U.S. patent application number 13/724984 was filed with the patent office on 2013-05-02 for two-part patch sensor for monitoring vital signs.
This patent application is currently assigned to SOTERA WIRELESS, INC.. The applicant listed for this patent is Sotera Wireless, Inc.. Invention is credited to Matthew John Banet, Kenneth Robert Hunt, Zhou Zhou.
Application Number | 20130109937 13/724984 |
Document ID | / |
Family ID | 39370080 |
Filed Date | 2013-05-02 |
United States Patent
Application |
20130109937 |
Kind Code |
A1 |
Banet; Matthew John ; et
al. |
May 2, 2013 |
TWO-PART PATCH SENSOR FOR MONITORING VITAL SIGNS
Abstract
A two-component monitoring device and system for monitoring
blood pressure from a patient is disclosed herein. The
two-component monitoring device includes a disposable component and
a main component. The disposable component features: i) a backing
structure having a first aperture; and ii) first and second
electrodes, each electrode connected to the backing structure and
including an electrical lead and a conductive electrode material,
and configured to generate an electrical signal that passes through
the electrical lead when the conductive electrode material contacts
the patient. The main component includes: i) first and second
connectors configured to connect to the first and second electrical
leads to receive the first and second electrical signals; and ii)
an optical component comprising a light source that generates
optical radiation and a photodetector that detects the optical
radiation. The optical component inserts into the first aperture of
the disposable component. The main component optionally includes an
acoustic sensor. The system utilizes a processing device, connected
to the monitoring device by a cable which receives and processes a
plurality of signals to determine real-time blood-pressure values
for the patient.
Inventors: |
Banet; Matthew John; (Del
Mar, CA) ; Zhou; Zhou; (La Jolla, CA) ; Hunt;
Kenneth Robert; (Vista, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sotera Wireless, Inc.; |
San Diego |
CA |
US |
|
|
Assignee: |
SOTERA WIRELESS, INC.
San Diego
CA
|
Family ID: |
39370080 |
Appl. No.: |
13/724984 |
Filed: |
December 21, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11558538 |
Nov 10, 2006 |
|
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13724984 |
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Current U.S.
Class: |
600/324 |
Current CPC
Class: |
A61B 5/021 20130101;
A61B 5/6833 20130101; A61B 7/00 20130101; A61B 5/02125 20130101;
A61B 5/0059 20130101; A61B 5/04085 20130101; A61B 5/14551 20130101;
A61B 5/68335 20170801; A61B 5/04012 20130101; A61B 5/411 20130101;
A61B 5/0205 20130101 |
Class at
Publication: |
600/324 |
International
Class: |
A61B 5/0205 20060101
A61B005/0205; A61B 5/1455 20060101 A61B005/1455; A61B 5/04 20060101
A61B005/04; A61B 5/00 20060101 A61B005/00; A61B 5/0408 20060101
A61B005/0408; A61B 7/00 20060101 A61B007/00 |
Claims
1. A system for monitoring a left ventricular ejection time from a
patient, the system comprising: a monitoring device comprising: a
patch sensor component comprising: i) a backing structure, ii) a
first electrode and a second electrode, each of the first and
second electrodes connected to the backing structure and comprising
an electrical lead in contact with a conductive electrode material,
the first electrode configured to measure a first signal from the
patient that passes through the conductive electrode material and
the electrical lead of the first electrode, and the second
electrode configured to measure a second signal from the patient
that passes through the conductive electrode material and the
electrical lead of the second electrode, iii) an acoustic sensor
comprised by the backing structure and configured to measure a
physiological property from the patient to generate a third signal,
iv) an optical component comprising a light source that generates
optical radiation and a photodectector that detects the optical
radiation and generates a fourth signal, and, a processing device
configured to receive and collectively process the first signal or
a processed version thereof, the second signal or a processed
version thereof, and the third signal or a processed version
thereof, and the fourth signal or a processed version thereof to
determine the left ventricular ejection time for the patient, and a
cable for transmitting signals between the monitoring device and
the processing device.
2. The system of claim 1, wherein the first electrode is disposed
at a first end of the backing structure, and the second electrode
is disposed at on opposing second end of the backing structure.
3. The system of claim 1, wherein the electrical lead of each of
the first electrode and the second electrode comprises a metal
component.
4. The system of claim 3, wherein the metal component is
substantially cylindrical and configured to removably connect with
the first connector or second connector of the main component.
5. The system of claim 4, wherein the metal component further
comprises and Ag/AgCl coating.
6. The system of claim 5, wherein the conductive electrode material
is a conductive solid gel.
7. The system of claim 5, wherein the conductive electrode material
is a conductive liquid gel.
8. The system of claim 1, wherein the backing structure is a
flexible foam material.
9. The system of claim 1, wherein the backing structure further
comprises an adhesive layer.
10. The system of claim 1, wherein the backing structure has an
aperture, and the acoustic sensor is configured to insert into the
aperture.
11. The system of claim 10, wherein the backing structure further
comprises an impedance-matching gel disposed over the
aperature.
