U.S. patent application number 17/215233 was filed with the patent office on 2021-07-15 for wearable device with multimodal diagnostics.
The applicant listed for this patent is GraftWorX, Inc.. Invention is credited to Ramkumar ABHISHEK, Anthony F. FLANNERY, JR., Samit Kumar GUPTA, Francis HONORE, James REICH.
Application Number | 20210212616 17/215233 |
Document ID | / |
Family ID | 1000005482240 |
Filed Date | 2021-07-15 |
United States Patent
Application |
20210212616 |
Kind Code |
A1 |
HONORE; Francis ; et
al. |
July 15, 2021 |
WEARABLE DEVICE WITH MULTIMODAL DIAGNOSTICS
Abstract
Systems and methods to non-invasively measure sub-cutaneous
processes in a patient are disclosed. Examples of systems may
optically detect biological fluid properties. The optical detection
techniques described herein may be incorporated into a wearable
monitoring system. Examples of wearable monitoring systems may
simultaneously measure a plurality of sensory modalities. Systems
of the present disclosure may be mounted on the skin of a
patient.
Inventors: |
HONORE; Francis; (San
Francisco, CA) ; REICH; James; (San Francisco,
CA) ; FLANNERY, JR.; Anthony F.; (Bainbridge Island,
WA) ; GUPTA; Samit Kumar; (Menlo Park, CA) ;
ABHISHEK; Ramkumar; (Menlo Park, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GraftWorX, Inc. |
Menlo Park |
CA |
US |
|
|
Family ID: |
1000005482240 |
Appl. No.: |
17/215233 |
Filed: |
March 29, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16082249 |
Sep 4, 2018 |
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PCT/US2018/024925 |
Mar 28, 2018 |
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17215233 |
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62626559 |
Feb 5, 2018 |
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62478469 |
Mar 29, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/6833 20130101;
A61B 5/14552 20130101; A61B 5/6824 20130101; A61B 5/4528 20130101;
A61B 5/14535 20130101; A61B 2562/0223 20130101; A61B 5/4875
20130101; A61B 5/1455 20130101; A61B 5/0261 20130101; A61B
2560/0252 20130101; A61B 5/02427 20130101; A61M 1/3656 20140204;
A61B 2562/0204 20130101 |
International
Class: |
A61B 5/1455 20060101
A61B005/1455; A61B 5/024 20060101 A61B005/024; A61B 5/026 20060101
A61B005/026; A61B 5/145 20060101 A61B005/145; A61B 5/00 20060101
A61B005/00 |
Claims
1. A method for monitoring subcutaneous processes in a patient
comprising: sensing a plurality of sensory modalities using a
sensor assembly comprising one or more sensors mounted on a
wearable patch, the one or more sensors selected from the group
consisting of an acoustic sensor, a strain gauge, an optical
sensor, a conductivity sensor, a temperature sensor, a pressure
sensor, and a chemical sensor, where the sensory modalities are
received as electrical signals representing the sensory modalities;
converting the electrical signals to a plurality of corresponding
sensor data signals; and transmitting the one or a plurality of
sensor data signals to a sensor data processing system.
2. The method of claim 1 where the step of sensing the plurality of
sensory modalities comprises any one or more of: sensing sound
using an acoustic sensor; sensing movement or orientation of a
patient body part using an accelerometer; sensing temperature using
a temperature sensor; sensing a stretch or compression of the
wearable patch using a strain gauge; sensing electromagnetic
signals using an optical sensor; sensing moisture using a moisture
sensor; sensing conductivity using a conductivity sensor; sensing
pressure using a pressure sensor; and sensing a chemical using a
chemical sensor.
3. The method of claim 1 where the step of sensing the plurality of
sensory modalities comprises sensing a differential measurement of
skin temperature from two temperature sensors.
4. The method of claim 1 where the step of transmitting the one or
a plurality of sensor data signals to the sensor data processing
system comprises: transmitting the one or a plurality of sensor
data signals to a local hub, where the local hub transmits the
sensor data signal to a remote sensor data processor for processing
of the one or a plurality of sensor data signals.
5. The method of claim 1 where the device can be placed into a
shelf mode where power is either disconnected or placed into a low
power mode.
6. The method of claim 5 where shelf mode is either invoked by a
microcontroller device or automatically entered, based on readings
from any one or more of: magnetic sensors or switches; optical
sensors; motion, acceleration or tilt sensors; temperature sensors;
capacitive proximity sensors; and mechanical switches.
7. The method of claim 5 where shelf mode can invoked by a
microcontroller device and exited based on readings from any one or
more of: magnetic sensors or switches; optical sensors; motion,
acceleration or tilt sensors; temperature sensors; capacitive
proximity sensors; and mechanical switches.
8. The method of claims 6 where the above sensors interact with
product packaging or an adhesive backing liner in order to exit
shelf mode when the patch is removed from the product packaging.
Description
CROSS-REFERENCE
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/082,249, filed Sep. 4, 2018, which is a
U.S. national stage entry under 35 U.S.C. .sctn. 371 of
International Patent Application No. PCT/US2018/024925, filed Mar.
28, 2018, which claims the benefit of U.S. Provisional Application
No. 62/626,559, filed Feb. 05, 2018, and U.S. Provisional
Application No. 62/478,469, filed Mar. 29, 2017, which applications
are each incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present disclosure relates to methods and systems using
sensors to non-invasively measure subcutaneous processes in a
patient. More particular1y, the present disclosure relates to
systems and methods for measuring one or more fluid properties
including systems and methods for measuring one or a plurality of
biological fluid properties using optical devices. Additionally,
the present disclosure relates to systems and methods for
simultaneously measuring a plurality of sensory modalities and
processing the measurements to detect physiological phenomenon in
the patient's body.
[0003] There is a current need for non-invasive techniques to
quantitatively measure one or more physiological properties, for
example, one or a plurality of biological fluid properties in the
physiological environment of the subject or patient, in order to
derive clinically relevant metrics to evaluate the state of
patients. For example, in dialysis patients there is a current need
for measurement of blood and flow related parameters at their
dialysis access location, where the parameters include but are not
limited to blood hematocrit, hemoglobin concentration, oxygen
saturation, heart rate and flow rate, and percentage change in
blood volume. Additionally, in total knee arthroplasty (TKA)
patients, there is a current need for measurement of parameters
relating to, for example, premature implant failure, including
synovial fluid white blood cell (WBC) concentration, range of
motion, skin temperature, and crepitus associated with a range of
disease states.
[0004] In an example, stethoscopes are effective tools used in the
hospital and doctor's office during physical exams for noninvasive
detection of physiologic sounds. Several designs have gained
popularity amongst clinicians, such as the Littmann.TM.
stethoscope, and the Welch-Allyn.TM. stethoscope. These devices
have been designed to be portable devices that are
clinician-centric and can be easily be moved from one location to
another on a patient during a single visit, and also easily used
across several patients. Physiological issues such as blocked blood
flow, abnormal lung sounds, heart murmurs, etc. occur at specific
locations on the body (e.g. the arm for a blocked arteriovenous
fistula, the neck for an obstruction in the carotid artery, the
chest or back for abnormal air flow in the lungs, etc.) and are
typically detectable using stethoscopes during patient-doctor
exams. These physiological issues cannot however be effectively
tracked outside of the clinic. The stethoscope requires the
patient's presence in the clinic to be used by a doctor trained in
interpreting the noise heard on the stethoscope. This makes
management of patients more difficult and leads to poor patient
outcomes, since the patient cannot be monitored for a developing
health issue until it has caused the patient damage.
[0005] It would be advantageous for noninvasive methods and devices
that may be used to monitor physiological phenomenon to allow
greater patient mobility. Existing stethoscope designs may hinder
patient mobility. These devices are also necessarily rigid due to
their under1ying architecture. Stethoscopes often have a "cup" or
other form of diaphragm that is used to provide acoustic impedance
matching from the skin to another medium. These components add to
the overall bulk and rigidity of existing stethoscopes. The bulk
and rigidity of existing stethoscopes does add to the ease of use
for these devices in their classic use case, typically, a clinician
moving the stethoscope from one location to another easily to
perform a complete physical examination on a patient during their
visit. However, this removes them as practical devices that could
be used as a long-term, low-profile more portable device for remote
monitoring of patient health.
[0006] Additionally, the stethoscope is limited to detecting a
single sensory modality. The doctor listens for sounds that
indicate blocked blood flow, abnormal lung sounds, heart murmurs,
for example. The ability to sense more sensory modalities may
enable a device to be configured for a wide range of applications.
Similar1y, techniques that measure biological fluid flow may
provide useful diagnostic information to clinicians which may
improve patient outcomes.
SUMMARY OF THE INVENTION
[0007] Systems and methods of the present disclosure addresses at
least some of these needs by providing systems and methods for
measuring one or more biological fluid properties using optical
devices. The present disclosure enables a non-invasive systems such
as an optical system and method to measure one or more
physiological properties, such as the properties of biological
fluids flowing though, or present in, for example, a vessel or
bursa in its physiological environment at a finite depth below the
skin surface. Additionally, the present disclosure enables wearable
systems and methods for simultaneously measuring one or a plurality
of sensory modalities. Such sensory modalities may comprise any one
or more of the optical devices disclosed in the present
application; however, in alternative embodiments, the systems and
methods for simultaneously measuring one or a plurality of sensory
modalities may not comprise an optical sensory modality.
[0008] In an aspect, an optical detection device is provided. The
optical detection device may comprise one or more photodetectors
configured to mount on a skin surface of a patient. The one or more
photodetectors may be configured to receive light from beneath the
skin surface and to generate an electrical signal indicative of the
light received. The optical detection device may comprise at least
two light sources configured to emit light at different wavelengths
and at controllable intensity levels, wherein the light sources are
configured to be mounted on the skin surface at variable distances
from the photodetector; wherein the light sources may be configured
to illuminate the volume of tissue beneath the skin surface, and
wherein the photodetector may detect light generated by the light
sources and reflected from particles and tissue structure in the
illuminated tissue. The optical detection device may comprise a
communications interface configured to receive the one or a
plurality electrical signals indicative of intensity from the
photodetector and to communicate the one or a plurality of
electrical signals to a sensor data processing system, where the
intensity of the light received is used to measure one or a
plurality of properties of biological fluids flowing in a vessel in
the volume of tissue.
[0009] Optionally, in any embodiment, the intensity of the light
received is used to determine a vessel depth of a fluid vessel in
the tissue. Optionally, in any embodiment, the intensity of the
light received is used to determine a position of the system
relative to the vessel. Optionally, in any embodiment, the
intensity of the light received is used to measure one or a
plurality of fluid properties inside the vessel. Optionally, in any
embodiment, the one or a plurality of fluid properties comprise one
or more of: blood oxygenation; heart rate; chemical composition;
analyte concentration; cell concentration; leukocyte concentration;
erythrocyte concentration; particle concentration; blood flow rate;
hematocrit; and hemoglobin concentration.
[0010] In another aspect, a method for determining one or a
plurality of biological fluid properties from a patient is
provided. The method may comprise emitting a first illumination of
a volume of tissue below a skin surface of a patient from a first
light source a first distance away from a photodetector positioned
on the skin surface, where the first light source emits the first
illumination at a first intensity to generate a first optical
radiation pattern in a first hemispherical volume having a first
radius. The method may comprise receiving a first set of electrical
signals representing reflection intensities communicated from the
photodetector positioned to receive light reflected below the skin
surface from the first illumination. The method may comprise
emitting a second illumination of the volume of tissue below the
skin surface from a second light source a second distance from the
photodetector, where the second light source emits the second
illumination at a second intensity to generate a second optical
radiation pattern in a second hemispherical volume having a second
radius. The method may comprise using the first set of electrical
signals and the second set of electrical signals to measure one or
a plurality of fluid properties of a vessel in the volume of tissue
below the skin surface.
[0011] Optionally, in any embodiment, the first light source is
configured to emit light at a first wavelength and the second light
source is configured to emit light at a second wavelength.
Optionally, in any embodiment, the step of emitting the first
illumination comprises applying a plurality of optical drive
signals to the first light source to generate a first plurality of
output intensities at the first wavelength. Optionally, in any
embodiment, the step of receiving the first set of electrical
signals comprises detecting a plurality of reflection intensities
for each of the first plurality of output intensities, converting
the plurality of reflection intensities to one or a plurality of
electrical signals, converting the one or a plurality of electrical
signals to digital data values corresponding to the one or a
plurality of electrical signals and storing the digital data values
of the one or a plurality of electrical signals as the plurality of
first wavelength intensities for each of the output intensities in
a memory. Optionally, in any embodiment, the step of emitting the
second illumination comprises applying the plurality of optical
drive signals to the second light source to generate a second
plurality of intensities at the second wavelength. Optionally, in
any embodiment, the step of receiving the second set of electrical
signals comprises detecting a plurality of reflection intensities
for each of the second plurality of output intensities, converting
the plurality of reflection intensities to one or a plurality of
electrical signals, converting the one or a plurality of electrical
signals to digital data values corresponding to the one or a
plurality of electrical signals, and storing the digital data
values of the one or a plurality of electrical signals as the
plurality of second wavelength intensities for each of the output
intensities in the memory. Optionally, in any embodiment, the step
of using the sets of signals to measure one or a plurality of fluid
properties comprises determining a plurality of radii for each of
the first and second illuminations corresponding to the plurality
of first wavelength reflection intensities and the plurality of
second wavelength reflection intensities. Optionally, in any
embodiment, the step of using the sets of signals to measure one or
a plurality of fluid properties comprises determining a depth of a
vessel in the volume of tissue illuminated in the steps of emitting
based on the plurality of radii at each of the first wavelength and
the second wavelength. Optionally, in any embodiment, the step of
using the sets of signals to measure one or a plurality of fluid
properties comprises determining a diameter of the vessel based on
the plurality of radii at each of the first wavelength and the
second wavelength.
