GB2150332A

GB2150332A - Heartbeat monitor

Info

Publication number: GB2150332A
Application number: GB08326790A
Authority: GB
Inventors: Martin Robin Bowman
Original assignee: Michael John Tranter
Current assignee: Michael John Tranter
Priority date: 1983-10-06
Filing date: 1983-10-06
Publication date: 1985-06-26
Also published as: GB2150332B; GB8326790D0

Abstract

A simple device for monitoring heartbeats includes a microphone (11) adapted to pick up cardiac noise and other sounds, filter means (23) to isolate a component of the signal corresponding to heartbeat pulses, and control means (25, 26) responsive to such heartbeat pulse component to inhibit actuation of alarm means. Conveniently, the device is formed as two separate units, comprising a detector unit (10) for securing to the body, and a remote unit (20) with a radio link between them. The detector unit may conveniently be housed in a pocket in a close-fitting garment. <IMAGE>

Description

SPECIFICATION Heartbeat monitor This invention relates to a device for monitoring heartbeats, especially but not exclusively in infants, to provide an alarm signal in the absence of a heartbeat.

Very sophisticated and hence expensive equipment is available in hospitals for monitoring heartbeat and other life functions in detail, but such equipment is far too costly and complex for use in normal domestic circumstances, and yet in view of the undesirably high incidence of "cot deaths", a simple and economical monitoring unit for home use would be of great value, and the object of the present invention is to provide such a unit.

In accordance with the invention, we provide a monitoring device comprising audio transducer means for application to suitable part of the human body to provide an electrical analogue signal derived from cardiac noise and other sounds picked up thereby, electrical filter means for isolating a component of such signal corresponding to heartbeat pulses, alarm means for producing an audible or visual alarm signal, and control means responsive to said heartbeat pulse component produced by the filter means to inhibit actuation of the alarm means.

In a particularly advantageous embodiment, the alarm means is actuated in response to a charge stored on a capacitor, and the control means responds to said pulse component to discharge the capacitor and thereby inhibit operation of the alarm means. This can readily be achieved by deriving a low-going signal from said pulse component and applying said signal to the capacitor through a rectifier of appropriate polarity to discharge the capacitor through the rectifier during such low-going pulse. The capacitor is conveniently arranged in a charging circuit with a relatively long time constant so that the voltage level on the capacitor rises towards the level required to actuate the alarm over a period corresponding to several heartbeats.

Conveniently, the device is formed as two separate units, namely a detector unit for securing to the body and a remote unit for processing the output of the transducer which is incorporated in the detector unit. Whilst in some cases the detector unit may be designed to be strapped to the wearer's body, or secured by means of adhesive, it is preferably adapted to be held in a pocket formed or provided in a close fitting garment, such as a vest.

Whilst in some cases it would be possible for the two units to be connected physically be means of a wire for transmission of the analogue signal from the transducer to the remote unit, it is preferred for the detector unit to include a low power radio transmitter to transmit a signal to a radio receiver incorporated in the remote unit. In this way, movement of the infant wearing the detector unit is in no way impeded, and the remote unit may be positioned in any suitable location, even in a different room.

In one embodiment, the detector unit is adapted to interfit with the remote unit when not in use, so that a battery in the detector unit can be recharged from the remote unit. A switch may be arranged to switch off the detector unit when it is fitted to the remote unit for charging. A back-up battery may be provided in the remote unit in case of failure of the mains electricity supply by which the remote unit would normally be energised, and a switch may be provided for operation by the detector unit to switch off the remote unit and re-charge any backup battery provided therein when the detector unit is assembled with the remote unit.

These and various features of the invention will now be described by way of example, with reference to the accompanying drawings, wherein: Figure 1 shows a schematic block diagram of the electronic circuitry; Figure 2 illustrates certain signals as processed by such circuits; and Figure 3 illustrates the way in which a detector unit may be carried detachably by a garment.

As illustrated, the device comprises two separate units 10 and 20. Unit 10 is a detector which incorporates a low power radio transmitter whereby signals are supplied to a receiver which is incorporated in the remote unit 20. In this case, the detector unit 10 incorporates a cardiac noise detector in the form of an f.e.t. microphone 11 which produces an analogue signal which is fed to a V.H.F. transmitter circuit 12 having an aerial 13 which is conveniently formed as part of a printed circuit. The unit 10 includes a rechargeable battery (not shown) as the power source and preferably has contacts (not shown) whereby such battery can be charged in the manner as hereinafter described.

The remote unit 20, as previously mentioned, includes a receiver 22 connected to an aerial 21, tuned to the preferably fixed frequency of the transmitter 12 so as to provide an output signal (a) which corresponds to the output of the microphone 11 and includes specifically cardiac noise, other noise detected in the body, and possibly also extraneous noise so that the signal typically is of the kind shown at (a) in Figure 2. This signal is supplied to a low pass filter circuit 23 which produces a smoothed output signal (b). As can be seen from Figure 2, the transmitted signal (a) typically includes two close pulses P1, P2, separated by a longer time interval, the two close pulses corresponding to a single, composite heartbeat.

The filter circuit 23 also includes a half wave rectifier and a smoothing circuit so that the filtered signal (b) is generally as shown in Figure 2 with broad humps P3,, P3b corresponding to the original pulses P1, P2. This signal is preferably applied to a light emitting diode 24 to provide a visual indication that the apparatus is working satisfactorily, and to a detector circuit 25 which includes a squaring amplifier which in this case is arranged to provide a signal (c) including a negative-going pulse P4 corresponding to each pair of pulses P1, P2. The signal (c) is fed to an alarm circuit 26 which includes a capacitor C which is charged through a relatively high value resistance R so that the charging circuit has a relatively long time constant.The signal (c) is applied to the capacitor C through a reverse diode D. This forms a reversed diode pump circuit whereby each negative-going pulse P4 discharges the capacitor C.

In the interval between the pulses P4, the capacitor begins to re-charge so that the voltage signal (d) which appears across the capacitor is of shallow saw-tooth form.

However, in the absence of heartbeat pulses P1, P2, the consequent absence of negative-going square pulses P4 will allow the capacitor C to continue to charge at the rate determined by the time constant at the capcitor circuit so that the voltage appearing across the capacitor will approach the line voltage applied to the resistor. The signal (d) from the capacitor is applied to a comparator or other form of detector which is arranged to a comparator or other form of alarm device when the voltage on the capacitor exceeds a predetermined value, which may typically be approximately two thirds of the line voltage.

The device is accordingly of very simple design, and can be made economically by mass production methods involving only two printed circuit boards. In a preferred arrangement, the detector unit 10 can be physically connected to the remote unit 20 for storage when not in use, and for recharging of its battery. For this purpose, the remote unit 10 is preferably adapted to be operated from a mains electricity supply, and the two units inter-fit in such a way as to operate switches which de-energise both units and connects a trickle charger incorporated in the remote unit 20 to the rechargeable battery included in the detector unit 10. The remote unit 20 may itself include a rechargeable back-up battery which is likewise placed on charge when the detector unit is coupled to the remote unit.

Thus, in use, it is only necessary to plug the remote unit into a mains supply socket and then remove the detector unit for use as required.

Conveniently, the detector unit 10 may be placed in a pouch 31 provided in a garment such as a vest 30. Such vest may be made of a stretch fabric so as to fit a range of sizes snugly. The pouch 31 may include shaped padding which is adapted to hold the unit 10 securely in position, and if necessary an opening 32 may be formed in the vest in register with the microphone 11 to enable the latter to be in direct contact with the wearer's skin.

We have found that such an arrangement is entirely satisfactory, and that it is not necessary for the detector unit to be positioned accurately over the wearer's heart. The use of a printed circuit aerial 13 is quite adequate for the short transmission distances envisaged and obviates the need for any wires or projection which might be dangerous when the device is used with a young baby. The remote unit 20 may be placed at any suitable location up to several metres away from the detector unit 10, and the latter may include any suitable form of alarm, such as a buzzer or siren, or it may include provision for connection to an external alarm.

