GB2431998A

GB2431998A - Motion alarm for patient's mattress able to detect epileptic seizure

Info

Publication number: GB2431998A
Application number: GB0522363A
Authority: GB
Inventors: Michael John Dines
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-11-02
Filing date: 2005-11-02
Publication date: 2007-05-09
Anticipated expiration: 2025-11-02
Also published as: GB0522363D0; GB2431998B

Abstract

A detector device is adapted to register movements of a person located on a bed or the like, such as may be caused by an epileptic seizure. An aligned pair of plates (2) are spaced apart beneath a mattress or the like. At least one plate (2) is resiliently deformable. A sensor (4, 5) is disposed between the plates to detect changes in load exerted thereon. Transducer 4 may comprise a PVDF piezoelectric device. Motion Alarm may also be used to detect cessation of breathing or if a patient leaves their bed. The sensor data may be electronically recorded and the time of seizure events may be logged.

Description

EPILEPTIC SEIZURE ALARM

The patent invention relates to a system to monitor a sleeping person. More particularly, but not exclusively it relates to a monitoring and alarm system to check a sleeping person for epileptic seizures and the like.

Many medical conditions may lead to particular problems, should acute episodes occur while a sufferer is asleep. For example, epileptic seizures, and the resulting muscle spasms, may result in physical injury, and there is a rare syndrome known as Sudden Unexpected Death in Epilepsy. Thus, rapid intervention may be required. However, it is impractical for sleepers to be watched over continuously by carers, even in a hospital or care home, so automatic monitoring arrangements are required.

Alarms to detect epileptic seizures experienced by a sleeping person have been known for a number of years. One form of alarm uses a tilt switch housed in an enclosure to provide an electrical trigger to operate an alarm when the person moves in bed. This type of alarm does provide a primitive method to alert of a seizure but is prone to many false alarms, since normal movements during sleep will often cause the alarm to operate. Also, if the user experiences only mild seizures there may not be enough movement to cause the tilt switch to change position to operate the alarm.

Another type of alarm uses a microphone enclosed in a housing to detect the thumping sounds created on a mattress by limb movement when an epilepsy sufferer experiences a seizure. This method, although more reliable than a tilt switch, is still dependent on there being a moderate level of movement to enable the seizure to be detected reliably.

If for example, a person does not experience significant convulsions during a seizure there is little to no chance of the seizure being detected. Certain types of seizure may for example result in only facial twitching or very slight limb movements. These seizures would also go undetected. The alarm is also restricted by the person's weight. A baby or child under three years of age will not have enough body weight to produce enough detectable movement, and larger children and adults with low body weights may not produce accurate detection. In addition, current alarms do not allow seizure events to be recorded or stored electronically.

It is hence an object of the present invention to provide a reliable means of detecting when a person with epilepsy, even a small child or baby, is experiencing a seizure when in bed, based on a minimal amount of movement and with a high degree of accuracy. It is also an object of the invention to detect cessation of breathing; to detect a person leaving their bed; and to be able to provide a record by electronically stored or transmitted means of data relating to a person's seizure activity. A further object of the invention is to provide a means of remote patient care in which generated alarm signals are used to operate automatically telephone communication equipment or the like to alert emergency services or care givers that a person requires help.

According to a first aspect of the present invention, there is provided a detector device adapted to register movements of a person located on a bed or the like, comprising an aligned pair of plate means spaced apart each from the other with at least one said plate means being resiliently deformable, and sensor means so disposed between said plate means as to detect changes in a load exerted thereon.

Preferably, each said plate means is resiliently deformable.

Advantageously, the plate means are connected by spacer means located adjacent a respective margin of each plate means, optionally adjacent each corner of polygonal plate means.

The plate means may then bow resiliently together under compressive loads.

The sensor means may be disposed generally centrally of the plate means.

The sensor means is preferably provided with means, for example electrical wiring means, to transmit signals indicating detected changes in loading to signal processing means located remotely from the detector device.

