AU654910B2 - Method and apparatus for ambulatory monitoring of wake or sleep status - Google Patents

Description

P/00/011 28/5/91 Regulation 3.2

AUSTALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: METHOD AND APPARATUS FOR AMBULATORY MONITORING OF WAKE OR SLEEP STATUS The following statement is a full description of this invention, including S the best method of performing it known to me S 'The invention relates to a new method for ambulatory monitoring of wake or sleep status, in which the physiological parameters of levator palpebrae superioris (LPS) muscle electromyographic (EMG) activity is detected by using a pair of surface electrodes with a reference electrode and the bodily posture is detected by using a hollow body. The binary coded form of LPS EMG activity and the coded form of bodily posture are stored on a cassette tape for off-line analysis. The invention furthermore relates to an ambulatory apparatus necessary for the practice of this method. The apparatus comprises an EMG activity detection unit, a bodily posture detection unit and a data storage unit. The apparatus permits an ambulatory monitoring of wake or sleep status continuously for a period of 24 to 48 hours, which is comparable in its meaningfulness to the monitoring of cardiac arrythmias based on Holter test.

Sleep disorders have been classified into four main groups: the hypersomnias, ^f insomnias, the sleep-wake schedule disorders, and the parasomnias. The hypersomnia group includes a large number of individual conditions: narcolepsycataplexy syndrome, idiopathic hypeisomnia, the many symptomatic hypersomnias, the recurrent hypersomnias Kleine-Levin syndrome, menstrual hypersomnia, bipolar affective illness), substance-related forms depressants, tolerance or withdrawal from stimulants), and those related to respiratory r -2disorders in sleep especially obstructive and mixed sleep apnea, and nocturnal hypoventilation).

The hypersomnias are of clinical importance for several reasons. The first is their high incidence. Narcolepsy is much more common than previously believed, with current prevalence figures being 40 to 70 per 100,000. It is therefore, about onehalf as common as Parkinson's disease and more common than multiple sclerosis.

The second reason concerns their marked socioeconomic effects. And the third reason is their typical chronicity, and their usual poor response to treatment, which is the main cause of the marked socioeconomic effects.

The usual studies of the sleep-wake features of hypersomniac patients have been performed in sleep laboratories in special clinics, in which a diagnosis can be performed by in-laboratory overnight polysomnography and the Multiple Sleep Latency Test or its variants. Such studies are extremely time-consuming and expensive, requiring three shifts of support staff with attendant overnight work 15 and tie up an entire laboratory room for a prolonged period. As many parameters have to be recorded the performance can only be done by confining the patient.

In addition to the high cost, such confinement has the disadvantage that the patient's sleep is disturbed by strange surroundings. This diminishes the value of such study. So ambulatory sleep-wake monitoring technique has been developed, but the current diagnosis of wake or sleep is still based on the electroencephalographic (EEG) activity, particularly the cha.iges of the frequencies and amplitudes of EEG. Although the ambulatory EEG has already been developed and used in the sleep study, the measurement of EEG activity is still a time-consuming and costly as it needs an expensive equipment, specially trained technologist and highly required for the patients. So for the purpose of clinical -B practice and further reducing the cost of monitoring wake or sleep status a new i method and a related apparatus is developed.

Physiologically when people fall into sleep the eyes close. It has been proved that i Y^ involuntary blink ceases entirely as people fall into sleep. So as early as in 1942 Duke-Elder states that the occurrence of bilateral blink movements may be used as a test for the simulation of sleep" (Nature; 1950:81-82). Therefore, monitoring blinking and bodily posture (upright, supine,lateral and prone postures) can be |i used to diagnose whether the patient is in wake or sleep state on this particular posture and how frequently the patient changes posture during sleep. And the IL wffi waw i :i< -3relationships between the occurrence of sleep and bodily posture can also reveal how easily the patient fall into sleep.

A blink is a temporary closure of both eyes, involving movements of the upper and lower lids. Blinking is a function of all vertebrates living in contact with air and possessing eyelids. In adults bilateral blinking movements occur periodically at regular intervals during all the waking hours as long as the eyes are open. Each individual appears to have a definite rhythm in which blinks occurring at short intervals may somtimes be followed by longer inter-blink periods but for the same individual the distribution of the movements is very constant provided the environmental condition do not vary. The rate of the blinking is influenced by a variety of factors, psychological, pharmacological and environmental. Anxiety increases the rate, inattention reduces it, alcohol at first increases the rate and then, as its depressant effect becomes established, diminishes it.

