Abstract:
Devices and methods for altering gaseous flow within a lung to improve the expiration cycle of an individual, particularly individuals having chronic obstructive pulmonary disease. The methods and devices create channels in lung tissue and maintain the patency of these surgically created channels in tissue. Maintaining the patency of the channels allows air to pass directly out of the lung tissue which facilitates the exchange of oxygen ultimately into the blood and/or decompresses hyper-inflated lungs.

Description:
REFERENCE TO RELATED APPLICATION 
     This application is a continuation of International Application Number PCT/US2004/023304 filed Jul. 19, 2004 which claims the benefit under 35 U.S.C. §119(e) of Provisional Application No. 60/488,332 filed Jul. 18, 2003, the contents of which are incorporated herein in their entirety. 
    
    
     FIELD OF THE INVENTION 
     This is directed to methods and devices for altering gaseous flow within a lung to improve the expiration cycle of an individual, particularly individuals having chronic obstructive pulmonary disease. The methods and devices create channels in lung tissue and maintain the patency of these surgically created channels in tissue. Maintaining the patency of the channels allows air to pass directly out of the lung tissue which facilitates the exchange of oxygen ultimately into the blood and/or decompresses hyper-inflated lungs. 
     BACKGROUND OF THE INVENTION 
     The American Lung Association (ALA) estimates that nearly 16 million Americans suffer from chronic obstructive pulmonary disease (COPD) which includes diseases such as chronic bronchitis, emphysema, and some types of asthma. The ALA estimated that COPD was the fourth-ranking cause of death in the U.S. The ALA estimates that about 14 million and 2 million Americans suffer from emphysema and chronic bronchitis respectively. 
     Those inflicted with COPD face disabilities due to the limited pulmonary functions. Usually, individuals afflicted by COPD also face loss in muscle strength and an inability to perform common daily activities. Often, those patients desiring treatment for COPD seek a physician at a point where the disease is advanced. Since the damage to the lungs is irreversible, there is little hope of recovery. Most times, the physician cannot reverse the effects of the disease but can only offer treatment and advice to halt the progression of the disease. 
     To understand the detrimental effects of COPD, the workings of the lungs requires a cursory discussion. The primary function of the lungs is to permit the exchange of two gasses by removing carbon dioxide from arterial blood and replacing it with oxygen. Thus, to facilitate this exchange, the lungs provide a blood gas interface. The oxygen and carbon dioxide move between the gas (air) and blood by diffusion. This diffusion is possible since the blood is delivered to one side of the blood-gas interface via small blood vessels (capillaries). The capillaries are wrapped around numerous air sacs called alveoli which function as the blood-gas interface. A typical human lung contains about 300 million alveoli. 
     The air is brought to the other side of this blood-gas interface by a natural respiratory airway, hereafter referred to as a natural airway or airway, consisting of branching tubes which become narrower, shorter, and more numerous as they penetrate deeper into the lung. Specifically, the airway begins with the trachea which branches into the left and right bronchi which divide into lobar, then segmental bronchi. Ultimately, the branching continues down to the terminal bronchioles which lead to the alveoli. Plates of cartilage may be found as part of the walls throughout most of the airway from the trachea to the bronchi. The cartilage plates become less prevalent as the airways branch. Eventually, in the last generations of the bronchi, the cartilage plates are found only at the branching points. The bronchi and bronchioles may be distinguished as the bronchi lie proximal to the last plate of cartilage found along the airway, while the bronchiole lies distal to the last plate of cartilage. The bronchioles are the smallest airways that do not contain alveoli. The function of the bronchi and bronchioles is to provide conducting airways that lead air to and from the gas-blood interface. However, these conducting airways do not take part in gas exchange because they do not contain alveoli. Rather, the gas exchange takes place in the alveoli which are found in the distal most end of the airways. 
     The mechanics of breathing include the lungs, the rib cage, the diaphragm and abdominal wall. During inspiration, inspiratory muscles contract increasing the volume of the chest cavity. As a result of the expansion of the chest cavity, the pleural pressure, the pressure within the chest cavity, becomes sub-atmospheric. Consequently, air flows into the lungs and the lungs expand. During unforced expiration, the inspiratory muscles relax and the lungs begin to recoil and reduce in size. The lungs recoil because they contain elastic fibers that allow for expansion, as the lungs inflate, and relaxation, as the lungs deflate, with each breath. This characteristic is called elastic recoil. The recoil of the lungs causes alveolar pressure to exceed atmospheric pressure causing air to flow out of the lungs and deflate the lungs. ‘If the lungs’ ability to recoil is damaged, the lungs cannot contract and reduce in size from their inflated state. As a result, the lungs cannot evacuate all of the inspired air. 
     In addition to elastic recoil, the lung&#39;s elastic fibers also assist in keeping small airways open during the exhalation cycle. This effect is also known as “tethering” of the airways. Tethering is desirable since small airways do not contain cartilage that would otherwise provide structural rigidity for these airways. Without tethering, and in the absence of structural rigidity, the small airways collapse during exhalation and prevent air from exiting thereby trapping air within the lung. 
     Emphysema is characterized by irreversible biochemical destruction of the alveolar walls that contain the elastic fibers, called elastin, described above. The destruction of the alveolar walls results in a dual problem of reduction of elastic recoil and the loss of tethering of the airways. Unfortunately for the individual suffering from emphysema, these two problems combine to result in extreme hyperinflation (air trapping) of the lung and an inability of the person to exhale. In this situation, the individual will be debilitated since the lungs are unable to perform gas exchange at a satisfactory rate. 
     One further aspect of alveolar wall destruction is that the airflow between neighboring air sacs, known as collateral ventilation or collateral air flow, is markedly increased as when compared to a healthy lung. While alveolar wall destruction decreases resistance to collateral ventilation, the resulting increased collateral ventilation does not benefit the individual since air is still unable to flow into and out of the lungs. Hence, because this trapped air is rich in CO 2 , it is of little or no benefit to the individual. 
     Chronic bronchitis is characterized by excessive mucus production in the bronchial tree. Usually there is a general increase in bulk (hypertrophy) of the large bronchi and chronic inflammatory changes in the small airways. Excessive amounts of mucus are found in the airways and semisolid plugs of this mucus may occlude some small bronchi. Also, the small airways are usually narrowed and show inflammatory changes. 
     Currently, although there is no cure for COPD, treatment includes bronchodilator drugs, and lung reduction surgery. The bronchodilator drugs relax and widen the air passages thereby reducing the residual volume and increasing gas flow permitting more oxygen to enter the lungs. Yet, bronchodilator drugs are only effective for a short period of time and require repeated application. Moreover, the bronchodilator drugs are only effective in a certain percentage of the population of those diagnosed with COPD. In some cases, patients suffering from COPD are given supplemental oxygen to assist in breathing. Unfortunately, aside from the impracticalities of needing to maintain and transport a source of oxygen for everyday activities, the oxygen is only partially functional and does not eliminate the effects of the COPD. Moreover, patients requiring a supplemental source of oxygen are usually never able to return to functioning without the oxygen. 
     Lung volume reduction surgery is a procedure which removes portions of the lung that are over-inflated. The portion of the lung that remains has relatively better elastic recoil, providing reduced airway obstruction. The reduced lung volume also improves the efficiency of the respiratory muscles. However, lung reduction surgery is an extremely traumatic procedure which involves opening the chest and thoracic cavity to remove a portion of the lung. As such, the procedure involves an extended recovery period. Hence, the long term benefits of this surgery are still being evaluated. In any case, it is thought that lung reduction surgery is sought in those cases of emphysema where only a portion of the lung is emphysematous as opposed to the case where the entire lung is emphysematous. In cases where the lung is only partially emphysematous, removal of a portion of emphysematous lung which was compressing healthier portions of the lung allows the healthier portions to expand, increasing the overall efficiency of the lung. If the entire lung is emphysematous, however, removal of a portion of the lung removes gas exchanging alveolar surfaces, reducing the overall efficiency of the lung. Lung volume reduction surgery is thus not a practical solution for treatment of emphysema where the entire lung is diseased. 
     Both bronchodilator drugs and lung reduction surgery fail to capitalize on the increased collateral ventilation taking place in the diseased lung. There remains a need for a medical procedure that can alleviate some of the problems caused by COPD. There is also a need for a medical procedure that alleviates some of the problems caused by COPD irrespective of whether a portion of the lung, or the entire lung is emphysematous. The production and maintenance of collateral openings through an airway wall allows air to pass directly out of the lung tissue responsible for gas exchange. These collateral openings serve to decompress hyper inflated lungs and/or facilitate an exchange of oxygen into the blood. 
     It was found that creation of collateral channels in COPD patients allowed expired air to pass out of the lungs and decompressed hyper-inflated lungs. Such methods and devices for creating and maintaining collateral channels are discussed in U.S. patent application Ser. No. 09/633,651, filed on Aug. 7, 2000; U.S. patent application Ser. Nos. 09/947,144, 09/946,706, and 09/947,126 all filed on Sep. 4, 2001; U.S. Provisional Application No. 60/317,338 filed on Sep. 4, 2001; U.S. Provisional Application No. 60/334,642 filed on Nov. 29, 2001; U.S. Provisional Application No. 60/367,436 filed on Mar. 20, 2002; and U.S. Provisional Application No. 60/374,022 filed on Apr. 19, 2002 each of which is incorporated by reference herein in its entirety. 
     It was found that creating an opening/channel through an airway wall overcomes the shortcomings associated with bronchodilator drugs and lung volume reduction surgery. To further improve the benefit provided by the channel a need further remains to extend the duration of which the channel remains open (e.g., patency of the opening). Surgically creating a hole in tissue triggers a healing cascade. The body&#39;s natural healing response sets into motion, amongst other things, cell proliferation which can result in a build-up of scar tissue. This tissue overgrowth can occlude or otherwise close the surgically created opening. Additionally, in the event an implant is deployed in the surgically created opening to maintain the patency of the opening, the implant may become encapsulated or filled with tissue thereby occluding the channel. 
     Drug eluting coronary-type stents are not known to overcome the above mentioned events because these stents are often substantially cylindrical (or otherwise have a shape that conforms to the shape of a tubular blood vessel). Hence, they may slide and eject from surgically created openings in an airway wall leading to rapid closure of any channel. Additionally, the design and structure of the coronary-type stents reflect the fact that these stents operate in an environment that contains different tissues when compared to the airways not to mention an environment where there is a constant flow of blood against the stent. Moreover, the design of coronary stents also acknowledges the need to avoid partial re-stenosis of the vessel after stent placement. In view of the above, implants suited for placement in the coronary are often designed to account for factors that may be insignificant when considering a device for the airways. 
     Not surprisingly, experiments in animal models found that placement of a paclitaxel drug eluting vascular stent into the opening did not yield positive results in maintaining the patency of the opening. The shortcomings were both in the physical structure of the stent along with the failure to control the healing cascade caused by creation of the channel. 
     An understanding of the distinctions between the healing response in the coronary versus the airways may explain this outcome. For purposes of our discussion, the healing response in both the coronary and the lungs may be divided into approximately four stages as measured relative to the time of the injury: 1) acute phase; 2) sub-chronic phase; 3) chronic phase; and 4) late phase. 
