U.S. patent application number 13/874372 was filed with the patent office on 2014-10-30 for compression depth monitor with variable release velocity feedback.
This patent application is currently assigned to ZOLL Medical Corporation. The applicant listed for this patent is ZOLL Medical Corporation. Invention is credited to Guy R. Johnson.
Application Number | 20140323928 13/874372 |
Document ID | / |
Family ID | 51789817 |
Filed Date | 2014-10-30 |
United States Patent
Application |
20140323928 |
Kind Code |
A1 |
Johnson; Guy R. |
October 30, 2014 |
Compression Depth Monitor with Variable Release Velocity
Feedback
Abstract
A system for facilitating the effective administration of
cardiopulmonary resuscitation (CPR) by providing feedback regarding
release velocity, which is the velocity of the chest while
resiliently expanding during the upstroke of a CPR compression
cycle. The feedback is provided, indicating whether the CPR
provider has substantially released the chest, through a control
systems which analyzes sensor input corresponding to chest
displacement to determine chest compression depth and release
velocity, compares the determined release velocity to a desired
release velocity threshold. The desired release velocity is
determined based on the depth of compression. The desired release
velocity may be determined based on assumed or target compression
depth, selected by a CPR provider and input into the control
system, or the desired release velocity may be determined
adaptively, based on the chest compression depth achieved during
compressions and/or the rate of compressions, as determined by the
control system.
Inventors: |
Johnson; Guy R.;
(Chelmsford, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ZOLL Medical Corporation |
Chelmsford |
MA |
US |
|
|
Assignee: |
ZOLL Medical Corporation
Chelmsford
MA
|
Family ID: |
51789817 |
Appl. No.: |
13/874372 |
Filed: |
April 30, 2013 |
Current U.S.
Class: |
601/41 |
Current CPC
Class: |
A61H 2201/5043 20130101;
A61H 2201/5064 20130101; A61H 2201/5007 20130101; A61H 2201/5084
20130101; A61H 31/007 20130101; A61N 1/3993 20130101; A61H
2201/5079 20130101; A61H 2201/5092 20130101; A61H 31/005
20130101 |
Class at
Publication: |
601/41 |
International
Class: |
A61H 31/00 20060101
A61H031/00 |
Claims
1. A system for facilitating the effective administration of
cardiopulmonary resuscitation (CPR), said system comprising: a
housing or other structure adapted to be held in fixed relationship
to the chest of a CPR recipient during chest compressions; a sensor
connected to the housing or other structure, the sensor operable to
provide at least one signal corresponding to motion of the chest;
an output device for providing prompts to a CPR provider; and a
control system operable to receive a signal corresponding to motion
of the chest, said control system programmed to determine the depth
of compressions from a signal corresponding to motion of the chest,
and determine release velocity during a release portion of a CPR
compression cycle from a signal corresponding to motion of the
chest, and programmed to determine whether the CPR provider is
substantially releasing the chest following chest compressions; and
further programmed to operate the output device to provide the CPR
provider with information as to whether the chest is being
substantially released following chest compressions; wherein the
control system is programmed to determine whether the CPR provider
has substantially released the chest based on a desired release
velocity threshold, and is further programmed to determine the
desired release velocity based on the depth of compression.
2. The system of claim 1 wherein the control system is programmed
to determine whether the CPR provider has substantially released
the chest based on a desired release velocity threshold, and is
further programmed to determine the desired release velocity
adaptively, based on the determined depth of compression.
3. The system of claim 1 wherein the control system is programmed
to determine the desired release velocity based on the compression
depth determined for a single compression.
4. The system of claim 1 wherein the control system is programmed
to determine the desired release velocity based on the compression
depth determined for a series of chest compressions.
5. The system of claim 1 wherein the control system is programmed
to determine the desired release velocity based on the compression
depth determined for a series of chest compressions, and compare
the average release velocity achieved over said series of
compressions to the desired release velocity to determine whether
the CPR provider is substantially releasing the chest following
compressions.
6. The system of claim 2 wherein the control system is programmed
to determine whether the CPR provider is substantially releasing
the chest following compressions based on the average release
velocity.
7. The system of claim 2 wherein the control system is programmed
to determine whether the CPR provider is substantially releasing
the chest following compressions based on the peak release velocity
determined during the release portion of the CPR compression
cycle.
8. The system of claim 2 wherein the control system is programmed
to determine whether the CPR provider is substantially releasing
the chest following compressions based on the average release
velocity determined during a window of time in the release portion
of the CPR compression cycle.
9. The system of claim 1 wherein the control system is programmed
to determine the desired release velocity based on the compression
rate, in addition to the determined compression depth.
10. The system of claim 1 wherein the sensor comprises an
accelerometer operable to sense acceleration of the chest and
provide acceleration signals corresponding to acceleration of the
chest, and the control system is programmed to determine the depth
of compressions from the acceleration signals and determine release
velocity from the accelerations signals.
11. The system of claim 1 wherein the sensor comprises an velocity
sensor operable to sense velocity of the chest and provide velocity
signals corresponding to the velocity of the chest, and the control
system is programmed to determine the depth of compressions from
the velocity signals and determine release velocity from the
velocity signals.
12. The system of claim 1 wherein the sensor comprises an
displacement sensor operable to sense displacement of the chest and
provide displacement signals corresponding to the displacement of
the chest, and the control system is programmed to determine the
depth of compressions from the displacement signals and determine
release velocity from the displacement signals.
