Patent Description:
Sleep diagnosis is a medical field wherein a patient's sleep is monitored during a certain time, e.g. one or more nights. Based on the monitoring, different sleep events may be identified such as for example apnoeic events, snoring or limb movements.

Sleep events may be determined by a polysomnography (PSG) during which different body functions are monitored such as the brain by electroencephalography (EEG), the eye movements by electrooculography (EOG), the muscle activity or skeletal muscle activation by electromyography (EMG), heart rhythm by electrocardiography (ECG), and respiratory airflow. Despite it being considered as the gold standard, this technique has several drawbacks. First, the test itself may require hospitalization or set-up of the test in the home environment by a healthcare professional. Second, the interpretation of the test is not fully automated, requiring a sleep technician to manually analyse the recorded signals thereby introducing inter-scorer variation and limiting the diagnostic accuracy. Third, the test may interfere with the person's sleep due to the complex wiring and overall overhead thereby influencing critical clinical parameters such as supine sleep time, sleep onset, arousals during sleep, and so forth. Forth, sleeping disorders such as sleep apnoea are known to have a high inter-night variability, and the current diagnostic systems are not suited for a multi-night study due the clinical shortcomings, lack of convenience, and high cost per examination.

<CIT> discloses a solution that monitors changes in the peripheral arterial tone for detecting a change in the physiological condition of a patient, e.g. an apnoeic event. In <CIT>, the arterial tone is defined as the degree of "active tension" which the smooth muscle fibres surrounding the arteries impart. When activated (usually by sympathetic nerve endings or by blood borne or locally elaborated mediators), these fibres contract and in so doing reduce the calibre of the arteries. When the degree of active tension is high, this results in a state of vasoconstriction and conversely, when the degree of active tension is low vasodilation occurs. To this end, <CIT> further discloses an apparatus for detecting such a change in the physiological condition of a patient comprising at least i) a probe to be applied to the distal end of the digit of the patient adapted to sense the peripheral arterial tone of the digit ; and ii) a processor adapted to receive signals from the probe and to provide an output indicating changes in the peripheral arterial tone of the digit, thereby indicating a physiological state or medical condition of the patient. The probe further comprises a membrane for applying a static pressure field around the distal end of the digit of the patient, including the extreme digit tip of the distal end which static pressure field is sufficient to (a) substantially prevent venous pooling in said distal end, (b) substantially prevent uncontrolled venous backflow at said distal end, and (c) partially unload the wall tension of, but not to occlude, the arteries in said distal end when the digit is at heart level or below.

A disadvantage of the above solution is that the apparatus has many components, making it, although portable, still cumbersome to wear and expensive. Moreover, it is impractical due to the need for a probe to apply a static pressure field around the distal end of the digit of the patient for avoiding venous blood pooling. During use, the apparatus may therefore hinder the person and affect sleep quality or even sleep posture. <CIT> discloses a system to detect sleep events based on an optical sensor. The system comprises wireless communication means and determines sympathetic arousals from a peripheral arterial tone signal. <CIT> discloses a system to determine a sleep condition from the envelope of a pulse wave. Other relevant prior art is provided in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>.

It is an object of the present invention to alleviate the above identified problems and to provide a solution for diagnosing sleep by the peripheral arterial tone that is easy to use, does not hinder the patient, and is cheap.

This object is achieved, according to a first aspect of the invention, by a system for diagnosing sleep comprising an apparatus configured to be attached to a patient; the apparatus comprising i) an optical sensor configured to measure a blood volume pulse of the patient; and ii) a wireless communication interface configured to wirelessly transmit the measured blood volume pulse. The system further comprises means for performing i) obtaining the wirelessly transmitted measured blood volume pulse; ii) deriving from the blood volume pulse the peripheral arterial tone; and iii) determining occurrences of sleep events from changes in the peripheral arterial tone.

The blood volume pulse is the output signal of the optical sensor and is characterized by the amount of light that is reflected or absorbed by a tissue. The apparatus does not perform any processing on the blood volume pulse but transmits it wirelessly for further processing by the remote means. In other words, the peripheral arterial tone nor the derived sleep events are determined by the apparatus but by the remote means. The wireless communication interface is preferably a low power communication interface, e.g. a Bluetooth Low Energy, BLE, wireless interface.

