Patent Description:
The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

One existing technique for determining biological parameters relating to a subject, such as cardiac function, involves the use of bioelectrical impedance. This involves measuring the electrical impedance of a subject's body using a series of electrodes placed on the skin surface. Changes in electrical impedance at the body's surface are used to determine parameters, such as changes in fluid levels, associated with the cardiac cycle or oedema.

Accordingly, complex signal processing is required to ensure measurements can be interpreted. Typically devices for achieving this utilise custom hardware configurations that are application specific. As a result, the devices can typically only be used in a limited range of circumstances.

<CIT> relates to a method for generating impedance images of the chest, comprising:
acquiring electrical data of the chest; obtaining electrocardiograph data of a patient; analyzing the electrocardiograph data to obtain information about breathing parameters at the time the electrical data was acquired; and reconstructing at least one impedance image of the chest from the electrical data and the information about breathing parameters; wherein the information about breathing parameters reduces the sensitivity of the at least one impedance image to breathing parameters.

<CIT> relates to an impedance model of tissue is useful for describing conductivity reconstruction in tissue. Techniques for determining and mapping conductivity distribution in tissue supply useful information of anatomical and physiological status in various medical applications. Electrical Impedance Tomography (EIT) techniques are highly suitable for analyzing conductivity distribution. Electrical characteristics of tissue include resistive elements and capacitive elements. EIT techniques involve passing a low frequency current through the body to monitor various anatomical and physiological characteristics. The system can interrogate at multiple frequencies to map impedance. Analytical techniques involve forward and inverse solutions to boundary value analysis to tissue characteristics.

<CIT> relates to an apparatus and a method for determining an approximate value for the stroke volume and the cardiac output of a person's heart. The apparatus and method employ a measured electrical impedance, or admittance, of a part of a person's body, namely, the thorax. This part of a person's body is chosen because its electrical impedance, or admittance, changes with time as a consequence of the periodic beating of the heart. Accordingly, the measured electrical admittance or impedance can provide information about the performance of the heart as a pump.

<CIT> relates to a postpartum supporting apparatus configured to measure a body bioelectrical impedance and to use it as an index of a body fat condition. The apparatus comprises a first CPU at the level of its main body and a second CPU at the level of an associated controlling device.

In one broad aspect of the present invention seeks to provide an apparatus for performing impedance measurements on a subject as recited in claim <NUM>.

It will be appreciated that the broad forms of the invention may be used individual or in combination, and may be used for diagnosis of the presence, absence or degree of a range of conditions and illnesses, including, but not limited to oedema, pulmonary oedema, lymphodema, body composition, cardiac function, and the like.

An example of the present invention will now be described with reference to the accompanying drawings, in which:.

An example of apparatus suitable for performing an analysis of a subject's bioelectric impedance will now be described with reference to <FIG>.

As shown the apparatus includes a measuring device <NUM> including a processing system <NUM> coupled to a signal generator <NUM> and a sensor <NUM>. In use the signal generator <NUM> and the sensor <NUM> are coupled to respective electrodes <NUM>, <NUM>, <NUM>, <NUM>, provided on a subject S, via leads L, as shown. An optional external interface <NUM> can be used to couple the measuring device <NUM> to one or more peripheral devices <NUM>, such as an external database or computer system, barcode scanner, or the like.

In use, the processing system <NUM> is adapted to generate control signals, which causes the signal generator <NUM> to generate one or more alternating signals, such as voltage or current signals, which can be applied to a subject S, via the electrodes <NUM>, <NUM>. The sensor <NUM> then determines the voltage across or current through the subject S, using the electrodes <NUM>, <NUM> and transfers appropriate signals to the processing system <NUM>.

Accordingly, it will be appreciated that the processing system <NUM> may be any form of processing system which is suitable for generating appropriate control signals and interpreting an indication of the measured signals to thereby determine the subject's bioelectrical impedance, and optionally determine other information such as the cardiac parameters, presence absence or degree of oedema, or the like.

The processing system <NUM> may therefore be a suitably programmed computer system, such as a laptop, desktop, PDA, smart phone or the like. Alternatively the processing system <NUM> may be formed from specialised hardware. Similarly, the I/O device may be of any suitable form such as a touch screen, a keypad and display, or the like.

It will be appreciated that the processing system <NUM>, the signal generator <NUM> and the sensor <NUM> may be integrated into a common housing and therefore form an integrated device. Alternatively, the processing system <NUM> may be connected to the signal generator <NUM> and the sensor <NUM> via wired or wireless connections. This allows the processing system <NUM> to be provided remotely to the signal generator <NUM> and the sensor <NUM>. Thus, the signal generator <NUM> and the sensor <NUM> may be provided in a unit near, or worn by the subject S, whilst the processing system <NUM> is situated remotely to the subject S.

In one example, the outer pair of electrodes <NUM>, <NUM> are placed on the thoracic and neck region of the subject S. However, this depends on the nature of the analysis being performed. Thus, for example, whilst this electrode arrangement is suitable for cardiac function analysis, in lymphoedema, the electrodes would typically be positioned on the limbs, as required.

Once the electrodes are positioned, an alternating signal is applied to the subject S. This may be performed either by applying an alternating signal at a plurality of frequencies simultaneously, or by applying a number of alternating signals at different frequencies sequentially. The frequency range of the applied signals may also depend on the analysis being performed.

In one example, the applied signal is a frequency rich current from a current source clamped, or otherwise limited, so it does not exceed the maximum allowable subject auxiliary current. However, alternatively, voltage signals may be applied, with a current induced in the subject being measured. The signal can either be constant current, impulse function or a constant voltage signal where the current is measured so it does not exceed the maximum allowable subject auxiliary current.

A potential difference and/or current are measured between an inner pair of electrodes <NUM>, <NUM>. The acquired signal and the measured signal will be a superposition of potentials generated by the human body, such as the ECG, and potentials generated by the applied current.

Optionally the distance between the inner pair of electrodes may be measured and recorded. Similarly, other parameters relating to the subject may be recorded, such as the height, weight, age, sex, health status, any interventions and the date and time on which they occurred. Other information, such as current medication, may also be recorded.

To assist accurate measurement of the impedance, buffer circuits may be placed in connectors that are used to connect the voltage sensing electrodes <NUM>, <NUM> to the leads L. This ensures accurate sensing of the voltage response of the subject S, and in particular helps eliminate contributions to the measured voltage due to the response of the leads L, and reduce signal loss.

This in turn greatly reduces artefacts caused by movement of the leads L, which is particularly important during dialysis as sessions usually last for several hours and the subject will move around and change positions during this time.

A further option is for the voltage to be measured differentially, meaning that the sensor used to measure the potential at each electrode <NUM>, <NUM> only needs to measure half of the potential as compared to a single ended system.

