Patent Publication Number: US-6216038-B1

Title: Broadcast audible sound communication of programming change in an implantable medical device

Description:
This application is a continuation-in-part of U.S. patent application Ser. No. 09/282,593 filed Mar. 31, 1999, now U.S. Pat. No. 6,044,301 and entitled AUDIBLE SOUND CONFIRMATION OF PROGRAMMING CHANGE IN AN IMPLANTABLE MEDICAL DEVICE, which is a continuation of U.S. patent application Ser. No. 09/069,516 filed Apr. 29, 1998, now U.S. Pat. No. 6,070,102 and entitled AUDIBLE SOUND CONFIRMATION OF PROGRAMMING AN IMPLANTABLE MEDICAL DEVICE. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to improved methods and apparatus for providing transmission of implantable medical device (IMD) information and patient warnings or messages via broadcast radio signals that can be received and reproduced as human understandable voiced statements or other audible sounds. 
     BACKGROUND OF THE INVENTION 
     Early IMDs such as implantable cardiac pacemakers were designed to operate in a typically single operating mode governed by fixed operating parameters without any ability to change the operating mode or otherwise communicate percutaneously with external equipment. In time, it became apparent that it would be clinically desirable to vary certain of the operating parameters and/or modes of operation. An initial approach employed with implanted cardiac pacemakers involved use of miniature rheostats that could be directly accessed by a needle-like tool inserted through the patient&#39;s skin to adjust a resistance in the pacing rate or pulse width setting circuit. Later, miniaturized reed switches were incorporated into the pacing rate or pulse width circuits that responded to magnetic fields applied through the skin by an external magnet placed over the implant site. The pulse width, pacing rate and a limited number of pacing modes could be adjusted in this manner. 
     It was also realized that the operation of an implantable cardiac pacemaker could be observed, for example, by use of a standard EKG machine and timing of intervals between pacing pulse spikes in the ECG tracing recorded from skin electrodes on the patient. The applied magnet was used to close a reed switch to change the pacing mode to an asynchronous pacing mode and to encode the fixed pacing rate or pulse amplitude or width to a value reflecting a current operating parameter. One use of this technique was to monitor impending battery depletion through observation of a change in the pacing rate from a preset or programmed pacing rate in response to a battery voltage drop, as described, for example, in U.S. Pat. No. 4,445,512. This approach could only provide a low band pass data channel, of course, to avoid interfering with the primary function of pacing the patient&#39;s heart when necessary. 
     Moreover, pacing pulses conducted through elongated pacing lead conductors caused electromagnetic signals that could be heard as noise impulses on AM radio bands when a radio antenna was held over the implanted lead. In this way, the delivery of pacing pulses could be confirmed without an EKG machine, and a rough determination of the pacing rate could be made by stop watch timing successive noise impulses. An output circuit inductor was incorporated into certain pacemaker models that was caused to “ring” when a pacing pulse was delivered for the duration of the pacing pulse. The duration of the noise impulse picked up by the radio was proportional to the pacing pulse width, and it was at least theoretically possible to measure the pacing pulse width from the duration of the noise impulse. 
     As digital circuit technology advanced, it was recognized that control of operating modes and parameters of implanted medical devices could be realized in digital or binary circuits employing memorized control states or operating parameter values. In order to change an operating mode or parameter value, “programmers” were developed based on radio frequency (RF) downlink data communication from an external programmer transceiver to a telemetry transceiver and memory incorporated within the IMD. 
     Through the use of such telemetry systems, it became possible to provide uplink data telemetry to transmit the contents of a register or memory within the IMD to the telemetry receiver within the programmer employing the same RF transmission capabilities. Today, both analog and digital data can be transmitted by uplink RF telemetry from the implanted medical device to the external programmer. In the context of implantable cardiac pacemakers, the analog data typically includes battery status, sampled intracardiac electrocardiogram amplitude values, sensor output signals, pacing pulse amplitude, energy, and pulse width, and pacing lead impedance. The digital data typically includes statistics related to performance, event markers, current values of programmable parameters, implant data, and patient and IMD identification codes. 
     The telemetry transmission system that evolved into current common use relies upon the generation of low amplitude magnetic fields by current oscillating in an LC circuit of an RF telemetry antenna in a transmitting mode and the sensing of is currents induced a closely spaced RF telemetry antenna in a receiving mode. Short duration bursts of the carrier frequency are transmitted in a variety of telemetry transmission formats. In the MEDTRONIC® product line, the RF carrier frequency is set at 175 kHz, and the RF telemetry antenna of the IMD is typically coiled wire wound about a ferrite core that is located within the hermetically sealed enclosure. The RF telemetry antenna of the external programmer is contained in a programming head together with a permanent magnet that can be placed on the patient&#39;s skin over the IMD to establish a magnetic field within the hermetically sealed enclosure of the IMD. 
     In an uplink telemetry transmission from an implanted medical device, it is desirable to limit the current drain from the implanted battery as much as possible simply to prolong device longevity. However, as device operating and monitoring capabilities multiply, it is desirable to be able to transmit out ever increasing volumes of data in real time or in as short a transmission time as possible with high reliability and immunity to spurious noise. As a result of these considerations, many RF telemetry transmission data encoding schemes have been proposed or currently are used that attempt to increase the data transmission rate. 
     At present, a wide variety of IMDs are commercially released or proposed for clinical implantation that are programmable in a variety of operating modes and are interrogatable using RF telemetry transmissions. Such medical devices include implantable cardiac pacemakers, cardioverter/defibrillators, pacemaker/cardioverter/defibrillators, drug delivery systems, cardiomyostimulators, cardiac and other physiologic monitors, electrical stimulators including nerve and muscle stimulators, deep brain stimulators, and cochlear implants, and heart assist devices or pumps, etc. As the technology advances, IMDs become ever more complex in possible programmable operating modes, menus of available operating parameters, and capabilities of monitoring increasing varieties of physiologic conditions and electrical signals. These complexities place ever increasing demands on the programming and interrogation system and the medical care providers using them. 
     In our Statutory Invention Registration H1347, we disclose an improvement to programmers of this type adding audio voiced statements that accompany their operations to assist the medical care provider using them. For example, we propose adding voiced statements that track interactive operation of a programmer and implanted medical device during programming and patient follow-up sessions that can be heard by the medical care provider using the programmer. Such voiced statements would augment or replace the visual display of such information or minimal audible tones (e.g., beeps) that are displayed or emitted in use of the external programmer or pacing system analyzer. 
     Other approaches than reliance upon RF telemetry transmissions have also been developed for providing real time warnings to the patient that the IMD is malfunctioning or is about to deliver a therapy in response to a detected need. Audible beeping alarms have been proposed to be incorporated into the IMD to warn the patient of battery depletion as disclosed for example in U.S. Pat. Nos. 4,345,603 and 4,488,555, incorporated herein by reference. Similarly, the application of low energy stimulation to electrodes on or near the IMD to “tingle” the patient upon battery depletion have been proposed in U.S. Pat. Nos. 4,140,131, and 5,076,272, incorporated herein by reference, and also in the above-incorporated &#39;603 patent. Use of the audible beeping alarm incorporated into an implantable cardioverter/defibrillator to warn the patient of impending delivery of a cardioversion shock is disclosed for example in U.S. Pat. No. 4,210,149, incorporated herein by reference. 
     Moreover, it has been proposed to employ acoustic beeping warnings of implantable cardiac pacemaker battery depletion in an external monitor which apparently is directly coupled with an implanted cardiac pacemaker in U.S. Pat. No. 4,102,346. Acoustic voice recordings have been incorporated into external medical devices to provide warnings or instructions for use as disclosed in U.S. Patent Nos. 5,285,792, 4,832,033, and 5,573,506, incorporated herein by reference. 
     As noted above, the historical development of IMDs has been marked by ever increasing sophistication and complexity in design and operation. However, in certain circumstances, it is desirable to provide simplified IMDs having limited features and controllable operating modes and parameters for use in developing countries or that can be controlled by the patient. 
     As an example of the former case, a simplified and low cost programmable, single chamber cardiac pacemaker pulse generator is disclosed in commonly assigned U.S. Pat. Nos. 5,391,188 and 5,292,342, incorporated herein by reference, specifically intended to meet demand in emerging countries. In order to avoid the need for expensive external programmers, the low cost pacemaker disclosed therein is designed to employ a simplified programming scheme and a simple EKG display coupled to skin contact electrodes for simply displaying the pacing pulse artifact and patient&#39;s ECG. In this low cost implantable cardiac pacemaker, programming is effected by repeated timed applications of the magnetic field to the IMD as described therein to incrementally increase or decrease pacing rate, pacing pulse width amplitude, etc. The magnetic field can be manually applied and removed and the field polarity can be reversed. A magnetic field sensor and associated programming circuitry within the IMD responds to the application and polarity of the magnetic field to make the incremental changes. The medical care provider must closely watch the EKG display and calculate the changes in pacing rate from the observed changes in pacing interval and scale changes in pulse amplitude. This requires good hand-eye coordination and rapid mental calculation to determine just when the desired rate or amplitude change has been accomplished. 
     In the latter case, neurological stimulation devices and drug delivery systems are available for implantation in a patients&#39; body, and external programmers for providing limited adjustment of stimulation therapies and delivery of drugs are provided to the patients to allow them to adjust the delivered therapy. Such devices include the MEDTRONIC® Itrel® implantable nerve stimulator and Synchromed® drug infusion system. The patients are allowed to adjust the stimulation and drug therapies by transmitting “increase” and “decrease” commands. The implanted medical device responds to the programmed command, but the response is not communicated back to the patient who may remain concerned that the desired adjustment has not been made. 
     All of the above-described RF telemetry systems require complex circuitry, and bulky antennas as described above and are expensive to implement into an IMD. The RF telemetry transceiver in the IMD consumes electrical energy from the device battery while it is in use. Moreover, the telemetry systems all require use of an expensive and complex external programmer that establishes the telemetry protocol, encodes and transmits the downlink telemetry transmissions, and receives, decodes and displays and/or records the uplink telemetry transmissions. The uplink telemetered data from the IMD and device operations, e.g., delivery of pacing pulses by an implantable cardiac pacemaker, are recorded and/or displayed only visually, requiring careful visual observation by the medical care provider operating the programmer. Similarly, confirmation of acceptance of a programmed change in an operating mode or parameter value can only be observed using a recorder or visible display of a confirmation received in an uplink telemetry transmission. It is desirable to provide a simple way to confirm the acceptance of a programmed change that would not require use of special purpose RF telemetry equipment by the patient or medical care provider and RF telemetry capability in the IMD. This is especially the case in programming limited operating modes and parameter values by a patient using a limited function programmer. As will become apparent from the following, the present invention satisfies many of these needs. 
     References to and incorporation by reference of earlier publications or patents made anywhere in this specification are intended to simply indicate the state of the art and/or that certain conventional structure, circuits, and the like, may be employed in the practice of the present invention. The disclosures of such referenced materials are not intended to limit the scope of the present invention to particular implementations shown therein. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to improving the above-described prior art systems for communicating with an IMD of the above described types to confirm programming changes made to the IMD of a device operation or function. In one aspect of the present invention, the communication is effected employing voiced statements or sounds that are stored in the IMD and transmitted by the IMD in an uplink transmission as modulated radio frequency signals. 
     In another aspect of the present invention, a simplified system is provided for receiving the uplink communication to the patient or medical care provider of radio frequency signals comprising a conventional radio that is tuned to the frequency of the signals broadcast from the IMD and can be listened to by the patient and/or a medical care provider attending the patient. The IMD includes a radio frequency transmitter and antenna employing amplitude or frequency modulation in the commercially available AM or FM bands to effect a broadcast or transmissions of the voiced statements or musical tones. A frequency at the low end of the AM or FM band that typically is not occupied by a broadcast station is preferred so that a simple, readily available, and inexpensive AM or FM radio can be employed to receive and reproduce the broadcasts or transmissions. However other broadcast bands, e.g., CB, UHF/VHF television and weather radio bands, and corresponding receivers could be used. 
     The present invention thus provides a system and method for generating radio frequency transmissions of audible voiced statements or other audible sounds, e.g., musical tones, from an IMD that can be received by a radio tuned to the transmission frequency, particularly to confirm programming changes. The transmitted or broadcast radio frequency signals are received, demodulated and reproduced by the radio receiver as voiced statements or other audible sounds that are listened to and understood by the medical care provider or the patient to confirm acceptance of a programming command. The transmitted and audibly reproduced IMD information can also include voiced statements of patient identification, IMD identification, and dates of implantation and last interrogation or programming in IMDs capable of being programmed with such data. 
