WO2008029316A2

WO2008029316A2 - An apparatus, a monitoring system and a method for spectroscopic bioimpedance measurements

Info

Publication number: WO2008029316A2
Application number: PCT/IB2007/053411
Authority: WO
Inventors: Claudia H. Igney; Eberhard Waffenschmidt
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Phlips Electronics N.V.
Priority date: 2006-09-05
Filing date: 2007-08-27
Publication date: 2008-03-13
Also published as: WO2008029316A3

Abstract

The invention relates to a bioimpedance measuring apparatus 20 for measuring the bioimpedance of a portion of a body, the apparatus comprising a transmitter 22, 24 for applying a perturbing signal at different frequencies to the portion of the body; a sensor 22 for detecting a response signal S from the body related to the said bioimpedance, wherein the perturbing signal comprises an alternating magnetic field, the sensor being arranged as a coil integrated in a resonant circuit with adjustable resonant frequency. The invention further relates to a monitoring system and a method of enabling a spectroscopic bioimpedance measurement.

Description

AN APPARATUS, A MONITORING SYSTEM AND A METHOD FOR SPECTROSCOPIC BIOIMPEDANCE MEASUREMENTS

FIELD OF THE INVENTION

The invention relates to a bioimpedance measuring apparatus for measuring the bioimpedance of a portion of a body, the apparatus comprising a transmitter for applying a perturbing signal at different frequencies to the portion of the body and a sensor for detecting a response signal from the body related to the said bioimpedance.

The invention further relates to a monitoring system.

The invention still further relates to a method of enabling a spectroscopic bioimpedance measurement of a portion of a body, said method comprising the steps of providing an apparatus comprising a transmitter for applying a perturbing signal at different frequencies to the portion of the body and a sensor for detecting a response signal from the body related to the said bioimpedance.

An apparatus as is set forth in the opening paragraph is known from US 2005/0192488 Al. The known apparatus is arranged to inject radio -frequency alternating current into a portion of the body between a pair of electrodes at a single site for a single sensor module. The known arrangement comprises a source of alternating current operating at several frequencies in the range of 1 MHz to 5 GHz and is further arranged to measure the phase and magnitude across the portion of the body between the electrode pair. The resultant phase and magnitude information from the RF-impedance spectroscopy block of the known apparatus is sampled by the data acquisition system so that signal processing is performed to determine local composition information, such as water and glucose level. The disadvantage of the known apparatus is in that it operates using invasive electrodes and in that special safety means are to be provided to ensure that the maximum level of injected current does not surpass a safe mode of operation. Additionally, the known arrangement is complicated in its architecture.

DESCRIPTION OF THE INVENTION

It is an object of the invention to provide a simple, yet safe and reliable spectroscopy bioimpedance measurement apparatus.

To this end in the apparatus according to the invention the perturbing signal comprises an alternating magnetic field, the sensor being arranged as a coil integrated in a resonant circuit with adjustable resonant frequency.

The technical measure of the invention is based on the insight that contactless non- invasive methods for measurements of a body signal allow an easy and comfortable means of controlling vital parameters, like heart rate, tissue water content and blood glucose level, notably to supervise the user without the need of applying any kind of invasive devices to the user's body. According to the technical measure of the invention a sole sensor operating in a resonant circuit provides a simple, reliable and low cost solution for spectroscopic measurement system of the bioimpedance. For distinguishing between different tissue classes spectroscopic measurements are performed by changing the resonant frequency of the resonant circuit and by applying the alternating magnetic field to the portion of the body with the said changed frequency.

Measurement of the bioimpedance is known per se. The operating principle is as follows: using an inductor loop an alternating magnetic field is induced in a portion of a body, notably a patient. This alternating magnetic field causes eddy currents in the tissue of the body. Depending on the type of tissue, these eddy currents are stronger or weaker. These eddy currents cause losses in the tissue, which can be measured as a decrease of the quality factor of the inductor loop. The quality factor is a measure of the time of free oscillations of the resonant circuit. The eddy currents also cause a secondary magnetic loop or an induced voltage in a second inductor loop. Preferably, for changing the resonant frequency of the resonant circuit, a value of the capacitance integrated in the resonant circuit is changed. This can be done, for example, by arranging a plurality of different capacitors and by selecting a value of the net capacitance by operating a suitable switch. Alternatively, it is possible to add some length of connecting tracks, such that their parasitic capacity adds to the resonant capacity. Preferably, a tunable capacitor is used or a ceramic capacitor having non-linear dielectric properties. The tunable capacitor is preferably realized using a semiconductor diode and varying it's DC offset.

The monitoring system according to the invention comprises the apparatus as is described with reference to the foregoing.

