Medical device

Abstract

The invention relates to a medical device (1) comprising: an oscillation unit (2) which can be brought into direct or indirect contact with a portion (3) of a liquid line (4), an actuation unit (9) which is designed to excite the oscillation unit (2) to vibrate by applying an electrical voltage, in particular an AC voltage, and an evaluation unit (10) which is designed to determine an impedance of the excited oscillation unit (2) and to determine a gas volume (6) in the portion (3) of the liquid line (4) taking into account the impedance.

Description

[0001] Medical device

[0002] Description

[0003] Technical field

[0004] The present disclosure relates to a medical device that makes it possible to determine a gas volume in a section of a liquid line.

[0005] The purpose of this disclosure is to provide a medical device capable of determining the volume of gas in a section of a liquid line. In particular, the device is intended not only to determine whether gas is present in the liquid line, but also to enable the determination of the volume of gas within the liquid line.

[0006] This problem is solved by the medical device according to claim 1. Advantageous embodiments of the present disclosure are the subject of dependent claims and / or are disclosed in the following description and / or the figures.

[0007] A medical device as disclosed comprises an oscillation unit, a control unit, and an evaluation unit. The oscillation unit can be brought into direct or indirect contact with a section of a fluid line. The control unit is configured to excite the oscillation unit to oscillation by applying an electrical voltage, in particular an alternating voltage. The evaluation unit is configured to determine the impedance of the excited oscillation unit and to determine the gas volume in the section of the fluid line, taking the impedance into account.

[0008] Accordingly, the gas volume in the section of the liquid line is determined based on the impedance of the electrically excited oscillation unit, whose electromechanical behavior is influenced by the gas volume in the section of the liquid line.

[0009] This means that the oscillation unit performs a mechanical oscillation due to electrical excitation and the associated volumetric expansion in at least one spatial direction. Due to the contact, the electromechanical oscillation of the oscillation unit excites the fluid line and consequently also its contents to oscillation. The mechanical properties of the system excited to oscillation, consisting of at least the oscillation unit, the fluid line, and the fluid contents, influence the impedance of the oscillation unit, so that the impedance of the oscillation unit allows conclusions to be drawn about the fluid contents of the fluid line.

[0010] In other words, the gas volume in the section of the fluid line influences the oscillation behavior of the system, which can be considered a spring-mass-damper system. The oscillation behavior of the system affects the impedance of the oscillation unit, which is why the gas volume in the section of the fluid line can be determined from the impedance of the oscillation unit.

[0011] Impedance is an electromechanical impedance, i.e., the electrical impedance of the electromechanically oscillating unit. It is also referred to as AC resistance and can be decomposed into the amplitude ratio of the AC voltage and the AC current, and the phase shift between the AC voltage and the AC current.

[0012] The fluid line can contain a liquid, a liquid with a gas phase, or a gas phase. The proportion of gas to liquid in a given section of the fluid line can therefore be classified by its impedance. The length of the fluid line section is determined by the length of the contact area between the oscillating unit and the fluid line.

[0013] The medical device may preferably be a device for fluid delivery or a device for monitoring, regulating, or controlling the fluid delivery device. The oscillation unit may be directly attached to the fluid line or be at least partially enclosed by a casing. The oscillation unit may also be fixed to a housing section against which the fluid line rests.

[0014] The liquid line is preferably a flexible hose, in particular made of transparent polyvinyl chloride or polyethylene. The diameter of the liquid line can be between 2 mm and 20 mm, preferably between 3 mm and 8 mm, and in particular 4 mm.

[0015] The control unit generates an electrical voltage, preferably a sinusoidal, and in particular frequency-variable, alternating voltage, and applies it to the oscillation unit. For this purpose, the control unit is preferably electrically connected to the oscillation unit, i.e., wired.

[0016] The control unit and the evaluation unit can preferably be combined in the same unit or logic unit.

[0017] Preferably, the evaluation unit can be configured to detect an electric current flowing through the oscillation unit.

[0018] The electrical voltage applied by the control unit causes the electric current to flow through the oscillating unit. This current, or amperage, can be detected by the evaluation unit or a connected measuring unit. Detection can be understood as determining a measured value of the electric current, recording it, and storing it. This allows the control unit to process the measured value of the current flowing through the oscillating element.

