Abstract:
An AED includes defibrillation circuitry housed within an enclosure, a first processor programmed to periodically test the operability of the defibrillation circuitry and a second processor in communication with the first processor. The AED further includes a visual indicator, such as a red/green LED, positioned at the exterior of the enclosure that is operatively connected to the second processor. The second processor is programmed to control the visual indicator in response to the periodic test results provided to it by the first processor.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 10/678,593, entitled “Automatic External Defibrillator with Active Status Indicator,” filed Oct. 2, 2003, which is a continuation-in-part of U.S. patent application Ser. No. 10/453,312, filed Jun. 3, 2003, which is a continuation of U.S. patent application Ser. No. 09/960,859, filed Sep. 21, 2001 now U.S. Pat. No. 6,577,102. The complete disclosure of each of the above-identified applications is hereby fully incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates generally to external defibrillators, and more specifically to automatic external defibrillators (AED) having active status indicators that provide a continuous indication related to the operational readiness of the defibrillator. The invention further relates to AEDs having other operation indicators that provide indications related to the condition of the defibrillator during use. 
         [0004]    2. Description of Related Art 
         [0005]    Conventional AEDs perform periodic self-tests to determine the operational readiness of the defibrillator. Some defibrillators perform such self-tests automatically when they are turned on. Other defibrillators perform self-tests on a periodic basis regardless of the on/off state of the defibrillator. The results of these tests, however, may not be indicated until subsequent turn-on of the AED or may not be readily apparent to the user of the AED. 
         [0006]    Hence, those skilled in the art have recognized a need for providing a continuous, active indication of the operational readiness of an external defibrillator regardless of the on/off state of the defibrillator. The need for additional indications of the condition of a defibrillator during use has also been recognized. The invention fulfills these needs and others. 
       SUMMARY OF THE INVENTION 
       [0007]    Briefly, and in general terms, the invention is directed to an AED that provides a continuous, active indication of the operational readiness of the defibrillator. This active indication is provided by a visual indicator carried by the enclosure of the AED. The visual indicator may be a single LED capable of displaying different first and second colors, e.g., red and green. Alternatively the visual indicator may be two separate LEDs or may be a mechanical type indicator having different first and second positions, each having an associated color. 
         [0008]    An AED incorporating aspects of the invention includes defibrillation circuitry housed within an enclosure, a first processor programmed to periodically test the operability of the defibrillation circuitry and a second processor in communication with the first processor. The AED further includes a visual indicator, as described above, positioned at the exterior of the enclosure that is operatively connected to the second processor. The second processor is programmed to control the visual indicator in response to the periodic test results provided to it by the first processor. Alternatively, the first and second processors may be combined into a single processor. 
         [0009]    In one configuration, the second processor is programmed to 1) cause the indicator to continuously present a first color, e.g., green, when the defibrillator is on and the periodic test result is that the defibrillation circuitry is operating normally; 2) cause the indicator to intermittently present the first color when the defibrillator is off and the periodic test result is that the defibrillation circuitry is ready to operate normally; 3) cause the indicator to continuously present a second color, e.g., red, when the defibrillator is on and the periodic test result has detected an error in the defibrillation circuitry and 4) cause the indicator to intermittently present the second color when the defibrillator is off and the periodic test result has detected an error in the defibrillation circuitry. 
         [0010]    In another aspect, the invention is directed to an AED that provides visual and/or audible indications of the condition of a defibrillator during use. These indications relate to the operation of the AED in conjunction with the electrode pad assembly used to monitor a patient&#39;s heart activity and administer defibrillation shocks. 
         [0011]    An AED related to this aspect of the invention includes defibrillation circuitry housed within an enclosure and an electrode pad assembly adapted for electrical communication with the defibrillation circuitry at one end and a patient at the other end. The AED further includes a processor programmed to monitor the operation of the defibrillation circuitry and electrode pad assembly and a visual indicator positioned at the exterior of the enclosure and operatively connected to the processor. The AED may also include a speaker. The processor is programmed to control the visual indicator and/or speaker in response to the results of the operation monitoring. 
