MONITORING SYSTEM

• US 20100100003A1
• Filed: 01/14/2008
• Published: 04/22/2010
• Est. Priority Date: 01/15/2007
• Status: Active Grant

• Current Assignee: ImpediMed Limited
• Original Assignee: ImpediMed Limited
• Inventors: Bruinsma, Ian John, Daly, Christopher Newton, Chetham, Scott
• Granted Patent: US 8,594,781 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 5/6824 Arm or wrist
• CPC Class Codes: A61B 5/6829 Foot or ankle

Abstract

A method for performing impedance measurements on a subject. The method includes, in a processing system, causing at least one electrical signal to be applied to the subject via first leads operatively connected to first electrodes provided on the subject, determining a first indication indicative of at least one first electrical signal measured via second leads operatively disconnected from second electrodes positioned on the subject, determining a second indication indicative of at least one second electrical signal measured via second leads operatively connected to second electrodes positioned on the subject, and determining from the indications and the at least one applied signal, at least one instantaneous impedance value.

Claims

1. A method for performing impedance measurements on a subject, the method including, in a processing system:

a) causing at least one electrical signal to be applied to the subject via first leads operatively connected to first electrodes provided on the subject;

b) determining a first indication indicative of at least one first electrical signal measured via second leads operatively disconnected from second electrodes positioned on the subject;

c) determining a second indication indicative of at least one second electrical signal measured via second leads operatively connected to second electrodes positioned on the subject; and

,

d) determining from the indications and the at least one applied signal, at least one instantaneous impedance value.

2. A method according to claim 1, wherein the second leads are connected to the second electrodes via respective switches, and wherein the method includes, in the processing system, causing the switches to be selectively opened and closed to allow the first and second indications to be determined.

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

a) opening the switches;

b) determining the first indication;

c) closing the switches; and

,

d) determining the second indication.

4. A method according to claim 1, wherein each second lead includes a lead pair, and wherein each lead pair includes a lead operatively connected to the second electrodes and a lead operatively disconnected to the second electrodes, and wherein the method includes, in the processing system:

a) determining the first indication using the lead operatively disconnected to the second electrodes; and

,

b) determining the second indication using the lead operatively connected to the second electrodes.

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

a) determining a number of frequencies;

b) selecting a next frequency from the number of frequencies;

c) causing the at least one electrical signal to be applied to the subject at the selected frequency;

d) determining the first and second indications; and

,

e) repeating steps (b), (c) and (d) for each of the number of frequencies.

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

a) determining at least one impedance measurement to be performed; and

,

b) determining the number of frequencies using the determined impedance measurement.

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

a) determining an indication of the at least one signal applied to the subject; and

,

b) determining the at least one instantaneous impedance value using the determined indication.

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

a) modifying the second indication using the first indication; and

,

b) using the modified second indication to determine the at least one instantaneous impedance value.

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

a) determining at least one first instantaneous impedance value using the first indication;

b) determining at least one second instantaneous impedance value using the second indication; and

,

c) determining the at least one instantaneous impedance value using the first and second instantaneous impedance values.

10. A method according to claim 1, wherein the method includes, in the processing system, using the first and second indications to account for inductive coupling between the first and second leads.

11. Apparatus for performing impedance measurements on a subject, the apparatus including, a processing system for:

a) causing at least one electrical signal to be applied to the subject via first leads operatively connected to first electrodes provided on the subject;

b) determining a first indication indicative of at least one first electrical signal measured via second leads operatively disconnected from second electrodes positioned on the subject;

c) determining a second indication indicative of at least one second electrical signal measured via second leads operatively connected to second electrodes positioned on the subject; and

,

d) determining from the indications and the at least one applied signal, at least one instantaneous impedance value.

12. Apparatus according to claim 11, wherein the apparatus includes switches for selectively operatively connecting the second electrodes to the second leads.

13. Apparatus according to claim 11, wherein the processing system is for opening and closing the switches to thereby selectively operatively connect the second electrodes to the second leads.

14. Apparatus according to claim 11, wherein the apparatus includes buffer circuits for coupling the second leads to the second electrodes.

15. Apparatus according to claim 14, wherein the apparatus includes switches positioned between the buffer circuits and the second electrodes for selectively operatively connecting the second leads to the second electrodes.

16. Apparatus according to claim 11, wherein each second lead includes a lead pair, and wherein each lead pair includes a lead operatively connected to the second electrodes and a lead operatively disconnected to the second electrodes.

45. Apparatus according to claim 43 or claim 11, wherein the leads include:

a) a first cable for coupling the measuring device to the signal generator to thereby allow the measuring device to control the signal generator to apply a first signal to the subject;

b) a second cable for coupling the measuring device to the signal generator to thereby allow the measuring device to determine a parameter relating to the first signal applied to the subject; and

,

c) a third cable for coupling the measuring device to the sensor generator to thereby allow the measuring device to determine a voltage measured at the subject.

