Abstract:
External portable medical devices, such as portable external defibrillators (PEDs), have long standby times and may be required to indicate their operational status to a user while conserving battery power. Frequently, numerous PEDs are scattered throughout one or more large facility, which may make identifying a PED that is indicating an operational status that requires attention more difficult. To conserve power and provide more effective notice, a PED may use a broadcast transmitter, which minimizes power usage, to communicate the PED&#39;s status to a remote monitor that is connected to a relatively unlimited power supply. The remote monitor may then provide a wide variety of sensory alerts to indicate the status of the PED without concern for the power consumption associated with the sensory alert.

Description:
TECHNICAL FIELD 
     The present invention is generally directed to external portable medical devices, and relates more particularly to the remote monitoring of Portable External Defibrillators (PEDs) to provide alerts of conditions on the PEDs while minimizing power consumption from the PED&#39;s battery. 
     BACKGROUND OF THE INVENTION 
     External defibrillators (“EDs”) are emergency medical devices designed to supply a controlled electric shock (i.e., therapy) to a person&#39;s heart during cardiac arrest. This electric shock is delivered by pads that are put into contact with the person&#39;s body. 
     During a cardiac arrest, the heart loses its normal electrical rhythm, commonly referred to as cardiac arrhythmia, and may adopt a fibrillation or tachycardia rhythm. As a result, the heart is unable to pump blood properly through a person&#39;s body. Unless a timely rescue attempt using an ED is made to restore the normal electrical rhythm, death can result. 
     To provide a timelier rescue attempt for a person experiencing cardiac arrest, some EDs have been made portable and have been designed to be operated by non-medical personnel. These portable EDs (PEDs) have gained acceptance by those outside the medical profession and have been deployed in myriad locations outside of traditional medical settings. Due to the life saving benefits of PEDs, more and more non-medical users are purchasing and deploying PEDs in their respective environments. This allows for a rescue attempt without the delay associated with bringing the person to a medical facility, or bringing a medical facility to the person (e.g., a life support ambulance). 
     Individuals as well as businesses are purchasing and deploying PEDs. As time is of the essence during any rescue attempt, multiple PEDs may be purchased by any particular individual or user to allow placement at multiple locations. In the case of an individual, this could be on several floors of a home, and in the case of a business, this could be for placement throughout a facility (e.g., factory, office building, or large retail center). Thus, regardless of where the victim is within the home/facility, access to a PED would only be seconds, or minutes, away. 
     Many of these deployed PEDs rely on battery power. More specifically, they use a battery as their primary source of power and are stored disconnected from a power grid (e.g., the battery is not constantly being charged). As these PEDs are standby devices that are used infrequently, typically a PED will remain in storage for long periods of time until, if ever, called upon to perform a rescue attempt. 
     Battery powered PEDs have a fixed battery life (e.g., the batteries must be recharged or replaced after some interval of time). Typically, battery life is measured in terms of months or even years. Minimizing power consumed (i.e., battery drain) by the PED while in storage to maximize PED availability is critical for a rescue attempt. More specifically, battery life is determined by two main factors, battery aging and battery usage. Battery aging results from the ongoing chemical reaction taking place in the battery, thus sets the maximum battery life possible. Battery usage, however, is due to such factors as tasks the PED must perform during storage to assure proper functioning, such as simple maintenance checks, and shortens battery life. It should be appreciated that regardless of the reason, a battery will lose power over time. Unfortunately, if the battery is not serviced there will come a point in the life of a PED where the PED will be unable to provide the necessary life saving shock during a rescue attempt due to a low battery condition. 
     In addition to battery life issues, PEDs may also have other issues. As mentioned above, the battery may provide power for performing maintenance checks to assure proper functioning. It is thus always possible that the PED may have a maintenance issue that requires action to allow the PED to function properly. 
     As a result of battery life issues and maintenance issues, a PED may require both scheduled maintenance (e.g., battery replacement) and unscheduled maintenance to assure that it is always ready to provide its life saving therapy when called upon. 
     To this end, PEDs incorporate various sensory alerts (i.e., devices that the senses (such as eyes or ears, can detect) to notify a user when maintenance is needed. For example, a PED may incorporate mechanical means, such as a status indicator (e.g., a flag that changes colors—from green (i.e., in service) to red (i.e., maintenance needed, or out-of-service)). These types of passive sensory alerts have the benefit of being very low power, but are subtle and can easily be missed, such as when the PED is not stored in plain sight (e.g., in a closet), or in low lighting. Active sensory alerts, such as an auditory (e.g., beeping alarm) or visual (e.g., a flashing light), provide a more noticeable signal, but use much more power. 
     It should be appreciated that sensory alerts are ideally provided before the PED reaches the point where it cannot function in a rescue attempt, but must be provided when the PED is no longer capable of performing a rescue attempt. It should also be appreciated that sensory alerts, particularly of the active types, depending upon their robustness can use significant battery power. Thus, there is a tradeoff between power usage for sensory alerts that command attention, and retaining power for a rescue attempt. In the most extreme and undesirable situation, a sensory alert meant to indicate simply a need for maintenance to preserve an existing rescue attempt capability (e.g., a low but usable battery) could actually drain sufficient power from the PED battery so the PED would not be able to perform a rescue attempt. 
