WO2014197257A1

WO2014197257A1 - Methods, systems, and devices for measuring information related to blood pressure

Info

Publication number: WO2014197257A1
Application number: PCT/US2014/039845
Authority: WO
Inventors: David W. STEUERMAN
Original assignee: Northern Fields, Llc
Priority date: 2013-06-05
Filing date: 2014-05-28
Publication date: 2014-12-11

Abstract

A computer-implemented method includes obtaining first and second signals corresponding to a person?s heart rate, measured at first and second locations on the person, respectively; determining a first peak in the first signal, the first peak corresponding to a specific heartbeat of the person; determining a second peak in the second signal corresponding to the same specific heartbeat as the first peak; determining a time difference between the first peak and the second peak; and presenting information corresponding to systolic blood pressure of the person based on the time difference between the first peak and the second peak. The first signal may be obtained with a microphone and the second signal may be obtained with a camera.

Description

METHODS, SYSTEMS, AND DEVICES FOR MEASURING INFORMATION RELATED TO BLOOD PRESSURE

COPYRIGHT STATEMENT

[0001] This patent document contains material subject to copyright protection. The copyright owner has no objection to the reproduction of this patent document or any related materials in the files of the United States Patent and Trademark Office, but otherwise reserves all copyrights whatsoever.

CROSS-REFERENCE TO RELATED APPLICATION

[0002] This application claims the benefit of U.S. Provisional

Application No. 61/831,576, titled "Methods, Systems, And Devices For Measuring Information Related To Blood Pressure," filed June 5, 2013, the entire contents of which are hereby fully incorporated herein for all purposes.

FIELD OF THE INVENTION

[0003] This invention relates generally to measurement of human biometric information, and more particularly to measuring time-of- flight (TOF) of blood flow in a human body.

BACKGROUND

[0004] Hypertension (high blood pressure) is a critical health issue for more than 30% of American adults. High blood pressure costs over $90 billion annually in the form of healthcare services, medications, and lost days of productivity. Furthermore, hypertension greatly increases the risk of heart attack and stroke, the number one and number three leading causes of death in the United States, respectively. One of the primary approaches to prevent and combat hypertension is to simply inform people about their cardiovascular health and perform regular assessments.

[0005] While knowing one's actual blood pressure is valuable, understanding its range and variability over time, e.g., throughout the course of the day, week, month, or year, is critically useful. These trends allow one to move away from snapshots that will likely be non-representative and toward a more holistic view of the health of one's circulatory system. Trends can be used to inform an individual of how his body is responding to age, a new job, or modifications to his behavior.

[0006] Many medical practitioners recommend that their patients take regular blood pressure measurements. However, such measurements typically require the use of an inflatable cuff or the like. As such, it is typically inconvenient to make such measurements at arbitrary times or locations.

[0007] It is therefore useful and desirable to be able to easily and conveniently obtain measurements relating to blood pressure. It is also useful and desirable to be able to obtain measurements relating to blood pressure without the use of an inflatable cuff or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 depicts a device according to embodiments hereof;

[0009] FIG. 2 depicts a flow chart of the process according to

embodiments hereof;

[00010] FIGS. 3(a)-3(b) depict measured heart rate signals according to embodiments hereof;

[00011] FIG. 4 shows an overlay of portions of the signals in FIGS. 3(a)- 3(b); and

[00012] FIG. 5 describes aspects of computing according to embodiments hereof.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS

GLOSSARY AND ABBREVIATIONS

[00013] As used herein, unless used otherwise, the following terms or abbreviations have the following meanings:

[00014] BP means blood pressure;

[00015] PPT means pulse transit time;

[00016] SBP means systolic blood pressure; [00017] TOF means time of flight.

BACKGROUND

[00018] Assuming an individual's circulatory system is relatively stable (no unexpected changes in arterial size, elasticity, and number), measuring the time it takes blood to travel through the individual's body provides insight into his cardiovascular health.

