U.S. patent application number 11/180396 was filed with the patent office on 2006-02-23 for automatic defibrillator module for integration with standard patient monitoring equipment.
Invention is credited to Patrick Bradley, David Clark, Raymond W. Cohen, Dongping Lin, Gary Mezack, Mike Norton.
Application Number | 20060041278 11/180396 |
Document ID | / |
Family ID | 24086941 |
Filed Date | 2006-02-23 |
United States Patent
Application |
20060041278 |
Kind Code |
A1 |
Cohen; Raymond W. ; et
al. |
February 23, 2006 |
Automatic defibrillator module for integration with standard
patient monitoring equipment
Abstract
A defibrillator module is described which includes a cardiac
sensor, a pulse generator and a controller that generates commands
responsive to intrinsic cardiac signals for the operation of said
pulse generator. The defibrillator module synergistic and arranged
so that it can be coupled to a generic patient monitor so that the
two can share certain functions. For example, operational
parameters and other signals indicative of the operation of the
defibrillator module can be shown to the clinician by the patient
monitor. Data between the defibrillator module and the patient
monitor is exchanged using either a standard or a customized
protocol.
Inventors: |
Cohen; Raymond W.; (Orange,
CA) ; Lin; Dongping; (Irvine, CA) ; Norton;
Mike; (Riverside, CA) ; Bradley; Patrick;
(Corona del Mar, CA) ; Mezack; Gary; (Norco,
CA) ; Clark; David; (Irvine, CA) |
Correspondence
Address: |
GOTTLIEB RACKMAN & REISMAN PC
270 MADISON AVENUE
8TH FLOOR
NEW YORK
NY
100160601
US
|
Family ID: |
24086941 |
Appl. No.: |
11/180396 |
Filed: |
July 13, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09523912 |
Mar 9, 2000 |
|
|
|
11180396 |
Jul 13, 2005 |
|
|
|
Current U.S.
Class: |
607/5 |
Current CPC
Class: |
A61N 1/3925 20130101;
A61N 1/3904 20170801 |
Class at
Publication: |
607/005 |
International
Class: |
A61N 1/39 20060101
A61N001/39 |
Claims
1-22. (canceled)
23. A composite monitoring system comprising: a patient monitor
disposed in a monitor housing and including a sensor arranged to
sense a physiological characteristic of a patient and a signal
processor coupled to said sensor and adapted to process the signal
from said sensor and an output member; and a defibrillator module
disposed in a defibrillator housing and adapted to be selectively
coupled to said patient monitor, said defibrillator module
including a pulse generator responsive to commands to generate
therapeutic pulses for the patient, and a data generator arranged
to generate indication signals indicative of an operation of said
defibrillator module; said patient monitor and said defibrillator
module cooperating when coupled to transfer said indication signal
to said output member wherein said output member generates output
signals corresponding to one of said patient characteristic and
said indication signals.
24. The defibrillator assembly of claim 23 wherein said
defibrillator module is adapted in one of several operational mode,
including a pacing mode for applying pacing to the patient.
25. A method of providing patient treatment comprising: providing a
patient monitor adjacent to a patient, said patient monitor being
adapted to measure a patient characteristic; providing a
defibrillator adapted to selectively provide shock therapy to the
patient, said patient monitor and said defibrillator being adapted
to operate independently of each other; and associating said
defibrillator and said patient monitor to allow said defibrillator
and said patient monitor to receive data to or from each other.
26. A method of combining a patient monitoring network and an
external defibrillator comprising: providing a patient monitoring
network; providing an external defibrillator, wherein said patient
monitoring network is operational independently of said external
defibrillator and said external defibrillator is operational
independently of said external defibrillator; and coupling said
patient monitoring network and said external defibrillator to
couple to each other for exchanging information.
Description
BACKGROUND OF THE INVENTION
[0001] A. Field of Invention
[0002] This invention pertains to an external defibrillator module
arranged and constructed to provide anti-tachyarrhythmia therapy to
a patient. In particular, an automatic external defibrillator
module is described which has several operational modes including a
fully automatic mode in which shocks are delivered without any
manual intervention, an advisory mode, a manual mode, and a pacer
mode. Moreover, the invention pertains to a defibrillator module
which is arranged and constructed for integration with patient
monitoring equipment for sharing certain functions and information
using a standard or customized protocol.
[0003] B. Description of the Prior Art
[0004] Defibrillators are devices which apply electric therapy to
cardiac patients having an abnormally high heart rhythm or
fibrillation. Two kinds of defibrillators are presently available:
internal defibrillators which are implanted subcutaneously in a
patient together with leads extending through the veins into the
cardiac chambers, and external defibrillators which are attached
(usually temporarily) to the patient. External defibrillators are
used in most instances in case of an emergency, for example, when a
patient has either suffered cardiac arrest or when a cardiac arrest
is imminent. Typically, therefore external defibrillators are
manual devices which must be triggered by a physician or other
trained personnel. Internal or implantable defibrillators (and
cardioverters) are implanted as a permanent solution for patients
having specific well-defined cardiac deficiencies which cannot be
treated successfully by other means. They generally operate in an
automatic mode.
[0005] Commonly-owned U.S. Pat. No. 5,474,574 discloses an external
defibrillator. Commonly-owned U.S. Pat. Nos. 4,576,170 and
5,474,574, incorporated herein by reference discloses external
defibrillators.
