WO2000043060A1

WO2000043060A1 - Flow directing device and system for supplying breathable gas to a patient

Info

Publication number: WO2000043060A1
Application number: PCT/AU2000/000033
Authority: WO
Inventors: Michel Calluaud
Original assignee: Resmed Limited
Priority date: 1999-01-21
Filing date: 2000-01-21
Publication date: 2000-07-27
Also published as: AUPP826899A0

Abstract

The flow directing device (20) comprises an inlet (18) supplying breathable gas, a first outlet (22) communicating with the inlet (18) and a mask (24) for supplying the gas to a patient, and a second outlet (26) communicating with the inlet (18) and an opening (36) to atmosphere. The flow resistance from the inlet (18) towards the first outlet (22) is relatively high. The flow resistance from the inlet (18) towards the second outlet (26) is relatively low. The device (20) is adapted such that, during the absence of inhalation, the pressure at the second outlet (26) is lower than the pressure at the inlet (18) and the first outlet (22) and gas flows to atmosphere (36). During inhalation at least some gas flows to the mask (24). The device (20) may be used in a system with a blower (14), a control unit (76) and one or two spool valves (72, 92).

Description

FLOW DIRECTING DEVICE AND A SYSTEM FOR SUPPLYING

BREATHABLE GAS TO A PATIENT

FIELD OF THE INVENTION

The present invention relates to a flow directing device and a system for supplying breathable gas to a patient's airways incorporating same.

The invention has been developed primarily for use in Continuous Positive Airway Pressure (CPAP) treatment apparatus used in the CPAP treatment of, for example, Obstructive Sleep Apnea (OSA) and other ventilatory assistance treatments such as Non Invasive Positive Pressure Ventilation (NIPPV) and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to these particular uses. BACKGROUND OF THE INVENTION

CPAP treatment is a common ameliorative treatment for breathing disorders including OSA. CPAP treatment, as described in US Patent No. 4,944,310, provides pressurized air or other breathable gas to the entrance of a patient's airways at a pressure elevated above atmospheric pressure, typically in the range 4-20cm H2O.

It is also known for the level of treatment pressure to vary during a period of treatment in accordance with patient need, that form of CPAP being known as automatically adjusting nasal CPAP treatment, as described in US Patent No. 5,245,995.

NIPPV is another form of treatment for breathing disorders which can involve a relatively higher pressure of gas being provided in the patient mask during the inspiratory phase of respiration and a relatively lower pressure or atmospheric pressure being provided in the patient mask during the expiratory phase of respiration. In other NIPPV modes the pressure can be made to vary in a complex manner throughout the respiratory cycle. For example, the pressure at the mask during inspiration or expiration can be varied through the period of treatment.

Typically, the ventilatory assistance for CPAP or NIPPV treatment is delivered to the patient by way of a nasal mask. Alternatively, a mouth mask or full face mask or nasal prongs can be used. In this specification any reference to a mask is to be understood as incorporating a reference to a nasal mask, mouth mask, full face mask or nasal prongs.

In this specification any reference to CPAP treatment is to be understood as embracing all of the above described forms of ventilatory treatment or assistance. A CPAP apparatus broadly comprises a flow generator constituted by a continuous source of air or other breathable gas such as a hospital piped supply or a blower. In the latter case, an electric motor drives the blower and is typically controlled by a servo-controller under the control of a microcontroller unit. In either case, the gas supply is connected to a conduit or tube (hereinafter referred to as "the_ inlet conduit"), which in turn is connected to a patient mask which incorporates, or has in close proximity, an exhaust to atmosphere for venting exhaled gases.

The patient mask generally includes one or more openings or diffusers through which passes a continuous flow of gas for entraining and thus withdrawing exhaled (CO2 rich) gases from within the mask. This continuous flow is known as CO2 washout flow and generally requires a flow of about 20-40 1/min.

