Measurement device and measurement method for determining at least one respiration parameter

Abstract

To provide a measurement device and a measurement method for determining at least one respiration parameter that do not restrict mobility.SOLUTION: An AC electromagnetic field is emitted to a body and is received in an opposite side of the body, a phase of the received AC electromagnetic field is compared with a phase of the emitted AC electromagnetic field, as a function of time, and at least one respiration parameter is determined from a result of the comparison.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a measurement device and method for determining at least one respiratory parameter, whereby an electromagnetic field is irradiated onto a body and received on the opposite side of the body, the phase of the received alternating field is then compared to the phase of the irradiated alternating field as a function of time, and at least one respiratory parameter is determined from the results of the comparison. [Background technology]

[0002] Respiratory monitoring has many practical applications. For example, the measurement of respiratory activity in specific situations or during exercise plays a central role in many scientific tests. Such tests provide a better understanding of respiratory behavior as a function of external influences.

[0003] Respiration monitoring is also important for mechanical ventilation of patients, where, for example, replacing spontaneous breathing with artificial respiration should be avoided.

[0004] Most established methods combine electrocardiogram (ECG) and impedance cardiography (ICG) to estimate the cardiac component, subtract it from the impedance signal, and obtain the respiratory component from the resulting signal. The detection of respiratory parameters is derived indirectly through the estimation of the cardiac component and therefore necessarily depends on the quality of the cardiac model. Moreover, mainly the respiratory frequency is determined in the process. It is not possible to provide direct information on tidal volume and spontaneous breathing.

[0005] Another method is to measure chest and abdominal expansion using respiratory inductive plethysmography (RIP). Here, two elastic bands are placed around the patient's chest and abdomen. Coils are incorporated into the bands and change inductance as the bands expand. This method can appear uncomfortable and restrictive for the patient due to the elastic bands. A similar method can be considered using strain gauges, but it does not offer any additional advantages. Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to provide a measuring device and a method for determining at least one respiratory parameter which, although making it possible to determine the corresponding parameter, is comfortable to wear and does not restrict the mobility of the wearer. [Means for solving the problem]

[0007] This object is achieved by a measuring device for determining at least one respiratory parameter according to claim 1, a method for measuring at least one respiratory parameter according to claims 10 and 12, a respiratory apparatus according to claim 24, a device for injecting a contrast agent according to claim 25 and a device for imaging according to claim 26. The respective dependent claims provide advantageous embodiments of the measuring device according to the invention and the method according to the invention.

[0008] According to the invention, a measuring device for determining at least one respiratory parameter is provided. The measuring device comprises at least one transmitting structure and at least one receiving structure. Advantageously, the at least one transmitting structure may be an antenna or an electrode. Preferably, the at least one receiving structure is an antenna or an electrode.

[0009] The at least one transmitting structure and / or the at least one receiving structure are preferably designed to be attachable externally to a human, animal or phantom body. The transmitting structure and / or the receiving structure can for example be designed to be adhesive. A conductive contact between the transmitting structure and / or the receiving structure and the body may be advantageous but is not necessary.

[0010] The measuring device according to the invention includes at least one signal generator electrically coupled to at least one transmitting structure. An AC voltage that can be applied to the transmitting structure can be generated by the signal generator. In this way, an alternating electromagnetic field can be generated by the transmitting structure.

[0011] In an advantageous embodiment of the invention, the antennas of the receiving and transmitting structures are arranged so as to be interleaved in the near field. The antennas of the transmitting structure are then coupled to the corresponding antennas of the receiving structure in the sense that a coupling impedance is formed between the antennas. This impedance Z 12 can be expressed as follows for the example of two dipoles acting as transmitting and receiving antennas:

number

[0012] In this process, permittivity terms dominate and the antennas are closer in relation to the wavelength (H. Wheeler, “The Radiansphere around a Small Antenna,” Proc. IRE, vol. 47, no. 8, pp. 1325-1331, 1959). Therefore, if the measurement is based on detecting the change in permittivity, it is advantageous to have the wavelength λ as large as possible, for example to make the ratio of r (the distance between the antennas) to λ (the wavelength) as small as possible. Advantageously, an optimal wavelength (or frequency) is selected, which is small enough to see a clear shift in the phase between inspiration and expiration with respect to the body, but large enough to still obtain significant coupling in the above sense. However, the invention can also be implemented when the antennas are not placed in the near field, i.e. are not coupled in the above sense.

