Patent Publication Number: US-2022226115-A1

Title: Balloons for prosthetic valve delivery apparatus and methods of assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT Patent Application No. PCT/US2020/054410, filed Oct. 6, 2020, which claims the benefit of U.S. Provisional Application No. 62/911,861, filed Oct. 7, 2019, U.S. Provisional Application No. 62/925,722, filed Oct. 24, 2019, U.S. Provisional Application No. 62/981,412, filed Feb. 25, 2020, U.S. Provisional Application No. 63/051,244, filed Jul. 13, 2020, and U.S. Provisional Application No. 63/086,940, filed Oct. 2, 2020, all of which applications are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The present disclosure concerns embodiments of a balloon for a transcatheter delivery device used for implanting a medical device, such as a prosthetic heart valve, and embodiments of a method for assembly a delivery device. 
     BACKGROUND 
     Endovascular delivery devices are used in various procedures to deliver prosthetic medical devices or instruments to locations inside the body that are not readily accessible by surgery or where access without surgery is desirable. Access to a target location inside the body can be achieved by inserting and guiding the delivery device through a pathway or lumen in the body, including, but not limited to, a blood vessel, an esophagus, a trachea, any portion of the gastrointestinal tract, a lymphatic vessel, to name a few. In one specific example, a prosthetic heart valve can be mounted in a crimped state on the distal end of a delivery device and advanced through the patient&#39;s vasculature (e.g., through a femoral artery and the aorta) until the prosthetic valve reaches the implantation site in the heart. The prosthetic valve is then expanded to its functional size such as by inflating a balloon on which the prosthetic valve is mounted, or by deploying the prosthetic valve from a sheath of the delivery device so that the prosthetic valve can self-expand to its functional size. 
     Balloon-expandable prosthetic valves typically are preferred for replacing calcified native valves because the balloon of the delivery device can apply a sufficient expansion force to expand and anchor the frame of the prosthetic valve against the surrounding calcified tissue. In one known technique for delivering a prosthetic heart valve, the prosthetic heart valve may be crimped on a valve retaining portion of a balloon of the delivery device prior to insertion into the patient&#39;s body. The delivery device may include proximal and distal shoulders arranged inside the balloon and which retain the crimped prosthetic valve on the balloon as the delivery device is advanced through the patient&#39;s vasculature. 
     Forming and folding the balloon during assembly of the delivery device is a time consuming and labor-intensive process. Thus, improvements in the way the balloon is formed and assembled in the delivery device are desirable. 
     SUMMARY 
     Disclosed herein are balloon catheters, balloon assemblies for balloon catheters, as well as related methods of forming balloon assemblies and balloon catheters. The balloon catheters can be used to deliver a medical device, tools, agents, or other therapy to a location within a body of a subject. In some embodiments, balloon catheters can be used to deliver an implantable medical device, such as a prosthetic valve, such as to a heart of the subject. In some embodiments, balloon catheters can be a component of a delivery apparatus that can used to deliver a prosthetic valve or other implantable medical device. 
     Certain embodiments of the disclosure concern a balloon assembly including an inflatable balloon having an inflated state and a deflated state. The inflatable balloon in the deflated state can include a valve retaining portion, a distal tapered portion connected to a distal end of the valve retaining portion, a proximal tapered portion connected to a proximal end of the valve retaining portion, a distal leg connected to the distal end of the distal tapered portion, and a proximal leg connected to the proximal end of the proximal tapered portion. The valve retaining portion can have a generally cylindrical shape and one or more axial folds. A proximal end of the distal tapered portion can have a larger diameter than a distal end of the distal tapered portion and the valve retaining portion. A distal end of the proximal tapered portion can have a larger diameter than a proximal end of the proximal tapered portion and the valve retaining portion. The distal tapered portion can include one or more axial folds. The proximal tapered portion can include one or more axial folds. The proximal end of the distal tapered portion can include a first radial fold connected to a second radial fold. The first and second radial folds can form a pocket extending distally at the proximal end of the distal tapered portion. 
     In some embodiments, the balloon assembly can include a restraining member extending around an outer surface of the valve retaining portion so as to prevent the one or more axial folds of the valve retaining portion from unfolding. 
     In some embodiments, the balloon assembly can include a cover that encloses the inflatable balloon. The cover can include a proximal end portion, a distal end portion, and an intermediate portion between the proximal end portion and the distal end portion. The proximal end portion can define a proximal recess that is shaped to substantially match a shape of the proximal tapered portion of the inflatable balloon. The distal end portion can define a distal recess that is shaped to substantially match a shape of the distal tapered portion of the inflatable balloon. The intermediate portion can define an intermediate recess that is shaped to substantially match a shape of the valve retaining portion of the inflatable balloon. 
     In some embodiments, the cover can include a first cover piece and a second cover piece that are complimentarily structured such that they can be matingly assembled together for enclosing the inflatable balloon in the deflated state. 
     In some embodiments, the balloon assembly can include an outer sleeve extending over the cover so as to prevent the first and second cover pieces from separating from each other. 
     In some embodiments, the inflatable balloon can include an internal lumen extending through the tapered proximal portion, the valve retaining portion, and the tapered distal portion. 
     In some embodiments, the proximal tapered portion of the inflatable balloon can include a proximal end portion. The one or more axial folds of the proximal tapered portion do not extend into the proximal end portion of the proximal tapered portion. 
     In some embodiments, the distal tapered portion of the inflatable balloon can include a distal end portion. The one or more axial folds of the distal tapered portion do not extend into the distal end portion of the distal tapered portion. 
     In some embodiments, the distal end of the proximal tapered portion can include a radial fold that forms an obtuse or right angle relative to the valve retaining portion. 
     In some embodiments, the first radial fold at the proximal end of the distal tapered portion can form an obtuse or right angle relative to the valve retaining portion, and the second radial fold can form an acute angle relative to the valve retaining portion. 
     Certain embodiments of the disclosure concern another balloon assembly having an inflatable balloon that has an inflated state and a deflated state. The inflatable balloon in the deflated state can include a valve retaining portion, a distal tapered portion connected to a distal end of the valve retaining portion, a proximal tapered portion connected to a proximal end of the valve retaining portion, one or more axially extending folds along at least sections of the distal tapered portion and the proximal tapered portion, a distal leg connected to the distal end of the distal tapered portion, and a proximal leg connected to the proximal end of the proximal tapered portion. The valve retaining portion can have a generally cylindrical shape and one or more axial folds. A proximal end of the distal tapered portion can have a larger diameter than a distal end of the distal tapered portion and the valve retaining portion. A distal end of the proximal tapered portion can have a larger diameter than a proximal end of the proximal tapered portion and the valve retaining portion. The inflatable balloon can be in an unassembled state apart from a delivery catheter. 
     In some embodiments, the balloon assembly can further include a restraining member extending around an outer surface of the valve retaining portion so as to prevent the one or more axial folds of the valve retaining portion from unfolding. 
     In some embodiments, the balloon assembly can further include a cover that encloses the inflatable balloon. The cover can include a proximal end portion, a distal end portion, and an intermediate portion between the proximal end portion and the distal end portion. The proximal end portion can define a proximal recess that is shaped to substantially match a shape of the proximal tapered portion of the inflatable balloon, and the distal end portion can define a distal recess that is shaped to substantially match a shape of the distal tapered portion of the inflatable balloon. 
     In some embodiments, the cover can include a first cover piece and a second cover piece that are complimentarily structured such that they can be matingly assembled together for enclosing the inflatable balloon. 
     In some embodiments, the balloon assembly can further include an outer sleeve extending over the cover so as to prevent the first and second cover pieces from separating from each other. 
     In some embodiments, the inflatable balloon can include an internal lumen extending through the tapered proximal portion, the valve retaining portion, and the tapered distal portion. 
     In some embodiments, the one or more axially extending folds do not extend into a proximal end portion of the proximal tapered portion. 
     In some embodiments, the one or more axially extending folds do not extend into a distal end portion of the distal tapered portion. 
     In some embodiments, the proximal end of the distal tapered portion can include a first radial fold connected to a second radial fold. The first and second radial folds can form a pocket extending distally at the proximal end of the distal tapered portion. 
     In some embodiments, the first radial fold at the proximal end of the distal tapered portion can form an obtuse or right angle relative to the valve retaining portion, and the second radial fold can form an acute angle relative to the valve retaining portion. 
     Certain embodiments of the disclosure also concern a method for assembling a delivery device. The method can include forming an inflatable balloon in a deflated state. The balloon in the deflated state can have a valve retaining portion, a distal tapered portion connected to a distal end of the valve retaining portion, a proximal tapered portion connected to a proximal end of the valve retaining portion, a distal leg connected to a distal end of the distal tapered portion, and a proximal leg connected to a proximal end of the proximal tapered portion. The method can further include inserting a distal shoulder mounted on a first shaft of the delivery device through the distal leg and into the distal tapered portion of the inflatable balloon, inserting a proximal shoulder mounted on a second shaft of the delivery device through the proximal leg and into the proximal tapered portion of the inflatable balloon, securing the distal leg of the inflatable balloon to the distal shoulder, and securing the proximal leg of the inflatable balloon to the second shaft and/or the proximal shoulder. 
     In some embodiments, the method can further include placing a restraining member around an outer surface of the valve retaining portion. 
     In some embodiments, the method can further include enclosing the inflatable balloon with a cover. The cover can include a first cover piece and a second cover piece that are complimentarily structured such that they can be matingly assembled together for enclosing the inflatable balloon. The cover can define an internal recess whose geometry substantially matches a shape of the inflatable balloon in the deflated state. 
     In some embodiments, the method can further include placing a sleeve over the cover to prevent the first and second cover pieces from separating from each other. 
     In some embodiments, a proximal end of the distal shoulder can have a larger diameter than a diameter of the distal leg. Inserting the distal shoulder through the distal leg can include radially compressing the proximal end of the distal shoulder. 
     In some embodiments, a distal end of the proximal shoulder can have a larger diameter than a diameter of the proximal leg. Inserting the proximal shoulder through the proximal leg can include radially compressing the distal end of the proximal shoulder. 
     In some embodiments, forming the inflatable balloon can include forming the valve retaining portion in a generally cylindrical shape, the diameter of which being smaller than both a diameter of a proximal end of the distal tapered portion and a diameter of a distal end of the proximal tapered portion. 
     In some embodiments, forming the inflatable balloon can include forming one or more axially extending folds along at least sections of the distal tapered portion and the proximal tapered portion. 
     In some embodiments, forming the inflatable balloon can include forming a distal end portion of the distal tapered portion, and the distal end portion can be free of any of the one or more axially extending folds. 
     In some embodiments, forming the inflatable balloon can include forming a proximal end portion of the proximal tapered portion, and the proximal end portion can be free of any of the one or more axially extending folds. 
     In some embodiments, forming the inflatable balloon can include forming a radial fold at the distal end of the proximal tapered portion, and the radial fold can form an obtuse or right angle relative to the valve retaining portion. 
     In some embodiments, forming the inflatable balloon can include forming a radial fold at the proximal end of the distal tapered portion, and the radial fold can form an obtuse or right angle relative to the valve retaining portion. 
     In some embodiments, forming the inflatable balloon can include forming a first radial fold connected to a second radial fold at the proximal end of the distal tapered portion. The first and second radial folds can form a pocket extending distally at the proximal end of the distal tapered portion. 
     In some embodiments, the distal shoulder can include one or more distal shoulder fins extending at least partially radially outwardly. Inserting the distal shoulder assembly into the distal tapered portion can include snuggly placing the one or more distal shoulder fins adjacent to at least some of the one or more axially extending folds in the distal tapered portion. 
     In some embodiments, the proximal shoulder can include one or more proximal shoulder fins extending at least partially radially outwardly. Inserting the proximal shoulder assembly into the proximal tapered portion can include snuggly placing the one or more proximal shoulder fins adjacent to at least some of the one or more axially extending folds in the proximal tapered portion. 
     In some embodiments, inserting the distal shoulder into the distal tapered portion can include aligning a marker located on the first shaft with a predefined position on the valve retaining portion of the inflatable balloon or the proximal shoulder. 
     Certain embodiments of the disclosure concern another method for assembling a delivery device. The method can include forming an inflatable balloon in a deflated state. The balloon in the deflated state can have a distal portion, a proximal portion, and a valve retaining portion between the distal portion and the proximal portion. The method can further include forming a plurality of axially extending folds along at least sections of the distal and proximal portions of the inflatable balloon, and after forming the inflatable balloon and forming the plurality of axially extending folds, mounting the inflatable balloon in the deflated state on a delivery device. 
     In some embodiments, mounting the inflatable balloon on the delivery device can include inserting a distal shoulder mounted on a first shaft of the delivery device through a distal leg of the balloon and inserting a proximal shoulder mounted on a second shaft of the delivery device through a proximal leg of the balloon. The distal leg can be connected to a distal end of a tapered portion of the distal portion of the inflatable balloon, and the proximal leg can be connected to a proximal end of a tapered portion of the proximal portion of the inflatable balloon. 
     In some embodiments, a proximal end of the distal shoulder can have a larger diameter than a diameter of the distal leg. Inserting the distal shoulder through the distal leg can include radially compressing the proximal end of the distal shoulder. 
     In some embodiments, a distal end of the proximal shoulder can have a larger diameter than a diameter of the proximal leg. Inserting the proximal shoulder through the proximal leg can include radially compressing the distal end of the proximal shoulder. 
     In some embodiments, mounting the inflatable balloon on the delivery device can include inserting the distal shoulder into the tapered portion of the distal portion of the inflatable balloon, and inserting the proximal shoulder into the tapered portion of the proximal portion of the inflatable balloon. 
     In some embodiments, the distal shoulder can include one or more distal shoulder fins extending at least partially radially outwardly. Inserting the distal shoulder into the tapered portion of the distal portion can include snuggly placing the one or more distal shoulder fins adjacent to at least some of the plurality of axially extending folds in the tapered portion of the distal portion. 
     In some embodiments, the proximal shoulder can include one or more proximal shoulder fins extending at least partially radially outwardly. Inserting the proximal shoulder into the tapered portion of the proximal portion can include snuggly placing the one or more proximal shoulder fins adjacent to at least some of the plurality of axially extending folds in the tapered portion of the proximal portion. 
     In some embodiments, inserting the distal shoulder into the tapered portion of the distal portion can include aligning a marker on the first shaft with a predefined position on the valve retaining portion of the inflatable balloon or the proximal shoulder. 
     In some embodiments, forming the inflatable balloon can include forming a distal end portion of the distal portion, and the distal end portion can be free of any of the plurality of axially extending folds. 
     In some embodiments, forming the inflatable balloon can include forming a proximal end portion of the proximal portion, and the proximal end portion can be free of any of the plurality of axially extending folds. 
     In some embodiments, forming the inflatable balloon can include forming the valve retaining portion in a generally cylindrical shape, the diameter of which being smaller than both a diameter of a proximal end of the distal portion and a diameter of a distal end of the proximal portion. 
     In some embodiments, forming the inflatable balloon can include forming a radial fold at the distal end of the proximal portion, and the radial fold can form an obtuse or right angle relative to the valve retaining portion. 
     In some embodiments, forming the inflatable balloon can include forming a radial fold at the proximal end of the distal portion, and the radial fold can form an obtuse or right angle relative to the valve retaining portion. 
     In some embodiments, forming the inflatable balloon can include forming a first radial fold connected to a second radial fold at the proximal end of the distal portion. The first and second radial folds can form a pocket extending distally at the proximal end of the distal portion. 
     In some embodiments, mounting the inflatable balloon on the delivery device can include securing the distal leg to the distal shoulder, and securing the proximal leg to the second shaft and/or the proximal shoulder. 
     In some embodiments, the method can further include placing a restraining member around the valve retaining portion. 
     In some embodiments, the method can further include enclosing the inflatable balloon with a cover. The cover can include a first cover piece and a second cover piece that are complimentarily structured such that they can be matingly assembled together for enclosing the inflatable balloon. The cover can define an internal recess whose geometry substantially matches a shape of the inflatable balloon in the deflated state. 
     In some embodiments, the method can further include placing a sleeve around the cover to prevent the first and second cover pieces from separating from each other. 
     Certain embodiments of the disclosure also concern a prosthetic valve delivery assembly including a delivery device. The delivery device can include a shaft and an inflatable balloon mounted on the shaft in a deflated state. The balloon in the deflated state can include a valve retaining portion having a generally cylindrical shape, a distal tapered portion connected to a distal end of the valve retaining portion, a proximal tapered portion connected to a proximal end of the valve retaining portion. The proximal end of the distal tapered portion can include a first radial fold connected to a second radial fold. The first and second radial folds can form a pocket extending distally at the proximal end of the distal tapered portion. 
     In some embodiments, the prosthetic valve delivery assembly can further include a restraining member extending around an outer surface of the valve retaining portion. 
     In some embodiments, the prosthetic valve delivery assembly can further include a cover. The cover can include a first cover piece and a second cover piece that are complimentarily structured such that they can be matingly assembled together for enclosing the inflatable balloon. The cover can define an internal recess whose geometry substantially matches a shape of the inflatable balloon in the deflated state. 
     In some embodiments, the prosthetic valve delivery assembly can further include an outer sleeve extending over the cover so as to prevent the first and second cover pieces from separating from each other. 
     In some embodiments, the balloon in the deflated state can include one or more axially extending folds along at least sections of the distal tapered portion and the proximal tapered portion. 
     In some embodiments, the distal tapered portion can include a distal end portion that is free of any of the one or more axially extending folds. 
     In some embodiments, the balloon can further include a distal leg connected to a distal end of the distal tapered portion and a proximal leg connected to a proximal end of the proximal tapered portion. 
     In some embodiments, the delivery device can include a distal shoulder mounted on the first shaft extending through the distal leg and into the distal tapered portion of the inflatable balloon, and a proximal shoulder mounted on a second shaft of the delivery device extending through the proximal leg and into the proximal tapered portion of the inflatable balloon. 
     In some embodiments, the distal leg can be secured to the distal shoulder and the proximal leg can be secured to the second shaft or the proximal shoulder. 
     In some embodiments, a proximal end of the distal shoulder can have a larger diameter than a diameter of the distal leg, and a distal end of the proximal shoulder can have a larger diameter than a diameter of the proximal leg. 
     In some embodiments, the distal shoulder can include one or more distal shoulder fins which extend at least partially radially outwardly and are adjacent to at least some of the one or more axially extending folds in the distal tapered portion. The proximal shoulder can include one or more proximal shoulder fins extending at least partially radially outwardly and are adjacent to at least some of the one or more axially extending folds in the proximal tapered portion. 
     In some embodiments, the first shaft can include a marker that aligns with a predefined position on the valve retaining portion of the inflatable balloon. 
     In some embodiments, the first shaft can extend through the valve retaining portion, and the first shaft can be separated from the valve retaining portion by an axially extending gap. 
     In some embodiments, the distal end of the proximal tapered portion can include a radial fold that forms an obtuse or right angle relative to the valve retaining portion. 
     In some embodiments, the first radial fold at the proximal end of the distal tapered portion can form an obtuse or right angle relative to the valve retaining portion, and the second radial fold can form an acute angle relative to the valve retaining portion. 
     Certain embodiments of the disclosure also concern another method for assembling a delivery device. The method can comprises forming an inflatable balloon in a deflated state, the balloon in the deflated state having a distal portion, a proximal portion, and a valve retaining portion between the distal portion and the proximal portion; placing the balloon inside of a cover; inserting a shaft of a delivery device through an opening of the cover and into the balloon while the balloon is inside the cover; and securing the balloon to a surface of the delivery device. 
     Certain embodiments of the disclosure also concern a balloon cover for a balloon catheter. The balloon cover can include an outer shell and an inner sleeve disposed within the outer shell. The inner sleeve can have an inner surface defining a lumen that is configured to receive at least a portion of a balloon of the balloon catheter. The inner sleeve can be deformable under pressure exerted against the inner surface by the balloon upon inflation of the balloon, thereby radially expanding the lumen from a first diameter to a second diameter, wherein the second diameter is larger than the first diameter. 
     Certain embodiments of the disclosure also concern a medical assembly. The medical assembly can include a balloon catheter having an inflatable balloon and a balloon cover. The balloon cover can include an outer shell and an inner member disposed within the outer shell, and the inner member can have an inner surface defining a lumen. The balloon can be disposed in the lumen of the inner member. The inner member can be radially deformable when the balloon is inflated and exerts pressure radially outwardly against the inner surface of the inner member. 
     Certain embodiments of the disclosure further concern a method of inflating a balloon of a balloon catheter. The method can include fluidly connecting the balloon to a fluid source. The balloon can be in a deflated state and is disposed inside of a balloon cover. The method can further include injecting an inflation fluid from the fluid source into the balloon so as to at least partially inflate the balloon to a partially inflated state. The balloon cover can include an outer shell and an inner member disposed inside the outer shell and around the balloon. Inflating the balloon from the deflated state to the partially inflated state can deform a lumen of the inner member from an initial state to a deformed state. The lumen can have a first diameter in the initial state and a second diameter in the deformed state, and the second diameter can be larger than the first diameter. 
     Certain embodiments of the disclosure also concern a balloon cover for a balloon catheter. The balloon cover can include an outer shell and an inner sleeve disposed within the outer shell. The inner sleeve can have an inner surface defining a lumen that is configured to receive at least a portion of a balloon of the balloon catheter. The inner sleeve can include first and second separable portions, each having an interior surface defining a section of the lumen. The first portion can have longitudinal edges that are configured to matingly engage respective longitudinal edges of the second portion to form the lumen. The lumen can have a first diameter when the balloon is deflated and a second diameter when the balloon is inflated, the second diameter being larger than the first diameter. 
     Certain embodiments of the disclosure also concern a balloon cover for a balloon catheter. The balloon cover can include an outer shell and an inner sleeve disposed within the outer shell. The inner sleeve can have an inner surface defining a lumen that is configured to receive at least a portion of a balloon of the balloon catheter. The lumen can have a first diameter when the balloon is deflated and a second diameter when the balloon is inflated, the second diameter being larger than the first diameter. The inner sleeve can have a fixed axial length when the lumen expands from the first diameter to the second diameter. 
     Certain embodiments of the disclosure also concern a medical assembly. The assembly can include a balloon catheter having an inflatable balloon and a balloon cover. The balloon cover can include an outer shell and an inner member disposed within the outer shell. The inner member can have an inner surface defining a lumen. The balloon can be disposed in the lumen of the inner member. The lumen can be configured to expand to a second diameter when the balloon is inflated and contract to a first diameter when the balloon is deflated, the second diameter being larger than the first diameter. 
     Certain embodiments of the disclosure further concern a method of inflating a balloon of a balloon catheter. The method can include receiving the balloon disposed inside of a balloon cover, wherein the balloon is in a deflated state, and injecting an inflation fluid from a fluid source into the balloon so as to at least partially inflate the balloon to a partially inflated state. The balloon cover can include an outer shell and an inner member disposed inside the outer shell and around the balloon. Inflating the balloon from the deflated state to the partially inflated state can deform a lumen of the inner member from an initial state to a deformed state. The lumen can have a first diameter in the initial state and a second diameter in the deformed state, and the second diameter is larger than the first diameter. 
     Certain embodiments of the disclosure further concern a balloon cover for a balloon catheter having a first shell member and a second shell member configured to matingly engage each other so as to enclose a distal end portion of the balloon catheter. The first shell member can include a plurality of first wedges and first cavities and the second shell member can include a plurality of second wedges and second cavities. The first wedges and first cavities can be configured to interlock with the corresponding second cavities and second wedges when the first and second shells are matingly engaged with each other. 
     Certain embodiments of the disclosure further concern a medical assembly including a balloon catheter having an inflatable balloon, and a balloon cover including a first shell member and a second shell member. The first and second shell members can be configured to matingly engage with each other to define a lumen that is configured to receive at least the inflatable balloon. The first shell member can include a plurality of first wedges and first cavities and the second shell member can include a plurality of second wedges and second cavities. The first wedges and first cavities can be configured to interlock with the corresponding second cavities and second wedges when the first and second shells are matingly engaged with each other. 
     Certain embodiments of the disclosure also concern a balloon cover for a balloon catheter including a first shell member and a second shell member. The first and second shell members can be configured to matingly engage with each other to define a lumen that is configured to receive a distal portion of the balloon catheter. The lumen can include a balloon section configured to receive a balloon mounted on the distal end portion of the balloon catheter. The balloon section can include a proximal compartment configured to receive a proximal portion of the balloon, a distal compartment configured to receive a distal portion of the balloon, and an intermediate compartment between the proximal and distal compartments, wherein the intermediate compartment can be configured to receive a valve retaining portion of the balloon. The distal compartment can include a proximal region, a distal region, and a middle region between the proximal and distal regions. The distal region can have a smaller diameter than the proximal region and the middle region can have a smaller diameter than the distal region. 
     Certain embodiments of the disclosure also concern a balloon cover for a balloon catheter including a first shell member and a second shell member, wherein the first and second shell members can be configured to matingly engage with each other so that inner walls of the first and second shell members define a lumen adapted to receive a distal portion of the balloon catheter. The lumen can include a balloon section configured to receive a balloon mounted on the distal end portion of the balloon catheter. The balloon section can include a proximal compartment configured to receive a proximal portion of the balloon, a distal compartment configured to receive a distal portion of the balloon, and an intermediate compartment between the proximal and distal compartments. The intermediate compartment can be configured to receive a valve retaining portion of the balloon. Inner walls of the first and second shell members can be shaped to create a depression in at least one portion of the balloon when the balloon is retained in the lumen. 
     Certain embodiments of the disclosure also concern a medical assembly including a balloon catheter having an inflatable balloon. The balloon can have a proximal portion, a distal portion, and valve retaining portion between the proximal and distal portions. The assembly can also include a compression member configured create at least one depression in the balloon. 
     Certain embodiments of the disclosure also concern a balloon cover assembly for a balloon catheter including a cover body defining a lumen configured to receive a balloon folded on a distal portion of the balloon catheter. The balloon can include a proximal portion, a distal portion, and a valve retaining portion connecting the proximal and distal portions. The assembly can further include at least one compression member configured to radially compress at least one portion of the balloon. 
     Certain embodiments of the disclosure also concern a method including folding a balloon on a distal portion of a delivery device when the balloon is in a deflated state. The balloon can have a proximal portion, a distal portion, and a valve retaining portion connecting the proximal and distal portions. A distal end of the distal portion can have a smaller diameter than a proximal end of the distal portion, a distal end of the proximal portion can have a larger diameter than a proximal end of the proximal portion, and the valve retaining portion can have a smaller diameter than the proximal end of the distal portion and the distal end of the proximal portion. The method can further include radially compressing the distal portion of the balloon at a location between the distal and proximal ends of the distal portion. 
     The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a prosthetic heart valve, according to one embodiment. 
         FIG. 2A  is a perspective view of a prosthetic heart valve, according to another embodiment. 