[0006] Several patient monitoring systems are presently available
in modular form which allow a clinician or other health
professional to monitor and display various physiological
parameters of a patient. Typically these units include several
subassembly modules which cooperate to acquire data from the
patient, to store the data electronically and to display
information about a patient's physiological status. The systems may
also be adapted to generate audible and/or visual alarms when
certain criteria are met. Some systems may also be integrated into
a communications network covering, for example, a part or even a
whole hospital and on which data is exchanged for various purposes.
Monitoring systems of this kind are available from GE Marquette
Medical Systems of Milwaukee, Wis.; Agilent Technologies of
Andover, Mass.; Spacelabs Medical of Redmond, Wash., and many other
companies. However, typically these systems are passive in that
their main purpose is to monitor, collect information and generate
alarms. These systems cannot provide therapy.
OBJECTIVES AND SUMMARY OF THE INVENTION
[0007] An objective of the present invention is to provide an
automatic defibrillator module which is capable of detecting a
current cardiac condition of a patient and of providing appropriate
therapy to the patient, when needed.
[0008] A further objective is to provide an automatic defibrillator
module which can be interfaced with a existing or future patient
monitoring systems in a manner which allows the system and the
module to share information and other common functions.
[0009] Yet another objective is to provide an external
defibrillator module with several modes of operation, including an
automatic mode in which shocks are applied on demand in accordance
with preprogrammed shock parameters and without any prompting from
an attendant, an advisory mode in which an attendant is alerted to
a shockable rhythm however the application of shocks must be
initiated by the attendant, a manual mode in which the attendant
determines how and when shocks should be applied and the
preprogrammed shock parameters are ignored, and a pacer mode for
pacing certain cardiac events.
[0010] Other objectives and advantages of the invention will become
apparent from the following description of the invention.
[0011] Briefly, a composite monitoring system constructed in
accordance with this invention comprises a patient monitor
including a sensor arranged to sense a physiological characteristic
of a patient and a signal processor coupled to said sensor and
adapted to process the signal from said sensor and an output
member; and a defibrillator module adapted to be selectively
coupled to said patient monitor, said defibrillator module
including a pulse generator responsive to commands to generate
therapeutic pulses for the patient, and a data generator arranged
to generate indication signals indicative of an operation of said
defibrillator module; wherein said patient monitor and said
defibrillator module cooperating when coupled to transfer said
indication signal to said output member whereby said output member
generates output signals corresponding to one of said patient
characteristic and said indication signals. The patient monitor may
include a display that can be used to show signals or data
associated with either the physiological characteristics being
monitored or information pertaining to the operation of the
defibrillator module. The patient monitor could also include
audible and visual alarms, a printer, and a connection to a network
through which data could be sent to a remote location. All these
components could be shared between the patient monitor and the
defibrillator module. Data between the defibrillator module and the
patient monitor is exchanged using either a protocol standardized
for the monitor or by using a customized protocol.
BRIEF DESCRIPTION OF THE FIGURES
[0012] FIG. 1 shows a block diagram of a combined patient monitor
and automatic defibrillator system;
[0013] FIG. 2 shows a somewhat schematic isometric view of the
automatic defibrillator module for the system of FIG. 1; and
[0014] FIG. 3 shows a block diagram for the control assembly of the
automatic defibrillator module incorporated into the system of FIG.
1.
[0015] FIG. 4a shows a circuit illustrating the "totem-poling" of
two SCRs so that the combination of the two devices can withstand a
higher voltage than a single device;
[0016] FIGS. 4b, 4c and 4d are, respectively, the substrate
construction, circuit symbol and I=V characteristics of a Shockley
diode;
[0017] FIG. 4e is a circuit diagram of a breakover USD;
[0018] FIGS. 4f, 4g and 4h are, respectively, a circuit diagram,
circuit symbol and I=V characteristics of a breakunder USD;
[0019] FIGS. 5a and 5b are, respectively, the circuit symbol and a
circuit diagram for a breakunder USD with hysteresis;
[0020] FIG. 6 is a circuit diagram of a defibrillator using a first
implementation for the pulse generator;
[0021] FIG. 7 is a circuit diagram of a of defibrillator using a
second implementation of a pulse generator;
[0022] FIG. 8 is an example of the waveform that can be produced by
the implementation of FIG. 7;
[0023] FIG. 9 is a circuit diagram of a defibrillator showing a
third implementation of the pulse generator;
[0024] FIG. 10 is a circuit diagram of a fourth implementation of
the pulse generator;
[0025] FIG. 11 illustrates a pulse generator with the output
circuit being implemented as a single encapsulated integrated
circuit component;
[0026] FIG. 12a is a circuit diagram of a fifth implementation of
the pulse generator; and
[0027] FIG. 12b is an example of the waveform that can be produced
by the embodiment of FIG. 12a.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Referring now to FIG. 1, a combined system 10 constructed in
accordance with this invention includes a generic patient monitor
12 which is connected to one or more sensors 14 extending to the
patient (not shown). The sensors 14 are used to obtain one or more
physiological indicia from the patient, such as temperature,
pressure, heart rate, respiration function, and so on. The monitor
12 includes a data processor 16, a display 18, a power supply 20,
and data interface 22, which may for example be a standard serial
or parallel port or any other data interface that may be used to
exchange information with other components and/or a communications
network (not shown). The monitor 12 may also include an audible
alarm 24, a visual alarm 26 and a printer 28.
