Abstract:
A valve for use in a CPAP system or any stem at a pressure above ambient which vents the pressurised gases from the blower during expiration. Due to the pressure-flow characteristics of the blower this results in the patient having a much lower airway pressure during expiration making breathing easier. The valve includes a movable member which blocks flow from the blower to the patient during exhalation and vents externally. During inhalation gases flow normally from the blower to the patient.

Description:
BACKGROUND TO THE INVENTION 
   i) Field of the Invention 
   This invention relates to valves particularly though not solely for inclusion in the breathing circuit of a respirator. 
   ii) Summary of the Prior Art 
   A medical breathing circuit such as might be used in a Continuous Positive Airway Pressure Respirator (CPAP) includes an inspiratory gases tube which has one end thereof connected to the patient through an interface. For example through an endotracheal breathing tube extending into the trachea and ending just above the lungs. The other end thereof is connected to a respirator providing pressurised gases. The connection to the respirator may be direct or a self contained humidifier may be interposed. 
   One disadvantage of CPAP treatment is that it effectively reverses the normal breathing function. The patient has to relax to breath in and requires effort to breath out. Since normal breathing requires the exact opposite, the use of CPAP is sometimes difficult initially. 
   A number of devices exist to reduce the effort required by the patient to exhale. For example U.S. Pat. No. 5,657,752 assigned to Airways Associates describes a variable orifice venting aperture member in the nasal mask to help vent the exhalations. U.S. Pat. No. 5,065,756 assigned to New York University includes vent holes in the face mask for rapid discharge of exhaled air. U.S. Pat. 4,655,213 assigned to New York University includes a threshold valve to release air from the mask. Alternatively electronic methods exist such as that described in U.S. Pat. 5,803,065 assigned to Respironics have been used to improve the effectiveness of CPAP therapy. 
   However to some degree these existing devices are still somewhat ineffective. Also in some cases these apparatus include a bulky face mask and strapping which may be uncomfortable for the user. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a valve for a respiratory breathing circuit which will obviate the above disadvantage or will at least provide healthcare providers with a useful choice. 
   Accordingly in a first aspect the invention consists in a device for controlling the gas flow between a pressurised gases supply and a user, comprising: 
   a body portion including a first opening adapted to be in fluid communication with a pressurised gases supply, a second opening adapted to be in fluid communication with a user 
   a first auxiliary outlet in said body portion, and 
   valve means adapted such that during a user&#39;s inhalation, the flow of gases from said first opening is directed to said second opening, and during a user&#39;s exhalation, the flow of gases from said first opening is directed to said first auxiliary outlet. 
   In a second aspect the present invention consists in a system for supplying gases to a user at a pressure above ambient including a pressurised gases supply; gases delivery means for supplying said gases to said user in fluid communication with said pressurised gases supply and said user; and flow control means disposed within said gases delivery means or in fluid communication therewith, said flow control means comprising: 
   a body portion including a first opening adapted to be in fluid communication with said pressurised gases supply, a second opening adapted to be in fluid communication with said user 
   a first auxiliary outlet in said body portion, and 
   valve means adapted such that during said user&#39;s inhalation, the flow of gases from said first opening is directed to said second opening, and during said user&#39;s exhalation, the flow of gases from said first opening is directed to said first auxiliary outlet. 
   To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a blown out perspective view of the present invention, showing the components that fit together to form the valve, 
       FIG. 1B  is a blown out perspective view of the movable valve member according to the preferred embodiment of the present invention, 
       FIG. 2  is a cutaway view of the present invention during inhalation, 
       FIG. 3  is a cutaway view of the present invention during exhalation, 
       FIG. 4  is a graph of a typical pressure/flow rate characteristics of a respirator, 
       FIG. 5  is a block diagram of a typical breathing assistance apparatus circuit, according to the preferred embodiment of the present invention, 
       FIG. 6  is a graph illustrating the typical pressure profile experienced by a patient according to traditional CPAP methods, and 
       FIG. 7  is a graph illustrating the typical pressure profile experienced by a patient according to the preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention attempts to provide a simple to manufacture device which attempts to improve comfort levels for a user undergoing CPAP therapy. This is done by providing a four-way valve in the conduit between the respirator and the patient which allows both gases to flow to the patient and exhalations to be expelled to flow through the same conduit. This makes exhaling easier for the user, without the need for additional apparatus to be worn by the user. If the gases supplied to the user are to be humidified, the valve is positioned between the respirator and the humidifier, i.e. upstream of the humidifier. 