17. A method for use in performing impedance measurements on a subject, wherein the method includes, in a processing system:

a) causing a first signal to be applied to the subject;

b) determining an indication of a second signal measured across the subject;

c) using the indication of the second signal to determine any imbalance;

d) determining a modified first signal in accordance with the imbalance;

e) causing the modified first signal to be applied to the subject to thereby allow at least one impedance measurement to be performed.

18. A method according to claim 17, wherein the second signal is a voltage sensed at respective second electrodes and wherein the method includes, in the processing system:

a) determining the voltage sensed at each of the second electrodes;

b) determining a first voltage using the voltage sensed at each of the second electrodes; and

,

c) determining the imbalance using the first voltage.

19. A method according to claim 18, wherein the first voltage is a common mode signal.

20. A method according to claims 17, wherein the method includes, in the processing system, determining the modified first signal so as to minimise the imbalance.

21. A method according to claims 17, wherein the first signal is a voltage applied to the subject using the first electrodes and the second signal is a voltage sensed at respective second electrodes, and wherein the method includes, in the processing system, performing the impedance measurement by:

a) determining a current flow caused by applying the first signal to the subject;

b) determining the voltage sensed at each of the second electrodes;

c) determining a second voltage using the voltage sensed at each of the second electrodes;

d) determining an impedance parameter using the determined current flow and the second voltage.

22. A method according to claim 21, wherein the second voltage is a differential voltage.

23. A method according to claim 17, wherein the first signal is a voltage applied to the subject using the first electrodes, and wherein the method includes, in the processing system, performing the impedance measurement by:

a) determining a current flow caused by applying the first signal to the subject;

b) comparing the current flow to a threshold; and

,

c) selectively halting application of the first signal to the subject depending on the results of the comparison.

24. A method according to claim 17, wherein the method includes, in the processing system, performing impedance measurements at each of a number of frequencies by:

a) causing a first signal to be applied to the subject at a first frequency;

b) determining an indication of a second signal measured across the subject;

c) using the indication of the second signal to determine an imbalance;

d) determining a modified first signal in accordance with the imbalance;

e) causing the modified first signal to be applied to the subject to thereby allow at least one impedance measurement to be performed at the first frequency; and

,

f) repeating steps a) to e) for at least one second frequency.

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

a) generating control signals, the control signals being used to apply one or more signals to the subject;

b) receiving an indication of the one or more signals applied to the subject;

c) receiving an indication of one or more signals measured across the subject; and

,

d) performing at least preliminary processing of the indications to thereby allow impedance values to be determined.

26. (canceled)

27. Apparatus for performing impedance measurements, the apparatus including a processing system for:

a) causing a first signal to be applied to the subject;

b) determining an indication of a second signal measured across the subject;

c) using the indication of the second signal to determine an imbalance;

d) determining a modified first signal in accordance with the imbalance;

e) causing the modified first signal to be applied to the subject to thereby allow at least one impedance measurement to be performed.

28. Apparatus according to claim 27, wherein the processing system is for:

a) generating control signals, the control signals being used to apply one or more signals to the subject;

b) receiving an indication of the one or more signals applied to the subject;

c) receiving an indication of one or more signals measured across the subject; and

,

d) performing at least preliminary processing of the indications to thereby allow impedance values to be determined.

29. Apparatus according to claim 27, wherein the apparatus includes at least one signal generator for:

a) receiving one or more control signals;

b) amplifying the control signals to thereby generate the first signal;

c) applying the first signal to the subject via a first electrode; and

,

d) providing an indication of a parameter relating to the first signal applied to the subject.

30. Apparatus according to claim 29, wherein the apparatus includes a respective signal generator for each first electrode.

31. Apparatus according to claim 29, wherein the first signal is a voltage, and wherein the signal generator is for providing an indication of the current flow through the subject.

32. Apparatus according to claim 27, wherein the apparatus includes at least one sensor for measuring the second signals via second electrodes.

33. Apparatus according to claim 32, wherein the apparatus includes a respective sensor for each second electrode.

34. Apparatus according to claim 27, wherein the apparatus includes a differential amplifier for amplifying second signals measured at each of two second electrodes.

35. Apparatus according to claim 34, wherein the differential amplifier generates at least one of:

a) a differential voltage indicative of the voltage measured at the second electrodes; and

,

b) a common mode signal indicative of any imbalance.

36. Apparatus according to claim 27, wherein the apparatus includes an electrode system including:

a) a first substrate having the signal generator and sensor mounted thereon; and

,

b) a second substrate having at least two conductive pads mounted thereon, the conductive pads being for coupling the signal generator and the sensor to a subject in use.