[0029] The data processor 16 in monitor 12 collects information
from the patient through the sensors, processes this information
and based on its programming, generates reports on the status of
the patient. This status may be shown on display 18, and
selectively a hard copy of the reports may be provided by printer
28. The status information may also be transmitted to remote
locations via the interface 22 and the communications network. The
monitor 12 may also include a memory 30 for logging the information
regarding the status of the patient. The data processor 16 may also
be adapted to determine if certain of the physiological parameters
exceed certain preselected ranges or threshold values, these ranges
or threshold values being selected to correspond to indicate
abnormal or dangerous conditions for the patient. When such an
event is detected, the data processor can activate the audible
and/or the visual alarms 24, 26 to indicate that a danger condition
has been detected.
[0030] As seen in FIG. 1, associated with monitor 12 there is
provided an automatic defibrillator module (ADM) 32. The ADM is
connected to its own set of sensors or defibrillator pads 34 via a
cable 36. The purpose of providing the ADM 32 as a module rather
than a stand-alone unit is so that it can share some of the
functions and components of the monitor 12. For this purpose, the
ADM 32 is connected to monitor 12 via a data cable 38. Power to the
ADM 32 can be provided by the power supply via a cable 40, or
alternatively, the cable 40 may be connected to a standard line
voltage outlet (not shown).
[0031] Referring now to FIG. 2, the ADM 32, in this configuration,
consists of three assemblies: a battery pack 42, an assembly 44
including an AC power supply and biphasic pulse generator and a
control board 46. The battery pack 42 consists of one or more
batteries, which may be re-chargable by using energy from the AC
power supply. The AC power supply is connected by cable 40 to
monitor 12 or other line voltage source. The battery pack is used
to provide high energy to the biphasic pulse generator of assembly
44. This energy is used as backup power source in the event of a AC
power failure. The defibrillation pulses are transmitted by the
cable 36 to the patient. For this purpose, the assembly 44 the
cable 36 is provided with a connector 48 which mates with a
connector 50 on the assembly 44.
[0032] The control assembly 46 contains the components required to
control the operation of the ADM 32. As seen in FIG. 2, the
assembly 46 includes a front face 52 formed with a display 54. Also
provided on face 52 are a control knob 56 and a plurality of panel
switches 58. Built into each of the switches 58 is an indication
light 60. These lights are optional and may be omitted.
[0033] The control assembly 46 is further provided with two serial
ports 62, 64. Serial port 62 is connected via cable 38 to monitor
12. The other port 64 may be used to connect the ADM 32 to other
components.
[0034] The overall functionality of each component is more
important than the number and the functional partition of
assemblies. Another implementation may comprise more or less
assemblies.
[0035] FIG. 3 shows a block diagram of the ADM 32. The control
assembly 46 includes a microprocessor or controller 66, a flash
memory 68 and a custom control IC 70 which may be made using, for
example, an FPGA design. The microprocessor 66 is connected to the
serial port 62, switches 58, indicator lights 60 and the flash
memory 68 and the custom IC 70 so that it can control the operation
of the ADM 32. The flash memory 68 is used to store various
operational parameters of the ADM 32 which can be either preset or
selected by a clinician. These parameters can be set through the
menu control knob 58 in conjunction with the switches 60 or via the
patient monitor.
[0036] The lights 60 are activated either by the microprocessor 66
or by the custom IC 70. As discussed above, the ADM 32 is capable
of generating audible as well as visual indication signals. The
audible signals can be transmitted to the monitor 12 and/or to
external speakers 72 (not shown in FIGS. 1 and 2). These audible
signals can be generated by the microprocessor 66 and/or the custom
IC 70.
[0037] Component 50 includes a power supply 74, a battery charger
76, an alarm power unit 78 and a biphasic pulse generator 80 (all
shown in FIG. 3). The alarm power unit 78 provides the power
required to drive the speakers 72 (if present). The battery charger
76 is used to charge the battery pack 42.
[0038] The biphasic pulse generator 80 receives dc power either
from the power supply 74 or from the battery pack 42. The pulse
generator 80 generates biphasic pulses in accordance with commands
from the microprocessor 66.
[0039] A somewhat preferred implementation for the biphasic pulse
generator 80 is now described, it being understood that this
implementation does not constitute a part of the subject invention,
and that other implementations may be used as well.
[0040] The pulse generators described herein use devices or
circuits having the characteristics of Shockley diodes, and which
are referred to herein as uncontrolled solid state devices (USDs)
as defined above. Unlike SCRs and IGBTs, a Shockley Diode does not
require a gate drive signal to initiate it from a high impedance
state to a state of lower impedance. FIG. 4b shows the substrate
construction of a Shockley diode as a four layer silicon device
with respective doping densities P1, N1, P2 and N2.
[0041] FIG. 4c shows the symbol used to denote a Shockley diode;
note that there are only two connecting terminals. Essentially, a
Shockley diode is uni-directional in that it can only change from
its default high impedance state to a state of reduced impedance
when the polarity of the applied signal is in a particular
direction to forward bias the device, see FIG. 4d. Applying a
signal of opposite polarity will fail to change the device's state
unless the voltage exceeds its reverse breakdown voltage (Vr). A
characteristic of a Shockley diode is that as a voltage is applied
across the device in the forward bias direction, the device will
only change to its lower impedance state if the voltage exceeds a
predetermined threshold (Vth). Shockley diodes, however, are not
readily commercially available and those that are typically only
capable of withstanding small voltages and currents. However, this
limitation can be overcome by arranging other commercially
available devices to perform the equivalent function for high
voltages and currents.
