A gas inflation/evacuation system and sealing system for use with occlusive devices such as occlusive balloons in vascular procedures. The gas inflation/evacuation system is removably connectible to a proximal portion of a guidewire assembly and includes an evacuation system to evacuate the guidewire assembly and an inflation system for introducing a biocompatible gas under pressure into the guidewire assembly to inflate an occlusive device a plurality of times. A sealing system is also removably connectible to the proximal portion of the guidewire assembly and selectively seals an extended sealable section at the proximal portion of the guidewire assembly at one of a plurality of separate locations to form an airtight seal of the guidewire assembly. Each time a deflation of the occlusive device is desired in order to reestablish blood flow to the vessel downstream of the occlusive device, the extended sealable section at the proximal portion of the guidewire assembly preferably is cut distal to the location of the last seal to quickly deflate the occlusive device.