Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
  • A61N1/00—Electrotherapy; Circuits therefor
  • A61N1/18—Applying electric currents by contact electrodes
  • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
  • A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
  • A61N1/372—Arrangements in connection with the implantation of stimulators
  • A61N1/37211—Means for communicating with stimulators
  • A61N1/37252—Details of algorithms or data aspects of communication system, e.g. handshaking, transmitting specific data or segmenting data
  • A61N1/3727—Details of algorithms or data aspects of communication system, e.g. handshaking, transmitting specific data or segmenting data characterised by the modulation technique

Definitions

• the present invention generally relates to
• implantable medical devices and more particularly, pertains to telemetry schemes for percutaneously
• the communication between the implant and the external world was at first primarily indirect.
• the operation of an implantable cardiac pacer could be observed, for example, in the electrocardiogram of the patient.
• data could be sent from the implanted cardiac pacer by modulating the stimulation pulses in some manner. This can only provide a low bandpass channel, of course, without interfering with the clinical application of the device.
• Change of the pacing rate to indicate battery condition was a commonly used application of this technique.
• the data to be transmitted is of two basic types, namely, analog and digital.
• the analog information can include, for example, battery voltage, intracardiac electrocardiogram, sensor signals, output amplitude, output energy, output current, and lead impedance.
• the digital information can include, for example, statistics on performance, markers, current values of programmable parameters, implant data, and patient and unit identifiers.
• RF telemetry systems are known to be used in connection with implantable medical devices, such as cardiac pacemakers.
• An example of a pulse interval modulation telemetry system used for transmitting analog and digital data, individually and serially, from an implanted pacemaker to a remote programmer is disclosed in U.S. Patent No. 4,556,063 issued to Thompson et al., herein incorporated by reference.
• An example of a modern pacemaker programmer for use with programmable cardiac pacemakers having RF telemetric capabilities is disclosed in U.S. Patent No. 4,550,370 issued to Baker, herein incorporated by reference.
• the telemetry format which is used under these systems, as well as other prior telemetry systems have not been entirely adequate for reasons described above and a need for significant improvement has continued. As will become apparent from the following, the present invention satisfies that need.
• the present invention percutaneously transmits all data from the implantable medical device in a digital format. It is pulse position modulated on an RF carrier. To accomplish this, the analog quantities must be
• electrocardiograms or before storage in the memory of the device, as in the case of historical values of pacing rate for subsequent transmission for trend analysis.
• the data to be sent is initially analog or digital, it is transmitted in the same format, i.e., as digital information.
• the RF carrier is pulse position modulated to conserve battery energy. In this manner, only a short burst of the carrier, e.g., one cycle, is actually needed to transmit a given unit of data. The time position of that burst relative to a synchronizing standard determines the value of the data unit
• a frame of about 2 milliseconds is defined. Within this frame are positioned a synchronizing burst, a frame identifier burst, and one or more data bursts.
• the synchronizing burst is positioned at a fixed position in the frame.
• the frame identifier and data are variables, such that the corresponding bursts occur within a range of time within the frame.
• the range in which a burst is found defines the nature or type of the variable.
• the position in the range defines the value of the variable.
• the transmission protocol provides data rates which are sufficient to transfer clinically useful EGM
• This modulation scheme provides flexibility of use, for example, with complex medical devices where transmission of increased volumes of data is desirable in real time, such as cardiac devices having dual-chamber or multisensor capabilities, and for controlling particular conditions such as tachyarrhythmia.
• FIG. 1 is a simplified schematic view of an
• FIG. 2 is a conceptual view of one frame of the improved telemetry format of the present invention
• FIG. 3 is a view of the actual transmission pattern of two frames of the improved telemetry format
• FIG. 4 is a block diagram of a portion of an
• implantable medical device for implementation of the improved telemetry format
• FIG. 5 is a simplified flowchart showing the basic function of software to perform the telemetry uplink operation of the improved telemetry format
• FIG. 6 is a block diagram of the circuitry of the telemetry uplink hardware for implementing the improved telemetry format
• FIG. 7 is a block diagram of the circuitry of the telemetry timing for implementing the improved telemetry format.
• FIG. 8 is a schematic diagram of the driver
• a preferred embodiment of the present invention is disclosed relating to use of the improved telemetry format with an implantable cardiac pacer, which may be programmable.
• an implantable cardiac pacer which may be programmable.
• those of skill in the art will be readily able to adapt the teachings found herein to other implantable medical devices.
• the telemetry format taught herein can be used for bi-directional
• FIG. 1 is a simplified schematic diagram of the present invention as employed in a cardiac pacing system.
• An implantable pulse generator 10 is implanted in the patient under the outer skin barrier 28.
• Implantable pulse generator 10 is electrically coupled to the heart of the patient using at least one cardiac pacing lead 12 in a manner known in the art.
• Percutaneous telemetry data is transmitted from implantable pulse generator 10 by an RF uplink 26 utilizing the improved telemetry format to a receiving antenna 22, which is coupled to a programmer 20 via a cable 24.
• Receiving antenna 22 also contains a magnet which activates a reed switch in implantable pulse generator 10 as a safety feature, as taught in U.S. Patent No. 4,006,086 issued to Alferness et al., herein incorporated by reference.
• the telemetry data is demodulated and presented to the attending medical personnel by programmer 20.
• FIG. 2 is a schematic diagram of the protocol of RF uplink 26 using the improved telemetry format.
• the uplink uses a damped 175 kilohertz RF carrier which is pulse position modulated, as described in detail below.
• Shown at 30, the basic timing unit of the format is a frame, having a duration of t n5 . It will be understood by those skilled in the art, however, that the present invention can be practiced using fixed-length frames having periods of shorter or longer duration.
• implantable pulse generator 10 comprises a standard
• a unique synchronizing signal is positioned within a first fixed range of each frame 30. This signal
• a synchronizing RF pulse 32 which is located at a time t n1 within frame 30. To properly function as a synchronizing pulse, it must be located at a fixed point within the first fixed range of frame 30, as shown at 34.
• a four-bit frame identifier code is positioned within a second fixed range of each frame 30, such second fixed range comprising an identifier range 38.
• Identifier range 38 uses a total of eleven basic clock cycles as shown.
• This identifier code comprises an identifier RF pulse 36 which is pulse position modulated within the identifier range 38. The position of
• identifier pulse 36 within identifier range 38 identifies the nature or type of data found within each frame 30 which is being transmitted, such as peak sense, peak pressure, sense threshold and others, as described in further detail below. Shown at 40, time interval t n2 thus uniquely represents the value of identifier pulse 36, which value in turn identifies the data type being transmitted within frame 30.
• Each frame 30 transfers one eight-bit byte of data along with the identifier code. This data is divided into two portions comprised of four bits of data each. A first portion of this data, namely the four least
• a second portion of this data namely the four most significant bits of the data byte, is positioned within a fourth fixed range of frame 30, such fourth fixed range comprising an upper nibble range 48.
• a lower nibble pulse 42 is pulse position modulated within lower nibble range 44, such that its value is uniquely identified by its location, such as at a time t n3 shown at 45.
• An upper nibble pulse 46 is also pulse position modulated within upper nibble range 48, such that its value is uniquely identified by its location, such as at a time t n4 shown at 50.
• Lower nibble range 44 and upper nibble range 48 each comprise sixteen basic clock cycles, permitting each of the sixteen unique values of the four-bit nibble to be specified.
• suitable guardbands are positioned between each of the ranges within the frame to uniquely identify the synchronizing pulses, thereby avoiding undefined and erroneous data transmission.
• FIG. 3 is a diagram of two frames of RF uplink 26, wherein a first frame corresponds to Word 1 shown at 70, and a second frame corresponds to Word 2 shown at 72. A count of clock cycles is indicated along an upper
• Each basic clock cycle has a duration of 30.52 microseconds.
• the first frame at 70 is initiated by an RF pulse 52.
• a synchronizing RF pulse 54 is shown uniquely identified as precisely four clock cycles later. Because the
• Synchronizing pulse 54 is used to provide frame synchronization between the transmitter (i.e., implantable pulse generator 10) and the receiver (i.e., programmer 20).
• An identifier RF pulse 56 is located within
• identifier range 38 which range is defined as nine to nineteen basic clock cycles from the beginning of frame 70.
• identifier pulse 56 is located at clock cycle nineteen. This identifies the frame as a particular type of data transfer, namely, "Sense Threshold" as indicated in Table 1 below.
• a lower nibble RF pulse 58 is located within lower nibble range 44, which range is defined as twenty-four to thirty-nine basic clock cycles from the beginning of frame 70.
• lower nibble pulse 58 is located at clock cycle thirty-one, specifying a binary value of seven on a scale of zero to fifteen.
• An upper nibble RF pulse 60 is located at clock cycle fifty-eight within upper nibble range 48, which range is defined as forty-four to fifty-nine basic clock cycles from the beginning of frame 70, and is demodulated in similar fashion.
• FIG. 4 is a block diagram of that portion of
• implantable pulse generator 10 which is associated with formatting and transmission of RF uplink 26.
• Most of the unique hardware which embodies the present invention is located on a single substrate, being a custom chip device indicated generally by arrow 105.
• the remainder is microprocessor-based logic indicated generally by arrow 100, comprising microprocessor 102, random access memory (RAM) 104, and parallel bus 106.
• RAM random access memory
• microprocessor-based logic 100 is described in further detail below.
• Chip 105 has an analog-to-digital (A/D) converter 108 which receives a number of analog inputs 110 from a multiplexer (not shown).
• A/D converter 108 permits data to be transferred via RF uplink 26 to be digitized as necessary, so that all data is transmitted in a
• Circuitry (CRC) for generating and analyzing the cyclic redundancy code used to forward error detect telemetry data transmitted over RF uplink 26 is indicated at 112. In the preferred embodiment, it is also used for data received by implantable pulse generator 10 via a downlink (not shown). Circuitry (DMA) for providing direct memory access to RAM 104 is indicated at 114, thus permitting multiple byte transfers without constant management by microprocessor 102.
• Data buffer 116 includes storage for twelve bits of data. This storage is partitioned into a four-bit section 119 for storage of the frame identifier code, and an eight-bit section 117 for storage of the lower nibble and upper nibble of a frame. Data buffer 116 thus stores all of the variables for one complete frame. Data buffer 116 is used to stage the variables for the frame which may be received from RAM 104, A/D converter 108, CRC 112, or elsewhere along parallel bus 106.
• Telemetry control 120 consists primarily of a telemetry status register. This register stores the telemetry commands and status as loaded by microprocessor 102. The contents of the register are thus used to gate the data at the proper time of the defined protocol.
• Up-link timing 118 decodes the twelve bits of data stored in data buffer 116 to produce a set of timing signals which key bursts of RF energy at the appropriate times to pulse position modulate the 175 kilohertz carrier. Up-link timing 118 also keys bursts of RF energy at the fixed positions within the frame
• FIG. 5 is a basic flowchart showing the overall function of the microprocessor-based logic 100. The role is essentially one of initiation of the transfer, rather than management of each detail of the transmission.
• Software associated with RF uplink 26 is started at element 130, usually by a down-linked command to transfer data.
• Element 132 schedules the requested transmission via the up-link facilities. This scheduling prioritizes uplink transmission requests. Lower priority is given to continuous real time transfers, such as EGM and battery voltage, whereas higher priority is given to single occurrence transmissions of status information.
• element 134 determines whether an uplink transmission is currently in progress. If an uplink transmission is in progress, element 132 reschedules the request.
• element 136 initiates the uplink transmission by activating telemetry control 120. Exit is via element 138. While some additional management of the process is required during the transmission, a description of such further details has been omitted, since it is not
• FIG. 6 is a block diagram showing the major data and control signals of telemetry control and data buffer 121 (which includes data buffer 116 and telemetry control 120 shown in FIG. 4), and also of up-link timing 118.
• a primary function of data buffer 116 is the staging of the twelve variable bits of a given frame which correspond to a four-bit frame identifier ID, and dual-nibble data comprising a four-bit lower nibble LN and a four-bit upper nibble UN.
• the data is received over an eight-bit, parallel bus 159 and can be from any one of several sources.
