FI108275B - Multichannel impedance measuring method - Google Patents

Description

108275

The present invention relates to a multichannel impedance measurement method according to the preamble of claim 1.

In many methods for measuring impedance of various bodies, such as measurements of the body impedance of a human I ', current of a known magnitude is applied through two or more electrodes attached to the body, and the potential difference between two or more electrodes is measured. At least two pairs of electrodes are used in tetrapolar impedance measurement. One pair of electrodes 10 is used to supply current and another pair is used to measure the voltage, whereby the effect of the electrode impedances can be reversed. The impedance or, more often, the real part of the impedance can be calculated from the ratio of the supplied current to the measured voltage; resistance. When measuring from multiple locations, changes in the impedance of a body or human body in different areas can be examined.

15 A fundamental feature of non-invasive bioimpedance measurement methods is the indirect measurement principle, which measures changes in body conductivity caused by changes in physiological or anatomical factors and aims to determine physiological or anatomical quantities. When measuring the impedance of a body or part of it, the resulting impedance signal can be influenced by many factors, which are impossible to distinguish by conventional impedance measurement methods. changes are detected in different ways.

Bioimpedance measurements have several applications. The most commonly used are the so-called.

: * f 25 plethysmographic measurements, methods used to measure tissue composition such as extracellular fluid volume, and impedance tomography. In these two '' viewfinder mentions, most often only single channel measurements are used.

• »·; Impedance plethysmography measurements are usually based on one frequency, whereas the other two use more frequencies. In these known impedance measurement methods, which use multiple frequencies, the changes are often used to determine the impedance behavior of the target in different frequency ranges.

. ,,,: This information can be used to evaluate tissue composition.

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Impedance plethysmography aims to determine the impedance of the whole body or part of the body, as well as the cyclic impedance changes caused by heart pumping.

These variables can be used to estimate various blood flow parameters such as the stroke volume (SV) pumped by the heart j at one time. Conventional methods have not proven to be very reliable, which would be an important feature in clinical use of measurements. Conventionally, SV is determined using a single supply and one measurement channel measuring the whole body or torso, whereby all impedance modifying factors are added to the measured impedance signal and the effects of the various factors cannot be distinguished. For impedance measurement, several simultaneous voltage measurement channels may be used.

10 In these known voltage measurement multichannel impedance measurement methods, the potentials generated by the current supplied to the object to be measured can be measured at multiple points. Measured potentials can provide information about the conductivity of an object, which may vary within the object according to location and / or time. Because the measurement range of each measurement depends on the position of both the current supplied and the voltage measurement electrodes, more measurements can be made by changing the position of the current supply points to provide more information on the conductivity distribution of the target. This multi-channel multichannel method is precisely used in impedance tomography, where a tomography image of the subject can be obtained by mathematical methods from the data of all independent measurements. Further information on the impedance of the target can be obtained, possibly also by using more frequencies in the measurement of the impedance frequency behavior and thus the composition of the tissues.

: 1 j ': For power supply in multichannel applications, each channel is supplied with::; current of different frequency and measuring the corresponding frequency of the respective voltage measuring electrodes of each power supply channel. For example, two: #: 25 simultaneous channels using two feeds and two corresponding measuring electrode arrays [1] · '· *' The problem with the known multi-channel impedance measurements is that • «· '...: changing the position of the power supply points, have to. ): ':': make a large number of measurements at different points in time, which takes time: '"; 30 times, and especially the variations in the impedance of a target as a function of time, cannot be measured.:. at one time from all measuring channels since only one power supply channel is used. use multiple power supply channels by measuring just one supply channel for one measurement requires multiple measurements of 3 to 108275 at a time to measure all possible counterparts, particularly when measuring dynamic changes such as monitoring of changes in blood volume and volume in humans leading to better conductivity of other tissues. with impedance tomography devices, it is possible to measure by changing the position of the power supply channel to measure very quickly all possible combinations of measuring electrode assemblies. t are only samples taken at different points in time. In addition, measuring instrumentation is sensitive to interference when rapidly changing power supply channels. In some known impedance tomography devices, current from multiple electrodes can be supplied and the current of each electrode can be adjusted to optimally distribute the electric field in the body for image formation [3-6]. These methods allow for faster imaging. However, this method also requires multiple current supply distributions to obtain the image. Plethysmographic measurements can be performed in multiple channels to map impedance changes in various organs and parts of the body and to determine the origin of impedance changes by multiple measurements [1]. Thus, for example, in multi-channel SV measurement, the signals obtained at different points in time may not provide sufficiently accurate information on the origin of the impedance changes, and not all information provided by the measuring electrodes can be used to determine SV.

. It is an object of the invention to eliminate these drawbacks and to provide an impedance measurement method which can measure the impedance of an object and its changes::: in all parts of the body to be measured, such as the body, such that concurrent.

This purpose can be achieved in accordance with the invention by using a plurality of simultaneous · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · Power Supply Channels and Measuring Channels, using different coding in each Power Supply Channel; and measurement channels • · · • · ·. * 'Impedance determines. In this case, for example, due to changes in the body 's circulatory system i ♦::: impedance changes can better estimate the circulatory system:. : 30 parameters and its physiological subscriber activity.

Specifically, the method of the invention is characterized by: •; · · · Is shown in the characterizing part of claim 1. Preferred embodiments of the invention are set forth in the dependent claims.

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The invention will now be described in more detail with reference to the accompanying drawings, which illustrate the use of the method of the invention.

In the known tetrapolar impedance measurement shown in Fig. 1, at least four switching points are used, e.g., the electrode is not ... 4. The constant current source Li terminals Lia 5 and Lib are connected to two supply points, for example no and e4- Current II voltage is measured from two remaining switching points. Mi terminal Mia is connected to switching point e2 and terminal

The mib is connected to the switching point e ^. The voltage-to-current ratio gives the impedance proportional to the conductivity distribution of the body, p, consisting of the conductivity pi of the body and the conductance of the inhomogeneities of the body (p2 pi P4).

It is known that voltage measurement can be made simultaneously from other possible free measuring points es ... n. For example, switches for selecting a voltage channel or multi-channel voltage measurement Mi ... "can be used to find out more about the conductivity distribution pv in different parts of the object not only the position of the voltage measuring electrodes but also the position of the power supply electrodes will affect the measurement sensitivity of the measurement in different parts of the body by transferring the power supply to other switching points.

In known multichannel metering systems, the power supply is switched manually or, for example, by computer control using various switching devices [2]. In this case, measurements. "20 occurs at different times. It is also known to use the method of FIG. 2, which also uses multiple power supply channels L1 ... Ln, whose input currents L ... In have different frequencies and: · 'measure multiple channels simultaneously. However, in known measurement systems': "; the measurement is made by measuring the current for each power supply channel. at one frequency · · · V · voltage measurement Ui ... Un [1] giving one impedance value for each measurement • · · V * 25 Zlimi ··· Z ^ Mn · If other tetrapolar measurements from electrode positions are required, new measurements must be made.

Figure 3 shows a device according to the invention. According to the idea of the invention, all independent measurements provided by the electrode system can be measured, if necessary, by using a plurality of electrically separated power supply channels L] • ...: 30 n with currents (li ... In) for example, its own frequency or other code is used as the identifier, and several voltage measurement channels M2 ... k · Each voltage measurement Ui ... Uk measures; : the impedances Zlimi, Zlim2 ··· Zl2M2 between all current supplied currents Ui (n..n) - Uk (ii.n) · All power supply pair, for example LiajaLib, and voltage measurement pair, for example 5 108275 M2 and M2a ... the ratio of the input current, e.g., Li, and the measured voltage, e.g., U2, is determined by the identification code of the current supply generator, e.g., Li.

An example of how the invention is used to measure the impedance of the human body to monitor cardiac and circulatory function using a so-called. 12-lead ECG electrode locations. The electrodes of the 12-lead ECG set are connected to the voltage measuring and power supply terminals of the device. Standard ECG electrodes can be used as electrodes, whereby each electrode is used for both measurement and power supply, or alternatively a dual electrode is used at each electrode site, whereby power supply and voltage measurement can be performed with their own electrodes.

