Abstract:
A fluid pressure indicating device is disclosed. The fluid pressure indicating device includes a base defining an aperture therethrough, a plate separated from the base by a variable distance, the plate defining a hole therethrough, a shaft including a helical surface disposed within the hole of the plate, a first bellows extending between the base and the plate, and a second bellows extending between the base and the plate, the second bellows disposed around the first bellows, the first bellows and the second bellows defining a first chamber therebetween. The first bellows and the second bellows expand or contract in response to a difference between a pressure inside the first chamber and a pressure outside the first chamber. The variable distance between the base and the plate varies upon expansion or contraction of the first bellows and the second bellows, such that the shaft rotates relative to the plate.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/784,546, filed on Mar. 14, 2013, the disclosure of which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to pressure indicators. More particularly, the present invention relates to a pressure indicator suitable for an inflatable cuff of an endotracheal tube. 
       BACKGROUND OF THE INVENTION 
       [0003]    Inflatable cuffs have been proposed for applying occlusive pressure to a flow lumen of a patient&#39;s body, or for sealing between a medical instrument and a flow lumen of a patient&#39;s body. For example, an endotracheal tube may include an inflatable cuff that conforms to the contours of a patient&#39;s trachea when inserted into the trachea and inflated to seal a gap between the endotracheal tube and the trachea. Further, pressure indicators have been proposed for monitoring a fluid pressure within an inflatable cuff. 
         [0004]    U.S. Pat. No. 4,727,887 (hereinafter “the &#39;887 patent”) describes an artificial sphincter with an occlusion cuff for applying occlusive pressure to a flow lumen of a patient&#39;s body (e.g., a urethra). The &#39;887 patent further proposes a combination hypodermic manometer including a piston assembly which is adapted for reciprocal movement through a fluid-filled sleeve. As the piston assembly of the ×887 patent is moved through the sleeve, a bellows is compressed, thereby changing a height of fluid within a manometer fluidly coupled to the bellows. However, accuracy of the hypodermic manometer of the &#39;887 patent may depend upon orientation of the manometer with respect to gravity, making it difficult to use with accuracy in practice. Moreover, a rupture or leak of the bellows poses the risk of mixing the manometer fluid with the fluid in contact with the occlusive cuff. 
         [0005]    Pressure indicators including a bellows within a hollow housing made of a transparent material, such that an indicator mark on the bellows is visible through the housing, are known for use with pressure cuff devices. However, such devices may have long axial lengths to provide sufficient indication precision, and may not work with opaque housing materials. 
         [0006]    Accordingly, methods and apparatus for indicating pressure in an inflatable cuff are desired that provide sufficient precision with a small and inexpensive indicator, and provide accuracy that is insensitive to its spatial orientation. 
       SUMMARY OF THE INVENTION 
       [0007]    The foregoing needs are met, to a great extent, by the present invention, wherein in one aspect an apparatus is provided that in some embodiments includes a plate defining a hole therethrough, and a shaft rotatable about an axis, the shaft including a helical surface disposed within the hole through the plate, wherein a portion of the plate is in fluid communication with a fluid whose pressure is to be measured. 
         [0008]    One aspect of the present invention advantageously provides a fluid pressure indicating device including a base defining a base aperture therethrough; a plate separated from the base by a variable distance, the plate defining a hole therethrough; a shaft rotatable about a first axis, the shaft including a helical surface disposed within the hole of the plate; a first bellows extending between the base and the plate; and a second bellows extending between the base and the plate, the second bellows disposed around the first bellows, the first bellows and the second bellows defining a first chamber therebetween. The first bellows and the second bellows expand or contract in response to a difference between a pressure inside the first chamber and a pressure outside the first chamber, and the variable distance between the base and the plate varies upon expansion or contraction of the first bellows and the second bellows, such that the shaft rotates relative to the plate. 