         [0012]    These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings which illustrate by way of example the features of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1A  illustrates a top sectional view of an AED with a battery pack installed; 
           [0014]      FIG. 1B  illustrates a top sectional view of the AED with the battery pack removed; 
           [0015]      FIG. 2  illustrates a bottom view of the battery pack; 
           [0016]      FIG. 3  illustrates a side sectional view of the AED including the battery pack; 
           [0017]      FIG. 4  illustrates a side sectional view of the battery pack including first and second battery units; 
           [0018]      FIG. 5  illustrates a block diagram of one configuration of circuitry contained within the battery pack and the AED; 
           [0019]      FIG. 6  illustrates a block diagram of another configuration of circuitry contained within the battery pack and the AED; and 
           [0020]      FIG. 7  is a perspective view of an AED including an active status indicator. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]      FIG. 1A  illustrates a top sectional view of the Semi-Automatic External Defibrillator (“AED”)  100  that includes a battery system, for example battery pack  110 . The AED  100  is a device to treat cardiac arrest that is capable of recognizing the presence or absence of ventricular fibrillation or rapid ventricular tachycardia or other shockable cardiac arrhythmias, and is capable of determining, without intervention by an operator, whether defibrillation should be performed. Upon determining that defibrillation should be performed, the AED automatically charges and requests delivery of electrical energy to electrodes that attach to a patient to deliver the energy to the patient&#39;s heart. 
         [0022]    The battery pack  110  provides power to components such as electronics and a charger located in the AED  100 . The charger charges a capacitor  564  ( FIG. 5 ) of the AED  100  that provides the electrical energy to the electrodes attached to the patient. The AED  100  includes a generally rectangular shaped battery well  120  that is constructed and arranged to house the battery pack  110 . The battery pack  110  is sized to slide in and out of the battery well  120  to releasably connect a power supply of the battery pack  110  to the AED  100 . 
         [0023]      FIG. 1B  illustrates a top sectional view of the AED  100  and the battery well  120  with the battery pack  110  removed. An entrance  210  of the battery well  120  accommodates alignment of the battery pack  110  within the battery well  120 . 
         [0024]      FIG. 2  illustrates a bottom view of the battery pack  110 . Referring to  FIGS. 1B and 2 , an opposite end of the battery well  120  includes a wedge-shaped feature  230  that corresponds to a wedge-shaped receptacle  235  located in the battery pack  110 . When inserting the removable battery pack  110  to the AED  100 , the battery pack  110  is guided along by the battery well  120  to the wedge-shaped feature  230 . The battery pack  110  is aligned at the end of its travel by the wedge shaped feature  230  in the battery well  120  via the corresponding wedge shaped receptacle  235  in the battery pack  110 . 
         [0025]    Referring to  FIG. 1A , to maintain the battery pack  110  in a connected position relative to the AED  100 , the battery pack  110  includes a latch  130  that retains the battery pack  110  within the battery well  120  when the battery pack is fully inserted into the battery well  120 . An end of the latch  130  connects with a spring  132  to bias the latch in a normally extended position. In the normally extended position, a latching end  134  of the latch  130  extends to enter a corresponding slot  136  located in the AED  100 . The latch  130  is moveable in a plane parallel to the spring  132  to compress the spring  132  to release the latching end  134  from the slot  136 . When the latching end  134  is released from the slot  136 , an ejection spring  137  located on the AED  100  pushes on the battery pack  110  to eject the battery pack  110  from the battery well  120 . The battery pack  110  includes a slot  138  from which the latch  130  extends. Even in a fully contracted position, the latch  130  extends past the slot  138 . 
         [0026]    The battery pack  110  also includes a printed circuit board (PCB)  140  including exposed electrical terminals  150  to connect the printed circuit board  140  to electrical circuitry contained in the AED  100 , as described in more detail below. The PCB  140  includes electrical components that connect to circuitry of the AED  100  when the battery pack  110  is installed in the AED  100 . The battery pack  110  includes a window  160  that is located proximate to a visual indicator, such as light emitting diode (LED)  550  ( FIG. 5 ). The window  160  allows an operator to view the LED  550  when the battery pack  110  is removed from the AED  100 . Thus, the operator can determine a status of at least one of the AED  100  and the battery pack  110  independent of the battery pack  110  being connected to the AED  100 . It should be appreciated that the AED  100  could also include a window located proximate to the battery pack window  160  so that an operator can view the LED  550  when the battery pack is inserted in the AED  100 . 
         [0027]      FIG. 3  illustrates a side sectional view of the AED  100  including the battery pack  110 . The electrical terminals  150  of the PCB  140  contact a connector  310  located within the AED  100 , to electrically connect the battery pack PCB  140  with an AED PCB  320 . 
