GB2425181A

GB2425181A - Wearable physiological monitoring device

Info

Publication number: GB2425181A
Application number: GB0507486A
Authority: GB
Inventors: Justin Pisani; Peter Howard; Daniel Cade; Stephen Ward
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-04-14
Filing date: 2005-04-14
Publication date: 2006-10-18
Anticipated expiration: 2025-04-14
Also published as: GB2458389A; GB2425181B; GB0507486D0; GB2458389B; GB0906368D0

Abstract

A wearable monitoring device comprises a body worn unit and a processing unit 40. The body worn portion includes at least three electrodes 51-54 arranged in a substantially triangular configuration to measure various physiological parameters, and may be a strap-on harness 57, an item of clothing or a self-adhesive patch (figure 6). Additional sensors may be provided on the body worn unit (e.g. thermometer 42, pulse oximetry sensor, an accelerometer). The processing unit is removably attached to the body worn unit using snap rivets 58, 59, 60, 63, 64 and eyelets 44, and comprises sensor electronics to analyse the data and transmit it to a remote site (by wired or wireless means). The monitoring device measures physiological parameters such as ECG, respiration (using motion or impedance measurements), skin surface temperature, body gravitational load, skin surface electrical impedance, blood oxygen level, orientation, and motion. Also disclosed is an alternative configuration where the device is remotely mounted to the patient (figure 8).

Description

SENSOR

Background to the invention

The invention relates to a compact non-invasive personal sensor device capable of monitoring the health and welfare of an ambulatory user in real time by the collection and analysis of a plurality of physiological signals.

The types of physiological signals to be collected, analysed and transmitted within the single unit include, for example, Electrocardiogram (ECG), Respiration Effort, Body Skin Temperature, Body Impedance, Skin Surface Impedance, Blood oxygen level, pulsatile waveform, Body Orientation, Body Motion, Body gravitational load and activity level.

Devices which extract, process and display one or more of the above signals are known in the art, but are generally intended for the monitoring of patients with known or suspected ailments, within a clinical environment. Typically, these units connect to the patient using separate sensors, either by wire or wireless means, and then process the recovered signals in a remote unit which is not intended to be worn by the user. Thus, such devices are not intended for true ambulatory use and also rely on easy access to the user's body in order to connect the sensor and probes in several locations.

Ambulatory monitors are also known in the art, but typically record a single or a few parameters such as two channels of a users ECG. Such devices are intended for infrequent use. Such devices typically store data in a data logging unit which the user is required to also carry, which is then taken to a medical expert for review and analysis after the monitoring session has completed. Hence such devices are not suited to use in real time.

An object of this invention is to provide a simple body worn device which is particularly suited for use by people engaged in activities which could result in injury and trauma.

Important Features Accordingly, this invention provides a compact bodyworn unit comprising of a compact sensor electronics module capable of collecting a plurality of physiological signals, analysing those signals, and selectively transmitting the signals and/or the analysis of them over a communications link, which may be wired or wireless.

Typical users of such a device may be engaged in hazardous activities and in order to minimise the risk of injury be required to wear protective clothing which provides a limitation on the body area which may be used for collecting physiological signals. It is an essential feature of such as sensor that it mounts in a position which has a low probability of conflict with the user's apparel and minimises the area on the body needed to connect sensors to the user's skin.

Accordingly, the sensor electronics module connects to single sensor connection device arranged in an approximately triangular shape to fit on and around the thoracic cavity and containing a plurality of sensor electrodes which in conjunction with the sensor electronics module provide: * Two or more distinct views of the Users Electrocardiogram (ECG).

Those skilled in the art will be aware that the provision of two or more distinct electrical views of heart allows an improvement in the detection and accuracy of heart beat electrical activity by allowing the electrical activity to be compared on each view and improved immunity to noise which is more prevalent.

* Respiration Effort derived from electrical impedance changes within the body due to thoracic cavity and abdominal movement which occurs during breathing.

* Respiration Effort derived from measuring thoracic cavity expansion and contraction using an external sensor fitted around part of the chest circumference.

* Sp02 Blood Oxygen and Pulsatile Waveform extraction by measuring the blood oxygenation variations on the sternum * Thoracic Cavity Skin Surface Impedance * Correct electrode contact confirmation by measuring impedance between electrodes.

* Activity, Impact and Body Position levels derived from 2 or 3 axes of g force measurement made using accelerometer devices contain in the sensor electronics module.