12. A monitoring device comprising: i) a backing structure; ii) a
first electrode and a second electrode, each of the first and
second electrodes disposed on the backing structure and comprising
an electrical lead in contact with a conductive electrode material,
the first electrode configured to generate a first signal from the
patient that passes through the conductive electrode material and
the electrical lead of the first electrode, and the second
electrode configured to generate a second signal from the patient
that passes through the conductive electrode material and the
electrical lead of the second electrode; iii) an acoustic sensor
comprised by the backing structure and configured to measure a
physiological property from the patient to generate a third signal;
iv) a first connector and a second connector, the first connector
configured to removably connect to the first electrode to receive
the first signal and the second connector configured to removably
connect to the second electrode to receive the second signal, and
v) an optical component comprising a light source that generates
optical radiation and a photodector that detects the optical
radiation and generates a fourth signal; and a processing device
configured to receive and collectively process the first signal or
a processed version thereof, the second electrode connects to a
second portion of the backing material.
13. The monitoring device of claim 12, wherein the first electrode
connects to a first portion of the backing structure, and the
second electrode connects to a second portion of the backing
material.
14. The monitoring device of claim 12, wherein each of the first
and second electrical leads comprises a metal component.
15. The monitoring device of claim 14, wherein the metal component
comprises a substantially cylindrical component configured to snap
into a connector comprised by the circuit board component.
16. The monitoring device of claim 14, wherein the metal component
comprises an Ag/AgCl coating.
17. The monitoring device of claim 12, wherein the conductive
electrode comprises a conductive gel.
18. The monitoring device of claim 12, wherein the backing
structure comprises a flexible foam material.
19. The monitoring device of claim 12, wherein the backing
structure further comprises an adhesive layer.
Description
CROSS REFERENCES TO RELATED APPLICATION
[0001] The present invention is a continuation of U.S. patent
application Ser. No. 11/558,538 filed Nov. 10, 2006, which is
hereby incorporated in its entirety including all tables, figures
and claims.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to medical devices for
monitoring vital signs, e.g. blood pressure.
[0004] 2. Description of the Related Art
[0005] Pulse transit time (`PTT`), defined as the transit time for
a pressure pulse launched by a heartbeat in a patient's arterial
system, has been shown in a number of studies to correlate to both
systolic and diastolic blood pressure. In these studies PTT is
typically measured with a conventional vital signs monitor that
includes separate modules to determine both an electrocardiogram
(ECG) and pulse oximetry. During a PTT measurement, multiple
electrodes typically attach to a patient's chest to determine a
time-dependent ECG characterized by a sharp spike called the `QRS
complex`. This feature indicates an initial depolarization of
ventricles within the heart and, informally, marks the beginning of
the heartbeat. Pulse oximetry is typically measured with a
clothespin-shaped device that clips to the patient's index finger,
and includes optical systems operating in both the red and infrared
spectral regions. In addition to measuring a pulse oximetry value,
this method yields a time-dependent waveform, called a
plethysmograph, that indicates both heart rate and a time-dependent
volumetric change in an underlying artery (e.g. in the finger)
caused by the propagating pressure pulse.
[0006] In many studies PTT is calculated from the time separating
the onset of the QRS complex to the foot of the plethysmograph.
Alternatively, PTT can be calculated as the time separating signals
measured by two sensors (e.g. optical or pressure sensors), each
sensitive to the propagating pressure pulse, placed at different
locations on the patient's body. In both cases, PTT depends
primarily on arterial tone, arterial compliance, the propagation
distance (closely approximated by the patient's arm length), and of
course blood pressure. Typically a high blood pressure results in a
shorter PTT.
[0007] A number of issued U.S. Patents describe the relationship
between PTT and blood pressure. For example, among others, U.S.
Pat. Nos. 5,316,008; 5,857,975; 5,865,755; and 5,649,543 each teach
an apparatus that includes conventional sensors that measure an ECG
and plethysmograph that are processed to measure PTT. U.S. Pat.
Nos. 6,511,436; 6,599,251; and 6,723,054 each teach an apparatus
that includes a pair of optical or pressure sensors, each sensitive
to a propagating pressure pulse, that measure PTT. As described in
these patents, a microprocessor associated with the apparatus
processes the PTT value to estimate blood pressure.
[0008] PTT-based measurements of blood pressure are complicated by
a number of factors, one of which is the many time-dependent
processes associated with each heartbeat that may correlate in a
different way with blood pressure, or in fact may not correlate at
all. For example, prior to the initial depolarization of the
ventricles (marked by the QRS complex), the mitral valve opens and
lets blood flow from the left atrium into the left ventricle. This
causes the ventricle to fill with blood and increase in pressure.
After the onset of the QRS, the mitral valve closes and the aortic
valve opens. When the heart contracts, blood ejects into the aorta
until the aortic valve closes. The time separating the onset of the
QRS and the opening of the aortic valve is typically called the
pre-injection period, or `PEP`. The time separating opening and
closing of the aortic valve is called the left ventricular ejection
period, or `LVET`. LVET and PEP, along with additional
time-dependent properties associated with each heartbeat, are
typically included in a grouping of properties called systolic time
intervals, or `STIs`.
