WO2018013569A1

WO2018013569A1 - Multi-sensor blood pressure measurement system

Info

Publication number: WO2018013569A1
Application number: PCT/US2017/041540
Authority: WO
Inventors: Milan RAJ; Bryan Mcgrane; Roozbeh Ghaffari; Paolo Depetrillo
Original assignee: Mc10, Inc.
Priority date: 2016-07-11
Filing date: 2017-07-11
Publication date: 2018-01-18
Also published as: CN109688910A; EP3481293A4; EP3481293A1

Abstract

A system for sensing blood pressure in a user is disclosed. The system includes a master sensor device including a clock signal generator generating a clock signal, a transceiver transmitting the clock signal, and a pulse sensor sensing a pulse of the user. The master sensor device is attached on a first location on the user. A first slave sensor device is attached at a second location on the user remote from the first location. The slave sensor device includes a pulse sensor sensing the pulse of the user and a transceiver receiving the clock signal from the master sensor device. The first slave sensor device synchronizes the sensing of the pulse to the clock signal. The transceiver transmits a time stamp signal to the master sensor. The blood pressure of the user is determined based on a pulse transit time or pulse arrival time between the sensing of the pulse by the master sensor device and the first slave sensor device.

Description

MULTI-SENSOR BLOOD PRESSURE MEASUREMENT SYSTEM

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of and priority to U.S. Provisional Application No. 62/360,807, filed July 11, 2016, entitled "MULTI-SENSOR BLOOD PRESSURE MEASUREMENT SYSTEM," which is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates generally blood pressure monitoring. More particularly, aspects of this disclosure relate to using sensors attached to a body to determine blood pressure based on pulse transit time and pulse arrival time.

BACKGROUND

[0003] Integrated circuits (ICs) are the cornerstone of the information age and the foundation of today's information technology industries. The integrated circuit, a.k.a. "chip" or "microchip," is a set of interconnected electronic components, such as transistors, capacitors, and resistors, which are etched or imprinted onto a semiconducting material, such as silicon or germanium. Integrated circuits take on various forms including, as some non-limiting examples, microprocessors, amplifiers, Flash memories, application specific integrated circuits (ASICs), static random access memories (SRAMs), digital signal processors (DSPs), dynamic random access memories (DRAMs), erasable programmable read only memories (EPROMs), and programmable logic. Integrated circuits are used in innumerable products, including computers (e.g., personal, laptop and tablet computers), smartphones, flat-screen televisions, medical instruments, telecommunication and networking equipment, airplanes, watercraft and automobiles.

[0004] Advances in integrated circuit technology and microchip manufacturing have led to a steady decrease in chip size and an increase in circuit density and circuit performance. The scale of semiconductor integration has advanced to the point where a single semiconductor chip can hold tens of millions to over a billion devices in a space smaller than a U.S. penny. Moreover, the width of each conducting line in a modern microchip can be made as small as a fraction of a nanometer. The operating speed and overall performance of a semiconductor chip (e.g., clock speed and signal net switching speeds) has concomitantly increased with the level of integration. To keep pace with increases in on-chip circuit switching frequency and circuit density, semiconductor packages currently offer higher pin counts, greater power dissipation, more protection, and higher speeds than packages of just a few years ago.

[0005] The advances in integrated circuits have led to related advances within other fields. One such field is sensors. Advances in integrated circuits have allowed sensors to become smaller and more efficient, while simultaneously becoming more capable of performing complex operations. Other advances in the field of sensors and circuitry in general have led to wearable circuitry, a.k.a. "wearable devices" or "wearable systems." Within the medical field, as an example, wearable devices have given rise to new methods of acquiring, analyzing, and diagnosing medical conditions of patients. Related to the medical field, other wearable devices have been created within the sports and recreational fields for the purpose of monitoring physical activity and fitness. For example, a user may don a wearable device, such as a wearable running coach, to measure the distance traveled during an activity (e.g., running, walking, etc.), and measure the kinematics of the user's motion during the activity.

SUMMARY

[0006] One example of a body function that is desirable to monitor is blood pressure and more specifically, to monitor resting and ambulatory blood pressure continuously over an extended period of time. An adequate blood pressure level is necessary for blood to travel from the heart around the body. A blood pressure that is too low (hypotension) may lead to inadequate blood flow, or hypoperfusion, of critical organs. A blood pressure level that is too high (hypertension) may, over time, have detrimental health effects on organs such as the heart (myocardial infarction), the brain (stroke, hemorrhage), and kidneys (renal failure). Unfortunately, traditional blood pressure measurement methods such as using an external cuff that constricts around a patient's arm cannot provide continuous monitoring of blood pressure.

[0007] Another method for blood pressure measurement is the use of pulse transit time (PTT) and pulse arrival time (PAT). A pulse generated from a pressure wave in blood flow is sensed by a first sensor and the time for the pulse to reach a second sensor along the same arterial path is measured. Pulse transit time (PTT) is the time delay of the pressure wave traveling between two points along a blood vessel and is typically measured optically. Pulse Arrival Time (PAT) is the time gap between the electrical pulse signal of the heart and the mechanical impulse of the pressure wave at an extremity (such as the wrist). Knowing PTT or PAT, and the distance between the two points of measurement, one can determine the Pulse Wave Velocity (PWV). Knowing the basic properties of the blood vessel wall, and the PWV, one can calculate the mean pressure exerted on the wall along the arterial path, and thus obtain blood pressure. The PWV and the basic properties of the vessel wall may be pre-determined constants and incorporated in a function based on the PTT or PAT to determine blood pressure.

[0008] Thus, there is a need for a reliable system for determining blood pressure using PTT. There is also a need for a system that uses sensors at different locations on the body that may be synchronized to accurately determine PTT. There is also a need for a system that may determine localized blood pressure in a specific region of a body.

[0009] According to some embodiments, an example system for sensing blood pressure of a user is disclosed. The system has a master sensor device including a clock signal generator generating a clock signal, a transceiver transmitting the clock signal, and a pulse sensor sensing a pulse at a first location on the user. A first slave sensor device is attached at a second location on the user remote from the first location. The slave sensor device includes a pulse sensor sensing the pulse of the user at the second location and a transceiver receiving the clock signal from the master sensor device. The first slave sensor device synchronizes the sensing of the pulse to the clock signal and the transceiver transmits a time stamp signal to the master sensor device. A controller determines blood pressure of the user based on a pulse transit time or a pulse arrival time between the sensing of the pulse by the master sensor device and the first slave sensor device.

[0010] Another example is a sensor device worn on the chest of a user. The sensor device includes a clock signal generator generating a clock signal, an electro cardiogram sensor to sense a pulse of the user and a transceiver coupled to the clock signal generator. The transceiver transmits a clock signal to a slave sensor device worn on the user at a location remote from the chest and receives a time stamp signal from the slave sensor device sensing the pulse. A processor is coupled to the transceiver. The processor determines the blood pressure of the user based on a pulse transit time or a pulse arrival time determined from the time stamp signal and a time when the electro cardiogram sensor senses the pulse.

