Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2001-01-16
2002-11-26
Evanisko, George R. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S005000
Reexamination Certificate
active
06487448
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to defibrillators and, more particularly, to converting a monophasic defibrillator to a defibrillator capable of applying a biphasic defibrillation pulse to a patient.
BACKGROUND OF THE INVENTION
One of the most common and life-threatening medical conditions is ventricular fibrillation, a condition where the human heart is unable to pump the volume of blood required by the human body. The generally accepted technique for restoring a normal rhythm to a heart experiencing ventricular fibrillation is to apply a strong electric pulse to the heart using an external cardiac defibrillator. External cardiac defibrillators have been successfully used for many years in hospitals by doctors and nurses, and in the field by emergency treatment personnel, e.g., paramedics.
Conventional external cardiac defibrillators first accumulate a high-energy electric charge on an energy storage capacitor. When a switching mechanism is closed, the stored energy is transferred to a patient in the form of a large current pulse. The current pulse is applied to the patient via a pair of electrodes positioned on the patient's chest. The switching mechanism used in most contemporary external defibrillators is a high-energy transfer relay. A discharge control signal causes the relay to complete an electrical circuit between the storage capacitor and a wave shaping circuit whose output is connected to the electrodes attached to the patient.
The relay used in contemporary external defibrillators has traditionally allowed a monophasic waveform to be applied to the patient. A typical monophasic defibrillator is shown in FIG.
1
. As illustrated in
FIG. 1
, a host control circuit
10
activates a capacitor-charging circuit
12
to charge a storage capacitor C
1
up to a high voltage level. Once capacitor C
1
is charged, the defibrillator is ready to apply a defibrillation pulse. To apply a defibrillation pulse, the host control circuit
10
activates control line XFER, which closes relay switches SW
1
and SW
2
. Relay switches SW
1
and SW
2
may be mechanical relays or solid state switching devices, and in some cases may be replaced by a single relay switch, such as switch SW
1
. Once relay switches SW
1
and SW
2
are closed, a monophasic defibrillation pulse travels from the capacitor C
1
to the patient
14
. The path of the pulse energy is from the positive terminal of the capacitor C
1
to a line
20
and through switch SW
1
. Next, the pulse passes through a line
30
and through the patient
14
in the direction of arrow
16
. Finally, the pulse passes through a line
32
, switch SW
2
, and another line
22
to the negative terminal of the capacitor C
1
.
Once the storage capacitor C
1
is charged, if the operator decides not to apply a defibrillation pulse to the patient, the capacitor is then discharged by the control signal DUMP. The control signal DUMP may also be activated by a “time-out” period, or when the power to the defibrillator is turned off, or by other selected events. To discharge the capacitor C
1
, the host control circuit
10
activates the control signal DUMP so as to close the switch SW
3
and short out the remaining energy from the capacitor C
1
through switch SW
3
and a dump resistor R
1
. Dump resistor R
1
limits the current from the capacitor C
1
through the switch SW
3
so as to prevent damage to the circuit components. by discharging capacitor C
1
relatively slowly.
While contemporary external defibrillators such as those described above have traditionally applied a monophasic waveform to a patient, it has recently been discovered that there may be certain advantages to applying a biphasic rather than a monophasic waveform to the patient. For example, preliminary research indicates that a biphasic waveform may limit the resulting heart trauma associated with the defibrillation pulse.
While defibrillators applying biphasic waveforms may have certain advantages, the cost of upgrading from monophasic to biphasic defibrillators can be significant. Consumers and manufacturers who have made substantial investments in the purchase and development of conventional monophasic defibrillators are faced with the costly expense of purchasing or developing entirely new biphasic defibrillators if they wish to upgrade to biphasic technology.
The present invention is directed to providing an apparatus that overcomes the foregoing and other disadvantages. More specifically, the present invention is directed to an upgrade kit for converting a conventional monophasic defibrillator into a defibrillator that is capable of applying a high-energy, biphasic defibrillation pulse to a patient.
SUMMARY OF THE INVENTION
In accordance with this invention, a defibrillator that applies monophasic defibrillation pulses to a patient may be converted into a defibrillator capable of providing biphasic defibrillation pulses. This conversion is significantly less expensive than the purchase or development of an entirely new biphasic defibrillator and reduces the training required for those who are already familiar with the controls for operating the monophasic defibrillator.
In accordance with further aspects of this invention, the upgrade kit is easily connected to and at least partially controlled by the control circuit of the monophasic defibrillator. The upgrade kit connects to easily accessible circuit components such as the terminals of the storage capacitor. In addition, an upgrade control circuit of the upgrade kit uses some of the control signals that are commonly available in most monophasic defibrillator control circuits. More specifically, the control signals for performing functions such as activating the monophasic pulse, and for dumping unwanted stored energy, may be used. These signals are commonly available in most monophasic defibrillator control circuits and are carried by control lines that can be easily coupled to and implemented by the upgrade kit. For the defibrillation pulse control signal, the upgrade kit is able to compensate for any delay time in the relay switches of the original defibrillator by delaying the activation of the faster upgrade kit switches until the slower relay switches have had time to close.
In accordance with further aspects of this invention, the upgrade kit uses a discharge method that will allow it to apply a proper biphasic defibrillation pulse regardless of the initial energy settings of the host defibrillator. The upgrade kit accomplishes this by using two measurements that are taken near the beginning of the biphasic defibrillator pulse and using the ratio of the two measurements to determine the desired length of the biphasic pulse. The desired length of the biphasic pulse may be determined by a look-up table in the upgrade control circuit. Use of this method allows the upgrade kit to apply a proper biphasic defibrillation pulse without needing information regarding the energy level to which the storage capacitor has been charged. This eliminates the need for a serial interface between the host control circuit in regard to the selection of energy levels to which the storage capacitor may be charged.
As will be readily appreciated from the foregoing description, the upgrade kit of the present invention is easily inserted into a conventional monophasic defibrillator. By using control signals that are readily available, and by not requiring a serial interface between the host and upgrade kit control circuits, the installation of the upgrade kit is simplified. The resulting upgraded defibrillator is less costly than a new biphasic defibrillator but is capable of providing the advantageous biphasic defibrillation pulses to a patient.
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patent: 5044367 (1991-09-01), Endres et al.
patent: 5163427 (1992-11-01), Keimel
patent: 5199429 (1993-04-01), Kroll et al.
patent: 5201865 (1993-04-01), Kuehn
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patent: 5352239 (1994-10-01), Pless
pa
Borschowa Lawrence A.
Nova Richard C.
Sullivan Joseph L.
Christensen O'Connor Johnson & Kindness PLLC
Evanisko George R.
Physio-Control Manufacturing Corporation
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