During patient inhalation, additional gas in excess of the CO₂ washout flow flows from the blower to the mask to satisfy the patient's inspiratory needs. During patient exhalation, some of the exhaled gas is forced into the inlet conduit connecting the mask to the blower and the remainder passes to atmosphere through the diffusers. At the end of exhalation, any of the exhaled gas that flowed into the inlet conduit is eventually washed out to atmosphere through the diffusers as a result of the continuous CO2 washout flow described above.

This known arrangement has several disadvantages. Firstly, during inspiration, the pressure at the mask is lower than the pressure at the outlet of the blower. This is because the gas flow delivered to the patient (approximately 5-10 1/min), and the additional continuous flow through the difftiser (approximately 20-40 1/min), results in a pressure drop along the inlet conduit due to its internal frictional resistance. During exhalation, the gas flow within the inlet conduit stops and the mask pressure increases to approach the pressure at the blower outlet.

Secondly, during expiration, some of the exhaled gas is forced into the inlet conduit towards the blower. This exhaled air has a high C0₂ content and must be washed out of the mask before the inspiration commences. This necessitates a larger washout gas flow and a correspondingly larger and more expensive blower than would be needed if the exhaled gas did not enter the inlet conduit.

Thirdly, the continuous washout gas flow, in combination with the exhaled gas passing through the diffusers, produces noise in close proximity to the patient and/or bed partner which reduces sleep comfort and can lead to patient non-compliance. Fourthly, the continuous washout gas flow can be directed toward the patient or the bed partner which again reduces sleep comfort and can also lead to patient non- compliance.

Fifthly, the large washout gas flow places an additional load on the blower which increases the noise produced by the motor and blower assembly. This also reduces the sleep comfort of the patient and/or bed partner and can also lead to patient non-compliance.

It is an object of the present invention to substantially overcome or at least ameliorate one or more of the disadvantages of the prior art. SUMMARY OF THE INVENTION

Accordingly, in a first aspect, the present invention provides a flow directing device comprising: an inlet adapted for receiving a supply of breathable gas; a first outlet in fluid communication with the inlet and a mask for communicating the supplied breathable gas to a wearer's airways, the flow resistance from the inlet towards the first outlet being relatively high; and a second outlet in fluid communication with the inlet and an opening to atmosphere, the flow resistance from the inlet towards the second outlet being relatively low, wherein the device is adapted such that, during an absence of inhalation, the pressure at the second outlet is lower than the pressure at the inlet and the first outlet and the supplied gas is directed towards the second outlet and so to said opening, and, during inhalation, the pressure at the first outlet is lowered below the pressure at the inlet and the second outlet and at least some of the supplied gas is directed to the first outlet and so to the mask.

The absence of inspiration desirably includes exhalation or pauses in breathing. Desirably, when the supplied gas is directed from the inlet to the second outlet, gas is also drawn from the first outlet to the second outlet.

The device preferably includes means to smoothly direct the supplied gas towards the second outlet and away from the first outlet. The gas being smoothly directed towards the second outlet follows the path of least resistance, as determined by the relative pressure gradients in each direction, from the inlet towards the second outlet, not the first outlet. The directing means is preferably in the form of a tapered annular channel converging towards the second outlet. The first outlet and the second outlet are desirably axially aligned with the annular channel. The inlet is desirably axially or radially aligned with the annular channel. The inlet of the device is preferably cylindrical. The first and second outlets are preferably also cylindrical, the internal diameter of the first outlet being less than the internal diameter of the second outlet.

The inlet is preferably supplied gas through an inlet conduit connected to a breathable gas supply apparatus. The first outlet is preferably directly connected to an inlet of the mask or indirectly connected by a flexible conduit interposed between the first outlet and the mask inlet. The second outlet is preferably connected to one end of an outlet conduit, the other end of the outlet conduit being connected to the opening. The opening is preferably positioned, in use, remote the patient mask. In one form, the opening is positioned, in use, at, or near, the breathable gas supply apparatus. The opening preferably includes a diffuser adapted to allow adjustment of the flow resistance of the opening.