This way, the number of components in the apparatus are limited such that it can be made small, portable and does not interfere with the patient during the sleep diagnosis. As the actual processing of the blood volume pulse is performed remotely, the apparatus is very energy efficient. Therefore, the apparatus may be used for several nights in a row without recharging or swapping batteries. Furthermore, smaller batteries such as button cells may be used to further miniaturize the apparatus. The miniaturisation of the apparatus further allows for a simultaneous recording of sleep events and the provision of therapy, such as when it is incorporated into a positional therapy or mandibular advanced device, both being devices which may be used to treat sleep disordered breathing.

According to an embodiment, the apparatus is configured to be attached to the skin of the patient.

The apparatus may further comprise an adhesive for attaching the apparatus to the skin of the patient. Due to the lightweight and small construction, the apparatus can just stick to the skin without further means than the adhesive. There is thus no need for further straps or for further wiring to other components.

The apparatus may further be configured to be attached to at least one of the group consisting of a nostril, an ear, a forehead, a finger, inside a mouth, and a toe. Again, due to small size, the apparatus may be easily attached onto any of these locations without further disturbing the patient's sleep. The apparatus is thus not limited to be attached to a finger but may be used in locations which allows for a better signal reception due to the proximity of vascular beds causing the measurements site to be well perfused such as at the nostril, the ear or even inside the mouth, e.g. onto the gum or the cheek.

According to a preferred embodiment, the peripheral arterial tone is further determined by calculating an envelope of the blood volume pulse. In other words, the peripheral arterial tone is approximated by taking the envelope of the blood volume pulse. Experiments have shown that this approximation may be used for derivation of the various sleep events disclosed herein, either from the blood volume pules measurements alone or in combination with other physiological measurements.

A sleep event may for example comprise at least one of the group consisting of sleep disordered breathing events, periods of intense snoring, limb movements, cortical arousals, autonomic arousals, periods of bruxism, hypnic jerks, tossing events, and turning events.

Preferably, the optical sensor is a reflectance based optical sensor comprising a light emitter and a light sensor. Such a sensor is configured to measure the light reflected from the tissue. As both the light emitter and receptor are located on the same side of the tissue, the apparatus may again be further miniaturized. For example, all components of the apparatus may be located on a single circuit board.

More preferably the apparatus comprises a flat surface around the optical sensor This way, a uniform compression is achieved around the sensing area thereby avoiding venous blood pooling which could disturb the measurements. Furthermore, no further means for applying a static pressure field such as a probe around the finger are needed.

Advantageously, the system further comprises a wraparound configured to attach the apparatus against the skin of the patient. Such a wraparound may further aid to press the sensor area against the tissue. This further aids in obtaining the uniform compression, advantageously in combination with the flat surface, to avoid venous blood pooling. Furthermore, the wraparound does not peel off as may the case with an adhesive applied to the underside of the apparatus.

According to an embodiment, the optical sensor further comprises a light emitter, a light sensor and the apparatus further comprises means for performing:.

By the above steps, the senor may be calibrated without performing any signal processing on the measured signal, i.e., there is no need to derive first a DC and AC component from the signal. Therefore, as the further signal components are of no use for the apparatus, further processing circuitry and additional energy consumption can be avoided. This allows for the further miniaturization of the apparatus.

The above calibration procedure may further be performed periodically, when detecting that light sensor is saturated or near saturation, and/or when detecting a significant drop in the measured light.

According to an embodiment, the means comprise a mobile communication device configured to receive the wirelessly transmitted measured blood volume pulse.

The mobile communication device is preferably located near the patient when in use allowing for a low power signal transmission. It may for example correspond to a mobile phone, a smartphone, a tablet computer or a laptop computer.

Advantageously, the mobile communication device is further configured to perform the deriving of the peripheral arterial tone and/or the determining of the sleep events. The mobile communication device may be further configured to wirelessly transmit the measured blood volume pulse to a remote service for performing the deriving and/or determining. This allows for a centralized cloud-based solution wherein the determining of the sleep events is done off-site. This further allows to combine measurements from different patients to further improve the determining of the sleep events.

The means may further comprise at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the controller.

The present disclosure relates to a system for diagnosing sleep of a patient. By a sleep diagnosis, sleep disorders may be discovered and treated adequately. An embodiment of such a system will be further described with reference to <FIG>, <FIG> and <FIG>. <FIG> illustrates an outside view of an apparatus <NUM> which is part of the system. The apparatus <NUM> is configured to be attached by one side <NUM> to a tissue of the patient, for example onto a fingertip <NUM>. At the side <NUM>, apparatus <NUM> comprises a reflectance based optical sensor <NUM>. This sensor is configured to measure the blood volume pulse when attached to the patient. When attached, the sensor emits light onto the tissue of the patient and measures the reflected light. The so-measured signal is then indicative for the blood volume pulse in the tissue where the sensor is attached to.

Apparatus <NUM> may be dimensioned such that is sticks to the skin of the patient during use by an adhesive applied on the side <NUM>. To further improve the adherence to the skin, apparatus <NUM> may further comprise flaps <NUM> having an adhesive layer.

Alternatively, or complementary, as further illustrated in <FIG>, apparatus <NUM> may be attached to a finger <NUM> or a toe by a wraparound <NUM>, i.e. by a means <NUM> for holding the apparatus <NUM> attached to the finger <NUM> wherein the means is configured to wrap around the finger <NUM> and apparatus <NUM> thereby holding the apparatus <NUM> against the finger <NUM>. Wraparound <NUM> may comprise an adhesive on one side for sticking the wraparound <NUM> to the topside <NUM> of the apparatus <NUM> one the one side and for sticking the wraparound to the finger <NUM> and/or to the wraparound's <NUM> other side when in use. Wraparound <NUM> may further comprise a region <NUM> indicating the side of the wraparound which is to be attached to the topside <NUM> of the apparatus <NUM>. By the wraparound, the sensor area <NUM> may be pushed or pressed against the skin thereby creating a uniform compression around the sensor are <NUM> which avoids venous blood pooling. The problem of blood pooling may be avoided without the need for pressure controlling circuitry such as for example an actively or passively pressurized membrane. By the wraparound <NUM>, the adhesive is further protected against peeling off as may be the case when only an adhesive is applied on the apparatus <NUM> or the flaps <NUM>.

The apparatus <NUM> may have a flat surface around the optical sensor at the side <NUM>. The optical sensor <NUM> is further recessed with respect to this flat surface. This way, when the apparatus <NUM> is pressed against the tissue of the patient, an even more uniform compression is obtained further avoiding the venous blood pooling. Advantageously, the adhesive is applied on this flat surface to further aid the adherence of the apparatus to the skin. The flaps <NUM>, <NUM> may further aid in applying the pressure and keeping the device in place.

Apparatus <NUM> may further be dimensioned such that the sensor may be attached to different kinds of tissue. For example, apparatus <NUM> may be attached onto different positions of the patient's skin including a nostril, an ear, the forehead, a finger and a toe. Alternatively, the apparatus may be attached to a soft tissue inside the patient's mouth such as to the gum or the cheek.

<FIG> illustrates the different components of apparatus <NUM> for determining the blood volume pulse. Apparatus <NUM> comprises a battery <NUM> for powering the different electrical components <NUM>, <NUM> and <NUM>. As already described, apparatus <NUM> comprises a reflectance based optical sensor <NUM>. Optical sensor <NUM> is powered by the battery <NUM>, e.g. a button cell. Optical sensor <NUM> comprises a light emitter <NUM>, e.g. a light emitting diode, for transmitting light into the attached tissue. Optical sensor <NUM> also comprises a light sensor for sensing the light transmitted by emitter <NUM> and reflected back onto the sensor <NUM>. Sensor <NUM> may for example correspond to a photodiode.

Apparatus <NUM> further comprises control circuitry <NUM> for controlling the optical sensor <NUM>, i.e., for enabling or disabling the sensor and for receiving the measured blood volume pulse values from the sensor <NUM>. Control circuitry <NUM> may further comprise a memory component for temporarily storing the obtained measurements. Control circuitry <NUM> is further coupled to a wireless interfacing circuitry <NUM> and configured to forward the measurements to the wireless interfacing circuitry <NUM>. Wireless interface <NUM> may support a short range and/or low power wireless communication protocol for efficient transmission of the measurements to a receiving part of the system. Wireless interface <NUM> may for example operate according to the Bluetooth Low Energy, BLE, protocol as defined by the Bluetooth Special Interest Group or according to a Near Field Communication, NFC, protocol. Operation by such protocols together with forwarding of the raw sensor <NUM> data allows miniaturization of apparatus <NUM> such that it fits on a finger or a nostril and allows operation during multiple nights.

<FIG> illustrates a system <NUM> for diagnosing sleep of a patient according to an embodiment. System <NUM> comprises the apparatus <NUM> configured to measure and wirelessly transmit the blood volume pulse of the patient during sleep. System <NUM> further comprises a mobile communication device <NUM> further configured to receive the blood volume pulse measurements transmitted by apparatus <NUM>. Apparatus <NUM> and device <NUM> may be configured to exchange the blood volume pulse measurements in a continuous manner or in a periodic manner. In the latter case, apparatus <NUM> stores the measurements during a certain time windows and the transmits the stored measurement in batch to the mobile device <NUM>.

<FIG> illustrates further steps performed by the system <NUM> for diagnosing the sleep of the patient based on the obtained blood volume measurements wherein the first step <NUM> is the obtaining of these measurements. The following steps may be performed by any suitable computing system. The steps may for example all be performed on mobile device <NUM>. Alternatively, mobile device <NUM> may forward the blood volume measurements to another remote computing system <NUM> which on its turn performs the further steps. Remote computing system <NUM> may correspond to a remote cloud-based computing service accessible over the Internet or over a private network. The steps may also be partly performed on device <NUM> and partly on the remote computing system <NUM>.

In step <NUM> the peripheral arterial tone is derived from the measured blood volume pulse. This may be done by deriving the envelope of the obtained blood volume pulse measurements. This process is illustrated in <FIG>. In <FIG> the measured blood volume pulse <NUM> is shown on the vertical axis as a function of time according to the horizontal axis. In step <NUM>, the upper envelope <NUM> and lower envelope <NUM> of the BVP <NUM> is determined. As the BVP <NUM> is an oscillating signal with a periodicity determined by the hearth beat of the patient, the upper envelope <NUM> is determined as a smooth curve outlining the upper extremities of the BVP <NUM> and the lower envelope <NUM> is determined by the lower extremities of the BVP <NUM>. The difference between the upper and lower envelopes <NUM> and <NUM> is then indicative for the peripheral arterial tone <NUM> as illustrated in <FIG>.

In the next step <NUM>, one or more sleep events are determined by inspecting the changes in the peripheral arterial tone <NUM>, e.g. by inspecting the decrease <NUM>, <NUM> in the amplitude of the peripheral arterial tone and/or the increase <NUM>, <NUM> in the amplitude of the peripheral arterial tone, optionally in combination with the measured BVP <NUM>. A sleep event may for example comprise a sleep disordered breathing events such as apnoeic events, periods of intense snoring, limb movements either as periodic or single events, cortical arousals, autonomic arousals, periods of bruxism, hypnic jerks, tossing events, and turning events. For example, an apnoeic event may be determined by considering the temporal proximity of a peripheral arterial tone amplitude decrease <NUM>, <NUM>, a blood oxygen desaturation, and a decrease of the inter pulse interval of the blood volume pulse. An autonomic arousal may be determined by considering the temporal proximity of a peripheral arterial tone amplitude decrease <NUM>, <NUM> and a decrease of the inter-pulse-interval of the blood volume pulse. A bruxism event may be determined by the temporal proximity of a peripheral arterial tone amplitude decrease <NUM>, <NUM> and a decrease of the inter-pulse-interval of the blood volume pulse, under the absence of limb movement. A periodic limb movement event may be determined by the temporal proximity of a peripheral arterial tone amplitude decrease <NUM>, <NUM> and a decrease of the inter-pulse-interval of the blood volume pulse, under the presence of limb movement.

<FIG> illustrates steps performed by control circuitry <NUM> of apparatus <NUM> for calibrating the optical sensor <NUM>, more specifically for determining the optimal light output of the light emitter <NUM> of the apparatus <NUM>. To this end, apparatus <NUM> may perform a calibration cycle <NUM> from time to time, e.g. when the apparatus <NUM> has been attached to the tissue of the patient before going to sleep. <FIG> illustrates the current <NUM> to the light emitter <NUM> as a function of time and the current <NUM> received by the light sensor <NUM> as a function of time. The current <NUM> is a direct representation of the light output of the light emitter <NUM> and the current <NUM> is a direct representation of the light received by the sensor <NUM>. Typically, the higher the light output of the emitter, the higher the signal to noise ratio of the sensor <NUM> as long as the sensor <NUM> does not saturate. During a first time interval <NUM>, the current <NUM> to the light emitter is gradually increased while the current <NUM> from the light sensor <NUM> is constantly measured. At a certain point in time <NUM>, the light sensor <NUM> is saturated and, therefore, its output current <NUM> stagnates. This point in time <NUM> determines the saturation current <NUM> for the light emitter <NUM>. Thereupon, the current <NUM> is decreased below this saturation current <NUM> up to a working point current <NUM>. This decrease may be relative, e.g. by between <NUM>% and <NUM>%, or may be absolute. After the working point of the emitter <NUM> is set, the calibration phase ends at time <NUM> and normal operation of the apparatus <NUM> resumes. Control circuitry <NUM> may further be configured to reperform the calibration upon certain calibration triggering events. A first calibration event may be the expiration of a timer such the calibration is performed periodically. A second calibration event may be the detection of a saturation of the light sensor <NUM> during normal operation, e.g. by detecting the saturation point <NUM> during normal operation. A third calibration event may be when a significant drop in the measured light is detected. Such drop may cause a decrease in signal quality and be due to a position switch of the patient, causing the light sensor to move relative to the skin or tissue which may further create an airgap between sensor and skin.

<FIG> shows a suitable computing system <NUM> for implementing the steps with reference to <FIG>. Computing system <NUM> may in general be formed as a suitable general-purpose computer and comprise a bus <NUM>, a processor <NUM>, a local memory <NUM>, one or more optional input interfaces <NUM>, one or more optional output interfaces <NUM>, a communication interface <NUM>, a storage element interface <NUM>, and one or more storage elements <NUM>. Bus <NUM> may comprise one or more conductors that permit communication among the components of the computing system <NUM>. Processor <NUM> may include any type of conventional processor or microprocessor that interprets and executes programming instructions. Local memory <NUM> may include a random-access memory (RAM) or another type of dynamic storage device that stores information and instructions for execution by processor <NUM> and/or a read only memory (ROM) or another type of static storage device that stores static information and instructions for use by processor <NUM>. Input interface <NUM> may comprise one or more conventional mechanisms that permit an operator or user to input information to the computing device <NUM>, such as a keyboard <NUM>, a mouse <NUM>, a pen, voice recognition and/or biometric mechanisms, a camera, etc. Output interface <NUM> may comprise one or more conventional mechanisms that output information to the operator or user, such as a display <NUM>, etc. Communication interface <NUM> may comprise any transceiver-like mechanism such as for example one or more Ethernet interfaces that enables computing system <NUM> to communicate with other devices and/or systems, for example with other apparatus <NUM>, mobile device <NUM> or computing system <NUM>. The communication interface <NUM> of computing system <NUM> may be connected to such another computing system by means of a local area network (LAN) or a wide area network (WAN) such as for example the internet. Storage element interface <NUM> may comprise a storage interface such as for example a Serial Advanced Technology Attachment (SATA) interface or a Small Computer System Interface (SCSI) for connecting bus <NUM> to one or more storage elements <NUM>, such as one or more local disks, for example SATA disk drives, and control the reading and writing of data to and/or from these storage elements <NUM>. Although the storage element(s) <NUM> above is/are described as a local disk, in general any other suitable computer-readable media such as a removable magnetic disk, optical storage media such as a CD or DVD, -ROM disk, solid state drives, flash memory cards,. could be used. Computing system <NUM> may thus correspond to or be part of mobile communication device <NUM> or remote computing system <NUM>.

Claim 1:
A system (<NUM>) configured to diagnose sleep comprising an apparatus (<NUM>) configured to be attached to a patient; the apparatus comprising:
an optical sensor (<NUM>) configured to measure a blood volume pulse (<NUM>) of the patient; and
a wireless communication interface (<NUM>) configured to wirelessly transmit (<NUM>) the measured blood volume pulse;
and wherein the system further comprises means (<NUM>, <NUM>) for performing:
obtaining (<NUM>) the wirelessly transmitted measured blood volume pulse;
deriving (<NUM>) from the blood volume pulse a signal that approximates peripheral arterial tone (<NUM>) by calculating an envelope of the obtained blood volume pulse measurements; and
determining occurrences of sleep events from changes (<NUM>, <NUM>, <NUM>, <NUM>) in the approximated peripheral arterial tone.