Method and apparatus for estimating neural recruitment

An implantable device for applying neural stimulus to neural tissue, 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 delivering stimulus pulses via the one or more stimulus electrodes to neural tissue;
• measurement circuitry for obtaining a measurement of a neural signal sensed at the one or more sense electrodes;
• and
• a control unit configured to:
• control the stimulus source to deliver a therapeutic pulse to neural tissue via the one or more stimulus electrodes, the therapeutic pulse having a first pulse width;
• control the stimulus source to deliver a probe pulse to the neural tissue having a second pulse width after the therapeutic pulse, wherein the second pulse width is less than the first pulse width, and wherein the probe pulse evokes a neural response;
• control the measurement circuitry to measure the neural response evoked by the probe pulse;
• determine a neural recruitment caused by the probe pulse based on the neural response;
• and
• determine a parameter for a subsequent therapeutic pulse based on the neural recruitment.

A method of applying stimulus to a tissue, the method comprising:

• delivering, by a plurality of stimulus electrodes, a plurality of therapeutic pulses having a first pulse width,
• delivering a plurality of probe pulses having a second pulse width interleaved with at least some therapeutic pulses of the plurality of therapeutic pulses, wherein the second pulse width is less than the first pulse width, and wherein the plurality of probe pulses evoke neural responses,
• measuring, after a probe pulse of the plurality of probe pulses and prior to a subsequent therapeutic pulse of the plurality of therapeutic pulses, a neural response evoked by the probe pulse of the plurality of probe pulses via one or more sense electrodes;
• determining a neural recruitment caused by the probe pulse of the plurality of probe pulses based on the neural response;
• and
• determining a parameter for the subsequent therapeutic pulse based on the neural recruitment.

An implantable device for applying neural stimulus to neural tissue, 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 delivering stimulus pulses via the one or more stimulus electrodes to neural tissue;
• measurement circuitry for obtaining a measurement of a neural signal sensed at the one or more sense electrodes;
• and
• a control unit configured to:
• control the stimulus source to deliver a plurality of therapeutic pulses to neural tissue via the one or more stimulus electrodes, the plurality of therapeutic pulses having a first pulse width;
• control the stimulus source to deliver a plurality of probe pulses to the neural tissue having a second pulse width interleaved with at least some therapeutic pulses of the plurality of therapeutic pulses, wherein the second pulse width is less than the first pulse width, and wherein the plurality of probe pulses evoke neural responses;
• control the measurement circuitry to measure, after a probe pulse of the plurality of probe pulses and prior to a subsequent therapeutic pulse of the plurality of therapeutic pulses, a neural response evoked by the probe pulse of the plurality of probe pulses;
• determine a neural recruitment caused by the probe pulse of the plurality of probe pulses based on the neural response;
• and
• determining a parameter for the subsequent therapeutic pulse based on the neural recruitment.