[0011] Another example is a method of measuring blood pressure of a user. A master sensor device is attached at a first location of the user. A first slave sensor device is attached at a second location of the user. The second location is remote from the first location. A clock synchronization signal is sent from the master sensor device to the slave sensor device. A pulse of the user is sensed via the master sensor at an initial time. The pulse of the user is sensed via the first slave sensor device. A timestamp signal of the sensed pulse is sent from the first slave sensor device. A pulse transit time or a pulse arrival time is determined from the timestamp signal and the initial time via a controller. Blood pressure is determined based on the pulse transit time or a pulse arrival time via the controller.

[0012] The above summary is not intended to represent each embodiment or every aspect of the present disclosure. Rather, the foregoing summary merely provides an exemplification of some of the novel aspects and features set forth herein. The above features and advantages, and other features and advantages of the present disclosure, will be readily apparent from the following detailed description of representative embodiments and modes for carrying out the present invention when taken in connection with the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The disclosure will be better understood from the following description of exemplary embodiments together with reference to the accompanying drawings, in which:

[0014] FIG. 1 shows a system of multiple wearable sensor devices used for sensing blood pressure in a user;

[0015] FIG. 2 is a block diagram of one of the wearable sensor devices in FIG. 1;

[0016] FIG. 3A is a graph showing the sampled ECG signal of the master sensor device and the sampled accelerometer signal of a slave device in FIG. 1 at the carotid artery;

[0017] FIG. 3B is a close-up view of the plotted waveforms of the sensed pulse signals of the master sensor device and the slave sensor device in FIG. 3 A;

[0018] FIG. 4 is a graph showing the sampled ECG signal of the master sensor device and the sampled accelerometer signal of a slave device in FIG. 1 at the wrist; [0019] FIG. 5 is a flow diagram showing the process of measuring blood pressure in the system in FIG. 1;

[0020] FIG. 6 is a flow diagram showing the synchronization process used by the process in FIG. 5;

[0021] FIG. 7 A is a diagram of the process of measuring pulse arrival time;

[0022] FIG. 7B is a diagram of the process of measuring pulse transit time between two slave sensor devices;

[0023] FIG. 8 is a diagram of the process of measuring localized blood pressure; and

[0024] FIG. 9 is a diagram of a treatment system including a system to determine localized blood pressure measurement.

[0025] The present disclosure is susceptible to various modifications and alternative forms, and some representative embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0026] The inventions according to this disclosure can be embodied in many different forms. There are shown in the drawings, and will herein be described in detail, representative embodiments with the understanding that the present disclosure is to be considered as an illustration of the principles of the present disclosure and is not intended to limit the broad aspects of the disclosure to the embodiments illustrated. To that extent, elements and limitations that are disclosed, for example, in the Abstract, Summary, and Detailed Description sections, but not explicitly set forth in the claims, should not be incorporated into the claims, singly or collectively, by implication, inference, or otherwise. For purposes of the present detailed description, unless specifically disclaimed: the singular includes the plural and vice versa; and the word "including" means "including without limitation." Moreover, words of approximation, such as "about," "almost," "substantially," "approximately," and the like, can be used herein in the sense of "at, near, or nearly at," or "within 3-5% of," or "within acceptable manufacturing tolerances," or any logical combination thereof, for example. [0027] FIG. 1 is a diagram of a user 100 that has a network of wearable sensor devices 110, 112, 114, 116, 118 and 120 that are attached to the body of the user 100 in different locations. One or more of the sensor devices 110, 112, 114, 116, 118 and 120 can be in communication with a smart device such as a user device 130. The user device 130 can be a computing device such as a smart phone, a tablet, a laptop or desktop computer, a personal digital assistant or a network of computers (e.g., a cloud or a cluster). In this example, one sensor device 110 can optionally serve as a master sensor device and can be attached near the chest 140 of the user 100. The other sensor devices 112, 114, 116, 118 and 120 can be attached to different regions of interest on the body of the user 100. For example as shown, the sensor device 112 is attached to the right wrist 142 of the user 100, sensor device 114 is attached to the left wrist 144 of the user 100, sensor device 116 is attached to the right foot 146 of the user 100, sensor device 118 is attached to the left ankle 148 of the user 100, and sensor 120 is attached to the neck 150 of the user 100 near the carotid artery. Although the sensor devices 110, 112, 114, 116, 118 and 120 are used for non-invasive blood pressure monitoring, they can have additional sensors and provide other measurement and sensing functions in relation to the user 100.

[0028] The user device 130 allows programming and control of the sensor devices 110, 112, 114, 116, 118 and 120. In this example, the sensor device 110 can be programmed or configured as a "master" device and the other sensor devices 112, 114, 116, 118 and 120 can be programmed or configured as "slave" devices. In accordance with some embodiments of the invention, each of the sensor devices 110, 112, 114, 116, 118 and 120 can be similar and can be programmed or configured to take the role of a master or slave. In the event of a failure or error, a slave device can be reconfigured to take the role of the master, or the master can be reconfigured to take the roles of a slave. As will be explained, time stamp data of a sensed pulse associated with a pressure wave of blood being pumped through blood vessels can be recorded by each slave sensor device 112, 1 14, 116, 118 and 120. The time stamp data of the slave sensor can be synchronized with respect to a time stamp signal from the master sensor device 110 indicating the initial time the pulse was sensed by the master sensor device 110.

[0029] The time data from each of the sensor devices 110, 112, 114, 116, 118 and 120 associated with the sensed pulses can be uploaded (e.g., through the user device 130) to a cloud storage server 160 periodically and analyzed by applications running on the cloud application server 162 using post-processing techniques. The user can access these applications or the output of the applications by accessing the cloud server 162 such as through a website. As will be explained below, a subset or all of the sensors 110, 112, 114, 116, 118 and 120 can be used to capture blood pressure related data such as pulse transit time and/or time stamps for detection of a pulse. Thus blood pressure can be determined using at least two time-synced sensor devices from the sensor devices 110, 112, 114, 116, 118 and 120. In one example, the sensors 110, 112, 114, 116, 118 and 120 send pulse data to the user device 130. The user device 130 determines blood pressure measurements based on the collected data. Alternatively, the determination of blood pressure measurements may be performed on one of the sensors 110, 112, 114, 116, 118 and 120 or on the cloud application server 162.

