ANALYSING IMPEDANCE MEASUREMENTS

• US 20120330167A1
• Filed: 12/20/2010
• Published: 12/27/2012
• Est. Priority Date: 12/21/2009
• Status: Abandoned Application

• Current Assignee: ImpediMed Limited
• Original Assignee: ImpediMed Limited
• Inventors: Gaw, Richelle Leanne, Ziegelaar, Brian William
• Application Number:
  US13/517,340
• Publication Number:
  US 20120330167A1
• Time in Patent Office: Days
• US Class Current: 600/481
• CPC Class Codes: A61B 2562/0214 Capacitive electrodes
• CPC Class Codes: A61B 5/02007 Evaluating blood vessel condition, e.g. elasticity, compliance
• 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 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence

Abstract

A method for use in analysing impedance measurements performed on a subject, the subject being arranged such that body fluid levels in at least one leg segment of the subject changes between a first time and a second time, the method including, in a processing system, at the first time, determining at least one first impedance value indicative of the impedance of the at least one leg segment of the subject; at the second time, determining at least one second impedance value indicative of the impedance of the at least one leg segment of the subject; and, determining an indicator based on the at least one first and at least one second impedance values, the indicator being indicative of changes in the body fluid levels.

Claims

1. A method for use in analysing impedance measurements performed on a subject, the subject being arranged such that body fluid levels in at least one leg segment of the subject changes between a first time and a second time, the method including, in a processing system:

a) at the first time, determining at least one first impedance value indicative of the impedance of the at least one leg segment of the subject;

b) at the second time, determining at least one second impedance value indicative of the impedance of the at least one leg segment of the subject; and

,

c) determining an indicator based on the at least one first and at least one second impedance values, the indicator being at least partially indicative of a rate of change of intra-cellular fluid levels in the at least one leg segment, and being usable in the assessment of venous insufficiency.

2. A method according to claim 1, wherein the indicator is indicative of a change between the at least one first impedance value and the at least one second impedance value.

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

a) comparing the indicator to a reference; and

,

b) providing an indication of the results of the comparison to allow determination of a presence, absence or degree of venous insufficiency.

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

a) determining the at least one first impedance value with the subject in a first orientation; and

b) determining the at least one second impedance value with the subject in a second orientation.

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

a) determining the at least one first impedance value with the subject in a first orientation; and

,

b) after positioning the subject in a second orientation for a predetermined time period, determining the at least one second impedance value with the subject in the first orientation.

6. A method according to claim 1, wherein the method includes:

a) positioning the subject in a first orientation for a predetermined time period; and

,

b) positioning the subject in a second orientation;

and wherein the method further includes, in the processing system;

c) determining the at least one first and second impedance values with the subject in the second orientation.

7. A method according to claim 1, wherein the torso of the subject remains in a constant orientation, and when the subject is in the first orientation a first leg of the subject is positioned in a first position, and when the subject is in the second orientation the first leg of the subject is positioned in a second position.

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

a) determining a plurality of impedance values with the subject in a single orientation; and

,

b) determining the indicator based on the plurality of impedance values.

9. A method according to claim 1, wherein the method includes, in the processing system, examining at least one change in the impedance values over time, the at least one change in the impedance values being used in the assessment of venous insufficiency.

10. A method according to claim 9, wherein the method includes, in the processing system, using a rate of change in the assessment of venous insufficiency by determining whether the rate of change is at least one of:

a) constant;

b) non-constant; and

,

c) logarithmic.

11. A method according to claim 10, wherein the method includes, in the processing system:

a) comparing the rate of change to a reference; and

,

b) providing an indication of the results of the comparison to allow determination of a presence, absence or degree of venous insufficiency.

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

a) determining the at least one first impedance value using a plurality of impedance measurements performed at a plurality of different frequencies; and

,

b) determining the at least one second impedance value using a plurality of impedance measurements performed at a plurality of different frequencies.

13. A method according to claim 1, wherein at least one impedance measurement is measured at a measurement frequency of at least one of:

a) less than 100 kHz;

b) less than 50 kHz; and

,

c) less than 10 kHz.

14. A method according to claim 13, wherein the method includes, in the processing system, using the at least one impedance measurement as an estimate of a resistance of the subject at a zero measurement frequency.

15. A method according to claim 1, wherein at least one impedance measurement is measured at a measurement frequency of at least one of:

a) greater than 200 kHz;

b) greater than 500 kHz; and

,

c) greater than 1000 kHz.

16. A method according to claim 15, wherein the method includes, in the processing system, using the at least one impedance measurement as an estimate of a resistance of the subject at an infinite measurement frequency.

17. A method according to claim 1, wherein the at least one first and second impedance values are based on impedance parameter values.

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

a) determining a plurality of impedance measurements; and

,

b) determining at least one impedance parameter value from the plurality of impedance measurements.

19. A method according to claim 18, wherein the impedance parameter values include at least one of:

R₀ which is the resistance at zero frequency;

R_∞

which is the resistance at infinite frequency; and

,

Z_c which is the resistance at a characteristic frequency.

20. A method according to claim 17, wherein the method includes, in the processing system, determining the parameter values using the equation:

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

a) determining values for impedance parameters R₀ and R_∞

from the measured impedance values; and

,

b) calculating a value for impedance parameter R_i which is the resistance of intracellular fluid, using the equation;

22. A method according to claim 1, wherein the method includes, in the processing system, determining the indicator using at least one of the equations:

23. A method according to claim 1, wherein the method includes, in the processing system, causing the impedance measurements to be performed.

24. A method according to claim 23, wherein the method includes, in the processing system:

a) causing one or more electrical signals to be applied to the subject using a first set of electrodes;

b) measuring electrical signals across a second set of electrodes applied to the subject in response to the applied one or more signals; and

,

c) determining from the applied signals and the measured signals at least one measured impedance value.

25. A method according to claim 1, wherein the indicator is used in the assessment of venous insufficiency.

26. A method according to claim 1, wherein the method includes determining a presence, absence or degree of venous insufficiency using the indicator.

27. A method according to claim 26, wherein, if the subject does not have venous insufficiency, the method includes:

a) determining a rate of change of extracellular fluid levels in the at least one leg segment; and

b) using the rate of change of extracellular fluid levels to determine the presence, absence or degree of lymphoedema.

28. Apparatus for use in analysing impedance measurements performed on a subject, the apparatus including a processing system for:

a) at a first time, determining at least one first impedance value indicative of the impedance of the at least one leg segment of the subject;

b) at a second time, determining at least one second impedance value indicative of the impedance of the at least one leg segment of the subject; and

,

c) determining an indicator based on the at least one first and at least one second impedance values, the indicator being at least partially indicative of a rate of change of intra-cellular fluid levels in the at least one leg segment, and being usable in the assessment of venous insufficiency.

29. Apparatus according to claim 28, wherein the apparatus includes a processing system for:

a) causing one or more electrical signals to be applied to the subject using a first set of electrodes;

b) measuring electrical signals across a second set of electrodes applied to the subject in response to the applied one or more signals; and

,

c) determining from the applied signals and the measured signals at least one measured impedance value.

30. Apparatus according to claim 29, wherein the apparatus includes:

a) a signal generator for generating electrical signals; and

,

b) a sensor for sensing electrical signals.