FIELD OF THE INVENTION

The present invention relates to a monitoring device for monitoring a physiological parameter of a subject using a concentrated electromagnetic field.. The invention further relates to a method for monitoring a physiological parameter of a subject using the concentrated electromagnetic field.

BACKGROUND OF THE INVENTION

Unobtrusive continuous vital sign (physiological characteristic) monitoring is highly desired for ambulatory patients in hospital or for people at home. One way to measure vital signs such as heart rate and breathing rate in an unobtrusive way is to measure magnetic induction impedance modulations in the subject's chest. This can be done using an excitation magnetic field that covers the volume of the lung and/or heart of the subject. The magnetic induction (i.e. the generation of eddy currents in the tissue due to the application of an external alternating magnetic field) will be modulated by intra-thoracic fluid movements due to heart beats and breathing. These modulations can be measured and used to determine physiological characteristics of the subject, such as breathing rate, breathing depth, heart rate and other physiological characteristics.

As respiratory activity correlates with the conductivity distribution modulations within the thorax, magnetic induction (also called electromagnetic induction) has been employed for monitoring respiration. Magnetic induction causes time varying magnetic fields in the tissues of the human body. These time varying magnetic fields cause eddy currents in the tissue, which in turn emit a secondary magnetic field. The eddy currents (also called Foucault currents) are loops of electric current induced within the tissue, due to Faraday's law of induction. The strength of such eddy current and consequent generated secondary magnetic field is proportional to the conductivity of the tissue/object receiving the first magnetic field. Variations in the tissues conductivity cause a modulation of the secondary magnetic field.

For biological tissues, the strength of such eddy current is depending on the amount of water and the concentration of ions (conductivity) within said biological tissue as well as the volume of air within a lung varies during the respiration cycle, thereby causing a change of conductivity of the lungs. Consequently, the generated eddy current will therefore be modulated by the breathing cycle. Such modulation may be detected by magnetic induction impedance measurement, thereby allowing the detection of breathing rate and breathing depth.

Application EP16153320.3 discloses a robust measurement of a secondary magnetic field (based on eddy currents) that is generated in a tissue of interest, which is further robust to movements and/or motions of a subject during a measurement period.

However, application EP16153320.3 has the disadvantage that it is sensitive to disturbances by electrical field artifacts, which can occur, e.g., due to sensor movement and/or cable movement or electrical influences in the surroundings of the sensor. Those disturbances result in worsening the signal quality.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome this disadvantage by providing the monitoring device for monitoring a physiological parameter of a subject, the monitoring device comprising an excitation unit comprising:

an excitation ferromagnetic core and a first excitation coil wound thereon, said excitation core being shaped for generation a first electromagnetic field on a first side of the excitation unit, wherein the first excitation coil wound on said excitation core is configured to create a spatially concentrated electromagnetic field in a region of interest within a body tissue of the subject, the excitation unit further comprising:

a first detection coil arranged to generate a first receiver signal from a secondary electromagnetic field which is modulated by the physiological parameter and originates from the first electromagnet ic field concentrated within the region of interest, the first detection coil being arranged on the first side of the excitation unit and oriented substantially orthogonal with respect to the first excitation coil and in alignment with the secondary magnetic field,

where the monitoring device is arranged to generate a physiological parameter signal from the first receiver signal.

By placing the detection coil on the same side of the excitation unit and orthogonally oriented with respect to the excitation coil, the detection unit will be aligned with the secondary magnetic field for optimal detection and thus signal quality, leading to less sensitivity to disturbances as the signal obtained is stronger. This mutual excitation/ detection coils arrangement reduces a magnetic field flux, caused by the first magnetic field, through the detection coil, thereby increasing a sensitivity of the detection coil to the secondary magnetic field. An additional improvement of the detection coil sensitivity is achieved by the concentration of the magnetic field lines in the region of interest. The focusing effect of the solid core allows concentrating first magnetic field created by the excitation coil in the region of interest, which in turn increases the intensity of the secondary magnetic field. Further, a spatial localization of the first magnetic field within the region of interests allows to place the detection coil in the vicinity of the region of interests but beyond a direct influence of the first magnetic field, thereby further increasing a signal to noise ratio of the receiver signal originating from the secondary electromagnetic field. The monitoring device is based on the concept of measuring a field distortion of the known magnetic field. In contrast to the prior art, the present device allows reducing the influence of the emitted, by the excitation unit, first electromagnetic field to the detection coil due to the excitation unit's arrangement. This permits detecting even small variation of the secondary electromagnetic field with reduced technical effort. In other words, the fact that the first magnetic field is concentrated in the region of interest allows position the detection coil closer to said region of interest, while still avoiding a substantial flux of the first magnetic field line through the detection coil.

