Abstract:
The volume of a hyperinflated lung compartment is reduced by sealing a distal end of the catheter in an airway feeding the lung compartment. Air passes out of the lung compartment through a passage in the catheter while the patient exhales. A one-way flow element associated with the catheter prevents air from re-entering the lung compartment as the patient inhales. Over time, the pressure of regions surrounding the lung compartment cause it to collapse as the volume of air diminishes. Residual volume reduction effectively results in functional lung volume expansion. Optionally, the lung compartment may be sealed in order to permanently prevent air from re-entering the lung compartment. The invention further discloses a catheter with a transparent occlusion element at its tip that enables examination of the lung passageway through a viewing scope.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a divisional of U.S. patent application Ser. No. 12/407,709 (Attorney Docket No. 20920-720.502), filed Mar. 19, 2009 (now U.S. Pat. No. ______), which is a continuation-in-part of International Application No. PCT/US08/56706 (Attorney Docket No. 20920-720.601), filed Mar. 12, 2008, which claims the benefit of U.S. patent application Ser. No. 11/685,008 (Attorney Docket No. 20920-720.501), filed, Mar. 12, 2007, the full disclosures of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to medical methods and apparatus. More particularly, the present invention relates to methods and apparatus for endobronchial residual lung volume reduction by passive deflation of hyperinflated segments with functional lung volume expansion as a result. 
         [0004]    Chronic obstructive pulmonary disease is a significant medical problem affecting 16 million people or about 6% of the U.S. population. Specific diseases in this group include chronic bronchitis, asthmatic bronchitis, and emphysema. While a number of therapeutic interventions are used and have been proposed, none are completely effective, and chronic obstructive pulmonary disease remains the fourth most common cause of death in the United States. Thus, improved and alternative treatments and therapies would be of significant benefit. 
         [0005]    Of particular interest to the present invention, lung function in patients suffering from some forms of chronic obstructive pulmonary disease can be improved by reducing the effective lung volume, typically by resecting diseased portions of the lung. Resection of diseased portions of the lungs both promotes expansion of the non-diseased regions of the lung and decreases the portion of inhaled air which goes into the lungs but is unable to transfer oxygen to the blood. Lung volume reduction is conventionally performed in open chest or thoracoscopic procedures where the lung is resected, typically using stapling devices having integral cutting blades. 
         [0006]    While effective in many cases, conventional lung volume reduction surgery is significantly traumatic to the patient, even when thoracoscopic procedures are employed. Such procedures often result in the unintentional removal of healthy lung tissue, and frequently leave perforations or other discontinuities in the lung which result in air leakage from the remaining lung. Even technically successful procedures can cause respiratory failure, pneumonia, and death. In addition, many older or compromised patients are not able to be candidates for these procedures. 
         [0007]    As an improvement over open surgical and minimally invasive lung volume reduction procedures, endobronchial lung volume reduction procedures have been proposed. For example, U.S. Pat. Nos. 6,258,100 and 6,679,264 describe placement of one-way valve structures in the airways leading to diseased lung regions. It is expected that the valve structures will allow air to be expelled from the diseased region of the lung while blocking reinflation of the diseased region. Thus, over time, the volume of the diseased region will be reduced and the patient condition will improve. 
         [0008]    While promising, the use of implantable, one-way valve structures is problematic in at least several respects. The valves must be implanted prior to assessing whether they are functioning properly. Thus, if the valve fails to either allow expiratory flow from or inhibit inspiratory flow into the diseased region, that failure will only be determined after the valve structure has been implanted, requiring surgical removal. Additionally, even if the valve structure functions properly, many patients have diseased lung segments with collateral flow from adjacent, healthy lung segments. In those patients, the lung volume reduction of the diseased region will be significantly impaired, even after successfully occluding inspiration through the main airway leading to the diseased region, since air will enter collaterally from the adjacent healthy lung region. When implanting one-way valve structures, the existence of such collateral flow will only be evident after the lung region fails to deflate over time, requiring further treatment. 
