CA1183576A - Telemetry system for a medical device - Google Patents
Telemetry system for a medical deviceInfo
- Publication number
- CA1183576A CA1183576A CA000387385A CA387385A CA1183576A CA 1183576 A CA1183576 A CA 1183576A CA 000387385 A CA000387385 A CA 000387385A CA 387385 A CA387385 A CA 387385A CA 1183576 A CA1183576 A CA 1183576A
- Authority
- CA
- Canada
- Prior art keywords
- analog
- digital
- information
- current level
- tank circuit
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
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
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/0002—Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network
- A61B5/0004—Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network characterised by the type of physiological signal transmitted
- A61B5/0006—ECG or EEG signals
-
- 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
-
- G—PHYSICS
- G08—SIGNALLING
- G08C—TRANSMISSION SYSTEMS FOR MEASURED VALUES, CONTROL OR SIMILAR SIGNALS
- G08C19/00—Electric signal transmission systems
- G08C19/16—Electric signal transmission systems in which transmission is by pulses
- G08C19/24—Electric signal transmission systems in which transmission is by pulses using time shift of pulses
Landscapes
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Public Health (AREA)
- Biomedical Technology (AREA)
- Veterinary Medicine (AREA)
- Animal Behavior & Ethology (AREA)
- General Health & Medical Sciences (AREA)
- Physics & Mathematics (AREA)
- Radiology & Medical Imaging (AREA)
- Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
- Pathology (AREA)
- Physiology (AREA)
- Computer Networks & Wireless Communication (AREA)
- Biophysics (AREA)
- General Physics & Mathematics (AREA)
- Heart & Thoracic Surgery (AREA)
- Medical Informatics (AREA)
- Molecular Biology (AREA)
- Surgery (AREA)
- Electrotherapy Devices (AREA)
- Measurement Of The Respiration, Hearing Ability, Form, And Blood Characteristics Of Living Organisms (AREA)
Abstract
ABSTRACT
Conventional digital modems have not been applicable to pacemaker telemetry systems since their use would require the periodic conversion of analog data to a numerical value prior to transmission. In contrast, the pulse interval telemetry system of the present invention is capable of transmitting analog data without conversion to a numerical value, and is capable of sequentially transmit-ting both digital and analog data. This data is individually and serially trans-mitted in either an analog or digital format to a remote receiver. The apparatus of this invention includes a resonant tank circuit for producing a radio frequen-cy carrier signal. This tank circuit is operative at periodic intervals deter-mined by the output frequency or period of a variable frequency oscillator (VFO).
Thus, the VFO output modulates the time interval between consecutive pulses of the carrier signal. Sources of digital and analog information are interfaced to the VFO to vary the VFO output period. In the digital mode the VFO output is varied to a first preselected period to encode a logic one) and to a second pre-selected period to encode a logic zero. In the analog mode the VFO output is continuously variable over a limited range about a nominal time period to encode the analog data. An additional feature of the invention is the use of the VFO
output to synchronize the translation of digital data from a parallel format in memory to a serial format suitable for telemetry transmission.
Conventional digital modems have not been applicable to pacemaker telemetry systems since their use would require the periodic conversion of analog data to a numerical value prior to transmission. In contrast, the pulse interval telemetry system of the present invention is capable of transmitting analog data without conversion to a numerical value, and is capable of sequentially transmit-ting both digital and analog data. This data is individually and serially trans-mitted in either an analog or digital format to a remote receiver. The apparatus of this invention includes a resonant tank circuit for producing a radio frequen-cy carrier signal. This tank circuit is operative at periodic intervals deter-mined by the output frequency or period of a variable frequency oscillator (VFO).
Thus, the VFO output modulates the time interval between consecutive pulses of the carrier signal. Sources of digital and analog information are interfaced to the VFO to vary the VFO output period. In the digital mode the VFO output is varied to a first preselected period to encode a logic one) and to a second pre-selected period to encode a logic zero. In the analog mode the VFO output is continuously variable over a limited range about a nominal time period to encode the analog data. An additional feature of the invention is the use of the VFO
output to synchronize the translation of digital data from a parallel format in memory to a serial format suitable for telemetry transmission.
Description
S7~
This invention relates to implantable medical devices such as pace-makers, and more particularly, to a telemetry system for transmitting information from the pacemaker to a remote receiver for diagnostic purposes.
Pacemakers for providillg stimulating pulses to the heart in the absence of natural cardiac activity are well-known. ~riginally, such pacemakers were fabricated from discrete analog componen~s. More recently designed pace-makers employ digital circuitry realized in monolithic form. The additional com-plexity resulting from monolithic digital implementation has been used to provide desirable pacemaker features, including programmability. One exarnple of such prior art is United States Patent No. ~,276,8~3 to McDonald et al. issued July 7, 1981. This Patent discloses a pacemaker having a number of programmable fea-tures including the pacing rate and pulse width. Information concerning these operating parameters is stoTed in digital form in the pacemaker's memory. After implantation it is desirable to read out these memory locations Eor diagnostics purposes. ~dditional information which is useful for diagnostic purposes, such as lead impedance, battery voltage, and the patient's intracardiac electrogram are inherently analog in nature and not directly compatible with the other digi~
tal information within the pacemaker. Consequently, conventional digital modems have not been applicable to pacemaker telemetry systems since their use would require the periodic conversion of the aforementioned analog data to a numerical value prior to transmission.
In contrast, the pulse interval telemetry system oE the present invention is capable of transmitting analog data without conversion to a numeri-cal value, and is capable of sequentially transmitting both digital and analog data. This data is individually and serially transmitted in either an analog or digital format to a remote receiver.