         FIG. 2B  is a perspective view of the prosthetic valve of  FIG. 2A  with the components on the outside of the frame shown in transparent lines for purposes of illustration. 
         FIG. 3  is a perspective view of a delivery for a prosthetic heart valve, according to one embodiment. 
         FIG. 4  is an enlarged, cross-sectional view of the distal end portion of the delivery apparatus of  FIG. 3 . 
         FIG. 5  is an enlarged, side elevation view of the distal end portion of the delivery apparatus of  FIG. 3 . 
         FIG. 6  is an enlarged, cross-sectional view of the distal end portion of a delivery apparatus, according to another embodiment. 
         FIG. 7  shows a section of the distal end portion of the delivery apparatus shown in  FIG. 6 . 
         FIG. 8  shows the distal end portion of the delivery apparatus of  FIG. 6  and a cover assembly, shown in cross-section, enclosing the balloon of the delivery apparatus. 
         FIG. 9  is an exploded view of the cover assembly of  FIG. 8 . 
         FIG. 10  shows the cover assembly of  FIG. 8  is a disassembled state with the distal end portion of the delivery apparatus placed in one of the cover portions of the cover assembly. 
         FIG. 11  is a side elevation view of a balloon for a delivery device, according to another embodiment. 
         FIG. 12  is a side elevation view of the balloon of  FIG. 11  nested inside a balloon cover, according to one embodiment. 
         FIG. 13  is a perspective view showing the balloon cover in an open position with the balloon inside the cover. 
         FIG. 14  is an illustration of method for assembling a delivery device using the balloon of  FIG. 11 , according to one embodiment. 
         FIG. 15  is a side cross-sectional view of a delivery device formed by the method shown in  FIG. 14 . 
         FIG. 16  is a side elevation view of the delivery device of  FIG. 15 . 
         FIG. 17  is a perspective view of a balloon cover, according to another embodiment, shown in an open state. 
         FIG. 18  is a perspective view of a portion of a balloon catheter where a balloon mounted on the balloon catheter is disposed inside the balloon cover of  FIG. 17  shown in a closed state. 
         FIG. 19  is a longitudinal cross-sectional view of the portion of the balloon catheter including the balloon and the balloon cover depicted in  FIG. 18 . 
         FIG. 20  is a perspective view of a balloon cover, according to an alternative embodiment, shown in an open state. 
         FIG. 21  is a longitudinal cross-sectional view of the balloon cover depicted in  FIG. 20 , shown in a closed state. 
         FIG. 22A  is a perspective view of a distal end portion of a balloon catheter received in a balloon cover, according to another embodiment, with the balloon cover shown in section. 
         FIG. 22B  is a cross-sectional view of the distal end portion of the balloon catheter received in the balloon cover depicted in  FIG. 22A . 
         FIG. 23A  is a perspective view of the balloon cover of  FIG. 22A , showing two shell members of the balloon cover separated from each other to define an open state of the balloon cover. 
         FIG. 23B  is a cross-sectional view of the balloon cover depicted in  FIG. 23A , showing the shell members in a closed state. 
         FIG. 24  is a side elevation view of a distal end portion of a delivery device comprising a folded balloon, according to another embodiment. 
         FIG. 25  is a side elevation view of the delivery device of  FIG. 25  showing the folded balloon having a different shape. 
         FIG. 26  is a perspective view of a balloon cover configured to retain the balloon depicted in  FIG. 25 , according to one embodiment, wherein two shell members of the balloon cover are separated from each other so that the balloon cover is in an open state. 
         FIG. 27  is a cross-sectional view of the balloon cover depicted in  FIG. 26 , wherein the two shell members are in a closed state. 
         FIG. 28  is a cross-sectional view of a distal portion of the balloon cover in the closed state, wherein a distal end portion of a delivery device and a balloon are retained within the balloon cover. 
         FIG. 29  is a side elevation view of a balloon folded on a distal end portion of a delivery device, according to an alternative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a prosthetic heart valve  10 , according to one embodiment. The illustrated prosthetic valve is adapted to be implanted in the native aortic annulus, although in other embodiments it can be adapted to be implanted in the other native annuluses of the heart (e.g., the pulmonary, mitral, and tricuspid valves). The prosthetic valve can also be adapted to be implanted in previously implanted prosthetic valves and other tubular organs or passageways in the body. The prosthetic valve  10  can have four main components: a stent or frame  12 , a valvular structure  14 , an inner skirt  16 , and a perivalvular outer sealing member or outer skirt  18 . The prosthetic valve  10  can have an inflow end portion  20 , an intermediate portion  22 , and an outflow end portion  24 . 
     The valvular structure  14  can comprise three leaflets  26 , collectively forming a leaflet structure, which can be arranged to collapse in a tricuspid arrangement, although in other embodiments there can be greater or fewer number of leaflets (e.g., one or more leaflets  26 ). The leaflets  26  can be secured to one another at their adjacent sides to form commissures  28  of the leaflet structure  14 . The lower edge of valvular structure  14  can have an undulating, curved scalloped shape and can be secured to the inner skirt  16  by sutures (not shown). In some embodiments, the leaflets  26  can be formed of pericardial tissue (e.g., bovine pericardial tissue), biocompatible synthetic materials, or various other suitable natural or synthetic materials as known in the art and described in U.S. Pat. No. 6,730,118, which is incorporated by reference herein. 
     The frame  12  can be formed with a plurality of circumferentially spaced slots, or commissure windows  30  that are adapted to mount the commissures  28  of the valvular structure  14  to the frame. The frame  12  can be made of any of various suitable plastically-expandable materials (e.g., stainless steel, a cobalt chromium alloy, etc.) or self-expanding materials (e.g., a nickel titanium alloy (NiTi), such as nitinol) as known in the art. When constructed of a plastically-expandable material, the frame  12  (and thus the prosthetic valve  10 ) can be crimped to a radially collapsed configuration on a delivery catheter and then expanded inside a patient by an inflatable balloon or equivalent expansion mechanism. When constructed of a self-expandable material, the frame  12  (and thus the prosthetic valve  10 ) can be crimped to a radially collapsed configuration and restrained in the collapsed configuration by insertion into a sheath or equivalent mechanism of a delivery catheter. Once inside the body, the prosthetic valve can be advanced from the delivery sheath, which allows the prosthetic valve to expand to its functional size. 
     Suitable plastically-expandable materials that can be used to form the frame  12  include, without limitation, stainless steel, a biocompatible, high-strength alloys (e.g., a cobalt-chromium or a nickel-cobalt-chromium alloys), polymers, or combinations thereof. In particular embodiments, frame  12  is made of a nickel-cobalt-chromium-molybdenum alloy, such as MP35N® alloy (SPS Technologies, Jenkintown, Pa.), which is equivalent to UNS R30035 alloy (covered by ASTM F562-02). MP35N® alloy/UNS R30035 alloy comprises 35% nickel, 35% cobalt, 20% chromium, and 10% molybdenum, by weight. Additional details regarding the prosthetic valve  10  and its various components are described in WIPO Patent Application Publication No. WO 2018/222799, which is incorporated herein by reference. 
       FIG. 2A  is a perspective view of a prosthetic heart valve  50 , according to another embodiment. The valve  50  can have three main components: a stent or frame,  52 , a valvular structure  54 , and a sealing member  56 .  FIG. 2B  is a perspective view of the prosthetic valve  50  with the components on the outside of the frame  52  (including the sealing member  56 ) shown in transparent lines for purposes of illustration. 
     Like the valvular structure  14 , the valvular structure  54  can comprise three leaflets  60 , collectively forming a leaflet structure, which can be arranged to collapse in a tricuspid arrangement. Each leaflet  60  can be coupled to the frame  52  along its inflow edge  62  (the lower edge in the figures; also referred to as “cusp edges” of the leaflets) and at commissures  64  of the valvular structure  54  where adjacent portions of two leaflets are connected to each other. A reinforcing element (not shown), such as a fabric strip, can be connected directly to the cusp edges of the leaflets and to the struts of the frame to couple the cusp edges of the leaflets to the frame. 
     Similar to the frame  12 , the frame  52  can be made of any of various suitable plastically-expandable materials or self-expanding materials as known in the art and described above. The frame  52  in the illustrated embodiment comprises a plurality of circumferentially extending rows of angled struts  72  defining rows of cells, or openings,  74  of the frame. The frame  52  can have a cylindrical or substantially cylindrical shape having a constant diameter from an inflow end  66  to an outflow end  68  of the frame as shown, or the frame can vary in diameter along the height of the frame, as disclosed in U.S. Patent Publication No. 2012/0239142, which is incorporated herein by reference. 
     The sealing member  56  in the illustrated embodiment is mounted on the outside of the frame  52  and functions to create a seal against the surrounding tissue (e.g., the native leaflets and/or native annulus) to prevent or at least minimize paravalvular leakage. The sealing member  56  can comprise an inner layer  76  (which can be in contact with the outer surface of the frame  52 ) and an outer layer  78 . The sealing member  56  can be connected to the frame  52  using suitable techniques or mechanisms. For example, the sealing member  56  can be sutured to the frame  52  via sutures that can extend around the struts  72  and through the inner layer  76 . In alternative embodiments, the inner layer  76  can be mounted on the inner surface of the frame  52 , while the outer layer  78  is on the outside of the frame  52 . 
     The outer layer  78  can be configured or shaped to extend radially outward from the inner layer  76  and the frame  52  when the prosthetic valve  50  is deployed. When the prosthetic valve is fully expanded outside of a patient&#39;s body, the outer layer  78  can expand away from the inner layer  76  to create a space between the two layers. Thus, when implanted inside the body, this allows the outer layer  78  to expand into contact with the surrounding tissue. 
     Additional details regarding the prosthetic valve  50  and its various components are described in U.S. Patent Publication No. 2018/0028310, which is incorporated herein by reference. 
       FIGS. 3-5  show various embodiments and components of a delivery device  100  (also referred to as a “delivery apparatus”), according to one embodiment, for implanting a prosthetic heart valve (e.g., a valve  10  or  50 ) in a patient. The delivery device  100  also can used to implant other types of expandable prosthetic medical devices (such as a stent or graft) in a patient&#39;s body. 
     Referring to  FIG. 3 , the delivery device  100  in the illustrated embodiment is a balloon catheter comprising a handle  102 , a steerable, outer first shaft  104  extending from the handle  102 , an intermediate second shaft  105  (see  FIG. 4 ) extending from the handle  102  coaxially through the steerable outer shaft  104 , and an inner third shaft  106  extending from the handle  102  coaxially through the intermediate shaft  105  and the steerable shaft  104 , an inflatable balloon  108  extending from a distal end of the intermediate shaft  105 , and a nosecone  110  arranged at a distal end of the delivery device  100 . A distal end portion  112  of the delivery device  100  includes the balloon  108 , the nosecone  110 , and a balloon shoulder assembly. A prosthetic medical device, such as a prosthetic heart valve may be mounted on a valve retaining portion of the balloon  108 , as described further below with reference to  FIG. 4 . As described further below, the balloon shoulder assembly is configured to maintain the prosthetic heart valve or other medical device at a fixed position on the balloon  108  during delivery through the patient&#39;s vasculature. 
     The handle  102  can include a steering mechanism configured to adjust the curvature of the distal end portion  107  of the outer shaft  104 . In the illustrated embodiment, for example, the handle  102  includes an adjustment member, such as the illustrated rotatable knob  134 , which in turn is operatively coupled to the proximal end portion of a pull wire (not shown). The pull wire extends distally from the handle  102  through the outer shaft  104  and has a distal end portion affixed to the outer shaft at or near the distal end of the outer shaft  104 . Rotating the knob  134  is effective to increase or decrease the tension in the pull wire, thereby adjusting the curvature of the distal end portion  107  of the outer shaft  104  and therefore the distal end portion  112  of the delivery device. 
       FIG. 4  shows an embodiment of the distal end portion  112  of the delivery device  100 . As shown in  FIG. 4 , the delivery device  100  is configured to mount a prosthetic valve (e.g., prosthetic heart valve)  114  in a crimped state over the balloon  108  for insertion of the delivery device  100  and prosthetic valve  114  into a patient&#39;s vasculature. 
     As shown in  FIG. 4 , at a proximal end of the distal end portion  112 , the inner shaft  106  extends distally beyond the steerable shaft  104  and the intermediate shaft  105  and through the balloon  108 . The balloon  108  can be supported on a balloon shoulder assembly  118 . The balloon shoulder assembly  118  includes a proximal shoulder  120  connected to a distal end of the intermediate shaft  105  and a distal shoulder  122  mounted on the inner shaft  106 . The balloon  108  includes a proximal end portion  126  surrounding and/or folded over the proximal shoulder  120  and a distal end portion  128  surrounding and/or folded over the distal shoulder  122 . In some embodiments, the proximal end portion  126  of the balloon  108  may be secured to the outer surface of the intermediate shaft  105 . In some embodiments, the distal end portion  128  of the balloon  108  may be secured to the outer surface of the nosecone  110  (as shown), which can be mounted on or coupled to the inner shaft  106 . 
     In the illustrated embodiment, the nosecone  110  and the distal shoulder  122  can be a one-piece or unitary component, that is, the nosecone  110  is a distal portion of the unitary component and the distal shoulder  122  is a proximal portion of the unitary component. In other embodiments, the nosecone  110  and the distal shoulder  122  can be separate components, and each can be mounted on the inner shaft  106  next to each other or at axially spaced locations. 
     The proximal shoulder  120  and the distal shoulder  122  are spaced apart from one another, in an axial direction relative to a central longitudinal axis  124  of the delivery device  100 . As a result, the balloon  108  defines a valve-retaining portion  130  in the space that separates the proximal shoulder  120  and the distal shoulder  122  (e.g., between flared ends of the proximal shoulder  120  and the distal shoulder  122 ). As shown in  FIG. 4 , the prosthetic valve  114  can be crimped onto the valve retaining portion  130  of the balloon  108 , between the proximal shoulder  120  and the distal shoulder  122 , thereby preventing or reducing axial movement of the prosthetic valve  114  relative to the balloon  108  during insertion of the delivery device  100  into the patient and delivery of the prosthetic valve  114  to the target implantation site. 
     The outer diameter of the inner shaft  106  can be sized such that an annular space  132  is defined between the inner shaft  106  and the intermediate shaft  105  along the entire length of the intermediate shaft  105 . The annular space  132  may be fluidly coupled to one or more fluid passageways of the delivery device  100  which can be fluidly connectable to a fluid source (e.g., a syringe) that can inject an inflation fluid (e.g., saline) into the delivery device. In this way, fluid from the fluid source can flow through the one or more fluid passageways, through the annular space  132 , and into the balloon  108  to inflate the balloon  108  and expand and deploy the prosthetic valve  114 . For example, the handle  102  can have a fluid port  103  (see  FIG. 3 ) configured to be coupled to the fluid source. In use, inflation fluid from the fluid source can be injected into the fluid port  103 , through one or more fluid passageways in the handle  102 , through the annular space  132 , and into the balloon  108 . 
       FIG. 4  illustrates the flow of fluid (indicated by arrows  109 ) through the annular space  132  and through passages in the proximal shoulder  120  and distal shoulder  122 . The fluid can then flow into the proximal and distal end portions  126 ,  128  of the balloon  108  to expand the valve  114 . 
     The shafts  104 ,  105 , and  106  of the delivery device  100  can be formed from any of various suitable materials, such as nylon, braided stainless steel wires, or a polyether block amide (commercially available as Pebax®), to name a few. The shafts  104 ,  105 , and  106  can have longitudinal sections formed from different materials in order to vary the flexibility of the shafts along their lengths. The inner shaft  106  can have an inner liner or layer formed of Teflon® to minimize sliding friction with a guide wire. The shafts  104 ,  105 , and  106  can also be axially and/or rotatably movable relative to each other and/or the handle portion  102 . 
     Further details of the balloon shoulder assembly, the steering mechanism, and other components of the delivery device are disclosed in U.S. Publication Nos. 2007/0005131, 2009/0281619, 2013/0030519, and 2017/0065415, which are incorporated herein by reference. 
     In some embodiments, the delivery device  100  need not include a steering mechanism or a shaft  104  (in which case the shaft  105  is the outer shaft of the delivery device). In some embodiments, the delivery device  100  need not include a shaft  104  and can include a steering mechanism configured to adjust the curvature of the shaft  105  (e.g., the pull wire can extend through the shaft  105 ). 
       FIG. 5  shows a side view of an exterior of the distal end portion  112  of the delivery device  100 , including the prosthetic valve  114  crimped on the balloon  108  mounted on the distal end portion  112  of the delivery device. As explained above, the balloon shoulder assembly including the proximal shoulder  120  and distal shoulder  122  supports the balloon  108  thereon. 
     As shown in  FIG. 5 , the balloon  108  includes the proximal end portion  126  surrounding and/or folded over the proximal shoulder  120 , the distal end portion  128  surrounding and/or folded over the distal shoulder  122 , and the valve retaining portion  130  located between the proximal end portion  126  and the distal end portion  128 . As shown in  FIG. 5 , the prosthetic valve  114  is crimped on and around the valve retaining portion  130  of the balloon  108 . 
       FIGS. 6-7  illustrates a distal end portion  112  of the delivery apparatus, according to another embodiment. In this embodiment, as shown, the balloon  108  includes a proximal portion  140 , a distal portion  142 , and a valve retaining portion  144  located between the proximal portion  140  and the distal portion  142 . 
     The valve retaining portion  144  in the illustrated configuration has a generally cylindrical shape. The distal portion  142  is connected to a distal end of the valve retaining portion  144 . The distal portion  142  can have a tapered shape, and therefore can be referred to as a “distal tapered portion.” For example, a proximal end  150  of the distal portion  142  can have a larger diameter than a distal end  152  of the distal portion  142 . The proximal portion  140  is connected to a proximal end of the valve retaining portion  144 . The proximal portion  140  can also have a tapered shape, and therefore can be referred to as a “proximal tapered portion.” For example, a distal end  154  of the proximal portion  140  can have a larger diameter than a proximal end  156  of the proximal portion  140 . 
     The valve retaining portion  144  can have one or more axially extending folds or pleats  146 . Such axial folds  146  can be tightly compressed in order to minimize the profile of the balloon and the prosthetic heart valve  114  crimped thereon. The axial length of the valve retaining portion  144  is approximately the same as or slightly longer than the axial length of the prosthetic heart valve  114  in its crimped configuration. 
     As shown in  FIG. 6 , both the diameter of the proximal end  150  of the distal portion  142  (D 1 ) and the diameter of the distal end  154  of the proximal portion  140  (D 2 ) are larger than the diameter of the valve retaining portion  144 . In some embodiments, the diameters D 1  and D 2  are configured to be about the same or slightly larger than the outer diameter of the prosthetic heart valve  114  when it is crimped over the valve retaining portion  144 . Thus, when the balloon  108  and the prosthetic heart valve  114  crimped thereon are enclosed by a balloon cover (described below), the cover will not scratch or damage the frame of the prosthetic heart valve  114 . 
     The distal tapered portion  142  can shield the valve struts against contacting the inner surface of a loader device and the inner surface of an introducer sheath during an implantation procedure device, thereby preventing or minimizing damage to those components (a loader device and an introducer sheath can be used to introduce the delivery device and the prosthetic valve into a patient&#39;s vasculature, as known in the art). In addition, the distal tapered portion  142  can reduce the insertion forces when advancing the delivery device  100  across the patient&#39;s native valve. The proximal tapered portion  140  can act as a landing support or stop for the prosthetic heart valve when being pushed through the loader, the introducer sheath and the patient&#39;s vasculature. In addition, the proximal tapered portion  140  can facilitate retrieving the delivery device from the patient&#39;s vasculature after the valve implantation. 
     In some embodiments, the inner shaft  106  also define a lumen that is sized to receive a guide wire that can extend coaxially through the inner shaft  106  and through the nosecone of the delivery apparatus. This allows the delivery apparatus  100  to be advanced over a guide wire previously inserted into the patient&#39;s vasculature, as known in the art. 
     In some embodiments, the inner shaft  106  can include a radiopaque marker  135  which is aligned with a predefined portion of the balloon  108 . For example, the marker  135  can be aligned with the center of the valve retaining portion  144  of the balloon  108 . The marker  135  can be used for aligning the prosthetic valve  114  with the native valve under fluoroscopy during an implantation procedure. 
     In the illustrated embodiment, a balloon shoulder assembly comprises a distal shoulder  160  mounted on the distal end portion of the inner shaft  106  and a proximal shoulder  170  mounted on or connected to a distal end portion of the intermediate shaft  105  (such as shown in  FIG. 4 ), which assist in retaining the prosthetic valve  114  on the valve retaining portion  144  of the balloon during delivery through a patient&#39;s vasculature. The distal shoulder  160  can include a flared distal collar member  162  and a cylindrical shaft portion  163 . The distal collar member  162  can have one or more distal shoulder fins  164 , which extend at least partially radially outwardly from the shaft portion  163 . The proximal shoulder  170  can include a flared proximal collar member  172  and a cylindrical shaft portion  173 . The proximal collar member  172  can have one or more proximal shoulder fins  174 , which extend at least partially radially outwardly from the shaft portion  173 . 
     The shaft portion  163  of the distal collar  160  can be affixed to the distal end portion of the inner shaft  106  using any known means, such as by welding, an adhesive, mechanical fasteners, etc. The shaft portion  173  of the proximal shoulder  170  can be affixed to the distal end portion of the shaft  105  using any known means, such as by welding, an adhesive, mechanical fasteners, etc. 
     The outer diameter of the inner shaft  106  can be sized such that an annular space  132  ( FIG. 4 ) is defined between the inner shaft and the intermediate shaft so as to define a fluid passageway through which an inflation fluid can flow from the handle into the balloon as previously described. As shown, the inner shaft  106  is separated from the valve retaining portion  144  of the balloon  108  by an axially extending gap  137 , which allows an inflation fluid to flow from the proximal tapered portion  140  to the distal tapered portion  142  of the balloon  108 . 
       FIG. 6  illustrates the flow of fluid (indicated by arrows  141 ) through the annular space  132 , the proximal tapered portion  140 , the axially extending gap  137 , and the distal tapered portion  142  to expand the balloon  108 . In addition, the balloon  108  can be deflated by withdrawing the inflation fluid from the balloon  108  through the fluid passageway described above back into a reservoir of the source of the inflation fluid. 
       FIG. 6  shows that the balloon  128  can further include a distal leg  180  connected to the distal end  152  of the distal tapered portion  142 , and a proximal leg  182  connected to the proximal end  156  of the proximal tapered portion  140 . The balloon  128  can define an internal lumen extending from the proximal leg  182 , through the tapered proximal portion  140 , the valve retaining portion  144 , the tapered distal portion  142 , and to the distal leg  180 . 
     The proximal leg  182  can be secured to the intermediate shaft  105 . For example, a proximal end portion  183  of the proximal leg  182  can be secured to an outer surface of the shaft  105 . In some embodiments, the proximal end portion  183  of the proximal leg  182  can have a tapered shape that has a gradually reduced diameter in the proximal direction so as to provide a tapered transition from the proximal leg  182  to the outer surface of the shaft  105 . Securing the proximal leg  182  to the shaft  105  can be achieved using any known means, including, but not limited to thermal bonding, gluing, mechanical locking, etc. 
     The distal leg  180  can be secured to the distal shoulder  160 , such as to a distal end portion of the shaft portion  163 . Securing the distal leg  180  to the distal shoulder  160  can be achieved using any known means, including, but not limited to thermal bonding, gluing, mechanical locking, etc. In  FIG. 6 , a small gap is shown between the distal leg  180  and the shaft portion  163  for purposes of illustration. However, it should be understood that the distal leg  180  can be in contact with and secured to the shaft portion  163  along the entire length of the distal leg  180  such that there is no gap between these two components. 
     In particular embodiments, as shown, the distal shoulder  160  can have a nosecone portion  166  connected to and extending distally from the shaft portion  163 . The nosecone portion  166  can be integrally connected to the shaft portion  163 . The nosecone portion  166  can include a first tapered portion  167 , a cylindrical portion  168  extending distally from the first tapered portion  167 , and a second tapered portion  169  extending distally from the cylindrical portion  168  and defining a terminal distal end of the nosecone portion and the delivery device. The first tapered portion  167  has an outer diameter that gradually reduces from the shaft portion  163  to the cylindrical portion  168 . The second tapered portion has an outer diameter that gradually reduces in diameter from the cylindrical portion  168  to its terminal distal end. 
     The tapered portions  167 ,  169  can facilitate crossing of the native valve leaflets by further reducing frictional forces when advancing the delivery device through the patient&#39;s native valve. 
     In some embodiments, one or more sections of the nosecone portion  166 , such as the cylindrical portion  168  and/or the second tapered portion  169 , can be color-coded to indicate the size of the balloon  108  and the prosthetic heart valve  114  intended to be used with the delivery device  100 . 
     In some embodiments, the distal tapered portion  142  of the balloon can include one or more axial pleats or folds  143  when the balloon is in a deflated state ready for insertion into a patient&#39;s vasculature. In some embodiments, the proximal tapered portion  140  of the balloon can include one or more axial pleats or folds  145  when the balloon is in a deflated state ready for insertion into a patient&#39;s vasculature. In some embodiments, the axial folds  143  or  145  can form an oblique angle relative to a longitudinal axis of the valve retaining portion  144 . The folds  143 ,  145  reduce the overall profile of the distal end portion  112  of the delivery device to facilitate passage of the delivery device through the introducer sheath and the patient&#39;s vasculature. 
     In some embodiments, the distal tapered portion  142  can have a distal end section  147  that is free of any folds. For example, the one or more axial folds  143  of the distal tapered portion  142  desirably do not extend into the distal end section  147 . During insertion of the delivery device through a native heart valve (e.g., a native aortic valve, which typically is calcified), the pleat-free distal end portion  147  (which has a relatively smooth outer surface) pushes open and passes through the patient&#39;s native valve first before the pleated balloon section (e.g., the section of the distal tapered portion containing the axial folds  143 ) passes through the native valve. Thus, the distal end section  147  creates a pleat gap that can facilitate smooth crossing of the patient&#39;s native valve when the delivery device is advanced through the native valve. 
     Likewise, the proximal tapered portion  140  can have a proximal end section  149  that is free of any folds. For example, the one or more axial folds  145  of the proximal tapered portion  140  desirably do not extend into the proximal end section  149 . When retracting the delivery device from the native valve during an implantation procedure, such as for re-positioning the prosthetic valve, the pleat-free proximal end section  149  (which has a relatively smooth outer surface) pushes open and passes through the patient&#39;s native valve first before the pleated balloon portion (e.g., the section of the proximal tapered portion containing the axial folds  145 ) passes through the native valve. Thus, the proximal end section  149  creates a pleat gap that can facilitate smooth crossing of the patient&#39;s native valve during retraction of the delivery device. The proximal end section  149  can also facilitate retrieval of the delivery device back through the introducer sheath after valve implantation. 
