Determining estimated neural threshold with ECAP signals
Systems, devices, and techniques are described for analyzing evoked compound action potential (ECAP) signals to determine an estimated neural threshold of a patient. In one example, a method includes controlling, by processing circuitry, delivery of a plurality of stimulation pulses to a patient, wherein each stimulation pulse of the plurality of stimulation pulses is at least partially defined by a different respective value of a stimulation parameter; receiving, by the processing circuitry, ECAP signal information, wherein the ECAP signal information comprises ECAP signals sensed by sensing circuitry and elicited by the plurality of stimulation pulses; determining, by the processing circuitry and based on the ECAP signal information, ECAP characteristic values for each of the ECAP signals elicited by the plurality' of stimulation pulses; and determining, by the processing circuitry and based on the ECAP characteristic values, an estimated neural threshold of the patient.
1 . A system comprising:
processing circuitry configured to:
control delivery of a plurality of stimulation pulses to a patient, wherein each stimulation pulse of the plurality of stimulation pulses is at least partially defined by a different respective value of a stimulation parameter;
receive evoked compound action potential (ECAP) signal information, wherein the ECAP signal information comprises ECAP signals sensed by sensing circuitry and elicited by the plurality of stimulation pulses;
determine, based on the ECAP signal information, ECAP characteristic values for each of the ECAP signals elicited by the plurality of stimulation pulses;
determine a relationship between the ECAP characteristic values and the different respective values of the stimulation parameter; and
determine, based on the relationship between the ECAP characteristic values and the different respective values of the stimulation parameter, an estimated neural threshold of the patient for stimulation.
2 . The system of claim 1 , wherein the processing circuitry is further configured to control stimulation circuitry to generate and deliver stimulation therapy based on the estimated neural threshold.
3 . The system of claim 1 , wherein the processing circuitry is further configured to iteratively increase the value of the stimulation parameter until the estimated neural threshold is determined.
4 . The system of claim 3 , wherein the stimulation parameter comprises one of a pulse amplitude, pulse width, pulse rate, or duty cycle.
5 . The system of claim 1 , wherein the stimulation parameter is a stimulation amplitude, wherein the processing circuitry is further configured to store data on a storage device, the data defining a correlation curve defining the relationship between the ECAP characteristic values and the different respective values of the stimulation amplitude, wherein the correlation curve includes a first region where change in the value of the stimulation amplitude is defined in part by residual artifact, and a second region where change in the stimulation amplitude is defined in part by patient neural response, and wherein the first region is prior to the estimated neural threshold and the second region is after the estimated neural threshold.
6 . The system of claim 5 , wherein the processing circuitry is configured to determine the estimated neural threshold at least in part on a curvature of an inflection region of the correlation curve.
7 . The system of claim 6 , wherein the relationship is defined by:
E
(
I
)
=
R
(
I
,
I
t
h
r
,
σ
)
·
S
Resp
+
I
·
S
a
r
t
+
N
;
wherein:
R
(
I
,
I
thr
,
σ
)
=
(
σlog
(
exp
(
-
I
-
I
thr
σ
)
+
1
)
+
(
I
-
I
thr
)
)
;
E(I) comprises an estimated neural response at a given stimulation current I;
I thr comprises an estimated threshold for neural activation;
σ comprises a parameter defining a rate of transition between a linear region of data and a curved region of data;
S art comprises is a rate of growth of an artifact with current; and
S resp comprises a rate of growth in the linear region of data.
8 . The system of claim 1 , wherein one of the ECAP characteristic values comprises a direct measurement between an N1 peak and a P2 peak of the ECAP signal information.
9 . The system of claim 1 , wherein the ECAP characteristic values comprise the ECAP signal information with an artifact removed therefrom.
10 . The system of claim 9 , wherein, to remove the artifact, the processing circuitry is configured to:
model the artifact as a sum of a single exponential component plus a linear component; and
remove the sum from each ECAP signal.
11 . The system of claim 10 , wherein, to model the artifact, the processing circuitry is configured to estimate a minimum of an error function by weighting the error function higher in a first region than in a second region, wherein the first region is prior to a patient neural response and the second region is after the patient neural response.
12 . The system of claim 9 , wherein, to remove the artifact, the processing circuitry is configured to pass the ECAP signal through a high-pass filter.
13 . The system of claim 1 , further comprising:
stimulation generation circuitry configured to:
generate a first train of electrical stimulation pulses at a first frequency to a first target tissue; and
generate a second train of electrical stimulation pulses at a second frequency to a second target tissue different from the first target tissue, wherein:
at least some electrical stimulation pulses of the first train of electrical stimulation pulses are interleaved with at least some electrical stimulation pulses of the second train of electrical stimulation pulses, and wherein the first frequency is greater than the second frequency; and
the processing circuitry is further configured to determine amplitude values for the first and second trains of electrical stimulation pulses as respective percentages of the estimated neural threshold.
14 . The system of claim 1 , wherein the stimulation parameter comprises a first stimulation parameter, and wherein the processing circuitry is configured to determine an initial value of a second stimulation parameter different from the first stimulation parameter based on ECAP characteristic values determined from different values of the second stimulation parameter.
15 . The system of claim 1 , wherein an implantable medical device or an external programming device comprises at least a portion of the processing circuitry.
16 . The system of claim 1 , wherein the estimated neural threshold is representative of a perception threshold of the patient for stimulation.
17 . A method comprises:
controlling, by processing circuitry, delivery of a plurality of stimulation pulses to a patient, wherein each stimulation pulse of the plurality of stimulation pulses is at least partially defined by a different respective value of a stimulation parameter;
receiving, by the processing circuitry, evoked compound action potential (ECAP) signal information, wherein the ECAP signal information comprises ECAP signals sensed by sensing circuitry and elicited by the plurality of stimulation pulses;
determining, by the processing circuitry and based on the ECAP signal information, ECAP characteristic values for each of the ECAP signals elicited by the plurality of stimulation pulses;
determining, by the processing circuitry, a relationship between the ECAP characteristic values and the different respective values of the stimulation parameter; and
determining, by the processing circuitry and based on the relationship between the ECAP characteristic values and the different respective values of the stimulation parameter, an estimated neural threshold of the patient for stimulation.
18 . The method of claim 17 , further comprising controlling stimulation circuitry to generate and deliver stimulation therapy based on the estimated neural threshold.
19 . The method of claim 17 , wherein the stimulation parameter is a stimulation amplitude, and wherein the method further comprises storing data on a storage device, the data defining a correlation curve defining the relationship between the ECAP characteristic values and the different respective values of the stimulation amplitude, wherein the correlation curve includes a first region where change in the value of the stimulation amplitude is defined in part by residual artifact, and a second region where change in the stimulation amplitude is defined in part by patient neural response, and wherein the first region is prior to the estimated neural threshold and the second region is after the estimated neural threshold.
20 . The method of claim 17 , wherein the ECAP characteristic values comprise the ECAP signal information with an artifact removed therefrom, and wherein the method comprises:
to remove the artifact, modeling the artifact as a sum of a single exponential component plus a linear component, wherein modeling the artifact comprises estimating a minimum of an error function by weighting the error function higher in a first region than in a second region, wherein the first region is prior to a patient neural response and the second region is after the patient neural response; and
removing the sum from each ECAP signal.
21 . A computer-readable storage medium comprising instructions that, when executed by processing circuitry, causes the processing circuitry to:
control delivery of a plurality of stimulation pulses to a patient, wherein each stimulation pulse of the plurality of stimulation pulses is at least partially defined by a different respective value of a stimulation parameter;
receive evoked compound action potential (ECAP) signal information, wherein the ECAP signal information comprises ECAP signals sensed by sensing circuitry and elicited by the plurality of stimulation pulses;
determine, based on the ECAP signal information, ECAP characteristic values for each of the ECAP signals elicited by the plurality of stimulation pulses;
determine a relationship between the ECAP characteristic values and the different respective values of the stimulation parameter; and
determine, based on the relationship between the ECAP characteristic values and the different respective values of the stimulation parameter, an estimated neural threshold of the patient for stimulation.