measurements are corrected by a correction signal when a force sensor is used, which force sensor is applied to the filling conduit. BACKGROUND

[0002] Generally, it is possible to measure the internal pressure of a conduit by means of a pressure measuring line. In this case, the (first) conduit, in which the internal pressure is to be measured, is connected to the pressure measuring line (second conduit), which in turn transmits the pressure to be measured to a (piezoelectric) pressure sensor / pressure transducer. For this purpose, the pressure measuring line is connected to the (first) conduit by means of a T-piece. At the upper (free) end of the pressure measuring line, the pressure sensor is preferably arranged with a luer lock connection. A gas cushion is located between the liquid column present in the pressure measuring line and the pressure transducer, which gas cushion changes (expands or becomes smaller) when the pressure in the (first) conduit changes, which in turn leads to a corresponding deflection of the pressure transducer.

[0003] This pressure measurement method and / or measurement system has disadvantages, in particular in the case where, for example, blood or another air-oxidizing liquid connected to the extracorporeal circuit is flowing through the (first) conduit, liquid-air contact occurs within the pressure measuring line, the manufacturing and assembly costs of the conduit are increased due to the T-piece, and the cleaning of the pressure measuring line is made more difficult due to this measurement arrangement. Furthermore, there is a risk of direct contact of the pressure sensor / pressure transducer with the liquid and a risk of bacteria entering the machine and / or a risk of contamination of the machine. Furthermore, the blood conduit delivery system becomes more confusing, there is a work effort to screw the luer lock connection, and the connection can wear out.

[0004] In order to avoid blood-air contact, which is disadvantageous, for example in detail in the case of application situations such as dialysis, so-called "pressure chambers" are being used. In this case, the pressure is not transmitted directly from the blood to, for example, a gas cushion, but the blood and the air are separated from one another by a diaphragm. Due to a change in pressure within the (first) conduit, the membrane is deflected, and this force effect is transmitted to the pressure sensor by means of a gas cushion connected to the membrane, which pressure sensor measures the internal pressure of the conduit. This means that, also in this known design, the gas cushion is provided as a pressure transmission medium between the membrane and the pressure sensor, although direct contact between the gas cushion and the fluid flowing in the (first) conduit is avoided. Furthermore, this measurement arrangement has the disadvantage that it makes high material and manufacturing costs necessary.

[0005] For this reason, in EP 1 357 372 A1, for example, a clamping device is provided in which a (first) catheter is clamped, the internal pressure of which is to be measured. The internal pressure of the catheter is measured non-invasively, which case means that the internal pressure is measured by means of a force through the outer wall of the catheter and not, for example, by means of a T-shaped branching mechanism for the connection between the interior of the container and the measuring sensor system. The expansion of the catheter due to a change in the internal pressure of the catheter is transmitted to a force sensor which emits a force signal by means of a force transmission member. A change in the force signal is converted into a pressure change by means of a scaling factor. In the case of a pressure change, only the deformation of the catheter at the gap of the support body which extends longitudinally through the clamping device is thus evaluated in order to generate a force signal.

[0006] However, when measuring the internal pressure of a catheter by means of a clamping device, the viscoelastic behavior of the catheter must be taken into account. This case means that, when the catheter is clamped, a recovery force is generated in the form of a drift signal which is superimposed on the force signal and / or the pressure signal for the measurement. In the case of longer measurement times, the recovery force has the effect that the internal pressure in the (first) catheter appears to drop, even if the conditions are constant. In order to solve this problem, it has been assumed to date that the pressure signal can be corrected by means of a reference to the ambient air. This case means that the viscoelastic behavior is checked by filling the catheter with air before it is actively used. The recovery signal which is thus received is then subtracted from the indicated pressure curve when actively used (in a catheter filled with a liquid such as blood). However, a catheter filled with a medium / liquid behaves differently compared to the catheter when it is in the condition in which it is filled with air. This is the reason why the pressure signal with reference to the ambient air does not provide an indication of the pressure signal of the filled catheter.

[0007] In order to be able to correct this distorted pressure signal, the document DE 197 47 254 C2 provides a method for correcting a pressure signal which is measured by means of a clamping device as already described above. For this purpose, the course of the recovery force is reproduced in the form of a relaxation function which depends on the catheter and is known in advance (determined). The parameters of this function are determined from the measured force signal. By means of this relaxation function, the force signal can be corrected and the pressure signal can be determined by means of a linear relationship to the force signal. SUMMARY

[0008] For this background, the task of the present disclosure is to further improve the correction of the force signal and to correct the drift signal by means of a reference signal which is caused by the mechanical properties of the (first) catheter before and during the active use of the (first) catheter (active use of the catheter means, for example, a catheter which is connected to a patient and / or a catheter during a treatment). Furthermore, the relative pressure change of the catheter as well as the absolute internal pressure should preferably be determined with a pressure accuracy of ± 10 mmHg.

[0009] This task is solved by the method according to the invention and the device according to the invention. Advantageous implementations of the invention are described as follows.

[0010] The invention relates first of all to a method for referencing / calibrating at least one pressure sensor or force sensor configured to measure a catheter internal pressure in a catheter filled with a fluid, wherein the at least one pressure sensor or force sensor is located in an extracorporeal circuit, preferably resting directly on the catheter and integrated into or inserted into a clamping device, the method comprising the steps of referencing / calibrating a pressure signal or force signal emitted by the at least one pressure sensor or force sensor from a force reference signal or pressure reference signal measured by a force reference sensor or pressure reference sensor not designed as a clamping device and using at least one force reference sensor or pressure reference sensor on the dialysis fluid side, which is a force reference sensor or pressure reference sensor in the dialysis fluid circuit and which is configured to detect the catheter internal pressure in the dialysis fluid circuit, in detail for referencing / calibrating a venous pressure sensor or force sensor.

[0011] Advantageously, the method further comprises the step of using a force reference sensor or pressure reference sensor arranged on the dialysis fluid inlet side on a dialysis fluid inlet catheter or using a force reference sensor or pressure reference sensor arranged on the dialysis fluid outlet side on a dialysis fluid outlet catheter side for referencing / calibrating a venous pressure sensor or force sensor arranged on a venous section of a catheter downstream of a dialyzer in an extracorporeal circuit.

[0012] The method can further comprise the steps of providing a bypass operation in which dialysis fluid does not flow through the dialyzer but not through the bypass line and a main connection operation in which the dialysis fluid flows through the dialyzer.

[0013] The method is further advantageous in that it comprises the steps of switching from the main connection operation to the bypass operation; waiting for a predetermined time period, preferably at least 10 seconds, in order to allow a pressure equalization to occur in the dialyzer between the dialysis fluid side and the blood side across the semipermeable membrane of the dialyzer.

[0014] An advantageous embodiment of the method is characterized in that it comprises the steps of operating a pump delivering the fluid and referencing the venous pressure sensor or force sensor by a pressure reference sensor or force reference sensor on the dialysis fluid outlet side.

[0015] Another advantageous embodiment of the method is characterized by the fact that the method comprises the steps of stopping a pump delivering the fluid; closing a venous catheter clamp that is a catheter clamp in a venous section of the catheter; and referencing the venous pressure sensor or force sensor by a force reference sensor or pressure reference sensor on the dialysis fluid inlet side and / or a force reference sensor or pressure reference sensor on the dialysis fluid outlet side.

[0016] Preferably, the method further comprises the steps of performing a dialyzer specific calibration / reference in order to take into account the influence of the dialyzer in the calibration / reference; and / or taking into account a pulsation of a pump roller rotor of a fluid delivery pump in the calibration / reference; and / or taking into account an influencing variable that causes a shift deviation of a pressure curve in the calibration / reference.

[0017] The present invention further relates to an apparatus comprising: an extracorporeal circuit; a dialyzer; a dialysis fluid circuit / dialysate circuit; at least one pressure sensor or force sensor arranged in the extracorporeal circuit, integrated into a clamping device and configured to measure a catheter internal pressure in a catheter filled with a fluid; at least one force reference sensor or pressure reference sensor for referencing a pressure signal or force signal emitted by the at least one pressure sensor or force sensor, which is not designed as a clamping device; wherein the apparatus is configured for the reference at least one pressure sensor or force sensor arranged in the extracorporeal circuit, at least one force reference sensor or pressure reference sensor on the dialysis fluid side, which is a force reference sensor or pressure reference sensor in the dialysis fluid circuit and which is configured to detect the catheter internal pressure in the dialysis fluid circuit.

[0018] Advantageously, an arterial pressure sensor or force sensor and a dialyzer input pressure or force sensor and a venous pressure sensor or force sensor are provided in the extracorporeal circuit as pressure sensors or force sensors integrated into clamping devices.

[0019] Preferably, the catheter has an arterial section and a venous section, wherein the arterial pressure sensor or force sensor and the dialyzer input pressure or force sensor are arranged on the arterial section and the venous pressure sensor or force sensor is arranged on the venous section.

[0020] Furthermore, the apparatus is preferably configured for referencing a venous pressure sensor or force sensor that is a pressure sensor or force sensor on a venous section of the catheter downstream of the dialyzer, a dialysis fluid inlet side force reference sensor or pressure reference sensor arranged on a dialysis fluid inlet catheter, or a force reference or pressure reference sensor on the dialysis fluid outlet side arranged on a dialysis fluid outlet catheter.

[0021] Preferably, the force reference sensor or pressure reference sensor on the dialysis fluid inlet side is arranged on the dialysis fluid inlet conduit between the dialyzer and the first shut-off valve and / or the force reference sensor or pressure reference sensor on the dialysis fluid outlet side is arranged on the dialysis fluid outlet conduit between the dialyzer and the second shut-off valve.

[0022] The method is further advantageous in case the dialysis fluid inlet conduit is connected to the dialysis fluid outlet conduit by a bypass line upstream of the first shut-off valve and downstream of the second shut-off valve.

[0023] The advantageous embodiment is characterized by the fact that the first shut-off valve is arranged on the dialysis fluid inlet conduit downstream of a first branching point at which the bypass line branches off from the dialysis fluid inlet conduit, the second shut-off valve is arranged on the dialysis fluid outlet conduit downstream of a second branching point at which the bypass line passes to the dialysis fluid outlet conduit, and a third shut-off valve is arranged on the bypass line such that the device is configured to allow the dialysis fluid to flow selectively through the dialyzer or the bypass line, wherein the force reference sensor or pressure reference sensor on the dialysis fluid side is arranged on the dialysis fluid inlet conduit downstream of the first shut-off valve and upstream of the dialyzer and / or the force reference sensor or pressure reference sensor on the dialysis fluid outlet side is arranged on the dialysis fluid outlet conduit downstream of the dialyzer and upstream of the second shut-off valve.

[0024] In an advantageous manner, the device is configured to carry out and / or apply the above-described method for referencing / calibrating the pressure sensor or force sensor.

[0025] The method according to the invention and the device according to the invention make it possible to dispense with a pressure sensor at the upper end of the pressure measuring line and / or the pressure measuring line arranged in the T-piece with a luer lock connection and / or in the extracorporeal circuit, so that a conventional force reference sensor or pressure reference sensor is not required in the extracorporeal circuit. Preferably, for all pressure sensors or force sensors arranged in the extracorporeal circuit (arterial pressure or force sensor, dialyzer input pressure or force sensor, venous pressure or force sensor), a so-called sensor is used, thus a clamp on the pressure sensor or force sensor, the pressure sensor or force sensor is pressed against the catheter and integrated and / or inserted into the clamping device. The essence of the invention is that the force reference sensor or pressure reference sensor in the dialysis fluid circuit serves as a reference / calibration for the pressure measurement of the clamp on the sensor in the extracorporeal circuit (adjustment / height correction of the blood fluid pressure and the dialysis fluid pressure). In this respect, the invention makes use of the fact that the pressure on the dialysis fluid side is equal to the pressure on the blood side through the semipermeable filter membrane of the dialyzer. Thus, the reference value for the pressure measurement in the extracorporeal circuit can be measured on the dialysis fluid side.

[0026] In this case, the following advantages are achieved by the method according to the invention and the device according to the invention: The manufacturing and assembly costs of the blood catheter delivery system are greatly reduced and the availability is improved. The time / work costs required for setting up the blood treatment device are reduced, there is a lower likelihood of a leakage occurring and the cleanliness of the blood catheter delivery system is improved. The contact of blood with air and associated coagulation is reduced and / or completely eliminated, so that anticoagulants can be saved, which reduces the treatment costs. In addition to the above, the connection can no longer be worn, as the connection no longer exists, the intrusion of bacteria and the bacterial-related contamination of the machine can be prevented and cleaning is made easier.

[0027] In the following, two embodiments of the invention are described in detail with reference to the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 A diagram illustrating the pressure curve in the clamping device over time is drawn by way of example;

[0029] Figure 2A A clamping device in which the catheter is clamped is illustrated;

[0030] Figure 2B A diagram is illustrated, the aforementioned diagram illustrating the progress of the drift signal compared to the reference signal;

[0031] Figure 3A A dialysis machine front in a state before the catheter is actively used is illustrated;

[0032] Figure 3B An alternative arrangement of two sensors is illustrated;

[0033] Figure 4 diagram, the preceding diagram illustrates the drift behavior of a catheter in a closed clamping device;

[0034] Figure 5 diagram, the preceding diagram illustrates the progression of the drift signal at constant catheter internal pressure and a correction function mapping the drift behavior of the catheter;

[0035] Figure 6 diagram, the preceding diagram illustrates the determination of the pressure signal from the drift signal / force signal graphically;

[0036] Figure 7 diagram, the preceding diagram illustrates the front of a dialysis machine during active use of the catheter by a patient connected to the machine;

[0037] Figure 8 diagram, the preceding diagram illustrates the pressure curve over time on the first pressure sensor when the process is carried out by means of an example;

[0038] Figure 9 diagram, the preceding diagram illustrates the pressure curve of a conventional pressure sensor, a first pressure reference sensor and a first pump;

[0039] Figure 10A diagram, the preceding diagram illustrates the pressure curve of two conventional pressure sensors and a second pressure reference sensor;

[0040] Figure 10B diagram, the preceding diagram illustrates the time progression of the (analog) blood pump flow and the blood pressure of the patient;

[0041] Figure 11A diagram, the preceding diagram illustrates the deviation between the calculated pressure signal and the reference signal due to temperature drift;

[0042] Figure 11B diagram, the preceding diagram relates to Figure 11A in the diagram, and illustrates the temperature profile of the fluid in the catheter at the first pressure sensor and the second pressure sensor;

[0043] Figure 12A diagram, the preceding diagram illustrates the deviation of the pressure signal of the second pressure reference sensor from the corresponding pressure reference signal and the linear correction signal;

[0044] Figure 12B diagram, the preceding diagram relates to Figure 12A in the diagram, and illustrates the curves of the pressure signal corrected by the linear correction signal and the pressure reference signal;

[0045] Figure 13A diagram, the preceding diagram illustrates the deviation of the pressure signal of the second pressure reference sensor from the corresponding pressure reference signal and the polynomial correction signal;

[0046] Figure 13B a diagram is drawn, which diagram relates to Figure 13A a diagram in the figure, and a curve of the pressure signal and the pressure reference signal corrected by the polynomial correction signal is drawn;

[0047] Figure 14 a front part of a dialysis machine in a state before active use of a catheter according to the second embodiment is drawn;

[0048] Figure 15 pressure measurement points in the area around the dialyzer according to the second embodiment are drawn;

[0049] Figure 16 a front part of a dialysis machine during active use of a catheter connected to a patient using the machine according to the second embodiment is drawn;

[0050] Figure 17 a pressure curve of a sensor according to the second embodiment is drawn;

[0051] Figure 18A a pressure behavior of a dialyzer with low permeability when in use is drawn;

[0052] Figure 18B a pressure behavior of a dialyzer with high permeability when in use is drawn; and

[0053] Figure 19 a pressure behavior of a sensor after offset correction is drawn. DETAILED DESCRIPTION

[0054] Embodiments of the present disclosure are described in the following on the basis of the drawings. It should be noted that the values illustrated are merely exemplary and not limiting.

[0055] First embodiment

[0056] The first embodiment described in the following forms the basis of the present invention and / or represents the basis on which the present invention has been developed. The present invention essentially relates to a method for indirect blood pressure measurement by means of a clamping device (force-pressure clamping). In detail, a method is described in the following, in which the viscoelastic properties of the catheter material are taken into account in the force / pressure measurement.

[0057] General procedure

[0058] Figure 1 By way of example, an example of a pressure curve of a pressure sensor (in this case, a PBE pressure sensor explained in more detail below) in millimeters of mercury (mmHg) over time (in seconds (s)) is drawn.

[0059] In phase 1, the catheter is inserted in two clamping devices, at least one pressure sensor is integrated into each of the two clamping devices, and the two clamping devices are measuring the pressure in form of a force signal on the dialysis machine, and the catheter is filled with fluid. The catheter delivery system is filled by varying the flow pump speed of at least one pump. In this phase, the leakage test is also performed on the machine and on the catheter.

[0060] In phase 2, the pressure in the catheter remains constant. After a short transitional phase, the step a) of recursive analysis and prediction of at least one correction function for finding a correction signal for correcting the drift signal is performed by means of a force reference signal or a pressure reference signal, which is measured by a first force reference sensor or a pressure reference sensor at a constant internal pressure of the catheter and a constant internal temperature of the catheter. In step a), the correction function f is determined in terms of time t by two constants a0, b for the viscoelastic behavior of the catheter before treatment. The two constants a0 and b are determined by means of an arithmetic procedure, which is called "fitting" in the following. This procedure is explained in the following. By means of this function, the drift signal in form of a force signal of the respective pressure sensor is determined.

[0061] In phase 3, a pressure drop can be detected, which is corrected by means of the correction function determined in step a) from the force signal. Furthermore, the corrected force signal of the pressure sensor is converted into a corrected pressure signal by means of the pressure reference signal of the pressure reference sensor, which is provided for this purpose by a linear relationship between the reference signal and the corrected force signal. In this case, the pressure reference sensor is a conventional pressure sensor. Phase 3 thus depicts the sequence of step b) of the first calibration of the pressure signal or the force signal, which is measured by the first pressure sensor or the force sensor and corrected by means of the correction signal, the force reference signal or the pressure reference signal, which is measured by the first force reference sensor or the pressure reference sensor, wherein step b) takes place before the start of the treatment. Thus, in step b), the corrected force signal is calibrated before the treatment by the pressure reference signal of the corresponding pressure reference sensor. The calibration can also be performed by a second constant pressure level.

[0062] A conventional pressure sensor means a pressure sensor, which is not integrated into any clamping device, and wherein no restoring force influences the pressure signal. In the conventional pressure sensor case, the internal pressure of the catheter is determined, for example, by a T-piece or a pressure chamber or the like, as it has been explained above.

[0063] At stage 4, after a predetermined time after the start of the treatment, preferably after 5 minutes, the newly corrected force signal is again calibrated by the pressure reference signal of the corresponding pressure reference sensor. At stage 4, the second calibration step c) of the pressure signal or force signal measured by the first pressure sensor or force sensor and corrected by means of the calibration function is thus carried out by the force reference signal or pressure reference signal, which is measured by the second force reference or pressure reference sensor.

[0064] At stage 5, a treatment progress is illustrated during which the PBE pressure is largely constant. It can be seen that the corrected PBE pressure signal and the reference signal overlap with each other, which means that the correction of the pressure signal is sufficient and also works in the case of a varying pressure (see the time interval between approximately 2600 and 2700 s).

[0065] In the following, the clamping device acting as a pressure sensor, the setup of the machine for which the method according to the application is used and the steps a) to c) are described in detail and by means of examples. Furthermore, alternative variations of the present disclosure will be as follows.

[0066] BACKGROUND

[0067] Figure 2A A (first) catheter 1 is illustrated, the internal pressure of which can be measured by a force sensor 2. For this purpose, the catheter 1 is clamped in a clamping device 3. The clamping device clamps the catheter 1 and the expansion or contraction of the catheter 1 is transmitted to the force sensor 2 by a force transmission member 4. The force change measurable by the force sensor 2 is proportional to the change in the internal pressure in the catheter 1.

[0068] Figure 2B A graph is illustrated, which shows a pressure curve of the drift signal over time and a pressure curve of the reference signal. The depicted pressure signal / drift signal illustrates the pressure progress in the catheter 1, which is clamped into the clamping device 3 at time t0. The reference pressure has a value of 0 mmHg (ambient pressure) over the entire time progress illustrated. The pressure signal illustrates a pressure increase at time t0, and below a pressure curve is illustrated which decreases logarithmically, which can be explained by the restoring force of the catheter. The drift signal has to be subtracted from the actually measured signal in order to equalize the absolute pressure to the reference pressure.

[0069] Setup for carrying out the method according to the present disclosure.

[0070] Figure 3AThe front of a dialysis machine 6 to which a (first) catheter 1 is attached, the internal pressure of the (first) catheter 1 is measured at various points. The dialysis machine 6 has an extracorporeal circuit. The catheter 1 has an arterial section la / arterial branch and a venous section lb. The arterial section la of the catheter 1 is connected to the machine 6 by a first substitution port SP1 and the venous section lb of the catheter 1 is connected to the machine 6 by a second substitution port SP2. In the illustrated embodiment, the catheter 1 is not connected to a patient, which situation means that the catheter is not in active use and thus in a pre-treatment state. This situation is the reason why the catheter 1 is not filled with blood in this situation but with another fluid which is here the washout fluid.

[0071] The fluid is first delivered into the arterial section la by a dialysate input flow pump FPE which is arranged outside the front of the dialysis machine 6. Even before the fluid is in the area of the front of the dialysis machine 6, a first pressure reference sensor PHOP records and / or measures the internal pressure of the catheter. Thus, the pressure reference sensor PHOP is again located at the substitution port SP and is an additional pressure sensor compared to the conventional dialysis machine 6. After the fluid has entered the front of the dialysis machine 6, the fluid first passes through an arterial catheter clamp SAKA which is usually open. Subsequently, the fluid passes through a first clamping device which is also referred to as PA pressure sensor and / or first pressure sensor PA and thus as first force sensor. The first clamping device is integrated into the front side of the dialysis machine 6. The PA sensor measures the pressure in the arterial section la of the catheter 1. The pressure reference sensor PHOP can be used for referencing the first pressure sensor PA which is carried out later on, since the pressure reference sensor PHOP has a higher measurement accuracy compared to the first pressure sensor PA.

[0072] Subsequently, the fluid reaches a first pump which continues to pump the fluid, a blood pump BP. Finally, the fluid passes through a second clamping device which is also referred to as PBE pressure sensor and / or second pressure sensor PBE and thus as second force sensor. The PBE pressure sensor measures the dialyzer input pressure at a point downstream of the blood pump BP in the flow direction of the medium in the catheter. After the PBE pressure sensor, the fluid can pass through the dialyzer 8. But in the bypass circuit situation through the bypass 10, it is also possible that the fluid does not flow through the dialyzer but bypasses the dialyzer. Downstream of the dialyzer / bypass in the direction of the fluid flow, the venous section lb is located which is here illustrated as a dashed line. At a point downstream of the dialyzer / bypass and upstream of the air eliminator 12, air trapped in the fluid is removed from the fluid, the fluid in the venous section lb passes a conventional pressure pickup which is referred to as PV measurement point. The conventional pressure pickup can for example be designed as a T-piece or as a pressure chamber.

[0073] After the PV measurement point, the fluid passes through the air trap 12, then the air detector 14 and finally the normally open venous line clamp SAKV. The venous line clamp SAKV and the arterial line clamp SAKA are only closed in case of a fault and they block the patient access in the treatment situation. This error can be, for example, that the air detector detects an amount of air greater than a certain threshold. After the fluid has passed the venous line clamp SAKV, the venous line clamp SAKV flows through the substitution port SP2 by means of the pump volume of the dialysate output flow pump FPA, which is located in the front outside of the dialysis machine 6.

[0074] Furthermore, Figure 3A It is shown that the dialysis machine 6 is connected to a CPU, which comprises a first, a second and a third calculation section. In the course of the process, the CPU can control the dialysate input flow pump FPE, the dialysate output flow pump FPA, the pressure reference sensor PHOP, the pressure reference sensor PV, the first pressure sensor PA, the second pressure sensor PBE, the blood pump BP, the arterial line clamp SAKA and the venous line clamp SAKV.

[0075] Figure 3B An alternative arrangement of the blood pump BP and the first and second pressure sensors PA, PBE is shown. In this case, the first (arterial) pressure sensor PA is located directly at the blood inlet of the blood pump BP and the second (dialyzer inlet) pressure sensor PBE is located directly at the blood outlet of the blood pump BP. In this case, both pressure sensors PA, PBE are integrated into the blood pump BP and the tubing material, the temperature and the point in time of insertion of the tubing of both pressure sensors PA, PBE are identical. The drift behavior that can be expected is identical for both pressure sensors PA, PBE as well. Thus, the pressure difference P PBE -P A The pressure difference P PBE -P A Should correspond to the difference of the corrected pressures P PBE_korr -P A_korr By comparing the two pressure differences (uncorrected pressure difference and corrected pressure difference), the correction correctness of the correction function described later can be evaluated. In case the difference between the pressure differences is greater than a predetermined amount, a recalibration of the system is recommended.

[0076] Step a)

[0077] Similar to Figure 2B , Figure 4The signal progress of the clamped catheter after the closing of the clamping device is plotted. But the force signal of the first pressure sensor PA is plotted here as an example in the form of a voltage value in units of volts (V) over time t in seconds (s). At the time t0(t0=0s), the clamping device is closed. From Figure 2B The known signal progress is plotted over the time period before and during the treatment. The reduction of the signal progress can be explained by the viscoelastic properties of the catheter material, which influence the pressure transmission between the force sensor and the fluid in the catheter. The elastic part of the catheter generates a restoring force. The viscous part of the catheter causes a slow irreversible deformation of the catheter. Due to this catheter deformation, the restoring force decreases and thus again the force of the catheter pressing on the pressure sensor. The curve of the restoring force plotted in Figure 4 is also called a drift signal. In order to be able to represent the force signal and / or the pressure signal of the force sensor as a signal that depends only on the internal pressure of the catheter, it is proposed to determine the drift signal, so that the drift signal can then be calculated / eliminated from the measured force signal and / or pressure signal, which case means that the drift signal is subtracted from the measured force signal.

[0078] The viscoelastic behavior of the catheter can generally be described by means of an exponential form of the decay factor. By this case, the drift signal can be described as a mathematical regular function with the following equation / formula (1):

[0079] f(t) = a0-t -b (1)

[0080] In this case, t is the time and a0and b are unknown constants. f(t) has the unit V, since the force signal is transmitted as a voltage value.

[0081] For other uses of the equation, it is proposed to determine the constants a0and b by fitting. For this purpose, it is necessary to produce a constant internal pressure of the catheter by adjusting the pump draw ratio of the pump BP and FPE or FPA. In addition, a constant internal temperature of the catheter is required. The eluate flowing through the catheter is preheated to approximately 36°C, which is the temperature of the blood, during the treatment. The temperature remains constant, so that the internal pressure of the catheter is also constant. In addition, the force signal of the pressure sensor, in this case the first pressure sensor PA, is determined in the measurement. But another pressure sensor, such as the force signal of the second pressure sensor PBE, can also be used. The force signal progress of the first pressure sensor PA over time can be seen in Figure 5 .

[0082] In Figure 5In the middle, the force signal is plotted as voltage in units of Volt [V] as a function of time t in seconds [s]. In the time range from 0 s up to about 1200 s, a condition exists before the active use of the catheter, during so-called "priming", which means before the treatment. Before the treatment, no patient is connected to the dialysis machine 6, and in this situation, the dialysis machine 6 is implemented as described in connection with Figure 3A has been described and plotted. In the time range starting at about 1200 s, the voltage signal during the treatment, also called "treatment", is plotted. During the treatment, the patient is connected to the dialysis machine 6, which is implemented as described in connection with Figure 7 has been described and plotted.

[0083] In order to be able to determine the constants a0and b by means of the force signal, the individual signal values f(t = ti) and f(t = t2) of the force signal are determined in a fit at two specific time points ti and t2in the area before the treatment. In the example plotted in Figure 5 , the time points ti = 600 s and t2= 800 s have been chosen. The following system of equations results for the equations (2) and (3) that must be solved in order to obtain the constants a0and b:

[0084] I f (t = ti) = a0- ti -b (2)

[0085] II f (t = t2) = a0- t2 -b (3)

[0086] From equation I, which means formula (2), a0can be expressed as follows

[0087] a0= f(t = ti) · ti b (4)

[0088] By inserting a0in the form as plotted in formula (4) into formula (3), b results in the form as plotted in formula (5), where b now only depends on the known time points ti, t2and the corresponding signal values f(t = ti) and f(t = t2) of the force signal and can thus be calculated:

[0089] b = ln(f(t = t2)) - ln(f(t = ti)) / (ln(ti) - ln(t2)) (5)

[0090] After determining the value of b, this value can be inserted into formula (4) to obtain the value of the constant a0, and equation (1) represents the viscoelastic behavior of the conduit used. The value of a0 is 1.19 and the value of b is 0.03, obtained by using the time points t1 and t2 selected above and the voltage value applicable in this test.

[0091] Step a) is implemented here as an example for the PA pressure sensor, and is implemented in a similar manner for the PBE pressure sensor.

[0092] Step b)

[0093] Next, the measured force signal is calibrated and converted into a pressure signal using an appropriate pressure reference signal. This is performed before treatment and when the internal pressure of the catheter changes, for example, when the internal pressure decreases, or when it decreases by a second constant pressure level that is different from the first pressure level. For example, when the catheter is disconnected from the replacement ports SP1, SP2, the internal pressure of the catheter decreases, which is necessary to prepare for treatment. Alternatively, the second pressure level can be adjusted by different pumping ratios of the blood pump and the flow pump. Step b) is performed with reference to the first pressure sensor PA.

[0094] First, the drift signal f(t) with values ​​calculated for a0 and b is derived from the force signal P measured by the first pressure sensor PA. s_gem Subtract the force signal, which is transmitted as a voltage value (in V). Therefore, the corrected force signal P... S_Korr It has the following equation (Formula (6)):

[0095] P S_Korr = P S_gem – f(t) (6)

[0096] Next, the first pressure reference sensor PHOP is used to record the pressure reference value P in mmHg. PHOP This isometry plot is drawn on the associated voltage value P in V. S_Korr Above, the associated voltage value P S_Kor Using examples Figure 6 As shown in the illustration.

[0097] exist Figure 6 In the diagram, the measured pressure reference value P PHOP Plot several points on the Y-axis, where these points are above the calculated voltage value P on the X-axis. S_korr Furthermore, the linear process is plotted for these points. Matching this situation, line A is mathematically determined, and this operation is most appropriately performed through these points; thus, it represents the pressure value P. A_Korr The pressure correction value P calculated by itS_korr The relationship between P and P can be mathematically stated in the form of equation (7) as follows:

[0098] P A_Korr = m - P S_korr + t (7)

[0099] Here, m is the weft of the straight line, which case is also referred to as a scaling value, and t is the pressure reference value at which the straight line intersects the Y-axis, and which is also referred to as an offset value. In the depicted example, a value of 5278 mmHg / V results for the scaling value, and a value of 23 mmHg results for the offset value.

[0100] Thus, P, which means the correction of the first pressure sensor PA and thus the correct pressure signal P A_korr Is known before the treatment, and step b) is completed.

[0101] Step b) is carried out for the PBE pressure sensor in a similar manner to the procedure depicted here for the PA pressure sensor, but here it is not the PHOP pressure reference sensor that is used as a reference, but the PV pressure reference sensor is used as a reference.

[0102] For example, since the value of the internal pressure of the catheter and / or the internal temperature of the catheter can change from the state before the treatment to the state during the treatment, it is recommended that the correction of the measured force signal for the first and / or second pressure sensor can be carried out repeatedly during the treatment.

[0103] Step c)

[0104] The settings depicted in Figure 2A are generally changed as depicted in Figure 7 . In Figure 7 , it can be seen that the arterial segment la and the venous segment lb are connected to the patient. In this case, the patient's heart replaces the dialysis fluid inflow and dialysis fluid outflow pumps. The (arm) artery connected to the arterial segment la and the patient's (arm) vein connected to the venous segment lb are connected to each other by an artificial connection 16, in detail by a patient shunt. Thus, the same blood pressure and the same blood flow value exist in the patient's vein and in the artery (which can also be referred to in general terms as a blood vessel). By setting a bypass on the dialyzer, the same blood pressure and the same blood flow value also exist in the arterial segment la and the venous segment lb, and thus in the entire system consisting of the catheter and the patient's blood vessels. For experiments, it is conceivable to simulate an experimental patient circuit, which has a water pump, a heated water bath and a back pressure valve.

[0105] The principle for calibration and referencing is the same for step b) as for step c). Again, the measured force signal of the pressure sensor is corrected by the correction signal found in step a) and from the relationship between the correction pressure signal and the correction force signal known from step b) (see equation (6), wherein the scaling value and the offset value are determined in step b)), the correction pressure signal can be calculated.

[0106] Step c) can be performed for the first pressure sensor PA and the second pressure sensor PBE. But here, the conventional PV pressure reference sensor acts as a pressure reference sensor not only for the PBE pressure sensor but also for the PA pressure sensor in order to allow a synchronous referencing of the PA pressure signal and the PBE pressure signal.

[0107] For the sake of simplicity, it is possible to reference the pressure signal of the second pressure sensor PBE together with the auxiliary pressure reference sensor PV by switching the dialyzer flow to bypass. Due to the manufacturing-dependent identicalness of the conduits at the location of the PA clamp device and at the location of the PBE clamp device, it is possible to apply the correction function found for the PBE pressure signal also for the PA pressure signal, however, it should be noted that this method is not as generally accurate as the method described previously, wherein one correction function is determined for the PA pressure signal and for the PBE pressure signal, respectively.

[0108] Result of the method according to the present application

[0109] After filtering and scaling the corrected pressure signal, the signal can be compared to the corresponding directly measured pressure reference signal. This comparison is by way of example for the corrected pressure signal P A_korr and the corresponding pressure reference signal P PHOP is depicted in Figure 8 .

[0110] In the diagram in Figure 8 , it can be seen that the course of the calculated pressure correction signal P A_Korr and the course of the directly measured pressure reference signal P PHOP are congruent. This means that the mathematical correction function from (1) together with the calculated values for a0and b can eliminate the drift course, but this only works if the internal pressure of the conduit and the internal temperature of the conduit are constant. For example, if the internal pressure of the conduit changes when the second point voltage f(t2) is taken, the correction function is not suitable to describe the course of the drift signal.

[0111] Referencing capability

[0112] In the following, Figure 9 and Figure 10AThe pressure curve of a conventional used pressure sensor for measuring arterial pressure P A and dialyzer input pressure P PBE is plotted in comparison to the pressure curve of the corresponding pressure reference sensor PHOP and PV.

[0113] In Figure 9 , the pressure curve PA_herk of a conventional first pressure sensor for measuring arterial pressure is compared to the pressure curve of a first pressure reference sensor PHOP before therapy. The pressure curve in mmHg is plotted over time in s. Furthermore, the pressure curve of a blood pump BP repeatedly having a pressure of 0 is plotted. The blood pump BP is repeatedly stopped in order to generate constant pressure values of the PA_herk sensor and the PHOP sensor.

[0114] It can be seen that the course of both pressure signals of the PA_herk pressure sensor and the PHOP pressure reference sensor is similar and runs parallel to each other, here with a parallel shift of the curves of approximately 20 mmHg pressure difference. The difference between the course of both pressure signals is due to the height difference of the first pressure sensor PA_herk and the first pressure reference sensor PHOP. In the present embodiment, the first pressure reference sensor PHOP is installed at a higher position than the first pressure sensor PA (see in Figure 2A ).

[0115] Although the pressure difference between the conventional pressure sensor and the pressure reference sensor has to be taken into account, the comparison in Figure 9 shows that the pressure reference sensor is suitable as a reference sensor for arterial pressure.

[0116] In Figure 10A , the pressure curve of a first conventional pressure sensor PA_herk for measuring arterial pressure and a second conventional pressure sensor PBE_herk for measuring dialyzer input pressure is plotted in comparison to the pressure curve of a second pressure reference sensor PV over time t in s in mmHg during therapy. Figure 10B A plot is plotted in which the time course of the blood pump flow in ml / min and the simulated patient pressure in mmHg is plotted, which has been recorded at the same time as the pressure values from Figure 10A .

[0117] Within the range where the blood pump flow is 0, meaning the time during which the blood pump stops, the pressure signals from the PA_herk, PBE_herk, and PV sensors are adjusted to each other and remain constant. Within this constant pressure range, the pressure curves of the two pressure sensors, PA_herk and PBE_herk, are essentially superimposed, and there is a pressure difference of approximately 20 mmHg between them and the pressure curve of the pressure reference sensor PV. This difference can be explained by the height difference between the pressure sensors PA_herk and PBE_herk and the pressure reference sensor PV.

[0118] Furthermore, what applies here is that, although the pressure difference between the traditional pressure sensor and the pressure reference sensor must be taken into account, Figure 9 The comparison diagram shows that the second pressure reference sensor is suitable as a reference sensor for arterial pressure and dialyzer input pressure during treatment.

[0119] Temperature drift

[0120] Up to this point, the above description has assumed a constant internal pressure and a constant internal temperature within the catheter. However, between steps b) and c), meaning between the pre-treatment phase and the treatment phase, a temperature difference may exist within the filled catheter, which can cause a linear deviation between the reference sensor value and the pressure sensor value.

[0121] This bias is illustrated by examples. Figure 11A The diagram illustrates the PBE pressure sensor and the PV pressure reference sensor. Figure 11B The associated temperature profiles at the measurement points of the PBE pressure sensor and the PV pressure reference sensor are plotted. To determine the temperature at these two measurement points, it is necessary to integrate the temperature sensors into the PBE clamping device and / or the PA clamping device. Here, calibration prior to treatment (up to approximately 900 seconds) occurs at T1, for example, at 35.8°C, while calibration during treatment occurs at T2, for example, at 37.2°C. The temperature difference ΔT (=T2-T1) at 1.4°C between the pre-treatment and treatment periods is plotted... Figure 11B The calculated PBE pressure signal does not follow the PV reference signal during treatment, but deviates from it linearly. The investigation has shown that the deviation between the pressure signal and the reference signal is linearly proportional to the temperature deviation before and during treatment. The pressure signal can be corrected using an empirically determined correction function.

[0122] Figure 12A Plot the pressure deviation between the pressure signal and the reference signal, and the straight line B found for the pressure deviation over time t (in seconds). In the example, the linear equation has the following form, as plotted in formula (8):

[0123] PBESignal = -0.0064182 [mmHg / °C] - AT [°C] + 3.4282 [mmHg] (8)

[0124] Figure 12B The PBE pressure signal is plotted, corrected by means of the determined formula (8), the PBE pressure signal is now again plotted superimposed with the PV reference signal.

[0125] As an alternative to a linear relationship of the deviation between the pressure signal and the reference signal and the temperature deviation before and during the treatment, a polynomial relationship can also exist. But a stronger computational power is needed in order to calculate the corresponding formula, although this relationship can represent a more precise deviation compared to a linear relationship.

[0126] Similarly to Figure 12A , Figure 13A The pressure deviation between the pressure signal and the reference signal and the polynomial C calculated for the pressure deviation over time t (in seconds) are plotted. In the example, the PBE pressure signal follows a polynomial deviation plotted in formula (9):

[0127]

[0128] Figure 13A The PBE pressure signal corrected by means of the determined formula (9) is plotted, the PBE pressure signal is now again plotted superimposed with the PV reference signal.

[0129] Modification of the first embodiment

[0130] The reference pressure measurement of the pressure signals PBE and PA in step c) (during the treatment) can alternatively also be performed by means of the closed venous catheter clamp SAKV and by means of the closed arterial catheter clamp SAKA.

[0131] For this purpose, the dialyzer flow is generally switched to the bypass as in the first embodiment and the catheter clamps SAKV and SAKA are closed. A pressure tight connection is created in the catheter. The blood pump BP is stopped. But due to a delay, the blood pump BP continues to rotate for a short time after the stop, so that a negative pressure builds up in the arterial catheter section and a positive pressure builds up in the venous catheter section, the arterial catheter section and the venous catheter section having the same pressure ratio to each other over time, meaning they have a fixed ratio to each other. The PBE pressure signal is calibrated by means of the PV pressure reference sensor. The PA pressure signal can again be calibrated by means of the PV pressure reference sensor.

[0132] Since the patient is attributed to the closed catheter clamp SAKV and SAKA is cut off from the extracorporeal circuit, this alternative version in step c) can be carried out independently of the patient. But in this case, the blood is no longer circulated in the extracorporeal circuit, so that blood clots can form in the extracorporeal circuit and the temperature can drop. But the coagulation of the blood and its temperature drop depend on the duration of the blood pump stoppage, which should therefore be as short as possible.

[0133] SUMMARY

[0134] In short, according to a first embodiment of the present disclosure, a method for calibrating a first force sensor / first pressure sensor is provided, which measures a first pressure, in particular an arterial pressure, in a fluid-filled (first) catheter, preferably a dialyzer catheter (blood catheter), in the form of a force signal, in an extracorporeal (blood) circuit. The pressure sensor is directly connected to the (first) catheter and integrated / inserted into a first clamping device in order to correct a drift signal caused by a correction function by means of a pressure reference signal picked up by a first (separate) pressure reference sensor. For this purpose, the following steps are carried out according to the present disclosure:

[0135] a) a recursive analysis and prediction of at least one correction function for finding a correction signal for correcting the drift signal is carried out by means of a corresponding pressure reference signal measured by the first force reference sensor at a constant internal pressure of the catheter and at a constant internal temperature of the catheter;

[0136] b) the force signal measured by the first force sensor and corrected by means of the correction signal is first calibrated by a pressure reference signal measured by the first pressure reference sensor before the active use of the catheter; and

[0137] c) the force signal measured by the first force sensor and corrected by means of the (previously predicted) correction function is then calibrated by a pressure reference signal measured by a second (separate) pressure reference sensor during the active use of the catheter.

[0138] In other words, a method for online correction of force-pressure signals is provided, which method according to the present disclosure is applied to the filled (first) catheter before and during the active use of the (first) catheter. This means that a first calibration of the (test / simulation) force signal generated by the first force sensor is first carried out before the active use of the (first) catheter by means of a pressure reference signal determined by means of a pressure reference sensor and a correction function. Then, a second calibration of the (second) force signal has a correction by means of the correction function carried out during the active use of the catheter, i.e. on the basis of a pressure reference signal, which is / has preferably generated by a second pressure reference sensor.

[0139] In particular, a mathematical correction function and a two-point calibration are applied for this purpose in a way that makes it possible to measure absolute pressure. The pressure measurement is carried out by means of a force sensor integrated into the clamping device. The mathematical correction function is determined from the measured (test) force-pressure signal and a reference pressure, which is determined by means of a (separate) pressure reference sensor (which has a different construction and / or different installation compared to the force sensor) and which provides a drift signal, preferably within a few minutes after the (first) catheter is inserted into the guide clamping device at a constant internal pressure of the catheter and at a constant internal temperature of the catheter. The pressure reference sensor preferably has a higher measurement accuracy compared to the corresponding pressure / force sensor. Then a first calibration is carried out, in which the internal pressure of the catheter and the internal temperature of the catheter are constant during the recording of the pressure / force signal for determining the correction function. During a subsequent re-calibration (second calibration), the (first) catheter is subjected to a constant known pressure, and the correction function is again determined from the pressure data that have been measured during this period. This reference method thus includes a calibration procedure not only before but also during active use of the catheter, meaning that the reference method is carried out before and during the treatment of a patient (dialysis).

[0140] This method enables pressure measurement by means of the clamping device directly on the filled (first) catheter as part of the catheter system. From this type of pressure measurement, a luer lock connection as used in the prior art is not required in the region of the clamping device. This results in lower manufacturing costs and improved usability of the catheter delivery system. The improved usability of the catheter delivery system can be demonstrated by the fact that, compared to conventional systems, fewer connectors have to be connected, and therefore machines using such a catheter delivery system can be set up more quickly, leaks occur less frequently, and the catheter delivery system is arranged more clearly. Furthermore, this catheter delivery system has the advantage that catheter fluid-air contact is reduced and / or avoided. In the case where the fluid / liquid flowing through the (first) catheter is blood, the risk of blood clotting is thus reduced. As a result, less anticoagulant needs to be added to the blood, which reduces disposal costs. In addition to the above, there is no wear on the pressure connection (luer lock connection) on the machine side, and the risk of contamination due to the pressure measurement is suppressed.

[0141] However, an advantage of the method according to the present disclosure is that the reference measurement during active use of the (first) catheter provides significantly more accurate values compared to a separate reference measurement before active use of the catheter. The correction function determined in the method according to the present disclosure can be carried out independently of the catheter material or the catheter size and can thus also be universally used for known catheter systems.

[0142] The method can be implemented in such a way that, in addition to the first pressure, a second pressure measured by a second force sensor / second pressure sensor integrated into the second clamping device can be measured and corrected. In this case, the force signal of the second force sensor is calibrated during the first calibration by a pressure reference signal measured by a second pressure reference sensor and during the second calibration. In this way, the internal pressure of the catheter can be measured and corrected at two different locations in the extracorporeal circuit without fluid-air contact.

[0143] Another aspect of the method according to the present disclosure provides that the (first) catheter (e.g. an extracorporeal blood catheter of a dialysis machine or a blood pump) comprises an arterial section (blood inlet section) and a venous section (blood outlet section). In this case, the first and / or second pressure / force sensor and the first pressure reference sensor are preferably arranged at the arterial section. A second pressure reference sensor, which can be a pressure / force sensor for checking the internal pressure of the catheter in the venous section, which pressure / force sensor (only one) does not cooperate with a clamping device, is arranged at the venous section. This means that the pressure in the venous section of the (first) catheter is measured (as only one) by the second pressure reference sensor, preferably according to a conventional pressure measurement method, e.g. by a T-piece or a flexible membrane (with increased accuracy). This means that the second pressure reference sensor (as only one) is further preferably connected to the machine to which the (first) catheter is connected by a luer lock connection. The reference is thus performed by means of a pressure reference sensor, which is more expensive but has a higher accuracy compared to the sensor integrated into the clamping device. The first pressure reference sensor is arranged in the region of the arterial catheter section and preferably has a piezoelectric element for pressure measurement.

[0144] Furthermore, it can be a condition that a constant internal pressure of the catheter can be achieved by adjusting the pump draw ratio between the first pump, in detail the blood pump, and the second pump, in detail the dialysate inflow flow pump or the dialysate outflow flow pump. It is particularly reliable and simple to achieve a constant pressure in the catheter by adjusting the pump draw ratio between these two pumps. For the method according to the present disclosure, a constant pressure in the filled catheter is of essential importance.

[0145] Furthermore, the method can be implemented in such a way that the drift signal is and / or corresponds to the restoring force of clamping the catheter.

[0146] Furthermore, it can be envisaged that the (corrected) force signal is converted into a pressure signal by means of a corresponding pressure reference signal by linear recursion and / or that the force signal is calibrated by a pressure reference signal. This linear recursion enables a simple calculation of the pressure signal from the respective force signal.

[0147] Preferably, in the case of the use of two force sensors, the first force sensor is arranged, in detail integrated, at the inlet opening / blood inlet of the first pump, and the second force sensor is arranged, in detail integrated, at the outlet opening / blood outlet of the first pump. In this case, the expected drift behavior at the location of both force sensors should again be identical, since the catheter material at the location of the force sensors, the temperature in the catheter and the insertion time of the catheter into the corresponding clamping device are identical.

[0148] Furthermore, according to the first embodiment of the present disclosure, a device is provided, which has an extracorporeal circuit and at least one pressure / force sensor, in detail an arterial pressure / force sensor and / or a dialyzer input pressure / force sensor. This pressure / force sensor is integrated into the clamping device in order to measure the internal pressure of the catheter in the fluid-filled catheter having an arterial section and a venous section. Furthermore, the device has at least one pressure reference sensor for a reference pressure signal / force signal, which is emitted by the at least one pressure sensor. The at least one pressure reference sensor, in detail an arterial reference sensor and / or a venous pressure reference sensor, is not designed as a clamping device and / or is not intended to be integrated into the clamping device (design without clamping device). Furthermore, the device preferably comprises at least a first pump and a second pump. The device is provided and adapted to apply the method according to at least one of the aforementioned aspects of the present disclosure, which calibrates the pressure signal of the at least one pressure sensor by means of the reference signal of the at least one pressure reference sensor.

[0149] Finally, according to the first embodiment of the present disclosure, a calibration device is provided for calibrating the measurement of at least a first (internal) pressure of a catheter, preferably an arterial pressure. This first pressure is measured in the extracorporeal (blood) circuit inside a fluid circuit, in detail a catheter filled with fluid / liquid / blood (not part of the device), by means of a first pressure sensor / force sensor of the calibration device directly adjacent to the catheter or can be brought to be directly adjacent to the catheter (externally). In this case, the pressure / force sensor is integrated into a first clamping device. The first pressure is calibrated in order to correct a drift signal caused by the (first) catheter (catheter material) by means of a correction function from a pressure reference signal, which is picked up / generated by a first pressure reference sensor of the calibration device. The calibration device has the following units or sections:

[0150] a) a first calculation section (CPU unit / program step), which is provided and adapted for the analysis and prediction of at least one correction function in order to find a correction signal for correcting a drift signal by means of a corresponding (force / )pressure reference signal, which is measured / generated by the first pressure reference sensor at a constant internal pressure of the catheter and at a constant internal temperature of the catheter;

[0151] b) a second calculation section (CPU unit / program step) is provided and adapted to first calibrate the force signal measured by the first pressure / force sensor (PA) by a pressure reference signal measured / generated by the first pressure reference sensor before the operational use of the catheter and then to correct the force signal by means of the correction signal.

[0152] c) a third calculation section (CPU unit / program step) is provided and adapted to then calibrate the force signal measured by the first pressure / force sensor by a (force / )pressure reference signal measured / generated by the second pressure reference sensor during the active (operational) use of the catheter.

[0153] Second embodiment

[0154] The second embodiment according to the present application is basically based on the first embodiment, so that in the following only the differences to the first embodiment are essentially explained.

[0155] In the first embodiment, the first pressure sensor PA and the second pressure sensor PBE on the arterial section la of the catheter 1 are designed as pressure sensors or force sensors integrated / inserted into the clamping device. On the other hand, in the venous section lb of the catheter 1, a conventional pressure sensor (force or pressure reference sensor PV) is provided which is required for the reference / calibration, which is realized as a T-piece or a pressure chamber, for example.

[0156] In the second embodiment according to the present application, a (third) pressure sensor PV is also provided in the venous section lb of the catheter, which is designed as a pressure sensor or force sensor integrated / inserted into the clamping device. Thus, three / all pressure sensors PA, PBE, PV for measuring the blood pressure without a conventional pressure transducer connected by a luer lock connection. The second embodiment according to the present application basically provides a method and a device for reference / calibration on the dialysis liquid side / dialysis fluid side.

[0157] The second embodiment according to the present application is referred to Figures 14 to 19 in the following.

[0158] Figure 14 A front part of a dialysis machine 6 to which the (first) catheter 1 is attached is illustrated, the internal pressure of the (first) catheter 1 is measured at various points. The dialysis machine 6 has an extracorporeal circuit. The catheter 1 has an arterial section la / arterial branch and a venous section lb / venous branch. The arterial section la of the catheter 1 is connected to the machine 6 by a first substitution port SP1 and the venous section lb of the catheter 1 is connected to the machine 6 by a second substitution port SP2. In the illustration Figure 14In the embodiment in Fig. 1 the catheter 1 is not (yet) connected to a patient, which situation means that the catheter is not in active use and thus in a pre-treatment state. For this reason the catheter 1 here is not filled with blood but with another fluid which here is a wash-out fluid.

[0159] The fluid is first transported through an input flow pump FPE which is arranged outside the front of the dialysis machine 6. Even before the fluid is in the area of the front of the dialysis machine 6 a first pressure reference sensor PHOP takes and / or measures the internal pressure of the catheter. Thus the pressure reference sensor PHOP is also located at the substitution port SP1 and is an additional pressure sensor compared to the conventional dialysis machine 6. After the fluid has entered the front of the dialysis machine 6 the fluid first passes through an arterial catheter clamp SAKA which is usually open. Then the fluid passes through a first clamping device which is also called PA pressure sensor and / or first pressure sensor PA and thus first force sensor. The first clamping device is integrated into the front side of the dialysis machine 6. The PA sensor measures the pressure in the arterial section 1a of the catheter 1. The pressure reference sensor PHOP can be used in order to reference the first pressure sensor PA because the pressure reference sensor PHOP has a higher measurement accuracy compared to the first pressure sensor PA.

[0160] Then the fluid reaches a first pump, the blood pump BP, which continues to transport the fluid. Finally the fluid passes through a second clamping device which is also called PBE pressure sensor and / or second pressure sensor PBE and thus second force sensor. The PBE pressure sensor measures the dialyzer input pressure at a point downstream of the blood pump BP in the flow direction of the medium in the catheter. After the PBE pressure sensor the fluid can pass through the dialyzer 8. But in a bypass loop situation through the bypass 10 it is also possible that the fluid does not flow through the dialyzer but bypasses the dialyzer. Downstream of the dialyzer / bypass in the direction of the fluid flow is the venous section 1b (this section is here drawn as a dashed line). At a point downstream of the dialyzer / bypass and upstream of the air eliminator 12 air trapped in the fluid is removed from the fluid, the fluid in the venous section 1b passes through a third clamping device which is called PV pressure sensor and / or third pressure sensor PV and thus third force sensor. The PV pressure sensor measures the dialyzer output pressure at a point downstream of the dialyzer 8. But the PV pressure sensor can also be located only downstream of the air eliminator 12 as it is the case in the setup of Figure 16 Fig. 2.

[0161] As Figure 14The diagram further illustrates that after the PV measurement point, the fluid passes through the degasser 12, then through the air detector 14, and finally through the intravenous catheter clamp SAKV. After the fluid has passed through the intravenous catheter clamp SAKV, the fluid flows through the replacement port SP2 by means of the pump capacity of the output flow pump FPA, which is located at the front exterior of the dialysis machine 6.

[0162] During treatment, arterial segment 1a and venous segment 1b are connected to the patient (see [link to treatment]). Figure 16 In this condition, the patient's heart is replaced by the inlet flow pump FPE and the outlet flow pump FPA. Air detector 14 is not depicted. Figure 16 It is available in the middle, but preferably provided during treatment.

[0163] As in Figure 14 , Figure 15 and Figure 16 The diagram illustrates a dialysis machine 6 including a dialysate inlet conduit / line 20 and a dialysate outlet conduit / line 22. A bypass conduit / line 24 branches off from the dialysate inlet conduit 20 at a first branch point 26. Downstream of the first branch point 26, a first shut-off valve 28 is provided. The first shut-off valve 28 is configured to allow or prevent fluid flow through the dialyzer 8. A second branch point 30 is located at the dialysate outlet conduit 22, at which the bypass conduit 24 extends into the dialysate outlet conduit 22. A second shut-off valve 32 is located upstream of the second branch point 30 on the dialysate outlet conduit 22. The second shut-off valve 32 is arranged to allow or prevent fluid flow through the dialyzer 8. A third shut-off valve 34 is located on the bypass conduit 24. The third shut-off valve 34 is arranged to allow or prevent fluid flow through the bypass conduit 24.

[0164] A force reference sensor or pressure reference sensor PDE is installed on the dialysate inlet conduit 20 downstream of the first shut-off valve 28 and upstream of the dialyzer 8. A force reference sensor or pressure reference sensor PDA is installed on the dialysate outlet conduit 22 downstream of the dialyzer 8 and upstream of the second shut-off valve 32 on the dialysate outlet side.

[0165] However, according to the present invention, only one of the force reference sensor PDE or the pressure reference sensor PDA, preferably the force reference sensor or the pressure reference sensor PDA, may be provided in principle. This means that only the force reference sensor or the pressure reference sensor PDA, or only the force reference sensor or the pressure reference sensor PDE, or not only the force reference sensor or the pressure reference sensor PDA but also the force reference sensor and the pressure reference sensor PDE, may be provided.

[0166] Figure 14The dialysis machine 6 is connected to a CPU which comprises a first computing section, a second computing section and a third computing section. In this respect, the CPU can control the input flow pump FPE, the output flow pump FPA, the pressure reference sensor PHOP, the pressure reference sensor PDA, the pressure reference sensor PDE, the first pressure sensor PA, the second pressure sensor PBE, the third pressure sensor PV, the blood pump BP, the arterial catheter clamp SAKA, the venous catheter clamp SAKV, the first shut-off valve 28, the second shut-off valve 32 and the third shut-off valve 34, etc., and / or receive information / signals from the sensors.

[0167] In detail, the CPU can control the shut-off valves 28, 32, 34 in such a way that the dialysis fluid / dialysate flows through the dialyzer 8 or the bypass line 24 as required. In the case where the first shut-off valve 28 and the second shut-off valve 32 are closed and the third shut-off valve 34 is open, the dialysis fluid flows through the bypass line 24 and does not flow through the dialyzer 8. This operation is referred to as bypass operation hereinafter. In the case where the first shut-off valve 28 and the second shut-off valve 32 are open and the third shut-off valve 34 is closed, the dialysis fluid flows through the dialyzer 8 and does not flow through the bypass line 24. This operation is referred to as main connection operation hereinafter.

[0168] Since it has already been explained, the PBE pressure sensor which measures the pressure at the inlet of the dialyzer 8 and the PV pressure sensor which measures the pressure at the outlet of the dialyzer 8 are designed as force sensors or pressure sensors which are integrated / inserted into the clamping device (so-called on-sensor clamping). In order to be able to operate the PBE pressure sensor and the PV pressure sensor with the desired accuracy, these pressure sensors must be essentially referenced / calibrated. According to the present application, this referencing / calibration is carried out by means of a reference measurement on the dialysis fluid side from at least one of the force reference sensor or pressure reference sensor PDA and the force reference sensor or pressure reference sensor PDE.

[0169] The referencing / calibration can essentially be carried out by means of a pressure equalization curve. A typical pressure equalization curve is depicted in Figure 17 . Figure 17 The actual pressure curve of PV (PV_Actual), the actual pressure curve of PBE (PBE_Actual) and the actual pressure curve of PDA are depicted. In detail, the course of the test measurement can be understood, in which an alternating switching between bypass operation B and main series operation H has been carried out. The switching takes place in each case at times tl, t2, t3, etc. marked on the time axis.

[0170] It can be appreciated that after the autonomous connection operation H is switched to the bypass operation B, the pressure equalizes after about 10 seconds. In detail, when the dialysis fluid flow through the dialyzer 8 is stopped (bypass operation), the pressure equalization between the blood side and the dialysis fluid side / dialysate side can take place through the semipermeable filter membrane of the dialyzer 8. With this background, the reference / calibration preferably takes place in the bypass operation B.

[0171] Basically, in order to carry out the reference / calibration, all the relevant influencing factors which influence the profile of the pressure equalization curve must be known and must be passed on and taken into account.

[0172] In addition thereto, it must be considered here whether the pressure equalization curve has been recorded with the blood side running (dynamic situation) or without the blood side running (static situation). In the Figure 17 The pressure equalization curve illustrated in Fig. 2 has been recorded, for example, in the static situation without the blood side running. In the dynamic situation, for example, in addition to the blood pressure pressure curve, the pulsation of the blood pump roller rotor must be taken into account. However, since the pulsation of the blood pump roller rotor propagates in the system in a known manner, the pulsation can be taken into account in a simple manner by a median filter.

[0173] In addition to the described case, a shift change / shift deviation of the curve must also be taken into account. The shift change depends, for example, on the pressure difference between the blood side and the dialysis fluid side, the size of the dialyzer, the volume on the dialysis fluid side, and the position of the pressure transducers and / or the position of the pressure sensors relative to one another, which can be included by the gravitational pressure of the water column. For example, in the case where the shift deviation / shift change / pressure difference is taken into account and / or compensated by a correction value, the reference / calibration can in principle be carried out not only in the bypass operation B but also in the main connection operation H.

[0174] With regard to the number of adjustments, it should be taken into account that these depend on several factors, such as on the pressure difference between the blood side and the dialysis fluid side, the size of the dialyzer, the volume on the dialysis fluid side, the compliance / volume expandability / flexibility of the catheter delivery system, and the position of the pressure transducers, which are preferably as close as possible to the dialyzer 8, preferably directly on the flushing bridge.

[0175] Furthermore, the influence of the dialyzer must also be taken into account. In other words, a dialyzer-specific calibration must also be carried out. For example, it is conceivable that the calibration / reference is calculated by the CPU of the dialysis machine from an average value of a large number of different dialyzer calibration curves. It is also conceivable that the dialyzer is characterized in a preparation phase by applying a constant pressure in order to determine the transmembrane pressure.

[0176] Figure 18A and Figure 18BThe pressure behavior of the dialyzer 8, in detail of the semipermeable membrane of the dialyzer 8, is illustrated under low permeability and under an ultrafiltration rate greater than 0. On the other hand, Figure 18A and Figure 18B The pressure curves of PV, PBE and PDA are illustrated in each case. In this case, Figure 18A The pressure behavior of the dialyzer 8, in detail of the semipermeable membrane of the dialyzer 8, is illustrated under low permeability and under an ultrafiltration rate greater than 0. On the other hand, Figure 18B The pressure behavior of the dialyzer 8, in detail of the semipermeable membrane of the dialyzer 8, is illustrated under high permeability and under an ultrafiltration rate greater than 0. In other words, Figure 18A The permeability of the dialyzer 8 is lower than Figure 18B The permeability of the dialyzer 8. In view of this situation, Figure 18A and Figure 18B It is explained that when the force sensor or pressure sensor in the extracorporeal circuit is referenced / calibrated by the force reference sensor or pressure reference sensor in the dialysis fluid circuit, a dialyzer-specific calibration / reference is required.

[0177] As soon as all influencing factors are known and communicated to the rate and, a good agreement between PV and PDA / PDE exists and a reference is possible. In this respect, Figure 19 The pressure curves of PV_Actual, PBE_Actual and PDA after offset correction are illustrated.

[0178] With regard to Figure 16 , the following is proposed for the reference / calibration: the blood pump BP continues to rotate (operating blood side and / or dynamic conditions) and the dialysis fluid flow is switched to the bypass operation B. After 10 seconds, a reference of PV by PDA takes place and a correction of the force sensor measurement at PV is carried out. Alternatively, a reference of PV by PDE (and / or PDA) can be carried out. Since the PDE sensor is located on the inlet side of the dialyzer 8, a negative pressure arises here when the blood pump and the bypass circuit are operating, which has a different negative pressure than the negative pressure of PV. However, when the venous catheter clamp SAKV is closed and the blood pump is stopped, the same pressure is present at all pressure sensors PBE, PV, PDA and PDE and a reference / calibration can take place. The only disadvantage in this case is that the lack of blood circulation can lead to blood clotting.

Claims

1. A method for calibrating at least one pressure or force sensor (PA, PBE, PV) configured to measure a catheter internal pressure in a catheter (1) filled with a fluid, wherein the at least one pressure or force sensor (PA, PBE, PV) is located in an extracorporeal circuit and integrated into or inserted into a clamping device (3), the method comprising the steps of: calibrating a pressure or force signal output by the at least one pressure or force sensor (PA, PBE, PV) with a force or pressure reference signal measured by a force or pressure reference sensor (PHOP, PDA, PDE) not realized as a clamping device (3); and using at least one dialysis fluid side force or pressure reference sensor (PDA, PDE) for calibrating at least one pressure or force sensor (PA, PBE, PV) arranged in the extracorporeal circuit, the at least one dialysis fluid side force or pressure reference sensor (PDA, PDE) being a force or pressure reference sensor in a dialysis fluid circuit and being configured to detect the catheter internal pressure in the dialysis fluid circuit; wherein the method is performed before a patient is connected to the catheter (1); characterized in that in the extracorporeal circuit, an arterial pressure or force sensor (PA) and a dialyzer inlet pressure or force sensor (PBE) and a venous pressure or force sensor (PV) are provided as pressure or force sensors (PA, PBE, PV) integrated into a clamping device (3); and a force or pressure reference sensor (PHOP) arranged upstream of an arterial section (la) of the extracorporeal circuit calibrates the arterial pressure or force sensor (PA), and the at least one dialysis fluid side force or pressure reference sensor (PDA, PDE) calibrates the dialyzer inlet pressure or force sensor (PBE) and the venous pressure or force sensor (PV).

2. The method according to claim 1, further comprising the step of: using a dialysis fluid inlet side force or pressure reference sensor (PDE) arranged on a dialysis fluid inlet catheter (20) or using a dialysis fluid outlet side force or pressure reference sensor (PDA) arranged on a dialysis fluid outlet catheter (22) for calibrating a venous pressure or force sensor (PV) arranged on a venous section of the catheter downstream of a dialyzer (8) in the extracorporeal circuit.

3. The method according to claim 2, further comprising the step of: providing a bypass operation in which dialysis fluid does not flow through the dialyzer (8) but through a bypass line (24) and a main connection operation in which the dialysis fluid flows through the dialyzer (8).

4. The method according to claim 3, further comprising the steps of: switching from the main connection operation to the bypass operation; waiting for a predetermined time period to allow a pressure equalization to occur in the dialyzer (8) between a dialysis fluid side and a blood side across a semipermeable membrane of the dialyzer (8).

5. The method of claim 4, further comprising the steps of: operating a pump (BP) delivering the fluid; and calibrating the venous pressure or force sensor (PV) by the dialysis fluid outlet side force or pressure reference sensor (PDA).

6. The method of claim 4, further comprising the steps of: stopping the pump (BP) delivering the fluid; closing a venous line clamp (SAKV) being a line clamp in a venous section (lb) of the line (1); and calibrating the venous pressure or force sensor (PV) by the dialysis fluid inlet side force or pressure reference sensor (PDE) and / or the dialysis fluid outlet side force or pressure reference sensor (PDA).

7. The method of any of the preceding claims 1 to 6, further comprising the steps of: performing a dialyzer specific calibration in order to take into account the influence of a dialyzer (8) in the calibration; and / or taking into account a pulsation of a pump roller rotor of a fluid delivery pump (BP) in the calibration; and / or taking into account influencing variables causing a shift of a pressure curve.

8. A blood treatment apparatus, comprising: an extracorporeal circuit; a dialyzer (8); a dialysis fluid circuit; at least one pressure or force sensor (PA, PBE, PV) arranged in the extracorporeal circuit, integrated into a clamping device (3) and configured to measure a line internal pressure in a line (1) filled with a fluid; at least one force or pressure reference sensor (PHOP, PDA, PDE) not designed as a clamping device for calibrating a pressure or force signal output by the at least one pressure or force sensor (PA, PBE, PV); wherein the apparatus is configured for calibrating at least one pressure or force sensor (PA, PBE, PV) arranged in the extracorporeal circuit with at least one dialysis fluid side force or pressure reference sensor (PDA; PDE) being a force or pressure reference sensor in the dialysis fluid circuit and being configured to detect the line internal pressure in the dialysis fluid circuit; characterized in that in the extracorporeal circuit, an arterial pressure or force sensor (PA) and a dialyzer input pressure or force sensor (PBE) and a venous pressure or force sensor (PV) are provided as pressure or force sensors (PA, PBE, PV) integrated into a clamping device (3); and a force or pressure reference sensor (PHOP) arranged upstream of an arterial section (la) of the extracorporeal circuit calibrates the arterial pressure or force sensor (PA), and the at least one dialysis fluid side force or pressure reference sensor (PDA, PDE) calibrates the dialyzer input pressure or force sensor (PBE) and the venous pressure or force sensor (PV).

9. The blood treatment apparatus according to claim 8, characterized in that The catheter (1) has an arterial section (1a) and a venous section (1b), wherein the arterial pressure or force sensor (PA) and the dialyzer input pressure or force sensor (PBE) are arranged on the arterial section (1a) and the venous pressure or force sensor (PV) is arranged on the venous section (1b).

10. The blood treatment apparatus according to claim 8, characterized in that The blood treatment apparatus is configured to use, for calibrating the venous pressure or force sensor (PV) as a pressure or force sensor on the venous section (1b) of the catheter (1) downstream of the dialyzer (8), a dialysis fluid inlet side force or pressure reference sensor (PDE) arranged on a dialysis fluid inlet catheter (20) or a dialysis fluid outlet side force or pressure reference sensor (PDA) arranged on a dialysis fluid outlet catheter (22).

11. The blood treatment apparatus according to claim 10, characterized in that The dialysis fluid inlet side force or pressure reference sensor (PDE) is provided on the dialysis fluid inlet catheter (20) between the dialyzer (8) and a first shut-off valve (28) and / or the dialysis fluid outlet side force or pressure reference sensor (PDA) is provided on the dialysis fluid outlet catheter (22) between the dialyzer (8) and a second shut-off valve (32).

12. The blood treatment apparatus according to claim 11, characterized in that Upstream of the first shut-off valve (28) and downstream of the second shut-off valve (32), the dialysis fluid inlet catheter (20) is connected to the dialysis fluid outlet catheter (22) by a bypass line (24).

13. The blood treatment apparatus of claim 10, characterized in a first shut-off valve (28) is provided on the dialysis fluid inlet catheter (20) downstream of a first branching point (26) at which the bypass line (24) branches off from the dialysis fluid inlet catheter (20), a second shut-off valve (32) is provided on the dialysis fluid outlet catheter (22) upstream of a second branching point (30) at which the bypass line (24) passes into the dialysis fluid outlet catheter (22), and a third shut-off valve (34) is provided on the bypass line (24), such that the apparatus is configured to allow dialysis fluid to flow selectively through the dialyzer (8) or the bypass line (24), wherein: the dialysis fluid inlet side force or pressure reference sensor (PDE) is arranged on the dialysis fluid inlet catheter (20) downstream of the first shut-off valve (28) and upstream of the dialyzer (8), and / or the dialysis fluid outlet side force or pressure reference sensor (PDA) is arranged on the dialysis fluid outlet catheter (22) downstream of the dialyzer (8) and upstream of the second shut-off valve (32).

14. The blood treatment apparatus of the preceding claim 8, characterized by being characterized by being configured to carry out and / or apply the method for calibration of claim 1.

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