• Control lines EGMDATA at 150, PRSDATA at 151, DLDMA at 153, DMADS at 155, LDANDAT at 156, ENCRC at 161 and LDCRC at 171 specify the source.
• the output of A/D converter 108 of FIG. 4 is presented separately to data buffer 116 as an eight-bit parallel transfer to ADC(0-7) at 154 (see FIG. 6).
• the output of CRC 112 is presented separately to data buffer 116 as an eight-bit parallel transfer to CRC(0-7) at 160, since those devices are located on the same substrate.
• Telemetry control 120 outputs a number of control signals, including EGMGAIN at 162, RVPGAIN at 163,
• EGMTELEN at 164, ANULON at 165, RAMULON at 166, MEMEN at 167, PRSTELEN at 168, HDRCRCEN at 169 and EGMNPRS at 170.
• These control outputs are used to enable and control inputs to data buffer 116.
• the key outputs of telemetry control and data buffer 121 are TELRST at 182, which resets up-link timing 118 and initiates the beginning of a frame, and a parallel data transfer at 184, which transfers the frame identifier ID, lower nibble LN and upper nibble UN to up-link timing 118.
• Up-link timing 118 receives the frame-initiating control signal TELRST at 182 and the parallel data transfer (ID, LN and UN) at 184.
• a primary function of up-link timing 118 is to key the transmission of 175 kilohertz RF energy at the proper times to indicate start of frame, frame synchronization, frame identifier, lower nibble and upper nibble. Timing for this function is provided by the 32.768 kilohertz crystal clock to uplink timing 118 with clock signal XTAL at 186.
• An output TELCLK is provided at 188 which keys the actual burst of RF carrier at the proper times.
• FIG. 7 is a block diagram of up-link timing 118.
• a frame timing generator 202 provides the desired timing for a frame according to clock input XTAL at 186, in a manner hereinabove explained. Thus, each frame is comprised of sixty-four basic clock cycles. The process is initiated by receipt of the frame-initiating control signal TELRST at 182, which enables uplink when in a low state and disables uplink when in a high state.
• the initial clock cycle of a frame contains a burst of RF energy which is keyed by control signal TELCLK at 188, which is also used to trigger the start of the data decoding by an uplink word multiplexer 200.
• a telemetry pulse timer 204 determines the appropriate timing for a burst to be provided to frame timing generator 202, and a
• Each of the four-bit quantities thus results in the keying of a burst of RF energy at the appropriate time within each frame.
• FIG. 8 is a circuit diagram for the drive circuit for generating the RF carrier.
• a control signal TELCLK at 188 provides the timing information for keying the carrier.
• a non-overlap generator 220 functions as a delay device to save current by preventing output
• control signal TELCLK at 188 causes one transition by non-overlap generator 220.
• Inverters 222, 224, 226 and 228 are scaled to provide efficient switching with sufficient drive to the gates of
• Transistors 230 and 232 drive the signal off of chip 105 to ANTDR at 234 to an antenna circuit.
• a tuned circuit of discreet components, capacitor 236 and coil 238, are located external to chip 105. Each transition thus causes this tuned circuit to resonate at 175 kilohertz, thereby generating one uplink burst.
• mag_state EQU 6 0006 401 mag_state EQU 6 ;Magnet state, mode and rate are
• uplink_memory EQU 6 'Uplink include memory block
• Uptiink includes CRC and header
• This macro uplinks the interrogate block of size INTRRG_SIZ and *
• statbyt uplnk_stat
• This macro is used to uplink measured values.
• the TLM module processes magnet mode operations while the reed *
• the uplink consists of confirmation and confirmation + *
• Routines defined in this module include: *
• uplink_flags UPLNK GN_SET
• uptnk_stat (uplnk_stat AND UPLNK_CLR_MSK);
• uplnk_stat uplnk_stat OR DNLK_OVF_ERR;

Landscapes

• Health & Medical Sciences (AREA)
• Engineering & Computer Science (AREA)
• Biomedical Technology (AREA)
• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
• Radiology & Medical Imaging (AREA)
• Life Sciences & Earth Sciences (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Mobile Radio Communication Systems (AREA)
• Electrotherapy Devices (AREA)
• Selective Calling Equipment (AREA)
• Radio Relay Systems (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=23859694

Family Applications (1)

Country Status (5)

Families Citing this family (14)

Family Cites Families (5)

• 1991
  • 1991-01-15 EP EP19910904210 patent/EP0512058A1/de not_active Ceased
  • 1991-01-15 JP JP50439991A patent/JPH05503646A/ja active Pending
  • 1991-01-15 WO PCT/US1991/000309 patent/WO1991010471A1/en not_active Application Discontinuation
  • 1991-01-15 AU AU72595/91A patent/AU636962B2/en not_active Ceased
  • 1991-01-15 CA CA 2070432 patent/CA2070432A1/en not_active Abandoned

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events