Cardiac monitoring system and method

Abstract

The cardiac monitoring system (100) includes an array of force-sensitive resistors (10) across a sensor surface (50). Each resistor (10) is configured to change its respective resistance (R) in response to an amount of static pressure (P) applied to the sensor surface (50) by a subject (200) at a respective location on the force-sensitive resistor (10). An array of piezoelectric transducers (20) is interspersed among the array of force-sensitive resistors (10). Each transducer (20) is configured to generate a respective time-dependent electrical signal (S) in response to a respective vibration (F) applied to the sensor surface (50) by the subject (200) at a respective location on the transducer (20). A controller (30) is configured to determine the heart rate (H1) of the subject (200) based on a combination of the measured resistances (R) of the force-sensitive resistors (10) and the time-dependent electrical signals (S) of the piezoelectric transducers (20).

Description

[Technical field]

[0001] The present disclosure relates to systems and methods for measuring heart rate. [Background technology]

[0002] For example, piezoelectric sensors can be used to perform ballistocardiography (BCG) to measure heart rate, respiration rate, and even pulse wave velocity in a semi-contact manner through clothing or bedding / mattress (e.g., chair / bed). Preferably, the sensor needs to be in close proximity to the relevant part of the body to transmit vibrations. Unfortunately, this contact information is difficult to extract from the sensor signal. As a result, artifacts are very common, which is exacerbated when the subject's position is not defined.

[0003] US Patent Application Publication No. 2018 / 0337325A1 describes a multi-element piezoelectric sensor for physiological measurements in a bed. The monitoring system can perform a first scan of all the piezoelectric sensors. The first scan can be, for example, a high-level scan to roughly determine where the user is located along the mat. The monitoring system can perform a second scan of one or more piezoelectric sensors, such as piezoelectric sensors potentially located in the immediate vicinity of the user's body. The piezoelectric sensors potentially located in the immediate vicinity of the user's body can be, for example, piezoelectric sensors that measure force or can be piezoelectric sensors located adjacent to piezoelectric sensors that do not measure force.

[0004] However, piezoelectric sensors typically generate time-dependent signals that may require individual and continuous monitoring, and it can be difficult to balance accuracy over different time scales and pressure ranges. There remains a need for further improvements in accurate heart rate monitoring. Summary of the Invention

[0005] Aspects of the present disclosure relate to cardiac monitoring systems and methods. As described herein, the cardiac monitoring system preferably uses a sensor surface having a combination of (membrane-based) force-sensitive resistors and piezoelectric transducers. The force-sensitive resistors can be configured to measure the amount of pressure applied to the sensor surface by the subject. For example, the force-sensitive resistors may change their resistance depending on the pressure. The piezoelectric transducers can be, for example, interspersed between the force-sensitive resistors and configured to measure the vibrations applied to the sensor surface at the respective locations of the transducers by the subject. For example, the piezoelectric transducers can generate a time-dependent electrical signal that depends on the vibrations. The subject's heart rate can be determined based on a combination of the respective signals from different types of sensors, for example, the measured resistances of the force-sensitive resistors and the time-dependent electrical signal of the piezoelectric transducer.

[0006] Using force sensitive resistors, the (static) pressure profile of the subject can be determined more accurately than using piezoelectric sensors. For example, the force sensitive resistors can be arranged in a (relatively) dense grid, for example with shared scan lines in a passive matrix configuration. As will be appreciated, the force sensitive resistors may be better suited to measure a range of different pressure signals and may be used in a dense grid to accurately determine the pressure profile. The accurate pressure profile information of the force sensitive resistors can be used to better select which of the piezoelectric transducers produces the best signal. For example, the pressure profile can be used to determine the area of ​​the body where heart rate vibrations are most prominent. The piezoelectric transducers can be arranged in a (relatively) low density grid, for example, to allow for a relatively small number of dedicated circuit lines between the transducers and the controller. In this way, rapidly changing signals such as heart rate can be clearly and accurately measured from specific locations. This can improve reliability and data integrity. Data from pressure sensors can also be used for many other applications such as respiration, posture detection, etc. This can further improve the applications of the sensors.

[0007] These and other features, aspects, and advantages of the presently disclosed apparatus, systems, and methods will become better understood from the following description, appended claims, and accompanying drawings. [Brief description of the drawings]

[0008] [Figure 1A] FIG. 1A illustrates an exemplary embodiment of a cardiac monitoring system. [Figure 1B] FIG. 1B shows a cross-sectional view of a cardiac monitoring system having a force sensitive resistor and a piezoelectric transducer. [Diagram 2] FIG. 2 shows a schematic layout of sensors on a sensor surface in a cardiac monitoring system and their connections to a controller. [Figure 3A]FIG. 3A shows an example of machine learning to improve heart rate determination using neural networks. [Figure 3B] FIG. 3B shows an example of machine learning to improve heart rate determination using neural networks. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The terms used to describe certain embodiments are not intended to limit the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural, unless the context clearly dictates otherwise. The term "and / or" includes any and all combinations of one or more of the associated listed items. It will be understood that the terms "comprises" and / or "comprises" specify the presence of a stated feature, but do not preclude the presence or addition of one or more other features. Furthermore, when a particular step of a method is referred to as following another step, it will be understood that the other step may directly follow, unless otherwise specified, or that one or more intermediate steps may be performed prior to performing the particular step. Similarly, when a connection between structures or components is described, it will be understood that the connection may be established directly or through an intermediate structure or component, unless otherwise specified.

[0010] Aspects of the present disclosure relate to performing data fusion to improve the reliability of piezoelectric sensors for the detection of other physiological parameters such as heart rate or respiration rate. Preferably, a combination of piezoelectric sensors and membrane-based pressure sensors is used. For example, based on the pressure sensor distribution, the piezoelectric sensor with the highest probability of good signal integrity can be selected.

[0011] In some embodiments, a quasi-static pressure distribution on an object, e.g., a bed, a sheet, a crib, clothing, is first detected based on pressure sensor technology, e.g., thermoplastic polyurethane (TPU) technology. The pressure distribution can be used to extract heart rate and / or respiration rate measurements using piezoelectric sensors, which are most likely to provide accurate data. Preferably, the piezoelectric sensors are printed.

[0012] In some embodiments, the pressure sensor is used to reconstruct how someone is laying on the sensor. This can aid in the readout of the piezo sensor, for example, since the pressure sensor can provide a low-power solution to detect whether a person or object is present on the sensor system. The resulting pressure distribution can then be used to reconstruct a model of the person on the pressure sensor. In one embodiment, the piezo sensor is read out only when a human body is detected. This can save computationally intensive analysis in other situations where it is not needed. In another or further embodiment, based on a combination of physical positions with respect to the body and body parts, e.g., arms, legs, neck, the sensor located on the best body part for detecting BCG is extracted, and within this group of piezo sensors, the piezo sensor within the optimal pressure range is selected.

[0013] In some embodiments, a piezo sensor, which is likely not in contact with the body, is used for noise cancellation, e.g., to remove extraneous (e.g., parasitic) vibrations. In other or further embodiments, a sensor located in a part of the body where a BCG signal should not be present is used to remove other vibrations, e.g., related to breathing and not related to heart rate, or vice versa (if breathing rate is measured). In some embodiments, the subject's breathing rate is simultaneously extracted from the pressure sensor signal, the piezo sensor providing redundancy to the resulting signal. Advantageously, motion artifacts can be actively suppressed since the subject's movements are detected using the pressure sensor. Alternatively or additionally, motion artifacts can be removed spatially and / or temporally.

[0014] The use of a piezoresistive sensor array can provide data directly related to improving signal quality by defining the most accurate locations for measuring and measuring real-time spatial and temporal low-frequency movements, e.g., less than 1 Hz. It will be appreciated that using absolute pressure distributions provides much more relevant data for improving measurements, as compared to using only piezo sensors, for example. Advantageously, static pressure sensor information can be used to better filter the piezo data and to complement the piezo sensor data (in the case of respiration rate).

[0015] In some embodiments, stretchable inks and TPU technology are used for the manufacture of the sensor. Thus, the sensor may be placed closer to the human body, which improves the reliability of the signal. In other or further embodiments, the measurement may be complemented by incorporating a (printed) temperature sensor on the sensor surface, for example to measure the temperature of a bed or chair.

[0016] The present invention will now be described more fully with reference to the accompanying drawings, which show embodiments of the invention. In the drawings, absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. The embodiments may be described with reference to schematic and / or cross-sectional illustrations of possibly idealized embodiments and intermediate structures of the invention. In the description and drawings, like numbers refer to like elements throughout. Relative terms and derivatives thereof should be construed to refer to an orientation as described below or as shown in the drawings under discussion. These relative terms are for convenience of description and do not require that the system be constructed or operated in a particular orientation, unless specifically stated otherwise.

[0017] FIG. 1A illustrates an exemplary embodiment of a cardiac monitoring system 100 .

[0018] In some embodiments, for example as shown, the cardiac monitoring system 100 comprises a sensor surface 50, for example an array of force sensitive resistors 10 across a substrate. In one embodiment, each resistor 10 is configured to change its respective resistance value "R" in response to an amount of (quasi)static pressure "P" applied to the sensor surface 50 at a respective location of the force sensitive resistor 10 by the subject 200. In other or further embodiments, the system comprises an array of piezoelectric transducers 20 interspersed among the array of force sensitive resistors 10, for example on the same or another (overlapping) substrate. In one embodiment, each transducer 20 is configured to generate a respective time-dependent electrical signal S in response to a respective vibration "F" applied to the sensor surface 50 by the subject 200 at a respective location of the transducer 20. In a preferred embodiment, for example as shown, the controller 30 is configured to determine the heart rate "H1" of the subject 200 based on a combination of the measured resistance value "R" of the force sensitive resistors 10 and the time-dependent electrical signal "S" of the piezoelectric transducers 20.

[0019] The cardiac monitoring system 100 described herein may find application in a variety of settings and situations. In one embodiment, for example, as shown, an aspect or application may be embodied as a bed 300 comprising the cardiac monitoring system 100 as described herein. In some embodiments, the mattress of the bed 300 comprises the cardiac monitoring system 100 for the subject 200 to lie on. In some embodiments, the sensor surface 50 is embedded in the mattress, for example, as shown. Alternatively, the sensor surface 50 may be located on top of the mattress. In other or further embodiments, the sensor surface 50 may be located between one or more sheets or other beds. For example, the subject 200 may be a patient requiring continuous monitoring lying in a hospital bed. The cardiac monitoring system may also be incorporated into other types of furniture, for example, a chair (not shown). For example, the system may be incorporated into the bottom and / or rear of a chair, for example, a regular chair or an automobile seat. For example, the sensor surface 50 including the force sensitive resistor 10 and the piezoelectric transducer 20 may be clamped onto the seat back and placed on top of the seat bottom. Alternatively or additionally, the sensor surface 50 may be embedded within an inner layer of the seat, for example within the inside of the seat cushion.

[0020] In a preferred embodiment, as shown, for example, the controller 30 receives as inputs the measured resistance "R" of the force sensitive resistor 10 and the time-dependent electrical signal "S" of the piezoelectric transducer 20, and generates as an output the heart rate "H1". Thus, the cardiac monitoring system 100 can provide continuous, real-time measurement and analysis of the heart rate of the subject 200, even when the subject (200) is in non-direct contact with the sensor surface 50. In some embodiments, as shown, for example, the controller 30 can be provided as an external device to the bed 300. For example, the controller 30 is connected with an electrical connection to the bed 300. Alternatively, the controller 30 may be provided as part of the bed 300. In one embodiment, as shown, for example, a display device is connected to the controller 30. The heart rate can also be output in other ways, for example, as an electrical data signal for further processing, or as an audible or tactile signal.

[0021] In some embodiments, a secondary cardiac monitor 40 may be provided temporarily or permanently and coupled to the controller 30, as shown in FIG. 1A. In some embodiments, the secondary cardiac monitor 40 is attached to the subject 200, e.g., on the wrist or chest, for a period of time to generate a secondary heart rate measurement H2 that can be used as a reference value. For example, the secondary cardiac controller 30 may compare the secondary heart rate measurement H2 with a primary measurement of heart rate "H1". In the illustrated embodiment, the secondary heart rate measurement H2 is measured using separate equipment, e.g., a dedicated secondary cardiac monitor 40 based on electrical signals (electrocardiogram) from the cardiac region. In some embodiments, the secondary cardiac monitoring device 40 may be provided temporarily to check and / or correct the primary cardiac monitoring system 100. Alternatively, the secondary cardiac monitor, e.g., electrodes on the chest, may be removed once the network is trained, as described below in FIGS. 3A and 3B.

[0022] In some embodiments, for example, as shown, the weight, position or movement of the subject may create a static or quasi-static pressure "P" on the sensor surface 50. For example, the pressure "P" may be relatively high in certain areas, e.g., in the subject's chest area compared to the subject's legs. In a preferred embodiment, the pressure profile is used to determine where the heart rate is measured. Static pressure can be distinguished from dynamic vibrations "F", such as heart rate, e.g., based on time scale. As will be appreciated, force sensitive resistors are typically capable of measuring static pressure, i.e., even if the pressure is constant in time. Of course, the pressure will change, e.g., due to the subject moving, resulting in a new (static) pressure being measured. This can be contrasted with measurements using piezoelectric sensors, which are typically more sensitive to vibrations or pressure changes.

[0023] FIG. 1B shows a cross-sectional view of a cardiac monitoring system 100 including a force sensitive resistor 10 and a piezoelectric transducer 20.

[0024] In a preferred embodiment, the force sensitive resistors 10 are disposed on or across the sensor surface 50. Most preferably, the force sensitive resistors 10 are distributed at equal intervals on the sensor surface 50. This may allow for easy correspondence between the respective signals and the location of the sensors. In alternative or further embodiments, the force sensitive resistors 10 may vary in distribution, orientation, number and / or shape. This may, for example, allow for a higher concentration of sensors at the relevant locations.

[0025] Typically, each of the force-sensitive resistors 10 includes a force-sensitive material 14, e.g., a conductive composite material, or other material that changes its resistance when a force is applied in a membrane configuration. In one embodiment, e.g., as shown, a force-sensitive material 14 disposed on a first stretchable substrate 17, e.g., a polyurethane (TPU) substrate, facing a series of electrodes 12, 13, e.g., a TPU substrate, in which the force-sensitive material 14 is disposed on an opposing second substrate 11. In another or further embodiment, e.g., as shown, the force-sensitive material 14 is disposed between the substrates 17, 11 and held away from the electrodes 12, 13 by a spacer material 15 that surrounds the force-sensitive material 14. In some embodiments, e.g., as shown, the first substrate 17 and / or the second substrate 11 are configured to deflect toward the opposing substrate under the influence of a static pressure "P" applied to the force-sensitive resistor 10. Thus, the force-sensitive material 14 contacts the electrodes 12, 13 and changes its resistance "R". In another or further embodiment, when no pressure is applied, the sensor acts like an infinite resistor, i.e. an open circuit. Preferably, the more pressure is applied to the surface of the sensor, the more the electrodes 12, 13 touch the force-sensitive material 14, and the lower the resistance. Preferably, the force-sensitive resistor has a diameter D10 of the order of a few millimeters, for example between 1 millimeter and 50 millimeters, preferably between 5 millimeters and 20 millimeters, for example 10 millimeters.

[0026] In a preferred embodiment, piezoelectric transducers 20 are interspersed between the force sensitive resistors 10. Typically, each of the piezoelectric transducers 20 includes a layer of piezoelectric material 24. Preferably, the piezoelectric material 24 is made of a polymer that has a piezoelectric effect, such as PVDF-TrFE. The piezoelectric effect can be understood as the phenomenon whereby an electric charge and a corresponding electric field can build up in a certain material in response to an applied mechanical stress. For example, the piezoelectric transducers 20 can detect small changes in pressure, acceleration, temperature, strain, or force and convert them into an electrical signal.

[0027] In one embodiment, for example as shown, the piezoelectric material 24 is sandwiched between a bottom electrode 22 and a top electrode 23. In some embodiments, the bottom electrode 22 is disposed on a substrate 21, for example a TPU substrate. Preferably, the piezoelectric transducer 20 is configured to generate a respective time-dependent electrical signal S in response to a time-dependent mechanical stress applied to the piezoelectric material 24. Preferably, the piezoelectric transducer has a diameter D20 of the order of a few millimeters, for example between 1 millimeter and 50 millimeters, preferably between 5 millimeters and 20 millimeters, for example 10 millimeters.

[0028] FIG. 2 shows a schematic layout of sensors 10 , 20 on a sensor surface 50 in a cardiac monitoring system 100 and their respective connections to a controller 30 .

[0029] As described herein, the sensor surface 50 may be formed by one or more substrates housing the sensors. For example, the force sensitive resistors 10 and / or the piezoelectric transducers 20 may be distributed (interspersed) on a single substrate, or each type of sensor may be disposed on its own substrate. The present illustration shows the force sensitive resistors 10 and the piezoelectric transducers 20 disposed on top of the substrate 50, but in other embodiments the substrates 11, 21 of the sensor may be part of the sensor surface.

[0030] In one embodiment, for example as shown, each of the force sensitive resistors 10 is coupled to a pair of shared circuit lines 30h, 30v. For example, each shared circuit line connects a plurality of force sensitive resistors 10 to a controller 30. Thus, the resistance value "R" of each force sensitive resistor 10 can be determined, for example, by scanning a respective shared circuit line pair 30h, 30v connected to said force sensitive resistor 10. For example, as shown in FIG. 2, a first row of force sensitive resistors 10 is horizontally coupled to the shared circuit line 30h, and a first row of force sensitive resistors 10 is also coupled to the shared circuit line 30v. In another or further embodiment, for example, the plurality of shared circuit lines 30v, 30h are coupled to the controller 30 from one side and to ground on the other side. Of course, other configurations are possible.

[0031] In alternative or further embodiments, for example as shown, each of the piezoelectric transducers 20 is separately coupled to a dedicated circuit line 30p and to the controller 30. A dedicated circuit line 30p can typically be used since the piezoelectric transducers 20 generate, for example, a single time-dependent electrical signal that is preferably detected individually. For example, the first piezoelectric transducer 20 on the first column of the array is individually coupled to a dedicated circuit line 30p, from one side to the controller 30 and from the other side to ground. In other embodiments, any other suitable means for coupling the force sensitive resistors 10 and the piezoelectric transducers 20 to the controller 30 are contemplated.

[0032] In a preferred embodiment, the sensor surface 50 includes many more force sensitive resistors 10 than piezoelectric transducers 20. For example, the force sensitive resistors are arranged in a relatively high density grid, while the piezoelectric transducers are arranged in a relatively low density grid. For example, the number of force sensitive resistors 10 can be at least two, three, four or five times higher than the number of piezoelectric transducers 20. It will be appreciated that it is easier to connect many more force sensitive resistors 10 than piezoelectric transducers 20, for example for different signals and / or connections. This can be advantageously used to provide a better measurement of the pressure profile using the force sensitive resistors 10, while using a small number of scattered piezoelectric transducers 20 to measure the heart rate at a particular location, for example based on the profile.

