Method and apparatus for measurement of neural response

Patent metadata

Field	Value
Publication number	US-9386934-B2
Application number	US-201214117144-A
Country	US
Kind code	B2
Filing date	May 11, 2012
Priority date	May 13, 2011
Publication date	Jul 12, 2016
Grant date	Jul 12, 2016

Abstract

A method for measuring a neural response to a stimulus. Measurement circuitry is settled prior to a stimulus, by connecting a sense electrode to the measurement circuitry to allow the measurement circuitry to settle towards a bio-electrically defined steady state. Charge is recovered on stimulus electrodes by short circuiting the stimulus electrodes to each other. An electrical stimulus is then applied from the stimulus electrodes to neural tissue, while keeping the sense electrode disconnected from the measurement circuitry. After the stimulus, a delay is imposed during which the stimulus electrodes are open circuited and the sense electrode is disconnected from the measurement circuitry and from the stimulus electrodes. After the delay, a neural response signal present at the sense electrode is measured by connecting the sense electrode to the measurement circuitry.

First claim

The invention claimed is:

1. A method for measuring a neural response to a stimulus, the method comprising:
settling measurement circuitry prior to a stimulus, by connecting a sense electrode to the measurement circuitry to allow the measurement circuitry to settle towards a bio-electrically defined steady state;
recovering charge on stimulus electrodes by short circuiting the stimulus electrodes to each other;
applying an electrical stimulus from the stimulus electrodes to neural tissue, while keeping the sense electrode disconnected from the measurement circuitry;
imposing a delay during which the stimulus electrodes are open circuited and the sense electrode is disconnected from the measurement circuitry and from the stimulus electrodes; and
after the delay, measuring a neural response signal present at the sense electrode by connecting the sense electrode to the measurement circuitry.

2. The method of claim 1 , wherein the sense electrode is open circuited during the post-stimulus delay so as to be disconnected from all other electrodes of the array, to prevent charge transfer to the sense electrode from other non-stimulus electrodes.

3. The method of claim 1 , wherein repeated measurement cycles are undertaken, and wherein the measurement amplifier is allowed to accumulate a bio-electrically defined steady state bias point over multiple cycles without re-setting the bias point each cycle.

4. The method of claim 1 , wherein the settle period is sufficiently long to permit the electrodes and circuitry to reach an equilibrium, as permitted by a stimulus rate.

5. The method of claim 1 , wherein the delay is in the range of substantially zero to 1 ms.

6. The method of claim 5 , wherein the delay is in the range of substantially 50 to 200 μs.

7. The method of claim 1 , wherein the delay is set to a value which ensures the measurement amplifier is not saturated and therefore performs linearly at all times when connected without experiencing clipping.

8. The method of claim 7 , wherein a feedback loop is implemented to determine a suitable minimum delay which avoids amplifier saturation for a given stimulus.

9. The method of claim 1 , wherein the signal from each sense electrode is passed to a sample-and-hold circuit at the input of a measurement amplifier.

10. The method of claim 1 , wherein a buffer or follower amplifier is provided between the sense electrode and the measurement amplifier, so that the high reverse impedance of the buffer effectively prevents switching transients from being conveyed to the sense electrode, thereby avoiding artefact which may arise upon the sense electrode if subjected to such transients.

11. The method of claim 1 , wherein the buffer amplifier is configured to give current gain to drive a storage capacitor of a sample and hold circuit.

12. The method of claim 10 , wherein a series capacitor is interposed between the sense electrode and the buffer to avoid DC transfer with the tissue.

13. The method of claim 1 , wherein the stimulus and sense electrodes are selected from an implanted electrode array.

14. The method of claim 1 , wherein each electrode of the electrode array is provided with an associated measurement amplifier, configured so as to avoid the need to switch the sense electrode(s) to a shared measurement amplifier.

15. The method of claim 1 , while recovering charge by short circuiting the stimulus electrodes together, the sense electrode is disconnected from the measurement circuitry, for example by setting a sample-and-hold circuit to “hold”.

16. The method of claim 1 , wherein an averaged CAP measurement is obtained by (i) delivering a first stimulus of a first polarity, and obtaining a first measurement of a CAP evoked by the first stimulus; (ii) delivering a second stimulus of a second polarity opposite to the first polarity, and obtaining a second measurement of a CAP evoked by the second stimulus; and (iii) taking an average of the first measurement and the second measurement to obtain an averaged measurement.

17. The method of claim 16 , further comprising obtain a curve of the averaged measurement vs. stimulus amplitude in order to obtain information regarding the recruitment effected by each stimulus.

18. The method of claim 17 , wherein the recruitment information is used for feedback control by the implant.

19. The method of claim 1 , when applied contemporaneously with administration of a drug, in order to gauge efficacy of drug delivery.

20. The method of claim 19 , wherein drug delivery is controlled by feedback based on CAP measurements.

21. The method of claim 1 , wherein the CAP is recorded within approximately 3 cm of the stimulus site.

22. The method of claim 1 , wherein the stimulus comprises a bi-phasic pulse, and the stimulus electrodes are configured with no capacitors so as to permit the stimulus electrode current to be interrupted or forced to zero, such as at those times where it would interfere with measurement.

23. A method of claim 1 , further comprising obtaining a compound action potential (CAP) measurement and providing feedback control of a neural stimulus using an implanted control unit, wherein the implanted control unit uses the obtained CAP measurement to control the delivery of subsequent neural stimuli by the implant.

Assignees

• Parker John Louis
• Single Peter Scott Vallack
• Karantonis Dean Michael
• Saluda Medical Pty Ltd

Inventors

• Parker John Louis
• Single Peter Scott Vallack
• Karantonis Dean Michael

Classifications

• A61N1/36135

  using physiological parameters · CPC title

• A61B5/6846

  specially adapted to be brought in contact with an internal body part, i.e. invasive · CPC title

• A61N1/36071

  Pain · CPC title

• A61M2230/08

  Other bio-electrical signals · CPC title

• A61B5/7203

  for noise prevention, reduction or removal · CPC title