[0012] Optionally, in any embodiment, the method further comprises
the first light source configured to emit light at a first at a
first wavelength and the second light source configured to emit
light at a second wavelength. Optionally, in any embodiment, the
step of emitting the first illumination comprises applying a
plurality of optical drive signals to the first light source to
generate a first plurality of output intensities at the first
wavelength. Optionally, in any embodiment, the step of receiving
the first set of electrical signals comprises detecting a plurality
of reflection intensities for each of the first plurality of output
intensities, converting the plurality of reflection intensities to
one or a plurality of electrical signals, converting the one or a
plurality of electrical signals to digital data values
corresponding to the one or a plurality of electrical signals, and
storing the digital data values of the one or a plurality of
electrical signals as the plurality of first wavelength intensities
for each of the output intensities in a memory. Optionally, in any
embodiment, the step of emitting the second illumination comprises
applying the plurality of optical drive signals to the second light
source to generate a second plurality of intensities at the second
wavelength. Optionally, in any embodiment, the step of receiving
the second set of electrical signals comprises detecting a
plurality of reflection intensities for each of the second
plurality of output intensities, converting the plurality of
reflection intensities to one or a plurality of electrical signals,
converting the one or a plurality of electrical signals to digital
data values corresponding to the one or a plurality of electrical
signals, and storing the digital data values of the one or a
plurality of electrical signals as the plurality of second
wavelength intensities for each of the output intensities in the
memory. Optionally, in any embodiment, the step of using the sets
of signals to measure one or a plurality of fluid properties
comprises determining a plurality of radii for each of the first
and second illuminations corresponding to the plurality of first
wavelength reflection intensities and the plurality of second
wavelength reflection intensities. Optionally, in any embodiment,
the step of using the sets of signals to measure one or a plurality
of fluid properties comprises analyzing the plurality of radii for
the first illumination to determine a first intersection of the
first hemispherical volume of the first optical radiation pattern
at each output intensity and the vessel. Optionally, in any
embodiment, the step of using the sets of signals to measure one or
a plurality of fluid properties comprises analyzing the plurality
of radii for the second illumination to determine a second
intersection of the second hemispherical volume of the second
optical radiation pattern at each output intensity and the vessel.
Optionally, in any embodiment, the step of using the sets of
signals to measure one or a plurality of fluid properties comprises
identifying the first light source as a primary light source when
the first intersection is greater than the second intersection and
identifying the second light source as the primary light source
when the second intersection is greater than the first
intersection.
[0013] Optionally, in any embodiment, the method further comprises
moving the first and second light sources and the photodetector to
a location on the skin surface in a direction transverse to the
vessel such that the difference between the first intersection and
the second intersection is expected to be less when the steps may
be repeated after moving the first light source, the second light
source, and photodetector.
[0014] Optionally, in any embodiment, the method further comprises
the first light source configured to emit light at a first
wavelength and the second light source configured to emit light at
a second wavelength. Optionally, in any embodiment, the method
further comprises applying an optical drive signal to the first
light source to generate a first output intensity at the first
wavelength. Optionally, in any embodiment, the method further
comprises receiving a first wavelength reflection intensity for the
first output intensity at the first wavelength. Optionally, in any
embodiment, the method further comprises storing a digital data
value as the first wavelength intensity for the first output
intensity in a memory. Optionally, in any embodiment, the method
further comprises applying the optical drive signal to the second
light source to generate a second output intensity at the second
wavelength. Optionally, in any embodiment, the method further
comprises receiving a first wavelength reflection intensity for the
second output intensity. Optionally, in any embodiment, the method
further comprises storing a digital data value as the second
wavelength intensity for the second output intensity in the memory.
Optionally, in any embodiment, the method further comprises
calculating a ratio of reflection intensities by dividing the first
wavelength reflection intensity by the second reflection intensity
when the first wavelength corresponds to a red light and the second
wavelength corresponds to an infrared light, storing the ratio of
reflection intensities as corresponding to an oxygenation level of
a fluid in the vessel.
[0015] Optionally, in any embodiment, the method further comprises
the first light source configured to emit light at a first
wavelength and the second light source configured to emit light at
a second wavelength. Optionally, in any embodiment, the method
further comprises periodically performing a measurement for the
first light source and the second light source. Optionally, in any
embodiment, the periodically performing a measurement comprises
applying a plurality of optical drive signals to the first light
source to generate a plurality of first output intensities at the
first wavelength. Optionally, in any embodiment, the periodically
performing a measurement comprises receiving a plurality of first
wavelength reflection intensities for each of the first output
intensities at the first wavelength. Optionally, in any embodiment,
the periodically performing a measurement comprises storing digital
data values as the plurality of first wavelength intensity for the
first output intensities in a memory. Optionally, in any
embodiment, the periodically performing a measurement comprises
applying a plurality of optical drive signals to the second light
source to generate a plurality of second output intensities at the
second wavelength. Optionally, in any embodiment, the periodically
performing a measurement comprises receiving a plurality of second
wavelength reflection intensities for each of the second output
intensities at the second wavelength. Optionally, in any
embodiment, the periodically performing a measurement comprises
storing digital data values as the plurality of second wavelength
intensities for the second output intensities in a memory.
Optionally, in any embodiment, the periodically performing a
measurement comprises identifying signal artifacts in each of the
first wavelength reflection intensities and in each of the second
wavelength reflection intensities. Optionally, in any embodiment,
the periodically performing a measurement comprises analyzing at
each period, the signal artifacts identified in the first
wavelength reflection intensities and the second wavelength
reflection intensities to determine a period of time between the
signal artifacts. Optionally, in any embodiment, the periodically
performing a measurement comprises using the period of time between
the signal artifacts to determine a heart rate.
[0016] In another aspect, a device for sensing information relating
to subcutaneous processes in a patient is provided. Optionally, in
any embodiment, the wearable device comprises a wearable patch
configured to attach to a body part of a patient; a sensor assembly
mounted on the wearable patch, the sensor assembly comprising one
or more sensors selected from the group consisting of an acoustic
sensor, a strain gauge, an optical sensor, a conductivity sensor, a
pressure sensor, and an chemical sensor. Optionally, in any
embodiment, the wearable device comprises a signal converter
configured to receive the one or a plurality of electrical signals
from the plurality of sensors and to convert the signals to one or
a plurality of sensor data signals comprising a data representation
of at least one of the one or a plurality of electrical signals;
and a communications interface configured to communicate the one or
a plurality of sensor data signals to a sensor data processing
system.
[0017] Optionally, in any embodiment, the sensor assembly further
comprises one or more sensors selected from the group consisting of
an accelerometer, a temperature sensor, and a moisture sensor.
Optionally, in any embodiment, the sensor assembly comprises one or
more of an ultrasonic transducer and an ultrasonic sensor.
Optionally, in any embodiment, the sensor assembly comprises an
acoustic sensor having a substantially flat sensitivity between
about 20 Hz. and about 20 kHz. Optionally, in any embodiment, the
sensor assembly comprises an accelerometer having a sensitivity
along three axes from 0 Hz. to about 500 Hz. Optionally, in any
embodiment, the sensor assembly comprises a strain gauge having a
sensitivity to a mechanical strain between about 0.1 Hz. and about
20 Mhz. Optionally, in any embodiment, the sensor assembly
comprises a temperature sensor having a resolution below about
0.1.degree. C. Optionally, in any embodiment, the sensor assembly
comprises a temperature sensor and the signal converter is
configured to sample one or a plurality of electrical signals
representing a temperature reading from the temperature sensor at
about 8 Hz. Optionally, in any embodiment, the sensor assembly
comprises two temperature sensors configured to provide a
differential temperature measurement. Optionally, in any
embodiment, the sensor assembly comprises one or more of an
acoustic sensor and an accelerometer. Optionally, in any
embodiment, the acoustic sensor is a piezoelectric device.
Optionally, in any embodiment, the piezoelectric device is made of
a material selected from any one or more of polyvinylidene fluoride
(PVDF), lead zirconate (PZT), a composite including either PVDF or
PZT materials. Optionally, in any embodiment, the acoustic sensor
is a microphone. Optionally, in any embodiment, the microphone is
implemented using a microelectromechanical system. Optionally, in
any embodiment, the communication interface comprises a wireless
transmitter to transmit the one or a plurality of sensor data
signals to the sensor data processing system. Optionally, in any
embodiment, the wireless transmitter communicates radio frequency
(RF) signals. Optionally, in any embodiment, the radio frequency
signals are communicated using a near field communication protocol.
Optionally, in any embodiment, the wireless transmitter
communicates using a cellular communications system. Optionally, in
any embodiment, the wireless transmitter communicates using a
wireless local area network system or a near field magnetic
communication system.
[0018] In another aspect, a system for monitoring a patient is
provided. Optionally, in any embodiment, the system comprises a
wearable patch configured to attach to a body part of a patient.
Optionally, in any embodiment, the wearable patch comprises a
sensor assembly comprising a plurality of sensors configured to
detect a corresponding plurality of sensory modalities and generate
one or a plurality of electrical signals representing the sensory
modalities; a signal converter configured to receive the one or a
plurality of electrical signals from the plurality of sensors and
to convert the signals to one or a plurality of sensor data signals
comprising a data representation of at least one of the one or a
plurality of electrical signals; a communications interface
configured to communicate the one or a plurality of sensor data
signals; and a local hub configured to wirelessly receive the one
or a plurality of sensor data signals from the wearable patch using
a first protocol, and to transmit the one or a plurality of sensor
data signals using a second protocol.
[0019] Optionally, in any embodiment, the local hub transmits the
one or a plurality of sensor data signals to a remote sensor data
processor configured to receive the one or a plurality of sensor
data signals using the second protocol and to process the one or a
plurality of sensor data signals to monitor and alert for
thrombosis development or clinically actionable levels of stenosis
in a vessel. Optionally, in any embodiment, the first protocol is
2.4 to 2.485 GHz radiofrequency communications protocol, a near
field communication protocol, a wireless local area network
protocol, or a near field magnetic protocol. Optionally, in any
embodiment, the second protocol is a cellular protocol or an
Internet protocol. Optionally, in any embodiment, the remote sensor
data processor comprises a processor and a storage medium storing
computer-executable instructions that when executed are operable to
perform phonoangiography using a break frequency to estimate an
internal diameter of a carotid artery for the patient. Optionally,
in any embodiment, the storage medium stores computer-executable
instructions that when executed are operable to determine the break
frequency by calculating a frequency power spectrum for a sound
measurement and identifying a highest frequency after which a power
level drops significantly.
[0020] In another aspect, a method for monitoring subcutaneous
processes in a patient is provided. Optionally, in any embodiment,
the method comprises sensing a plurality of sensory modalities
using a sensor assembly comprising one or more sensors mounted on a
wearable patch, the one or more sensors selected from the group
consisting of an acoustic sensor, a strain gauge, an optical
sensor, a conductivity sensor, a temperature sensor, a pressure
sensor, and a chemical sensor, where the sensory modalities are
received as one or a plurality of electrical signals representing
the sensory modalities; converting the one or a plurality of
electrical signals to a plurality of corresponding one or a
plurality of sensor data signals; and transmitting the one or a
plurality of sensor data signals to a sensor data processing
system.
[0021] Optionally, in any embodiment, the step of sensing the
plurality of sensory modalities comprises any one or more of:
sensing sound using an acoustic sensor; sensing movement or
orientation of a patient body part using an accelerometer; sensing
temperature using a temperature sensor; sensing a stretch or
compression of the wearable patch using a strain gauge; sensing
electromagnetic signals using an optical sensor; sensing moisture
using a moisture sensor sensing conductivity using a conductivity
sensor; sensing pressure using a pressure sensor; and sensing a
chemical using a chemical sensor.
[0022] Optionally, in any embodiment, the step of sensing the
plurality of sensory modalities comprises sensing a differential
measurement of skin temperature from two temperature sensors.
Optionally, in any embodiment, the step of transmitting the one or
a plurality of sensor data signals to the sensor data processing
system comprises: transmitting the one or a plurality of sensor
data signals to a local hub, where the local hub transmits the
sensor data signal to a remote sensor data processor for processing
of the one or a plurality of sensor data signals.
[0023] Optionally, in any embodiment, the device can be placed into
a shelf mode where power is either disconnected or placed into a
low power mode. In some embodiments shelf mode can be automatically
entered based on readings from any one or more of: magnetic sensors
or switches; optical sensors; motion, acceleration or tilt sensors;
temperature sensors; capacitive proximity sensors; and mechanical
switches. Optionally, in any embodiment, shelf mode can invoked by
a microcontroller device and exited based on readings from any one
or more of: magnetic sensors or switches; optical sensors; motion,
acceleration or tilt sensors; temperature sensors; capacitive
proximity sensors; and mechanical switches.
[0024] Optionally, in any embodiment, the above sensors interact
with product packaging or an adhesive backing liner in order to
exit shelf mode when the patch is removed from the product
packaging. Optionally, in any embodiment, the device can be placed
into a shelf mode where power is either disconnected or placed into
low power modes. Optionally, in any embodiment, shelf mode is
either invoked by a microcontroller device or automatically
entered, based on readings from any one or more of: magnetic
sensors or switches; optical sensors; motion, acceleration or tilt
sensors; temperature sensors; capacitive proximity sensors; and
mechanical switches. Optionally, in any embodiment, shelf mode can
be invoked by a microcontroller device and exited based on readings
from any one or more of: magnetic sensors or switches; optical
sensors; motion, acceleration or tilt sensors; temperature sensors;
capacitive proximity sensors; and mechanical switches. Optionally,
in any embodiment, the above sensors interact with product
packaging or an adhesive backing liner in order to exit shelf mode
when the patch is removed from the product packaging.
[0025] Optionally, in any embodiment, the device can be placed into
a shelf mode where power is either disconnected or placed into a
low power mode. Optionally, in any embodiment, shelf mode is either
invoked by a microcontroller device or automatically entered, based
on readings from any one or more of: magnetic sensors or switches;
optical sensors; motion, acceleration or tilt sensors; temperature
sensors; capacitive proximity sensors; and mechanical switches.
Optionally, in any embodiment, shelf mode can invoked by a
microcontroller device and exited based on readings from any one or
more of: magnetic sensors or switches; optical sensors; motion,
acceleration or tilt sensors; temperature sensors; capacitive
proximity sensors; and mechanical switches. Optionally, in any
embodiment, the above sensors interact with product packaging or an
adhesive backing liner in order to exit shelf mode when the patch
is removed from the product packaging.
[0026] Additional aspects and advantages of the present disclosure
will become readily apparent to those skilled in this art from the
following detailed description, wherein only illustrative
embodiments of the present disclosure are shown and described. As
will be realized, the present disclosure is capable of other and
different embodiments, and its several details are capable of
modifications in various obvious respects, all without departing
from the disclosure. Accordingly, the drawings and description are
to be regarded as illustrative in nature, and not as
restrictive.
INCORPORATION BY REFERENCE
[0027] All publications, patents, and patent applications mentioned
in this specification are herein incorporated by reference to the
same extent as if each individual publication, patent, or patent
application was specifically and individually indicated to be
incorporated by reference.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The invention can be better understood by referring to the
following figures. The components in the figures are not
necessarily to scale, emphasis instead being placed upon
illustrating the principles of the invention. In the figures, like
reference numerals designate corresponding parts throughout the
different views.
