WO2020178268A1

WO2020178268A1 - Method and device for detecting contractions of the diaphragm

Info

Publication number: WO2020178268A1
Application number: PCT/EP2020/055506
Authority: WO
Inventors: Roman Kusche; Martin Ryschka
Original assignee: Technische Hochschule Lübeck
Priority date: 2019-03-06
Filing date: 2020-03-03
Publication date: 2020-09-10
Also published as: DE102019203052B4; DE102019203052A1

Abstract

The invention relates to a method for detecting contractions of the diaphragm and to a detection device for carrying out a detection of contractions of the diaphragm using such a method, wherein said method is characterized by the detection of at least a first signal related to the diaphragm muscle using a first measurement frequency and of at least a second signal related to the diaphragm muscle using at least a second measurement frequency. The detection of the contractions of the diaphragm is carried out as a function of the result of the evaluation of the phases of the first and the second signal related to the diaphragm muscle. The signals related to the diaphragm muscle can be bioimpedance signals. The system makes it possible to distinguish between muscle contractions and interfering signals.

Description

Method and device for the detection of diaphragmatic contractions

The entire content of the priority application DE 10 2019 203 052.1 is hereby incorporated by reference into the present application.

The invention relates to a method for the detection of diaphragmatic contractions and a detection device for performing a detection of diaphragmatic contractions by such a method.

In addition to filling the lungs with fresh air and checking the exhaled air, information about the contraction of the diaphragm, which is responsible for natural breathing, is of particular interest for ventilation technology.

So far, the muscle contractions of the diaphragm have mostly been detected using diaphragm electromyography (diEMG). This is a well-known method for detecting stimulation of the respiratory muscles. One problem with this procedure is that the

Frequency range (approx. 5 Hz to 500 Hz) of the useful signal is heavily overlaid by interference. In addition, the signal amplitudes are very low.

The patent application DE 10 2018 205 306.5 (as yet unpublished) shows an orthotic or prosthesis system and a method for controlling or regulating orthotics or prostheses. The muscle signal that is responsible for moving the orthosis or prosthesis is recorded and evaluated using multifrequency complex bioimpedance measurements, and this information is used to control an actuator that moves the orthosis or prosthesis.

The invention is based on the object of a method for the detection of

To provide diaphragmatic contractions and a detection device for performing such a method, each of which has an improved immunity to interference.

In particular, it is desirable to be as good as possible between interfering influences and

actual diaphragm muscle contraction to be able to differentiate. This object is achieved by a method for the detection of diaphragmatic contractions according to claim 1 and a detection device according to claim 15. Advantageous embodiments of the invention are contained in the subclaims.

The method according to the invention for the detection of diaphragmatic contractions has the following steps:

Attaching to the user at least one pair of electrodes, which are provided for contacting the body, for recording diaphragmatic muscle-related signals of a user;

Acquisition of at least one first diaphragm muscle-related signal using a first measurement frequency and at least one second

diaphragm muscle-related signal using at least one second measurement frequency;

Evaluating a phase of the first diaphragmatic muscle-related signal and a phase of the second diaphragmatic muscle-related signal;

Detecting at least one diaphragmatic contraction as a function of the result of the evaluation of the phases of the first and the second diaphragm muscle-related signal.

In the following, the diaphragmatic muscle-related signals are also referred to only briefly as "signals".

The evaluation of the phase of the respective first signal and the phase of the respective second signal makes it possible to distinguish a “real” signal related to the diaphragm muscle from an interference signal. It has been found that the phase of the bioimpedance of the muscle or muscle group measured along a muscle or a muscle group, in particular a diaphragm muscle or a diaphragm muscle group, exhibits a typical change in the frequency behavior during the contraction versus the relaxation. Typical interference signals, such as those caused by the electrode-skin junctions, on the other hand, do not show this phase behavior.

In a preferred embodiment of the invention, a phase response of the respective first and respective second signals is evaluated. As will be described below, the phase response of a diaphragmatic muscle-related signal can have certain characteristics that do not occur in the event of an interference signal. So can a "real"

Diaphragmatic muscle-related signal can be distinguished from any other type of signal, here called interference signal.