[0030] FIG. 2 shows an example of a wearable sensor device 200 such as the sensor device 110 in FIG. 1 in accord with aspects of the present disclosure. The wearable device 200 can provide conformal sensing capabilities, providing mechanically transparent close contact with a surface (such as the skin or other portion of the body) to provide measurement and/or analysis of physiological information from the user 100. According to some embodiments, the wearable device 200 senses, measures, or otherwise quantifies the motion of at least one body part of a user upon which the wearable device 200 is located. Additionally, or in the alternative, according to some embodiments, the wearable device 200 senses, measures, or otherwise quantifies the temperature of the environment of the wearable device 200, including, for example, the skin and/or body temperature at the location that the wearable device 200 is coupled to the body of a user. Additionally, or in the alternative, according to some embodiments, the wearable device 200 senses, measures, or otherwise quantifies other characteristics and/or parameters of the body (e.g., human or animal body) and/or surface of the body, including, for example, electrical signals associated with cardiac activity (e.g., ECG), electrical signals associated with muscle activity (e.g., electromyography (EMG)), changes in electrical potential and impedance associated with changes to the skin (e.g., galvanic skin response), electrical signals of the brain (e.g., electroencephalogram (EEG)), bioimpedance monitoring (e.g., body-mass index, stress characterization, and sweat quantification), and optically modulated sensing (e.g., photoplethysmography (PPG) and pulse-wave velocity), and the like.

[0031] The wearable device 200 described herein can be formed as a patch. The patch can be flexible and stretchable, and can include stretchable and/or conformal electronics and conformal electrodes disposed in or on a flexible and/or stretchable substrate. Alternatively, the wearable device 200 can be rigid but otherwise attachable to a user. In accordance with some embodiments of the invention, the wearable device 200 can include portions that are stretchable and/or conformable and portions that are rigid. Thus, the wearable device 200 can be any device that is wearable on a user, such as coupled to the skin of the user, to provide measurement and/or analysis of physiological information of the user. For example, the wearable device can be adhered to the body by adhesive, held in place against the body by tape or straps, or held in place against the body by clothing. The more conformal the sensing device is more likely to stay in position on the skin and produce more reliable and accurate sensor data.

[0032] In general, the wearable device 200 of FIG 2 can include at least one processor 201 and one or more associated memory storage modules 203. The wearable device 200 can further include one or more sensors, such as an accelerometer 205 and/or a temperature sensor 213 and/or an optical sensor 217. The wearable device 200 can optionally include one or more wireless transceivers, such as transceiver 207, for communicating with other sensor devices such as the master sensor device 110 or other computing devices such as the user device 130 in FIG. 1. The wearable device 200 can also include a power source 209 that provides power for the components of the wearable device 200. In accordance with some embodiments, the wearable device 200 can be configured to draw power from a wireless connection or an electromagnetic field (e.g., an induction coil, an NFC reader device, microwaves, and light).

[0033] The processor 201 can be a controller that is configured to control the wearable device 200 and components thereof based on computer program code. Thus, the processor 201 can control the wearable device 200 to measure and quantify data indicative of temperature, motion and/or other physiological data, and/or analyze such data indicative of temperature, motion and/or other physiological data according to the principles described herein.

[0034] The memory storage module 203 can be configured to save the generated sensor data (e.g., the time when a pulse in blood flow is sensed, accelerometer 205 information, temperature sensor 213 information, or other physiological information, such as ECG, EMG, etc.) or information representative of acceleration and/or temperature and/or other physiological information derived from the sensor data. Further, according to some embodiments, the memory storage module 203 can be configured to store the computer program code that controls the processor 201. In some implementations, the memory storage module 203 can be volatile and/or non-volatile memory. For example, the memory storage module 203 can include flash memory, static memory, solid state memory, removable memory cards, or any combination thereof. In certain examples, the memory storage module 203 can be removable from the wearable device 200. In some implementations, the memory storage module 203 can be local to the wearable device 200, while in other examples the memory storage module 203 can be remote from the wearable device 200. For example, the memory storage module 203 can be internal memory of a smartphone such as the user device 130 in FIG. 1 that is in wired or wireless communication with the wearable device 200, such as through radio frequency communication protocols including, for example, WiFi, Zigbee, Bluetooth®, medical telemetry and near-field communication (NFC), and/or optically using, for example, infrared or non-infrared LEDs. In such an example, the wearable device 200 can optionally communicate (e.g., wirelessly) with a user device 130 such as a smartphone via an application (e.g., program) executing on the smartphone.

[0035] In some embodiments, the generated data, including the temperature information, the acceleration information, and/or the other physiological information (e.g., ECG, EMG, etc.), can be stored on the memory storage module 203 for processing at a later time. Thus, in some embodiments, the wearable device 200 can include more than one memory storage module 203, such as one volatile and one non-volatile memory storage module 203. In other examples, the memory storage module 203 can store the information indicative of motion (e.g., acceleration information), temperature information, physiological data, or analysis of such information indicative of motion, temperature, physiological data according to the principles described herein, such as storing historical acceleration information, historical temperature information, historical extracted features, and/or historical locations. The memory storage module 203 can also store time and/or date information about when the information was received from the sensor.

[0036] Although described as the processor 201 being configured according to computer program code in the form of software and firmware, the functionality of the wearable device 200 can be implemented based on hardware, software, or firmware or a combination thereof. For example, the memory storage module 203 can include computer program code in the form of software or firmware that can be retrieved and executed by the processor 201. The processor 201 executes the computer program code that implements the functionality discussed below with respect to determining the on-body status of the wearable device 200, the location of the wearable device 200 on a user, and configuring functionality of the wearable device 200 (e.g., based on the on-body status and sensed location). Alternatively, one or more other components of the wearable device 200 can be hardwired to perform some or all of the functionality.

[0037] The power source 209 can be any type of rechargeable (or single use) power source for an electronic device, such as, but not limited to, one or more electrochemical cells or batteries, one or more photovoltaic cells, or a combination thereof. In the case of the photovoltaic cells, the cells can charge one or more electrochemical cells and/or batteries. In accordance with some embodiments, the power source 209 can be a small battery or capacitor that stores enough energy for the device to power up and execute a predefined program sequence before running out of energy, for example, an NFC based sensing device.

[0038] As discussed above, the wearable device 200 can include one or more sensors, such as the accelerometer 205, a temperature sensor 213, electrical contacts 215 (e.g., electrical contacts or electrodes), and/or an optical sensor 217. In accordance with some embodiments, one or more of the sensors, such as accelerometer 205, the optical sensor 217 and/or electrical contacts 215, can be separate components from the wearable device 200. That is, the wearable device 200 can be connected (by wire or wirelessly) to each sensor (e.g., accelerometer 205, temperature sensor 213, electrical contacts 215, optical sensor 217). This enables the wearable device 200 to sense conditions at one or more locations that are remote from the wearable device 200. In accordance with some embodiments, the wearable device 200 can include one or more integral sensors in addition to one or more remote sensors.

[0039] The accelerometer 205 measures and/or generates acceleration information indicative of a motion and/or acceleration of the wearable device 200, including information indicative of a user wearing, and/or body parts of the user wearing, the wearable device 200. In accordance with one embodiment, the accelerometer 205 within the wearable device 200 can include a 3- axis accelerometer that generates acceleration information with respect to the x-axis, the y-axis, and the z-axis of the accelerometer based on the acceleration experienced by the wearable device 200. Alternatively, the wearable device 200 can include three independent accelerometers (not shown for illustrative convenience) that each generate acceleration information with respect to a single axis, such as the x-axis, the y-axis, or the z-axis of the wearable device 200. Alternatively, the wearable device 200 can include an inertial measurement unit (IMU) that measures the velocity, the orientation, and the acceleration using a combination of one or more accelerometers, gyroscopes, and magnetometers. Thus, although generally referred to herein as an accelerometer 205, the accelerometer 205 can be any motion sensing element or combination of elements that provides acceleration information.

