Baby monitoring system

Abstract

A system (100) for monitoring physiological parameters of a baby. The system (100) comprises a wearable device (102) and a controller module (150). The wearable device (102) comprises a flexible support element (104), configured to conform with a profile of the skin of the baby, at least two optical PPG sensors for SpO2 measurement, each optical PPG sensor supported in contact with the baby's skin by the flexible support element, and at least two ECG electrodes (106, 108), each ECG electrode (106, 108) supported in contact with the baby's skin by the flexible support element (104), or at least two ECG electrode contacts, each for receiving an ECG electrode that is supported in contact with the baby's skin by the flexible support element (104). The controller module (150) comprises a wireless transmitter configured to transmit data indicating the physiological parameters to a base station. The physiological parameters comprise a heart rate and / or pulse rate and an SpO2 measurement. The wearable device (102) may be a wearable patch device or a wearable band device.

Description

[0001] BABY MONITORING SYSTEM

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a system for monitoring physiological parameters of a baby, and to related methods.

[0004] BACKGROUND

[0005] An estimated 10% of newborn babies require some form of assistance or resuscitation at birth (in the UK about 72,000 / year and globally around 14 million / year). For high- risk infants, such as those born preterm or following birthing difficulties, resuscitation increases risk of dying or developing life-long disabilities including cerebral palsy. Brain injury at or soon after birth occurs in -3,500 babies each year in England.

[0006] Optimal resuscitation practice in the first ‘golden minutes’ of life can reduce the risk of death and brain injury. Current evidenced-based international resuscitation guidelines recommend that multiple physiological parameters are monitored to ensure optimal care, including heart rate, oxygen saturation and temperature. Monitoring these parameters requires multiple sensors and devices, many of which perform poorly as they are not designed for the unique delivery room environment. Failure to monitor these physiological parameters makes it more challenging to reliably maintain these parameters within acceptable ranges. A failure to maintain such parameters within acceptable ranges increases the risk of death or significant morbidity including brain injury.

[0007] Improving newborn monitoring has the potential to advance resuscitation practice, reduce death or severe morbidity, and significantly reduce healthcare costs.

[0008] Research is underway to develop suitable systems for monitoring physiological parameters of neonates. A recent review paper (Wu, Ellen, et al. "Wireless Monitoring Systems for Vital Signs in Neonates and Infants: a Systematic Review." Neonatology Today 17.8 (2022)) concluded by stating that “Our review here suggests a tremendous unmet clinical need and a gap in evidence for novel wearable monitoring platforms for neonates and infants — too often, vulnerable populations such as these are overlooked when it comes to medical technology innovation”. Although there has been some progress in the development of suitable systems, there is considerable room for improvement and further development. The present invention is intended to address or ameliorate some of the above-mentioned problems.

[0009] SUMMARY

[0010] According to a first aspect, there is provided a system for monitoring physiological parameters of a baby, the system comprising: a wearable device comprising: a flexible support element, configured to conform with a profile of the skin of the baby; at least two optical PPG sensors for SpO2 measurement, each optical PPG sensor supported in contact with the baby’s skin by the flexible support element; and at least two ECG electrodes, each ECG electrode supported in contact with the baby’s skin by the flexible support element or at least two ECG electrode contacts, each for receiving an ECG electrode that is supported in contact with the baby’s skin by the flexible support element; and a controller module comprising a wireless transmitter and configured to transmit data indicating the physiological parameters to a base station, the physiological parameters comprising: i) a heart and / or pulse rate; and ii) an SpO2 measurement.

[0011] The physiological parameters may further comprise a respiration rate. A respiration rate may be determined from PPG sensor, for example by filtering a PPG signal with a bandpass filter that passes only frequencies corresponding with an expected breathing rate, then determining a frequency with a maximum power spectral density in the filtered signal. Any other suitable method may also be used (for example performing an FFT and picking the peak in the range of frequencies corresponding with an expected respiration rate, or machine learning, and / or approaches that fuse data obtained via ECG electrodes and PPG sensors).

[0012] The system may comprise the base station. The base station may comprise a display, on which an indication of the physiological parameters is shown. The controller module may be configured to receive or determine the physiological parameters from signals obtained from the wearable device. For example, the heart rate may be determined by the controller module in response to signals obtained from the wearable device. As a further example, the SpO2 measurement may be determined by the controller module in dependence on signals obtained from the wearable device.

[0013] The data indicating the physiological parameters may comprise data from which the physiological parameters can be determined. For example, the data may comprise raw measurements of the output from a photodiode (e.g. obtained in a transimpedance configuration) of each PPG sensor, and the base station may be configured to determine an SpO2 measurement from the data.

[0014] The determination of the SpO2 measurement and / or the heart rate may be performed at the controller module or the base station.

[0015] The physiological parameters may comprise a temperature of the baby (e.g. a skin temperature). The wearable device may comprise a temperature sensor, configured to measure the skin temperature of the baby, and to transmit a signal indicating the temperature of the baby to the controller module. A core temperature of the baby may be inferred from a skin temperature.