37. Apparatus according to claim 27, wherein the apparatus includes at least one lead for at least partially connecting a measuring device to first and second electrodes, the lead including:

a) at least two connections for connecting the measuring device and the signal generator, and the measuring device and the sensor; and

,

b) a shield for each of the at least two connections, the shields being electrically connected, and connected to a reference potential in each of the measuring device and the electrode system.

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

a) at least two electrode systems, each electrode system including;

i) a signal generator for applying a first signal to be applied to the subject;

ii) a sensor for sensing a second signal across the subject;

iii) a first electrode for coupling the signal generator to the subject; and

,

iv) a second electrode for coupling the sensor to the subject; and

,

b) a measuring device for controlling the electrode systems to allow impedance measurements to be performed; and

,

c) at least two leads for connecting the measuring device to the electrode systems, the leads being arranged to at least one of

i) extend from the measuring device in different directions to thereby reduce inductive coupling therebetween; and

,

ii) minimise the lead length.

39. Apparatus according to claim 27, wherein the apparatus includes an interface for coupling the processing system to a computer system, the processing system being for:

a) generating control signals in accordance with commands received from the computer system; and

,

b) providing data indicative of measured impedance values to the computer system to allow impedance values to be determined.

40. Apparatus according to claim 39, wherein the processing system is an FPGA.

41. Apparatus according to claim 39, wherein the computer system is for:

a) generating commands for controlling the processing system;

b) receiving data indicative of measured impedance values from the processing system; and

,

c) determining impedance values using the data.

42. (canceled)

43. Apparatus for use in performing impedance measurements on a subject, wherein the apparatus includes leads for connecting a measuring device to an electrode system, the electrode system including a signal generator and a sensor, the leads including:

a) at least two connections for connecting the measuring device and the signal generator, and the measuring device and the sensor; and

,

b) a shield for each of the at least two connections, the shields being electrically connected, and connected to a reference potential in each of the measuring device and the electrode system.

44. Apparatus according to claim 43, wherein the reference potential is a ground potential.

46. Apparatus according to claim 43, wherein the electrode system includes:

a) a first substrate having the signal generator and sensor mounted thereon; and

,

b) a second substrate having at least two conductive pads mounted thereon, the conductive pads being for coupling the signal generator and the sensor to a subject in use.

47. (canceled)

48. Apparatus for use in performing impedance measurements on a subject, wherein the apparatus includes:

a) at least two electrode systems, each electrode system including;

i) a signal generator for applying a first signal to be applied to the subject;

ii) a sensor for sensing a second signal across the subject;

iii) a first electrode for coupling the signal generator to the subject; and

,

iv) a second electrode for coupling the sensor to the subject; and

,

b) a measuring device for controlling the electrode systems to allow impedance measurements to be performed; and

,

c) at least two leads for connecting the measuring device to the electrode systems, the leads being arranged to at least one of;

i) extend from the measuring device in different directions to thereby reduce inductive coupling therebetween; and

,

ii) minimise the lead length.

49. Apparatus according to claim 48, wherein the apparatus includes:

a) four electrode systems; and

,

b) four leads extending from the measuring device in four different directions.

50. Apparatus according to claim 48, wherein the apparatus includes a support for supporting a subject'"'"'s limbs to thereby position the measuring device substantially between the subject'"'"'s knees.

51. Apparatus according to any claim 48, wherein each lead includes:

a) a first cable for coupling the measuring device to the signal generator to thereby allow the measuring device to control the signal generator to apply a first signal to the subject;

b) a second cable for coupling the measuring device to the signal generator to thereby allow the measuring device to determine a parameter relating to the first signal applied to the subject; and

,

c) a third cable for coupling the measuring device to the sensor generator to thereby allow the measuring device to determine a voltage measured at the subject.

52. Apparatus according to claim 48, wherein the electrode system includes:

a) a first substrate having the signal generator and sensor mounted thereon; and

,

b) a second substrate having at least two conductive pads mounted thereon, the conductive pads being for coupling the signal generator and the sensor to a subject in use.

53. (canceled)

54. A method of using apparatus for performing impedance measurements on a subject, wherein the apparatus includes:

a) at least two electrode systems, each electrode system including;

i) a signal generator for applying a first signal to be applied to the subject;

ii) a sensor for sensing a second signal across the subject;

iii) a first electrode for coupling the signal generator to the subject; and

,

iv) a second electrode for coupling the sensor to the subject; and

,

b) a measuring device for controlling the electrode systems to allow impedance measurements to be performed; and

,

c) at least two leads for connecting the measuring device to the electrode systems, wherein the method includes, arranging the leads to at least one of;

i) extend from the measuring device in different directions to thereby reduce inductive coupling therebetween; and

,

ii) minimise the lead length.

