WO2003026730A1

WO2003026730A1 - Flow switch

Info

Publication number: WO2003026730A1
Application number: PCT/NZ2002/000192
Authority: WO
Inventors: Mehdi Shahbazpour; Michael John Blood Trousdell; Craig Robert Prentice
Original assignee: Fisher & Paykel Healthcare Limited
Priority date: 2001-09-25
Filing date: 2002-09-25
Publication date: 2003-04-03

Abstract

A flow switch for a CPAP breathing system uses a Coanda effect to switch a flow of CPAP gases away from a patient outlet port (3) during patient exhalation. The flow switch has an inlet passage (2) leading to a constricted nozzle (5). A chamber (6) immediately downstream from the constricted nozzle (5) has a patient outlet passage (3) and a vent passage (4). A first wall (7) extends from the nozzle to patient outlet passage (3). A second wall (8) extends from the nozzle (5) to the vent passage (4). Separation between the wall grows moving away from the nozzle (5). Provision is made for influencing flow from the nozzle toward the first wall (7) during patient inhalation. The flow attaches to the first wall (7) during patient inhalation, and to the second wall (8) during patient exhalation.

Description

"FLOW SWITCH"

BACKGROUND TO THE INVENTION

Field of Invention

The present invention relates to a CPAP system and in particular to a flow switch for switching supplied gases between a patient outlet and a vent outlet.

Summary of the Prior Art

One of the disadvantages of CPAP treatment for obstruction sleep apnea is that it effectively reverses the normal breathing function. The patient is supplied with gases at above ambient temperatures through a conduit and face mask. The patient relaxes to breath in but requires additional effort to breath out against the applied positive pressure.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a flow switch for a CPAP breathing system which goes someway to overcoming the above mentioned disadvantage or which will at least give the public a useful choice.

Accordingly in a first aspect the invention consists in a flow switch for a CPAP breathing system including: an inlet passage leading to a constricted nozzle, a chamber immediately downstream of said constricted nozzle, a patient outlet passage from said chamber, a vent passage from said chamber, said chamber including first and second walls extending away from said nozzle, on opposite sides of said nozzle, with growing separation between said walls moving away from said nozzle; said first wall leading to said patient outlet passage, and said second wall leading to said vent passage; and flow directing means for influencing flow from said nozzle towards said first wall during patient inhalation.

In a further aspect the invention consists in a flow switch as described above wherein the flow directing means comprises a control pressure port opening in said first wall adjacent said nozzle, said opening presenting a pressure which varies according to the patient breathing cycle.

In a further aspect the invention consists in a flow switch as described above wherein the chamber is configured such that the exit flow from said nozzle creates a smaller separation bubble against said first wall than against said second wall.

In a still further aspect the invention consists in a system for breathing assistance comprising: a CPAP delivery device, a patient interface, a breathing circuit connecting between said CPAP delivery device and said patient interface, and a flow switch as described above interposed in said circuit or integrated in said CPAP delivery device or patient interface.

In a further aspect the present invention may broadly be said to consist in a flow switch for a CPAP breathing system which uses the coanda effect to switch a flow of CPAP gases away from a patient outlet port during patient exhalation.

This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

The invention consists in the forgoing and also envisages constructions of which the following gives examples.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an isometήc view of a flow switch device according to a preferred embodiment of the present invention as viewed from the outlet end of the device.

Figure 2 is a plan view one half component of the device according to the preferred embodiment, showing the internal passages; the other half component being symmetrical.

Figure 3 is an isometric view of the upper half component of the device of Figure 1, turned over to show the cavities forming the flow passages thereof.

Figure 4a - 4b are plan elevations equivalent to that of Figure 2, demonstrating the air flows during operation of the device in use. In particular:

Figure 4a shows the device with flow attached to the patient outlet and the patient inhaling, and,

Figure 4b shows the device with flow attached to the vent outlet and the patient exhaling.

Figure 5 is a plan view of one half component of the device according to the preferred embodiment, showing the geometric parameters than can be varied to vary the relative size and position of the separation bubbles adjacent the walls.

