A controlled pressure inflation-deflation device inflates a balloon to occlude a blood vessel by moving a large plunger to provide incremental pressure increases within a syringe. A releasable latch moves a second plunger, positioned within a syringe formed by an inner columnar opening in the large plunger, between an occlusion position and a perfusion position. A three-position switch has a release position to allow the large plunger to move freely, an adjust position to provide the incremental pressure increases, and a lock position to lock the location of the plunger. Pressures at which various balloons (e.g., folded balloons) achieve or nearly achieve a substantially circular cross-section may be extrapolated by inflating balloons with pressures equal and/or greater than the first occlusion pressure. Balloons may be pre-inflated up to or below the first occlusion pressure to achieve a substantially circular cross-section, prior to increasing the balloon to an occlusion pressure.
