U.S. patent application number 15/754006 was filed with the patent office on 2018-09-06 for device and system for monitoring of pulse-related information of a subject.
The applicant listed for this patent is KONINKLIJKE PHILIPS N.V.. Invention is credited to Ronaldus Maria Aarts, Ihor Olehovych Kirenko, Caifeng Shan.
Application Number | 20180249918 15/754006 |
Document ID | / |
Family ID | 54012036 |
Filed Date | 2018-09-06 |
United States Patent
Application |
20180249918 |
Kind Code |
A1 |
Kirenko; Ihor Olehovych ; et
al. |
September 6, 2018 |
DEVICE AND SYSTEM FOR MONITORING OF PULSE-RELATED INFORMATION OF A
SUBJECT
Abstract
The present invention relates to a wearable device for obtaining
signals from a subject for use in the monitoring of pulse-related
information of the subject. To enable the use of such a device in
the monitoring of pulse-related information of the subject, which
provides for unobtrusive, reproducible, easy to use, and simple
measurements, the device comprises a device body (20), a PPG signal
sensing unit (21) for acquiring a first photoplethysmography, PPG,
signal from a first body location of the subject's body, and an
imaging unit (22) for acquiring a sequence of images from a second
body location of the subject's body different from the first body
location, said sequence of images being configured for deriving a
second PPG signal for the second body location of the subject's
body. Said PPG signal sensing unit and said imaging unit are
mounted in or at the device body and are configured to
simultaneously acquire the first PPG signal and the sequence of
images.
Inventors: |
Kirenko; Ihor Olehovych;
(Veldhoven, NL) ; Aarts; Ronaldus Maria; (Geldrop,
NL) ; Shan; Caifeng; (Veldhoven, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KONINKLIJKE PHILIPS N.V. |
EINDHOVEN |
|
NL |
|
|
Family ID: |
54012036 |
Appl. No.: |
15/754006 |
Filed: |
August 24, 2016 |
PCT Filed: |
August 24, 2016 |
PCT NO: |
PCT/EP2016/069967 |
371 Date: |
February 21, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/6803 20130101;
A61B 5/02125 20130101; A61B 5/14552 20130101; A61B 5/02427
20130101; A61B 5/02433 20130101; A61B 5/6843 20130101; A61B 5/0017
20130101; A61B 5/0024 20130101; A61B 5/6824 20130101; A61B 5/681
20130101; A61B 5/6898 20130101; A61B 5/7278 20130101; A61B 5/0002
20130101; A61B 5/02438 20130101; A61B 5/0295 20130101; A61B 5/0261
20130101; A61B 5/6844 20130101; A61B 5/0077 20130101 |
International
Class: |
A61B 5/024 20060101
A61B005/024; A61B 5/00 20060101 A61B005/00; A61B 5/026 20060101
A61B005/026 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 25, 2015 |
EP |
15182289.7 |
Claims
1. Wearable device for obtaining signals from a subject for use in
the monitoring of pulse transit time and/or pulse arrival time,
said device comprising: a device body, a PPG signal sensing unit
for acquiring a first photoplethysmography, signal from a first
body location of the subject's body, wherein the PPG signal sensing
unit is in front of or in contact with the first body location when
the wearable device is worn by the subject, and an imaging unit for
acquiring a sequence of images from a second body location of the
subject's body different from the first body location, said
sequence of images being configured for deriving a second PPG
signal for the second body location of the subject's body, wherein
said PPG signal sensing unit and said imaging unit are mounted in
or at the device body and are configured to simultaneously acquire
the first PPG signal and the sequence of images, and a processing
unit for deriving the second PPG signal from said sequence of
images, wherein the processing unit is configured to determine the
pulse transit time and/or pulse arrival time based on the first PPG
signal and the second PPG signal.
2. Wearable device as claimed in claim 1, wherein the processing
unit determines the pulse transit time and/or pulse arrival time
based on time delay between the peaks of the first PPG signal and
the second PPG signal.
3. Wearable device as claimed in claim 1, wherein said PPG signal
sensing unit comprises an optical sensing unit, in particular a
contact sensor.
4. Wearable device as claimed in claim 1, wherein said PPG signal
sensing unit comprises another imaging unit.
5. Wearable device as claimed in claim 1, further comprising a
distance unit for obtaining the distance between said first and
second body locations and/or the distances between the first body
location and the second body location, respectively, and the heart,
wherein said processing unit is configured to use the obtained
distance or distances in determining the pulse-related
information.
6. Wearable device as claimed in claim 5, wherein said distance
unit is configured to obtain the distance or distances through
measurement, in particular from an image of the sequence of images
acquired by the imaging unit, or through input.
