U.S. patent application number 16/403658 was filed with the patent office on 2019-08-22 for integrated resuscitation.
The applicant listed for this patent is ZOLL Medical Corporation. Invention is credited to Gary A. Freeman, Mark Totman.
Application Number | 20190254594 16/403658 |
Document ID | / |
Family ID | 35395896 |
Filed Date | 2019-08-22 |
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United States Patent
Application |
20190254594 |
Kind Code |
A1 |
Freeman; Gary A. ; et
al. |
August 22, 2019 |
INTEGRATED RESUSCITATION
Abstract
A method for treating a patient includes providing a
defibrillation and pacing device configured to be worn on a
continuous basis by a patient, the defibrillation and pacing device
comprising a (i) capacitor and associated circuitry and (ii) an
activity sensor. The method includes placing on the patient
electrodes configured to detect an ECG of the patient, monitoring
the ECG signals and activity of the patient, determining from at
least the ECG signal and activity of the patient whether the
patient meets an at least one of a bradycardia condition and
asystole condition, and, if it is determined that the patient meets
the bradycardia condition, providing pacing therapy.
Inventors: |
Freeman; Gary A.; (Waltham,
MA) ; Totman; Mark; (Hilton Head, SC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ZOLL Medical Corporation |
Chelmsford |
MA |
US |
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|
Family ID: |
35395896 |
Appl. No.: |
16/403658 |
Filed: |
May 6, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15478573 |
Apr 4, 2017 |
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16403658 |
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13271613 |
Oct 12, 2011 |
9713445 |
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15478573 |
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12794719 |
Jun 4, 2010 |
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13271613 |
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10954633 |
Sep 30, 2004 |
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12794719 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N 1/37288 20130101;
A61N 1/3968 20130101; A61B 5/0402 20130101; A61H 2201/5097
20130101; A61N 1/39046 20170801; A61H 2201/5007 20130101; A61B
5/7282 20130101; A61B 7/02 20130101; A61H 31/007 20130101; A61N
1/3625 20130101; A61B 5/0245 20130101; A61H 31/005 20130101; A61H
2230/207 20130101; A61B 5/1118 20130101; A61B 5/02438 20130101;
A61B 5/1116 20130101; A61B 5/14551 20130101; A61H 2201/5043
20130101; A61H 2201/5084 20130101; A61H 2230/04 20130101; A61N
1/3993 20130101; A61N 1/0472 20130101; A61H 2201/5048 20130101;
A61B 5/04012 20130101; A61H 2201/5061 20130101; A61N 1/046
20130101; A61N 1/0492 20130101; A61H 2031/002 20130101; A61N
1/39044 20170801; A61B 5/4836 20130101; A61N 1/3987 20130101 |
International
Class: |
A61B 5/00 20060101
A61B005/00; A61N 1/39 20060101 A61N001/39; A61N 1/04 20060101
A61N001/04; A61N 1/362 20060101 A61N001/362; A61H 31/00 20060101
A61H031/00; A61B 5/11 20060101 A61B005/11; A61B 5/024 20060101
A61B005/024; A61B 5/0402 20060101 A61B005/0402; A61B 5/1455
20060101 A61B005/1455; A61B 7/02 20060101 A61B007/02; A61B 5/04
20060101 A61B005/04; A61B 5/0245 20060101 A61B005/0245 |
Claims
1. A method for treating a patient comprising: providing a
defibrillation and pacing device configured to be worn on a
continuous basis by a patient, the defibrillation and pacing device
comprising a (i) capacitor and associated circuitry and (ii) an
activity sensor; placing on the patient electrodes configured to
detect an ECG of the patient; monitoring the ECG signals and
activity of the patient; determining from at least the ECG signal
and activity of the patient whether the patient meets an at least
one of a bradycardia condition and asystole condition; and if it is
determined that the patient meets the bradycardia condition,
providing pacing therapy.
2. The method of claim 1, further comprising providing at least two
electrical therapy electrodes adapted to be worn by the patient for
an extended period of time.
3. The method of claim 2, wherein the extended period of time
comprises at least 30 days.
4. The method of claim 2, wherein the at least two electrical
therapy electrodes are configured to provide at least one of
defibrillation and pacing therapy to the patent.
5. The method of claim 1, further comprising providing a power
source coupled to the capacitor.
6. The method of claim 1, further comprising providing a processor
coupled to the patient electrodes and the power source.
7. The method of claim 1, further comprising providing at least one
of a speaker and a display configured to provide prompts.
8. The method of claim 7, wherein the prompts comprise at least one
of spoken and visual prompts.
9. The method of claim 1, further comprising providing a prompt
based on an estimated current activity of the patient.
10. The method of claim 1, further comprising providing a prompt
based on the ECG signals and other physiological parameters.
11. The method of claim 10, wherein the prompt is an audible alarm
sounded to the patient for indicating the detection of a
physiological condition requiring treatment.
12. The method of claim 1, further comprising determining whether
the patient is moving based on the monitored activity of the
patient.
13. A long term wearable cardiac monitoring system for monitoring a
cardiac condition of a patient, comprising: a power source; one or
more electrodes electrically attached to an ECG monitoring unit,
the one or more electrodes configured to be held against the skin
of the patient for an extended period of time; circuitry for
receiving an ECG signal of the patient via the one or more
electrodes; an energy delivery unit coupled to the power source
configured to provide pacing therapy to the patient; and at least
one processor operatively coupled to the circuitry for receiving
the ECG signal of the patient and the energy delivery unit
configured to provide pacing, the at least one processor configured
to: monitor the received ECG signal of the patient, detect at least
one of a bradycardia condition and an asystole condition in the
patient for which pacing is indicated, and provide a pacing therapy
to the patient via the energy delivery unit upon detecting the at
least one of the bradycardia condition and the asystole condition
in the patient.
14. The long term wearable cardiac monitoring system of claim 13,
wherein the extended period of time comprises at least 30 days.
15. The long term wearable cardiac monitoring system of claim 13,
further comprising an activity sensor, wherein the at least one
processor receives information from the activity sensor on whether
or not the patient is moving.
16. The long term wearable cardiac monitoring system of claim 13,
further comprising a display configured to provide a visual
prompt.
17. The long term wearable cardiac monitoring system of claim 13,
further comprising a speaker configured to provide an audible
prompt.
18. The long term wearable cardiac monitoring system of claim 17,
further comprising an activity sensor, wherein the prompt is based
on an estimated current activity of the patient.
19. The long term wearable cardiac monitoring system of claim 17,
wherein the prompt is provided based on the monitored ECG signal
and other physiological parameters.
20. The long term wearable cardiac monitoring system of claim 17,
wherein the prompt is sounded to the patient for indicating the
detection of a physiological condition requiring treatment.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of and claims priority to
U.S. application Ser. No. 15/478,573, filed on Apr. 4, 2017, which
is a continuation application of and claims priority to U.S.
application Ser. No. 13/271,613, filed on Oct. 12, 2011, now U.S.
Pat. No. 9,713,445 issued on Jul. 25, 2017, which is a continuation
application of and claims priority to U.S. application Ser. No.
