A system for deploying a device to a distal location across a diseased vessel, comprising a sheath comprising an expandable distal portion comprising a porous wall defining a lumen there-through, the distal portion having a collapsed configuration, wherein the sheath has a first cross-sectional outer diameter and a first lumen inner diameter, and an expanded configuration, wherein the sheath has a second cross-sectional outer diameter and a second lumen inner diameter； wherein in the collapsed configuration, the sheath is configured to be advanced across at least a portion of the diseased vessel to a position adjacent the distal location and wherein said system comprises a removable expansion retention member configured to retain the expandable sheath in the collapsed configuration.