7. Wearable device as claimed in claim 1, further comprising an
illumination unit mounted in or at the device body for illuminating
said first and/or second body location.
8. Wearable device as claimed in claim 1, further comprising an
image recognition unit for detecting when said second body part is
shown in the images of the acquired sequence of images and a
control unit for controlling the PPG signal sensing unit to start
acquiring the first PPG signal if it is detected that the second
body part is shown in an image.
9. Wearable device as claimed in claim 1, further comprising
mounting equipment for mounting the device body at the subject's
body.
10. Wearable device as claimed in claim 1, wherein said wearable
device is a wrist worn device, in particular a watch or heart rate
monitor, glasses, camera, multimedia player, mobile phone or smart
phone.
11. Wearable device as claimed in claim 1, wherein said wearable
device is a wrist worn device, wherein said PPG signal sensing unit
is arranged at the bottom of the device body and the imaging unit
is arranged at the front or a side surface of the device body.
12. Wearable device as claimed in claim 1, wherein said PPG signal
sensing unit is mounted at a first position in or at the device
body facing said first body location when the wearable device is
worn by the subject and wherein said imaging unit is mounted at a
second position in or at the device body facing said second body
location when the wearable device is worn by the subject.
13. Wearable device as claimed in claim 1, wherein said processing
unit is further configured to determine pulse wave velocity,
hemodynamic information and/or blood pressure changes of the
subject.
14. System for monitoring of pulse transit time and/or pulse
arrival time, said system comprising: a wearable device comprising:
a PPG signal sensing unit for acquiring a first
photoplethysmography, signal from a first body location of the
subject's body, wherein the PPG signal sensing unit is in front of
or in contact with the first body location when the wearable device
is worn by the subject; an imaging unit for acquiring a sequence of
images from a second body location of the subject's body different
from the first body location, said sequence of images being
configured for deriving a second PPG signal for the second body
location of the subject's body; and an output unit for outputting
said first PPG signal and said sequence of images via a
communication network to another entity for processing, and the
another entity comprising: an input unit for obtaining the first
PPG signal and the sequence of images acquired by the wearable
device via the communication network; and a processor for deriving
a second PPG signal from said sequence of images and for
determining the pulse transit time and/or the pulse arrival time
from said first and second PPG signals.
15. The system according to claim 14, wherein the another entity is
at least one of a remote server, a wireless communication device,
and a computer.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a wearable device for
obtaining signals from a subject for use in the monitoring of
pulse-related information of the subject. Further, the present
invention relates to a system for monitoring of pulse-related
information of a subject.
BACKGROUND OF THE INVENTION
[0002] Vital signs of a person, for example the heart rate (HR),
the respiration rate (RR) or the arterial blood oxygen saturation
(SpO2), serve as indicators of the current health state of a person
and as powerful predictors of serious medical events. For this
reason, vital signs are extensively monitored in inpatient and
outpatient care settings, at home or in further health, leisure and
fitness settings.
[0003] One way of measuring vital signs is plethysmography.
Plethysmography generally refers to the measurement of volume
changes of an organ or a body part and in particular to the
detection of volume changes due to a cardio-vascular pulse wave
traveling through the body of a subject with every heartbeat.
[0004] Photoplethysmography (PPG) is an optical measurement
technique that evaluates a time-variant change of light reflectance
or transmission of an area or volume of interest. PPG is based on
the principle that blood absorbs light more than surrounding
tissue, so variations in blood volume with every heart beat affect
transmission or reflectance correspondingly. Besides information
about the heart rate, a PPG waveform can comprise information
attributable to further physiological phenomena such as the
respiration. By evaluating the transmittance and/or reflectivity at
different wavelengths (typically red and infrared), the blood
oxygen saturation (SpO2) can be determined. Different kinds of such
contact sensor are commonly known and used, including contact
finger pulse oximeters, contact forehead pulse oximeter sensors,
contact pulse sensors, etc.
[0005] Recently, non-contact, remote photoplethysmography (rPPG)
devices (also called camera PPG devices) for unobtrusive
measurements have been described in many publications, e.g. in
Verkruysse et al., "Remote plethysmographic imaging using ambient
light", Optics Express, 16(26), 22 Dec. 2008, pp. 21434-21445,
which demonstrates that photoplethysmographic signals can be
measured remotely using ambient light and a conventional consumer
level video camera, using red, green and blue color channels.