         [0028]      FIG. 4  illustrates a side sectional view of the battery pack  110 . The battery pack  110  includes a first power supply, such as battery unit  410 . The battery unit  410  powers essential power needs of the AED during a main operating mode, for example when the AED is powered on. An essential power need includes, for example, the power necessary to charge the capacitor  564  to delivery energy to the patient. The battery unit  410  is preferably not being drained of power when the AED is powered off. 
         [0029]    The battery unit  410  includes one or more battery cells, or other power supplies, that are electrically connected together. The power supply may include other forms of energy storage, for example based on chemical or kinetic principles, such as a flywheel storage device. The battery cells can include, for example, ⅔ A size batteries and/or C size batteries. The number of batteries used varies depending on a particular application but typically includes five or ten ⅔ A size batteries or four C size batteries. The five ⅔ A size batteries or four C size batteries are connected in series. Also, two sets connected in parallel of five ⅔ A batteries connected in series can be used for the battery unit  410 . The battery unit  410  preferably powers electronics and a charger located in the AED  100 . 
         [0030]    The battery pack  110  also includes a secondary power supply, such as secondary battery  420 . The secondary battery  420  powers at least a portion of at least one of the AED and the battery pack  110  in an alternate mode, such as when at least a portion of the AED is powered off. Those skilled in the art will appreciate that the secondary battery  420  could also be used to power the AED during other modes, such as a sleep mode or when the AED is powered on. The secondary battery  420  typically includes a single 9 Volt battery, but other power supplies could be used, such as other sized batteries or other forms of energy storage. In a preferred embodiment, the battery pack  110  accommodates replacement of the secondary battery  420 . The secondary battery  420  can be sized smaller than the battery unit  410  and contain energy sufficient to power, for example, electric circuitry of the AED  100  and the battery PCB  140 . 
         [0031]    The secondary battery  420  can be used to power circuitry exclusive of a state of the battery unit  410  and without draining power from the battery unit. Diodes  502  ( FIG. 5 ) electrically isolate the battery unit  410  from the secondary battery  420 . Electric circuitry of the battery pack PCB  140  is described in more detail below with regard to  FIG. 5 . Such circuitry includes a socket to removably receive a memory device ( FIG. 4 ), such as a memory card  430  or a multi-media card (MMC). 
         [0032]    When the AED  100  is powered on and attached to the patient, the memory card  430  records the patient&#39;s electrocardiogram (ECG) signals, audio signals received from a microphone located on the AED  100 , and other operational information such as results of an analysis done on the patient by software of the AED  100 . The memory card  430  may also hold files that may be used to upgrade the software of the AED  100  or to provide user training mode software for the AED. 
         [0033]      FIG. 5  shows a block diagram illustrating battery pack circuitry  500  contained with the battery pack  110 , for example, on the battery pack PCB  140 , and main unit circuitry  505 . The circuitry  500  includes a main power switch  510 . The main power switch  510  connects with a digital logic, such as micro-controller  520 , that turns the main power switch  510  on and off and controls other circuitry  500  of the battery pack PCB  140 . In addition to or in place of the micro-controller  520 , the digital logic can also include a microprocessor, a programmable logic device (PLD), a gate array and a custom integrated circuit. Other digital logic could also be used such as a Programmable Interface Controller (PIC) manufactured by Microchip Technologies, located in Chandler, Ariz. 
         [0034]    The micro-controller  520  connects with a main AED connector  530  that connects circuitry of the battery pack PCB  140  to circuitry of the AED  100 . When the operator engages a power switch  592  located on the AED  100 , the micro-controller  520  receives a signal from the main unit connector  530  indicating that the power switch has been engaged. Thereafter, the micro-controller  520  enables the main power switch  510  to provide an electrical power between the battery unit  410  of battery pack  110  and the electronics of the AED  100 . The battery pack PCB  140  also includes a main battery connector  540  to connect the battery unit  410  to the main unit connector  530  and other circuitry of the battery pack PCB  140 . 
         [0035]    The micro-controller  520  also controls a visual indicator, such as LED  550  and an audio indicator, such as sounder  560  that are used to automatically communicate information to the operator. For example, when the AED  100  fails a self-test, the operator is notified by a chirping sound from the sounder  560 . Moreover, the LED  550  blinks green to indicate that a status of components of the AED  100  is within an acceptable operating range. Those skilled in the art can appreciate the opposite could be true, i.e., that a blinking light indicates a fault condition. According to a preferred embodiment, if the LED  550  is not blinking an error exists, for example, in the circuitry  500 , or the battery unit  410  or secondary battery  420  are depleted. The micro-controller  520  monitors a signal of a comparator connected to secondary battery  420  to monitor a status of the secondary battery  420 , for example, to determine whether or not power of the secondary battery  420  is low or depleted. 
