Oedema detection

• US 9,149,235 B2
• Filed: 12/20/2013
• Issued: 10/06/2015
• Est. Priority Date: 06/18/2004
• Status: Active Grant

• Current Assignee: ImpediMed Limited
• Original Assignee: ImpediMed Limited
• Inventors: Ward, Leigh, Cornish, Brian
• Primary Examiner(s): HINDENBURG, MAX F
• Application Number:
  US14/136,463
• Publication Number:
  US 20140107522A1
• Time in Patent Office: 655 Days
• Field of Search: 600/547
• US Class Current: 1/1
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/4869 Determining body composition
• 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 of detecting tissue oedema in a subject. The method includes determining a measured impedance for first and second body segments. An index indicative of a ratio of the extra-cellular to intra-cellular fluid is then calculated for each body segment, with these being used to determine an index ratio based on the index for the first and second body segments. The index ration can in turn be used to determine the presence, absence or degree of tissue oedema, for example by comparing the index ratio to a reference or previously determined index ratios.

Claims

1. A method of diagnosing tissue oedema in a body region, the method including:

calculating, using a processor of a processing system, an index R_i/R_e as indicative of the ratio of extracellular fluid to intracellular fluid;

where;

R_e is the resistance of extracellular fluid determined from R_e=R₀; and

, R_i is the resistance of intracellular fluid determined from

2. The method of claim 1, wherein the method includes:

calculating of the index R_i/R_e is made prior to an event likely to cause oedema; and

,

comparing to a measurement of the index R_i/R_e made after the event.

3. The method of claim 1, additionally including, in the processing system:

determining a measured impedance for first and second body segments;

for each body segment, and using the measured impedance, determining the index R_i/R_e;

determining an index ratio based on the index R_i/R_e for the first and second body segments;

determining the presence, absence or degree of tissue oedema based on the index ratio.

4. The method of claim 3, additionally including, in the processing system:

comparing the index ratio to at least one reference; and

determining the presence, absence or degree of tissue oedema based on the results of the comparison.

5. The method of claim 4, wherein the reference includes at least one of:

a predetermined threshold;

a tolerance determined from a normal population; and

a predetermined range.

6. The method of claim 4, wherein the reference includes an index ratio previously determined for the subject.

8. The method of claim 4, wherein the first and second body segments are different types of body segment.

9. The method of claim 4, wherein the first and second body segments are limbs.

10. The method of claim 4, wherein the first body segment is a leg and the second body segment is an arm.

11. The method of claim 4, additionally including, in the processing system:

determining a plurality of measured impedances for each body segment, each measured impedance being measured at a corresponding measurement frequency; and

determining the index ratio based on the plurality of measured impedances.

12. The method of claim 1, additionally including, in the processing system, determining parameter values of parameters R₀ and R_∞

using the equation;

13. The method of claim 12, wherein the method includes, in the processing system:

determining the impedance of each body segment at four discrete frequencies; and

determining values for the parameters by solving the equation using four simultaneous equations.

14. The method of claim 1, additionally including, in the processing system, determining parameter values of parameters R₀ and R_∞

by;

determining an impedance locus using the measured impedance values; and

using the impedance locus to determine the parameter values.

15. The method of claim 1, additionally including, in the processing system, displaying an indication of at least one of:

the parameter values of parameters R₀ and R_∞

;

the ratio of extra-cellular to intra-cellular fluid; and

an indication of the at least one of the presence, absence or degree of tissue oedema in the subject.

16. The method of claim 1, additionally including, in the processing system:

applying an alternating current signal at four or more discrete frequencies;

measuring an impedance at each frequency;

solving the equation;

17. The method of claim 16, additionally including diagnosing tissue oedema by determining the presence, absence or degree of tissue oedema.

18. The method of claim 16, additionally including, in the processing system:

determining the impedance at four discrete frequencies; and

determining values for the parameters by solving the equation using four simultaneous equations.

19. The method of claim 16, additionally including, in the processing system:

determining values of one or more of the parameters R₀, R_∞

, τ and

α

for first and second body regions;

comparing the results from the first body region with the results from the second body region to obtain an indication of the presence of tissue oedema.

20. The method of claim 19, additionally including, in the processing system:

comparing the parameters R₀ and R_∞

for each body region; and

,

indicating tissue oedema if the difference is outside a tolerance determined from a normal population.

21. The method of claim 16, additionally including, in the processing system, indicating tissue oedema by displaying the indication as a position on a scale.

48. The method of claim 1, wherein the indicator indicates if the body region is “

unaffected”

, “

possibly affected”

or “

affected”

.

49. The method of claim 1, wherein the method is performed on a body region at risk of oedema.

50. The method of claim 1, additionally including:

applying an alternating current at four or more discrete frequencies via a first pair of electrodes;

measuring an impedance at each of the four or more discrete frequencies via a second pair of electrodes; and

using the measured impedance in diagnosing tissue odema in the body region.

7. The method of 6, wherein the previously determined index ratio is determined prior to the subject undergoing at least one of:

surgery; and

treatment.

22. An apparatus for diagnosing tissue oedema in a body region, the apparatus including a processing system configured to:

calculate, using a processor of the processing system, an index R_i/R_e as indicative of the ratio of extracellular fluid to intracellular fluid;

where;

R_e is the resistance of extracellular fluid determined from R_e=R₀;

R_i is the resistance of intracellular fluid determined from

23. The apparatus of claim 22, wherein measuring of the index R_i/R_e is made prior to an event likely to cause oedema, and the processing system is configured to compare to a measurement of the index R_i/R_e made after the event.

24. The apparatus of claim 22, wherein the processing system is configured to:

determine a measured impedance for first and second body segments;

for each body segment, and using the measured impedance, determine the index R_i/R_e;

determine an index ratio based on the index R_i/R_e for the first and second body segments; and

determine the presence, absence or degree of tissue oedema based on the index ratio.

25. The apparatus of claim 24, wherein the processing system is configured to:

compare the index ratio to at least one reference; and

determine the presence, absence or degree of tissue oedema based on the results of the comparison.

26. The apparatus of claim 25, wherein the reference includes at least one of:

a predetermined threshold;

a tolerance determined from a normal population; and

a predetermined range.

27. The apparatus of claim 25, wherein the reference includes an index ratio previously determined for the subject.

28. The apparatus of claim 27, wherein the previously determined index ratio is determined prior to the subject undergoing at least one of:

surgery; and

treatment.

29. The apparatus of claim 25, wherein the first and second body segments are different types of body segment.

30. The apparatus of claim 25, wherein the first and second body segments are limbs.

31. The apparatus of claim 25, wherein the first body segment is a leg and the second body segment is an arm.

32. The apparatus of claim 25, wherein the processing system is configured to:

determine a plurality of measured impedances for each body segment, each measured impedance being measured at a corresponding measurement frequency; and

,

determine the index ratio based on the plurality of measured impedances.

33. The apparatus of claim 22, wherein the processing system is configured to determine parameter values of parameters R₀ and R_∞

using the equation;

34. The apparatus of claim 33, wherein the processing system is configured to:

determine the impedance of each body segment at four discrete frequencies; and

determine values for the parameters by solving the equation using four simultaneous equations.

35. The apparatus of claim 22, wherein the processing system is configured to determine parameter values of parameters R₀ and R_∞

by;

determining an impedance locus using the measured impedance values; and

using the impedance locus to determine the parameter values.

36. The apparatus of claim 22, wherein the processing system is configured to display an indication of at least one of:

the parameter values of parameters R₀ and R_∞

;

the ratio of extra-cellular to intra-cellular fluid; and

,

an indication of the at least one of the presence, absence or degree of tissue oedema in the subject.

37. The apparatus of claim 22, wherein the processing system is configured to:

apply an alternating current signal at four or more discrete frequencies;

measure an impedance at each frequency;

solve the equation;

38. The apparatus of claim 37, wherein the processing system is configured to diagnose tissue oedema by determining the presence, absence or degree of tissue oedema.

39. The apparatus of claim 37, wherein the processing system is configured to:

determine the impedance at four discrete frequencies; and

determine values for the parameters by solving the equation using four simultaneous equations.

40. The apparatus of claims 37, wherein the processing system is configured to:

determine values of one or more of the parameters R₀, R_∞

, τ and

α

for first and second body regions; and

compare the results from the first body region with the results from the second body region to obtain an indication of the presence of tissue oedema.

41. The apparatus of claim 40, wherein the processing system is configured to:

compare the parameters R_o and R_∞

for each body region; and

indicate tissue oedema if the difference is outside a tolerance determined from a normal population.

42. The apparatus of claim 27, wherein the processing system is configured to indicate tissue oedema by displaying the indication as a position on a scale.

43. The apparatus of claim 22, wherein the apparatus includes:

a current supply for generating an alternating current at each of a plurality of frequencies;

at least two supply electrodes for applying the generated alternating current to the body region;

at least two measurement electrodes for detecting a voltage across the body region; and

,

a sensor coupled to the measurement electrodes for determining the voltage, the sensor being coupled to the processing system to thereby allow the processing system to determine the measured impedances.

44. The apparatus of claim 43, wherein the current supply generates an alternating current at four or more discrete frequencies across a frequency range.

45. The apparatus of claim 22, wherein the apparatus includes a two-channel bioimpedance meter.

46. The apparatus of claim 45, wherein current is passed between supply electrodes on first and second body segments and a voltage is sensed between measurement electrodes on the first and second body segments.

47. The apparatus of claim 22, wherein the apparatus displays an indication of whether the body region is “

unaffected”

, “

possibly affected”

or “

affected”

.

51. A bioimpedance apparatus for detecting the presence of oedema, the bioimpedance apparatus including:

a processing system configured to calculate an index R_i/R_e indicative of the ratio of extracellular fluid to intracellular fluid, where;

R_∞

is the resistance of the body region at infinite applied frequency

R₀ is the resistance of the body region at zero applied frequency

R_e is the resistance of extracellular fluid determined from R_e=R₀; and

R_i is the resistance of intracellular fluid determined from

52. The bioimpedance apparatus of claim 51, wherein the apparatus includes:

a current supply for generating an alternating current at each of a plurality of frequencies;

at least two supply electrodes for applying the generated alternating current to the body region;

at least two measurement electrodes for detecting a voltage across the body region; and

,

a sensor coupled to the measurement electrodes for determining the voltage, the sensor being coupled to the processing system to thereby allow the processing system to determine the measured impedances.