U.S. patent application number 09/810813 was filed with the patent office on 2003-10-09 for electrotherapy apparatus.
Invention is credited to Ochs, Dennis E., Powers, Daniel J..
Application Number | 20030191510 09/810813 |
Document ID | / |
Family ID | 23355639 |
Filed Date | 2003-10-09 |
United States Patent
Application |
20030191510 |
Kind Code |
A1 |
Ochs, Dennis E. ; et
al. |
October 9, 2003 |
Electrotherapy apparatus
Abstract
An electrotherapy apparatus includes a connecting mechanism
coupled between an energy source and a pair of electrodes for
contacting a patient. A controller coupled to the energy source
configures the energy source to provide a selected one of a
plurality of energy levels. The controller actuates the connecting
mechanism to couple the energy source to the electrodes. A sensor
coupled to the controller measures a parameter or parameters
related to the energy delivered to the patient through the
electrodes. The controller performs an operation using the output
received from the sensor. Based upon the operation, the controller
actuates the connecting mechanism to decouple the energy source
from the electrodes. In an embodiment of the electrotherapy
apparatus, the energy source includes a high voltage power supply
for charging a capacitor to a selected one of a plurality of
initial voltages. The sensor includes a voltage sensor to measure
the voltage across the capacitor and a current sensor to measure
the current supplied by the capacitor. The connecting mechanism
includes electronic switches coupled between the capacitor and the
electrodes to permit application of an electrotherapy waveform in
either polarity. The controller performs the operation using the
measured voltages and currents to control the electronic switches.
The operation may include computing the patient impedance,
determining a time constant of the voltage or current, determining
a quantity of charge delivered to the patient, or determining the
time required for the voltage or current to substantially equal a
predetermined fraction of the voltage or current.
Inventors: |
Ochs, Dennis E.; (Bellevue,
WA) ; Powers, Daniel J.; (Issaquah, WA) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P.O. BOX 3001
BRIARCLIFF MANOR
NY
10510
US
|
Family ID: |
23355639 |
Appl. No.: |
09/810813 |
Filed: |
December 13, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09810813 |
Dec 13, 2000 |
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09345590 |
Jun 30, 1999 |
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6317635 |
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Current U.S.
Class: |
607/62 |
Current CPC
Class: |
A61N 1/3937
20130101 |
Class at
Publication: |
607/62 |
International
Class: |
A61N 001/18 |
Claims
What is claimed is:
1. An electrotherapy apparatus for performing electrotherapy on a
patient through a first electrode and a second electrode, the
electrotherapy apparatus comprising: an energy source to provide
energy for performing the electrotherapy; a connecting mechanism
configured for coupling and decoupling the energy source,
respectively, to and from the first electrode and the second
electrode; a first sensor configured for measuring a first
parameter related to the energy supplied to the patient by the
energy source; and a controller arranged to receive the first
parameter from the first sensor and configured to perform an
operation, using the first parameter, for actuating the connecting
mechanism to decouple the energy source from the first electrode
and the second electrode.
2. The electrotherapy apparatus as recited in claim 1, further
comprising: a second sensor configured for measuring a second
parameter related to the energy supplied to the patient by the
energy source with the controller arranged to receive the second
parameter and configured to perform the operation using the second
parameter.
3. The electrotherapy apparatus as recited in claim 2, wherein: the
first parameter includes a voltage supplied by the energy source to
the patient; the second parameter includes a current supplied by
the energy source to the patient; and the operation includes
determining a patient impedance using the first parameter and the
second parameter.
4. The electrotherapy apparatus as recited in claim 3, wherein: the
controller includes a configuration to control the energy source to
provide a selected one of a plurality of energy levels for the
electrotherapy and to perform the operation using a value
corresponding to the selected one of the plurality of energy levels
for the electrotherapy.
5. The electrotherapy apparatus as recited in claim 4, wherein: the
operation includes determining the patient impedance based upon a
plurality of values of the first parameter and a plurality of
values of the second parameter.
6. The electrotherapy apparatus as recited in claim 5, wherein: the
controller includes a configuration to actuate the connecting
mechanism to perform a first phase of the electrotherapy having a
first duration based upon the operation and to actuate the
connecting mechanism to perform a second phase of the
electrotherapy having a second duration based upon the
operation.
7. The electrotherapy apparatus as recited in claim 1, wherein: the
operation includes determining a time constant based upon the first
parameter.
8. The electrotherapy apparatus as recited in claim 7, wherein: the
controller includes a configuration to control the energy source to
provide a selected one of a plurality of energy levels for the
electrotherapy and to perform the operation using a value
corresponding to the selected one of the plurality of energy levels
for the electrotherapy.
9. The electrotherapy apparatus as recited in claim 8, wherein: the
controller includes a configuration to actuate the connecting
mechanism to perform a first phase of the electrotherapy having a
first duration based upon the operation and to actuate the
connecting mechanism to perform a second phase of the
electrotherapy having a second duration based upon the
operation.
10. The electrotherapy apparatus as recited in claim 9, wherein:
the first parameter includes either a current or a voltage supplied
by the energy source to the patient.
11. The electrotherapy apparatus as recited in claim 1, wherein:
the operation includes determining a first time interval beginning
with the first sensor measuring a first value of the first
parameter and ending with the first sensor measuring a second value
of the first parameter substantially equal to a predetermined
fraction of the first value; and the controller includes a
configuration to actuate the connecting mechanism to couple the
energy source to the first electrode and the second electrode and
to decouple the energy source from the first electrode and the
second electrode at the end of a second time interval determined by
the operation and having a first duration based upon the first time
interval.
12. The electrotherapy apparatus as recited in claim 11, wherein:
the controller includes a configuration to actuate the connecting
mechanism to couple the energy source to the first electrode and
the second electrode after the second time interval and to decouple
the energy source from the first electrode and the second electrode
at the end of a third time interval determined by the operation and
having a second duration based upon the first time interval.