     In some embodiments, the axial folds  145  can extend the entire length of the proximal tapered portion  140  (i.e., no pleat gap in the proximal tapered portion). In some embodiments, the axial folds  143  can extend the entire length of the distal tapered portion  142  (i.e., no pleat gap in the distal tapered portion). 
     As shown in  FIG. 6 , the proximal tapered portion  140  of the balloon  108  can be folded around the distal end of the proximal collar member  172  so as to form an obtuse radial fold  188  that extends radially inwardly to a radial section  190  that extends radially inwardly to the proximal end of the valve retaining portion  144 . The obtuse radial fold  188  provides secure nesting of the prosthetic valve  114  while facilitating passage through the introducer sheath. In the illustrated embodiment, there is a slight gap between the fold  188  and the distal end of the shoulder  170 . However, in alternative embodiments, the balloon can be folded snugly around the distal end of the shoulder  170  such that there is little or no gap between the fold  188  and the shoulder  170 . Moreover, the axially extending folds  145  desirably contact and extend along the proximal collar member  172  in the deflated state of the balloon. 
     The distal tapered portion  142  of the balloon  128  can be folded around the distal collar member  162 . As shown in  FIGS. 6 and 7 , in certain embodiments, the distal tapered portion  142  of the balloon  108  can include a first radial fold  184  connected to a second radial fold  185  that extends to the distal end of the valve retaining portion  144 . The first radial fold  184  can form an obtuse or right angle relative to the valve retaining portion  144 , and the second radial fold  185  can form an acute angle relative to the valve retaining portion  144 . As such, the first and second radial folds  184 ,  185  together form an S-shaped curve around the proximal end of the distal collar member  162 . The intersection of the fold  185  and the valve retaining portion  144  can form a pocket  186  (or “tuck”). The axially extending folds  143  desirably contact and extend along the distal collar member  162  in the deflated state of the balloon. 
     The pocket  186  formed by radial folds  184 ,  185  can help keep the prosthetic heart valve  114  stable during valve deployment. As noted above, the axial length of the valve retaining portion  144  is approximately the same as or slightly longer than the axial length of the prosthetic heart valve  114  crimped thereon. As the balloon  108  is inflated during valve deployment, the prosthetic heart valve  114  is radially expanded and axially foreshortened. Without the pocket  186 , such foreshortening of the prosthetic heart valve  114  during radial expansion can create an axial gap between the distal end of the prosthetic valve and the adjacent portion of the balloon, potentially causing the prosthetic heart valve  114  to shift in position. However, the radial folds  184 ,  185  forming the pocket  186  can mitigate such undesired shift in position of the prosthetic valve. As the inflation fluid flows through the axially extending gap  137  and into the distal tapered portion  142 , the radial folds  184 ,  185  are unfolded under the pressure of the inflation fluid, causing the pocket  186  to unfold in the proximal direction and maintain contact against the prosthetic valve  114 . Thus, the unfolding pocket provides an extra volume within the distal tapered portion  142  which can occupy or offset the axial gap that otherwise would be created by valve foreshortening. Accordingly, the radially expanding prosthetic heart valve  110 , despite its axial shortening, can remain stable along the valve retaining portion  144 . 
     In the illustrated embodiment, there is a slight gap between the folds  184 ,  185  and the proximal end of the distal collar member  162 . However, in alternative embodiments, the balloon can be folded snugly around the proximal end of the distal collar member  162  such there is no such gap. In such embodiments, the S-shaped curve can extend around the distal collar member such that the pocket  186  is located within the interior of the distal collar member  162 . 
     In another embodiment, the proximal portion  140  of the balloon  108  can be folded in the same manner as the distal portion  142  such that it also forms an S-shaped curve. In another embodiment, the distal portion  142  can have one obtuse fold  188  and the proximal portion  140  can have folds  184 ,  185  forming an S-shaped curve. In another embodiment, each of the proximal and distal portions  140 ,  142  can have one obtuse fold  188 . 
     As noted above, the proximal collar member is placed snuggly adjacent to at least some of the axially extending folds  145  formed along the proximal tapered portion  140 , and the distal collar member is placed snuggly adjacent to at least some of the axially extending folds  143  formed along the distal tapered portion  142 . Such snug placement of the proximal and distal collar members next to respective balloon folds  143 ,  145  can help improve stability of the crimped prosthetic valve  114 . 
       FIGS. 8-10  show a protective cover assembly  200  for protecting and maintaining the shape of the folded balloon  108  during shipping and storage prior to use, according to one embodiment. After the delivery device  100  is fully assembled, the balloon  108  can be folded at the manufacturing site so as to include the various folds described above. The cover assembly  200  can help retain the folds in the balloon until the delivery device is removed from its packaging for crimping the prosthetic valve on the balloon at the point of use. 
     As shown, the cover assembly  200  in the illustrated embodiment can include first and second cover portions  202   a ,  202   b  and a sleeve  204 . The cover portions  202   a ,  202   b  are configured to receive and enclose the distal end portion  112  of the delivery device. The first cover portion  202   a  can be placed around one half of the distal end portion  112  and the second cover portion  202   b  can be placed around the other half of the distal end portion  112  and mate with the first cover portion  202   a . The mating cover portions  202   a ,  202   b  form an enclosure that encloses or houses the distal end portion  112  of the delivery device, including the folded balloon  108 , and optionally the distally end portion of the shaft  105 . The sleeve  204  can be slid over the cover portions  202   a ,  202   b  to hold those components together during shipping and storage. 
     Each of the cover portions  202   a ,  202   b  can include a distal recess portion  206 , an intermediate recess portion  208 , and a proximal recess portion  210 . The distal recess portion  206  can be shaped to correspond to the shape of the distal end portion  142  of the balloon and the nosecone portion  166 . The intermediate recess portion  208  can be shaped to correspond to the shape of the valve retaining portion  144  of the balloon. The proximal recess portion  210  can be shaped to correspond to the shape of the proximal end portion  140  of the balloon, and optionally the distal end portion of the shaft  105 . 
     Thus, when situated inside the cover assembly  200 , the folded balloon  108  can be prevented from expanding substantially or otherwise deviating from its folded shape. In addition, the cover assembly  200  can protect the balloon  208  from scratches, tears, etc., during shipping and storage. Further, the cover assembly  200  can also facilitate pressure and/or vacuum testing of the balloon  108 . More specifically, the balloon  108  can be tested in the cover assembly  200  by introduction of gas, fluid, or vacuum at the assembly location, and/or in the operating room prior to crimping of the prosthetic heart valve, because the balloon is held in its folded configuration by the contoured cavity of the cover assembly  200 . Therefore, the physician does not need to perform any folding steps after balloon testing and prior to crimping the prosthetic heart valve on the balloon  108 . 
     In the illustrated embodiment, the cover portions  202   a ,  202   b  are completely separable from each other. However, in other embodiments, the cover portions  202   a ,  202   b  can be connected to each other along adjacent longitudinal edges by a hinge that allows the cover portions  202   a ,  202   b  to open and close around the distal end portion  112  of the delivery device (similar to the cover  400  shown in  FIG. 13 , described below). In lieu of or in addition to the sleeve  204 , the cover portions  202   a ,  202   b  can include complimentary latch portions that retain the cover portions in the closed state around the distal end portion  112  of the delivery device (similar to the latch portions  406   a ,  406   b  of  FIG. 13 , described below). 
       FIG. 11  shows an inflatable balloon  300  folded in a deflated state, according to another embodiment. The balloon  300  can be referred to an “off-device formed balloon,” in that it can be fully formed and folded prior to being assembled on the delivery device (e.g., delivery device  100 ). 
     Similar to the balloon  108 , the balloon  300  in the illustrated embodiment can include a valve retaining portion  302  having a generally cylindrical shape, a distal tapered portion  304  connected to a distal end of the valve retaining portion  302 , a proximal tapered portion  306  connected to a proximal end of the valve retaining portion  302 , a distal leg  308  connected to a distal end of the distal tapered portion  304 , and a proximal leg  310  connected to a proximal end of the proximal tapered portion  306 . The balloon  300  can be formed using techniques known in the art. 
     In some embodiments, the balloon  300  can include one or more markings or indicia that identify certain attributes of the balloon, such as its size, for use in assembly of the delivery device. For example, a laser marking  312  can be placed on the proximal leg  310 . Likewise, an optional laser marking  314  can be placed on the distal leg  308  of the balloon. It should be understood that the markings  312  or  314  can be placed on other sections of the balloon. Also, other types of markings can be used, such as markings formed by printing, painting, or etching markings on the balloon. 
     The valve retaining portion  302  can include a plurality of tightly compressed axially extending folds  316 . In addition, the balloon  302  can include one or more axially extending folds  318  formed along the distal tapered portion  304  and the proximal tapered portion  306 . 
     As further shown in  FIG. 11 , the distal end  320  of the proximal tapered portion  306  can have a radial fold  322  which forms an obtuse or right angle relative to the valve retaining portion  302  (similar to fold  188  of  FIG. 6 ). The proximal end  324  of the distal tapered portion  304  can have a radial fold  326  which forms an obtuse or right angle relative to the valve retaining portion  302  (similar to fold  188  of  FIG. 6 ). The obtuse angled radial folds  322 ,  326  can provide a secure valve nesting zone while passing the delivery device through the loader and the introducer sheath of the delivery system. 
     Although not shown, in other embodiments, one or both of the distal tapered portion  304  and the proximal tapered portion  306  can have two radial folds forming an S-shaped curve (similar to folds  184 ,  185  of  FIG. 6 ). 
     As shown in  FIG. 11 , the distal tapered portion  304  can have a distal end section  328  that is free of any folds. Likewise, the proximal tapered portion  306  can have a proximal end section  330  that is free of any folds. As described above in connection with the embodiment of  FIG. 6 , the distal end section  328  creates a pleat gap that can facilitate smooth crossing of the patient&#39;s native valve during valve delivery. The proximal end section  330  creates a pleat gap that can facilitate smooth crossing of the patient&#39;s native valve during retraction of the delivery device (such as for repositioning the prosthetic valve) and retrieval of the delivery device back through the introducer sheath after valve implantation. 
     After forming the balloon  300  and created the folds, the balloon can be enclosed in a protective cover  400 , as depicted in  FIGS. 12-13 , until it is ready to be assembled in a delivery device. Similar to cover  200 , the cover  400  has an internal geometry that generally matches the shape of the folded balloon  300 . In the illustrated embodiment, the cover  400  can include first and second complementary cover portions  402   a ,  402   b , each of which is configured to receive one half of the balloon. The cover portions  402 ,  402   b  can be connected by a hinge  404  to form a clam shell configuration that allow the cover portions  402   a ,  402   b  to open and close around the balloon. 
     The first and second cover portions  402   a ,  402   b  can include respective latch portions  406   a  and  406   b . When the cover portions  402   a ,  402   b  are placed around the balloon in a closed state, the latch portion  406   a  can engage the latch portion  406   b  to retain the cover portions in the closed state. In certain embodiments, the latch portion  406   a  can form a releasable snap fit connection with the latch portion  406   b.    
     Each over portion  402   a ,  402   b  can have a distal recess portion  408 , an intermediate recess portion  410 , and a proximal recess portion  412 . The distal recess portion  408  can have a shape that substantially corresponds to the shape of the distal tapered portion  304  and the distal leg  310 . The intermediate recess portion  410  can have a shape that substantially corresponds to the shape of the valve retaining portion  302 . The proximal recess portion  412  can have a shape that substantially corresponds to the shape of the proximal tapered portion  306  and the proximal leg  310 . 
     In lieu of or in addition to the latch portions  406   a ,  406   b , the cover  400  can be placed inside of a sleeve  414  (as shown in  FIG. 12 ) to retain the cover portions  402   a ,  402   b  in the closed state around the balloon. 
     In alternative embodiments, the cover portions  402   a ,  402   b  can be completely separable (similar to the embodiment of  FIGS. 8-10 ) and can be retained in the closed state by the sleeve  414  or other retaining means. 
     In certain embodiments, in lieu of or in addition to the cover  400 , a restraining member  350 , such as in the form of a sleeve, can be placed around the valve retaining portion  302  of the balloon. The restraining member  350  can assist in retaining the valve retaining portion  302  of the balloon in a compressed and folded state until the balloon  300  is assembled onto a delivery device, as described below. The restraining member  350  can be formed from a relatively thin sheet of polymeric material, such as polyester, polyurethane, or fluorinated ethylene propylene (FEP). In some embodiments, the restraining member  350  can be removed by the manufacturer after assembly of the delivery device. In other embodiments, the restraining member can be kept in place after assembly and removed by an end user prior to crimping a prosthetic valve on the balloon. Moreover, it should be understood that the restraining member  350  can be used with other embodiments disclosed herein, such as the balloon  108 . In other embodiments, the restraining member  350  is not used and only the cover  400  is used to retain the valve retaining portion  302  in its compressed and folded state. 
       FIGS. 17-19  show another balloon cover  600  for a folded balloon  680  mounted on a delivery catheter  670 , according to an alternative embodiment. 
     As described herein, the balloon  680  can be any of the balloons  108 ,  208 ,  300  disclosed above or any other types of foldable balloons, and the delivery catheter  670  can be the same delivery devices  100 ,  500  described above, or any other types of delivery devices for implanting a balloon-inflatable prosthetic valve, as known in the art. 
     For example, in the depicted embodiment, the delivery device  670  can include an outer shaft  672 , an inner shaft  674  extending through a central lumen of the outer shaft  672 , and a nose cone  676  coupled to the inner shaft  674 . The balloon  680  can be supported on a shoulder assembly of the delivery device  670 . The shoulder assembly can include a proximal shoulder  690  connected to a distal end of the outer shaft  672  and a distal shoulder  692  mounted on the inner shaft  674 . The balloon  680  can have a proximal end portion  682  surrounding and/or folded over the proximal shoulder  690 , a distal end portion  684  surrounding and/or folded over the distal shoulder  692 , and a valve retaining portion  686  located between the proximal end portion  682  and the distal end portion  684 . The proximal end portion  682  of the balloon  680  may be secured to the distal end portion of the outer shaft  672 . The distal end portion  684  of the balloon  680  may be secured to an outer surface of the nose cone  676 . 
     As shown, the balloon cover  600  can include an outer shell  602  and an inner sleeve  604  disposed within the outer shell  602 . The inner sleeve  604  can have an inner surface  606  defining a lumen  608 . In an example embodiment, the lumen  608  is configured to receive the valve retaining portion  686  of the balloon  680 . 
     Prior to crimping a prosthetic valve on the balloon of a delivery device, the user typically performs a cyclic “de-airing” process that involves pushing inflation fluid into the balloon and then withdrawing the fluid out of the balloon, such as with a syringe fluidly connected to the handle of the delivery device. The de-airing process can be more effective when the balloon is allowed to at least partially inflate. However, inflation of the balloon outside of a balloon cover can result in un-folding of the balloon, which can inhibit or prevent the balloon from returning to its folded state when the inflation fluid is removed from the balloon. As described more fully below, the inner sleeve  604  can be deformable under pressure exerted against the inner surface  606  by the balloon  680  upon inflation of the balloon  680 , thereby radially expanding the diameter of the lumen  608 . This allows at least partial inflation of the balloon while performing the de-airing procedure while the balloon is contained within the cover. During the de-airing process, the deformable inner sleeve  604  can prevent complete unfolding of the balloon and/or assist the balloon in returning to its fully folded state after the inflation fluid is removed from the balloon. 
     In some embodiments, the outer shell  602  can be more rigid than the inner sleeve  604 . For example, the inner sleeve  604  can be made of an elastomer such as natural rubbers, styrene-butadiene block copolymers, polyisoprene, polybutadiene, ethylene propylene rubber, ethylene propylene diene rubber, silicone elastomers, fluoroelastomers, polyurethane elastomers, nitrile rubbers, or a mixture of these materials. The inner sleeve  604  can also include a shape memory material as described further below. The outer shell  602  can be made of a non-deformable material such as polyvinyl chloride, glass, poly(methyl methacrylate), acrylonitrile butadiene styrene, styrene acrylonitrile, polystyrene, silicone, cellulose, polyester, polyolefins, polyethylene, metal, ceramic, or a mixture of these materials. 
     In the depicted embodiments, the outer shell  602  includes a first shell member  602   a  and a second shell member  602   b . The first and second shell members  602   a ,  602   b  can be connected by a hinge  610  forming a clam shell configuration that allows the shell members  602   a ,  602   b  to open and close around the balloon  680 . 
     In certain embodiments, the first and second shell members  602   a ,  602   b  can include respective latch portions. When the first and second shell members  602   a ,  602   b  are placed around the balloon  680  and the inner sleeve  604  in a closed state, the respective latch portions can engage each other, as illustrated in  FIG. 18 , to retain the shell members  602   a ,  602   b  in the closed state. 
     For example, as best shown in  FIG. 17 , one latch portion can be configured as a ridge  612   a  extending outwardly from the first shell member  602   a , and another latch portion can be configured as a cantilevered tab  612   b  extending outwardly from the second shell member  602   b . The ridge  612   a  can have an enlarged rim or edge portion  614   a  along its free longitudinal edge, and the tab  612   b  can have a corresponding slot  614   b . The slot  614   b  can be so positioned and sized as to allow the enlarged rim  614   a  to extend through to form a snap-fit when the shell members  602   a ,  602   b  are placed around the balloon  680  and the inner sleeve  604  in a closed state. 
     In some embodiments, the width of the slot  614   b  can be slightly smaller than the width of the enlarged rim  614   a  and the tab around the slot  614   b  can be made of an elastic or deformable material. Thus, by pressing the ridge  612   a  and the tab  612   b  against each other, the slot  614   b  can enlarge slightly to allow the enlarged rim  614   a  to extend therethrough and then revert back to its original size and shape after the rim  614   a  passes through the slot  614   b . The narrower slot  614   b  relative to the enlarged rim  614   a  prevents the rim  614   a  from inadvertently sliding back through the slot  614   b  in the opposite direction, thus ensuring a tight interlocking between the ridge  612   a  and the tab  612   b . To open the shell members  602   a ,  602   b , a user can separate the ridge  612   a  from the tab  612   b , e.g., by manually pulling the enlarged rim  614   a  out of the slot  614   b . In some embodiments, the tab  612   b  can have a plurality of bumps and/or indents  616  located on its surface so as to provide friction points for a user&#39;s finger to firmly grab the tab  612   b  for engaging or disengaging the ridge  612   a  and the tab  612   b.    
     It should be understood that the latching mechanism described above is merely an example embodiment. Other latching mechanisms that are known in the art can also be used to couple and decouple between the shell members  602   a ,  602   b , such as hook-and-loop fasteners, clips, buckles, magnetic fasteners, etc. 
     In the depicted embodiment, when the shell members  602   a ,  602   b  are in the closed state, outer shell  602  can define a proximal recess  620 , a distal recess  622 , and an intermediate recess  624  located between the proximal recess  620  and the distal recess  622 . 
     The proximal recess  620  can have a tapered shape such that a proximal end of the proximal recess  620  has a smaller diameter than a distal end of the proximal recess  620 . In certain embodiments, the shape of the proximal recess  620  can substantially correspond to the shape of the proximal end portion  682  of the balloon  680 . 
     The distal recess  622  can have a tapered shape such that a distal end of the distal recess  622  has a smaller diameter than a proximal end of the distal recess  622 . In some embodiments, the shape of the distal recess  622  can substantially correspond to the shape of the distal end portion  684  of the balloon  680 . 
     The intermediate recess  624  can have a generally cylindrical shape that is configured to receive the inner sleeve  604 . 
     In the depicted embodiment, the shell members  602   a ,  602   b  have about the same circumferential size such that each defines a half section of the proximal recess  620 , the distal recess  622 , and the intermediate recess  624 . In other embodiments, the shell members  602   a ,  602   b  can have different circumferential sizes such that one of the shell members defines a smaller section whereas the other shell member defines the remaining (i.e., a larger) section of the recesses  620 ,  622 , and  624 . 
     In the depicted embodiment, the inner sleeve  604  has first and second portions  604   a ,  604   b . Each portion has a semi-cylindrical interior surface  606   a  or  606   b  defining a half section of the lumen  606 . 
     In other embodiments, the first and second portions  604   a ,  604   b  can have different circumferential sizes such that one portion defines a less-than-half section whereas the other portion defines the remaining (i.e., larger-than-half) section of the lumen  608 . 
     In the depicted embodiment, the first portion  604   a  of the inner sleeve  604  has two longitudinal edges  618   a  that are configured to matingly engage two respective longitudinal edges  618   b  of the second portion  604   b  of the sleeve  604  to form the lumen  606 . Thus, when the longitudinal edges  618   a  of the first portion  604   a  are aligned with the respective longitudinal edges  618   b  of the second portion  604   b , the inner sleeve  604  can enclose the valve retaining portion  686  of the balloon  680  in a closed state. 
     In some embodiments, the first and second portions  604   a ,  604   b  are completely separable at both pairs of longitudinal edges  618   a ,  618   b . In other embodiments, the first and second portions  604   a ,  604   b  can be hingely connected along one pair of longitudinal edges  618   a ,  618   b  while they can be separable at the other pair of longitudinal edges  618   a ,  618   b.    
     As described herein, the inner sleeve  604  can be radially deformable when the balloon  680  is inflated and exerts pressure radially outwardly against the inner surface  606  of the inner sleeve  604 , such as during a de-airing procedure. In other words, inflating the balloon  680  from a deflated state to an inflated state can deform the lumen  606  of the inner sleeve  604  from an initial state to a deformed state. The lumen  608  can have a first diameter in the initial state and a second diameter in the deformed state, and the second diameter is larger than the first diameter. 
     In the depicted embodiment, the inner surface  606  of the inner sleeve  604  can maintain enclosure of the lumen  608  in a circumferentially continuous manner when the lumen  608  is radially expanded by inflating the balloon  680  from the deflated state to the inflated state. In other words, the inner surface  606  can be circumferentially continuous where there is no gap between either engaging pairs of longitudinal edges  618   a ,  618   b  through which a portion of the balloon  680  can extend. Thus, the two semi-cylindrical interior surfaces  606   a  or  606   b  can form a full cylindrical interior surface that defines the lumen  608  irrespective of the lumen&#39;s diameter. 
     In some embodiments, the inner sleeve  604  can further define a tapered proximal opening  626  located at a proximal end of the lumen  608  and a tapered distal opening  628  located at a distal end of the lumen  608 . The tapered proximal opening  626  connects the middle portion  630  of the lumen  608  to the proximal recess  620  and the tapered distal opening  628  connects the middle portion  630  of the lumen  608  to the distal recess  622 . 
     In some embodiments, at least when the balloon  680  is in the deflated state (i.e., the lumen  608  is in the initial state), the middle portion  630  of the lumen  608  can have a diameter that is smaller than both the tapered proximal opening  626  and the tapered distal opening  628 . 
     In some embodiments, the tapered proximal opening  626  can be configured to receive a junctional region of the balloon  680  where the valve retaining portion  686  connects with the proximal end portion  682 , and the tapered distal opening  628  can be configured to receive a junctional region of the balloon  680  where the valve retaining portion  686  connects with the distal end portion  684 . 
     In some embodiments, the axial length of the inner sleeve  604  is configured to be about the same as the axial length of the intermediate recess  624  of the outer shell  602  so that the inner sleeve  604  and the valve retaining portion  686  of the balloon  680  can snuggly fit into the intermediate recess  624 . In some embodiments, the axial length of the inner sleeve  604  is configured to remain fixed when inflating the balloon  680  from the deflated state to the inflated state. Thus, the inner sleeve  604  and the valve retaining portion  686  can remain snuggly fit inside the intermediate recess  624  regardless of whether the balloon  680  is in a deflated or inflated state. 
     In an example embodiment, the inner sleeve  604  includes an inner wall portion  632  that surrounds the lumen  608  and one or more legs  634  extending radially outwardly from the inner wall portion  632  and spaced apart axially from each other along the length of the inner wall portion  632 . Specifically, the inner wall portion  632  can be divided into two half wall portions  632   a ,  632   b  which respectively define the semi-cylindrical interior surfaces  606   a  and  606   b  of the first and second separable portions  604   a ,  604   b . When both the inner sleeve  604  and the outer shell  602  are in the closed state, the one or more legs  634  can press against an inner surface  636  of the outer shell  602  so as to form one or more cavities  638  between the inner wall portion  632  of the inner sleeve  604  and the inner surface  636  of the outer shell  602 . 
     In the depicted example, the inner sleeve  604  has seven legs  634  which divides the space between the inner wall portion  632  and the inner surface  636  into six cavities  638 . In other embodiments, the number (N) of legs can be less than 7 (e.g., 2, 3, 4, 5, 6) or more than 7 (e.g., 8, 9, or more), and the number of cavities can be N−1. 
     As illustrated in  FIG. 19 , the one or more legs  634  can be parallel to each other. In some embodiments, each of the one or more legs  634  can extend circumferentially around the inner wall portion  632 . 
     For example, each leg  634  can be divided into a pair of half legs that are respectively located on the two half wall portions  632   a ,  632   b . Each of the half legs can extend circumferentially around the corresponding half wall portion  632   a  or  632   b  for about 180 degrees so that when the two half wall portions  632   a ,  632   b  are aligned together to enclose the lumen  608 , the pair of half legs abut each other to form a complete leg  634  that completely encircles the inner wall portion  632  (i.e., the leg  634  extends circumferentially around the inner wall portion  632  for 360 degrees). As such, a cavity between two adjacent, complete legs can be a closed space that is isolated from any of its neighboring cavities. 
     In other embodiments, some of the legs  634  may not fully encircle the inner wall portion  632 . For example, a leg may extend circumferentially along one or more discontinuous segments of the inner wall portion  632  such that two cavities on opposite sides of the leg are connected to each other through a gap in the leg. 
     In some embodiments, the one or more legs  634  can be compressible in the radial direction. For example, when inflating the balloon  680  from the deflated state to the inflated state, the lumen  608  can be radially expanded from the initial state (with a relatively smaller diameter) to the deformed state (with a relatively larger diameter). Correspondingly, the legs  634  can be compressed from an initial radial length to a shortened radial length. Thus, the space occupied by the cavities  638  between the legs  634  can be reduced from an initial volume to a reduced volume. 
     Conversely, when deflating the balloon  680  from the inflated state to the deflated state, the lumen  608  can revert back from the deformed state to the initial state. For example, the legs  634  can be made of an elastomer or a shape memory material, including any of various polymers or alloys. Thus, the legs  634  can recover their initial radial length after the radial pressure exerted by the inflated balloon is removed. Correspondingly, the space of each cavities  638  between the legs  634  can revert back to its initial volume. Note that the contracting lumen  608  can press inwardly against the balloon  680  and help prevent the folded balloon  680  (in deflated state) from unfolding. 
