Implantable neurostimulator with refractory stimulation

1. A method, comprising:

applying a first electrical signal to a nerve to evoke an action potential, said nerve thereafter entering a refractory period in which said nerve is refractory to further induction of action potentials; and

after applying said first electrical signal, altering said refractory period by applying a second electrical signal to said nerve during said refractory period, wherein said second electrical signal is effective to alter said refractory period and is unable to stimulate said nerve to evoke an action potential.

2. The method of claim 1 wherein applying said second electrical signal during said refractory period comprises providing current during a relative refractory period.

3. The method of claim 1 wherein applying said second electrical signal during said refractory period comprises providing current for a period of time that extends past said nerve's intrinsic refractory period.

4. The method of claim 1 wherein said refractory period comprises an absolute refractory period and a relative refractory period, and wherein applying said second electrical signal to said nerve during said refractory period comprises beginning to apply said second electrical signal to said nerve during said relative refractory period.

5. The method of claim 1 wherein altering said refractory period comprises shortening said refractory period by applying said second electrical signal having a polarity opposite that of a polarity of the first electrical signal.

6. The method of claim 1 wherein altering said refractory period comprises extending said refractory period by applying said second electrical signal having a polarity that is the same as a polarity of the first electrical signal.

7. The method of claim 1 wherein applying said second electrical signal to said nerve comprises applying said second electrical signal during a relative refractory period of a select nerve fiber type while not applying said second electrical signal during the refractory period of another nerve fiber type.

8. A method, comprising:

applying a first electrical signal to a nerve to evoke an action potential;

wherein said first electrical signal or said action potential evokes action potentials in non-target tissue;

said non-target tissue thereafter entering a refractory period in which the nontarget tissue is refractory to further induction of action potentials; and

after applying said first electrical signal, altering said refractory period of the non-target tissue by applying a second electrical signal to said nerve during said refractory period, wherein said second electrical signal is effective to alter said refractory period and has an insufficient magnitude to trigger an action potential in said non-target tissue.

9. The method of claim 8 wherein applying said second electrical signal during said refractory period comprises providing current during a relative refractory period.

10. The method of claim 8 wherein applying said second electrical signal during said refractory period comprises providing current for a period of time that extends past the non-target tissue's intrinsic refractory period.

11. The method of claim 8 wherein said refractory period comprises an absolute refractory period and a relative refractory period, and wherein applying said second electrical signal to said nerve during said refractory period comprises beginning to apply said second electrical signal to said nerve during said relative refractory period.

12. The method of claim 8 wherein altering said refractory period of the non-target tissue comprises shortening said refractory period by applying said second electrical signal having a polarity opposite that of a polarity of the first electrical signal.

13. The method of claim 8 wherein altering said refractory period of the non-target tissue comprises extending said refractory period by applying said second electrical signal having a polarity that is the same as a polarity of the first electrical signal.

14. The method of claim 8 wherein applying said second electrical signal to said nerve comprises applying said second electrical signal during a relative refractory period of a select nerve fiber type while not applying said second electrical signal during the refractory period of another nerve fiber type.

15. An implantable neurostimulator, comprising:

an electrical signal generator; and

an electrode coupled to said electrical signal generator and adapted to couple to a nerve;

wherein said electrical signal generator applies a first electrical signal to said nerve to evoke an action potential, said nerve thereby entering a refractory period in which said nerve is in a refractory state, and during said refractory period after applying said first electrical signal, said electrical signal generator alters said refractory period by applying a second electrical signal to said nerve, said second electrical signal being effective to alter said refractory period and unable to stimulate said nerve to evoke an action potential.

16. The implantable neurostimulator of claim 15 wherein said electrical signal generator extends said refractory period of said nerve.

17. The implantable neurostimulator of claim 15 wherein said electrical signal generator extends a relative refractory period of said nerve.

18. The implantable neurostimulator of claim 15 wherein said electrical signal generator shortens said refractory period of said nerve.

19. The implantable neurostimulator of claim 15 wherein said electrical signal generator shortens a relative refractory period of said nerve.

20. The implantable neurostimulator of claim 15 wherein said electrical signal generator applies said second electrical signal during a refractory period of a select nerve fiber type while not applying said second electrical signal during the refractory period of another nerve fiber type.

21. An implantable neurostimulator, comprising:

an electrical signal generator; and

an electrode coupled to said electrical signal generator and adapted to couple to a nerve to thereby provide therapy to a target nerve fiber;

wherein said electrical signal generator applies a first electrical signal to a nerve to evoke an action potential in the target nerve which causes an action potential to be evoked in a non-target nerve fiber or tissue, said non-target nerve fiber or tissue thereby entering a refractory period in which the non-target nerve fiber or tissue is in a refractory state, and during said refractory period after applying said first electrical signal, said electrical signal generator alters said refractory period of said non-target nerve fiber or tissue by applying a second electrical signal to said target nerve, said second electrical signal being effective to alter said refractory period and unable to trigger an action potential in said non-target nerve fiber or tissue.

22. The implantable neurostimulator of claim 21 wherein said first and second electrical signals have opposite polarities to each other and said refractory period is thereby shortened.

23. The implantable neurostimulator of claim 21 wherein said first and second electrical signals have a common polarity to each other and said refractory period is thereby extended.