The invention provides a medical device having a catheter and one or more expandable constricting/occluding members. The catheter is adapted for use with therapeutic or diagnostic devices, including an angioplasty/stent catheter and an atherectomy catheter. The constrictor/occluder is mounted at the distal end 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 are disclosed for preventing distal embolization during extracranial or intracranial carotid artery, vertebral artery, or coronary artery procedures, or procedures involving any vessel having collateral flow by reversing flow in the diseased vessel.