[0006] Remote PPG utilizes light sources or, in general radiation
sources, disposed remotely from the subject of interest. Similarly,
also a detector, e.g., a camera or a photo detector, can be
disposed remotely from the subject of interest, i.e. without
contact to the subject. Therefore, remote photoplethysmographic
systems and devices are considered unobtrusive and well suited for
medical as well as non-medical everyday applications. This
technology particularly has distinct advantages for patients with
extreme skin sensitivity requiring vital signs monitoring such as
Neonatal Intensive Care Unit (NICU) patients with extremely fragile
skin or premature babies.
[0007] Current methods for evaluation of blood pressure changes are
based on measurement of pulse transit time (PTT) or pulse arrival
time (PAT). The first approach estimates the transit time between
one signal carrying the arterial pulse wave (pulse wave signal) and
another signal such as the electrocardiogram (ECG). The time
interval between the ECG fiducial point (typically the R peak) and
a fiducial point marking the pulse arrival is referred to as the
PAT. The PTT is the time difference between the aortic valve
opening and the pulse wave arrival. The second approach estimates
the BP from the PTT between two pulse wave signals measured at
different parts of the body.
[0008] These methods require placement of contact PPG (and/or ECG)
sensors at two body locations, at least, preferably at large
distance from each other. This might require significant time
investment and efforts to estimate changes of blood pressure based
on PTT. Moreover, in order to follow the trend of changes of blood
pressure over long periods of time (e.g. days), the location for
placement of contact sensors, as well as position of a body should
be the same for every measurement. Furthermore, the two sensors
needs to be synchronized to millisecond level in order to provide
accurate PTT measurement. Finally, contact sensors are sensitive to
motion of a person, and are sensitive to correct placement.
[0009] Those disadvantages of current methods of PTT measurement
limit the use of such approach beyond professional healthcare
environment (e.g. at home, on the go, etc.). Therefore, there is a
need for a system, which can remove disadvantages of current
systems for PTT-based measurement of pulse-related information such
as e.g. blood pressure changes, pulse transit time and/or pulse
arrival time.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide a
wearable device for obtaining signals from a subject for use in the
monitoring of pulse-related information of the subject, which
provides for unobtrusive, reproducible, easy to use, and simple
measurements, preferably using existing type of devices that are
used in everyday life. Further, it is another object of the present
invention to provide a corresponding system for monitoring of
pulse-related information of a subject.
[0011] In a first aspect of the present invention a wearable device
for obtaining signals from a subject for use in the monitoring of
pulse transit time and/or pulse arrival time is presented. The
wearable device includes
[0012] a device body,
[0013] a PPG signal sensing unit for acquiring a first
photoplethysmography, PPG, signal from a first body location of the
subject's body, wherein the first PPG signal sensing unit is in
contact with the first location, and
[0014] an imaging unit for acquiring a sequence of images from a
second body location of the subject's body different from the first
body location, said sequence of images being configured for
deriving a second PPG signal for the second body location of the
subject's body,
wherein said PPG signal sensing unit and said imaging unit are
mounted in or at the device body and are configured to
simultaneously acquire the first PPG signal and the sequence of
images, a processing unit for deriving the second PPG signal from
said sequence of images, wherein the processing unit is configured
to determine the pulse transit time and/or pulse arrival time based
on the first PPG signal and the second PPG signal.
[0015] In a further aspect of the present invention a system for
monitoring of pulse transit time and/or pulse arrival time is
presented, the system comprising
[0016] a wearable device comprising
[0017] a PPG signal sensing unit for acquiring a first
photoplethysmography, (PPG), signal from a first body location of
the subject's body, wherein the first PPG signal sensing unit is in
contact with the first location;
[0018] an imaging unit for acquiring a sequence of images from a
second body location of the subject's body different from the first
body location, said sequence of images being configured for
deriving a second PPG signal for the second body location of the
subject's body; and
[0019] an output unit for outputting said first PPG signal and said
sequence of images, wherein the said outputted first PPG signal and
sequence of images are sent to another entity for processing via a
communication network,
[0020] wherein the another entity comprising: an input unit for
obtaining the first PPG signal and the sequence of images acquired
by the wearable device via the communications network, and
[0021] a processor for deriving a second PPG signal from said
sequence of images and for determining the pulse transit time
and/or pulse arrival time from said first and second PPG
signals.
[0022] Preferred embodiments of the invention are defined in the
dependent claims. It shall be understood that the claimed system
has similar and/or identical preferred embodiments as the claimed
device and as defined in the dependent claims.
