Abstract:
A sensor and guide wire assembly ( 21; 41; 61; 81 ) for intravascular measurements of a physiological variable in a living body includes a sensor element ( 22; 42; 62; 82 ) mounted at a distal sensor portion ( 23; 43; 63; 83 ) of a guide wire ( 24; 44; 64; 84 ), wherein the sensor portion exhibits a maximal cross-sectional dimension which is larger than a maximal cross-sectional dimension of guide wire portions ( 28, 30; 48, 50; 68, 70 ) located proximally of the sensor portion.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to a sensor mounted in a distal portion of a guide wire for intravascular measurements of physiological variables in a living body, and in particular to the design of said distal portion. 
       BACKGROUND OF THE INVENTION 
       [0002]    Sensor and guide wire assemblies in which a sensor, adapted for measurements of physiological variables in a living body, such as blood pressure and temperature, is mounted at a distal portion of a guide wire are known. 
         [0003]    For example, the U.S. Pat. No. Re. 35,648, which is assigned to the present assignee, discloses a sensor and guide wire assembly comprising a sensor element, an electronic unit, signal transmitting cables connecting the sensor element to the electronic unit, a flexible tube having the signal cables and the sensor element disposed therein, a solid metal wire, and a coil attached to the distal end of the solid wire. The sensor element comprises a pressure sensitive device, e.g. a membrane, with piezoresistive elements electrically connected in a Wheatstone bridge-type of circuit arrangement mounted thereon. The entire contents of the &#39;648 patent are incorporated herein by reference for additional details of equipment, methods, and techniques for such measurements. 
         [0004]    The sensor element is usually provided in the form of a silicon chip, which besides the pressure sensitive device also comprises integrated electronic circuits. For various reasons it is desired to include ever more functionality in the electronic circuits. This need has so far been met by the general miniaturization trend that exists in the chip technology, which allows more functionality and more complex circuits to be integrated in a comparatively smaller area, or, in the three-dimensional case, in a smaller volume. Such miniaturization is extremely important within the field of guide wire mounted sensors, because the outer diameter of the sensor guide wire is in practice limited by the inner diameter of a catheter which in a so-called PCI (Percutan Coronar Intervention) is used for the treatment of a stenosis present in a blood vessel and which is threaded over the sensor guide wire and advanced to the site of interest. The standard inner diameter of such catheters is 0.35 mm (0.014 inches); and consequently the standard outer diameter of most guide wires, and in particular of sensor guide wires, is therefore 0.35 mm (0.014 inches). 
         [0005]    However, the miniaturization of electronic circuits and chips is a difficult task, and it is far from certain that the chips industry can provide sensor chips which fulfil the future requirements for mounting in a guide wire adapted for intravascular measurements. 
         [0006]    Consequently, there is a need for a guide wire design that provides more space for a sensor element, while at the same time allows use together with a standard catheter. 
       SUMMARY OF THE INVENTION 
       [0007]    Embodiments of the present invention are directed to a sensor and guide wire assembly comprising a sensor element which is mounted in a distal portion of a guide wire. According to embodiments of the invention, a distal portion is provided which has a larger diameter than the rest of the guide wire, to thereby provide more space for the sensor element. The inventor has observed that a catheter very rarely (or never) is advanced over the distal tip of the guide wire, and has realized that a distal portion of a guide wire can have a larger diameter than the rest of the guide wire. A hollow distal portion having a larger diameter provides more space for a sensor element (and/or other devices) mounted within this distal portion. 
         [0008]    According to the different embodiments disclosed below, an enlarged distal sensor portion can include the entire distal end of the sensor guide wire, but can also be restricted to the sensor portion, with the short distal end portion of the guide wire being smaller than the enlarged sensor portion. 
         [0009]    Further, the sensor and guide wire assembly can be of a relatively well-known design (see, e.g., the above-referenced Re  35 , 648 ), with electrical leads that extend along the length of the guide wire and connect the sensor element to a male connector at the proximal end of the sensor guide wire; or the sensor and guide wire assembly can be of a wireless type, in which the sensor element wirelessly communicates with an external unit. Especially in the latter case, there is a need for very complex electronics and therefore a need for more space within the guide wire. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic illustration of a sensor and guide wire assembly according to the prior art. 
           [0011]      FIG. 2  shows a cross-sectional view of a first embodiment of a sensor and guide wire assembly according to the present invention. 