[0029] FIG. 1 is a block diagram of an example of a system for
measuring biological one or a plurality of fluid properties;
[0030] FIGS. 2A and 2B are an isometric and a top view,
respectively, of an example of an optical measuring system for
measuring one or a plurality of biological fluid properties in the
system in FIG. 1;
[0031] FIGS. 3A and 3B are a side and a top view, respectively, of
an example of the optical measuring system of FIGS. 2A and 2B used
for measuring the depth of biological fluid carrying vessels below
the skin surface;
[0032] FIGS. 4A and 4B are a top view centered and a top view
off-axis, respectively, of an example of the optical measuring
system of FIGS. 2A and 2B used for determining a position of the
system relative to the biological fluid carrying vessels below the
skin surface;
[0033] FIGS. 5 and 6 are side views of an example of the optical
system of FIGS. 2A and 2B illustrating use of an analytical model
for determining and analyzing optical reflectance data in measuring
one or a plurality of biological fluid properties;
[0034] FIG. 7 is a graph illustrating a determination of a minimum
threshold LED current to illuminate the tissue sufficiently to
reach the vessel;
[0035] FIG. 8 is a graph of current at the photodetector,
I.sub.del, as a function of the depth, d, of the fluid vessel for
different LED to photodetector spacings;
[0036] FIG. 9 is a graph of ratio reflected intensity at each
spacing as a function of hematocrit;
[0037] FIG. 10 is a schematic diagram of the system in FIGS. 2A and
2B illustrating a variation in vessel axis with respect to the
hemispherical radiation volume induced by the LEDs;
[0038] FIG. 11 is a flowchart illustrating operation of a system
for measuring one or a plurality of biological fluid properties
using an example of the system in FIGS. 2A and 2B positioned on the
skin surface of a patient;
[0039] FIGS. 12A and 12B are front views at extension and at
flexion of a knee of a patient with a system for measuring one or a
plurality of biological fluid properties thereupon;
[0040] FIG. 13A is a flow chart illustrating operation of the
system in FIGS. 2A and 2B positioned on a skin surface superior to
the patella of a patient;
[0041] FIG. 13B is a block diagram of an example of a system for
measuring one or a plurality of biological fluid properties from an
optical sensor on a skin surface superior to the patella of a
patient;
[0042] FIG. 14 depicts an arm having a synthetic bridge graft
between an artery and a vein;
[0043] FIG. 15 is a block diagram of an example implementation of a
wearable patch with a sensor assembly and a wireless communication
interface;
[0044] FIG. 16A is a block diagram of another example
implementation of a wearable patch with a sensor assembly and a
wireless communication interface;
[0045] FIG. 16B is a flow diagram for an example state machine for
the wearable patch of FIG. 16A;
[0046] FIG. 17A is a perspective bottom view of an example of a
wearable patch;
[0047] FIG. 17B is a top view of an example of a wearable
patch;
[0048] FIG. 18 is a flowchart illustrating operation of a method
for monitoring subcutaneous processes in a patient wearing a
wearable patch; and
[0049] FIG. 19 is a block diagram of an example system for
monitoring a patient wearing a wearable patch.
DETAILED DESCRIPTION OF THE INVENTION
I. Optical Detection of Biological Fluid Properties
[0050] 1. System Overview
[0051] Disclosed herein are systems and methods for measuring one
or a plurality of biological fluid properties from a patient's
body. Examples of systems comprise an optical system comprising at
least two light sources, at least one photodetector, and data
processing resources for analyzing the data collected using the
light sources and photodetector. The light sources are identified
as light-emitting diodes (LEDs) throughout this description,
however, any suitable light source with a controllable intensity
and in some implementations, different wavelengths, may be used as
well. The LEDs are controlled to illuminate a region in the tissue
below the LEDs. The photodetector senses light reflected from, or
transmitted through, the tissue below the LEDs and generates a
current corresponding to the intensity of the reflected light. The
distances between the LEDs and photodetector are known and the
position of each LED relative to each other, to the photodetector,
and to any fluid vessels below the skin surface is also known.
[0052] Any number of LEDs may be used in the system depending on
the measurements to be taken and the sensitivity desired. The
different LEDs may be needed for emitting light at different
wavelengths, or for illuminating the tissue from different
positions on the skin surface. Multiple photodetectors may be used
as well to measure intensities at different wavelengths, or at
different positions on the skin surface.
[0053] FIG. 1 is an example of a system 100 for measuring
biological fluid vessel properties. The system 100 in FIG. 1
comprises at least two light sources (LEDs in the described
example) 102a, 102b, a photodetector 104, a signal converter 106,
and a communication interface 108. The LEDs 102, the photodetector
104, the signal converter 106, and communications interface 108 may
be mounted in or on a casing, substrate or other holding structure
in a manner that allows each LED 102a, 102b to contact the
patient's skin S. The casing or substrate may be any suitable
structure. In one example implementation, the LEDs 102 and the
photodetector 104 are disposed on a flexible, stretchable substrate
formed as a type of patch with an adhesive that would allow the
patient to wear the system for constant monitoring. The stretchable
substrate, for example extended polytetrafluoroethylene (ePTFE),
enables a wider range of adherent form factors, including on or
near articulating joints. The substrate contains corrugated traces
that allow the device to stretch without disrupting electrical
connections. These traces may be placed by a physical vapor
deposition process when the substrate is at maximum stretch. Rigid
and flexible electronics components can then be assembled on the
deposited traces using, for instance, a reflow soldering process.
This can be done either while the substrate is still at stretch or
after it has reverted to its resting dimensions. Where the
substrate is ePTFE, the device is able to dynamically stretch by
more than 20% of its total length, even when populated by rigid
electronics components, due to the material's ability to stretch by
.about.50% when unpopulated.
[0054] The LEDs 102a, 102b are mounted in the structure so as to
contact the skin to irradiate the tissue below the skin with a
light having an intensity controlled by a current level. Each LED
102a, 102b is driven to illuminate the tissue by a corresponding
current I.sub.LED1 and I.sub.LED2, respectively. The system in FIG.
1 depicts two LEDs, however, additional LEDs may be used.
[0055] The photodetector 104 is also mounted on the skin to receive
reflectance values corresponding to light reflected from scattering
off the structure in the tissue beneath the skin. The photodetector
104 detects the light and emits a current, I.sub.del, corresponding
to the intensity of the reflected light. One photodetector 104 is
used in the system 100 in FIG. 1. In other examples, additional
photodetectors may be used.
[0056] The signal converter 106 and communications interface 108
are optional and represent a connection by which reflectance values
may be communicated to a processing system for analysis. A simple
hardwired connection may be used to connect the system to a
processing system. The signal converter 106 and communications
interface 108 allow for the system 100 to be implemented on a
wearable patch to allow for remote monitoring of the patient. The
signal converter 106 may modulate or encode a signal to be
communicated to a processing system. The communications interface
108 may then communicate the signal wirelessly via antenna 112.
[0057] The system 100 may receive power from a power supply 103,
which may be a simple battery. The power supply may comprise a
wakeup sensor to trigger the power supply 103 to start the system
100 when the system 100 is moved from a storage state to an
operable state. The wakeup sensor may for example be implemented as
a magnetic sensor that keeps the power off in proximity to a
magnetized packaging, but then triggers the power on when moved
away from the magnetized packaging. The wakeup sensor may also be a
piezoelectric film that remains in a quiescent state until it is
stretched, inducing a voltage to activate the device. Other
modalities may be used for the wakeup sensor such as light or
pressure.
[0058] FIGS. 2A and 2B are an isometric and a top view,
respectively, of an example of an optical measuring system 200 for
measuring biological fluid properties in the system in FIG. 1. The
system 200 in FIGS. 2A and 2B comprises two LEDs L1, L2 and one
photodetector PD (housing not shown). Additional LEDs or
photodetectors may be used. FIGS. 2A and 2B shows the position of
each component on the skin relative to a biological fluid carrying
vessel 210 with a diameter, D, at a finite depth, d, in the tissue
T below the skin surface S. The LEDs L1, L2, each emit
corresponding optical radiation patterns to illuminate the tissue.
The optical radiation patterns are illustrated in FIGS. 2A and 2B
as two separate hemispherical volumes (in FIGS. 2A and 2B, L1
generates an optical radiation pattern shown as a hemispherical
volume with radius R.sub.1 and L2 generates an optical radiation
pattern shown as a hemispherical volume with radius R.sub.2). The
LEDS, L1, L2, may be selected to emit at different wavelengths,
such as for example, green, yellow, red, infrared (IR), or other
wavelengths.
[0059] The two LEDs L1, L2 are shown to be located at a
center-to-center distance of r.sub.1, r.sub.2 from the
photodetector and placed along the axis of the vessel 210. The
hemispherical volumes representing the optical radiation patterns
are depicted as each having a radius R.sub.1 and R.sub.2 for L1, L2
respectively. The radius R.sub.1, R.sub.2 of the optical radiation
pattern is dependent on the light wavelength and the corresponding
absorption and scattering properties of the tissue and its
constituents at the wavelength. It is noted that the system 100 in
FIG. 1 is one of many example implementations and its description
herein is not intended to limit the many possible implementations
that are feasible to achieve the intended function of the system.
The example system 200 in FIGS. 2A and 2B implements a minimum two
LEDs located at a known distance from at least one photodetector.
While the system is functional with two LEDs and one photodetector,
more LEDs and photodetectors can be used to increase the
measurement performance as detailed in the description below.
[0060] FIGS. 3A, 3B 4A, and 4B below illustrate how the system in
FIGS. 1, 2A, and 2B may be used to obtain different measurements of
properties of biological fluid vessels. The system may be modified
in various ways as described below by using more than two LEDs or
by using LEDs with different wavelengths. It is to be understood
that the descriptions below are not intended as limiting the system
to any one implementation. [0061] 2. Measurement Techniques
Measuring the Depth of the Fluid Vessel below the Skin Surface
[0062] FIGS. 3A and 3B are a side and a top view, respectively, of
an example of the optical measuring system of FIGS. 2A and 2B used
for measuring the depth of biological fluid carrying vessels below
the skin surface. In FIG. 3A, the side view depicts the optical
radiation pattern in the tissue induced by one of the at least two
LEDs L1, L2 portrayed as a series of hemispherical volumes with
increasing radii R1, R2, R3, R4, R5, R6 and R7 corresponding to
increasing light intensity. FIG. 3B depicts the same radiation
pattern from the top, alongside the photodetector PD with the
hemispherical pattern centered about LED L1 for illustration
purposes.
[0063] Each of the at least two LEDs can enable emission of light
at increasing intensities by increasing the power, via the current
I.sub.LED, supplied to the LEDs. As shown in FIGS. 3A and 3B light
emitted into the tissue undergoes absorption and scattering due to
the tissue and its constituents. The absorption and scattering is
depicted in FIGS. 3A and 3B by the hemispherical optical radiation
pattern with radius R, and a portion of this light (arrow Refl) is
scattered back into the photodetector, thus enabling the
measurement of optical reflectance characteristics within this
region of influence. An increase in light intensity results in the
light emitted in the tissue to penetrate deeper, and consequently,
enable the measurement of optical reflectance characteristics
within regions of influence that are increasing in size,
corresponding to hemispherical radiation volumes with increasing
radii R1, R2, R3, R4, R5, R6 and R7 centered about the position of
the LED. This enables a spatial, depth-based optical reflectance
measurement of the biological fluid carrying vessel at a finite
depth in the tissue. Changes observed in the optical reflectance
measurement with increasing light intensity, and consequently
increasing radiation volume radius, can be used to determine the
depth, d (from R3 to R4), and diameter, D (from R6 to R7), of the
vessel.
[0064] One example method for determining the depth of a vessel
comprises the steps of: [0065] a. generating a light from a first
light source positioned on a skin surface above a fluid vessel at
each of a plurality of intensity levels, each intensity level
corresponding to a radius of a hemispherical region of
influence;
[0066] b. measuring a first plurality of reflectance values each
corresponding to each of the plurality of intensity levels of the
first light;
[0067] c. generating a light from a second light source positioned
on the skin surface proximal to the first light source at each of
the plurality of intensity levels;
[0068] d. measuring a second plurality of reflectance values
corresponding to each of the plurality of intensity levels;
[0069] e. determining a vessel depth and a vessel diameter from
changes in reflectance values with increasing light intensity.
[0070] The techniques described above may be used to determine the
optical intensity required to `meaningfully` irradiate and sense
the region of the vessel below the LED L1 (R7 in FIG. 3A).
Detection of the Position of the System over the Fluid Vessel
[0071] FIGS. 4A and 4B are a first top view and a second top view
of an example of the optical measuring system of FIGS. 2A and 2B
used for determining a position of the system relative to the
biological fluid carrying vessels below the skin surface. In FIG.
4A, the top view depicts the two LEDs L1, L2 and photodetector PD
centered about the vessel axis VA with their corresponding optical
radiation patterns induced in the tissue portrayed as two separate
hemispherical volumes (L1 & L2). In FIG. 4B, the second top
view depicts the same radiation patterns but with the two LEDs L1,
L2 and photodetector PD offset with respect to the vessel axis
VA.
[0072] The two LEDs L1, L2 and the photodetector PD enable the
measurement of the tissue's optical reflectance characteristics
within a region of influence corresponding to the LED's optical
radiation pattern centered about the position of the LEDs (see FIG.
4A, L1 generates a first radiation pattern, and L2 generates a
second radiation pattern). The light intensity of each LED can be
independently adjusted to irradiate the region below the LEDs with
their respective optical radiation pattern radii intersecting the
vessel (see R4 to R7 in FIG. 3A). The system as shown in FIGS. 4A
and 4B enables a two-point, spatial measurement of the optical
reflectance characteristics of the biological fluid carrying vessel
at a finite depth in the tissue. The relative level of signal
strength of the optical reflectance measurement at the
photodetector PD due to light from LEDs L1 and L2 can be used to
determine the relative position of the system over the vessel. For
example, FIGS. 4A and 4B depicts two cases, centered and off-axis,
respectively. A scan of different light intensities at each LED, L1
and L2 would result in a set of reflectance values corresponding to
each LED that provide a data pattern corresponding to the
intersection of the fluid vessel and the two hemispherical
irradiation volumes. The data pattern for the LEDs in the case in
which the LEDs, L1 and L2, centered would be substantially the
same. The data pattern for the LEDs in the case in which the LEDs
are off-axis would be different. The differences in the data
patterns in the off-axis case would make it possible to determine
which LED is the primary LED light source for use in biological
fluid properties or flow measurements inside the vessel. The LED
for which the intersection of the hemispherical irradiation volume
and vessel is maximized (such as for example, LED L2 in FIGS. 4A
and 4B) would be deemed the primary LED. If it is desired to center
the LEDs and the photodetector over the vessel, the LEDs and
photodetector can be moved in a direction transverse to the vessel
such that the intersection of the irradiation volume and vessel is
more equal for each LED. The process may be repeated until a
substantially centered system over the vessel is achieved.
Measurement of Fluid Properties including Particle Concentration
and Flow Rate Inside a Vessel
[0073] Referring to FIGS. 2A and 2B, the two LEDs L1, L2 and
photodetector PD in the system 200 enable the measurement of the
tissue's optical reflectance characteristics within a region of
influence corresponding to the LED's optical radiation pattern
centered about the position of the LED (see FIGS. 4A and 4B, LED L1
generates a radiation pattern with radius r1 and the LED L2
generates a radiation pattern with radius r2). The optical light
intensity of the LEDs can be adjusted to irradiate the region below
the LEDs with their respective optical radiation pattern radii
reaching beyond the bottom of the vessel (R>d+D, see R7 in FIG.
3A). The LEDs L1, L2 may be configured to emit light at two
different optical wavelengths .lamda.1, .lamda.2. This enables a
two-wavelength measurement of the optical reflectance
characteristics of the biological fluid in the vessel, where the
fluid exhibits different optical absorption and scattering
characteristics at the two wavelengths. The relative level of
signal strength of the optical reflectance measurement at the
photodetector PD due to light at the two wavelengths .lamda.1,
.lamda.2. (from LEDs L1 and L2 ) can be used to determine the one
or a plurality of properties of the biological fluid. The one or a
plurality of properties that may be determined include, but are not
limited to, chemical composition and analyte concentration,
particular1y where the analyte is a specific type of cell.
[0074] In one example implementation, one LED that can emit light
in the infrared and one LED that can emit red light may be used to
measure oxygenation levels in blood flowing through the vessel. For
example, the oxygenation levels may be measured by calculating the
ratio of optical reflectance measured at the two wavelengths. In
addition, the frequency of repetitive signal artifacts observed in
the optical reflectance measured at one or more wavelengths may
also be analyzed allowing for the determination of the heart rate.
While the system may be implemented with two LEDs at different
wavelengths and one photodetector, a more robust system may
comprise additional LEDs or wavelengths and photodetectors that can
be used to increase the measurement performance. For example, the
use of an additional LED that emits light at green wavelength can
provide an improved heart rate measurement by sensing the blood
flowing through the vessel.
[0075] In another example implementation, one LED that can emit
light in the infrared and one LED that can emit yellow light may be
used to measure the white blood cell (WBC) concentration in the
synovial fluid in a subcutaneous bursa. For example, the WBC
concentration may be measured by calculating the ratio of optical
reflectance and/or transmittance measured at the two wavelengths by
at least one, but possibly more, photodetectors. [0076] 3. Model of
System and Tissue Interaction
[0077] The feasibility and strength of the measurement techniques
described above may be validated by modeling the system and tissue
interaction using analytical and finite element method (FEM)
formulations. The modeling also informs the system parameters
(including but not limited to components and their related control
parameters) that may be adjusted to achieve the intended function
of measuring one or a plurality of properties of biological fluids
flowing through, or present in, a vessel or a bursa in its
physiological environment at a finite depth below the skin surface.
These system parameters comprise but are not limited to optimal
number of LEDs, number of photodetectors (PD), light wavelengths,
LED light intensity, and LED & PD spacings and position.
Model Objectives:
[0078] The main objective of the analytical formulation is to
quantitatively model the LED light source L and the optical
absorption and scattering experienced by the light in the tissue,
in order to determine the optical reflectance measured at the
photodetector. The fundamental theory behind the formulation is
particle diffusion, wherein light is treated as a particle which
undergoes absorption and scattering in the tissue depending on the
optical properties.
Model Formulation:
[0079] FIG. 5 is a side view depicting the cross-section of the
optical radiation pattern in the tissue T induced by one of the at
least two LEDs L, where the optical radiation pattern is
represented as a hemispherical volume with radius R; Parameters
defined for the analytical model include: [0080] 1. L-PD spacing r,
[0081] 2. random tissue voxel position (p, z), [0082] 3. vessel
depth d and diameter D, [0083] 4. vessel radial dilation about its
axis during pulsatile fluid flow .DELTA.D.
[0084] By using particle diffusion theory.sup.1, the following
analytical expression can be derived for the steady-state (DC)
photon flux at a random tissue voxel position (p, z): [0085]
.sup.1J. M. Schmitt, "Simple Photon Diffusion Analysis of the
Effects of Multiple Scattering on Pulse Oximetry," IEEE
Transactions on Biomedical Engineering, vol. 38, no. 12, Dec. 1991.
(incorporated by reference)
[0085] .psi. dc .function. ( .rho. ) = P .mu. s .times. 2 .times.
.pi. .times. .rho. 2 .function. [ C 1 .times. e - .alpha. .times.
.rho. .function. ( 1 .rho. + .alpha. ) + C 2 .times. e .alpha.
.times. .rho. .function. ( 1 .rho. - .alpha. ) ] ##EQU00001##
[0086] where, [0087] Photon flux [0088] P-Optical power emitted by
the LED [0089] .mu.a-absorption coefficient of tissue [0090]
.mu.s-transport-corrected scattering coefficient of tissue [0091] a
{square root over (3.mu..sub.a.mu..sub.s)} C1, C2-constants that
are calculated depending on the boundary conditions (BC) at the
hemispherical optical radiation volume (BC1: p=r, z=R) and LED
(BC2: p=0, z=0).
[0092] For Boundary Condition BC1: As shown in FIG. 5, the optical
absorption and scattering phenomena encountered by the light is
expected to differ at the tissue-vessel boundary (R=d) depending on
the absorption (.mu..sub..alpha..sup.b) and scattering
(.lamda..sub.s.sup.b) coefficients of the fluid relative to that of
the tissue. This boundary can be modeled using a Robin-type
boundary condition2:
Photon .times. .times. flux .times. .times. .psi. .function. (
.rho. ) + 2 .times. k b .times. d .times. .psi. .function. ( p ) d
.times. .rho. = 0 .times. .times. at .times. .times. .rho. = R
##EQU00002##
where, the diffusion coefficient in fluid is
k b = 1 3 .times. ( .mu. a b + .mu. s b ) . ##EQU00003##
[0093] For boundary condition BC2-the flux density at the LED can
be defined as:
lim .rho. -> 0 .times. [ - 4 .times. .times. .pi. .times.
.times. k .times. .times. .rho. 2 .times. d .times. .times. .psi.
.function. ( .rho. ) d .times. .times. .rho. ] = P ##EQU00004##
[0094] By applying boundary conditions BC1 and BC2 to the
steady-state photon flux, C1 and C2 can be determined:
C 1 = 1 ( 1 - e - 2 .times. .times. .alpha. .times. .times. R )
.times. ( 1 - 2 .times. .times. k b R + 2 .times. .times. k b
.times. .alpha. ) ##EQU00005## C 2 = 1 ( 1 - e 2 .times. .alpha.
.times. .times. R ) .times. ( 1 - 2 .times. .times. k b R - 2
.times. .times. k b .times. .alpha. ) ##EQU00005.2## [0095] .sup.2
M. Schweiger et al., "The Finite element method for the propagation
of light in scattering media: Boundary and source conditions,"
Medical Physics, vol. 22, no. 11, pt. 1, Nov. 1995. The steady
state current (I.sub.dc) due to the optical reflectance from the
tissue measured at the photodetector, with an area PD.sub.area and
conversion factor at the specific LED wavelength, spectral
sensitivity SS, can be defined as:
[0095] I dc = PD area .times. SS .times. .psi. dc .function. (
.rho. = r ) = PD area .times. SS .times. P .mu. s .times. 2 .times.
.times. .pi. .times. .times. r 2 [ C 1 .times. e - .alpha. .times.
.times. r ( 1 r + .alpha. ) + C 2 .times. e .alpha. .times. .times.
r ( 1 r - .alpha. ) ] ##EQU00006##
[0096] FIG. 6 is an example of the system as shown in FIG. 5, where
the vessel radial dilation about its axis during pulsatile fluid
flow .DELTA.D is approximated by an increase in the hemispherical
optical radiation pattern radius by dR, which physically
constitutes the increase in fluid corresponding to the pulsatile
dilation of the vessel.
[0097] The pulsatile fluid flow in the vessel manifests itself as a
radial vessel dilation .DELTA.D about its axis as depicted in FIG.
5. In order to investigate the time-varying photodetector current
(I.sub.ac) during pulsatile fluid flow, the increase in fluid
corresponding to the pulsatile dilation of the vessel is
approximated by an increase in the hemispherical optical radiation
pattern radius by .DELTA.R (see FIG. 6). With this approximation,
the time-varying photodetector current (I.sub.ac) can be defined
as:
I ac = .DELTA. .times. .times. R .times. dI dc dR = .DELTA. .times.
.times. R .times. .times. PD area .times. SS .times. .alpha.
.times. .times. P .mu. s .times. .pi. .times. .times. r 2 [ ( e - 2
.times. .alpha. .times. .times. R .times. C 1 - k b .alpha. .times.
.times. R 2 ) .times. e - .alpha. .times. .times. r 1 - e - 2
.times. .alpha. .times. .times. R .times. ( 1 r + .alpha. ) - ( e 2
.times. .alpha. .times. .times. R .times. C 2 + k b .alpha. .times.
.times. R 2 ) .times. e .alpha. .times. .times. r 1 - e 2 .times.
.alpha. .times. .times. R .times. ( 1 r - .alpha. ) ]
##EQU00007##
Measurement of biological fluid carrying vessel depth below skin
surface:
[0098] A technique for measuring the depth of a vessel below the
skin surface on which the system is positioned was described above
with reference to FIGS. 3A and 3B. One way to simplify the
technique and to enable the measurement of one or a plurality of
properties of biological fluids flowing through the vessel (having
a diameter, D) in its physiological environment at a finite depth,
d, below the skin surface, is to ascertain the minimum, threshold
optical light intensity or LED current I.sub.LEDth. The minimum,
threshold optical light intensity current, I.sub.LEDth, is the
level of current needed to drive the LED in order to irradiate the
region below the LEDs and for the respective optical radiation
pattern radii of the LEDs to reach the vessel (R>d, see R3 in
FIGS. 3A and 3B). Irradiating the tissue to a sufficient depth
enables vessel depth measurement.
[0099] The I.sub.LEDth operating point may be determined using the
analytical model used to analyze the measured data by calibrating
it to the photodetector technical specifications, including but not
limited to the minimum detectable current, I.sub.PDmin and the
maximum usable current, I.sub.PDmax. In addition, the measured
photodetector DC current I.sub.dc at increasing LED power can be
used to further calibrate the model for the subject's tissue
characteristics.
I del .function. ( I LED ) = I ac .function. ( I LED ) I dc
.function. ( I LED ) - I PDmin I dc .function. ( I LED )
##EQU00008##
where,
I del .function. ( I LED ) > I PDmin I PDmax ##EQU00009##
can be used to determine the minimum, threshold LED current
I.sub.LEDth needed to reach the vessel.
[0100] FIG. 7 is a graph illustrating how a minimum threshold LED
current to illuminate the tissue sufficiently to reach the vessel
may be determined. The LEDs may then be energized at a range of
currents while measuring and calculating I.sub.del(I.sub.LED) 702
and
I PDmin I PDmax .times. 704. ##EQU00010##
The I.sub.del(I.sub.LED) 702 and
I PDmin I PDmax .times. 704 ##EQU00011##
are plotted as a function of I.sub.LED as shown in FIG. 7. The
point of intersection of the I.sub.del(I.sub.LED) plot and the
I PDmin I PDmax ##EQU00012##
plot indicates the minimum, threshold LED current I.sub.LEDth
needed to reach the vessel.
[0101] FIG. 8 is a graph of current at the photodetector,
L.sub.del, as a function of the depth, d, of the fluid vessel for
different LED-to-photodetector spacings. FIG. 8 shows an example
plot of I.sub.del with LED-PD spacing of r.sub.i=5.3 mm, 802, and
FIG. 8 also shows an example plot of I.sub.del with LED-PD spaceing
of r.sub.2=6.5, 804. FIG. 8 shows the system can be appropriately
configured to be sensitive to vessels with varying depths by
adjusting the LED to photodetector center-to-center spacing r (see
FIGS. 2A and 2B). As shown in FIG. 8, the analytical model predicts
that the system sensitivity to deeper vessels increases as the
LED-PD spacing r increases. [0102] 4. Biological Fluid Property
Measurement Inside Vessel:
[0103] In order to enable the measurement of one or a plurality of
properties of biological fluids flowing through a vessel (diameter
D) in its physiological environment at a finite depth d below the
skin surface, in addition the minimum, threshold optical light
intensity or LED current I.sub.LEDth needed to reach the vessel,
one needs to be able to ascertain the optimal optical light
intensity or LED current I.sub.LEDopt needed to irradiate the
region below the LEDs and their respective optical radiation
pattern radii to reach beyond the bottom of the vessel (R>d+D,
see R7 in FIGS. 2A and 2B). This operating point can be determined
empirically by detecting an inflection point in
I.sub.del(I.sub.LED) by sweeping I.sub.LED after crossing the
threshold LED current I.sub.LEDth.
[0104] Once this inflection point is found for the at least two
LEDs L1, L2, the optimal LED current I.sub.LEDopt can be determined
for each of the at least two LEDs in the system and this operating
point maintained when performing biological fluid property
measurement inside the vessel. For example, the at least two LEDs
L1, L2 can be designed to emit light at two different optical
wavelengths .lamda..sub.1, .lamda..sub.2. The relative level of
signal strength of the optical reflectance
measurement at the photodetector i.e.
I del .function. [ L .times. .times. 1 ] I del .function. [ L
.times. .times. 2 ] ##EQU00013##
can be used to determine the one or a plurality of properties of
the biological fluid. These properties comprise but are not limited
to chemical composition and analyte concentration. One envisioned
embodiment of this invention is the use of two LEDs that can emit
light at infrared and red wavelengths to measure oxygenation levels
in blood flowing through the vessel, by calculating the ratio of
optical reflectance measured at the two wavelengths. Further, by
analyzing the frequency of the repetitive signal artifacts observed
in the optical reflectance measured at one or more wavelengths, the
heart rate can be determined.
Particle Concentration and Flow Rate of the Biological Fluid:
[0105] In order to measure the particle concentration and flow rate
of the biological fluid in the vessel, the LEDs L1, L2 can be
configured to emit light at the same optical wavelength, but
located at different center-to-center spacing from the
photodetector r.sub.1, r.sub.2. Following the determination and
setting of the operating point, i.e. the optimal LED current
I.sub.LEDopt for each of the at least two LEDs L1, L2, the relative
level of signal strength of the optical reflectance measurement at
the photodetector, i.e.
R = I del .function. [ L .times. .times. 1 ] I del .function. [ L
.times. .times. 2 ] , ##EQU00014##
due to light from LEDs L1 and L2 can be used to determine one or a
plurality of properties of the biological fluid.
[0106] One envisioned embodiment of this invention is the use of
two LEDs that can emit light at the same infrared wavelength to
measure the red blood cells concentration (hematocrit) and flow
rate of blood in the vessel, by calculating the ratio of optical
reflectance measured using LEDs L1 and L2. Using the analytical
model, this ratio,
R = I del .function. [ L .times. .times. 1 ] I del .function. [ L
.times. .times. 2 ] , ##EQU00015##
can be calculated and its sensitivity to hematocrit can be
determined (see Graph below). The effect of hematocrit hct and
blood oxygenation SpO2 can be incorporated into the analytical
model by defining the absorption (.mu..sub.a.sup.b) coefficient,
and hence the diffusion coefficient k.sub.b, of the fluid as a
function of hct and SpO2.sup.3: [0107] .sup.3J. M. Schmitt, "Simple
Photon Diffusion Analysis of the Effects of Multiple Scattering on
Pulse Oximetry," IEEE Transactions on Biomedical Engineering, vol.
38, no. 12, Dec. 1991.
[0107] k b = 1 3 .times. ( .mu. a b .function. [ hct , Sp .times.
.times. O .times. .times. 2 ] + .mu. s b ) ##EQU00016##
[0108] FIG. 9 includes example plots of ratio,
R = I del .function. [ L .times. .times. 1 ] I del .function. [ L
.times. .times. 2 ] , ##EQU00017##
as a tunction of hematocrit with an LED-PD spacing of r.sub.1-5.3
mm and r.sub.2-6.5 mm for L1 and L2, which indicates the ratio's
sensitivity to increasing hematocrit. It should be noted, the
negative values correspond to LED currents I.sub.LED below the
minimum, threshold optical light intensity or LED current
I.sub.LEDth needed to reach the vessel.
[0109] Further, blood volume flow rate Q can be estimated from the
changes in the measured hematocrit hct using the ratio R over a
cycle of pulsatile blood flow (i.e. one heart beat) in the vessel
manifesting as a radial vessel dilation .DELTA.D about its
axis.sup.4. The blood volume under interrogation Vol.sub.inter in
the vessel can be ascertained using the analytical model, by
calculating the intersection of the LEDs' hemispherical irradiation
volume and vessel at the operating point, i.e. optimal LED current
I.sub.LEDopt for each of the at least two LEDs L1, L2. The blood
volume flow rate measurement can be averaged over multiple cycles
in order to increase measurement performance. [0110] .sup.4 R. R.
Steuer et al., "Noninvasive transcutaneous determination of access
blood flow rate," Kidney International, vol. 60, pp. 284-291,
2001.
[0110] Q = Vol inter 1 R .times. dR dt .times. dt ##EQU00018##
[0111] The calculated interrogation volume Vol.sub.inter can be
further adjusted to account for the variation in orientation of the
vessel axis portrayed in FIG. 10. FIG. 10 is a schematic diagram of
the system in FIGS. 2A and 2B illustrating a variation in vessel
axis with respect to the hemispherical radiation volume induced by
the LEDs. The system can account for this variation by using
imaging sensors to detect the vessel axis position and refine the
calculated interrogation volume Vol.sub.inter. Alternatively, a
correction factor C can be used to refine the interrogation volume
Vol.sub.inter calculated using the analytical model, wherein C[d,D]
can be defined as a function of the vessel depth d and diameter D
by calculating the distribution of the volume intersection of the
hemispherical optical radiation and a cylinder.sup.5. [0112]
.sup.5W. Gille, "Chord Length Distributions of the Hemisphere,"
Journal of Mathematics and Statistics, vol. 1, no. 1, pp. 24-28,
2005.
[0113] Once the hematocrit, vessel dimensions, and volumetric flow
rate have been determined, a number of clinical conditions can be
monitored using the methods and embodiments described herein in
conjunction with an appropriate remote monitoring system. When
utilized as part of a remote monitoring system, the capabilities
described herein can allow clinicians to better monitor a number of
conditions, including but not limited to:
[0114] Arteriovenous (AV) Access Maturation [0115] After an AV
access is surgically created, there is often a maturation period
that needs to occur for the body to adapt to the presence of new
vessel. In the cases of a native AV access (referred to as a
fistula), this maturation period can take up to 12 weeks. During
this time, the patient is at high risk for access closure. If the
access becomes closed, or fails to mature, the patient must then
endure an additional surgery and subsequent maturation period,
which can further delay the start of their dialysis treatments.
Ultimately, this creates more risk for the patient, added cost to
the healthcare system and complicates management of these patients
for clinicians. [0116] The most common cause of the access failing
to mature is the development of a juxta-anastamotic stenosis, which
reduces flow into the newly formed access. This condition is easily
correctable if detected ear1y enough, and when corrected leads to
successful access maturation in most patients. [0117] Monitoring
the volumetric flow rate through a patient's AV access is a
well-established way of assessing access maturation. A "mature" AV
access is defined as one that can sustain 600 mL/min of flow.
[0118] Tracking the volumetric flow rate in an AV access during the
maturation period is something that is impractical through
in-clinic measurements, but could be addressed through a remote,
at-home monitoring system. Incorporation of the methods and
embodiments disclosed herein into a remote monitoring system would
enable tracking of the maturation process of a patient's AV access.
In such a system, the clinician could be alerted if the access
needed intervention (e.g. to correct a juxta-anastamotic stenosis)
or if the patient's AV access had matured and was ready to begin
dialysis.
[0119] AV Access Health [0120] After an AV access has matured and
the patient has begun dialysis, the only reliable methodology for
detecting a blockage within a patient's AV access remains a
physical examination carried out by a trained nephrologist. This
examination is recommended to be carried out once a week-something
which is impractical given the volume of patients seen by a
dialysis clinic. [0121] A remote monitoring solution that
automatically tracks the health of an AV access and can detect
blockages in said access would enable better outcomes and
compliance with clinically recommended best-practices. [0122]
Tracking volumetric flow rate is a clinically accepted approach for
determining the health of a patient's AV access, and for
determining whether the patient needs an intervention to preserve
the health of the access. Incorporation of the methods and
embodiments disclosed herein into a remote monitoring system would
enable tracking of the health of a patient's AV access. In such a
system, the clinician could be alerted if the access needed
intervention (e.g. to correct a blockage). This would enable
practical, and reliable monitoring of access health-leading to
better outcomes and lower costs.
[0123] Dialysis Patient Dry Weight/Fluid Status [0124] When a
patient is on dialysis estimation of their "dry weight" is
essential to understanding both end-dialysis weight targets and the
necessary rate of dialysis to appropriately manage a patient's
fluid level. No reliable metrics exist today to track this
important parameter, and this value is determined predominantly
through clinical judgment. [0125] It is generally accepted that
hematocrit levels are inversely proportional to patient blood
volume, so long as a patient is not hemorrhaging or undergoing any
other significant trauma that could lead to blood loss. The
monitoring of hematocrit level can be more reliably used to make a
determination on a patient's fluid status, if measured in
conjunction with additional vitals such as heart rate, blood
pressure, and flow. [0126] The embodiments and methods disclosed
herein could be incorporated with a remote monitoring system to
track fluid status of a patient on dialysis and to develop a
quantified assessment of dry weight over the course of multiple
dialysis sessions. This technology could be applied to vessels
close to the surface of the skin such as an AV access, radial
artery, brachial artery, carotid artery, etc. The flexibility of
this approach could allow for fluid status monitoring for patients
on peritoneal dialysis as well as for those on hemodialysis.
[0127] Fluid Overload or Dehydration in Congestive Heart Failure
Patients [0128] Congestive heart failure (CHF) patients often must
undergo hospitalization for fluid overload or dehydration, which
has a significant effect on increasing the mortality rates for
these patients. The goal for CHF patient management is to provide
fluid management that enables the patient to stay in fluid balance,
without becoming dehydrated or overloaded. [0129] Hematocrit, blood
pressure, oxygen saturation, and blood flow rate are all useful
metrics in diagnosing a patient's fluid status. The methods and
embodiments described herein could be used in conjunction with a
remote monitoring system to detect and monitor fluid status of
patients and thus enable fluid management of patients with
congestive heart failure. An exemplary embodiment of such a system
would determine a patient's fluid level through measurement of
hematocrit, heart rate, blood pressure and oxygen saturation. After
determining the patient's fluid level, the system would provide a
recommendation on the patient's intake of fluid and sodium for that
day, while also notifying the clinician that such a recommendation
had been made. In this embodiment, if a patient were at risk of
becoming overloaded or dehydrated, the system would alert the
clinician so that additional recommendations and tests could be
carried out. [0130] The embodiments and methods described herein
could be utilized in a wearable device that is used as part of a
remote monitoring system to provide non-invasive fluid management
for heart failure patients. The wearable device could be worn over
a suitable blood vessel close enough to the surface of the skin,
such as an AV access, radial artery, brachial artery, carotid
artery, cephalic vein, etc.
[0131] Fluid Status for Patients in Critical Care Units [0132]
Patients in critical care units who are hypotensive are candidates
for fluid bolus therapy to preserve blood pressure and cardiac
function. However, in 50% of cases, patients are operating at peak
cardiac output, and providing additional fluids will exacerbate any
cardiac issues rather than solving the observed hypotension. [0133]
The most reliable method of determining a patient's suitability for
fluid bolus is to perform a fluid challenge and test the
cardiovascular fluid response. Cardiovascular fluid response has
traditionally been monitored using a pulmonary artery catheter
(PAC). This requires a surgical procedure to be carried out on an
already critical patient. Another approach is to monitor
bioimpedance noninvasively using electrodes on the patient's chest
and torso. This approach doesn't require a surgical procedure, but
is still a complicated process since multiple electrodes have to be
applied in the correct locations to get a measurement. Moreover,
this system is very costly for critical care units and is difficult
to uniformly use across all patients. [0134] A wearable, low-cost
solution for monitoring fluid status in critical care patients
would offer a significant advantage over current approaches for
fluid status monitoring. [0135] The methods and embodiments
described herein could be incorporated into a remote monitoring
system that comprises a wearable sensor to provide monitoring and
measurement of patient fluid status. The measurement of hematocrit,
in conjunction with other metrics (heart rate, blood pressure,
oxygen saturation and flow rate) could provide an accurate estimate
of fluid status without the need for a surgical procedure, or
costly equipment. The wearable sensor could be applied over any
suitable vessel lose enough to the surface of the skin, such as an
AV access, radial artery, brachial artery, carotid artery, cephalic
vein, etc. [0136] 4. Example Method For Measuring Fluid Vessel
Properties
[0137] In an example implementation, the system may operate as
illustrated in the flowchart 1100 in FIG. 11. At step 1102, the
system may be placed on the surface of a patient's skin at a
position above a fluid vessel disposed in the tissue below the
skin. The LEDs are energized at step 1104 for a quick scan of the
tissue. The LEDs emit light at different intensities and
reflectance signals are received at the photodetector for each
intensity. The reflectance values are analyzed to determine if the
fluid vessel has been detected (decision block 1106). If the fluid
vessel is not detected ("NO" path from decision block 1106), the
system may be re-positioned on the skin surface and the method
begins again at step 1102. The reflectance values may provide the
user with some indication as to which direction and the user may
use the reflectance values to guess as to a distance and direction
from the current position of the system. If the vessel is detected
("YES" path from decision block 1106), the position of the system
relative to the fluid vessel may be determined at step 1108. The
system may be in an off-axis position relative to the vessel, and
likely not centered over the vessel. The system may illuminate each
light source with different levels of intensities to measure
reflectance values allowing the system to determine which light
source is a primary light source (i.e. the light source having an
illumination volume that covers more of the vessel than the other
light source). The light source and the photodetector can be moved
in a direction transverse to the blood vessels such that the light
sources cover a more equal part of the vessel. This process of
repositioning the light sources and photodetector may be repeated
until the light sources and photodetector are substantially
centered over the vessel. Steps 1102 through 1108 may then be
repeated.
[0138] At step 1110, the system at a known position relative to the
fluid vessel may be used to determine a depth of the fluid vessel
and the diameter of the vessel. The system may also determine
certain operating parameters used in determining the properties of
the vessel, such as for example, a threshold LED current,
I.sub.LEDth, an optimum LED current, I.sub.LEDopt, for each LED.
The threshold LED current for each LED is the minimum current level
needed to irradiate the region below the LEDs and for their
respective optical radiation radii to reach the vessel. The optimum
LED current is a current level needed to irradiate the region below
LEDs and for their respective optical radiation radii to reach
beyond the bottom of the vessel. Also, at step 1110, the LEDs and
the photodetector may perform scans the tissue beneath the LEDs at
different intensities and in some cases at different wavelengths to
obtain reflectance values at each intensity.
[0139] At steps 1112 and 1114, the reflectance values received from
performing the scan in step 1110 may be analyzed to determine
certain properties or obtain measurements of the fluid vessel. The
properties comprise blood oxygenation (SpO2), heart rate,
hematocrit, hemoglobin concentration, analyte concentration,
chemical composition, particle flow rate, blood flow rate, and/or
other properties.
[0140] In another example implementation, the system may operate as
illustrated in the flowchart 1300 in FIG. 13A. At step 1320, the
system may be placed on the surface of a patient's skin at a
position superior to the patella PA as shown in FIGS. 12A and 12B.
The LEDs are energized at step 1340 for a quick scan of the tissue.
The LEDs emit light at different intensities and reflectance
signals are received at the photodetector PD for each intensity.
The reflectance values are analyzed to determine the depth of the
bursa SB containing synovial fluid (step 1340). Once the depth of
the bursa has been determined, the device will read z-values from
the onboard accelerometer and the resistance signal from the
piezoelectric film PI to determine the knee's angle of flexion
(decision block 1360). If the angle of flexion is greater than
45.degree. , the device will read data from all onboard sensors,
including but not limited to the photodetector array 1304 A-B, MEMS
microphone 1309, temperature 1307 and accelerometer. If, at the
time of interrogation of the accelerometer and piezo 1305, the
angle of knee flexion is less than 45.degree. , the device will
wait 15 seconds before interrogating the angle of flexion again.
