Method and apparatus to provide safety checks for neural stimulation

• US 20070255319A1
• Filed: 04/28/2006
• Published: 11/01/2007
• Est. Priority Date: 04/28/2006
• Status: Active Grant

• Current Assignee: Cortigent Incorporated
• Original Assignee: Second Sight Medical Products, Inc.
• Inventors: Greenberg, Robert, Roy, Arup, Little, James, Tang, Kea-Tiong, Reinhold, John, Yadav, Sumit, Zhou, Chunhong, Maksy, Pishoy, Dai, Rongqing, McClure, Kelly, Zhou, Dao, Castro, Richard
• Granted Patent: US 9,913,985 B2
• Time in Patent Office: Days
• US Class Current: 607/2
• CPC Class Codes: A61N 1/00 Electrotherapy; Circuits therefor A61N2/00 takes precedence; irradiation apparatus A61N5/00
• CPC Class Codes: A61N 1/0543 Retinal electrodes
• CPC Class Codes: A61N 1/0551 Spinal or peripheral nerve electrodes
• CPC Class Codes: A61N 1/08 Arrangements or circuits for monitoring, protecting, controlling or indicating for external stimulators A61N1/3603; for implantable neurostimulators A61N1/36128; for heart stimulators A61N1/37; for defibrillators A61N1/3925
• CPC Class Codes: A61N 1/3603 Control systems
• CPC Class Codes: A61N 1/36046 of the eye
• CPC Class Codes: A61N 1/36142 for improving safety
• CPC Class Codes: A61N 1/36185 Selection of the electrode configuration

Abstract

In electrically stimulating neural tissue it is important to prevent over stimulation and unbalanced stimulation which would cause damage to the neural tissue, the electrode, or both. It is critical that neural tissue in not subjected to any direct current or alternating current above a safe threshold. Further, it is important to identify defective electrodes as continued use may result in neural and further electrode damage. The present invention presents system and stimulator control mechanisms to prevent damage to neural tissue.

Claims

1. A method of stimulating neural tissue comprising:

providing a neural stimulator including a plurality of electrodes suitable to stimulate neural tissue;

testing the impedance of all electrodes;

calculating an average impedance;

calculating a difference from said average impedance for each electrode; and

determining bad electrodes based on said difference and a predetermined value.

2. The method according to claim 1, wherein said average is a median.

3. The method according to claim 1, wherein said average is a mean.

4. The method according to claim 1, further comprising calculating a standard deviation of said impedances, and wherein said predetermined value is a multiple of said standard deviation.

5. The method according to claim 4, wherein said predetermined value is four times said standard deviation.

6. The method according to claim 1, further comprising repeating said steps of calculating based of a subset of said electrodes after eliminating electrodes known to be bad.

7. The method according to claims 6, wherein said standard deviation is obtained from all electrodes but applied to said subset of said electrodes.

8. The method according to claim 1, wherein said standard deviation is the greater of a calculated standard deviation and predetermined minimum value.

9. The method according to claims 6, further comprising maintaining a record of said impedances overtime and determining bad electrodes by impedance changes over time.

10. The method according to claim 1, wherein said step of stimulating neural tissue is stimulating visual neurons to form artificial vision.

11. A method of stimulating neural tissue comprising:

providing a neural stimulator including a plurality of electrodes suitable to stimulate neural tissue;

determining a safe level for all electrodes;

receiving input for neural stimulation;

calculating a sum of stimulation on all electrodes based on said input for neural stimulation;

reducing the stimulation on each electrode by the amount necessary not to exceed said safe level for all electrodes; and

stimulating said neural tissue according to a reduced stimulation level.

12. The method according to claim 11, where said step of reducing comprises reducing the stimulation on each electrode in equal proportion.

13. The method according to claim 11, wherein said step of receiving input for neural stimulation comprises receiving input from multiple sources and said step of calculating a sum of stimulation includes a sum from all sources.

14. The method according to claim 11, wherein said step of stimulating neural tissue is stimulating visual neurons to form artificial vision.

15. A method of stimulating Neural tissue comprising:

providing a neural stimulator including a plurality of electrodes suitable to stimulate neural tissue;

receiving input for neural stimulation;

determining an desired cathodic pulse based on said input;

calculating a anodic pulse to balance said cathodic pulse; and

Stimulating neural tissue according to said cathodic and anoodic pulses.

16. The method according to claim 15, wherein said anodic pulse has a predetermined amplitude and varies pulse width to balance said cathodic pulse.

17. The method according to claim 15, further comprising shorting said electrodes to ground after said anodic pulse.

18. The method according to claim 15, further comprising appending a pulse to compensate for imbalance.

19. The method according to claim 15, wherein said step of stimulating neural tissue is stimulating visual neurons to form artificial vision.

20. A neural stimulator comprising:

a neural stimulation controller;

a plurality of electrodes suitable to stimulate neural tissue driven by said neural stimulation controller;

means for testing the impedance of all electrodes;

means for calculating an average impedance;

means for calculating a difference from said average impedance for each electrode; and

means for determining bad electrodes based on said difference and a predetermined value.

21. A neural stimulator comprising

a neural stimulation controller;

a plurality of drivers controlled by said neural stimulation controller;

a plurality of electrodes suitable to stimulate neural tissue driven by said plurality of drivers;

a plurality of switches connection the output of said drivers to a common line; and

a comparator comparing voltage on said common line to a predetermined reference voltage.

22. The neural stimulator according to claim 21, further comprising a capacitor coupling said common line to a ground.

23. The neural stimulator according to claim 21, further comprising switching means for disabling said plurality of drivers when leakage current is detected by said comparator.

24. The neural stimulator according to claim 21, further comprising transmitting means for transmitting a error signal when leakage current is detected by said comparator.

25. A method of stimulating neural tissue comprising:

providing a neural stimulator including a plurality of electrodes suitable to stimulate neural tissue;

testing the capacitance of all electrodes;

recording changes in capacitance over time; and

determining bad electrodes based on said change in capacitance.

26. The method according to claim 25, wherein said change in capacitance is measured as a phase shift.

27. A method of stimulating neural tissue comprising:

providing a neural stimulator including a plurality of electrodes suitable to stimulate neural tissue;

determining a maximum charge per phase for each electrode;

receiving input for neural stimulation;

calculating a discrete integral of the wave form of the input;

reducing the stimulation on each electrode by the amount necessary not to exceed said safe level for all electrodes; and

stimulating said neural tissue according to a reduced stimulation level.

28. A method of stimulating neural tissue comprising:

providing a neural stimulator including a plurality of electrodes suitable to stimulate neural tissue;

stimulating neural tissue in accordance with external input;

testing total power dissipation of said neural stimulator;

comparing said total power dissipation to a predetermined maximum power dissipation; and

reducing stimulation if the total power dissipation exceeds said predetermined maximum power dissipation.

29. The method according to claim 28, wherein reducing stimulation is discontinuing stimulation.

30. The method according to claim 28, wherein testing total power dissipation is controlled via an RF power control loop.

31. The method according to claim 28, wherein testing total power dissipation is testing with an instantaneous current sum check.

32. The method according to claim 28, wherein testing total power dissipation is testing with a thermistor in the neural stimulator.

33. A method of stimulating neural tissue comprising:

providing a neural stimulator including a plurality of stimulating electrodes and one common electrode, suitable to stimulate neural tissue;

stimulating neural tissue in accordance with external input using balanced biphasic pulses in opposite phases at the same time across said stimulating electrodes; and

disallowing stimulation waveforms on said electrodes that overlap non-contiguously during opposite phases with other said electrodes in the array in a bipolar or multipolar configuration.

34. A method of stimulating neural tissue comprising:

providing a neural stimulator including a plurality of electrodes suitable to stimulate neural tissue;

measuring electrode impedance using driver output voltage;

stimulating neural tissue according to external input;

measuring an after stimulation driver output voltage; and

calculating leakage current using electrode impedance and after stimulation driver output voltage.