The functions of the blinking movements are probably threefold. They undoubtedly play an extremely important protective role in moistening the cornea and sweeping it clean. The movements help the drainage of tears. It is possible that they tend to eliminate blurring of images during the actual movements of the eyes. Therefore as long as the eyes are open during waking hours the blinking does not cease.

The LPS is the main skeletal muscle providing the dominent forces that. act on the eye lid. The tonically active LPS raises the eye lid and holds it up. During blink or eye closing the LPS transiently turns off, allowing the upper eyelid fall. Therefore the intermittent activity of LPS directly relates to blink.

Therefore a new method to monitor wake or sleep status is developed as specified in claim 1. Wake or sleep status is monitored through detecting the LPS EMG i activity together with the bodily postures. i There are three types of EMG electrodes, needle electrode, wire electrodes and surface electrodes. The first two are invasive and can only be performed in laboratory by special trained technologist. The surface EMG electrodes are noninvasive and easy to be applied just like to place a small piece of stick tape on the skin. So there is no problem for the patients to perform placing the surface i electrodes themselves. Based cn this method the present invention provides a new method and a new appararus to continuously monitor wake or sleep status, which -4measures the surface LPS EMG activity by placing two surface electrodes just above eyebrow with one reference electrode placed on forehead as specified in claim 2, through measuring the phasic LPS EMG activity during blinking to reflect the wake status. The measurement of the surface LPS EMG activity is much easier to be done than the measurement of EEG activity and the patient even does not feel any uncomfortable at all. So the surface LPS EMG activity can be continuously measured.

The method described has the following two disadvantages comparing with the current EEG method. It measures LPS EMG activity during blinking, which indicates whether the eyes are open or closed. So if the patients close their eyes voluntarily while they are still awake, this method still takes it as sleep. But this problem can be easily solved by just telling the patients "don't do that intentionally". It permits only a relatively rough diagnosis of sleep. It can not provide further information about sleep staging. But it has the advantages that it costs far less to make a portable EMG amplifier than to make a portable EEG amplifier and it is much easier to apply the surface electrodes to measure LPS EMG activity than to apply EEG electrodes.

The surface electrodes placed above eyebrow can pick up two muscles' (occipitofrontalis and LPS EMG activities, occipitofrontalis EEG activity and some noise signals. Relative to EMG activity, the occipitofrontalis EEG signals are too small and can be ignored. Through bandpass filter the noise signals can be totally ruled out. Normally EMG signals mainly come from LPS. Therfore the phasic EMG changes picked up by these two surface electrodes mainly represent the LPS EMG activity.

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I '25 As the LPS EMG activity picked up by the two surface electrodes is generated from a group of muscle fibers and composed of a group of muscle fiber action potential, which is called raw LPS EMG signals. In order to simplify the procedure to seperate the tonic and phasic LPS EMG activity, the raw LPS EMG signals are integrated and 1 further converted into a binary code form by a peak detection unit as specified in claim 3. Therefore, the intermittent LPS EMG activity piked up by these two electrodes occurring during blinking is processed and finally changed into quality square-waved electrical signals. t The blinking and bodily posture are detected synchronous'y as specified in claim 4. By analysing the relationships between posture and blinking, it can reveal in i i: what posture the patient falls into sleep and how frequently the patient changes posture during the sleeping period. This is important for the diagnosis of sleep disorders because it helps to know how easily and how frequently the patient falls into sleep and whether the patient sleeps well.

The apparatus according to the invention for the practice of the method described and claimed is specified in claims 5 to 7. it is a portable appararus which contains means for detecting the LPS EMG activity and means for detecting bodily postures.

The present apparatus consists of an EMG activity detection unit, bodily posture detection unit and a data recording unit. The EMG signal is sensed by two surface electrodes, amplified, bandpass filtered integrated and peak detected. So the LPS EMG activities are converted from quantity data into quality data and then recorded on a cassette tape in a binary coded form. The bodily posture detected through a hollow body device are also recorded on the tape in coded form. The quality data makes it easier to rapidly playback and analysis the data. The recording unit is a small cassette tape recorder.

The means for measuring LPS EMG activity include two disc electrodes (preferable S, silver-silver chloride electrodes which are commei-ially available), which are placed just above eyebrow to sense the LPS EMG activity. The skin is cleaned with alcohol to remove the dead surface layer of the skin to lower the electrical impedance before applying the electrodes. Electrode gel (commercially available) is used to improve the contact between the electrodes and skin. Then the electrodes are fastened to the skin by adhesive rings. The muscle fiber action potential is conducted through skin, electrode gel and the silver-silver chloride disc electrodes, then transmitted through cable wires to the EMG amplifier.

