Abstract:
In one embodiment, a balloon catheter is provided for use during annuloplasty. Preferably, the balloon includes a distal, noncompliant portion and a proximal semi-compliant portion which allows for sequential inflation, reliable positioning, and compliance measurement.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 13/231,807 filed Sep. 13, 2011 entitled Positionable Valvuloplasty Catheter, which claims priority to U.S. Provisional Application Ser. No. 61/382,446 filed Sep. 13, 2010 entitled Positionable Valvuloplasty Catheter, both of which are hereby incorporated herein by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The following patents are hereby incorporated by reference in their entirety: U.S. Pat. Nos. 7,618,432; 7,744,620; and 7,951,111. 
         [0003]    This invention is related to balloon catheters used for locating a position within a blood vessel or tubular member of the body, dilating tissue found within the tubular member, and measuring the compliance characteristics of tissue or the tubular member. Specifically, this device is intended for locating the balloon across the aortic annulus and aortic sinus, dilating the diseased aortic valve leaflets, and measuring the compliance characteristics of the annulus or sinus region. 
         [0004]    Currently cylindrically shaped balloons are used to perform valvuloplasty procedures wherein the stenotic aortic valve leaflets are dilated or pushed back into the space of the aortic sinus. This procedure is typically performed under fluoroscopic guidance while the heart is beating. Movement of the heart, flow of blood, and inaccuracies in of fluoroscopic guidance do not always allow for accurate placement of the valvuloplasty catheter across the aortic annulus and sinus. 
         [0005]    Recently dog-bone-shaped balloons have been presented (see U.S. Pat. No. 7,618,432) that provide for improved positioning across the aortic annulus and sinus. Also, dog-bone-shaped balloons have been presented that are able to measure the diameter of the aortic annulus as well as indicate the compliance characteristics of the aortic annulus (see U.S. Pat. No. 7,951,111). 
         [0006]    Dilation of the aortic valve leaflets into the aortic sinus can cause the sinus to become overly distended and potentially encounter dissection or tearing which can result in patient death. Under current fluoroscopic visualization the physician does not know when the balloon has made contact with the leaflets, does not know if the aortic sinus is being overdistended, and he does not have information indicating the compliance characteristics of the aortic sinus or annulus. Such information would be useful to the clinician to ensure safety to the patient during dilation of the stenotic aortic valve leaflets to obviate annulus and sinus dissection and to ensure adequate dilation of the leaflets. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention is a balloon catheter used for dilating tubular members of the body such as dilating stenotic aortic valve leaflets found in the aortic root. The balloon catheter has a balloon that is comprised of one region or portion that inflates earlier than the rest of the balloon to help position the balloon in the correct location within the tubular member. This portion of the balloon is made of a non-compliant (nc) material that is folded up during delivery and is unfolded as it is inflated at relatively low pressures. Another region or portion of the balloon is formed from a semi-compliant (sc) material or elastomeric material that undergoes expansion as pressure is increased within the balloon. Additionally, a waist region with a length that is larger than the aortic annulus and a diameter that is smaller than the aortic annulus and smaller than the bulb portion is located in either the nc portion or the sc portion. 
         [0008]    For valvuloplasty applications the sc portion is inserted across the stenotic aortic valve leaflets while the nc portion is located in the left ventricular outflow tract (LVOT) upstream of the aortic annulus. A smaller diameter waist portion is located across the aortic annulus. Upon inflation to low pressures from zero to 0.5 atm the nc distal portion inflates first and allows the catheter to be pushed into place by the pulsating blood or pulled back proximally into position with the distal portion of the balloon located just upstream of the aortic annulus. Since it is sized larger than the valve annulus, the nc distal portion lodges itself in the valve region and prevents the balloon from being actively pushed via blood pressure and flow in a direction downstream toward the aorta. The sc proximal portion remains relatively small in diameter with only mild or no contact with the aortic valve leaflets thereby allowing the sc portion to be easily pulled further if needed through the opening provided by the stenotic aortic valve leaflets. 
