A device for measuring pressure in an extracorporeal blood circulation circuit

Abstract

The present invention relates to a method for referencing at least one pressure or force sensor (PA, PBE, PV) configured to measure intratubing pressure in a fluid-filled tube (1), the method comprising the steps of: referencing a force or pressure reference 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) located in an extracorporeal circuit and integrated into or inserted in a clamping device (3) and not designed as a clamping device (3); and using at least one dialysis fluid-side force or pressure reference sensor (PDA, PDE) that is a dialysis fluid circuit force or pressure reference sensor and is configured to detect intratubing pressure of the dialysis fluid circuit for referencing the at least one pressure or force sensor (PA, PBE, PV) located in the extracorporeal circuit. The present invention further relates to a device configured to use at least one dialysis fluid side force or pressure reference sensor (PDA, PDE) for referencing at least one pressure or force sensor (PA, PBE, PV) arranged in the extracorporeal circuit, the force or pressure reference sensor being a dialysis fluid circuit force or pressure reference sensor and configured to detect the pressure inside the tubing of the dialysis fluid circuit.

Description

[Technical field]

[0001] The present disclosure relates to methods and devices for calibrating pressure measurements and / or force sensor measurements for determining intratubal pressure in an extracorporeal circuit when using a force sensor applied to a filled tube, to correct measurements determined by pressure measurements with a correction signal. [Background technology]

[0002] Generally, it is possible to measure the pressure inside a tube by means of a pressure measuring line. In this case, the (first) tube, whose internal pressure is to be measured, is connected to a pressure measuring line (second tube), which transmits the measured pressure to a (piezoelectric) pressure sensor / pressure transducer. For this purpose, the pressure measuring line is connected to the (first) tube via a T-piece. At the (free) upper end of the pressure measuring line, a pressure sensor is preferably arranged with a Luer lock connection. An air cushion is arranged between the liquid column present in the pressure measuring line and the pressure transducer, which changes (increases or decreases) when the pressure in the (first) tube changes, resulting in a corresponding deflection of the pressure transducer.

[0003] Such a pressure measurement method and / or measurement system has the disadvantages, inter alia, that liquid-air contact occurs in the pressure measurement line, for example if blood connected to the extracorporeal circuit or another air-oxidizing liquid flows through the (first) tube, the manufacturing and assembly costs of the tube increase due to the T-shaped part, and cleaning of the pressure measurement line becomes more difficult as a result of this measurement set-up. In addition, there is a risk of direct contact of the pressure sensor / pressure transducer with the liquid, germs getting into the device, and / or machine contamination. Furthermore, the blood tubing system becomes more obscure, there is an expenditure of labor for screwing into the Luer lock connection, and the connections may wear out.

[0004] To avoid contact between blood and air, which is particularly disadvantageous in cases such as dialysis, so-called "pressure pods" are used. Here, pressure is not transmitted directly from, for example, blood to an air cushion, but blood and air are separated from each other by a flexible membrane. Due to pressure changes in the (first) tube, the membrane deflects and the effect of this force is transmitted via the air cushion connected to the membrane to a pressure sensor measuring the internal pressure of the tube. This means that, also in this known design, an air cushion is provided as pressure transmission medium between the membrane and the pressure sensor, but direct contact between the air cushion and the fluid flowing in the (first) tube is avoided. In addition, this measurement setup has the disadvantage of involving high material and manufacturing costs.

[0005] For this reason, for example in EP 1 357 372, a clamping device is provided in which a (first) tube is clamped and the internal pressure of the (first) tube is measured. The internal pressure of the tube is measured non-invasively, i.e. by force measurement through the outer wall of the tube, but not, for example, through a T-shaped branch for connection between the interior of the container and a measurement sensor system. The expansion of the tube due to a change in the internal pressure of the tube is transmitted via a force transmission means to a force sensor, which emits a force signal. The change in the force signal is converted proportionally to the pressure change by means of a proportionality factor. Thus, in the case of a pressure change, only the deformation of the tube in the gap extending through the longitudinal direction of the support of the clamping device is evaluated in order to generate a force signal.

[0006] However, when measuring the tube internal pressure via a clamping device, the viscoelastic behavior of the tube must be taken into account. This is because, when the tube is clamped, restoring forces arise in the form of a drift signal, which overlaps with the measured force and / or pressure signal. For long measurement times, the restoring forces have the effect that the internal pressure of the (first) tube appears to drop even if the conditions are constant. To solve this problem, it was previously assumed that the pressure signal could be corrected by referencing it with ambient air. This means that before the tube is actively used, the viscoelastic behavior is examined by filling the tube with air. The resulting received restoring signal is then subtracted from the indicated pressure curve (of a tube filled with a liquid such as blood) when actively used. However, a tube filled with a medium / liquid behaves differently than when it is in an air-filled state. For this reason, a pressure signal referenced with ambient air does not provide an indication of the pressure signal of a filled tube.

[0007] In order to be able to correct such distorted pressure signals, DE 197 47 254 provides a method for correcting the pressure signal measured via the clamping device as described above. For this purpose, the course of the restoring force is reproduced in the form of a relaxation function which is tube-dependent and known (determined) in advance. The parameters of this function are determined from the measured force signal. With the aid of this relaxation function the force signal can be corrected and the pressure signal can be determined via a linear relationship with the force signal. Summary of the Invention [Problem to be solved by the invention]

[0008] Against this background, the object of the present invention is to further improve the correction of the force signal and to correct the drift signal caused by the mechanical properties of the (first) tube before and during active use of the (first) tube (where active use of the tube means, for example, a tube connected to a patient and / or a tube during treatment) by means of a reference signal. Furthermore, not only the absolute internal pressure of the tube but also the relative pressure changes shall be determined, preferably with a pressure accuracy of ±10 mmHg. [Means for solving the problem]

[0009] This problem is solved by a method according to claim 1 and a device according to claim 8. Advantageous embodiments of the invention are the subject matter of the dependent claims.

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

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

[0012] The method may further include providing a bypass operation in which the dialysis fluid flows through the bypass line without passing through the dialyzer, and a main connection operation in which the dialysis fluid flows through the dialyzer.

[0013] It is further advantageous if the method includes the steps of switching from main connection operation to bypass operation and waiting a predetermined time, preferably at least 10 seconds, to allow pressure equalization in the dialyzer between the dialysis fluid side and the blood side across the semi-permeable filter membrane of the dialyzer.

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

[0015] Another advantageous embodiment of the method is characterized in that it includes the steps of stopping the pump delivering the fluid, closing a venous tubing clamp, which is a tubing clamp on the venous section of the tubing, and referencing the venous pressure sensor or force sensor via a force or pressure reference sensor on the dialysis fluid inlet side and / or a force or pressure reference sensor on the dialysis fluid outlet side.

[0016] Preferably, the method further comprises a step of performing a dialyzer-specific calibration / referencing to take into account the influence of the dialyzer in the referencing / calibration, and / or a step of taking into account pulsation of the pump roller rotor of the fluid delivery pump in the referencing / calibration, and / or a step of taking into account influencing variables causing an offset deviation of the pressure curve in the referencing / calibration.

[0017] The present invention further relates to a device comprising an extracorporeal circuit, a dialyzer, a dialysis fluid circuit / dialysate circuit, at least one pressure or force sensor arranged in the extracorporeal circuit, integrated in a clamping device and configured to measure the internal tubing pressure in a fluid-filled tube, and at least one force or pressure reference sensor not designed as a clamping device for referencing / calibrating the pressure or force signal emitted by the at least one pressure or force sensor, the device being configured to use, for referencing of the at least one pressure or force sensor arranged in the extracorporeal circuit, at least one force or pressure reference sensor on the dialysis fluid side, which is a force or pressure reference sensor of the dialysis fluid circuit and configured to detect the internal tubing pressure of the dialysis fluid circuit.

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

[0019] Preferably, the tubing has an arterial section and a venous section, the arterial pressure or force sensor and the dialyser input pressure or force sensor are located in the arterial section and the venous pressure or force sensor is located in the venous section.

[0020] Furthermore, the device is preferably configured for use for referencing a venous pressure or force sensor which is a pressure or force sensor in the venous section of the tubing downstream of the dialyzer, a dialysis fluid inlet side force or pressure reference sensor located in the dialysis fluid inlet tubing, or a dialysis fluid outlet side force or pressure reference sensor located in the dialysis fluid outlet tubing.

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

[0022] It is further advantageous if upstream of the first shut-off valve and downstream of the second shut-off valve the dialysis fluid inlet tube is connected to the dialysis fluid outlet tube via a bypass line.