Whilst the device is particularly suitable for use with very young babies, it will be appreciated that it may be used for any age group.

Thus, in a further embodiment, the detector unit 10 may be provided with a strap or harness for securing to the wearer's body. In some cases, the signal from the microphone 11 may be applied to the filter circuit 23 directly by means of a wire whereby the two units are physically connected so that the use of a radio transmitter and receiver is obviated. In other cases, the two units may be combined into a single device, again obviating the need for a radio transmitter and receiver, which would then be fully portable and powered by a rechargeable battery. In a further embodiment, the circuitry included in the remote unit 20 could be duplicated in the detector unit 10 so as to provide a dual alarm signal, one from the detector unit itself, and one from the remote unit.

It will be see that by relying on a microphone to pick up general cardiac noise, the device is particularly simple to use, and does not require the use of electrodes attached to the skin, or adhesive contact with the wearer's skin. No sophisticated electronics are employed and there are no controls which an unskilled user may inadvertently set incorrectly.

The use of a reverse diode pump circuit to detect the absence of heartbeats is particularly simple, but it will be appreciated that other forms of circuit could be employed for this purpose. For example, the squared pulse from the amplifier 25 could be used to gate the input of constant frequency pulses from a standard clock to a pulse counter arranged to produce an alarm output if the count does not reach a predetermined value within a specified time period.

Claims

1. A monitoring device comprising audio transducer means for application to a suitable part of the human body to provide an electrical analogue signal derived from cardiac noise and other sounds picked up thereby, electrical filter means for isolating a component of such signal corresponding to heartbeat pulses, alarm means for producing an audible or visual alarm signal, and control means response to said heartbeat pulse component producted by the filter means to inhibit actuation of the alarm means.

2. A monitoring device according to Claim 1 wherein the alarm means is arranged to be actuated in response to a charge stored on a capacitor, and the control means is arranged to respond to said pulse component to discharge the capacitor and thereby inhibit operation of the alarm means.

3. A monitoring device as claimed in Claim 2 wherein said control means is arranged to derive a low-going signal from said pulse component and apply said signal to the capacitor through a rectifier of appropriate polarity to discharge the capacitor through the rectifier during such low-going pulses.

4. A monitoring device as claimed in Claim 3 wherein the capacitor is arranged in a charging circuit with a time constant such that the voltage level on the capacitor rises towards the level required to actuate the alarm over a period corresponding to several heartbeats.

5. A monitoring device as claimed in any one of the preceding claims which is formed as two separate units comprising a detector unit for securing to the body and a remote unit for processing the output of the transducer means which is incorporated in the detector unit.

6. A monitoring device as claimed in Claim 5 wherein the detector unit is adapted to be held in a pocket formed or provided in a close-fitting garment.

7. A monitoring device as claimed in Claim 5 or Claim 6 wherein the detector unit includes a lowpower radio transmitter to transmit a signal to a radio receiver incorporated in the remote unit.

8. A monitoring device as claimed in Claim 7 wherein the detector unit is adapted to interfit with the remote unit, when not in use, so that a battery in the detector unit can be re-charged from the remote unit.

9. A monitoring device as claimed in Claim 8 wherein the detector unit incorporates a switch arranged to switch off said unit when it is fitted to the remote unit for charging.

10. A monitoring device as claimed in Claim 8 wherein the remote unit is arranged to be energised from a mains electricity supply system and incorporates a back-up battery.

11. A monitoring device as claimed in Claim 10 wherein said back-up battery is arranged to be charged from said mains electricity supply system to which the remote unit is connected.

12. A monitoring device as claimed in Claim 1 and substantially as hereinbefore described.

13. Any novel feature or novel combination of features disclosed herein and/or shown in the accompanying drawings.