Neural Measurement

• US 20170049345A1
• Filed: 05/05/2015
• Published: 02/23/2017
• Est. Priority Date: 05/05/2014
• Status: Active Grant

• Current Assignee: Saluda Medical Pty Ltd.
• Original Assignee: Saluda Medical Pty Ltd.
• Inventors: Single, Peter Scott Vallack
• Granted Patent: US 10,368,762 B2
• Time in Patent Office: 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 5/30 Input circuits therefor
• CPC Class Codes: A61B 5/311 for nerve conduction study [NCS]
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61N 1/0529 Electrodes for brain stimulation
• CPC Class Codes: A61N 1/0541 Cochlear electrodes
• CPC Class Codes: A61N 1/0551 Spinal or peripheral nerve electrodes
• CPC Class Codes: A61N 1/36128 Control systems
• CPC Class Codes: A61N 1/36135 using physiological parameters

Abstract

Measuring a neural response to a stimulus comprises applying an electrical stimulus, then imposing a delay during which the stimulus electrodes are open circuited. During the delay, a neural response signal present at sense electrodes is measured with a measurement amplifier, while ensuring that an impedance between the sense electrodes is sufficiently large that a voltage arising on the sense electrode tissue interface in response to the stimulus is constrained to a level which permits assessment of the neural response voltage seen at the sense electrode. For example the input impedance to the measurement amplifier (Z_IN) can be

$Z_{\mathrm{IN}}>Z_C\frac{\left(V_{S1}-V_{S2}\right)}{V_E},$

where Z_C is the sense electrode(s) constant phase element impedance, V_s1−V_s2 is the differential voltage arising on the sense electrode tissue interface, and V_E is the neural response voltage seen at the sense electrode.

Claims

1. A method for measuring a neural response to a stimulus, the method comprising:

applying an electrical stimulus from stimulus electrodes to neural tissue;

imposing a delay during which the stimulus electrodes are open circuited; and

during the delay, measuring a neural response signal present at sense electrodes with a measurement amplifier, while ensuring that an impedance between the sense electrodes is sufficiently large that a voltage arising on the sense electrode tissue interface in response to the stimulus is constrained to a level which permits assessment of the neural response voltage seen at the sense electrode.

2. The method of claim 1 wherein a differential measurement of the neural response is obtained by using two sense electrodes, and wherein the voltage arising on the sense electrode tissue interface in response to the stimulus is the differential voltage arising between the two sense electrodes in response to the stimulus.

3. The method of claim 1 wherein the input impedance to the measurement amplifier (Z_IN) is defined as:

4. The method of claim 3 wherein Z_IN is limited by:

Z_IN>

A×

Z_C(V_s1−

V_s2)/V_E

where A is a scalar provided to give sufficient margin of V_E over (V_S1−

V_S2)

5. The method of claim 4 wherein A is greater than 0.067.

6. The method of claim 5 wherein A is greater than 0.5.

7. The method of claim 5 wherein A is greater than 1.

8. The method of claim 5 wherein A is greater than 2.

9. The method of claim 1, further comprising providing a sense electrode capacitor in series between the sense electrode and the measurement amplifier, the sense electrode capacitor being chosen to have a capacitance which ensures that the voltage arising across the capacitor in response to the stimulus is constrained to a level which permits assessment of the neural response voltage seen at the sense electrode.

10. The method of claim 1 further comprising obtaining neural measurements repeatedly over time and monitoring for changes in the neural response to a given stimulus.

11. The method of claim 10 further comprising providing feedback control of a therapy delivered to the patient.

12. An implantable device for measuring a neural response to a stimulus, the device comprising:

a plurality of electrodes including one or more nominal stimulus electrodes and one or more nominal sense electrodes;

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

a measurement amplifier for amplifying a neural response signal sensed at the one or more sense electrodes, wherein an impedance between the sense electrodes is sufficiently large that a voltage arising on the sense electrode tissue interface in response to the stimulus is constrained to a level which permits assessment of the neural response voltage seen at the sense electrode; 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 apply an electrical stimulus from the stimulus electrodes to neural tissue, the control unit further configured to impose a delay during which the stimulus electrodes are open circuited, and the control unit further configured to, during the delay, measure a neural response signal present at the sense electrodes with the measurement amplifier.

13. The device of claim 12 wherein the control unit is further configured to obtain a differential measurement of the neural response by using two sense electrodes, and wherein the voltage arising on the sense electrode tissue interface in response to the stimulus is the differential voltage arising between the two sense electrodes in response to the stimulus.

14. The device of claim 12 wherein the input impedance to the measurement amplifier (Z_IN) has a value:

15. The device of claim 14 wherein Z_IN is limited by:

Z_IN>

A×

Z_C(V_S1−

V_S2)/V_E

where A is a scalar provided to give sufficient margin of V_E over (V_S1−

V_S2)

16. The device of claim 15 wherein A is greater than 0.067.

17. The device of claim 16 wherein A is greater than 0.5.

18. The device of claim 16 wherein A is greater than 1.

19. The device of claim 16 wherein A is greater than 2.

20. The device of claim 13, further comprising a sense electrode capacitor in series between the or each sense electrode and the measurement amplifier, the or each sense electrode capacitor having a capacitance which ensures that the voltage arising across the capacitor in response to the stimulus is constrained to a level which permits assessment of the neural response voltage seen at the sense electrode.