13. The system of claim 1 wherein the control system is programmed
to determine whether the CPR provider has substantially released
the chest based on a desired release velocity threshold, and is
further programmed to determine the desired release velocity based
on the target depth of compression, where the control system
further programmed to accept input from a user regarding the target
depth of compression as assessed at the time CPR is provided.
14. The system of claim 13 wherein the control system is programmed
to compare the average release velocity achieved over a series of
compressions to the desired release velocity to determine whether
the CPR provider is substantially releasing the chest following
compressions.
15. The system of claim 13 wherein the control system is programmed
to determine whether the CPR provider is substantially releasing
the chest following compressions based on the average release
velocity.
16. The system of claim 13 wherein the control system is programmed
to determine whether the CPR provider is substantially releasing
the chest following compressions based on the peak release velocity
determined during the release portion of the CPR compression
cycle.
17. The system of claim 13 wherein the sensor comprises an
accelerometer operable to sense acceleration of the chest and
provide acceleration signals corresponding to acceleration of the
chest, and the control system is programmed to determine the depth
of compressions from the acceleration signals and determine release
velocity from the accelerations signals.
18. The system of claim 13 wherein the sensor comprises an velocity
sensor operable to sense velocity of the chest and provide velocity
signals corresponding to the velocity of the chest, and the control
system is programmed to determine the depth of compressions from
the velocity signals and determine release velocity from the
velocity signals.
19. The system of claim 13 wherein the sensor comprises an
displacement sensor operable to sense displacement of the chest and
provide displacement signals corresponding to the displacement of
the chest, and the control system is programmed to determine the
depth of compressions from the displacement signals and determine
release velocity from the displacement signals.
20. A method for facilitating the effective administration of
cardiopulmonary resuscitation (CPR), said method comprising:
operating a sensor for generating a signal corresponding to motion
of a cardiac arrest victim's chest to determine motion of the
cardiac arrest victim's chest during CPR chest compressions;
operating a control system with an output device, wherein said
control system is operable to receive a signal corresponding to
motion of the chest, said control system programmed to determine
the depth of compressions from a signal corresponding to motion of
the chest, and determine release velocity during a release portion
of a CPR compression cycle from a signal corresponding to motion of
the chest, and programmed to determine whether the CPR provider is
substantially releasing the chest following chest compressions; and
further programmed to operate the output device to provide the CPR
provider with information as to whether the chest is being
substantially released following chest compressions; wherein the
control system is programmed to determine whether the CPR provider
has substantially released the chest based on a desired release
velocity threshold, and is further programmed to determine the
desired release velocity based on the depth of compression; and
providing, through the output device, a prompt to the CPR provider
whether the chest is being substantially released following chest
compressions.
Description
FIELD OF THE INVENTIONS
[0001] The inventions described below relate to the field of
CPR.
BACKGROUND OF THE INVENTIONS
[0002] Chest compression monitoring during the course of CPR is now
possible with the Real CPR Help.RTM. and CPR-D-padz technology
marketed by ZOLL Medical Corporation. This technology is described
in U.S. Pat. Nos. 6,390,996, 7,108,665, and 7,429,250, and includes
the use of an accelerometer to measure accelerations of the chest
and calculating the depth of each compression from the acceleration
signal. The technology is used in ZOLL's Real CPR Help.RTM.
compression depth monitoring system to provide real-time rate and
depth CPR feedback for manual CPR providers. Commercially, it is
implemented in ZOLL's electrode pads, such as the
CPR-D.cndot.Padz.RTM. electrode pads. It is also implemented for
training use in the PocketCPR.RTM. chest compression monitor and
PocketCPR.RTM. iPhone app.
[0003] Halperin, et al., CPR Chest Compression Monitor, U.S. Pat.
No. 6,390,996 (May 21, 2002), as well as Palazzolo, et al., Method
of Determining Depth of Chest Compressions During CPR, U.S. Pat.
No. 7,122,014 (Oct. 17, 2006), described chest compression monitors
capable of determining chest compression depth accurately during
repeated rapid chest compressions required by CPR. The devices of
Halperin and Palazzolo were adapted to be placed between the CPR
provider's hand and the patient's sternum during CPR. In both
cases, the CPR chest compression monitor is held in fixed
relationship to the chest during use, and the chest compression
module is operable to determine the depth of each chest compression
based on acceleration data from accelerometers in the chest
compression module, without input from other sources, especially
without input of data from other sensors fixed in space or remote
from the compression module. The disclosures of U.S. Pat. Nos.
6,390,996, 7,108,665, and U.S. Pat. No. 7,429,250 to Halperin, and
U.S. Pat. No. 7,122,014 to Palazzolo are hereby incorporated by
reference.
[0004] Geheb, et al., Method and Apparatus for Enhancement of
Compressions During CPR, U.S. Pat. No. 7,720,235 (May 22, 2007)
provides an enhancement a CPR chest compression monitor. In
addition to providing feedback regarding depth of compression, this
system measures or computes the velocity of the chest compression
module, and compare the upward velocity of the chest compression
module with a predetermined desired velocity. The system advises,
through a display or audio prompt, whether the CPR provider is
substantially releasing the chest from compression, or failing to
do so. The disclosure of U.S. Pat. No. 7,720,235 is hereby
incorporated by reference. Complete release ensures that that the
thorax of the CPR victim will expand without hindrance of the CPR
provider's weight on the chest, and encourage (or at least avoid
hindering) the creation of negative pressure in the chest which
encourages venous return and filling of the heart.
[0005] The techniques of Halperin, Palazzolo and Geheb are
accomplished by various ZOLL defibrillator systems which include
and AED box and compression modules (the compression modules are
combined with sensing and defibrillating electrodes in a convenient
sheet which facilitates proper placement (see FIG. 2). In these
systems, a compression monitor which includes accelerometers to
sense movement is secured to the patients chest. The CPR provider
pushes down on the patient's chest while the compression monitor is
trapped between the CPR provider's hands and the patient's chest,
so that it generates acceleration signals that correspond to the
acceleration of the patient's chest. The AED box includes a control
system, a display and speaker, and a defibrillator. The control
system (a computer) is programmed to interpret the acceleration
signals calculate compression depth and velocity (specifically,
release velocity), and generate visual displays and/or audio
prompts to be displayed or played to guide the CPR provider. (The
control system also analyzes ECG signals obtained from the
electrodes, to determine if defibrillating shock should be applied,
and may prompt the user to apply shock or automatically operate the
defibrillator to apply shock to the patient.) The control system
comprises at least one processor and at least one memory including
program code with the memory and computer program code configured
with the processor to cause the system to perform the functions
described throughout this specification.
[0006] As currently implemented, the system provides positive or
negative feedback regarding release velocity based on a
predetermined desirable release velocity of 300 inches (762 cm) per
minute, which corresponds to an assumed compression depth of 1.5
inches (38.1 cm).
[0007] The threshold of release velocity used to determine whether
actual release velocity achieved during CPR is determined through
clinical experience, and the systems described above use a single
set threshold, programmed into the control system. In some cases,
it is desirable to provide greater release velocity, or acceptable
to achieve lesser release velocity. For instance, where compression
depth achieved is significantly greater than the desired 2 to 2.5
inches (5.08-6.35 cm), it is desirable to release the chest more
quickly than is the case for compressions of standard depth, and
for compressions of lesser depth, it may be acceptable to release
the chest with a lower release velocity.
SUMMARY
[0008] The devices and methods described below provide for feedback
regarding release velocity of CPR chest compressions based on a
user-entered compression depth target or the measured depth of
compression. The system may be enhanced in that feedback based on
release velocity is based on preconfigured release velocity values
corresponding to assumed or desired depth targets, as determined by
the CPR provider. For example, the CPR provider may enter a desired
target depth of 1.5, 2.0 or 2.5 inches (3.81, 5.08 or 6.35 cm), and
the control system will operate to provide feedback which varies
according to the selected depth. The CPR compression depth
monitoring system, and the method accomplished by the system, may
also be enhanced in that feedback based on release velocity is
based on the measured depth of compression. The control system is
programmed to adaptively determine the depth of compression, or a
moving average of depth of compression for a series of
compressions, and determine the release velocity of a compression,
or a moving average of release velocity for the series of
compressions, and determine, based on the actual compression depth,
the desired release velocity threshold, and advise the CPR provider
with feedback as to whether or not the achieved release velocity
meets the release velocity desired for particular depth of
compression. The system is adaptive, in the sense that it is
programmed to make adjustments in the threshold in response to
changes in the actual performance of the chest compression depth
and/or rate during the course of CPR on each cardiac arrest
victim.
[0009] The system can be implemented with accelerometer-based
compression monitors, or compression monitors based on other
sensing and measuring devices, such a velocity sensors, optical
sensors, magnetic sensors, or any other sensor or combination of
sensors that provide signals corresponding to movement of the chest
(the anterior surface of the thorax) of the CPR victim.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 illustrates the use of a chest compression monitor in
use on a patient, with a rescuer providing manual chest
compressions.
[0011] FIG. 2 is a top view of the electrode assembly FIG. 1.
[0012] FIG. 3 illustrates the chest compression monitor as
implemented in ZOLL Medical's Real CPR Help.RTM. chest compression
monitor.
[0013] FIG. 4 illustrates the relationship of acceleration,
velocity and compression depth for CPR compressions
[0014] FIG. 5 is a table correlating measured compression depth to
desired release velocities.
[0015] FIG. 6 is a graph corresponding to the table of FIG. 4.
[0016] FIGS. 7 and 8 illustrate the output provided by an AED.
DETAILED DESCRIPTION OF THE INVENTIONS
[0017] FIG. 1 illustrates the use of a chest compression monitor in
use on a patient 1, with a rescuer 2 providing manual chest
compressions. As part of the resuscitation effort, the rescuer has
applied an ECG electrode assembly 3 on the patient's chest. This
assembly includes a sternum electrode 4, an apex electrode 5, and
sternal bridge 6. A chest compression monitor 7 is disposed within
the sternal bridge, sandwiched between layers of foam that comprise
the bridge. The bridge, along with the cross-hair indicia, serves
as a template for proper placement of the chest compression monitor
over the sternum of the victim which, together with the
configuration of the bridge, ensures that the sternal and apex
electrodes are properly placed (for patients of a wide variety of
sizes). The electrode assembly is connected to a defibrillator 8
(through cable 9) which is fitted with a control system or systems
capable of controlling (and programmed to control) ECG and
defibrillating functions and capable of controlling (and programmed
to control) the compression monitor functions of interpreting
sensor signals (acceleration signals, velocity signals, or distance
signals, for example) from the compression monitor, determining the
depth of compressions from those sensor signals, and generating and
providing feedback to the rescuer. The feedback may be both audio
feedback (voice prompts) provided through an annunciator or visual
feedback provided on a display. These compression monitor functions
can also be accomplished by a control system built into the
compression monitor itself, as described in Halperin and as
implemented in our PocketCPR.RTM. device. The feedback can include
prompts to compress more deeply, prompts to compress at a faster or
slower rate, and prompts to quickly and completely release the
chest of the patient after each compression.
