Patent Description:
Pulse wave velocity gives an indication of a subject's cardiovascular health. Therefore it is useful to provide apparatus, methods and computer programs for determining pulse wave velocity within a subject.

<CIT> discloses sensors that use accelerometers to register body-surface movements and vibrations generated by cardiac forces. These enable non-obtrusive evaluation, monitoring, and high-fidelity mapping of cardiac mechanical and electromechanical forces and central arterial blood pressure. D1 provides wearable product incorporating the sensors.

<CIT> discloses devices and methods for estimating blood pressure. A pulse-transit-time-based blood pressure model is used.

<CIT> discloses a method of performing personal authentication using a feature of a ballistocardiogram of an individual.

According to various, but not necessarily all, examples of the disclosure there is provided an apparatus comprising means for: receiving a first ballistocardiograph signal, travelling in a first direction, indicative of a first change in direction of a pulse wave, wherein the first change in direction of the pulse wave occurs at a first point within an arterial system of a subject at a first time, the pulse wave having a velocity; receiving a second ballistocardiograph signal, travelling in a second direction, indicative of a second change in direction of the pulse wave, wherein the second change in direction of the pulse wave occurs at a second point within the arterial system of the subject at a second time, wherein the second direction is, at least partially, perpendicular to the first direction; determining the pulse wave velocity based on the first time, the second time and an estimate of a distance within the arterial system of the subject between the first point and the second point.

The first ballistocardiograph signal may correspond to the pulse wave travelling through an aorta of a subject and the second ballistocardiograph signal may correspond to the pulse wave travelling through an iliac artery of a subject.

The first direction may be a vertical direction and the second direction may be a horizontal direction.

The distance travelled by the pulse wave between the first time and the second time may be received as an input.

The first ballistocardiograph signal and the second ballistocardiograph signal may be received from sensors comprised within a chair.

The first ballistocardiograph signal and the second ballistocardiograph signal may be received from accelerometers comprised within the seat of a chair.

According to various, but not necessarily all, examples of the disclosure there is provided a system comprising an apparatus as described above and a chair configured to enable a subject to sit with their legs, at least partially, perpendicular to their torso wherein the chair comprises one or more sensors and/or accelerometers configured to detect ballistocardiograph signals.

According to various, but not necessarily all, examples of the disclosure there is provided a method comprising: receiving a first ballistocardiograph signal, travelling in a first direction, indicative of a first change in direction of a pulse wave, wherein the first change in direction of the pulse wave occurs at a first point within an arterial system of a subject at a first time, the pulse wave having a velocity; receiving a second ballistocardiograph signal, travelling in a second direction, indicative of a second change in direction of the pulse wave, wherein the second change in direction of the pulse wave occurs at a second point within the arterial system of the subject at a second time, wherein the second direction is, at least partially, perpendicular to the first direction; determining the pulse wave velocity based on the first time, the second time and an estimate of a distance within the arterial system of the subject between the first point and the second point.

The first ballistocardiograph signal may correspond to the pulse wave travelling through an aorta of a subject and the second ballistocardiograph signal may correspond to the pulse wave travelling through a femoral artery of a subject.

According to various, but not necessarily all, examples of the disclosure there is provided a computer program comprising computer program instructions that, when executed by processing circuitry cause: receiving a first ballistocardiograph signal indicative of a pulse wave travelling in a first direction at a first time, the pulse wave having a pulse velocity; receiving a second ballistocardiograph signal indicative of the pulse wave travelling in a second direction at a second time, wherein the second direction is, at least partially perpendicular to the first direction; determining the pulse wave velocity based on the first ballistocardiograph signal and the second ballistocardiograph signal.

According to various, but not necessarily all, examples of the disclosure there is provided a physical entity embodying the computer program as described above.

According to various, but not necessarily all, examples of the disclosure there is provided an apparatus comprising: a chair configured to enable a subject to sit with their legs, at least partially, perpendicular to their torso; sensing means configured to detect a first ballistocardiograph signal indicative of a pulse wave, having a pulse wave velocity, travelling in a first direction at a first time and a second ballistocardiograph signal indicative of the pulse wave travelling in a second direction at a second time, wherein the second direction is, at least partially perpendicular to the first direction.

The sensing means may be comprised in a seat of the chair.

The sensing means may comprise one or more accelerometers.