Si 25 The means for detecting the patient's posture contain a hollow body fastened on the patient's upper body by adhesive ring. The hollow body is composed of a hollow decagon in which is a electrically conductive metal ball.There are seven i corners in the decagon. Five of the seven corners represent five body postures, supine, left-sided, right-sided, upright and prone postures. Each corner acts as an opened switch waiting for the coniductive metal ball to connect. The hollow decagon is oriented. For example, in sipine, lying on left or right side, or in upright postures, the ball will come to rest in one of the comers due to gravity. The posture signals originating from the hollow body are analysed by a decoder and also binary coded then recorded on the tape in a coded form.

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h: .i i iii -CI- IIII--Y-YI~-I~ 0 -6- To assist with understanding the invention, the following figures are described:- Figure 1 is a perspective view of a mobile detection and recording apparatus, Figure 2 shows a perspective view of the apparatus in working position on a patient's body, Figure 3 is a block circuit diagram of the detection and recording apparatus.

Figure 1 consists of the actual detection 1 and signal processing and recording 2 unit with a pushbutton switch 3 on the front and the following different pickups: three EMG electrodes 4 and one posture detector 5. The leads runing from the electrodes and posture detector are combined in a single cable 6 which is then connected by a plug 7 to the signal processing and recording unit 2.

Figure 2 shows where the surface LPS muscle electromyographic electrodes 4 and the posture detector 5 are placed.

Two silver-silver chloride disc electrodes 4 (commercially available) are fastened to 1 cm above the middle of eyebrow with one reference electrode 4 fastened on the forehead with adhesive rings. The posture detector 5 is preferably fastened to the upper middle of chest with an adhesive ring in a specific orientation indicated by the instructions printed on its exterior.

Figure 3 shows the signal processing in the signal processing and recording unit 2. The signals picked up by the EMG electrodes are amplified, filtered to get rid of noise by a bandpass filter, integrated and then fed to a peak detection unit to convert the signals into binary coded form. The signals originating from the posture detector are analysed by a decoder and recorded synchronously on a tape together with the coded form of LPS muscle EMG activity.

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Claims (1)

1. 7- 7.- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. Method for the ambulatory monitoring of wake or sleep status, in which, by means of a mobile apparatus, the physiological parameters: Sa) levator palpebrae superioris muscle electromyographic activity and S b) bodily posture of the patient are detected and recorded in coded form on a tape o recorder. covene S 2. Method according to claim 1, o characterized in that, the levator palpebrae superioris muscle electromyographic activity is measured by using two surface electrodes placed above eyebrow with one reference electrode a" o placed or forehead. o n 3. Method according to claims 1 and 2, o o characterized in that, after amplification the levator palpebrae superioris muscle electromyographic o e9 signals are fed to integration and peak detection to converte the signals into binary coded form. 4. Method according to claim 1, characterized in that the signals from the levator palpebrae superioris muscle electromyographic activity sensor and bodily posture sensor are recorded synchronously on a tape in coded form. Mobile apparatus for detection and recording of physiological parameteres of a patient for the practice of the method according to any one of claims 1 to 4 comprising: means for sensing the electromyographic activity of levator palpebrae superioris S.t- muscle by surface electrodes, means for detecting blinking on the basis of levator palpebrae superioris muscle electromyographic activity, means for detecting the bodily posture of the patient, and means for continuously detecting and synchronously recording these two phasiological parameters to the tape in coded form. _I ,sq ro o ro o~o El I DO 0~ OI I D -9- 6. Mobile apparatus according to claim characterized in that the means for the detection of blink include two surface electromyographic electrodes with one reference electrode, which are then connected to the 5. electromyographic amplifier, bandpass filter, integrator and peak detection processing unit. 7. Mobile apparatus according to claim characterized in that the means for detecting the bodily postures contain a hollow body fastened to the upper middle of chest, which is then connected to a decoder to analyse !he posture and to give a coded form signal representing the posture. "YVMtI7-X-/A Sf--- (Name of Applicant) (BLOCK LETTERS) S(Date) (Date) '4- 5 Aki s 0 ~fr i~ :a ti~ ABSTRACT A method and an apparatus are described for the ambulatory monitoring of wake or sleep status, which is based on the physiological parameters of levator palpebrae muscle electromyographic activity and bodily posture. The levator palpebrae muscle electromyographic activity is measured by using two surface electrodes placed above eyebrow. The bodily posture is detected by using a hollow body fastened to the upper part of chest. The processed electromyographic signal and bodily posture signal are recorded on a cassette tape in a coded form for off- line analysis. The ambulatory apparatus comprises an electromyographic activity detection unit, a bodily posture detection unit and a tape recording unit. j ii