delineated by the lumen tube 15 and its inner circumference by the guide tube 14 the control structure carries an annular seal 22 which circumscribes the guide tube 14 an annular thumb screw 24 is threaded into the control structure 16 for controllably compressing the seal 22 to effect a fluid tight seal between the structure and the guide tube 14 the guide tube 14 has a plurality of position indicating indicia 25 near its proximal end the indicia 25 function to indicate to an operator relative longitudinal spacing of the distal ends of the guide and lumen tubes 14 15 an annular angioplasty balloon 26 is provided the balloon 26 has a proximal end connected to the distal end of the lumen tube at 28 the distal end of the balloon 26 is connected to the distal end of the guide tube 14 at 30 as indicated by a comparison of fig1 and 2 the guide tube is relatively moveable when the seal 22 is released between a retracted position as shown in fig1 and an extended position as shown in fig2 thus the balloon is adjustable between the position of fig1 where the balloon is folded on itself and the position of fig2 where the balloon 26 is fully extended the effect of this adjustment is to vary an inflation deflation volume 32 which is essentially fully defined by the balloon 26 in the retracted position of fig1 the inflation space 32 is perimetrically defined by the balloon 26 with its inner circumference defined by the guide tube 14 when the guide tube and balloon are in their fully extended positions as shown in fig2 fig1 a is a foreshortened sectional view of an.