[0018] FIG. 2 is a top view of the electrode assembly of FIG. 1,
which includes the chest compression monitor 7. In this view, the
location of the sternal electrode 4 and apex electrode 5, and the
chest compression monitor 7 within the bridge 6 are more clearly
shown. The chest compression monitor is disposed within a housing
or on an equivalent structure, which itself is disposed within the
electrode locating bridge shown in FIG. 1, sandwiched between
layers of foam, so that, when applied to the patient, the CPR chest
compression monitor is disposed over the sternal notch of the
patient. This chest compression monitor and its housing are
referred to as a puck in the developing art.
[0019] FIG. 3 illustrates the chest compression monitor 7 as
implemented in ZOLL Medical's Real CPR Help.RTM. chest compression
monitor and CPR stat padz or CPR-D-Padz.RTM.. The puck includes a
housing 12 with a housing bottom portion 13 and housing top portion
14. The housing bottom portion has a slightly convex bottom surface
15 (which opposes the chest, or anterior surface of the patient's
thorax), to conform to the patient's sternal notch. The housing top
portion has a slightly concave top surface 16 (superficial,
relative to the patient) which facilitates hand placement over the
puck during use. The accelerometer assembly 17 that measures
acceleration of the puck is disposed in its packaging and on a
mounting board 18, within the housing. Typically, the accelerometer
assembly is a multi-axis accelerometer assembly, with two or three
distinct accelerometers arranged orthogonally to each other,
capable of detecting acceleration on two or three orthogonal axes.
Preferably, the axes are aligned in the compression monitor to
coincide with the compression axis 19 (typically, the vertical axis
which corresponds to the anterior/posterior axis of the patient
when supine) and one or two axes orthogonal to the compression axis
(typically two horizontal axes). With this arrangement, chest
compression depth can be measured, as described in the Halperin
patents. The accelerometer assembly may also comprise separate
accelerometers, with two or three accelerometers rotatably mounted
to the housing. As described in Halperin and Palazzolo, the
accelerometers produce an acceleration signal corresponding to
acceleration of the chest wall achieved during CPR compressions,
and the control system processes this acceleration signal to
determine compression depth. Also, as described in Geheb, the
control system processes this acceleration signal to determine
velocity, including the velocity of the chest wall during the
period when the CPR provider should be releasing the chest to allow
it to expand (the release velocity).
[0020] The chest compression monitor, as illustrated in FIGS. 1, 2
and 3, comprises a housing adapted to be held in fixed relation to
the chest, specifically the anterior surface of the thorax over the
sternum, so that during CPR compressions the movement of the chest
compression monitor and sensors of the monitor closely correspond
to downward and upward motion of the chest wall of the patient.
[0021] The accelerometer-based compression monitor is presented as
the most convenient configuration for obtaining information
regarding compression depth and release velocity. However, any
device operable to sense compression depth and release velocity, or
to sense signals or obtain data from which compression depth and
release velocity may be derived or determined, may be used in place
of the accelerometer based compression monitor. Thus, means for
determining release velocity can include the accelerometers
described above, velocity sensors which directly measure velocity,
and distance sensors of proximity sensors which track the
displacement of the compression module. For example, the proximity
sensors, including and ultrasonic distance sensor arrangement,
optical distance sensors, magnetic motion sensors, RFID sensors and
emitter/detector arrangements, for example those described in
Freeman and Herken, Chest Compression Belt with Belt Position
Monitoring System, U.S. Provisional App. 61/654,642 filed Jun. 1,
2012, incorporated herein by reference in its entirety, can be used
to measure the actual displacement of the chest, and the control
system can readily determine the velocity as the derivative of the
displacement curve. Velocity can be measured directly using an
imposed magnetic field and inductive sensors, for example, as
disclosed in Geheb, by placing a magnet on one side of the thorax
(on or under the back of the patient) and an inductive coil on the
opposite surface of the thorax (on the chest wall, or anterior
surface of the chest) to detect voltage based on induction of
current in the coil, which varies with the speed of coil through
the magnetic field. A rheostat and mechanical linkage fixed to the
puck may used to measure the displacement, as described in Gruben
et al., Sternal Force Displacement Relationship During
Cardiopulmonary Resuscitation, 115 Journal of Biomedical
Engineering 195 (May 1993)(which describes the use of mechanical
linkages incorporating position sensing transducers to measure
chest displacement during CPR), and from displacement data the
control system can calculate the release velocity.
[0022] Geheb, et al., Method and Apparatus for Enhancement of
Compressions During CPR, U.S. Pat. No. 7,720,235 (May 22, 2007) and
Centen, et al., Reference Sensor For CPR Feedback Device, U.S. Pub.
2012/0083720 (Apr. 5, 2012) disclose a system for measuring chest
compression depth using a magnetic field generator under the
patient and a inductive coil, which senses movement through the
magnetic field, as a velocity sensing system. This system can be
used as a velocity sensor in the system described above, from which
compression depth can be determined. Centen, Optical Techniques For
The Measurement Of Chest Compression Depth And Other Parameters
During CPR, U.S. Pub. 2011/0040217 (Feb. 17, 2011) discloses a
system for measuring chest compression depth using infrared optical
illumination and detection of the reflected infrared light from the
patient. This system can be used as a distance sensor in the system
described above, from which velocity of the chest wall movement can
be determined.
[0023] These and any other means for determining velocity may be
used. Also, though a single sensor, and a single type of sensor,
are sufficient to provide the necessary information to determine
velocity and chest displacement, multiple sensors and sensor types
can be used in any permutation. For example, a velocity sensor can
be used to directly measure velocity, and an displacement sensor or
measurement device (operable independently from the velocity
sensor) can be used to directly measure displacement, such that the
control system can determine velocity from the velocity sensor and
determine displacement from the displacement sensor.
[0024] FIG. 4 illustrates the relationship of acceleration,
velocity and compression depth (displacement) for CPR compressions.
Any one of these values may be measured, and others may be
determined, through straightforward integration or derivation, of
the measured signal. As shown in FIG. 4, acceleration, chest wall
velocity and chest wall displacement correspond to each other
during a compression cycle (a compression cycle includes a
downstroke, an upstroke (a release portion), and perhaps some delay
between a downstroke and a successive upstroke, or between an
upstroke and a successive downstroke). When the CPR provider pushes
on the patient's chest, the chest and the compression module held
in fixed relation to the chest are accelerated downwardly,
experiencing a downward acceleration depicted as a negative
acceleration A.sub.down. Near the end of the downstroke, the
acceleration A.sub.down slows to zero, and reverses to an upward
acceleration A.sub.up as the CPR provider releases the compression
and natural resilience of the thorax leads to expansion and upward
rebound of the chest wall. This is reflected in the positive
acceleration A.sub.up which quickly slows to zero as the chest
reaches its fully expanded position. Upward movement decelerates at
A.sub.slow, and then returns to zero at the completion of the
compression cycle. The cycles continue as the CPR provided
repeatedly compresses the chest. The velocity curve follows the
acceleration curve, with peak downward velocity V.sub.peakdown
occurring when the downward acceleration A.sub.down falls to zero,
and upward or release velocity V.sub.up increasing while the upward
acceleration A.sub.up is positive, and V.sub.peakup occurring when
A.sub.up falls to zero. The displacement of the chest reaches its
deepest extent D.sub.peak when the downward velocity returns to
zero, and returns to the original chest position during the period
of upward velocity. As these curves are strictly related to each
other, each curve can be determined for the others, and data
regarding one parameter can be analyzed to determined the other
values. The upward velocity, which we refer to as the release
velocity, is of primary concern in the inventions described herein,
and it can be determined either by directly measuring the velocity
(while the valuable displacement data can be determined from the
measured velocity), or by measuring acceleration, from which
velocity data and displacement data can be determined, or by
measuring displacement directly to obtain the valuable chest
compression depth measurement and determining release velocity from
the displacement data.
[0025] FIG. 5 is a table correlating measured compression depth to
desired release velocities. FIG. 5 indicates the average velocity
of the chest wall, and thus the compression module, for various
measured compression depths and measured compression rates. For
example, in the ideal situation in which compressions are
accomplished at the recommended rate of 100 compressions per minute
and the recommended depth of 2 inches (5 cm)(on average), the
average of the absolute value of the instantaneous velocity of the
compression module is 400 inches (1016 cm) per minute. When
compression are deeper, such as 3 inches (7.62 cm) per compression,
at the same rate, the average instantaneous velocity of the
compression module is 600 inches (1524 cm) per minute.
[0026] When compressions are accomplished at a more rapid rate, the
average instantaneous velocity is greater. So, for example, 2 inch
(5.08 cm) compressions at a rate of 120 compression per minute
results in a average instantaneous velocity of 440 inches (1016 cm)
per minute. Thus the table reflects the average instantaneous
velocity of the compression module for compressions at various
combinations of depth and rate. The indicated average instantaneous
velocities can be taken as minimum upward or "release" velocities
of the compression module during the upstroke needed to ensure
substantial release of the chest that promotes refilling beneficial
to CPR. Accounting for the rapidity of the downstroke, some delay
at both the bottom of the compression stroke, and some delay
between each complete compression cycle (up and down) and the
downward stroke of the next compression, the average instantaneous
velocity is a desirable goal for the instantaneous velocity of the
upstroke of each compression. The threshold may be adjusted, as
clinical experience dictates, to higher or lower velocities. Also,
peak velocity during the upstroke may be used as the parameter to
be compared to desirable release velocity goals, and velocity
during specific period of time during the upstroke (such as the
window of time immediately after release (that is, the start of the
upstroke, ignoring a portions of the upstroke which is likely to be
quite slow (the last few milliseconds, in which the chest wall is
nearly fully rebounded, and likely to be moving slowly upwardly)).
Where peak release velocity is used to determine the adequacy of
release, peak velocities of about 15% to 25% above the average
velocities shown in FIG. 5 will be taken as the threshold against
which the control system compared measured peak velocity to
determine if the chest has been substantially released. Where
velocity during a portion of the upstroke is used, average velocity
during a small window of time in the upstroke (a window of time
that is shorter than the entire release portion) that meets or
exceeds a value of about 10% above the average velocities shown in
FIG. 5 will be taken as the threshold against which the control
system compared measured "window" velocity to determine if the
chest has been substantially released. The window may be a period
of 50 to 100 milliseconds immediately at the beginning of the
upstroke or near the beginning of the upstroke.
[0027] FIG. 6 is a graph corresponding to the table of FIG. 5.