In another embodiment the excitation core is shaped symmetrically with respect to the first excitation coil to define a volume enclosed in between two ends of the core; and the first detection coil is arranged within said volume.

This relative arrangement of the excitation ferromagnetic core and the first detection coil allows to further spatially concentrate the first electromagnetic field in the region of interest, while symmetrically compensating the first field's magnetic line fluxes through the detection coil. This arrangement permits placing the detection coil on the same side of the excitation unit closer to the region of interest.

In an embodiment the excitation unit further comprises a second excitation ferromagnetic core and a second excitation coil wound thereon, said second excitation coil is arranged to generate a second concentrated electromagnetic field, being identical to the first electromagnetic field, on an second side of the excitation unit, opposite to the first side of the excitation unit, and the excitation unit further comprises a second detection coil arranged to generate a second receiver signal from the second concentrated electromagnetic field and the monitoring device is arranged to subtract the second receiver signal from the first receiver signal to compensate for cross-talk between the first excitation coil and the first detection coil when generating the physiological parameter signal.

The second concentrated magnetic field is generated by the second excitation coil and detected by the second detection coil. The arrangement of the second excitation/ detection coil pair allows creating the second concentrated magnetic field having the same magnetic field lines distribution as well as field intensities. The second magnetic field can be seen as a mirrored first magnetic field with respect to the first side of the excitation unit. The cross talk between the second pair of coils (the second excitation coil and the second detection coil) is identical to the cross talk of the first pair of coils (the first excitation coil and the first detection coil) that perform the actual physiological parameter and can thus be subtracted, yielding the desired physiological parameter signal with greatly reduced disturbance due to cross talk. In addition, external disturbances that affect both pairs of coils also automatically get removed from the physiological parameter signal.

In yet another embodiment the excitation unit further comprises a first ferromagnetic detection core with the first detection coil wound thereon and/or a second ferromagnetic detection core with the second detection coil wound thereon.

An application of the ferromagnetic core with a detection coil allows to localize (focus) the detector's sensitivity to the region of interest, thereby further improving signal to noise ratio of the physiological parameter signal.

In a further embodiment, the excitation unit is arranged to operate using a floating ground, to electrically isolate the excitation unit from the detection unit.

Normally, both the excitation and receiving electronics have an electrical connection to the ground. This might make the whole system sensitive to all sorts of artifacts, including wire movements and sensor movements. It was noticed that magnetic induction measurements were disturbed by a movement artifact caused by rhythmic movement of the skin, and/or disturbed by the mechanic impact of the heart (sort of ballostography).

However, usage of the floating ground in the excitation unit enables a fully electrical separate excitation unit from the detection unit, which prevents any undesirable ground currents thus reducing noise in the system.

In a further embodiment, the first detection coil and the second detection coil are arranged to have an electrical field shielding.

The electrical field shielding enables eliminates any remaining electrical disturbances of the first receiver signal from stray electromagnetic fields. It is essential to only detect a magnetic field without any electrical disturbances, which is what the first detection coil is intended to do.

In a further embodiment, the monitoring device is configured to be connectable to a portable electronic device. Within this embodiment, the skilled in the art will see that the processing unit may be totally, or partially embedded into a portable electronic device, for instance a mobile phone, a smart phone, a tablet, a (smart-/health-) watch, or any other devices comprising a processor (or processing unit) that can be carried by the subject in his/her activity of daily life. This embodiment is advantageous as it enables a simple monitoring device without any advanced processing capabilities, thereby increasing its robustness and ease to use. The advanced processing and / or interfacing is in that case performed by the portable electronic device.

In a further embodiment, the physiological parameter signal is one or more of heart rate, breathing rate, breathing depth and pulmonary edema or any other physiological characteristic that can be measured by modulations of a eddy current caused by fluid (liquid, such as blood, plasma and/or gas, such as breathing air) movement(s) within the body, for instance intra-thoracic fluid shift.