The current measurement system may also have buffers placed in the connectors between the electrodes <NUM>, <NUM> and the leads L. In one example, current can also be driven or sourced through the subject S symmetrically, which again greatly reduced the parasitic capacitances by halving the common-mode current. Another particular advantage of using a symmetrical system is that the micro-electronics built into the connectors for each electrode <NUM>, <NUM> also removes parasitic capacitances that arise when the subject S, and hence the leads L move.

The acquired signal is demodulated to obtain the impedance of the system at the applied frequencies. One suitable method for demodulation of superposed frequencies is to use a Fast Fourier Transform (FFT) algorithm to transform the time domain data to the frequency domain. This is typically used when the applied current signal is a superposition of applied frequencies. Another technique not requiring windowing of the measured signal is a sliding window FFT.

In the event that the applied current signals are formed from a sweep of different frequencies, then it is more typical to use a processing technique such as multiplying the measured signal with a reference sine wave and cosine wave derived from the signal generator, or with measured sine and cosine waves, and integrating over a whole number of cycles. This process rejects any harmonic responses and significantly reduces random noise.

Other suitable digital and analog demodulation techniques will be known to persons skilled in the field.

Impedance or admittance measurements are determined from the signals at each frequency by comparing the recorded voltage and current signal. The demodulation algorithm will produce an amplitude and phase signal at each frequency.

An example of the operation of the apparatus for performing impedance analysis will now be described with reference to <FIG>.

At step <NUM>, the processing system <NUM> operates to generate control signals which are provided to the signal generator <NUM> at step <NUM>, thereby causing the signal generator to apply an alternating current signal to the subject S, at step <NUM>. Typically the signal is applied at each of a number of frequencies fi to allow multiple frequency analysis to be performed.

At step <NUM> the sensor <NUM> senses voltage signals across the subject S. At step <NUM> the measuring device, operates to digitise and sample the voltage and current signals across the subject S, allowing these to be used to determine instantaneous impedance values for the subject S at step <NUM>.

A specific example of the apparatus will now be described in more detail with respect to <FIG>.

In this example, the processing system <NUM> includes a first processing system <NUM> having a processor <NUM>, a memory <NUM>, an input/output (I/O) device <NUM>, and an external interface <NUM>, coupled together via a bus <NUM>. The processing system <NUM> also includes a second processing system <NUM>, in the form of a processing module. A controller <NUM>, such as a micrologic controller, may also be provided to control activation of the first and second processing systems <NUM>, <NUM>.

In use, the first processing system <NUM> controls the operation of the second processing system <NUM> to allow different impedance measurement procedures to be implemented, whilst the second processing system <NUM> performs specific processing tasks, to thereby reduce processing requirements on the first processing system <NUM>.

Thus, the generation of the control signals, as well as the processing to determine instantaneous impedance values is performed by the second processing system <NUM>, which may therefore be formed from custom hardware, or the like. In one particular example, the second processing system <NUM> is formed from a Field Programmable Gate Array (FPGA), although any suitable processing module, such as a magnetologic module, may be used.

The operation of the first and second processing systems <NUM>, <NUM>, and the controller <NUM> is typically controlled using one or more sets of appropriate instructions. These could be in any suitable form, and may therefore include, software, firmware, embedded systems, or the like.

The controller <NUM> typically operates to detect activation of the measuring device through the use of an on/off switch (not shown). Once the controller detects device activation, the controller <NUM> executes predefined instructions, which in turn causes activation of the first and second processing systems <NUM>, <NUM>, including controlling the supply of power to the processing systems as required.

The first processing system <NUM> can then operate to control the instructions, such as the firmware, implemented by the second processing system <NUM>, which in turn alters the operation of the second processing system <NUM>. Additionally, the first processing system <NUM> can operate to analyse impedance determined by the second processing system <NUM>, to allow biological parameters to be determined. Accordingly, the first processing system <NUM> may be formed from custom hardware or the like, executing appropriate applications software to allow the processes described in more detail below to be implemented.

It will be appreciated that this division of processing between the first processing system <NUM>, and the second processing system <NUM>, leads to a number of benefits that will become apparent from the remaining description.

In this example, the second processing system <NUM> includes a PCI bridge <NUM> coupled to programmable module <NUM> and a bus <NUM>, as shown. The bus <NUM> is in turn coupled to processing modules <NUM>, <NUM>, <NUM>, which interface with ADCs (Analogue to Digital Converters) <NUM>, <NUM>, and a DAC (Digital to Analogue Converter) <NUM>, respectively.

The programmable module <NUM> is formed from programmable hardware, the operation of which is controlled using the instructions, which are typically downloaded from the first processing system <NUM>. The firmware that specifies the configuration of hardware <NUM> may reside in flash memory (not shown), in the memory <NUM>, or may be downloaded from an external source via the external interface <NUM>. Alternatively, the instructions may be stored within inbuilt memory on the second processing system <NUM>. In this example, the first processing system <NUM> typically selects firmware for implementation, before causing this to be implemented by the second processing system <NUM>. This may be achieved to allow selective activation of functions encoded within the firmware, and can be performed for example using configuration data, such as a configuration file, or instructions representing applications software or firmware, or the like, as will be described in more detail below.

In either case, this allows the first processing system <NUM> to be used to control operation of the second processing system <NUM> to allow predetermined current sequences to be applied to the subject S. Thus, for example, different firmware would be utilised if the current signal is to be used to analyse the impedance at a number of frequencies simultaneously, for example, by using a current signal formed from a number of superposed frequencies, as compared to the use of current signals applied at different frequencies sequentially.

An example of a specific form of signal generator <NUM> in the form of a current source circuit, is shown in <FIG>.

As shown the current source includes three fixed or variable gain differential amplifiers A<NUM>, A<NUM>, A<NUM> and three op-amps A<NUM>, A<NUM>, A<NUM>, a number of resistors R<NUM>,. R<NUM> and capacitors C<NUM>,. C<NUM>, interconnected as shown. The current source also includes leads <NUM>, <NUM> (corresponding to the leads L in <FIG>) which connect the current source to the electrodes <NUM>, <NUM> and a switch SW for shorting the leads <NUM>, <NUM> as will be described in more detail below.

Connections <NUM>, <NUM> can also be provided for allowing the current applied to the subject S to be determined. Typically this is achieved using the connection <NUM>. However, the connection <NUM> may also be used as shown in dotted lines to allow signal losses within the leads and other circuitry to be taken into account.

In general the leads used are co-axial cables with a non-braided shield and a multi strand core with a polystyrene dielectric. This provides good conductive and noise properties as well as being sufficiently flexible to avoid issues with connections from the measuring device <NUM> to the subject S. In this instance, resistors R<NUM>, R<NUM> decouple the outputs of the amplifiers A<NUM>, A<NUM> from the capacitances associated with cable.