[0013] When antennas are arranged in the near field of each other, it is advantageous if the distance between the antennas is less than or equal to four wavelengths λ, advantageously less than or equal to three wavelengths λ, advantageously less than or equal to two wavelengths λ. Optionally, the IEEE definition of the near field may be used as a basis, where the outer boundary is defined as the distance λ / (2π) from the antenna surface, where λ is the wavelength in free space (see IEEE Standard for Terms for Antennas, IEEE Std 145-2013). Therefore, it is advantageous if the distance between the antennas of an antenna pair is less than or equal to λ / (2π).

[0014] The coupled system of transmitting and receiving structures advantageously operates at the resonant frequency of the transmitting antenna and / or at the resonant frequency created in the transmitting antenna by the receiving antenna.

[0015] It is advantageous if the transmitting and receiving antennas each form a shared resonance by coupling in the above sense. The quality of the resonance can be particularly advantageously adapted or changed to suit the specific application. In the process, a high quality leads to a high sensitivity with a smaller dynamic range. Correspondingly, a low quality leads to a low sensitivity with a larger dynamic range. Here, the dynamics is defined as the measurement range that can be unambiguously assigned to the phase offset [0...2π]. If the phase offset exceeds 2π, the phase offset no longer unambiguously corresponds to the distance between the antennas. This is not necessarily a problem, since it is also possible to identify the distance between the antennas based on the progression of the phase offset. However, it is advantageous to select the wavelength so that it does not exceed the range from 0 to 2π when the breath passes through the full amplitude.

[0016] For example, a high quality may be suitable for use with newborns or premature infants, since the volume range that must be measured is small except at high resolution, whereas a low quality may be suitable for use with adults, since a large volume range must be measured, but a low resolution is sufficient.

[0017] In an advantageous embodiment of the invention, the transmitting antenna and / or the receiving antenna can have a meander-shaped configuration. The antenna can be applied particularly advantageously to a substrate with a high permittivity. In this way, the electrical length of the antenna is increased compared to its mathematical or geometrical length.

[0018] It is also advantageously possible to use ceramic antennas as transmitting and / or receiving antennas, in which case the waves run on the ceramic. It is also possible to use patch antennas.

[0019] This results in a clearer measurement range for the antenna pair and less interference from high permittivity bodies (such as arms and hands) entering the near field of the antenna from the outside. Such directional characteristics can be achieved, for example, by a grounded surface behind the antenna, i.e. distal to the body. Alternatively or additionally, antenna topologies with non-unipolar radiation characteristics can be used. Advantageously, it is also possible to introduce a low-permittivity body behind the antenna, i.e. distal to the body. Another option is to place an absorber material distal to the body.

[0020] In an advantageous embodiment, the antennas can be differentially contacted: for this purpose, the antennas can be contacted, for example, with a twisted conductor pair, which has two currents, the two currents being phase shifted by 180°.

[0021] The antennas may generally be located away from the body, in particular a dielectric or insulating material may be present between the antennas and the body, in particular in special cases air may be present between the antennas and the body.

[0022] In any embodiment, at least one of the transmitting and / or receiving antennas may be located on a surface, such as a support surface for the patient or a side element of a patient bed.

[0023] In an advantageous embodiment of the invention, the transmitting structure can be identical to the receiving structure. In this case, there is one structure, for example one antenna, which functions as transmitting and receiving structure. This can make use of the fact that the resonant frequency of the antenna changes as a result of the change in the dielectric constant of the body. This change can be determined as a signal. For example, a frequency that varies with time can be applied to the antenna and it can be determined in each case what frequency resonance is present. From this resonance, the respiratory parameter can be determined. Alternatively, it is also possible to apply a frequency at which a resonance is present at a certain distance in the respiration process and determine the change in resonance or the phase over time. The respiratory parameter can then be determined. In particular, it is advantageous to use an antenna with directional characteristics as described above to irradiate only within the body to be measured.