[0023] The present invention is based on the idea to make use of
the benefits of remote and reflective PPG approaches to design a
new PPG sensor arrangement combining two separate sensors enabling
simultaneously obtaining two PPG signals from different portions of
the user's body in a simple, unobtrusive, reproducible, easy to use
manner. The proposed wearable device thus comprises two separate
sensor units, wherein at least one of the sensor units is an
imaging unit, such as a 2D camera or 2D image sensor. The two
sensor units are e.g. placed at different sides of a device to
obtain separate sensor signals (PPG signals) from different body
locations. In this way pulse-related information of the subject can
be obtained particularly including one or more of pulse transit
time, pulse arrival time, pulse wave velocity, hemodynamic
information and/or blood pressure changes of the subject.
[0024] Contrary to known systems using several contact PPG sensors
placed on body parts (e.g. legs, arms, forehead), synchronized with
each other or/and with ECG, all the information used according to
the present invention comes from one single wearable device.
[0025] The present invention provides a reliable and efficient
device and system that can provide pulse-related information
automatically, continuously and in a non-obtrusive way. It enables
a continuous measurement of transit time of a pressure pulse when
travelling through the body. Further, pulse transit time (PTT) can
be determined and pulse wave velocity (PWV) values can be
calculated, e.g. in the following way:
PWV=D/PTT,
where D is the distance difference between the travelling distances
from the heart to the points of measurement (i.e. the points of
measurement of the first PPG signal and the sequence of images, in
particular the particular region within the images, from which the
second PPG signal is derived). For instance, if the PAT of face and
hand are measured, the distance D corresponds to the distance
difference between "travelling distance from heart to face" and
"travelling distance from heart to hand". The pulse transit time is
generally defined as:
PTT=PATd-PATp,
where PATp is the pulse arrival time (PAT) of the pressure pulse at
the point closer to the heart and PATd is the arrival time of the
pressure pulse at extremity. Using signals from various body sites,
e.g. from the forehead and hand, allows to detect PTT measurements,
which are not affected by the pre-ejection period (PEP). More
precisely, in mathematical terms, taking the difference of at least
two measured PAT cancels the PEP contribution and only the PTT
difference remains. Alternatively, calculation of the PTT can be
done in the frequency domain.
[0026] Further, according to the present invention PAT measures can
be obtained and hemodynamic information about the hemodynamic
status of the subject can be derived from said one or more PAT
measures. Non-limiting examples of such PAT measures are the PAT
foot, PAT 20%, PAT50%, PAT80%, the PAT top, the PTT and/or the PEP.
From a combination of the acquired signals such PAT measures can be
easily obtained and monitored to detect changes of the hemodynamic
status of the subject.
[0027] Further, changes of blood pressure can be monitored based on
analysis of changes of PTT and PAT values. The calculation itself
is generally known, e.g. from WO 2013/171599 A1, WO 2010/020914 A1
or WO 2009/136341 A2. Generally, the pulse arrival time (PAT) is
the sum of the pre-ejection period (PEP), determined by a measure
of the aortic closure and pulse transit time (PTT), as e.g.
described in X. Aubert, J. Muehlsteff, "Non-Invasive Cuff-less
Measurements of the Arterial Blood Pressure: What does
Pulse-Transit-Time tell us all about?", Proc. ESGCO'06, Jena,
Germany, May 2006 and J. Muehlsteff, X. Aubert, M. Schuett,
"Cuff-less Estimation of Systolic Blood Pressure for Short Effort
Bicycle Tests: The Prominent Role of the Pre-Ejection Period",
EMBC'06, New York, 2006.
[0028] A definition how to obtain the blood pressure can e.g. be
found in B M McCarthy, B O'Flynn and A Mathewson "An Investigation
of Pulse Transit Time as a Non-Invasive Blood Pressure Measurement
Method", J. Phys.: Conf. Ser. 307 012060 as follows: Blood pressure
can be related to PTT directly by
P e = P b - 2 .gamma. PTT b .DELTA. PTT ##EQU00001##
where P.sub.b is the base blood pressure level, PTT.sub.b is the
value of PTT corresponding to the pressure P.sub.b, while
.DELTA.PTT is the change in the PTT and .gamma. is a coefficient
ranging from 0.016 to 0.018 (mmHg.sup.-1).
[0029] The proposed device may e.g. be wrist worn device, such as a
watch, at which the two sensor units are placed in a way to provide
a view on two different body parts, such as for instance face and
wrist of a person. Therefore, a practical embodiment of such device
may be a watch placed on a wrist of a subject with a 2D optical
sensor on top of the watch and another optical sensor on the
bottom. In this embodiment, estimation of PTT is achieved by
measuring PPG signals from a face of a person and from the wrist,
followed by an analysis of the time delay between peaks of the
detected pulse signals to extract PTT (or PAT).
