Abstract:
An implantable lead and lead body, method of manufacturing the same, and a system and method for stimulating a portion of a body is disclosed. In one advantageous embodiment, a lead body assembly is formed by placing an inner layer of extrusion material on a mandrel, wrapping a plurality of conductors coated with extrusion material around the inner layer, and placing an outer layer of extrusion material over the plurality of conductors. Heat shrink tubing is placed over the lead body assembly and the lead body assembly is heated to melt the extrusion material. The melted extrusion material is compressed around the plurality of conductors. The assembly is then cooled and the heat shrink tubing is removed. The solidified extrusion material forms a protective wall that encapsulates the plurality of conductors in the lead body.

Description:
CROSS-REFERENCE TO RELATED PATENT DOCUMENTS  
       [0001]     The present disclosure is related to the inventions disclosed in the following United States patent applications:  
         [0002]     United States Patent Application No. [Attorney Docket Number 03-003] filed concurrently herewith, entitled “System and Method for Providing a Medical Lead Body With Dual Conductor Layers”; and  
         [0003]     United States Patent Application No. [Attorney Docket Number 03-009] filed concurrently herewith, entitled “System and Method for Providing A Medical Lead Body Having Conductors That Are Wound in Opposite Directions.” 
         [0004]     These patent applications are commonly owned by the assignee of the present invention. The disclosures of the related United States patent applications are incorporated herein by reference for all purposes as if fully set forth.  
       TECHNICAL FIELD OF THE INVENTION  
       [0005]     The present invention generally relates to medical leads and, more particularly, to a system and method for manufacturing an implantable lead that includes a lead body having conductors that are located between an inner layer of extrusion material and an outer layer of extrusion material.  
       BACKGROUND OF THE INVENTION  
       [0006]     Electrical signals may be used in a variety of medical applications to provide electrical stimulation to various parts of the body of a patient. For example, electrical signals may be used to modulate the amount of pain perceived by a patient by electrically stimulating a site near one or more nerves of the patient. A source of electrical signals may be implanted within the body of a patient. Electrical signals are conducted from the source of electrical signals to the stimulation site of the patient through a lead implanted within the body of the patient.  
         [0007]     A lead generally includes a thin, flexible, lead body that contains electrically conducting conductors (e.g., wires) that extend from a first end of the lead (the proximal end) to a second end of the lead (the distal end). The lead body includes insulating material for covering and electrically insulating the electrically conducting conductors. The proximal end of the lead further includes an electrical contact that may be coupled to a source of electrical signals and the distal end of the lead includes an electrode that may be placed at the stimulation site within the body of the patient.  
         [0008]     A prior art manufacturing process that the inventors developed for a lead involved placing a plurality of electrically conducting conductors on a layer of extrusion material placed on an underlying mandrel. This method was developed for only up to four conductors, because the conductors ran longitudinally along the length of the mandrel. Because only four wires were used, concern about insulating the conductors were minimized by evenly spacing the wires along the length, something that was simplified because of placement of the wires along the length of the mandrel. Greater than four conductors caused concern for mass production because of narrowing spacing requirements tended to cause conductor interference and shorts, since it became more difficult to evenly space the conductors.  
         [0009]     After the conductors were in place on the extrusion material on the mandrel in this method, the conductors were then covered with another layer of extrusion material and a heat shrink process is applied to melt the extrusion material. The extrusion material was then cooled to form a lead body that encapsulates the conductors.  
         [0010]     Different prior art conductors suggest that the conductors may be wound around a cylindrically shaped mandrel in a spiral manner. Here, a mechanical comb is utilized in the prior art winding process to keep the conductors separated as the conductors are wound around the mandrel. The use of a mechanical comb can sometimes cause the pitch of the conductors to vary. The term “pitch” refers to the distance along the axis of the mandrel that represents one turn of conductor around the mandrel.  
         [0011]     The use of mechanical combs can also sometimes damage the conductors. Prior art manufacturing methods can also result in a lead body that has variable (non-uniform) conductor pitches for the conductors in the lead body. Prior art manufacturing methods can also result in a lead body that has variable (non-uniform) wall thicknesses. Prior art manufacturing methods also can result in the creation of lead bodies that have relatively large diameters.  
         [0012]     Larger electrode-carrying catheters in the prior art (such as those used in cardiology applications) may utilize electrically conducting wires that are spirally wound around a cylindrically shaped wire core. For example, U.S. Pat. No. 5,417,208 issued to Winkler describes an electrode-carrying catheter that comprises insulated wires (or non-insulated wires) that are spirally wound under hand tension around a cylindrically symmetrical wire core. The wires are embedded in a soft plastic covering (such as polyurethane having a durometer hardness of 80A available under the trade name Tecoflex) over-extruded over the wire core. The wires are embedded in the plastic covering to preclude accidental movement of the wires with respect to the wire core. Subsequently, an insulating layer of plastic is over-extruded over the soft core covering layer. This insulating layer forms a hard outer layer.  
         [0013]     There is a need in the art for an improved system and method for manufacturing a lead body. In particular, there is a need in the art for a system and method for manufacturing a lead body that is capable of protecting and accurately placing electrically conducting conductors within the lead body during the manufacturing process. There is also a need in the art for a system and method for manufacturing a lead body that has a minimal diameter.  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention is directed to a system and method for manufacturing a medical lead that includes a lead body composed of a plurality of conductors that have been previously coated with extrusion material before the plurality of conductors are assembled to form the lead body.  
         [0015]     In one advantageous embodiment of the present invention, a lead body assembly is formed by placing an inner layer of extrusion material on a mandrel. A plurality of conductors is coated with extrusion material and each coated conductor is wrapped around the inner layer of extrusion material on the mandrel. An outer layer of extrusion material is then placed over the plurality of conductors that are coated with extrusion material. Heat shrink tubing is then placed over the lead body assembly and the lead body assembly is heated to melt the extrusion material. The melted extrusion material is compressed around the plurality of conductors as the heat shrink tubing shrinks. The lead body assembly is then cooled to form a lead body and the heat shrink tubing is removed. The solidified extrusion material forms a protective wall that encapsulates the plurality of conductors in the lead body. The lead body is then removed from the mandrel.  
         [0016]     In another advantageous embodiment of the present invention, a lead body assembly is formed by coating a plurality of conductors with extrusion material and wrapping each of the coated conductors around a mandrel. An outer layer of extrusion material is then placed over the plurality of conductors that are coated with extrusion material. Heat shrink tubing is then placed over the lead body assembly and the lead body assembly is heated to melt the extrusion material. The melted extrusion material is compressed around the plurality of conductors as the heat shrink tubing shrinks. The lead body assembly is then cooled to form a lead body and the heat shrink tubing is removed. The solidified extrusion material forms a protective wall that encapsulates the plurality of conductors in the lead body. The lead body is then removed from the mandrel.  
         [0017]     In another advantageous embodiment of the present invention, a lead body assembly is formed by placing an inner layer of extrusion material on a mandrel. A plurality of conductors is coated with extrusion material and each coated conductor is wrapped around the inner layer of extrusion material on the mandrel. Heat shrink tubing is then placed over the lead body assembly and the lead body assembly is heated to melt the extrusion material. The melted extrusion material is compressed around the plurality of conductors as the heat shrink tubing shrinks. The lead body assembly is then cooled to form a lead body and the heat shrink tubing is removed. The solidified extrusion material forms a protective wall that encapsulates the plurality of conductors in the lead body. The lead body is then removed from the mandrel.  
         [0018]     In another advantageous embodiment of the present invention, a lead body assembly is formed by coating a plurality of conductors with extrusion material and wrapping each of the coated conductors around a mandrel. Heat shrink tubing is then placed over the lead body assembly and the lead body assembly is heated to melt the extrusion material. The melted extrusion material is compressed around the plurality of conductors as the heat shrink tubing shrinks. The lead body assembly is then cooled to form a lead body and the heat shrink tubing is removed. The solidified extrusion material forms a protective wall that encapsulates the plurality of conductors in the lead body. The lead body is then removed from the mandrel.  
         [0019]     The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions and the accompanying drawings, wherein like numbers designate like objects, and in which:  
         [0021]      FIG. 1  illustrates a perspective view of a lead constructed in accordance with the present invention;  
         [0022]      FIG. 2  illustrates a lead of the present invention connected to a stimulation source including an implantable pulse generator (IPG);  
         [0023]      FIG. 3  illustrates a lead of the present invention connected to a stimulation source including a radio frequency receiver;  
         [0024]      FIG. 4  illustrates a cross sectional view of a first embodiment of a lead body assembly of the present invention comprising an inner layer of extrusion material, a plurality of conductors coated with a layer of extrusion material, and an outer layer of extrusion material;  
         [0025]      FIG. 5  illustrates a cross sectional view of a first embodiment of the lead body of the present invention formed by subjecting the lead body assembly shown in  FIG. 4  to melting and compression;  
         [0026]      FIG. 6  illustrates a cross sectional view of a second embodiment of a lead body assembly of the present invention comprising a plurality of conductors coated with a layer of extrusion material and an outer layer of extrusion material;  
         [0027]      FIG. 7  illustrates a cross sectional view of a second embodiment of the lead body of the present invention formed by subjecting the lead body assembly shown in  FIG. 6  to melting and compression;  
         [0028]      FIG. 8  illustrates a cross sectional view of a third embodiment of a lead body assembly of the present invention comprising an inner layer of extrusion material and a plurality of conductors coated with a layer of extrusion material;  
         [0029]      FIG. 9  illustrates a cross sectional view of a third embodiment of the lead body of the present invention formed by subjecting the lead body assembly shown in  FIG. 8  to melting and compression;  
         [0030]      FIG. 10  illustrates a cross sectional view of a fourth embodiment of a lead body assembly of the present invention comprising a plurality of conductors coated with a layer of extrusion material;  
         [0031]      FIG. 11  illustrates a cross sectional view of a fourth embodiment of the lead body of the present invention formed by subjecting the lead body assembly shown in  FIG. 10  to melting and compression;  
         [0032]      FIG. 12  illustrates a perspective side view of a mandrel showing how an exemplary conductor may be coiled around the axial length of the mandrel.  
         [0033]      FIG. 13  illustrates a perspective side view of a mandrel showing how a plurality of conductors may be placed along the axial length of the mandrel.  
         [0034]      FIG. 14  is a flow diagram illustrating the steps of an advantageous embodiment of a method for making a first embodiment of the lead body of the present invention;  
         [0035]      FIG. 15  is a flow diagram illustrating the steps of an advantageous embodiment of a method for making a second embodiment of the lead body of the present invention;  
         [0036]      FIG. 16  is a flow diagram illustrating the steps of an advantageous embodiment of a method for making a third embodiment of the lead body of the present invention; and  
         [0037]      FIG. 17  is a flow diagram illustrating the steps of an advantageous embodiment of a method for making a fourth embodiment of the lead body of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]      FIGS. 1 through 17 , discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably modified medical lead.  
         [0039]      FIG. 1  illustrates an advantageous embodiment of a lead  100  of the present invention. Lead  100  includes a flexible lead body  120  having a proximal end  110  and a distal end  130 . Proximal end  110  of lead body  120  is coupled to an electrical contact  140 . Distal end  130  of lead body  120  is coupled to electrode  160 . Electrical contact  140  includes portions of lead body  120  and a plurality of contact electrodes  150  (also sometimes referred to as ring electrodes  150 ). Electrode  160  includes portions of lead body  120  and a plurality of band electrodes  170  (also sometimes referred to as ring electrodes  170 ). Although four contact electrodes  150  and four band electrodes  170  are shown in  FIG. 1 , it is understood that the present invention is not limited to the use of exactly four contact electrodes  150  or four band electrodes  170 .  
         [0040]      FIG. 2  and  FIG. 3  illustrate different embodiments of a system ( 200 ,  300 ) for generating and applying a stimulus to a tissue or to a certain location of a body. In general terms, the system ( 200 ,  300 ) includes a stimulation or energy source ( 210 ,  310 ) and a lead  100  for application of the stimulus. The lead  100  shown in  FIG. 2  and in  FIG. 3  is the lead of the present invention.  
         [0041]      FIG. 2  illustrates a lead  100  of the present invention connected to a stimulation source  210 . The stimulation source  210  shown in  FIG. 2  includes an implantable pulse generator (IPG). As is well known in the art, an implantable pulse generator (IPG) is capable of being implanted within a body (not shown) that is to receive electrical stimulation from the stimulation source  210 . An exemplary implantable pulse generator (IPG) may be one manufactured by Advanced Neuromodulation Systems, Inc., such as the Genesis® System, part numbers  3604 ,  3608 ,  3609 , and  3644 . Reference numeral  200  refers to the system including the lead  100  and the stimulation source  210 .  
         [0042]     Electrical contact  140  is not visible in  FIG. 2  because electrical contact  140  is situated within a receptacle (not shown) of stimulation source  210 . Electrical contact  140  is electrically connected to a generator (not shown) of electrical signals within stimulation source  210 . Stimulation source  210  generates and sends electrical signals via lead  100  to electrode  160 . Electrode  160  is located at a stimulation site (not shown) within the body that is to receive electrical stimulation from the electrical signals. A stimulation site may be, for example, adjacent to one or more nerves in the central nervous system (e.g., spinal cord). The band electrodes  170  of electrode  160  conduct electrical signals from electrode  160  to the stimulation site. Stimulation source  210  is capable of controlling the electrical signals by varying signal parameters (e.g., intensity, duration, frequency) in response to control signals that are provided to stimulation source  210 .  
         [0043]      FIG. 3  illustrates a lead  100  of the present invention connected to a stimulation source  310 . The stimulation source  310  shown in  FIG. 3  includes a radio frequency (RF) receiver. As is well known in the art, a stimulation source  310  comprising a radio frequency (RF) receiver is capable of being implanted within the body (not shown) that is to receive electrical stimulation from the stimulation source  310 . Exemplary RF receiver  310  may be those RF receivers manufactured by Advanced Neuromodulation Systems, Inc., such as the Renew® System, part numbers  3408  and  3416 . Reference numeral  300  refers to the system including the lead  100  and the stimulation source  310 . System  300  may also include the optional components  320  and  340  described below.  
         [0044]     Electrical contact  140  is not visible in  FIG. 3  because electrical contact  140  is situated within a receptacle (not shown) of stimulation source  310 . Electrical contact  140  is electrically connected to a generator (not shown) of electrical signals within stimulation source  310 . Stimulation source  310  generates and sends electrical signals via lead  100  to electrode  160 . Electrode  160  is located at a stimulation site (not shown) within the body that is to receive electrical stimulation from the electrical signals. A stimulation site may be, for example, adjacent to one or more nerves in the central nervous system (e.g., spinal cord). The band electrodes  170  of electrode  160  conduct electrical signals from electrode  160  to the stimulation site. Stimulation source  310  is capable of controlling the electrical signals by varying signal parameters (e.g., intensity, duration, frequency) in response to control signals that are provided to stimulation source  310 .  
         [0045]     As shown in  FIG. 3 , the radio frequency (RF) receiver within stimulation source  310  is capable of receiving radio signals from a radio frequency (RF) transmitter  320 . The radio signals are represented in  FIG. 3  by radio link symbol  330 . Radio frequency (RF) transmitter  320  and controller  340  are located outside of the body that is to receive electrical stimulation from stimulation source  310 . A user of stimulation source  310  may use controller  340  to provide the control signals for the operation of stimulation source  310 . Controller  340  provides the control signals to radio frequency (RF) transmitter  320 . Radio frequency (RF) transmitter  320  transmits the control signals to the radio frequency (RF) receiver in stimulation source  310 . Stimulation source  310  uses the control signals to vary the signal parameters of the electrical signals that are transmitted through electrical contact  140 , lead body  120 , and electrode  160  to the stimulation site. Exemplary RF transmitter  320  may be those RF transmitters manufactured by Advanced Neuromodulation Systems, Inc., such as the Renew® System, part numbers  3508  and  3516 .  
         [0046]      FIG. 4  illustrates a cross sectional view of a first embodiment of a lead body assembly  115  of the present invention. Lead body assembly  115  includes (1) an inner layer  410  of extrusion material, (2) a plurality of conductors  420  in which each conductor  420  is coated with a layer of extrusion material  430 , and (3) an outer layer  440  of extrusion material. A lumen  450  is formed by the inner wall of inner layer  410 . The portions of the first embodiment of lead body assembly  115  shown in  FIG. 4  are collectively referred to with reference numeral  400 .  
         [0047]     An advantageous embodiment of a method for making the first embodiment of lead body  120  (shown in  FIG. 5 ) will now be described. An inner layer  410  of extrusion material is placed on a cylindrically shaped mandrel (not shown). After the lead body  120  is removed from the mandrel, the space formerly occupied by the mandrel will form lumen  450  within inner layer  410 . Each conductor  420  of the plurality of conductors  420  is coated with a layer  430  of the same extrusion material that is used to form inner layer  410 . Alternatively, the extrusion material used to form layer  430  may not be the same type of extrusion material that is used to form inner layer  410 . Each conductor  420  of the plurality of conductors  420  is cylindrically wrapped around (i.e., coiled around) the inner layer  410  of extrusion material. The layer  430  of extrusion material around each conductor  420  ensures that the conductors  420  are uniformly spaced. An outer layer  440  of extrusion material is placed over the plurality of conductors  420 . The outer layer  440  of extrusion material forms an external coating over the plurality of conductors  420  as shown in  FIG. 4 .  
         [0048]     In an alternative embodiment of the method of the present invention, each conductor  420  of the plurality of conductors  420  is not coiled around the inner layer  410  of extrusion material, but instead is placed lengthwise along the axial length of inner layer  410 . An outer layer  440  of extrusion material is placed over the plurality of conductors  420  in the same manner as in the case of the coiled conductors  420 .  
         [0049]     The extrusion material is formed of an insulating material typically selected based upon biocompatibility, biostability and durability for the particular application. The extrusion material may be silicone, polyurethane, polyethylene, polyimide, polyvinylchloride, PTFT, EFTE, or other suitable materials known to those skilled in the art. Alloys or blends of these materials may also be formulated to control the relative flexibility, torqueability, and pushability of the lead body  120 . Depending on the particular application, the diameter of the lead body  120  may be any size, though a smaller size is more desirable for neurological and myocardial mapping/ablation leads and neuromodulation and stimulation leads.  
         [0050]     The conductors may take the form of solid conductors, drawn-filled-tube (DFT), drawn-brazed-strand (DBS), stranded conductors or cables, ribbons conductors, or other forms known or recognized to those skilled in the art. The composition of the conductors may include aluminum, stainless steel, MP35N, platinum, gold, silver, copper, vanadium, alloys, or other conductive materials or metals known to those of ordinary skill in the art. The number, size, cross-sectional shape, and composition of the conductors will depend on the particular application for the lead body  120 .  
         [0051]     As previously mentioned, the conductors may be configured along the lead body  120  in a straight orientation or cylindrically or helically wound around the lumen  450  at the center of the lead body  120 . The conductors are typically insulated from the lumen  450 , and from each other, and from the external surface of the lead body  120  by the extrusion material. As also previously mentioned, the extrusion material may be of single composition, or of multiple layers of the same or different materials.  
         [0052]     In one embodiment of the invention, the combined portions  400  of lead body assembly  115  are then covered with heat shrink tubing (not shown) and heat is applied. The heat melts the layers ( 410 ,  430  and  440 ) of extrusion material and the melted extrusion material flows together to form an integral body. The heat shrink tubing holds and compresses the melted extrusion material around the conductors that are located within the extrusion material to create a unitary body lead  500  as shown in  FIG. 5 . The conductors  420  in unitary body lead  500  are contained in the unitary core, that comprises a unitary or unified wall  510 , lumen  520  and conductors  420 . The conductors  420  are each within the wall  510  of the unitary body lead  500  and may be centered within the unitary wall  510 .  
         [0053]     Thus, once formed as described above, there is no need to have a separate or secondary electrical insulation material (separate from the extrusion material that forms wall  510 ) surrounding the conductors as in the prior art. This is because the unitary construction of wall  510  acts as the electrical insulation material and forms the unitary core of the unitary body. This is true for embodiments of this invention including those described below.  
         [0054]     Wall  510  is formed from the layers that include the layers ( 410 ,  430  and  440 ) of extrusion material shown in  FIG. 4 . As known, the various extrusion materials may be of a like kind or may be formulated using different materials such that when formed as a unitary body, the lead body will have a desired consistence, flexibility, electrically conductive properties, or other such functionality as may be desired. This holds true for all embodiments of the invention described below.  
         [0055]     In the embodiment described above, the unitary body lead  500  is cooled and the heat shrink tubing removed. Lumen  520  is formed when the unitary body lead  500  is removed from the mandrel (not shown). There may be some release of coiled tension in the conductors  420  when the heat shrink tubing is removed. This holds true for all embodiments of the invention described below.  
         [0056]     While the previous paragraphs describe one embodiment of forming the unitary body, those skilled in the art will recognize that other like methods may be used. For example, some of the other possible ways of forming the lead without heat shrink could be: a single hot die, successively smaller dies wherein the dies are used to draw the product to a final outside diameter. Other methods could be a compression mold or hot die drawing or other methods familiar to those in the arts. In fact, as those skilled will understand, any heating method that results in the wires becoming imbedded in a homogenous plastic or unitary body may be used. This holds true for all embodiments of the invention described below.  
         [0057]     The present invention provides a layer  430  of extrusion material around each conductor  420 . This protective layer  430  of extrusion material provides an electrical barrier between each of the conductors  420 . This process also provides a significant improvement over the prior art method that uses a mechanical comb in the winders to try to keep the conductors  420  separate. The protective layer  430  of extrusion material also allows the present invention to create leads that are smaller and thinner than prior art leads.  
         [0058]     The method of the present invention provides several advantages over prior art methods. Advantages of the method of the present invention include: (1) more accurate conductor placement during the process of coiling the conductor around a mandrel, (2) more accurate conductor pitches, (3) improved pitch consistency, (4) more conductor protection during the process of coiling the conductor around the mandrel, and (5) precise centering of the conductors within the resulting unitary body.  
         [0059]     In addition, the apparatus and method of the present invention makes possible the construction of lead bodies that have a smaller diameter than prior art lead bodies. That is, the lead bodies of the present invention may be made thinner than prior art lead bodies. In general, the inventive lead body diameter will be smaller than 34 French and can be smaller than 9 French. (This holds true for the embodiments described below). The cylindrically symmetrical embodiment of the lead body  120  of the invention can also better withstand lateral stretching than prior art lead bodies.  
         [0060]     The lead body assembly  115  shown in  FIG. 4  has been described as having cylindrical symmetry. It is noted that other types of geometrical cross-sectional shapes (e.g., rectangular) could be used if a different shape is desired for a particular application.  
         [0061]     The lead body assembly  115  shown in  FIG. 4  and the lead body  120  shown in  FIG. 5  have been shown as having eight conductors  420 . The use of eight conductors  420  is merely an example. It is understood that more than eight conductors  420  may be used. It is also understood that fewer than eight conductors  420  may be used.  
         [0062]      FIG. 6  illustrates a cross sectional view of a second embodiment of a lead body assembly  115  of the present invention. Lead body assembly  115  includes (1) a plurality of conductors  620  in which each conductor  620  is coated with a layer of extrusion material  630 , and (2) an outer layer  640  of extrusion material. A lumen  650  is formed by the plurality of coated conductors  620 . The portions of the second embodiment of lead body assembly  115  shown in  FIG. 6  are collectively referred to with reference numeral  600 .  
         [0063]     An advantageous embodiment of a method for making the second embodiment of lead body  120  (shown in  FIG. 7 ) will now be described. A plurality of conductors  620  is provided in which each conductor  620  is coated with a layer  630  of extrusion material. Each conductor  620  of the plurality of conductors  620  is cylindrically wrapped around (i.e., coiled around) a cylindrically shaped mandrel (not shown). After the lead body  120  is removed from the mandrel, the space formerly occupied by the mandrel will form lumen  650  within the plurality of coated conductors  620 . The layer  630  of extrusion material around each conductor  620  ensures that the conductors  620  are uniformly spaced. An outer layer  640  of extrusion material is placed over the plurality of conductors  620 . The outer layer  640  of extrusion material forms an external coating over the plurality of conductors  620  as shown in  FIG. 6 .  
         [0064]     In an alternative embodiment of the method of the present invention, each conductor  620  of the plurality of conductors  620  is not coiled around the cylindrically shaped mandrel, but instead is placed lengthwise along the axial length of the cylindrically shaped mandrel. An outer layer  640  of extrusion material is placed over the plurality of conductors  620  in the same manner as in the case of the coiled conductors  620 .  
         [0065]     The combined portions  600  of lead body assembly  115  are then covered with heat shrink tubing (not shown) and heat is applied. The heat melts the layers ( 630  and  640 ) of extrusion material and the melted extrusion material flows together to form an integral body. The heat shrink tubing holds and compresses the melted extrusion material around the conductors that are located within the extrusion material to create a unitary body lead  700  as shown in  FIG. 7 . The conductors  620  in unitary body lead  700  may each be centered within the wall  710  of the unitary body lead  700 . Wall  710  is formed from the layers that include the layers ( 630  and  640 ) of extrusion material shown in  FIG. 6 . The unitary body lead  700  is cooled and the heat shrink tubing removed. Lumen  720  is formed when the unitary body lead  700  is removed from the mandrel (not shown). There may be some release of coiled tension in the conductors  620  when the heat shrink tubing is removed.  
         [0066]     The lead body assembly  115  shown in  FIG. 6  has been described as having cylindrical symmetry. It is noted that other types of geometrical cross-sectional shapes (e.g., rectangular) could be used if a different shape is desired for a particular application.  
         [0067]      FIG. 8  illustrates a cross sectional view of a third embodiment of a lead body assembly  115  of the present invention. Lead body assembly  115  includes (1) a plurality of conductors  820  in which each conductor  820  is coated with a layer of extrusion material  830 , and (2) an inner layer  810  of extrusion material. A lumen  840  is formed by the inner wall of inner layer  810 . The portions of the third embodiment of lead body assembly  115  shown in  FIG. 8  are collectively referred to with reference numeral  800 .  
         [0068]     An advantageous embodiment of a method for making the third embodiment of lead body  120  (shown in  FIG. 9 ) will now be described. An inner layer  810  of extrusion material is placed on a cylindrically shaped mandrel (not shown). After the lead body  120  is removed from the mandrel, the space formerly occupied by the mandrel will form lumen  840  within inner layer  810 . Each conductor  820  of a plurality of conductors  820  is coated with a layer  830  of extrusion material. Each conductor  820  of the plurality of conductors  820  is cylindrically wrapped around (i.e., coiled around) the inner layer  810  of extrusion material. The layer of extrusion material  830  around each conductor  820  ensures that the conductors  820  are uniformly spaced as shown in  FIG. 8 .  
         [0069]     In an alternative embodiment of the method of the present invention, each conductor  820  of the plurality of conductors  820  is not coiled around inner layer  810  of extrusion material, but instead is placed lengthwise along the axial length of the inner layer  810  of extrusion material.  
         [0070]     The combined portions  800  of lead body assembly  115  are then covered with heat shrink tubing (not shown) and heat is applied. The heat melts the layers ( 810  and  820 ) of extrusion material and the melted extrusion material flows together to form an integral body. The heat shrink tubing holds and compresses the extrusion material around the conductors that are located within the extrusion material to create a unitary body lead  900  as shown in  FIG. 9 . The conductors  820  in unitary body lead  900  may each be centered within the wall  910  of the unitary body lead  900 . Wall  910  is formed from the layers that include the layers ( 810  and  830 ) of extrusion material shown in  FIG. 8 . The unitary body lead  900  is then cooled and the heat shrink tubing removed. Lumen  920  is formed when the unitary body lead  900  is removed from the mandrel (not shown). There may be some release of coiled tension in the conductors when the heat shrink tubing is removed.  
         [0071]     The lead body assembly  115  shown in  FIG. 8  has been described as having cylindrical symmetry. It is noted that other types of geometrical cross-sectional shapes (e.g., rectangular) could be used if a different shape is desired for a particular application.  
         [0072]      FIG. 10  illustrates a cross sectional view of a fourth embodiment of a lead body assembly  115  of the present invention. Lead body assembly  115  includes a plurality of conductors  1020  in which each conductor  1020  is coated with a layer of extrusion material  1030 . A lumen  1040  is formed by the plurality of conductors  1020 . The portions of the fourth embodiment of lead body assembly  115  shown in  FIG. 10  are collectively referred to with reference numeral  1000 .  
         [0073]     An advantageous embodiment of a method for making the fourth embodiment of lead body  120  (shown in  FIG. 11 ) will now be described. Each conductor  1020  of a plurality of conductors  1020  is coated with a layer  1030  of extrusion material. Each conductor  1020  of the plurality of conductors  1020  is cylindrically wrapped around (i.e. coiled around) a cylindrically shaped mandrel (not shown). After the lead body  120  is removed from the mandrel, the space formerly occupied by the mandrel will form lumen  1040  between the plurality of conductors  1020 . The layer of extrusion material  1030  around each conductor  1020  ensures that the conductors  1020  are uniformly spaced as shown in  FIG. 10 .  
         [0074]     In an alternative embodiment of the method of the present invention, each conductor  1020  of the plurality of conductors  1020  is not coiled around a cylindrically shaped mandrel, but instead is placed lengthwise along the axial length of the mandrel.  
         [0075]     The combined portions  1000  of lead body assembly  115  are then covered with heat shrink tubing (not shown) and heat is applied. The heat melts the layers  1030  of extrusion material around the plurality of conductors  1020  and the melted extrusion material flows together to form an integral body. The heat shrink tubing holds and compresses the extrusion material around the conductors  1020  that are located within the extrusion material to create a unitary body lead  1100  as shown in  FIG. 11 . The conductors  1020  in unitary body lead  1100  may each be centered within the wall  1110  of the unitary body lead  1100 . Wall  1110  is formed from the layers that include the layers  1030  of extrusion material shown in  FIG. 10 . The unitary body lead  1100  is then cooled and the heat shrink tubing removed. Lumen  1120  is formed when the unitary body lead  1100  is removed from the mandrel (not shown). There may be some release of coiled tension in the conductors when the heat shrink tubing is removed.  
         [0076]     The lead body assembly  115  shown in  FIG. 10  has been described as having cylindrical symmetry. It is noted that other types of geometrical cross-sectional shapes (e.g., rectangular) could be used if a different shape is desired for a particular application.  
         [0077]      FIG. 12  illustrates a perspective side view of a mandrel  1210  showing how an exemplary conductor  1220  may be coiled around the axial length of the mandrel  1220 . Other conductors (not shown in  FIG. 12 ) may also be coiled around mandrel  1210  adjacent to conductor  1220 .  
         [0078]      FIG. 13  illustrates a perspective side view of a mandrel  1310  showing how a plurality of conductors may be placed along the axial length of the mandrel  1310 . Two exemplary conductors,  1320  and  1330 , are shown in  FIG. 13  placed along the length of mandrel  1310 . Other conductors (not shown in  FIG. 13 ) may also be placed along the length of mandrel  1310  adjacent to conductors  1320  and  1330 .  
         [0079]      FIG. 14  illustrates a flow chart depicting the steps of one advantageous embodiment of the process of the present invention for making the first embodiment of lead body  120 . The steps of the method are collectively referred to with reference numeral  1400 .  
         [0080]     An inner layer of extrusion material is placed on a cylindrical mandrel (step  1410 ). A plurality of conductors is provided in which each conductor is coated with extrusion material (step  1420 ). Each coated conductor is then wrapped around (or placed on) the inner layer of extrusion material (step  1430 ). An outer layer of extrusion material is then placed over the plurality of coated conductors on the inner layer (step  1440 ).  
         [0081]     The assembly of the inner layer, the coated conductors, and the outer layer is then covered with heat shrink tubing and heat is applied to melt the layers of extrusion material (step  1450 ). The heat shrink tubing compresses the extrusion material around the conductors to form a unitary body lead (step  1460 ). The unitary body lead is then cooled and the heat shrink tubing is removed (step  1470 ).  
         [0082]      FIG. 15  illustrates a flow chart depicting the steps of an advantageous embodiment of the method of the present invention for making the second embodiment of lead body  120 . The steps of the method are collectively referred to with reference numeral  1500 .  
         [0083]     A plurality of conductors is provided in which each conductor is coated with extrusion material (step  1510 ). Each coated conductor is then wrapped around (or placed on) a cylindrical mandrel (step  1520 ). An outer layer of extrusion material is then placed over the plurality of coated conductors on the cylindrical mandrel (step  1530 ).  
         [0084]     The assembly of the coated conductors and the outer layer is then covered with heat shrink tubing and heat is applied to melt the layers of extrusion material (step  1540 ). The heat shrink tubing compresses the extrusion material around the conductors to form a unitary body lead (step  1550 ). The unitary body lead is then cooled and the heat shrink tubing is removed (step  1560 ).  
         [0085]      FIG. 16  illustrates a flow chart depicting the steps of an advantageous embodiment of the method of the present invention for making the third embodiment of lead body  120 . The steps of the method are collectively referred to with reference numeral  1600 .  
         [0086]     An inner layer of extrusion material is placed on a cylindrical mandrel (step  1610 ). A plurality of conductors is provided in which each conductor is coated with extrusion material (step  1620 ). Each coated conductor is then wrapped around (or placed on) the inner layer of extrusion material (step  1630 ).  
         [0087]     The assembly of the inner layer and the coated conductors is then covered with heat shrink tubing and heat is applied to melt the layers of extrusion material (step  1640 ). The heat shrink tubing compresses the extrusion material around the conductors to form a unitary body lead (step  1650 ). The unitary body lead is then cooled and the heat shrink tubing is removed (step  1660 ).  
         [0088]      FIG. 17  illustrates a flow chart depicting the steps of an advantageous embodiment of the method of the present invention for making the fourth embodiment of lead body  120 . The steps of the method are collectively referred to with reference numeral  1700 .  
         [0089]     A plurality of conductors is provided in which each conductor is coated with extrusion material (step  1710 ). Each coated conductor is then wrapped around (or placed on) a cylindrical mandrel (step  1720 ). The assembly of the coated conductors is then covered with heat shrink tubing and heat is applied to melt the layers of extrusion material (step  17930 ). The heat shrink tubing compresses the extrusion material around the conductors to form a unitary body lead (step  1740 ). The unitary body lead is then cooled and the heat shrink tubing is removed (step  1750 ).  
         [0090]     It may be advantageous to set forth definitions of certain words and phrases that may be used within this patent document: the terms “include” and “include,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely.  
         [0091]     While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims.