GB2312309A

GB2312309A - Sleep detection and alarm system

Info

Publication number: GB2312309A
Application number: GB9607969A
Authority: GB
Inventors: Richard Ian Wolman
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-04-17
Filing date: 1996-04-17
Publication date: 1997-10-22
Also published as: GB9607969D0

Abstract

A system for waking an individual upon onset of sleep comprises a wearable device and an alarm, the wearable device comprising a sleep detector 1,2,3 for determining the sleep/wake state of an individual when wearing the device, a signal generator 3 that provides an activating signal for the alarm 4 upon detection of a sleep state by the detector 1,2,3, and manually operable alarm reset means 5. The wearable device preferably comprises the alarm 4. The system may comprise a

Description

SLEEP DETECTION AND ALARM SYSTEM The present invention relates to a system which on detection of the onset of sleep in an individual activates an alarm with the aim of waking the individual. In particular, the invention relates to such a system that comprises a portable device, preferably to be worn on the wrist.

Various ways for the determination of the waking or sleeping state of individuals are available.

Typical ways of determining the onset of sleep include measurements of pulse, respiration and muscle movement and also polysomnographic recording. As the sleeping state is approached, these physiological signs show fundamental changes which may be measured.

It has been found (Mullany DJ et al, Sleep, 1980, 3:82-91) that one particularly successful method of unobtrusively identifying the sleeping state is based on wrist activity. Cole et al (American Sleep Disorders Association and Sleep Research Society, 1992, 15(5), 461469) published an automatic sleep/wake identification method based on this work. Wrist activity is measured and stored as a function of time using a commercially available Mini-Motionlogger Actigraph (motional transducer). This is available from Ambulatory Monitoring Inc, 731 Saw Mill Road, Ardsley, New York, USA. Mini Motionlogger Actigraph is a trade mark. This record of wrist activity is then extracted from the actigraph at a later time by an additional device and analysed using a computer. Optionally, an algorithm essentially averages the measured wrist activity over a set period of time.

Periods of low activity are equated with the sleeping state and periods of high activity with the waking state.

The duration of wrist movements during sleep and sleepiness is substantially greater than during awake, alert periods.

In order to test the accuracy of this method, Cole et al simultaneously made polysomnographic measurements on the same subjects. There is a better than 80% agreement of the assignment of sleeping and waking states between the two methods in most patients, the accuracy being insensitive to small changes in the averaging algorithm.

Some vehicles such as aircraft have sleep detectors.

For example, in one system a camera measures movement, usually-eye movement, to detect the sleeping state. The system may then attempt to wake the subject with an alarm of some form, typically by blowing air on the subject or by playing a recorded message. Various disadvantages are associated with such devices, not least the fact that the subject has a very restricted range of movement if the system is to be effective.

The present inventor has realised the advantages of providing a device comprising a portable, preferably wearable, sleep detector and alarm. A wearer of the device may have complete freedom of movement and should be woken on onset of sleep. The sleep detector may be appropriately calibrated so as to determine onset of sleep, i.e. that a subject is in a sleep state as opposed to awake, at a certain level of sleepiness or drowsiness rather than when the subject is fully asleep.

Thus, according to the present invention there is provided a system for waking an individual upon onset of sleep, the system comprising a sleep detector and a manually resettable alarm. The sleep detector is a component of a portable, preferably wearable device that generally also comprises manually operable reset means for the alarm. A signal generator provides an activating signal for the alarm upon detection of a sleep state by the detector.

The alarm is preferably included in the portable or wearable device but may be separate, provided a suitable activating signal is generated by the signal generator.

For instance, the alarm may be remote from the device, e.g. in a building or vehicle, in which case it may be activated by an optical signal such as infra-red or by a radio signal.

The device is preferably wearable on the wrist, though embodiments may be provided for wearing on any part of the body, for example on the leg or round the neck.

For attachment to the body, the device may comprise a strap or belt and buckle. One advantage of using a wearable device is the lack of restriction on movement of the wearer, particularly if the alarm is included in the wearable device. A further, important advantage may arise from the alarm reset means being included in the wearable device, that is the need for a positive physical movement in order to reset the alarm. For instance, if the device is worn on a wrist of one arm of an individual, operation of the alarm reset will require use of the other arm.

This action is likely to require conscious effort, in turn requiring a certain level of awareness or awakening.

A system according to the present invention has a range of important applications. For example, it may be used by truck drivers, motorists or coach drivers, airline pilots, and so on. Other applications may include workers manning dangerous machinery, possibly at a range of sites or positions where conventional sleep detection apparatus would not be able to keep track of the operatives.

The system may also be used by medical staff or security guards who may cover large areas during their shifts. Security guards often work in isolation where the system would be particularly useful.

The sleep detector may comprise a motion sensor.

The motion sensor may comprise a motional transducer such as an actigraph system for measuring the duration of movements of the wearer. The motion sensor may comprise a device for measuring the frequency of movements of the wearer. The motion sensor may comprise an accelerometer which converts measured acceleration of the sensor into a signal.

The portable or wearable device may comprise a signal processor that may comprise a memory for recording the signal generated by the motion sensor and a computer or computing element for interpreting the measured data in order to determine the sleep/wake state of the wearer.

An averaging algorithm such as the Webster algorithm may be used in the determination of the waking or sleeping state, the algorithm (Webster et al, Sleep (1982) 5: 389399; see also Cole, et al) using measured velocity as a function of time to determine the sleeping or waking state.

A suitable algorithm may use measured acceleration as a function of time to determine the sleeping or waking state.

A digital or an analogue circuit may be employed.

The sleep detector may comprise a device for measuring blood pressure or pulse rate.

Use of a non-invasive mode of determination of the sleep/wake state, which is generally the case in the present invention, allows for various advantages including minimal discomfort to the subject, simplicity of operation and an absence of side-effects. It allows for prolonged use of the system in wide variety of different situations.

Preferably, in the present invention, the alarm emits a sound, for example a buzz, ring, tone, siren or recorded or synthesized message. The alarm may aim to wake the wearer by inducing vibrations in a surface of the device in contact with the skin, or in any other suitable way likely to wake a sleeping or sleepy person.

No existing sleep detection system reliably determines if the subject has been woken by the alarm.

There is a danger therefore that the subject sleeps through the alarm, or sleeps long enough to be in or cause danger and/or be in neglect of his duties.

The system according to the present invention may therefore comprise a second, e.g. remote alarm, that is preferably activated in the event that the first alarm is not switched off by operation of the reset means within an allotted time.

Thus, in further preferred embodiments of the present invention the system comprises a second alarm and a second signal generator that provides an activating signal for the second alarm if the first alarm is not after its activation reset within a pre-determined time.

The pre-determined or allotted time may be variable. The activating signal for the second alarm may be optical or a radio signal, for example.

When such embodiments are employed, the first alarm is activated upon detection of a sleep state in the subject. Should the subject not reset the alarm within a pre-determined time, suggesting that the subject has not been woken by the alarm, the second alarm will be activated. This alarm may be designed to be a further attempt to wake the subject, e.g. by emitting a louder or more piercing sound, or, more preferably, may be remote from the wearer and designed to alert someone else, e.g a manager, supervisor or controller, to the onset of the sleep in the wearer. This may prompt emergency action, for example machinery operated by the subject may be turned off, or other pre-arranged procedure as appropriate.

Embodiments of the present invention will now be described in detail by way of example and not limitation, and with reference to the following figures: Figure 1 is a block diagram of one embodiment of the device.

Figure 2 is a second block diagram of another embodiment of the invention, including a remote alarm and a means of activating said alarm.

All documents mentioned are incorporated herein by reference.

The embodiment of the present invention illustrated in Figure 1 comprises a transducer 1, memory 2, processor 3, alarm 4 and alarm reset 5. Onset of sleep is determined as follows: The transducer 1 is part of a device to be worn on the wrist and detects wrist motion, information about which is then stored in memory 2. The processor 3 processes the stored data in real time and generates a signal that activates the alarm 4 if a sleep state is detected. The device comprising the sleep detector comprises a manual reset button 5, operation of which resets the alarm 4.

The action of resetting the alarm manually, and so having to make some physical motion to stop the alarm, is more effective than just the alarm alone in waking an individual wearing the device.

The embodiment of the present invention illustrated in Figure 2 is a system comprising a second, remote alarm.

Components 1-5 are as in the embodiment illustrated in Figure 1 and described above, but the wrist-worn device further comprises a delay circuit 6 and an emitter 7.

Determination of the wake/sleep state of a wearer is as described above with reference to Figure 1. A signal from the processor 3 is passed to the alarm 4 as before to activate the alarm 4 upon detection of a sleep state in the subject.

In this embodiment, however, the signal from the processor 3 is also sent to an emitter 7 which in turn generates a signal that activates the remote alarm 9 following receipt of the signal by receiver 8. Between the emitter 7 and processor 3 is a delay circuit 6 that delays the signal from the processor 3 from reaching the emitter 7 for a pre-determined length of time, which may be varied according to operating preferences. As previously, the alarm may be reset manually by operation of the reset 5. Resetting the alarm 4 also prevents the signal from the processor 3 from activating the emitter 7.

Provided the alarm 4 is reset before the signal activates the emitter 7, i.e. within the pre-determined time of delay by the delay circuit 6, the second alarm 9 is not activated.

If on the other hand the first alarm 4 is not reset within the pre-determined time, emitter 7 is activated and generates a radio signal. Receipt of the signal by the remote receiver 8 leads to activation of the second alarm 9. This may alert a supervisor or manager to the onset of sleep in the individual wearing the sleep detector, who may for example be operating dangerous machinery. The supervisor or manager may then take appropriate action.

Claims

1. A system for waking an individual upon onset of sleep, the system comprising a wearable device and an alarm, the wearable device comprising a sleep detector for determining the sleep/wake state of an individual when wearing the device, a signal generator that provides an activating signal for the alarm upon detection of a sleep state by the detector, and manually operable alarm reset means.

2. A system according to claim 1 wherein the wearable device comprises the alarm.

3. A system according to claim 1 or claim 2 wherein the sleep detector comprises a motion sensor.

4. A system according to claim 3 wherein the motion sensor comprises an accelerometer.

5. A system according to any of the preceding claims wherein the sleep detector comprises a blood pressure measuring device.

6. A system according to any of the preceding claims wherein the sleep detector comprises a pulse rate measuring device.

7. A system according to any of the preceding claims wherein the alarm emits a sound on activation.

8. A system according to any of the preceding claims wherein the wearable device is for the wrist.

9. A system according to any of the preceding claims comprising a second alarm and a second signal generator that provides an activating signal for the second alarm if the first alarm is not after its activation reset within a pre-determined time.

10. A system according to claim 9 wherein the activating signal for the second alarm is optical.

11. A system according to claim 10 wherein the activating signal for the second alarm is a radio signal.

12. A system substantially as herein described with reference to Figure 1.

13. A system substantially as herein described with reference to Figure 2.