     In the rigid and controlled medical environment, PEDs are constantly monitored and checked to assure the PED&#39;s operational status, thus low subtle sensory alerts are effective. However, in the less rigid and uncontrolled non-medical environment, the robustness of the sensory alert needed to assure action may use a significant amount of power. Thus, there is a need in the art for a more effective method of monitoring PEDs and alerting those in charge of the PED&#39;s maintenance when a PED is in need of maintenance to assure that it is ready to support a rescue attempt when called upon to do so. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a portable emergency medical device interacts via a transmitter with a monitor, which is remote from the portable emergency medical device. As a result of the interaction, the monitor can make an assessment of the operational status of the portable emergency medical device, and, if appropriate, alerts a user of its need for service. 
     More specifically, the portable emergency medical device has self-diagnostic tests that determine the operational status of the device. These self-diagnostic tests, which may be activated sua sponte, are capable of determining, for example, whether the portable emergency medical device is ready to perform its function or not. Based on the outcome of the self-diagnostic tests, the portable emergency medical device communicates its operational status to a user by transmitting a signal to the monitor. 
     One feature of the present invention is to provide a remote capability to assess and notify a user of the operational status of a battery powered portable emergency medical device using as little battery power of the portable emergency medical device as possible. As a result, battery power of the portable emergency medical device is conserved for a rescue attempt. In addition, the monitor, which has a power supply independent of the portable emergency medical device, can have sensory alerts that are considerably more robust than those in a portable emergency medical device. Further, the monitor can be located in an area more favorable to a user detecting and acting upon an alert from a sensory alert. 
     Other features, attainments, and advantages will become apparent to those skilled in the art upon a reading of the following descriptions when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a plan view of a system for monitoring a PED according to one exemplary embodiment of the invention. 
         FIG. 2  is a functional block diagram illustrating a PED which is part of the system according to one exemplary embodiment of the invention. 
         FIG. 3  is an exemplary condition information data stream. 
         FIG. 4  is a functional block diagram illustrating a remote monitor of the system according to one exemplary embodiment of the invention. 
         FIG. 5  illustrates a plan view of the system of  FIG. 1  incorporating a repeater. 
         FIG. 6  illustrates a plan view of a system having multiple PEDs being monitored by a single monitor. 
         FIG. 7  is a logic flow diagram illustrating exemplary steps for generating a condition information stream according to one exemplary embodiment of the invention. 
         FIG. 8  is a logic flow diagram illustrating exemplary steps for processing a condition information stream. 
         FIG. 9  is a logic flow diagram illustrating exemplary steps for providing an alert when a monitor fails to receive an expected condition information stream. 
         FIG. 10  illustrates a plan view of an enhanced system according to one exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The term “portable emergency medical device” as used herein means a medical device intended by its design to be readily movable (e.g., carried) by a typical human being of ordinary strength, and to be a self-contained medical device (e.g., has an integrated portable power source (e.g., battery, crank generator)), which performs a medical procedure (e.g., a defibrillator) that is stored in a location, such as on a shelf or in a closet, and for use is retrieved and associated with a body, such as that of a human, to perform the medical procedure for which it was created. The term “broadcast transmitter/receiver combination” as used herein means a broadcast transmitter and broadcast receiver that work in combination that need not be collocated, but are not as a precondition to transmitting and receiving data required to establish first their mutual co-existence and compatibility (e.g., Wi-Fi and Bluetooth). Thus all things being equal, a broadcast transmitter transmits its data consuming less power from a power source. 
     Common examples of broadcast transmitter/receiver combinations are radio transmitters and radios, television transmitters and televisions, and generally most remote control devices and the device they control (e.g., television remotes and televisions). A common feature of broadcast transmitter/receiver combinations is that the broadcast transmitter upon an initiating transmission does not transmit to a known, particular broadcast receiver, or know if any broadcast receiver is within range. 
     It is possible, that a second receiver associated with a broadcast transmitter may receive a confirmation transmission from a second transmitter associated with the broadcast receiver to indicate that the broadcast transmitter should continue broadcasting, or indicate a successful transmission. A common example of this is a walkie-talkie wherein a first walkie-talkie makes an initial transmission using its broadcast transmitter and then waits for a second walkie-talkie to respond, indicating its presence, before making another transmission and so on. 
     The term “battery” as used herein means a cell (e.g., a D cell) or group of cells (e.g., two D cells in series) for providing power. 