Each current supply channel formed by two or more electrodes is supplied with a current signal of its own specific frequency and the voltage measurement channels measure the potential differences caused by current at the surface of the body. In this case, a large number of independent measurements, which accumulate several thousand already with the number of electrodes 15 of the 12-lead measurement, can be simultaneously measured. Different measurements provide information on the impedance of different parts of the body, which can be used to study cardiovascular function. Not all of this information, measured at the same time, is available with current measurement methods. By adjusting the current supply or the weighting of the voltage measuring electrodes, i.e. the relative current intensity or voltage weighting factor of the various electrodes, the measurement sensitivity can be changed. "20 distributions in the body. Since the device of the invention can, if necessary, perform all independent measurements simultaneously, assuming that the system is: linear at the frequencies used, the change in measurement sensitivity described above can be accomplished by weighting the measurements of suitable input and measuring electrode pairs. .

• t · V '25 The device can be implemented, for example, as follows: the power supply channels and the voltage measurement channels are electrically isolated and independent, so that their operation does not interfere with each other. Each voltage measurement channel may have its own tuned measuring section for each of the supplied • · · • «frequencies, e.g. implemented by the Phase Lock Loop technique.

: A: Easier to implement and simpler in structure, using all of the,,,,,, 30, wideband measuring amplifiers that receive the input frequencies and size; the analogue to digital conversion of the measurement signal, followed by computational separation of the components of the different input frequencies (Figure 3, block D). This 6 108275 also allows for freer choice of frequencies, programmability of the instrument, and adaptation of the measurement protocol to suit each measurement situation.

A particular advantage of the method according to the invention is that the dynamic impedance changes can be recorded on several channels simultaneously than in the known multichannel impedance measurements, since independent impedance measurements forming different positions of the power supply electrodes can be performed simultaneously. This allows e.g. monitoring of impedance fluctuations caused by cardiac activity in real time across a large number of channels.

Likewise, it is possible to accelerate the impedance tomography measurement because the 10 methods can simultaneously measure more impedance measurements than the known methods.

References 15 [1] Kunishige H, Khono Y, Sakanaka M, Kira Y, Ohotomo T, Shimizu I, Kitamura H.Simultaneous recording of impedance pulse wave on ascending aorta and pulmonary artery branch, Proceedings of the Vth ICEBI, Aug 1981, Tokyo , Japan, p. 11-12.

[2] Kauppinen, Hyttinen, "Method for Measuring Your Bioimpedance" Patent Application No. "• 20 982289: ':: [3] US5390110: Layer Stripping Process for Impedance Imaging · [4] US5284142: Three-Dimensional Impedance Imaging processes • · ·:.: 25 [5] US5381333: Current patterns for electrical impedance tomography * »•« «* ...; [6] US5544662: High-speed electric tomography • · • «♦ •« ♦ • · 1 ·>

Claims (8)

A method for a multi-channel tetrapolar impedance measurement using multiple current supply channels and voltage measurement channels, characterized in that several simultaneous current supply channels and measurement channels are used in the measurement, at each flow current channel one encryption is different from each other, when voltage measurement channel, an impedance between all supply and measurement channels can be defined. Multichannel tetrapolar impedance measurement method according to claim 1, characterized in that each electrically independent current supply channel is measured encoded signal on the basis of which the signal source can be identified from said voltages. Multichannel tetrapolar impedance measurement method according to claims 1-2, characterized in that an identifier which has been supplied to power supply channels can be a frequency characteristic of each channel or something other identifier such as a digital code. Multichannel tetrapolar impedance measurement method according to claims 1-3, characterized in that different current supply channels in the impedance measurement are electrically independent and can thus use the same electrodes. Multichannel tetrapolar impedance measurement method according to claims 1-4, characterized in that the identifier can be identified by means of a measurement instrumentation of the voltage, such as identification of a frequency with the Phase Lock Loop technique, or with calculating means from a numerically changed signal of a voltage which every voltage channel has been measured. Multichannel tetrapolar impedance measurement method according to claims 1-5, characterized in that from each impedance signal which has been measured, a timing signal describing impedance variations in relation to the time of part of the object formed by measurement and measurement channels can be formed. Multichannel tetrapolar impedance measurement method according to claims 1-5, characterized in that measurement connections consisting of several electrodes and signals obtained by emphasizing several electrodes can be reconstructed from the single signals of the current supply and 4 voltage measurement connections. Multichannel tetrapolar impedance measurement method according to claims 1-5, characterized in that simultaneously measured signals of several measurement couplings can be used to form an image by means of impedance tomographic means.