12/794,719, filed on Jun. 4, 2010, now abandoned, which application
is a continuation application of and claims priority to U.S.
application Ser. No. 10/954,633, filed on Sep. 30, 2004, now
abandoned. The entire content of each application is incorporated
herein by reference in its entirety.
TECHNICAL FIELD
[0002] This invention relates to resuscitation systems
incorporating defibrillation therapy and resuscitation prompts.
BACKGROUND OF THE INVENTION
[0003] Resuscitation can generally include clearing a patient's
airway, assisting the patient's breathing, chest compressions, and
defibrillation.
[0004] The American Heart Association's Basic Life Support for
Health Care Providers textbook provides a flow chart at page 4-14
of Chapter 4 that lists the steps of airway clearing, breathing,
and circulation (known as A, B, and C), for situations in which
there is no defibrillator readily accessible to the rescuer.
[0005] Defibrillation (sometimes known as step D) can be performed
with the use of an automatic external defibrillator (AED) Most
automatic external defibrillators are actually semi-automatic
external defibrillators (SAED), which require a clinician to press
a start button, after which the defibrillator analyzes the
patient's condition and provides a shock to the patient if the
electrical rhythm is shockable and waits for user intervention
before any subsequent shock. Fully automatic external
defibrillators, on the other hand, do not wait for user
intervention before applying subsequent shocks. As used below,
automatic external defibrillators (AED) include semi-automatic
external defibrillators (SAED).
[0006] Both types of defibrillators typically provide an oral stand
clear warning before the application of each shock, and then the
clinician is expected to stand clear of the patient and may be
required to press a button indicating that the clinician is
standing clear of the patient. The controls for automatic external
defibrillators are typically located on a resuscitation control
box.
[0007] AEDs are used typically by trained providers such as
physicians, nurses, fire department personnel, and police officers.
There might be one or two people at a given facility that has an
AED who have been designated for defibrillation resuscitation
before an ambulance service arrives. The availability of on-site
AEDs along with rescuers trained to operate them is important
because if the patient experiences a delay of more than 4 minutes
before receiving a defibrillation shock the patient's chance of
survival can drop dramatically. Many large cities and rural areas
have low survival rates for defibrillation because the ambulance
response time is slow, although many suburbs have higher survival
rates because of the faster ambulance response time due to lack of
traffic and availability of hospitals and advanced life
support.
[0008] Trained lay providers are a new group of AED operators, but
they rarely have opportunities to defibrillate. For example,
spouses of heart attack victims may become lay providers, but these
lay providers can be easily intimidated by an AED during a medical
emergency. Consequently, such lay providers can be reluctant to
purchase AEDs, or might tend to wait for an ambulance to arrive
rather than use an available AED, out of concern that the lay
provider might do something wrong.
[0009] There are many different kinds of heart rhythms, some of
which are considered shockable and some of them are not. For
example, a normal rhythm is considered non-shockable, and there are
also many abnormal non-shockable rhythms. There are also some
abnormal non-viable non-shockable, which means that the patient
cannot remain alive with the rhythm, but yet applying shocks will
not help convert the rhythm.
[0010] As an example of a non-shockable rhythm, if a patient
experiences asystole, the heart will not be beating and application
of shocks will be ineffective. Pacing is recommended for asystole,
and there are other things that an advanced life support team can
do to assist such patient, such as the use of drugs. The job of the
first responder is simply to keep the patient alive, through the
use of CPR and possibly defibrillation, until an advanced life
support team arrives. Bradycardias, during which the heart beats
too slowly, are non-shockable and also possibly non-viable. If the
patient is unconscious during bradycardia, it can be helpful to
perform chest compressions until pacing becomes available.
Electro-mechanical dissociation (EMD), in which there is electrical
activity in the heart but it is not making the heart muscle
contract, is non-shockable and non-viable, and would require CPR as
a first response. Idio-ventricular rhythms, in which the normal
electrical activity occurs in the ventricles but not the atria, can
also be non-shockable and non-viable (usually, abnormal electrical
patterns begin in the atria). Idio-ventricular rhythms typically
result in slow heart rhythms of 30 or 40 beats per minute, often
causing the patient to lose consciousness. The slow heart rhythm
occurs because the ventricles ordinarily respond to the activity of
the atria, but when the atria stop their electrical activity, a
slower, backup rhythm occurs in the ventricles.
[0011] The primary examples of shockable rhythms, for which a first
responder should perform defibrillation, include ventricular
fibrillation, ventricular tachycardia, and ventricular flutter.
[0012] After using a defibrillator to apply one or more shocks to a
patient who has a shockable electrical rhythm, the patient may
nevertheless remain unconscious, in a shockable or non-shockable
rhythm. The rescuer may then resort to chest compressions. As long
as the patient remains unconscious, the rescuer can alternate
between use of the defibrillator (for analyzing the electrical
rhythm and possibly applying a shock) and performing
cardio-pulmonary resuscitation (CPR).
[0013] CPR generally involves a repeating pattern of five or
fifteen chest compressions followed by a pause. CPR is generally
ineffective against abnormal rhythms, but it does keep some level
of blood flow going to the patient's vital organs until an advanced
life support team arrives. It is difficult to perform CPR over an
extended period of time. Certain studies have shown that over a
course of minutes, rescuers tend to perform chest compressions with
less-than-sufficient strength to cause an adequate supply of blood
to flow to the brain. CPR prompting devices can assist a rescuer by
prompting each chest compression and breath.
[0014] PCT Patent Publication No. WO 99/24114, filed by
Heartstream, Inc., discloses an external defibrillator having PCR
and ACLS (advanced cardiac life support) prompts.
SUMMARY OF THE INVENTION
[0015] In a first aspect, the invention features a resuscitation
system for use by a rescuer for resuscitating a patient, comprising
at least two high-voltage defibrillation electrodes, a first
electrical unit comprising circuitry for providing resuscitation
prompts to the rescuer, a second electrical unit separate from the
first unit and comprising circuitry for providing defibrillation
pulses to the electrodes, and circuitry for providing at least one
electrical connection between the first and second units.
[0016] Preferred implementations of this aspect of the invention
may incorporate one or more of the following. The two electrodes
and the first unit may be built into a defibrillation electrode pad
assembly. The defibrillation electrodes may be detachable from the
defibrillation electrode pad assembly. The first unit may be
separate from the two electrodes, and may be connected to the two
electrodes by one or more cables. The first unit may be capable of
functioning and providing the resuscitation prompts without being
electrically connected to the second unit. The first unit may
comprise a source of electrical power and a processor. The first
unit may have circuitry for monitoring at least one physiological
parameter of the patient. The parameter may be an ECG signal. The
resuscitation prompts may comprise CPR prompts. The circuitry for
providing at least one electrical connection between the first and
second units may comprise at least one cable. The circuitry for
providing at least one electrical connection between the first and
second units may comprise at least one wireless connection. The
second unit may be connected directly to the defibrillation
electrodes by one or more cables that carry the defibrillation
pulses to the electrodes. The circuitry for providing at least one
electrical connection between the first and second units may
comprise at least one cable for delivering the defibrillation
pulses to the first unit, from where they are delivered to the
electrodes. The ECG signal may be detected using the defibrillation
electrodes. The first unit may comprise a speaker for providing the
resuscitation prompts. The resuscitation prompts may comprise
spoken and visual prompts. The first unit may comprise a microphone
and circuitry for storing sounds recorded during use of the unit.
