Sensor and system for determining physiological parameters using external pressure

Abstract

This invention discloses sensors and systems for determining physiological parameters such as blood pressure using external pressure. Such sensors and / or systems may be embodied in wearable user devices. Wearable user devices may include: a loop configured to apply pressure to a user's site at one or more substantially constant pressure levels; a photoacoustic sensor configured to acquire a photoacoustic signal generated from light incident on a blood vessel; and a wearable structure including the loop and the photoacoustic sensor. Techniques relating to wearable user devices may include: acquiring the photoacoustic signal from the user's site; determining a curve associated with the user, the curve including multiple spatial measurements of the blood vessel varying according to multiple discrete pressures, the curve realizing the determination of blood vessel characteristics; and determining physiological parameters at least based on the characteristics.

Description

[0001] Related applications

[0002] This application claims the benefit of priority to U.S. Patent Application No. 18 / 480831, filed October 20, 2023, entitled “SENSORS AND SYSTEMS FORDETERMINING A PHYSIOLOGICAL PARAMETER USING EXTERNAL PRESSURE”, which has been assigned to the assignee of this application and whose entire contents are incorporated herein by reference for all purposes. Technical Field

[0003] This disclosure generally relates to devices and systems that use biometric sensors (e.g., in conjunction with circadian rhythms).

[0004] Related technical descriptions

[0005] Various sensing technologies and algorithms are being implemented in devices for a wide range of biometric and biomedical applications, including health and wellness monitoring. This drive is partly due to the limitations of traditional measurement devices for continuous, non-invasive, and / or mobile monitoring. Some of these devices are or include photoacoustic sensors. While some previously deployed devices provide acceptable results, improvements in detection devices and systems are still expected. Summary of the Invention

[0006] The systems, methods, and apparatus disclosed herein have several aspects, none of which alone is responsible for the desired properties disclosed herein.

[0007] In one aspect of this disclosure, a wearable user device is disclosed. In some embodiments, the wearable user device may include: a loop configured to apply pressure to a user's site at one or more substantially constant pressure levels; a photoacoustic sensor configured to acquire a photoacoustic signal generated from light incident on a blood vessel of the user, the photoacoustic signal being correlated with one or more dimensions of the user's blood vessel when the pressure is applied to the user's site, the one or more dimensions of the blood vessel and the pressure being correlated with characteristics of the blood vessel that enable the determination of the user's blood pressure; and a wearable structure including the loop and the photoacoustic sensor.

[0008] In another aspect of this disclosure, a method for determining a user's physiological parameters is disclosed. In some embodiments, the method may include: acquiring a photoacoustic signal from a site of the user using a photoacoustic sensor while simultaneously applying multiple discrete pressures to the site of the user at multiple corresponding times, the photoacoustic signal being generated from light incident on a blood vessel of the user; determining multiple dimensions of the blood vessel and multiple spatial measurements of the blood vessel corresponding to the multiple dimensions based on the photoacoustic signal; determining a curve associated with the user, the curve including the multiple spatial measurements of the blood vessel varying according to the multiple discrete pressures, the curve realizing the determination of the characteristics of the blood vessel at a given pressure; and determining the user's physiological parameters based at least on the characteristics of the blood vessel.

[0009] In another aspect of this disclosure, an apparatus is disclosed. In some embodiments, the apparatus may include: a component for applying pressure to a user's site at a substantially constant pressure level; a component for obtaining a photoacoustic signal generated from light incident on the user's blood vessel, wherein the photoacoustic signal is correlated with one or more dimensions of the user's blood vessel when the pressure is applied to the user's site, the one or more dimensions of the blood vessel and the pressure being correlated with characteristics of the blood vessel that enable the determination of the user's blood pressure; and a wearable component including the component for applying the pressure to the user's site and the component for obtaining the photoacoustic signal.

[0010] In another aspect of this disclosure, a non-transitory computer-readable device is disclosed. In some embodiments, the non-transitory computer-readable device may include a storage medium comprising a plurality of instructions configured to, when executed by one or more processors, cause the device to: acquire a photoacoustic signal from a user's site using a photoacoustic sensor, while simultaneously applying a plurality of discrete pressures to the user's site at a plurality of corresponding times, the photoacoustic signal being generated from light incident on a blood vessel of the user; determine a plurality of dimensions of the blood vessel and a plurality of spatial measurements of the blood vessel corresponding to the plurality of dimensions based on the photoacoustic signal; determine a curve associated with the user, the curve including the plurality of spatial measurements of the blood vessel varying according to the plurality of discrete pressures, the curve realizing the determination of the characteristics of the blood vessel at a given pressure; and determine the user's physiological parameters at least based on the characteristics of the blood vessel.

[0011] Details of one or more specific embodiments of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, drawings, and claims. Note that the relative dimensions in the following drawings may not be drawn to scale. Attached Figure Description

[0012] Figure 1This shows an example of a blood pressure monitoring device based on photoacoustic volume plethysmography (which may be referred to herein as PAPG).

[0013] Figure 2 This is a block diagram showing example components of a sensor device according to some disclosed specific implementations.

[0014] Figure 3 This shows an example of heart rate waveform (HRW) features that can be extracted based on some specific implementations.

[0015] Figure 4A The image shows example monitoring devices designed to be worn around the wrist, based on some specific implementations.

[0016] Figure 4B The image shows example monitoring devices designed to be worn on a finger, based on some specific implementations.

[0017] Figure 4C The image shows example monitoring devices designed to be installed on earplugs according to some specific implementations.

[0018] Figures 5A to 5D It is a graph showing examples of externally applied pressure (e.g., using a ring belt) that varies over time according to some specific implementation.

[0019] Figure 6 Ultrasound images depicting blood vessels at different pressure levels.

[0020] Figure 7 Depicts the size and spatial measurements of blood vessels under constant external pressure that varies over time.

[0021] Figure 8 This shows an example of a device configured to perform a receiver-side beamforming process.

[0022] Figure 9A and Figure 9B Depicting beamforming photoacoustic images based on blood vessel-based ultrasound images according to some specific implementations.

[0023] Figure 10 It is a graph of example curves of arterial space measurements that vary according to the external pressure applied based on some specific implementation criteria.

[0024] Figure 10A and Figure 10B Examples of arterial spatial measurements corresponding to external pressure applied during diastole and systole, based on some specific implementations, are provided.

[0025] Figure 11 It is a chart of a set of example data points showing the variation of arterial size under applied external pressure based on some specific implementation criteria.

[0026] Figure 12 It is a chart of a set of example data points showing the variation of arterial cross-sectional area under applied external pressure based on some specific implementation criteria.

[0027] Figure 13 It is a flowchart based on some disclosed specific implementations of methods for determining a user's physiological parameters.

[0028] Figure 14 It is a flowchart of another method for determining a user's physiological parameters, based on some disclosed specific implementations.

[0029] Similar reference numerals and names in the various figures indicate similar elements. Detailed Implementation

[0030] The following description is directed to certain implementations and is intended to describe various aspects of this disclosure. However, those skilled in the art will readily recognize that the teachings herein can be applied in a variety of different ways. Some of the concepts and examples provided in this disclosure are particularly applicable to blood pressure monitoring applications or the monitoring of other physiological parameters. However, some specific implementations may also be applicable to other types of biosensing applications and other fluid flow systems. The described specific implementations can be implemented in any device, apparatus, or system that includes the means disclosed herein. Furthermore, it is contemplated that the described specific implementations may be included in or associated with a variety of electronic devices, such as, but not limited to: mobile phones, cellular phones with multimedia-enabled networks, mobile TV receivers, wireless devices, smartphones, smart cards, wearable devices (such as wristbands, armbands, wrist straps, rings, headbands, patches, chest straps, and anklets, etc.), Bluetooth. ® Devices, personal data assistants (PDAs), wireless email receivers, handheld or portable computers, netbooks, laptops, smartbooks, tablets, printers, copiers, scanners, fax machines, GPS receivers / navigators, cameras, digital media players, game consoles, wristwatches, clocks, computers, television monitors, flat panel displays, electronic reading devices (e.g., e-readers), mobile health devices, computer monitors, automotive displays (including odometer and speedometer displays, etc.), cockpit controls and / or displays, camera view displays (such as displays of vehicle rearview cameras), building structures, microwave ovens, refrigerators, stereo systems, cassette recorders or players, DVD players, CD players, VCRs, radios, portable memory chips, washing machines, dryers, washer / dryer units, parking meters, car doors, Internet of Things (IoT) devices, etc. Therefore, this teaching is not intended to be limited to the specific implementations depicted and described with reference to the accompanying drawings; rather, this teaching has a broad applicability, as will be apparent to those skilled in the art.

[0031] There is an urgent need in clinical and consumer applications for accurate, non-invasive, and continuously monitorable wearable devices, such as those for measuring physiological parameters like a user's blood pressure. Specifically, non-invasive blood pressure monitoring is desired. Continuous blood pressure monitoring opens pathways for the efficient and effective diagnosis and treatment of cardiovascular diseases (e.g., hypertension), cardiovascular event detection, and stress monitoring. It also enables daily spot checks of cardiovascular diseases, including blood pressure, as well as nighttime sleep monitoring. A good user experience is achieved during nighttime sleep monitoring. For example, user discomfort should be minimized as much as possible during the operation of the wearable device, including during sleep.

[0032] Sensing mechanisms capable of collecting biometric data and measuring physiological properties, such as pulse wave velocity (PWV), arterial compliance, and arterial measurements (such as diameter, cross-sectional area, volume, and / or dilation), could be a step in the right direction. PWV and compliance are properties that vary with arterial wall stiffness and tension, blood density, body posture, and blood pressure. Therefore, accurate and convenient acquisition of these properties is of great importance for blood pressure estimation.

[0033] Specifically, compliance can be determined for each individual user and information can be provided to help accurately estimate the user's blood pressure. In some embodiments disclosed herein, photoacoustic signals can be recorded while applying different pressures to the user. For example, a band worn by the user can be inflated to different pressure levels, and signal analysis obtained at such different pressure levels can provide compliance information to the user. Photoacoustic signals have the unique advantage of being able to measure physiological parameters such as arterial size and / or dilation. Size measurements (such as diameter or semi-axis) can be combined with information about arterial stiffness (e.g., compliance) to achieve blood pressure estimation. Such parameters, along with other known information, can be used to derive and estimate the user's blood pressure (relative to the artery on which the photoacoustic measurement is performed).

[0034] More specifically, compliance curves can be determined based on spatial parameters, such as arterial volume or cross-sectional area at different pressure levels. Compliance can be defined as the difference in spatial parameters relative to pressure level differences. In other words, compliance at a given pressure level can be derived from the slope of the compliance curve. Depending on the need, photoacoustic signals can also be obtained for initial calibration of age or individual physiology, as well as for intermittent recalibration of wearable device offset or positioning. Additional features and information can help estimate or predict a user's blood pressure, such as multiple band pressures applied after compliance information is obtained, zero-pressure arterial size (e.g., vessel diameter extrapolated from measured data at zero applied external pressure), or heart rate waveform (HRW) characteristics. Such information helps provide useful contextual information or alternative methods for estimating blood pressure.

[0035] Furthermore, in some specific implementations, machine learning can be used to train machine learning models or artificial intelligence models capable of predicting a user's physiological parameters (e.g., blood pressure). Additionally, some or all of the sensor-based measurements can be retained or discarded based on any discrepancies between the sensor-based estimates and the predictions generated by the model.

[0036] Specific embodiments of the subject matter described in this disclosure can be implemented to achieve one or more of the following potential advantages: Physiological characteristics (e.g., arterial compliance) can be derived to accurately estimate difficult-to-obtain physiological parameters, such as blood pressure, in a simplified manner. Unique compliance curves can be measured for each specific user at discrete time points, and measurements can be performed passively while the user is asleep, rather than as a continuous process requiring manual intervention or operation by the user. The data used to create the compliance curves is also compatible with machine learning or deep learning implementations, where the data can be used as input to machine learning or artificial intelligence models, further improving the accuracy of blood pressure measurement.

[0037] Additional details will follow the initial description of the relevant systems and technologies.

[0038] Figure 1 This shows an example of a blood pressure monitoring device based on photoacoustic volume plethysmography (referred to herein as PAPG). Figure 1 The same example shows arteries, veins, arterioles, venules, and capillaries within a body part (in this example, finger 115). In some examples, Figure 1 The light source shown can be coupled to a light source system (not shown) located away from a body part (e.g., finger 115). In some embodiments, the light source can be an opening in an optical fiber or other waveguide. Such openings can also be connected to openings in interfaces that can contact body parts. In some embodiments, the light source system may include one or more LEDs, one or more laser diodes, etc. In this example, the light source emits transmitted light (in some examples, green, red, infrared, and / or near-infrared (NIR) light), which penetrates the tissue of finger 115 in the illuminated area.