         [0009]    Upon further inflation from 0.1 to 2 atm, the sc proximal portion of the balloon contacts the stenotic leaflets and begins to push them outward against the aortic sinus. Balloon contact with the leaflets can be observed by noting an inflection point and an increase in the slope of the dP/dV curve that is higher than that normally observed for the dP/dV compliance curve for the sc portion of the balloon. 
         [0010]    A computerized control system and display can be used to monitor the pressure versus volume slope and determine if a change in slope is occurring. The computer can detect an inflection point in the pressure-volume curve and can record the pressure at the time of the inflection as well as calculate slope changes. These calculations can then be used to determine the compliance of the tissues that are being contacted and expanded by the balloon. Further description of the computerized system is found in the US patent application by Drasler referenced earlier. 
         [0011]    Further inflation of the balloon from 0.5 atm to higher than 2 atm causes the sc portion of the balloon to further dilate the leaflets outward. The stenotic leaflets can come into contact with the aortic sinus; this contact will be noted by an inflection point and an increase in the slope of the dP/dV curve. Observation of the slope of the dP/dV compliance curve following contact of the leaflets with the sinus reflects the compliance of the stenotic leaflets, the sinus, and the sc portion of the balloon. Subtraction of the balloon compliance allows the physician to assess the compliance of the aortic tissues and determine if further dilation is warranted. This subtraction can be accomplished automatically with the computer control system and the tissue compliance can be displayed on a monitor. 
         [0012]    The balloon structure in one preferred embodiment can have a dogbone shape in its fully expanded conformation. The dogbone shape can provide an improved locking of the balloon on each side, upstream and downstream, of the annulus. Also, the dogbone shape can allow the stenotic leaflets to be dilated in a hyperextended manner while maintaining a lower dilation diametric magnitude for the annulus. 
         [0013]    The waist of the dogbone-shaped balloon of the present invention can be formed from the nc material and attain a diameter that is approximately equal to or somewhat smaller than the annulus diameter. Alternately, the balloon waist can be formed from a sc material and expansion of the waist can allow it to come into contact with the annulus thereby providing compliance data from the slope of the dP/dV curve to also be indicative of the annulus diameter and compliance. 
         [0014]    In yet another embodiment, the balloon of the present invention can be shaped such that it forms a generally cylindrical shape after it is fully inflated. In this embodiment, the nc distal portion is inflated first at lower pressures while the sc proximal portion resists expansion due to its elastomeric character. Further expansion at higher pressures from 0.2 atm to approximately 2 to 4 atm causes the sc proximal portion to expand out to its fully expanded conformation. 
         [0015]    The present invention can include limiting fibers located in the proximal sc portion of the balloon. These limiting fibers are intended to limit the amount of expansion that the sc proximal portion of the balloon can expand. The expansion limitation can be in the diametric direction, the axial direction, or both. Such limiting fibers can be wrapped fibers such as an elastomeric monofilament material wrapped via a helical wind with a multi-filament non-compliant material. The limiting fibers are either bonded or attached to the sc proximal portion of the balloon. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    These and other aspects, features and advantages of which embodiments of the invention are capable of will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings, in which 
           [0017]      FIGS. 1A-1C  illustrate an embodiment of a balloon catheter according to the present invention. 
           [0018]      FIGS. 2A and 2B  illustrate another embodiment of a balloon catheter according to the present invention. 
           [0019]      FIGS. 3A and 3B  illustrate another embodiment of a balloon catheter according to the present invention. 
           [0020]      FIGS. 4A and 4B  illustrate another embodiment of a balloon catheter according to the present invention. 
           [0021]      FIGS. 5A and 5B  illustrate example pressure vs. volume graphs measured with regard to the balloon catheters of the present invention. 
           [0022]      FIGS. 6A and 6B  illustrate another embodiment of a balloon catheter according to the present invention. 
           [0023]      FIGS. 7A-7C  illustrate another embodiment of a balloon catheter according to the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0024]    Specific embodiments of the invention will now be described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements. 