     In the coronary, after trauma caused by the placement of a coronary stent, the healing process begins in the acute phase with thrombus and acute inflammation. During the sub-chronic phase, there is an organization of the thrombus, an acute/chronic inflammation and early neointima hyperplasia. In the following chronic phase, there is a proliferation of smooth muscle cells along with chronic inflammation and adventitial thickening. In the late stage of the healing process there is chronic inflammation, neointimal remodeling, medial hypertrophy and adventitial thickening. Based upon the observations in a rabbit model, the healing response in the airway begins with a fibrinous clot, edema hemorrhage, and fibrin deposition. In the sub-chronic phase there is re-epithelialization, mucosal hypertrophy, squamous metaplasia, fibroplasias and fibrosus. In the chronic phase, while the epithelium is intact and there is less mucosal hypertrophy, there is still fibroplasia and fibrosis. In the late stage the respiratory epithelium is intact and there is evidence of a scar. 
     In view of the above, a need remains to create channels in airways of COPD patients. A need also remains for methods and devices for creating the channels and placing conduits therein such that the patency of the opening is extended. 
     SUMMARY OF THE INVENTION 
     The invention includes methods and devices for treating a lung suspected of having chronic obstructive pulmonary disease through the creation of collateral channels. The invention also includes extending the duration during which these channels remain open (e.g., maintaining patency.) 
     In one variation, the invention includes a method comprising selecting a treatment site in an airway of the lung, creating a hole in an airway wall of the airway; and expanding the hole in the airway wall. 
     Selecting the treatment site may include visual inspection of the site or inspection for the presence or absence of a blood vessel underneath the surface of the airway wall. 
     Selection of the site may be performed or aided by non-invasive imaging. Such imaging may include x-ray, ultrasound, Doppler, acoustic, MRI, PET, and computed tomography (CT) scans. Furthermore, a substance may be administered into the lungs to assist in the selection of the treatment site. For example, the substance may comprise a hyperpolarized gas, a thermochromatic dye, a regular dye, and/or a contrast agent. 
     Variations of the invention include the use of a less-traumatic holemaker for creation of the channel (note that a channel includes a hole that is created and subsequently expanded.) The less traumatic holemaker may include a piercing member (e.g., a needle, a cannula, a blade, a tube, a rod or other similar structure). The less traumatic holemaker may also include devices which minimize the collateral damage to tissue (e.g., low temperature RF devices, pulsating RF, low temperature laser, ultrasound, high pressure water, etc.) 
     In particular, the devices and methods prevent closure of the channel such that air may flow through the channel and into the airway. Such channels may be made by a variety of methods as discussed in the patents incorporated by reference above. For example, the channel may be made via a surgical incision, a needle, a rotary coring device, etc. Furthermore, the channel may be made by an energy based device, e.g., RF device, laser, etc. However, it has been noted that use of low temperature devices, e.g., mechanical devices, to create the channel result in less trauma to surrounding tissue and thereby minimize the healing response of the tissue. Accordingly, such modes of creating the channel often result in less occlusion of the channel. 
     The method includes expanding the hole by inserting a conduit into the hole. Furthermore, the method may comprise partially expanding the hole by deploying the conduit in the hole, and then fully expanding the hole by expanding the conduit within the hole. 
     Preventing closure may be performed using various approaches including, but not limited to, biochemical, electrical, thermal, irradiation, or mechanical approaches (or any combination thereof). 
     The method may also include delivering a bio-active composition, as described herein, to maintain patency of the channel or conduit. The bio-active composition may be delivered to the airway wall prior to creation of the channel, subsequent to creation of the channel, and/or after insertion and deployment of the conduit. The bio-active composition may also be delivered through a drug eluting process, either through a composition placed on the conduit, or via delivery of a separate eluting substance. 
     Biochemical approaches include delivery of medicines that inhibit closure of the surgically created channel. The medicines may be delivered locally or systematically. In one variation, a delivery catheter includes a dispense lumen that sends a drug to the target site. Also, bioactive substances may be delivered to the channel tissue using various delivery vehicles such as a conduit. The bioactive substance may be disposed on an exterior surface of the conduit such that it interacts with the channel tissue when the conduit is placed at the injury site. Also, bioactive substances may be delivered to the channel tissue before or after the conduit is positioned in the channel. The bioactive agent may also be delivered to the target site alone. That is, a medicine may be sent to the surgically created channel as the sole mechanism for maintaining the patency of the channel. 
     Also, systematic delivery of medicines may be carried out through digestion, injection, inhalation, etc. Systematic delivery of medicines may be provided alone or in combination with other techniques described herein. For example, a patient having undergone the procedures described herein may be prescribed steroids and/or COX-2 inhibitors in an attempt to prolong the effects of the treatment. 
     Any of the conduits discussed herein may also include at least one visualization feature disposed on a portion of the tissue barrier. The visualization feature may be a stripe circumferentially disposed about at least a portion of the center section. The visualization feature serves to aid in placement or deployment of the conduit in a target site. 
     Another conduit for maintaining the patency of a channel created in tissue comprises a radially expandable center section and extension members as described above. A bioactive substance is disposed on at least a portion of a surface of the conduit. Also, when the conduit is radially expanded it has an overall length and an inner diameter such that a ratio of the overall length to the inner diameter ranges from 1/6 to 2/1. The conduit may also be provided such that this ratio ranges from 1/4 to 1/1 and perhaps, 1/4 to 1/2. A tissue barrier may be disposed on at least a portion of the exterior surface corresponding to the center section. The tissue barrier may be comprised of various materials including but not limited to polymers and elastomers. An example of a material which may be used for the tissue barrier is silicone. Additional matrixes of biodegradable polymer and medicines may be associated with the tissue barrier such that controlled doses of medicines are delivered to the tissue opening. 
     The invention includes a hole-making catheter for creating and dilating an opening within tissue, the catheter comprising an elongate shaft having a proximal portion and a distal portion, and at least one lumen extending through the proximal end; a balloon having an interior in fluid communication with the lumen, the balloon located on the distal portion of the elongate shaft, the balloon having an uninflated state and an inflated state; a piercing member located at the distal portion of the elongate shaft, the piercing member being extendable and retractable within the elongate shaft; and a depth limiter stop located on the exterior of the distal portion of the elongate shaft, proximal to the balloon and larger in working diameter than the uninflated balloon, which limits the maximum penetration of the catheter into tissue. 
     The piercing member may include a body portion having a lumen extending therethrough. The lumen of the piercing member may be in fluid communication with a central lumen of the elongate shaft. In some variations of the invention an obturator is used within the device, where the obturator is slidably located within the lumen of the elongate body and piercing member. 
     The elongate body and/or piercing member may have multiple lumens. For example, they may be constructed from multi-lumen tubing. In some variations, the piercing member is retractable within the elongate shaft. 
     The balloon member may consist of a distensible balloon or a non-distendsible balloon. For either type of balloon, the working diameter may closely match the outer diameter of the piercing member. 
     The invention may also include an implant located about the balloon of the device. In use, the piercing member would create a channel within the tissue, the device is then further advanced until the implant is located within the channel. Inflation of the balloon then deploys the implant within the channel thereby improving the patency of the channel. 
     Implants for the present invention include, but are not limited to, a stent, conduit, grommet, valve, graft, anchor, etc. 
     It should be noted that since the device must often access airways deep within the lung, the elongate shaft may be comprised of a flexible material. In particular, the elongate shaft may be sufficiently flexible to pass through a fully articulated bronchoscope. 
     The piercing member of the current invention may also be used to deliver bio-active agents to the site of the collateral channel. As described herein, such agents may increase the duration of patency of the channels and/or implants. 
     The invention includes a balloon catheter for deploying a device within an opening in tissue, the balloon catheter comprising an elongate shaft having a proximal portion, a distal portion, a proximal end, a distal end; and at least one lumen extending through the proximal end, a balloon having an interior in fluid communication with the lumen, the balloon located on the distal end portion of the elongate shaft, a guide member extending distally from the distal end of the elongate shaft, the guide member comprising a rounded surface at an end opposite to the elongate shaft, where the guide member has sufficient column strength to penetrate the opening in tissue, the guide member further comprising at least one resistance surface a such that when the body enters the opening, the resistance surface exerts resistance against tissue upon removal of the guide member from the opening. 
     The resistance surface may have an increased diameter greater to provide resistance upon removal from tissue. It may alternatively, or in combination, comprise a rough surface to provide added friction upon removal of the device. 
     The guide member may be tapered, rounded, partially-spherical, elliptical, prolate, cone-shaped, triangular, or any similar shape. It is contemplated that there may be more than one resistance surface on the guide body. Moreover, the guide body may have a wavy/variable diameter shape providing several resistance surfaces on the areas of increased diameter. 
     The device may also be used with an implant that may be located about the balloon where upon expansion of the balloon, the implant deploys. The implant may be selected from a stent, conduit, grommet, valve, graft, and anchor. 
     In another variation of the invention, the balloon catheter may further comprise a dilating member located distally of the balloon. The dilating member may be is located on the distal portion of the shaft between the distal end and the balloon and may comprise a tapered section, a second balloon, or other similar structure. 
     In some variations of the invention, the dilating member may be retractable within the elongate shaft. 
     The device may also include a needle assembly moveably located in the instrument lumen, where the needle assembly is advanceable through a hole-making lumen and out of the opening in the rounded surface. 
     The balloon catheter may be constructed to be sufficient flexibility to advance through a fully articulated bronchoscope. 
     The balloon catheter may also be configured to deliver bio-active substances (e.g., drugs, medicines, compounds, etc.) to the tissue, either via the elongate tube or the guide member. Furthermore, the device may be adapted to provide suction to clear the target site. 
     The invention includes a hole-making catheter for creating and dilating an opening within tissue, the catheter comprising; an elongate shaft having a proximal portion and a distal portion, and at least one lumen extending through the proximal end; a nondistensible balloon having an interior in fluid communication with the lumen, the nondistensible balloon located on the distal portion of the elongate shaft; and a piercing member located at the distal portion of the elongate shaft, the piercing member being extendable and retractable within the elongate shaft. 
     The invention includes an implant delivery system for deploying the implant within a wall of tissue, the system comprising; an elongate shaft having a distal portion, a proximal end, a distal end, at least one lumen extending through the proximal end; a balloon member having an interior in fluid communication with the lumen, the balloon member located on the distal portion of the elongate shaft; a piercing member distally located to the distal end of the elongate shaft within the second lumen, the solid piercing member having a sharpened distal end adapted to penetrate tissue; and an expandable implant located about the balloon member. 
     The preceding illustrations are examples of the invention described herein. It is contemplated that, where possible, combinations of features/aspects of specific embodiments or combinations of the specific embodiments themselves are within the scope of this disclosure. 
     This application is also related to the following applications 60/420,440 filed Oct. 21, 2002; 60/387,163 filed Jun. 7, 2002; Ser. No. 10/235,240 filed Sep. 4, 2002; Ser. No. 09/947,144 filed Sep. 4, 2001; Ser. No. 09/908,177 filed Jul. 18, 2001; Ser. No. 09/633,651 filed Aug. 7, 2000; and 60/176,141 filed Jan. 14, 2000; Ser. No. 10/080,344 filed Feb. 21, 202; Ser. No. 10/079,605 filed Feb. 21, 2002; Ser. No. 10/280,851 filed Oct. 25, 2002; and Ser. No. 10/458,085 filed Jun. 9, 2003. Each of which is incorporated by reference herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1C  illustrate various states of the natural airways and the blood-gas interface. 
         FIG. 1D  illustrates a schematic of a lung demonstrating a principle of the invention described herein. 
         FIG. 2A  illustrates a side view of a conduit in an undeployed state. 
         FIG. 2B  illustrates a side view of the conduit of  FIG. 2A  shown in a deployed shape. 
         FIG. 2C  illustrates a front view of the conduit shown in  FIG. 2B . 
         FIG. 2D  is a cylindrical projection of the undeployed conduit shown in  FIG. 2A . 
         FIG. 2E  illustrates a side view of another variation of a conduit in an undeployed shape. 
         FIG. 2F  illustrates a side view of the conduit of  FIG. 2E  in a deployed state. 
         FIG. 2G  is a cylindrical projection of the undeployed conduit shown in  FIG. 2E . 
         FIG. 3A  illustrates a side view of a conduit having a tissue barrier in a deployed state. 
         FIG. 3B  illustrates a side view of a conduit having a tissue barrier. 
         FIG. 3C  is a front view of the conduit shown in  FIG. 3B . 
         FIG. 3D  illustrates a conduit positioned in a channel created in a tissue wall. 
         FIG. 3E  is a cross sectional view of the conduit shown in  FIG. 3B  taken along line  3 E- 3 E. 
         FIGS. 3F-3G  depict another conduit including a membrane that supports a bioactive substance; the bioactive substance may be coated on the membrane. 
         FIGS. 4A-4C  a variation of selecting a site, creating a channel at the site using a less traumatic hole-maker, and expanding the channel. 
         FIGS. 4D-4K  illustrate variations of piercing members for creating collateral channels. 
         FIGS. 5A-5C  illustrate a method for deploying a conduit. 
         FIGS. 5D-5E  illustrate a method for deploying a conduit within another implant. 
         FIGS. 6A-6B  illustrate a method for deploying a conduit at an angle. 
         FIGS. 7A-7B  illustrate placement of a conduit within a channel by using a guide member. 
         FIGS. 8A-8F  illustrate additional variations of guide bodies for use with catheters of the present invention. 
         FIGS. 9A-9B  illustrate additional features for use with guide bodies of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Described herein are devices (and methods) for improving the gas exchange in the lung. In particular, methods and devices are described that serve to maintain collateral openings or channels through an airway wall so that air is able to pass directly out of the lung tissue and into the airways. This facilitates exchange of oxygen into the blood and decompresses hyper inflated lungs. 
     By “channel” it is meant to include, but not be limited to, any opening, hole, slit, channel or passage created in the tissue wall (e.g., airway wall). The channel may be created in tissue having a discrete wall thickness and the channel may extend all the way through the wall. Also, a channel may extend through lung tissue which does not have well defined boundaries such as, for example, parenchymal tissue. 
     The channels may be maintained by preventing or inhibiting tissue from growing into or otherwise blocking the channel. Chemical, electrical, light, mechanical, or a combination of any two or more of these approaches may be performed to maintain the channel openings. For example, the channel walls may be treated with a bioactive agent which inhibits tissue growth. The bioactive agent may be delivered locally or systematically. Also, the channels may be treated with rf energy, heat, electrical energy, or radiation to inhibit tissue overgrowth. These treatments may be performed once, periodically, or in response to the severity of the channel blockage. For example, the tissue blockage may be periodically removed with a laser or another tissue-removal tool. Also, mechanical devices and instruments may be deployed in the channel to prevent tissue growth from blocking the channel. Mechanical devices include without limitation conduits, valves, sponges, etc. These mechanical devices may be deployed permanently or temporarily. If deployed temporarily, the devices are preferably left in the channel for a sufficient amount of time such that the channel tissue heals coaxially around the device. 
       FIGS. 1A-1C  are simplified illustrations of various states of a natural airway and a blood gas interface found at a distal end of those airways.  FIG. 1A  shows a natural airway  100  which eventually branches to a blood gas interface  102 . 
     Although not shown, the airway comprises an internal layer of epithelial pseudostratified columnar or cuboidal cells. Mucous secreting goblet cells are also found in this layer and cilia may be present on the free surface of the epithelial lining of the upper respiratory airways. Supporting the epithelium is a loose fibrous, glandular, vascular lamina propria including mobile fibroblasts. Deep in this connective tissue layer is supportive cartilage for the bronchi and smooth muscle for the bronchi and bronchioles. 
       FIG. 1B  illustrates an airway  100  and blood gas interface  102  in an individual having COPD. The obstructions  104  impair the passage of gas between the airways  100  and the interface  102 .  FIG. 1C  illustrates a portion of an emphysematous lung where the blood gas interface  102  expands due to the loss of the interface walls  106  which have deteriorated due to a bio-chemical breakdown of the walls  106 . Also depicted is a constriction  108  of the airway  100 . It is generally understood that there is usually a combination of the phenomena depicted in  FIGS. 1A-1C . Often, the states of the lung depicted in  FIGS. 1B and 1C  may be found in the same lung. 
       FIG. 1D  illustrates airflow in a lung  118  when conduits  200  are placed in collateral channels  112 . As shown, collateral channels  112  (located in an airway wall) place lung tissue  116  in fluid communication with airways  100  allowing air to pass directly out of the airways  100  whereas constricted airways  108  may ordinarily prevent air from exiting the lung tissue  116 . While the invention is not limited to the number of collateral channels which may be created, it is to be understood that 1 or 2 channels may be placed per lobe of the lung and perhaps, 2-12 channels per individual patient. However, as stated above, the invention includes the creation of any number of collateral channels in the lung. This number may vary on a case by case basis. For instance, in some cases in an emphysematous lung, it may be desirable to place 3 or more collateral channels in one or more lobes of the lung. 
     Although  FIG. 1D  depicts a mechanical approach to maintaining channels in the airway walls, the channel openings may be maintained using a variety of approaches or combinations of approaches. 
     As shown in  FIGS. 2A-2G , the conduits described herein generally include a center section  208  and at least one extension member (or finger)  202  extending from each end of the center section. The extension members, as will be discussed in more detail below, are capable of deflecting or outwardly bending to secure the conduit in an opening created in an airway wall thereby maintaining the patency of the opening. The extension members may deflect such that opposing extension members may form a V, U or other type of shape when viewed from the side. 
     Additionally, the conduits shown in  FIGS. 2A-2G  include a center-control segment  235 ,  256  which restricts or limits radial expansion of the center section. The center-control segments are adapted to straighten as the center section is radially expanded. Once the center-control segments become straight or nearly straight, radial expansion of the conduit is prevented. In this manner, the radial expansion of the conduit may be self controlled. 
     It is understood that the conduits discussed herein are not limited to those shown in the figures. Instead, conduits of various configurations may be used as described herein. Such conduits are described in the following patent applications Ser. No. 09/908,177 filed Jul. 18, 2001; PCT/US03/12323 filed Apr. 21, 2003; Ser. No. 09/947,144 filed Sep. 4, 2001; Ser. No. 10/235,240 filed Sep. 4, 2002; and Ser. No. 10/458,085 filed Jun. 9, 2003 the entirety of each of which is hereby incorporated by reference. 
     Conduit States 
     The conduits described herein may have various states (configurations or profiles) including but not limited to (1.) an undeployed state and (2.) a deployed state. 
     The undeployed state is the configuration of the conduit when it is not secured in an opening in an airway wall and, in particular, when its extension members (or fingers) are not outwardly deflected to engage the airway wall.  FIG. 2A  is a side view of a conduit  200  in an undeployed state. As shown in this figure, extension members  202 A,  202 B extend straight from the ends  210 ,  212  respectively of center section  208 . The extension members shown in this example are parallel. However, the invention is not so limited and the extension members need not be parallel. 
     The deployed state is the configuration of the conduit when it is secured in a channel created in an airway wall and, in particular, when its extension members are outwardly bent to engage the airway wall such that the conduit is fixed in the opening. An example of a conduit in its deployed configuration is shown in  FIGS. 2B and 2C .  FIG. 2B  is a side view of a conduit in its deployed state and  FIG. 2C  shows a front view of the conduit of  FIG. 2B . 
     Center Section of the Conduit 
     As shown in  FIGS. 2A-2D , the conduit includes a center section  208  having a short passageway. This center section may be a tubular-shaped open-frame (or mesh) structure having a plurality of ribs. Also, as explained in more detail below, the center section may be a sheet of material. 
     The axial length of the center section or passageway may be relatively short. In  FIGS. 2A-2D , the passageway&#39;s length is about equal to the width of a wire segment or rib. Here, the center section serves as a bridge or junction for the extension members and it is not required to be long. The axial length of the passageway may therefore be less than 1 mm and even approach 0 mm. In one example, the length of the center section is less than twice the square root of a cross sectional area of the center section. However, the center section may also have passageways which have lengths greater than 1 mm. 
     The overall length (L) of the conduit may be distinguished from the length of the center section because the overall length includes the lengths of the extension members. Further, the overall length (L) is dependent on which state the conduit is in. The overall length of the conduit will typically be shorter when it is in a deployed state as shown in  FIG. 2B  than when it is in an undeployed state as shown in  FIG. 2A . The overall length (L) for a deployed conduit may be less than 6 mm and perhaps, between 1 and 20 mm. 
       FIG. 2C  shows a front view of the conduit  200  shown in  FIG. 2B .  FIG. 2C  shows the passageway having a hexagonal (or circular) cross section. The cross-section, however, is not so limited. The cross section may be circular, oval, rectangular, elliptical, or any other multi-faceted or curved shape. The inner diameter (D 1 ) of the center section, when deployed, may range from 1 to 10 mm and perhaps, from 2 to 5 mm. Moreover, in some variations, the cross-sectional area of the passageway, when deployed, may be between 0.2 mm 2  to 300 mm 2  and perhaps between 3 mm 2  and 20 mm 2 . 
     The diameter of the center section, when deployed, thus may be significantly larger than the passageway&#39;s axial length (e.g., a 3 mm diameter and an axial length of less than 1 mm). This ratio of the center section length to diameter (D 1 ) may range from about 0:10 to 10:1, 0.1:6 to 2:1 and perhaps from 1:2 to 1:1. 
     The diameter of the center section, when deployed, may also be nearly equal to the overall length (L) of the conduit  200 . This overall length (L) to diameter (D 1 ) ratio may range from 1:10 to 10:1, 1:6 to 2:1, and perhaps from 1:4 to 1:1. However, the invention is not limited to any particular dimensions or ratio unless so indicated in the appended claims. Rather, the conduit should have a center section such that it can maintain the patency of a collateral channel in an airway wall. The dimensions of the center section (and the conduit as a whole) may be chosen based on the tissue dimensions. When the channel is long in its axial length, for example, the length of the center section may likewise be long or identical to the channel&#39;s length. 
     Extension Members of the Conduit 
     As mentioned above, extending from the ends of the center section  208  are extension members  202 A,  202 B which, when the conduit is deployed, form angles A 1 , A 2  with a central axis of the passageway. When viewed from the side such as in  FIG. 2B , opposing extension members may have a V, U, or other shape. The extension members  202 A,  202 B may thus outwardly rotate until they sandwich tissue (not shown) between opposing extension members. 
     The angles A 1 , A 2  may vary and may range from, for example, 30 to 150 degrees, 45 to 135 degrees and perhaps from 30 to 90 degrees. Opposing extension members may thus form angles A 1  and A 2  of less than 90 degrees when the conduit is deployed in a channel. For example, angles A 1  and A 2  may range from 30 to 60 degrees when the conduit is deployed. 
     The conduits of the present invention are effective and may maintain a surgically created opening despite not substantially sandwiching tissue between opposing extension members as described above. Additionally, it is not necessary for the conduits of the present invention to prevent air from flowing along the exterior of the conduit. That is, air may move into (and through) spaces between the exterior of the conduit and the interior wall of the tissue channel. Thus, fluidly sealing the edges of the conduit to prevent side flow or leakage around the conduit is not crucial for the conduits to be effective. However, the conduits of the present invention are not so limited and may reduce or eliminate side flow by, for example, increasing the angles A 1  and A 2  and adding sealant around the exterior of the conduit. 
     Moreover, the angle A 1  may be different than angle A 2 . Accordingly, the conduit may include proximal extension members which are parallel (or not parallel) to the distal extension members. Additionally, the angle corresponding to each proximal extension member may be different or identical to that of another proximal extension member. Likewise, the angle corresponding to each distal extension member may be different or identical to that of another distal extension member. 
     The extension members may have a length between 1 and 20 mm and perhaps, between 2 and 6 mm. Also, with reference to  FIG. 2C , the outer diameter (D 2 ) of a circle formed by the free ends of the extension members may range from 2 to 20 and perhaps, 3 to 10 mm. However, the invention is not limited to the dimensions disclosed above. Furthermore, the length of the distal extension members may be different than the length of the proximal extension members. The length of the distal extension members may be, for example, longer than that of the proximal extension members. Also, the lengths of each proximal extension member may be different or identical to that of the other proximal extension members. Likewise, the lengths of each distal extension member may be different or identical to that of the other distal extension members. 
     The number of extension members on each end of the center section may also vary. The number of extension members on each end may range from 2-10 and perhaps, 3-6. Also, the number of proximal extension members may differ from the number of distal extension members for a particular conduit. Moreover, the extension members may be symmetrical or non-symmetrical about the center section. The proximal and distal extension members may also be arranged in an in-line pattern or an alternating pattern. The extension members or the center section may also contain barbs or other similar configurations to increase adhesion between the conduit and the tissue. The extension members may also have openings to permit tissue ingrowth for improved retention. 
     The shape of the extension members may also vary. They may be open-framed and somewhat petal-shaped as shown in  FIGS. 2A-2D . In these figures, the extension members  202 A,  202 B comprise wire segments or ribs that define openings or spaces between the members. However, the invention is not so limited and the extension members may have other shapes. The extension members may, for example, be solid or they may be filled. 
     In another variation the conduit is constructed to have a delivery state. The delivery state is the configuration of the conduit when it is being delivered through a working channel of a bronchoscope, endoscope, airway or other delivery tool. The maximum outer diameter of the conduit in its delivery state must therefore be such that it may fit within the delivery tool, instrument, or airway. 
     In one variation, the conduit is radially expandable such that it may be delivered in a smaller working channel of a scope while maximizing the diameter to which the conduit may expand upon deployment. For example, sizing a conduit for insertion into a bronchoscope having a 2 mm or larger working channel may be desirable. Upon deployment, the conduit may be expanded to have an increased internal diameter (e.g., 3 mm.) However, the invention is not limited to such dimensions. It is contemplated that the conduits  200  may have center sections that are expanded into a larger profile from a reduced profile, or, the center sections may be restrained in a reduced profile, and upon release of the restraint, return to an expanded profile. 
     Additionally, the conduit need not have a smaller delivery state. In variations where the center section is not able to assume a second smaller delivery profile, a maximum diameter of the first or deployed profile will be sufficiently small such that the conduit may be placed and advanced within an airway or a working channel of a bronchoscope or endoscope. Also, in cases where the conduit is self-expanding, the deployed shape may be identical to the shape of the conduit when the conduit is at rest or when it is completely unrestrained. 
     Additionally the conduit may be partially expanded in its proximal region in the delivery state, as shown in figure X. The partially expanded portion would still me sized small enough to fit within the working channel of the bronchoscope, but would be significantly larger (e.g., 0.5-2 mm) larger that the distal portion of the conduit. This partial expansion allows for easy placement of the conduit by providing a physical stop for the conduit within the airway wall. After the conduit is placed the entire conduit can be expanded to its intended expanded shape. 
     The partial expansion state can also be achieved by partially inflating the proximal section of the conduit with a separate balloon on the delivery device. Another possible method is to design the conduit to preferentially expand the proximal section before the distal section, thereby partially expanding the conduit to create the size differential, placing the stent inside the airway wall with the aid of the stop, and then fully expanding the conduit. 
     Control Members 
     The conduit  200  shown in  FIGS. 2A-2D  also includes diametric-control segments, tethers, or leashes  235  to control and limit the expansion of the center section  208  when deployed. This center-control segment  235  typically is shaped such that when the conduit radially expands, the center-control segment bends until it is substantially straight or no longer slack. Such a center-control segment  235  may be circular or annular shaped. However, its shape may vary widely and it may have, for example, an arcuate, semi-circular, V, or other type of shape which limits the expansion of the conduit. 
     Typically, one end of the center-control segment is attached or joined to the center section at one location (e.g., a first rib) and the other end of the center-control segment is connected to the center section at a second location (e.g., a rib adjacent or opposite to the first rib). However, the center-control segments may have other constructs. For example, the center-control segments may connect adjacent or non-adjacent center section members. Further, each center-control segment may connect one or more ribs together. The center-control segments may further be doubled up or reinforced with ancillary control segments to provide added control over the expansion of the center section. The ancillary control segments may be different or identical to the primary control segments. 
       FIG. 2B  illustrates the conduit  200  in its deployed configuration. As discussed above, the center-control segments  235  may bend or otherwise deform until they maximize their length (i.e., become substantially straight) such as the center-control segments  235  shown in  FIG. 2B . However, as discussed above, the invention is not so limited and other types of center-control segments may be employed. 
     As shown in  FIGS. 2E-2G , control segments  252  may also be used to join and limit the expansion of the extension members  254  or the control segments may be placed elsewhere on the conduit to limit movement of certain features to a maximum dimension. By controlling the length of the control segments, the shape of the deployed conduit may be controlled. In the conduit shown in  FIGS. 2E-2G , the conduit includes both center-control segments  256  and distal control segments  252 . The center-control segments are arcuate shaped and join adjacent rib sections of the center section and the distal-control segments are arcuate and join adjacent distal extension members. 
       FIG. 2F  illustrates the conduit in a deployed configuration and shows the various control members straightening as the extension members and center section deploy. The proximal extension members, however, are not restricted by a control member and consequently may be deflected to a greater degree than the distal extension members. Accordingly, a conduit having control members connecting, for example, regions of the center section and having additional control segments connecting extension members, may precisely limit the maximum profile of a conduit when it is deployed. This is desirable where overexpansion of the conduit is hazardous. 
     This also serves to control the deployed shape of the conduit by, for instance, forcing angle A 1  to differ from angle A 2 . Using control segments in this manner can provide for cone-shaped conduits if the various types of control-segments have different lengths. For example, providing longer proximal-control segments than distal-control segments can make angle A 1  larger than angle A 2 . Additionally, cylindrical-shaped conduits may be provided if the center-control segments and the extension-control segments are sized similarly such that angle A 1  equals angle A 2 . Again, the control segments straighten as the conduit expands and the conduit is thus prevented from expanding past a predetermined amount. 
     The control segments, as with other components of the conduit, may be added or mounted to the center section or alternatively, they may be integral with the center section. That is, the control segments may be part of the conduit rather than separately joined to the conduit with adhesives or welding, for example. The control segments may also be mounted exteriorly or interiorly to the members to be linked. Additionally, sections of the conduit may be removed to allow areas of the conduit to deform more readily. These weakened areas provide another approach to control the final shape of the deployed conduit. Details for creating and utilizing weakened sections to control the final shape of the deployed conduit may be found in U.S. patent Ser. No. 09/947,144 filed on Sep. 4, 2001. 
     Manufacture and Materials 
     The conduit described herein may be manufactured by a variety of manufacturing processes including but not limited to laser cutting, chemical etching, punching, stamping, etc. For example, the conduit may be formed from a tube that is slit to form extension members and a center section between the members. One variation of the conduit may be constructed from a metal tube, such as stainless steel, 316L stainless steel, titanium, titanium alloy, nitinol, MP35N (a nickel-cobalt-chromium-molybdenum alloy), etc. Also, the conduit may be formed from a rigid or elastomeric material that is formable into the configurations described herein. Also, the conduit may be formed from a cylinder with the passageway being formed through the conduit. The conduit may also be formed from a sheet of material in which a specific pattern is cut. The cut sheet may then be rolled and formed into a tube. The materials used for the conduit can be those described above as well as a polymeric material, a biostable or implantable material, a material with rigid properties, a material with elastomeric properties, or a combination thereof. If the conduit is a polymeric elastic tube (e.g. a thermoplastic elastomer), the conduit may be extruded and cut to size, injection molded, or otherwise formed. 
     Additionally, the conduits described herein may be comprised of a shape memory alloy, a super-elastic alloy (e.g., a NiTi alloy), a shape memory polymer, or a shape memory composite material. The conduit may be constructed to have a natural self-assuming deployed configuration, but is restrained in a pre-deployed configuration. As such, removal of the restraints (e.g., a sheath) causes the conduit to assume the deployed configuration. A conduit of this type could be, but is not limited to being, comprised from an elastic polymeric material, or shape memory material such as a shape memory alloy. It is also contemplated that the conduit could comprise a shape memory alloy such that, upon reaching a particular temperature (e.g., 98.5° F.), it assumes a deployed configuration. 
     Also, the conduit described herein may be formed of a plastically deformable material such that the conduit is expanded and plastically deforms into a deployed configuration. The conduit may be expanded into its expanded state by a variety of devices such as, for example, a balloon catheter. 
     The conduit&#39;s surface may be modified to affect tissue growth or adhesion. For example, an implant may comprise a smooth surface finish in the range of 0.1 micrometer to 0.01 micrometer. Such a finish may serve to prevent the conduit from being ejected or occluded by tissue overgrowth. On the other hand, the surface may be roughened or porous. The conduit may also comprise various coatings and tissue barriers as discussed below. 
     Tissure Barrier 
       FIG. 3A  illustrates another variation of a conduit  200  having a tissue barrier  240 . The tissue barrier  240  prevents tissue ingrowth from occluding the collateral channel or passage of the conduit  200 . The tissue barrier  240  may coaxially cover the center section from one end to the other or it may only cover one or more regions of the conduit  200 . The tissue barrier may completely or partially cover the conduit so long as the ends are at least partially open. Moreover, the tissue barrier may only be placed on the center section of the conduit. The tissue barrier  240  may be located about an exterior of the conduit&#39;s surface, about an interior of the conduit&#39;s surface, or the tissue barrier  240  may be located within openings in the wall of the conduit&#39;s surface. Furthermore, in some variations of the invention, the center section  208  itself may provide an effective barrier to tissue ingrowth. The tissue barrier, of course, should not cover or block the entrance and exit of the passageway such that air is prevented from passing through the conduit&#39;s passageway. However, in some constructs, the tissue barrier may partially block the entrance or exit of the passageway so long as air may continue to pass through the conduit&#39;s passageway. 
     The tissue barrier may be formed from a material, mesh, sleeve, or coating that is a polymer or an elastomer such as, for example, silicone, fluorosilicone, polyurethane, PET, PTFE, or expanded PTFE. Other biocompatible materials will work, such as a thin foil of metal, etc. The coatings may be applied, for example, by either dip coating, molding, spin-coating, transfer molding or liquid injection molding. Alternatively, the tissue barrier may be a tube of a material and the tube is placed either over and/or within the conduit. The tissue barrier may then be bonded, crimped, heated, melted, shrink fitted or fused to the conduit. The tissue barrier may also be tied to the conduit with a filament of, for example, a suture material. 
     Still other techniques for attaching the tissue barrier include: solvent swelling applications and extrusion processes; wrapping a sheet of material about the conduit, or placing a tube of the material about the conduit and securing the tube to the conduit. The tissue barrier may be secured on the interior of the conduit by positioning a sheet or tube of material on the inside of the center section and securing the material therein. 
     The tissue barrier may also be formed of a fine mesh with a porosity or treatment such that tissue may not penetrate the pores. For example, a ChronoFlex™ DACRON® or TEFLON® mesh having a pore size of 100-300 microns may be saturated with collagen or another biocompatible substance. This construct may form a suitable tissue barrier. The mesh may be coaxially attached to a frame such as the open frame structures disclosed above. Still other suitable frames include a continuous spiral metallic or polymeric element. Given the mesh&#39;s radial strength or lack thereof, the use of a reinforcement element serves to prevent the implant from collapsing. Also, as described below, other substances may be applied to the exterior surface of the conduit to control elution of various medicines. 
       FIGS. 3B and 3C  respectively illustrate a side view and a front view of another conduit  300  having a partial tissue barrier coating. The conduit  300  includes a center section  310 , a plurality of extension members  320 , and a partial tissue barrier  330 . The conduit  300  is thus different than that shown in  FIG. 3A  in that the center section is longer and that the tissue barrier  330  only partially covers the extension members  320 . In particular, the center section  310  shown in  FIGS. 3B-3C  is cylindrical or tubular-shaped. This shape may be advantageous when a relatively long passageway is desired. Also, it is to be understood that the overall (or three dimensional) shape of the center section, when deployed, is not limited to the shape shown here. Rather, it may have various shapes such as, for example, rectangular, tubular, conical, hour-glass, hemi-toroidal, etc. 
     Additionally, the tissue barrier  330  covers only a first region  350  of the extension members and leaves a second region  340  of the extension members uncovered. The second or free region  340  of the extension members  320  is shown as being open-framed. However, the invention is not so limited. The second region of the extension members may be solid and it may include indentations, grooves, and recesses for tissue ingrowth. Also, the extension members may include small holes for tissue ingrowth. For example, the second region of the extension members may have a dense array of small holes. In any event, the conduits described herein may include at least one region or surface which is susceptible to tissue ingrowth or is otherwise adherent to the tissue. Accordingly, tissue ingrowth at the second region  340  of the extension members is facilitated while tissue growth into the passageway  325  is thwarted. 
     As shown in  FIG. 3D , tissue growth  360  into the uncovered region  340  further secures the extension members to the tissue wall  370 . Free region  340  of the extension members may also include tissue growth substances such as epithelial growth factors or agents to encourage tissue ingrowth. Accordingly, conduit  300  may be configured to engage the tissue wall  370  as well as to allow tissue to grow into predetermined regions of the conduit. 
     Visualization Feature 
     The conduit shown in  FIG. 3A  also includes a visualization ring or marker  242 . The marker  242  is visually apparent during a procedure. The marker is observed as the conduit is placed in a collateral channel and, when the marker is even with the opening of the channel, the conduit may be deployed. In this manner, the visualization feature facilitates alignment and deployment of the conduits into collateral channels. 
     The visualization ring or mark may be a biocompatible polymer and have a color such as white. Also, the visualization feature may protrude from the center section or it may be an indentation(s). The visualization mark may also be a ring, groove or any other physical feature on the conduit. Moreover, the visualization feature may be continuous or comprise discrete segments (e.g., dots or line segments). 
     The visualization feature may be made using a number of techniques. In one example, the mark is a ring formed of silicone and is white. The polymeric ring may be spun onto the tissue barrier. For example, a clear silicone barrier may be coated onto the conduit such that it coaxially covers the extension members and the center section as shown in  FIG. 3A . Next, a thin ring of white material such as a metal oxide suspended in clear silicone may be spun onto the silicone coating. Finally, another coating of clear silicone may be applied to coat the white layer. The conduit thus may include upwards of 1-3 layers including a tissue barrier, a visualization mark layer, and a clear outer covering. 
     The shape of the visualization mark is not limited to a thin ring. The visualization mark may be large, for example, and cover an entire half of the conduit as shown in  FIG. 3B . The visualization mark may, for example, be a white coating disposed on the proximal or distal half of the conduit. The visualization mark thus may extend from an end of the extension members to the center section of the conduit. As explained in more detail below, when such a device is deposited into a channel created in lung tissue, the physician may observe when one-half of the conduit extends into the channel. This allows the physician to properly actuate or deploy the conduit to secure the conduit in the tissue wall. 
     Accordingly, the visualization member is made visually apparent for use with, for example, an endoscope. The visualization feature, however, may also be made of other vision-enhancing materials such as radio-opaque metals used in x-ray detection. It is also contemplated that other elements of the conduit can include visualization features such as but not limited to the extension members, tissue barrier, control segments, etc. 
     In some variations of the invention, it was found that incorporation of a bioactive, as discussed herein, or other substance into the coating caused a coloration effect in the composition layer (e.g., the polymer turns white). This coloration obscures the support member structure in the layer making it difficult to identify the edges and center of the support member or implant. As discussed herein, placement of the implant may depend upon positioning the center of the implant within the opening in tissue. If the support member structure is identifiable, then one is able to visually identify the center of the implant. When the composition colors obscures the support member or renders the implant otherwise opaque, it may become difficult to properly place the device. This may be especially true when the composition layer extends continuously over the support member. 
     Additionally, the coloration may render the visualization mark difficult to identify especially under direct visualization (e.g., using a scope) In some cases it was undesirable to simply add additional substances on or in the composition layer for marking because such substances could possibly interfere with the implant&#39;s ability to deliver the substance as desired. To address these issues, a variation of the invention includes a delivery device for delivering an expandable implant (such as those described herein and in the cases referenced herein), where the delivery device includes an expandable member having an expandable implant located about the expandable member. Where the implant and the expandable member are of different visually identifiable colors or shades such that they distinction is easy to identify under endoscopic or bronchoscopic viewing. 
     In one example, as shown in  FIG. 9C , a balloon catheter has a colored sleeve  306  located about the balloon. The sleeve  306  comprises a visually identifiable color where selection of the colors should ease identification of the implant an endoscopic visualization system (e.g., blue or a similar color that is not naturally occurring within the body.) The implant is placed about the sleeve  306  where the proximal and distal areas of the implant would be identifiable by the difference in color. Such a system allows a medical practitioner to place the implant  200  properly by using the boundary of the implant  200  to guide placement in the tissue wall. The sleeve  306  may be fashioned from any expandable material, such as a polymer. Optionally, the sleeve  306  may also provide an elastic force to return the balloon to a reduced profile after expansion of the balloon. Such a system allows for identification without affecting the properties of the implant. 
     It should be noted that variations of the invention include coloring the balloon itself, or other expandable member, a color that meets the above criteria. 
     In another variation, the visualization mark may comprise providing a contrast between the implant and a delivery catheter. In one example the implant is appears mostly white and while mounted on a contrasting color inflation balloon. In this example the implant would be placed over a blue deflated balloon catheter. The proximal and distal areas of the implant would be flanked by the deflated blue balloon, thus giving the appearance of a distinct distal and proximal end of the implant. This would allow a physician to place the implant properly by using the blue flanks as a guide for placing the central white portion in the tissue wall. Similarly, a colored flexible sheath covering the balloon would also suffice. 
     It is noted that while the visualization features described above are suitable for use with the implants described herein, the inventive features are not limited as such. The features may be incorporated into any system where placement of an implant under direct visualization requires clear identification of the implant regardless of whether the implant is opaque or colored. 
     Bioactive Agents 
     As discussed above, the bio-active substance or combination of bioactive substances is selected to assists in modifying the healing response as a result of the trauma to the lung tissue resulting from creation of the collateral channel. As noted above, the term lung tissue is intended to include the tissue lining the airway, the tissue beneath the lining, and the tissue within the lung but exterior to the airway (e.g., lung parenchyma.) The purpose of modifying the healing response is to further extend the patency of the channel or implant to increase the duration which trapped gasses may exit through the implant into the airways. The term antiproliferative agent is intended to include those bioactive substances that directly modify the healing response described herein. 
     The bioactive substances are intended to interact with the tissue of the surgically created channels and in particular, lung tissue. These substances may interact with the tissue in a number of ways. They may, for example, 1.) accelerate cell proliferation or wound healing to epithelialize or scar the walls of the surgically-created channel to maintain its patent shape or 2.) the substances may inhibit or halt tissue growth when a channel is surgically created through an airway wall such that occlusion of the channel due to tissue overgrowth is prevented. Additionally, other bioactive agents may inhibit wound healing such that the injury site (e.g., the channel or opening) does not heal leaving the injury site open and/or inhibit infection (e.g., reduce bacteria) such that excessive wound healing does not occur which may lead to excessive tissue growth at the channel thereby blocking the passageway. 
     A variety of bioactive substances may be used alone or in combination with the devices described herein. Examples of bioactive substances include, but are not limited to, antimetabolites, antithrobotics, anticoagulants, antiplatelet agents, thorombolytics, antiproliferatives, antinflammatories, agents that inhibit hyperplasia and in particular restenosis, smooth muscle cell inhibitors, growth factors, growth factor inhibitors, cell adhesion inhibitors, cell adhesion promoters and drugs that may enhance the formation of healthy neointimal tissue, including endothelial cell regeneration. The positive action may come from inhibiting particular cells (e.g., smooth muscle cells) or tissue formation (e.g., fibromuscular tissue) while encouraging different cell migration (e.g., endothelium, epithelium) and tissue formation (neointimal tissue). 
     Still other bioactive agents include but are not limited to analgesics, anticonvulsives, anti-infectives (e.g., antibiotics, antimicrobials), antineoplastics, H2 antagonists (Histamine 2 antagonists), steroids, non-steroidal anti-inflammatories, hormones, immunomodulators, mast cell stabilizers, nucleoside analogues, respiratory agents, antihypertensives, antihistamines, ACE inhibitors, cell growth factors, nerve growth factors, anti-angiogenic agents or angiogenesis inhibitors (e.g., endostatins or angiostatins), tissue irritants (e.g., a compound comprising talc), poisons (e.g., arsenic), cytotoxic agents (e.g., a compound that can cause cell death), various metals (silver, aluminum, zinc, platinum, arsenic, etc.), epithelial growth factors or a combination of any of the agents disclosed herein. 
     Examples of agents include pyrolitic carbon, titanium-nitride-oxide, taxanes, fibrinogen, collagen, thrombin, phosphorylcholine, heparin, rapamycin, radioactive 188Re and 32P, silver nitrate, dactinomycin, sirolimus, everolimus, Abt-578, tacrolimus, camptothecin, etoposide, vincristine, mitomycin, fluorouracil, or cell adhesion peptides. Taxanes include, for example, paclitaxel, 10-deacetyltaxol, 7-epi-10-deacetyltaxol, 7-xylosyl-10-deacetyltaxol, 7-epi-taxol, cephalomannine, baccatin III, baccatin V, 10-deacetylbaccatin III, 7-epi-10-deacetylbaccatin III, docetaxel. 
     Of course, bioactive materials having other functions can also be successfully delivered in accordance with the present invention. For example, an antiproliferative agent such as methotrexate will inhibit over-proliferation of smooth muscle cells and thus inhibit restenosis. The antiproliferative is desirably supplied for this purpose until the tissue has properly healed. Additionally, localized delivery of an antiproliferative agent is also useful for the treatment of a variety of malignant conditions characterized by highly vascular growth. In such cases, an implant such as a implant could be placed in the surgically created channel to provide a means of delivering a relatively high dose of the antiproliferative agent directly to the target area. A vasodilator such as a calcium channel blocker or a nitrate may also be delivered to the target site. The agent may further be a curative, a pre-operative debulker reducing the size of the growth, or a palliative which eases the symptoms of the disease. For example, tamoxifen citrate, Taxol® or derivatives thereof Proscar®, Hytrin®, or Eulexin® may be applied to the target site as described herein. 
     Variations of the invention may also include fibrinolytics such as tPA, streptokinase, or urokinase, etc. Such fibrinolytics prevent or reduce the accumulation of fibrin within the opening. Accumulation of fibrin in the opening may result from inflammation of the tissue. The fibrin may form a structure which makes it easier for tissue to grow into the opening using the fibrin structure as a framework. Use of fibrinolytics, either topically, locally, or on the implant, serves to remove or hinder the network of fibrin from forming within the opening (or implant) and therefore aids in modifying the healing response. 
     In the event that poisonous and toxic compounds are delivered, they should be controlled so that inadvertent death of tissue does not occur. The poisonous agent should be delivered locally or only be effective locally. One method for delivering the bioactive agent locally is to associate the bioactive agent with an implant. For example, the implants described herein may include a bioactive substance or medicine deposited onto the interior, the exterior, or both the interior and exterior surfaces of the implant. The bioactive substance may remain on the implant so that it does not leach. Cells that grow into the surgically created channel contact the poison and die. Alternatively, the bioactive agent may be configured to gradually elute as discussed below. 
     When used in the lungs, the implant modifies the healing response of the lung tissue (e.g., at the site of newly created hole/channel) for a sufficient time until the healing response of the lung tissue subsides or reduces such that the hole/channel becomes a persistent air path. For example, the implant and bioactive substance will modify the healing response for a sufficient time until the healing response is reduced and, from a visual observation, the body treats the opening essentially as a natural airway passage rather than as an injury to the airway wall. 
     In one variation of the invention which modifies the healing response as describe above, the implant provides a steady release rate of bio-active substance as well as has a sufficient amount of available bio-active substance to modify the healing response of the lung tissue. As noted herein, the term lung tissue is intended to include the tissue lining the airway, the tissue beneath the lining, and the tissue within the lung but exterior to the airway (e.g., lung parenchyma.) Such a delivery profile allows for a concentration gradient of drug to build in these tissues adjacent to the delivery site of the implant. 
     It is believed that forming the concentration gradient affects the healing response of the lung tissue so that the implant does not become occluded as a result of the healing response. Because the implant is often placed in the airway wall it is exposed to the healing process of the multiple tissues. Providing a sufficient amount of bio-active substance allows for the formation of a concentration of the bio-active substance across these various tissues. In one variation of the invention it is believed that the fluids from these tissues enter into the composition layer of the device. The fluids then combine with the bio-active substances and migrate out of the composition layer to settle into the lung tissue. A concentration gradient forms when the drug ‘saturates’ local tissue and migrates beyond the saturated tissues. Furthermore, by providing a sufficient delivery rate, the healing response may be affected or suppressed during the critical time immediately after the wounding caused by creation of the collateral channel when the healing response is greatest. 
     To select a proper combination of drug and polymer, it is believed that the solubility parameter of the polymer must be matched with the bio-active substance to provide an acceptable slow elution rate from the polymer. Next, the polymer itself must be selected to have the proper attributes, such as a proper diffusion coefficient (to slow fluid entering and departing from the implant), and proper mechanical expansion properties (to allow for the significant expansion of the polymer to accommodate formation of the grommet shape.) 
     The solubility parameter is defined as the square root of the cohesive energy of the molecules in a compound. The level of control that a polymer has over the elution of a drug is the difference between the solubility parameters of the polymer and the solubility parameter of the drug. To select a polymer with the approximate diffusion a polymer with a high internal density could be selected to be less permeable to a complex molecule such as paclitaxel. Using a polymer with high internal density also accommodated the significant expansion required of the polymer to form the structure necessary to grommet about the airway wall. An example of the polymer selection is found below. 
     It is also important to note that paclitaxel is a taxane that is regarded as a microtubule stabilizer. The benefits of a microtubule stabilizing substance for use in vascular drug eluting stents is discussed, for example, in U.S. Pat. No. 5,616,608 to Kinsella et al. This type of drug operates to enhance microtubule polymerization which inhibits cell replication by stabilizing microtubules in spindles which block cell division. In contrast to the vascular applications, the implant for use in the present invention may use microtubule stabilizing substances such as taxanes (e.g., paclitaxel) as well as those microtubule destabilizing substances that are believed to promote microtubule disassembly in preventing cell replication. Such destabilizing substances include, but are not limited to vincristine, vinblastine, podophylotoxin, estramustine, noscapine, griseofulvin, dicoumarol, a vinca alkaloid, and a combination thereof. 
     Additionally, the exterior surface of the implant may be treated via etching processes or with electrical charge to encourage binding of the bioactive substances to the implant. The exterior surface may also be roughened to enhance binding of the medicine to the surface as discussed in U.S. Patent Application Publication No. 2002/0098278. See also U.S. Patent Application Publication Nos. 2002/0071902, 2002/0127327 and U.S. Pat. No. 5,824,048 which discuss various techniques for coating medical implants. 
     Although the implant may comprise a frame or body with a bioactive matrix disposed or otherwise associated therewith, the invention is not so limited. In one variation, the support member is formed from a polymer and the composition is joined to the polymeric support member. Alternatively, the bioactive substances may be placed directly onto the polymeric support member. 
     Various additional substances may be used incorporated into the device to reduce an adverse reaction resulting from possible contact with the implant and the airway wall. Adverse reactions include, but are not limited to, granulation, swelling, and mucus overproduction. These substance may may also be inhaled, injected, orally applied, topically applied, or carried by the implant. These substances may include anti-inflammatory, infection-fighting substances, steroids, mucalytics, enzymes, and wound healing-accelerating substances. Examples of these substances include but are not limited to, acetylcysteine, albuterol sulfate, ipratropium bromide, dornase alfa, and corticosteroids. 
     As noted above, conventional vascular drug eluting devices are not designed for exposure multiple tissue environments. Moreover, those devices are placed in an environment where a constant flow of blood creates an environment requiring a different delivery mechanism and rate. As noted herein, experiments with conventional coronary drug eluting implants demonstrated that such devices were unsuitable. 
     Channel Creation Devices and Methods 
     As discussed above, the use of low temperature devices, (e.g., mechanical devices, newer generation RF-type devices, etc.) to create the channel may result in less trauma to surrounding tissue and minimize the healing response of the tissue.  FIGS. 4A-4C  illustrates creation of the collateral channel and selecting a treatment site in the airway  100 . As will be discussed in more detail below, a single device may be used to select the site and create the channel. Moreover, another variation of the invention includes using such a device to deploy the conduit at the target site. However, the invention also contemplates using separate devices to perform each step or a combination of steps. 
     As shown in  FIG. 4A , a device  602  is advanced, for example, via a bronchoscope  404 , into the airway  100 . A potential treatment site is then inspected to determine whether or not a blood vessel is in proximity to the site. Naturally, if a blood vessel is detected, the surgeon has the option of selecting a different site. The device  602  may be a Doppler ultrasound device, a thermal device, an imaging device, etc. 
       FIG. 4B  illustrates another variation of selecting a site for a channel. In this variation, a piercing member (e.g., a blade affixed to a shaft, a needle, cannula, sharpened tube or rod, etc.,)  604  is advanced into the airway wall. Once the piercing member  604  is inserted into the airway wall, the surgeon may inspect the area for blood to determine whether the device punctured a blood vessel. After the opening is created the surgeon may also remove collect a biopsy of material behind the airway wall. If the opening is large enough as created by a balloon, as described herein, the surgeon may use forceps to visually obtain the sample. This may preferable to a blind method of obtaining biopsies, considering that the risk of bleeding may be reduced because the area has been scanned for blood vessels. 
     The piercing member  604  may have a lumen and may be open at a distal end or closed. In those cases where the piercing member  604  is hollow and has an opening at or near the distal end, the surgeon may aspirate the site using the piercing member  604  to determine whether a blood vessel is present and/or penetrated. For example, flashback catheters contain chambers which will fill with blood upon the penetration of a vessel by the distal tip of the catheter. The piercing member may be incorporated to have a flashback chamber to detect the presence of blood flow from a penetrated vessel. Using these approaches, a target site may not be selected until after a hole is made in the airway  100  wall. It should be noted that a piercing member may be of a diameter which results in closure of the puncture site upon removal of the piercing member. Alternatively, the piercing member may be of a sufficient size or construction that the hole remains open upon removal of the piercing member. In any case, the piercing member or another device may be used to mark the site of the opening (e.g., via ink, dye, physical marker, via application of electrical energy, etc.) Furthermore, the invention includes use of both a detecting device as described above in combination with a piercing member. For example, the site may be inspected by the detecting device prior to insertion of a piercing member. 
     The piercing member lumen may also used to deliver therapeutic fluids to the lungs. For example, in case of bleeding after channel creation the physician may apply epinephrine or saline the lungs. Alternatively the physician may use the piercing member to apply epinephrine to the airway wall prior to creation of the channel, to prevent bleeding. This may be done by injecting directly into the airway wall at or about the site of passage creation; singly or in a surrounding pattern of multiple applications. The physician may also use the piercing member lumen to apply any of the bioactive agents discussed herein, before or after passage creation. 
     Because it may be desirable to reach remote airways within the lung, it may be necessary to fully articulate the scope  404  to access and inspect a desirable site. Therefore, to inspect the site and create an opening, it may be desirable to maintain the scope  404  in a fixed position and simply advance/retract various components of the scope or devices in the scope. Accordingly, a piercing member may be selected to have a length that will sufficiently pass through the airway wall, while being small enough that it will also pass through a fully articulated bronchoscope. Furthermore, the piercing member may have sections of varying stiffness where a distal portion, (that is sufficient stiff to penetrate the tissue) may be of a length such that it is able to advance through a fully articulated bronchoscope. For example, the piercing member may comprised of a sharpened cannula which has a length from between 2 mm to 30 mm. The diameter may range between 16 Ga to 25 Ga or larger. The cannula may be affixed to a catheter having a relatively flexible proximal portion. In any case, the length of the piecing member  604  may vary as needed. 
     The piercing member is not limited to a cannula, it may be of solid construction, such as a sharpened rod or wire. Additionally the piercing member may be adapted with an elongate member, such as a wire, rod, or tube, which extends throughout the device. The purpose of the elongate member is to provide column strength to the piercing member and necessary bending resistance to the catheter, because it has been found that the device must have high column strength to effectively pierce the airway wall, otherwise the device will deflect and not create a passageway. The elongate member may be utilized to expose and retract the piercing member within the catheter, as the elongate member may extend throughout the device to a user interface. The elongate member and piercing member may also be constructed from one piece of material, thereby making them one part. Alternatively the elongate member may be a separate part welded, bonded, mechanically attached, or a combination thereof, to the piercing member. 
     However, it is understood, that the current invention is not limited to any particular length of the piercing member. Furthermore, the piercing member may be comprised of a resilient polymer, a polymer with a reinforced structure (e.g., a braid, coil, etc.), a super-elastic alloy, a metallic material with sufficient resilience, etc, such that it may navigate through a fully articulated bronchoscope yet return to its original profile upon exiting the working channel of the scope. 
     In some variations of the invention, the piercing member of the device may be retractable within a lumen of an elongate shaft so as to prevent damage to the bronchoscope or to tissue as the device advances to the target site. Additionally the piercing member may be retracted after the initial piercing of the airway wall, and blunt trauma may be used to further push the remaining portion of the catheter into the airway wall. This technique may help avoid additional bleeding and pneumothoraxes from an exposed piercing member. The catheter may be advanced to tortuous locations, therefore the device may incorporate low friction materials to make it easier to reach the treatment site. The materials may be selected from a group of low friction polymers, for example PTFE. Low friction materials may also be applied as a coating onto the pierced member or elongate member, for example PTFE or titanium nitride. Reducing the contact surface area between the members may also help to reduce friction. Adding or removing material from the surfaces of members is one way to reduce contact surface area. For example attaching a closed coiled spring around the piercing member or elongate member, effectively reduces the surface area contacted between the elongate member and lumen because only the peaks of the coils contact the lumen. 
     In additional variations of the invention, as shown in  FIG. 4C , a balloon catheter may be configured with a piercing member  604 . In this variation the balloon  614  advances into the opening created by the piercing member (in which case the piercing member either retracts into the catheter or advances with the catheter.) The balloon  614  would then deploy to dilate the opening for ease of later inserting a conduit. Alternatively, a conduit may be located on the balloon itself and deployed on inflation of the balloon. Examples of variations of such a balloon catheter may be found below. Furthermore, the needle may be affixed to a tapered introducer type device which is able to dilate the opening. 
     The piercing member  604  may also be used to deliver bioactive substances (as described herein) to the site of the opening. In such a case, the piercing member  604  may deliver the bioactive substance during creation of the opening (e.g., see  FIG. 4B ) or after dilation of the opening (see e.g.,  FIG. 4C ). In another variation of the invention, the piercing member  604  may be have a multi-lumen cross-section with different lumens being reserved, for example, for inflating the balloon, aspirating the site for blood, drug delivery, and suction of mucous/fluids at the site. In any of the variations described herein, an obturator (not shown) may be used to fill a lumen during advancement of the piercing member into tissue so that the lumen does not become blocked with tissue or other debris. The obturator may be a guide-wire, polymeric column of material, etc. 
       FIG. 4D  illustrates a variation of a balloon catheter  606  having a piercing member  604 . In this variation, the balloon catheter  606  comprises two lumens  608 ,  610 . One lumen  608  is fluidly coupled to the interior of the balloon  614  while the second lumen  610  extends through the piercing member  604 . It is understood that the device  606  may be configured to have any number of lumens as required. As discussed above, the piercing member  604  may either be fixedly attached to the distal end of the balloon catheter  606 . Alternatively, the piercing member  604  may be retractable into the balloon catheter  606  so that it does not cause damage to lung parenchyma when the catheter  606  is inserted into the airway  100  wall. As illustrated, the balloon catheter  606  may have a tapered section  612  between the piercing member  604  and the balloon  614  to assist in insertion of the balloon  614  into the opening  112 . 
       FIG. 4E  illustrates an additional variation of a piercing member  604  according the present invention. As illustrated, the piercing member  604  may have a number of ports  616  (e.g., openings, holes, etc.). The ports  616  may allow for either aspiration of blood or delivery of bio-active substances as described herein. Furthermore, although the piercing members  604  shown herein are configured with a beveled tip, it is contemplated that the tip may be any type of tip sufficient to penetrate the airway wall. For instance, the tip may be non-beveled with sharpened edges, the tip may be a trocar tipped needle, or any other available needle tip configuration. The piercing member  604  of  FIG. 4E  is also shown with an obturator placed therein. In this configuration, the obturator  618  blocks the lumen of the piercing member  604  at the distal end. Moreover, as shown, a portion of the obturator  618  may be sized such that it is smaller than a lumen of the piercing member  604  to allow for delivery of substances or aspiration through the ports  616 . 
       FIG. 4F  illustrates yet another variation of a balloon catheter  606  having a piercing member  604 . In this variation, as indicated by the arrow, the piercing member  604  is capable of being retracted into the catheter  606 . The ability to retract the piercing member  604  into the catheter  606  reduces the possibility of the piercing member  604  causing damage to any lung tissue that is behind the airway wall. Clearly, this variation combines the channel-making step with the conduit deployment step. Also, as shown in the figure, the catheter  606  may have a conduit  202  placed over the balloon  614 . Such a variation may create the opening or channel and then deploy the conduit  200  with a single device. 
       FIG. 4G  illustrates another variation of a balloon catheter  606  where the piercing member  604  is slidably located within the catheter  606 . In this variation, the catheter  606  contains an outer and inner sheaths  620 ,  622  which define two lumens. The lumen defined by the inner sheath  622  extends to the distal end of the catheter  606  and may be used to deliver bioactive substances, for suction, or for irrigation. 
     It is also contemplated that variations of the invention include a piercing member which is affixed to the catheter. Alternatively, the piercing member could have a flexible body that extends through the catheter to a proximal hub which is able to be coupled to a vacuum source, a source of medication, etc. Furthermore, either the piercing member and/or balloon catheter may be “pre-loaded” with a bioactive substance. Such a feature allows improves the precision of amount of substance delivered to the desired site. 
     As mentioned above, the piercing member  604  may be of a sufficient size or construction that the hole remains open upon removal of the piercing member. Once variation of this as shown in  FIG. 4H , where the device has a conical tip  658  with a lumen extending through out. A piercing member  604  is extendable past the distal tip to pierce the airway wall, after the initial opening is made, the rest of the device can be driven into the airway wall, gradually expanding the hole to a desirable diameter which allows the conduit to be subsequently placed. 
     The makeup of airway tissue may require a considerable amount of force to create a channel with the piercing device. Therefore, it will generally be easier to create a channel if the device has sufficient column strength to avoid bending of the device when applying a force at the proximal end of the device. 
     Additional variations of the invention may incorporate a nondistensible balloon to overcome the toughness of the airway tissue. Nondistensible balloons are generally made up of relatively inelastic materials consisting of PET, nylons, polyurethanes, polyolefins, PVC, and other crosslinked polymers. The makeup of airway tissue may be very tough and resist radial expansions. Therefore it will be generally easier to expand the channel in the airway wall using high pressure nondistensible balloons (&gt;6 atm), which generally inflate in a uniform shape. 
     Nondistensible balloons will occupy a greater mass than distensible balloons because they in an inelastic predetermined form. Too much balloon mass will have too large of a working diameter, which in turn will hinder entry into a channel. Working diameter is the smallest effective diameter opening the uninflated nondistensible balloon can be inserted into. Therefore it is desirable to have the uninflated nondistensible balloon to have a working diameter close to the diameter of the piercing device  604 . This can be attained by using a thin walled balloon, using a balloon with a small distal profile, by using a balloon with a distal end which is close in actual diameter to the diameter of the piercing member or by using a balloon which folds into a low profile state, or a combination of these. 
     As shown in  FIG. 4I , a device of insufficient sharpness will “tent” the airway wall  450 . Tenting occurs when a device is placed against an airway wall with significant force but with no puncturing of the airway wall. The airway wall will deflect and become displaced until the device is withdrawn. If the tissue becomes tented there remains a significant amount of potential energy placed by the device onto the airway wall. The potential energy may unexpectedly becomes realized, when the device eventually punctures the airway, which may cause the device to suddenly plunge into the parenchyma to an unintended depth. Plunging may in turn cause unintended damage to the patient. A depth limiting feature  654  may overcome this problem. 
     Variations of the invention include a depth limiting feature that may prevent inadvertent advancement of the device when creating the channel. One example of this may be a circular tube  654  placed over the device and set at a fixed distance (e.g. 10 mm) from the distal tip of the piercing member, proximal to the balloon, as shown in  FIG. 4J . If the device does tent and plunge into the airway wall the front face of the tube may halt the plunging effect by acting as a barrier. Another example would be a secondary balloon, proximal to the channel expansion balloon, placed in a similar position to the circular tube as described above. Another example would be a folding basket formed from the outer lumen of the device, or constructed from wire. 
     As shown in  FIG. 4K , variations of the invention may include a distal collar  650  on the distal portion of the piercing member  604  to precisely limit the maximum extension and retraction of the piercing member  604 . The distal collar  650  would be attached to the piercing member and travel between two set collar stops  652  which are attached to the lumen  656  the piercing member travels in. This feature has multiple benefits; first, it has the safety setting a maximum distance for the piercing member to extend, around 2-3 mm has been found to be sufficient in most cases. Thus, the maximum penetration of the piercing member  604  is limited which may prevent unintentional damage to the lung tissue. 
     The collar  650  protects the bronchoscope by preventing deflection of the distal tip. Deflection can take place when there is a significant amount of gap between the inner sheath  622  and the distal tip of the piercing member in the retracted mode. When the device is being maneuvered through a bronchoscope in a torturous configuration, the lumen  656  can deflect while the stiffer piercing member will not, and thus the piercing member may pierce through the deflected lumen  656  and subsequently into the bronchoscope. By setting a small gap (e.g. &lt;1 mm) this deflection may be eliminated, and the scope protected. 
     The collar  650  also allows the piercing member to be reliably extended. It was found that when a similar feature was placed at the proximal section of the device the piercing member could not reliably be extended to a set distance beyond the distal tip. This is because when in a torturous configuration the outer sheath  620  of the device may have a tendency to stretch or compress. As a result the tubing may stretch to such a degree that when the piercing member is fully extended it still may not fully extend past the distal tip of the lumen  656 . By locating the collar  650  in the distal portion of the lumen  656  (e.g. less than 2 inches from the distal tip) the stretching or compression is minimized or eliminated. 
     Conduit Deployment Devices and Methods 
       FIGS. 5A-5C  illustrate a way to deploy a conduit in a channel. Referring to  FIG. 5A , a delivery device  400  is loaded with a conduit  200 . An access scope-type device  404  (e.g., an endoscope, a bronchoscope, or other device) may optionally be used to place the delivery device  400  into a collateral channel  112 . A guide wire  402  may be used to place the delivery device  400  into the collateral channel  112 . The guide wire  402  may be a conventional guide-wire or it may simply be comprised of a super-elastic material. The use of a guide wire is optional as the invention contemplates placement of the conduit  200  using only the delivery device  400 . 
       FIG. 5A  also illustrates articulation (or bending) of the deliver device  400  to access the collateral channel  112 . However, the invention also contemplates articulation of the access device  404 . The access device  404  may be articulated such that the delivery device  400  may advance straight into the collateral channel  112 . Accordingly, the delivery device  400  may exit straight from the access device  404  or it may be articulated into the opening. 
