REOKARDIOGRAFIYA (Greek rheos a current, a flow + kardia heart + grapho to write, represent; synonym: impedance cardiography, precardiac reografiya, chest reografiya, transthoracic reografiya) — the method of a research of cordial activity based on measurement of the changes of an impedance of a thorax connected with dynamics of a krovenapolneniye of heart and large vessels during a cardial cycle. The river in various options is applied to the phase analysis of cordial reduction, studying of a hemodynamics in a small circle of blood circulation, but its main purpose — noninvasive definition of a stroke output of blood, a cut make with the help to both a bipolar, and tetrapolar reografiya. The last has advantages to R. on the accuracy of the received results compared to results of reference methods including Fick's method (see. Blood circulation, methods and devices for a research ).
Theoretical bases of a reokardiografiya
Already in Holzer, Poltser and Marko's early studies (W. Holzer, To. Polzer u A. Marko, 1945), offered the term «reokardiografiya», an attempt of assessment of a stroke output of blood on changes of amplitude of a reokardiogramma (RKG) was made. Development of evidence-based ways of definition of this indicator is connected with A. A. Kedrov's works (1941, 1948) who showed that the relation of a volumetric gain of blood (ΔV) to its initial volume (V) in the studied body part is proportional to the relation of a gain of an impedance (ΔZ) to a basic impedance (Z) on the same site from where
ΔV = (ΔZ*V)/z (1)
values V are necessary For calculation ΔV on a formula (1), to-rye in each research cannot be measured. It demanded transformations of a formula (1) introduction instead of the V coefficient of proportionality between ΔV and ΔZ/Z, to-ry it was dependent on electrical resistivity of blood (r) and from geometry of the studied body part, in particular from distance (L) between potential electrodes. In relation to reografichesky definition of a stroke output of heart (UO = ΔV) one of the main options of such transformation of a formula (1) following:
UO = (p*L 2 *ΔZ) / Z 2 (2)
Accuracy of definition of UO on a formula (2) in an essential measure depends on the accuracy of measurement of size ΔZ, the equivalent size of a stroke output of blood. Use for this purpose of the maximum amplitude of RKG was insufficiently reasonable because during a systole along with inflow of blood also its outflow, therefore, a reografichesky index less required size takes place.
For definition of a true equivalent of a stroke output of blood a number of ways of extrapolation of a reografichesky curve was offered. The main of them are shown in fig. 1. So Feyfar and Zaits (Z. Fejfar, F. Zajic, 1954), proceeding from the assumption that a systolic part of RKG is the vector sum of a brothel and outflow, considered an impedance at the end of a systole corresponding to a half of a stroke output and ΔZ determined size as the doubled amplitude of RKG during the second cardiac sound (fig. 1, a). Graphic extrapolation of the descending part of a reogramma (fig. 1, c) formed the basis of definition ΔZ on Naybora (J. Nyboer, 1959) and according to Herrman (G. R. Herrman, 1962). Extrapolation of the ascending part of a reogramma in the time slice equal to the period of exile of blood from heart is closest to a true equivalent of a stroke output of blood, according to W. G. Kubicek et al. (1966) (fig. 1, d). This principle is applied in the most exact way of definition of UO by means of tetrapolars - ache R., expressing ΔZ as works of amplitude (h) of the differential RKG calibrated in ohms a second and time of exile of blood (e) in seconds (fig. 2). In the latter case the formula for definition of UO takes a form:
UO = (p*L 2 * h*e) / Z 2 (3).
The formula (3) is main for definition of UO by means of R., all sizes entering it can be measured, and size r is accepted by a constant with values apprx. 150 ohms-cm.
Measurement impedance (see) at tetrapolar option P. it is based on the law of Ohm (ratios of current, tension and impedance) applicable in case of uniform electric field. The last in many respects depends on placement of electrodes. Researches Sacks (R. N. Cooley, 1970) showed that for the maximum penetration of the probing current in a biological object the distance between current and potential electrodes shall be not less than 3 cm. Otherwise, because of irregularity of electric field, the impedance of only superficially located fabrics is measured. The last is possible when at Kubichek's way current and potential electrodes are imposed in close proximity to each other on a neck and a thorax. Placement of current electrodes at considerable distance from measuring is provided in modifications of a method Yu. T. The gunner et al. (1977), on a cut tone electrodes are imposed on the head and the left shin, and measuring — on a neck and a thorax. At this modification of a method it is necessary to enter coefficient of the amendment into a formula (3) = 0,9 that in the work with the size taken for a constant r gives the overal coefficient equal 135, and the formula for calculation of UO has an appearance:
UO = (135*L 2 * h*e) / Z 2 (4).
Because resistance of volume conductors, to the Crimea belongs a thorax, depends not only on their length, but also cross-section, Yu. T. Pushkar et al. (1980) consider it expedient to enter into a formula (3) the size of perimeter (Q) of a thorax in centimeters, at the same time the formula will be transformed, taking the following form:
UO = (0,45*Q 2 * L*h*e) / Z 2 (5).
M. K. Oskolkova and soavt. (1980) consider that at children at the age of 11 — 15 years it is necessary to include in a formula (3) the size of a circle of a thorax, and also digital ratios of growth (N) and age (V) of the child, calculating a stroke output on a formula:
UO = [(0,1*Q 2 * L*h*e) / Z] * (H/B) (6).
In this case strict physical and mathematical justification of the equation is replaced with empirically found coefficients aiming to coordinate estimated values with the sizes of a stroke output of blood found other methods.
The aspiration to enter into the equation (3) various amendments confirm certain restrictions of a method, to-rye come to light at considerable deviations of anthropometrical indicators from average norms, and also at children and in cases of disturbances of electrolytic balance.
high precision of measurements of an impedance, a possibility of use of the ordinary bipolar reo-counts measuring dynamics of ohmic resistance by means of a Wheatstone bridge is necessary for a reokardiografiya == As at reografichesky definition of a stroke output of blood (a reografytip of RG1 — 01, 4 — RG — 1, etc.) » In (>much it is limited. So, e.g., the admissible error of counting of a reograf 4 — RG — 1, equal 25 ohms, can exceed the actual size of a basic impedance of separate zones. Certain difficulties arise also at calibration of RKG and disbalance of the bridge owing to the changing transfer resistance between electrodes and the surface of skin of the patient. These defects are considerably eliminated at a four-electrode way of measurements on tetrapolar reograf like a reopletizmograf of RPG — 202, in Krom measuring and generating chains are divided. The studied body part is connected to a source of current of high frequency by means of two generating (current) electrodes, and remove the electric signal proportional to an impedance from two potential (measuring) electrodes. As measurements in a tetrapolar reograf are carried out without bridge scheme — in size of power failure on potential electrodes, there is an opportunity to make exact counting of a basic impedance and its pulse fluctuations, without resorting to repeated calibrations in the course of the research. Thanks to considerable decrease in influence of transfer resistance on results of measurements, record of a tetrapolar reogramma is possible also at the movement of the patient during functional trials.
Technique of a research
At record RKG on a tetrapolar reopletizmograf of the RPG type — the 202nd potential electrodes in the form of a narrow metal tape, or more convenient electrodes like Minnesota (the strip of a foil 7 mm wide pasted on an adhesive tape) fix around a neck and around a thorax at the level of a xiphoidal shoot. Knaruzhi from them is placed by the same current (generating) electrodes, on the Crimea the probing current of high frequency comes to the studied zone. The distance between potential electrodes (L) is measured in centimeters. After fixing of electrodes register on the multichannel electrocardiograph (allowing simultaneous record of carotid pulse or the phonocardiogram) a calibration signal of 1 ohms/sec. for a differential reogramma. The scale of record can be regulated randomly handles of strengthening of electrocardiographic channels, but for the subsequent calculations it is the most convenient to adhere to amplitude of calibration signals, equal 10 mm. Attaching then current and potential electrodes to special nests of a block of a reopletizmograf, determine by a scale of the indicator the size of a basic (interelectrode) impedance of Z in ohms. After that register differential RKG and measure its amplitude (h) in ohms a second (on the proportional relation to amplitude of a calibration signal) and duration of the period of exile (e) in seconds. Duration of the period of exile can be measured on an interval between the beginning of a systolic part of differential RKG and the foot of its intsizura. However in many cases this point does not manage to be identified accurately, then the end of the period of exile is defined at first the II tone of the synchronous phonocardiogram (minus a time lag of a reogramma). More exact results gives definition of the period of exile on a differential curve of a central pulse (fig. 2). The received sizes L, Z, h, e substitute in a formula (4) and receive values of a stroke output of blood in millimeters.
Use of a reokardiografiya
Simplicity and availability of a method, a possibility of its use at any weight of a condition of patients, and also in the course of exercise and other functional loads promotes broad use of R., especially for dynamic researches of a stroke output of heart in clinical conditions, for conducting functional and pharmacological trials, and also for control of changes of a hemodynamics under the influence of specific influences on healthy faces (sports loadings, hypo - and hyper barium etc.).
For control of cordial activity in the course of rendering urgent kardiol. the help and monitor observation in chambers of an intensive care various modifications of reografichesky techniques as, e.g., a technique of an integral reografiya of a body according to M. I. Tyshchenko (1971), at a cut electrodes place in distal departments of extremities are developed. Along with the original technique according to M. I. Tyshchenko providing a bipolar way of measurements, A. P. Golikov and soavt. (1980) its tetrapolar option by means of the reconstructed model of a reopletizmograf RPG-202 is developed. Development of automatic systems like the offered G. I. Sidorenko, L in this respect is of considerable interest. 3. P Olonets and soavt. devices for continuous definition of an equivalent of shock emission and peripheric resistance on the basis of a bipolar reokardiograf, or the PKAG-01 polycardioanalyzer for the automated definition of a stroke output of blood and the analysis of a tetrapolar chest reogramma.
The sizes of shock and minute volumes of blood received by reografichesky methods can be used for calculation of a number of complex indicators hemodynamics (see), such as rate of volume flow of a blood-groove in an aorta, the power of cordial reductions, peripheric resistance, etc. that allows to study more fully the major parameters characterizing a functional condition of blood circulation.
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I. M. Kayevitser.