In a preferred embodiment of the invention, a phase of the respective first signal with, in particular

frequency-dependent, reference phase compared in order to determine a first phase change at least qualitatively;

a phase of the respective second signal with, in particular

frequency-dependent, reference phase compared to a second

To determine phase change at least qualitatively; and

the first phase change and the second phase change are evaluated, in particular compared with one another.

In this way, the characteristics of a real diaphragmatic muscle-related signal or an interfering signal can be recognized and evaluated.

In a preferred embodiment of the invention, the reference phase is a phase, in particular a predetermined phase, which essentially corresponds to a measurement in a relaxed state of a diaphragmatic muscle.

Using such a reference phase can help ensure that the signals are correctly identified.

According to a preferred embodiment of the invention, it is also determined whether the first phase change is a phase change in the same direction as the second phase change, or in an opposite direction.

The “direction” of a phase change is to be understood here as whether the amount of the phase becomes smaller or larger as a result of the phase change.

The directions of the first and second phase change can be used to distinguish between real diaphragm muscle-related signals and interference signals. According to one embodiment, the first and the second signal are further assessed as belonging to a diaphragmatic muscle contraction if the first and the second

Phase change are phase changes in opposite directions.

In this way, a real diaphragmatic muscle-related signal can be reliably recognized.

Accordingly, according to one embodiment, the first and second signals can be assessed as belonging to a disturbance if the first and second phase change

Phase changes are in the same direction.

A malfunction or an interference signal can thus be correctly identified.

According to one embodiment, the first measurement frequency is more than approx. 60 kHz and the second measurement frequency is less than approx. 60 kHz.

The inventors have found that the phase response below a frequency of approx. 60 kHz differs from the phase response above a frequency of approx. 60 kHz, depending on whether the signal to be evaluated is a real diaphragm muscle-related signal or an interference signal. A reliable differentiation can therefore be made for a measurement below and above approx. 60 kHz.

According to a preferred embodiment of the invention, the first measurement frequency is significantly greater than 60 kHz and / or the second measurement frequency is significantly smaller than 60 kHz.

This enables the distinction between the two types of signals to be made with even greater reliability.

In a preferred embodiment of the invention, the at least first and second diaphragmatic muscle-related signal is a complex bioimpedance signal.

The characteristic phase behavior described above occurs in particular with a bioimpedance signal. In addition to the phase, the complex bioimpedance signal also contains information about the amount of bioimpedance. In a preferred embodiment of the invention, a diaphragmatic electromyography (diEMG) is performed simultaneously and / or one after the other and / or overlapping in time using the same or different electrodes.

The combination of diEMG and bioimpedance measurement provides information on both the stimulation of the diaphragm and its actual contraction. Quantitative measurements can therefore be used to determine the "training status" of the

To determine the diaphragm, d. H. how strongly the diaphragm muscles have to be stimulated in order to generate a certain geometric change in diaphragm muscles.

In a preferred embodiment of the invention, the condition of the electrode-skin junctions is also measured.

The interface between the electrodes and the skin is a common cause of an interference signal. If a diEMG is also carried out using the same electrodes, the reliability of the diEMG can be determined.

In a preferred embodiment of the invention, the detection of the at least one first diaphragmatic muscle-related signal is carried out simultaneously and / or successively and / or overlapping in time with different geometric positions of the electrodes.

In this way, preferably by averaging the multiple first diaphragmatic muscle-related signals obtained in this way, a more precise signal can be obtained than by detecting only a single signal, deviations in the signal caused by different geometric positions of the electrodes being reduced.

In a preferred embodiment of the invention, an electrocardiogram (EKG) is additionally derived simultaneously from the electrodes used.

A simultaneous EKG eliminates the need for additional electrodes, which are necessary for simultaneous monitoring of diaphragm and heart muscle activity. The invention also relates to a detection device for performing the method according to the invention; this has: a pair of electrodes, which are provided for contacting the body, for recording diaphragmatic muscle-related signals of a user;

an evaluation unit which is set up to evaluate a phase of at least one diaphragm muscle-related signal of the electrodes;

a detection unit which is set up to include at least one

To detect diaphragmatic contraction as a function of the result of the evaluation of the phase of the at least one diaphragmatic muscle-related signal.

In a preferred embodiment of the invention, the detection device has a

Ventilator on or can be connected to a ventilator, wherein the ventilation of a patient can be controlled and / or regulated and / or influenced by the detection device.

