Blood pressure monitoring device

Abstract

There is provided a wearable device 1 for monitoring a blood pressure of a person, comprising: a strap 2 for extending around a chest of the person or a limb of the person; and a sensor unit 4 removably attachable to the strap 2 for being secured to the person by the strap 2, the sensor unit 4 comprising an optical sensor for detecting one or more physiological parameters relating to the person's blood pressure; wherein when the sensor unit 4 is attached to the strap 2, a majority of the sensor unit 4 is located on a first side 20 of the strap 2 and a projection portion 24 of the sensor unit 4 including the sensor extends through an opening in the strap 2 to a second side 26 of the strap 2; and wherein the sensor unit 4 comprises a port 50 located such that the strap 2 covers the port 50 when the sensor unit 4 is attached to the strap 2.

Description

[0001] BLOOD PRESSURE MONITORING DEVICE

[0002] Field

[0003] The present specification relates to a wearable device for monitoring a blood pressure of a person, and to a method of monitoring a blood pressure of a person using the wearable device.

[0004] Background

[0005] The blood pressure of a person is a useful indication of the health status of the person, and a relatively high or low blood pressure can indicate various underlying health issues. It is therefore important to monitor the person’s blood pressure to detect any changes that may occur.

[0006] Some conventional blood pressure monitoring devices, such as an inflatable cuff, enable a single reading of the person’s blood pressure. Such devices require repeated readings to be taken at specified intervals to create a picture of the person’s blood pressure over time. Other conventional blood pressure monitoring devices enable continuous readings, which allow the person’s blood pressure to be continuously monitored over a period of time.

[0007] Wearable blood pressure monitoring devices integrate continuous blood pressure measurement technology in wearable articles, such as wrist bands, socks, etc. Such devices provide a convenient measurement device which enables the person to continue their normal activities while their blood pressure is being monitored.

[0008] Summary

[0009] In a first aspect, there is provided a wearable device for monitoring a blood pressure of a person, comprising: a strap for extending around a chest of the person or a limb of the person (e.g., the upper arm of the person); and a sensor unit removably attachable to the strap for being secured to the person by the strap, the sensor unit comprising a sensor for detecting one or more physiological parameters relating to the person’s blood pressure; wherein when the sensor unit is attached to the strap, a majority of the sensor unit is located on a first side of the strap (i.e., the first side of the strap being the side which faces away from the person when worn) and a projection portion of the sensor unit including the sensor extends through an opening in the strap to a second side of the strap (i.e., the side of the strap facing and in contact with the person when worn); and wherein the sensor unit comprises a port located in the projection portion such that the strap covers the port when the sensor unit is attached to the strap. The sensor may be an optical sensor, such as a PPG sensor. The ‘person’ may be a healthy person, a person that has an underlying health condition or a person that has a suspected health condition.

[0010] The sensor unit may comprise a plurality of sensors. By way of example, the sensors may comprise a PPG sensor, an ECG sensor, an accelerometer, a gyroscope, a temperature sensor, etc. Data from such other sensors like the ECG sensor, motion sensors, temperature sensor, may be used to help improve the blood pressure data from the PPG sensor.

[0011] The person may wear the device by passing the strap around their chest, with the first side of the strap facing away from the person and the second side of the strap facing toward the person. The sensor unit can be easily attached to the strap by inserting the projection portion into the opening, before or after the person has fixed the strap around their chest. The person may also wear the device around one of their limbs in a similar manner where that is a preferred way of wearing the device.

[0012] Since the majority of the sensor unit is located on the first side of the strap, with the optical sensor extending through to the second side so as to access the person to take measurements therefrom (e.g. by contacting the person’s skin), the device is more comfortable to wear compared to devices in which the majority of the sensor unit is on the same side of the strap as the optical sensor (i.e. , the side contacting the person’s body). The device can also provide more reliable measurements because better skin contact can be provided between the optical sensor and the person, and because ambient light reaching the sensor is reduced since the belt “surrounds” the sensor.

[0013] The strap enables the wearable device to be chest-worn. The sensor can therefore take measurements from the chest (for example, PPG measurements) which can be more accurate than measurements taken at other areas of the body, such as the wrist or arm, due to the chest being less sensitive to noise caused by motion and other factors like body surface temperature and body position. In addition, the person’s chest provides the opportunity to monitor other physiological parameters, such as an ECG signal.

[0014] A suitable length strap may also enable the wearable device to be worn on a limb of the person, for example, on the upper arm, where it is preferred to wear the device in that manner.

[0015] The wearable device may be particularly suited for long term usage. For example, the strap enables the person to wear the device under their clothes, providing discreet and comfortable blood pressure monitoring. It is beneficial for wearable blood pressure monitoring devices to be comfortable for the person to wear in order to encourage long term usage. Additionally, if the person is comfortable, the blood pressure measurements are more likely to be reflective of an actual health condition of the person, rather than being influenced by discomfort or anxieties of the person. An example of such influence is colloquially known as ‘white coat hypertension’, which is when a person’s blood pressure increases when their blood pressure is being measured by a medical professional, caused by the stress of having the measurement taken rather than because the person’s blood pressure is high due to a health condition. Furthermore, because the strap can be detached from the sensor unit, the strap can be washed without damaging the sensor unit and then re-worn repeatedly. This is beneficial compared to single use attachment means such as adhesive patches which need to be disposed of after one use.

[0016] The one or more physiological parameters detected by the sensor(s) may include a heart rate of the person, heart rate variability (HRV), electrocardiogram (ECG), oxygen saturation, sleep, respiration rate, body surface temperature, pulse wave velocity, and / or any other parameter related to the person’s blood pressure.

[0017] The wearable device may also measure or determine other parameters related to the person’s blood pressure or for providing information that can provide context for the blood pressure. The other parameters might relate to heart diagnoses (such as arrythmia, tachycardia and bradycardia), activity level, step count, posture, and / or activity categories of the person’s activity. These other parameters may be determined by the optical sensor or by other sensing devices of the sensor unit, such as an accelerometer, a gyroscope, etc. The blood pressure determination may be additionally based on these other parameters or associated with them in a data set.

[0018] The sensor unit may be configured to process signals from the sensor(s), e.g. signals representative of the measured physiological parameters(s), to determine the person’s blood pressure. For example, the sensor unit may comprise a processor configured to determine the person’s blood pressure based on the one or more physiological parameters and optionally one or more of the other parameters.

[0019] Additionally or alternatively, the sensor unit may be arranged for communication with a remote device for the signal processing. For example, the sensor unit may be configured to transmit information regarding the one or more physiological parameters to the remote device for processing. The remote device may be configured to receive the information via an electrical cable connectable to the sensor unit port, or wirelessly (e.g. via Bluetooth (RTM) or other known wireless data transfer technology). The remote device may comprise a mobile phone, a computer, etc. Thus, the wearable device can be worn for a predetermined period of time (e.g. 1 day) to collect data on the physiological parameter(s) of the person and store the data (for example, using memory storage of the sensor unit), and then the data can be transmitted to the remote device wirelessly or by detaching the sensor unit from the strap and plugging the sensor unit into the remote device. The remote device can then process the data and determine the person’s blood pressure measurements over the period of time and / or analyse the person’s blood pressure measurements for patterns of behaviour over the period of time. The sensor unit can then be reattached to the strap (if it was detached for wired data transfer), and the person can wear the wearable device again to monitor the blood pressure over another predetermined period of time. If the data transfer is performed wirelessly, the data can be transferred to the remote device while the wearable device is in use (i.e. while the sensor unit is attached to the strap and being worn by the person) or once the sensor unit has been detached from the strap.

[0020] Therefore, there may be provided a system comprising the wearable device as described herein and a remote device, wherein the remote device is configured to receive information regarding the one or more physiological parameters from the sensor unit, and to process the information to determine the person’s blood pressure and / or analyse the blood pressure measurements.

[0021] The majority of the sensor unit being located on the first side of the strap may mean at least 50% of the volume of the sensor unit is located on the first side, i.e., on a side of the strap facing away from the person wearing the wearable device. Optionally, at least 60% or at least 70% of the volume of the sensor unit is located on the first side. Optionally, all of the sensor unit except the projection portion is located on the first side of the strap.

[0022] The sensor unit may comprise a main portion. The main portion may comprise the majority of the sensor unit and may be located on the first side of the strap. The main portion may comprise a housing and one or more electronic components of the sensor unit, such as a processor, a battery, a control circuit, etc. The battery may comprise a rechargeable battery, such as an Li-ion battery. In this way, the battery may take up a majority of the main portion and have a substantially cuboid form within the main portion. The battery, control electronics and user interface components, such as LEDs and / or one or more buttons, may take up substantially the whole of an internal space of the main portion within the housing. The battery may have a generally rectangular footprint which is larger in area than the opening in the strap for the projecting portion, the battery extending over the opening in the strap (the opening may be a circular opening as viewed from the first side).

[0023] The main portion may comprise a strap-engaging surface, also referred to herein as a ‘first surface’, which abuts the first side of the strap when the sensor unit is attached to the strap. The first surface of the main portion may have a larger area than the area of the opening to prevent the main portion from entering the opening.

[0024] The projection portion of the sensor unit may project from the main portion, e.g. from the first surface of the main portion. Thus, in use, the main portion of the sensor unit may abut the first side of the strap so that the strap can support and stabilise the sensor unit, and the projection portion may extend from the main portion through the opening in the strap to provide the sensor with access to the person (e.g. to contact the person’s skin) for measuring the one or more physiological parameters. The sensor unit may comprise a display feature for displaying information to the person. The display feature may comprise an LED and / or a screen, for example. The person may therefore be able to obtain a visual indication of their blood pressure or a status of the device (e.g. a low power status) by observing the display feature. The display feature may preferably be located on the main portion, which is located on the first (external) side of the strap in use, so that the person can easily observe the display feature without needing to remove the strap or detach the sensor unit from the strap.

[0025] The sensor unit may comprise an input component configured to provide user control of the device. For example, the input component may optionally comprise a button or a touch-operated screen, or any other suitable component which enables the user to provide inputs to the device. The input may for example cause the device to provide a display of a current blood pressure determination, to allow the user to adjust settings of the device, etc. For some embodiments it may be preferable to only display minimal information, such as that the device is switched on, is charged or needs charging, or is transmitting data, so that the person is not able to observe the measured parameters and potentially let that influence their behaviour. The input component may preferably be located on the main portion so that the person can easily control the sensor unit without needing to remove the strap or detach the sensor unit from the strap.

[0026] The optical sensor may comprise any optical component suitable for obtaining information about the one or more physiological parameters. For example, the optical sensor may comprise a photoplethysmography (PPG) sensor. The PPG sensor may be configured to measure pulsating blood volume changes by illuminating a pulsatile tissue of the person using a light source, such as an LED, and measuring the light intensity received by a photoreceptor after the light has been reflected by the tissue. The pulsatility of the tissue then creates variations in the received light intensity in the PPG measurements.

[0027] A PPG sensor may be used to detect a heart rate of the person and / or other parameters that are identifiable from a PPG signal, such as heart rate variability, oxygen saturation, sleep, respiration rate, and pulse wave velocity, etc. Any suitable type of analysis may be used to calculate the blood pressure from the PPG sensor data, such as pulse wave analysis. The pulse wave analysis may involve morphological analysis of the signal obtained from the PPG sensor, which is known to resemble a blood pressure waveform.

[0028] The sensor unit may comprise a sensor surface for contacting the person’s skin. The sensor surface may be a distal end surface of the projection portion of the sensor unit (i.e., located distally from the main portion). The sensor surface may protrude from the opening when the sensor unit is attached to the strap, so that when the strap is being worn by the person the sensor surface can make good contact with the person’s skin. Direct skin-to-sensor contact may enable more reliable readings of the physiological parameter(s).

[0029] The sensor unit may comprise emitter and receiver components for emitting and receiving sensor signals to and from the person across the sensor surface. The emitter and receiver components may be housed within the projection portion of the sensor unit.

[0030] The sensor unit can thus be easily fitted to the strap by aligning the projection portion with the opening, inserting the projection portion into the opening until the first surface of the main portion abuts the first side of the strap and the optical sensor (e.g. in particular the sensor surface of the optical sensor) protrudes from the opening, and then fastening the sensor unit to the strap. The wearable device can therefore be easily worn, operated and removed by the person, without the need for expertise e.g. from a medical professional. Moreover, since the bulkier main portion is located on the first side of the strap away from the person, and only the projection portion extends through the opening to the second side, improved comfort for the person is provided whilst also improving the reliability of the sensor readings.

[0031] The wearable device may be manufactured with the battery (and optionally other sensors) in the main portion and with the port and the optical sensor (and optionally other sensors) in the projection portion. The main portion may have a generally rectangular shape, e.g. to generally conform to or mirror the shape of the battery. The projection portion may have a generally cylindrical shape. The port and the optical sensor (and optionally other sensors) may abut the battery and be sealed, e.g. in plastic, to form the projection portion. The optical sensor and the one or more other sensors may be provided on the same chip within the sensor unit.

[0032] The strap may comprise a plate portion surrounding the opening. The plate portion may comprise a rigid material. One or more arms of the strap may comprise a flexible material. Thus, the flexible arms may enable the strap to wrap around the person’s chest (or arm), whilst the rigid plate portion may provide structural integrity and support for the sensor unit to hold it stably against the person. A well-supported sensor unit can ensure good skin contact of the sensor surface to the person, thus improving reliability of the sensor readings. The plate portion may comprise a first plate section on the first side of the strap and a second plate section on the second side of the strap.

[0033] The wearable device may comprise one or more attachment features configured to allow the sensor unit to be removably attached to the strap (e.g. to the plate portion of the strap). For example, the attachment feature(s) may comprise a push fit connector or feature, such as push studs (sometimes referred to as snap fasteners, that may engage with a snapping action), or other suitable connection system using a screw, a hook and loop fastener, magnets, etc. In a preferred arrangement, the sensor unit may comprise a pair of protrusions, which may be in the form of studs, arranged either side of the projection portion to engage with a pair of recesses provided on the strap. The recesses may be in the form of sockets for the projections with the protrusions I studs engaging the sockets in a pushfitting manner to secure the sensor unit to the strap. Since the sensor unit is removably attachable, it can be affixed to and removed from the strap by the person as desired. This can enable the sensor unit to be removed from the strap e.g. to be electrically charged up, and then reattached to the strap for blood pressure monitoring, without needing to remove the strap from the person.

