Patent Publication Number: US-2006020347-A1

Title: Implanted bronchial isolation devices and methods

Description:
REFERENCE TO PRIORITY DOCUMENT  
      This application claims priority of co-pending U.S. Provisional Patent Application Ser. No. 60/551,476 entitled “Implanted Bronchial Isolation Devices and Methods”, filed Mar. 8, 2004. Priority of the filing date of Mar. 8, 2004 is hereby claimed, and the disclosure of the Provisional Patent Application is hereby incorporated by reference. 
    
    
     BACKGROUND  
      Pulmonary diseases, such as chronic obstructive pulmonary disease, (COPD), reduce the ability of one or both lungs to fully expel air during the exhalation phase of the breathing cycle. Such diseases are accompanied by chronic or recurrent obstruction to air flow within the lung. Because of the increase in environmental pollutants, cigarette smoking, and other noxious exposures, the incidence of COPD has increased dramatically in the last few decades and now ranks as a major cause of activity-restricting or bed-confining disability in the United States. COPD can include such disorders as chronic bronchitis, bronchiectasis, asthma, and emphysema.  
      It is known that emphysema and other pulmonary diseases reduce the ability of one or both lungs to fully expel air during the exhalation phase of the breathing cycle. One of the effects of such diseases is that the diseased lung tissue is less elastic than healthy lung tissue, which is one factor that prevents full exhalation of air. During breathing, the diseased portion of the lung does not fully recoil due to the diseased (e.g., emphysematic) lung tissue being less elastic than healthy tissue. Consequently, the diseased lung tissue exerts a relatively low driving force, which results in the diseased lung expelling less air volume than a healthy lung. The reduced air volume exerts less force on the airway, which allows the airway to close before all air has been expelled, another factor that prevents full exhalation.  
      The problem is further compounded by the diseased, less elastic tissue that surrounds the very narrow airways that lead to the alveoli, which are the air sacs where oxygen-carbon dioxide exchange occurs. The diseased tissue has less tone than healthy tissue and is typically unable to maintain the narrow airways open until the end of the exhalation cycle. This traps air in the lungs and exacerbates the already-inefficient breathing cycle. The trapped air causes the tissue to become hyper-expanded and no longer able to effect efficient oxygen-carbon dioxide exchange.  
      In addition, hyper-expanded, diseased lung tissue occupies more of the pleural space than healthy lung tissue. In most cases, a portion of the lung is diseased while the remaining part is relatively healthy and, therefore, still able to efficiently carry out oxygen exchange. By taking up more of the pleural space, the hyper-expanded lung tissue reduces the amount of space available to accommodate the healthy, functioning lung tissue. As a result, the hyper-expanded lung tissue causes inefficient breathing due to its own reduced functionality and because it adversely affects the functionality of adjacent healthy tissue.  
      Some recent treatments include the use of devices that isolate a diseased region of the lung in order to reduce the volume of the diseased region, such as by collapsing the diseased lung region. According to such treatments, one or more flow control devices are implanted in airways feeding a diseased region of the lung to regulate fluid flow to the diseased lung region in order to fluidly isolate the region of the lung. These implanted flow control devices can be, for example, one-way valves that allow flow in the exhalation direction only, occluders or plugs that prevent flow in either direction, or two-way valves that control flow in both directions. However, such devices are still in the development stages.  
      Thus, there is much need for improvement in the design and functionality of such flow control devices.  
     SUMMARY  
      Disclosed are methods and devices for regulating fluid flow to and from a region of a patient&#39;s lung, such as to achieve a desired fluid flow dynamic to a lung region during respiration and/or to induce collapse in one or more lung regions. In one aspect, a flow control device suitable for implanting in a bronchial passageway is described. The flow control device comprises a valve defining a variable-sized mouth through which fluid can flow through the valve to regulate fluid flow through the bronchial passageway. The mouth increases in size in response to fluid flow in a first direction and decreases in size in response to fluid flow in a second direction&gt; The mouth is open when the valve is in a default state.  
      In another aspect, there is described a fluid flow control device suitable for implanting in a bronchial passageway, comprising: a frame configured to retain the flow control device within the bronchial passageway; a seal coupled to the frame, the seal configured to seal against internal walls of the bronchial passageway; and a valve coupled to the frame, the valve having lips that define a variable-sized mouth through which fluid can flow through the valve, wherein the lips move away from one another to increase the size of the mouth in response to fluid flow in a first direction and move toward one another to decrease the size of the mouth in response to fluid flow in a second direction, and wherein the lips are at least partially spaced apart to define an open mouth when the valve is exposed to no fluid flow.  
      In another aspect, there is described a fluid flow control device suitable for implanting in a bronchial passageway, comprising a frame configured to retain the flow control device within the bronchial passageway; a seal coupled to the frame, the seal configured to seal against internal walls of the bronchial passageway; and a valve that resists fluid flow in an inspiratory direction through the bronchial passageway, wherein the valve&#39;s resistance to fluid flow varies as a function of a pressure differential across the valve.  
      In another aspect, there is described a fluid flow control device suitable for implanting in a bronchial passageway, comprising a frame configured to retain the flow control device within the bronchial passageway; a seal coupled to the frame, the seal configured to seal against internal walls of the bronchial passageway; and a valve that resists fluid flow in an inspiratory direction through the bronchial passageway, wherein the valve transitions to a state of increased resistance to fluid flow in response to an increase in a rate of fluid flow through the bronchial passageway.  
      In another aspect, there is described a flow control device suitable for implanting in a bronchial passageway, comprising a valve element that transitions between an open configuration that permits fluid flow in an inspiratory direction and a closed configuration that blocks fluid flow in the inspiratory direction, wherein a default state of the valve element is the open configuration.  
      The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     DESCRIPTION OF DRAWINGS  
       FIG. 1  shows an anterior view of a pair of human lungs and a bronchial tree with a flow control device implanted in a bronchial passageway to bronchially isolate a region of the lung.  
       FIG. 2  illustrates an anterior view of a pair of human lungs and a bronchial tree.  
       FIG. 3A  illustrates a lateral view of the right lung.  
       FIG. 3B  illustrates a lateral view of the left lung.  
       FIG. 4  illustrates an anterior view of the trachea and a portion of the bronchial tree.  
       FIG. 5A  shows a perspective view of an exemplary flow control device that can be implanted in a body passageway.  
       FIG. 5B  shows a perspective, cross-sectional view of the flow control device of  FIG. 5A .  
       FIG. 6A  shows a side view of the flow control device of  FIG. 5A .  
       FIG. 6B  shows a cross-sectional, side view of the flow control device of  FIG. 5A .  
       FIG. 7  shows another embodiment of a flow control device.  
       FIG. 8  shows a bi-leaflet valve with open mouth for use in a flow control device.  
       FIG. 9  shows a trilobular valve for use in a flow control device.  
       FIGS. 10A and 10B  shows two views of a bronchial isolation device with an open-mouth flap valve.  
       FIG. 11  shows an open, oval-mouth valve for use in a flow control device.  
       FIG. 12  shows a valve in a fully open state.  
       FIG. 13  shows a valve in a partially closed state.  
       FIG. 14  shows a valve in a fully closed state.  
       FIG. 15  shows a sharp-corner, open-mouth valve for us in a flow control device.  
       FIG. 16A-16C  show various views of a high-flow valve with pleated sides.  
       FIG. 17  shows a mandrel and a dipped parallel-lipped valve manufactured using the mandrel for use in a flow control device.  
       FIG. 18  shows a bonded parallel-lipped Heimlich valve.  
       FIG. 19  shows another embodiment of a valve for use in a flow control device. 
    
    
     DETAILED DESCRIPTION  
      Disclosed are methods and devices for regulating fluid flow to and from a region of a patient&#39;s lung, such as to achieve a desired fluid flow dynamic to a lung region during respiration and/or to induce collapse in one or more lung regions. Pursuant to an exemplary procedure, an identified region of the lung (referred to herein as the “targeted lung region”) is targeted for treatment. The targeted lung region is then bronchially isolated to regulate airflow into and/or out of the targeted lung region through one or more bronchial passageways that feed air to the targeted lung region.  
      As shown in  FIG. 1 , the bronchial isolation of the targeted lung region is accomplished by implanting a flow control device  110  (sometimes referred to as a bronchial isolation device) into a bronchial passageway  115  that feeds air to a targeted lung region  120 . The flow control device  110  regulates fluid flow through the bronchial passageway  115  in which the flow control device  110  is implanted. The flow control device  110  can regulate airflow through the bronchial passageway  115  using a valve that permits fluid flow in a first direction (e.g., the exhalation direction) while limiting or preventing fluid flow in a second direction (e.g., the inhalation direction).  
      The valve includes coaptation regions, such as lips, that are moveable toward and away from one another so as to define a variable sized opening through which fluid can flow. When exposed to fluid flow in the first direction (e.g., the exhalation direction), the coaptation regions are urged away from one another to increase the size of the opening therebetween and permit an increasing amount of fluid flow through the valve. When exposed to fluid flow in the second direction (e.g., the inhalation direction), the coaptation regions are urged toward one another to decrease the size of and/or completely close the opening to decrease and/or completely prevent fluid flow through the valve. Flow through the valve is completely prevented when the coaptation regions are completely shut such that there is no opening for fluid to flow through the valve.  
      In conventional flow control devices, the valve is closed in a default state such that there is no gap or opening between the coaptation regions of the valve. The coaptation regions separate from one another to form an opening for fluid flow in the first direction when the valve cracking pressure is exceeded. For such a valve, there is a tendency for the coaptation regions, such as the valve lips, to stick together so as to resist opening and thereby increase the valve cracking pressure. The sticking force between the coaptation regions can be stronger when the valve is implanted in a lung, as mucous can coat the valve lips and form surface tension that must be overcome to separate the lips and open the valve.  
      As described in detail below, the flow control device  110  can include a valve that is “normally-open” in a default state such that at least a portion of the coaptation regions are separated from one another to define an opening therebetween. Because the coaptation regions are separated from one another in a default state, such a valve has a reduced cracking pressure as there is a little or no tendency for the coaptation regions to stick together. In addition, the gap between the coaptation regions reduces or eliminates the effect of surface tension caused by mucous on the valve. A normally-open valve also permits increased fluid flow in the first direction (relative to a valve that is closed in the default state), as the default open state of the valve reduces bulk resistance to flow in the first direction. Various embodiments and features of normally-open valves are described in more detail below.  
      Exemplary Lung Regions  
      Throughout this disclosure, reference is made to the term “lung region”. As used herein, the term “lung region” refers to a defined division or portion of a lung. For purposes of example, lung regions are described herein with reference to human lungs, wherein some exemplary lung regions include lung lobes and lung segments. Thus, the term “lung region” as used herein can refer, for example, to a lung lobe or a lung segment. Such nomenclature conform to nomenclature for portions of the lungs that are known to those skilled in the art. However, it should be appreciated that the term “lung region” does not necessarily refer to a lung lobe or a lung segment, but can refer to some other defined division or portion of a human or non-human lung.  
       FIG. 2  shows an anterior view of a pair of human lungs  210 ,  215  and a bronchial tree  220  that provides a fluid pathway into and out of the lungs  210 ,  215  from a trachea  225 , as will be known to those skilled in the art. As used herein, the term “fluid” can refer to a gas, a liquid, or a combination of gas(es) and liquid(s). For clarity of illustration,  FIG. 2  shows only a portion of the bronchial tree  220 , which is described in more detail below with reference to  FIG. 5 .  
      Throughout this description, certain terms are used that refer to relative directions or locations along a path defined from an entryway into the patient&#39;s body (e.g., the mouth or nose) to the patient&#39;s lungs. The path of airflow into the lungs generally begins at the patient&#39;s mouth or nose, travels through the trachea into one or more bronchial passageways, and terminates at some point in the patient&#39;s lungs. For example,  FIG. 2  shows a path  202  that travels through the trachea  225  and through a bronchial passageway into a location in the right lung  210 . The term “proximal direction” refers to the direction along such a path  202  that points toward the patient&#39;s mouth or nose and away from the patient&#39;s lungs. In other words, the proximal direction is generally the same as the expiration direction when the patient breathes. The arrow  204  in  FIG. 2  points in the proximal or expiratory direction. The term “distal direction” refers to the direction along such a path  202  that points toward the patient&#39;s lung and away from the mouth or nose. The distal direction is generally the same as the inhalation or inspiratory direction when the patient breathes. The arrow  206  in  FIG. 2  points in the distal or inhalation direction.  
