Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR DETERMINING
BATTERY CAPACITY IN A DEFIBRILLATOR
Reference To Pending Prior Patent Applications
This patent application claims benefit of pending
prior U.S. Provisional Patent Application Serial No.
60/592,788, filed 07/30/2004 by Kyle R. Bowers for
METHOD AND SYSTEM FOR DETERMINING DEFIBRILLATOR BATTERY
CAPACITY (Attorney Docket No. ACCESS-5 PROV), which
patent application is hereby incorporated herein by
reference.
Field Of The Invention
The present invention relates generally to the
measurement of battery capacity. More particularly,
the present invention relates to the measurement and
determination of the remaining capacity of a battery or
battery pack in a defibrillator system.
Background Of The Invention
Approximately 350,000 deaths occur each year in
the United States, due to sudden cardiac arrest (SCA).
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Many of these deaths can be prevented if effective
defibrillation is administered within 3-5 minutes of
SCA.
Sudden cardiac arrest is the onset of an abnormal
heart rhythm, lack of pulse and absence of breath,
leading to a loss of consciousness. If a pulse is not
restored within a few minutes, death occurs. Most
often, SCA is due to ventricular fibrillation, a
chaotic heart rhythm that causes an uncoordinated
quivering of the heart muscle. The lack of coordinated
heart muscle contractions results in insufficient blood
flow to the brain and other organs. Unless this
chaotic rhythm is terminated, allowing the heart to
restore its own normal rhythm and thus normal blood
flow to the brain and other organs, death ensues.
Rapid defibrillation is the only known means to
restore the normal heart rhythm and prevent death after
SCA due to ventricular fibrillation. For each minute
that passes after the onset of SCA, the mortality rate
increases by 10%. If defibrillated within 1-2 minutes,
a patient's survival rate can be as high as 90% or
more. At 7-10 minutes, the patient's survival rate
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drops below 10%. Therefore, the only way to increase
the survival chances for an SCA victim is through early
defibrillation.
Automatic External Defibrillators (AEDs) can
provide early access to defibrillation, but they must
be portable so they can be easily carried to a victim
of SCA, easy-to-use so that they can be properly
utilized when SCA occurs, and easily maintained. In
addition, AEDs must be inexpensive, so that they can be
broadly deployed.
Additionally, AEDs require a portable energy
source to enable the device to be deployed quickly to
treat a victim of SCA. Often, the victim may be in a
remote or difficult-to-reach area, making compact and
portable AEDs attractive to police, EMT, Search-And-
Rescue and other rescue or emergency services.
AEDs must remain in a standby mode for extended
periods of time. Most current AEDs are rated for two
years of standby and must be able to complete a
sufficient number of shocks at the end of this period.
However, during this two-year standby period, the
battery pack may discharge significantly and thus may
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not have sufficient capacity to provide therapy,
especially in situations which may require many
defibrillation shocks and an extended period of
monitoring time.
Currently, many AEDs use a battery monitoring
circuit, also known as a "smart battery", to provide a
"fuel gauge" for remaining capacity. This technique
requires the use of low power analog and digital
circuitry within the battery pack or the device to
constantly monitor battery capacity. Most of these
devices also monitor battery temperature in order to
accurately gauge capacity. As those skilled in the art
can appreciate, the disadvantage of this technique is
that the additional circuitry, components and
connections needed to monitor battery capacity may add
significant cost to the battery pack and/or the AED
itself. As is well known to those skilled in the art,
this technique has been historically problematic and
has been an issue with portable AEDs that use either
disposable or rechargeable battery packs.
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Summary Of The Invention
The present invention addresses the deficiencies
described above by providing a novel method and
apparatus for determining the capacity of a battery
and/or a number of battery cells contained in a battery
pack.
In accordance with the present invention, the
defibrillation system contains a battery or battery
pack, a circuit to charge the defibrillation capacitor
or capacitors, and a circuit to deliver a biphasic
waveform.
In accordance with the present invention, the
defibrillation system contains an LCD display and voice
playback circuitry, an audio amplifier and a speaker to
notify the user of events during device operation.