FIGS. 5 and 6 illustrate a linear relationship between the desired
or achieved compression depth and rate and the desired release
velocity. However, for some patients, such as elder patients or
pediatric or infant patients, the optimal relationship may not be
linear, and there may be an upper limit to release velocity based
on the resilience of a particular patient, such that the release
above a certain threshold may not be possible without active
decompression. For such cases, the relationship between compression
depth and/or rate and the desired release velocity may be adjusted,
such that lower release velocity is considered adequate and
feedback is provided based on lower release velocity goals.
[0028] In one mode of operation which implements the method insofar
as desired release velocity is determined based on the depth of
compression and/or the rate of compression, an input means such as
a keyboard, selector dial, soft key, or other input can be provided
so that the CPR provider or other user can indicate to the control
system a desired depth and/or rate of compression for a particular
CPR session, and the control system can be programmed to receive
and interpret this input and provide release velocity feedback
based on this predetermined depth and/or rate. Thus, the system is
configurable in the field, at the point of use, by the CPR provider
who decides and inputs the optimal configuration based on an
individual assessment of the cardiac arrest victim. The desired
depth and/or rate is predetermined in the sense that the CPR
provider, just prior to the application of CPR compressions,
assesses the patient and decides the appropriate depth of
compression and/or rate of compression, and inputs this to the
control system. In this manner, the release velocity feedback and
the chest compression feedback can be provided based on the
predetermined depth and rate targets, so that the system can be
used to assist in CPR for a wider variety of patients including
pediatric patients. For pediatric patients, the depth and rate may
vary with the sized of the patient, so that a system that sets the
desired release velocity to match the depth chosen by a CPR
provider is beneficial. For example, for compression of small
children, the chest compression goal is currently 2.5 cm (1 inch)
of compression depth. Before providing CPR chest compressions to
the child in cardiac arrest, a CPR provider may provide input the
control system, indicating that the CPR provider has determined
that compressions of 2.5 cm (1 inch), at 100 compressions per
minute, are appropriate for this cardiac arrest victim. This is a
user-determined chest compression depth and/or rate target. The
control system then operates to determine the appropriate release
velocity (either by calculation using a formula provided in the
software which the control system operates under or by reference to
a table of stored values) for the user determined chest compression
depth and/or rate. In this mode, the control system is programmed
to be user-configured in the field, at the point of use, and is
programmed to accept user input regarding desired compression depth
and/or rate goals, or accept user input regarding patient age
and/or size, and select appropriate release velocity goals, against
which it compares the measured release velocity, and provides
corresponding output indicating that the CPR provider achieved, or
failed to achieve, the desired release velocity. The threshold is
chosen by the control system to match the average instantaneous
velocity of the compression module necessary to achieve the
user-entered compression depth and/or rate. Thus, according to the
table, the control system would indicate that the CPR provider has
fully released the compression if release velocity meets or exceeds
200 inches (508 cm) per minute, if the user has configured the
system for a user-entered goal of 1 inch (2.54 cm) compression, 300
inches (762 cm) per minute for a user-entered goal 1.5 inch (3.8
cm) compression, 400 inches (1016 cm) per minute for a user entered
goal of 2 inch (5.08) compression, 500 inches (1270 cm) per minute
for a user-entered goal of 2.5 inch (6.35 cm) compression and 600
inches (1524 cm) per minute for a user-entered goal of 3 inch (7.62
cm) compression. The thresholds can be more or less finely
granulated.
[0029] In other modes of operation, the control system is
programmed to adaptively determine whether a compression, or a
series of compressions, has been fully released based on the depth
of the compression, or the series of compressions, rather than on
the basis of a predetermined threshold value or a user-configured
threshold value. The determined threshold varies with the measured
compression depth, and the control system is programmed to choose
the threshold, against which it compares the measured release
velocity, depending on the measured compression depth, and provide
corresponding output indicating that the CPR provider achieved, or
failed to achieve, the desired release velocity. This may be
accomplished without regard to compression rate. The threshold is
chosen by the control system to match the average instantaneous
velocity of the compression module necessary to achieve the
measured compression depth at a presumed rate (for example, the
recommended rate of 100 compressions per minute). Thus, according
to the table, the control system would indicate that the CPR
provider has fully released the compression if release velocity
meets or exceeds 200 inches (508 cm) per minute for a inch (2.54
cm) compression, 300 inches (762 cm) per minute for a 1.5 inch (3.8
cm) compression, 400 inches (1016 cm) per minute for a 2 inch
(5.08) compression, 500 inches (1270 cm) per minute for a 2.5 inch
(6.35 cm) compression and 600 inches (1524 cm) per minute for a 3
inch (7.62 cm) compression. The thresholds can be more or less
finely granulated.
[0030] In the user-configurable mode described above, the control
system can be programmed to assess the release velocity based on
average velocity on the upstroke or release, or the peak velocity
detected on the upstroke.
[0031] The determined threshold may also vary with the measured
compression rate, and the control system is programmed to choose
the threshold, against which it compares the measured, depending on
the measured compression rate, and provide corresponding output
indicating that the CPR provider achieved, or failed to achieve,
the desired release velocity. This may be accomplished without
regard to compression depth. The threshold is chosen by the control
system to match the average instantaneous velocity of the
compression module necessary to achieve the measured compression
depth at a presumed compression depth (2 inches (5.08 cm), for
example). Thus, according to the table, the control system would
indicate that the CPR provider has fully released the compression
if release velocity meets or exceeds 320 inches (812 cm) per minute
for a compression rate of 80 compression per minute, 360 inches
(914 cm) per minute for a compression rate of 90 compression per
minute, 400 inches (1016 cm) per minute for a compression rate of
100 compression per minute, 440 inches (1118 cm) per minute for a
compression rate of 110 compression per minute and so on. The
thresholds can be more or less finely granulated.