[0024] Advantageously, two insulated conductors can be arranged around the patient's chest, for example as circumferential conductors. In this process, one conductor is guided, for example ventrally across the chest region and one conductor is guided, for example dorsally across the back region. The patient's chest can thus be arranged like a dielectric between the conductor pair. Breathing changes the dielectric constant of the chest and with it the propagation time of the electromagnetic waves guided by the conductors through the chest. This can be detected as a change in phase over time. It is advantageous in the process to apply the conductor pair differentially, i.e. a voltage rises in one conductor and a voltage falls to the same extent in the second conductor, and is reversed as soon as the polarity of the alternating electromagnetic field is reversed. Furthermore, it is advantageous to shield the conductors on one side in order to reduce external disturbances.

[0025] In an advantageous embodiment, it is also possible to provide information regarding respiration (inhalation or exhalation) via the attenuation of the waves, both transmitted (S21 parameter) and reflected (S11 parameter). In addition to the phase information, the attenuation can be measured as an additional parameter supporting the determination of the respiratory parameters, or the attenuation can be detected independently by the device according to the invention and used for the determination of at least one respiratory parameter.

[0026] The measuring device of the invention also comprises a comparison unit capable of comparing the phase of the signal provided by the receiving structure with the phase of the alternating voltage applied to the transmitting structure. The fact that the receiving structure provides a signal can be understood to mean that the receiving structure generates the signal, but the receiving structure does not have to be an active element. It can also be understood to mean that the signal is received from the receiving structure in the sense that the signal originates from and is received by the receiving structure. The comparison unit can be electrically coupled to the receiving structure for this purpose. Advantageously, a comparison of the phase between the signals received from at least two receiving structures is possible.

[0027] According to the invention, the measuring device further comprises an evaluation unit capable of determining at least one respiratory parameter from the result of a comparison of the phase of the signal received from the receiving structure with the phase of the alternating voltage and / or the phase of the alternating electromagnetic field generated by the transmitting structure.

[0028] The measuring device is preferably configured to carry out the method according to the invention for measuring at least one respiratory parameter. In this method, an alternating electromagnetic field is irradiated into the body, for example of a human, animal or dummy, via at least one transmitting structure, where an alternating voltage is generated by a signal generator that is applied to the at least one transmitting structure. The alternating electromagnetic field irradiated into the body is received by at least one receiving structure, preferably on the opposite side of the body, after passing through the body. In this process, the opposite side can preferably be any side located opposite to the side where the alternating electromagnetic field is irradiated, with respect to the axis of the body. In the comparison step, the phase of the signal received from the at least one receiving structure is compared with the phase of the AC voltage as a function of time, and from the result of this comparison, at least one respiratory parameter is determined. Optionally, it is also possible to arrange the transmitting or receiving structure on the left side of the chest, and correspondingly to arrange the receiving or transmitting structure on the left side of the abdomen, and correspondingly to arrange the receiving or transmitting structure on the right side of the abdomen, so that the signal passes through the lungs and the diaphragm.

[0029] The transmitting structure may advantageously be connected to the signal generator via a cable. In this case, the phase of the alternating voltage is preferably measured at a resistor through which the cable is fed. Similarly, the receiving structure may be connected to the comparing unit via a cable. It is then advantageously possible to measure the phase of the signal received from the receiving structure at a terminator, advantageously connected between the comparing unit and a reference potential. Advantageously, the phase of the output of the signal generator, or a reference defined therefor, or a time-constant reference, is compared with the phase of the receiving input of the comparing unit, or a reference defined therefor, or a time-constant reference.

[0030] The fact that the phase of the signal received from the receiving structure is compared with the phase of the AC voltage or with the phase of the irradiated alternating electromagnetic field preferably means that the difference between these phases is found.

[0031] In particular, in the process, it is preferred that this phase difference between the phase of the received signal and the phase of the AC voltage or illumination signal can be determined as a function of time. This phase difference is therefore preferably determined for several different points in time, and the respiratory parameters are then determined from the time progression of the phase difference.