[0040] According to some embodiments, the accelerometer 205 includes a detection range of ±4 times the force of gravity (Gs). However, the range can vary, such as being ±10 Gs or ±2 Gs. Further, the accelerometer 205 can have a sampling rate of 50 hertz (Hz) such that each second the accelerometer 205 generates 150 points of acceleration information, or 50 points within each axis. However, the sampling rate can vary, such as being 20 Hz to 100 Hz.

[0041] According to some embodiments, one or more sensors of the wearable device 200, such as the accelerometer 205, can include a built-in temperature sensor, such as the temperature sensor 211 within the accelerometer 205. For example, the temperature sensor 211 within the accelerometer 205 can be used to calibrate the accelerometer 205 over a wide temperature range and to measure the temperature of the area of the body that the accelerometer 205 is coupled to. Other temperature sensors included with other device components can also be used. Other than the accelerometer 205, and temperature sensor 211, other subcomponents or elements of the wearable device 200 can include one or more microelectromechanical system (MEMS) components within the wearable device 200 that is designed to measure motion or orientation (e.g., angular-rate gyroscope, etc.). Alternatively, or in addition, the wearable device 200 can include a discrete temperature sensor, such as the temperature sensor 213 which can be positioned in a different location from the wearable device 200. The wearable device 200 can use the temperature information detected by the temperature sensor 211 and/or the temperature sensor 213 according to various methods and processes. For purposes of convenience, reference is made below to the temperature sensor 211. However, such reference is not limited to apply only to the temperature sensor 211, but applies to any one or more temperature sensors within or connected to the wearable device 200.

[0042] The electrical contacts 215 can be formed of conductive material (e.g., copper, silver, gold, aluminum, a hydrogel, conductive polymer, etc.) and provide an interface between the wearable device 200 and the skin of the user 100, for receiving electrical signals (e.g., ECG, EMG, etc.) from the skin. The electrical contacts 215 can include one or more electrical contacts 215, such as two electrical contacts 215, electrically connecting the skin of the user 100 to an amplifier circuit that can be part of an analog front end circuit 216, to amplify and condition electrical signals (e.g., ECG, EMG, etc). With two electrical contacts 215, one contact can be electrically configured as a positive contact and the other contact can be electrically configured as a negative contact. However, in some aspects, there may be more than two electrical contacts, such as four electrical contacts 215 (e.g., two positive and two negative electrical contacts), six electrical contacts 215, etc.

[0043] The optical sensor 217 can include one or more light emitters that can emit red, green, infrared light or a combination thereof and one or more optical transducers (e.g., photodiode, CCD sensors). Using the one or more optical transducers, the optical sensor 217 can sense the wavelength of the reflected light. In this example, the optical sensor 217 illuminates the skin and the reflected light changes intensity based on the concentration of oxygen in a blood vessel. Thus, a pulse can be detected as a change in the amount of the reflected light due to a change in the concentration of oxygen in a blood vessel and thus the reflected light detected by the optical sensor 217. Of course other sensors can be included on the wearable device 200 to detect the pulse such as an acoustic sensor to measure the mechanoacoustic signatures of the pulse.

[0044] In addition to the above-described components, the wearable device 200 can include one or more additional components without departing from the spirit and scope of the present disclosure. Such components can include a display (e.g., one or more light-emitting diodes (LEDs), liquid crystal display (LCD), organic light-emitting diode (OLED)), a speaker, a microphone, a vibration motor, a barometer, a light sensor, a photoelectric sensor, or any other sensor for sensing, measuring, or otherwise quantifying parameters and/or characteristics of the body. In other embodiments of the invention, the wearable device 200 can include components for performing one or more additional sensor modalities, such as, but not limited to, hydration level measurements, conductance measurements, and/or pressure measurements. For example, the wearable device 200 can be configured to, or include one or more components that, perform any combination of these different types of sensor measurements, in addition to the accelerometer 205 and temperature sensor 211.

[0045] Referring back to the temperature sensor 211, according to some embodiments, the primary purpose of the temperature sensor 211 is for calibrating the accelerometer 205. Accordingly, the temperature sensor 211 does not rely on direct contact to an object to detect the temperature. By way of example, the temperature sensor 211 does not require direct contact to the skin of a user when coupled to the user to determine the skin temperature. For example, the skin temperature affects the temperature information generated by the wearable device 200 without direct contact between the temperature sensor 211 and the skin. Accordingly, the temperature sensor 211 can be fully encapsulated and, therefore, be waterproof for greater durability. The thermal conductivity of the encapsulating material can be selected to control the ability of the temperature sensor 211 to detect the temperature without direct contact.

[0046] In accordance with some embodiments, a user's blood pressure can be measured using two or more sensor devices, such as the wearable sensing device 200. In this example, the master sensor device 110 in FIG. 1 measures electrocardiogram (ECG) data at the chest of the user 100 via the electrical contacts or electrodes 215 in FIG. 2. Another (or several) sensor devices such as the sensor devices 112, 114, 116, 118 and 120 can be placed at different locations on the body of the user 100 such as the wrists 142 and 144, feet 146 ankle 148, and neck 150 and configured to measure photoplethysmography (PPG) or accelerometer data to detect the pulse at the location of the sensor. Of course, other types of sensors on the sensor devices such as the optical sensor 217 or an acoustic sensor can be used to detect the pulse. As shown in FIG. 1, the master sensor device 110 can be configured to periodically or continuously transmit its clock synchronization data in a clock timestamp signal via the transceiver 207. The clock timestamp signal can include analog and/or digital signals, information and data. In one example, the transceiver 207 can send the clock timestamp signal at an interval of 30 seconds via a low energy Bluetooth signal, although other intervals in the range of 1-60 seconds can be used. The slave sensor devices 112, 114, 116, 118 and 120 can include one or more transceivers 207 configured to listen for the clock timestamp signal in the Bluetooth low energy signal and capture the clock timestamp signal in order to synchronize the local clock on the slave sensor device. In accordance with some embodiments, of the invention the slave device 112, 114, 116, 118 and 120 can synchronize its local clock by resetting the time in software to match the timestamp from the master device 110 clock such that the time stamp of the slave device 112, 114, 116, 118 and 120 will be synchronized with the master device 110. In accordance with some embodiments of the invention, the slave device 112, 114, 116, 118 and 120 can keep track of the difference in time between master device 110 time stamp and the local slave clock and apply the difference to each time stamp that is created when a local PPG or pulse signal is detected. The timestamps applied by the slave sensor devices to the PPG data are therefore synchronized with the clock of the master sensor device 110. Synchronization accuracy of at least 1 ms is achievable for the sensor devices 110, 112, 114, 116, 118 and 120.

