WO2008029362A2

WO2008029362A2 - Real time monitoring system and method of electrical signals relating to an athlete's heart action

Info

Publication number: WO2008029362A2
Application number: PCT/IB2007/053580
Authority: WO
Inventors: Ruan Van Den Heever; Willem Christiaan Venter; Dawid Daniël Jacobus MALAN
Original assignee: North-West University
Priority date: 2006-09-07
Filing date: 2007-09-05
Publication date: 2008-03-13
Also published as: WO2008029362A3; ZA200901508B

Abstract

A monitoring system for monitoring the heart activity of an athlete while being active, comprises a base station (12) comprising a wireless transceiver (20) connected to a computing device (14). At least one relay station RS#1 to RS#4 is locatable in the region of an activity area (22). Mounted on the body of the athlete (24.1 to 24.n) is a monitoring apparatus (30) for monitoring an electrical signal relating to the heart activity of the athlete. A wireless communications link comprising a first channel (f1) enables communications of data relating to the signal monitored between the at least one relay station and the base station. A second channel (f2) enables communications of the data between the monitoring apparatus on the athlete and the at least one relay station. The computing device is configured to process the data and user selectively to output the heart rate and/or an ECG of the athlete.

Description

REAL TIME MONITORING SYSTEM AND METHOD OF ELECTRICAL SIGNALS RELATING TO AN ATHLETE'S HEART ACTION

INTRODUCTION AND BACKGROUND This invention relates to a system, apparatus and a method for monitoring in real time, electrical signals relating to a mammal's heart action. The invention more particularly relates to such a system, apparatus and method for use while a subject mammal is exercising or participating in sporting activities.

Apparatus for producing an electrocardiogram is well known in the art. However, the known apparatus is not suitable for use with subject mammals while exercising or participating in sports. There is a need for apparatus and a system to enable a trainer or coach of an athlete to monitor the heart rate, and preferably other parameters of an electrical signal relating to the athlete's heart activity in real time, while the athlete is participating in a sporting activity. For example, it may enable the coach to determine (perhaps with the aid of historical data) whether the athlete is over-exerting herself, alternatively is under performing and, in team sports, whether the athlete should perhaps be substituted. Problems associated with the monitoring of signals relating to the heart activity of an athlete include noise, such as network interference, motion artifacts, electro-myographic interference, baseline wander due to respiration, abrupt base-line changes due to jumping and other jerking actions, instrumentation noise as a result of electromagnetic interference and composite noise comprising one or more of the aforementioned noise types.

OBJECT OF THE INVENTION Accordingly, it is an object of the present invention to provide a system, apparatus and method with which the applicant believes the aforementioned disadvantages and/or problems may at least be alleviated.

SUMMARY OF THE INVENTION

According to the invention there is provided a heart activity monitoring system comprising:

- a base station comprising a wireless transceiver connected to a computing device; - at least one relay station locatable in the region of an activity area; at least one monitoring apparatus for monitoring an electrical signal relating to the heart activity of a mammal in the activity area and which apparatus is mountable on a body of the mammal; - a wireless communications link comprising a first channel for enabling communications of data relating to the signal monitored between the at least one relay station and the base station and a second channel for enabling communications of the data between the monitoring apparatus on the mammal and the at least one relay station; and

- the computing device being configured to process the data and to provide data relating to at least one parameter of a signal relating to the heart activity of the mammal.

The first channel may be associated with a carrier signal having a first frequency and the second channel may be associated with a carrier signal having a second frequency, and the first frequency may be different from the second frequency.

The system may comprise at least a first relay station and a second relay station. More relay stations may be provided if required. The base station may be configured to transmit an interrogation signal on the first channel to the first relay station, the first relay station may be configured in response, to broadcast the interrogation signal on the second channel to cover at least a first part of the activity area, the first relay station may be configured to receive a response signal from an interrogated apparatus on the second channel, and if no response is received, the first relay station may be configured to cause the second relay station to broadcast the interrogation signal on the second channel to cover a second part of the activity area.

