Abstract:
A compact, simplified, totally pneumatic demand valve designed for coupling between a source of pressurized gas and a recipient user is provided which achieves a high degree of sensitivity and flow control without expensive, bulky valving arrangements characteristic of prior demand valves. Preferably, the demand valve includes a valve body presenting a gas flow passageway, together with pneumatically coupled sensing and slave diaphragms; the slave diaphragm is interposed in the flow passageway and prevents gas flow during the exhalation phases of the patient&#39;s breathing cycle. During inhalation sensed by the sensing diaphragm, the slave diaphragm is shifted to open the gas flow passageway in the valve, thus permitting passage of gas to the patient. The valve is designed for coupling to a fixed orifice flow controller, which may be positioned either downstream or upstream of the valve as desired.

Description:
This is a continuation of application Ser. No. 07/787,775, filed Nov. 6, 1991, now abandoned; which is a continuation of application Ser. No. 07/680,028, filed Mar. 28, 1991, now abandoned; which is a continuation of application Ser. No. 07/305,446, filed Feb. 1, 1989, now abandoned; which is a continuation of application Ser. No.07/027,943, filed Mar. 19, 1987, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is broadly concerned with a demand-type pneumatic valve particularly adapted for administering medicinal gas, normally oxygen, to a patient undergoing respiratory therapy. More particularly, it is concerned with a compact, to tally pneumatic demand valve useful in a wide variety of contexts, including hospital, home care and ambulatory settings. 
     2. Description of the Prior Art 
     The traditional approach in administration of a medicinal gas such as oxygen is to connect the patient via a cannula to a source of pressurized gas, with the gas being administered on a more or less continuous basis. In the case of oxygen, however, studies have indicated that, in the continuous administration mode, significant quantities of oxygen are lost. That is to say, during the normal breathing cycle, the patient will inhale, exhale and pause before beginning the next inhalation; as a consequence, oxygen delivered to the patient during the exhale and pause portions of the breathing cycle are essentially wasted. 
     In response to this problem, it has been known in the past to provide valves of the so-called demand type, i.e., valves adapted to open only during the inspiration period of the patient&#39;s breathing cycle. Thus, U.S. Pat. No. 4,054,133 to Myers describes a demand-type valve of the pneumatic variety. 
     The Myers valve makes use of a sensing diaphragm arrangement made up of a pair of interconnected flexible diaphragms which cooperatively define a chamber. An adjustable spring engages one of these diaphragms in an attempt to provide a measure of sensitivity control. Moreover, the Myers device includes a rather complicated arrangement associated with the dual diaphragm structure designed to prevent the wastage of control volumes of gas, which typically may account for only 4 or 5% of the volume of gas used. As a consequence, the Myers design is inherently costly, and is believed prone to malfunction because of the inability to precisely respond to the changing pressure conditions induced during the patient&#39;s breathing cycle. 
     Thus, while the concept of a demand valve is known, there is a real and unsatisfied need in the art for a simplified, low cost, compact pneumatic demand valve. 
     SUMMARY OF THE INVENTION 
     The demand valve of the invention overcomes the noted difficulties and provides a greatly improved pneumatic demand valve designed for coupling between a source of pressurized gas, such as oxygen, and a breathing gas recipient, in order to supply gas to the recipient as needed on a demand basis. The demand valve broadly includes a body presenting a gas flow passageway there through having an inlet adapted for connection to the gas source and an outlet adapted for connection to the recipient. The valve body further has an internal sensing chamber having a port adapted for coupling to the recipient for transmission of the changing pressure conditions induced by the recipient&#39;s breathing to the sensing chamber. In practice, a dual lumen cannula is coupled to the device of the invention, with one of the lumen being a gas supply passageway for delivering quantities of oxygen on a demand basis. The remaining lumen is connected to the aforementioned sensing chamber port and leads to the nasal cavities of the patient, whereby to transmit to the sensing chamber the patient-induced pressure variations attendant to normal breathing. 
     The demand valve also includes sensing means in the form of only a single shiftable diaphragm operatively disposed in and forming a part of the sensing chamber and shiftable between a position corresponding to inhalation by the recipient, and a position corresponding to exhalation by the recipient. Such shifting is in response to the pressure conditions within the sensing chamber induced by the recipient&#39;s breathing and transmitted through the aforementioned cannula lumen. 
     The overall demand valve further includes a slave diaphragm operably interposed in the gas flow passageway and movable between a gas flow-blocking position and a gas flow-permitting position. In the gas flow-blocking position, the slave diaphragm engages an adjacent seat forming a part of the gas flow passageway through the body, and resists the forces exerted thereagainst by the pressurized gas. Means generally in the form of a small pilot passageway or orifice is provided for passing pressurized gas to a region adjacent the other face of the slave diaphragm, i.e., the face remote from that engageable with the passageway seat, so that the pressurized gas exerts pressure against both faces of the slave diaphragm. 
     Finally, the valve includes means operatively coupling the sensing diaphragm and the slave diaphragm for movement of the slave diaphragm from the flow-blocking position thereof to its flow-permitting position, in response to shifting of the sensing diaphragm from the exhalation to the inhalation positions thereof. Correspondingly, the coupling means provides for movement of the slave diaphragm from the flow-permitting to the flow-blocking positions thereof in response to shifting of the sensing diaphragm from the inhalation to the exhalation positions. This diaphragm coupling means preferably includes a port separate from the patient outlet and leading to the atmosphere for passage of pressurized gas from the region adjacent the other face of the s lave diaphragm to the atmosphere, upon shifting of the sensing diaphragm from the exhalation to the inhalation positions. Also, spring means is provided for engaging the slave diaphragm and biasing the same in a preselected direction. The combination of atmospheric venting and spring means serves to give precise coupling between the sensing and slave diaphragms. 
     In particularly preferred forms, the relief passageway is provided for communicating the adjacent faces of the sensing and slave diaphragms, with the relief passageway presenting a seat for engagement by the sensing diaphragm. Advantageously, the ratio between the effective area of the sensing diaphragm, and the effective area presented by the relief passageway seat, is at least about 35,000 to 1. This relatively large ratio is afforded by precision drilling of the appropriate relief passageway in the valve body, and makes it possible to significantly reduce the size of the overall valve while at the same time enhancing the sensitivity thereof. As used herein, the sensitivity of the valve apparatus refers to the pressure level required in the sensing cavity of the valve to induce movement of the sensing and slave diaphragms from a flow-preventing to a flow-permitting position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view with parts cut away showing a complete demand valve/flow controller in accordance with the invention, with a dual lumen cannula operatively coupled to the valve/flow controller apparatus; 
     FIG. 2 is a fragmentary, enlarged view in vertical section illustrating the internal construction of the preferred demand valve; 
     FIG. 3 is an essentially schematic, vertical sectional view depicting the preferred demand valve device, shown during exhalation; 
     FIG. 4 is a view similar to that of FIG. 3, but showing the operation of the demand valve during inhalation; 
     FIG. 5 is an essentially schematic, vertical sectional view illustrating another embodiment of the demand valve of the invention, shown during the exhalation phase of operation thereof; and 
     FIG. 6 is a view similar to that of FIG. 5, but showing the operation of the demand valve during inhalation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to the drawing, a complete breathing assist apparatus 10 in accordance with the invention is illustrated in FIG. 1. Broadly speaking, the device 10 is in the form of a combined demand valve/flow controller unit 12 having a demand valve 14 operatively coupled with a selectable, multiple orifice flow controller 16. The demand valve includes an inlet 18 adapted for connection to a source of oxygen or other medicinal gas, illustrated by arrow 20. Valve 14 also has a sensing port 22 which is important for reasons to be described. The flow controller 16 on the other hand is of conventional construction and includes a gas outlet 24 adapted to supply gas to a recipient. 
     The overall assist apparatus 10 further includes a dual lumen cannula 26 having a pair of elongated flexible tubes in the form of a gas supply tube 28 and a sensing tube 30. The gas supply tube 28 is operatively connected to outlet 24 as shown, and, adjacent the recipient, divides at juncture 32 to present two branch legs 34, 36. The latter are interconnected by means of a nasal delivery structure 38 including a pair of spaced apart gas delivery tubes 40 respectively insertable into the patient&#39;s nasal cavities. The sensing tube 30 is operatively coupled to port 22 as depicted, and, adjacent the recipient, divides at juncture 41 to present two branch legs 41a and 41b; these legs are in turn connected to structure 38 as shown. A pair of short sensing tubes 42 are respectively located within the spaced delivery tubes 40 as shown, and these are coupled with the legs 41a, 41b. The function of sensing tube 30 is to convey and transmit, via the tubes 42 and the remainder of the tube body, the pressure conditions induced during the patient&#39;s breathing efforts, such pressure conditions being transmitted to port 22. 
     Attention is next directed to FIG. 2 which illustrates in detail the preferred demand valve 14. Specifically, the valve 14 includes interconnected upper, intermediate and lower body components respectively numbered 44, 46 and 48. The components 44, 46, 48 are interconnected by means of screws 50 or other appropriate fasteners, in order to present a complete valve housing. 