[0030] Another practical embodiment of such device may be a
head-mounted device (such as Google Glass) worn by a subject on
his/her head. The device may have two optical sensors, one looking
forward (outward), and another one looking backward (inward). The
forward-looking sensor may preferably be a 2D camera sensor to
remotely measure PPG signals at a body part such as a hand. The
backward-looking sensor is looking at a skin area in face or is
attached to a skin area in face, i.e. can be either a 2D camera
sensor or a single spot photo-sensor. In this way, PTT may be
estimated by measuring PPG signals at two different body parts.
Similar to above embodiment, an analysis of the time delay between
peaks of the detected pulse signals provides PTT and/or PAT.
[0031] Further pulse-related signals can be derived from the PPG
signals and the extracted PTT in both embodiments.
[0032] In an embodiment the device further comprises an output unit
for outputting said first PPG signal and said sequence of images
for processing by another entity. The other entity may e.g. be a
computer, tablet, smartphone, central server (e.g. of a hospital),
or generally any device of e.g. the user, a caregiver or a
physician.
[0033] In another embodiment the device further comprises a
processing unit for deriving a second PPG signal from said sequence
of images and for determining pulse-related information from said
first and second PPG signals.
[0034] There are various options for implementing the PPG signal
sensing unit. In one embodiment said PPG signal sensing unit
comprises an optical sensing unit, in particular a contact sensor.
In another embodiment said PPG signal sensing unit comprises
another imaging unit. It depends on the particular application,
costs, use etc. how the PPG signal sensing unit may preferably be
implemented.
[0035] The distance difference between the travelling distances
from the heart to said first and second body locations,
respectively, may generally be known or estimated, e.g. based on
the information at which position of the device body the PPG signal
sensing unit and the imaging unit are arranged and which direction
they are oriented, which allows an estimation from which body
location the respective signal will be obtained. In another
embodiment the device may further comprise a distance unit for
obtaining the distance between said first and second body locations
and/or the distances between the first body location and the second
body location, respectively, and the heart, wherein said processing
unit is configured to use the obtained distance(s) in determining
the pulse-related information. For instance, from said distances
the distance difference between the travelling distances from the
heart to said first and second body locations can be determined,
which is then used in determining the pulse-related information.
Alternatively, the distance unit may be configured to directly
obtain the different distances between the respective body location
and the heart, from which the distance difference can then be
obtained. The use of such a distance unit increases the accuracy of
the determination of the distance, which leads to more accurate
results of the determined pulse-related information.
[0036] Said distance unit may thus be configured to obtain the
distance through measurement, in particular from an image or the
sequence of images acquired by the imaging unit, or through input
from e.g. the user. Hence, image processing may be used to
recognize the body portions and, there from, to determine the
distance between them and/or the distance of the respective body
portion to the heart, or the distances and/or the distance
difference may directly be estimated within one or more images of
the sequence of images.
[0037] In a preferred embodiment the device further comprises an
illumination unit mounted in or at the device body for illuminating
said first and/or second body location. The illumination unit may
be a source of multi-wavelength dedicated illumination. It may e.g.
be attached to a skin area or placed close to a skin area; it may
e.g. be arranged next to the PPG signal sensing unit and/or the
imaging unit to illuminate the respective body portion from which
the respective signal is acquired.
[0038] The device may further comprise an image recognition unit
for detecting when said second body part is shown in the images of
the acquired sequence of images and a control unit for controlling
the PPG signal sensing unit to start acquiring the first PPG signal
if it is detected that the second body part is shown in an image.
Hence, according to this embodiment, the device can start
measurement when the skin area of the other body part (such as
face, hand, wrist, elbow, leg) appears in the field of view of the
imaging unit and can stop measurements when no skin area appears
any more in the field of view. This particularly saves battery
power and processing power.
[0039] The device may further comprise mounting equipment for
mounting the device body at the subject's body. This may e.g.
include a strap, wristband, headband, body band, etc., i.e. any
kind of equipment, by which the device can be held at the subject's
body.
[0040] As already mentioned briefly, said wearable device may be a
wrist worn device, in particular a watch or heart rate monitor,
glasses, camera, multimedia player, mobile phone or smart phone.
Generally, any device, which allows mounting of the two sensing
units such that they can simultaneously acquire separate PPG
signals from different body locations, can be used.
[0041] In yet another embodiment there may be made use of a wrist
worn device having a built in PPG sensor, which communicates with
the other sensors in any of the above mentioned embodiment. Hereby,
using the time difference between both sensors will lead to the
PTT.
[0042] In a practical implementation said wearable device is a
wrist worn device, wherein said PPG signal sensing unit is arranged
at the bottom of the device body and the imaging unit is arranged
at the front or a side surface of the device body.