In a second aspect, the present invention provides a system for providing breathable gas to a patient's airways, the system comprising: a breathable gas supply apparatus adapted to provide a supply of breathable gas pressurized above atmospheric pressure; an inlet conduit for communicating the breathable gas supply to the inlet of the flow directing device of the first aspect; a mask for connecting to the first outlet of the flow directing device of the first aspect, the mask adapted to communicate the gas supplied thereto to the patient's airways; and an outlet conduit for connecting to the second outlet of the flow directing device of the first aspect.

Preferably, the system also includes a first controllable flow restrictor adapted to restrict the flow of gas through the outlet conduit during patient inhalation. In one form, the first controllable flow restrictor is a first spool valve driven between maximum and minimum restriction positions by an electromagnetic actuator.

Desirably, the system also includes a second controllable flow restrictor adapted to restrict the flow of gas to the inlet conduit during patient exhalation. In one form, the second controllable flow restrictor is a second spool valve driven between maximum and minimum restriction positions by an electromagnetic actuator. In the minimum restriction position, the gas supply preferably passes through the second spool valve before the inlet conduit. In the maximum restriction position, the gas supply preferably passes through a fixed orifice and the second spool valve before the inlet conduit. This embodiment has application in bi-level CPAP treatment. The first and second spool valves are preferably driven by a common electromagnetic actuator.

The first spool valve is desirably at the maximum restriction position whilst the second spool valve is at the minimum restriction position and vice versa.

The system preferably also includes a control unit. The control unit desirably determines patient inspiration and exhalation from signals received from flow and/or pressure sensors in the inlet conduit and/or outlet conduit. The control unit is adapted to control the electromagnetic actuator in response to determining patient inspiration and expiration. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic view of a first system for supplying breathable gas incorporating a first embodiment of a flow directing device according to the invention;

Fig. 2 is an enlarged cross-sectional view of the flow directing device shown in Fig. 1;

Fig. 3 is a schematic view of a second system for supplying breathable gas incorporating the first embodiment of the flow directing device according to the invention during inspiration;

Fig. 4 is a schematic view of the system shown in Fig. 3 during expiration; Fig. 5 is a schematic view of a third system for supplying breathable gas incorporating the first embodiment of the flow directing device according to the invention during inspiration;

Fig. 6 is a schematic view of the system shown in Fig. 5 during expiration; and

Fig 7 is an enlarged cross-sectional view of a second embodiment of a flow directing device according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figs. 1 shows a first system 10 for providing breathable gas to a patient's airways. The system 10 comprises a breathable gas supply apparatus 12 having a blower 14 adapted to provide a supply of breathable gas pressurized above atmospheric pressure. An inlet conduit 16 communicates the breathable gas supply from the blower 14 to an inlet 18 of a first embodiment of a flow directing device 20.

The flow directing device 20 also includes a first outlet 22 connected to a patient mask 24 and a second outlet 26 connected to an outlet conduit 28. The flow directing device 20 is shown in enlarged detail in Fig. 2. The fιrst_ outlet 22 and the second outlet 26 are generally cylindrical and share a common longitudinal axis 29. The inlet 18 is also cylindrical and extends radially between the first outlet 22 and the second outlet 26.

The flow directing device 20 is configured to provide differing amounts of flow resistance to the flow paths from the inlet 18 to the first outlet 22 and from the inlet 18 to the second outlet 26. Firstly, the internal diameter of the first outlet 22 is less than that of the second outlet 26. Secondly, gas travelling from the inlet 18 to the second outlet 26 is relatively smoothly directed to the second outlet 26 by curved internal surfaces 30 and 32 which define an annular channel 33 that converges towards the second outlet 26. The converging of the internal surfaces 30 and 32 also causes the gas to accelerate when passing through the channel 33. Thus, the momentum of the supplied gas is smoothly directed through the channel 33 and towards the second outlet 26. However, for gas to travel from the inlet 18 to the first outlet 22 it must undergo an approximately 180 degree change in direction at end 34 of the channel 33 against its momentum.

