IMPEDANCE MEASUREMENTS

• US 20100087750A1
• Filed: 05/25/2007
• Published: 04/08/2010
• Est. Priority Date: 05/30/2006
• Status: Active Grant

• Current Assignee: James Matthew Mcgree, John Anthony Eccleston, Leigh Cordwin Ward, Stephen Brent Duffull
• Original Assignee: ImpediMed Limited
• Inventors: Duffull, Stephen Brent, Eccleston, John Anthony, McGree, James Matthew, Ward, Leigh Cordwin
• Granted Patent: US 8,761,870 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• 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

Abstract

A method of determining frequencies for use in performing impedance measurements. The method includes determining estimates for parameter values representing an impedance response for at least one subject, using the estimated parameter values to determine a design and using the design to determine frequencies for use in impedance measurements.

Claims

1. A method of determining frequencies for use in performing impedance measurements, the method including:

a) determining estimates for parameter values representing an impedance response for at least one subject;

b) using the estimated parameter values to determine a design; and

,

c) using the design to determine frequencies for use in impedance measurements.

2. A method according to claim 1, wherein the method includes, determining the estimates for the parameter values at least in part using a model of the subject'"'"'s impedance response.

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

a) determining a residual variance model having a predetermined distribution; and

,

b) determining the estimates for the parameter values at least in part using the selecting variance model.

4. A method according to claim 3, wherein the method of determining the residual variance model includes using an expectation maximization algorithm.

5. A method according to claim 1, wherein the method includes determining a range of parameter values representing the impedance response of a number of subjects.

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

a) determining a Fisher information matrix for a model of the impedance response of the at least one subject; and

,

b) determining a design using the Fisher information matrix.

7. A method according to claim 6, wherein the model includes at least one of:

a) A Cole model; and

,

b) A residual variance model.

8. A method according to claim 6, wherein the model includes determining the design by optimising the determinant of the Fisher information matrix.

9. A method according to claim 6, wherein the design is a D-optimal design.

10. A method according to claim 1, wherein the method includes determining a design space to take into account practical limitations.

11. A method according to claim 10, wherein the method includes, modifying the design by at least one of:

a) restricting the frequencies; and

,

b) providing an error structure as a function of frequency.

12. A method according to claim 1, wherein the method is performed at least in part using a processing system.

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

a) determining impedance data representing the impedance response of the at least one subject; and

,

b) using the impedance data to determine the estimates for the parameter values.

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

a) determining an impedance model; and

,

b) using the impedance model and the estimated parameter values to determine the design.

15. A method according to claim 14, wherein the method includes, in the processing system:

a) calculating a Fisher information matrix for the model; and

,

b) using the Fisher information matrix to determine the design.

16. A method according to claim 15, wherein the method includes, in the processing system, optimising a determinant of the Fisher information matrix for the model.

17. A method according to claim 16, wherein the method includes, in the processing system:

a) receiving limits on applicable frequencies; and

,

b) using the limits and the design to determine the frequencies.

18. A method according to claim 1, wherein the method includes, in the processing system, determining frequencies for use in impedance measurements within the ranges:

a) 0-50 kHz;

b) 2-200 kHz;

c) 50-500 kHz; and

,

d) 200-1000 kHz.

19. A method according to claim 18, wherein the frequencies are within the ranges:

a) 0-24 kHz;

b) 5-74 kHz;

c) 77-200 kHz;

d) 530-1000 kHz.

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

a) 14 kHz

b) 57 kHz

c) 188 kHz

d) 679 kHz.

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

a) 4.1844 kHz

b) 56.9201 kHz

c) 187.5397 kHz

d) 679.1141 kHz.

22. Apparatus for determining frequencies for use in performing impedance measurements, the apparatus including, a processing system for:

a) determining estimates for parameter values representing an impedance response for at least one subject;

b) using the estimated parameter values to determine a design; and

,

c) using the design to determine frequencies for use in impedance measurements.

23. (canceled)

25. A method according to claim 23, wherein a restricted range of frequencies can be defined by the ranges:

a) 0-24 kHz;

b) 5-74 kHz;

c) 77-200 kHz;

d) 530-1000 kHz.

26. A method according to claim 23, wherein the frequencies are approximately:

a) 14 kHz

b) 57 kHz

c) 188 kHz

d) 679 kHz.

27. A method according to claim 23, wherein the frequencies are:

a) 14.1844 kHz

b) 56.9201 kHz

c) 187.5397 kHz

d) 679.1141 kHz.

28. A method according to claim 23, wherein the method includes determining one or more impedance parameter values based on the plurality of measured impedance values.

30. Apparatus according to claim 28, the measuring device including:

a) a current source for applying current signals to the subject;

b) a voltage sensor for measuring voltages signals across the subject; and

,

c) a processing system could to the current source and the voltage sensor for;

i) causing the current signals to be applied to the subject; and

,

ii) determining the impedance using the applied current signals and measured voltage signals.

24. A method of measuring the impedance of a subject, the method including, in a measuring device:

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

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

c) determining from the applied signals and the measured signals at least one measured impedance value at each of the four frequencies, wherein the four frequencies are in the ranges;

i) 0-50 kHz;

ii) 2-200 kHz;

iii) 50-500 kHz; and

,

iv) 200-1000 kHz.

29. Apparatus for measuring the impedance of a subject the apparatus including a measuring device for:

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

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

c) determining from the applied signals and the measured signals at least one measured impedance value at each of the four frequencies, wherein the four frequencies are in the ranges;

i) 0-50 kHz;

ii) 2-200 kHz;

iii) 50-500 kHz; and

,

iv) 200-1000 kHz.

31. (canceled)