Abstract:
A method of dimensionally stabilizing a lumen of a multi-lumen device during manufacture wherein one or more minor lumens may contain a fluid that maintains patency of the one or more minor lumens without the need for a solid core within. The at least one second lumen tube may be in fluid communication with a fluid source during the manufacturing process, such as during extrusion and/or mesh overlay steps. Preventing collapse of the one or more minor lumens during manufacture using a fluid instead of a solid core allows the lumens to have any of a variety of shapes and configurations that would be difficult, cost prohibitive, or impossible for a solid core to be used. Also, obviating the need for a solid core within one or more lumens reduces cost and production complexity. The fluid may be a non-compressible liquid or a pressurized gas.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     n/a 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     n/a 
     FIELD OF THE INVENTION 
     The present invention relates to methods and systems for manufacturing a steerable catheter and/or sheath for medical devices, in particular, intravascular and intracardiac sheaths. 
     BACKGROUND OF THE INVENTION 
     Medical devices such as intravascular and intracardiac catheters are commonly used for a variety of medical procedures, such as in cardiovascular, neurologic, endoscopic, neurovascular, renal, and other applications. For example, these steerable devices may be used in minimally invasive procedures such as cardiac ablation, mapping, stent delivery, and imaging. In performing procedures such as these, it is often desirable, if not essential, that the catheter is steerable in order to navigate the catheter through the patient&#39;s vasculature to the desired treatment location. For medical devices that are themselves not steerable, a steerable catheter sheath may be used to guide the medical device to a treatment desired treatment location. 
     Steerable sheaths and steerable catheters may include multiple longitudinal lumens. In the case of a steerable catheter, for example, the catheter body may include a major or central lumen through which a push rod, rigid or semi-rigid guidewire lumen, or shaft may be passed. In the case of a steerable sheath, for example, the sheath may include a major or central lumen through which a second device or catheter may be passed. In both cases, the catheter or sheath may include one or more minor lumens for one or more pull wires used for steering. 
     Manufacturing methods for steerable catheters and sheaths have improved over the years. Many such devices that once required tedious hand assembly or time-intensive ram extrusion can now be produced using extrusion techniques that allow for multilayer extrusion of a device. For example, a sheath may be produced with an inner layer consisting of a lubricious material such as polytetrafluoroethylene (PTFE), a middle layer consisting of a braided steel matrix for strength and torque transmission, and an outer layer consisting of a thermoplastic or similar material. Although the manufacturing process is becoming more efficient, there are still several aspects of steerable catheter and sheath production that are inefficient and costly. 
     One example of a limitation in steerable catheter and sheath production is the creation of the minor lumens. A thin layer of PTFE, for example, having a wall thickness of about 0.025 mm (approximately 0.001 inch), is commonly used for the minor lumens. Although this material is valued for its low coefficient of friction, it is not very rigid and easily collapses during the manufacturing process, particularly when used for the small-diameter minor lumens. To prevent collapse, a rigid mandrel is inserted into each minor lumen to prevent collapse during braiding, reflow, or other manufacturing steps. Although effective in maintaining patency of the minor lumens, the use of mandrels adds cost and complexity to the manufacturing process. 
     Additionally, extrusion may be used to manufacture steerable catheters and sheaths. However, these multi-lumen devices are commonly produced using a discrete extrusion and/or fusing method, in which a usable length of catheter body or sheath, for example, less than six feet (such as around three feet), is extruded at a time. Each length of catheter body or sheath may be manufactured in a series of steps or “passes.” As an example, a polymer tube is extruded and cut to a desired length, creating discrete polymer tubes. Each tube is then slid over a length of mandrel, and a stainless steel braided wire mesh is overlayed over each discrete tube. Then, another polymer tube is slid over the mandrel, first polymer tube, and mesh layer, and the whole assembly is heated in an oven to fuse the materials together and create discrete lengths of catheter or sheath body. Undergoing each step for a discrete length of catheter or sheath is inefficient and adds increased labor requirements and operational costs. 
     It is therefore desired to provide efficient and cost-effective methods of manufacturing steerable catheter bodies and steerable sheaths. In one aspect, it is desirable to provide a method of manufacturing these multi-lumen devices without the need for a mandrel, which incurs additional production cost. In another aspect, it is desirable to provide a method of manufacturing these multi-lumen devices using an efficient extrusion process. 
     SUMMARY OF THE INVENTION 
     The present invention advantageously provides a method and system for producing a multi-lumen medical device. In one embodiment, the method may include extruding at least one layer of material to form an elongate body with a first lumen and a second lumen, the first lumen having a removable core composed of a solid therein and the second lumen having a fluid therein during extrusion of the at least one layer of material. The patency of the second lumen may be maintained by the fluid, regardless of the shape or configuration of the second lumen. The device may include a plurality of second lumens, and each second lumen may have fluid therein. The fluid may be a non-compressible liquid, for example, water, a mixture of water and isopropyl alcohol, silicone fluid, or a combination thereof. If the device includes a plurality of second lumens, each second lumen may have non-compressible liquid therein. Alternatively, the fluid may be a pressurized gas, for example, atmospheric air, nitrogen, or combination thereof. The step of extruding at least one layer of material to form an elongate body may include extruding a layer of first material to define an elongate body having a first lumen and a second lumen and extruding a layer of second material over the layer of first material. The method may further include depositing a mesh layer over the first layer of material. The pressurized gas may have a first pressure during extruding the layer of first material and a second pressure during depositing the mesh layer over the layer of first material and extruding the layer of second material over the mesh layer. The first pressure may be less than the second pressure. The second lumen may be in fluid communication with a source of pressurized gas, the source of pressurized gas being transitionable between delivering pressurized gas at the first pressure and pressurized gas at the second pressure. Alternatively, the second lumen may be in fluid communication with a first source of pressurized gas delivering pressurized gas at the first pressure and in fluid communication with a second source of pressurized gas delivering gas at the second pressure. The first layer of material may define the first and second lumens, or the first and second lumens may each be defined by a first and second lumen tube, respectively, over which the first layer of material may be extruded. In this case, the second lumen tube may be in fluid communication with a source of fluid. 
     A method of producing a multi-lumen elongate body for a medical device may include extruding a first layer of material over a first lumen tube and at least one second lumen tube to form an elongate body with a first lumen and at least one second lumen, the at least one second lumen tube being in fluid communication with a source of fluid that is either pressurized gas or non-compressible liquid, depositing a mesh layer over the elongate body, and extruding a second layer of material over the mesh layer. The first lumen tube may contain a removable solid core. Further, the at least one second lumen tube may contain pressurized gas at a first pressure during the step of extruding a first layer of material and may contain a pressurized gas at a second pressure during the steps of depositing a mesh layer over the elongate body and extruding a second layer of material over the mesh layer, the second pressure being greater than the first pressure. The at least one second lumen tube may contain one of water, a mixture of water and isopropyl alcohol, silicone fluid, and combination thereof. The first lumen tube may also contain pressurized gas at a first pressure during the step of extruding a first layer of material and may also contain a pressurized gas at a second pressure during the steps of depositing a mesh layer over the elongate body and extruding a second layer of material over the mesh layer, the second pressure being greater than the first pressure. 
     A method of producing a multi-lumen medical device may include providing a first lumen tube and providing at least one second lumen tube, each of the first lumen tube and the at least one second lumen tube being in fluid communication with a fluid source; delivering fluid from the fluid source into the first lumen tube and the at least one second lumen tube; extruding a first layer of material over the first lumen tube to form an elongate body having a length, a first lumen, and at least one second lumen; depositing a mesh layer over the length of the elongate body; and extruding a second layer of material over at least a portion of the mesh layer. The fluid source may be a compressed gas, and the method may further include: delivering to the first lumen and the at least one second lumen compressed gas having a first pressure before the step of extruding a first layer of material; delivering to the first lumen and the at least one second lumen compressed gas having a second pressure before the step of depositing a mesh layer over the length of the elongate body; and delivering to the first lumen and the at least one second lumen compressed gas having the second pressure before the step of extruding a second layer of material over at least a portion of the mesh layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1  shows a cutaway view of an exemplary multi-lumen medical device; 
         FIG. 2  shows a cross-sectional view of a multi-lumen medical device with mandrels inserted into the major and minor lumens during prior art manufacturing methods; 
         FIG. 3  shows a cross-sectional view of a multi-lumen medical device with a mandrel inserted into the major lumen during manufacturing, the multi-lumen medical device having a minor lumen composed of a non-collapsible material; 
         FIG. 4  shows a cross-sectional view of a multi-lumen medical device having a non-round minor lumen composed of a non-collapsible material; 
         FIG. 5  shows a cross-sectional view of a multi-lumen medical device having two minor lumens composed of a non-collapsible material; 
         FIG. 6  shows a cross-section view of a multi-lumen medical device having a plurality of minor lumens composed of a non-collapsible material; 
         FIG. 7A  shows a cross-sectional view of a multi-lumen medical device having a minor lumen and a major lumen having non-compressible liquid or pressurized gas within, with the major and minor lumens each being defined by a lumen tube; 
         FIG. 7B  shows a cross-sectional view of a multi-lumen medical device having a minor lumen and a major lumen having non-compressible liquid or pressurized gas within, with the major and minor lumens each being defined by the inner layer; 
         FIG. 8  shows a cross-sectional view of a multi-lumen medical device with mandrel inserted into the major lumen during manufacturing, the multi-lumen medical device having a non-round minor lumen with non-compressible liquid or pressurized gas within; 
         FIG. 9  shows a cross-sectional view of a multi-lumen medical device having a major lumen and two minor lumens with non-compressible liquid or pressurized gas within; 
         FIG. 10  shows a cross-sectional view of a multi-lumen medical device having a major lumen and a plurality of minor lumens with non-compressible liquid or pressurized gas within; 
         FIG. 11  shows a cross-sectional view of a multi-lumen medical device in which a minor lumen is disposed between a braided mesh layer and an outer thermoplastic layer; 
         FIG. 12  shows a cross-sectional view of a multi-lumen medical device in which a minor lumen is disposed within the matrix of a braided mesh layer; 
         FIG. 13  shows a cutaway view of the multi-lumen medical device in which the minor lumen is disposed within the matrix of a braided mesh layer; 
         FIG. 14A  shows a schematic view of a first step in a continuous extrusion multi-lumen medical device manufacturing process; 
         FIG. 14B  shows a schematic view of a second step in a continuous extrusion multi-lumen medical device manufacturing process; 
         FIG. 14C  shows a schematic view of a third step in a continuous extrusion multi-lumen medical device manufacturing process; 
         FIG. 15  shows a cross-sectional view of an unfinished multi-lumen medical device body after the first step of the continuous extrusion process; 
         FIG. 16  shows a cross-sectional view of an unfinished multi-lumen medical device body after the second step of the continuous extrusion process; and 
         FIG. 17  shows a cross-sectional view of a finished multi-lumen medical device body after the third step of the continuous extrusion process. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1 , a cutaway view of an exemplary multi-lumen steerable catheter is shown. Although the methods and configurations shown and described herein may be used for, at least, steerable catheters and steerable sheaths, any type of multi-lumen device capable of being produced as shown and described here is referred to herein for simplicity as “steerable catheter,” “catheter,” or “elongate body.” For example, the methods and configurations shown and described herein may be used for multi-lumen catheters or sheaths that are not steerable or have a plurality of minor lumens with fewer than all minor lumens housing a pull wire (such as catheters having one or more minor lumens for fluid injection or return, electrical connection to the console, housing sensors, or other non-pull wire uses). Also, although the individual layers of the steerable catheter are shown having difference lengths, it will be understood that this is for the sake of illustration only, and that all layers, including those not shown, may be coterminous. Of note, the device components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Moreover, while certain embodiments or figures described herein may illustrate features not expressly indicated on other figures or embodiments, it is understood that the features and components of the penetration device disclosed herein may be included in a variety of different combinations or configurations without departing from the scope and spirit of the invention. 
     As shown in  FIG. 1 , a non-limiting example of a catheter  10  may include a major lumen  12  and one or more minor lumens  14 . In use, the one or more minor lumens  14  may each contain a pull wire  16 . The steerable catheter may be manufactured with several layers of material, such as an inner layer  18 , a braided mesh middle layer  20 , and an outer layer  22 . However, it will be understood that more or fewer layers, and/or different layers than those shown in  FIG. 1 , may be used. Additionally, although a slight gap is shown between each layer for clarity, it will be understood that the layers may be in contact or substantially in contact with each other. 
     Before the finished catheter  10  is produced, the major  12  and minor  14  lumen may be each be a tube  24 ,  26  of material composed of, for example, polytetrafluoroethylene (PTFE). During the first pass of an extrusion process, each tube  24 ,  26  for the major  12  and minor  14  lumens may be coated with a layer of material to form the inner layer  18 . In currently known devices, the major lumen tube  24  and the minor lumen tube  26  may be composed of PTFE. In the present invention, however, the minor lumen tube  26  may be a non-collapsible tube composed of a material having a higher durometer than PTFE, such as polyimide, nylons, fluorinated ethylene propylene (FEP), polyether ether ketone (PEEK), ethylene tetrafluoroethylene (ETFE), or combinations thereof. In either case, the inner layer  18  may be composed of the same material as the major lumen tube  24 , for example, PTFE, which may help the device maintain flexibility. After the inner layer is deposited over the major lumen tube  24  and the minor lumen tube  26 , the inner layer may be substantially circular in cross section. Alternatively, the inner layer may be extruded to have any desired shape, including those that are not circular in cross section. 
     After the first pass of extrusion is finished, the inner layer  18  may be covered in a layer of braided mesh  20 . This braided mesh middle layer  20  may be braided, coiled, or woven about the inner layer  18  using a plurality of individual wires or threads, which may be composed of, for example, stainless steel. Alternatively, the braided mesh  20  may be pre-woven and placed about the inner layer  18  as a sheet or sheath. However, depending on the type and number of layers used, desired configuration, and/or intended use, the braided mesh layer  20  may be at a different location, overlayed on the inner layer  18  in a different manner, and/or may have a configuration other than a braided or woven mesh. 
     Referring now to  FIG. 2 , a cross-sectional view of a multi-lumen steerable catheter during prior art manufacturing methods is shown. Extrusion methods may be used to produce the catheter, as discussed in  FIG. 1 . However, currently known methods of producing a catheter having one or more minor lumens involve the use of a mandrel in each lumen to ensure that the lumens remain open during the entire process. As shown in  FIG. 2 , for example, a mandrel  30  is disposed within the major lumen  12  and a mandrel  32  is disposed within each minor lumen  14 . Although a small gap is shown between the mandrels  30 ,  32  and the lumen tubes  24 ,  26  in  FIG. 2  for illustration purposes only, it will be understood that the mandrels  30 ,  32  will be at least substantially in contact with the inner surfaces of the lumen tubes  24 ,  26  during the manufacturing process, with no or very little gap present. The mandrels may be passed through the extruder in the first pass for each length of catheter body, so that the inner layer  18  is extruded around the mandrels. For example, this may be used if the catheter  10  is extruded such that the major  12  and minor  14  lumens are defined by the inner layer  18 , rather than by individual tubes  24 ,  26  about which the inner layer  18  is extruded. Alternatively, such as when tubes  24 ,  26  are used, the mandrels may be disposed within the major lumen tube  24  and the minor lumen tube  26  prior to the first pass extrusion, in order to support the tubes during the first pass, mesh overlay, and second pass. After the extrusion process is complete, the mandrels  30 ,  32  are removed. This is in contrast to the current invention, in which cores are not required to preserve patency of the minor lumens  14  during manufacture, such as during extrusion and mesh layer overlay. 
     Referring now to  FIGS. 3-6 , cross-sectional views of multi-lumen medical devices are shown, the devices having one or more minor lumens composed of a non-collapsible material. For example, the device may be a catheter. Unlike the currently known catheter shown in  FIG. 2 , the multi-lumen catheter of  FIGS. 3-6  are manufactured using one or more minor lumens  14  each defined by a minor lumen tube  34  that is composed of a material having a higher durometer than PTFE. For example, the minor lumen tubes  34  may be composed of polyimide, nylons, fluorinated ethylene propylene (FEP), polyether ether ketone (PEEK), ethylene tetrafluoroethylene (ETFE), or combinations thereof. The more rigid minor lumen tubes  34  may enable the minor lumens to remain open, that is, not collapse, without a mandrel  32  being disposed within during the manufacturing process. This makes production more cost efficient because the cost of the mandrels are saved, makes production less labor intensive, and makes the product less susceptible to human error and damage. Although a small gap is shown between the mandrel  30  and the major lumen tube  24  in  FIG. 3  for illustration purposes only, it will be understood that the mandrel  30  will be at least substantially in contact with the inner surfaces of the lumen tube  24  during the manufacturing process, with no or very little gap present. Alternatively, the major lumen tube  24  may also be composed of a non-collapsible material, like the one or more minor lumen tubes  34 , that obviates the need for the mandrel  30  to maintain patency of the major lumen  12  during manufacture (as shown in  FIGS. 4-6 ). Although a mandrel  30  is shown in only some figures, it will be understood that a mandrel  30  may or may not be used in the major lumen  12  of any of the configurations shown and described herein. 
     The catheter  10  shown in  FIG. 3  includes a single minor lumen  14  having a substantially circular cross section.  FIG. 4  shows a non-limiting example of a minor lumen  14  having a non-circular cross section. Although the minor lumen  14  in  FIG. 4  is shown as being substantially ellipsoidal, it will be understood that the minor lumen  14  can have any cross-sectional shape sufficient to house fluid, a pull wire, electrical wires, sensors, or other component. Non-circular minor lumen cross sections may be impractical or impossible in currently catheters and methods of production that require the use of a mandrel in each minor lumen  14 . By eliminating the need to use a mandrel, the non-collapsible minor lumen tube  34  may make any of a variety of minor lumen cross sections possible.  FIG. 5  shows an exemplary embodiment having two minor lumens  14 A,  14 B each defined by a non-collapsible tube  34 A,  34 B, respectively, and  FIG. 6  shows an exemplary embodiment having four minor lumens  14 A,  14 B,  14 C,  14 D each defined by a non-collapsible lumen  34 A,  34 B,  234 C,  34 D, respectively. Further multi-lumen embodiments having one or more non-collapsible minor lumen tubes  34  are possible and contemplated other than those shown and described herein. 
     Referring now to  FIGS. 7A-10 , cross-sectional views of multi-lumen catheters are shown, the catheters having one or more minor lumens, the one or more minor lumens containing a non-compressible liquid or pressurized gas. Like the multi-lumen catheters shown in  FIGS. 3-6 , the multi-lumen catheters shown in  FIGS. 7A-10  do not require a mandrel to preserve patency of the minor lumens  14  during manufacture, including during extrusion and mesh layer overlay, which may offer the advantages discussed regarding  FIGS. 3-6 . Although the minor lumens  14  in  FIGS. 7A-10  may be defined by tubes  36  composed of a non-collapsible material such as polyimide, nylons, fluorinated ethylene propylene (FEP), polyether ether ketone (PEEK), ethylene tetrafluoroethylene (ETFE), or combinations thereof, the tubes  36  may alternatively be composed of PTFE or other suitable material. Alternatively, the minor lumens  14  may not be defined by a tube (as shown, for example, in  FIGS. 7A and 8-10 ), but may instead be extruded such that they are defined by the inner layer itself  18  (as shown, for example, in  FIG. 7B ). Although a small gap is shown between the mandrel  30  and the lumen tube  24  in  FIG. 8  for illustration purposes only, it will be understood that the mandrel  30  will be at least substantially in contact with the inner surfaces of the lumen tube  24 , or the portion of the inner layer  18  defining the major lumen  12 , during the manufacturing process, with no or very little gap present, if a mandrel  30  is used. Alternatively, the major lumen tube  24  may also contain a non-compressible liquid or pressurized gas, like the one or more minor lumen tubes  36 , that obviates the need for the mandrel  30  to maintain patency of the major lumen  12  during manufacture (as shown in  FIGS. 7A, 7B, 9, and 10 ). Although a mandrel  30  is shown in only some figures, it will be understood that a mandrel  30  may or may not be used in the major lumen  12  of any of the configurations shown and described herein. 
     In order to preserve patency of the major lumen  12  and/or minor lumens  14  during manufacture, the lumens  12 ,  14  may be filled with a non-compressible fluid and/or a pressurized gas. The fluid within the lumens  12 ,  14  in  FIGS. 7A-10  are collectively referred to with the number “ 38 ” and the term “fluid core.” For example, the minor lumens  14  and/or major lumen  12  may be filled with a fluid core  38  of water, a combination of water and isopropyl alcohol, air (for example, atmospheric air such as a combination of at least oxygen and nitrogen, and optionally also including gases such as argon and carbon dioxide), nitrogen, silicone fluid, or combinations thereof. Other non-compressible fluids and/or gases may also be used. If a gaseous fluid core  38  is used, the pressure of the gas may be adjusted at different stages in the manufacturing process. For example, the minor lumens  14  and/or major lumen  12  may be filled with a fluid core  38  of compressed air at a first pressure during the first extrusion pass. A relatively low pressure within the lumens  12 ,  14  may be used during the first pass because there may be little to no external pressure exerted on the lumens  12 ,  14  that would require substantial pressure within the lumens  12 ,  14  in order to maintain patency. During subsequent stages such as mesh layer overlay and a second extrusion pass, however, the pressure of the gas within the lumens may be increased to a pressure sufficient to withstand the external pressure exerted as, for example, the mesh layer is overlayed on the inner layer  18  and the outer layer, such as a thermoplastic, is extruded over the mesh layer. Further, the pressure should be such that the internal pressure does not cause rupture or damage to the lumens  12 ,  14 . The lumens  12 ,  14  may be in fluid communication with a source of fluid  39  during production (as shown in  FIGS. 14A-14C ). As a non-limiting example, the fluid source may contain a pressurized gas during each stage of production, with the pressure being adjusted to the desired pressure for each step. Alternatively, the lumens  12 ,  14  may be in fluid communication with a first source of pressurized air during the first pass extrusion, and in fluid communication with a second source of pressurized air during the mesh overlay step and the second pass extrusion, the second source of pressurized air being at a higher pressure than the first source of pressurized air. As the manufacturing process may include additional steps that likewise exert pressure on the lumens  12 ,  14 , the increased pressure of the gas within the lumens  12 ,  14  may preserve patency of the lumens  12 ,  14  during these steps as well. 
     The catheter  10  shown in  FIGS. 7A and 7B  includes a single minor lumen  14  having a substantially circular cross section. Additionally, use of a fluid core  38  of non-compressible fluid or pressurized gas instead of a rigid mandrel in the lumens may allow for the use of any of a variety of minor lumen cross sections, other than just circular or substantially circular, because the fluid flows into and offers support for any shape.  FIG. 8  shows an exemplary embodiment having a minor lumen  14  with a non-circular cross-sectional shape. Although the minor lumen  14  in  FIG. 8  is shown as being substantially ellipsoidal, it will be understood that the minor lumen  14 , or the major lumen  12 , can have any cross-sectional shape sufficient to house fluid, a pull wire, electrical wires, sensors, or other component. Non-circular minor lumen cross sections may be impractical or impossible in currently catheters and methods of production that require the use of a mandrel in each lumen  12 ,  14 . By eliminating the need to use a mandrel, the fluid core  38  may make any of a variety of lumen cross sections possible.  FIG. 9  shows an exemplary embodiment having two minor lumens  14 A,  14 B each defined by a non-collapsible tube  34 A,  34 B, respectively, and  FIG. 10  shows an exemplary embodiment having four minor lumens  14 A,  14 B,  14 C,  14 D each defined by a non-collapsible lumen  34 A,  34 B,  234 C,  34 D, respectively. Further multi-lumen embodiments having one or more non-collapsible minor lumen tubes  34  are possible and contemplated other than those shown and described herein. In this embodiment, the fluid source  39  in fluid communication with the lumens  12 ,  14  shown in  FIGS. 14A-14C  may contain a non-compressible liquid. 
     Referring now to  FIGS. 11-13 , cross-sectional views of two exemplary multi-lumen catheters are shown. The minor lumens  14  in  FIGS. 3-10  are shown as being located beneath the mesh layer  20 ; however, the minor lumens  14  may alternatively be placed in other locations. In the non-limiting embodiment shown in  FIG. 11 , the minor lumen  14  may be located on the outside of the mesh layer  20 , between the mesh layer  20  and the outer layer  22 . During manufacture, the major lumen  12  may be formed by covering the major lumen tube  24  with an inner layer  18  during a first pass extrusion, and then the mesh layer  20  may be overlaid on the inner layer  18 . As shown and described in  FIGS. 3-10 , a mandrel  30  may or may not be used in the major lumen  12 . After the mesh layer  20  is in place, a minor lumen tube  40  may be added on top of the mesh layer  20  and passed through a second extrusion pass, creating the outer layer  22  over the mesh layer  20  and minor lumen  14 . In the non-limiting embodiment shown in  FIGS. 12 and 13 , the minor lumen  14  may be part of the mesh layer  20 . For example, the major lumen tube  24  may be covered with a first inner layer  18 A during a first pass extrusion, and then the minor lumen tube  40  may be interwoven with (for example, being passed through the openings in the braid, weave, or mesh pattern) or covered in a layer of mesh  20  that is also interwoven with the layer of mesh  20  surrounding the first inner layer  18 A. The elongate body may then be passed through a second extrusion pass, which may add more of the inner layer material in a second inner layer  18 B on top of the mesh layer  20 , and a third extrusion pass, which may create the outer layer  22  over the mesh layer  20  and/or second inner layer  18 B and minor lumen tube  40 . Alternatively, the minor lumens  14  may be included in other configurations than those shown and described in  FIGS. 3-13 . Although a small gap is shown between the mandrel  30  and the lumen tube  24  in  FIGS. 11-13  for illustration purposes only, it will be understood that the mandrel  30  will be at least substantially in contact with the inner surfaces of the lumen tube  24  during the manufacturing process, with no or very little gap present. 
     Referring now to  FIGS. 14A-17 , a schematic view of a three-step continuous extrusion process is shown. Although manufacturing a steerable (or non-steerable) multi-lumen catheter  10  may involve more than three steps,  FIG. 14  shows a process including a first extrusion pass, a mesh layer overlay, and a second extrusion pass for illustration. As discussed in the Background section, currently known manufacturing processes for multi-lumen devices involve manufacturing a usable length at a time. For example, for use in a medical device including an 86.4 cm multi-lumen catheter body for intravascular use, each approximately 86.4-cm length of catheter body may be manufactured individually, which each length undergoing, for example, a first extrusion pass, an overlay step, and a second extrusion pass. In  FIG. 14 , however, a more efficient method is shown, in which the first and second extrusion passes and the mesh overlay step may each be performed continuously for a length of product that is longer than a typical usable length. That is, a catheter body length of, for example, approximately 100 to approximately 5000 feet may undergo each step at a time, rather than each usable length at a time, and the finished length may then be cut to a desired length. Additionally, the methods shown and described herein maintain patency, or prevent collapse, of the lumens during manufacturing processes that include more than one step, including extrusion. 
     In the non-limiting process shown in  FIGS. 14A-14C , a length of major lumen tubing  44  contained on a first spool  46  and at least one length of minor lumen tubing  48  contained on a second spool  50  may be passed through an extruder  52  in a first extrusion pass. During the first extrusion pass shown in  FIG. 14A , an inner layer  18  composed of, for example, PTFE or other suitable biocompatible material, may be deposited over the major lumen tubing  44  and at least one minor lumen tubing  48 . This first pass may create a length (for example, between approximately 100 to approximately 5000 feet) of unfinished catheter body  54  that includes the major lumen  12 , at least one minor lumen  14 , and the inner layer  18  (as shown in  FIG. 15 ). 
     The major lumen tubing  44  and the minor lumen tubing  48  may each be composed of a commonly used material such as PTFE, or at least the one or more minor lumen tubing  48  and major lumen tubing  24  may be composed of a non-collapsible material such as polyimide, nylons, fluorinated ethylene propylene (FEP), polyether ether ketone (PEEK), ethylene tetrafluoroethylene (ETFE), or combinations thereof, as shown and described in  FIGS. 3-6 . Alternatively, the first pass extrusion may produce an unfinished catheter body  54  that includes the inner layer  18 , with the inner layer  18  defining both the major lumen  12  and the at least one minor lumen  14 . In either configuration, the at least one minor lumen  14  and/or the major lumen  12  may be filled with a non-compressible fluid or a pressurized gas. For example, the at least one minor lumen  14  and/or the major lumen  12  may be in fluid communication with a source of fluid  39 , such as a source of pressurized gas or a source of non-compressible liquid, during each step of the manufacturing process. Alternatively, the major lumen  12  and/or at least one minor lumen  14  may contain a core material  56  that preserves patency of the lumens  12 ,  14  during the manufacturing process. For example, the core material may be composed of metal, such as silver-plated copper. The unfinished catheter body  54  may be wound about a third spool  58  after passing through the first pass extruder  52 . If it is desired to produce a catheter  10  similar to that shown in  FIG. 11 , in which a minor lumen  14  is located outside the mesh layer  20 , or in  FIGS. 12 and 13 , in which a minor lumen  14  passes through the weave or braid of the mesh layer  20 , only the major lumen tubing  44  may be passed through the first extruder  52 , with the minor lumen tubing  48  being added in subsequent steps. 
     After the inner layer  18  is extruded over the major lumen tubing  44  and the at least one minor lumen tubing  48 , the unfinished catheter body  54  may be passed through a water bath  59  to cool the inner layer material before the unfinished catheter body  54  is wound about the third spool  58 . The third spool  58  may then be transferred to, or remain in, a suitable location for the mesh overlay step. 
     Once in a suitable location for the mesh overlay step shown in  FIG. 14B , the unfinished catheter body  54  may be passed from the third spool  58  to a fourth spool  60 . As the unfinished catheter body  54  is passed from the third spool  58  to the fourth spool  60 , the mesh layer may be overlayed on the length of the inner layer  18 , or individual wires or threads (which may be composed of, for example, stainless steel) may be braided, coiled, or woven about the inner layer  18 , producing a length of intermediate unfinished catheter body  62  that includes the major lumen  12 , at least one minor lumen  14 , an inner layer  18 , and a mesh layer  20  (as shown in  FIG. 16 ). This intermediate unfinished catheter body  62  may have the same length as the unfinished catheter body  54 , for example, between approximately 100 feet and approximately 5000 feet. If it is desired to produce a catheter  10  similar to that shown in  FIGS. 12 and 13 , in which a minor lumen  14  passes through the weave or braid of the mesh layer  20 , at least one length of minor lumen tubing  48  may be placed proximate the unfinished product  54  as a weaving machine  64  weaves the mesh wires or threads  66  about the at least one minor lumen tubing  48 , so as to weave the at least one minor lumen tubing  48  into the mesh layer  20 . Alternatively, the at least one length of minor lumen tubing  48  may be woven into the mesh layer  20  in a separate process, and the mesh layer  20  with integrated one or more minor lumens  14  may be overlayed on the unfinished product  54  in a sheet. Also, although not shown, it is contemplated that at least one length of minor lumen tubing  48  may be placed proximate the unfinished product beneath the mesh layer during the mesh overlay step, rather than placing the at least one length of minor lumen tubing  48  proximate the major lumen tubing  44  during the first extrusion pass. That is, the at least one minor lumen  14  may be created during the first extrusion pass or the mesh overlay step. 
     After the mesh overlay step, the intermediate unfinished catheter body  62  may be passed from the fourth spool  60  through a second extruder  68  and, optionally, onto a fifth spool  70 , in a second extrusion pass shown in  FIG. 14C . Alternatively, the intermediate unfinished catheter body  62  may be passed through the first extruder  52  in a second extrusion pass. During the second extrusion pass, an outer layer  22  composed of, for example, a thermoplastic or other suitable biocompatible material, may be extruded over the intermediate unfinished catheter body  62 . This second pass may create a length of finished catheter body  72  that is the same length as in the first pass and mesh overlay step. For example, the length may be between approximately 100 feet and approximately 5000 feet. Further, the finished catheter body  72  may include a major lumen  12 , at least one minor lumen  14 , an inner layer  18 , a mesh layer  20 , and an outer layer  22  (as shown in  FIG. 17 ). Optionally, the outer layer  22  may not be added to the entire length of the intermediate unfinished catheter body  62 . Rather, a distal portion of the intermediate unfinished catheter body  62  may have an exposed area of mesh layer  20  that is not covered by the outer layer  22 . In another option, the outer layer  22  may be extruded over the intermediate unfinished catheter body  62  in sections. For example, the outer layer  22  may be extruded in discrete sections of approximately 3.5 feet, with a section of approximately 0.5 foot (approximately six inches) of exposed mesh layer  20 . That is, the second extrusion pass may produce a length of finished catheter body  72  that includes discrete sections in which the outer layer  22  is not deposited. This may be accomplished by, for example, switching the extruder between an on mode, in which material is deposited on the catheter body, and an off mode, in which material is not deposited on the catheter body as the intermediate unfinished catheter body  62  passes through the extruder. Once the second extrusion pass is complete, the finished catheter body  72  may be cut in the exposed mesh sections into usable lengths, with each end of each usable length having an exposed portion of mesh layer or a portion having no outer layer  22 . These end portions may facilitate various finishing steps, such as balloon attachment, pull wire insertion, electrode attachment, and the like. In contrast to the present invention, currently known methods necessitate an additional step of removing the outer layer  22  in the catheter body usable length end portions in order to finish the device. 
     If it is desired to produce a catheter similar to that shown in  FIG. 11 , in which a minor lumen  14  is located outside the mesh layer  20 , at least one length of minor lumen tubing  48  may be placed proximate the intermediate unfinished catheter body  62  and passed through the first  52  or second  68  extruder in the second extrusion pass, and the outer layer  22  may be extruded over the at least one minor lumen tubing  48  and intermediate unfinished catheter body  62 . The finished catheter body  72  may be passed through a water bath  74  to cool the finished catheter body  72  before it is wound about the fifth spool  70  (as shown in path A in  FIG. 14C ). Alternatively, instead of being wound about the fifth spool  70 , the finished catheter body  72  may be cut into one or more shorter lengths (as shown in path B in  FIG. 14C ). As a non-limiting example, the finished catheter body  72  may be cut into a plurality of shorter catheter bodies  72 A,  72 B,  72 C,  72 D, etc., each having a desired usable length (for example, approximately six feet or less). 
     As the finished catheter body  72  exits the water bath  74 , it may be wound about the fifth spool  70  for storage, shipping, transportation, or sale, and each desired usable length of catheter body  72  may be cut from the length wound about the spool  70 . Alternatively, the finished catheter body  72  may be cut into usable lengths immediately upon exiting the second extrusion pass. The core material  56 , if used, may be removed from the major lumen  12  either before or after the finished catheter body  72  is cut into usable lengths. Likewise, additional components such as pull wires and/or distal polymer segments may be added either before or after the finished catheter body  72  is cut into usable lengths. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.