The defibrillation electrodes may be built into an electrode pad
assembly and a handle for providing an upward lifting force on the
assembly may be provided. The handle may comprise a flexible sheet
material. The handle may comprise a substantially rigid
material.
[0017] In a second aspect, the invention features a resuscitation
system for resuscitating a patient, comprising at least two
electrical therapy electrodes adapted to be worn by the patient for
extended periods of time, circuitry for monitoring the ECG of the
patient, an activity sensor adapted to be worn by the patient and
capable of providing an output from which the patient's current
activity can be estimated, and at least one processor configured
for estimating the patient's current activity by analyzing the
output of the activity sensor, analyzing the ECG of the patient,
and determining whether electrical therapy should be delivered to
the electrodes.
[0018] Preferred implementations of this aspect of the invention
may incorporate one or more of the following. The processor may be
configured for estimating whether the patient is moving. The
activity sensor may comprise an accelerometer, and the processor
may be configured for integrating the output of the accelerometer
to provide an estimate of velocity and/or displacement. The
processor may be configured to process the output of the activity
sensor and use the result of the processing to modify at least one
threshold in a technique used for determining a physiological
status of patient. The physiological status may comprise
determining a risk of impending heart attack or cardiac arrest. The
resuscitation system may include a speaker for issuing spoken
prompts to the patient, and the processor may decide on the nature
of the spoken prompt based on the estimated current activity of the
patient. The patient's current activity may comprise estimating the
orientation of the patient. Estimating the orientation of the
patient may comprise determining whether the patient lying on his
back. The electrodes may be defibrillation electrodes and the
electrical therapy may comprise a defibrillation pulse. The
invention may further comprise an activity sensor adapted to be
worn by the patient and capable of providing an output from which
the patient's current activity can be estimated, and at least one
processor configured for estimating the patient's current activity
by analyzing the output of the activity sensor. The at least one
processor may be located in the first unit. At least some of the
resuscitation prompts delivered by the first unit may be dependent
on the estimated current activity of the patient. The current
activity may comprise whether the patient is lying on his back, and
at least one resuscitation prompt issued when the patient is not on
his back may be an instruction to roll the patient on their back
prior to beginning CPR.
[0019] In a third aspect, the invention features a resuscitation
system for resuscitating a patient, comprising at least two
electrical therapy electrodes adapted to be worn by the patient for
extended periods of time, circuitry for monitoring the ECG of the
patient, an activity sensor adapted to be worn by the patient and
capable of providing an output from which the patient's current
activity can be estimated, and at least one processor configured
for estimating the patient's current activity by analyzing the
output of the activity sensor, analyzing the ECG of the patient,
and determining whether the patient has an elevated probability of
cardiac arrest.
[0020] Preferred implementations of this aspect of the invention
may incorporate one or more of the following. The processor may be
configured for determining whether the patient's current activity
includes increased physical activity. The processor may be
configured for determining an activity level parameter
representative of the patient's activity level. The decision of an
elevated probability of cardiac arrest may be based on the activity
level parameter and a parameter may be derived from the patient's
ECG. The decision of an elevated probability of cardiac arrest may
be based on the activity level parameter and a measurement of blood
pressure. The invention may further comprise the capability of
delivering at least one test pulse through the electrodes at a time
based, at least in part, on an estimate of the patient's current
activity, wherein the test pulse is of a type configured to produce
a ventricular premature beat (VPB). The time based on an estimate
of the patient's current activity may be shortly after waking in
the morning. Prior to delivering the test pulse, the system may
issue a prompt to the patient requesting administration of the test
pulse and the system may wait for the patient to indicate his
consent to administration of the test pulse.
[0021] Among the many advantages of the invention (some of which
may be achieved only in some of its various aspects and
implementations) are that the invention may permit wider
distribution and availability of the first unit, which provides
resuscitation prompting, than of the second unit, which provides
defibrillation therapy. The first unit's relatively lower cost may
make it possible for the first unit to be more widely distributed
than the second unit. Wider distribution of the first unit may mean
more successful rescues, as a patient can be stabilized and
prepared for defibrillation using the first unit.
[0022] The unit may be worn on a continuous basis by a person at
higher risk of a heart attack such as someone who has recently
undergone bypass surgery or one who has experienced a myocardial
infarction. The early warning of a heightened risk of an impending
cardiac arrest provided by the device will allow the wearer of the
device to phone a physician or emergency service in advance of the
actual cardiac arrest, thus reducing fatality rates of cardiac
arrest by early prevention and treatment of the underlying
physiological abnormalities rather than treating the consequences
of the arrest. The activity sensor provides a means of determining
whether or not the wearer of the device is awake or not, thereby
providing an accurate way of providing voice prompts and
physiological tests in synchrony with the wearer's daily schedule
in a non-interfering manner. When used in conjunction with a
communication link to medical providers such as an EMS system, the
activity sensor also provides a means of determining the state of
the victim, whether the victim is vertical or horizontal, and
moving, thus potentially lowering false alarm rates and accuracy of
diagnosis. The activity sensor may also be used to adjust the
thresholds used for various alarms and heart attack risk detection
methods. The wearer can activate a keying input on the device
indicating chest pain, and in conjunction with the additional ECG,
and activity sensor data, the device can more reliably calculate
relative risk of impending heart attack or cardiac arrest and with
a communication means, potentially contact emergency services
directly without intervention of the wearer.
[0023] Other features and advantages of the invention will be found
in the detailed description, drawings, and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a drawing of a defibrillation electrode pad
according to the invention, positioned over the chest of a
patient.
[0025] FIG. 2 is a view of the front display panel of a
resuscitation control box according to the invention that houses
electronic circuitry and provides audible and visual prompting.
[0026] FIG. 3 is a cross-sectional drawing of the defibrillation
electrode pad of FIG. 1 taken along line 3-3.
[0027] FIG. 4 is a cross-sectional drawing of the defibrillation
pad of FIG. 1 taken along line 4-4.
[0028] FIG. 5 is a circuit diagram illustrating the circuit
interconnections between the defibrillation electrode pad of FIG. 1
and the resuscitation control box of FIG. 2.
[0029] FIGS. 6A and 6B are a flowchart illustrating the initial
routine of a resuscitation system according to the invention.
[0030] FIGS. 7A, 7B, and 7C are a flowchart illustrating the
"circulation help" routine of the resuscitation system.
[0031] FIG. 8 is a flowchart illustrating the "breathing help"
routine of the resuscitation system.
[0032] FIGS. 9A and 9B are a flowchart illustrating the "airway
help" routine of the resuscitation system.
[0033] FIG. 10 is a block diagram of the electronic circuitry of an
alternative implementation.
[0034] FIG. 11 is a drawing of the defibrillation electrode
assembly of another alternative.
[0035] FIGS. 12A-12C are diagrammatic views of three possible
implementations of first and second units.
[0036] FIGS. 13A and 13B are drawings of two alternative
implementations of the electrode pad assembly in which a handle is
provided for the rescuer.