     Turning now to the drawings,  FIG. 1  illustrates a system for monitoring a portable emergency medical device (generally referred to by reference number  10 ) which includes a portable emergency medical device  12  (illustrated as and hereinafter referred to as a Portable External Defibrillator (PED)). A PED  12  generally includes a base unit  14 , having the necessary programmable circuitry for performing the medical procedure of the PED (well known to those skilled in the art), and a set of pads  16  associated therewith. For this particular PED  12 , the pads from the set of pads  16  are appropriately placed on a body (not shown) and an electrical shock generated in the base unit  14  is passed through the body when the “SHOCK” button is depressed. Within the base unit  14 , is a battery  18  for powering the PED  12  and a broadcast transmitter  22  of a broadcast transmitter/receiver combination. 
     The system  10  further includes a broadcast receiver  26 , which is the receiver of the broadcast transmitter/receiver combination. The broadcast transmitter  22  transmits a condition information stream  24  to the broadcast receiver  26  that is in a monitor  28 . The monitor  28  is remote from the PED  12 . 
     The monitor  28  is powered by a power supply  30 , which is independent of the PED&#39;s battery  18 . Therefore, the battery  18  of the PED  12  is not powering the monitor  28 . As a result, the power available to the PED  12  from its battery  18  is not altered by the power consumed by the monitor  28 . It should, therefore, be appreciated that where the PED  12  is attached to a power grid (e.g., for battery charging) and the monitor  28  is attached to the same power grid, the two power supplies would still be considered independent within the context of this invention, as the operation of one does not change the power available to the other. 
       FIG. 2  is a block diagram of the PED  12 . Underlined reference numbers indicate structure depicted in  FIG. 1 . 
     As shown in  FIG. 2 , the broadcast transmitter  22  is electrically connected to the PED&#39;s  12  programmable circuitry  34 . As illustrated, the broadcast transmitter  22  includes a transmitter  36  connected to an antenna  38 . 
     The broadcast transmitter  22  may be capable of generating a signal of constant frequency and amplitude, so that when it is turned “on” then “off” and back “on” the same signal is produced. A transmitter that may be used with the present invention is an Elsie RF transmitter. The Elsie RF transmitter includes a Surface Acoustic Wave (SAW) stabilized Colpitts oscillator with a carrier frequency of 433.92 MHz. As those skilled in the transmitter design arts will appreciate, depending on the geographical location where the transmitter is to be utilized and the range of the transmitter, governmental regulations may dictate which frequencies may be used. 
     In this illustrative example, the broadcast transmitter  22  is controlled by an active status indicator (ASI) processor  40  of the programmable circuitry  34 . The ASI Processor  40  cooperates with a Main Processor  42 , of the programmable circuitry  34 , to conduct and then report the results of at least some self-diagnostic test of the PED  12 . 
     More specifically, the PED  12  has a STANDBY mode, a MANUAL-TEST mode, an AUTO-TEST mode, and an ON mode. The MANUAL-TEST mode, AUTO-TEST mode, and ON mode may all have self-diagnostic testing to determine the capability of the PED  12  programmable circuitry  34  to perform a rescue attempt. The STANDBY mode is the lowest energy consuming mode. 
     In the STANDBY mode, the PED  12  has a running clock  44  and an active status indicator (ASI)  46 . As illustrated, the clock  44  is associated with the ASI Processor  40 . The ASI  46  indicates, in this case by solid or blinking green or red lights, the last known operational status (e.g., ready with no maintenance needed, ready but maintenance needed, not ready) of the PED  12 . The ASI  46  is controlled by the ASI Processor  40 . 
     The PED  12  may be automatically put into the AUTO-TEST mode from the STANDBY mode sua sponte (i.e., as a result of its own action) by the PED. The PED  12  may go into AUTO-TEST mode periodically (e.g., when a time interval is reached). More specifically, in this illustrative example in the STANDBY mode the clock  44  maintains time and causes the ASI Processor  40  to come “on” at a fixed interval, to accomplish the routine task of operating the ASI  46 . 
     Programming in the ASI Processor  40  tracks the number of “on” intervals and when a sufficient number is accumulated sends a “wake-up” signal  48  to the Main Processor  42 ; thereby beginning the AUTO-TEST mode. Upon receiving the “wake-up” signal  48 , the Main Processor  42  is powered and programming in the Main Processor determines the time from the clock  44 , and based on that time determines the self-diagnostic test required and then performs the self-diagnostic test. At the end of a self-diagnostic test, programming in the Main Processor  42  puts the PED  12  back into the STANDBY mode. 
     In order to minimize battery power consumption during the AUTO-TEST mode, different self-diagnostic tests may be performed at different times. For example, there may be daily, weekly, monthly, and quarterly self-diagnostic tests. As those skilled in the art appreciate, to maximize battery life there should be an inverse relationship between the frequency of a self-diagnostic test and the power it consumes. Thus, a daily self-diagnostic test should consume less power than a weekly self-diagnostic test and so on. 
     As stated above, the self-diagnostic tests vary to balance effective self-diagnostic testing of the PED  12  and PED battery  18  life. For example, the daily self-diagnostic test may include powering up the Main Processor  42  to check software integrity, basic operation of electronic circuitry, and pad presence. The weekly self-diagnostic tests could add such elements to the daily self-diagnostic test as advanced circuit and battery integrity, broadcast transmitter integrity, patient interface circuitry, defibrillation electrode analysis, and capacitor/discharge circuit evaluation using partial charging. The monthly self-diagnostic tests could add to weekly self-diagnostic test discharge at the partial charge. The quarterly self-diagnostic test could add to the monthly regimen a simulated full ON condition with discharge. 
