Method and apparatus for measurement of neural response

• US 10,278,600 B2
• Filed: 06/16/2016
• Issued: 05/07/2019
• 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): Dougherty, Sean P
• Assistant Examiner(s): Fernandes, Patrick
• Application Number:
  US15/184,787
• Publication Number:
  US 20170071490A1
• Time in Patent Office: 1,055 Days
• 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. An implantable device for measuring a neural response to a stimulus, the device comprising:

a plurality of electrodes including at least one nominal stimulus electrode and at least one nominal sense electrode;

a stimulus source for providing a stimulus to be delivered from the one or more stimulus electrodes to neural tissue;

measurement circuitry for amplifying a neural signal sensed at the one or more sense electrodes; and

a control unit configured to control application of a stimulus to the neural tissue and measurement of an evoked neural response, the control unit configured to settle the measurement circuitry prior to a stimulus by connecting the at least one sense electrode to the measurement circuitry to allow the measurement circuitry to settle towards a bio-electrically defined steady state, the control unit further configured to recover charge on the stimulus electrodes by short circuiting the stimulus electrodes to each other, the control unit further configured to cause the stimulus source to apply an electrical stimulus from the stimulus electrodes to neural tissue while keeping the at least one sense electrode disconnected from the measurement circuitry, the control unit further configured to impose 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 the control unit further configured to measure a neural response signal present at the sense electrode by connecting the at least one sense electrode to the measurement circuitry after the delay.

2. The device of claim 1, wherein the control unit is further configured to open circuit the at least one sense electrode during the post-stimulus delay so the at least one sense electrode is disconnected from all other electrodes of the array, to prevent charge transfer to the at least one sense electrode from other non-stimulus electrodes.

3. The device of claim 1, wherein the control unit is further configured to undertake repeated measurement cycles and to allow a measurement amplifier to accumulate a bio-electrically defined steady state bias point over multiple cycles without re-setting the bias point each cycle.

4. The device of claim 1, wherein the control unit is further configured to cause the settle period to be sufficiently long to permit the electrodes and the measurement circuitry to reach an equilibrium, as permitted by a stimulus rate.

5. The device of claim 1, wherein the control unit is further configured to provide for the delay to be in the range of substantially zero to 1 ms.

6. The device of claim 5, wherein the control unit is further configured to provide for the delay to be in the range of substantially 50 to 200 μ

s.

7. The device of claim 1, wherein the control unit is further configured to provide for the delay to take a value which ensures a measurement amplifier is not saturated and therefore performs linearly at all times when connected without experiencing clipping.

8. The device of claim 7, further comprising a feedback loop configured to seek a suitable minimum delay which avoids amplifier saturation for a given stimulus.

9. The device of claim 1, configured to pass the signal from the at least one sense electrode to a sample-and-hold circuit at the input of the measurement circuitry.

10. The device of claim 1, further comprising a buffer or follower amplifier connected between the at least one sense electrode and a measurement amplifier, so that the high reverse impedance of the buffer effectively prevents switching transients from being conveyed to the sense electrode.

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

12. The device of claim 10, further comprising a series capacitor interposed between the at least one sense electrode and the buffer to avoid DC transfer with the tissue.

13. The device of claim 1, further comprising an electrode array, and wherein the control unit is further configured to select the at least one stimulus electrode and the at least one sense electrode from electrodes of the electrode array.

14. The device of claim 13, further comprising a respective measurement amplifier associated with each electrode of the electrode array, configured so as to avoid the need to switch the at least one sense electrode to a shared measurement amplifier.

15. The device of claim 1, wherein the control unit is further configured to disconnect the at least one sense electrode from the measurement circuitry, while recovering charge by short circuiting at least two of the at least one stimulus electrodes together.

16. The device of claim 15, wherein the control unit is configured to disconnect the at least one sense electrode from the measurement circuitry by setting a sample-and-hold circuit to “

hold”

.

17. The device of claim 1, wherein the control unit is further configured to obtain an averaged CAP measurement 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.

18. The device of claim 17, wherein the control unit is further configured to obtain a curve of the averaged measurement vs. stimulus amplitude in order to obtain information regarding the recruitment effected by each stimulus.

19. The device of claim 18, wherein the control unit is further configured to use the recruitment information for feedback control of a future stimulus.

20. The device of claim 1, wherein the control unit is further configured to control drug delivery by feedback based on CAP measurements.

21. The device of claim 1, wherein the at least one sense electrode is within 3 cm of the at least one stimulus electrode.

22. The device of claim 1, wherein the stimulus source is configured to deliver a bi-phasic pulse, and wherein the at least one stimulus electrode is configured with no capacitors so as to permit a stimulus electrode current to be interrupted or forced to zero.