[0032] Both compression depth and compression rate can be taken
into account to refine the system described in the preceding
paragraphs. As illustrated in the chart of FIG. 4, the velocity
threshold can be varied according to both depth and rate of
compression. In this case the threshold is chosen by the control
system to match the average instantaneous velocity of the
compression module necessary to achieve the measured compression
depth and compression rate determined by the compression module.
The determined threshold varies with both the measured compression
depth and the measured compression rate, and the control system is
programmed to choose the velocity threshold, against which it
compares the measured velocity, depending on the measured
compression depth and rate, and provide corresponding output
indicating that the CPR provider achieved, or failed to achieve,
the desired release velocity. The threshold is chosen by the
control system to match the average instantaneous velocity of the
compression module necessary to achieve the measured compression
depth at a presumed compression depth (2 inches (5 cm), for
example).
[0033] In each of these three modes, the system is adaptive, in the
sense that it is programmed to make adjustments in the threshold in
response to changes in the actual performance of the chest
compression depth and/or rate during the course of CPR on each
cardiac arrest victim. The system adaptively determines the desired
threshold for release velocity based on the determined compression
depth, the determined compression rate, or a combination of the
desired compression depth and compression rate, and applies that
adaptively determined threshold to compare with the determined
release velocity to determine if the release velocity meets the
desired threshold.
[0034] In each of the three adaptive modes described above, the
control system can be programmed to assess the release velocity
based on average velocity on the upstroke or release, or the peak
velocity detected on the upstroke.
[0035] FIG. 7 illustrates the output provided by an AED. The
control system operates to provide visual output in a portion of
display to provide feedback and/or provide prompts to the CPR
provider. The display is provided in the front panel of an AED box
21, such as ZOLL's R Series automatic external defibrillator. The
AED can accomplish various functions, including ECG monitoring,
defibrillation, pacing, and monitoring of other parameters. When
used for CPR feedback, the display includes a graph 22 of the CPR
victims ECG, a bar graph 23 representing compression depth, a
"dashboard" display area 24 for numerical displays 25 of
compression depth and compression rate, a progress bar representing
release velocity 26, and a diamond shaped icon 27 used to indicate
a CPR index, which is determined based on an analysis of both the
release velocity and the compression depth. The diamond shaped icon
is filled according to an index determined based on rate and depth.
We refer to the index as the Perfusion Performance Index. The
progress bar representing release velocity, item 26, is referred to
as the compression release bar. The control system will operate
this display to fill the compression release bar to an extent
corresponding to the release velocity determined by the control
system from the sensors used to determine release velocity. The
control system is programmed to fill the bar completely when it
detects release at an upward velocity meeting or exceeding the
desired threshold of release velocity, and fill the compression
release bar to a proportionately lesser extent when release
velocity is slower than the desired threshold. Thus, for example,
release velocity of half the desired release velocity will lead to
a display in which the compression release bar is half full, and
release velocity of 75% of desired release velocity will lead to a
display in which the compression release bar is 75% full. In FIG.
7, the compression release bar is only partially filled, indicating
that measured release velocity is low compared to the desired
threshold, the compression depth is low, hovering around 1.5 inches
(3.81 cm) per compression, and the CPR index diamond is only
partially filled, indicating inadequate release velocity, poor
compression depth, and thus inadequate CPR performance. (Also in
FIG. 7, the ECG is indicative of fibrillation, and the blood oxygen
level (SpO2%) is very low, as would be expected of a cardiac arrest
victim.)
[0036] FIG. 8 illustrates the dashboard display area 24 with the
display, generated by the control system, to reflect a different
state of performance of CPR. In this Figure, the release velocity
is improved, vis-a-vis the display of FIG. 7, as shown in the
release velocity bar graph 26 and the compression depth over the
past several compressions is closer to the ideal of 2-2.5 inches
(5.08-6.35 cm), so the diamond shaped icon 27 is more fully filled
with a color contrasting that of the background. With the displays
of FIGS. 7 and 8, a CPR provider can readily determine from the
output of the system that the quality of chest compressions and is
good or bad, and can then adjust the effort used to compress the
CPR victim or the rapidity of release, until the displays indicate
optimal compression depth and release velocity.
[0037] Whether release velocity is satisfactory may be determined
for each and every compression, or for a series of compressions, or
as an average over a series of compressions. When determined on the
basis of a series of compressions, the control system tracks a
number of compressions, keeping track of those compressions which
are fully releases and those compressions that are not fully
released. The system designers pre-determine an acceptable
compliance rate, and the control system is programmed to issue a
prompt and generate the display accordingly. For example, the
system may be programmed to track 10 compressions and their
associated compression depths and release velocities, and issue a
prompt indicated unacceptable release velocity if 2 of the 10
compressions are not fully released (these numbers are, of course,
merely exemplary). When determined on the basis of an average over
a series of compressions, the system designers pre-determine an
acceptable average release velocity, weighted for compression
depth, and the control system is programmed to issue a prompt and
generate the display accordingly. The control system tracks a
number of compressions, keeping track of those compressions and
release velocities for each compression. If the average release
velocity is less that an acceptable percentage of the desired
release velocities, the control system will issue a prompt for more
complete release. Alternatively, the control system can average the
compression depth, and average the release velocity, and issue a
prompt when the average release velocity fall below the threshold
for the average compression depth. Thus, it is not necessary to
issue a confirmation for every single compression with complete
release or a prompt after every single compression with inadequate
release.
