CN102008304A - Signal simulation method for electrical impedance gastric motility detection - Google Patents

Abstract

The invention discloses a method for simulating and detecting an impedance gastric motility signal. Stomach and tissues surrounding the stomach are simulated by using an elastic solid medium and a liquid medium with different conductivity; the elastic solid medium is pressed by a shifting fork for deformation; and a motor drives the shifting fork to move along the elastic solid medium according to a preset mode under the control of a mechanical electric control unit to generate deformation propagation so as to simulate a gastric peristalsis process. When current is injected from an exciting electrode, the boundary of the liquid medium and the solid medium deforms to change field conductivity distribution; the voltage variation of the boundary is measured from a detection electrode, is amplified, demodulated and transformed and is input into a computer to calculate and analyze an impedance signal; and the impedance change caused by conductivity change is calculated by a sensitivity coefficient method.

Description

A kind of signal imitation method that is used for the detection of electrical impedance gastric motility

Technical field

The present invention relates to the biomedical signals measuring field, be mainly used in the bio-electrical impedance gastric motility and detect the simulation that stomach moves and the electrical impedance signal changes in the research.

Background technology

The detection technique of the biomedical information that the medical science electrical impedance technology is a kind of electrical characteristics of utilizing biological tissue and organ and Changing Pattern extraction thereof and Human Physiology, pathological condition is relevant.It injects small AC measurment curtage by the electrode system that places body surface to detected object usually, detects corresponding electrical impedance and situation of change thereof, then according to different application purposes, obtains relevant physiology and pathological information.

The motion of stomach is the process that electrical activity-machinery of a complexity shrinks and conducts, and it is begun by the myoelectrical activity of pipe smooth muscle, forms dividing a word with a hyphen at the end of a line property contraction vertical, annular smooth muscle, and initiation body of stomach, gastric antrum shrink and propagate to the pylorus of far-end.It defers to the rhythm and pace of moving things of electrical activity, also depends on the influence of the factors such as amplitude, time limit, direction and conduction distance that conductivity is shunk, and also is subjected to the restriction of multiple factors such as food species, gut hormone react, make a variation between daytime simultaneously.

Stomach is that the human body internal ratio is easier to one of organ that extracts electrical impedance information, in the active stage of stomach, as gastric emptying or stomach shrink, during wriggling, because it is bigger that the form of stomach, volume and content thereof are formed the change of situation, its electrical property change is very obvious, Changing Pattern is corresponding with gastric motility situation, and dependency is strong.Adopt bioimpedance method can realize noinvasive, sensitivity, extract and gastric motility corresponding electrical characteristics of situation and change information thereof exactly.

Body of stomach is in the encirclement of other organ and tissue, it is to realize by the electrode that is positioned over the epigastrium body surface that the bio-electrical impedance gastric motility detects, promptly form a metastable electric field in human body upper abdomen zone, and produce a Potential distribution at body surface from exciting electrode injection and effusive electric current.Because coat of the stomach and gastric content are different with the electrical conductivity of peripheral organs and tissue, when stomach shrinks, when wriggling, will produce disturbance to this metastable electric field, thereby change the distribution of aforementioned electrostatic field, form new electric field, and this variation can be reflected on the Potential distribution of body surface.Detection system is measured the potential change of body surface by being positioned over stomach at the locational detecting electrode of body surface projection, and variation that just can perception body internal impedance reflects the contraction and the wriggling of body of stomach.In fact, the beating of heart, breathing and position motion etc. all can produce corresponding impedance variation, but we can extract the gastric motility impedance signal according to the frequecy characteristic of stomach motion.

In sum, the generation of gastric motility impedance signal is the process of a complexity, and the nonlinear properties that become when being can not be used the Linear Network element simulation.But in the debugging of research that the bio-electrical impedance gastric motility detects and detecting instrument, calibration operation, still need to simulate the method that the stomach movement resistance changes.