The device may also provide haptic feedback to alert the patient to
the need to flex their knee. This data is transmitted via a
wireless communications protocol such as Bluetooth.RTM. Low Energy
(BLE) to a remote hub unit. The hub unit relays the received data
to a cloud serve via a 3G cellular network. In the cloud server,
the data is analyzed to diagnose a variety of disease states,
including but not limited to periprosthetic joint infection,
loosening of the orthopedic implant, fracture of the orthopedic
implant, and fracture of the bone surrounding the orthopedic
implant. This diagnosis is made using a composite of multiple
measurements taken over the course of multiple days.
[0141] It is noted that the example method in FIG. 11 is only one
example of the use of the systems described herein. Other methods
may be used as well.
[0142] It is noted that the example system in FIGS. 1 and 13B are
examples of systems incorporating a system for measuring biological
fluid properties. The optical detection techniques described herein
may be incorporated into a wearable monitoring system described
below, such as for example, the system of FIGS. 15 and 16.
Additionally or alternatively, an optical sensor of the present
disclosure may comprise an example, variation, or embodiment of
optical systems for measuring biological fluid properties described
herein.
II. Wearable Monitoring System
[0143] 1. System Overview
[0144] Disclosed herein are systems and methods for monitoring a
patient. In an example implementation, a system for monitoring a
patient comprises a wearable device, or a wearable patch,
configured to attach to a body part of a patient. The wearable
patch incudes a sensor assembly mounted on the wearable patch. The
sensor assembly comprises a plurality of sensors configured to
detect a corresponding plurality of sensory modalities and generate
one or a plurality of electrical signals representing the sensory
modalities. The wearable patch comprises a signal converter
configured to receive the one or a plurality of electrical signals
from the plurality of sensors and to convert the signals to one or
a plurality of sensor data signals comprising a data representation
of at least one of the one or a plurality of electrical signals. A
communications interface communicates the one or a plurality of
sensor data signals to a sensor data processing system. The
wearable patch is attached to a patient to take measurements based
on the sensors included in the sensor assembly. The data from the
sensors is communicated to the sensor data processing system.
[0145] As used herein, the terms "close proximity," "local,"
"locally," "substantially close," or "near" in reference to a
patient wearing a wearable device or patch shall mean within a
distance at which the communication interface on the wearable patch
communicates using Bluetooth.RTM. , Near-Field Communication (NFC),
near field magnetic communication, a wired connection, or any
wireless technology configured for communication with a building.
Communications over distances typically by cellular, WiFi.TM. to
the Internet, the Internet, satellite, or any other technology
configured for communication beyond a building shall be understood
to be "remote," "far," or at a "long distance."
[0146] In an example implementation, the communication interface on
the wearable patch transmits one or a plurality of sensor data
signals, processed measurements, or alerts indicating that more
thorough examination of the patient may be required, to a local hub
using a first protocol configured for local or near distance
communications. The local hub communicates the one or a plurality
of sensor data signals to a remote sensor data processor over a
second protocol configured for long distance communication. The
first protocol may comprise Bluetooth.RTM. , near field
communication protocols, near field magnetic protocols, or any
communication protocol configured to provide communications over a
short distance. The second protocol may comprise cellular
communications, WiFi.TM. communication via the Internet, satellite
communications, and other long distance communications protocols.
In the second protocol, a local hub is not required. In one
example, a local hub may be implemented as an application on a
smartphone using Bluetooth.RTM. to receive one or a plurality of
sensor data signals from the wearable patch. The wearable patch and
the smartphone may process the one or a plurality of sensor data
signals to a desired extent, or may simply relay the one or a
plurality of sensor data signals to the remote sensor data
processor using a WiFi.TM. connection to the Internet or a cellular
data connection.
[0147] The sensor data processing system, which may comprise the
local hub and the remote sensor data processor may comprise an
interface to a patient medical records database, any suitable
database, or a web portal. The sensor data processing system may
also comprise an alerting system to send notifications of
conditions requiring urgent attention to a doctor or any other
specified person. The notifications may be sent using any suitable
communications system such as, for example, notification via
e-mail, notification on a website, notification by text message, or
any other suitable signaling mechanism.
[0148] The sensor assembly on the wearable patch may comprise any
combination of sensors. For example, sensors included in example
implementations of the sensor assembly may comprise any combination
of the following:
[0149] 1. acoustic sensors
[0150] 2. accelerometers
[0151] 3.strain gauges
[0152] 4. temperature sensors
[0153] 5. pressure sensors
[0154] 6. optical sensors
[0155] 7. moisture sensors
[0156] 8. conductivity sensors
[0157] 9. chemical sensors
[0158] In some implementations, an ultrasonic transducer may be
disposed in the sensor assembly along with ultrasonic sensors to
obtain ultrasonic imaging of a desired body part.
[0159] In some implementations, the sensor assembly may be
configured for specific applications by selecting sensors that
provide information that may be used to determine a state of a
certain condition. In one example, the wearable patch may be
configured to monitor an arteriovenous (AV) fistula on a dialysis
patient. The wearable patch may comprise a sensor assembly having
an acoustic sensor, an accelerometer, a strain gauge, and two
thermometers. The acoustic sensor may be a microphone designed to
have a flat sensitivity between 20 Hz and 20 kHz. The accelerometer
may be selected to be sensitive along three axes from DC to 500 Hz.
The strain gauge may be selected to have a sensitivity to
mechanical strain between 0.1 Hz to 20 MHz. The temperature sensors
may be selected to have resolutions below 0.1.degree. C. and sample
up to 8 Hz.
[0160] In the example application, the wearable patch may be
applied to the surface of a patient's arm over an AV fistula, which
may be used for kidney dialysis. Dialysis patients may have a
fistula (natural vein) or synthetic graft inserted to provide
access to blood flow for dialysis treatments. FIG. 14 depicts an
arm having a synthetic bridge graft used as an AV fistula between
an artery and a vein. Referring to FIG. 14, an arm 1400 having an
arteriovenous (AV) access 1402 inserted to receive blood from an
artery 1404 and to transport the blood to a vein 1406. A first
catheter 1408 is inserted into the AV access 1402 on the arterial
side to transport blood to a dialysis machine (not shown). A second
catheter 1410 is inserted on a venous side to transport blood from
the dialysis machine back into the vein 1406.
[0161] The AV access 1402 may become occluded over time during use
and prevent the patient from receiving dialysis treatment. The
blockage can typically either be acute from thrombosis or occur
over time through stenosis. If blockage is detected ear1y enough,
there are treatments that can unclog the AV access (e.g.
thrombectomy, angioplasty) while preserving the access. If a
thrombosis forms, clinicians must intervene prior to the thrombus
hardening (typically occurs within 48-72 hours) in order to
successfully treat the patient and preserve the access. If left
untreated, the access may need to be replaced which leads to 4-12
weeks of catheter-based dialysis in the patient's treatment.
Central catheters carry several risk factors for patients (e.g.
infection, easily blocked, etc.) and as a result, their long-term
inclusion in a patient's dialysis protocol is considered to be an
indicator of poor quality of care for the dialysis patient by
organizations such as the Center for Medicare Services (CMS) and
the National Kidney Foundation.
[0162] The output of the microphone provides an acoustic signature
of the flow within the fistula. The accelerometer provides several
pieces of information. For example, the accelerometer generates
data indicative of the orientation of the arm with respect to
gravity from the DC component of all three axes. The accelerometer
may also be used to determine if the arm is in motion during the
reading of the data, which in turn may be used to determine if the
motion of the arm was sufficient to affect the readings from the
other sensors. The accelerometer may also provide a ballistic
cardiographic measurement in the location of the fistula. The
strain gauge provides information about the strength of the
pressure wave through the fistula as it forces expansion on the
surface of the skin. The two temperature sensors provide a
differential measurement of skin temperature in the region of the
fistula relative to a location without significant arterial flow.
Thermography is as a tool for determining the state of healthy
blood flow in the periphery.
[0163] The sensor assembly fitted with the above-described sensors
provides multiple and simultaneously collected data streams at any
given time. The combination of these simultaneous data streams
provides a more complete and accurate assessment of the quality of
blood flow within the fistula, more than any single data stream can
provide individually. The specific signature of the multiple data
streams processed together can provide diagnostic information to
the clinician as to the source of any change in the condition of
the fistula.
[0164] FIG. 15 is a block diagram of an example implementation of a
wearable patch 1500 comprising a sensor control module 1501 and a
power module 1503. It is noted that the block diagram in FIG. 15 is
schematic such that components are described in functional bocks
for clarity with no intent to limit the described examples to any
number of modules. An example implementation may comprise separate
hardware modules implementing the sensor control module 1501 and
the power module 1503. In other implementations, a single hardware
module, e.g. a circuit board, may comprise components of both the
sensor control module 1501 and the power module 1503.
[0165] The sensor control module 1501 comprises a sensor assembly
1502 and a wireless communication interface 1506. The sensor
assembly 1502 comprises N sensors, sensor 1502a, sensor 1502b, and
additional sensors up to sensor 1502n. Each sensor 1502a-n detects
a corresponding sensory modality and converts the sensory modality
to an electrical signal. The electrical signal is communicated to a
signal converter to convert the electrical signal to a suitable
data representation of the one or a plurality of properties
indicated by the electrical signal. For example, the acoustic
sensor may be a microphone or a piezoelectric transducer. Sound is
converted to one or a plurality of electrical signals in a
well-known manner producing a signal having a frequency and an
amplitude. The electrical signal may be processed by amplifying the
signal and filtering the signal to reduce any noise that may be in
the signal. The electrical signal may then be input to a signal
converter 1504 to convert the electrical signal to data. The signal
converter 1504 may comprise an analog-to-digital converter (ADC) to
generate a series of digital samples representing a voltage level
at each part of a wave formed by the electrical signal. The signal
converter 1504 may also comprise a processor to perform, for
example, digital signal processing techniques to either reduce the
data set to comprise only the most meaningful data, to filter out
signal anomalies, or to perform other similar functions. The
processor may also comprise functions to manage the operation of
the wearable patch 1500. For example, the processor may be
programmed to implement an operating system, such as for example, a
state machine in which the components are controlled according to
various states. Other types of operating systems may also be used,
such as an infinite loop of control functions for acquiring sensor
data, and managing the power during times in which the wearable
patch is not acquiring sensor data. The processor may operate using
interrupt schemes, or polling of input/output (I/O) devices to
control the functions of the wearable patch 1500. The processor may
be programmed to perform minimal processing of the data, or to
perform signal conditioning functions or to perform more high level
functions such as analysis sufficient to determine if an alert
should be communicated. In some implementations, the digital signal
processing and other high level functions may be performed by the
sensor data processing system, which may be at the local hub in a
system that comprises the local hub.
[0166] Each sensor 1502 may be connected to provide one or a
plurality of electrical signals to the signal converter 1504 to
form channels of sensor data. The signal converter 1504 may be
configured to provide signal processing functions tailored to the
sensor 1502 connected to the signal converter 1504. The signal
converter 1504 may also comprise functions to format the
simultaneously collected data as a sensor data signal in a manner
that permits the sensor data signal to be communicated. The signal
converter 1504 communicates the sensor data signal to the
communication interface 1506 for transmission to the sensor data
processing system. In some implementations, the sensor data may be
combined into a single sensor data signal. In other
implementations, the sensor data may be formatted in one or a
plurality of sensor data signals that correspond to each sensor
from which the data is obtained. That is, the sensor data signal
may be communicated as a single data stream that combines the
sensor data from each sensor, or as multiple data streams each
having the sensor data from a corresponding sensor.
[0167] The communication interface 1506 may be configured to
operate using any suitable communications protocol. A wireless
communication protocol is preferred, although a wired communication
protocol may be used as well. In an example implementation in which
the wearable patch 1500 communicates with a local hub, which then
communicates with a remote sensor data processor, the communication
interface 1506 may comprise functions enabling communication using
communication protocols for short distance communication. The
communications interface 1506 may also communicate using
communication protocols for short distance communication to
transmit one or a plurality of sensor data signals to a locally
placed sensor data processing system. The system data processing
system may provide monitoring functions, diagnostic functions, and
may interface with locally or remotely located databases or web
portals. The system data processing system may also comprise
functions to send alerts by email, text messages, or other
available formats.
[0168] The power module 1503 comprises an energy source 1507 such
as, for example, a battery or other portable energy source that may
be of limited capacity. The power module 1503 may be configured to
operate in a low power state. In an example implementation, the
power module 1503 may be configured to operate in a state in which
the components on the sensor control module 1501 are isolated from
the energy source 1507 be a power switch 1508 as shown in FIG. 15.
The low power state, or the state in which power is switched off
permit the wearable patch to implement functions that conserve
energy.
[0169] In an example implementation, the power module 1503 may
comprise a wakeup sensor 1509 to change the state of the power
switch 1508 to provide power to the sensor control module 1501 to
begin operate, such as acquisition of sensor data. The wakeup
sensor 1509 may be implemented using a watchdog timer that times
up, or down, to, or from. a time period. When the time period
elapses, the watchdog timer may switch the power switch 1508 to
power the sensor control module 1501 and to signal the processor to
perform needed functions, such as acquisition of sensor data, or
other processing functions. In example implementations, the wakeup
sensor 1509 may comprise a sensor that detects activity at one or
more of the sensors 1502a-1502n. For example, the wakeup sensor
1509 may comprise a signal detecting function in which an
electrical signal from one or more sensors of sufficient magnitude
to constitute a meaningful signal from the sensors is detected as a
trigger to power the signal control module 1501 to begin
acquisition.
[0170] In some implementations, the wakeup sensor 1509 may be a
sensor of selected states that indicate conditions for which power
should be provided to the signal control module 1501. For example,
the wakeup sensor 1509 may comprise any combination of the
following:
[0171] 1. Magnetic sensors or switches
[0172] 2. Optical sensors
[0173] 3. Motion, acceleration or tilt sensors
[0174] 4. Temperature sensors
[0175] 5. Capacitive proximity sensors
[0176] 6. Mechanical switches
[0177] The wearable patch 1500 may also comprise functions and
components to support long term storage of the wearable patch 1500.
For example, the wearable patch 1500 may operate in a "shelf mode."
The shelf mode may be entered via explicit control (e.g. a command)
received from a device communicating over the communication
interface 1506. In some implementations, the shelf mode may be
entered based on one of the sensors 1502a-n (which may comprise the
wakeup sensor 1509). In some implementations, the shelf mode may be
entered based on a specific shelf sensor 1510 as shown in FIG. 15.