[0019] Preferably, the evaluation unit is configured to calculate the impedance of the oscillation unit using a Fourier transform of the applied electrical voltage and the measured electrical current. The Fourier transform can preferably be performed as a discrete Fourier transform (DFT) or a fast Fourier transform (FFT).

[0020] The evaluation unit can detect the electrical voltage applied by the control unit or receive information about the applied electrical voltage from the control unit.

[0021] This allows the impedance of the oscillating element to be assigned to the applied electrical voltage, i.e., in particular to a frequency of the applied alternating voltage.

[0022] Preferably, the control unit is configured to excite the oscillation unit over a predetermined frequency range. The evaluation unit can be configured to detect an amplitude response and / or a phase response of the impedance over the predetermined frequency range. The predetermined frequency range is preferably between 1.7 MHz and 2.1 MHz.

[0023] This means that the control unit can supply the oscillation unit with alternating current of different frequencies within the specified frequency range.

[0024] The amplitude response can represent the amplitude ratio, i.e., the real part, of the complex-valued impedance over the given frequency range. The phase response can represent the argument, i.e., the phase shift, of the complex-valued impedance over the given frequency range.

[0025] The measurement of impedance as a function of the frequency of the excitation of the oscillation unit can be called electromechanical impedance spectroscopy.

[0026] The gas volume in the liquid line section can have varying degrees of influence on the impedance of the oscillation unit depending on the excitation frequency. Since excitation and measurement occur at different frequencies within the specified frequency range, the frequencies relevant to the gas volume being determined can also be evaluated. This allows for a more precise determination of the gas volume in the liquid line section than is possible when evaluating a single frequency.

[0027] It is further advantageous for the evaluation unit to have a memory. This memory can store reference values ​​for the impedance or at least one reference curve for the amplitude response and / or the phase response. The evaluation unit can be configured to determine the gas volume by comparing the determined, i.e., measured, impedance(s) with the reference values, or the amplitude response and / or the phase response with the respective reference curve.

[0028] The reference values ​​can be impedance values ​​for specific frequencies within the specified frequency range.

[0029] The reference curve can be a value curve of the amplitude ratio and / or the phase shift over the specified frequency range.

[0030] The reference values ​​and / or the reference profile can be linked to a state of the contents in the section of the liquid line and / or a value representing the volume of gas present in that section. The state can also be the absence of gas, i.e., a gas volume of 0. The value can, in particular, be a volume measurement. Furthermore, the state and / or the value can be stored in the memory.

[0031] The comparison of the determined (i.e., measured) impedance with the reference values, or the amplitude response and / or phase response with the respective reference curve, can be performed using a correlation coefficient. The correlation coefficient represents a measure of the degree of linear relationship between two interval-scaled characteristics. For this purpose, the determined impedance, its amplitude ratio, or its phase shift is set in relation to the mean of all considered frequencies for each frequency and correlated with the reference value for that frequency from the reference values ​​or the reference curve, which is itself set in relation to the mean of all considered frequencies.A correlation coefficient of 1 can represent a match between the state of the contents in the section of the liquid line and the state associated with the reference values ​​or the reference profile, and / or a match between the gas volume in the section of the liquid line and the value associated with the reference values ​​or the reference profile.

[0032] The gas volume in a section of the liquid pipeline can be determined using the correlation coefficient. This can be done by determining the correlation coefficient with reference values ​​or a reference curve associated with a specific state, particularly the absence of gas in the section of the liquid pipeline and / or with a gas volume of 0. The gas volume in this section can then be determined based on this correlation coefficient. Alternatively, correlation coefficients can be determined for multiple reference values ​​or reference curves associated with different states and / or values. The gas volume can then be determined based on the state or value of the reference values ​​or reference curve whose correlation coefficient is closest to 1.

[0033] This allows the gas volume in the section of the liquid line to be determined based on the course of the specified impedance, i.e., a course of the amplitude response and / or the phase response, over the specified frequency range.

[0034] According to an optional aspect of the disclosure, the control unit is configured to excite the oscillation unit with one or more predefined frequency reference points. The frequency reference points are preferably located between 1.7 MHz and 2.1 MHz. The evaluation unit can be configured to detect the impedance of the one or more predefined frequency reference points. The evaluation unit can include a memory in which reference values ​​for the impedance are stored. The evaluation unit can be configured to determine the gas volume by comparing the determined impedance(s) with the reference values.