     In some embodiments, the inner surface  636  of the outer shell  602  can have a receptacle configured to receive at least one of the legs  634  so as to securely couple the inner sleeve  604  to the outer shell  602 . 
     For example, as depicted in  FIG. 19 , the first and second shell members  602   a ,  602   b  can have a pair of receptacles  640   a ,  640   b , such as in the form of openings in the shell members  602   a ,  602   b , located at the center (along the axial direction) of their respective inner surface. A pair of half legs located at the center (along the axial direction) of the two half wall portions  632   a ,  632   b  (which can be joined together to form the middle leg) can have enlarged foot portions  642   a ,  642   b . The pair of receptacles  640   a ,  640   b  can be configured to matingly receive the respective foot portions  642   a ,  642   b  so that the first and second separable portions  604   a ,  604   b  of the inner sleeve can be securely coupled to the respective first and second shell members  602   a ,  602   b.    
     In some embodiments, the receptacle and the coupling leg can be located off the center (along the axial direction) of the balloon cover. In some embodiments, a plurality of receptacles can be spaced apart on the outer shell  602  along the axial direction, and each receptacle can be configured to matingly receive a corresponding leg of the inner sleeve  604 . In some embodiments, the inner surface  636  of the outer shell  602  can have one or more protrusions that are configured to matingly engage corresponding one or more receptacles located on the legs  634  of the inner sleeve  604 . In some embodiments, the legs  634  of the inner sleeve  604  and the inner surface  636  of the outer shell  602  can be securely coupled together by other mechanisms, such as gluing, tongue-and-groove joints, clips, buckles, magnetic fasteners, etc. 
     In some embodiments, the inner sleeve  604  and the outer shell  602  can be removably coupled together (i.e., they can be separated apart). In other embodiments, the inner sleeve  604  and the outer shell  602  can be fixedly coupled together (i.e., the inner sleeve  604  cannot be removed from the outer shell  602 ). 
     In other embodiments, the inner sleeve  604  can include only the inner wall portion  632  without the legs  634 . For example, the inner wall portion  632  can be made of a compressible or viscoelastic material such as polyurethane foam, latex, or other types of shape memory foams, or superelastic alloys that have shape memory properties. Thus, when inflating the balloon  680  from the deflated state to the inflated state, the inflating force of the balloon  680  can compress the inner wall portion  632  and reduce its thickness, thus increasing the diameter of the lumen  608 . Conversely, when deflating the balloon  680  from the inflated state to the deflated state, the inner wall portion  632  can revert back to its original shape with a larger wall thickness, thus decreasing the diameter of the lumen  608 . Thus, the contracting lumen  608  can press inwardly against the balloon  680  and help retain the deflated balloon  680  in its folded shape. 
       FIGS. 20-21  show another balloon cover  700 , according to an alternative embodiment. 
     Similar to the balloon cover  600 , the balloon cover  700  can have an outer shell  702  and an inner sleeve  704  disposed within the outer shell  702 , and the outer shell  702  can be more rigid than the inner sleeve  704 . The outer shell  702  can include a first shell member  702   a  and a second shell member  702   b , which are connected to each other by a hinge  710 . Thus, the shell members  702   a ,  702   b  can form a clam shell configuration, allowing them to open and close around a balloon mounted on a delivery catheter (not shown). Likewise, the first and second shell members  702   a ,  702   b  can include respective latch portions  712   a ,  712   b , which can be configured to engage each other to retain the shell members  702   a ,  702   b  in the closed state. 
     As shown in  FIG. 20 , the inner sleeve  704  can have first and second separable sleeve portions  704   a ,  704   b . The first sleeve portion  704   a  includes a wall portion  732   a  and five rib portions  734   a  extending radially inwardly from the wall portion  732   a , and the second sleeve portion  704   b  includes a wall portion  732   b  and five rib portions  734   b  extending radially inwardly from the wall portion  732   b.    
     Although each of the first and second sleeve portions  704   a ,  704   b  has five rib portions, it should be understood that the number of rib portions in each sleeve portion can be less than five (e.g., from one to four) or more than five, and the same principles described herein apply. 
     In some embodiments, the rib portions  734   a ,  734   b  are distributed uniformly along the longitudinal axis of the respective sleeve portions  704   a ,  704   b . In other embodiments, the rib portions  734   a ,  734   b  can be distributed non-uniformly along the longitudinal axis of the respective sleeve portions  704   a ,  704   b.    
     The wall portion  732   a  includes a plurality of wall segments  736   a  separated by the rib portions  734   a , and the wall portion  732   b  includes a plurality of wall segments  736   b  separated by the rib portions  734   b . The number of wall segments in each sleeve portion can be the number of rib portions on the sleeve portion plus one (six in the depicted example). 
     Each wall segment  736   a  of the first sleeve portion  704   a  has two longitudinal edges  740   a  and a wall surface  742   a  extending between the two longitudinal edges  740   a . Similarly, each wall segment  736   b  of the second sleeve portion  704   b  has two longitudinal edges  740   b  and a wall surface  742   b  extending between the two longitudinal edges  740   b.    
     Each rib portion  734   a  of the first sleeve portion  704   a  has two radial edges  744   a  and a rib surface  746   a  extending between the two radial edges  744   a . Similarly, each rib portion  734   b  of the second sleeve portion  704   b  has two radial edges  744   b  and a rib surface  746   b  extending between the two radial edges  744   b.    
     In addition, the first sleeve portion  704   a  includes a proximal end plate  733   a  and a distal end plate  735   a  that are generally parallel to the rib portions  734   a , and the second sleeve portion  704   b  includes a proximal end plate  733   b  and a distal end plate  735   b  that are generally parallel to the rib portions  734   b . The proximal end plate  733   a  has a pair of radial edges  743   a  and an inner surface  747   a  extending between the pair of radial edges  743   a . The distal end plate  735   a  has a pair of radial edges  745   a  and an inner surface  748   a  extending between the pair of radial edges  745   a . Similarly, the proximal end plate  733   b  has a pair of radial edges  743   b  and an inner surface  747   b  extending between the pair of radial edges  743   b . The distal end plate  735   b  has a pair of radial edges  745   b  and an inner surface  748   b  extending between the pair of radial edges  745   b.    
     As described herein, the first and second sleeve portions  704   a ,  704   b  can be matingly coupled together so that the inner sleeve  704  is in a closed state around the balloon. 
     For example, the two radial edges  744   a  of each rib portion  734   a  of the first sleeve portion  704   a  can be configured to matingly engage (e.g., through an interlocking mechanism) two radial edges  734   b  of a corresponding rib portion  734   b  of the second sleeve portion  704   b  so that the rib surfaces  746   a  of the first sleeve portion  704   a  can adjoin corresponding rib surfaces  746   b  of the second sleeve portion  704   b  to form five rib enclosures  750 . In other words, five rib enclosures  750  can be formed by matingly engaging five respective pairs of rib portions  734   a ,  734   b . In some embodiments, all rib enclosures  750  have about the same diameter. 
     In addition, the two longitudinal edges  740   a  of each wall segment  736   a  of the first sleeve portion  704   a  can be configured to align with or matingly engage two longitudinal edges  740   b  of a corresponding wall segment  736   b  of the second sleeve portion  704   b  so that the wall surfaces  742   a  of the first sleeve portion  704   a  can adjoin corresponding wall surfaces  742   b  of the second sleeve portion  704   b  to form six wall enclosures  752  separated by five pairs of rib portions  734   a ,  734   b . In some embodiments, all wall enclosures  752  have about the same diameter. 
     Further, the pair of radial edges  743   a  of the proximal end plate  733   a  can be configured to align with or matingly engage the pair of radial edges  743   b  of the proximal end plate  733   b  so that the inner surfaces  747   a ,  747   b  of the proximal end plates  733   a ,  733   b  can be adjoined to form a proximal opening  726 . Similarly, the pair of radial edges  745   a  of the distal end plate  735   a  can be configured to align with or matingly engage the pair of radial edges  745   b  of the distal end plate  735   b  so that the inner surfaces  748   a ,  748   b  of the distal end plates  735   a ,  735   b  can be adjoined to form a distal opening  728 . In some embodiments, the proximal and distal openings  726 ,  728  can have tapered shapes similar to the proximal and distal openings  626 ,  628  described above. 
     In some embodiments, the rib enclosures  750  can define a lumen which is configured to receive the valve retaining portion (e.g.,  686 ) of the balloon (e.g.,  680 ). For example, when the first and second sleeve portions  704   a ,  704   b  are matingly coupled together, all rib enclosures  750  can have about the same diameter, which is about the same as the diameter of the valve retaining portion of the balloon in its compressed or folded state. Thus, the valve retaining portion of the folded balloon can be retained within the plurality of rib enclosures  750 , which are spaced apart from each other and distributed along the length of the inner sleeve  704 . 
     In some embodiments, when inflating the balloon retained within the rib enclosures  750 , the inner sleeve  704  can be deformed under pressure exerted against the rib surfaces  746   a ,  746   b  by the balloon, thereby radially expanding the diameter of the rib enclosures  750 . 
     For example, the first and second sleeve portions  704   a ,  704   b  can further include a plurality of legs (not shown) extending radially outwardly from the wall portions  732   a ,  732   b  to the inner surface of respective outer shell members  702   a ,  702   b . Such legs can be compressible in the radial direction similar to the legs  634  described above. Thus, when inflating the balloon from the deflated state to the inflated state, the rib enclosures  750  can be radially expanded from the initial state (with a relatively smaller diameter) to the deformed state (with a relatively larger diameter) while the legs are compressed from an initial radial length to a shortened radial length. Conversely, when deflating the balloon from the inflated state to the deflated state, the rib enclosures  750  can revert back from the deformed state to the initial state while the legs recover to their initial radial length after the radial pressure exerted by the inflated balloon is removed. 
     Alternatively, the rib portions  734   a ,  734   b  can be made of a compressible or viscoelastic material having shape memory properties. Thus, when inflating the balloon from the deflated state to the inflated state, the inflation force of the balloon can radially compress the rib portions  734   a ,  734   b , thus increasing the diameter of the rib enclosures  750 . Conversely, when deflating the balloon from the inflated state to the deflated state, the rib portions  734   a ,  734   b  can revert back to their original shape, thus decreasing the diameter of the rib enclosures  750 . 
     In some embodiments, inflating the balloon not only can increase the diameter of the rib enclosures  750 , but also can transmit the force to the diameter of the wall segments  736   a ,  736   b  and cause corresponding increase the diameter of the wall enclosures  752 . Conversely, when the balloon is deflated, both the rib enclosures  750  and the wall enclosures  752  can return to their original (smaller) diameters. 
     In other embodiments, inflating the balloon can increase the diameter of the rib enclosures  750  without changing the diameter of the wall enclosures  752 . This can occur, for example, when the rib portions  734   a ,  734   b  are made of a compressible or viscoelastic material while the wall segments  736   a ,  736   b  are made of a more rigid material. 
     Generally, the diameter of the wall enclosures  752  is larger than the diameter of the rib enclosures  750 , regardless the balloon is in the deflated state or inflated state. In some embodiments, when the balloon is in the inflated state, while sections of the balloon are retained within the rib enclosures  750 , portions of the balloon outside the rib enclosures  750  may partially bulge into the wall enclosures  752 . 
     In some embodiments, any two adjacent rib portions can be configured to have a circumferential offset such that the two radial edges of one of the two adjacent rib portions extend angularly relative to respective two radial edges of the other adjacent rib portion. 
     For example, as shown in  FIG. 20 , the five rib portions  734   a  of the first sleeve portion  704   a  are configured to have alternate rotational positions such that the corresponding radial edges of the first, third, and fifth rib portions (numbering from the most distal one to the most proximal one) extend in a first angular direction, whereas the corresponding radial edges of the second and fourth rib portions extend in a second angular direction that has a circumferential offset relative to the first angular direction. The five rib portions  734   b  of the second sleeve portion  704   b  have similar alternate rotational positions. 
       FIG. 21  shows a cross-section of the cover  700  when the first and second sleeve portions  704   a ,  704   b  are in a closed configuration. The locations where adjacent radial edges  734   a ,  734   b  mate with each other form parting lines  760   a ,  760   b ,  760   c ,  760   d ,  760   e . As shown, each parting line  760   a - e  is circumferentially offset from an adjacent parting line with respect to a central longitudinal axis of the cover  700 . The offset between the parting lines minimizes the risk of the balloon extending outwardly through the parting lines when the balloon in inflated during use. 
     In some embodiments, the plurality of rib portions do not have alternate rotational orientations. For example, the plurality of rib portions on a sleeve portion can be configured to rotate clockwise (or counter-clockwise) progressively from the most distal rib portion to the most proximal rib portion. In other embodiments, the plurality of rib portions on a sleeve portion can be randomly rotated or rotated in a predefined pattern so that no two adjacent rib portions have radial edges extending in the same angular direction. 
       FIGS. 22-23  show another balloon cover  800  configured to receive a delivery device, such as a delivery device  870 , according to yet another embodiment. 
     As shown, the balloon cover  800  includes a first shell member  802   a  and a second shell member  802   b  that are configured to matingly engage each other. When the first and second shell members  802   a ,  802   b  are mating engaged with each other, the balloon cover  800  is in a closed state, as shown in  FIGS. 22B and 23B . The respective inner surfaces (or “inner walls”)  804   a ,  804   b  of the shell members  802   a ,  802   b  can define a lumen  806  that is configured to receive a distal end portion of the balloon catheter  870 , including an inflatable balloon  880  mounted thereto. When the shell members  802   a ,  802   b  are disengaged from each other, the balloon cover  800  is in an open state, as shown in  FIG. 23A . 
     In the depicted embodiment, the delivery device  870  includes an outer shaft (not shown), an intermediate shaft  876  (also referred to as a “balloon shaft”) extends through a lumen of the outer shaft, an inner shaft  878  extends through a lumen of the balloon shaft  876 , and a nosecone  874  connected to the distal end portion of the inner shaft  878 . Similar to the examples described above (see e.g.,  FIGS. 6-7 ), the delivery device  870  can include a shoulder assembly  890  connected to the distal end portion of balloon shaft  876 , and the balloon  880  can be folded onto the shoulder assembly  890 . 
     In the depicted embodiment, the first shell member  802   a  has two opposing first longitudinal edges  840   a  and the second shell member  802   b  has two opposing second longitudinal edges  840   b . The first longitudinal edges  840   a  can be configured to mate with the corresponding second longitudinal edges  840   b  to form two longitudinal parting lines. 
     In some embodiments, the shell members  802   a ,  802   b  can be completely separable from each other, i.e., both first longitudinal edges  840   a  can be separated from respective longitudinal edges  840   b  (see e.g.,  FIG. 23A ). In alternative embodiments, the first and second shell members  802   a ,  802   b  can be connected to each other along one (and only one) pair of longitudinal edges  840   a ,  840   b  by a hinge (similar to the hinges  610  or  710  described above), thereby allowing the first and second shell members  802   a ,  802   b  to open and close around the distal end portion of the balloon catheter  870 . 
     In certain embodiments, the first and second shell members  802   a ,  802   b  can have respective latches (similar to the latches  406   a  and  406   b , or  612   a  and  612   b  described above) which are configured to engage each other so as to retain the first and second shell members  802   a ,  802   b  matingly engaged (i.e., in the closed state). 
     In other embodiments, the balloon cover  800  can further include a sleeve (not shown, similar to the sleeve  204  described above) configured to slide over the first and second shell members  802   a ,  802   b  so as to retain the first and second shell members matingly engaged (i.e., in the closed state). 
     In the depicted embodiment, the lumen  806  can include a proximal shaft section  808  configured to receive a distal end portion of the intermediate shaft  876  of the delivery device  870 , a distal nosecone section  812  configured to receive the nosecone  874  of the balloon catheter  870 , and an intermediate balloon section  810  configured to receive the balloon  880  mounted on the shoulder assembly  890  of the delivery device  870 . The balloon section  810  is located between the shaft section  808  and the nosecone section  812 . 
     In another embodiment, the balloon cover  800  can be configured to have a lumen that only includes the balloon section  810  without the shaft section  808  or nosecone section  812 . In yet an alternative embodiment, the balloon cover  800  can be configured to have a lumen that includes only the balloon section  810  and one of the shaft section  808  and nosecone section  812 . 
     As shown, the balloon section  810  can include a proximal shoulder portion  814  (also referred to as the “proximal compartment”) configured receive a proximal portion  882  of the balloon  880  mounted on a proximal shoulder  892  of the shoulder assembly  890 , a distal shoulder portion  816  (also referred to as the “distal compartment”) configured to receive a distal portion  884  of the balloon  880  mounted on a distal shoulder  894  of the shoulder assembly  890 , and an intermediate portion  818  (also referred to as the “intermediate compartment”) between the proximal and distal shoulder portions  814 ,  816 . The intermediate portion  818  can be configured to receive a valve retaining portion  886  of the balloon  880  located between the proximal and distal portions  882 ,  884  of the balloon. 
     Generally, except for the wedges and cavities as described below, the proximal shoulder portion  814  of the lumen can have a shape that substantially corresponds to the outer contour of the proximal portion  882  of the balloon folded on the proximal shoulder  892 . Similarly, the distal shoulder portion  816  of the lumen can have a shape that substantially corresponds to the outer contour of the distal portion  884  of the balloon folded on the distal shoulder  894 , and the intermediate portion  818  of the lumen can have a shape that substantially corresponds to the outer contour of the folded valve retaining portion  886  of the balloon. Specifically, in the depicted embodiment, the proximal shoulder portion  814  tapers radially outwardly from its proximal end to its distal end, and the distal shoulder portion  816  tapers radially outwardly from its distal end to its proximal end. The intermediate portion  818  has a generally cylindrical shape. The intermediate portion  818  has a smaller diameter than the proximal end of distal shoulder portion  814  and the distal end of the proximal shoulder portion  816 . 
     Generally, the diameter of the lumen can vary along its axial length. For example, as described above, the balloon portions  882 ,  884  folded around the respective shoulders  892 ,  894  can have respective tapered shape and the valve retaining portion  886  can have a smaller diameter than the balloon portions  882 ,  884 . Accordingly, the intermediate portion  818  of the lumen can have a smaller diameter than a distal end portion of the proximal shoulder portion  814  and a proximal end portion of the distal shoulder portion  816 . 
     In another embodiments, the shoulder assembly  890  of the delivery device  870  includes the distal shoulder  894  but has no proximal shoulder  892 . In such circumstances, while the distal portion  884  of the balloon  880  can be mounted on the distal shoulder  894  of the shoulder assembly  890 , the proximal portion  882  of the balloon  880  can be mounted on the distal end of the intermediate shaft  876 , similar to the embodiments shown in  FIGS. 24-25  below. The portion  814  of the balloon section  810  of the lumen defined by the balloon cover  800  can still be configured to receive the proximal portion  882  of the balloon  880  (despite the absence of proximal shoulder  892 ), similar to the embodiment shown in  FIG. 27  below. 
     In some embodiments, the nosecone section  812  of the lumen can have a neck portion  820 . The neck portion  820  can be formed by two matching semi-annular rings  822   a ,  822   b  protruding radially inwardly from the respective inner surfaces  804   a ,  804   b  of the first and second shell members, Thus, when the balloon  800  is in the closed state, the two semi-annular rings  822   a ,  822   b  can form neck portion  820  that has a smaller diameter than the remaining portions of the nosecone section  812 . By constraining the space at the distal end portion of the lumen, the narrower neck portion  820  can help maintain the folded shape of the balloon  880 . 
     In some embodiments, the shaft section  808  of the lumen can include a plurality of central passages or apertures  824 . Each central passage can be formed by a corresponding pair of opposing rib members  826   a ,  826   b  extending radially inwardly from respective inner surfaces  804   a ,  804   b  of the first and second shell members  802   a ,  802   b . Each rib member  826   a  (or  826   b ) can have two radial edges  828   a  (or  828   b ) and a semicircular rib surface  830   a  (or  830   b ) extending between the two radial edges  828   a  (or  828   b ) such that when the balloon  800  is in the closed state, the two rib surfaces  830   a ,  830   b  can jointly define an inner surface of the respective central passage  824 . As shown, any two adjacent central passages  824  can be separated by a chamber  832  located between the rib members  826   a ,  826   b  that form the two adjacent central passages  824 . 
     Generally, the diameter of the chamber  832  (measured across the inner surface  804   a ,  804   b ) is larger than the diameter of the central passages  824  (measured across the rib surfaces  830   a ,  830   b ). In some embodiments, the plurality of passages  824  can have varying diameters (e.g., in  FIG. 23B , the diameter of the left two passages is smaller than the four passages on the right side). In other embodiments, the plurality of passages  824  can have about the same diameter. 
     In some embodiments, when the balloon cover  800  encloses the distal end portion of the balloon catheter  870  (including the balloon  880  mounted thereto), the balloon cover  800  can have a small cavity (e.g., at about the location where the arrow  808  points to in  FIG. 22A ) configured to receive a distal end of the outer shaft. In some embodiments, this cavity (the proximal portion of shaft section  808  of the cover) is sized to receive a distal portion of an outer shaft and a tip portion of the outer shaft, such as outer shaft  972  and tip portion  973  of  FIG. 24 . When the balloon cover  800  is in the open state with the distal end portion of the balloon catheter disposed in one of shell members  802   a ,  802   b , slightly pushing the balloon  800  in a proximal direction causes the proximal portion  882  of the folded balloon  800  to “puff up” or more closely conform to the shape of the proximal compartment  814  of the cover, which can help maintain the desired shape of the balloon during storage of the balloon catheter. 
     According to one exemplary embodiment, the first shell member  802   a  includes a plurality of first wedges  842   a  juxtaposed with a plurality of first cavities  844   a  and the second shell member  802   b  includes a plurality of second wedges  842   b  juxtaposed with a plurality of second cavities  844   b . The first wedges  842   a  and first cavities  844   a  are configured to interlock with the corresponding second cavities  842   b  and second wedges  844   b  when the balloon cover  800  is in the closed state. 
     For example, the first cavities  844   a  can be so positioned and sized to receive the corresponding second wedges  842   b  and the second cavities  844   b  can be so positioned and sized to receive the corresponding first wedges  842   a . Thus, when the balloon  880  is in the closed state (see e.g.,  FIGS. 22B and 23B ), the first wedges  842   a  are offset with the second wedges  842   b  such that the plurality of first wedges  842   a  are received by the plurality of second cavities  844   b  and the plurality of second wedges  842   b  are received by the plurality of first cavities  844   a.    
     As described herein, the interlocking between the wedges  842   a ,  842   b  and corresponding cavities  844   a ,  844   b  advantageously allow the balloon cover  800  to hold certain areas of the balloon  880  (e.g., areas contacting with wedges) tighter than others (e.g., areas not contacting with edges), according to design need. In addition, the interlocking nature of the design can mitigate the risk of sliding and/or misaligning between the shell members  802   a ,  802   b  (thus reducing the risk of damage to the balloon) during manufacture, transportation, and/or storage of the balloon assembly comprising the balloon  880  and the balloon cover  800 . 
     As shown, the first and second wedges  842   a ,  842   b , and the first and second cavities  844   a ,  844   b  are located in the balloon section  810  of the lumen. In the depicted embodiment, the wedges  842   a ,  842   b  and cavities  844   a ,  844   b  are distributed in the proximal shoulder portion  814 , the distal shoulder portion  816 , as well as the intermediate portion  818 . In other embodiments, the wedges  842   a ,  842   b  and cavities  844   a ,  844   b  can be distributed in only selected part(s) of the balloon section  810 . 
     As shown, the first wedges  842   a  and first cavities  844   a  can be located adjacent and along with the first longitudinal edges  840   a , and the second wedges  842   b  and second cavities  844   b  can be located adjacent and along with the second longitudinal edges  844   b.    
     As shown, the first wedges  842   a  can protrude above the first longitudinal edges  840   a  and the cavities  844   a  can be recessed below the first longitudinal edges  840   a . Similarly, the second wedges  842   b  can protrude above the second longitudinal edges  840   b  and the cavities  844   b  can be recessed below the second longitudinal edges  840   b.    
     In the depicted embodiment, the first wedges  842   a  and first cavities  844   a  located along the two opposing first longitudinal edges  840   a  are symmetric about an axial axis of the first shell member  802   a , and the second wedges  842   b  and second cavities  844   b  located along the two opposing second longitudinal edges  840   b  are symmetric about an axial axis of the second shell member  802   b . In other embodiments, the wedges  842   a ,  842   b  and cavities  844   a ,  844   b  may be located asymmetric about respective axial axis of the shell members. 
     In the depicted embodiment, the wedges  842   a ,  842   b  and cavities  844   a ,  844   b  are distributed about uniformly along the axial axis of the balloon cover (i.e., the wedges and cavities on a cover member are axially spaced apart from each other at about equal distances). In other embodiments, the wedges  842   a ,  842   b  and cavities  844   a ,  844   b  can be distributed non-uniformly along the axial axis of the balloon cover. For example, the wedges  842   a ,  842   b  and cavities  844   a ,  844   b  located in the intermediate portion  818  can be configured to have a density (i.e., smaller distances between adjacent wedges or cavities) than the wedges  842   a ,  842   b  and cavities  844   a ,  844   b  located on the proximal shoulder portion  814  and/or distal shoulder section  816 , or vice versa. 
     In the depicted embodiment, the wedges  842   a ,  842   b  are about the same size and shape. In other embodiments, the wedges  842   a ,  842   b  can be configured to have different sizes and/or shapes (and the cavities  844   a ,  844   b  can have corresponding sizes and/or shapes to receive the respective wedges  842   a ,  842   b ). For example, the cross section of the wedges  842   a  and/or  842   b  can be square, rectangle, circle, oval, or other shapes. In another example, the cross section of the wedges  842   a  and/or  842   b  in the intermediate portion  818  can be configured to have a smaller (or larger surface area) than the wedges  842   a ,  842   b  and cavities  844   a ,  844   b  located on the proximal shoulder portion  814  and/or distal shoulder section  816 . 
     In some embodiments, the shell members  802   a ,  802   b  can be made of a rigid material (similar to the outer shells  602  and  702  described above) so that the lumen  806  cannot be deformed by partial inflation of the balloon  880 . In other embodiments, the shell member  802   a ,  802   b  can be made of an elastic material (similar to the inner shells  604  and  704  described above) such that the lumen  806  may partially deform (e.g., increase in diameter) due to partial inflation of the balloon  880 . In some embodiments, the shell member  802   a ,  802   b  can be configured to function in a similar manner as the inner shells  604  and  704 , e.g., by including components similar to the legs  634  or rib portions  734  described above, and then including another outer shell outside the shell member  802   a ,  802   b.    
       FIGS. 24-25  show the distal end portion of a delivery device  970  for a prosthetic valve, according to another embodiment. The delivery device  970  in the illustrated embodiment comprises an inflatable balloon  980  for expanding a prosthetic heart valve within a patient&#39;s body. 