When in shelf mode, the various components of the wearable patch
1500 may be commanded to enter a low power mode, or may be cut off
from power by the power switch 208, or other switches selectively
inserted to control selected sensors 1502. The shelf mode can be
exited based on the wakeup sensor 1509, any one or more of the
other sensors, 1502, or via the specific shelf sensor 1510, which
may be configured to automatically detect the wearable patch 1500
being put into service. This shelf sensor 1510 may be implemented
using any combination of the following:
[0178] 1. Magnetic sensors or switches
[0179] 2. Optical sensors
[0180] 3. Motion, acceleration or tilt sensors
[0181] 4. Temperature sensors
[0182] 5. Capacitive proximity sensors
[0183] 6. Mechanical switches
[0184] This shelf sensor 1510 may interact with the packaging 1500
in which the wearable patch is stored prior to deployment on a
patient. When the wearable patch 1500 is in its packaging, it is in
shelf mode thereby precluding a connection of the power from the
energy source 1507 to the sensor control module 1501. In some
implementations, the packaging may be configured to generate a
magnetic field which is detected by a shelf sensor 1510 capable of
sensing magnetic fields to prevent the wearable patch 1500 from
being activated and thereby consuming power. In an example
implementation, the wearable patch 1500 may be provided with an
adhesive liner during manufacturing. The adhesive liner is
configured so that a user would remove the adhesive liner during
application of the wearable patch 1500 on the patient. The adhesive
liner may be made of a material that generates a magnetic field.
When the magnetic adhesive liner is removed to apply the wearable
patch 1500 on the patient, the magnetic field is removed as well so
that the shelf sensor 1510 can no longer detect the magnetic field.
When the magnetic field is not detected, the wearable patch 1500 is
taken out of shelf mode and allows the energy source 1507 to power
the sensor control module 1501.
[0185] In other implementations, the packaging may be opaque to
light and the shelf sensor 1510 may be a light sensor. If the
wearable patch 1500 is in its packaging, the shelf sensor 1510 does
not detect light and keeps the wearable patch 1500 in the shelf
mode precluding the energy source 1507 powering the sensor control
module 1501. When the wearable patch 1500 is removed from the
packaging, the shelf sensor 1510 is exposed to ambient light
allowing the shelf sensor 1510 to sense the ambient light and
determine that the wearable patch 1500 has been removed from its
packaging. The shelf sensor 1510 changes to a state in which it is
no longer in shelf mode to enable the delivery of power to the
sensor control module 1501. [0186] 2. Example Implementation of a
Wearable Patch.
[0187] FIG. 16A is a block diagram of another example
implementation of a wearable patch 1600 with a sensor assembly 1602
and a wireless communication interface 1606. The wearable patch
1600 in FIG. 16A comprises a sensor assembly comprising an
accelerometer 1602a, a microphone 1602b, a piezoelectric sensor
1602c, and two temperature sensors 1602d. The sensors 1602 indicate
specific components that may be used as the sensors in the sensor
assembly in FIG. 16A. The accelerometer 1602a may be implemented
using a Bosch BMA280 accelerometer. The microphone 1602b may be
implemented using a Knowles SPH1642 MEMS microphone. The strain
gauge 1602c in FIG. 1602c is indicated as being a custom piezo
sensor. The temperature sensors 1602d may be implemented using two
TI TMP 112 temperature sensors. It is noted that the specific parts
identified for implementing the sensors 1602 in the sensor assembly
are only examples of components that may be used as each sensor.
Many components are available for use as each sensor. Those of
ordinary skill in the art will appreciate that suitable sensors may
be selected based on the specific requirements of specific
implementations.
[0188] It is noted that the example described below is for a
wearable patch intended for operation by communicating to a local
hub, which then communicates data to a remote sensor data
processor.
[0189] The sensors 1602 in FIG. 16A are connected to communicate
with a processor 1604. which comprises ADC functionality and other
signal conditioning functions. The processor 1604 converts the one
or a plurality of electrical signals from each sensor to one or a
plurality of sensor data signals for communication via the
communication interface 1606.
[0190] The wearable patch 1600 in FIG. 16A is one example
implementation of a wearable device for simultaneously obtaining
data from multiple sensory modalities detected using multiple
sensors. The operation of the wearable patch 1600 in FIG. 16A is
described as follows. Those of ordinary skill in the art understand
the implementation details described below are provided as
examples, and are also able to identify and use alternatives.
[0191] The wearable patch 1600 is configured to capture data from 4
or fewer analog channels plus devices connected by an
inter-integrated circuit (I2C) bus. One channel is used to
communicate one or a plurality of electrical signals representing
sound from an analog MEMS microphone. An example of an analog MEMS
microphone that may be used in the wearable patch 1600 in FIG. 16
is a SPH1642 MEMS microphone from Knowles. The remaining channels
correspond to the Bosch BMA280 accelerometer, the two TI
temperature sensors running over the I2C bus and 1 charge-amplified
channel for piezo sensing. [0192] 3. Sensor Read Process.
[0193] Data may be sampled for a predetermined read duration time
(such as for example, 5 seconds) on selected channels. The
temperature sensors may be sampled once, at the beginning of the
measurement. Analog microphone data may be sampled by an ADC, such
as for example, the 12 bit SAR ADC function on the processor, at a
selected sample rate (for example, 4 kHz) at a selected resolution
(for example, 12 bits). Data from the accelerometer may be sampled
at a selected accelerometer sampling rate (for example, 1 kHz), at
a selected resolution, which may also be 12 bits of resolution. The
accelerometer may also be set to an anti-aliasing cutoff frequency
(for example, 500 Hz).
[0194] The microphone 1602b may be operated in differential mode.
In the illustrated example, operating in a differential mode may
allow for an amplitude of 0.79 VRMS maximum, achieved at 123 dBA
SPL. If 2 channels or fewer are used, the analog front end may
comprise a 2nd order Butterworth type II anti-aliasing filter with
a-6 dB predetermined cutoff frequency (for example, 1.6 kHz). If
3-4 channels are needed at the same frequency, the sampling rate
may be increased and a single pole anti-aliasing filter may be used
with a -3 dB frequency of around 4 KHz in the illustrated
example.
[0195] The gain of the front end for each analog channel may be
independently programmable via a configuration block, for example,
by selecting among resistors, for example, on several output ports.
Gains of 1.times., 5.times. and 20.times. may be pre-installed on
switchable input pins. A digital filter may be implemented to block
60 Hz AC frequency noise from the microphone, piezo and
accelerometer channels. Data may be captured into RAM in a 251 byte
(each half) double buffer. Once a buffer is filled, data capture
may continue in the second buffer, and data in the first buffer may
be filtered, delta compressed, and stored in FRAM without
interrupting data capture.
[0196] Data reads may comprise a UTC timestamp in 32 bit unsigned
Unix time. Unsigned 32 bit is used to save bytes, since there will
be no data from before Jan. 1, 1970. This is followed by a 16-bit
millisecond offset from that time (in the first packet) and a
sequence number thereafter.
[0197] 4. Sensor Suite Selection.
[0198] Several classes or types of sensors may be used in the
sensor assembly and selected based on their ability to transduce
clinically relevant data. Sensor suites may be configured in which
the sensors are selected for their relevance to specific
applications. The wearable patch 1600 in FIG. 16A comprises one or
more of the following sensors to perform the indicated
functions:
[0199] 1. Microphone-a microphone may be incorporated into the
wearable patch to measure the acoustic signature of blood flow
through the fistula. This is consistent with current clinical
practices and most closely resembles the use of a stethoscope to
assess the health of an AV fistula. [0200] a. The microphone may be
a MEMS microphone that is held directly against the skin by the
surrounding adhesive of the wearable device. The MEMS microphone
may also be protected by a thin-film porous membrane such as made
from polytetrafluoroethylene (PTFE) that allows good acoustic
coupling to the skin while protecting the MEMS microphone from
moisture and particles. [0201] b. The microphone may be made of a
piezoelectric material, such as for example, polyvinylidene
fluoride (PVDF) or lead zirconate titanate (PZT). PVDF has an
acoustic impedance very similar to biological tissue. A PVDF sensor
that is conformally attached to the skin can offer unique benefits
to stethoscope design by allowing for elimination of impedance
matching components that add to the bulk of traditional
stethoscopes. The PVDF sensor may be attached directly on the skin
in the area of the fistula using a biocompatible adhesive with
suitable acoustic impedance. An exemplary adhesive would be a
hydrogel adhesive, which typically has comparable acoustic
impedance to biological tissue and PVDF. [0202] 2.
Accelerometer--the accelerometer allows for:
[0203] Detection of fistula health by monitoring the vibration or
thrill that can be detected from the flow of a healthy fistula
[0204] Detection of arm motion that would interfere with a good
read. [0205] Use as in inclinometer to monitor the orientation of
the arm relative to gravity.
[0206] 3. Temperature sensor: [0207] Pair of temperature sensors at
different locations on the user's arm differentially may be used to
infer blood flow in the fistula.
[0208] 4. Piezoelectric sensor (strain gauge) may take the form of
a stretched piezoelectric diaphragm or a piezoelectric sensor in
compression driven by a diaphragm and will produce an AC acoustic
signal. [0209] 5. Power Management/Shelf Mode.
[0210] The wearable patch 1600 comprises a shelf mode wakeup sensor
1610, which may be implemented as shown in FIG. 16 using a,
normally closed magnetic reed switch connected to a battery 1612.
The shelf mode wakeup sensor 1610 cuts off power from the battery
1612 to the rest of the system when the shelf mode wakeup sensor
1610 is open. The wearable patch 1600 may be stored prior to
deployment in packaging that comprises a magnetic adhesive backing
liner 1614 applied to adhesive on the wearable patch 1600. When the
magnetic adhesive backing liner 1614 is attached to the wearable
patch 1600, the shelf mode wakeup switch 1610 is kept in an open
state by the magnetic field from the adhesive backing liner 1614
thereby keeping battery power disconnected from the other
components. When the adhesive backing liner 1614 is removed during
deployment of the wearable patch 1600 on the patient's body, the
shelf mode wakeup switch 1614 closes, thereby restoring power to
the remaining components on the wearable patch 1600. Once power is
present, the wearable patch microcontroller 1604 actuates a shelf
mode lockout switch 1616, which prevents the shelf mode wakeup
switch 1614 from returning the device to shelf mode without an
explicit command from the microcontroller 1604 to unlock the shelf
mode lockout switch 1616.
[0211] The wearable patch 1600 in FIG. 16B comprises a power switch
1620, which may be implemented using a nanoboost converter with
integrated load switch. In the illustrated example, the power
switch 1620 applies battery voltage to two 3.0 V. buses: 1. Vcc,
which is used to power the processor 1604, and 2. Vsec, which is
used to power the sensors and a memory module 1622. The power
switch 1620 consumes power at nA levels in a quiescent (low
power/low demand) state.
[0212] The wearable patch 1600 also comprises a wakeup sensor 1618,
which may be implemented using an Ambiq 1805 nanopower RTC+switch.
The wakeup sensor 1618 maintains a timestamp and powers up the
processor 1604 on a time schedule. The processor 1604 provides
power to a secondary bus as needed by wearable patch 1600
application via a digital I/O output from the processor 1604
configured to drive the power switch 1620. Before entering a sleep
mode, the processor 304 deactivates the secondary bus.
[0213] Between data reads and transmits, the processor 1604 may
enter a deep sleep mode with the watchdog timer (wakeup sensor
1618) set to wake it on schedule. The boost converter load switch
(power switch 1620) may be used to shut off all power to the memory
1622, the accelerometer 1602a and the microphone 1602b. [0214] 6.
Firmware Flow.
[0215] A. Modes of Operation. Operation of the wearable patch 1600
may be implemented using a state machine according to a state
diagram, such as the state diagram depicted in FIG. 16B. The state
diagram in FIG. 16B operates using 8 basic states of operation as
follows:
[0216] 1. Shelf--the device has been put on the shelf for long-term
storage. Power is disconnected from the system and can only be
reconnected by actuating the shelf mode switch.
[0217] 2. Sleep--the mode the device enters between timed wakeups.
It can be awoken by either the watchdog timer or the wakeup
switch.
[0218] 3. Boot--the device is reading configuration settings and
initializing operation. At this point, the shelf mode lockout
switch is actuated, preventing the patch from returning to shelf
mode without an explicit command.
[0219] 4. Wake--a transient state immediately after a watchdog
timer wakeup where the system decides whether to sample data,
advertise for a connection or do nothing.
[0220] 5. Advertising--sending advertisements and waiting for
someone to connect and authenticate.
[0221] 6. Acquire--In the Acquire mode, the device samples data
from the ADC or I2C bus into internal buffers.
[0222] 7. Transmit--In the Transmit mode, the device streams data
notifications to the hub. The Transmit mode can be interrupted by
the reed switch, but the device is not listening for commands.
[0223] 8. Command--In the Command mode, the device listens for, or
responds to commands communicated over the communication interface
(e.g. Bluetooth.RTM. Low Energy (BLE) interface).
[0224] B. Flow.
[0225] The state diagram in FIG. 16B shows the flow of control
between modes. Note that when the reed switch is triggered from
sleep or command modes, the system is triggered to first acquire,
then transmit all stored packets. This is shown here via a
parameter "chain" that is set when the reed switch is triggered,
and is automatically cleared upon return to command mode.
[0226] In an example implementation, each mode may operate as
follows:
[0227] (1) Shelf Mode
[0228] The system is disconnected from the battery.
[0229] (2) Boot Mode
[0230] The shelf mode lockout switch is actuated, preventing the
device from going back to shelf mode without an explicit
command.
[0231] The processor reads a configuration settings block into a
configuration data structure.
[0232] All interrupts and 10 pins are initialized.
[0233] A watchdog timer is set to wake up every 1 hour, for
example.
[0234] (3) Sleep Mode
[0235] The wearable patch may be put in a deep sleep mode, which
refers to a function of the processor in this example, with the
watchdog timer set to wake up at the next event. The wake up at the
next event may be a sensor read event or an advertising wakeup,
occurring after a predetermined time period, such as for example,
every 1 hour.
[0236] It may be assumed that the advertising wakeup will happen
more frequently than the read period, and the read period
(currently, is 3 hours) will be a multiple of that time
interval.
[0237] (4) Advertising
[0238] The processor turns on advertising for a selected time
period, for example, 30 seconds at a selected advertising
frequency, for example, 2 Hz rate. The advertising is provided for
display or printout on a connectable peripheral device.