The activity area may comprise, but is not limited to at least one of a sports field, exercise area, race track, athletics track, athletics field and the like.

According to another aspect of the invention there is provided a method of monitoring heart activity of a mammal in an activity region, the method comprising the steps of: from a base station adjacent the region, transmitting an interrogation signal on a first channel to a first relay station; - causing the relay station to broadcast on the second channel the interrogation signal to cover at least a first part of the activity region; - at a monitoring apparatus on a mammal in the first part, causing the interrogation signal to be received; causing the monitoring apparatus to respond on the second channel with a signal comprising data relating to the heart activity of the mammal;

- at the relay station receiving the response signal; and causing the relay station to transmit the response signal to the base station on the first channel.

According to yet another aspect of the invention there is provided monitoring apparatus for monitoring an electrical signal relating to the heart activity of a mammal, the apparatus comprising: first and second electrodes mountable on the body of the mammal; - the first and second electrodes being connectable to respective first and second inputs of a first amplifier stage; the first amplifier stage having a first output for providing a difference signal relating to a difference between a first signal at the first input and a second signal at the second input; - the first amplifier stage further comprising a second output for providing a signal common to the first and second signals; a second amplifier stage having an input and an output; the input of the second amplifier stage being connected to the second output of the first amplifier stage and the second amplifier stage being configured to provide at the output of the second amplifier stage an inverted and amplified signal corresponding to said common signal; and the output of the second amplifier stage being connectable to a third electrode mountable on the body of the athlete to feed back to the body the inverted amplified signal, thereby to cancel common mode noise in the first and second signals.

The first output of the first amplifier stage may be connected to an analogue band pass filter to reject signals below 1 Hz, preferably below 0.5Hz, thereby to reduce base-line wander and to reject out of band signals above 120Hz.

The analogue band pass filter may comprise a class Il Chebychev filter.

The monitoring apparatus may comprise a controller comprising a processor, typically in the form of a microcontroller, and an output of the band pass filter may be connected to an analogue to digital (A/D) converter to digitize an output signal from the band pass filter. The A/D converter may be implemented by the mircorcontroller.

The microcontroller may further be configured to implement a digital filter, preferably an adaptive digital filter, to reduce network noise at about 50 Hz or about 60Hz.

An output of the digital filter may be connected to a digital to analogue (D/A) converter for converting the digitally filtered signal to an analogue signal.

An output of the digital to analogue converter may be connected to a analogue low pass filter, with cut off frequency at about 1 20Hz.

The low pass filter may be non-inverting and may comprise an amplifier. An output of the low pass filter may be connected to a serial capacitor, to remove DC shift in the signal.

The capacitor may be connected to a voltage pull-up stage and an output of the pull-up stage may be connected to an input of the A/D converter of the microcontroller. The microcontroller may be configured periodically to sample the signal at the output of the pull-up stage and the A/D converter may be configured to convert successive samples into digital data.

The microcontroller may further comprise an encoder for encoding the digital data with a suitable error correcting code. The encoder may be a Manchester encoder.

The apparatus may further comprise a wireless transceiver, typically a radio frequency (RF) transceiver, connected to a data output of the microcontroller. The microcontroller may be configured to cause the transceiver to broadcast an RF carrier carrying the encoded data.

The monitoring apparatus may be mounted on an item of clothing worn by the athlete. The item of clothing may be a sports vest and the apparatus may typically be mounted on one printed circuit board, which may be locatable in a pocket on the vest. The apparatus may be suitably covered with padding material. In other embodiments, the monitoring apparatus may be carried on a special purpose carrier adapted to be mounted on the body of the athlete. The invention also includes within its scope an item of sports clothing, such as a sports vest, carrying the monitoring apparatus as hereinbefore defined.

