Expandable balloon

1. An expandable balloon for insertion in a vessel of the human or animal body, the balloon being movable between a collapsed condition and an expanded condition to expand the vessel, wherein a plaque disrupting member is disposed on an outer surface of the balloon when in the expanded condition, the plaque disrupting member extending over a lengthwise portion of the balloon, and the balloon having, when in the expanded condition, a centre line which follows a substantially helical path, wherein the plaque disrupting member is arranged helically on the balloon outer surface with substantially the same pitch as a helical centre line of the balloon, and wherein the plaque disrupting member is fixed at one end thereof relative to the balloon outer surface and is not attached to the balloon outer surface over a lengthwise extending portion of the balloon and, wherein the plaque disrupting member comprises a holder at its other end which is movable relative to the balloon outer surface.

2. A balloon as claimed in claim 1 , wherein the helical centre line rotates around a longitudinal axis, and the plaque disrupting member is arranged so that when the balloon is in the expanded condition it faces radially outwardly with respect to the longitudinal axis.

3. A balloon as claimed in claim 1 , wherein the helical arrangement of the plaque disrupting member has the same handedness as the helical centre line of the balloon.

4. A balloon as claimed in claim 1 , wherein the helical arrangement of the plaque disrupting member has the opposite handedness to the helical centre line of the balloon.

5. A balloon as claimed in claim 1 , comprising a plurality of plaque disrupting members provided at a circumferential interval or at circumferential intervals around the balloon outer surface.

6. A balloon as claimed in claim 1 , wherein when the balloon is in the collapsed condition, it is divided into a plurality of pleats which are wrapped around a central shaft.

7. A balloon as claimed in claim 6 , wherein the pleats each have a radially inner fold line, and wherein the radially inner fold line extends helically around the central shaft.

8. A balloon as claimed in claim 6 , wherein the plaque disrupting member is provided on the balloon outer surface so as to face radially outwardly when the balloon is in the collapsed condition.

9. A balloon as claimed in claim 6 , wherein the plaque disrupting member is provided on the balloon outer surface so as to be covered by at least one of the pleats when the balloon is in the collapsed condition.

10. A balloon as claimed in claim 1 , wherein the holder is arranged to be axially movable.

11. A balloon as claimed in claim 1 , wherein the holder is arranged to be rotatably movable.

12. A balloon as claimed in claim 1 , wherein the holder comprises a ring.

13. A balloon as claimed in claim 1 , wherein the plaque disrupting member extends continuously over a lengthwise portion of the balloon.

14. A balloon as claimed in claim 1 , wherein the plaque disrupting member extends over a lengthwise portion of the balloon as a plurality of plaque disrupting members arranged at longitudinal intervals.

15. A balloon as claimed in claim 1 , wherein the plaque disrupting member comprises a cutting blade or wire.

16. A balloon as claimed in claim 1 , wherein the balloon has, when in the expanded condition, the helical centre line which follows a substantially helical path so that the balloon has a helical shape, and the balloon is configured so that when the balloon is expanded in the vessel the balloon expands the vessel to a helical shape corresponding to the helical shape of the expanded balloon as constrained by the vessel.

17. A method of treating a plaque in a vessel of the human or animal body, the method comprising deploying a balloon in a collapsed condition to a treatment site and expanding the balloon to expand the vessel, wherein a plaque disrupting member is disposed on an outer surface of the balloon, the plaque disrupting member extending over a lengthwise portion of the balloon, so that when the balloon is in the expanded condition the plaque disrupting member exerts pressure on the plaque, and the balloon having, when in the expanded condition, a centre line which follows a substantially helical path, wherein the plaque disrupting member is arranged helically on the balloon outer surface with substantially the same pitch as a helical centre line of the balloon, and wherein the plaque disrupting member is fixed at one end thereof relative to the balloon outer surface and is not attached to the balloon outer surface over a lengthwise extending portion of the balloon and, wherein the plaque disrupting member comprises a holder at its other end which is movable relative to the balloon outer surface.

18. A method as claimed in claim 17 , comprising determining the shape of a plaque, and using a balloon with a plaque disrupting member extending helically generally to follow the shape of the plaque.

19. The method as claimed in claim 17 , wherein the plaque disrupting member comprises a cutting blade or wire.

20. The method as claimed in claim 17 , wherein the balloon has, when in the expanded condition, a helical shape, and the balloon is configured so that when the balloon is expanded in the vessel the balloon expands the vessel to a helical shape corresponding to the helical shape of the expanded balloon as constrained by the vessel.