DEMAND VALVE FOR BREATHING APPARATUS

CROSS-REFERENCE TO APPLICATION

[0001] This application claims the benefit of Australian Provisional Application No.

AU 2007900927, filed February 23, 2007, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] The present invention relates to a demand valve for use in a mechanical breathing apparatus. In particular, the present invention relates to apparatus that reduces the effort of breathing, particularly during exhalation.

[0003] Aspects of the invention may be used for Non-invasive Positive Pressure

Ventilation (NPPV) and for continuous positive airway pressure (CPAP) therapy of sleep disordered breathing (SDB) conditions such as obstructive sleep apnea (OSA). However, aspects of the invention may have application in other fields.

BACKGROUND OF THE INVENTION

[0004] U.S. Patent No. 7,066,175 discloses a demand valve for a breathing apparatus including a supply inlet port adapted to be connected to a pressurized source of oxygen and an outlet port adapted to be connected to the inlet of a patient's breathing appliance. The demand valve includes a valve assembly for connecting/disconnecting the inlet port to and from the outlet port. However, such demand valve doe not allow scavenging of exhausted gas.

SUMMARY OF THE INVENTION

[0005] One aspect of the invention relates to a demand valve for a breathing apparatus. The demand valve includes a housing, a valve assembly, and a diaphragm coupled to the valve assembly. The housing defines a chamber and includes a demand port adapted to be in fluid communication with the entrance of a patient's airways, an inlet port adapted to be in fluid communication with a supply of breathable gas at a positive pressure, and an exhaust

port adapted to allow gas to exit the housing. The valve assembly includes an inlet valve adapted to at least partially close the inlet port and an exhaust valve adapted to at least partially close the exhaust port. The diaphragm is constructed and arranged to be responsive to pressure within the chamber in order to effect movement of the valve assembly to selectively close the inlet and exhaust ports.

[0006] Another aspect of the invention relates to a breathing apparatus including a housing defining a chamber with a variable volume. The housing includes a demand port adapted to be in fluid communication with the entrance of a patient's airways, an inlet port adapted to be in fluid communication with a supply of breathable gas at a positive pressure, and an exhaust port adapted to allow gas to exit the housing. The housing is constructed and arranged to expand during an expiration phase of the patient's breathing cycle and to contract during an inspiration phase of the patient's breathing cycle to thereby forcibly vent at least a portion of exhausted gas to the exhaust port.

[0007] Another aspect of the invention relates to a method for supplying breathable gas to a patient. The method includes providing a patient interface for communication with a patient, setting a PAP device to generate a supply of breathable gas at a substantially constant positive pressure, and controlling the flow of breathable gas to be delivered to the patient interface upon patient inhalation, and at least partially stopped or impeded from proceeding to the patient interface upon patient exhalation.

[0008] Another aspect of the invention relates to a method for supplying breathable gas to a patient. The method includes providing a chamber with a variable volume between a patient interface for communication with a patient and a PAP device structured to generate a supply of breathable gas at a substantially constant positive pressure, and expanding the volume during an expiration phase of the patient's breathing cycle and contracting the volume during an inspiration phase of the patient's breathing cycle to thereby forcibly vent at least a portion of exhausted gas to atmosphere.

[0009] Other aspects, features, and advantages of this invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings facilitate an understanding of the various embodiments of this invention. In such drawings:

[0011] Fig. 1 is a schematic view of a breathing apparatus including a demand valve according to an embodiment of the present invention;

[0012] Fig. 2A illustrates a demand valve according to an embodiment of the present invention, the demand valve arranged to provide pressurized gas to a patient;

[0013] Fig. 2B illustrates the demand valve of Fig. 2A with the demand valve arranged to scavenge gas from the patient;

[0014] Fig. 3 A illustrates a demand valve according to another embodiment of the present invention, the demand valve arranged to provide pressurized gas to a patient;

[0015] Fig. 3 B illustrates the demand valve of Fig. 3 A with the demand valve arranged to scavenge gas from the patient;

[0016] Fig. 4 illustrates a demand valve according to another embodiment of the present invention, the demand valve arranged to scavenge gas from the patient;

[0017] Fig. 5 A is a graph illustrating pressure applied to the chamber of the demand valve from a supply of pressurized breathable gas during expiration and inhalation phases of the patient's breathing cycle; and

[0018] Fig. 5B is a graph illustrating pressure within a chamber during expiration and inhalation phases of the patient's breathing cycle for the demand valve and for a typical CPAP device.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

[0019] The following description is provided in relation to several embodiments which may share common characteristics and features. It is to be understood that one or more features of any one embodiment may be combinable with one or more features of the other embodiments. In addition, any single feature or combination of features in any of the embodiments may constitute additional embodiments.

