Using scrum methodology helps manage changing requirements during the course of product development. But how do we handle requirement changes within a sprint?

At CI we use the following process. All the changes initiated by the Product Owner are to be logged into a change tracker. This needs to be approved by any of the members of the Change Control Board. The member should preferrably not be the Product Owner. After approval, the Scrum Master computes the Backlog Churn. If the Churn is greater than the set percentage, re-prioritization of backlog is done by the Product Owner. If not the changes are done in the current sprint itself. This has helped us in managing change effectively.