Monitoring system

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 while the at least one electrical signal is applied to the subject via first leads;

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 while the at least one electrical signal is applied to the subject via first leads; 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 while the at least one electrical signal is applied to the subject via first leads;

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 while the at least one electrical signal is applied to the subject via first leads; 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.

17. 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 while the at least one electrical signal is applied to the subject via first leads;

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 while the at least one electrical signal is applied to the subject via first leads; and,

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

18. 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 while the at least one electrical signal is applied to the subject via first leads;

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 while the at least one electrical signal is applied to the subject via first leads; and,

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

19. 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 while the at least one electrical signal is applied to the subject via first leads;

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 while the at least one electrical signal is applied to the subject via first leads; and,

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

20. 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 while the at least one electrical signal is applied to the subject via first leads;

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 while the at least one electrical signal is applied to the subject via first leads; and,

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