Heartrate measurement

Abstract

PPG data is obtained 502 by an instrumented mouthguard. Outlier data is removed and then high frequency noise components are removed 504. The processed data is segmented into windows 506, each contain

Description

Heart rate measurement is a common health management tool used for general health monitoring and for optimizing performance in various sports. The valid monitoring of internal load during sports training and competition, such as during heart rate activity zones, assists in making informed decisions concerning training load and recovery activity prescription based on the demands of the sport. If the nature, such as magnitude, of these demands, is known training can then be planned to maximise performance within competition. Advancements in and miniaturization of heart rate monitoring technologies have made possible measuring including, to all intents and purposes, constant measuring of a participant’s heart rate during sport performances using a variety of sensors, typically wrist or chest strap mounted sensors. Wrist mounted methods typically utilize an optical approach to heart rate calculation called photoplethysmography (PPG). PPG is an optical measurement technique that detects blood volume changes in the microvascular bed of tissue through the absorption and / or reflection of infrared light. PPG outputs an oscillating signal with repeating, distinctive peaks, with the time between peaks used to calculate instantaneous heart rate. Wrist worn PPG measures carry the benefit of being comfortable to wear but there appears to be large variations in the validity and reliability of data obtained from different devices and examined exercise intensities, with a general trend towards an increase in error rate the higher the exercise intensity due to motion artefacts. That is to say, disruption in sensor data reliability occurs due to the greater intensity of movement occurring commensurate with a greater intensity of exercise causing sensors to move with respect to the skin surface and separate from the skin surface. Chest strap mounted sensors have demonstrated higher levels of reliability in data collection and hence greater validity of the data when compared to wrist worn optical sensors, most likely due to reduced motion artefacts because the chest has a smaller range of movement compared to a wrist. However, there are some sports where both chest strap and wrist worn measures are either impractical or not permitted under sport safety guidelines. Such sports are typically combat sports and include mixed martial arts, boxing, kickboxing and Muay Thai (all competing under the umbrella of ‘combat sports’). Hence, other measures are required. An option to traditional heart rate measures is the integration of PPG sensors into mouthguards. In combat sports, athletes are required to wear mouthguards during competition and their use is unlikely to be prohibited in the future because the device is not worn externally on the body. The human oral cavity has a rich arterial blood supply via the posterior superior and middle superior alveolar artery, which is high in oxygen content. Modern mouthguards are configured such that they are coupled rigidly to the upper dentures thereby minimising the degree of motion artefacts that may be possible. A mouthguard device having electronics embedded in it supplied by the applicant, such as PPG sensors or acceleration sensors together with associated and circuitry for example, is referred to herein as an instrumented Mouth Guard (IMG). Notwithstanding the rigid coupling of the IMG, there are still significant contributors to ‘noise’ within the IMG PPG signal, such as low frequency physiological body processes (breathing and temperature fluctuations) and within mouth moisture, which can diffuse and complicate PPG output data. Complex data processing methodologies are required to effectively process the PPG data and transmit it live, “in play”, from the IMG. An example of an IMG including PPG sensor electronics is disclosed in Australian Patent Application Publication Number AU2021107530A4. Aspects and embodiments in accordance with the present invention have been devised with the foregoing in mind. SUMMARY According to a first aspect of the invention, there is provided a computer implemented method for measurement of heart rate using photoplethysmography, PPG, data obtained by an instrumented mouthguard comprising: a) receiving data comprising a PPG data indicative of the heartrate of a wearer of the instrumented mouthguard; b) applying a first processing to the received data to remove outlier data to generate first processed data; c) applying a second processing to the first processed data to remove high frequency noise components to generate second processed data; d) segmenting the second processed data into one or more windows; each window configured to contain the same predefined number of samples; e) for each window: (i). identifying respective peak PPG values, wherein a respective peak PPG value is a PPG value that is above a threshold value; (ii). determine one or more instantaneous heart rate values, wherein an instantaneous heart rate value is the difference between two successive respective peak PPG values in the window; (iii). remove anomalous instantaneous heartrate values, wherein an anomalous instantaneous heart rate value is determined based on human physiological range; (iv). discarding a window for which the ratio of the maximum instantaneous heart rate value to the minimum instantaneous heart rate value in the window is greater than a threshold ratio; (v). discarding a window for which the standard deviation of the window is greater than the standard deviation of the second processed data derived at feature c) above; and f) calculate a trailing moving average of the instantaneous heartrate values of a respective ones of a plurality of windows; and g) providing to a user interface respective trailing moving averages to provide an indication of the heart rate of a wearer. Optionally or additionally, the second processing is determined based on the expected heart rate / activity intensity. This provides for the processing to be focussed on a target range of heart rate / activity intensity thereby reducing the amount of processing that would otherwise be necessary. Optionally, a Butterworth filter is used for the second processing for the expected heart rate determined to be in the range of 50 to 100 beats per minute, BPM, and a Chebyshev filter is used for the second processing for the expected heart rate determined to be in the range of 100 to 220 BPM. A Butterworth filter and a Chebyshev filter are respective implementations of filters comprising a 3dB roll-off width greater than the 3dB roll-off width Optionally, the first processing comprises applying a Hampel filter. Such a filter removes the measured values which do not correspond to possible physical heart rates. Optionally, the threshold value derived at feature e)(i) is determined in accordance with the following relationship: Maximum Window Value — Minimum Window Value Selection Threshold = ------------------------------------------------- 4 Optionally, the threshold value derived at feature e)(i) is further determined in accordance with the following relationship: Mean All Windows Selection Threshold Revised Selection Threshold = -------------------------------------------—— Standard Deviation All Windows Selection Threshold Optionally, feature e)(iii) further comprises comparing the instantaneous heart rate values to a range of expected values of instantaneous heart rate. Optionally, wherein the range of expected values of instantaneous heart rate is 40 to 210 beats per minute (BPM). This is the expected range of a typical human and so using this range removes values that are considered to be non-physical. Optionally, wherein the one or more windows overlap. Such an overlap provides increased control over averaging of previous and future windows. Optionally, the threshold ratio in feature e)(iv) is 4. According to a second aspect of the present invention, there is provided an instrumented mouth guard for measurement of a heart rate comprising: a sensor configured to detect a PPG signal indicative of the heart rate of a wearer of the instrumented mouthguard; and a processor configured to implement the method of the first aspect of the invention. Such a mouthguard will be able to detect the heart rate of a wearer using only a simple optical sensor. According to a third aspect of the invention, there is provided a computer readable carrier medium carrying computer readable program elements implementable by a processor to perform the method of the first aspect of the invention. According to a fourth aspect of the invention, there is provided a computer readable storage medium storing computer readable program elements implementable in a processor to perform the method of the first aspect of the invention. According to a fifth aspect of the invention there is provided a system for measurement of a heart rate comprising: one or more instrumented mouth guards for measurement of a heart rate according to the second aspect of the invention; a monitoring station operatively configured to communicate with the one or more instrumented mouth guards; wherein the monitoring station is configured to communicate data received from the one or more instrumented mouthguards to one or more devices. The system allows the mouthguards to be used while “in play” and transmits data to a device such as a computer off pitch. This provides live monitoring of the heart rate which can be used to monitor player health or provide information about the player to viewers watching the pitch. Optionally, the communication between the monitoring station and the one or more instrumented mouthguards is wireless communication and / or wired communication link. Advantageously, a wireless communication allows freedom of movement for the wearers while using the mouthguard. Optionally, the data is PPG data indicative of the heartrate of a wearer. BRIEF DESCRIPTION OF THE DRAWINGS One or more specific embodiments in accordance with aspects of the present invention will be described, by way of example only, and with reference to the following drawings in which: Fig. 1 illustrates a mouthguard according to one or more embodiments of the present invention in which embedded and / or encapsulated components are arranged; Fig. 2 illustrates a system for providing a monitoring environment for monitoring acceleration and PPG signals measured by a mouthguard worn participants in a sporting event, according to one or more embodiments of the present invention; Fig. 3 illustrates a schematic block diagram of the components of a mouthguard according to one or more embodiments of the present invention; Fig. 4 illustrates an example PPG signal as a function of time measured by a mouthguard according to one or more embodiments of the present invention; Fig. 5 is an illustrative example of a process flow diagram of a method of measuring a heart rate using PPG signals measured from a mouthguard according to one or more embodiments of the present invention; Fig. 6 is an example of a PPG signal which has been filtered according to one or more embodiments of the present invention; Fig. 7 is an example window of a PPG signal showing instantaneous heart beats according to one or more embodiments of the present invention; and Fig. 8 is an illustrative example of a process flow diagram of a method of measuring a heart rate using PPG signals measured from a mouthguard according to one or more embodiments of the present invention. DETAILED DESCRIPTION An IMG (also known as a gumshield or mouthguard) is a piece of protective equipment worn by participants in sports, particularly contact sports. An IMG is typically worn in an upper part of the mouth of the participant and is generally configured to cover at least a portion of the upper teeth of the participant. Most typically, an IMG is configured to cover at least a portion of a vestibular (outer) surface of upper teeth of the wearer, at least a portion of a palatal (inner) surface of upper teeth of the wearer, and at least a portion of incisal and occlusal surfaces (i.e. “biting” and “chewing” surfaces) of upper teeth of the wearer. In general outline, an IMG according to one or more embodiments of the present invention can form a part of a system for the detection, measurement, characterisation, transmission, and / or reporting of impact events causing acceleration to be experienced by participants and of PPG data acquired by appropriate sensors. The sensor and / or monitoring element components are embedded and / or encapsulated in material from which the IMG is formed. Fig. 1 illustrates an example IMG 10 according to one or more embodiments of the present invention in which embedded and / or encapsulated components are arranged in a first arrangement. Reference is made to the descriptions of related IMGs in United Kingdom Patent Applications Publication Numbers GB2570726A1 and GB2572677A1 which are incorporated herein by reference. In the illustrated IMG 10 of Fig. 1, components are shown positioned in walls of the IMG that are locatable at the rear of a mouth of a wearer when the IMG is located correctly in the mouth. The components are connected electronically by means of wires or circuit board (which may be flexible) and are communicatively coupled to a transceiver for transmitting data received from the components to a monitoring station in real-time (not shown in Fig.1). These components operate to collect and process impact event data, which can then be transmitted to the monitoring station via the transceiver. Various terms used in dentistry are used in describing the IMG 10 of one or more embodiments of the present invention. The terms used in this disclosure are listed below: • Anterior - The direction towards the front of the head or the lips, as opposed to posterior, which refers to the directions towards the back of an individual's head. The term anterior teeth refers to incisors and canines, as opposed