[00019] Pulse transit time (PTT) is the time between two pulse waves propagating on the same cardiac cycle from two separate arterial sites. PTT has been shown to have a correlation with systolic blood pressure (SBP) and has been reported to be suitable for indirect BP measurements (Continuous blood pressure measurement by using the pulse transit time: comparison to a cuff-based method, Heiko Gesche et al, Eur J Appl Physiol, DOI

10.1007/s00421-01 1-1983-3, Springer- Verlag 201 1). PTT has been shown to be quasi-linear to low BP values, but increase exponentially at higher pressures (Pruett et al (1988) Measurement of pulse-wave velocity using a beat-sampling technique. Ann Biomed Eng 16:341- 347; and Callaghan et al (1984) The relationship between arterial pulse-wave velocity and pulse frequency at different pressures. J Med Eng Technol 8: 15-18).

[00020] In some aspects, a device that measures the time required for blood to travel from point A to point B on a human body provides insights into the circulatory system and blood pressure (assuming that points A and B are at different distances from the heart along the arterial system). This approach to characterize a dynamic system is referred to as a time of flight (TOF) technique.

[00021] FIG. 1 depicts a device 102 according to embodiments hereof. As shown in FIG. 1, device 102 includes one or more cameras 104, and one or more microphones 106. The camera(s) 104 and microphone(s) 106 may be connected in a known manner to a computing system 108. The computing system 108 includes memory 110 and one or more processors 112 connected to the memory/storage 110. Memory/storage 110 may include RAM, persistent storage, or the like, and includes application(s) 114 according to embodiments hereof. The memory/storage 110 may also include application data 116.

[00022] The device 102 may be a smartphone (e.g., an iPhone or the like), and the application(s) 114 may be one or more applications running as so- called "apps" on that smartphone.

[00023] FIG. 2 is a flow chart of an exemplary process using the application(s) 114 according to embodiments hereof. Those of ordinary skill in the art will appreciate and understand, upon reading this description, that this process shown in FIG. 2 is merely exemplary, and that variations thereof are contemplated and are considered part of the invention. At least some of the acts of the process are performed by the computing system 108 running the application(s) 114 using the processor(s) 112.

[00024] In operation, an individual needs to take two simultaneous heart rate measurements using device 102. One measurement is taken using the camera(s) 104 while the other measurement is taken using the microphone(s) 106. The individual starts the application 114 in the usual manner and begins to measure his heart rate (S202). To obtain a heart rate measurement using the camera(s) 104, the individual places his fingertip over a camera and begins measurement of his heart rate (at his fingertip) using that camera (at S204). This process may use, e.g., the approach described in U.S. Patent Publication No. 20100268094, titled "Consumer electronic camera photoplethysmograph," filed April 15, 2010, published October 21, 2010, the entire contents of which are fully incorporated herein for all purposes. The application 114 stores information relating to the measurements obtained using the camera in application data 116 in the memory/storage 110. While measuring heartbeat with the camera (at S204) the individual also holds the microphone to his chest and measures his heart rate using sound picked up by the microphone(s) 106 (at S206). The application 114 stores information relating to the measurements obtained using the microphone(s) in application data 116 in the

memory/storage 110. [00025] The application 116 needs to obtain at least some overlapping heart rate measurements from both the camera(s) 104 and the microphone(s) 106. It should be appreciated that the individual may begin either measurement (with camera or with microphone) first.

[00026] Although a particular device may have multiple cameras and microphones, those of ordinary skill in the art will appreciate and understand, upon reading this description, that only one camera is needed and only one microphone is needed.

[00027] Once the system (application 116) determines that it has sufficient overlapping measurements, the device may provide an indication to the individual so that he knows that he can stop measurement. Similarly, if either the camera or microphone measurements are inadequate, the application may advise the individual accordingly. For example, the individual may need to reposition the microphone and/or his finger in order to obtain a proper measurement.

[00028] Having obtained sufficient overlapping measurements (at S202), the application 116 proceeds to find and correlate peaks in the measured data. FIG. 3(a) shows a normalized audio signal as measured by the microphone 106. This signal corresponds to measurement data obtained by the

microphone(s) 106 in S206.

[00029] The time delay between adjacent peaks in the signal may be used to determine the individual's heart rate. FIG. 3(b) shows a normalized signal from the camera during the same time period as that of FIG. 3(a). This delay between the peaks in the signal in FIG. 3(b) can also be used to calculate the individual's heart rate. The peak labeled A in FIG. 3(a) corresponds to the same heartbeat as the peak labeled B in FIG. 3(b). Accordingly, the time between peak A and peak B corresponds to the pulse transit time (PTT) and may be determined by the application 116 (at 210).

[00030] FIG. 4 shows a region of the measurement period of FIGS. 3(a)- 3(b), including the peaks A and B. In the example shown in FIGS. 2A-2B and 4, the PTT is approximately 665 ms. [00031] Once the PTT has been determined, it may be presented to the individual (at 212), e.g., as a numerical value and/or graphically on a display of the device 102. This value could also be used as an input to generate a cardiovascular health score or index.

[00032] The application 116 may to determine multiple PTT values from the store data (by looping through steps 208 to 212) or by taking additional measurements and repeating steps 202 to 212.

[00033] Peak detection (at S208) may use any known technique. For example, the data would be baseline subtracted, normalized and then signals that are greater than a given threshold would be identified as peaks. Least square fitting routines could also be employed to search for Gaussian or Lorentzian line shapes for example. Peak identification is aided by the fact that peak-width parameters are stable and the time delay between adjacent peaks is well-bounded (typical heart rates are between 50 and 180 beats per minute).

[00034] The correlation of two peaks, one in each of the signals, may be done by selecting a peak in one of the signals and then locating the first peak in the other signal at a subsequent time.

[00035] It should be appreciated that the measurements taken optically with the camera should use the same clock as measurements taken with the microphones.

[00036] As noted above, the PTT may be correlated with systolic blood pressure. In some embodiments the system may present the individual with information corresponding to his blood pressure. While not necessarily giving an actual blood pressure measurement, the individual can be notified that his blood pressure may be low, normal, or high. In some cases it may be useful to calibrate the application for a particular individual by providing the application with actual blood pressure measurements corresponding to or taken at the same time as the PTT and heart rate measurements.

[00037] Thus is provided a method to readily evaluate an individual's circulatory health and better understand his blood pressure by making hemodynamic measurements. [00038] While it is understood, as noted above, that PTT may be a proxy for blood pressure, it should be appreciated that PTT is, in and of itself, a useful measure of circulatory health and could be used to generate a health score or index.

[00039] Those of ordinary skill in the art realize and understand, upon reading this description, that a precise relationship between PTT and blood pressure may be measured or determined in some way. For example, using a known relationship from fluid dynamics, put in physiological terms, a formula relating PTT to blood pressure may be derived.

[00040] For example, beginning with the analytical expression called the Moens-Korteweg formula, one can derive a formula relating PTT to pressure as:

P_e = P_b + ΔΡ

Where P_e is the estimation of the blood pressure, P_b is the baseline blood pressure for the individual, and ΔΡ is the change in blood pressure.

Where γ is a coefficient that represents the characteristic response of the blood vessels during blood flow, T_b is the baseline pulse transit time, ΔΤ is the observed change in pulse transit time.

[00041] Although described here using a camera and a microphone, it should be appreciated that detection of a cardiovascular pulse wave may be performed by a variety of instruments or mechanisms. Those of ordinary skill in the art would appreciate and understand, upon reading this description, that other techniques or mechanisms may be used to obtain the two readings, as long as they are measuring heart rate at two distinct locations that are different distances from the heart. It should be understood that the "distance" from the heart refers to a vascular distance. [00042] In summary, a preferred device has both a microphone (if a second microphone is available it could be used for background noise cancellation) and an optical sensor, each of which can produce a signal as function of time. These time -varying signal streams must be plotted on a universal time axis where the time difference between events can be accurately determined. The primary microphone is held to the chest near the heart and the optical sensor is trained on the skin of the individual (typically by covering it with a finger). When the sensors simultaneously record traces as a functions of time, the signals are plotted on the same time axis. This is accomplished by translating the individual data streams into a universal clock time set forth by an internal or external reference (e.g. Global Positioning System Clock).

Cardiovascular waves are identified in each trace.

[00043] The pulse transit time (PTT) is calculated for each pair of pulses; one from microphone and the second from the optical sensor. In each pair the t=0 time is defined as an easily consistently identifiable feature in the audio signal, e.g., the peak. Additionally, a peak is readily identifiable in the optical signal and begins to peak at a later time t'.

[00044] In some aspects, the invention provides a device, system, and method for measuring time-of- flight of blood flow in a human subject.

COMPUTING

[00045] The services, mechanisms, operations, and acts shown and described above are implemented, at least in part, by software running on one or more computers or computer systems or devices (such as smartphones and the like). It should be appreciated that each user device is, or comprises, a computer system.

[00046] Programs that implement such methods (as well as other types of data) may be stored and transmitted using a variety of media (e.g. , computer readable media) in a number of manners. Hard-wired circuitry or custom hardware may be used in place of, or in combination with, some or all of the software instructions that can implement the processes of various embodiments. Thus, various combinations of hardware and software may be used instead of software only.

[00047] One of ordinary skill in the art will readily appreciate and understand, upon reading this description, that the various processes described herein may be implemented by, e.g., appropriately programmed general purpose computers, special purpose computers and computing devices. One or more such computers or computing devices may be referred to as a computer system.

[00048] FIG. 5 is a schematic diagram of a computer system 500 upon which embodiments of the present disclosure may be implemented and carried out.

[00049] According to the present example, the computer system 500 includes a bus 502 (i.e., interconnect), one or more processors 504

(corresponding, e.g., to processor(s) 112 in FIG. 1), one or more

communications ports 514, a main memory 506, removable storage media (not shown), read-only memory 508, and a mass storage 512 (collectively

corresponding, e.g., to memory/storage 110 in FIG. 1). Communication port(s) 514 may be connected to one or more networks by way of which the computer system 500 may receive and/or transmit data.

[00050] As used herein, a "processor" means one or more

microprocessors, central processing units (CPUs), computing devices, microcontrollers, digital signal processors, or like devices or any combination thereof, regardless of their architecture. An apparatus that performs a process can include, e.g. , a processor and those devices such as input devices and output devices that are appropriate to perform the process.

[00051] Processor(s) 504 can be (or include) any known processor, such as, but not limited to, an Intel® Itanium® or Itanium 2® processor(s), AMD® Opteron® or Athlon MP® processor(s), or Motorola® lines of processors, and the like. Communications port(s) 514 can be any of an S-232 port for use with a modem based dial-up connection, a 10/100 Ethernet port, a Gigabit port using copper or fiber, or a USB port, and the like. Communications port(s) 514 may be chosen depending on a network such as a Local Area Network (LAN), a Wide Area Network (WAN), a Content Delivery Network (CDN), or any network to which the computer system 500 connects. The computer system 500 may be in communication with peripheral devices (e.g. , display screen 516, input device(s) 518) via Input / Output (I/O) port 520. Some or all of the peripheral devices may be integrated into the computer system 500, and the input device(s) 518 may be integrated into the display screen 516 (e.g., in the case of a touch screen).

[00052] Main memory 506 can be Random Access Memory (RAM), or any other dynamic storage device(s) commonly known in the art. Read-only memory 508 can be any static storage device(s) such as Programmable Readonly Memory (PROM) chips for storing static information such as instructions for processor(s) 504. Mass storage 512 can be used to store information and instructions.

[00053] Bus 502 communicatively couples processor(s) 504 with the other memory, storage and communications blocks. Bus 502 can be a PCI / PCI-X, SCSI, a Universal Serial Bus (USB) based system bus (or other) depending on the storage devices used, and the like. Removable storage media 510 can be any kind of external flash drives, hard-drives, floppy drives, Compact Disc - Read Only Memory (CD-ROM), Compact Disc - Re-Writable (CD-RW), Digital Versatile Disk - Read Only Memory (DVD-ROM), etc.

[00054] Embodiments herein may be provided as one or more computer program products, which may include a machine-readable medium having stored thereon instructions, which may be used to program a computer (or other electronic devices) to perform a process. As used herein, the term "machine- readable medium" refers to any medium, a plurality of the same, or a combination of different media, which participate in providing data (e.g., instructions, data structures) which may be read by a computer, a processor or a like device. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks and other persistent memory. Volatile media include dynamic random access memory, which typically constitutes the main memory of the computer. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise a system bus coupled to the processor. Transmission media may include or convey acoustic waves, light waves and electromagnetic emissions, such as those generated during radio frequency ( F) and infrared (IR) data

communications.

