Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-08-11
2002-04-09
Layno, Carl (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06370428
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to electrotherapy circuits and in particular to a method for configuring an external defibrillator based on environmental characteristics.
Electro-chemical activity within a human heart normally causes the heart muscle fibers to contract and relax in a synchronized manner that results in the effective pumping of blood from the ventricles to the body's vital organs. Sudden cardiac death is often caused by ventricular fibrillation (VF) in which abnormal electrical activity within the heart causes the individual muscle fibers to contract in an unsynchronized and chaotic way. The only effective treatment for VF is electrical defibrillation in which an electrical shock is applied to the heart to allow the heart's electrochemical system to re-synchronize itself. Once organized electrical activity is restored, synchronized muscle contractions usually follow, leading to the restoration of cardiac rhythm.
FIG. 1
is an illustration of a defibrillator
10
being applied by a user
12
to resuscitate a patient
14
suffering from cardiac arrest. In cardiac arrest, otherwise known as sudden cardiac arrest, the patient is stricken with a life threatening interruption to their normal heart rhythm, typically in the form of ventricular fibrillation (VF) or ventricular tachycardia (VT) that is not accompanied by a palpable pulse (shockable VT). In VF, the normal rhythmic ventricular contractions are replaced by rapid, irregular twitching that results in ineffective and severely reduced pumping by the heart. If normal rhythm is not restored within a time frame commonly understood to be approximately 8 to 10 minutes, the patient
14
will die. Conversely, the quicker defibrillation can be applied after the onset of VF, the better the chances that the patient
14
will survive the event.
The defibrillator
10
may be in the form of an automatic external defibrillator (AED) capable of being operated by users with a wide variety of skill levels ranging from first responders to physicians, including emergency medical technicians trained in defibrillation (EMT-Ds), police officers, flight attendants, security personnel, occupational health nurses, and firefighters. AEDs can also be used in areas of the hospital where personnel trained in ACLS (advanced cardiac life support) are not readily available.
Having a simple, easily understood user interface in an AED is particularly important in applications where the first responder may have only infrequent need to use the AED. Because training and refresher courses may be relatively infrequent, coupled with a high stress emergency situation in which the AED is designed to be used in, the user interface design is therefore critical.
In more recent AED designs such as the Heartstream Forerunner® defibrillator, the AED functions have been logically grouped into step 1, “power on”; step 2, “analyze”; and step 3, “shock.” More sophisticated audio prompts have been added in addition to the visual prompts provided by the LCD display. The transition from step 1 to step 2 may be initiated by the defibrillator, such as upon detection of patient contact between the defibrillation electrodes to begin the ECG analysis as soon as possible. Proceeding from step 2 to step 3 according to the AED personality requires the user to press a shock button upon recognition of a shockable rhythm by the ECG analysis algorithm. In this way, the AED personality is commonly understood to mean semi-automatic rather than fully automatic defibrillation.
The step 1, 2, and 3 methodology, with some variation among manufacturers, is commonly understood and accepted as the AED personality. After step 3, the AED can continue the ECG analysis as a background process to watch for shockable rhythms and alert the user
12
.
In
FIG. 1
according to step 1 of the AED personality, the defibrillator
10
is turned on and a pair of electrodes
16
is applied across the chest of the patient
14
by the user
12
in order to acquire an ECG signal from the patient's heart. According to step 2 of the AED personality, the defibrillator
10
then analyzes the ECG signal to detect ventricular fibrillation (VF). If VF is detected, the defibrillator
10
signals the user
12
that a shock is advised. According to step 3 of the AED personality, the user
12
then presses a shock button on the defibrillator
10
to deliver the defibrillation pulse to resuscitate the patient
14
.
The defibrillator
10
thus forms a nexus between a population of patients
14
and a population of users
12
. The behavior of the defibrillator
10
is critical in maximizing both the efficacy of the resuscitation effort and patient safety across the two populations and also across the variety of circumstances in which the defibrillator
10
may be used. It has been found that the behavior of the defibrillator
10
may be optimized according to a set of meaningful parameters across the population of patients
14
, the population of users
12
, and the various circumstances in which the defibrillator
10
may be employed.
The configuration parameters of the defibrillator
10
that determine the behavior of the defibrillator
10
are often complex and arcane, bearing little resemblance to the environmental characteristics. It would be desirable to be able to map the set of environmental characteristics to the set of configuration parameters to ease the process of configuring the defibrillator
10
.
The population of patients
14
spans the entire human population since sudden cardiac arrest (SCA) can potentially affect anyone. The human population can be further categorized using environmental characteristics that have been found to be meaningful for defibrillation and resuscitation purposes. For example, the patient
14
may have a transthoracic impedance (“patient impedance”) that spans a range commonly understood to be 20 to 200 ohms. It is desirable that the defibrillator
10
provide an impedance-compensated defibrillation pulse that delivers a desired amount of energy to any patient across the range of patient. The patient's age group, generally categorized as infant, adult, and geriatric, may determine the minimum amount of energy needed for effective defibrillation as well as the appropriate resuscitation protocols that determine how the defibrillator is to be applied. It would be desirable that the behavior of the defibrillator
10
be optimized according to a set of patient characteristics.
The population of users
12
includes first responders with little or infrequent training in the use of defibrillators, designated first responders who may have more frequent training as a secondary part of their jobs, and EMTs, paramedics, and physicians who have higher levels of medical training and more frequent opportunities to use defibrillators. This classification takes into account the level of user (operator) training and as well as the familiarity of the user
12
with the defibrillation process. It would be desirable that the behavior of the defibrillator
10
be optimized according to the type of user
12
.
The circumstances in which the defibrillator
10
will be applied will vary widely. Defibrillation could take place in the victim's home, on board an airliner or ship, on the street, or any other of a variety of locations. The geographic location of the defibrillation is an environmental characteristic that substantially affects the time required to get more advanced cardiac care on scene with the patient as well as the transport time needed to get the patient
14
to a hospital. It would be desirable that the behavior of the defibrillator
10
be optimized according to transport time.
In many situations such as a drowning, cardiac arrest is preceded by respiratory arrest. It has been found that cardio-pulmonary resuscitation (CPR) is best applied more aggressively before attempting defibrillation in such cases. It is thus desirable that the defibrillator behavior be modified for such applications to emphasize the use of CPR before attempting defibri
Gliner Bradford E.
Lyster Thomas D.
Snyder David E.
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