         [0025]    The present invention includes a balloon dilatation catheter for positioning within a tubular vessel of the body and dilating a stenotic portion of the vessel. When used for valvuloplasty, the distal region or portion of the balloon is positioned in the left ventricular outflow tract and is inflated first to help position the balloon to a desirable location. The proximal region or portion of the balloon is positioned adjacent to the stenotic aortic valve leaflets such that they can be pushed back against the sinus. This dilation of the aortic valve leaflets can be accomplished as a stand-alone balloon aortic valvuloplasty (BAV) procedure or it can be performed as a pre-dilatation prior to implanting an aortic valve. The procedure can also be performed to dilate out other valves of the body or other stenotic regions of any tubular vessel of the body. 
         [0026]      FIGS. 1A-1C  illustrate a first embodiment of a dilatation device  100  according to the present invention. A balloon  102  is disposed at the distal end of a catheter shaft  104  and includes a distal non-compliant (nc) portion  102 A and a proximal semi-compliant (sc) portion  1026 . The sc portion  1026  is joined to the nc portion  102 A at a junction  102 C located between the proximal end and the distal end of the balloon. 
         [0027]    The balloon waist  102 D of this embodiment is found in the distal nc portion  102 A and extends from the junction  102 C to the distal bulb  102 E. Since the waist  102 D and distal bulbous portion  102 E are composed of nc material, they both will inflate earlier than the sc portion  1026 . Further, even at relatively low pressures such as about 0.1-0.5 atmospheres the waist  102 D and distal nc portion  102 A can substantially attain their final diameter. 
         [0028]    The length  102 F of the waist  102 D (including the angled, shoulder or transition region adjacent the junction  102 C) in a preferred embodiment is about 4-10 mm (and can range from 2-15 mm). The nc balloon waist  102 D ensues that the waist cannot grow during further balloon inflation and therefore will reduce accidental dissection of the aortic annulus. The diameter of the waist is preferably constructed to be about 1-3 mm smaller than the aortic annulus diameter (but may also range between zero to 10 mm smaller). 
         [0029]    The sc portion  1026  can be formed from polyurethane, silicone, lower durometer nylon, other thermoplastic elastomer, thermoset elastomer or material that can expand outwards to a larger diameter upon application of internal pressure. The nc portion  102 A can be formed from polyethyleneterephthalate (PET), nylon, Pebax, or other polymeric material that does not expand appreciably upon application of internal pressure within the balloon. 
         [0030]    The balloon  102  may include a sc polyurethane thermoplastic elastomer layer that extends throughout the entire proximal and distal portion. The nc portion  102 A can be located as a second, outer layer at the distal portion of the balloon  102  while the proximal portion leaves the polyurethane layer exposed to allow for expansion. Hence, the balloon  102  can have a proximal portion that is compliant and a distal portion that is non-compliant. 
         [0031]    This “layered” approach to creating the balloon  102  can be accomplished by coextruding a nc material over a sc material and ablating the nc material away from the portion of the balloon that is sc. Alternately, a separate nc balloon can be formed and a distal portion can be excised from it and bonded to the sc inner polyurethane layer located in the distal portion of the balloon. Other methods for forming the balloon are described in the U.S. Pat. Nos. 7,618,432; 7,744,620; and 7,951,111 which were previously incorporated by reference. 
         [0032]    In one embodiment, the sc portion  102 B can have a maximum inflation size that is limited by one or more embedded filaments or fibers. For example, the proximal sc portion  102 B of the balloon  102  can have a layer of braided polymeric filaments  132  (seen on balloon  130  in  FIG. 4A ) or a layer of a helically wound polymeric filament  142  (seen on balloon  140  in  FIG. 4B ). The layers  132  or  142  can be embedded within the balloon wall or otherwise attached to the balloon wall. The polymeric filament is formed, in one example, from an internal core of polyurethane and wrapped with a spiral wrap of PET. This filament can be braided or wound onto the sc proximal balloon portion  102 B as shown in  FIGS. 4A and 4B . 
         [0033]    These braids can also be included on the nc waist  102 D which thereby restricts the fully expanded diameter of the waist region  102 D to a desired size. In this regard, a braid that expands to a larger diameter may begin at junction  102 G. 
         [0034]    This support structure can also help to reduce the amount of length change encountered by the proximal portion as it is exposed to increasing pressures. The methods for providing such a braid or helical wind are described in more depth in the U.S. Pat. Nos. 7,618,432; 7,744,620; and 7,951,111 which were previously incorporated by reference. 