13. The electrotherapy apparatus as recited in claim 12, wherein:
the controller includes a configuration to control the energy
source to provide a selected one of a plurality of energy levels
for the electrotherapy and to perform the operation to determine
the second time interval and the third time interval using a value
corresponding to the selected one of the plurality of energy levels
for the electrotherapy.
14. The electrotherapy apparatus as recited in claim 13, wherein:
the first parameter includes either a current or a voltage supplied
by the energy source to the patient.
15. The electrotherapy apparatus as recited in claim 1, wherein:
the first parameter includes a current supplied by the energy
source to the patient; the operation includes determining a charge
delivered to the patient using the first parameter and determining
a first time interval beginning with the coupling of the energy
source to the first electrode and the second electrode and ending
with the charge delivered to the patient substantially equaling a
predetermined value; and the controller includes a configuration to
actuate the connecting mechanism to couple the energy source to the
first electrode and the second electrode and to decouple the energy
source from the first electrode and the second electrode at the end
of a second time interval determined by the operation and having a
first duration based upon the first time interval.
16. The electrotherapy apparatus as recited in claim 15, wherein:
the controller includes a configuration to actuate the connecting
mechanism to couple the energy source to the first electrode and
the second electrode after the second time interval and to decouple
the energy source from the first electrode and the second electrode
at the end of a third time interval determined by the operation and
having a second duration based upon the first time interval.
17. The electrotherapy apparatus as recited in claim 16, wherein:
the controller includes a configuration to control the energy
source to provide a selected one of a plurality of energy levels
for the electrotherapy and to perform the operation to determine
the second time interval and the third time interval using a value
corresponding to the selected one of the plurality of energy levels
for the electrotherapy.
18. The electrotherapy apparatus as recited in claim 17, wherein:
the energy source includes a capacitor coupled to a power supply;
and the energy source includes a configuration to charge the
capacitor to a selected one of a plurality of voltages
corresponding to the selected one of the plurality of energy
levels.
19. The electrotherapy apparatus as recited in claim 18, wherein:
the operation includes determining the first time interval based
upon a time required for the charge delivered to the patient to
substantially equal a selected one of a plurality of predetermined
values, including the predetermined value, corresponding to the
selected one of the plurality of voltages.
20. The electrotherapy apparatus as recited in claim 19, wherein:
the controller includes a configuration to determine a maximum
allowable current and a minimum allowable current based upon the
selected one of the plurality of voltages and to actuate the
connecting mechanism to decouple the energy source from the first
electrode and the second electrode for a value of the first
parameter greater than the maximum allowable current or less than
the minimum allowable current.
21. In an electrotherapy apparatus including an energy source and a
controller, a method for performing electrotherapy on a patient
comprising: coupling the energy source to the patient; measuring a
first parameter related to energy supplied to the patient;
performing an operation upon the first parameter using the
controller; and decoupling the energy source from the patient based
upon the operation.
22. The method as recited in claim 21, further comprising:
measuring a second parameter related to the energy supplied to the
patient after coupling the energy source to the patient, where
performing the operation includes using the second parameter.
23. The method as recited in claim 22, wherein: the first parameter
includes a current supplied by the energy source to the patient;
the second parameter includes a voltage supplied by the energy
source to the patient; and performing the operation includes
determining a patient impedance using the first parameter and the
second parameter.
24. The method as recited in claim 23, further comprising:
selecting one of a plurality of energy levels for performing the
electrotherapy before coupling the energy source to the patient,
where performing the operation includes using a value corresponding
to the selected one of the plurality of energy levels.
25. The method as recited in claim 24, further comprising:
measuring a plurality of values of the first parameter before
determining the patient impedance; and measuring a plurality of
values of the second parameter before determining the patient
impedance, where determining the patient impedance includes using
the plurality of values of the first parameter and the plurality of
values of the second parameter.
26. The method as recited in claim 25 further comprising: coupling
the energy source to the patient after decoupling the energy source
from the patient; and decoupling the energy source from the patient
after a time interval based upon the operation.
27. The method as recited in claim 21, wherein: performing the
operation includes determining a time constant using the first
parameter.
28. The method as recited in claim 27, further comprising:
selecting one of a plurality of energy levels for performing the
electrotherapy before coupling the energy source to the patient,
where performing the operation includes using a value corresponding
to the selected one of the plurality of energy levels.
29. The method as recited in claim 28, further comprising: coupling
the energy source to the patient after decoupling the energy source
from the patient; and decoupling the energy source from the patient
after a time interval based upon the operation.
30. The method as recited in claim 29, wherein: the first parameter
includes either a current or a voltage supplied by the energy
source to the patient.
31. The method as recited in claim 21, wherein: the first parameter
includes a current supplied by the energy source to the patient;
performing the operation includes determining a charge delivered to
the patient using the first parameter and determining a first time
interval beginning with the coupling of the energy source to the
patient and ending with the charge delivered to the patient
substantially equaling a predetermined value; and decoupling the
energy source includes decoupling the energy source at the end of a
second time interval determined by the operation and having a first
duration based upon the first time interval.
32. The method as recited in claim 31, further comprising:
selecting one of a plurality of energy levels for the energy source
to perform the electrotherapy before coupling the energy source to
the patient, where performing the operation includes using a value
corresponding to the selected one of the plurality of energy levels
to determine the first time interval.
33. The method as recited in claim 32, further comprising:
determining a maximum allowable current and a minimum allowable
current using the value corresponding to the selected one of the
plurality of energy levels; determining a value of the first
parameter after coupling the energy source to the patient; and
actuating the connecting mechanism to decouple the energy source
from the first electrode and the second electrode for the value of
the first parameter greater than the maximum allowable current or
for the value of the first parameter less than the minimum
allowable current.
