Variable stiffness catheter

1. A variable stiffness catheter comprising:

an outer layer having a bore with an inner surface;

an inner layer disposed within the bore and being coaxial with the outer layer, the inner layer having an outer surface;

a first coil having a first helical axis coaxial with the inner layer and comprising a first wire wrapped around the first helical axis in a first plurality of turns disposed between the inner surface and the outer surface, the first coil being fixed in place relative to the outer layer and the inner layer; and

a second coil having a second helical axis coaxial with the inner layer, the second coil being comprising a second wire wrapped around the second helical axis in a second plurality of turns disposed between the first inner surface and the second inner surface, and between turns of the first plurality of turns, the second coil being rotatable about the second helical axis relative to the outer layer, the inner layer, and the first coil.

2. The variable stiffness catheter of claim 1 further comprising a tube disposed between the inner surface and the outer surface, the tube being proximal to the first coil and the second coil and having a distal end coupled to a proximal end of the second coil.

3. The variable stiffness catheter of claim 2 wherein the tube is comprised of stainless steel.

4. The variable stiffness catheter of claim 1 wherein the first wire and the second wire are comprised of stainless steel.

5. The variable stiffness catheter of claim 1 wherein the first wire has a first cross section and the second wired has a second cross section and wherein the first cross section and the second cross section are substantially equal.

6. The variable stiffness catheter of claim 1 wherein the first wire has a first cross section and the second wired has a second cross section and wherein the first cross section and the second cross section are different from one another.

7. The variable stiffness catheter of claim 1 wherein the first coil is biased to have a distal helical axis curved relative to the first helical axis.

8. The variable stiffness catheter of claim 7 wherein the second coil has a first position that constrains the distal helical axis to be coaxial with the first helical axis and a second position that does not constrain the distal helical axis.

9. The variable stiffens catheter of claim 1 wherein an inner surface of the outer layer extends into a space between adjacent turns of the first coil and wherein the inner surface has a helical groove in the space between adjacent turns sized to receive the second coil.

10. The variable stiffness catheter of claim 1 wherein an outer surface of the inner layer extends into a space between adjacent turns of the first coil and wherein the outer surface has a helical groove in the space between adjacent turns sized to receive the second coil.

11. The variable stiffness catheter of claim 1 wherein the first wire has a round cross section.

12. The variable stiffness catheter of claim 1 wherein the second wire has a rectangular cross section.

13. A variable stiffness catheter comprising:

a wall having an inner surface and an outer surface;

a first coil disposed in the wall between the inner surface and the outer surface, the first coil being fixed in place relative to the wall;

a helical channel disposed in the wall between the inner surface and the outer surface between adjacent turns of the first coil; and

a second coil disposed in the helical channel, the second coil being movable within the helical channel.

14. The variable stiffness catheter of claim 13 wherein the wall is comprised of an outer layer comprising a first material and an inner layer comprising a second material.

15. The variable stiffness catheter of claim 13 wherein the wall is comprised of a single layer of material.

16. The variable stiffness catheter of claim 13 wherein the second coil is coated with a nonstick material.