Preferably, the sensor means comprises a piezoelectric element.

The piezoelectric element may comprise a flexible piezocable, optionally containing a flexible piezo material such as polyvinylidene fluoride (PVDF).

Alternatively, the sensor means may comprises a spacer body extending part-way between the plate means in an unloaded condition of the detector device.

The piezoelectric element may be mounted to a first plate means, with the spacer body extending from the piezoelectric element towards the second plate means.

Alternatively, the piezoelectric element may be mounted to a first plate means, with the spacer body extending from the second plate means towards the piezoelectric element.

The spacer body may be so dimensioned that under an anticipated load on the detector device it bridges a gap between the plate means.

Alternatively or additionally, the sensor means may comprise a pair of electrical contact means, one mounted to each of the plate means.

The detector device is preferably adapted to be disposed extending generally horizontally beneath a recumbent person.

Advantageously, the detector device is disposable beneath a mattress or the like on which a person will lie, for example between a mattress and a bed base.

The detector device may be less than twenty millimetres thick overall.

The detector device may be at least two hundred millimetres across, optionally measuring three hundred millimetres or more in each horizontal, in use, direction.

Preferably, the sensor device is so sufficiently sensitive as to detect changes in load on the plate means resulting from breathing.

According to a second aspect of the present invention, there is provided a monitoring apparatus adapted to monitor a condition of a person lying on a bed or the like, comprising a detector device as described in the first aspect above.

Preferably, the monitoring apparatus comprises signal processing means.

Advantageously, the monitoring apparatus comprises alarm means.

Said alarm means may comprise audible and/or visual alarm means.

The monitoring apparatus may comprise means to alert persons, such as care providers or emergency services, located remotely from the detector device.

Said alerting means may comprise wireless communication means.

Said alerting means may comprise a public telecommunications network.

Said alerting means may comprise communication means dedicated solely thereto.

Preferably, the monitoring apparatus is provided with data recording means.

Advantageously, the data recording means is adapted to transmit recorded data to persons, such as care providers, located remotely from the detector device.

Preferably, the detector device is linked to a remainder of the monitoring apparatus by electrical or optical cable means.

Alternatively or additionally, the detector device may be linked to a remainder of the monitoring device by wireless communication means.

The remainder of the monitoring apparatus may then be located remotely from the detector device.

Preferably, the signal processing means is adapted to establish a reference movement level, for example comprising normal breathing movements.

The signal processing unit may then produce an alarm indication in response to a deviation from said reference movement level.

Advantageously, the signal processing unit is adapted to produce a first said alarm indication in response to an onset of said deviation and a second said alarm indication in response to a prolonged period of said deviation.

A duration of said prolonged period may be selectably adjustable.

Said first alarm indication may be adapted not to wake the person monitored. -7..

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a schematic perspective view of a bed sensor unit embodying the present invention; Figure 2 is a schematic scrap elevation of a central portion of the bed sensor unit shown in Figure 1; and Figure 3 is a flow chart of a monitoring and alarm system embodying the present invention and incorporating the bed sensor unit shown in Figure 1.

Referring now to the figures and to Figure I and 2 in particular, a bed sensor unit 1 comprises two identical rectangular sheets 2 of a substantially rigid, slightly resiliently flexible plastics material, each measuring approximately 450 millimetres by 300 millimetres and being approximately three millimetres thick. The sheets 2 are aligned, each with the other, and are spaced approximately five millimetres apart by four spacer bodies 3, one located adjacent each corner.

A piezoelectric element 4 is mounted to a surface of a first rectangular sheet 2, substantially centrally thereot facing the second sheet 2. A small cylindrical contact element 5 is mounted to the piezoelectric element 4. Here, the contact element is between five and ten millimetres in diameter, and is so dimensioned that, when no load is exerted on the sensor unit 1, there is a gap 6 between opposing faces of the contact element 5 and the second sheet 2 of between one and three millimetres. This allows central portions of the rectangular sheets 2 to bow slightly together when the sensor unit I is under load. The contact element 5 is held in place with a suitable adhesive. An electrical cable 7 extends from the piezoelectric element 4 to a signal processor (see Figure 3) so as to pass thereto electrical signals that are produced when the piezoelectric element 4 has varying loads imposed thereon.

In use, the bed sensor unit I is positioned between a mattress and a base of a user's bed.

Once the user is lying in bed, the gap 6 will lessen and may even disappear, and the piezoelectric element 4 will then be able to react to changes in the load exerted thereon, e.g. as the user moves his or her body.

A signal processor unit for the monitoring and alarm system would conveniently be located adjacent to the user's bed, where it would be visible to the user and/or to care givers. The signal processor unit is mains powered with battery backup, and is provided with a secure on/off switch so that it may not be switched off accidentally. It should be switched on whenever the user is lying on the bed.

The user's movements, even minute movements including chest movements caused by breathing, result in changes in pressure on the plastic sheets 2 of the sensor unit 1.

There are two possible mechanisms by which these bodily movements could be registered.

The small amplitude movements would be transferred to the upper sheet 2 which might make or break contact with the contact element 5 secured to the piezoelectric element 4, resulting in an electrical current being generated by the piezoelectric element 4. Alternatively, if the upper sheet 2 is already so sufficiently bowed as to make contact continuously with the contact element 5, variations in load imposed on the upper sheet 2 would be transmitted through the contact element 5 to the piezoelectric element 4. When the load thereon varies, the piezoelectric element 4 would produce an electrical current. In either case, the electrical currents would be passed down the cable 7 to a remainder of a monitoring and alarm system (represented in Figure 3).

In the monitoring and alarm system, the small electrical current from the sensor unit 1 is fed to a signal amplifier 8 to increase the signal to a usable level. From the amplifier 8, the signal is fed into a pulse generator circuit 9 that is used to generate clock pulses with a mark space ratio dependent on the degree of movement applied to the sensor unit 1. Normal breathing would therefore produce a regular series of clock pulses. The regular breathing pattern, after a brief timed interval, is processed by an encoder/decoder 10 which activates the monitor system and may also produce an output signal for a normal time clock to be used to record and store the time and date. An LCD or other visual means could be used to confirm that the monitor system is ready for use.

Should a person suffering from epilepsy experience a seizure on a bed monitored by the system described, the dramatic change in movement would result in a much faster and continuous stream of clock pulses being generated by the pulse generator 9. The encoder/decoder 10 identifies such increased clock pulse rates and causes a timer to commence counting while producing a preliminary alarm output via an instant alarm circuit 11 linked to a warning device 12. The preliminary alarm signals could be an audible beep andlor a flashing visual warning enclosed within the signal processor unit to warn nearby caregivers such as a nurse in a hospital ward, but which would not disturb the person being monitored. Alternatively or additionally, it could be transmitted to a remote location. Since epileptic seizures can vary in length, this feature of the invention is set up to offer very quick detection of unusual body movement. The timer, still running as part of a delayed alarm circuit 17, would reach a full alarm condition if the increased speed pulses were still present -10 -when a preselected delay period had elapsed (the delay period could be adjusted beforehand to suit a particular person's medical history). An alarm signal would then be fed into an alarm output control circuit 13. The alarm output control circuit 13 is provided with external connections to devices to be used to generate an alarm. These could comprise alarm devices 14 hard-wired to the system and/or a communications port 15 into which a selected alarm or communications system could be plugged. For example, a telephone auto dialler connected to port 15 could be used to send an alarm message to a remote monitoring system, to a pager, or to emergency services. A radio transmitter could be plugged in to the port 15 so that it may signal a receiver of a wireless alarm system. Another option is a hard-wired switching contact that could be used to trigger a conventional nurse call system.

The monitoring and alarm system is also provided with an event recorder 16, allowing a full record of both severe and transient seizures to be retained and studied later. An increasing number of transient seizures, each insufficient to result in a full alarm condition, might, for example, indicate to a carer that a severe seizure is increasingly likely. The event recorder 16 may be readable locally aridlor may transmit logged data remotely via the communications port 15.

Because the sensor unit I initially detects breathing movements, the monitoring and alarm system could be programmed to generate a warning/alarm instantly, or after a timed period, to warn caregivers if a person were to stop breathing. Also, if the person were to leave their bed, the drop in load could be used to generate an instant alarm signal which would be sent to care givers to warn of a patient walking around, who might potentially be at risk from falling.

This method of detecting a seizure is believed to be far more reliable than current methods as described above because it continually monitors the movement of the user and will respond to irregular movement patterns very quickly with a higher degree of control. This type of sensor could be used with young children, babies and adults, the only amplification required being of the signal from the piezoelectric element which would therefore be a standard setting rather than needing careful adjustment. It would not require any complicated setting-up procedures to be performed by the user or caregivers, nor would it be affected by different bed types. The sensor would operate on virtually any bed, as the slightest change in pressure on the two plastics sheets 2 would produce a recordable electrical signal, even with movements attenuated through thick mattresses, for example.

The monitoring and alarm system of the present invention has several advantages over existing systems. It provides a means of detecting minute movements from a person lying on a bed, including chest movements caused by breathing. It will be able to record electronically seizure occurrences by date and time. It will be able to operate an alarm in response to cessation of breathing, and it will be able to produce an alarm if a person leaves their bed.

It is believed that the same approach may be useable to produce monitors for baby movement and breathing, so as to monitor for SIDS (Sudden Infant Death Syndrome) or the like.

Claims

CLAIMS

1. A detector device to register movements of a person, located on a bed comprising an aligned pair of plate means spaced apart each from the other, one being resiliently deformable, and sensor means so disposed between said plate means as to detect changes in a load exerted thereon.

2. A device as claimed in claim 1, wherein each said plate means is resiliently deform ahi e.

3. A device as claimed in either claim I or claim 2, wherein the plate means are connected by spacer means located adjacent respective margins of each plate means, optionally adjacent each corner of polygonal plate means.

4. A device as claimed in any one of the preceding claims, wherein the sensor means is provided with means to transmit signals indicating detected changes in loading to signal processing means remote from the detector device.

5. A device as claimed in any one of the preceding claims, wherein the sensor means comprises a piezoelectric element, such as a flexible piezocable.

6. A device as claimed in claim 5, wherein the piezoelectric element containing a flexible piezo material such as polyvinylidene fluoride (PVDF).

7. A device as claimed in any one of claims I to 4, wherein the sensor means comprises a spacer body extending part-way between the plate means when in their unloaded condition.

8. A device as claimed in claim 7, wherein the piezoelectric element is mounted to a first plate means, with the spacer body extending from the piezoelectric element towards the second plate means.

9. A device as claimed in claim 7, wherein the piezoelectric element is mounted to a first plate means, with the spacer body extending from the second plate means towards the piezoelectric element.

10. A device as claimed in any one of claims 1 to 4, wherein the sensor means comprises a pair of electrical contact means, one mounted to each of the plate means.

11. A device as claimed in any one of the preceding claims, which is adapted to be disposable beneath a mattress or the like on which a person will lie, for example between a mattress and a bed base.

12. A detector device to register movement of a person substantially as described herein with reRrence to the Figures of the accompanying drawings.

13. A monitoring apparatus adapted to monitor a condition of a person lying on a bed comprising a detector device as claimed in any one of the preceding claims.

14. An apparatus as claimed in claim 13, further comprising audible and/or visual alarm means.

15. An apparatus as claimed in either claim 13 or claim 14, wherein the monitoring apparatus is provided with data recording means, which is adapted to transmit recorded data to persons, such as care providers, located remotely from the detector device.

16. An apparatus as claimed in any one of claims 13 to 15. further comprising a signal processing unit adapted to produce a first alarm indication in response to an onset of a deviation from a presetable norm, and a second alarm indication in response to a prolonged period of said deviation.