In accordance with the present invention, the
defibrillation system contains a microprocessor and
circuitry that measures the battery terminal or battery
pack terminal voltage, digitizes the signal and stores
the data in local memory for analysis.
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In another aspect of the present invention, the
defibrillation system stores the battery data in flash
memory for post-incident analysis.
In another aspect of the present invention, the
defibrillation system applies filtering techniques
before and/or after storing the measured battery
voltage signal data.
In another aspect of the invention, the
defibrillation system uses an algorithm to determine
the remaining capacity of the battery or battery pack.
In another aspect of the present invention, the
defibrillation system stores in memory the measured
battery terminal or battery pack terminal voltage and
its associated operational mode. The different
operating modes draw various levels of current from the
battery or battery pack. The algorithm then uses this
stored data to determine the remaining capacity of the
battery or battery pack.
In another aspect of the present invention, the
defibrillation system stores in memory how long the
device has been used. The algorithm then uses this
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stored data to determine the remaining capacity of the
battery or battery pack.
In another aspect of the present invention, the
defibrillation system stores in memory the measured
battery terminal or battery pack terminal voltage and
how long the device has been used. The algorithm then
uses this stored data to determine the remaining
capacity of the battery or battery pack.
In another aspect of the present invention, the
defibrillation system stores in memory the measured
battery terminal or battery pack terminal voltage and
how many times the device has been used with its
installed battery or battery pack. The algorithm then
uses this stored data to determine the remaining
capacity of the battery or battery pack.
In another aspect of the present invention, the
defibrillation system stores in memory the measured
battery terminal or battery pack terminal voltage and
how many times the device has been used to charge its
internal capacitors with its installed battery or
battery pack. The algorithm then uses this stored data
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to determine the remaining capacity of the battery or
battery pack.
In another aspect of the present invention, the
defibrillation system stores in memory how many times
the device has been used to deliver a biphasic shock to
a patient with its installed battery or battery pack.
The algorithm then uses this stored data to determine
the remaining capacity of the battery or battery pack.
In another aspect of the present invention, the
defibrillation system stores in memory the measured
battery terminal or battery pack terminal voltage and
how many times the device has been used to deliver a
biphasic shock to a patient with its installed battery
or battery pack. The algorithm then uses this stored
data to determine the remaining capacity of the battery
or battery pack.
In another aspect the present invention, the
algorithm uses the stored data to determine the
remaining capacity of the battery or battery pack and
informs the user audibly and/or visually that the
battery or battery pack is low.
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In another aspect the present invention, the
algorithm uses the stored data to determine the
remaining capacity of the battery or battery pack and
informs the user that the battery or battery pack needs
to be replaced.
In another aspect the present invention, the
algorithm uses the data to determine the remaining
capacity of the battery or battery pack and informs the
user of the number of shocks left.
In another aspect the present invention, the
algorithm uses the data to determine the remaining
capacity of the battery or battery pack and informs the
user of the remaining monitor time.
In another aspect the present invention, the
algorithm uses the data to determine the remaining
capacity of the battery or battery pack and informs the
user of the general battery capacity as it relates to
typical use, as for example, by displaying a "fuel
gauge".
In one form of the invention, there is provided a
method for determining the remaining battery capacity
of a battery in a defibrillator, the method comprising:
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applying an algorithm that calculates remaining
battery capacity of a battery using measured battery
voltage value in conjunction with historical
information previously stored in the defibrillator.
In another form of the invention, there is
provided a defibrillator comprising:
at least one battery;
at least one capacitor;
a circuit to charge the at least one capacitor
from the at least one battery;
a circuit to deliver a biphasic waveform from the
at least one capacitor to the patient;
user notification apparatus for notifying the user
of events during defibrillator operation; and
a data acquisition circuit that measures the
terminal voltage of the at least one battery, digitizes
the signal and stores the data in memory for analysis.