The apparatus of this invention includes a resonant tank circuit for producing a radio frequency carrier signal. This tank circuit is operative 7~
at periodic intervals determined by the output frequency or period of a variable frequency oscillator (VF0). Thus, the ~FO output mod~llates the time interval between consecutive pulses of the carrier signa].
Sources of digital and analog information are interfaced to the VF0 to vary the VF0 output period. In the digital mode the VFO output is varied to a first preselected period to encode a logic one, and to a second preselected period to encode a logic zero. In the analog mode the VF0 output is continuously variable over a limited range about a nominal time period to encode the analog data.
An additional feature of the invention is the use of the VF0 output to synchronize the translation of digital data from a parallel format in memory to a serial format suitable for telemetry transmission.
Thus 9 in accordance with one broad aspect of the invention, there is provided a pulse interval modulation telemetry system for sequentially transmitting analog and digital information from an implantable medical device to a remote rece:iver comprising an energy storage capacitor means, a resonant tank circuit and antenna means for providing an oscillatory signal upon the application of a burst of energy thereto, variable frequency oscillator means responsive to the charging rate of said energy storage capacitor means for periodically energizing said tank circuit and antenna means with said bursts oE energy, and circuit means comprising a plurality of current sources for selectively estab:lishing charging rates for sa:Ld storage capacitGr means which correspond respectively to a logic one and logic zero levels of said digital information and the instantaneous value oE said analog information relative to at least one nominal reference value, wherein said circuit means is constructed to respond to three input control signals so as to establish said first preselected interval with a first one 3~ii7~
of said control signals, said second preselected interval with a second one of said control signals and said nominal value with a third one of said control signals.
In accordance with another broad aspect of the in-vention, there is provided a pulse interval modulation telemetry system for transmitting elther analog or digital information from an implantable pacemaker compris-ing a resonant tank circuit and antenna means for generating a oscil].atory signal upon the application of a burst of energy thereto, circuit means controlled by an input current level comprising a variable frequency oscillator means constructed to provide energization to said resonant tank circuit and antenna means for time intervals that are determined by the magnitude of said input current level which may assume first and second values, which correspond to logic one and logic zero digital information, and to an instantaneous value relative to at least one nominal reference ~alue, which corresponds to analog information, wherein said energization to said tank circuit and antenna means is supplied by said variable frequency osci'lator means.
In accordance with another broad aspect oE the invention there is provided, in a transmitter for transmitting signals from an implantable medical device which are representative of either analog or digital values comprising a signal controlled variable frequency oscillator means having a control terminal, signal application means Ear selectlvely presenting information signals representa-tive o:E said digital and analog ~lues to said control terminal to vary the frequency of said oscillator means in response thereto relative to a nominal output frequency of said oscillator 33~7~
means that exists when said information signals are not being supplied, a tank circuit and antenna means having a predetermined ringing frequency of oscillation when pulsed with energy, and drive circuit means coupled to said oscillator means and to said tank circuit and antenna means for supplying pulses o:E energy to said tank circuit and antenna means a-t a rate that is proportional to the output frequency of said oscillator means whereupon said pulses are radiated :Erom said tank circuit and antenna means as damped ringing signals; the improvement wherein said signal application means comprises a selectively activated digital signa.l means which in a first o state provides a first digital current level s;.gnal to said control terminal that is representative of a digital "one" and in a second state provides a second digital current level signal to said control terminal that is re-presentative of a digital "zero"J firs~ and second sources of analog in$ormation, a selectively actuated analog signal means which, when selected provides either a first analog current level signal in accordance with the information content of said first source or a second analog current level signal in accordance with the information content of said second source, means for selecting either said first or said second analog current level signal and means -~r selectively adding said first digital current level signal to said first analog current level signal and for selectively adding said second digital current level signal to said second analog current level signal and means for providing said added current level signals to said con~
trol terminal.
~ 3a ;
3~
The invention will now be further discussed in conjunction with the accompanying drawings, in which:
FIGU~E 1 is a block diagr~m of the function elements of the system for encoding and transmitting information from the implanted medical clevice.
FIGURE 2 is a truth table showing the relationship between the encoding scheme and the corresponding states of the various current sources of the system;
FIGURE 3 is a waveform diagram showing the analog and digital data format; and FIGURE 4 is a schematic diagram showing the VFO, and current sources in a form suitable for implementation in a bipolar integrated circuit.
- 3b -3~ir76 As previously described, the pulse interval modulation telemetry system is used to transmit analog and digital information from the implanted medical device to a remote receiver. In the context of a pacemaker application the analog information may include battery voltage, lead impedance, or the patient's intracardiac electrogram. Similarly, typical digital data may include programmed pulse width and rate settings as well as iclentification information. An example oE a pacemaker suitable for use as a source of digital information is taught by the previously mentioned United States Patent No. 4,276,883. This ~ ~33~
application discloses a digit lly imp]emented pacemaker having memory for storing digi~ally programmed information shown in FIGURE 6H of th~ reference patent.
This information is stored in a parallel format as a sequence of binary digits.
A suitable source for analog information such as the patient's intracardiac electrogram may be found in United S~ates Patent No. 4,266,551 to Stein et al., issued May 12~ 1981. The circuitry disclosed in this patent may be used to provide a source of intracardiac analog information to the telemetry system of the present inventionO
As shown schematically in FIGURE 1 the heart 10 has an indwelling catheter 11 for sensing cardiac depolarizations and for stimulating cardiac tissue~ Pacer logic receives signals via sense amplifier 34 and delivers stimu-lating pulses by way of output amplifier 33. The pacer logic 12 shown operates under the control of parameter data stored in memory 15. The memory 15 contains the parameter data in parallel form which is seriali~ed for data transmission by shift register 16 which forms a portion of the telemetry system.
