Patent Publication Number: US-2022226617-A1

Title: Guidewire and method of use

Description:
BACKGROUND 
     Conventional guidewires for angioplasty and other vascular procedures usually comprise an elongated core member with one or more tapered sections near the distal end thereof and a flexible body such as a helical coil disposed about the distal portion of the core member. A shapeable member, which may be the distal extremity of the core member or a separate shaping ribbon which is secured to the distal extremity of the core member extends through the flexible body and is secured to a rounded tip at the distal end of the flexible body. 
     In a typical coronary procedure, a guidewire having a preformed distal tip is percutaneously introduced into a patient&#39;s peripheral artery, e.g., the guidewire crosses a lesion to be dilated, then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient&#39;s coronary anatomy over the previously introduced guidewire until the balloon of the dilatation catheter is properly positioned across the lesion. Once in position across the lesion, the procedure is performed. 
     A requirement for guidewires is that they have sufficient column strength to be pushed through a patient&#39;s vascular system or other body lumen without kinking. However, guidewires must also be flexible enough to avoid damaging the blood vessel or other body lumen through which they are advanced. Efforts have been made to improve both the strength and flexibility of guidewires to make them more suitable for their intended uses, but these two properties are for the most part, diametrically opposed to one another in that an increase in one usually involves a decrease in the other. 
     Some guidewires have been formed from a superelastic alloy such as a nitinol (nickel-titanium or NiTi) alloy, to achieve both flexibility and strength. When stress is applied to nitinol alloy exhibiting superelastic characteristics at a temperature at or above which the transformation of martensite phase to the austenite phase is complete, the specimen deforms elastically until it reaches a particular stress level where the alloy then undergoes a stress-induced phase transformation from the austenite phase to the martensite phase. As the phase transformation proceeds, the alloy undergoes significant increases in strain but with little or no corresponding increases in stress. The strain increases while the stress remains essentially constant until the transformation of the austenite phase to the martensite phase is complete. Thereafter, further increase in stress are necessary to cause further deformation. 
     If the load on the specimen is removed before any permanent deformation has occurred, the martensitic phase of the specimen will elastically recover and transform back to the austenite phase. The reduction in stress first causes a decrease in strain. As stress reduction reaches the level at which the martensite phase transforms back into the austenite phase, the stress level in the specimen will remain essentially constant until the transformation back to the austenite phase is complete, i.e., there is significant recovery in strain with only negligible corresponding stress reduction. After the transformation back to austenite is complete, further stress reduction results in elastic strain reduction. This ability to incur significant strain at relatively constant stress upon the application of a load and to recover from the deformation upon the removal of the load is commonly referred to as superelasticity. These properties to a large degree allow a guidewire core of a superelastic material to have both flexibility and strength. 
     While the properties of the guidewire formed of the superelastic material were very advantageous, it was found that the guidewires and guiding members formed of materials having superelastic characteristics did not have optimum push and torque characteristics. 
     As is known in the art, many materials used for guidewire construction have desirable mechanical properties, but are difficult to assemble to other guidewire components using conventional technology such as soldering or use of polymer adhesives due to inherent surface properties such as tenacious oxide layers. In one prior art guidewire, a nitinol wire is joined to the proximal end of a stainless steel wire by either a hypotube/glue arrangement, or dissimilar weld. This joint typically has an abrupt stiffens transition from the nitinol to the stainless steel, has complex manufacturing steps, and is expensive to manufacture. 
     The present invention allows for the design of a guidewire with a unitary core, rather than a core with proximal and distal segments joined together. Additionally, the core member of the present invention may be used with other wire designs to create guidewires with improved superelasticity and kink-resistance. 
     SUMMARY OF THE INVENTION 
     It is an important aspect of the guidewire disclosed herein to utilize the structural features of a metal alloy having high yield strength for pushability and torque performance combined with a metal alloy having a high degree of elasticity for flexibility and trackability performance. 
