CN205658910U - Human impedance admittance measuring instrument of high accuracy - Google Patents

Abstract

The utility model discloses a human impedance admittance measuring instrument of high accuracy, move looks ware, the differential voltage input utmost point, first adder frequency selective amplifier, first synchronous detection circuit, transimpedance amplifier, second adder frequency selective amplifier, second synchronization detection circuit, first -order differentiator and display including first to fourth measuring electrode, scaling circuit, fiduciary level, sine wave generator, triangle generator, buffer, the controllable amplifier of difference formula gain, the permanent width of cloth, wherein, first, second synchronous detection circuit comprise lock -in amplifier and low pass filter, and lock -in amplifier's output is connected with low pass filter's input. The utility model discloses a lock -in amplifier replaces general high frequency amplitude modulation demodulation circuit to improve the interference killing feature of instrument greatly, obviously improved measurement accuracy.

Description

High-precision human impedance-admittance measuring instrument

Technical field

This utility model relates to a kind of High-precision human impedance-admittance measuring instrument.

Background technology

Impedance-admittance volume diagram instrument configuring electrocardiograph or during polygraph, can direct convenience measure human body The impedance-admittance parameter at the positions such as breast, lung, liver, brain and first differential figure thereof.Thus obtain the stroke volume of human body, breathe, arteries and veins Fight, the physiological parameter such as cardiac index, cerebral blood flow.It is that a kind of atraumatic measures the convenience of Human Physiology electrical quantity and useful instrument Device.

In the measurements, regarding blood vessel as cylinder, blood of its flowing is equivalent to conductor, and free fat is equivalent to one by one Slight electric capacity.Therefore the blood vessel of human body can be considered the doublet of electric capacity and resistance on the whole, and its equiva lent impedance is:

$Z=\frac{R(1-j\mathrm{\ω}CR)}{1+{\mathrm{\ω}}^2{R}^2{C}^2}......\left(1\right)$

Wherein:

Vascular cross-section amasss

L unit length

ε dielectric constant

By R, C equation substitution (1) formula:

$Z=\frac{\mathrm{\ρ}L/A\·(1-j\mathrm{\ω}K\mathrm{\ϵ}\mathrm{\ρ})}{1+{\mathrm{\ω}}^2{\mathrm{\ρ}}^2{K}^2{\mathrm{\ϵ}}^2}$

The partial differential that Z carries out A obtains:

$\frac{dZ}{dA}=\frac{-\mathrm{\ρ}L(1-j\mathrm{\ω}K\mathrm{\ϵ}\mathrm{\ρ})}{A^2(1+{\mathrm{\ω}}^2{\mathrm{\ρ}}^2{K}^2{\mathrm{\ϵ}}^2)}$

After phase shift, both members obtains with divided by Z:

$\frac{dZ}{Z}=-\frac{dA}{A}......\left(2\right)$

Thus derive rate of change and the cross correlation of vascular cross-section rate of change of vascular hindrance, for quantitative study blood vessel Change provides Mathematics Proof.

The partial derivative of time and the proportionate relationship of blood entrance elastic vessel instantaneous delivery are derived as follows by impedance variation:

If length of vessel L is constant, according to conservation of mass theorem:

$\frac{\∂\left(D_0\mathrm{\Δ}AL\right)}{\∂t}\·\mathrm{\Δ}t=D_0{A}_0{U}^{\·}\mathrm{\Δ}t......\left(a\right)$

Δ V=Δ A L...... (b) again

Can obtain:

D0 blood specific gravity

A0 non-fluid injection body section

Q^·The instantaneous delivery of injection end

Δ A blood injects cross section increment after blood vessel

U^·Inject transient liquid flow velocity

According to Nyb₀Er relational expression: Δ Z=ρ L Δ A/ Δ A₀ ²......(d)

And Δ A=2 π r₀Δr......(e)

Wherein: r₀Vessel radius

Δ r radius increment

Again:

$\frac{\∂Z}{\∂t}=\frac{\∂\mathrm{\ρ}L}{{{\mathrm{\πr}}_0}^2}\·\frac{\∂r}{\∂t}......\left(f\right)$

E () substitutes into

Push away:

Instantaneous delivery formula measures the instantaneous blood stroke volume of human heart for impedance method undoubtedly and heart amount number provides one Individual good approach.According to hydrodynamics understand, as long as by during instantaneous delivery to pulsation liquid integration in injection length, Pushing away often to fight the volume injecting liquid, its expression formula is:

SV_Z=∫₀TQ^·Dt=(A₀ ²/ρ)ΔZ^t=ρ (L/Z₀)²ΔZ^t

Wherein: SV_ZFor liquid volume of often fighting

ΔZ—ΔZmax

Due to Δ Z^t=dT/dtmax T^·(Kabkicek is theoretical)

Wherein: T^·Being equivalent to the left ventricular ejection time on impedance differential map, it starts and baseline friendship up at dZ/dtmax Point, terminates to synchronize and second heart sound.

And then obtain: SV_Z=ρ (L/Z₀)²·dZ/dtmax·T·......(4)

Wherein: Z0 is human body basal impedance

L is for measuring interelectrode distance

ρ is blood resistivity

Simultaneously according to SV_Z.HR and BSA body surface area, can be in the hope of CI cardiac index:

CSI=HR 8V/BSA 1000 (liter/min/square metre) ... (5)

Wherein: according to Xu Shi Shi Ke get

BSA=0.0061cm (height)+0.0128kg (body weight)-0.1529

HR heart rate

Through substantial amounts of it is demonstrated experimentally that it is a kind of simple and effective means that impedance method measures physiological parameter.

Existing human body impedance admittance measurement circuit typically uses Amplitude Modulation High Frequency demodulator circuit.Human body in place, It is a big conductor, the space around it also exists the electromagnetic field of various alternation, according to the law of electromagnetic induction Understanding, this all will produce induction field and electric current with surface in human body.Owing to human body is a non-conductor, these disturb electricity Field sometime up to several volts even tens volts.Owing to it greatly exceed useful signal, cause strong interference, in general circuit, Although using difference channel in input stage, to improve the suppression to common mode interference signal, but because of the asymmetry of differential pair element General all more than 1%, thus common mode rejection ratio all can not do the highest, and more helpless to differential mode interference and noise, this Just leverage the accuracy of measurement result.

Utility model content

This utility model aims to provide a kind of High-precision human impedance-admittance measuring instrument, with solve that prior art exists by In the poor problem causing certainty of measurement low of interference free performance.

The technical solution of the utility model is:

A kind of High-precision human impedance-admittance measuring instrument, including first to fourth measurement electrode, scaling circuit, standard electric Flat, sine-wave generator, triangular-wave generator, buffer, differential type gain controlled amplifier, permanent width phase shifter, differential voltage Input pole, first adder frequency-selective amplifier, the first synchro detection circuit, trans-impedance amplifier, second adder frequency-selective amplifier, Second synchro detection circuit, first differential device and display；Wherein, the outfan of fiduciary level amplifies with differential type gain controllable One input of device connects, and two outfans of sine-wave generator are defeated with the second of differential type gain controlled amplifier respectively Enter the input of end and permanent width phase shifter to be connected；The outfan of differential type gain controlled amplifier and the input of buffer Connecting, the outfan of buffer and the outfan of scaling circuit are all measured electrode with first and are connected；Two of the permanent width phase shifter defeated Go out end respectively with an input and an input of second adder frequency-selective amplifier of first adder frequency-selective amplifier End connects；Two inputs of differential voltage input pole connect the second measurement electrode and the 3rd respectively and measure electrode, differential electrical The outfan of pressure input pole is connected with another input of first adder frequency-selective amplifier, this first adder frequency-selective amplifier Outfan and the first synchro detection circuit input connect, the outfan of the latter pass through a pair of ter end permutator (K1) First be associated between the 3rd input of differential type gain controlled amplifier and first differential device and the input of display turn Change connection；The input of trans-impedance amplifier and outfan measure the another of electrode and second adder frequency-selective amplifier with the 4th respectively One input connects, and the outfan of second adder frequency-selective amplifier and the input of the second synchro detection circuit connect, the latter Outfan by the second of described duplex three end permutator (K1) be associated in the input of first differential device and display with Between 3rd input of differential type gain controlled amplifier, conversion connects；The input of described first differential device passes through one Three end permutatoies (K2) are changed between triangular-wave generator and the input of display and are connected；This first differential device and display The input of device is by electric capacity output impedance or the variable signal of admittance；The first described synchro detection circuit or second synchronizes inspection Wave circuit is made up of lock-in amplifier and low pass filter, and the outfan of lock-in amplifier connects with the input of low pass filter Connect.

As the preferred structure of one of the present utility model, described lock-in amplifier is by integrated single functional simulation multiplication Device SA602A is constituted.

As the preferred structure of another kind of the present utility model, first to fourth described measurement electrode is by compound on surface The silver plate or the filamentary silver that have silver chloride are made.

Major advantage of the present utility model includes: use lock-in amplifier to replace general Amplitude Modulation High Frequency demodulator circuit, from And it is greatly improved the capacity of resisting disturbance of instrument instrument, hence it is evident that improve certainty of measurement.

Accompanying drawing explanation

Fig. 1 be this utility model embodiment totally constitute block diagram；

Fig. 2 is the embodiment circuit diagram of first, second synchro detection circuit in Fig. 1.

Detailed description of the invention

Seeing Fig. 1, this utility model one High-precision human impedance-admittance measuring instrument, including first to fourth measurement electrode 16～19, (10V/0.1 Ω) scaling circuit 1, fiduciary level 2, sinusoidal wave (50KHz) generator 3, triangular-wave generator 13, slow Rush device 4, differential type gain controlled amplifier 5, permanent width phase shifter 6, differential voltage input pole 7, first adder frequency-selective amplifier 8, the first synchro detection circuit 9, trans-impedance amplifier 10, second adder frequency-selective amplifier the 11, second synchro detection circuit 12, Rank differentiator 14 and display 15.Wherein, the outfan of fiduciary level 2 and an input of differential type gain controlled amplifier 5 End connects, the outfan of sine-wave generator 3 respectively with the second input of differential type gain controlled amplifier 5 and permanent amplitude shift phase The input of device 6 connects；The outfan of differential type gain controlled amplifier 5 is connected with the input of buffer 4, buffer 4 The outfan of outfan and scaling circuit 1 is all measured electrode 16 with first and is connected；Two outfans of permanent width phase shifter 6 respectively with One input of first adder frequency-selective amplifier 8 and second adder frequency-selective amplifier 11 connects；Differential voltage input pole 7 Two inputs connect the second measurement electrode 17 and the 3rd respectively and measure electrode 18, the outfan of differential voltage input pole 7 with Another input of first adder frequency-selective amplifier 8 connects, and the outfan of this first adder frequency-selective amplifier 8 and first is together The input of step detecting circuit 9 connects, and the outfan of the latter is associated in described by the first of a pair of ter end permutator (K1) Differential type gain controlled amplifier 5 the 3rd input and the input of first differential device 14 and display 15 between conversion even Connect.The input of trans-impedance amplifier 10 and outfan measure electrode 19 and second adder frequency-selective amplifier 11 with the 4th respectively Another input connects, and the outfan of second adder frequency-selective amplifier 11 and the input of the second synchro detection circuit 12 are even Connecing, the outfan of the latter is associated in described first differential device 14 by the second of described duplex three end permutator (K1) and shows Show to change between the input of device 15 and the 3rd input of differential type gain controlled amplifier 5 and be connected.Described first differential The input of device 14 by three end permutatoies (K2) triangular-wave generator 13 and display 15 input (this end also with K1 First 3 ends and second 2 ends connect) between conversion connect；This first differential device 14 and the input of display 15 By isolation capacitance C output △ Z or △ Y-signal.Outfan output dy/dt or the dz/dt signal of first differential device 14.

Described first～the 4th is measured electrode 16-19 and is made up of the silver plate or filamentary silver being compounded with silver chloride on surface.

Seeing Fig. 2, the first described synchro detection circuit 9 or the second synchro detection circuit 12 are by integrated single functional simulation Lock-in amplifier and low pass filter that multiplier SA602A is constituted form, the outfan of lock-in amplifier and low pass filter Input connects.

This utility model is in addition to the first synchro detection circuit 9 and the second synchro detection circuit 12, and remaining is conventional electricity Road.

One, operation principle of the present utility model is described as follows:

Complete machine duty (see Fig. 1) is divided into two kinds of situations to carry out, and both dmittance chart was measured and wave arrestment figure is measured, and was provided with breast Portion, pulmonary's regulating liver-QI, four switches measuring electrode 16-19 at these four positions of brain and 10V (0.1 Ω) scaling circuit 1 and triangle The calibration switch of wave producer 13, in order to the impedance-admittance of different parts is made different selections.

1, admittance measurement:

When K1 puts 1, carry out admittance measurement.Concrete work process is: first by high-gain amplifier integrated circuit 5G24 The sine-wave generator 3 of composition produces the constant amplitude high-frequency signal of 2V, 50KHz, decays to about 100mv after decay；Differential type Gain controlled amplifier 5 is after 50mv standard DC level compares control, and the high frequency letter of human body about 50mv transported to by buffered device 4 Number.Then, the amplitude modulated high-frequency signal drawn from tested position, the choosing being made up of 5G24 is added to through differential voltage input stage 7 After audio amplifier amplifies, deliver to the first synchro detection circuit 9, produce a direct current ripple control level and deliver to differential type gain controllable Amplifier 5, after comparing, adjusts output level, makes whole signal source system can load change frequency from wide model conspicuous for 0-200 Keep tested position all-the-time stable on 50mv voltage when enclosing fluctuation, thus reach the dynamic constant-voltage characteristic of high stable width.

Current detecting system, by the trans-impedance amplifier 10 being made up of 5G24, the high-frequency electrical of reflection human body admittance change Circulation changes high frequency voltage into, then delivers to the second synchro detection circuit 12 through second adder frequency-selective amplifier 11, finally obtains The alternating low frequency signal of one reflection human body admittance change, i.e. Δ y.A part is shown as y0 by display 15.Δ y is re-fed into one Rank differentiator 14, to t derivation, sends dy/dt differential ripple signal through first differential device 14.Deliver to electrocardiogram or multiple tracks the most again Physiograph describes one and connects admittance oscillogram, thus completes the measurement to human body admittance.

2, impedance measurement:

As K1 to 2, instrument carries out impedance diagram measurement.At this moment, signal source is born with current detection circuit one electric current of composition Feedback constant current closed loop, meanwhile, becomes voltage current transformation by buffer 4 changing-over after differential type gain controlled amplifier 5 Device, to improve signal source output impedance.Specific works process and voltage source controlled state are essentially identical, and institute is visibly different is mark Quasi-Automatic level control differential type gain controlled amplifier 5, obtain is the high-frequency constant current source characteristic of constant output 1.6mA.And voltage Measure loop is then connected with first differential device 14, complete to projection human body impedance change ± the tracing of U.

Scaling block, as K2 to 1, utilizes the triangular wave through verification that first differential device 14 is carried out auto-scaling.K3 to 1 Time, utilize string in loop 0.1 Ω resistance (in the scaling circuit 1) change measured, Δ y, Δ E manually to be calibrated.

Two, main circuit wants design objective:

1. dmittance chart is measured

(1) constant pressure source

A () concussion frequency and waveform 50KHz ± 5% are sinusoidal wave

(b) constant voltage value 50mv (virtual value)

When () constant-pressure stable degree is supported on 10 Ω-100 Ω change c, change in voltage is less than 1%

(d) frequency characteristic 0-200Hz

(2) Δ y leading indicator

A () output voltage amplitude is more than 10mv/10 σ

(b) frequency characteristic 0.5Hz-200Hz

(3) dy/dt leading indicator

A () output voltage amplitude is more than 10mv/1v/s

(b) frequency characteristic 5-200Hz

(c) signal to noise ratio

2 resistances are measured

(1) constant-current source

A () frequency of oscillation and waveform 50KHZ ± 5% are sinusoidal wave

(b) constant current value 1.6mA (virtual value)

When () constant current degree of stability is supported on 10 Ω-100 Ω change c, curent change is less than 1%

(d) frequency characteristic 0-200Hz

(2) Δ z leading indicator

A () output voltage amplitude is more than 10mv/0.1 Ω

(b) frequency characteristic 0.5-200Hz

(3) dz/dt leading indicator

A () output voltage amplitude is more than 10mv/0.1 Ω/s

(b) frequency characteristic 5-200Hz

(c) signal to noise ratio

3 calibrations

(1) calibration of Δ y and Δ E is square wave (manually)

(2) calibration of dy/dt and dz/dt is that (triangular wave is changed the square wave correction of 0.1 Ω, the width of calibration signal by 30 Ω Degree can be adjustable at 0-0.4 Ω) square wave.

Three, the feature of complete machine:

This utility model uses lock-in amplifier to replace general Amplitude Modulation High Frequency demodulator circuit, thus is greatly improved instrument instrument The capacity of resisting disturbance of device.Human body is in place, but is a big conductor, also exists each in the space around it Planting the electromagnetic field of alternation, according to the law of electromagnetic induction, this all will produce induction field and electric current with surface in human body.By Being a non-conductor in human body, these electric interfering fields are sometime up to a few volt even tens volts.Owing to it greatly exceed useful Signal, causes strong interference, in general circuit, although use difference channel in input stage, to improve common mode interference signal Suppression, but because the asymmetry of differential pair element is general all more than 1%, thus common mode rejection ratio all can not do the highest, and And it is more helpless to differential mode interference and noise.Lock-in amplifier is used to replace as synchronizing indicator for this this utility model Common average detection circuit, improves the interference free performance of complete machine.

Lock-in amplifier (Lock-in Amp) is a kind of Weak Signal Detecting Circuit, and it utilizes Theory of correlation detection, will be deep The weak signal extraction being embedded in noise is out.The lock-in amplifier being made up of integrated single functional simulation multiplier SA602A is such as Shown in Fig. 2, require to set biasing at IC interior according to analog multiplier, reduce sheet external circuit, use debugging simple Convenient.

F in Fig. 2₁T () is made up of useful signal s (t) and the signal being mixed into noise N (t), f_rT () is not done by noise The signal disturbed, and often and s (t) with frequency not homophase, the two has a great dependency, and noise N (t) and f_rT () is It is incoherent, so after coherent detection, noise will be suppressed, and s (t) will be extracted.Assume s (t) and f_rT () is all Sine, and meet ω₀=ω_r, it may be assumed that

So, multiplier output u₀₁(t) be:

Integrator (low pass filter that actually a cut-off frequency is the lowest) subsequently, by all 2 ω₀、ω₀Component All filter, only leave Section 1 (DC component), then:

K in formula₁For multiplier transmission coefficient, K₂For low pass filter transmission coefficient.

If the regulation permanent good fortune phase shifterMake phase contrastOr 180 °, then:

Visible, the output voltage of correlator depends solely on measured signal s (t) and unrelated with noise.

Upper cut-off frequency f of low pass filter in figure_HFor:

$f_H=\frac{1}{2{\mathrm{\πR}}_6{C}_5}=\frac{1}{2\mathrm{\π}\×{10}^5\×{10}^{-6}}Hz=1.6Hz$

Visible, frequency band is the narrowest, the DC quantity that only output is relevant with signal amplitude and phase contrast, and 2 ω₀、ω₀Component and making an uproar Sound all can be filtered out.

Have employed and suppress the method for carrier frequency to improve gain, prevent issuable clipping distortion, improve signal to noise ratio, simultaneously Also improve circuit to various different basal impedance measurement requirement abilities.At this moment because the basic Z0 impedance of human body is relatively big, with breast As a example by portion, there are about 30 Ω, and changing value is the least, at 0.1 below Ω, when measuring impedance in order to 10mv/0.1 Ω's to be reached Output, the gain of whole testing circuit will reach about 1000 times, as a example by constant-current source output 1.6mA measures electric current, hinder at 30 Ω Anti-upper blood pressure lowering 48mv.

Therefore, if gain is overall gain at the end of detector stage.At this moment carrier frequency peak value will reach more than tens volts.If Survey admittance, the gain of 50mv/10 Ω to be reached, overall gain about 80dB to be reached under some circumstances, therefore be so can not be normal Work.Conventional method is to reduce predetection high frequency peak gain to prevent amplitude limit.But so will make sensitivity and signal to noise ratio Decline.Some impedance diagram instrument utilize the starting voltage dead angle of transistor characteristor characteristic curve, make pipe work in Class B state, to carrier frequency Signal carries out carrier wave amplification, though certain gain and signal to noise ratio so can be improved, but the impact of temperature (fluctuation of initial angle), carry Waveform serious distortion after ripple, it is impossible to Z is made quantitative analysis, the most easily introduces harmonic wave interference.Therefore, we use and draw from signal source Go out one group of CF signal.The high-frequency signal of poor with carrier signal 180 ° is obtained, by summing circuit by positive amplitude modulation through phase locking unit Frequency-portions suppression major part in CF signal, to meet the needs of normal circuit operation.

(differential type gain controllable amplifies to have employed difference electronics attenuation type gain-controlled voltage amplifier in signal source circuit Device 5), its advantage is: gain reduction amount (dB) and control between voltage in certain scope linearly functional relationship, and has Attenuation is big, i.e.The features such as wide dynamic range.In signal source circuit, integrated the banishing of 5G24 is used to constitute Follow circuit and voltage-current converter circuit, further increase the dynamic characteristic of constant-current source and constant pressure source.

Additionally, measuring circuit also have employed trans-impedance amplifier 10 in current measurement input stage, to eliminate general Current Mutual Inductance The linearity error that device brings, improves the performance of decay.

Claims (3)

1. a High-precision human impedance-admittance measuring instrument, including: first measures electrode, the second measurement electrode, the 3rd measurement electricity Pole, the 4th measurement electrode, scaling circuit, fiduciary level, sine-wave generator, triangular-wave generator, buffer, differential type gain Controllable amplifier, the permanent width phase shifter, differential voltage input pole, first adder frequency-selective amplifier, the first synchro detection circuit, across Impedance amplifier, second adder frequency-selective amplifier, the second synchro detection circuit, first differential device and display；It is characterized in that: The outfan of fiduciary level is connected with an input of differential type gain controlled amplifier, two outputs of sine-wave generator End is connected with the second input, the input of perseverance width phase shifter of differential type gain controlled amplifier respectively；Differential type gain can The outfan of control amplifier is connected with the input of buffer, and the outfan of buffer and the outfan of scaling circuit are all with first Measurement electrode connects；Two outfans of permanent width phase shifter respectively with first adder frequency-selective amplifier and second adder frequency-selecting One input of amplifier connects；Two inputs of differential voltage input pole connect the second measurement electrode and the 3rd respectively Measuring electrode, the outfan of differential voltage input pole is connected with another input of first adder frequency-selective amplifier, and this is first years old The outfan of adder frequency-selective amplifier and the input of the first synchro detection circuit connect, the output of the first synchro detection circuit End is by the first of a pair of ter end permutator the 3rd input and first differential being associated in differential type gain controlled amplifier Between device and the input of display, conversion connects；The input of trans-impedance amplifier and outfan respectively with the 4th measure electrode and Another input of second adder frequency-selective amplifier connects, and the outfan of second adder frequency-selective amplifier and second synchronizes inspection The input of wave circuit connects, and the outfan of the second synchro detection circuit is by the second of described duplex three end permutator Change between described first differential device and the input of display and the 3rd input of differential type gain controlled amplifier Connect；The input of described first differential device passes through the input at triangular-wave generator Yu display of the three end permutatoies Between end, conversion connects；The input of this first differential device and display is by electric capacity output impedance or the variable signal of admittance； The first described synchro detection circuit or the second synchro detection circuit are made up of lock-in amplifier and low pass filter, and locking is amplified The outfan of device is connected with the input of low pass filter.

High-precision human impedance-admittance measuring instrument the most according to claim 1, it is characterised in that described lock-in amplifier It is made up of integrated single functional simulation multiplier SA602A.

High-precision human impedance-admittance measuring instrument the most according to claim 1, it is characterised in that described first to fourth Measure electrode to be made up of the silver plate or filamentary silver being compounded with silver chloride on surface.