Abstract:
The pulmonary oxygen flow control system delivers oxygen from a source of pressure to a nasal cannula worn by the patient. Between the source and the nasal cannula is a pendant flow structure which includes an orifice followed by a gas dynamic valve. When the downstream pressure in the cannula is high, the gas dynamic valve diverts the oxygen flow through the orifice to a flexible reservoir. Upon inhalation, the pressure at the cannula falls so that the gas dynamic valve delivers the orifice flow to the cannula and also utilizes a Venturi effect to withdraw oxygen from the reservoir and deliver it to the cannula. The cannula has nasal tubes which have angular faces and which are positioned farther into the nares to deliver the oxygen more efficiently.

Description:
FIELD OF THE INVENTION 
   This invention teaches a novel method of delivering oxygen to patients with severe lung disease that requires them to be prescribed supplemental oxygen. Because oxygen is delivered more efficiently, small and more portable oxygen canisters may be carried by patients on ambulatory and portable oxygen systems. 
   BACKGROUND OF THE INVENTION 
   The collective of knowledge and understanding of pulmonary rehabilitation has shown that patients with chronic lung diseases (CLD) such as chronic obstructive pulmonary disease (COPD), can live comfortable, productive and enjoyable lives if they can remain active. Patients on long-term home oxygen are limited by the portability of their system. It has been demonstrated that patients with CLD will live longer by using their oxygen continuously and that depriving them of oxygen during exertion may cause dangerous tissue hypoxia (lack of oxygen). As their impairment gradually worsens, these patients live progressively more confined existence. They find it difficult to leave their homes and gradually find themselves limited to living space of a chair or bed. This severely hurts their ability to live quality lives, and they become depressed and a burden to their families. The goal of pulmonary rehabilitation is to reverse this trend, mobilize and make these patients more active. Pulmonary rehabilitation is remarkably effective in meeting this goal. 
   The physiological goal of oxygen therapy is to maintain arterial oxygen saturation above 90 percent for all living conditions including wakeful rest, sleep and exertion. Because of the unique capacity for hemoglobin on the red blood cell to carry oxygen, little is gained by maintaining oxygen saturation above 90 percent, except to assure that it does not drop below 90 percent. Adding much more oxygen is wasteful and will impose an unnecessary weight burden for the patient using portable oxygen. 
   The Oxygen consensus 
   Conferences and the most recent conference of the American Thoracic Society and European Respiratory Society Standards for the Diagnosis and Treatment of COPD have emphasized the importance of maintaining an active lifestyle and the importance of a portable oxygen system. 
   In response to the need for mobility, coupled with the necessity for oxygen therapy in order to protect the body tissues from tissue hypoxia, there is a need to deliver oxygen to patient more efficiently. Providing adequate supplies of oxygen improves oxygen transport to the muscles, improving both strength and endurance and becoming an essential ingredient in pulmonary rehabilitation. The oxygen therapy apparatus disclosed in U.S. Pat. No. 4,572,177, co-invented by me together with Robert E. Phillips and Ben A. Otsap, teaches an oxygen conservation system. That system is very useful in the conservation of oxygen. This disclosure teaches further advancement in controlling the flow of oxygen to the patient to improve upon alveolar gas exchange and oxygen transport to the exercising muscle. 
   SUMMARY OF THE INVENTION 
   In order to aid in the understanding of this invention, it can be stated in essentially summary form that it is directed to the efficient delivery of oxygen to the patient. The system has a structure preferably in the form of a small reservoir chamber for storing oxygen during exhalation, when it is ordinarily wasted so that volume can be delivered upon the next inhalation. It includes the functions of metering, switching, storing and releasing oxygen. The system includes a nasal cannula, which receives the oxygen from the structure at an advantageous time during inhalation so that most of the oxygen effectively participates and contributes to alveolar gas exchange. 
   It is a purpose and advantage of this invention to provide an oxygen flow control system which includes gas dynamic switching that regulates, stores and releases oxygen to the nasal cannula, timed to the portion of the inspiratory cycle in which alveolar gas exchange takes place. 
   It is another purpose and advantage of this invention to provide a structure with a gas dynamic valve so that oxygen flow is diverted to storage except during the beginning of inhalation. 
   It is another purpose and advantage of this invention to provide an oxygen flow control system which permits a nasal cannula structure of lightweight tubing over the users ears on its way to the nasal prongs of the nasal cannula. 
   It is another purpose and advantage of this invention to provide an oxygen flow control system which includes an oxygen switch which switches oxygen flow to the storage reservoir inside the cannula when the cannula pressure rises to exhalation pressure and directs the oxygen flow when the cannula pressure at the nasal prongs drops to inspiratory pressure. 
