the following detailed description should be read with reference to the drawings in which similar parts in different figures are numbered the same . the drawings , which are not necessarily to scale , depict exemplary embodiments and are not intended to limit the scope of the invention . those skilled in the art will recognize that many of the examples provided have suitable alternatives which may also be utilized . it is well known in the stent delivery art that an entire catheter may be repositioned within a vessel to properly position and seat a stent . however , moving the entire catheter places unwanted strain along the entire length of the vessel . in order to ensure that the inner balloon may be repositioned to properly seat the stent , without requiring that the entire catheter be repositioned , the present invention provides for a stent delivery system having an independently moveable inner balloon for stent seating . the present invention relates to a high pressure medical device deployment catheter . fig1 illustrates a catheter , indicated generally at 20 , for deploying a stent 24 . as shown , catheter 20 has two balloons , a shorter mobile high pressure inner balloon 30 within a longer low pressure outer balloon 40 distally mounted upon an inner tube or shaft 32 . the inner balloon 30 is capable of independent movement relative the inner tube 32 . in an alternative embodiment , the outer balloon 40 may be capable of independent motion as well . in an embodiment where the respective balloons 30 and 40 are individually or both capable of independent movement , the balloons 30 and 40 will respectively include proximal extensions 51 and 53 . where the inner balloon 30 is capable of independent motion the inner balloon 30 may be manipulated as well as inflated from the proximal end of the catheter 20 through proximal extension 51 . likewise , where the outer balloon 40 is independently mobile , the outer balloon 40 may be manipulated and inflated at the proximal end of the catheter 20 through proximal extension 53 . in order for either the inner balloon 30 or outer balloon 40 to be capable of independent motion relative to the inner tube 32 , the balloons must respectively be equipped with a sliding seal 60 . slidable seal 60 forms a fluid - tight seal against the inner tube 32 during balloon inflation . the slidable seal 60 will be discussed in greater detail below . disposed about inner tube 32 , and located proximal of the catheter tip 28 is a medical device mounting region upon which a medical device such as a stent 24 is mounted . in operation catheter 20 is inserted into a vessel and advanced to a treatment site . once properly in position , the outer balloon 40 may be inflated under low pressure to initially expand stent 24 and / or dilitate the vessel walls . in an embodiment where outer balloon 40 is not independently mobile , outer balloon 40 may be inflated from within inner tube 32 through low pressure inflation lumen 50 . similarly , in an embodiment where the inner balloon 30 is not independently mobile , the inner balloon may be inflated via internal lumen 54 . because the low - pressure outer balloon 40 is designed to initially expand stent 24 and to pre dilate a vessel , the balloon will typically be constructed to be highly compliant and readily expandable . the low - pressure balloon 40 is designed to readily expand to a predetermined diameter when inflated with low pressure . an example of some appropriate low pressure volumes may be within the range between 4 and 12 atmospheres , however the required low - pressure values may vary greatly depending on several factors . in order to ensure proper seating of stent 24 into the vessel , inner balloon 30 is positioned under stent 24 and inflated . inner balloon 30 may be inflated with a relatively high pressure fluid , from within inner tube 32 , through the high pressure inflation lumen 54 or where the inner balloon is mobile through proximal extension 51 as previously discussed . actual pressure values may vary greatly in actual use , however an example of an appropriate range of values for high pressure inflation may be between 10 and 20 atmospheres . in a preferred embodiment shown in fig2 both the inner balloon 30 and outer balloon 40 are longitudinally independently mobile relative to the inner tube 32 . inner balloon 30 includes proximal extension 51 which extends all the way to the proximal end of the catheter 20 where the proximal extension 51 and eventually the balloon 30 may be directly inflated and manipulated . by effectively extending the balloon 30 all the way to the proximal end of the catheter , the proximal extension 51 provides a user with the ability to independently position balloon 30 by manipulating the proximal extension 51 while holding the inner tube 32 stationary . outer balloon 40 is also capable of independent movement and inflation via proximal extension 53 . in contrast to outer balloon 40 , inner balloon 30 is preferably designed to continue to expand only marginally when inflated at high pressure . the construction and manufacture of inner balloon 30 provides the inner balloon with sufficient strength to gradually push against and possibly through plaque buildups and other interferences when inflated at high pressure . in the embodiment shown in fig3 the catheter may be configured with a retractable outer sheath 48 , and a retraction member 49 . in this embodiment retractable outer sheath 48 surrounds the outer balloon 40 and stent 24 . in an embodiment where the inner balloon 30 is located distally or proximally of the outer balloon 40 , as best shown by fig5 and 6 , the stent 24 and outer sheath 48 would be disposed about the outer balloon 40 . in an alternative