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A method embodiment comprises generating a neural stimulation signal for a neural stimulation therapy. The signal is generated during a duty cycle of a stimulation period to provide the neural stimulation therapy with an intensity at a therapy level for a portion of the duty cycle. In various embodi

A method embodiment comprises generating a neural stimulation signal for a neural stimulation therapy. The signal is generated during a duty cycle of a stimulation period to provide the neural stimulation therapy with an intensity at a therapy level for a portion of the duty cycle. In various embodiments, a ramp up protocol is implemented to begin the duty cycle, a ramp down protocol is implemented to end the duty cycle, or both the ramp up protocol and the ramp down protocol are implemented. The ramp up protocol includes ramping up the intensity from a non-zero first subthreshold level for the neural stimulation therapy at the beginning of the duty cycle to the therapy level. The ramp down protocol includes ramping down the intensity from the therapy intensity level to a non-zero second subthreshold level for the neural stimulation therapy at the end of the duty cycle.

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1. A method, comprising: generating a neural stimulation signal only during a duty cycle of a stimulation period to provide intermittent neural stimulation for a neural stimulation therapy, including: generating the neural stimulation signal during the duty cycle of the stimulation period to provide

1. A method, comprising: generating a neural stimulation signal only during a duty cycle of a stimulation period to provide intermittent neural stimulation for a neural stimulation therapy, including: generating the neural stimulation signal during the duty cycle of the stimulation period to provide the neural stimulation therapy with an intensity at a therapy level for a portion of the duty cycle, the neural stimulation signal including a stimulation pulse train; andimplementing a ramp up protocol to begin the duty cycle, a ramp down protocol to end the duty cycle, or both the ramp up protocol to begin the duty cycle and the ramp down protocol to end the duty cycle; wherein the ramp up protocol includes a programmed value for at least one programmable ramp up parameter, and wherein implementing the ramp up protocol includes stepping up the intensity from a zero value before the duty cycle when the neural stimulation signal is not generated to a non-zero first subthreshold level for the neural stimulation therapy at the beginning of the duty cycle, and implementing a programmed ramp up algorithm to ramp up the intensity from the non-zero first subthreshold level at the beginning of the duty cycle to the therapy level; andwherein the ramp down protocol includes a programmed value for at least one programmable ramp down parameter, and wherein implementing the ramp down protocol includes implementing a programmed ramp down algorithm to ramp down the intensity from the therapy level to a non-zero second subthreshold level for the neural stimulation therapy at the end of the duty cycle, and stepping down the neural stimulation intensity from the non-zero second subthreshold level at the end of the duty cycle to the zero value after the duty cycle. 2. The method of claim 1, wherein implementing the ramp up protocol or the ramp down protocol includes changing at least one of an amplitude, a frequency, or a pulse width of the stimulation pulse train. 3. The method of claim 1, further comprising stimulating at least one of an autonomic neural target using the neural stimulation signal, the autonomic neural target including a vagus nerve, a cardiac nerve, or a cardiac fat pad, wherein implementing the ramp up protocol or the ramp down protocol includes avoiding or reducing overshoot or rebound of a target autonomic response. 4. The method of claim 1, further comprising: monitoring a physiologic response at the beginning or the end of the duty cycle; andautomatically adjusting according to the monitored physiologic response the at least one programmable ramp up parameter, the at least one programmable ramp up parameter, or both the at least one programmable ramp up parameter and the at least one programmable ramp up parameter, wherein: the monitored physiologic response includes a heart rate response, a blood pressure response, or a heart rate variability response;the at least one programmable ramp up parameter includes a non-zero first sub-threshold level parameter, a ramp up duration parameter, or a therapy level intensity parameter; andthe at least one programmable ramp down parameter includes the therapy level intensity parameter, a non-zeros second subthreshold level parameter, or a ramp-down duration parameter. 5. The method of claim 4, wherein the heart rate response includes a change in heart rate or an acceleration of heart rate, and wherein the blood pressure response includes a change in mean blood pressure, or an acceleration of mean blood pressure. 6. The method of claim 4, wherein automatically adjusting according to the monitored physiologic response the at least one programmable ramp up parameter or the at least one programmable ramp down parameter further includes: programming the therapy level intensity parameter to a desired therapy intensity according to the monitored heart rate response or the monitored blood pressure response; andprogramming the first subthreshold level parameter or the second subthreshold level parameter to a percentage of the programmed therapy level intensity. 7. The method of claim 6, wherein the percentage is between approximately 50% to approximately 90%. 8. The method of claim 4, wherein automatically adjusting according to the monitored physiologic response the at least one programmable ramp up parameter or the programmable ramp down parameter further includes adjusting the ramp up duration parameter or the ramp down duration parameter in adaptation to the monitored physiologic response and a desired physiological response to the neural stimulation. 9. The method of claim 8, wherein the adjusted ramp up duration parameter or the adjusted ramp down duration parameter is within a range between approximately 1 to approximately 15 seconds or between approximately 10% to approximately 60% of the duration of the duty cycle. 10. The method of claim 1, further comprising detecting a circadian rhythm and adjusting according to the detected circadian rhythm the at least one programmable ramp up parameter or the programmable ramp down parameter. 11. A neural stimulator, comprising: a neural stimulation delivery system configured to generate a neural stimulation signal only during a duty cycle of a stimulation period to provide intermittent neural stimulation for a neural stimulation therapy; anda controller configured to control the neural stimulation delivery system using at least one programmable parameter to: generate the neural stimulation signal during the duty cycle of the stimulation period to provide the neural stimulation therapy with an intensity at a therapy level for a portion of the duty cycle, the neural stimulation signal including a stimulation pulse train; andimplement a protocol selected from the group of protocols consisting of: a ramp up protocol to begin the duty cycle by stepping up the intensity from a zero value before the duty cycle when the neural stimulation signal is not generated to a non-zero first subthreshold level for the neural stimulation therapy at the beginning of the duty cycle, and the ramp up protocol further including a programmed ramp up algorithm to ramp up the intensity from the non-zero first subthreshold level at the beginning of the duty cycle to the therapy level;a ramp down protocol, including a programmed ramp down algorithm to ramp down the intensity from the therapy level and ending with a non-zero second subthreshold level for the neural stimulation therapy at the end of the duty cycle, and the ramp down protocol further including stepping down the neural stimulation intensity from the non-zero second subthreshold level at the end of the duty cycle to the zero value after the duty cycle; anda protocol that includes both the ramp up protocol to begin the duty cycle and the ramp down protocol to end the duty cycle. 12. The stimulator of claim 11, wherein in implementing the ramp up protocol or the ramp down protocol the controller is configured to change at least one of an amplitude, a frequency, or a pulse width of the stimulation pulse train. 13. The stimulator of claim 11, further comprising a physiologic sensor configured to sense a physiologic response at the beginning or the end of the duty cycle, wherein: the physiologic sensor includes at least one of a heart rate sensor, a blood pressure sensor, or a heart rate variability sensor; andthe controller is configured to use the send physiologic response to automatically adjust the at least one programmable parameter selected from a group of parameters consisting of: a non-zero first sub-threshold level parameter; a ramp up duration parameter; a therapy level intensity parameter; a non-zero second subthreshold level parameter; and a ramp-down duration parameter. 14. The stimulator of claim 13, wherein the controller is further configured to: use the sensed heart rate response or the sensed blood pressure response to program the therapy level intensity parameter to a desired therapy intensity; andprogram the first subthreshold level parameter or the second subthreshold level parameter to a percentage of the determined therapy level intensity. 15. The stimulator of claim 13, wherein the controller is configured to adjust the ramp up duration parameter or the ramp down duration parameter in adaptation to the sensed physiologic response and a desired physiological response to the neural stimulation. 16. The stimulator of claim 15, wherein the controller is further configured to maintain the adjusted ramp up duration parameter or the adjusted ramp down duration parameter within a predetermined duration range. 17. The stimulator of claim 11, further comprising a circadian rhythm detector configured to detect a circadian rhythm, wherein the controller is configured to use the detected circadian rhythm to automatically adjust the at least one programmable parameter for the ramp up protocol, the ramp down protocol or both the ramp up and ramp down protocols. 18. The stimulator of claim 11, wherein the neural stimulation delivery system is configured to stimulate an autonomic neural target including a vagus nerve, a cardiac nerve, or a cardiac fat pad. 19. The stimulator of claim 18, wherein the neural stimulation delivery system is configured to stimulate an intravascular site proximate to the autonomic neural target. 20. The stimulator of claim 11, further comprising a cardiac pacing system, wherein: the stimulator is an implantable stimulator configured to generate the neural stimulation signal for heart failure therapy; andthe cardiac pacing system includes an implantable pulse generator configured to generate cardiac resynchronization pacing for heart failure therapy.