Figure 6 shows a plan elevation in cross section of the flow switch device according to an alternative embodiment of the present invention, in which flow switching is influenced by a pair of pressure ports on opposite sides of the nozzle outlet.

Figure 7 is an illustration of a CPAP apparatus including a flow switch according to the embodiment of Figure 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One of the disadvantages of the CPAP treatment for obstructive sleep apnea is that it effectively reverses the normal breathing function. The patient has to relax to breath in and requires effort to breath out. The device of the present invention attempts to reduce the effort required by the patient to exhale.

The device 1 includes an input connection 2 and two outlet connections 3, 4. One outlet connection is connected to the mask worn by the patient, and the other outlet connection 4 acts as a vent to the atmosphere. The main function of the device is to direct the CPAP flow to the vent 4 at the time of exhalation and to redirect it to the patient outlet 3 when exhalation is completed. By doing so the pressure faced by the patient is reduced when exhaling, and less effort is required to exhale. This is achieved in part by utilising a phenomenon known as the Coanda Effect, which is associated with fluid jets.

Consider a jet of air emerging from a nozzle into a cavity where air has near zero velocity. Due to its turbulent behaviour, the jet carries with it some of the surrounding air. The jet spreads and its mass flow rate increases with distance downstream. This extra mass comes from the surrounding air. If a wall is placed near the jet the air around the jet has very little room to move. This results in high velocity gradients and ultimately in a low-pressure vortex in the space between the jet and the wall. The low pressure vortex causes the jet to bend towards the wall and the jet attaches the wall some distance downstream. This is called the Coanda Effect and the region in vortex is called the separation bubble.

If there is a wall on either side of the jet, the jet will bend towards the wall with the smallest separation bubble. This means that regions of differing pressures are created on either side of the jet, inducing a resultant force which will push the jet until it is forced to become detached. One way of detaching the flow from the wall is to create a pressure gradient along the wall. This can be achieved by blocking the flow downstream or applying aback flow to it. Once the jet is detached from the wall, it becomes unstable and if the pressure gradient is applied long enough it will flick to the other wall and attach to it. Another way of detaching flow is to alter the pressure balance between either side of the jet at the nozzle.

Referring to Figures 1 to 3 the device according to the preferred embodiment of the present invention comprises a component for including in a CPAP gases supply circuit. The component is formed from a pair of symmetric half shells which have cavities formed in their abutting faces. With the half-shells connected the cavities form a series of internal passages between inlet port 2, patient outlet 3 and vent outlet 4. These passages include a nozzle 5 immediately after the inlet port 2 and a chamber 6 immediately after the nozzle 5. The chamber is bifurcated to have a pair of legs 13, 14 extending to the patient outlet and vent outlet respectively.

The chamber 6 has a ceiling surface 12 and a corresponding parallel floor. It includes side wall surfaces 7 and 8 extending from near the nozzle 5 to jom the chamber legs 13 and 14 respectively. The nozzle 5 is configured to provide a flow jet into the chamber 6 in a first direction ('the first direction'), preferably chosen to correspond with the flow inlet direction into the inlet port 2. The patient outlet wall 7 is positioned closer to the first direction than is the vent outlet wall 8. In the preferred embodiment of the invention the relative closeness of wall 7 to the first direction compared to the closeness of wall 8 to the first direction is achieved by different relative inclinations of these walls away from the first direction. In particular the angle between the wall 7 and the first direction, represented by arrow 20, is less than the angle between the wall 8 and the first direction 20.

Alternatively the creation of a smaller "separation bubble" adjacent the wall which will set the default flow path, can be achieved by several other means. With reference to Figure 5, changing the combination of geometric parameters such as setback (D_x & D₂), nozzle width (W), nozzle to splitter gap (L) and wall angle (θ_x & θ₂), will affect the size and position of the separation bubble that forms adjacent each inclined wall. This will determine the bias and therefore the inclination of the jet towards the corresponding wall with the smallest separation bubble.

