Impedance-based measuring method for hemodynamic parameters

The invention relates to a method for measuring the electrical impedance or its time

Changes to a human body, in particular for an impedance cardiography (ICG) measurement to determine hemodynamic parameters, whereby a measurement current is impressed via current electrodes, which are spaced from one another on the body surface by a current electrode measuring length, and voltage measurement Electrodes the electrical impedance or its change over time is determined.

There is often a need in medicine to measure the mechanical action of the heart. Using various methods, such as echocardiography, with or without io color Doppler, the impact force, inotropy, contractility and the ejection fraction (ejection

Fraction) measured. Furthermore, the amount of blood that is ejected from the heart within a heartbeat, the stroke volume and other hemodynamic parameters are often determined. From this, if the heart rate is known, the cardiac output (CO = cardiac output = cardiac output = CO) can be calculated. The function of the heart can be derived from the variables mentioned and the diagnosis of heart diseases can be made or diagnosed. new physiological knowledge can be gained. However, patients with severe heart disease cannot really be monitored by means of echocardiography in intensive care units or during anesthesia, because an examiner would have to be constantly present. Because of the importance of this problem, there are many more

Methods for measuring CO in medicine. For example, a catheter is inserted into the pulmonary artery and / or into the aorta and there the decrease in the concentration of the mentioned indicator substance is measured within a measuring section by means of an indicator substance, which can be, for example, heat, cold, table salt or lithium, and then by means of the Fick 'principle, the CO measured. The disadvantage of this method is the introduction of a catheter into a human vessel with all the resulting complications, such as bleeding and infection. This is an invasive procedure that involves high costs because of the disposable catheter and high risks for the patient (',]. In addition, the principle of thermodilution or the dye dilution has a large margin of error, so that the mean value of several measurements is usually used in order to obtain a plausible value.

Under physical stress or in other conditions in which the body temperature changes, the thermodilution also delivers incorrect values.

Attempts have recently been made to use Fick's principle for measuring cardiac output by measuring gases in the breath. This is possible because there is a very rapid exchange of gas between blood and breathing air, so that the concentrations in these two media can in fact be equated. If a gas is added to the breathing air, its concentration also increases in the blood.If the burial of the gas is ended, the gas in the blood and also in the breathing air decreases, whereby the decrease in concentration in the unit of time again results according to the Fick principle

CO can be measured. One method that has particularly proven its worth is CO₂Rebreathing. A loop is introduced into the patient's airways and the patient breathes his own exhaled air again for a certain period of time, causing an increase in CO₂-Concentration in the blood is coming. The disadvantage of these methods is that the patient has to be provided with a mouthpiece and breathing has to be as constant as possible so that an even concentration of the breathing gases in the breathing air and in the blood is guaranteed. This is why this procedure is mainly used in anesthesia with constant tidal volume and constant breathing rate. In spontaneously breathing patients, the disadvantage of breathing through a tube system with a mouthpiece remains, which considerably increases the dead space for breathing and also increases the breathing resistance and thus the exertion of breathing. In addition, the accuracy of the method decreases sharply with spontaneous breathing. Another method consists of a similar method, whereby instead of the CO₂ an inert gas that is inhaled and which also rapidly equilibrates with the blood is used to measure the CO.

Another method is to measure stroke volume and other hemodynamic

AT 413 189 Β

Parameter from the pulse shape, which is taken from a peripheral artery. A change in the pulse shape is also caused by a change in the stroke volume and other hemodynamic parameters, from which the change in the stroke volume and other hemodynamic parameters can be derived indirectly via a transfer function. This method must be calibrated once at the beginning using one of the methods described above, and it is also not sufficiently precise. Another method is to measure an indicator substance such as indigo green transcutaneously on the capillaries of the ear or fingers, which greatly reduces the accuracy of Fick's principle.

io Another method is the impedance cardiography IKG. In this case, a constant alternating current field is applied to the thorax, and the change in the alternating voltage that is created by this alternating current field indicates a change in the fluid content in the thorax. More precisely, the alternating current resistance (impedance) is measured with this method, which is a measure of the change in the thoracic fluid content. This change in the fluid content in the thorax in turn serves as a measure of the amount of blood ejected per stroke. The cardiac output (CO = SV * HR) can then be calculated from the stroke volume and other hemodynamic parameters (SV) and the heart rate (HR).

Usually, a pair of electrodes that conduct the current to the body is attached above or on the upper and below or on the lower thorax border. Within this pair of electrodes, a second pair of electrodes is attached to measure the resulting alternating voltage. This inner pair of electrodes must maintain the correct distance from one another, namely the upper voltage electrode must be at least at the level of the glottis and the lower electrode at the level of the xiphoid. The distance between the two

Electrode is therefore dependent on the length of the thorax and is described as electrode measuring length L in the following. The impedance Z (t) = u (t) / l is calculated₀, where u (t) is the changing alternating voltage and l₀ is the alternating current impressed in the body with a constant effective current strength.

So far, either circular electrodes or point electrodes, similar to EKG electrodes, have been used for this purpose. In the patent application Medical Electrode ['] a new electrode arrangement was described in which two strip electrodes are attached to the same film over a short distance in parallel, the spacing of which is precisely predetermined and reproducible by the common carrier film. One of these strip electrodes, which run parallel to the strip electrodes and is applied to this common carrier film, is used to apply the measuring current, the other strip electrode running parallel to the strip electrode is provided for deriving the measuring voltage. The upper pair of electrodes can be attached to the neck, for example, and the lower electrode pairs can be attached to the left and right of the lower thoracic aperture. This electrode arrangement shows a much better reproducibility of the

Results than the previously used ring electrodes or better than those in the patent application US 4,450,527 SRAMEK [^iv] (Fig. 1a + Fig. 1b) described photo electrodes.

Disadvantages of the described impedance method have been that the results either according to the KUBICEK equation [^v, or according to the SRAMEK equation [⁴, 'j, both of which were derived from very simplistic assumptions about the human body. These assumptions are only partially correct, which is why there is also a considerable error in the calculation of the stroke volume and other hemodynamic parameters and the cardiac output.

Equation 1 shows the KUBICEK equation for calculating the stroke volume and other hemodynamic parameters from the change in the impedance signal:

SV ^ P '- LVETidZIdt} ™, (1)

AT 413 189 Β

Where L is the measurement length between two electrodes measured in [cm] on the body surface, with p the specific resistance of the blood in [Qcm], with Zo the basic impedance in [Ω], with (dZ / dt)_max is the maximum level of the 1st derivative of the electrical resistance or impedance change according to the time in [Ω / sec] due to the cardiac action and LVET, which is the left ventricular expansion time [sec].

As can be seen, on the one hand the electrode measuring length L is included in this equation as a square, this electrode measuring length currently being measured on the thorax surface. Furthermore, the specific resistance p of the blood is linearly incorporated into the formula, the specific resistance of the blood primarily depending on the red blood cell content of the blood. Under the law of LAMBERTS ET. AL. [^{, x}] p is calculated approximately from the hematocrit Hkt using the formula p _ 7 »| 24 θθ, 000358 Hkt to the power of 2 (2) or estimated from a similar formula or simply kept constant in other methods. This does not take into account the fact that it is not only the hematocrit that changes the conductivity of the blood, but also the ion concentration in the plasma and the proteins in it. That is why it will never be possible to determine the exact conductivity or resistance of the blood from an empirically obtained equation that takes only one and not all blood components into account. Furthermore, the conductivity of the blood also changes due to the flow velocity, since at higher velocities the erythrocytes align themselves longitudinally in the blood flow and thus enlarge the cross-section of the liquid. At even higher speeds and the resulting turbulence, the resistance of the blood can increase again.

