Fluid level indicator determination

• US 9,615,767 B2
• Filed: 10/21/2010
• Issued: 04/11/2017
• Est. Priority Date: 10/26/2009
• Status: Active Grant

• Current Assignee: ImpediMed Limited
• Original Assignee: ImpediMed Limited
• Inventors: Gaw, Richelle Leanne, Thomas, Brian John
• Primary Examiner(s): Henson, Devin
• Assistant Examiner(s): Kremer, Matthew
• Application Number:
  US13/503,833
• Publication Number:
  US 20130131538A1
• Time in Patent Office: 2,364 Days
• Field of Search: None
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/4878 Evaluating oedema
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F

Abstract

A method for use in analyzing impedance measurements on a subject is described. The method can include, in a processing system, determining at least one impedance value at each of a number of frequencies, each impedance value representing the impedance of a segment of the subject, determining a dispersion parameter value indicative of a dispersion of the impedance values and, determining an indicator based at least on part on the dispersion parameter value.

Claims

1. A method for use in diagnosing a presence, absence or degree of oedema in a subject suspected of having the oedema by using impedance measurements performed on the subject, the method being performed using an apparatus including:

a first set of electrodes for applying to the subject;

a signal generator for applying excitation electrical signals to the subject using the first set of electrodes;

a second set of electrodes for applying to the subject;

a sensor for measuring measured electrical signals across the second set of electrodes; and

,

a processing system including at least one of a programmable computer system or a field-programmable gate array,

the method including, in the processing system;

causing the impedance measurements to be performed by;

causing the excitation electrical signals to be applied to the subject using the signal generator;

determining the measured electrical signals across the subject using the sensor; and

,

determining, using an indication of the excitation electrical signals and an indication of the measured electrical signals, impedance values at each of a number of frequencies for first and second body segments of the subject, each impedance value representing an impedance of the respective body segment, wherein the first body segment is a body segment of the subject that is suspected of being affected by the oedema and the second body segment is a body segment of the subject that is suspected of being unaffected by the oedema;

determining impedance parameter values for the first and second body segments based on the impedance values for the respective body segment, the impedance parameter values including;

R_∞

representing an impedance at infinite applied frequency;

R₀ representing an impedance at zero applied frequency; and

,

X_c representing a reactance at a centre of a circle defined by the impedance values for the respective body segment;

determining first and second dispersion parameter values for the first and second body segments respectively, each dispersion parameter value being indicative of a dispersion of the impedance values for the respective body segment, each dispersion parameter value being based on a ratio of;

a difference between R_∞

and R₀ for the respective body, and,

X_c for the respective body segment;

determining an indicator using the first and the second dispersion parameter values; and

,

displaying a representation of the indicator, to thereby allow the presence, the absence or the degree of the oedema in the subject to be diagnosed.

2. A method according to claim 1, wherein at least one of the first and second body segments is a dominant limb and the other of the first and second body segments is a non-dominant limb.

3. A method according to claim 1, wherein the method includes, in the processing system:

determining a predicted dispersion parameter value for the first body segment using the second dispersion parameter value; and

,

determining the indicator using the first and predicted dispersion parameter values.

4. A method according to claim 3, wherein the predicted dispersion parameter value is determined to take into account at least one of:

limb dominance; and

,

differences in limb types.

5. A method according to claim 3, wherein the method includes, in the processing system, determining the predicted dispersion parameter value using at least one reference value derived from a reference normal population.

6. A method according to claim 5, wherein the reference normal population is selected based on at least one of:

limb dominance;

differences in limb types;

ethnicity;

age;

gender;

weight; and

,

height.

7. A method according to claim 5, wherein the at least one reference value is determined based on a linear regression of the first and second dispersion parameter values measured for the reference normal population.

8. A method according to claim 3, wherein the method includes, in the processing system, determining the predicted dispersion parameter value using an equation of the form:

DP_p=aDP₂+K,

where;

DP₂ is the second dispersion parameter value;

DP_p is the predicted dispersion parameter value;

a is a multiplier reference value determined based on a relationship between the first and second dispersion parameter values in a reference population; and

,

K is a constant reference value determined based on the relationship between the first and second dispersion parameter values in the reference population.

9. A method according to claim 8, wherein the first body segment is a leg segment of the subject and the second body segment is an arm segment of the subject, and, for a male subject, the predicted dispersion parameter value for the leg segment based on the second dispersion parameter value for the arm segment is based on:

a value of a in a range 0.15 to 0.022; and

,

a value of K in a range 0.62 to 0.72.

10. A method according to claim 8, wherein the first body segment is a leg segment of the subject and the second body segment is an arm segment of the subject, and, for a female subject, the predicted dispersion parameter value for the leg segment based on the second dispersion parameter value for the arm segment is based on:

a value of a in a range 0.44 to 0.41; and

,

a value of K in a range 0.43 to 0.46.

11. A method according to claim 3, wherein the method includes, in the processing system, determining the indicator using the equation:

12. A method according to claim 11, wherein the scaling factor is selected so that a threshold value indicative of the presence or the absence of the oedema is an integer value.

13. A method according to claim 3, wherein the method includes, in the processing system, determining the indicator using the equation:

14. A method according to claim 1, wherein the method includes, in the processing system, determining the indicator based on the equation:

Ind=sf(DP₂−

DP₁)

where;

Ind is the indicator;

DP₁ is the first dispersion parameter value for the first body segment;

DP₂ is the second dispersion parameter value for the second body segment; and

,

sf is a scaling factor.

15. A method according to claim 1, wherein each dispersion parameter value is indicative of a distribution of the impedance measurements for the respective body segment.

16. A method according to claim 1, wherein the dispersion parameter is based on the value of:

17. A method according to claim 1, wherein the representation of the indicator includes a linear scale including:

a linear indicator;

a scale; and

,

a pointer, the pointer being positioned on the scale in accordance with the indicator.

18. A method according to claim 17, wherein the method includes, in the processing system, displaying the representation including an indication of a change in indicator value from at least one of a previous indicator value and a baseline indicator value.

19. A method according to claim 1, wherein the method includes, in the processing system:

determining at least one threshold using a reference; and

,

displaying the at least one threshold as part of the representation.

20. Apparatus for use in diagnosing a presence, absence or degree of oedema in a subject suspected of having the oedema by using impedance measurements performed on the subject, the apparatus including:

a first set of electrodes for applying to the subject;

a signal generator for applying excitation electrical signals to the subject using the first set of electrodes;

a second set of electrodes for applying to the subject;

a sensor for measuring measured electrical signals across the second set of electrodes; and

,

a processing system including a processor, a memory, and an I/O device, the processing system for;

causing the impedance measurements to be performed by;

causing the excitation electrical signals to be applied to the subject using the signal generator;

determining the measured electrical signals across the subject using the sensor; and

,

determining, using an indication of the excitation electrical signals and an indication of the measured electrical signals, impedance values at each of a number of frequencies for first and second body segments of the subject, each impedance value representing an impedance of the respective body segment, wherein the first body segment is a body segment of the subject that is suspected of being affected by the oedema and the second body segment is a body segment of the subject that is suspected of being unaffected by the oedema;

determining impedance parameter values for the first and second body segments based on the impedance values for the respective body segment, the impedance parameter values including;

R_∞

representing an impedance at infinite applied frequency;

R₀ representing an impedance at zero applied frequency; and

,

X_c representing a reactance at a centre of a circle defined by the impedance values for the respective body segment;

determining first and second dispersion parameter values for the first and second body segments respectively, each dispersion parameter value being indicative of a dispersion of the impedance values for the respective body segment, each dispersion parameter value being based on a ratio of;

a difference between R_∞

and R₀ for the respective body segment, and,

X_c for the respective body segment;

determining an indicator using the first and the second dispersion parameter values; and

,

displaying a representation of the indicator, to thereby allow the presence, the absence or the degree of the oedema in the subject to be diagnosed.

21. A method for use in diagnosing a presence, absence or degree of oedema in a subject suspected of having the oedema by using impedance measurements performed on the subject, the method being performed using an apparatus including:

a first set of electrodes for applying to the subject;

a signal generator for applying excitation electrical signals to the subject using the first set of electrodes;

a second set of electrodes for applying to the subject;

a sensor for measuring measured electrical signals across the second set of electrodes; and

,

a processing system including a processor, a memory, and an I/O device, the method including, in the processing system;

causing the impedance measurements to be performed by;

causing the excitation electrical signals to be applied to the subject using the signal generator;

determining the measured electrical signals across the subject using the sensor; and

,

determining, using an indication of the excitation electrical signals and an indication of the measured electrical signals, impedance values at each of a number of frequencies for first and second body segments of the subject, each impedance value representing an impedance of the respective body segment, wherein the first body segment is a body segment of the subject that is suspected of being affected by the oedema and the second body segment is a body segment of the subject that is suspected of being unaffected by the oedema;

determining impedance parameter values for the first and second body segments based on the impedance values for the respective body segment, the impedance parameter values including;

R_∞

representing an impedance at infinite applied frequency;

R₀ representing an impedance at zero applied frequency; and

,

X_c representing a reactance at a centre of a circle defined by the impedance values for the respective body segment;

determining first and second dispersion parameter values for the first and second body segments respectively, each dispersion parameter value being indicative of a dispersion of the impedance values for the respective body segment, each dispersion parameter value being based on a ratio of;

a difference between R_∞

and R₀ for the respective body segment, and,

X_c for the respective body segment;

determining an indicator using the first and the second dispersion parameter values; and

,

displaying a representation of the indicator, to thereby allow the presence, the absence or the degree of the oedema in the subject to be diagnosed.