cardiac catheterization is conducted using a probe having a balloon assembly , in which a spring has a resting axially elongated configuration and a torsed , axially shortened configuration . an inflatable balloon is twisted about the spring and mechanically linked to the spring . a flexible sheath is disposed about the spring within the balloon , the sheath and the wall of the balloon defining a chamber to contain a fluid flowing therein and thereout for inflation of the balloon and deflation of the balloon so as to energize and de - energize the spring .