[0032] Advantageously, the propagation time of the electromagnetic waves through the body can be inferred from a comparison of the phase of the alternating voltage with the phase of the received signal, and such propagation time is preferably determined as a function of time, such that at least one respiratory parameter can be ascertained from the chronological progression of the propagation time.

[0033] The phase or propagation time corresponds to the instantaneous expansion of the body between the transmitting and receiving structures and, optionally, to the change in the dielectric properties of the volume between the transmitting and receiving structures. The alternating electromagnetic field is preferably irradiated to the chest and / or abdomen of the body via at least one transmitting structure. For this purpose, at least one transmitting structure can be attached to the chest or abdomen. The alternating electromagnetic field is then preferably received by at least one receiving structure on the opposite side of the chest and / or abdomen. In this process, it is particularly preferred that the transmitting and receiving structures are attached laterally in the abdomen and / or chest, so that the electromagnetic waves pass laterally through the body.

[0034] In this case, the phase or the propagation time corresponds to the instantaneous expansion of the lungs (including the diaphragm, the costal arches, etc.). If the expansion of the lungs changes due to breathing, then the phase difference or the propagation time also changes. The change in the phase difference or the propagation time is due, on the one hand, to the expansion of the body or chest during inspiration and, on the other hand, to the change in the dielectric properties of the body area through which the electromagnetic wave passes. On the one hand, the tissues and organs of the body move and, on the other hand, the amount of air in the lungs changes, which changes the electrical properties.

[0035] Advantageously, the breathing depth of the person, animal or phantom can be derived, for example, via the phase deviation, i.e. the difference between the minimum and maximum phase difference in a selected time window, in which case the at least one breathing parameter can be the volume of a breath of air of the person, animal or dummy.

[0036] In an advantageous embodiment of the invention, the irradiated alternating electromagnetic field or the alternating voltage applied to the transmitting structure may be generated at a variable and / or changing frequency. At least one respiratory parameter may then be advantageously determined at one of a number of frequencies at which the coupling between the irradiated and the received alternating electromagnetic field or between the transmitting structure and the receiving structure is maximum and / or the amplitude of the received alternating electromagnetic field or the signal received from the receiving structure is maximum. It is also possible to select a frequency for the determination of the respiratory parameter at which the maximum change is the phase difference between the phase of the signal received from the receiving structure and the phase of the AC voltage over the respiratory cycle. In this way, an optimal measuring frequency can be ascertained. The optimal measuring frequency may be different for different persons, animals or phantoms, depending in particular on the size of the body.

[0037] Advantageously, it is also possible to measure simultaneously at multiple frequencies and compare the values ​​of at least one respiratory parameter determined at different frequencies with one another or offset them with one another, for example by averaging. It is also possible to transmit the multiple frequencies successively at short intervals in time, or to transmit the multiple frequencies simultaneously in frequency division multiplexing, and to use each measurement frequency for a plausibility check, for example the assessment of the temporal gradients. This plausibility check can be used, inter alia, to eliminate movement artefacts from the measuring series. It is also possible to use the different measurement frequencies by adaptive filtering techniques, correlation filters or methods of machine learning to improve the signal quality.

[0038] In an advantageous embodiment of the invention, at least one transmitting structure may be connected to the signal generator via a first cable. In this process, the first cable preferably has a predetermined wave impedance. The transmitting structure is then preferably fed via a first resistor, the value of which is equal to the wave impedance of the first cable. At least one receiving structure is advantageously connected to the comparison unit via a second cable, the second cable preferably has a predetermined wave impedance. The receiving structure is then preferably terminated via a second resistor, the value of which is equal to the wave impedance of the second cable. For example, the first and second resistors, together with the wave impedances of the first and second cables, may be 50 ohms. Optionally, the wave impedance of the transmitting structure may also be equal to the wave impedance of the cable. The same is preferably true for the wave impedance of the receiving structure.

[0039] Advantageously, the AC voltage and / or the irradiated alternating electromagnetic field is generated at a frequency of 10 MHz or more, preferably 30 MHz or more, preferably 100 MHz or more, and / or 1000 MHz or less, preferably 500 MHz or less, preferably 300 MHz or less.