34. The method as recited in claim 33, further comprising: coupling
the energy source to the patient after decoupling the energy source
from the patient; decoupling the energy source from the patient
after a third time interval where performing the operation includes
determining the third time interval using the value corresponding
to the selected one of the plurality of energy levels.
35. The method as recited in claim 21, wherein: measuring the first
parameter includes measuring a first value of the first parameter
and a second value of the first parameter; performing the operation
includes determining a first time interval beginning with measuring
the first value of the first parameter and ending with the second
value of the first parameter substantially equal to a predetermined
fraction of the first value of the first parameter; performing the
operation includes determining a second time interval based upon
the first time interval; and decoupling the energy source from the
patient occurs at the end of the second time interval.
36. The method as recited in claim 35, further comprising:
selecting one of a plurality of energy levels for the energy source
to perform the electrotherapy before coupling the energy source to
the patient where performing the operation includes using a value
corresponding to the selected one of the plurality of energy levels
to determine the first time interval.
37. The method as recited in claim 36, further comprising: coupling
the energy source to the patient after decoupling the energy source
from the patient; and decoupling the energy source from the patient
after a third time interval where performing the operation includes
determining the third time interval using the value corresponding
to the selected one of the plurality of energy levels.
38. The method as recited in claim 37, wherein: the first parameter
includes either a current or a voltage supplied by the energy
source to the patient.
39. A defibrillator for delivering a multi-phasic waveform to a
patient through a first electrode and a second electrode,
comprising: a capacitor having a first terminal and having a second
terminal, with the capacitor to store charge used for delivery of
the multi-phasic waveform to the patient; a first sensor configured
for measuring a first parameter related to the energy supplied to
the patient by the capacitor; a connecting mechanism coupled
between the first terminal and the second terminal of the capacitor
and the first electrode and the second electrode to permit the
first terminal of the capacitor to selectively couple to one of the
first electrode and the second electrode and to permit the second
terminal of the capacitor to selectively couple to one of the first
electrode and the second electrode; a controller arranged to
receive the first parameter from the sensor and configured to
perform an operation, using the first parameter, for actuating the
connecting mechanism to decouple the capacitor from the first
electrode and the second electrode; and a power supply configured
for charging the capacitor to an initial voltage determined by the
controller.
40. The defibrillator as recited in claim 39, further comprising: a
second sensor configured for measuring a second parameter related
to the energy supplied to the patient by the capacitor with the
controller arranged to receive the second parameter and configured
to perform the operation using the second parameter.
41. The defibrillator as recited in claim 40, wherein: the first
parameter includes a voltage supplied by the capacitor to the
patient; the second parameter includes a current supplied by the
capacitor to the patient; and the operation includes determining a
patient impedance using the first parameter and the second
parameter.
42. The defibrillator as recited in claim 41, wherein: the
controller includes a configuration to control the power supply to
charge the capacitor to a selected one of a plurality of initial
voltages, including the initial voltage, and to perform the
operation using a value corresponding to the selected one of the
plurality of initial voltages for the multi-phasic waveform.
43. The defibrillator as recited in claim 42, wherein: the
operation includes determining the patient impedance based upon a
plurality of values of the first parameter and a plurality of
values of the second parameter.
44. The defibrillator as recited in claim 43, wherein: the
multi-phasic waveform includes a bi-phasic waveform having a first
phase and a second phase each having a duration dependent upon the
operation.
45. The defibrillator as recited in claim 39, wherein: the
operation includes determining a time constant based upon the first
parameter.
46. The defibrillator as recited in claim 45, wherein: the
controller includes a configuration to control the power supply to
charge the capacitor to a selected one of a plurality of initial
voltages, including the initial voltage, and to perform the
operation using a value corresponding to the selected one of the
plurality of initial voltages for the multi-phasic waveform.
47. The defibrillator as recited in claim 46, wherein: the
multi-phasic waveform includes a bi-phasic waveform having a first
phase and a second phase each having a duration dependent upon the
operation.
48. The defibrillator as recited in claim 47, wherein: the first
parameter includes either a current or a voltage supplied by the
capacitor to the patient.
49. The defibrillator as recited in claim 39, wherein: the
operation includes determining a first time interval beginning with
the first sensor measuring a first value of the first parameter and
ending with the first sensor measuring a second value of the first
parameter substantially equal to a predetermined fraction of the
first value; and the controller includes a configuration to actuate
the connecting mechanism to couple the capacitor to the first
electrode and the second electrode and to decouple the capacitor
from the first electrode and the second electrode at the end of a
second time interval determined by the operation and based upon the
first time interval.
50. The defibrillator as recited in claim 49, wherein: the
controller includes a configuration to actuate the connecting
mechanism to couple the energy source to the first electrode and
the second electrode after the second time interval and to decouple
the energy source from the first electrode and the second electrode
at the end of a third time interval determined by the operation and
based upon the first time interval.
51. The defibrillator as recited in claim 50, wherein: the
controller includes a configuration to control the power supply to
charge the capacitor to a selected one of a plurality of initial
voltages, including the initial voltage, and to perform the
operation using a value corresponding to the selected one of the
plurality of initial voltages for the multi-phasic waveform.
52. The defibrillator as recited in claim 51, wherein: the
multi-phasic waveform includes a bi-phasic waveform having a first
phase and a second phase each having a duration dependent upon the
operation.
53. The defibrillator as recited in claim 52, wherein: the first
parameter includes either a current or a voltage supplied by the
capacitor to the patient.
54. The defibrillator as recited in claim 39, wherein: the first
parameter includes a current supplied by the capacitor to the
patient; the operation includes determining a charge delivered to
the patient using the first parameter and determining a first time
interval beginning with the coupling of the capacitor to the first
electrode and the second electrode and ending with the charge
delivered to the patient substantially equaling a predetermined
value; and the controller includes a configuration to actuate the
connecting mechanism to couple the capacitor to the first electrode
and the second electrode and to decouple the capacitor from the
first electrode and the second electrode at the end of a second
time interval determined by the operation and based upon the first
time interval.
55. The defibrillator as recited in claim 54, wherein: the
controller includes a configuration to actuate the connecting
mechanism to couple the capacitor to the first electrode and the
second electrode after the second time interval and to decouple the
capacitor from the first electrode and the second electrode at the
end of a third time interval determined by the operation and based
upon the first time interval.
56. The defibrillator as recited in claim 55, wherein: the
controller includes a configuration to control the power supply to
charge the capacitor to a selected one of a plurality of initial
voltages, including the initial voltage, and to perform the
operation to determine the second time interval and the third time
interval using a value corresponding to the selected one of the
plurality of initial voltages for the multi-phasic waveform.
57. The defibrillator as recited in claim 56, wherein: the
operation includes determining the first time interval based upon a
time required for the charge delivered to the patient to
substantially equal a selected one of a plurality of predetermined
values, including the predetermined value, corresponding to the
selected one of the plurality of initial voltages.
58. The defibrillator as recited in claim 57, wherein: the
controller includes a configuration to determine a maximum
allowable current and a minimum allowable current based upon the
selected one of the plurality of initial voltages and to actuate
the connecting mechanism to decouple the energy source from the
first electrode and the second electrode for a value of the first
parameter greater than the maximum allowable current or less than
the minimum allowable current.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the field of electrotherapy. More
particularly, this invention relates to a hardware implementation
of an electrotherapy apparatus and a method for using the
electrotherapy apparatus.
BACKGROUND OF THE INVENTION
[0002] Some electrotherapy apparatuses used to perform
electrotherapy dynamically control the electrotherapy waveform
applied to the patient in response to real time impedance
measurements made upon the patient. Hardware implementations of
these electrotherapy apparatuses measure such parameters as the
charge delivered to the patient or the voltage of the
electrotherapy waveform applied to the patient to estimate the
impedance. In response to these measurements, the electrotherapy
apparatuses adjust the electrotherapy waveform delivered to the
patient to improve the effectiveness of the electrotherapy.
[0003] Electrotherapy apparatuses that dynamically control the
electrotherapy waveform applied to the patient have implemented
threshold comparison functions in hardware. The hardware has
included such things as comparators using voltage references to
determine when a measured parameter has reached a threshold value.
A cost savings and a reliability improvement could be realized if
the hardware required for implementing the threshold comparison
could be simplified. A need exists for an electrotherapy apparatus
having reduced hardware complexity.
SUMMARY OF THE INVENTION
[0004] Accordingly, an implementation of an electrotherapy
apparatus having reduced hardware and a method for using the
electrotherapy apparatus have been developed. An electrotherapy
apparatus for performing electrotherapy on a patient through a
first electrode and a second electrode includes an energy source to
provide energy for performing the electrotherapy and a connecting
mechanism configured for coupling and decoupling the energy source,
respectively, to and from the first electrode and the second
electrode. The electrotherapy apparatus also includes a first
sensor configured for measuring a first parameter related to the
energy supplied to the patient by the energy source. Additionally,
the electrotherapy apparatus includes a controller arranged to
receive the first parameter from the first sensor. The controller
is configured to perform an operation, using the first parameter,
for actuating the connecting mechanism to decouple the energy
source from the first electrode and from the second electrode.
[0005] An electrotherapy apparatus includes an energy source and a
controller. A method for performing electrotherapy on a patient
includes coupling the energy source to the patient. The method also
includes measuring a first parameter related to energy supplied to
the patient. Additionally, the method includes performing an
operation upon the first parameter using the controller. The method
further includes decoupling the energy source from the patient
based upon the operation.
[0006] A defibrillator for delivering a multi-phasic waveform to a
patient through a first electrode and a second electrode includes a
capacitor having a first terminal and having a second terminal. The
capacitor stores charge used for delivery of the multi-phasic
waveform to the patient. The defibrillator further includes a first
sensor configured for measuring a first parameter related to the
energy supplied to the patient by the capacitor. Additionally, the
defibrillator includes a connecting mechanism coupled between the
first terminal and the second terminal of capacitor and the first
electrode and the second electrode. The connecting mechanism
permits the first terminal of the capacitor to selectively couple
to one of the first electrode and the second electrode and to
permit the second terminal of the capacitor to selectively couple
to one of the first electrode and the second electrode. The
defibrillator also includes a controller arranged to receive the
first parameter from the sensor. The controller is configured to
perform an operation, using the first parameter, for actuating the
connecting mechanism to decouple the capacitor from the first
electrode and the second electrode. The defibrillator also includes
a power supply configured for charging the capacitor to an initial
voltage determined by the controller.
DESCRIPTION OF THE DRAWINGS
[0007] A more thorough understanding of the invention may be had
from the consideration of the following detailed description taken
in conjunction with the accompanying drawings in which:
[0008] FIG. 1 shows a high level block diagram of an electrotherapy
apparatus.
[0009] FIG. 2 shows a high level flow diagram of a method for using
the electrotherapy apparatus shown in FIG. 1 to apply
electrotherapy to a patient.
[0010] FIG. 3 shows an exemplary electrotherapy waveform that could
be applied to a patient using the electrotherapy apparatus shown in
FIG. 1.
[0011] FIG. 4 shows a simplified schematic of an embodiment of the
electrotherapy apparatus shown in FIG. 1.
DETAILED DESCRIPTION OF THE DRAWINGS
[0012] The present invention is not limited to the embodiments
disclosed in this specification. Although the exemplary embodiments
of the electrotherapy apparatus will be discussed in the context of
an external defibrillator, the principles illustrated are
applicable to an internal defibrillator. Additionally, although one
of the exemplary embodiments of the electrotherapy apparatus is
configured for delivering a bi-phasic electrotherapy waveform, the
principles illustrated are applicable to an electrotherapy
apparatus which delivers other electrotherapy waveforms such as a
mono-phasic electrotherapy waveform, multi-phasic electrotherapy
waveform, a damped sinusoid electrotherapy waveform, or the
like.
[0013] Compensation for impedance variations between patients
involves the measurement of one or more parameters related to the
energy delivered to the patient. These parameters could include,
for example, voltage or current supplied to the patient by the
electrotherapy apparatus. The measured parameters, or the results
of computations on the measured parameters, are compared to
threshold values. Based upon the result of the comparison, the
electrotherapy waveform is adjusted during its application to
compensate for impedance variations between patients. Previously,
comparison of the measured values of the parameters to the
threshold values was done using dedicated hardware by using
comparators. Additionally, the threshold values themselves have
typically been set using dedicated hardware such as voltage
references. The voltage references have been implemented in a
variety of ways, such as by using voltage dividers, zener diodes,
or integrated circuit voltage references.
[0014] A reduction in hardware complexity could be achieved by
performing an operation on the parameters using programmable
hardware. By using firmware or software to control the hardware
with the threshold values specified in the code, the additional
hardware complexity that would be required to implement the
threshold comparison functions is eliminated. An additional
advantage achieved under program control is the capability to
easily configure the electrotherapy apparatus to deliver one of a
plurality of energy levels. Under program control, the operation
performed on the parameters is adjusted depending upon the selected
energy level and the different threshold values that can be coded
in the software, or firmware, are easily selected.
[0015] Yet another advantage of an implementation under program
control is the improved reliability achieved by reducing the
hardware required. A hardware implementation using a plurality of
threshold values for delivering one of a plurality of possible
energy levels to the patient would require additional hardware to
establish a plurality of reference values and a plurality of
comparators to perform the comparison. Alternatively, a switching
mechanism could be used to selectively connect the plurality of
reference values to a single comparator. This increased complexity
decreases the reliability of the electrotherapy apparatus.
[0016] Shown in FIG. 1 is a high level block diagram of an
electrotherapy apparatus 30, such as a defibrillator. The
electrotherapy apparatus 30 performs electrotherapy on patients and
compensates for impedance variations between patients by
dynamically controlling the electrotherapy waveform applied to the
patients. The implementation of electrotherapy apparatus 30 shown
in FIG. 1 is a reduced hardware implementation. In the
electrotherapy apparatus 30, functions previously implemented using
dedicated hardware are accomplished by the operation performed in
controller 38 under program control, thereby reducing the hardware
complexity needed for electrotherapy apparatus 30.
[0017] Electrotherapy apparatus 30 includes an energy source 32 to
provide the energy for the electrotherapy waveform. Energy source
32 may include, for example, a single capacitor or a capacitor bank
arranged to act as a single capacitor. A connecting mechanism 34
selectively connects and disconnects energy source 32 to and from a
pair of electrodes 36 contacting a patient, with the impedance of
the patient represented here as a resistive load 37. Connecting
mechanism 34 selectively connects energy source 32 to resistive
load 37 to provide an electrotherapy waveform. Connecting mechanism
34 can selectively connect either side of energy source 32 to
either one of electrodes 36 to provide an electrotherapy waveform
of either polarity. Controller 38 actuates the connecting mechanism
34 to couple energy source 32 to electrodes 36 or to decouple
energy source 32 from electrodes 36.
[0018] Electrotherapy apparatus 30 could be configured to provide a
variety of electrotherapy waveforms to a patient, such as a
mono-phasic electrotherapy waveform, a truncated exponential
bi-phasic waveform, a damped sinusoidal waveform, or the like.
Energy source 32, connecting mechanism 34, and controller 38 could
be designed to selectively permit delivery of any of these types of
electrotherapy waveforms to the patient. Additionally, the
electrotherapy waveforms may be delivered by energy source 32 using
a selected one of a plurality of energy levels set by controller
38.
[0019] Controller 38 is coupled to sensor 42 and receives the
output it generates. Sensor 42 measures a parameter, or parameters,
related to the energy delivered to the patient. Sensor 42 may be,
for example, a voltage sensor, a current sensor, or sensor 42 could
be configured to measure both voltage and current. Controller 38
uses the values of the parameter or parameters provided by sensor
42 to control connecting mechanism 34. The operation performed by
controller 38 could include comparing threshold values to the
output received from sensor 42. Based upon the result of this
comparison, controller 38 actuates connecting mechanism 34 to
control the duration of the electrotherapy waveform applied to
resistive load 37. Connecting mechanism 34 can be actuated to
either couple energy source 32 to patient electrodes 36 or decouple
energy source 32 from patient electrodes 36 based upon the
operation. The operation could include directly determining the
duration of the electrotherapy waveform based upon the results of
the comparison. Alternatively, the operation performed by
controller 38 on the values of the parameter or parameters received
from sensor 42 may include integrating a current measured by sensor
42 to determine the charge delivered to the patient. Or, it could
include determining patient impedance, computing a time constant,
or determining the time required for a current or voltage to
substantially equal a predetermined fraction of the initial voltage
or current. In this alternative, the operation would also include
comparing the results of these computations to threshold values
accessed by controller 38.
[0020] Using controller 38, operating under program control, to
perform the operation using the values output from sensor 42 and
threshold values simplifies the hardware needed to implement
electrotherapy apparatus 30. For example, in previous
implementations of electrotherapy apparatuses, integrations were
performed in hardware using analog integrators. The result of the
integration was compared to a threshold value using dedicated
hardware. By using controller 38 to perform the integration and
comparison to the threshold value under program control, the
dedicated hardware is eliminated. An additional benefit from
performing integration under program control is the ability to
achieve a greater dynamic range in the integration more easily than
using dedicated hardware. This allows for dynamic control of the
electrotherapy waveform using threshold values (that may, for
example, be specified in terms of the charge delivered to the
patient) that can be more simply implemented over a broader range
of values with greater accuracy than for a dedicated hardware
integrator. Similarly, determining patient impedance, time
constants, or the time required for voltages or currents to
substantially equal predetermined threshold values, is more easily
done over a wide range of energy levels by performing the operation
using controller 38 than by using dedicated hardware.
[0021] In electrotherapy apparatus 30, threshold values for other
parameters, such as the maximum allowable current supplied
(indicating the possibility of a short circuit) or the minimum
current supplied by the electrotherapy apparatus 30 (indicating a
possible open circuit) may be implemented in the software or
firmware operating controller 38. Performing these comparisons
under program control allows a reduction in the hardware needed to
perform the over current and under current detection functions.
Previously, dedicated hardware (in addition to that needed for
dynamic waveform control) was used to accomplish the over current
and under current detection.
[0022] Shown in FIG. 2 is a high level flow diagram of a method for
using the hardware shown in FIG. 1 to perform electrotherapy.
First, in step 100, controller 38 initializes energy source 32 in
preparation for delivering an electrotherapy waveform to resistive
load 37. Next, in step 102, controller 38 actuates connecting
mechanism 34 to couple energy source 32 to resistive load 37
through electrodes 36. Then, in step 104, sensor 42 measures a
parameter, or parameters, related to the energy delivered to
resistive load 37. Next, in step 106, controller 38 performs an
operation on the output received from sensor 42 for determining
control of connecting mechanism 34. The operation may include
determining the charge delivered to the patient, determining a
patient impedance, determining a time constant, or determining the
time required for a current or voltage to substantially equal a
predetermined fraction of the initial voltage or current. Then, in
step 108, controller 38 actuates connecting mechanism 34 to
decouple energy source 32 from electrodes 36 to control the
electrotherapy waveform applied to resistive load 37
(representative of the patient impedance) based upon the parameter.
The decoupling is done based upon the operation to compensate for
impedance variations between patients.
[0023] Shown in FIG. 3 is an exemplary electrotherapy waveform that
could be applied to a patient using electrotherapy apparatus 30.
Although the exemplary electrotherapy waveform shown in FIG. 3 is a
bi-phasic waveform, it should be recognized that electrotherapy
apparatus 30 could be configured to deliver a mono-phasic waveform
or an electrotherapy waveform having more than two phases.
[0024] Shown in FIG. 4 is a simplified block diagram showing an
embodiment of electrotherapy apparatus 30 that performs the
operation under firmware control. The embodiment of electrotherapy
apparatus 30 shown in FIG. 4 can be configured for delivering a
multi-phasic electrotherapy waveform to the patient, such as the
bi-phasic waveform shown in FIG. 3. Although FIG. 4 shows a
specific electrotherapy apparatus that performs the operation, the
disclosed principles are broadly applicable to electrotherapy
apparatuses.
[0025] A limitation of a dedicated hardware implementation using
multiple threshold values for delivery of multiple energy levels to
the patient is the complexity of the dedicated hardware required.
The implementation of this capability would require dedicated
hardware to set the multiple threshold values and dedicated
hardware to selectively compare the output from the sensors to the
threshold values. However, in the embodiment of the electrotherapy
apparatus 30 shown in FIG. 4, these functions are easily
implemented in the firmware that operates controller 212.
[0026] The embodiment of the electrotherapy apparatus 30 shown in
FIG. 4 includes sensors to measure the voltage and current supplied
by capacitor 200 to patient impedance 202 through first electrode
204 and second electrode 206. Measurement of the voltage supplied
by capacitor 200 is performed by voltage sensor 208. Voltage sensor
208 could, for example, be implemented using a voltage divider
network and a buffer amplifier coupled to the voltage divider. The
voltage divider generates a scaled version of the voltage on
capacitor 200 for the buffer amplifier. The voltage from the
voltage divider is coupled to the buffer amplifier. Measurement of
the current supplied by capacitor 200 is performed by current
sensor 210. Current sensor 210 could, for example, be implemented
using a sense resistor coupled in series with capacitor 200 and an
amplifier coupled across the sense resistor. The sense resistor
generates a voltage proportional to the current flowing from
capacitor 200. The voltage output from the amplifier is a scaled
version of the voltage across the sense resistor. Voltage sensor
208 and current sensor 210 are each coupled to controller 212.
Controller 212 measures the output from each of these sensors.
Controller 212 can use the values of the parameters measured by
voltage sensor 208 and current sensor 210 to dynamically control
the electrotherapy waveform supplied to the patient. Dynamic
control could be based upon the current supplied to the patient,
the charge supplied to the patient, the voltage supplied to the
patient, or a combination of these.
[0027] Controller 212 performs the operation on the values of the
parameters received from one or both of voltage sensor 208 and
current sensor 210. Based upon the operation, switches SW1, SW2,
SW3, SW4, and SW5 are closed and opened to deliver a multi-phasic
electrotherapy waveform to patient impedance 202 through first
electrode 204 and second electrode 206. The duration of each of the
phases of the multi-phasic waveform are determined by the operation
performed by controller 212 on the values of the parameters
received from one or both of voltage sensor 208 and current sensor
210. By controlling the duration of the phases, the embodiment of
the electrotherapy apparatus 30 can deliver differently shaped
electrotherapy waveforms to the patient. The operation performed by
controller 212 that determines the durations of each of the phases
could be accomplished by computations using the values of the
measured parameters. Alternatively, the operation performed by
controller 212 that determines the durations of each of the phases
could be accomplished with values in a lookup table accessed by
controller 212 using the values of the measured parameters.
[0028] The operation performed by controller 212 on the values of
the parameters measured by voltage sensor 208 and current sensor
210 depends upon the method chosen to implement the dynamic
electrotherapy waveform control. For example, controller 212 could
measure either the voltage or current supplied over a period of
time after the application of the electrotherapy waveform to
compute a time constant. The time constant is dependent upon the
value of capacitor 200 and the resistance in series with this
capacitance. The series resistance includes the patient impedance
and the resistance in the discharge path of the capacitor. Control
of the electrotherapy waveform based upon the time constant value
would involve sampling either the voltage or current supplied by
capacitor 200, computing the time constant of the electrotherapy
waveform from these values, and then dynamically controlling the
waveform using the computed time constant value. One way to
determine the time constant value would involve computing the slope
of the logarithm of the voltage versus time curve for the
electrotherapy waveform applied to the patient. Using the time
constant value, the durations of the phases of the electrotherapy
waveform would be selected from a lookup table or computed by
controller 212. For a bi-phasic electrotherapy waveform, the
information in the lookup table would have first phase durations
corresponding to ranges of time constant values. The duration of
the second phase could also be specified in the lookup table or
computed based upon the duration of the first phase.
[0029] Alternatively, the operation performed by controller 212
could dynamically control the electrotherapy waveform applied to
the patient based upon a time interval required for the voltage or
current supplied to the patient to substantially equal a
predetermined fraction of a value of voltage or current measured
during application of the electrotherapy waveform. This value of
voltage or current could be the peak value of the voltage or
current measured near the beginning of the electrotherapy waveform.
Or, this value of voltage or current could be measured at other
times during the application of the electrotherapy waveform. For
example, this value of voltage or current could be measured after
the instant at which the peak current or voltage occurs.
[0030] For dynamic waveform control based upon measurements by
voltage sensor 208, controller 212 could read the voltage measured
by voltage sensor 208 (the voltage across capacitor 200 which
closely approximates the voltage applied to patient impedance 202)
at the time capacitor 200 is coupled to patient impedance 202. This
corresponds to the peak value of the voltage supplied to the
patient during application of the electrotherapy waveform.
Alternatively, because controller 212 is used in selecting the
initial voltage to which capacitor 200 is charged, controller 212
could use the value of the selected initial voltage of capacitor
200 as the peak voltage supplied by capacitor 200. In another
alternative, the voltage on capacitor 200 after the occurrence of
the peak voltage could be measured and used by controller 212 to
perform the operation. The operation performed by controller 212
would include computing a threshold value as a predetermined
fraction of the value of the voltage on capacitor 200 (either
measured or selected). The time interval required for the voltage
across capacitor 200 to substantially equal the threshold value
changes depending upon the magnitude of patient impedance 202. The
time interval will be shorter for low impedance patients than it is
for high impedance patients. Based upon this time interval, the
operation performed with controller 212 would also include
computing, or selecting from a lookup table, the durations of the
phases of the multi-phasic electrotherapy waveform, such as the
first phase or the second phase of a bi-phasic waveform.
[0031] Dynamic control of the electrotherapy waveform could also be
accomplished by determining a time interval required for the
current supplied by capacitor 200 to substantially equal a
predetermined fraction of the peak value of the current supplied by
capacitor 200. To accomplish this, the controller 212 would read
the measurement of the current supplied by capacitor 200 made by
current sensor 210 to determine the peak current supplied to
patient impedance 202. Typically, when electrotherapy is applied,
the current supplied to patient impedance 202 will rise from zero
to a peak value shortly after capacitor 200 is coupled to the
patient. The rise time from zero to the peak value is limited by
the inductance in the path through which the current flows. After
reaching the peak value, the current will decay toward zero at a
rate determined primarily by the value of capacitor 200 and the
series resistance (which includes patient impedance 202). The
operation performed by controller 212 would include computing a
threshold value as a predetermined fraction of the peak value of
the current. As an alternative to measuring the peak current to
compute a threshold value, controller 212 could read the
measurement of the current supplied by capacitor 200 after the
occurrence of the peak current. The threshold value would be
computed as a predetermined fraction of this measured current.
[0032] The time interval required for the current supplied to
patient impedance 202 to substantially equal the threshold value of
the current changes depending upon the magnitude of patient
impedance 202. The time interval will be shorter for low impedance
patients than it is for high impedance patients. The operation
performed by the controller 212 would further include determining
the time interval required for the current supplied by capacitor
200 to substantially equal the threshold value. Based upon this
time interval, the operation performed by controller 212 would also
include computing, or selecting from a lookup table, the durations
of the phases of the multi-phasic electrotherapy waveform, such as
the first phase and the second phase of a bi-phasic electrotherapy
waveform.
[0033] In yet another dynamic electrotherapy waveform control
technique, the operation performed by controller 212 would involve
determining the value of patient impedance 202. Controller 212
would read the voltage and current values from, respectively,
voltage sensor 208 and current sensor 210. The operation performed
by controller 212 would include computing the value of patient
impedance 202 based upon the voltage and current values.
Computation of patient impedance 202 by controller 212 could be
done using a single voltage value and a single current value
measured substantially simultaneously, or, alternatively, a
plurality of pairs of voltage values and current values measured
substantially simultaneously at various times after the start of
the electrotherapy waveform.
[0034] The plurality of pairs of voltage values and current values
would be used by the controller to calculate multiple instantaneous
values of the patient impedance during application of the
electrotherapy waveform. The operation performed by controller 212
could include averaging these values of patient impedance.
Averaging of the impedance values provides a more accurate
measurement of the patient impedance than would be obtained from
single measurements of voltage and current. The measurements and
computation of the patient impedances would be done relatively
early in the application of the electrotherapy waveform so that the
results could be used to adjust the electrotherapy waveform based
upon the calculated patient impedance. Based upon the computed
impedance value, the operation performed by controller 212 would
also include computing, or selecting from a lookup table, the
durations of the phases of the multi-phasic electrotherapy
waveform, such as the first phase and the second phase of a
bi-phasic electrotherapy waveform.
[0035] An additional technique for dynamic control of the
electrotherapy waveform determines the duration of the phases of a
multi-phasic electrotherapy waveform depending based upon the
charge delivered to the patient. Controller 212 reads the values of
current measured by current sensor 210 after application of the
electrotherapy waveform to the patient. The operation performed by
controller 212 includes integrating these current values to
determine the charge delivered to the patient over the time in
which the measurements were made. The operation performed by
controller 212 further includes determining a time interval
required for delivering a predetermined quantity of charge to the
patient. Based upon the time interval, the operation performed by
controller 212 would also include computing, or selecting from a
lookup table, the durations of the phases of the multi-phasic
electrotherapy waveform, such as the first phase and the second
phase of a bi-phasic electrotherapy waveform.
[0036] An energy source, such as high voltage power supply 214, is
used to charge capacitor 200 to an initial voltage determined by
controller 212. The initial voltage to which capacitor 200 is
charged sets the energy level of the electrotherapy waveform to be
applied to patient impedance 202. The initial voltage is selected
by controller 212 from one of a plurality of possible initial
voltages values. Selecting from a plurality of initial voltages
values for charging capacitor 200 is done in response to operator
input. An operator may need to select the initial voltage because
electrotherapy will be applied to the heart, or to a pediatric
patient.
[0037] Controller 212 dynamically controls the electrotherapy
waveform applied to patient impedance 202 based upon the parameters
supplied by the sensors. Dynamic control of the electrotherapy
waveform permits patients having a wide range of impedances to
receive optimal levels of energy. Depending upon the technique used
to perform the dynamic waveform control, the operation performed by
controller 212 may need to account for the initial voltage to which
capacitor 200 is charged to deliver optimal levels of energy to
patients having varying impedances. The threshold values used in
the operation performed by controller 212 may change depending upon
the initial voltage to which capacitor 200 is charged. In
performing the operation, controller 212 would use a threshold
value corresponding to the selected one of the plurality of initial
voltage values. For dynamic electrotherapy waveform control based
upon the operation, the threshold values used by controller 212
would be computed or selected from a lookup table dependent upon
the energy level applied to the patient. For each of the plurality
of initial voltages to which capacitor 200 could be charged, there
would be a corresponding threshold value used in the operation
performed by controller 212. Using a plurality of threshold values
is easily done because the different threshold values are selected
by the firmware of controller 212.
[0038] In addition to dynamic electrotherapy waveform control, the
embodiment of electrotherapy apparatus 30 shown in FIG. 4 is also
well suited to the detection of over-current and under-current
conditions during the application of electrotherapy. Current sensor
210 measures the current supplied by capacitor 200 at the end of
the first 100 micro-seconds following application of the
electrotherapy waveform to detect the over-current or under-current
condition. The threshold values that indicate the presence of
either an over-current condition or an under-current condition
change with the energy level used for the electrotherapy.
[0039] Detection of either an over-current or an under-current
condition results in termination of the electrotherapy waveform.
The presence of an under-current condition indicates the
possibility of damaged electrodes or electrodes that are not
connected to the patient. The presence of an over-current condition
indicates the possibility of a short circuit. The threshold values
for the over-current and the under-current detection can be
computed from the initial voltage to which capacitor 200 is
charged. The initial voltage could be obtained by reading the
output of voltage sensor 208. Alternatively, the threshold values
for the over-current and the under-current detection can be
selected from a lookup table based upon the initial voltage to
which capacitor 200 is charged. The threshold values are computed
by controller 212 using the upper and lower limits of the expected
values of patient impedance 202 (respectively, 180 ohms and 25
ohms) and subtracting or adding a small value to provide for
possible measurement error. The values of the measured current read
from current sensor 210 are compared by controller 212 to the
corresponding threshold values to determine whether an over-current
or an under-current condition is present.
[0040] Operation of the embodiment of electrotherapy apparatus 30
shown in FIG. 4 will be explained for the case in which switch SW5
is an insulated gate bipolar transistor and switches SW1-SW4 are
silicon controlled rectifiers. However, it should be recognized
that other types of electronic or electro-mechanical switches could
be used to deliver the electrotherapy waveform. For other types of
switching devices, the order in which switches SW1-SW5 are actuated
may be different. Additionally, operation of the embodiment of
electrotherapy apparatus 30 will be explained for the case in which
the multi-phasic waveform applied includes a bi-phasic
waveform.
[0041] In preparation for delivering a bi-phasic electrotherapy
waveform, controller 212 configures high voltage power supply 214
to charge capacitor 200 to a selected initial voltage. Then
controller 212 closes switch SW5 to prepare for delivering the
first phase of a bi-phasic waveform. Next, switches SW1 and SW4 are
closed to begin the first phase of the bi-phasic electrotherapy
waveform. After the beginning of the first phase, voltage sensor
208 measures the voltage across capacitor 200 and current sensor
210 measures the current supplied by capacitor 200. Based upon the
values of either the voltage or the current or the values of both
the voltage and the current, controller 212 performs an operation
to determine the duration of the first phase and the second phase.
At the end of the time interval determined for the first phase,
controller 212 opens switch SW5. This interrupts current flow
through switches SW1 and SW4 and opens these switches, completing
the first phase. After 400 micro-seconds, controller 212 closes
switch SW5 to prepare for delivering the second phase of the
bi-phasic waveform. Then, 50 micro-seconds later, switches SW2 and
SW3 are closed to begin the second phase. At the end of the time
interval determined for the second phase, controller 212 opens
switch SW5. This interrupts current flow through switches SW2 and
SW3 and opens these switches completing the second phase.
[0042] Although several embodiments of the invention have been
disclosed, various modifications may be made without departing from
the scope of the appended claims.
* * * * *