Measurements of bio impedance has been shown to allow a non-contact detection of several vital parameters, like breath action and depth, heart rate, change of the heart volume and the blood glucose level. Further parameters that can be measured using the bio impedance measurement are fat or water content of the tissue. The monitoring system according to the invention is preferably arranged to measure a signal representative of these vital parameters. Usually, it is not sufficient to measure bioimpedance with one frequency and it is important to use setup to measure with different frequencies. Such setup has an additional advantage, because if the difference between two frequencies is measured, the measurement is not as dependent on exact positioning as it is for a single frequency measurement. Therefore, the monitoring system according to the invention is simple, low cost and reliable in use and can easily be used to monitor any relevant vital sign, like ones mentioned above, of the individual. Preferably, for durable measurements, the monitoring system according to the invention is integrated into a wearable article, like an elastic belt, wrist watch, or piece of clothing in tight contact with the body.

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

DESCRIPTION OF THE DRAWINGS Figure 1 presents a schematic view of an embodiment of a resonant bioimpedance apparatus according to the invention.

Figure 2 presents a schematic view of architecture of a monitoring system according to the invention.

Figure 3 presents a schematic view of an embodiment of the monitoring system integrated in a wearable article.

Figure 4 presents a further embodiment of the monitoring system according to the invention.

Figure 1 presents a schematic view of an embodiment of a resonant bioimpedance apparatus according to the invention. The resonant bioimpedance apparatus 20 comprises a winding 22, which is preferably implemented as a planar spiral winding. More preferably the planar spiral winding is integrated on a printed circuit board or on any other suitably selected isolating material. A transmitter of alternating magnetic field 20 is realized as a resonating circuit by means of electrically connecting the winding 22 to a DC blocking capacitance 24. In order to realize a measurement using different resonating frequencies the bioimpedance apparatus 20 is provided with a means 26, which causes a corresponding change in the resonant frequency when a value of the net capacitance 26 is changed. This can be done, for example, by arranging a plurality of different capacitors and by selecting a value of the net capacitance by operating a suitable switch. Alternatively, it is possible to add some length of connecting tracks, such that their parasitic capacity adds to the resonant capacity. Preferably, a tunable capacitor is used or a ceramic capacitor having non-linear dielectric properties. An other preferred solution is realized by using a semiconductor diode and varying it's DC offset. The apparatus 20 may be arranged in such a way that winding 22 is conceived to detect a response signal S of the portion of the body. Alternatively, the apparatus 20 may be provided with a further resonant circuit to measure the induced voltage in response to alternating magnetic field applied by the resonating circuit 22, 24.

According to the technical measure of the invention a sole winding operating in a resonant circuit with variable resonant frequencies provides a simple, reliable and low cost solution for measurement system of the bio impedance. For distinguishing between different tissue classes spectroscopic measurements are performed by changing the resonant frequency of the resonant circuit and by applying the alternating magnetic field to the portion of the body with the said changed frequency. Preferably, the bioimpedance apparatus 20 is integrated in a monitoring system, which will be described in more detail with reference to Figures 2 - 4.

Figure 2 presents a schematic view of architecture of a monitoring system according to the invention. The monitoring system 1 comprises the bioimpedance apparatus 6 provided with one or more resonating circuits 8, 9, preferably acting as individual transmit- and detect components. Preferably, resonant circuits 8, 9 are arranged to perform corresponding spectroscopic bioimpedance measurements and to pick corresponding electrical signals S 1 , S2 related to a suitable vital sign being monitored, when brought close to the individual's skin or in contact with individual's skin. Suitable vital signs that could be measured using the monitoring system according to the invention comprise, but not limited to, breath action and depth, heart rate, change of the heart volume, the blood glucose level and fat or water content of the tissue The signals Sl, S2 from the sensors is supplied to the front-end electronics 7 of the monitoring system 1. The front-end electronics 7 is arranged to analyse the said signals in order to derive a suitable health-related parameters which are further used by the monitoring system 1 for suitable analysis. The front-end electronics 7 comprises an input amplifier and analogue processing circuit 11, an ADC unit 12, a μ-processor 13 and a control unit 5. The control unit 5 comprises a sensor signal interpretation unit 14 provided with event extraction means 15.

The monitoring system 1 operates as follows: when the sensors are put close to or in contact with the individual's skin, they provide a corresponding input signals Sl, S2 to the front-end electronics 7. The front-end electronics 7 provides means for receiving the signals from the sensing means, performs suited analogue processing by means of the analogue processing circuit 11. The processed raw data is converted into a digital format by means of the ADC 12 and is forwarded to the control unit 5, where a suitable health-related parameter of the individual is being analysed. For example, for ventilation applications the control unit 5 can comprise a per-se known peak detector to determine characteristics of inhalation peak and intervals between such peaks. The control unit 5 comprises a signal interpretation unit 14 arranged to derive a predetermined event 15. For example, for ventilation applications said feature can be a frequency, an amplitude or a signal to noise ratio of the signal. Preferably, a reference value of the predetermined event is stored in a look-up table (not shown) of the memory unit 17. Additionally, the system can be arranged as a self-learning system, where a threshold value for the predetermined event is being adjusted and stored in the look-up table in cases a pre-stored reference value does not correspond to deteriorated condition of the individual being monitored. This feature is particularly important for monitoring exercising and/or revalidating people. The control unit 5 further comprises an event detection means 14a arranged to verify whether a predetermined event has occurred, like a threshold value of the amplitude of the response signals Ml, M2. In case the event has occurred, for example a condition of the individual is below a predetermined allowable level; the indicator means 16 is actuated by the detection means 14a to warn the individual and/or the surrounding.