[0034] The sensor unit may comprise at least one electrode for receiving electrocardiogram (ECG) signals. The at least one electrode may be in the form of an electrical connector that is adapted to couple with (mechanically and electrically) a recess or socket in the strap. The at least one electrode of the sensor unit may project from the first surface of the main portion. The at least one electrode of the sensor unit may comprise an attachment feature of the sensor unit that is configured to attach to a corresponding attachment feature of the strap. For example, the at least one electrode of the sensor unit may be a stud, e.g. a metal stud, configured to attach to a corresponding recess(es) in the strap (e.g., corresponding recesses extending at least partially through the plate portion of the strap). The recesses in the strap may comprise a conductive material and may be in the form of a socket for the at least one electrode of the sensor unit, providing a second electrical connector. A male I female electrical connector arrangement may be provided by the electrodes of the sensor unit and strap.

[0035] The strap may comprise at least one ECG electrode for taking ECG measurements, more preferably a pair of spaced ECG electrodes, preferably in the form of pads, so that a potential difference between the ECG electrodes may be measured.

[0036] Thus the at least one ECG electrode of the strap may be configured to detect electrical activity of the person’s heart, such as through electric signals produced by heartbeats of the person. The at least one ECG electrode of the strap may be configured to be in contact with the person when the wearable device is in use. The at least one ECG electrode of the strap may therefore be located on the second side of the strap. The at least one ECG electrode of the strap may be in communication with the at least one electrode of the sensor unit through wires and / or the recesses of the strap. In this way, ECG signals taken by the at least one ECG electrode of the strap may be communicated to the sensor unit via the at least one electrode of the sensor unit. The ECG signals may then be processed within the sensor unit (e.g., using the processor of the sensor unit), or once the sensor unit is removed from the person may be communicated to the remote device via the electrical cable or wirelessly and processed within the remote device. The processed ECG signals may be used to identify a number of heart-related issues, such as arrhythmia, coronary heart disease, heart attack, and / or cardiomyopathy.

[0037] The wearable device may comprise a fastener for fastening the strap around the person’s chest. For example, opposing ends of the strap may be connectable together to form a loop, with each opposing end comprising complementary fastening features, such as a hook and loop fastener, push-fit connector components, a buckle, magnets, etc. One end of the strap may comprise a buckle that clamps the other end of the strap (which may be a ‘free’ end with no additional fastening features provided). The ends of the strap may be configured for the person to tie together, in a knot for instance. This may enable the user to easily wear and remove the device. Alternatively, the wearable device may comprise a continuous loop which can be fitted to a person’s body and hold the sensor unit thereto, without the need for fastening. The strap may be elasticated to provide sufficient tension to hold the sensor unit against the person. Other configurations may be provided, such as a shorter length strap or an elasticated strap for wearing the device on a limb of the person, for example, their upper arm.

[0038] A length of the strap may be selected depending on the size of the person (e.g., a strap for a child person is likely to be smaller than a strap for an adult person). The length of the strap may be adjustable to enable the strap to be used with different body sizes. The strap may be at least 40 cm in length, for instance. The fastener for fastening the strap around the person’s chest may be configured to set the length of the strap at various lengths, which may be discrete or continuously adjustable. For example, a belt buckle may be insertable in a plurality of discrete belt holes, or each opposing end of the strap may have a hook and loop fastener portion which enables the two ends to be connected by overlapping them to the desired size and then fastening the ends together.

[0039] The port may comprise an electrical socket of the sensor unit configured for receiving an electrical cable. Since the port is covered by the strap when the sensor unit is attached to the strap, the electrical cable may only be connectable to the sensor unit when the sensor unit is detached from the strap. This provides safety benefits since the person cannot attempt to charge the device while wearing it (which might otherwise cause electrical shocks, for example).

[0040] The electrical cable may be configured to charge the sensor unit, e.g. by charging a battery of the sensor unit. The electrical cable may be configured to transfer data between the sensor unit and a remote device, e.g. to upload sensor data from the sensor unit to the remote device for processing. The electrical cable may be configured to simultaneously transfer data and charge the sensor unit. The port may therefore be an electrical charging port, a data port, or a combined electrical charging port and data port. For example, the port may comprise a USB port or any other universal connection port. By locating the port such that the strap (in a thickness direction) covers the port when the sensor unit is attached to the strap, the port is protected (at least in part) from potential damage e.g. by debris falling into the port, from dust, and to an extent from moisture, etc. Also, the risk from electric shocks is reduced since the port is not accessible (e.g. by the person) while the sensor unit is attached to the strap. Therefore, safety of the device is improved.

[0041] The port may be located on the first surface of the main portion so that when the sensor unit is attached to the strap, the port is covered by the first side of the strap. Alternatively, the port may be located on the projection portion of the sensor unit so that when the sensor unit is attached to the strap, the port is covered by a part of the strap that surrounds the opening (i.e. an internal surface of the opening). In other words, because the projection portion extends through the opening, the port can be located on the part of the projection portion that sits in the opening so that the thickness of the opening of the strap covers the charging port. Advantageously, when the port is located on the projection portion and the projection portion projects from the first surface of the main portion, an electrical cable connected to the port may be supported at least in part by the main portion. This may reduce the likelihood of damage to the cable while it is connected to the sensor unit, e.g. from bending of the cable.

[0042] The sensor unit may be sealed so as to prevent moisture ingress. For example, the main portion and the projection portion may be waterproof or at least water resistant. This avoids potential moisture-related damage, e.g., from sweat from the person or other liquids which come into contact with the sensor unit.

[0043] In a second aspect, there is provided a method of monitoring a blood pressure of a person using the wearable device of the first aspect, the method comprising: attaching the sensor unit to the strap such that the majority of the sensor unit is located on the first side of the strap, the projection portion of the sensor unit including the optical sensor extends through the opening in the strap, and the port is covered by the strap; arranging the wearable device around the person’s chest or around a limb of the person (e.g., around the upper arm); detecting the one or more physiological parameters using the sensor; and determining the person’s blood pressure based on the one or more physiological parameters.

[0044] Some benefits may be realised by locating the majority of the sensor unit on the outside of the strap (i.e., greater than 50% of the volume of the sensor unit is on the outside of the strap, and less than 50% of the volume of the sensor unit is extending through the opening in the strap to the second side of the strap), even when the port is not covered by the strap.

[0045] Thus, in a broader aspect there is provided a wearable device for monitoring a blood pressure of a person, comprising: a strap for extending around a chest of the person or a limb of the person; and a sensor unit removably attachable to the strap for being secured to the person by the strap, the sensor unit comprising an optical sensor (and optionally other sensors) for detecting one or more physiological parameters relating to the person’s blood pressure; wherein when the sensor unit is attached to the strap, a majority of the sensor unit is located on a first side of the strap and a projection portion of the sensor unit including the optical sensor extends through an opening in the strap to a second side of the strap.

[0046] Optionally, the sensor unit comprises a port located such that the strap covers the port when the sensor unit is attached to the strap.

[0047] Also, some benefits may be realised by covering the port by the strap when the sensor unit is attached to the strap, even when the majority of the sensor unit is not located on the outside of the strap.

[0048] Thus, in another broader aspect, there is provided a wearable device for monitoring a blood pressure of a person, comprising: a strap for extending around a chest of the person or a limb of the person; and a sensor unit removably attachable to the strap for being secured to the person by the strap, the sensor unit comprising a sensor for detecting one or more physiological parameters relating to the person’s blood pressure; wherein the sensor unit comprises a port located such that the strap covers the port when the sensor unit is attached to the strap.

[0049] Optionally, when the sensor unit is attached to the strap, a majority of the sensor unit is located on a first side of the strap and a projection portion of the sensor unit including the sensor extends through an opening in the strap to a second side of the strap.

[0050] The broader aspects may include any of the features of the preceding aspects.

[0051] Certain embodiments of the disclosure will now be described, by way of example only, and with reference to the accompanying drawings.

[0052] Figure 1 shows a front perspective view of a wearable device;

[0053] Figure 2 shows a rear perspective view of the wearable device of Figure 1 ;

[0054] Figure 3 shows a top view of the wearable device of Figure 1 ;

[0055] Figure 4 shows a front view of the sensor unit of the wearable device of Figure 1 ;

[0056] Figure 5 shows a top view of the sensor unit of Figure 4;

[0057] Figure 6 shows a rear perspective view of the sensor unit of Figure 4;

[0058] Figure 7 shows a rear perspective view of the wearable device of Figure 1 with the strap partially cut away;

[0059] Figure 8 shows a schematic representation of a sensor unit comprising a plurality of sensor devices; Figure 9 shows a schematic representation of a sensor unit comprising a multisensor chip;

[0060] Figure 10 shows a rear perspective view of the strap of the wearable device of Figure 1; and

[0061] Figure 11 shows a front perspective view of the strap of Figure 10.

[0062] Detailed Description

[0063] A wearable device 1 for monitoring a blood pressure of a person according to an embodiment is shown in Figures 1, 2 and 3. The wearable device 1 comprises a strap 2 and a sensor unit 4 attached to the strap 2. The sensor unit 4 is removably attached to the strap 2 so that the sensor unit 4 can be detached from the strap 2 as desired, e.g. to charge the sensor unit or wash the strap.

[0064] The strap 2 is for extending around a chest of the person whose blood pressure is to be monitored. The wearable device 1 is therefore a chest-worn device.

[0065] In an alternative embodiment (not shown), the strap 2 may be made shorter for fitting around a limb of the person, for example, around the upper arm of the person.

[0066] The strap 2 comprises a central portion 6 to which the sensor unit 4 is attachable, and first and second arms 8, 10 extending outwardly from the central portion 6. The arms 8, 10 comprise a flexible material such as a fabric to enable them to wrap around the person.

[0067] Each arm 8, 10 comprises a fastening feature 12, 14 at an end thereof, enabling the arms 8, 10 to be fastened together to secure the strap 2 to the person. In this example, the first arm 8 comprises a loop 12 and the second arm 14 comprises a hook 14 for engaging the loop. The arms 8, 10 can thus be connected together by inserting the hook 14 into and through the loop 12.

[0068] Other strap arrangements are envisaged, for example, where the arms 8, 10 are of different lengths to that indicated in the figures e.g., to position an adjustment feature to one side of the person, or where ends of the strap 2 connect closer to the sensor unit 4. The format shown in the figures, however, is likely to be more familiar to a person because of existing heart rate monitors.

[0069] The length of the strap 2 can be selected to fit around the particular person’s chest, as indicated by the broken lines 16. The length of the strap 2 is adjustable using a length adjustment mechanism 18 located on the second arm 10. This enables size adjustments of the strap 2 so that the same strap 2 can fit persons within a range of sizes. A suitable strap may also be provided for wearing the device on a limb of the person.

[0070] The sensor unit 4 is attached to a first side 20 of the strap 2. The sensor unit 4 comprises a main portion 22 located on the first side 20 of the strap 2 and a projection portion 24 which extends through an opening 36 in the strap 2 to a second side 26 of the strap 2 (see Figures 10 and 11, which show the opening 36 in the strap 2 with the sensor unit 4 removed). When the wearable device 1 is worn by a person, the second side 26 of the strap 2 faces toward the person and the first side 20 of the strap 2 faces away from the person.

[0071] The central portion 6 of the strap 2 comprises a plate portion 28 having a first plate section 30 on the first side 20 of the strap 2 (see Figure 1) and a second plate section 32 on the second side 26 of the strap 2 (see Figure 2). The plate sections 30, 32 comprise a rigid material such as hard plastic or metal.

[0072] Figures 2 and 3 show the projection portion 24 of the sensor unit 4 protruding from the opening 36 in the strap 2. The projection portion 24 comprises a sensor (or sensors) including an optical sensor for measuring one or more physiological parameters of the person. The optical sensor may be a PPG sensor 60 and may have one or more LEDs for emitting light on to the person’s skin. The sensor or sensors are internal to the sensor unit 4 and may only be visible via a sensor surface 34 on the projection portion 24 which is for contact with the person where one or more physiological parameters are sensed. The sensor surface 34 of the sensor unit 4 is located at a distal end of the projection portion 24 so that when the wearable device 1 is worn by the person, the sensor surface 34 contacts the person’s skin. The sensor surface 34 may provide a window to allow light from the PPG sensor 60 to be directed on to the person’s skin. The sensor surface 34 may protrude, as shown, beyond the surface of the strap 2 which is in contact with the person. In this way, the strap and the skin of the person can help to ‘surround’ the PPG sensor and reduce effects of ambient light.

[0073] Other components of the optical sensor (and / or other sensors), such as emitter and / or receiver components, are housed within the projection portion 24 and / or the main portion 22 of the sensor unit 4. As shown schematically in Figure 8, the sensor unit 4 may, in addition to the PPG sensor 60, comprise an ECG sensor 62 (which can observe ECG signals received by ECG electrodes 58 in the strap 2 via conductive protrusions 48 in the sensor unit 4), motion detectors 64, 66 (such as a gyroscope 64 and / or an accelerometer 66), a temperature sensor 68, etc. These other sensors may be housed in the main portion 22 of the sensor unit 4 (as shown in Figure 8), or in in the projection portion 24 of the sensor unit.

[0074] The sensor unit 4 is shown in more detail in Figures 4, 5 and 6.

[0075] The main portion 22 comprises a first surface 38 (see Figure 6) which abuts the first side 20 of the strap 2 when the sensor unit 4 is attached to the strap 2, and a second surface 40 (see Figure 4) which faces away from the strap 2 when the sensor unit 4 is attached to the strap 2. The main portion 22 comprises three LEDs 42 which display information to the person, e.g. regarding battery status, wireless connectivity to a remote device, etc. The main portion 22 also comprises a button 44 on a top surface 46 thereof which allows the person to control the sensor unit 4, e.g. to turn the sensor unit 4 on and off.

[0076] The main portion 22 comprises attachment features in the form of two protrusions 48 extending outward from the first surface 38, as shown in Figures 5 and 6. The protrusions 48 are received in corresponding recesses 54 in the strap (see Figure 11) to form a push-fit connection between the sensor unit 4 and the strap 2. The protrusions 48 comprise electrodes that are configured to communicate, via recesses 54, with ECG electrodes 58 of the strap 2. The two protrusions 48 on the sensor unit 4, arranged either side of the projection portion 24, may provide electrical connections to the ECG electrodes 58 in the strap 2 as well as mechanical attachment of the sensor unit 4 to the strap 2, so as to keep the port 50 covered by the strap 2 when the sensor unit 4 is in place on the strap 2.

[0077] The projection portion 24 extends outwardly from the first surface 38 of the main portion 22. The projection portion 24 comprises the sensor surface 34 and a port 50. The port 50, in the illustrated embodiment, is located on a top surface 52 of the projection portion 24. The port 50 is for receiving an electrical cable, such as a charging cable and / or a data transfer cable. The main portion 22 may help to support a cable when located in the port e.g., to help the person slide an end of the cable into the port 50, or to shield the cable from accidental deflection when it is lodged in the port 50, and thereby help to minimise damage to the port 50, which might cause the device to fail.

[0078] The main portion 22 is substantially rectangular in cross-sectional shape, with rounded corners to provide a more ergonomic design. The substantially rectangular form of the main portion 22 may assist the location and form of components like a battery and / or control electronics within the sensor unit 4. The projection portion 24 has a substantially cylindrical shape. A substantially cylindrical shape may assist integration of components like the sensor (or sensors) within the sensor unit 4. A substantially cylindrical shape may also offer ease of use benefits when attaching the sensor unit 4 to the strap 2. The projection portion 24 may include flat portions to resist twisting within the opening 36, and may be rounded-off towards a surface of the projection portion 24 which is for contact with the person’s skin. In this way, the form of the projection portion 24 may help to guide the sensor unit 4 during attachment and support it during use, while also presenting a smooth surface where it protrudes for contact with the person. Other shapes could be provided.

[0079] As shown in Figure 7, the port 50 is located on the sensor unit 4 such that when the sensor unit 4 is attached to the strap 2, the port 50 is hidden within the strap 2. In Figure 7, part of the strap 2 has been cut away and it can be seen that the port 50 is covered by the thickness of the strap 2, in particular by the second plate section 32. The second plate section 32 may be formed from a material which has sufficient compliance to bend and follow the shape of the person’s body in use while being stiff enough to support and retain the sensor unit 4. The second plate section 32 may be of a thickness of more than 1mm, optionally more than 2mm, in order to provide an opening depth which is greater than the thickness of a majority of a remainder of the strap 2, so that the depth of the opening 36 may support the projection portion 24 while also hiding the port 50 within the strap 2.

[0080] Figure 7 also shows one of the electrodes 48 (studs) of the sensor unit 4 projecting from the first surface 38 of the main portion 22. The electrodes 48 are received by recesses 54 (not visible in Figure 7 but visible in Figure 11) that extend at least partially through the plate portion 28, and are covered by an outer portion of the second plate section 32 to form a socket. In this way, the electrodes 48 of the sensor unit 4 and the recesses 54 are configured to provide a pair of male I female electrical connectors that push-fit together. The electrodes 48 communicate through the recesses 54, which are made of a conductive material, with ECG electrodes 58 provided in the strap 2. The strap ECG electrodes 58 are located on the second side 26 of the strap 2 such that they arranged to make contact with the person during use. The ECG strap electrodes 58 are configured to take ECG signals by observing the electrical activity of the person’s heart, such as through detecting variations in electrical potential produced by the heartbeats of the person. The ECG signals are communicated from the strap ECG electrodes 58 to the sensor unit 4 via the electrical connection provided by the electrodes 48.

[0081] Figures 8 and 9 schematically show the various components of the sensor unit 4. As can be seen from Figure 8, the sensor unit 4 comprises PPG sensor 60 and port 50 within the projection portion 24, and comprises other sensors 62, 64, 66, 68 and conductive protrusions 48 within the main portion 22. The main portion 22 of the sensor unit 4 further comprises a battery 70, a memory storage 72, and a processor 74. The battery 70 may provide power to the various components of the sensor unit 4, and may be a rechargeable battery chargeable through port 50. The memory storage 72 may be configured to store data obtained from the various sensors, and said data may be accessible (e.g., using a remote device) from the memory storage 72 via either a wired connection to the sensor unit 4 through port 50, or through a wireless connection such as Bluetooth. The data from the sensors may be directly stored in memory storage 72, or may be firstly processed by processor 74. In this case, the memory storage 72 may store the processed sensor data. The processor 74 may be configured to determine blood pressure from the sensor data and analyse said blood pressure to determine a pattern of behaviour.

[0082] Whilst shown as separate devices in Figure 8, the sensors 62, 64, 66, 68 may alternatively be integrated into a single chip 76 within the sensor unit 4, as shown in Figure 9. In this case, the chip 76 provides the PPG sensor functionality as well as that of the other sensors 62, 64, 66, 68, and is housed in the projection portion 24 of the sensor unit. The chip 76 can observe ECG signals via conductive protrusions 48, which are electrically connected to ECG electrodes 58 in the strap.

[0083] Figures 10 and 11 show the strap 2 of the wearable device 1 without the sensor unit 4 included. The opening 36 is visible extending from the first side 20 to the second side 26 of the strap, in particular through the first plate section 30 and the second plate section 32.

[0084] The perimeter surface 56 of the opening 36 has substantially the same size and shape as the outer surface of the projection portion 24, so that the projection portion 24 can extend through the opening 36 and be seated therein without allowing excessive relative movement between the strap 2 and the sensor unit 4. The sensor unit 4 is therefore held more stably by the strap 2. This also reduces the amount of light leakage through the opening 36 when the sensor unit 4 is attached to the strap 2, which might otherwise interfere with the sensor readings. Furthermore, when the perimeter surface 56 of the opening 36 covers the port 50 (e.g. as shown in Figure 7), then a close match between the size and shape of the opening 36 and the projection portion 24 enables the port 50 to be covered and protected more effectively by the strap 2.

[0085] Figure 11 also shows two recesses 54 in the first plate section 30 which in use engage with the corresponding attachment features (protrusions 48) of the sensor unit 4 to attach the sensor unit 4 to the strap 2. Other attachment features could be provided in addition to or instead of the corresponding protrusions 48 and recesses 54 depicted in the Figures, and / or the number of attachment features could be more or fewer than two. The perimeter surface 56 of the opening 36 may also be provided with compliant / resilient material to grip the projection portion 24 when fitted in the opening 36. In this way the material of the opening 36 may act as a grommet to help aid retention of the projection portion 24 in the strap 2.

Claims

CLAIMS:

1. A wearable device for monitoring a blood pressure of a person, comprising: a strap for extending around a chest of the person or around a limb of the person; and a sensor unit removably attachable to the strap for being secured to the person by the strap, the sensor unit comprising an optical sensor for detecting one or more physiological parameters relating to the person’s blood pressure; wherein when the sensor unit is attached to the strap, a majority of the sensor unit is located on a first side of the strap and a projection portion of the sensor unit including the optical sensor extends through an opening in the strap to a second side of the strap; and wherein the sensor unit comprises a port located such that the strap covers the port when the sensor unit is attached to the strap.

2. A wearable device as claimed in claim 1 , wherein the optical sensor comprises a photoplethysmography (PPG) sensor.

3. A wearable device as claimed in claim 1 or 2, wherein the sensor unit comprises a sensor surface for contacting the person’s skin, wherein the sensor surface protrudes from the opening on the second side of the strap when the sensor unit is attached to the strap.

4. A wearable device as claimed in any preceding claim, wherein the port is located on the projection portion of the sensor unit.

5. A wearable device as claimed in any preceding claim, wherein the sensor unit comprises a processor configured to determine the person’s blood pressure based on the one or more physiological parameters, or wherein the sensor unit is configured to transmit information regarding the one or more physiological parameters to a remote device for processing.

6. A wearable device as claimed in any preceding claim, wherein the one or more physiological parameters include a heart rate, heart rate variability, ECG, oxygen saturation, sleep, respiration rate, body surface temperature, and / or pulse wave velocity of the person along with other features of the optical sensor and other sensors of the sensor unit.

7. A wearable device as claimed in any preceding claim, wherein the sensor unit comprises a main portion having a first surface which abuts the first side of the strap when the sensor unit is attached to the strap, and wherein the projection portion of the sensor unit projects from the first surface.

8. A wearable device as claimed in any preceding claim, comprising a fastener for fastening the strap around the person’s chest.

9. A wearable device as claimed in any preceding claim, wherein a length of the strap is adjustable.

10. A wearable device as claimed in any preceding claim, wherein the sensor unit comprises a display feature for displaying information to the person, wherein the display feature optionally comprises an LED and / or a screen.

11. A wearable device as claimed in any preceding claim, comprising an input component configured to provide user control of the device, wherein the input component is optionally a button or a touch-operated screen.

12. A wearable device as claimed in any preceding claim, wherein the strap comprises a plate portion surrounding the opening and wherein the sensor unit is removably attachable to the plate portion.

13. A wearable device as claimed in any preceding claim, comprising an attachment feature configured to allow the sensor unit to be removably attached to the strap, wherein the attachment feature optionally comprises a push fit connector, a screw, a hook and loop fastener, or a magnet.

14. A wearable device as claimed in any preceding claim, wherein the port comprises an electrical charging port, a data port, or a combined electrical charging port and data port; wherein the port is optionally a USB port or any other universal connection port.

15. A method of monitoring a blood pressure of a person using the wearable device of any preceding claim, the method comprising: attaching the sensor unit to the strap such that the majority of the sensor unit is located on the first side of the strap, the projection portion of the sensor unit including theoptical sensor extends through the opening in the strap, and the port is covered by the strap; arranging the wearable device around the person’s chest or around a limb of the person; detecting the one or more physiological parameters using the sensor unit; and determining the person’s blood pressure based on the one or more physiological parameters.

Images