Examples of the disclosure relate to apparatus, methods and computer programs for determining pulse wave velocity using ballistocardiograph signals. The apparatus <NUM> comprises means for receiving a first ballistocardiograph signal <NUM> and a second ballistocardiograph signal <NUM>. The first ballistocardiograph signal <NUM> is indicative of a pulse wave, having a pulse wave velocity, travelling in a first direction at a first time and the second ballistocardiograph signal <NUM> is indicative of the pulse wave travelling in a second direction at a second time, wherein the second direction is, at least partially, perpendicular to the first direction. The means of the apparatus <NUM> are also configured for determining the pulse wave velocity based on the first ballistocardiograph signal <NUM> and the second ballistocardiograph signal <NUM>.

The apparatus <NUM> therefore enables the pulse wave velocity within the aorta of a subject to be determined which can provide an indication of the cardiovascular health of a subject.

<FIG> schematically illustrates an apparatus <NUM> according to examples of the disclosure. The apparatus <NUM> illustrated in <FIG> may be a chip or a chip-set. In some examples the apparatus <NUM> may be provided within a system which is configured to measure the ballistocardiograph signals of a subject. In some examples the apparatus <NUM> could be located remotely to the system for measuring the ballistocardiograph signals of a subject but could be configured to receive the signals via any suitable communication link.

In the example of <FIG> the apparatus <NUM> comprises a controller <NUM>. In the example of <FIG> the implementation of the controller <NUM> may be as controller circuitry. In some examples the controller <NUM> may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware).

As illustrated in <FIG> the controller <NUM> may be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program <NUM> in a general-purpose or special-purpose processor <NUM> that may be stored on a computer readable storage medium (disk, memory etc.) to be executed by such a processor <NUM>.

The memory <NUM> is configured to store a computer program <NUM> comprising computer program instructions (computer program code <NUM>) that controls the operation of the apparatus <NUM> when loaded into the processor <NUM>. The computer program instructions, of the computer program <NUM>, provide the logic and routines that enables the apparatus <NUM> to perform the methods illustrated in <FIG>. The processor <NUM> by reading the memory <NUM> is able to load and execute the computer program <NUM>.

The apparatus <NUM> therefore comprises: at least one processor <NUM>; and at least one memory <NUM> including computer program code <NUM>, the at least one memory <NUM> and the computer program code <NUM> configured to, with the at least one processor <NUM>, cause the apparatus <NUM> at least to perform: receiving a first ballistocardiograph signal <NUM> indicative of a pulse wave travelling in a first direction at a first time, the pulse wave having a pulse velocity; receiving a second ballistocardiograph signal <NUM> indicative of the pulse wave travelling in a second direction at a second time, wherein the second direction is, at least partially perpendicular to the first direction; determining the pulse wave velocity based on the first ballistocardiograph signal <NUM> and the second ballistocardiograph signal <NUM>.

As illustrated in <FIG> the computer program <NUM> may arrive at the apparatus <NUM> via any suitable delivery mechanism <NUM>. The delivery mechanism <NUM> may be, for example, a machine readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a Compact Disc Read-Only Memory (CD-ROM) or a Digital Versatile Disc (DVD) or a solid state memory, an article of manufacture that comprises or tangibly embodies the computer program <NUM>. The delivery mechanism may be a signal configured to reliably transfer the computer program <NUM>. The apparatus <NUM> may propagate or transmit the computer program <NUM> as a computer data signal. In some examples the computer program <NUM> may be transmitted to the apparatus <NUM> using a wireless protocol such as Bluetooth, Bluetooth Low Energy, Bluetooth Smart, 6LoWPan (IPv<NUM> over low power personal area networks) ZigBee, ANT+, near field communication (NFC), Radio frequency identification, wireless local area network (wireless LAN) or any other suitable protocol.

The computer program <NUM> comprises computer program instructions for causing an apparatus <NUM> to perform at least the following: receiving a first ballistocardiograph signal <NUM> indicative of a pulse wave travelling in a first direction at a first time the pulse wave having a pulse velocity; receiving a second ballistocardiograph signal <NUM> indicative of the pulse wave travelling in a second direction at a second time, wherein the second direction is, at least partially perpendicular to the first direction; determining the pulse wave velocity based on the first ballistocardiograph signal <NUM> and the second ballistocardiograph signal <NUM>.

The computer program instructions may be comprised in a computer program <NUM>, a non-transitory computer readable medium, a computer program product, a machine readable medium. In some but not necessarily all examples, the computer program instructions may be distributed over more than one computer program <NUM>.

References to "computer-readable storage medium", "computer program product", "tangibly embodied computer program" etc. or a "controller", "computer", "processor" etc. should be understood to encompass not only computers having different architectures such as single/multi- processor architectures and sequential (Von Neumann)/parallel architectures but also specialized circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry.