Figure 3 presents a schematic view of an embodiment of the monitoring system integrated in a wearable article. This particular embodiment shows a monitoring system 30, integrated on a piece of a wearable article 30a, for example on an elastic belt. Preferably, the coil 32 is arranged as a planar spiral winding, more preferably integrated in a printed circuit board or on any other isolating substrate. For the integration into wearables a flexible substrate, like polyimide "Flexfoil" may be used. Flexible coils may also be stitched or woven into fabric using thin insulated wire. The monitoring system 30 comprises a resonant circuit with a sensor winding 32, which is preferably manufactured on a flexible printed circuit board 31. Still preferably, the board 31 is sealed in a water- impermeable unit 34 so that the whole monitoring system can be washable. This feature is particularly advantageous for monitoring systems arranged for continuous monitoring, for example of a health-related parameter. The winding 32 is preferably powered from a rechargeable battery 37 in the receiver circuit. To measure the signal S from the body (not shown), an input electronic circuit 36 is used. This electronic circuit may have a similar architecture as one described with reference to Figure 2. Preferably, the monitoring system is also arranged with indicators 39 conceived to warn the individual when a pre-determined event has occurred. Preferably, data related to a vital sign are measured, like blood pressure, heart rate, respiration rate, etc.

Figure 4 presents a schematic view of a further embodiment of the monitoring system according to the invention. The wearable monitoring system 40 according to the invention is arranged as a body- wear 41 for an individual P. The monitoring system 40 comprises a flexible carrier 43 arranged for supporting suitable bio impedance measurement apparatus 45. Preferably, for improving a wearing comfort, the carrier 43 is implemented as an elastic belt, whereto, for example, a number of sensors (not shown) is attached. It must be noted that although in the current embodiment a T-shirt is depicted, any other suitable wearables are possible, including, but not limited to an underwear, a brassier, a sock, a glove, a hat. The bioimpedance measurement apparatus 45 is arranged to measure a signal representative of a physiological condition of the individual P. Preferably, the coil, forming part of a resonant circuit with adjustable resonant frequency, is woven or stitched into the fabric of a suitable wearable in a form of a spiral. This solution is most comfortable and flexible. The purpose of such monitoring may be a medical one, for example, a monitoring of a temperature, a heart condition, a respiration rate, or any other suitable parameter. Alternatively, the purpose of monitoring may be fitness- or sport-related, whereby an activity of the individual P is being monitored. For this purpose the bioimpedance measurement apparatus 45 is brought close to or in contact with the individual's skin. Due to the elasticity of the carrier 43, the sensor or sensors experience a contact pressure which keeps it substantially in place during a movement of the individual P. The measured signal is forwarded from the bioimpedance measurement apparatus 45 to the control unit 47 for purposes of signal analysis or other data processing. The control unit 47 may be coupled to a suitable alarming means (not shown).

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.

Claims

CLAIMS:

1. A bioimpedance measuring apparatus (20) for measuring the bioimpedance of a portion of a body, the apparatus comprising: a transmitter (22, 24) for applying a perturbing signal at different frequencies to the portion of the body; a sensor (22) for detecting a response signal (S) from the body related to the said bioimpedance; characterized in that the perturbing signal comprises an alternating magnetic field, the sensor being arranged as a coil (22) integrated in a resonant circuit (22, 24) with adjustable resonant frequency.

2. An apparatus according to Claim 1, wherein the resonant circuit comprises a tunable capacitance (26).

3. An apparatus according to Claim 1, wherein the resonant circuit comprises a ceramic capacitor with non linear dielectric properties.

4. A monitoring system (1) for monitoring a vital sign of an individual comprising an apparatus according to any one of the preceding Claims.

5. A monitoring system (40) according to Claim 4, wherein the sensor is integrated in a wearable article (41).

6. A method of enabling a spectroscopic bioimpedance measurement of a portion of a body, said method comprising the steps of: providing an apparatus comprising a transmitter for applying a perturbing signal at different frequencies to the portion of the body and a sensor for detecting a response signal from the body related to the said bioimpedance, the perturbing signal comprising an alternating magnetic field, the sensor being arranged as a coil integrated in a resonant circuit with adjustable resonant frequency; positioning the apparatus in a vicinity of the portion of the body; applying alternating electromagnetic field to the said portion with different frequencies; detecting respective response signals representative of the bioimpedance of the said portion of the body.