[0040] In an advantageous embodiment of the invention, two, three, four or more transmitting structures can be provided and / or two, three, four or more receiving structures can be provided, which allows more accurate measurement results to be obtained. If multiple transmitting structures and multiple receiving structures are used, time division multiplexing of all transmitting structures can find the optimal transmitting structure-receiving structure pairing.

[0041] In case one transmission structure and multiple reception structures are provided, multiple results confirmed by multiple signals of different reception structures can be used to check the validity of the results. For example, if the gradient is very high in all reception structures, it means that the measured body is moving. In this case, the measurements can be discarded. Also, in case of multiple transmission structures, such a validity check can be performed in a time division multiplexing process. It is also possible to take into account the time offset of the different reception signals if the temporal resolution of the determination of the phase difference is selected high enough. A rapid change in the temporal relationship of the individual measurements may also indicate body movement. Furthermore, it is also possible to use the different reception signals by adaptive filtering techniques, correlation filters or machine learning methods to improve the signal quality.

[0042] The combination of two transmission structures with two reception structures, one transmission structure with three reception structures, and one transmission structure with two reception structures have proven to be particularly advantageous. For example, when using two transmission structures and two reception structures, multiplexing between the same pair can be advantageous. One transmission structure and multiple reception structures are particularly advantageous for the above-mentioned plausibility check, since the signals of different reception structures can be compared with each other.

[0043] In an advantageous embodiment of the invention, it is possible to determine whether inspiration or expiration is occurring as a respiratory parameter. For this purpose, the gradient of the phase difference between the phase of the received signal and the phase of the irradiated alternating electromagnetic field can be determined, for example, as the time derivative of the phase difference. The sign of the gradient indicates whether inspiration or expiration is occurring. The determination of sequences of local minima in the phase difference and local maxima in the phase difference can also be used to determine whether inspiration or expiration is present. For example, if a local maximum follows a local minimum, it can be determined that inspiration is present. If a local minimum follows a local maximum, it can be determined that expiration is present. This exemplary determination can be performed analogously in similar examples for other reference directions, for example also depending on the number of wavelengths that are fitted in the body. For example, the start of inspiration or expiration can be determined by forming the derivative of the phase difference with respect to time, by averaging, correlation, etc. of the rising or falling edges.

[0044] The respiratory frequency can be determined as a respiratory parameter. It can be determined, for example, from the time interval between two maximum phase differences or between two minimum phase differences, the respiratory frequency being the reciprocal of the time interval. Similarly, it is possible to determine the time interval between the minimum / maximum phase difference and the maximum / minimum phase difference. In this process, the time interval corresponds to the duration of a particular respiratory phase. It is also possible to determine the respiratory frequency from the time signal by Fourier transformation. All that is required here is to ascertain the rate with the maximum absolute value from the spectrum determined by Fourier transformation.

[0045] The tidal volume can also be determined as a respiratory parameter. The tidal volume correlates with the difference between the local minimum and maximum of the phase difference. In the simplest case, it can be assumed that the correlation between this difference and the tidal volume is linear. For a more accurate determination, the function between the tidal volume and the aforementioned difference can be analytically approximated or experimentally measured.

[0046] In an advantageous embodiment of the invention, the method according to the invention can be used to control a mechanical ventilation. The mechanical ventilation produces a regular breathing cycle, which means that the difference between the phase of the emitted and the phase of the received alternating electromagnetic field progresses regularly. When the person receiving the ventilation performs spontaneous breathing, this regular breathing cycle is interrupted in a characteristic way. The method according to the invention can then be advantageously used to send a signal to the breathing device to start inhalation or exhalation. The breathing device can then advantageously start to support inhalation (air supply) or exhalation (interruption of mechanical ventilation) so as to support the person and not provide ventilation contrary to spontaneous breathing. The different received signals can be taken into account in the calculations, for example by adaptive filtering techniques, correlation filters or machine learning methods.

[0047] The method or the device of the invention can also be used in devices that inject contrast agents (e.g. CT / MRI / Ultrasound) in order to optimally adapt the injection of contrast agent to breathing, in which the injection can advantageously be performed when the patient is just starting to exhale, or when the patient is starting to inhale, or when the patient is holding his breath.