     As shown, the delivery device  970  includes a first shaft  972  (which is an outer shaft in the illustrated embodiment), a second shaft  976  (which is an intermediate shaft in the illustrated embodiment; also referred to as a “balloon shaft”) extending through a lumen of the outer shaft  972 , a third shaft  978  (which is an inner shaft in the illustrated embodiment) extending through a lumen of the intermediate shaft  976 , and a nosecone  974  connected to the distal end portion of the inner shaft  978 . The inner shaft  978  can have a guidewire lumen for receiving a guidewire  979 , as known in the art. The balloon  980  can have a proximal end portion  982   p  affixed to a stepped down end portion of the balloon shaft  976  and a distal end portion  984   d  affixed to the nosecone  974 . 
     In the depicted embodiment, a flexible tip member  973  is fixedly coupled to a distal end of the outer shaft  972 . A distal end of the flexible tip member  973  can have a larger diameter than the diameter of the outer shaft  972 . The delivery device  970  can include a shoulder assembly  990  connected to the distal end portion of the inner shaft  978 , and at least a distal portion  984  of the balloon  980  can be folded around the shoulder assembly  990 . 
     As shown, the shoulder assembly  990  in the illustrated embodiment includes only a distal shoulder  994  (there is no proximal shoulder, in contrast to the shoulder assembly  890  described above). While the distal portion  984  of the balloon is folded around the distal shoulder  994 , a proximal portion  982  of the balloon can be folded directly around a section  992  of the inner shaft  978  that is located proximal to the distal shoulder  994 . A valve retaining portion  986  of the balloon  980  (which is located between the proximal portion  982  and the distal portion  984 ) can be positioned along a portion of the inner shaft  978  that connects the distal shoulder  994  and the shaft section  992 . As shown, when the balloon  980  is in a deflated and folded state, the valve retaining portion  986  can have a generally cylindrical shape. As shown, both the proximal end portion  984   p  of the distal portion  984  and the distal end portion  982   d  of the proximal portion  982  have larger diameters than the valve retaining portion  986  of the balloon  980 . In the depicted embodiment, the largest diameter of the folded balloon  980  can be located at the proximal end portion  984   p  of the distal portion  984 . 
     The proximal end portions of the shafts  972 ,  976 , and  978  can be coupled to a handle of the delivery  970  (e.g., the handle  102 ). In certain embodiments, the shafts  972 ,  976 ,  978  are moveable axially (in distal and proximal directions) and rotationally relative to each other. Further details of the delivery device  970  are disclosed in U.S. Application No. 63/069,567, filed Aug. 24, 2020, which is incorporated herein by reference. 
       FIGS. 24-25  show that the balloon  980  can assume different shapes during use. 
     For example, in the embodiment shown in  FIG. 24 , the proximal portion  982  of the balloon tapers radially inwardly from its distal end portion  982   d  to its proximal end portion  982   p . In contrast, in the embodiment shown in  FIG. 25 , the proximal portion  982  of the balloon is shaped to form two parts having different shapes: a proximal part  981  and a distal part  983 . While the distal part  983  tapers radially inwardly from its distal end to its proximal end, the proximal part  981  has a generally constant diameter along its length. In one example embodiment, the proximal part  981  and the distal part  983  have equal or substantially equal lengths. In other embodiments, the proximal part  981  and the distal part  983  have different lengths. 
     In addition, in the embodiment shown in  FIG. 24 , the distal portion  984  of the balloon tapers radially inwardly from its proximal end portion  984   p  to its distal end portion  984   d . In contrast, in the embodiment shown in  FIG. 25 , the distal portion  984  of the balloon has a generally gourd or hourglass shape characterized by a radial depression in its middle part. Specifically, the distal portion  984  of the balloon tapers radially inwardly from its proximal end portion  984   p  toward a radially depressed middle portion  984   m , and then tapers radially outwardly toward its distal end portion  984   d.    
     The balloon  980  shaped as shown in  FIG. 24  can be retained in the balloon cover  200 ,  400 ,  600 ,  700 , or  800  described above. The shape of the balloon  980  as shown in  FIG. 25  can be formed by the balloon cover  900  as depicted in  FIGS. 26-27  and described more fully below. 
     Prior to introducing the delivery device  970  into a patient, a prosthetic valve can be crimped onto the valve-retaining portion  986  of the balloon  980 . As previously described, prior to crimping, the balloon  980  can undergo a cyclic de-airing process whereby the inflation fluid is introduced into the balloon and then withdrawn from the balloon. The process of introducing inflation fluid into the balloon and then withdrawing the inflation fluid can be repeated one or more times as needed. During the de-airing process, the tip  973  of the outer shaft  972  typically is positioned proximal to the balloon to facilitate the flow of inflation fluid into the proximal portion  982  of the balloon  980 . In some embodiments, the de-airing process can be carried out while the balloon  980  is contained within a balloon cover. Following the de-airing process, the balloon cover can be removed from the balloon and the outer shaft  972  can be moved relative to the intermediate shaft  976  (and the inner shaft  978 ) to a distal position extending over the proximal part  981  of the proximal portion  982  of the balloon (as shown in phantom in  FIG. 25 ). When the outer shaft  972  is moved distally over the proximal part  981 , residual fluid in the proximal portion of the balloon from the de-airing process can be pushed distally into the valve-retaining portion  986  and the distal portion  984  of the balloon. Following the de-airing process, the shape of the folded balloon depicted in  FIG. 25  can be advantageous than the one depicted in  FIG. 24  in at least two aspects. 
     First, the tapered shape of the proximal portion  982  of balloon shown in  FIG. 24  can press against the flexible tip member  973  and resist the distal advancement of the outer shaft  972  relative to the intermediate shaft  976  and the balloon  980  due to the gradual increase of the diameter of the balloon from the proximal end portion  982   p  to the distal end portion  982   d  and/or the presence of residual fluid in the proximal portion of the balloon. In contrast, the smaller diameter of cylindrically-shaped proximal part  981  depicted in  FIG. 25  facilitates axial movement between the outer shaft  972  and the intermediate shaft  976  with less resistance, especially when the inner diameters of the lumen of the outer shaft  972  and the lumen of the flexible tip member  973  are configured to be about the same as or slightly larger than the outer diameter of the proximal part  981  of the balloon. 
     Second, when the residual inflation fluid in the proximal portion  980  of the balloon is “squeezed” or pushed into the distal portion  984  of the balloon by advancing the outer shaft  972 , the displaced residual fluid can dilate the distal portion  984  of the balloon and increase the outer diameter at the proximal end portion  984   p , thus increasing the overall crimp profile of the delivery device  970 . Moreover, the effect of the displaced inflation fluids can be even more pronounced when the proximal portion  982  has the tapered shape shown in  FIG. 24 . In contrast, undesirable inflation of the proximal end portion  984   p  can be avoided by creating the depression along the middle portion  984   m  as shown in  FIG. 25 . Thus, when the displaced inflation fluid is pushed into the distal portion  984  of the balloon, the middle portion  984   m  can receive the inflation fluid and partially inflate from the hourglass shape (shown in solid lines) to the tapered conical shape  984   m ′ (shown in dashed lines) having a diameter that gradually and continuously decreases from the proximal end portion  984   p  to the distal end portion  984   d  (shown in dashed lines Thus, the radially depressed middle portion  984   m  effectively creates a negative radial depression that can compensate for the displaced residual fluid, thereby preventing or minimizing inflation of the proximal end portion  984   p  of the balloon distal portion. In this manner, increasing the overall crimp profile of the delivery device  970  as a result of advancing the outer shaft can be avoided. 
     Generally, the maximum diameter of the balloon and the crimped prosthetic valve typically is the location where the inflow end of the prosthetic valve comes in contact with the proximal end portion  984   p  of the balloon distal portion and therefore the overall crimp profile of the delivery device can be determined by the diameter at this location. For the balloon shaped as shown in  FIG. 24 , in some examples, the displaced inflation fluid can increase the diameter of the balloon at the inflow end of the prosthetic valve (at location  984   p ) by about 0.25 mm. In contrast, for the balloon shaped as shown in  FIG. 25 , in some examples, the displaced inflation fluid causes a slight increase of the diameter of the balloon at the inflow end of the prosthetic valve (e.g., an increase of about 0.12 mm). Thus, by changing the balloon shape from  FIG. 24  to  FIG. 25 , the increase in diameter of the balloon at the inflow end of the prosthetic valve due to the displaced inflation fluid can be reduced by over 50% (e.g., from about 0.25 mm to about 0.12 mm). 
     Various techniques and mechanisms can be used to achieve the balloon shape shown in  FIG. 25 , including a balloon cover having an internal cavity that is shaped to produce the desired shape of the balloon. 
       FIGS. 26-27  show a balloon cover  900  configured to receive the delivery device  970  and the balloon  980  folded thereon, according to one embodiment. Specifically, the balloon cover  900  is configured to receive and create the final shape the balloon  980  shown in  FIG. 25 . For example,  FIG. 28  shows a distal portion of the balloon cover  900  that retains the distal portion  984  of the hourglass-shaped balloon depicted in  FIG. 25 . As described more fully below, the balloon cover  900  is similar to the balloon cover  800  described above, except for the shape of the lumen that is configured to receive the balloon. 
     As shown, the balloon cover  900  includes a first shell member  902   a  and a second shell member  902   b  that are configured to matingly engage each other. When the first and second shell members  902   a ,  902   b  are mating engaged with each other, the balloon cover  900  is in a closed state, as shown in  FIG. 27 . The respective inner surfaces (or “inner walls”)  904   a ,  904   b  of the shell members  902   a ,  902   b  can define a lumen  906  that is configured to receive the distal end portion of the delivery device  970 , including the balloon  980  folded thereon. When the shell members  902   a ,  902   b  are disengaged from each other, the balloon cover  900  is in an open state, as shown in  FIG. 26 . The first and second shell members  902   a ,  902   b  can be matingly coupled together or separated from each other along respective longitudinal edges  940   a ,  940   b . Similar to the balloon cover  800 , the shell members  902   a ,  902   b  can be made of a rigid material or an elastic material, and they can be completely separable from or connected to each other with a hinge (e.g., such as shown in  FIG. 13 or 17 ). 
     Similar to the balloon cover  800 , the first shell member  902   a  has a plurality of first wedges  942   a  alternating with a plurality of first cavities  944   a  along the length of the first shell member. The second shell member  902   b  has a plurality of second wedges  942   b  alternating with a plurality of second cavities  944   b  along the length of the second shell member. The first wedges  942   a  and first cavities  944   a  are configured to interlock with corresponding second cavities  944   b  and second wedges  942   b  when the balloon cover  900  is in the closed state. In the depicted embodiment, the first wedges  942   a  and first cavities  944   a  are perpendicular to the first longitudinal edges  940   a , and the second wedges  942   b  and second cavities  944   b  are perpendicular to the second longitudinal edges  940   b . As shown, the first and second wedges  942   a ,  942   b  can protrude above the respective first and second longitudinal edges  940   a ,  940   b , and the first and second cavities  944   a ,  944   b  can be recessed below the respective first and second longitudinal edges  940   a ,  940   b  when the cover is in the closed state. 
     Like the balloon cover  800 , the lumen  906  of the balloon cover  900  includes a balloon section  910  configured to receive the balloon  980  folded on the distal end portion of the delivery device  970 , a shaft section  908  configured to receive a distal end portion of the intermediate shaft  976 , and a nosecone section  912  configured to receive the nosecone  974 . The balloon section  910  is located between the shaft section  908  and the nosecone section  912 . As shown, the balloon section  910  includes a proximal compartment  914  configured to receive the proximal portion  982  of the balloon, a distal compartment  916  configured to receive the distal portion  984  of the balloon, and an intermediate compartment  918  between the proximal and distal compartments  914 ,  916  and which is configured to receive the valve retaining portion  986  of the balloon. A distal end  914   d  of the proximal compartment  914  can have a smaller diameter than a proximal end  916   p  of the distal compartment  916 , and the intermediate compartment  918  can have a smaller diameter than the distal end  914   d  of the proximal compartment  914 . 
     The shaft section  908  and nosecone section  912  of the balloon cover  900  can be similar to the respective shaft section  808  and nosecone section  812  of the balloon cover  800 . The intermediate compartment  918  of the balloon cover  900  can be similar to the intermediate portion  818  of the balloon cover  800 . However, the proximal compartment  914  and/or the distal compartment  916  of the balloon cover  900  can have different shapes than the corresponding compartments  814 ,  816  of the balloon cover  800 . 
     Specifically, the proximal compartment  914  can include a proximal part  913  and a distal part  911  that are shaped to receive the corresponding proximal part  981  and distal part  983  of the balloon depicted in  FIG. 25 . As shown in  FIG. 26 , the distal part  911  tapers radially inwardly from its distal end to its proximal end, and the proximal part  913  has a substantially constant diameter along its axial length. In the depicted embodiment, the proximal part  913  has about the same axial length as the distal part  911 . In other embodiments, the proximal part  913  and the distal part  911  can have different lengths so long as they match the respective lengths of the proximal part  981  and distal part  983  of the balloon. 
     In addition, as shown in  FIG. 26 , the distal compartment  916  includes a proximal region  915 , a distal region  917 , and a middle region  916   m  between the proximal and distal regions  915 ,  917 . Generally, the distal region  917  has a smaller diameter than the proximal region  915 , and the middle region  916   m  has a smaller diameter than the distal region  917 . Specifically, in the illustrated embodiment, the distal compartment  916  tapers radially inwardly from the proximal region  915  to the middle region  916   m  and then tapers radially outwardly from the middle region  916   m  to the distal region  917 . A distal end  917   d  of the distal region  917  can have a smaller diameter than a proximal end  915   p  of the proximal region  915 . As best shown in  FIG. 28 , the distal compartment  916  has a generally gourd or hourglass shape that is configured to receive the distal portion  984  of the balloon depicted in  FIG. 25 . 
     In certain embodiments, the deflated balloon can be initially folded to achieve the shape depicted in  FIG. 24 . The folded balloon can include axial and/or radial folds as shown in  FIGS. 6, 8 and 10 . A compression mechanism or compression member can be applied to radially compress the distal portion  984  of the balloon to form the hourglass shape depicted in  FIG. 25 . 
     In certain embodiments, a radial protrusion from the inner walls of the shell members at the middle region  916   m  can be used as a compression mechanism to radially compress and retain the middle portion  984   m  of the balloon distal portion. For example, as shown in  FIGS. 26 and 28 , a first semicircular radial protrusion  920   a  can extend radially inwardly from the inner wall  904   a  of the first shell member  902   a  and a second semicircular radial protrusion  920   b  can extend radially inwardly from the inner wall  904   b  of the second shell member  902   b . The first and second semicircular radial protrusions  920   a ,  920   b  can form a circular radial protrusion that extends radially inwardly when the first and second shell members  902   a ,  902   b  are matingly engaged with each other. 
     In certain embodiments, the shape of the lumen  906  can be defined by inner surfaces of the wedges  942   a ,  942   b . When the two shell portions  902   a ,  902   b  are in the closed state, the distal compartment  916  of the lumen can have a smooth hourglass cross-sectional profile, and the distal portion  984  of the balloon will assume that shape when shell portions  902   a ,  902   b  are closed around the balloon. In the embodiment shown in  FIG. 28 , the radial protrusions  920   a ,  920   b  can be defined by inner surfaces of the wedges  942   a ,  942   b , which correspond to the smallest diameter along the middle portion  916   m  of the distal compartment. Thus, wedges  942   a ,  942   b  at the middle portion  916   m  can function as compression members to compress the distal portion  984  of the balloon to form the hourglass shape depicted in  FIG. 25 . 
     In certain embodiments, the balloon cover  900  can further shape the proximal portion  982  of the balloon from the initial shape of  FIG. 24  to the final shape of  FIG. 25 . For example, the proximal portion  982  of the balloon having an initially tapered shape of  FIG. 24  can be reformed by the proximal compartment  914  of the balloon cover to the shape shown in  FIG. 25  (i.e., having the tapered distal part  983  and the cylindrical proximal part  981 ) when shell portions  902   a ,  902   b  are closed around the balloon. 
       FIG. 30  illustrates another compression mechanism or compression member configured to radially compress and retain the distal portion  984  of the balloon. As shown, the compression member can include an annular band or ring  922  configured to be placed around the middle portion  984   m  of the distal portion  984  of the balloon. In one embodiment, the band  922  can be made from a relatively rigid and non-elastomeric material (e.g., a rigid plastic) having a fixed inner diameter equal to the final, desired diameter of the middle portion  984   m  of the balloon distal portion. In use, the band  922  can be slid over the nosecone  974  and onto the middle portion  984   m  of the balloon distal portion. When placed on the balloon, the band  922  creates a radial depression along the middle portion  984   m . In another embodiment, the band  922  can made from an elastomeric material (e.g., rubber or a synthetic elastomer, such as polyurethane), such as an O-ring, which can expand to facilitate sliding the band over the nosecone. The inner diameter of the band is sized such that when placed on the balloon, the band creates a radial depression along the middle portion  984   m  of the balloon distal portion. Also, when positioned on the balloon, the elastomeric band can allow for at least partial inflation of the balloon distal portion  984  during the de-airing process. After the de-airing process, the band  922  can be removed from the balloon by sliding it distally over the nosecone  974 . In some embodiments, the band  922  can have sufficient elasticity to permit full inflation of the distal portion  984  of the balloon or at least sufficient inflation for full deployment of the prosthetic valve and can be left on the balloon during the implantation procedure. 
     In another embodiment, the band  922  can be formed by wrapping a flexible cord or string, such as a suture, around the middle portion  984   m  of the balloon distal portion and tying the two ends of the cord together. The cord can be sufficiently tightened around the middle portion  984   m  to create the radial depression. 
     In some embodiments, after the band  922  is placed around the middle portion, the distal end portion of the delivery device  970  can be placed in a balloon cover (including any of the embodiments of balloon covers disclosed herein) for storage and subsequent de-airing. 
     In certain embodiments, the compression member can include a flexible sheath  924  connected to the band  922 , as shown in  FIG. 29 . The sheath  924  is configured to surround a distal part of the distal portion  984  of the balloon. A distal end  924   d  of the sheath  924  can be connected to the distal end portion  984   d  of the distal portion of the balloon and/or the nosecone  974 . 
     In certain embodiments, the sheath  924  can comprise an elastic or deformable material so that it can be radially expanded when the distal portion  984  of the balloon is inflated, such as during the de-airing process. For example, the sheath  924  can be configured to be movable between a radially compressed configuration and a radially expanded configuration. When the sheath  924  is in the radially compressed configuration, the band  922  can radially compress the middle portion  984   m  of the balloon to create a radial depression. When the sheath  924  is in the radially expanded configuration (e.g., after radially expanding the distal portion  984  of the balloon), the band  922  can be radially expanded. In some embodiments, after the band  922  and the sheath  924  are placed over the balloon, the distal end portion of the delivery device  970  can be placed in a balloon cover (including any of the embodiments of balloon covers disclosed herein) for storage and subsequent de-airing. 
     After the de-airing process, the band  922  and the sheath  924  can be removed from the balloon by rolling up the band and the sheath in the distal direction until the rolled-up band and sheath is on the nosecone. In some embodiments, the band  922  and the sheath  924  can allow for sufficient inflation of the balloon for valve deployment and can be kept in place over the balloon during the implantation procedure. 
     In some embodiments, there is no separate structure forming the band  922 . Instead, the band  922  can be an integral portion of the proximal end portion  924   p  of the sheath  924 . In one example, the sheath  924  can be relatively thicker and less resilient along the proximal end portion  924   p  compared to remaining portion of the sheath  924  such that the proximal end portion  924   p  can apply a sufficient inward force on the middle portion  984   m  of the balloon distal portion to create a radial depression along that portion of the balloon. 
     Although in the examples described above, a compression mechanism or compression member is disposed in the distal compartment of the balloon cover to radially compress the distal portion of the balloon, it is to be understood that similar compression mechanisms or compression members can also be placed at other locations (e.g., the proximal compartment and/or the intermediate compartment) of the balloon cover depending on the needs of the design (e.g., to radially compress a certain portion of the balloon to conform to a specified diameter or shape at that portion). For example, it may be desirable to create a depression in the proximal portion of a balloon, which can facilitate sliding of the outer shaft  972  over the proximal portion of the balloon. 
     In certain embodiments, for example, the proximal compartment  914  and/or the intermediate compartment  918  can be formed with a compression member (e.g., a radial protrusion) to create a depression in the portions of the balloon in those compartments. In some embodiments, the cover  900  can include one or more compression members (e.g., radial protrusions) at one or more locations along the length of the cover, including the proximal compartment  914 , the intermediate compartment  918 , and/or the distal compartment  916 . Similarly, the device of  FIG. 29  can be sized such that the band  922  can be placed around any portion of the balloon, including the proximal portion, the intermediate portion or the distal portion of the balloon. 
     It should be understood that the compression mechanisms described above are merely example embodiments. Other embodiments can be employed to radially compress the middle portion  984   m  of the balloon or other portions of the balloon so that the compressed section of the balloon has a generally gourd or hourglass shape. 
     As described below, the balloon cover  600  (or cover  200 ,  400 ,  700 ,  800 , or  900 ) can facilitate de-airing of the balloon  680  by employing a compressible inner member or layer defining the inner chamber for receiving a balloon. 
     Prior to crimping a prosthetic valve onto the balloon, the balloon typically needs to undergo a cyclic de-airing process that involves pushing an inflation fluid into the balloon and then drawing the fluid out (e.g., with a syringe) to create a vacuum in the balloon. The de-airing process is more successful when the balloon is allowed to at least partially inflate. However, inflation of a folded balloon without a balloon cover can result in un-folding of the balloon, which may not then return to its compressed, folded shape. On the other hand, rigid balloon covers may prevent inflation of the balloon entirely. 
     The balloon cover  600  (or  200 ,  400   700 ,  800 , or  900 ) disclosed herein can overcome such problems. Advantageously, the flexible inner sleeve  604  (or  704 ; similarly, covers  200 ,  400 ,  700   800 ,  900  can include a flexible or deformable inner sleeve or layer forming the chamber for receiving the balloon) allows the folded balloon  680  to partially inflate within the inner sleeve  604  (or  704 , or similar components of covers  200 ,  400 ,  700 ,  800 ,  900 ) during the de-airing process without becoming unfolded. Specifically, when an inflation fluid is injected into the folded balloon  680 , the balloon  680  can partially inflate, pressing against the inner sleeve  604  which deforms (e.g., by increasing the diameter of the lumen and shortening the legs) to accommodate the partially inflated balloon  680 . The degree of flexibility of the inner sleeve  604  limits the partial inflation of the balloon  680 . For example, the maximum diameter the balloon  680  can be inflated to can be limited by the largest diameter of the lumen  608  (or rib enclosures  750 , or  810 ) can be extended to, which can be further limited by the shortest radial length the legs  634  can be compressed to and is inherently limited by the diameter of the intermediate recess  624  of the outer shell  602 . 
     When the vacuum is created in the balloon  680  after drawing the inflation fluid out of the balloon, the flexible inner sleeve  604  (or  704 , or similar components of covers  200 ,  400 ,  700 ,  800 ,  900 ) can revert back to its original shape (e.g., by decreasing the diameter of the lumen  608  (or rib enclosures  750 , or  810 ) and lengthening the legs  634 ). Thus, the contracting inner sleeve  604  (or  704 ,  800 ,  900 ) can press inwardly against the balloon  680  and help return the balloon  680  to its original (folded) shape. 
     An example method of assembling the balloon  680  within the balloon cover  600  is described below (and similar method can also be applied to assemble the balloon  680  within the balloon cover  200 ,  400 ,  700 ,  800 , or  900 ). 
     According to one embodiment, the balloon  680  (in the deflated state) can be folded over the shoulder assembly (including the proximal shoulder  690 , the distal shoulder  692  and the valve retaining portion  686 ) of the delivery device  670  as shown in  FIG. 19 . The folded balloon  680  can be placed within the lumen  608  of the inner sleeve  604 , e.g., by aligning the corresponding longitudinal edges  618   a ,  618   b  of the first and second portions  604   a ,  604   b  to enclose the valve retaining portion  686  of the balloon  680 . Then, the inner sleeve  604  and the balloon  680  can be placed within the outer shell  602 . For example, the shell members  602   a ,  602   b  can be placed around the balloon  680  such that the proximal end portion  682  of the balloon  680  is placed inside the proximal recess  620  of the outer shell  602 , the distal end portion  684  of the balloon is placed inside the distal recess  622  of the outer shell  602 , and the inner sleeve  604  is placed inside the intermediate recess  624  of the outer shell  602 . Then, the outer shell  602  can be locked, e.g., by extending the enlarged rim  614   a  through the slot  614   b  to form a snap-fit between the shell members  602   a ,  602   b.    
     An example method of de-airing of the balloon  680  inside the balloon cover  600  is described below, and it should be understood that the same method can also apply to de-airing the balloon inside the other balloon covers disclosed herein. 
     According to one embodiment, the balloon  680  can be fluidly connected to a fluid source (e.g., a syringe). The fluid source can inject a predetermined amount of inflation fluid (e.g., saline) into the balloon  680  so as to inflate the balloon  680  to a partially inflated state. In the partially inflated state, the balloon  680  can still remain partially folded (e.g., at least some of the adjacent folds remain partially overlapped with each other) and can revert back to its original (folded) shape after removal of the inflation pressure. As described above, inflation of the balloon  680  can deform the lumen  608  of the inner sleeve  604  from its initial state (with a relatively smaller diameter) to the deformed state (with a relatively larger diameter). Then, the inflation fluid can be removed from the balloon  680  (e.g., withdrawn back into the inflation source) to create a vacuum inside the balloon  680 . The vacuum can cause the balloon  680  to return from its partially inflated state to the deflated state. The lumen  608  of the inner sleeve  604  can also revert back from the deformed state (with a relatively larger diameter) to its initial state (with a relatively smaller diameter), thereby press inwardly against the balloon  680  and help return the balloon  680  to its original (folded) shape. In some embodiments, the steps of (a) inflating the balloon  680  from the deflated state to the partially inflated state and (b) deflating the balloon  680  from the partially inflated state to the deflated state can be repeated in a plurality of cycles. 
       FIG. 14  illustrates a method of assembling a delivery device to include the balloon  300 , according to one embodiment.  FIGS. 15-16  show a fully assembled delivery device  500  with the folded balloon  300  mounted thereon. The delivery device  500  includes many of the same components of the delivery device  100  of  FIGS. 3-7 . Thus, the same components in  FIGS. 15-16  are given the same respective reference numbers and are not described further. 