[0035] The frequency support points can be individual frequencies at which the impedance of the oscillation unit is influenced by the gas volume in the section of the liquid line. The frequency support points are preferably frequencies at which a change in gas volume leads to a significant change in impedance.

[0036] This allows the gas volume in the section of the liquid line to be determined based on individual excitation frequencies.

[0037] Preferably, the evaluation unit includes a pattern recognition unit configured to determine the gas volume by inputting the specified impedance or amplitude response and / or phase response.

[0038] The pattern recognition unit can detect regularities, repetitions, similarities or laws of the specific impedance or the specific amplitude response and / or the specific phase response.

[0039] This allows the gas volume in the section of the liquid pipeline to be determined using patterns.

[0040] Pattern recognition can be trained offline or statically during a development phase. Furthermore, the pattern recognition unit can be trained adaptively and / or adapted online during operation, during a set change (i.e., a change of the fluid line), or after venting.

[0041] The pattern recognition unit can be combined with a determination of the gas volume, taking into account reference values ​​and / or the reference curve and / or the correlation coefficient. Accordingly, two values ​​for the gas volume are available, which can be averaged, for example, for the purpose of increased robustness. According to an optional aspect of the disclosure, the oscillation unit comprises at least one oscillation element. The oscillation element can, in particular, be a piezoelectric element.

[0042] The oscillating element can be an electromechanical exciter and / or sensor. Materials that undergo a change in length and / or volume when an electrical voltage is applied can be used for this purpose. Piezoelectric elements, such as piezoceramics or piezoelectric crystals, are particularly suitable.

[0043] This allows for a coupling of the electrical excitation and the mechanical vibration behavior.

[0044] Preferably, the oscillation unit has a further oscillation element which can be brought into contact with the fluid line at a predetermined angle to the oscillation element. Preferably, the angle between the oscillation elements can be 90° or 180°.

[0045] This means that the oscillating elements can contact the liquid line from two sides, preferably from two adjacent sides (i.e., in two spatial directions), or from two opposite sides. The control unit can be configured to excite the oscillating elements to oscillation by applying electrical voltages, particularly alternating voltages. The evaluation unit can be configured to determine two impedances of the excited oscillating elements and to determine the gas volume in the section of the liquid line, taking these impedances into account.

[0046] One oscillating element can act as a transmitter, and another as a receiver. Multiple oscillating elements can also perform measurements from two spatial directions. This allows the gas volume to be determined based on a specific transmission between the transmitter and receiver and / or based on measurements from two spatial directions. In particular, this allows the gas volume of gas bubbles that do not fill the entire cross-section of the liquid line to be determined. The determined transmission can be compared with reference values ​​or a reference transmission curve to determine the gas volume. Furthermore, transmission properties such as mechanical structural properties or a complex-valued transfer function as a function of frequency can be determined and evaluated to calculate the gas volume in a section of the liquid line.

[0047] The oscillation unit can have multiple oscillation elements. The control unit can be designed to control the oscillation elements simultaneously or sequentially.

[0048] According to another optional aspect of the disclosure, the one oscillation element or the multiple oscillation elements each have two pairs of electrodes.

[0049] One electrode pair of the oscillating element can act as a transmitter, while the other electrode pair can act as a receiver. Multiple electrode pairs of the oscillating element can also perform measurements from two spatial directions. Furthermore, an oscillating unit with two electrode pairs can be configured to generate complex signal modulation.

[0050] Preferably, the oscillation unit has a reflector which is arranged on a side of the fluid line opposite the oscillation element or elements.

[0051] The reflector can be designed to contact the fluid line. The reflector can be made of a material with a higher density than the material of the casing or housing in which the oscillation unit is at least partially located. This allows the electromechanical oscillation of the oscillation unit, which can be transmitted from the fluid line to the reflector, to be reflected by the reflector. The gas volume in the section of the fluid line can also be determined based on the reflection and / or reflectance of the excited oscillation. The reflection and / or reflectance can be compared with reference values ​​or correlated with a reference curve for reflection and / or reflectance.

[0052] It is further advantageous that the medical device has a receptacle for the fluid line and a flap to secure the fluid line within the receptacle. The oscillation unit can be located in the receptacle and / or in the flap.

