in the descriptions below , specific designs for bronchial flow restrictors are described . the restrictors can be placed in any bronchial airway , but generally the airways between and including the lobar bronchus and sub - sub - segmental bronchi are the desired airways to restrict . the restrictor is intended to impede air flow in both the inspiratory and expiratory direction usually about equally , and either permanently or temporarily . flow limitation can be from 10 % to 99 . 99 % reduction of flow , usually being from 99 % to 99 . 9 % of the unrestricted flow , depending on the clinical need . the flow limitation will have at least one of two physiologic effects . in instances where the lung region distal to the restrictor is generally free from collateral ventilation , the restrictor will induce a controlled atelectasis . the distal lung region will collapse , although at a significantly slower rate of collapse than would be the case with complete occlusion of air flow into the region , and the risk of pneumothorax will be significantly reduced . in other instances where the lung region downstream from the flow restrictor is exposed to significant levels of collateral ventilation , the restricted air flow into and from the region will induce hypoxia . the resulting reduced oxygen concentrations distal to the restrictor will catalyze the von euler reflex to shunt pulmonary perfusion to other , usually more healthy and functional , bronchopulmonary regions of the lung that have not been treated with a restrictor , and thus improve the ventilation - perfusion efficiency of the lung . fig1 a and 1b illustrate a bronchial flow restrictor ( bfr ) 10 constructed of an elastic wire frame 12 which is laminated with an elastomeric membrane 14 . on the proximal end 16 of the bfr , the membrane 14 is incomplete or perforated , creating at least one vent hole 18 . on the distal section 20 of the bfr , apertures 22 are formed in the membrane 14 to create a path for the gas flow . the size and shape of the vent hole 18 and apertures 22 can vary in order to provide a desired flow resistance within the range defined elsewhere herein . this general design permits collapsibility of the bfr for insertion into a small catheter for delivery into the lung , allowing self - expansion of the bfr when released from the catheter . the stepped configuration of this particular design allows the bfr to be placed at or near an airway bifurcation or airway narrowing . for example , the larger proximal end may be placed in a proximal airway so that the distal smaller section 20 extends into the next generation airway which is smaller because it is distal to the proximal airway . the flow restrictions can be fabricated by the techniques described for fabrication of fully occlusive elements and one - way valves set forth in u . s . pat . no . 6 , 527 , 761 and commonly assigned , copending application ser . no . 11 / 280 , 592 , the full disclosures of which are incorporated herein by reference . fig2 a - 2d describe a modified configuration 10 ′ of the previously described bfr in which distal gas flow apertures 24 are positioned to be within the lumen of the distal airway da after the bfr has been expanded from a radially constrained diameter in the airway to an unconstrained diameter which creates a dilated pocket dp ( fig2 d ) in the airway . thus , the gas flow through apertures 24 is not obstructed by the bronchial wall . fig3 is a cross - sectional view of bfr 30 in which a housing 32 includes a gas flow orifice tube 34 on its distal end 36 . the housing can have a “ uni - body ” construction , typically being molded or cast from silicone or another biocompatible elastomer . in some instances , the housing 32 can have composite construction of wire frame with silicone membrane coating , or be formed from a variety of materials and construction methods . it can be collapsible and self expanding for a catheter based delivery . in other designs , the bfr can be malleable to allow plastic deformation and expansion by a balloon or other expandable deployment on the delivery catheter . fig4 illustrates a bfr 40 in which a housing 42 comprises a plurality of windows 44 in a wall of a distal section 46 in order to permit gas flow in and out of the housing . an orifice 48 at the opposite proximal end completes the gas flow path such that the device restricts but does not obstruct gas flow . as with previously described embodiments , the housing 42 can have a uni - body construction or comprise a wire frame with silicone or other membrane covering . it can be either collapsible and self expanding or balloon expandable . fig5 a and 5b illustrate bfr 50 which has gas or fluid transport channels 52 shaped or formed into an outer surface or periphery of the housing body 54 . the channels 52 will leave a space or gap between the airway wall in which the bfr is implanted and the surface of the bfr , thus providing a path for fluid flow in both directions . as mentioned previously , the housing 54 can have a uni - body or composite construction . the housing 54 can be collapsible and self expanding or balloon expandable . fig6 illustrates a bfr 60 in which a housing 62 houses a funnel - shaped ( or hourglass - shaped ) diaphragm 64 which provides a gas flow orifice 66 in the center of the diaphragm . distal and proximal apertures 68 and 69 , respectively , allow air flow into and out of the housing 62 , and the tapered orifice 66 defined by the diaphragm 64 restricts the flow . the diameter of the orifice 66 can be selected to provide a desired flow resistance . the housing 62 can have a uni - body construction or be a wire braided structure encapsulated with silicone or other elastomere . the diaphragm can be a flexible silicone material or other elastomere in order to facilitate compressibility of the bfr 60 for insertion into the lung via a delivery catheter lumen . fig7 illustrates bfr 70 in which a gas flow tube 72 is axially aligned in a housing 74 . construction of the housing 74 can be similar to any of the concepts previously described . the gas flow tube 72 can be constructed of any tubular material , preferably being a flexible polymer . flexibility is advantageous since a flexible tube will facilitate insertion into the lung . the housing 74 can have any of the constructions described previously . fig8 a and b and 9 a and b illustrate non - covered , tightly packed wire braid flow restrictors 80 and 90 . the tight backing of the wire braid can eliminate the need for a membrane cover to achieve occlusion while providing a perforate or foraminous surface 82 and 92 , respectively , to permit a controlled flow of air therethrough . referring now to fig1 , the respiratory system of a patient starts at the mouth and extends through the vocal cords and into the trachea where it then joins the main stem bronchi b which leads into the right lung rl and the left lung ll . the bronchi going into the right lung divide into the three lobar bronchi which lead into the upper lobe rul , the middle lobe rml and the lower lobe rll . the lobes of the right lung include a total of ten segments ( three in the rul , two in the rml , and five in the rll ) which are discrete units of the lung separated from each other by a fibrous septum generally referred to as a lung wall . the left lung ll includes only an upper lobe lul and a lower lobe lll , where the individual lobes include four to five segments each each lung segment , also referred to as a bronchopulmonary segment , is an anatomically distinct unit or compartment of the lung which is fed air by a tertiary bronchus and which oxygenates blood through a tertiary artery . normally , the lung segment and its surrounding fibrous septum are intact units which can be surgically removed or separated from the remainder of the lung without interrupting the function of the surrounding lung segments . in some patients , however , the fibrous septum separating the lobes or segments may be perforate or broken , thus allowing air flow between the segments , referred to as “ collateral ventilation .” use of a delivery catheter 100 for placement of a bfr in accordance with the principles of the present invention is shown generally in fig1 and 12 . the catheter 100 is advanced through the mouth , down through the trachea t , and through the main bronchus into the left lung ll . a distal end 102 of catheter 100 is advanced into the left lung ll , and further advanced to an airway aw which feed a diseased lung region dr . the catheter 100 may be introduced through the main bronchus b and into the left lung ll without the use of a bronchoscope or other primary introducing catheter , as illustrated in fig1 . alternatively , the catheter 100 may be introduced through a conventional bronchoscope ( not shown ) which is positioned in the main bronchus above the branch between the right and left lungs . alternatively , the catheter 100 may be introduced into the lung through a scope , such as a visualizing endotracheal tube ( not shown ) which is capable of advancing into the branching airways of the lung is advantageous in that it facilitates positioning of the delivery catheter 100 at the desired airway leading to a target lung segment . construction and use of a visualizing endotracheal tube is taught , for example , in u . s . pat . no . 5 , 285 , 778 , the full disclosure of which is incorporated herein by reference . it would be possible , of course , to utilize both the bronchoscope and the endotracheal tube in combination for positioning the delivery catheter 100 in the desired lung segment airway . after the distal end 102 of the delivery catheter 100 has been positioned in the main airway or bronchus feeding the diseased region dr , the catheter can optionally be immobilized , for example by inflating a balloon or cuff 104 . after immobilizing the distal end of the catheter , a pusher or other element 106 can be advanced in order to eject the bronchial flow restrictor bfr in the bronchus , where it optionally self - expands to anchor in place . although not illustrated , it would also be possible to use an inflatable balloon or other deployment device on the catheter 100 in order to position a plastically deformable restrictor at a desired location . referring now to fig1 a and 13b , after the bronchial flow restrictor bfr has been placed in the airway leading to a diseased region dr , illustrated as a first lung segment ls 1 , air flow into and out of the segment as the patient inhales and exhales will be restricted by placement of the bfr , as generally described above . as shown in fig1 a and 13b , the first lung segment ls 1 is surrounded by a fibrous septum fs which is generally intact so that little or no collateral ventilation with adjacent lung segments ls 2 and ls 3 will occur . thus , as shown in fig1 b , the reduced air flow into and out of the treated lung segment ls 1 will induce atelectasis and cause the treated segment to deflate . deflation of the treated segment ls 1 , in turn , allows the adjacent , healthier lung segments ls 2 and ls 3 to expand and provide improved patient blood oxygenation . moreover , the slower rate of atelectasis reduces the risk to the patient of pneumothorax , as discussed above . referring now to fig1 a and 14b , in other instances , the diseased lung region dr may have a perforated or otherwise damaged region of the fibrous septum dfs which permits collateral ventilation between the diseased region ( ls 1 ) and an adjacent lung region ls 2 . in those instances , air entering via the collateral channels is already low in oxygen and placement of the bronchial flow restrictor bfr will significantly reduce the amount of oxygenated air entering the diseased region ls 1 / dr via the feeding bronchus . as shown in fig1 b , over time , the reduced and non - oxygenated air exchange with the diseased region dr will induce hypoxia in the region ( shown with the cross - hatching ) which will catalyze the von euler reflex to shunt pulmonary perfusion to other healthier regions of the lung , such as adjacent healthy segments ls 2 and ls 3 . it will be appreciated , however , that the induced lung collapse and induced hypoxia may occur to differing degrees in even the same treated region . in particular , the shift between lung collapse and hypoxia may depend , at least in part , on the degree to which collateral ventilation exists between the diseased region and adjacent healthier lung regions . thus , although it may be desirable to perform a diagnostic on the patient to determine whether or not a particular diseased region is subject to collateral ventilation ( as taught , for example , in commonly owned , copending application ser . no . 11 / 296 , 951 , filed on dec . 7 , 2005 , the full disclosure of which is incorporated herein by reference ), it would not be necessary . treatment of diseased lung regions using the bronchial flow restrictors of the present invention may be advantageous regardless of the collateral ventilation status of a particular region . 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 .
lung conditions are treated by implanting a flow restrictor in a passageway upstream from a diseased lung segment . the restrictor will create an orifice at the implantation site which inhibits air exchange with the segment to induce controlled atelectasis and / or hypoxia . controlled atelectasis can induce collapse of the diseased segment with a reduced risk of pneumothorax . hypoxia can promote gas exchange with non - isolated , healthy regions of the lung even in the absence of lung collapse .