     Although the balloon  300  is shown in  FIGS. 14-16  for purposes of illustration, it should be understood that the method described below can be to assemble a delivery device having other balloons, such as the balloon  108 , or a balloon that does not have any folds. Although less desirable, in other embodiments, a balloon can be folded after being assembled onto a delivery device. For example, the balloon  300  without any folds (e.g., folds  316 ,  318 ,  322 ,  326 ) can be assembled onto a delivery device (as described below), after which the balloon can be folded. 
     Referring to  FIG. 14 , a distal shoulder  160  (which can include a nosecone portion  166 ) can be mounted on the distal end portion of a first shaft  106  (which can be the inner shaft of the delivery device) to form a first sub-assembly  502  of the delivery device. A proximal shoulder  170  can be mounted on the distal end portion of a second shaft  105  (which can be an intermediate shaft of the delivery device) to form a second sub-assembly  504  of the delivery device. 
       FIG. 14  shows the balloon  300  removed from its protective cover  400  during the assembly process. In other embodiments, the protective cover  400  (or cover  200 ,  600 ,  700 ,  800 , or  900 ) can be kept in place surrounding the balloon during the assembly process. The restraining member  350  (not shown in  FIG. 14 ) can be removed from the balloon just prior to the assembly process described below or after the balloon is assembled onto the delivery device, or alternatively, the restraining member  350  can be left in place for removal by the end user prior to crimping a prosthetic valve onto the balloon. 
     In the direction indicated by arrow  506  in  FIG. 14  (left to right in  FIG. 14 ), the proximal end of the first shaft  106  can be inserted into an open distal end  340  of the distal leg  308 . The first shaft can then be inserted through the balloon  300 , through the proximal shoulder  170 , and through the second shaft  105 , after which the distal shoulder  160  can be at least partially inserted into the distal tapered portion  304  of the balloon. Because the distal collar member  162  is larger in diameter than the distal leg  306 , the distal collar member  162  can be radially compressed, and then inserted into and through the distal collar member  162 . The distal shoulder  160  can be inserted into the balloon until the distal leg  308  extends over the shaft portion  163  of the distal shoulder  160 . Because the distal collar member  162  is made of a resilient material, it can radially expand back to its original shape once it is passed through the distal leg  308 . The distal leg  308  of the balloon can then be secured to the distal shoulder  160  (e.g., to the shaft portion  163 ) by means of thermal bonding, gluing, mechanical locking, or any other suitable techniques or methods. 
     In the direction indicated by arrow  508  in  FIG. 14  (right to left in  FIG. 14 ), the proximal shoulder  170  can be inserted into an open distal end  342  of the proximal leg  310  of the balloon and inserted through the balloon until the proximal collar member  172  resides within the proximal tapered portion  306  of the balloon and the proximal leg  310  extends over the shaft portion  173  of the proximal shoulder  170 . Because the proximal collar member  172  is larger in diameter than the proximal leg  310 , the proximal collar member  172  can be radially compressed before it is inserted into and through the proximal leg  310 . Because the proximal collar member  172  is made of a resilient material, it can radially expand back to its original shape once it is passed through the proximal leg  310 . The proximal leg  310  of the balloon can then be secured to the proximal shoulder  170  (e.g., to the shaft portion  173 ) by means of thermal bonding, gluing, mechanical locking, or any other suitable techniques or methods. 
     For purposes of illustration, there are shown small gaps between the legs  308 ,  310  and the shaft portions  163 ,  173 . However, it should be understood, the legs  308 ,  310  can be in contact with the shaft portions  163 ,  73  once they are secured to the shaft portions  163 ,  173 . 
     One or more components of the balloon  300  and the distal and proximal shoulders  160 ,  170  can include markings or indicia to facilitate alignment of the balloon with respect to the distal and proximal shoulders  160 ,  170 . For example, the distal leg  308  can include one or more markings that are aligned with corresponding one or more markings on the shaft portion  163  of the distal shoulder  160 . Likewise, the proximal leg  308  can include one or more markings that are aligned with corresponding one or more markings on the shaft portion  173  of the proximal shoulder  170 . Once the distal and proximal legs  308 ,  310  are aligned with the shaft portions  163 ,  173 , respectively, using the markings, the mating components can be affixed to each other as described above. The markings can be any type of marking, including markings printed or painted on the components, markings formed by laser etching, or markings molded into the components. 
     The required axial distance L 1  between the distal shoulder  160  and the proximal shoulder  170 , and therefore the distance between the distal tapered portion  304  and the proximal tapered portion  306  of the balloon, can be predetermined and can be selected to allow a prosthetic valve to be crimped between the distal tapered portion  304  and the proximal tapered portion  306 . Desirably, the axial distance L 1  is selected such that when the prosthetic valve is crimped onto the balloon, the distal tapered portion  304  and the proximal tapered portion  306  can contact adjacent ends of the crimped prosthetic valve. When assembling the first sub-assembly  502  with the second sub-assembly  504 , this distance can be set by measuring a predetermined offset between a component on the first sub-assembly  502  with a component on the second sub-assembly  504 , such as a distance L 2  between the proximal shoulder  170  and the marker band  135 . For example, when inserting the shaft  106  into the shaft  105 , the position of the shaft  106  relative to the shaft  105  can be adjusted until the distance between the proximal shoulder  170  and the marker band  135  is a predetermined distance L 2 , which corresponds to a predetermined distance L 1  between the distal and proximal tapered portions  304 ,  306  of the balloon. 
     In alternative embodiments, other offsets can be used to set the distance L 1 , including (but not limited to): (i) an axial distance between the proximal shoulder  170  and the distal shoulder  160 ; (ii) an axial distance between the proximal shoulder  170  and the distal end of the valve retaining portion  302  of the balloon; and (iii) an axial distance between the distal shoulder and the proximal end of the valve retaining portion  302  of the balloon. 
     In certain embodiments, the axial position of the shaft  106  relative to the shaft  105  is fixed, such as by securing these components directly to each other, such as by welding, an adhesive, mechanical fasteners, etc. The proximal end portions of the shafts  105 ,  106  can then be coupled to a handle (e.g., handle  102 ). Alternatively, the proximal end portions of the shafts  105 ,  106  can be secured to a handle (e.g., handle  102 ) at fixed locations, which fixes the positions of the shafts  105 ,  106  relative to each other. 
     In some embodiments, a steerable outer shaft  104  (such as shown in  FIG. 3 ), can be assembled over the shafts  105 ,  106 . 
     As noted above, in some embodiments, the protective cover  400  (or cover  200 ,  600 ,  700 ,  800 , or  900 ) can be kept in place surrounding the balloon  300  during the assembly process. As shown in  FIG. 13 , the cover  400  has distal and proximal openings  414 ,  416 , which can be sized to allow components of the delivery device to be inserted into the cover  400  and through the openings  340 ,  342  of the balloon while the balloon is inside of the cover  400 . 
     The cover  400  can facilitate alignment of the balloon with components of the delivery apparatus. For example, it sometimes can be difficult for the assembler to visually locate specific locations on the balloon  300  when aligning the balloon relative to the distal and proximal shoulders  160 ,  170 . Instead, the assembler can visually locate specific portions on the cover and align those portions with the distal and proximal shoulders (or other components of the delivery apparatus to which the balloon is secured). 
     For example, a specific location on the distal recessed portion  408  of the cover corresponding to a specific location of the leg portion  308  disposed within the recessed portion  408  can be aligned with a predetermined location of the distal shoulder  160 . Similarly, a specific location of the proximal recess portion  412  corresponding to a specific location of the leg portion  310  disposed within the recessed portion  412  can be aligned with a predetermined location of the proximal shoulder  170 . Optionally, one or more markers can be included on the cover  400  at these locations to further facilitate the alignment process. Moreover, because the cover  400  is more rigid than the balloon  300 , the cover  400  can further facilitate the alignment process because the balloon can be more easily manipulated (e.g., pushed and pulled) relative to the sub-assemblies  502 ,  504  when positioning and aligning the balloon by grasping and moving the cover instead of grasping the balloon directly. 
     Once the balloon  300  is aligned relative to the predetermined locations on the distal and proximal shoulders (or other locations on the sub-assemblies  502 ,  504 ), the assembler optionally can open the cover  400  prior to affixing the distal and proximal legs  308 ,  310  to the distal and proximal shoulders  160 ,  170 , such as by welding or applying an adhesive to these components. After securing the balloon in place, the cover  400  can be re-closed and left in place for the remainder of the assembly process and/or for shipping and storage. 
     If the cover is removed from the balloon prior to assembly, the cover  400  can be placed back on the balloon  300  for shipping and storage. Alternatively, another cover can be placed around the balloon if the initial cover  400  is not re-useable. The assembly of the delivery device and the cover can be further placed in a sterile package for shipping and storage, as known in the art. It should be understood that the features and use of the cover  400  described above can apply to covers  200 ,  600 ,  700 ,  800  and  900 . 
     An off-device formed balloon, such as balloon  300  described above, has a number of advantages. For example, a finished off-device balloon can be inspected to verify that it matches dimensional specifications prior to being assembled onto the delivery device. Importantly, off-device balloons can be produced in large numbers and their performance can be tested on dummy devices prior to being released to stock and used to manufacture finished delivery devices. This will not only reduce the variability in balloon performance due to manufacturing parameter shifts, but also allow volume production of the off-device formed balloons in one facility and then transport of the balloons to another facility for mounting of the balloons to delivery devices. The latter can automate the delivery device assembly process and improve the production capacity due to the elimination of time-consuming balloon forming steps on the catheter manufacturing line. Further, the manufacturing line for assembling the delivery device requires less physical space and fewer production operators. 
     Thus, in certain embodiments, a manufacturer can produce any number of fully formed and folded balloons (e.g., balloons  300 ), and optionally place the balloons in covers (e.g., covers  200 ,  400 ,  600 ,  700 ,  800 , and  900 ). The preformed and pre-folded balloons can then be placed into stock for assembling delivery devices in another manufacturing area at the assembly site or shipped to another facility for assembling the delivery devices if the preformed and pre-folded balloons are produced at a different site from where the delivery devices are assembled. 
     In certain embodiments, a prosthetic valve (e.g., valve  10  or  50 ) intended for use with a certain delivery device can be stored in a container or jar containing a hydrating fluid. At the point of use, the user can remove the prosthetic valve from its container, remove the delivery device from its packaging, place the prosthetic valve around the balloon (e.g., balloon  108  or  300 ) and crimp the prosthetic valve onto the balloon between the distal and proximal shoulders (e.g., shoulders  160 ,  170 ). In some embodiments, the prosthetic valve can be crimped on the delivery device at a location offset from the valve-mounting portion of the balloon, such as at a location on the proximal portion of the balloon, or on a portion of a shaft proximal to the balloon, such as disclosed in U.S. Publication No. 2013/0030519, which is incorporated herein by reference. Once inserted into the body and prior to deployment, the prosthetic valve can be moved (e.g., pushed) from its crimped location to the valve-mounting portion of the balloon. 
     In alternative embodiments, a prosthetic valve can have dry or substantially dry leaflets that can be stored without a hydrating fluid, such as disclosed in U.S. Pat. Nos. 8,007,992 and 8,357,387, which are incorporated herein by reference. In such cases, the prosthetic valve can be crimped onto the balloon of a delivery device (or at a location offset from the balloon) by the manufacturer and the assembly comprising the delivery device and the crimped prosthetic valve can be placed in sterile package for shipping and storage until use by a health care provider. For example, in some cases, a prosthetic valve can be crimped onto a balloon at the same site where the delivery device is assembled, or alternatively, the fully assembled delivery device can be shipped to another facility where the prosthetic valve is crimped onto the delivery device and packaged for delivery to an end user. 
     Any of the delivery devices disclosed herein can be used to implant a prosthetic valve (e.g., valve  10  or  50 ) to a native valve (the aortic, mitral, tricuspid, or pulmonary valve) using any of various delivery techniques. For example, when implanting the prosthetic valve within the native aortic valve, the delivery apparatus and the prosthetic valve can be inserted into and through a femoral artery, and through the aorta to the native aortic valve (known as transfemoral delivery). Once the prosthetic valve is positioned at the desired implantation site, the balloon can be inflated to radially expand the prosthetic valve into engagement with surrounding tissue of the native valve. In another delivery approach, the delivery apparatus and the prosthetic valve can be inserted through a surgical opening in the apex of the heart and advanced to position the prosthetic valve within the native aortic valve (known as transapical delivery). 
     General Considerations 
     It should be understood that the disclosed embodiments can be adapted to deliver and implant prosthetic devices in any of the native annuluses of the heart (e.g., the pulmonary, mitral, and tricuspid annuluses), and can be used with any of various delivery approaches (e.g., retrograde, antegrade, trans septal, transventricular, transatrial, etc.). 
     For purposes of this description, certain aspects, advantages, and novel features of the embodiments of this disclosure are described herein. The disclosed methods, apparatus, and systems should not be construed as being limiting in any way. Instead, the present disclosure is directed toward all novel and nonobvious features and aspects of the various disclosed embodiments, alone and in various combinations and sub-combinations with one another. The methods, apparatus, and systems are not limited to any specific aspect or feature or combination thereof, nor do the disclosed embodiments require that any one or more specific advantages be present or problems be solved. The technologies from any example can be combined with the technologies described in any one or more of the other examples. In view of the many possible embodiments to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated embodiments are only preferred examples and should not be taken as limiting the scope of the disclosed technology. 
     Although the operations of some of the disclosed embodiments are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed methods can be used in conjunction with other methods. Additionally, the description sometimes uses terms like “provide” or “achieve” to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms may vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art. 
     As used herein, with reference to the prosthetic valve, delivery apparatus and other components of the delivery assembly, “proximal” refers to a position, direction, or portion of a device that is closer to the handle of the delivery assembly that is outside the patient, while “distal” refers to a position, direction, or portion of a device that is further away from the handle. The terms “longitudinal” and “axial” refer to an axis extending in the proximal and distal directions, unless otherwise expressly defined. 
     As used in this application and in the claims, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means “comprises.” Further, the terms “coupled” and “connected” generally mean electrically, electromagnetically, and/or physically (e.g., mechanically or chemically) coupled or linked and does not exclude the presence of intermediate elements between the coupled or associated items absent specific contrary language. 
     Directions and other relative references (e.g., inner, outer, upper, lower, etc.) may be used to facilitate discussion of the drawings and principles herein, but are not intended to be limiting. For example, certain terms may be used such as “inside,” “outside,”, “top,” “down,” “interior,” “exterior,” and the like. Such terms are used, where applicable, to provide some clarity of description when dealing with relative relationships, particularly with respect to the illustrated embodiments. Such terms are not, however, intended to imply absolute relationships, positions, and/or orientations. For example, with respect to an object, an “upper” part can become a “lower” part simply by turning the object over. Nevertheless, it is still the same part and the object remains the same. As used herein, “and/or” means “and” or “or”, as well as “and” and “or”. 
     Additional Description of Embodiments of Interest 
     Clause 1. A balloon assembly, comprising: 
     an inflatable balloon having an inflated state and a deflated state, wherein the inflatable balloon in the deflated state comprises: 
     a valve retaining portion having a generally cylindrical shape and one or more axial folds; 
     a distal tapered portion connected to a distal end of the valve retaining portion, a proximal end of the distal tapered portion having a larger diameter than a distal end of the distal tapered portion and the valve retaining portion; 
     a proximal tapered portion connected to a proximal end of the valve retaining portion, a distal end of the proximal tapered portion having a larger diameter than a proximal end of the proximal tapered portion and the valve retaining portion; 
     a distal leg connected to the distal end of the distal tapered portion; and 
     a proximal leg connected to the proximal end of the proximal tapered portion; 
     wherein the distal tapered portion comprises one or more axial folds, the proximal tapered portion comprises one or more axial folds, and wherein the proximal end of the distal tapered portion comprises a first radial fold connected to a second radial fold, the first and second radial folds forming a pocket extending distally at the proximal end of the distal tapered portion. 
     Clause 2. The balloon assembly of clause 1, further comprising a restraining member extending around an outer surface of the valve retaining portion so as to prevent the one or more axial folds of the valve retaining portion from unfolding. 
     Clause 3. The balloon assembly of any of clauses 1-2, further comprising a cover that encloses the inflatable balloon, wherein the cover comprises a proximal end portion, a distal end portion, and an intermediate portion between the proximal end portion and the distal end portion, wherein the proximal end portion defines a proximal recess that is shaped to substantially match a shape of the proximal tapered portion of the inflatable balloon, the distal end portion defines a distal recess that is shaped to substantially match a shape of the distal tapered portion of the inflatable balloon, and the intermediate portion defines an intermediate recess that is shaped to substantially match a shape of the valve retaining portion of the inflatable balloon. 
     Clause 4. The balloon assembly of clause 3, wherein the cover comprises a first cover piece and a second cover piece that are complimentarily structured such that they can be matingly assembled together for enclosing the inflatable balloon in the deflated state. 
     Clause 5. The balloon assembly of clause 4, further comprising an outer sleeve extending over the cover so as to prevent the first and second cover pieces from separating from each other. 
     Clause 6. The balloon assembly of any of clauses 1-5, wherein the inflatable balloon comprises an internal lumen extending through the tapered proximal portion, the valve retaining portion, and the tapered distal portion. 
     Clause 7. The balloon assembly of any of clauses 1-6, wherein the proximal tapered portion of the inflatable balloon comprises a proximal end portion, wherein the one or more axial folds of the proximal tapered portion do not extend into the proximal end portion of the proximal tapered portion. 
     Clause 8. The balloon assembly of any of clauses 1-7, wherein the distal tapered portion of the inflatable balloon comprises a distal end portion, wherein the one or more axial folds of the distal tapered portion do not extend into the distal end portion of the distal tapered portion. 
     Clause 9. The balloon assembly of any of clauses 1-8, wherein the distal end of the proximal tapered portion comprises a radial fold that forms an obtuse or right angle relative to the valve retaining portion. 
     Clause 10. The balloon assembly of any of clauses 1-9, wherein the first radial fold at the proximal end of the distal tapered portion forms an obtuse or right angle relative to the valve retaining portion, and the second radial fold forms an acute angle relative to the valve retaining portion. 
     Clause 11. A balloon assembly, comprising: 
     an inflatable balloon having an inflated state and a deflated state, wherein the inflatable balloon in the deflated state comprises: 
     a valve retaining portion having a generally cylindrical shape and one or more axial folds; 
     a distal tapered portion connected to a distal end of the valve retaining portion, a proximal end of the distal tapered portion having a larger diameter than a distal end of the distal tapered portion and the valve retaining portion; 
     a proximal tapered portion connected to a proximal end of the valve retaining portion, a distal end of the proximal tapered portion having a larger diameter than a proximal end of the proximal tapered portion and the valve retaining portion; 
     one or more axially extending folds along at least sections of the distal tapered portion and the proximal tapered portion; 
     a distal leg connected to the distal end of the distal tapered portion; and 
     a proximal leg connected to the proximal end of the proximal tapered portion; 
     wherein the inflatable balloon is in an unassembled state apart from a delivery catheter. 
     Clause 12. The balloon assembly of clause 11, further comprising a restraining member extending around an outer surface of the valve retaining portion so as to prevent the one or more axial folds of the valve retaining portion from unfolding. 
     Clause 13. The balloon assembly of any of clauses 11-12, further comprising a cover that encloses the inflatable balloon, wherein the cover comprises a proximal end portion, a distal end portion, and an intermediate portion between the proximal end portion and the distal end portion, wherein the proximal end portion defines a proximal recess that is shaped to substantially match a shape of the proximal tapered portion of the inflatable balloon, and the distal end portion defines a distal recess that is shaped to substantially match a shape of the distal tapered portion of the inflatable balloon. 
     Clause 14. The balloon assembly of clause 13, wherein the cover comprises a first cover piece and a second cover piece that are complimentarily structured such that they can be matingly assembled together for enclosing the inflatable balloon. 
     Clause 15. The balloon assembly of clause 14, further comprising an outer sleeve extending over the cover so as to prevent the first and second cover pieces from separating from each other. 
     Clause 16. The balloon assembly of any of clauses 11-15, wherein the inflatable balloon comprises an internal lumen extending through the tapered proximal portion, the valve retaining portion, and the tapered distal portion. 
     Clause 17. The balloon assembly of any of clauses 11-16, wherein the one or more axially extending folds do not extend into a proximal end portion of the proximal tapered portion. 
     Clause 18. The balloon assembly of any of clauses 11-17, wherein the one or more axially extending folds do not extend into a distal end portion of the distal tapered portion. 
     Clause 19. The balloon assembly of any of clauses 11-18, wherein the proximal end of the distal tapered portion comprises a first radial fold connected to a second radial fold, the first and second radial folds forming a pocket extending distally at the proximal end of the distal tapered portion. 
     Clause 20. The balloon assembly of clause 19, wherein the first radial fold at the proximal end of the distal tapered portion forms an obtuse or right angle relative to the valve retaining portion, and the second radial fold forms an acute angle relative to the valve retaining portion. 
     Clause 21. A method for assembling a delivery device, the method comprising: 
     forming an inflatable balloon in a deflated state, the balloon in the deflated state having a valve retaining portion, a distal tapered portion connected to a distal end of the valve retaining portion, a proximal tapered portion connected to a proximal end of the valve retaining portion, a distal leg connected to a distal end of the distal tapered portion, and a proximal leg connected to a proximal end of the proximal tapered portion; 
     inserting a distal shoulder mounted on a first shaft of the delivery device through the distal leg and into the distal tapered portion of the inflatable balloon; 
     inserting a proximal shoulder mounted on a second shaft of the delivery device through the proximal leg and into the proximal tapered portion of the inflatable balloon; 
     securing the distal leg of the inflatable balloon to the distal shoulder; and 
     securing the proximal leg of the inflatable balloon to the second shaft and/or the proximal shoulder. 
     Clause 22. The method of clause 21, further comprising placing a restraining member around the valve retaining portion. 
     Clause 23. The method of any of clauses 21-22, further comprising enclosing the inflatable balloon with a cover, wherein the cover comprises a first cover piece and a second cover piece that are complimentarily structured such that they can be matingly assembled together for enclosing the inflatable balloon, and wherein the cover defines an internal recess whose geometry substantially matches a shape of the inflatable balloon in the deflated state. 
     Clause 24. The method of clause 23, further comprising placing a sleeve over the cover to prevent the first and second cover pieces from separating from each other. 
     Clause 25. The method of any of clauses 21-24, wherein a proximal end of the distal shoulder has a larger diameter than a diameter of the distal leg, and inserting the distal shoulder through the distal leg comprises radially compressing the proximal end of the distal shoulder. 
     Clause 26. The method of any of clauses 21-25, wherein a distal end of the proximal shoulder has a larger diameter than a diameter of the proximal leg, and inserting the proximal shoulder through the proximal leg comprises radially compressing the distal end of the proximal shoulder. 
     Clause 27. The method of any of clauses 21-26, wherein forming the inflatable balloon comprises forming the valve retaining portion in a generally cylindrical shape, the diameter of which being smaller than both a diameter of a proximal end of the distal tapered portion and a diameter of a distal end of the proximal tapered portion. 
     Clause 28. The method of clause 27, wherein forming the inflatable balloon comprises forming one or more axially extending folds along at least sections of the distal tapered portion and the proximal tapered portion. 
     Clause 29. The method of clause 28, wherein forming the inflatable balloon comprises forming a distal end portion of the distal tapered portion, wherein the distal end portion is free of any of the one or more axially extending folds. 
     Clause 30. The method of any of clauses 28-29, wherein forming the inflatable balloon comprises forming a proximal end portion of the proximal tapered portion, wherein the proximal end portion is free of any of the one or more axially extending folds. 
     Clause 31. The method of any of clauses 27-30, wherein forming the inflatable balloon comprises forming a radial fold at the distal end of the proximal tapered portion, the radial fold forming an obtuse or right angle relative to the valve retaining portion. 
     Clause 32. The method of any of clauses 27-31, wherein forming the inflatable balloon comprises forming a radial fold at the proximal end of the distal tapered portion, the radial fold forming an obtuse or right angle relative to the valve retaining portion. 
     Clause 33. The method of any of clauses 27-31, wherein forming the inflatable balloon comprises forming a first radial fold connected to a second radial fold at the proximal end of the distal tapered portion, the first and second radial folds forming a pocket extending distally at the proximal end of the distal tapered portion. 
     Clause 34. The method of any of clauses 28-33, wherein the distal shoulder comprises one or more distal shoulder fins extending at least partially radially outwardly, and inserting the distal shoulder assembly into the distal tapered portion comprises snuggly placing the one or more distal shoulder fins adjacent to at least some of the one or more axially extending folds in the distal tapered portion. 
     Clause 35. The method of any of clauses 28-34, wherein the proximal shoulder comprises one or more proximal shoulder fins extending at least partially radially outwardly, and inserting the proximal shoulder assembly into the proximal tapered portion comprises snuggly placing the one or more proximal shoulder fins adjacent to at least some of the one or more axially extending folds in the proximal tapered portion. 
     Clause 36. The method of any of clauses 21-35, wherein inserting the distal shoulder into the distal tapered portion comprises aligning a marker located on the first shaft with a predefined position on the valve retaining portion of the inflatable balloon or the proximal shoulder. 
     Clause 37. A method for assembling a delivery device, the method comprising: 
     forming an inflatable balloon in a deflated state, the balloon in the deflated state having a distal portion, a proximal portion, and a valve retaining portion between the distal portion and the proximal portion; 
     forming a plurality of axially extending folds along at least sections of the distal and proximal portions of the inflatable balloon; and 
     after forming the inflatable balloon and forming the plurality of axially extending folds, mounting the inflatable balloon in the deflated state on a delivery device. 
     Clause 38. The method of clause 37, wherein mounting the inflatable balloon on the delivery device comprises inserting a distal shoulder mounted on a first shaft of the delivery device through a distal leg of the balloon and inserting a proximal shoulder mounted on a second shaft of the delivery device through a proximal leg of the balloon, wherein the distal leg is connected to a distal end of a tapered portion of the distal portion of the inflatable balloon, and the proximal leg is connected to a proximal end of a tapered portion of the proximal portion of the inflatable balloon. 
     Clause 39. The method of clause 38, wherein a proximal end of the distal shoulder has a larger diameter than a diameter of the distal leg, and inserting the distal shoulder through the distal leg comprises radially compressing the proximal end of the distal shoulder. 
     Clause 40. The method of any of clauses 38-39, wherein a distal end of the proximal shoulder has a larger diameter than a diameter of the proximal leg, and inserting the proximal shoulder through the proximal leg comprises radially compressing the distal end of the proximal shoulder. 
     Clause 41. The method of any of clauses 38-39, wherein mounting the inflatable balloon on the delivery device comprises inserting the distal shoulder into the tapered portion of the distal portion of the inflatable balloon, and inserting the proximal shoulder into the tapered portion of the proximal portion of the inflatable balloon. 
