Patent Description:
In modern clinical medicine, a respiratory apparatus is commonly used for patients with respiratory illnesses such as acute respiratory distress syndrome, severe asthma and chronic obstructive pulmonary disease, as well as used for anesthesia and respiratory management during surgery, first aid resuscitation, and even domestic use for supportive treatment. A respiratory apparatus is a vital medical device that can prevent and treat respiratory failure, reduce complications and prolong the patient's life.

Current respiratory apparatuses possess a number of drawbacks. For example, when air is drawn into a respiratory apparatus by a blower, noise is generated by the friction between the air flow and the gas inlet passage. The noise is particularly obvious when the respiratory apparatus is used in a quiet environment or when the patient is sleeping, potentially causing a physical and mental annoyance to the patient. Further, it can be difficult to monitor the gas composition or gas flow rate when there are substantial high frequency noises. The high frequency noises may be generated when supplying a high pressure gas and these can affect the detection conducted by a sensor in the respiratory apparatus.

It is therefore desirable to provide an improved respiratory apparatus with a sensor working effectively to monitor the gas flow and gas content, and/or a respiratory apparatus with reduced noises.

<CIT> discloses a system for reducing the noise generated by the mechanical ventilator, and the system includes a gas source, a manifold and a sound dampening apparatus.

<CIT> discloses a respiratory device, which includes an air inlet, an oxygen inlet, an inlet muffler and an outlet muffler.

The present invention provides a respiratory apparatus which can at least solve the technical problem of the noise generated by /at the gas inlet of the current respiratory apparatus, and/or improve the measurement of concentration of gas to be delivered to a user.

According to the invention, there is provided a respiratory apparatus including a first gas inlet for supplying a first gas to the respiratory apparatus; a second gas inlet connectable to a pressurized gas source to supply a pressurized gas; a mixing chamber for mixing the first gas and the pressurized gas, and a noise-damping member disposed downstream of the mixing chamber, where the respiratory apparatus further includes a flow sensor for determining a flow rate of the mixed stream of gas towards the humidifying chamber; and the noise-damping member (<NUM>) is cylindrical, has a cylindrical body insertable into the flow sensor and an end portion with a diameter greater than the diameter of the cylindrical body.

In an example, the respiratory apparatus further comprises a noise reduction device mounted on the respiratory apparatus, wherein the noise reduction device is in fluid communication with the first gas inlet. The noise reduction device comprises a body having a side wall and a noise reduction device gas outlet, and a cover configured to be detachably engageable with the body for forming a noise-reduction device gas inlet and a gas passage. Without intending to be limited by theory, it is believed that the respiratory apparatus of the present invention substantially minimize possible noises generated during supply of the pressurized gas and the supply of atmospheric air driven by a blower. The noise-damping member herein is particularly useful to improve the measurement conducted by one or more sensors arranged on, or in the respiratory apparatus, and especially those susceptible to frequency noises.

The figures herein are for illustrative purposes only and are not necessarily drawn to scale.

The present invention relates to a respiratory apparatus which requires a supply of a pressurized gas. The respiratory apparatus may be, but is not limited to, a humidifier, a respirator, a nebulizer, a continuous positive air pressure machine, an automatic positive air pressure machine, etc..

In an embodiment of the present invention, the respiratory apparatus includes a first gas inlet for supplying a first gas to the respiratory apparatus; a second gas inlet connectable to a pressurized gas source to supply a pressurized gas; a mixing chamber for mixing the first gas and the pressurized gas, and a noise-damping member disposed downstream of the mixing chamber. The first gas inlet and the second inlet are separate from each other allowing two streams of gas to enter the respiratory independently. In this context, the pressurized gas entered via the second gas inlet is considered as a second gas.

The gas useful herein typically includes atmospheric air, air enriched with oxygen gas, etc., as desired. In an embodiment, the first gas is atmospheric air which may be supplied to the respiratory apparatus at ambient room temperature, higher than room temperature, or lower than room temperature, as desired. In an embodiment, the first gas is at the ambient pressure of the surrounding environment and at ambient room temperature. In an embodiment, the second gas or the pressurized gas is provided by a pressurized gas source which may be, but not limited to, a compressed oxygen gas tank. The pressurized gas may be oxygen which is at a higher pressure than the surrounding environment. Other suitable pressurized gas may also be used according to the desired operation.

