ANALYSING IMPEDANCE MEASUREMENTS

• US 20110060239A1
• Filed: 01/09/2009
• Published: 03/10/2011
• Est. Priority Date: 01/22/2008
• Status: Abandoned Application

• Current Assignee: ImpediMed Limited
• Original Assignee: ImpediMed Limited
• Inventors: Gaw, Richelle Leanne
• Application Number:
  US12/867,224
• Publication Number:
  US 20110060239A1
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: H04W 72/51 based on terminal or device properties
• CPC Class Codes: H04W 72/52 based on load

Abstract

A method for use in analysing impedance measurements performed on a subject, the method including, in a processing system determining at least one impedance value indicative of the impedance of at least one leg segment of the subject; and determining an indicator using the at least one impedance value, the indicator being indicative of extracellular fluid levels in the at least one leg segment and being used in the assessment of venous insufficiency.

Claims

1. ) A method for use in analysing impedance measurements performed on a subject, the method including, in a processing system:

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

,

b) determining an indicator using the at least one impedance value, the indicator being indicative of extracellular fluid levels in the at least one leg segment and being used in the assessment of venous insufficiency.

2. ) A method according to claim 1, wherein the method includes, in a 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.

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

a) determining a first indicator value with the subject in a first orientation;

b) determining a second indicator value with the subject in a second orientation; and

,

c) determining an indicator change based on a difference between the first and second fluid indicator values, the indicator change being used in the assessment of venous insufficiency.

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

a) comparing the indicator 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.

5. ) A method according to claim 1, wherein the method includes, in a processing system, determining an index using the at least one impedance value, the index being indicative of a ratio of extracellular to intracellular fluid levels in the at least leg segment, the index being used in the assessment of venous insufficiency.

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

a) comparing the index 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.

7. ) A method according to claim 6, wherein the method includes, diagnosing the presence of venous insufficiency if:

a) an indicator is less than first reference; and

,

b) an index is greater than a second reference.

8. ) A method according to claim 5, wherein the method includes, in a processing system:

a) determining a first index value with the subject in a first orientation;

b) determining a second index value with the subject in a second orientation; and

,

c) determining an index change based on a difference between the first and second fluid index values, the index change being used in the assessment of venous insufficiency.

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

a) determining a first indicator value with the subject in a first orientation;

b) after positioning the subject in a second orientation for a predetermined time period, determining a second indicator value with the subject in the first orientation; and

,

c) determining a difference between the first and second fluid indicator values, the difference being used in the assessment of venous insufficiency.

10. ) A method according to claim 9, wherein the method includes, in the processing system:

a) monitoring the difference;

b) determining the time taken for the difference fall below a reference; and

,

c) providing an indication of the time taken to allow determination of a presence, absence or degree of venous insufficiency.

11. ) A method according to claim 1, wherein the method includes, in a processing system:

a) determining a pre-treatment indicator value prior to treatment of the subject;

b) determining a post-treatment indicator value following treatment of the subject for venous insufficiency; and

,

c) determining an indicator change based on a difference between the pre-treatment and post-treatment indicator values, the indicator change being used in the assessment of venous insufficiency.

12. ) A method according to claim 11, wherein the method includes, diagnosing the presence of venous insufficiency if the indicator change is greater than a reference.

13. ) A method according to claim 1, wherein the method includes, in the processing system, using a reference that is at least one of:

a) an indicator or index determined for another limb of the subject;

b) a reference determined from a sample population; and

,

c) a previous indicator or index determined for the subject.

14. ) A method according to claim 1, wherein the method includes, in the processing system, displaying at least one of:

a) an indicator;

b) an index ratio;

c) an index;

d) an indicator change;

e) an index change;

f) one or more impedance parameter values; and

,

g) results of a comparison.

15. ) A method according to claim 1, wherein the at least one impedance value 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.

17. ) A method according to claim 1, wherein the method includes measuring at least one second impedance value, the at least one second impedance value being 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.

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

a) determining a plurality of impedance values; and

,

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

20. ) A method according to claim 19, 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.

21. ) A method according to claim 20, 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 the index (I) using the equation;

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

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

16. ) A method according to claim 16, 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.

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

24. ) A method according to claim 18, wherein the method includes, in the computer 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. ) Apparatus for use in analysing impedance measurements performed on a subject, the apparatus including a processing system for:

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

b) determining an indicator using the at least one impedance value, the indicator being indicative of extracellular fluid levels in the at least leg segment and being used in the assessment of venous insufficiency.

26. ) Apparatus according to claim 25, 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.

27. ) Apparatus according to claim 26, wherein the apparatus includes:

a) a signal generator for generating electrical signals; and

,

b) a sensor for sensing electrical signals.

28. ) A method for use in assessing the presence, absence or degree of venous insufficiency, the method including, in a processing system:

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

,

b) determining an indicator using the at least one impedance value, the indicator being indicative of extracellular fluid levels in the at least leg segment and being used in the assessment of venous insufficiency.

29. ) A method for use in analysing impedance measurements performed on a subject, the method including, in a processing system:

a) determining at least one impedance value indicative of the impedance of at least one body segment of the subject;

b) determining an indicator using at least one impedance value, the indicator being indicative of extracellular fluid levels in the at least one body segment;

c) determining an index using at least one impedance value, the index being indicative of a ratio of extracellular to intracellular fluid levels in the at least one body segment;

d) comparing the indicator to a first reference;

e) comparing the index to a second reference; and

,

f) providing an indication of the results of the comparisons.

30. ) A method according to claim 29, wherein the method includes, in the processing system, determining the indicator using an impedance measurement performed at a single low frequency.

31. ) A method according to claim 29, wherein the 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.

32. ) A method according to claim 31, 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.

33. ) A method according to claim 29, wherein the method includes measuring at least one second impedance value, the at least one second impedance value being 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.

34. ) A method according to claim 33, wherein the method includes, in the processing system, using the at least one second impedance measurement as an estimate of a resistance of the subject at an infinite measurement frequency.

35. ) A method according to claim 29, wherein the method includes, in the processing system:

a) determining at least two impedance values; and

,

b) determining at least one impedance parameter value from the at least two impedance values.

36. ) A method according to claim 35, wherein the method includes, in the processing system:

a) at each of three frequencies, determining first and second parameter values for first and second impedance parameters relating to the impedance of at least one body segment of the subject;

b) solving simultaneous equations representing a circle defined with respect to the first and second impedance parameters to thereby determine circle parameter values, the equations being solved using the first and second parameter values at each of the three frequencies;

c) using the circle parameter values to determine a third impedance parameter value at a respective frequency; and

,

d) using the third impedance parameter value to determine an indicator indicative of relative fluid levels within the body segment of the subject.

37. ) A method according to claim 36, wherein the first and second parameter values are resistance and reactance values.

38. ) A method according to claim 35, 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.

39. ) A method according to claim 38, 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 the index (I) using the equation;

40. ) A method according to claim 38, wherein the method includes, in the processing system, determining the parameter values using the equation:

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

a) determining at least one impedance value indicative of the impedance of at least one body segment of the subject;

b) determining an indicator using at least one impedance value, the indicator being indicative of extracellular fluid levels in the at least one body segment;

c) determining an index using at least one impedance value, the index being indicative of a ratio of extracellular to intracellular fluid levels in the at least one body segment;

d) comparing the indicator to a first reference;

e) comparing the index to a second reference; and

,

f) providing an indication of the results of the comparisons.

42. ) Apparatus according to claim 41, wherein the processing system is 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.

43. ) Apparatus according to claim 41, wherein the apparatus includes:

a) a signal generator for generating electrical signals; and

,

b) a sensor for sensing electrical signals.

44. ) A method for use in distinguishing the presence of oedema and lymphoedema in a subject, the method including, in a processing system:

a) determining at least one impedance value indicative of the impedance of at least one body segment of the subject;

b) determining an indicator using at least one impedance value, the indicator being indicative of extracellular fluid levels in the at least one body segment;

c) determining an index using at least one impedance value, the index being indicative of a ratio of extracellular to intracellular fluid levels in the at least one body segment;

d) comparing the indicator to a first reference;

e) comparing the index to a second reference; and

,

f) providing an indication of the results of the comparisons, the results being used to distinguish oedema and lymphoedema.