[0038] The diamond-shaped icon 27 provides a quick, overall
indicator of how well the rescuer's combined rate and depth of
chest compressions match the AHA/ERC recommendations for adult CPR.
The CPR Compression Indicator, also known as Perfusion Performance
Indicator (PPI), is first displayed as an empty diamond. The
control system operates to alter this icon, filling it as
compressions begin, and gradually filling it as compressions
continues, until consistent chest compression depth exceeding
AHA/ERC 2010 guidelines of 2.0 inches (5.08 cm) and rate exceeding
90 compressions per minute (cpm) are achieved simultaneously, at
which point the control system completely fills the diamond icon.
Should the chest compression rate or depth begin to fall below the
configured target levels, the indicator will only partially fill to
indicate the need for more rigorous efforts. Following the
cessation of compressions, the indicator's fill level gradually
decreases until a hollow outline is displayed after a short period
of time.
[0039] In addition to the visual display, the control system can
also be programmed to operate a speaker which provides audio prompt
to the CPR provider. For example, when release velocity for a
compression or a series of compression is lower than the desired
release velocity, the control system can generate a audio prompt
such as "Release Fully," and when release velocity is satisfactory,
the control system can generate an audio prompts such as "Good
Release" or "Good Compression." The audio prompt may be either
verbal or non-verbal.
[0040] In use, a CPR provider will place the chest compression
monitor on the victim's chest, over the victim's sternum. If the
chest compression monitor is embedded in an electrode assembly,
this will be done by placing the electrode assembly on the chest so
that the chest compression monitor is properly located over the
sternum. If the chest compression monitor is incorporated into a
stand-alone device, such as a puck or a smart phone, this may be
done by trapping the device between the CPR provider's hands and
the patient's chest. The CPR provider will then press down on the
chest, keeping the chest compression monitor between his hands and
the victim's chest (or otherwise in fixed relation to the victim's
chest), so that the chest compression monitor moves up and down in
fixed relation with the patient's chest. The CPR provider will
operate an associated control system, and energize the sensors in
the chest compression module, to analyze the sensor signals to
determine chest compression depth, velocity of the compression
monitor (including release velocity), and, optionally, the rate of
compression, and determine the desired release velocity based on
the determined chest compression depth (and, optionally, the chest
compression rate), compare the determined release velocity to the
desired release velocity, and operate an output device to provide
prompts indicating whether the release velocity meets or fails meet
the desired release velocity (and whether the chest compression
depth meets the desired chest compression depth). If the system is
used in a user-configurable mode, the CPR provider will operate an
associated control system, and energize the sensors in the chest
compression module, to analyze the sensor signals to determine
chest compression depth, velocity of the compression monitor
(including release velocity), and, optionally, the rate of
compression, and determine the desired release velocity based on
the user-entered chest compression depth target (and, optionally,
the chest compression rate)(or the user-entered patient
information), compare the determined release velocity to the
desired release velocity, and operate an output device to provide
prompts indicating whether the release velocity meets or fails meet
the desired release velocity (and whether the chest compression
depth meets the desired chest compression depth).
[0041] Thus, the system is used in a method for facilitating the
effective administration of cardiopulmonary resuscitation (CPR).
The method includes operating a sensor for generating a signal
corresponding to motion of a cardiac arrest victim's chest to
determine motion of the cardiac arrest victim's chest during CPR
chest compressions, in tandem with operating a control system with
an output device to provide prompts in response to the motion
signals. The control system is operable to receive a signal
corresponding to motion of the chest, and programmed to determine
the depth of compressions from a signal corresponding to motion of
the chest, and determine release velocity during a release portion
of a CPR compression cycle from a signal corresponding to motion of
the chest, and programmed to determine whether the CPR provider is
substantially releasing the chest following chest compressions, and
further programmed to operate the output device to provide the CPR
provider with information as to whether the chest is being
substantially released following chest compressions. Specifically,
the control system is programmed to determine whether the CPR
provider has substantially released the chest based on a desired
release velocity threshold, which it is programmed to determine
based on (1) the CPR provider's target chest compression depth
and/or compression rate, as entered by the operator or (2) the
actual depth of compression and/or compression rate as measured by
the sensors. The control system then provides, through the output
device, a prompt to the CPR provider whether the chest is being
substantially released following chest compressions. As the CPR
provider performs CPR chest compressions on the patient, with the
goal of meeting approved standards of depth, rate and release
velocity, the CPR provider monitors the outputs, occasionally
viewing the output displays and listening to audio prompts as the
are provided by the system, and adjusts the effort of chest
compression if the output indicates that depth, rate, or release
velocity differs from the desired thresholds.
[0042] While the preferred embodiments of the devices and methods
have been described in reference to the environment in which they
were developed, they are merely illustrative of the principles of
the inventions. The elements of the various embodiments may be
incorporated into each of the other species to obtain the benefits
of those elements in combination with such other species, and the
various beneficial features may be employed in embodiments alone or
in combination with each other. Other embodiments and
configurations may be devised without departing from the spirit of
the inventions and the scope of the appended claims.
* * * * *