In use, the current source circuit receives current control signals I+, I- from the DAC <NUM>, with these signals being filtered and amplified, to thereby form current signals that can be applied to the subject S via the electrodes <NUM>, <NUM>.

In use, when the amplifiers A<NUM>,. A<NUM> are initially activated, this can lead to a minor, and within safety limits, transient current surge. As the current is applied to the subject, this can result in the generation of a residual field across the subject S. To avoid this field effecting the readings, the switch SW is generally activated prior to measurements being taken, to short the current circuit, and thereby discharge any residual field.

Once the measurement is commenced, an indication of the current applied to the subject can be obtained via either one of the connections <NUM>, <NUM>, that are connected to the ADC <NUM>, as shown by the dotted lines.

This allows the current supplied across the subject to be accurately determined. In particular, by using the actual applied current, as opposed to estimating the current applied on the basis of the control signals I+, I-, this takes into account non-ideal behaviour of the components in the current source, and can also take into account the effects of the leads <NUM>, <NUM>, on the applied current.

In one example, the amplifier A<NUM> and associated components may be provided on a housing coupled to the electrodes <NUM>, <NUM>, allowing more accurate sensing of the current applied to the subject. In particular, this avoids measuring of cable effects, such as signal loss in the leads L.

The above is an example of a non-symmetric current source and it will be appreciated that symmetric current sources may alternatively be used.

An example of the buffer used for the voltage electrodes is shown in <FIG>. In this example, each electrode <NUM>, <NUM>, will be coupled to a buffer circuit 50A, 50B.

In this example, each buffer 50A, 50B includes amplifiers A<NUM>, A<NUM>, and a number of resistors R<NUM>,. , R<NUM>, interconnected as shown. In use, each buffer 50A, 50B, is connected a respective electrode <NUM>, <NUM> via connections <NUM>, <NUM>. The buffers 50A, 50B are also connected via leads <NUM>, <NUM> to a differential amplifier <NUM>, acting as the signal sensor <NUM>, which is in turn coupled to the ADC <NUM>. It will therefore be appreciated that a respective buffer circuit 50A, 50B is connected to each of the electrodes <NUM>, <NUM>, and then to a differential amplifier, allowing the potential difference across the subject to be determined.

In one example, the leads <NUM>, <NUM> correspond to the leads L shown in <FIG>, allowing the buffer circuits 50A, 50B to be provided in connector housing coupled to the electrodes <NUM>, <NUM>, as will be described in more detail below.

In use, the amplifier A<NUM> amplifies the detected signals and drives the core of the cable <NUM>, whilst the amplifier A<NUM> amplifies the detected signal and drives the shield of the cables <NUM>, <NUM>. Resistors R<NUM> and R<NUM> decouple the amplifier outputs from the capacitances associated with cable, although the need for these depends on the amplifier selected.

Again, this allows multi-core shielded cables to be used to establish the connections to the voltage electrodes <NUM>, <NUM>.

An example of operation of the apparatus will now be described with reference to <FIG> to 6C.

At step <NUM> an operator selects an impedance measurement type using the first processing system <NUM>. This may be achieved in a number of ways and will typically involve having the first processing system <NUM> store a number of different profiles, each of which corresponds to a respective impedance measurement protocol.

Thus, for example, when performing cardiac function determination, it will be typical to use a different applied current sequence and a different impedance analysis, as compared to performing lymphoedema measurements, body composition, pulmonary oedema, or the like. The profile will typically be stored in the memory <NUM>, or alternatively may be downloaded from flash memory (not shown), or via the external interface <NUM>.

Once an appropriate measurement type has been selected by the operator, this will cause the first processing system <NUM> to load desired code module firmware into the programmable module <NUM> of the second processing system <NUM> at step <NUM>, or cause embedded firmware to be activated. The type of code module used will depend on the preferred implementation, and in one example this is formed from a wishbone code module, although this is not essential.

At step <NUM>, the second processing system <NUM> is used to generate a sequence of digital control signals, which are transferred to the DAC <NUM> at step <NUM>. This is typically achieved using the processing module <NUM>, by having the module generate a predetermined sequence of signals based on the selected impedance measurement profile. This can therefore be achieved by having the second processing system <NUM> program the processing module <NUM> to cause the module to generate the required signals.

The DAC <NUM> converts the digital control signals into analogue control signals I+, I- which are then applied to the current source <NUM> at step <NUM>.

As described above, the current source circuit shown in <FIG> operates to amplify and filter the electrical control signals I+, I- at step <NUM>, applying the resulting current signals to the electrodes <NUM>, <NUM> at step <NUM>.

During this process, and as mentioned above, the current circuit through the subject can optionally be shorted at step <NUM>, using the switch SW, to thereby discharge any residual field in the subject S, prior to readings being made.

At step <NUM>, the measurement procedure commences, with the voltage across the subject being sensed from the electrodes <NUM>, <NUM>. In this regard, the voltage across the electrodes is filtered and amplified using the buffer circuit shown in <FIG> at step <NUM>, with the resultant analogue voltage signals V being supplied to the ADC <NUM> and digitised at step <NUM>. Simultaneously, at step <NUM> the current applied to the subject S is detected via one of the connections <NUM>, <NUM>, with the analogue current signals I being digitised using the ADC <NUM> at step <NUM>.

The digitised voltage and current signals V, I are received by the processing modules <NUM>, <NUM> at step <NUM>, with these being used to performed preliminary processing of the signals at step <NUM>.

The processing performed will again depend on the impedance measurement profile, and the consequent configuration of the processing modules <NUM>, <NUM>. This can include for example, processing the voltage signals V to extract ECG signals. The signals will also typically be filtered to ensure that only signals at the applied frequencies fi, are used in impedance determination. This helps reduce the effects of noise, as well as reducing the amount of processing required.

At step <NUM> the second processing system <NUM> uses the processing signals to determine voltage and current signals at each applied frequency fi, with these being used at step <NUM> to determine instantaneous impedance values at each applied frequency fi.

The ADCs <NUM>, <NUM> and the processing modules <NUM>, <NUM> are typically adapted to perform sampling and processing of the voltage and current signals V, I in parallel so that the voltage induced at the corresponding applied current are analysed simultaneously. This reduces processing requirements by avoiding the need to determine which voltage signals were measured at which applied frequency. This is achieved by having the processing modules <NUM>, <NUM> sample the digitised signals received from the ADCs <NUM>, <NUM>, using a common clock signal generated by the processing module <NUM>, which thereby ensures synchronisation of the signal sampling.

Once the instantaneous impedance values have been derived, these can undergo further processing in either the first processing system <NUM>, or the second processing system <NUM>, at step <NUM>. The processing of the instantaneous impedance signals will be performed in a number of different manners depending on the type of analysis to be used and this in turn will depend on the selection made by the operator at step <NUM>.