     In one embodiment, an elongated tubular member has a proximal end and a distal end and includes an inner core member and an outer layer over the inner core member. The inner core member is formed from a first metal alloy and the outer layer is formed from a second metal alloy that is different than the first metal alloy. A feather edged joint defining a tapered transition segment is formed between the outer layer and the inner core member. Preferably a section of the outer layer is ground down to form the feather edged joint. The tapered transition segment extends from a first point on the outer layer where the nominal transverse wall thickness is constant, to a second point where the nominal transverse wall thickness of the outer layer is zero. In other words, the tapered segment extends between the first point where the wall thickness of the outer layer is thickest and then tapers (from the grinding process) to the second point where the wall thickness of the outer layer has been ground down to zero and the inner core member is exposed. In this embodiment, the inner core member is further ground at certain points along its length to form multiple tapered sections along a distal segment of the inner core member. Importantly, no portion of the outer layer surrounds the inner core member distal of the second point. 
     In one embodiment, a drawn filled tube has a proximal end and a distal end and includes an inner core member and an outer layer over the inner core member. The inner core member is formed from a first metal alloy and the outer layer is formed from a second metal alloy that is different than the first metal alloy. A feather edged joint defining a tapered transition segment is formed between the outer layer and the inner core member. Preferably a section of the outer layer is ground down to form the feather edged joint. The tapered transition segment extends from a first point on the outer layer where the nominal transverse wall thickness is constant, to a second point where the nominal transverse wall thickness of the outer layer is zero. In other words, the tapered segment extends between the first point where the wall thickness of the outer layer is thickest and tapered (from the grinding process) to the second point where the wall thickness of the outer layer has been ground down to zero and the inner core member is exposed. In this embodiment, the inner core member is ground at certain points along its length to form multiple tapered sections along a distal segment of the inner core member. Importantly, no portion of the outer layer surrounds the inner core member distal of the second point. 
     In one embodiment, the drawn filled tubing guidewire has a parabolic grind at a distal section thereof to take advantage of the nitinol inner core member. 
     In another embodiment, a pressure sensor is attached to a sensor pocket formed in a proximal section of a drawn filled tubing guidewire. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal cross-sectional view of a guidewire depicting an outer layer surrounding an inner core member. 
         FIG. 2  is a transverse cross-sectional view of the guidewire of  FIG. 1  taken along line  2 - 2 . 
         FIG. 3  is a longitudinal cross-sectional view of the guidewire of  FIG. 1  depicting a feather edged joint. 
         FIG. 4  is a transverse cross-sectional view of the guidewire of  FIG. 3  taken along line  4 - 4 . 
         FIG. 5  is a transverse cross-sectional view of the guidewire of  FIG. 3  taken along line  5 - 5 . 
         FIG. 6  is a longitudinal cross-sectional view of the guidewire depicting the feather edged joint and multiple distal section tapers. 
         FIG. 7  is a graph depicting the bending stiffness of a drawn filled tubing guidewire of the invention compared to a commercially available guidewire. 
         FIG. 8  is a graph depicting the bending stiffness of a drawn filled tubing guidewire of the invention compared to a commercially available guidewire. 
         FIG. 9  is a graph depicting the bending stiffness constant diameter wires including of a drawn filled tubing guidewire of the invention compared to a commercially available guidewire. 
         FIG. 10  is an elevational view of a prior art guidewire depicting a distal section having multiple tapered sections. 
         FIG. 11  is an elevational view of a guidewire depicting a distal section having a parabolic grind profile. 
         FIG. 12  is a graph depicting the bending stiffness along the distal section of the guidewires shown in  FIGS. 10 and 11 . 
         FIG. 13 . is a perspective view of a drawn filled tubing guidewire depicting a pressure sensor and sensor pocket. 
         FIG. 14  is a longitudinal cross-sectional view of the drawn filled tubing guidewire of  FIG. 13 . 
         FIG. 15  is a partial perspective view of the guidewire shown in  FIG. 13  depicting the pressure sensor attached to the sensor pocket. 
         FIG. 16A  is a longitudinal cross-sectional view of the guidewire shown in  FIG. 15  depicting a polymer sleeve covering the power and data cable. 