In the formula according to SRAMEK, 17% of the body height is entered instead of the electrode measurement length, because empirically it has been shown that the thorax length makes up approx. 17% of the total body length. Another assumption in this formula is the divisor 4.25, which is derived from the estimated relationship between electrode measurement length and abdominal circumference, as well as an estimated constant ratio between a cylindrical thorax model and a frustoconical thorax model (US 4,450,527, column 5, line 50 ff .) results. Thus the length of the body H is even included in the formula in cubic form.

³⁵ sV = (°¹⁷'^Η)³ LVET- (3)

4.25 Z_O^{k 1}

Bernstein [*] has further corrected this formula by multiplying the above formula by a correction factor of 8.

δ = ß (WreaWVidea.) (4) where ß is a Blood volume index, and W_ideai and W_reai is the ideal45 weight and real weight of a person.

The ideal weight for men is:

W ideal = 0.534 H-17.36 (5)

The ideal weight for women is:

W ideal = 0.534 H - 27.36 (6)

H denotes the height of the person in [cm].

It can be seen that different units of measurement are mixed up in all equations. This means that the equations obtained have a genuinely derived, more believable

Math to do nothing. By introducing anthropometric quantities into the

Equation, an indirect measure for the stroke volume and other hemodynamic parameters of the heart in healthy subjects is also directly included in the calculation of the stroke volume and other hemodynamic parameters. In healthy people, the CO fits the surface of the body like a tailor-made suit. Thus, a parameter is included in the formula that has nothing to do with the measurement of stroke volume and other hemodynamic parameters, namely the patient's body size. Therefore, a large patient automatically has a larger stroke volume and other, larger hemodynamic parameters than a small patient by including the height or the height-dependent electrode measurement length L between glottis and xiphoid in the calculation formula. Also in Kubicek's formula that was given above, a measure for the dimensions of the body is directly included in the formula.

As shown in FIG. 1, the measurement length between the electrodes correlates surprisingly well with the size of the patient when correctly applied to the upper and lower thoracic aperture.

In the case of people with healthy hearts, the correspondence between the stroke volume measured in blood and other hemodynamic parameters with the impedance cardiography according to the above statements is good because the body size is actually a measure of the cardiac output. A tall, heavy person actually has to bring much more blood to the tissues in a unit of time than a small, delicately built person. This principle is no longer valid in the case of cardiac patients, which is why the correlation between the actual cardiac output and the cardiac output measured by means of impedance cardiography is very poor or nonexistent, because suddenly the body mass no longer has the meaning introduced into the formula. There is therefore an enormous bias in the direction of normal and thus falsely high values ​​in heart patients.

In addition, the value determined by means of impedance cardiography is falsified in the wrong direction, namely in those too high CO values, due to the following phenomenon. In patients with heart failure, there is in most cases more body water in the thorax than in people with healthy heart because of the disease. This increased thoracic fluid content naturally lowers the basic impedance Zo in Ω. This value is inverted (SRAMEK) or inverted quadratically (KUBICEK) into the respective calculation formulas and falsifies the calculated value of the CO upwards, which can lead to fatal misdiagnoses. In the case of healthy heart patients, Zo is a measure of the thoracic geometry; in heart failure patients with increased thoracic fluid content, this is not the case.

This is clearly demonstrated in FIG. 2. Here, the ejection fraction (EF) was measured echocardiographically on patients with and without heart failure using the Simpson method, and the ejection fraction was compared with the CO. The echocardiographic parameter EF was chosen instead of the echocardiographically measured CO because it can be measured much more precisely. As can be seen, there is no connection whatsoever between CO and ejection fraction, which one would expect in and of itself if impedance cardiography had informative value in heart failure.

For this reason, impedance cardiography has not really caught on with cardiologists, at least in Europe, because the agreement with the actual stroke volume and other hemodynamic parameters may be good in healthy people, but in heart patients, where the value is really important for the diagnosis, the accuracy is very bad in

Despite this, the method is now being used more and more in America because it has been shown that the relative changes in stroke volume and other hemodynamic parameters can be followed well, so that the effects of pharmacological interventions can be well traced

AT413 189 Β can also track if the absolute values ​​may be wrong.

In addition, none of the devices on the market would be able to output a value for the stroke volume and other hemodynamic parameters or the cardiac output, if at least the body size or the thorax length between the electrodes, i.e. another measure for the body size, was not entered beforehand. If an incorrect value is entered, which can easily happen in practice, the result would be further falsified.

However, a device for determining cardiac output should also provide a reliable value if there is no a priori knowledge of body size and weight, as is of course also the case with the gold standard of thermodilution, or with other methods that use Fick's principle use like the method of CO₂ Rebreathing, or other breathing gas methods, is possible. As soon as a priori knowledge of the body measurements is also used , the measurement result is already influenced in the direction in which the measured value of the cardiac output should go, i.e. bias is introduced into the equation, which results in falsely good results in people with healthy heart the method pretends. In addition, in the case of an electrically measured cardiac output, only electrically measured parameters should also find a place in the equation.

In the method of determining the body composition given in US Pat The length measurement of the examined segment can be carried out. This is done with the centimeter measurement and a caliper as e.g. in Fig. 5 US 5,335,667 A shown. In practice, this measuring method is too imprecise, since the actually effective measuring length differs from patient to patient and every change in the position of the body during the measurement results in significant fluid displacements. These fluid shifts influence the venous return flow to the heart and thus the cardiac output, resp. also causes venous insufficiency when the body is straightened up along the longitudinal axis.

Furthermore, US Pat. No. 5,086,781 A reveals a method for measuring the body impedance at different frequencies, although this publication also does not take account of the actual effective length that is present when measuring the impedance in the patient's body.

In US 5,114,424 A and in US 5,000,753 flat neutral electrodes are disclosed which are not suitable for an impedance measurement or for the determination of an electrically measured measurement length, especially since with these a current output as wide as possible (HF surgery) in the Body should be aimed at, which is unsuitable for a length determination.

The object of the invention is therefore to provide a method of the type mentioned at the beginning, in particular for determining the stroke volume or, in general, also for measuring other hemodynamic parameters such as inotropy, ejection fraction, by means of impedance cardiography, which helps avoid the aforementioned disadvantages.

According to the invention, this is achieved in that the impedance or its time derivative is determined for at least two different voltage electrode measurement lengths or at least two different current electrode measurement lengths along the essentially same body segment through which the measurement current flows.

Attaching an additional current electrode or voltage electrode results in a change in the measuring length L of the current electrodes and / or voltage electrodes

AT 413 189 soil in relation to a further electrode element, preferably in the longitudinal direction of the

Body, and thus in the main flow direction of the blood. Simultaneously or alternately, the measurement of the impedance and its change in the thorax can be carried out with the shorter and longer electrode measuring length. This change in the electrode measuring length L should be constant, known or calculable.