In an example, the mixing chamber is in fluid communication with the first and second gas inlet. The mixing chamber has two separate ports, a first port and a second port for respectively receiving the first gas and the second gas from the first and second gas inlet. The first port and the second port may be arranged on different surface of the mixing chamber so that when the two streams of gas enter into the mixing chamber, they may, for example, generate a vortex and mix with each other resulting in a mixed stream of gas. In a particular embodiment, the first port is arranged to be perpendicular to or at angle with respect to the second port so as to thoroughly mix the two streams of gas.

The mixing chamber of the present invention has a gas outlet for discharging the mixed stream of gas towards other parts of the respiratory apparatus for example a humidifying chamber, a drug adding chamber, a heating chamber or the like. In an embodiment, the mixed stream of gas is discharged towards a humidifying chamber for further processing before delivering to a user so that the delivered gas is at the optimum conditions.

However, it has been found that the mixing of a first gas and a second gas may cause enough noise and/or noise of a frequency (e.g., a whining or whistling noise) to bother users, especially when they are attempting to rest and/or sleep. It has further been found that this noise can be especially loud and/or annoying due to the frequency thereof. In addition, it has been found that the noise can be exacerbated when a gas is mixed with a pressurized gas.

Accordingly, the respiratory apparatus herein includes a noise-damping member disposed downstream of the mixing chamber for minimizing possible noises generated during supply of the pressurized gas. The noise-damping member is particularly useful to improve the measurement conducted by one or more sensors arranged on, or in the respiratory apparatus. It is particularly advantageous for the respiratory apparatus having an ultrasonic sensor which is susceptible to high frequency noises.

In an embodiment, the noise-damping member is in fluid communication with the mixing chamber, for example along the flow path of the mixed stream of gas discharging from the mixing chamber. The provision of the noise-damping member along the flow path effectively minimizes possible noises generated during operation. The noise-damping member is useful to absorb and/or reduce the noises generated in particular high frequency noises. In an embodiment, the noise-damping member is made of a sound absorbing material particularly, but not limited to, a sintered material. The sound absorbing material may be a porous material, for example, porous ceramic, porous plastics or porous polymeric foams, for absorbing noise. In an embodiment, the sound absorbing material is a sintered plastic, optionally porous, selected from sintered polyethylene (PE), sintered polyamide (PA), sintered polytetrafluoroethylene (PTFE), or sintered polyvinylidene fluoride (PVDF). In another embodiment, the noise-damping member is made of a metallic sintered material, optionally porous, and may include one or more of silver, nickel, titanium, aluminum, steel, stainless steel, bronze and the like.

The noise-damping member may be configured in any shape to be positioned along the flow path so as to absorb or reduce the undesirable noises. In an embodiment, the noise-damping member may be cylindrical, or in the form of a C-shape or a mesh. In another embodiment, the noise-damping member may be configured as a membrane or a filter which is permeable to gas, and such a noise-damping member may further act as a turbulence filter to minimize turbulence in the gas before discharging the gas to other part of the respiratory apparatus, thereby reducing noises. The respiratory apparatus may include more than one noise-damping member and each noise-damping member may be configured in different shape and provided at different position along the flow path, and preferably downstream of the mixing chamber.

Furthermore, it has been surprisingly found that the absorption and/or reduction of the undesirable noises helps to improve the accuracy of the measurements conducted by the sensor, especially an ultrasonic sensor; or a high frequency ultrasonic sensor.

In an embodiment, the respiratory apparatus has a sensor for determining the concentration of one or more gas components in the first gas, the pressurized gas or the mixed stream of gas. The sensor may be an ultrasonic sensor particularly a high frequency ultrasonic sensor. In an embodiment, an ultrasonic sensor is arranged downstream of the mixing chamber to determine the concentration of the mixed stream of gas, and/or before entering next processing chamber such as the humidifying chamber. In a particular embodiment, the ultrasonic sensor is disposed downstream of the noise-damping member so as to effectively minimize the noises generated.

In order to better monitor the air flow in the respiratory apparatus, the respiratory apparatus may further include a flow sensor for determining a flow rate of the gas in particular the mixed stream of gas towards the humidifying chamber. Flow sensors that are typically known in the art may be applied in the present invention anywhere within flow path.

The respiratory apparatus of the present invention may further include a noise reduction device and that the noise reduction device is in fluid communication with the first gas inlet. The combination with the noise reduction device can further help to reduce possible noises generated at the first gas inlet.