       FIG. 5B  illustrates deployment of the conduit  200 . In particular, balloon member  406  is shown in an expanded state resulting in (1) the conduit&#39;s center section being radially expanded and (2) the conduit&#39;s extension members being outwardly deflected such that opposing extension members sandwich portions of the tissue wall  422 . Diametric-control members  424  are also shown in this figure. The diametric or center-control segments limit the center section&#39;s radial expansion. In this manner, conduit  200  is securely placed in the channel to maintain a passageway through the airway wall  422 . 
       FIG. 5C  illustrates the deployed conduit  200  once the delivery device  400  is removed from the site. It should be noted that dilation of the collateral channel or opening  112  may be performed by mere insertion of the conduit  200  and/or delivery device  400 . 
     It should be noted that deployment of conduits is not limited to that shown in  FIGS. 5A-5C , instead, other means may be used to deploy the conduit. For example, spring-loaded or shape memory features may be actuated by mechanical or thermal release and unlocking methods. Additionally, mechanical wedges, lever-type devices, scissors-jack devices, open chest surgical placement and other techniques may be used to deploy the conduit. Again, the conduit  200  may be comprised of an elastic or super-elastic material which is restrained in a reduced profile for deployment and expands to its deployed state upon mechanical actuator or release. 
     In one additional variation of the invention, as shown in  FIGS. 5D , a conduit  201  may be deployed within a second structure such as a second conduit or stent. Such an approach may be used to increase retention of the conduits within the channel as well as prevent closing of the channel. For example, an initial conduit  200  or stent may be deployed within the channel  112 . This first conduit or stent may have certain properties that make it more acceptable to implantation within the body without generating an aggressive tissue healing response. For instance, the stent may be a drug eluting stent, or the conduit may be constructed from a bio-compatible metal without any additional tissue barrier. Once the initial stent or conduit is placed within the channel  112  a second conduit may be deployed within the first conduit. As shown in  FIG. 5D , a first conduit  200  (or stent) is placed within the channel  112 .  FIG. 5D  illustrates a second conduit  201  advanced towards the first conduit  200 .  FIG. 5E  illustrates the second conduit  201  deployed within the first conduit  200 . The second conduit  201  may have additional properties that permit the channel to remain patent. For example, the second conduit  201  my have a tissue barrier as discussed above, or other construction that generates an aggressive healing response within the lung. Therefore, the first conduit  200 , being more conducive to implantation, will serve to anchor both conduits  200 ,  201  as the tissue either does not grow, or it grows around the outer conduit  200 . The second conduit, for example, may have a tissue barrier placed thereon. Once the second conduit  201  is deployed within the first conduit  200 , the tissue barrier of the second conduit  201  will prevent tissue from growing through the stent structure. It should be noted that the structure of a conduit within a conduit may be incorporated into a single composite structure. 
     In use, the conduit  200  is deployed with the distal side towards the parenchymal tissue  460  while the proximal side remains adjacent or in the airway  450 . Of course, where the proximal and distal extension members are identical, the conduit may be deployed with either side towards the parenchymal tissue. 
       FIGS. 6A-6B  illustrate another example of deploying a conduit  500  in a channel  510  (or opening) created in a tissue wall  520 . Referring to  FIG. 6A , a delivery tool  530  carrying a deployable conduit  500  is inserted into the channel  510 . The delivery tool  530  is extended straight from an access catheter  540  such that the delivery tool forms an angle             with the tissue wall  520 . It is to be understood that while the tissue wall of airway  522  is shown as being thin and well defined, the present invention may be utilized to maintain the patency of channels and openings which have less well defined boundaries. The delivery tool is further manipulated until the conduit is properly positioned which is determined by, for example, observing the position of a visualization mark  552  on the conduit relative to the opening of the channel  510 .
       FIG. 6B  illustrates enlarging and securing the conduit in the channel using an expandable member or balloon  560 . The balloon  560  may be radially expanded using fluid (gas or liquid) pressure to deploy the conduit  500 . The balloon may have a cylindrical shape (or another shape such as an hourglass shape) when expanded to 1.) expand the center section and 2.) deflect the proximal and distal sections of the conduit such that the conduit is secured to the tissue wall  520 . During this deployment step, the tissue wall  520  may distort or bend to some degree but when the delivery tool is removed, the elasticity of the tissue tends to return the tissue wall to its initial shape. Accordingly, the conduits disclosed herein may be deployed either perpendicular to (or non-perpendicular to) the tissue wall. 
       FIG. 7A  illustrates another variation of deploying a conduit  200  into an opening  112 . In some variations of the invention, prior to deployment of the conduit  200 , the channel  112  may have a diameter or size that may require an additional dilation or expansion of the channel  112  for proper deployment of the conduit  200 . For example, the channel  112  may be created by a piercing member, as described above, where the channel  112  nearly closes upon removal of the piercing member. However, the devices and method described herein are not limited to channels  112  of any particular size. The channels may in fact be larger than a diameter of the conduit  200  in its un-deployed state. 
     In any case, after creation of the channel  112  the surgeon may advance a balloon catheter  630  containing a conduit  200  towards the site of the opening  112 . The variation of the balloon catheter  630  depicted in the figure also includes a guide body  632 . Because the opening  112  may be difficult to locate, the guide body  632  may serve various functions to assist in locating the opening  112  and placing the conduit  200 . For example, as shown in  FIG. 7A , the guide body  632  may have a rounded front surface. This allows probing of the catheter  630  against the airway  100  wall to more easily locate the opening  112 . The rounded surface of the guide body  632  will not drag on the airway tissue. 
     As shown in  FIG. 7B , once inserted into the opening  112 , the guide body  632  provides an additional function of temporarily anchoring the device  630  within the opening  112 . The ability to temporarily anchor the device  630  into the opening  112  may be desirable due to the natural tidal motion of the lung during breathing. The increased surface area of the guide body  632  requires increased resistance upon remove the guide body  632  from the opening  112 . Such a feature lessens the occurrence of unintended removal of the device from the site as the lung tissue moves. As shown in  FIG. 7B , after insertion into the airway  100  wall, a portion of the guide body  632  serves as a resistance surface to provide the temporary anchoring function. Additional variations of the guide body  632  are shown below. 
       FIGS. 8A-8F  illustrate additional variations of guide bodies  632  for use with the present invention. As shown, the guide body  632  is located on the distal end of the balloon catheter  630 . The guide body  632  will have a front surface  634  that is preferably smooth such that it can easily be moved over the airway wall. Proximal to the front surface  634 , the guide body  632  will have at least one resistance surface  636  which is defined as an area that causes increased resistance upon removal of the guide body  634  from the airway wall. As shown, the resistance surface  636  will be adjacent to an area of reduced diameter  638  to which allows the guide body  632  to nest within the opening  112  in the airway wall. The guide body  632  may have any number of shapes as shown in the figures. 
       FIG. 8F  illustrates another variation of a guide body  632  having a resistance surface  636  which comprises an area of increased surface roughness such that the surface will drag upon the airway wall or tissue surrounding the channel  112 . Such a feature may be combined with the variations of the guide members provided above. 
     The balloon catheters  630  of the present invention may include a dilating member between the guide body  632  and balloon  614 . In the variation shown in  FIG. 8A , the dilating member comprises a tapered section. However, the invention is not limited as such. For example, the dilating member may comprise a second inflatable balloon, or other expanding device. The dilating members may also be retractable within the elongate shaft. 
       FIGS. 9A and 9B  depict cross sections of examples of a balloon catheter  630  having a guide body  632  that includes a lumen  642  which terminates at a surface of the guide body  632 . The lumen  642  may be used for suction, irrigation, or deliver bio-active substances, etc. The catheter  630  may also have an additional lumens  646 ,  646 ,  648  as shown, for inflation of the balloon  614  and for additional suction  644 , and for communication with the guide body lumen  642 . As shown in  FIG. 8B , the lumen may also be used to advance a piercing member  604  to the airway wall to create the channel  112 . 
     Any of the balloons described herein may be distensible balloons (e.g., they assume a predetermined shape upon expansion) or elastic balloons (e.g., simply expand). Use of a distensible balloon permits control in dilating the opening  112  or placement of the conduit. 
     All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. To the extent there is a conflict in a meaning of a term, or otherwise, the present application will control. Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims. It is also contemplated that combinations of the above described embodiments/variations or combinations of the specific aspects of the above described embodiments/variations are within the scope of this disclosure. 
     EXAMPLE 
     Implant 
     Implants comprising stainless steel mesh frame fully encapsulated with a composition comprising silicone (as described below) and paclitaxel were implanted in several canine models. Visual observation indicated that, on average, the passage through the implants of the present invention remained unobstructed and were associated with significantly reduced fibrotic and inflammatory responses, in canine models, at a considerably higher rate than an implant without any drug adjunct or coronary drug eluting stents (as shown in  FIG. 12 ). 
     The composition comprised approximately a 9% paclitaxel to silicone ratio with approximately 400 micrograms of paclitaxel per implant. Measurements found that approximately 30% of the paclitaxel released after 60 days. In general, for implants with the paclitaxel/silicone composition, observations of chronic inflammation, epithelial metaplasia and fibrosis were all very mild. 
     For paclitaxel as the bioactive substance, polymers with solubility parameters between 5-25 (MPa) ^½ were believed to provide sufficient elution rates. The polymer used in the example device has good diffusivity for lipophilic drug (such as paclitaxel) because the side methyl group on the silicone may be substituted with more lipophilic hydrocarbon molecules containing vinyl group or groups in addition polymerization by platinum catalyst. 
     The composition for the example may be as follow: polymer part: polydimethylsiloxane, vinyldimethyl terminated, any viscosity; and/or polydimethylsiloxane, vinylmonomethyl terminated, any viscosity. The cross-linker part: polydimethylsiloxane, any viscosity; and or polymonomethylsiloxane, any viscosity. Platinum catalyst part and/or cross-linker part: platinum; and/or platinum-divinyltetramethyldisiloxane complex in xylene, 2-3% Pt; and/or platinum-divinyltetramethyldisiloxane complex in vinyl terminated polydimethylsiloxane, 2-3% Pt; and/or platinum-divinyltetramethyldisiloxane complex in vinyl terminated polydimethylsiloxane, ˜1% Pt; platinum-Cyclovinylmethylsiloxane complex, 2-3% Pt in cyclic vinyl methyl siloxane. 
     These components may be combined in different ratios to make the polymer. The hydrocarbon side chain off the silicone back bone makes this polymer system unique and may result in a “zero-order”-like release profile. The amount of vinyl siloxane cross-linker may determine the rate of the drug release and diffusivity of the polymer to the drug. There are other types of polydimethylsiloxanes such as: trimethylsiloxy terminated polydimethylsiloxane in various viscosities, (48-96%) dimethyl (4-52%) diphenylsiloxane copolymer in various viscosities, dimethylsiloxane-ethylene oxide copolymer, dimethyl diphenylsiloxane copolymer, polymethylhydrosiloxane, trimethylsilyl terminated at various viscosities, (30-55%) methyldro-(45-70%) dimethylsiloxane copolymer at various viscosities, polymethylphenylsiloxane, polydimethylsiloxane silanol terminated at various viscosities, polydimethylsiloxane aminopropyldimethyl terminated at various viscosities. For paclitaxel a release profile was found to be acceptable with a polymer system consisting of polydimethylsiloxane vinyl terminated at various viscosity and a range of platinum-mono, di, tri and/or tetramethyldisiloxane complex.