Patent Application
20250090029
This disclosure relates generally to photoacoustic devices and more specifically to controlling light sources of photoacoustic devices.
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 are, or include, photoacoustic devices. Although some previously-deployed photoacoustic devices and systems can provide acceptable results, improved photoacoustic devices and systems would be desirable.
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, a receiver system and a control system configured for electrical communication with the light source system and the receiver system. The receiver system may be, or may include, an ultrasonic receiver system. In some examples, the receiver system may include an array of ultrasonic receiver elements. 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.
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. The control system may be configured to control the light source system to direct two or more pulse groups of light towards a target object during a total light transmission time interval. The target object may be part of a human body or an animal body. In some examples, each pulse group time interval within the total light transmission time interval may be separated from a successive pulse group time interval by an “off time interval” during which no light is being transmitted towards the target object. The control system may be configured to receive, via the receiver system, receiver signals corresponding to acoustic waves caused by photoacoustic (PA) responses of a target object to the two or more pulse groups. The control system may be configured to determine one or more heart rate waveforms of the human or animal body based on the receiver signals.
In some examples, the control system may be configured to estimate one or more cardiac features based, at least in part, on the one or more heart rate waveforms. In some such examples, estimating the one or more cardiac features may involve estimating blood pressure.
According to some examples, an exposure duration equals one pulse group time interval plus one off time interval. In some such examples, the average optical power density during the exposure duration may be in a range from 0.01-1.00 W/cm2. In some examples, the average optical power density during the exposure duration is less than a maximum permissible exposure (MPE) published by American National Standards Institute for Safe Use of Lasers corresponding to wavelength(s) of transmitted light.
Other innovative aspects of the subject matter described in this disclosure can be implemented in a method. The method may involve directing two or more pulse groups of light towards a target object during a total light transmission time interval, the target object being part of a human or animal body. In some examples, each pulse group time interval within the total light transmission time interval may be separated from a successive pulse group time interval by an off time interval during which no light is being transmitted towards the target object. The method may involve receiving acoustic signals corresponding to photoacoustic (PA) responses of a target object to the two or more pulse groups and determining one or more heart rate waveforms of the human or animal body based on the acoustic signals.
In some examples, the method may involve estimating one or more cardiac features based, at least in part, on the one or more heart rate waveforms. In some such examples, estimating the one or more cardiac features may involve estimating blood pressure.
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.
Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings and the claims. Note that the relative dimensions of the following figures may not be drawn to scale.
Like reference numbers and designations in the various drawings indicate like elements.
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, such as photoacoustic plethysmography (PAPG)-capable 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 PAPG-based devices. One challenge is that the signal-to-noise ratio (SNR) for signals of interest, such as signals corresponding to ultrasound caused by the photoacoustic response of arterial walls, is low. For example, the signals corresponding to arterial walls are generally significantly lower in amplitude than signals corresponding to the photoacoustic response of skin. SNR can be enhanced by reducing uncorrelated noise. Some currently-implemented methods involve providing sequential pulses of laser light to a target object using a continuous pulse repetition frequency (PRF), then averaging data corresponding to photoacoustic (PA) responses of the target object over multiple (such as 100 or more) samples. SNR can also be enhanced by increasing the power of the light source. However, it is essential to avoid harming a person's skin by using an overly powerful light source, such as a laser light source, for a PAPG-based method. The American National Standards Institute for Safe Use of Lasers publishes maximum permissible exposure (MPE) standards indicating average power limits and single-pulse limits for various wavelengths of transmitted laser light for the safety of skin and eyes exposed to laser light.
Some disclosed devices include a light source system, an ultrasonic receiver system and a control system. According to some implementations, the control system may be configured to control the light source system according to a pulse group-based drive scheme. Some disclosed examples involve directing two or more pulse groups of light towards a target object during a total light transmission time interval. In some such examples, each pulse group time interval within the total light transmission time interval may be separated from a successive pulse group time interval by what will be referred to herein as an “off time interval.” The off time interval is a time interval during which no light is being transmitted towards the target object. However, in some alternative examples, instead of the off time interval there may be a “lower-intensity” time interval between successive pulse group time intervals during which the light being transmitted towards the target object has a much lower intensity than the light transmitted during the pulse group time intervals, a “lower-PRY” time interval between successive pulse group time intervals during which the light being transmitted towards the target object has a much lower PRF, or both. In some alternative examples, the lower-intensity interval may be a time interval during which the light being transmitted towards the target object has one tenth of the intensity of light transmitted during the pulse group time intervals, 1/100th of the intensity of light transmitted during the pulse group time intervals, 1/1000th of the intensity of light transmitted during the pulse group time intervals, 1/10000th of the intensity of light transmitted during the pulse group time intervals, etc. In some alternative examples, the time interval between successive pulse group time intervals may be a time interval during which the light being transmitted towards the target object has the same intensity as the light transmitted during the pulse group time intervals, but which is a “lower-PRY” time interval during which the light is transmitted at one tenth of the PRF, 1/100th of the PRF, 1/1000th of the PRF, 1/10000th of the PRF, etc. In some implementations, the control system may be configured for receiving receiver signals corresponding to acoustic waves caused by photoacoustic (PA) responses of a target object to the two or more pulse groups and for determining one or more heart rate waveforms, one or more blood vessel features, or both, based on the receiver signals. In some examples, the control system may be configured for estimating one or more cardiac features based, at least in part, on the one or more heart rate waveforms, the one or more blood vessel features, or both. According to some examples, estimating the one or more cardiac features may involve estimating blood pressure.