     In the MANUAL-TEST mode, which is activated by a user, a user activates a self-diagnostic test. Depending upon the sophistication of the PED  12 , the user may be able to select a particular self-diagnostic test from a selection of self-diagnostic tests. A check pad self-diagnostic test can be activated by depressing a test button  50 . Where there is only a single self-diagnostic test available in the MANUAL-TEST mode, it should test as much of the PED  12  as possible, including but not limited to charging and discharging (internally only). The self-diagnostic test(s) available in the MANUAL-TEST mode may be the same as those in other modes. 
     When the PED  12  is put into ON mode, the PED has a power-on self-diagnostic test, which may be the same as a self-diagnostic test in other modes. In this illustrative example, the ON mode is manually activated by an ON/OFF Button  52 . When the ON/OFF Button  52  is in the ON position, the PED  12  prepares to give a patient a shock by activating all the necessary circuits, and performing the power-on self-diagnostic test to determine availability to perform the rescue mission. It should be appreciated that to effectuate a rescue, charging of a capacitor  54 , which is part of the PED&#39;s defibrillator system  56  that is part of the programmable circuitry  34 , will be required. When and how the capacitor  54  is charged is well known in the art. The defibrillator system  56  further includes a charger circuit  58  and a discharge circuit  60 . 
     When a self-diagnostic test is performed, data obtained from the self-diagnostic test may be transmitted by the broadcast transmitter  22  to the broadcast receiver  26  in the condition information stream  24 . It is not necessary that every time a self-diagnostic test is performed a condition information stream  24  be generated, or, if generated, be transmitted. 
     As shown in  FIG. 2 , the condition information stream  24  may be created by the ASI Processor  40  or the Main Processor  42 . If created by the Main Processor  42 , the Main Processor may obtain input from itself, the battery  18 , the defibrillator system  56 , the pad connector  62  and the memory  66 , depending upon the self-test preferred. Generally, the ASI Processor  40  generates a condition information stream  26  when the Main Processor  42  fails to provide a timely condition information stream  24  to the ASI Processor  40 . As a means of assuring the condition information stream  24  is not lost, the ASI Processor  40  may also send a copy of it into memory  66 . 
     As illustrated in  FIG. 3 , the condition information stream  24  may have several parts. In this illustrative example, the condition information stream  24  is 152 bits in length and includes a message preamble  24 A of 8 bits, a fixed value  24 B of 8 bits, an RF message ID  24 C of 8 bits, and a data payload  64 . The data payload  64  may include a unique sequence  24 D of 8 bits, a PED Serial No.  24 E of 32 bits, a PED Model No.  24 F of 32 bits, an ASI status word  24 G of 16 bits, a defibrillator error code  24 H of 16 bits, an event code  24 I of 8 bits, and an error detector  24 J of 16 bits. As those skilled in the art will appreciate, the illustrated condition information stream  24  is but one example, however, the data payload as used herein means that part of the condition information stream contains at least some data that may change to indicate a change in the operational status (e.g., out-of-service) of the PED  12 . 
     The message preamble  24 A may be a series of bits, generally all the same (e.g., 1s or 0s). The message preamble  24 A provides the time and signal necessary for programming in the monitor  28  to set the broadcast receiver  26  thresholds to receive the balance of the incoming condition information stream  24 . It is not necessary that the broadcast receiver  26  receive the entire message preamble  24 A, or that each bit of the message preamble be properly framed (i.e., interpreted). 
     The fixed value  24 B is a predetermined, known series of bits that provides a framing reference. In other words, the fixed value  24 B provides a means for programming in the monitor  28  to determine how to begin reading the condition information stream  24  by providing a known value, and also may identify the data stream as being relevant to the monitor  28 . In other words, the broadcast receiver  26 , thus the monitor  28 , is always waiting to receive a condition information stream  24 . Thus, any data stream on the broadcast receiver&#39;s  26  frequency will be detected by the broadcast receiver, and the monitor  28  needs a means to determine if it is a condition information stream  24 . The Message ID  24 B may be an 8 bit word, such as a “D.” 
     The RF Message ID  24 C is a value that assists in the differentiation of data payloads. More specifically, the RF Message ID  24 C defines the digital format of the data payload  64  of the condition information stream  24 . The data payload  64  of the condition information stream  24  contains some number of bits that must be subdivided to extract information, and the monitor&#39;s  28  programming must know the format. For example, the RF Message ID  24 C could be 8 bits that translate into a word, such as “S.” An “S” indicates a data payload  64  having an “S” structure. The “S” structure, which would be known by the monitor&#39;s  28  programming, could mean the unique sequence  24 D, discussed below, is 8 bits, the PED Serial Number  24 E, discussed below, is 32 bits, etc. A change in RF Message ID  24 C would indicate a change in the number of bits or how the bits are partitioned within the data payload  64 . 