[0042] FIG. 4e is a high voltage, high current, implementation of a
"breakover" USD, equivalent to a Shockley diode, using a DIAC and a
TRIAC. Note that the overall circuit of FIG. 3 has only two
terminals, an anode A' and a cathode K'. The TRIAC will change to a
state of low impedance allowing a high current to flow when an
appropriate voltage is applied to its gate terminal g. The
combination of resistors R1 and R2 form a voltage divider, dividing
the voltage V down to a voltage Vb, referenced to the cathode K',
at the base of the transistor T1, where Vb=V[R2/(R1+R2)]. The
emitter follower configuration of transistor T1 keeps the voltage
applied to the DIAC at point X at approximately 0.7 Volts below the
voltage Vb.
[0043] The DIAC will remain in its default high impedance state
unless the voltage across it exceeds its threshold voltage Vd.
Unless this voltage threshold is exceeded therefore, the USD will
remain high impedance between A' and K'. If, however, the voltage
at X exceeds the DIAC's threshold Vd, the DIAC will fold back and
allow a voltage to appear at the gate of the TRIAC, and the TRIAC
will then change to its low impedance state allowing a high current
to flow between A' and K'. The overall voltage at which the USD
changes state can therefore be accurately set by the voltage
divider R1/R2. If the USD is desired to change to its low impedance
state when the voltage V across it, i.e. across the terminals A'
and K', reaches a certain threshold Vth, then the values of R1 and
R2 are chosen such that this voltage Vth causes the voltage at X to
be equal to the DIAC threshold voltage Vd; i.e. one solves the
equation Vd=[Vth(R2/(R1+R2))]-0.7 for R1 and R2. Resistor R3 limits
the current flow into the gate terminal of the TRIAC and prevents
the gate from being damaged by the relatively high voltage across
the terminals A' and K'. Note that with the state change of the
device being determined by the ratio of R1 and R2, and the supply
to the DIAC being performed by R3 through the current gain of T1,
the values of both R1 and R2 can be kept high. Using high impedance
values for R1 and R2 means that in the high impedance state there
is very little current leakage through the USD. The diode D1
opposes any current flow in the reverse bias direction and in
effect determines the reverse breakdown characteristics for the
USD.
[0044] Note that any device which can be placed in a low impedance
state from an initial state of high impedance could be used in
place of the TRIAC in FIG. 4e, for example the USD could have
employed a combination of IGBTs, SCRs, FETs (field effect
transistors) or BJTs (bipolar junction transistor). The various
implementations possible will be known to those skilled in the
art.
[0045] FIG. 4f shows another USD where the device has been
configured to change to a state of low impedance if the
instantaneous voltage across the anode A' and cathode K' exceeds a
well defined threshold V1, yet does not exceed an even higher
voltage threshold Vh. In other words, if the voltage V applied
across the device in FIG. 4f is within a well specified range from
V1 to Vh the device will enter its low impedance state, while if it
is outside this range, the device will remain in its default high
impedance mode. With this particular characteristic the device is
termed a "breakunder" USD. FIGS. 4g and 4h show the device's
circuit symbol and I-V characteristics respectively.
[0046] The implementation of the breakunder USD in FIG. 4f is
similar to that of the breakover device in FIG. 4e. The main
difference is the presence of a capacitor C1 and a second
transistor T2. Capacitor C1 limits the rate of change of voltage
across R1. This in turn limits the rate of change of voltage across
the DIAC. Since the voltage across the DIAC is slow to rise, if the
voltage Y at the base of T2, as determined by the voltage divider
R4/R5, rises above the forward bias voltage across T2's base
emitter-junction before the DIAC voltage reaches its threshold Vd,
the transistor T2 will turn on to short the gate of the TRIAC to K'
and thus inhibit any current flow into the gate of the TRIAC. Using
this arrangement, the upper voltage threshold Vh can be set by the
voltage divider R4/R5 and the lower threshold V can be set as
before by R1/R2.
[0047] Any breakunder device can further be arranged so that, once
a voltage has been applied across its terminals large enough to
exceed the upper threshold Vh so keeping the device in the high
impedance state, if the applied voltage drops in magnitude the
device will remain in the high impedance state. In this mode, in
order to change to the low impedance state, the current must be
reduced to almost zero and then re-applied. This later device is
referred to as a breakunder USD with hysteresis.
[0048] FIG. 5a shows the circuit symbol for a breakunder USD with
hysteresis. FIG. 5b shows an implementation of the device based
upon the breakunder device shown in FIG. 4. Only the differences
will be described. A transistor T2 now forms a second emitter
follower supplying a second DIAC, DIAC2. The voltage at point Y is
designed to have a value equal to the threshold of DIAC2 when the
voltage V across A', K' is equal to an upper threshold Vh. From
FIG. 5b it can be seen that, unlike the voltage at point X, the
voltage at point Y will instantaneously follow V and will be a
proportion of V according to the ratio set by R4 and R5. If the
voltage V causes the voltage at Y to exceed the voltage threshold
of DIAC2, then a second TRIAC, TRIAC2, will enter a low impedance
state. As soon as TRIAC2 enters its low impedance state, the
voltage Vb at the base of T1 will reduce to almost zero. Once
TRIAC2 has entered a low impedance state T1 cannot supply any
current to DIAC1 and therefore the gate of TRIAC1. This "feedback"
enhancement of FIG. 4 has introduced a level of hysteresis in to
the arrangement. The only way now for TRIAC1 to enter its low
impedance state is for the voltage across A', K' to be reduced to
zero and then a new voltage applied which has a value between the
lower threshold set by R1, R2 and DIAC1 and the upper threshold set
by R4, R5 and DIAC2. This device has essentially three modes, two
high impedance and one low impedance. If the instantaneous voltage
applied to the arrangement is below the lower threshold V1, then
the combination of R1, R2 and T1 means that DIAC1 does not pass
current and TRIAC1 remains in it's high impedance state. If the
applied voltage is greater than the lower threshold V1 and less
than the upper threshold Vh, then the combination of R4, R5 and T2
means that DIAC2 does not pass current and with DIAC1 now passing
current, once the voltage across C1 has had sufficient time to
rise, to the gate of TRIAC1, TRIAC1 enters its low impedance state.
If, however, the applied voltage is greater than the upper
threshold Vh, then the combination of R4, R5 and T2 means that
DIAC2 does pass current to the gate of TRIAC2 thereby inhibiting
DIAC1 and keeping TRIAC1 in its high impedance state.
[0049] It should be noted that any of the USDs of FIGS. 4e to 5
could be implemented as doped silicon layers in a single discrete
integrated device. None of the devices require any external control
and have the characteristic that they will conduct if the voltage
across their two terminals A' and K' is either above and/or below a
specified threshold. Another characteristic is that once in their
low impedance state, they can only be returned to their high
impedance state if the current flow through them is reduced to near
zero. At exactly which current they will drop-out is dependent upon
the particular device used.
[0050] FIG. 6 shows a basic implementation of a defibrillator,
designed to provide a monophasic output voltage pulse across a pair
of patient electrodes A and B. The defibrillator has an energy
source 160, in this instance a capacitor which is charged up by a
charging circuit 162, and an output circuit for connecting the
voltage on the capacitor across the electrodes A, B upon the
occurrence of a control signal 164. The output circuit comprises a
first current path connecting the +ve side of the energy source 160
to the electrode A and a second current path connecting the -ve
side of the energy source to the electrode B. The first current
path contains a breakover USD, USD1(bo), while the second current
path contains an IGBT, IGBT1. The breakover USD1(bo) will allow the
current from the energy source 160 to flow through the load
(patient) connected across the output electrodes A and B if the
voltage applied from the energy source is large enough to exceed
its threshold. The breakover USD1(bo) can be constructed as
described with reference to FIG. 4e.
[0051] Initially, both sides of the load see a high impedance into
A and B. Applying a gate drive pulse 164 to IGBT1 turns the latter
on and drops the entire energy source voltage across USD1(bo).
Provided the energy source is charged to a voltage above the
threshold for USD1(bo), the latter will change to its low impedance
state. The energy source now begins to discharge into the load.
Removing the drive pulse 164 from the gate of IGBT1 after a
pre-determined time period causes IGBT1 to return to its high
impedance state and the current in the circuit reduces to
approximately zero. With almost zero current flow, the device
USD1(bo) recovers and the load once again sees a high impedance on
both sides of A and B.
[0052] The use of the USD between electrode A and the +ve terminal
of the energy source means that there is no isolated controlling
circuit connection required. The only controlling element in the
circuit of FIG. 6 is the gate of IGBT1 and this is referenced to
the circuit ground so no isolation barrier is needed. The
conventional diode D1 is used to prevent current flow back into the
charging circuitry when charging is complete. The output generated
by the circuit of FIG. 6 is a simple monophasic truncated
exponential waveform.
[0053] Although FIG. 6 shows only one USD in the first current
path, it will be understood that the voltage that can be withstood
by the output circuit in the high impedance state can be increased
by totem-poling two or more USDs in the first current path, as
described previously. Two or more USDs in series actually behave
just like a single USD with a threshold Vth which is the sum of the
thresholds of the individual devices.
[0054] FIG. 7 shows an implementation of a defibrillator designed
to provide a biphasic truncated exponential output voltage pulse
across the patient electrodes A and B. Essentially, the
implementation of FIG. 6 has been modified to add third and fourth
current paths, shown by dashed lines. The third current path
connects the +ve side of the energy source 160 to the electrode B
and the fourth current path connects the -ve side of the energy
source to the electrode A. The third current path contains two
"totem-poled" SCRs, SCR1 and SCR2, while the fourth current path
contains a further IGBT, IGBT2. The first and second current paths
are as before, except that the first current path is shown with two
totem-poled breakover USDs, USD1(bo) and USD2(bo). The USDs may be
as shown in FIG. 3. For reasons previously described, the SCRs have
isolated gate drives.
[0055] In operation, the energy source 160 is first charged to a
voltage exceeding the threshold Vth of the totem-poled USDs. Then,
at time t0 (see FIG. 8), the device IGBT1 is given a gate pulse 64
placing it into its low impedance state. This places substantially
the entire voltage of the energy source across the totem-poled USDs
(two USDs are used as previously stated to increase the voltage
that the circuit can withstand). The USDs therefore turn on (the
devices SCR1, SCR2 and IGBT2 remaining in their high impedance
state), and a current flows through the load from electrode A to
electrode B. As energy is removed from the energy source by the
load, the voltage applied by the energy source decays. At a later
time t1, the IGBT1 has its gate signal removed and it returns to
its high impedance state. This causes the current in the circuit to
reduce to almost zero so returning the devices USD1(bo) and
USD2(bo) to their high impedance states. The instant t1 is chosen
so that at that point the voltage remaining on the energy source is
below the threshold Vth of the totem-poled devices USD1(bo) and
USD2(bo).
[0056] Now, at a time t2 following shortly after t1, the devices
IGBT2, SCR1 and SCR2 are given simultaneous gate drive pulses 64'
to place them in their low impedance state. Now a discharge current
flows in the opposite direction through the load, i.e. from
electrode B to electrode A. After a further pre-determined time
period has elapsed the gate drive to device IGBT2 is removed at t3
and the current flowing in the circuit is reduced almost to zero.
Again this causes the two SCRs to also return to their high
impedance state. The resulting output is as shown in FIG. 8.
[0057] In this circuit isolated gate drives are required for the
SCRs. However, only two such isolated gate drives are required in
this case. The methods used by prior art would have required at
least four isolated gate drive circuits. Also only four devices are
required to be controlled in total instead of the six control lines
previously necessary.
[0058] FIG. 9 shows a third implementation of the pulse generator.
This differs from the implementation of FIG. 7 in that the
totem-poled SCRs, SCR1 and SCR2, have been replaced by totem-poled
breakunder USDs with hysteresis, USD3(bu) and USD4(bu).
[0059] In operation, the energy source 160 is first charged to a
voltage greater than the threshold Vth of the totem-poled breakover
USDs and also greater than the upper voltage threshold Vh of the
totem-poled breakunder USDs. Then, at time t0 (see FIG. 8, which
also apples in this case), the device IGBT1 is given a gate pulse
164 placing it into its low impedance state. This places
substantially the entire voltage of the energy source across the
totem-poled breakover USDs, USD1(bo) and USD2(bo). All other
devices remain in their high impedance state (the breakunder USDs
because the voltage is above their upper threshold Vh; this is
important because otherwise they would turn on and bypass the
load). The breakover USDs therefore turn on and a current flows
through the load from electrode A to electrode B. As energy is
removed from the energy source by the load, the voltage applied by
the energy source decays. At a later time t1, the IGBT1 has its
gate signal removed and it returns to its high impedance state.
This causes the current in the circuit to reduce to almost zero so
returning the devices USD1(bo) and USD2(bo) to their high impedance
states. The instant t1 is chosen so that at that point the voltage
remaining on the energy source is below the threshold Vth of the
totem-poled devices USD1(bo) and USD2(bo) but between the upper and
lower voltage thresholds V1, Vh of the totem-poled devices USD3(bu)
and USD4(bu).
[0060] Now, at a time t2 following shortly after t1, the device
IGBT2 is given a gate drive pulse 64' to place it in its low
impedance state. Now the devices USD3(bu) and USD4(bu) turn on,
because the voltage applied across them is between their upper and
lower voltage thresholds, and a discharge current flows in the
opposite direction through the load, i.e. from electrode B to
electrode A. After a further pre-determined time period has elapsed
the gate drive to device IGBT2 is removed at t3 and the current
flowing in the circuit is reduced almost to zero. Again this causes
USD3(bu) and USD4(bu) to return to their high impedance state. The
resulting output is as shown in FIG. 8.
[0061] Of particular note is that for this arrangement there are no
isolated connection gate control connections to any of the devices
in the circuit. Also only two devices (IGBT1 and IGBT2) require
control signals and these are both direct electrical connections
referenced to circuit ground. This is a significant saving in size
and component cost. Furthermore, to control the entire circuit only
requires two control signals rather than the five that would be
otherwise be necessary. The control circuit can now simply pulse
one IGBT, IGBT1, to produce the first phase of the output waveform
and pulse the second IGBT, IGBT2, to produce the second phase of
the output.
[0062] FIG. 10 shows a fourth implementation of the pulse
generator. This differs from the implementation of FIG. 9 in that
the two IGBTs, IGBT1 and IGBT2, have been replaced by a breakover
USD, USD5(bo), and a breakunder USD, USD6(bu), respectively. Also,
an IGBT (IGBT3) has been added in common to the second and fourth
current paths. For simplicity the circuit uses single USDs
(USD1(bo) and USD3(bu) respectively) in the first and third current
paths, although as described two or more such devices can be
totem-poled in each path to increase the ability of the circuit to
withstand higher voltages. Although this arrangement has added
another circuit element, IGBT3, the output circuit is fully
automatic and all devices connected to the load across A and B are
uncontrolled. The only controlling signal required is the signal to
the gate of IGBT3 in the common ground return.
[0063] In operation, having charged the energy storage device 160
to a voltage greater in magnitude than the threshold of breakover
devices USD1(bo) and USD5(bo), and also high enough not to enter
the threshold range which would place USD3(bu) and USD6(bu) into
their low impedance state, a gate drive pulse 64 applied to IGBT3
will turn on USD1(bo) and USD5(bo) and cause current to follow
through the load in the direction from A to B. Removing the gate
drive to IGBT3 after a pre-determined time interval will, as
before, reduce the current in the circuit to almost zero and all
devices will return to their high impedance states. Provided the
voltage across the energy storage device is now less than the
threshold for USD1(bo) and USD5(bo), and furthermore providing the
voltage is within the threshold required to allow the break-under
devices USD3(bu) and USD6(bu) to enter their low impedance states,
the application of a second gate pulse 164 to IGBT3 will cause the
current to flow through the load in the opposite direction from B
to A. Again, this causes the biphasic waveform of FIG. 8 to be
generated.
[0064] Note that not only is there no requirement for any isolated
connections to any of the devices but only one single device needs
to have a gate drive signal applied in order for the whole circuit
to be fully operated. It will be appreciated that this arrangement
means that the whole output circuit including USD1(bo), USD5(bo),
USD3(bu), USD6(bu) and IGBT3 could be easily implemented as a
single integrated solid state component. This would further mean
that the entire output stage would be a single encapsulated
integrated module only requiring 5 connections. These connections
would be a common ground connection, an input from an energy
source, two output connections to the electrodes A and B and a
single input control connection referenced to the common ground
which would control the module. FIG. 11 shows the block diagram of
a circuit including such an integrated circuit 66--note that even
the gate drive circuit for the IGBT can be included in the module,
leaving the control terminal into the circuit requiring a standard
TTL type signal. This represents an enormous saving in terms of
cost, size and complexity.
[0065] In a fifth implementation of the pulse generator, which is a
modification of that shown in FIG. 10, and may likewise be formed
with the output circuit as a single integrated circuit component,
the energy source is a programmable active power supply 168, rather
than a passive capacitor. Referring to FIG. 12a, here the energy
source is designed to supply a programmed constant DC voltage, and
with this voltage set at a level above the conducting threshold Vth
of breakover devices USD1(bo) and USD5(bo) and greater than the low
impedance threshold range of break-under devices USD3(bu) and
USD6(bu), the current again flows through the load from A to B.
Setting the programmable power supply then to supply a voltage of
zero volts for a pre-determined time interval causes all the
devices to return to their high impedance state. Further setting it
to supply a voltage which is less than the thresholds for USD1(bo)
and USD5(bo), and within the threshold range required to allow the
breakunder devices USD3(bu) and USD6(bu) to enter their low
impedance state, will cause the current to flow in the opposite
direction from B to A. The resulting waveform can be seen by way of
example in FIG. 12b. It would also be possible to have several
energy sources selectable by placing additional USDs within the
circuit arrangement. Which energy source is to be used to supply
the output circuit could then be selected at whatever times are
desirable to achieve the pulse shape required.
[0066] It should be appreciated that further current paths
containing USDs or other solid state devices could be added between
the energy source and the electrodes A and B in any of the circuits
described above, thereby allowing a third, fourth or subsequent
phase to be added in a pre-determined polarity.
[0067] It should also be appreciated that further protective
components may be necessary for reliable operation of the circuits
in practice. By way of example, an inductor could be placed in
series with the output of the energy source to limit the rate of
change of current in the circuit. Such additions are well known to
those skilled in the art.
[0068] In FIGS. 1-3 the cable 36 terminating in connector 48 may
have several wires. In FIG. 3 three such wires are shown, 48A, 48B
and 48C. Wires 48A and 48B provide a dual purpose. They are used to
sense intrinsic cardiac activity, i.e., an ECG. Sensed signals are
sent to the custom IC 70 which performs signal processing on these
signals and then sends them to the microprocessor 66. The
microprocessor uses the ECG to determine the current condition of
the patient.
[0069] The second function of the wires 48A, 48B is to provide
defibrillator pulses from the pulse generator 80.
[0070] An impedance detection circuit 82 may also be provided. This
circuit may be connected across the wires 48A, 48B and used to
detect the impedance of pads (not shown) used to apply the
defibrillator pulses. This impedance is provided to the custom IC
70 and may be used to confirm that the wires 48A, 48B are not open
and that the pads are attached to the patient properly.
[0071] Preferably the cable 36 and its terminating block 34A which
are uniquely identified by an ID code stored in a memory 84. The
terminating block 34 is connected to the electrodes or pads
attached to the patient (not shown). The code stored in memory 84
can be obtained by the custom IC 70 using the third wire 48C. This
code is checked before any pulses are applied to insure that the
proper cable is used with the ADM 32.
[0072] The ADM 32 is operated as follows. First, it is attached
mechanically and electrically to monitor 12 so that the two can
form a single, integrated, composite system 10. The mechanical
connection is not described here since it can be implemented using
brackets or other coupling elements well known in the art. The
electrical connections include the cable 40 for the power supply
(if used) and a serial cable 38.
[0073] Once the ADM 32 is mounted, it can be configured, for the
patient. For this purpose, the clinician operates the keys on face
52 to enter into a configuration mode or via the patient monitor.
In this mode the clinician can select the parameters associated
with the defibrillator therapy to be administered to the patient.
The clinician can also set whether the ADM 32 operates in a fully
automatic mode, an advisory mode, a manual mode, or a pacer mode.
Typically, in an automatic mode the ADM 32 monitors the status of
the patient and if fibrillation is detected then pulses from the
biphasic pulse generator are delivered to the patient
automatically. In the advisory mode, the ADM32 monitors the patient
and generates audio and/or visual indication of the patient's
status, including an indication of a fibrillation episode, makes
the device ready to deliver defibrillation pulses, however,
defibrillation pulses are not applied unless they are delivered by
the clinician. In the manual mode the operation of the ADM 32 is
under the complete control of the clinician. In the pacer mode, the
clinician selects the pacing protocol and delivers the pacing
pulses to the patient. The clinician enters the parameters required
for all these operations via the knob 56 and switches 58 in
response to prompts shown in the display 54. In the Figures, the
same wires are shown for both sensing the intrinsic cardiac
activity of the patient and delivering the high voltage biphasic
defibrillator pulses. Of course, separate wires, terminating in
appropriate electrodes and/or pads may be used as well. In this
manner, the ADM 32 can deliver defibrillation (or other kinds of),
therapy to a patient using any of the protocols well known in the
art. An external defibrillator describing some protocols that may
be used is described in commonly owned co-pending application Ser.