[0016] The system may be configured to determine a plurality of preliminary SpO2 measurements, each of the preliminary SpO2 measurements obtained from signals from one of the PPG sensors.

[0017] The system may be configured to determine the SpO2 measurement as the most reliable of the plurality of preliminary SpO2 measurements. The most reliable of the plurality of SpO2 measurements may be determined based on a signal metric determined from each SpO2 measurement.

[0018] The system may be configured to determine the SpO2 measurement by combining at least some of the plurality of preliminary SpO2 measurements. For example, where there are three preliminary SpO2 measurements, the measurement that is most different from the average may be discarded as unreliable, and the average of the remaining two preliminary SpO2 measurements determined as the SpO2 measurement. In some embodiments combining may comprise simply taking an average (mean) measurement. A preliminary SpO2 measurement may be discarded as unreliable if a pulse rate indicated by the corresponding PPG sensor is not within a predetermined threshold (e.g. 5 bpm) of a pulse rate indicated by at least one other PPG sensor or of a pulse rate determined from an RR interval of an ECG measurement from the ECG electrodes . Other reliability metrics can be used such as: PPG skewness; baseline variability; signal to noise ratio; threshold / range of acceptance for both red and infra red perfusion indices as well as PPG AC amplitude; etc. The SpO2 measurement may determined over a sliding window (for example of 5-15 seconds) in order to capture several pulsatile pulses thereby removing outliers.

[0019] The wearable device may be a wearable patch device and the flexible support element may be a flexible patch configured to adhere to and conform with a baby’s skin.

[0020] The flexible patch may comprise a polymer layer with a thickness of 100 microns or less, or 75 microns or less, or 50 microns or less. The polymer layer may comprise or consist mainly or entirely of LDPE, or another similar polymer material (e.g. MDPE, polyester, PET etc).

[0021] An elastic modulus of the polymer layer may be less than 10 GPa or less than 5 GPa.

[0022] The flexible patch may have a surface area of at least 60cm2, 50cm2or 40cm2.

[0023] The at least two optical PPG sensors may be disposed in a sensor subsystem of the wearable device, and the sensor subsystem may be disposed centrally in the flexible patch.

[0024] A minimum distance of at least 20mm or 15mm or 10mm may be provided between an edge of the sensor subsystem and an edge of the flexible patch. An edge of the sensor subsystem may be defined as an edge of a flexible printed circuit board region that is populated by the PPG sensors (exclusive of ECG electrodes).

[0025] The sensor subsystem may comprise a cut out bite configured as an alignment aid and / or for facilitating access to the cardiac muscle of the baby for chest compressions. The wearable device may comprise a reflector disposed over the sensor subsystem (e.g. over a whole surface of the sensor subsystem). The reflector may be configured to reflect incident radiant heat and other stray light sources (including ambient) away from the sensor subsystem.

[0026] The controller module may be spaced apart from the wearable device by a cable that is at least 8cm or at least 10cm long. The cable may be less than 20cm long or less than 15cm long. The cable may be between 9cm and 12cm long. If the cable is too long it increases the risk of entanglement (with the baby or with something else in the region of the baby). The controller module may comprise a power source (e.g. battery) configured to power the wearable device via the cable.

[0027] The controller module may comprise a processor or microcontroller. The wearable device may comprise an analog readout circuit, configured to provide digital signals to the microcontroller of the controller module.

[0028] In certain embodiments, in which the wearable device is a wearable patch device, the system may be configured to route the cable over the shoulder of the baby when the ECG electrodes are properly positioned about the baby’s heart.

[0029] The wearable device may be a wearable band device, and the flexible support element may be a chest wearable band configured to urge the wearable band device into contact with the baby’s chest or back. Such an arrangement facilitates comfortable skin to skin (kangaroo care) for parents and family in a hospital or home setting.

[0030] The band may comprise a fabric material. The fabric material may comprise an elastic material (i.e. the band may be an elastic band, capable of lengthening elastically by at least 5% or at least 10%). The elastic material may, for example, comprise spandex / elastane (polyether-polyurea copolymer). The elastic fabric material may comprise at least 5% spandex or at least 8% spandex or at least 10% spandex.

[0031] The band may comprise a hook and loop fastening system. The band may be formed into a loop by fastening a loop region to a hooked region of the band. The wearable device may comprise two or more sensor subsystems interconnected by a flexible printed circuit board.

[0032] Each sensor subsystem may comprise a loop through which the band is threaded. The loop may be rigid and formed from a polymer material (i.e. a hard polymer material).

[0033] Each sensor subsystem may comprise at least one of the at least two PPG sensors. For example, there may be two subsystems, and each subsystem may comprise a PPG sensor.

[0034] The wearable device may comprise an ECG electrode contact at each end of the flexible printed circuit board, each ECG electrode contact configured to receive an ECG electrode (e.g. by a snap fit connection). The advantage that this offers is that inexpensive, standard off the shelf neonatal electrodes can be utilised without disposing of the main sensor configuration. For example, neonatal electrodes may comprise a conductive hydrogel with relatively low adhesion forces.

