Nasal cannula

Abstract

A nasal cannula for delivering air to a patient's nares. Two delivery tubes are provided to supply air to a pair of nasal inserts each of which conform to the shape of the nare. Properly placed bleed ports reduce noise and reduce carbon dioxide retained in the system. The cannula is positioned on the face with the aid of a strap system.

1. A nasal cannula for use with a constant positive pressure air supply, comprising:
 first and second nasal inserts for insertion into a patient's nares; 
 said inserts adapted for a sealing relationship with the patient's nares; 
 a left and a right delivery tube, each coupled to both of said nasal inserts, each of said delivery tubes is sufficient to provide all of the air required by the patient; 
 a coupler located remote from said nasal inserts for coupling said cannula to a source of respiration gas; 
 two tubular bleed ports having an internal lumen directly opening into said delivery tubes connecting an interior of the cannula with an exterior of the cannula; 
 each of said bleed ports having a characteristic area expressed as a bleed port diameter called BPD, and separated by a distance called L; 
 each of said tubular bleed ports located beneath each of said nasal inserts such that a first bleed port is located beneath a first insert and a second bleed port is located beneath a second insert, for preferentially intercepting expired gas during exhalation; 
 the sum total of said bleed port diameters, called the Total Bleed Port Diameter (TBPD), have a T BPD/L ratio of between 0.1 and 0.5 such that for the two bleed ports: 0.5>2*BPD/L>0.1 
 
     
     
       2. A nasal cannula for use with a constant positive pressure air supply, supplying air (F) at between about 10 to 50 liters/minutes, said cannula comprising:
 first and second nasal inserts for insertion into a patient's nares; 
 said inserts adapted for a sealing relationship with the patients nares; 
 a left and right delivery tube coupled to both of said nasal inserts, each of said delivery tubes is sufficient to provide all of the air (F) required by the user; 
 each nasal insert communicates with both the left delivery tube and right delivery tube; 
 a coupler located remote from said nasal inserts for coupling said cannula to a source of respiration air; 
 at least two bleed ports having an internal lumen directly opening into said delivery tubes connecting the interior of the cannula with the exterior of the cannula; 
 said bleed port active during exhalation to remove respired air from the cannula; 
 each of said bleed ports located beneath each of said nasal inserts for preferentially intercepting expired gas during exhalation; 
 each of said bleed ports has an individual diameter size (BPD) which is approximated by 
 
       
         
           
             
               
                 
                   ( 
                   BPD 
                   ) 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 Bleed 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 Port 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 Diameter 
               
               = 
               
                 2 
                 ⁢ 
                 
                   
                     
                       X 
                       * 
                       IDS 
                     
                     
                       π 
                       * 
                       F 
                     
                   
                 
               
             
           
         
       
       where IDS is the immediate dead space volume of the delivery tubes proximate the nares, and ‘X’ is the cross section area of the cylinder volume of the delivery tubes between said bleed ports. 
     
     
       3. A nasal cannula for use with a constant positive pressure air supply for supplying air (F) between about 10 to 50 liters/minutes, said cannula comprising:
 first and second nasal inserts for insertion into a patient's nares; said inserts adapted for a sealing relationship with the patients nares; 
 a left and right delivery tube coupled to both of said nasal inserts, each of said delivery tubes is sufficient to provide all of the air (F) required by the user, 
 each nasal insert communicates with both the left delivery tube and right delivery tube; 
 a coupler located remote from said nasal inserts for coupling said cannula to a source of respiration gas; 
 at least two bleed ports having an internal lumen directly opening into said delivery tubes connecting the interior of the cannula with the exterior of the cannula; 
 said bleed port active during exhalation to remove respired air from the cannula; 
 each of said bleed ports located beneath each of said nasal inserts for preferentially intercepting expired gas during exhalation; 
 said bleed ports when two in number and they have a separation distance (L) which is approximated by; 
 
       
         
           
             
               
                 
                   
                     ( 
                     L 
                     ) 
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   bleed 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   port 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   separation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   distance 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   is 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   approximately 
                 
                 ≈ 
                 
                   
                     A 
                     * 
                     F 
                   
                   
                     X 
                     2 
                   
                 
               
               ; 
             
           
         
       
       where ‘A’ is a constant of proportionality an ‘X’ is the cross sectional area of the delivery tubes. 
     
