The invention provides a medical device having a catheter and one or more expandable constricting/occluding members. The catheter has a lumen communicating with a port at its distal end. The lumen and port are adapted for introduction of therapeutic or diagnostic devices, including an angioplasty/stent catheter and an atherectomy catheter, into a vertebral or basilar artery. The constrictor/occluder is mounted proximal to the port of the catheter. Manometers may be mounted distal to one or more constrictors for measuring pressure distal to the constrictor(s). Methods of using the devices for preventing distal embolization during vertebral and/or basilar procedures by reversing blood flow in the vertebral artery toward the subclavian artery are disclosed.