[0023] An advantageous embodiment is characterized in that a first shut-off valve is provided in the dialysis fluid inlet tube downstream of a first branch point where the bypass line branches off from the dialysis fluid inlet tube, a second shut-off valve is provided in the dialysis fluid outlet tube upstream of a second branch point where the bypass line passes into the dialysis fluid outlet tube, and a third shut-off valve is provided in the bypass line, so that the device is configured to allow dialysis fluid to flow selectively through the dialyzer or the bypass line, and a force or pressure reference sensor on the dialysis fluid inlet side is arranged in the dialysis fluid inlet tube downstream of the first shut-off valve and upstream of the dialyzer, and / or a force or pressure reference sensor on the dialysis fluid outlet side is arranged in the dialysis fluid outlet tube downstream of the dialyzer and upstream of the second shut-off valve.

[0024] In an advantageous manner, the device is configured to implement and / or apply the above-mentioned methods for referencing / calibrating a pressure 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 measuring line in the T-piece of the luer lock connection and / or a pressure sensor at the upper end of the pressure measuring line in the extracorporeal circuit, so that conventional force or pressure reference sensors are not required in the extracorporeal circuit. Preferably, for all pressure or force sensors in the extracorporeal circuit (arterial pressure or force sensor, dialyzer input pressure or force sensor, venous pressure or force sensor), so-called clamp-on sensors are used, thus pressure or force sensors supporting the tube and integrated and / or inserted in the clamping device. The gist of the invention is that a force or pressure reference sensor in the dialysis fluid circuit is used for referencing / calibration of the pressure measurements of the clamp-on sensors in the extracorporeal circuit (adjustment / height correction of blood and dialysis fluid pressures). 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 semi-permeable filter membrane of the dialyzer. The reference value for the pressure measurement in the extracorporeal circuit can therefore be measured on the dialysis fluid side.

[0026] Herein, 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 tubing system are significantly reduced and the ease of use is improved; the time / labor expenditure required to set up the blood processing device is reduced, the possibility of possible leaks is reduced and the clarity of the blood tubing system is improved; the contact of the blood with air and the associated clotting is reduced and / or completely eliminated, thus saving on anticoagulants and thus reducing the cost of treatment; in addition to this, the absence of connections means that they cannot wear out, preventing the ingress of germs and the associated contamination of the device, and facilitating cleaning.

[0027] Two embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. [Brief description of the drawings]

[0028] [Figure 1] 1 shows a diagram illustrating the pressure curve of a clamping device over time. [Figure 2A] 1 shows a clamping device with which the tube is clamped. [Figure 2B] 1 shows a diagram illustrating the course of a drift signal compared to a reference signal; [Figure 3A] 1 shows the front of the dialysis machine before active use of the tubing. [Figure 3B] 1 shows an alternative arrangement of two sensors. [Figure 4] FIG. 13 shows a diagram illustrating the drift behavior of a tube in a closed clamping device. [Diagram 5] 1 shows a diagram illustrating the course of the drift signal at constant internal tube pressure and a correction function that maps the drift behavior of the tube. [Figure 6] FIG. 1 shows a graphical illustration of the determination of a pressure signal from a drift / force signal. [Figure 7] 1 shows the front of the device during active use of the tubing with a patient connected to the dialysis machine. [Figure 8] 1 shows a diagram illustrating a pressure curve at a first pressure sensor over time as a process is performed. [Figure 9] FIG. 2 shows a diagram illustrating pressure curves of a conventional pressure sensor, a first pressure reference sensor, and a first pump. [Figure 10A] FIG. 2 shows a diagram illustrating pressure curves for two conventional pressure sensors and a second pressure reference sensor. [Figure 10B] A diagram showing the (simulated) blood pump flow and patient blood pressure over time is shown. [Figure 11A] FIG. 1 shows a diagram illustrating the deviation between the calculated pressure signal and the reference signal due to temperature drift. [Figure 11B] 11B is a diagram showing the temperature profile of the fluid in the tube at the first pressure sensor and the second pressure sensor, in relation to the diagram of FIG. 11A. [Figure 12A] 1 shows a diagram illustrating the deviation between the pressure signal of a second pressure reference sensor and the corresponding pressure reference signal, and a linear correction signal. [Figure 12B] 12A, which shows the curves of the pressure signal and the pressure reference signal corrected by a linear correction signal. [Figure 13A] FIG. 13 shows a diagram illustrating the deviation of the pressure signal of a second pressure reference sensor from the corresponding pressure reference signal and the polynomialized correction signal. [Figure 13B] 13B is a diagram showing curves of the pressure signal and the pressure reference signal corrected by a polynomialized correction signal, which is related to the diagram of FIG. 13A. [Figure 14] 1 shows the front part of the dialysis machine before active use of the tube according to the second embodiment. [Figure 15] 4 shows pressure measurement points in the area around the dialyzer according to the second embodiment. [Figure 16] 13 shows the front of the device during active use of the tubing with a patient connected to the dialysis machine according to the second embodiment. [Figure 17] 4 shows a pressure curve of a sensor according to a second embodiment. [Figure 18A] 1 shows the pressure behavior when a dialyzer with low permeability is used. [Figure 18B] 1 shows the pressure behavior when a high permeability dialyzer is used. [Figure 19] Shows the pressure behavior of the sensor after offset compensation DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Embodiments of the present disclosure are described below based on the accompanying drawings, in which it is noted that the values ​​shown are only exemplary and are not limiting.

[0030] (First embodiment) The first embodiment described below forms the basis of the invention and / or represents the basis on which the invention was developed. It essentially relates to a method for indirect blood pressure measurement using a clamping device (force-pressure clamp). In particular, a method is described below in which the viscoelastic properties of the tube material are taken into account in the force / pressure measurement.

[0031] Overall Procedure FIG. 1 shows, by way of example, a pressure curve in millimeters of mercury (mmHg) of a pressure sensor (in this case a PBE pressure sensor, described in more detail below) with time t in seconds (s).

[0032] In stage 1, the tubing is inserted into two clamping devices, each incorporating at least one pressure sensor measuring the pressure on the dialysis machine in the form of a force signal, and the tubing is filled with fluid. The tubing system is filled by varying the pumping flow rate of at least one pump. Leak tests are also performed on the machine and tubing at this stage.

[0033] In step 2, the pressure inside the tube is kept constant. After a short transition phase, step a of recursive analysis and prediction of at least one correction function for determining a correction signal for correcting the drift signal is carried out by the corresponding force or pressure reference signal measured by the first force or pressure reference sensor at constant internal pressure of the tube and at constant internal temperature of the tube. In step a, a correction function f is determined as a function of time t with two constants a0, b related to the viscoelastic behavior of the tube before treatment. The two constants a0 and b are determined by a mathematical operation, hereinafter called "fitting", which will be described later. With this function, the drift signal in the form of a force signal of the respective pressure sensor is determined.

[0034] In step 3, a pressure drop can be detected, which is used to correct the force signal by the correction function determined in step a. Furthermore, the corrected force signal of the pressure sensor is converted into a corrected pressure signal using a pressure reference signal of a pressure reference sensor provided for this purpose via a linear relationship between the reference signal and the corrected force signal. In this specification, the pressure reference sensor is a conventional pressure sensor. Thus, step 3 shows a sequence of step b of a first calibration of the pressure or force signal measured by the first pressure or force sensor and corrected by means of a correction signal together with the force or pressure reference signal measured by the first force or pressure reference sensor, step b being performed before the start of the treatment. Thus, in step b, the corrected force signal has been calibrated by the pressure reference signal of the corresponding pressure reference sensor before the treatment. The calibration can also be performed via a second constant pressure level.

[0035] By conventional pressure sensors we mean pressure sensors that are not integrated into any clamping device and whose restoring forces do not influence the pressure signal. In the case of conventional pressure sensors, the internal pressure of the tube is determined, for example, via a T-piece or a pressure pod (as explained above).

[0036] In step 4, after a predefined time from the start of the treatment, preferably 5 minutes, the newly corrected force signal is again calibrated by the pressure reference signal of the corresponding pressure reference sensor. In step 4, a step c of a second calibration of the pressure or force signal measured by the first pressure or force sensor and corrected with the correction function is thus performed by the force or pressure reference signal measured by the second force or pressure reference sensor.

[0037] In stage 5, the treatment progress is shown while the PBE pressure is nearly constant. It can be seen that the corrected PBE pressure signal and the reference signal are superimposed on each other, which means that the correction of the pressure signal is sufficient and still works even with changing pressure (see time interval around 2600-2700 seconds).

[0038] In the following, the clamping device acting as a pressure sensor, the setup of the apparatus in which the method according to the invention is used, and steps a to c are described in detail by way of example. Furthermore, alternative variants of the present disclosure are subsequently described.

[0039] (background) 2A shows a (first) tube 1, the internal pressure of which can be measured by a force sensor 2. For this purpose, the tube 1 is clamped with a clamping device 3. Said clamping device clamps the tube 1, the expansion or contraction of which is transmitted to the force sensor 2 via force transmission means 4. The change in force that can be measured by the force sensor 2 is proportional to the change in the internal pressure of the tube 1.