     The present invention may be implemented in simplified, low cost programming and/or interrogation schemes to provide the sole uplink transmission of IMD information including stored data and operating states or device operations as well as the confirmation of the programmed change thereof. Such voiced statements or musical tones are generated during the programming of such an IMD by a medical care provider following a simplified programming protocol employing timed, manual applications of a magnetic field to the IMD. However, the present invention may also be implemented into sophisticated RF telemetry programming and interrogation methods and protocols to selectively replace or augment uplink RF telemetry transmissions and display of IMD information during interrogation of the IMD data, operating modes and parameters and during reprogramming of operating modes and parameters. In any such implementation, the patient and/or medical care provider is immediately apprised of the acceptance of the programming command, the change in the programmed operating modes and parameter values, operations or states without needing to analyze visually presented data. 
     Changes in operating parameter values are made sequentially in a programming sequence employing any programming command transmission methodology, and each change is confirmed, in accordance with the present invention, by an audible voiced statement or musical tone. For example, ascending or descending scale musical tones can be transmitted accompanying each incremental increase or decrease, respectively, in the programmed parameter value to signify that the parameter value is being changed. In certain IMDs one or more ascending or descending scale musical tone can be transmitted following each increase or decrease in the parameter value, and the actual value need not be voiced in a voice statement produced by the radio in response to the broadcast signal. 
     Audio drive signals that generate the voiced statements or other audible sounds, e.g., musical tones, are advantageously recorded in solid state, non-volatile, analog memory locations having specified memory addresses within the IMD. The voiced statements are preferably recorded in the language appropriate to the patient or the country or population where the patient resides at the point of manufacture or distribution. In one embodiment where sufficient non-volatile memory is available, the voiced statements can be recorded in multiple languages, and the appropriate language can be selected for use by a programmed selection command. In the more sophisticated IMDs having RF telemetry capabilities, the specific language can be selected by a downlink RF telemetry command. In a low cost IMD disclosed herein, a repeated sequence of magnetic fields can be provided that, when decoded, can be used to select a language. The capability of recording the voiced statements or selecting pre-recorded voiced statements in the locally prevailing language allows a more flexible, less error prone and safer audible feedback and control. A physician or other medical care provider can select the language of the voiced statements if a patient moves to a country or locale where the prevailing language differs from that prevailing in the country or locale departed by the patient. 
     A plurality of audio drive signals of voiced statements or musical tones conveying or signifying the above listed types of IMD information are stored in the analog memory. In a hardware embodiment, the appropriate audio drive signals are accessed in both interrogation and programming sequences by logic circuitry that generates their unique memory addresses. In a microcomputer based embodiment, an operating algorithm is used to sequentially generate the addresses of the appropriate audio drive signals. The appropriate audio drive signals are retrieved and applied to the RF transmitter to generate the AM or FM transmissions during interrogation or programming sequences. At other times, a monitored condition, state or impending or consummated operation of the implantable medical device or a condition or state of the patient causes a message trigger signal to be generated in response thereto. The unique memory address of the message or warning to be broadcast is determined from the message trigger signal. 
     To conserve energy, the AM or FM transmissions are low power, short in duration, and have a range of a few feet or meters in order to conserve energy, to avoid use of bulky components in the IMD, and to avoid interference. The antenna may comprise a discrete radio frequency antenna within the IMD housing or an elongated conductor wire of a lead body if the IMD employs such an elongated lead. The existing RF telemetry antenna of the more sophisticated RF telemetry systems may also be employed or modified for employment in the practice of the present invention. The low power radio frequency signals can be picked up by a body worn low cost radio receiver located in a few feet or meters from the patient and emitted therefrom. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other advantages and features of the present invention will be appreciated as the same becomes better understood by reference to the following detailed description of the preferred embodiment of the invention when considered in connection with the accompanying drawings, in which like numbered reference numbers designate like parts throughout the figures thereof, and wherein: 
     FIG. 1 is a simplified schematic view of communication between a programmable IMD in a patient and a medical care provider effecting interrogation and programming thereof using audible voiced statement or musical tone feedback emitted by an external radio receiving the AM or FM transmissions from the IMD; 
     FIG. 2 is a block diagram of an exemplary pacemaker implantable pulse generator (IPG) circuit employed in the system of FIG.  1  and operated in accordance with FIGS. 3A-3C and  4  when a magnet is applied to the patient&#39;s skin over the IPG; 
     FIGS. 3A-3C are timing diagrams depicting successive applications of the magnet to the IPG of FIG. 2, and the responses of the IPG to the applied magnetic fields, including device operations and voiced statements generated in the interrogation and programming sequences; 
     FIG. 4 is a chart depicting the memory address locations of voiced statements transmitted by the IMD in the interrogation and programming sequences illustrated in FIGS. 3A-3C; 
     FIG. 5 is an expanded block diagram of the audio feedback circuit block of FIG. 2 illustrating how the audio drive signals that are modulated in an AM/FM transmitter to broadcast or transmit the voiced statements shown in the interrogation and programming sequences illustrated in FIGS. 3A-3C are generated; 
     FIG. 6 is a block diagram of the analog storage/playback IC of FIG. 5; 
     FIG. 7 is a timing diagram depicting the generation of a two word message in the block diagram of FIG. 5; 
     FIG. 8 is a block diagram of a microcomputer based IMD operating system intended to be used in conjunction with a controller and monitor or therapy delivery system of one of the types depicted in FIG. 10 that is capable of being interrogated or programmed by successive applications of a magnetic field and of transmitting IMD information for reception by a radio; 
     FIG. 9 is a block diagram of a microcomputer based IMD operating system intended to be used in conjunction with a controller and monitor or therapy delivery system of one of the types depicted in FIG. 10 that is capable of being interrogated or programmed using an RF telemetry transmission system and of transmitting IMD information for reception by a radio; 
     FIG. 10 is a block diagram of a digital controller/timer circuit usable with the operating systems of FIG. 8 or  9  and with one of the depicted monitors and therapy delivery devices 
     FIG. 11 is a chart depicting the memory address locations of audio drive signals for voiced statements or musical tones transmitted during interrogation and programming sequences of an implantable drug delivery apparatus of FIG. 10 having an operating system of FIG. 8 or  9 ; and 
     FIG. 12 is a chart depicting the memory address locations of audio drive signals for voiced statements or musical tones transmitted in interrogation and programming sequences of an implantable electrical stimulation apparatus of FIG. 10 having an operating system of FIG. 8 or  9 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     The preferred embodiments of the present invention disclose uses of audio voiced statements or musical tones emitted by a conventional, low cost AM or FM or other band radio that receives radio frequency transmissions or broadcasts from an IMD in the course of a communication session involving interrogation or programming of device operating modes or parameters or provision of a patient warning or other message. The musical tones or voiced statements can may be listened to by the physician or other medical care provider to augment or substitute for visual displays or to otherwise confirm programming changes or listened to by the patient to confirm patient initiated programming. The present invention may be implemented in all of the above referenced IMDs that provide monitoring and/or delivery of a therapy to a patient. The present invention may be implemented in simplified, low cost programming schemes to provide the sole uplink transmission of IMD information. The audible voiced statements preferably also assist the medical care provider in following a programming or interrogation protocol during an initial implantation or follow-up session. 
     The present invention may also be implemented into sophisticated RF telemetry programming and interrogation methods and protocols to selectively replace or augment uplink RF telemetry transmissions of device operating modes, states, operations and parameter values. In this case, the modulation of the transmitted audio drive signals may be at the prevailing RF carrier frequency of such RF telemetry transmissions, e.g. at 175 kHz. Or, the AM or FM band telemetry system described herein may be employed incorporating a radio receiver into the programmer. 
     The following description in reference to FIGS. 1-7 is directed to various preferred embodiments of the invention implemented in the housing of a low cost, single chamber, implantable cardiac pacemaker IPG that is programmed using a permanent magnet. This implementation can be incorporated into a more complex, dual chamber, programmable pacemaker or pacemaker/cardioverter/defibrillatorIPG as described in reference to FIGS. 8-10. Other uses of audible communications attendant to programming or interrogation of the IMDs identified in FIG. 10 are then described. Particular uses with implantable substance delivery systems and implantable electrical stimulators are illustrated in FIGS. 11 and 12, respectively. Those of skill in the art will be readily able to adapt the teachings found herein to the IMDs listed herein and others to be devised in the future. 
     FIG. 1 is a simplified schematic illustration of the audio feedback of data from an IMD  100  implanted in a patient  102  that occurs during interrogation or during programming to confirm changes in device operating mode or parameter values or the generation of a warning at other times. For convenience of illustration, the IMD  100  is preferably a cardiac pacemaker comprising a pacemaker IPG  110  and a pacing lead  120  which extends from the IPG connector  112  to one or more pace/sense electrodes located in or on the patient&#39;s atrium or ventricle in the conventional manner. The pacemaker IPG  110  is therefore illustrated as either a programmable, single chamber atrial or ventricular IPG operating in an atrial demand or ventricular demand pacing mode. Moreover, in the preferred embodiments described below, the pacemaker IPG  110  has the operating architecture of the low cost, single chamber pacemaker IPG disclosed in the above-incorporated, commonly assigned &#39;188 and &#39;342 patents incorporating the audio feedback features of the present invention as described below. 
     In the embodiment of FIGS. 2-7, a telemetry or communication session is established with the IMD by application and removal of the permanent magnet  130  by the physician or other medical care provider to the patient&#39;s skin over the IPG  110  according to protocols described below. The magnetic field constitutes a communication link signal that is detected by the IPG  110  to establish the communication session. The interrogation of IMD information and programming of the pacemaker IPG  110  operating modes and parameter values is effected during the communication session. 
     The magnetic field polarity is sensed by a magnetic field sensor  70  within the housing of the pacemaker IPG  110 . The interrogation and programming protocol is recognized by decoding and logic circuitry coupled to the magnetic field sensor in a manner described below. In accordance with the low cost pacemaker preferred embodiments of the invention, each protocol causes stored voiced statements to be transmitted as a radio frequency signal by a radio frequency transmitter  31 , e.g. an AM or FM band transmitter. The transmitter  31  operates in conjunction with an antenna which may comprise a discrete radio frequency antenna within the IMD housing or, in the case of cardiac pacemakers, ICDs and nerve or muscle stimulation devices, may comprise the elongated conductor wire of a lead body, e.g. lead  120 . The transmitter  31  could take the form of the MOTOROLA® MC13176 one-chip AM/FM transmitter tuned to an appropriate band. 
     The physician or other medical care provider tunes an AM or FM radio  142  to the appropriate AM or FM RF transmission frequency and listens for the voiced statements or musical notes emitted by radio speaker  144  while applying and removing the magnet  130  to the patient&#39;s skin in the sequence established by the protocol. While not specifically illustrated, it will be understood that the medical care provider can also use an EKG display or recorder to observe pacing pulse artifacts in the manner described in the above-incorporated, commonly assigned &#39;188 and &#39;342 patents. The AM or FM transmissions  146  are at low power to conserve energy and minimize IMD size and avoid interference issues, so radio  142  may need to be close by or worn on the patient&#39;s body. 
     This same procedure can be employed by the patient to provide a therapy, or monitor a condition, or to alter the parameters of a therapy, e.g. to commence or alter the strength of electrical nerve stimulation or to deliver a bolus of an analgesic drug to control pain. 
     FIG. 2 is a block diagram depicting the major components of a small, lightweight, limited function, implantable pacemaker IPG circuit  10  in accordance with one embodiment of the present invention and is a modification of FIG. 1 of the above-incorporated, commonly assigned &#39;188 and &#39;342 patents. The modification involves the incorporation of battery monitor circuit  17 , the audio feedback circuit  25 , the RF transmitter  31 , the RF antenna  117  (or connection with the lead terminal  12  through capacitor  129 ), filter and amplifier circuit  33 , optional activity sensor  116  and rate response circuit  35 , and connection lines with certain of the other circuit blocks. It should be understood that the even numbered circuit blocks in FIG. 2 may take the form of those circuits disclosed in detail in the above-incorporated, commonly assigned &#39;188 and &#39;342 patents and equivalents thereto. Specific embodiments of those circuits have also been identified in the above-incorporated, commonly assigned &#39;188 and &#39;342 patents with reference to prior patents for the purposes of illustration only. References to such circuits is not intended to limit the scope of the present invention to particular implementations of these circuits. It is believed by the inventors that the selection of particular circuits is not critical to the present invention so long as they function as a whole to perform the operations of the present invention. 
     Pacemaker IPG circuit  10  is encased within a hermetically sealed housing of IPG  110  implanted within the patient  102  and is coupled at IPG connector  112  to an atrial or ventricular cardiac pacing lead  120  as shown in FIG.  1 . Pacemaker IPG circuit  10  provides single chamber pacing and may be used in conjunction with a ventricular pacing lead or an atrial pacing lead to provide ventricular or atrial demand pacing in the conventional VVI or AAI and related programmable pacing modes. 
     It is to be understood throughout the present disclosure that various internal electronic components comprising pacemaker IPG circuit  10  are coupled to a power source  11 , including a battery  13 , e.g., a commercially available magnesium oxide (MgO 2 ) camera battery or the like. For the sake of clarity, the connection of all of the circuit blocks with power source  11  is not shown in FIG.  2 . However, the power source  11  is shown coupled with a battery monitor  17  for providing a warning trigger signal representative (in this case) of battery voltage to the Elective Replacement Indicator (ERI) input of audio feedback circuit  25  to trigger a voiced battery status during device interrogation as described below in reference to FIGS. 3A-3C. In accordance with another aspect of the present invention, the warning trigger signal also can be used to periodically trigger the generation of a radio frequency warning that is broadcast to and received by the external radio  142 . The radio audible sound emitted by speaker  144  of radio  142  can be heard by the patient  102  to alert the patient that the battery voltage is depleted and to take appropriate action. Other messages can also be conveyed to the patient from the IMD in this manner. 
     The battery monitor  17  periodically compares the output voltage of the battery against a reference voltage therein selected to provide the ERI warning trigger signal to the ERI input when battery voltage falls below the reference voltage. Such a battery monitor  17  follows the teachings of commonly assigned U.S. Pat. No. 4,313,079, incorporated by reference herein. Although it is not depicted in this embodiment, it will be understood that the ERI signal can also be applied to the up-down control circuit  90  to adjust the pacing rate to a percentage of the programmed pacing rate and applied to the activity rate response circuit  35  (if present) to disable its operation. For example, the up/down circuit  90  is responsive to the ERI signal to adjust a programmed pacing rate of 70 ppm downward to an ERI rate of 58 ppm, for example, during normal VVI or AAI pacing. 
     Pacemaker IPG circuit  10  includes an output and pump circuit  14  which responds to a pacing trigger signal generated by pulse width one-shot  16  by delivering pacing (PACE) pulses to terminal  12  and the atrial pacing lead or ventricular pacing lead attached to it. Output and pump circuit  14  may correspond generally to the pacing pulse output circuit disclosed in commonly assigned U.S. Pat. No. 4,476,868 incorporated by reference herein or other conventional pacing pulse output circuits. Output and pump circuit  14  further includes a programmable amplitude control circuit disclosed in detail in the above-incorporated &#39;342 patent which allows for programming the pacing pulse amplitude by way of an amplitude programming signal applied to the pump (P) input. In the preferred embodiment, the pacing pulse amplitude is programmable between a high, medium and low amplitude. 
     The patient&#39;s intrinsic electrical cardiac activity is monitored by means of a conventional filter circuit  18  and sense amplifier  20  coupled to terminal  12  for filtering and amplifying intrinsic electrical cardiac signals from the patient&#39;s heart. Filter circuit  18  performs basic band-pass filtering operations on the raw atrial or ventricular electrical cardiac signal, and provides the conditioned signal to the input of a conventional sense amplifier  20 . The sense amplifier  20  is configured to detect a P-wave or R-wave and provide a SENSE output signal on line  21 . The SENSE output of sense amplifier  20  is conducted on line  21  to the clock (CL) input of D flip-flop  46 . 
     In accordance with this embodiment of the present invention, timing operations of pacemaker IPG circuit  10  is controlled by a slow, e.g., 10 Hz, master timing clock signal generated by  10  Hz oscillator circuit  22  which is enabled via line  40  from one output of rate limit decode circuit  26 . The 10 Hz oscillator circuit  22  is shown and described in detail in reference to FIG. 10 of the above-incorporated, commonly assigned &#39;188 and &#39;342 patents. Each time that the 10 Hz oscillator circuit  22  is enabled, it emits four 10 Hz pulses over a 400 mSec time period; then it remains dormant until it is enabled again. The 10 Hz timing clock signal generated by oscillator circuit  22  is applied via line  24  to the negative CL inputs of a rate limit decode circuit  26 , a blanking decode circuit  28  and a refractory decode circuit  30 , and to one input of an AND gate  32 . Rate limit decode circuit  26 , blanking decode circuit  28 , and refractory decode circuit  30  define an upper rate limit period, a blanking period, and a refractory period, respectively, by counting 10 Hz clock cycles provided on line  24  to their negative CL inputs. 
     The conventional blanking circuit  28  provides a blanking signal to sense amplifier  20  when a Pacing pulse is delivered or a SENSE signal is generated that extends therefrom for a blanking interval, e.g., 100 mSec corresponding to one 10 Hz clock cycle. It is to be understood that a blanking period comprising a greater number of clock cycle counts may be defined, depending upon the desired length of the blanking interval and the actual oscillation rate of oscillator circuit  22 . The blanking signal effectively disconnects the input of the sense amplifier from the terminal  12  for the blanking time period to allow pacing pulse induced artifacts that would otherwise saturate sense amplifier  20  to dissipate and to avoid double sensing of an intrinsic P-wave or R-wave. 
     Refractory decode circuit  30  defines a refractory period which follows every SENSE or PACE cardiac event. Refractory decode circuit  30  measures the refractory period by counting 10 Hz dock cycles from line  24 , just as blanking decode circuit measures the blanking interval. In the presently preferred embodiment of the invention, it is believed that a refractory period on the order of 300 mSec or so is appropriate. In that instance, refractory decode circuit  30  can define the refractory period as lasting for three 10 Hz clock cycles. 
     A logic low level refractory output signal is provided by refractory decode circuit  30  during the refractory period on line  44  and is applied to the D input of a D flip-flop  46 . The output on line  21  from sense amplifier  20  is applied to the CL input of flip-flop  46 . The Q output of D flip-flop  46  is maintained at a logic low level and cannot be switched to a logic high level as long as the logic low level refractory output signal is provided by refractory decode circuit  30  to the D input. But, after the refractory period has expired, the refractory signal on line  44  applied to the D input returns to a logic high level. At this point, the assertion of a SENSE signal on line  21 , caused by a sensed event as described below, clocks the Q output of D flip-flop  46  on line  48  to a logic high level, non-refractory sense signal. 
     The logic high or low level on line  48  is applied to one input of AND gate  32 ; and the 10 Hz clock signal is applied to the other input of AND gate  32 , as previously noted. If the refractory period has not expired, the output of AND gate  32  and the signal level on line  50  remains at a logic low level. If the refractory period has expired, line  48  will go to a logic high level upon detection of a SENSE event. A SENSE signal on line  21  occurring after expiration of the 300 mSec refractory period switches the Q output of D flip-flop  46  to a logic high level. Then, the next positive excursion of the 10 Hz clock signal will switch the output of AND gate  32  to a logic high level. The output of AND gate  32  is conducted on line  50  to the reset (R) input of flip-flop  46 . In this way, the Q output of D flip-flop  46  is switched to a logic low level when the signal on line  50  goes to a logic high level at the next clock signal following a sense signal that occurs after expiration of the refractory period. 
     The non-refractory sense signal on line  48  is also applied to one input of an OR gate  52 , and the pulse width trigger signal on line  55  is applied to the other input of OR gate  52 . The output of OR gate  52  is conducted on line  56  to the set (S) inputs of rate limit, blanking and refractory decode circuits  26 ,  28 , and  30 . A logic high level pulse on line  56  corresponding to either a non-refractory sense signal or a pulse width trigger signal sets and restarts the upper rate limit interval, blanking interval, and refractory interval. In addition, when the rate limit decode circuit is set, it applies the logic high level enabling signal on line  40  to enable the 10 Hz oscillator circuit  22  which again emits the four, 10 Hz clock pulses. 
     Rate limit decode circuit  26  defines an upper rate limit for delivery of stimulating pulses by pacemaker IPG circuit  10 . In the presently disclosed embodiment of the invention, it is believed that an upper rate limit of one pacing pulse every 400 mSec, or a maximum pacing rate of 150 PPM, is appropriate. In this case, rate limit decode circuit  26  defines an upper rate limit interval which lasts for the four successive 10 Hz clock cycles applied to its CL input. The output O from rate limit decode circuit  26  goes to a logic low level for the 400 mSec period when the logic high level signal on line  56  is applied to the S input of rate limit decode logic  26  following each SENSE and PACE event as described above. This logic low level signal is applied on line  62  to the D input of D flip-flop  54 , and it prevents the D flip-flop output Q from being switched from a logic low level to a logic high level in response to a logic high level or transition at the CL input of D flip-flop  54 . After the 400 mSec upper rate limit interval has elapsed, the O output signal on line  62  from rate limit circuit  26  returns to a logic high level. 
     A rate one-shot and TMT circuit  58  (hereinafter referred to simply as rate/TMT circuit  58 ) determines the base pacing rate, which is the rate at which pacing pulses are delivered to terminal  12  in the absence of a SENSE output on line  21  during the pacing escape interval. The pacing escape interval between output pulses produced by rate/TMT circuit  58  at its output O is programmable, within a range from 460 to 1200 mSec to establish programmable pacing rates in 10 PPM increments between 130 PPM and 50 PPM, respectively, for example. Rate/TMT circuit  58  includes a re-triggerable monostable multivibrator which produces an output signal at its output (O) that is applied to the CL input of D flip-flop  54  via line  60  when the programmed escape interval times out. If the 400 mSec upper rate period has timed out, the Q output of D flip-flop  54  is switched to a logic high level in response to the output signal on line  60 , providing a pulse width trigger signal to the trigger (T) input of the pacing pulse one-shot  16  via line  55 . During the 400 mSec upper rate interval, an output signal on line  60  from rate/TMT circuit  58  cannot switch the Q output of the D flip-flop  54  to a logic high level and generate the pulse width trigger signal. 
     At this point, it should be noted that a logic high level pulse width trigger signal on line  55  is also directed through the OR gate  52  and line  56  to the S inputs of rate limit, blanking and refractory decode circuits  26 ,  28 , and  30 . The logic high level pulse width trigger signal on line  56  restarts the upper rate limit interval, blanking interval, and refractory interval on expiration of the pacing escape interval following expiration of the 400 mSec rate limit interval. 
     The programmed pacing escape interval is automatically restarted within the rate/TMT circuit  58  when the output pulse is generated on line  60 . The programmed pacing escape interval is also restarted in the rate/TMT circuit  58  in response to a SENSE event. A rising edge transition of a reset signal occurring on line  84  from the output of AND gate  82  that is applied to the R input of rate/TMT circuit  58  restarts the pacing escape interval. The non-refractory sense signal on line  48  from the Q output of D flip-flop  46  is coupled to one input of AND gate  82 , and the normally logic high level output of NOR gate  76  is coupled to the other input of AND gate  82 . The Q output of the D flip-flop  46  goes to a logic high level in response to a SENSE event on line  21  after expiration of the refractory interval indicating a non-refractory sense event. The rising edge transition is conveyed via line  48 , AND gate  82  and line  84  to the R input of rate/TMT circuit  58  and restarts the pacing escape interval. As long as a rising edge transition appears at the R input of rate/TMT circuit  58  more frequently than the programmed pacing escape interval, the output signal on line  60  will stay at a logic low level, and generation of pulse width trigger signals at the Q output of D flip-flop  54  will be inhibited. 
     The pulse width trigger signal output by flip-flop  54  is conducted on line  55  to the T input of pulse width one-shot  16  which responds by producing a pace trigger pulse on line  64  having a duration that defines the pulse width of the pacing pulse produced by output and pump circuit  14 . The pacing pulse width is programmable within a range from 0.1 to 1.0 mSec, for example, in a manner described in greater detail in the above-incorporated, commonly assigned &#39;188 and &#39;342 patents. Pace trigger pulses output from pulse width one-shot  16  are applied via line  64  to the T input of output and pump circuit  14  which responds by applying the programmed amplitude pacing pulse to terminal  12  and the pacing lead attached to it via coupling capacitor  66 . Pace trigger pulses from pulse width one-shot  16  are also applied on line  64  to the R input of D flip-flop  54  to terminate the pulse width trigger signal by terminating the logic high level latched or stored at the Q output of D flip-flop  54 . 
     In this manner, pacing pulses are generated on demand and applied to the pacing lead depicted in FIG. 1 The programming of the pacing rate and pacing pulse amplitude and width is accomplished in this embodiment in the manner described and illustrated in detail in the above-incorporated, commonly assigned &#39;188 and &#39;342 patents. The programming circuitry and protocol disclosed therein utilizes a solid state semiconductor device which is sensitive to application of an external magnetic field in order to eliminate the conventionally used, costly, bulky, and energy consuming RF telemetry circuitry and components. A solid-state magnetic field sensor (MAGFET)  70  suitable for use in an IMD telemetry system is disclosed in commonly assigned U.S. Pat. No. 5,438,990 to Wahistrand et al., incorporated herein by reference in its entirety. In the absence of an applied magnetic field, both the N and S output signals on lines  72  and  74  are at a logic zero or low level. As noted in the &#39;990 patent, MAGFET circuit  70  is capable of discerning between external magnetic fields of two different polarity orientations (e.g., between a field oriented north-south and a field oriented south-north). Accordingly, MAGFET circuit  70  produces two logic high output signals, N (north) on line  72 , and S (south) on line  74 . The N signal is asserted, for example, upon detection by MAGFET circuit  70  of an applied magnetic field of N-S orientation. Similarly, the S signal is asserted upon detection of an applied magnetic field of S-N orientation. 