As a result of these features, when gas is being supplied to the inlet 18, and the first outlet 22 and the second outlet 26 are only restricted by connection to the mask 24 and the outlet conduit 28 respectively, (and the mask 24 and outlet conduit 28 are open to atmosphere) the pressure at the second outlet 26 is lower than the pressure at the inlet 18 and the first outlet 22 and gas is thus directed from the inlet 18 to the second outlet 26. The Venturi effect of the gas flowing to the second outlet 26 also creates a relatively low pressure region in the first outlet 22 which entrains and draws gas from the first outlet 22 to the second outlet 26.

The conditions described above are essentially static. In use, and during patient exhalation, the pressure in the mask 24 increases which also increases the pressure at the first outlet 22 to higher than the inlet 18 and the first outlet 22. This further increases the washout effect described above. During patient inhalation, the pressure in the mask 24 and the first outlet 22 is lowered below that of the inlet 18 and second outlet 26 and some of the supplied gas is directed from the inlet 18 to the first outlet 22 and so to the mask 24 for breathing by the patient. In this way, the flow directing device 20 provides a CO₂ gas washout flow that continuously removes any exhaled gas from the mask 24.

The main advantage of the system 10 and the flow directing device 20 is it allows the gas washout flow to be directed through the outlet conduit 28 to vent to atmosphere at a position remote the patient and/or their bed partner. Accordingly, the noise created by the washout flow venting is reduced from a patient and/or bed partner perspective and the gas flow is not directed towards the patient and/or their bed partner thereby increasing their sleep comfort.

In the system shown in Fig. 1, the outlet conduit 28 is conveniently terminated at a diffuser 36 located within the casing or housing of the breathable gas supply apparatus 12. The flow resistance of the diffuser 36 is adjustable to suit the flow and pressure breathing requirements of the patient.

A second embodiment of a flow directing device 60 is shown in Fig. 7. The second embodiment functions in a consistent manner to the first embodiment and like reference numerals to those used in describing the first embodiment will be used to denote like features in the second embodiment.

The main difference in the second embodiment is that inlet 18 and the second outlet 26 are arranged coaxially about the axis 29. The second outlet 26 is supported within the inlet 18 by radial connector 62. Multiple fins or ribs can also be used. The second embodiment allows the inlet conduit 16 and the outlet conduit 28 to be arranged coaxially. This advantageously reduces the number of tubes the patient has to accommodate in their sleeping environment and reduces the risk of tangling and the like. Further, coaxial conduits permit heat exchange from the relatively warmer exhaled gas to the relatively cooler supplied gas which results in warming of the supplied gas and increased patient comfort.

Fig's. 3 and 4 show a second system 70 for supplying breathable gas to a patient's airways that utilizes the first embodiment of the flow directing device 20. Like reference numerals to those used in describing the first system 10 will be used to denote like features in the second system 70. The second system 70 is similar to the first system 10 except for the addition of a first controllable flow restriction device in the outlet conduit 28 in the form of first spool valve 72. The first spool valve 72 is driven by an electromagnetic actuator 74 between positions of maximum and minimum restriction of the outlet conduit 28. The system 70 also includes a control unit 76 which is adapted to determine when the patient is inhaling or exhaling from signals received from pressure and/or flow sensors 78 and 80 located in the inlet conduit 16 and the outlet conduit 28 respectively. Determining inspiration and exhalation from such signals is well known in the art.

When the control unit 76 senses inspiration it energizes the actuator 74 into driving the first spool valve 72 to a maximum restriction position, as shown in Fig. 3. In the preferred form shown, the first spool valve 72 fully occludes the flow area of the outlet conduit 28 in the maximum restriction position. This restriction, in combination with the patient inhaling, causes the pressure at the first outlet to be lower than the pressure at the inlet 18 and the second outlet 26 and results in at least some of the gas supply being directed to the first outlet 22 and so to the patient mask 24 for breathing. When the control unit 76 senses exhalation it energizes the actuator 74 into driving the first spool valve 72 to a minimum restriction position, as shown in Fig. 4. In the preferred form shown, the first spool valve 72 provides no obstruction to the flow area of the outlet conduit 28 in the minimum restriction position. This lack of restriction, in combination with the patient exhaling, causes the pressure at the second outlet 26 to be lower than the pressure at the inlet 18 and the first outlet 22 and results in at least some of the gas supply being directed to the second outlet 26 and so to the outlet conduit 28 and the diffuser 36.