[0048] The method according to the invention or the device according to the invention can also be used for imaging such as CT, X-ray, CBCT, MRI, ultrasound etc. to record respiratory parameters (e.g. inspiration, expiration, instantaneous chest and / or abdominal expansion) during image capture. In this way, for example, fusion of different partial images can be optimized to the effect that in the scanning imaging process, only partial images having the same respiratory parameters are combined to form a total image, or partial images are recorded only when the respiratory parameters are appropriate (e.g., only at the end of expiration, end of inspiration, or in defined states), or the temporal progression of the respiratory parameters during recording of the partial images and / or the total image is used to modify the image data or for combined evaluation.

[0049] In an advantageous embodiment of the invention, the alternating electromagnetic field can be applied, preferably successively in time, using a number of different frequencies, and it is then preferably possible to determine at least one respiratory parameter from a comparison of the phase of the received alternating electromagnetic field with the phase of the applied alternating electromagnetic field, the results thus obtained being compared with each other and / or offset with each other in order to obtain a final value of the particular respiratory parameter.

[0050] In an advantageous embodiment of the invention, the temporal change in the difference between the phase of the received and the phase of the applied alternating electromagnetic field can be represented as a function of time, for example in a graphical display, so that the change in at least one respiratory parameter over time can be observed. In this way, for example, long-term tests can be performed (for example, trends can be monitored) and direct feedback can be communicated.

[0051] The AC voltage is preferably applied to the transmitting structure such that the current potentially flowing through the body is below the permissible patient auxiliary current, for example below 100 μA.

[0052] In an advantageous embodiment of the invention, at least one further electrode and / or at least one further measurement frequency can be used and evaluated in order to determine and remove at least one disturbance variable, such as the influence of the heartbeat and / or body movements, from the calculation of the respiratory parameter. In this way, the influence of the heartbeat can be extracted from the signal, for example, by means of a scaled Fourier linear combiner or by means of other adaptive filtering techniques. Advantageously, it is also possible to remove at least one disturbance variable from the calculation of the at least one respiratory parameter determined in the above manner, for example by means of a frequency filter, an adaptive filter, a correlation filter and / or a smoothing filter and / or a differentiation of the signal. Other smoothing methods can be used, such as, for example, a moving average or Savitzky-Golay.

[0053] The measured signal can also be correlated with other measurement signals, such as instantaneous respiratory state (inhalation, exhalation), pressure and / or flow values, provided or measured by the respiratory device or its surroundings.

[0054] The method according to the invention can in many advantageous embodiments be implemented as a non-diagnostic method. For example, it can be used to scientifically understand the respiratory behavior. For this purpose, the respiratory behavior or at least one respiratory parameter can be monitored by the method according to the invention while a test subject performs a specific task or is exposed to a specific stress. In an advantageous application of the method according to the invention, the body can be a phantom body, as used for example for breathing exercises during first aid classes or crash tests. By using the method according to the invention, the influence of respiratory activity and of externally acting forces on such a body can be investigated.

[0055] According to the invention there is further provided a breathing apparatus adapted to carry out the method described above and to control breathing on the basis of at least one breathing parameter, such a breathing apparatus can for example also be used during diving. [Brief description of the drawings]

[0056] [Figure 1] The basic design of the measurement device of the present invention is shown in a block diagram. [Diagram 2] 4 shows curves of the phase of the received signal at different measurement frequencies. [Diagram 3] The phase deviation for different respiratory rates is shown. [Figure 4] As an example, a determination of the phase difference between the emitted and received signals is shown, as well as an exemplary determination of a respiratory parameter. [Diagram 5] The phase difference between unobstructed and obstructed breathing is shown. [Figure 6] 1 shows a meandering antenna structure. [Figure 7] The antenna structure shown in FIG. 6 is shown in side view. [Figure 8] 1 shows an embodiment of a transmitting and receiving structure in the form of a circumferential conductor. [Figure 9] 1 illustrates an embodiment of a transmitting structure and a receiving structure positioned away from a patient. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] The invention will now be described by way of example only with reference to several figures, in which the same reference numbers indicate the same or corresponding features, and in which the features described in the embodiments can also be implemented independently of the specific embodiments and can be combined between the embodiments.