         [0009]    For these reasons, it would be desirable to provide improved and alternative methods and apparatus for effecting residual lung volume reduction in hyperinflated and other diseased lung regions. The methods and apparatus will preferably allow for passive deflation of an isolated lung region without the need to implant a one-way valve structure in the lung. The methods and apparatus will preferably be compatible with known protocols for occluding diseased lung segments and regions after deflation, such as placement of plugs and occluding members within the airways leading to such diseased segments and regions. Additionally, such methods and devices should be compatible with protocols for identifying and treating patients having diseased lung segments and regions which suffer from collateral flow with adjacent healthy lung regions. At least some of these objectives will be met by the inventions described hereinbelow. 
         [0010]    2. Description of the Related Art 
         [0011]    Methods for performing minimally invasive and endobronchial lung volume reduction are described in the following U.S. Pat. Nos. and published patent applications: U.S. Pat. Nos. 5,972,026; 6,083,255; 6,258,100; 6,287,290; 6,398,775; 6,527,761; 6,585,639; 6,679,264; 6,709,401; 6,878,141; 6,997,918; 2001/0051899; and 2004/0016435. Balloon catheter devices for use in body passageways have previously been described in U.S. Pat. Nos. 4,976,710; 4,470,407; 4,681,093 and 6,174,307, and. U.S. Pat. No. 4,976,710 describes an angioscope with a transparent occlusion balloon at its distal end. Similarly, U.S. Pat. No. 6,174,307 describes an endovascular catheter with a transparent portion near the distal tip that can be used to view the body passageway. Similarly, issued U.S. Pat. Nos. 4,470,407 and 4,681,093 also describe endovascular devices with a transparent expandable balloon covering the lens. Though these catheters utilize the balloons to view the passageways, their use for viewing pulmonary passageways is limited in several aspects. Practically, the use of these devices in pulmonary passageways would be limited to those passageways large enough to accommodate a similarly constructed bronchoscope. These devices are also limited by the fact that treatment is limited to the exact site of visualization, rather than at a point distal to the visualization point. Further, the flexibility of these devices would be limited by the inherent properties of a visualization catheter. Hence, it would be beneficial to have a catheter that is flexible and to use it to visualize points that are distal to the location of the distal tip of the catheter. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention provides methods and apparatus for passively reducing the residual volume (the volume of air remaining after maximal exhalation) of hyperinflated or otherwise diseased lung compartments or segments. By “passively reducing,” it is meant that air can be removed from the diseased lung region without the use of a vacuum aspiration to draw the air from the region. Typically, such passive reduction will rely on a non-implanted one-way flow element, structure, or assembly which permits air to be exhaled or exhausted from the lung region while preventing or inhibiting the inspiration of air back into the lung region. By non-implanted, it is meant that some portion of the element, structure, or assembly will be temporarily placed in an airway or bronchus leading to the lung region in a manner that allows that portion to be removed later, typically within days or hours, without the need for surgical intervention Thus, the methods of the present invention will not require the permanent implantation of valves or other structures prior to actually achieving the desired residual lung volume reduction, as with the one-way implantable valve structures of the prior art. 
         [0013]    The methods and apparatus of the present invention can be terminated and all apparatus removed should it appear for any reason that the desired residual lung volume reduction is not being achieved. Commonly, such failure can be the result of collateral flow into the diseased lung region from adjacent healthy lung region(s). In such cases, steps can be taken to limit or stop the collateral flow and allow resumption of the passive lung volume reduction protocols. In other cases, it might be desirable or necessary to employ open surgical, thoracoscopic, or other surgical procedures for lung resection. 
         [0014]    Patients who successfully achieve residual volume reduction of hyperinflated or other diseased lung regions in accordance with the principles of the present invention will typically have those regions sealed permanently to prevent reinflation. Such sealing can be achieved by a variety of known techniques, including the application of radiofrequency or other energy for shrinking or sealing the walls of the airways feeding the lung region. Alternatively, synthetic or biological glues could be used for achieving sealing of the airway walls. Most commonly, however, expandable plugs will be implanted in the airways leading to the deflated lung region to achieve the sealing. 
         [0015]    In a first aspect of the present invention, methods for reducing the residual volume of a hyperinflated lung compartment comprise sealingly engaging a distal end of a catheter in an airway feeding the lung compartment. Air is allowed to be expelled from the lung compartment through a passage in the catheter while the patient is exhaling, and air is blocked from re-entering the lung compartment through the catheter passage while the patient is inhaling. As the residual volume diminishes, the hyperinflated lung compartment reduces in size freeing up the previously occupied space in the thoracic cavity. Consequently, a greater fraction of the Total Lung Capacity (TLC), which is the volumetric space contained in the thoracic cavity that is occupied by lung tissue after a full inhalation becomes available for the healthier lung compartments to expand and the volume of the lung available for gas exchange commonly referred to in clinical practice as the lung&#39;s Functional Vital Capacity (FVC) or Vital Capacity (VC) increases, the result of which is effectively a functional lung volume expansion. 
         [0016]    The hyperinflated lung compartment will usually be substantially free of collateral flow from adjacent lung compartments, and optionally the patient can be tested for the presence of such collateral flow, for example using techniques taught in copending, commonly assigned application Ser. No. 11/296,951 (Attorney Docket No.: 017534-002820US), filed on Dec. 7, 2005; Ser. No. 11/550,660 (Attorney Docket No. 017534-003020US), filed on Oct. 18, 2006; and application Ser. No. 11/428,762 (Attorney Docket No. 017534-003010US), filed on Jul. 5, 2006, the full disclosures of which are incorporated herein by reference. 
         [0017]    Alternatively, the methods of the present invention for reducing residual lung volume can be performed in patients having collateral flow channels leading into the hyperinflated or other diseased lung compartment. In such cases, the collateral flow channels may first be blocked, for example, by introducing glues, occlusive particles, hydrogels or other blocking substances, as taught for example in copending application Ser. No. 11/684,950 (Attorney Docket No. 017534-004000US), filed on Mar. 12, 2008, the full disclosure of which is incorporated herein by reference. In other cases, where the flow channels are relatively small, those channels will partially or fully collapse as the residual lung volume is reduced. In such cases, the patient may be treated as if the collateral flow channels did not exist. The effectiveness of reduction in hyperinflation however will depend on the collateral resistance between the hyperinflated compartment and the neighboring compartments, as illustrated in  FIG. 9 , where residual volume reduction is negligible when the resistance to collateral flow Rcoll is very small (significant collateral flow channels) and maximally effective when Rcoll is very high (no collateral flow channels). 
         [0018]    In all of the above methods, it may be desirable to introduce an oxygen-rich gas into the lung compartment while or after the lung volume is reduced in order to induce or promote absorption atelectasis. Absorption atelectasis promotes absorption of the remaining or residual gas in the compartment into the blood to further reduce the volume, either before or after permanent sealing of the lung volume compartment or segment. 
         [0019]    In a second aspect, the present invention provides catheters for isolating and deflating hyperinflated and other diseased lung compartments. The catheter comprises a catheter body, an expandable occluding member on the catheter body, and a one-way flow element associated with the catheter body. The catheter body usually has a distal end, a proximal end, and at least one lumen extending from a location at or near the distal end to a location at or near the proximal end. At least a distal portion of the catheter body is adapted to be advanced into and through the airways of a lung so that the distal end can reach an airway which feeds a target lung compartment or segment to be treated. The expandable occluding member is disposed at or near the distal end of the catheter body and is adapted to be expanded in the airway which feeds the target lung compartment or segment so that said compartment or segment can be isolated with access provided only through the lumen or catheter body when the occluding member is expanded. 
         [0020]    The catheter of the present invention can be used in conjunction with, or independent of, a viewing scope such as a bronchoscope. Since it is generally configured to be narrower than a visualization tube such as a bronchoscope, the catheter may be introduced into narrower passageways and is used to isolate a portion of lung tissue. 
         [0021]    In one embodiment of the catheter, the expandable occluding element is disposed near the distal end of the catheter body. In this embodiment, the expandable occluding element is configured such that both the proximal and distal ends of the expandable occluding element are attached to the outer surface of the catheter body. 
         [0022]    In another embodiment of the catheter, the expandable occluding element is disposed at the distal end of the catheter body, and is configured to form a cover over the rim of the lumen. This embodiment prevents or inhibits entry of mucus into the lumen, and prevents the catheter tip from contacting the airway wall. A method of manufacturing this embodiment of the catheter is also disclosed. One end of the occluding element is attached to the internal surface of the central passageway at the tip of the catheter. The occluding element is then inverted over the catheter body and a second end of the occluding element is attached to the outer surface of the catheter body. The expandable occluding element is optionally transparent to enable viewing the body passageway (for example during diagnostic or treatment procedures). 
         [0023]    The one-way flow element is adapted to be disposed within or in-line with the lumen of the catheter body in order to allow flow in a distal-to-proximal direction so that air will be expelled from the isolated lung compartment or segment as the patient exhales. The one-way flow element, however, inhibits or prevents flow through the lumen in a proximal-to-distal direction so that air cannot enter the isolated lung compartment or segment while the patient is inhaling. 
         [0024]    For the intended endobronchial deployment, the catheter body will typically have a length in the range from 20 cm to 200 cm, preferably from 80 cm to 120 cm, and a diameter near the distal end in the range from 0.1 mm to 10 mm, preferably from 1 mm to 5 mm. The expandable occluding member will typically be an inflatable balloon or cuff, where the balloon or cuff has a width in the range from 1 mm to 30 mm, preferably from 5 mm to 20 mm, when inflated. The one-way flow element is typically a conventional one-way flow valve, such as a duck-bill valve, a flap valve, or the like, which is disposed in the lumen of the catheter body, either near the distal end or at any other point within the lumen. Alternatively, the one-way flow element could be provided as a separate component, for example, in a hub which is detachably mounted at the proximal end of the catheter body. In other instances, it might be desirable to provide two or more one-way flow elements in series within the lumen or otherwise provided in-line with the lumen in order to enhance sealing in the inspiratory direction through the lumen. In a particular illustrated embodiment, a one-way flow control assembly is provided as part of an external console attached in-line with the catheter lumen. The flow-control assembly comprises a valve that is controlled electrically or through other means, sensors for sensing flow and pressure in the lumen, and a valve controller for controlling the valve based on input from the sensors. The sensors monitor flow to detect the beginning of an inhalation cycle and pressure to detect the beginning of an exhalation cycle. Based on the input from the sensors, the valve controller opens the valve at the beginning of the exhalation cycle to deflate the lung region and closes the valve at the beginning of the inhalation cycle to prevent reinflation of the lung region. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1   a  is a perspective view of an isolation and deflation catheter constructed in accordance with the principles of the present invention. 
           [0026]      FIG. 1   b  illustrates an embodiment of the occluding element covering the distal end of the catheter. 
           [0027]      FIGS. 1   c  and  1   d  show a method of manufacture of the embodiment of the occluding element shown in  FIG. 1   b.    
           [0028]      FIGS. 2-4  illustrate alternative placements of one-way flow elements within a central lumen of the catheter of  FIG. 1 . 
           [0029]      FIG. 5   a  shows an alternative embodiment of a one-way flow element comprising a valve controller coupled to sensors and an electrically-controlled valve. 
           [0030]      FIG. 5   b  shows an external console housing the one-way flow element shown in  FIG. 5   a.    
           [0031]      FIG. 6   a  shows a flowchart and  FIG. 6   b  show flow and pressure graphs, illustrating the operation of the one-way flow element shown in  FIG. 5   a.    
           [0032]      FIG. 7  illustrates the trans-esophageal endobronchial placement of the catheter of  FIG. 1  in an airway leading to a diseased lung region in accordance with the principles of the present invention. 
           [0033]      FIGS. 8   a - 8   d  illustrate use of the catheter as placed in  FIG. 7  for isolating and reduction of the volume of the diseased lung region in accordance with the principles of the present invention. 
           [0034]      FIG. 9  is a graph showing the relationship between collateral resistance Rcoll and residual volume reduction in an isolated lung compartment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    Referring to  FIGS. 1   a  and  1   b , an endobronchial lung volume reduction catheter  10  constructed in accordance with the principles of the present invention includes an elongate catheter body  12  having a distal end  14  and a proximal end  16 . Catheter body  12  includes at least one lumen or central passage  18  extending generally from the distal end  14  to the proximal end  16 . Lumen  18  will have a distal opening  19  at or near the distal end  14  in order to permit air or other lung gases to enter the lumen and flow in a distal-to-proximal direction out through the proximal end of the lumen. Additionally, catheter body  12  will have an expandable occluding member or element  15  at or near the distal end  14 , to occlude an air passageway during treatment. 
