Fluid level determination

1. A method for use in determining fluid levels within a subject, the method including, in a processing device that is configured to:

a) determine at least one impedance value measured for the subject, wherein the at least one impedance values are measured by applying one or more drive signals to the subject using a first set of electrodes and measuring one or more sense electrical signals across a second set of electrodes applied to the subject;

b) determine physical dimensions for at least part of at least one segment of the subject;

c) use the physical dimensions to determine a shape factor at least partially indicative of a shape of the at least one segment; and,

d) calculate a fluid indicator indicative of the fluid levels in the segment at least in part using the at least one impedance value and the shape factor;

wherein the physical dimensions are measured for the subject by:

i) capturing at least one image of the subject;

ii) determining a silhouette of the subject from the at least one image; and

iii) measuring the physical dimensions from the silhouette.

2. A method according to claim 1 , wherein the method includes, in a processing device that is being configured to:

a) determine an impedance parameter value using the impedance value measured, the impedance parameter value being indicative of an impedance at zero frequency; and,

b) calculate the fluid indicator using the impedance parameter value.

3. A method according to claim 2 , wherein the method includes, in a processing device that is being configured to:

a) determine a number of impedance measurements, the number of impedance measurements including at least one impedance measurement at each of a number of measurement frequencies; and,

b) determine the impedance parameter value using the number of impedance measurements.

4. A method according to claim 1 , wherein the physical dimensions include a length and circumference of the at least one segment.

5. A method according to claim 1 , wherein the method includes, in a processing device that is configured to, determine a whole of body fluid indicator by:

a) determining a whole of body impedance measurement;

b) determining physical dimensions for segments including at least:

i) a torso;

ii) an arm; and,

iii) a leg;

c) using the physical dimensions to determine a whole body shape factor; and,

d) calculating the fluid indicator at least in part using the whole of body impedance measurement and the whole body shape factor.

6. A method according to claim 1 , wherein the method includes, in a processing device that is configured to, determine a segmental fluid indicator indicative of a fluid volume of the at least one segment by:

a) determining a segmental impedance measurement for the at least one segment;

b) determining physical dimensions for the at least one segment;

c) using the physical dimensions to determine a segmental shape factor; and,

d) calculating the fluid indicator at least in part using the segmental impedance measurement and the segmental shape factor.

7. A method according to claim 1 , wherein the fluid indicator is indicative of at least one of:

a) extracellular fluid levels; and,

b) intracellular fluid levels.

8. A method according to claim 1 , wherein the method includes, in the processing device that is configured to:

a) cause at least one drive signal to be applied to the subject using a signal generator;

b) determine at least one sense signal measured across the subject using a sensor; and,

c) determine at least one impedance value using an indication of the drive signal and the sensed signal.

9. Apparatus for use in measuring fluid levels within a subject, the apparatus including:

a) a signal generator that is configured to apply one or more drive signals to the subject using a first set of electrodes;

b) a sensor that is configured to measure one or more sense electrical signals across a second set of electrodes applied to the subject; and,

c) a processing device that is configured to:

i) determine at least one impedance value measured for the subject using the drive and sense electrical signals;

ii) determine physical dimensions for at least part of at least one segment of the subject;

iii) use the physical dimensions to determine a shape factor at least partially indicative of a shape of the at least one segment; and,

iv) calculate a fluid indicator indicative of the fluid levels in the segment at least in part using the at least one impedance value and the shape factor;

wherein the physical dimensions are measured for the subject by the processor that is configured to:

(1) capture at least one image of the subject;

(2) determine a silhouette of the subject from the at least one image; and

(1) measure the physical dimensions from the silhouette.