55. (canceled)

56. A method for use in determining body composition, the method including, in a processing system:

a) causing a first signal to be applied to the subject;

b) determining an indication of a second signal measured across the subject;

c) using the indication of the second signal to determine any imbalance;

d) determining a modified first signal in accordance with the imbalance;

e) causing the modified first signal to be applied to the subject to thereby allow at least one impedance measurement to be performed.

57. A method of using apparatus for use in determining body composition, wherein the apparatus includes:

a) at least two electrode systems, each electrode system including;

i) a signal generator for applying a first signal to be applied to the subject;

ii) a sensor for sensing a second signal across the subject;

iii) a first electrode for coupling the signal generator to the subject; and

,

iv) a second electrode for coupling the sensor to the subject; and

,

b) a measuring device for controlling the electrode systems to allow impedance measurements to be performed; and

,

c) at least two leads for connecting the measuring device to the electrode systems, and wherein the method includes, arranging the leads to at least one of;

i) extend from the measuring device in different directions to thereby reduce inductive coupling therebetween; and

,

ii) minimise the lead length.

58. A method for use in diagnosing the presence, absence or degree of oedema, the method including, in a processing system:

a) causing a first signal to be applied to the subject;

b) determining an indication of a second signal measured across the subject;

c) using the indication of the second signal to determine any imbalance;

d) determining a modified first signal in accordance with the imbalance;

e) causing the modified first signal to be applied to the subject to thereby allow at least one impedance measurement to be performed.

59. A method for use in diagnosing the presence, absence or degree of oedema, wherein the apparatus includes:

a) at least two electrode systems, each electrode system including;

i) a signal generator for applying a first signal to be applied to the subject;

ii) a sensor for sensing a second signal across the subject;

iii) a first electrode for coupling the signal generator to the subject; and

,

iv) a second electrode for coupling the sensor to the subject; and

,

b) a measuring device for controlling the electrode systems to allow impedance measurements to be performed; and

,

c) at least two leads for connecting the measuring device to the electrode systems, and wherein the method includes, arranging the leads to at least one of;

i) extend from the measuring device in different directions to thereby reduce inductive coupling therebetween; and

,

ii) minimise the lead length.

60. A method for use in diagnosing the presence, absence or degree of oedema, wherein the method includes:

a) causing at least one electrical signal to be applied to the subject via first leads operatively connected to first electrodes provided on the subject;

b) determining a first indication indicative of at least one first electrical signal measured via second leads operatively disconnected from second electrodes positioned on the subject;

c) determining a second indication indicative of at least one second electrical signal measured via second leads operatively connected to second electrodes positioned on the subject; and

,

d) determining from the indications and the at least one applied signal, at least one instantaneous impedance value.

61. A method for use in diagnosing the presence, absence or degree of oedema, wherein the method includes:

a) causing at least one electrical signal to be applied to the subject via first leads operatively connected to first electrodes provided on the subject;

b) determining a first indication indicative of at least one first electrical signal measured via second leads operatively disconnected from second electrodes positioned on the subject;

c) determining a second indication indicative of at least one second electrical signal measured via second leads operatively connected to second electrodes positioned on the subject; and

,

d) determining from the indications and the at least one applied signal, at least one instantaneous impedance value.

62. Apparatus for use in diagnosing the presence, absence or degree of oedema, wherein the apparatus includes a processing system for:

a) causing at least one electrical signal to be applied to the subject via first leads operatively connected to first electrodes provided on the subject;

b) determining a first indication indicative of at least one first electrical signal measured via second leads operatively disconnected from second electrodes positioned on the subject;

c) determining a second indication indicative of at least one second electrical signal measured via second leads operatively connected to second electrodes positioned on the subject; and

,

d) determining from the indications and the at least one applied signal, at least one instantaneous impedance value.

63. A method for use in determining body composition, wherein the method includes:

a) causing at least one electrical signal to be applied to the subject via first leads operatively connected to first electrodes provided on the subject;

b) determining a first indication indicative of at least one first electrical signal measured via second leads operatively disconnected from second electrodes positioned on the subject;

c) determining a second indication indicative of at least one second electrical signal measured via second leads operatively connected to second electrodes positioned on the subject; and

,

d) determining from the indications and the at least one applied signal, at least one instantaneous impedance value.

64. Apparatus for use in determining body composition, wherein the apparatus includes a processing system for:

a) causing at least one electrical signal to be applied to the subject via first leads operatively connected to first electrodes provided on the subject;

b) determining a first indication indicative of at least one first electrical signal measured via second leads operatively disconnected from second electrodes positioned on the subject;

c) determining a second indication indicative of at least one second electrical signal measured via second leads operatively connected to second electrodes positioned on the subject; and

,

d) determining from the indications and the at least one applied signal, at least one instantaneous impedance value.