Abstract:
A sensing guidewire device used to measure physiological parameters within a living body. In one embodiment, the device is used to measure the fractional flow reserve (FFR) across a stenotic lesion in a patient&#39;s vasculature. The device includes a sensor that is adapted to be affixed near the distal end of a guidewire. The guidewire contains a corewire, processed to enclose electrical conductors in a sealed, off-centered interstice or channel, with an outer diameter approximate to the outer diameter of the device, running substantially the full length of the device, and has a homogenous outer surface. The enclosed eccentric channel provides space for electrical conductors to move freely. The corewire can have a tapered segment to create desirable flexibility. A solid connector comprised of alternating conductive and insulating elements for connecting the conductors to an external device is disclosed. The guidewire can be advanced through a patient&#39;s blood vessels, returning pressure measurements across vessel blockages that allow for accurate assessment of blockage severity and lead to better clinical outcomes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional patent application No. 62/290,779 entitled “Guidewire with sensor”, filed Feb. 3, 2016, and from U.S. Provisional patent application No. 62/379,814 entitled “Modular Sensing Guidewire”, filed Aug. 26, 2016, both of which are incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to the field of measuring physiological parameters within a living body. 
       BACKGROUND OF THE INVENTION 
       [0003]    While there are different ways to measure physiological parameters, the most accurate measurements often require having the sensor in close physical proximity to the anatomy of interest. Characterizing stenotic lesions within a blood vessel can be done by passing a sensor through the stenotic lesion to measure directly pressure drop or other physiological parameters. In minimally invasive non-surgical techniques, the way to gain access to the anatomy is by inserting a guidewire from outside a patient&#39;s body, through the patient&#39;s vasculature, to the anatomical site of interest. The guidewire&#39;s ability to successfully navigate through vasculature and across stenotic lesion sites without injury is an important performance parameter that determines user preference, whether the guidewire contains a sensor or not. 
         [0004]    Looking at current practice for the characterization of stenotic lesions, and in particular those relating to coronary artery disease (CAD), an access guidewire is inserted into a patient&#39;s vasculature. Once a desired location has been accessed, a catheter is fed over the access guidewire which is then removed leaving the catheter in a place to facilitate advancement of a second guidewire designed for use in the coronary vasculature. This guidewire can include a sensor at its distal tip. The sensor guidewire is advanced through the catheter. Upon exiting the catheter, the sensor guidewire is advanced through the vasculature where blood pressure or other important physiological parameters are measured. Stenotic lesions are characterized by abnormal or abrupt changes in blood pressure or flow, so the device operator can identify the location of a clinically significant stenotic lesion by making a measurement before and after the blockage. 
         [0005]    Fractional Flow Reserve (FFR) is a ratio of blood pressure measurements before and after a stenotic lesion under hyperemic conditions. Data collected using this methodology has established important thresholds for guiding therapeutic decisions. Importantly, the guidewire must be able to be advanced through the vasculature and across the lesion site to make this measurement. 
         [0006]    Currently, treatment of stenoses in arteries is predominantly guided by x-ray imaging techniques. In interventional cardiology, one such x-ray technology is fluoroscopy. Angiography is a technique of injecting radiopaque dye into arteries using fluoroscopic equipment, which has proven to be useful in identifying stenotic lesions. However, patients with CAD often have blockages at more than one site. This creates a challenge for the operator treating the patient. An operator must correctly determine which of multiple blockages are causing the symptoms which prompted the procedure. An angiogram presents a two dimensional view of a three dimensional phenomena, blood flow through a vessel. Angiographic images can over-represent or under-represent the perceived degree of blockage. Important clinical studies have shown that patients treated using a FFR pressure wire to guide treatment instead of fluoroscopy alone have improved outcomes. These studies have shown that not treating a clinically significant stenotic lesion has a deleterious impact on patient outcomes. Less intuitively, treating stenotic lesions that are clinically insignificant also have a deleterious impact on patient outcomes. Thus, a patient afflicted with multiple stenotic lesions is best served by only treating clinically significant lesions and leaving the clinically insignificant lesions untreated. Clinical studies have consistently demonstrated that treatment guidance for blocked coronary arteries using physiological measurements have consistently outperformed image guidance alone in improving patient outcomes. 
         [0007]    Most coronary guidewires used today do not have sensors. Non-sensing guidewires have designs optimized to cross stenotic lesions in coronary arteries. The most frequently used coronary guidewires employ a solid corewire. A solid wire enables the superior pushing capability needed to advance the device in the body, is kink resistant, and has exceptional tip control needed to navigate through bends, twists and turns in vessel vasculature. It also provides stable support for delivering catheters and stents. Stability means the coronary guidewire does not back out of the artery and lose position as therapeutic devices are advanced over the guidewire. A coronary guidewire is typically approximately 355 microns in diameter or less. Consequently, optimizing material characteristics is an important aspect in extracting maximum performance from such a miniature device. A solid corewire is typically made using a cold work forming process that enhances mechanical strength. Guidewires of this type, which are most frequently used, while optimized in design for crossing stenotic lesions lack sensing capabilities to measure abnormal pressure drops using FFR techniques, which are needed to effectively guide treatment. 
         [0008]    Prior art patents related to guidewire capabilities are numerous, including, for example, U.S. Pat. Nos. 4,958,642 and 5,226,423, which describe guidewire assemblies with sensors and interconnect cables. While these devices enable making FFR measurements, they are less than optimal in their performance with respect to navigating through anatomy, and are expensive to manufacture. Such FFR guidewires use long, hollow tubular structures to route wires needed to connect the sensor at the tip of the wire to a processor outside the patient&#39;s body. The sensor guidewire&#39;s hollow tube is unable to be processed in the same manner as a solid corewire to enhance mechanical strength, compromising the mechanical performance of these sensing guidewires compared to non-sensing guidewires. A hollow tube&#39;s inherently lower strength makes it more susceptible to kinking, taking a curved set and generally deforming more readily than a guidewire made from a cold drawn solid corewire. Moreover, such FFR guidewires use multiple discrete components assembled together requiring expensive labor intensive processes. These designs also lack the seamless and progressive guidewire transition from stiff to flexible that traditional non-sensing guidewires offer with their unitary solid corewire construction. 
         [0009]    In U.S. Pat. No. 5,406,960 a corewire with grooves is used in a coronary guidewire. The grooved corewire provides space to place radiopaque bands to enhance visibility under fluoroscopy. 
         [0010]    U.S. Pat. No. 5,797,856 describes a tubular member coaxially disposed on a solid corewire to make a guidewire with improved torque transmission capabilities. However, a clearance of 0.001-0.003 inches is specified between the inner flexible member and outer tubular member, which compromises guidewire performance, given the entire guidewire outer diameter could be as small as 0.014 inches. Moreover, the outer and inner members are secured using adhesive or threading, which precludes the insertion of wiring needed to power a sensor and to transmit electrical signals from the sensor to an external instrument. 
         [0011]    U.S. Pat. Nos. 8,231,537 and 8,277,386 describe a sensor assembly with a solid corewire with wires routed external to the solid corewire within channels in a tubular insulator. This construction yields a solid core of inadequate diameter because of the space required to contain individual conductors and a sleeve to cover them. 
         [0012]    U.S. Patent App. No. 2010/0228112, and related U.S. Pat. Nos. 8,852,125, 8,226,578 and 8,551,022, may provide a helically grooved corewire for use in a sensor guidewire for better predictability in guidewire movement. The helical winding is intended to preclude energy from being built up during guidewire rotation. In one embodiment the electrical wires in the grooves are left uncovered in order to achieve maximal corewire outer diameter, which, however, exposes delicate electrical wiring during use, potentially reducing device reliability and increasing risk of patient injury. In another embodiment, a proximal cover is fitted over the corewire to protect the microcables. The cover reduces the outer diameter of the corewire, thereby compromising the guidewire handling performance. 
         [0013]    U.S. Patent App. Nos. 2013/0296722 and 2013/0237864 describe a guidewire using a different electrical circuit to measure pressure which allows replacing a hollow tubular member with a solid core. Such highly miniaturized complex electrical circuit components and a sensor to fit into a guidewire, are significant and expensive technological challenges, which are difficult to overcome in today&#39;s cost constrained healthcare environment. 
         [0014]    U.S. Patent App. No. 2015/0032027 describes a guidewire with grooves cut into a solid core using secondary processes like grinding, machining or laser etching. Insulated wires are inserted into the grooves to provide electrical conduction. How to contain the electrical wires in the grooves is not addressed, and as the electrical wires are subjected to severe bending, torque, and manipulation, such manipulation can unravel the wires set into the channels. Stress acting on the structure is greatest at the outer surface, consequently, the electrical conductors when spirally wound or adhered onto the solid core are subjected to forces that can break the wires causing device failure. Loose wires extending from a device advanced by pushing through delicate vasculature presents safety risks to the patient. 
         [0015]    Pressure or sensor wires utilizing hollow tubes to route wires or other signal conductors necessitate the use of a connection cable to relay signals from the sensor to an external instrument. Typically, a subassembly for connection is built into the proximal most segment of the hollow tube. The interconnecting subassembly must provide for secure engagement and coupling to a cable to pass signals from the sensor to an external instrument. These couplings are prone to damage because of frail designs necessitated, in part, by the use of hollow tubes. They are also prone to failure because of susceptibility to contamination from blood, saline or other liquids commonly spilled on the device during the course of use. 
         [0016]    Prior art sensor guidewires have significant design and performance shortcomings, and are expensive due to labor intensive assembly and manufacturing costs, and consequently represent a small fraction of the guidewires used in today&#39;s coronary interventions. 
         [0017]    There remains a need for a sensor guidewire that can navigate tortuous vascular anatomy with the same degree of success as non-sensing guidewires. Such a device would ideally eliminate the hollow tube currently employed as a structural element, in order to improve flexibility. Moreover, an improved delivery platform utilizing existing electrical circuit and sensor components is desirable in order to reduce development expenses, commercialization timelines and device cost. A more robust and reliable connection to a cable to route signals from the pressure or sensor wire to an external instrument is needed. Additionally, there is a need for a modern technology platform, modular in construction, that reduces the manufacturing costs and provides for tailoring guidewire handling performance characteristics to provide a range of models to suit user&#39;s individual preferences. 
       SUMMARY OF THE INVENTION 
       [0018]    The device of the present application utilizes a high strength corewire of a diameter and cross-sectional area approximate to a non-sensing guidewire corewire intended for the same application. This is accomplished using a novel structure including a flexible distal segment, an intermediate corewire, and an interconnecting proximal subassembly segment. 
         [0019]    The initially solid corewire is processed so that the outer surface has a circular cross-sectional configuration, and has formed within it interstices or an internal channel or channels, which are positioned offset from the centerline of the device to accommodate electrical conductors. The internal channels are formed as a closed channel, or channels which are closed during processing, and are non-centered, non-coaxial, with respect to the central axis of the corewire. The internal channels are large enough so that the conductors can nest within them but small enough so as to preserve the mechanical integrity of the corewire. The shape of the internal channels may be of any cross-sectional configuration, but is optimized to enable high volume, cost efficient manufacturing. The device is composed of a modular assembly of building blocks that can be easily and inexpensively tailored to provide a range of performance characteristics to suit individual user preferences. The corewire functions as a structural backbone that extends substantially the full length of the sensing guidewire. 
         [0020]    The conductors are contained within the internal channels of the corewire to protect the conductors and preserve the corewire&#39;s mechanical characteristics by maximizing the diameter of the corewire. Stress due to bending moment is zero at the neutral axis, or the center longitudinal axis of the cross-sectional area of the corewire, and increases to the largest stresses acting on the outer diameter of the corewire. Such stresses warrant extra measures to protect the relatively fragile conductors, however doing so while maximizing the corewire outer dimension requires a novel form, which has only recently been made possible by improved manufacturing techniques. This novel guidewire device with a corewire with internal closed channels also preserves the tactility of the corewire without having to assemble a separate cover over the corewire, which may require expensive secondary operations to adhere into a single form, for example, using threading or adhesives, as in the prior art. 
         [0021]    A miniaturized sensor is mounted and may be attached to the corewire near its distal tip in a flexible distal segment. The electrical conductors connect to this sensor and are routed within the internal channel or channels of the corewire to a proximal connector or interconnecting subassembly. The flexible distal segment of the device has a tapered corewire of a smaller diameter, by design to offer increased flexibility where desired, that may eliminate the need for the internal channel or channels to extend the full length of the corewire. The flexible distal segment may be formed from the same corewire material or from different corewire material that is joined to the proximal segment. The electrical conductors can be placed adjacent to the corewire of the flexible distal segment or loosely wound in a spiral pattern around the flexible distal segment of the corewire. 
         [0022]    A spring coil or sleeve can be placed over the electrical conductors and corewire to contain the conductors within the boundaries of the device&#39;s overall diameter in the flexible distal segment where the corewire diameter is reduced. Components may be bound to the corewire with provisions to allow for free movement of the electrical conductors through the bond joints. Importantly, the overall diameter of the device is maintained at or less than the specified maximum needed to transport compatible devices like catheters or stents over the guidewire body. For coronary guidewires, this diameter is less than approximately 0.014 inches or 355 microns. 
         [0023]    The diameter of the corewire is maximized by containing the conductors within the internal channel or channels of the corewire, and avoiding use of an additional covering surrounding the entire corewire diameter. This enables the maximum diameter corewire. While this design creates special challenges in manufacturing, manufacturing methods have been optimized to enable high volume, efficient manufacturing which offers the potential to greatly reduce the manufacturing costs normally associated with sensor guidewires. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0024]      FIG. 1  shows a patient positioned supine on an operating table with the invention inserted into the body, a cable outside the body connecting the invention to an instrument and an instrument outside the body to display the physiological measurements. 
           [0025]      FIG. 2  shows the modular components of the guidewire device of the present application, including the interconnecting proximal subassembly segment, intermediate corewire (with internal channel), and flexible distal segment (with a sensor subassembly). 
           [0026]      FIG. 2A  shows an enlarged schematic view of the sensor subassembly highlighted in  FIG. 2 . 
           [0027]      FIG. 3  shows a schematic side view of the guidewire subassembly with the electrical wires inside the corewire&#39;s internal channel and a sensor shown disposed along the flexible distal segment of the corewire. 
           [0028]      FIG. 4  shows an isometric view of the guidewire subassembly with the sensor wires shown extending from outside of the channel on the proximal end of the corewire and sensor disposed along the distal flexible segment. 
           [0029]      FIG. 5A  shows a cross-sectional view of the assembled corewire, electrical conductor wires placed within the internal channels of the corewire, taken along the line A-A of  FIG. 3 . 
           [0030]      FIG. 5B  shows a cross-sectional view of an alternative embodiment of the assembled corewire, electrical conductor wires placed within the internal channels, taken along the location of the line A-A of  FIG. 3 . 
           [0031]      FIG. 6A  shows a schematic depiction of a reel to reel continuous process for embedding electrical conductors within the channel of an open channel corewire, highlighting the device&#39;s suitability for efficient manufacturing processes. 
