Embodiments of the present invention relate to wearable multi-sensor arrays for unobtrusive and continuous health status monitoring. Embodiments relate further to methods for generating pulse wave velocity imaging and thereby estimating central blood pressure. Still further, embodiments of the present invention relate to multi-sensor array designs and methods for estimating blood pressure.
Pulse wave velocity (PWV) is an important physiological parameter for evaluating arterial stiffness, which is an independent predictor of cardiovascular morbidity and mortality, as well as a potential indicator to track blood pressure changes. PWV is typically assessed by the arrival time of a pressure wave propagating through the arterial tree for a certain distance between the proximal and distal arterial sites. Pulse transit time (PTT) has a reciprocal relationship with PWV, and can be obtained from two pulse signals. PTT can be used for BP estimation without the need for a cuff. The estimated BP can be obtained by calibration with a cuff-based BP device that measures brachial BP. Despite the fact that cuff-less BP measuring is noninvasive and continuous, PTT-based methods can only provide peripheral BP. However, emerging evidence suggests that central blood pressure is more closely related to future cardiovascular events than is brachial pressure. There are several methods available for assessing central blood pressure. The invasive cardiac catheterization is the gold standard for measurement of central BP, but it is highly invasive and limited to only clinical settings. In addition, noninvasive methods can be used, such as the applanation tonometry of the carotid artery, applanation tonometry of the radial artery, and cuff-based oscillometry at the brachial artery. However, these methods require skilled medical professionals for operation and/or applanation against the artery and the occluded inflation cuff. Thus, they are not suitable for long-term continuous and unobtrusive applications.
Current techniques for PWV imaging include ultrasound methods and magnetic resonance imaging (MRI). These techniques provide good resolution, but they have several disadvantages, including bulky size, the requirement of skilled medical staff for operation, and being limited to clinical usage. Therefore, they are not suitable for continuous long-term applications.
Embodiments of the subject invention provide novel and advantageous systems, devices, and methods for pulse wave velocity (PWV) imaging that enable precise central blood pressure (BP) estimation. In many embodiments, a multi-sensor array can provide two-dimensional PWV, thereby achieving the PWV imaging and precise central BP estimation. The multi-sensor array can be integrated in daily objects (e.g., clothing or a bed), which results in noninvasive, unobtrusive, continuous, low-cost monitoring of BP that is easy to use and does not require a medical professional. Embodiments are therefore suitable for long-term monitoring for cardiovascular disease. In addition, embodiments can also provide electrocardiogram (ECG) imaging, photoplethysmogram (PPG) imaging, and monitoring for other physiological parameters such as heart rate, SpO2, BP, and respiration.
In one embodiment, a system for PWV imaging can comprise: a plurality of sensor units, each sensor unit including at least one electrical sensor for detecting ECG signals of a user and at least one optical sensor for detecting PPG signals of said user, wherein each optical sensor includes a light source emitting light at a first wavelength and a photodetector, a front-end circuit in operable communication with the plurality of sensor units, the front-end circuit comprising at least one amplifier and filter circuit to amplify and filter the ECG and PPG signals and at least one analog-to-digital converter to digitize the filtered ECG and PPG signals; and at least one processor in operable communication with the front-end circuit to calculate pulse transmit time (PTT) from the ECG and PPG signals, thereby generating PWV imaging. The plurality of sensor units and the front-end circuit can be provided on an everyday object, such as a wearable garment (e.g., a shirt, a vest, or pants) or a bed.
Embodiments of the subject invention provide novel and advantageous systems, devices, and methods for pulse wave velocity (PWV) imaging that enable precise central blood pressure (BP) estimation. In many embodiments, a multi-sensor array can provide two-dimensional PWV, thereby achieving the PWV imaging and precise central BP estimation. The multi-sensor array can be integrated in daily objects (e.g., clothing or a bed), which results in noninvasive, unobtrusive, continuous, low-cost monitoring of BP that is easy to use and does not require a medical professional. Embodiments are therefore suitable for long-term monitoring for cardiovascular disease. In addition, embodiments can also provide electrocardiogram (ECG) imaging, photoplethysmogram (PPG) imaging, and monitoring for other physiological parameters such as heart rate, SpO2, BP, and respiration.
PWV is an important physiological parameter for evaluating arterial stiffness and tracking BP changes, as well as an independent predictor of cardiovascular morbidity and mortality. Current techniques for PWV measurement are through detecting arterial pulses at two different peripheral sites, so the measured PWV is one-dimensional and provides limited information about the cardiovascular system. In addition, existing cuff-less BP measurement methods based on PWV recording are available only for peripheral BP estimation. Central BP (CBP) is a better indicator for future cardiovascular events as compared to peripheral BP pressure (e.g., brachial pressure), but existing cuff-less BP based on PWV recording methods based on PWV recording cannot determine or estimate CBP.
Embodiments of the subject invention include multi-sensor layouts (e.g., multi-sensor arrays) that enable two-dimensional PWV measurements, as well as precise CBP estimation. A multi-sensor layout can include a plurality of sensor pairs, with each sensor node including one or more ECG electrodes and one or more PPG optical sensors. These sensor pairs provide PWV imaging and lead to CBP estimation, in addition of physiological monitoring of ECG imaging, PPG imaging, and physiological parameters including but not necessarily limited to heart rate, SpO2, BP, and respiration. Each sensor element can be utilized as a pixel and can be assembled in various ways to achieve different resolutions that adapt to different applications. A multi-sensor layout can be incorporated into an everyday object, such as a wearable garment (e.g., a shirt, a vest, pants) or a bed, such that noninvasive and continuous monitoring can be performed without the need for a medical professional.
With PTT calculated from the ECG and PPG from each sensor set, the spatially resolved PWV can be obtained and thereby the PWV imaging can be reconstructed (e.g., with time-space transform). Further, the CBP can be estimated through a source location method based on the PWV imaging. Systems of embodiments of the subject invention can be embedded into wearable objects (e.g., a shirt, a vest, pants) and can be used for ambulatory, clinical, and home monitoring of cardiovascular diseases (e.g., for the elderly and patients with cardiovascular risk factors), thereby providing early prediction and prevention of cardiovascular events and mortality.
To improve the accuracy, signals from other sites of the body, for example the ear 35, arm 36, and/or finger 47, can be extracted and used as a calibration to the signals extracted from the chest and the back 34. These signals can be processed by a signal processing box 38.
In an embodiment, the customized algorithm 41 for CBP estimation can utilize a method of system identification, for example, the Multiple Input Single Output (MISO) with AutoRegressive eXogenous input (ARX), though embodiments are not limited thereto. With the features extracted from the PWV imaging, the central BP can be calculated through the system transfer function:
where Hk(t) is the sub-system function for the kth feature Xk(t) obtained from the element ui,j(f) collected from the sensor located at (i,j), and E(n) is the exogenous factors (e.g., age, gender, etc.) relevant to the nth subject.
The methods and processes described herein can be embodied as code and/or data. The software code and data described herein can be stored on one or more machine-readable media, which may include any device or medium that can store code and/or data for use by a computer system. When a computer system reads and executes the code and/or data stored on a machine-readable medium, the computer system performs the methods and processes embodied as data structures and code stored within the computer-readable storage medium.