According to a second aspect of the invention it is provided a method of the kind set forth in the opening paragraphs, the method comprising the steps of a) emitting a first concentrated electromagnetic field in a region (tissue) of interest of the subject b) generating a first receiver signal from a secondary electromagnetic field which is modulated by the physiological parameter and originates from first concentrated electromagnetic field within the region of interest, and c) generating a first physiological parameter signal from the first receiver signal.

Additionally, a further step of the method according to the invention consists emitting second concentrated electromagnetic field, being identical to the first concentrated electromagnetic field and directed opposite to the first electromagnetic field, generating a second receiver signal from the second concentrated electromagnetic field, and subtracting the second receiver signal from the first receiver signal, wherein generating the first physiological parameter signal is based on the subtracting the second receiver signal from the first receiver signal. The advantages of the method according to the present invention are analogous to the corresponding advantages for the monitoring device according to the present invention.

According to a fourth aspect of the invention, it is provided a computer program product of the kind set forth in the opening paragraphs comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the steps, and further steps, of the method according to the present invention. The advantages of the computer program according to the present invention are analogous to the corresponding advantages for the monitoring device and/or the monitoring system according to the present invention.

This and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

It will be appreciated by those skilled in the art that two or more of the above- mentioned options, implementations, and/or aspects of the invention may be combined in any way deemed useful.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, similar reference characters generally refer to the same parts throughout different views. Also, the drawings are not necessarily to scale, with the emphasis instead generally being placed upon illustrating the principles of the invention.

Fig. 1 illustrates a monitoring device in operation on a subject according to the present invention;

Fig. 2 illustrates an excitation unit according to the present invention;

Fig. 3 illustrates a schematic representation of an excitation unit having two pairs of excitation and detection coils according to the present invention;

Fig.4 illustrates a schematic representation of an excitation unit having two pairs of excitation and detection coils according the present invention;

Fig. 5 illustrates a schematic representation of the excitation unit of Fig. 4 using a floating ground according the present invention;

Fig. 6 illustrates the excitation unit of Fig. 4 using selective shielding according to the present invention; and

Fig.7 illustrates a method for monitoring a physiological parameter of a subject.

DETAILED DESCRIPTION OF EMBODIMENTS

Certain embodiments will now be described in greater detail with reference to the accompanying drawings. In the following description, like drawing reference numerals are used for like elements, even in different drawings. The matters defined in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of the exemplary embodiments. In addition, well-known functions or constructions are not described in detail since they would obscure the embodiments with unnecessary detail. Moreover, expressions such as "at least one of, when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

The device 100 for measuring a physiological characteristic of a subject 101 is shown in Fig. 1. The excitation unit 103, comprising an excitation coil, generates a focused magnetic field 104. Said alternating magnetic field creates an eddy current in the tissue of interest 102. The induced eddy current in turn creates another alternating magnetic field 105, a so-called secondary magnetic field. The strength of the secondary magnetic field 105 is proportional to the eddy current. A detection coil (not shown on the Fig. 1) which detects the secondary magnetic field 105, senses the strength of the eddy current.

The strength of the generated eddy current is proportional to the conductivity of the tissue in the region (tissue) of interest 102. For biological tissues, such conductivity is related to the relative or absolute amount of water therein and the concentration of ions within the said tissues. For instance, since inhaled air has a much lower conductivity than lung tissue, the eddy current generated in lungs will be modulated by the breathing cycle (inhalation and expiration) because of intra-thoracic fluid movements. In the heart, the generated eddy current is modulated between the systolic and diastolic phase by intrathoracic fluid movements as a results of heartbeat cycle. These modulations are found in a first receiver signal from the secondary electromagnetic field 105 detected by the detection coil in the excitation unit 103.

The penetration depth of an electromagnetic field depends on its frequency and the amount of water within the exposed tissue and the concentration of ions (therefore its conductivity) and variations therein will modulate the eddy currents in the tissue.