           [0032]      FIG. 6B  shows a schematic depiction of a reel to reel continuous process for forming an outer strip of material over the open channel of an open channel corewire, forming the internal channel of the corewire within which the conductors are routed. 
           [0033]      FIG. 7A  shows a cross sectional view, taken along the line B-B of  FIG. 6B , of an outer strip of material being seated over the electrical conductor wires within a closable channel of the corewire prior to closing the channel during manufacturing. 
           [0034]      FIG. 7B  shows a cross sectional view, taken along the line C-C of  FIG. 6B , of an assembled corewire formed from the outer strip of material and corewire with the electrical conductor wires contained within the closed internal channel. 
           [0035]      FIG. 8  shows a schematic depiction for an alternate process of forming the internal channel by drawing an outer cover, or tube, over the channeled corewire with conductors contained within the channel of the corewire. 
           [0036]      FIG. 9A  shows a cross sectional view, taken along the line D-D of  FIG. 8 , of an outer cover being seated over the electrical conductor wires within a closable channel of the corewire prior to closing the channel during manufacturing. 
           [0037]      FIG. 9B  shows a cross sectional view, taken along the line E-E of  FIG. 8 , of an assembled corewire formed from outer cover and corewire with the electrical conductor wires contained within the closed internal channel. 
           [0038]      FIG. 10  shows a process flow chart for assembly of the guidewire. 
           [0039]      FIG. 11  shows an electrical connector composed of assembled alternating conductors and insulators assembled into one contiguous part. 
           [0040]      FIG. 12A  shows an electrical connector integrated into the proximal end or segment of the guidewire. 
           [0041]      FIG. 12B  shows a receiving connector with electrical contacts that completes the connection between the sensor and display system when the receiving connector is engaged with the electrical connector. 
       
    
    
     DETAILED DESCRIPTION 
       [0042]    The guidewire device  12  is a device capable of measuring physiological parameters within a body. As shown in  FIG. 1 , it is adapted for introduction into a body  11  through a puncture into a vessel and delivery through the vasculature. It is comprised of an interconnecting proximal subassembly  21 , an intermediate corewire  22 , and a distal flexible segment  23 . The assembled corewire  24  is an elongate member with an internal channel or channels  41  housing electrical conductor wires  31  routed from the conductors  113  in the interconnecting proximal subassembly  21  to the sensor  28  mounted within the sensor subassembly  29 . The electrical conductors or wires  31  provide communication of electrical signals from outside the body  11  to the sensor  28 , and from the sensor  28  to an instrument  15  outside the body  11 . An outer coating (not shown) to enhance lubricity or modify the surface friction of the device can be deposited on the outer surface of the sensing guidewire  12 . The coating may be polytetrafluoroethylene (PTFE), also known by its trade name Teflon™, a hydrophilic polymer coating, parylene or other materials commonly used for coating guidewires. Spring coils  26  made from stainless steel or platinum can be mounted over the assembled corewire  24  in the flexible distal segment  23 , where a reduced diameter solid corewire is preferred for flexibility in navigating tortuous coronary vasculature. A connector  13  to the sensor guidewire  12  is mounted on the proximal end of the device where it connects to the interconnecting subassembly  21 . The connector  13  enables a physical engagement of the pressure sensing guidewire  12  to a cable assembly  14  and provides a means for transmission of electrical signals from the sensor  28 , through the cable assembly  14 , to an instrument  15  outside the body  11 . 
         [0043]    The corewire  24  can be constructed from diamond drawn, cold worked wire which offers enhanced tensile strength. The fabrication of cold drawn wire is known to those with ordinary skill in the art. A grade of stainless steel such as 302, 304V, 316 LVM or other grades are suitable materials. In one embodiment the stainless steel corewire serves as the base material for both the proximal corewire segment and the flexible distal segment, which is made flexible by a secondary grinding process to reduce the outer diameter. Alternatively, nitinol #1, nitinol #2 or nitinol #3 or other grades of nitinol could be used. Another alternative is to have a proximal corewire segment made of cold drawn stainless steel and a flexible distal segment made of nitinol. The cold drawn stainless steel proximal segment is joined to a tapered nitinol flexible distal segment. In this case, the proximal corewire segment is made of a different material from the distal flexible segment. It is anticipated that other combinations of materials, suitable for use as a guidewire corewire, can be used to construct the corewire assembly. Corewire materials suitable for this purpose are readily available from entities such as Fort Wayne Metals, http://fwmetals.com, or Lake Region Medical (Greatbatch), http://www.lakeregionmedical.com. 
         [0044]    An initial outer surface channel, or a closed internal channel  41 , can be shaped during the cold drawing process to create the final internal channel or channels within the corewire  24 . Where the closed internal channels  41  are formed during the manufacture of the drawn cold worked corewire, conducting wires  31  may be fed into the internal channels  41  post-processing. Alternatively, as shown in  FIG. 6A , conducting wire  31  may be pre-placed within the open channel of the corewire  61  prior to formation of the closed internal channels. The closed channel can be formed after the wire drawing process as a secondary operation. This can be accomplished by grinding, laser etching, or any number of other comparable processes used to remove material. The final material properties can be tailored by a post forming process exposing the cold drawn wire to elevated temperatures and different gaseous atmospheres in an annealing process. Annealing is performed to optimize the properties of the corewire, including to reduce the brittleness of the hardened metal wire. 
         [0045]    Electrical conductor wires  31  are positioned within the internal channels  41 , as shown in  FIG. 4 . Typically, 3-wire medical electrical cables or trifilar wires are used, which are commonly known to those of ordinary skill in the art from a variety of manufacturers. The internal channel may be sized in such a way as to permit free movement of the conductors within it. The maximum diameter of the corewire  24  is substantially the same as that of a standard solid corewire outer diameter. To accomplish such a maximum diameter, a cross-sectional profile is utilized such that the electrical conductors  31  are contained within the outermost surface diameter of the corewire. This provides for superior mechanical properties compared with prior art sensor wires. This minimizes loss in bend stiffness and torque of the final guidewire assembly. This structure enables superior lesion crossing and catheter/stent delivery capability in comparison with current FFR guidewires. The unitary structure also offers improved kink resistance, superior torque-ability and offers the operator similar tactile feedback to non-sensing guidewires. 
         [0046]    To place the electrical conductors  31  within the channels  41  of the corewire  24 , it is advantageous if the outer circumference of the corewire is formed around them. This can be accomplished by several processing techniques, including sealing a strip to cover the channel, as shown in  FIGS. 7A-7B , where a strip  62  of cold drawn stainless steel can be inserted over or covering the channel and then processed to form a bond for sealing the strip within the corewire. The sequence of processing steps may include heat and pressure to seal the strip to the corewire. A secondary grinding operation can be used to reduce the outer diameter of the final assembly. Welding, soldering or other joining processes known in the art can be employed to create the bond. The strip  62  of stainless steel can take any number of shapes including circular, rectangle, an arc or a tube. In the event a tube, or stainless steel tubing sheath, is used in place of a solid metal strip, the tube may be pre-loaded to contain the electrical conducting wires  31 . Such a pre-loaded tube may be used similarly to the thin metal strip  62 , by placing it within the opening of the channel  71  and then processing it, through drawing and grinding or other processes known in the art, to rebuild the outer diameter so it is uninterrupted and contiguous. The end result is the formation of a closed internal channel  41 . 
         [0047]    Another method to accomplish this is to form a stainless steel tube around and on the solid corewire, as shown in  FIG. 8 , by drawing it through a die, or a series of progressive or reduction dies, to force a small amount of material into or covering the open channel. Thereafter, the outer diameter of the in-process subassembly may be reduced using common processes, such as centerless grinding. Importantly, this technique can be tailored to preserve the open space between the outer tube and inner solid corewire to allow free movement of the conductors. This seal may be created through interference fit, cold working, weld, or other joining methods familiar to those skilled in the art. Once the tube  81  is sufficiently joined to the corewire  61  and over the conductors  31 , a secondary grinding process may be used to bring the oversized corewire down to the size of a standard corewire. At this point, the tubing once (or twice or more) compressed and applied around the circumference of the solid corewire has been completely removed from the corewire with the exception of a small amount of material inside the channel, along the lines shown in  FIG. 9B , yielding the closed channel corewire  24 . Alternatively, to obtain desired advantages during manufacturing such as a closer initial fit between the tube and corewire, a thicker or heavier walled tube may be used over the corewire, for example, approximately 0.003 inch tube wall thickness, as compared to a thinner tube wall thickness of approximately 0.0015 inches. 
         [0048]    The preferred material for the strip  62  or tube  81  is the same as the solid corewire, which may be a desired grade of stainless steel or nitinol. This ensures nearly homogenous properties and promotes joining, regardless of the process used to join the materials. The final assembled corewire  24  is sufficiently circular and contains the electrical conductors  31  within its interstices or internal closed channels  41 . The process can be performed in a continuous reel-to-reel process offering significant cost-savings. Prior art FFR devices are typically constructed in batch processes that are necessarily labor intensive and prone to manufacturing yield loss. 
         [0049]    Alternatively, the centerless grinding process used with the present device, is intended to remove most of the outer tubing or strip, in order to improve flexibility, and can be controlled to leave a small amount of the tubing or strip intact, providing for increased sealing integrity. It is contemplated that other suitable materials can also be used for the strip, including metallic and polymeric materials, providing a protective seal and suitable for use in a continuous reel-to-reel process designed for low cost manufacturing. While using a continuous manufacturing process offers the potential cost savings, the design is also amenable to conventional batch assembly process techniques. 
         [0050]    The sensor guidewire device design incorporating the aforementioned processed corewire  24  enables access across vascular blockages with a sensor  28  that can be attached to the flexible distal end of the corewire  23 . The superior structural properties offered by use of a maximized corewire outer diameter obviates the need for the frequent guidewire exchanges often employed with current FFR devices thus reducing the cost and the time required to perform the procedure. 
         [0051]    The closed internal channel  41  inside of the corewire provides a protected space for routing the electrical conductors  31  from the sensor  28  to equipment  15  outside the body  11 . The internal channel  41  defined by the outer strip  62  and corewire  24  may be partially filled by the electrical conductors  31  to enable free and unencumbered movement so as to avoid tugging on the electrical connections to the sensor or other immobilized components as the device is advanced through the patient body. Alternatively, or additionally, extra electrical conductor wire  31  length in the flexible distal segment  23  of the device can provide freedom of longitudinal wire movement adjacent to fixed conductor wires within the internal channels  41 . In this embodiment the extra length in the distal segment enables free movement where the guidewire is designed to be distorted by vascular anatomy, as the flexible distal end  23  is the first portion of the guidewire  12  that is advanced into a patient&#39;s body  11  through the most tortuous paths and blockages in the vasculature. 
         [0052]    To secure the sensor to the guidewire, the current device affixes the sensor  28  to the guidewire  12  according to at least one of many techniques. Among these techniques is providing a sensor subassembly comprised of a cradle or tubular sensor subassembly  29  with an inner lumen of sufficient size to accept the sensor. The corewire  24  can be fixedly secured onto the sensor subassembly so that it can pass through to the distal most end of the device where it forms a distal tip  27 , along with a surrounding spring sleeve or coil  26 , as shown in  FIG. 2 . 
         [0053]    Alternatively, to make room within the sensor subassembly  29 , the corewire can be attached and terminated at the proximal section of the subassembly and a second wire affixed to the distal end of the housing. The surrounding sleeve  25  can be affixed to the corewire by a number of means including soldering or adhesive bonding. Likewise, the corewire can be attached to the sensor subassembly housing using similar bonding techniques. Other known bonding techniques have been contemplated. Electrical wiring  31  can likewise be connected to the sensor  28 . By providing the sensor  28  and a completed sensor subassembly  29  electrical testing can be performed prior to final assembly, thus providing opportunity for cost savings. This sensor sub assembly structure can be easily attached to the aforementioned assembled corewire  24  subassembly enabling the sensor subassembly  29  to be used with different guidewire designs of the same diameter while benefiting from the savings of a guidewire utilizing high volume manufacturing. In other words, corewires of different designs can be easily interchanged with this modular sensor subassembly. This design reduces manufacturing cost and provides for a means to vary guidewire performance characteristics, enabling the manufacture of guidewires offering a variety of handling characteristics to better appeal to a broader group of users. 
         [0054]    Current FFR guidewires have failed to provide the functionality of the current device due to an inability to successfully carry the signal from the sensor  28  to an outside instrument or monitor  15  without compromising the guidewire&#39;s vascular blockage crossing capability. The current device solves this problem. 
         [0055]      FIG. 1  shows a patient  11  who is undergoing a procedure with the sensing guidewire device  12 . The proximal end or segment  20  of the sensing guidewire  12  is attached to a connector or interconnecting subassembly  13  that provides the sensing guidewire with electrical interconnection and communication with an instrument cable  14 . The flexible distal segment  23  of the sensing guidewire is inserted into the patient in this Figure, from whence it collects data that is transmitted via the instrument monitor cable  14  to an instrument  15 . The instrument can also supply power to the sensing guidewire. 
         [0056]      FIG. 2  shows the fully assembled guidewire device  12  in detail. It is separated into three discrete segments: interconnecting subassembly  21 , intermediate corewire segment  22 , and flexible distal segment  23 . The device has completely internalized the electrical conductors  31  within the corewire  24 . This enables both protection for the wires as well as optimization of the mechanical characteristics of the guidewire. A sleeve  25 , sensor subassembly  29 , and spring coil  26  are assembled over a section of corewire  24  with reduced diameter for increased flexibility, the flexible distal segment  23 . The sensor  28  is shown within the sensor subassembly  29  guidewire. The interconnecting subassembly connects the sensor to an external monitor through wires  31  routed from the sensor to the connector  111 . 
         [0057]      FIG. 3  shows a subassembly of the sensing guidewire in more detail. The sensing guidewire includes an assembled core  24  that extends from the proximal end  21  towards the distal tip  27 . The assembled corewire subassembly includes at least one internal channel  41  that extends from the proximal end  21  towards the distal end. In this figure, the channel is not shown as it is an internal feature of the corewire. The channel can be formed either asymmetrically, concentric, or parallel to the axis of the assembled core, or between those extremes. Other designs for the channel would be apparent to a person of ordinary skill in the art, including zigzag and wave shapes. Within the flexible distal end  23  of the sensing guidewire, the diameter of the corewire can vary, resulting in a tapered end. Towards the distal end of the tapered segment of corewire, a sensor  28  and, optionally, a sensor housing or subassembly  29  are secured. In one embodiment, the sensor is affixed in a cantilevered position with respect to the tapered section. Other embodiments would be readily apparent to a person of ordinary skill in the art, including affixing the sensor inside a separate tubular sensor housing at the distal end of the solid corewire or directly onto the distal end of the corewire, on a flattened surface. The tubular sensor housing can be made from materials similar to that used for the corewire, thus enabling the use of common bonding techniques like welding, soldering or bonding with adhesive. 
         [0058]    At least one electrical conductor wire  31  runs from the sensor  28  near the distal tip to the proximal end of the corewire, spanning substantially the complete length of the device. In the preferred embodiment, three wires are contained in the channel  41 , though configurations containing one, two, or more than three wires are also readily apparent to one of ordinary skill in the art. The preferred embodiment is a three wire configuration fused together to form a trifilar wire assembly. Medical wire of the type used are well known to those of ordinary skill in the art, and can be procured readily from suppliers like MWS Wire Industries, http://www.mwswire.com. Over the length of the sensing guidewire  12  that includes the closed internal channel, the conductor wire  31  lies within the channel. In one embodiment, the size of the channel is greater than the greatest diameter of the conductor wires  31  so that the wires can move freely, or slide longitudinally, within the channel  41 . In another embodiment, the conducting wire is sized to fill the space within the channel  41 . 
         [0059]      FIG. 4  shows the assembled core at a different angle and closer perspective. In this embodiment, the assembled core includes a single triangular shaped internal channel  41 , although in different embodiments the assembled core has other numbers of channels. The channel has a substantially triangular cross-sectional configuration, although other shapes would be obvious to a person of ordinary skill in the art, including U-shaped depressions of any height-to-width ratio (including zero) and rectangular openings. In one embodiment of the invention, the height of the channel is about 0.0028 inches and the width of the channel is approximately 0.0060 inches. In another embodiment, the ratio of the width of the channel to the height of the channel is about 2:1. 
         [0060]      FIGS. 5A and 5B  show alternate cross-sections of corewire taken at the A-A plane in  FIG. 3 . The channel  41  is shown with sufficient space to enable the conductor wires  31  to move freely. In order to ensure the performance of the sensing guidewire, the at least one conductor wire is housed so it cannot easily break; since it is expected that the sensing guidewire will be bent, twisted, and otherwise deformed, the conductor wire or wires need to be protected from disconnection or breakage. In one embodiment, the conducting wire lies freely in the closed internal channel and has an overall length that, if straightened, is greater than the length of the sensing guidewire  12 . When the sensing guidewire is bent, turned, or twisted, the conducting wire can move within the interstitial space defined by the channel  41 . The channel can accommodate, over the length of the sensing guidewire, the additional length of the connecting wire. And when the sensing guidewire is bent in a direction that shortens the length needed for the conducting wires  31 , the excess conducting wire can gather within the channel  41 . Other techniques to protect conducting wires  31  from breakage include using coatings within the channel to reduce friction and/or covering the conductors with thicker layers of insulation. Adhering the conducting wires to other support materials, such as stainless steel, may also provide support during assembly and clinical use. 
         [0061]      FIGS. 6A and 6B  show steps of one possible continuous manufacturing process for assembling the electrical conductor wires  24  within the channel  41  of the corewire. In  FIG. 6A  a reel-to-reel process is shown where a channeled corewire  61  has electrical wires placed within the open channel such that they are within the outer diameter of the corewire.  FIG. 6B  shows an outer strip of metal material  62 , in a preferred embodiment composed of a similar metal to that of the corewire, initially wrapped over top of the conductor wires  31  and seated on top of the open channel to form a closed internal channel  41 . The strip is processed through grinding, cold working, or other processes familiar to those skilled in the art into a contiguous and homogenous outer surface of the solid corewire. It is anticipated that the strip can be formed from materials of varying shapes and dimensions, so long as they are able to be placed within the channel in a way that reliably forms the corewire internal channel  41  through the assembly process and provides for a robust seal and desired guidewire handling. In the preferred embodiment, a metal material such as stainless steel is used to close the internal channel, as it offers more protection and better space efficiency within the closed internal channel, as it is less fragile, and does not sag into the channel or abrade during use. However, various polymeric materials may be suitable for this purpose, for example polyimide or thermoplastic polymers such as PET (polyethylene terephthalate), nylon, polyurethane and co-polymers of these materials, such as polyether block amide (PEBA) such as PEBAST, commercially available from Arkema, or a polyester block co-polymer such as HytrelT, commercially available from DuPont. Likewise, polyether polyurethanes with carbon atoms linked in open chains, for example paraffins, olefins and acetylenes, such as TecoflexT, commercially available from Lubrizol, may also be suitable. Still further polymer materials from the polyurethane class of thermoplastic polymers such as PellthaneT, available from the Dow Chemical Company, and Tecothane, available from Lubrizol, may also provide alternative solutions. 
         [0062]      FIGS. 7A and 7B  show cross-sectional views of the process described in  FIG. 6B . In  FIG. 7A , the cross-sectional view at plane B-B in  FIG. 6B , the strip  62  is shown seated on top of an open channel  71  containing the electrical wires  31 . In  FIG. 7B , the cross-sectional view at plane C-C in  FIG. 5B , the same strip  62  has been joined to the corewire to form the assembled corewire  24  with an internal channel  41 . 
         [0063]      FIG. 8  shows another continuous process for assembling the electrical wires within the corewire&#39;s closed internal channels  41 . In this process a metal tube  81  is placed over top of a corewire with an open channel  61 , electrical conductors  31  contained within the channel. The tube is drawn down on top of the corewire through a die, effectively joining it to the outer surface of the corewire to form an assembled corewire with internalized channels  24 . This corewire may then be ground down to a standard guidewire diameter. The majority of the tube  81  is effectively removed from the corewire during this process. This effectively maximizes the corewire diameter. In an alternative embodiment, a small amount of the tubular outer layer may be left in place to enhance the integrity of the sealed internal channel. 
         [0064]      FIGS. 9A and 9B  show cross-sectional views of the process described in  FIG. 8 . In  FIG. 9A , the cross-sectional view at plane D-D in  FIG. 8 , the tube  81  is shown concentric to the corewire with an open channel  61 , covering the channel containing the electrical wires. In  FIG. 9B , the cross-sectional view at plane E-E in  FIG. 8 , the tube  81  has been joined to the corewire and then ground away to form the assembled corewire with an internal channel  41 . 
         [0065]      FIG. 10  shows a process flow chart for assembling the guidewire using the corewire and electrical conductor wires. This process is one example that may be employed. Other processes may be employed to achieve the same end. For example, a method for manufacturing the sensing guidewire device is also contemplated where stainless steel wire is drawn through a die or dies, and the resulting cold drawn corewire forms a closed internal channel having a cross-sectional configuration which is off-set from a central axis of the corewire and has a sufficient size to enable free movement of a conducting wire positioned within the closed internal channel, and a conducting wire is fed through the closed internal channel of the corewire from a distal end to a proximal end. Optionally, the loose fitting conductor can be partially pulled out from the corewire to enhance processing. Processes may include soldering or bonding to other conductor segments. 
         [0066]      FIG. 11  shows an embodiment of a solid plug style connector  111  with alternating bands of insulators  112  and conductors  113 . These individual components of the solid plug are joined together with adhesive or other means. 
         [0067]      FIG. 12A  shows an embodiment of a cylinder or solid plug  111  located within the internal diameter of an insulated solid plug covering  121 . This solid plug  111  is constructed to function as a part of the corewire  24  by providing mechanical support for the interconnecting subassembly  21 . The solid plug  111  may be joined to the corewire  24  and covering  121  with an adhesive  124  or through other conventional means. The interconnecting subassembly  23  is slid inside the connector  13 , shown in  FIG. 12B , to electrically connect the sensor  28  to an external instrument  15 . In this embodiment, the solid plug includes alternating insulators  112  and conductors  113 . The conductors  113  can be made from, for example, a platinum alloy (Pt—Ir); the insulators can be made from, for example, a polymer such as PEEK. While the insulators and conductors are shown here as having substantially identical diameters, the insulators could be made thinner than the conductors and vice versa. As shown in  FIG. 12A , each conductor  113  is in electrical communication, through a solder joint  123  or other contact, with one of the electrical conducting wires  31  or one lead from a conducting wire that includes multiple leads. The wires  31  are shown to be wound around the outer diameter of the plug several times, but can be arranged without winding in other embodiments. For example, another embodiment of the solid plug  111  may have an irregularly shaped outer diameter in order to allow for the wires to lay within the maximum diameter of the solid plug. The electrical wires contained within the internal diameter of the body of the outer insulating cover  121  are visible once the solid plug is placed within this recessed area. This allows for simpler manufacturing of the connections between the wires and the conducting elements of the solid plug. 
         [0068]    The solid plug conductors  113  are electrically connected to the wires  31 , through solder joints  123  or other electrical interconnections, and engage with the connector  13  along connecting pins  125  when the connector  13  is engaged over the covering  121  along the line shown in  FIG. 12A / 12 B. The connecting pins  125  are each designed to contact one of the solid plug conductors  113  through openings  122  in the solid plug covering  121 . The pins  125  may be spring-loaded to facilitate engagement and removal of the connector  13 . In place of pins flexible metal wires may be used. There must be at least three openings  122  in the solid plug covering  101  shown in  FIG. 10A , including an opening on the most proximal end of the covering formed by the inner dimension of the tube, but other embodiments may include more to assist in creating an electrical connection so long as they do not overlap the path of the electrical wires  31 . The openings  122  help locate and secure the connector  13  onto the guidewire and also help seal the connection between the solid plug conductors  113  and connecting pins  125  from disturbance by outside fluids or debris. In another embodiment of the sensing guidewire, the solid plug is part of the connector and is slid into the recessed area of the guidewire during a clinical procedure. 
         [0069]    While other benefits of this solid plug connector concept will be apparent to people of ordinary skill in the art, some of the benefits are that a solid device provides a more robust connection between the sensing guidewire electrical wires and the connector. In addition, the area of electrical connection is protected within the recessed area, thereby preventing short-circuits caused by fluids such as blood. A further improvement provided by the solid plug connector is to facilitate manufacture by making it easier to visualize where the connecting wires connect with respect to the conductors. 
         [0070]    Certain embodiments of the invention have been described with specificity in order to improve understanding of the invention. However, many variations and modifications will become apparent to a person of ordinary skill in the art. It is therefore expected and intended that the certain changes and modifications may be practiced which will still fall within the scope of the appended claims.