Detect in the research at present bio-electrical impedance, generally use resistance-capacitance network to simulate the electrical impedance characteristics and the variation thereof of tested biological tissue, adopt two dimension or three-dimensional resistance-capacitance network to constitute the basic electrical impedance characteristics of tested tissue, use the resistance-capacitance card module to change partial electrical impedance characteristics then, with the impedance specific regions of simulated tissue inside, this method is in field extensive uses such as electrical impedance tomography, electrical impedance bioelectrical impedance analysis.But, if in the bio-electrical impedance gastric motility detects, adopt resistance-capacitance network to simulate the wriggling of gastrointestinal tissue, then can produce following problem:

The first, according to the principle that the bio-electrical impedance gastric motility detects, this method is to utilize the different and realization of the electrical conductivity of Different Organs and tissue.Because gastrointestinal is in the encirclement of other organs and tissue substantially, its the motion all be by self smooth muscle (stringer, annular) shrink and to cause, on body surface (border), there is not tangible external movement, be that its impedance variation is under the fixed prerequisite in border, move by the adjacent interfaces of organ or tissue and produce with different electrical conductivity.Therefore, it is very difficult simulating this variation with linear resistance-capacitance network.

Second, the bio-electrical impedance gastric motility detects and is different from Static Detection such as electrical impedance tomography, electrical impedance bioelectrical impedance analysis, gastrointestinal peristalsis is the fluctuation of advancing along digestive tract in the digestion process, the impedance variation that is produced all changes on time and space, simulate such impedance variation, it also be very complicated for it to realize.

In order to address the above problem, the present invention proposes the method for a kind of electrical impedance gastric motility signal imitation.

Summary of the invention

The gastric motility signal imitation method that the present invention proposes, be to adopt to exert pressure at the interface of solid-state and liquid medium with different electrical conductivity, cause the mechanical creeping at interface, the electrical impedance that forms with the motion of simulation internal organs changes, and can be by this variation of electrode detection that is distributed in the medium periphery.

This method is used a tank, injects the liquid of a certain electrical conductivity in the tank, settles pair of exciting and a plurality of impedance bioelectrical measurement electrode on the cell wall, and electrode is realized being electrically connected with the liquid in the groove by the hole on the cell wall.Place one in the liquid in tank and have the solid elastomer that is different from liquid electric conductivity, and make its be suspended at the cell wall detecting electrode near, so just constituted and had the solid-state of two kinds of different electrical conductivity and liquid medium system.When the exciting electrode injection current, electric current enters system from an exciting electrode, behind the solid-state and liquid medium of flowing through, flows out from another exciting electrode.Because two media has different electrical conductivity, a temporary transient stable electric field can be formed, as shown in Figure 1 in tested zone.When the motion of simulation stomach, with a thin shift fork that is dipped in the liquid medium, compressing elastic solid medium, make it to produce deformation, cause two kinds of interface displacements between the different electrical conductivity media, thereby former Electric Field Distribution is changed, and cause that the current potential that is distributed in borderline detecting electrode changes.Like this, by measuring the potential change on the detecting electrode, under the condition of known deformation quantity and distribution of conductivity, can calculate the impedance variation that mimic stomach motor process produces according to following method.

The impedance electric field theory of Geselowitz is the variation of a certain regional electrical conductivity in the computed volume conductor and the main theoretical basis of the reform of Chinese economic structure of the impedance variation that causes also is the theoretical basis that electrical impedance method is measured gastric motility.

(x, y z), are formed by stacking by the distribution of conductivity of liquid medium in the tank and solid state medium if the initial conductivity in whole tank zone is distributed as σ.(A is B) with (C D) pastes on the border that is placed on the zone electrode pair.If φ represents exciting current I _φ(A, B) upward the voltage of time domain distributes, φ to be added to electrode pair _CDExpression electrode pair (C, the voltage that D) measures this moment.ψ represents exciting current I _ψ(C, D) upward the voltage of time domain distributes, ψ to be added to electrode pair _ABExpression electrode pair (A, the voltage that B) measures this moment.Definition transfer impedance Z is:

$Z=\frac{{\mathrm{\φ}}_{\mathrm{CD}}}{I_{\mathrm{\φ}}}=\frac{{\mathrm{\ψ}}_{\mathrm{AB}}}{I_{\mathrm{\ψ}}}$