         FIG. 16B  is a transverse cross-sectional view taken along lines  16 B- 16 B depicting the polymer sleeve covering the power and data cable. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1-6  illustrate features of a guidewire  10  embodying features of the invention. A composite elongated tubular member  12  has a proximal end  14  and a distal end  16 . The elongated tubular member has an inner core member  18  that extends from the proximal end  14  to the distal end  16  and preferably is a solid core wire formed from a linear elastic alloy or a superelastic alloy. An outer layer  20  covers or surrounds the inner core member  18  along elongated tubular member  12 . A wall thickness  21  of the outer layer  20  is shown in  FIGS. 1, 3  and  6  and is sometimes referred to herein as a single wall thickness  21 . The outer layer  20  is formed from a precipitation hardenable material such as 35N LT, stainless steel, L605, MP35, MP35N, cobalt chromium, titanium, NiTiCo, NiTiCr, NiTi ternary alloys and similar metal alloys. More specifically, the outer layer  20  extends from the proximal end  14  in a distal direction to the distal end  16 . It is preferred that the outer layer  20  tightly surrounds the inner core member  18  with no space or gaps between the structures. The inner core member  18  is preferably formed from linear elastic or superelastic alloys and can include NiTi, CuNiTi, NiTiCr, NiTiCo, and similar metal alloys. The elongated tubular member  12  is typically drawn filled tubing (DFT) that is commercially available from several sources such as Fort Wayne Metals, Fort Wayne, Ind. 
     In one embodiment, shown in  FIGS. 1-6 , a portion of the outer layer  20  is ground down to expose the inner core member  18 . The outer layer has a proximal end  22  and a distal end  24  and a proximal segment  26  that extends from the proximal end  22  to a first point  28  that is closer to the distal end  24  than the proximal end  22 . In this embodiment, a feather edged joint  30  is formed by grinding down the outer layer  20  from the first point  28  to a second point  32 . The outer layer  20  is ground down so that the feather edged joint  30  forms a tapered transition segment  34  that gradually tapers from the first point  28  to the second point  32 . The tapered transition segment  34  of the feather edged joint  30  extends a length along the elongated tubular member  12  beginning at the first point  28  where the nominal transverse wall thickness of the outer layer  20  is a constant, and ends at the second point  32  where the nominal transverse wall thickness of the outer layer  20  is zero. The length of the tapered transition segment  34  extends from first point  28  to the second point  32  and preferably is in the range of 0.079 inch (2.0 mm) to 1.000 inch (25.4 mm). Importantly, one critical aspect of the invention is to form a joint between two dissimilar metals such as 35N LT (the outer layer  20 ) and linear elastic or superelastic nitinol (the inner core member  18 ), which traditionally is difficult or impossible to achieve by welding, brazing, or the like. The feather edged joint  30  provides a seamless transition between the two metals thereby significantly improving the structural aspects of the joint as well as enhancing the tactile feel for the physician. In this embodiment, the inner core member  18  is further ground down to form multiple distal tapers to enhance flexibility in the distal portion of the guidewire. Starting at the second point  32  on the inner core member  18  and moving distally to a third point  36 , the inner core member  18  has a first constant diameter section  40 . Starting at the third point  36  and moving distally to a fourth point  42 , the inner core member  18  is ground down to form a first tapered section  38 . The inner core member  18  has a second constant diameter section  48  extending from the fourth point  42  to a fifth point  46 . The inner core member  18  is ground down to form a second tapered section  44  extending from the fifth point  46  to a sixth point  50 . The inner core member  18  has a third constant diameter section  52  that extends from the sixth point  52  to the distal end  16  of the elongated tubular member  12 . Importantly, the nitinol distal portion of the guidewire having multiple tapers allows the guidewire to maneuver through tortuous anatomy without permanent deformation of the guidewire. 
     The overall length and diameter of guidewire  10  may be varied to suit the particular procedures in which it is to be used and is dependent on the materials from which it is constructed. Generally, the length of the guidewire  10  ranges from about 65 cm to about 350 cm, and more typically ranging from about 160 cm to about 200 cm. In one embodiment, the guidewire  10  is 180 cm long. 
     Commercially available guidewires for coronary and peripheral anatomy typically have lengths of about 175 cm or about 330 cm. Guidewire diameters generally range from about 0.008 inch to about 0.035 inch (0.2 to 0.9 mm), and more typically range from about 0.01 inch to about 0.018 inch (0.25 to 0.55 mm). Commercially available guide wires for coronary and peripheral use typically have diameters of 0.014 inch and 0.018 inch (0.036 mm and 0.46 mm, respectively). 
     As can be seen in Table 1, standard guidewire diameters are 0.014 inch, 0.018 inch, and 0.035 inch for most coronary and peripheral vessel applications. While other guidewire diameters are contemplated, these diameters comprise the vast majority of commercially available guidewires. Table 1 shows the ranges of diameters for a drawn filled tubing guidewire including nominal diameters and preferred diameters for the disclosed invention. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 (inches) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Standard 
                   