   Referring now to  FIGS. 1   a ,  1   b  we see the valve in more detail. The valve body  100  has two ends  102 ,  104  adapted for connection to a typical respiratory conduit and an enlarged centre section  106  which houses the axially moveable valve member  108 . The centre section  106  includes two apertures  110  and  112  on its periphery, located either side of an imaginary central point. 
   The valve member  108  is of a generally hollow cylindrical construction and includes two matching apertures  114 ,  116  on its periphery again located either side of an imaginary centre point. Also part of the valve member  108  is a partition  118  which joined to the inner periphery of the valve member in between the two apertures  114 ,  116 . Attached in the centre  122  of the partition  118  is a one-way valve  120  which only allows inhalatory gases to pass and at least partially blocks exhalatory gases. 
   In the preferred embodiment of the present invention the one way valve  120  is a sealing rubber flap attached to the partition on the patient side. This allows gas to pass from respirator to user (inhalation), but only on a minimal level from user to respirator (exhalation) in  FIGS. 2 and 3 . This is because the flap is designed to be not quite large enough to entirely seal around the aperture. Thus a small amount of exhalatory gases may pass. 
   Referring now to  FIGS. 2 and 3 , the operation of the valve is now explained. 
   During a patient inhalation the valve member is in the open position as shown in FIG.  2 . The gas flow is as designated by arrow  130 , which forces the movable member  108  towards the patient, until it hits the inspiratory stops  134 . The apertures in the body portion  110 ,  112  in this position are closed off and do not match up with the apertures in the valve member  114 ,  116 . In this case the one-way valve is effectively in open position and provides low resistance through the valve from the respirator to the patient. 
   When the patient exhales, shown in  FIG. 3 , back pressure results on the patient side of the valve due to the one-way valve  120 . This pressure forces the valve member  108  to move towards the respirator, until it hits the expiratory stops  136 . Once forced to the “closed” position, the apertures  110 ,  112  in the body portion and the apertures in the valve member  114 ,  116  align. This means that gases from the respirator are discharged into the atmosphere, shown by arrow  140  and the exhalatory gases from the patient, shown by arrow  150 , are also discharged into the atmosphere. This means that the back pressure that the patient experiences while exhaling is much reduced due to the typical pressure flow rate characteristics of the respirator shown in FIG.  4 . During inhalation the respirator might operate at point  200 . Whereas during exhalation, due to the high flow rate through aperture  110  into the atmosphere, operation might be at point  202  with correspondingly low pressure seen by the patient. 
   It will be appreciated that the aperture in the valve used to vent the patient&#39;s exhalations is only one possible embodiment of the present invention. It would be equally viable to have, for example, a pressure release valve in the circuit near the patient. The advantage of the present invention however is the reduced pressure delivered by the respirator, during exhalation. 
   Each of the valve body portion  102  and valve member  108  may be simply manufactured by injection moulding, for example a polycarbonate plastics material or other suitable plastics material. 
   A typical respiratory humidification circuit such as might employ the present invention is shown diagrammatically in  FIG. 5 , and includes the respirator  230 , humidifier  231 , and the associated respiratory breathing tubes  233  and  234 . A patient  236  under treatment is shown connected to the system. As indicated in  FIG. 5  the valve of the present invention is connected between the humidifier  231  and the outlet port of the respirator  230  and is indicated by reference numeral  237 . 
   A typical pressure profile as might be experienced by a patient treated using the present invention is shown in FIG.  7 . This illustrates the high pressure during inhalation  300 , the point at which the valve vents the respirator output  301 , and the relatively low pressure during exhalation  302 . This compares with a typical pressure profile of a patient treated without the present invention shown in FIG.  6 . This illustrates that the pressure experienced during exhalation  308  is similar to that during inhalation  306 . 
   It will be appreciated from the above description that during exhalation the patient does not have to exert as much force to exhale as would normally be the case with traditional cpap therapy. Thus the present invention provides a simple method of improving the quality of CPAP therapy without increasing the bulk of the apparatus worn by the patient.