[0039] exist Figure 1In the example shown, blood vessels (and components of the blood itself) are heated by incident light from a light source and emit sound waves 102. In this example, the emitted sound waves 102 include ultrasound. According to this specific embodiment, an ultrasound receiver detects the sound wave emission 102; in this example, the ultrasound receiver is a piezoelectric receiver. The photoacoustic emission 102 from the irradiated tissue detected by the piezoelectric receiver can be used to detect changes in blood volume in the irradiated area of ​​the finger 115, corresponding to physiological data within the irradiated tissue of the finger 115, such as heart rate waveforms. Although some tissue areas shown as irradiated are offset from those shown as generating photoacoustic emission 102, this is only for illustrative purposes. It should be understood that the irradiated tissue is, in fact, the tissue that generates photoacoustic emission. Furthermore, it should be understood that the highest intensity of the photoacoustic emission typically occurs on the same axis as the highest irradiation intensity.

[0040] Systems based on optical technologies (e.g., systems based on photoplethysmography (PPG)) and Figure 1 The key difference between PAPG-based methods in China is that... Figure 1 The sound waves shown travel much slower than the reflected light waves involved in the PPG. Therefore, Figure 1 The depth differentiation based on sound wave arrival time shown is feasible, while depth differentiation based on light wave arrival time in PPG may not be feasible. This depth differentiation enables some of the disclosed specific implementations to separate sound waves received from different blood vessels.

[0041] Based on some such examples, this depth discrimination is able to distinguish arterial heart rate waveforms from venous heart rate waveforms and other heart rate waveforms. Therefore, the blood pressure estimation of the PAPG method based on depth discrimination is generally more accurate than that of the PPG-based method.

[0042] Figure 2 This is a block diagram showing example components of a sensor device 200 according to some specific embodiments. In this example, the sensor device 200 includes an interface 201, a receiver system 202, a light source system 204, and a ring system 205. In some cases, the waveguide system may be included as a separate part of the sensor device 200, or in some cases, it may be part of the light source system 204. Some specific embodiments of the sensor device 200 may include a control system 206, an interface system 208, a noise reduction system 210, or combinations thereof.

[0043] This document discloses various examples of interface 201, and various configurations of receiver system 202 and light source system 204. Some examples are described in more detail below.

[0044] In some embodiments, interface 201, receiver system 202, and light source system 204 may be components of a photoacoustic (PAPG) sensor of sensor device 200. That is, in some embodiments, sensor device 200 may include a PAPG sensor and a loop system 205. In the various specific embodiments described herein, the PAPG sensor and / or its components may operate in conjunction with loop system 205, for example, to time the acquisition of photoacoustic measurements relative to the operation of loop system 205. Example configurations of example components of sensor device 200 will be described in more detail below.

[0045] Some of the disclosed PAPG sensors described herein may include a pressure plate, a light source system, and an ultrasonic receiver system. According to some embodiments, the light source system may include a light source configured to generate and direct light. In some embodiments, the pressure plate may include an anti-reflective layer, a mirror layer, or a combination thereof. According to some embodiments, the pressure plate may have an outer surface or a layer on an outer surface whose acoustic impedance is configured to approximate the acoustic impedance of human skin. In some embodiments, the pressure plate may have a surface adjacent to the ultrasonic receiver system, or a layer on the surface adjacent to the ultrasonic receiver system, whose acoustic impedance is configured to approximate the acoustic impedance of the ultrasonic receiver system.

[0046] Some of the disclosed PAPG sensors described herein may include an interface, a light source system, and an ultrasonic receiver system. Some such devices may not include a rigid pressure plate. According to some embodiments, the interface may be a solid flexible interface constructed of one or more suitable materials having desired properties or multiple properties (e.g., acoustic properties such as acoustic impedance, material softness, etc.). In some embodiments, the interface may be a flexible interface capable of contacting a target object that may be close to or in contact with the interface. Such interfaces may differ significantly from pressure plates. In some embodiments, the light source system may be configured to guide light using one or more optical waveguides (e.g., optical fibers) configured to direct light to the target object. According to some embodiments, the interface may have an outer surface or a layer on the outer surface whose acoustic impedance is configured to approximate that of human skin. Such an outer surface may have contact portions that can be contacted by a user or a part of the user's body (e.g., fingers and wrist). In some examples, the optical waveguides may be embedded in one or more acoustic matching layers configured to direct light transmitted by the optical waveguides toward tissue very close to it. The outer surface and / or other portions of the interface may be flexible, bendable, flexible, or otherwise at least partially conformable to the shape and contour of a user's body part. In some embodiments, the interface may have a surface adjacent to the ultrasonic receiver system, or a layer on the surface adjacent to the ultrasonic receiver system, whose acoustic impedance is configured to approximate the acoustic impedance of the ultrasonic receiver system.

[0047] In some specific implementations of receiver system 202, including an ultrasonic receiver system, interface 201 may be configured to interact with a user's body part (such as...). Figure 1 The interface of the contact portion that the finger 115 (shown) contacts.

[0048] In some embodiments, the light source system 204 may include one or more light sources. In some embodiments, the light source system 204 may include one or more light-emitting diodes (LEDs). In some embodiments, the light source system 204 may include one or more laser diodes. According to some embodiments, the light source system 204 may include one or more vertical-cavity surface-emitting lasers (VCSELs). In some embodiments, the light source system 204 may include one or more edge-emitting lasers. In some embodiments, the light source system 204 may include one or more neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers.

[0049] Therefore, the light source system 204 may include, for example, an array of laser diodes, light-emitting diodes (LEDs), or either or both. The light source system 204 may be configured to generate and emit optical signals. In some examples, the light source system 204 may be configured to transmit light in one or more wavelength ranges. In some examples, the light source system 204 may be configured to transmit light in the 500 nanometer (nm) to 600 nanometer (nm) wavelength range. According to some examples, the light source system 204 may be configured to transmit light in the 800 nm to 950 nm wavelength range. According to some examples, the light source system 204 may be configured to transmit light in the infrared or near-infrared (NIR) region of the electromagnetic spectrum (approximately 700 nm to 2500 nm). One or both of these wavelength ranges are suitable for a variety of applications, taking into account factors such as skin reflectivity, flux, absorption coefficients of blood and various tissues, and skin safety limits. For example, wavelength ranges of 500 nm to 600 nm and 800 nm to 950 nm are suitable for obtaining photoacoustic responses from relatively small and shallow blood vessels, such as those found in a finger, with a diameter of approximately 0.5 mm and a depth in the range of 0.5 mm to 1.5 mm. For example, wavelength ranges of 800 nm to 950 nm, or approximately 700 nm to 900 nm, or approximately 600 nm to 1100 nm are suitable for obtaining photoacoustic responses from relatively large and deep blood vessels, such as those found in an adult wrist, with a diameter of approximately 2.0 mm and a depth in the range of 2 mm to 3 mm. In some specific implementations, the light source system 204 may be configured, for example, to switch wavelengths based on signals(s) from the control system 206 to capture acoustic information from different depths.

[0050] In some embodiments, the light source system 204 may be configured to emit light of various wavelengths, which may be selectable to trigger acoustic emission primarily from a specific type of substance. For example, because hemoglobin in blood absorbs near-infrared light very strongly, in some embodiments, the light source system 204 may be configured to emit light of one or more wavelengths in the near-infrared range to trigger acoustic emission from hemoglobin. However, in some examples, the control system 206 may control the wavelength(s) of light emitted by the light source system 204 to preferentially sense acoustic waves in blood vessels, other soft tissues, and / or bones. For example, an infrared (IR) light-emitting diode (LED) may be selected, and short pulses of IR light may be emitted to illuminate a portion of the target object and generate acoustic emission, which is then detected by the receiver system 202. In another example, IR LEDs and red LEDs or other colors, such as green, blue, white, or ultraviolet (UV), may be selected, and each light source sequentially emits short pulses of light, with an ultrasound image obtained after each light source emits light. In other embodiments, one or more light sources of different wavelengths may be illuminated sequentially or simultaneously to generate acoustic emission detectable by an ultrasound receiver. Image data from an ultrasound receiver can be combined to determine the location and type of material within a target object. This image data is obtained using light sources of different wavelengths at different depths within the target object (e.g., varying distance gating delay (RGD)). Image contrast is possible because substances within the body typically absorb light of different wavelengths to varying degrees. When substances absorb light of a specific wavelength, they may heat to varying degrees and emit acoustic waves under the influence of short light pulses of sufficient intensity. Depth contrast can be obtained using different wavelengths and / or different intensities of light at each selected wavelength. That is, continuous images can be obtained at a fixed RGD (which corresponds to a fixed depth within the target object) using varying light intensities and wavelengths to detect material and its location within the target object. For example, photoacoustic detection can be used to detect hemoglobin, blood glucose, or blood oxygen in blood vessels within a target object such as a finger.

[0051] According to some embodiments, the light source system 204 can be configured to emit light pulses with a pulse width of less than about 100 nanoseconds. In some embodiments, the pulse width of the light pulses may be between about 10 nanoseconds and about 500 nanoseconds or longer. According to some examples, the light source system 204 can be configured to emit multiple light pulses at a pulse repetition frequency between 10 Hz and 100 kHz. Alternatively or additionally, in some embodiments, the light source system 204 can be configured to emit multiple light pulses at a pulse repetition frequency between about 1 MHz and about 100 MHz. Alternatively or additionally, in some embodiments, the light source system 204 can be configured to emit multiple light pulses at a pulse repetition frequency between about 10 Hz and about 1 MHz. In some examples, the pulse repetition frequency of the light pulses may correspond to the acoustic resonant frequency of the ultrasonic receiver and the substrate. For example, a set of four or more light pulses can be emitted from the light source system 204 at a frequency corresponding to the resonant frequency of the acoustic resonant cavity in the sensor stack, thereby enabling the accumulation of received ultrasonic waves and obtaining a higher resulting signal strength. In some embodiments, filtered light or a light source with a specific wavelength for detecting the selected substance may be included in the light source system 204. In some embodiments, the light source system 204 may contain a light source such as red, green, and blue LEDs for a display, which may be enhanced by light sources of other wavelengths (such as IR and / or UV) and light sources with higher optical power. For example, high-power laser diodes or electronic flash units (e.g., LED or xenon flash units) with or without filters may be used for short-term irradiation of the target object.

[0052] According to some examples, the light source system 204 may also include one or more light guiding elements configured to guide light from the light source system 204 to a target object along a first axis. In some examples, the one or more light guiding elements may include at least one diffraction grating. Alternatively or additionally, the one or more light guiding elements may include at least one lens.

[0053] In various configurations, the light source system 204 may include an anti-reflective (AR) coating, a mirror, a light-blocking layer, and shielding to minimize crosstalk.

[0054] Depending on the specific implementation, the light source system 204 may include various types of driving circuitry. In some disclosed embodiments, the light source system 204 may include at least one multi-junction laser diode, which may generate less noise than a single-junction laser diode. In some examples, the light source system 204 may include driving circuitry (also referred to herein as a driving circuitry system) configured to cause the light source system 204 to emit light pulses with pulse widths ranging from 3 nanoseconds to 1000 nanoseconds. According to some examples, the light source system 204 may include driving circuitry configured to cause the light source system 204 to emit light pulses at pulse repetition frequencies ranging from 1 kHz to 100 kHz.

[0055] In some example implementations, some or all of the light sources of the light source system 204 may be arranged on or along an axis parallel to or at an angle relative to a central axis associated with the pressure plate or interface 201. Optical signals may be emitted toward a target object (e.g., a blood vessel), which may cause the target object to generate ultrasound. One or more receiver elements of the receiver system 202 may detect such ultrasound.