                   
                   
                   
                   
                   
                 Preferred 
               
            
           
           
               
               
               
               
               
            
               
                 Guidewire 
                 Overall DFT 
                 Preferred 
                 Nitinol Core 
                 Nitinol Core 
               
               
                 Diameters 
                 Wire Diameters 
                 Overall DFT 
                 Diameters 
                 Diameters 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
                 G 
                 H 
                 I 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 0.014 
                 0.013 
                 0.014 
                 0.0132 
                 0.0135 
                 0.0092 
                 0.0128 
                 0.0094 
                 0.0125 
               
               
                 0.018 
                 0.0165 
                 0.018 
                 0.017 
                 0.0175 
                 0.0142 
                 0.0148 
                 0.0143 
                 0.0145 
               
               
                 0.035 
                 0.029 
                 0.035 
                 0.028 
                 0.032 
                 0.025 
                 0.03 
                 0.026 
                 0.029 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 (inches)  
               
               
                 Double Wall Thickness  
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Wall  
                 Wall  
               
               
                 D-F  
                 D-H  
                 E-G  
                 E-I  
                 Thickness  
                 Thickness 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 0.004  
                 0.0038  
                 0.0007  
                 0.001  
                 0.0025  
                 0.0012  
               
               
                 0.0028  
                 0.0027  
                 0.0027  
                 0.003  
                 0.0029  
                 0.0015  
               
               
                 0.003  
                 0.002  
                 0.002  
                 0.003  
                 0.0035  
                 0.0018 
               
               
                   
               
            
           
         
       
     
     Referring to Table 1, a standard guidewire diameter for a DFT wire of 0.014 inch (column A) can range from 0.013 inch to 0.014 inch, as shown in columns B and C respectively. A preferred overall diameter DFT wire for the 0.014 inch wire (column A) can range from 0.0132 inch to 0.0135 inch, as shown in columns D and E respectively. The nominal nitinol core diameter range is shown in columns F and G, and the preferred nitinol core diameter range is shown in columns H and I. From Table 1, one can determine the overall diameter range for each of the three standard guidewires listed in column A, as well as the diameter ranges of the nitinol core wire. 
     The wall thickness of the outer layer  20  is derived from the dimensions set forth in Table 1. Referring to Table 2, by subtracting the preferred overall diameter of the DFT wire in column D from the nitinol core diameter in column F (0.0132 inch−0.0092 inch=0.004 inch), the wall thickness of the outer layer  20  is derived, as shown in column D-F. Since there are two wall thicknesses in the diameter dimension, the “average” wall thickness column in Table 2 is divided by two to obtain the wall thickness of the outer layer. For example, the preferred wall thickness for a 0.014 inch diameter guidewire is calculated by subtracting D (0.0132) from H (0.0094) to equal 
     
       
         
           
             
               
                 0 
                 . 
                 0 
               
               ⁢ 
               038 
                 
                inch 
             
             2 
           
         
       
     
     to equal 0.0019 inch wall thickness. The column headed “average” is calculated by the formula 
     
       
         
           
             
               
                 
                   ( 
                   
                     D 
                     - 
                     H 
                   
                   ) 
                 
                 + 
                 
                   ( 
                   
                     E 
                     - 
                     I 
                   
                   ) 
                 
               
               2 
             
             , 
           
         
       
     
     which is the total average wall thickness of the outer layer. The average wall thickness of a single layer of the outer layer is calculated in the column headed “average/2” and is calculated using the formula 
     
       
         
           
             
               
                 
                   ( 
                   
                     D 
                     - 
                     H 
                   
                   ) 
                 
                 + 
                 
                   ( 
                   
                     E 
                     - 
                     I 
                   
                   ) 
                 
               
               2 
             
             ÷ 
             2. 
           
         
       
     
     For example, in one embodiment, a 0.014 inch diameter DFT guidewire has an “average/2” outer layer single wall thickness  21  of 0.0012 inch 
     
       
         
           
             
               
                 
                   ( 
                   
                     D 
                     - 
                     H 
                   
                   ) 
                 
                 - 
                 
                   ( 
                   
                     E 
                     - 
                     I 
                   
                   ) 
                 
               
               2 
             
             ÷ 
             2. 
           
         
       
     
     In another embodiment, a 0.018 inch diameter DFT guidewire has an “average/2” outer layer single wall thickness  21  of 0.0015 inch. In another embodiment, a 0.035 inch diameter DFT guidewire has an “average/2” outer layer single wall thickness  21  of 0.0018 inch. 
     The guidewire  10  disclosed herein is formed from drawn filled tubing (DFT) and after processing as disclosed herein, including forming a feather edged joint  30 , has bending stiffness characteristics similar or superior to commercially available guidewires. As shown in the graphs of  FIGS. 7 and 8 , the bending stiffness of a DFT guidewire  10  is compared to that of a commercially available guidewire manufactured and sold by Abbott Cardiovascular Systems, Inc., Santa Clara, Calif. The bending stiffness from the distal tip of each guidewire to about 50 mm is similar and shows a high degree of flexibility due to a very low bending stiffness. From about 50 mm to about 150 mm, the DFT guidewire  10  has a higher bending stiffness than the commercial guidewire, which means that DFT guidewire  10  has better pushability and torque response than the commercial guidewire. 
     Referring to the graph in  FIG. 9 , the bending stiffness of a constant diameter guidewire of 0.0135 inch was compared among a superelastic nitinol guidewire, a 304V stainless steel guidewire, and a DFT guidewire. As can be seen in  FIG. 9 , the superelastic nitinol guidewire has a low and relatively constant bending stiffness. The DFT guidewire and the 304V stainless steel guidewire have similar high and relatively constant bending stiffness. Thus, comparing the graphs from  FIGS. 7 and 8  to  FIG. 9 , it can be seen that once the DFT guidewire  10  has the distal portion of the outer layer removed and the multiple tapers formed in the distal portion, the DFT guidewire performs as well or better than the commercially available guidewires. 
     The bending stiffness of the drawn filled tubing (DFT) disclosed herein can also be altered by applying a parabolic grind along the nitinol distal section of the guidewire. A parabolic grind profile was described in commonly owned and commonly assigned U.S. Ser. No. 16/671,044 filed Oct. 31, 2019, the entire contents of which are incorporated herein by reference. Rather than grinding the nitinol inner core member  18  as shown in  FIG. 6  with a first tapered section  38  and a second tapered section  44 , a parabolic grind can be applied instead. Thus, referring to  FIGS. 31-33  of U.S. Ser. No. 16/671,044, now renumbered as  FIGS. 10-12  herein, the distal section of the guidewire is reduced in cross-section to be more flexible when navigating tortuous vessels, such as coronary arteries. The distal section of the guidewire must be both flexible and pushable, that is the distal section must flex and be steerable through the tortuous arteries, and also have some stiffness so that it can be pushed or advanced through the arteries without bending or kinking. A prior art guidewire is shown in  FIG. 10  and has a distal section comprised of tapered sections and core sections with no taper. The resulting bending stiffness is shown in the graph in  FIG. 12  wherein the bending stiffness decreases at each tapered position, and the bending stiffness remains constant along the core section that is not tapered. The tapered distal section of the prior art guidewire of  FIG. 10  provides abrupt changes in bending stiffness that can reduce the tactile feel to the physician when advancing the guidewire through tortuous anatomy. In fact, in some prior art guidewires, the abrupt change in bending stiffness can result in the distal tip of the guidewire to kink or prolapse into a side branch vessel. Prolapse can be dangerous to the patient in that the artery can be damaged or punctured. Importantly, it is preferred to maintain the outer diameter of the core section as far distal as possible to maintain torque. Each tapered section loses torque, which is critical in advancing the guidewire through tortuous vessels. 
     In keeping with the invention, a parabolic distal section  62  of a guidewire  60  is shown in  FIG. 11  wherein a significant portion of the distal section has been ground to form a continuous taper. More specifically, the continuous taper is formed by a parabolic grind along parabolic distal section  62  of the guidewire  60 . The parabolic grind provides a smooth curvilinear transition along section  62  that is highly flexible and yet maintains a linear change in stiffness as shown in the graph of  FIG. 12 . Not only is parabolic distal section  62  flexible, but it has a linear change in stiffness thereby providing excellent torque and tactile feedback to the physician when advancing the guidewire through tortuous anatomy. A tapered section  64  that is not curvilinear (not a parabolic grind section) is located on the guidewire  60  distal of the parabolic distal section  62  and it provides reduced bending stiffness and a linear change in bending stiffness as shown in the graph of  FIG. 12 . It is intended that the parabolic grind profile be applied to only the nitinol inner core member along the parabolic distal section  62 . 
     Bending stiffness can be measured in a variety of ways. Typical methods of measuring bending stiffness include extending a portion of the sample to be tested from a fixed block with the sample immovably secured to the fixed block and measuring the amount of force necessary to deflect the end of the sample that is away from the fixed block a predetermined distance. A similar approach can be used by fixing two points along the length of a sample and measuring the force required to deflect the middle of the sample a fixed amount. Those skilled in the art will realize that a large number of variations on these basic methods exist including measuring the amount of deflection that results from a fixed amount of force on the free end of a sample, and the like. Other methods of measuring bending stiffness may produce values in different units of different overall magnitude, however, it is believed that the overall shape of the graph will remain the same regardless of the method used to measure bending stiffness. 
     The embodiments of the drawn filled tubing (DFT) guidewire disclosed herein are particularly suitable for use in conjunction with a pressure sensor. During some medical interventions, it may be desirable to measure and/or monitor the blood pressure within a blood vessel. For example, some medical devices may include pressure sensors that allow a clinician to monitor blood pressure. Such devices may be useful in determining fractional flow reserve (FFR), which may be understood as the pressure after a stenosis relative to the pressure before the stenosis. A number of pressure sensing devices, however, may pose technical challenges for steering, tracking, torqueing or otherwise navigating the device within the vasculature. For example, medical devices may include a relatively stiff pressure sensor located at or near the distal tip of the device and/or a sensor housing (in which the sensor is mounted) that may also be relatively stiff. Disclosed herein are a number of medical device that include pressure sensing capabilities and may be more easily steered, tracked, torqued, and/or otherwise navigated through the anatomy. The DFT guidewire of the present invention is used to carry a pressure sensor through the coronary and peripheral vessels to measure blood pressure and possibly FFR, as well as other measurements. 
     In one embodiment, shown in  FIGS. 13-16B , a drawn filled tubing (DFT) guidewire  70  is processed according to the embodiment shown in  FIGS. 1-6 . The difference, however, is in this embodiment the proximal section  72  is adapted to carry a pressure sensor  74  (or any other type of measuring device). The pressure sensor  74  can be any sensor known in the art and may include a semiconductor (e.g., silicon wafer) pressure sensor, piezoelectric pressure sensor, a fiber optic or optical pressure sensor, a Fabry-Perot type sensor, an ultrasound transducer and/or ultrasound pressure sensor, a magnetic pressure sensor, a solid-state pressure sensor, and the like. In this embodiment, a sensor pocket  76  is formed in the proximal section  72  of the drawn filled tubing  70  for mounting the pressure sensor  74 . The sensor pocket  76  can be formed by grinding the outer surface  78  of DFT guidewire  70  to a depth and shape that is configured to receive the pressure sensor  74  without compromising the integrity of the DFT guidewire  70 . Also, it is preferred that the pressure sensor  74  be configured so as to not disrupt blood flow or impede the movement of the DFT guidewire  70  through the vasculature. Preferably, the sensor pocket  76  is positioned on the DFT guidewire  70  just proximal of the tapered transition segment  80  where the outer layer  82  is first ground down to form the tapered transition segment  80 . The grinding procedure for forming the sensor pocket  76  can be performed by any method well known in the prior art. 
     Pressure sensors  74  are well known in the art and can take many different sizes and shapes. As shown in  FIG. 15 , for example, the pressure sensor  74  has a contoured outer surface  84  to conform to the curved outer surface  78  of the DFT guidewire  70  so that there are no sharp edges that could cause injury to the vasculature. The pressure sensor  74  can be attached to the sensor pocket  76  by any known means including adhesive, laser welding, soldering, brazing, and the like. 
     In further reference to  FIGS. 13-16B , a power and data transmission cable  86  is attached to the pressure sensor  74  and the cable  86  extends proximally along the outer surface  78  of the DFT guidewire  70  to a location outside of the patient so that it can be attached to the appropriate monitoring equipment. A polymer sleeve  88  is formed over the cable  86  and at least a portion of the outer surface  78  of the DFT guidewire  70  in order to protect the cable  86  and prevent it from interfering with the movement of the guidewire in the vasculature. While a polymer sleeve  88  is preferred, other covers are contemplated such as polymer bands, radiopaque marker bands, braided materials, and the like. 
     It is preferred that the sensor pocket  76  and the attached pressure sensor  74  be positioned very close to the tapered transition segment  80 , but proximal thereto. In one embodiment, a distal edge  90  of the sensor pocket  76  is a length  94  between 0.1 mm and 30.0 mm from a first point  92  which marks the beginning of the tapered transition segment  80 . In another embodiment, the length  94  is between 0.1 mm and 10.0 mm. 
     Referring to  FIG. 14 , the depth of the sensor pocket  76  is shown to be equal to the thickness of the outer layer  82 . Depending on the thickness of the pressure sensor  74 , the depth of the sensor pocket  76  can be more or less than depicted in  FIG. 14 , and extends into an inner core member  96  which is formed from nitinol as previously described. It is preferred that the depth of the sensor pocket  76  into the inner core member be minimal, however, it is possible that the sensor pocket  76  extends half way through the diameter of the DFT guidewire  70 , which means the pocket would extend well into the nitinol inner core member  96 . 
     Guidewires like the ones disclosed herein typically will have one or more coils attached to the distal end as well as a solder structure, neither of which are shown. Further, the drawn filled tubing is manufactured by know means and need not be further described. The multiple distal tapers are formed by centerless grinding machines and the method of grinding is well known and need not be further described. 
     With respect to the embodiment shown in  FIGS. 13-16B , the DFT guidewire  70  has an inner core member  96  extending the entire length of the guidewire  70 . In some embodiments, it is preferred that the inner core member  96  extend only in a distal portion of the guidewire so that the outer layer  82  covers only a short length of the proximal end of the inner core member  96 . In one embodiment, the outer layer  82  overlaps and covers less than 2.5 cm of the proximal end of the inner core member  96 . 
     While the present invention has been described and illustrated in terms of its use as an intravascular guidewire, it will be apparent to those skilled in the art that the present invention can be applied to other medical devices. Moreover, modifications and improvements may be made to the above-described exemplary embodiments without departing from the scope of the invention.