Abstract:
A valve, particularly suited for use with a patient ventilation system to regulate respiration gas flow to and from the lungs of a patient has a substantially parallel, co-axial, arrangement of inner and outer fluid flow passages for conducting gas through the valve to and from a common flow conduit connected to the patient&#39;s lungs, each passage having gas flowing therein in a different direction. A cuff is provided which is inflatable to control the flow of fluid through the valve. The cuff is disposed so as to be able to form a fluid-tight seal against one or other of the facing surfaces of the inner and the outer flow passages when inflated, and to block flow through the outer passage in a timed relationship with the breathing cycle of the patient.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a valve and in particular to a valve of the type which is connectable to common flow path for inspiration and expiration gas in a patient ventilation system to provide separate the flows paths of the inspiration and expiration gases. 
     2. Description of the Prior Art 
     Known patient ventilation systems, such as respirators, ventilators and anaesthetic delivery systems, have associated tubing circuits. These tubing circuits commonly include an inspiration gas line for delivering breathing gas from the ventilation system to a patient and an expiration gas line for taking expired gas from the patient to the air or other expiration gas receiving facility. In common usage the tubing circuit may need to be frequently removed for cleaning or replacement, perhaps on a daily basis, in order to minimize the possibility of bacterial growth within the circuit which could infect the patient. Additionally, long lengths of flexible tubing in an inspiration branch and a,separate expiration branch make the determination of the patient&#39;s tidal volume and lung-thorax compliance difficult since the tubing tends to expand and contract radially in response to pressure variations during a breathing cycle. Patient comfort needs also to be considered and some patients, especially “home-care” patients, wish to move around in their “care environment”, and obviously the smaller the amount of tubing the easier and more comfortable it will be for them as they move. It is therefore desirable to minimize the length and the number of tubes within the circuit. 
     This may be achieved by providing a common flow path for the inspiration and the expiration gases which therefore replaces two gas lines with only one for a part of the tubing circuit. In order to be able to do this, a valve arrangement is required that is able to separate inspiration and expiration gas flows in order to prevent the patient from re-breathing expired gases, or to enable the inspiration gas and the expiration gas to be treated separately within the ventilation system. 
     One known valve which is used in ventilation systems to achieve this result is disclosed in U.S. Pat. No. 5,002,050. This valve has a valve body with an inlet for inspiration gas, an outlet for expiration gas and a common inlet/outlet for connecting the valve to the airway of a patient. Concentrically arranged inner and outer gas flow conduits are also provided, each having one end connected to the common inlet/outlet via a common gas flow passage and opposite ends respectively connected to the inlet and the outlet. A differential area valving means is located towards the end of the inner conduit and is arranged so that inspiration gas always impinges on its larger surface area. This inspiration gas provides operational control of the valve so that its opening and closing is dependent on the pressure exerted by the inspiration gas on the valving means. The valving means is slidable along the common axis of the valve in response to the flow of pressurized inspiration gas through the valve to seal the end of the common gas flow passage and block gas communication between the valve outlet and the common passage. When the pressure exerted on the differential area valving means by the expiration gas exceeds that exerted by the inspiration gas, the valving means slides in the opposite direction to unblock the end of the common passage way and permit egress of expiration gas past the valving means, into the outer conduit and out of the valve through the outlet. Further check valves are attached to the differential area valving means which permit only a unidirectional flow through the valving means. 
     This arrangement, however, is mechanically complex and the seal itself is made over a relatively small area, which is the end of a pipe, so that small particles may prevent a proper seal being formed. Moreover, once fabricated, and the differential area of the valving means set, the operation of the valve is controllable mainly by varying the relative pressures of inspiration and expiration gas acting on the different areas. Thus, the operation of the valve is controlled basically by varying the amount of gas within the inspiration line of the tubing circuit. This line has a relatively large volume, compared with that of the valve, and this leads to a relatively slow response of the valve to inspiration gas changes. 
     A further known valve is disclosed in U.S. Pat. No. 5,538,002 which has a pair of concentric tubes arranged to form a narrow channel therebetween through which breathing gas is supplied to a patient. The inner tube is arranged to connect the respiratory system of the patient to the outside and an inflatable cuff is disposed within the inner channel to expand and seal against itself as breathing gas passes through the outer, narrow channel. A disadvantage with this self-sealing arrangement is that a relatively poor gas seal may be formed. This is because if the cuff is substantially fully expanded to form the seal then the region of contact between the two surfaces is small, and if the cuff is less expanded wrinkles may form in the contacting surfaces which can lead to a poor seal or to the surfaces being separable at low pressures. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a structurally simple valve, useable in patient ventilation systems, in which a relatively large sealing area can be provided and in which operation of the actual valving components occurs substantially independently of the relative pressures of the inspiration and expiration gases within the tubing circuit. 
     The above object is achieved in accordance with the principles of the present invention in a valve having a substantially parallel, concentric arrangement of an inner fluid flow passage and an outer fluid flow passage for respectively conducting fluid through the valve to and from a common flow conduit, in opposite directions in the respective passages, and a cuff which is inflatable to control the flow of fluid through the valve, the cuff being inflatable to form a fluid-tight seal against one or the other of the facing surfaces of the inner and outer flow passages, so as to block fluid flow through the outer passage. 
     Thus, by providing a valving element in the form of an inflatable cuff that seals between overlapping regions of the outer surface of an inner conduit and the inner surface of an outer conduit which are arranged to be substantially parallel to, and preferably co-axial with one another, a seal is formed across a large area of the external surface of the cuff. Additionally, by having the inside of the cuff connectable with an external pressurized fluid source then the opening and closing of the valve need not rely on either of the inspiration gas or the expiration gas. Moreover, the valve is of a relatively simple construction with the valving element having only one moving part i.e. the inflatable cuff. 
     Preferably the degree of inflation of the cuff is controllable to provide a variable area flow restriction which may serve, for example, as a Positive End Expiratory Pressure (PEEP) valve useable in a ventilation system to regulate the exhaled gas flow to keep the lungs at a positive pressure throughout the expiratory phase of a patient&#39;s breathing cycle. Such PEEP ventilator operating modes are well known in the art but are achieved here in a novel manner. Additionally or alternatively, the variable area flow restriction may be used in conjunction with a differential pressure flow meter so that the size of the inflated cuff is varied in order to maintain the linearity of the meter over a large dynamic flow range. The operating principles of variable area flow restriction flow meters are well known in the art and are described, for example in U.S. Pat. Nos. 4,938,077 and 4,006,634. 
     The cuff may be formed integrally with the valve, attached to one or other of the inner and the outer conduit so as to provide a unitary design. This may be achieved, for example, by locating the cuff on the outer surface of the inner passage so that it inflates to seal against the inner surface of the outer passage. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of an embodiment of a valve constructed in accordance with the principles of the present invention. 
     FIG. 2 shows a schematic representation of a tubing circuit of a patient ventilation system including the inventive valve. 
     FIG. 3 shows an alternative embodiment of a valve constructed in accordance with the principles of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 1, a valve  1  has, in this example, [two body sections  2 , 3 ] a first body section  2  and a second body section  3  which when interfitted, together form an outer fluid flow passage  4  and an inner fluid flow passage  5  co-axial therewith, and a common flow passage  6  through the valve  1 . An inflatable cuff  7  is secured around its periphery to the external surface  40  of the inner flow passage  5 , for example by using a suitable bonding agent. A further fluid passage  8  is a formed within the body section  2  and is connectable to a source of pressurized fluid (not shown) for inflating the cuff  7  to form a fluid tight seal against the inner surface  41  of the outer flow passage  4  block the outer flow passage  4 , as illustrated in FIG. 1. A first connection piece  11  and a second connection piece  12  are formed on the first and second body sections  2  and  3  respectively, to facilitate the external connection of the valve  1  to fluid flow conduits (for example the tubing section  14  shown connected to the common flow passage  6 ). 
     The body section  2  is also provided with apertures  9  which, when the two body sections  2 , 3  are interfitted, are in fluid communication with the inner passage  4  of the valve  1 . These apertures  9  thus provide for fluid communication external of the valve  1  and are co-operatively disposed with the cuff  7  so that, when expanded, the cuff  7  can block fluid flow to and from the apertures  9  to control fluid flow through the valve  1 . 
     In the present example, a flow restriction  13  is located within the common flow passage  6  and flow channels  15  are provided in pressure communication with the common flow passage  6  either side of the flow restriction  13 . These channels are connectable to a standard differential pressure flow meter  16  to provide flow measurements for fluid proceeding in both directions within the valve  1  i.e. into and out of the common flow passage  6 . 
     As shown in FIG. 1, the valve  1  is configured with the connection piece  11  acting as an inlet for fluid flow through inner flow passage  5  and in to the common flow passage  6 . The apertures  9  then act as outlets for fluid flowing from the common flow passage  6  and through the outer passage  4 . Pressurized fluid flows through the fluid passage  8  to the cuff  7  to inflate it and seal the outer passage  4  when fluid flows through the valve  1  from the inner passage  5 . To reverse the direction of flow through the valve  1  the cuff  7  is deflated by removing the pressurized fluid therefrom and fluid can flow from the common flow passage  6  to the apertures  9 . 
     As shown in FIG. 2, one use of the valve of the present invention, such as the embodiment shown in FIG. 1, is to control the flow of respiration gases (the flow directions of which are shown in FIG. 2 by the arrows) within a tubing circuit of a patient ventilation system, such as might include a ventilator or a respirator, as further described below. 
     The valve  1  is connected between connected between the lungs of a patient  17  and a known patient ventilation system  18  to control the flow of gas between the patient  17  and the ventilation system  18 . An inspiration gas line  19  passes from the ventilation system  18  and seals in a gas tight connection to the connection piece  11  of the inner gas passage  5 . An expiration gas line  20  passes from the ventilation system  18  and is connected in a gas tight seal with the body section  2  to enclose the outlet apertures  9 . The inspiration line  19  and the expiration line  20  are configured concentrically for at least part of their lengths proximal the valve  1 . A small bore lumen tubing  21  connects the cuff passage  8  with a pressurized gas source  22 . This gas source  22  preferably contains or supplies a gas which is harmless to humans in order to minimize harm to the patient in case of its unexpected leakage into the valve  1 . The gas source  22  is operatively inked to the ventilator system  18  so that supply of the pressurized gas to the cuff  7  can be timed with an operating cycle of the ventilation system  18 , for example inflation of the cuff  7  may be triggered at the onset of the mechanical assisted inspiration phase of a patient&#39;s breathing cycle. 
     The common flow passage  6  of the valve  1  is connected in a gas-tight seal with a common flow conduit  14 , which may be an inlet to a face mask (not shown) or an endotracheal tube, through which both inspiration gas to the lungs  17  and expiration gas from the lungs  17  alternately flow. 
     In use, the ventilation system  18  supplies a volume of inspiration gas as an output into the inspiration tubing  19  during an inspiration phase of the patient and also triggers the supply of pressurized gas from the source  22  to inflate the cuff  7  and block the outer passage  4  and prevent gas flow through the apertures  9 . The volume of inspiration gas therefore passes through the valve  1  from the inlet connection  11 , through the inner passage  5  and to the common gas flow conduit  14 . From the conduit  14  the inspiration gas is delivered into the lungs  17 . During an expiration phase of the patient&#39;s breathing cycle a valve arrangement (not shown) within the ventilation system  18  closes to prevent supply of inspiration gas to the inner passage  5 . The gas within the cuff  7  is removed, to be vented to the atmosphere or recovered for re-use by the source  22 , and the outer passage  4  is unblocked as the cuff  7  deflates. Expiration gas passing from the lungs  17  into the common flow passage  6  of the valve  1  can flow through the outer passage  4 , through the apertures  9  and into the expiration gas line  20  from where it is recovered by the ventilation system  18 . Thus the cuff  7  acts as a valving arrangement to block and unblock the outer passage  4  of the valve  1  as it respectively inflates and deflates during the breathing cycle of the patient. Additionally, or alternatively, by controlling the manner in which the cuff  7  is deflated a variable area flow restriction in the expiration gas path may be provided. This may be used to control the expiration pressure of the patient while the exhaled gas passes the partially deflated cuff  7  a nd so provides a PEEP mode of ventilation the therapy. 
     FIG. 3 shows a further embodiment of the valve of the present invention. Similar to the valve of FIG. 1, the valve  31  has a first body section  32  and a second body section  33  which, when interfitted, form an inner fluid flow passage  35  and an outer fluid flow passage  34 . The body portion  32  is provided with apertures  39  which in the assembled valve  31  provide fluid communication between the outer flow passage  34  and external of the valve  31 . Different to FIG. 1 is that the first and second body sections  32  and  33  are of lengths such that no common flow passage is formed within the valve  31 . Instead the body section  33  is connectable directly to a common flow passage  314 . Sealed around the external surface  340  of the inner flow passage  35  is an inflatable cuff  37  which when inflated forms a fluid-tight seal against the inner surface  341  of the outer flow passage  34 . The inflation and deflation of the cuff  37  is controlled by a pressurized gas source (not shown) which is connectable to the fluid passage  38 . Ports  315  are provided in pressure communication with the outer flow passage  34 , one either side of the cuff  37 . A differential pressure flow meter  316  is connectable to the ports  315 . The inflation of the cuff  7  is controlled to vary size the flow restriction it forms when partially inflated so as to provide a more linear response across the dynamic range of the meter  316 . 
     It will be appreciated by those skilled in the art that the valves described above are examples of a valve according to the present invention. Modifications may be made to the valves described above while remaining within the scope of the invention. For example, the inner conduit may be adapted to carry the expiration gas and the outer the inspiration the inspiration gas; or the inflatable cuff may be fixedly located against the inner wall of the outer flow passage so as to seal against the outer wall of the inner flow passage when inflated; or the two part body may be formed as a single part, for example by using plastic injection molding techniques in its construction. Moreover, a one-way valve may be placed within the flow passage not to be sealed by the cuff to prevent a reverse flow through that passage instead of relying on existing valves normally present within the ventilation system, as are used in the above examples. 
     Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.