DEVICES, METHODS AND SYSTEMS FOR MEASURING PULSE WAVE VELOCITY

Some disclosed devices include a light source system, an ultrasonic receiver system and a control system. The control system may be configured to receive first sensor signals, including ultrasonic receiver signals, from the ultrasonic receiver system and to estimate one or more blood vessel features based on the first sensor signals. The control system may be configured to receive second sensor signals from a second sensor and to estimate a PWV based on the first sensor signals and the second sensor signals. The control system may be configured to estimate blood pressure based, at least in part, on the one or more blood vessel features and the PWV.

TECHNICAL FIELD

This disclosure relates generally to measuring pulse wave velocity and more specifically to measuring pulse wave velocity with devices configured to be worn by, or attached to, a person.

DESCRIPTION OF RELATED TECHNOLOGY

A variety of different sensing technologies and algorithms are being implemented in devices for various biometric and biomedical applications, including health and wellness monitoring. This push is partly a result of the limitations in the usability of traditional measuring devices for continuous, noninvasive and ambulatory monitoring. Some such devices may be, or include, photoacoustic devices. Although some previously-deployed devices and systems can provide acceptable results, improved devices and systems would be desirable.

SUMMARY

The systems, methods and devices of this disclosure each have several aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.

One innovative aspect of the subject matter described in this disclosure can be implemented in an apparatus. The apparatus may include a light source system and a receiver system. The light source system may be configured for providing light to a target object on an outer surface of the apparatus The receiver system may be, or may include, an ultrasonic receiver system. The receiver system may be configured to receive ultrasonic waves generated by the target object responsive to the light from the light source system. In some implementations, a mobile device (such as a wearable device, a cellular telephone, etc.) may be, or may include, at least part of the apparatus.

In some implementations, the apparatus may include a control system. The control system may include one or more general purpose single- or multi-chip processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) or other programmable logic devices, discrete gates or transistor logic, discrete hardware components, or combinations thereof. According to some examples, the control system may be configured to receive first sensor signals from at least a first ultrasonic sensor of the ultrasonic receiver system. The first sensor signals may be, or may include, ultrasonic receiver signals. In some examples, the control system may be configured to estimate one or more blood vessel features based on the first sensor signals. According to some examples, the control system may be configured to receive second sensor signals from a second sensor, or from a second sensor system. In some examples, the control system may be configured to estimate a pulse wave velocity based, at least in part, on the first sensor signals and the second sensor signals. According to some examples, the control system may be configured to estimate blood pressure based, at least in part, on the one or more blood vessel features and the pulse wave velocity.

According to some examples, the apparatus may be configured to be worn by, or attached to, a person. In some examples, the apparatus may be, or may include, a watch, an ear bud, headphones, an ear clip, a chest strap, an arm strap, a head band, or eye wear. In some examples, the apparatus may be configured to be worn on the person's wrist. According to some examples, the second device may be configured to be worn by, or attached to, the person's finger or the person's arm.

In some examples, the second sensor signals may include signals from a photoplethysmography sensor, signals from a photoacoustic plethysmography sensor, microphone signals, signals from an accelerometer, capacitive sensor signals, signals from a radio frequency sensor, signals from a magnetic sensor, electrocardiogram signals, signals from an ultrasonic sensor, signals from a pressure sensor, signals from a camera, or combinations thereof.

According to some examples, the apparatus also may include an interface system In some examples, the second sensor signals may be received, via the interface system, from a second device. In some examples, the control system may be further configured to estimate a distance between the first ultrasonic sensor and the second sensor. According to some examples, the second sensor may be a component of the ultrasonic receiver system. In some examples, the apparatus may be a component of a weighing scale, a component of an automobile, a component of an exercise machine or a component of a game controller.

According to some examples, the one or more blood vessel features may include blood vessel diameter, blood vessel distension, volumetric flow, or combinations thereof. In some examples, the ultrasonic receiver system may include an array of ultrasonic receiver elements.

In some examples, the pulse wave velocity may be a regional pulse wave velocity and the control system may be further configured to estimate a local pulse wave velocity. According to some examples, the second sensor signals may include signals from a sensor array. In some examples, the sensor array may be a two-dimensional sensor array.

Other innovative aspects of the subject matter described in this disclosure can be implemented in one or more methods. Some such methods may involve receiving first sensor signals from at least a first ultrasonic sensor of an ultrasonic receiver system. In some examples, the first sensor signals may be, or may include, ultrasonic receiver signals corresponding to ultrasonic waves generated by a target object responsive to light from a light source system. Some methods may involve estimating one or more blood vessel features based on the first ultrasonic receiver signals. Some methods may involve receiving second sensor signals from a second sensor, estimating a pulse wave velocity based, at least in part, on the first ultrasonic receiver signals and the second sensor signals and estimating blood pressure based, at least in part, on the one or more blood vessel features and the pulse wave velocity. Some methods may involve estimating a distance between the first ultrasonic sensor and the second sensor.

According to some examples, the second sensor signals may be received from a second device. In some examples, the first sensor signals may correspond to ultrasonic waves generated within a person's wrist. According to some examples, the second sensor signals may be obtained from the person's finger or the person's arm. According to some examples, the second sensor signals may include signals from a photoplethysmography sensor, signals from a photoacoustic plethysmography sensor, microphone signals, signals from an accelerometer, capacitive sensor signals, signals from a radio frequency sensor, signals from a magnetic sensor, electrocardiogram signals, signals from an ultrasonic sensor, signals from a pressure sensor, signals from a camera, or combinations thereof.

In some examples, the pulse wave velocity may be a regional pulse wave velocity. According to some examples, the method may involve estimating a local pulse wave velocity.

According to some examples, the second sensor signals may include signals from a sensor array. In some examples, the sensor array may be a two-dimensional sensor array. According to some examples, the one or more blood vessel features may include blood vessel diameter, blood vessel distension, volumetric flow, or combinations thereof. According to some examples, receiving the first sensor signals may involve receiving signals from an array of ultrasonic sensors of the ultrasonic receiver system.

Some or all of the methods described herein may be performed by one or more devices according to instructions (e.g., software) stored on non-transitory media. Such non-transitory media may include memory devices such as those described herein, including but not limited to random access memory (RAM) devices, read-only memory (ROM) devices, etc. Accordingly, some innovative aspects of the subject matter described in this disclosure can be implemented in one or more non-transitory media having software stored thereon. The software may include instructions for controlling one or more devices to perform one or more disclosed methods.

Some such methods may involve receiving first sensor signals from at least a first ultrasonic sensor of an ultrasonic receiver system. In some examples, the first sensor signals may be, or may include, ultrasonic receiver signals corresponding to ultrasonic waves generated by a target object responsive to light from a light source system. Some methods may involve estimating one or more blood vessel features based on the first ultrasonic receiver signals. Some methods may involve receiving second sensor signals from a second sensor, estimating a pulse wave velocity based, at least in part, on the first ultrasonic receiver signals and the second sensor signals and estimating blood pressure based, at least in part, on the one or more blood vessel features and the pulse wave velocity. Some methods may involve estimating a distance between the first ultrasonic sensor and the second sensor.

According to some examples, the second sensor signals may be received from a second device. In some examples, the first sensor signals may correspond to ultrasonic waves generated within a person's wrist. According to some examples, the second sensor signals may be obtained from the person's finger or the person's arm. According to some examples, the second sensor signals may include signals from a photoplethysmography sensor, signals from a photoacoustic plethysmography sensor, microphone signals, signals from an accelerometer, capacitive sensor signals, signals from a radio frequency sensor, signals from a magnetic sensor, electrocardiogram signals, signals from an ultrasonic sensor, signals from a pressure sensor, signals from a camera, or combinations thereof.

In some examples, the pulse wave velocity may be a regional pulse wave velocity. According to some examples, the method may involve estimating a local pulse wave velocity.

According to some examples, the second sensor signals may include signals from a sensor array. In some examples, the sensor array may be a two-dimensional sensor array. According to some examples, the one or more blood vessel features may include blood vessel diameter, blood vessel distension, volumetric flow, or combinations thereof. According to some examples, receiving the first sensor signals may involve receiving signals from an array of ultrasonic sensors of the ultrasonic receiver system.

DETAILED DESCRIPTION

The following description is directed to certain implementations for the purposes of describing various aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein can be applied in a multitude of different ways. Some of the concepts and examples provided in this disclosure are especially applicable to blood pressure monitoring applications. However, some implementations also may be applicable to other types of biological sensing applications, as well as to other fluid flow systems. The described implementations may be implemented in any device, apparatus, or system that includes an apparatus as disclosed herein. In addition, it is contemplated that the described implementations may be included in or associated with a variety of electronic devices such as, but not limited to: mobile telephones, multimedia Internet enabled cellular telephones, mobile television receivers, wireless devices, smartphones, smart cards, wearable devices such as bracelets, armbands, wristbands, rings, headbands, patches, etc., Bluetooth® devices, personal data assistants (PDAs), wireless electronic mail receivers, hand-held or portable computers, netbooks, notebooks, smartbooks, tablets, printers, copiers, scanners, facsimile devices, global positioning system (GPS) receivers/navigators, cameras, digital media players, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, electronic reading devices (e.g., e-readers), mobile health devices, computer monitors, auto displays (including odometer and speedometer displays, etc.), cockpit controls and/or displays, camera view displays (such as the display of a rear view camera in a vehicle), architectural structures, microwaves, refrigerators, stereo systems, cassette recorders or players, DVD players, CD players, VCRs, radios, portable memory chips, washers, dryers, washer/dryers, parking meters, automobile doors, autonomous or semi-autonomous vehicles, drones, Internet of Things (IoT) devices, etc. Thus, the teachings are not intended to be limited to the specific implementations depicted and described with reference to the drawings; rather, the teachings have wide applicability as will be readily apparent to persons having ordinary skill in the art.

Non-invasive health monitoring devices have various potential advantages over more invasive health monitoring devices such as cuff-based or catheter-based blood pressure measurement devices. However, it has proven to be difficult to design satisfactory wearable devices that are capable of estimating cardiac-related features, such as blood pressure. Some methods for estimating blood pressure require accurate pulse wave velocity (PWV) measurements. One challenge of obtaining accurate PWV measurements with wearable devices is that two-point or multi-point measurements along an artery are needed. However, most wearable health monitoring devices have compact designs, which makes it difficult to place the sensors of such devices along a blood vessel to obtain a precise PWV measurement.

Some disclosed devices include a light source system, an ultrasonic receiver system and a control system. The control system may be configured to receive first sensor signals from at least a first ultrasonic sensor of the ultrasonic receiver system. The first sensor signals may be, or may include, ultrasonic receiver signals. The control system may be configured to estimate one or more blood vessel features based on the first sensor signals. The one or more blood vessel features include blood vessel diameter, blood vessel distension, volumetric flow, or combinations thereof.

The control system may be configured to receive second sensor signals from a second sensor, or from a second sensor system. The control system may be configured to estimate a PWV based, at least in part, on the first sensor signals and the second sensor signals. If the second sensor system resides more than 50 millimeters from at least the first ultrasonic sensor of the ultrasonic receiver system, the PWV may be considered to be a regional PWV. If the second sensor system resides less than 50 millimeters from at least the first ultrasonic sensor of the ultrasonic receiver system, the PWV may be considered to be a local PWV. The control system may be configured to estimate blood pressure based, at least in part, on the one or more blood vessel features and the PWV.

Particular implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. Various disclosed configurations are capable of obtaining accurate PWV measurements and accurate measurements of one or more blood vessel features such as blood vessel diameter, blood vessel distension, etc. Accordingly, measurements from such devices may be used to obtain accurate estimates of blood pressure.

FIG.1is a block diagram that shows example components of an apparatus according to some disclosed implementations. In this example, the apparatus100includes an ultrasonic receiver system102, a control system106and a light source system104. Some implementations of the apparatus100may include a platen101, an interface system108, a noise reduction system110, or combinations thereof. As with other disclosed implementations, in some alternative implementations the apparatus100may include more components, fewer components, different components, or combinations thereof.

In some implementations, the platen101—if present—may be configured to increase an intensity of ultrasonic energy received by at least a portion of the ultrasonic receiver system. In some such implementations, the platen101may include an acoustic waveguide. According to some implementations, the platen101may include an acoustic lens system. The acoustic lens system may, for example, reside on, or proximate, an outer surface of the platen101. The acoustic lens system may, for example, include a spherical lens or a cylindrical lens.

According to some examples, the platen101(or another portion of the apparatus) may include one or more anti-reflective layers. In some examples, one or more anti-reflective layers may reside on, or proximate, one or more outer surfaces of the platen101.

In some examples, at least a portion of the outer surface of the platen101may have an acoustic impedance that is configured to approximate an acoustic impedance of human skin. The portion of the outer surface of the platen101may, for example, be a portion that is configured to receive a target object, such as a human digit. (As used herein, the terms “finger” and “digit” may be used interchangeably, such that a thumb is one example of a finger.) A typical range of acoustic impedances for human skin is 1.53-1.680 MRayls. In some examples, at least an outer surface of the platen101may have an acoustic impedance that is in the range of 1.4-1.8 MRayls, or in the range of 1.5-1.7 MRayls.

Alternatively, or additionally, in some examples at least an outer surface of the platen101may be configured to conform to a surface of human skin. In some such examples, at least an outer surface of the platen101may have material properties like those of putty or chewing gum.

In some examples, at least a portion of the platen101may have an acoustic impedance that is configured to approximate an acoustic impedance of one or more receiver elements of the ultrasonic receiver system102. According to some examples, a layer residing between the platen101and one or more receiver elements may have an acoustic impedance that is configured to approximate an acoustic impedance of the one or more receiver elements. Alternatively, or additionally, in some examples a layer residing between the platen101and one or more receiver elements may have an acoustic impedance that is in an acoustic impedance range between an acoustic impedance of the platen and an acoustic impedance of the one or more receiver elements.

In this example, the ultrasonic receiver system102includes one or more ultrasonic receiver elements. Various examples and configurations of ultrasonic receiver systems102are disclosed herein. In some examples, the ultrasonic receiver system102may include an array of ultrasonic receiver elements. According to some such examples, the ultrasonic receiver system102may include a two-dimensional array of ultrasonic receiver elements. In some examples, the ultrasonic receiver system102may include an array of electrodes arranged on a piezoelectric receiver layer, such as a layer of PVDF polymer, a layer of PVDF-TrFE copolymer, or a layer of piezoelectric composite material. In some implementations, other piezoelectric materials may be used in the piezoelectric layer, such as aluminum nitride (AlN) or lead zirconate titanate (PZT). The ultrasonic receiver system102may, in some examples, include an array of ultrasonic transducer elements, such as an array of piezoelectric micromachined ultrasonic transducers (PMUTs), an array of capacitive micromachined 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 ultrasonic transmitters as well as ultrasonic receivers. According to some examples, the ultrasonic receiver system102may be, or may include, an ultrasonic receiver array. In some examples, the apparatus100may include one or more separate ultrasonic transmitter elements. In some such examples, the ultrasonic transmitter(s) may include an ultrasonic plane-wave generator.

According to some implementations, the light source system104may include one or more light-emitting diodes (LEDs). In some implementations, the light source system104may include one or more laser diodes. According to some implementations, the light source system104may include one or more vertical-cavity surface-emitting lasers (VCSELs). In some implementations, the light source system104may include one or more edge-emitting lasers. In some implementations, the light source system may include one or more neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers. The light source system104may, in some examples, include an array of light-emitting elements, such as an array of LEDs, an array of laser diodes, an array of VCSELs, an array of edge-emitting lasers, or combinations thereof.

The light source system104may, in some examples, be configured to transmit light in one or more wavelength ranges. In some examples, the light source system104may configured for transmitting light in a wavelength range of 500 to 600 nanometers. According to some examples, the light source system104may configured for transmitting light in a wavelength range of 800 to 950 nanometers.

The light source system104may include various types of drive circuitry, depending on the particular implementation. In some disclosed implementations, the light source system104may include at least one multi-junction laser diode, which may produce less noise than single-junction laser diodes. In some examples, the light source system104may include a drive circuit (also referred to herein as drive circuitry) configured to cause the light source system to emit pulses of light at pulse widths in a range from 3 nanoseconds to 1000 nanoseconds. According to some examples, the light source system104may include a drive circuit configured to cause the light source system to emit pulses of light at pulse repetition frequencies in a range from 1 kilohertz to 100 kilohertz.

In some implementations, the light source system104may be configured for emitting various wavelengths of light, which may be selectable to trigger acoustic wave emissions primarily from a particular type of material. For example, because the hemoglobin in blood absorbs near-infrared light very strongly, in some implementations the light source system104may be configured for emitting one or more wavelengths of light in the near-infrared range, in order to trigger acoustic wave emissions from hemoglobin. However, in some examples the control system106may control the wavelength(s) of light emitted by the light source system104to preferentially induce acoustic waves in blood vessels, other soft tissue, and/or bones. For example, an infrared (IR) light-emitting diode LED may be selected and a short pulse of IR light emitted to illuminate a portion of a target object and generate acoustic wave emissions that are then detected by the ultrasonic receiver system102. In another example, an IR LED and a red LED or other color such as green, blue, white or ultraviolet (UV) may be selected and a short pulse of light emitted from each light source in turn with ultrasonic images obtained after light has been emitted from each light source. In other implementations, one or more light sources of different wavelengths may be fired in turn or simultaneously to generate acoustic emissions that may be detected by the ultrasonic receiver. Image data from the ultrasonic receiver that is obtained with light sources of different wavelengths and at different depths (e.g., varying RGDs) into the target object may be combined to determine the location and type of material in the target object. Image contrast may occur as materials in the body generally absorb light at different wavelengths differently. As materials in the body absorb light at a specific wavelength, they may heat differentially and generate acoustic wave emissions with sufficiently short pulses of light having sufficient intensities. Depth contrast may be obtained with light of different wavelengths and/or intensities at each selected wavelength. That is, successive images may be obtained at a fixed RGD (which may correspond with a fixed depth into the target object) with varying light intensities and wavelengths to detect materials and their locations within a target object. For example, hemoglobin, blood glucose or blood oxygen within a blood vessel inside a target object such as a finger may be detected photoacoustically.

According to some implementations, the light source system104may be configured for emitting a light pulse with a pulse width less than about 100 nanoseconds. In some implementations, the light pulse may have a pulse width between about 10 nanoseconds and about 500 nanoseconds or more. According to some examples, the light source system may be configured for emitting a plurality of light pulses at a pulse repetition frequency between 10 Hz and 100 kHz. Alternatively, or additionally, in some implementations the light source system104may be configured for emitting a plurality of light pulses at a pulse repetition frequency between about 1 MHz and about 100 MHZ. Alternatively, or additionally, in some implementations the light source system104may be configured for emitting a plurality of 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 an acoustic resonant frequency of the ultrasonic receiver and the substrate. For example, a set of four or more light pulses may be emitted from the light source system104at a frequency that corresponds with the resonant frequency of a resonant acoustic cavity in the sensor stack, allowing a build-up of the received ultrasonic waves and a higher resultant signal strength. In some implementations, filtered light or light sources with specific wavelengths for detecting selected materials may be included with the light source system104. In some implementations, the light source system may contain light sources such as red, green and blue LEDs of a display that may be augmented with light sources of other wavelengths (such as IR and/or UV) and with light sources of higher optical power. For example, high-power laser diodes or electronic flash units (e.g., an LED or xenon flash unit) with or without filters may be used for short-term illumination of the target object.

The control system106may include one or more general purpose single- or multi-chip processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) or other programmable logic devices, discrete gates or transistor logic, discrete hardware components, or combinations thereof. The control system106also may include (and/or be configured for communication with) one or more memory devices, such as one or more random access memory (RAM) devices, read-only memory (ROM) devices, etc. Accordingly, the apparatus100may have a memory system that includes one or more memory devices, though the memory system is not shown inFIG.1. The control system106may be configured for receiving and processing data from the ultrasonic receiver system102, e.g., as described below. If the apparatus100includes an ultrasonic transmitter, the control system106may be configured for controlling the ultrasonic transmitter. In some implementations, functionality of the control system106may be partitioned between one or more controllers or processors, such as a dedicated sensor controller and an applications processor of a mobile device.

In some examples, the control system106may be configured to control the light source system104to emit light towards a target object on an outer surface of the apparatus100. In some such examples, the control system106may be configured to receive signals from the ultrasonic receiver system102corresponding to ultrasonic waves generated by the target object responsive to the light from the light source system104.

In some examples, the control system106may be configured to receive first sensor signals from at least a first ultrasonic sensor of the ultrasonic receiver system. The first sensor signals may be, or may include, ultrasonic receiver signals. In some such examples, the first sensor signals may be, or may include, ultrasonic receiver signals from an ultrasonic receiver array. The ultrasonic receiver array may include a linear array, a two-dimensional array, etc. Receiving the first sensor signals from an ultrasonic receiver array may be potentially advantageous, because such signals may allow for more reliable location of a blood vessel, such as an artery.

According to some examples, the control system106may be configured to estimate one or more blood vessel features based on the first sensor signals. The blood vessel feature(s) may include blood vessel diameter, blood vessel distension, volumetric flow, or combinations thereof.

In some examples, the control system106may be configured to receive second sensor signals from a second sensor, or from a second sensor system. The second sensor signals may be, or may include, signals from a photoplethysmography sensor, signals from a photoacoustic plethysmography sensor, microphone signals, signals from an accelerometer, capacitive sensor signals, signals from a radio frequency sensor, signals from a magnetic sensor, electrocardiogram signals, signals from an ultrasonic sensor, signals from a pressure sensor, signals from a camera, or combinations thereof. According to some examples the second sensor, or the second sensor system, may be part of the same apparatus that includes the ultrasonic receiver system102. However, in other examples the second sensor, or the second sensor system, may be part of another apparatus. In some such examples, the second sensor signals may be, or may include, signals from a sensor array, signals from a receiver array, etc. The array may, in some examples, be a two-dimensional array.

According to some examples, the control system106may be configured to estimate a pulse wave velocity based, at least in part, on the first sensor signals and the second sensor signals. In some examples, the control system106may be configured to estimate one or more cardiac features based, at least in part, on the one or more blood vessel features and the pulse wave velocity. According to some examples, the cardiac features may be, or may include, blood pressure.

Some implementations of the apparatus100may include the interface system108. In some examples, the interface system108may include a wireless interface system. In some implementations, the interface system108may include a user interface system, one or more network interfaces, one or more interfaces between the control system106and a memory system and/or one or more interfaces between the control system106and one or more external device interfaces (e.g., ports or applications processors), or combinations thereof. According to some examples in which the interface system108is present and includes a user interface system, the user interface system may include a microphone system, a loudspeaker system, a haptic feedback system, a voice command system, one or more displays, or combinations thereof. According to some examples, the interface system108may include a touch sensor system, a gesture sensor system, or a combination 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.

In some examples, the interface system108may include, a force sensor system. The force sensor system (if present) may be, or may include, a piezo-resistive sensor, a capacitive sensor, a thin film sensor (for example, a polymer-based thin film sensor), another type of suitable force sensor, or combinations thereof. If the force sensor system includes a piezo-resistive sensor, the piezo-resistive sensor may include silicon, metal, polysilicon, glass, or combinations thereof. An ultrasonic fingerprint sensor and a force sensor system may, in some implementations, be mechanically coupled. In some such examples, the force sensor system may be integrated into circuitry of the ultrasonic fingerprint sensor. In some examples, the interface system108may include an optical sensor system, one or more cameras, or a combination thereof.

According to some examples, the apparatus100may include a noise reduction system110. For example, the noise reduction system110may include one or more mirrors that are configured to reflect light from the light source system104away from the ultrasonic receiver system102. In some implementations, the noise reduction system110may include one or more sound-absorbing layers, acoustic isolation material, light-absorbing material, light-reflecting material, or combinations thereof. In some examples, the noise reduction system110may include acoustic isolation material, which may reside between the light source system104and at least a portion of the ultrasonic receiver system102, on at least a portion of the ultrasonic receiver system102, or combinations thereof. In some examples, the noise reduction system110may include one or more electromagnetically shielded transmission wires. In some such examples, the one or more electromagnetically shielded transmission wires may be configured to reduce electromagnetic interference from circuitry of the light source system104, receiver system circuitry, or combinations thereof, that is received by the ultrasonic receiver system102. In some examples, the one or more electromagnetically shielded transmission wires, sound-absorbing layers, acoustic isolation material, light-absorbing material, light-reflecting material, or combinations thereof may be components of the ultrasonic receiver system102, the light source system104, or both. Despite the fact that the ultrasonic receiver system102, the light source system104and the noise reduction system110are shown inFIG.1as being separate elements, such components may nonetheless be regarded as elements of the noise reduction system110.

The apparatus100may be used in a variety of different contexts, many examples of which are disclosed herein. In some implementations, a wearable device may include the apparatus100. The wearable device may be, or may include, a bracelet, one or more devices configured to be attached to an arm, such as an armband or an arm strap, one or more devices configured to be attached to a wrist, such as a wristband or a watch, one or more devices configured to be attached to a finger, such as a ring or a finger strap, a headband, one or more ear buds, headphones, one or more car clips, a chest strap, eye wear-such as glasses or goggles- or a patch. Accordingly, in some examples the apparatus100may be configured to be worn by, or attached to, a person.

However, in some examples, at least a portion of the apparatus100may not be configured to be worn by, or attached to, a person. For example, in some implementations a mobile device may include the apparatus100. In some such examples, the mobile device may be, or may include, a smart phone. In some examples, the apparatus100may be, or may include, a component of a weighing scale, such as a component residing in or on a portion of the weighing scale that is configured to receive a person's foot or feet. According to some examples, the apparatus100may be, or may include, a component of an automobile, such as a component residing in or on a portion of a steering wheel, a door handle, an arm rest, etc. In some examples, the apparatus100may be, or may include, a component of an exercise machine, such as a component configured to receive a person's foot (such as a pedal), a component configured to receive a person's hand (such as a handle, a hand grip, a lever or a bar), etc. According to some examples, the apparatus100may be, or may include, a component of a game controller.

FIG.2Ashows components of an apparatus according to one example. In this example, the apparatus100includes apparatus portions200aand200b. In this example, the apparatus portion200ais configured to be worn on a person's wrist. Accordingly, in this example the apparatus portion200aincludes a sensor205a, an adjustable wrist band215, a housing portion220aand a display210that resides in or on a portion of the housing portion220a. In this example, the apparatus portion200bis configured to be worn on a person's finger and includes a sensor205b. Here, the apparatus portion200bis electrically connected to the apparatus portion200avia the electrical interface208. As with other disclosed examples, the types, numbers, sizes and arrangements of elements shown inFIG.2Aare merely examples.

The sensor205a, which is also labeled as “Sensor1” inFIG.2A, is an example of what may be referred to herein as a first sensor, or a first sensor system. In this example, the sensor205aresides within the housing portion220aon a side of the housing portion220athat faces a person's wrist when the adjustable wrist band215is fastened to the person's wrist. In other words, the display210resides in or on a first side of the housing portion220a—which may be referred to as an outer side—and the sensor205aresides in or on a second side of the housing portion220athat faces a person's wrist when the adjustable wrist band215is fastened to the person's wrist. The second side may be referred to herein as an inner side.

In some examples, the sensor205amay be, or may include, a PAPG sensor. However, in some examples the sensor205amay be, or may include, another type of sensor, such as an ultrasonic sensor capable of transmitting and receiving ultrasonic waves. In some examples in which the sensor205ais, or includes, a PAPG sensor, the sensor205amay include instances of the ultrasonic receiver system102, the light source system104and the control system106that are described with reference toFIG.1. In some examples, the ultrasonic receiver system102may include a sensor array, which in some examples may be a two-dimensional sensor array. According to some examples, the control system106may be configured to control the light source system104to emit light towards the wrist of a person wearing the apparatus portion200a.

In some examples, the control system106may be configured to receive first sensor signals from the ultrasonic receiver system102. The first sensor signals may be ultrasonic receiver signals corresponding to ultrasonic waves generated by a blood vessel within the person's wrist, blood within the blood vessel, or a combination thereof, responsive to the light from the light source system104. . . . According to some examples, the control system106may be configured to estimate one or more blood vessel features based on the first sensor signals. The blood vessel feature(s) may include blood vessel diameter, blood vessel distension, volumetric flow, or combinations thereof.

The sensor205b, which is also labeled as “Sensor2” inFIG.2A, is an example of what may be referred to herein as a second sensor, or a second sensor system. In this example, the sensor205bresides within the housing portion220bon a side of the housing portion220athat faces a person's finger when a person's finger is within the housing portion220b. In other words, the sensor205bresides in an inner side of the housing portion220b.

In some examples, the sensor205bmay be, or may include, a PAPG sensor. The PAPG sensor may, in some examples, be another instance of the PAPG sensor that is described with reference to the sensor205a. In some examples, the ultrasonic receiver system102of the PAPG sensor may include a sensor array, which in some examples may be a two-dimensional sensor array. However, in some examples the sensor205bmay be, or may include, another type of sensor, such as a photoplethysmography (PPG) sensor, a microphone, an accelerometer, a capacitive sensor, a radio frequency sensor, a magnetic sensor, an electrocardiogram sensor, an ultrasonic sensor, a pressure sensor, etc. According to some examples the control system106(not shown) may receive second sensor signals from the sensor205band may be configured to estimate a pulse wave velocity (PWV) based, at least in part, on signals from the sensor205aand the sensor205b. In some examples, the second sensor signals may be, or may include, signals from a sensor array, which in some examples may be a two-dimensional sensor array.

With the type of implementation illustrated inFIG.2A, if the apparatus100is worn by an adult the sensor205awill generally reside more than 50 millimeters from the sensor205b. Therefore, the PWV may be considered to be a regional PWV. The control system106may be configured to estimate blood pressure based, at least in part, on the one or more blood vessel features and the PWV. According to some examples, the control system106may be configured to estimate a distance between the sensor205aand the sensor205b. In some such examples, the control system106may be configured to estimate a distance between the sensor205aand the sensor205busing an ultrasonic transmitter in the sensor205aand an ultrasonic receiver in the sensor205b, using an ultrasonic transmitter in the sensor205band an ultrasonic receiver in the sensor205a, or both. By emitting ultrasonic waves at one sensor and receiving ultrasonic waves at other sensor, the control system106may be configured to estimate the distance between the sensor205aand the sensor205bby multiplying the travel time for the ultrasonic waves by the speed of sound in air.

FIG.2Bshows components of an apparatus according to another example. As with the example shown inFIG.2A, the apparatus100is configured to be worn on a person's wrist and includes an adjustable wrist band215, a housing220and a display210that resides in or on a portion of the housing220. However, unlike the example shown inFIG.2A, in this example the apparatus100does not include apparatus portions200aand200b, but instead includes the sensors205aand205bwithin the housing220. As with other disclosed examples, the types, numbers, sizes and arrangements of elements shown inFIG.2Bare merely examples.

The sensors205aand205bare also labeled as Sensors1and2, respectively, inFIG.2B. In this example, the sensors205aand205bboth reside within the housing220on a side of the housing220that faces a person's wrist when the adjustable wrist band215is fastened to the person's wrist. In other words, the display210resides in or on a first side of the housing220—which may be referred to as an outer side—and the sensors205aand205breside proximate a second side of the housing220, which may be referred to as an inner side.

In some examples, the sensor205amay be, or may include, a PAPG sensor. According to some such examples, the sensor205balso may be, or may include, a PAPG sensor. However, in some examples the sensor205a, the sensor205b, or both, may be, or may include, another type of sensor, such as an ultrasonic sensor capable of transmitting and receiving ultrasonic waves. In some examples in which the sensor205ais, or includes, a PAPG sensor, the sensor205amay include instances of the ultrasonic receiver system102, the light source system104and the control system106that are described with reference toFIG.1. Likewise, in some examples in which the sensor205bis, or includes, a PAPG sensor, the sensor205bmay include instances of the ultrasonic receiver system102, the light source system104and the control system106that are described with reference toFIG.1. According to some examples, the control system106may be configured to control the light source system104to emit light towards the wrist of a person wearing the apparatus100.

In some examples, the control system106may be configured to receive first sensor signals from the ultrasonic receiver system102of the sensor205a, the sensor205b, or both. The first sensor signals may be ultrasonic receiver signals corresponding to ultrasonic waves generated by a blood vessel within the person's wrist, blood within the blood vessel, or a combination thereof, responsive to the light from the light source system104. In some alternative examples, the first sensor signals may be ultrasonic receiver signals corresponding to ultrasonic waves generated by the apparatus100and reflected from a blood vessel within the person's wrist, blood within the blood vessel, etc. According to some examples, the control system106may be configured to estimate one or more blood vessel features based on the first sensor signals. The blood vessel feature(s) may include blood vessel diameter, blood vessel distension, volumetric flow, or combinations thereof.

As noted above, in some examples the sensor205bmay be, or may include, a PAPG sensor. However, in some examples the sensor205bmay be, or may include, another type of sensor, such as a photoplethysmography (PPG) sensor, a microphone, an accelerometer, a capacitive sensor, a radio frequency sensor, a magnetic sensor, an electrocardiogram sensor, an ultrasonic sensor, a pressure sensor, etc. According to some examples the control system106(not shown) may receive second sensor signals from the sensor205band may be configured to estimate a PWV based, at least in part, on first sensor signals from the sensor205aand second sensor signals from the sensor205b.

With the type of implementation illustrated inFIG.2B, the sensor205amay or may not reside more than 50 millimeters from the sensor205b, depending on the dimensions of the housing220. In this example, the sensor205aand the sensor205bare separated by a distance D. In some examples D may be more than 50 millimeters, in which case the estimated PWV may be considered to be a regional PWV. The control system106may be configured to estimate blood pressure based, at least in part, on the one or more blood vessel features and the PWV. However, in other examples D may be less than 50 millimeters, in which case the estimated PWV may be considered to be a local PWV.

FIG.3Ashows components of an apparatus according to another example. As with the example shown inFIG.2B, the sensors205aand205breside within the housing220of the apparatus100. The sensors205aand205bmay, in some examples, be as described with reference toFIG.2B. In this example, as in the example shown inFIG.2B, the apparatus100also includes a display210that resides in or on a portion of the housing220. However, in the example shown inFIG.3A, the apparatus100is configured to be worn on a person's upper arm—in other words, above the person's elbow—instead of on a person's wrist. Accordingly, in this example the apparatus100includes an adjustable arm band315. As with other disclosed examples, the types, numbers, sizes and arrangements of elements shown inFIG.2Aare merely examples.

According to some examples the control system106(not shown) may receive sensor signals from the sensor205aand the sensor205band may be configured to estimate a PWV based, at least in part, on signals from the sensor205aand the sensor205b. With the type of implementation illustrated inFIG.3A, the sensor205awill generally reside more than 50 millimeters from the sensor205b. In other words, D will generally be more than 50 millimeters, in which case the estimated PWV may be considered to be a regional PWV. The control system106may be configured to estimate blood pressure based, at least in part, on the one or more blood vessel features and the PWV. However, in other examples D may be less than 50 millimeters, in which case the estimated PWV may be considered to be a local PWV.

In some implementations, the sensor205amay reside more than 50 millimeters from the sensor205b, but there also may be one or more sensors residing between the sensors205aand205b, for example including at least a sensor205c. The sensor205cmay be another instance of the sensor205aor the sensor205b. According to some such implementations, the control system106may be configured to estimate a regional PWV based on signals from the sensor205aand the sensor205band may be configured to estimate a local PWV based on signals from the sensor205aand the sensor205c, on signals from the sensor205band the sensor205c, or both.

FIG.3Bshows components of an apparatus according to another example. As with other disclosed examples, the types, numbers, sizes and arrangements of elements shown inFIG.3Bare merely examples.

The example shown inFIG.3Bis similar in some ways to the example shown inFIG.2A. In both examples, the apparatus100includes apparatus portions200aand200b. In both examples, the apparatus portion200aincludes a sensor205a, a housing portion220aand a display210that resides in or on a portion of the housing portion220a. In both examples, the apparatus portion200bis configured to be worn on a person's finger and includes a sensor205b. In both examples, the apparatus portion200bis electrically connected to the apparatus portion200a. The sensors205aand205bshown inFIG.3Bmay, in some examples, be as described with reference toFIG.2A.

However, in the example shown inFIG.3B, the electrical interface is not a wire or a cable, as shown in the example ofFIG.2A. According to the example shown inFIG.3B, the apparatus portions200aand200b, as well as the housing portion220aand the housing portion220b, are physically and electrically coupled to one another. Therefore, both of the apparatus portions200aand200bare configured to be worn on a person's finger.

The example shown inFIG.3Bhas some potential advantages relative to the example ofFIG.2A. One such potential advantage is that in the example shown inFIG.3B, the relative positions of the sensors205aand205bare both fixed and known, whereas in the example shown inFIG.2Athe relative positions of the sensors205aand205bare not fixed and may be challenging to determine with accuracy.

According to some examples the control system106(not shown) may receive sensor signals from the sensor205aand the sensor205band may be configured to estimate a PWV based, at least in part, on signals from the sensor205aand the sensor205b. With the type of implementation illustrated inFIG.3B, the sensor205awill generally reside less than 50 millimeters from the sensor205b, in which case the estimated PWV may be considered to be a local PWV. However, in other examples the sensor205awill reside more than 50 millimeters from the sensor205b, in which case the estimated PWV may be considered to be a regional PWV. The control system106may be configured to estimate blood pressure based, at least in part, on the one or more blood vessel features and the PWV.

FIGS.4A and4Bshow alternative apparatus examples. In these examples, the apparatus100is configured to be worn in a human ear, on a human ear, or both. As with other disclosed examples, the types, numbers, sizes and arrangements of elements shown inFIGS.4A and4Bare merely examples.

FIG.4Ashows examples of bone, muscles and blood vessels in and near the back of a human ear400, including the mastoid process, muscle tissue attached to the mastoid process, muscle tissue attached to the posterior area of the ear400, the posterior auricular artery, and branches thereof. In the example shown inFIG.4A, the sensors205aand205breside within the housing220in positions such that, when the apparatus100is worn in the ear400, both of the sensors205aand205bare positioned on the posterior auricular artery.

According to some examples the control system106(not shown) may receive sensor signals from the sensor205aand the sensor205band may be configured to estimate a PWV based, at least in part, on signals from the sensor205aand the sensor205b. When the type of implementation illustrated inFIG.4Ais worn by an adult, the sensor205awill generally reside more than 50 millimeters from the sensor205b, in which case the estimated PWV may be considered to be a regional PWV. However, in other examples—such as when the type of implementation illustrated inFIG.4Ais worn by a child—the sensor205awill reside less than 50 millimeters from the sensor205b, in which case the estimated PWV may be considered to be a local PWV. The control system106may be configured to estimate blood pressure based, at least in part, on the one or more blood vessel features and the PWV.

FIG.4Bshows an alternative example of an apparatus100that is configured to be worn on, and in, the ear400. In this example, the sensor205aresides in the housing portion220a, which is configured to reside proximate, or within, an ear concha. According to this example, the sensor205bresides in the housing portion220b, which is configured to wrap around the outside of the ear400. In this example, the housing portions220aand220bare configured to position the sensors205aand205bsuch that the sensors205aand205bare on opposite sides of the same volume of the ear400. According to this example, the housing portion220cis configured to be inserted into an ear canal of the ear400.

According to some examples the control system106(not shown) may receive sensor signals from the sensor205aand the sensor205band may be configured to estimate a PWV based, at least in part, on signals from the sensor205aand the sensor205b. The control system106may be configured to estimate blood pressure based, at least in part, on the one or more blood vessel features and the PWV.

In some examples, the apparatus100shown inFIG.4A, the apparatus100shown inFIG.4B, or both, also may include at least one loudspeaker. The at least one loudspeaker may, for example, reside in the housing portion220c. In some such examples, the control system (not shown) may be configured to control the at least one loudspeaker to play back audio content. According to some examples, the apparatus100shown inFIGS.4A and4Balso may include at least one microphone. In some such examples, the control system (not shown) may be configured to control the at least one loudspeaker to provide hearing aid functionality that is based, at least in part, in microphone signals received from the at least one microphone.

FIGS.5A and5Bshow alternative examples. In these examples, the system505includes devices that are configured to be worn on a human finger. As with other disclosed examples, the types, numbers, sizes and arrangements of elements shown inFIGS.5A and5Bare merely examples.

According to the examples shown inFIGS.5A and5B, the apparatus500aincludes Sensor1, which is also referred to as sensor205a. In the examples shown inFIGS.5A and5B, the apparatus500ais an instance of the apparatus100ofFIG.1and is PAPG-capable. However, as described with reference toFIG.2Aand elsewhere herein, in some alternative examples the sensor205amay be, or may include, another type of sensor.

In the example shown inFIG.5A, the apparatus500ais a smart watch. Here, the apparatus500band the apparatus500care both configured to be worn on a human finger. In this example, the sensor205bresides in the housing520band the sensor205cresides in the housing520c.

One may observe that the implementation shown inFIG.5Ais similar to that shown inFIG.2A. The sensors205band205cofFIG.5Amay be instances of the sensor205bthat is described with reference toFIG.2A. However, in the example shown inFIG.5A, the apparatus500band the apparatus500care both configured for electrical connectivity with the control system506. In this example, the control system106(not shown) of the apparatus500ais configured for wireless communication with the control system506. Accordingly, the control system106may receive signals from the sensors205band205cvia the control system506. In some examples, the control system106or the control system506may be configured to estimate PWV, blood pressure, etc., based on signals from the sensors205aand205b, based on signals from the sensors205aand205c, or based on signals from the sensors205a,205band205c.

In the example shown inFIG.5B, both the apparatus500aand the apparatus500bare configured to be worn on a human finger. In this example, the sensor205aresides in the housing520aand the sensor205bresides in the housing520b. In this example, the control system106(not shown) of the apparatus500ais configured for wireless communication with the apparatus500b. In some examples, the control system106may be configured to estimate PWV, blood pressure, etc., based on signals from the sensors205aand205b.

FIG.6shows examples of possible sensor locations on a human wrist and finger. As with other disclosed examples, the types, numbers, sizes and arrangements of elements that are described with reference toFIG.6are merely examples.

FIG.6shows examples of bones and arteries in a wrist and hand, with3of the4possible sensor locations corresponding to positions along the radial artery. In some alternative examples, 2 or more sensor locations may correspond to positions along another artery, such as the ulnar artery.

According to some examples, an instance of the sensor205amay be positioned at location1and an instance of the sensor205bmay be positioned at location2, location3or location4. The sensors205aand205bmay be as described with reference toFIG.2A. In some such examples, at least the sensor205ais, or includes, a PAPG sensor. However, in some examples the sensor205amay be, or may include, one of the other types of sensors disclosed herein. According to this example, the sensor205aincludes an array of sensor elements602, which in this instance are, or include, ultrasonic receiver elements of an ultrasonic receiver system102. In this example—as suggested by the dashed outlines—the sensor205balso may include an array of sensor elements602. The type of sensor elements602will depend in the particular implementation(s) of the sensor205b. Although the arrays of sensor elements602shown inFIG.6are linear arrays, in some examples the arrays of sensor elements602may be two-dimensional arrays. Arrays of sensor elements have the potential advantage—as compared to individual sensors—of being able to more clearly identify the position of a blood vessel, such as the radial artery. However, according to some alternative examples, the sensor205a, the sensor205b, or both, may be individual sensors.

In some alternative examples, an instance of the sensor205amay be positioned at location1, location2or location3. In some such examples, an instance of the sensor205bmay be positioned at one or more of the other 3 locations. According to some such examples, an instance of the sensor205bmay be positioned at two of the other 3 locations or at all 3 of the other 3 locations.

In some examples, the sensor(s) at location1, location2, location3, or combinations thereof, may reside in a single apparatus that is configured to be attached to the wrist605, such as a smart watch, a health monitoring device with a wrist band, etc. In this example, if a sensor resides at location4, the sensor will reside in an apparatus that is configured to be attached to a human finger. In some alternative implementations, location4may be at a corresponding position of another digit of the hand610, such as the thumb615, the middle finger620, etc.

FIG.7is a flow diagram that shows examples of some disclosed operations. The blocks ofFIG.7may, for example, be performed by the apparatus100ofFIG.1or by a similar apparatus. As with other methods disclosed herein, the method outlined inFIG.7may include more or fewer blocks than indicated. Moreover, the blocks of methods disclosed herein are not necessarily performed in the order indicated. In some instances, one or more of the blocks shown inFIG.7may be performed concurrently.

In this example, block705involves receiving first sensor signals from at least a first ultrasonic sensor of an ultrasonic receiver system. In this example, the first sensor signals include ultrasonic receiver signals corresponding to ultrasonic waves generated by a target object responsive to light from a light source system. The target object may be a finger, a wrist, etc., depending on the particular example. The first sensor signals may, in some examples, be received from an instance of the sensor205athat is disclosed herein.

According to this example, block710involves estimating one or more blood vessel features based on the first ultrasonic receiver signals. The one or more blood vessel features may include blood vessel diameter, blood vessel distension, volumetric flow, or combinations thereof.

According to this example, block715involves receiving second sensor signals from a second sensor. The second sensor signals may, in some examples, be received from an instance of the sensor205bthat is disclosed herein.

In this example, block720involves estimating a pulse wave velocity based, at least in part, on the first ultrasonic receiver signals and the second sensor signals. According to this example, block725involves estimating blood pressure based, at least in part, on the one or more blood vessel features and the pulse wave velocity.

According to some examples, the second sensor signals may be received from a second device. However, in some examples, the second sensor signals may be received from a second sensor of the same device that includes the ultrasonic receiver system. In some examples, the second sensor signals may be signals from a photoplethysmography sensor, signals from a PAPG sensor, microphone signals, signals from an accelerometer, capacitive sensor signals, signals from a radio frequency sensor, signals from a magnetic sensor, electrocardiogram signals, signals from an ultrasonic sensor, signals from a pressure sensor, signals from a camera, or combinations thereof.

In some examples, the first sensor signals may correspond to ultrasonic waves generated within a person's wrist. In some such examples, the second sensor signals may be obtained from the person's finger. In some alternative examples, the second sensor signals may be obtained from the person's arm.

According to some examples, method700may involve estimating a distance between the first ultrasonic sensor and the second sensor. However, in some examples the distance between the first ultrasonic sensor and the second sensor may be known. In some such examples, a single device may include the first ultrasonic sensor and the second sensor.

In some examples, the first sensor signals, the second sensor signals, or both, may include signals from a sensor array. According to some examples, the sensor array may be a two-dimensional sensor array. According to some examples, method700may involve extracting and evaluating heart rate waveform (HRW) features.

FIG.8shows examples of heart rate waveform (HRW) features that may be extracted according to some implementations of the method ofFIG.10. The horizontal axis ofFIG.8represents time and the vertical axis represents signal amplitude. The cardiac period is indicated by the time between adjacent peaks of the HRW. The systolic and diastolic time intervals are indicated below the horizontal axis. During the systolic phase of the cardiac cycle, as a pulse propagates through a particular location along an artery, the arterial walls expand according to the pulse waveform and the elastic properties of the arterial walls. Along with the expansion is a corresponding increase in the volume of blood at the particular location or region, and with the increase in volume of blood an associated change in one or more characteristics in the region. Conversely, during the diastolic phase of the cardiac cycle, the blood pressure in the arteries decreases and the arterial walls contract. Along with the contraction is a corresponding decrease in the volume of blood at the particular location, and with the decrease in volume of blood an associated change in the one or more characteristics in the region.

The HRW features that are illustrated inFIG.8pertain to the width of the systolic and/or diastolic portions of the HRW curve at various “heights,” which are indicated by 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” of 50% of the maximum amplitude. In some implementations, the 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 implementations, additional HRW features may be used for blood pressure estimation. Such additional HRW features may, in some instances, include the sum and ratio of the SW and DW at one or more “heights,” e.g., (DW75+SW75), DW75/SW75, (DW66+SW66), DW66/SW66, (DW50+SW50), DW50/SW50, (DW33+SW33), DW33/SW33, (DW25+SW25), DW25/SW25 and/or (DW10+SW10), DW10/SW10. Other implementations may use yet other HRW features for blood pressure estimation. Such additional HRW features may, in some instances, include sums, differences, ratios and/or other operations based on more than one “height,” such as (DW75+SW75)/(DW50+SW50), (DW50+SW50/(DW10+SW10), etc.

FIG.9shows examples of devices that may be used in a system for estimating blood pressure based, at least in part, on pulse transit time (PTT). As with other figures provided herein, the numbers, types and arrangements of elements are merely presented by way of example. According to this example, the system900includes at least two sensors. In this example, the system900includes at least an electrocardiogram sensor905and a device910that is configured to be mounted on a finger of the person901. In this example, the device910is, or includes, an apparatus configured to perform at least some PAPG methods disclosed herein. For example, the device910may be, or may include, the apparatus300ofFIG.3or a similar apparatus.

As noted in the graph920, the PAT includes two components, the pre-ejection period (PEP, the time needed to convert the electrical signal into a mechanical pumping force and isovolumetric contraction to open the aortic valves) and the PTT. The starting time for the PAT can be estimated based on the QRS complex—an electrical signal characteristic of the electrical stimulation of the heart ventricles. As shown by the graph920, in this example the beginning of a pulse arrival time (PAT) may be calculated according to an R-Wave peak measured by the electrocardiogram sensor905and the end of the PAT may be detected via analysis of signals provided by the device910. In this example, the end of the PAT is assumed to correspond with an intersection between a tangent to a local minimum value detected by the device910and a tangent to a maximum slope/first derivative of the sensor signals after the time of the minimum value.

There are many known algorithms for blood pressure estimation based on the PTT and/or the PAT, some of which are summarized in Table 1 and described in the corresponding text on pages 5-10 of Sharma, M., et al.,Cuff-Less and Continuous Blood Pressure Monitoring: a Methodological Review(“Sharma”), in Multidisciplinary Digital Publishing Institute (MDPI) Technologies 2017, 5, 21, both of which are hereby incorporated by reference.

Some previously-disclosed methods have involved calculating blood pressure according to one or more of the equations shown in Table 1 of Sharma, or other known equations, based on a PTT and/or PAT measured by a sensor system that includes a PPG sensor. As noted above, some disclosed PAPG-based implementations are configured to distinguish artery HRWs from other HRWs. Such implementations may provide more accurate measurements of the PTT and/or PAT, relative to those measured by a PPG sensor. Therefore, disclosed PAPG-based implementations may provide more accurate blood pressure estimations, even when the blood pressure estimations are based on previously-known formulae.

Other implementations of the system900may not include the electrocardiogram sensor905. In some such implementations, the device915, which is configured to be mounted on a wrist of the person901, may be, or may include, an apparatus configured to perform at least some PAPG methods disclosed herein. For example, the device915may be, or may include, the apparatus200ofFIG.2or a similar apparatus. According to some such examples, the device915may include a light source system and two or more ultrasonic receivers. One example is described below with reference toFIG.11A. In some examples, the device915may include an array of ultrasonic receivers.

In some implementations of the system900that do not include the electrocardiogram sensor905, the device910may include a light source system and two or more ultrasonic receivers. One example is described below with reference toFIG.11B.

FIG.10shows a cross-sectional side view of a diagrammatic representation of a portion of an artery1000through which a pulse1002is propagating. The block arrow inFIG.10shows the direction of blood flow and pulse propagation. As diagrammatically shown, the propagating pulse1002causes strain in the arterial walls1004, which is manifested in the form of an enlargement in the diameter (and consequently the cross-sectional area) of the arterial walls-referred to as “distension.” The spatial length L of an actual propagating pulse along an artery (along the direction of blood flow) is typically comparable to the length of a limb, such as the distance from a subject's shoulder to the subject's wrist or finger, and is generally less than one meter (m). However, the length L of a propagating pulse can vary considerably from subject to subject, and for a given subject, can vary significantly over durations of time depending on various factors. The spatial length L of a pulse will generally decrease with increasing distance from the heart until the pulse reaches capillaries.

As described above, some particular implementations relate to devices, systems and methods for estimating blood pressure or other cardiovascular characteristics based on estimates of an arterial distension waveform. The terms “estimating,” “measuring,” “calculating,” “inferring,” “deducing,” “evaluating,” “determining” and “monitoring” may be used interchangeably herein where appropriate unless otherwise indicated. Similarly, derivations from the roots of these terms also are used interchangeably where appropriate; for example, the terms “estimate,” “measurement,” “calculation,” “inference” and “determination” also are used interchangeably herein. In some implementations, the pulse wave velocity (PWV) of a propagating pulse may be estimated by measuring the pulse transit time (PTT) of the pulse as it propagates from a first physical location along an artery to another more distal second physical location along the artery. It will be appreciated that this PTT is different from the PTT that is described above with reference toFIG.15. However, either version of the PTT may be used for the purpose of blood pressure estimation. Assuming that the physical distance ΔD between the first and the second physical locations is ascertainable, the PWV can be estimated as the quotient of the physical spatial distance ΔD traveled by the pulse divided by the time (PTT) the pulse takes in traversing the physical spatial distance ΔD. Generally, a first sensor positioned at the first physical location is used to determine a starting time (also referred to herein as a “first temporal location”) at which point the pulse arrives at or propagates through the first physical location. A second sensor at the second physical location is used to determine an ending time (also referred to herein as a “second temporal location”) at which point the pulse arrives at or propagates through the second physical location and continues through the remainder of the arterial branch. In such examples, the PTT represents the temporal distance (or time difference) between the first and the second temporal locations (the starting and the ending times).

The fact that measurements of the arterial distension waveform are performed at two different physical locations implies that the estimated PWV inevitably represents an average over the entire path distance ΔD through which the pulse propagates between the first physical location and the second physical location. More specifically, the PWV generally depends on a number of factors including the density of the blood ρ, the stiffness E of the arterial wall (or inversely the elasticity), the arterial diameter, the thickness of the arterial wall, and the blood pressure. Because both the arterial wall elasticity and baseline resting diameter (for example, the diameter at the end of the ventricular diastole period) vary significantly throughout the arterial system, PWV estimates obtained from PTT measurements are inherently average values (averaged over the entire path length ΔD between the two locations where the measurements are performed).

In traditional methods for obtaining PWV, the starting time of the pulse has been obtained at the heart using an electrocardiogram (ECG) sensor, which detects electrical signals from the heart. For example, the starting time can be estimated based on the QRS complex—an electrical signal characteristic of the electrical stimulation of the heart ventricles. In such approaches, the ending time of the pulse is typically obtained using a different sensor positioned at a second location (for example, a finger). As a person having ordinary skill in the art will appreciate, there are numerous arterial discontinuities, branches, and variations along the entire path length from the heart to the finger. The PWV can change by as much as or more than an order of magnitude along various stretches of the entire path length from the heart to the finger. As such, PWV estimates based on such long path lengths are unreliable.

In various implementations described herein, PTT estimates are obtained based on measurements (also referred to as “arterial distension data” or more generally as “sensor data”) associated with an arterial distension signal obtained by each of a first arterial distension sensor1006and a second arterial distension sensor1008proximate first and second physical locations, respectively, along an artery of interest. In some particular implementations, the first arterial distension sensor1006and the second arterial distension sensor1008are advantageously positioned proximate first and second physical locations between which arterial properties of the artery of interest, such as wall elasticity and diameter, can be considered or assumed to be relatively constant. In this way, the PWV calculated based on the PTT estimate is more representative of the actual PWV along the particular segment of the artery. In turn, the blood pressure P estimated based on the PWV is more representative of the true blood pressure. In some implementations, the magnitude of the distance ΔD of separation between the first arterial distension sensor1006and the second arterial distension sensor1008(and consequently the distance between the first and the second locations along the artery) can be in the range of about 1 centimeter (cm) to tens of centimeters-long enough to distinguish the arrival of the pulse at the first physical location from the arrival of the pulse at the second physical location, but close enough to provide sufficient assurance of arterial consistency. In some specific implementations, the distance ΔD between the first and the second arterial distension sensors1006and1008can be in the range of about 1 cm to about 30 cm, and in some implementations, less than or equal to about 20 cm, and in some implementations, less than or equal to about 10 cm, and in some specific implementations less than or equal to about 5 cm. In some other implementations, the distance ΔD between the first and the second arterial distension sensors1006and1008can be less than or equal to 1 cm, for example, about 0.1 cm, about 0.25 cm, about 0.5 cm or about 0.75 cm. By way of reference, a typical PWV can be about 15 meters per second (m/s). Using an ambulatory monitoring device in which the first and the second arterial distension sensors1006and1008are separated by a distance of about 5 cm, and assuming a PWV of about 15 m/s implies a PTT of approximately 3.3 milliseconds (ms).

The value of the magnitude of the distance ΔD between the first and the second arterial distension sensors1006and1008, respectively, can be preprogrammed into a memory within a monitoring device that incorporates the sensors (for example, such as a memory of, or a memory configured for communication with, the control system306that is described above with reference toFIG.3). As will be appreciated by a person of ordinary skill in the art, the spatial length L of a pulse can be greater than the distance ΔD from the first arterial distension sensor1006to the second arterial distension sensor1008in such implementations. As such, although the diagrammatic pulse1002shown inFIG.10is shown as having a spatial length L comparable to the distance between the first arterial distension sensor1006and the second arterial distension sensor1008, in actuality each pulse can typically have a spatial length L that is greater and even much greater than (for example, about an order of magnitude or more than) the distance ΔD between the first and the second arterial distension sensors1006and1008.

Sensing Architecture and Topology

In some implementations of the ambulatory monitoring devices disclosed herein, both the first arterial distension sensor1006and the second arterial distension sensor1008are sensors of the same sensor type. In some such implementations, the first arterial distension sensor1006and the second arterial distension sensor1008are identical sensors. In such implementations, each of the first arterial distension sensor1006and the second arterial distension sensor1008utilizes the same sensor technology with the same sensitivity to the arterial distension signal caused by the propagating pulses, and has the same time delays and sampling characteristics. In some implementations, each of the first arterial distension sensor1006and the second arterial distension sensor1008is configured for photoacoustic plethysmography (PAPG) sensing, e.g., as disclosed elsewhere herein. Some such implementations include a light source system and two or more ultrasonic receivers, which may be instances of the light source system104and the receiver system102ofFIG.1. In some implementations, each of the first arterial distension sensor1006and the second arterial distension sensor1008is configured for ultrasound sensing via the transmission of ultrasonic signals and the receipt of corresponding reflections. In some alternative implementations, each of the first arterial distension sensor1006and the second arterial distension sensor1008may be configured for impedance plethysmography (IPG) sensing, also referred to in biomedical contexts as bioimpedance sensing. In various implementations, whatever types of sensors are utilized, each of the first and the second arterial distension sensors1006and1008broadly functions to capture and provide arterial distension data indicative of an arterial distension signal resulting from the propagation of pulses through a portion of the artery proximate to which the respective sensor is positioned. For example, the arterial distension data can be provided from the sensor to a processor in the form of voltage signal generated or received by the sensor based on an ultrasonic signal or an impedance signal sensed by the respective sensor.

As described above, during the systolic phase of the cardiac cycle, as a pulse propagates through a particular location along an artery, the arterial walls expand according to the pulse waveform and the elastic properties of the arterial walls. Along with the expansion is a corresponding increase in the volume of blood at the particular location or region, and with the increase in volume of blood an associated change in one or more characteristics in the region. Conversely, during the diastolic phase of the cardiac cycle, the blood pressure in the arteries decreases and the arterial walls contract. Along with the contraction is a corresponding decrease in the volume of blood at the particular location, and with the decrease in volume of blood an associated change in the one or more characteristics in the region.

In the context of bioimpedance sensing (or impedance plethysmography), the blood in the arteries has a greater electrical conductivity than that of the surrounding or adjacent skin, muscle, fat, tendons, ligaments, bone, lymph or other tissues. The susceptance (and thus the permittivity) of blood also is different from the susceptances (and permittivities) of the other types of surrounding or nearby tissues. As a pulse propagates through a particular location, the corresponding increase in the volume of blood results in an increase in the electrical conductivity at the particular location (and more generally an increase in the admittance, or equivalently a decrease in the impedance). Conversely, during the diastolic phase of the cardiac cycle, the corresponding decrease in the volume of blood results in an increase in the electrical resistivity at the particular location (and more generally an increase in the impedance, or equivalently a decrease in the admittance).

A bioimpedance sensor generally functions by applying an electrical excitation signal at an excitation carrier frequency to a region of interest via two or more input electrodes, and detecting an output signal (or output signals) via two or more output electrodes. In some more specific implementations, the electrical excitation signal is an electrical current signal injected into the region of interest via the input electrodes. In some such implementations, the output signal is a voltage signal representative of an electrical voltage response of the tissues in the region of interest to the applied excitation signal. The detected voltage response signal is influenced by the different, and in some instances time-varying, electrical properties of the various tissues through which the injected excitation current signal is passed. In some implementations in which the bioimpedance sensor is operable to monitor blood pressure, heartrate or other cardiovascular characteristics, the detected voltage response signal is amplitude- and phase-modulated by the time-varying impedance (or inversely the admittance) of the underlying arteries, which fluctuates synchronously with the user's heartbeat as described above. To determine various biological characteristics, information in the detected voltage response signal is generally demodulated from the excitation carrier frequency component using various analog or digital signal processing circuits, which can include both passive and active components.

In some examples incorporating ultrasound sensors, measurements of arterial distension may involve directing ultrasonic waves into a limb towards an artery, for example, via one or more ultrasound transducers. Such ultrasound sensors also are configured to receive reflected waves that are based, at least in part, on the directed waves. The reflected waves may include scattered waves, specularly reflected waves, or both scattered waves and specularly reflected waves. The reflected waves provide information about the arterial walls, and thus the arterial distension.

In some implementations, regardless of the type of sensors utilized for the first arterial distension sensor1006and the second arterial distension sensor1008, both the first arterial distension sensor1006and the second arterial distension sensor1008can be arranged, assembled or otherwise included within a single housing of a single ambulatory monitoring device. As described above, the housing and other components of the monitoring device can be configured such that when the monitoring device is affixed or otherwise physically coupled to a subject, both the first arterial distension sensor1006and the second arterial distension sensor1008are in contact with or in close proximity to the skin of the user at first and second locations, respectively, separated by a distance ΔD, and in some implementations, along a stretch of the artery between which various arterial properties can be assumed to be relatively constant. In various implementations, the housing of the ambulatory monitoring device is a wearable housing or is incorporated into or integrated with a wearable housing. In some specific implementations, the wearable housing includes (or is connected with) a physical coupling mechanism for removable non-invasive attachment to the user. The housing can be formed using any of a variety of suitable manufacturing processes, including injection molding and vacuum forming, among others. In addition, the housing can be made from any of a variety of suitable materials, including, but not limited to, plastic, metal, glass, rubber and ceramic, or combinations of these or other materials. In particular implementations, the housing and coupling mechanism enable full ambulatory use. In other words, some implementations of the wearable monitoring devices described herein are noninvasive, not physically-inhibiting and generally do not restrict the free uninhibited motion of a subject's arms or legs, enabling continuous or periodic monitoring of cardiovascular characteristics such as blood pressure even as the subject is mobile or otherwise engaged in a physical activity. As such, the ambulatory monitoring device facilitates and enables long-term wearing and monitoring (for example, over days, weeks or a month or more without interruption) of one or more biological characteristics of interest to obtain a better picture of such characteristics over extended durations of time, and generally, a better picture of the user's health.

In some implementations, the ambulatory monitoring device can be positioned around a wrist of a user with a strap or band, similar to a watch or fitness/activity tracker.FIG.11Ashows an example ambulatory monitoring device1100designed to be worn around a wrist according to some implementations. In the illustrated example, the monitoring device1100includes a housing1102integrally formed with, coupled with or otherwise integrated with a wristband1104. The first and the second arterial distension sensors1106and1108may, in some instances, each include an instance of the ultrasonic receiver system302and a portion of the light source system304that are described above with reference toFIG.3. In this example, the ambulatory monitoring device1100is coupled around the wrist such that the first and the second arterial distension sensors1106and1108within the housing1102are each positioned along a segment of the radial artery1110(note that the sensors are generally hidden from view from the external or outer surface of the housing facing the subject while the monitoring device is coupled with the subject, but exposed on an inner surface of the housing to enable the sensors to obtain measurements through the subject's skin from the underlying artery). Also as shown, the first and the second arterial distension sensors1106and1108are separated by a fixed distance ΔD. In some other implementations, the ambulatory monitoring device1100can similarly be designed or adapted for positioning around a forearm, an upper arm, an ankle, a lower leg, an upper leg, or a finger (all of which are hereinafter referred to as “limbs”) using a strap or band.

FIG.11Bshows an example ambulatory monitoring device1100designed to be worn on a finger according to some implementations. The first and the second arterial distension sensors1106and1108may, in some instances, each include an instance of the ultrasonic receiver102and a portion of the light source system103that are described above with reference toFIG.1.

In some other implementations, the ambulatory monitoring devices disclosed herein can be positioned on a region of interest of the user without the use of a strap or band. For example, the first and the second arterial distension sensors1106and1108and other components of the monitoring device can be enclosed in a housing that is secured to the skin of a region of interest of the user using an adhesive or other suitable attachment mechanism (an example of a “patch” monitoring device).

FIG.11Cshows an example ambulatory monitoring device1100designed to reside on an earbud according to some implementations. According to this example, the ambulatory monitoring device1100is coupled to the housing of an earbud1120. The first and second arterial distension sensors1106and1108may, in some instances, each include an instance of the ultrasonic receiver302and a portion of the light source system304that are described above with reference toFIG.3.

Implementation examples are described in the following numbered clauses:1. An apparatus, including: a light source system configured for providing light to a target object on an outer surface of the apparatus; an ultrasonic receiver system configured to receive ultrasonic waves generated by the target object responsive to the light from the light source system; and a control system configured to: receive first sensor signals from at least a first ultrasonic sensor of the ultrasonic receiver system, the first sensor signals including ultrasonic receiver signals; estimate one or more blood vessel features based on the first sensor signals; receive second sensor signals from a second sensor; estimate a pulse wave velocity based, at least in part, on the first sensor signals and the second sensor signals; and estimate blood pressure based, at least in part, on the one or more blood vessel features and the pulse wave velocity.2. The apparatus of clause 1, where the apparatus is configured to be worn by, or attached to, a person.3. The apparatus of clause 2, where the apparatus includes a watch, an ear bud, headphones, an ear clip, a chest strap, an arm strap, a head band, or eye wear.4. The apparatus of clause 2 or clause 3, further including an interface system, where the second sensor signals are received, via the interface system, from a second device.5. The apparatus of clause 4, where the apparatus is configured to be worn on the person's wrist and where the second device is configured to be worn by, or attached to, the person's finger or the person's arm.6. The apparatus of clause 4 or clause 5, where the control system is further configured to estimate a distance between the first ultrasonic sensor and the second sensor.7. The apparatus of any one of clauses 1-6, where the second sensor signals comprise signals from a photoplethysmography sensor, signals from a photoacoustic plethysmography sensor, microphone signals, signals from an accelerometer, capacitive sensor signals, signals from a radio frequency sensor, signals from a magnetic sensor, electrocardiogram signals, signals from an ultrasonic sensor, signals from a pressure sensor, signals from a camera, or combinations thereof.8. The apparatus of any one of clauses 1-7, where the apparatus includes the second sensor.9. The apparatus of clause 8, where the apparatus is configured to be worn by, or attached to, a person.10. The apparatus of clause 8, where the apparatus is a component of a weighing scale, a component of an automobile, a component of an exercise machine or a component of a game controller.11. The apparatus of any one of clauses 8-10, where the second sensor is a component of the ultrasonic receiver system.12. The apparatus of clause 11, where the ultrasonic receiver system includes an array of ultrasonic receiver elements.13. The apparatus of any one of clauses 1-12, where the one or more blood vessel features include blood vessel diameter, blood vessel distension, volumetric flow, or combinations thereof.14. The apparatus of clause any one of clauses 1-13, where the pulse wave velocity is a regional pulse wave velocity and where the control system is further configured to estimate a local pulse wave velocity.15. The apparatus of any one of clauses 1-14, where the second sensor signals comprise signals from a sensor array.16. The apparatus of clause 15, where the sensor array is a two-dimensional sensor array.17. An apparatus, including: a light source system configured for providing light to a target object on an outer surface of the apparatus; an ultrasonic receiver system configured to receive ultrasonic waves generated by the target object responsive to the light from the light source system; and control means for: receiving first sensor signals from at least a first ultrasonic sensor of the ultrasonic receiver system, the first sensor signals including ultrasonic receiver signals; estimating one or more blood vessel features based on the first sensor signals; receiving second sensor signals from a second sensor; estimating a pulse wave velocity based, at least in part, on the first sensor signals and the second sensor signals; and estimating blood pressure based, at least in part, on the one or more blood vessel features and the pulse wave velocity.18. The apparatus of clause 17, where the apparatus is configured to be worn by, or attached to, a person.19. The apparatus of clause 18, where the apparatus includes a watch, an ear bud, headphones, an ear clip, a chest strap, an arm strap, a head band, or eye wear.20. The apparatus of clause 18 or clause 19, further including an interface system, where the second sensor signals are received, via the interface system, from a second device.21. A method, including: receiving first sensor signals from at least a first ultrasonic sensor of an ultrasonic receiver system, the first sensor signals including ultrasonic receiver signals corresponding to ultrasonic waves generated by a target object responsive to light from a light source system; estimating one or more blood vessel features based on the first ultrasonic receiver signals; receiving second sensor signals from a second sensor; estimating a pulse wave velocity based, at least in part, on the first ultrasonic receiver signals and the second sensor signals; and estimating blood pressure based, at least in part, on the one or more blood vessel features and the pulse wave velocity.22. The method of clause 21, where the second sensor signals are received from a second device.23. The method of clause 22, where the first sensor signals correspond to ultrasonic waves generated within a person's wrist and where the second sensor signals are obtained from the person's finger or the person's arm.24. The method of clause 22 or clause 23, further including estimating a distance between the first ultrasonic sensor and the second sensor.25. The method of any one of clauses 21-, where the second sensor signals comprise signals from a photoplethysmography sensor, signals from a photoacoustic plethysmography sensor, microphone signals, signals from an accelerometer, capacitive sensor signals, signals from a radio frequency sensor, signals from a magnetic sensor, electrocardiogram signals, signals from an ultrasonic sensor, signals from a pressure sensor, signals from a camera, or combinations thereof.26. The method of any one of clauses 21-25, where the one or more blood vessel features include blood vessel diameter, blood vessel distension, volumetric flow, or combinations thereof.27. The method of any one of clauses 21-26, where the pulse wave velocity is a regional pulse wave velocity and where the method involves estimating a local pulse wave velocity.28. The method of any one of clauses 21-27, where the second sensor signals comprise signals from a sensor array.29. The method of clause 28, where the sensor array is a two-dimensional sensor array.30. The method of any one of clauses 21-29, where receiving the first sensor signals involves receiving signals from an array of ultrasonic sensors of the ultrasonic receiver system.

It will be understood that unless features in any of the particular described implementations are expressly identified as incompatible with one another or the surrounding context implies that they are mutually exclusive and not readily combinable in a complementary and/or supportive sense, the totality of this disclosure contemplates and envisions that specific features of those complementary implementations may be selectively combined to provide one or more comprehensive, but slightly different, technical solutions. It will therefore be further appreciated that the above description has been given by way of example only and that modifications in detail may be made within the scope of this disclosure.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Further, the drawings may schematically depict one more example processes in the form of a flow diagram. However, other operations that are not depicted can be incorporated in the example processes that are schematically illustrated. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the illustrated operations. Moreover, various ones of the described and illustrated operations can itself include and collectively refer to a number of sub-operations. For example, each of the operations described above can itself involve the execution of a process or algorithm. Furthermore, various ones of the described and illustrated operations can be combined or performed in parallel in some implementations. Similarly, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations. As such, other implementations 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 desirable results.