No. 09/452,507 filed Dec. 1, 1999 entitled AUTOMATIC EXTERNAL
CARDIOVERTER/DEFIBRILLATOR WITH TACHYARRHYTHMIA DETECTOR USING A
MODULATION (AMPLITUDE AND FREQUENCY) DOMAIN FUNCTION, incorporated
herein by reference. Of course other protocols and modes of
operation may be used as well.
[0074] Importantly, during its operation, ADM 32 continuously
exchanges data with the monitor 12 over the serial cable 38. For
example, the ADM 32 needs to generate a digital representation of
the ECG for its determination of the patient's status. This digital
ECG is transmitted to the monitor for its display 18. Under the
direction of the microprocessor 66, the ADM 32 may send various
other information to the monitor 12, including, for example, its
current mode of operation (manual, advisory, automatic). The ADM 32
may also send data descriptive of various stages of its operation,
including data indicative of the status of the patient, the voltage
on the capacitors of the biphasic pulse generator, time required to
charge the capacitors to a nominal voltage, time with the next
pulse is applied, time expired since the last pulse, number of
pulses applied to the patient, readiness of the ADM to apply a
pulse, etc. The ADM 32 may also include a self-testing feature. The
results of this self test may also be sent to the monitor. The
information sent to the monitor 10 may be shown immediately on
display 18, may be sent to the printer 28 for a hard copy and may
also be stored in the memory of the monitor (not shown). In
addition, the data from the ADM 32 may be transmitted to other
sites if the monitor is connected to a network.
[0075] The monitor 10 may also send data to the ADM 32, including
acknowledgments of the data received. Typically monitor 12 may be
capable of monitoring one or more physiological functions of the
patient such as blood pressure, arterial pulse oximetry
(SpO).sub.2, carbon dioxide (CO.sub.2), respiration, and cardiac
output. Some monitors may be capable of generating a digital ECG
signal. While it is expected that the ECG signal detected by the
ADM 32 through its electrodes may be more reliable, the external
ECG signal from the monitor may be used as a backup in case the ECG
signal cannot be detected locally, or as a means of confirming the
validity of the local ECG signal by the ADM. Moreover, the ADM 32
may be adapted to determine the condition of the patient and other
information based on other physiological parameters of the patient
as well. For example, the ADM 32 may use any of the physiological
parameters derived by the monitor 12 to determine whether the
patient has a cardiac condition which needs therapy to be delivered
by the ADM 32. These other physiological parameters may be provided
to the ADM 32 by the monitor 12 as well.
[0076] In addition, the memory 68 may be insufficient for data
logging purposes. Therefore the ADM 32 may send some data for
storage in memory 30 of monitor 12. The monitor 12 can then return
this data to the ADM 32 as requested.
[0077] As described above, the ADM 32 is adapted to perform a
self-test and to monitor the status of the patient. If the
self-test indicates that the ADM 32 may be malfunctioning, or if a
patient condition is detected which should be brought to the
attention of the clinician, the ADM 32 is adapted to generate an
alarm signal. This alarm signal may be used to activate the audible
and visual signals on the ADM 32 and/or the monitor 12. In
addition, these signals may be transmitted to a remote location via
the communications network connected to interface 22. The
communications network may be a wired or wireless network.
Therefore the term `network` is used herein very broadly to cover
any analog or digital communications network capable of
transmitting information from the system 10 to another location,
including local area networks, wide area networks, Internet
connections, paging cellular telephones, telemetry, and satellite
communications, just to name a few.
[0078] Some monitors presently available are designed so that they
can be interfaced with other apparatus, like the ADM 12 using a
standard protocol such as Spacelabs Universal Flexport Protocol. If
no such protocol is available for a particular monitor, the ADM 32
can be programmed so that it can communicate with monitor 12 using
the unique protocol characteristic of the monitor 12.
[0079] In summary, an automatic defibrillator module is described
which can be integrated with a patient monitoring device such that
the two can share various functions. More specifically, the ADM 32
includes the components necessary to analyze the condition of the
patient and to generate, if necessary, therapeutic pulses. Data
from the ADM 32, including a digital ECG and other signals
indicative of the operation of the ADM 32 are sent to the monitor
12 for display, printing, and/or storage. Thus, the ADM 32 may or
may not have its own ECG display, a printer or data logging memory.
It is expected that the overall combination of a monitor and ADM
requires less space, is cost-effective and very flexible since the
same ADM can be used with many different patient monitors from
different manufacturers.
[0080] In the embodiment described above, programming information
for the ADM 32 is entered using the controls on the face of the ADM
while patient specific information is displayed or otherwise
provided on the monitor 12. Of course other arrangements may be
made as well. For example, the programming information may be
entered from the monitor 12 and/or some of the patient specific
information can be displayed by the ADM 32. Moreover, the ADM 32
may also incorporate a printer which may be dedicated for
information from the ADM 32 or may be shared by the monitor 12.
Moreover, the ADM 32 may also be arranged to sense other
physiological parameters besides ECG as well and to transmit the
same to the monitor 12.
[0081] Obviously, numerous modifications may be made to this
invention without departing from its scope as defined in the
appended claims.
* * * * *