     The unique sequence  24 D is a unique value for each condition information stream  24  from a given broadcast transmitter  22 . The unique sequence  24 D provides the ability for the monitor&#39;s programming to differentiate condition information streams  24  from a given broadcast transmitter  22 , thus PED  12 . 
     Where the unique sequence  24 D is an ordered value known to the monitor&#39;s  28  programming, the unique sequence  24 D can be used to place the various condition information streams  24  from a PED  12  in order. It could also be used by the monitor&#39;s  28  programming to determine if a particular condition information stream  24  was not collected by the monitor  28 ; thus, an alert should be issued. Typically, ordered values are well known ordinal schemes, such as 1, 2, 3, etc. 
     The unique sequence  24 D may provide the monitor&#39;s  28  programming the ability to determine if it missed receiving a particular condition information stream  24 . 
     The PED Serial No.  24 E is a unique identifier of a particular PED  12 . The PED Serial No.  24 E is generally assigned by the manufacturer. 
     The PED Model No.  24 F is an identifier that relates a PED  12  to a particular group of PEDs. The PED Model No.  24 F is assigned by the manufacturer. 
     The PED Status Word  24 G identifies an operational condition of a PED  12 . A reasonable PED Status Word  24 G is best read as a status bit field. More specifically, the PED Status Word  24 G has 16 bits numbered  0 - 15 . Each bit can have a 1 or 0 status, and each bit can be associated with a particular issue. For example, bit  0  could be related to primary battery condition. If it is a 0 the primary battery is fine, if 1, the primary battery is low. Similarly, for bit  6 , a 0 could indicate pads connected, while a 1 could indicate no pads connected. 
     The defibrillator error code  24 H provides a code relevant to an identified failure. In this example, the defibrillator error code  24 H is 16 bits, which can potentially provide up to 65,565 error codes. 
     Taken together, or individually, the PED Status Word  24 G and the defibrillator error code  24 H provide operational status information, which may generate an alert. This is discussed in detail below. 
     The event code  24 I indicates the event, e.g., AUTO-TEST, MANUAL TEST, or ON, that generated the condition information stream  24 . 
     The error detector  24 J provides a check (e.g., CRC 16 ) of some or all the data within the condition information stream  24 . More specifically, the error detector  24 J is constructed from all, or some, of the information in the condition information stream  24 . Generally, the Message Preamble  24 A will be excluded. The error detector  24 J provides a means for the monitor&#39;s  28  programming to check the content of the condition information stream  24  for accuracy of receipt. 
     It should be appreciated that some of the contents of the condition information stream  24  (e.g., defibrillator error code  24 H) are generated based on self-diagnostic test results. Therefore, there is no requirement that all condition information streams  24  from a PED  12  be the same. And as used herein, the phrase “condition information stream” when used in conjunction with a PED includes the limitation that all condition information streams  24  from a PED are not required to be the same. 
     To facilitate data transfer, the condition information stream  24  may use a known coding scheme. One possible coding scheme is Manchester Coding. Manchester coding (also referred to as Phase Encoding, or PE) is a line code coding scheme in which the encoding of each data bit (e.g., 1 or 0) has at least one transition and occupies the same time duration (i.e., has the same time duration). As a result, this type of line code is considered self-clocking (e.g., the clock signal can be recovered from the encoded data). Thus, the condition information stream  24  does not need to have a separate clock signal. 
     Manchester coding can be achieved by essentially turning the broadcast transmitter  22  (See  FIG. 2 ), more specifically the transmitter  36 , “on” and “off.” This procedure is commonly referred to as On-Off Keying (OOK) or Amplitude Shift Keying (ASK). When this is done, the frequency and amplitude of the signal from the broadcast transmitter  22  may remain constant. 
     The distance over which data can be transmitted, all other conditions being the same, is inversely related to baud rate at which the message is sent. The ability to decode accurately the condition information stream  24  can be increased by incorporation of a return-to-zero (RZ) data code. 
     Turning the broadcast transmitter  22  “on” and “off” to send the condition information stream  24  minimizes battery usage. Since the broadcast transmitter  22  is only “on” to send some portion of the condition information stream  24 , a majority of the time the broadcast transmitter  22  is not powered. This approach, thus, uses minimal battery power. 
     The broadcast transmitter  22  may operate on a different schedule than the schedule for self-diagnostic tests. For example, the self-diagnostic tests may run every hour with the broadcast transmitter  22  transmitting only once in a 24 hour period, as long as the status of the PED  12  is acceptable. Ideally, the broadcast transmitter  22  should transmit immediately if a problem has been detected. 
     As a practical matter, when the broadcast transmitter  22  is operated, the condition information stream  24  could be transmitted several times at fixed or random intervals. Multiple transmission are particularly important to avoid collisions between conditions information stream  24  from multiple PEDs  12  that are being monitored by a single monitor (this case is discussed below). This multiple transmission gives the broadcast receiver  26  in the monitor  28  several opportunities to receive the transmission. It should be appreciated that if a problem has been detected the transmission could be more frequent in time and more robust in energy. 