DETAILED DESCRIPTION
[0037] There are a great many possible implementations of the
invention, too many to describe herein. Some possible
implementations that are presently preferred are described below.
It cannot be emphasized too strongly, however, that these are
descriptions of implementations of the invention, and not
descriptions of the invention, which is not limited to the detailed
implementations described in this section but is described in
broader terms in the claims.
[0038] With reference to FIG. 1, a defibrillation electrode pad 10,
which includes high-voltage apex defibrillation electrode 12 and
high-voltage sternum defibrillation electrode 14, is placed on the
patient's chest 16 and includes a region 18 on which a user may
press to perform CPR. Legends on pad 10 indicate proper placement
of the pad with respect to the patient's collarbones and the chest
centerline and the proper placement of the heel of the rescuer's
hand.
[0039] A low-profile button panel 20 is provided on the electrode
assembly. Button panel 20 has buttons 22, including buttons A
(Airway Help), B (Breathing Help), C (Circulation Help) and PAUSE,
and may also include adjacent light emitting diodes (LEDs) 24 that
indicate which button has been most recently pressed. Button panel
20 is connected by a cable 23 to a remote resuscitation control box
26, shown in FIG. 2. Button panel 20 provides rigid support
underneath buttons A, B, C, and PAUSE against which the switches
can be pushed in order to ensure good switch closure while the
electrode rests on a patient. Button panel 20 includes components
that make electrical contact with silver/silver-chloride electrical
circuit components screen-printed on a polyester base of
defibrillation electrode pad 10, as is described in detail
below.
[0040] A pulse detection system based on shining light through the
patient's vascular bed, e.g., a pulse oximetry system 52, is
incorporated into defibrillation electrode pad 10. Pulse oximetry
system 52 includes a red light-emitting diode, a near-infrared
light-emitting diode, and a photodetector diode (see FIG. 5)
incorporated into defibrillation electrode pad 10 in a manner so as
to contact the surface of the patient's chest 16. The red and
near-infrared light-emitting diodes emit light at two different
wavelengths, which is diffusely scattered through the patient's
tissue and detected by the photodetector diode. The information
obtained from the photodetector diode can be used to determine
whether the patient's blood is oxygenated, according to known
noninvasive optical monitoring techniques.
[0041] In another implementation, the pulse detection system is a
phonocardiogram system for listening to the sound of the victim's
heart, rather than a pulse oximetry system. The phonocardiogram
system includes a microphone and an amplifier incorporated within
the electrode pad. Because a heart sound can be confused with
microphone noise, the signal processing that must be performed by
the microprocessor inside the control box will be more difficult in
connection with a phonocardiogram system than in connection with a
pulse oximetry system. Nevertheless, there are programs available
that can enable the microprocessor to determine whether an ECG
signal is present as opposed to microphone noise.
[0042] Pulse oximetry is a well-developed, established technology,
but it requires good contact between the light sources and the
victim's skin so that light can shine down into the victim's
vascular bed. Many victims have lots of chest hair, which can
interfere with good contact. It may be desirable for different
types of electrode pads to be available at a given location (one
having a pulse oximetry system and one having a phonocardiogram
system) so that a rescuer can select an appropriate electrode pad
depending on the nature of the victim.
[0043] In another implementation, instead of providing a
low-profile button panel, a button housing can be provided that is
affixed to an edge of the defibrillation electrode. The housing may
be in the form of a clamshell formed of single molded plastic
element having a hinge at an edge of the clamshell around which the
plastic bends. The two halves of the clamshell can be snapped
together around the electrode assembly.
[0044] The resuscitation control box (FIG. 2) includes an internal
charge storage capacitor and associated circuitry including a
microprocessor, an further includes off/on dial 28, and a "READY"
button 30 that the rescuer presses immediately prior to application
of a defibrillation shock in order to ensure that the rescuer is
not in physical contact with the patient. The microprocessor may be
a RISC processor such as a Hitachi SH-3, which can interface well
with displays and keyboards, or more generally a processor capable
of handling DSP-type (digital signal processing) operations.
[0045] The resuscitation control box has printed instructions 32 on
its front face listing the basic steps A, B, and C for
resuscitating a patient and giving basic instructions for
positioning the defibrillation electrode pad on the patient. A
speaker 32 orally prompts the user to perform various steps, as is
described in detail below.
[0046] For example, the resuscitation control box instructs the
user, by audible instructions and also through a display 34 on the
resuscitation control box, to check the patient's airway and
perform mouth-to-mouth resuscitation, and if the patient's airway
is still blocked, to press the A (Airway Help) button on the button
panel (FIG. 1), upon which the resuscitation control box gives
detailed prompts for clearing the patient's airway. If the
patient's airway is clear and the patient has a pulse but the
patient does not breathe after initial mouth-to-mouth
resuscitation, the resuscitation control box instructs the user
press the B (Breathing Help) button, upon which the resuscitation
control box gives detailed mouth-to-mouth resuscitation prompts.
If, during the detailed mouth-to-mouth resuscitation procedure, the
rescuer checks the patient's pulse and discovers that the patient
has no pulse, the resuscitation control box instructs the user to
press the C (Circulation Help) button.
[0047] During the circulation procedure, the resuscitation control
box receives electrical signals from the defibrillation electrodes
and determines whether defibrillation or CPR should be performed.
If the resuscitation control box determines that defibrillation is
desirable, the resuscitation control box instructs the user to
press the "ready" button on the resuscitation control box and to
stand clear of the patient. After a short pause, the resuscitation
control box causes a defibrillation pulse to be applied between the
electrodes. If at any point the resuscitation control box
determines, based on the electrical signals received from the
electrodes, that CPR is desirable, it will instruct the user to
perform CPR.
[0048] Thus, the key controls for the system are on the electrodes
attached to the patient rather than the resuscitation control box.
This is important because it enables the rescuer to remain focused
on the patient rather than the control box. The resuscitation
control box gets its information directly from the electrodes and
the controls on the electrodes.
[0049] The resuscitation control box can sense electrical signals
from the patient's body during pauses between CPR compressions.
Also, as is described below, a compression-sensing element such as
an accelerometer or a force-sensing element is provided in the
region of the defibrillation electrode pad on which the user
presses to perform CPR. The purpose of the compression-sensing or
force-sensing element is to allow the resuscitation control box to
prompt the user to apply additional compression or force, or to
prompt the user to cease CPR if the user is performing CPR at an
inappropriate point in time.
[0050] Referring to FIG. 4, in one implementation, each electrode
12, 14 (only electrode 12 is shown) of defibrillation electrode pad
10 includes a polymer-based ink containing a silver/silver-chloride
suspension, which is screen-printed on a polyester or plastic base
36. The ink is used to carry the defibrillation current. The
screen-printing process first involves applying a resist layer to
the polyester base 36. The resist layer is basically a loose mesh
of nylon or the like, in which the holes have been filled in at
some locations in the mesh. Then, the silver/silver-chloride ink is
applied as a paste through the resist layer in a squeegee-like
manner. The ink squeezes through the screen and becomes a solid
layer. The ink may then be cured or dried. The
silver/silver-chloride ink provides good conductivity and good
monitoring capabilities.