In another form of the invention, there is
provided a method for determining battery capacity in a
defibrillator comprising:
recording historical data comprising at least one
from the group consisting of:
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how long it has been since the battery was
last charged;
how the defibrillator has been used since the
battery was last charged, including a record of when
the defibrillator was in idle mode and when the
defibrillator was in shocking mode;
how many shocks have been delivered since the
battery was last recharged;
how long has it been since the defibrillator
was last used in shocking mode; and
how many times the battery has been recharged
over its lifetime;
measuring the current battery voltage; and
applying an algorithm to calculate remaining
battery capacity, using the measured battery voltage
and the recorded historical data.
In another form of the invention, there is
provided apparatus for determining the battery capacity
in a defibrillator comprising:
apparatus for recording historical data comprising
at least one from the group consisting of:
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how long it has been since the battery was
last charged;
how the defibrillator has been used since the
battery was last charged, including -a record of when
the defibrillator was in idle mode and when the
defibrillator was in shocking mode;
how many shocks have been delivered since the
battery was last recharged;
how long has it been since the defibrillator
was last used in shocking mode; and
how many times the battery has been recharged
over its lifetime;
apparatus for measuring the current battery
voltage; and
apparatus for applying an algorithm to calculate
remaining battery capacity, using the measured battery
voltage and the recorded historical data.
Brief Description Of The Drawings
These and other objects and features of the
present invention will be more fully disclosed or
rendered obvious by the following detailed description
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of the preferred embodiments of the invention, which is
to be considered together with the accompanying
drawings wherein like numbers referto like parts and
further wherein:
Fig. 1 is an illustration of a battery pack
containing battery cells;
Fig. 2 shows how the battery pack is inserted into
the defibrillator;
Fig. 3 is a schematic drawing showing the cell
arrangement of the battery pack;
Fig. 4 is block diagram of the defibrillator
components;
Fig. 5 is a profile of a new battery pack run in
the defibrillator for a number of continuous shock
cycles, wherein two voltages, i.e., the minimum voltage
during charging (Vchg(min)) and the recovered voltage
in between shocks (Vrecover), are measured;
Fig. 6 is a profile of a used battery pack run in
the defibrillator for a number of continuous shock
cycles, wherein two voltages, i.e., the minimum voltage
during charging (Vchg(min)) and the recovered voltage
in between shocks (Vrecover), are measured;
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Fig. 7 is a profile of a depleted battery-pack run
in the defibrillator for a number of continuous shock
cycles, wherein two voltages, i.e., the minimum voltage
during charging (Vchg(min)) and the recovered voltage
in between shocks (Vrecover), are measured;
Fig. 8 is an oscilloscope display showing the
battery voltage drop during a defibrillator charge
cycle; and
Fig. 9 is a flow diagram showing a preferred
algorithm for determining battery capacity.
Detailed Description Of The Preferred Embodiments
The present invention discloses a system and
method for determining the remaining capacity in the
battery pack of a defibrillator.
Looking first at Figs. 1 and 2, there is shown the
battery pack 5 of a defibrillator 15. It should be
appreciated that the present invention may be applied
the entire battery pack 15 or to individual cells of
the battery pack.
In current defibrillator systems, it is difficult
to determine the remaining capacity of the battery
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cells of a defibrillator. The battery pack voltage
during idle mode (i.e., during the monitoring mode)
yields little information about the remaining battery
capacity due to the lack of cell load. In addition, as
the batteries become depleted over time, the internal
impedance of the cell increases. When the
defibrillator begins charging the capacitors to deliver
a shock, the battery load is significantly increased,
thereby lowering the cell voltage. In cases where the
battery is depleted, the battery cell impedance is high
and the voltage may decrease to a level insufficient to
charge the capacitors and provide defibrillation
therapy.
The varying capacities of battery cells are
illustrated in Figs. 5-7.
Fig. 5 is the profile of a new battery pack
measured while the defibrillator is running in AED mode
for a number of continuous shock cycles. AED mode is
defined as three shocks per minute followed by one
minute of rest. The battery profile in Fig. 5 shows
two voltage measurements. The first measured voltage,
Vchg(min) 80, is the minimum voltage reached during the
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charge cycle (i.e., while the defibrillator is
delivering shocks). The second measured voltage,
(Vrecover) 85, is the battery voltage present when the
battery has recovered after a charging cycle (i.e.,
while the battery is "resting" between shocks). As can
be seen in the profile of Fig. 5, the measured
Vchg(min) 80 is relatively flat with a slight increase
in voltage over the first thirty shocks, followed by a
slight decrease in approximately the last twelve shocks
before the voltage decreases sharply after the last
shock (approximately shock number 43 in Fig. 5). This
decrease is due,.to a rise in cell temperature as the
defibrillator is delivering shocks. However, the
measured Vrecover 85 shows little indication that the
battery is depleting at any point measured.
Fig. 6 shows the profile of a used battery pack,
also measured while the battery pack is run in a
defibrillator for a number of continuous shock cycles.
As can be seen, the two voltages measured (Vchg(min) 80
and Vrecover 85) exhibit characteristics similar to
that of a new battery, with the exception that
Vchg(min) 80 has a lower baseline voltage and the used
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battery pack has a smaller shock capacity than the new
battery pack.
Fig. 7 shows the profile of a depleted battery
pack. While the depleted battery pack is capable of
delivering several shocks, both voltages (Vchg(min) 80
and Vrecover 85) are gradually decreasing. The
depleted battery pack has a much lower shock capacity
than both the new and used battery packs (Figs. 5 and
6, respectively). It should be appreciated that the
depleted battery in this case should not be confused
with a deeply discharged battery. A deeply discharged
battery is unable to sustain a voltage even under a
nominal load.
As can be seen in Fig. 7, a depleted battery pack,
does not provide the defibrillator with a reliable
source of power. Yet, it is critical in life saving
situations that the device reliably notify the user
that the battery is low. Many current AED units use a
battery monitoring circuit, also known as a "smart
battery", to provide a "fuel gauge" for remaining
battery capacity. This technique requires the use of
low power analog and digital circuitry within the
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battery.pack, or within the device, to constantly
monitor battery capacity. Many current devices also
monitor battery cell temperature to accurately gauge
capacity. The disadvantage of this technique is that
the additional circuitry, components and connections
which are needed for battery monitoring add significant
cost to the battery pack and/or the AED unit itself.
Therefore, this "fuel gauge" technique has been
historically problematic and has been an issue with
portable AEDs with both disposable and rechargeable
battery packs.
To overcome these issues, the AED of the present
invention uses a data acquisition system that measures
the current battery voltage and stores the data, along
with historical information, for analysis, thereby
eliminating the need for using additional circuitry,
components and connections.
Looking again at Figs. 1 and 2, there is shown the
battery pack 5 of the defibrillator 15. Battery pack 5
preferably comprises Lithium Manganese Dioxide type
cells, however, the method and apparatus of the present
invention may be applied to other cell chemistries as
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well including, but not limited to, Alkaline Manganese
Dioxide or rechargeable types, Nickel-Metal Hydride
types or Lithium Ion types, etc. A preferred
embodiment of the battery pack uses five battery cells,
however, the battery pack may easily implement a
different number of battery cells. The voltage of each
of the five single battery cells is 3V, therefore, the
defibrillator supply voltage is 15V. The present
invention could also be utilized with more or less
battery cells and/or other supply voltages.
Battery pack 5, preferably placed in a plastic
housing, is inserted into defibrillator 15 as shown in
Fig. 2.
A schematic of the five-cell arrangement 20,
comprising five individual cells 10, each with a supply
voltage of 3V, is shown in Fig. 3.
A block diagram of the defibrillator components is
shown in Fig. 4. Defibrillator 15 contains a data
acquisition system including, but not limited to,
microprocessor 25, programmable logic device (PLD) 30,
memory (not shown) and analog-to-digital converter 40.
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The preferred embodiment of the invention uses
microprocessor 25 to execute instructions to (i) sample
data, (ii) store the data into memory, and (iii)
process the data to determine the remaining battery
capacity. In a preferred embodiment, programmable
logic device 30 controls the interface to analog-to-
digital converter 40 and stores the sampled data into a
local memory buffer. Programmable logic device 30 then
interrupts microprocessor 25 to sample the data
contained in the buffer, via data-bus 45 connected
between microprocessor 25 and PLD 30. Microprocessor
25 may also directly interface to analog-to-digital
converter 40 and use internal timing to interrupt
microprocessor 25 for sampling frequency.
Additionally, microprocessor 25 may be a
microcontroller and have memory, analog-to-digital
converter 40 and other peripherals on a single chip.
The defibrillator also contains LCD screen 50, as
well as a voice synthesizer and speaker for instructing
the rescuer. Defibrillator 15 also contains all the
necessary components for defibrillation including, but
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not limited to, charger circuit 60, battery pack 10,
capacitors 65 and an H-bridge circuit 70.
The defibrillator data acquisition system samples
the battery voltage once every 45 mS (22.22Hz) and
stores the data into random access memory (RAM). The
data acquisition system may also store the battery data
onto a removable multi-media flash card for
post-incident review. Defibrillator 15 is also capable
of storing the battery data into EEPROM, Flash or other
types of memory well known in the art.
Defibrillator 15 does not need to implement a
digital filter, however, a digital filter, such as, but
not limited to, an averaging filter (smoothing filter),
low-pass filter or other filters well known in the art,
may easily be implemented.
Defibrillator 15 may also store historical
information into RAM. Such data may contain
information about the period of time since the device
was last used, the number of times the device has been
used, the operational mode of the device and the number
of shocks that have been delivered. The device may
additionally store its historical information onto a
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removable multi-media flash card for post-incident
review. Defibrillator 15 is also capable of storing
its historical information into EEPROM, Flash or other
types of memory well known in the art.
In one embodiment of the present invention, the
method for determining the remaining battery capacity
of defibrillator 15 may apply an algorithm that uses
battery voltage values in conjunction with the device's
historical information. Different thresholds for
different modes of the defibrillator operation may be
used when applying the algorithm to determine the
remaining battery capacity of defibrillator 15. As
shown in Fig. 8, for example, voltage 100 drops
significantly when the defibrillator begins to charge.
The method of the present invention uses a
predetermined threshold for when the defibrillator is
in idle mode (monitor mode) and applies an algorithm
using multiple thresholds for when the defibrillator is
in charge mode (charging the capacitors in preparation
to provide a shock). The algorithm takes into account,
among other things, how long it has been since the
defibrillator was last used, how many times the
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capacitors have been charged and how many times the
defibrillator has delivered a shock.
As shown in the flow diagram of Fig. 9, the
defibrillator uses three predetermined thresholds
based, on the number of shocks delivered, to determine
the charge remaining in the battery pack. The method
of the present invention preferably uses a threshold of
7.39 volts for one to three shocks, a threshold of 7.87
volts for three to six shocks, and a threshold of 9.03
volts for more than six shocks. When in idle (i.e.,
monitoring) mode, the method of the present invention
uses a single threshold of 10 volts. When the
defibrillator battery cell's voltage falls below the
predetermined threshold, the algorithm will determine
that a battery capacity remaining is capable of, for
example, a minimum of six shocks, although in some
cases may be able to deliver up to a maximum of twelve
shocks. The rescuer is notified to replace the'battery
by means of visual and audible messages.
It should be appreciated that the method for
determining the remaining battery capacity of
defibrillator 15 uses delays between modes to allow the
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battery voltage to recover. As can be seen in Fig. 8,
it can take several hundred milliseconds for the
battery to recover after charge mode.
The algorithm used in the metho.d for determining
remaining battery capacity also takes into account the
total number of shocks de-livered. When the device has
reached a predetermined threshold for the number of
shocks delivered, the device proceeds to notify the
user to replace the battery. In one embodiment of the
present invention, the defibrillator may use a twenty-
shock count threshold.
In addition, the algorithm used in the method of
the present invention for determining remaining battery
capacity also takes into account the total time the
device has been used. When the device has reached a
predetermined threshold for the total time of use, the
device proceeds to notify the user to replace the
battery. In one embodiment of the present invention,
the defibrillator may use a two-hour time threshold.
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Modifications
It is to be understood that the present invention
is by no means limited to the particular constructions
herein disclosed and/or shown in the drawings, but also
comprises any modifications or equivalents within the
scope of the invention.
