In some examples, a catheter includes an expandable member configured to expand radially outward from a collapsed configuration to an expanded configuration. The expandable member is configured to be expanded and contracted in a controlled manner, e.g., in response to user actuation or automatically under the control of control circuitry of a device. For example, in some examples, control circuitry of a device can be configured to control the expandable member to expand and contract according to a predetermined expansion frequency or according to an expansion frequency determined based on a cardiac cycle of a patient.