[0056] Various examples of receiver system 202 disclosed herein may include, among them, an ultrasonic receiver system, an optical receiver system, or a combination thereof. In some embodiments, receiver system 202 includes an ultrasonic receiver system having one or more receiver elements. In embodiments including an ultrasonic receiver system, an ultrasonic receiver and an ultrasonic transmitter may be combined in an ultrasonic transceiver. In some embodiments, receiver system 202 may include a piezoelectric receiver layer, such as a PVDF polymer layer or a PVDF-TrFE copolymer layer. In some embodiments, a single piezoelectric layer may be used as an ultrasonic receiver. In some implementations, other piezoelectric materials, such as aluminum nitride (AlN) or lead zirconate titanate (PZT), may be used in the piezoelectric layer. In some examples, receiver system 202 may include an array of ultrasonic transducer elements, such as an array of piezoelectric micromechanical ultrasonic transducers (PMUTs), an array of capacitive micromechanical ultrasonic transducers (CMUTs), etc. In some such examples, a piezoelectric receiver layer, PMUT elements in a single-layer array of PMUTs, or CMUT elements in a single-layer array of CMUTs may be used as both an ultrasonic transmitter and an ultrasonic receiver. According to some examples, receiver system 202 may be or may include an array of ultrasonic receivers. In some examples, sensor device 200 may include one or more individual ultrasonic transmitter elements or an array of one or more individual ultrasonic transmitter elements. In some examples, the ultrasonic transmitter(s) may include an ultrasonic plane wave generator.

[0057] In some embodiments, at least a portion of the sensor device 200 (e.g., receiver system 202, light source system 204, or both) may include one or more sound-absorbing layers, sound-insulating materials, light-absorbing materials, light-reflecting materials, or combinations thereof. In some examples, sound-insulating material may be disposed between at least a portion of the light source system 204 and the receiver system 202. In some examples, at least a portion of the sensor device 200 (e.g., receiver system 202, light source system 204, or both) may include one or more electromagnetically shielded transmitting lines. In some such examples, the one or more electromagnetically shielded transmitting lines may be configured to reduce electromagnetic interference received by the receiver system 202 from the light source system 204.

[0058] In some embodiments, sensor device 200 may include loop system 205. In some specific embodiments, loop system 205 may include a pump, airbag, and / or pressure sensor. Further components of loop system 205 may include vents, pump drivers, controllers, printed circuit boards, temperature sensors, memory, processors, valves, nozzles, tubing, power sources or batteries, physical structures (e.g., wearable structures, housings, and loops), or combinations thereof.

[0059] A pump can be configured to draw air into an airbag to create positive pressure within the airbag. The airbag can be a bag constructed to be pressurized by the air contained therein. In some configurations, a pump driver (including, for example, circuitry, logic, or a processor) controls the pump and draws air into the airbag. Voltage can be applied to the pump by the pump driver or a controller to control the airflow. In some implementations, the pressure caused by the air can be kept constant over a period of time. This pressure can be gradually changed by adjusting the voltage level. Therefore, an external pressure can be applied and maintained at discrete pressure levels. A vent can also be controlled by a controller to allow air to escape from the airbag, thereby reducing the pressure. A pressure sensor can be used to detect the pressure within the airbag, thereby generating pressure data for the operation described herein. The pressure can be adjusted to a specified level based on the detected pressure.

[0060] Control system 206 may include one or more general-purpose single-chip or multi-chip processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or combinations thereof. Control system 206 may also include one or more memory devices (and / or be configured to communicate with them), such as one or more random access memory (RAM) devices, read-only memory (ROM) devices, etc. Therefore, sensor device 200 may have a memory system including one or more memory devices, although... Figure 2The memory system is not shown. Control system 206 can be configured to receive and process data from receiver system 202, for example, as described below. If sensor device 200 includes an ultrasonic transmitter, control system 206 can be configured to control the ultrasonic transmitter. In some implementations, the functionality of control system 206 can be divided among one or more controllers or processors, such as between a dedicated sensor controller and an application processor in a mobile device.

[0061] In some examples, control system 206 may be communicatively coupled to light source system 204 and configured to control the light source system to emit light toward a target object on the outer surface of interface 201. In some such examples, control system 206 may be configured to receive signals from an ultrasound receiver system (including one or more receiver elements) corresponding to ultrasound waves generated by the target object in response to light from the light source system. In some examples, control system 206 may be configured to identify one or more vascular signals, such as arterial or venous signals, from the ultrasound receiver system. In some such examples, the one or more arterial or venous signals may be or may include one or more vessel wall signals corresponding to ultrasound waves generated by one or more arterial or venous walls of the target object. In some such examples, the one or more arterial or venous signals may be or may include one or more arterial blood signals or one or more venous blood signals, corresponding respectively to ultrasound waves generated by blood within an artery or blood within a vein of the target object. In some examples, control system 206 may be configured to determine or estimate one or more physiological parameters or cardiac characteristics based at least in part on one or more arterial signals, one or more venous signals, or combinations thereof. According to some examples, physiological parameters may be or may include blood pressure. In some methods, blood pressure can be estimated at least in part based on PWV, as will be discussed below.

[0062] In some examples, control system 206 may be communicatively coupled to receiver system 202. Receiver system 202 may be configured to detect acoustic signals from a target object. Control system 206 may be configured to select at least one of a plurality of receiver elements of receiver system 202. Such selected receiver element(s) may correspond to the optimal signal from the plurality of receiver elements. In some embodiments, the selection of at least one receiver element may be based on information about detected acoustic signals (e.g., arterial or venous signals) from the plurality of receivers. For example, the signal quality or signal strength of some signals (based on, for example, signal-to-noise ratio (SNR)) may be relatively higher than that of others or above a predetermined threshold or percentile, which may indicate the optimal signal. In some specific embodiments, control system 206 may also be configured to determine or estimate at least one characteristic of a blood vessel, such as PWV (indicating arterial stiffness), arterial size, or both, based on information about the detected acoustic signals.

[0063] Some specific implementations of sensor device 200 may include interface system 208. In some examples, interface system 208 may include a wireless interface system. In some specific implementations, interface system 208 may include a user interface system, one or more network interfaces, one or more interfaces between control system 206 and memory system, and / or one or more interfaces between control system 206 and one or more external device interfaces (e.g., ports or application processors), or combinations thereof. According to some examples where interface system 208 is present and includes a user interface system, the user interface system may include a microphone system, a speaker system, a haptic feedback system, a voice command system, one or more displays, or combinations thereof. According to some examples, interface system 208 may include a touch sensor system, a gesture sensor system, or combinations thereof. The touch sensor system (if present) may be or may include a resistive touch sensor system, a surface capacitive touch sensor system, a projected capacitive touch sensor system, a surface acoustic wave touch sensor system, an infrared touch sensor system, any other suitable type of touch sensor system, or combinations thereof.

[0064] In some examples, interface system 208 may include a force sensor system. The force sensor system, if present, may be or may include a piezoresistive sensor, a capacitive sensor, a thin-film sensor (e.g., a polymer-based thin-film sensor), other suitable types of force sensors, or combinations thereof. If the force sensor system includes a piezoresistive sensor, the piezoresistive sensor may include silicon, metal, polycrystalline silicon, glass, or combinations thereof. In some embodiments, the ultrasonic fingerprint sensor and the force sensor system may be mechanically coupled. In some embodiments, the force sensor system may be mechanically coupled to a pressure plate. In some such examples, the force sensor system may be integrated into the circuitry of the ultrasonic fingerprint sensor. In some examples, interface system 208 may include an optical sensor system, one or more cameras, or combinations thereof.

[0065] According to some examples, sensor device 200 may include a noise reduction system 210. For example, noise reduction system 210 may include one or more mirrors configured to reflect light from light source system 204 away from receiver system 202. In some embodiments, noise reduction system 210 may include one or more sound-absorbing layers, sound-insulating materials, light-absorbing materials, light-reflecting materials, or combinations thereof. In some examples, noise reduction system 210 may include sound-insulating materials disposed between, on, or in combination with at least a portion of light source system 204 and receiver system 202. In some examples, noise reduction system 210 may include one or more electromagnetically shielded transmission lines. In some such examples, the one or more electromagnetically shielded transmission lines may be configured to reduce electromagnetic interference received by the receiver system from circuitry of the light source system, receiver system circuitry, or combinations thereof.

[0066] In some embodiments, sensor device 200 may be a wearable device configured to be worn by a user around, for example, the wrist, fingers, arm, leg, ankle, or another limb, or another part of the body. In an example embodiment, sensor device 200 may be in the form of a watch and wearable around the wrist. The loop system 205 may apply pressure around the wrist while the skin at the wrist contacts through interface 201, and photoacoustic measurements can be performed by manipulating the properties of receiver system 202 and light source system 204. However, the embodiments described herein are not limited to this. In some cases, not all components of sensor device 200 may be worn. For example, loop system 205 may be wearable around a limb (similar to a blood pressure monitor), but other components (such as receiver system 202 and light source system 204) may be in a separate PAPG sensor assembly and / or not in the wearable housing to collect photoacoustic measurements.

[0067] Figure 3This shows an example of heart rate waveform (HRW) features that can be extracted based on some specific implementations. Figure 3 The horizontal axis represents time, and the vertical axis represents signal amplitude. The cardiac cycle is indicated by the time between adjacent peaks of the HRW (Heart Rate Wave). The systolic and diastolic time intervals are indicated below the horizontal axis. During the systolic phase of the cardiac cycle, as the pulse travels along the artery through a specific location, the arterial wall expands according to the pulse waveform and the elastic properties of the arterial wall. Accompanying this expansion is a corresponding increase in blood volume at the specific location or region, and with the increase in blood volume, one or more properties in that region change accordingly. Conversely, during the diastolic phase of the cardiac cycle, blood pressure in the artery decreases and the arterial wall constricts. Accompanying this constriction is a corresponding decrease in blood volume at the specific location, and with the decrease in blood volume, one or more properties in that region change accordingly.

[0068] Figure 3 The illustrated HRW features relate to the width of the systolic and / or diastolic portions of the HRW curve at different “heights,” expressed as a percentage of the maximum amplitude. For example, the SW50 feature is the width of the systolic portion of the HRW curve at a “height” that is 50% of the maximum amplitude. In some embodiments, HRW features used for blood pressure estimation may include some or all of the SW10, SW25, SW33, SW50, SW66, SW75, DW10, DW25, DW33, DW50, DW66, and DW75 HRW features. In other embodiments, additional HRW features may be used for blood pressure estimation. In some examples, such additional HRW features may include the sum and ratio of SW and DW at one or more “heights,” such as (DW75 + SW75), DW75 / SW75, (DW66 + SW66), DW66 / SW66, (DW50 + SW50), DW50 / SW50, (DW33 + SW33), DW33 / SW33, (DW25 + SW25), DW25 / SW25, (DW10 + SW10), and / or DW10 / SW10. Other implementations may use yet another number of HRW features for blood pressure estimation. In some examples, such additional HRW features may include sums, differences, ratios, and / or other calculations based on more than one “height,” such as (DW75 + SW75) / (DW50 + SW50) and (DW50 + SW50 / (DW10 + SW10), etc.

[0069] In some implementations, the monitoring device can be positioned around the user's wrist as a strip or band, similar to a watch or fitness / activity tracker. Figure 4AThis illustrates an example device 400 designed to be worn around the wrist according to some specific embodiments. In some embodiments, the example device 400 may include a sensor device 200 such that components of the sensor device 200 interact with the user, for example, through the user's skin. In the illustrated example, the monitoring device 400 includes a housing 402 integrally formed, coupled, or otherwise integrated with a wristband 404. In some examples, each of the first artery sensor 406 and the second artery sensor 408 may include an example of the ultrasound receiver system described above and a portion of a light source system. In this example, the example device 400 is coupled around the wrist such that the first artery sensor 406 and the second artery sensor 408 within the housing 402 are each positioned along a segment of the radial artery 410 (it should be noted that when the monitoring device is coupled to a subject, the sensors are typically concealed from the exterior or outer surface of the housing facing the subject, but exposed on the inner surface of the housing, allowing the sensors to obtain measurements from the underlying artery through the subject's skin). Also as shown, a fixed distance is maintained between the first artery sensor 406 and the second artery sensor 408. In some other specific implementations, example device 400 may be similarly designed or adapted to use strips or bands around the forearm, upper arm, ankle, lower leg, thigh, or fingers (all of which are referred to below as "limbs") for positioning.

[0070] Figure 4B The illustration shows an example device 400 designed to be worn on a finger according to some specific embodiments. In some examples, each of the first artery sensor 406 and the second artery sensor 408 may include the aforementioned example of an ultrasound receiver and a portion of a light source system.

[0071] In some other embodiments, the devices disclosed herein can be positioned on a user’s area of ​​concern without the use of strips or bands. For example, the first arterial sensor 406 and the second arterial sensor 408, along with other components of the monitoring device, can be enclosed in a housing that is secured to the user’s skin in the area of ​​concern using an adhesive or other suitable connection mechanism (an example of a “patch” monitoring device).

[0072] Figure 4C This illustrates an example device 400 designed to be mounted on an earbud according to some specific implementation. According to this example, the monitoring device 400 is coupled to the housing of the earbud 420. In some examples, each of the first arterial sensor 406 and the second arterial sensor 408 may include the aforementioned example of an ultrasound receiver and a portion of a light source system.

[0073] Example signal acquisition and analysis

[0074] As noted elsewhere, the sensor device (e.g., sensor device 200) may be worn at least partially by the user to apply pressure at different discrete pressure levels and acquire photoacoustic signals and measurements. This pressure applied by the sensor device may be referred to herein as external pressure or externally applied pressure. In some specific implementations, data segments may be collected, for example, under multiple external pressures applied by an annular system. For example, photoacoustic signals may be acquired by the sensor device (e.g., using receiver system 202 and light source system 204) within time periods corresponding to external pressures. That is, photoacoustic measurements acquired for each pressure level are used to obtain information about the target object (e.g., blood vessels). Figures 5A to 5D This will be explained and discussed now.

[0075] Figure 5A This is a graph 500 showing an example of how externally applied pressure (e.g., using a ring system) varies over time according to some specific implementation. In this example, three discrete pressure levels are shown: a first pressure level 502a, a second pressure level 502b, and a third pressure level 502n. The ring system can apply such pressure at a constant level over a set time period. In a non-limiting example, the first pressure level 502a could be 30 mmHg or approximately 30 mmHg applied during a first time period, the second pressure level 502b could be 40 mmHg or approximately 40 mmHg applied during a second time period, and the third pressure level 502n could be 50 mmHg or approximately 50 mmHg applied during a third time period. The pressure levels can be preset or selected based on the user's blood pressure status (e.g., hypotension, hypertension, or normal blood pressure). That is, the target ring inflation pressure or range may differ for users with different blood pressures. An approximate pressure level can refer to a pressure level with an associated range or error, such as ±1 mmHg, ±2 mmHg, ±3 mmHg, or ±0.1%, ±0.2%, ±0.5%, ±1%, etc., and each time period can last for a few seconds or longer (e.g., 3 seconds, 10 seconds, 60 seconds or longer). The pressure can be low enough (e.g., 100 mmHg or lower, 90 mmHg or lower, or other low pressures) that the user will not feel discomfort, but high enough to exert sufficient pressure on the target object (e.g., blood vessels).

[0076] Within each of these time periods, photoacoustic signals can be acquired and stored. Comprehensive analysis of photoacoustic signals from multiple pressure levels allows for the acquisition of highly correlated features and the extraction of significant information, such as other compliance information. Other types of information (e.g., artery size, spatial parameters such as area or volume, dilatancy / PWV, etc.) can also be determined from the correlated features.

[0077] In some cases, there may be a transition period between each pressure level; for simplicity, this transition period is not shown. During the transition period, the pressure level may, for example, change from 30 mmHg to 40 mmHg or from 40 mmHg to 50 mmHg (or decrease from 50 mmHg to 40 mmHg or 30 mmHg), each of which may take a few seconds or longer. A longer transition period makes the change in applied pressure less noticeable to the user, thus improving the comfort of the wearable device.

[0078] Figure 5B This is a graph 510 showing another example of how externally applied pressure changes over time according to some specific implementation. In this example, the pressure level may begin at a first pressure level 502 and increase over time (similar to how this increase is performed in graph 500). The pressure level may reach a maximum pressure level 504 and decrease over time. Each incremental increase or decrease may be associated with a transition period for airbag inflation or deflation, respectively. In a non-limiting example, the pressure may begin at an initial first pressure level 502 of 30 mmHg or approximately 30 mmHg during a first time period, increase to a maximum pressure level 504 of 100 mmHg or approximately 100 mmHg during a subsequent time period, and return to the first pressure level 502 of 30 mmHg or approximately 30 mmHg during yet another subsequent time period. However, pressure levels may be applied in any order. In one of several methods, the maximum pressure level 504 may be 90 mmHg (or less); the range of applied pressure may be from 30 mmHg to 90 mmHg (or approximately so). In another approach, the first pressure level 502 can be 40 mmHg (or greater). During each of these time periods, a photoacoustic signal can be acquired and stored.

[0079] The sequence shown in Figure 510 may be useful for individual users' calibration. More specifically, this can be achieved by proceeding from a wider range of pressure levels (in this case, 30 mmHg to 100 mmHg), as opposed to those discussed below. Figure 5C A larger set of photoacoustic measurements can be obtained from a smaller range or constant pressure level.

[0080] Figure 5C and Figure 5DGraphs 520 and 530 illustrate examples of an externally applied pressure that is substantially constant over time (e.g., using a ring belt system) according to some specific implementations. Graph 520 shows a lower constant pressure (e.g., about 40 mmHg or less), while graph 530 shows a higher constant pressure (e.g., about 90 mmHg). In some contexts, substantially constant can refer to, for example, ±1 mmHg, ±2 mmHg, ±3 mmHg, etc., or an associated range or error of ±0.1%, ±0.2%, ±0.5%, ±1%, etc. A substantially constant pressure can be applied for a period of time, such as 3 seconds, 5 seconds, 10 seconds, 30 seconds, 60 seconds, or longer. Once the so-called compliance curve is determined (e.g., possibly by using...), Figure 5B As shown in Figure 510 (pressure level calibration), applying constant pressure can determine a user's physiological parameters, such as blood pressure.

[0081] Depending on the pressure applied to the blood vessel, its properties may change. Characteristics of the blood vessel may include, for example, arterial compliance, dilation, stiffness, size (e.g., diameter), and pulse wave velocity (PWV). For example, these characteristics may change because pressure causes the blood vessel to flatten more during at least a portion of the pulse. As a result, the blood vessel may have an elliptical or nearly elliptical shape, with both a long axis and a short axis.

[0082] Figure 6 Ultrasound images of blood vessel 602 at different pressure levels illustrate the elliptical shape and size based on externally applied pressure. As can be seen, blood vessel 602 is essentially circular. In some cases, blood vessel 602 may still exhibit elliptical characteristics, where the diameter across one axis (major axis 606) is slightly longer than the diameter across the other axis (minor axis 604). Pressure levels increasing from level 1 to level 8 (above 0 mmHg) are shown. For example, pressure level 1 may correspond to 20 mmHg. When a larger level of external pressure is applied, the difference between the diameter across the minor axis 604 and the diameter across the major axis 606 becomes larger. That is, blood vessel 602 appears flatter at larger external pressure levels, and blood vessel 602 becomes more elliptical. Therefore, Figure 6 The size of blood vessel 602 changes with external pressure.

[0083] Figure 7The dimensions and spatial measurements of blood vessel 602 under constant external pressure vary over time. The applied pressure level corresponds to the pressure magnitude that causes blood vessel 602 to form a distinct elliptical shape (e.g., 60 mmHg). Over time, blood vessel 602 may still expand due to the force of blood pulsation as it flows through the user's cardiovascular system. The minor axis length 712 may change over time along with the major axis length 714. The difference between the normalized minor axis length 722 and the normalized major axis length 724 shows that the expansion of blood vessel 602 along the minor axis is more pronounced than along the major axis. Therefore, the cross-sectional area 716 of blood vessel 602 may change at corresponding times (e.g., during a pulse).

[0084] Photoacoustic sensing can be used to capture at least some of the aforementioned characteristics of blood vessels, wherein photoacoustic signals can be acquired and stored by a sensor device (e.g., using receiver system 202 and light source system 204). Examples of characteristics that can be derived from photoacoustic sensing include artery size and dilation. Other characteristics and parameters (e.g., compliance and PWV) can be derived from photoacoustic measurements.

[0085] In some methods, a "beamforming" image can be generated from a photoacoustic signal. Multiple channels or sources of photoacoustic data can be used to generate such an image. In this document, a beamforming image can refer to an image generated as a result of a "delay and summation" process using multiple receiver elements of a receiver system. More specifically, a delay can be applied to the ultrasonic receiver signal by performing a correlation operation on the input ultrasonic receiver signal. For example, a control system can perform a correlation operation on different first and second ultrasonic receiver signals and determine that by applying a first time shift to the first ultrasonic receiver signal, the first ultrasonic receiver signal will be strongly correlated with a third ultrasonic receiver signal. Similarly, a control system can perform a correlation operation on the second and third ultrasonic receiver signals and determine that by applying a second time shift to the second ultrasonic receiver signal, the second ultrasonic receiver signal will be strongly correlated with the third ultrasonic receiver signal.

[0086] Figure 8 An example of an apparatus configured to perform a receiver-side beamforming process is shown. In this example, the receiver-side beamforming process is a delay-plus-summation beamforming process. As for other disclosed examples, Figure 8 The types, quantities, sizes, and arrangements of the components shown, as well as the associated methods, are merely examples.

[0087] In this example, a source emitting ultrasonic waves 102 is shown, which are detected by active ultrasonic receiver elements 202a, 202b, and 202c of an ultrasonic receiver element array. The ultrasonic receiver element array is part of the ultrasonic receiver system 202. In some examples, ultrasonic waves 102 may correspond to the photoacoustic response of a target object to light emitted by the light source system 204 of the sensor device 200. In this example, active ultrasonic receiver elements 202a, 202b, and 202c provide ultrasonic receiver signals 815a, 815b, and 815c to the control system 206, respectively.

[0088] According to this example, the control system 206 includes a delay module 805 and a summing module 810. In this example, the delay module 805 is configured to determine whether a delay should be applied to each of the ultrasonic receiver signals 815a, 815b, and 815c, and if it is determined that a delay should be applied, to determine how much delay should be applied. According to this example, the delay module 805 determines that a delay d0 of t2 should be applied to ultrasonic receiver signal 815a, a delay d1 of t1 should be applied to ultrasonic receiver signal 815b, and a delay should not be applied to ultrasonic receiver signal 815c. Therefore, the delay module 805 applies the delay of t2 to ultrasonic receiver signal 815a, generating ultrasonic receiver signal 815a', and applies the delay of t1 to ultrasonic receiver signal 815b, generating ultrasonic receiver signal 815b'.

[0089] In some examples, delay module 805 can determine how much delay (if any) to apply to the ultrasonic receiver signal by performing correlation operations on the input ultrasonic receiver signal. For example, delay module 805 can perform correlation operations on ultrasonic receiver signals 815a and 815c, and can determine that by applying a time shift of t2 to ultrasonic receiver signal 815a, ultrasonic receiver signal 815a will be strongly correlated with ultrasonic receiver signal 815c. Similarly, delay module 805 can perform correlation operations on ultrasonic receiver signals 815b and 815c, and can determine that by applying a time shift of t1 to ultrasonic receiver signal 815b, ultrasonic receiver signal 815b will be strongly correlated with ultrasonic receiver signal 815c.

[0090] According to this example, the summation module 810 is configured to sum the ultrasonic receiver signals 815a', 815b', and 815c, producing a summed signal 820. It can be observed that the amplitude of the summed signal 820 is greater than the amplitude of any one of the ultrasonic receiver signals 815a, 815b, or 815c. In some cases, the signal-to-noise ratio (SNR) of the summed signal 820 may be greater than the SNR of any one of the ultrasonic receiver signals 815a, 815b, or 815c.

[0091] In other words, according to this example, the control system can be configured to sum the first time-shifted ultrasonic receiver signal, the second time-shifted ultrasonic receiver signal, and the third ultrasonic receiver signal to produce a summed signal. The amplitude of the summed signal may be greater than the amplitude of any one of the first, second, or third ultrasonic receiver signals. The signal-to-noise ratio (SNR) of the summed signal may be greater than the SNR of any one of the first, second, or third ultrasonic receiver signals. Therefore, a cleaner, stronger, and less noisy signal can be obtained by using multiple receiver elements and performing time shifts on some of the ultrasonic signals.

[0092] Figure 9A A beamformed photoacoustic image 906 is depicted based on an ultrasound image 904 of blood vessels 602, 902 according to some specific implementation. The ultrasound image 904 can depict an image at any low contact pressure. From the ultrasound image 904 to the photoacoustic image 906, the axial depth (how deep into the tissue) and lateral distance (how wide) of the blood vessel 902 can be determined, as shown by the dashed lines, by correlating the edge portion of the blood vessel 602 in the ultrasound image 904 with the posterior and anterior walls of the blood vessel 902 shown in the beamformed photoacoustic image 906.

[0093] Figure 9B A beamformed photoacoustic image 906 is depicted in more detail. The anterior and posterior walls of the vessel 902 can be detected in the beamformed photoacoustic image 906 based on signal intensity. In some specific implementations, an elliptical or circular boundary 908 can be fitted onto the beamformed photoacoustic image 906, and the major axis 910a and minor axis 910b can be determined. Half of the major axis 910a is called the semi-major axis, and half of the minor axis 910b is called the semi-minor axis, collectively referred to as the semi-axis. In some example methods, image processing, algorithmic processing, or machine learning and training can be used to determine the boundaries of the vessel 902, from which the major and minor axes can be estimated using axial depth and lateral distance. The major and minor axes of the vessel 902 are dimensions that can be used to determine the cross-sectional area and / or volume of the vessel 902, the significance of which will become apparent in the discussion below.

[0094] Now for reference Figure 10This diagram displays a graph of example curves 1000 showing the variation of arterial space measurements under applied external pressure according to some specific implementation. This curve may be referred to herein as a compliance curve. In some methods, the dimensions of a target object, such as its diameter (e.g., major and / or minor axes), can be obtained by inflating a band of a sensor device (such as sensor device 200 embodied in a wearable device) and performing photoacoustic measurements from the target object (e.g., a blood vessel) at different discrete pressure levels. In some examples, photoacoustic measurements of blood vessels can be used to obtain the arterial diameter at the corresponding pressure level.

[0095] In some specific implementations, spatial measurements of the blood vessel, such as area (cross-sectional area) or volume, can be calculated or inferred from the artery diameter. More specifically, for round or nearly round blood vessels, the well-known formula A can be used. circle = π r 2 To estimate the cross-sectional area, and V can be used. circle = π r 2 l To estimate the volume, where r It is the radius (half the diameter of the obtained artery), and l It refers to the length of the blood vessel segment in question. l The value of can be any constant, within a range of minimum and / or maximum lengths chosen for accurate estimation of vascular hydrodynamics. This range is determined based on the size of the wearable device and / or the actual photoacoustic response of the segment of interest. In some methods, length is not considered because it is constant, for example, where the parameter of interest is based on area change or the ratio of initial volume to final volume.

[0096] For elliptical blood vessels, when the applied external pressure exceeds a threshold (e.g., 20 mmHg or higher), the single diameter is considered inaccurate, and the elliptical area and volume of the cross-section can be derived as follows: A ellipse = π a b ,in a It is the radius of the major axis (half the obtained artery diameter), and b It is the radius of the minor axis. In other words, a It is the length of the semi-minor axis, and b It is the length of the semi-minor axis. In some methods, V ellipse = π a b l ,inl This refers to the length of the vessel segment in question. In alternative methods, V... ellipsoid = (4 / 3) π a b c ,in c It is the length of the third half-axis along the segment of blood vessel of interest. c or l The value can be any constant, within the minimum and / or maximum length range chosen for an accurate estimate of the hydrodynamics of the blood vessel, the range being determined based on the size of the wearable device and / or the actual length of the segment of interest.

[0097] Since the area and volume of a circular or elliptical blood vessel are related by a constant, either of the derived spatial measurements (e.g., area or volume) can be used to derive curve 1000 and obtain a similar curve profile. Arterial spatial measurement can broadly refer to the cross-sectional area or volume associated with a blood vessel in this paper. In some methods, curve 1000 can be fitted to data points representing the derived spatial measurements corresponding to the applied external pressure. Curves (or lines) such as exponential curves, polynomial curves (quadratic, cubic, quartic, etc.), logarithmic curves, etc., can be determined. Normalized curves (ranging from 0 to 1 on either or both axes) can also be derived. In some methods, a trained machine learning model can be used to generate curve 1000. For example, a dataset of the applied external pressure and arterial dimensions (e.g., diameter, semi-axis) and / or arterial spatial measurements (e.g., cross-sectional area, volume) can be input into a machine learning model trained on a "benchmark ground truth," which can then generate curve 1000 based on the input.

[0098] As can be seen from curve 1000, the greater the applied pressure, the flatter the blood vessel, and the smaller its area or volume. Therefore, the compliance curve shows a decreasing trend with increasing external pressure. The relationship between arterial volume or area and applied pressure can be determined at each measured pressure level on curve 1000. The corresponding spatial measurement 1002 can be identified at a given applied external pressure level 1004. An advantage of applying external pressure is, for example, improved signal quality from applying a substantially constant pressure via a ring.

[0099] Furthermore, the slope 1006 at the point on curve 1000 corresponding to a given applied external pressure level 1004 can be identified. Slope 1006 provides information about the user's compliance. Compliance (C) can also be expressed as C = dV / dP or C = dA / dP, where P is the applied external pressure. Compliance information is based on the elastic properties of blood vessels and is a determinant of pulse pressure wave velocity. Individual compliance may vary based on physiology, activity, chronic diseases, etc., and can change with individual states. For example, a user may be relaxed, agitated, post-exercise, or asleep, all of which can affect blood flow, heart rate, blood pressure, etc. These user states correspond to different arterial compliance values. Therefore, compliance information obtained individually for each user at different pressure levels can provide a larger dataset, a wider measurement range, and richer features.

[0100] Intermittent recalibration of the compliance curve and / or sensor device may also be performed to account for changes in the user's physiology or the placement of the sensor device, thus adapting to changes in vascular position. Recalibration can also correct for any offsets in the sensor system or encirclement system. Depending on the method, recalibration can be performed at various time intervals. In some examples, recalibration may be performed every two to three months, monthly, weekly, daily (e.g., immediately before or during sleep to minimize disruption to the user's waking activities), or manually. The choice of recalibration frequency requires consideration of numerous variables.

[0101] In some variations, more than one compliance curve may be determined, for example, for the systolic and diastolic diameters measured separately for systole and diastole. Systolic blood pressure is the highest blood pressure during ventricular contraction (systole), and diastolic blood pressure is the lowest blood pressure recorded before the next systole (diastole). During phases of the heart rhythm where blood pressure is relatively low (such as in diastole), the blood vessels may be relatively smaller due to reduced pressure within the vessels. On the other hand, during periods of elevated blood pressure (such as in systole), the blood vessels may be larger because of the greater pressure within them.

[0102] Figure 10A Examples of curves 1010, which correspond to the external pressure applied during diastole, are shown according to some specific implementations. Figure 10B An example is illustrated by curve 1020, corresponding to an arterial spatial measurement of the applied external pressure during systole, relative to curve 1000, according to some specific implementation. The profile of each of curves 1010 and 1020 is similar to that of curve 1000; from curves 1010 and 1020, they may represent mean pressure or have wider error bars associated with the spatial measurement. These multiple compliance curves provide context for estimation to extract additional compliance information.

[0103] However, additional information is needed to determine PWV and blood pressure.

[0104] Figure 11 This is a graph of a set of example data points showing the variation of arterial size under applied external pressure according to some specific implementation. As previously mentioned, the size (e.g., the diameter of a target object, such as a blood vessel) can be measured, for example, by photoacoustic signals collected under different external pressures. Each hollow circle represents the associated arterial size 1102, for example, by a band worn by a user (e.g., the band system 205 of sensor device 200). However, arterial size is difficult to obtain under zero applied pressure because contact with the skin is required to obtain the photoacoustic signal used to determine the arterial size. Any air gap will cause inaccurate photoacoustic measurements.

[0105] Therefore, in some specific implementations, photoacoustic measurements under several external pressures and the corresponding dimensional measurements can be used to extrapolate arterial dimensions at zero pressure. In some methods, curve 1110 can be fitted to arterial dimension measurement 1102, such as exponential curves, polynomial curves (quadratic, cubic, quartic, etc.), logarithmic curves, etc. In some methods, line 1112 can be fitted to arterial dimension measurement 1102. The zero-pressure arterial dimension 1104 can be determined based on extrapolation.

[0106] In some implementations, machine learning models can be used to determine arterial size at zero pressure. These models are trained to output arterial size based on multiple discrete pressures and / or corresponding multiple arterial sizes as inputs.

[0107] This artery size (e.g., zero-pressure artery diameter) can serve as the basis for zero-pressure space measurements (such as zero-pressure cross-sectional area (or volume)). This zero-pressure space measurement can provide additional information for estimating blood pressure, as described below.

[0108] In some implementations, the shape of the heart rate waveform (HRW) at different external pressure levels can also provide useful information or context. Because the shape of the HRW changes with different applied external pressures, HRW characteristics corresponding to high, low, or no applied external pressure can aid in blood pressure estimation. For example, evaluating the obtained HRW characteristics and comparing them with corresponding known arterial sizes or known HRW characteristics at applied pressures can verify whether the arterial size is as expected (or not). If it is as expected and verified, the arterial size and compliance curve can be used for blood pressure estimation. If not, recalibration (or resizing) or a new measurement can be performed.

[0109] Finally, compliance information and zero-pressure arterial size can be used to determine vascular properties (e.g., pressure wv) and thus blood pressure. The following version of the Bramwell-Hill equation (Equation 1) provides the relationship between arterial dilatation, pressure changes, and pressure wv: (Equation 1) Modifying equation 1, we get: (Equation 2) Assuming that PWV remains relatively constant over a cardiac cycle, integrating equation 2 yields the following equation 3: (Equation 3) P(t) can be further defined as follows, where P i (t) is the blood pressure to be determined, and P e (t) is the known applied external pressure: (Equation 4) In the equations provided in this paper, A is the average cross-sectional area under a given external pressure, which can be obtained using the photoacoustic measurements described above. dP / dA (or dP / dV) is the reciprocal of compliance. (See above regarding...) Figure 10 As described, compliance curves can be used to obtain dP / dA (or dP / dV), such as by identifying the slope (dA / dP) of curve 1000 under a given external pressure. ρ This refers to blood density, and it can be assumed that each user's blood density is a constant value (although blood density may vary slightly from person to person and is not universally fixed). In some cases, components such as oscillators used for measuring fluid density can be used to measure and determine this. ρ This allows users to make more personalized settings.

[0110] Therefore, compliance information can be used to estimate PWV and blood pressure. The above method can be used for continuous blood pressure monitoring, where photoacoustic measurements of size and other characteristics (e.g., dilation, compliance) can be used to estimate blood pressure.

[0111] In some methods (e.g., in the absence of a compliance profile), biometric sensors (e.g., photoacoustic sensors, acoustic sensors) are used to detect external pressure P. e PWV is measured under (t), and similarly, the cross-sectional area A(t) can be measured. A0 is P e (0) and P i The unknown cross-sectional area of ​​(0), where P i (0) is the unknown reference blood pressure, and P e (0) is the known reference external pressure.

[0112] P0 is P i (0) and P e Reference pressure for the difference between (0): (Equation 5) In summary, blood pressure P can be determined by applying different external pressures at different times. i (t) and the applied external pressure P e (t). Combining equations 3–5, we can obtain: (Equation 6) Now P can be i (t) (blood pressure to be determined) is formulated as follows: (Equation 7) From this, information about multiple discrete pressure levels (e.g., three or more pressure levels) at different times can be used. For example, the different corresponding annular pressures P at t1, t2, and t3. e (t1), P e (t2) and P e (t3) can be applied to the user to obtain a set of equations: (Equation 8a) (Equation 8b) (Equation 8c) Three different external pressures were applied at three different times. Three unknowns included the undetermined blood pressure P. i (t) (which is equal to P) i (t1), P i (t2) and P i (t3), because it is assumed that the user's blood pressure remains relatively constant at t1, t2, and t3), P i (0) and A0 can be solved using equations 8a and 8c.

[0113] In another approach, the zero-pressure condition can be considered, where P e (t) = 0. In this case, P(t) equals P i (t) (blood pressure to be determined), according to Equation 4. This can be seen in relation to... Figure 11 The zero-pressure artery size (area or volume) is determined by extrapolation, as shown. This information can be applied using the methods described above to estimate blood pressure.

[0114] In another approach, other variables related to blood vessels can be used to determine blood pressure. Consider the Shapiro equation: (Equation 9) Here, pi It is the blood pressure in the blood vessels, p e It is the external pressure applied to the blood vessel (e.g., through the circumference), κ p It is the critical pressure for vascular collapse, A is the current cross-sectional lumen area, A0 is the cross-sectional lumen area under stress-free conditions, and n is a constant that depends on one or more factors that vary from person to person to provide... Figure 12 The fit shown.

[0115] Figure 12 This is a graph of a set of example data points showing the variation of the arterial cross-sectional area 1202 under applied external pressure, based on specific implementation criteria. The arterial cross-sectional area 1202 can be obtained from experimental data. The example range of applied external pressure can be 60 mmHg to 85 mmHg. The example range of arterial cross-sectional area can be from 0 to 1 (mm). 2 / mm 2 The normalized range of (). In some cases, equation 9 can be used to fit curve 1210 to the data points of arterial cross-sectional area 1202. Therefore, blood pressure p can be determined based on the applied external pressure and empirical measurements. i .

[0116] In some implementations, machine learning models can be used to predict physiological parameters, such as a user's blood pressure. A machine learning model can refer to a computational algorithm that indicates the relationship between input and output variables. In some implementations, the machine learning model can be trained. Training a machine learning model may involve determining weight values, etc., associated with the machine learning model, wherein the relationship between input and output variables is at least partially based on the determined weight values. In one specific implementation, the machine learning model can be trained in a supervised manner using a training set that includes labeled training data. In a more specific example, the labeled training data may include inputs and manually annotated outputs, which are approximated by the machine learning model using the determined weight values. In another specific implementation, the machine learning model can be trained in an unsupervised manner, wherein the weight values ​​are determined without manually labeled training data.

[0117] An example training process for a machine learning model may involve providing training data that includes: known photoacoustic signal data, known arterial spatial measurements (e.g., area, volume), known external pressure levels, known associated compliance information and / or known null conditional arterial dimensions, and a "benchmark" or known output characteristic or parameter, such as known PWV, blood pressure, or cardiac features (e.g., peak or HRW features). In some approaches, a portion of the training data (e.g., 20%) may be used as part of the validation set for the machine learning model. Using this training data and validation set, one or more loss functions may be implemented. A loss function is an optimization function in which the error is iteratively minimized, for example, by gradient descent. An effective learning rate may also be set during training, which determines the "steps" taken by gradient descent to find the minimum error.

[0118] As a result, a trained machine learning model can be generated. In some implementations, this trained machine learning model can be used to further improve the accuracy and reliability of the estimated physiological characteristics or parameters. For example, estimates derived from measurements from the disclosed sensor device and various derivations based on photoacoustic measurements can be provided to the machine learning model (stored at the sensor or host device and / or accessible by its control system) for comparison with vascular physiological characteristics (e.g., PTT, PWV, heart rate) or user physiological parameters (e.g., blood pressure) estimated by the machine learning model. If there is a difference greater than a threshold between the sensor-based estimate and the prediction generated by the model, the obtained estimate can be further evaluated or discarded. If discarded, the prediction generated by the model can be used, or additional measurements can be performed by the sensor. In cases where there are two or more sensors on the user and a difference exists between the sensor estimates and the model predictions, fewer sensors, rather than all sensors, can be used as backups. On the other hand, if the difference is less than a threshold, the sensor-based estimate can be selected or retained for further processing, transmission to the host device, reporting, display to the user, etc.

[0119] Example Method

[0120] Figure 13 This is a flowchart of a method 1300 for determining a user's physiological parameters, based on some disclosed specific implementations. It is used to perform... Figure 13The functional structures illustrated in one or more of the boxes shown can be performed by hardware and / or software components of a computerized device or system (which may be implemented as a wearable device in some embodiments). Components of this device or system may include, for example, one or more sensors, a control system (including one or more processors), memory, and / or a computer-readable device including a storage medium storing computer-readable and / or computer-executable instructions configured to cause the control system, one or more processors, or the device to perform the operations represented by the boxes below when executed by the control system. Example components of the device are illustrated in... Figure 2 The above text describes it in more detail.

[0121] Figure 13 The block can be executed, for example, by device 200 or by similar device or components thereof (e.g., a control system). Similar to other methods disclosed herein, Figure 13 The methods outlined herein may include more or fewer boxes than those shown. Furthermore, the boxes in the methods disclosed herein are not necessarily executed in the indicated order. In some examples, Figure 13 One or more of the items shown in the box can be executed simultaneously.

[0122] At block 1310, method 1300 may include using a photoacoustic sensor to obtain a photoacoustic signal from a user's site, while simultaneously applying multiple discrete pressures to the user's site at multiple corresponding times, the photoacoustic signal being generated by light incident on the user's blood vessels. In some embodiments, a loop of a wearable device may be used to apply multiple discrete pressures to the user's site, the user's site including the user's skin, the wearable device including the photoacoustic sensor and the loop.

[0123] In some embodiments, the photoacoustic sensor may be configured to engage with a user's body part, including the user's skin. In some embodiments, the wearable device may include a wearable structure, and the wearable structure may be configured to be worn around a user's limb. A limb may be, for example, a wrist, finger, ankle, or other suitable body part.

[0124] Components for performing functionality at frame 1310 may include interface 201, receiver system 202 and light source system 204, ring system 205 and / or such as Figure 2 Other components of the apparatus shown.

[0125] At block 1320, method 1300 may include determining multiple dimensions of a blood vessel and multiple spatial measurements corresponding to the multiple dimensions of the blood vessel based on photoacoustic signals. In some embodiments, the multiple dimensions may include multiple diameters of the blood vessel or multiple semi-axes of the blood vessel; and the method may further include deriving multiple spatial measurements from the diameters of the blood vessel or the multiple semi-axes of the blood vessel, and associating the multiple spatial measurements with characteristics of the blood vessel, the multiple spatial measurements including multiple cross-sectional areas or multiple volumes associated with the blood vessel. Examples of semi-axes are semi-major axes and semi-minor axes. In some cases (e.g., in determining the volume of an elliptical blood vessel), a third semi-axe is another example of a semi-axe.

[0126] In some implementations, method 1300 may include determining multiple dimensions using an image processing algorithm applied to an image representation of the photoacoustic signal, a machine learning model trained to obtain a first axis and a second axis based on the photoacoustic signal, or a combination thereof. In some cases, multiple spatial measurements of a blood vessel may be determined based on multiple dimensions, a first axis, a second axis, or a combination thereof.

[0127] Components for performing the functionality at block 1320 may include control system 206 and / or, for example, Figure 2 Other components of the apparatus shown.

[0128] At block 1330, method 1300 may include determining a curve associated with a user, the curve comprising multiple spatial measurements of a blood vessel varying according to multiple discrete pressures, the curve realizing the determination of the characteristics of the blood vessel at a given pressure. In some embodiments, the characteristics of the blood vessel may include the compliance of the blood vessel.

[0129] In some implementations, vascular compliance can be obtained from a user-associated compliance profile determined based on a calibration procedure. In some embodiments, the compliance profile may include multiple spatial parameters of the vascular body varying according to multiple discrete pressures, the spatial parameters being determined based on multiple dimensions of the vascular body determined from photoacoustic signals obtained when multiple discrete pressures are applied to the user's site at multiple corresponding times. In some embodiments, the calibration procedure for the wearable user equipment may include obtaining multiple spatial parameters of the vascular body corresponding to multiple discrete pressures applied to the user's site by a band at multiple corresponding times, the multiple spatial parameters associated with the vascular body being related to multiple dimensions of the vascular body determined from photoacoustic signals, and the compliance profile including multiple spatial parameters varying according to multiple discrete pressures. Examples of multiple discrete pressures may range from 30 mmHg to 100 mmHg. In some cases, the pressure applied to the user's site may be about 40 mmHg or lower. In some cases, the pressure applied to the user's site may be about 90 mmHg or lower. However, the multiple discrete pressures can be other pressure values, such as above 0 mmHg but below 30 mmHg, or above 100 mmHg until the user feels discomfort. In some methods, the multiple spatial parameters of the blood vessel may include multiple cross-sectional areas associated with the blood vessel at a corresponding discrete pressure among multiple discrete pressures applied to the user's site by the ring at a corresponding time. In some other methods, the multiple spatial parameters of the blood vessel may include multiple arterial volumes associated with the blood vessel at a corresponding discrete pressure among multiple discrete pressures applied to the user's site by the ring at a corresponding time. In some cases, the multiple spatial parameters of the blood vessel may include multiple cross-sectional areas associated with the blood vessel at a corresponding discrete pressure among multiple discrete pressures applied to the user's site by the ring at a corresponding time. In some implementations, the pulse wave velocity (PWV) of the blood vessel may be correlated with the compliance of the blood vessel, and the PWV may be obtained in other ways using photoacoustic sensors and a second photoacoustic sensor not used by the wearable user device. In some implementations, the slope of the compliance curve may correspond to the compliance at the pressure applied to the user's site by the ring.

[0130] In some implementations, the dimensions of the blood vessel may include a first axis and a second axis; one or more spatial parameters of the blood vessel may be derived from at least the first and second axes; and one or more spatial parameters and pressure of the blood vessel may be associated with the characteristics of the blood vessel. Examples of spatial parameters may be the volume or cross-sectional area associated with the blood vessel. In some specific implementations, the first and second axes may be determined using image processing algorithms applied to image representations of photoacoustic signals, machine learning models trained to obtain the first and second axes based on photoacoustic signals, or combinations thereof.

[0131] Components for performing the functionality at block 1330 may include control system 206 and / or, for example, Figure 2 Other components of the apparatus shown.

[0132] At block 1340, method 1300 may include determining a user's physiological parameters based at least on vascular characteristics. In some embodiments, the user's physiological parameters may include the user's blood pressure. In some specific embodiments, determining the user's physiological parameters may include determining the user's blood pressure based at least on characteristics; wherein the characteristics may include vascular compliance; the method may further include determining the vascular pulse wave velocity (PWV) based at least on compliance; and determining the user's blood pressure may include determining the user's blood pressure based at least on PWV.

[0133] Components for performing the functionality at block 1340 may include control system 206 and / or, for example, Figure 2 Other components of the apparatus shown.

[0134] In some implementations, the characteristics of the blood vessels can further determine the pulse wave velocity associated with the blood vessels. In some implementations, the user's blood pressure can be determined. In some implementations, the user's blood pressure can be determined at least based on estimated parameters of the blood vessels, including the diameter of the blood vessels associated with zero pressure, and the user's blood pressure can be determined by: (i) extrapolation of multiple diameters varying based on multiple discrete pressures applied to the user's site by a band, or (ii) a machine learning model trained to determine the diameter based on multiple discrete pressures.

[0135] In some implementations, the band may be further configured to apply pressure to the user's site at multiple substantially constant pressure levels, which are different from each other; and the user's blood pressure may be determined based at least on the multiple substantially constant pressure levels, for example, using equations 8a to 8c.

[0136] In some implementations, the wearable device may further include a control system, wherein the control system may be configured to determine the characteristics of the blood vessels and the user's blood pressure based at least on the characteristics of the blood vessels.

[0137] In some implementations, method 1300 may further include determining the pulse wave velocity (PWV) of a blood vessel based at least on the vessel's compliance, the PWV being obtained in other ways using a photoacoustic sensor and an unused second photoacoustic sensor.

[0138] In some implementations, method 1300 may further include: applying pressure to the user's site at a substantially constant pressure level after determining a curve associated with the user; and determining the characteristics of the blood vessels corresponding to the substantially constant pressure level based on the slope of the curve.

[0139] In some implementations, method 1300 may further include, after determining the curve, applying pressure to the user's site at multiple substantially constant pressure levels, the multiple substantially constant pressure levels being different from each other. In some specific implementations, the user's physiological parameters may be further determined based at least on the multiple substantially constant pressure levels.

[0140] Figure 14 This is a flowchart of a method 1400 for determining a user's physiological parameters, based on some disclosed specific implementations. It is used to perform... Figure 14 The functional structures illustrated in one or more of the boxes shown can be performed by hardware and / or software components of a computerized device or system (which may be implemented as a wearable device in some embodiments). Components of this device or system may include, for example, one or more sensors, a control system (including one or more processors), memory, and / or a computer-readable device including a storage medium storing computer-readable and / or computer-executable instructions configured to cause the control system, one or more processors, or the device to perform the operations represented by the boxes below when executed by the control system. Example components of the device are illustrated in... Figure 2 The above text describes it in more detail.

[0141] Figure 14 The block can be executed, for example, by device 200 or by similar device or components thereof (e.g., a control system). Regarding other methods disclosed herein, Figure 14 The methods outlined herein may include more or fewer boxes than indicated. Furthermore, the boxes in the methods disclosed herein are not necessarily executed in the indicated order. In some examples, Figure 14 One or more of the items shown in the box can be executed simultaneously.

[0142] At box 1410, method 1400 may include applying pressure to a user's site at a substantially constant pressure level. As above, examples of a substantially constant pressure level may include about 30 mmHg, about 100 mmHg, or lower.

[0143] Components for performing functionality at block 1410 may include the belt system 205 and / or, as well as... Figure 2 Other components of the apparatus shown.

[0144] At box 1420, method 1400 may include determining the compliance of a user's blood vessels corresponding to a substantially constant pressure level based on a compliance curve. For example, it may be derived from... Figure 10 The curve 1000 shown determines the slope of the applied external pressure, where the slope corresponds to the compliance of the blood vessels.

[0145] Components for performing the functionality at block 1420 may include control system 206 and / or, for example, Figure 2Other components of the apparatus shown.

[0146] At box 1430, method 1400 may include determining a user's physiological parameters based at least on characteristics. In some embodiments, the user's physiological parameters may include blood pressure.

[0147] Components for performing the functionality at block 1430 may include control system 206 and / or, for example, Figure 2 Other components of the apparatus shown.

[0148] As used in this article, the phrase “at least one of the items” refers to any combination of these items, including a single member. As an example, “at least one of a, b, or c” is intended to cover: a, b, c, ab, ac, bc, and abc.

[0149] The various exemplary logics, logic blocks, modules, circuits, and algorithmic processes described in conjunction with the specific implementations disclosed herein can be implemented as electronic hardware, computer software, or a combination of both. The interchangeability of hardware and software has been broadly described in terms of functionality and illustrated in the various exemplary components, blocks, modules, circuits, and processes described above. Whether such functionality is implemented in hardware or software depends on the specific application and the design constraints imposed on the overall system.

[0150] Hardware and data processing means for implementing the various exemplary logic, logic blocks, modules, and circuits described herein can be implemented or executed using general-purpose single-chip or multi-chip processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor can be a microprocessor, or any conventional processor, controller, microcontroller, or state machine. A processor can also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors combined with a DSP core, or any other such configuration. In some specific implementations, specific processes and methods can be performed by circuitry specific to a given function.

[0151] In one or more aspects, the described functionality may be implemented in hardware, digital electronic circuits, computer software, firmware, including the structures disclosed in this specification and their structural equivalents or any combination thereof. Specific implementations of the subject matter described in this specification may also be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a computer storage medium for execution by a data processing apparatus or for controlling the operation of a data processing apparatus.

[0152] If implemented in software, the functions can be stored as one or more instructions or codes on or transmitted via a computer-readable medium such as a non-transitory medium. The processes of the methods or algorithms disclosed herein can be implemented in a processor-executable software module that can reside on a computer-readable medium. Computer-readable media include both computer storage media and communication media, including any medium capable of transferring a computer program from one location to another. Storage media can be any available medium accessible to a computer. By way of example and not limitation, non-transitory media can include RAM, ROM, EEPROM, CD-ROM or other optical disc storage devices, disk storage devices or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and is accessible to a computer. Additionally, any connection can be appropriately referred to as a computer-readable medium. As used herein, disks and optical discs include compact optical discs (CDs), laser discs, optical discs, digital versatile optical discs (DVDs), floppy disks, and Blu-ray discs, wherein disks typically magnetically reproduce data, while optical discs optically reproduce data using lasers. Combinations of the above should also be included within the scope of computer-readable media. Additionally, the operation of a method or algorithm may reside as a set of code and instructions or any combination of code and instructions on a machine-readable medium and a computer-readable medium that may be incorporated into a computer program product.

[0153] Various modifications to the specific embodiments described herein may be apparent to those skilled in the art, and the general principles defined herein may be applied to other specific embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not intended to be limited to the specific embodiments shown herein, but is to be accorded the widest scope consistent with the claims, principles, and novel features disclosed herein. The word “exemplary” (if any) is used herein specifically to mean “serving as an example, instance, or illustration.” Any specific embodiment described herein as “exemplary” is not necessarily to be construed as superior to or better than other specific embodiments.

[0154] Certain features described in this specification in the context of a single embodiment may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented individually or in any suitable sub-combination in multiple embodiments. Furthermore, although features may be described above as operating in certain combinations and even originally claimed in this way, one or more features from the claimed combination may be removed from that combination in some cases, and the claimed combination may be for sub-combinations or variations thereof.

[0155] Similarly, although operations are depicted in a specific order in the figures, this should not be construed as requiring such operations to be performed in the shown specific order or sequential order, or to perform all illustrated operations to achieve the desired result. In some environments, multitasking and parallel processing are advantageous. Furthermore, the separation of the various system components in the embodiments described above should not be construed as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. Additionally, other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve the desired result.

[0156] It should be understood that unless features in any particular embodiment of the description are explicitly identified as incompatible with each other, or the surrounding context suggests that they are mutually exclusive and not easily combined in a complementary and / or supporting sense, the general conception and ideas of this disclosure may be selectively combined with specific features of those complementary embodiments to provide one or more comprehensive but slightly different technical solutions. Therefore, it should also be understood that the above description is given by way of example only and may be modified in detail within the scope of this disclosure.

[0157] Various modifications to the specific embodiments described in this disclosure will be apparent to those skilled in the art, and the general principles defined herein may be applied to other specific embodiments without departing from the spirit or scope of this disclosure. Therefore, the following claims are not intended to limit the specific embodiments shown herein, but are intended to be consistent with the maximum scope of this disclosure, the principles disclosed herein, and the novel features.

[0158] Furthermore, certain features described in the context of a single embodiment in this specification may also be implemented in combination within that single embodiment. Conversely, individual features described in the context of a single embodiment may also be implemented individually or in any suitable sub-combination in multiple embodiments. Moreover, while some features are described above as working in a particular combination and even initially claimed in this way, in some cases, one or more features from the claimed combination may be extracted from that combination, and the claimed combination may involve sub-combinations or variations thereof.

[0159] Similarly, although operations are depicted in a specific order in the figures, this should not be construed as requiring such operations to be performed in the indicated specific order or sequential order, or to perform all illustrated operations to achieve the desired result. Furthermore, the figures may schematically depict one or more example processes in the form of flowcharts. However, other operations not depicted may be incorporated into the schematically illustrated example processes. For example, one or more additional operations may be performed before, after, simultaneously with, or between any of the illustrated operations. Moreover, the various agents in the described and illustrated operations may themselves include and collectively include several sub-operations. For example, each of the aforementioned operations may itself involve the execution of a process or algorithm. Furthermore, in some embodiments, the various agents in the described and illustrated operations may be combined or performed in parallel. Similarly, the separation of various system components in the above embodiments should not be construed as requiring this separation in all embodiments. Thus, other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve the desired result.

[0160] Specific implementation examples are described in the following numbered clauses: Clause 1: A wearable user device comprising: a loop configured to apply pressure to a user's site at one or more substantially constant pressure levels; and a photoacoustic sensor configured to receive a photoacoustic signal generated from light incident on a blood vessel of the user, the photoacoustic signal being correlated with one or more dimensions of the user's blood vessel when the pressure is applied to the user's site, the one or more dimensions of the blood vessel and the pressure being correlated with characteristics of the blood vessel, the characteristics of the blood vessel enabling the determination of the user's blood pressure; and a wearable structure comprising the loop and the photoacoustic sensor.

[0161] Clause 2: The wearable user device according to Clause 1, wherein: the characteristics of the blood vessel include the compliance of the blood vessel; and the compliance of the blood vessel can be obtained from a compliance curve associated with the user, the compliance curve being determined based on a calibration procedure.

[0162] Clause 3: A wearable user device according to any one of Clauses 1 to 2, wherein the compliance curve includes a plurality of spatial parameters of the blood vessel that vary according to a plurality of discrete pressures, the plurality of spatial parameters being determined based on a plurality of dimensions of the blood vessel determined from photoacoustic signals obtained when the plurality of discrete pressures are applied to the user’s site at a plurality of corresponding times.

[0163] Clause 4: A wearable user device according to any one of Clauses 1 to 3, wherein the calibration procedure of the wearable user device includes obtaining a plurality of spatial parameters of the blood vessel corresponding to a plurality of discrete pressures applied to the user's site by the ring at a plurality of corresponding times, the plurality of spatial parameters associated with the blood vessel being related to a plurality of dimensions of the blood vessel determined from the photoacoustic signal, and the compliance curve including the plurality of spatial parameters varying according to the plurality of discrete pressures.

[0164] Clause 5: A wearable user device according to any one of Clauses 1 to 4, wherein the plurality of spatial parameters of the blood vessel include a plurality of cross-sectional areas associated with the blood vessel at the respective discrete pressures of the plurality of discrete pressures applied to the user's site by the annulus at corresponding times.

[0165] Clause 6: A wearable user device according to any one of Clauses 1 to 5, wherein the pulse wave velocity (PWV) of the blood vessel is related to the compliance of the blood vessel, and the PWV may be obtained in other ways using the photoacoustic sensor and a second photoacoustic sensor not used by the wearable user device.

[0166] Clause 7: A wearable user device according to any one of Clauses 1 to 6, wherein the slope of the compliance curve corresponds to the compliance under the pressure applied by the loop to the user's site.

[0167] Clause 8: A wearable user device according to any one of Clauses 1 to 7, wherein the one or more dimensions of the blood vessel include a first axis and a second axis of the blood vessel; one or more spatial parameters of the blood vessel are derived from at least the first axis and the second axis; and the one or more spatial parameters of the blood vessel and the pressure are related to the characteristics of the blood vessel.

[0168] Clause 9: A wearable user device pursuant to any one of Clauses 1 to 8, wherein the first axis and the second axis are determined using an image processing algorithm applied to an image representation of the photoacoustic signal, a machine learning model trained to obtain the first axis and the second axis based on the photoacoustic signal, or a combination thereof.

[0169] Clause 10: A wearable user device according to any one of Clauses 1 to 9, wherein the characteristics of the blood vessel further enable the determination of the pulse wave velocity associated with the blood vessel.

[0170] Clause 11: A wearable user device according to any one of Clauses 1 to 10, wherein the user's blood pressure is determined at least based on the pulse wave velocity associated with the blood vessel.

[0171] Clause 12: A wearable user device according to any one of Clauses 1 to 11, wherein the user's blood pressure is determined at least based on estimated parameters of the blood vessel, the estimated parameters of the blood vessel including the diameter of the blood vessel at zero pressure, and the user's blood pressure can be determined by: (i) extrapolation of a plurality of diameters varying according to a plurality of discrete pressures applied to the user's site by the band, or (ii) a machine learning model trained to determine the diameter based on the plurality of discrete pressures.

[0172] Clause 13: A wearable user device according to any one of Clauses 1 to 12, wherein the characteristics of the blood vessel include the pulse wave velocity of the blood vessel determined using the photoacoustic signal; the ring is further configured to apply the pressure to the user's site at a plurality of substantially constant pressure levels, the plurality of substantially constant pressure levels being different from each other; and the user's blood pressure is determined at least based on the pulse wave velocity and the plurality of substantially constant pressure levels.

[0173] Clause 14: A wearable user device according to any one of Clauses 1 to 13, wherein the photoacoustic sensor is configured to engage with the user's body part, the user's body part including the user's skin.

[0174] Clause 15: A wearable user device according to any one of Clauses 1 to 14, wherein the wearable structure is configured to be worn around the user's limbs.

[0175] Clause 16: A wearable user device according to any one of Clauses 1 to 15, wherein the pressure applied to the user's site comprises a pressure of about 40 mmHg or less.

[0176] Clause 17: A wearable user device according to any one of Clauses 1 to 16, wherein the pressure applied to the user's site comprises a pressure of about 90 mmHg or less.

[0177] Clause 18: The wearable user device according to any one of Clauses 1 to 17 further includes a control system, wherein the control system is configured to determine the characteristics of the blood vessel and the user's blood pressure based at least on the characteristics of the blood vessel.

[0178] Clause 19: A method for determining a user's physiological parameters, the method comprising: acquiring a photoacoustic signal from a site of the user using a photoacoustic sensor while simultaneously applying a plurality of discrete pressures to the site of the user at a plurality of corresponding times, the photoacoustic signal being generated from light incident on a blood vessel of the user; determining a plurality of dimensions of the blood vessel and a plurality of spatial measurements of the blood vessel corresponding to the plurality of dimensions based on the photoacoustic signal; determining a curve associated with the user, the curve including the plurality of spatial measurements of the blood vessel varying according to the plurality of discrete pressures, the curve realizing the determination of characteristics of the blood vessel at a given pressure; and determining the user's physiological parameters based at least on the characteristics of the blood vessel.

[0179] Clause 20: The method according to Clause 19, wherein the physiological parameters of the user include the user's blood pressure.

[0180] Clause 21: The method according to any one of Clauses 19 to 20, wherein the characteristics of the blood vessel include the compliance of the blood vessel.

[0181] Clause 22: The method according to any one of Clauses 19 to 21 further comprises determining the pulse wave velocity (PWV) of the blood vessel based at least on the compliance of the blood vessel, the PWV being otherwise obtained using the photoacoustic sensor and an unused second photoacoustic sensor.

[0182] Clause 23: The method according to any one of Clauses 19 to 22, the method further comprising, after determining the curve associated with the user, applying pressure to the site of the user at a substantially constant pressure level; and determining the characteristics of the blood vessel corresponding to the substantially constant pressure level based on the slope of the curve; wherein determining the physiological parameters of the user includes determining the user's blood pressure based at least on the characteristics.

[0183] Clause 24: The method according to any one of Clauses 19 to 23, wherein the characteristic includes the compliance of the blood vessel; the method further includes determining the pulse wave velocity (PWV) of the blood vessel based at least on the compliance; and determining the blood pressure of the user includes determining the blood pressure of the user based at least on the PWV.

[0184] Clause 25: The method according to any one of Clauses 19 to 24, wherein the plurality of dimensions includes a plurality of diameters of the blood vessel or a plurality of semi-axes of the blood vessel; and the method further includes deriving the plurality of spatial measurements from the diameters of the blood vessel or the plurality of semi-axes of the blood vessel, and relating the plurality of spatial measurements to the characteristics of the blood vessel, the plurality of spatial measurements including a plurality of cross-sectional areas associated with the blood vessel or a plurality of volumes associated with the blood vessel.

[0185] Clause 26: The method according to any one of Clauses 19 to 25, the method further comprising using an image processing algorithm applied to an image representation of the photoacoustic signal, a machine learning model trained to obtain the first axis and the second axis based on the photoacoustic signal, or a combination thereof, to determine the plurality of dimensions.

[0186] Clause 27: The method according to any one of Clauses 19 to 26, wherein the plurality of discrete pressures are applied to the user's body part using a loop of a wearable device, the user's body part including the user's skin, the wearable device including the photoacoustic sensor and the loop.

[0187] Clause 28: The method according to any one of Clauses 19 to 27, the method further comprising, after determining the curve, applying the pressure to the user's site at a plurality of substantially constant pressure levels, the plurality of substantially constant pressure levels being different from one another; wherein the determination of the user's physiological parameter is further based at least on the plurality of substantially constant pressure levels.

[0188] Clause 29: An apparatus comprising: means for applying pressure to a site of a user at a substantially constant pressure level; means for obtaining a photoacoustic signal generated from light incident on a blood vessel of the user, wherein the photoacoustic signal is correlated with one or more dimensions of the blood vessel of the user when the pressure is applied to the site of the user, the one or more dimensions of the blood vessel and the pressure being correlated with characteristics of the blood vessel, the characteristics of the blood vessel enabling the determination of the user's blood pressure; and a wearable means comprising the means for applying the pressure to the site of the user and the means for obtaining the photoacoustic signal.

[0189] Clause 30: A non-transitory computer-readable device comprising a storage medium including a plurality of instructions configured to, when executed by one or more processors, cause the device to: acquire a photoacoustic signal from a site of a user using a photoacoustic sensor, while simultaneously applying a plurality of discrete pressures to the site of the user at a plurality of corresponding times, the photoacoustic signal being generated from light incident on a blood vessel of the user; determine a plurality of dimensions of the blood vessel and a plurality of spatial measurements of the blood vessel corresponding to the plurality of dimensions based on the photoacoustic signal; determine a curve associated with the user, the curve including the plurality of spatial measurements of the blood vessel varying according to the plurality of discrete pressures, the curve realizing the determination of characteristics of the blood vessel at a given pressure; and determine the physiological parameters of the user based at least on the characteristics of the blood vessel.

Claims

1. A wearable user device, the wearable user device comprising: A ring belt configured to apply pressure to a user's site at one or more substantially constant pressure levels; and A photoacoustic sensor configured to acquire a photoacoustic signal generated from light incident on a user's blood vessel, wherein the photoacoustic signal is correlated with one or more dimensions of the user's blood vessel when pressure is applied to the user's site, the one or more dimensions of the blood vessel and the pressure are correlated with characteristics of the blood vessel, the characteristics of the blood vessel enabling the determination of the user's blood pressure; and A wearable structure, the wearable structure including the loop and the photoacoustic sensor.

2. The wearable user device according to claim 1, wherein: The characteristics of the blood vessel include the compliance of the blood vessel; and The compliance of the blood vessel can be obtained from a compliance curve associated with the user, which is determined based on a calibration procedure.

3. The wearable user device of claim 2, wherein the compliance curve includes a plurality of spatial parameters of the blood vessel that vary according to a plurality of discrete pressures, the plurality of spatial parameters being determined based on a plurality of dimensions of the blood vessel determined from photoacoustic signals obtained when the plurality of discrete pressures are applied to the user's site at a plurality of corresponding times.

4. The wearable user device of claim 2, wherein the calibration procedure of the wearable user device includes obtaining a plurality of spatial parameters of the blood vessel corresponding to a plurality of discrete pressures applied to the user's site by the ring at a plurality of corresponding times, the plurality of spatial parameters associated with the blood vessel being related to a plurality of dimensions of the blood vessel determined from the photoacoustic signal, and the compliance curve including the plurality of spatial parameters varying according to the plurality of discrete pressures.

5. The wearable user device of claim 4, wherein the plurality of spatial parameters of the blood vessel includes a plurality of cross-sectional areas associated with the blood vessel at a respective discrete pressure of the plurality of discrete pressures applied to the user's site by the annulus at a corresponding time.

6. The wearable user device of claim 2, wherein the pulse wave velocity (PWV) of the blood vessel is related to the compliance of the blood vessel, and the PWV may be obtained in other ways using the photoacoustic sensor and a second photoacoustic sensor not used by the wearable user device.

7. The wearable user device of claim 2, wherein the slope of the compliance curve corresponds to the compliance under the pressure applied by the loop to the user's site.

8. The wearable user device according to claim 1, wherein: The one or more dimensions of the blood vessel include a first axis and a second axis of the blood vessel; One or more spatial parameters of the blood vessel are derived from at least the first axis and the second axis; and The one or more spatial parameters of the blood vessel and the pressure are related to the characteristics of the blood vessel.

9. The wearable user device of claim 8, wherein the first axis and the second axis are determined using an image processing algorithm applied to an image representation of the photoacoustic signal, a machine learning model trained to obtain the first axis and the second axis based on the photoacoustic signal, or a combination thereof.

10. The wearable user device of claim 1, wherein the characteristics of the blood vessel further enable the determination of a pulse wave velocity associated with the blood vessel.

11. The wearable user device of claim 10, wherein the user's blood pressure is determined at least based on the pulse wave velocity associated with the blood vessel.

12. The wearable user device of claim 10, wherein the user's blood pressure is determined at least based on estimated parameters of the blood vessel, the estimated parameters of the blood vessel including the diameter of the blood vessel at zero pressure, and the user's blood pressure can be determined by: (i) extrapolation of a plurality of diameters varying according to a plurality of discrete pressures applied to the user's site by the annulus, or (ii) a machine learning model trained to determine the diameter based on the plurality of discrete pressures.

13. The wearable user device according to claim 1, wherein: The characteristics of the blood vessel include the pulse wave velocity of the blood vessel determined using the photoacoustic signal; The ring is further configured to apply the pressure to the user's site at multiple substantially constant pressure levels, which are different from one another. as well as The user's blood pressure is determined at least based on the pulse wave velocity and the plurality of substantially constant pressure levels.

14. The wearable user device of claim 1, wherein the photoacoustic sensor is configured to engage with the user's body part, the user's body part including the user's skin.

15. The wearable user device of claim 1, wherein the wearable structure is configured to be worn around the user's limbs.

16. The wearable user device of claim 1, wherein the pressure applied to the user's site comprises a pressure of about 40 mmHg or less.

17. The wearable user device of claim 1, wherein the pressure applied to the user's site comprises a pressure of about 90 mmHg or less.

18. The wearable user device of claim 1, further comprising a control system, wherein the control system is configured to determine the characteristics of the blood vessel and the user's blood pressure based at least on the characteristics of the blood vessel.

19. A method for determining a user's physiological parameters, the method comprising: A photoacoustic sensor is used to obtain a photoacoustic signal from the user's body part, and multiple discrete pressures are applied to the user's body part at multiple corresponding times. The photoacoustic signal is generated from light incident on the user's blood vessels. Based on the photoacoustic signals, multiple dimensions of the blood vessel and multiple spatial measurements of the blood vessel corresponding to the multiple dimensions are determined; Determine a curve associated with the user, the curve comprising multiple spatial measurements of the blood vessel varying according to the multiple discrete pressures, the curve realizing the determination of the characteristics of the blood vessel at a given pressure; and The user's physiological parameters are determined at least based on the characteristics of the blood vessels.

20. The method of claim 19, wherein the physiological parameter of the user includes the user's blood pressure.

21. The method of claim 19, wherein the property of the blood vessel includes the compliance of the blood vessel.

22. The method of claim 21, further comprising determining the pulse wave velocity (PWV) of the blood vessel based at least on the compliance of the blood vessel, the PWV being otherwise obtained using the photoacoustic sensor and an unused second photoacoustic sensor.

23. The method according to claim 19, further comprising: After determining the curve associated with the user, pressure is applied to the user's site at a substantially constant pressure level; as well as The characteristics of the blood vessel corresponding to the substantially constant pressure level are determined based on the slope of the curve; The determination of the user's physiological parameters includes, at least based on the characteristic, determining the user's blood pressure.

24. The method according to claim 23, wherein: The characteristics include the compliance of the blood vessels; The method further includes determining the pulse wave velocity (PWV) of the blood vessel based at least on the compliance; and Determining the user's blood pressure includes determining the user's blood pressure based at least on the PWV.

25. The method according to claim 19, wherein: The plurality of dimensions includes a plurality of diameters of the blood vessel or a plurality of semi-axises of the blood vessel; and The method further includes deriving the plurality of spatial measurements from the diameter of the blood vessel or the plurality of semi-axises of the blood vessel, and relating the plurality of spatial measurements to the characteristics of the blood vessel, the plurality of spatial measurements including a plurality of cross-sectional areas associated with the blood vessel or a plurality of volumes associated with the blood vessel.

26. The method of claim 19, the method further comprising using an image processing algorithm applied to an image representation of the photoacoustic signal, a machine learning model trained to obtain a first axis and a second axis of the blood vessel based on the photoacoustic signal, or a combination thereof, to determine the plurality of dimensions; The plurality of spatial measurements of the blood vessel are determined based on the plurality of dimensions, the first axis, the second axis, or a combination thereof.

27. The method of claim 19, wherein the plurality of discrete pressures are applied to the user's body part using a loop of a wearable device, the user's body part including the user's skin, the wearable device including the photoacoustic sensor and the loop.

28. The method of claim 19, wherein the plurality of discrete pressures are in the range of 30 mmHg to 100 mmHg.

29. An apparatus comprising: A component used to apply pressure to a user's part at a substantially constant pressure level; A component for obtaining a photoacoustic signal generated from light incident on the user's blood vessel, wherein when pressure is applied to the user's site, the photoacoustic signal is related to one or more dimensions of the user's blood vessel, the one or more dimensions of the blood vessel and the pressure are related to the characteristics of the blood vessel, the characteristics of the blood vessel enabling the determination of the user's blood pressure; as well as A wearable component, the wearable component including a component for applying the pressure to the user's body part and a component for obtaining the photoacoustic signal.

30. A non-transitory computer-readable device, the non-transitory computer-readable device comprising a storage medium, the storage medium comprising a plurality of instructions configured to, when executed by one or more processors, cause the device to: A photoacoustic sensor is used to obtain photoacoustic signals from a user's body part, and multiple discrete pressures are applied to the user's body part at multiple corresponding times. The photoacoustic signals are generated from light incident on the user's blood vessels. Based on the photoacoustic signals, multiple dimensions of the blood vessel and multiple spatial measurements of the blood vessel corresponding to the multiple dimensions are determined; Determine a curve associated with the user, the curve comprising multiple spatial measurements of the blood vessel varying according to the multiple discrete pressures, the curve realizing the determination of the characteristics of the blood vessel at a given pressure; and The user's physiological parameters are determined at least based on the characteristics of the blood vessels.

Images