[0058] FIG. 1 shows an example design of a measuring device according to the invention in the form of a block diagram. Respiratory parameters are determined in the process by irradiating an alternating electromagnetic field through the body 1. The alternating electromagnetic field is irradiated into the body 1 by a transmitting structure 2, which may be for example an antenna or an electrode, and is received by a receiving structure 3, which may also be an antenna or an electrode. To generate the irradiated signal, an AC voltage, here supplied via a cable (for example a coaxial cable), is applied to the transmitting electrode 2. Such a cable may have a defined wave impedance. In the process, the AC voltage is amplified by a transmitting amplifier 4 with a terminating resistance, the value of which is preferably equal to the wave impedance of the cable, via which the transmitting electrode 2 is connected to the transmitting amplifier 4.

[0059] An AC voltage is supplied to the transmission amplifier 4 via an oscillator 5, which generates an AC voltage with a defined frequency and phase. For this purpose, the oscillator 5 is controlled by a control unit 6, which may be controlled by a suitable interface, for example a human-machine interface or a machine-to-machine interface.

[0060] The alternating field emitted from the transmitting electrode 2 into the body 1 is received by a receiving structure 3, which is connected, for example, via a coaxial cable, to a receiving amplifier 8 having a termination resistance. The absolute value of the termination resistance is preferably equal to the wave impedance of the cable, via which the receiving amplifier 8 is connected to the receiving electrode 3. The receiving amplifier 8 is connected to a phase detector 9, which can measure the phase of the signal received by the receiving structure 3 and amplified by the receiving amplifier 8. The phase detector 9 is further connected to an oscillator 5, which generates the transmission signal. The phase detector 9 receives information from the oscillator 5 about the phase of the emitted signal. The phase detector 9 can thereby compare the phase of the emitted signal with the phase of the detected signal and determine, for example, the phase difference between these signals. It is particularly preferred that this phase difference is determined as a function of time, i.e. for at least two or more time points. The phase detector 9 can then send the preferably time-dependent phase difference to an evaluation unit 10, which determines at least one respiratory parameter from the phase difference. The evaluation unit 10 can for this purpose carry out suitable calculation or correction steps, such as averaging, differentiation, determination of minimum and maximum values, adaptive filtering, correlation filtering and frequency filtering, etc. The evaluation unit 10 can then pass the ascertained results, i.e. the respiratory parameters, to an interface 7, which is accessible to a person or a machine, such as a respiratory device.

[0061] FIG. 2 shows the time course curves of the phase during natural breathing at three different measurement frequencies, represented by dotted, dashed and solid lines. The dashed lines show the measurements at twice the frequency of the dotted lines, and the solid lines show the measurements at three times the frequency of the dotted lines. It is clear that the measurements at three times the frequency of the dotted lines show the largest phase deviation and are therefore the most suitable measurement frequency.

[0062] Figure 3 shows the phase deviation for different breathing volumes. The phase deviation is plotted on the vertical axis and the breathing volume is plotted against the reference volume on the horizontal axis. It is clear that there is an approximately proportional relationship between breathing volume and phase shift. The higher the breathing volume, the larger the phase shift.

[0063] Fig. 4 shows, as an example, how to determine the progression of the breathing volume from the transmitted and received signals. The time curves of the transmitted signal (high amplitude) and the received signal (low amplitude) are plotted in part (A) of Fig. 4. Between the transmitted and received signals there exists a phase offset Phi. The phase offset Phi is the time difference between the same phases, such as the maximum or minimum, of the transmitted and received signals multiplied by the angular frequency.

[0064] This phase offset Phi, also called the phase difference, is plotted against time in seconds in part (B) of FIG. 4. A progression of the phase offset is obtained, as shown by the dotted line. As shown here as an example, the phase offset increases during inspiration. During expiration the phase offset decreases. The reciprocal of the distance between adjacent maxima or minima is the respiratory frequency.

[0065] Figure 4(C) shows the chronological progression of the phase offset or phase difference, where ΔPhi is plotted, which is the difference between the maximum and minimum phase offsets Phi plotted in Figure 4(B). Since the respiration rate increases with time, ΔPhi increases with time.