         [0035]    The balloon catheter  100  is typically introduced into the femoral arterial vasculature and advanced such that the balloon  102  is positioned with its distal portion  102 A located in the left ventricular outflow tract  14  (LVOT) as shown in  FIG. 1B . Upon inflation to a relatively low pressure of about 0.1-1.0 atm (preferably about 0.2-0.5 atm) the distal portion  102 A of the balloon  102  is expanded such that the bulbous distal portion  102 A lodges just upstream of the aortic valve annulus  12  as the catheter shaft  104  is place under tension or gently pulled by the clinical operator. The junction  102 C of this embodiment is preferably located at a position along the balloon length such that it positions just downstream of the annulus  12  during use. 
         [0036]    The balloon waist  102 D, which is also formed from nc material in this embodiment, can locate adjacent to the annulus as also shown in  FIG. 1B . The waist portion  102 D preferably has a diameter at the previously described low inflation pressure of approximately 18-22 mm (range from 16-26 mm) and the distal bulb portion  102 E preferably has a diameter of 22-25 mm (range 20-30 mm). Generally, the waist  102 D is smaller than the distal portion  102 E by between about 1-8 mm and more preferably 2-6 mm. 
         [0037]    At the previously described low inflation pressure, the proximal portion  102 B of the balloon  102  expands to or remains mostly deflated to a relatively smaller diameter than the waist  102 C and distal portion  102 A. Preferably the diameter of proximal portion  102 B has a diameter such that upon application of tension to the shaft, the proximal balloon portion will slide easily through the opening found between the stenotic aortic valve leaflets  16  and will allow the balloon  102  will come into position as shown in  FIG. 1B . Typically, the flow area for blood through a stenotic aortic valve is equal to or larger than approximately 0.4 cm 2  and has a diameter of approximately 7 mm. The diameter of the proximal portion  102 B of the balloon is preferably about 7 mm (range from about 5-18 mm) at a pressure between about 0.2-0.5 atm when it is being pulled back into position as just described. 
         [0038]    The balloon catheter of the present invention can also be positioned via the venous system or trans-apically. In the apical approach, the catheter is introduced through a thoracotomy in the patient&#39;s chest and enters into the apex of the heart. With this apical approach, the balloon shaft extends from the balloon through the apex of the heart and therefore the nc portion  102 A and the sc portion  102 B are located in the reverse positions on the shaft as that of the device  100  in  FIGS. 1A and 1B  (used with a femoral approach). It is to be understood that the present invention is equally applicable to the apical, trans-venous or femoral approach, however, only the femoral approach will described hereafter. 
         [0039]    Upon positioning the balloon nc distal bulb portion  102 E just upstream of the annulus, and the waist  102 D across the aortic annulus, the pressure can be increased within the balloon to cause the sc proximal portion  102 B to expand. The compliance of the sc proximal portion  102 B generally follows a pressure-volume curve with a balloon compliance slope  200 , dP/dV, that is associated with the modulus of the sc balloon material as shown in  FIG. 5A . This dP/dV slope can be monitored by measuring the pressure via a pressure transducer  110  located in the balloon  102  (as seen  FIG. 1B ) or in fluid communication with the balloon (not shown). The change in balloon volume can be monitored by the amount of fluid delivered to the balloon via a delivery syringe that is connected to the balloon inflation lumen. Additional details relating to a system for monitoring balloon pressure and volume change can be found in U.S. Pat. Nos. 7,618,432; 7,744,620; and 7,951,111 which were previously incorporated by reference. 
         [0040]    During a procedure, the inflated balloon  102  initially follows the balloon compliance slope  200 , as seen in  FIG. 5A . Contact of the proximal portion  102 B of the balloon  102  with the stenotic leaflets  16  creates an increased slope of dP/dV, described here as the balloon/leaflet slope  202 . This slope is higher than the balloon compliance slope  200  alone, due to additional resistance to expansion offered by the leaflets  16 . 
         [0041]    Continuing to inflate the balloon  102  can cause the leaflets  16  to fracture their fibrous and calcified structures and result in a drop in the slope of the balloon/leaflet compliance curve that may approach or be similar to the balloon compliance slope  200 . This reduced slope is labeled as a balloon/fractured leaflet slope  206  in  FIG. 5A . 
         [0042]    Further inflation of the balloon  102  can cause the proximal sc portion  102 B of the balloon to push the leaflets  16  outward into contact with the wall of the sinus  10  as shown in  FIG. 1C . Upon contact with the sinus wall  10 , an inflection point  204  is observed in the slope of the balloon/leaflet curve as the slope increases. This increased slope is described as the balloon/leaflet/sinus slope  208  and shown in  FIG. 5A . The leaflets generally achieve desirable fractures when they are forced into intimate contact with the wall of the aortic sinus as shown in  FIG. 1C  and therefore, slope  208  may indicate to the user that this desirable expansion has occurred. In the embodiments of this specification, this contact may occur, for example above approximately 2 atm of pressure inside the balloon  102 . 
         [0043]    Provided that the leaflets have been significantly fractured, the balloon/leaflet/sinus slope  208  provides valuable information regarding the compliance of the sinus region. If the slope continues to increase above the balloon/leaflet slope, then the clinical operator knows that contact has been made with the sinus and obtains information regarding the compliance of the sinus  10 . 
         [0044]    The proximal sc portion  102 B of the balloon  102  expands to a diameter that is larger than the diameter of the waist portion  102 D, preferably ranging from 20-26 mm. This larger diameter for the sc proximal portion  102 B may provide an improved hyperextension for the aortic valve leaflets  16  and also may help to lock the balloon  102  in a desirable position on each side of the annulus  12 . 
         [0045]    Assessment of the compliance of the leaflets and the leaflets/sinus can be obtained by subtracting the balloon compliance slope  200  (i.e., the compliance slope of the balloon alone in  FIG. 5A ) from the compliance of the balloon/leaflet slope  202  or the compliance of the balloon/leaflet/sinus slope  208 . This balloon compliance slope  200  “subtraction” can be seen in the dP/dV curve of  FIG. 5B , which shows the un-fractured leaflet compliance slope  210 , the fractured leaflet compliance slope  212 , and the leaflet/sinus compliance slope  214 . The compliance of the leaflets can change as the fibrous tissues become fractured. The compliance of the leaflets/sinus can help the clinical operator to ensure safety to the patient by discontinuing dilation if the sinus tissue appears to be weak or beginning to fracture. 
         [0046]      FIGS. 2A and 2B  illustrate another embodiment of a balloon catheter  120  similar to that described in  FIGS. 1A-1C  having a balloon  122  with a nc distal portion  122 A, a sc proximal portion  122 B, and an interface  122 C between the sc and nc portions of the balloon. However, when fully expanded, the balloon  120  achieves a generally stepped-shaped balloon ( FIG. 2B ). 
         [0047]    As shown in  FIG. 2A , the distal nc portion  122 A of the balloon  122  inflates first at relatively low pressures to help position the nc distal portion of the balloon  122  just upstream of the annulus  12  in the LVOT as described with regard to the device  100 . The balloon  122  is pulled back by the clinical operator such that the proximal sc portion  122 B slides easily through the opening formed by the stenotic aortic valve leaflets  16  and across the aortic annulus. Upon further inflation as shown in  FIG. 2B , the proximal sc portion  122 B expands outwards to form a generally cylindrical shape with a diameter that is similar to that found crossing the annulus. Preferably, the balloon diameter adjacent to the annulus is approximately 20-23 mm (range 18-26 mm). The diameter of the nc distal portion  122 A is preferably slightly larger, such as between about 22-28 mm (however a range of 20-30 is also possible). 
         [0048]      FIGS. 3A and 3B  illustrate another embodiment of a balloon catheter  140  that is generally similar to the previously described embodiments, including a balloon  142 , having a distal nc portion  142 A, a proximial sc portion  142 B, a junction interface  142 C between the two portions  142 A,  142 B, and a narrowed waist portion  142 D. 