[0053] The receptacle can be designed to clamp the fluid line in a form-fitting and / or force-fluid manner in a position where the oscillation unit contacts the fluid line.

[0054] The flap can be designed to allow removal of the fluid line from the receptacle in an open position. The flap can be designed to prevent removal of the fluid line from the receptacle in a closed position.

[0055] This prevents accidental removal of the fluid line from the medical device, particularly due to movement of the fluid line or the medical device.

[0056] The gas volume in the section of the liquid line can be determined with the valve closed.

[0057] Preferably, the medical device is a medical pump or a clamp. The medical pump can, in particular, be an infusion pump. The medical pump can be used to pump fluids. The clamp can be designed to be attached to the fluid line.

[0058] Furthermore, the evaluation unit can be configured to output a signal when a predetermined gas volume or a predetermined total volume of gas pumped is reached. The predetermined gas volume can, for example, be set to 10 pl. The signal can be used to stop the pumping of the liquid. The signal can also be used to issue an audible and / or visual warning via a suitable output device.

[0059] This allows the flow of the liquid to be stopped if a gas bubble of a specified volume or larger is detected in the section of the liquid line. Furthermore, flow can be stopped if the total volume of gas conveyed through the liquid line exceeds a specified value within a given time period or since the start of flow. The total gas volume can be calculated, in particular, by integrating the determined gas volumes in the section of the liquid line, the volume of the liquid line in that section, and a flow rate. The integration can be approximated as the sum of gas volumes per unit time.

[0060] The determination of the gas volume in the section of the liquid pipeline can be carried out repeatedly, especially before and during pumping.

[0061] In addition to the correlation coefficient, the gas volume in the section of the liquid line can be determined by evaluating the determined impedance via integration, normalization or a relative change in impedance, a matrix of reference values ​​or a threshold value.

[0062] Furthermore, a method for measuring gas volume in a section of a liquid pipeline can comprise the following steps: Applying an electrical voltage, in particular a preferably frequency-variable alternating voltage, to an oscillating unit; measuring the electrical voltage and the electrical current flowing through the oscillating unit; determining the impedance of the oscillating unit using a Fourier transform of the measured electrical voltage and current; comparing or correlating the impedance with a reference value; and outputting a result.

[0063] In addition to determining the gas volume in the liquid line section, operating states of the medical device can be determined, such as the absence of liquid flow, the filling of the liquid line with water, the presence of gas bubbles in the liquid line, the opening or closing of the valve, the occurrence of a defect in the oscillating element, a recommendation to replace the oscillating element, microcracks, aging, or contamination. This allows decision values ​​to be provided for further control logic. Furthermore, preventive maintenance can be requested.

[0064] Reference values ​​or profiles can be determined for a known condition within a section of the fluid line. These reference values ​​or profiles can be preset for the medical device or manually trained on it. This can be done during manufacturing, functional testing, and / or maintenance. Furthermore, reference values ​​or profiles can be adaptively adjusted or externally specified via communication.

[0065] Different liquids and / or different fluid lines may require different reference values ​​or reference profiles for determining the gas volume in the fluid line. This may necessitate inputting or specifying a type of liquid and / or fluid line into the medical device. Input can be done manually via a control panel. Alternatively, the medical device may be configured to automatically detect the type of liquid and / or fluid line.

[0066] Brief description of the figures Fig. 1 shows a schematic representation of the medical device according to a first embodiment of the present disclosure;

[0067] Fig. 2 shows a schematic representation of the medical device with a representation of an oscillation element;

[0068] Fig. 3 shows a schematic representation of the medical device with an oscillating element with two electrode pairs;

[0069] Fig. 4 shows a schematic representation of the medical device with a reflector;

[0070] Fig. 5 shows a medical device with two oscillation elements;

[0071] Fig. 6 shows a schematic representation of another embodiment of the medical device in the form of a clamp in a view with a horizontal longitudinal axis of a fluid line;

[0072] Fig. 7 shows a schematic representation of the further embodiment of the medical device in the form of the clamp in a view with the longitudinal axis of the fluid line orthogonal to the plane of the image;

[0073] Fig. 8 shows an isometric view of another embodiment of the medical device in the form of an infusion pump with a gas bubble with a volume of 8 pl;

[0074] Fig. 9 shows the isometric view of the further embodiment of the medical device in the form of the infusion pump with a gas bubble with a volume of 24 pl;

[0075] Fig. 10 shows an amplitude response and a phase response of the electromechanical impedance of the oscillation unit of the medical device; and Fig. 11 shows a table of correlation coefficients.

[0076] Detailed description of embodiments

[0077] Fig. 1 shows a medical device 1 according to the disclosure. The medical device 1 has an oscillation unit 2, which contacts a section 3 of a liquid line 4 from one side. A liquid 5 and a gas bubble 6 are located in the liquid line 4. The gas bubble 6 is located in section 3 of the liquid line 4. The oscillation unit 2 is connected to a logic unit 7 via a transfer line 8. The logic unit 7 has a control unit 9 and an evaluation unit 10. The control unit 9 and the evaluation unit 10 communicate with the oscillation unit 2 via the transfer line 8. The evaluation unit 10 comprises a memory 11 and a pattern recognition unit 12.

[0078] Fig. 2 shows an embodiment of the medical device 1 according to the disclosure from Fig. 1 with an oscillation element 13 present in the oscillation element 13. The oscillation element 13 is formed within the oscillation unit 2. Two electrodes 14a, 14b of an electrode pair 14 are formed on the oscillation element 13, which are connected to the transfer line 8 via electrical lines 15.

[0079] Fig. 3 shows an embodiment of the medical device 1 according to the disclosure from Fig. 1 with the oscillation element 13 formed within the oscillation unit 2. Two pairs of electrodes 14 are formed on the oscillation element 13. Each pair of electrodes 14 has two electrodes 14a, 14b, 14c, 14d, each formed on opposite sides. The two electrodes 14c, 14d of the second electrode pair 14 are each formed on opposite sides adjacent to the sides on which the electrodes 14a, 14b of the first electrode pair 14 are formed. Fig. 4 shows an embodiment of the medical device 1 according to the disclosure from Fig. 2, in which the oscillation unit 2 has a reflector 16. The reflector 16 is arranged on a side of the liquid line 4 opposite the oscillation element 13 and is located at section 3 of the liquid line 4.

[0080] Fig. 5 shows an embodiment of the medical device 1 according to the disclosure from Fig. 2, in which the oscillation unit 2 has two oscillation elements 13. The second oscillation element 13 is formed on a side of the fluid line 4 opposite the first oscillation element 13 and rests against section 3 of the fluid line 4. The two oscillation elements 13 are arranged inside the oscillation unit 2. The unit is C-shaped and extends behind the fluid line 4. The second oscillation element 13 is connected to a separate electrical line 15 and a separate transfer line 8. The transfer lines 8 connect the oscillation unit 2 to the logic unit 7.

[0081] Fig. 6 shows a further embodiment of the medical device 1 according to the disclosure from Fig. 1 in the form of a clamp 17. In the view of Fig. 6, a longitudinal axis of the fluid line 4 lies horizontally in the plane of the image. The logic unit 7 with control unit 9 and evaluation unit 10 with memory 11 and pattern recognition unit 12, as well as the transfer line 8 and the oscillation unit 2, are enclosed by a clamp housing 18. To receive the fluid line 4, the clamp housing 18 has a recess 19. The fluid line 4 rests against the clamp housing 18 along the recess 19. The recess 19 is designed and configured to clamp the fluid line 4 in a form-fitting manner. The oscillation unit 2 rests against the clamp housing 18 on one side opposite the fluid line 4.

[0082] Fig. 7 shows the embodiment of the medical device 1 according to the disclosure from Fig. 1 in the form of the clamp 17. In the view of Fig. 7, the longitudinal axis of the fluid line 4 is orthogonal to the plane of the image. The receptacle 19 has a C-shaped cross-section in this view. The fluid line 4 rests against the clamp housing 18 at a vertex of the receptacle 19. The receptacle 19 is designed and configured to clamp the fluid line 4 positively at the vertex. The oscillation unit 2 rests against the clamp housing 18 on a side opposite the fluid line 4.

[0083] Fig. 8 shows another embodiment of the medical device 1 in the form of an infusion pump 20. The infusion pump 20 has an oscillation unit 2 with two oscillation elements 13, which are partially enclosed by an oscillation housing 22. The fluid line 4 is located between the oscillation elements 13, so that the oscillation elements 13 contact the fluid line 4 on two opposite sides. The oscillation housing 22 forms a receptacle 24 which clamps the fluid line 4 in a form-fitting manner. In section 3 of the fluid line 4, there is a gas bubble 6 with a volume of 8 pl inside the fluid line 4. The remaining part of the fluid line 4 is completely filled with the fluid 5. Inside an infusion pump housing 23 of the infusion pump 20 is the logic unit 7 with the control unit 9 (not shown in Fig. 8) and the control unit 9 (shown in Fig. 8).The evaluation unit 10 (not shown) with memory 11 and pattern recognition unit 12 is integrated into the infusion pump housing 23. These are connected to the oscillation unit 2 by means of the transfer line 8 (not shown in Fig. 8). A hinged flap 21 is mounted on the infusion pump housing 23. When the flap 21 is open, the fluid line 4 can be removed from the infusion pump 20. When the flap 21 is closed, it prevents the fluid line 4 from being removed from the receptacle 24 or from the infusion pump 20. The edges of the oscillation housing 22 and the infusion pump housing 23, which lie behind the transparent fluid line 4, are shown with dashed lines in Fig. 8.

[0084] Fig. 9 shows a further embodiment of the medical device 1 in the form of the infusion pump 20 from Fig. 8. In this illustration, a gas bubble 6 with a volume of 24 pl is present inside the fluid line 4.

[0085] Fig. 10 shows a Bode plot, i.e., a plot of the amplitude response and a plot of the phase response, of the impedance of oscillation unit 2. The two plots show an amplitude ratio in decibels (dB) and a phase shift in radians (rad) over a frequency between 1.4 megahertz (MHz) and 2.1 MHz. Both plots show five curves of the amplitude ratio and the corresponding phase shift. Each curve is associated with a state. Four curves correspond to different states in section 3 of the liquid line 4. The fifth curve represents a comparison measurement of the first curve. The first curve is represented by a solid line (-) and shows the impedance of oscillation unit 2 when section 3 of the liquid line 4 is filled with water.A second curve is shown with a dash-dot-dot-dash line (-■ ■-) and depicts the impedance of oscillation unit 2 when section 3 of liquid line 4 is filled with air. A third curve is shown with a dotted line (■ ■ ■ ■) and depicts the impedance of oscillation unit 2 when section 3 of liquid line 4 is filled with an air bubble with a volume of 8 pl in water. A fourth curve is shown with a dash-dot-dash line (-■-) and depicts the impedance of oscillation unit 2 when section 3 of liquid line 4 is filled with an air bubble with a volume of 24 pl in water. A fifth curve is shown with a dashed line (- -) and again depicts the impedance of oscillation unit 2 when section 3 of liquid line 4 is filled with water. All five amplitude ratio curves exhibit a W-shaped graph.At frequencies below 1.7 MHz and above 2.05 MHz, the curves are tangent to values ​​below 0 dB. Between these values, the curves exhibit three or four local maxima. All five phase shift curves have a W-shaped graph. At frequencies below 1.7 MHz and above 2.05 MHz, the curves are tangent to values ​​of approximately -1 rad. Between these values, the curves exhibit three or four local minima. In the range from 1.7 MHz to 2.05 MHz, the first four curves vary and show a dependence of the resonance behavior on the gas volume in section 4 of the liquid line. The first and fifth curves, i.e., the curves for the states with water, are identical.

[0086] Fig. 11 shows a table with correlation coefficients of the phase response for the different states in section 3 of the liquid line 4 from Fig. 10. The first curve, represented by the solid line (-) in Fig. 10, serves as the reference curve for the correlation coefficient. In this curve, section 3 of the liquid line 4 is filled with water. A second row assigns a correlation coefficient of 1.00 to the curve when section 3 of the liquid line 4 is filled with water. A third row assigns a correlation coefficient of 0.77 to the curve when section 3 of the liquid line 4 is filled with an air bubble with a volume of 8 pl in water. A fourth row assigns a correlation coefficient of 0.69 to the curve when section 3 of the liquid line 4 is filled with an air bubble with a volume of 24 pl in water.A fifth line assigns a correlation coefficient of 0.47 to the curve when section 3 of liquid line 4 is filled with air. Using this correlation coefficient against the reference curve with water, the gas volume of the gas bubble 6 in section 3 of liquid line 4 can thus be determined.

[0087] Reference symbol list

[0088] 1 medical device

[0089] 2 oscillation units

[0090] Section 3

[0091] 4. Liquid line

[0092] 5 Liquid

[0093] 6 Gas bubble

[0094] 7 Logic Unit

[0095] 8 Transfer line

[0096] 9 Control unit

[0097] 10 evaluation units

[0098] 11 storage

[0099] 12 Pattern Recognition Unit

[0100] 13 Oscillating element

[0101] 14 electrode pairs

[0102] 14a, 14b, 14c, 14d Electrode

[0103] 15 Electrical wiring

[0104] 16 Reflector

[0105] 17 terminal

[0106] 18 terminal boxes

[0107] 19th entry

[0108] 20 infusion pumps

[0109] 21

[0110] 22 oscillation housings

[0111] 23 infusion pump housings

[0112] 24 recordings

Claims

Claims 1. Medical device (1) comprising: an oscillation unit (2) which can be brought into contact directly or indirectly with a section (3) of a liquid line (4), a control unit (9) which is configured to excite the oscillation unit (2) to oscillation by applying an electrical voltage, in particular an alternating voltage, and an evaluation unit (10) which is configured to determine an impedance of the excited oscillation unit (2) and to determine a gas volume (6) in the section (3) of the liquid line (4) taking into account the impedance.

2. Medical device (1 ) according to claim 1 , characterized in that the evaluation unit (10) is configured to detect an electric current flowing through the oscillation unit (2).

3. Medical device (1 ) according to claim 2, characterized in that the evaluation unit (10) is configured to calculate the impedance of the oscillation unit (2) using a Fourier transform of the applied electrical voltage and the detected electrical current.

4. Medical device (1) according to one of claims 1 to 3, characterized in that the control unit (9) is configured to excite the oscillation unit (2) over a predetermined frequency range, preferably 1.7 MHz to 2.1 MHz, and the evaluation unit (10) is configured to detect an amplitude response and / or a phase response of the impedance over the predetermined frequency range.

5. Medical device (1) according to claim 4, characterized in that the evaluation unit (10) has a memory (11) in which Reference values ​​for the impedance or at least one reference curve for the amplitude response and / or the phase response are stored, and the evaluation unit (10) is designed to determine the gas volume (6) by comparing the determined impedance with the reference values ​​or the amplitude response and / or the phase response with the respective reference curve.

6. Medical device (1) according to one of claims 1 to 3, characterized in that the control unit (9) is configured to excite the oscillation unit (2) with one or more predetermined frequency reference points, preferably between 1.7 MHz and 2.1 MHz, the evaluation unit (10) is configured to detect the impedance of the one or more predetermined frequency reference points, and the evaluation unit (10) has a memory (11) in which reference values ​​for the impedance are stored, and is configured to determine the gas volume (6) by comparing the determined impedance(s) with the reference values.

7. Medical device (1 ) according to one of claims 1 to 6, characterized in that the evaluation unit (10) has a pattern recognition unit (12) which is configured to determine the gas volume (6) by inputting the specified impedance or amplitude response and / or phase response.

8. Medical device (1) according to one of claims 1 to 7, characterized in that the oscillation unit (2) comprises at least one oscillation element (13), in particular a piezoelectric element.

9. Medical device (1) according to claim 8, characterized in that the oscillation unit (2) has a further oscillation element (13) which can be brought into contact with the fluid line (4) at a predetermined angle, preferably 90° or 180°, offset from the oscillation element (13).

10. Medical device (1) according to claim 8 or 9, characterized in that the oscillation element(s) (13) has two electrode pairs (14).

11. Medical device (1) according to claim 8 or 9, characterized in that the oscillation unit (2) has a reflector (16) which is arranged on a side of the fluid line (4) opposite the oscillation element(s) (13).

12. Medical device (1) according to any one of claims 1 to 11, characterized by a receptacle (24) for the fluid line (4) and a flap (21) for securing the fluid line (4) in the receptacle (24), wherein the oscillation unit (2) is arranged in the receptacle (24) and / or in the flap (21).

13. Medical device (1) according to one of claims 1 to 12, characterized in that this is a medical pump, in particular an infusion pump (20), or a clamp (17).

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