[0043] In a practical implementation said PPG signal sensing unit
is mounted at a first position in or at the device body facing said
first body location when the wearable device is worn by the subject
and said imaging unit is mounted at a second position in or at the
device body facing said second body location when the wearable
device is worn by the subject.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] These and other aspects of the invention will be apparent
from and elucidated with reference to the embodiment(s) described
hereinafter. In the following drawings
[0045] FIG. 1 schematically shows a first embodiment of a system
and device according to the present invention,
[0046] FIG. 2 shows an electrocardiogram and a photoplethysmogram
for measuring a pulse arrival time according to the state of the
art;
[0047] FIG. 3 shows an electrocardiogram and two PPG signals
obtained at different locations for illustrating the determination
of PTT and PWV;
[0048] FIG. 4 shows a second embodiment of a device according to
the present invention in the form of a wrist worn device,
[0049] FIG. 5 shows a third embodiment of a device according to the
present invention in the form of glasses,
[0050] FIG. 6 shows a fourth embodiment of a device according to
the present invention in the form of a smartphone, and
[0051] FIG. 7 schematically shows a fifth embodiment of a device
according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0052] FIG. 1 schematically shows a first embodiment of a system 1
and a device 2 according to the present invention. The system 1 for
monitoring of pulse transit time, pulse arrival time and/or blood
pressure of a subject comprises a wearable device 2 for obtaining
signals from a subject for use in the monitoring of pulse-related
information, such as pulse transit time, pulse arrival time, blood
pressure, pulse wave velocity and/or hemodynamic status of the
subject. Detailed practical embodiments of such a wearable device
will be explained in more detail below. The system 1 further
comprises an input unit 3, e.g. a (wireless or wired) data
interface, for obtaining (i.e. receiving or retrieving) a first PPG
signal 10 and a sequence of images 11 acquired by the wearable
device 2 and a processor 4 for deriving a second PPG signal from
said sequence of images 11 and for determining, as output signal
12, the desired pulse-related information from said first and
second PPG signals.
[0053] In one embodiment the elements of the system 1 are
integrated into a common device together with the wearable device
2, e.g. the input unit 3 and the processor 4 may be integrated into
the wearable device 2. In another embodiment, as shown in FIG. 1,
the input unit 3 and the processor 4 may be arranged separate from
the wearable device 2, e.g. in a computer 5 or workstation, to
which the data acquired by the wearable device 2 are transmitted
(e.g. via a network, such as Bluetooth, Wifi or a communications
network).
[0054] The wearable device 2 comprises a device body 20, a PPG
signal sensing unit 21 for acquiring the first PPG signal 10 from a
first body location of the subject's body and an imaging unit 22,
e.g. a camera, for acquiring the sequence of images 11 from a
second body location of the subject's body different from the first
body location. Hereby, said sequence of images is configured for
deriving the second PPG signal for the second body location of the
subject's body. The PPG signal sensing unit 21 and the imaging unit
22 are mounted in or at the device body 20 and are configured to
simultaneously acquire the first PPG signal 10 and the sequence of
images 11.
[0055] In the embodiment shown in FIG. 1 the wearable device 2
comprises an output unit 23 for outputting said first PPG signal 10
and said sequence of images 11 for processing by another entity,
such as the computer 5, a wireless communication device/a mobile
communication device, a remote server(s), etc. The computer 5 may
be arranged at a separate location, e.g. at a caregiver, doctor or
hospital, to which the data are transmitted, e.g. via a
communications network or the internet 30. The processor may also
be located in the cloud and may return the result of the
calculation back to the wearable device 2 for presenting the result
to the user or another person.
[0056] Generally, said PPG signal sensing unit 21 may be any kind
of sensing unit that is able to acquire a PPG signal from the
subject's body. The PPG sensing unit comprises an optical sensing
unit, in particular a contact sensor (e.g. a pulse oximeter as
conventionally used in a finger clip sensor or in a wristband). In
another embodiment the PPG sensing unit comprises another imaging
unit, e.g. another camera.
[0057] FIG. 2 shows, for illustration purposes, an
electrocardiogram and a photoplethysmogram for evaluating the pulse
arrival time according to the state of the art. The
electrocardiogram and the photoplethysmogram are detected at
different positions on the human body in order to measure the pulse
transit time and to detect trends in the blood pressure from the
pulse arrival time.
[0058] The pulse arrival time is usually determined as a time frame
from a maximum peak R of the electrocardiogram to a certain point
in time of the photoplethysmogram. The pulse arrival time may be
detected as a time frame from the maximum R of the
electrocardiogram to a minimum value F of the photoplethysmogram as
a foot pulse arrival time PAT.sub.foot or to a maximum value T of
the photoplethysmogram as a top pulse arrival time PAT.sub.top or
as a time to the maximum slope of the photoplethysmogram between
the maximum and the minimum value of the photoplethysmogram.
