WO2018023146A1

WO2018023146A1 - Method and device for detecting a pulmonary hypertension based on impedance cardiograms

Info

Publication number: WO2018023146A1
Application number: PCT/AT2017/060198
Authority: WO
Inventors: Michael PIENN; Horst Olschewski; Gabor Kovacs; Zoltan Balint
Original assignee: Ludwig Boltzmann Gesellschaft Gmbh
Priority date: 2016-08-05
Filing date: 2017-08-04
Publication date: 2018-02-08
Also published as: AT518396A4; AT518396B1

Abstract

The invention relates to a method and to a device (1) for processing impedance cardiograms (ICG) in order to assess the presence of a pulmonary hypertension (PH) of a person (P), comprising a unit (2) for recording and/or storing the temporal progression of the impedance (Z(t)) of the person (P) as an impedance cardiogram (ICG). The invention further relates to an impedance cardiograph (8) having such a device (1). According to the invention, a calculation device (3) for detecting the minimum of the first derivative of the impedance (Z(t)) after the time ((dZ/dt) _min) at the beginning of the ejection time during a heartbeat of the person (P) and for determining a change in the impedance (Z(t)) after/according to the minimum of the slope/gradient ((dZ/dt)_min) corresponding indicator (I_PH) for the presence of pulmonary hypertension (PH) is provided.

Description

METHOD AND DEVICE FOR DETECTING PULMONARY HYPERTONIA BASED ON

I MPEDAN CARDIOGRAM MEN

The invention relates to a method and a device for processing impedance cardiograms for the assessment of the presence of pulmonary hypertension of a person as well as an impedance cardiograph having such a device.

The characterization of the temporal course of the impedance provides information about changes in the blood flow in the thorax. This is of great importance for the detection of pulmonary hypertension (PH), ie hypertension in the pulmonary circulation. PH is often the result of chronic obstructive pulmonary disease (COPD) or other diseases, such as heart failure, pulmonary embolism, pulmonary fibrosis, congenital heart disease, etc., but may also occur without obvious causes (idiopathic pulmonary arterial hypertension, IPAH). PH is often difficult to diagnos ^¬ tizieren because many of the symptoms occur, such as fatigue, shortness of breath and dizziness also occur in other diseases. The unknown number of patients with pulmonary hypertension is considered high. Every year about 2-3 people / 1 000 000 people are diagnosed with IPAH, but this accounts for only about 5% of all cases with PH. The Mortalitätsra ^¬ th in IPAH - three years after detection - is untreated about 50%. If the disease is recognized late, the annual treatment costs can amount to 300,000 euros. An early detection is therefore essential. The PH in COPD, pulmonary fibrosis or heart failure also worsens the prognosis considerably.

To date, PH has mainly been detected by invasive examination with the right heart catheter (Swan-Ganz catheter). A thin catheter is inserted into the jugular vein or other large vein of the body and passed through the right atrium of the heart and the right ventricle into the pulmonary artery (PA). The pressure is constantly being measured. In healthy people, the mean pressure in the pulmonary artery (mPAP) is 14.0 ± 3.3 mmHg. PH occurs when the mPAP reaches 25 mmHg or exceeds. From the outside, the direct measurement of the pressure conditions in the PA is not possible.

A non-invasive estimation of the mPAP can be performed with Doppler-Sono ^¬ graphy. The speed ei ^¬ nes decline in blood flow is measured from the right ventricle into the right atrium and thereby closed the pressure conditions. Since this technique requires special equipment and a specially ^¬ les Training of the examiner and therefore can be applied only to a small part of the population at risk, this method is not suitable for widespread screening. Due to the relatively rough estimation of pulmonary pressure, this method is only used for a first screening, which is followed by further investigations.

In radiological examinations of the thorax by means of X-ray, computed tomography (CT) or magnetic resonance tomography (MRI), further indications from the morphology can be found on PH. These include the determination of the diameter of PA and aorta, the thickening of the heart muscle, in particular of the right heart, the magnification of the right heart itself and the change in curvature of the cardiac septum due to the changed pressure conditions ^¬ nit. By means of appropriate methods, functional parameters can also be determined in these investigations. The

Reduction of the compliance of the PA to the pressure changes during a heartbeat (distensibility) can be used as a ^diagnostic parameter. However, in this case be with electrocardiogram-triggered recordings Need Beer ^¬ Strengthens that lead in the case of CT studies, an increased radiation dose or when MRI studies to a longer study period. The evaluation of a contrast medium flow through the pulmonary vessels by means of dynamic

Recordings are described for example in AT 512 393 Bl. This method allows assessment of blood flow through the pulmonary vessels without triggering and therefore provides an easy way to obtain diagnostically relevant statements.

As shown in US 2010/0094122 A1, the distribution of blood flow velocities can be measured in MRI studies with phase contrast imaging. At elevated pressure in the PA a vortex forms in the main stem of the PA, which can be represented in this way. Similarly, the time can be measured, in which a downward flow of blood is provided by the vortex and be related to the duration of the heartbeat or the average flow velocity in a heartbeat measured ^¬ the. By these latter methods, a diagnosis of PH with MRI is possible. The disadvantage here is the effort and associated with an MRI study the costs, which exclude this type of investigation, for example as routine or pre ^¬ care investigation.

Object of the present invention is to provide an above-mentioned method and apparatus by which a pulmonary hypertension as quickly and easily he ^¬ can be known without costly equipment or a long ^¬ wieriges training of the examiner would be necessary. The method and device are intended to enable diagnosis without invasive surgery, to be as robust as possible to the user experience and to avoid costly and expensive CT or MRI examinations. Disadvantages of known methods and devices are to be eliminated or at least reduced.

The inventive method of the initially defined type achieves this object in that the minimum of the ers ^¬ th derivative of the impedance is detected after the time from the time profile of the Impe ^¬ impedance during a heart beat of the person and from the time variation of the impedance after the Minimum of the slope is a change of the impedance corresponding indicator for the presence of pulmonary hypertension is determined. The method according to the invention enables a rapid, simple and above all non-invasive assessment of the ^{presence of} pulmonary hypertension in a reliable manner. It has been found that by assessing the time course of the thoracic impedance signal, in particular the sy ^¬ stolic increase of the impedance cardiogram, after the minimum of the first derivative of the impedance after the time, a reliable statement about the presence of pulmonary hypertension can be made. An impedance cardiogram can be recorded quickly and easily, and above all, noninvasively, by applying a constant alternating current to the thorax of four electrodes is impressed on the person to be examined and four more electrodes, the resulting voltage is recorded. For assessing the absence of pulmonary hypertension, various parameters of the Impedanzkardiogramms have issued ^¬ during the systolic rise in Impedanzkardiogramms be appropriate here, which are described below and individually or can be used in combination as an indicator of the presence of pulmonary hypertension.

According to a feature of the invention, the maximum change in the slope of the impedance is determined as an indicator from the time characteristic of the impedance to the minimum of the slope of the impedance. The maximum change in the slope of the impedance can be determined relatively easily from the impedance cardiogram and provides a possibility of a reliable indicator of the presence of pulmonary hypertension.

Alternatively or additionally, from the time characteristic of the impedance to the minimum of the slope of the impedance, the maximum of the slope can also be determined as an indicator.

Furthermore, it is possible and expedient to determine the mean change in the slope of the impedance as an indicator from the temporal course of the impedance to the minimum of the slope of the impedance.

It is advantageous if the above parameters from the time variation of the impedance corresponding indicator is detected in a time window after the minimum of the slope of the change in impedance, with the time window preferably between 50 and 200 ms, preferably 100 ms be ^¬ wearing. By applying such a time window artifacts can be reduced or eliminated and the determination of the

Indicators for the presence of pulmonary hypertension are facilitated or accelerated.

From the time characteristic of the impedance to the minimum of the slope of the impedance, the time duration from the minimum of the impedance to the reaching of a predetermined value of the impedance as an indicator can furthermore be determined. Also this characteristic from the time course of the impedance of the thorax of the person to investi ^¬ sponding is an alternative or additional possibility for assessing the absence of pulmonary hypertension.

Finally, from the temporal course of the impedance to the minimum of the slope of the impedance, the area under the time profile of the first derivative of the impedance between a first predetermined time after the minimum of the slope of the impedance and a second predetermined time as an indicator can be determined. The predetermined times are selected according to experience and can also be adapted accordingly to the persons to be examined, for example, on their gender or age.

Advantageously, the temporal courses of the impedance are smoothed with suitable filters. By smoothing the characteristics of the impedance artifacts can be eliminated and the Aussa ^¬ ge be improved on the presence of pulmonary hypertension. Different filter methods can be implemented in hardware or software.

By averaging the temporal courses of the impedance of several heartbeats, preferably of at least 10 heart beats, artefacts can be reduced and more reliable statements can be obtained from the evaluation of the impedance characteristics.

In order to obtain a particularly simple and rapid statement about the possible presence of pulmonary hypertension, the indicator determined is preferably compared with a preset indicator. The default indicator will be

selected from empirical values in accordance with the investigation procedure or methods.

It has been found to be particularly advantageous if the default value of the indicator is changed depending on ^{data of} the person. For example, in depen ^¬ dependence on sex, age or weight of the person

different pre-set values of the indicator of pulmonary hypertension are used. Furthermore, it is possible to calculate and quantify the deviation of the determined indicator from the preset indicator. In this way, a first assessment of the severity of pulmonary hypertension can be made, which can provide important information for appropriate follow-up with other methods.

If the determined indicator exceeds or falls below the preset indicator, a warning can also be issued automatically. This facilitates the use of the method according to the invention even further and makes fewer demands on the user of the method and reduces wei ^¬ ters the error probability.

The warning may be visual, audible and / or mechanical in the form of a vibration or the like. be issued.

The indicator can online, that are determined during the recording of In ^¬ pedanzkardiogramms or offline at any later date after taking a Impedanzkardiogramms by the stored impedance cardiogram is softwa ^¬ remäßig processed and as a result,

Indicator or indicators of the presence of pulmonary hypertension are given or a quantification or probability for the presence of pulmonary hypertension is calculated and output.

The object of the invention is also achieved by an above-mentioned device for processing impedance cardiograms, wherein a processing device for detecting the minimum of the first derivative of the impedance after the time during a heartbeat of the person and for determining an indicator corresponding to the change of impedance from the time course the impedance is formed after the minimum of the slope for the presence of pulmonary hypertension. Such a device can be relatively easily and inexpensively manufactured and can be implemented both hardware and software imple ^¬ . For the further advantages of such a device, reference is made to the above description of the method for processing impedance cardiograms. The processing device may be designed to determine the maximum change in the slope of the impedance, the maximum of the slope of the impedance or the mean change in the slope of the impedance from the time profile of the impedance to the minimum of the slope of the impedance as an indicator.

Furthermore, it is advantageous if the processing device for determining the impedance corresponding to the indicator from the time course of the impedance in a time window of preferably between 50 and 200 ms, more preferably 100 ms, is formed after the minimum of the slope.

Alternatively or in addition to the parameters described above, the processing device can also be used to determine the time duration from the minimum of the impedance until reaching a predetermined value of the impedance and / or to determine the area under the time characteristic of the first derivative of the impedance between a first predetermined time be formed after the minimum of the slope of the impedance and a second predetermined time from the time course of the impedance to the minimum of the slope of the impedance as an indicator.

According to a further feature of the invention, a filter is provided for smoothing the temporal characteristics of the impedance.

In order to reduce artifacts, it is also possible to provide a filter for averaging the temporal courses of the impedance of a plurality of heartbeats, preferably of at least 10 heartbeats.

An automated evaluation of Impedanzkardiogramms in Hin ^¬ view can be done in the presence of pulmonary hypertension through a comparison means for comparing the detected indicator with a preset value of the indicator.

If an actuating device for changing the preset value of the indicator is provided as a function of data of the ^person , an adaptation of the preset Value of the indicator can be made depending on the person examined.

Via an indicator connected to the comparison device, it is possible to indicate that the determined indicator is above or below the preset indicator so that the operator of the device can quickly be informed about the result of the measurement.

The object according to the invention is also achieved by an impedance cardiograph having an apparatus for processing impedance cardiograms described above for assessing the presence of pulmonary hypertension of a person. In this case, the device according to the invention can be realized by a hardware construction or by an appropriate software.

The invention will be further elucidated on the basis of particularly preferred exemplary embodiments, to which, however, it should not be restricted, and with reference to the drawing. Show:

Fig. 1 shows schematically the positioning of the electrodes, when recording an impedance cardiogram on the human thorax;

2A to 2D, the temporal profiles of an Electrocardiogram ^¬ program, the impedance of the first derivative of the impedance with respect to time as well as the second derivative of the impedance with respect to time.

3 shows a block diagram of an impedance cardiograph equipped with the device according to the invention; and

Fig. 4 is a block diagram of an embodiment of a driving Ver ^¬ for processing Impedanzkardiogrammen for assessing the absence of pulmonary hypertension.

FIG. 1 schematically shows the positioning of the electrodes 10, 11 during the recording of an impedance cardiogram ICG on the thorax of a person P. Via four external electrodes 10, a constant alternating current I _AC generated in an alternating current source 9 is passed through the thorax of the person P. About the four Internal electrodes 11, the resulting voltage at the thorax is detected by the Imdepanzkardiographen 8 and determines the time course of the impedance Z (t). The modifications of the ^¬ impedance Z (t) by the pulse-synchronized variation of the

Blood volume in the thoracic aorta and the orientation of the orientation of the erythrocytes, when the blood is pumped from the left ventricle is pumped into the aorta. The outer electrodes 10, also called current electrodes and the inner electrodes 11, also called the measuring electrodes may be prepared by conventional adhesive electrodes as they are ver ^¬ applies also in the electrocardiography be realized. Typically, impedance cardiography is used to determine cardiac output. In the subject invention, an indicator I _PH for the presence of pulmonary hypertension PH is derived from the temporal course of the impedance Z (t), which allows a rapid and ^simple diagnosis of the pulmonary hypertension PH by means of a non-invasive measurement method.

Figures 2A to 2D show the time courses of the electrocardiogram, the thoracic impedance Z (t), the first derivative of the impedance after the time dZ / dt and the second

Deriving the impedance after the time d ² Z / dt ² using an example. The electrocardiogram ECG shown in FIG. 2A shows the evoked during a heartbeat electrical Erre ^¬ supply the heart muscle with the characteristic P-wave, the following QRS complex and the subsequent T-wave.

The corresponding impedance cardiogram ICG, so the time Ver ^¬ course of the thoracic impedance Z (t) is shown in Fig. 2B. This may be the average course over several heartbeats, in particular at least 10 heartbeats, in order to reduce or even eliminate artifacts. The course of the impedance Z (t) is characterized by a minimum and a maximum during a heartbeat.

Fig. 2C shows the first derivative of the impedance over time dZ / dt with a temporal resolution of, for example, 2 ms. For historical and practical reasons, the first derivative of the impedance dZ / dt multiplied by -1 is always used for further processing. The first derivative of the impedance dZ / dt was filtered with a low-pass filter to reduce periodic disturbances from the power grid, and interpolated by means of a so-called spline filter to a temporal resolution of 1ms. The impedance cardiogram was triggered to the R wave in the QRS complex of the electrocardiogram taken simultaneously, and the respective waveforms over a plurality of heart beats ^¬, preferably min. 10 heart beats are averaged. In the first derivative of the impedance over the time dZ / dt, the minimum (dZ / dt) min was detected and from this to the minimum

(dZ / dt) min following rise various parameters are determined, which can serve as reliable indicators I _PH for the presence of pulmonary hypertension PH. For example, the maximum change in the slope of the impedance (d ² Z / dt ² ) _max , the maximum of the slope (dZ / dt) _max , the mean change in slope

(d ² Z / dt ² ) _mean , the time period At _PH between the minimum of the impedance Z _mln until reaching a predetermined value of the impedance Z _bes t or the surface AUC _N i- _N2 under the time course of the first derivative of the impedance dZ / dt between a first predetermined time t _Ni and a second predetermined time t _N2 as appropriate parameters for the formation of an indicator I _PH ge ^¬ suitable. This surface AUC _N i- _N2 corresponds, as shown in Fig. 2B is ^¬ lines, the distance between the impedance Z (t _N2) and the impedance Z (t _N i) · Instead of the surface AUC _N i- _N2 can also be the surface AUC _mln - _max, which is the area under the time curve of the first derivative of the impedance dZ / dt between the minimum of the first derivative of the impedance (dZ / dt) min and the maximum of the first derivative of the Impe ^¬ impedance (dz / dt) _max , are used as a parameter or indicator I _PH . The one or more indicators I _PH can be automatically compared with a preset indicator I _PHN and also automatically issued a warning in case of deviation.

3 shows a block diagram of a possible device 1 for processing impedance cardiograms ICG for the assessment of the presence of pulmonary hypertension PH of a person P according to the present invention, wherein the device 1 can be integrated in an impedance cardiograph 8. Impedanzkardio- graph 8 has a device 2 for receiving and / or storage of the time course of the impedance Z (t) of the person P on. The apparatus 1 for processing the impedance cardio ICG includes a processing device 3 for detecting the minimum of the first derivative of the impedance after the time (dZ / dt) _mln during a heartbeat of the person P and Ermitt ^¬ ment of a change of the impedance Z (t) corresponding indicator I p _H out the time course of the impedance Z (t) after the minimum of the slope (dZ / dt) _mln for the presence of pulmonary hypertension PH. If necessary, filtering of the impedance cardiogram ICG can take place via a filter 4. A

Comparing means 5 compares the at least one identified indicator I _PH with a preset value _Ι ΡΗΝ which can be gegebe ^¬ appropriate, adjusted by an actuator 6, and, for example, adapted to the particular person P. A display 7 gives an optical, acoustic or mechanical warning, or a combination thereof, a warning if the at least one indicator I _PH deviates from the preset indicator I _PHN .

4 shows a block diagram of an embodiment variant of the method according to the invention for processing impedance cardiograms ICG for the assessment of the presence of pulmonary hypertension PH of a person P. According to query 101, between the recording (block 102) of an impedance cardiogram ICG or the data stored in a memory Impedance cardiogram ICG (block 103). In blocks 104 and 105, the Impedanzkardiogramme from the current recording or from memory are read and supplied to the query 106, in the entschie ^¬ is, whether a filtering of the data is to be performed or not. If affirmative is made, according to block 107, a entspre ^¬ sponding restrict Impedanzkardiogramme ICG. Since after ^¬ , or if no filtering of the data has been selected, takes place in accordance with block 108, a calculation and processing of the temporal characteristics of the impedance Z (t). According to query 109 it is decided whether the default values of the indicator I _PHN ad ^¬ should be aptiert. If appropriate, according to block 110, a person-specific adaptation of the preset values of the indicator I _PHN takes place. Otherwise, the general preset values of the indicators I _{PHN are} loaded in block 111. In method step 112, a comparison is made of the curve parameters of the temporal characteristics of the impedance Z (t ) determined indicators I _PH with the preset value of the indicator I _PHN - Comparative an exceeded or the indicator I _PH so takes place in accordance with block 114 from the preset value of the Indi ^¬ kators I _PHN r yields according to block 113, the output of the

Indicators I _PH and a corresponding audible, visual and / or mechanical warning. If no or too little exceeded or the indicator I _PH from voreingestell ^¬ th value of the indicator I _PHN instead, the output of the in ^¬ indicators I _PH occurs without warning (block 115).

The present method and the device for processing impedance cardiograms ICG for the assessment of the presence of pulmonary hypertension PH of a person P allows a ra ^¬ cal, especially noninvasive and simple assessment of the presence of pulmonary hypertension PH, which possibly by further investigations, possibly also invasive Methods that need to be verified.

Claims

Claims:

A method for processing impedance cardiograms (ICG) for the assessment of the presence of pulmonary hypertension (PH) of a person (P), wherein the time course of the impedance (Z (t)) of the person (P) is recorded as an impedance cardiogram (ICG) and or or is stored, characterized in that from the time variation of the impedance (Z (t)) during a cardiac ^¬ beat of the person (P) the minimum of the first derivative of the impedance with respect to time ((dZ / dt) _mln) is detected, and from the time characteristic of the impedance (Z (t)) to the minimum of the slope ((dZ / dt) _mln ) an indicator (I _PH ) corresponding to the change in the impedance (Z (t)) for the presence of pulmonary hypertension (PH).

2. The method according to claim 1, characterized in that from the time course of the impedance (Z (t)) to the minimum of the slope of the impedance ((dZ / dt) _mln ), the maximum change in the slope of the impedance ((d ² Z / dt ² ) _max ) is determined as an indicator (I _PH ).

3. The method of claim 1 or 2, characterized in that from the time course of the impedance (Z (t)) to the minimum of the slope of the impedance ((dZ / dt) _mln ) the maximum of the slope ((dZ / dt) _max ) is determined as an indicator (I _PH ).

4. The method according to any one of claims 1 to 3, characterized in that from the time course of the impedance (Z (t)) to the minimum of the slope of the impedance ((dZ / dt) _mln ), the mean change in the slope ((d ² Z / dt ² ) _mea n) of the impedance (Z (t)) is determined as an indicator (I _PH ).

5. The method according to any one of claims 1 to 4, characterized in that from the time course of the impedance (Z (t)) in a time window (At) after the minimum of the slope ((dZ / dt) _mln ) of the change of Impedance (Z (t)) corresponding indicator (I _PH ) is determined, wherein the time window (At) is preferably between 50 and 200 ms, preferably 100 ms.

6. The method according to any one of claims 1 to 5, characterized characterized in that from the time course of the impedance (Z (t)) to the minimum of the slope of the impedance ((dZ / dt) _mln ) the time duration (At _PH ) of the minimum of the impedance (Z _mln ) until reaching a predetermined Value of the impedance (Z _best ) is determined as an indicator (I _PH ).

7. The method according to any one of claims 1 to 6, characterized in that from the time course of the impedance (Z (t)) to the minimum of the slope of the impedance ((dZ / dt) _mln ) the area

(AUC _N i- _N2) under the time curve of the first derivative of the impedance (dZ / dt) predetermined between a first time

(t _N i) after the minimum of the slope of the impedance ((dZ / dt) _mln ) and a second predetermined time (t _N2 ) is determined as an indicator (I _PH ).

8. The method according to any one of claims 1 to 7, characterized in that the temporal courses of the impedance (Z (t)) are smoothed with suitable filters.

9. The method according to any one of claims 1 to 8, characterized in that the temporal courses of the impedance (Z (t)) meh ^¬ rerer heartbeats, preferably of at least 10 heartbeats, are averaged.

10. The method according to any one of claims 1 to 9, characterized in that the determined indicator (I _PH ) is compared with a pre ^¬ presented indicator (I _PHN ).

11. Method according to claim 10, characterized in that the preset value of the indicator (I _PH N) is changed as a function of ^{data of} the person (P).

12. The method according to claim 10 or 11, characterized in that the deviation (Δΐ _ΡΗ ) of the determined indicator (I _PH ) from the preset indicator (I _PHN ) is calculated and quantified.

13. The method according to any one of claims 10 to 12, characterized in that when exceeding or ^{falling below} the determined ^¬ th indicator (I _PH ) on the preset indicator (I _PHN ) a warning is issued.

14. The method according to claim 13, characterized in that an optical, acoustic and or or mechanical warning ^¬ is given.

15. The method according to any one of claims 1 to 14, characterized in that the indicator (I _PH ) is determined online.

16. The method according to any one of claims 1 to 15, characterized in that the indicator (I _PH ) is determined offline.

17. An impedance cardiogram (ICG) processing apparatus (1) for assessing the presence of pulmonary hypertension (PH) of a person (P), comprising means (2) for receiving and / or storing the time course of the impedance (Z (Z). t)) of the person (P) as an impedance cardiogram (ICG), characterized in that a processing device (3) for detecting the minimum of the first derivative of the impedance after the time ((dZ / dt) min) during a heartbeat of the person (P) and one of the change in impedance to determine (Z (t)) corresponding indicator (I _PH) from the time profile of the Impe ^¬ impedance (Z (t)) to the minimum of the slope ((dZ / dt) _mln) is designed for the presence of pulmonary hypertension (PH).

18. Device (1) according to claim 17, characterized in that the processing device (3) for determining the maximum change in the slope of the impedance ((d ² Z / dt ² ) _max ) from the time course of the impedance (Z (t) ) is formed after the minimum of the slope of the impedance ((dZ / dt) _mln ) as an indicator (I _PH ).

19. Device (1) according to claim 17 or 18, characterized in that the processing device (3) for determining the maximum of the slope ((dZ / dt) _max ) from the time course of the impedance (Z (t)) to the minimum the slope of the impedance ((dZ / dt) min) as an indicator (I _PH ) is formed.

20. Device (1) according to any one of claims 17 to 19, characterized in that the processing means (3) for determining the mean change in the slope ((d ² Z / dt ² ) _mea n) of Impedance (Z (t)) from the time course of the impedance (Z (t)) to the minimum of the slope of the impedance ((dZ / dt) _mln ) as an indicator (I _PH ) is formed.

21. Device according to one of claims 17 to 20, characterized in that the processing device (3) for determining the change of the impedance (Z (t)) corresponding indicator (I _PH ) from the time course of the impedance (Z (t) ) in a time window (At) of preferably between 50 and 200 ms, particularly preferably of 100 ms, after the minimum of Stei ^¬ tion ((dZ / dt) min) is formed.

22. Device (1) according to one of claims 17 to 21, characterized in that the processing device (3) for determining the time duration (At _PH ) of the minimum of the impedance (Z _mln ) until reaching a predetermined value of the impedance (Z _best ) is formed from the time characteristic of the impedance (Z (t)) after the minimum of the slope of the impedance ((dZ / dt) _mln ) as an indicator (I _PH ).

23. Device (1) according to one of claims 17 to 22, characterized in that the processing device (3) for determining the area (AUC _N i- _N2 ) under the time profile of the first derivative of the impedance (dZ / dt) between a first predetermined time (t _N i) according to the minimum of the slope of the ^¬ impedance ((dZ / dt) _m i _n) and a second predetermined time (t _L2) from the time variation of the impedance (Z (t)) to the Minimum of the slope of the impedance ((dZ / dt) _mln ) as indicator (IPH) is out forms.

24. Device (1) according to one of claims 17 to 23, characterized in that a filter (4) for smoothing the temporal courses of the impedance (Z (t)) is provided.

25. Device (1) according to one of claims 17 to 24, characterized in that a filter (4) for averaging the temporal courses of the impedance (Z (t)) of several heartbeats, preferably of at least 10 heartbeats, is provided.

26. Device (1) according to any one of claims 17 to 25, characterized in that a comparison device (5) for Verglei ^¬ surfaces of the indicator detected (I _PH) with a preset value of the indicator (I _PHN) is provided.

27. Device (1) according to claim 26, characterized in that an actuating device (6) for changing the preset value of the indicator (I _PHN ) in dependence on data of the person (P) is provided.

28. Device (1) according to claim 26 or 27, characterized in that a comparator (5) connected to the display (7) for indicating an overshoot or undershooting of the detected indicator (I _PH ) provided by the preset indicator (I _PHN ) is.

29. Impedance cardiograph (8) with a device (1) according to one of claims 17 to 28.