[0020] In this specification, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear. [0021] The term "air" will be taken to include breathable gases, for example air with supplemental oxygen. It is also acknowledged that the apparatus described herein may be designed for use with fluids other than air.

1. Breathing Apparatus

[0022] Fig. 1 is a schematic view of a breathing apparatus 2 including a demand valve

10 according to an embodiment of the present invention. As illustrated, the breathing apparatus 2 includes a positive airway pressure (PAP) device or flow generator 4 structured to generate a supply of air or breathable gas at a positive pressure, a patient interface 6 (e.g., full-face mask, nasal mask, etc.) structured to provide a seal with the patient's face, and a demand valve 10 between the PAP device 4 and the patient interface 6. [0023] In an embodiment, the demand valve 10 includes an inlet in fluid communication with the outlet of the PAP device 4 (e.g., via an air delivery tube) and an outlet in fluid communication with the inlet of the patient interface (e.g., via an air delivery tube), as described below. However, it should be appreciated that the demand valve may be at least partially incorporated into the PAP device and/or the patient interface, e.g., demand valve incorporated into the housing of the PAP device.

2. Demand Valve

[0024] Figs. 2A and 2B illustrate a demand valve 10 for use in a breathing apparatus according to an embodiment of the present invention. As illustrated, the demand valve 10 includes a housing 20 defining a chamber 22, a valve assembly 30, and a diaphragm 40 coupled to the valve assembly 30 that is responsive to pressure within the chamber 22 in order to regulate a supply of pressurized breathable gas to a patient and assist with scavenging or venting exhausted gas to atmosphere.

2.1 Housing

[0025] The housing 20 includes a demand port 24, an inlet port 26, and an exhaust port 28. The demand port 24 is adapted to be connected to the entrance of a patient's airways (e.g., via an air delivery tube and some form of patient interface or mask). The inlet port 26 is adapted to be connected to a supply of air or breathable gas at a positive pressure (e.g., via an air delivery tube and a PAP device), hi an embodiment, the air or breathable gas is provided at a relatively constant positive pressure, e.g., between 2-30 CmH ₂ O for the treatment of obstructive sleep apnea or other respiratory diseases or conditions, although other fields of use are also considered. However, the air or breathable gas may be provided at variable or bi- level pressures. The exhaust port 28 is adapted to allow air or gas (e.g., exhausted CO ₂ ) to exit the housing 20, e.g., to atmosphere.

[0026] The chamber 22 is in constant fluid communication with the demand port 24 and is in variable fluid communication with the inlet and exhaust ports 26, 28, as described in greater detail below. A baffle wall 25 is provided between the inlet and exhaust ports 26, 28 and defines an exhaust chamber 35 adjacent the exhaust port 28.

2.2 Valve Assembly

[0027] The valve assembly 30 includes a valve 50 and a mechanical arm 60 to interconnect the valve 50 with the diaphragm 40. As shown in Figs. 2A and 2B, the valve 50 includes an inlet valve 52 engageable with an inlet valve seat 27 adjacent the inlet port 26 and an exhaust valve 54 engageable with an exhaust valve seat 29 adjacent the exhaust port 28. As illustrated, the inlet and exhaust valves 52, 54 are coupled to one another, e.g., by a mechanical link 55.

[0028] The mechanical arm 60 is responsive to movement of the diaphragm 40, which is responsive to pressure within the chamber 22 as described in greater detail below. The mechanical arm 60 is arranged to create a mechanical advantage such that movement of the diaphragm 40 moves the valve 50 relative to the inlet and exhaust ports 26, 28. Specifically, the mechanical arm 60 includes a first and second links 62, 64. The first link 62 is pivotally mounted to the housing 20 via an off-center hinge 65 (which creates the mechanical advantage) and includes a first end 62(1) pivotally mounted to the valve 50 and a second end 62(2). The second link 64 includes a first end 64(1) in communication or coupled with the

diaphragm 40 and a second end 64(2) pivotally mounted to the second end 62(2) of the first link 62.

[0029] As shown in Figs. 2A and 2B, the coupled inlet and exhaust valves 52, 54 include a generally I-shaped cross-sectional configuration, and the inlet port 26 includes an axis that is generally aligned or coaxial with an axis of the exhaust port 28. This arrangement allows the coupled valves 52, 54 to move generally linearly to open one of the inlet and exhaust ports 26, 28 while closing the other, and vice versa. While generally aligned, the baffle wall 25 prevents short circuiting of the incoming gas directly to the exhaust chamber

35 or exhaust port 28.

[0030] hi an embodiment, it may be possible for the coupled valves 52, 54 to assume an intermediate position so that both the inlet and exhaust ports 26, 28 are simultaneously open. That is, the valves may not entirely open/close respective ports, but may at least partially open/close the ports to regulate flow through the inlet/exhaust ports during inhalation/exhalation phases of the patient's breathing cycle.

[0031] However, the valve and/or housing may include other suitable configurations.

For example, in Figs. 3 A and 3B, the valve may be in the form of a piston 250 including a plunger portion 252 and a head portion 254. In use, the plunger portion 252 is structured to open/close the inlet port 26 and the head portion 254 is structured to open/close the exhaust port 28.

[0032] The piston-type valve may include different configurations, e.g., depending on the structure of the housing and inlet/exhaust ports thereof. For example, Fig. 4 illustrates a piston-type valve 350 including a plunger portion 352 with an angled side wall.

2.3 Diaphragm

[0033] The diaphragm 40 (e.g., flexible membrane) is provided to the housing 20 and is structured to allow the volume of the chamber 22 to change responsive to pressure within the chamber 22. In its initial or relaxed position, the diaphragm assumes a generally flat configuration, as shown in Fig. 2A. When deformed or expanded (due to pressure within the chamber 22), the diaphragm balloons outwardly and assumes a generally contoured or bulbous configuration, as shown in Fig. 2B. It should be appreciated that the diaphragm may

assume other suitable configurations in its relaxed or expanded positions, e.g., diaphragm may be slightly curved (inward or outward) in its relaxed position.

[0034] In the illustrated embodiment, the diaphragm 40 may have inherent resiliency and/or may be coupled to a biasing structure (e.g., spring 42) so that the diaphragm is biased to its relaxed position. The spring rate provided by the diaphragm 40 may be adjustable. [0035] In use, increased pressure within the chamber 22 causes the diaphragm 40 to expand from its relaxed position to its expanded position (against biasing thereof), and decreased pressure within the chamber 22 allows the diaphragm 40 to resiliently return to its relaxed position. Movement of the diaphragm 40 effects movement of the mechanical arm 60 which in turn effects movement of the valve 50 to open and close the inlet and exhaust ports 26, 28, i.e., the coupled inlet and exhaust valves 52, 54 are arranged to open and close respective inlet and exhaust ports 26, 28 responsive to pressure within the chamber 22.

2.4 Operation

[0036] The housing chamber 22 is in fluid communication with the demand port 24, which is coupled to a patient interface provided to the patient's face. The demand valve 10 is structured to supply pressurized breathable gas to the patient interface (e.g., upon patient inhalation) and allow exhausted gas to exit to atmosphere (e.g., upon patient exhalation). [0037] In the absence of a supply of pressurized breathable gas to the demand valve

10, the diaphragm 40 assumes its relaxed position so that the exhaust valve 54 is held in contact with the exhaust seat 29 adjacent the exhaust port 28 (e.g., see Fig. 2A). Thus, the inlet port 26 is open and the exhaust port 28 is closed to prevent any inward leakage of atmospheric air into the demand valve 10. In an alternative embodiment, the demand valve 10 be arranged so that the coupled valves 52, 54 assume an intermediate position when the diaphragm 40 is in its relaxed position so both the inlet and exhaust ports 26, 28 are simultaneously, slightly open.

[0038] When a supply of pressurized breathable gas is supplied to the demand valve

10 (e.g., from PAP device coupled to the inlet port 26), the pressurized breathable gas passes through the inlet port 26, through the chamber 22, through the demand port 24, and into the patient interface for inhalation by the patient (e.g., see Fig. 2A). As illustrated, during the inhalation phase of the patient's breathing cycle, the baffle wall 25 is provided between the

inlet and exhaust ports 26, 28 to direct the pressurized breathable gas towards the demand port 24.

[0039] When the patient stops inhaling, the incoming gas will start to pressurize the chamber 22 and begin expanding the diaphragm 40. As shown in Fig. 2B, when the patient exhales, the exhausted gas will further increase the pressure within the chamber 22 which causes the diaphragm 40 to further expand. As the diaphragm 40 reaches its expanded position, the mechanical arm 60 pivots about the off-center hinge 65 to cause the inlet valve 52 to engage the inlet valve seat 27 adjacent the inlet port 26. Due to the off-center hinge 65, the diaphragm 40 may have a relatively low spring constant, yet the desired movement of the valve 30 can still be effected (e.g., even against pressure from the inlet port 26). This movement closes to the inlet port 26 to stop or nearly stop the supply of pressurized breathable gas, while allowing the exhaust valve 54 to open the exhaust port 28 to allow the exhausted gas to exit the chamber 22.

[0040] When the patient inhales again, the pressure within the chamber 22 decreases which causes the diaphragm 40 to resiliently return to its initial position (e.g., under biasing from inherent resiliency, a biasing structure, and/or ambient pressure on the outside of the diaphragm). As the diaphragm 40 reaches its relaxed position, the mechanical arm 60 pivots about the off-center hinge 65 to cause the exhaust valve 54 to engage the exhaust valve seat 29 adjacent the exhaust port 28. This movement closes to the exhaust port 28 to prevent gas from exiting the chamber 22, while allowing the inlet valve 52 to open the inlet port 26 to allow pressurized breathable gas to enter the chamber 22 and proceed through the demand port 24 to the patient interface.

[0041] Fig. 5 A includes a graph illustrating pressure (P _s ) applied to the chamber from the supply of pressurized breathable gas during expiration and inhalation phases (E, I) of the patient's breathing cycle, and Fig. 5B includes a graph illustrating pressure (P _c ) within the chamber during expiration and inhalation phases (E, I) of the patient's breathing cycle for the demand valve (in dashed lines) and for a typical CPAP device (in solid lines). [0042] As shown in Fig. 5 A, the supply of pressurized gas applied to the chamber is stopped or nearly stopped during the exhalation phase (E), the supply of pressurized gas is opened during the inhalation phase (I), and the supply of pressurized gas is partially opened/stopped as the inlet valve transitions between open/closed positions (e.g., both inlet

and exhaust ports open). This arrangement reduces breathing effort especially during patient exhalation as described below.

[0043] As shown in Fig. 5B, the pressure within the chamber for the demand valve (in dashed lines) increases during patient expiration and decreases during patient inspiration. The pressure in the chamber may even be a negative value, i.e., a vacuum in certain cases. As described above, this arrangement controls movement of the diaphragm which effects movement of the inlet and exhaust valves. Specifically, the higher pressure during expiration results in expansion of the diaphragm and an increase in the volume of the chamber, and the lower pressure during inspiration results in contraction of the diaphragm and a decrease in the volume of the chamber. As illustrated in dashed lines, the pressure swing between expiration and inspiration is not significant due to the variable volume of the chamber and/or the regulation of the supply of pressurized gas. In contrast, the pressure swing for a chamber of a typical CPAP device (in solid lines) has substantial pressure swings because it does not include a diaphragm to vary the chamber volume and/or it is not structured to stop or at least partially stop the supply of pressurized gas during exhalation, nor increasing venting/exhaust during exhalation.