         [0009]    Another aspect of the present invention advantageously provides an expandable cuff system including a tube defining a lumen therein; an expandable bladder in fluid communication with the lumen; and a fluid pressure indicator. The fluid pressure indicator includes a plate defining a hole therethrough, and a shaft rotatable about a first axis, the shaft including a helical surface disposed within the hole through the plate. A portion of the plate is in fluid communication with the expandable bladder through the lumen. 
         [0010]    Yet another aspect of the present invention advantageously provides a fluid pressure indicating device including a base defining a base aperture therethrough; a plate separated from the base by a variable distance, the plate defining a hole therethrough; a shaft rotatable about a first axis, the shaft including a helical surface disposed within the hole of the plate; first means for defining a variable volume extending between the base and the plate; and second means for defining the variable volume extending between the base and the plate, the second means for defining the variable volume disposed around the first means for defining the variable volume. The first means for defining the variable volume and the second means for defining the variable volume define a first chamber therebetween. A volume of the first chamber expands or contracts in response to a difference between a pressure inside the first chamber and a pressure outside the first chamber, and the variable distance between the base and the plate varies upon expansion or contraction of the volume of the first chamber, such that the shaft rotates relative to the plate. 
         [0011]    There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
         [0012]    In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, the phraseology and terminology employed herein, as well as the Abstract, are for the purpose of description and should not be regarded as limiting. 
         [0013]    As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. Therefore, the claims shall be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  presents a schematic view of a pressure cuff system according to an embodiment of the present invention. 
           [0015]      FIG. 2  presents a schematic view of a pressure cuff system according to another embodiment of the present invention. 
           [0016]      FIG. 3  presents a schematic view of an endotracheal tube system according an embodiment of the present invention. 
           [0017]      FIG. 4  shows a cross section of the endotracheal tube system illustrated in  FIG. 3  along section  3 - 3 . 
           [0018]      FIG. 5  presents a perspective view of a pressure indicator according to an embodiment of the present invention. 
           [0019]      FIG. 6  shows an exploded view of the pressure indicator in  FIG. 5 . 
           [0020]      FIG. 7  shows an exploded view of a variant of the pressure indicator according to another embodiment of the present invention. 
           [0021]      FIG. 8  shows a top view of the pressure indicator in  FIG. 5 . 
           [0022]      FIG. 9  shows a cross sectional view of the pressure indicator in  FIG. 8  along section  9 - 9 . 
           [0023]      FIG. 10  shows an upper perspective view of a bellows assembly according to an embodiment of the present invention. 
           [0024]      FIG. 11  shows a lower perspective view of the bellows assembly illustrated in  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. An embodiment in accordance with the present invention provides a pressure indicator for detecting an inflation pressure applied to an inflatable cuff. 
         [0026]      FIG. 1  presents a schematic view of a pressure cuff system  10  according to an embodiment of the present invention. The pressure cuff system  10  includes an inflatable cuff  12  in fluid communication with a pressurized fluid source  14  through a supply channel  16 . The pressure cuff system  10  further includes a pressure indicator  18  in fluid communication with the supply channel  16 , such that a flow of pressurizing fluid from the pressurized fluid source  14  flows through the pressure indicator  18  en route to the inflatable cuff  12 . The pressurizing fluid may include any liquid fluid, such as water, or any gaseous fluid, such as air, for example. 
         [0027]    The pressure cuff system  10  may include a first valve  20  disposed in the supply channel  16 , and a second valve  24  branching off from the supply channel  16  and in fluid communication therewith. In one embodiment of the present invention, the first valve  20  is a check valve oriented such that the first valve  20  permits flow only in a direction from the pressurized fluid source  14  toward the inflatable cuff  12 . In another embodiment of the present invention, the first valve  20  is a normally-closed, spring-loaded isolation valve that is configured to be opened by a syringe luer engaging the pressure cuff system  10  as the pressurized fluid source  14 . In yet another embodiment of the present invention, the valve  24  is a manually operated bleed valve. In still yet another embodiment of the present invention, the valve  24  is a spring-loaded pressure relief valve that is configured to vent pressure from the inflatable cuff  12  at a threshold high pressure. 