         [0036]    Regarding the main unit circuitry  505 , a digital signal processor (DSP)  562  processes instructions and data of the AED  100 . The DSP  562  connects with a charger circuit  563  and discharger circuit  565  to control the charging and discharging of main unit capacitor  564 . The capacitor charger  563  connects the battery unit  410  to the capacitor  564 . The capacitor  564  connects to a discharge circuit  565  that connects to patient interface  566  to deliver shocks to the patient. 
         [0037]    The micro-controller  520  also controls an active status indicator (ASI), which in one embodiment is a red and green LED  567  located on the AED  100 . In an alternate embodiment the ASI may include two separate LEDs, a red LED and a green LED. The micro-controller  520  connects to the red and green LED  567 , for example, via pins of the main unit connector  530 . The micro-controller  520  causes the LED  567  to blink green when the AED  100  is operating properly and causes the LED  567  to blink red when components of the AED are not within the acceptable operating range, for example, a component of the AED  100  failed during a self-test procedure. If the LED  567  is not blinking when the battery pack  110  is installed into the AED  100 , components of the AED  100  and the battery pack  110  should be checked. The operation of the AED self-test procedures and the ASI are described further below. The battery pack LED  550  is preferably disabled when the battery pack  110  is installed. 
         [0038]    The secondary battery  420  powers the micro-controller  520 , the LED  550  and the LED  567 , which helps to maintain the integrity of the battery unit  410  that provides power to electronics and the capacitor charger located in the AED  100 . A secondary battery connector  570  connects the secondary battery  420  to the circuitry of the battery pack PCB  140 . 
         [0039]    The battery pack circuitry  500  also includes an electrically erasable programmable read only memory (EEPROM)  580  connected to the micro-controller  520  and the main unit connector  530 . The EEPROM  580  stores information that may be relevant to an owner, service person or operator of the AED  100 . The EEPROM  580  stores information regarding, for example, the number of shocks the battery unit  410  has been used for, that the AED  100  has been activated, the date of manufacture of the battery pack  110  and status information regarding a status of components of the battery pack  110  and the AED  100 . The DSP  562  of the AED  100  connects to a bus that connects to a real time clock (RTC)  590 , the EEPROM  580  and the micro-controller  520 . Typically once per power up of the AED  100 , the DSP accesses the RTC  590  to set a main unit clock of the AED  100  that is located in the DSP. 
         [0040]    The main unit circuitry  505  also includes a switch  592 , such as an ON/OFF switch, that connects to the micro-controller  520  via the main unit connector  530 . A shock switch  594  connects to the DSP  562  to allow an operator to administer a shock to the patient. A speaker  596  and indicator LEDs  598  connect to the DSP  562  to supply instructions or other information to the operator. Front end circuitry  599  connects between the DSP  562  and the patient interface  566  to process and/or provide the DSP  562  with information from the patient. 
         [0041]    With reference to  FIG. 6 , in another configuration, the AED  10  consists of a main AED  12  and a removable battery pack  14 . The main AED  12  includes a PIC processor  16 , which is used to control power to the AED, a digital signal processor (DSP)  18 , which is the main processor for the AED, and AED circuitry  20 , which consists of the remainder of the AED circuitry. For a description of additional AED circuitry including the high-voltage circuitry used to generate and deliver defibrillation shock, see U.S. Pat. Nos. 5,607,454 and 5,645,571, the disclosures of which are hereby incorporated by reference. Alternate circuitry, within the purview of one of ordinary skill in the art, may be developed and employed. Thus, the scope of this invention is not intended to be limited to the circuitry described in the incorporated references. 
         [0042]    The battery pack  14  is similar to that previously described with reference to  FIG. 5 , except that some components, including the micro-controller  520  ( FIG. 5 ), i.e., the PIC processor, have been moved to the main AED  12  ( FIG. 6 ). The battery pack  14  includes a battery  22 , which contains multiple battery cells, a real-time clock  24 , which keeps time and can generate an output signal on a regular basis, a power switch  26 , which is used to couple the battery  22  to the main AED  12 , and a 9V battery  20  used to provide power to the PIC processor  16  during the times that the power switch  26  is off. 
         [0043]    The DSP  18  is configured to run a number of self-tests that check the operation of the DSP  18  and the AED circuitry  20  on a periodic basis to ensure that the AED is fully operational. When the main AED  12  is powered off, the PIC  16  is placed in a standby mode. The real-time clock  24 , which is permanently powered from the battery  22 , issues a periodic signal, typically every five seconds. This signal is routed to the PIC  16  and causes the PIC to “wake up” from standby mode. At that time, the PIC  16  flashes an ASI  30  to indicate AED status and also decrements a count of the number of times that it has been woken up since the count was last set. When this count reaches zero, indicating that approximately 24 hours have elapsed since the count was last set, the PIC  16  turns the power switch  26  on which applies power to the AED causing the DSP  18  to execute startup code. 
         [0044]    During the startup sequence, the DSP  18  communicates with the PIC  16  to determine the reason for the power-up. Typical reasons are that the user pressed the on/off button on the AED or that the PIC  16  has initiated a self-test. If the reason is a self-test, the DSP  18  executes self-test code which tests a portion or a majority of the AED circuitry  20 . The results of the self-test are communicated to the PIC  16  which then displays the AED status by blinking the ASI  30 . The PIC may also be configured to sound a sounder, e.g., speaker  32 . When the test is complete, the DSP  18  sets the wake-up counter to a value which will cause the PIC  16  to wake up the DSP  18  approximately 24 hours later and initiates main AED  12  shut-down. The PIC  16  then turns off power to the main AED  12  by switching off the power switch  26 . In this manner the AED is tested on a regular basis. 
         [0045]    A typical testing schedule is to do the following self-tests at the intervals indicated:
       Every day: basic circuitry tests.   Once a week: basic circuitry tests, basic battery tests and basic high voltage circuit tests,   Once a month: basic circuitry tests, additional battery tests and comprehensive high voltage circuit tests, including a partial-voltage internal shock.   Once every three months: basic circuitry tests, additional battery tests and comprehensive high voltage circuit tests, including a full-voltage internal shock.       
 
         [0050]    Tests are performed in a “silent mode” where no user interface elements are exercised and the user is not able to tell that the tests are being executed. The user may also independently initiate a self-test by holding down the on/off button  42  ( FIG. 7 ) on the AED for five seconds while turning the unit on. This will cause an extended self-test, similar in scope to the “once every three months” test, to execute. 
         [0051]    With reference to  FIG. 7 , the ASI  30  is located on the upper right side of the AED enclosure  34 . The status indications provided by the ASI are as follows:
       Steady-on green: the AED is on and operating normally.   Blinking green: the AED is off (in the stand-by mode) and is ready to operate normally.   Steady-On red: the AED is on and has detected an error.   Blinking red: the AED is off (in the stand-by mode) and the AED or battery pack needs servicing.   Off: battery pack not installed, AED defective, or the 9V battery is discharged.       
 
         [0057]    Regarding the “blinking red” status, anytime the ASI  30  blinks red, the PIC  16  causes the speaker  32  to beep periodically to call attention to the AED. The ASI  30  is powered by the replaceable 9V battery  28  in the battery pack  14 . If the 9V battery  28  has discharged, active status indication will not be available. In this case, the 9V battery  28  should be replaced. Once the 9V battery  28  has been replaced, the ASI  30  will once again flash a status indication. If the 9V battery  28  is depleted, the AED will still be fully functional and can be used in the on-state normally. 
         [0058]    When the ASI  30  is blinking red, additional indications of the reasons for the blinking may be obtained by turning the AED on through the on/off button  42 . These additional indications are provided by voice prompts programmed into the DSP  18  and output over the speaker  32 . These voice prompts include: 
         [0059]    “Power on self-test failed, error ‘xxx”’—indicates that the AED has failed the power-on self-test and is non-operational and needs servicing. The code number xxx indicates the type of problem that the unit is experiencing. 
         [0060]    “Battery pack self-test failed, error ‘xxx’”—indicates that the AED&#39;s battery pack is non-operational and needs servicing. The code number xxx indicates the type of problem that the unit is experiencing. 
         [0061]    “Error ‘xxx’, service required”—indicates that the AED has detected an internal error, is non-operational and needs servicing. The code number xxx indicates the type of problem that the unit is experiencing. 
         [0062]    “Battery pack low”—indicates that the battery pack capacity is low and should be replaced soon. The AED will still be able to deliver at least a minimum of six defibrillation shocks the first time this message is spoken. 