In opera~ion~ the transmission of data is remotely initiated by the closure of a magnetically actuated reed switch within the pacemaker in the well-known manner. DigitaL data is then transmitted twice to a remote receiver where it is decoded and checked for errors. The digital data transmission is followed by the transmission of analog data in an analog format. The ~elemetry system is disabled by removing the magnet from the pacemaker site which opens the reed switch and disables the telemetry circuitry.
Additionally, the telemetry circuitry of the present invention in-cludes a receiver blanking circuit which permits the transmission of analog or digital data to be interrupted by the remote programmer thus truncating the transmission of telemetry information so that the pacemaker may receive higher priority programming information from the remote programmer. This function is ~ ~35i7~
achieved by digital circuitry which detects the presence of a lohg duration burst of ~E energy from the remote programmer which is received by the pacemaker and which is decoded to turn off the ~elemetry transmission systems and ~o prepare the digi~al circuitry for the reception of program~ing information from the re-mote programmer.
Oscillators . . _ Referring to FIGURE 1 the radio frequency carrier signal is devel-oped by a radio frequency oscillator tank in FIGURE 1. The tank circuit 1~ is energized at periodic intervals determined by a variable frequency oscillator ~VFO) 12. Radio frequency energy from the resonant tank circuit 1~ is coupled to antenna 16 which radiates this energy to a remote receiver (not shown).
The repetition rate of the variable frequency oscillator is set by a number of cooperating current sources which establish a net charging rate at the input node 18 of the VFO 12. When operating in the digi~al mode for the transmission of digital information the current sources establish a first char-acteristic charging rate for encoding a logic one and a second characteristic charging rate for encoding a logic zero.
As shown in FIGURE 1, three cooperating current sources 26, 28 and 30, are energized by control logic, operating swi~ches 20, 22, 2~. When each of these current sources is turned on, a chara~teristic current I, .5I or .25I is supplied to the capacitor 32 which establishes a voltage at node 18. When the voltage on capacitor 32 reaches a trip level, the VFO ou-tput will change state initiating a burst of RF energy from the tank circuit 1~. Consequently, the time period between successive bursts of radio frequency energy will be deter-mined by the number of current sources which are on. The truth table FIGURE 2 indicates the relationship between the encoding scheme of the present invention and the states of the various current sources. As indicated in the diagraml the 35i7~
logic "one" signal is encoded by energizing current source 30 by closing switch 24, which provides a constant cwrrent charging rate to capacitor 32 of magnitude I. In the preferred embodiment this characteristic charging ra~e results in a pulse interval of 1,000 microseconds. Similarly, a logic "zero" is encoded by energizing the two current sources 28 and 30 resulting in a net charging current of 1.5I which results in a shorter, 667 microsecond pulse interval. This is accomplished by closure of switches 22 and 2~.
In the analog mode, an alternate pair of current sources 26 and 30 are energized to provide a nominal charging rate corresponding to an 800 micro-second pulse interval. A suitable analog signal such as the intracardiac electro-gram derived from the pacemaker lead system is used to modulate one of the current sources 26 to vary the nominal charging rate in a positive or negative direction.
This current modulation results in a varying pulse interval which corresponds to the amplitude variations of the intracardiac signal.
As shown in FIGURE 3, digital data corresponding ~o a serial stream of logic one and logic zeroes is encoded by time periods between shorter and longer time period between bursts of radio frequency energy. It is important to note that the longer interval of 1,000 microseconds is not an even multiple of the shorter time period of 667 microseconds used to encode a logic zero. This scheme results in a lower error rate than systems wherein the logic zero and logic one are related as integer multiples. As shown in the lower analog traces of FIGURE 3, a nominal time period of 800 microseconds corresponds to the zero level of the analog signal to be transmitted. Bositive and negative excursions indicated by the phantom wave traces are used to encode the minimum and maximum excursions about the nominal value.
Although the telemetry system has been described with reference to only a single analog channel, it should be clear that a time division multiplex-~83~ii76 ing scheme could be employed to simultaneously transmit more than one channel of analog data 36 as shown in FIGURE 1. The sequential transfer of more than one analog channel is desirable for use with dual chamber pacemakers whose perform-ance depends upon intrinsic at~ial and ventricular el~ctrogr~ns. One possible scheme for achieving this time division multiplexing is using a multiplexor 35, shown in FIGURE 2 wherein an additional analog channel, labelled "Analog B") is encoded by activating both current sources 28 and 26.
In a similar fashion, other analog signal sources 36 such as lead impedance or battery voltage could be suitably buffered and applied to variable current source 26 to establish a charging rate proportional to ~he analog signal.
Control Lo~ic and Current Sources The block diagram of FIGURE 1 shows the two constant current sources 28 and 30 and one variable current source 26 energized by suitable switching means interfaced to control logic 38. In practice, the switching and current sourcing function may be combined by the use of bipolar transistors which have a characteristic collector-emitter current which corresponds to the magnitude of injected basa current. One suitable bipolar implcmentation for these current sources is shown in FIGURE 4. Referring now to FIGURE ~ the op0ration of this circuit is initiated by a reed switch closure connecting node lOO to the positive supply voltage. This connection supplies bias current to transistors 102, 104, 106, 108 which, in turn, supply bias current to transistors 110, 111, 112, 113, 114, 116~ 118, 120 and to transistors 122, 124 and 126. Input node 99 inter-faces the current source system with the sources of digital and analog data.
This node 99 is connected to the positive supply voltage through a tri-state buffer when a logic "zero" is to be transmitted. The node 99 is connected to ground through the tri-state buffe-r for the transmission o~ "analog" information.
The node 99 is disconnected and is floating when the tri~state buffer is in the _~_ 7~`
high impedance configuration for the transmission of a logic "one".
For the transmission of a logic "one"~ transistor 118 is off and transistor 120 supplies approximately 225 nanoamps of current to the junction of the base of transistor 128 and the VF0 capacitor 32. Assuming that capacitor 32 is near ground pote~tial, then transistors 129, 130, 132, 134 and 136 are off.
The voltage on capacitor 32 increases because of the charging current supplied by transistor 120 until ~he bases of transis~ors 128 and 129 are equal. This allows current flow in transistors 129 and 138. When the collector-emi~tter cur-rent of transistor 129 exceeds the current flow through transistor 138, excess current flows into transistor 134, which turns it on. This, in turn, turns on transis~or 136 which sinks current through the tank circuit 14 and causes the emission of a pulse of radio frequency. The circuit formed by transistors 130, and 134 form a latch arrangement which will not change state until the capacitor 32 discharges to approximately 0.5 volt whereupon these transistors shut off.
The discharge of capacitor 32 takes approximately 2 microseconds and determines the time transistor 13G is on, which determines the width of the pulse applied to the tank circuit. When capacitor 32 is discharged, transistor 129 is off and *ransistor 128 is on which permits the cycle to begin again.
When a logic "one" is applied to input node 99, transistor 118 is activated which adds additional current to the VF0 input node 18, shortening the time required to reach the trip level of the VF0 circuit, thus shortening the pulse interval time to approximately 667 microseconds.
When input node 99 is grounded through the operation control logic, the analog transmission mode is enabled and an analog voltage signal applied to the base of transistor 142 is converted to a proportional charging current by transistors 142, 144, 1~6, 148, 140. As the analog voltage varies, the current of transistor 148 is modulated and the result of pulse interval is shifted with ._9_ 3S7~
respect to the nominal 800 microsecond pulse interval.
Although the current sources and VFO have ~een shown implemented in bipolar technology, it should be appreciated that equivalent structures exist in other technologies including metal oxide semiconductor technologies, and that other modifications may be made without departing from the scope of the invention.
This invention relates to implantable medical devices such as pace-makers, and more particularly, to a telemetry system for transmitting information from the pacemaker to a remote receiver for diagnostic purposes.
Pacemakers for providillg stimulating pulses to the heart in the absence of natural cardiac activity are well-known. ~riginally, such pacemakers were fabricated from discrete analog componen~s. More recently designed pace-makers employ digital circuitry realized in monolithic form. The additional com-plexity resulting from monolithic digital implementation has been used to provide desirable pacemaker features, including programmability. One exarnple of such prior art is United States Patent No. ~,276,8~3 to McDonald et al. issued July 7, 1981. This Patent discloses a pacemaker having a number of programmable fea-tures including the pacing rate and pulse width. Information concerning these operating parameters is stoTed in digital form in the pacemaker's memory. After implantation it is desirable to read out these memory locations Eor diagnostics purposes. ~dditional information which is useful for diagnostic purposes, such as lead impedance, battery voltage, and the patient's intracardiac electrogram are inherently analog in nature and not directly compatible with the other digi~
tal information within the pacemaker. Consequently, conventional digital modems have not been applicable to pacemaker telemetry systems since their use would require the periodic conversion of the aforementioned analog data to a numerical value prior to transmission.
In contrast, the pulse interval telemetry system oE the present invention is capable of transmitting analog data without conversion to a numeri-cal value, and is capable of sequentially transmitting both digital and analog data. This data is individually and serially transmitted in either an analog or digital format to a remote receiver.
The apparatus of this invention includes a resonant tank circuit for producing a radio frequency carrier signal. This tank circuit is operative 7~
at periodic intervals determined by the output frequency or period of a variable frequency oscillator (VF0). Thus, the ~FO output mod~llates the time interval between consecutive pulses of the carrier signa].
Sources of digital and analog information are interfaced to the VF0 to vary the VF0 output period. In the digital mode the VFO output is varied to a first preselected period to encode a logic one, and to a second preselected period to encode a logic zero. In the analog mode the VF0 output is continuously variable over a limited range about a nominal time period to encode the analog data.
An additional feature of the invention is the use of the VF0 output to synchronize the translation of digital data from a parallel format in memory to a serial format suitable for telemetry transmission.
Thus 9 in accordance with one broad aspect of the invention, there is provided a pulse interval modulation telemetry system for sequentially transmitting analog and digital information from an implantable medical device to a remote rece:iver comprising an energy storage capacitor means, a resonant tank circuit and antenna means for providing an oscillatory signal upon the application of a burst of energy thereto, variable frequency oscillator means responsive to the charging rate of said energy storage capacitor means for periodically energizing said tank circuit and antenna means with said bursts oE energy, and circuit means comprising a plurality of current sources for selectively estab:lishing charging rates for sa:Ld storage capacitGr means which correspond respectively to a logic one and logic zero levels of said digital information and the instantaneous value oE said analog information relative to at least one nominal reference value, wherein said circuit means is constructed to respond to three input control signals so as to establish said first preselected interval with a first one 3~ii7~
of said control signals, said second preselected interval with a second one of said control signals and said nominal value with a third one of said control signals.
In accordance with another broad aspect of the in-vention, there is provided a pulse interval modulation telemetry system for transmitting elther analog or digital information from an implantable pacemaker compris-ing a resonant tank circuit and antenna means for generating a oscil].atory signal upon the application of a burst of energy thereto, circuit means controlled by an input current level comprising a variable frequency oscillator means constructed to provide energization to said resonant tank circuit and antenna means for time intervals that are determined by the magnitude of said input current level which may assume first and second values, which correspond to logic one and logic zero digital information, and to an instantaneous value relative to at least one nominal reference ~alue, which corresponds to analog information, wherein said energization to said tank circuit and antenna means is supplied by said variable frequency osci'lator means.
In accordance with another broad aspect oE the invention there is provided, in a transmitter for transmitting signals from an implantable medical device which are representative of either analog or digital values comprising a signal controlled variable frequency oscillator means having a control terminal, signal application means Ear selectlvely presenting information signals representa-tive o:E said digital and analog ~lues to said control terminal to vary the frequency of said oscillator means in response thereto relative to a nominal output frequency of said oscillator 33~7~
means that exists when said information signals are not being supplied, a tank circuit and antenna means having a predetermined ringing frequency of oscillation when pulsed with energy, and drive circuit means coupled to said oscillator means and to said tank circuit and antenna means for supplying pulses o:E energy to said tank circuit and antenna means a-t a rate that is proportional to the output frequency of said oscillator means whereupon said pulses are radiated :Erom said tank circuit and antenna means as damped ringing signals; the improvement wherein said signal application means comprises a selectively activated digital signa.l means which in a first o state provides a first digital current level s;.gnal to said control terminal that is representative of a digital "one" and in a second state provides a second digital current level signal to said control terminal that is re-presentative of a digital "zero"J firs~ and second sources of analog in$ormation, a selectively actuated analog signal means which, when selected provides either a first analog current level signal in accordance with the information content of said first source or a second analog current level signal in accordance with the information content of said second source, means for selecting either said first or said second analog current level signal and means -~r selectively adding said first digital current level signal to said first analog current level signal and for selectively adding said second digital current level signal to said second analog current level signal and means for providing said added current level signals to said con~
trol terminal.
~ 3a ;
3~
The invention will now be further discussed in conjunction with the accompanying drawings, in which:
FIGU~E 1 is a block diagr~m of the function elements of the system for encoding and transmitting information from the implanted medical clevice.
FIGURE 2 is a truth table showing the relationship between the encoding scheme and the corresponding states of the various current sources of the system;
FIGURE 3 is a waveform diagram showing the analog and digital data format; and FIGURE 4 is a schematic diagram showing the VFO, and current sources in a form suitable for implementation in a bipolar integrated circuit.
- 3b -3~ir76 As previously described, the pulse interval modulation telemetry system is used to transmit analog and digital information from the implanted medical device to a remote receiver. In the context of a pacemaker application the analog information may include battery voltage, lead impedance, or the patient's intracardiac electrogram. Similarly, typical digital data may include programmed pulse width and rate settings as well as iclentification information. An example oE a pacemaker suitable for use as a source of digital information is taught by the previously mentioned United States Patent No. 4,276,883. This ~ ~33~
application discloses a digit lly imp]emented pacemaker having memory for storing digi~ally programmed information shown in FIGURE 6H of th~ reference patent.
This information is stored in a parallel format as a sequence of binary digits.
A suitable source for analog information such as the patient's intracardiac electrogram may be found in United S~ates Patent No. 4,266,551 to Stein et al., issued May 12~ 1981. The circuitry disclosed in this patent may be used to provide a source of intracardiac analog information to the telemetry system of the present inventionO
As shown schematically in FIGURE 1 the heart 10 has an indwelling catheter 11 for sensing cardiac depolarizations and for stimulating cardiac tissue~ Pacer logic receives signals via sense amplifier 34 and delivers stimu-lating pulses by way of output amplifier 33. The pacer logic 12 shown operates under the control of parameter data stored in memory 15. The memory 15 contains the parameter data in parallel form which is seriali~ed for data transmission by shift register 16 which forms a portion of the telemetry system.
In opera~ion~ the transmission of data is remotely initiated by the closure of a magnetically actuated reed switch within the pacemaker in the well-known manner. DigitaL data is then transmitted twice to a remote receiver where it is decoded and checked for errors. The digital data transmission is followed by the transmission of analog data in an analog format. The ~elemetry system is disabled by removing the magnet from the pacemaker site which opens the reed switch and disables the telemetry circuitry.
Additionally, the telemetry circuitry of the present invention in-cludes a receiver blanking circuit which permits the transmission of analog or digital data to be interrupted by the remote programmer thus truncating the transmission of telemetry information so that the pacemaker may receive higher priority programming information from the remote programmer. This function is ~ ~35i7~
achieved by digital circuitry which detects the presence of a lohg duration burst of ~E energy from the remote programmer which is received by the pacemaker and which is decoded to turn off the ~elemetry transmission systems and ~o prepare the digi~al circuitry for the reception of program~ing information from the re-mote programmer.
Oscillators . . _ Referring to FIGURE 1 the radio frequency carrier signal is devel-oped by a radio frequency oscillator tank in FIGURE 1. The tank circuit 1~ is energized at periodic intervals determined by a variable frequency oscillator ~VFO) 12. Radio frequency energy from the resonant tank circuit 1~ is coupled to antenna 16 which radiates this energy to a remote receiver (not shown).