       FIG. 4  is a block diagram of the monitor  28  and the transmitter  22  depicted in  FIG. 1  interacting with a central monitor. Underlined reference numbers indicate structure depicted in  FIG. 1 . 
     Referring to  FIG. 4 , the monitor  28  contains the broadcast receiver  26 , having a receiver  67  which is connected to an antenna  68 , and programmable circuitry, having a processor  70  associated with memory  72 . The broadcast receiver  26  is capable of receiving a condition information stream  24  from the broadcast transmitter  22  within a PED  12 . The processor  70  contains programming to decode the condition information stream  24  and act upon the information contained therein. 
     The monitor  28  may also include a sensory alert  74 , a transmitter  76  connected to antenna  78 , and a network connection  80 . The sensory alert  74  can be of almost any type of sensory alarm, such as visual or audible device. It should be remembered that the monitor  28  is utilizing a main power source  30  that is separate from the battery  18  of the PED  12 . Ideally, the monitor  28  is plugged into a constant ON power grid (e.g., in the US a standard  120   v  outlet). Thus, the sensory alert  74  can be as robust as desired to get the attention of personnel (e.g., maintenance personnel) without worry that the battery  18  of the PED  12  is being drained. 
     The sensory alert  74  may have one or more sensory alarms (i.e., output devices that at least one of the senses of a human can detect) for getting the attention of a human. For example, the sensory alarms devices may include speakers for generating sounds (e.g., commands such as “action required,” or noise), horns (e.g., beeping sounds), lights (e.g., blinking lights or solid colors), or mechanical devices (e.g., flags to be deployed upon detection of a problem). As the monitor  28  is connected to the main power source  30  that will not affect the power available to the PED  12 , these sensory alarms may be quite robust. 
     In addition, the monitor  28  could include a network connection  80  for incorporating the monitor into an intranet or internet. In addition, the monitor  28  could include a transmitter  76 , with antenna  78 , for transmitting condition information, or merely an alarm condition, to a central monitor  82 , having its own antenna  84 . It is possible that the transmitter  76 , with antenna  78 , could be a cell phone and the central monitor  82 , with antenna  84 , could be a cell phone. It is certainly possible that a standard transmitter/receiver combination could be used. 
     The monitor&#39;s broadcast receiver  26  is ideally constantly on and ready to receive a condition information stream  24  from a broadcast transmitter  22 . The monitor  28  therefore needs a reliable power source (e.g., main power source  30  being a power grid), but it may have backup power  86 . 
     In operation, the transmitter  24  is operated to send a condition information stream  24  as a result of a self-diagnostic test. Generally, the condition information stream  24  will be sent as part of the PED  12  turn off routine. In the ON mode, however, the condition information stream  24  maybe sent at anytime from immediately after the test is performed until a turn off routine is encountered. 
     As an initial matter, the broadcast receiver  26  would receive notice that the broadcast transmitter  22  is active by receiving the message preamble  24 A. The message preamble  24 A would allow programming in the monitor  28  to adjust the broadcast receiver  26  gain to receive the balance of the condition information stream  24 . The balance of the condition information stream  24  would then be received. If the condition information stream  24  were being sent multiple times, the broadcast receiver  26  would receive all condition information streams. 
     The monitor&#39;s processor  70 , which is part of the monitor&#39;s circuitry, contains programming to process the condition information stream  24  to extract and analyze the data contained therein. As part of the analysis, the PED Status Word  24 G and defibrillator error code  24 H would be analyzed to determine if an alert using the sensory alert  74  is needed to alert a person that the PED needs attention. More specifically, the programming should be able to distinguish between those PED Status Words  24 G and defibrillator error codes  24 H that require an alert due to a PED condition and those which were reporting that the PED is in operating order, which generally would not generate an alert. 
     The monitor&#39;s processor  70  may also contain programming to determine the failure to receive a condition information stream  24 . More specifically, the self-diagnostic system of the PED  12  may be designed to perform periodic checks of the PED. In addition, it may be designed to transmit periodically the results of those checks to the monitor  28 . Thus, the processor  70  of the monitor  28  could be programmed to recognize when a periodic transmission of a condition information stream  24  was missed based on when it was to occur, recognize when a condition information stream has not been received within a given time period, or analyze the unique sequences  24 D within various condition information streams to determine if a specific condition information stream was missed. Ideally, the processor  70  of the monitor  28  would have the ability to learn when the next transmission was expected and await its arrival. This could be accomplished by providing the monitor  28  with the periodic interval and then initializing the monitor with a first condition information stream  24 . 
     Referring to  FIG. 5 , the system  10  in addition to a PED  12  and monitor  28  may include a repeater  88 . As discussed above, there is a trade-off of power usage (i.e., battery) by the PED&#39;s broadcast transmitter  22  and the range of that transmitter. Thus, requiring the monitor  28  to be remote from, but close enough to, the PED  12  to receive the condition information stream  24 . This distance, however, can be increased by the use of a repeater  88 . 