<FIG> illustrates an example system <NUM> comprising an apparatus <NUM> and one or more sensors <NUM>. A communication link <NUM> is provided between the apparatus <NUM> and the one or more sensors <NUM>. The system <NUM> is configured to enable a first ballistocardiograph signal <NUM> and a second ballistocardiograph signal <NUM> to be obtained and used to determine the pulse wave velocity of a subject.

The apparatus <NUM> could be an apparatus <NUM> as shown in <FIG>. The apparatus <NUM> could comprise a controller <NUM>, processor <NUM> and memory <NUM> as described.

The apparatus <NUM> could be configured to establish a communication link <NUM> with the one or more sensors <NUM> so as to enable information obtained by the one or more sensors <NUM> to be provided to the apparatus <NUM>. The communication link <NUM> could also enable control signals, and/or any other suitable information, to be transmitted from the apparatus <NUM> to the one or more sensors <NUM>.

In some examples the communication link <NUM> could comprise a wireless communication link which uses a wireless protocol such as Bluetooth, Bluetooth Low Energy, Bluetooth Smart, 6LoWPan (IPv<NUM> over low power personal area networks) ZigBee, ANT+, near field communication (NFC), Radio frequency identification, wireless local area network (wireless LAN) or any other suitable protocol. In some examples the communication link <NUM> could comprise a wired connection or any other suitable type of connection.

The one or more sensors <NUM> may comprise any means which enables ballistocardiograph signals <NUM>, <NUM> to be detected from a subject. The one or more sensors <NUM> are configured to detect the ballistic force of the pulse of the subject. The one or more sensors <NUM> may be configured to detect the ballistic force of the pulse as it travels through the aorta and iliac artery of a subject. The one or more sensors <NUM> could comprise accelerometers, force sensors, or any other suitable means or combination of such means.

The one or more sensors <NUM> are configured within the system <NUM> so as to enable a first ballistocardiograph signal <NUM> to be detected at a first time and a second ballistocardiograph signal <NUM> to be detected at a second time. The second time may be after the first time.

The one or more sensors <NUM> are configured within the system <NUM> so as to enable ballistocardiograph signals <NUM>, <NUM> travelling in different directions to be detected. In examples of the disclosure the first ballistocardiograph signal <NUM> is indicative of a pulse wave travelling in a first direction and the second ballistocardiograph signal <NUM> is indicative of a pulse wave travelling in a second direction. The first and second direction could be perpendicular, or at least partially perpendicular to each other. The first ballistocardiograph signal <NUM> could be caused by the pulse travelling through a first artery while the second ballistocardiograph signal could be caused by the pulse travelling through a second artery. The subject could be positioned so that the first and second artery extend in different directions. For example, the first artery could be the aorta while the second artery could be the iliac artery and the subject could be arranged in a seated position so that the iliac artery extends in a different direction to the aorta.

In some examples the same sensor <NUM> could be configured to detect the ballistocardiograph signals <NUM>, <NUM> representing the pulse wave travelling in different directions. This may enable the system <NUM> to be operable with a single sensor <NUM>. For instance an accelerometer may be configured to detect forces in different directions.

In other examples the system <NUM> could comprise a plurality of sensors <NUM> where different sensors <NUM> are configured to detect the different ballistocardiograph signals <NUM>, <NUM>. For example, a first force sensor <NUM> could be positioned to detect the first ballistocardiograph signal <NUM> and a second force sensor <NUM> could be positioned to detect the second ballistocardiograph signal <NUM>.

In some but not necessarily all examples, the one or more sensors <NUM> may be configured to communicate data from the one or more sensors <NUM> with or without local storage of the data in a memory at one or more sensors <NUM> and with or without local processing of the data by circuitry or processors at the one or more sensors <NUM>.

The data may, for example, be measurement data from the one or more sensors <NUM> or data produced by the processing of measurement data from one or more sensors <NUM>, such as, for example, an indication of the times at which the ballistocardiograph signals <NUM>, <NUM> were detected.

The data may be stored in processed or unprocessed format remotely at one or more devices. In some examples the data may be stored on a remote server.

The data may be processed remotely by one or more apparatus <NUM> which may be provided in one or more devices. The data may be partially processed locally and partially processed remotely by the one or more apparatus <NUM> in one or more devices.

The data may be communicated to the apparatus <NUM> in the one or more remote devices wirelessly via short range radio communications such as Wi-Fi or Bluetooth, for example, or over long range cellular radio links. The one or more sensors <NUM> may be coupled to a communications interface such as, for example, a radio transceiver for communication of data.