[0035] The controller module may be removable to allow for hot swapping of a fully recharged module, for example to interrupt the monitoring session. The controller module may be held in place by magnetic or snap fix coupling.

[0036] The baby may be a neonate (i.e. under 28 days old).

[0037] According to a second aspect, there is provided the wearable device of the first aspect, including any optional features thereof, optionally also including any of features described with reference to example embodiments. According to a third aspect, there is provided the controller module of the first aspect, including any optional features thereof, optionally also including any of the features described with reference to example embodiments.

[0038] According to a fourth aspect, there is provided a method of monitoring physiological parameters of a baby, comprising: attaching a wearable device to the baby, wherein attaching the wearable device comprises conforming a flexible support element to a profile of the skin of the baby; connecting the wearable device to a controller module via a cable and a connector; at the wearable device, detecting signals indicative of the physiological parameters; transmitting the signals to the controller module; transmitting further signals, indicative of the physiological parameters to a base station comprising a display; displaying, at the base station, the physiological parameters based on the further signals; wherein the physiological parameters comprise: i) heart and / or pulse rate; and ii) an SpO2 measurement.

[0039] The physiological parameters may further comprise a respiration rate and / or a skin temperature of the baby.

[0040] The flexible support element may comprise a flexible patch or a chest wearable band. The physiological parameters may further comprise a temperature of the baby.

[0041] The features of the first aspect may be combined with those of the fourth aspect, and the features of the fourth aspect may be combined with those of the first aspect. The method of the fourth aspect may comprise the use of any of the features mentioned with reference to the first aspect and described with reference to the example embodiments. The system of the first aspect may comprise features described with reference to the example embodiments.

[0042] BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Example embodiments will be described, with reference to the accompanying drawings. These embodiments are not intended to limit the scope of the present disclosure, but may be useful in understanding the appended claims.

[0044] Figure 1 is a top view of an example system comprising a wearable patch device with a controller module attached to the wearable patch device;

[0045] Figure 2 is a bottom view of the example system of Figure 1 ; Figure 3 is a top view of the example system of Figure 1 with the controller module not present (with the system arranged with stiff card backing for transport);

[0046] Figure 4 is an exploded diagram of the wearable patch device of Figures 1 to 3;

[0047] Figure 5 is a block diagram showing features of an example wearable device;

[0048] Figure 6 is an exploded diagram of an example controller module;

[0049] Figure 7 is a block diagram showing features of an example controller module;

[0050] Figure 8 is an exploded diagram of a charging dock for two controller modules;

[0051] Figure 9 is a rendering of the system of Figure 1 being worn by a baby;

[0052] Figure 10 is a further rendering of the system of Figure 1 being worn by a baby, showing a base station comprising a display;

[0053] Figure 1 1 shows a system comprising a wearable band device and controller module;

[0054] Figure 12 is a top and side view of the wearable band device of Figure 11 ;

[0055] Figure 13 is a bottom view of the wearable band device of Figure 11 ;

[0056] Figure 14 is an orthographic top view and bottom view of the band of the system of Figure 11 ;

[0057] Figure 15 shows two views of the controller module of Figure 11 ;

[0058] Figure 16 is a front view and side view of a charging station for the controller module of Figure 15;

[0059] Figure 17 shows the system of Figure 1 1 in use, in a hospital context, with a baby wearing the wearable band device about its chest and the sensors and electrodes in contact with the front of the baby; and Figure 18 shows the system of Figure 1 1 in use, in a kangaroo care context, with a baby resting on its mother’s chest and wearing the wearable band device about its chest with the sensors and electrodes in contact with the back of the baby.

[0060] DETAILED DESCRIPTION

[0061] Referring to Figures 1 and, a system 100 is shown. The system 100 is for monitoring physiological parameters of a baby and more specifically is designed for use with neonates (for example in the context of neo-natal intensive care). The system 100 comprises wearable device 102, controller module 150 and cradle 122.

[0062] The wearable device 102 comprises flexible support element 104, sensor module 110, ECG electrodes 106, 108, lead 120 and controller module connector 115.

[0063] The wearable device 102 in this example is a wearable patch device, and the flexible support element is a flexible patch 104 that is configured to adhere to and conform with a baby’s skin without the use of conventional adhesives (which have the potential to injure a newborn baby’s skin on removal). The flexible patch 104 may instead be adhered by surface tension forces resulting from being applied to a wet baby, and / or be adhered by relatively weak adhesion resulting from ECG hydrogel between the flexible patch 104 and the baby.

[0064] Improved adhesion with low adhesion forces per unit area can be achieved by the flexible patch 104 having a relatively large area and being relatively flexible. The relatively large area will mean that a low adhesion per unit area is sufficient to keep the wearable device attached, and the high flexibility will help the flexible patch 104 to achieve reliable adhesion over the whole area. A relatively stiff patch would tend to make contact only in limited areas, and would tend to work its way unstuck with movement of the baby.