[0051] Thus, the ink can be applied as pattern, as opposed to a
solid sheet covering the entire polyester base. For example, U.S.
Pat. No. 5,330,526 describes an electrode in which the conductive
portion has a scalloped or daisy shape that increases the
circumference of the conductive portion and reduces burning of the
patient. A conductive adhesive gel 38 covers the exposed surface of
each electrode.
[0052] In addition, electrical circuit components are also be
screen printed on the base, in the same manner as flat circuit
components of membrane-covered, laminated panel controls.
[0053] Referring to FIG. 3, a rigid piece 40 of hard plastic, such
as PVC or polycarbonate, is laminated beneath substrate 36 and
supports buttons A, B, C, and PAUSE. The rigid plastic piece 40 is
glued onto substrate 36. Buttons A, B, C, and PAUSE consist of
small metal dome snap-action switches that make contact between an
upper conductive ink trace 42 and lower conductive ink traces 44,
46, 48, and 50. Buttons A, B, C, and PAUSE serve as controls that
can be activated by the user that are physically located either on
or immediately adjacent to the electrode assembly itself. Each of
buttons A, B, C, and PAUSE may be associated with an adjacent
light-emitting diode (LED). For example, LEDs may be glued, using
conductive epoxy, onto silver/silver-chloride traces on substrate
36. An embossed polyester laminate layer 54 covers conductive ink
trace 42 of buttons A, B, C, and PAUSE, and a foam layer 56 is
laminated beneath rigid plastic piece 40.
[0054] Referring again to FIG. 4, defibrillation electrode pad 10
includes an extension piece that is placed directly over the
location on the patient's body where the rescuer performs chest
compressions. This extension piece includes substrate 36, and a
semi-rigid plastic supporting member 58 laminated underneath
substrate 36 that covers the chest compression area. Semi-rigid
supporting member 58 provides somewhat less rigidity than rigid
plastic piece 409 provided at the location of buttons A, B, C, and
PAUSE (illustrated in FIG. 3).
[0055] In implementations having a force-sensing element, a
polyester laminate 60, and a force-sensing resistor having two
layers of carbon-plated material 62 and 64, are laminated between
polyester substrate 36 and semi-rigid supporting member 58. A
suitable construction of the force-sensing resistor is illustrated
in the FSR Integration Guide & Evaluation Parts Catalog with
Suggested Electrical Interfaces, from Interlink Electronics. The
electrical contact between the two carbon-plated layers of material
increases with increased pressure, and the layers of force-sensing
resistive material can provide a generally linear relationship
between resistance and force. Conductive ink traces 66 and 68
provide electrical connections to the two layers of the
force-sensing resistor.
[0056] During chest compressions, the rescuer's hands are placed
over the extension piece, and the force-sensing resistor of the
extension piece is used to sense the force and the timing of the
chest compressions. The force-sensing resistor provides information
to the resuscitation control box so that the resuscitation control
box can provide the rescuer with feedback if the rescuer is
applying insufficient force. The resuscitation control box also
provides coaching as to the rate at which CPR is performed. In
certain situations, the resuscitation control box indicates to the
rescuer that CPR should be halted because it is being performed at
an inappropriate time, such as immediately prior to application of
a defibrillation shock when the rescuer's hands should not be
touching the patient, in which case the resuscitation control box
will also indicate that the rescuer should stay clear of the
patient because the patient is going to experience a defibrillation
shock.
[0057] As is noted above, during CPR the rescuer pushes on the
patient's chest through the extension piece in the vicinity of the
electrodes. If the resuscitation control box were to perform
analysis during the chest compressions, the chest compressions
would be likely to affect the sensed electrical rhythm. Instead,
during the pauses between sets of compressions (for example, the
pause after every fifth chest compression), the resuscitation
control box can perform an electrocardiogram (ECG) analysis. The
resuscitation control box might discover, for example, that the
patient who is undergoing CPR is experiencing a non-shockable
rhythm such as bradycardia, in which case the CPR is required in
order to keep the patient alive, but then the resuscitation control
box may discover that the rhythm has changed to ventricular
fibrillation in the midst of CPR, in which case the resuscitation
control box would instruct the rescuer to stop performing CPR so as
to allow the resuscitation control box to perform more analysis and
possibly apply one or more shocks to the patient. Thus, the rescuer
is integrated into a sophisticated scheme that allows complex
combinations of therapy.
[0058] In another implementation, a compression-sensing element
such as an accelerometer may be used in place of a force-sensing
element. The accelerometer, such as a solid-state ADXL202
accelerometer, is positioned at the location where the rescuer
performs chest compressions. In this implementation, the
microprocessor obtains acceleration readings from the accelerometer
at fixed time intervals such as one-millisecond intervals, and the
microprocessor integrates the acceleration readings to provide a
measurement of chest compression. The use of an accelerometer is
based on the discovery that it is more important to measure how
deeply the rescuer is compressing the chest than to measure how
hard the rescuer is pressing. In fact, every victim's chest will
have a different compliance, and it is important that the chest be
compressed about an inch and a half to two inches in a normal sized
adult regardless of the victim's chest compliance.
[0059] FIG. 5 is a circuit diagram illustrating the circuit
interconnections between the defibrillation electrode pad of FIG. 1
through the cable to the resuscitation control box of FIG. 2.
Sternum electrode 14 is connected to HV+ at the resuscitation
control box, and apex electrode 12 is connected to HV-. A ground
GND is connected to the upper conductive ink trace of buttons A, B,
C, and PAUSE and to one of the layers of the force-sensing
resistor. The other layer of the force-sensing resistor is
connected to CPR_FORCE, and the lower conductive ink traces
associated with buttons A, B, C, and PAUSE are connected to
BUTTON_DETECT through resistors R1, R2, R3, and R4. As an
alternative to the use of a force-sensing resistor, a
compression-sensing accelerometer 76 may be employed, in which case
CPR_FORCE is replaced by CPR_ACCEL connected to accelerometer 76.
Red light-emitting diode 70, near-infrared light-emitting diode 72,
and photodetector diode 74 of the pulse oximetry system are
connected to RLED, ILED, and ISENSE respectively, as well as ground
AGND. As an alternative to the use of a pulse oximetry system, a
phonocardiogram system may be employed, in which case RLED, ILED,
and ISENSE is replaced by SENSE connected to microphone 78 and
amplifier 80.
[0060] FIGS. 6-9 illustrate the routine of the resuscitation
system, which is based on steps A, B, and C (airway, breathing, and
circulation). Because step C includes defibrillation as well as
chest compressions, all of the aspects of resuscitation are tied
together in one protocol (actually, if defibrillation were
considered to be a step D distinct from step C, the sequence of
steps would be A, B, D, C).
[0061] The first thing the rescuer must do upon arriving at the
patient is to determine whether the patient is unconscious and
breathing. The rescuer opens the patient's airway, administers
breaths to the patient if the patient is not breathing, and checks
to determine whether a pulse is present. If there is no pulse,
rather than perform chest compressions as in standard CPR, the
rescuer allows the resuscitation control box to analyze the
patient's electrical rhythm, and if the resuscitation control box
determines that the rhythm is shockable, the resuscitation control
box causes one or more shocks to be applied to the patient, and
then the rescuer performs chest compressions. Thus, there is
provided a first response system that can keep the patient viable
until an advanced life support time arrives to perform advanced
techniques including pacing, further defibrillation, and drug
therapy.