Accordingly, it will be appreciated by persons skilled in the art that a range of different current sequences can be applied to the subject by making an appropriate measurement type selection. Once this has been performed, the FPGA operates to generate a sequence of appropriate control signals I+, I-, which are applied to the subject S using the current supply circuit shown in <FIG>. The voltage induced across the subject is then sensed using the buffer circuit shown in <FIG>, allowing the impedance values to be determined and analysed by the second processing system <NUM>.

Using the second processing system <NUM> allows the majority of processing to be performed using custom configured hardware. This has a number of benefits.

Firstly, the use of an second processing system <NUM> allows the custom hardware configuration to be adapted through the use of appropriate firmware. This in turn allows a single measuring device to be used to perform a range of different types of analysis.

Secondly, this vastly reduces the processing requirements on the first processing system <NUM>. This in turn allows the first processing system <NUM> to be implemented using relatively straightforward hardware, whilst still allowing the measuring device to perform sufficient analysis to provide interpretation of the impedance. This can include for example generating a "Wessel" plot, using the impedance values to determine parameters relating to cardiac function, as well as determining the presence or absence of lymphoedema.

Thirdly, this allows the measuring device <NUM> to be updated. Thus for example, if an improved analysis algorithms is created, or an improved current sequence determined for a specific impedance measurement type, the measuring device can be updated by downloading new firmware via flash memory (not shown) or the external interface <NUM>.

It will be appreciated that, in the context of the invention, the processing is performed partially by the second processing system <NUM>, and partially by the first processing system <NUM>. However, more generally in the context of this disclosure, it is also possible for processing to be performed by a single element, such as an FPGA, or a more generalised processing system.

As the FPGA is a custom processing system, it tends to be more efficient in operation than a more generic processing system. As a result, if an FPGA alone is used, it is generally possible to use a reduced overall amount of processing, allowing for a reduction in power consumption and size. However, the degree of flexibility, and in particular, the range of processing and analysis of the impedance which can be performed is limited.

Conversely, if only a generic processing system is used, the flexibility is enhanced at the expensive of a decrease in efficiency, and a consequent increase in size and power consumption.

Accordingly, the above described example strikes a balance, providing custom processing in the form of an FPGA to perform partial processing. This can allow for example, the impedance values to be determined. Subsequent analysis, which generally requires a greater degree of flexibility can then be implemented with the generic processing system.

A further disadvantage of utilising an FPGA alone is that it complicates the process of updating the processing, for example, if improved processing algorithms are implemented.

An example of an electrode connection apparatus is shown in <FIG>.

In particular, in this example, the connector includes circuitry provided on a substrate such as a PCB (Printed Circuit Board) <NUM>, which is in turn mounted in a housing <NUM> as shown. The housing <NUM> includes an arm <NUM> which is urged toward a contact <NUM> provided on the substrate <NUM>. The substrate <NUM> is then coupled to a respective one of the ADCs <NUM>, <NUM> or the DAC <NUM>, via appropriate leads shown generally at L, such as the leads <NUM>, <NUM>, <NUM>, <NUM>.

In use, the connector couples to a conductive electrode substrate <NUM>, such as a plastic coated in silver, and which in turn has a conductive gel <NUM>, such as silver/silver chloride gel thereon. The arm <NUM> urges the conductive electrode substrate <NUM> against the contact <NUM>, thereby electrically coupling the conductive gel <NUM> to the circuit provided on the substrate <NUM>.

This ensures good electrical contact between the measuring device <NUM> and the subject S, as well as reducing the need for leads between the electrodes <NUM>, <NUM> and the input of the voltage buffers, removing the requirement for additional leads, which represents an expense, as well as a source of noise within the apparatus.

In this example, the edges and corners of the housing <NUM>, the arm <NUM> and the substrate <NUM> are curved. This is to reduce the chance of a subject being injured when the connector is attached to the electrode. This is of particular importance when using the electrodes on lymphodema suffers, when even a small nip of the skin can cause severe complications.

To further enhance the useability of the housing, the housing may be formed from a material that has a low coefficient of friction and/or is spongy or resilient. Again, these properties help reduce the likelihood of the subject being injured when the housing is coupled to the electrode.

A further development of the apparatus will now be described with reference to <FIG>.

In this example, the second processing system <NUM> is formed from two respective FPGA portions 17A, 17B. The two FPGA portions 17A, 17B are interconnected via an electrically isolated connection shown generally by the dotted line 17C. The electrically isolated connection could be achieved for example using an inductive loop connections, wireless links or the like.

This split in the FPGA can be used to ensure that the measuring device <NUM> is electrically isolated from the subject S. This is important for example when taking readings with a high degree of accuracy.

In this example, the second processing system <NUM> will typically be implemented such that the operation of the second FPGA portion 17B is substantially identical for all measurement types. As a result, there is no requirement to upload firmware into the second FPGA portion 17B to allow different types of impedance analysis.

In contrast to this, the first FPGA portion 17A will typically implement firmware depending on the impedance measurement type in a manner substantially as described above.

It will therefore be appreciated that this provides a mechanism by which the measuring device <NUM> is electrically isolated from the subject, whilst still allowing the benefits of use of the second processing system <NUM> to be achieved.

Alternatively, equivalent electrical isolation can be obtained by providing a single FPGA electrically isolated from the first processing system <NUM>.

In this example, the second FPGA portion 17B can be provided into a subject unit, shown generally at <NUM>, which includes the lead connections.

This allows a single measuring device <NUM> to communicate with a number of different subject units, each of which is associated with a respective subject S. This allows the measuring device <NUM> to provide centralised monitoring of a number of different subjects via way of a number of subject units <NUM>. This in turn allows a number of subjects to be analysed in sequence without having to reconnect each subject S each time an analysis is to be performed.

To assist in interpreting the impedance measurements, it is useful to take into account electrical properties of the connecting leads and associated circuitry.

To achieve this, the leads and corresponding connections can be encoded with calibration information. This can include, for example, using specific values for respective ones of the resistors in the current source, or buffer circuits shown in <FIG> and <FIG>. Thus for example, the value of the resistors R<NUM>, R<NUM>, R<NUM> can be selected based on the properties of the corresponding leads.

In this instance, when the leads are connected to the measuring device <NUM>, via the corresponding ADCs <NUM>, <NUM>, the processing modules <NUM>, <NUM> can be to interrogate the circuitry using appropriate polling signals to thereby determine the value of corresponding resistor. Once this value has been determined, the second processing system <NUM> can use this to modify the algorithm used for processing the voltage and current signals to thereby ensure correct impedance values are determined.