[0009] PTT and LVET can be measured with a number of different
techniques, such as impedance cardiography (`ICG`) and by measuring
a time-dependent acoustic waveform, called a phonocardiogram
(`PCG`), with an acoustic sensor. The PCG, characterized by
acoustic signatures indicating the closing (and not opening) of the
mitral and aortic valves, is typically coupled with an ECG to
estimate PEP and LVET. For example, U.S. Pat. Nos. 4,094,308 and
4,289,141 each teach an apparatus that measures a PCG and ECG, and
from these waveforms estimates PEP and LVET. U.S. Pat. No.
7,029,447 teaches an apparatus using transit times calculated from
an ICG measurement to determine blood pressure.
[0010] Studies have also shown that a property called vascular
transit time (`VTT`), measured from features in both a PCG and
plethysmograph, can correlate to blood pressure. Such a study, for
example, is described in an article entitled `Evaluation of blood
pressure changes using vascular transit time`, Physiol. Meas. 27,
685-694 (2006). In addition, studies have shown that PEP and LVET,
taken alone, can correlate to blood pressure. These studies
typically require multiple sensors placed on the patient's body to
measure time-dependent waveforms that are processed to determine
PEP and LVET. Studies that relate these properties to blood
pressure, for example, are described in `Systolic Time Intervals in
Man`, Circulation 37, 149-159 (1968); `Relationship Between
Systolic Time Intervals and Arterial Blood Pressure`, Clin.
Cardiol. 9, 545-549 (1986); `Short-term variability of pulse
pressure and systolic and diastolic time in heart transplant
recipients`, Am. J. Physiol. Heart Circ. Physiol. 279, H122-H129
(2000); and `Pulse transit time measured from the ECG: an
unreliable marker of beat-to-beat blood pressure`, J. App.l
Physiol. 100, 136-141 (2006).
SUMMARY OF THE INVENTION
[0011] The sensor according to this invention makes cuffless blood
pressure measurements using a two-part patch sensor featuring a
disposable component that includes a pair of electrodes and a
non-disposable component that features optical and acoustic
sensors. When snapped together, the disposable and non-disposable
components form an adhesive sensor with a form factor similar to a
conventional band-aid that typically attaches to a patient's chest,
just below their sternal notch. During operation, the sensor
measures optical, electrical, and acoustic waveforms from the
patient, which a microprocessor then analyzes as described in
detail below to determine blood pressure and other vital signs. In
this way, the sensor replaces a conventional cuff to make a rapid
measurement of blood pressure with little or no discomfort to the
patient.
[0012] Specifically, in one aspect, the invention provides system
for monitoring blood pressure from a patient that includes a patch
sensor component featuring: i) a backing material comprising a
first opening; and ii) first and second electrodes, each electrode
connected to the backing material and including an electrical lead
and a conductive electrode material. The electrode generates an
electrical signal that passes through the electrical lead when the
conductive electrode material contacts the patient. The patch
sensor component connects to a circuit board component that
includes: i) first and second connectors that connect to the first
and second electrical leads to receive the first and second
electrical signals; and ii) an optical component, featuring a light
source photodetector, that detects the optical radiation after it
irradiates the patient to generate an optical waveform. The optical
component inserts into the first opening of the patch sensor
component when the first and second connectors connect,
respectively, to the first and second electrical leads. A
monitoring device, connected to the circuit board component by a
cable, receives and process the optical waveform (or a processed
version thereof) and the first and second electrical signals (or
processed versions thereof) to determine blood-pressure
information.
[0013] The patient typically wears the sensor on or just below the
`sternal` notch of their chest, proximal to their heart. In this
location the sensor simultaneously measures optical, electrical,
and acoustic signals. These signals are then processed with an
algorithm described below to measure blood pressure and other vital
signs. The measurement is possible because: 1) the proximity of
this area to the heart allows the acoustic sensor to measure
acoustic signals caused by closure of the mitral and aortic valves;
2) an abundance of capillaries in the sternal notch, meaning
optical signals can be measured in a reflective mode; and 3) the
strong electrical activity of the heart in this area, meaning
electrical signals can be measured with a high signal-to-noise
ratio even when the electrodes are relatively close together.
[0014] In embodiments, the first and second electrodes removably
connect, respectively, to first and second portions of the backing
material, and the first opening that receives the optical component
is disposed between the first and second portions. Typically both
the first and second electrical leads comprise a metal snap
component, e.g. a substantially cylindrical `male` component
configured to snap into a `female` connector on the circuit board
component. In embodiments, the metal snap component comprises an
Ag/AgCl coating and the conductive electrode material comprises a
conductive solid or liquid gel. The combination of these materials
is known in the art to improve the quality of electrical signals
collected from the patient.