[0062] If the resuscitation control box determines that it should
apply one or more defibrillation shocks to the patient, it is
important that the rescuer not be anywhere near the patient when
the shocks are applied to the patient. Prior to application of each
shock, the resuscitation control box instructs the rescuer to
please press the "ready" button when everybody is clear of the
patient. The pressing of the "ready" button verifies that the
rescuer's hands are off of the patient.
[0063] When the resuscitation control box detects a shockable
rhythm, the resuscitation control box provides shocks of
appropriate duration and energy (such as a sequence of shocks of
increasing energy from 200 Joules to 300 Joules to the highest
setting, 360 Joules, with the resuscitation control box performing
analysis after each shock to determine whether another shock is
required). If the defibrillation therapy is successful, the
patient's rhythm is typically converted from ventricular
fibrillation, ventricular tachycardia, or ventricular flutter to
bradycardia, idio-ventricular rhythm, or asystole, all of which
require CPR. It is rare to convert to a normal rhythm. Once the
resuscitation control box has caused defibrillation shocks to be
applied to the patient, the resuscitation control box automatically
senses the patient's condition, and depending on the patient's
condition will either prompt the responder to perform CPR or will
not prompt the respond to perform CPR.
[0064] Defibrillation equipment can be somewhat intimidating to
rescuers who are not medical professionals because the equipment
can lead the rescuer to feel responsibility for having to save a
loved one's life. It is important that the defibrillation equipment
reduce this sense of responsibility. In particular, when the
rescuer presses the "ready" button, rather than apply a shock
immediately that will cause the patient's body to jump
dramatically, the resuscitation control box will thank the rescuer
and instruct the rescuer to remain clear of the patient and then
wait for about two seconds (the resuscitation control box may
describe this period to the rescuer as being an internal safety
check, even if no substantial safety check is being performed).
This process has an effect similar to a conversation that hands
responsibility to the resuscitation control box, which makes the
decision whether to apply the shock. Thus, the system maintains the
rescuer safety features of a semi-automatic external defibrillator,
because the rescuer must press the "ready" button before each
shock, while appearing to operate more as a fully automatic
external defibrillator because the time delay immediately prior to
each shock leaves the rescuer with the impression that operation of
the equipment is out of the hands of the rescuer. The use of CPR
prompts in combination with the defibrillation also adds to the
sense that the rescuer is simply following instructions from the
resuscitation control box.
[0065] With reference to FIGS. 6-9, when the rescuer turns the
resuscitation control box on (step 101), the resuscitation control
box first informs the rescuer that the rescuer can temporarily halt
prompting by pressing the PAUSE button (step 102), and then, after
a pause, instructs the rescuer to check responsiveness of patient,
and if the patient is non-responsive to call an emergency medical
service (EMS) (steps 103, 104). The resuscitation control box then
instructs the rescuer to check the patient's airway to determine
whether the patient is breathing (steps 105-107).
[0066] After a pause, the resuscitation control box then instructs
the rescuer that if the patient is breathing the patient should be
placed on the patient's side, unless trauma is suspected, and that
the rescuer should press the PAUSE button (steps 108-109). Then the
resuscitation control box instructs the rescuer to perform
mouth-to-mouth resuscitation if the patient is not breathing (steps
110-114). Then the resuscitation control box instructs the rescuer
to press an Airway Help button A if the patient's airway is
blocked, so that the resuscitation control box can give prompts for
clearing obstructed airways (steps 115 of FIG. 6B and 147-158 of
FIGS. 9A-9B).
[0067] Next, after a pause (step 116a), if the resuscitation
control box does not include pulse oximetry or phonocardiogram
capability (step 116b), the resuscitation control box instructs the
rescuer to check the patient's pulse (step 117). After another
pause, the resuscitation control box instructs the rescuer to press
a Breathing Help button B if the patient's pulse is okay but the
patient is not breathing, so that the resuscitation control box can
give prompts for assisting the patient's breathing (steps 118 and
119 of FIG. 7A and 140-146 of FIG. 8). Light-emitting diodes
adjacent the various buttons indicate which button has been pressed
most recently (only one light remains on at a time). The
resuscitation control box next prompts the rescuer to contact an
emergency medical system (step 120) and to open the patient's shirt
or blouse and attach the adhesive pads (steps 122f-122h).
[0068] If the resuscitation control box does include pulse oximetry
or phonocardiogram capability (step and 116b), the resuscitation
control box prompts the rescuer to open the patient's shirt or
blouse and attach the adhesive pads (steps 121 and 122a). If the
pulse oximetry or phonocardiogram system does not provide a valid
pulsatile reading (step 122b), then the flow chart proceeds to step
117. If the pulse oximetry or phonocardiogram system does provide a
valid pulsatile reading and detects a pulse (steps 122b and 122c),
then the resuscitation control box begins the breathing help
routine (steps 122d of FIG. 7B and step 140 of FIG. 8). If the
pulse oximetry or phonocardiogram system does not detect a pulse,
then the resuscitation control prompts the rescuer to contact an
emergency medical system (step 122e), measures the impedance of the
patient to determine whether it is within an acceptable range for
application of shocks (step 123) and determines whether the
patient's rhythm is shockable (steps 124). If the rhythm is
shockable, the resuscitation control box causes a sequence of
shocks to be applied to the patient, each shock requiring the
rescuer first to press the "READY" button on the resuscitation
control box (steps 124-131). After the last shock in the sequence,
or if the rhythm is non-shockable, the resuscitation control box
prompts the rescuer in CPR (steps 132-139). The flowchart then
returns to step 117.
[0069] FIG. 8 shows the steps 140-146 for prompting the rescuer to
assist the patient's breathing. After 12 breaths have been
completed (step 144), the pulse oximetry or phonocardiogram system
attempts to detect a pulse (step 145a), or, if the system does not
include a pulse oximetry or phonocardiogram system, the
resuscitation control box prompts the rescuer to check the
patient's pulse. If no pulse is present, the resuscitation control
box prompts the rescuer to press a Circulation Help button C (step
145b) that brings the rescuer back to the circulation portion of
the flowchart. Otherwise, if a pulse is detected, then the flow
chart of FIG. 8 returns to step 142.
[0070] The combined defibrillation and CPR resuscitation assembly
provided can be less intimidating than conventional AEDs because
the assembly is not devoted solely to defibrillation. Moreover, the
resuscitation assembly is less intimidating because it accommodates
common skill retention problems with respect to necessary
techniques ancillary to defibrillation such as mouth-to-mouth
resuscitation and CPR, including the appropriate rates of chest
compression, the proper location for performing compressions, the
proper manner of tilting the patient's head. In addition, because
the rescuer knows that it may never even be necessary to apply a
defibrillation shock during use of the resuscitation assembly, the
rescuer may be more comfortable using the resuscitation assembly
for mouth-to-mouth resuscitation and CPR. Unlike previous CPR
prompting devices, the rescuer would be required to place the
electrode assembly on top of the patient, but the rescuer would do
this with the belief that the resuscitation assembly will be
sensing the patient's condition and that the likelihood that the
resuscitation assembly is actually going to apply a shock is low.