In this way it is made possible that the control or regulation of the

Ventilator by stimulating the contraction and / or relaxation of the

Diaphragm takes place or is influenced, whereby natural breathing can be supported.

Further features, advantages and possible applications of the invention emerge from the following description in connection with the respective figure. Show:

1 shows part of a system for the detection of diaphragmatic contractions in

schematic representation according to an embodiment;

2 shows the course of the magnitude of a bioimpedance signal for different

Measurement frequencies;

3 shows the course of the phase of a bioimpedance signal at different

Measurement frequencies; 4 shows the course of the amount of a bioimpedance signal for different

Measurement frequencies, and

Fig. 5 shows the course of the phase of a bioimpedance signal with different

Measurement frequencies.

1 shows part of a system 100 for detecting diaphragmatic contractions according to an exemplary embodiment of the present invention. On the left in FIG. 1, the torso is indicated with skin 1 and muscle 2. It goes without saying that the muscle 2 described here is representative of muscles or muscle groups, in particular for diaphragm muscles or diaphragm muscle groups.

A set of electrodes 11 of the system 100 for the detection of diaphragmatic contractions contact the skin 1, the set of electrodes in the example shown consisting of four electrodes 11, namely two electrodes each for impressing current and two electrons for measuring voltage. The bioimpedance can be determined in a manner known per se from the measured voltage and the measured or previously known current.

If necessary, as shown in FIG. 1, further sensors can be present and, if necessary, contact the skin 1.

The electrodes 11 are connected to an evaluation unit 10 in which the current and voltage signals can be further processed and / or stored. The right part of FIG. 1 schematically illustrates the further processing of the current and voltage signals or the further processing of signals derived from the current and voltage signals. These functions can be implemented either in the evaluation unit 10 or in an evaluation unit (not shown) coupled to it.

As will be explained in more detail below, the phase cp and the amount | Z | the bioimpedance Z can be determined and further processed. Optionally, as indicated in FIG. 1, further measured variables, such as an electromyography (EMG) and / or mechanomyography (MMG) signal, can also be determined and, if necessary

are further processed. The inventors have recognized that both the amount | Z | as well as changing the phase cp of the bioimpedance upon muscle contraction. They found that the phase change, depending on the measurement frequency, has a characteristic that can be used to differentiate between “real” muscle-related signals and interference signals. The term “real” muscle-related signals is preferably understood to mean that these are signals that indicate an actually occurring muscle contraction or the like. can be traced back. In contrast to this, interference signals are preferably those signals which are at least partially, preferably predominantly, and more preferably essentially exclusively, due to interference. Such a disruptive influence can be, for example, insufficient contact between an electrode 11 and the skin 1.

Fig. 2 shows an example of the frequency response of the amount | Z | the bioimpedance in

Dependence on the measurement frequency f used for a muscle. The upper curve 20 shows the course of the amount | Z | the bioimpedance in a relaxed state of the muscle and the lower curve 21 the course of the amount | Z | the bioimpedance during muscle contraction. As FIG. 2 clearly shows, the amount | Z | decreases the bioimpedance during a muscle contraction in the entire frequency range shown.

The phase cp of the bioimpedance shown in FIG. 3 has a different profile in the frequency range shown. The curve, which corresponds to a relaxed muscle state, is provided with the reference number 22 in a left-hand area and with the reference number 26 in a right-hand area. The curve sections 25 and 24 represent the phase of the bioimpedance during a muscle contraction can be seen, the curve 22, 26 intersects the curve 24, 25 at a point 23. This means that the phase at a measurement frequency that corresponds to the intersection 23 (approx. 60 kHz), due to a muscle contraction compared to the relaxed state does not change. At lower measurement frequencies (to the left of the intersection 23), the phase cp of the bioimpedance decreases due to a muscle contraction. In contrast, the phase cp increases at higher measurement frequencies (to the right of the intersection point 23) due to a muscle contraction.

Referring to FIG. 3 (and correspondingly also to FIG. 5 explained below)

It should be noted that decreasing the phase here means that the phase becomes "even more negative". The amount of the phase therefore increases when the phase is reduced as illustrated in FIG. 3. The frequency response of the phase cp of the bioimpedance shown in FIG. 3 can according to

Embodiments of the present invention are evaluated to a

Recognize muscle contraction and in particular to distinguish it from an interfering signal.

With regard to the measurement of the bioimpedance and the evaluation of the phase of the

There are several variants of bioimpedance, which are briefly described here. In the following, the term “cut frequency”, abbreviated fs, is referred to several times. This cut frequency corresponds to the measurement frequency at the point of intersection 23, which could be different under certain circumstances for different muscles or for different people. If necessary, this cutting frequency could be determined empirically on a case-by-case basis.

Version 1 :

The bioimpedance or the phase cp of the bioimpedance are measured at two different measurement frequencies f1 and f2, where f1 is smaller, in particular significantly smaller than fs, and where f2 is larger, in particular significantly larger, than fs. From these

Measurements result in the phases cp1 and cp2 for the measurement frequencies f1 and f2, respectively. The phases cp1 and cp2 are then compared in the evaluation unit 10 with a reference phase cpR. The reference phase cpR can have been stored in the evaluation unit 10 in advance. The reference phase cpR can in particular be the phase cp of the bioimpedance in the relaxed muscle state, that is to say as shown by curve 22, 26. Although it can make sense to determine the reference phase cpR for many different frequencies and store it, it would also be possible to determine and save the reference phase cpR only for the two measurement frequencies f1 and F to be used.

In the evaluation unit 10, in particular by a comparator 13 (FIG. 1), the phases cp1 and cp2 are now compared with corresponding reference phases cpR1 and cpR2.

Such a comparison can reveal phase changes, i. H. Phase differences, cpD1 and cpD2 are determined. These phase changes or phase differences thus correspond to the changes in the phases caused by the muscle contraction at the respective measurement frequencies. The comparator provides 13 for the two

Measuring frequencies phase changes in different directions fixed (resp. Phase differences with different signs), the signal measured by the electrodes 11 is evaluated as a real signal of a muscle contraction.

If, on the other hand, the comparator 13 detects phase changes in the same direction or phase differences with the same sign, the signal measured by the electrodes 11 is evaluated as an interference signal, or at least not as an interfering signal

Belonging to muscle contraction.

If no phase change or difference can be detected, or if the

Phase change or phase difference has not exceeded a minimum value, the signal is not assessed as belonging to a muscle contraction, i.e. H. in this case the measurement is preferably interpreted in such a way that the muscle is in the relaxed state.

Variant 2:

The second variant differs from the first in particular in that one of the measurement frequencies f 1, f2 is close to the cutting frequency fs, in particular im

Essentially the same as the cutting frequency. The evaluation is adjusted accordingly. This means in particular that a signal detected by the electrodes 11 is evaluated as a real muscle-related signal if for that measurement frequency that is

(essentially) differs from the cutting frequency fs, a phase change or phase difference is determined, for the other measurement frequency, which is close to or equal to the cutting frequency fs, but no or only a very small phase change or difference is determined.

In contrast, the signal is assessed as not belonging to a muscle contraction if there is no or only a very slight change in phase for both measurement frequencies, or if there is a phase change in the same direction for both measurement frequencies.

In the first and second variant, it would be possible to only carry out the evaluation qualitatively, i.e. only to determine in which directions the phases change (or whether there is any phase change at all), without (further) taking into account the size of the change. Such a qualitative evaluation would be sufficient to distinguish a real muscle-related signal from an interference signal. Variation 3:

This variant is similar to the second variant. In the third variant, the

Measurement frequencies f1 and f2 are selected so that either both are greater or both are less than the cutting frequency fs. However, one of the frequencies should be significantly closer to the cut frequency than the other. After this variant it would be necessary to use the

Phase change or phase difference not only qualitative (phase change in the same or different directions, phase differences with the same or

different signs, no significant phase change), but also to be evaluated quantitatively, because it would be expected that with a muscle contraction the phases at the different measurement frequencies would change in the same direction, but that the size of the changes would be different.

