Oedema Detection

• US 20080319336A1
• Filed: 06/17/2005
• Published: 12/25/2008
• Est. Priority Date: 06/18/2004
• Status: Active Grant

• Current Assignee: ImpediMed Limited
• Original Assignee: Qutbluebox Pty Ltd.
• Inventors: Cornish, Bruce, Ward, Leigh
• Granted Patent: US 8,744,564 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• 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 ratio 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 detecting tissue oedema in a subject, the method including, in a processing system:

a) determining a measured impedance for first and second body segments;

b) for each body segment, and using the measured impedance, determining an index indicative of a ratio of the extra-cellular to intra-cellular fluid;

c) determining an index ratio based on the index for the first and second body segments;

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

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

a) comparing the index ratio to at least one reference; and

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

3. A method according to claim 2, wherein the reference includes at least one of:

a) a predetermined threshold;

b) a tolerance determined from a normal population; and

c) a predetermined range.

4. A method according to claim 2, wherein the reference includes an index ratio previously determined for the subject.

5. A method according to claim 4, wherein the previously determined index ratio is determined prior to the subject undergoing at least one of:

a) surgery; and

b) treatment.

6. A method according to claim 1, wherein the first and second body segments are different types of body segment.

7. A method according to claim 1, wherein the first and second body segments are limbs.

8. A method according to claim 1, wherein the first body segment is a leg and the second body segment is an arm.

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

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

,

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

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

a) determining values for parameters R0 and R00 from the measured impedance values; and

,

b) calculating the index (I) using the equation;

11. A method according to claim 10, wherein the method includes, in the processing system, determining the parameter values using the equation:

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

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

and,

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

13. A method according to claim 10, wherein the method includes, in the processing system, determining the parameter values by:

a) determining an impedance locus using the measured impedance values; and

b) using the impedance locus to determine the parameter values.

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

a) the parameter values;

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

,

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

15. Apparatus for detecting tissue oedema in a subject, the apparatus including a processing system for:

a) determining a measured impedance for first and second body segments;

b) for each body segment, and using the measured impedance, determining an index indicative of a ratio of the extra-cellular to intra-cellular fluid;

c) determining an index ratio based on the index for the first and second body segments;

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

16. Apparatus according to claim 15, wherein the apparatus includes:

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

b) at least two supply electrodes for applying the generated alternating current to a subject;

c) at least two measurement electrodes for detecting a voltage across the subject;

and,

d) 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.

17. (canceled)

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

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

b) measuring an impedance at each frequency;

c) solving the equation;

19. A method according to claim 18, wherein the method includes diagnosing tissue oedema by determining the presence, absence or degree of tissue oedema.

20. A method according to claim 18, wherein the method includes:

a) determining the impedance at four discrete frequencies; and

,

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

21. A method according to claim 18, wherein the method includes:

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

, τ and

α

for first and second body regions; and

b) 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.

22. A method according to claim 21, wherein the includes:

a) comparing the parameters R₀ and R_∞

for each body region; and

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

23. A method according to claim 21, wherein the method includes:

a) calculating an index R_i/R_e as indicative of the ratio of extracellular fluid to intracellular fluid;

where

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

R_i is the resistance of intracellular fluid determined from

24. A method according to claim 18, wherein the method includes indicating tissue oedema by displaying the indication as a position on a scale.

25. (canceled)

26. Apparatus for detecting tissue oedema, the apparatus including:

a) a current supply for applying an alternating current to an anatomical region at four or more discrete frequencies across a frequency range;

b) a monitor for monitoring the bioelectrical impedance of said region; and

c) a processing system for;

i) analysing the bioelectrical impedance by solving;

27. Apparatus according to claim 26, wherein the current supply includes a proximal electrode and distal electrode in electrical connection with a power source.

28. Apparatus according to claim 26, wherein the monitor includes a first connection and second connection for location on or near the anatomical region.

29. Apparatus according to claim 26, wherein the monitor includes display means to display the signals indicative of bioimpedance.

30. Apparatus according to claim 26, wherein the processing system is suitably programmed to perform analysis of data to provide an indication of the presence of tissue oedema.

31. (canceled)

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

a) calculating an index R_i/R_e as indicative of the ratio of extracellular fluid to intracellular fluid;

where

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

R_i is the resistance of intracellular fluid determined from

33. A method according to claim 32, wherein the method includes:

a) measuring of R_i/R_e made prior to an event likely to cause oedema; and

,

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

34. (canceled)

35. Apparatus for diagnosing tissue oedema in a body region, the apparatus including a processing system for:

a) calculating an index R_i/R_e as indicative of the ratio of extracellular fluid to intracellular fluid;

where

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

R_i is the resistance of intracellular fluid determined from

36. (canceled)