Preferably, however, the lock will allow the forming element to be released so that the physician can release tension on the device 40 in the event of momentary over tightening. [0119] The forming element 56 and support 58, with or without the tubular body discussed below, may be surrounded by a tubular jacket of ePTFE or a polyester fabric such as DACRON, or other material which is wrapped or sti