An apparatus for modulating the pressure of a fluid such as a gas within the expandable portion of a guide wire catheter. The apparatus features a means for controllably gripping and releasing the open, proximal end of a tubular guide wire, means for introducing a fluid to a desired pressure and volume into the expandable portion of the tubular guide wire through the open end, and, while maintaining the pressure and volume of fluid in the tubular guide wire, a means for sealing the open end of said tubular guide wire to seal the fluid in the tubular guide wire. In a preferred embodiment, the apparatus also features a deflation tool for re-opening the sealed tubular guide wire and letting the fluid out. In a particularly preferred embodiment, the pressure and volume of fluid in the tubular guide wire is maintained by utilizing an apparatus to crimp the end of the tubular guide wire, effectively sealing the inside bore of the tubular guide wire. Here, a deflation tool might comprise a means of severing the crimp from the rest of the tubular guide wire, unsealing the bore of the tubular guide wire. Preferably, the crossing profile of the crimped tubular guide wire is no greater than what it was prior to crimping. Using this apparatus, the tubular guide wire can be re-sealed and re-opened as necessary.