to premolars and molars, which are posterior teeth; • Distal - The direction towards the gums beyond the tooth furthest from the midline (i.e. the 'most posterior tooth' or last tooth) in each quadrant of a dental arch, as opposed to mesial, which refers to the direction towards the midline; • Incisal - The direction towards the biting edge of front teeth. This is a related term to occlusal, which relates to the analogous location on rear teeth; • Mandibular - Relating to the mandible, or lower jaw; • Maxillary - Relating to the maxilla, or upper jaw; • Mesial - The direction towards the midline in a dental arch, as opposed to distal, which refers to the direction towards the gums beyond the tooth furthest from the anterior midline (the 'most posterior tooth' or last tooth) in each quadrant; • Midline - Roughly, an imaginary vertical line dividing the left and right sides of the mouth at the teeth; • Occlusal - The direction towards the biting surface of rear teeth. This is a related term to incisal, which relates to the analogous location on anterior teeth; • Palatal - The side of a tooth adjacent to (or the direction towards) the palate, as opposed to vestibular, which refers to the side of a tooth adjacent to (or the direction towards) the inside of the cheek or lips of the mouth respectively; • Posterior - The direction towards the back of an individual's head, as opposed to anterior, which refers to the directions towards an individual's lips. The term posterior teeth refers to premolars and molars, as opposed to incisors and canines, which are anterior teeth; • Quadrant - The arrangement of teeth in a mouth is divided into four quarters. Upper and lower sets of teeth form an oval, which is divided into quadrants: Upper right quadrant: upper right first incisor to upper right wisdom tooth; Upper left quadrant: upper left first incisor to upper left wisdom tooth; Lower right quadrant: lower right first incisor to lower right wisdom tooth; Lower left quadrant: lower left first incisor to lower left wisdom tooth; and • Vestibular - The side of a tooth that is adjacent to (or the direction towards) the inside of the cheeks and lips, as opposed palatal, which refers to the side of a tooth adjacent to the palate. Additionally, reference is made to monitoring acceleration. In at least some implementations, a device used to measure acceleration is termed an “accelerometer”. The terms “acceleration measurement”, “acceleration monitoring” and the like include use of devices known as “accelerometers”. The terms may be used interchangeably depending on context. As illustrated in Fig. 1, the IMG 10 comprises a body 12 that defines a formation to be located around at least a portion of maxillary teeth of a wearer (i.e. teeth in the upper jaw of the wearer - hereinafter “upper teeth”), to cover, surround, and / or envelope the upper teeth of the wearer. The body 12 is formed from a plastics, resin, and / or rubber material. The body 12 comprises a first wall 14 configured to cover at least a portion of an outer surface of the upper teeth of the wearer (i.e. the surface of the upper teeth that faces the inside of the upper lip and the cheek). In dentistry terminology this surface is known as a vestibular surface. The body 12 comprises a second wall 16 configured to cover at least a portion of an inner surface of the upper teeth of the wearer (i.e. the surface of the upper teeth that faces the palate). In dentistry terminology this surface is known as a palatal surface. The body 12 comprises a third wall 18 connecting the first and second walls 14, 16 and configured to cover at least a portion of biting edges and chewing surfaces of the upper teeth of the wearer (i.e. the edges and surfaces of the upper teeth that are opposed to the lower teeth). In dentistry terminology, these surfaces are known as incisal and occlusal surfaces. The first wall 14, the second wall 16 and the third wall 18 of the body 12 define a channel 20 for receiving a plurality of teeth of a wearer. In the illustrated examples of Fig. 1, the channel 20 is structured such that, when worn, it covers teeth that include the incisors of a wearer when the IMG 10 is inserted. In plan view, the body 12 of the IMG 10 presents a generally symmetrical U-shaped configuration with “arms” extending away from a mid-line (denoted by a dashed line 22 in Fig. 1). The first wall 14, the second wall 16, and the third wall 18 in one arm define a portion of the channel 20 that can receive teeth of an upper left quadrant. The first wall 14, the second wall 16, and the third wall 18 in the other arm define a portion of the channel 20 that can receive teeth of an upper right quadrant. The IMG 10 also defines an open area 24, located between the two arms, which can allow a tongue of the wearer to touch their upper palate when the IMG 10 is being worn. This may allow the user to maintain verbal communication with other participants (e.g. teammates) without requiring removal of the IMG. The IMG 10 includes a power source 26 (e.g. an electrical power battery) that is electrically connected to a system for monitoring acceleration 28 and a system for PPG signal acquisition 30. Typically, the power source 26 is of a type compatible with a wireless charger to allow recharging of the power source, i.e., the power source 26 may be wirelessly rechargeable, which allows the power source 26 to be charged / recharged without requiring removal from the IMG 10. In the illustrated example of Fig. 1, the power source 26 and the system for monitoring acceleration 28 are located in a portion of the same arm of the IMG. The portion in which they are located is in a distal direction from the midline 22. The power source 26 is located in the second wall 16 and the system for monitoring acceleration 28 is located in the first wall 14. The power source 26, the system for monitoring acceleration 28, and the system for PPG signal acquisition 30 are electrically connected using a suitable connection (not shown) that runs from the power source 26, through the third wall 18 to system for monitoring acceleration 28. As mentioned, the system for PPG signal acquisition is an optical measurement technique that detects blood volume changes in the microvascular bed of tissue through the absorption and / or reflection of infrared light as it commonly known in the field of medical devices and / or sports devices. PPG outputs an oscillating signal with repeating, distinctive peaks, with the time between peaks used to calculate instantaneous heart rate. Optionally, the power source 26 and / or the system for monitoring acceleration 28 and / or the system for PPG signal acquisition 30 may be located in a different area of the IMG 10 in one or more embodiments and the invention is not limited to this configuration. In the illustrated example of Fig. 1, the components of the IMG 10, described above, are encapsulated (i.e. wholly embedded) within material forming the IMG 10. Of course, the components of the IMG 10 described above is a non-exhaustive list of components and the IMG 10 