         [0036]    As mentioned above, in one embodiment the expandable occluding member is disposed near the distal end of the catheter body to seal the passageway, while in an alternate embodiment the expandable occluding element forms a cover of the rim of the catheter lumen in order to seal the passageway, prevent or inhibit mucus entry into the lumen, and shield the passageway wall from the tip of the catheter. In the alternate embodiment, the expandable occluding member may be transparent to allow viewing of the passageway. These embodiments will now be described in more detail with reference to the Figures. 
         [0037]    In one embodiment of the catheter, as shown in  FIG. 1   a , the expandable occluding element  15  is located at or near the distal end  14 . In this embodiment, the expandable occluding element  15  is configured such that the proximal and distal ends of the expandable occluding element  15  are attached to the outer surface of the catheter body  12 . An auxiliary lumen  17 A extends from the inflation port  17  to the occluding element  15  to provide for expansion of the occluding element. 
         [0038]    In an alternate embodiment, as shown in  FIG. 1   b , the expandable occluding element  15  is disposed at the distal end of the catheter body  12 , and is configured to form a cover over the rim of the distal opening  19  of the catheter body  12 . In this embodiment, the proximal end of the occluding element  15  is attached to the outer surface of the catheter body  12 , while the inner surface of the occluding element  15  wraps over the rim of the catheter body  12  and is attached to the inner surface of the catheter body  12 . Inflation lumen  17 A is used to inflate the occluding element  15  through inflation port  17 B. When inflated, the occluding element  15  will form a cover (or “lip”), over the rim of the catheter body  12 , thereby preventing or inhibiting entry of mucus into the lumen  18  of the catheter, and preventing or inhibiting the opening  19  from contacting the walls of the passageway. The inflated occluding element  15  also helps prevent or inhibit accidental placement of the catheter tip into an airway segment that is smaller than the intended airway segment. Additionally or optionally, the occluding element  15  and the distal portion of the catheter body  12  comprise a transparent material to enable viewing past the occluding element  15 . 
         [0039]    Manufacture of the second embodiment of the catheter  10  is shown in  FIGS. 1   c  and  1   d . As shown in  FIG. 1   c , one end  15 A of the occluding element  15  is circumferentially attached to the inner wall of the lumen, using any suitable technique such as thermal bonding or adhesive bonding. Then, the occluding element  15  is inverted over the catheter tip and catheter body  12 , as shown in  FIG. 1   d . The second end  15 B of the occluding element  15 , which is now proximal to the tip of the catheter, is attached circumferentially to the outer surface of the catheter body  12 , using any suitable technique such as thermal bonding or adhesive bonding. The occluding element  15  thus encloses the outer rim of the distal end of the catheter. Further, the occluding element  15  is configured such that it is fed for inflation by an inflation port  17 B leading from an inflation lumen  17 A. Though the figures describe a preformed balloon-like occluding element  15 , any suitable material of any shape may be used to manufacture the occluding element  15  in the described manner, as should be obvious to one of ordinary skill in the art. For example, as described above, some portion of the catheter body  12  and/or of the occluding element  15  may be configured to be transparent. Optionally, a hub  20  will be provided at the proximal end, for example as shown in  FIG. 1   a , but the hub is not a necessary component of the catheter. 
         [0040]    Additionally and optionally, catheter  10  is configured to be introducible into the passageway via a viewing scope such as a bronchoscope (not shown). Use of the scope, in conjunction with a catheter  10  comprising one or more transparent components as described above, enables enhanced viewing of the body passageway during diagnostic or treatment procedures, by allowing a user to view the body passageway through the transparent element  15 . Additionally, a transparent occluding element  15  could serve as a lens to be used in conjunction with the scope. When so used, light from the scope would interact with the occluding element  15  in such a manner as to enable more enhanced viewing than would be obtained without the use of a transparent occluding element  15 . Examples of such enhanced viewing could include: obtaining wide angle or fish-eye views or a greater field of vision, telephoto properties (macro, zoom, etc.) or color filtration. These can be achieved by manipulating the material properties of the occluding element  15 . 