      The lungs include a right lung  210  and a left lung  215 . The right lung  210  includes lung regions comprised of three lobes, including a right upper lobe  230 , a right middle lobe  235 , and a right lower lobe  240 . The lobes  230 ,  235 ,  240  are separated by two interlobar fissures, including a right oblique fissure  226  and a right transverse fissure  228 . The right oblique fissure  226  separates the right lower lobe  240  from the right upper lobe  230  and from the right middle lobe  235 . The right transverse fissure  228  separates the right upper lobe  230  from the right middle lobe  235 .  
      As shown in  FIG. 2 , the left lung  215  includes lung regions comprised of two lobes, including the left upper lobe  250  and the left lower lobe  255 . An interlobar fissure comprised of a left oblique fissure  245  of the left lung  215  separates the left upper lobe  250  from the left lower lobe  255 . The lobes  230 ,  235 ,  240 ,  250 ,  255  are directly supplied air via respective lobar bronchi, as described in detail below.  
       FIG. 3A  is a lateral view of the right lung  210 . The right lung  210  is subdivided into lung regions comprised of a plurality of bronchopulmonary segments. Each bronchopulmonary segment is directly supplied air by a corresponding segmental tertiary bronchus, as described below. The bronchopulmonary segments of the right lung  210  include a right apical segment  310 , a right posterior segment  320 , and a right anterior segment  330 , all of which are disposed in the right upper lobe  230 . The right lung bronchopulmonary segments further include a right lateral segment  340  and a right medial segment  350 , which are disposed in the right middle lobe  235 . The right lower lobe  240  includes bronchopulmonary segments comprised of a right superior segment  360 , a right medial basal segment (which cannot be seen from the lateral view and is not shown in  FIG. 3A ), a right anterior basal segment  380 , a right lateral basal segment  390 , and a right posterior basal segment  395 .  
       FIG. 3B  shows a lateral view of the left lung  215 , which is subdivided into lung regions comprised of a plurality of bronchopulmonary segments. The bronchopulmonary segments include a left apical segment  410 , a left posterior segment  420 , a left anterior segment  430 , a left superior segment  440 , and a left inferior segment  450 , which are disposed in the left lung upper lobe  250 . The lower lobe  225  of the left lung  215  includes bronchopulmonary segments comprised of a left superior segment  460 , a left medial basal segment (which cannot be seen from the lateral view and is not shown in  FIG. 3B ), a left anterior basal segment  480 , a left lateral basal segment  490 , and a left posterior basal segment  495 .  
       FIG. 4  shows an anterior view of the trachea  225  and a portion of the bronchial tree  220 , which includes a network of bronchial passageways, as described below. In the context of describing the lung, the terms “pathway” and “lumen” are used interchangeably herein. The trachea  225  divides at a lower end into two bronchial passageways comprised of primary bronchi, including a right primary bronchus  510  that provides direct air flow to the right lung  210 , and a left primary bronchus  515  that provides direct air flow to the left lung  215 . Each primary bronchus  510 ,  515  divides into a next generation of bronchial passageways comprised of a plurality of lobar bronchi. The right primary bronchus  510  divides into a right upper lobar bronchus  517 , a right middle lobar bronchus  520 , and a right lower lobar bronchus  522 . The left primary bronchus  515  divides into a left upper lobar bronchus  525  and a left lower lobar bronchus  530 . Each lobar bronchus,  517 ,  520 ,  522 ,  525 ,  530  directly feeds fluid to a respective lung lobe, as indicated by the respective names of the lobar bronchi. The lobar bronchi each divide into yet another generation of bronchial passageways comprised of segmental bronchi, which provide air flow to the bronchopulmonary segments discussed above.  
      As is known to those skilled in the art, a bronchial passageway defines an internal lumen through which fluid can flow to and from a lung or lung region. The diameter of the internal lumen for a specific bronchial passageway can vary based on the bronchial passageway&#39;s location in the bronchial tree (such as whether the bronchial passageway is a lobar bronchus or a segmental bronchus) and can also vary from patient to patient. However, the internal diameter of a bronchial passageway is generally in the range of 3 millimeters (mm) to 10 mm, although the internal diameter of a bronchial passageway can be outside of this range. For example, a bronchial passageway can have an internal diameter of well below 1 mm at locations deep within the lung.  
      Flow Control Device  
      Some of the breathing patterns that are characteristic of patients with severe emphysema are that the patients are able to inhale very easily and yet exhale with great difficulty. The destruction of lung parenchyma in the diseased regions of the lung leads to a loss of elastic recoil for the diseased lung region. The resulting imbalance in elastic recoil between diseased and healthier lung regions results in the diseased lung regions filling with air easily and first during inspiration. However, the diseased regions empty last and with great difficulty during expiration, as there is little or no elastic recoil remaining in the diseased lung regions to assist in the expelling of air. Adding to this difficulty, the distal airways in the diseased lung regions collapse during exhalation due to the loss of tethering forces that hold the airways open during exhalation in normal lung regions. As pleural pressure increases at the beginning of expiration, these distal airways partially or fully collapse, thus decreasing the exhalation flow, and increasing the work and time required for the patient to fully exhale.  
      To help ease the symptoms of emphysema and to improve breathing mechanics, implantation of one-way flow control devices or valve bronchial isolation devices has been employed, as described in several prior U.S. patent applications, including “Methods and Devices for use in Performing Pulmonary Procedures”, Ser. No. 09/797,910, filed Mar. 2, 2001 and “Bronchial Flow Control Devices and Methods of Use”, Ser. No. 10/270,792, filed Oct. 10, 2002, which are incorporated herein by reference. In the aforementioned patent applications, at least some of the bronchial isolation devices include one-way valves that remain closed and sealed in a default state, such as when there is no pressure differential across the valve.  
       FIGS. 5A-6B  show an exemplary embodiment of a flow control device  110  that generally includes a valve, a frame or anchor, and a seal member for sealing against a wall of a bronchial passageway. It should be appreciated that the flow control device  110  shown in  FIGS. 5A-6B  is exemplary and that the frame, seal member, and valve can vary in structure. For example, the valve does not have to be configured with a central opening for fluid flow. Rather, the valve can be configured to interact with the walls of the bronchial passageway to permit or block fluid flow in that the valves contact or withdraw from the bronchial walls to block or permit fluid flow. The flow control device  110  has a general outer shape and contour that permits the flow control device  110  to fit entirely or at least partially within a body passageway, such as within a bronchial passageway.  