The preferred construction of the flow switch device includes a pair of symmetrical half shells. The half shells form upper and lower halves of the device. Each half shell includes either the lower or upper half of each of the flow features referred to above. Such a half shell is depicted in Figures 2 and 3. In particular an upper half shell 10 includes a block of material within with the flow passages are formed as a series of cavities in one face. These cavities include the chamber 6 with side walls 7, 8 and ceiling 12, the chamber legs 13 and 14, nozzle 5, inlet port 2 and outlet ports 3 and 4.

The half shell 10 demonstrates some aspects of the construction in more detail. The chamber 6 is a substantially constant height. The nozzle 5 is formed as a vertical slot extending between the ceiling and floor of the chamber 6 at one end of the chamber 6. The gases inlet 2 for the component includes a cylindrical portion 17 and tapering faces 16 leading to the nozzle 5. The patient outlet port 3 includes a cylindrical portion 18 for connecting with a patient site connector and tapering faces 15 providing a transition between patient leg 13 of chamber 6 and the cylindrical portion 18. The vent port 4 includes a cylindrical portion 30 for connecting with a conduit connector and tapering faces 32 providing a transition between vent leg 28 of chamber 6 and the cylindrical portion 30.

In use the vent port 4 may be connected with a flow or pressure regulating device. The flow or pressure regulating device may be chosen according to individual requirements of the flow switch and the individual patient. For example the regulating device may comprise an opening of suitable size. The opening size may be set according to the CPAP pressure to be similar to the flow restraint provided by a patient during inhalation.

In the completed construction depicted in Figure 1 the upper half shell 10 and lower half shell 11 are joined to form the completed flow switching unit. The flow switching unit has cylindrical inlet port 2 and cylindrical patient outlet port 3. The inlet port 2 is for connection with a supply side connector. The patient outlet port 3 is for connection with a patient side connector, for example on a CPAP delivery mask or the like. It will be appreciated that the device according to the present invention could instead be incorporated as a part of a CPAP delivery mask, other CPAP patient interface or into the CPAP delivery machine, rather than being a stand alone component.

Each of the components 10, 11 may be constructed from a suitable plastic material by suitable manufacturing technique. For example they might be manufactured from polypropylene by injection moulding. They may be joined by any technique suitable to the chosen material, for example hot plate welding, ultrasonic welding, adhesive fixing, fixing by mechanical fasteners such as screws, or mechanically fixing by interaction of inbuilt clips or engagements.

In use CPAP gases flow enters the device 1 at inlet port 2 and is passed through nozzle 5. It is thus turned into a jet and enters the cavity 6 after the nozzle. The flow will choose to attach to the wall 7 with smaller mclination angle since it has a smaller separation bubble. This preferred wall 7 takes the flow to the patient output 3. This flow situation is depicted in Figure 4a

When the patient breathes back against this flow, this increases the pressure at the patient outlet 3. This creates a pressure gradient on the patient outlet wall 7 and causes the flow to detach from the patient wall 7 and attach to the opposite wall 8 that leads to the vent outlet 4. This flow situation is depicted in Figure 4B.

When the exhalation load is lifted from the patient outlet 3 , a slight suction force applied by the patient is sufficient to switch the flow back to the patient wall 7.

An alternative embodiment of the present invention is illustrated in Figures 6 and 7. In this alternative embodiment creation and size of the separation bubble is influenced by a pair of pressure ports located on opposite sides of the nozzle outlet. One of these pressure ports provides a prevailing pressure related to the prevailing pressure inside the patient mask. The other port provides a reference pressure against which flow switching is effectively determined.

In Figures 6 and 7 features in common with the first embodiment illustrated with reference to Figures 1 to 3 share the same reference numerals. In contrast to the embodiment of Figures 1 to 3 the attachment of the flow to one or other wall (7 or 8) of the chamber 6 is not primarily influenced by the chamber geometry. Accordingly chamber geometry may be symmetric, or may be selected to work with the chosen reference pressure/control pressure continuation.