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 include PAPG-capable devices that can provide a higher SNR, as compared to previously-deployed PAPG-capable devices. Some such examples involve a pulse group-based drive scheme for the light source system in which each pulse group time interval within the total light transmission time interval is separated from a successive pulse group time interval by an off time interval. Some examples involve increasing the PRF during a pulse group time interval, as compared to the PRF used in previously-implemented continuous PRF drive schemes. Some such examples have the potential benefits of decreasing uncorrelated noise and thereby increasing the SNR, while remaining below the MPE limits for maximum average optical power density, etc. Moreover, some disclosed examples have the potential benefit of saving power by driving the light source system for less time and potentially using less overall power.
According to some examples, the platen 101 (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 platen 101.
In some examples, at least a portion of the outer surface of the platen 101 may have an acoustic impedance that is configured to approximate an acoustic impedance of human skin. The portion of the outer surface of the platen 101 may, 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 platen 101 may 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 platen 101 may be configured to conform to a surface of human skin. In some such examples, at least an outer surface of the platen 101 may have material properties like those of putty or chewing gum.
In some examples, at least a portion of the platen 101 may have an acoustic impedance that is configured to approximate an acoustic impedance of one or more receiver elements of the receiver system 102. According to some examples, a layer residing between the platen 101 and 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 platen 101 and 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 some examples, the receiver system 102 may include 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). In some examples, the receiver system 102 may include an array of ultrasonic receiver elements. The array may be a linear array, a two-dimensional array, etc. In some examples, the array may include an array of electrodes residing on a layer of piezoelectric material. The receiver system 102 may, 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 receiver system 102 may be, or may include, an ultrasonic receiver array. In some examples, the apparatus 100 may 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 system 104 may include one or more light-emitting diodes (LEDs). In some implementations, the light source system 104 may include one or more laser diodes. According to some implementations, the light source system 104 may include one or more vertical-cavity surface-emitting lasers (VCSELs). In some implementations, the light source system 104 may 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 system 104 may, 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 system 104 may, in some examples, be configured to transmit light in one or more wavelength ranges. In some examples, the light source system 104 may configured for transmitting light in a wavelength range of 500 to 600 nanometers. According to some examples, the light source system 104 may configured for transmitting light in a wavelength range of 800 to 950 nanometers.
The light source system 104 may include various types of drive circuitry, depending on the particular implementation. In some disclosed implementations, the light source system 104 may include at least one multi-junction laser diode, which may produce less noise than single-junction laser diodes. In some examples, the light source system 104 may 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 system 104 may 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 system 104 may 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 system 104 may 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 system 106 may control the wavelength(s) of light emitted by the light source system 104 to 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 receiver system 102. 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 system 104 may 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 system 104 may 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 system 104 may 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 system 104 at 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 system 104. 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 system 106 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. The control system 106 also 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 apparatus 100 may have a memory system that includes one or more memory devices, though the memory system is not shown in
In some examples, the control system 106 may be configured to control the light source system 104 to direct two or more pulse groups of light towards a target object during a total light transmission time interval. In some such examples, each pulse group time interval within the total light transmission time interval may be separated from a successive pulse group time interval by an “off time interval.” In some instances, the off time interval may be a time interval during which no light is being transmitted towards the target object. However, in some alternative examples, the time interval between successive pulse group time intervals may be a time interval during which the light being transmitted towards the target object has much lower intensity than the light transmitted during the pulse group time intervals, a much lower PRF, or both. According to some alternative examples, the time interval between successive pulse group time intervals may be a time interval during which the light being transmitted towards the target object has an intensity lower than a first threshold, a PRF lower than a second threshold, or both. In some alternative examples, the time interval between successive pulse group time intervals may be a lower-intensity time interval during which the light being transmitted towards the target object has one tenth of the intensity of light transmitted during the pulse group time intervals, 1/100th of the intensity of light transmitted during the pulse group time intervals, 1/1000th of the intensity of light transmitted during the pulse group time intervals, 1/10000th of the intensity of light transmitted during the pulse group time intervals, etc. In some alternative examples, the time interval between successive pulse group time intervals may be a “lower-PRF” time interval during which the light being transmitted towards the target object has the same intensity as the light transmitted during the pulse group time intervals, but one tenth of the PRF, 1/100th of the PRF, 1/1000th of the PRF, 1/10000th of the PRF, etc. In some alternative examples, the time interval between successive pulse group time intervals may be a time interval during which the light being transmitted towards the target object has a different intensity—for example, a lower intensity—than the light transmitted during the pulse group time intervals and is also transmitted at a different PRF (for example, a lower PRF).