[0065] The sensor subsystem 110 disposed approximately in the centre of the flexible patch 104. In this example the flexible patch 104 has an area of approximately 64 cm2(including the region occupied by the sensor subsystem) but in general an area of at least 50 cm2is desirable. The edge regions of the flexible patch 104 may be particularly important for adhesion, to prevent peeling from an edge. For example the area of the edge regions of the flexible patch (i.e. not including the sensor subsystem) may be at least 55 cm2, or at least 40 cm2. A distance from an edge of the sensor subsystem 110 to an edge of the flexible patch 104 may be a minimum of at least 27mm, and preferably at least 20mm or at least 15mm.

[0066] The flexible patch 104 in this example is made from LDPE, and has a thickness of ~50 microns. In general, materials with a thickness of less than 100 microns or 75 microns, and an elastic modulus of less than 10 GPa or less than 5 GPa may be preferable for achieving reliable adhesion with low adhesion force per unit area.

[0067] The sensor subsystem 110 comprises three optical PPG sensors. Each optical PPG sensor comprises a photodiode 111 and a pair of adjacent light emitting diodes (LEDs) (the position of which can be seen above the photodiodes 211a-c in Figure 4). Each pair of LEDs has different wavelengths - typically red and infra-red. The photodiode 111 detects the light from the adjacent LEDs after it has interacted with the adjacent tissue. The photocurrent is converted by adjacent transimpedance amplifiers into voltage. This voltage is digitised by an adjacent ADC into a digital data stream for transmission along lead 120 to the controller module 150 housed in the cradle 122.

[0068] As is known in the art, a peripheral blood oxygen saturation SpO2 can be determined from an R value that is determined as:

[0069] Where AC represents the pulsatile amplitude or AC component peak to trough value and DC represents the DC component of light measured by the photodiode, for red light and infra-red light respectively. The value of R can be related to the SpO2 value by a lookup table or similar approach. R is inversely related to SpO2, typically in a linear fashion.

[0070] In example system 100 there are three PPG sensors (but this is not essential, and variations are possible with two or four or more PPG sensors) . It is useful that there is more than one PPG sensor, because for neonatal care it is very important that the measured physiological parameters are reliable. Including a plurality of PPG sensors means that the signal quality can be determined, for example with reference to a quality of agreement between a first PPG sensor and a second PPG sensor. The three sensors provided in this example allow for improved reliability of signals over an implementation with two sensors. Any suitable method (e.g. data fusion, spectral matrix decomposition) can be used for combining signals from multiple redundant sensors. For example, a correlation between a pulsatile component of a PPG sensor and an RR interval or heart rate obtained from the ECG electrodes may provide an indication that the signal from the PPG sensor is reliable. A machine learning approach may also be used to identify a suitable method for data fusion (e.g. in which signals from the sensors are provided to an artificial neural network which has been trained to reliably determine the underlying physiological parameters using suitable labelled data such as a heart rate or pulse rate from another PPG sensor).

[0071] The ECG electrodes 106, 108 in this embodiment are formed integrally with the flexible patch 104, and are spaced apart from the sensor subsystem 110, which is disposed centrally within the flexible patch 104. As shown more clearly in Figure 9, the wearable device 102 is configured to be placed on the baby’s chest with the lead 120 running diagonally over the left shoulder of the baby so that the controller module 150 can rest on the mattress near the baby’s shoulder. When in use in the intended configuration, the first ECG electrode 106 is offset from the sensor subsystem 110 in the inferior and lateral directions and the second ECG electrode 108 is offset from the subsystem 110 in the medial direction.

[0072] In this example, each of the first and second electrodes 106, 108 comprise silver chloride, and the electrode radius is at least 5mm. The electrodes 106, 108 are preferably spaced apart (centroid to centroid) by at least 50mm so that they can be placed in different positions relative to the heart in order to detect electrical potentials associated with the heart.

[0073] In general, any arrangement in which the ECG electrodes 106, 108 are spaced apart from a central region of the flexible patch 104 will be suitable for obtaining ECG measurements from which an RR rate can be determined used well known methods (corresponding with the heart rate). System 100 has two electrodes, but this is not essential and other embodiments may comprise more electrodes, for example three or four electrodes.

[0074] The sensor subsystem 110 further comprises an analog front end or analog readout circuit, configured to receive analog signals from the PPG photodiodes 111 and the ECG electrodes 106, 108. The analog readout circuit may, for example, comprise a packaged integrated circuit that is configured for readout of PPG and ECG signals (an example of such a device is the Analog Devices ADPD4100, but any suitable circuit can be used). The analog readout circuit is configured to convert the signals from the PPG photodiodes 111 and the ECG electrodes 106, 108 to digital signals, from which SpO2 and / or heart rate can be determined by a controller (comprising a processor). An example of a suitable digital signal protocol is I2C.

[0075] The sensor subsystem 110 further comprises a temperature sensor. The temperature sensor may be any suitable device, capable of providing accurate measurements of body temperature (e.g. accurate within 0.2 or 0.1 degree C). An example of a suitable device is the Analog Devices MAX30208, which provides a digital (I2C) output indicating temperature, accurate to within 0.1 degree C.

[0076] In certain embodiments, in order to keep the size and mass of the wearable device to a minimum (which is especially important in the context of neonatal monitoring) , the battery and controller for the system 100 are housed off the wearable device 102 in a controller module 150 (with the wearable device 102 not including a battery) . The wearable device 102 in system 100 is connected to the controller module 150 by lead 120. The lead 120 ends in a controller module connector 115, which is configured to engage with a corresponding connector of the controller module 150 to enable the controller module 150 (located inside the cradle 122) to receive the digital signals derived from the output of the ECG electrodes 106, 108 and the PPG photodiodes 111.

[0077] In the example of Figures 1 to 4, the wearable device 102 is configured to connect to a controller module 150 that comprises pogo pins, and the system 100 is configured to magnetically urge the connector 115 into contact with pogo pins of the controller module 150. A cradle 122 is provided in system 100 for this purpose. Figure 4 shows some of the elements of the wearable device 102 in an exploded view. Specifically, the elements shown are: silk screen / ink layer 202, solder mask layer 204, bottom cover layer 206, silver / silver chloride layer 208, bottom copper layer 210, polyimide layer 212, top copper layer 214, top cover layer 216, stiffener 218 and metalized film 220. To the right of the exploded view of the elements is a view of the layout of the sensor subsystem 110 of the wearable device 230, showing the positions of photodiodes 211a-c analog readout circuit 231 , LEDs 1-6, and temperature sensor 232.

[0078] The metalized film 220 helps to prevent stray light reaching the PPG photodiodes 21 la-c and also helps avoid any heating of the sensor subsystem 110 by incident light or radiant heat sources (which are often present in a hospital setting).

[0079] The sensor subsystem 1 10 includes a “bite” 112 cut out from a corner thereof, which serves as both an aid to proper alignment on the baby’s chest, and also allows access to the baby’s heart muscle in the event that emergency compressions are required. As illustrated in Figure 9, the “bite” region should be aligned centrally on the baby’s chest over the baby’s heart muscle (approximately on the internipple line). The cutout bite region 112 therefore serves as an alignment aid.

[0080] Two power rails are provided to the wearable device 102 from the controller module 150, via the pogo pins and pogo contacts. The power for the analog readout circuit, memory and temperature sensor are sent over one pogo pin pair, and the power for the LEDs is sent over another pogo pin pair. The power is only switched on when the controller module 150 is connected to the cradle 122.

[0081] The wearable device 102 comprises an onboard memory. The onboard memory is used to adjust for the variance in the electrical properties of the patch, and stores calibration data that provides for compensation for any variation in the electrical and optical properties of each patch and within a patch i.e. central LED wavelengths for example. The calibration data can be obtained by calibration during production. This allows any wearable device 102 to be paired with any controller module 150, since the calibration data for the wearable device 102 is stored on the wearable device 102. Figure 5 shows a functional block diagram of the wearable device 102, which comprises: pogo contacts 402, dock sensor 403, regulator 405, LEDs 404, photodiodes 406, ECG electrodes 408, analog readout circuit 410, memory 412 and temperature sensor 414.

[0082] As already discussed, the pogo contacts 402 connect with the controller module 150, and provide incoming power from the controller module 150 to the wearable device 102, and carry digital signals from the wearable device 102 to the controller module 150. The analog readout circuit 410 receives and digitises signals from the ECG electrodes 408 and photodiodes 406. The analog readout circuit 410 comprises LED drive circuits for driving the LEDs 404, and receives and digitises signals from the photodiodes 406. The LEDs are pulsed on and off such that the photodiodes can also capture the stray light in what is called an ambient phase when the LEDs are off - allowing subtraction of such optical interference. The photodiodes 406 are held in contact with the flexible patch 104, which is in turn held in contact with the skin of the baby. The signals from the photodiodes 406 and ECG electrodes are captured at a rate of at least 100 samples per second, and preferably at least 200 samples per second.

[0083] The regulator 405 regulates the voltage received by the analog readout circuit 410. The regulator regulates the output from a battery power source (in the controller 550) to maintain a stable DC power supply for semiconductor components of the wearable device 502. The dock sensor 403 is configured to determine when the controller module 150 is received in cradle 122.

[0084] An output from the readout circuit comprises digital (I2C) signals that are transmitted to the controller module 150 via the pogo contacts 402. The output from the temperature sensor 414 is also digital, and is provided to the controller module 150 via the pogo contacts 402.

[0085] Figure 6 shows an exploded view of the controller module 150, comprising a top cover 302, light guide 304, screws 306, printed circuit board 308, pogo pin housing 310, magnets 312, pogo pins 314, battery 316, housing 318, gas permeable vent cover 320 and label 322.