[0040] FIG. 2B shows a graph displaying the pressure curve of the drift signal and the pressure curve of the reference signal over time. The pressure signal / drift signal depicted shows the course of the pressure in the tube 1 clamped in the clamping device 3 at time t0. The reference pressure has a value of 0 mmHg (ambient pressure) throughout the depicted time course. The pressure signal shows a pressure rise at time t0, followed by a logarithmically decreasing pressure curve that can be explained by the restoring force of the tube. The drift signal must be subtracted from the measured signal so that the absolute pressure is equal to the reference pressure.

[0041] (Setup for carrying out the method according to the present disclosure) FIG. 3A shows the front part of the dialysis machine 6, to which the (first) tube 1 is attached, the internal pressure of which is measured at various points. The dialysis machine 6 has an extracorporeal circuit. The tube 1 has an arterial section / branch 1a and a venous section 1b. Via a first substitution port SP1, the arterial section 1a of the tube 1 is connected to the machine 6, and via a second substitution port SP2, the venous section 1b of the tube 1 is connected to the machine 6. In the illustrated embodiment, the tube 1 is not connected to a patient, which means that the tube is not in active use and is therefore in a pre-treatment state. For this reason, the tube 1 is not filled with blood, but with another fluid (here the eluate).

[0042] First, the fluid is delivered to the arterial tube section 1a via the 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, the first pressure reference sensor PHOP records and / or measures the internal pressure of the tube. The pressure reference sensor PHOP is therefore also arranged at the substitution port SP. It is an additional pressure sensor to the conventional dialysis machine 6. After the fluid enters the front of the dialysis machine 6, it first passes through the arterial tube clamp SAKA, which is normally open. Then the fluid passes through the first clamping device, also called the PA pressure sensor and / or the first pressure sensor PA and therefore the first force sensor. The first clamping device is integrated in the front of the dialysis machine 6. The PA sensor measures the pressure in the arterial section 1a of the tube 1. The pressure reference sensor PHOP has a higher measurement accuracy than the first pressure sensor PA and therefore can be used for referencing the first pressure sensor PA (to be carried out later).

[0043] The fluid then reaches the first pump, the blood pump BP, which continues to pump the fluid. Finally, the fluid passes through a second clamping device, also called the PBE pressure sensor and / or the second pressure sensor PBE, therefore the 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 tube. After the PBE pressure sensor, the fluid can pass through the dialyzer 8. However, in the case of a bypass circuit via the bypass 10, it is also possible for the fluid to bypass without passing through the dialyzer. Downstream of the dialyzer / bypass in the flow direction of the fluid, the venous tube section 1b (shown here in dashed lines) is arranged. Downstream of the dialyzer / bypass and upstream of the air trap 12, where the air trapped in the fluid is removed from the fluid, the fluid in the venous tube section 1b passes through a conventional pressure capture, called the PV measuring point. The conventional pressure capture can be designed, for example, as a T-shaped part or as a pressure pod.

[0044] After the PV measuring point, the fluid passes through the deaerator 12, then the air detector 14 and finally through the normally open venous tube clamp SAKV. The venous tube clamp SAKV and the arterial tube clamp SAKA are closed only in case of a malfunction, preventing the patient's access in case of treatment. Such a malfunction may be, for example, that the air detector detects an air volume greater than a certain threshold. After the fluid has passed through the venous tube clamp SAKV, it flows out of the substitution port SP2 using the pumping capacity of the dialysate output flow pump FPA, which is arranged outside the front of the dialyzer 6.

[0045] 3A further shows that the dialysis machine 6 is connected to a CPU with a first computing section, a second computing section and a third computing section, in the process of which 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 tube clamp SAKA and the venous tube clamp SAKV.

[0046] FIG. 3B shows a blood pump BP and an alternative arrangement of the first pressure sensor PA and the second pressure sensor PBE. In this case, the first (arterial) pressure sensor PA is placed directly at the blood inlet of the blood pump BP, and the second (dialyser inlet) pressure sensor PBE is placed directly at the blood outlet of the blood pump BP. In this case, both pressure sensors PA and PBE are integrated into the blood pump BP, and the tubing material, temperature, and insertion point of the tubing of both pressure sensors PA and PBE are identical. The predictable drift behavior is likewise identical for both pressure sensors PA and PBE. Thus, the differential pressure P of both pressure sensors is PBE -P A can be determined without correction for drift, i.e. without calibration. PBE -P A is the corrected pressure P throughout the treatment PBE_korr -P A_Korr The correctness of the correction function described below can be assessed by comparing the two differential pressures (uncorrected and corrected). If these pressure differences differ by more than a predetermined amount, recalibration of the system is advisable.

[0047] (Step a) Similarly to FIG. 2B, FIG. 4 shows the signal course of the clamped tube after the clamping device is closed. However, the force signal of the first pressure sensor PA is shown here by way of example in the form of voltage values ​​in volts (V) over time t in seconds (s). At time t0 (t0=0s) the clamping device is closed. The signal course already known from FIG. 2B is shown for the period before and during treatment. The decrease in the signal course can be explained by the viscoelastic properties of the tube material, which influence the pressure transmission between the force sensor and the fluid in the tube. The elastic part of the tube generates a restoring force. The viscous part of the tube causes a slow and irreversible deformation of the tube. Due to this deformation of the tube, the restoring force decreases and so does the force with which the tube presses against the force sensor. The curve of the restoring force shown in FIG. 4 is also called the drift signal. In order to be able to represent the force signal and / or pressure signal of the force sensor as a signal that depends only on the internal pressure of the tube, it is desirable to calculate / remove the drift signal from the measured force signal and / or pressure signal, i.e. to determine the drift signal so that it can be subtracted from the measured force signal.

[0048] The viscoelastic behavior of the tube can generally be described by an exponentially decaying coefficient, which allows the drift signal to be described as a mathematical correction function with the following equation: f(t)=a0 t -b (1)

[0049] Here, t is time, a0 and b are unknown constants. The force signal is emitted as a voltage value, so f(t) has units of V.

[0050] To further utilize this equation, it is desirable to determine the constants a0 and b by fitting. For this purpose, it is necessary to generate a constant internal pressure in the tube by adjusting the pumping ratio of the pump BP and the FPE or FPA. In addition, a constant internal temperature of the tube is required. The eluate flowing in the tube is preheated to 36 ° C, approximately the same as the temperature of the blood during treatment. Said temperature is kept constant so that the internal temperature of the tube is also constant. Furthermore, the force signal of a pressure sensor, in this case the first pressure sensor PA, is determined in the measurement. However, the force signal of another pressure sensor, for example the second pressure sensor PBE, can also be used. The course of the force signal of the first pressure sensor PA over time can be seen in Figure 5.

[0051] In FIG. 5 the force signal is shown as voltage with units of volts [V] as a function of time t in seconds [s]. In the time range from 0 seconds to about 1200 seconds there is a state before active use of the tube during the so-called "priming", which means before treatment. Before treatment, the patient is not connected to the dialysis machine 6, which in this case is realized as described and shown in relation to FIG. 3A. In the time range starting from about 1200 seconds the voltage signal during treatment is shown, also called "treatment". During treatment, the patient is connected to the dialysis machine 6, which is realized as described and shown in relation to FIG. 7.

[0052] To be able to determine the constants a0 and b using the force signals, the signal values ​​of each of the force signals f(t=t1) and f(t=t2) are determined in a fitting at two specific points at time t1 and t2 in the pre-treatment area. In the example shown in FIG. 5, the points at time t1=600 seconds and t2=800 seconds are selected. The following simultaneous equations are given by Equation (2) and Equation (3), which must be solved to obtain the constants a0 and b: I f(t=t1)=a0·t1 -b (2) II f(t=t2)=a0·t2 -b (3)

[0053] From Equation I, i.e., Equation (2), a0 can be expressed as follows: a0 = f(t = t1) t1 b (4)

[0054] By substituting a0 of the form shown in equation (4) into equation (3), b is given by equation (5), which now depends only on the known time instants t1, t2 and the corresponding signal values ​​of the force signals f(t=t1) and f(t=t2) and can therefore be calculated as follows: b=ln(f(t=t2))-ln(f(t=t1)) / (ln(t1)-ln(t2)) (5)

[0055] After determining the value of b, the value of the constant a0 is obtained by substituting this value into equation (4), where equation (1) describes the viscoelastic behavior of the tube used. Using the times t1 and t2 selected above and the voltage values ​​applicable in this test, the value of a0 is 1.19 and the value of b is 0.03.

[0056] Step a is performed here as an example for a PA pressure sensor and is performed in analogy for a PBE pressure sensor.