     In more detail, it will be seen that the upper body component 44 is in the form of a substantially planar, circular in plan plate 52 presenting a lower chamber-defining wall surface 53 and a central, internal, depending stop 54. The righthand edge of plate 52 as shown in FIG. 2 is bored for reception of the elongated tubular port 22. 
     Intermediate body component 46 is designed to mate with upper component 44, and accordingly includes an upper wall surface 56 which, in conjunction with lower wall surface 53 of component 44, defines an internal recess 58. Furthermore, the intermediate component 46 includes a circular, essentially square in cross-section channel 60 in surrounding relationship to recess 58. 
     A sensing diaphragm 62 is located within recess 58 and is in the form of a circular, unbiased elastomeric body having a central reinforcing element therewithin, a downwardly extending, semicircular in cross-section, integral bead 66, and an essentially square in cross-section outermost peripheral connection rib 68. As illustrated, rib 68 is seated within channel 60, and the complete diaphragm 62 is maintained in position by virtue of the interconnection of the components 44, 46, serving to retain the peripheral connection bead 66. 
     The sensing diaphragm 62 in effect divides overall recess 58 into an upper sensing chamber 70 and a lower relief passageway 72. The port 22 is in communication with sensing chamber 70, whereas body component 44 is bored as at 74 to present an outlet or relief port communicating with passageway 72 and the atmosphere. 
     The intermediate body portion 46 is further provided with a central, stepped bore 76. The bore 76 presents a lowermost, radially expanded section 78, an upright spring-receiving section 80, and an uppermost section 82 presenting a bore 83 therethrough. An axially bored member 84 is seated within bore 83, with the bore 86 therethrough terminating in an uppermost restricted seat portion 88. 
     Finally, it will be observed that intermediate body portion 46 is provided with an angled bore 90 leading from expanded section 78 to the lower wall surface 92 presented by body component 46. The terminus of bore 90 is radially outwardly spaced from the expanded lower section 78 of bore 76, for reasons to be described. 
     The lower body component 48 includes an upper wall surface 94, an opposed lower surface 96, and a depending circular flange 98. The flange 98 is adapted to interfit with the upper end of flow controller 16 and to be connected thereto by means of fasteners 100. 
     The lower body component is provided with an inlet bore 102 adapted to receive the inlet tube 18. The inlet bore 102 in turn communicates with an upright, circular in cross-section pressurized gas chamber 104 which aligns with radially expanded section 78 of intermediate body component 44 as illustrated. An angled pilot bore 106 extends radially outwardly from the gas chamber 104 and terminates in opposed relationship to the end of bore 90 provided in intermediate body component 44. The upper wall surface 94 is relieved as at 108 and receives an O-ring 110 as well as an apertured metallic disc 112. In this fashion, compression of the body components 46, 48 serves to create a seal and hence a continuous gas flow passageway between chamber 104 and the expanded section of bore 76; the importance of the feature will be explained hereinafter. 
     The slave diaphragm 114 is situated atop and defines the upper surface of gas flow chamber 104. The diaphragm 114 includes an upstanding semicircular in cross-section marginal bead and is of elastomeric construction. The diaphragm 114 further is held in place by compression between the adjacent surfaces of body components 44, 46, and for this purpose, upper surface 94 of lower body component 48 is appropriately relieved as at 95 to receive the outermost marginal edge of the diaphragm 114. 
     A metallic actuator body 116 is in engagement with the upper surface of diaphragm 114 and includes an upright central section. A biasing spring 118 receiving the central section of the body 116 is interposed between the latter and the upper portion of body component 44 defining the aperture 82. This serves to bias diaphragm 114 downwardly as will be readily apparent. 
     The lower body component 48 has an innermost, central, upstanding, annular wall 120 which defines a central gas flow path 122 and an uppermost diaphragm seat 124 of reduced cross-sectional dimensions. 
     As noted, diaphragm 114 serves as the uppermost wall of gas chamber 104. This diaphragm also serves as the bottom or lower wall of a biasing chamber 125 defined by the stepped bore 76 and the diaphragm itself. Here again, the importance of this structure will be explained hereinafter. 
     The flow controller 16 is of entirely conventional design and provides a selector (not shown) for selecting any one of a number of differently sized, fixed dimension orifices which serve to deliver to the patient fixed rates of gas flow, e.g., 2, 4 or 6 liters per minute. 
     In overall context, it will thus be seen that the demand valve 14 presents a continuous gas flow passageway from the source of pressurized gas to the patient outlet. In particular, this passageway (see FIG. 3) is defined by the inlet 18, chamber 104 and flow path 122 leading to the flow controller 16 and ultimately outlet 24. Slave diaphragm 114 is operably interposed in this flow passageway, namely by engagement with the uppermost end of annular wall 120. Moreover, the sensing diaphragm 62 is pneumatically coupled with the slave diaphragm 114 for operation of the latter in response to operation of the sensing diaphragm. 
     In order to clearly explain the operation of demand valve 14, attention is directed to schematic FIGS. 3 and 4, which respectively show operation of the valve during exhalation and inhalation. 
     Thus, during exhalation (see FIG. 3), the pressure within sensing chamber 70 is positive, as indicated by arrow 126, such pressure conditions being induced by the patient and transmitted via cannula lumen 30 and port 22 from the patient. In this orientation, it will be seen that sensing diaphragm 62 is in engagement with the seat portion 88 of bore 86 thereby effecting a seal between biasing chamber 125 and relief passageway 72. The diaphragm 114 is retained in its sealing orientation by virtue of two factors, namely passage of gas from chamber 104 through the bores 90, 106 (shown for purposes of simplification in FIGS. 3 and 4 by means of pilot orifice 90/106 directly through the diaphragm itself) so as to substantially equalize pressure against both faces of the diaphragm 114, and the biasing of spring 118. Thus, pressure equalization is effected because of the pressurized gas acting simultaneously against both faces of diaphragm 114 during this sequence of operation, and this together with spring 118 closes the overall gas flow passageway through the demand valve 14. 
     During inhalation however (see FIG. 4), the negative pressure as indicated by arrow 127 induced within chamber 70 causes sensing diaphragm 62 to raise from engagement with seat 88. This establishes communication between biasing chamber 125 and relief passageway 72. As a consequence, the biasing gas within chamber 125 passes into the passageway 72 and is immediately exhausted to the atmosphere through communicating passageway 74. When this occurs, the pressure within chamber 104 is sufficient to raise slave diaphragm 114 from seat 124, thereby opening the gas flow passageway through the valve and permitting gas to travel from chamber 104 through flow path 122 and into flow controller 16. As described above, the flow controller 16 is of conventional design and includes selectable fixed orifice means schematically referred to by the throat 128; the flow controller creates, during inhalation, a fixed back pressure within the demand valve downstream of slave diaphragm 114. 
     FIGS. 5 and 6 illustrate another embodiment in accordance with the invention which is in many respects identical with that shown in FIGS. 3 and 4, and accordingly the same reference numerals are employed where appropriate, except with a letter designation &#34;a&#34;. The principal difference between the embodiment of FIGS. 5 and 6 as compared with the preferred embodiment is that in the second embodiment the flow controller device 16a is upstream of the demand valve 14a. In order to provide this type of flow controller/demand valve orientation, the oxygen supply referred to by the arrow 20a first passes through the fixed throat 128a of the flow controller and thence into the path 122a of demand valve 14a. In terms of internal construction, the valve 14a is different in that the slave diaphragm 114a is inverted as compared with the embodiment of FIGS. 3-4, i.e., the marginal bead thereof opens upwardly as opposed to downwardly. Furthermore, the equalization orifice 90/106a is located in the center of the diaphragm and thus communicates with path 122a. Finally, in this orientation, it is necessary to position biasing spring 118a in surrounding relationship to the annular wall 120a so as to exert an upward biasing force against slave diaphragm 114a. 
     The operation of the embodiment of FIGS. 5-6 is in most respects identical to that described above. Thus, during the exhalation phase of operation illustrated in FIG. 5, the pressure conditions within sensing chamber 70a maintain diaphragm 62a in engagement with seat 88a. At this same time, pressurized gas is located within path 122a and biasing chamber 125a by virtue of pilot orifice 90/106a or its equivalent. This serves to maintain slave diaphragm 114a in engagement with seat 124a to prevent flow of gas to the patient. 
     When the patient inspires, the negative pressure within sensing chamber 70a causes diaphragm 62a to lift, whereby biasing gas within chamber 125a passes into passageway 72a and ultimately to the atmosphere through communicating passageway 74a. This creates an inequality of forces on the diaphragm 114a, whereby the latter is lifted thus opening the gas flow passageway through the valve 114a so that gas may pass through path 122a, chamber 104a and ultimately out the outlet 24a to the patient. 
     In both of the above described embodiments however, it will be seen that the sensing and slave diaphragms are pneumatically coupled for operation of the slave diaphragm in response to movement of the sensing diaphragm; the latter is in turn moved in response to the patient&#39;s breathing efforts as transmitted through the cannula. 
     A very desirable feature of the invention results from its fail safe characteristics. Specifically, a fail safe demand device is one that, upon a mechanical failure of one or more components, establishes a continuous flow of oxygen to be delivered to the recipient at the prescribed rate.