     Clause 42. The method of clause 41, wherein the distal shoulder comprises one or more distal shoulder fins extending at least partially radially outwardly, and inserting the distal shoulder into the tapered portion of the distal portion comprises snuggly placing the one or more distal shoulder fins adjacent to at least some of the plurality of axially extending folds in the tapered portion of the distal portion. 
     Clause 43. The method of any of clauses 41-42, wherein the proximal shoulder comprises one or more proximal shoulder fins extending at least partially radially outwardly, and inserting the proximal shoulder into the tapered portion of the proximal portion comprises snuggly placing the one or more proximal shoulder fins adjacent to at least some of the plurality of axially extending folds in the tapered portion of the proximal portion. 
     Clause 44. The method of any of clauses 41-43, wherein inserting the distal shoulder into the tapered portion of the distal portion comprises aligning a marker on the first shaft with a predefined position on the valve retaining portion of the inflatable balloon or the proximal shoulder. 
     Clause 45. The method of any of the claims  37 - 44 , wherein forming the inflatable balloon comprises forming a distal end portion of the distal portion, wherein the distal end portion is free of any of the plurality of axially extending folds. 
     Clause 46. The method of any of the claims  37 - 45 , wherein forming the inflatable balloon comprises forming a proximal end portion of the proximal portion, wherein the proximal end portion is free of any of the plurality of axially extending folds. 
     Clause 47. The method of any of clauses 37-46, wherein forming the inflatable balloon comprises forming the valve retaining portion in a generally cylindrical shape, the diameter of which being smaller than both a diameter of a proximal end of the distal portion and a diameter of a distal end of the proximal portion. 
     Clause 48. The method of clause 47, wherein forming the inflatable balloon comprises forming a radial fold at the distal end of the proximal portion, the radial fold forming an obtuse or right angle relative to the valve retaining portion. 
     Clause 49. The method of any of clauses 47-48, wherein forming the inflatable balloon comprises forming a radial fold at the proximal end of the distal portion, the radial fold forming an obtuse or right angle relative to the valve retaining portion. 
     Clause 50. The method of any of clauses 47-48, wherein forming the inflatable balloon comprises forming a first radial fold connected to a second radial fold at the proximal end of the distal portion, the first and second radial folds forming a pocket extending distally at the proximal end of the distal portion. 
     Clause 51. The method of any of the claims  38 - 50 , wherein mounting the inflatable balloon on the delivery device comprises securing the distal leg to the distal shoulder, and securing the proximal leg to the second shaft and/or the proximal shoulder. 
     Clause 52. The method of any of clauses 37-51, further comprising placing a restraining member around the valve retaining portion. 
     Clause 53. The method of any of clauses 37-52, further comprising enclosing the inflatable balloon with a cover, wherein the cover comprises a first cover piece and a second cover piece that are complimentarily structured such that they can be matingly assembled together for enclosing the inflatable balloon, and wherein the cover defines an internal recess whose geometry substantially matches a shape of the inflatable balloon in the deflated state. 
     Clause 54. The method of clause 53, further comprising placing a sleeve around the cover to prevent the first and second cover pieces from separating from each other. 
     Clause 55. A prosthetic valve delivery assembly, comprising: 
     a delivery device comprising: 
     a shaft; and 
     an inflatable balloon mounted on the shaft in a deflated state; 
     wherein the balloon in the deflated state comprises a valve retaining portion having a generally cylindrical shape, a distal tapered portion connected to a distal end of the valve retaining portion, a proximal tapered portion connected to a proximal end of the valve retaining portion; and wherein the proximal end of the distal tapered portion comprises a first radial fold connected to a second radial fold, the first and second radial folds forming a pocket extending distally at the proximal end of the distal tapered portion. 
     Clause 56. The prosthetic valve delivery assembly of clause 55, further comprising a restraining member extending around an outer surface of the valve retaining portion. 
     Clause 57. The prosthetic valve delivery assembly of any of clauses 55-56, further comprising a cover, wherein the cover comprises a first cover piece and a second cover piece that are complimentarily structured such that they can be matingly assembled together for enclosing the inflatable balloon, and wherein the cover defines an internal recess whose geometry substantially matches a shape of the inflatable balloon in the deflated state. 
     Clause 58. The prosthetic valve delivery assembly of clause 57, further comprising an outer sleeve extending over the cover so as to prevent the first and second cover pieces from separating from each other. 
     Clause 59. The prosthetic valve delivery assembly of any of clauses 55-58, wherein the balloon in the deflated state comprises one or more axially extending folds along at least sections of the distal tapered portion and the proximal tapered portion. 
     Clause 60. The prosthetic valve delivery assembly of clause 59, wherein the distal tapered portion comprises a distal end portion that is free of any of the one or more axially extending folds. 
     Clause 61. The prosthetic valve delivery assembly of any of clauses 55-60, wherein the balloon further comprises a distal leg connected to a distal end of the distal tapered portion and a proximal leg connected to a proximal end of the proximal tapered portion. 
     Clause 62. The prosthetic valve delivery assembly of clause 61, wherein the delivery device comprises a distal shoulder mounted on the first shaft extending through the distal leg and into the distal tapered portion of the inflatable balloon, and a proximal shoulder mounted on a second shaft of the delivery device extending through the proximal leg and into the proximal tapered portion of the inflatable balloon. 
     Clause 63. The prosthetic valve delivery assembly of clause 62, wherein the distal leg is secured to the distal shoulder and the proximal leg is secured to the second shaft or the proximal shoulder. 
     Clause 64. The prosthetic valve delivery assembly of any of clauses 62-63, wherein a proximal end of the distal shoulder has a larger diameter than a diameter of the distal leg, and a distal end of the proximal shoulder has a larger diameter than a diameter of the proximal leg. 
     Clause 65. The prosthetic valve delivery assembly of any of clauses 62-64, wherein the distal shoulder comprises one or more distal shoulder fins which extend at least partially radially outwardly and are adjacent to at least some of the one or more axially extending folds in the distal tapered portion, and wherein the proximal shoulder comprises one or more proximal shoulder fins extending at least partially radially outwardly and are adjacent to at least some of the one or more axially extending folds in the proximal tapered portion. 
     Clause 66. The prosthetic valve delivery assembly of any of clauses 62-65, wherein the first shaft comprises a marker that aligns with a predefined position on the valve retaining portion of the inflatable balloon. 
     Clause 67. The prosthetic valve delivery assembly of any of clauses 62-66, wherein the first shaft extends through the valve retaining portion, and the first shaft is separated from the valve retaining portion by an axially extending gap. 
     Clause 68. The prosthetic valve delivery assembly of any of clauses 55-67, wherein the distal end of the proximal tapered portion comprises a radial fold that forms an obtuse or right angle relative to the valve retaining portion. 
     Clause 69. The prosthetic valve delivery assembly of any of clauses 55-68, wherein the first radial fold at the proximal end of the distal tapered portion forms an obtuse or right angle relative to the valve retaining portion, and the second radial fold forms an acute angle relative to the valve retaining portion. 
     Clause 70. A method for assembling a delivery device, the method comprising: 
     forming an inflatable balloon in a deflated state, the balloon in the deflated state having a distal portion, a proximal portion, and a valve retaining portion between the distal portion and the proximal portion; 
     placing the balloon inside of a cover; 
     inserting a shaft of a delivery device through an opening of the cover and into the balloon while the balloon is inside the cover; and 
     securing the balloon to a surface of the delivery device. 
     Clause 71. The method of clause 70, wherein forming the balloon further comprises forming a plurality of axially extending folds along at least sections of the distal and proximal portions of the inflatable balloon. 
     Clause 72. The method of clause 70, wherein the cover is more rigid than the balloon. 
     Clause 73. The method of clause 70, the method further comprises aligning a location of the cover with a location on the delivery device prior to securing the balloon to a surface of the delivery device. 
     Clause 74. The method of clause 70, wherein the act of inserting comprises inserting a first shaft of the delivery through a first opening of the cover and through the balloon in a first direction and inserting a second shaft of the delivery device through a second opening of the cover and through the balloon in a second direction, opposite the first direction. 
     Clause 75. A balloon cover for a balloon catheter, comprising: 
     an outer shell; and 
     an inner sleeve disposed within the outer shell, wherein the inner sleeve has an inner surface defining a lumen that is configured to receive at least a portion of a balloon of the balloon catheter; 
     wherein the inner sleeve is deformable under pressure exerted against the inner surface by the balloon upon inflation of the balloon, thereby radially expanding the lumen from a first diameter to a second diameter, wherein the second diameter is larger than the first diameter. 
     Clause 76. The balloon cover of clause 75, wherein the inner sleeve has a fixed axial length when the lumen expands from the first diameter to the second diameter. 
     Clause 77. The balloon cover of any of clauses 75-76, wherein the outer shell is more rigid than the inner sleeve. 
     Clause 78. The balloon cover of any of clauses 75-77, wherein the inner sleeve is made of an elastomer. 
     Clause 79. The balloon cover of any of clauses 75-78, wherein the inner sleeve comprises first and second separable portions, each having a semi-cylindrical interior surface defining a section of the lumen, wherein the first portion has longitudinal edges that are configured to matingly engage respective longitudinal edges of the second portion to form the lumen. 
     Clause 80. The balloon cover of any of clauses 75-79, wherein the outer shell comprises a first shell member and a second shell member, the second shell member being hingely connected to the first shell member. 
     Clause 81. The balloon cover of clause 80, wherein the first shell member comprises a first coupling member, the second shell member comprises a second coupling member, wherein the first coupling member is configured to be releasably connected to the second coupling member so that the first and second coupling members can be matingly coupled to each other to form a clam shell. 
     Clause 82. The balloon cover of clause 81, wherein the first coupling member comprises a ridge extending outwardly from the first shell member, the second coupling member comprises a cantilevered tab extending outwardly from the second shell member, wherein the ridge is configured to extend through a slot on the tab to form a snap-fit lock. 
     Clause 83. The balloon cover of any of clause 75-82, wherein the inner sleeve comprises an inner wall portion that surrounds the lumen and one or more legs extending outwardly from the inner wall portion, wherein the one or more legs press against an inner surface of the outer shell so as to form one or more cavities between the inner wall portion of the inner sleeve and the inner surface of the outer shell. 
     Clause 84. The balloon cover of clause of 83, wherein the one or more legs have a first length when the lumen of the inner sleeve has the first diameter and are compressed to a second length when the lumen of the inner sleeve changes to the second diameter, the second length being shorter than the first length. 
     Clause 85. The balloon cover of any of clauses 83-84, wherein the inner surface the outer shell comprises a receptacle configured to receive at least one of the one or more legs so as to securely couple the inner sleeve to the outer shell. 
     Clause 86. The balloon cover of any of clauses 83-85, wherein the one or more legs are parallel to each other and extend circumferentially around the inner wall portion. 
     Clause 87. The balloon cover of any of clauses 75-86, wherein the inner sleeve further defines a tapered proximal opening located at a proximal end of the lumen and a tapered distal opening located at a distal end of the lumen, wherein a middle portion of the lumen has a smaller diameter than both the tapered proximal opening and the tapered distal opening before radially expanding the lumen. 
     Clause 88. The balloon cover of any of clauses 75-87, wherein the inner surface of the inner sleeve maintains enclosure of the lumen in a circumferentially continuous manner when the lumen is radially expanded to the second diameter. 
     Clause 89. The balloon cover of any of clauses 75-88, wherein the outer shell comprises a proximal recess configured to receive a proximal shoulder member of the balloon catheter, a distal recess configured to receive a distal shoulder member of the balloon catheter, and an intermediate recess between the proximal and distal recesses, wherein the inner sleeve is disposed in the intermediate recess. 
     Clause 90. A medical assembly, comprising: 
     a balloon catheter comprising an inflatable balloon; and 
     a balloon cover comprising an outer shell and an inner member disposed within the outer shell, the inner member having an inner surface defining a lumen; 
     wherein the balloon is disposed in the lumen of the inner member; 
     wherein the inner member is radially deformable when the balloon is inflated and exerts pressure radially outwardly against the inner surface of the inner member. 
     Clause 91. The assembly of clause 90, wherein the inner member maintains a fixed axial length when the lumen is radially expanded by inflating the balloon. 
     Clause 92. The assembly of any of clauses 90-91, wherein the outer shell is more rigid than the inner member. 
     Clause 93. The assembly of any of clauses 90-92, wherein the inner member is made of an elastomer. 
     Clause 94. The assembly of any of clauses 90-93, wherein the inner member comprises first and second separable portions, each having a semi-cylindrical interior surface defining a section of the lumen, wherein the first portion has longitudinal edges that are configured to matingly engage respective longitudinal edges of the second portion to form the lumen. 
     Clause 95. The assembly of any of clauses 90-94, wherein the outer shell comprises a first shell member and a second shell member, the second shell member being hingely connected to the first shell member. 
     Clause 96. The assembly of clause 95, wherein the first shell member comprises a first coupling member, the second shell member comprises a second coupling member, wherein the first coupling member is configured to be releasably connected to the second coupling member so that the first and second coupling members can be matingly coupled to each other to form a clam shell. 
     Clause 97. The assembly of clause 96, wherein the first coupling member comprises a ridge extending outwardly from the first shell member, the second coupling member comprises a cantilevered tab extending outwardly from the second shell member, wherein the ridge is configured to extend through a slot on the tab to form a snap-fit lock. 
     Clause 98. The assembly of any of clause 90-97, wherein the inner member comprises an inner wall portion that surrounds the lumen and one or more legs extending outwardly from the inner wall portion, wherein the one or more legs press against an inner surface of the outer shell so as to form one or more cavities between the inner wall portion of the inner member and the inner surface of the outer shell. 
     Clause 99. The assembly of clause of 98, wherein the one or more legs are shortened when the lumen is radially expanded by inflating the balloon. 
     Clause 100. The assembly of any of clauses 98-99, wherein the inner surface the outer shell comprises a receptacle configured to receive at least one of the one or more legs so as to securely couple the inner member to the outer shell. 
     Clause 101. The assembly of any of clauses 98-100, wherein the one or more legs are parallel to each other and extend circumferentially around the inner wall portion. 
     Clause 102. The assembly of any of clauses 90-101, wherein the inner member further defines a tapered proximal opening located at a proximal end of the lumen and a tapered distal opening located at a distal end of the lumen, wherein a middle portion of the lumen has a smaller diameter than both the tapered proximal opening and the tapered distal opening before inflating the balloon. 
     Clause 103. The assembly of any of clauses 90-102, wherein the outer shell comprises a proximal recess, a distal recess, and an intermediate recess between the proximal and distal recesses, wherein the inner member is disposed in the intermediate recess, a proximal shoulder member of the balloon catheter is disposed in the proximal recess, and a distal shoulder member of the balloon catheter is disposed in the distal recess. 
     Clause 104. The assembly of clause 103, wherein the proximal recess has a tapered shape such that a proximal end of the proximal recess has a smaller diameter than a distal end of the proximal recess, and the distal recess has a tapered shape such that a distal end of the distal recess has a smaller diameter than a proximal end of the distal recess. 
     Clause 105. The assembly of any of clauses 90-104, wherein the inner surface of the inner member maintains enclosure of the lumen in a circumferentially continuous manner when the lumen is radially expanded by inflating the balloon. 
     Clause 106. A method of inflating a balloon of a balloon catheter, comprising: 
     fluidly connecting the balloon to a fluid source, wherein the balloon is in a deflated state and is disposed inside of a balloon cover; and 
     injecting an inflation fluid from the fluid source into the balloon so as to at least partially inflate the balloon to a partially inflated state; 
     wherein the balloon cover comprises an outer shell and an inner member disposed inside the outer shell and around the balloon; 
     wherein inflating the balloon from the deflated state to the partially inflated state deforms a lumen of the inner member from an initial state to a deformed state, wherein the lumen has a first diameter in the initial state and a second diameter in the deformed state, wherein the second diameter is larger than the first diameter. 
     Clause 107. The method of clause 106 further comprising removing the inflation fluid from the balloon so as to return the balloon from the partially inflated state to the deflated state, which causes the lumen of the inner member to revert back from the deformed state to the initial state. 
     Clause 108. The method of any of clauses 106-107, wherein the inner member maintains a fixed axial length when the lumen changes between the initial state and the deformed state. 
     Clause 109. The method of any of clauses 106-108, wherein the outer shell is more rigid than the inner member. 
     Clause 110. The method of any of clauses 106-109 further comprising inserting the balloon into the lumen of the inner member. 
     Clause 111. The method of any of clauses 106-110 further comprising forming the lumen using first and second separable portions of the inner member, each portion having a semi-cylindrical interior surface, wherein forming the lumen comprises matingly engaging longitudinal edges of the first portion with respective longitudinal edges of the second portion so that their respective interior surfaces are joined together to form a circumferentially continuous inner surface. 
     Clause 112. The method of any of clauses 106-111 further comprising locking the outer shell, wherein the outer shell comprises first and second shell members that are fixedly connected to each other at a hinged portion, wherein locking the outer shell comprises coupling unhinged portions of the first and second shell members together to form a clam shell. 
     Clause 113. The method of any of clause 106-112, wherein the inner member comprises an inner wall portion that surrounds the lumen and one or more legs extending outwardly from the inner wall portion, wherein the one or more legs press against an inner surface of the outer shell so as to form one or more cavities between the inner wall portion of the inner member and the inner surface of the outer shell. 
     Clause 114. The method of any of clauses 106-113 further comprising placing a proximal shoulder member of the balloon catheter in a proximal recess of the outer shell, placing a distal shoulder member of the balloon catheter in a distal recess of the outer shell, and placing the inner member in an intermediate recess between the proximal and distal recesses. 
     Clause 115. A balloon cover for a balloon catheter, comprising: 
     an outer shell; and 
     an inner sleeve disposed within the outer shell, wherein the inner sleeve has an inner surface defining a lumen that is configured to receive at least a portion of a balloon of the balloon catheter; 
     wherein the inner sleeve comprises first and second separable portions, each having an interior surface defining a section of the lumen, wherein the first portion has longitudinal edges that are configured to matingly engage respective longitudinal edges of the second portion to form the lumen; 
     wherein the lumen has a first diameter when the balloon is deflated and a second diameter when the balloon is inflated, the second diameter being larger than the first diameter. 
     Clause 116. The balloon cover of clause 115, wherein the inner sleeve has a fixed axial length when the lumen expands from the first diameter to the second diameter. 
     Clause 117. The balloon cover of any of clauses 115-116, wherein the outer shell is more rigid than the inner sleeve. 
     Clause 118. The balloon cover of any of clauses 115-117, wherein the inner sleeve is made of an elastomer. 
     Clause 119. The balloon cover of any of clauses 115-118, wherein the outer shell comprises a first shell member and a second shell member, the second shell member being hingely connected to the first shell member. 
     Clause 120. The balloon cover of clause 119, wherein the first shell member comprises a first coupling member, the second shell member comprises a second coupling member, wherein the first coupling member is configured to be releasably connected to the second coupling member so that the first and second coupling members can be matingly coupled to each other to form a clam shell. 
     Clause 121. The balloon cover of any of clause 115-120, wherein the inner sleeve comprises an inner wall portion that surrounds the lumen and one or more legs extending outwardly from the inner wall portion, wherein the one or more legs press against an inner surface of the outer shell so as to form one or more cavities between the inner wall portion of the inner sleeve and the inner surface of the outer shell. 
     Clause 122. The balloon cover of clause of 121, wherein the one or more legs have a first length when the lumen of the inner sleeve has the first diameter and are compressed to a second length when the lumen of the inner sleeve changes to the second diameter, the second length being shorter than the first length. 
     Clause 123. The balloon cover of any of clauses 121-122, wherein the inner surface the outer shell comprises a receptacle configured to receive at least one of the one or more legs so as to securely couple the inner sleeve to the outer shell. 
     Clause 124. The balloon cover of any of clauses 122-123, wherein the one or more legs are parallel to each other and extend circumferentially around the inner wall portion. 
     Clause 125. A balloon cover for a balloon catheter, comprising: 
     an outer shell; and 
     an inner sleeve disposed within the outer shell, wherein the inner sleeve has an inner surface defining a lumen that is configured to receive at least a portion of a balloon of the balloon catheter; 
     wherein the lumen has a first diameter when the balloon is deflated and a second diameter when the balloon is inflated, the second diameter being larger than the first diameter; 
     wherein the inner sleeve has a fixed axial length when the lumen expands from the first diameter to the second diameter. 
     Clause 126. The balloon cover of clause 125, wherein the outer shell is more rigid than the inner sleeve. 
     Clause 127. The balloon cover of any of clauses 125-126, wherein the inner sleeve is made of an elastomer. 
     Clause 128. The balloon cover of any of clauses 125-127, wherein the inner sleeve comprises first and second separable portions, each having a semi-cylindrical interior surface defining a section of the lumen, wherein the first portion has longitudinal edges that are configured to matingly engage respective longitudinal edges of the second portion to form the lumen. 
     Clause 129. The balloon cover of any of clauses 125-128, wherein the outer shell comprises a first shell member and a second shell member, the second shell member being hingely connected to the first shell member. 
     Clause 130. The balloon cover of clause 129, wherein the first shell member comprises a first coupling member, the second shell member comprises a second coupling member, wherein the first coupling member is configured to be releasably connected to the second coupling member so that the first and second coupling members can be matingly coupled to each other to form a clam shell. 
     Clause 131. The balloon cover of any of clause 125-130, wherein the inner sleeve comprises an inner wall portion that surrounds the lumen and one or more legs extending outwardly from the inner wall portion, wherein the one or more legs press against an inner surface of the outer shell so as to form one or more cavities between the inner wall portion of the inner sleeve and the inner surface of the outer shell. 
     Clause 132. The balloon cover of clause of 131, wherein the one or more legs have a first length when the lumen of the inner sleeve has the first diameter and are compressed to a second length when the lumen of the inner sleeve changes to the second diameter, the second length being shorter than the first length. 
     Clause 133. The balloon cover of any of clauses 130-131, wherein the inner surface the outer shell comprises a receptacle configured to receive at least one of the one or more legs so as to securely couple the inner sleeve to the outer shell. 
     Clause 134. The balloon cover of any of clauses 125-133, wherein the inner sleeve further defines a tapered proximal opening located at a proximal end of the lumen and a tapered distal opening located at a distal end of the lumen, wherein a middle portion of the lumen has a smaller diameter than both the tapered proximal opening and the tapered distal opening before inflating the balloon. 
     Clause 135. A medical assembly, comprising: 
     a balloon catheter comprising an inflatable balloon; and 
     a balloon cover comprising an outer shell and an inner member disposed within the outer shell, the inner member having an inner surface defining a lumen; 
     wherein the balloon is disposed in the lumen of the inner member; 
     wherein the lumen is configured to expand to a second diameter when the balloon is inflated and contract to a first diameter when the balloon is deflated, the second diameter being larger than the first diameter. 
     Clause 136. The assembly of clause 135, wherein the inner member maintains a fixed axial length when the lumen expands from the first diameter to the second diameter or contracts from the second diameter to the first diameter. 
     Clause 137. The assembly of any of clauses 135-136, wherein the outer shell is more rigid than the inner member. 
     Clause 138. The assembly of any of clauses 135-137, wherein the inner member comprises first and second separable portions, each having a semi-cylindrical interior surface defining a section of the lumen, wherein the first portion has longitudinal edges that are configured to matingly engage respective longitudinal edges of the second portion to form the lumen. 
     Clause 139. The assembly of any of clauses 135-138, wherein the outer shell comprises a first shell member and a second shell member, the second shell member being hingely connected to the first shell member. 
     Clause 140. The assembly of clause 139, wherein the first shell member comprises a first coupling member, the second shell member comprises a second coupling member, wherein the first coupling member is configured to be releasably connected to the second coupling member so that the first and second coupling members can be matingly coupled to each other to form a clam shell. 
     Clause 141. The assembly of any of clause 135-140, wherein the inner member comprises an inner wall portion that surrounds the lumen and one or more legs extending outwardly from the inner wall portion, wherein the one or more legs press against an inner surface of the outer shell so as to form one or more cavities between the inner wall portion of the inner member and the inner surface of the outer shell. 
     Clause 142. The assembly of clause of 141, wherein the one or more legs are shortened from a first length to a second length when the lumen expands from the first diameter to the second diameter and returns from the second length to the first length when the lumen contracts from the second diameter to the first diameter, the first length being larger than the second length. 
     Clause 143. The assembly of any of clauses 141-142, wherein the inner surface the outer shell comprises a receptacle configured to receive at least one of the one or more legs so as to securely couple the inner member to the outer shell. 
     Clause 144. The assembly of any of clauses 135-143, wherein the outer shell comprises a proximal recess, a distal recess, and an intermediate recess between the proximal and distal recesses, wherein the inner member is disposed in the intermediate recess, a proximal shoulder member of the balloon catheter is disposed in the proximal recess, and a distal shoulder member of the balloon catheter is disposed in the distal recess. 
     Clause 145. A method of inflating a balloon of a balloon catheter, comprising: 
     receiving the balloon disposed inside of a balloon cover, wherein the balloon is in a deflated state; and 
     injecting an inflation fluid from a fluid source into the balloon so as to at least partially inflate the balloon to a partially inflated state; 
     wherein the balloon cover comprises an outer shell and an inner member disposed inside the outer shell and around the balloon; 
     wherein inflating the balloon from the deflated state to the partially inflated state deforms a lumen of the inner member from an initial state to a deformed state, wherein the lumen has a first diameter in the initial state and a second diameter in the deformed state, wherein the second diameter is larger than the first diameter. 
     Clause 146. The method of clause 145 further comprising removing the inflation fluid from the balloon so as to return the balloon from the partially inflated state to the deflated state, which causes the lumen of the inner member to revert back from the deformed state to the initial state 
     Clause 147. The method of any of clauses 145-146, wherein the inner member maintains a fixed axial length when the lumen changes between the initial state and the deformed state. 
     Clause 148. The method of any of clauses 145-147, wherein the outer shell is non-deformable when inflating the balloon from the deflated state to the partially inflated state. 
     Clause 149. The method of any of clauses 145-148 further comprising connecting the balloon to the fluid source. 
     Clause 150. The method of any of clauses 145-149 further comprising forming the lumen using first and second separable portions of the inner member, each portion having an interior surface, wherein forming the lumen comprises matingly engaging longitudinal edges of the first portion with respective longitudinal edges of the second portion so that their respective interior surfaces are joined together to form a circumferentially continuous inner surface. 
     Clause 151. The method of any of clauses 145-150 further comprising locking the outer shell, wherein the outer shell comprises first and second shell members that are fixedly connected to each other at a hinged portion, wherein locking the outer shell comprises coupling unhinged portions of the first and second shell members together to form a clam shell. 
     Clause 152. The method of any of clause 145-151, wherein the inner member comprises an inner wall portion that surrounds the lumen and one or more legs extending outwardly from the inner wall portion, wherein the one or more legs press against an inner surface of the outer shell so as to form one or more cavities between the inner wall portion of the inner member and the inner surface of the outer shell. 