The Sensor Electronics Module is self supported by the Sensor Connection Device and can be easily mounted and dismounted from the Sensor Connection Device without the need for special tools by the use of suitable connectors. The shape and ergonomics of the Sensor Connection Device are such that the user can correctly apply the device without the need for specialist medical assistance or training and that they can be used by both male and female users.

The Sensor Electronics module is battery powered either by primary or rechargeable means.

Preferably, in order to provide user flexibility in mounting the sensor to the body, the Sensor Connection Device may be realised in a variety of means to best suit that user, including, for example, a disposable adhesive electrode array, a re-usable strap based harness assembly or as an integrated element within clothing such as a vest or top.

An additional object of this aspect of the invention is to allow the continued useful use of the device by a medic once a user has been injured. In this circumstance it may be preferable to not have the sensor electronics module mounted on the body which may interfere with the medics need to access the body in order to provide care. In this circumstance, the medic could remove or take a new Sensor Electronics Module and use a version of a Sensor Connection Device which allows the Sensor Electronics Module to be remotely connected to electrodes and sensors on the body. The position of these sensors and electrodes can be determined by the medic to meet clinical need, thus providing the medic with a basic vital signs monitoring capability as commonly used in triage of casualties.

Introduction to the Drawings

With reference to the drawings: FIGURE 1 shows a diagram of the preferred sensor locations on a user.

FIGURE 2 shows a diagram of the sensor electronics module and sensor connection device where the sensor connection device is achieved using a strap based harness.

FIGURE 3 shows a rear view of the user wearing the device described in FIGURE 2 FIGURE 4 shows how the sensor electronics module interconnects to strap based harness sensor connection device.

FIGURE 5 shows how the strap based harness sensor collection device sensors and electrodes are arranged.

FIGURE 6 shows a diagram of an adhesive sensor connection device.

FIGURE 7 shows a diagram of how the sensor electronics module may be combined into clothing.

FIGURE 8 shows a diagram of how a remote sensor connection device can be provided for a medic.

FIGURE 9 shows a block diagram of the sensor electronics device.

Preferred Embodiment In a preferred embodiment, with reference to FIGURE 1, the signals of interest may be derived from an approximately triangular set of electrodes applied to the central thoracic cavity.

By the use of differential electrical amplification the hearts electrical activity can be measured between electrodes [1] and [3], [1] and [2], and [3] and [2]. Those skilled in the art will be aware that whilst the electrode spacing is small, for example 10 cms, the proximity of the sensor to the heart will compensate to allow a reasonable signal to noise ratio to be achieved.

Respiration effort may be measured across electrodes [1] and [2] simultaneously, by presenting a high frequency AC signal from a constant current source, such that variation in the impedance of the diaphragm due to respiration will result in a voltage waveform which approximates to respiration effort. This signal may be used to derive respiration rate after appropriate filtering.

This same technique can also be used to determine the impedance of the electrode [1], [2], [3] connection to the skin and to flag a "lead-off" condition if they exceed a certain threshold.

Those skilled in the art will also be aware that blood oxygen percentage level and pulsatile waveform can also be measured using the established technique of pulse oximetery and a reflectance type sensor placed on the sternum bone within the same approximate area [4].

The use of this sensor may be optional depending on the user's requirements.

With reference to FIGURE 2, the Sensor Electronics Module [10] electrically and mechanically connects to the Sensor Connection Device which is derived using a strap based harness [20].

The strap harness Sensor Collection Device [20] is made up of a central mounting point [11] made, for example, of a suitable non- conductive body conformal material, for example leather or vinyl, which is cut to follow the approximate contours of the central thoracic cavity.

The central mounting point [11] is attached, for example, by means of clothing stitching, to semi flexible straps which are passed around the body to secure the connection device in place and hold the device to the body with a degree on tension such that unwanted movement of the device is minimised. Those skilled in the art will be aware that such strap device may be individually adjusted using integral adjusters commonly found in clothing straps to allow for variation in user body sizes. In addition, the strap harness may be produced in varying sizes (for example small, medium and large) to cope with larger user to user size variations.

One strap passes horizontally around the trunk [20] and may also contain within it a semi elastic variable resistance sensor whose resistance varies when expanded and contracted, in this case by the movement of the user's chest with breathing. This sensor may be made from a thin, for example 4 mm thick, rectangular cross section of silver loaded flexible material such as SantopreneTM. Those skilled in the art will also be aware that the sensor could also be achieved by inlaying loops of wire within the strap [20] and measuring the variation in inductance achieved by the same chest expansion and contraction which will cause the loops of wire to change in proximity to each other.

The top part of the central mounting point [11] is held in place by two vertical straps [21] and [22] which act to tension the upper part of the mounting point [11]. The Electrode material is attached by, for example, by normal clothing thread to the body facing side of the strap harness assembly at the appropriate points to achieve the desired electrode positions [30], [31], [33]. The double straps [21],[22] are advantageous in that they act to hold the uppermost electrode [33] in place when the user is walking and the upper body yaws with the associated arm movement. In addition the point at which the straps [21], [22] attach to the central mounting point [11] provide an aperture to place the reflectance pulse oximetery sensor [32] in position.

Referring to FIGURE 3, at the rear of the user, the vertical straps [37], [38] run down the back and connect to the horizontal strap [36]. The horizontal strap has a clasp [35] to allow the strap to be separated for ease of application and removal. This clasp also provides for adjustment of the circumference of the horizontal belt to the users precise trunk circumference at that point by allowing the amount of belt length to be varied by adjusting the position of the clasp on the belt [34].

FIGURE 4 shows the central mounting point [43]. Electrical and mechanical connection is achieved using electrically conductive male snap rivets and eyelets [44] (for example Micron E391282-085 and E31 1-a2cl). The Sensor Electronics Module [40] contains the matching female snap fixing allowing the module to be connected to the central mounting point by pressing the two parts together. Additionally, the Sensor Electronics Module provides extra electrical interconnect to allow charging of its internal battery, wired transfer of data, and connection to the pulse oximetery sensor.

This can be achieved for example by recessed plated copper terminals [47] moulded into the module housing [46]. Connection to these terminals can be made by a corresponding set of male sprung contacts of matching dimensions [48] mounted on the central mounting point [43] of the sensor connection device, such that when the two devices are brought together electrical contact is made between the sprung contacts [49] and the recessed terminals [47]. The sensor electronics module also contains an elevated thermally conductive probe [42] which contacts the user's skin and contains internally a temperature measuring device such as a thermistor to measure skin temperature.

FIGURE 5 shows the body facing side of the central mounting point [50]. The snap rivets [58],[59],[60],[63],[64] pass through the mounting point and allow electrical connection to the electrodes [50],[52],[54] which are on the opposite side to the Sensor Electronics Module connections. Those skilled in the art will be aware that this can be achieved by a number of means including for example flexible wires, flexible conductive printed circuit boards, or by direct connection to the electrode material.

The electrode material used for [51],[52],[53],[54] may be made of a fabric woven from silver loaded thread, or by the use of conductive flexible material such as silver loaded SantopreneTM. Additional snap rivets [60]. [63] connect via wires to the respiration chest belt sensor contained within part of the circumference of the horizontal straps [57].

The reflectance pulse oximetery sensor [62] is held within the assembly with an aperture [68] to allow the sensor head to protrude and contact the body and is electrically connected by wire to the rear of the electrical connector block [65]. Positive pressure on the sensor can be achieved for example, by placing sprung close cell foam [67] between the sensor [69] and the central mounting point material [66].

A protective, waterproof fabric layer would be overlayed on the rear of the central mounting point [50] to cover the electrical connections and protect from damage.

FIGURE 6 shows the preferred embodiment of an adhesive Senor Connection Device. The device comprises of a sculpted adhesive membrane [72] (for example the Intellicoat 5230 range) to hold the sensor to the skin. The three electrodes [73],[74] and [75] are provided by a circular hydrogel disk (for example Ludlow RG63B) of which one side contacts the skin and the other side a flexible polyester membrane [76] , printed with conductive silver /silver chloride ink tracks [77] to connect between the electrode points and the snap rivets [79] arranged in the same locations as used in the earlier strap harness example. [71] is a release liner material (eg: Flexcon 94PRTPFW) used to protect the adhesive membrane before application to the body.

Those skilled in the art will also be aware that alternative electrode assemblies are commonly provided with conductive snap fittings (eg: Ambu BlueSensor L) and that these could also be used.

FIGURE 7 shows how the sensor connection device may be incorporated into a user's apparel either as part of a vest [82] which may be constructed from a suitable fabric such a LycralM and has sewn internal to the vest electrodes of the style discussed earlier and connects to the Sensor Electronics Module [80] via the same conductive snap rivet method as discussed earlier. The vest can also have integrated into it a flexible semi-conductive strap [81] as discussed earlier to detect user's respiratory chest movement. [83] shows an alternate example of a top targeted at a female user constructed out of similar materials and methods.

FIGURE 8 shows how the sensor can be remotely mounted from the user by a medic.

Commonly used ECG electrodes [91], [90] and [92] are used to connect to the users skin providing an ECG signal view as desired by the medic. For example the configuration in FIGURE 8 provides an ECG view those skilled in the art will recognise as Lead I between [90] and [91] and Lead II between [91] and [92]. Such conventional ECG views may offer an advantage of familiarity to a medic.

Respiratory effort may also be measured between [91] and [92]. The electrodes connect to the sensor electronics module [94] by a special remote sensor connection device which has a connection plate comprising of a plastic carrier and aforementioned conductive snap rivets connecting to flying electrode wires with a suitable termination to connect to the electrodes.

Additionally, the device contains a wired connection to a pulse oximeter device [95] for example, the NONIN XPOD, which provides a variety of sensor clip assemblies [96] to connect to the users body for example as a finger, toe or ear clip. In this configuration, the medic may observe the sensor output by means of a portable computing device, for example an IPAQ, communicating to the sensor electronics module by wire or wireless means (for example BluefoothTM) Referring to FIGURE 10, a preferred embodiment of the sensor electronics module may be achieved as follows: ECG measurements are taken from the subject from electrodes sensors attached to the skin and connected to the electronics via connections [100], [101], and [102].

Considering a single channel of ECG1 as shown, using a differential input allows the ECG signal to be differentially amplified by the amplifier [116], greatly reducing the effect of noise, particularly mains electrical hum. After amplification, the ECG signal is filtered using a band pass filter [117] to select only those frequencies of interest, which will be in the region of 0.05Hz to 150Hz. This is followed by further amplification [118] and low- pass filfering [119] before presentation of the signal to an AID input [120] of the microprocessor unit [131], which may be an embedded microcontroller such as a Philips 80C51. Additional noise immunity may be provided by, for example reducing the ECG bandwidth to for example 2Hz to 100Hz when a user is moving and this may be controlled by the microcontroller which is able to detect the presence of motion via the accelerometer [104]. The additional ECG2 and 3 channels would be provided using the same methodology.

Impedance respiration effort is measured using a simple current source amplifier [121] to drive an impedance signal to the RE and LE electrode connections [100] and [102]. The frequency of the current source amplifier output could be in the range of 50-150kHz. The same electrodes are used to sense the voltage using a differential amplification stage [114] and [112], band pass filtering [115] and [113], and a simple AM diode detector [123] and then further amplification [122] and low-pass filtering [125] before presentation of the signal to an AID input [126] of the microprocessor unit [131].

A chest belt sensor is used to provide an alternative method of measuring respiration effort [103]. The sensor [103] is physically attached to the subject as part of the aforementioned sensor connection device, and electrically connected as part of an impedance measurement network, with its centre point fed into an amplification stage [109] and a band pass filter [107]. Further amplification may be provided [110] and low-pass filtering [108] can be applied before presentation of the signal to an AID input [128] of fhe microprocessor unit [131].

Respiration measurements may also be derived from the ECG signal. It is well known in the art that, in a normal subject, the R-R interval characteristic of the ECG signal varies over time, and this variation is associated with the respiration rate. This is known as Respiratory Sinus Arrhythmia (RSA). In this embodiment of the invention, respiration data are derived by measuring the variations in R-R interval. This requires that normal beats are identified, so that abnormal beats and artefacts are nof included in the analysis. To do this requires analysis of the beats which is performed by the microcontroller [131].

The preferred embodiment has provision for a accelerometer [104], which is assumed to be a digital two-axis device, for example the Analog Devices AD XL2O2E, but may also be a three axis device, or two two-axis devices placed orthogonally. This can provide information either of the subject's motion, or of their orientation (upright or prone). It is shown connected digitally to the microprocessor [131] via connections [129] which include provision for an enable control signal to improve power management.

Skin temperature is shown being measured by a simple thermistor [6], the output of which is amplified [7] before being presented to an AID input [130] of the microprocessor unit [131].

It will be clear to those skilled in the art that other methods of deriving the physiological parameters would be possible, and that other parameters could also be measured using well-known techniques.

The circuits described are powered by a cell or cells which may be either primary (for example Alkaline LRO3 cells) or secondary rechargeable (for example Varta LIP 553048) which may be regulated to provide a stable and controlled voltage to the circuit elements.

After analysing the signals presented to it, the microprocessor [131] processes the signals further and may undertake further signal condition, filtering and numerical computation in order to derive secondary measures from the signals recovery, either in isolation or in conjunction with other signals and sends the required data either to an rf transmitter [134] which may be for example, a wireless transceiver such as a Bluetooth radio modem (for example a Wireless Futures BluewavelM or a LigbeeTM radio transceiver. Alternately a wire based communications driver [135] can be used. This communications driver also provides a serial data communication interface for the connection of a pulse oximeter sensor to the unit.

Claims

We Claim: 1. A compact body worn, anatomically shaped, monitoring device intended for use by a ambulatory user which enables the measurement, processing, analysis and onward transmission of multiple physiological parameters where said device comprises of; a sensor electronics module unit which processes analyses and transfers the physiological information to remote device for capture, display, analysis or further processing either by wired or wireless means.

a body worn connection unit containing three or more electrodes arranged in an approximately triangular configuration of which the upper point is placed approximately at the sternum and the lower points approximately on the abdomen.

and is able to measure and process; two or more distinct views of the user's electrocardiogram (ECG).

Respiration effort by measuring electrical impedance or motion changes.

skin surface temperature.

body gravitational load in vertical and horizontal axes.

skin surface electrical impedance.
2. A device as in Claim 1 where the sensor electronics module is anatomically shaped to fit the users thoracic cavity in an approximately triangular, three lobed arrangement, shaped to fit between the sternum and abdomen.
3. A device as in Claim I where the sensor connection unit consists of a central connection conformal material piece shaped to fit between the users sternum and abdomen in an approximate triangular, three lobed configuration, where the central connection piece contains the means to connect and support the sensor electronics module by three or more electrically conductive snap rivet fittings and in turn connect these fitting to three or more body contacting conductive electrodes and sensors, and is retained in place by a horizontal flexible fabric strap and two vertical fabric straps extending from the sternum point over each shoulder and reconnecting to the horizontal strap where the two meet on the user back.
4. A device as in Claim 1 where the Sensor Electronics Module contains addition high density electrical interconnect terminals which may be connected to via a male electrically conductive set of spring contacts of similar dimensions held within the body worn connection unit and enables the connection of: wired computing terminals.

pulse oximetery module held within the sensor connection unit.

other sensors.

a power source to recharge power cells contained within the Sensor Electronics Module.
5. A device as in Claim 3 where the horizontal strap also contains the means to measure the users breathing related chest movement by the incorporation of an variable impedance sensor which connects to the sensor electronics module via conductive snap fittings or by the interconnect defined in Claim 3.
6. A device as in Claim 3 where said straps contain adjusters to allow the user to tension the sensor connection unit to the body optimally.
7. A device as in Claim 3 where the sensor connection unit is produced in sizes to allow fitment to a broader range of body sizes.
8. A device as in Claim 1 where the sensor connection unit consist a conductive adhesive patch laminate structure of three electrodes conforming to the same triangular electrode configuration and where the adhesive patch uses the same connection fitting types and locations to allow it to connect to the same Sensor electronics module without need for modification.
9. A device as in Claim 1 where the sensor connection unit consist of a fabric vest structure containing three or more electrodes conforming to the same triangular electrode configuration and where vest uses the same connection fitting types and locations to allow it to connect to the same sensor electronics module without need for its modification.
10. A device as in Claim 7 also contains the means to measure the users breathing related chest movement by the incorporation of an horizontal variable impedance sensor which connects to the sensor electronics module via conductive snap fittings or by the interconnect defined in Claim 4.
11. A device as in Claim 1 where the sensor electronic module can communicate with external devices in order to transfer it physiological signals, or derivations of said signals by processing performed by the sensor electronics module
12. A device as in Claim 1, where the sensor connection unit consist a contact plate to connect electrically to the sensor electronics module and offers three or more individual electrode wires which may be used to connect to individual electrodes at other locations on the body and also to a separate pulse oximeter module.
13. A device as in Claim 1, where the sensor electronics module utilises two of the ECG views of the user to improve the performance of the detection of heart beat electrical activity by using both views to determine if such a beat has occurred.
14. A sensor electronics device for measuring a users ECG where the sensor detects the presence of motion by measuring gravitational load variation on the body using an accelerometer and uses evidence of motion to reduce the bandwidth of the ECG signal receiver thus improving the signal to noise of the ECG.
15. A measuring device substantially as herein before described with reference to or as shown in accompanying drawings.
16. A measuring system substantially as herein before described with reference to or as shown in accompanying drawings.