RU2273452C2 - Method for diagnosing water balance disorders in extracellular fluid of body - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: method involves measuring human body dimensions, electric impedance of legs Z_L, trunk Z_T and arms Z_A in sounding them with low frequency current and potential electrodes placed on distal extremity parts, determining extracellular fluid volume of human body parts with additional current electrodes being placed on the left and right sides of the neck. Sounding currents are passed through in turn between the neck and leg electrodes on the same side. Total impedance of the right trunk part and leg Z_RTL and one of the left trunk part and leg Z_LTL. Trunk impedance is determined as Z_T = 0.5(Z_RTL + Z_LTL - Z_L). Combined impedance Z_CT of arms and thoracic trunk part is measured when passing sounding current from arm to arm. Thoracic trunk part impedance is determined as Z_TT= Z_CT - Z_A. Extracellular fluid volume of abdominal trunk part is determined as difference V_A of trunk volume V_T and thoracic trunk part V_TT. When calculating trunk volume, geometric body size is taken as distance l from plane passing through upper arm surface to the middle of radiocarpal articulation when the arm is arranged along the trunk. When calculating thoracic trunk part volume, the value is equal to 0.4*l. Water balance disorders in extracellular fluid of body are is found to take place with discrepancy in extracellular fluid volume ratios of trunk to the thoracic part volume is equal to 1.77±0.05 in men and to 1.78±0.06 in women.

EFFECT: high accuracy of the method.

2 dwg, 5 tbl

Description

The invention relates to medicine, namely to non-invasive methods for determining fluid volumes in parts of the body in which an alternating electric current is used as a probing signal.

Modern diagnostic methods make it possible to conduct comprehensive studies without violating the integrity of the skin of the patient. This is achieved through the use of probe radiation with high penetrating power, for example: x-ray, ultrasound or magnetic, as well as electric current. As a result of interaction with body tissues, the signals of the probe radiation change their parameters, on the basis of which it is possible to obtain a number of characteristics that reflect the structure of the body and the state of organs and tissues.

A known method for determining the volume of body fluid during hemodialysis is carried out by measuring the impedance of the legs at low and high frequencies and determining the volumes of extracellular, cellular and total body fluids based on the relationship of impedance with the volume of electrically conductive fluid in the measured part of the body, which can be used to judge the body's water balance (K.Sakamoto, H. Kanai, K.Sakurai Estimation of the fluid distribution change during hemodialysis by the electrical admittance method. Oslo, Proceedings of the XI international conference on electrical bioimpedance, 2001, 377-380).

The disadvantage of this method is the low accuracy due to the fact that the fluid volumes of the whole organism are estimated indirectly, additionally using the parameters of the change in blood parameters (hematocrit).

The closest analogue is a method for determining the violation of the water balance of the extracellular fluid of the body using a device for determining the volumetric content of extracellular fluid in the tissues of a biological object (Patent SU No. 1826864, class A 61 B 5/05, publ. 1993), which consists in measuring growth ( geometric size of the body), imposing potential and current electrodes on the distal parts of the limbs, measuring the impedance of the arms, trunk and legs when probing tissues with a low-frequency current and determining, based on the measured parameters, extracellular volumes full-time fluid.

The disadvantage of this method is the low accuracy of determining the volume of body fluid and volumes in the upper (thoracic) and lower (abdominal) parts, which is due to the high uneven distribution of the probe current in the body, which does not allow to accurately determine the violation of the water balance of the body. Additionally, the uneven distribution of the current density arises due to the fact that the tissues of the thoracic and abdominal regions differ significantly both in the anatomical structure and in the amount of fluid contained in them, for example, the thoracic region is largely filled with the air volume of the trachea and lungs.

The objective of the invention is to eliminate these drawbacks by increasing the accuracy of determining the volume of extracellular fluid of the body and its thoracic and abdominal regions by ensuring uniform distribution of the probe current in the body volume and using more accurate values characterizing the geometric dimensions of the body when determining the volume of parts of the body.

To do this, in the method for determining the violation of the water balance of the extracellular fluid of the body, including measuring the geometric size of the body, the electrical impedance of the hands Z _P , the body Z _T and legs Z _H when they are probed with a low-frequency current through current and potential electrodes superimposed on the distal parts of the limbs, determine extracellular fluid volume of the parts of the body, it is proposed to additionally impose current electrodes on the left and right parts of the neck, sequentially pass probe currents between the electrodes of one nominal neck sides and legs, and to measure the total impedance of the right side of the torso and the right foot Z _PTN and left sides of the trunk and left leg Z _LTN, the impedance Z of the trunk defined as _T = 0.5 _(PTN + Z Z -Z _{LTN H} ), when a probe current is passed between the hands, measure the joint impedance of the hands and the thoracic part Z _CP , and determine the impedance for the thoracic part of the body as Z _TT = Z _CP -Z _P and the volume of extracellular fluid of this part of the body, while the volume of extracellular fluid of the abdominal part of the body determine as the difference between volumes of the torso and thoracic part of the body, and as the geometric size of the body when calculating the volume of the body, use the distance l from the plane passing through the upper surface of the shoulder to the middle of the wrist joint with the arm along the body, and when calculating the volume of the thoracic part - a value of 0, 4l, in this case, the violation of the water balance of the extracellular fluid of the body is judged if the ratio of the volume of extracellular fluid of the abdominal body to the volume of the thoracic parts of the body to a value of 1.77 ± 0.05 for men and 1.78 ± 0.06 for women.

The invention is illustrated by drawings, reflecting the equivalent spatial scheme of the spatial conjugation of the impedance of body parts, where: in Fig.1 shows an equivalent circuit showing the impedance of the analyzed parts of the body; figure 2 shows a diagram of an algorithm for measuring the impedance of body parts.

The method for determining the violation of the water balance of the extracellular fluid of the body is as follows.

To measure the impedance of the body parts, the tetrapolar method is used, in which pairs of current and potential electrodes are applied to the distal parts of the forearms and legs, and additional current electrodes are applied to the left and right parts of the neck. The impedance in the selected leads is measured by means of a probing current of low frequency, the switching of which between current electrodes is carried out by means of a current switch controlled through an interface by a controller (Fig. 2). Signals from potential electrodes through a potential switch, a voltage meter and an interface are sent to the controller, which also controls the potential switch, which ensures registration in the selected leads.

To determine the impedance of the body Z _T and its thoracic Z _TT and abdominal Z _AT parts, the signal is measured in the following leads, including the impedance of the following parts of the body (figure 1):

Z _P = Z _PR + Z _PT + Z _PN , where:

Z _P - the impedance of the right side of the body, which is measured with the passage of current between the right hand and the right foot by measuring between them the lead voltage for the right side of the body;

Z _PN - impedance of the right leg;

Z _PT - the impedance of the right side of the body;

Z _PR - impedance of the right hand.

Z _L = Z _LR + Z _LT + Z _LN , where:

Z _L - the impedance of the left side of the body, which is measured with the passage of current between the left hand and left foot by measuring the lead voltage between the left side of the body;

Z _LN - impedance of the left leg;

Z _LT - the impedance of the left side of the body;

Z _LR - impedance of the left hand.

Z _H = Z _PN + Z _LN , where:

Z _H - the impedance of the legs, which is measured by the passage of current between the legs by measuring the voltage between them;

Z _PTN = 2 _PT + Z _PN, where:

Z _PTN - the impedance of the right side of the body and the right leg, which is measured by the passage of current between the right side of the neck and the right foot by measuring the voltage between the right hand and the right foot;

Z _LTN = Z _LT + Z _LN

Z _LTN - the impedance of the left side of the body and the left foot, which is measured by the passage of current between the left side of the neck and the left foot by measuring the voltage between the left hand and the left foot;

Z _CP = Z _PR + Z _TT + Z _PR , where:

Z _CP - the impedance of the upper body, which is measured by the passage of current between the right hand and the left hand by measuring between them the voltage of abduction for the upper body;

Z _TT - impedance of the thoracic part of the body.

To measure Z _T, it is necessary that the probing current (I _Z ) be evenly distributed throughout the entire electrically conductive volume of the body. This condition is satisfied, to the greatest extent, with the location of the current electrodes on the neck and leg. With this arrangement of the electrodes increases the uniformity of distribution of the I _W in cross-sectional area of the trunk and longitudinal orientation is achieved _Z direction I along the entire length of the body. The value of Z _{T is} obtained as a result of two successive measurements of the impedance: Z _PTN and Z _LTN , as well as measurements of Z _H , which can be performed before or after sequential measurement of the impedance Z _PTN and Z _LTN :

Z _T = 0.5 · (Z _PTN +2 _LTN -Z _N )

The peculiarity of the Z _T measurement is that it is made between two imaginary "electric boundaries": the first passes at the level of the hip joints along the lower streamline as it passes through the legs, the second along the line passing in the upper plane between the shoulders, i.e. on the highest equipotential surface in the shoulder area. Together with a uniform distribution of _IZ in the body due to the fixation of current electrodes on the neck and legs and taking into account the successive measurement of the impedance of the right and left parts of the body, it is possible to obtain the value Z _T , which reliably displays the impedance of the body.

The impedance of the right hand Z _PR is determined from the measurement results of the impedance Z _P and the impedance Z _PTN :

Z _P -Z _PTN = Z _PR

The impedance of the left hand Z _LR is determined from the measurement results of the impedance Z _L and the impedance Z _LTN :

Z _L -z _LTN = Z _LR

The impedance of the thoracic part of the trunk Z _TT is determined from the measurement results of the impedance Z _CP and the impedance Z _PR and Z _LR :

Z _TT = Z _CP -Z _PR -Z _LR

The impedance of the abdominal part of the body Z _AT is determined from the measurement results of the impedance Z _T and impedance Z _TT :

Z _AT = Z _T -Z _TT

Tissue impedance (Z _LF ), measured at a low frequency (5 kHz), is due to the passage of current through a space filled with extracellular fluid.

The volumes of extracellular (V _BH ) body fluid are determined according to the well-known biophysical model based on their impedance (Z _BH ), specific resistance of body fluid (ρ), and body length (l) according to the following formulas:

V _BH = ρ · l ² / Z _BH , where:

Z _LF - tissue impedance measured at a low frequency (LF) of 5 kHz.

As the base length (l), the distance from the plane passing through the upper surface of the shoulder to the middle of the wrist joint is measured and based on its size and known anthropometric ratios, the values used as the length for the studied parts of the body are determined:

l _T = 1; l _TT = 0.4 · 1; Where:

l _T is the value used to determine the volume of the body;

l _TT is the value used to determine the volume of the thoracic part of the body.

The value of resistivity (ρ) used to determine the volume of fluid was clarified during the bioimpedance control of medical procedures that carry out fluid deficiency in the body: hemodialysis, plasmapheresis. For a probe current frequency of 5 kHz and impedance measurement by the tetrapolar method: ρ = 70 Ohm · cm.

The impedance values: Z _P , Z _L , Z _H , Z _PTN , Z _LTN , Z _CP receive, using the analyzer ABC-01 (Medass) or a similar device, for example, made according to the above diagram (figure 2).

The metrological reliability of the method is clearly demonstrated during the control of fluid volumes in patients who, during therapy, created a quantitative dynamics of extracellular fluid volumes. In the first case, this occurred after the injection of saline into the vein of the arm. With this procedure, for the first time after administration, the volume of extracellular fluid of the thoracic region mainly changes. In the second case, the volume of extracellular fluid was monitored during the replacement of the solution in the abdominal cavity in a patient undergoing peritonial dialysis. With this procedure, the volume of extracellular fluid in the abdominal region changes.

The impedance measurements were carried out with the ABC-01 MEDASS instrument using 5 pairs of electrodes placed on the legs of the wrist and neck. The impedance of the arms, trunk, and legs was measured at a low (5 kHz) frequency. As the "basic interelectrode distance" - "l", the distance from the plane passing through the upper surface of the shoulder to the middle of the wrist joint was measured with an accuracy of 1 cm.

The normal values of the ratio of the volumes of extracellular fluid of the abdominal and thoracic regions (V _A / V _TT ) for men and women were obtained by examining 140 healthy volunteers aged 16 to 55 years, of which 80 men and 60 women with normal blood pressure, and whose body mass index was 19-25.

The range of l values for men ranged from 49 to 62 cm. Based on the measured l values, the impedance measurements were divided (in 1 cm increments) into 14 groups with indices: 49 m ÷ 62 m. The values of the measured volumes of extracellular fluid for the thoracic region of the subjects were in the range 1.76 ÷ 2.83 L, and for the abdominal region in the range e 3.16 ÷ 5.05 L. Statistical analysis of the average values of V _A / V _{TT of the} analyzed groups of men “49 m ÷ 62 m” showed that with an increase in the value of “l” the values of V _A / V _TT remain relatively stable and are expressed by the following average statistical values of 1.77 ± 0.05 .

The range of “1” values for women ranged from 46 to 56 cm. Based on the measured “1” values, the impedance measurements were divided (in 1 cm increments) into 11 groups with indices: “46 w ÷ 56 w”. The values of the measured extracellular volumes liquids for the thoracic region of the subjects were in the range of 1.27 ÷ 2.18 l, and for the abdominal region in the range of 2.61 ÷ 3.88 l. The results of a statistical analysis of the mean values of "A / T" for groups of women "46 w ÷ 56 w", carried out similarly as for groups of men amounted to 1.78 ± 0.06.

Example 1

Patient M., 18 years old, weight 47 kg, l = 51 cm. Bioimpedance control of fluid volumes in the body was carried out before the PF procedure and at the time of administration of 300 ml. saline before plasmapheresis. The impedance values measured in the leads before the introduction of saline are shown in Table 1, and the calculated impedance values for body parts before and during the introduction in Table 2:

Table 1 Impedance in leads, Ohm Z _P Z _L Z _h Z _PTN Z _LTN Z _CP 641.5 555.4 534.9 319.0 294.0 601.3 table 2 The entered volume, ml Impedance of body parts and areas of the body, Ohm Torso Z _T Thoracic Z _TT Abdominal Z _A 0 39.07 8.22 30.35 +200 37.77 7.37 30,4 +250 37.08 7.13 29.95 +300 36.93 6.78 30.15

The volume values: V _{BH of} liquids calculated according to the formulas of the biophysical model are shown in the table:

Table 3 Body parts The volume of fluid in parts of the body and areas of the body, l. Before the introduction of saline 0.2 L introduced 0.25 L introduced Introduced 0.3 L Torso 4.68 4.85 4.93 4.95 Thoracic 1,67 1.76 1.79 1.81 Abdominal 3.01 3.09 3.14 3.14 Attitude 1.80 1.76 1.75 1.73 V _A / V _TT Volume change extracellular 0 0.17 0.25 0.27 liquids

The analysis of the obtained values of the volumes of fluid (Table 3) shows: the values by which the volume of extracellular fluid of the body increases during the introduction of physiological saline are in good agreement with the volumes introduced;

the value of the ratio V _A / V _TT during the injection of physiological saline into the vein decreases, thus, the capabilities of the method for displaying the process of redistribution of extracellular fluid between the abdominal and thoracic regions of the body are reliably demonstrated.

Example 2

Patient G., 35 years old, weight 51.4 kg, l = 54 cm, peritoneal dialysis is performed for the first month, the volume of the injected solution is 2.5% into the abdominal cavity: 2.5 liters.

Determined by the proposed method, changes in fluid volumes in parts of the body during one procedure for replacing a solution in the stomach: "full stomach → empty stomach → full stomach". The dynamics of changes in extracellular fluid volumes are shown in table 4.

Table 4 Body parts The volume of fluid in body parts and areas of the body, l full belly empty stomach full belly Hands 1.24 1.24 1.23 Torso 8.98 7.44 8.72 Thoracic 3.10 2.63 2.91 Abdominal 5.88 4.81 5.81 Ratio V _A / V _TT 0 1,54 0.26 Volume change extracellular 1.90 1.83 2.00 liquids

During the procedure for replacing the solution in the abdomen, the volumes of extracellular fluid significantly decreased only in the body by 1.54 L and remained at the same level in the hands. The extracellular volume in the abdominal region decreased by 1.07 L, after which it increased by 1.0 L, which is in good agreement with the dynamics of the volumes of the replaced solution. The dynamics of changes in the volume of fluid in the body of 0.26 l is in good agreement with the dynamics of the volumes of the drained 2.7 l and flooded solutions 2.5 l (difference 0.2 l).

The results obtained in the form of: a synchronous decrease in the values of extracellular fluid volumes during the procedure demonstrate the capabilities of the method to display the dynamics of fluid volumes in body parts at short time intervals.

During the procedure, the calculation of the volume of the cell fluid should be made with a correction that takes into account the increased electrical conductivity of the injected solution, in the given example, the concentration of the solution is 2.5%, i.e. more than twice the concentration of the isotonic solution.

A change in the magnitude of the ratio V _A / V _TT reliably reflects the dynamics of an increase in the volume of extracellular fluid in the abdominal region relative to the thoracic.

Compared with the prototype, which determines the volume of fluid in parts of the body by sensing with a low-frequency current, the claimed method has the following advantages:

the accuracy of determining the impedance of the body, and consequently, the volume of its fluid is increased due to a more uniform distribution of the probe current in the thoracic region, not covered by the prototype and is ≈20% of the total body volume;

the accuracy of determining the volumes of extracellular fluid of the thoracic and abdominal regions of the body in the proposed method allows to reliably determine the dynamics of volumes in the regions during procedures for the introduction or replacement of solutions to patients.