         [0041]    The technique of using a transparent, expandable element on a catheter may also be used independently. For example, in one embodiment, a catheter may be equipped with a transparent expandable element similar to that shown in  FIG. 1   b . In such an embodiment, the transparent expandable element serves as an image enhancer or diagnostic lens, and need not be fully occlusive. Similar to the above description, when used in conjunction with a viewing scope, it would enable more enhanced diagnostic viewing than would be obtained without the use of a transparent expandable element. Examples of such enhanced viewing could include: obtaining wide angle or fish-eye views or a greater field of vision, telephoto properties (macro, zoom, etc.) or color filtration. These can be achieved by manipulating the material properties of the transparent expandable element. Additionally, the transparent expandable element may be configured to allow for therapeutic procedures, such as delivery of a therapeutic electromagnetic energy (e.g., laser, infrared, etc.) to the lung or other tissue. In such a case, the surface, shape, material, size or other properties of the lens can be chosen to allow a user to manipulate the therapeutic laser energy. For example a user could focus or diffuse the energy by moving the source of laser energy back and forth relative to the transparent expandable occluding element. 
         [0042]    The present invention relies on placement of a one-way flow element within or in-line with the lumen  18  so that flow from an isolated lung compartment or segment (as described hereinbelow) may occur in a distal-to-proximal direction but flow back into the lung compartment or segment is inhibited or blocked in the proximal-to-distal direction. As shown in  FIGS. 2-4 , a one-way flow element  22  may be provided in the lumen  18  near the distal end  14  of the catheter body  12 , optionally being immediately proximal of the distal opening  19 . As shown, the one-way flow element  22  is a duck-bill valve which opens as shown in broken line as the patient exhales to increase the pressure on the upstream or distal side of the valve  22 . As the patient inhales, the pressure on the upstream or distal side of the valve is reduced, drawing the valve leaflets closed as shown in full line. 
         [0043]    Alternatively or additionally, the one-way flow element  22  could be provided anywhere else in the lumen  18 , and two, three, four, or more such valve structures could be included in order to provide redundancy. 
         [0044]    As a third option, a one-way valve structure  26  in the form of a flap valve could be provided within the hub  20 . The hub  20  could be removable or permanently fixed to the catheter body  12 . Other structures for providing in-line flow control could also be utilized, as will be presently described. 
         [0045]    In addition to the passive one-way valve structures described above, one-way flow functionality may be provided using an actively controlled one-way flow control assembly. One-way flow can be controlled by measuring the flow and pressure through the lumen and using this information to determine the beginning and end of inhalation and exhalation cycles and thereby determining whether the valve should remain open or closed. In one embodiment, the one-way flow control assembly is provided as part of an external console attached in-line with the catheter lumen. The console comprises a channel for air flow to which the proximal end of the catheter connects via a standard connector. When the patient exhales, air is forced through the catheter lumen into the console&#39;s air channel, and then exits through an exhaust port of the console. The one-way flow control assembly comprises a valve that is within or in-line with the catheter lumen and can be opened or closed by a valve controller to control the air flow through the air channel. The valve controller opens and closes the valve based on input from flow and pressure sensors within or in-line with the catheter lumen. The sensors measure the air flow and air pressure to detect the inhalation and exhalation cycles of the patient. Based on input from the sensors, the valve controller opens the valve at the beginning of the exhalation cycle, and closes the valve at the beginning of the inhalation cycle. The valve controller may control the valve electrically, magnetically, mechanically or through other means known in the art. 
         [0046]      FIG. 5   a  shows an illustration of such an actively controlled one-way flow control assembly provided as part of an external console. The external console  60  comprises an air channel  61 , a connector  62 , and an exhaust port  64 . Catheter  10  is detachably coupled to air channel  61  using a standard connector  62 , such that air channel  61  is in-line with lumen  18 . Preferably, a filter  63  is provided between the air channel  61  and lumen  18  to maintain sterility of air channel  61  and promote reusability of console  60 . Additionally, air flowing into air channel  61  is expelled through exhaust port  63 . Console  60  comprises a one-way flow assembly  70  in-line with lumen  18  of catheter  10 . 
         [0047]    One-way flow assembly  70  comprises an electrically controlled valve  71 , a flow sensor  73 , a pressure sensor  74 , and a valve controller  75 . In one embodiment, valve  71 , flow sensor  73 , and pressure sensor  74  are disposed within air channel  61 . Valve controller  75  provides one-way flow functionality by opening and closing valve  71  based on flow and pressure signals received from sensors  73  and  74 , respectively. When valve  71  is closed, it prevents air from flowing into the lumen of catheter  10  (during inhalation); during exhalation, valve  71  remains open and allows air to flow out of the isolated lung compartment. 
         [0048]    In one embodiment, valve  71  is a solenoid-based valve. Alternatively, valve  71  may be any other valve that can be opened and closed via an electrical control signal. Flow sensor  73  and pressure sensor  74 , respectively, measure air flow and pressure in lumen  18 . Valve controller  75  receives a flow indicator signal  76  from the flow sensor  73  and a pressure indicator signal  77  from pressure sensor  74  and produces a valve control signal  78  to open or close valve  71 . Alternatively, one or more of flow sensor  73 , pressure sensor  74 , and valve  71  may reside within lumen  18  and be in communication with valve controller  75  via connections between the catheter  10  and console  60 . 
         [0049]      FIG. 5   b  shows one embodiment of an external console  60  connected to catheter  10 . External console  60  optionally comprises a visual display  79  that receives and displays flow and pressure data as sensed by sensors  73  and  74 , for example, via a connection  72  to the controller  75 . Optionally, visual display  79  is a touch-screen display allowing a user to interact with console  60 . 
         [0050]      FIGS. 6   a  and  6   b  illustrate the operation of one-way flow assembly  70 .  FIG. 6   a  is a flowchart showing the operational steps of valve controller  75  as it produces the electrical valve control signal  78  to open or close valve  71  based on input from flow sensor  73  and pressure sensor  74 .  FIG. 6   b  is a graph showing exemplary signals generated by the flow sensor  73  (top panel) and pressure sensor  74  (bottom panel) during a series of respiration cycles. The flow and pressure direction during exhalation is herein referred to as the positive flow and pressure direction and plotted on the positive ordinate of the graphs in  FIG. 6B , and the flow and pressure direction during inhalation is referred to as the negative flow direction and plotted on the negative ordinate of  FIG. 6B . 
         [0051]    Initially, the patient may breathe normally through lumen  18  of catheter  10 . Once the treatment is initiated—which could be accomplished using the touch-screen display  79 —valve controller  75  waits for the completion of an inhalation cycle, until flow sensor  73  indicates a flow value that is greater than a specified flow threshold value. This is shown as step  81  in  FIG. 6   a  and shown as the first flow and pressure cycle in  FIG. 6B  lasting for a period indicated as  81   p . The flow threshold value is chosen to indicate the beginning of an exhalation cycle.  FIGS. 6   a  and  6   b  and the present description assume an exemplary flow threshold value of zero. Optionally, the flow threshold value is configurable to a value other than zero. 
         [0052]    In step  82  in  FIG. 6   a  (also indicating the positive flow and pressure in  FIG. 6   b ), valve controller  75  maintains valve  71  in an open state during exhalation until flow sensor  73  receives a flow value less than or equal to zero. Thus, as is illustrated in  FIG. 6   b , step  82  lasts for a period indicated as  82   p  as long as flow sensor  73  senses an air flow value greater than zero. 
         [0053]    When flow sensor  73  senses a flow value that is less than or equal to zero, valve controller  75  closes valve  71  in step  83  in  FIG. 6   a  and no air flows through the lumen into the lung compartment. As is shown in  FIG. 6   b , Step  83  occurs contemporaneously with the flow value reaching zero or lower at the point in time denoted  83   p . Typically, the flow reduces to zero at the end of exhalation, at which point valve controller  75  closes the valve  71 . 
         [0054]    The following steps of valve controller  75  refer to a pressure threshold value. The pressure threshold value is chosen to indicate the beginning of an exhalation cycle. This value is configurable, and in what follows, an example pressure threshold value of zero is assumed. 
         [0055]    Ideally, it is desirable that valve controller  75  reopen valve  71  when the pressure increases to or above the pressure threshold value. Realistically, given hardware imperfections, the pressure as sensed and reported by pressure sensor  74  at the end of exhalation may fluctuate around zero, causing chatter of valve  71 . To prevent valve chatter, in step  84 , valve controller  75  maintains valve  71  in a closed state while the pressure remains above a specified minimum pressure value, denoted as min_pressure in  FIGS. 6   a  and  6   b . This minimum pressure—min_pressure—is configurable and set to a value appreciably less than the specified pressure threshold value. Thus, as is further shown in  FIG. 6   b , valve  71  remains closed during the period  84   p.    
         [0056]    Optionally, during step  84 , valve controller  75  also monitors pressure to ensure that valve  71  will open if the patient starts exhalation prior to the pressure decreasing to below min_pressure, To this end, during step  84 , valve controller  75  is optionally configured to open valve  71  if pressure increases to a value that is above the pressure threshold value by an amount referred to as a safeguard offset value. The safeguard offset value is configurable. 
         [0057]    During step  85  in  FIG. 6   a , once the pressure passes below “min_pressure”, valve controller  75  maintains valve  71  in a closed state until the pressure increases to or passes the pressure threshold value. Referring to  FIG. 6   b , step  85  lasts the duration between the achievement of min_pressure in step  84  and the attainment of the pressure threshold value, with the period denoted as  85   p  in  FIG. 6   b.    
         [0058]    When the pressure increases to or passes the pressure threshold value, the valve controller  75  opens the valve  71  at step  86  in  FIG. 6   a . Thus, referring to  FIG. 6   b , the opening of the valve in step  86  occurs at point  86   p  and is contemporaneous with the pressure increasing to or passing a zero value. This allows air to empty from the lung compartment in communication with lumen  18 . 
         [0059]    Thereafter, as the patient resumes inhalation, the valve controller  75  resumes operation at Step  82  (close valve  71  and prevent airflow into the target lung compartment), for a new respiration cycle, until the lung reduction process is terminated. 
         [0060]    Use of the endobronchial lung volume reduction catheter  10  to reduce the residual volume of a diseased region DR of a lung L is illustrated beginning in  FIG. 7 . Catheter  10  is introduced through the patient&#39;s mouth, down past the trachea T and into a lung L. The distal end  14  of the catheter  10  is advanced to the main airway AW leading into the diseased region DR of the lung. Introduction and guidance of the catheter may be achieved in conventional manners, such as described in commonly-owned U.S. Pat. Nos. 6,287,290; 6,398,775; and 6,527,761, the full disclosures of which are incorporated herein by reference. 
         [0061]    Referring now to  FIGS. 8A-D , functioning of the one-way valve element in achieving the desired lung volume reduction will be described. After the distal end  14  of the catheter  10  is advanced to the feeding airway AW, an expandable occluding element  15  is expanded to occlude the airway. The expandable occluding element may be a balloon, cuff, or a braided balloon as described in copending applications 60/823,734 (Attorney Docket No. 017534-003800US), filed on Aug. 28, 2006, and 60/828,496 (Attorney Docket No. 017534-003900US) filed on Oct. 6, 2006, the full disclosures of which are incorporated herein by reference. At that point, the only path between the atmosphere and the diseased region DR of the lung is through the lumen  18  of the catheter  10 . As the patient exhales, as shown in  FIG. 8A , air from the diseased region DR flows outwardly through the lumen  18  and the one-way valve element  22 , one-way flow assembly  70 , or any other one-way flow structure, causing a reduction in residual air within the region and a consequent reduction in volume. Air from the remainder of the lung also passes outward in the annular region around the catheter  10  in a normal manner. 
         [0062]    As shown in  FIG. 8B , in contrast, when the patient inhales, no air enters the diseased regions DR of the lung L (as long as there are no significant collateral passageways), while the remainder of the lung is ventilated through the region around the catheter. It will be appreciated that as the patient continues to inhale and exhale, the air in the diseased region DR is incrementally exhausted, further reducing the lung volume as the external pressure from the surrounding regions of the lung are increased relative to the pressure within the diseased region. As shown in  FIG. 8C , after sometime, typically seconds to minutes, air flow from the isolated lung segment will stop and a maximum or near-maximum level of residual lung volume reduction within the diseased region DR will have been achieved. At that time, the airway AW feeding the diseased region DR can be occluded, by applying heat, radiofrequency energy, glues, or preferably by implanting an occluding element  30 , as shown in  FIG. 8D . Implantation of the occluding element may be achieved by any of the techniques described in commonly-owned U.S. Pat. Nos. 6,287,290; and 6,527,761, the full disclosures of which have been previously incorporated herein by reference. 
         [0063]    While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description should not be taken as limiting the scope of the invention which is defined by the appended claims.