Variation 4:

According to this variant, it is sufficient to determine and evaluate only one phase, i.e. only at one measuring frequency. The measurement frequency is preferably above the cutting frequency fs and is in particular significantly higher than the cutting frequency fs, i.e. in a frequency range for which curve 24 (muscle contraction) in FIG. 3 is significantly higher than curve 26 (relaxed state). It will turn the

Phase change evaluated relative to a reference phase, for example by forming a phase difference. This can in turn be carried out in the comparator 13. If the comparator 13 determines that the phase determined from the measurement is greater than the reference phase, the signal is assessed as belonging to a muscle contraction. Otherwise, the signal is either evaluated as an interference signal (the phase determined from the measurement is smaller than the reference phase) or as belonging to a relaxed muscle (no phase change).

Further explanations

It has already been mentioned that the method for the detection of diaphragmatic contractions according to embodiments of the invention can recognize real muscle-related signals, i.e. in particular signals attributable to a muscle contraction, with greater reliability and in particular can distinguish them from interfering signals than according to Approaches in the prior art was possible. In this context, it is useful to explain the course of the amount | Z | the bioimpedance or the phase cp of the bioimpedance of a possible interference signal. In this connection, reference is made to FIGS. 4 and 5.

4 shows the frequency-dependent course of the amount | Z | the bioimpedance for a given muscle condition. Here, the lower curve 28 shows the course with good electrode-skin contact of the negative current electrode, and curve 27 shows the course with poor electrode-skin contact. A bioimpedance that is larger in amount (upper curve 27) therefore corresponds to a poorer contact than a smaller one in terms of amount

Bioimpedance (lower curve 28). An evaluation of the signals that relate solely to the amount | Z | which supports bioimpedance, but could be unreliable under certain circumstances

Deliver results. For example, an increase in the amount of bioimpedance can either mean that the muscle has relaxed (more) compared to a comparable state, or that the electrode-skin contact has worsened.

5 shows the frequency response of the phase of bioimpedance in the case of good electrode-skin contact (upper curve 29) and in the case of poor electrode-skin contact (lower curve 30). The frequency response of the phase shown in FIG. 5 does not have the characteristic frequency response shown in FIG. 3 for real muscle-related signals.

In particular, the curves 29 and 30 do not intersect. The differences between a real muscle-related signal (FIG. 3) and an interference signal, such as poor electrode-skin contact (FIG. 5), become particularly clear when a measurement and evaluation is carried out according to the first variant described above. In the two measurements with the two measurement frequencies f1 and f2 (with f1 <fs <f2), the evaluation described above provides one for a real muscle-related signal

Phase change in different directions. For an interfering signal such as Legs

Deterioration of the electrode-skin contact, on the other hand, provides a

Phase change in the same direction. Because of this, the

Evaluation unit 10 differentiate between a real muscle-related signal and an interference signal.

The same applies to the other variants described above. According to embodiments of the invention, two or more measurements can be carried out at two or more different frequencies by means of the same set of electrodes 11 (using more than one measuring channel). The measurements could take place quasi-simultaneously, ie with short intervals that are not noticeable to a user. Alternatively, the measurements could be made at the two or more different frequencies using different sets of electrodes.

As shown in Fig. 1, the evaluation unit 10 according to the shown

Embodiment an A / D converter (ADC) 14, which the determined phase of the

Converts bioimpedance and possibly also the amount of bioimpedance and / or other measured or derived variables into a digital format. The digital data output by the A / D converter can be temporarily stored in an intermediate memory (buffer) 15 and optionally by an expanded one

Signal processing unit 16 are further processed. In particular, such further processing can include the control of a ventilator.

Fig. 1 indicates yet another advantage of embodiments of the invention. Embodiments of the invention provide that additional measurement methods and / or signal processing components are only switched on when a muscle contraction has been detected by means of the method described above, in particular by the comparator 13. This is indicated in FIG. 1 by an arrow which originates from the comparator 13 and leads to the symbol of an on / off switch 17 of the unit 16. In this way, processes or components with, under certain circumstances, a comparatively high energy requirement can be executed or operated in a more energy-saving manner, which can reduce the energy requirement of the entire system.

According to a further embodiment of the invention, it is possible to arrange several electrodes (sets) 11 in an electrode array. This enables a high geometric resolution to be achieved.

Advantages (or further advantages) of at least some embodiments of the invention are: Inexpensive and simple system, for example because no

(significantly) higher circuit complexity compared to already known ones

Systems

(Significant) increase in the measurement reliability of diaphragmatic muscle contractions. Small number of electrodes required

Possible extensions / variants:

Like the other components, the comparator can be implemented digitally as well as analog.