[0239] The wearable patch may be bonded to a single hub, via an LE
Secure encrypted private address. Connection will automatically
occur if the wearable patch is bonded. If the patch is not bonded,
it will be open for pairing or commands from any hub that has the
appropriate out-of-band (OOB) shared secret key.
[0240] (5) Wake
[0241] The Wake State operates as follows:
[0242] The Wake state is a transient state which evaluates the time
and decides whether to acquire data or advertise in order try to
make a connection to a hub. Note that data acquisition from sensors
is started before an attempt is made to make a connection in order
to save the power of running the PA/LNA during acquisition.
[0243] (6) Command
[0244] When a connection is made, the local hub can issue
commands.
[0245] In command mode, any characteristic can be activated as
described in the BLE Characteristics section below.
[0246] If a selected time period (e.g. 30 seconds) elapses after
completion of the most recent command, the device automatically
enters sleep mode.
[0247] (7) Acquire
[0248] Data may be captured automatically every 3 hours, or when
requested via commands over the BLE interface.
[0249] To capture data, the patch may turn on power to a sensor and
the onboard op amps. The patch then waits a fixed delay period,
e.g. 2 seconds, for the wearable patch to stabilize. The wearable
patch will then take measurements.
[0250] Data may be compressed as it arrives from the ADC or digital
sensor. Data may be compressed for storage in a 251-byte buffer
using a delta encoder (encoders are independent, on a per channel
basis). When the buffer fills, the data may be copied to the FRAM,
in time sorted order as a circular buffer-of-buffers.
[0251] (8) Transmit
[0252] Data is transmitted to the local hub at a maximum rate in
251-byte BLE 4.2 packets. Each packet may comprise its own
timestamp. The system may proceed to transmit the new packets in
the buffer. Once the final packet is transmitted, the wearable
patch may send an END-OF-BUFFER indication.
[0253] The wearable patch may receive a command requesting
transmission of all buffers. In response to receiving the command
requesting transmission of all buffers, the wearable patch
transmits all buffers are transmitted sequentially and marked as
SENT.
[0254] FIG. 16B is a block diagram of the processor 1604in FIG.
16A. In the example described above with reference to FIG. 3A, the
processor is implemented using a Cypress PSOC BLE module, which is
based on a Cortex M3 ARM core, contains 256 MB FLASH, 32 KB RAM and
supports BLE 4.2.
[0255] FIG. 17A is a perspective bottom view of an example of a
wearable patch. FIG. 17B is a top view of an example of a wearable
patch attached to a patient's arm. The wearable patch is intended
to be worn over a fistula and configured to communicate to a nearby
sensor data processing system, which may comprise a local hub for
forwarding data to a backend, or remote sensor data processor.
[0256] The wearable patch may be formed with 1 or 2 parts. FIG. 17A
depicts an example wearable patch formed in 2 parts. If the
wearable patch is in 1 part, then the adhesive may be a replaceable
component (3-7.times./week) and the device may be configured to
house electronics components, while still enabling adequate
coupling of the sensor to the skin for conformal attachment. If the
wearable patch is formed in 2 parts, the part connected to the skin
could be a flexible adhesive layer with the sensor assembly and the
second part would comprise the encapsulated electronics. The
mechanical features on both parts that connect the two parts would
also comprise electrical connectors that would enable communication
between the sensor assembly and the electronics (processor,
communications interface, etc.). The mechanical features in
particular on the sensor/adhesive part would be flexible to enable
conformal attachment of the sensor assembly and adhesive to the
skin, while still allowing for secure mating with the rigid,
encapsulated electronics. The overall size of the wearable patch,
including the height, may be an important factor that affects
comfort. The wearable patch may be powered by a battery, which
would likely be the largest component. [0257] 7. Power
Consumption.
[0258] The expected power consumption of the wearable patch may
help determine the size of the battery required to operate between
recharges. The power may be dominated by the standby current since
the duty cycle is low (3 hours off, 5 seconds on). [0259] 8. Method
for Monitoring a Patient.
[0260] Determining either a thrombosis alert or level of stenosis
requires a few steps of signal processing to get data from the
sensor, digitized, and analyzed. The above description with
reference to FIG. 16A of the example implementation of a wearable
sensor comprises a detailed description of how data may be
extracted from the sensors shown in FIG. 16A using the components
in FIG. 16A. In general, the data extraction process involves the
steps of:
[0261] 1. sensing a plurality of sensory modalities using a sensor
assembly comprising a plurality of sensors mounted on a wearable
patch, where the sensory modalities are received as one or a
plurality of electrical signals representing the sensory
modalities;
[0262] 2. converting the one or a plurality of electrical signals
to a plurality of corresponding one or a plurality of sensor data
signals; and
[0263] 3. transmitting the one or a plurality of sensor data
signals to a sensor data processing system.
[0264] FIG. 18 is a flowchart illustrating operation of an example
of a method for obtaining data from a sensor assembly. The method
in FIG. 18 may be performed using any suitable sensor assembly
connected to a signal converter, which may be implemented using a
processor that uses a real time clock timer, an ADC function and
signal processing capabilities including for example, Fast Fourier
Transform (FFT) tools, digital filtering functions, and signal
detection algorithms.
[0265] The method illustrated in FIG. 18 begins at step 1802 in
which the processor is in a sleep mode, and a real-time clock (RTC)
timer is set to wake the processor periodically. The processor
enables the analog front end (AFE) and the ADC function at step
1804. The AFE refers to the sensor assembly, which when enabled,
begins to receive sensory modalities corresponding to the sensors
in the sensor assembly. The sensory modalities are converted to one
or a plurality of electrical signals. Sampling may then be enabled
for each sensor as indicated in step 1806. The one or a plurality
of electrical signals sampled by the ADC function may be sampled at
10 k samples/sec for 2 seconds; however, the sampling rate may be
adapted for each sensor modality. The digital samples representing
the electrical signal from the sensors may be processed using
digital signal processing functions, such as for example, the
functions listed above, as deemed useful for each signal as
indicated in step 1808. At step 1810, the communications interface
is awakened for transmission of the sensor data. The processor
generates the sensor data signal from the digital signal processing
functions and formats the sensor data signal according to a
suitable communication protocol. The sensor data signal is then
transmitted at step 1812 via the communication interface.
[0266] The wearable patch may transmit results wirelessly after the
sensing operation. In an example implementation, Bluetooth.RTM.
Smart.TM. is a low power radio technology that may be used to
communicate to a relay or local hub. The local hub transfers the
results to a backend system, such as the remote sensor data
processor in the network. Storage and further processing of the
sensor data may be performed on the remote sensor data processor,
which may be implemented on a remote server. A front-end interface
may be configured to communicate alerts to a clinician.
[0267] FIG. 19 is a block diagram of an example system architecture
for a system for monitoring a patient wearing a wearable patch. The
system in FIG. 19 comprises a patch 1902 connected to a local hub
1904 via a BLE connection. Any other suitable local communication
protocol may be used as well. The local hub is connected to a
carrier network 1906 using a cellular link. The carrier network is
a cellular data system, but may be any other suitable network
infrastructure, such as the Internet where connection to the
Internet is achieved using a WiFi.TM. system, a hardwired Ethernet
connection, or any other infrastructure that may be used for
communicating remotely. In the example in FIG. 19, the carrier
network connects the home hub over the Internet to an Amazon Web
Service (AWS) 1908. The AWS is a cloud-based computing service.
Other cloud-based services are available from Microsoft, Oracle and
other, and may be used as well.
[0268] 9. Determining a Level of Stenosis.
[0269] Examples of a wearable patch may be used as part of a system
to monitor and alert for thrombosis development or clinically
actionable levels of stenosis in a vessel such as an AV fistula or
graft. Alerts may be triggered by the system and lead to a clinical
pathway whereby the patient is examined by a care provider and put
through a diagnostic pathway including but not limited to duplex
ultrasound, fistulogram and/or arteriograms. The results of the
diagnostic studies combined with the monitoring result from the
patch could lead to a corrective intervention such as a drug
prescription, thrombectomy or angioplasty to clear the blocked
fistula. In some cases, the diagnostic process may lead to another
surgery for the patient to place a new fistula, HERO graft or
central venous catheter.
[0270] The wearable patch may be worn to enable an AV fistula or
Graft to reach maturation, or to help lengthen the lifetime of an
AV fistula or graft. The wearable patch may be worn by the patient
and communicate data and alerts multiple times in a given day. The
patient may remove the electronics from the patch (if the device is
constructed as a two-part patch) periodically, or replace
disposable components of the patch (e.g. adhesive) depending upon
the specific protocol.
[0271] During a clinician or home visit, the wearable patch may be
removed and charged to replenish the battery. In the case of an AV
fistula patient, the battery-charging may be performed during the
dialysis session.
[0272] Standard clinical protocols typically require a check of the
patency of an AV fistula or graft during a physical examination on
routine visits to a clinician. The clinician can "feel the thrill"
of a bruit, and also listen for the bruit using a conventional
stethoscope. A change of the character of the bruit to a higher
pitch can indicate the presence of stenosis or thrombosis. Various
methods may be used to quantify the stenosis using the digital
output of a stethoscope, or to determine if a thrombosis has
formed. One example is to use a break frequency to estimate the
internal diameter of the carotid artery in patients. This technique
is referred to as phonoangiography. The break frequency may be
determined a number of ways. A frequency power spectrum may be
calculated for an acoustic sensor output and used to identify the
highest frequency after which the power drops off significantly. A
higher break frequency is correlated with a narrower vessel, and
thus a higher level of stenosis. Break frequency values typically
fall between 10 and 1000 hz., where a value closer to 1000 would
indicate a significant degree of stenosis (>50%). In AV
fistulas, metrics such as the break frequency may be utilized to
determine either thrombosis or stenosis.
[0273] A key difference may exist for the utilization of break
frequency for AV fistulas as opposed to a carotid artery. In the
carotid artery, a bruit is indicative of unhealthy flow, while in
the AV fistula a bruit is indicative of healthy flow. Thus, the
correlation in AV fistula may be reversed from those found in the
carotid artery, with a lower level of bruit (i.e. a lower break
frequency) indicating a higher degree of stenosis or potentially
even thrombosis. Additional analytic methods are possible for AV
fistulas/grafts such as using autoregression to calculate the power
spectral density. The advantage of such a method is that it may be
more effective at quantifying stenosis levels at lower flow rates.
A combination of different analytical methods would likely be
beneficial to determine the level of stenosis or if a potential
thrombosis has occurred in an AV access.
[0274] The wearable stethoscope patch would enable this analysis by
detecting these signals and automatically transmitting them for
analysis over the course of a patient's life and treatment.
[0275] It will be understood that one or more of the processes,
sub-processes, and process steps described herein may be performed
by hardware, firmware, software, or a combination of two or more of
the foregoing, on one or more electronic or digitally-controlled
devices. The software may reside in a software memory (not shown)
in a suitable electronic processing component or system such as,
for example, the processor. The software memory may comprise an
ordered listing of executable instructions for implementing logical
functions (that is, "logic" that may be implemented in digital form
such as digital circuitry or source code, or in analog form such as
an analog source such as an analog electrical, sound, or video
signal). The instructions may be executed within a processing
module, which comprises, for example, one or more microprocessors,
general purpose processors, combinations of processors, digital
signal processors (DSPs), application specific integrated circuits
(ASICs), field-programmable gate array (FPGAs), etc. Further, the
schematic diagrams describe a logical division of functions having
physical (hardware and/or software) implementations that are not
limited by architecture or the physical layout of the functions.
The examples of systems described herein may be implemented in a
variety of configurations and operate as hardware/software
components in a single hardware/software unit, or in separate
hardware/software units.
[0276] The executable instructions may be implemented as a computer
program product having instructions stored therein which, when
executed by a processing module of an electronic system, direct the
electronic system to carry out the instructions. The computer
program product may be selectively embodied in any non-transitory
computer-readable storage medium for use by or in connection with
an instruction execution system, apparatus, or device, such as an
electronic computer-based system, processor-containing system, or
other system that may selectively fetch the instructions from the
instruction execution system, apparatus, or device and execute the
instructions. In the context of this disclosure, a
computer-readable storage medium is any non-transitory means that
may store the program for use by or in connection with the
instruction execution system, apparatus, or device. The
non-transitory computer-readable storage medium may selectively be,
for example, an electronic, magnetic, optical, electromagnetic,
infrared, or semiconductor system, apparatus, or device. A
non-exhaustive list of more specific examples of non-transitory
computer readable media include: an electrical connection having
one or more wires (electronic); a portable computer diskette
(magnetic); a random access memory (electronic); a read-only memory
(electronic); an erasable programmable read only memory such as,
for example, flash memory (electronic); a compact disc memory such
as, for example, CD-ROM, CD-R, CD-RW (optical); and digital
versatile disc memory, i.e., DVD (optical). Note that the
non-transitory computer-readable storage medium may even be paper
or another suitable medium upon which the program is printed, as
the program may be electronically captured via, for instance,
optical scanning of the paper or other medium, then compiled,
interpreted, or otherwise processed in a suitable manner if
necessary, and then stored in a computer memory or machine
memory.
[0277] It will also be understood that the term "in signal
communication" or "in electrical communication" as used herein
means that two or more systems, devices, components, modules, or
sub-modules are capable of communicating with each other via
signals that travel over some type of signal path. The signals may
be communication, power, data, or energy signals, which may
communicate information, power, or energy from a first system,
device, component, module, or sub-module to a second system,
device, component, module, or sub-module along a signal path
between the first and second system, device, component, module, or
sub-module. The signal paths may comprise physical, electrical,
magnetic, electromagnetic, electrochemical, optical, wired, or
wireless connections. The signal paths may also comprise additional
systems, devices, components, modules, or sub-modules between the
first and second system, device, component, module, or
sub-module.
[0278] More generally, terms such as "communicate" and "in . . .
communication with" (for example, a first component "communicates
with" or "is in communication with" a second component) are used
herein to indicate a structural, functional, mechanical,
electrical, signal, optical, magnetic, electromagnetic, ionic or
fluidic relationship between two or more components or elements. As
such, the fact that one component is said to communicate with a
second component is not intended to exclude the possibility that
additional components may be present between, and/or operatively
associated or engaged with, the first and second components.
[0279] While preferred embodiments of the present invention have
been shown and described herein, it will be obvious to those
skilled in the art that such embodiments are provided by way of
example only. Numerous variations, changes, and substitutions will
now occur to those skilled in the art without departing from the
invention. It should be understood that various alternatives to the
embodiments of the invention described herein may be employed in
practicing the invention. It is intended that the following claims
define the scope of the invention and that methods and structures
within the scope of these claims and their equivalents be covered
thereby.
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