         [0049]    In this embodiment, the junction  142 C is located such that it is positioned upstream of the annulus  12  (i.e. positioned upstream relative to the previously described embodiments). The waist  142 D is included in the proximal sc region  142 B. 
         [0050]    In use, increasing pressure inflates the distal nc region  142 A, similar to that described in the earlier embodiments and causes the balloon  142  to position just upstream of the annulus in the LVOT  14 . Upon placing the shaft  104  under tension, the proximal sc region  142 B is pulled through the stenotic aortic valve opening and the aortic annulus. 
         [0051]    Upon further inflation to higher pressures, the proximal sc region  142 B expands into contact with the leaflets  16  and an inflection point is noted as the slope increases to a balloon/leaflet slope  202  of the dP/dV curve, as described with regard to  FIG. 5A . Further inflation pushes the leaflets  16  back towards the aortic sinus  10  until the leaflets  16  crack or fracture (slope  206 ) and also extends the waist portion  142 D out into contact with the annulus  12 . Contact of the leaflets with the aortic sinus  10  or contact of the balloon with the annulus  12  increase in the slope of the dP/dV curve (balloon/leaflet/sinus), creating another inflection point. This increased slope can be indicative of the compliance of the aortic sinus  10  or the annulus  12  or both as described earlier with regard to  FIG. 5A . For this embodiment, the slope of the balloon/leaflet/sinus compliance curve  208  could also be reflective of the annulus compliance, since the proximal sc balloon portion  142 B and the waist  142 D can both make contact with the leaflets  16  and the annulus  12  respectively. 
         [0052]    Preferably, this balloon  142  maintains a bulbous shape in its fully expanded configuration with the waist  142 D ranging between about 1-5 mm smaller in diameter than either the proximal bulb  142 B or the distal bulb  142 A. The proximal and distal bulbs preferably have a diameter that ranges between about 21-28 mm. The waist length extends axially from about 4-10 mm (range 2-15 mm). 
         [0053]    Another embodiment of a balloon catheter  150  is shown inflated to an initial, relatively low pressure (e.g., between about 0-0.5 atm) in  FIG. 6A  and inflated to a final, higher pressure (e.g., between about 1-4 atm) in  FIG. 6B . The balloon  152  has two bulbs or bulb regions  152 A,  152 B located on each end of a waist region  152 C. The waist or waist region  152 C can be considered the combination of the central waist  152 E plus the bevel regions  152 D. Two bevels or bevel regions  152 D connect each of the bulbs  152 A,  152 B with the central waist region  152 E. 
         [0054]    When the balloon  152  is fully expanded, the diameter of each bulb, DB, is preferably about 24-30 mm and the diameter of the central waist  152 E, Dw, is preferably about 15-24 mm. The bulb diameter ranges from 2-10 mm larger than the central waist diameter. The waist length is about 5-15 mm in this initial, low pressure state (about 0.1-0.5 atm.). 
         [0055]    As seen in  FIG. 6B , increased pressure and expansion of the balloon  152  causes the waist region  152 C (i.e., the waist region  152 E and/or beveled regions  152 D) become shorter in length. In its initial configuration shown in  FIG. 6A , the balloon  152  has a relatively long length of its central waist  152 C that extends from the outer edge of the beveled region  152 D on one side of the balloon  152  to the outer edge of the beveled region  152 D on the other side. As the balloon  152  is expanded under pressure to its final configuration as shown in  FIG. 6B , the length of the waist  152 C extends a shorter distance from the outer ends of the beveled regions  152 D. The waist length at pressures ranging from 1-4 atm is approximately 4-10 mm (range 2-12 mm). 
         [0056]    This shortening of waist region  152 C provides an advantage over other balloons by allowing the longer waist to be placed more easily across the aortic annulus  12  and across the stenotic leaflets  16  prior to full inflation of the balloon  152 . Upon inflating the balloon to its final configuration, the waist will reduce in length to position the distal bulb region  152 A against the upstream side of the annulus  12  and the proximal bulb  152 B to push the leaflets  16  outwards against the wall of the aortic sinus  10 . Thus the larger waist length is more easily positioned and properly located across the annulus  12 , preventing the annulus  12  from being accidentally expanded by either of the bulbs  152 A,  152 B or exposed to any significant forces that could cause tearing or dissection. Also, the shortening of the length of the waist  152 C can open the stenotic leaflets  16  more efficiently by providing an expansion force by the bulb region  1526  that is directed at the outflow ends of the valve leaflets  16  to initiate leaflet opening. This action of opening leaflets  16  at the outflow ends provides a more consistent separation of the leaflets  16  that has particular benefit to opening stenotic bileaflet valves without as much potential for causing leaflet avulsion. 
         [0057]    The diameter of the central waist region  152 C, Dw, can remain approximately the same diameter from its initial to final configuration during inflation of the balloon  152 . Alternately, an increase in central waist diameter within a predetermined range may also occur. Preferably, this central waist diameter range is approximately 2-6 mm smaller than the diameter of the bulbs  152 A,  1526  and smaller than the diameter of the annulus  12 . 
         [0058]    Preferably, the bulb diameter remains approximately the same diameter between its initial to final configuration although some diameter growth can be generally expected depending upon the material of construction. For example, a nylon balloon bulb material may grow in diameter by approximately 5-15% and a PET balloon bulb material may grow in diameter from 3-10% depending upon its wall thickness and processing conditions. Other typical medical device balloon materials are also contemplated including other generally noncompliant materials such as pebax, polyethylene, and others commonly used in the industry or semi-compliant (sc) materials including polyurethanes, silicones, lower durometer nylons, pebax, and copolymers of such materials. 
         [0059]    The manufacture of this balloon  152  can be accomplished using a single material for the entire balloon, two or more balloon materials such as an inner balloon of one material and an outer balloon of another material, or a portion of one balloon inside or outside of another balloon material. For example, a nc material such as PET can be formed with a bulbous shape; the bulbous ends can be excised from the balloon and bonded over the bulbous ends of a balloon formed from a sc material such as nylon or polyurethane. Such balloon construction can include bonding or thermal forming or attachment of one balloon portion or region around another balloon portion or region, or balloon fabrication can include a coextrusion of two or more different materials that are then formed into a balloon. Further, the balloon or a portion of the balloon can be formed with a braided structure either bonded to or embedded within a portion of the balloon wall or the entire balloon wall. 
         [0060]    In one example construction, plastic tubing can be extruded and blown into a balloon with a diameter similar to that of the desired central waist diameter. Preferably, this balloon attains a molecular circumferential orientation and a diameter that is smaller than the diameter of an aortic annulus  12 . The blown balloon is then placed into a bulbous mold and the end regions or bulb regions are heated or annealed to allow molecular rearrangement. The central waist region can be cooled to ensure that the central waist will retain its circumferential molecular alignment. Upon further inflation of the balloon into the bulbous mold the bulb regions can regain molecular circumferential orientation to retain the large bulb diameter. It is noted that this construction method can be also used to form a bulbous or hour-glass shaped balloon out of a single polymeric material such that the waist will retain a smaller diameter and will not expand outwards to the diameter of the larger bulb diameters as the internal pressure is increased up to approximately 3-5 atmospheres. The polymeric material can be, for example, PET, nylon, pebax, or other nc or sc material that is suitable for forming such a balloon. Cooling temperatures and heating temperatures will vary according to the melting temperature and glass transition temperatures for these materials. 
         [0061]    The beveled regions may require less orientation because they have not been expanded out to as large of a diameter. Also, thermal annealing of the beveled regions can be greater than that of the bulb regions, if necessary, to provide enhanced bevel growth under pressure. These bevel regions may then have a tendency during use, to grow to a relatively larger diameter than the central waist region when the pressure is increased. A portion of the bevel region can grow to a diameter that is equivalent or nearly equal to the diameter of a bulb region. This increase in diameter of the bevel regions then causes the waist length to reduce during balloon inflation and safely dilate the aortic valve leaflets with proper positioning of the bulbs on each side of the annulus, with more efficient dilation of the aortic valve leaflets, and without causing dilation to the annulus. 
         [0062]    Yet other embodiments for constructing a balloon catheter  160  with a “shrinking” waist are shown in  FIGS. 7A-7C . Specifically,  FIGS. 7A and 7B  illustrate two alternate configurations of a balloon  162  at a relatively low pressure, while  FIG. 7C  illustrates the balloon  162  at a relatively higher pressure. The expansion of the central waist  162 C (including central waist  162 E and beveled regions  162 D) are controlled or limited by the inclusion of braided fibers. Depending on several characteristics of the braid, expansion is limited. 
         [0063]    In  FIG. 7A , the central waist  162 C is preferably constructed out of either a semi-compliant (sc) material or a noncompliant (nc) material. A braid (i.e., braided fiber elements) are attached or embedded and preferably oriented the circumferential direction. In one example, the braid fiber angle with respect to the longitudinal axis of the balloon is about 75-85 degrees. The braid size, angle, material and orientation prevents the central waist  162 E from becoming equal to or larger than the annulus diameter. 
         [0064]    Alternately, a spiral winding of noncompliant fiber, such as Dacron, can be attached or embedded to the central waist  162 E to prevent diametric expansion. In this alternate construction, the central waist  162  can be folded (if composed of nc material) to attain a low profile as require for delivery of the balloon into the tubular vessel or access site into the body. 
         [0065]    The diameter of the central waist  162 E and the central waist braid angle in one embodiment is preferably similar in its initial, relatively low pressure configuration (e.g.,  FIGS. 7A or 7B ) to that in the final higher pressure configuration ( FIG. 7C ). The bevel region  162 D is preferably formed from a semi-compliant material with a bevel braid angle that is more axially directed than the central waist braid angle in the initial configuration. For example, the bevel braid angle is between about 45-75 degrees with respect to the axial direction. In this embodiment, the waist region  152 C preferably enlarges in diameter by stretching of its sc material and thereby changing the relative angles of the nc braid fibers. 
         [0066]    The bulb regions  162 A,  162 B can be formed from a nc material without a braid. Alternately, a sc material can be used with a braid. In either construction, the bulb regions  162 A,  162 B preferably inflate easily at low pressures and should reach the final bulb diameter at relatively low pressures below about 0.5 atm. 
         [0067]    As this balloon  162  is inflated, the bevel regions  162 D expand outwards to effectively “move” the regions  162 D towards the center of the central waist region  162 E. This new shape for the bevel regions  162 D is formed and is controlled by the expanding braid and also is controlled by the shape of the material used to form the bevel regions. The braid fibers used in the waist  162 C can be formed from Dacron, or other plastic monofilament fiber, or multifilament fiber, or metal monofilament fiber or multifilament metal fiber. 
         [0068]    The manufacture of the balloon  162 ′ in  FIG. 7B  may include a braided material that is embedded or attached to the waist  162 C. In the initial, relatively low pressure configuration shown in  FIG. 7B , the central waist  162 E initially expands to a relatively small diameter which can be achieved by increasing the axially configuration or orientation of the braid angle. The waist can have a significantly smaller central waist diameter, Dw, than its final central waist diameter, Dw, as shown in  FIG. 7C . 
         [0069]    The beveled regions  162 D are also preferably formed from a sc material with attached or embedded braided fibers. As the balloon  162 ′ is inflated, the central waist  162 E and beveled regions  162 D expand outward until the braid angle becomes generally circumferentially oriented, thereby stopping the outward expansion. Also, upon inflation of the balloon  162 ′ to its final configuration, the central waist  162 E may shorten in length due to the presence of the attached braid. The bevel regions  162 D expand outward in diameter relative to the central waist region  162 E due to a different braid configuration. As the bevel braid angle becomes more circumferentially oriented in the final configuration, expansion become restricted. 
         [0070]    The bulb regions  162 A,  162 B are preferably formed of a nc material that attains the final bulb diameter at a relatively low pressure below 0.5 atm. Other materials are contemplated and can also be used for the bulb material including a braided sc material that is formed at a diameter that is similar in its initial low pressure configuration to the final higher pressure configuration. As the balloon  162 ′ is inflated, the waist length will reduce in length as the bevel regions  162 E migrate closer to the central waist  162 E as shown in  FIG. 7C . 
         [0071]    Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.