The system <NUM> may be part of a larger, distributed network such as the Internet of Things. The Internet of Things may comprise a plurality of devices that may be configured to communicate via the internet. The devices may or may not be local to each other.

The processing of the data, whether local or remote, may be for the purpose of health monitoring, data aggregation, patient monitoring, vital signs monitoring or other purposes.

<FIG> illustrates a chair <NUM> comprising one or more sensors <NUM> which may be used in some examples of the disclosure to enable the ballistocardiograph signals <NUM>, <NUM> to be detected. In the example of <FIG> a subject <NUM> is sitting in the chair <NUM>.

The chair <NUM> is configured to enable a subject <NUM> to sit with their legs <NUM>, at least partially perpendicular to their torso <NUM>. The seated position may enable a first artery to be positioned to extend in a different direction to a second artery. In the examples shown in <FIG> the subject's aorta <NUM> extends from the subject's heart <NUM> in a vertical direction while the subject's iliac artery <NUM> in the top of the legs <NUM> extends in a horizontal direction.

In the example of <FIG> the chair <NUM> comprises a seat portion <NUM> and a back rest <NUM>. The seat portion <NUM> is configured to provide a horizontal or substantially horizontal surface for the subject <NUM> to sit on. The seat portion <NUM> may be a rigid portion so that the ballistocardiograph signals <NUM>, <NUM> do not cause deformation of the seat portion <NUM>. This may enable the ballistocardiograph signals <NUM>, <NUM> to be detected.

The back rest <NUM> comprises a portion that is, at least partially, perpendicular to the seat portion <NUM>. The back rest <NUM> is configured to support the back of the subject <NUM> when the subject <NUM> is seated on the seat portion <NUM>. The back rest <NUM> may enable the subject <NUM> to sit in an upright position for the duration of time that the ballistocardiograph signals <NUM>, <NUM> are to be measured.

The sensors <NUM> provide sensing means for detecting the ballistocardiograph signals <NUM>, <NUM>. The sensors <NUM> are configured to detect a first ballistocardiograph signal <NUM> indicative of a pulse wave travelling in a first direction <NUM> at a first time and a second ballistocardiograph signal <NUM> indicative of the pulse wave travelling in a second direction <NUM> at a second time, wherein the second direction <NUM> is, at least partially perpendicular to the first direction <NUM>.

In the example chair <NUM> shown in <FIG> the sensors <NUM> are provided in the seat portion <NUM> of the chair <NUM>. The same sensors <NUM> may be configured to detect both the first ballistocardiograph signal <NUM> and the second ballistocardiograph signal <NUM>.

The sensor <NUM> may be provided close to the surface of the seat portion to enable the ballistocardiograph signals <NUM>, <NUM> to be detected. In the example of <FIG> a single sensor <NUM> is provided which is configured to detect ballistocardiograph signals in the first direction and also the second direction. The sensor <NUM> could comprise one or more accelerometers or any other suitable means.

In the example of <FIG> the seat portion <NUM> of the chair <NUM> is mounted on a spring <NUM> which is coupled to a rigid base portion <NUM>. The spring <NUM> extends perpendicularly, or substantially perpendicularly, to the seat portion <NUM>. The spring may provide means for enabling movement of the seat portion <NUM> so that the sensor <NUM> can detect the movement. In some examples the spring <NUM> may also act to damp external vibrations and so may reduce noise in the signals provided by the one or more sensors <NUM>. Other means for enabling movement of the seat portion <NUM> could be used in other examples of the disclosure.

In the example system <NUM> of <FIG> the first ballistocardiograph signal <NUM> corresponds to the pulse wave travelling through the aorta <NUM> of the subject <NUM> and the second ballistocardiograph signal <NUM> corresponds to the pulse wave travelling through an iliac artery <NUM> of the subject <NUM>. The forces that are detected by the sensors <NUM> may comprise recoil forces related to the pulse waves. In this example the first direction <NUM> is a vertical direction as indicated by the vertical arrow in <FIG> and the second direction <NUM> is a horizontal direction as indicated by the horizontal arrow in <FIG>. In other examples the directions could be substantially vertical and substantially horizontal. In other examples the directions do not need to be aligned with the vertical and horizontal.

In examples of the disclosure, the change in the direction of the pulse wave can be detected by the one or more sensors <NUM>. This gives an indication of the time at which the same pulse wave is at two different points within the arterial system of the subject <NUM>. In examples of the disclosure the distance between these two points can be determined by making an external measurement of the subject <NUM>. For instance a tape measure can be used to measure the length of the subject's aorta <NUM> or any other suitable distance. In such cases the apparatus <NUM> would receive an input indicative of the distance travelled by the pulse wave. The pulse wave velocity can be determined from the time it takes the pulse to travel between the two different points of the arterial system.

The same type of wave could be detected at the different points within the arterial system. In examples of the disclosure the pulse wave that is detected by the sensors <NUM> could comprise an I wave. The I wave may be the largest component of the pulse wave within the arteries. Other components of the pulse wave could be detected in other examples of the disclosure.

In the example of <FIG> the sensors <NUM> are provided in the seat of the chair <NUM>. The sensors <NUM> could comprise an accelerometer or any other suitable means which may be configured to detect the ballistocardiograph signals <NUM>, <NUM> in at least two different directions. In other examples the sensors <NUM> could be provided in different positions so as to enable the different ballistocardiograph signals <NUM>, <NUM> to be detected. For instance a first force sensor could be provided in the seat portion <NUM> of the chair <NUM> to detect the first ballistocardiograph signal <NUM> and a second force sensor could be provide in the back rest <NUM> of the chair <NUM> so as to detect the second ballistocardiograph signal <NUM>. Other configurations of the sensors <NUM> could be used in other examples of the disclosure.

<FIG> illustrates a method that could be implemented using the apparatus <NUM>, systems <NUM> and chairs <NUM> described above.

The method comprises, at block <NUM>, receiving a first ballistocardiograph signal <NUM> indicative of a pulse wave travelling in a first direction <NUM> at a first time, the pulse wave having a pulse wave velocity. In examples of the disclosure the first ballistocardiograph signal <NUM> could be a pulse wave travelling through the aorta <NUM> of a subject <NUM>. The pulse wave could be travelling in a vertical or substantially vertical direction.

The method also comprises, at block <NUM>, receiving a second ballistocardiograph signal <NUM> indicative of the pulse wave travelling in a second direction <NUM> at a second time, wherein the second direction <NUM> is, at least partially perpendicular to the first direction <NUM>. In examples of the disclosure the second ballistocardiograph signal <NUM> could be a pulse wave travelling through the iliac artery of the subject <NUM>. The pulse wave could be travelling in a horizontal or substantially horizontal direction.

The method also comprises, at block <NUM>, determining the pulse wave velocity based on the first ballistocardiograph signal <NUM> and the second ballistocardiograph signal <NUM>. The pulse wave velocity can be determined from the time it takes the pulse wave to travel between the aorta <NUM> and the iliac artery <NUM> or any other suitable points in the arterial system.

In some examples the method could also comprise blocks that are not shown in <FIG>. For example in some examples the received ballistocardiograph signals <NUM>, <NUM> could be processed to remove noise and/or artefacts. For example the received ballistocardiograph signals <NUM>, <NUM> could be filtered to remove artefacts caused by the subject <NUM> breathing.

In some examples the received ballistocardiograph signals <NUM>, <NUM> could also be processed to remove artefacts caused by motion of the user. In some examples the motion artifacts caused by the motion of the subject <NUM> could be limited by the subject keeping still for the duration of the ballistocardiograph measurements.

The technical effects of examples of the disclosure are therefore an effective and accurate system and process for determining the pulse wave velocity of a subject <NUM>. The system <NUM> and method are non-invasive and do not require any electrodes or direct electrical connections to the skin of the subject <NUM>. The measurements can be made while the subject <NUM> is seated in a chair <NUM> and so may be a convenient and non-intrusive method of making the measurements.

If it is intended to use 'comprise' with an exclusive meaning then it will be made clear in the context by referring to 'comprising only one. ' or by using 'consisting'.

Although embodiments have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims.

The term 'a' or 'the' is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use 'a' or 'the' with an exclusive meaning then it will be made clear in the context. In some circumstances the use of 'at least one' or 'one or more' may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer and exclusive meaning.

Claim 1:
An apparatus (<NUM>) comprising means for:
receiving a first ballistocardiograph signal (<NUM>), travelling in a first direction, indicative of a first change in direction of a pulse wave, wherein the first change in direction of the pulse wave occurs at a first point within an arterial system of a subject at a first time, the pulse wave having a velocity;
receiving a second ballistocardiograph signal (<NUM>), travelling in a second direction, indicative of a second change in direction of the pulse wave, wherein the second change in direction of the pulse wave occurs at a second point within the arterial system of the subject at a second time, wherein the second direction is, at least partially, perpendicular to the first direction;
determining the pulse wave velocity based on the first time, the second time and an estimate of a distance within the arterial system of the subject between the first point and the second point.