Method and apparatus for measurement of neural response

• US 9,386,934 B2
• Filed: 05/11/2012
• Issued: 07/12/2016
• Est. Priority Date: 05/13/2011
• Status: Active Grant

• Current Assignee: Saluda Medical Pty Ltd.
• Original Assignee: Saluda Medical Pty Ltd.
• Inventors: Parker, John Louis, Single, Peter Scott Vallack, Karantonis, Dean Michael
• Primary Examiner(s): Eiseman, Adam J
• Assistant Examiner(s): FERNANDES, PATRICK M
• Application Number:
  US14/117,144
• Publication Number:
  US 20150164354A1
• Time in Patent Office: 1,523 Days
• US Class Current: 1/1
• CPC Class Codes: A61B 5/24 Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
• CPC Class Codes: A61B 5/4848 Monitoring or testing the effects of treatment, e.g. of medication
• CPC Class Codes: A61B 5/6846 specially adapted to be brought in contact with an internal body part, i.e. invasive
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7285 for synchronising or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal A61B6/5205, A61B6/541, A61B8/5207, A61B8/543 take precedence
• CPC Class Codes: A61M 2230/08 Other bio-electrical signals
• CPC Class Codes: A61M 5/1723 using feedback of body parameters, e.g. blood-sugar, pressure measurement of body parameters A61B5/00
• CPC Class Codes: A61N 1/36071 Pain
• CPC Class Codes: A61N 1/36125 Details of circuitry or electric components
• CPC Class Codes: A61N 1/36135 using physiological parameters
• CPC Class Codes: A61N 1/36146 specified by the stimulation parameters

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.

Claims

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 μ

s.

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.