In some implementations, the control system 106 may be configured for receiving receiver signals from the receiver system 102 corresponding to acoustic waves caused by photoacoustic (PA) responses of a target object to the two or more pulse groups and for determining one or more heart rate waveforms, one or more blood vessel features, or both, based on the receiver signals. In some examples, the control system 106 may be configured for estimating one or more cardiac features based, at least in part, on the one or more heart rate waveforms, the one or more blood vessel features, or both. According to some examples, estimating the one or more cardiac features may involve estimating blood pressure. In some examples, the control system 106 may be configured for receiving receiver signals from the receiver system 102 corresponding to acoustic waves caused by PA responses of a target object to the two or more pulse groups and for determining one or more cardiac features, such as blood pressure, based on the receiver signals. In some such examples, the control system 106 may be configured for determining one or more cardiac features without an intermediate process of determining one or more heart rate waveforms, one or more blood vessel features, or both, based on the receiver signals. In some examples, the control system 106 may be configured to implement a neural network that has been trained to estimate one or more cardiac features, potentially including blood pressure, using the receiver signals as input. The neural network may, for example, have been trained using blood pressure measurements from a blood pressure measuring device, such as a cuff-based, catheter-based or other blood pressure measuring device, as the “ground truth” for the neural network training process.
As noted elsewhere, according to some examples the receiver system 102 may include an array of receiver elements. In some such examples, the control system 106 may be configured to apply a receiver-side beamforming process to the ultrasonic receiver signals, to produce a beamformed ultrasonic receiver image. According to some examples, the control system 106 may be configured to detect a blood vessel within the targe object based, at least in part, on the beamformed ultrasonic receiver image. In some such examples, the control system 106 may be configured to estimate one or more blood vessel features based, at least in part, on the beamformed ultrasonic receiver image. In some examples, the control system 106 may be configured to estimate one or more cardiac features based, at least in part, on one or more arterial signals, on the blood vessel features. According to some examples, the cardiac features may be, or may include, blood pressure.
Some implementations of the apparatus 100 may include the interface system 108. In some examples, the interface system 108 may include a wireless interface system. In some implementations, the interface system 108 may include a user interface system, one or more network interfaces, one or more interfaces between the control system 106 and a memory system and/or one or more interfaces between the control system 106 and one or more external device interfaces (e.g., ports or applications processors), or combinations thereof. According to some examples in which the interface system 108 is 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 system 108 may 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 system 108 may 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 system 108 may include an optical sensor system, one or more cameras, or a combination thereof.
According to some examples, the apparatus 100 may include a noise reduction system 110. For example, the noise reduction system 110 may include one or more mirrors that are configured to reflect light from the light source system 104 away from the receiver system 102. In some implementations, the noise reduction system 110 may 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 system 110 may include acoustic isolation material, which may reside between the light source system 104 and at least a portion of the receiver system 102, on at least a portion of the receiver system 102, or combinations thereof. In some examples, the noise reduction system 110 may 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 system 104, receiver system circuitry, or combinations thereof, that is received by the receiver system 102. 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 receiver system 102, the light source system 104, or both. Despite the fact that the receiver system 102, the light source system 104 and the noise reduction system 110 are shown in
The apparatus 100 may be used in a variety of different contexts, many examples of which are disclosed herein. For example, in some implementations a mobile device may include the apparatus 100. In some such examples, the mobile device may be a smart phone. In some implementations, a wearable device may include the apparatus 100. The wearable device may, for example, be a bracelet, an armband, a wristband, a watch, a ring, a headband or a patch. Accordingly, in some examples the apparatus 100 may be configured to be worn by, or attached to, a person.
However, for PAPG-enabled devices for human subjects that are used in the United States and use lasers as light sources, it is essential that the average power limits and single-pulse limits for the wavelength(s) of transmitted laser light be less than or equal to the maximum permissible exposure (MPE) standards published the American National Standards Institute for Safe Use of Lasers (the ANSI Z136.1 standards). For example, for a laser light source having a wavelength in the 400 nm to 1400 nm range and a total exposure duration t of 10−7 s to 10 s, the MPE is 1.1 CA t0.25, where CA is a wavelength-dependent correction factor. CA is 1.0 for wavelengths in the 400-700 nm range, 100.002(λ-700) for wavelengths in the 700-1050 nm range and 5.0 for wavelengths in the 1050-1400 nm range. For a laser light source having a wavelength in the 400 nm to 1400 nm range and a total exposure duration t of 10 s to 30,000 s, the MPE is 0.2 CA.
Uncorrelated noise amplitude is proportional to 1/sqrt(N), where N represents the number of samples. In some examples, N may be 100 or more. According to some continuous PRF examples in which the PRF is 3.2 KHz and the required effective PRF for a particular use case is 25 Hz, N=3.2 KHz/25 Hz=128 samples. Different implementations may involve averaging different numbers of samples.
One cannot have both high peak optical power density and high PRF, due to MPE constraints. Because peak optical power density is proportional to the resulting PA signal, some PAPG-enabled device implementations may prioritize peak optical power density at the expense of high PRF. Maximum average optical power density=peak optical power density*pulse width*PRF. Some continuous PRF implementations maximize peak optical power density and optimize pulse width for PA signal amplitude. Thus, PRF is capped, which in turn caps the noise reduction possible through averaging.