     Logic circuit  78  receives the logic high level N or S signal on line  72  or  74  from MAGFET circuit  70 . Logic circuit  78  detects applications of the magnetic field in the N-S or S-N field orientation, respectively, and removals of the magnetic fields. As illustrated below in reference to FIG. 3B, logic circuit  78  issues control signals to an up/down control circuit  90  via a plurality of control lines designated collectively as  92  in FIG.  2 . Logic circuit  78  includes digital logic circuitry for detecting and counting magnet removal and replacement cycles as described in the above-incorporated, commonly assigned &#39;188 and &#39;342 patents and asserts various control signals in response thereto for effecting programming of pacing rate, pacing pulse width and pacing pulse amplitude. 
     For example, in response to detection of one magnet removal/replacement cycle, logic circuit  78  asserts a control signal to up/down control circuit  90  causing it to enter a pacing rate programming mode. In the rate programming mode, another control signal is derived from the N or S magnet polarity signal on line  72  or  74  that orders that the pacing rate is to be incrementally increased or decreased, respectively. 
     Up/down control circuit  90  produces a plurality of output signals which are conducted on lines  94 ,  96 , and  98  to the program (P) inputs of rate/TMT circuit  58 , pulse width one-shot  16 , and output/pump circuit  14 , respectively. The signals on lines  94 ,  96 , and  98  are analog reference currents which are described in detail in the above-incorporated, commonly assigned &#39;188 and &#39;342 patents. The reference currents on lines  94  and  96  determine the duration of output pulses from the rate/TMT circuit  58  and the pulse width one-shot  16 , respectively, and hence determine the programmed pacing rate and pulse width. The reference current on line  98  determines the output pulse amplitude from the output/pump circuit  14  by generating a reference voltage on resistor  15 . This reference voltage is used in conjunction with a comparator and a charging circuit in output/pump circuit  14  to charge an output capacitor to a programmed voltage amplitude as is well known in the art. 
     For example, in the case of the pacing rate parameter, up/down control circuit  90  provides a reference current on line  94  to the P input of rate/TMT circuit  58 . An incremental decrease in the reference current level on line  94  results in an increase in the pacing escape interval established by rate/TMT circuit  58 . Similarly, an incremental increase in the reference current level on line  94  results in an incremental decrease in pacing interval established by rate one-shot  58 . Pulse width one-shot  16  is controlled in a similar fashion by the reference current on line  96 . The pacing pulse amplitude of the pacing pulse generated by output/pump circuit  14  is directly controlled by the voltage developed on resistor  15  which is in turn controlled by the voltage on line  98  developed by up-down control circuit  90 . 
     The interrogation and programming protocol of this embodiment of the invention is based upon initially detecting the application of the external magnetic field as illustrated in FIG.  1  and initially entering the TMT mode. Following completion of the TMT and interrogation mode, the external magnet  130  is removed and applied again successively in accordance with the protocol disclosed in the above-incorporated, commonly assigned &#39;188 and &#39;342 patents for programming operating modes and parameter values and the like. The number of programmable modes and parameter values of pacemaker IPG circuit  10  is relatively more limited than is typically the case with more sophisticated programmable cardiac pacemakers. For example, in this embodiment, the base pacing rate, pacing pulse width, and pacing pulse amplitude parameters are programmable within selected ranges. A single chamber asynchronous and triggered pacing mode and other parameters, e.g., sense amplifier sensitivity, refractory period, and activity thresholds and gain factors described in the above-incorporated, commonly assigned &#39;096 patent, could be made programmable. The pacing upper rate limit and A-V delay interval could also be made programmable in a programmable dual chamber pacemaker context. There must be some arrangement for selecting which parameter or mode is to be programmed in order to separately program the different parameter values and operating modes. The identification of the parameter or mode to be programmed has been accomplished in some prior pacemakers by downlink RF telemetry transmitting a code identifying it together with the new value or mode to the receiver of the implanted pacemaker. 
     In the TMT mode, the rate/TMT circuit  58  provides a preset number, e.g., three, output pulses on line  60  at a TMT pacing rate to the D flip-flop  54  to provide three corresponding pulse width trigger pulses at its Q output. The non-refractory sense event signals that might be generated by D flip-flop  46  in response to SENSE signals are blocked from resetting the rate/TMT circuit  58 . The AND gate  82  is blocked by the logic low level signal output on line  80  from NOR gate  76  caused by a logic high (N or S) level on one of its inputs. In this manner, the amplifier circuit  20  continues to operate but its output signals are effectively disabled as long as a magnetic field is sensed by the MAGFET  70 . 
     The asynchronous TMT sequence assists the medical care provider in determining whether the currently programmed, pacing pulse width and pulse amplitude settings are sufficient to achieve “capture” of the patient&#39;s heart, that is sufficient to cause it to contract. The TMT sequence in the presently disclosed embodiment of the invention may be one such as is disclosed in commonly assigned U.S. Pat. No. 4,273,132 to Hartlaub, incorporated herein by reference in its entirety. The pacing pulses generated during the TMT sequence can have a higher than normal pacing rate to distinguish the TMT sequence from the asynchronous pacing pulses that precede and follow it. At least one of the TMT pacing pulses is reduced either in amplitude or pulse width to a percentage of the programmed amplitude or pulse width. In the conventional programming system described in the above-incorporated &#39;132 patent, the medical care provider observes the patient&#39;s cardiac activity on an EKG monitor during this time and observes whether or not the three pacing pulses all result in a cardiac contraction. If one (or more) TMT pacing pulse does not capture the heart, the medical care provider can increase either the programmed pulse width or pulse amplitude and conduct the TMT sequence again to verify that the pacing pulse energy is sufficient to capture the heart with an adequate safety margin. 
     After rate/TMT circuit  58  performs the TMT, the IPG circuit  10  commences asynchronous pacing at a nominal rate, e.g., 70 PPM, or at the programmed rate or at the ERI rate, if that function is employed, for as long as either the N or S magnetic field continues to be detected by MAGFET  70 . According to the operating modes described in the above-incorporated, commonly assigned &#39;188 and &#39;342 patents, a protocol of manual removals and re-applications of the N or S magnetic field by appropriate movements of the poles of magnet  130  in FIG. 1 is followed to program pacing rate, pulse width and/or amplitude. 
     Referring to FIG. 2, the following operations are accomplished within the audio feedback circuit  25  in a manner to be described in greater detail below. Briefly, when the N or S signal is generated on lines  72  or  74 , the output signal of the NOR gate  76  is applied on line  80  to the audio feedback circuit  25  as a MAGNET signal. The MAGNET signal causes power to be applied from power supply  11  to components of the audio feedback circuit  25  described below which are normally not powered in order to conserve energy of battery  13 . The audio feedback circuit  25  includes logic circuitry for designating memory addresses for the analog musical tone or voiced statements which are retrieved from analog memory and applied as audio drive (A-D) signals to the AM/FM transmitter  31  to be transmitted as described below. The AM/FM transmitter  31  is only powered by the SW signal and coupled to the audio drive signal (ADS) output when necessary during an interrogation or programming session or delivery of a message to the patient to conserve battery energy. 
     The pace trigger signals on line  64  and the non-refractory SENSE output signals of the flip-flop  46  on line  48  are conducted to the respective PACE and SENSE inputs of the audio feedback circuit  25 . Signals representative of the pacing pulse amplitude, pacing rate and pacing pulse width established in up/down control circuit  90  are conducted on lines  91 ,  93  and  95  to the AMP, RATE and PW inputs, respectively, of the audio feedback circuit  25 . The ERI signal on line  23  is applied to the ERI input of audio feedback circuit  25  when battery voltage falls below the reference voltage in battery monitor  17  as described above. 
     The audio feedback circuit  25  also includes a PACE/SENSE event counter that is activated to count PACE trigger pulses and SENSE event signals occurring after the MAGNET signal is received. The event counter initially counts the PACE trigger pulses of the TMT sequence and then counts the asynchronous PACE trigger pulses during the asynchronous interrogation mode for as long as the MAGNET signal is present. In the illustrated embodiment, upon termination of the MAGNET signal, the PACE/SENSE counter counts a fixed number of PACE trigger signals and SENSE signals. That count (CNT) is applied on line  73  to the logic circuit  78  for timing re-applications of the magnetic field. The count of the PACE/SENSE event counter is used to address voiced statements to be emitted in time synchronization with each PACE and SENSE event. 
     In accordance with this embodiment of the present invention, audio feedback circuit  25  and AM/FM transmitter  31  are energized during the TMT to retrieve from analog memory and transmit the voiced statement “PACE” at each pacing pulse of the TMT and “TMT PACE” at the delivery of the final reduced energy pacing pulse of the sequence. The PACE/SENSE event counter count is used to append the correct voiced statement to the pacing pulses delivered in the TMT sequence. Then, a series of voiced statements are retrieve and transmitted in an interrogation sequence commencing after the TMT and continuing until they are completed, whether or not the magnetic field continues to be applied. In the embodiment of FIGS. 2-4, the voiced statements include, manufacturer, device model and serial number identification, battery status, and parameter values including pacing rate, pacing pulse width, and pacing pulse amplitude. However, if the pacing mode and other operating parameters, e.g. sense amplifier sensitivity, refractory period, activity threshold, etc., are made programmable, then the voiced statements could include other statements of such programmed modes and parameter values. 
     Fixed rate pacing pulses are delivered following completion of this TMT sequence as long as the magnetic field is not disturbed. In accordance with this embodiment, the delivery of each pacing pulse is accompanied by a retrieved and transmitted “PACE” statement until the magnetic field is removed. In an alternative variation, only a fixed number of the “PACE” statements may be retrieved and transmitted, and the magnetic field may be left in place to maintain fixed rate pacing for prolonged diagnostic or treatment purposes. The RF transmission of the “PACE” statements ceases when a fixed count, e.g., ten, of the PACE/SENSE event counter is reached. The PACE/SENSE event counter can be turned off at that point or can continue to count PACE trigger signals. Moreover, when the magnetic field is thereafter removed, a fixed number of asynchronous pacing pulses can be delivered accompanied by the retrieved and transmitted “PACE” statement to assist timing of re-application of the magnetic field to enter the programming mode. 
     The pacing mode returns to the programmed mode, which is typically the AAI or VVI mode, but could be a triggered mode (AAT or WT), if no magnetic field is re-applied and sensed during the delivery of the fixed number of asynchronous mode pacing pulses. It would be possible to temporarily place the IPG in an inhibited mode to determine for certain whether intrinsic cardiac events are being sensed, but such a test may not be safe for the patient. Preferably, the retrieved and transmitted “PACE” or “SENSE” statements are emitted for a further fixed number, e.g., ten, of PACE trigger or SENSE event signals counted by the PACE/SENSE event counter following removal of the magnetic field and termination of the asynchronous mode. The PACE trigger pulse at the end of the pacing escape interval in the absence of a non-refractory SENSE event continues to be accompanied by a retrieved and transmitted “PACE” statement until the count is reached. As shown in FIG. 2, non-refractory SENSE events are counted and trigger RF transmission of the “SENSE” statement, but it is possible to alternatively count and transmit the “SENSE” statement on both refractory and non-refractory SENSE events. 
     One preferred embodiment in the sequence of events involved in interrogating and/or programming pacemaker IPG  10  may be better understood with reference to the time lines of FIGS. 3A,  3 B and  3 C. In FIGS. 3A,  3 B, and  3 C, pacing pulses are represented by solid vertical lines designated P 0 , P 1 , etc. and sense events are represented by broken vertical lines designated S 1 , S 2 , etc. FIG. 3A depicts the interrogation of the pacemaker IPG identification, the programmed pacing rate and pulse amplitude, the battery condition and the retrieved and transmitted pace and sense events. In FIG. 3A, it is assumed that pacemaker IPG  10  is operating normally up to time T 1 , at which time the magnet  130  is applied as shown in FIG.  1 . In response to detection of the programming magnet at T 1 , pacemaker IPG circuit  10  commences the TMT delivery of three pacing pulses P 1 , P 2 , and P 3  at the asynchronous rate of 100 PPM, for example. Pacing pulses P 1  and P 2  are at the programmed pulse amplitude, but pacing pulse P 3  is at a reduced pulse amplitude to determine if the patient&#39;s heart can be captured by the reduced energy pacing pulse. Artifacts of these three pacing pulses may be observed by a medical care provider on an EKG monitor, which also shows the PQRST complex evoked by the pacing pulse if the pacing pulse energy exceeds the patient&#39;s pacing threshold. The retrieved “START TMT” statement is transmitted by AM/FM transmitter  31  shortly after the MAGNET signal is generated. The “PACE”, “PACE” and “TMT PACE” statements are retrieved and transmitted synchronously with the next three PACE trigger signals of the TMT sequence. 
     Pacemaker IPG circuit  10  remains in the asynchronous (AOO) or VOO) mode in which pacing pulses P 4  through P n  are delivered at the programmed or nominal asynchronous rate, e.g., 70 PPM, after the TMT sequence is completed at time T 2  in FIG.  3 A. Alternatively, the asynchronous rate may be the decreased rate of 58 ppm if the ERI signal is present and applied to the up/down control circuit  90  as described immediately above. It is to be understood that the interval of asynchronous pacing between time T 2  and time T 3  in FIG. 3A may last an indefinite period of time, so long as the programming magnet  130  remains in place. However, the retrieved and transmitted “PACE” statements may continue only until a predetermined number “n” are retrieved and transmitted and then stop to save battery energy. At time T 3 , the magnet is removed, and the pacemaker IPG returns to the programmed pacing mode, e.g., the AAI or VVI mode, at the programmed pacing rate and pacing pulse amplitude and width. Alternatively, a further number, e.g., ten, asynchronous pacing pulses can be delivered after T 3  and prior to the reversion to the programmed pacing mode. This feature allows the removal of the magnet at any time after T 1  and allows the TMT, uplink telemetry, and asynchronous pacing to continue to completion after such removal as just described above. 
     Returning to time T 2 , the audio feedback circuit  25  commences to retrieve and apply A-D signals to the AM/FM transmitter  31  in the depicted interrogation sequence to cause the AM/FM transmitter  31  to transmit the analog voice statements. In this example, the retrieved and transmitted voice statements include a number of phrases selected from those depicted in the memory address list of FIG.  4 . The pacemaker manufacturer, model and unique serial number are retrieved and transmitted, followed by the retrieved and transmitted phrases stating the programmed pacing rate, the programmed pulse width, the programmed high, medium or low pacing pulse amplitude, and the battery status. The battery status statement “BATTERY OK” is retrieved and transmitted if the logic level at the ERI input to audio feedback circuit  25  indicates normal, beginning of life, battery energy. The battery status statement “BATTERY DEPLETED” is retrieved and transmitted if the ERI signal is generated by battery monitor  17  in response to detection of a depleted, end of life, battery energy. It should be noted that the medical care provider can leave the magnet  130  in place as shown in FIG. 1 or remove it at any time during the interrogation sequence described above. The retrieval and transmission of voiced statements continues to completion even if the magnet is removed before all the statements of the interrogation sequence are retrieved and transmitted. The “PACE” statement is suppressed at pacing pulses P 4  through P 7 , for example, while these identification and status statements of the interrogation sequence are retrieved and transmitted. The “PACE” statements are retrieved and transmitted after the interrogation sequence is completed for as long as the magnet continues to be applied or until the predetermined count “n” is reached. 
     At time T 3  in FIG. 3A, the magnet  130  is removed from the patient  102  in FIG. 1; and the MAGNET signal is no longer applied to the MAGNET input of audio feedback circuit  25 . As shown in FIG. 3A, the audio feedback circuit  25  starts the internal event counter of ten PACE or SENSE events, for example, within which one or more re-applications of a magnetic field must be sensed by MAGFET  70  to continue with programming pacing rate, pulse width or amplitude. The sense amplifier  20  is no longer effectively disabled, and non-refractory sense signals pass through the AND gate  82  and reset the pacing escape interval being timed out in rate/TMT circuit  58 . The termination of each escape interval by a non-refractory sense event or the time out of the escape interval is applied to the SENSE and PACE inputs of the audio feedback circuit  25  which counts them. The audio feedback circuit  25  continues to retrieve from memory and supply the A-D signals to the AM/FM transmitter  31  to modulate and transmit the statements “PACE” or “SENSE” on delivery of each pacing pulse, as at P n+1  and P N+10  and each SENSE signal at S n+2  and S n+3  shown in FIG.  3 A. During this sequence, the medical care provider can use the radio to receive, demodulate and emit the “PACE” and “SENSE” voiced statements (or musical tones signifying the same) and correlate them to a visual display of the same events. The retrieval and transmission of voiced statements cease when a predetermined count of PACE and SENSE events accumulates in the event counter in the audio feedback circuit  25 . 
     The illustration of FIG. 3A assumes that a magnetic field is not re-applied during the ten pace and sense events (counted by an event counter and supplied to logic block  78  on line  73 ) following time T 3 . FIG. 3B depicts a programming protocol sequence that is initiated by a single re-application of the permanent magnet that provides the MAGNET signal on line  80  during the above-described sequence after T 3  but before the ten pace or sense events are counted. In this time period, the medical care provider or physician can listen to and count the number of retrieved, transmitted and radio emitted “PACE” and “SENSE” statements and time reapplication of the magnet  130  to the patient&#39;s skin. The single re-application of the magnetic field within this ten event window is decoded in logic circuit  78  at the completion of the  10  event window to commence a pacing rate programming sequence in which base pacing rate is programmed. 
     FIG. 3C depicts a programming protocol sequence that is initiated by two re-applications of the permanent magnet that provides a signal N or S on line  72  or  74  during the above-described sequence after T 3  but before the ten events are counted. The two re-applications of the magnetic field within the ten event count window is decoded in logic circuit  78  to commence a pacing pulse amplitude programming sequence in which pacing pulse amplitude is programmed. Similarly, three reapplications of the magnetic field within the ten event count window is decoded in logic circuit  78  to commence a pacing pulse width programming sequence in which pacing pulse width is programmed 
     Programming any of these three programmable parameters is accomplished by first initiating the TMT and interrogation sequence described above with reference to FIG.  3 A. Then, after time T 3 , the appropriate number (one, two, or three) of magnet removal/replacement cycles must be performed within the ten event count window to switch logic circuit  78  into the programming mode for programming the desired parameter. This approach and the ability to hear the retrieved and transmitted “PACE” and “SENSE” statements emitted by the radio makes it easy to reliably apply and remove the permanent magnet  130  from the patient&#39;s skin the required number of times after the initial removal of the permanent magnet  130  from the patient&#39;s skin at time T 3  to select the desired parameter to re-program. 
     In the magnet removal/re-application cycles depicted in FIGS. 3B and 3C, it will be observed that the re-applied magnet  130  is held in place to provide the selected N-S or S-N magnetic field to the MAGFET  70  during the subsequent programming modes. Therefore, the continuously generated N or S signal is applied through the NOR gate  76  to one input of AND gate  82  to effectively disable the sense amplifier  20  and to commence pacing in the asynchronous mode. Pacing pulses are then delivered at the current programmed pacing rate, pacing pulse width and pulse amplitude. The logic circuit  78  decodes the applied number of removals and replacements of the magnet  130  and provides the corresponding programming mode control signals to the up/down control circuit  90  via lines  92 . 
     Once in the decoded programming mode, up/down control circuit  90  adjusts the corresponding parameter value up or down, by an incremental amount at each asynchronous pacing cycle, depending upon the polarity of the detected magnetic field. For example, rate programming mode is initiated by completing the TMT and interrogation mode and then removing and replacing the magnet once as shown in FIG.  3 B. The up/down control circuit  90  increases the pacing rate by an incremental amount (e.g. 5 PPM or 10 PPM) each pacing cycle so long as the N signal remains present on line  72 , signifying detection of the N-S oriented magnetic field. Conversely, up/down control circuit  90  decreases the pacing rate by a like incremental amount each pacing cycle so long as the S signal is present on line  74 , signifying the S-N oriented magnetic field. Programming the pacing rate to a desired level is thus accomplished by maintaining a S-N or N-S oriented magnetic field over MAGFET circuit  70  for enough pacing cycles to reach the desired level. When the desired rate is reached, rate programming is terminated by simply removing the magnet. 
     In the above-incorporated, commonly assigned &#39;188 and &#39;342 patents verification of the pacing rate change is effected by observing the delivery of redundant pacing pulses signifying the parameter being programmed by their number on the running EKG display. In the programming of rate, two such pacing pulses separated by 5 msec are generated at the end of each pacing cycle as also shown in FIG.  3 B. In the programming of pulse amplitude, three such pacing pulses separated by 5 mSec are generated at the end of each pacing cycle as also shown in FIG.  3 C. Presumably, four such pacing pulses are generated at the end of each pacing cycle in order to signify that pacing pulse width is being programmed. The number of redundant pacing pulses show which parameter is being programmed but do not reveal the programmed parameter value. Mistakes in counting the pacing cycles can occur, and it is not easy to observe or measure incremental changes in these parameter values from the EKG tracing that is being printed or displayed on a video screen. It is necessary to know what the starting parameter value is and to mentally calculate the change from that value by counting the escape intervals until the end parameter value should be obtained. If the starting pacing pulse width or amplitude or pacing rate is not known and cannot be measured, then it may be necessary to follow the programming sequence to increase or decrease the programmed parameter value to its upper or lower limit. This upper or lower limit is reached by counting out the maximum number of escape intervals corresponding to the total number of possible incremental values. Then, the new parameter value is programmed by decrementing the parameter value from the maximum value or incrementing the parameter value from the minimum parameter value by the number sufficient to arrive at the desired programming value. 
     In accordance with a further feature of the present invention, the audio feedback circuit  25  and the AM/FM transmitter  31  are employed to retrieve and transmit statements of the programmed parameter value at the end of each escape interval. In this way, it is not necessary to employ the redundant and energy wasteful pacing pulses, and it is not necessary to calculate the correct number of pacing cycles required to make a correct change in the parameter value or to count the pacing cycles. This results in a simplified, more reliable, and less error prone programming function with benefits of reduced costs and improved patient safety. 
     Thus, in FIGS. 3B and 3C, the redundant pacing pulses employed in the above-incorporated, commonly assigned &#39;188 and &#39;342 patents are depicted, but it will be understood that they are not necessary in the practice of the present invention. Upon entering a programming mode via one, two or more removal/replacement cycles of the magnet, the voiced statement of the parameter that is being programmed, e.g., “Programming Rate” or “Programming Amplitude” is retrieved from analog memory, transmitted and picked up and reproduced by the external radio. 
     Additionally, at each incremental change, the change in pacing rate, pulse width or pulse amplitude is retrieved and transmitted as depicted in FIGS. 3B and 3C. In this embodiment, particularly at high pacing rates, it may be necessary to make the incremental programmed changes and transmit the changed value only at the end of every second or third or fourth escape interval to provide sufficient time for the complete phrase to be transmitted and heard from the radio receiving it. Or is the phrase may be shortened to simply state the number for pacing rates which are multiples of either 5 or 10 and pulse widths which are stated in milliseconds. Additionally, ascending or descending scale musical tones can be transmitted and emitted by the radio prior to or following each incremental increase or decrease, respectively, in the programmed parameter value to signify that the parameter value is being changed. As noted below, in certain IMDs one or more ascending or descending scale musical tone can be transmitted following each increase or decrease in the parameter value, and the actual value need not be retrieved and transmitted in an transmitted voice statement. 
     FIG. 4 sets forth an exemplary list of pacing rates, pulse widths and pulse amplitudes that are retrieved and transmitted in the programming modes and that are coded to memory addresses of the analog storage array described below with reference to FIG.  6 . For example, voiced statements of pulse widths in a range of 0.1 mSec to 1.0 mSec at 0.1 mSec increments and pacing rates between 50 PPM and 100 PPM at 5 PPM increments are stored in memory. Voiced statements of pacing pulse amplitudes “AMPLITUDE LOW”, “AMPLITUDE MEDIUM” and “AMPLITUDE HIGH” for three programmable amplitudes, for example, are also stored in memory. 
     FIG. 5 is an expanded block diagram of the audio feedback circuit  25  of FIG.  2  and includes an analog storage/playbackIC  200 , timing control logic circuit  202  and address generation logic circuit  204 . In addition, a sound input block  206  is depicted in broken lines to illustrate recording and storage of analog retrieved and transmitted voiced statements and/or musical tones in analog memory in the analog storage/playbackIC  200 . Recording typically takes place in the course of manufacturing the pacemaker IPG or other IMD, although such recording may take place after manufacture of the pacemaker IPG is completed. The analog storage/playbackIC  200  is preferably one of the ISD33000 Series, ChipCorder® single-chip voice record/playback devices sold by Information Storage Devices, Inc. (ISD) located in Los Alton Hills, Calif., and particularly, the model ISD33060 depicted in FIG.  6 . Such analog storage/playbackICs are disclosed in U.S. Pat. No. 4,890,259, incorporated herein by reference, and other related ISD patents. 
     In FIG. 5, the timing control circuit  202  is interconnected with the IPG circuit to receive the PACE trigger pulse on line  64 , the SENSE event signal on line  48 , and a MAGNET signal on line  80  whenever the N (UP) or S (DOWN) signal is present on lines  72  and  74 , respectively. Timing control circuit  202  establishes the protocols depicted in FIGS. 3A-3C and described above and generates the commands depicted in FIG. 5 that are applied to the address generation circuit  204  or the AM/FM transmitter  31  and logic  78 . These commands are generated particularly during the TMT mode, the asynchronous interrogation mode, and the subsequent normal operating mode depicted in FIG.  3 A. The SW signal generated by timing control circuit  202  enables power up of the AM/FM transmitter  31  only during transmission time windows to conserve energy. 
     The address generation circuit  204  also receives the ERI signal from battery monitor  17  on line  23  and the pulse amplitude (AMP), the pacing rate (RATE), and the pulse width (PW) programmed operating parameter values from up/down control circuit  90  on lines  91 ,  93  and  95 , respectively. During the asynchronous interrogation mode of FIG. 3A, the AMP, RATE and PW programmed parameters and the ERI signal are converted to the memory addresses listed in FIG. 4 for the programmed values and battery condition. These commands prompt the address generation circuit  204  to select and apply the memory addresses for the voiced statements identified above and listed in FIG. 4 to the ADDRESS input line to the analog storage/playback IC  200 . 
     It would be possible to combine voiced statements retrieved in tandem from two memory addresses to form a retrieved and transmitted phrase as shown in FIG.  7 . For example, the PACE signal and the programmed pacing RATE value can be employed to select the addresses in tandem to voice a “PACE XX PPM” phrase from the “PACE” statement and the “XX PPM” rate statements depicted at two addresses in FIG. 4 (where “XX” is the presently programmed value). 
     During the programming modes illustrated in FIGS. 3B and 3C, the increased or decreased AMP, RATE and PW programmed parameter values are similarly converted to the memory addresses listed in FIG.  4  and applied to the ADDRESS input of the analog storage/playbackIC  200 . 
     The address generation circuit  204  also supplies the “not chip enable” (NCE) command and the PLAY command to the analog storage/playbackIC  200  in order to start or trigger playback at the addresses supplied to the ADDRESS bus. The recorded voiced statement or other audible sound that is addressed is supplied as the A-D signal through playback filter and amplification stage  208  to the AM/FM transmitter  31  of FIG.  2 . When the retrieved A-D signal statement is completed, the logic level on the “not end of message” (NEOM) line switches to alert the timing control  202  to queue up the next command to the address generation block  204 . The above-described sequence of retrieved and transmitted statements of device identification, operating conditions and mode or states and programmed parameter values are sequentially generated in the interrogation mode by the “hand shake” cooperation between timing control  202  and analog storage/playbackIC  200 . Similarly, each device operation, i.e., PACE trigger pulse or SENSE event signal causes the timing control  202  to instruct the address generation circuit  204  to supply the address for the retrieved and transmitted “PACE or “SENSE” statement to the ADDRESS input of the analog storage/playbackIC  200 . The address generation circuit  204  also supplies the “power down” (PWR_DWN) logic level to the analog storage/playbackIC  200  in order to place the analog storage/playbackIC  200  in a “zero power” mode when not in use. 
     The sound input block  206  is used to record voiced statements and/or musical tones through line  211  at predetermined addresses in analog storage/playback IC  200 . The sound input block  206  supplies the addresses and provides a record command signal on play/record line and the not chip enable (NCE) signal on the NCE line. The NCE input receives an enable logic level to commence recording of the voiced statement (or musical tone) that is addressed on the ADDRESS bus. 
     FIG. 5 also includes additional circuitry to retrieve a recorded message or warning as an A-D signal when appropriate to transmit a warning to the radio indicating device malfunction and impending delivery of a therapy, where appropriate. A variety of IMD monitoring means can be provided for periodically or continuously monitoring a condition, state or impending operation of the implantable medical device or a condition or state of the patient and for providing a message trigger signal in response thereto. Voiced statements can also be stored and transmitted advising the patient to contact his/her physician or medical care provider. 
     The ERI signal is one such message trigger signal that will trigger the address generation and retrieval of the above-described “BATTERY DEPLETED” A-D signal to be transmitted by AM/FM transmitter  31 . A timer is employed in the address generation block that responds to the ERI signal and periodically enables the generation of the address of this warning to the patient, e.g., once every hour, so that it is not continually generated. The ERI warning can be automatically set OFF when an interrogation or programming sequence is conducted in accordance with FIGS. 3A-3C to allow those functions to be completed. Moreover, in more complex, multi-programmable embodiments than illustrated in FIG. 2, this function can be programmed on or off by the medical care provider employing the programmer to transmit the appropriate programmed command. 
     FIG. 6 is a simplified block diagram of the analog storage/playbackIC  200 , and it includes components for recording voiced statements and sounds in a non-volatile analog storage array  210 . Analog storage/playbackIC  200  also retrieves the recorded statements and sounds and forwards them on analog outputs A-D+ and A-D-− to the filter and amplifier stage  208  which processes them to provide the A-D signal to the AM/FM transmitter  31 . The ISD33060 ChipCorder® analog storage/playback IC  200  is a CMOS device that operates at 3 volts and provides playback of 60 seconds of analog voice recordings stored in non-volatile analog storage array  210 . The analog voice recordings are addressed via decoders  212  coupled to the ADDRESS buffers  214  and applied to the analog output amplifier  226  as described below. The analog storage array is a multilevel storage, EEPROM array that is proprietary to ISD and is described in detail in the above-incorporated ISD &#39;259 patent. 
     The CMOS device includes power conditioning circuit  230  that is intended to be coupled to external components forming a regulated power supply coupled with the power source  11  for supplying power to the other depicted circuits. A device control circuit  232  is also coupled with the other depicted circuits and governs device operations depending on the intended application. In accordance with the present invention, the PWR_DWN signal from the address generation block  204  is applied to the PD input to device control circuit to enter the zero power mode to minimize battery drain at all times other than during voice recording or playback. It is alleged that audio or voiced statements stored in non-volatile analog storage array  210  can be retained 100 years without consuming any power. A PLAY or RECORD logic level is applied to the P/NR input during playback or recording of voiced statements. The NCE input receives an enable logic level to commence recording the voiced statements in memory at the specified address to enable location and the playback of the voiced statement that is addressed on the ADDRESS bus. The NEOM logic level signal is outputted from the device control circuit  232  and applied to the timing control  202  when the voiced statement or phrase is completed in order to allow the next voiced statement or phrase to be addressed as noted above. 
     An on-chip oscillator is provided by the internal clock  234  that can be also driven by external clock signal XCLK (not employed in the practice of the present invention). The internal clock  234  provides clock signals to internal timing circuit  236  which provides a sampling frequency to sampling clock  238  and to the 5-pole active anti-aliasing filter  222  and to the 5-pole active smoothing filter  218 . 
     The audio sound or voice recording section of the CMOS device includes the speech or audio input amplifier  220  for amplifying the audio input signal at ANA I N and applying the amplified signal coupled to anti-aliasing filter  222 . The filtered input signal is sampled by sampling clock  238  and the sampled analog values are stored directly into memory cells through analog transceivers  216  for later retrieval when addressed via decoders  212 . The manner of storage and the assignment of addresses is described in the above-incorporated ISD &#39;259 patent. A further pre-amplifier  240  and AGC circuit  242  are provided on the IC but are not employed in the practice of the present invention. 
     In accordance with one feature of the present invention, the voiced statements are recorded in a particular human language at completion of manufacture of the pacemaker IPG circuit  10  (or other IMD circuit), but before the circuit  10  is enclosed in the IPG housing. Alternatively, the sound or voiced statement recordings are supplied to the vendor, ISD in this instance, and recorded in the analog storage array  210  before the analog storage/playbackIC  200  is delivered. In another alternative approach, the pacemaker IPG or other IMD could be provided with a feedthrough for direct coupling with the ANA IN terminal of amplifier  220  for recording the voiced statements in the manner described in the above-incorporated, commonly assigned &#39;096 patent. In this variation, it would be possible for a distributor or a physician implanting the medical device in a given country or region to employ the local language in storing the voiced statements. In accordance with a further aspect of the present invention, musical tones can also be recorded through audio input amplifier  220  at certain memory locations for use in conjunction with recorded voiced statements. 
     In accordance with another feature of the present invention, the voiced statements can be recorded in more than one language, and the medical care provider or physician can select the language to be used. In more sophisticated IMDs having RF telemetry capabilities, the specific language can be selected by a downlink RF telemetry command. In the low cost pacemaker IPG  10  described above, a further repeated sequence of successive removals and replacements of magnet  130  within the specified time period, can be detected by appropriate circuitry in logic circuit  78  and applied to address generation circuit  204  to select a language to be used. 
     Regardless of how voiced statements are recorded in analog storage array  210 , the analog voice samples of the retrieved and transmitted statements are sequentially retrieved from storage locations in the analog storage array  210  when they are addressed via decoders  212 . The analog voice samples are sequentially retrieved through the analog transceivers  216  at the sampling clock frequency and applied to the 5-pole active smoothing filter  218  to recompose the words of the phrase in a natural cadence and speech form. The reconstituted words pass through the multiplexor  224  and are applied to the input terminals of the output amplifier  226  where they are amplified and output at output terminals A-D+ and A-D−. The auxiliary input to multiplexor  224  is not employed in the present invention. 
     It will be understood that this preferred embodiment of the invention may be modified to provide differing programming and interrogation sequences. The MEDTRONIC® Champion™ single chamber, pacemaker IPG system shares a similar architecture and operating system as the preferred embodiment described above but is programmed by successive magnet removals and re-applications and indicates programmed operating modes and parameters in a somewhat different manner. The system includes the MEDTRONIC® Model 9710 programmer which only detects and displays pacing intervals on a display to facilitate ECG interpretation using the method described in commonly assigned U.S. Pat. No. 4,226,245 to Benneft, incorporated herein by reference. Even when the intervals are displayed, it is difficult to program the pacing rate while viewing and interpreting the pacing interval display in order to count pacing intervals and synchronize the generation of the programming command to counted intervals. This method is prolonged and subject to error. The present invention may be implemented into the Champion™ systems to transmit voiced statements during an interrogation sequence and transmitted “PACE” and “SENSE” statements that are received by the radio to aide in understanding the TMT operation and to time re-programming. 
     In the Champion™ IPG, the programmed pacing rate is reduced by a measurable percentage in response to an ERI signal so that the medical care provider can observe the current rate and interpret that the battery is depleted from that observed pacing rate. For example, the programmed pacing rate of 75 PPM may be reduced to 58 PPM when the battery voltage falls below an ERI threshold voltage. A reed switch is included in addition to the MIAGFET that is closed by an applied magnetic field to commence an interrogation sequence that culminates in a TMT after the magnet is removed rather than commencing with the TMT sequence. The applied magnet closes the reed switch and causes the pacing mode to change to the asynchronous mode and the programmed pacing rate to be restored in an initial sequence of 3-4 asynchronous pacing pulses. Then, the asynchronous pacing rate changes to the ERI rate, if the battery voltage is below the ERI threshold, or remains at the programmed pacing rate for a second sequence of asynchronous pacing pulses. The medical care provider observes the pacing artifacts on an ECG display and compares the observed escape intervals to determine whether there is an apparent difference and draws a conclusion that the battery voltage is or is not depleted requiring replacement of the IPG. The magnet is then removed, and the pacing mode returns to the inhibited mode at a preset escape interval corresponding to 75 PPM, for example, and a fixed number of pacing escape intervals are counted in a third sequence. The TMT sequence of four asynchronous pacing pulses at an elevated pacing rate and a programming window sequence including the TMT sequence and seven more pacing pulses are commenced at the end of that count. Again, the medical care provider observes the ECG display to determine if the reduced energy pacing pulse of the TMT sequence captures the heart. 
     In this embodiment of the present invention, the retrieval and transmission of voiced statements during the interrogation mode of FIG. 3A, including the battery status, can be commenced and completed in the initial sequence of fixed rate pacing pulses at the programmed pacing rate. The second sequence could be augmented by retrieved and transmitted “PACE XX PPM” statements (where “XX” is the presently programmed value) emitted by the radio synchronously with each PACE trigger. Similarly, the pacing pulses of the TMT sequence could be augmented by retrieved and transmitted “PACE” and “TMT PACE” statements emitted by the radio, and the pacing pulses of the programming window sequence could be augmented by retrieved and transmitted “PACE” and “SENSE” statements emitted by the radio. 
     Only the pacing rate and pacing pulse amplitude are programmable in the Champion™ pacemaker IPG. In the programming sequences of the Champion™ pacemaker IPG, the N-S and S-N magnetic fields are used to program the pacing rate and pulse width, respectively. The programmed parameter value is incremented when the magnetic field is quickly applied and removed twice in rapid succession in an increment window between three successive pacing pulses. The programmed parameter value is decremented when the magnetic field is quickly applied and removed once. In either case, it is necessary to wait until three escape intervals lapse with PACE trigger pulses before the parameter value can be again incremented or decremented. Once a desired parameter value is achieved, no more magnetic fields are applied, and the pacing mode reverts to the inhibited pacing mode after ten pacing pulses are delivered from the last application of a magnetic field. 
     In this embodiment, the present invention can be implemented to voice “PACE” statements and thereby assist in timing the application(s) of the magnetic fields sufficiently far apart and within the increment window to avoid mis-programming. The retrieved and transmitted “PACE” statements can augment the delivery of the final ten pacing pulses. 
     The above-described embodiments of the pacemaker IPG are implemented in custom integrated circuits or more sophisticated, micro-computer based operating systems incorporating the analog storage IC  200  and distributing the timing control and address generation functions of FIG. 5 among other system components. This approach can be used for a number of IMDs, e.g. electrical stimulators of the type disclosed in commonly assigned U.S. Pat. No. 4,520,825 to Thompson et al., incorporated herein by reference. 
     FIGS. 8 and 9 are block diagrams of such microcomputer based IMD operating systems intended to be used in conjunction with a controller and monitor or therapy delivery system of one of the types depicted in FIG.  10 . The system of FIG. 8 can be programmed or interrogated employing a simple magnet application and removal approach as described above, whereas the system of FIG. 9 employs RF telemetry programming and interrogation techniques known in the art. The micro-computer based system of FIGS. 8 and 9 comprises a microprocessor  152  coupled by a data and command bus  150  with RAM  154 , ROM  156 , analog storage/playback IC  200 , filter and amplifier stage  208 , the battery monitor  17  and the digital controller/timer circuit  158  of FIG.  10 . The digital controller/timer circuit  158  is coupled with a specific monitor or therapy delivery system  160   a - 160   i  as shown in FIG.  10 . Other components or circuit blocks that are used in a specific IMD may also be connected with the data and control bus  150 . 
     The analog storage/playbackIC  200  is configured as described above in reference to FIG.  6 . Audio drive signals for transmitting voiced statements or musical tones are stored in the analog storage array  210  of FIG. 6 using the sound input block  206  and associated signals in the manner described above. The sound input block  206  may not be present in the IMD or may be disabled if the A-D signals are recorded during manufacture of the IMD and no option is provided to allow recording by a distributor or physician. If the sound input block  206  is present and enabled, it would be coupled with the data and control bus  150  to allow its usage particularly in the embodiment of FIG. 9 where appropriate commands could be received in a downlink telemetry transmission. 
     In these embodiments, it is not necessary to employ the timing control circuit  202  or the address generation circuit  204  of FIG. 5 to control the operation of the analog storage/playbackIC  200 . In this micro-computer based operating system, the timing of operations of the analog storage/playbackIC  200  as described above are governed by interrogation and programming algorithms stored in ROM  156  and enabled by microprocessor 152 . The memory location addresses for the A-D signals stored in the analog storage array  210  are also stored in ROM  156  and selectively retrieved and applied to the address buffers  214  in accordance with the interrogation and programming algorithm. 
     The IMD of FIG. 8 or  9  in conjunction with FIG. 10 is powered by the battery  13  in the power source  11 , and battery voltage is monitored by the battery monitor  17 . The battery voltage is either encoded in battery monitor  17  and supplied to data and command bus  150  or an ERI warning trigger signal is developed in the battery monitor  17  in the manner described above and encoded and supplied to data and command bus  150  to the microprocessor  152 . During an interrogation sequence, the battery voltage itself or a simplified voiced statement that the battery voltage is “OK” or “depleted” is transmitted by AM/FM transmitter  31  as described above. 
     At other times, if the encoded battery data signifies that the battery  13  is depleted to an ERI voltage, the microprocessor  152  commences a warning routine to cause the AM/FM transmitter  31  to transmit a warning statement or musical tone at an audible volume that the patient can hear. During the warning routine, the microprocessor periodically (e.g., once every hour) retrieves the address of the appropriate A-D signal and directs it on data and control bus  150  to the address buffers  214  of analog storage/playback IC  200 . The NCE and NEOM commands are also applied on data and control bus  150 . The filter and amplifier stage  208  amplifies the A-D signal and applies it to the AM/FM transmitter 31  for transmission to the radio. 
     Other warning routines may also be included in the microcomputer based operating system for providing such audible sound warnings emitted by the radio to the patient when a triggering event occurs. The triggering event can include certain operations of the IMD or other changed conditions or states of the IMD. For example, in the context of an implantable drug delivery system, the patient can be warned that the medication supply is depleted. In the context of an implantable cardiac monitor or cardioverter/defibrillator, the patient can be warned that an arrhythmia has been detected by the arrhythmia detection algorithm and to take appropriate action. The onset of the malignant condition of the patient is detected, and the warning trigger signal is generated in response to the detection. The patient is warned to seek medical assistance or take other precautions by RF transmission of the audible warning. In the case of a cardioverter/defibrillator, the patient can be advised to get in a resting position before the cardioversion/defibrillation shock is delivered. 
     In each case, the triggering event causes the microprocessor  152  to retrieve and apply the commands for operating the analog storage/playback IC  200  and provide the addresses of the appropriate A-D signal to retrieve it from nonvolatile analog storage array  210  from the RAM  154  or ROM  156 . The analog storage/playbackIC  200  retrieves the addressed A-D signal and applies it through the filter and amplifier stage  208  to the AM/FM transmitter  31  which transmits the AM or FM voiced statement or musical tone warning to the patient. 
     In FIG. 8, an interrogation and programming system responsive to successive applications of a magnetic field to a MAGFET  70  is illustrated for interrogating IMD information and for programming device operating modes and parameter values. The MAGFET  70  detects the polarity of the applied magnetic field and generates the corresponding N and S signals on lines  72  and  74 , respectively, in the manner described above in reference to FIG.  2 . The N and S signals are applied to logic circuit  78 , and logic circuit  78  develops an appropriate encoded signal that is applied on data and control bus  150  to microprocessor 152  to initiate the programming or interrogation algorithm. Thus, a communication session is established by applying the magnet  130  to the patient&#39;s skin as shown in FIG.  1  and described. The magnetic field constitutes a communication link signal that is detected by the MAGFET  70  to establish the communication session. 
     In FIG. 9, the communication session is established using an RF telemetry transmission based, programming and interrogation system for interrogating IMD information and for programming device operating modes and parameter values. The programming head (not shown) of the programmer (not shown) typically includes a permanent magnet that closes reed switch  166  and generates downlink RF telemetry signals that are received by the RF telemetry antenna  168  and applied to the RF telemetry transmitter/receiver circuit  164 . The received downlink RF telemetry signals are decoded by the RF telemetry transmitter/receiver circuit  164  and then encoded for transmission on data and control bus  150  and constitute communication link signals. Uplink RF telemetry transmissions of IMD information received on data and control bus  150  are generated in the RF telemetry transmitter/receiver circuit  164  and applied to RF telemetry antenna  168  in an uplink telemetry transmission routine. The microprocessor  152  commences an uplink RF telemetry transmission routine and supplies data and control signals on data and control bus  150  to RF telemetry transmitter/receiver circuit  164 . 
     The system of FIG. 9 can be configured in many different ways to share the uplink communication capabilities of the audible sounds generated by the AM/FM transmitter  31  with high speed RF telemetry uplink transmissions for receipt by a programmer. In a simple application, the RF telemetry transmission system can be used to receive programming and interrogation commands, and the interrogated data and programming confirmation can be transmitted back at a frequency in the AM or FM band to be received by a radio incorporated into the programmer or a separate radio. It should be noted that the 175 kHz telemetry antenna in the IMD could be employed to also transmit the AM or FM frequency signal. The single antenna can be designed with a switching circuit to operate optimally at both RF frequencies depending on the switch state. 
     In the system of FIG. 8, the patient can be provided with a magnet to program limited operating modes or parameter values and received audible sound feedback confirming such programming or to interrogate certain IMD information. It will be understood that the interrogation and programming system of FIG. 8 can be included in the operating system of FIG. 9 to allow the patient to use the magnet for the same purpose. Or the patient can be provided with a limited function programmer for RF telemetry downlink transmission of limited interrogation and programming commands that are responded to by the audible sound RF transmission of the corresponding IMD information. 
     In this regard, the high volume, audible sound RF transmission capability can also be employed during programming or interrogation routines that the patient is allowed to self initiate. For example, if the patient is supplied with a limited programmer or magnet for increasing or decreasing dosage of a drug or a symptom alleviating electrical stimulation, the programmed change can be confirmed by RF transmission of a voiced statement or musical tone received and played back by the radio. In each case, the programmed change causes the microprocessor to retrieve and apply the commands for operating the analog storage/playbackIC  200  and the addresses of the appropriate A-D signal. The analog storage/playbackIC  200  retrieves the addressed A-D signal and applies it through the filter and amplifier stage  208  to the AM/FM transmitter  31  which transmits the voiced statement or musical tone confirming the change to the patient. Examples are described below in reference to FIGS. 11 and 12. 
     FIG. 10 is a block diagram of a digital controller/timer circuit  158  usable with the operating systems of FIGS. 8 or  9  and with a therapy delivery device  160   a - 160   h  or physiologic monitor  160   i . It will be understood that many of the identified therapy delivery devices  160   a - 160   h  also have monitoring capabilities that accumulate physiologic data for later interrogation. It will be understood that the logic  78  and the RF telemetry transmitter/receiver  164  of FIGS. 8 and 9 can be incorporated within the digital controller/timer circuit  158  in any particular therapy delivery device and monitoring configuration. In each IMD configuration case, the digital controller/timer circuit  158  and the appropriate programmable operating algorithm  162  govern all operating functions. 
     With respect to therapy delivery device configurations, the IMD may be configured to operate an implantable heart assist device or pump  160   a  implanted in patients awaiting a heart transplant operation. In this case, the derived relative blood pressure and/or temperature values may be used to modulate the action of the pump to maintain adequate cardiac output. Or it may be configured to include any one or a combination of the anti-tachycardia pacer  160   b , anti-bradycardia pacer  160   c , cardioverting apparatus  160   d  and/or defibrillating apparatus  160   e  having suitable leads and electrodes extending from the implantable therapy delivery medical device  100  to the patient&#39;s heart  10  for sensing the electrogram (EGM) and delivering pacing pulses or cardioversion/defibrillation shocks. The IMD may be configured to include the substance delivery apparatus  160   f  which is coupled to a suitable catheter extending to a site of the patient&#39;s body to deliver a substance, e.g., a therapeutic or diagnostic agent or drug, from a substance reservoir. For example, a drug to treat hypertension may be delivered to the patient&#39;s heart  10  or vascular system. 
     In accordance with one aspect of the present invention, the memory stores an audio drive signal indicative of the delivery of a substance to body tissue. The audio drive signal related to the delivery of the substance is applied to the radio frequency transmitter. The radio frequency transmitter broadcasts a modulated radio frequency signal capable of being detected and demodulated by the radio receiver to produce a human understandable voiced statement or the other audible sound indicative of the delivery of the substance. In accordance with another aspect of the present invention, the depletion of the substance reservoir is periodically monitored or interrogated. An audio drive signal signifying the quantity of substance delivered or remaining in the substance reservoir is stored at a memory location having a specified memory address. The deliveries of boluses of the substance are monitored. The quantity of substance delivered or remaining in the reservoir is measured or calculated upon each delivery or upon receipt of a substance quantity interrogation command, and the stored audio drive signal signifying the quantity of substance delivered or remaining in the reservoir is retrieved from the memory location. The radio frequency transmitter broadcasts a modulated radio frequency signal capable of being detected and demodulated by the radio receiver to produce the human understandable voiced statement or the other audible sound message indicative of the quantity of substance delivered or remaining in the reservoir. 
     The IMD may be configured as a MEDTRONIC® Transform™ Cardiomyostimulator 160 g having suitable leads extending to the patient&#39;s heart and the skeletal muscle wrapped about the heart to sense the cardiac EGM and time delivery of the muscle stimulation pulses. Again, the derived relative blood pressure and/or temperature values may be used to modulate the muscle stimulation rate to maintain adequate cardiac output. The IMD may also be configured as an electrical stimulator  160   h , including nerve and muscle stimulators, deep brain stimulators, and cochlear implants, for applying electrical stimulation therapies to electrodes at appropriate locations of the patient&#39;s body. 
     Finally, the IMD can also be configured as an implantable monitoring system for monitoring physiologic conditions, e.g., a cardiac monitor for monitoring the patient&#39;s heart EGM and/or for monitoring blood pressure, temperature and blood gas or pH. The MEDTRONIC® Reveal™ implantable loop recorder has surface electrodes and records a 42 minute segment of EGM when the patient feels the effects of an arrhythmic episode and activates the recording function by applying a magnet over the site of implantation. The MEDTRONIC® Chronicle™ implantable hemodynamic recorder employs the leads and circuitry disclosed in commonly assigned U.S. Pat. Nos. 5,535,752 and 5,564,434, incorporated by reference herein, to record the EGM and absolute blood pressure values for predetermined time intervals. 
     A wide variety of IMD information can be conveyed in any of these therapy delivery or monitoring systems by way of retrieved and transmitted voiced statements or musical tones stored in the analog storage array  210  of the analog storage/playbackIC  200 . Two specific examples are set forth in FIGS. 11 and 12 that show how the present invention can be employed to simplify interrogation and programming of IMDs that typically provide for limited function programming by the patient to relieve symptoms felt by the patient. 
     In these embodiment, the patient is typically supplied with a patient activator or programmer to turn a therapy on or off and/or to increase or decrease a therapy parameter. Specifically, the above-referenced MEDTRONIC® Itrel® implantable nerve stimulator and Synchromed® drug infusion system are provided with such patient activators to allow the patient to adjust the stimulation and drug therapies to relieve pain symptoms. In accordance with the following described embodiments of the present invention, musical tones are transmitted by the IMD to the radio when it is programmed by the patient to adjust the stimulation and drug therapies using such a patient activator or a magnet. A series of ascending scale musical tones can be transmitted to the radio upon delivery of an increased stimulation energy or medicinal bolus therapy in response to use of the patient activator or magnet. Similarly, a series of descending scale musical tones can be transmitted to the radio upon delivery of an decreased stimulation energy or medicinal bolus therapy in response to use of the patient activator or magnet. Moreover, the programmed stimulation energy or bolus volume can also be retrieved and transmitted to the radio in accompaniment with the ascending or descending scale musical tones or chimes. 
     FIG. 11 is a chart depicting the memory address locations of A-D signals for transmitting voiced statements or musical tones in interrogation and programming sequences of an implantable drug delivery apparatus  160   f  of FIG. 10 having an operating system of FIG. 8 or FIG.  9 . The chart of FIG. 11 depicts the memory address locations for retrieving and transmitting voiced statements or musical tones in an interrogation sequence of current IMD information at analog memory addresses “00”-“0D” followed by a programming sequence for increasing or decreasing a drug infusion rate at addresses “0E” and “0F”. In the interrogation and programming sequences, the medical care provider can commence the interrogation using either a programmer in the case of a configuration using the operating system of FIG. 9 or a magnet  130  in the case of a configuration using the operating system of FIG.  8 . 
     Assuming the latter case and assuming that the IMD  100  of FIG. 1 is a drug delivery system incorporating the drug delivery apparatus  160   f , the medical care provider applies the magnet  130  over the MAGFET  70  which produces either the N or S signal on line  72  or  74  of FIG.  8 . The logic circuit  78  responds by providing an interrupt to the microprocessor  152  to commence the interrogation routine. The analog memory address “01” is provided on bus  150  to analog storage/playbackIC  200  which transmits the voiced statement “Data Start” or a musical tone at an identifiable audible frequency. Then, the interrogation routine sequentially selects the programmed one of the addresses “02”-“05” for the current infusion rate, “06”-“0A” for the remaining drug quantity, and “0B” or “0C” for the battery condition. The A-D signals cause the RF transmission of voiced statements in these cases. Then, the “End Data” statement or a further musical tone at the same or a different frequency than the “Data Start” frequency is transmitted by providing address “0D” on bus  150  to the analog storage/playbackIC  200 . 
     During the interrogation sequence, the battery voltage is monitored and the appropriate one of the addresses “0B” or “0C” are provided to the analog storage/playbackIC  200  at the specified point in the sequence. The detection of the magnet  130  causes the microprocessor  152  to suspend the periodic RF transmission of the battery depletion warning that would take place at other times if the battery  13  is depleted to the ERI voltage. Similarly, the detection of the magnet  130  causes the microprocessor  152  to suspend the periodic RF transmission of the drug depletion warning that would take place at other times if the drug quantity is depleted to the “Less than 2 days remaining” or a lower quantity. However, it will be understood that during the normal operation, these voiced statement or musical tone warnings at addresses “0A” and “0C” are transmitted to the radio. 
     The magnet  130  can be withdrawn to end the interrogation sequence or it can be left in place or rotated end to end to commence the programming sequence to increase or decrease the rate of delivery of the drug. In either case, the programming sequence commences with a rate increasing mode by providing the address “0F” to cause the RF transmission of the “rate increasing” voiced statement or the ascending scale musical tone. Then, within the time of a few seconds, the medical care giver can either leave the magnet  130  in place to continue in the rate increasing mode or reverse it end to end to cause the programming sequence to switch to a rate decreasing mode. In the former case, after a few seconds, the rate is incrementally increased by a command provided from the microprocessor  152 , and the current programmed rate is stored in RAM  154  for periodic use by digital controller/timer circuit  158  in the drug delivery routine. Then, the analog memory address for the A-D signal for the voiced statement of the increased rate is applied by the microprocessor  152  on the data and control bus  150  to the analog storage/playbackIC  200  to cause the retrieval and RF transmission of the voiced statement to the radio to confirm the rate change. At this point, assuming that the maximum rate has not been reached, the medical care provider can choose to increase the rate by the next rate increment by leaving the magnet  130  in place for a few seconds and by repeating the process. Or, the medical care provider can choose to terminate the programming sequence at the new programmed rate by simply removing the magnet  130  before the next rate change is retrieved and transmitted. A similar process is followed if it is desired to decrease the drug delivery rate by reversing the magnetic field and using the memory address “0F” to generate the descending scale musical tone or “Rate decreasing” voiced statement. 
     In this case of a configuration using the programming and interrogation system of FIG. 8, the patient  102  can also be provided with a magnet  130  and instructions to follow to increase or decrease a dug delivery therapy to treat pain, for example. In this case, it will be assumed that the IMD is programmed at manufacture with musical tones using the audible sound input  206  at addresses “00”, “0A”, “0D” rather than the equivalent voiced statements. The patient  102  is advised to apply the magnet  130  and to follow the above described routine until the ascending scale musical tone is heard. Then, the rate can be increased or decreased by following the steps described above. For safety reasons, the maximum rate that the patient can program may be limited in a manner described, for example, in commonly assigned U.S. Pat. No. 5,443,486 to Hrdlicka et al., incorporated herein by reference. 
     FIG. 12 is a chart depicting the memory address locations of A-D signals for transmitting voiced statements or musical tones in interrogation and programming sequences of an implantable electrical stimulator  160   h  of FIG. 10 having an operating system of FIG. 8 or FIG. 9 or a hard wired equivalent thereto. Such implantable electrical stimulators include but are not limited to stimulators to electrically stimulate the spinal cord, peripheral nerves, muscles and muscle groups, the diaphragm, parts of the brain, body organs and the like with electrical pulses delivered to electrodes located at the desired site of stimulation. Commercially available electrical stimulators of this type include the MEDTRONIC® Itrel Il® electrical stimulator, Itrel III® electrical stimulator, and the Matrix® electrical stimulator, and a dual channel Itrel® electrical stimulator. 
     The chart of FIG. 12 depicts the memory addresses for A-D signals for transmitting voiced statements or musical tones in an interrogation sequence of current IMD information at address locations “00”-“1D” and in a programming sequence of the programmable parameter values and modes at address locations “00”-“14” and “18”-“1D”. The chart of FIG. 12 also shows the memory address locations “0E” and “1F” for transmitting ascending scale and descending scale musical tones in a programming sequence for increasing or decreasing a stimulation parameter, e.g., pulse amplitude or pulse width or pulse rate or electrodes at address locations “00”-“14” and “18”-“1D”. In the interrogation and programming sequences, the medical care provider can commence the interrogation using either a programmer in the case of a configuration using the operating system of FIG. 9 or a magnet  130  in the case of a configuration using the operating system of FIG.  8 . The patient can be provided with a limited function programmer for programming one or more of the programmable parameter values and operating modes. 
     The following description assumes that a magnet programming and interrogation system is used and assuming that the IMD  100  of FIG. 1 is an electrical stimulator  160   h  with the lead  120  applied to a muscle other than the heart. The medical care provider applies the magnet  130  over the MAGFET  70  which produces either the N or S signal on line  72  or  74  of FIG.  8 . The logic circuit  78  responds by providing an interrupt to the microprocessor  152  to commence the interrogation routine. The memory address “15” is provided on bus  150  to analog storage/playback IC  200  which retrieves stored voiced statements identifying the IMD. Then, the interrogation routine sequentially selects the programmed one of the addresses “00”-“06” for the current pulse rate, “07”-“0E” for the current (I. e., previously programmed) pulse width, and “0F”-“14” for the current pulse amplitude. The interrogation continues with the selection of the address “16” or “17” for the battery condition, the address “18” or “19” for the cycle ON or OFF state, and the addresses “1A”-“1D” of the programmed electrode configuration. The A-D signals are applied to the AM/FM transmitter to cause the RF transmission of the voiced statements in these cases. In the illustration of FIG. 1, these retrieved voiced statements are transmitted and received, demodulated and emitted by the radio  142  to be heard by the medical care provider. 
     During the interrogation sequence, the battery voltage is monitored and the appropriate one of the addresses “16” or “17” are provided to the analog storage/playbackIC  200  at the specified point in the sequence. The detection of the magnet  130  causes the microprocessor  152  to suspend the periodic RF transmission of the battery depletion warning that would take place at other times if the battery  13  is depleted to the ERI voltage. However, it will be understood that during the normal operation, the voiced statement or musical tone warning at address “16” are applied to the AM/FM transmitter to cause the RF transmission of the voiced statement. In the illustration of FIG. 1, these retrieved voiced statements are transmitted and received, demodulated and emitted by the radio  142  to be heard by the medical care provider. 
     At this point, the magnet  130  can be withdrawn to end the interrogation sequence or it can be left in place or rotated end to end to commence the programming sequence to increase or decrease any of the programmable parameters, i.e., the pulse rate, width, amplitude, the cycle state and the electrodes. The programming sequence commences with a rate increasing mode by providing the address “1E” to cause the RF transmission of the “increasing value” voiced statement or the ascending scale musical tone. Then, within the time of a few seconds, the medical care giver can either leave the magnet  130  in place to continue in the increasing mode or reverse it end to end to cause the programming sequence to switch to a decreasing mode. A system of successive magnet placements and removals similar to that employed in the sequence illustrated in FIGS. 3A-3C can be employed to successively program each parameter value and operating mode. 
     Assuming that the stimulation pulse rate is being programmed to an increased pulse rate, after continued application of the magnet for a few seconds, the pulse rate is incrementally increased by a command provided from the microprocessor  152 . The new current programmed pulse rate is stored in RAM  154  for periodic use by digital controller/timer circuit  158  in the stimulation delivery routine. Then, the address “1E” for the A-D signal for the voiced statement of the increased rate is applied by the microprocessor  152  on the data and control bus  150  to the analog storage/playback IC  200  to cause the RF transmission of the voiced statement or ascending scale musical tone to confirm the rate change. At this point, assuming that the maximum pulse rate has not been reached, the medical care provider can choose to increase the pulse rate by the next rate increment by leaving the magnet  130  in place for a few seconds and by repeating the process. Or, the medical care provider can choose to terminate the programming sequence at the new programmed pulse rate by simply removing the magnet  130  before the next rate change is retrieved and transmitted. A similar process is followed if it is desired to decrease the drug delivery rate. 
     In this case of a configuration using the programming and interrogation system of FIG. 8, the patient  102  can also be provided with a magnet  130  and instructions to follow to increase or decrease a drug delivery therapy to treat pain, for example. In this case, it will be assumed that the IMD is programmed at manufacture with musical tones using the audible sound input  206  at analog memory addresses “1E”, and “1F”, rather than the equivalent voiced statements. The patient  102  is advised to apply the magnet  130  and to follow the above described routine until the ascending scale musical tone is heard. Then, the rate can be increased by leaving the magnet in place while the ascending scale musical tone continues or decreased by reversing the polarity of the magnetic field and listening for the decreasing scale musical tone. 
     These embodiments of the present invention depicted in FIGS. 8-10 and employing IC  200  of FIG. 6 are described above in the context of a micro-computer based IMD operating system where the programming and interrogation sequences are governed by algorithms stored in ROM  156  and that cooperate with logic circuitry and registers in the digital controller/timer circuit  158 . The algorithm takes the place of the timing control circuit  202  and the address generation circuit  204  and the interconnections therebetween and with the analog storage/playback IC  200  of FIG.  5 . It will be understood that such a circuit of FIG. 5 could be employed in a micro-computer based operating system. Conversely, it will be understood that these embodiments can also be practiced in a hardware based system that does use the circuit of FIG. 5 to sequentially address the analog memory addresses in the sequences described above with reference to FIGS. 11 and 12 and in other sequences that can be devised using the therapy delivery and monitoring systems of FIG.  10 . 
     The preceding specific embodiments are therefore to be understood as illustrative of the many ways in which the principles of the invention may be practiced. It is to be understood, therefore, that other expedients known to those of skill in the art or disclosed herein may be employed without departing from the invention or the scope of the appended claims. 
     It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described without actually departing from the spirit and scope of the present invention.