     It should be appreciated that the system  10  could further include any number of repeaters  88 . More specifically, the range of the broadcast transmitter  22  is limited by the power drain on the PED battery  18  one wishes to tolerate. Thus, repeaters  88  attached to independent power sources  90  could be used to extend the distance between a PED  12  and its associated monitor  28 . 
     As shown in  FIG. 6 , multiple PEDs  12  may be associated with a single monitor  28 . As those skilled in the art will appreciate, if one monitor  28  is monitoring several PEDs  12  the monitor should be able to distinguish between PEDs and identify the relevant PED. More specifically, if the monitor  28  receives a condition information stream  24  from a particular PED  12  indicating a problem, the monitor should be able to indicate the specific PED with the problem. There are many ways to accomplish this objective. The most straightforward method is to use the PED Serial Number  24 E in the condition information stream  24  (see  FIG. 3 ). 
       FIG. 7  shows a method for generating a condition information stream  24  for a PED  12 . As shown in  FIG. 2 , the PED  12  includes a clock  44 , an ASI Processor  40 , and a Main Processor  42 . 
     Continuing with  FIG. 7 , the clock  44  contains a timer, step  91 , which when activated sends a “wake-up” signal to the ASI  40 . More specifically, the clock  44  is programmed with a baseline time and then one second intervals are generated. The timer, step  91 , is set to a given number of seconds (e.g., 5). As time passes and is recorded in the time index, step  92 , the time index is evaluated, step  94 , to determine if the timer should be activated. At the appointed interval (e.g., 5), the timer activates and sends a “wake-up” signal to the ASI Processor  40 . 
     When the ASI Processor  40  is awakened, step  96 , the ASI Processor  40  commands the ASI  46 , step  98 , to display as required based on the last self-diagnostic test. Also, the ASI Processor  40  has programming which contains a counter for self-diagnostic testing, step  99 , which may have a fixed value. More specifically, the counter for self-diagnostic testing, step  99  determines when the ASI Processor  40  should send a “wakeup” signal to the Main Processor  42 . When the “wake-up” signal is sent is determined by the counter for self-diagnostic testing. For example, if a daily self-diagnostic test is desired, the fixed value of the counter for self-diagnostic testing assuming that the ASI is awakened every 5 seconds is 17,280, calculated as follows—86,400 seconds/day divided by 5 seconds. Thus, every time the ASI Processor  40  is turned “on,” a counter index, step  100 , is advanced one, and the new counter index is compared to the counter for self-diagnostic test to determine if the counter has be tripped, step  102 . If the two values are equal, the ASI Processor  40  sends a “wake-up” signal to the Main Processor  42  and the counter index is reset, step  104 . It should be appreciated that the ASI Processor  40  turns itself “off” after performing its ASI  46  function, step  98 , if no “wake-up” signal is sent to the Main Processor  42 . 
     If a “wake-up” signal is sent to the Main Processor  42 , the Main Processor is powered up, step  106 . Upon power up, the Main Processor  42  obtains from the clock  44  the baseline date and the present number of cumulative seconds from the baseline date, step  108 . Further, in step  108  using a calendar algorithm, the Main Processor  42  determines the date. Using this date, the Main Processor  42  programming identifies the proper self-diagnostic test. As mentioned above, the PED  12  may contain several self-diagnostic tests, such as daily, weekly, monthly, or quarterly. Based on the date and programming within the Main Processor  42 , the Main Processor selects the appropriate self-diagnostic test for the date and performs the self-diagnostic test, step  110 . 
     After completion of the self-diagnostic test, step  110 , the programming of the Main Processor  42  creates an appropriate condition information stream  24  and sends that CIS to the ASI Processor  40 , step  112 . To maximize the chances of receipt by the broadcast receiver  26 , the condition information stream  24  may be sent multiple times over a short time period (e.g., one-half hour). Multiple times are prudent because of potential interference from, for example, other PEDs reporting, or failure of the PED to receive the entire message. Where a single condition information stream  24  is sent multiple times, there is a potential it will be received multiple times. The monitor&#39;s programming should be able to determine if the same condition information stream  24  has been received multiple times by evaluating the unique sequence  24 D. In addition, the programming of the monitor  28  should be capable of taking partial condition information streams  24  which it can identify as being a single information stream and constructing the single information stream. 
     When the counter index is tripped, step  102 , to send a “wake-up” signal to the Main Processor  42 , the ASI Processor&#39;s  40  programming begins waiting for a condition information stream  24  from the Main Processor, step  114 . More specifically, the ASI Processor  40  sets a time limit of receiving a condition information stream  24  from the Main Processor  42 . If the Main Processor  42  sends a condition information stream  24  within this time period, the ASI Processor  40  will broadcast the condition information stream  24  from the Main Processor, step  116 . In the event, the ASI Processor  40  does not receive a timely condition information stream  24  from the Main Processor  42 , the ASI Processor  40  will generate a condition information stream  24  and broadcast that condition information stream, step  118 . As a result of the condition information stream broadcast, programming in ASI Processor  40  will update the ASI  46 , step  120 . 
