Abstract:
A defibrillator configurable for optimal behavior across a broad spectrum of patients, users, and circumstances is provided. A set of environmental characteristics that represent the patient population, the user population, and the possible circumstances are determined and then applied to a configure algorithm to determine an optimal behavior of the defibrillator as reflected through the set up parameters. The set of environmental characteristics can be entered manually or determined from dispatch data supplied by computerized dispatch systems. The optimal behavior can also be achieved using adaptation algorithms such as fuzzy logic and neural networks that allow the defibrillator to obtain measurements of the environmental characteristics and alter its behavior based on those measurements.

Description:
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&#39;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&#39;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&#39;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&#39;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&#39;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 defibrillation. The application of CPR can be monitored by the defibrillator  10  with feedback given to the user  12 . In U.S. application Ser. No. 08/965,347, titled “External defibrillator with CPR prompts and ACLS prompts and Method of Use”, filed Jun. 30, 1999 and assigned to the assignee of the present invention, the incorporation of prompts for CPR and other cardiac care is discussed. 
     The location of the defibrillator such with the staff of a public swimming pool or life guard facility would allow optimization of the defibrillator behavior for resuscitation of drowning victims. It would therefore be desirable that the behavior of the defibrillator  10  can be optimized for maximizing the resuscitation efficacy and patient safety based on the environment characteristics in which the defibrillator  10  is to be applied. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a medical device that is configurable for optimal behavior across a broad spectrum of patients, users, and circumstances is provided. The defibrillator is an example of a medical device having a user interface that typically includes front panel buttons, a liquid crystal display (LCD), and an audio speaker. The behavior of the defibrillator as reflected through the user interface is determined according to a set of set up parameters. 
     A set of environmental characteristics that represent the patient population, the user population, and the possible circumstances are first determined. The environmental characteristics are chosen that are relevant to determining the behavior of the defibrillator as reflected through the user interface. 
     The set of environment characteristics are then applied to a configure routine to determine an optimal behavior of the defibrillator. Optimal behavior of the defibrillation provides for achieving resuscitation of the patient in a manner which optimizes defibrillation efficacy and patient safety. Other optimal behaviors such as maximizing defibrillator battery life may also be achieved according to application requirements. 
     Maximizing defibrillation efficacy means that the defibrillation process is as reliable and error free as possible, given the particular patient, user, and circumstance. For example, an inexperienced user will require more frequent and detailed prompts from the defibrillator than a physician. A pediatric patient will typically require different defibrillation protocols such as lower energy levels than an adult patient for maximum defibrillation efficacy and patient safety. A patient suffering from respiratory arrest followed by cardiac arrest requires increased emphasis on CPR. 
     Maximizing patient safety means that the defibrillation process minimizes the possibility of injury to the patient and as well as to the user. For example, the inexperienced user may not know to refrain from touching the patient when the defibrillator is analyzing the heart rhythm. Such touching and movement introduce measurement artifacts which impede the process of detecting a shockable heart rhythm such as VF. The defibrillator can be adapted with increased user prompts to not touch the patient, adjusting the shock advisory algorithm to be more conservative in detecting shockable rhythms, and increased emphasis on artifact detection. 
     The optimal behavior can also be achieved using adaptation algorithms such as fuzzy logic and neural networks that allow the defibrillator to obtain measurements of the environmental characteristics and alter its behavior based on those measurements. Monitoring a pattern of usage may uncover differences in the environmental characteristics not anticipated when the defibrillator was originally configured. Providing for a control program that changes the configuration parameters allows the behavior of the defibrillator to be adjusted responsive to new environmental characteristics. 
     Defibrillators are one example of a medical device that may benefit from the ability to be configured to match the environmental characteristics. Other such medical devices may include cardiac monitors and drug delivery devices. 
     A feature of the present invention is to provide a method for configuring a medical device based on environmental characteristics. 
     Another feature of the present invention is to provide a configurable medical device. 
     A further feature of the present invention is to provide a configurable defibrillator. 
     Another feature of the present invention is to provide a defibrillator that may be configured according to environmental characteristics. 
     Another feature of the present invention is to provide a defibrillator capable of adapting to new environmental characteristics. 