      The valve is configured to regulate fluid flow through a bronchial passageway in which the device  110  is implanted. The valve opens and vents fluid (such as gas or liquid, including mucous) when the pressure across the valve due to flow in a first direction, such as the exhalation direction, exceeds the rated cracking pressure of the valve. Thus, the valve opens in response to fluid flow in the first direction. The valve moves towards a closed configuration in response to fluid flow in a second, opposite direction such as the inhalation direction.  
      With reference to  FIGS. 5A-6B , the flow control device  110  extends generally along a central axis  605  (shown in  FIGS. 5B and 6B ). The flow control device  110  includes a main body that defines an interior lumen  610  through which fluid can flow along a flow path. The dimensions of the flow control device  110  can vary based upon the bronchial passageway in which the flow control device  110  is configured to be implanted. The valve does not have to be precisely sized for the bronchial passageway it is to be placed within. Generally, the diameter D (shown in  FIG. 6A ) of the flow control device  110  in the uncompressed state is larger than the inner diameter of the bronchial passageway in which the flow control device  110  will be placed. This will permit the flow control device  110  to be compressed prior to insertion in the bronchial passageway and then expand upon insertion in the bronchial passageway, which will provide for a secure fit between the flow control device  110  and the bronchial passageway.  
      The flow of fluid through the interior lumen  610  is controlled by a valve  612  that is disposed at a location along the interior lumen such that fluid must flow through the valve  612  in order to flow through the interior lumen  610 . It should be appreciated that the valve  612  could be positioned at various locations along the interior lumen  610 . The valve  612  can be made of a biocompatible material, such as a biocompatible polymer, such as silicone. As discussed in more detail below, the configuration of the valve  612  can vary based on a variety of factors, such as the desired cracking pressure of the valve  612 .  
      The valve  612  can be configured to permit fluid to flow in only one-direction through the interior lumen  610 , to permit regulated flow in two-directions through the interior lumen  610 , or to prevent fluid flow in either direction.  
      With reference still to  FIGS. 5A-6B , the flow control device  110  includes a seal member  615  that provides a seal with the internal walls of a body passageway when the flow control device is implanted into the body passageway. The seal member  615  is manufactured of a deformable material, such as silicone or a deformable elastomer. The flow control device  110  also includes an anchor member or frame  625  that functions to anchor the flow control device  110  within a body passageway.  
      As shown in  FIGS. 5A-6B , the seal member  615  can includes a series of radially-extending, circular flanges  620  that surround the outer circumference of the flow control device  110 . The configuration of the flanges can vary. For example, as shown in  FIG. 6B , the radial length of each flange  620  can vary. It should be appreciated that the radial length could be equal for all of the flanges  620  or that the radial length of each flange could vary in some other manner. In addition, the flanges  620  can be oriented at a variety of angles relative to the longitudinal axis  605  of the flow control device.  
      As mentioned, the anchor member  625  functions to anchor the flow control device  110  in place when the flow control device is implanted within a body passageway, such as within a bronchial passageway. The anchor member  625  has a structure that can contract and expand in size (in a radial direction and/or in a longitudinal direction) so that the anchor member can expand to grip the interior walls of a body passageway in which the flow control device is positioned. In one embodiment, as shown in  FIGS. 5A-6B , the anchor member  625  comprises an annular frame that surrounds the flow control device  110 .  
      The frame  625  can be formed from a super-elastic material, such as Nickel Titanium (also known as Nitinol), such as by cutting the frame out of a tube of Nitinol or by forming the frame out of Nitinol wire. The super-elastic properties of Nitinol can result in the frame exerting a radial force against the interior walls of a bronchial passageway sufficient to anchor the flow control device  110  in place.  
      It should be appreciated that the configurations, including the sizes and shapes, of the frame  625  and the seal member  615  can vary from those shown in the figures. The seal  615  and/or the frame  625  can contract or expand in size, particularly in a radial direction. The default state is an expanded size, such that the flow control device  110  will have a maximum diameter (which is defined by either the seal  615  or the frame  625 ) when the flow control device  110  is in the default state. The flow control device  110  can be radially contracted in size during insertion into a bronchial passageway, so that once the flow control device  110  is inserted into the passageway, it expands within the passageway.  
      At least a portion of the valve  612  is optionally surrounded by a rigid or semi-rigid valve protector member  637  (shown in  FIGS. 5B and 6B ), which is a tubular member or annular wall that is contained inside the seal member  615 . In another embodiment, the valve protector can comprise a coil of wire or a ring of wire that provides some level of structural support to the flow control device. The valve protector  637  can be concentrically located within the seal member  615 . Alternately, the valve  612  can be completely molded within the seal member  615  such that the material of the seal member  615  completely surrounds the valve protector. The valve protector has sufficient rigidity to maintain the shape of the valve member against compression.  
      In one embodiment, the valve protector member  637  has two or more windows  639  comprising holes that extend through the valve protector member, as shown in  FIG. 6B . The windows  639  can provide a location where a removal device, such as graspers or forceps, can be inserted in order to facilitate removal of the flow control device  110  from a bronchial passageway.  
      As mentioned, the structural configuration of the flow control device can vary. For example,  FIG. 7  shows a perspective view of another embodiment of a flow control device  110  that includes a frame  625 , a valve  612  mounted in the frame  625 , and a membrane  627 . The frame  625  and the membrane  627  can collectively or individually seal with an internal wall of a bronchial passageway.  
      Normally-Open Valves  
      As mentioned, the valve in a flow control device opens and vents fluid (such as gas or liquid, including mucous) when the pressure differential across the valve due to flow in the first direction, such as the exhalation direction, exceeds the rated cracking pressure of the valve. Applicant has determined that the lower the cracking pressure and the higher the level of fluid flow in the first direction through the valve once it has cracked, the better the performance of the flow control device for certain circumstances. This is because a greater amount of fluid (gas or liquid) will be expelled from the target lung region through the valve during exhalation.  