     Continuing with  FIG. 8 , the monitor  28  has a constant on (24 hours per day 7 days a week) receiver  67 , step  122 . The receiver  67  stands ready to receive a condition information stream  24 . In addition, the programming of the monitor  28  may be programmed to know which PEDs  12  it is monitoring, step  124 . This knowledge may be based on knowing the PED&#39;s serial number. 
     Upon receiving a condition information stream, step  126 , the programming in the monitor  28  checks, step  128 , the log of PED units of interest to confirm it is a PED  12  being monitored by this monitor. If it is not, it is ignored, or an error may be reported, step  130 . If it is, the condition information stream  24  is stored in the receiver log, step  132 , and decoded and analyzed to determine if it contains alert information, step  134 . If alert information is detected (e.g., an ASI Status  24 G, or defibrillator error code  24 H indicating a problem), step  136 , the proper sensory alert  74  is activated, step  134 . 
     The steps shown in  FIGS. 7 and 8  are for the AUTO-TEST Mode. As those skilled in the art will appreciate, the steps for other self-diagnostic test modes, such as self-diagnostic tests and startup self-diagnostic testing in an ON condition, are similar. More specifically, the other self-diagnostic test modes should result in the transmission of a condition information stream. The primary differences, however, are that the self-diagnostic testing will not be started by the clock; it should not result in disrupting the AUTO-TEST (e.g., increasing the index counter, step  120 ); and the specific self-diagnostic test is pre-determined (e.g., not determined by the Main Processor). 
     As shown in  FIG. 9 , the monitor  28  programming may include a subroutine (generally referred to by reference number  150 ) which determines whether a condition information stream from a particular broadcast transmitter  22  has not been received in a timely fashion. In step  152 , the monitor&#39;s programming (most likely in memory) has a log of when to expect a particular condition information stream. Based on this log, the monitor&#39;s computer programming looks to confirm receipt of an expected conditional information stream. If the expected conditional information stream has been received, the subroutine is simply terminated, step  156 . If not, the monitor  28  issues an alert, step  158 . 
     More specifically, it is desirable that each PED  12  conduct AUTO-TEST self-diagnostic tests on a periodic interval (e.g., every 24 hours). Thus, these self-diagnostic tests should generate a condition information stream  24  at least every 24 hours. The monitor  28  thus should have knowledge that at least one condition information stream  24  should be received from a particular broadcast transmitter  22  every 24 hours, within some reasonable tolerance. In the event a condition information stream  24  is not received in a timely fashion, the monitor&#39;s programming should activate an alert. 
       FIG. 10  is an enhanced version of the system  210  depicted in  FIG. 1 . In this enhanced version, like components are given the same reference number preceded by the number  2 . In this enhanced system  210 , there are multiple monitors  228  for receiving a given condition information steam  224  from a given PED  212   a . Depending upon information in the data payload  64  (see  FIG. 3 ), the multiple monitors could perform several services. It should be appreciated that each monitor  228  if in range of the PED  212   a  will receive the condition information stream  224 , thus the flexibility of the enhanced system  210  is based on how each monitor  228  acts upon the condition information stream. 
     In the most basic enhanced system  210 , each monitor  228  is identical. In other words, each monitor  228  receives the condition information stream  224  and analyzes the condition information stream in the same way. In reality, one monitor  228  is backing up the other. 
     In another alternative, the monitors  228  are programmed to handle the same condition information stream  224  in different ways. For example, one monitor  228   a  may be located in a maintenance area and another monitor  228   b  may be located in a medical area. Thus, when the condition information stream  224  contains information indicating a requirement for maintenance, only monitor  228   a  alerts. However, when the condition information stream  224  indicates a rescue attempt, the other monitor  228   b  alerts. The ability of the programming in the monitor  228  to distinguish between a maintenance event and a rescue attempt could be accomplished by evaluating the event code  24 I in the data payload  64 . (See  FIG. 3 ). 
     In yet another enhancement, some monitors  228  could be programmed to work with more than one PED  212 . In the illustrative example, all condition information streams  224  are acted upon by the medical monitor  228   b  if the condition information stream contains information indicating a rescue attempt. However, for non-medical condition information streams, monitor  228   a  reacts to condition information stream  224 A from one PED  212   a , and monitor  228   c  reacts to condition information stream  224 B from the other PED  212   b . It should be appreciated that repeaters  88  may be incorporated into this enhanced system  210 . 
     Alternate embodiments of the monitoring system will become apparent to one of ordinary skill in the art to which the present invention pertains without departing from its spirit and scope. In particular, those skilled in the art will recognize alternate circuitry and programming. Thus, although this invention has been described in exemplary form with a certain degree of particularity, it should be understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts or steps may be resorted to without departing from the spirit or scope of the invention. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description.