It should be appreciated by those skilled in the art that machine-readable media (e.g., computer-readable media) include removable and non-removable structures/devices that can be used for storage of information, such as computer-readable instructions, data structures, program modules, and other data used by a computing system/environment. A machine-readable medium includes, but is not limited to, volatile memory such as random access memories (RAM, DRAM, SRAM), and non-volatile memory such as flash memory, various read-only-memories (ROM, PROM, EPROM, EEPROM), magnetic and ferromagnetic/ferroelectric memories (MRAM, FeRAM), and magnetic and optical storage devices (hard drives, magnetic tape, CDs, DVDs); network devices, or other media now known or later developed that is capable of storing computer-readable information/data. Computer-readable media should not be construed or interpreted to include any propagating signals. A machine-readable medium of the subject invention can be, for example, a compact disc (CD), digital video disc (DVD), flash memory device, volatile memory, or a hard disk drive (HDD), such as an external HDD or the HDD of a computing device, though embodiments are not limited thereto. A computing device can be, for example, a laptop computer, desktop computer, server, cell phone, or tablet, though embodiments are not limited thereto.
The subject invention includes, but is not limited to, the following exemplified embodiments.
A system for pulse wave velocity (PWV) imaging, the system comprising:
a plurality of sensor units, each sensor unit including at least one electrical sensor for detecting electrocardiogram (ECG) signals of a user and at least one optical sensor for detecting photoplethysmogram (PPG) signals of said user, wherein each optical sensor includes a light source emitting light at a first wavelength and a photodetector;
a front-end circuit in operable communication with the plurality of sensor units, the front-end circuit comprising at least one amplifier and filter circuit to amplify and filter the ECG and PPG signals and at least one analog-to-digital converter to digitize the filtered ECG and PPG signals; and
at least one processor in operable communication with the front-end circuit to calculate pulse transmit time (PTT) from at least two signals out of the at least one ECG signal and the at least one PPG signal (e.g., one ECG signal and one PPG signal, or two PPG signals), thereby generating PWV imaging.
The system according to embodiment 1, wherein the front-end circuit further comprises a microcontroller to process the signals from the at least one analog-to-digital converter and transmit the digital signals.
The system according to any of embodiments 1-2, wherein the front-end circuit further comprises a power source.
The system according to embodiment 1, wherein the power source comprises at least one (rechargeable) battery.
The system according to any of embodiments 1-4, further comprising a remote terminal in operable communication with the front-end circuit and comprising a display to display PWV images based on the ECG and PPG signals obtained from the plurality of sensor units.
The system according to embodiment 5, wherein the microcontroller wirelessly communicates with the remote terminal.
The system according to embodiment 6, wherein the front-end circuit (e.g., the microcontroller) communicates via Bluetooth with the remote terminal Embodiment 8. The system according to embodiment 2, further comprising a remote terminal in operable communication with the microcontroller and comprising a display to display PWV images based on the ECG and PPG signals obtained from the plurality of sensor units, wherein the microcontroller transmits the signals wirelessly (e.g., via Bluetooth) to the remote terminal.
The system according to any of embodiments 5-8, wherein the remote terminal comprises the at least one processor.
The system according to any of embodiments 1-9, wherein the at least one processor performs a first algorithm to calculate PTT from the at least two signals out of the at least one ECG signal and the at least one PPG signal (e.g., one ECG signal and one PPG signal, or two PPG signals), thereby generating the PWV imaging, by treating each sensor unit as an individual pixel.
The system according to any of embodiments 1-10, wherein the at least one processor performs a second algorithm to estimate central blood pressure (CBP), of a user of the system, from the obtained PWV imaging.
The system according to embodiment 11, wherein the second algorithm comprises utilizing a method of system identification.
The system according to embodiment 12, wherein the second algorithm comprises utilizing Multiple Input Single Output (MISO) with AutoRegressive eXogenous input (ARX).
The system according to any of embodiments 11-13, wherein the CBP is calculated through the system transfer function:
where Hk(t) is sub-system function for the kth feature Xk(t) obtained from element ui,j(t) collected from a sensor located at (i,j), and E(n) represents exogenous factors (e.g., age, gender, etc.) relevant to the nth subject.
The system according to any of embodiments 1-14, wherein the plurality of sensor units are provided in an array (e.g., an N*M array, where N is number of rows, M is number of columns, and N>M, N=M, or N<M are all valid).
The system according to any of embodiments 1-15, wherein each light source is a light emitting diode (LED).
The system according to any of embodiments 1-16, wherein the first wavelength is an infrared wavelength in a range of from 850 nm to 950 nm.
The system according to any of embodiments 1-17, wherein each photodetector is a photodiode or a phototransistor.
The system according to any of embodiments 1-18, wherein each light source is spaced apart from the photodetector of the same sensor unit by a distance of 5 mm.
The system according to any of embodiments 1-19, wherein the at least one processor performs a third algorithm to generate ECG imaging and PPG imaging based on the ECG signals and PPG signals, respectively, detected from the sensor units.
The system according to any of embodiments 1-20, wherein the at least one processor performs a fourth algorithm to obtain at least one of blood pressure, heart rate, SpO2, and respiration of a user of the system.
The system according to any of embodiments 5-21, wherein the remote terminal displays physiological parameters of a user of the system.
The system according to any of embodiments 1-14 or 16-22, wherein the plurality of sensor units are provided in a circular arrangement.
The system according to any of embodiments 1-14 or 16-22, wherein the plurality of sensor units are provided in an oval arrangement.
The system according to any of embodiments 1-14 or 16-22, wherein the plurality of sensor units are provided in an irregularly-shaped arrangement.
The system according to any of embodiments 1-25, further comprising a wearable garment in which the plurality of sensor units are provided.
The system according to embodiment 26, wherein the front-end circuit is also provided on the wearable garment.
The system according to any of embodiments 26-27, wherein the wearable garment is a shirt.
The system according to any of embodiments 26-27, wherein the wearable garment is a vest.
The system according to any of embodiments 1-25, further comprising a bed on which the plurality of sensor units are provided.
The system according to embodiment 30, wherein the front-end circuit is also provided on the bed.
The system according to any of embodiments 1-31, wherein each optical sensor comprises at least two light sources operating at different spectral ranges, wherein each respective photodetector PPG signals from different depths of peripheral arteries of a user of the system.
The system according to embodiment 32, wherein the at least one processor performs a fifth algorithm to generate PWV imaging of blood vessels at different depths of sensing sites of the sensor units.
The system according to any of embodiments 32-33, wherein the at least one processor performs a sixth algorithm to generate PPG imaging based on the PPG signals collected at different depths of sensing sites of the sensor units.
The system according to any of embodiments 1-34, further comprising a PPG body sensor network for collecting PPG signals from different sites of a user, separate from the plurality of sensor units, thereby increasing the accuracy of PTT determination.
The system according to embodiment 35, wherein the PPG body sensor network for collecting PPG signals from different sites of a user is configured to collect PPG signals from at least one of a brachial artery, a radial artery, a fingertip, am earlobe, and a toe.
The system according to any of embodiments 1-36, further comprising a BP body sensor network for collecting BP readings from different sites of a user, separate from the plurality of sensor units, thereby increasing the accuracy of BP determination.
The system according to any of embodiments 1-37, further comprising a plurality of e-textile electrodes positioned to contact a user of the system to generate a reference ECG signal to be used as a reference signal during the calculation of PTT.
The system according to embodiment 38, comprising at least three e-textile electrodes.
The system according to embodiment 38, comprising exactly three e-textile electrodes.
The system according to any of embodiments 38-40, wherein the e-textile electrodes are provided in or on a surface of a wearable garment or bed having the plurality of sensor units provided thereon.
A method of obtaining pulse wave velocity (PWV) imaging, the method comprising:
providing the system according to any of embodiments 1-41 to a user-, and
positioning the system such that the plurality of sensor units are in contact with the user, and
obtaining PWV imaging of the user by utilizing the system.
It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.
All patents, patent applications, provisional applications, and publications referred to or cited herein (including those in the “References” section) are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.