In addition to the advantages of the first system 10, the volume of gas supplied by blower 12 of the second system 70 is advantageously reduced. More particularly, during inspiration, there is no washout flow of 20-40 1/min as the only gas flowing through the system 12 is the 5-10 1/min that is being inhaled by the patient. This lower flow rate reduces the pressure drop between the blower 14 and the mask 24 that is caused by the internal frictional resistance of the gas passing through the inlet conduit 16. Fig's. 5 and 6 show a third system 90 for providing breathable gas to a patient's airways that also utilizes the first embodiment of the flow directing device 20. Like reference numerals to those used in describing the second system 70 will be used to denote like features in the third system 90.

The third system 90 is similar to the second system 70 except for the addition of a second controllable flow restriction device in the inlet conduit 16 in the form of a second spool valve 92. The second spool valve 92 is also driven by the electromagnetic actuator 74 between positions of maximum and minimum restriction of the inlet conduit 16.

When the control unit 76 senses inhalation it energizes the actuator 74 into driving the first spool valve 72 to a maximum restriction position and simultaneously driving the second spool valve 92 to a minimum restriction position, as shown in Fig. 5. In the preferred form shown, the gas supply flows past the second spool valve 92 into the inlet conduit 16. This unrestricted gas supply flow to the inlet conduit 16, in combination with the patient inhaling and the restricted outlet conduit 28, causes the pressure at the first outlet 22 to be lower than the pressure at the inlet 18 and the second outlet 26 and results in at least some of the supplied gas being directed to the first outlet 22.

When the control unit 76 senses exhalation it energizes the actuator 74 into driving the first spool valve 72 to a minimum restriction position and simultaneously drives the second spool valve 92 to a maximum restriction position, as shown in Fig. 6. In the preferred form shown, the maximum restriction position of the second spool valve 92 diverts the gas supply through a fixed orifice 94 before it can enter the inlet conduit 16. This restricted gas supply flow to the inlet conduit 16, in combination with the patient exhaling and the unrestricted outlet conduit 28, causes the pressure at the second outlet 26 to be lower than the pressure at the inlet 18 and the first outlet 26 and results in at least some of the gas supply being directed to the second outlet 26. Further, the second spool valve 92 also reduces the gas supply pressure to the patient during inspiration and the system 90 thereby provides gas supply in a bi-level regime. Further, the bi-level pressure supply can be achieved very simply and with a constant output blower, thereby obviating the need for an expensive and complicated blower motor speed control system.

The diffuser 36 and the fixed orifice 94 are generally configured such that the pressure of the gas supplied during expiration is approximately 50-60% of the pressure of the gas supplied during inspiration. However, this can be adjusted depending on the particular treatment being administered and individual patient requirements.

Although the invention has been described with reference to a preferred embodiment, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

CLAIMS:

1. A flow directing device comprising: an inlet adapted for receiving a supply of breathable gas; a first outlet in fluid communication with the inlet and a mask for communicating the supplied breathable gas to a wearer's airways, the flow resistance from the inlet towards the first outlet being relatively high; and a second outlet in fluid communication with the inlet and an opening to atmosphere, the flow resistance from the inlet towards the second outlet being relatively low, wherein the device is adapted such that, during an absence of inhalation, the pressure at the second outlet is lower than the pressure at the inlet and the first outlet and the supplied gas is directed towards the second outlet and so to said opening, and, during inhalation, the pressure at the first outlet is lowered below the pressure at the inlet and the second outlet and at least some of the supplied gas is directed to the first outlet and so to the mask.

2. The device as claimed in claim 1 , wherein the absence of inspiration includes exhalation or pauses in breathing.

3. The device as claimed in claim 1, wherein when the supplied gas is directed from the inlet to the second outlet, gas is also drawn from the first outlet to the second outlet.

