In typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient and advanced through the aorta until the distal end is in the ostium of the desired coronary artery.  Using fluoroscopy, a guide wire is then advanced through the guiding catheter and across the site to be treated in the coronary artery.  A balloon catheter is advanced over the guide wire to the treatment site.  The balloon is then expanded to reopen the artery.  The catheter may have a guide wire lumen which is as long as the catheter (such as with an over the wire catheter--OTW) or it may be a rapid exchange catheter wherein the guide wire lumen is substantially shorter than the catheter.  Alternatively, a fixed wire balloon catheter could be used.  This device features a guide wire which is affixed to the catheter and cannot be removed. 
To help prevent arterial closure, repair dissection, or prevent restenosis, a physician can implant an intravascular prosthesis, or a stent, for maintaining vascular patency inside the artery at the lesion.  The stent may either be a self-expanding stent or a balloon expandable stent.  For the latter type, the stent is often delivered on a balloon and the balloon is used to the expand the stent.  The self-expanding stents may be made of shape memory materials such as nitinol or constructed of other metals but of a design which exhibits self expansion characteristics. 
In certain known stent delivery catheters, a stent and an optional balloon are positioned at the distal end of the catheter, around a core lumen.  The stent and balloon are held down and covered by a sheath or sleeve.  When the distal portion is in its desired location of the targeted vessel the sheath or sleeve is retracted to expose the stent.  After the sheath is removed, the stent is free to self-expand or be expanded with a balloon. 
A number of sheath designs are known in the art including those disclosed in U.S. Pat.  No.  4,732,152 to Wallsten ('152), U.S. Pat.  No.  4,848,343 to Wallsten ('343), U.S. Pat.  No.  4,875,480 to Imbert, U.S. Pat.  No.  5,662,703 to Yurek et al. (' 703), U.S. Pat.  No.  5,690,644 to Yurek ('644) and WO 94/15549, all of which disclose using a sleeve formed of a doubled-over section of membrane to compress and contain the stent. 
Wallsten '152 and Wallsten '343 disclose the use of lubricants on the interior walls of the membrane.  Moreover, fluid may be introduced into the chamber that is formed, in part, by the walls of the doubled-over membrane. 
The Imbert device contains small holes in the sleeve to allow for the expulsion of gas therefrom upon the introduction of a fluid into the region between the inner and outer walls.  The holes are not sized to allow for fluid flow therethrough. 
Yurek '703 discloses a stent that is retained distal to the inner tube by a folded over sheath.  The outer layer of the sheath, although not the inner layer, is disclosed as being porous.  The Yurek '644 patent and WO 94/15549 disclose a catheter in which a stent is mounted on an inner tube and retained by a double walled hose having micropores in the outer wall of the hose.  The micropores allow for the flow of fluid therethrough.  The Yurek catheter is of the rapid-exchange design. 
U.S. Pat.  No.  5,445,646 to Euteneuer et al.,  incorporated herein in its entirety by reference, discloses a stent delivery apparatus comprising a single layer sheath retaining sleeve means for retaining the stent in its delivery configuration attached to a slipping sleeve means for releasing the stent to self-expand.  The slipping sleeves may be activated hydraulically by delivering a fluid to the area in between the inner and outer layers of the slipping sleeve. 
While the use of rolling membranes is known, it is desirable to provide a medical device delivery system with a rolling retractable sheath in which the frictional interactions between the inner and outer walls of the sheath are reduced without requiring hydraulic activation.  A rolling membrane eliminates the problem of sliding friction that is common with sliding sheaths as the rolling membrane, literally, rolls off of the stent.  This, in turn, results in a lesser likelihood of the stent being damaged as the sheath is removed from over it.  It is also desirable to provide such a system with a sealed rolling retractable sheath to prevent any lubricants interior to the sheath from interacting with any bodily fluids.  It is also desirable to provide such a system having a rolling retractable sheath whose inner and outer walls exhibits different physical properties such as hoop strength and creep resistance.  The creep resistance of the outer wall is of particular value in preventing the stent from growing in profile and thereby deforming the catheter sheath.  Finally, it is desirable to provide a medical device delivery system which is self-priming. 
The present invention addresses these needs in its various embodiments as described below.