[0015] In other embodiments, the backing material comprises a
flexible foam material and is coated on one side with an adhesive
layer. Typically the adhesive layer is designed to effectively
secure the sensor to the patient's skin, and is covered with a
protective plastic coating when the sensor is not in use. This
keeps both the adhesive layer and solid or liquid gel from drying
out.
[0016] The backing material typically includes a second opening,
with the acoustic sensor configured to insert into the second
opening when the first and second connectors on the backing
material connect, respectively, to the first and second electrical
leads. To increase coupling of acoustic signals into the acoustic
sensor, the backing material can additionally include an
impedance-matching gel disposed over the second opening. During
use, the electrical leads of the patch sensor component snap into
their mated connectors on the circuit board component, and the
acoustic sensor inserts into the second opening and contacts the
impedance-matching gel. The impedance-matching gel is sandwiched
between the acoustic sensor and the patient's skin when the
two-part sensor is attached to the patient. This improves coupling
of acoustic signals into the acoustic sensor, thereby increase the
quality of the measured signal.
[0017] In another aspect, the invention provides a system for
measuring blood pressure values that features a main component
comprising an optical sensor, an acoustic sensor, a first receptor,
and a second receptor. A disposable component removably attaches to
the main component. The disposable component features: i) a
polymeric body with an exterior surface and an interior surface
coated with an adhesive film; ii) a first electrode; iii) a second
electrode; iv) a first aperture; and v) a second aperture. During
use, the optical sensor extends through the first aperture, the
acoustic sensor extends through the second aperture, and the first
and second electrodes connect to, respectively, the first and
second receptors of the main component. A processing device
calculates a real-time blood pressure value from the electrical
signals from the first and second electrodes, an optical signal
from the optical sensor, and an acoustic signal from the acoustic
sensor.
[0018] The invention has many advantages. In particular, it
provides a low-profile, disposable sensor that measures a variety
of vital signs, particularly blood pressure, without using a
conventional cuff. This and other information can be transferred to
a central monitor through a wired or wireless connection to better
characterize a patient. For example, with the system a medical
professional can continuously monitor a patient's blood pressure
and other vital signs during their day-to-day activities.
Monitoring patients in this manner increases patient care and the
accuracy of a blood-pressure measurement while minimizing erroneous
measurements due to, e.g., `white coat syndrome`.
[0019] Once collected, information describing the blood pressure
can be viewed using an Internet-based website, a personal computer,
or simply by viewing a display on the device. Blood-pressure
information measured continuously throughout the day provides a
relatively comprehensive data set compared to that measured during
isolated medical appointments. This approach identifies trends in a
patient's blood pressure, such as a gradual increase or decrease,
which may indicate a medical condition that requires treatment. The
system also minimizes effects of `white coat syndrome` since the
monitor automatically and continuously makes measurements away from
a medical office with basically no discomfort to the patient.
[0020] These and other advantages are described in detail in the
following description, and in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is an exploded view of the two-part patch sensor
according to the invention wherein the non-disposable sensor
housing connects to the disposable patch sensor;
[0022] FIG. 2 is a front view of the disposable patch sensor of
FIG. 1;
[0023] FIG. 3 is a front view of the non-disposable sensor housing
of FIG. 1 containing a sensor board;
[0024] FIG. 4A is a schematic front view of an external, secondary
electrode that connects to the two-part patch sensor of FIG. 1 to
improve the quality of the electrical waveform;
[0025] FIG. 4B is a front view of a secondary electrode connector
that connects to the secondary electrode of FIG. 4A;
[0026] FIG. 5A is a schematic view of the two-part patch sensor of
FIG. 1 connected to a patient's chest;
[0027] FIG. 5B is a schematic view of the two-part patch sensor of
FIG. 1 and the secondary electrode of FIG. 4B connected to a
patient's chest;
[0028] FIG. 6A is a graph of time-dependent electrical, optical,
and acoustic waveforms measured with the two-part patch sensor
connected to the patient in FIG. 5A;
[0029] FIG. 6B is a graph of the time-dependent electrical,
optical, and acoustic waveforms shown in FIG. 6A plotted over a
relatively short time scale;
[0030] FIG. 7 is a schematic diagram of processing components used
to process waveforms measured by the two-part patch sensor of FIG.
1 to determine a patient's blood pressure;
[0031] FIG. 8A is a schematic view of a two-piece, non-disposable
sensor housing attached to a disposable patch; and,
[0032] FIG. 8B is a schematic view of a three-piece, non-disposable
sensor housing attached to a disposable patch.
DETAILED DESCRIPTION OF THE INVENTION
[0033] FIGS. 1, 2, and 3 show a two-part patch sensor 10 according
to the invention that features a disposable adhesive patch sensor 5
that attaches to a non-disposable sensor housing 6 to measure
optical, electrical, and acoustic waveforms from a patient's chest.
The optical, acoustic and electrical waveforms represent,
respectively, capillary blood flow, mitral and aortic valve
closures, and electrical activity generated by the patient's heart.