Different implementations may involve different parameters, including but not limited to different numbers of pulse groups in the total light transmission time interval. In various disclosed examples, the average optical power density during the exposure duration is less than the MPE published by American National Standards Institute (ANSI) for Safe Use of Lasers, such as the ANSI Z136.1 standards, as well as the International Standard for the Safety of Laser Products (IEC 60825-1), corresponding to wavelength(s) of transmitted light. In some such examples, the pulse group time interval may be in a range from 0.0014 to 7 seconds. According to some examples, the off time interval may be in a range from 2 to 5 seconds, for example 2.0 seconds, 2.5 seconds, 3.0 seconds, 3.5 seconds, 4.0 seconds, 4.5 seconds, 5.0 seconds, etc.
In some examples, the width of each light pulse in a pulse group may be in a range from 50 to 500 nanoseconds. According to some examples, the total light transmission time interval may be in a range from 9 and 25 seconds. In some examples, the PRF of light pulses in a pulse group may be in a range from 0.5 to 200 kilohertz. According to some examples, each light pulse in a pulse group may have a peak amplitude in a wavelength range from 600 to 1064 nanometers. In some examples, the average optical power density during the exposure duration may be in a range from 0.01-1.00 W/cm2.
In some examples in which PA techniques are used to estimate blood pressure, a pulse group time interval of multiple seconds (such as 2.5 seconds, 3.0 seconds, etc.) may be required for slow heart rate waveforms (HRWs) having a period of up to 2 seconds. However, for other use cases, or for use cases involving HRWs having a period of less than 2 seconds, this constraint may not exist.
Both skin and eye laser safety are necessary conditions to meet laser safety requirements. The disclosed implementations can also meet eye safety requirements when used properly. In many disclosed implementations, for example, when the device is used properly, light is transmitted directly against the skin in a wearable device and therefore the user's eyes are protected.
According to this example, the receiver system 102, is, or includes, an ultrasonic receiver system. In this example, the receiver system 102 includes the receiver stack portion 102a and the receiver stack portion 102b. In this example, the receiver stack portion 102a includes piezoelectric material 215a, an electrode layer 220a on a first side of the piezoelectric material 215a and an electrode layer 222a on a second side of the piezoelectric material 215a. According to some examples, a layer of anisotropic conductive film (ACF) may reside between each of the electrode layers 220a and 220b and the piezoelectric material 215a. In this example, the electrode layer 222a resides between the piezoelectric material 215a and a backing layer 230a. The electrode layers 220a and 220b include conductive material, which may be, or may include, a conductive metal such as copper in some instances. The electrode layers 220a and 220b may be electrically connected to receiver system circuitry, which is not shown in
In this example, the receiver stack portion 102b includes piezoelectric material 215b, an electrode layer 220b on a first side of the piezoelectric material 215b and an electrode layer 222b on a second side of the piezoelectric material 215b. Here, the electrode layer 222b resides between the piezoelectric material 215b and a backing layer 230b. According to this example, the receiver stack portion 102a resides proximate a first side of the light guide component 240a and the receiver stack portion 102b resides proximate a second side of the light guide component 240a. In this example, the piezoelectric materials 215a and 215b are configured to produce electric signals in response to received acoustic waves, such as the photoacoustic waves PA1 and PA2.
According to this example, the light source system 104 includes at least a first light-emitting component (the light-emitting component 235a in this example), at least a first light guide component (the light guide component 240a in this example) and light source system circuitry 245a. The light-emitting component 235a may, for example, include one or more light-emitting diodes, one or more laser diodes, one or more VCSELs, one or more edge-emitting lasers, one or more neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers, or combinations thereof.
The light guide component 240a may include any suitable material, or combination of materials, for causing at least some of the light emitted by the light-emitting component 235a to propagate within the light guide component 240a, for example due to total internal reflection between one or more core materials and one or more cladding materials of the light guide component 240a. In such examples, the core material(s) will have a higher index of refraction than the cladding material(s). In one specific and non-limiting example, the core material may have an index of refraction of approximately 1.64 and the cladding material may have an index of refraction of approximately 1.3. In some examples, the core material(s) may include glass, silica, quartz, plastic, zirconium fluoride, chalcogenide, or combinations thereof. According to some examples, the cladding material(s) may include polyvinyl chloride (PVC), acrylic, polytetrafluoroethylene (PTFE), silicone or fluorocarbon rubber. The light guide component 240a may, in some examples, include one or more optical fibers. As used herein, the terms “light guide” and “light pipe” may be used synonymously.
In some examples, the width W3 of the light guide component 240a may be in the range of 0.25 mm to 3 mm, for example 0.5 mm, 1.0 mm, 1.5 mm, etc. According to some examples, the width W2 of the space between the receiver stack portion 102a and the receiver stack portion 102b may be in the range of 0.5 mm to 5 mm, for example 1.0 mm, 1.5 mm, 2 mm, 2.5 mm, etc. In some examples, the space 233a between the receiver stack portion 102a and the light guide component 240a and the space 233b between the receiver stack portion 102b and the light guide component 240a, if any—in other words, the space(s) between W2 and W3, if any—may include light-absorbing material. According to some examples, the spaces 233a and 233b, if any, may include air. In some examples, the spaces 233a and 233b, if any, may include sound-absorbing material, preferably sound-absorbing material having a relatively low Grüneisen parameter.
In this example, the light source system 104 is configured to emit light through a first area of the platen towards a target object that is in contact with the first area of the platen 101. According to this example, the light source system 104 is configured to transmit light-represented in
The platen 101 may include any suitable material, such as glass, acrylic, polycarbonate, combinations thereof, etc. In some examples, the width W1 of the platen 101 may be in the range of 2 mm to 10 mm, for example 4 mm, 5 mm, 6 mm, etc. According to some examples, the thickness of the platen 101 (in the z direction of the coordinate system shown in
In this example, the platen 101 includes platen areas 201a, 201b and 201c. In this example, the platen area 201a resides adjacent the light guide component 240a. Accordingly, at least the platen area 201a includes transparent material in this example. According to some examples, the platen 101 may include one or more anti-reflective layers. In some examples, one or more anti-reflective layers may reside on the platen 101, or proximate the platen 101, for example on or proximate the outer surface 208a.
According to this example, the platen area 201b resides proximate the receiver stack portion 102a and the platen area 201c resides proximate the receiver stack portion 102c. In this example, a mirror layer 205a, a matching layer 210a and an adhesive layer 215a reside between the platen area 201b and the receiver stack portion 102a. Similarly, in this example a mirror layer 205b, a matching layer 210b and an adhesive layer 215b reside between the platen area 201c and the receiver stack portion 102b. The matching layers 210a and 210b may have an acoustic impedance that is selected to reduce the reflections of acoustic waves caused by the acoustic impedance contrast between one or more layers of the receiver stack portions 102a and 102b that are adjacent to, or proximate, the matching layers 210a and 210b. According to some examples, the matching layers 210a and 210b may include polyethylene terephthalate (PET). In some examples, the adhesive layers 215a and 215b may include pressure-sensitive adhesive (PSA) material.
In the example shown in
In these examples, the outlines of the receiver stack portion 102a and the receiver stack portion 102b (and, in
According to the example shown in
In the example shown in
According to the example shown in
In this example, the receiver stack portion 102a and the receiver stack portion 102b are portions of a receiver stack ring 305a. According to this example, the receiver stack ring 305a is configured to surround the light guide component 240a. In this example, the receiver stack ring 305a includes the receiver stack portions 102a and 102b, as well as the platen areas 201b and 201c. According to this example, the receiver stack ring 305b is configured to surround the receiver stack ring 305a. In this example, the receiver stack ring 305b includes the receiver stack portions 102c and 102d, as well as the platen areas 201j and 201k.
In
In this example, the light source system also includes the light guide component 240b, which is configured to transmit the light 250b from the light-emitting component 235b to the light guide component 250a. Accordingly, in this example the light source system includes at least a second light-emitting component and at least a second light guide component, the second light guide component being configured to transmit light from the second light-emitting component to at least a portion of the first light guide component. According to this example, the light guide component 240b is also configured to transmit the light 250a from the light-emitting component 235a to the light guide component 250a. Although the light guide component 240b is shown as having 90-degree bends, this is merely an example. In some implementations, the light guide component 240b may include flexible material, such as one or more optical fibers, allowing the light guide component 240b to form arcuate shapes and more gradual bends.
In this example, a source is shown emitting ultrasonic waves 601, which are detected by active ultrasonic receiver elements 655a, 655b and 655c of an array of ultrasonic receiver elements 602. The array of ultrasonic receiver elements 602 is part of a receiver system 102. The ultrasonic waves 601 may, in some examples, correspond to the photoacoustic response of a target object to light emitted by a light source system 104 of the apparatus 101. In this example, the active ultrasonic receiver elements 655a, 655b and 655c provide ultrasonic receiver signals 615a, 615b and 615c, respectively, to the control system 106.
According to this example, the control system 106 includes a delay module 605 and a summation module 610. In this example, the delay module 605 is configured to determine whether a delay should be applied to each of the ultrasonic receiver signals 615a, 615b and 615c, and if so, what delay to apply. According to this example, the delay module 605 determines that a delay d0 of t2 should be applied to the ultrasonic receiver signal 615a, that a delay d1 of t1 should be applied to the ultrasonic receiver signal 615b and that no delay should be applied to the ultrasonic receiver signal 615c. Accordingly, the delay module 605 applies a delay of t2 to the ultrasonic receiver signal 615a, producing the ultrasonic receiver signal 615a′, and applies a delay of t1 to the ultrasonic receiver signal 615b, producing the ultrasonic receiver signal 615b′.
In some examples, the delay module 605 may determine what delay, if any, to apply to an ultrasonic receiver signal by performing a correlation operation on input ultrasonic receiver signals. For example, the delay module 605 may perform a correlation operation on the ultrasonic receiver signals 615a and 615c, and may determine that by applying a time shift of t2 to the ultrasonic receiver signal 615a, the ultrasonic receiver signal 615a would be strongly correlated with the ultrasonic receiver signal 615c. Similarly, the delay module 605 may perform a correlation operation on the ultrasonic receiver signals 615b and 615c, and may determine that by applying a time shift of t1 to the ultrasonic receiver signal 615b, the ultrasonic receiver signal 615b would be strongly correlated with the ultrasonic receiver signal 615c.
According to this example, the summation module 610 is configured to sum the ultrasonic receiver signals 615a′, 615b′ and 615c, producing the summed signal 620. One may observe that the amplitude of the summed signal 620 is greater than the amplitude of any one of the ultrasonic receiver signals 615a, 615b or 615c. In some instances, the signal-to-noise ratio (SNR) of the summed signal 620 may be greater than the SNR of any of the ultrasonic receiver signals 615a, 615b or 615c.
In this example, block 705 involves directing two or more pulse groups of light towards a target object during a total light transmission time interval. The target object may be a finger, a wrist, etc., depending on the particular example. According to this example, each pulse group time interval within the total light transmission time interval is separated from a successive pulse group time interval by an off time interval. In this example, no light is being transmitted towards the target object during the off time interval. However, in some alternative examples, the time interval between successive pulse group time intervals may be a lower-intensity time interval during which the light being transmitted towards the target object has a much lower intensity than the light transmitted during the pulse group time intervals, for example one tenth of the intensity of light transmitted during the pulse group time intervals, 1/100th of the intensity of light transmitted during the pulse group time intervals, 1/1000th of the intensity of light transmitted during the pulse group time intervals, 1/10000th of the intensity of light transmitted during the pulse group time intervals, etc. In some alternative examples, the time interval between successive pulse group time intervals may be a lower-PRF time interval during which the light being transmitted towards the target object has the same intensity as the light transmitted during the pulse group time intervals, but one tenth of the PRF, 1/100th of the PRF, 1/1000th of the PRF, 1/10000th of the PRF, etc. In some alternative examples, the time interval between successive pulse group time intervals may be a time interval during which the light being transmitted towards the target object has a different intensity—for example, a lower intensity—than the light transmitted during the pulse group time intervals and is also transmitted at a different PRF (for example, a lower PRF).
According to this example, block 710 involves receiving acoustic signals corresponding to photoacoustic (PA) responses of a target object to the two or more pulse groups. In some examples, block 710 may involve receiving, by the control system, receiver signals corresponding to acoustic waves caused by PA responses of a target object to the two or more pulse groups.
In this example, block 715 involves determining one or more heart rate waveforms based on the acoustic signals. Alternatively, or additionally, block 715—or another aspect of method 700—may involve determining one or more blood vessel features. In some examples, method 700 may involve estimating one or more cardiac features based, at least in part, on the one or more heart rate waveforms, the one or more blood vessel features, or both. According to some examples, estimating the one or more cardiac features may involve estimating blood pressure.
In some examples, block 715—or another aspect of method 700—may involve determining one or more cardiac features, such as blood pressure, based on the receiver signals. In some such examples, method 700 may involve determining one or more cardiac features without an intermediate process of determining one or more heart rate waveforms, one or more blood vessel features, or both, based on the receiver signals. In some examples, method 700 may involve implementing—for example, via the control system 106 of
According to some examples, an exposure duration may equal one pulse group time interval plus one off time interval. In some examples, the average optical power density during the exposure duration is less than or equal to the MPE published by American National Standards Institute for Safe Use of Lasers (the ANSI Z136.1 standards), as well as the International Standard for the Safety of Laser Products (IEC 60825-1), corresponding to wavelength(s) of transmitted light. In some such examples, the pulse group time interval may be in a range from 0.0014 to 7 seconds. According to some examples, the off time interval may be in a range from 2 to 5 seconds.
In some examples, the width of each light pulse in a pulse group may be in a range from 50 to 500 nanoseconds. According to some examples, the total light transmission time interval may be in a range from 9 and 25 seconds. In some examples, the PRF of light pulses in a pulse group may be in a range from 0.5 to 200 kilohertz. According to some examples, each light pulse in a pulse group may have a peak amplitude in a wavelength range from 600 to 1064 nanometers. In some examples, the an average optical power density during the exposure duration may be in a range from 0.01-1.00 W/cm2.
According to some examples, one or more criteria for controlling a light source system according to a pulse group-based method may be based, at least in part, on one or more observed cardiac events. As noted elsewhere herein, in some examples in which PA techniques are used to estimate blood pressure, a pulse group time interval of 2.5 seconds, 3.0 seconds, or more may be required for slow heart rate waveforms (HRWs) having a period of up to 2 seconds. However, for other use cases, or for use cases involving HRWs having a period of less than 2 seconds, this constraint may not exist. Some examples may involve measuring one or more HRW criteria, such as an HRW period, a pulse rate, etc., according to any convenient method. Some such examples may involve measuring one or more HRW criteria using PAPG-based methods, photoplethysmography (PPG)-based methods, electrocardiogram-based methods, or other methods. Some such examples may involve determining a pulse group time interval, an off time interval, or both, according to an HRW period, a pulse rate, etc. Some examples may involve determining the start time of a pulse group time interval, an off time interval, or both, according to a measured or expected cardiac event start time. In some examples, the average optical power density during the exposure duration is less than or equal to the MPE published by American National Standards Institute for Safe Use of Lasers (the ANSI Z136.1 standards), as well as the International Standard for the Safety of Laser Products (IEC 60825-1), corresponding to wavelength(s) of transmitted light.
In some examples, one or more criteria for controlling a light source system according to a pulse group-based method may be based, at least in part, on observed apparatus motion. According to some such examples, the apparatus 100 may include a motion sensor system. The motion sensor system may, for example, include one or more accelerometers, one or more gyroscopes, or one or more other types of motion sensors. In some examples, the control system 106 may temporarily prevent the light source system 104 from emitting light pulses when motion sensor system data indicate that the apparatus motion is at or above an apparatus motion threshold.
The HRW features that are illustrated in
As noted in the graph 920, 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 graph 920, in this example the beginning of a pulse arrival time (PAT) may be calculated according to an R-Wave peak measured by the electrocardiogram sensor 905 and the end of the PAT may be detected via analysis of signals provided by the device 910. 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 device 910 and 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 system 900 may not include the electrocardiogram sensor 905. In some such implementations, the device 915, which is configured to be mounted on a wrist of the person 901, may be, or may include, an apparatus configured to perform at least some PAPG methods disclosed herein. For example, the device 915 may be, or may include, the apparatus 200 of
In some implementations of the system 900 that do not include the electrocardiogram sensor 905, the device 910 may include a light source system and two or more ultrasonic receivers. One example is described below with reference to
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 to
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 AD 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 p, 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 AD 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 sensor 1006 and a second arterial distension sensor 1008 proximate first and second physical locations, respectively, along an artery of interest. In some particular implementations, the first arterial distension sensor 1006 and the second arterial distension sensor 1008 are 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 AD of separation between the first arterial distension sensor 1006 and the second arterial distension sensor 1008 (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 AD between the first and the second arterial distension sensors 1006 and 1008 can 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 AD between the first and the second arterial distension sensors 1006 and 1008 can 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 sensors 1006 and 1008 are 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 AD between the first and the second arterial distension sensors 1006 and 1008, 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 system 106 that is described above with reference to
In some implementations of the ambulatory monitoring devices disclosed herein, both the first arterial distension sensor 1006 and the second arterial distension sensor 1008 are sensors of the same sensor type. In some such implementations, the first arterial distension sensor 1006 and the second arterial distension sensor 1008 are identical sensors. In such implementations, each of the first arterial distension sensor 1006 and the second arterial distension sensor 1008 utilizes 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 sensor 1006 and the second arterial distension sensor 1008 is 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 system 104 and the receiver system 302 of
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 sensor 1006 and the second arterial distension sensor 1008, both the first arterial distension sensor 1006 and the second arterial distension sensor 1008 can 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 sensor 1006 and the second arterial distension sensor 1008 are in contact with or in close proximity to the skin of the user at first and second locations, respectively, separated by a distance AD, 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.
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 sensors 1106 and 1108 and 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).
Implementation examples are described in the following numbered clauses:
1. A method, including: directing two or more pulse groups of light towards a target object during a total light transmission time interval, the target object being part of a human or animal body, each pulse group time interval within the total light transmission time interval being separated from a successive pulse group time interval by an off time interval during which no light is being transmitted towards the target object; receiving acoustic signals corresponding to photoacoustic (PA) responses of a target object to the two or more pulse groups; and determining one or more heart rate waveforms of the human or animal body based on the acoustic signals.
2. The method of clause 1, further including estimating one or more cardiac features based, at least in part, on the one or more heart rate waveforms.
3. The method of clause 2, where estimating the one or more cardiac features involves estimating blood pressure.
4. The method of any one of clauses 1-3, where each pulse group time interval is in a range from 0.0014 to 7 seconds.
5. The method of any one of clauses 1-4, where each off time interval is in a range from 2 to 5 seconds.
6. The method of any one of clauses 1-5, where the total light transmission time interval is in a range from 5 to 25 seconds.
7. The method of any one of clauses 1-6, where a width of each light pulse in a pulse group is in a range from 50 to 500 nanoseconds.
8. The method of any one of clauses 1-7, where a pulse repetition frequency (PRF) of light pulses in a pulse group is in a range from 0.5 to 200 kilohertz.
9. The method of any one of clauses 1-8, where each light pulse in a pulse group has a peak amplitude in a wavelength range from 600 to 1064 nanometers.
10. The method of any one of clauses 1-9, where an exposure duration equals one pulse group time interval plus one off time interval.
11. The method of clause 10, where an average optical power density during the exposure duration is in a range from 0.01-1.00 W/cm2.
12. The method of clause 10 or clause 11, where an average optical power density during the exposure duration is less than a maximum permissible exposure (MPE) published by American National Standards Institute for Safe Use of Lasers corresponding to wavelength(s) of transmitted light.
13. The method of any one of clauses 1-12, where the off time interval is greater than the pulse group time interval.
14. The method of clause 13, where an exposure duration equals one pulse group time interval plus one off time interval and where a ratio of off time interval to pulse group time interval is such that over the exposure duration the average optical power density is below a threshold.
15. One or more non-transitory computer-readable media having instructions for performing a method stored thereon, the method including: directing two or more pulse groups of light towards a target object during a total light transmission time interval, the target object being part of a human or animal body each pulse group time interval within the total light transmission time interval being separated from a successive pulse group time interval by an off time interval during which no light is being transmitted towards the target object; receiving acoustic signals corresponding to photoacoustic (PA) responses of a target object to the two or more pulse groups; and determining one or more heart rate waveforms of the human or animal body based on the acoustic signals.
16. The one or more non-transitory computer-readable media of clause 15, further including estimating one or more cardiac features based, at least in part, on the one or more heart rate waveforms.
17. An apparatus, including: a light source system; a receiver system; and a control system configured for electrical communication with the light source system and the receiver system, the control system being configured to: control the light source system to direct two or more pulse groups of light towards a target object during a total light transmission time interval, the target object being part of a human or animal body, each pulse group time interval within the total light transmission time interval being separated from a successive pulse group time interval by an off time interval during which no light is being transmitted towards the target object; receive, via the receiver system, receiver signals corresponding to acoustic waves caused by photoacoustic (PA) responses of a target object to the two or more pulse groups; and determine one or more heart rate waveforms of the human or animal body based on the receiver signals.
18. The apparatus of clause 17, where the control system is further configured to estimate one or more cardiac features based, at least in part, on the one or more heart rate waveforms, where estimating the one or more cardiac features involves estimating blood pressure.
19. The apparatus of any one of clauses 16-18, where each pulse group time interval is in a range from 0.0014 to 7 seconds.
20. The apparatus of any one of clauses 16-19, where each off time interval is in a range from 2 to 5 seconds.
21. The apparatus of any one of clauses 16-20, where the total light transmission time interval is in a range from 9 and 25 seconds.
22. The apparatus of any one of clauses 16-21, where a width of each light pulse in a pulse group is in a range from 50 to 500 nanoseconds.
23. The apparatus of any one of clauses 16-22, where a pulse repetition frequency (PRF) of light pulses in a pulse group is in a range from 0.5 to 200 kilohertz.
24. The apparatus of any one of clauses 16-23, where each light pulse in a pulse group has a peak amplitude in a wavelength range from 600 to 1064 nanometers.
25. The apparatus of any one of clauses 16-24, where an exposure duration equals one pulse group time interval plus one off time interval.
26. The apparatus of clause 25, where an average optical power density during the exposure duration is in a range from 0.01-1.00 W/cm2.
27. The apparatus of clause 25 or clause 26, where an average optical power density during the exposure duration is less than a maximum permissible exposure (MPE) published by American National Standards Institute for Safe Use of Lasers corresponding to wavelength(s) of transmitted light.
28. An apparatus, including: a light source system; a receiver system; and control means for: controlling the light source system to direct two or more pulse groups of light towards a target object during a total light transmission time interval, the target object being part of a human or animal body, each pulse group time interval within the total light transmission time interval being separated from a successive pulse group time interval by an off time interval during which no light is being transmitted towards the target object; receiving, via the receiver system, acoustic signals corresponding to photoacoustic (PA) responses of a target object to the two or more pulse groups; and determining one or more heart rate waveforms of the human or animal body based on the acoustic signals.
29. The apparatus of clause 28, where the control means includes means for estimating one or more cardiac features based, at least in part, on the one or more heart rate waveforms.
30. The apparatus of clause 29, where estimating the one or more cardiac features involves estimating blood pressure.
As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.
The various illustrative logics, logical blocks, modules, circuits and algorithm processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. The interchangeability of hardware and software has been described generally, in terms of functionality, and illustrated in the various illustrative components, blocks, modules, circuits and processes described above. Whether such functionality is implemented in hardware or software depends upon the particular application and design constraints imposed on the overall system.
The hardware and data processing apparatus used to implement the various illustrative logics, logical blocks, modules and circuits described in connection with the aspects disclosed herein may be implemented or performed with a general purpose single- or multi-chip processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, or, any conventional processor, controller, microcontroller, or state machine. A processor also may be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. In some implementations, particular processes and methods may be performed by circuitry that is specific to a given function.
In one or more aspects, the functions described may be implemented in hardware, digital electronic circuitry, computer software, firmware, including the structures disclosed in this specification and their structural equivalents thereof, or in any combination thereof. Implementations of the subject matter described in this specification also may be implemented as one or more computer programs, i.e., one or more modules of computer program instructions, encoded on a computer storage media for execution by, or to control the operation of, data processing apparatus.
If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium, such as a non-transitory medium. The processes of a method or algorithm disclosed herein may be implemented in a processor-executable software module which may reside on a computer-readable medium. Computer-readable media include both computer storage media and communication media including any medium that may be enabled to transfer a computer program from one place to another. Storage media may be any available media that may be accessed by a computer. By way of example, and not limitation, non-transitory media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that may be used to store desired program code in the form of instructions or data structures and that may be accessed by a computer. Also, any connection may be properly termed a computer-readable medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. Additionally, the operations of a method or algorithm may reside as one or any combination or set of codes and instructions on a machine readable medium and computer-readable medium, which may be incorporated into a computer program product.
Various modifications to the implementations described in this disclosure may be readily apparent to those having ordinary skill in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Thus, the disclosure is not intended to be limited to the implementations shown herein, but is to be accorded the widest scope consistent with the claims, the principles and the novel features disclosed herein. The word “exemplary” is used exclusively herein, if at all, to mean “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other implementations.
Certain features that are described in this specification in the context of separate implementations also may be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also may be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination may in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.
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. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve desirable results.
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.
Various modifications to the implementations described in this disclosure may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Thus, the following claims are not intended to be limited to the implementations shown herein, but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein.
Additionally, certain features that are described in this specification in the context of separate implementations also can be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also can be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.
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.