may include other components such as processors, data storage, microcontrollers, or other sensors. System Diagram Fig. 2 illustrates a system 200 for providing a monitoring environment for monitoring acceleration and motion as a function of time sustained by participants in a sporting event. The system 200 operates to aggregate data representative of temporal acceleration that occurs during impact events, the data being received from the system for monitoring acceleration 28 in IMGs 10 worn by game participants. Additionally, the system 200 is operative to aggregate data representative of a heart beat, in the form of a PPG signal, as described above. The data can be conveyed to technicians, via the system 200, for assessing the physiological measurements and data of the athlete or merely recording an event to be used in analysis on aggregated data. The system 200 comprises a monitoring station 32 that is in wireless communication with one or more IMGs 10. The monitoring station 32 can communicate data received from the one or more IMGs to one or more devices (not shown in Fig. 2) either wirelessly or by wired communication link. The monitoring station 32 includes a processor 34, a user interface 36, memory 38, and a transceiver 40. The monitoring station 32 wirelessly receives data representative of accelerations experienced by participants from each of the systems for monitoring acceleration 28 and the PPG signal data measured by the system for PPG signal acquisition 30. Signals from each of IMGs 10 are received at an antenna 42 coupled to the transceiver 40. The received signals are passed to the processor 34, which operates to process the data. The processed data is communicated to a memory 38 for storage and can also be communicated to the user interface 36, which is configured for communicating the data to a display device (e.g. via a communications network). In this example system 200, the method of data transfer between the IMGs 10 and monitoring unit 32 is not disclosed in detail and is merely an example of how the physiological data is recorded and transferred off of the IMG 10 for further processing. IMG Component System Fig. 3 is an illustrative block diagram showing schematic representations of the components of the IMG 10 (e.g. the power source 26 and the system for monitoring acceleration 28) in more detail. Such components collectively, individually or in sum or in part providing processing resources for the IMG 10. As mentioned, the IMG 10 comprises the system for monitoring acceleration 28, which further comprises an a three-axis linear accelerometer 52 (“accelerometer” 52) and a gyroscope unit 54. Each of the accelerometer 52 and the gyroscope unit 54 are communicatively coupled to a processor 56 by way of Inter-Integrated Circuit (I2C) buses 58 and 60 respectively. The accelerometer 52 is operative to monitor linear accelerations of the IMG 10. The accelerometer 52 is operative to measure a linear acceleration in each orthogonal direction (x, y, z), e.g. of a Cartesian coordinate reference frame. A combination of respective acceleration values may be used to derive a linear acceleration vector. The gyroscope unit 54 is operative to measure angular velocity to provide data representative of angular rotation. The gyroscope unit 54 is operative to measure angular velocity with respect to each orthogonal direction (x, y, z), e.g. of a Cartesian coordinate reference frame. A combination of respective angular velocity values may be used to derive a angular velocity vector. Fig. 3 also shows the system for PPG acquisition 30 which is communicatively coupled to the processor 56 by way of Inter-Integrated Circuit (I2C) bus 62. The IMG 10 also comprises a transceiver 48 which is electrically coupled to the processor 56 via an SPI bus 61. The transceiver 48 is operative to communicate data signals containing data representative of acceleration monitored and measured by the system for monitoring acceleration 48 and data representative of a processed heart rate , or an instantaneous heart rate measured by the system for PPG acquisition 30 to the monitoring station 32 (not shown in this figure - see Fig. 2) via an antenna 50. External data can also be received by the IMG 10 from an external source via the antenna 50 and transceiver 48. Received external data may comprise, for example, a negative-acknowledgement signal (e.g. to indicate an error in data previously sent from the system for monitoring acceleration 28 and to request that the data be re-sent), software updates, time stamp information or the like. The processor 56 is also electrically coupled to the memory 46 via the SPI bus 61, which serves to store data measured and monitored by the components of the IMG 10 thereon. PPG Data Fig. 4 is in illustrative example of a PPG signal 400 measured and acquired by the above-mentioned system for PPG acquisition 30 during operation of an IMG utilizing the system in a test subject. The PPG signal 400 shows on a measure of received optical signal as a function of time (x-axis). The temporal units here are shown as a sample number, which can easily be converted to time with the knowledge of the sampling frequency. In this embodiment, the sampling frequency is 100Hz. As will be appreciated by a person skilled in the art, the optical measurement technique detects blood volume changes in the microvascular bed of tissue through the absorption and / or reflection of infrared light as commonly used in pulse oximeters. Typically, PPG outputs an oscillating signal with repeating, distinctive peaks, with the time between peaks used to calculate the instantaneous heart rate. However, the PPG signal 400 is the result of measurements from an IMG, which due to its location in a users’ mouth, lacks the distinctive repeating peaks normally expected. The location within a user’s mouth introduces different sources of noise which would not be present in a wrist mounted or chest mounted device. Such mouth specific noises may be from movements of the IMG within the mouth when a user coughs, talks, swallows, experiencing impacts. The movement artifacts will be measured by the system for PPG acquisition 30 and result in additional peaks in the “pure” signal. It should also be noted that breathing contributes to the noise measured by the IMG, which at higher exercise intensities introduces noise frequencies which cross over with potential heart rate frequencies. The line 402 shows the PPG sensor value changing as a function of time in an irregular manner, with example peaks 404, 406, 408, and 410 being spaced at different intervals. Other examples of the sources of artifacts and noise can be motion artifacts, optical signal quality degradation due to saliva in the mouth, and other sensor noise. The contributing noise factors make it difficult to extract accurate heart rate values from the PPG signal 400. Typically, a signal such as that of PPG signal 400 would be discarded leaving gaps in the overall PPG signal that must be dealt with, for example utilising interpolation, concurrent accelerometer readings, or signal reconstruction using concurrent ECG readings. Accordingly, it is an aspect of the present invention to address such a technical problem. Offline Method A general outline of a computer implemented method of classification of PPG signals measured by an IMG, such as the example described in relation to Figs. 1 to 3 will now be described with reference to process flow control diagram 500 illustrated in Fig. 5 and Figs. 6 and 7. At step 502 the PPG signal is received by a processor, such as the one described in relation to the monitoring station 32 in Fig. 2. The PPG signal is filtered at step 504 to reduce noise artifacts, which comprises a first and second processing step. The received PPG signal is first processed to remove impulsive outliers, which are defined as data points that occur over a short duration of less than three samples and the magnitude of three standard deviations higher than the surrounding samples. In this described embodiment, the impulsive outliers are removed with a Hampel filter to produce a first processed data. The first processed data proceeds to a second processing step to remove low and high frequency noise components using a bandpass filter. The second processing step applies an adaptive filter which is determined based on the expected heart rate of the wearer of the IMG. For low intensity activities the expected heart rate will be similarly lower and thus the bandpass filter used is a Butterworth filter. The Butterworth filter is used for lower heart rate applications because it has a smooth and flat frequency response in the passband and the stop band. If the wearer of the IMG is expected to be performing a high intensity activity, such as MMA, boxing, or the like, a 12th order Chebyshev type II filter will be used as part of the adaptive filter regime 504. Due to the higher intensity of activity, the type of noise artefacts in the received PPG signal will be different and thus a Chebyshev bandpass filter is used. Initially frequencies are passed between 0.5Hz and 5Hz with 10dB of stopband attenuation. However, when a very high heart rate was expected (above 120bpm) the Chebyshev bandpass filter was further adjusted to pass frequencies between 0.8Hz and 6Hz with 40dB of stopband attenuation. A Chebyshev filter is used because it has a steeper and sharper frequency response than a Butterworth filter. This means that the filter achieves a faster transition from the passband to the stopband, resulting in a narrower bandwidth and a higher selectivity. Reference is made to Fig. 6 which is an illustrative graph showing the PPG signal from Fig. 4 once it has been filtered in step 504. As can be seen, the PPG signal 602 has a more “regular” peak pattern. The peaks can be seen to be more evenly distributed and have a more even magnitude, which allows the peaks representing instantaneous heart beats to be identified with greater ease and accuracy than otherwise would be the case. The aim of the filtering described above is to remove the presence of frequency components outside the specified frequency range of reasonable heart rates, for example, 50 - 300 BPM. Once the PPG signal has been filtered, it is segmented into one or more temporal windows at step 506. That is, the full received PPG signal is split into segments of a determined length of time, or number of samples. The windowing applied can be simply the total signal cut into segments of n samples with the end of one window being the start of the next; or a window of n samples may be selected with the start of the next window beginning n / 2 samples into the previous, thus creating an overlap between subsequent windows of n / 2. Such a windowing technique provides increased control over averaging of previous and future windows. In one embodiment, for each window only an extra second of signal is added, which mitigates against large increases or decreases or average output heart rate. Of course, the overlap value of n / 2, or 1 second, is an arbitrary overlap and other values can easily be envisaged to tailor the level of overlap required. For each window the peaks relating to individual heart beats within the window are identified using a peak finding regime. An example window of PPG signal 702 is show in Fig. 7 which shows the filtered PPG signal on the y-axis and the number of samples in the x-axis. The sampling rate for the data in this graph was taken at 200Hz, which is different from the data showing in Fig. 6. However, as explained further below, this only results in a minor change in the temporal unit conversion once the peak positions have been identified. The PPG signal 702 has three distinctive peaks 704, 706, and 708 with some smaller minor peaks 710 and 712. The difficulty is in correctly determining which peaks are representative of a heart beat and which is overcome with the following peak detection regime. Initially, a threshold value for the window is determined as: Window Threshold = ----------------------------------- (1). Equation (1) above shows that an initial window threshold value is set determined based on the maximum and minimum values within the window. In the example shown in Fig. 7, the window threshold value will be around a signal value of 2.5, which is indicated by dashed line 714. In some embodiments, the peak detection regime will determine the local peaks to above this window threshold value using the “Peakfinder” function on Matlab™. The function uses user defined thresholds to find transition points that are above or below the threshold and designates them as a peak or valley. In another embodiment, a revised threshold value is determined to take into account the amount of noise / variance within the PPG signal as a whole. The new revised threshold takes the window threshold defined above in equation (1) or all windows in the PPG signal in the following manner: _. . , ... Mean All Windows Selection Threshold Revised Threshold = --------------------------------------- (2). Standard Deviation All Windows Selection Threshold As will be apparent, this is related to the Coefficient of Variation, being its inverse. Using such a revised threshold results in improved peak detection accuracy. Once the peaks have been located as described above, the location within the window is identified and then the number of samples between successive peaks is calculated, which is denoted the peak interval and thus the instantaneous heart rate in step 510. To convert the peak interval to instantaneous heart rate in units of beats per minute (BPM), the following can be used: Instantenous Heart Rate (bpm) = --------------- x 60 (3). ' 7 Peak Interval ' ' As illustrated in Fig. 7, each window will have a number of successive peaks and thus values of instantaneous heart rate. Typically, the values of instantaneous heart rate vary and is not usually the final number that is output to a user or wearer of the IMG because of the variation between instantaneous heart rate values. Therefore, is typical to output some sort of statistical calculation based on instantaneous heart rate values within a window, such as a mean value or the like. However, before an average heart rate for the window is calculated, the instantaneous heart rate values for a particular window are subjected to a signal quality assessment to make sure that the value that is output to the user or wearer of the IMG is accurate and precise. Once the instantaneous heart rate values have been calculated for the window, they are assessed in step 512. In this described embodiment, instantaneous heart rate value determined to be outside of physiological possible parameters are removed 514. For example, instantaneous heart rate values falling below 40BPM or above 210BPM are considered to be in physical and therefore removed from the particular set of instantaneous heart rate values for this window. One particular way of removing the nonphysical instantaneous heart rate value from the window would be to designate it as ‘not a number’ (NaN), which means that it will not be regarded in further calculations. The second step of the instantaneous heart rate assessment 512 consists of comparing the ratio of the maximum instantaneous heart rate value to the minimum instantaneous heart rate value within the window. If this ratio is greater than a predetermined ratio, sometimes called a threshold ratio, the entire sample window is designated as NaN. The reason for doing this is true heart rate values typically only fluctuate by around 10-15% beat-to-beat. If one ‘beat’ in a window that is identified as 60bpm and another as 140bpm, it is assumed that noise is present in the window or an inappropriate beat has been chosen. Finally, in the third step of the instantaneous heart rate assessment 512 the standard deviation of the PPG values in the window is calculated and compared to the standard deviation of the entire sample of PPG values. If the standard deviation of the sample window is calculated to be twice that of the standard deviation of the entire filtered PPG signal, then the window is designated NaN. The third step removes high peaks from the sample, which could be present due to noise factors such as movement of the IMG within the user’s mouth or instrument noise. Only the values of instantaneous heart rate determined to be within physiologically possible parameters are used to calculate an average heart rate for the window in step 516, which is output as a moving average across a determined number of windows to a user at step 518. The moving average is calculated based on the last 40 previous windows. On-IMG Analysis The method described in relation to Fig. 5 requires the data recorded by the IMG 10 to be transferred off the device to the monitoring station 32 (see Fig. 2 and the description thereto). The measured PPG signal is either stored in a memory on the IMG or transferred off in data packets, which will not be described here in detail. Once the data is transferred to the monitoring station 32, various suitable processing resources implement the method 500 to provide a measurement of the heart rate of the wearer of the IMG. This method 500 provides a “retrospective” analysis of the heart rate and, due to the fact the entire signal must be transferred off the device, it requires valuable processing resources, memory, power, and time. Therefore, in a second embodiment the approach taken in relation to Fig. 5 is modified so that it may be implemented on the IMG 10 to provide a “live” measurement of the heart rate which can be transferred off the IMG 10. A general outline of a further embodiment of a computer implemented method of classification of PPG signals measured by an IMG, such as the example described in relation to Figs. 1 to 3, will now be described with reference to process flow control diagram 800 illustrated in Fig. 8. Fig. 8 is very similar to Fig. 5 with like processes being represented by the same reference numeral except incremented by 300 (for example the “filter data” step 504 is the same as step 804). At process control flow step 801 the data acquisition starts and the system for PPG acquisition 30 commences measurement of the data indicative of a PPG signal. The process of how the IMG 10 begins data acquisition will not be described in detail here but can be found in patent application GB 2572677 B1, which is incorporated herein by reference. The PPG signal is continuously captured and processed on a window-by-window basis. A first window of PPG signal 803 is taken and sent into the pipeline to extract instantaneous heart rate values and subsequently an average heart rate for the window is calculated. In this embodiment, the window length is 3 seconds, meaning that after an initial three seconds (t = 0s to t = 3s) the PPG data for the window is processed. Similar to step 504, the PPG signal within the current window is filtered at step 804 to reduce noise artifacts that may be present. Since this is substantially the same as step 504, it will not be described again here. Once the data is filtered to minimise any noise artifacts, the peaks within the window are detected in process control flow step 809. At step 809 the peaks are identified using a moving window with a length corresponding to an odd number of samples of PPG data. The reason for the window being an odd number of samples is to ensure that the centre of the window falls on a sample (i.e., if there were an even number of samples, the centre of the window would be the position between two respective samples). The peak detection method compares the value of the central sample to the maximum sample value within the window. If the central sample is the maximum sample value, i.e., has the highest PPG value in the window, then the sample value is identified as a peak value that could be representative of a heart beat. The window length determines the sensitivity of the peak detection method. If the sample length is too short then spurious noise peaks that are not representative of heart beats could potentially be misidentified. Conversely, if the window length is too long then sequential heart beat peaks could be ignored and not identified. Both instances will result in a less accurate assessment of the instantaneous heartrate (see discussion of 812 below). Therefore, careful selection of the peak window is chosen to reduce this. In an embodiment, a window length of is 41 samples is chosen as the optimum length considering the above. Suitably, the window length is variable depending on the expected heartrate of the user. For example, activities that are expected to have higher heart rate might use a window length that is shorter than that of a lower heart rate. Once the peaks have been detected and identified as described above, the location within the window is identified and the number of samples between successive peaks is calculated, which is denoted the “peak interval”. This corresponds to the instantaneous heart rate in step 810. To convert the peak interval to instantaneous heart rate in units of beats per minute (BPM) equation (3) can be used as described above. At process control flow step 812, the instantaneous heart rate values for the window are assessed. The first step of the process 812 is the same as that of 512 in that any nonphysical values of instantaneous heart rate is removed by assigning NaN. The second step of the instantaneous heart rate assessment 812 is also the same as that of corresponding step 512 and consists of comparing the ratio of the maximum instantaneous heart rate value to the minimum instantaneous heart rate value within the window. Once the instantaneous heart rate values within the window have been verified, the average heart rate for the window is calculated in step 816. The average heart rate for the window is stored in a buffer 818. The process then returns to the next window, which has the same length in time as the present window but will have its start and end times moved forward by one second. That is, the PPG data measured from t = 1s to t = 4s is used for the next window. Therefore, in this windowing scheme, steps 804 to 816 are performed on every second for the subsequent three seconds. Each average heart rate for the window calculated in step 816 is added to and stored in the buffer at step 818 until there are a sufficient number of stored values to calculate a moving average. That is a moving average of the values stored in the buffer 818 for a given set period, one example being the last 30 seconds of measurements. Of course, until data has been recorded for the set period of the moving average, it will not be for the full period. Calculating the moving average smooths the beat to beat variations of the heartrate between each window 803. The advantage of processing and estimating the heart rate on the IMG 10 is that the amount of data that must be transferred off the device is reduced significantly. Instead of the entire PPG signal being transferred off the IMG 10, only the processed heartrate values are. This reduces the overall battery consumption and data transfer requirements, thus the IMG 10 could potentially be used for a longer period of time. Additionally, the arrangement of this embodiment permits calculation of the wearer’s heart rate live while being used in play. In the example embodiments described above, the sample rate of the system for PPG acquisition is 100Hz. However, it must be noted that this is merely one example of such a sample rate, and the methods and apparatus described can easily be adapted to accommodate such a change. The method described in relation for Fig. 5 is described as being data transmitted from an IMG to a monitoring unit. However, the method could be implemented on the IMG itself with appropriate processing resources. The moving average calculated in step 516 is described as being for the last 40 windows, which is of course one example of many different potential moving average schemes. It can be easily envisaged by a person skilled in the art that other numbers of windows such as 30, 50, 100 etc can be used. The absolute magnitude of PPG signal is dependent upon sensor signal strength and can change person to person (or from IMG to IMG), which is why the magnitude of the data shown between Figs. 4, 6, and 7 varies. All references made herein to orientation (e.g. front, rear, upper, lower, anterior and posterior) are made for the purposes of describing relative spatial arrangements of features and are not intended to be limiting in any sense. It will be understood by those skilled in the art that the drawings are merely diagrammatic and that further items of equipment may be required in a commercial apparatus. The position of such ancillary items of equipment forms no part of the present invention and is in accordance with conventional practice in the art. Insofar as embodiments of the invention described above are implementable, at least in part, using a software-controlled programmable processing device such as a general purpose processor or special-purposes processor, digital signal processor, microprocessor, or other processing device, data processing apparatus or computer system it will be appreciated that a computer program for configuring a programmable device, apparatus or system to implement methods and apparatus is envisaged as an aspect of the present invention. The computer program may be embodied as any suitable type of code, such as source code, object code, compiled code, interpreted code, executable code, static code, dynamic code, and the like. The instructions may be implemented using any suitable high-level, low-level, object-oriented, visual, compiled and / or interpreted programming language, such as, Liberate, OCAP, MHP, Flash, HTML and associated languages, JavaScript, PHP, C, C++, Python, Nodejs, Java, BASIC, Perl, Matlab, Pascal, Visual BASIC, ActiveX, assembly language, machine code, and so forth. A skilled person would readily understand that term “computer” in its most general sense encompasses programmable devices such as referred to above, and data processing apparatus and computer systems. Suitably, the computer program is stored on a carrier medium in machine readable form, for example the carrier medium may comprise memory, removable or non-removable media, erasable or non-erasable media, writeable or re-writeable media, digital or analog media, hard disk, floppy disk, Compact Disk Read Only Memory (CD-ROM), Company Disk Recordable (CD-R), Compact Disk Rewriteable (CD-RW), optical disk, magnetic media, magneto-optical media, removable memory cards or disks, various types of Digital Versatile Disk (DVD) subscriber identity module, tape, cassette solid-state memory, optical carrier signal, electrical signal, or radiowave. As used herein any reference to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. Moreover, one or more features of different embodiments may be combined to create further embodiments not specifically described herein, and any one or more features may be combined consistent with their technical and operational compatibility. To the extent that one or more features from respective embodiments may not be combined without being inconsistent with the technical and / or operational compatibility such features from respective embodiments may be selected for combination which do not have such technical and / or operational compatibility. All such embodiments are contemplated within the scope of this disclosure. As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). In addition, use of the “a” or “an” are employed to describe elements and components of the invention. This is done merely for convenience and to give a general sense of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise. In view of the foregoing description, it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention. For example, the various electronic components and power supply have been disposed in particular locations in the specific embodiments described herein. It will be evident to a person of ordinary skill in the art that the outright components and power supply may be disposed in other locations as benefits or benefits any particular design of mouthguard.

Claims

1: A computer implemented method for measurement of heart rate using photoplethysmography, PPG, data obtained by an instrumented mouthguard comprising:a) receiving data comprising a PPG data indicative of the heartrate of a wearer of the instrumented mouthguard;b) applying a first processing to the received data to remove outlier data to generate first processed data;c) applying a second processing to the first processed data to remove high frequency noise components to generate second processed data;d) segmenting the second processed data into one or more windows; each window configured to contain the same predefined number of samples;e) for each window:(i). identifying respective peak PPG values, wherein a respective peak PPG value is a PPG value that is above a threshold value;(ii). determine one or more instantaneous heart rate values, wherein an instantaneous heart rate value is the difference between two successive respective peak PPG values in the window;(iii). remove anomalous instantaneous heartrate values, wherein an anomalous instantaneous heart rate value is a value based on subject physiological responses;(iv). discarding a window for which the ratio of the maximum instantaneous heart rate value to the minimum instantaneous heart rate value in the window is greater than a threshold ratio;(v). discarding a window for which the standard deviation of the window is greater than the standard deviation of the second processed data derived at feature c) above; andf) calculate a trailing moving average of the instantaneous heartrate values of a respective ones of a plurality of windows; andg) providing to a user interface respective trailing moving averages to provide an indication of the heart rate of a wearer.

2. A computer implemented method according to claim 1, wherein the second processing is determined based on the expected heart rate / activity intensity.

3. A computer implemented method according to claim 2, wherein a filter having a smooth and flat frequency response in the passband and the stop band is used for the second processingfor an expected heart rate determined to be in the range of 50 to 100 beats per minute, BPM, and a filter having a sharper and faster decay is used for the second processing for the expected heart rate determined to be in the range of 100 to 220 BPM4. A computer implemented method according to claim 2, wherein a Butterworth filter is used for the second processing for the expected heart rate determined to be in the range of 50 to 100 beats per minute, BPM, and a Chebyshev filter is used for the second processing for the expected heart rate determined to be in the range of 100 to 220 BPM.

5. A computer implemented method according to any preceding claim, wherein the first processing comprises applying a Hampel filter.

6. A computer implemented method according to any preceding claim, wherein the threshold value derived at feature e)(i) is determined in accordance with the following relationship: Maximum Window Value — Minimum Window Value Selection Threshold = -------------------------------------------------47. A computer implemented method according to claim 6, wherein the threshold value derived at feature e)(i) is further determined in accordance with the following relationship:Mean All Windows Selection ThresholdRevised Selection Threshold = -------------------------------------------——Standard Deviation All Windows Selection Threshold8. A computer implemented method according to any preceding claim, wherein feature e)(iii) further comprises comparing the instantaneous heart rate values to a range of expected values of instantaneous heart rate.

9. A computer implemented method according to claim 8, wherein the range of expected values of instantaneous heart rate is 40 to 210 beats per minute (BPM).

10. A computer implemented method according to any preceding claim, wherein the one or more windows overlap.

11. A computer implemented method according to any preceding claim, wherein the threshold ratio in feature e)(iv) is 4.

12. An instrumented mouth guard for measurement of a heart rate comprising:a sensor configured to detect a PPG signal indicative of the heart rate of a wearer of the instrumented mouthguard; anda processor configured to implement the method of any preceding claim.

13. A computer readable carrier medium carrying computer readable program elements implementable by a processor to perform the method of any of claims 1 to 10.

14. A computer readable storage medium storing computer readable program elements implementable in a processor to perform the method of any of claims 1 to 10.

15. A system for measurement of a heart rate comprising:one or more instrumented mouth guards for measurement of a heart rate according to claim 12;a monitoring station operatively configured to communicate with the one or more instrumented mouth guards;wherein the monitoring station is configured to communicate data received from the one or more instrumented mouthguards to one or more devices.

16. A system according to claim 15, wherein the communication between the monitoring station and the one or more instrumented mouthguards is wireless communication and / or wired communication link.

17. A system according to claim 15 or claim 16, wherein the data is PPG data indicative of the heartrate of a wearer.Application No: GB2416350.3 Examiner: Stephen JenningsClaims searched: 1-17 Date of search: 4 April 2025Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance A - US 2019 / 0125261 Al (LATHROP et al.) see paragraph [0027] A - WO 2017 / 070343 Al (THE UNIV OF FLORIDA RES FOUND INC) see paragraph [0038] A - US 2020 / 0323493 Al (ARORA et al.) see paragraph [0030] A - US 2024 / 0194333 Al (LEE et al.) see paragraph [0033] A - US 2024 / 0180436 Al (DAGHER et al.) see paragraph [0048] A - US 2018 / 0338727 Al (MUKHOPADHYAY et al.) see paragraphs [0028] and [0039]Categories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if combined with one or more other documents of same category. P Document published on or after the declared priority date but before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB, EP, WO &US patent documents classified in the following areas of the UKCX :www.gov.uk / ipoInternational Classification:Subclass Subgroup Valid From A61B 0005 / 024 01 / 01 / 2006www.gov.uk / ipo

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