A cable 11 containing a shielded wire for each signal transports
the waveforms to a main console (the components of which are shown
in FIG. 8) that processes them to measure a patient's vital signs,
particularly blood pressure. One such processing technique, for
example, is described in detail in co-pending U.S. patent
application Ser. No. 11/470,708, entitled Hand-Held Vital Signs
Monitor, filed Sep. 7, 2006, the pertinent contents of which are
hereby incorporated by reference.
[0034] The patch sensor 5 features a sterile backing 9 composed of
a polymeric material (e.g. foam) that supports electrodes 20, 21
and makes measurements by adhering to a patient's skin; after use
it is discarded. The sensor housing 6 encloses a circuit board
component 36 that supports solid-state, non-disposable optical 42
and acoustic 41 sensors, described in detail below, and is designed
to be used with multiple disposable patch sensors. The patch sensor
5 contains primary 20 and a secondary 21 electrodes, each composed
of a cylindrical `male` electrical lead 3, 4 coated with Ag/AgCl
that snaps into a mated female connector 40, 43 on the sensor board
6. The electrical leads 3, 4 contain a bottom portion that extends
through the foam backing 9 and contacts a conductive `solid gel`
22, 24 that sticks to the patient during operation. The solid gel
22, 24 has an electrical impedance (approximately 100,000 ohms*cm)
that approximates the patient's skin to improve coupling of
electrical signals into the electrodes 20, 21.
[0035] The sterile foam backing 9 (approximate dimensions:
L.about.9 cm, W.about.4.5 cm, T.about.0.1 cm) includes clear
apertures 7, 8 positioned to match the orientation and geometry of,
respectively, the optical 42 and acoustic 41 sensors
surface-mounted on the circuit board component 36. The clear
aperture 8 for the acoustic sensor 41 is additionally covered by a
non-conductive, water-based solid gel 23 that approximates the
acoustic impedance of the patient's skin to improve coupling of
acoustic signals from the patient into the acoustic sensor 41. The
foam's back surface is coated with a non-allergenic adhesive 25 so
that it securely sticks to the patient's skin during operation.
Before the patch sensor 5 is used, a thin, plastic adhesive backing
(not shown in the figure) covers the adhesive 25 and the solid gels
22, 23, 24 to prevent them from drying out.
[0036] During operation a medical professional snaps the male
electrical leads 3, 4 of the patch sensor 5 into the female snap
connectors 43, 40 on the circuit board component 36. This action
secures the sensor housing 6 and circuit board component 36 to the
disposable patch sensor 5 and presses the acoustic 41 and optical
42 sensors through, respectively, the clear holes 8, 7 on the foam
backing 9. The optical sensor 42 presses completely through its
clear hole 7 and is exposed so that it directly contacts the
patient's skin, whereas the acoustic sensor 41 presses partially
through its clear hole 8 and contacts the non-conductive solid gel
23. The medical professional then peels off the protective backing
and sticks the combined patch sensor 10, featuring the
non-disposable housing 6, circuit board component 36, and
disposable patch sensor 5, onto the patient. To make a measurement,
the optical sensor 42 and electrodes 20, 21 each contact the
patient directly, while the acoustic sensor 41 contacts the
impedance-matched solid gel 23, which in turn contacts the patient.
As shown in FIG. 5A, the patch sensor 10 preferably attaches to the
patient 150 just below their sternal notch, and connects to a
console 100 typically located proximal to the patient 150. The
sternal notch, as described above, is an ideal location wherein the
patch sensor 10 can effectively measure optical, electrical, and
acoustic signals.
[0037] To improve the quality of the electrical waveform, the
two-part patch sensor 10 may connect to a secondary two-part
electrode 60, shown in FIGS. 4A and 4B, which is similar to a
conventional ECG electrode. The two-part electrode 60 features a
disposable electrode 70 that, like the disposable patch sensor
shown in FIGS. 1-3, includes a sterile foam backing 69 that
supports an Ag/AgCl-coated male electrical lead 72 that contacts an
impedance-matching solid gel 71. An adhesive layer 75 coats the
foam backing 69 so that it sticks to the patient's skin. During
use, the male electrical lead 72 snaps into a female snap connector
86 housed by a secondary electrode connector 82. A shielded cable
84 connects the secondary two-part electrode 60 to the primary
two-part patch sensor described above. In a preferred embodiment,
electrodes 20, 21 measure, respectively, a positive signal and
ground signal, while the two-part electrode 60 measures a negative
signal. An electrical amplifier in the main console then processes
the positive, negative, and ground signals to generate an
electrical waveform, described in detail below, that is similar to
a single-lead ECG. FIG. 5B, for example, shows how the secondary
two-part electrode 60 connects to the two-part patch sensor 10'
through the cable 84; the combined system then attaches to a
patient 150' and connects to the console 100' through a cable 11'
to measure the patient's vital signs.