   Other purposes and advantages of this invention will become apparent from the following description because the Summary set forth above is inherently incapable of indicating the many purposes, advantages, features and facets which are important to the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view the preferred embodiment of the oxygen delivery cannula system of this invention. 
       FIG. 2  is an enlarged front view of the nasal cannula with the supply tubes broken away. 
       FIG. 3  is an isometric view of the pendant structure with the near half of the upper structure broken away to show the upper portion of the pendant structure in section. 
       FIG. 4  is a longitudinal section through the pendant structure, as seen generally along line  4 - 4  of  FIG. 3 . 
       FIG. 5  is a longitudinal section taken through the pendant structure, as seen generally along line  5 - 5  of  FIG. 3 . 
       FIG. 6  is a schematic plan view showing flow during inspiration. 
       FIG. 7  is a schematic plan view showing flow during exhalation or non-flow at the cannula. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The oxygen delivery cannula system of this invention is generally indicated at  10  in  FIG. 1 . It includes an oxygen supply tube  12  which is connected by fitting  14  to a continuous source of gaseous oxygen under pressure. The supply tube  12  is connected to pendant structure  16 , the structure of which is described in detail below. Outlet tubes  18  and  20  receive oxygen from the pendant structure and are connected to the ends of nasal cannula  22 . The nasal cannula  22  delivers gaseous oxygen to the patient  24 , shown in dashed lines. 
   As seen in  FIGS. 3 ,  4 , and  5  the pendant structure  16  is formed of three substantially rigid parts made of injection moldable synthetic polymer composition material, and a flexible reservoir. Bottom panel  26  is the lower most panel in the pendant structure assembly. It is substantially circular in outline and is formed with a plurality of spaces and walls for various functional purposes. Its underside lies against the user&#39;s chest. Inlet opening  28  receives the supply tube  12 , while outlet openings  30  and  32  receive the outlet tubes  20  and  18 , respectively. Upright walls, one of which is indicated at  34  in  FIGS. 4 and 5  define an inlet channel  36 . These walls extend to walls which define an internal orifice slot  38 . Beyond orifice slot  38 , upright walls  40 ,  42 ,  44  and  46  form a Y-shaped outlet passage  48 . The Y-shaped outlet passage  48  terminates in outlet openings  30  and  32 . These walls are best seen in  FIGS. 6 and 7 . Between orifice slot  38  and Y-shaped outlet passage  48 , the side walls of the flow passage are formed into right and left lobes  50  and  52 . The body panel  26  thus defines the principal passages which have, at this point, open tops, so that the structure can be readily injection-molded of thermoplastic synthetic polymer composition material. 
   Passage cover  54  overlies the inlet channel and overlies the passages and lobes. The passage cover  54  acts to close the top of the passages except for reservoir openings  56  and  58  which are over the lobes. The passage cover  54  preferably covers only the passages to leave some reservoir spaces  60  and  62  on each side of the lobes and the Y-shaped outlet passage. 
   The flexible reservoir membrane  64  has a circular seal lip  66  which is clamped between body panel  28  and cover  68 , see  FIGS. 3 ,  4  and  5 . The flexible material of the reservoir membrane extends inwardly from the seal lip and lies down against the top rib  70  of the body panel  26  for a short distance inward from the circular seal lip. The flexible reservoir membrane is formed in a doorknob shape, which is a figure of revolution formed with two flat walls, which terminate in a hemi-circle of revolution. The flexible material of the flexible reservoir membrane  64  is elastomeric but rolls instead of stretches so that it does not exert significant pressure on the contained gas. The reservoir membrane elastomeric material very slightly favors flow into the reservoir. The space  69  under the flexible membrane  64  and the spaces  60  and  62  form the total reservoir volume space. The doorknob shape of the flexible reservoir membrane permits it to increase and decrease in its interior volume without stretching. In order to prevent the reservoir space outside of the flexible reservoir from exerting other than atmospheric pressure on the flexible reservoir, cover  68  is vented by vent slots  71 , which have sufficient opening to not limit reservoir movement. 
   Outlet tubes  18  and  20  are positioned in connector ports  32  and  30 . The outlet tubes  18  and  20  are usually clear flexible polymer tubes and are sized to extend over the patient&#39;s ears to retain the two cannula tubes  72  and  74  in the patient&#39;s nares. The nasal cannula  22  is a one-piece structure, including the cannula tubes  72  and  74 . It is preferably a polymer material and has the tubes  18  and  20  pressed therein. The length of the cannula tubes is such as to extend farther into the nares. This is possible because the cannula tubes have faces  76  and  78 , which are formed at a 45 degree angle with respect to the direction of outlet oxygen through the tubular cannula and at approximately 90 degree angle with respect to each other. The angular cut provides a larger oxygen discharge area and thus a lower velocity than a square cut. This angle also distributes the oxygen toward the septum and toward the interior nasal passages. 
