Transmission of information from an implanted medical device

• US 20040039423A1
• Filed: 08/20/2002
• Published: 02/26/2004
• Est. Priority Date: 08/20/2002
• Status: Active Grant

• Current Assignee: TC1 LLC (Abbott Laboratories)
• Original Assignee: Thoratec LLC
• Inventors: Dolgin, Alexander
• Granted Patent: US 6,772,011 B2
• Time in Patent Office: Days
• US Class Current: 607/27
• CPC Class Codes: A61M 2205/3523 using telemetric means
• CPC Class Codes: A61M 2205/8243 by induction
• CPC Class Codes: A61M 60/205 Non-positive displacement blood pumps
• CPC Class Codes: A61M 60/873 specially adapted for wireless or transcutaneous energy transfer [TET], e.g. inductive charging
• CPC Class Codes: A61N 1/37223 Circuits for electromagnetic coupling
• CPC Class Codes: A61N 1/3727 characterised by the modulation technique
• CPC Class Codes: A61N 1/3787 from an external energy source

Abstract

An implanted medical apparatus and external power source use the same coils for energy transfer to the implanted medical device as used for transmission of control signals from the implanted device. In one example, implanted circuitry generates a feedback control signal indicative of the load voltage level of a load-generating medical device and superimposes the feedback signal on an inductor capacitor (LC) tank circuit for detection by the external powering apparatus. The external powering apparatus uses the feedback signal to control the energy transfer to the implanted medical device, thus regulating the load voltage at the load-generating medical device. The feedback control signal may be a sequence of pulses whose frequency indicates the load voltage level. Other information besides load voltage level may also be transmitted from the implanted device, such as telemetry and logic information.

Claims

1. An implantable device requiring electrical power from an external power source for operation, comprising:

an LC tank circuit that receives power from the external power source;

a load-generating device to which the received power is delivered; and

feedback circuitry that senses a load voltage level of the power delivered to the load-generating device, produces a feedback signal indicative of the load voltage level, and superimposes the feedback signal on the LC tank circuit for communication to the external power source.

2. The implantable device of claim 1 wherein the feedback signal comprises a series of pulses, the frequency that the pulses are generated being indicative of the load voltage level.

3. The implantable device of claim 2 wherein the feedback circuitry comprises:

an error amplifier that receives the load voltage level, compares the load voltage level to a reference voltage, and generates a difference signal indicative of the load voltage level; and

a controller that receives the difference signal and generates the feedback signal.

4. The implantable device of claim 2 wherein the pulses are generated at varying frequencies within a specified range with a center frequency, and that center frequency indicates that the load voltage level is the desired level and no adjustment needs to be made to the amount of power the external power source is delivering, while frequencies above and below the center frequency indicate that the amount of power the external power source is delivering needs to be adjusted to bring the load voltage level back to the desired level.

5. The implantable device of claim 4 wherein the center frequency is about one kilohertz.

6. The implantable device of claim 4 wherein the frequency range of the feedback signal differs from the frequency of a power signal produced by the external power source so that in the external power source, the power signal may be filtered to extract the feedback signal.

7. The implantable device of claim 6 wherein the frequency range of the feedback signal is less than the frequency of the power signal.

8. The implantable device of claim 2 wherein the feedback circuitry comprises a switch that receives the feedback signal and is coupled with the LC tank circuit so that during the time the feedback signal is pulsed high the switch closes and the LC tank circuit is short-circuited to superimpose the feedback signal on the LC tank circuit.

9. The implantable device of claim 8 further comprising a rectifier that comprises:

first and second diodes, the first diode being coupled to a first terminal of the LC tank circuit and the second diode being coupled to a second terminal of the LC tank circuit, and the first and second diodes both having a forward bias directed toward a positive terminal of the load-generating device; and

first and second transistor switches whose current conducting terminals are coupled, respectively, between the first terminal of the LC tank circuit and the negative terminal of the load-generating device and between the second terminal of the LC tank circuit and the negative terminal of the load-generating device;

wherein the first and second transistor switches serve as the switch and each receives the feedback signal at its gate, and the first and second transistor switches are activated by the pulses in the feedback signal.

10. An implantable device requiring electrical power from an external power source for operation, comprising:

an LC tank circuit that receives a power signal from the external power source;

a rectifier that rectifies the power signal;

a load-generating device to which the rectified power signal is delivered;

a voltage-to-frequency converter that senses a load voltage level of the power delivered to the load-generating device and produces a pulsed feedback signal comprising a series of pulses, the frequency that the pulses are generated being indicative of the load voltage level; and

a switch that superimposes the pulsed feedback signal on the LC tank circuit for communication to the external power source.

11. The implantable device of claim 10 wherein the rectifier and the switch utilize common components.

12. The implantable device of claim 10 wherein the voltage-to-frequency converter comprises:

an error amplifier that receives the load voltage level, compares the load voltage level to a reference voltage, and generates a difference signal indicative of the load voltage level; and

a controller that receives the difference signal and generates the feedback signal.

13. The implantable device of claim 10 wherein the pulses are generated at varying frequencies within a specified range with a center frequency, and that center frequency indicates that the load voltage level is the desired level and no adjustment needs to be made to the amount of power the external power source is delivering, while frequencies above and below the center frequency indicate that the amount of power the external power source is delivering needs to be adjusted to bring the load voltage level back to the desired level.

14. The implantable device of claim 13 wherein the frequency range of the feedback signal differs from the frequency of the power signal so that in the external power source, the power signal may be filtered to extract the feedback signal.

15. The implantable device of claim 10 wherein the rectifier comprises:

first and second diodes, the first diode being coupled to a first terminal of the LC tank circuit and the second diode being coupled to a second terminal of the LC tank circuit, and the first and second diodes both having a forward bias directed toward a positive terminal of the load-generating device; and

first and second transistor switches whose current conducting terminals are coupled, respectively, between the first terminal of the LC tank circuit and the negative terminal of the load-generating device and between the second terminal of the LC tank circuit and the negative terminal of the load-generating device;

wherein the first and second transistor switches serve as the switch and each receive the feedback signal at their gates, the first and second transistor switches being activated by the pulses in the feedback signal.

16. A medical system with transcutaneous energy transfer comprising:

an external electrical power source having a power driver and a primary LC tank circuit; and

an implantable device requiring electrical power from an external power source for operation, comprising;

a secondary LC tank circuit that receives power from the external power source;

a load-generating device to which the received power is delivered; and

feedback circuitry that senses a load voltage level of the power delivered to the load-generating device, produces a feedback signal indicative of the load voltage level, and superimposes the feedback signal on the secondary LC tank circuit for communication to the external power source.

17. The medical system of claim 16 wherein the feedback signal comprises a series of pulses, the frequency that the pulses are generated being indicative of the load voltage level.

18. The medical system of claim 17 wherein the power driver comprises:

a sensor that senses the feedback signal communicated from the implantable device;

a decoder that receives the feedback signal sensed by the sensor, determines the frequency of the pulses in the feedback signal, and generates a voltage signal indicative of the frequency of the pulses; and

a pulse-width modulator and driver that receives the voltage signal and generates a power signal transferring a desired amount of energy to the implantable device.

19. The medical system of claim 18 wherein the power signal is a rectangular pulse whose duty cycle varies the amount of energy transferred to the implanted device.

20. The medical system of claim 19 wherein the frequency range of the feedback signal differs from the frequency of the power signal so that in the external power source, the power signal may be filtered to extract the feedback signal.

21. The medical system of claim 18 wherein the power driver further comprises a tuning circuit that monitors a voltage component and a current component of the power signal and tunes the power signal so that the signal components have an ideal timing relationship.

22. The medical system of claim 17 wherein the feedback circuitry comprises:

an error amplifier that receives the load voltage level, compares the load voltage level to a reference voltage, and generates a difference signal indicative of the load voltage level; and

a controller that receives the difference signal and generates the feedback signal.

23. The medical system of claim 17 wherein the feedback circuitry comprises a switch that receives the feedback signal and is coupled with the secondary LC tank circuit so that during the time the feedback signal is pulsed high the switch closes and the secondary LC tank circuit is short-circuited to superimpose the feedback signal on the secondary LC tank circuit.

24. The medical system of claim 23 further comprising a rectifier that comprises:

first and second diodes, the first diode being coupled to a first terminal of the secondary LC tank circuit and the second diode being coupled to a second terminal of the secondary LC tank circuit, and the first and second diodes both having a forward bias directed toward a positive terminal of the load-generating device; and

first and second transistor switches whose current conducting terminals are coupled, respectively, between the first terminal of the secondary LC tank circuit and the negative terminal of the load-generating device and between the second terminal of the secondary LC tank circuit and the negative terminal of the load-generating device;

wherein the first and second transistor switches serve as the switch and each receive the feedback signal at their gates, the first and second transistor switches being activated by the pulses in the feedback signal.

25. An external power source for an implantable device requiring electrical power from an external power source for operation, the external power source comprising:

an electrical power supply;

a pulse-width modulator and driver for generating a power signal;

an LC tank circuit for transmitting electrical energy; and

a sensor that senses a feedback signal provided by the implantable device through the LC tank circuit, the feedback signal indicative of a load voltage level;

wherein the external power source varies the amount of power delivered to the implantable device in response to the feedback signal.

26. The external power source of claim 25 wherein the feedback signal comprises a series of pulses, the frequency that the pulses are generated being indicative of the load voltage level.

27. The external power source of claim 26 further comprising a decoder that receives the feedback signal sensed by the sensor, determines the frequency of the pulses in the feedback signal, and generates a voltage signal to be received by the pulse-width modulator and driver that is indicative of the frequency of the pulses.

28. The external power source of claim 26 wherein the power signal is a rectangular pulse whose duty cycle varies the amount of energy transferred to the implanted device.

29. The external power source of claim 28 wherein the frequency range of the feedback signal differs from the frequency of the power signal so that the power signal may be filtered to extract the feedback signal.

30. The external power source of claim 25 further comprising a tuning circuit that monitors a voltage component and a current component of the power signal and tunes the power signal so that the signal components have an ideal timing relationship.

31. The external power source of claim 26 further comprising a circuit that senses the rate of change of current through the LC tank circuit, and wherein the feedback signal further comprises a signal indicative of the rate of change of current through the LC tank circuit.

32. The external power source of claim 31 wherein the circuit that senses the rate of change of current through the LC tank circuit is an R-C circuit that receives a current therethrough indicative of the current through the LC tank circuit and that has a capacitor with a voltage thereon indicative of the rate of change of current through the LC tank circuit.

33. An implantable device requiring electrical power from an external power source for operation, comprising:

an LC tank circuit that receives power from the external power source;

a load-generating device to which the received power is delivered; and

circuitry that senses a condition, produces a signal indicative of the condition, and superimposes the signal on the LC tank circuit for communication to the external power source.

34. The implantable device of claim 33 wherein the signal comprises one or more pulses.

35. The implantable device of claim 34 wherein the load generating device is a blood pump.

36. The implantable device of claim 35 wherein the condition being sensed is whether the blood pump is in an operating state or a fault state.

37. The implantable device of claim 35 wherein the condition being sensed is whether the blood pump is operating on primary components or redundant components.

38. The implantable device of claim 34 wherein the condition being sensed is a charge condition for an internal battery.

39. The implantable device of claim 34 wherein the circuitry comprises a switch that receives the signal and is coupled with the LC tank circuit so that during the time the signal is pulsed high the switch closes and the LC tank circuit is short-circuited to superimpose the signal on the LC tank circuit.

40. The implantable device of claim 34 further comprising a rectifier that comprises:

first and second diodes, the first diode being coupled to a first terminal of the LC tank circuit and the second diode being coupled to a second terminal of the LC tank circuit, and the first and second diodes both having a forward bias directed toward a positive terminal of the load-generating device; and

first and second transistor switches whose current conducting terminals are coupled, respectively, between the first terminal of the LC tank circuit and the negative terminal of the load-generating device and between the second terminal of the LC tank circuit and the negative terminal of the load-generating device;

wherein the first and second transistor switches serve as the switch and each receive the signal at their gates, the first and second transistor switches being activated by the pulses in the signal.