CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2019/062313, filed on 14 May 2019, which claims the benefit of European Patent Application No. 18172328.9, filed on 15 May 2018. These applications are hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to the field of medical emergency signaling and user-activated medical alarm systems. In particular, the present invention relates to a wrist-worn medical alert device for conveying an emergency message to a caregiver. The present invention furthermore relates to a corresponding system and method as well as to a corresponding computer program for carrying out said method.

BACKGROUND OF THE INVENTION

Elderly and dependent people are at increased risk regarding medical emergencies and accidents at home. Medical emergencies may arise e.g. when a stroke or heart attack occurs, caused by home accidents, when moving and handling objects, or due slips and falls. In such situations, medical care may be critical. The time elapse from the moment the medical emergency happens to the moment assistance is provided should be minimal, as it may become vital for the individual.

A medical home alarm can refer to an alarm system designed to signal the presence of a hazard requiring urgent attention and to summon assistance such as emergency medical personnel, family members or neighbors. Typical systems have a wireless pendant or transmitter that can be activated by the user in case of emergency. When the medical alarm is activated, the signal can be transmitted to an alarm monitoring company's central station, other emergency agency or other programmed contact. Medical personnel or other assistance can then be dispatched to the site where the alarm was activated. There are different technologies which are able to alert medical assistance.

Firstly, there are so-called health buttons or emergency buttons, wherein a user may manually set off a call for help by pressing an alert button on his personal device. Medical alarm devices may be implemented in different forms such as, for example, a pendant worn around the neck, a small device worn on the belt, or a wristband. Moreover, a user may simply use his smartphone to call for assistance.

However, depending on the severity of the patient's condition, the patient may not be able to properly operate the medical alarm device. For example, the patient may not be able to reach over to activate a wrist-worn alarm button with the other hand.

Automatic monitoring systems, such as fall detection systems, have proven very helpful in such situations.

Further, there are passive systems, similar to a dead-man's switch, which may trigger an alarm if no activity has been detected for a predetermined period of time. However, a drawback of this solution is that a significant amount of time may elapse until assistance can be provided. However, in particular for stroke patients, the time elapsed from the moment the medical emergency happens to the moment assistance is provided is crucial.

In the different application scenario of patient monitoring in hospitals, automatic monitoring systems are widely used. An alarm may e.g. be triggered if a vital sign parameter such as a blood oxygen saturation value falls below a predetermined threshold. However, when using such monitoring systems outside of the well-controlled environment of and intensive care unit (ICU) or hospital, there is a risk of triggering a large number of false alarms. As a solution, WO 2013/071014, paragraph [0012], discloses a body worn patient monitor comprising an alarm system that takes a patient's motion into consideration when processing vital sign measurements. Since motion typically disrupts the RED/IR PPG waveforms for blood oxygen saturation (SpO2) measurement, it is suggested to exclude certain noise-corrupted artifacts from the SpO2 calculations. Hence, the risk of false alarms can be reduced. Moreover, the motion sensor can be used as a fall detector regardless of the SpO2 values of the patient.

However, such systems may only cover a limited number of emergency situations. An alarm may not be triggered when it is needed the most.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved medical alert device. In particular, it would be desirable to provide a medical alert device that can be more easily operated by a user. In particular, it would be desirable to facilitate the dispatch of an alert message in a wider range of emergency situations.

In a first aspect of the present disclosure a wrist-worn medical alert device for conveying an emergency message to a caregiver is presented, wherein the medical alert device is adapted to be worn at a wrist of a subject, the device comprising:a PPG (photoplethysmography) unit adapted to acquire a first PPG signal at first wavelength (λ1) and a second PPG signal at second wavelength (λ2) over time at the wrist of the subject;a processing unit adapted to receive the first and second PPG signals and to determine a finger movement of one or more fingers of the subject based on the first and second PPG signals; anda communication unit adapted to transmit, based on the determined finger movement, an emergency message to (a communication apparatus of) the caregiver.

In a further aspect of the present disclosure a medical alert system for conveying an emergency message to a caregiver is presented, the system comprising the aforementioned wrist-worn medical alert device; and a base station configured to forward an emergency message from the wrist-worn medical alert device to a caregiver.

In another aspect of the present disclosure, a medical alert method for conveying an emergency message to a caregiver is presented, the method comprising the steps of:receiving first and second PPG signals, said first PPG signal being acquired at a first wavelength (λ1) and said second PPG signal being acquired at a second wavelength (λ2) over time at a wrist of a subject;determining a finger movement of one or more fingers of the subject based on the first and second PPG signals; andtransmitting, based on the determined finger movement, an emergency message to (a communication apparatus) of the caregiver.

In yet further aspects of the present invention, there is provided a corresponding a computer program which comprises program code means for causing a computer to perform the steps of the method disclosed herein when said computer program is carried out on a computer as well as a non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method disclosed herein to be performed. It shall be understood that receiving first and second PPG signals in this context can refer to receiving data indicative of first and second PPG signals acquired at a wrist of the subject. Correspondingly, transmitting an emergency message to the caregiver can refer to dispatching or sending data indicative of an emergency message to the caregiver. Reference can be made to a computer-based signal processing method.

Preferred embodiments of the invention are defined in the dependent claims. It shall be understood that the claimed method, system, computer program and medium can have similar and/or identical preferred embodiments as the claimed system, in particular as defined in the dependent claims and as disclosed herein.

Photoplethysmography (PPG) is a known technique for determining vital sign parameters such as the heart rate or blood oxygen saturation of a subject. In intensive care units (ICUs), it is known to automatically issue an alarm if a vital sign parameter does not fall within a predetermined healthy range. For example, an alert may be issued if the blood oxygen saturation drops below a predetermined threshold.

The present invention is based on the idea that a medical emergency condition is not necessarily immediately reflected by a vital sign parameter. Hence, a vital sign-based alert system may only cover a limited number of emergency situations. Nonetheless, wrist-worn devices for vital signs monitoring are becoming increasingly popular for continuous monitoring of vital signs for fitness, leisure and health applications. Motion is usually considered an artifact in PPG measurements. For example, a movement of fingers may substantially distort acquired PPG signals. Therefore, it is usually an object to suppress any motion and corresponding signal portions are usually disregarded to minimize the occurrence of false alarms based on SpO2 measurements.

On the other hand, a convention health button or emergency button does not rely on vital signs measurements. However, such a health button requires that the user is still in a position to reach and activate the health button in order to set off an alarm.

The inventor recognized that a wrist-worn medical alert can be provided wherein an emergency message is generated based on a finger movement of one or more fingers that is determined from PPG measurements at a first and at a second wavelength. The first wavelength and the second wavelength can be different, for example, red and green or red and infrared can be used. Hence, instead of considering a motion signal as an artifact and disregarding the respective signal portions, it is suggested to actually use said finger movement to trigger a user-activated medical alert.

During an emergency some body parts might have become immobilized, such as one or both upper limbs, and operating a conventional patient alert device may be impossible. A conventional health button or emergency button does not rely on vital signs measurements. However, such a health button requires that the user is still in a position to reach the health button in order to set off an alarm and does not have problems operating the device e.g. due to dizziness. The proposed solution overcomes such drawbacks since moving the fingers requires minimal effort and can be done in any body position and without being consciously aware of the device itself.

Often, a wrist-worn device for continuous monitoring of vital signs may be available anyway. An advantage of the proposed solution can be that the functionality of existing PPG based vital sign monitoring devices may be expanded at low cost. For example, a wrist-worn vital sign monitor may already comprise a PPG sensor and a communication interface. A wrist-worn monitoring device may be adapted to automatically raise an alert if a vital sign is not within a predetermined range, e.g. triggered by a vital sign indicative of the cardiovascular status. Having the possibility to manually trigger an alert may further improve the robustness of detect an event which needs medical attention.

A synergistic effect may be reached in that the PPG sensor may be used both for a vital-sign based medical alert as well as for a user-activated medical alert. A wrist-worn monitoring device may automatically raise an alert e.g. triggered by the cardiovascular status. Having the possibility to raise actively/manually an alert by moving the fingers, may increase the robustness to detect an event which needs medical attention. Hence, in addition or in the alternative to monitoring a cardiovascular state, it is suggested to use PPG for a user-activated alert system in case of emergency. The proposed solution of raising an alert may be lifesaving when other methods are not accessible, unavailable or out of reach.

According to an aspect of the present disclosure, a medical alarm or emergency message may thus be triggered by a recognized finger movement or gesture rather than a vital sign parameter. The first and second PPG signals may undergo pattern recognition as will be described further below.

In order to detect and identify finger movements in PPG signals, the technologies disclosed in WO2015/121100 A1 for the different application scenario of an input device for controlling a computer may advantageously be used. The disclosure of this earlier application of the same applicant is incorporated herein by reference in its entirety. In the present case, a much simpler PPG device may be used. In particular, in contrast to the aforementioned reference the PPG unit may not be adapted to generate light detection signals acquired at spatially different locations on the wrist (with different PPG sensors). In contrast to the device described in WO2015/121100 A1, the device according to the present disclosure may not be adapted to distinguish between different fingers. In the context of the present disclosure, light traveling through different regions of the tissue can be understood as using different wavelengths at the same location traveling through different layers of the tissue.

In an embodiment, the wrist-worn medical alert device can be adapted to establish an audio and/or video connection to a communication apparatus of the caregiver. Thereby, the caregiver may communicate with the subject to determine if and what kind of further assistance is required.

The processing unit can comprise a pattern recognition unit adapted to recognize a finger movement pattern of one or more fingers of the subject based on the first and second PPG signals. The communication unit can be adapted to transmit, based on the recognized finger movement pattern, an emergency message to the caregiver. For example, by moving one or more fingers in a certain rhythmic pattern, e.g. moving one finger up and down periodically, the PPG signals are disturbed and this disturbance can be extract as a pattern from the PPG signals. Depending on the recognized pattern, an alert may be raised. Examples of alert signals may be an alarm sound and/or a message delivered to the caregiver e.g. via the internet or a smart phone. A pattern may be determined by comparison with a predetermined waveform or spectrum.

The communication unit can be adapted to establish a connection to a first caregiver based on a first determined pattern; and to establish a connection to a second, different caregiver based on a second determined pattern. For example, if the subject does not require urgent assistance, he may choose a first finger movement pattern to establish a connection to a family member or neighbor. However, in an urgent medical case, he may choose a second finger movement pattern to establish a connection to a doctor. Hence, the pattern recognition unit may be adapted to recognize several different patterns.

In addition, or in the alternative, the communication unit can be adapted to transmit a first message based on a first determined pattern; and to transmit a second message based on a second determined pattern. In this way the user may convey different messages depending on the type of pattern generated with the finger movements. For example, different emergency messages or different severity levels may be indicated. Moreover, different messages may also be transmitted during communication with a caregiver. For example, the subject may not be able to speak but may transmit different messages such as yes/no or use messages such as Morse code for communication. For example, when an emergency message has been received by a caregiver a communication link may be established between the user and the caregiver, e.g. using audio/video. In case the user is not able to speak, the method can be used to communicate by replying to questions with fingers movements in patterns corresponding to ‘yes’ and ‘no’.

In an embodiment, the processing unit can be adapted to determine (in particular based on the first and/or second PPG signal) a vital sign parameter of the subject and to adapt a threshold for determining the finger movement (or a threshold for pattern recognition) based on the determined vital sign parameter. An advantage of this embodiment is that an adaptive determination of finger movements or adaptive pattern recognition can be provided. For example, an emergency situation may correlate with arousal of the subject. Hence, there is a higher probability that the subject intends to issue emergency message if the subject the vital sign indicates a poor health state or if arousal of the subject is detected. A decision threshold may thus be lowered to more quickly respond to a finger movement in case of an emergency situation. An advantage can be that false alarms caused by finger movements can be reduced. This may complement the notion above to increase robustness by manually triggering an alert if the vital-sign based medical alert fails

In an embodiment, the wrist-worn medical alert device can further comprise a motion sensor, such as e.g. an accelerometer or gyroscope, adapted to detect a motion of the subject, wherein the wrist-worn medical alert device is adapted not to generate an emergency message if the detected movement exceeds a predetermined threshold. An advantage of this embodiment is that false alarms can be suppressed. It is thus possible to further increase the accuracy. For example, only if no motion is determined or motion below threshold is determined by the accelerometer, an alert is issued. Moreover, the motion sensor may serve to avoid false alarms, i.e. to rule out motion components in the PPG signal stemming from movements other than finger movements.

In an embodiment, the wrist-worn medical alert device may further comprise a posture sensor adapted to determine a posture of the subject, wherein the wrist-worn medical alert device is adapted to adapt decision threshold for determining the finger movement and/or pattern recognition and/or to adapt a message content of the emergency message based on the determined posture. An advantage of this embodiment is that more meaningful alarms may be provided. For example, false alarms may be reduced since a standing subject is less likely to need medical assistance than a subject lying on the floor.

In an embodiment, the wrist-worn medical alert device can be operable in a learning mode, in which the device is adapted to learn patterns and corresponding emergency messages, and in a normal operation mode, in which the device is adapted to generate the emergency message corresponding to the learned patterns. An advantage of this embodiment is that the finger movement patterns can be adapted to the capabilities of the user. For example, a partially disabled subject may wish to perform different patterns than other subjects.

In an embodiment, the device wrist-worn medical alert device can be adapted to recognize at least one default pattern and to transmit a default emergency message to a communication apparatus of a caregiver upon determining the default pattern. An advantage of this embodiment is that the device can be shared or temporally assigned, e.g. to different patients during recovery.

In an embodiment, the processing unit can be adapted to monitor a ratio of the first and second PPG signals and to determine a finger movement of one or more fingers of the subject if the ratio changes by more than a predetermined threshold. For example, the processing unit may be adapted to analyze the amplitudes of red and green PPG signals acquired at red and green wavelengths to determine if an alert is to be issued.

In a further refinement, the first PPG signal is indicative of a measurement using red light and wherein the second PPG signal is indicative of a measurement using green light; and the processing unit can be adapted to determine a finger movement if an amplitude of the first (red) PPG signal is larger than an amplitude of the second (green) PPG signal. The red PPG signal has the property that during motion the signal amplitude is larger than the amplitude of the green signal, and when there is no motion, the amplitude of the red signal is smaller than the amplitude of the green signal (which may only contain the pulse component stemming from the heart contractions). Using this property of the signals, motion components triggered by finger movements can be detected.

Referring to the medical alert system, the base station can be configured to forward an emergency message from the wrist-worn medical alert device to a caregiver. An advantage of this embodiment is that the base station may serve as a relay. Thereby, the requirements and cost of the wrist-worn device in terms of one or more of cost, compatibility with transmission standards and power consumption may be reduced.