Thus, the proposed method allows to increase the accuracy of non-invasive determination of extracellular volumes in the trunk and its regions by measuring the parameters of the trunk in a more complete volume.

Example 3

Patient U., 24 years old, weighing 56 kg, l = 57 cm, multiple organ failure syndrome, which developed against the background of diffuse fibro-purulent peritonitis, underwent a continuous procedure of veno-venous hemofiltration for 24 hours. Bioimpedance control of fluid volumes in the body was carried out before and after the procedure, as well as on the 6th and 8th day after its completion, the measurement results are shown in Table 5.

The volume of fluid in the patient, measured before the procedure showed that the patient is in a state of dehydration. Based on what, hemofiltration was carried out in a hemodilution mode with a positive balance during the procedure equal to 1.8 liters. Additionally, during the procedure, massive infusion therapy was carried out in a volume of 8.0 liters. Diuresis during the procedure was 3.0 liters, and discharge by drainage was 3.1 liters. Therefore, the patient received 9.8 liters of fluid during the procedure, and 6.1 liters were withdrawn by him during the same period. Under normal conditions of temperature and humidity in the room, the body loses by means of perspiration from 0.8-1.0 liters of water, forming the so-called imperceptible losses. Given the patient’s normal body temperature and mechanical ventilation with humidified oxygen, the loss from perspiration was 0.8 l and, therefore, the total amount of fluid excreted by the body during the procedure was 6.9 l. Based on what, during the procedure, the patient achieved a positive fluid balance in the amount of 2.9 liters.

According to the results of bioimpedance measurements, the patient’s fluid volume during the procedure increased: in the body by 2.96 liters (Table 5), and in the arms and legs, respectively, by 0.15 and 0.68 liters. Based on what, the positive fluid balance measured by the bioimpedance method was 3.79 l.

Analysis of the calculated (2.9 L) and measured (3.79 L) fluid balance in the patient during the procedure showed that their difference is 0.89 L, which is 16.7 (relative to the total volume of fluid involved in the procedure) 9.8 + 6.9) L, is 5.3%. These results indicate that the proposed method allows you to accurately control the dynamics of fluid volumes in patients who undergo lengthy infusion procedures with large volumes.

The value of the ratio of volumes V _A / V _TT during the procedure did not change and amounted to 1.81. Therefore, we can conclude that the procedure regarding the distribution of fluid in the body was carried out adequately, and the normalization of this parameter on the 6th day to 1.76 additionally reflects the overall positive dynamics in the treatment.

Thus, the proposed method allows to increase the accuracy of non-invasive determination of extracellular fluid volumes in the trunk and its regions by measuring the trunk impedance in a more complete volume, as well as to reliably evaluate the occurring disturbances in the extracellular fluid water balance between the abdominal and thoracic regions, which allows you to adjust the treatment tactics and reduce the number of complications in the treatment of the excretory system of the body.

Claims (1)

A method for determining the violation of the water balance of the extracellular fluid of the body, including measuring the geometric size of the body, the electrical impedance of the hands Z _P , the body Z _T and legs Z _H when they are probed with a low-frequency current by current and potential electrodes superimposed on the distal parts of the limbs, determining the extracellular volume of fluid parts of the body, characterized in that they additionally impose current electrodes on the left and right parts of the neck, sequentially pass probing currents between the electrodes of the same ennyh neck sides and legs, and the total impedance measured right side of the torso and the right foot Z _PTN, and the left part of the trunk and left leg Z _LTN, the impedance Z of the trunk is determined as _T = 0.5 _(PTN + Z Z -Z _{LTN H} ), when a probe current is passed between the hands, the joint impedance of the hands and thoracic part Z _{CT is} measured and the impedance for the thoracic part of the body is determined as Z _TT = Z _CP -Z _P and the volume of extracellular fluid of the abdominal part of the body V _A is determined as the difference between the volumes of the body V _T and thoracic part of the body V _TT , and in quality In terms of body geometry, when calculating the volume of the body, use the distance l from the plane passing through the upper surface of the shoulder to the middle of the wrist joint with the arm along the body, and when calculating the volume of the thoracic part, the value is 0.4l, while water balance is disturbed extracellular fluid of the body is judged if the ratio of the volumes of extracellular fluid of the abdominal part of the body to the volume of the thoracic part of the body does not match the value for men 1.77 ± 0.05, and for women 1 78 ± 0.06.

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