The repetition rate of the variable frequency oscillator is set by a number of cooperating current sources which establish a net charging rate at the input node 18 of the VFO 12. When operating in the digi~al mode for the transmission of digital information the current sources establish a first char-acteristic charging rate for encoding a logic one and a second characteristic charging rate for encoding a logic zero.
As shown in FIGURE 1, three cooperating current sources 26, 28 and 30, are energized by control logic, operating swi~ches 20, 22, 2~. When each of these current sources is turned on, a chara~teristic current I, .5I or .25I is supplied to the capacitor 32 which establishes a voltage at node 18. When the voltage on capacitor 32 reaches a trip level, the VFO ou-tput will change state initiating a burst of RF energy from the tank circuit 1~. Consequently, the time period between successive bursts of radio frequency energy will be deter-mined by the number of current sources which are on. The truth table FIGURE 2 indicates the relationship between the encoding scheme of the present invention and the states of the various current sources. As indicated in the diagraml the 35i7~
logic "one" signal is encoded by energizing current source 30 by closing switch 24, which provides a constant cwrrent charging rate to capacitor 32 of magnitude I. In the preferred embodiment this characteristic charging ra~e results in a pulse interval of 1,000 microseconds. Similarly, a logic "zero" is encoded by energizing the two current sources 28 and 30 resulting in a net charging current of 1.5I which results in a shorter, 667 microsecond pulse interval. This is accomplished by closure of switches 22 and 2~.
In the analog mode, an alternate pair of current sources 26 and 30 are energized to provide a nominal charging rate corresponding to an 800 micro-second pulse interval. A suitable analog signal such as the intracardiac electro-gram derived from the pacemaker lead system is used to modulate one of the current sources 26 to vary the nominal charging rate in a positive or negative direction.
This current modulation results in a varying pulse interval which corresponds to the amplitude variations of the intracardiac signal.
As shown in FIGURE 3, digital data corresponding ~o a serial stream of logic one and logic zeroes is encoded by time periods between shorter and longer time period between bursts of radio frequency energy. It is important to note that the longer interval of 1,000 microseconds is not an even multiple of the shorter time period of 667 microseconds used to encode a logic zero. This scheme results in a lower error rate than systems wherein the logic zero and logic one are related as integer multiples. As shown in the lower analog traces of FIGURE 3, a nominal time period of 800 microseconds corresponds to the zero level of the analog signal to be transmitted. Bositive and negative excursions indicated by the phantom wave traces are used to encode the minimum and maximum excursions about the nominal value.
Although the telemetry system has been described with reference to only a single analog channel, it should be clear that a time division multiplex-~83~ii76 ing scheme could be employed to simultaneously transmit more than one channel of analog data 36 as shown in FIGURE 1. The sequential transfer of more than one analog channel is desirable for use with dual chamber pacemakers whose perform-ance depends upon intrinsic at~ial and ventricular el~ctrogr~ns. One possible scheme for achieving this time division multiplexing is using a multiplexor 35, shown in FIGURE 2 wherein an additional analog channel, labelled "Analog B") is encoded by activating both current sources 28 and 26.
In a similar fashion, other analog signal sources 36 such as lead impedance or battery voltage could be suitably buffered and applied to variable current source 26 to establish a charging rate proportional to ~he analog signal.
Control Lo~ic and Current Sources The block diagram of FIGURE 1 shows the two constant current sources 28 and 30 and one variable current source 26 energized by suitable switching means interfaced to control logic 38. In practice, the switching and current sourcing function may be combined by the use of bipolar transistors which have a characteristic collector-emitter current which corresponds to the magnitude of injected basa current. One suitable bipolar implcmentation for these current sources is shown in FIGURE 4. Referring now to FIGURE ~ the op0ration of this circuit is initiated by a reed switch closure connecting node lOO to the positive supply voltage. This connection supplies bias current to transistors 102, 104, 106, 108 which, in turn, supply bias current to transistors 110, 111, 112, 113, 114, 116~ 118, 120 and to transistors 122, 124 and 126. Input node 99 inter-faces the current source system with the sources of digital and analog data.
This node 99 is connected to the positive supply voltage through a tri-state buffer when a logic "zero" is to be transmitted. The node 99 is connected to ground through the tri-state buffe-r for the transmission o~ "analog" information.
The node 99 is disconnected and is floating when the tri~state buffer is in the _~_ 7~`
high impedance configuration for the transmission of a logic "one".
For the transmission of a logic "one"~ transistor 118 is off and transistor 120 supplies approximately 225 nanoamps of current to the junction of the base of transistor 128 and the VF0 capacitor 32. Assuming that capacitor 32 is near ground pote~tial, then transistors 129, 130, 132, 134 and 136 are off.
The voltage on capacitor 32 increases because of the charging current supplied by transistor 120 until ~he bases of transis~ors 128 and 129 are equal. This allows current flow in transistors 129 and 138. When the collector-emi~tter cur-rent of transistor 129 exceeds the current flow through transistor 138, excess current flows into transistor 134, which turns it on. This, in turn, turns on transis~or 136 which sinks current through the tank circuit 14 and causes the emission of a pulse of radio frequency. The circuit formed by transistors 130, and 134 form a latch arrangement which will not change state until the capacitor 32 discharges to approximately 0.5 volt whereupon these transistors shut off.
The discharge of capacitor 32 takes approximately 2 microseconds and determines the time transistor 13G is on, which determines the width of the pulse applied to the tank circuit. When capacitor 32 is discharged, transistor 129 is off and *ransistor 128 is on which permits the cycle to begin again.
When a logic "one" is applied to input node 99, transistor 118 is activated which adds additional current to the VF0 input node 18, shortening the time required to reach the trip level of the VF0 circuit, thus shortening the pulse interval time to approximately 667 microseconds.
When input node 99 is grounded through the operation control logic, the analog transmission mode is enabled and an analog voltage signal applied to the base of transistor 142 is converted to a proportional charging current by transistors 142, 144, 1~6, 148, 140. As the analog voltage varies, the current of transistor 148 is modulated and the result of pulse interval is shifted with ._9_ 3S7~
respect to the nominal 800 microsecond pulse interval.
Although the current sources and VFO have ~een shown implemented in bipolar technology, it should be appreciated that equivalent structures exist in other technologies including metal oxide semiconductor technologies, and that other modifications may be made without departing from the scope of the invention.
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A pulse interval modulation telemetry system for sequentially transmitting analog and digital information from an implantable medical device to a remote receiver comprising an energy storage capacitor means, a resonant tank circuit and antenna means for providing an oscillatory signal upon the application of a burst of energy thereto, variable frequency oscillator means responsive to the charging rate of said energy storage capacitor means for periodically energizing said tank circuit and antenna means with said bursts of energy, and circuit means comprising a plurality of current sources for selectively establishing charging rates for said storage capacitor means which correspond respectively to a logic one and logic zero levels of said digital information and the instantaneous value of said analog information relative to at least one nominal reference value, wherein said circuit means is constructed to respond to three input control signals so as to establish said first preselected interval with a first one of said control signals, said second preselected interval with a second one of said control signals and said nominal value with a third one of said control signals.
2. A pulse interval modulation telemetry system as claimed in Claim 1 wherein the bursts of energy applied to said tank circuit and antenna means are supplied by said variable frequency oscillator means.
3. A pulse interval modulation telemetry system for transmitting either analog or digital information from an implantable pacemaker comprising a resonant tank circuit and antenna means for generating a oscillatory signal upon the application of a burst of energy thereto, circuit means controlled by an input current level comprising a variable frequency oscillator means constructed to provide energization to said resonant tank circuit and antenna means for time intervals that are determined by the magnitude of said input current level which may assume first and second values, which correspond to logic one and logic zero digital information, and to an instantaneous value relative to at least one nominal reference value, which corresponds to analog information, wherein said energization to said tank circuit and antenna means is supplied by said variable frequency oscillator means.
4. A pulse interval modulation telemetry system as claimed in Claim 3 wherein said circuit means is constructed to respond to three input control signals so as to establish said first preselected interval with a first one of said control signals, said second preselected interval with a second one of said control signals and said nominal value with a third one of said control signals.
5. The telemetry system of Claim 3 wherein said circuit means comprises a plurality of scaled current sources, at least two of which are selectively operated to encode logic one and logic zero information, and at least one of which is selectively operated to encode analog information.
6. The telemetry system of Claim 5 further comprising storage means for storing said digital information in a parallel format and for converting said stored digital information to a serial bit stream format and delivering means for delivering said bit stream digital information to said circuit means.
7. The telemetry system of Claim 6 wherein said circuit means is constructed to respond to three input control signals so as to establish said first preselected interval with a first one of said control signals, said second preselected interval with a second one of said control signals and said nominal value with a third one of said control signals.
8. In a transmitter for transmitting signals from an implantable medical device which are representative of either analog or digital values comprising a signal controlled variable frequency oscillator means having a control terminal, signal application means for selectively presenting infor-mation signals representative of said digital and analog values to said control terminal to vary the frequency of said oscillator means in response thereto relative to a nominal output frequency of said oscillator means that exists when said information signals are not being supplied, a tank circuit and antenna means having a predetermined ringing frequency of oscillation when pulsed with energy, and drive circuit means coupled to said oscillator means and to said tank circuit and antenna means for supplying pulses of energy to said tank circuit and antenna means at a rate that is proportional to the output frequency of said oscillator means whereupon said pulses are radiated from said tank circuit and antenna means as damped ringing signals; the improvement wherein said signal application means com-prises a selectively activated digital signal means which in a first state provides a first digital current level signal to said control terminal that is representative of a digital "one" and in a second state provides a second digital current level signal to said control terminal that is representative of a digital "zero", first and second sources of analog information, a selectively actuated analog signal means which, when selected provides either a first analog current level signal in accordance with the information content of said first source or a second analog current level signal in accordance with the information content of said second source, means for selecting either said first or said second analog current level signal and means for selectively adding said first digital current level signal to said first analog current level signal and for selectively adding said second digital current level signal to said second analog current level signal and means for providing said added current level signals to said control terminal.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000452931A CA1187140A (en) | 1980-10-07 | 1984-04-26 | Telemetry system for a medical device |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US19480780A | 1980-10-07 | 1980-10-07 | |