In addition to this, the resistance value can also act as a lead identifier, to allow the measuring device to identify the leads and ensure that only genuine authorised leads are utilised. Thus, for example, if the determined resistance value does not correspond to a predetermined value this can be used to indicate that non-genuine leads are being used. In this instance, as the lead quality can have an effect on the accuracy of the resultant impedance analysis, it may desirable to either generate an error message or warning indicating that incorrect leads are in use. Alternatively, the second processing system <NUM> can be adapted to halt processing of the measured current and voltage signals. This allows the system to ensure that only genuine leads are utilised.

This can further be enhanced by the utilisation of a unique identifier associated with each lead connection circuit. In this instance, a unique identifier can be encoded within an IC provided as part of the current source or voltage buffer circuits. In this instance, the measuring device <NUM> interrogates the unique identifier and compared to unique identifiers stored either in local memory, or in a central database, allowing genuine leads to be identified.

This process can also be used to monitor the number of times a lead has been used. In this instance, each time a lead is used, data reflecting lead usage is recorded. This allows the leads to have a predesignated use quota life span, and once the number of times the lead is used reaches the quota, further measurements using the leads can be prevented. Similarly, a temporal limitation can be applied by providing an expiry date associated with the lead. This can be based on the date the lead is created, or first used depending on the preferred implementation.

It will be appreciated that when recording lead usage, issues may arise if this is recorded locally. In particular, this could allow a lead to be re-used with a different measuring device. To avoid this, the leads can be configured with a ID which is set by the measuring device on first use. This can be used to limit usage of the leads to a single measuring device.

This can be used to ensure that the leads are correctly replaced in accordance with a predetermined lifespan thereby helping to ensure accuracy of measure impedance values.

A further variation to the apparatus is shown in <FIG>.

In this example, the apparatus is adapted to provide multiple channel functionality allowing different body segments to undergo impedance analysis substantially simultaneously. In this instance, this is achieved by providing first and second processing modules 32A, 32B, 33A, 33B, 34A, 34B, first and second ADCs and DACs 37A, 37B, 38A, 38B, 39A, 39B as well as first and second voltage and current circuits 11A, 11B, 12A, 12B, in parallel, as shown.

Thus, the measuring device <NUM> includes two separate impedance measuring channels indicated by the use of reference numerals A, B. In this instance, this allows electrodes to be attached to body segments, such as different limbs, with measurements being taken from each segment substantially simultaneously.

As an alternative to the above described arrangement, multiple channels could alternatively be implemented by utilising two separate second processing modules <NUM>, each one being associated with a respective channel. Alternatively, the signals applied to each channel could be applied via multiplexers positioned between the ADCs <NUM>, <NUM> and the DAC <NUM> and the electrodes.

It will be appreciated that whilst two channels are shown in the above example, this is for clarity only, and any number of channels may be provided.

<FIG> shows an example of an impedance measuring apparatus including a switching arrangement. In this example, the measuring device <NUM> includes a switching device <NUM>, such as a multiplexer, for connecting the signal generator <NUM> and the sensor <NUM> to the leads L. This allows the measuring device <NUM> to control which of the leads L are connected to the signal generator <NUM> and the sensor <NUM>.

In this example, a single set of leads and connections is shown. This arrangement can be used in a number of ways. For example, by identifying the electrodes <NUM>, <NUM>, <NUM>, <NUM> to which the measuring device <NUM> is connected, this can be used to control to which of the leads L signals are applied, and via which leads signals can be measured. This can be achieved either by having the user provide an appropriate indication via the input device <NUM>, or by having the measuring device <NUM> automatically detect electrode identifiers, as will be described in more detail below.

Alternatively, however the arrangement may be used with multiple leads and electrodes to provide multi-channel functionality as described above.

An example of an alternative electrode configuration will now be described with reference to <FIG>.

In this example, the electrode connector is formed from a housing <NUM> having two arms <NUM>, <NUM> arranged to engage with an electrode substrate <NUM> to thereby couple the housing <NUM> to the substrate <NUM>. A contact <NUM> mounted on an underside of the arm <NUM>, is urged into contact and/or engagement with an electrode contact <NUM> mounted on a surface of the electrode substrate <NUM>. The electrode also includes a conductive gel <NUM>, such as a silver/silver chloride gel, electrically connected to the contact <NUM>. This can be achieved, either by using a conductive track, such as a silver track, or by using a conductive substrate such as plastic coated in silver.

This allows the lead L to be electrically connected to the conductive gel <NUM>, allowing current to be applied to and/or a voltage measured from the subject S to which they are attached. It will be appreciated that in this example the above described housing <NUM> may also contain the buffer circuit <NUM>, or all or part of the current source circuit shown in <FIG>, in a manner similar to that described above with respect to <FIG>.

Alternatively more complex interconnections may be provided to allow the measuring device <NUM> to identify specific electrodes, or electrode types.

This can be used by the measuring device <NUM> to control the measurement procedure. For example, detection of an electrode type by the processing system <NUM> may be used to control the measurements and calculation of different impedance parameters, for example to determine indicators for use in detecting oedema, monitoring cardiac function, or the like.

Similarly, electrodes can be provided with visual markings indicative of the position on the subject to which the electrode should be attached. For example a picture of a left hand can be shown if the electrode pad is to be attached to a subject's left hand. In this instance, identification of the electrodes can be used to allow the measuring device <NUM> to determine where on the subject the electrode is attached and hence control the application and measurement of signals accordingly.

An example of this will now be described with reference to <FIG>. In this example the contact <NUM> is formed from a contact substrate <NUM>, such as a PCB, having a number of connector elements <NUM>, <NUM>, <NUM>, <NUM>, formed from conductive contact pads, typically made of silver or the like. The connector elements are connected to the lead L via respective electrically conductive tracks <NUM>, typically formed from silver, and provided on the contact substrate <NUM>. The lead L includes a number of individual wires, each electrically coupled to a respective one of the connector elements <NUM>, <NUM>, <NUM>, <NUM>.

In this example the electrode contact <NUM> on the electrode substrate <NUM> typically includes an electrode contact substrate <NUM>, including electrode connector elements <NUM>, <NUM>, <NUM>, <NUM>, typically formed from silver contact pads or the like. The electrode connector elements <NUM>,. <NUM> are positioned so that, in use, when the electrode connector <NUM> is attached to an electrode, the connector elements <NUM>. <NUM> contact the electrode connector elements <NUM>,. <NUM> to allow transfer of electrical signals with the measuring device <NUM>.

In the examples, of <FIG>, the connector element <NUM> is connected to the conductive gel <NUM>, via an electrically conductive track <NUM>, typically a silver track that extends to the underside of the electrode substrate <NUM>. This can be used by the measuring device <NUM> to apply a current to, or measure a voltage across the subject S.