[0086] The controller module 150 is configured to power the wearable device 102 via cable 120 from the battery 316. The system 100 comprises a controller module cradle 122 for facilitating connection between the controller module 150 and controller module connector 115 in which the controller 150 and connector 115 are urged together magnetically. The pogo pins 314 on the controller module 150 are spring loaded, and make electrical contact with corresponding contacts on the connector 115. This magnetic engagement is robust and also very straightforward to engage and disengage.

[0087] The controller module 150 comprises a processor or microcontroller, which receives digital signals from the analog readout circuit via cable 120 and connector 115. The processor of the controller module 150 may determine physiological parameters of the baby from these signals, the parameters comprising at least heart rate and SpO2 (and optionally also comprising respiration rate and skin temperature) . The controller module 150 also receives signals indicating the temperature of the baby from the sensor subsystem 110. The controller module 150 wirelessly transmits signals to a base station comprising a display. The base station is configured to display (on the display) at least some of the physiological parameters, for example a graph of heart rate, SpO2 , respiration rate and temperature.

[0088] Figure 7 shows a functional block diagram of the controller module 150, which comprises: pogo pins 401 , electrically controlled switch 422, comparator 424, regulator 426, EEPROM 428, indicator LED 454, microcontroller 430, battery management IC 434, Bluetooth module 432 and battery 436.

[0089] The controller module 150 (and in turn the wearable device 102) is powered by a battery 436, which is rechargeable. The battery management IC 434 charges and measures the battery state (e.g. state of charge, voltage etc). The battery management IC 434 is controlled by the microcontroller 430, for example over I2C.

[0090] The controller module 150 will not communicate or supply power to the wearable device 102 until the patch detect circuit is engaged. This is achieved through the switch 422 and comparator 424 on the controller module 150. Once the controller module 150 is connected to the wearable device 102, the controller module 150 supplies power to the wearable device and establishes an I2C connection between the microcontroller 430 and the analog readout circuit 410. The data received by the controller module 150 may be processed by the microcontroller 430 to determine the physiological parameters. For example, the heart rate may be determined by the microcontroller using signals obtained from the wearable device 102. The SpO2 measurement may be determined by the microcontroller in dependence on PPG sensor signals obtained from the wearable device 102.

[0091] The controller module 150 is configured to transmit data using the Bluetooth module 432 indicating the physiological parameters to a base station. The data may comprise the measured physiological parameters, as determined by the controller module 150, or may comprise more raw data from the sensors of the wearable device 102. For example, the data may comprise each signal from the photodiodes of the PPG sensors of the wearable device 102, and the base station may determine the physiological parameters therefrom. Similarly the raw ECG signals may be sent to the base station for further processing in order to determine a heart rate.

[0092] The indicator LED 454 provides a user interface for the controller module 150. In an example, the indicator LED 454 comprises a red LED, green LED and amber LED. A continuously lit green LED indicates that the controller module is powered on and connected wirelessly to a base station and ready to use. A flashing green LED indicates that the controller module is on but not yet connected wirelessly to a base station. A red LED indicates a warning, for one of the following reasons: connection to the wearable device is faulty, battery voltage is low. The orange LED indicates that the controller module 150 is charging.

[0093] Figure 8 shows a charging dock 350, for charging a controller module 150. This charging dock 350 is capable of charging two controller modules 150 at the same time (but this is not essential). The charging dock 350 comprise two sockets 361 , each socket 361 configured to receive a controller module 150 and charge it. Each charging socket comprises pogo contacts through which the controller module is charged via its pogo pins 362. The controller module 150 is preferably magnetically urged into engagement with the socket 361 , for example by a magnet in the controller module 150 and a ferroelectric element in the charging dock 350.

[0094] The charging dock 350 comprises: lid 360, PCB 365, housing 370, screws 371 and rubber feet 372. The sockets 361 are defined in the shape of the lid 360, and an opening is defined in the base of each socket 361 so that the pogo pins of the controller module 150 can make contact with contacts on the underlying PCB 365. The PCB 365 and lid 360 are held in place connected to the housing 370 by the screws 371. The base of the housing 370 is provided with rubber feet 372.

[0095] The screws 371 are merely one way to assemble the dock, and any other suitable approach can be used - for example the charging dock may snap together.

[0096] Referring to Figure 9, the system 100 is shown in use on a baby 130. The wearable device 102 is adhered to the chest of the baby, with the “bite” 122 positioned centrally on the internipple line [better definition from intercostal] . The ECG electrodes 106, 108 are consequently positioned on either side of the heart. The cable 120 is positioned over the left shoulder of the baby 130, with the controller module 150 on the mattress next to the left shoulder of the baby 130.

[0097] Figure 10 shows the system 100 comprising wearable device 102 and controller module 150 in the same position as shown in Figure 9. In Figure 10 a base station 160 comprising a display is visible. The display is showing: top) a graph of the ECG readout, and a numerical indication of heartrate; middle) a graph showing a PPG readout with a numerical readout of SpO2 level; bottom) a graph of temperature and respiration rate.

[0098] Figure 11 to 18 show alternative embodiments to the patch based wearable device of Figures 1 to 5, in which the flexible support element comprises a chest wearable band.

[0099] Figure 11 shows a system 500 comprising a wearable device 502, controller module 550 and flexible support element 540. The flexible element 540 in this embodiment is a chest wearable band 540 on which the wearable device 502 is mounted.

[0100] Figures 12 and 13 show the wearable device 502 configured for use with the band 540. The wearable device 502 comprises: first sensor subsystem 521 ; second sensor subsystem 531 ; cable 530, connector 505, first ECG contact 522 and second ECG contact 532.

[0101] The first and second sensor subsystems 521 , 531 respectively comprise a loop 523, 533 through which the band 540 may be threaded. The first and second sensor subsystems 521 , 531 each comprise a PPG sensor, each having two LEDs 525, 535 and a photodiode 524, 534. One of the sensor subsystems 531 comprises a temperature sensor 536, and the wearable device 502 comprises an analog to digital readout circuit (not visible in the drawings). The first sensor subsystem 521 and second sensor subsystem 531 are interconnected (electronically and physically) by a flexible printed circuit board: the wearable device 502 comprises a flexi-rigid PCB comprising rigid regions in each sensor subsystem 521 , 531 , a flexible sensor subsystem interconnect 519 and end regions bearing the ECG contacts 522, 532. The first ECG contact 522 is outboard of the first sensor subsystem 521 at one end of the wearable device 502 and the second ECG contact 532 is outboard of the second sensor subsystem 531 at the other end of the wearable device 502. Each of the ECG contacts 522, 532 is a button type contact, configured to make a snap connection to an ECG contact with a corresponding button connector. Snap on electrodes 527, 537 are shown connected to the ECG contacts in Figure 11. Alternatively other ECG attachments can be used such as adhesive, plugs and pincers.

[0102] A separation distance between the first sensor subsystem and the second sensor subsystem may be at least 1cm. A separation distance between the centre of each of the ECG contacts 522, 532 may be at least 3cm or at least 4cm.

[0103] The operation of the sensors and electronics of the wearable device 502 is very similar to that of the wearable device 102, and the description of the sensors and electronics for that device are equally applicable to this device. In this example wearable device 502 the pogo pin connectors are part of the connector of the wearable, rather than part of the controller module 550. There are two PPG sensors (one in each sensor subsystem 521 , 532), but in other embodiments there may be more PPG sensors. The wearable device 502 comprises a temperature sensor (536 ???) in at least one of the sensor subsystems 521 , 531. A common analog readout circuit with digital output may be provided in a single sensor subsystem 521 , connected to the photodiodes 525, 535 and ECG electrode connectors 522, 532 associated with each of the sensor subsystems 521 , 531.

[0104] The cable 530 in this device is longer than the cable 120 of the wearable patch device 102, because the controller module 550 is configured to be worn clipped to the clothing of a carer. Since this device is intended for use in kangaroo care, it can be expected that the carer holding the baby will manage / ameliorate any possible tangling of the cable 530. The cable 530 may be at least 15cm long, or at least 20cm long. The cable may be less than 100cm long or less than 70cm long. The cable may be between 30cm and 70cm long.

[0105] Figure 14 shows the chest wearable band 540. The band 540 comprises an elastic fabric material, for example comprising at least 5% spandex (for example -90% nylon and -10% spandex). One side 541 of the band 540 comprises loops suitable for engagement with a fastener comprising a plurality of hooks (i.e. a hook and loop system). In this way the band 540 can be fastened around the chest of the baby with the correct amount of tension to gently secure the ECG electrodes and sensor subsystems 521, 531 in contact with the baby’s skin. The band 540 comprises a portion with hooks, for engagement with the loops that are present on the looped side 541 of the band 540. The opposite side 544 of the band 540 is smooth. At an end of the band 540 there is a hooked portion 543, which may be bonded to the main body of the band 540.

[0106] Figure 15 shows the controller module 550, which is similar in operation to the controller module 150 described above. The controller module 550 comprises a clip 551 , and is designed to be worn by a carer of the baby (e.g. a parent or nurse) clipped to the clothing of the carer. The connector 505 connects the wearable device 502 to the controller module 550. In controller module 550 a magnetic force is not used, and a connector clip 515 is instead used to retain the connector 505 in engagement with the controller module 550. The connector clip 515 comprises a catch with a protrusion that engages with a corresponding recess in the controller module 550.

[0107] The controller module 550 comprises indicator LEDs 554 that perform the same function as the LED indicator 154 described with reference to system 100. There are three separate indicator LEDs shown in controller module 550 - these may be red, amber and green.

[0108] Figure 16 shows a charging dock 560 for charging the controller module 550. The charging dock 560 comprises a recess 565 for receiving the controller module 550 for charging. A connector comprising pogo pins is provided within the recess that connects to pogo contacts 556 of the controller module 550 when the controller module 550 is received in the recess 565. Figure 17 shows the system 500 in use, with the wearable device 502 worn on the chest of a newborn baby, which is cradled in the arms of a nurse. The nurse is wearing the control module 550 clipped to their collar, and the wearable device 502 is connected to the controller module 550. The controller module 550 is in wireless communication with a base station 570 comprising a display. The display of the base station is displaying: top) a graph of the ECG readout, and a numerical indication of heartrate; middle) a graph showing a PPG reading with a numerical readout of SpO2 level; bottom) a graph of temperature and a numerical indication of the current temperature. The base station 570 is mounted on a pole (which may in turn be on wheels), and the pole also carries a charging dock 560.

[0109] Figure 18 shows the system 500 in use, with the wearable device 502 worn on the back of a newborn baby, which is lying on the chest of its mother. The mother is wearing the control module 550 clipped to their clothing, and the wearable device 502 is connected to the controller module 550. The controller module 550 is in wireless communication with a base station 570 comprising a display (not shown in Figure 18), which may provide the same information as described with reference to Figure 17.

[0110] Although example embodiments have been described, these are not intended to limit the scope of the invention which should be determined with reference to the appended claims.

Claims

CLAIMS1. A system for monitoring physiological parameters of a baby, the system comprising: a wearable device comprising: a flexible support element, configured to conform with a profile of the skin of the baby; at least two optical PPG sensors for SpO2 measurement, each optical PPG sensor supported in contact with the baby’s skin by the flexible support element; and at least two ECG electrodes, each ECG electrode supported in contact with the baby’s skin by the flexible support element or at least two ECG electrode contacts, each for receiving an ECG electrode that is supported in contact with the baby’s skin by the flexible support element; and a controller module comprising a wireless transmitter and configured to transmit data indicating the physiological parameters to a base station, the physiological parameters comprising: i) a heart rate and / or pulse rate; and ii) an SpO2 measurement.

2. The system of claim 1 , wherein the wearable device comprises a temperature sensor configured to measure a skin temperature of the baby and the physiological parameters further comprise the skin temperature of the baby.

3. The system of claim 1 or 2, wherein the system is configured to determine a plurality of preliminary SpO2 measurements, each of the preliminary SpO2 measurements obtained from signals from one of the PPG sensors.

4. The system of claim 3, wherein the system is configured to determine the SpO2 measurement by combining at least some of the preliminary SpO2 measurements.

5. The system of claim 3, wherein the system is configured to determine the SpO2 measurement by selecting the most reliable of the preliminary SpO2 measurements.

6. The system of any preceding claim, wherein the wearable device is a wearable patch device and the flexible support element is a flexible patch configured to adhere to and conform with a baby’s skin.

7. The system of claim 6, wherein the flexible patch comprises a polymer layer with a thickness of 100 microns or less.

8. The system of claim 6 or 7, wherein an elastic modulus of the polymer layer is less than 5 GPa.

9. The system of any of claims 6 to 8, wherein the flexible patch has a surface area of at least 50cm2.

10. The system of any of claims 6 to 9, wherein the at least two optical PPG sensors are disposed in a sensor subsystem of the wearable device, and the sensor subsystem is disposed centrally in the flexible patch.

11. The system of claim 10, wherein a minimum distance of at least 20mm is provided between an edge of the sensor subsystem and an edge of the flexible patch.

12. The system of claim 10 or 11 , wherein the sensor subsystem comprise a cut out bite configured as an alignment aid and / or for facilitating access to the cardiac muscle of the baby for chest compressions.

13. The system of any of claims 10 to 12, wherein the wearable device comprises a reflector disposed over the area of the sensor subsystem, the reflector configured to reflect incident radiant heat and light away from the sensor subsystem.

14. The system of any preceding claim, wherein the controller module may be spaced apart from the wearable device by a cable that is at least 8cm long.

15. The system of claim 13, wherein the wearable device is a wearable patch device, and wherein the system is configured to route the cable over the shoulder of the baby when the ECG electrodes are properly positioned about the baby’s heart.

16. The system of any of claims 1 to 5 or claim 14, wherein the wearable device is a wearable band device, and the flexible support element is a chest wearable band configured to urge the wearable band device into contact with the baby’s chest or back.

17. The system of claim 16, wherein the band comprises an elastic material.

18. The system of claim 16 or 17, wherein the band comprises a hook and loop fastening system.

19. The system of any of claims 16 to 18, wherein the wearable device comprise two or more sensor subsystems interconnected by a flexible printed circuit board.

20. The system of claim 19, wherein each sensor subsystem comprises a loop through which the band is threaded.

21. The system of claim 19 or 20, wherein each sensor subsystem comprises a PPG sensor.

22. The system of any of claims 19 to 21 , wherein the wearable device comprises an ECG electrode contact at each end of the flexible printed circuit board, each ECG electrode contact configured to receive an ECG electrode.

23. The system of any preceding claim, wherein the physiological parameters comprise a respiration rate.

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