[0038] FIGS. 6A and 6B show graphs 151, 152 of the time-dependent
electrical waveform 160, optical waveform 162, and acoustic
waveform 164 measured by the above-described sensors. Each waveform
160, 162, 164 includes time-dependent features that repeat with
each heartbeat. For example, the electrical waveform 160 looks
similar to a conventional ECG and features a QRS complex featuring
a sharp spike that indicates an initial depolarization of the
ventricle. Because of its well-defined features, the QRS complex is
relatively easy to detect with a computational algorithm, and
serves as an effective `marker` that indicates each individual
heartbeat. The optical waveform 162 is measured from underlying
capillaries in the patient's chest and features a slowly varying
pulse that indicates an increase in volume in the capillaries
caused by a propagating pressure wave. Finally, the acoustic
waveform features two `beats`, each representing a collection of
acoustic frequencies, that occur with each heartbeat. The first and
second beats represent the sounds made following closure of,
respectively, the heart's mitral and aortic valves; these are the
conventional `lub` and `dub` heard through a stethoscope.
[0039] FIG. 6B graphs a portion of the waveforms highlighted by a
box 166 of FIG. 6A, and indicates how a microprocessor preferably
analyzes the various features of the electrical waveform 160',
optical waveform 162', and acoustic waveform 164' to determine a
variety of systolic time intervals. These systolic time intervals
are then further processed to determine a patient's real-time blood
pressure. Co-pending U.S. patent application Ser. No. 11/470,708,
entitled Hand-Held Vital Signs Monitor and filed Sep. 7, 2006,
previously incorporated herein by reference, describes this
processing method in detail. As described above, the QRS complex in
the electrical waveform 160', which is caused by initial
depolarization of the heart muscle, serves as a marker indicating
the start of each heart beat. At a later time, the mitral valve
opens and blood flows from the heart's left atrium into the left
ventricle. The mitral valve then closes, causing the first beat in
the acoustic waveform 164', and the aortic valve opens shortly
thereafter. The opening of the aortic valve does not result in a
feature in the acoustic waveform 164' (only closing valves do
this), but is assumed to follow within approximately 10
milliseconds after the closing of the mitral valve. The time
difference between the onset of the QRS complex and the opening of
the aortic valve is called the `pre-injection period`, or PEP.
Since the technique described herein does not explicitly measure
the opening of the aortic valve, but rather the closure of the
mitral valve, it is labeled PEP*. Once the aortic valve opens, the
heart pumps a bolus of blood through the aorta, resulting in a
pressure wave that propagates through the patient's arterial
system. The propagation time of the pressure wave is a strong
function of the patient's blood pressure, along with their vascular
compliance and resistance. When the pressure wave reaches
capillaries in the patient's chest, the rise in pressure causes the
capillaries to increase in volume with blood, which in turn
increases the amount of optical radiation from the LED of the
optical sensor 20 that the flowing blood absorbs. The photodetector
in the optical sensor 20 detects this as a time-dependent pulse
characterized by a relatively sharp rise time and a slower decay,
as indicated by the optical waveform 162'. The time difference
between the estimated opening of the aortic valve and the onset of
the pulse's rise time is the `vascular transit time` (VTT*).
Typically the VTT* decreases with higher blood pressure. The second
beat in the acoustic waveform 164' represents the closure of the
aortic valve, and the time period separating this from the
estimated opening of the aortic valve is called the `left
ventricular ejection period` (LVET*). Finally, the onset of the QRS
complex and the foot of the plethysmograph is the pulse transit
time (PTT*). Note that the transit time essentially represents the
time from when the heart begins to beat to when the pressure wave
appears underneath the optical sensor 20. To reach this point, the
vascular pathway that the pressure wave must travel is somewhat
complicated: it extends through the aorta, the subclavian artery, a
series of smaller arteries proximal to the patient's ribs, and
finally through relatively small capillaries attached to these
arteries.
[0040] Other properties known to correlate to blood pressure can
also be measured from the optical waveform 162, electrical waveform
160, and acoustic waveform 164. For example, the rise and fall
times of the optical waveform 162 can meet this criterion, and thus
these properties can be measured from the optical waveform 162. In
addition, in some cases the optical waveform 162 will include a
primary and secondary peak, separated by a feature called the
`dicrotic notch`. The microprocessor can be programmed to take a
second derivative of the waveform to determine the ratio of the
primary and second peaks, and this property has been shown to
correlate to blood pressure. In addition, variability in the
patient's heartbeat, as measured from each of the electrical
waveform 160, optical waveform 162, and acoustic waveform 164, can
indicate variation in the patient's blood pressure, and can also be
processed by the microprocessor. Heart rates from these three
waveforms can be calculated and averaged together to yield a very
accurate measure of the patient's real-time heart rate.
[0041] FIG. 7 shows a preferred configuration of electronic
components featured within the console 100 that process the
above-described information to measure a patient's vital signs. A
data-processing circuit 111 connects to an
optical/electrical/acoustic signal processing circuit 106 that
controls the optical sensor 41, acoustic sensor 42, and electrodes
20, 21, 71. During operation, signals from these sensors
independently pass through a two-stage amplifier system 105 that
includes first 101 and second 103 amplifier stages separated by a
high-pass filter 102. A typical circuit board used in this
application features a separate two-stage amplifier system 105 for
the optical, electrical, and acoustic signals; a single amplifier
is shown in FIG. 7 for simplicity. The first 100 and second 103
amplifiers independently amplify analog input signals, while the
high-pass filter 102 removes low-frequency noise and DC component
in the signals to further improve their quality. Signals that pass
through the two-stage amplifier system 105 are then sent to an
analog-to-digital converter 107 connected to a microprocessor 108.
The analog-to-digital converter 107 can be integrated within the
microprocessor 108, or can be an independent chipset. In either
case, the analog-to-digital converter 107 digitizes the analog
optical, electrical, and acoustic waveforms to generate arrays of
data points that can be processed by the microprocessor 108 using
the algorithms described above to determine blood pressure, heart
rate, and pulse oximetry using techniques described herein and
known in the art.
[0042] To communicate with external wireless devices and networks,
the data-processing circuit 111 connects to a wireless transceiver
118 that communicates through an antenna 109 to a matched
transceiver embedded within an external component. The wireless
transceiver 118 can be a short-range wireless transceiver, e.g. a
device based on 802.11, Bluetooth.TM., Zigbee.TM., or part-15
wireless protocols. Alternatively, the wireless transceiver 118 can
be a cellular modem operating on a nation-wide wireless network,
e.g. a GSM or CDMA wireless network. The data-processing circuit
111 can also display information on a touchable interactive liquid
crystal display (`LCD`) 112, and transmit and receive information
through a serial port 110. A battery 117 powers all the electrical
components within the console 100, and is preferably a metal
hydride battery (generating 3-7V, and most preferably about 3.7V)
that can be recharged through a battery-recharge interface 114.
[0043] In addition to those methods described above, a number of
additional methods can be used to calculate blood pressure from the
optical, electrical, and acoustic waveforms. These are described in
the following co-pending patent applications, the contents of which
are incorporated herein by reference: 1) CUFFLESS BLOOD-PRESSURE
MONITOR AND ACCOMPANYING WIRELESS, INTERNET-BASED SYSTEM (U.S. Ser.
No. 10/709,015; filed Apr. 7, 2004); 2) CUFFLESS SYSTEM FOR
MEASURING BLOOD PRESSURE (U.S. Ser. No. 10/709,014; filed Apr. 7,
2004); 3) CUFFLESS BLOOD PRESSURE MONITOR AND ACCOMPANYING WEB
SERVICES INTERFACE (U.S. Ser. No. 10/810,237; filed Mar. 26, 2004);
4) VITAL SIGN MONITOR FOR ATHLETIC APPLICATIONS (U.S. Ser. No.
______; filed Sep. 13, 2004); 5) CUFFLESS BLOOD PRESSURE MONITOR
AND ACCOMPANYING WIRELESS MOBILE DEVICE (U.S. Ser. No. 10/967,511;
filed Oct. 18, 2004); and 6) BLOOD PRESSURE MONITORING DEVICE
FEATURING A CALIBRATION-BASED ANALYSIS (U.S. Ser. No. 10/967,610;
filed Oct. 18, 2004); 7) PERSONAL COMPUTER-BASED VITAL SIGN MONITOR
(U.S. Ser. No. 10/906,342; filed Feb. 15, 2005); 8) PATCH SENSOR
FOR MEASURING BLOOD PRESSURE WITHOUT A CUFF (U.S. Ser. No.
10/906,315; filed Feb. 14, 2005); 9) PATCH SENSOR FOR MEASURING
VITAL SIGNS (U.S. Ser. No. 11/160,957; filed Jul. 18, 2005); 10)
WIRELESS, INTERNET-BASED SYSTEM FOR MEASURING VITAL SIGNS FROM A
PLURALITY OF PATIENTS IN A HOSPITAL OR MEDICAL CLINIC (U.S. Ser.
No. 11/162,719; filed Sep. 9, 2005); 11) HAND-HELD MONITOR FOR
MEASURING VITAL SIGNS (U.S. Ser. No. 11/162,742; filed Sep. 21,
2005); 12) CHEST STRAP FOR MEASURING VITAL SIGNS (U.S. Ser. No.
11/306,243; filed Dec. 20, 2005); 13) SYSTEM FOR MEASURING VITAL
SIGNS USING AN OPTICAL MODULE FEATURING A GREEN LIGHT SOURCE (U.S.
Ser. No. 11/307,375; filed Feb. 3, 2006); 14) BILATERAL DEVICE,
SYSTEM AND METHOD FOR MONITORING VITAL SIGNS (U.S. Ser. No.
11/420,281; filed May 25, 2006); 15) SYSTEM FOR MEASURING VITAL
SIGNS USING BILATERAL PULSE TRANSIT TIME (U.S. Ser. No. 11/420,652;
filed May 26, 2006); 16) HAND-HELD VITAL SIGNS MONITOR, (U.S. Ser.