     Other features, attainments, and advantages will become apparent to those skilled in the art upon a reading of the following description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an illustration of a typical scenario of a defibrillator being applied by a user to resuscitate a patient suffering from cardiac arrest; 
     FIG. 2 is an illustration of a typical defibrillator and set of electrodes; 
     FIG. 3 is a simplified block diagram of the defibrillator; 
     FIG. 4 is an illustration of the process of configuring a defibrillator with a set of configuration parameters according to the prior art; 
     FIG. 5 is an illustration showing process of mapping a set of environmental characteristics to the set of configuration parameters according to the present invention; 
     FIGS. 6A and 6B are illustrations of several alternative embodiments of the process of applying a configure algorithm to determine configuration parameters based on environmental characteristics, either in a host computer or in the defibrillator, according to the present invention; 
     FIG. 7 is an illustration showing an example of an embodiment of the configure routine; and 
     FIG. 8 is a block diagram of an alternative embodiment of the present invention that allows the defibrillator to adapt itself to new environmental characteristics. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2 is an illustration of the defibrillator  10  configured as an automatic external defibrillator (AED). The user interface of the defibrillator  10  includes an on-off button  34 . A condition indicator  36  indicates the readiness of defibrillator  10  for use. A display  32 , typically implemented with LCD technology, provides for visual prompts to the user  12  and may be used to graphically display ECG waveforms and CPR prompts. A speaker  38  provides for audio prompts such as by voice or tones to the user  12 . A shock button  30  is pressed by the user  12  responsive to prompts from the defibrillator  10  such as illuminating the shock button  30  and generating audio prompts. A pair of electrodes  16  is plugged into a jack  17  to couple the patient  14  to the defibrillator  10 . 
     FIG. 3 is a simplified block diagram of a defibrillator  10  according to the present invention. The pair of electrodes  16  for coupling to the patient  14  are connected to an ECG front end  18  and further connected to an HV switch  28 . The ECG front end  18  provides for detection, filtering, and digitizing of the ECG signal from the patient  14 . The ECG signal is in turn provided to a controller  26  which runs a shock advisory algorithm that is capable of detecting ventricular fibrillation (VF) or other shockable rhythm that is susceptible to treatment by electrotherapy. 
     The shock button  30  is pressed by the user  12  to initiate the delivery of a defibrillation pulse through the pair of electrodes  16  after the controller  26  has detected VF or other shockable rhythm. A battery  24  provides power for the defibrillator  10  in general and in particular for a high voltage charger  22  that charges the capacitors in an energy storage circuit  20 . Typical battery voltages are 12 volts or less, while the energy storage circuit  20  may be charged to 1500 volts or more. A charge voltage control signal from the controller  26  determines the charge voltage in the energy storage circuit  20 . The shock button  30 , display  32 , speaker  38 , and condition indicator  36  collectively form a user interface  42 . 
     The energy storage circuit  20  is connected to the HV switch  28  which operates to deliver the defibrillation pulse across the pair of electrodes  16  to the patient  14  in the desired polarity and duration response to the switch control signal from the controller  26 . The HV switch  28  is preferably constructed using an H bridge to deliver biphasic defibrillation pulses in the preferred embodiment but could readily be adapted to deliver monophasic or multiphasic defibrillation pulses and still realize the benefits of the present invention. 
     FIG. 4 illustrates the process of manually configuring the defibrillator  10  according to the prior art. A set of configuration parameters  50 , including the parameters A-M shown as an example, are entered individually by setting the user interface  42  to a configuration mode. Each of the configuration parameters  50  defines various set-up options that are particular to the defibrillator  10 . For example, speaker volume, ECG display on/off, manual operation enable, defibrillation energy levels over three successive shocks, timeout length to pause for CPR, and so on are all configuration parameters that can be individually changed. Such parameters could be changed using the user interface  42  directly or down-loaded to the defibrillator  10  via a data card, serial port, or infrared (“IrDA”) port from a host computer. The set of configuration parameters  50  is then stored in a memory  40  to define the behavior of the defibrillator  10 . 
     The prior art technique of configuring the defibrillator  10  shown in FIG. 4 suffers from the problem of having to change individual parameters which may require referencing product manuals or other user documentation to understand their function as well as their relation to other parameters. Changing one parameter may affect other parameters. At the same time, adapting the defibrillator  10  to new situations is difficult because there is no clear mapping between the environmental characteristics and the set of configuration parameters  50 . 
     FIG. 5 is an illustration showing a process of applying a set of environmental characteristics to a configure routine  44  to obtain the set of configuration parameters  50  according to the present invention. A set of environmental characteristics  60  that include operator type  62 , circumstances  64 , and protocol  66  are presented in a host computer  46  to a user in order to configure the defibrillator  10 . The set of environmental characteristics  60  is chosen to reflect the most relevant characteristics of the environment in which the defibrillator  10  is to be applied that would allow its behavior to be optimized. Optimized behavior means that the defibrillator  10  behaves in a manner that maximizes the chances of successful resuscitation and also maximizes patient safety in a given environment. For example, the chance of successful resuscitation can be maximized both by reducing the chance of error in operating the defibrillator  10  and also by maximizing the speed in which the defibrillator  10  can be deployed. However, speed and error-free operation are typically traded off according to the operator type  62 . 
     The operator type  62  is organized according to a taxonomy of training levels ranging from a highly skilled physician requiring little in the way of guidance from the defibrillator  10  to the first responder who may require substantially more guidance. Such guidance, such as in the form of audible or visual prompts provided by the user interface  42 , can add a substantial amount of time to the defibrillation process which, in the case of the operator type  62  as physician, adds little value. The operator type  62  is thus chosen as a one of the set of environmental characteristics  60  because it has been shown to have a strong correlation in determining the optimal behavior of the defibrillator  10 . 
     Similarly, circumstances  64 , which may include a variety of factors such as transport time, patient age, and type of arrest, and may have a strong correlation in determining the optimal behavior of the defibrillator  10 . Transport time  68 , grouped into short and long, may be an important factor in maximizing patient safety. For example, on board an airliner, the defibrillator  10  may be applied in long transport time situations typically exceeding an hour. The defibrillator  10  may be optimized to have a behavior that allows for an ECG monitoring mode to assist in patient care and battery saving features to allow for extended operation. 
     Patient age  70  is another example of a factor that may have a strong correlation in determining the optimal behavior of the defibrillator  10 . It is known that pediatric patients require less defibrillation energy than adult patients. The behavior of the defibrillator  10  in terms of defibrillation energy could then be adjusted downward maximize pediatric patient safety. Geriatric patients on the other hand, could require an entirely different behavior depending on their physiology. 
     Type of arrest  72  is a further example of a factor that may have strong correlation in determining the optimal behavior of the defibrillator  10 . If cardiac arrest is preceded by respiratory arrest, which is commonly found in drowning victims, the chances of successful resuscitation are enhanced through increased emphasis on CPR (cardiopulmonary resuscitation) rather than simply applying a defibrillation pulse. The defibrillator  10 , based on the type of arrest  72  typically determined by the anticipated application, could then be optimized to prompt the user to first perform CPR on the patient and act as a monitor in order to provide feedback on the efficacy of the CPR effort. 
     Protocol  72  is determined by the medical director of the region in which the defibrillator  10  is applied. The medical director may choose from a variety of defibrillation protocols, such as AHA (American Heart Association) protocol, a European protocol, or a local protocol which may be any of a variety of variations. Protocols commonly determine the number of successive defibrillation pulses that may be applied, their respective defibrillation energies, and other factors that must be rigidly adhered to in order for the defibrillator  10  to be acceptable for use in that jurisdiction. Because of the interaction between the protocol and the various other environmental characteristics, the present invention allows for optimization of the defibrillator  10  in conforming with the protocol  66 . For example, the protocol  66  may allow for different defibrillation energy levels based on the patient age  64 . 
     The set of environmental characteristics  60  is applied to the configure routine  44  which operates to map the set of environment characteristics  60  to the set of configuration parameters  50 . The configure routine  44  is preferably written as a set of software instructions which may be executed by a microprocessor, controller, host computer, or other commonly available processors. The operation of the configure routine  44  is given in more detail below. 
     FIG. 6A and 6B illustrate alternative processes of configuring a defibrillator according to the present invention. In FIG. 6A, a host computer  46  running a software program for the configure routine  44  is used to produce the set of configuration parameters  50  which are then downloaded to the defibrillator  10 . The environmental characteristics may be entered into the host computer  46  by an operator typically through a graphical user interface (GUI) using techniques commonly known in the art. The download process from the host computer  46  to the defibrillator  10  could take place through any of variety of communication forms, including RS-232 serial bus, IrDA, and universal serial bus (USB) or via an internet or local area network link. The set of configuration parameters  50  would typically reside in a memory  40  within the defibrillator  10  for determining the behavior of the defibrillator  10  through the user interface  42 . 
     The typical application of the host computer  46  is in the case of a medium to large emergency medical service (EMS) that may deploy a large number of defibrillators  10 . Maintaining the defibrillators  10  and ensuring their proper behavior is made easier through automated techniques using the host computer  46 . At the same time, variations in the defibrillators  10  can be accommodated through their assigned users. 
     Defibrillators assigned to various departments within an EMS jurisdiction such as the fire department, the police department, and the parks department may each have different behaviors optimized for their situations based on the differences in the set of environmental characteristics  60 . For example, differences in the type of operator type  62  among the various groups may be significant. The fire fighter is typically an EMT with relatively frequent exposure to medical emergencies whereas the parks department employee may only be a designated first responder who receives occasional in-service training as part of their job. It may be readily appreciated that an entirely new set of environmental characteristics  60  based on the relevant subsets within an EMS system could be created to optimize the behavior of the defibrillator  10 . 
     In FIG. 6B, the set of environmental characteristics  60  may be entered directly into the defibrillator  10  with the help of the user interface  42 . The environmental characteristics are provided to the configure routine  44  which is preferably executed by the controller  26  to obtain the set of configuration parameters  50  which are then stored in the memory  40 . The use of the configure routine  44  within the defibrillator  10  allows for adaptive behavior based on differences in the set of environmental characteristics  60 . 
     A defibrillator with AED and manual personalities is discussed in U.S. Pat. No. 6,021,349, titled “Automatic External Defibrillator With Manual Features”, issued Oct. 31, 2000, that is assigned to the assignee of the present invention and is incorporated herein by reference. Based on the operator type  62 , which was assumed to be either a first responder or an EMT, an expanded set of manual modes is made available to the user. The present invention allows such a mapping of operator type  62  to configuration parameters  50  to be readily determined and more readily modifiable to allow for optimized behavior. 
     The environmental characteristics  60  can be dynamically applied to the defibrillator  10  for specific situations. The patient circumstances, type of call that was dispatched, and type of operator can be manually entered into the defibrillator  10  via the user interface  42 . The environmental characteristics  60  can also be applied to the defibrillator  10  in an automated fashion. Computerized dispatch systems (not shown) commonly employed in many metropolitan areas send dispatch data to mobile data terminals mounted in emergency vehicles. This dispatch data can be dynamically applied to configure the defibrillator  10 . The environmental characteristics from the dispatch data could be gathered either by the host computer  46  or applied directly to the defibrillator  10  via a wireless link such as an IrDA port. For example, the dispatch data “pediatric drowning with CPR in progress” could be readily parsed into the set of environmental characteristics  60  which could then be applied to the defibrillator  10  while en route to the scene. 
     FIG. 7 is an illustration showing an example of the operation of the configure routine  44 . As shown in this simplified example, the set of environmental characteristics  60  which includes the protocol  66 , operator type  62 , and patient age  70  are provided as inputs to a matrix  45  containing various sets of configuration parameters  50 . Based on this mapping structure, an appropriate set of configuration parameters is selected and provided to the defibrillator  10 . If more elements are added to the set of environmental characteristics  60 , an n-dimensional matrix may be constructed to accommodate the additional elements. Other methods of selecting an appropriate set of configuration parameters such as using decision tree structures, look up tables and data bases may be readily applied. 
     Constructing the matrix or data base within the configure routine  44  may be done after selection of the set of environmental characteristics  60  and the variables required for each of the set of configuration parameters  50 . Many of the choices in defining the matrix  45  may be made on the basis of expert knowledge on which behaviors are optimal for each permutation of the environmental characteristics  60 . Other choices may be arrived at through reasonable experimentation to determine an optimal behavior. 
     Constructing the matrix  45  in this manner has the advantages of forcing choices of defibrillator behavior to be made among the various permutations of environmental characteristics  60  as part of an overall process rather than a series of ad hoc decisions made over time. The information contained in the matrix  45  thus represents the collective knowledge that determines the defibrillator  10  behavior. The embodiment of the configure routine  44  as illustrated in FIG. 7 allows a static mapping of the set of environmental characteristics  60  to the sets of configuration parameters  50  in a fixed and predictable manner and requires relatively little processor power to implement. 
     FIG. 8 is a block diagram of the method and apparatus for configuring the defibrillator  10  according to alternative embodiment of the present invention. The set of configuration parameters  50  are generated responsive to the set of environmental characteristics  60  which are provided to an optimizer  100 . The optimizer  100  performs the functions of the configure routine  44  based on the set of environmental characteristics  60 . In addition, a set of performance objectives  102  are provided to the optimizer  100  to further refine the behavior of the defibrillator  10  based on usage information that is measured by a usage monitor  104 . The set of performance objectives  102  may include a set of goals that are conflicting or require trade-offs. As shown, the set of performance objectives include goals  106 ,  108 , and  110  labeled “Maximize Patient Safety”, “Minimize User Error”, and “Maximize Battery Life”. 
     The usage monitor  104  should be capable of providing a measure of the patterns of usage of the defibrillator  10  to allow for optimization of each of the goals  106 - 110 . For example, the usage monitor  104  can be used to measure the duty cycle of the defibrillator  10 . In the hospital emergency department, the defibrillator  10  may be used weekly while in a first responder environment the defibrillator  10  may not be used for years. The usage monitor  104  can determine such a pattern of use and optimize the behavior of the defibrillator  10  for the goal  110  of maximizing battery life. For example, the frequency of self test operations, which consume a substantial amount of energy from the battery  24 , can be reduced based on a low duty cycle of use determined by the usage monitor  104 . 
     As a further example, the usage monitor  104  can be used to monitor a pattern of inputs during actual use of the defibrillator  10 . Multiple erroneous key presses may indicate confusion by the user  12  that can be detected by the usage monitor  104  and provided to the optimizer  100 . The frequency and types of prompts from the user interface  42  can be altered to provide further detail in order to optimize the goal of minimizing user error. The usage monitor  104  can also be coupled to a shock advisory algorithm within the controller  26  which provides an indication of the level of artifact present in the ECG signal which may indicate the patient is being moved or CPR is in progress. The goal  106  of maximizing patient safety could be optimized by changing the parameters of the shock advisory algorithm to a more robust standard from a more aggressive standard. 
     The optimizer  106  is an algorithm that may be implemented through a variety of techniques including fuzzy logic, neural networks, and other non-linear control programs. Fuzzy logic, for example, is particularly suitable for describing human decision making process which cannot be precisely described in conventional mathematical terms. For reasoning purposes, numeric variables are mapped onto a fuzzy set of linguistic variables by a set of membership functions which permit replacing the original numeric measurement by confidences attached to each linguistic term. For example, the usage pattern during actual use of the defibrillator can be mapped into the linguistic variables “skilled operator”, “semi-skilled operator”, or “confused operator” based on the pattern of operation determined by the usage monitor. The usage pattern could be mapped into the linguistic variables “frequent” and “non-frequent”. Rules could then be written such as “If the operator is confused and the usage pattern is infrequent, then maximize the level of prompting.” In this way, the defibrillator  10  may provide for optimization of its behavior based on the set of environmental characteristics  60  and also on the set of performance objectives  102 . 
     It will be obvious to those having ordinary skill in the art that many changes may be made in the details of the above-described preferred embodiments of the invention without departing from the spirit of the invention in its broader aspects. The present invention may be applied to any medical device which entails complex configuration parameters in order to adapt to differing environmental characteristics. Therefore, the scope of the present invention should be determined by the following claims.