     Clause 153. The method of any of clauses 145-152 further comprising placing a proximal shoulder member of the balloon catheter in a proximal recess of the outer shell, placing a distal shoulder member of the balloon catheter in a distal recess of the outer shell, and placing the inner member in an intermediate recess between the proximal and distal recesses. 
     Clause 154. The method of any of clauses 145-153 further comprising cyclically inflating the balloon from the deflated state to the partially inflated state followed by deflating the balloon from the partially inflated state to the deflated state in a plurality of cycles. 
     Clause 155. The balloon cover of any of clauses 75-78, wherein the inner sleeve comprises first and second separable sleeve portions, each of which comprises a wall portion and one or more rib portions extending radially inwardly from the wall portion, wherein each wall portion comprises a plurality of wall segments separated by the one or more rib portions, each wall segment comprising two longitudinal edges and a wall surface extending between the two longitudinal edges, and wherein each rib portion comprises two radial edges and a rib surface extending between the two radial edges. 
     Clause 156. The balloon cover of clause 155, wherein the two radial edges of each rib portion of the first sleeve portion are configured to matingly engage two radial edges of a corresponding rib portion of the second sleeve portion so that the rib surfaces of the first sleeve portion adjoin corresponding rib surfaces of the second sleeve portion to form one or more rib enclosures that define the lumen, and wherein the two longitudinal edges of each wall segment of the first sleeve portion are configured to matingly engage two longitudinal edges of a corresponding wall segment of the second sleeve portion so that the wall surfaces of the first sleeve portion adjoin corresponding wall surfaces of the second sleeve portion to form a plurality of wall enclosures separated by the one or more rib portions. 
     Clause 157. The balloon cover of clause 156, wherein the plurality of wall enclosures define a third diameter when the lumen is in the first diameter, wherein the third diameter is larger than the first diameter. 
     Clause 158. The balloon cover of clause 157, wherein the plurality of wall enclosures define a fourth diameter when the lumen is in the second diameter, wherein the fourth diameter is larger than the second diameter. 
     Clause 159. The balloon cover of any of clauses 155-158, wherein any two adjacent rib portions of the first or second sleeve portion are configured to have a circumferential offset such that the two radial edges of one of the two adjacent rib portions extend angularly relative to respective two radial edges of the other adjacent rib portion. 
     Clause 160. A balloon cover for a balloon catheter, comprising: 
     a first shell member and a second shell member, wherein the first and second shell members are configured to matingly engage with each other to define a lumen that is configured to receive a distal portion of the balloon catheter; 
     wherein the first shell member comprises a plurality of first wedges juxtaposed with a plurality of first cavities and the second shell member comprises a plurality of second wedges juxtaposed with a plurality of second cavities; 
     wherein the first wedges are offset with the second wedges such that when the first and second shell members are matingly engaged with each other, the plurality of first wedges are received by the plurality of second cavities and the plurality of second wedges are received by the plurality of first cavities. 
     Clause 161. The balloon cover of clause 160, wherein the first and second shell members are completely separable from each other. 
     Clause 162. The balloon cover of clause 160, wherein the first and second shell members are connected to each other along adjacent longitudinal edges by a hinge that allows the first and second shell members to open and close around the distal end portion of the balloon catheter. 
     Clause 163. The balloon cover of clause 162, wherein the first and second shell members comprise respective latches which are configured to engage each other so as to retain the first and second shell members matingly engaged. 
     Clause 164. The balloon cover of any of clauses 160-163, further comprising a sleeve configured to slide over the first and second shell members so as to retain the first and second shell members matingly engaged. 
     Clause 165. The balloon cover of any of clauses 160-164, wherein the lumen comprises a shaft section configured to receive a distal end portion of an outer shaft of the balloon catheter, a nosecone section configured to receive a nosecone of the balloon catheter, and a balloon section configured to receive a balloon mounted on a shoulder assembly of the balloon catheter, wherein the balloon section is located between the shaft section and the nosecone section. 
     Clause 166. The balloon cover of clause 165, wherein the balloon section comprises a proximal shoulder portion configured to receive a proximal portion of the balloon mounted on a proximal shoulder of the balloon assembly, a distal shoulder portion configured to receive a distal portion of the balloon mounted on a distal shoulder of the balloon assembly, and an intermediate portion between the proximal and distal shoulder portions, wherein the intermediate portion is configured to receive a valve retaining portion of the balloon located between the proximal and distal portions of the balloon. 
     Clause 167. The balloon cover of clause 166, wherein the lumen has a varying diameter defined by inner surfaces of the first and second shell members, wherein the intermediate portion has a smaller diameter than a distal end portion of the proximal shoulder portion and a proximal end portion of the distal shoulder portion. 
     Clause 168. The balloon cover of any of clauses 165-167, wherein the first and second wedges, and the first and second cavities are in the balloon section. 
     Clause 169. The balloon cover of any of clauses 165-168, wherein the nosecone section comprises a neck portion, wherein the neck portion has a smaller diameter than remaining portions of the nosecone section. 
     Clause 170. The balloon cover of any of clauses 165-169, wherein the shaft section comprises a plurality of central passages, each central passage being formed by a corresponding pair of opposing rib members extending radially inwardly from respective inner walls of the first and second shell members, wherein each rib member comprises two radial edges and a semicircular rib surface extending between the two radial edges such that the two rib surfaces of the opposing rib members jointly define an inner surface of the respective central passage, wherein any two adjacent central passages is separated by a chamber located between the rib members forming the two adjacent central passages, wherein the chamber has a larger diameter than the plurality of central passages. 
     Clause 171. The balloon cover of any of clauses 160-170, wherein the first shell member has two opposing first longitudinal edges and the second shell member has two opposing second longitudinal edges, wherein the first longitudinal edges are configured to mate with the corresponding second longitudinal edges to form two longitudinal parting lines. 
     Clause 172. The balloon cover of clause 171, wherein the first wedges and first cavities are located adjacent and along with the first longitudinal edges, and the second wedges and second cavities are located adjacent and along with the second longitudinal edges. 
     Clause 173. The balloon cover of clause 172, wherein the first wedges and first cavities located along the two opposing first longitudinal edges are symmetric about an axial axis of the first shell member, and the second wedges and second cavities located along the two opposing second longitudinal edges are symmetric about an axial axis of the second shell member. 
     Clause 174. The balloon cover of any of clauses 171-173, wherein the first and second wedges protrude above the respective first and second longitudinal edges and the first and second cavities recess below the respective first and second longitudinal edges. 
     Clause 175. A balloon cover for a balloon catheter, comprising: 
     a first shell member and a second shell member configured to matingly engage each other so as to enclose a distal end portion of the balloon catheter; 
     wherein the first shell member comprises a plurality of first wedges and first cavities and the second shell member comprises a plurality of second wedges and second cavities, and wherein the first wedges and first cavities are configured to interlock with the corresponding second cavities and second wedges when the first and second shells are matingly engaged with each other. 
     Clause 176. The balloon cover of clause 175, wherein the first and second shell members are completely separable from each other. 
     Clause 177. The balloon cover of clause 175, wherein the first and second shell members are connected to each other along adjacent longitudinal edges by a hinge that allows the first and second shell members to open and close around the distal end portion of the balloon catheter. 
     Clause 178. The balloon cover of clause 177, wherein the first and second shell members comprise respective latches which are configured to engage each other so as to retain the first and second shell members matingly engaged. 
     Clause 179. The balloon cover of any of clauses 177-178, further comprising a sleeve configured to slide over the first and second shell members so as to retain the first and second shell members matingly engaged. 
     Clause 180. The balloon cover of any of clauses 175-179, wherein inner surfaces of the first and second shell members define a lumen, the lumen comprising a shaft section configured to receive a distal end portion of an outer shaft of the balloon catheter, a nosecone section configured to receive a nosecone of the balloon catheter, and a balloon section configured to receive a balloon mounted on a shoulder assembly of the balloon catheter, wherein the balloon section is located between the shaft section and the nosecone section. 
     Clause 181. The balloon cover of clause 180, wherein the balloon section comprises a proximal shoulder portion configured receive a proximal portion of the balloon mounted on a proximal shoulder of the balloon assembly, a distal shoulder portion configured to receive a distal portion of the balloon mounted on a distal shoulder of the balloon assembly, and an intermediate portion between the proximal and distal shoulder portions, wherein the intermediate portion is configured to receive a valve retaining portion of the balloon located between the proximal and distal portions of the balloon. 
     Clause 182. The balloon cover of clause 181, wherein the lumen has a varying diameter defined by inner surfaces of the first and second shell members, wherein the intermediate portion has a smaller diameter than a distal end portion of the proximal shoulder portion and a proximal end portion of the distal shoulder portion. 
     Clause 183. The balloon cover of any of clauses 180-182, wherein the first and second wedges, and the first and second cavities are in the balloon section. 
     Clause 184. The balloon cover of any of clauses 180-183, wherein the nosecone section comprises a neck portion, wherein the neck portion has a smaller diameter than remaining portions of the nosecone section. 
     Clause 185. The balloon cover of any of clauses 180-184, wherein the shaft section comprises a plurality of central passages, each central passage being formed by a corresponding pair of opposing rib members extending radially inwardly from respective inner walls of the first and second shell members, wherein each rib member comprises two radial edges and a semicircular rib surface extending between the two radial edges such that the two rib surfaces of the opposing rib members jointly define an inner surface of the respective central passage, wherein any two adjacent central passages is separated by a chamber located between the rib members forming the two adjacent central passages, wherein the chamber has a larger diameter than the plurality of central passages. 
     Clause 186. The balloon cover of any of clauses 175-185, wherein the first shell member has two opposing first longitudinal edges and the second shell member has two opposing second longitudinal edges, wherein the first longitudinal edges are configured to mate with the corresponding second longitudinal edges to form two longitudinal parting lines. 
     Clause 187. The balloon cover of clause 186, wherein the first wedges and first cavities are located adjacent and along with the first longitudinal edges, and the second wedges and second cavities are located adjacent and along with the second longitudinal edges. 
     Clause 188. The balloon cover of clause 187, wherein the first wedges and first cavities located along the two opposing first longitudinal edges are symmetric about an axial axis of the first shell member, and the second wedges and second cavities located along the two opposing second longitudinal edges are symmetric about an axial axis of the second shell member. 
     Clause 189. The balloon cover of any of clauses 186-188, wherein the first and second wedges protrude above the respective first and second longitudinal edges and the first and second cavities recess below the respective first and second longitudinal edges. 
     Clause 190. A medical assembly, comprising: 
     a balloon catheter comprising an inflatable balloon; and 
     a balloon cover comprising a first shell member and a second shell member; 
     wherein the first and second shell members are configured to matingly engage with each other to define a lumen that is configured to receive at least the inflatable balloon; 
     wherein the first shell member comprises a plurality of first wedges and first cavities and the second shell member comprises a plurality of second wedges and second cavities, and wherein the first wedges and first cavities are configured to interlock with the corresponding second cavities and second wedges when the first and second shells are matingly engaged with each other. 
     Clause 191. The assembly of clause 190, wherein the first and second shell members are completely separable from each other. 
     Clause 192. The assembly of clause 190, wherein the first and second shell members are connected to each other along adjacent longitudinal edges by a hinge that allows the first and second shell members to open and close around the distal end portion of the balloon catheter. 
     Clause 193. The assembly of clause 192, wherein the first and second shell members comprise respective latches which are configured to engage each other so as to retain the first and second shell members matingly engaged. 
     Clause 194. The assembly of any of clauses 190-193, further comprising a sleeve configured to slide over the first and second shell members so as to retain the first and second shell members matingly engaged. 
     Clause 195. The assembly of any of clauses 190-194, wherein the balloon catheter comprises a first shaft, a second shaft extending through a lumen of the first shaft, a shoulder assembly configured to mount the balloon thereto, and a nosecone, wherein the shoulder assembly comprises a proximal shoulder and a distal shoulder that are axially spaced apart from each other, wherein the proximal shoulder is connected to a distal end portion of the second shaft, and the distal shoulder is connected to the nosecone. 
     Clause 196. The assembly of clause 195, wherein the lumen comprises a shaft section configured to receive a distal end portion of the first shaft, a nosecone section configured to receive the nosecone, and a balloon section configured to receive the balloon mounted on a shoulder assembly. 
     Clause 197. The assembly of clause 196, wherein the balloon section comprises a proximal shoulder portion configured receive a proximal portion of the balloon mounted on the proximal shoulder, a distal shoulder portion configured to receive a distal portion of the balloon mounted on the distal shoulder, and an intermediate portion between the proximal and distal shoulder portions, wherein the intermediate portion is configured to receive a valve retaining portion of the balloon located between the proximal and distal portions of the balloon. 
     Clause 198. The assembly of clause 197, wherein the lumen has a varying diameter defined by inner surfaces of the first and second shell members, wherein the intermediate portion has a smaller diameter than a distal end portion of the proximal shoulder portion and a proximal end portion of the distal shoulder portion. 
     Clause 199. The assembly of any of clauses 196-198, wherein the first and second wedges, and the first and second cavities are in the balloon section. 
     Clause 200. The assembly of any of clauses 196-199, wherein the nosecone section comprises a neck portion, wherein the neck portion has a smaller diameter than remaining portions of the nosecone section. 
     Clause 201. The assembly of any of clauses 196-200, wherein the shaft section comprises a plurality of central passages, each central passage being formed by a corresponding pair of opposing rib members extending radially inwardly from respective inner walls of the first and second shell members, wherein each rib member comprises two radial edges and a semicircular rib surface extending between the two radial edges such that the two rib surfaces of the opposing rib members jointly define an inner surface of the respective central passage, wherein any two adjacent central passages is separated by a chamber located between the rib members forming the two adjacent central passages, wherein the chamber has a larger diameter than the plurality of central passages. 
     Clause 202. The assembly of any of clauses 190-201, wherein the first shell member has two opposing first longitudinal edges and the second shell member has two opposing second longitudinal edges, wherein the first longitudinal edges are configured to mate with the corresponding second longitudinal edges to form two longitudinal parting lines. 
     Clause 203. The assembly of clause 202, wherein the first wedges and first cavities are located adjacent and along with the first longitudinal edges, and the second wedges and second cavities are located adjacent and along with the second longitudinal edges. 
     Clause 204. The assembly of clause 203, wherein the first wedges and first cavities located along the two opposing first longitudinal edges are symmetric about an axial axis of the first shell member, and the second wedges and second cavities located along the two opposing second longitudinal edges are symmetric about an axial axis of the second shell member. 
     Clause 205. The assembly of any of clauses 202-204, wherein the first and second wedges protrude above the respective first and second longitudinal edges and the first and second cavities recess below the respective first and second longitudinal edges. 
     Clause 206. A balloon cover for a balloon catheter, comprising: 
     a first shell member and a second shell member, wherein the first and second shell members are configured to matingly engage with each other to define a lumen that is configured to receive a distal portion of the balloon catheter; 
     wherein the lumen comprises a balloon section configured to receive a balloon mounted on the distal end portion of the balloon catheter, wherein the balloon section comprises a proximal compartment configured to receive a proximal portion of the balloon, a distal compartment configured to receive a distal portion of the balloon, and an intermediate compartment between the proximal and distal compartments, wherein the intermediate compartment is configured to receive a valve retaining portion of the balloon; 
     wherein the distal compartment comprises a proximal region, a distal region, and a middle region between the proximal and distal regions, wherein the distal region has a smaller diameter than the proximal region, and the middle region has a smaller diameter than the distal region. 
     Clause 207. The balloon cover of clause 206, wherein the proximal compartment comprises a proximal part and a distal part, wherein the distal part tapers radially inwardly from a distal end of the distal part to a proximal end of the distal part, and the proximal part has a substantially constant diameter along its axial length. 
     Clause 208. The balloon cover of any one of clauses 206-207, wherein the proximal region of the distal compartment tapers radially inwardly from a proximal end of the proximal region to a distal end of the proximal region, and wherein the distal region of the distal compartment tapers radially inwardly from a distal end of the distal region to a proximal end of the distal region. 
     Clause 209. The balloon cover of any one of clauses 206-208, wherein the intermediate compartment of the balloon section has a smaller diameter than a proximal end of the distal compartment and a distal end of the proximal compartment of the balloon section. 
     Clause 210. The balloon cover of any one of clauses 206-209, wherein the lumen comprises a shaft section configured to receive a distal end portion of an intermediate shaft of the balloon catheter and a nosecone section configured to receive a nosecone of the balloon catheter, wherein the balloon section is located between the shaft section and the nosecone section. 
     Clause 211. The balloon cover of any one of clauses 206-210, wherein the first shell member has two opposing first longitudinal edges and the second shell member has two opposing second longitudinal edges, wherein the first longitudinal edges are configured to mate with the corresponding second longitudinal edges to form two longitudinal parting lines. 
     Clause 212. The balloon cover of clause 211, wherein the first shell member comprises a plurality of first wedges and first cavities and the second shell member comprises a plurality of second wedges and second cavities, and wherein the first wedges and first cavities are configured to interlock with corresponding second cavities and second wedges when the first and second shells are matingly engaged with each other. 
     Clause 213. The balloon cover of clause 212, wherein the first wedges and first cavities are perpendicular to the first longitudinal edges, the second wedges and second cavities are perpendicular to the second longitudinal edges. 
     Clause 214. The balloon cover of any one of clauses 212-213, wherein the first and second wedges protrude above the respective first and second longitudinal edges, and the first and second cavities are recessed below the respective first and second longitudinal edges. 
     Clause 215. The balloon cover of any one of clauses 212-214, wherein the first wedges and first cavities are disposed along the first longitudinal edges, and the second wedges and second cavities are disposed along the second longitudinal edges. 
     Clause 216. A balloon cover for a balloon catheter, comprising: 
     a first shell member and a second shell member, wherein the first and second shell members are configured to matingly engage with each other so that inner walls of the first and second shell members define a lumen adapted to receive a distal portion of the balloon catheter; 
     wherein the lumen comprises a balloon section configured to receive a balloon mounted on the distal end portion of the balloon catheter, wherein the balloon section comprises a proximal compartment configured to receive a proximal portion of the balloon, a distal compartment configured to receive a distal portion of the balloon, and an intermediate compartment between the proximal and distal compartments, wherein the intermediate compartment is configured to receive a valve retaining portion of the balloon; 
     wherein inner walls of the first and second shell members are shaped to create a depression in at least one portion of the balloon when the balloon is retained in the lumen. 
     Clause 217. The balloon cover of clause 216, wherein the inner walls of the first and second shell members comprise at least one radial protrusion that extends radially inwardly to create the depression in the at least one portion of the balloon. 
     Clause 218. The balloon cover of clause 217, wherein the radial protrusion comprises a first semicircular radial protrusion extending radially inwardly from the inner wall of the first shell member and a second semicircular radial protrusion extending radially inwardly from the inner wall of the second shell member, wherein the first and second semicircular radial protrusions form a circular radial protrusion when the first and second shell members are matingly engaged with each other. 
     Clause 219. The balloon cover of any one of clauses 216-218, wherein the inner walls of the first and second shell members along the distal compartment are shaped to create a depression in the distal portion of the balloon. 
     Clause 220. The balloon cover of clause 219, wherein the distal compartment comprises a proximal region and a distal region interconnected by a middle region, wherein the distal compartment tapers radially inwardly from the proximal region to the middle region and then tapers radially outwardly from the middle region to the distal region. 
     Clause 221. The balloon cover of clause 220, wherein a distal end of the distal region has a smaller diameter than a proximal end of the proximal region. 
     Clause 222. The balloon cover of any one of clauses 216-221, wherein the proximal compartment comprises a proximal part and a distal part, wherein the distal part tapers radially inwardly from a distal end of the distal part to a proximal end of the distal part, and the proximal part has a substantially constant diameter along its axial length. 
     Clause 223. The balloon cover of any of clauses 216-222, wherein a distal end of the proximal compartment has a smaller diameter than a proximal end of the distal compartment, and the intermediate compartment has a smaller diameter than the distal end of the proximal compartment. 
     Clause 224. The balloon cover of any one of clauses 216-223, wherein the lumen comprises a shaft section configured to receive a distal end portion of an intermediate shaft of the balloon catheter and a nosecone section configured to receive a nosecone of the balloon catheter, wherein the balloon section is located between the shaft section and the nosecone section. 
     Clause 225. The balloon cover of any one of clauses 216-224, wherein the first shell member comprises a plurality of first wedges alternating with a plurality of first cavities along a length of the first shell member and the second shell member comprises a plurality of second wedges alternating with a plurality of second cavities along a length of the second shell member, wherein the first wedges are offset from the second wedges such that when the first and second shell members are matingly engaged with each other, the plurality of first wedges are received by the plurality of second cavities and the plurality of second wedges are received by the plurality of first cavities. 
     Clause 226. A medical assembly, comprising: 
     a balloon catheter comprising an inflatable balloon, the balloon comprising a proximal portion, a distal portion, and valve retaining portion between the proximal and distal portions; 
     and a compression member configured to create at least one depression in the balloon. 
     Clause 227. The medical assembly of clause 226, wherein the compression member is configured to radially compress the distal portion of the balloon between proximal and distal ends of the distal portion of the balloon such that the distal portion of the balloon has a generally hourglass shape. 
     Clause 228. The medical assembly of any one of clauses 226-227, further comprising a balloon cover having a lumen configured to the receive the balloon, wherein the lumen comprises a balloon section comprising a proximal compartment configured to receive the proximal portion of the balloon, a distal compartment configured to receive the distal portion of the balloon, and an intermediate compartment configured to receive the valve retaining portion of the balloon, wherein the distal compartment comprises the compression member. 
     Clause 229. The medical assembly of clause 228, wherein the distal compartment comprises a proximal region and a distal region interconnected by the middle region, wherein the compression member comprises a radial protrusion extending inwardly from an inner wall of the middle region. 
     Clause 230. The medical assembly of any one of clauses 228-229, wherein the balloon catheter comprises a balloon shaft, an inner shaft extending through a lumen of the balloon shaft, a nosecone, and a distal shoulder located within the distal portion of the balloon. 
     Clause 231. The medical assembly of clause 230, wherein the lumen of the balloon cover comprises a shaft section configured to receive a distal end portion of the balloon shaft and a nosecone section configured to receive the nosecone, wherein the balloon section is located between the shaft section and the nosecone section. 
     Clause 232. The medical assembly of any one of clauses 230-231, wherein the proximal portion of the balloon comprises a proximal part and a distal part, wherein the distal part tapers radially inwardly from a distal end of the distal part to a proximal end of the distal part, and the proximal part has a substantially constant diameter along its axial length. 
     Clause 233. The medical assembly of any one of clauses 226-227, wherein the compression member comprises an annular band configured to extend around the balloon. 
     Clause 234. The medical assembly of clause 230, wherein the annular band is connected to a sheath, wherein a distal end of the sheath is connected to a distal end of the balloon so that the sheath at least partially covers the distal portion of the balloon. 
     Clause 235. The medical assembly of any one of clauses 226-234, further comprising a prosthetic valve disposed on the valve retaining portion of the balloon in a radially crimped state. 
     Clause 236. A balloon cover assembly for a balloon catheter, comprising: 
     a cover body defining a lumen configured to receive a balloon folded on a distal portion of the balloon catheter, wherein the balloon comprises a proximal portion, a distal portion, and a valve retaining portion connecting the proximal and distal portions; and at least one compression member configured to radially compress at least one portion of the balloon. 
     Clause 237. The balloon cover assembly of clause 236, wherein the compression member comprises a radial protrusion of an inner wall of the cover body, wherein the radial protrusion extends radially inwardly into the lumen to contact the at least one portion of the balloon. 
     Clause 238. The balloon cover assembly of clause 237, wherein the radial protrusion encircles the lumen. 
     Clause 239. The balloon cover assembly of clause 236, wherein the compression member comprises an annular band configured to extend around the at least one portion of the balloon. 
     Clause 240. The balloon cover assembly of clause 239, wherein the annular band is radially compressible around the at least one portion of the balloon. 
     Clause 241. The balloon cover assembly of any of clauses 239-240, wherein the compression member further comprises a sheath connected to the annular band. 
     Clause 242. The balloon cover of clause 241, wherein a distal end of the sheath is connected to the distal end of the distal portion of the balloon. 
     Clause 243. The balloon cover assembly of clause 236, wherein compression member comprises a suture that can be tightened around the at least one portion of the balloon. 
     Clause 244. The balloon cover assembly of any of clauses 236-243, wherein the compression member is configured to radially compress the at least one portion of the balloon such that the at least one portion of the balloon has a generally hourglass shape. 
     Clause 245. The balloon cover assembly of any of clauses 236-244, wherein the cover body comprises first and second separable shell portions defining the lumen. 
     Clause 246. The balloon cover assembly of any of clauses 236-245, wherein the at least one compression member is configured to radially compress the distal portion of the balloon at a location between proximal and distal ends of the distal portion of the balloon. 
     Clause 247. A method comprising: 
     folding a balloon on a distal portion of a delivery device when the balloon is in a deflated state, wherein balloon has a proximal portion, a distal portion, and a valve retaining portion connecting the proximal and distal portions, wherein a distal end of the distal portion has a smaller diameter than a proximal end of the distal portion, a distal end of the proximal portion has a larger diameter than a proximal end of the proximal portion, and the valve retaining portion has a smaller diameter than the proximal end of the distal portion and the distal end of the proximal portion; and radially compressing the distal portion of the balloon at a location between the distal and proximal ends of the distal portion. 
     Clause 248. The method of clause 247, wherein after radially compressing the distal portion of the balloon, a diameter of the distal portion of the balloon at the location between the distal and proximal ends is smaller than that of the distal and proximal ends of the distal portion of the balloon. 
     Clause 249. The method of any one of clauses 247-248, wherein radially compressing the distal portion of the balloon comprises placing the balloon into a balloon cover having a compression member that radially compresses the distal portion of the balloon. 
     Clause 250. The method of clause 249, wherein the compression member comprises a radial protrusion of an inner wall of the balloon cover. 
     Clause 251. The method of any one of clauses 247-248, wherein radially compressing the distal portion of the balloon comprises placing an annular band around the distal portion of the balloon. 
     Clause 252. The method of clause 251, further comprising placing a balloon cover over the balloon after placing the annular band around the distal portion of the balloon. 
     Clause 253. The method of any one of clauses 249, 250 or 252, further comprising injecting an inflation fluid into the balloon and withdrawing the inflation fluid from the balloon while the balloon is within the balloon cover. 
     Clause 254. The method of clause 253, further comprising removing the balloon cover from the balloon and sliding a shaft of the delivery device over a proximal portion of the balloon. 
     Clause 255. The method of clause 254, wherein sliding the shaft of the delivery device over the proximal portion of the balloon causes the distal portion of the balloon to partially inflate. 
     In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims.