Device for measuring electrical impedance in parts of the body

 

The invention relates to medical equipment, namely to diagnostic devices for measuring impedance in specified parts of the body, and can be used for non-invasive determination of volumes of body fluids. The device includes a current generator, two current switching unit, respectively, right and left, three pairs of current electrodes, respectively, first, second and third levels of fixation designed for fixing on the legs, arms and the two sides of the neck, controlled potential switch, two pairs of potential electrodes, respectively, first and second levels, fixing, detector, analog-to-digital Converter and the control unit and data processing. Current switching blocks each contain three series-connected switch first, second, third levels. The device also has current and potential electrodes of the fourth level with the possibility of fixing respectively on the forehead in the projection of the frontal sinuses and the nose, while the right switch unit includes a switch of the fourth level. The current generator may have a control from the control unit and data processing. Switches made in the form of relays sealed Bereket more uniform distribution of the excitation current in the conductive volume of the trunk. 3 C.p. f-crystals, 6 ill. table 2.

The invention relates to medical equipment, namely to diagnostic devices for measuring impedance in specified parts of the body by remote scanning probe current, and can be used for non-invasive determination of volumes of body fluids.

Diagnostic information in the measurement of electrical impedance of body parts is obtained by analysis of the parameters of the AC probe current when its volume passing through the tissues of the body. To measure with high precision electrical impedance (Z0section of the body is used tetrapolar method in which the excitation current (IC) is passed through the current electrodes (TE), and the voltage drop (Uoon the examined part of the body is measured by the potential electrodes (PE).

Diagnostic devices that use alternating current as the probing signal, are the most non-invasive among modern technical means, displaying the amount of fluid in the body. This is achieved through the use of probing signals of low power, for example not more than the ache energy of the probing signal in the body: alternating current causes polar molecules and ions to make only vibrational motion.

In the diagnostic plan of the device for measuring the impedance of the body parts are used as transducers in instrumentation, reflecting the dynamics of the clinical condition of the patient: the parameters of the circulatory, respiratory and water balance.

A device for measuring the impedance of tissue containing a dual frequency unit current generators, current and potential electrodes, a detector, an analog-to-digital Converter and display unit, which allows to measure the impedance parts of the body between the electrodes [1]. However, this device does not allow the measurement of impedance areas of the body, which is an integral part of the total volume of tissue through which passes the probe current. While the electrodes of the device are located directly on the border of the studied area and in some cases are a hindrance in her manipulations.

The closest technical solution is a device for determining the volumetric contents of the extracellular and intracellular fluid in the tissues of a biological object, containing four pairs of potential-current electrodes, a current generator, a managed switch, detector, analog-to-digital Converter and the processing unit and display the measurements at low and high frequencies, to determine the volume of fluid [2]. The impedance of the body of the device is measured using electrodes placed on the arms and legs. Such arrangement of the electrodes does not create interference for procedural manipulation in the area of the body. But when measuring the impedance of the body of the probe current is passed between the right (left) hand and the left (right) foot and measure the voltage drop on the trunk between the left (right) and the right (left) foot. In the shoulder region of the probe current changes its direction almost opposite, resulting in the upper part of the trunk occurs uneven distribution and decreases the accuracy of the measurement of the impedance of the trunk. The torso contains not less than half of the total volume of body fluid. The measurement error of the impedance of the body significantly reduces the accuracy of determining the volume of liquid not only the body, but for the entire body. The uneven distribution of the excitation current in the shoulder area reduces the accuracy of measurement of the impedance of the hands, because its calculation uses the value of the impedance of the trunk.

The technical result of the invention is to improve the accuracy of measurement of the impedance of the body and hands, due to the more uniform distribution of soneto for measuring electrical impedance in parts of the body, contains the current generator controlled current switch, two pairs of current electrodes, respectively, first and second levels of fixation, two pairs of potential electrodes, respectively, first and second levels of fixation, which are connected with inputs controlled potential switch, the outputs of which through the detector and analog-to-digital Converter connected to the control unit and data processing, control outputs of which are connected to respective control inputs of current and potential switches and the input of the start of analog-to-digital Converter, and the electrodes of the first level is made with the ability to commit to the right and left legs, and the electrodes of the second level can be locked on the right and left hands, put a pair of current electrodes of the third level is made with the possibility of their fixation on the right and left parts of the neck, and the current switch is designed as two respectively of the right and left of the current switching blocks, each of which is connected to the outputs of the generator current and is made in three series-connected switches, respectively, first, second and third levels, and the second exit right switch per the La of the first level is connected to the electrode of the first level with fixation on the right foot, the second outputs of the left and right switches of the second and third levels respectively connected to the electrodes of the second and third levels with fixation on the right and left arms and the left and right parts of the neck.

In addition, the device may include current and potential electrodes of the fourth level, is made with the possibility of fixing respectively on the forehead in the projection of the frontal sinuses and the nose, thus the right of the current switching unit includes a switch of the fourth level, the input of which is connected to the second output of the switch of the third level, and the output current electrode of the fourth level, and the potential electrode of the fourth level connected with additional input potential of the switch.

In addition, the device processing unit and the display unit may contain additional control output connected with the control input of the current generator.

At that, the device switches can be made in the form of sealed relay with changeover contact group.

The invention is illustrated by drawings, where:

- Fig.1 shows a structural diagram of a device for measuring electrical impedance of body parts when fixing electrodes on three levels is when you commit electrodes at four levels;

- Fig.3 shows the equivalent circuit of a managed switch for probing high frequency current.

- Fig.4 shows an equivalent diagram showing the passage of the excitation current in the right part of the body;

- Fig.5 shows an equivalent diagram showing the passage of the excitation current in the left part of the body;

- Fig.6 shows the block diagram of algorithm of the device using a control unit and data processing.

Device for measuring electrical impedance of body parts (Fig.1) contains the current generator 1, the outputs of which are connected to control inputs of the right 2 and left 3 current switching blocks, the potential switch 4. Blocks 2 and 3 contain each of the switches of the first, second and third levels, respectively, 5-7 and 8-10. Current electrodes 11 and 12 of the first level of fixation designed for electrical contact with the right and left legs (H). The electrode 11 is connected to the switch 8, and the electrode 12 to the switch 5. Current electrodes 13 and 14 of the second level of fixation designed for electrical contact with the right and left hands (P) and connected respectively with the switches of the second layer 6 and 9. Current electrodes 15 and 16 of the third level pre-commit what aalami third layer 7 and 10. Potential electrodes 17, 18 of the first level of fixation intended for contact with the foot, and the potential electrodes 19, 20 second-level fixation intended for contact with the hands, connected to inputs of the controlled potential switch 4, the output of which through the detector 21 and an analog-to-digital Converter 22 is connected to the unit 23 of the control and data processing, control outputs which are connected to control inputs of the switch 4 Converter 22 and switch blocks 2, 3.

The device may contain (Fig.2) in unit 2, the switch 24, connected in series with the switch 7, and a current electrode 25 and the potential electrode 26 of the fourth level of fixation intended for contact to the head (G), respectively, with the forehead and nose, and the electrode 25 is connected to the output of the switch 24 and the electrode 26 with the additional input of switch 4.

Switches 5-10, 24 can be made in the form of sealed relay with changeover contact group 27 (Fig.3).

The generator 1 may be performed by control unit 23.

Device for measuring electrical impedance in parts of the body works as follows.

Based on tasks probing Argaka ICgiven shape and frequency. When running the generator 1 without control input, it automatically generates the output signal with a given amount of current, frequency and form (for example, a current of 100 μa, containing two harmonic components at frequencies of 5 kHz and 500 kHz). When running the generator 1 with the control input it only performs the function of stabilizing the value of current at its output at a given level, and the signal that defines the shape and frequency of the probe current ICformed the programming mode of the unit 23 and with its additional output to the input of the generator 1. Determination of the impedance of the body part is made by passing the excitation current ICbetween the two current electrodes fixed on certain parts of the body and simultaneous measurement of the voltage drop between the two potential electrodes, also recorded on the appropriate parts of the body. The output signal of the block 23, arriving on blocks 2, 3 and switch 4, establish contacts 27 switches 5-10, 24 in combination connection current electrodes 11-16, 25 in accordance with a logical sequence, formed in the block 23. The output signal of the block 23 at the input of switch 4, the mouth of the to through the respective switches 5-10, 24 is fed to two current electrodes and two potential relevant electrode through the switch 4 is connected to the input of the detector 21. To the input of the detector 21 receives the tension between the potential electrodes during the passage of ICin the body, it outputs a voltage proportional to the amplitude of the input voltage, which is in digital form after analog-to-digital conversion in the Converter 22 is supplied to the block 23, where it is memorization, conversion to impedance parameters and display. The frequency of measurement of the impedance is set to the programming mode of the unit 23 (Fig.6).

The algorithm of operation of the device (Fig.6) shows the temporal sequence of the generation of control signals, the block 23 and the processing sequence of the signals received at its data input when calculating impedance "hands", "body", "legs". They are calculated on the basis of measurement values of impedance 5 leads. In the unit 23 sequentially for each lead generated signals that control the state of switches 5-10 blocks 2 and 3, and block 4 - control signals connecting electrodes 17-20.

The Converter 22 is continuous with the period of 10 MS serial the conversion of low or high frequency signal to the transmitter 22 receives from block 23.

During the "t" measure impedance in one lead is 15 transformations similar code. The first 3 values are ignored (Tpd) to avoid possible interference, and 12 later (magnetism) are averaged and used to calculate impedance. The total measurement time in one abstraction is: t=Tpd+Semitism. The period measuring impedance in all leads (Totw) is selected based on the ratio: Totw>n(Tpd+Semitism) where n is the number of leads.

Switching the excitation current ICfrom the output of the generator 1 through a pair of switches: 5, 8; 6, 9; 7, 10, which form three levels of connection of current ICto the body: "legs" (H), "hands" (R), "neck" (W), and the switch 24 performs switching of the head current electrode 25, related to the level of: "head" (G). The connection switches 5-10, 24 reduces the amount of parasitic capacitance that is connected in parallel to the output of the generator 1. Parasitic capacitance at the output of the generator 1 is formed due to the presence of switches 5-10, 24 in the open state pass-through tanksP. At a high-frequency capacity WithPcontinuum the output of the generator 1 and the portion of the current ICpasses through them instead of through electrodes 11-16, 25. Leakage current ICthrough capacityis locately 5-10, 24 in the current switch leads to capacity WithPare connected in series. Due to this reduced the total equivalent capacitance connected to the output of the generator 1. The smallest decrease of the accuracy of measurement of impedance at high frequency can be obtained with the use of relay switches with hermetically sealed switch group having a capacitance of 1 pF.

To measure the impedance of the trunk (ZTyou should require that the probe current ICwas evenly distributed throughout its conductive volume. This condition is met to the greatest extent, at the location of the pairs of current electrodes 15, 11 and 16, 12 at the neck and legs (Fig.4, Fig.5). With this arrangement of the electrodes 15, 11 and 16, 12 lie on an imaginary straight line running from the outer edge of the neck to the middle line of the foot. This arrangement of the electrodes creates a mainly longitudinal, oriented to the right or to the left uniform distribution of ICthroughout the length of the body. The impedance value of the trunk ZTreceive as a result of two measurements of the impedance of the trunk, together with the right and left legs (ZT+ZMO); (ZT+ZNL) and a separate measurement of the impedance of the two but the ICand between the potential electrodes 19, 17 measure voltage U1. Similarly, measure U2for the left part of the body between the electrodes 16 and 12 and potential electrodes 20, 18. The impedance of the legs (ZMO+ZNL) is measured by passing current ICbetween the electrodes 11, 12 by measuring the voltage UHbetween the potential electrodes 17, 18.

The mathematical expression U1U2UHand their transformations, respectively, equal to

U1=IC(ZT+ZMO);

U2=IC(ZT+ZNL);

UH=IC(ZNL+ZMO);

U1+U2-UH=2 ICZT;

ZT=1/2(U1+U2-UN)/IC;

(ZMO+ZNL)=UH/IC.

The feature of this measurement is that the impedance of the trunk is measured between imaginary "electric borders": the first takes place at the level of the hip joints in the midline of the distribution of current ICif it passes in the legs, second in line to the top plane between the shoulders, i.e. the higher the equipotential surfaces in the shoulder area. Together with a uniform distribution of Igiven the value reflecting the impedance of the trunk ZT.

The impedance of the right hand ZCRdetermined by measuring voltage U3between the potential electrodes 19, 17 by passing the ICbetween the electrodes 13, 11, and the impedance of the left hand ZLRby measuring the voltage U4between the potential electrodes 20, 18 by passing the ICbetween the electrodes 14, 12. The mathematical expression for determining the impedance of the arms is equal to

ZCR=(U3-U1)/IC; ZLR=(U4-U2)/IC.

To measure the impedance of the head ZGcurrent ICis passed between the electrodes 25 and 11 and the measured voltage U5between the electrodes 26 and 17. The mathematical expression for determining the impedance of the head is equal to

ZG=(U5-U1)/IC.

The magnitude of impedance arms, torso and feet, measured at low (5 kHz) and high (500 kHz) frequencies, can be used to determine the volume of extracellular and cellular fluids by well-known mathematical dependencies [3]. Determining the volume of liquid in the individual parts of the body, followed by summing their values also significantly increases the accuracy of determining the total volume of fluid in the body because dannemora, implements the claimed device was conducted at the Department of Nephrology hospital. Botkin (Moscow). Assessed the possibility of controlling the dynamics of fluid volume in a patient resulting from the procedure of hemodialysis (HD).

Example. Patient A. Conducted the procedure DG for 4 hours, the volume of ultrafiltration was 3.1 HP impedance Measurement 5 leads were made before and after DG. Calculation of quantities of liquid produced by the method described previously [3]. The test results are presented in table.1 - values of impedance, PL.2 - the volume of liquid is calculated based on the values of the impedance of the body parts.

The measured decrease in the total volume of fluid the patient was 3,26 l, which is in good agreement with the volume of ultrafiltration of 3.1 l (measurement error does not exceed 5%).

Thus, the device for measuring electrical impedance of body parts improves the accuracy of measuring the impedance of the trunk and hands, due to the more uniform distribution of the excitation current in the conductive volume of the trunk.

Sources of information

1. U.S. patent No. 4291708, class. And 61 In 5/05, 29.09.81.

Claims

1. Device for measuring electrical impedance in parts of the body that contains the current generator controlled current switch, two pairs of current electrodes, respectively, first and second levels of fixation, two pairs of potential electrodes, respectively, first and second levels of fixation, which are connected with inputs controlled potential switch, the outputs of which through the detector and analog-to-digital Converter connected to the control unit and data processing, control outputs of which are connected to respective control inputs of current and potential switches and the input of the start of analog-to-digital Converter, and the electrodes of the first level is made with the ability to commit to the right and left legs, and the electrodes of the second level can be locked on the right and left hands, characterized in that it introduced a pair of current electrodes of the third level is made with the possibility of their fixation on the right and left parts of the neck, and the current switch is made in the am generator current and is made in three series-connected switches, accordingly, the first, second and third levels, and the second exit right switch first level is connected to the electrode of the first level with fixation on the left leg, and the second output of the left switch of the first level is connected to the electrode of the first level with fixation on the right foot, the second outputs of the left and right switches of the second and third levels respectively connected to the electrodes of the second and third levels with fixation on the right and left arms and the left and right parts of the neck.

2. The device under item 1, characterized in that it contains current and potential electrodes of the fourth level, is made with the possibility of fixing respectively on the forehead in the projection of the frontal sinuses and the nose, thus the right of the current switching unit includes a switch of the fourth level, the input of which is connected to the second output of the switch of the third level, and the output current electrode of the fourth level, and the potential electrode of the fourth level connected with additional input potential of the switch.

3. The device according to PP.1 and 2, characterized in that the control unit and processing data contains additional control output connected with the control input of the generator is with a group of contacts.



 

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