[00055] The machine-readable medium may include, but is not limited to, floppy diskettes, optical discs, CD-ROMs, magneto-optical disks, ROMs, RAMs, erasable programmable read-only memories (EPROMs), electrically erasable programmable read-only memories (EEPROMs), magnetic or optical cards, flash memory, or other type of media/machine-readable medium suitable for storing electronic instructions. Moreover, embodiments herein may also be downloaded as a computer program product, wherein the program may be transferred from a remote computer to a requesting computer by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., modem or network connection).

[00056] Various forms of computer readable media may be involved in carrying data (e.g. sequences of instructions) to a processor. For example, data may be (i) delivered from RAM to a processor; (ii) carried over a wireless transmission medium; (iii) formatted and/or transmitted according to numerous formats, standards or protocols; and/or (iv) encrypted in any of a variety of ways well known in the art.

[00057] A computer-readable medium can store (in any appropriate format) those program elements that are appropriate to perform the methods.

[00058] As shown, main memory 506 is encoded with application(s) 522 that support(s) the functionality as discussed herein (an application 522 may be an application that provides some or all of the functionality of one or more of the mechanisms, e.g., application(s) 114, described herein). Application(s) 522 (and/or other resources as described herein) can be embodied as software code such as data and/or logic instructions (e.g. , code stored in the memory or on another computer readable medium such as a disk) that supports processing functionality according to different embodiments described herein.

[00059] During operation of one embodiment, processor(s) 504 accesses main memory 506 via the use of bus 502 in order to launch, run, execute, interpret or otherwise perform the logic instructions of the application(s) 522. Execution of application(s) 522 produces processing functionality of the service(s) or mechanism(s) related to the application(s). In other words, the process(es) 524 represents one or more portions of the application(s) 522 performing within or upon the processor(s) 504 in the computer system 500.

[00060] It should be noted that, in addition to the process(es) 524 that carries(carry) out operations as discussed herein, other embodiments herein include the application 522 itself (i.e., the un-executed or non-performing logic instructions and/or data). The application 522 may be stored on a computer readable medium (e.g., a repository) such as a disk or in an optical medium. According to other embodiments, the application 522 can also be stored in a memory type system such as in firmware, read only memory (ROM), or, as in this example, as executable code within the main memory 506 (e.g., within Random Access Memory or RAM). For example, application 522 may also be stored in removable storage media 510, read-only memory 508, and/or mass storage device 512.

[00061] Those skilled in the art will understand that the computer system 500 can include other processes and/or software and hardware components, such as an operating system that controls allocation and use of hardware resources.

[00062] As discussed herein, embodiments of the present invention include various steps or operations. A variety of these steps may be performed by hardware components or may be embodied in machine-executable instructions, which may be used to cause a general-purpose or special-purpose processor programmed with the instructions to perform the operations.

Alternatively, the steps may be performed by a combination of hardware, software, and/or firmware. The term "module" refers to a self-contained functional component, which can include hardware, software, firmware or any combination thereof.

[00063] One of ordinary skill in the art will readily appreciate and understand, upon reading this description, that embodiments of an apparatus may include a computer/computing device operable to perform some (but not necessarily all) of the described process.

[00064] Embodiments of a computer-readable medium storing a program or data structure include a computer-readable medium storing a program that, when executed, can cause a processor to perform some (but not necessarily all) of the described process.

[00065] Where a process is described herein, those of ordinary skill in the art will appreciate that the process may operate without any human

intervention. In another embodiment, the process includes some human intervention (e.g., a step is performed by or with the assistance of a human).

[00066] As used in this description, the term "portion" means some or all. So, for example, "A portion of X" may include some of "X" or all of "X". In the context of a conversation, the term "portion" means some or all of the conversation.

[00067] As used herein, including in the claims, the phrase "at least some" means "one or more," and includes the case of only one. Thus, e.g., the phrase "at least some ABCs" means "one or more ABCs", and includes the case of only one ABC.

[00068] As used herein, including in the claims, the phrase "based on" means "based in part on" or "based, at least in part, on," and is not exclusive. Thus, e.g., the phrase "based on factor X" means "based in part on factor X" or "based, at least in part, on factor X." Unless specifically stated by use of the word "only", the phrase "based on X" does not mean "based only on X."

[00069] As used herein, including in the claims, the phrase "using" means "using at least," and is not exclusive. Thus, e.g., the phrase "using X" means "using at least X." Unless specifically stated by use of the word "only", the phrase "using X" does not mean "using only X." [00070] In general, as used herein, including in the claims, unless the word "only" is specifically used in a phrase, it should not be read into that phrase.

[00071] As used herein, including in the claims, the phrase "distinct" means "at least partially distinct." Unless specifically stated, distinct does not mean fully distinct. Thus, e.g., the phrase, "X is distinct from Y" means that "X is at least partially distinct from Y," and does not mean that "X is fully distinct from Y." Thus, as used herein, including in the claims, the phrase "X is distinct from Y" means that X differs from Y in at least some way.

[00072] As used herein, including in the claims, a list may include only one item, and, unless otherwise stated, a list of multiple items need not be ordered in any particular manner. A list may include duplicate items. For example, as used herein, the phrase "a list of XYZs" may include one or more "XYZs".

[00073] It should be appreciated that the words "first" and "second" in the description and claims are used to distinguish or identify, and not to show a serial or numerical limitation. Similarly, the use of letter or numerical labels (such as "(a)", "(b)", and the like) are used to help distinguish and / or identify, and not to show any serial or numerical limitation or ordering.

[00074] No ordering is implied by any of the labeled boxes in any of the flow diagrams unless specifically shown and stated. When disconnected boxes are shown in a diagram the activities associated with those boxes may be performed in any order, including fully or partially in parallel.

[00075] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

I CLAIM:

1. A computer-implemented method, implemented by hardware in combination with software, the method comprising:

(A) obtaining a first signal of a heart rate of a person, measured at a first location on the person;

(B) obtaining a second signal of the heart rate of the person, measured at a second location on the person, said second location being distinct from the first location;

(C) determining a first peak in the first signal, the first peak corresponding to a specific heartbeat of the person;

(D) determining a second peak in the second signal, the second peak corresponding to the same specific heartbeat as the first peak in the first signal;

(E) determining a time difference between said first peak and said second peak; and

(F) presenting information corresponding to systolic blood pressure of the person based on the time difference between the first peak and the second peak.

2. The method of claim 1 wherein the first signal is obtained using a microphone.

3. The method of any one of claims 1 or 2 wherein the first location is a location on the person's chest.

4. The method of any one of claims 1-3 wherein the second signal is obtained using a camera.

5. The method of any one of claims 1-4, wherein the second location is on the person's finger.

6. The method of any one of claims claim 1-5, wherein the first signal is obtained using a microphone in a device, and wherein the second signal is obtained using a camera in the device.

7. The method of any one of claims 1-6, wherein the first location is a location on the person's chest adjacent the person's heart, and wherein the second location is a location on the person's finger.

8. The method of any of the preceding claims wherein the time difference corresponds to a pulse transit time.

9. Non- transitory computer-readable storage media containing instructions that when executed by one or more processors cause the one or more processors to perform the method of any one of claims 1-8.

10. A device comprising hardware, including a camera, a

microphone, at least one processor and software, in combination with said hardware:

(a) to obtain a first signal to a heart rate of a person, measured at a first location on the person;

(B) to obtain a second signal to the heart rate of the person, measured at a second location on the person, said second location being distinct from the first location; (C) to determine a first peak in the first signal, the first peak corresponding to a specific heartbeat of the person;

(D) to determine a second peak in the second signal, the second peak corresponding to the same specific heartbeat as the first peak in the first signal;

(E) to determine a time difference between said first peak and said second peak; and

(F) to present information corresponding to systolic blood pressure of the person based on the time difference between the first peak and the second peak.

1 1. The device of claim 10 wherein the first signal is obtained using a microphone.

12. The device of claims 10 or 1 1 wherein the first location is a location on the person's chest.

13. The device of any one of claims 10-12 wherein the second signal is obtained using a camera.

14. The device of any one of claims 10-13, wherein the second location is on the person's finger.

15. The device of any one of claims 10-14, wherein the first signal is obtained using a microphone in a device, and wherein the second signal is obtained using a camera in the device.

16. The device of any one of claims 10-15, wherein the first location is a location on the person's chest adjacent the person's heart, and wherein the second location is a location on the person's finger.

17. The device of any one of claims 10-16 wherein the time difference corresponds to a pulse transit time.

18. The device of any one of claims 10-17 wherein the device comprises a smartphone.

19. A system comprising the device of any one of claims 10-18.