[0044] Figs. 3 A and 3B illustrate movement of the piston-type valve 250 described above between a position to provide a supply of pressurized breathable gas (Fig. 3A) and a position to allow exhausted gas to exit the chamber (Fig. 3B). As illustrated, the plunger portion 252 of the piston-type valve 250 is structured to open/close the inlet port 26 and the head portion 254 of the piston-type valve 250 is structured to open/close the exhaust port 28. [0045] Fig. 4 illustrates the piston-type valve 350 described above in a position to close the inlet port 26 while opening the outlet port 28.

2.5 Reduced Breathing Effort

[0046] The demand valve 10 is structured to reduce breathing effort, especially during patient exhalation. Specifically, the demand valve 10 regulates the supply of pressurized gas so that pressurized gas is supplied to the patient when demanded (i.e., upon patient inhalation). When the patient exhales, the supply of pressurized gas is at least partially restricted (e.g., inlet port 26 closed) so that the patient does not have to exhale against pressurized gas, i.e., less effort to exhale. Further, the exhaust valve can be designed

significantly larger to vent higher flow to allow reduced work of exhalation to the patient. The flow generator also works with less effort as leak is not constant, especially during inhalation. [0047] Thus, the demand valve may allow a PAP device that supplies relatively constant positive pressure to simulate bi-level type therapy to a patient, i.e., higher pressure during inhalation and lower pressure during exhalation. It may be possible for the demand valve to be used with PAP devices structured to supply VPAP or Bi-level therapy.

2.6 Scavenging

[0048] The demand valve 10 may be structured to provide forced venting or scavenging of exhausted gas (e.g., efficient washout of CO ₂ ) to the exhaust port 28. Specifically, at the end of exhalation as the patient begins to inhale and the diaphragm 40 begins to resiliency return or contract to its initial position to open the inlet port 26, the movement of the diaphragm 40 along with the pressurized gas entering the chamber 22 creates a blast of pressure to force all the gas within the chamber 22 to exit the housing 22. That is, the blast of pressure forces gas to exit through the exhaust port 28 (until it is closed by the exhaust valve 54) as well as urge the supply of pressurized gas towards the demand port 24. In this embodiment, both the inlet and outlet valves 52, 54 may be slightly open at the same time to assist scavenging.

2.7 Exhaust Flow Restrictor

[0049] As illustrated, the housing 20 includes internal walls adjacent the exhaust port

28 that define an exhaust flow restrictor 70. The exhaust flow restrictor 70 (which may be adjustable) is structured to restrict the flow of gas to the exhaust port 28 communicated with atmosphere. As a result, pressure increase in the chamber 22 (i.e., upon exhalation) will increase the pressure drop across the exhaust flow restrictor 70 which allows gas to gradually vent to atmosphere when the exhaust port 28 is opened, i.e., exhaust flow restrictor 70 restricts flow so flow does not exceed the maximum flow rate at the exhaust port 28. hi addition, the exhaust flow restrictor 70 may help control the rate at which the diaphragm 40 expands.

[0050] In one form of the invention, pressure from the PAP device is used to counterbalance the diaphragm 40. By controlling the pressure in the PAP device one may

control the diaphragm 40 and hence the venting through the exhaust valve 54. See for example International Patent Application PCT/IB2007/001837 the contents of which are hereby expressly incorporated by cross-reference.

[0051] In one form the exhaust valve 54 includes a conical valve plunger that allows finer control over the rate of flow through the valve.

[0052] In one form inlet valve 52 includes a piston element that allows a range of different flows through the outlet valve while the inlet valve remains closed. For example, the piston element may completely close the inlet valve in a range of different positions (part- way through, all the way through) while the exhaust valve is moving through a range of different degrees of openness.

[0053] In one form the position of the arm 60 is relayed to a flow generator, e.g. via a rotation sensor at axis 65 that would provide appropriate breath data to the machine which could enhance therapy further; e.g. reduce pressure further on exhalation.

[0054] In one form the diaphragm has an adjustable spring constant.

[0055] While the invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment. In addition, while the invention has particular application to patients who suffer from OSA, it is to be appreciated that patients who suffer from other illnesses (e.g., congestive heart failure, diabetes, morbid obesity, stroke, bariatric surgery, etc.) can derive benefit from the above teachings. Moreover, the above teachings have applicability with patients and non-patients alike in non-medical applications.