         [0028]    The pressurized fluid source  14  could include any pump, such as, for example, a syringe, an elastic bulb, a rotary pump, or a positive displacement pump; a plenum pressurized with a fluid; combinations thereof; or any other means for delivering a pressurized fluid known to persons with ordinary skill in the art. The inflatable cuff  12  could include an elastic membrane or other structure that expands upon pressurization known to persons with ordinary skill in the art. 
         [0029]      FIG. 2  presents a schematic view of a pressure cuff system  10  according to an alternate embodiment of the present invention. In  FIG. 2 , the pressure indicator  18  is in fluid communication with the supply channel  16  through a branch channel  25 . Here, the pressure indicator  18  has an inlet in fluid communication with the supply channel  16  but no outlet. 
         [0030]    Referring now to  FIGS. 3 and 4 , it will be appreciated that  FIG. 3  presents a schematic view of an endotracheal tube system  26  according an embodiment of the present invention; and  FIG. 4  shows a cross section of the endotracheal tube system  26  illustrated in  FIG. 3  along section  3 - 3 . The endotracheal tube system  26  includes an elongated tube  28 , defining a main lumen  30  (see  FIG. 4 ) therein. The inflatable cuff  12  is disposed around an outer periphery  32  of the elongated tube  28 . In one embodiment, the inflatable cuff  12  defines an annular volume therein, which surrounds the elongated tube  28 . 
         [0031]    The elongated tube  28  may further define an inflation lumen  34  (see  FIG. 4 ), which is fluidly coupled to a volume within the inflatable cuff  12 . The supply channel  16  may be fluidly coupled to the inflation lumen  34 , thereby effecting fluid communication between the inflatable cuff  12  and the pressurized fluid source  14 . 
         [0032]      FIG. 5  presents a perspective view of a pressure indicator  18  according to an embodiment of the present invention. The pressure indicator  18  includes a housing  36  that defines an inlet port  38  and may define an exit port  40 . The pressure indicator  18  may be fluidly coupled to the supply channel  16  (see  FIG. 1 ) through both the inlet port  38  and the exit port  40 , or coupled to the supply channel  16  (see  FIG. 2 ) through only the inlet port  38  when there is no exit port  40 . The pressure indicator  18  may include a pointer  42  and pressure indicia  44 . 
         [0033]      FIG. 6  shows an exploded view of the pressure indicator  18  in  FIG. 5 . An internal surface  46  of the housing  36  further defines a cavity  48  therein. The cavity  48  of the housing  36  receives a shaft  50  having a helical surface  52 , and a bellows assembly  54 . The bellows assembly  54  includes at least one bellows  56  a plate  58 . The plate  58  defines a hole  60  therethrough, where the hole  60  receives the helical surface  52  of the shaft  50 . 
         [0034]    The pressure indicator  18  may include a housing top  62  disposed on the housing  36 . In one embodiment of the present invention, the pressure indicia  44  are disposed on the housing top  62 . Alternatively, the pressure indicia  44  may be disposed on the plate  58 . The housing top  62  may define a hole  64  therethrough, such that the hole  64  receives the shaft  50 . A pointer  42  may be coupled to a first end  68  of the shaft  50 , such that the pointer  42  rotates in unison with the shaft  50 . The pressure indicator  18  may further include a window  70  disposed on the housing top  62 , such that the pointer  42  is disposed between the housing top  62  and the window  70 . 
         [0035]    At least a portion of the window  70  is permeable to visible light such that a user of the pressure indicator  18  can see at least a portion of the housing top  62 , the pointer  42 , or combinations thereof. Further, all of the window  70  may be substantially transparent or translucent. In one embodiment, translucent pressure indicia  71  may be disposed on the window  70 , such that the pointer  42  is visible through the translucent pressure indicia  71  and the window  70 . 
