Non-invasive method and device for collecting measurements representing body activity and determining cardiorespiratory parameters of the human body based upon the measurements collected

• US 5,469,859 A
• Filed: 06/24/1993
• Issued: 11/28/1995
• Est. Priority Date: 06/24/1992
• Status: Expired due to Fees

• Current Assignee: N.I. Medical Ltd.
• Original Assignee: N.I. Medical Ltd.
• Inventors: Tsoglin, Alexander, Frinerman, Yafim
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US08/082,606
• Time in Patent Office: 887 Days
• Field of Search: 128/671, 128/723, 128/734
• US Class Current: 600/536
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295

Abstract

A medical device, utilizing a non-invasive method for determining the main cardiorespiratory parameters of a patient'"'"'s body, and employing a method of operation wherein two or four electrodes are applied to the patient'"'"'s body in a manner enabling integral bioimpedance measurements of the total body of a patient to be effected. High stability amplitude alternating current is passed through the electrodes into the body so as to obtain an integral impedance curve of the body and derive therefrom simultaneous automatic separation of an active component. The desired cardiorespiratory parameters of the body are calculated from the active component of the integral bioimpedance, using empiric formulae applicable to integral bioimpedance measurements; the calculation being accomplished based on the average data obtained during a respiration cycle.

Claims

1. A non-invasive method for determining of the main cardiorespiratory parameters of a human body, comprising the steps of:

attaching electrodes to the body in a manner so as to enable the measuring of integral bioimpedance measurements of the total body of a patient;

transmitting a high stability amplitude alternating current through said electrodes and into said body;

obtaining an integral impedance curve of said body from the connected electrodes upon transmission of the high stability amplitude alternating current;

transmitting the integral impedance curve to a measuring device;

converting the impedance curve to a working signal;

transmitting the working signal to a computer;

simultaneously and automatically separating an active component from said integral impedance;

calculating cardiorespiratory parameters; and

applying the computerized calculation of the cardiorespiratory parameters of said body from the active component of said integral bioimpedance, using empiric formulae applicable, to integral bioimpedance measurements;

the computerized calculation being based on the bioimpedance measurements measured during a respiration cycle.

2. The method according to claim 1, further including the step of:

calculating, in said computer, parameters relating to extracellular fluids of the patient'"'"'s body;

said parameters being based on bioimpedance measurements measured at two different current frequencies.

3. The method according to claim 1, further comprising the steps of:

attaching four electrodes to the extremities of a patient'"'"'s body;

said four electrodes being combined into two pairs, each pair being used both for current injection and voltage measuring.

4. The method according to claim 1, further comprising the step of:

attaching two electrodes at two distal parts of the patient'"'"'s extremities respectively, so as to include the patient'"'"'s body as part of an electrical circuit formed between said electrodes.

5. The method according to claim 4, further comprising the steps of attaching one of the two electrodes to a distal part of a left arm, and attaching the second electrode at a distal part of a right leg of the patient.

6. The method according to claim 1, further including the steps of:

preliminarily attaching four of said electrodes to respective distal parts of extremities of the patient;

measuring an integral impedance between each pair of said electrodes placed on each arm and leg; and

selecting, for determination of the main cardiorespiratory parameters of the human body, the pair of electrodes characterized by a lowest integral impedance.

7. The method according to claim 1, further comprising the step of attaching the electrodes in a bipolar manner.

8. The method according to claim 1, further comprising the step of attaching the electrodes in a tetrapolar manner.

9. The method according to claim 1, further including the step of continuously examining each electrode'"'"'s contact by continuously setting a local capacitance between the electrode and the patient'"'"'s skin during said measurement, and activating an alarm whenever said capacitance exceeds a minimal threshold.