     
       4. A nasal cannula for use with a constant positive pressure air supply, comprising:
 left and right delivery tubes, each tube having a size sufficient to provide all the air required by a patient;   first and second nasal inserts for insertion into a patient's nares, said inserts connected to and extending at an angle relative to respective portions of said tubes;   said nasal inserts each being elongated and comprising a soft, compliant material configured to conform to the cross-section of a nare of a patient when inserted into a nare up to a location where the inner cross-section of the nare equals the outer cross-section of the insert to effect said sealing relationship with the patient's nares; and   two tubular bleed ports, each bleed port having an open internal lumen directly opening into a respective delivery tube and connecting an interior of the delivery tube with an exterior of the delivery tube; and   wherein each bleed port is located directly opposite and aligned with a respective nasal insert, said bleed ports comprising together one of three air exit paths leading away from the nasal inserts.   
     
     
       5. The nasal cannula as claimed in claim 4, including a soft flange located at a distal terminal end of each nasal insert, each flange readily conformable with a patient's nare and enabling a sealing with the interior of a nare in which the insert is placed when the insert is inserted up to a location where the cross-section of the flange equals the cross-section of the nare. 
     
     
       6. The nasal cannula as claimed in claim 5, wherein said left and right delivery tubes include portions adjacent to the nasal inserts, wherein said delivery tube portions adjacent to the nasal inserts, the nasal inserts and the flanges are made in one integral piece. 
     
     
       7. The nasal cannula as claimed in claim 6, wherein said delivery tube portions adjacent the nasal inserts, the nasal inserts and the flanges are made of silicone rubber. 
     
     
       8. The nasal cannula as claimed in claim 4, further comprising a coupler located remote from said nasal inserts for enabling coupling said delivery tubes to a source of respiration gas. 
     
     
       9. The nasal cannula as claimed in claim 4, wherein each bleed port extends inwardly of an inner wall of a respective delivery tube, and comprises a bleed tube that extends toward a respective nasal insert. 
     
     
       10. The nasal cannula as claimed in claim 4, wherein said delivery tubes include portions generally aligned adjacent to the nasal inserts so as to feed pressurized air towards a central area between the delivery tubes beneath the nasal inserts, and wherein each bleed port comprises a bleed tube extending into the interior of a respective delivery tube from an inner wall thereof in a direction generally normal to the direction of motion of the air supply flowing in the respective delivery tube, each bleed tube further extending toward and parallel with a respective nasal insert. 
     
     
       11. The nasal cannula as claimed in claim 10, each bleed tube terminating at a location spaced inwardly from an inner wall of a respective delivery tube and directly opposite an inner end of a respective nasal insert at its juncture with a delivery tube. 
     
     
       12. The nasal cannula as claimed in claim 11, wherein each delivery tube has a wall thickness, and each bleed tube has a characteristic height that is at least twice and less than 10 times the wall thickness of a respective delivery tube at the location of the bleed tube. 
     
     
       13. The nasal cannula as claimed in claim 10, wherein the bleed tube has a tapered outer shape, tapering inwardly from the respective delivery tube inner wall towards each nasal insert. 
     
     
       14. The nasal cannula as claimed in claim 10, wherein the cannula, including nasal inserts, bleed tubes, and at least part of the delivery tubes adjacent to the nasal inserts, are made in a single unitary and integral piece. 
     
     
       15. The nasal cannula as claimed in claim 14, wherein the cannula, including said nasal inserts, bleed tubes and said at least part of the delivery tubes adjacent to the nasal inserts, are made of silicone rubber.