         [0036]      FIG. 7  shows an exploded view of a variant of the pressure indicator  18  according to another embodiment of the present invention. In  FIG. 7 , a disk  72  is coupled to the shaft  50 , such that the disk  72  rotates in unison with the shaft  50 . Pressure indicia  44  may be disposed on the disk  72  and an indicating mark  74  may be disposed on the window  70 , such that the indicating mark  74  does not move relative to the housing  36 . It will be appreciated that the non-limiting embodiment shown in  FIG. 7  may include any of the features shown in  FIG. 6 , either individually or in combination. 
         [0037]    Referring now to  FIGS. 8 and 9 , it will be appreciated that  FIG. 8  shows a top view of the pressure indicator  18  in  FIG. 5 , and  FIG. 9  shows a cross sectional view of the pressure indicator  18  along section line  9 - 9  in  FIG. 8 . As shown in  FIG. 9 , the housing  36  further includes a base  76  and a wall  78  extending from the base  76 . The internal surface  46  of the housing  36  may be a surface of the wall  78  that faces the bellows assembly  54 . 
         [0038]    The bellows assembly  54  includes an outer bellows  80  and an inner bellows  82 , such that the outer bellows  80  is disposed around the inner bellows  82 . Both the outer bellows  80  and the inner bellows  82  extend between the base  76  of the housing  36  and the plate  58 . Further, both the outer bellows  80  and the inner bellows  82  are attached to the base  76  and the plate  58  by sealed connections at longitudinal ends of each bellows. The sealed connections between the bellows  80 ,  82  and the base  76  and the plate  58  may include welds, adhesives, fasteners such as screws or rivets, combinations thereof, or other fasteners known to persons of ordinary skill in the art. 
         [0039]    The housing  36  further defines a flow channel  84  therethrough. In one embodiment, the flow channel  84  is in fluid communication with both the inlet port  38  and the exit port  40 . In an alternate embodiment, where the pressure indicator  18  is connected to a branch channel  25  off of the supply channel  16  of a pressure cuff system  10  (See  FIG. 2 ), the flow channel  84  is only in fluid communication with an inlet port  38 . The outer bellows  80 , inner bellows  82 , base  76 , and the plate  58  define a first chamber  86  therein. The first chamber  86  may be in fluid communication with the flow channel  84  via one or more base apertures  88  extending through the base  76 . 
         [0040]    The housing  36 , the outer bellows  80 , the inner bellows  82 , and the plate  58  may define a second chamber  90 . The second chamber  90  may be sealed from an ambient environment  92  of the pressure indicator  18 . Alternatively, the housing  36  may define an aperture  94  therethrough, such that the second chamber  90  may be in fluid communication with the ambient environment  92  through the aperture  94 . 
         [0041]    The outer bellows  80  and the inner bellows  82  may include a flexible membrane having a substantially cylindrical shape. The bellows  80 ,  82  may be fabricated from a polymer, metal foil, textiles, papers, combinations thereof, or other similar materials known to persons with ordinary skill in the art. In one embodiment of the present invention, the bellows  80 ,  82  include a corrugated structure, which contributes to the resiliency of the bellows  80 ,  82 . In another embodiment of the present invention, the bellows  80 ,  82  are free from corrugations, yet derive resilience from elastic properties of the material forming the membrane. 
         [0042]    The plate  58  is separated from the base  76  by a variable distance  96 , depending upon a pressure difference between the first chamber  86  and the second chamber  90 . Resilience of the outer bellows  80  or the inner bellows  82  may bias the plate  58  toward the base  76  of the housing  36 . Moreover, resilience of the outer bellows  80  may bias the location of the plate  58  toward a position that minimizes the volume within the first chamber  86  and maximizes the volume within the second chamber  90 . As pressure is increased in the flow channel  84 , a pressure difference between the first chamber  86  and the second chamber  90  also increases, thereby extending the bellows  80 ,  82  in an axial direction of the shaft  50 . In turn, the variable distance  96  between the plate  58  and the base  76  increases with increasing pressure within the flow channel  84 . Further, a volume within the first chamber  86  increases with increasing pressure within the flow channel  84 . 