[0057] (Step b) The measured force signal is then corrected and converted into a pressure signal by a suitable pressure reference signal. This is done when the internal pressure of the tube changes, for example drops, during the pre-treatment phase, or via a second constant pressure level with a different pressure compared to the first pressure level. The internal pressure of the tube drops, for example, in case of separation of the tube from the replacement ports SP1, SP2, which is necessary for preparation of the treatment. Alternatively, the second pressure level can be adjusted via a different pumping ratio of the blood pump and the flow pump. Step b is implemented as an example of a first pressure sensor PA.

[0058] First, a drift signal f(t) having calculated values ​​of a0 and b is calculated based on a force signal P measured using a first pressure sensor PA. S_gemThis force signal is then output as a voltage value (V). The corrected force signal P S_korr has the following equality (equation (6)): P S_korr =P S_gem -f(t) (6)

[0059] Next, a first pressure reference sensor PHOP is used to obtain a pressure reference value P PHOP These values ​​are recorded along with the associated voltage values ​​P in V as illustrated in Figure 6. S_korr are plotted in the figure above.

[0060] In the diagram of Figure 6, the measured pressure reference value P PHOP is the calculated voltage value P on the X-axis S_korr , and a straight line course is shown for these points. Accordingly, most preferably a straight line A passing through these points is mathematically determined, so that the voltage value P S_korr and the pressure correction value P calculated from it. A_Korr This relationship can be mathematically expressed in the form of equation (7): P A_Korr =m P S_korr +t (7)

[0061] where m is the slope of the line, also called the scaling value, and t is where the line intersects the Y-axis, also called the offset value, and is the pressure reference value. In the example shown, the scaling value is 5278 mmHg / V, and the offset value is 23 mmHg.

[0062] As a result, the corrected, i.e. correct pressure signal P A_Korr is known prior to treatment and step b is completed.

[0063] (Step b) is performed for the PBE pressure sensor analogous to the procedure shown here for the PA pressure sensor, except that the PV pressure reference sensor is used as the reference rather than the PHOP pressure reference sensor used here as the reference.

[0064] For example, since the values ​​of the internal pressure of the tube and / or the internal temperature of the tube may change from a pre-treatment state to a treatment state, it is recommended that the correction of the measured force signal of the first pressure sensor and / or the second pressure sensor is repeatedly performed during the treatment.

[0065] (Step c) During the treatment, the setup shown in FIG. 2A changes as shown in FIG. 7. In FIG. 7, it can be seen that the arterial tube section 1a and the venous tube section 1b are connected to the patient. In this case, the patient's heart takes the place of the dialysate inflow and outflow pumps. The (arm) artery, connected to the arterial tube section 1a, and the (arm) vein of the patient, connected to the venous tube section 1b, are connected to each other via an artificial connection 16, in particular via a patient shunt. As a result, the same blood pressure and the same blood flow values ​​are present in the patient's veins and arteries (which can also be generally called blood vessels). By setting up a bypass of the dialyzer, the same blood pressure and the same blood flow values ​​are also present in the arterial tube section 1a and the venous tube section 1b, and thus in the entire system consisting of the tubes and the patient's blood vessels. For the experiment, it is conceivable to simulate an experimental patient circuit with a water pump, a heated water bath and a back pressure valve.

[0066] The calibration and referencing principle is the same in step c as in step b. Here too, the measured force signal of the pressure sensor is corrected by the correction signal determined in step a, and the corrected pressure signal can be calculated from the relationship between the corrected pressure signal and the corrected force signal found in step b (see equation (6) with the scaling and offset values ​​determined in step b).

[0067] Step c may be performed for the first pressure sensor PA and the second pressure sensor PBE, but here the conventional PV pressure reference sensor serves as a pressure reference sensor for the PA pressure sensor as well as the PBE pressure sensor to enable simultaneous referencing of the PA pressure signal and the PBE pressure signal.

[0068] To simplify the problem, it is possible to refer only to the pressure signal of the second pressure sensor PBE using the pressure reference sensor PV by switching the dialyzer flow to bypass. Due to the same characteristics depending on the manufacture of the tubes at the position of the PA clamping device and at the position of the PBE clamping device, it is possible to apply the correction function determined for the PBE pressure signal to the PA pressure signal as well, but it should be noted that this method is not as accurate as the above-mentioned method in which one correction function each is determined for the PA pressure signal and the PBE pressure signal.

[0069] (Results of the method according to the present invention) After filtering and scaling the corrected pressure signal, the signal can be compared to a corresponding directly measured pressure reference signal. This comparison yields the corrected pressure signal P A_korr and the corresponding pressure reference signal P PHOP An example of this is shown in FIG.

[0070] In the diagram of Figure 8, the calculated pressure correction signal P A_Korr and the directly measured pressure reference signal P PHOP It can be seen that the curves of a0 and b coincide. This means that the mathematical correction function according to (1) together with the calculated values ​​of a0 and b can eliminate the drift curve, but this is only valid if the internal pressure of the tube and the internal temperature of the tube are constant. If, for example, the internal pressure of the tube is changing when the second voltage value f(t2) is measured, the correction function is not suitable for describing the course of the drift signal.

[0071] (Referencing Possibility) In the following, in Figs. 9 and 10A, the arterial pressure P A and the dialyzer input pressure P PBE 4 shows the pressure curves of pressure sensors conventionally used to measure pressure PHOP and PV compared with the pressure curves of the corresponding pressure reference sensors PHOP and PV, respectively.

[0072] In FIG. 9, the pressure curve of a conventional first pressure sensor PA_herk for measuring arterial pressure is compared with a first pressure reference sensor PHOP before treatment. The pressure curve in mmHg is shown over time t in seconds. Additionally, the pressure curve of the blood pump BP is shown, which repeatedly goes to pressure 0. The blood pump BP is repeatedly stopped so that constant pressure values ​​of the PA_herk and PHOP sensors occur.

[0073] It can be seen that the profiles of the two pressure signals of the PA_herk and PHOP pressure sensors are similar and run parallel to each other. Here, the curves are translated with a pressure difference of about 20 mmHG. The difference in the profiles of the pressure signals of the two sensors is due to the difference in height between the first pressure sensor PA_herk and the first reference pressure sensor PHOP. In this embodiment, the first reference pressure sensor PHOP is mounted at a higher position than the first pressure sensor PA (see FIG. 2A).

[0074] Although the differential pressure between the conventional pressure sensor and the pressure reference sensor must be taken into account, the comparison of FIG. 9 shows that the pressure reference sensor is suitable as a reference sensor for arterial pressure.

[0075] In Fig. 10A the pressure curves 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 are shown compared to the pressure curve of a second pressure reference sensor PV in mmHg over time t in seconds during treatment. Fig. 10B shows a diagram of the blood pump flow rate in ml / min and the simulated patient pressure in mmHg over time, recorded simultaneously with the pressure values ​​of Fig. 10A.

[0076] In the range where the flow rate of the blood pump is 0, i.e. when the blood pump is stopped, the pressure signals of the PA_herk, PBE_herk and PV sensors are adjusted to each other and are constant. In these constant pressure ranges, the pressure curves of the two pressure sensors PA_herk and PBE_herk essentially coincide and there is a pressure difference with respect to the pressure curve of the pressure reference sensor PV, which here is about 20 mmHg and can be explained by the height difference of the pressure sensors PA_herk, PBE_herk and the pressure reference sensor PV.

[0077] Again, the differential pressure between the conventional pressure sensor and the pressure reference sensor must be considered, but a comparison of Figure 9 shows that the second pressure reference sensor is suitable as a reference sensor for arterial pressure and dialyzer input pressure during treatment.

[0078] (Temperature drift) Up to this point, the above description has assumed a constant internal pressure in the tube and a constant internal temperature in the tube. However, temperature differences may occur in the filled tube between steps b and c, i.e., between the pre-treatment and treatment phases, which may lead to a linear deviation between the reference sensor value and the pressure sensor value.

[0079] Such deviations are illustrated by the example of a PBE pressure sensor and a PV pressure reference sensor in the diagram of FIG. 11A. FIG. 11B shows the relevant temperature profiles at the measurement points of the PBE pressure sensor and the PV pressure reference sensor. To be able to determine the temperatures of these two measurement points, a temperature sensor must be integrated into the PBE clamping device and / or the PA clamping device. Here, the pre-treatment calibration (up to about 900 seconds) is performed at T1, e.g. 35.8°C, and the during-treatment calibration is performed at T2, e.g. 37.2°C. Due to the temperature difference ΔT (=T2-T1) before and during treatment, here 1.4°C, the calculated PBE pressure signal shown in FIG. 11B does not follow the PV reference signal during treatment but deviates linearly from it. It has been found in studies 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 experimentally determined correction function.

[0080] 12A shows the pressure deviation between the pressure signal and the reference signal and a line B determined for it over time t in seconds. In one example, the line equation has the following form shown in equation (8): PBE Signal =-0.0064182[mmHg / ℃]·ΔT[℃]+3.4282[mmHg] (8)

[0081] 12B shows the PBE pressure signal corrected using the derived equation (8), which is again shown to be coincident with the PV reference signal.