In order to be able to determine the measuring length actually effective between the electrodes in question during the impedance measurement, according to a further embodiment of the invention, an operative electrode measuring length can be calculated from the impedance values ​​determined for different electrode measuring lengths. In this way, the manual measurement of changes in the electrode measuring length can be dispensed with.

Another embodiment of the invention can consist in that the electrical impedance is measured at two or more measurement frequencies and the proportions of the intra- and extra-cellular space are determined, and that these variables are used to calculate the stroke volume and other hemodynamic parameters. This method can also be used in a conventional two-electrode system or in combination with this, independently of the defined change in the measuring length according to the invention. By choosing the two measurement frequencies, the property of the blood to assume a different resistance at different frequencies can be used to determine different hemodynamic parameters for which the specific resistance of the blood is important.

The number of different frequencies that are used for the method according to the invention is unlimited, and a continuous sweeping of a frequency band (sweep) is also within the scope of the invention. The phase angle between current and voltage at different frequencies can also be a measure for determining hemodynamic parameters.

An advantageous embodiment of the method according to the invention can consist in that the electrical impedance is measured at two measurement frequencies at the same time. The two frequencies can be separated using frequency filters (frequency multiplexers), for example. Alternatively, one and the other measuring frequency can be measured alternately in very short time windows. From the different impedance values ​​obtained with different

Frequencies can be measured, the body water distribution can be determined and conclusions can be drawn about the thorax geometry.

As already explained, one of the problems of impedance cardigraphy is the determination of the specific blood resistance, which plays a role in various formulas for calculating hemodynamic parameters. Since the decrease in the maximum temporal derivative of the impedance over time with increasing frequencies is a measure of the specific resistance of the blood, the objectives of the invention can be achieved in a method mentioned at the beginning in that the maximum temporal change in the measured impedance values ​​(dZ / dt) is determined at at least two measurement frequencies and from these the specific resistance of the blood in the body is determined. Such a measurement can be carried out with or without changing the measurement length between the voltage or current electrodes.

From the impedance changes, for example at a high and at a low measuring frequency, a ratio can be calculated that is a measure of the erythrocytes deformed by the acceleration in the aorta. From this ratio can be made by appropriate mathematical

Signal analysis, other parameters can be derived that are important for calculating the heartbeat volume.

Thus, according to a further development of the invention, the maximum change in time of the ge8

AT 413 189 Β measured impedance value, especially in relatively narrow time windows, at different times of the cardiac period. In this way, the changes in impedance values ​​are averaged over time over the cardiac period.

A mean value formation from the extreme values ​​of a cardiac period can be carried out according to a further variant of the invention in that the time windows are set in the event of a steep increase in the specific resistance and at the time of the minimum blood flow at the end of the diastole.

If time windows are placed as narrow sliding windows over the entire cardiac period, the accuracy of the method according to the invention can be increased.

Finally, a significant advantage of the method according to the invention is that an empirical equation that was obtained with the aid of a gold standard such as Fick's principle, for example, can be used for the measurement of hemodynamic parameters.

It has proven to be beneficial to change the electrode measuring length in the main flow direction of the blood, which is why, in a further embodiment of the method according to the invention, the measuring voltage values ​​are measured at different voltage electrode measuring lengths in the longitudinal direction of the body, in particular between the upper and lower thoracic aperture.

When using two spaced apart voltage electrodes, the measurement voltage is determined for a first voltage electrode measurement length and for a second voltage electrode measurement length that is different from the first, and the length relative to a reference electrode that is operative for the impedance determination is determined from the measurement values.

In order to also be able to determine the distance between the voltage electrodes by measuring electrical quantities, according to a further embodiment of the invention, the measuring voltage can furthermore be determined at a third voltage electrode measuring length different from the first and the second.

In addition, by attaching electrodes to the periphery or to the extremities, the total body impedance at different frequencies, and thus also the body water with its sub-fractions such as extracellular space and intracellular space, can be determined and further conclusions can be drawn from the relation of body water to the electrically participating thoracic volume the actual stroke volume and other hemodynamic parameters can be obtained. If the extremities are also measured with different frequencies, there is also the opportunity to determine the intracellular space and extracellular space and also to include these values ​​and their relationship to one another in an equation for calculating the CO. After the intracellular space and extracellular space have changed characteristically in heart diseases, further important conclusions can be drawn about the function of the heart. In heart failure, for example, there is a decrease in the intracellular space and an increase in the extracellular space.

A further embodiment of the invention can therefore consist in that the measurement current is impressed via two current electrodes on at least one body extremity, for example on a leg and / or on an arm.

So All substances involved in the impedance measurement in the body are subject to a frequency dependency, which can provide valuable information on the constitution of the organism to be measured.

The measurement current should therefore be impressed at different measurement frequencies and the associated measurement voltage values ​​determined. The frequencies used should be a

AT 413 189 B result in measurable changes in the impedance values ​​for blood.

An advantageous distribution of the measurement frequency values ​​results when the measurement current is impressed with a measurement frequency of 1 to 10 kHz, 40 kHz, 200 kHz and 800 kHz to 1 MHz.

Finally, another variant of the method according to the invention can consist in that the frequency of the alternating measuring current is continuously changed from a lower measuring frequency to an upper measuring frequency. In this way, noticeable changes in the impedance can be tracked over the entire measuring frequency range, the lower measuring frequency preferably being 1 kHz and the upper measuring frequency preferably being 1000 kHz.

An advantageous signal-to-noise ratio of the measured value determinations can be achieved if, in a further embodiment of the invention, the measuring current is impressed at several different voltage electrode measuring lengths and at several different measuring frequencies and the measuring voltage caused by the measuring current is measured.

In order to determine the character of the impedance (inductive or capacitive), it can also prove to be beneficial to determine the phase angle between the measuring current and the measuring voltage.

It is also advantageous if the amplitudes, areas and rise and fall tangents of the

EKG waves B, C, X and O can be used individually or together to calculate hemodynamic parameters.

Since the electrode element according to the invention described here and the method according to the invention that can be carried out with it do not have any great similarities to the previous impedance cardiography, the new term multi-site-frequency electromechanocardiography (msf-ELMECG or msf-EMCG) is used for the method and measuring system according to the invention described here. suggested that all electrically determinable parameters of cardiac output such as

Stroke volume, inotropy, ejection fraction and potentially other hemodynamic parameters such as pulmonary pressure can be determined.

The invention further relates to a medical electrode element for measuring the electrical impedance or their change over time on a human body, in particular for an impedance cardiography (IKG) measurement to determine hemodynamic parameters, with a first current electrode, which has a current connection for impressing an electrical alternating measuring current, and one that is spaced apart from it , first voltage electrode, which has a voltage connection for tapping an electrical measurement voltage, the distances between the electrodes being greater than the width or the

Diameters of the electrodes are for use in the method according to the invention.

The aims and objects of the invention mentioned at the outset are achieved in that at least one further voltage electrode with a voltage connection and / or at least one further current electrode with a current connection is or are provided, the at least one further Voltage electrode at a distance (d, d1) from the first voltage electrode and / or the at least one further current electrode is or are arranged at a distance (a) from the first current electrode.