The monitoring device 100 may be attached or coupled to a subject for instance via a biocompatible patch, flexible or semi-flexible, stretchable or semi-stretchable. As shown in Fig. 1 the monitoring device 100 may be also partly attached to the subject. The excitation unit 103 is attached to the subject, while box 106 corresponding to a monitor device and necessary electronics is separate. The monitor device 106 could be also merged with the excitation unit in one unit (not shown). Alternatively, the monitoring device may be embedded within for instance the garment material of a piece of clothing such as a shirt or a vest. Fig. 2 illustrates an excitation unit 103 according to the present invention. In accordance with the invention, an excitation unit 103 comprises excitation core 201 with a excitation coil 204 wound thereon and a detection core 202 with a detection coil 203 wound thereon each.

For example the excitation unit 103 comprises the excitation coil 204 mounted on a horseshoe shaped solid core 201. The core can be made of ferromagnetic material.

Examples, of such ferromagnetic materials can be ferrite, powder iron. Ferromagnetic materials have a property of concentrating (focusing) or channeling magnetic field lines. Commonly used solenoid shape coils are arranged to create magnetic field lines

symmetrically distributed with respect to a main axis of the solenoid coil. An application of a coil together with a ferromagnetic core allows redistributing the magnetic field lines such that they are concentrated within the solid core. Due to the increased losses in the ferromagnetic material and self-inductance effects it may be advantageous for the excitation unit 103 to be operated at alternating current frequencies below 10 MHz.

In the present embodiment, the horseshoe shaped solid core allows creating an omnidirectional magnetic field lines connecting two edges (ends) of the horseshoe as illustrated by an arrow in Fig. 2. Depending on the current direction in the coil the magnetic field lines exit the solid core on one end (edge) and enter the solid core at another end (edge), thereby defining a single direction for the magnetic field. The detection core 202 is positioned symmetrically within the excitation core 201. In this embodiment the detection core 202 is placed in equidistance from the sides of the horseshoe, where the (due to the orientation) induced voltage caused by the first electromagnetic field is the lowest. Further the plane of the detection core 202 is oriented orthogonally with respect to plane of the excitation core 201. The excitation coil 204 and the detection coil 203 are arranged on the same side (first side) of the excitation unit and the axis of the detection coil 203 is orientated substantially perpendicular to the axis 110 of the excitation coil 101 (normal alignment). This orientation favors the detection of the secondary magnetic field.

In such an emitter/detector arrangement the axis of the detection coil 203 is substantially orthogonal to the magnetic field lines of the concentrated magnetic field emitted by the excitation coil. This mutual excitation/ detection coils arrangement reduces a magnetic field flux, caused by the first magnetic field, through the detection coil 203 to substantially zero, thereby increasing a sensitivity of the detection coil to the secondary magnetic field. An additional improvement of the detection coil sensitivity is achieved by the concentration of the magnetic field lines outside of the detection coil's location. The focusing effect of the solid core allows concentrating first magnetic field created by the excitation coil in the region of interest, which in turn increases the intensity of the secondary magnetic field. Further, a spatial localization of the first magnetic field within the region of interests allows to place the detection coil in the vicinity of the region of interests but beyond a direct influence of the first magnetic field, thereby further increasing a signal to noise ratio of the receiver signal originating from the secondary electromagnetic field.

In Fig. 2 the detection coil 203 is illustrated to be placed within the horseshow inner volume, wherein the density of the magnetic field lines of the first magnetic field, is minimized. The shape of the ferromagnetic solid core may be symmetrical with respect to the coil (non- limiting to the horseshoe example illustrated) such that the core defines a volume enclosed in between two ends of the core (in Fig. 2 the two ends are shown be connected by the curved arrow). In this case, when the detection coil is arranged within the volume defined by the shape of the solid excitation core, the induced voltage in detection coil 203 caused by the first electromagnetic field is the minimized. The induced voltage can be further reduced to its lowest value, when the detection coil 203 is placed in equidistance from two ends of the solid core.

The arrangement of the functional elements of the excitation unit 103 minimizes the magnetic field flux through the detection coil caused by the first magnetic field 104, thereby increasing the detection coil 203 sensitivity to the secondary electromagnetic field 105. This allows implementing in the excitation unit 103 a signal circuitry with reduced dynamic range amplification requirements, which would give an additional advantage to the monitoring device cost reduction.

Fig. 3 illustrates a schematic representation of an excitation unit having two pairs of excitation and detection coils according to the present invention. The monitoring device comprises an excitation unit 103. The excitation unit 103 comprises a first excitation coil 305 generating a first concentrated electromagnetic field on a first side 301 of the excitation unit 103, the first excitation coil creates a spatially concentrated (focused) magnetic field within the region of interest in a body tissue 102 of the subject, the excitation unit 103 further comprises a second excitation coil 306 arranged to generate a second identical concentrated electromagnetic field on an second side 302 of the excitation unit 103, said second side 302 being opposite to the fisrt side 301 .

A first detection coil 308 (in non-limiting example wound upon a first ferromagnetic detection core) generates a first receiver signal from a secondary

electromagnetic field 105 which is modulated by the physiological parameter and originates from the first concentrated electromagnetic field 104 within the region of interest 102, the first detection coil 308 is on the first side of the excitation unit 301 and substantially orthogonally oriented with respect to the first excitation coil 305. The second detection coil 307 generates a second receiver signal from the second identical concentrated

electromagnetic field. The first detection coil 308 and the second detection coil 307 (in non- limiting example wound upon a second ferromagnetic detection core) are serially reverse connected to the input of a differential amplifier 304. By doing this the differential amplifier 304 subtracts the second receiver signal from the first receiver signal to compensate for cross-talk between the first excitation coil and the first detection coil when generating the physiological parameter signal. The arrangement of the elements of the excitation unit 103 imposes reduced requirement to the dynamic range of the amplifier (since the receiver signal amplitude would smaller and be mainly defined by the secondary field rather than interposed secondary and first magnetic fields), which allows reducing costs of the monitoring device.

The second identical concentrated magnetic field is generated by the second excitation coil 306 and detected by the second detection coil 307 due to cross talk between the coils 306, 307 and that the cross talk of the second pair 306 and 307 is identical to the cross talk of the first pair 305 and 308 and can thus be subtracted, yielding the desired physiological parameter signal with greatly reduced disturbance due to cross talk. As the second concentrated magnetic field is directed away from the tissue it does not cause any eddy currents and thus no modulated secondary electromagnetic is generated and thus the second detection coil only picks up the crosstalk signal from the second excitation coil. (Like a Wheatstone bridge, voltages are proportional with magnetic fields). The embodiment with two pairs of excitation and detection coils allows to compensate for a potential deviation from the orthogonal alignment of the first excitation and first detection coils. Therefore, this embodiment provides a further improvement in the sensitivity of the monitoring device.

In the Fig. 3 the differential amplifier 304 is shown for illustration proposes, however the two receiver signals can also be subtracted in the digital domain.

The excitation coils 305, 306 are shown connected in parallel to the driving source 309 but can also be used connected in series with the driving source 309.

The first receiver signal generated by the first detection coil 308 and the second receiver signal generated by the second detection coil 307 can be processed via a processing unit (not shown) within the monitoring device 100, or may be processed by an external processing unit (not shown), for instance a personal computer, a mobile phone, a smart phone, a tablet, a (smart-/health-)watch, or any other devices comprising a processor unit (for instance a processor, a microprocessor, an integrated circuit) that can be carried by the subject in his/her activities of daily life. The first receiver signal and the second receiver signal may be transferred to said external processing unit (not shown) via means of wire, for instance a USB cable, a one way or two ways audio cable, or wirelessly, for instance via Bluetooth, Wi-Fi, ZigBee or any other means that could be contemplated by the skilled in the art.

Fig 4. illustrates a schematic representation of an excitation unit 103 having two pairs of excitation and detection coils according the present invention. It is shown a more physical representation of the invention: two sets of coils in a bridge coil configuration, in contrast to Fig 3, which illustrates the schematic circuits of the bridge configuration. All numbered components on the Fig. 4 correspond to the same numbered components on the Fig 3. The second coil pair (the second excitation coil 306 and the second detection coil 307) are located on the second side 302 (opposite to the first side) of the excitation unit 103 away from the region of interest 102, thus the eddy currents in the tissue not being detected by the second detection coil 307. In the Fig 3 excitation circuit section (305, 306), detection circuit (307, 308) section and the differential amplifier 304 are connected to the same ground.

Fig 5. depicts a schematic representation of the excitation unit of Fig. 4 using a floating ground according the present invention.

In Fig. 4 the excitation and receiving electronics were connected to the same ground. This makes the whole system as shown in Fig. 4 sensitive to disturbance by ground currents in ground loops. However, electrically isolating the ground of the excitation circuit 401 (by making it floating) from the ground of the detection circuit 402, ground currents are prevented, and true magnetic induction measurements of vital signs can be performed, unaffected by ground currents of other parts of the electronic circuits.

Fig. 6 illustrates the excitation unit of Fig. 4 using selective shielding according to the present invention. The shielding 501, 502, 503, connected to ground is applied to both detection circuits and further suppresses disturbances by electrical fields.

The coil creates a magnetic field but also an (unwanted) electric field. The latest will be a source of extra (and quite dominant) cross-talk. Therefore, an electrical field shield (also called Faraday- shield) is applied. Care might be taken to ensure that this electrical field shield does not experience currents caused by the magnetic field. Strategic interruptions (cuts) in the shield should be placed to prevent those currents.

It is to be noted that Fig. 6 illustrates in one figure all four techniques used in the invention combined to improve the signal quality and eliminate disturbances by electrical field and magnetic fields. (1) a focused magnetic excitation beam using solid cores 305 in combination in a (2) "bridge coil configuration" 305, 306, 308, 307 using two sets of coils, for detecting the secondary magnetic field from the body 102, which is set up to (3) avoid ground loops 402. The system is further optimized by applying (4) smart shielding 501, 502, 503. It shall be noted that the detection coils 307 and 308 are shown to be wound upon corresponding ferromagnetic cores. An application of the ferromagnetic core with a detection coil allows to localize (focus) the detector's sensitivity to the region of interest, thereby further improving signal to noise ratio of the physiological parameter signal.

However, the detection coils can be also used without ferromagnetic cores.

The method depicted in Fig. 7 comprises a first step 601 of starting monitoring a physiological parameter of a subject.

A second step 602 of emitting a first concentrated electromagnetic field within a region of interest of the subject, for instance a lung, or the heart.

A third step 603 of generating a first receiver signal from a secondary electromagnetic field which is modulated by the physiological parameter and originates from first concentrated electromagnetic field within the region of interest.

A fourth step 604 consist in generating a first physiological parameter signal from the first receiver signal.

In order to compensate for the crosstalk between the excitation coil and the detection coil the method comprises further steps.

A fifth step 605 consists in emitting second identical concentrated electromagnetic field opposite in direction to the first concentrated electromagnetic field, which happens in simultaneously with the second step 602.

A sixth step 606 consist in generating a second receiver signal from the second identical concentrated electromagnetic field. This sixth step happens simultaneously with the third step 603.

A seventh step 607 consist of the subtraction of the second receiver signal from the first receiver signal obtained in the fourth step 604.

The steps 601 to 607 and any additional or intermediary steps of the method according to the present invention may be executed using a computer, a processor or a network such that these steps are computer implemented. To this extent, a computer program product is foreseen, said computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer, or processor, or network, the computer or processor or network is caused to perform the steps to and any additional or intermediary steps.

Aspects of the invention may be implemented in a computer program product, which may be a collection of computer program instructions stored on a computer readable storage device, which may be executed by a computer. The instructions of the present invention may be in any interpretable or executable code mechanism, including but not limited to scripts, interpretable programs, dynamic link libraries (DLLs) or Java classes. The instructions can be provided as complete executable programs, partial executable programs, as modifications to existing programs (e.g. updates) or extensions for existing programs (e.g. plugins). Moreover, parts of the processing of the present invention may be distributed over multiple computers or processors.

As discussed above, the processing unit, for instance a controller implements the control method. The controller can be implemented in numerous ways, with software and/or hardware, to perform the various functions required. A processor is one example of a controller that employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform the required functions. A controller may however be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions.

Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

In various implementations, a processor or controller may be associated with one or more storage media such as volatile and non- volatile computer memory such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that, when executed on one or more processors and/or controllers, perform at the required functions. Various storage media may be fixed within a processor or controller or may be transportable, such that the one or more programs stored thereon can be loaded into a processor or controller. While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

There is therefore provided an improved method, system and apparatus for measuring a physiological characteristic of a subject.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless

telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.