JPH0344785B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to implantable medical devices such as pacemakers, and more particularly to telemetry systems for transmitting information from a pacemaker to a remote receiving device for diagnostic purposes. ) regarding.

Pacemakers are well known for providing stimulation pulses to the heart when natural cardiac activity is not occurring. Initially, such pacemakers were assembled from analog discrete components. More recently designed pacemakers use digital circuitry implemented in monolithic form. The resulting complexity of monolithic digital implementations is used to provide programmability and provide desired pacemaker characteristics. An example of such prior art is
No. 4,276,883 (registered July 7, 1981) filed November 5, 1979 to McDonald et al. This patent discloses a pacemaker with a number of programmable features including pacing rate and pulse width. Information regarding these operating parameters is stored in the pacemaker's memory in digital form. After implantation, it is desirable to read these storage locations for diagnostic purposes. Additional information useful for diagnostic purposes, such as lead impedance, battery voltage, and the patient's intracardiac electrogram, is analog in nature and is not directly connected to other digital information within the pacemaker. are incompatible. For this reason, conventional digital modems cannot be applied to pacemaker telemetry devices (systems).
The reason is that in order to use those modems,
This is because the analog data described above needs to be periodically converted into numerical values before being transmitted.

In contrast to the above, the pulse interval telemetry device of the present invention is capable of transmitting analog data without conversion to numerical values and is capable of transmitting both digital and analog data sequentially. This data is transmitted individually and serially in analog or digital form to a remote receiving device.

In the present invention, the arrangement corresponding to the means for varying the pulse interval for the nominal value comprises a plurality of current sources selected in response to the type of information being encoded.

The device of the invention includes a resonant tank circuit for generating a radio frequency carrier signal. This tank circuit operates at periodic intervals determined by the output frequency or period of the variable frequency oscillator (VFO). The VFO output thus modulates the time interval between successive pulses of the carrier signal.

Digital and analog information sources are interfaced to the VFO to vary the VFO output period. In digital mode, the VFO output is varied at a first preselected period to encode a logic 1;
The second preselected period is changed to encode a logic zero. In analog mode, the VFO output is
It encodes analog data by constantly changing over a limited range of about the nominal time period.

Another feature of the invention is the use of the VFO output to synchronize the conversion of digital data from a parallel format in memory to a serial format suitable for remote transmission.

SUMMARY OF THE INVENTION The present invention enables different combinations of fixed value and variable value current sources by means of a telemetry logic code that energizes a tank coil, and by generating a ringing type variable frequency RF signal, digital data and A data telemetry device for use with an implantable medical device that transmits (transmits) analog data to a remote receiver.

General Description As mentioned above, pulse interval modulation telemetry devices are used to transmit analog and digital information from an implanted medical device to a remote receiving device. In pacemaker applications, analog information may include battery voltage, lead impedance, or the patient's intracardiac electrogram. Similarly, typical digital data will include programmed pulse width and rate settings along with identification information. An example of a pacemaker suitable for use as a digital information source is taught in US Pat. No. 4,276,883, filed Nov. 5, 1979, to McDonald et al., mentioned above. This patent is
A digitally implemented pacemaker is disclosed having a memory for storing digitally programmed information. This information is a series of two
Stored in parallel format as base digits.

A suitable analog source of information, such as a patient's intracardiac electrogram, is U.S. Pat.
12th registration). The circuitry disclosed in this patent may be used to provide an intracardiac analog information source for the telemetry system of the present invention.

As schematically illustrated in FIG. 1, a heart 10 includes an indwelling catheter 11 for sensing cardiac depolarization and stimulating cardiac tissue. The pacer logic receives signals via sense amplifier 34 and delivers stimulation pulses via output amplifier 33. The illustrated pacer logic 12 operates under the control of parameter data stored in memory 15. The memory 15 contains parameter data in parallel form, but the data is serialized for data transmission by a shift register 16 forming part of the telemetry device.

In operation, data transmission is initiated remotely by closure of a magnetically actuated reed switch within the pacemaker in a manner well known. The digital data is then transmitted twice to a remote receiving device where it is decoded and checked for errors. Following the transmission of digital data, analog data is transmitted in analog form. The telemetry device (system) is disabled by removing the magnet from the pacemaker side which opens the reed switch and disables the telemetry circuit.

Furthermore, the telemetry circuit of the present invention includes a receiver blanking circuit that allows the transmission of analog or digital data to be interrupted by a remote programmer, thus allowing the transmission of remote information. can be aborted, allowing the pacemaker to receive higher priority programming information from a remote programmer. This function is accomplished by digital circuitry that detects the presence of long duration bursts of RF energy from the remote programmer, which are received and decoded by the pacemaker and sent to the telemetry device (system ) to prepare the digital circuitry for receiving programming information from a remote programmer.

SUMMARY OF THE INVENTION A transmitter for transmitting a signal from an implantable medical device indicative of either an analog value or a digital value, comprising signal controlled variable frequency oscillator means having a control terminal, comprising information indicative of the digital value and the analog value. selectively providing a signal to said control terminal to cause the frequency of said oscillator means to change in response thereto with respect to the nominal output frequency of said oscillator means present when said information signal is not provided; signal application means; tank circuit and antenna means having a predetermined ringing frequency of oscillation when energized with pulsed energy; supplying pulsed energy to the tank circuit and antenna means at a rate proportional to the output frequency of;
a drive circuit whereby said pulse is emitted from said tank circuit and antenna means as an attenuated or ringing signal; applying a digital current level signal of 1 to the control terminal;
in a second state, selectively activated digital signal means for providing a second digital current level signal to the control terminal indicative of a digital zero value; and first and second analog information sources; selectively providing either a first analog current level signal according to the information content of the first information source or a second analog current level signal according to the information content of the second information source when means for selecting either said first or said second analog current level signal; and means for selecting either said first or said second analog current level signal;
means for selectively adding the second digital current level signal to the second analog current level signal; and means for selectively adding the second digital current level signal to the second analog current level signal; and means for applying it to the terminal.

Oscillator Referring to Figure 1, the radio frequency carrier signal is
It is generated by the tank circuit of the radio frequency oscillator of FIG. Tank circuit 14 is energized at periodic intervals determined by variable frequency oscillator (VFO) 13. Radio frequency energy from resonant tank circuit 14 is coupled to antenna 17, which radiates this energy to a remote receiving device (not shown).

The repetition rate of the variable frequency oscillator is VFO13
is set by a number of cooperating current sources which set the net charging rate at the input node 18 of the circuit. When operating in digital mode to transmit digital information, the current source sets a first characteristic charging rate to encode a logical 1 and a second characteristic charge rate to encode a logical 0. Set the charging rate.

As shown in FIG. 1, three cooperating current sources 26,
28 and 30 are powered by the control logic, operating switches 20, 22, and 24. Each of these current sources, when turned on, supplies a characteristic current I, 0.5I or 0.25I to capacitor 32, which generates a voltage at node 18. When the voltage on capacitor 32 reaches the trip level, the VFO output changes state and disconnects the RF from tank circuit 14.
Initiates a burst of energy. As a result,
The time interval between successive bursts of RF energy is determined by the number of current sources that are turned on. Truth table FIG. 2 shows the relationship between the encoding scheme of the present invention and the states of the various current sources. As shown, a logic “1” signal
4 and energizing current source 30, which provides a constant charging rate of magnitude I to capacitor 32. In the preferred embodiment, this characteristic charging rate results in a pulse interval of 1000 microseconds. Similarly, a logic "0" is encoded by energizing two current sources 28 and 30, resulting in a net charging rate of 1.5I, resulting in a shorter pulse interval of 667 microseconds. . This is done by closing switches 22 and 24.

In analog mode, another pair of current sources 26 and 30 are energized to provide a nominal charging rate corresponding to a pulse interval of 800 microseconds. A suitable analog signal, such as an intracardiac electrogram derived from a pacemaker lead system, modulates one of the current sources 26 to change the nominal charging rate in a positive or negative direction. used. This current modulation results in a variable pulse interval that corresponds to changes in the amplitude of the intracardiac signal.

As shown in Figure 3, digital data corresponding to a serial stream of logic 1s and logic 0s is generated by the time interval between the shorter time interval and the longer time interval between bursts of RF energy. It is encoded as follows. It is important to note that the longer time interval of 1000 microseconds is not an even multiple of the shorter time interval of 667 microseconds used to encode a logic zero. This configuration allows logical 0
The error rate is lower than that of a system in which the logic 1 and the logic 1 are integer multiples. As shown in the lower analog diagram of FIG. 3, the nominal time interval of 800 microseconds corresponds to the zero level of the transmitted analog signal. The positive and negative excursoins shown by the phantom waveform diagram are used to encode the minimum and maximum excursions for the nominal value.

Although the telemetry device has been described with respect to only a single analog channel, it is clear that a time division multiplexing configuration may be used to simultaneously transmit more than one channel of analog data 36 as shown in FIG. It is. Sequential transmission of one or more analog channels is desirable for use with dual chamber pacemakers whose performance relies on native atrial and ventricular electrograms. One possible configuration for achieving this time division multiplexing is to use the multiplexer 35 shown in FIG.
An additional analog channel, labeled , is encoded by energizing both current sources 28 and 26.

In a similar manner, other analog signal sources 36, such as wire impedance or battery voltage, can be appropriately buffered and applied to variable current source 26 to set a charging rate proportional to the analog signal.

CONTROL LOGIC AND CURRENT SOURCES (SIGNAL APPLICATION MEANS) The block diagram of FIG.
and one variable current source 26 are shown. In fact, the switching and current sourcing functions can be combined by using a bipolar transistor whose collector-emitter characteristic current corresponds to the magnitude of the injected base current. One suitable bipolar transistor embodiment for these current sources is shown in FIG. Referring to FIG. 4, the operation of this circuit is as follows:
It begins with the closure of a reed switch connecting node 100 to the positive supply voltage. This connection allows the bias current to flow through transistors 102 and 10.
4, 106, 108, and the bias current is sequentially supplied to transistors 110, 111, 112, 1.
13, 114, 116, 118, 120, and transistors 122, 124, 126.
Input node 99 interfaces the current source system with digital and analog data sources. This node 99, when a logic "0" is transmitted,
Connected to the positive supply voltage via a tri-state buffer. Node 99 is grounded through a three-state buffer to transmit "analog" information. When the three-state buffer is in a high impedance state to transmit a logic "1", node 99 is disconnected and floating.

To transmit a logic "1", transistor 118 is turned off and transistor 120 is connected between the base of transistor 128 and VFO capacitor 32.
delivers approximately 225 nanoamps of current to the connection point.
Assuming that capacitor 32 is near ground potential,
Transistors 129, 130, 132, 134 and 136 are turned off. The voltage on capacitor 32 increases due to the charging current provided by transistor 120 until the base currents of transistors 128 and 129 are equal. This causes current to flow through transistors 129 and 138. If the collector-emitter current of transistor 129 exceeds the current flowing through transistor 138, excess current flows into transistor 134, turning it on. It in turn turns on transistor 136, which reduces the current through tank circuit 14 and causes the radio frequency pulse to be emitted. The circuit formed by transistors 130 and 134 constitutes a latch circuit arrangement, which discharges capacitor 32 to approximately 0.5 volts and does not change state. When this discharge occurs, these transistors stop. Discharging capacitor 32 takes approximately 2 microseconds and determines the time that transistor 136 is on, which determines the width of the pulse applied to the tank circuit. When capacitor 32 discharges, transistor 129 is turned off and transistor 128 is turned on, thereby starting the cycle again.

When a logic "1" is applied to input node 99, transistor 118 is energized to draw additional current.
is added to the VFO input node 18, reducing the time required to reach the trip level of the VFO circuit.
As a result, the pulse interval time is reduced to approximately 667 microseconds.

When input node 99 is grounded through the arithmetic control logic, analog transmission mode is enabled and the analog voltage signal applied to the base of transistor 142 is connected to transistors 142, 144, 14.
6,148,140 into a proportional charging current. As the analog voltage changes, the current in transistor 148 is modulated and the resulting pulse interval is shifted with respect to a nominal 800 microsecond pulse interval.

Although the current source and VFO are shown implemented in bipolar technology, similar structures exist in other technologies, including MOS technology, and other modifications may be made without departing from the scope of the invention. We should recognize that.

Embodiments of the present invention will be listed below.

1 means for continuously varying said pulse interval for a nominal value in response to analog information; and encoding a logic one for serial transmission of digital information in a first preselected pulse interval;
Logic 0 at second preselected pulse interval
A pulse interval modulation telemetry device for transmitting both analog and digital information from an implantable medical device to a remote receiving device, comprising: means for setting the pulse interval to encode the pulse interval.

2 a digital data source; an analog data source; a fixed frequency oscillator for providing a carrier signal; variable frequency oscillator means for periodically energizing said fixed frequency oscillator to set a telemetry pulse interval; responsive to a digital data source, varying the variable frequency oscillator to a first preselected pulse interval that encodes digital data 1 and to a second preselected pulse interval that encodes digital data 0; and means responsive to an analog data source for continuously varying the variable frequency oscillator about a preselected nominal pulse interval for encoding the analog data. A pulse-interval modulation telemetry device that transmits information both from and to an implanted medical device.

3 a digital data source; an analog data source; fixed frequency oscillator means for providing a radio frequency telemetry carrier signal; frequency oscillator means, cooperating with said analog and digital data source;
a plurality of current sources for setting a charging rate proportional to the instantaneous value of said information; and a pulse-interval modulation telemetry system for sequentially transmitting analog and digital information from an implantable medical device to a remote receiving device. Device.

4 having memory means for storing digital information;
a fixed frequency oscillator for generating a telemetry carrier signal; and a fixed frequency oscillator for generating a telemetry carrier signal; a current level responsive to a frequency oscillator for providing a modulating signal that periodically energizes the fixed frequency oscillator at time intervals proportional to the magnitude of the current level.

5. The current source comprises a plurality of scaled current sources, at least two of which are selectively activated to encode logic 1 and logic 0 information; 5. The telemetry device of claim 4, wherein the telemetry device is selectively operative to encode analog information.

6. Telemetry device according to claim 4, further comprising means for converting digital data stored in parallel form in said memory into a serial bit stream supplied to said current source at a bit rate equal to said modulating signal. .

7. The current means further comprises: a first current source that sets a bias charging rate that is energized during the telemetry mode; a second current source configured to set a first rate of charge proportional to the logic zero state and a second current source proportional to the logic zero state; 4. A telemetry device according to claim 4 or claim 3, further comprising a third current source for setting a continuously varying charging rate proportional to magnitude.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the functional elements of a system for encoding and transmitting information from an implantable medical device. FIG. 2 shows a table of truth values illustrating the relationship between encoding configurations and the corresponding states of various current sources in the system. FIG. 3 is a waveform diagram showing analog and digital formats. FIG. 4 is a schematic diagram illustrating a type of VFO and current source suitable for implementation in a bipolar integrated circuit. In FIG. 1, 10 is a heart, 11 is a catheter, 12 is a pacer logic, 13 is a variable frequency oscillator (VFO), 14 is a tank circuit, 15 is a memory, 1
6 is a shift register, 17 is an antenna, 20,2
2 and 24 are reed switches, 26, 28, and 30 are current sources, 32 is a capacitor, 35 is a multiplexer CL, 36 is other analog data, and 38 is telemetry logic.

Claims (1)

Claims: 1. A transmitter for transmitting a signal from an implantable medical device indicating either an analog value or a digital value, comprising signal controlled variable frequency oscillator means having a control terminal, the transmitter comprising: selectively providing an information signal to said control terminal indicative of a value for causing a change in the frequency of said oscillator means in response to a nominal output frequency of said oscillator means present when said information signal is not provided; signal application means; tank circuit and antenna means having a predetermined ringing frequency of oscillation when energized with pulsed energy; a drive circuit for supplying pulsed energy to said tank circuit and antenna means at a rate proportional to said tank circuit and antenna means, whereby said pulse is radiated from said tank circuit and antenna means as an attenuated ringing signal; The signal applying means applies a first digital current level signal indicating a digital value of 1 to the control terminal in a first state;
selectively driven digital signal means for providing a second digital current level signal to said control terminal in a second state indicative of a digital zero value; and first and second analog information sources, when selected; selectively driven to provide either a first analog current level signal according to the information content of the first information source or a second analog current level signal according to the information content of the second information source. means for selecting either the first or second analog current level signal; and means for selecting either the first or second analog current level signal;
means for selectively adding the second digital current level signal to the second analog current level signal; and means for selectively adding the second digital current level signal to the second analog current level signal; A telemetry device for a medical device, comprising: means for applying to a terminal;