So there is at least one additional voltage electrode or an additional current electrode, which is attached to the body or that by attaching this additional current electrode and / or voltage electrode there is a change in the measuring length between the current electrodes and / or the measuring length L between the voltage electrodes of two electrode elements attached to the patient's body, preferably in the longitudinal direction of the body and thus in the main flow direction of the blood

AT 413189 Β and that the measurement of the impedance and its change in the thorax can take place simultaneously or alternately with the shorter and longer measuring length between the respective electrodes.

By introducing additional degrees of freedom, namely different measurement lengths between the voltage electrodes and the pairing of current-carrying electrodes, the actually electrically participating operative thorax length or the actually participating electrical operative thorax volume or volume can be made. Determine the actually measured operative specific resistance of the blood electronically with solutions of equations with several unknowns or use empirically obtained equations to bring this additional knowledge into a so-called black box model. So only electrically measured quantities are included in this formula. The problem of body size, namely that the stroke volume and other hemodynamic parameters are only correctly determined in healthy people on the basis of the anthropometric advance information, is thus eliminated.

A possible embodiment of the invention can now consist in that the at least one further voltage electrode is formed by a second voltage electrode which is arranged at a distance (d) from the first voltage electrode.

In this way, the measurement voltage can be tapped on the one hand at the first voltage electrode and on the other hand at the second voltage electrode in relation to a reference voltage electrode which is attached in a different area of ​​the body, and from the measured values ​​thus obtained with a known distance d between the first and of the second voltage electrode, an operative measurement length to the reference voltage electrode for the impedance value25 determination can be determined.

The distance d between the first and the second voltage electrode is known from the shape of the electrode element according to the invention, but it has proven to be favorable, as is an operative distance between the first and second voltage values ​​for the operative measurement length. To determine the electrode.

According to a further embodiment of the invention, this can be achieved in that the at least one further voltage electrode is formed by the second voltage electrode and a third voltage electrode, the third voltage electrode in one

Distance (d1) to the first voltage electrode is arranged.

A relatively high measurement volume, e.g. within the thorax, and thus meaningful measurement values ​​can be achieved for determining the body impedance if the first voltage electrode and the first current electrode and the at least one further voltage40 electrode and / or the at least one further current electrode are in Form of mutually parallel, electrically conductive strips are formed.

It has been found that there is a very high degree of reproducibility of the values ​​measured with the electrode element according to the invention if the ratio of the

The strip length to the electrode spacing is in the range between 4 and 10.

According to a further embodiment of the invention, the distance between the individual electrodes can be kept constant in that the first voltage electrode and the first current electrode as well as the at least one further voltage electrode and / or the at least one further current electrode are arranged on a common electrically insulating carrier material.

The carrier material can be formed by a carrier film, the first voltage electrode and the first current electrode as well as the at least one further voltage electrode and / or the at least one further current electrode on one side of the carrier film

1

AT 413 189 Β are applied to this and preferably provided with an electrically conductive adhesive layer. In this way, a constant spacing of the individual electrodes on the body surface is ensured while the method according to the invention is being carried out.

Another variant of the invention can consist in that the carrier material comprises several film strips with an adhesive surface on which the first voltage electrode and the first current electrode as well as the at least one further voltage electrode and / or the at least one further current electrode are applied, and that the film strips with the electrodes located thereon adhere in a substantially parallel arrangement on a common base carrier film, which base carrier film can be removed from the body surface after the film strips have been applied. After the base carrier film has been peeled off, only the film strips, each with an electrode, remain attached to the patient's body and are in electrical contact with the body surface. While this maintains a constant distance between the individual electrodes, the small total contact area results in a significant reduction in skin irritation, which is why the electrodes can be left in contact with the patient for longer.

In order to achieve the most reliable and easy-to-use connection with the connection cables required to operate the electrode element according to the invention, according to a further embodiment of the invention, the carrier film can taper at one longitudinal end to form a plug-in connection surface, on which the first voltage electrode and the first current electrode as well as the at least one further voltage electrode and / or the at least one further current electrode are guided in a closely spaced manner.

Another variant of the invention can consist in that the first voltage electrode and the first current electrode as well as the at least one further voltage electrode and / or the at least one further current electrode are designed in the form of spot electrodes, which through Spacers are arranged spaced from one another. In this way, the

Measurement of the impedance can also be carried out over very small contact areas on the body surface.

The invention also relates to a measuring system for measuring the electrical impedance or their change over time on a human body, in particular for an impedance35 cardiography (IKG) measurement to determine hemodynamic parameters, with an alternating measuring current source and a voltage measuring device as well as a medical electrode element according to the invention, the measuring current source with the current The electrode and the voltage measuring device can be connected to the first voltage electrode of the electrode element.

In previously used measuring systems for measuring the electrical impedance in the body, the measuring length between two electrode elements provided for the impedance measurement or at least the body size of the patient had to be measured, for example with the help of a tape measure. Measurement inaccuracies and the fact that the actual electrical measuring length deviates slightly from the distance between the respective electrodes to be measured on the body surface leads to falsifications or inaccuracies in the determination of the measurement result.

According to the invention, a changeover switch is provided, via which the voltage measuring device can be connected either to the first voltage electrode or to the at least one further voltage electrode.

From the known distance between the first and the further voltage electrode, the measurement length actually effective in relation to a reference electrode can be used to determine the

Impedance determined from the impressed current and the tapped voltage values

2

AT413 189 B.

Since the result of the impedance measurement on the patient's body is frequency-dependent, a further development of the invention can consist in that the measuring alternating current source has a, preferably continuously, changeable measuring frequency. In this way, the

Influence of body components such as blood, tissue and bones on the measurement result can be determined at different measurement frequencies.

In this context, a phase detector can be provided for determining the phase angle between the measuring current of the measuring current source and the measuring voltage measured by the voltage measuring device, so that a further measured variable can be obtained with the phase angle.

Since the various impedance values ​​that can be measured by the measuring system according to the invention depend on the position of the human body in space, it is advantageous to record the angle between the longitudinal axis of the body and a spatial reference point. A further embodiment of the measuring system according to the invention can therefore consist in providing a protractor for measuring the body inclination. This can preferably be arranged in a distributor piece.

The measuring electrodes of the measuring system according to the invention can also be used for other purposes, it being particularly advantageous if the electrode elements are connected to an EKG measuring device according to a further embodiment of the invention.

The invention is explained in detail below with reference to the embodiments shown in the accompanying drawings. It shows

3 shows a diagram which shows the relationship between the measured length measured on the body and the determined operative measured length between two voltage or current electrodes;

4A shows a diagram from which a comparison of the heartbeat volume determinations according to the conventional impedance cardiography and the rebreathing method emerges;

4B shows a diagram from which a comparison of the heartbeat volume determinations according to the inventive impedance cardiography (msf-ELMECG) and the rebreathing method emerges;

Fig. 5 shows a time-derived impedance signal, an electrocardiogram and a phonocardiogram of a patient;

6 shows an impedance signal derived with respect to time for a healthy and a sick patient in comparison;

7 shows an embodiment of the electrode element according to the invention;

8 shows a further embodiment of the electrode element according to the invention;

9 shows a schematic representation of an embodiment of the measuring system according to the invention;

Fig. 10 is a schematic representation of a further embodiment of the invention

Measuring system;

11 shows a schematic representation of a further embodiment of the measuring system according to the invention and

12 shows a schematic representation of a further embodiment of the measuring system according to the invention.

