fig1 to 8 illustrate certain embodiments of the invention . fig1 illustrates a central airway stent of conical shape having a tapered tube 3 with proximal open end 2 having a diameter greater than the distal open end 1 of the tube . the stent has a metallic mesh structure 5 with a lining 4 . in some embodiments , the lining may be of synthetic or natural polymeric material . in some embodiments , the metallic mesh may be of shape - memory alloy . fig2 illustrates a central airway stent of an accordion type structure having a tube 6 with a distal open end 1 , a proximal open end 2 and circumferential pleated elongation portion 7 having three pleats 8 . in other embodiments , the accordion type stent may have one or more pleats , such as , 2 to 4 pleats . each pleat may have an effective length of about 0 . 2 cm to about 1 cm when fully straightened . in some embodiments , the accordion type stent may have proximal open end 2 having a diameter greater than the distal open end 1 . the central airway stent may be repositioned by pulling the proximal open end 2 or the distal open end 1 sufficiently to at least partially straighten one or more of the pleats 8 . fig3 illustrates a central airway stent of a telescopic type structure , and its cross section , having a distal portion 9 , a proximal portion 10 , wherein a portion 11 of the tube lying between the proximal open end 2 and the distal open end 1 is invaginated toward the proximal open end 2 . the central airway stent may be repositioned by pulling the proximal open end 2 or the distal open end 1 sufficiently to at least partially decrease the length of the invaginated portion 11 which constitutes the elongation portion 7 for the stent of fig3 . in some embodiments , the telescopic type stent may have proximal open end 2 having a diameter greater than the distal open end 1 . the maximum length of the invaginated portion 11 of the telescoped stent may be from about 0 . 5 cm to about 3 cm , such as about 2 cm . fig4 illustrates a central airway stent of a telescopic type structure , and its cross section , having a distal tube 12 having a diameter less than the diameter of the a proximal tube 13 , wherein at least a portion of the distal tube 13 resides within the proximal tube 12 . the central airway stent may be repositioned by reducing the length of this elongation portion 7 of the distal tube that resides within the proximal tube to increase the length of the distal tube that is not within the proximal tube . in some embodiments , the telescopic stent may have tapered distal tube 13 residing within a tapered proximal tube 12 . fig5 illustrates a central airway stent of a telescopic type structure , and its cross section , having a distal tube 12 having a diameter less than the diameter of the a proximal tube 13 , wherein the tubes are completely separated from each other to provide a modular stent system . at least a portion of the distal tube 13 can suitably reside within the proximal tube 12 at the time of deployment . fig6 illustrates a cross section of a central airway stent of y type structure , having an elongation portion 7 , a distal tube 14 having a diameter less than the diameter of the a proximal tube 13 , wherein the distal bifurcated tube 14 branches into narrower tubes 15 and 16 that are suitably flexible to lie adjacent to each other in substantially parallel position while lodged in the deployment device 17 . the portion of the tube 14 and narrower tubes 15 and 16 where the bifurcation or branching occurs may be made of suitable synthetic or natural polymeric material to impart desired flexibility while other parts may be of more inflexible material so as to function effectively and maintain airflow . fig7 illustrates a cross section of a central airway stent of modular y type structure , having a distal tube 12 , a proximal tube 13 , and an elongation portion 7 wherein at least a portion of the distal tube 13 resides within the proximal tube 12 , and concentric tapered narrower tubes 18 and 19 . the narrower tubes 18 and 19 may be pushed out consecutively after the deployment of the main tubes , such that one narrow tube is deployed in each main bronchus to form a modular system , the tube 18 with the larger diameter being deployed in the left bronchus . fig8 illustrates a cross section of a central airway stent of y type structure , having a distal portion 9 , a proximal portion 10 , an elongation portion 7 with invaginated portion 11 , and an additional distal bifurcated tube 14 branched into narrower tubes 15 and 16 that are flexible enough to lie adjacent to each other in a substantially parallel position while lodged in the distal tube or distal end of the tube before deployment . the bifurcated tube 14 has a diameter less than the diameter of the distal portion 10 . the portion of the tube 14 and narrower tubes 15 and 16 where the bifurcation or branching occurs may be made of suitable synthetic or natural polymeric material to impart desired flexibility while other parts may be of more inflexible material so as to function effectively and maintain airflow . the central airway stents of the invention may be tapered or straight . the central airway stents may be circular , oval or squarish - oval in cross section . the central airway stents may be conical or of other suitable shapes . the narrower tubes 15 and 16 may be of identical size or one of the narrower tubes may be narrower or shorter than the other . the proximal open end 2 may have a diameter of about 16 mm to about 22 mm , such as , a diameter of about 20 mm , suitable for deployment in the trachea . the proximal open end 2 may have a diameter of about 10 mm to about 16 mm , such as , a diameter of about 14 mm , suitable for deployment in the main bronchi . the distal open end 1 may have a diameter of about 14 mm to about 22 mm , such as , a diameter of about 18 mm for deployment in the trachea . the distal open end 1 may have a diameter of about 8 mm to about 14 mm , such as , a diameter of about 10 mm , suitable for deployment in the main bronchi . the stent may have a length of from about 2 cm to about 10 cm , such as 2 cm , 3 cm , 4 cm , 5 cm , 6 cm , 8 cm , 9 cm , or 10 cm . the length of distal tube 12 , proximal tube 13 and narrower tubes 15 and 16 , or 18 and 19 are proportionate to the overall length of the stent and may be from about 0 . 5 cm to about 6 cm . similarly , the maximum length of the portion of the distal tube that lies inside the proximal tube of the telescoped stent may be from about 0 . 5 cm to about 3 cm , such as about 2 cm . the edges of the proximal open end 2 and the distal open end 1 of the tubes may be beveled , rounded or wedged so that positioning and repositioning in the trachea can be carried out smoothly without causing abrasions . the central airway stent may be made of synthetic , natural , or biodegradable material or made of metal , including shape - memory alloys . the construction of the tube may be covered , such as made from plain sheets , or open , such as made of meshed or woven metal wires , or polymeric threads . examples of suitable materials include silicon rubber , such as dow corning 3110 rtv ; polyurethane ; polyethylene terephthalate , such as dacron ®, polytetrafluoroethylene ( ptfe ), such as teflon ®; nickel titanium alloys , such as nitinol ; and other metal alloys , such as fept , fepd , fenicoti , fenic , femnsi or femnsicrni . the materials may be coated or otherwise infused with a therapeutic medicament that provides local treatment to the central airway . non - limiting examples of therapeutic medicaments include chemotherapeutic agents and anti - inflammatory agents . a central airway stent according to the present invention may also comprise agents for radiation therapy and delivery . according to the present invention , a central airway stent may comprise a biodegradable or bioabsorbable material . such a stent is advantageous for patients who require a stent for a period of weeks or months because , e . g ., their central airway tumor has been responsive to treatment . non - limiting examples of suitable biodegradable or bioabsorbable materials include , polycaprolactone ; poly ( l - lactide ), poly ( dl - lactide ); polyglycolide ; poly ( l - lactide - co - d , l - lactide ) 70 : 30 poly ( l - lactide - co - d , l - lactide ); 95 : 5 poly ( dl - lactide - co - glycolide ); 90 : 10 poly ( dl - lactide - co - glycolide ); 85 : 15 poly ( dl - lactide - co - glycolide ); 75 : 25 poly ( dl - lactide - co - glycolide ); 50 : 50 poly ( dl - lactide - co - glycolide ); 90 : 10 poly ( dl - lactide - co - caprolactone ); 75 : 25 poly ( dl - lactide - co - caprolactone ); 50 : 50 poly ( dl - lactide - co - caprolactone ); polydioxanone ; polyesteramides ; copolyoxalates ; polycarbonates and poly ( glutamic - co - leucine ). polydioxanone ; poly - 96l / 4d - lactic acid [ pla ], and type i collagen from bovine sources . suitable deployment devices include conventional deployment devices known in the art , which have been loaded with a central airway stent according to the present invention . examples of such suitable deployment devices are the aero ® tracheal over - the - wire delivery catheter and aero ® bronchial over - the - wire delivery catheter from merit medical endotek , and other deployment devices disclosed in u . s . pat . no . 6 , 409 , 750 , and u . s . patent application publication no . 2009 / 0319021 a1 . suitable deployment procedures include conventional methods known in the art , such as those disclosed in u . s . pat . no . 6 , 409 , 750 , and u . s . patent application publication no . 2009 / 0319021 a1 . for deployment , the patient is usually positioned in a supine position . access to the airway is obtained either through an endotracheal tube , rigid bronchoscope , laryngeal mask , suspension device , or other such airway designed to provide airway access . general anesthesia or other anesthesia with sedation can be used for stent deployment as suitable to the clinical situation . stents according to the invention are preloaded on the delivery system , which includes a relatively flexible introduction catheter . once appropriate position of the stent / delivery system has been confirmed by bronchoscopic evaluation and fluoroscopy , the sheath or thread that constrains the stent is slowly released , and the stent gradually expands within the airway , conforming to the walls of the bronchus or trachea . the radioopaque markers assist with correct positioning of the stent within the airway . examples of y tubes , where a distal tube or distal end of a tube branches into two narrower tubes that are flexible enough to lie adjacent to each other in substantially parallel position , include suitable tubes disclosed in u . s . pat . no . 5 , 480 , 431 , and u . s . patent application publication no . 2009 / 0319021 a1 . specific embodiments has been described above to illustrate the invention , and are not intended to be restrictive . modifications and equivalents will be apparent to those skilled in the art and are included within the scope of the invention . patents and publications cited in this application are hereby incorporated by reference in their entirety .
the present invention relates to central airway stents , and methods and devices for deploying such stents . the central airway stents are useful for maintaining or prolonging the patency of a central airway .