An apparatus for modulating the pressure of a fluid such as a gas within the expandable portion of a guide wire catheter. In one 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 be employed to sever the crimp from the rest of the tubular guide wire, unsealing the bore of the tubular guide wire. Using this apparatus, the tubular guide wire can be re-sealed and re-opened as necessary.