In particular for an impedance cardiography (ICG) measurement to determine hemodynamic parameters, e.g. the heartbeat volume, an alternating measuring current is impressed via current electrodes, which are spaced from one another on the body surface by a current electrode measuring length, and via voltage electrodes, those on the body surface, especially on the thorax surface, by a voltage electrode measuring length of 1 3

AT 413 189 Β are spaced apart from each other, a measuring voltage caused by the measuring current is tapped.

The electrical impedance or its change over time is calculated from the measurement current and the measurement voltage.

In the method according to the invention, the measurement voltage is determined with different voltage electrode measurement lengths between the voltage electrodes or with different current electrode measurement lengths between the current electrodes. The associated impedance values ​​are calculated from the resulting measurement voltage values, taking into account the voltage electrode measurement lengths or the io current electrode measurement lengths. The measurement length is preferably changed in the longitudinal direction of the body and thus in the main direction of the blood conveyed in it.

Furthermore, with at least two different measurement frequencies, better at least three to 4

Frequencies the impedance can be determined. This presupposes that the measuring alternating current source used for the measurement has a, preferably continuous, changeable measuring frequency.

The measurement frequencies should be so far apart that a measurable change in the impedance of blood can be observed, or that at the higher frequency the body membranes are penetrated by the electric current. The relevant frequencies mentioned are, for example, approx. 1 - 10 kHz, approx. 40 kHz, approx. 200 kHz and approx. 800 kHz to 1 MHz, although these are only rough guidelines for the desired frequency range. It is also proposed, instead of measuring individual frequencies, to carry out a frequency sweep over the entire frequency spectrum in question, from a lower measuring frequency to an upper measuring frequency, e.g. between 1 and 1000 kHz or over a section of interest in this range . In order to keep the signal-to-noise ratio of the measurements low, it can prove to be advantageous to measure alternately or simultaneously with several lengths and several frequencies. It can also prove to be beneficial to co-determine the phase angle of the impedance signal with a special electronic structure. For this purpose, a phase detector is provided for determining the phase angle between the measuring current of the measuring current source and the measuring voltage measured by the voltage measuring device.

As is known, according to the definition of the specific resistance, the impedance is:

Z₀= p * (LSA) (7) if p is the specific resistance of the measuring section, L is the measuring length and A is the cross-section of the measuring section.

There is now a second measuring section with the measuring length

L.₂ = L + d (8) present, where d is a constant or calculable distance between the two measurement lengths L and L.₂ is, then it can easily be deduced that the operative electrical measuring length U can be calculated using the following formula:

(9) ^Z02 *01

If this electrically measured length L is now set_O eg in the KUBICEK equation, all unknown length measures have now disappeared from the formula with the exception of the

AT 413 189 Β difference d (electrode spacing) precisely defined by the shape of the electrodes.

Such an electrode element according to the invention is formed from a triple electrode, namely a current electrode 70 and two voltage electrodes 72, 73, which are attached at a constant and known distance, preferably to maintain the constant distance on a common carrier film 2 ( Fig. 7).

The difference d is known from the shape of the electrodes 72, 73, but it can be just as electrically invalid as the length L. io measured on the thoracic surface to calculate L_O according to formula (9) also an operative d₀ to calculate. Since it is favorable to the inhomogeneous current field within the

Thorax not to intervene in these calculations of operative lengths, it is advisable to leave the current-carrying electrodes unchanged and to use only additional measuring electrodes.

The calculation of a d₀ makes it necessary, for example, to attach an additional measuring electrode 71 to an electrode element 80 according to the invention, as shown in FIG , 73 are arranged. The measuring current is impressed via an alternating measuring current source 52 which is connected between the current electrode 70 and a current electrode 60 of an electrode element 20 which is applied to the lower thorax aperture of the patient.

A voltage measuring device 51 is connected on the one hand to a voltage electrode 61 of the electrode element 20 and can be connected via a changeover switch 50 either to the first voltage electrode 73 or to a further, namely the second and third voltage electrode 72, 71. The measuring length between the voltage electrode 61 and the first voltage electrode 73 is L, the measuring length between the voltage electrode

61 and the second voltage electrode 72 is L2 and the measuring length between the voltage electrode 61 and the third voltage electrode 71 is finally equal to L3. Furthermore, L2 = L + d and L3 = L + d1 apply.

By controlling the switch 50, a total of three measurement voltages can be tapped, which correspond to the measurement lengths L, L2 and L3.

After calculating d₀ this value can then be substituted for d in equation (9).

A variant of the measuring system according to the invention, in which several current electrodes are provided instead of several voltage electrodes, is shown in FIG.

The starting point is again a quadruple electrode element 80 on which a voltage electrode 33 and three current electrodes 30, 31, 32 arranged at a defined distance from one another are provided. The measuring length between the current electrode 60 of the electrode 45 element 20 and the current electrode 32 is L, it increases to L4 for the current electrode 31 and to L5 for the current electrode 30, where L4 = L + a and L5 = L + a1 is.

The measuring current is impressed via the measuring alternating current source 52, which is connected on the one hand to the current electrode 60 of the electrode element 20 and on the other hand can be switched to the current electrodes 30, 31, 32 via the switch 50.

The voltage measuring device 51 is connected to the voltage electrode 61 of the electrode element 20 and connected to the voltage electrode 33, so that by measuring the voltage at three different measurement lengths L, L4 and L5, the current impression is the

Impedance and an operative measuring length can be determined, which results from analogous considerations to the exemplary embodiment according to FIG. 11.

3 shows the differences determined in practical tests between the actual length in cm measured on the body surface and the operative length calculated from Ohm's law for an electrode element according to the prior art. As can be seen, the relationship between the two lengths is extremely unsatisfactory, which indicates that there is no clinically relevant relationship between the length measured on the body surface and the operative length, as it results from the above formula. Above all, one can see in Fig. 3 observe that the measured length is significantly longer than the virtual length, which indicates that there must be significant changes in the diameter of the electrically participating thorax tissue between the electrodes, which apparently as electrical bellies shorten the virtual electrode distance, and in an unforeseeable way .

So you can see that up to now in the case of impedance cardiography, completely wrong theoretical considerations have been assumed. This is very easy to explain, since the distribution of electricity in the thorax is extremely inhomogeneous, and the conduction through the various media such as skin, bones, fat, lungs, heart and blood vessels is distributed differently. So far, the reproducibility of impedance cardiography was also very limited by these inhomogeneities. In order to be halfway reproducible, the electrodes had to be placed as precisely as possible in the same place on the thorax. This is possible in a short-term experiment, but not in the case of long-term observations over months and years. With the method according to the invention, this has become independent of the location of the electrodes, because the method always corrects itself automatically by measuring the operative measurement length, even if the

Relationships within the thorax should have changed, for example due to a different fluid distribution.

A very advantageous method is also to attach the current-carrying electrode to the extremities, because from these the current mainly flows along the large vessels and along the aorta. The measurement current is impressed via two current electrodes on at least one body extremity, for example on a leg and / or on an arm.

This results in a far more homogeneous current field in the thorax than if the current-carrying electrode is attached directly to the thorax. This would suffice to attach a single electrode or a double electrode to the lower thoracic aperture, as described, for example, in patent specification A392 / 2001. When attaching two double electrodes, e.g. the electrode described in A392 / 2001 or two adjacent individual electrodes on the periphery of the upper and lower extremities, the body fluid can then also be measured at the same time, namely by also measuring the whole body impedance. This is important because the fluid content of the thorax must be seen in relation to the fluid balance of the organism. Particularly in the case of heart failure, the fluid distribution in the thorax in relation to the total body fluid is very disturbed, which has made the use of impedance cardiography in heart failure impossible up to now.

Another main problem of impedance cardiography is the inclusion of the specific blood resistance, which should be included in the formula quantitatively. For this reason, at least in the KUBICEK equation, the specific blood resistance calculated from the hematocrit is included in the formula. QUAIL ET AL. [^xi] rewrote the KUBICEK equation and calculated the specific resistance from the stroke volume and other hemodynamic parameters that they determined with the help of an electromagnetic flow meter (EMF) in dogs:

_ SV_EMFZ§ ^PbIu» 1² . LVET (dZ / dt)_Max (10)

QUAIL ET AL. found that p_B.It depends on the hematocrit, but otherwise remains approximately constant. They replace ρ_Βω by a mean thoracic resistance p₀. If p₀ is approximately a constant in KUBICEK's equation, it can be replaced as follows:

Z

<img file="AT413189B_D0001.tif" />

Z₀A (7-11)

Now insert into KUBICEK's equation:

SV =

Z₀ A /²

LVET (dZI dt)_n¹⁵ SV = - LVET - (dZldt)_n (12a, b, c) sv = v_thorax_LVET (dZ / dt)_MaxZ_O \ N \ r have now mathematically eliminated the very difficult to determine specific resistance (resistivity p) from the equation for the stroke volume and other hemodynamic parameters. The prerequisite for this is that this specific blood resistance during the

Cardiac activity remains constant. According to SHANKAR ET AL. [”] The change in resistivity as a function of the activity of the heart is less than 5.5% and thus the equation is sufficiently precise.

An alternative would be to measure p at different points in time of cardiac activity, namely, for example, at the time of maximum blood flow, during systole, and also at the time of minimum blood flow, at the end of diastole. It is better, as is usual with impedance cardiography, to change the impedance over time (dZ / dt)_Max to be observed, since this value is determined by the heart's action and thus by the amount of blood from the heart (SV). For the new method only the property has to be used that the specific

Resistance of the blood p, especially the red blood cells (erythrocytes), is different at different frequencies of the alternating current. For example, the electrical resistance of the blood at 20 kHz is significantly higher than, for example, at 100 kHz, with the conductivity of the erythrocytes increasing at even higher frequencies, because at higher frequencies the erythrocytes behave like an electrical capacitor. This property can then be used to determine p; more precisely, the decrease in (dZ / dt) max at higher frequencies is a measure of the number of red blood cells, i.e. the specific resistance of the blood associated with the hematocrit. The greater the decrease of (dZ / dt)_Max when changing from a low to a high frequency, the greater the number of red blood cells, since the stroke volume at the specific

Heartbeat stays the same.

zp = f (Hkt) = F v

(dZ / diU_ freq2 J (13)

In the same way, in the case of a non-linear relationship, measurements can be made at more than 2 frequencies and all functions that may result from this can also be expressed as a non-linear regression equation. The function F can in both cases (2 frequencies, several frequencies) by comparative measurements with the conventional determination of the

Hematocrites Hkt can be determined empirically.

7

AT 413 189 Β

Another method of deriving the change in blood resistance during the cardiac cycle from electrically measured signals also results from the above

Method: WANG ET. AL. [”“] Have shown that the change in blood resistivity is '25% of the

Impedance change, so it is an important measure for calculating the correct SV. This change in blood resistivity is now a direct measure from the ratio between the two differentiated impedance signals measured at different frequencies (dZ / dQfreqi / idZ / dtJfreqz which represents a measure of the change in blood resistivity during the cardiac cycle a sliding narrow window can be placed over the cardiac cycle in order to determine the Ap (t) for each of these narrow windows. The maximum deflection of this signal Ap_Max can now also be used to determine the CO. So it is not absolutely necessary to determine the function F empirically beforehand.

Ap (f) = (dZ / cff) ^ (dZIdt) ^ (14)

An additional advantage of the method is that if the Ap (t) signal is determined with sufficient precision according to the above method, it can now also be determined whether the blood is flowing or not and what type of flow it is. In the case of laminar flow, the resistance decreases due to the alignment of the erythrocytes in the direction of flow, only to increase again at higher speeds due to the turbulence. The shape curve of the continuously measured Ap (t) values ​​can then be used to determine how long the blood flows and whether the blood flow is laminar or turbulent. The LVET (left25 ventricular ejection time), which is conventionally determined from the ICG signal directly or from the phonocardiogram, could thus also be determined by a measurement from the changing p.

The exact determination of the blood resistivity p, the correct operative length Lo, or the basic impedance Z_O, which is a measure for the thoracic geometry, is necessary for the determination of the correct SV, because the correct determination of the electrically participating thoracic volume V can be made from these variables_Thorax derive. This electrically participating thoracic volume V_Thorax is the important measure for determining the SV with the help of impedance cardiography, as can be seen from the general equation of the IKG (12c):

SV = V_thorax LVET- (12c)

As already described before, Kubicek calculates this V_Thorax from the electrode spacing L, the specific resistance of the blood p and the basic impedance Zo, SRAMEK or BERNSTEIN estimate V_ThOrax from the body size H and / or the weight of the patient W. Further improved formulas that are used in various ICG devices even process the patient's age in order to determine V_Tto determine horax.

However, as described above, these values ​​or linear dependencies of these values ​​can now be determined from electrically measurable quantities. Thus the V is also_Thorax can only be determined from different electrical quantities.

^ Thorax ^ thorax

I yL., P, ZQ, O, VV j (

d (dZldt \ max_freq1 ^ freql ^ -freql

2q2 - | (dZ / dt)_mgx__6vq2 Zfreq2 ^ fraq3 (15)

AT 413 189 Β

These quantities, which are now exclusively measured electrically, can not only be converted into any known

Formula for determining stroke volume and other haemodynamic parameters, such as the formulas of KUBICEK, SRAMEK or BERNSTEIN, but also in any equation for determining stroke volume and other haemo5 dynamic parameters; this could also be not derived, but empirically obtained equations, which by means of comparison with a gold standard such as the invasive Fick principle, thermodilution or the breathing gas method. So only electrically measured quantities remain in the equation, which results in a much greater precision. The quality of the individual signal is of subordinate importance, since measurements can be made with each heartbeat, i.e. around 70 times a minute, and the values ​​calculated from each individual heartbeat are either averaged or an exact template is determined from the impedance signal.

Similarly, the electrically determined parameters L and p can be incorporated into any known or newly developed equation for calculating the stroke volume and other hemodynamic parameters. The numerous parameters determined electrically in this way can also be used to calculate other important parameters of the mechanical heart function, for example the ejection fraction, contractility, inotropy, or pulmonary pressure, etc.

In our experience, it has proven to be at least as effective to use empirical formulas for stroke volume and other hemodynamic parameters, such as ejection fraction, inotropy, etc., which are created using the gold standard for the sizes listed above. The sizes Z01, Zo₂, (dZ / dt)_Max_freqi, (dZ / dtJma ^ fre ^, Z_freqi, Z_freq2,

Zfre ^ ..... are preferably related in a multiple regression analysis with the actual stroke volume and other hemodynamic parameters obtained by a gold standard method. The gold standard for the actual stroke volume and other hemodynamic parameters would of course primarily be Fick's principle, thermodilution or the breathing gas method. A multiple regression equation could be created from this, which empirically describes the best relationship between the above parameters and the actual stroke volume, so that there would be all inhomogeneities of the biological measurement, such as the fact that the thorax is not a geometrically precisely defined body and that the homogeneity of the propagation of electricity in the thorax in different tissues, such as fat,

Muscles, ribs, skin, lungs, vascular ligaments and the heart can never be described mathematically with sufficient accuracy. Because of the non-linearities, a multiple polynomial equation can also result. The use of whole-body impedance is also particularly important in these formulas, and this at several frequencies, e.g. at around 1-10 kHz, 40 kHz and 200 kHz and possibly also at much higher frequencies, because this takes into account the body water, the extracellular space and the intracellular water and their relation to the fluid content of the thorax. These formulas would include all the electrically measured quantities that have shown in a partial correlation analysis to be significantly related to the mechanical performance of the heart.

FIG. 4 shows, for example, a calculation of the CO obtained with the aid of a simple application of the method presented here in the case of unselected patients, that is to say also patients with cardiac insufficiency who had to undergo an operation due to a wide variety of diseases. During the operation, the NICO device, which was controlled via CO₂Rebreathing measures the CO, and which in ventilated patients shows excellent agreement with the thermodilution, the CO measured as the gold standard. In the upper part of the figure, the correlation of the NICO CO with conventional impedance cardiography is shown on the x-axis. As can be seen, r = 0.58, which corresponds to a clinically very poor and therefore unusable correlation. In the lower part of the figure, however, the comparison of the NICO-CO with a very simple version of the msf55 ELMECG is shown, in which the correlation coefficient is r = 0.84, which is already a clinical one

9

AT 413 189 Β corresponds to a very useful correlation. This correlation can be significantly improved with a more complex technical design.

5 shows the usual differentiated impedance signal with the usual nomenclature, namely the times A, B, C, X, Y and O, and the simultaneously registered EKG and phonocardiogram. The times of maximum blood flow are given between RZ and those of minimum blood flow immediately before the A wave. It should be noted that the sign of the impedance curves (ΔΖ and dZ / dt) is reversed in accordance with the convention.

io Another possibility to improve the msf-ELMECG results from the following approach:

Usually only the level of the dz / dt is currently used for the evaluation of the impedance cardiography, although much more information is hidden in the form of the impedance signal. In the case of heart failure, the shape of the impedance signal changes as shown in FIG. 6.

In the upper part of FIG. 6, a dZ / dt signal of a person with healthy heart can be seen, in the lower part the dZ / dt signal of a patient with heart failure. As can be seen, the (dZ / dt) max (C-point) becomes smaller in cardiac insufficiency, but there are additional changes, such as an increase in the amplitude of the X-wave and the O-wave.

As shown in this figure, instead of the sole (dZ / dt)_Max the amplitudes of the negative wave B, the positive amplitude of the wave C (the actual (dZ / dt)_Max), the negative wave X and the positive wave O, as well as the associated rise and fall steepnesses as well as area integrals can be included in the formula.

In addition, it may be necessary to know the position of the human body in space along the longitudinal axis, since the different Zo can enter the equation differently with different positions. For this purpose, it can prove to be beneficial to help determine the position of the body could be housed in the distributor piece so that it is hidden and can also be used again with every patient. In this case, the equations for determining stroke volume and other hemodynamic parameters would be corrected for the different body position.

With all these innovations, the method now appears for the first time to be physically accurate enough, exclusively electrically defined, of high precision and reproducibility and thus also suitable for the first time for the diagnosis of heart diseases and for monitoring in intensive care and anesthesia. In contrast to all other methods, only a few, comfortable to wear electrical electrodes have to be applied to the chest and extremities, which are also available for recording the ECG; Questionable length measurements no longer have to be carried out on the thorax, which can never be precise due to the asymmetrical shape of the thorax and the multiple electrodes with the necessary averaging; it is no longer necessary to enter the patient's height, which, as already stated, introduces undesirable, error-promoting bias into the equation; the patient no longer needs to have a catheter inserted into the pulmonary artery or another artery and no longer needs to breathe through a mouthpiece in a closed system. The application of a dye, which is measured transcutaneously, is thus superfluous.

FIG. 7 shows an example of an embodiment of the electrode elements according to the invention that are necessary for this purpose.

On this, a first current electrode 70 has a current connection 90 for impressing an electrical alternating measurement current, while in the case of a first voltage electrode 73 spaced apart therefrom, a voltage connection 93 for tapping off an electrical

Measurement voltage is formed.

AT413 189 Β

According to the invention, a further, here a second, voltage electrode 72 is provided with a voltage connection 92, which is arranged at a distance d from the first voltage electrode 73. Within the scope of the invention, several further voltage electrodes or several current electrodes can also be provided.

The first voltage electrode 73 and the first current electrode 70 as well as the at least one further voltage electrode 72 are designed in the form of mutually parallel, electrically conductive strips which are arranged on a common electrically insulating carrier material, in particular a carrier film 2. There are the first voltage electrode 73 io and the first current electrode 70 as well as the second voltage electrode 72 on one side of the

Carrier film 2 applied to this and preferably provided with an electrically conductive adhesive layer.

To simplify the production of an electrical contact with a measuring current source 15 or with a measuring voltage device, the carrier film 2 further tapers at one

Longitudinal end on one side to a plug connection surface 6, on which the first voltage electrode 73 and the first current electrode 70 as well as the second voltage electrode 72 are guided closely spaced. The carrier film 2 is preferably made of a skin-friendly, non-conductive, pliable material and can be designed continuously between the electrodes 70, 72, 73, as is shown in the exemplary embodiment according to FIG.

In the exemplary embodiment according to FIG. 8, however, the carrier material comprises a plurality of film strips 3 with an adhesive surface, to which the first voltage electrode 73 and the first current electrode 70 and the at least one further voltage electrode 72 are applied, the film strips 3 with the electrodes 70, 72, 73 located thereon in im

Adhere essentially parallel arrangement on a common base carrier film 4, which

Base carrier film 4 can be peeled off from the body surface after the film strips 3 have been applied.

The constant distance between the electrodes 70, 72, 73 is ensured by the fact that the base carrier film 4 is pulled off again after it has been attached to the thorax. This has the advantage that skin irritation from the large area of ​​a very wide carrier film 2 of the embodiment according to FIG. 7 is reduced to a very small area.

The electrode element 80 according to the invention shown in FIG. 8 has, in a known manner, preferably on the side facing the body initially a peel-off film which keeps the conductive coating of the electrodes 70, 72, 73 and the non-conductive adhesive of the base carrier film 4 moist is withdrawn immediately before use, as is well known from all medical electrodes.

Of course, additional voltage and current electrodes could also be applied to this carrier film 4, for example also an additional current electrode or also additional voltage electrodes around the operative electrode measurement length L_O or the operative distance d₀ to calculate even more precisely mathematically. The use of a common current electrode 70, on the other hand, has the advantage that the inhomogeneity of the electrical field in the thorax, both when measuring Z01 and Zo2, cannot change.

A further embodiment of the electrode element according to the invention for ensuring the constant distance can consist in that an additional carrier film is attached to the side facing away from the body, which is only applied after the finger-shaped

Carrier film is peeled off on the thorax. The carrier-carrier film should therefore not have any skin-irritating adhesive on the area between the carrier films.

As can also be seen from FIG. 8, the electrodes 70, 72, 73 are preferably in a lateral taper 6 in the area of ​​a plug connection 7 for an impedance measuring device

AT 413 189 Β the film strips 3 brought together in order to be able to use a narrow, inexpensive plug-in connection 7 that is practicable in everyday clinical practice.

9 shows a measurement setup on the body of a patient including the measurement system according to the invention. Electrode elements 7 and 8a are attached to the distal ends of extremities, such as arms and legs, which are used to measure the whole-body impedance, best at two, three or more frequencies, and which contain both current and voltage electrodes. In order to avoid an asymmetrical current distribution within the body, the electrode elements 7 and 8a are attached to both legs and to both arms in the embodiment shown, with the current applied to each half of the body being selected to be the same. Alternatively, you could have just one arm and only one

When a measuring current is introduced.

On the trunk there are also two triple electrode elements 80 and in the groin area

Neck area a triple electrode 80, each with a voltage electrode and two current electrodes attached. A measuring current is impressed via the current electrode of the upper (neck area) triple electrode element 80 and the current electrode of the left lower (groin area) triple electrode element 80, as well as between the current electrode of the upper triple electrode element 80 and the right lower triple electrode element 80, where the measuring current flowing through the left half of the body and the measuring current flowing through the right half of the body are preferably selected to be equal. By attaching the left and right lower electrode elements 80, a relatively large body volume is covered by the measurement. Alternatively, only one electrode element 80 extending over the entire front of the body in the groin area could be provided, but it has been shown that two electrode elements 80 arranged next to one another, as shown in FIG. 9, enable better reproducibility of the measurement results. The measurement voltages are tapped from the associated first and second voltage electrodes of the electrode elements 80 and processed further in the manner according to the invention to determine hemodynamic parameters.

All connections of the electrode elements 7, 8a, 80 are brought together via connection lines 10 in a distributor piece 9, which is fixed on the patient's body and contains a protractor 11, which is provided for determining the position of the patient's body relative to the horizontal To be able to record the influence of the same on the measurement result. The protractor 11 could of course also be attached elsewhere on the patient's body or on the bed on which the living being is located. A device for determining the impedance 12 is able, via a connection line 10a connected to the distributor piece 9, to carry out all the wiring of the voltage electrodes and also the current electrodes of the electrode elements 7, 8a, 80 automatically by means of an analog switch 13.

In addition to a current electrode, a first and a second voltage electrode, the electrode elements 80 can have a third voltage electrode or further voltage electrodes.

It is of course also conceivable to apply the known circular electrodes in 3 or multiple designs to the body, or to strive for a 3 or multiple design for spot electrodes. Any other electrode shape would also have to be designed in such a way that there is a variable distance at least between the current or voltage electrodes.

10 shows an example of an embodiment of a multiple spot electrode 14, whereby the constant electrode spacing can be ensured by the fact that the connecting cable between the electrodes is stretched to the maximum at the time of application to the body, and that a change is caused by the way in which the electrodes are attached of the electrical distance is achieved. So that the electrode gap is actually a 22

AT 413 189 B is held, a relatively stiff spacer 16 can also be present between the electrodes, and the connecting cable as an electrode spacer 16 can also be designed to be rigid, thereby ensuring that the distance is maintained. When calculating an operational difference d_O the electrodes can also be glued at any distance from each other and a spacer is not required.

'DALEN JE: The Pulmonary Artery Catheter - Friend, Foe, or Accomplice? JAMA, July 18, 2001 - Vol 286, No. 3: 348-350.

POLANCZYK CA, ROHDE LE, GOLDMAN L, COOK EF, THOMAS EJ, MARCANTONIO ER,

MANGIONE CM, LEE TH: Right Heart Cathertization and Cardiac Complications in Patients Undergoing Noncardiac Surgery. JAMA, July 18, 2001 - Vol 286, No. 3: 309-314.

^iH FORTIN J, NESSLER B, NESSLER W, SKRABAL F: Medical electrode, A 392/2001,

KL. A61B, submitted on March 13, 2001,^iv SRAMEK B: Noninvasive Continuous Cardiac Output Monitor US 4,450,527.22. May 1984^v KUBICEK, WG, INKARNEGIS, RP PATTERSON, DA WITSOE, RH MATTSON: Development 20 opment and evaluation of an impedance cardiac output system. Aerospace Medicine 37, 1208 1212 (1966)^vi KUBICEK, WG, FJ KOTTE, MU RAMOS, RP PATTERSON, DA WITSOE, JW LA BREE, W. REMOLE, TE LAYMAN, H. SCHOENING, D. SMITH: The minnesota impedance cardiograph - theory and applications. Biomed. Eng., 9, 410-416, (1974) 2^vii SRAMEK, B: Noninvasive technique for measurement of cardiac output by means of electrical impedance. Proceedings of the Vth ICEBI Tokyo, (1981)^viii SRAMEK, B.BO, DM ROSE, Α. MIYAMOTO: Stroke volume equation with a linear base impedance model and is accuracy, as compared to thermodilution and magnetic flowmeter techniques in humans and animals. Proceedings of the Vith ICEBI, Zadar, Yugoslavia, p. 38 (1983)^{, x} LAMBERTS, R., KR VISSER, WG ZIJLSTRA: Impedance cardiography. Van Gorcum, Assen, Holland (1984)^x BERNSTEIN, DP: A new stroke volume equation for thoracic electrical bioimpedance: Theory and rational. Critical Care Medicin 14, pp. 904-909 (1986)⁴⁰

QUAIL, AW, FM TRAUNGOTT, WL PORGES: Thoracic resistivity for stroke volume calculation in impedance cardiography J Appl. Physiol. (7981)^x SHANKAR, TMR, JG WEBSTER, SY SHAO: The contribution of vessel volume change and resistivity change to the electrical impedance pulse. IEEE Trans Biomed Engl, BME32: 192. (1985) xiiixiii wang | _ PATTERSON R: Multiple Source of the Impedance Cardiogram Based on 3-D Finite Difference Human Thorax Models. IEEE Transactions on Biomedical Engineering Vol .:

so 42, No: 2, February 2, 1995, 141-148