If, during this resuscitation process, the resuscitation control
box instructs the rescuer to press the "READY" button so that a
defibrillation shock can be applied, the rescuer will likely feel
comfortable allowing the shock to be applied to the patient.
Basically, the resuscitation assembly simply tells the rescuer what
to do, and by that point, given that the rescuer is already using
the assembly, the rescuer is likely simply to do what the rescuer
is told to do. Essentially, the rescuer will be likely to view the
resuscitation assembly as simply being a sophisticated CPR
prompting device with an additional feature incorporated into it,
and since rescuers are less likely to be intimidated by CPR
prompting devices than AEDs, they will be likely to use the
resuscitation assembly when it is needed.
[0071] FIGS. 10, 11, and 12A-12C show alternative implementations
in which an electrode pad assembly 10 is connected by a cable 212
to a first unit 214 containing the electronics for CPR prompting
and resuscitation control. Another cable 216 connects the first
unit to a second unit 218 containing the electronics for
defibrillation and pacing therapy. A third cable 220 could be
provided for making a direct connection from the second unit to the
electrodes (FIG. 12B). The first unit 214 could be configured to
receive the second unit 218 as an inserted module (FIG. 12C), in
which case the electrical connection between the units are made
internally without the use of cable 216. The primary function of
the first unit 214 is to provide processing and control for CPR
functions such as CPR prompts. The primary function of the second
unit 218 is to provide processing and control of electrical therapy
functions. The first unit includes a CPR processor 170, a battery
178, ECG circuitry 177 for amplifying and filtering the ECG signal
obtained from the defibrillation pads 12, 14, a microphone 78 for
recording the rescuer's voice as well as ambient sounds, an
accelerometer 76, a real time clock 187, and a speaker 182 for
delivering prompts to the rescuer. The second unit includes a
therapy processor 171, a battery 179, buttons and controls 180, and
memory 191.
[0072] The first unit could also be incorporated into the electrode
pad assembly rather than being a separate box. The electronics
could be provided on the rigid substrate 40 of the electrode pad
assembly (FIG. 1).
[0073] Separate batteries 178, 179 and controls 180, 181 may be
provided for the first (CPR) and second (therapy) units, thereby
allowing the electronics in the first unit to provide CPR prompting
to the operator without the need for the second unit. The cable 216
that connects the first and second units may be detachable. Memory
189 is provided in the first unit for storing information such as
voice recording, ECG data, chest compression data, or electronic
system status such as device failures that occur during daily self
checks of the electronics initiated by a real time clock
circuit.
[0074] The defibrillation electrode pad assembly 10 may incorporate
defibrillation electrodes composed of a material that can be held
against a patient's skin for extended periods of time (e.g., up to
30 days).
[0075] As shown in FIGS. 13A and 13B, the pad assembly 10 may also
incorporate features on its upper surface facing the rescuer that
provide a handle 195 for the rescuer during performance of CPR. The
handle could take the form of a fabric loop (FIG. 13B) or a more
rigid polymer member (FIG. 13A). The fabric could be sewn or
adhered by adhesive or ultrasonic bonding to the pad 10 (FIG. 13B).
The polymer handle could also be bonded by adhesive or ultrasonic
bonding to the pad (FIG. 13A). It has been shown in studies that
the maintenance of pressure on the chest during the decompression
phase of chest compression results in a significant decrease in the
effectiveness of the chest compressions. The handle 195 motivates
the rescuer to pull up at least slightly during the decompression
phase. The adhesive gel of the electrode pad, or other adhesive,
can extend under the region where the rescuer's hands are placed
during compression thus providing adhesion of the pad to the skin
while the rescuer pulls on the handle during the decompression
phase. Pulling up on the chest during the decompression phase has
been shown to heighten negative intrathoracic pressure, increasing
venous return and thus increasing blood flow during chest
compressions.
[0076] In another implementation, the first unit may be adapted to
be supported by the patient for long periods of time. The unit
could be incorporated into the electrode pad assembly as suggested
above, or it could be a separate unit configured to be worn by the
patient. In such an implementation, the electronics of the first
unit are designed to allow for long term monitoring of the
patient's condition via the ECG 177 and physiological monitoring
176 circuitry. If a physiological condition is detected that is
deemed hazardous to the patient by the CPR processor 170, based on
analysis of the ECG and other physiological parameters, an alarm is
sounded to the patient via the speaker 182.
[0077] An activity sensor and associated circuitry can inform the
CPR processor of whether the patient is moving. For example,
accelerometer 76 could serve as the activity sensor, and detect
whether or not the patient is moving. Patient motion may be
detected using a variety of different algorithms, including, for
example the following: The acceleration signal is integrated over
one-second intervals to provide an estimate of velocity. Velocity
is integrated over the same one-second intervals to provide an
estimate of displacement. The root means square velocity is
calculated for each one-second interval. If either the RMS velocity
exceeds 0.2 cm/s or the peak displacement exceeds 0.5 cm, the
patient is determined to be moving.
[0078] If the algorithm determines that a cardiac emergency event
is occurring, the first unit can send a message directly to a
medical emergency response system, such as 911. This can be done
using a variety of known communication techniques, e.g., Bluetooth,
cellular phone, Ultra Wideband (UWB). If the activity sensor has
determined that the patient is still moving during the cardiac
emergency, the unit could also issue a prompt indicating, "Call 911
Immediately!"
[0079] The first unit will be able to determine the orientation of
the patient, e.g., based on the accelerometer output. It can detect
if a patient has fallen down and initiate a message to the
emergency system. It can also determine whether the patient is
lying on his back, the proper orientation for doing CPR. Thus, a
specific prompt can be provided to the rescuer that tells them to
roll the patient on their back prior to beginning CPR, should the
device detect an improper orientation of the patient.
[0080] Other implementations may include signal analysis software
for predicting the risk of a heart attack. When a threshold is
exceeded in the value of that risk probability, a voice prompt may
be provided to the patient via the speaker 182 to contact the
medical emergency system. By using the motion detection
capabilities of the accelerometer to measure and track a patient's
activity level (PAL), and combining the activity level calculation
with measurements of the ECG 177, e.g., ST-segment elevation (STE),
the first unit is able to provide a predictor of the risk of an
impending heart attack or cardiac arrest. An ST segment elevation
exceeding a threshold such as 300 microvolts on the ECG provides an
indicator of impending heart attack. In the preferred embodiment,
ST segment elevation in the presence of increased physical activity
is an indication of further risk of potential cardiac arrest. The
calculation of risk probability may be accomplished by first
performing a logistic regression of variables such as STE and PAL
as predictors of cardiac arrest within 24 hours. The calculation
may take the form of a linear regression equation such as
0.24 STE+0.12 PAL=RISK.
Alternatively, nonlinear regression may be performed to allow for a
multiplicative term such as
0.24 STE+0.12 PAL+0.54(STE*PAL)=RISK.
The multiplicative term heightens the importance of STE in the
presence of PAL.
[0081] Parameters such as STE, PAL and RISK may additionally be
stored in memory and multiple readings and calculations performed
over time. The sequence of readings may then be analyzed for trends
in the physiological state of the patient that can augment the RISK
calculation taken at a single point in time. For instance, if STE
is found to be steadily rising over a series of readings, the voice
prompt may be triggered sooner than at a fixed threshold of 300
microvolts.
[0082] Additionally, the ECG may be analyzed to determine the
interval between adjacent R-waves of the QRS complexes and using
this interval to calculate heart rate variability as a running
difference between adjacent R-R intervals. It is known that the R-R
interval will vary following an ectopic beat or ventricular
premature contraction (VPC). In a healthy heart, the R-R interval
will decrease immediately following the VPC followed by a gradual
return to steady state; a heart with an increased risk of heart
attack will show a decreased level of variability. This effect is
sometimes called heart rate turbulence. Two variables are
calculated: (1) the Relative Change in R-R interval (RCRR) between
pre- and post-VPB R-R intervals,
RCRR=(R-R pre-VPB-R-R post-VPB)/R-R pre-VPB
and (2) the slope of the change of R-R interval (SRR) while it is
undergoing its post-VPB decrease. If the RCRR is non-negative and
the slope SRR does not steeper than -2 ms/R-R interval then the
patient is considered as at risk. Alternatively, the individual
calculations may be included along with STE and PAL to create an
integrated measurement vector as discussed in the preceding
paragraphs. Other signal analysis algorithms may incorporate
analysis of heart rate variability in the frequency domain, wavelet
domain or using non-linear dynamics-based methods.
[0083] Since VPBs are often rare events, the defibrillation
electrode pad 10 may include circuitry to stimulate the patient
with a single pulse of low enough amplitude to cause a VPB without
undue discomfort to the patient, under the patient's control. An
additional control is provided on the low-profile button panel 20
so that the patient may initiate the pulse under their control.
Alternatively, the device is programmed to automatically deliver
the pulse at regular intervals such as at 24-hour intervals, at a
time of day when the patient may conveniently have access to the
device, such as in the morning. While the pulse generator 186 may
be located in the second (therapy) unit, it is preferably contained
as part of the first (CPR) unit.
[0084] In another implementation, the activity monitoring
capability of the first unit may be utilized so that the activity
state of the patient is continuously monitored. Using the activity
monitoring capability and a real time clock 187, the first unit may
detect when a patient has woken up in the morning. After there has
been 10 minutes of regular motion detected, the unit may prompt the
patient that it would like to perform a test. If the patient
assents to the test indicated by a press of the TEST button on the
low-profile button panel 20, the unit will send out a small current
pulse, preferably a 40 millisecond pulse of 75 mA amplitude that is
synchronized to the patient's ECG so that it occurs approximately
200 mS prior to the R-wave and after the T-wave so as not to
introduce any arrhythmias. The pulse will safely cause a VPB in the
patient which can then be used to measure the autonomic response to
a VPB to provide regular calculations of the autonomic response to
a VPB as measured by such parameters, though not limited to, STE
and PAL, and providing a daily update to the RISK calculation.
[0085] Additional physiological measurement, preferably that of
blood pressure, may be incorporated into the RISK calculation. A
sudden change in systolic or mean arterial blood pressure of
greater than 10-15 points is indicative of an increased risk of
cardiac arrest. In the preferred embodiment, the blood pressure
measurement device would be a handheld, inflated cuff blood
pressure device 188. The blood pressure cuff 188 would have
wireless communication capability with the CPR Processor 170 and at
the conclusion of each measurement, the blood pressure reading
along with a date and time stamp would be stored in memory 189 of
the CPR Processor 170 for subsequent use in calculating RISK. This
scheme would allow the patient to carry the small blood pressure
cuff along with them during their daily activities and take blood
pressure measurements at regular intervals without having to return
home. Alternatively, the blood pressure measurement device may
communicate with the therapy processor and may additionally get
power from and be physically connected to the second (therapy) unit
by a cable. The patient will then be required to take regular blood
pressure readings at the second unit, typically a larger device
that may or may not be portable. Communication of the blood
pressure readings may be accomplished over a cable between the
first (CPR) and second units (therapy) units, e.g., cable 216, or
wirelessly, using such technology as Bluetooth.
[0086] The second unit 218 may in some implementations be thought
of as an energy delivery unit (EDU), in which case it would
incorporate a defibrillator 172, pacer 173, or other electrical
therapy 174. In some implementations, the EDU would be small and
light enough to be worn in a harness or belt to be carried around
continuously by the patient. The EDU 218 may in some cases not
contain a therapy processor 171, but be a "dumb" device that
requires the controls provided by connection to the processor in
the first (CPR) unit, e.g., on the defibrillator pad 10, in order
to deliver electrical therapy to the patient.
[0087] In some cases, the patient may not even own an EDU due to
the significant costs inherent in the high-voltage components
necessary. The patient would only own the first unit and
defibrillator pad, as the components incorporated in them are less
expensive, e.g., they can be manufactured from less-expensive,
consumer-type electronics. In such a case, when the patient did not
own the EDU, and had a heart attack, a bystander or family member
who encountered the cardiac arrest victim would be prompted to
begin CPR. It has been shown now in several studies that performing
good CPR for extended periods prior to delivery of a shock are not
only not detrimental to long term survival, but in fact increase
survival rates. CPR would thus begin with built-in prompting and
when the paramedic arrives with the defibrillator it can be
connected to the pads to deliver the electrical therapy. If the
first (CPR) unit is separate from the electrode pad assembly, the
EDU connection to the electrodes could be direct, or via a cable
connected to the first (CPR) unit. If the defibrillator is an EDU
or other compatible device, patient and performance data stored by
the first (CPR) unit may be downloaded to the defibrillator.
[0088] Many other implementations of the invention other than those
described above are within the invention, which is defined by the
following claims. For example, the defibrillation pads 10, 12 may
be separable from the CPR-prompting first unit and be connected at
the time that the EDU is brought to the scene; the defibrillation
pads may be connected both electrically and mechanically to the
CPR-prompting first unit at that time. A greater amount of the
control functionality may be put into the first unit, leaving
essentially only the circuitry for providing the defibrillation
pulses in the second unit. The first unit may be incorporated into
the defibrillation electrode pad assembly, or made a separate unit
connected to the pad assembly by one or more cables. The second
unit may connect to the first unit by one or more cables, or by a
wireless connection. The defibrillation pulses may pass through the
first unit (FIG. 12A), or be routed directly to the defibrillation
electrodes via one or more cables running from the second unit to
the electrodes (FIG. 12B). The second unit may connect to the first
unit by being plugged into the first unit (FIG. 12C), without the
need for a cable (e.g., the second unit could be a defibrillation
module that plugs into the first unit).
[0089] In some implementations the second (therapy) unit can
provide pacing therapy as well as defibrillation therapy. Pulse
detection methods other than pulse oximetry and phonocardiogram may
be employed. Any method capable of detecting a victim's pulse can
be used for pulse detection.
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