In addition, the method can be expanded to include information on changes in the amount of bioimpedance in the event of muscle contraction.

The anisotropic impedance behavior of muscle tissue can be exploited by carrying out several (quasi) simultaneous measurements on the same muscle group in different geometric electrode arrangements. Measurement of the state of the electrode-skin junctions. This information can also be used to determine how reliable the additional measurement of the EMG signal is.

The arterial pulse wave can also be detected using the bioimpedance measurement. From this information such as heart rate,

Derive pulse wave velocity, augmentation index, blood pressure and respiratory rate.

The resulting information gain by measuring at least two frequency points provides additional information about the contraction strength.

Possible areas of application of the invention are, among other things, ventilation technology and medical technology for examining the condition of the diaphragmatic muscles. List of reference symbols

1 skin

2 muscle

10 evaluation unit

1 1 pair of electrodes

12 additional sensors

13 comparators

14 A / D converter

15 buffers

16 signal processing unit

17 switches

20, 21, 27, 28 measurement curves (amount of bioimpedance)

22, 24, 25, 26, 29, 30 measurement curves (phase of bioimpedance)

23 Point of intersection of the measurement curves

100 system for the detection of diaphragmatic contractions

Claims

1. Procedure for the detection of diaphragmatic contractions with the following steps:

Acquiring at least one first diaphragm muscle-related signal using a first measurement frequency and at least one second diaphragm muscle-related signal using at least one second measurement frequency;

2. The method according to claim 1, characterized in that a phase response of the first and second signals are evaluated.

3. The method according to any one of the preceding claims, characterized by the further steps:

Comparing a phase of the first signal with a, in particular frequency-dependent, reference phase in order to determine a first phase change;

Comparing a phase of the second signal with the, in particular frequency-dependent, reference phase in order to determine a second phase change; and

Evaluating, especially comparing, the first

Phase change and the second phase change.

4. The method according to the preceding claim, characterized in that the reference phase is a, in particular previously determined, phase that is in Essentially a measurement in a relaxed state of a

Diaphragmatic muscle.

5. The method according to claim 3 or 4, characterized by the further step of determining whether the first phase change is a phase change in the same direction as the second phase change, or in one

opposite direction.

6. The method according to the preceding claim, characterized by the

further step of evaluating the first and second signals as belonging to a diaphragmatic muscle contraction if the first and second

Phase change are phase changes in opposite directions.

7. The method according to claim 5 or 6, characterized by the further step of evaluating the first and the second signal as belonging to a disturbance when the first and second phase changes are phase changes in the same direction.

8. The method according to any one of the preceding claims, characterized in that the first measurement frequency is more than approximately 60 kHz and the second

Measuring frequency is less than approx. 60 kHz.

9. The method according to any one of the preceding claims, characterized in that the first measurement frequency is significantly greater than 60 kHz and / or the second measurement frequency is significantly smaller than 60 kHz.

10. The method according to any one of the preceding claims, characterized in that the at least first and second diaphragmatic muscle-related signal is a bioimpedance signal.

1 1. Method according to one of the preceding claims, characterized in that a diaphragmatic electromyography (diEMG) is carried out over the same or different electrodes simultaneously and / or one after the other and / or overlapping in time.

12. The method according to any one of the preceding claims, characterized in that the state of the electrode-skin junctions is also measured.

13. The method according to any one of the preceding claims, characterized in that the detection of the at least one first diaphragmatic muscle-related signal is carried out simultaneously and / or successively and / or overlapping in time with different geometric positions of the electrodes.

14. The method according to any one of the preceding claims, characterized in that an electrocardiogram is additionally derived simultaneously through the electrodes used.

15. Detection device for the detection of diaphragmatic contractions, wherein the

The detection device is set up in particular to carry out a method according to one of the preceding claims and has: a pair of electrodes which are provided for contacting the body, for detecting diaphragm muscle-related signals of a user; an evaluation unit which is set up to evaluate a phase of at least one diaphragm muscle-related signal of the electrodes; a detection unit which is set up to include at least one

16. Detection device according to claim 15, characterized in that it has a ventilator or can be connected to a ventilator, and that the ventilation of a patient can be controlled and / or regulated and / or influenced by the detection device.