[0047] The form factor of the wearable device 200 allows positioning and repositioning of the sensor devices at different locations on the body of the user 100 in order to achieve the highest quality of data. In this example, the master sensor 110 placed on the chest 140 is set in electrocardiogram (ECG) mode in order to receive the time-point of a pulse associated with the R-wave from measuring the ECG of the heart of the user 100. The blood is pumped through blood vessels by the heart thereby sending the pulse and associated R-wave throughout the blood vessels. Alternatively, the master sensor 110 may measure PPG data to determine the time-point of the pulse. The pulse transit time or pulse arrival time is measured based on data from one or more of the other slave sensor devices 112, 114, 116, 118 and 120. The slave sensor device is attached at an extremity such as the wrist, ankle, or foot of the user 110. For example, the slave sensor device 112 is attached to the right wrist 142 of the user 100. The slave sensor device captures the time-point of the pulse associated with the pressure-wave using a photoplethysmography (PPG) sensor or accelerometer. The wearable device 200 can provide high quality ECG and PPG data as it conforms to the body and is coupled to the skin of the user 100 without bands or other fastening devices placing pressure on the arterial wall which would alter the measurement. This tight coupling also reduces the motion artifacts. The accelerometer 205 may be used to cancel out noise seen by the PPG sensor.

[0048] The slave sensor devices 112, 114, 116, 118 and 120 can be synchronized to the clock of the master sensor device 110. In accordance with some embodiments of the invention, the master sensor device 110 broadcasts timestamps in the form of a low energy communication signal at a known time interval to the other sensor devices 112, 114, 116, 118 and 120. The "slave" sensor devices can be configured to listen for the timestamp data and use it to synchronize the pulse data that is sensed to the clock of the master sensor device 110. In accordance with some embodiments, of the invention the slave device 112, 114, 116, 118 and 120 can synchronize its local clock by resetting the date and time information in software to match the timestamp from the master device 110 clock such that the time stamp of the slave device 112, 114, 1 16, 118 and 120 will be synchronized with the master device 110. In accordance with some embodiments of the invention, the slave device 112, 114, 116, 118 and 120 can keep track of the difference in time between master device 110 time stamp and the local slave clock and apply the difference to each time stamp that is created when a local PPG or pulse signal is detected. The master sensor device 110 and the slave sensor devices 112, 114, 116, 118 and 120 transmit the time data of the pulse at the extreme locations to the user device 130 for purposes of determining the pulse transit time.

[0049] Using the above methods, any number of "slave" sensor devices may be applied to the patient. For example, different sensor devices may be applied to locations on the body to determine changes in blood pressure at those specific regions of the body between the master sensor and each slave sensor device. This allows identification of vasodilation (dilation of blood vessels) at localized regions of the body that can provide a strong indicator of inflammation.

[0050] FIG. 3A is a graph 300 showing a visualization of the data stream from the master sensor device 110 and one of the slave sensor devices such as the slave sensor device 120 attached near the carotid artery of the user 100 in FIG. 1. A first trace 310 is the output of the ECG sensed from the electrodes 215 of the master sensor device 110. In this example, the ECG of the master sensor device 110 is sampled at 250 Hz and digitized to 16 bits. A second trace 320 is the output of the accelerometer 205 of the slave sensor device 120 located near the carotid artery in the neck 150. In this example, the accelerometer sensor is sampled at 500 Hz at ± 2 g mode at 16 bits. A pulse pressure wave is detected at a first time point 322 on the first trace 310. The pulse pressure wave is detected at a second time point 324 on the second trace 312. The time difference between the two time points 322 and 324 constitute the pulse arrival time between the heart and the neck 150 through the carotid artery.

[0051] FIG. 3B is a graph 350 showing a magnified view of the plotted waveforms of the first trace 310 representing the ECG sensor signal from the master sensor 110 and the second trace 320 representing the accelerometer sensor output from the slave sensor 120. FIG. 3B shows a closeup view of the pulse pressure wave at the first time point 322 on the first trace 310 and the second time point 324 on the second trace 320. As explained above, the trace data such as the first trace 310 and the second trace 320 and associated time stamps is sent to the user device 130 from the sensors 110 and 120 in FIG. 1 for pulse peak and foot detection.

[0052] FIG. 4 is a graph 400 showing a visualization of the data stream from the master sensor device 110 and one of the slave sensor devices such as the slave sensor device 112 attached near the wrist 142 of the user 100 in FIG. 1. A first trace 410 is the output of the ECG sensed from the electrodes 215 of the master sensor device 110. In this example, the ECG of the master sensor device 110 is sampled at 250 Hz and digitized to 16 bits. A second trace 420 is the output of the optical sensor 217 of the slave sensor device 120 located near the wrist 142. In this example, the optical sensor is sampled at 400 Hz at 18 bits. An electrical wave is detected at a first time point 422 on the first trace 410. A pulse pressure wave is detected at a second time point 424 on the second trace 412. The time difference between the two time points 422 and 424 constitute the pulse arrival time between the heart and the wrist 142 through the artery.

[0053] The relative blood pressure can be determined as a function of the pulse transit time and distance between the master and slave sensor device. The pulse transit time and the distance between the two points of measurement allows calculation of the Pulse Wave Velocity (PWV). The distance between respective sensors can be based on user input or determined from tables reflecting the estimated distance between the locations of the sensors based on the height and other biometric measurements of a user. The tables can be stored in memory on the user device 130. For example, the distance between the master sensor device 110 and sensor devices 112 and 114 on the user's wrists can be stored in memory on the user device 130. Similarly, the distance between the master sensor device 110 and the sensor device 116 on the user's foot may be stored in memory. Similarly, the distance between two slave sensor devices such as a sensor device attached to a wrist and a sensor device attached to a shoulder may be stored memory. Of course other methods may be used to determine the distance between respective sensors. A calibration measurement of blood pressure is made by a conventional cuff based blood pressure monitor and input to the user device 130. The calibration measurement may be used to determine the basic properties of the vessel wall. Knowing the basic properties of the vessel wall, and the PWV, the pressure exerted on the wall may be calculated and thus the blood pressure may be determined from the PTT or PAT.

[0054] Blood pressure is inversely proportional to the pulse transit time. By determining the pulse transit time from the master and slave sensors over a period of time, whether an individual's blood pressure has increased or decreased over time relative to an initial measurement at rest may be determined.

[0055] Absolute blood pressure may also be determined using the master and slave sensor devices. Absolute blood pressure is more difficult to determine due to the sensitive dependencies on displacement between sensors and individualized physiological metrics. Absolute blood pressure therefore involves generating a calibration constant for each new individual. This calibration would require measuring blood pressure using a blood pressure cuff and correlating that to a measured pulse transit time. Such data is sent to the master sensor device 110 or user device 130 to allow calibration. The equation for determining absolute blood pressure is as follows:

Where Ki and K₂ are constants derived from calibration. The determination of the pulse transit time may be made by the master sensor 110 after receiving time stamped pulse data from the slave sensor. Alternatively, such data may be received by the user device 130 in FIG. 1 for the determination of relative and absolute blood pressure.

