A medical guidewire system including an inner member having an outer diameter and an outer member having an inner diameter, the inner diameter being larger than the outer diameter. The inner and outer members are relatively slidable to adjust a stiffness of the guidewire system. The lumen of the outer member forms a gap for fluid flow therethrough. A connector to the inner member and a fluid infusion channel communicating with the gap for injection of fluid through the gap to exit a distal portion of the outer member.