Abstract:
A tube system for ventilation with an outer tube ( 1 ) and with an inner tube ( 3 ) arranged non-centrally in the radial direction in the interior of the outer tube ( 1 ) is shown and described. The coaxial type tube system may be provided for ventilation and for medical applications. The flow resistance for the gas is minimized by the inner tube ( 3 ) being designed such that it is linearly in contact with an inner wall ( 35 ) of the outer tube ( 1 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of German Patent Application 10 2014 011 188.1 filed Jul. 31, 2014, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention pertains to a flexible, extensible, coaxial tube system, especially for ventilating patients with ventilation systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    Tube systems for ventilation (also known as respiration) with two separate tube volumes extending in parallel have been sufficiently well known from the state of the art. They are used preferably in the field of medicine, especially for the purposes of ventilating patients, and they have an inspiratory line and an expiratory line connected to it, which facilitates the use. 
         [0004]    For example, it is known from the state of the art that two ventilation lines that are separated from one another can be provided by a tube with an axially extending, membrane-like partition being provided, so that two volumes that are separated from one another are generated thereby. However, the length of the tube system is defined as a fixed value in this variant (for example, Limb-O variant of Vital Signs). 
         [0005]    The tube system may also be designed as a coaxial tube system with an outer tube and an inner tube with a smaller diameter, and both tubes are usually designed as corrugated tubes in order to ensure the necessary flexibility. Furthermore, coaxial tube systems are known as well, whose length is variable. This property of a variable tube length is achieved by the outer tube and the inner tube being designed each as a folded tube, in which the folds spread out during longitudinal extension. Coaxial tube systems with the possibility of varying the length have the advantage over tube systems with fixed lengths that tube systems with different lengths are not needed for different applications, and, for example, the storage expenses of a medical institution is not increased due to the need to stock the tube systems in a plurality of lengths. Furthermore, situations in which a flexible length adaptation is desirable, for example, when changing the position of patients, may occur during the use of the tube systems. 
         [0006]    However, the tubes are connected to one another at their respective ends only in the coaxial tube systems with outer tube and inner tube and are in an undefined position in relation to one another between the ends. The coaxial tube systems with fixed or variable length known from the state of the art have the following drawback due to this design. First, the often sharp-edged folds of the inner tube and of the outer tube, which are needed for the flexibility and possibly for extensibility, generate a turbulent flow of the gas in areas in which the gap between the inner tube and the outer tube does not reach a critical value, which will then lead, on the whole, to an increased flow resistance for the gas. 
       SUMMARY OF THE INVENTION 
       [0007]    Therefore, based on the state of the art, an object of the present invention is to provide a coaxial type tube system, especially for ventilation and for medical applications, in which the flow resistance for the gas is minimized. 
         [0008]    This object is accomplished according to the present invention by a coaxial type tube system with an outer tube and with an inner tube arranged non-centrally in the interior of the outer tube in the radial direction, wherein the inner tube is designed such that it is linearly in contact with an inner wall of the outer tube. 
         [0009]    It is guaranteed hereby that the width of the radial gap between the inner tube and the inner wall of the outer tube is maximized in the radial direction opposite the side on which the inner tube is linearly in contact with the outer tube. It is avoided hereby, in particular, that the width of the gap drops below a critical value, below which turbulences, which develop on the profiled surfaces of the tubes, cause a massive increase in the flow resistance for the breathing gas in the intermediate space between the inner tube and the outer tube. 
         [0010]    The outer tube and the inner tube preferably have ends, and the ends of the outer tube are firmly connected to the ends of the inner tube. The positions of the outer tube and inner tube relative to one another are thus preset permanently. 
         [0011]    Furthermore, it is advantageous if the tube system has an outer tube and an inner tube, whose length is variable. The tube system can be adapted s a result to changed situations during the use of the tube system. 
         [0012]    Furthermore, it is preferred that the inner tube is designed such that it is under a prestress in the axial direction, which contracts the inner tube in the axial direction. It is achieved hereby that with the ends of the inner tube being arranged eccentrically at the outer tube, the inner tube is always in contact with the outer tube, because it seeks to minimize its length, so that a linear contact will become established in this manner between the outer tube and the inner tube. 
         [0013]    In a preferred embodiment, the inner tube has, in the longitudinal section, V-shaped sections and intermediate sections, which are located between the V-shaped sections and adjoin the free ends of the V-shaped sections. The tip of the V-shaped sections faces radially to the outside, while the intermediate sections are straight on the side facing the tube axis, and they have a curved shape to the outside, which protrudes radially to the outside to the same extent as the V-shaped sections. This makes a longitudinal extension possible due to the spreading out of the V-shaped sections, and the straight inner sides and the curved outer sides of the intermediate sections bring about a low flow resistance in both the inner tube and the intermediate space between the inner tube and the outer tube. 
         [0014]    The intermediate sections and the sections that are V-shaped in the longitudinal section for longitudinal extension may have a ring-shaped cross section. It is also conceivable that the intermediate sections and the sections having a V-shaped longitudinal section have a helical design in the axial direction between the ends of the inner tube. 
         [0015]    In another preferred embodiment, the profile of the inner tube has strips in the longitudinal section, which extend radially from the inside to the outside and are flatly connected to one another at their ends alternatingly at the top and at the bottom. The inner tube consequently comprises ring-shaped elements in the cross section. An inner tube with prestress in the longitudinal direction, where the outwardly facing connection sections of the strips can come to lie in corresponding recesses in the wall of the outer tube, can be designed in this manner as well. 
         [0016]    In another preferred embodiment, the inner tube has a spring element, which extends helically along the inner tube between the ends. A prestress, which contracts the tube in the axial direction and thus leads to a linear contact of the inner tube with the outer tube in the above-described manner, is generated by this spring element in the inner tube. 
         [0017]    Furthermore, it is preferred that an intermediate section consisting of a flexible material, which is bellows-like (bellows-shaped) in the longitudinal section of the inner tube, is formed in the inner tube between adjacent turns of the helical spring element, wherein the length of the flexible material between two adjacent turns in the axial direction of the inner tube corresponds to a multiple of the distance between two adjacent turns of the spring element in case of maximum longitudinal extension of the inner tube, wherein the diameter of the intermediate section corresponds to the external diameter of the inner tube, and wherein the folds of the intermediate section are in contact with the spring element radially on the outside. An inner tube designed in this manner has a great longitudinal extension potential, and the folds that are in contact cover the turns of the helical spring element even in case of an increased tube length. As a result, the inner tube has a smooth surface without sharp edges or tips, which could increase the flow resistance due to turbulences. 
         [0018]    In another preferred embodiment, the inner tube and the outer tube are also connected to one another in a positive-locking manner at an additional point between the ends of the tubes, in addition to their connection at the ends. It is also conceivable that the inner tube and the outer tube are connected to one another linearly by welding. A connection can also be established between the outer tube and the inner tube in this manner, for example, also by locking, as a consequence of which a linear contact will develop between the outer tube and the inner tube. 
         [0019]    According to another preferred embodiment, the outer tube and the inner tube have, in the longitudinal section, a folded contour, which is formed in the longitudinal direction alternatingly from a flank sloped in relation to the longitudinal direction and a radially outwardly extending flank. A radially outwardly extending flank of the folded contour of the inner tube is connected with a radially outwardly extending flank of the folded contour of the outer tube along a line extending in the longitudinal direction of the tube. The inner tube is connected in this manner to the outer tube over the entire length and forms a gap, whose width is maximized over the entire length of the tube, between the inner tube and the outer tube, as a result of which the flow resistance is reduced. 
         [0020]    The present invention will be explained below on the basis of a drawing showing only preferred exemplary embodiments. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    In the drawings: 
           [0022]      FIG. 1  is a longitudinal sectional view of a first exemplary embodiment of a coaxial type tube system according to the present invention; 
           [0023]      FIG. 2  is a cross sectional view of the exemplary embodiment from  FIG. 1 ; 
           [0024]      FIG. 3  is a partial longitudinal sectional view of a second exemplary embodiment of a coaxial type tube system according to the present invention; 
           [0025]      FIG. 4  is a partial longitudinal sectional view of a third exemplary embodiment of a coaxial type tube system according to the present invention; 
           [0026]      FIG. 5  is a partial longitudinal sectional view of a fourth exemplary embodiment of a coaxial type tube system according to the present invention; and 
           [0027]      FIG. 6  is a partial longitudinal sectional view of a fifth exemplary embodiment of a coaxial type tube system according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Referring to the drawings,  FIG. 1  shows a first exemplary embodiment of a coaxial type tube system in a longitudinal section, while  FIG. 2  shows the cross section of this tube system. 
         [0029]    It can be seen in these two views that the tube system has an outer tube  1  and an inner tube  3 , and the outer tube  1  has a symmetry axis  5  and the inner tube  3  has a symmetry axis  7 . These two symmetry axes  5 ,  7  are located at spaced locations from one another, so that the inner tube  3  is arranged eccentrically in the outer tube  1 . The outer tube  1  has folds  9  with two flanks  11 ,  13  each, which spread out during the extension of this variable-length tube system. 
         [0030]    In addition to the folds  9 , the outer tube  1  has in this embodiment a groove-like profile  15 , which extends circumferentially around the outer tube  1  and which is connected to a profile  19  extending circumferentially around the inner tube  3  on the radially outwardly directed outer side  17  of the inner tube  3  by locking in a positive-locking manner. This positive-locking connection of the profiles  15 ,  19  may be repeated several times at preset spaced locations over the entire length of the tube. However, these additional possible connection points of additional profiles  15 ,  19  are not shown in the detail view of the tube system, which is shown in  FIG. 1 . 
         [0031]    Just like the outer tube  1 , the inner tube  3  has folds  21  in the exemplary embodiment being shown here for changing the length, these folds being formed from two flanks  23 ,  25 , which spread out during pulling apart. The internal diameter  27  of the inner tube  3  is formed by the smallest distance of the radially inwardly facing inner wall  29 . The external diameter  31  of the inner tube  3  is formed by the greatest distance of the radially outwardly facing outer side  33 . 
         [0032]    The outer tube  3  has a radially inwardly directed inner wall  35 , whose smallest distance forms an internal diameter  37  of the outer tube. 
         [0033]    The inner tube  3  is in contact with the inner wall  35  of the outer tube  1  along a connection line  39  with its outer side  17  because of the meshing of the profiles  15 ,  19 . 
         [0034]    As can be seen in  FIG. 1  and even more clearly in the cross section shown in  FIG. 2 , a gap  41 , whose width is formed by the distance between the external diameter  31  of the inner tube  3  and the internal diameter  37  of the outer tube  1 , is formed on the side of the inner tube  3  that is located opposite the connection line  39 . It should be noted in this connection that the gap  41  has a constant maximum width over the entire length of the tube. It is achieved due to this broad gap  41  that the flow resistance for the gas flowing through the outer tube  1  is minimized. In particular, the inner tube is prevented from being able to be arranged freely in the interior of the outer tube  1  by the linear contact of the inner tube  3  with the outer tube  1 , so that even though the overall cross section would remain the same for the flow in the outer tube  1 , a narrower gap would be formed between the outer tube  1  and the inner tube  3 , which would lead to an increased flow resistance, especially because of the folds  9 ,  21  in both tubes. 
         [0035]    As was already described above, the extensible outer tube  1  is again designed as a folded tube in the exemplary embodiment of a coaxial type tube system shown in  FIG. 3 . The inner tube  3 , whose length can likewise be increased, has V-shaped sections  43  in the longitudinal sections, and the tips of these V-shaped sections are directed radially outwardly. The legs  45 ,  47  of the V-shaped sections  43  form an angle. The angle formed by the legs  45 ,  47  is an acute angle in this preferred exemplary embodiment and equals about 15° in the relaxed state of the inner tube  1 . An intermediate section  49  each is arranged between all V-shaped sections  43 . In the relaxed state of the inner tube  1 , the intermediate sections  49  have a length in the longitudinal direction of the tube that is a multiple of the open distance between the legs  45 ,  47  of the V-shaped sections  43  without extension of the inner tube. The intermediate sections  49  are straight on the inner side  51  facing the symmetry axis  7  of the inner tube  3 , and the radially outwardly facing side  53  has a curved shape. This curved outer side  53  projects radially to the outside by the same amount as the V-shaped sections  43 . The free ends of the legs  45 ,  47  of the V-shaped sections  43  adjoin the intermediate sections  49  on the inner side  51  thereof. This makes possible a longitudinal extension by spreading out the V-shaped sections  43 , and the straight inner sides  51  and the curved outer sides  53  of the intermediate sections  49 , whose shape does not change during an extension, ensure that there will be hardly any change in the flow resistance in both the inner tube  3  and the outer tube  1 . 
         [0036]    It should be mentioned in this connection that the profiles of the V-shaped sections  43  and of the intermediate sections  49 , which profiles are shown in the longitudinal section, may either have a ring-shaped cross section or a helical design in the axial direction. A restoring force of the inner tube  3  against extension or a corresponding prestress in the axial direction is achieved due to the elasticity of the V-shaped sections  43 . 
         [0037]    As was already described above, the extensible outer tube  1  is again designed as a folded tube in the exemplary embodiment according to  FIG. 4 . The likewise extensible inner tube  3  has ring-shaped elements, which are flatly connected to one another alternatingly at the top and at the bottom. 
         [0038]    This is embodied in the longitudinal section being shown by the strips  55 , which extend radially from the inside to the outside and are connected to one another flat alternatingly at the top and at the bottom. Due to the rigid, flat connection points  57  at the ends of the strips  55 , the strips  55  are slightly bent when pulled apart, which leads to an elasticity and hence to a restoring force against an extension or prestress in the axial direction if the strips  55  are made of a suitable material. 
         [0039]    As was already described above, the outer tube  1  is again designed as a folded tube in the embodiment shown in  FIG. 5 . The longitudinal section shows the inner tube  3  with a spring element  59  having a helical design in the axial direction, but the helical design of the spring element  59  cannot be shown in the longitudinal section. The turns of the spring element  59  are arranged at spaced locations from one another, and bellows-like intermediate sections  61  made of a flexible material are formed in the intermediate spaces of the turns. The bellows-like intermediate sections  61  are connected to the turns of the spring element  59  and are in contact with the spring element  59  on the outside. The bellows-like intermediate sections  61  are designed such that in the axial direction they have an overall length that corresponds to a multiple of the distance between two adjacent turns of the spring element  59  at maximum longitudinal extension of the inner tube  3 . The bellows-like intermediate sections  61  extend from a first connection point  63  with a turn of the spring element  59  axially in the direction of an adjacent turn, and the bellows-like intermediate sections  61  extend, bent slightly to the outside, past the adjacent turn and then back again from there in the direction of the connection point  63 , in order to be then connected to the adjacent turn at another connection point  63 ′. However, it should be noted here that all the connection points  63 ,  63 ′ are located on a contiguous line because of the helical course of the spring element  59 . 
         [0040]    The diameter of the intermediate section  61  corresponds to the external diameter  31  of the inner tube, and the folds of the intermediate sections  57  are in contact with the spring element  59  radially on the outside. Because of their length, they cover the spring element  59  even when the inner tube  3  is in the extended state, so that a smooth outer side  17  is formed, which ensures s low flow resistance in the outer tube  1 . 
         [0041]    While only one spring element  59  is provided in the exemplary embodiment shown in  FIG. 5 , it is also conceivable that a double helix is used, in which case the second spring element of the double helix is received in the bellows-like intermediate sections  61  and ensures that these extend in the longitudinal direction and are tightly in contact with the first spring element. 
         [0042]    In the above-described exemplary embodiments according to  FIGS. 3 through 5 , the linear contact of the inner tube  3  in the inner wall  35  of the outer tube  3  during the operation is brought about solely by the prestress in the inner tube  3 , which arises from the elastic design and causes the inner tube  3  to seek to minimize its length. The inner tube  3  is therefore in contact with the inner wall  35 , especially in case of a curved course of the entire tube system. 
         [0043]    As was already described above, the outer tube  1  is designed as a folded tube in the exemplary embodiment according to  FIG. 6  and has folds  9 , which are formed from two flanks  11 ′ and  13 ′. The inner tube  3  likewise has folds  21  in the longitudinal section, which are formed from two flanks  23 ′,  25 ′. The folds  9 ,  21  are pushed one into the other in the correct position in the embodiment being described here, so that one fold  21  of the inner tube  3  always protrudes into a fold  9  of the outer tube  1 . Every other fold  13 ′ of the folds  9  of the outer tube  1  and every other flank  25 ′ of the folds  21  of the inner tube  3  extend radially from the inside to the outside, while the other flanks  11 ′,  23 ′ may be oblique in relation hereto or curved. 
         [0044]    The folds  21  of the inner tube  3  are pushed into the folds  9  of the outer tube  1  to the extent that an overlapping area  65  of the folds  13 ′ and  25 ′ is formed, which extends from the radially outer end of the flank  25 ′ of the folds  21  of the inner tube  3  to the radially inner end of the flank  13 ′ of the folds  9  of the outer tube  1 . The inner tube  3  is connected to the outer tube  1  in a suitable manner, especially by bonding or welding, at this overlapping area  65  in the embodiment being shown here, so that a linear and in this case permanent contact is established hereby. 
         [0045]    A linear contact of the inner tube  3  with the inner wall  35  of the outer tube  3  is achieved in all exemplary embodiments, be it by positive-locking connection ( FIGS. 1 and 2 ) or prestress ( FIGS. 3 through 5 ) or by permanent connection such as welding or bonding ( FIG. 6 ), so that the width of the gap between the inner tube  3  and the outer tube  1  is maximum. This in turn leads to a minimization of the flow resistance in the outer tube  1 . 
         [0046]    While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.