Yet further included within the scope of the invention is a method of monitoring remotely and in real time a signal relating to heart activity of an active mammal, the method comprising the steps of sensing between two electrodes the signal on the body of the athlete, deriving a common mode noise signal, inverting the noise signal and feeding the inverted signal back to the body thereby to destruct the common mode noise signal, electronically filtering the sensed signal, converting the signal into digital data relating to the signal and transmitting the data via a wireless link to a remote base station.

BRIEF DESCRIPTION OF THE ACCOMPANYING DIAGRAMS

The invention will now further be described, by way of example only, with reference to the accompanying diagrams wherein: figure 1 is a diagrammatic view of a sports field and a high level block diagram of the system according to the system for monitoring remotely and in real time an electrical signal relating to the heart activity of an athlete taking part in sports on the field; figure 2 is a diagram of a sportsman on the field carrying electronic monitoring apparatus for monitoring the signal on his body; figure 3 is a block diagram of the electronic monitoring apparatus; figure 4 is a circuit diagram of at least part of an acquisition circuit forming part of the apparatus; figure 5 is a high level flow diagram of processes and a computer program running on a computing device at a base station of the system; figure 6 is a high level flow diagram of processes and computer programs running on controllers at relay stations of the system and figure 7 is a diagram similar to that in figure 6, with additional steps.

DESCRiPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

A system for monitoring remotely and in real time signals relating to heart activity of athletes while playing a sport, is generally designated by the reference numeral 10 in figure 1 . The system 10 comprises a base station 12, which may comprise a computing device 14 comprising one or more of a desk-top computer, lap-top computer, hand held device, etc. The computing device executes an application program for processing data received by the device 14 as will hereinafter be described and to display the processed data on a monitor or display 16. A keyboard 18 is also connected to the device to enable a human user to enter commands to the device. The device is further connected to a transceiver 20. The transceiver is preferably a wireless, more preferably, a radio frequency (RF) transceiver adapted to transmit and receive RF signals in the Industrial Standards Medical Devices (ISM) band, that is in the band between 430MHz and 434MHz.

In one application, the base station is established in the vicinity of an activity area, such as a sports field 22, on which two teams of players 24.1 to 24. n compete in a sport, such as rugby, soccer, cricket or any other team sport. In other applications the base station may be established at a training or exercising area, such as a gym. In yet other embodiments the base station may be set up in the vicinity of an athletics track or field and in yet other applications, in the vicinity of a horse racing track, for example, to monitor remotely and in real time, as will hereinafter be described, signals relating to heart activity of mammals active on the field, track or area.

In the application shown in figure 1 , the system comprises a plurality of relay stations RS#1 to RS#n mounted around the field 22. The relay stations are similar in configuration and each comprises a dual frequency transceiver 26 for receiving a first RF signal having a first carrier frequency fi and for broadcasting an interrogation signal on a second carrier frequency f2, so that it may be received by transceivers (shown at 32 in figure 3) forming part of apparatus 30 for monitoring signals relating to the heart activity of the players as will hereinafter be described. The transceivers 26 also serve to receive response data carried on the second frequency transmitted by the transceivers 32 on the players and for transmitting the data received from the transceivers 32 on the first frequency to the base station. It will be appreciated that the relay stations serve to improve RF coverage over the whole field 22 and also the range of communications between the base station 12 and apparatus 30 on the players. It will further be appreciated that in some applications fewer and even no relay stations may be required. In general, the base station 12 transmits to a first of the relay stations a request for data relating to a designated player or players. The request may be for data relating to the heart rate of the player, alternatively data required to construct to an ECG of the player. The first relay station then transmits an interrogation signal addressed by a unique address to the relevant apparatus on the body of the player. If the player is in range, the apparatus 30 transmits data relating to the signal monitored to the relay station. The relay station then forwards the data to the base station. If the player is not in range of the first relay station, the first relay station prompts a second relay station to go through the aforementioned steps, until the designated player is in range of one of the relay stations. In the case of the requested data being data relating to the heart rate of the player, the signal monitored by the apparatus 30 is locally processed and the data relating to the heart rate (typically a number per minute) is transmitted to the relay station and the base station. In the case of the requested being data required to construct an ECG of the player, digital data relating to successive samples over a predetermined period of a signal EC (which will be explained hereinafter) are transmitted to the relay station and the base station. In figure 2, there is shown a diagrammatic representation of player 24.1 carrying the apparatus 30 on his body. The apparatus 30 is preferably padded with suitable padding material and carried in a pocket 28 sewn in a sports vest 29 or the like.

The apparatus 30 is shown in more detail in figure 3. The apparatus 30 is preferably mounted on a single printed circuit board and comprises a battery, preferably a single battery 34. The battery is connected to a high frequency inverter 36, to provide with the battery a dual voltage supply. The apparatus 30 further comprises a controller

38 comprising an embedded PIC18F252 microcontroller 39 and signal acquisition circuitry 40 as will hereinafter be described. The circuitry 40 is connectable to the body of the player 24.1 by a first electrode 42, a second electrode 44 and a third electrode 46. An output of the acquisition circuitry 40 is connected to the controller 38 and the controller is connected to the transceiver 32. In some embodiments large parts of the apparatus 30 may be integrated on a single application specific integrated circuit (ASIC), thereby to reduce volume and mass.

The acquisition circuitry 40 comprises a first amplifier stage 50 comprising a differential amplifier 51 , for example an AD623AR, having a first input 52 connectable to first electrode 42 to sense a first signal on the body, a second input 54 connectable to second electrode 44 to sense a second signal on the body and a first output 56 where there is provided a signal relating to a difference between the first signal at the first input 52 and the second signal at the second input 54. The first amplifier stage further comprises a second output 58 where there is provided a noise signal common to the first signal and the second signal. The second output 58 of the first amplifier stage 50 is connected to a first input 60 of a second amplifier stage 62, to feed the common mode signal to the second amplifier stage 62. The second amplifier stage 62 comprises an inverting operational amplifier 63, such as one in the OP97 range manufactured by Analog Devices, and provides at an output 64 thereof an amplified and inverted form of the common mode signal. The output 64 is connectable via third electrode 46 to the body of the athlete 24.1 . In use, the third electrode 46 is applied to the body in a region close to the first and second electrodes 42,44.

The difference signal at first output 56 of the first amplifier stage 50 represents the signal (EC) relating to the heart activity of the subject.

The common signal at the second output 58 represents common noise in the first and second signals. The inverted and amplified signal at output 64 of the second amplifier stage 62 is used to destruct or cancel on the body of the player the common noise at the first and second electrodes 42 and 44, thereby to improve the quality of the difference signal at output 56. The difference signal (EC) at pin 6 of amplifier 51 relating to the heart action may be expressed as follows:

EC = ((Signal 1 + noise) - noise) - ((Signal 2 + noise) - noise) = Signal 1 - Signal 2

An analogue class Il Chebyshev band passes filter 70 is connected to the output 56 of the first amplifier stage 50, to cut off frequencies below 0.5 Hz, thereby to reduce base-line wander and frequencies above 120 Hz, to reject all out of band signals.

In order to attenuate network interference at about 50Hz or 60Hz, as the case may be, the signal is converted to the digital domain by a

10-bit A/D converter 72 implemented on the microcontroller 39. An adaptive digital filter 74 implemented in software running on the microcontroller 39 is used mathematically to attenuate the network interference. After the aforementioned digital filtering, the signal is again converted to the analogue domain by a D/A converter 76. In a final filtering stage 78, a non-inverting analogue low pass filter is used to reject all out of band (larger than 120Hz) noise. Capacitor 80 is used to eliminate DC shift and pull-up voltage stage 82 allows the analogue filtered EC signal to be pulled up to a suitable voltage level at 84.

The analogue signal at 84 is again converted to the digital domain by the 10-bit A/D converter implemented by the microcontroller 39. The analogue signal is sampled at adjustable inter-sampling periods, but say every 6 μs. The controller processes the sampled signal to determine the heart rate which is locally stored in a memory arrangement of the apparatus 30 and intermittently or periodically updated. In the event that the data requested is data relating to the heart rate, the stored data is transmitted. In the event that the data requested is data relating to the EC, the controller 38 causes the sampled data relating to the signal to be Manchester encoded and fed in serial form to the transceiver 32. The transceiver 32 broadcasts the second carrier signal f2 in the ISM band carrying the data. The second carrier signal with data is received by any one of the relay stations RS#1 to RS#4 and the relevant relay station then broadcasts the aforementioned data on the first carrier signal in the ISM band. The first carrier signal with data is received by the transceiver 20 at the base station 12. The data is transmitted to the computing device 14 where it is processed to extract one or more parameters relating to the signal, and to display that parameter on display 16 to the aforementioned human user, such as a sports coach or sports scientist. In this manner, data relating to the heart rates of all the players in a team on the field may be displayed simultaneously. The system may be configured, when an irregularity in the heart rate of any one player is detected, automatically to obtain sufficient data from the monitoring apparatus 30 on that player, to generate and display on display 16 an electrocardiogram (ECG) relating to that player. The system may also enable the human user to request the computing device 14 through keyboard 18, to source sufficient data from the monitoring apparatus 30 on any one selected athlete only, and to generate and display in real time on display 16 an ECG of the selected athlete.

The flow diagrams in figures 5, 6 and 7 are self-explanatory, but some features are highlighted hereinafter. Referring to figure 5 read with figure 1 , at 100, the user at the base station 12 is able to interrogate an apparatus 30 on a selected one of athletes 24.1 to

24. n, for data relating to the heart activity of the athlete, either in the form of data relating to a heart rate or sampled data over a predetermined period of time relating to signal EC, to enable the device 14 to reconstruct an ECG. In the event of heart rate data, when received, the data is stored for display at 102. In the event of the sampled data, the device 14 receives the data for the time period as shown at 104 and also monitors the signal strength (SS) as shown at 106. If the SS is too bad, the base station 12 causes a next one of the relay stations RS#1 to RS#4 to broadcast the request to the selected device 30 as hereinbefore described and as shown at 108 and if still not satisfactory, to hand over to yet a next relay station. Hence, only one relay station will be transmitting at a time. The base station is configured to activate the relay stations in a predetermined sequence, sequentially to cover a first part, second part and further parts of the field or region of activity.

In figure 6 there is shown in more detail the handling of heart rate data by the relay stations and the steps of sequentially handing over the communications with the targeted apparatus 30 from one relay station to a next.

In figure 7, there is shown in more detail the handling of the sampled data in the case where data to construct an ECG is requested. At 1 10, both channels on all the relay stations are opened to receive data. Each relay station is then able to receive on the second channel the sampled data from a targeted monitoring apparatus 30 as shown at loop 1 12 and if received, to forward the data on the first channel to the base station. Since the receiver of the first channel is also operative, and as shown at 1 14, the relay station is also able to respond to commands received from the base station.

Claims

1 . A heart activity monitoring system comprising: a base station comprising a wireless transceiver connected to a computing device; - at least one relay station locatable in the region of an activity area; at least one monitoring apparatus for monitoring an electrical signal relating to the heart activity of a mammal in the activity area and which apparatus is mountable on a body of the mammal; a wireless communications link comprising a first channel for enabling communications of data relating to the signal monitored between the at least one relay station and the base station and a second channel for enabling communications of the data between the monitoring apparatus on the mammal and the at least one relay station; and

2. A system as claimed in claim 1 wherein the first channel is associated with a carrier signal having a first frequency and the second channel is associated with a carrier signal having a second frequency, and wherein the first frequency is different from the second frequency.

3. A system as claimed in claim 1 or claim 2 comprising at least a first relay station and a second relay station.

4. A system as claimed in claim 3 wherein the base station is configured to transmit an interrogation signal on the first channel to the first relay station, wherein the first relay station is configured in response, to broadcast the interrogation signal on the second channel to cover at least a first part of the activity area, wherein the first relay station is configured to receive a response signal from an interrogated apparatus on the second channel, and wherein, if no response is received, the first relay station is configured to cause the second relay station to broadcast the interrogation signal on the second channel to cover a second part of the activity area.

5. A system as claimed in any one of claims 1 to 4 wherein the activity area comprises at least one of a sports field, exercise area, race track, athletics track and athletics field.

6. A system as claimed in any one of claims 1 to 5, wherein the at least on monitoring apparatus comprises: first and second electrodes mountable on the body of the mammal;

- the first and second electrodes being connectable to respective first and second inputs of a first amplifier stage;

- the first amplifier stage having a first output for providing a difference signal relating to a difference between a first signal at the first input and a second signal at the second input; - the first amplifier stage further comprising a second output for providing a signal common to the first and second signals; a second amplifier stage having an input and an output;

- the input of the second amplifier stage being connected to the second output of the first amplifier stage and the second amplifier stage being configured to provide at the output of the second amplifier stage an inverted and amplified signal corresponding to said common signal; and

- the output of the second amplifier stage being connectable to a third electrode mountable on the body of the athlete to feed back to the body the inverted amplified signal, thereby to cancel common mode noise in the first and second signals.

7. A method of monitoring heart activity of a mammal in an activity region, the method comprising the steps of:

- from a base station adjacent the region, transmitting an interrogation signal on a first channel to a first relay station; causing the relay station to broadcast on the second channel the interrogation signal to cover at least a first part of the activity region;

- at a monitoring apparatus on a mammal in the first part, causing the interrogation signal to be received; causing the monitoring apparatus to respond on the second channel with a signal comprising data relating to the heart activity of the mammal; at the relay station receiving the response signal; and causing the relay station to transmit the response signal to the base station on the first channel.

8. A monitoring apparatus for monitoring an electrical signal relating to the heart activity of a mammal, the apparatus comprising: first and second electrodes mountable on the body of the mammal;

9. Apparatus as claimed in claim 8 wherein the first output of the first amplifier stage is connected to an analogue band pass filter to reject signals below about 1 Hz and signals above about 120Hz.

10. Apparatus as claimed in claim 9 comprising an analogue to digital converter connected between the output of the band pass filter and a digital filter configured to reduce network noise at one of about 50 Hz and about 60Hz.

1 1 . Apparatus as claimed in claim 10 wherein an output of the digital filter is connected to a digital to analogue (D/A) converter for converting the digitally filtered signal to an analogue signal and wherein an output of the digital to analogue converter is connected to an analogue low pass filter, with cut off frequency at about 120Hz.

12. Apparatus as claimed in claim 1 1 wherein the low pass filter is non-inverting, comprises an amplifier and wherein an output of the low pass filter is connected to a serial capacitor.

13. Apparatus as claimed in claim 12 wherein the capacitor is connected to a voltage pull-up stage, wherein an output of the pull-up stage is connected to an input of an A/D converter, and wherein the A/D converter is configured periodically to sample the signal at the output of the pull-up stage and to convert successive samples into digital data.

14. Apparatus as claimed in claim 1 3 wherein the digital data is encoded with an error correction code.

1 5. Apparatus as claimed in claim 14 comprising a wireless transceiver for transmitting the encoded data.

16. Apparatus as claimed in any one of claims 8 to 15 mounted on an item of clothing for the mammal.

17. A method of monitoring remotely and in real time a signal relating to heart activity of an active mammal, the method comprising the steps of sensing between two electrodes the signal on the body of the athlete, deriving a common mode noise signal, inverting the noise signal and feeding the inverted signal back to the body thereby to destruct the common mode noise signal, electronically filtering the sensed signal, converting the signal into digital data relating to the signal and transmitting the data via a wireless link to a remote base station.