      In an effort to further improve the performance of the valve by lowering the cracking pressure and increasing the flow through the valve once cracked, the valve may be configured to be open in a default state. The valve is “open” in that there is an opening for fluid to flow through. The opening is typically defined by a gap between the coaptation regions of the valve, such as a gap between the lips of a valve. A valve that is open in the default state is referred to herein as a “normally-open” valve. In the default state, there is no pressure differential across the valve. Those skilled in the art will appreciate that a pressure differential can be achieved as a result of the valve being exposed to the flow of fluid. Thus, when a normally-open valve is in a default state, the coaptation regions of the valve are at least partially separated from one another to define a gap or opening therebetween.  
      As discussed above, exemplary implantable one-way valve flow control devices are shown in  FIG. 5A-7 . A valve of a flow control device includes regions (referred to herein as coaptation regions) that contact one another to block flow through the valve, and separate from one another to allow flow through the valve. The coaptation regions can contact one another along their entire length or area such that there is no gap between therebetween and the valve is completely closed. The coaptation regions can also partially contact one another such that there is at least a partial opening therebetween. For a normally-open valve, the coaptation regions at least form a partial opening in the default state.  
      The coaptation regions can comprise, for example, opposed lips that contact one another in a duckbill valve. For example, in the embodiment shown in  FIGS. 5A-6B , the valve  612  comprises a duckbill valve that includes two opposed, inclined walls or flaps  631  (shown in  FIGS. 5B and 6B ) that are oriented at an angle with respect to one another. The flaps  631  can open and close with respect to one another so as to form an opening between coaptation regions comprised of lips  801  ( FIG. 6B ). The relative positions of the lips  801  determines the size of the opening in the valve  612 . When the lips are in full contact with one another, there is no opening between the coaptation regions. The valve shown in  FIGS. 5A-6B  has such a configuration.  
      In conventional flow control devices, the valve coaptation regions are in full contact with one another in a default state, such as when there is no pressure differential across the valve. That is, the coaptation regions are in contact with one another such that there is no opening for fluid to flow through. As mentioned, the default state is the state of the valve when exposed to no fluid flow and, therefore, no pressure differential across the valve. When a valve is “closed” the valve coaptation regions contact one another so as to block flow through the valve when there is no pressure differential across the valve.  
      There are now described embodiments of valves that are normally-open in a default state. Thus, when there is no pressure differential across the valve, the coaptation regions (such as the lips of a duckbill valve) of the valve are not in contact with one another or only partially contact one another so as to form an opening therebetween. As discussed, such a valve has a reduced cracking pressure with respect to a valve that is closed in the default state. One reason for this is that the gap between the coaptation regions reduces or eliminates any “sticking force” between the coaptation region, which sticking force resists cracking of the valve. Another reason is that the gap between the lips reduces or eliminates surface tension that can be caused by mucous lining the coaptation regions. Such surface tension must be overcome in order to crack the valve. Furthermore, because the valve is at least partially open in the default state, bulk resilience of the valve is decreased so that the valve has less resistance to flow in the first direction than for a normally-closed valve at the same pressure. This can result in a higher flow through the valve in the first direction once the valve is cracked.  
       FIG. 8  shows an exemplary embodiment of a normally-open duckbill valve  805  that can be used in the flow control device  110 . The valve  805  is manufactured with a measurable gap  807  between the coaptation regions. The coaptation regions comprise two or more lips  810   a,    810   b  that are joined at opposing ends and that define the valve opening. The lips  810   a ,  810   b  do not contact one another along their length in a default state, but rather are separated to form the opening  807 . When the valve  805  is exposed to flow in the first direction (e.g., the expiration direction, represented by arrow  812  in  FIG. 8 ), the lips  810   a  and  810   b  are urged away from one another to increase the size of the opening  807 . Because the lips  810   a ,  810   b  do not contact one another in the default, there is no sticking force to overcome in order for the flow in the first direction to urge the lips apart from each other. When the valve  805  is exposed to flow in the second direction (e.g., the inspiratory direction, represented by arrow  814  in  FIG. 8 ) the lips  810   a  and  810   b  are urged toward one another. If exposed to a sufficient level of flow in the second direction, the lips  810   a  and  810   b  can fully contact one another to completely close the opening  807 .  
       FIG. 9  shows another embodiment of a normally-open valve  905  having a trilobular configuration. The trilobular valve  905  has a single, contoured wall that is shaped so as to form three lobes defined by outside corners  920  and inside corners  925 . The wall has coaptation regions comprised of lips  915  that define an opening  910  in a default state. When exposed to fluid flow in the first direction  812 , the lips  915  separate to increase the size of the opening  910 . When exposed to fluid flow in the second direction  814 , the lips  915  move toward one another to decrease the size of the opening  910 . The radius of the outside corners  920  and the inside corners  925  formed by the contours of the wall of the trilobular valve  905  can be gently curved as shown in  FIG. 9 , or can have a very sharp radius or can be sharp corners with no radius at all. Alternately, the valve may have four or more lobes.  
       FIGS. 10A and 10B  shows another embodiment of a flow control device  1010  that is similar in configuration to the device  110  described above. However, the flow control device  1010  has a valve  1020  having a flap valve configuration. The valve  1010  has a flap  1025  and a seat  1030 . The flap  1025  opens and closes relative to the seat  1030 . There is a measurable gap or opening  1040  between the flap  1025  and the seat  1030  in the default state of the valve  1010 . The flap  1025  moves away from the seat  1030  in response to fluid flow in the first direction  812  to increase the size of the opening  1040  through which fluid flows. The flap  1025  moves toward the seat  1030  in response to fluid flow in the second direction  814  to decrease the size of the opening  1040 . The flap  1025  can completely contact the seat  1030  to close the opening  1040  when exposed to a sufficient level of fluid flow in the second direction.  
      As discussed, the use of a valve that is “normally-open” has the effect of reducing or eliminating the cracking pressure. A flow control device equipped with a normally-open valve, when implanted into a bronchial passageway of a patient, opens wider more quickly in response to fluid flow in the expiratory direction and with a lower driving pressure with respect to a valve that is closed in its default state. This leads to greater exhalation of fluid during exhalation.  
      The size of the opening or amount of separation between the coaptation regions of the valve in the default state can vary. In one embodiment, the valve is completely open or near completely open in the default state. When a valve is “completely open” the valve allows its maximum level of flow therethrough or a flow level that is substantially near its maximum. When a valve is “partially open”, it allows less than the maximum level.  FIG. 11  shows an exemplary valve  1110  that has an opening  1115  defined by lips  1120 . The opening  1115  is oval-shaped in a default state. As in the previous valves, fluid flow in the first direction  812  urges the lips  1120  away from one another to increase the size of the opening  1115 . Fluid flow in the second direction  814 urges the lips  1120  toward each other to decrease and possibly close the opening  1115 .  
      In another embodiment, the valve is partially open in the default state and the valve opens more fully as the valve is exposed to fluid flow in a first direction, such as in the exhalation direction. The size of the opening decreases when exposed to fluid flow in the second direction, such as the inhalation direction. That is, the valve transitions from a partially open state toward a completely open state as the valve is exposed to an increasing level of fluid flow in the first direction. The valve might completely open when exposed to fluid flow in the first direction. How close the valve gets to being completely open depends on the level of flow in the first direction. When exposed to fluid flow in the second direction, the valve transitions from the partially open state toward the closed state. The valve might fully close depending on the level of flow in the second direction, although does not necessarily fully close. Thus, the opening in the valve increased as flow moves through the valve in the first direction, such as the exhalation direction. The valve shown in  FIG. 8  shows an example of a valve that opens more fully when exposed to fluid flow in the first direction.  
      Given the variability in the degree, location and effect of the destruction due to emphysema and the resulting loss of elastic recoil and increase in distal airway collapse in patients that have emphysema, it can be difficult to assign a sufficiently low cracking pressure for the valve of a flow control device. The cracking pressure should be sufficiently low such that the valve will easily crack open and vent fluid during all conditions of flow in a particular direction, such as exhalation. In a similar fashion, it can be difficult to assign a required level of flow through the valve, once cracked, that will ensure that fluid will vent through the valve during exhalation. It is desirable to have the cracking pressure be as low as possible, and the level of flow through the valve, once cracked, to be as high as possible. If the valve is configured to open in response to exhalation flow, this results in the valve cracking open more quickly once exhalation has begun, and once open, the maximum possible flow of fluid will occur through the valve. This will result in the maximum emptying of fluid from the targeting lung unit during exhalation, and the maximum benefit to the patient.  
      When a valve is designed to be biased closed such that the valve is completely closed in a default state, the geometrical and material properties inherent in such a valve can add some degree of cracking pressure and some limitation to the level of flow through the valve. Applicant has determined that a valve has beneficial properties when the valve is not biased completely closed such that the coaptation regions do not contact one another when there is zero pressure differential across the valve. Such a valve opens with less resistance to flow and therefore allows much greater flow through it during exhalation (with respect to a valve that is closed in the default state). It should be appreciated that a normally-open valve can be biased toward the closed position but that the bias is not so strong as to completely close the valve. Thus, a normally-open valve can be biased toward a partially-closed configuration.  
      As mentioned, when the coaptation regions of a valve contact one another in the default state, the coaptation regions, typically formed of an elastomeric material, tend to stick together. The resulting “sticking force” must be overcome in order to crack the valve open, thus increasing the cracking pressure. This “sticking force” may be reduced by coating the coaptation regions with a material that reduces sticking between the coaptation regions. Some possible coatings include polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), fluorinated ethylene-propylene (FEP) or other flouropolymer, parlylene, hydrophilic coatings such as hyaluronic acid, various ion implanted or otherwise applied coatings such as silver, alumina (Al 2 O 3 ) or sialon (SiO 2 /N/Al 2 O 3 ), etc. It should be appreciated that this is not a complete list of possible coatings or surface treatments, and other coatings or surface treatments that reduce the “sticking force” of the coaptation regions are possible. In addition, in order to ensure that the coaptation regions are always pressed together, a normally-closed valve is typically designed with some elastic resilience or spring bias so that some force from fluid flow through the valve must be applied to the coaptation regions in order to force them apart and allow fluid flow through the valve. This has the effect of raising the cracking pressure of the valve and of reducing the flow at a given driving pressure.  
      In designing a normally-open valve, there are a few design factors that can be considered. In general, if it is desired that the valve close at very low flows in the second direction (e.g., the inhalation direction), the valve will likely have some restriction to opening in response to fluid flow in the second direction (e.g., exhalation direction). If it is desired that the valve have the lowest possible restriction to exhaled flow, the valve will likely require a higher flow in the inhalation direction to close the valve. In addition, when closed, the valve may still allow a slight flow leak in the inhalation direction, which can be a disadvantage. Such a disadvantage may be more than compensated for by an increase in the flow through the valve in the exhalation direction. If the valve is of a duckbill or Heimlich type where there are two coaptation regions such as lips that come in contact with each other to seal the valve, the valve may be designed to have either of these characteristics or to be somewhere in between.  
      For example, if the valve is configured to be completely or almost completely open when there is no flow through the valve (such as for the valve  1110  shown in  FIG. 11 ), the valve will have a very high flow rate in a first direction (e.g. the exhalation direction) yet will require a threshold amount of flow in the second direction (e.g., the inhalation direction) to close the valve.  
      The valve can also be configured to allow flow at a low rate to move through the valve without ever completely closing the valve at all. That is, the valve is completely or partially open when exposed to no fluid flow and gradually closes when exposed to flow in the second direction such that the valve increasingly closes as the rate of fluid flow in the second direction increases. When closed to a maximum closing capacity, the valve may have some leak paths that allow a low level of flow in the second direction, such as the inhalation direction. Such a valve  1210  is shown in  FIG. 12  through  FIG. 15 . The valve  1210  is shown completely open in  FIG. 12 , which means that the valve is open to its maximum capacity. Alternately, the valve  1210  can be partially open in  FIG. 12 . In  FIG. 13 , the valve  1210  is partially closed in response to flow in the second direction (reverse flow). The lips of the valve are in partial contact with each other in  FIG. 13 . That is, the lips contact one another along a central region, but are separated from each other along opposed edges to form small openings at the opposed edges. It should be appreciated that the lips can contact each other at various locations along their length or area when in partial contact. In  FIG. 14 , the valve is completely closed by a higher level of flow in the second direction.  
      Thus, the valve provides increased resistance to fluid flow in the second direction as the level of fluid flow in the second direction increases. The valves described herein can be configured to provide increased resistance to fluid flow as the level or rate of fluid flow in the second direction increases. The fluid flow occurs as a result of a pressure differential across the valve. For example, the pressure differential may be such that fluid flows in the second direction (such as the inspiratory direction). In such a situation, the pressure on the proximal side of the valve is greater than the pressure on the distal side of the valve. As such a pressure differential increases, the valve&#39;s resistance to fluid flow in the inspiratory direction also increases. The resistance to fluid flow can gradually increase as the pressure differential and the rate of fluid flow increases. The valve&#39;s resistance to fluid flow can also suddenly increases when the pressure differential or rate of fluid flow increases beyond a threshold. The valve can resist fluid flow in an inspiratory direction through the bronchial passageway, wherein the valve transitions to a state of increased resistance to fluid flow in response to an increase in a rate of fluid flow through the bronchial passageway.  
      Depending on the design of the valve and the level of flow in the second direction, the valve may not necessarily reach the completely closed state shown in  FIG. 14 . Rather, the maximum closed state of the valve can be some variation of the valve as shown in  FIG. 13 , with the size(s) of the opening(s) between the lips being larger or smaller in the maximum closed state.  
      As shown in  FIGS. 12-14 , depending on the level of flow through the valve in the second direction (e.g., the inhalation direction), there may be leak paths through the valve, such as in the corners of the valve mouth. The leak paths can allow some fluid flow through the valve when exposed to flow in the second direction, such as during inhalation. The valve gradually closes when exposed to increasing flow in the second direction and opens when exposed to flow in the first direction. It should be appreciated that the first direction need not correspond to the expiration direction and that the second direction need not correspond to the inhalation direction.  
      The valve of the flow control device can be configured so that it does not close suddenly, and may behave more like a variable resistance valve in that the resistance to flow in the second direction increases as the level of flow in the second direction through the valve increases, as shown in  FIG. 12  through  FIG. 14 . Alternately, the valve may be configured to close quickly so that once a flow threshold required to close the valve is exceeded, the valve closes quickly. The valve in  FIG. 8  is such a valve. If the valve is configured such that the coaptation regions are very close together when there is no flow through the valve (as shown in  FIG. 8 ), the valve will have a lower flow in the first direction (e.g. exhalation direction) yet will close at a very low flow in the second direction (e.g. inhalation direction). When the valve is closed to a maximum, the valve may be designed to completely block flow in the second direction (such as under inhalation pressures and flows), or may allow a relatively low level of flow in the second direction. It should be appreciated that valves may be designed between these extremes and may be of other designs such as flap valves, trilobular valves, etc.  
       FIG. 15  shows another exemplary valve  1610 . The valve  1610  has coaptation regions comprised of lips  1612  that meet at opposed corners  1613 . The shape of the opening  1615  is defined by the lips  1612 . In the illustrated embodiment, the corners  1613  of the opening  1615  form a very sharp angle, such as, for example, in the range of  1  to  10  degrees. It should be appreciated that the foregoing corner angles are exemplary and can vary. For example, the corner angle could be greater than 10 degrees. When such a valve closes, the two lips  1612  meet or contact one another tightly without leaving any openings therebetween. In this way, leaks in the second direction (e.g., the inhalation direction) may be prevented or reduced, while at the same time retaining the low cracking pressure and high exhalation flow that come with a normally-open valve.  
      Another feature of the valve  1610  of  FIG. 15  is the length (when measured along the central axis of the device in the fluid flow direction) of the valve lips  1612 , which are longer than those found in the more standard duckbill valve shown mounted in the bronchial isolation device of  FIG. 5A-7 . In the valve  1610 , the lips  1612  are parallel to one another for an extended length, such as, for example, approximately 0.010 to 0.100 inches. It should be appreciated that the extended lip length can vary based on the relative size of the valve. This extended length of the coaptation regions where the lips are parallel lowers the pressure required to close the valve in the inhalation direction while maintaining the low cracking pressure of a normally-open bi-leaflet valve.  
      In order to lower the crack pressure as much as possible and to increase the flow through the valve once it is cracked, the wall thickness of the valve walls for a duckbill valve may be reduced relative to conventional valve. If the valve is constructed of silicone, either molded or dipped, an optimal wall thickness may be as low as 0.002″ or 0.003″. As mentioned previously, the valve may also be constructed of other elastomeric materials, such as urethane.  
      When the valve is constructed with thin walls, the valve may be less resistant to inversion, or turning inside-out, when pressure is applied across the valve in the flow direction that closes the valve (such as in the inhalation direction). When a valve inverts, the valve ceases to perform as a one-way valve, so it is desirable to avoid inversion during expected inhalation flows and pressures. If a valve such as that shown in  FIG. 15  is mounted into a flow control device, such as the device shown in  FIG. 5A-7 , the pressure at which inversion occurs may be greatly increased by bonding or otherwise attaching or “tethering” at least a portion  1620  of the valve, such as one side of the valve, to the inside of the valve protector member  637  ( FIG. 5A ) of the flow control device  110 .  
      The attachment to the valve protector member  637  on one side of the valve greatly raises the pressure required for the valve to invert, yet does not greatly increase cracking pressure or reduce flow through the valve. Alternately, the valve may be bonded to the valve protector in two or more locations. In an alternative embodiment, the wall thickness of the valve component may be tapered so that it is thicker at the base of the valve to reduce inversion potential, yet is thinner at the mouth of the valve in order to keep the crack pressure low and the flow high.  
      An alternate valve embodiment of a valve  2010  is shown in  FIG. 19 . In this embodiment, the valve  2010  has coaptation regions comprised of lips  2012  that meet at opposed corners  2013  in the same fashion as the valve shown in  FIG. 15 , however this embodiment differs in that the lips  2012  continue to be split apart around both sides of the valve  2014 . This modification allows the valve to open farther and allows a larger level of flow in the exhalation direction. There is an opening  2015  in the default state that is defined by the lips  2012 , however the valve may also be constructed without the opening  2015  in order to produce a valve which is not normally open in the default state.  
      An alternate valve embodiment of a valve  1710  is shown in  FIGS. 17A-17C . In this embodiment, the valve  1710  has pleated sides  1715  and a mouth  1720  that is open in a default state. The pleated sides  1715  allow the valve  1710  to close and seal with minimal flow in the second direction (e.g. inhalation direction), yet when the flow is reversed and fluid starts to move through the valve in the first direction (e.g. exhalation direction), the pleats allow the valve to open very widely, thus allowing a very high flow rate.  
      Active Valve  
      The valves described above have been “passive” in that the valves open or close in response to flow and pressure across the valves. The valves can also close in response to a bias built into the valve. The aforementioned designs generally entail trade-offs between design and material properties. A normally-closed valve has the advantage of minimizing retrograde flow through the valve at the expense of increased cracking pressure and resistance to flow in the exhalation direction. A normally-open valve has the advantage of reducing cracking pressure and reducing resistance to flow in a first direction (e.g., the exhalation direction), but at the expense of increases in flow prior to valve closing in the second direction or leaking after closure. Additionally, the physiological conditions at which valves must operate vary greatly between patients and even within the same patient under different conditions.  
      An “active” valve is actuated by some power source to open completely with little or no flow or pressure differential at the initiation of exhalation and then rapidly close and seal immediately at the initiation of inhalation. An active valve overcomes some drawbacks of passive valves. In a prior U.S. patent application entitled “Active Pump Bronchial Implant Devices and Methods of Use Thereof”, Ser. No. 10/298,387, which is incorporated here by reference and assigned to the same assignee as the instant application, the inventors described various devices and methods of implantable pumps that would actively move fluid through the bronchial anatomy regardless of pressure and flow conditions across the valve. Under some physiologic conditions or because of greater simplicity in design, the use of an active valve may be more desirable than a passive valve.  
      In one embodiment, the active valve is synchronized with the patient&#39;s breathing. One method is to convert the mechanical movement of the abdomen into an electrical pulse by having the patient wear an elastic belt with integrated pressure transducers about the abdomen. The pressure belt transmits this electrical signal, either wired, through radio waves or other methods, to a controller for the actuator of the implanted valve(s). Alternately sensing stimulation of the phrenic nerve during normal respiration can be used as the pacing signal to actuate the valve to open during exhalation and close during inhalation.  
      The active valve could be a flap valve, a bi-leaflet valve, a tri-leaflet valve, or any other valve that one skilled in the art could create.  
      Manufacture of Parallel-Lipped Valve  
      As discussed, a bi-leaflet or duckbill valve is configured with a relatively long coaptation region, such as lips that are parallel to each other as shown in  FIGS. 15 and 19 . This type of valve may be designed as a normally-open valve where the two parallel lips are spaced apart by a predetermined distance, or the valve may have the two lips that are in contact with each other along the length of the lips.  
      In an embodiment shown in  FIG. 17 , a mandrel  1810  is formed out of aluminum, stainless steel or other suitable material in the shape of the desired inside surfaces of the valve. The mandrel  1810  is then dipped in a silicone, urethane or other suitable dispersion to coat the outer surface of the mandrel  1810 . The coating is then cured in an appropriate fashion to form the valve, and the valve is stripped off of the mandrel  1810  as shown in  FIG. 17 . The tip  1705  of the valve is trimmed to expose the opening in the valve (as dipping will cover the tip of the mandrel thus closing off the opening at the valve mouth), thus leaving a valve with an open center lumen with parallel sealing surfaces. Of course, other methods of forming the normally-open, parallel-lipped valves such as injection molding, etc may be used.  
      Alternately, in the embodiment shown in  FIG. 18 , a parallel-lipped valve is normally-closed in that the lips are in contact with each other when there is no pressure differential across the valve. In this embodiment, the valve is formed by heat bonding two sheets of urethane to each other using a bonding die that is formed in the desired shape of the valve. Of course, other materials and methods could be used to form a normally-closed parallel lipped valve.  
      Tethered Flap Valve  
      For certain situations, it may be desirable to use a one-way flow control device that remains closed and sealed at all times when there is no flow through the device in either direction, yet still has as low a cracking pressure as possible in response to flow in the first direction, and once cracked, has as high a flow as possible through the valve. A flap valve is a style of valve that may be designed to have a low cracking pressure and a high flow once cracked. However, conventional flap valves do not remains closed and sealed with no flow through the valve. One way to improve the sealing of a flap valve is to add an elastic tether, formed for example from silicone, to the flap to assist in holding the valve down against the valve seat. For example, the flap valve  1010  shown in  FIGS. 10A and 10B  can have a tether mounted to the flap  1025  to urge the flap  1025  toward the seat  1030 .  
      When a pressure differential is applied to the valve in the exhalation direction, the tether is stretched and the valve opens. When there is no pressure across the valve, the tether holds the flap against the valve seat, thus preventing leakage through the valve. In an alternative embodiment, the tether is not elastic and does not stretch when the valve opens. Instead, the edges of the flap component deflect away from the valve seat when the valve opens.  
      Occluder  
      There are times when an implanted occlusion flow control device, instead of a one-way or two-way valve device, is clinically indicated for the isolation of lung tissue. The device shown in  FIG. 7  can be modified to act as an occluder. The valve  612  in  FIG. 7  is replaced with an occluding member that blocks flow through the flow control device. As mentioned, the device  110  in  FIG. 7  includes an elastically expandable frame  625  that is covered with an elastomeric membrane  627 . In one embodiment, the device has an expanded frame laser-cut from nitinol tubing that has been expanded and heat treated to set it in the shape shown. The frame  625  is dipped in a silicone dispersion so that all outer surfaces are covered in a thin silicone membrane.  
      When the device is compressed into a delivery catheter, it may be delivered through the trachea, using any of a number of well know delivery methods, to the target bronchial lumen, and released from the catheter. Once released, the device expands and grip the walls of the bronchial lumen, and due to the silicone membrane, blocks fluid (gas and liquid) flow through the lumen in both the inhalation and exhalation directions. The frame  625  can have points or prongs on the distal end to prevent migration of the device in the distal or inhalation direction.  
      Of course, the frame may be made of other materials and take other shapes, may be deformable or heat expandable rather than spring resilient, and the membrane may be formed from other materials (such as urethane) and may be manufactured using methods other than dipping. This particular device is compact enough to fit into a delivery catheter that can fit through the working channel of a bronchoscope that has an internal diameter of 2.2 mm, however it may be delivered using other methods.  
      A number of embodiments of the invention have been described. Neverthe-less, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.