[0059] FIG. 3 shows a diagram of an ECG (as a reference) and two
PPG signals, as used according to the present invention, obtained
at different body locations, e.g. at the face (PPG.sub.face) and
the hand (PPG.sub.hand) of a subject. Therein the pulse transit
time at the face (PTT.sub.face) and at the hand (PTT.sub.hand) are
indicated as well as their difference PTT.sub.diff. The pulse wave
velocity PWV is obtained by calculating PWV=D/PTT.sub.diff, where D
is the distance difference between the travelling distances from
the heart to the face and the hand, i.e. the positions where the
PPG signals were obtained from.
[0060] FIG. 4 shows a second embodiment of a device 2a according to
the present invention in the form of a wrist worn device. FIG. 4A
shows a cross-sectional side view, FIG. 4B shows the device 2a
mounted to the wrist of the subject. In this embodiment the device
2a is wearable on the wrist and may e.g. be a separate device or
integrated into a known device, such as a wrist worn watch,
smartphone, multimedia player, heart rate monitor, etc. The device
2a comprises, in this exemplary embodiment, two embedded optical
sensors arranged on different sides of the device 2a to measure PPG
signals of a subject from two different parts of the body.
[0061] On a front side 24 of the housing 20 of the device 2a a
camera 22a (representing the imaging unit), in particular a 2D
camera sensor, is arranged, and on a rear side 25 (facing the skin
of the subject, when worn by the subject using the wrist band 26)
of the housing 20 a single spot photo-sensor 21a (or,
alternatively, 2D camera sensor, representing the PPG signal
sensing unit) is arranged. In the current embodiment, the single
spot photo-sensor 21a is arranged to contact the skin of the wrist
of the subject. A 2D camera sensor can be either monochrome (a
single wavelength) sensor, or multi wavelength sensor (e.g. an
RGB). The single spot photo-sensor 21 preferably includes, like
known pulse oximeters, a dedicated light source 211, preferably in
the visible (preferably red) or near infrared spectrum, and a photo
detector 212.
[0062] In this embodiment the device 2a further integrates a
processing unit 27 for deriving a second PPG signal from said
sequence of images and for determining the pulse-related
information from said first and second PPG signals. As explained
earlier, the pulse related information is one of pulse transit
time, pulse arrival time, pulse wave velocity, hemodynamic
information, blood pressure changes, and combination thereof. This
processing unit 27 thus commonly represents the input unit 3 (e.g.
a data interface for obtaining the measured data from the sensor
21a and the camera 22a) and the processor 4 for determining the
desired pulse-related information of the device 1 shown in FIG. 1.
Further, a user interface 28, e.g. a display, is provided for
outputting the determined pulse-related information and/or other
information derived therefrom (e.g. an indication of the change of
blood pressure, a warning, an recommendation, a health status
information, etc.). Hence, all elements of the system are commonly
integrated into the device 2a.
[0063] FIG. 5 shows a third embodiment of a device 2b according to
the present invention in the form of glasses. FIG. 5A shows a
perspective view of the glasses 2b, FIG. 5B shows the glasses 2b
worn by the subject. In this embodiment, a first camera 21b
(representing the PPG signal sensing unit) is mounted on the rear
side of the frame 27 and a second camera 22b (representing the
imaging unit) is mounted on the front side of the frame 27. Both
cameras 21b, 22b may be 2D camera sensors for obtaining a sequence
of image frames over time, from which respective PPG signals can be
derived. As shown in FIG. 5B the first camera 21b faces the face of
the user (e.g. the temple, as indicated by 31) and the second
camera faces away from the user and can be used to acquire the
sequence of images e.g. from the hand or arm (as indicated by 32)
of the user of the glasses 2b, who directs his head and/or the arm
in a corresponding position. In the current embodiment, when the
glasses 2b is worn by the subject, the first camera 21b contacts
the skin of the subject in order to acquire the PPG signal.
[0064] The other elements of the system may also be integrated into
the glasses 2b, similar as explained above with respect to the
wrist worn device 2a. Alternatively, as shown in FIG. 5A, the
glasses may include an output unit 23b, e.g. a transmitter (e.g. a
Wifi or Bluetooth transmitter) for transmitting the respective data
to an external entity, e.g. a computer for processing and
outputting results.
[0065] FIG. 6 shows a fourth embodiment of device 2c according to
the present invention in the form of a smartphone. In this
embodiment the front side camera 21c is used as a PPG signal
sensing unit and rear side camera 22c is used as an imaging unit
(or vice versa). The smartphone 2c is used by holding one of the
cameras directly in front of or in contact with skin, e.g. of the
arm and orienting it such that the other camera faces a different
body part, e.g. the face, to obtain different sequences of images
from the two cameras 21c, 22c, which can be processed, preferably
using the processor of the smartphone, to derive two PPG signals
and the desired pulse-related information. Hence, preferably, all
elements of the system, i.e. the processing unit 27 and the user
interface 28, are commonly integrated into the smartphone 2c.
[0066] FIG. 7 schematically shows a fifth embodiment of a device 2d
according to the present invention. In addition to the elements of
the device 2 shown in FIG. 1, the device 2d further comprises one
or more additional elements.
[0067] One additional element may be a distance unit 29 for
obtaining the distance between said first and second body locations
and/or the distance between each of said body locations and the
heart to obtain the desired distance difference. In this case the
processing unit 27 of the device 2b (or the processor 4 of the
external entity 5 in another embodiment) is configured to use the
obtained distance difference in determining the pulse-related
information. The distance unit 29 may e.g. be configured to obtain
the distance(s) through measurement, in particular from an image of
the sequence of images acquired by the imaging unit, or through
input (e.g. by the user or another person, who measured the
distance(s) in advance).
[0068] In this way the estimation of blood pressure changes can be
further improved by taking into account the distance difference
between the different ROIs (regions of interest, i.e. location from
which the PPG signal are obtained) and the heart, such as the
distance difference between the face and the wrist of a person with
respect to the heart. The distance and/or the distance difference
can either be estimated automatically, or set manually, or
extracted from the known physiological data of a subject.
[0069] Another additional element may be an illumination unit 40
mounted in or at the device body 20 for illuminating said first
and/or second body locations. This further improves the acquisition
of PPG signals and the quality and robustness of the determined
pulse-related information.
[0070] Still further additional elements may be an image
recognition unit 41 for detecting when said second body part is
shown in the images of the acquired sequence of images and a
control unit 42 for controlling the PPG signal sensing unit 21 to
start acquiring the first PPG signal if it is detected that the
second body part is shown in an image. In this embodiment, device
2d starts measurement of two PPG signals from different body
locations after a person, in particular a desired body location to
be used for PPG signal acquisition, such as a face of a person, is
detected by the imaging unit 22.
[0071] Preferably, according to the present invention optical
sensors are used for both the PPG signal sensing unit 21 and the
imaging unit 22, e.g. arranged on opposite sides of the device 2
and working at the same wavelength. However, in other embodiments
the PPG signal sensing unit 21 is not an optical PPG sensor, but
any other sensor to measure a PPG signal, such as a capacitive
sensor or a pressure sensor.
[0072] In yet another embodiment, the measurements of PPG signals
are performed only if no motion of the respective body parts, e.g.
the face and/or wrist, is detected for a certain amount of time,
which may be detected by an evaluation of the images obtained by
the imaging unit 22.
[0073] A further improvement may be obtained by use of a
calibration measurement with a conventional blood pressure
measurement device, which may be used to calibrate the proposed
wearable device, in particular blood pressure information obtained
with the proposed wearable device. By use of such a calibration it
may be possible to derive blood pressure information from the
measurements made by the wearable device even without knowing the
distance information about the distances between the different body
locations or the distance difference discussed above.
[0074] This may be refined even further by making use of pattern
recognition for recognizing various parts of the body (e.g. the
face and/or hand). Individual calibration factors, obtained in
advance for the respective body part, may then be applied in the
real measurements and calculations by use of the wearable
device.
[0075] While the invention has been illustrated and described in
detail in the drawings and foregoing description, such illustration
and description are to be considered illustrative or exemplary and
not restrictive; the invention is not limited to the disclosed
embodiments. Other variations to the disclosed embodiments can be
understood and effected by those skilled in the art in practicing
the claimed invention, from a study of the drawings, the
disclosure, and the appended claims.
[0076] In the claims, the word "comprising" does not exclude other
elements or steps, and the indefinite article "a" or "an" does not
exclude a plurality. A single element or other unit may fulfill the
functions of several items recited in the claims. The mere fact
that certain measures are recited in mutually different dependent
claims does not indicate that a combination of these measures
cannot be used to advantage.
[0077] A computer program may be stored/distributed on a suitable
non-transitory medium, such as an optical storage medium or a
solid-state medium supplied together with or as part of other
hardware, but may also be distributed in other forms, such as via
the Internet or other wired or wireless telecommunication
systems.
[0078] Any reference signs in the claims should not be construed as
limiting the scope.
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