[0033] In one embodiment, the multiple shared circuit lines 30v, 30h and the dedicated circuit lines 30p form a matrix readout system. In another or further embodiment, the controller 30 is configured to determine a pressure profile based on the measured resistance values ​​(R) of the force sensitive resistors 10. In some embodiments, the pressure profile is used to determine a region of interest (RoI) based on the location of the corresponding force sensitive resistor 10 on the surface 50. For example, the region of interest is an area of ​​the sensor surface 50 in contact with the subject 200. In a preferred embodiment, the controller 30 is configured to analyze the shape and / or magnitude of the pressure profile to overlay the shape of the subject's body. In another or further preferred embodiment, the region of interest is determined at one or more specific locations in the pressure profile corresponding to respective locations on the subject's body.

[0034] In one embodiment, the controller 30 is configured to exclusively or primarily select the piezoelectric transducers 20 located within the region of interest to measure the respective time-dependent electrical signals "S". Thus, the heart rate "H1" is determined by measuring the vibrations "F" using a subset of the piezoelectric transducers 20 located on the surface 50 within the region of interest. For example, the region of interest is a region of the sensor surface 50 where the BCG signal of the subject 200 is optimal. In some embodiments, only the piezoelectric transducers 20 located in the region of interest are active. In this manner, it will be appreciated that the controller does not need to continuously monitor all the piezoelectric transducers 20 on the sensor surface 50.

[0035] In some embodiments, at least one of the piezoelectric transducers 20 outside the region of interest based on the force sensitive resistor 10 is used for noise cancellation. For example, after determining the region of interest, one or more piezoelectric transducers 20i outside the region of interest can be used to cancel noise by canceling any vibrations "F" detected by the inactive piezoelectric transducers 20i. In this way, it will be appreciated that vibrations "F" that are not induced by contact between the subject 200 and the sensor surface 50 are cancelled and any background noise is not taken into account while measuring the heart rate "H1".

[0036] 3A and 3B show an example of machine learning for improving the determination of heart rate "H1" using a neural network 30n.

[0037] In one embodiment, as shown in FIG. 3A, for example, the controller 30 comprises a neural network 30n configured to receive at least a resistance value "R" to determine a region of interest. For example, the resistance value "R" is provided as an input to the neural network 30n, and the neural network is trained to output a region of interest. In a preferred embodiment, a selection is made from one or more of the time-dependent electrical signals "S(t)" to determine a primary measure of heart rate "H1" based on the region of interest determined by the neural network, for example, as shown. In some embodiments, the network is trained for each individual subject, taking into account the subject's particular characteristics to provide optimal accuracy. In other or further embodiments, the network is trained generally to be used for other subjects as well. Combinations are also possible, for example, the network starts with a basic training that may be improved for a particular individual. For example, the trained network may comprise a set of weights (w), offsets, or other parameters that determine the network to output a region of interest and / or a heart rate based on the respective input signals.

[0038] In another or further embodiment, for example as shown in FIG. 3B, the time-dependent electrical signal "S(t)" may be input to the same or another neural network to determine a respective heart rate measurement. For example, the resistance value "R" and the time-dependent electrical signal "S" are provided as inputs to neural network 30n. In a preferred embodiment, neural network 30n is configured to output a value indicative of a primary measurement of heart rate "H1".

[0039] In some embodiments, for example, as shown in both Figures 3A and 3B, a primary measurement of heart rate "H1" is compared to a secondary measurement of heart rate "H2" obtained by an independent cardiac monitoring device 40 to train a neural network 30n. For example, the neural network 30n may be trained by comparing a direct or indirect output from the neural network 30n to a secondary heart rate of a secondary cardiac monitoring device 40. For example, the difference between the primary and secondary heart rate measurements may be fed back to the network as an error "Err", which may result in changes to the weights "w" or other parameters of the neuronal connections.

[0040] In some embodiments, a recurrent neural network (RNN) is used. This is a class of artificial neural networks in which the connections between nodes form a directed graph along a time sequence. This allows to show temporal dynamic behavior, for example a time-dependent heart rate signal. Other or similar artificial networks can also be used. Other or further values ​​H' can also be output from the neural network 30n or from the controller 30 in general. For example, the neural network 30n may output physiological parameters such as respiration rate, blood pressure, weight, posture detection, body position, body temperature, etc.

[0041] For clarity and concise description, features are described herein as part of the same or separate embodiments, but it will be understood that the scope of the present disclosure may include embodiments having all or some combination of the described features. Some aspects of the present disclosure relate to a non-transitory computer-readable medium storing instructions. In some embodiments, the non-transitory computer-readable, when executed by a controller in a cardiac monitoring system, causes the system to determine a heart rate of a subject directly or indirectly contacting the sensor surface. Another aspect of the present disclosure relates to a method for cardiac monitoring. In some embodiments, the method includes providing an array of force-sensitive resistors across the sensor surface. In one embodiment, each resistor is configured to change a respective resistance value in response to an amount of quasi-static pressure applied to the sensor surface at a respective location of the force-sensitive resistor by the subject. In another or further embodiment, the method includes providing an array of piezoelectric transducers interspersed among the array of force-sensitive resistors. In one embodiment, each transducer is configured to generate a respective time-dependent electrical signal in response to a respective vibration applied to the sensor surface at a respective location of the transducer by the object. In a preferred embodiment, the method includes determining the subject's heart rate based on a combination of the measured resistance of the force sensitive resistor and the time-dependent electrical signal of the piezoelectric transducer.

[0042] In interpreting the appended claims, it should be understood that the term "comprising" does not exclude the presence of elements or acts other than those recited in a given claim, the term "a" or "an" preceding an element does not exclude the presence of a plurality of such elements, reference signs in the claims do not limit their scope, a plurality of "means" can be represented by the same or different items or embodied structures or functions, any of the disclosed apparatus or parts thereof can be combined together or separated into different parts, unless otherwise specified. When one claim refers to another claim, this may indicate synergistic advantages achieved by the combination of their respective features. However, the mere fact that certain means are recited in mutually different claims does not indicate that a combination of these means cannot also be used advantageously. Thus, the present embodiments can include all practical combinations of the claimed inventions, and the invention of each claim can in principle refer to the invention of any preceding claim, unless the context clearly excludes otherwise.

Claims

1. an array of force sensitive resistors (10) across a sensor surface (50), each resistor (10) configured to change a respective resistance value (R) according to an amount of static pressure (P) exerted by a subject (200) on the sensor surface (50) at a respective location of the force sensitive resistor (10); an array of piezoelectric transducers (20) interspersed among said force-sensitive resistors (10), each transducer (20) configured to generate a respective time-dependent electrical signal (S) according to a respective vibration (F) applied to said sensor surface (50) by said subject (200) at a respective location of said transducer (20), said sensor surface (50) including more force-sensitive resistors (10) than said piezoelectric transducers (20); a controller (30) configured to determine a heart rate (H1) of the subject (200) based on a combination of the measured resistance (R) of the force sensitive resistor (10) and the time dependent electrical signal (S) of the piezoelectric transducer (20), the controller (30) is configured to measure a pressure profile using the force sensitive resistors (10), and based on the measured pressure profile, a controller configured to measure a heart rate at one or more specific locations of the sensor surface (50) using a subset of the piezoelectric transducers (20) between the force sensitive resistors (10); A cardiac monitoring system (100) comprising:

2. 2. The system of claim 1, wherein the controller (30) is configured to determine a pressure profile based on the measured resistance values ​​(R) of the force sensitive resistors (10), the pressure profile is used to determine a region of interest (RoI) based on the position of the corresponding force sensitive resistors (10) on a surface (50), and the heart rate (H1) is determined by measuring vibrations (F) using a subset of the piezoelectric transducers (20) located on the surface (50) within the region of interest (RoI).

3. The system of claim 1 or claim 2, wherein the controller (30) is configured to analyze the shape and / or magnitude of the pressure profile and overlay it on the shape of the subject's body, and a region of interest (RoI) is determined at one or more specific locations within the pressure profile corresponding to respective locations on the subject's body.

4. The system according to any one of claims 1 to 3, wherein at least one of the piezoelectric transducers (20) that is outside a region of interest (RoI) based on a force sensitive resistor (10) is used for noise elimination.

5. The system of any one of claims 1 to 4, wherein the resistance value (R) is provided as an input to a neural network (30n), the neural network being trained to output a region of interest (RoI), based on which a selection is made from one or more of the time-dependent electrical signals (S) for determining a primary measure of heart rate (H1).

6. 6. The system of claim 1, wherein the resistance value (R) and the time-dependent electrical signal (S) are provided as inputs to a neural network (30n), the neural network (30n) being configured to output a value indicative of a primary measure of the heart rate (H1).

7. 7. The system of claim 5 or claim 6, wherein the primary measurement of heart rate (H1) is compared with a secondary measurement of heart rate (H2) obtained by an independent cardiac monitoring device (40) to train the neural network (30n).

8. each of said force sensitive resistors (10) comprises a force sensitive material (14) disposed on a first substrate (17) facing a set of electrodes (12, 13) disposed on an opposing second substrate (11), said force sensitive material (14) being disposed between said substrates (17, 11) and held away from said electrodes (12, 13) by a spacer material (15) surrounding said force sensitive material (14), said first substrate and / or second substrate (17) being configured to deflect towards said opposing substrate under the effect of a static pressure (P) applied to said force sensitive resistor (10), thereby bringing said force sensitive material (14) into contact with said electrodes (12, 13) and changing said resistance value (R); A system according to any one of claims 1 to 7.

9. 9. The system of claim 1, wherein each of the piezoelectric transducers (20) comprises a layer of piezoelectric material (24) sandwiched between a lower electrode (22) and an upper electrode (23), and the piezoelectric transducers (20) are configured to generate a respective time-dependent electrical signal (S) in response to a time-dependent mechanical stress applied to the piezoelectric material (24).

10. 10. The system of claim 1, wherein each of the force sensitive resistors (10) is coupled to a pair of shared circuit lines (30h, 30v), each shared circuit line connecting a plurality of the force sensitive resistors (10) to the controller (30), and wherein a resistance value (R) of each of the force sensitive resistors (10) is determined by scanning a respective pair of the shared circuit lines (30h, 30v) connected to the force sensitive resistors (10).

11. The system of any one of claims 1 to 10, wherein each of the piezoelectric transducers (20) is separately coupled to the controller (30) with a dedicated circuit line (30p).

12. The system according to any one of the preceding claims, wherein the sensor surface (50) comprises at least twice as many force sensitive resistors (10) as there are piezoelectric transducers (20).

13. A bed or chair comprising a cardiac monitoring system (100) according to any one of the preceding claims.

14. A non-transitory computer readable medium storing instructions that, when executed by a controller (30) in a cardiac monitoring system (100) of any one of claims 1 to 13, cause the system to determine a heart rate (H1) of a subject (200) in direct or indirect contact with a sensor surface (50).

15. A method (100) for cardiac monitoring, comprising: providing an array of force sensitive resistors (10) across a sensor surface (50), each resistor (10) configured to change a respective resistance value (R) according to an amount of static pressure (P) exerted by a subject (200) on the sensor surface (50) at a respective location of the force sensitive resistor (10); providing an array of piezoelectric transducers (20) interspersed among said force sensitive resistors (10), each transducer (20) configured to generate a respective time-dependent electrical signal (S) according to a respective vibration (F) applied to said sensor surface (50) by said subject (200) at a respective location of said transducer (20), said sensor surface (50) including more force sensitive resistors (10) than said piezoelectric transducers (20); determining a heart rate (H1) of the subject (200) based on a combination of the measured resistance (R) of the force sensitive resistor (10) and the time dependent electrical signal (S) of the piezoelectric transducer (20); The force sensitive resistors (10) are used to measure a pressure profile, and a subset of the piezoelectric transducers (20) between the force sensitive resistors (10) are used to measure a heart rate at one or more specific locations on the sensor surface (50) based on the measured pressure profile. method.

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