[0056] FIG. 5 is a flow diagram of the process of determining blood pressure as function of PTT or PAT in the system shown in FIG. 1. Handshaking can be performed between the user device 130 and the master sensor device 110 and at least one of the slave sensor devices 112, 114, 116, 118, and 120 (500). The handshaking involves sending identification information for each of the sensor devices, a MAC address to the user device 130. The user device 130 sets initial configuration data such as the location of the respective sensor on the body, the sampling rate and applicable storage parameters (502). The user device 130 also sends an initial clock timestamp to the master sensor device 110 during the initial configuration process. The clock timestamp from the user device 130 is used by the master sensor device 110 to synchronize the rest of the slave devices 112, 114, 116, 118, and 120. The clock timestamp from the user device 130 is sent periodically to recalibrate the system. For example, the clock timestamp can be sent once a day or every time the user device 130 establishes initial communication with the master sensor device 110. The master sensor device 110 sends a signal that includes timestamp data to the slave sensor devices (504). In this example, the timestamp data signal is sent every 30 seconds from the master sensor device 110. The clock timestamp signal can be received by the slave sensor devices and each slave sensor device synchronizes the initial value of a time counter to the clock timestamp signal received from the master sensor device 110 (506). In this manner, the time counter of the slave sensor can be synchronized with the clock of the master sensor device 110.

[0057] In this example, the master sensor 110 continuously sends the output of the ECG signal received from the electrical contacts 215 in FIG. 2 to the user device 130. The output of the ECG signal includes a number of samples such as four samples associated with a particular timestamp. The user device 130 receives the ECG output from the master sensor 110 and senses an R-wave of the pulse from the ECG wave (508). The user device 130 records the timestamp data associated with the R-wave of the pulse (510).

[0058] The accelerometer on the slave sensor also continuously sends an output to the user device 130 based on a number of samples associated with a particular timestamp. The user device 130 senses the pulse based on sensing a foot of the PPG signal from the accelerometer output when the pressure wave reaches the location of the slave sensor (512). The user device 130 records the timestamp associated with the sample when the pulse is sensed (514). The pulse arrival time is determined by the user device 130 based on the timestamps from the R-wave and the pulse determined from the PPG signal (514). The blood pressure is determined from the pulse arrival time by the user device 130 (518). The blood pressure is then stored in the memory of the user device 130 (520). Of course, the master sensor 110 may also sample the PPG signal and send the signal to the user device 130 for determining pulse transit time.

[0059] The process described in FIG. 5 can be used for real time determination of blood pressure by the user device 130. Some or all of the operations described above may be performed by the master sensor 110. Alternatively, the timestamp data and respective signals may be transmitted to the cloud server 162 and some or all of the above operations may be performed by the cloud server 162. Alternatively, the master sensor 110 may store the waveform data and transmit the stored data periodically to the user device 130 for measurement of the blood pressure at a delayed time.

[0060] FIG. 6 is a flow diagram showing the synchronization process used by the handshake step 500 and initial configuration step 502 in FIG. 5. The user device 130 interfaces with the master sensor 110 via a Bluetooth low energy signal (600). The user device 130 in this example can send a time synchronization message that can include a timestamp (e.g. Unix/Epoch time stamp) and offset unit from the timestamp (e.g., in microseconds) to the master sensor 110 via the Bluetooth transceiver (602). The master sensor 110 can receive and apply the timestamp and offset from the user device 130 as an initial setting (604). In accordance with some embodiments, the processor 201 of the master sensor 110 can increment its clock with 15 bit precision per second (e.g., 30.52 microsecond increments). The master sensor 110 loads the timestamp to a data payload of a Bluetooth low energy transmission packet prior to the transmission of the packet (606). The transceiver 207 of the master sensor 110 broadcasts the timestamp data in a transmission packet to the slave sensors via a Bluetooth low energy transmission signal (608). The master sensor 110 continues to broadcast the time stamps at a predetermined frequency (e.g., once every 10 sec, 20 sec, or 30 sec.) (610).

[0061] The slave sensors such as the sensor devices 112 and 1 18 enable the transceiver 207 in receive mode and listen to the timestamp broadcast from the master sensor 110 (e.g., continuously or at a predetermined rate) (612). The slave sensor devices 112 and 118 can receive the timestamp packet from the master sensor 110 and parse the data for the timestamp (614). The slave sensors can store the timestamp from the master sensor device and add a transmission latency offset to the current local time setting of the slave sensor. For example, the processor 201 in the slave sensor increments a counter initialized from the received timestamp with 15 bit precision per second (616).

[0062] FIG. 7A is a block diagram of a procedure performed by the system in FIG. 1 to determine a pulse arrival time measurement. This procedure can be used in the blood pressure determination process described in FIG. 5 above. In this example, an ECG waveform 700 generated by the user 100 is measured by the master sensor 110. The user device 130 determines the time an R-wave peak 702 occurs in the ECG waveform 700 as measured by the master sensor 110. A PPG waveform 710 generated from blood flow in the user 100 is measured by the slave sensor 112 attached to the wrist of the user 100. The user device 130 also receives the time a foot 712 occurs in the PPG waveform 710 as measured by the slave sensor 112.

[0063] The user device 130 determines the time difference of the timestamps corresponding to the received peak measurements from the master sensor 110 and the slave sensor 112 (720). The user device 130 then determines the pulse arrival time (PAT) from the time difference (730).

[0064] FIG. 7B is a block diagram of a procedure performed by the system in FIG. 1 to determine a pulse transit time measurement between two slave sensors. In this example, a PPG waveform 750 generated from blood flow in the user 100 is sensed by a slave sensor 752. In this example the slave sensor 752 is attached the shoulder of the user 100, but other slave sensors such as the slave sensors 114, 116 and 118 may be used. The user device 130 receives the sensed waveform and determines the time a foot 754 occurs in the PPG waveform 750 as measured by the slave sensor 752. Another PPG waveform 760 generated from blood flow in the user 100 is measured by the slave sensor 112. The user device 130 also receives the sensed waveform 760 and determines the time a foot 762 occurs in the PPG waveform 760 as measured by the slave sensor 112.

[0065] The user device 130 determines the time difference of the timestamps corresponding to the received foot PPG measurements from PPG waveforms received from the first slave sensor 752 and the slave sensor 112 (770). Since the pulse travels via the blood flow, the pulse will first be detected by the first slave sensor 752 and then by the slave sensor 112 as the blood flows from the shoulder of the user 100 to the wrist. The user device 130 then determines the pulse transit time (PTT) from the time difference (780).