           [0012]      FIG. 3  shows a cross-sectional view of a second embodiment of a sensor and guide wire assembly according to the present invention. 
           [0013]      FIG. 4  shows a cross-sectional view of a third embodiment of a sensor and guide wire assembly according to the present invention. 
           [0014]      FIG. 5  shows a cross-sectional view of a fourth embodiment of a sensor and guide wire assembly according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0015]      FIG. 1  illustrates schematically the general design of a sensor and guide wire assembly  1  according to the prior art. The sensor and guide wire assembly  1  comprises a sensor element  2 , which is arranged in a distal portion  3  of a sensor guide wire  4 . More specifically, the sensor guide wire  4  comprises a distal tip  5 , a distal coil spring  6 , a jacket or sleeve  7 , a flexible distal tube  8 , which also could be in the form of a coil spring, a core wire  9 , and a proximal tube  10 . The distal coil spring  6  is attached to the distal tip  5 , and extends to the jacket  7 , which serves as a housing for the sensor element  2 . The flexible distal tube  8  extends between the jacket  7  and the proximal tube  10 . The sensor element  2  is mounted in a recess in a distal portion of the core wire  9 , and is through a window in the jacket  7  in fluid communication with the medium, e.g. blood, surrounding the sensor and guide wire assembly  1 . The sensor and guide wire assembly  1  comprises further a number of signal transmitting cables  11 , the distal ends of which are electrically connected to the sensor element  2  and which extend along the core wire  9  to the proximal end portion of the sensor guide wire  4 , where each signal transmitting cable  11  is electrically connected to a conductive member  12 . The conductive members  12  are electrically insulated from the core wire  9  as well as from each other by insulating members  13 , so as to form a male connector adapted for connection to a corresponding female connector of an external signal conditioning and display unit (not shown in  FIG. 1 ) for displaying the measured quantities, e.g. pressure, temperature and/or flow. 
         [0016]    From  FIG. 1 , which is intended to present the essential elements of a sensor and guide wire assembly according to prior art, it may be appreciated that there is only a limited amount of space available for the sensor element. Throughout the present specification, the term “sensor element” as applied to pressure measurement is meant to encompass both the pressure sensitive member, e.g. a membrane, as well as the electronic components and circuits that are connected to the pressure sensitive member. It is even contemplated that a sensor element comprises a pressure sensitive part and an electronic part, which are connected by at least one electrical lead. The latter arrangement is disclosed in the U.S. patent applications Ser. Nos. 11/063,744 and 11/359,761, both of which are assigned to the present assignee and whose entire contents are incorporated herein by reference for additional details of equipment, methods, and techniques for such arrangements. In a preferred embodiment of these patent applications, the pressure sensitive member and the electronic circuitry are incorporated in a silicon chip with integrated circuits. 
         [0017]    A first embodiment of a sensor and guide wire assembly  21  according to the present invention is disclosed in  FIG. 2 , which illustrates that the sensor and guide wire assembly  21  comprises a sensor element  22 , which is arranged in a distal portion  23  of a sensor guide wire  24 . More specifically, the sensor guide wire  24  comprises a distal tip  25 , a distal coil spring  26 , a jacket or sleeve  27 , a flexible distal tube  28 , a core wire  29 , and a proximal tube  30 . The distal coil spring  26  is attached to the distal tip  25 , and extends to the jacket  27 , which serves as a housing for the sensor element  22 . The flexible distal tube  28 , which also could be in the form of a coil spring, extends between the jacket  27  and the proximal tube  30 . The sensor element  22  is mounted in a recess in a distal portion of the core wire  29 , and is through a window in the jacket  27  in fluid communication with the medium, e.g. blood, surrounding the sensor and guide wire assembly  21 . The sensor and guide wire assembly  21  comprises further a number of signal transmitting cables  31 , the distal ends of which are electrically connected to the sensor element  22  and which extend along the core wire  29  to the proximal end portion of the sensor guide wire  24 , where each signal transmitting cable  31  is electrically connected to a conductive member  32 . The conductive members  32  are electrically insulated from the core wire  29  as well as from each other by insulating members  33 , so as to form a male connector adapted for connection to a corresponding female connector of an external signal conditioning and display unit (not shown in  FIG. 2 ). 