A pair of ports 100 and 108 are provided on opposite sides of the chamber 6 adjacent the nozzle outlet. Port 100 opens at the nozzle end of patient outlet wall 7. Port 108 opens at the nozzle outlet end of opposite wall 8. The control port 100 is provided with a prevailing pressure based on the pressure within the patient interface(usually a mask 132).

In one form this is through a direct pressure line connection between the patient mask cavity and the port 100. For example passage 106 leads to a control pressure port on an outer surface of the flow switch, and a pressure line 104 has a connector 102 engaged with this port. As indicated in Figure 7 the pressure line 104 extends to the patient mask where it communicates with the patient mask cavity. Thus the prevailing pressure within the patient mask 132 is transmitted to the control port 100.

In this embodiment with a discreet flow switch at an immediate point along the breathing conduit between a CPAP machine 134 and the nasal mask 132 a conduit 140 will connect between the flow switch 130 and the nasal mask 132. For convenience the pressure lme 104 maybe cHppedto the flow switch 130 by clip 142 and clipped at spaced intervals to the breathing conduit 140 by clips 144. The clips 144 may clip independently onto the conduit 140 and the pressure line 104.

Thus with patient breathing a negative pressure (on inhalation) in the nasal mask 132 will be transmitted to the control port 100. This will draw the flow toward patient outlet wall 7. During patient exhalation the positive pressure within the mask 132 will be transmitted to port 100. This increased pressure at the control port 100 will allow the flow to separate from wall 7 and attach temporarily to the opposite wall 8, drawn there by a lesser pressure. This lower pressure may be produced by the flow separation bubble generated from the chamber geometry or may be applied there by reference pressure port 108.

Where a reference pressure port 108 is provided in the inclined wall 8 of the chamber 6 a gas pressure is preferably applied to it that is related to the operating pressure of CPAP machine 134. For example the CPAP machine 134 may be provided with a reference pressure output for this purpose and be connected with the reference pressure port 108 by a reference pressure line 112. A passageway 114 in the flow switch 130 may extend from the reference pressure port 108 to an outer surface of the switch 130, with a connector 110 joining the reference pressure line 112 to the passage 114. The reference pressure line may be secured to the flow switch 130 by one or more clips 146, and the breathing circuit 148 by regularly spaced clips 150. For convenience the pressure line 112 may terminate adjacent the respiratory gases outlet port 152 of the CPAP machine. The connection for the conduit 148 and the pressure line 112 may be integrated into a single connector.

A wide variation is possible in this embodiment, in the form described and shown in the drawings is merely illustrative. For example, depending on the prevailing conditions, it may be necessary to amplify the control pressure at port 100 to account for a limited variation in mask pressure during breathing cycles. In that case a fluid amplifier may be provided at some point in the flow path between the patient mask and the control port 100.

The reference pressure port 108 may be provided with an operating pressure that is varied automatically CPAP pressure is increased, or may be varied manually (for example set for an individual user profile), may be varied independently of machine pressure or may be constant. It will be appreciated that this reference pressure at port 108 operates, together with the influence of any chamber geometry, as a threshold about which control port 100 switches the flow between walls 7 and 8. Chamber geometry is not the primary influencing factor in flow switching, although it can be selected to enhance or moderate the effects of the prevailing control and reference pressures.

Additional venting passages 120 and 122 may be provided toward the outlet end of chamber 6. The passage 120 extends between the vent outlet wall 8 and the outside surface of the flow switch. The passage 122 extends between the patient outlet wall 7 and the outside surface of the flow switch. In a switching situation the bubble between the flow jet and the wall to which it is attached grows under the influence of the higher pressure control port or by back pressure from the patient outlet, or both. It extends along the wall until it reaches the vent. The vent is at higher pressure than the separation bubble. Air rushes in through vent and helps the jet switch over to other wall.

The present invention uses the coanda effect in a switch for the purpose of venting the CPAP flow when the patient under CPAP treatment exhales. This reduces the pressure faced by the patient at the time of exhalation, improving the comfort level of the patient under treatment.

Claims

CLAIMS:

1. A flow switch for a CPAP breathing system including: an inlet passage leading to a constricted nozzle, a chamber immediately downstream of said constricted nozzle, a patient outlet passage from said chamber, a vent passage from said chamber, said chamber including first and second walls extending away from said nozzle, on opposite sides of said nozzle, with growing separation between said walls moving away from said nozzle; said first wall leading to said patient outlet passage, and said second wall leading to said vent passage; and flow directing means for influencing flow from said nozzle towards said first wall during patient inhalation.

2. A flow switch as claimed in claim 1 wherein said flow directing means comprises a control pressure port opening in said first wall adjacent said nozzle, said opening presenting a pressure which varies according to the patient breathing cycle.

3. A flow switch as claimed in claim 2 wherein said control pressure port presents a pressure which is a function of the pressure within the patient interface or mask.

4. A flow switch as claimed in claim 3 wherein a gases supply passage extends between said control pressure port opening and the inside of the patient interface or mask.

5. A flow switch as claimed in any one of claims 1 to 4 including a reference pressure port opening in said second wall adjacent said nozzle, said reference pressure port presenting a pressure within the range of said varymg pressure presented by said control pressure port.

6. A flow switch as claimed m claim 1 wherein said chamber is configured such that the exit flow from said nozzle creates a smaller separation bubble against said first wall than against said second wall.

7. A flow switch as claimed in claim 6 wherein the angle of said first wall relative to the initial flow exit direction from said nozzle is less than the angle of said second wall relative to the initial flow exit direction from said nozzles; said first wall leads to said patient outlet passage, and said second wall leads to said vent passage.

8. A flow switch as claimed in claim 6 wherein a setback distance to said first wall from the exit of said nozzle is less than a setback distance to said second wall from the exit of said nozzle; said first wall leads to said patient outlet passage, and said second wall leads to said vent passage.

9. A flow switch as claimed in claim 7 wherein a setback distance to said first wall from the exit of said nozzle is less than a setback distance to said second wall from the exit of said nozzle; said first wall leads to said patient outlet passage, and said second wall leads to said vent passage.

10. A flow switch as claimed in any one of claims 1 to 9 wherein said nozzle and said immediately subsequent chamber include a floor surface and a ceiling surface with a substantially constant separation between said floor surface and said ceiling surface, said nozzle being a slot with substantially constant profile from said floor surface to said ceiling surface.

11. A flow switch as claimed in claim 10 wherein said inlet passage is configured with a substantially cylindrical entry port for receiving a breathing circuit connector.

12. A flow switch as claimed in claim 11 wherein said inlet passage includes a tapering transition between said cylindrical portion and said nozzle slot.

13. A flow switch as claimed in claim 10 wherein said chamber is bifurcated at its end away from said nozzle to have a first leg extending to said patient outlet and a second leg extending to said vent passage.

14. A flow switch as claimed in claim 13 wherein preferably said patient outlet passage includes a substantially cylindrical exit port for receiving a breathing circuit connector.

15. A flow switch as claimed in claim 14 wherein said patient outlet passage includes a tapering transition between a cylindrical portion thereof and said first leg of said chamber.

16. A flow switch as claimed in claim 13 wherein preferably said vent passage includes a substantially cylindrical exit port for receiving a connection to a device for setting or varying pressure at the vent passage.

17. A flow switch for a CPAP breathing system which uses the coanda effect to switch a flow of CPAP gases away from a patient outlet port during patient exhalation.

18. A flow switch substantially as herein described with reference to and as illustrated by Figures 1 to 3 of the accompanying drawings.

19. A flow switch substantially as herein described with reference to and as illustrated by Figures 6 and 7 of the accompanying drawings.

20. A system for breathing assistance comprising: a CPAP delivery device, a patient interface, a breathing circuit connecting between said CPAP delivery device and said patient interface, and a flow switch as claimed in any one of claims 1 to 19 interposed in said circuit or integrated in said CPAP delivery device or patient interface.