Additionally, selective ones of the connector elements <NUM>, <NUM>, <NUM> are also interconnected in four different arrangements by respective connectors <NUM>136A, <NUM>136B, 1136C, 1136D. This allows the measuring device <NUM> to detect which of the electrode contacts <NUM>, <NUM>, <NUM> are interconnected, by virtue of the connectors, <NUM>136A, <NUM>136B, <NUM>136C, <NUM>136D, with the four different combinations allowing the four different electrodes to be identified.

Accordingly, the arrangement of <FIG> can be used to provide four different electrodes, used as for example, two current supply <NUM>, <NUM> and two voltage measuring electrodes <NUM>, <NUM>.

In use, the measuring device <NUM> operates by having the second processing system <NUM> cause signals to be applied to appropriate wires within each of the leads L, allowing the conductivity between the connecting elements <NUM>, <NUM>, <NUM>, to be measured. This information is then used by the second processing system <NUM> to determine which leads L are connected to which of the electrodes <NUM>, <NUM>, <NUM>, <NUM>. This allows the first processing system <NUM> or the second processing system <NUM> to control the multiplexer <NUM> in the example of <FIG>, to correctly connect the electrodes <NUM>, <NUM>, <NUM>, <NUM> to the signal generator <NUM>, or the signal sensor <NUM>.

In this example, the individual applying the electrode pads to the subject can simply position the electrodes <NUM>, <NUM>, <NUM>, <NUM> on the subject in the position indicated by visual markings provided thereon.

Leads may then be connected to each of the electrodes allowing the measuring device <NUM> to automatically determine to which electrode <NUM>, <NUM>, <NUM>, <NUM> each lead L connected and then apply current signals and measure voltage signals appropriately. This avoids the complexity of ensuring the correct electrode pads are connected via the correct leads L.

It will be appreciated that the above described process allows electrode identification simply by applying currents to the electrode connector. However, other suitable identification techniques can be used, such as through the use of optical encoding. This could be achieved for example, by providing a visual marker, or a number of suitably arranged physical markers on the electrode connector <NUM>, or electrode substrate <NUM>. These could then be detected using an optical sensor mounted on the connector <NUM>, as will be appreciated by persons skilled in the art.

Alternatively, the identifier for the electrodes may be identified by an encoded value, represented by, for example, the value of a component in the electrode, such as a resistor or capacitor. It will therefore be appreciated that this can be achieved in a manner similar to that described above with respect to lead calibration.

An example of an alternative electrode configuration will now be described with reference to <FIG>. In this particular example the electrode is a band electrode <NUM>, which includes a number of separate electrodes. In this example the electrode is formed from an elongate substrate <NUM> such as a plastic polymer coated with shielding material and an overlaying insulating material.

A number of electrically conductive tracks <NUM> are provided on the substrate extending from an end of the substrate <NUM> to respective conductive contact pads <NUM>, spaced apart along the length of the substrate in sequence. This allows a connector similar to the connectors described above, but with corresponding connections, to be electrically coupled to the tracks <NUM>.

The tracks <NUM> and the contact pads <NUM> may be provided on the substrate <NUM> in any one of a number of manners, including for example, screen printing, inkjet printing, vapour deposition, or the like, and are typically formed from silver or another similar material. It will be appreciated however that the tracks and contact pads should be formed from similar materials to prevent signal drift.

Following the application of the contact pads <NUM> and the tracks <NUM>, an insulating layer <NUM> is provided having a number of apertures <NUM> aligned with the electrode contact pads <NUM>. The insulating layer is typically formed from a plastic polymer coated with shielding material and an overlaying insulating material.

To ensure adequate conduction between the contact pads <NUM>, and the subject S, it is typical to apply a conductive gel <NUM> to the contact pads <NUM>. It will be appreciated that in this instance gel can be provided into each of the apertures <NUM> as shown.

A removable covering <NUM> is then applied to the electrode, to maintain the electrode's sterility and/or moisture level in the gel. This may be in the form of a peel off strip or the like which when removed exposes the conductive gel <NUM>, allowing the electrode to be attached to the subject S.

In order to ensure signal quality, it is typical for each of the tracks <NUM> to comprise a shield track <NUM>, and a signal track <NUM>, as shown. This allows the shield on the leads L, such as the leads <NUM>, <NUM>, <NUM> to be connected to the shield track <NUM>, with the lead core being coupled to the signal track <NUM>. This allows shielding to be provided on the electrode, to help reduce interference between applied and measured signals.

This provides a fast straight-forward and cheap method of producing band electrodes. It will be appreciated that similar screen printing techniques may be utilised in the electrode arrangements shown in <FIG>, and <FIG>.

The band electrode may be utilised together with a magnetic connector as will now be described with respect to <FIG>. In this example, the band electrode <NUM> includes two magnets 1201A, 1201B positioned at the end <NUM> of the substrate <NUM>. The connector, is formed from a connector substrate <NUM> having magnets 1281A, 1281B provided therein. Connecting elements <NUM> are also provided, and these would in turn be connected to appropriate leads L.

The magnets 1201A, 1281A; 1201B (not shown for clarity), 1281B can be arranged to align and magnetically couple, to urge the connector substrate <NUM> and the band electrode <NUM> together. Correct alignment of the poles of the magnets 1201A, 1281A; 1201B, 1281B can also be used to ensure both the correct positioning and orientation of the connector substrate <NUM> and band electrode, which can ensure correct alignment of the connecting elements <NUM>, with corresponding ones of the tracks <NUM>, on the band electrode <NUM>.

It will be appreciated that this can be used to ensure correct connection with the electrode, and that a similar magnetic alignment technique may be used in the connectors previously described.

In use, the band electrode may be attached to the subject's torso, as shown in <FIG>. The electrode will typically include an adhesive surface, allowing it to stick to the subject. However, a strap <NUM> may also be used, to help retain the electrode <NUM> in position. This provides an electrode that is easy to attach and position on the subject, and yet can be worn for an extended period if necessary. The band electrode <NUM> may also be positioned on the subject at other locations, such as on the side of the subject's torso, or laterally above the naval, as shown.

The band electrode <NUM> provides sufficient electrodes to allow cardiac function to be monitored. In the above example, the band electrode includes six electrodes, however any suitable number may be used, although typically at least four electrodes are required.

A further feature that can be implemented in the above measuring device is the provision of a signal generator <NUM> capable of generating a variable strength signal, such as a variable current. This may be used to allow the measuring device <NUM> to be utilised with different animals, detect problems with electrical connections, or to overcome noise problems.

In order to achieve this, the current source circuit shown in <FIG> is modified as shown in <FIG>. In this example, the resistor Rio in the current source circuit of <FIG> is replaced with a variable resistor VR<NUM>. Alteration of the resistance of the resistor VR<NUM> will result in a corresponding change in the magnitude of the current applied to the subject S.