   The outlet tubes  18  and  20  can be small and flexible because they handle only oxygen. This small diameter and good flexibility permit the tube to be comfortably positioned over the patient&#39;s ears. The pendant structure  16  controls the flow of oxygen from the orifice to and from the reservoir and to the outlet tubes  18  and  20  in such a manner that oxygen is conserved as compared to continuous flow, non-conserved oxygen. Assuming that the system is full of oxygen and there is flow through the orifice  38  of about ½ liter per minute (about ¼ of standard continuous flow oxygen), the patient starts to inhale. This reduces the outlet pressure at the cannula tubes, and oxygen immediately flows into the nasal passages. Oxygen flow in the pendant structure  16  is that shown in  FIGS. 6 and 7 . Oxygen is present at the cannula tubes at the beginning of inhalation, at which time that oxygen is most effective because it is drawn deeply into the lungs. 
   At the beginning of inhalation, the entire system is full of oxygen including all the way up to the cannula outlets. Also, pressure is reduced at the cannula outlets, and oxygen flows therefrom. The orifice  38  has the reservoir openings  56  and  58  adjacent thereto so that the orifice flow acts as a Venturi to withdraw oxygen from the reservoir  69 , see  FIG. 6 . A normal inhalation withdraws, with the help of this Venturi effect, oxygen from the reservoir. At the end of inhalation, the oxygen continues to flow from the orifice  38 , but the higher back pressure at the cannula outlets at the end of inhalation defeats the jet in the gas dynamic valve structure and causes the oxygen to flow to the reservoir, as shown in  FIG. 7 . The reservoir fills, and then the oxygen flows through the cannula tubes  18  and  20 , which are filled by oxygen flow so that oxygen is present at the cannula outlets at the beginning of the next inhalation. There is no significant exhalation into the cannula. 
   At the end of inhalation, the pressure builds up close to atmospheric in the tubes  18  and  20  up to the main passage  48 . This buildup of pressure defeats the jet and switches the flow of oxygen from the flow paths shown in  FIG. 6  to the flow shown in  FIG. 7 . Thus, the interior passages to the lobes  50  and  52  and the Y-shaped outlet passage  46  together with orifice  38  act as a gas dynamic valve. When the pressure in main passage  48  is about at atmospheric pressure, the flow is diverted into the reservoir through reservoir openings  56  and  58 . When the pressure in main passage  48  goes below atmospheric caused by inhalation by the patient, oxygen flow into passage  48  comes from the orifice  38  and entrains flow from the reservoir  64  through reservoir openings  56  and  58 , helped by venturi action. This permits an effective flow at the cannula during inhalation at a rate equivalent to 2 liters per minute of uninterrupted oxygen flow to fully supply the patient&#39;s needs, even though the actual flow rate through the orifice slot  38  is only about ½ liter per minute. During the ¾ of the time when the patient is not inhaling, the oxygen flow goes back into the reservoir. The reservoir has a volume of about 0.025 liter so that at a respiration rate of 20 breaths per minute, the ½ liter per minute oxygen flow through the orifice fills the reservoir and outlet tubes to the cannula. At the next breath, there is oxygen at the cannula. 
   The patient need not exhale through his nose to cause the gas dynamic valve to switch flow to the reservoir. The fact that he is no longer inhaling causes the back pressure to switch to filling the reservoir. No exhalation into the cannula or outlet tubes  18  and  20  occurs, but oxygen remains available at the cannula tubes in the nares. One advantage of this balance of pressure is that there is no need to exhale down through the outlet tubes back to the pendant to cause the pendant to switch from supply to reservoir-filling condition. This permits a smaller outlet tube which can be worn comfortable over the ear, as shown in  FIG. 1 . 
   Another advantage of not requiring exhalation into the cannula is that pursed-lip breathing can be exercised. This is a breathing condition in which exhalation is through pursed lips in order to raise the pressure in the lungs to increase the transfer of oxygen to the bloodstream. Pursed-lip breathing, as compared to regular breathing, can increase blood oxygen content in the order of 10 percentage points. This breathing method causes hyperinflation, increases oxygenation and breathing efficiency and reduces breathlessness. 
   This invention has been described in its presently preferred embodiment, and it is clear that it is susceptible to numerous modifications, modes and embodiments within the ability of those skilled in the art and without the exercise of the inventive faculty. Accordingly, the scope of this invention is defined by the scope of the following claims.