         [0018]    A comparison between  FIG. 1  and  FIG. 2  reveals that the sensor guide wire  24  shown in  FIG. 2  is provided with a jacket  27  which is enlarged in comparison with the corresponding jacket  7  of the sensor guide wire  4  illustrated in  FIG. 1 . The enlargement of the jacket  27  provides more space for the sensor element  22  (and/or other devices), which consequently can comprise more electrical components and more complex functionality. In the first embodiment illustrated in  FIG. 2 , the jacket  27  is not the only portion of the sensor guide wire  24  that has a diameter which is enlarged in comparison with the diameters of the more proximal portions of the sensor guide wire  24 . As can be seen, the diameters of the distal tip  25  and the distal coil spring  26  are also larger than the diameters of the flexible distal tube  28  and the proximal tube  30 . In other words, in this embodiment, an enlarged distal sensor portion  23  encompasses the distal tip  25 , the distal coil spring  26  and the jacket  27 , and constitutes the extreme distal portion of the sensor guide wire  24 . By making the diameter of the distal coil spring  26  equal to the diameter of the jacket  27  the assembly of the sensor and guide wire assembly  21  is simplified, because it is relatively easy to fit the distal coil spring  26  to the jacket  27  and to match the mechanical characteristics of these two elements to each other as there is no abrupt transition from the jacket  27  to the distal coil spring  26 . 
         [0019]      FIG. 3  illustrates a second, alternative embodiment of a sensor and guide wire assembly  41  according to the present invention, and shows that the sensor and guide wire assembly  41  comprises a sensor element  42 , which is arranged in a distal portion  43  of a sensor guide wire  44 . More specifically, the sensor guide wire  44  comprises a distal tip  45 , a distal coil spring  46 , a jacket or sleeve  47 , a flexible distal tube  48 , a core wire  49 , and a proximal tube  50 . The distal coil spring  46  is attached to the distal tip  45 , and extends to the jacket  47 , which serves as a housing for the sensor element  42 . The flexible distal tube  48 , which also could be in the form of a coil spring, extends between the jacket  47  and the proximal tube  50 . The sensor element  42  is mounted at a distal portion of the core wire  49 , and is through a window (not visible in  FIG. 3 ) in the jacket  47  in fluid communication with the medium, e.g. blood, surrounding the sensor and guide wire assembly  41 . The sensor and guide wire assembly  41  comprises further a number of signal transmitting cables  51 , the distal ends of which are electrically connected to the sensor element  42  and which extend along the core wire  49  to the proximal end portion of the sensor guide wire  44 , where each signal transmitting cable  51  is electrically connected to a conductive member  52 . The conductive members  52  are electrically insulated from the core wire  49  as well as from each other by insulating members  53 , so as to form a male connector adapted for connection to a corresponding female connector of an external signal conditioning and display unit (not shown in  FIG. 3 ). 
         [0020]    In contrast to the first embodiment depicted in  FIG. 2 , the jacket  47  constitutes the only portion of the sensor guide wire  44  that has an enlarged diameter; and in particular the distal tip  45  and the distal coil spring  46  have both a diameter that is equal to the diameter of the flexible distal tube  48  and the proximal tube  50 . Due to its small diameter, the distal end portion (i.e. the coil spring  46 ) of the sensor guide wire  44  can be made very flexible, which can be advantageous in some medical applications, such as when the sensor guide wire is manoeuvred through extremely tortuous vessels. 
         [0021]    As was briefly mentioned above, it is foreseen that a sensor element can communicate wirelessly with an external unit. In this case, the physical requirements put on the sensor element are considerably higher than in the wired case, because the sensor element must be able to receive energy via electromagnetic signals and communicate signals that are modulated in accordance with the sensed measurements. A schematic illustration of a wireless sensor and guide wire arrangement is shown in  FIG. 4 . In this third embodiment of the present invention, a sensor and guide wire assembly  61  comprises a sensor element  62 , which is arranged in a distal portion  63  of a sensor guide wire  64 . More specifically, the sensor guide wire  64  comprises a distal tip  65 , a distal coil spring  66 , a jacket or sleeve  67 , a flexible distal tube  68 , a core wire  69 , and a proximal tube  70 . The distal coil spring  66  is attached to the distal tip  65 , and extends to the jacket  67 , which serves as a housing for the sensor element  62 . The flexible distal tube  68 , which also could be in the form of a coil spring, extends between the jacket  67  and the proximal tube  70 . The sensor element  62  is mounted to a distal portion of the core wire  69 , and is through a window (not visible in  FIG. 4 ) in the jacket  67  in fluid communication with the medium, e.g. blood, surrounding the sensor and guide wire assembly  61 . 
         [0022]    The third embodiment discussed in conjunction with  FIG. 4  differs from the first and second embodiments of the present invention shown in  FIG. 2  and  FIG. 3 , respectively, in that there are no signal transmitting cables provided. The sensor element  62  is instead capable of communicating with an external unit by electromagnetic signals, i.e. there is a wireless communication between the sensor element  62  and the external unit (not shown in  FIG. 4 ). In this case, the physical requirements put on a sensor element are considerably higher than in the wired case, since the sensor element must be able to receive energy from some type of carrier signals and then communicate signals that are modulated in accordance with the sensed measurement. Other types of wireless communications are also possible, e.g. that the sensor is powered by a battery and only output signals are received by an external unit. Generally, the more functionality that is incorporated in a sensor element, the larger is the space required for the electronic circuits; and a sensor guide wire that provides a larger space for the sensor element is particularly advantageous for a wireless sensor and guide wire assembly. 
         [0023]    In the third embodiment of  FIG. 4 , the general structure of the sensor guide wire  64  is the same as in the first and second embodiments, i.e. the sensor guide wire  64 , like sensor guide wires  24  and  44 , respectively, comprises a core wire as well as proximal and distal tubes. When a wireless sensor element is used, the design of a sensor guide wire can be significantly changed, due to the fact that signal transmitting cables can be dispensed with. In a fourth embodiment of the invention, which is schematically illustrated in  FIG. 5 , a sensor and guide wire assembly  81  adapted for wireless communication comprises a sensor element  82 , which is arranged in a distal portion  83  of a sensor guide wire  84 . More specifically, the sensor guide wire  84  comprises a distal tip  85 , a distal coil spring  86 , and a housing  87 . The distal coil spring  86  is attached to the distal tip  85 , and extends to the housing  87 , in which the sensor element  82  is disposed. In this embodiment, it should be noted that there is no separate core wire and no proximal tube, as the sensor guide wire  84  is made from a solid wire, typically a metal wire. Further, the housing  87  is formed integrally with the solid wire that constitutes the sensor guide wire  84 , and it can furthermore be noted that the housing  87  only projects out from a part of the circumference of the sensor guide wire  84 . With this design, the mechanical characteristics of the sensor guide wire  84  can be improved, e.g. regarding torsional rigidity and bending stiffness. 
         [0024]    As already has been discussed, the present invention is based on the observation that a catheter which is threaded onto a sensor guide wire never is advanced over the distal end of the sensor guide wire, and an enlarged distal sensor portion will consequently not prevent an effective use of a combination of a sensor guide wire and a catheter. As the person skilled in the art will recognize, there is a significant difference between a (sensor) guide wire and a catheter, for example, in that a catheter completely lacks steering capability, i.e. the catheter must be guided to the site of interest by means of a guide wire. For a standard sensor guide wire having an outer diameter of 0.35 mm (0.014 inches), which corresponds to the inner diameter of a standard catheter, the enlarged sensor portion is preferably less than 2 mm, and in particular less than 1 mm. The enlarged portion may be, for example, 10% larger (or 25%, or 50%, or 100% larger) than the non-enlarged portion. 
         [0025]    Although the present invention has been described with reference to specific embodiments, also shown in the appended drawings, it will be apparent for those skilled in the art that many variations and modifications can be done within the scope of the invention as described in the specification and defined with reference to the claims below. It should in particular be noted that a sensor portion that is enlarged in comparison with the more proximal portions of a sensor guide wire can be symmetrical, i.e. having a larger diameter than the diameters of the more proximal portions but with the same centre, or can be asymmetric or non-circular, i.e. where only a sector of the cross-section has a larger radius than the more proximal portions, an example of which was illustrated in conjunction with  FIG. 5 , the important feature being that the sensor portion exhibits a maximal cross-sectional dimension that is larger than the maximal cross-sectional dimension of the guide wire portions located proximally of the sensor portion. Said cross-sectional dimension should be taken perpendicular to the central axis of the sensor guide wire. Consequently, the corresponding relationship and definition applies also for a distal end portion being smaller than the enlarged sensor portion, an example of which was discussed in conjunction with  FIG. 3 .