[ 0038 ] fig3 a shows an ett 19 constructed according to the invention . ett 19 includes a hollow tube , or tubular member , 19 a and a cuff , or balloon , 20 mounted near the distal end of tube 19 a . also , in ett 19 , hollow tube 19 a and cuff 20 are both made of silicone . the durometer ( or hardness ) of the silicone used to fabricate hollow tube 19 a may be about 80 shore a . a suitable source of silicone for fabricating tube 19 a is dow corning , midland , mich ., or wacker silicone in germany . tube 19 a may be about 30 - 40 cm in length for adult sizes . use of a silicone cuff 20 is advantageous because , as discussed above , silicone does not have the allergic effects associated with latex , and silicone has a longer shelf life than latex . use of a silicone tube 19 a facilitates attachment of cuff 20 to the tube 19 a since methods of adhering silicone to silicone are well known in the art . also , as discussed below , dimensions of the hollow tube 19 a and the cuff 20 are adjusted so as to advantageously provide an adequate air supply to the patient &# 39 ; s lungs during ippv and so as to insure that the cuff 20 reaches its pressure plateau before making circumferential contact with the inner lining of the trachea . accordingly , ett 19 facilitates measurement of the mucosal pressure and further facilitates avoidance of excessive mucosal pressures . also , use of the silicone cuff 20 provides improved seals with the trachea and avoids the wrinkles and microleaks associated with inelastic cuffs . in ett 19 , the cuff 20 is mounted to hollow tube 19 a in a region , or zone , 32 of reduced diameter . that is , in region 32 , the outer diameter of tube 19 a is reduced as compared with the outer diameter at other portions of tube 19 a . fig3 b shows a magnified view of the region 32 of reduced diameter . as shown , the outer diameter of region 32 , od 1 , is reduced from the outer diameter of the rest of hollow tube 19 a , od 2 . in contrast , the inner diameter id of hollow tube 19 a ( or the diameter of the airway lumen ) is substantially constant from the proximal end to the distal end of hollow tube 19 a . as a result of the differing outer diameters , the thickness ti of the wall of hollow tube 19 a in region 32 is less than the thickness t 2 of the wall of the remainder of hollow tube 19 a . an inflation lumen 30 is defined in the wall of hollow tube 19 a in the regions where the wall thickness is t 2 ( i . e ., in regions outside the zone 32 of reduced diameter ). as shown , cuff 20 is mounted to tube 19 a at extreme ends of region 32 at locations 24 and 26 ( i . e ., locations 24 and 26 are adjacent to the junctions between region 32 and other portions of the tube outside of region 32 ). typically , for an adult size ett , the distance between the mounting locations 24 and 26 is about three to five centimeters . also , a relatively short rigid extension tube 36 extends from inside lumen 30 , through cuff mounting location 24 , and into the interior volume of cuff 20 . accordingly , inflation and deflation of cuff 20 can be controlled by an air supply , such as a syringe , coupled to the proximal end of inflation lumen 30 ( near the proximal end of hollow tube 19 a ). since hollow tube 19 a is made from silicone , the thickness of the tube wall t 2 is greater than would be required if the tube were made of a more rigid material such as pvc . accordingly , for a given inner diameter , id , the outer diameter od 2 of hollow tube 19 a is greater than the outer diameter that would be required if hollow tube 19 a were made of pvc . the larger outer diameter od 2 of hollow tube 19 a increases the difficulty of insuring that a cuff attached to tube 19 a will reach its pressure plateau prior to making circumferential contact with the inner lining of the trachea . however , to compensate for the increased tube outer diameter , which is a consequence of using silicone to fabricate tube 19 a , the tube 19 a is provided with region 32 of reduced diameter . attaching cuff 20 to the region 32 of reduced diameter increases the amount by which the cuff expands before it makes circumferential contact with the inner lining of the trachea and thereby facilitates insuring that cuff 20 reaches its pressure plateau prior to making such circumferential contact . in one example embodiment of an adult size ett , the inner diameter id of tube 19 a is about seven millimeters , the wall thickness t 2 is about 1 . 625 millimeters , the wall thickness ti in region 32 is about 1 . 0 millimeters , the outer diameter od 1 of the tube 19 a in region 32 is about nine millimeters , and the outer diameter od 2 of the majority of tube 19 a is about 10 . 25 millimeters . the pressure plateau of cuff 20 is about thirty to thirty five centimeters of water and is reached when the cuff diameter is less than the smallest expected adult tracheal diameter ( e . g ., less than about 1 . 5 centimeters ). in yet another example embodiment of an adult size ett , the inner diameter id of tube 19 a is about eight millimeters , the wall thickness t 2 is about 1 . 625 millimeters , the wall thickness t 1 in region 32 is about 1 . 125 millimeters , the outer diameter od 1 of the tube 19 a in region 32 is about 10 . 25 millimeters , and the outer diameter od 2 of the majority of tube 19 a is about 11 . 25 millimeters . again , the pressure plateau of cuff 20 is about thirty to thirty five centimeters of water and is reached when the cuff diameter is less than the smallest expected adult tracheal diameter ( e . g ., less than about 1 . 5 centimeters ). as noted above , inflation lumen 30 is defined in the wall of hollow tube 19 a in the regions where the wall thickness is t 2 ( i . e ., in regions outside the region 32 of reduced diameter ). the presence of inflation lumen 30 in the wall of hollow tube 19 a is one aspect of the ett 19 that limits the tube &# 39 ; s minimum wall thickness . advantageously , the lumen 30 does not extend beyond the region 32 of reduced diameter , e . g ., the lumen extends from near the proximal end of the tube 19 a to the reduced diameter portion 32 . a relatively short rigid hollow tube 36 is inserted within the lumen 30 and extends through the balloon mounting location 24 to provide fluid communication between lumen 30 and the interior of cuff 20 . if the wall thickness t 1 of the region 32 of reduced diameter is too thin , the intra - cuff pressure of cuff 20 ( which is circumferentially applied to the outer wall of region 32 , and in effect squeezes region 32 inwards ), may be sufficient to cause the region 32 of reduced diameter to collapse . such collapse of any portion of hollow tube 19 a is of course not desired since it may occlude the airway lumen provided by the ett thereby preventing adequate ventilation of the lungs . one method of preventing such collapse is to fabricate the cuff 20 from silicone having a durometer of about 10 shore a . use of a silicone cuff with such a hardness allows the pressure plateau to occur as low as thirty to thirty five centimeters of water , a pressure which will not harm the tracheal mucosa or allow the tube to collapse under normal operating conditions . [ 0047 ] fig4 illustrates another method of preventing collapse of hollow tube 19 a , and in particular , of preventing collapse of region 32 of reduced diameter . fig4 shows a magnified sectional view of region 32 , when cuff 20 is deflated , of an alternative embodiment of ett 19 constructed according to the invention . in the embodiment illustrated in fig4 a spiral reinforcing wire , or other stiffening element , 42 is incorporated into the wall of hollow tube 19 a . reinforcing wire 42 provides radial strength to the hollow tube 19 a and increases the tube &# 39 ; s crush strength so that tube 19 a will not collapse when the cuff 20 is inflated . preferably , reinforcing wire 42 is located near the inside surface of hollow tube 19 a . providing a reinforcing wire at such a location facilitates allowing both the reinforcing wire 42 and the air supply lumen 30 to exist in the same tube 19 a . reinforcing wire 42 may extend along the entire length of hollow tube 19 a , or alternatively , may be disposed only proximal the region 32 of reduced diameter . it will be appreciated that many manufacturing methods may be used for fabricating tube 19 a such that it includes reinforcing wire 42 . for example , a reduced diameter tube ( i . e ., a tube having an inner diameter id equal to the desired inner diameter of tube 19 a and an outer diameter less than the outer diameter od 1 of region 32 ) may be extruded and then the reinforcing wire 42 may be disposed on the outer surface of the tube . a second tube may then be applied , or extruded over the reduced diameter tube and the wire . the second , or outer , tube may be heated and bonded with the reduced diameter tube to create a single tube 19 a . the region 32 of reduced diameter may then be formed by removing material from a portion of the outer surface of the tube . for example , the region 32 may be formed by placing the tube 19 a on a lathe and cutting material away from a portion of the outer surface of the tube . such manufacturing techniques may be used to form the region 32 of reduced diameter regardless of whether a reinforcing wire is incorporated into the tube . referring again to fig3 b , it can be seen that tube 19 a may be fabricated such that inflation lumen 30 initially extends from the proximal end of tube 19 a to a location 30 d near the distal end of tube 19 a . using a lathe or other device for cutting material away from a portion of tube 19 a so as to form region 32 of reduced diameter automatically connects inflation lumen 30 to the region 32 , at location 30 e , as long as enough material is removed from the outer portion of the tube to expose lumen 30 . rigid tube 36 may be used to thereafter couple inflation lumen 30 to the interior volume of cuff 20 as discussed above . [ 0050 ] fig5 shows a magnified sectional view of region 32 of reduced diameter , when cuff 20 is deflated , of another embodiment of ett 19 constructed according to the invention . as shown , the outer surface of tube 19 a in the region 32 of reduced diameter is characterized by a texture 50 , or a roughening . providing texture 50 advantageously reduces the likelihood that the cuff 20 will stick to the tube 19 a . it is generally not desirable for any portion of cuff 20 ( other than at locations 24 , 26 , where cuff 20 is bonded to tube 19 a ) to stick to the outer surface of tube 19 a because such sticking generally causes the cuff to inflate non - uniformly . non - uniform inflation of cuff 20 is undesirable because it generally results in formation of a less than optimal seal with the trachea . in one preferred embodiment , the texture 50 has the form of a threaded surface ( e . g ., as in the threads of a screw ) and comprises one or more spiral grooves cut into the outer surface of tube 19 a . in one embodiment , the grooves are 0 . 5 millimeters wide and 0 . 2 millimeters deep . the grooves may be cut , for example , using a high speed lathe . one advantage of having texture 50 be a spiral groove , is that this texture rapidly and evenly distributes air introduced from lumen 30 to the entire interior surface of the cuff , and thereby provides for uniform inflation of the cuff 20 . however , it will be appreciated that textures 50 other than spiral grooves may be used as well . for example , texture 50 can comprise longitudinal rather than spiral grooves , or a random or pseudo random roughening . [ 0052 ] fig6 shows a magnified view of region 32 of reduced diameter , when cuff 20 is deflated , of yet another embodiment of ett 19 constructed according to the invention . in previously discussed embodiments , the locations 24 , 26 , where cuff 20 is attached to tube 19 a , are in the region 32 of reduced diameter ( i . e ., locations 24 , 26 were located where the outer diameter of the tube 19 a is od 1 ). however , as shown in fig6 the locations 24 , 26 may be located outside of region 32 ( i . e ., locations 24 , 26 may be located where the outer diameter of tube 19 a is od 2 ). in this embodiment , the semi - rigid tube extension 36 ( shown , e . g ., in fig3 b ) may be eliminated . the embodiment illustrated in fig6 may be used for example when the material used to form cuff 20 is pre - stretched as discussed in more detail below . it may be desirable to tailor the region 32 of reduced diameter , and possibly portions of the tube 19 a adjacent to region 32 , to provide tube 19 a with a smooth surface so as to minimize irritation to the patient &# 39 ; natural airway during introduction and removal of ett 19 . for example , in the embodiment illustrated in fig6 the outer diameter of ett 19 may increase slightly at locations 24 , 26 thereby disturbing , or providing a “ step ” in , the otherwise smooth outer surface of tube 19 a . to eliminate this step , it may be desirable to remove a small portion of the outer surface of tube 19 a at locations 24 , 26 , so that when cuff 20 is attached , the outer surface of ett 19 is smooth and does not include a stepped surface at locations 24 , 26 . similarly , in the embodiments illustrated in fig3 b , 4 , and 6 , it may be desirable to taper the outer surface of tube 19 a adjacent region 32 so as to provide a smoothly changing outer diameter rather than a step . as discussed above , inclusion of region 32 increases the amount that cuff 20 will expand , and thereby increases the likelihood that cuff 20 will have reached its pressure plateau , prior to making circumferential contact with the inner lining of the trachea . accordingly , inclusion of region 32 of reduced diameter facilitates measurement of the mucosal pressure and further facilitates avoidance of excessive mucosal pressures , since the mucosal pressure generated by a silicone cuff may be measured using the procedure discussed above in connection with fig2 b . another method of increasing the likelihood that cuff 20 will have reached its pressure plateau prior to making circumferential contact with the inner lining of the trachea is to prestretch the cuff 20 prior to mounting it to tube 19 a , so that the cuff material is in a stretched state ( i . e ., beyond its natural resting dimensions ) even when the cuff is fully deflated . such stretching , or prestretching , reduces the additional amount that the cuff must stretch before reaching the pressure plateau . there is a limit to how much prestretching should be applied to the cuff . if the cuff is prestretched too much , the cuff will not be able to expand to the proper diameters safely . moreover , if additional cuff material is used for the cuff so that the cuff may become able to expand to the appropriate diameters , attachment points which affix the cuff to the tube may be too far apart . as presently conceived , the percent stretching desirable for the cuff is between 50 and 100 percent . that is , if a 3 centimeters linear length of cuff is stretched to 6 centimeters , the resultant stretch would be 100 percent . although stretching is clearly desirable , excess stretching can reduce the shelf life of the cuff . accordingly , one skilled in the art will recognize that the optimal amount of stretching in a design includes consideration of the shelf life . in one method of stretching the cuff prior to final mounting , a cuff , which may be a tubular piece of elastic material , may be mounted onto tube 19 a in an unstretched manner and then inflated . the inflated cuff is then pulled axially along the tube 19 a to invaginate part of the cuff on itself so that part of the cuff is “ doubled - up .” the part of the cuff that is doubled - up is then secured to the tube . thus the cuff is mounted on the tube 19 a in a stretched manner . this increases the likelihood that the pressure plateau is achieved before the cuff makes circumferential contact with the inner lining of the trachea . pre - stretching the cuff also reduces the likelihood that the cuff will stick to the tube . fig7 a - 7 c briefly illustrate this method of pre - stretching the cuff 20 . as shown in fig7 a , cuff material 20 is initially attached to tube 19 a and inflated . at this point , the left end of the cuff is attached to tube 19 a at location 26 and the right end of the cuff is attached to the tube 19 a at location 21 . as shown in fig7 b , the cuff is then pulled longitudinally to the right so as to stretch the cuff material . this step of stretching the cuff material by pulling it to the right may be accomplished for example manually . pulling the cuff to the right as shown in fig7 b results in all of the cuff material to the right of the attachment point at location 21 becoming “ doubled - up ”. as illustrated in fig7 c , the cuff is then squeezed inwardly towards the tube 19 a so that the right end of the cuff material contacts the tube 19 a , at location 24 . the right end of the cuff material is then attached to the tube 19 a at location 24 . this results in all cuff material between locations 24 and 26 being , in effect , longitudinally pre - stretched . for convenience of illustration , the region 32 of reduced diameter is not shown in fig7 a - 7 c , however , it will be appreciated that the steps illustrated therein may be performed so as to result in having the cuff 20 located within region 32 . the method described above in connection with fig7 a - 7 c results in pre - stretching the cuff material in a longitudinal direction prior to mounting the cuff 20 to tube 19 a . as an alternative to longitudinal stretching , the cuff material may also be stretched circumferentially prior to mounting cuff 20 to tube 19 a . fig8 a and 8b illustrate such circumferential prestretching . fig8 a shows a sectional side view of tube 19 a of an ett constructed according to the invention , the side view being taken in the general direction of line 9 - 9 as shown in fig3 b . in fig8 a , the circle labeled 19 a represents the outer periphery of the majority of hollow tube 19 a ( the outer diameter of which is od 2 ); the dashed circle labeled 32 represents the outer periphery of the region 32 of reduced diameter of tube 19 a ( the outer diameter of which is od 1 ); and the circle interior to 32 , the diameter of which is labeled id , represents the interior lumen , or airway passage , which extends from the proximal end to the distal end of hollow tube 19 a . in fig8 b , the circle labeled 20 represents a tube of elastic material , seen in a cross section taken in the same general direction as the cross section of fig8 a , that will be used to form cuff 20 . for convenience of illustration , the inflation lumen 30 is not shown in fig8 a . as shown , when the cuff material is in its natural resting ( unstretched ) state , its diameter is less than that of region 32 . so , placing the cuff material over tube 19 a and locating it in region 32 advantageously results in circumferentially pre - stretching the cuff material . it will be appreciated that the cuff material may also be pre - stretched both circumferentially and longitudinally . [ 0058 ] fig8 a shows the airway passage ( the diameter of which is id ) as being concentrically located within tube 19 a . however , it may be advantageous to form the airway passage so that it is eccentrically located within tube 19 a . fig9 shows an example of such an eccentrically located airway lumen . the eccentricity enables the tube 19 a to bend more easily along the portion of the tube with the increased thickness . the eccentricity can help reduce the pressure applied to the trachea when the ett 19 is in place . as with fig8 a , for convenience of illustration , the inflation lumen 30 is not shown in fig9 . as discussed above , tube 19 a is preferably fabricated from silicone . however , other materials may be used as well . in particular , it may be advantageous to form tube 19 a from a material that is harder than silicone such as pvc . use of a harder material such as pvc allows the outer diameter od 1 of the tube 19 a outside the region 32 to be reduced as compared with that of a silicone tube . in one embodiment , a region 32 of reduced diameter is formed in a pvc tube 19 a by reducing the external diameter by 10 % over the length of the tube onto which the cuff is mounted . as discussed above , adhering a silicone cuff 20 to a pvc tube 19 a is more difficult than adhering a silicone cuff to a silicone tube . however , shrink wrap material may be used to attach a silicone cuff 20 to a pvc tube 19 a . the shrink wrap material may be configured for example as a tube or annular ring , which is shrunk over the two materials so as to hold the cuff 20 to the tube 19 a . when shrink wrap material is used to hold cuff 20 to tube 19 a , the cuff 20 may tend to roll or slide in a longitudinal direction when the cuff is inflated . for example , referring to fig3 b , at location 24 the cuff 20 may tend to roll or slide to the left ( towards the proximal end of the ett 19 ) upon inflation . one advantage of placing locations 24 , 26 within the region 32 of reduced diameter , is that any such rolling or sliding will cause the shrink wrap material to abut into the thicker part of the tube 19 a ( i . e ., where the wall thickness is t 2 ) and this abutment tends to hold the shrink wrap material in place . additionally , since shrink wrap material adds thickness , it can be used to minimize or eliminate a “ step ” or rough spot , at the junction of region 32 with the rest of tube 19 a . accordingly , it can be advantageous for locations 24 , 26 to be at the extreme ends of region 32 so that the locations 24 , 26 abut the thicker part of the tube 19 a . however , as shown in fig6 it can also be advantageous for locations 24 , 26 to be outside of region 32 . alternatively , it is also possible to have one of locations 24 , 26 be within region 32 and have the other one be outside of region 32 . in addition , or as an alternative , to use of shrink wrap material , other methods , such as laser welding , heat welding , or use of adhesives , may be used for attaching cuff 20 to hollow tube 19 a . however , use of shrink wrap material is preferred for adhering a silicone cuff to a pvc tube , whereas other methods such as welding are preferred for adhering a silicone cuff to a silicone tube . the above description is intended to provide a representative example of the device defined in the claims . changes may be made in the apparatus disclosed above without departing from the scope of the invention recited in the claims . all the description contained above and shown in the drawing shall be interpreted in an illustrative and not in a limiting sense . for example , while etts have been discussed in detail , it will be appreciated that the invention may be applied to tracheostomy tubes as well . as such , the hollow tubes or tubular members used to form medical devices according to the invention need not be perfect tubes having uniform cross sections along their entire length . rather , the tubular members may include pre - formed bends , or angles ( as in the case of a tracheostomy tube ). also , the outer diameter of the tubular members need not be constant within the zone of reduced diameter or outside that zone . however , the outer diameter of at least a portion of the zone of reduced diameter will generally be smaller than the outer diameter of a portion of the tubular member adjacent to the zone of reduced diameter . also , whereas several different methods and structures have been discussed individually ( e . g ., textured outer surface , reinforcing member , pre - stretching ), it will be appreciated that they may be used alone or in combination . for example , an ett constructed according to the invention may include a reinforcing wire , a zone of reduced diameter having a textured outer surface , and a pre - stretched cuff .
the disclosed endotracheal tube includes a silicone tubular member that has a proximal end , a distal end , and a lumen extending through the member to supply air from the proximal end to the distal end . the tubular member defines a first zone and a second zone . at least a portion of the first zone has a first outer diameter . the second zone has a second outer diameter . the first outer diameter is less than the second outer diameter . the first and second zones are adjacent to one another and are configured for insertion into the trachea of a human patient . a silicon cuff is attached to the tubular member such that the cuff extends over at least a portion of the first zone . the silicone cuff is mounted such that when the cuff is inflated in a trachea , the cuff reaches its plateau pressure prior to circumferentially contacting the inner wall of the trachea so that an accurate pressure reading may be taken of the pressure the cuff exerts on an inner wall of the trachea .