         [0063]    “Replace battery pack”—indicates that the battery pack is almost discharged and that the AED may not be able to deliver defibrillation shocks. The battery pack should be immediately replaced. 
         [0064]    “Replace 9V battery”—indicates that the 9V battery in the battery pack needs to be replaced. The unit may not provide active status indication during standby mode in this condition, but the AED is still fully functional when turned on and may be used to treat patients. The 9V battery should be replaced as soon as possible. 
         [0065]    As previously indicated with reference to  FIG. 5 , a speaker  596  and indicator LEDs  598  are connected to the DSP  562  to supply instructions or other information to the operator. With further reference to  FIG. 7 , in one configuration of the AED, these indicators  36  are located on the front panel of the enclosure  34  and include a red “check pads” LED, a red “do not touch patient” LED and a green “analyzing” LED. 
         [0066]    As shown in  FIG. 6 , the indicator LEDs  36  are directly controlled by the DSP  18 . Each LED  36  has a separate control line  38  and driver circuit  40 . When the control line  38  is active the LED  36  is powered and lights up. The DSP  18  determines when to enable an LED  36  based on system state, i.e., connecting, motion, analyzing. The LED  36  can blink under software control by enabling and disabling the control line  38  at timed intervals. 
         [0067]    The DSP  18  enables an LED  36  under the following conditions. The “check pads” LED blinks when the DSP  18  detects that the patient electrodes are not properly applied. The “do not touch patient” LED blinks when the DSP  18  detects patient motion and at times when the operator should stay clear of the patient. The “analyzing” LED blinks when the DSP  18  is analyzing the patient&#39;s ECG Signal. The process of determining conditions that activate these LEDs is described below within the context of additional indications provided by voice prompts. 
         [0068]    In addition to the indications provided by the blinking LEDs  36 , the DSP  18  is programmed to output voice prompts over the speaker  32  in association with certain conditions. Voice prompts associated with the “check pads” LED include “connect pads” and “check pads”. “Connect pads” indicates that the DSP  18  has determined that the pads are not properly connected to the unit or not placed on the patient. This determination may be made by measuring the impedance across the pads. A high impedance is an indication that the pads are either not connected to the unit or not placed on the patient while a low impedance serves as an indication that the pads may be shorted together. What is considered “high” or “low” impedance is dependent on the electrical characteristics of electrode pad assembly and the internal defibrillator circuitry. “Check pads” indicates that the pads are making improper contact with the patient and that the impedance is out of range, i.e., either too high or too low, for proper ECG analysis and shock delivery. 
         [0069]    Voice prompts associated with the “do not touch patient” LED include “do not touch patient”, “stop motion” and “stop interference”. “Do not touch patient” indicates that the DSP  18  is in the process of analyzing the patient&#39;s heart rhythm and that the operator should not touch the patient. The DSP  18  is programmed to analyze ECG signals once it has determined that the electrode pads are making good connection to the patient. The “do not touch patient” message is spoken at the beginning of the ECG analysis period and also if motion or interference has been detected. “Stop motion” indicates that the DSP  18  has detected motion in the patient, such as may occur during the administering of CPR. “Stop interference” indicates that the DSP  18  has detected interference on the ECG signal. In each of these cases, the DSP  18  monitors the characteristics of the ECG signals for indications of patient motion, e.g., an unexpected spike in the signal, and signal interference, e.g., a signal pattern containing noise or a signal of weak amplitude. 
         [0070]    Voice prompts associated with the “analyzing” LED include “analyzing heart rhythm” and “analyzing interrupted”. “Analyzing heart rhythm” indicates that the DSP  18  is actively analyzing the patient&#39;s ECG signal. The DSP  18  will continue analyzing until it has determined whether a rhythm is shockable or non-shockable or analyzing is interrupted for some reason. “Analyzing interrupted” indicates that the DSP  18  has determined that accurate ECG analysis is not possible and has ceased analyzing. The DSP  18  determines this condition by monitoring the ECG signal as previously described with respect to patient motion, signal interference and check pads. While the other LEDs may blink during this process, the “analyzing” LED will not be lit during this message. 
         [0071]    While the invention has been described above by reference to various embodiments, it will be understood that many changes and modifications can be made without departing from the scope of the invention. It is therefore intended that the foregoing detailed description be understood as an illustration of the presently preferred embodiments of the invention, and not as a definition of the invention. It is only the following claims, including all equivalents, which are intended to define the scope of this invention.