10. The method according to claim 1 for calculating a plurality of said parameters further including the steps of:

obtaining hemodynamic parameters from the patient including Stroke Volume, Systolic Index, Pulse rate, Cardiac output, Heart Index, Reserve Index, Total Resistance Index, Index of Tone Stabilization;

obtaining respiratory parameters from the patient including Rate of respiration, Index of Respiration changes, Index of Respiration intensiveness, Index of Hemodynamic Security; and

obtaining additional parameters from the patient including Index of Respiratory Duration and Index of Tidal Respiratory Volume.

11. The method according to claim 10, further comprising the step of calculating a plurality of parameters characterizing extracellular fluids of the human body including Volume of Extracellular Fluids of the whole patient'"'"'s body and Index of Fluid Balance of the whole body based upon the parameters obtained.

12. The method according to claim 1, further comprising the step of calculating a basic hemodynamic parameter Stroke Volume according to the following equation:

##EQU12## where;

Hct_corr. --a corrected Haemotacrytis, being 145+0.35(Hct-40);

Hct--Haemotacrytis, obtained from the blood analysis of the patient;

K(shape*sex*age)--a complex coefficient of the individual patient'"'"'s body, being;

##EQU13## δ

r/R--the ratio characterizing the measured active bioimpedance component'"'"'s change;

H_corr. --the corrected height of the patient, given by;

##EQU14## α

+β

--duration of a cardiac cycle, being a sum of its anacrotic and catacrotic parts;

β

--duration of the catacrotic part of a cardiac cycle;

Kel--coefficient of electrolytic ions in the patient'"'"'s blood, calculated based on the blood analysis and being given by;

##EQU15##

13. A non-invasive medical device for determining at least one cardiorespiratory parameter of a human body, the device comprising:

at least two electrodes for attachment to the human body,

an electrical total body integral bioimpedance measuring device coupled to the at least two electrodes and including a high stability amplitude alternative current source and electronic means for automatically deriving an active component of said integral bioimpedance wherein the measuring device transmits a high stability amplitude alternative current through said at least two electrodes;

a computer coupled to the electrical integral bioimpedance measuring device for receiving a signal transmitted from the measuring device and calculating said at least one cardiorespiratory parameter from the active component of the integral bioimpedance based upon the received signal; and

display means connected to the computer for displaying said at least one cardiorespiratory parameter from the active component of the integral bioimpedance.

14. The device according to claim 13, comprising two electrodes, wherein:

said two electrodes are connected to the patient'"'"'s body in a bipolar manner, so as to be used both for current injection and voltage measurement; and

a single channel, the two electrodes being connected to the electrical bioimpedance measuring device via the single channel.

15. The device according to claim 13, comprising four electrodes, wherein:

said four electrodes are connected, in pairs, to two sections of the patient'"'"'s body in a tetrapolar manner, so that a first pair of the electrodes are used for current injection, and a second pair of the electrodes are used for voltage measurement; and

two channels, the four electrodes being connected to said electrical bioimpedance measuring unit via the two channels.

16. The device according to claim 13, wherein the current source transmits a high stability amplitude alternating current from the measuring device through the at least two electrodes and through the patient'"'"'s body when connected to the at least two electrodes, and wherein the patient'"'"'s body acts as a resistive capacitance (RC) impedance.

17. The device according to claim 16, wherein the current source has a stability factor of between 10^-5 to 10^-7, and based upon the stability factor variations in bioimpedance in a complete range of 10^-3 are able to be measured by the measuring device.

18. The device according to claim 16, wherein said current source delivers a current of 1 to 2 mA, at a frequency of 32 to 100 KHz through the at least two electrodes and to the patient'"'"'s body.

19. The device according to claim 13, wherein the electrical integral bioimpedance measuring device comprises:

a voltage pulse generator,

a first filter;

a detector, having an output, for detecting the integral bioimpedance signal obtained;

a transmitter;

a controllable gain amplifier having a first terminal coupled to the voltage pulse generator and having a second terminal coupled to the first filter,

a high stability amplitude alternative current source coupled to the first filter and having a pair of outlets connected to the at least two electrodes connected across the patient'"'"'s body,

a high precision amplifier, connected across said at least two electrodes for receiving a signal therefrom and having an outlet connected to the detector, and for providing simultaneous separation of its active component from its reactive component,

a low-pass filter, coupled to the output of the detector, and having an output for issuing a working signal,

a capacitor coupled to the output of the low-pass filter for dividing the working signal into a direct component and an alternating component,

a high scaling amplifier coupled to the capacitor for amplifying the alternating component,

a multiplexer having a pair of inlets respectively coupled to respective outputs of the low-pass filter and the high scaling amplifier, for alternately connecting either the direct or the alternating components to an input of said multiplexer wherein the outputs of the low-pass filter and high scaling amplifier act as outputs of the measuring device, and

an analog-to-digital (A/D) converter having an input connected to the output of the multiplexer and having an output connected to said computer via the transmitter.

20. The device according to claim 19, wherein the detector is provided with a switch control connected between the output of the first filter and the input of the high stability amplitude alternative current source.

21. The device according to claim 20, wherein the detector comprises:

an electronic switch;

an RC timing circuit;

a first operational amplifier having a pair of inputs connected to the high precision amplifier and a second operational amplifier connected at an inverting input thereof to the outlet of the first filter through the RC timing circuit, and at its outlet to the non-inverting input of said first operational amplifier through the electronic switch.

22. The device according to claim 19, wherein:

the electrical integral bioimpedance measuring device is provided with a self testing block for testing the device before obtaining the measurements;

the self testing block comprising;

a control device connected to the second outlet of the controllable gain amplifier, and

a means for simulating impedance connected across the patient'"'"'s body.

23. The device according to claim 19, wherein the analog-to-digital converter, the multiplexer and the transmitter are constituted by a micro-controller, the micro-controller having a plurality of input ports and at least one output port.

24. The device according to claim 23, further comprising:

an ECG measuring device having at least two inputs and an output; and

first and second ECG electrodes connected to respective ones of the at least two inputs of the ECG measuring device; and

wherein;

the inputs of the high precision amplifier are connected to the at least two electrodes,

the outputs of the electrical integral bioimpedance measuring device are connected to respective input ports of the micro-controller,

the output of the high precision amplifier is connected to a respective input port of the micro-controller,

the output of the ECG measuring device is connected to a respective input port of the micro-controller, and

the at least one output port of the micro-controller is connected to the computer via isolation circuits and a correction circuit.

25. The device according to claim 19, wherein the high stability amplitude alternative current source comprises:

an inverter;

two symmetric current sources connected to the voltage pulse generator via the controllable gain amplifier and the first filter, one of said symmetric current sources being connected to the first filter through an inverter, and the second symmetric current source being connected to the first filter directly for receiving an alternating voltage from the first filter;

the first of the symmetric current sources stabilizing a positive half-wave of the alternating voltage, and the second of the symmetric current sources stabilizing a negative half-wave alternating voltage received from the first filter;

and wherein each of the symmetric current sources comprises;

first, second and third high precision operational amplifiers, a first of the high precision operational amplifiers including an output, an inverting input and a non-inverting input, and having a high output resistance and being provided with an alternating signal from the first filter at the inverting input, and being further provided with a positive feedback formed by the second high precision, high speed operational amplifier, the second operational amplifier including an output, an inverting input and a non-inverting input;

said first and second operational amplifiers stabilizing the alternating current passing through the load;

the output of the first operational amplifier and the non-inverting input of the second operational amplifier forming a zero point;

the third operational amplifier, including an output an inverting input and a non-inverting input, is connected at its inverting input to the zero point, and at its output to the non-inverting input of said first operational amplifier in order to provide a zero voltage DC level at said zero point; and

said load, being constituted by a human body, is connected to the symmetric zero point of each of said two symmetric current sources through the at least two electrodes.