4. The device as claimed in claim 1. further including means to smoothly direct the supplied gas towards the second outlet and away from the first outlet.

5. The device as claimed in claim 4. wherein the directing means is a tapered annular channel converging towards the second outlet.

6. The device as claimed in claim 5. wherein the first outlet and the second outlet are axially aligned with the annular channel.

7. The device as claimed in claim 5. wherein the inlet is axially aligned with the annular channel.

8. The device as claimed in claim 5 , wherein the inlet is radially aligned with the annular channel.

9. The device as claimed in claim 8, wherein the inlet and the second outlet are arranged coaxially.

10. The device as claimed in claim 1 , wherein the inlet is cylindrical.

11. The device as claimed in claim 1 , wherein the first and second outlets are cylindrical, the internal diameter of the first outlet being less than the internal diameter of the second outlet.

12. The device as claimed in claim 1, wherein the inlet is supplied gas through an inlet conduit connected to a breathable gas supply apparatus.

13. The device as claimed in claim 1, wherein the first outlet is directly connected to an inlet of the mask.

14. The device as claimed in claim 1 , wherein the first outlet is indirectly connected to an inlet of the mask by a flexible conduit interposed between the first outlet and the mask inlet.

15. The device as claimed in claim 1, wherein the second outlet is connected to one end of an outlet conduit, the other end of the outlet conduit being connected to the opening.

16. The device as claimed in claim 15, wherein the opening is positioned, in use, remote the patient mask.

17. The device as claimed in claim 15, wherein the opening is positioned, in use, at the breathable gas supply apparatus.

18. The device as claimed in claim 15, wherein the opening is positioned, in use, near the breathable gas supply apparatus.

19. The device as claimed in claim 15, wherein the opening includes a diffuser adapted to provide adjustment of the flow resistance of the opening.

20. A system for providing breathable gas to a patient's airways, the system comprising: a breathable gas supply apparatus adapted to provide a supply of breathable gas pressurized above atmospheric pressure; an inlet conduit for communicating the breathable gas supply to the inlet of the flow directing device defined in claim 1 ; a mask for connecting to the first outlet of said flow directing device, the mask adapted to communicate the gas supplied thereto to the patient's airways; and an outlet conduit for connecting to the second outlet of said flow directing device.

21. The system as claimed in claim 20, further including a first controllable flow restrictor adapted to restrict the flow of gas through the outlet conduit during patient inhalation.

22. The system as claimed in claim 21, wherein the first controllable flow restrictor is a first spool valve driven between maximum and minimum restriction positions by an electromagnetic actuator.

23. The device as claimed in claim 22, further including a second controllable flow restrictor adapted to restrict the flow of gas to the inlet conduit during_, patient exhalation.

24. The device as claimed in claim 23, the second controllable flow restrictor is a second spool valve driven between maximum and minimum restriction positions by an electromagnetic actuator.

25. The device as claimed in claim 24, wherein, in the minimum restriction position, the gas supply passes through the second spool valve before the inlet conduit.

26. The device as claimed in claim 24, wherein, in the maximum restriction position, the gas supply passes through a fixed orifice and the second spool valve before the inlet conduit.

27. The device as claimed in claim 24, wherein the first and second spool valves are driven by a common electromagnetic actuator.

28. The device as claimed in claim 24, wherein the first spool valve is at the maximum restriction position whilst the second spool valve is at the minimum restriction position and vice versa.

29. The device as claimed in claim 20, further also including a control unit.

30. The device as claimed in claim 29, wherein the control unit determines patient inspiration and exhalation from signals received from a flow sensor in the inlet conduit.

31. The device as claimed in claim 29, wherein the control unit determines patient inspiration and exhalation from signals received from a pressure sensor in the inlet conduit.

32. The device as claimed in claim 29, wherein the control unit determines patient inspiration and exhalation from signals received from flow pressure sensors in the inlet conduit.

33. The device as claimed in claim 29, wherein the control unit is adapted to control the electromagnetic actuator in response to determining patient inspiration and expiration.