No. 11/470,708, filed Sep. 7, 2006); and, 17) BLOOD PRESSURE
MONITOR, (U.S. Ser. No. 11/530,076 filed Sep. 8, 2006).
[0044] Other embodiments are within the scope of the invention. For
example, FIG. 8A shows an embodiment where a non-disposable sensor
component 196 is separated into first 200 and second 205 pieces,
both of which connect to a disposable patch component 199 similar
to that shown in FIGS. 1 and 2. The disposable patch component 199
includes an adhesive backing that adheres to a patient during a
measurement. In this embodiment, the first piece 200 of the
non-disposable sensor component includes a soft rubber overmold
that covers a female snap connector (not shown in the figure). The
female snap connector connects to a matched male electrical lead
and electrode (not shown in the figure) that are similar,
respectively, to the electrical lead 3 and electrode 20 shown in
FIGS. 1 and 2. The second piece 205 includes a similar rubber
overmold that covers a female snap connector, optical sensor, and
acoustic sensor (also not shown in the figure) similar to the
connector 43, optical sensor 42, and acoustic sensor 41 shown in
FIG. 3. The second piece 205 connects to a portion of the
disposable patch component 199 that includes apertures for the
optical and acoustic sensors.
[0045] When separated into multiple components, the non-disposable
sensor component 196 is less rigid than that shown in FIG. 3, and
thus better conforms to contours in the patient's chest. This
allows the optical, acoustic, and electrical sensors to be closely
coupled to the patient's body when attached to the disposable patch
component 199, thereby improving the quality of the waveforms
collected during a measurement. The female snap connector holds the
optical and acoustic sensors in place for the measurement, during
which the corresponding waveforms are collected and passed through
a bifurcated cable 197 that attaches to a processing device (not
shown in the figure) similar to the processing device 100 shown in
FIG. 5A. A secondary two-part electrode, similar to the electrode
60 shown in FIG. 5B, connects to the processing device through a
separate cable to improve the signal-to-noise ratio of the
electrical waveform. The processing device processes the waveforms
as described above to determine the patient's blood pressure. An
additional foam adhesive patch covering top portions of the first
200 and second 205 pieces may be used in this embodiment to further
secure these pieces of the non-disposable sensor component to the
patient.
[0046] FIG. 8B shows a related embodiment of a non-disposable
sensor 195 separated into three separate pieces 200', 206, 207 that
attaches to a disposable patch sensor component 199' that adheres
to a patient during a measurement. Segmenting the sensor 195 in
this way further improves its flexibility and the manner in which
it couples to contours in a patient's chest during a measurement.
In this embodiment the first 200' and third 207 pieces of the
non-disposable sensor 195 include a soft rubber overmold that
covers a female snap connector (not shown in the figure) that
connect to a matched male electrical lead and electrode (not shown
in the figure) similar to that described above. A trifurcated cable
198 connects the non-disposable sensor 195 to a processing device
(not shown in the figure) similar to the processing device 100
shown in FIG. 5A.
[0047] During a measurement, the first 200' and third 207 pieces
snap into their mated connectors and are held firmly in place. The
second piece 206 includes a similar rubber overmold that covers
optical and acoustic sensors described above. This piece 206
loosely attaches to a portion the disposable sensor 199' that
includes apertures for the optical and acoustic sensors, and is
further secured using an additional foam adhesive patch. A
secondary electrode similar to that described above also connects
to the processing device. Once secured to the patient, optical,
acoustic, and electrical sensors measure waveforms that pass
through the cable 198 to the processing device, which then
processes them as described above to determine the patient's blood
pressure.
[0048] In still other embodiments, each piece of the three-part
non-disposable sensor described above connects to a separate
disposable sensor. In this embodiment, for example, the first 200'
and third 207 pieces of the non-disposable sensor 195 (i.e., the
pieces that include a female snap connector) connect to a standard,
disposable ECG electrode that includes an adhesive foam backing,
Ag/AgCl-coated snap connector, and solid gel. The second piece 206
(i.e. the piece that includes the optical and acoustic sensor)
connects to a disposable foam substrate with an adhesive backing
that includes apertures for the optical and acoustic sensors.
[0049] In still other embodiments, the second piece 205 of the
above-mentioned sensor described with reference to FIG. 8A, or the
second piece 206 of the above-described sensor described with
reference to FIG. 8B, includes only the optical sensor or the
acoustic sensor, but not both sensors.
[0050] In still other embodiments, the disposable portion of the
sensor includes the electrodes, and is a separate component that
simply adheres with an adhesive to the non-disposable portion that
includes the optical and acoustic sensors and a cable that connects
to the console. In this case the disposable and non-disposable
portions include matched electrical contacts that touch each other
when the two portions are adhered. This way electrical signals
measured by the electrodes can be passed to the non-disposable
portion and through the cable to the console, where they are
processed to determine the electrical waveform.
[0051] Other embodiments are also within the scope of the
invention.
* * * * *