A balloon catheter system comprising: a) an outer conduit; b) an inner conduit, suitable for passage over a guide wire, disposed within the lumen of said outer conduit such that the longitudinal axes of said inner and outer conduits are substantially parallel, and positionable such that the distal tip of said inner conduit extends beyond the distal tip of said outer conduit, wherein said inner conduit is capable of being moved along its longitudinal axis in relation to said outer conduit; c) an inflatable element whose proximal margin is attached to the outer surface of the distal tip of said outer conduit, and whose distal margin is attached to the outer surface of the portion of the inner conduit that extends beyond the distal tip of said outer conduit, and wherein the distal and/or proximal end portion(s) of said inflatable element are capable of intussuscepting upon proximal movement of said inner conduit in relation to said outer conduit; d) means for the introduction of an expansion fluid into the annular space formed between the inner surface of the outer conduit and the outer surface of the inner conduit and therefrom into the lumen of said inflatable element, and for the removal thereof; characterized by e) means for preventing pressure changes within said annular space upon axial movement of said inner conduit in relation to said outer conduit, wherein said means for preventing pressure changes comprise a syringe-like structure positioned at the proximal end of said catheter system, wherein the barrel portion of said syringe-like structure is formed by an expanded portion of the outer conduit, and wherein the plunger of said syringe-like structure co-axially surrounds the proximal end of the inner conduit, and is affixed thereto. a) an outer conduit; b) an inner conduit, suitable for passage over a guide wire, disposed within the lumen of said outer conduit such that the longitudinal axes of said inner and outer conduits are substantially parallel, and positionable such that the distal tip of said inner conduit extends beyond the distal tip of said outer conduit, wherein said inner conduit is capable of being moved along its longitudinal axis in relation to said outer conduit; c) an inflatable element whose proximal margin is attached to the outer surface of the distal tip of said outer conduit, and whose distal margin is attached to the outer surface of the portion of the inner conduit that extends beyond the distal tip of said outer conduit, and wherein the distal and/or proximal end portion(s) of said inflatable element are capable of intussuscepting upon proximal movement of said inner conduit in relation to said outer conduit; d) means for the introduction of an expansion fluid into the annular space formed between the inner surface of the outer conduit and the outer surface of the inner conduit and therefrom into the lumen of said inflatable element, and for the removal thereof; characterized by e) means for preventing pressure changes within said annular space upon axial movement of said inner conduit in relation to said outer conduit, wherein said means for preventing pressure changes comprise a syringe-like structure positioned at the proximal end of said catheter system, wherein the barrel portion of said syringe-like structure is formed by an expanded portion of the outer conduit, and wherein the plunger of said syringe-like structure co-axially surrounds the proximal end of the inner conduit, and is affixed thereto.