         [0043]    Movement of the plate  58  in a direction of the axis  97  of the shaft  50  rotates the shaft  50  through engagement of the helical surface  52  of the shaft  50  with the hole  60  through the plate  58 . The base  76  may include a rotational bearing  98  that engages a second end  100  of the shaft  50 , thereby allowing the shaft  50  to rotate about an axis  97  of the shaft  50 . Further, the housing top  62  may include a rotational bearing  102  that engages the shaft  50 . Accordingly, the rotational position of the shaft  50  relative to the housing  36 , and therefore also the rotational position of the pointer  42 , are functionally related to the pressure difference between the first chamber  86  and the second chamber  90 . As a result, the pressure indicia  44  may be designed to either quantitatively or qualitatively indicate a difference in pressure between the first chamber  86  and the second chamber  90  in cooperation with the pressure indicia  44 ,  71  on the housing  36 . 
         [0044]    In one embodiment of the present invention, the pressure indicia  44  quantitatively delineate pressure magnitudes sensed. In another embodiment of the present invention, the pressure indicia  44  qualitatively indicate a first range  104  where the pressure is too low, a second range  106  where the pressure is acceptable, and a third range  108  where the pressure is too high (see  FIG. 8 ). Further, unique colors may be associated with each of the first range  104 , the second range  106 , and the third range  108 . For example, the first range  104 , the second range  106 , and the third range  108  could be associated with the colors yellow, green, and red, respectively. Persons of skill in the art will appreciate that other similar pressure indicia  44  may be applied to the pressure indicator  18  based on the particular application. Further, it will be appreciated that the examples for pressure indicia  44  also apply to the translucent pressure indicia  71  (see  FIG. 6 ) previously discussed. 
         [0045]    The relationship between change in the variable distance  96  between the plate  58  and the base  76 , and the corresponding change in shaft  50  rotational position is determined by the thread pitch of the helical portion  52 . As a result, the thread pitch of the helical portion  52  of the shaft  50  could be selected such that fairly small changes in the variable distance  96  could result in noticeably large changes in the rotational position of the shaft  50  and pointer  42 . Accordingly, an overall dimension of the pressure indicator  18  may be minimized by utilizing small displacements in the variable distance  96  to indicate pressure via the pointer  42 , when such displacements of the variable distance  96  may not otherwise be apparent without the corresponding rotation of the shaft  50  and pointer  42 . 
         [0046]    Referring now to  FIGS. 10 and 11 , it will be appreciated that  FIG. 10  shows an upper perspective view of a bellows assembly  54  according to an embodiment of the present invention; and  FIG. 11  shows a lower perspective view of the bellows assembly  54  illustrated in  FIG. 10 . The bellows assembly  54  has an inner bellows  82  and an outer bellows  80 . In one embodiment, the inner bellows extends in a substantially longitudinal direction  110  from a first annular edge  112  toward an end cap  114 . An intersection of the inner bellows  82  and the end cap  114  may define a second annular edge  116 . 
         [0047]    The end cap  114  may extend in a substantially radial direction  118  from the second annular edge  116  toward the outer bellows  80 . An intersection of the end cap  114  and the outer bellows  80  may define a third annular edge  120 . The outer bellows  80  extends away from the end cap  114  in a substantially longitudinal direction alongside the inner bellows  82 . In another embodiment, the outer bellows  80  terminates at a fourth annular edge 
         [0048]    In one embodiment of the present invention, the bellows assembly  54  may be fabricated from a single, continuous piece of material. In another embodiment of the present invention, the inner bellows  82  and the end cap  114  may be fabricated from separate pieces of material and then be joined by welding, adhesive, or other fastening method known to persons with ordinary skill in the art. In yet another embodiment of the present invention, the outer bellows  80  and the end cap  114  may be fabricated from separate pieces of material and then be joined by welding, adhesive, or other fastening method known to persons with ordinary skill in the art. 
         [0049]    Although the pressure indicator  18  is useful to indicate a fluid pressure within a pressure cuff system  10 , the pressure indicator  18  can also be used to measure fluid pressure in other systems that could benefit from either quantitative or qualitative indication of a fluid pressure. 
         [0050]    The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.