[0082] As an alternative to the linear relationship between the deviation between the pressure signal and the reference signal for the temperature deviation before and during treatment, there may also be a polynomial relationship, but even though such a relationship may represent the deviation more accurately than a linear relationship, more computing power is required to calculate the corresponding equation.

[0083] 13A shows, similar to FIG. 12A, the pressure deviation between the pressure signal and the reference signal and the polynomial C calculated therefor over time t in seconds. In this example, the PBE pressure signal follows the polynomial deviation shown in equation (9): PBE Signal =2.6287 10 -6 ·[mmHg / ℃ 2 ]ΔT 2 [℃ 2 ]-0.018486[mmHg / ℃]·ΔT[℃]+15.8826[mmHg] (9)

[0084] FIG. 13A shows the PBE pressure signal corrected by the determined equation (9), which is again shown to match the PV reference signal.

[0085] (Modification of the first embodiment) Alternatively, the reference pressure measurement of the pressure signals PBE and PA in step c (during treatment) can be performed with the venous tube clamp SAKV closed and the arterial tube clamp SAKA closed.

[0086] For this purpose, as in the first embodiment, the dialyzer flow is switched to bypass and the tube clamps SAKV and SAKA are closed. A pressure-tight connection is formed in the tubes. The blood pump BP is stopped. However, due to a delay, the blood pump BP continues to rotate for a short time after stopping, so that a negative pressure accumulates in the arterial tube section and a positive pressure accumulates in the venous tube section, which have the same pressure ratio to each other over time, i.e. have a constant ratio to each other. The PBE pressure signal is calibrated by the PV pressure reference sensor. The PA pressure signal can be calibrated similarly by the PV pressure reference sensor.

[0087] This alternative version of step c can be performed independently of the patient, since the patient is isolated from the extracorporeal circuit by closed tube clamps SAKV and SAKA. However, in this case, blood clots may form in the extracorporeal circuit, and the body temperature may decrease, since blood no longer circulates through the extracorporeal circuit. However, blood clotting and its temperature decrease depend on the time the blood pump is stopped, which should be as short as possible.

[0088] (summary) In summary, 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) tube, preferably a dialyzer tube (blood tube), in the form of a force signal, for example in an extracorporeal (blood) circulation circuit. The pressure sensor is directly connected to the (first) tube and is integrated / inserted into a first clamping device in order to correct drift signals caused by the (first) tube by a correction function using a pressure reference signal captured by a first (separate) pressure reference sensor. For this purpose, the following steps are performed according to the present disclosure: (a) recursively analyzing and predicting at least one correction function to obtain a correction signal for correcting the drift signal with a corresponding pressure reference signal measured by a first pressure reference sensor at a constant internal pressure of the tube and a constant internal temperature of the tube; (b) a first calibration of the force signal measured by the first force sensor and corrected by the correction signal with a pressure reference signal measured by the first pressure reference sensor before active use of the tube; and (c) A second calibration of the force signal measured by the first force sensor and corrected by a (pre-predicted) correction function by a pressure reference signal measured by a second (separate) pressure reference sensor during active use of the tube.

[0089] In other words, a method for online correction of a force-pressure signal is provided, which according to the present disclosure is applied to a filled (first) tube before and during active use of the (first) tube. This means that a first calibration of the (test / simulated) force signal generated by the first force sensor is first performed before active use of the (first) tube by a pressure reference signal determined by a pressure reference sensor and a correction function. Then, a second calibration of the (second) force signal already corrected by the correction function is performed during active use of the tube, i.e. based on a pressure reference signal generated / preferably by a second pressure reference sensor.

[0090] Specifically, a mathematical correction function and a two-point calibration are applied for this purpose so that a measurement of the absolute pressure is possible. The pressure measurement is carried out via a force sensor integrated in the clamping device. The mathematical correction function is determined from the measured (test) force-pressure signal at constant internal pressure of the tube and constant internal temperature of the tube, preferably within a few minutes after the insertion of the (first) tube into the clamping device, and from a reference pressure determined via a (separate) pressure reference sensor (of different construction and / or different installation than the force sensor) and providing a drift signal. The pressure reference sensor preferably has a higher measurement accuracy than the corresponding pressure / force sensor. Then, during the recording of the pressure / force signal for determining the correction function, a first calibration is carried out in which the internal pressure of the tube and the internal temperature of the tube are constant. In a later recalibration (second calibration), the (first) tube is exposed to a constant known pressure and the correction function is again determined from the pressure data measured during this period. Such a referencing method thus includes a calibration procedure not only before active use of the tube, but also during active use of the tube, i.e. the referencing method is performed before and during the patient's (dialysis) treatment.

[0091] Such a method allows pressure measurement via a clamping device directly on the filled (first) tube as part of the tubing system. With this type of pressure measurement, the luer lock connection used in the prior art is not required in the area of ​​the clamping device. This results in a reduced manufacturing cost of the tubing system and an improved ease of use. The improved ease of use of the tubing system can be based on the fact that fewer connectors have to be connected compared to conventional systems, and therefore devices using such a tubing system can be set up faster, are less prone to leaks and the tubing system is more clearly arranged. Furthermore, this tubing system has the advantage that contact between the fluid and air in the tubes is reduced and / or avoided. Thus, if the liquid / liquid flowing through the (first) tube is blood, the risk of blood clotting is reduced. As a result, less anticoagulant needs to be added to the blood, which reduces the cost of treatment. In addition to this, the pressure connection (luer lock connection) on the device side is not worn out and the risk of contamination due to pressure measurement is also reduced.

[0092] However, an advantage of the method according to the present disclosure is that the reference measurement during active use of the (first) tube provides a significantly more accurate value than a reference measurement alone before active use of the tube. The correction function determined in the method according to the present disclosure can be performed independent of the tube material or tube dimensions and can therefore be used generally for unknown tubing systems.

[0093] The method can be implemented such that in addition to the first pressure, a second pressure can be measured and corrected, the second pressure being measured using a second force sensor / second pressure sensor integrated in the second clamping device. Herein, the force signal of the second force sensor is calibrated using a pressure reference signal measured by a second pressure reference sensor during the first calibration and during the second calibration. In this way, the internal pressure of the tube can be measured and corrected at two different positions in the extracorporeal circuit without any fluid-air contact.

[0094] A further aspect of the method according to the present disclosure provides that the (first) tube (e.g., an extracorporeal blood tube of a dialysis machine or a blood pump) comprises an arterial section (blood inlet section) and a venous section (blood outlet section). Herein, the first and / or second pressure / force sensor as well as the first pressure reference sensor are preferably arranged in the arterial section. The second pressure reference sensor, which may be a pressure / force sensor for checking the internal pressure of the tube in the (only) venous section not cooperating with the clamping device, is arranged in the venous section. This means that the pressure in the venous section of the (first) tube is (only) measured by the second pressure reference sensor, preferably according to conventional pressure measurement methods, for example via a T-piece or a (higher accuracy) flexible membrane. This means that the (only) second pressure reference sensor is further preferably connected via a Luer lock connection to the device to which the (first) tube is connected. In this way, the referencing is performed by a pressure reference sensor, which is more expensive compared to a sensor integrated in the clamping device, but has a higher accuracy. The first pressure reference sensor is arranged in the region of the arterial tube section and preferably comprises a piezoelectric element for pressure measurement.

[0095] Furthermore, it can be provided that by adjusting the pump ratio between a first pump, in particular a blood pump, and a second pump, in particular a dialysate inlet flow pump or a dialysate outlet flow pump, a constant internal pressure in the tube can be achieved. By adjusting the pump ratio between these two pumps, achieving a constant pressure in the tube is particularly reliable and simple. In the method according to the present disclosure, a constant pressure in the filled tube is of essential importance.

[0096] Additionally, the method may be implemented such that the drift signal is and / or corresponds to the restoring force of the clamped tube.

[0097] In addition to this, it is conceivable that the (corrected) force signals are converted to pressure signals via a linear regression with the corresponding pressure reference signals and / or the force signals are calibrated with the pressure reference signals, which linear regression allows for a simple calculation of the pressure signals from the respective force signals.

[0098] Preferably, in the case of two force sensors used, the first force sensor is arranged and in particular integrated at the inlet opening / blood inlet of the first pump and the second force sensor is arranged and in particular integrated at the outlet opening / blood outlet of the first pump. In this case, the tubing material at the position of the force sensor, the temperature in the tubing and the insertion time of the tubing into the corresponding clamping device are identical, so that the predicted drift behavior at the positions of the two force sensors should also be identical.

[0099] Further, according to a first embodiment of the present disclosure, a device is provided having an extracorporeal circuit and at least one pressure / force sensor, in particular an arterial pressure / force sensor and / or a dialyzer input pressure / force sensor. The pressure / force sensor is integrated into a clamping device for measuring the internal pressure of the tube in a fluid-filled tube having an arterial section and a venous section. Furthermore, the device has at least one pressure reference sensor for referencing the pressure / force signal emitted by the at least one pressure sensor. The at least one pressure reference sensor, in particular the arterial reference sensor and / or the venous pressure reference sensor, is not designed as a clamping device and / or is not intended to be integrated into a clamping device (design without a clamping device). Furthermore, the device preferably comprises at least a first pump and a second pump. A device is provided and configured for applying the method for calibrating the pressure signal of at least one pressure sensor by the reference signal of the at least one pressure reference sensor according to at least one of the preceding aspects of the present disclosure.

[0100] Finally, according to a first embodiment of the present disclosure, a calibration device is provided for calibrating the measurement of at least a first pressure (internal pressure) of a tube, preferably an arterial pressure. This first pressure is measured in the form of a force signal in a fluid circuit, in particular an extracorporeal (blood) circulation circuit, in a tube (not part of the device) filled with fluid / liquid / blood, by a first pressure / force sensor of the calibration device, which may be directly adjacent to the tube or directly (externally) adjacent to the tube. Herein, the pressure / force sensor is integrated in a first clamping device. The first pressure is calibrated to correct drift signals caused by the (first) tube (tube material) by a correction function using a pressure reference signal captured / generated by a first pressure reference sensor of the calibration device. The calibration device has the following units or sections: (a) a first calculation section (CPU unit / program step) provided and configured for analysis and prediction of at least one correction function for determining a correction signal for correcting the drift signal using a corresponding (force / ) pressure reference signal measured / generated by a first pressure reference sensor at a constant internal pressure of the tube and at a constant internal temperature of the tube; (b) a second computing section (CPU unit / program step) provided and configured for a first calibration of the force signal measured by the first force / pressure sensor (PA) using a pressure reference signal measured / generated by the first pressure reference sensor before operational use of the tube and subsequently corrected by a correction signal; (c) a third computing section (CPU unit / program step) provided and configured for a second calibration of the force signal measured by the first force / pressure sensor and subsequently corrected by the correction signal, using a (force / ) pressure reference signal measured / generated by a second pressure reference sensor during active (operating) use of the tube.

[0101] Second embodiment The second embodiment according to the present invention, as claimed in the claims, is substantially based on the first embodiment, so that in the following essentially only the differences from the first embodiment will be described.

[0102] In the first embodiment, the pressure sensors of the arterial section 1a of the tube 1, the first pressure sensor PA and the second pressure sensor PBE, are designed as pressure or force sensors integrated / inserted into the clamping device, while the venous section 1b of the tube 1 is provided with a conventional pressure sensor (force or pressure reference sensor PV) needed for referencing / calibration, realized for example as a T-piece or pressure pod.

[0103] In a second embodiment according to the invention, as claimed in the claims, a (third) pressure sensor PV is also provided in the venous section 1b of the tube, which is designed as a pressure sensor or a force sensor integrated / inserted in the clamping device. Thus, conventional pressure transducers connected via Luer lock connections are not used for the three / all pressure sensors PA, PBE, PV measuring the blood pressure. The second embodiment according to the invention essentially provides a method and a device for referencing / calibrating on the dialysate / dialysis fluid side.

[0104] A second embodiment according to the present invention will now be described with reference to FIGS.

[0105] FIG. 14 shows the front part of a dialysis machine 6, to which a (first) tube 1 is attached, the internal pressure of which is measured at various points. The dialysis machine 6 has an extracorporeal circuit. The tube 1 has an arterial section / branch 1a and a venous section / branch 1b. Via a first replacement port SP1, the arterial section 1a of the tube 1 is connected to the machine 6, and via a second replacement port SP2, the venous section 1b of the tube 1 is connected to the machine 6. In the embodiment shown in FIG. 14, the tube 1 is not (yet) connected to a patient, which means that the tube is not in active use, and therefore in a pre-treatment state. For this reason, the tube 1 is not filled with blood, but with another fluid (here the eluate).

[0106] The fluid is first transported to the arterial tube section 1a via the input flow pump FPE, which is arranged outside the front of the dialysis machine 6. Even before the fluid comes to the area of ​​the front of the dialysis machine 6, the first pressure reference sensor PHOP acquires and / or measures the internal pressure of the tube. The pressure reference sensor PHOP is therefore also arranged at the substitution port SP1 and is an additional pressure sensor to the conventional dialysis machine 6. After the fluid enters the front of the dialysis machine 6, it first passes through the arterial tube clamp SAKA, which is normally open. The fluid subsequently passes through the first clamping device, also called the PA pressure sensor and / or the first pressure sensor PA and therefore the first force sensor. The first clamping device is integrated in the front side of the dialysis machine 6. The PA sensor measures the pressure in the arterial section 1a of the tube 1. The pressure reference sensor PHOP has a higher measurement accuracy than the first pressure sensor PA and can therefore be used for referencing the first pressure sensor PA.

[0107] The fluid then reaches the first pump, the blood pump BP, which continues to transport the fluid. Finally, the fluid passes through a second clamping device, also called the PBE pressure sensor and / or the second pressure sensor PBE, thus the 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 tube. After the PBE pressure sensor, the fluid can pass through the dialyzer 8. However, in the case of a bypass circuit via the bypass 10, it is also possible for the fluid to bypass without passing through the dialyzer. Downstream of the dialyzer / bypass in the flow direction of the fluid is the venous tube section 1b (here shown in dashed lines). Downstream of the dialyzer / bypass and at a point upstream of the air trap 12, where the air trapped in the fluid is removed from the fluid, the fluid in the venous tube section 1b passes through a PV pressure sensor and / or a third pressure sensor PV, thus the third clamping device, also called the third force sensor. The PV pressure sensor measures the dialyzer output pressure at a point downstream of the dialyzer 8. However, the PV pressure sensor may be placed only downstream of the air trap 12, as is the case, for example, in the setup of FIG. 16 in which the therapy mode is shown.

[0108] As further shown in Figure 14, after the PV measurement point, the fluid passes through a deaerator 12, then an air detector 14, and finally through the venous tubing clamp SAKV. After the fluid passes through the venous tubing clamp SAKV, it flows out of the displacement port SP2 using the pumping capacity of the output flow pump FPA located outside the front of the dialysis machine 6.

[0109] During treatment, the arterial tube section 1a and the venous tube section 1b are connected to a patient (see FIG. 16). In this case, the patient's heart replaces the input flow pump FPE and the output flow pump FPA. An air detector 14 is not depicted in FIG. 16, but is preferably provided during treatment as well.

[0110] As shown in Figures 14, 15 and 16, the dialysis machine 6 includes a dialysis fluid inlet tube / line 20 and a dialysis fluid outlet tube / line 22. A bypass line / tube 24 branches off from the dialysis fluid inlet tube 20 at a first branch point 26. A first shutoff valve 28 is provided downstream of the first branch point 26. The first shutoff valve 28 is configured to allow or prevent fluid flow through / in the dialyzer 8. A second branch point 30 is provided in the dialysis fluid outlet tube 22, where the bypass line 24 passes into the dialysis fluid outlet tube 22. A second shutoff valve 32 is provided in the dialysis fluid outlet tube 22 upstream of the second branch point 30. The second shutoff valve 32 is arranged to allow or prevent fluid flow through / in the dialyzer 8. A third shutoff valve 34 is provided in the bypass line 24. The third shutoff valve 34 is arranged to allow or prevent fluid flow through the bypass line 24.

[0111] The dialysis fluid inlet tube 20 is provided with a force or pressure reference sensor PDE on the dialysis fluid inlet side downstream of the first shutoff valve 28 and upstream of the dialyzer 8. The dialysis fluid outlet tube 22 is provided with a force or pressure reference sensor PDA on the dialysis fluid outlet side downstream of the dialyzer 8 and upstream of the second shutoff valve 32.

[0112] However, according to the invention, only one of the force or pressure reference sensors PDE and PDA, preferably also a force or pressure reference sensor PDA, can in principle be provided, which means that only a force or pressure reference sensor PDA, or only a force or pressure reference sensor PDE, or not only a force or pressure reference sensor PDA but also a force and pressure reference sensor PDE can be provided.

[0113] 14 shows that the dialysis machine 6 is connected to a CPU with a first computing section, a second computing section and a third computing section. In this regard, 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 tube clamp SAKA, the venous tube clamp SAKV, the first shutoff valve 28, the second shutoff valve 32 and the third shutoff valve 34, etc., and / or can receive information / signals from sensors.

[0114] In particular, the CPU can control the shutoff valves 28, 32, 34 to allow dialysis fluid / dialysate to flow optionally through the dialyzer 8 or the bypass line 24. If the first shutoff valve 28 and the second shutoff valve 32 are closed and the third shutoff valve 34 is open, dialysis fluid flows through the bypass line 24 and not through the dialyzer 8. Hereinafter, this operation is referred to as bypass operation. If the first shutoff valve 28 and the second shutoff valve 32 are open and the third shutoff valve 34 is closed, dialysis fluid flows through the dialyzer 8 and not through the bypass line 24. Hereinafter, this operation is referred to as main connection operation.

[0115] As already 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 or pressure sensors integrated / inserted into a clamping device (so-called clamp-on sensors). In order that the PBE and PV pressure sensors can operate with the desired accuracy, they must essentially be referenced / calibrated. According to the invention, this referencing / calibration is performed by a reference measurement on the dialysis fluid side via at least one sensor from the force or pressure reference sensor PDA and the force or pressure reference sensor PDE.

[0116] Referencing / calibration can essentially be done by means of pressure equalization curves. A typical pressure equalization curve is shown in Figure 17. Figure 17 shows the actual pressure curves for PV (PV_Actual), PBE (PBE_Actual) and PDA. In particular it can be seen the course of a test measurement in which alternating switching between bypass operation B and main series operation H was performed. In each case switching occurs at times t1, t2, t3 etc. marked on the time axis.

[0117] It can be seen that the pressure is equalized about 10 seconds after switching from the main connection operation H to the bypass operation B. In particular, when the flow of dialysis fluid through the dialyzer 8 is stopped (bypass operation), the pressure between the blood side and the dialysis fluid side / dialysate side can be equalized via the semi-permeable filter membrane of the dialyzer 8. In this context, the referencing / calibration is preferably performed in the bypass operation B.

[0118] Essentially, to perform a referencing / calibration, all relevant factors that influence the profile of the pressure equalization curve must be known, calculated and taken into account.

[0119] In particular, it must be taken into account here whether the pressure equalization curve was recorded with the blood side moving (dynamic case) or without the blood side moving (static case). For example, the pressure equalization curve shown in FIG. 17 was recorded in the static case without the blood side moving. In the dynamic case, for example, the pulsation of the blood pump roller rotor must additionally be taken into account, which influences the pressure curve. However, as is known, the pulsation of the blood pump roller rotor propagates in the system and can be taken into account in a simple way by a mean value filter.

[0120] In addition, the offset variation / offset shift of the curve must be taken into account. The offset variation depends, for example, on the differential pressure between the blood side and the dialysis fluid side, on the size of the dialyzer, on the volume of the dialysis fluid side, and on the relative positions of the pressure sensors relative to each other, which may be included via the position of the pressure transducer and / or the gravity of the water column. For example, if the offset shift / offset variation / differential pressure is taken into account and / or corrected with a correction value, the referencing / calibration can in principle be performed not only in the bypass operation B but also in the main connection operation H.

[0121] Regarding the adjustment times, it should be taken into account that these depend on many factors such as, for example, the pressure difference between the blood side and the dialysis fluid side, the size of the dialyzer, the volume of the dialysis fluid side, the compliance / volume expandability / flexibility of the tubing system as well as the position of the pressure transducer, which is preferably placed as close as possible to the dialyzer 8, preferably directly on the flushing bridge.

[0122] Furthermore, the influence of the dialyzer must be taken into account; in other words, a dialyzer-specific calibration must also be performed. For example, for calibration / referencing it is conceivable that an average value from a number of different dialyzer calibration curves is calculated by the dialysis machine's CPU. It is also conceivable that the dialyzer is characterized in the preparation phase by the application of a constant pressure in order to determine the transmembrane pressure.

[0123] 18A and 18B show how the dialyzer 8, in particular the semipermeable membrane of the dialyzer 8, can affect and / or influence the pressure curve. In each case, FIG. 18A and FIG. 18B show the pressure curves of the PV, PBE and PDA. Herein, FIG. 18A shows the pressure behavior at low permeability of the dialyzer 8, in particular the semipermeable membrane of the dialyzer 8, and at ultrafiltration rates greater than 0. On the other hand, FIG. 18B shows the pressure behavior at high permeability of the dialyzer 8, in particular the semipermeable membrane of the dialyzer 8, and at ultrafiltration rates greater than 0. In other words, the permeability of the dialyzer 8 in FIG. 18A is lower than that of the dialyzer 8 in FIG. 18B. In view of this, FIG. 18A and FIG. 18B show that dialyzer-specific calibration / referencing is necessary when the force sensor or pressure sensor of the extracorporeal circuit is referenced / calibrated via the force reference sensor or pressure reference sensor of the dialysis fluid circuit.

[0124] As soon as all the influencing factors are known and taken into account, PV and PDA / PDE will be in good agreement and can be referred to. In this regard, Figure 19 shows the pressure curves of PV_Actual, PBE_Actual and PDA after offset correction.

[0125] With reference to FIG. 16, the referencing / calibration is proposed as follows: the blood pump BP continues to rotate (blood side progression and / or dynamic case) and the flow of dialysis fluid is switched to bypass operation B. After 10 seconds, the referencing of the PV via the PDA is performed and a correction of the force sensor measurement at the PV is performed. Alternatively, the referencing of the PV via the PDE (and / or PDA) may be performed. Since the PDE sensor is located on the inlet side of the dialyzer 8, a negative pressure occurs here during the operation of the blood pump and the bypass circuit, which negative pressure is different from the PV. However, when the venous tube 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 the referencing / calibration can be performed. The only drawback here is that the lack of blood circulation can lead to blood clotting. The following items are elements that are claimed in the international application: (Item 1) 1. A method for referencing at least one pressure or force sensor (PA, PBE, PV), comprising: said at least one pressure or force sensor is configured to measure intratube pressure in the fluid-filled tube (1) and is located in the extracorporeal circuit and is integrated into or inserted into the clamping device (3); The method comprises: referencing the pressure or force signal output by said 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); using at least one dialysis fluid side force or pressure reference sensor (PDA, PDE) for referencing at least one pressure or force sensor (PA, PBE, PV) arranged in the extracorporeal circuit; Including, The at least one dialysis fluid side force or pressure reference sensor (PDA, PDE) is a force or pressure reference sensor of a dialysis fluid circuit and is configured to detect the pressure in the tube of the dialysis fluid circuit. A method comprising: (Item 2) for referencing a venous pressure or force sensor (PV) located in the venous section of the tubing downstream of the dialyzer (8) of the extracorporeal circuit, using a dialysis fluid inlet force or pressure reference sensor (PDE) located in the dialysis fluid inlet tube (20); or using a dialysis fluid outlet force or pressure reference sensor (PDA) located in the dialysis fluid outlet tube (22); The method of claim 1, further comprising: (Item 3) 3. The method of claim 2, further comprising providing a bypass operation in which dialysis fluid flows through a bypass line (24) without passing through a dialyzer (8) and a main connection operation in which the dialysis fluid flows through the dialyzer (8). (Item 4) switching from the main connection operation to the bypass operation; waiting for a predetermined time, preferably at least 10 seconds, to allow the pressure in the dialyzer (8) to become equal between the dialysis fluid side and the blood side across the semi-permeable filter membrane of the dialyzer (8); The method of claim 3, further comprising: (Item 5) activating a pump (BP) to deliver said fluid; referencing the venous pressure sensor or force sensor (PV) via a force or pressure reference sensor (PDA) at the dialysis fluid outlet; The method according to item 4, further comprising: (Item 6) stopping a pump (BP) delivering said fluid; closing a venous tubing clamp (SAKV) on the venous section (1b) of the tubing (1); referencing the venous pressure sensor or force sensor (PV) via a force or pressure reference sensor (PDE) at the dialysis fluid inlet and / or a force or pressure reference sensor (PDA) at the dialysis fluid outlet; The method according to item 4, further comprising: (Item 7) performing a dialyser-specific referencing to take into account the influence of said dialyser (8) in said referencing; and / or taking into account the pulsation of the pump roller rotor of the fluid carrying pump (BP) in the referencing; and / or taking into account influencing variables that cause an offset deviation of the pressure curve in the referencing; The method according to any one of items 1 to 6, further comprising: (Item 8) A device, comprising: An extracorporeal circulation circuit; A dialysis machine (8); A dialysis fluid circuit / dialysis solution circuit; At least one pressure or force sensor (PA, PBE, PV) arranged in the extracorporeal circuit and integrated into a clamping device (3) and configured to measure the intratube pressure in the fluid-filled tube (1); at least one force or pressure reference sensor (PHOP, PDA, PDE) not designed as a clamping device for referencing the pressure or force signal output by said at least one pressure or force sensor (PA, PBE, PV); Equipped with The device is configured to use at least one dialysis fluid side force or pressure reference sensor (PDA, PDE) for referencing at least one pressure or force sensor (PA, PBE, PV) arranged in the extracorporeal circuit, the force or pressure reference sensor being a force or pressure reference sensor of the dialysis fluid circuit and configured to detect the pressure inside the tube of the dialysis fluid circuit. device. (Item 9) 9. The device according to item 8, characterized in that the extracorporeal circuit is provided with an arterial pressure sensor or force sensor (PA), a dialyzer input pressure sensor or force sensor (PBE), and a venous pressure sensor or force sensor (PV) as pressure or force sensors (PA, PBE, PV) integrated into the clamping device (3). (Item 10) The tube (1) has an arterial section (1a) and a venous section (1b), the arterial pressure sensor or force sensor (PA) and the dialyzer input pressure sensor or force sensor (PBE) are located in the arterial section (1a); The venous pressure sensor or force sensor (PV) is arranged in the venous section (1b), Item 9. The device according to item 9. (Item 11) for referencing a venous pressure sensor or force sensor (PV) which is a pressure sensor or force sensor in the venous section (1b) of the tubing (1) downstream of the dialyzer (8), a dialysis fluid inlet force or pressure reference sensor (PDE) located in the dialysis fluid inlet tube (20); or The device is configured to use a force reference sensor or pressure reference sensor (PDA) on the dialysis fluid outlet side, the force reference sensor or pressure reference sensor (PDA) being disposed on the dialysis fluid outlet tube (22). Item 8. The device according to item 8. (Item 12) 12. The device according to claim 11, characterized in that the dialysis fluid inlet force or pressure reference sensor (PDE) is provided in the dialysis fluid inlet tube (20) between the dialyzer (8) and a first shut-off valve (28) and / or the dialysis fluid outlet force or pressure reference sensor (PDA) is provided in the dialysis fluid outlet tube (22) between the dialyzer (8) and a second shut-off valve (32). (Item 13) 13. The device according to claim 12, characterized in that upstream of the first shut-off valve (28) and downstream of the second shut-off valve (32), the dialysis fluid inlet tube (20) is connected to the dialysis fluid outlet tube (22) via a bypass line (24). (Item 14) a first shutoff valve (28) is provided in the dialysis fluid inlet tube (20) downstream of a first branch point (26) where a bypass line (24) branches off from the dialysis fluid inlet tube (20); a second shutoff valve (32) is provided in the dialysis fluid outlet tube (22) upstream of a second branch point (30) where the bypass line (24) passes into the dialysis fluid outlet tube (22); The third shutoff valve (34) is provided in the bypass line (24), thereby the device is configured to selectively allow dialysis fluid to flow through the dialyzer (8) or the bypass line (24); the dialysis fluid inlet force or pressure reference sensor (PDE) is located in the dialysis fluid inlet tube (20) downstream of the first shutoff valve (28) and upstream of the dialyzer (8); and / or the dialysis fluid outlet force or pressure reference sensor (PDA) is arranged in the dialysis fluid outlet tube (22) downstream of the dialyzer (8) and upstream of the second shutoff valve (32), Item 12. The device according to item 11. (Item 15) A device according to any one of items 8 to 14, characterized in that it is configured to carry out and / or apply a method for referencing a pressure sensor or force sensor (PA, PBE, PV) according to any one of items 1 to 7.

Claims

1. A method for referencing at least one pressure or force sensor (PA, PBE, PV), comprising: said at least one pressure or force sensor is configured to measure intratube pressure in a fluid-filled tube (1) and is located in the extracorporeal circuit and is integrated into or inserted into a clamping device (3); The method comprises: referencing the pressure or force signal output by said 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); using at least one dialysis fluid side force or pressure reference sensor (PDA, PDE) for referencing at least one pressure or force sensor (PA, PBE, PV) arranged in the extracorporeal circuit; Including, said at least one dialysis fluid side force or pressure reference sensor (PDA, PDE) is a force or pressure reference sensor of a dialysis fluid circuit and is configured to detect the pressure in the tube of said dialysis fluid circuit; The method is performed before the tube is connected to a patient, the extracorporeal circuit is provided with an arterial pressure sensor or force sensor (PA), a dialyzer input pressure sensor or force sensor (PBE), and a venous pressure sensor or force sensor (PV) as pressure or force sensors (PA, PBE, PV) integrated into the clamping device (3); method.

2. for referencing a venous pressure or force sensor (PV) located in the venous section of the tubing downstream of the dialyzer (8) of the extracorporeal circuit, using a dialysis fluid inlet force or pressure reference sensor (PDE) located in the dialysis fluid inlet tube (20); or using a dialysis fluid outlet force or pressure reference sensor (PDA) located on the dialysis fluid outlet tube (22); The method of claim 1 further comprising:

3. 3. The method of claim 2, further comprising providing a bypass operation in which dialysis fluid flows through a bypass line (24) without passing through a dialyzer (8) and a main connection operation in which the dialysis fluid flows through the dialyzer (8).

4. switching from the main connection operation to the bypass operation; a step of waiting for a predetermined time so that the pressure inside the dialyzer (8) becomes equal between the dialysis fluid side and the blood side across the semipermeable filter membrane of the dialyzer (8); The method of claim 3 further comprising:

5. activating a pump (BP) to deliver said fluid; referencing the venous pressure sensor or force sensor (PV) via a force or pressure reference sensor (PDA) at the dialysis fluid outlet; The method of claim 4 further comprising:

6. stopping a pump (BP) delivering said fluid; Closing the venous tube clamp (SAKV) of the venous section (1b) of the tube (1); referencing the venous pressure sensor or force sensor (PV) via a force or pressure reference sensor (PDE) at the dialysis fluid inlet and / or a force or pressure reference sensor (PDA) at the dialysis fluid outlet; The method of claim 4 further comprising:

7. and / or performing a dialyser (8) specific referencing to take into account the influence of said dialyser (8) in said referencing; and / or taking into account the pulsation of the pump roller rotor of the fluid carrying pump (BP) in the referencing; and / or taking into account influencing variables that cause an offset deviation of the pressure curve in the referencing; The method of any one of claims 1 to 6, further comprising:

8. A device, comprising: An extracorporeal circulation circuit; A dialysis machine (8); a dialysis fluid circuit; at least one pressure or force sensor (PA, PBE, PV) arranged in the extracorporeal circuit, integrated in a clamping device (3) and configured to measure the intratube pressure in the fluid-filled tube (1); at least one force or pressure reference sensor (PHOP, PDA, PDE) not designed as a clamping device for referencing the pressure or force signal output by said at least one pressure or force sensor (PA, PBE, PV); Equipped with The device is configured to use at least one dialysis fluid side force or pressure reference sensor (PDA, PDE) for referencing at least one pressure or force sensor (PA, PBE, PV) arranged in the extracorporeal circuit, the force or pressure reference sensor being a force or pressure reference sensor of the dialysis fluid circuit and configured to detect the pressure inside the tube of the dialysis fluid circuit; the extracorporeal circuit is provided with an arterial pressure sensor or force sensor (PA), a dialyzer input pressure sensor or force sensor (PBE), and a venous pressure sensor or force sensor (PV) as pressure or force sensors (PA, PBE, PV) integrated into the clamping device (3); device.

9. The tube (1) has an arterial section (1a) and a venous section (1b), said arterial pressure sensor or force sensor (PA) and said dialyzer input pressure sensor or force sensor (PBE) are arranged in said arterial section (1a); characterised in that the venous pressure or force sensor (PV) is arranged in the venous section (1b), The device of claim 8.

10. for referencing a venous pressure sensor or force sensor (PV) which is a pressure sensor or force sensor in the venous section (1b) of the tube (1) downstream of the dialyzer (8), a dialysis fluid inlet force or pressure reference sensor (PDE) located in the dialysis fluid inlet tube (20); or The device is configured to use a force or pressure reference sensor (PDA) on the dialysis fluid outlet side, the force or pressure reference sensor being arranged on the dialysis fluid outlet tube (22), The device of claim 8.

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

12. 12. The device 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 tube (20) is connected to the dialysis fluid outlet tube (22) via a bypass line (24).

13. a first shutoff valve (28) is provided in the dialysis fluid inlet tube (20) downstream of a first branch point (26) where a bypass line (24) branches off from the dialysis fluid inlet tube (20); a second shutoff valve (32) is provided in the dialysis fluid outlet tube (22) upstream of a second branch point (30) where the bypass line (24) passes into the dialysis fluid outlet tube (22); A third shutoff valve (34) is provided in the bypass line (24), the device is configured to selectively allow dialysis fluid to flow through the dialyzer (8) or the bypass line (24); the dialysis fluid inlet force or pressure reference sensor (PDE) is located in the dialysis fluid inlet tube (20) downstream of the first shutoff valve (28) and upstream of the dialyzer (8); and / or the dialysis fluid outlet force or pressure reference sensor (PDA) is arranged in the dialysis fluid outlet tube (22) downstream of the dialyzer (8) and upstream of the second shutoff valve (32), The device of claim 10.

14. A device according to claim 8, characterized in that it is adapted to carry out and / or apply the method for referencing according to claim 1.

Images