embodiment of the invention as shown in fig4 the catheter 20 may avoid the requirement of a low pressure balloon and employ only a single moveable high pressure balloon 30 to seat a self - expanding stent after the stent 24 is freed by the retraction of sheath 48 . as may been seen in fig1 - 3 and 5 - 9 , inner balloon 30 will typically be shorter than outer balloon 40 . this design feature provides significant benefits when seating the stent in place . stent 24 will normally be the same or similar in length to the longer outer balloon 40 . inner balloon 30 may be positioned centrally relative to stent 24 . as the shorter inner balloon 30 is inflated inner balloon 30 will generally impinge only a central portion of the stent as dictated by the inner balloon &# 39 ; s shorter length and position . as shown in fig7 the resulting central expansion of the stent 24 will cause the edges of the stent to have reduced contact with a vessel wall . the extent of the contact is dependant on the design and construction of the stent . by minimizing the contact of the vessel wall and the edges of the stent during the stent seating process , the present high pressure dilation balloon protects the patient from edge dissections which would otherwise be more likely to occur . as best shown in fig . 8 , inner balloon 30 may be slidably sealed to the inner tube 32 . the slidable seal 60 allows the inner balloon 30 to be positioned with great accuracy directly under the stent 24 . slidable seal 60 is essentially a fold of inner balloon 30 that rests against inner tube 32 . slidable seal 60 forms a fluid - tight seal as the pressure being exerted upon the seal during inflation of inner balloon 30 forces the slidable seal 60 against the inner tube 32 . as shown in fig2 , 5 and 7 outer balloon 40 may also be equipped with a slidable seal 60 . as should be obvious from such an embodiment the slidable seal 60 as applied to the outer balloon may be a fold of the outer balloon material which rest against the inner tube 32 . regardless of the specific embodiment , once the stent 24 is properly set into position both outer balloon 40 and inner balloon 30 are deflated and the entire catheter 20 is withdrawn from the vessel . as mentioned above , the inventive catheter may contain the stent and balloons in a variety of spatial relationships . in additional embodiments the inner balloon 30 is initially positioned further distally ( see fig5 ) or proximally ( see fig6 ) relative to the stent 24 and outer balloon 40 . where inner balloon 30 is located outside of outer balloon 40 , inner balloon 30 remains capable of independent movement along the inner shaft 32 . depending on the specific embodiment desired outer balloon 40 may also be capable of independent movement relative to the inner balloon 30 such as in the embodiment shown in fig5 or the outer balloon may be secured to the inner tube 32 as shown in fig6 . in yet another embodiment of the present invention shown in fig9 stent 24 may be disposed about one or more inflation balloons 70 and 72 . in the embodiment shown only balloon 70 is capable of independent motion however multiple balloons could be mobile relative to the inner tube 32 . the proximal end of balloon 70 is equipped with a sliding seal 60 to allow the proximal extension 51 of balloon 70 to be drawn or advanced as desired without disturbing balloon 72 . balloon 72 may be inflated via lumen 50 . balloons 70 and 72 may be inflated at the same time to provide uniform initial expansion of stent 24 . in an embodiment where stent 24 is self expanding retractable sheath 48 may be included to retain the stent on the balloons prior to delivery . once stent 24 is expanded balloon 70 may be moved to specific areas of the stent and inflated thereby providing the stent with increased pressure for seating the stent or for compressing plaque or other interferences between the stent and vessel wall . in all of the embodiments described above , the balloon may be composed of suitable materials which include polyolefin copolymer , polyester , polyethylene terephthalate , polyethylene , polyether block amide , polyamide , polyimide , nylon , latex and urethane as well as other suitable balloon materials as are known in the art . in addition to being directed to the embodiments described above and claimed below , the present invention is further directed to embodiments having different combinations of the features described above and claimed below . as such , the invention is also directed to other embodiments having any other possible combination of the dependent features claimed below . the above examples and disclosure are intended to be illustrative and not exhaustive . these examples and description will suggest many variations and alternatives to one of ordinary skill in this art . all these alternatives and variations are intended to be included within the scope of the attached claims . those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims attached hereto .
a high pressure dilation medical device delivery catheter having a proximal and distal end comprising two tubes mounted generally concentrically about an inner tube . the balloons being characterized as a relatively short inner tube which is inflated with high pressure and a longer outer tube which is inflated with low pressure . the balloons have independent inflation lumens which extend toward the proximal end of the inner tube . a medical device mounting region is disposed about at least a portion of the outer balloon and may have a stent or other medical device mounted thereupon . a retractable outer sheath is further disposed about the medical device mounting region and is operatively connected near the proximal end of the catheter .