[0066] Fig. 5 shows a time curve of the phase measured with the method according to the invention, with portions of unobstructed and obstructed breathing. In the portion marked 51, the obstructed phase string can be seen. The phase deviation, i.e. the difference between the maximum and minimum phase difference, during obstructed breathing is much smaller than for unobstructed breathing. In this way, the method according to the invention can be used to identify obstructions. Furthermore, laboured breathing during the obstruction is also evident, which can be used, for example, to control mechanical ventilation.

[0067] 6 shows an example of an antenna structure 2 arranged on a substrate 61, which may have a high dielectric constant, allowing the electrical length of the antenna to be long compared to its geometric length. Here, the antenna is designed as a dipole antenna, with a short mechanical width compared to the electrical length (i.e. the length of the conductors 2a, 2b) by arranging the dipole arms 2a, 2b in a meander-shaped manner.

[0068] Figure 7 is a side view of one embodiment of the antenna shown in Figure 6, viewed in a direction parallel to the surface of the substrate 61. In this example, the antenna 2 is disposed on the substrate 61, which is disposed on a ground plane 72 on the opposite side of the antenna 2. The ground 72 can shield the antenna 2 from rear-side disturbances.

[0069] 8 shows an exemplary embodiment in which two insulated conductors 81a, 81b functioning as antennas are placed around the chest of a patient 82. In the process, one conductor 81a is guided ventrally, for example across the chest region, and one conductor 81b is guided dorsally, for example across the back region.

[0070] Here, a transmitting structure 83 as a differential design with terminals A and B that can be activated in phase opposition, with a ventral conductor 81a and a dorsal conductor 81b, and a receiving structure 84 (also different), are shown, where a voltage can be applied between terminals A and B. Measuring, for example, the impedance, makes it possible to infer changes in the body of a person 82.

[0071] Figure 9 shows an arrangement in which the transmitting antenna 2 and the receiving antenna 3 are placed away from the body of a person 91. Here, an alternating field 92 is emitted from the transmitting structure 83 and a respiration modulated field 93 is received by the receiving structure 84. The antennas are placed away from the body of the person 91. The alternating fields 92, 93 therefore pass through a region in the air.

[0072] The method according to the invention is advantageous compared to conventional methods, since the measurement can be performed directly and does not require any adjustment of the signal for the cardiac component. However, the cardiac component may be taken into account so as to increase the signal quality. Furthermore, since no determination of the conductivity is involved, artefacts and drifts of the measurement signal resulting from changes in the conductivity of the electrodes or the skin can be minimized. Furthermore, the method according to the invention has very low movement artefacts, which would occur if only the amplitude were considered. The wearing comfort of the user is considerably higher, since fewer electrodes and / or antennas are worn compared to a band around the chest. It is also possible to use existing ECG electrodes.

[0073] The described transmission measurements of the invention allow the measured volume to be clearly defined, which is advantageous over reflecting measurements, which are not clearly defined, since the penetration depth depends on the dielectric properties and therefore on the structure of the measured tissue. The method according to the invention allows to identify spontaneous breathing during mechanical ventilation. The measurements are inherently low in motion artifacts, which means that little post-processing is required and no additional sensor systems are required, but which can be used to enhance the signal quality. Compared to other measurements, the user is not restricted.

Claims

[Claim 1] A measuring device for determining at least one respiratory parameter, comprising: at least one transmitting structure through which an alternating electromagnetic field is irradiated onto a body; at least one receiving structure for receiving the alternating electromagnetic field irradiated to the body after passing through the body; a signal generator connected to the at least one transmitting structure and configured to generate an AC voltage that can be applied to the at least one transmitting structure; a comparison section for determining, as a comparison, the difference between the phase of the signal provided by the receiving structure and the phase of the AC voltage as a function of time; an evaluation unit for determining said at least one respiratory parameter from a comparison between the phase of the signal provided by said receiving structure and the phase of said alternating voltage; Equipped with The at least one respiratory parameter is Whether inspiration or expiration is occurring The beginning of inspiration or expiration, At the end of inspiration or expiration, Progression of inspiration and / or expiration At least one selected from the following: Measuring equipment.

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