[0066] The system of sensor devices on a user allows continuous and non-invasive blood pressure monitoring. The monitoring may be for absolute or relative blood pressure. The continuous blood pressure monitoring allows better data for improvements in health for healthy and unhealthy individuals. The non-intrusive patch sensor devices allow comfortable noninvasive tracking of blood pressure giving a better user experience. The monitoring allows higher accuracy due to sensor placement and sensor fusion. With the architecture of the wearable device 200, multiple patches may be attached to the body of the user 100 to measure localized blood pressure at a variety of locations typically inaccessible.

[0067] For example, localized blood pressure may be monitored in order to track inflammation and wound healing. FIG. 8 shows a user 800 with the application of slave sensors 810, 812, 814 and 816 on the right shoulder, right wrist, right thigh and right ankle respectively. Slave sensors 820, 822, 824 and 826 are applied on the left shoulder, left wrist, left thigh and left ankle respectively. FIG. 8 shows the measurement of localized blood pressure by a user device such as the user device 130 in FIG. 1. In this example, the blood pressure for each limb (right arm, left arm, left arm and left leg) may be measured. The ratio of the maximum blood pressures correlates to detection of peripheral arterial disease.

[0068] The localized blood pressure of the right arm may be determined by the transmission of the detection of a pulse from a PPG waveform measured by the slave sensors 810 and 812 and sent to a user device. The time difference is determined by a user device after detecting when the pulses occurred (830). The pulse transit time may then be determined by the time difference (832). The blood pressure of the right arm may then be determined from the PTT (834). Similarly, the localized blood pressure of the right leg may be determined by the transmission of a PPG waveform measured by the slave sensors 814 and 816 to a user device. The time difference is determined by a user device after detecting when the pulses occurred (840). The pulse transit time may then be determined by the time difference (842). The blood pressure of the right leg may then be determined from the PTT (844).

[0069] The localized blood pressure of the left arm may be determined by the transmission of the detection of a pulse from a PPG waveform measured by the slave sensors 820 and 822 to a user device. The time difference is determined by a user device (850). The pulse transit time may then be determined by the time difference (852). The blood pressure of the left arm may then be determined from the PTT (854). Similarly, the localized blood pressure of the left leg may be determined by the transmission of the detection of a pulse from a PPG waveform measured by the slave sensors 824 and 826 to a user device. The time difference is determined by a user device (860). The pulse transit time may then be determined by the time difference (862). The blood pressure of the left leg may then be determined from the PTT (864).

[0070] The ankle-brachial index of the right side of the user 800 may be determined by dividing the maximum blood pressure of the right leg by the maximum blood pressure of the arms (the higher blood pressure measured from the right and left arms). The ankle-brachial index of the left side of the user 800 may be determined by dividing the maximum blood pressure of the left leg by the maximum blood pressure of the arms (the higher blood pressure measured from the right and left arms).

[0071] Application of a number of "slave" patches to a subject at a variety of locations on the body to determine changes in blood pressure at those specific regions. This allows identification of vasodilation (dilation of blood vessels) at localized regions of the body which are a strong indicator of inflammation. This data may be used to track wound healing, as inflammation and vasodilation is usually an indicator of the body attempting to combat pathogens and speed healing.

[0072] FIG. 9 shows a treatment system 900 that relies on localized blood pressure monitoring to treat a wound. The system 900 includes a controller 902 that receives data from two slave sensor devices 910 and 912 on a patient. In this example, the two slave sensor devices 910 and 912 are attached to the thigh and the foot of the patient. The two slave sensor devices 910 and 912 allow the measurement of localized blood pressure in the leg. The controller 902 is also connected to a drug delivery device 920 that allows delivery of drugs to an injured area. It is to be understood that data may be taken by sensors located anywhere around a wound to determine the local blood pressure.

[0073] A wound results in an inflammatory response in an area of a patient. The skin includes an epidermal and subcutaneous layer composed of a complex network of cells that communicates chemically. These cells include skin cells, mast cells and dendrite cells. Oxygen carrying red and white blood cells travel through arteries that are composed of capillary endothelial cells. When an object pierces the epidermal layer of a person, an inflammation response is initiated causing mast cells to release histamine as a first line of defense. The histamine causes the arteries and capillaries to dilate (vasodilation), creating openings between the vessel-lining cells. The openings are large enough for white blood cells to pass through, promoting an attack on the infection area. This reaction causes a loss in blood pressure that is reflected in an increase in pulse transmit time.

[0074] The controller 902 monitors the blood pressure of the limb with the infected area via determining PTT from the time pulses are detected in the PPG signals received from the slave sensor devices 910 and 912. On detecting an increase in PTT indicating a loss of blood pressure from the reactions to an infection, the controller 902 activates the drug delivery device 920 to deliver drugs such as an anti-histamine or steroids to reduce and mitigate the infection.

[0075] In some embodiments, the aforementioned methods include at least those steps enumerated above. It is also within the scope and spirit of the present disclosure to omit steps, include additional steps, and/or modify the order of steps presented herein. It should be further noted that each of the foregoing methods can be representative of a single sequence of related steps; however, it is expected that each of these methods will be practiced in a systematic and repetitive manner.

[0076] While particular embodiments and applications of the present disclosure have been illustrated and described, it is to be understood that the present disclosure is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations can be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

CLAIMS What is claimed is:

1. A system for sensing blood pressure of a user, the system comprising:

a master sensor device including a clock signal generator generating a clock signal, a transceiver transmitting the clock signal, and a pulse sensor sensing a pulse at a first location on the user;

a first slave sensor device attached at a second location on the user remote from the first location, the slave sensor device including a pulse sensor sensing the pulse of the user at the second location, a transceiver receiving the clock signal from the master sensor device, wherein the first slave sensor device synchronizes the sensing of the pulse to the clock signal and the transceiver transmitting a time stamp signal to the master sensor device; and

a controller to determine blood pressure of the user based on a pulse transit time or a pulse arrival time between the sensing of the pulse by the master sensor device and the first slave sensor device.

2. The system of claim 1 further comprising a second slave sensor attached to a third location on the user remote from the first location, the second slave sensor device including a pulse sensor sensing the pulse of the user at the third location, a transceiver receiving the clock signal from the master sensor device, wherein the second slave sensor device synchronizes the sensing of the pulse to the clock signal and the transceiver transmitting a time stamp signal to the master sensor, wherein the controller determines another blood pressure of the user based on a pulse transit time or a pulse arrival time between the sensing of the pulse by the master sensor device and the second slave sensor device.

3. The system of claim 1, wherein the pulse sensor of the master slave device is an electrocardiogram (ECG) sensor or a photoplethysmography (PPG) sensor.

4. The system of claim 1, wherein the pulse sensor of the slave sensor device is a photoplethysmography (PPG) sensor.

5. The system of claim 1, wherein the pulse sensor of the slave sensor device is one of an accelerometer or an acoustic sensor.

6. The system of claim 1, wherein the controller receives a calibration signal including a calibration blood pressure measurement of the user and wherein the determination of blood pressure includes the calibration blood pressure measurement.

7. The system of claim 6, wherein the calibration blood pressure measurement is obtained by a pressure cuff device.

8. The system of claim 6, wherein the determined blood pressure is absolute blood pressure of the user.

9. The system of claim 1, wherein the master sensor device includes memory to store the time stamp signal received from the slave sensor device and an initial time associated with the sensing of the pulse by the master sensor device.

10. The system of claim 1, wherein the controller is in the master sensor device.

11. The system of claim 1, further comprising a user device including a transceiver, the user device in communication with the master sensor device.

12. The system of claim 11, wherein the controller is in the user device and wherein the user device determines the pulse transit time or the pulse arrival time based on received pulse data from the master sensor device and the slave sensor device.

13. The system of claim 1, wherein relative blood pressure is determined by measuring a second time pulse transit time or pulse arrival time associated with a second pulse sensed by the master sensor device and the slave sensor device.

14. The system of claim 1, wherein the first location is at the chest of the user, and the second location is one of an upper arm, a lower arm, a wrist, an upper leg, a lower leg, a foot, a neck or an ankle of the user.

15. The system of claim 14, wherein the determined blood pressure is associated with the second location on the user.

16. The system of device of claim 1, wherein the pulse is sensed continuously, periodically, and/or on demand of the controller.

17. The system of claim 1, wherein the blood pressure is determined continuously, periodically, and/or on demand.

18. The system of claim 1, wherein the first slave sensor device is mounted on the skin of the user.

19. A sensor device worn on the chest of a user, the sensor device comprising:

a clock signal generator generating a clock signal;

a pulse sensor to sense a pulse of the user;

a transceiver coupled to the clock signal generator, the transceiver transmitting a clock signal to a slave sensor device worn on the user at a location remote from the chest, the transceiver receiving a time stamp signal from the slave sensor device sensing the pulse; and a processor coupled to the transceiver, the processor determining blood pressure of the user based on a pulse transit time or a pulse arrival time determined from the time stamp signal and a time when the electro cardiogram sensor senses the pulse.

20. The sensor device of claim 19, wherein another slave sensor is attached to another location on the user, the another slave sensor device receiving the clock signal from the transceiver, and wherein the transceiver receives another time stamp signal from the another slave sensor device sensing the pulse, wherein the processor determines another blood pressure of the user based on a pulse transit time or a pulse arrival time determined from the another time stamp signal and the time when the electro cardiogram sensor senses the pulse.

21. The sensor device of claim 19, wherein the pulse sensor is an electro-cardiogram (ECG) sensor or a photoplethysmography (PPG) sensor.

22. The sensor device of claim 19, wherein the slave sensor device includes a photoplethysmography (PPG) sensor.

23. The sensor device of claim 19, wherein the pulse sensor of the slave sensor device is one of an accelerometer or an acoustic sensor.

24. The sensor device of claim 19, wherein the processor receives a calibration signal including a calibration blood pressure measurement of the user and wherein the determination of blood pressure includes the calibration blood pressure measurement.

25. The sensor device of claim 24, wherein the calibration blood pressure measurement is obtained by a pressure cuff device.

26. The sensor device of claim 24, wherein the determined blood pressure is absolute blood pressure of the user.

27. The sensor device of claim 19, further comprising a memory to store the time stamp signal received from the slave sensor device and the time when the electro cardiogram sensor senses the pulse.

28. The sensor device of claim 19, wherein the transceiver is in communication with a user device.

29. The sensor device of claim 19, wherein relative blood pressure is determined by measuring a second time pulse transit time or pulse arrival time associated with a second pulse sensed by the sensor device and the slave sensor device.

30. The sensor device of claim 19, wherein the remote location is one of an upper arm, a lower arm, a wrist, an upper leg, a lower leg, a foot, a neck or an ankle of the user.

31. The sensor device of claim 30, wherein the determined blood pressure is associated with the second location on the user.

32. The sensor device of claim 19, wherein the pulse is sensed continuously, periodically, and/or on demand of the process.

33. The sensor device of claim 19, wherein the blood pressure is determined continuously, periodically, and/or on demand.

34. A method of measuring blood pressure of a user, the method comprising:

attaching a master sensor device at a first location of the user;

attaching a first slave sensor device at a second location of the user, the second location being remote from the first location;

sending a clock synchronization signal from the master sensor device to the slave sensor device;

sensing a pulse of the user via the master sensor at an initial time;

sensing the pulse of the user via the first slave sensor device;

sending a timestamp signal of the sensed pulse from the first slave sensor device;

determining a pulse transit time or a pulse arrival time from the timestamp signal and the initial time via a controller; and

determining blood pressure based on the pulse transit time or pulse arrival time via the controller.

35. The method of claim 34 further comprising: attaching a second slave sensor to a third location on the user remote from the first location, the second slave sensor device including a pulse sensor sensing the pulse of the user at the third location,

receiving the clock synchronization signal from the master sensor device;

sensing of the pulse of the user via the second slave sensor device;

sending a second timestamp signal of the sensed pulse from the second slave sensor device; and

determining another blood pressure of the user based on a pulse transit time or pulse arrival time between the sensing of the pulse by the master sensor device and the second slave sensor device.

36. The method of claim 34, wherein the master sensor device senses the pulse via an electrocardiogram (ECG) sensor or a photoplethysmography (PPG) sensor.

37. The method of claim 34, wherein the slave sensor device senses the pulse via a photoplethysmography (PPG) sensor.

38. The method of claim 34, wherein the slave sensor device senses the pulse via one of an accelerometer or an acoustic sensor.

39. The method of claim 34, further comprising receiving a calibration signal including a calibration blood pressure measurement of the user, and wherein the determination of blood pressure includes the calibration blood pressure measurement.

40. The method of claim 39, wherein the calibration blood pressure measurement is obtained by a pressure cuff device.

41. The method of claim 39, wherein the determined blood pressure is absolute blood pressure of the user.

42. The method of claim 34, further comprising storing the time stamp signal received from the slave sensor device and an initial time associated with the sensing of the pulse by the master sensor device.

43. The method of claim 34, wherein the controller is in the master sensor device.

44. The method of claim 34, further comprising communicating a time signal from a user device to the master sensor device.

45. The method of claim 44, wherein the controller is in the user device and wherein the user device determines the pulse transit time or pulse arrival time based on received pulse data from the master sensor device and the slave sensor device.

46. The method of claim 34, wherein relative blood pressure is determined by measuring a second time pulse transit time or pulse arrival time associated with a second pulse sensed by the master sensor device and the slave sensor device.

47. The method of claim 34, wherein the first location is at the chest of the user, and the second location is one of an upper arm, a lower arm, a wrist, an upper leg, a lower leg, a foot, a neck or an ankle of the user.

48. The method of claim 47, wherein the determined blood pressure is associated with the second location on the user.

49. The method of claim 34, wherein the pulse is sensed continuously, periodically, and/or on demand of the controller.

50. The method of claim 34, wherein the blood pressure is determined continuously, periodically, and/or on demand.

51. The method of claim 34, wherein the first slave sensor device is mounted on the skin of the user.