To reduce noise and interference between the current source circuit and the control, which is typically achieved using the second processing module <NUM>, it is typical to electrically isolate the variable resistor <NUM> from the control system. Accordingly in one example, the variable resistor VR<NUM> is formed from a light dependent resistor. In this example, an light emitting diode (LED) or other illumination source can be provided, as shown at L<NUM>. The LED L<NUM> can be coupled to a variable power supply P of any suitable form. In use, the power supply P, is controlled by the second processing module <NUM>, thereby controlling the intensity of light generated by the LED Li, which in turn allows the resistance VR<NUM>, and hence the applied current, to be varied.

In order to operate the measuring device <NUM>, the first processing system <NUM> and the second processing system <NUM> typically implement the process described in <FIG>. In this example, at step <NUM> the user selects a measurement or an animal type utilising the input/output device <NUM>.

At step <NUM> the first processing system <NUM> and the second processing system <NUM> interact to determine one or more threshold values based on the selected measurement or animal type. This may be achieved in any one of a number of ways, such as by having the first processing system <NUM> retrieve threshold values from the memory <NUM> and transfer these to the second processing system <NUM>, although any suitable mechanism may be used. In general, multiple thresholds may be used to specify different operating characteristics, for signal parameters such as a maximum current that can be applied to the subject S, the minimum voltage required to determine an impedance measurement, a minimum signal to noise ratio, or the like.

At step <NUM> the second processing system <NUM> will activate the signal generator <NUM> causing a signal to be applied to the subject S. At step <NUM> the response signal at the electrodes <NUM>,<NUM> is measured using the sensor <NUM> with signals indicative of the signal being returned to the second processing system <NUM> at step <NUM>.

At step <NUM> the second processing system <NUM> compares the at least one parameter of the measured signal to a threshold to determine if the measured signal is acceptable at step <NUM>. This may involve for example determining if the signal to noise levels within the measured voltage signal are above the minimum threshold, or involve to determine if the signal strength is above a minimum value.

If the signal is acceptable, impedance measurements can be performed at step <NUM>. If not, at step <NUM> the second processing system <NUM> determines whether the applied signal has reached a maximum allowable. If this has occurred, the process ends at step <NUM>. However, if the maximum signal has not yet been reached, the second processing system <NUM> will operate to increase the magnitude of the current applied to the subject S at step <NUM> before returning to step <NUM> to determine a new measured signal.

Accordingly, this allows the current or voltage applied to the subject S to be gradually increased until a suitable signal can be measured to allow impedance values to be determined, or until either a maximum current or voltage value for the subject is reached.

It will be appreciated that the thresholds selected, and the initial current applied to the subject S in step <NUM> will typically be selected depending on the nature of the subject. Thus, for example, if the subject is a human it is typical to utilise a lower magnitude current than if the subject is a animal such as a mouse or the like.

An example of a process for updating the measuring device will now be described with reference to <FIG>.

In one example, at step <NUM> the process involves determining a measuring device <NUM> is to be configured with an upgrade, or the like, before configuration data is created at step <NUM>. At step <NUM> the configuration data is typically uploaded to the device before the device is activated at <NUM>. At <NUM> when the device commences operation the processing system <NUM> uses the configuration data to selectively activate features, either for example by controlling the upload of instructions, or by selectively activating instructions embedded within the processing system <NUM> or the controller <NUM>.

This can be achieved in one of two ways. For example, the configuration data could consist of instructions, such as a software or firmware, which when implemented by the processing system <NUM> causes the feature to be implemented. Thus, for example, this process may be utilised to update the operation of the firmware provided in the second processing system <NUM>, the processing system <NUM> or the controller <NUM> to allow additional functionality, improved measuring algorithms, or the like, to be implemented.

Alternatively, the configuration data could be in the form of a list of features, with this being used by the processing system <NUM> to access instructions already stored on the measuring device <NUM>. Utilisation of configuration data in this manner, allows the measuring device to be loaded with a number of as yet additional features, but non-operational features, when the device is sold. In this example, by updating the configuration data provided on the measuring device <NUM>, this allows these further features to be implemented without requiring return of the measuring device <NUM> for modification.

This is particularly useful in the medical industry as it allows additional features to be implemented when the feature receives approval for use. Thus, for example, techniques may be available for measuring or detecting lymphoedema in a predetermined way, such as through the use of a particular analysis of measured voltage signals or the like. In this instance when a device is sold, approval may not yet have been obtained from an administering body such as the Therapeutic Goods Administration, or the like. Accordingly, the feature is disabled by appropriate use of a configuration data. When the measurement technique subsequently gains approval, the configuration data can be modified by uploading a new updated configuration data to the measuring device, allowing the feature to be implemented.

It will be appreciated that these techniques may be used to implement any one of a number of different features, such as different measuring techniques, analysis algorithms, reports on results of measured impedance parameters, or the like.

An example of a suitable system for providing updates will now be described with respect to <FIG>. In this example, a base station <NUM> is coupled to a number of measuring devices <NUM>, and a number of end stations <NUM> via a communications network <NUM>, such as the Internet, and/or via communications networks <NUM>, such as local area networks (LANs), or wide area networks (WANs). The end stations are in turn coupled to measuring devices <NUM>, as shown.

In use, the base station <NUM> includes a processing system <NUM>, coupled to a database <NUM>. The base station <NUM> operates to determine when updates are required, select the devices to which updates are applied, generate the configuration data and provide this for update to the devices <NUM>. It will be appreciated that the processing system <NUM> may therefore be a server or the like.

This allows the configuration data to be uploaded from the server either to a user's end station <NUM>, such as a desk top computer, lap top, Internet terminal or the like, or alternatively allows transfer from the server via the communications network <NUM>, <NUM>, such as the Internet. It will be appreciated that any suitable communications system can be used such as wireless links, wi-fi connections, or the like.

In any event, an example of the process of updating the measuring device <NUM> will now be described in more detail with reference to <FIG>. In this example, at step <NUM> the base station <NUM> determines that there is a change in the regulatory status of features implemented within a certain region. As mentioned above this could occur for example following approval by the TGA of new features.

The base station <NUM> uses the change in regulatory status to determine new features available at step <NUM>, before determining an identifier associated with each measuring device <NUM> to be updated at step <NUM>. As changes in regulatory approval are region specific, this is typically achieved by having the base station <NUM> access database <NUM> including details of the regions in which each measuring device sold are used. The database <NUM> includes the identifier for each measuring device <NUM>, thereby allowing the identifier of each measuring device to be updated to be determined.

At step <NUM>, the base station <NUM> determines the existing configuration data, typically from the database <NUM>, for a next one of the measuring devices <NUM>, before modifying the configuration data to implement the new features at step <NUM>. The configuration data is then encrypted utilising a key associated with the identifier. The key may be formed from a unique prime number associated with the serial number, or partially derived from the serial number, and is typically stored in the database <NUM>, or generated each time it is required using a predetermined algorithm.

At step <NUM> the encrypted configuration data is transferred to the measuring device <NUM> as described above.

At step <NUM> when the device restarts and the first processing system <NUM> is activated, the first processing system <NUM> determines the encryption key, and uses this to decrypt the configuration data. This may be achieved in any one of a number of ways, such as by generating the key using the serial number or other identifier, and a predetermined algorithm. Alternatively, this may be achieved by accessing a key stored in the memory <NUM>. It will be appreciated that any form of encryption may be used, although typically strong encryption is used, in which a secret key is used to both encrypt and decrypt the configuration data, to thereby prevent fraudulent alteration of the configuration by users, as will be explained in more detail below.

At step <NUM>, the first processing system <NUM> activates software features within the second processing system <NUM> using the decrypted configuration data.

It will therefore be appreciated that this provides a mechanism for automatically updating the features available on the measuring device. This may be achieved either by having the second processing system <NUM> receive new firmware from the processing system <NUM>, or by activating firmware already installed on the second processing system <NUM>, as described above.

As an alternative to performing this automatically when additional features are approved for use, the process can be used to allow features to be activated on payment of a fee. In this example, a user may purchase a measuring device <NUM> with limited implemented functionality. By payment of a fee, additional features can then be activated as and when required by the user.

In this example, as shown in <FIG>, when the user selects an inactive feature at step <NUM>, the first processing system <NUM> will generate an indication that the feature is unavailable at step <NUM>. This allows the user to select an activate feature option at step <NUM>, which typically prompts the user to provide payment details at step <NUM>. The payment details are provided to the device manufacturer in some manner and may involve having the user phone the device manufacturer, or alternatively enter the details via a suitable payment system provided via the Internet or the like.

At step <NUM>, once the payment is verified, the process can move to step <NUM> to allow an automatic update to be provided in the form of a suitable configuration data. However, if payment details are not verified the process ends at <NUM>.

It will be appreciated by a person skilled in the art that encrypting the configuration data utilising a unique identifier means that the configuration data received by a measuring device <NUM> is specific to that measuring device. Accordingly, the first processing system <NUM> can only interpret the content of a configuration data if it is both encrypted and decrypted utilising the correct key. Accordingly, this prevents users exchanging configuration data, or attempting to re-encrypt a decrypted file for transfer to a different device.

It will be appreciated that in addition to, or as an alternative to simply specifying features in the configuration data, it may be necessary to upload additional firmware to the second processing system <NUM>. This can be used for example, to implement features that could not be implemented using the firmware shipped with the measuring device <NUM>.

In this example, it would be typical for the configuration data to include any required firmware to be uploaded, allowing this to be loaded into the second processing system <NUM>, using the first processing system <NUM>. This firmware can then either be automatically implemented, or implemented in accordance with the list of available features provided in the configuration data.

It will be appreciated that this provides a mechanism for updating and/or selectively activating or deactivating features, such as measuring protocols, impedance analysis algorithms, reports interpreting measured results, or the like. This can be performed to ensure the measuring device conforms to existing TGA or FDA approvals, or the like.

In order to provide a housing configuration with suitable electrical isolation for the subject an arrangement similar to that shown in <FIG> can be used.

In this example the measuring device <NUM> is provided in a housing <NUM> which includes a touch screen <NUM>, forming the I/O device <NUM>, together with three respective circuit boards <NUM>, <NUM>, <NUM>. In this instance the digital electronics including the second processing system <NUM> and the first processing system <NUM> are provided on the circuit board <NUM>. The circuit board <NUM> is an analogue circuit board and includes the ADCs <NUM>, <NUM>, the DAC <NUM>. A separate power supply board is then provided at <NUM>. The supply board typically includes an integrated battery, allowing the measuring device <NUM> to form a portable device.

It is also typical housing electrical/magnetic shielding from the external environment, and accordingly, the housing is typically formed from a mu-metal, or from aluminium with added magnesium.

Furthermore, whilst the above examples have focussed on a subject such as a human, it will be appreciated that the measuring device and techniques described above can be used with any animal, including but not limited to, primates, livestock, performance animals, such race horses, or the like.

The above described processes can be used for diagnosing the presence, absence or degree of a range of conditions and illnesses, including, but not limited to oedema, lymphodema, body composition, or the like.

It will also be appreciated above described techniques, such as electrode identification, device updates and the like may be implemented using devices that do not utilise the separate first processing system <NUM> and second processing system <NUM>, but rather use a single processing system <NUM>, or use some other internal configuration.

Claim 1:
Apparatus for performing impedance measurements on a subject, the apparatus including a processing system (<NUM>) coupled to a signal generator (<NUM>) and a sensor (<NUM>), the signal generator (<NUM>) and the sensor (<NUM>) being coupled to respective electrodes provided on the subject in use, and wherein in use:
a) the processing system (<NUM>) generates control signals which causes the signal generator (<NUM>) to generate one or more alternating signals which are applied to the subject, S, via the electrodes (<NUM>, <NUM>, <NUM>, <NUM>);
b) the sensor (<NUM>) determines the voltage across or current through the subject, S, using the electrodes (<NUM>, <NUM>, <NUM>, <NUM>), and transfers appropriate signals to the processing system (<NUM>); and,
c) the processing system (<NUM>) determines impedance values, wherein the processing system (<NUM>) includes first and second processing systems (<NUM>, <NUM>), and characterised in that in use:
i) the apparatus:
(<NUM>) receives configuration data, the configuration data being indicative of at least one feature;
(<NUM>) determines, using the configuration data, instructions representing the at least one feature; and,
(<NUM>) causes, using said instructions:
(a) at least one impedance measurement to be performed by the second processing system (<NUM>); and,
(b) at least one impedance measurement to be analysed by the first processing system (<NUM>)
ii) the first processing system (<NUM>) operates to:
(<NUM>) determine an impedance measurement procedure;
(<NUM>) select a subset of instructions corresponding to the measurement procedure from said instructions; and,
(<NUM>) control the second processing system (<NUM>) so as to ensure implementation of the selected subset of instructions;
iii) the second processing system (<NUM>):
(<NUM>) generates the control signals;
(<NUM>) receives an indication of the one or more signals applied to the subject, S;
(<NUM>) receives an indication of one or more signals measured across the subject, S;
(<NUM>) performs at least preliminary processing of the indications to thereby allow impedance values to be determined; and,
iv) the first processing system (<NUM>):
(<NUM>) analyses impedance values determined by the second processing system (<NUM>); and,
(<NUM>) determines biological parameters using the analysis.