| US194,807 | 1980-10-07 |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000452931A Division CA1187140A (en) | 1980-10-07 | 1984-04-26 | Telemetry system for a medical device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1183576A true CA1183576A (en) | 1985-03-05 |
Family
ID=22718976
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000387385A Expired CA1183576A (en) | 1980-10-07 | 1981-10-06 | Telemetry system for a medical device |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5789872A (en) |
| CA (1) | CA1183576A (en) |
| DE (1) | DE3139452A1 (en) |
| FR (1) | FR2491659B1 (en) |
| NL (1) | NL8104534A (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4493325A (en) | 1982-05-03 | 1985-01-15 | Medtronic, Inc. | Tachyarrhythmia pacer |
| US4558702A (en) * | 1983-01-21 | 1985-12-17 | Cordis Corporation | Cardiac pacer having input/output circuit programmable for use with unipolar and bipolar pacer leads |
| DE3722829C2 (en) * | 1987-07-07 | 2000-05-31 | Biotronik Mess & Therapieg | Method and arrangement for controlling the pulse delivery of an implantable electromedical device |
| US5137022A (en) * | 1990-07-13 | 1992-08-11 | Cook Pacemaker Corporation | Synchronous telemetry system and method for an implantable medical device |
| DE19930241A1 (en) | 1999-06-25 | 2000-12-28 | Biotronik Mess & Therapieg | Procedure for data transmission in implant monitoring |
| DE19930250A1 (en) | 1999-06-25 | 2001-02-15 | Biotronik Mess & Therapieg | Device for monitoring data, in particular from an electromedical implant |
| DE19930262A1 (en) | 1999-06-25 | 2000-12-28 | Biotronik Mess & Therapieg | Electromedical implant, especially pacemaker, has telemetry device transmitter containing oscillator with first transistor and resonator, buffer stage, antenna driver with second transistor |
| DE19930245A1 (en) | 1999-06-25 | 2000-12-28 | Biotronik Mess & Therapieg | Electromedical implant |
| DE19930256A1 (en) | 1999-06-25 | 2000-12-28 | Biotronik Mess & Therapieg | Near and far field telemetry implant |
| DE19930263A1 (en) | 1999-06-25 | 2000-12-28 | Biotronik Mess & Therapieg | Method and device for data transmission between an electromedical implant and an external device |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2143187A1 (en) * | 1971-08-28 | 1973-03-01 | Reeb Max Eckardt | ARRANGEMENT FOR WIRELESS TRANSMISSION OF MEASURED VALUES OVER SHORT DISTANCES, IN PARTICULAR FOR USE IN RADIO TELEMETRY PROBES |
| US4026305A (en) * | 1975-06-26 | 1977-05-31 | Research Corporation | Low current telemetry system for cardiac pacers |
| DE2643949C3 (en) * | 1976-09-29 | 1981-06-19 | Siemens AG, 1000 Berlin und 8000 München | Circuit arrangement for the pulsed transmission of analog voltage values of both polarities |
| FR2440199A1 (en) * | 1978-11-06 | 1980-05-30 | Medtronic Inc | ON-DEMAND CARDIAC STIMULATOR |
| AU527740B2 (en) * | 1978-11-06 | 1983-03-17 | Medtronic, Inc. | Digital cardiac pacemaker |
| US4223679A (en) * | 1979-02-28 | 1980-09-23 | Pacesetter Systems, Inc. | Telemetry means for tissue stimulator system |
-
1981
- 1981-09-30 FR FR8118454A patent/FR2491659B1/en not_active Expired
- 1981-10-03 DE DE19813139452 patent/DE3139452A1/en active Granted
- 1981-10-06 JP JP15936981A patent/JPS5789872A/en active Granted
- 1981-10-06 CA CA000387385A patent/CA1183576A/en not_active Expired
- 1981-10-06 NL NL8104534A patent/NL8104534A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| DE3139452A1 (en) | 1982-06-24 |
| NL8104534A (en) | 1982-05-03 |
| DE3139452C2 (en) | 1992-07-02 |
| JPS5789872A (en) | 1982-06-04 |
| FR2491659A1 (en) | 1982-04-09 |
| JPH0344785B2 (en) | 1991-07-09 |
| FR2491659B1 (en) | 1986-04-04 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4556063A (en) | Telemetry system for a medical device | |
| EP1408818B1 (en) | Low energy consumption rf telemetry control for an implantable medical device | |
| US5443486A (en) | Method and apparatus to limit control of parameters of electrical tissue stimulators | |
| USRE32361E (en) | Implantable telemetry transmission system for analog and digital data | |
| US5127404A (en) | Telemetry format for implanted medical device | |
| US4281664A (en) | Implantable telemetry transmission system for analog and digital data | |
| CA1183576A (en) | Telemetry system for a medical device | |
| US4453162A (en) | Efficient and fast-switching telemetry transmitter | |
| EP0443496A2 (en) | Telemetry apparatus for implantable tissue stimulator | |
| US4024875A (en) | Device for non-invasive programming of implanted body stimulators | |
| US4211235A (en) | Programmer for implanted pacer | |
| WO1986005675A1 (en) | Telemetry system for an implantable device | |
| US4203447A (en) | Security maintenance for programmable pacer reprogramming | |
| US4203448A (en) | Programmably variable voltage multiplier for implanted stimulator | |
| EP0001156B1 (en) | Programmable, implantable body function control apparatus and method for reprogramming said apparatus | |
| EP1252911A2 (en) | Bidirectional telemetry system and method for transmitting data at high transmission rate | |
| US4304237A (en) | Dual mode programmable pacer | |
| CA1187140A (en) | Telemetry system for a medical device | |
| US4169480A (en) | Demand pacer with programmable rate hysteresis | |
| US4202342A (en) | Programmable pacer with variable amplifier sensitivity and pacing rate | |
| EP0000987B1 (en) | Demand pacer with programmable rate hysteresis | |
| EP0000985A1 (en) | Program alteration security for programmable pacers | |
| CA1117217A (en) | Programmer for implanted pacer | |
| EP0000984B1 (en) | Programmable pacer with variable amplifier gain | |
| CA1114025A (en) | Programmably variable voltage multiplier for implanted stimulator |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |