GB2375012A

GB2375012A - Radio biotelemetry monitoring system

Info

Publication number: GB2375012A
Application number: GB0110222A
Authority: GB
Inventors: Brian Austin Reed
Original assignee: RE TECH ELECTRONICS Ltd
Current assignee: RE TECH ELECTRONICS Ltd
Priority date: 2001-04-26
Filing date: 2001-04-26
Publication date: 2002-10-30
Anticipated expiration: 2021-04-26
Also published as: GB2375012B; GB0110222D0

Abstract

With reference to Figure 1, a biotelemetry monitoring system 1 for use in collecting monitored data derived from several subjects 2a, 2b, is shown wherein each subject is provided with an individual data monitoring sensor 3, (Figures 2 and 3), operable to transmit said data by way of a first radio link 4 to a relay station 5 operable in turn to transmit said data to a data collection station 6 by way of a second radio link 7. In this example, the subjects 2a, 2b, are athletes undergoing training. With reference to Figures 2, monitoring each athlete is by way of electrodes 10 mounted on the skin of the athlete's body which transmit data signals 11 to an amplifier 12 and thence to a signal processing circuit 13. The circuit 13 is connected to a battery management circuit 14 and a temperature sensor 15. From the processing circuit 13 the data signals are passed to an ultra high frequency transmitter circuit 16 and then to the radio link 4 by way of an ultra high frequency loop antenna 17.

Description

BIOTELEMETRY MONITORING SYSTEMS This invention relates to biotelemetry monitoring systems. There are many applications for a high quality remote biotelemetry monitoring system for use in collecting high frequency biologically derived data such as eeg. (electroencephalogram where electrical events in the brain are recorded), emg. (electromyogram, where nerve impulses to muscles and the response thereto are recorded) and ecg (electrocardiogram). There are both animal and human applications in such areas as athletic training, early detection of seizures, and telemedicine.

The present invention provides such a biotelemetry monitoring system.

According to the invention, a biotelemetry monitoring system is provided for use in collecting monitored data derived from several subjects, wherein each subject is provided with an individual data monitoring sensor operable to transmit said data by way of a first radio link to a relay station (or subject receiver) operable in turn to transmit said data to a data collection station (or base station) by way of a second radio link.

Preferably the relay station is provided with encoder means whereby the individual data monitoring signals are encoded before transmission of the data to the data collection station.

An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings, wherein :- Figure 1 is a block diagram which illustrates the monitoring system, Figure 2 is a simplified diagram of a data monitoring sensor module, and Figure 3 is a block diagram which illustrates, in further detail, the sensor module of Figure 2.

With reference to Figure 1, a biotelemetry monitoring system 1 for use in collecting monitored data derived from several subjects 2a, 2b, is shown wherein each subject is

provided with an individual data monitoring sensor 3 module, (Figures 2 and 3), operable to transmit said data by way of a first radio link 4 to a relay station 5 (or subject receiver) operable in turn to transmit said data to a data collection station 6 (or base station) by way of a second radio link 7. In this example, the subjects 2a, 2b, are athletes undergoing training.

With reference to Figures 2, monitoring each athlete is by way of data derived from each athlete by way of electrodes 10 mounted on the skin of the athlete's body which transmit data signals 11 to an amplifier 12 and thence to a signal processing circuit 13. The circuit 13 is connected to a battery management circuit 14 and a temperature sensor 15.

From the processing circuit 13 the data signals are passed to an ultra high frequency transmitter circuit 16 and then to the radio link 4 by way of an ultra high frequency loop antenna 17.

With reference now to Figure 3, each sensor module 3 is small in size. Electrical power is provided by a small battery unit 20 having a battery management circuit 4 provided with a built-in battery low level warning circuit operable should the battery output fall below predetermined level. Each battery 21 comprises a button cell which provides a typical operating time of 10 hours or more. The warning signal could be visual and/or audible.

Depending on the intended application, different types of skin surface mounted electrodes are used by the sensor module 3. For emg. signals from large muscle groups two differentially sensed self adhesive electrodes produce good results. For low level eeg. signals, as illustrated, a. group of three larger electrodes, namely high, low and reference, produce signals with low levels of movement artifacts. For ecg. signals external electrodes may be used. The signals from the electrodes are sensed via a high gain, low noise differential amplifier 22. Owing to the high dynamic range of the different types of signals, the output of amplifier 22 is then amplitude compressed with a simple square law response by unit 23. This negates the need for any adjustment of the modules in use,

and allows simultaneous monitoring of eeg. and emg. signals from the same electrode site.

After peak limiting, the date signals are used to frequency modulate a uhf frequency of between 300 and 2000 MHz, using an amplifier 24, a limiter 25 a modulator 26, and an amplifier 27, before being fed to the antenna 17. The antenna 17 comprises a printed circuit component.

The carrier frequency is produced by a programmable crystal controlled synthesizer 28 connected to a frequency divider 29 and an oscillator 30, and a reference crystal 31. The synthesizer 28 has a channel programming input 32.

As many as eight different narrow band frequency modulated channels can be programmed into the sensor 3.

By adding a low frequency carrier, of say 2KHz, to the compressed signal, other parameters may be transmitted to base data collection station 6 (Figure 1). This is achieved by a modulator 35 and an oscillator 36.

By adding a small surface mounted thermistor 40 with amplifier 41 to the contact surface of the sensor module 3, the subject's surface temperature may be sensed. The resistance of the thermistor 40 is used to control the frequency of the low frequency carrier. By sensing the voltage of battery 21, and momentarily interrupting the low frequency carrier when it drops to a predetermined limit, a low level battery warning may be signalled to the data collection station 6 (Figure 1). As the battery voltage becomes more critical, the interruptions can be made more rapid.

Heart rate may be sensed by an additional electrode (not shown) connected to the sensor module 3 by a short cable. The potential of this electrode is compared with the reference electrode to sense ecg. signals. These trigger a monostable circuit to give short defined interruptions of the low frequency carrier, and so the heart rate may be recovered at the date collection station 6.

With further reference to Figure 1, where sensor modules on different channels 45 are illustrated, each relay station 5 is also battery powered, and can be belt or harness mounted for large subjects, or can be stationary rather than worn by the subject, where they are within a two meter range.

A relay station 5 simultaneously monitors the eight possible channels 45, decompresses them, and by synchronised time division multiplexing, encodes them to a higher power radio link for transmission to the data collection station 6. Programmable amplifiers for each sensor channel allow the relay station 5 to optimise its performance for the types of signal being sensed. This selection may be carried out automatically by sensing the amplitude and frequency content of the signal, or may be remotely selected at the data collection station 6. Depending on the configuration used, the data collection station 6 can be disposed as much as a kilometre away.

The data collection station 6 can have a single receiver set for each subject, or if remote control of the relay station 5 is required, together with error correction of the final signal link, transceivers would be used to provide a two-way link. Normally up to four subjects would be allowed for. The data collection station 6 would be mains or battery powered, and would output all the recovered biopotential signals simultaneously, in both analogue and digital formats, to allow a variety of recording and analysis equipment to be used.

The invention has the following innovative features :- (a) The ability to remotely monitor low level biopotentials with minimal distortion.

(b) The ability to monitor multiple sensors on several different subjects.

(c) To handle eeg., emg. , or ecg. signals without adjustment at the sensor.

(d) To transmit eeg. and emg. signals simultaneously from the same site.

(e) The ability to provide skin temperature and heart rate information.

Provision of the relay station (subject receiver) 5 allows the sensor modules 3 to be made very small and also allows a small power battery to be used. However, this means that the sensor modules 3 transmit at low power with a low range, say 2,0 metres. For

monitoring signals to reach the data recording equipment at the collection station (base station) 6, it is necessary to add the relay receiver/transmitter at station 5.

This low range does, however, have the advantage that different subjects can be monitored in close vicinity, say 2.0 or more meters, using the same frequency channels.

As long as intended sensor module 3 is closer than the nominated one, the use of frequency modulation will ensure there is interaction.

To montior ecg. two electrodes would be used, one fitted to the base or contact surface of the sensor module 3, as when two would be used for eeg. or emg. , and an extra one connected to the module by a length of wire, about half a meter, with an adhesive pad on it. The module could be attached with its electrode to convenient a site, such as the centre of the chest, and the wired electrode to the left side of the chest, for instance. If just heart rate is to be measured, and not the more detailed ecg. signal, which also indicates the action of the heart muscles, and hence health, the electrodes can be directly attached to the sensor module, and so close together. Almost anywhere on the chest will pick up the pulses from the hearts'large muscle group.

Claims

1. A biotelemetry monitoring system for use in collecting monitored data derived from several subjects, wherein each subject is provided with an individual data monitoring sensor operable to transmit said data by way of a first radio link to a relay station operable in turn to transmit said data to a data collection station by way of a second radio link.

2. A system as claimed in Claim 1, wherein the relay station is provided with encoder means whereby the individual data monitoring signals are encoded before transmission of data to the data collection station.

3. A system as claimed in Claim 1 or 2 powered by an electric battery, provided with means for emitting a warning should the battery output fall below a predetermined level.

4. A system as claimed in any one of Claims 1,2 or 3 wherein monitored data signals are first amplified, passed on to a signal processing circuit and then passed on to an ultra high frequency transmitter circuit before transmission to the relay station by way of said first radio link.

5. A system as claimed in Claim 4, provided with means for producing a carrier frequency, said means comprising a programmable crystal controlled synthesizer.

6. A system as claimed in any of Claims 1 to 5, wherein the individual data monitoring sensor comprises a plurality of electrodes mountable on the skin surface of the subject being monitored.

7. A system as claimed in any one of Claims 1 to 6, wherein the subject being monitored carries the relay station of the system.

8. A biotelemetry monitoring system substantially as hereinbefore described, with reference to the accompanying drawings.