Solid state medium is after producing deformation under the effect of thin fork in the system, and at a time, the conductivity variations in the tank zone can abstractly be at former field domain distribution of conductivity σ (x, y, electrical conductivity Δ σ (x, the y of the variation that superposeed on z), z), the distribution of conductivity that changes the back field domain be σ (x, y, z)+Δ σ (x, y, z), can cause being added in electrode pair (A, B) the exciting current I on _φRedistribute in conductor, thereby the voltage distribution that causes the zone becomes φ (σ+Δ σ) from φ (σ), transfer impedance becomes Z+ Δ Z by Z, can prove that impedance increment is:

$\mathrm{\ΔZ}=-{\∫}_{\mathrm{\Ω}}\mathrm{\Δ\σ}\frac{\▿\mathrm{\φ}(\mathrm{\σ}+\mathrm{\Δ\σ})}{I_{\mathrm{\φ}}}\·\frac{\▿\mathrm{\ψ}\left(\mathrm{\σ}\right)}{I_{\mathrm{\ψ}}}\mathrm{d\Ω}---\left(1\right)$

In (1) formula, with the gradient of voltage distribution

Launch at the σ place, have:

$\mathrm{\ΔZ}=-{\∫}_{\mathrm{\Ω}}\mathrm{\Δ\σ}\frac{\▿\mathrm{\φ}\left(\mathrm{\σ}\right)}{I_{\mathrm{\φ}}}\·\frac{\▿\mathrm{\ψ}\left(\mathrm{\σ}\right)}{I_{\mathrm{\ψ}}}\mathrm{d\Ω}+o\left[{\left(\mathrm{\Δ\σ}\right)}^2\right]---\left(2\right)$

O[(Δ σ in the formula) ²] be the high-order dimensionless of Δ σ, if Δ σ is enough little, can ignore for second in the formula (2), and voltage gradient

Be independent of electrical conductivity increment Delta σ.

Δ Z represents when being conductivity variations Δ σ, measures the increment of impedance phase for transfer impedance, can adopt the sensitivity coefficient method to calculate, and its iterative process can be described as:

$\mathrm{\Δ}{Z}^{\left(k\right)}=Z-Z^{\left(k\right)}=-{\∫}_{\mathrm{\Ω}}\mathrm{\Δ}{\mathrm{\σ}}^{\left(k\right)}\frac{\▿\mathrm{\φ}\left({\mathrm{\σ}}^{\left(k\right)}\right)}{I_{\mathrm{\φ}}}\·\frac{\▿\mathrm{\ψ}\left({\mathrm{\σ}}^{\left(k\right)}\right)}{I_{\mathrm{\ψ}}}\mathrm{d\Ω}---\left(3\right)$

In the formula, Z measures impedance, Z ^(k)Be that distribution of conductivity is σ ^(k)The time transfer impedance, k represents iterations.Z ^(k)Expression formula be:

$Z^{\left(k\right)}=\frac{{\mathrm{\φ}}_{\mathrm{CD}}}{I_{\mathrm{\φ}}}=\frac{{\mathrm{\ψ}}_{\mathrm{AB}}}{I_{\mathrm{\ψ}}}---\left(4\right)$

Formula (4) need be found the solution by Finite Element Method, sets up the corresponding relation between the resistance variations in total transmission impedance variation and the individual unit.At first discrete region is changed into n tetrahedron element (Fig. 2), suppose each unit Ω _jThe internal conductance rate is a constant, and establishing the right number of absolute electrode is m, then being changed to of i transfer impedance:

$\mathrm{\Δ}{Z}_i^{\left(k\right)}=Z_i-Z_i^{\left(k\right)}=-{\mathrm{\Σ}}_{j=1}^n{S}_{\mathrm{ij}}\mathrm{\Δ}{\mathrm{\σ}}_j^{\left(k\right)},i=\mathrm{1,2},...,m$

Here

$S_{\mathrm{ij}}=-{\∫}_{{\mathrm{\Ω}}_i}\frac{\▿\mathrm{\φ}}{I_{\mathrm{\φ}}}\·\frac{\▿\mathrm{\ψ}}{I_{\mathrm{\ψ}}}\mathrm{d\Ω}$

S _IjWhat represent is the sensitivity coefficient of i electrode pair j unitary electrical conductivity, Z _iWith

Represent that respectively (the unit electrical conductivity is the k time iteration i counter electrode to j unit

) measurement impedance and transfer impedance.

Sensitivity coefficient S _IjRelevant with the apex coordinate of the tetrahedron element of subdivision.The summit of subdivision unit if (Fig. 3) be numbered (i, j, m, n), apex coordinate is respectively (x _i, y _i), (x _j, y _j), (x _m, y _m), (x _n, y _n), subscript e represents a certain unit, and unitary electrical conductivity is steady state value σ ^e, volume is V ^e, then sensitivity coefficient is:

$S_{\mathrm{ij}}=-{\∫}_{{\mathrm{\Ω}}_i}\frac{\▿\mathrm{\φ}}{I_{\mathrm{\φ}}}\·\frac{\▿\mathrm{\ψ}}{I_{\mathrm{\ψ}}}d{V}_j=-\frac{1}{I_{\mathrm{\φ}}{I}_{\mathrm{\ψ}}}{\mathrm{\φ}}_e^T\frac{{\mathrm{bb}}^T+{\mathrm{cc}}^T+{\mathrm{dd}}^T}{{36V}^e}{\mathrm{\ψ}}_e$

Here, b ^T=(b _i, b _j, b _m, b _n), c ^T=(c _i, c _j, c _m, c _n),

d ^T＝(d _i，d _j，d _m，d _n)。

$b_i=-\left|\begin{array}{ccc}1& y_j& z_j\\ 1& y_m& z_m\\ 1& y_n& z_n\end{array}\right|$ $b_j=\left|\begin{array}{ccc}1& y_i& z_i\\ 1& y_m& z_m\\ 1& y_n& z_n\end{array}\right|$ $b_m=-\left|\begin{array}{ccc}1& y_i& z_i\\ 1& y_j& z_j\\ 1& y_n& z_n\end{array}\right|$ $b_n=\left|\begin{array}{ccc}1& y_i& z_i\\ 1& y_j& z_j\\ 1& y_m& z_m\end{array}\right|$

$c_i=\left|\begin{array}{ccc}1& x_j& z_j\\ 1& x_m& z_m\\ 1& x_n& z_n\end{array}\right|$ $c_j=-\left|\begin{array}{ccc}1& x_i& z_i\\ 1& x_m& z_m\\ 1& x_n& z_n\end{array}\right|$ $c_m=\left|\begin{array}{ccc}1& x_i& z_i\\ 1& x_j& z_j\\ 1& x_n& z_n\end{array}\right|$ $c_n=-\left|\begin{array}{ccc}1& x_i& z_i\\ 1& x_j& z_j\\ 1& x_m& z_m\end{array}\right|$

$d_i=-\left|\begin{array}{ccc}1& x_j& y_j\\ 1& x_m& y_m\\ 1& x_n& y_n\end{array}\right|$ $d_j=\left|\begin{array}{ccc}1& x_i& y_i\\ 1& x_m& y_m\\ 1& x_n& y_n\end{array}\right|$ $d_m=-\left|\begin{array}{ccc}1& x_i& y_i\\ 1& x_j& y_j\\ 1& x_n& y_n\end{array}\right|$ $d_n=\left|\begin{array}{ccc}1& x_i& y_i\\ 1& x_j& y_j\\ 1& m_m& y_m\end{array}\right|$

$V^e=\frac{1}{6}\left|\begin{array}{cccc}1& x_i& y_i& z_i\\ 1& x_j& y_j& z_j\\ 1& x_m& y_m& z_m\\ 1& x_n& y_n& z_n\end{array}\right|$

φ _eExpression I _φInjecting electrode is to (A, the node potential vector of unit e in the time of B), ψ _eExpression I _ψInjecting electrode is to (C, the node potential vector of unit e in the time of D).

The voltage of whole each node of subdivision field domain can be solved by following two nodal equiations:

K _φ＝I _φ

K _ψ＝I _ψ

Wherein,

$K_e=\frac{{\mathrm{\σ}}^e}{36V^e}\left[\begin{array}{cccc}{b}_i{b}_i+c_i{c}_i+d_i{d}_i& b_i{b}_j+c_i{c}_j+d_i{d}_j& b_i{b}_m+c_i{c}_m+d_i{d}_m& b_i{b}_n+c_i{c}_n+d_i{d}_n\\ b_i{b}_j+c_i{c}_j+d_i{d}_j& b_j{b}_j+c_j{c}_j+d_j{d}_j& b_j{b}_m+c_j{c}_m+d_j{d}_m& b_j{b}_n+c_j{c}_n+d_j{d}_n\\ b_i{b}_m+c_i{c}_m{d}_i{d}_m& b_m{b}_j+c_m{c}_j+d_m{d}_j& b_m{b}_m+c_m{c}_m+d_m{d}_m& b_m{b}_n+c_m{c}_n+d_m{d}_n\\ b_i{b}_n+c_i{c}_n+c_i{c}_n& b_n{b}_j+c_n{c}_j+d_n{d}_j& b_n{b}_m+c_n{c}_m+d_n{d}_m& b_n{b}_n+c_n{c}_n+d_n{d}_n\end{array}\right]$

The transfer impedance change vector of remembering the k time iteration is

Note conductivity variations vector is

Then have:

ΔZ ^(k)＝S ^(k)Δσ ^(k) (5)

Can calculate conductivity variations by formula (5) is Δ σ ^(k)The time transfer impedance Δ Z ^(k)

Owing to gastric peristalsis is that smooth muscle contraction and propagate along coat of the stomach forms, be the forms of motion of simulation stomach, adopt the mechanical movement of shift fork, promptly shift fork moves (Fig. 4) along the elastic solid dielectric surface, thus the propagation of generation deformation.For reaching this purpose, adopt a cover electric-controlled mechanical device, this device can experimental needs, produce motion multi-form, friction speed, realize the function that the simulation stomach moves, and its principle is as shown in Figure 5.

The present invention is further described below in conjunction with drawings and Examples.

Description of drawings

Fig. 1: system's Electric Field Distribution schematic diagram

Fig. 2: field domain three-dimensional dividing figure

Fig. 3: subdivision unit figure

Fig. 4: sketch map is moved in medium deformation

Fig. 5: system's schematic three dimensional views

1. exciting electrodes among the figure, 2. constant-current source, 3. detecting electrode, 4. liquid medium, 5. elastic solid medium, 6. electrical current distribution lines, 7. deformed region, 8. shift fork, 9. deformation moving direction, 10. tetrahedron subdivision unit, 11. slide blocks, 12. tanks, 13. motor, 14. leading screws, 15. computers, 16. detection system, 17. mechanical ECUs.

The specific embodiment

As shown in Figure 5, hardware system of the present invention comprises: exciting electrode (1), constant-current source (2), detecting electrode (3), tank (12), liquid medium (4), elastic solid medium (5), slide block (11), motor (13), leading screw (14), shift fork (8), detection system (16), computer (15), mechanical ECU (17).

In the embodiment shown in fig. 5, when system carries out stomach motion simulation experiment, at first, liquid medium (4) is injected tank (12), and elastic solid medium (5) is placed liquid according to the electrical conductivity of experiment needs configuration liquid medium (4) and elastic solid medium (5).The forms of motion of Chan Shenging is provided with the parameter of mechanical ECU as required, and shift fork (8) is pressed on the elastic solid medium (5), adjusts pressure.Electrical impedance stomach movement detection systems (16) is connected on exciting electrode (1) and the detecting electrode (3), is 50kHz by constant-current source (2) to the exciting electrode injected frequency, and peak-to-peak value is the alternating current of 1mA.Start mechanical ECU (17), shift fork moves along the elastic solid (Hookean body) medium in predetermined patterns, make detection system (16) can obtain the modulus of impedance analog signal of stomach motion, after amplifying, separate the mediation conversion, send into analysis and the processing that computer (15) carries out data.

Claims (1)

1. impedance gastric motility signal imitation method, the hardware system that this method adopts is by exciting electrode, constant-current source, detecting electrode, tank, liquid medium, the elastic solid medium, slide block, motor, leading screw, shift fork, the machinery ECU, detection system and computer constitute, it is characterized in that using elastic solid medium and liquid medium simulation stomach with two kinds of different electrical conductivity and the tissue that surrounds it, from the exciting electrode injection current, set up electric field, with shift fork compressing elastic solid medium, make it to produce deformation, change Electric Field Distribution, shift fork is moved along the elastic solid medium by motor-driven, cause the propagation of deformation, cause electric field to change continuously, produce the gastric motility impedance change signal.

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