Turning to the figures, <FIG> shows an embodiment of a respiratory apparatus <NUM> which is provided as a humidifier to supply humidified gas to a user. The respiratory apparatus <NUM> has a gas mixing mechanism (see <NUM> at <FIG>) therein for facilitating the supply of gas to a humidifying chamber <NUM> for processing. After processing, the humidified gas will be delivered to a user via a breathing circuit connected to a discharge port <NUM> on the humidifying chamber <NUM>.

With reference to <FIG>, <FIG> and <FIG>, the gas mixing mechanism <NUM> includes a first gas inlet <NUM> allowing entry of atmospheric air into a mixing chamber <NUM>, a second gas inlet <NUM> connectable to a pressurized gas source for supplying a pressurized gas in particular, but not limited to, high pressure oxygen gas, to the mixing chamber <NUM>. A sealing ring <NUM> may be provided between the second gas inlet <NUM> and the mixing chamber <NUM> to avoid or minimize leakage of the pressurized gas. The mixing chamber <NUM> also has a gas outlet <NUM> for discharging the mixed stream of gas, and a check valve <NUM>. The check valve <NUM> may be provided at a recess <NUM> on the mixing chamber <NUM> to prevent back flow of the gas. The check valve <NUM> can be of any design an ordinary skill person in the art can appreciate. In this embodiment, the check valve <NUM> includes a silicone film arranged to cover the opening 215a. The silicone film or a part of the silicon film covering the opening 215a only allows an unidirectional gas flow from the second gas inlet <NUM> to the surrounding, and the opening 215b allows gas flows into the mixing chamber <NUM>. For example, when the pressurized gas enters the respiratory apparatus <NUM> particularly into the mixing chamber <NUM>, the pressure may be high enough to lift up the silicone film covering the opening 215a, and allows the pressurized gas to flow away via the opening 215a. The leaked gas may return to the mixing chamber <NUM> via the opening 215b, but not the opening 215a.

In this embodiment, the mixing chamber has a first port <NUM> for receiving the first gas inlet <NUM> and a second port <NUM> for receiving the second gas inlet <NUM>. In this embodiment, the first gas port <NUM> is separate from, and aligned perpendicular to the second port <NUM>. The first port may be connected to a blower <NUM> for receiving atmospheric air from the ambient environment. When the pressurized gas enters the respiratory apparatus <NUM> via the second gas inlet <NUM>, the atmospheric air concurrently enters into the mixing chamber <NUM> via the first gas inlet <NUM> and mixes with the pressurized gas. The two streams of gas may then be thoroughly mixed in the mixing chamber <NUM>. The resultant mixed stream of gas is then discharged past a flow sensor <NUM> downstream of and connected to the mixing chamber <NUM>. In this embodiment, the flow sensor <NUM> is arranged to determine the flow rate of the mixed stream of gas after existing the mixing chamber <NUM> such that an operator can monitor the gas flow.

In this embodiment, a noise-damping member <NUM> is provided at one end; or the downstream end, of the flow sensor <NUM>. In <FIG>, the noise-damping member <NUM> is made of a sound absorbing material such as sintered porous PE that is capable of absorbing high frequency noises generated by the respiratory apparatus. In particular, the high frequency noises are typically those generated during the supply of the pressurized gas at the second gas inlet <NUM>, and/or those generated during the mixing of the two steams of gas in the mixing chamber <NUM>. The noise-damping member <NUM> is configured in cylindrical form with a size engagable with the flow sensor <NUM>. The noise- damping member <NUM> engages with the flow sensor <NUM> at one end and allows the mixed stream of gas to continue to flow to another part of the respiratory apparatus <NUM>. As shown in <FIG>, the noise-damping member <NUM> has a cylindrical body 217a insertable into the flow sensor <NUM> and an end portion 217b with a diameter greater than the diameter of the cylindrical body 217a. The end portion 217b limits the movement of the noise-damping member <NUM> in the respiratory apparatus <NUM> so as to keep the noise-damping member <NUM> in place. The end portion 217b may also facilitate the connection between the flow sensor <NUM> and other components of the respiratory apparatus <NUM>. Such a configuration of the noise-damping member <NUM> is useful in manufacturing process, and in minimizing noises with stable connection between the components.

In an embodiment, that is not covered by the claims, an additional noise-damping member <NUM> may be provided between the mixing chamber <NUM> and the flow sensor <NUM>. The additional noise-damping member <NUM> may be provided as a porous membrane allowing gas to pass through. This can help to minimize turbulence in the mixed stream of gas before said gas enters the flow sensor <NUM>. This arrangement can further help to reduce the noises. The additional noise-damping member <NUM> can be made of the sound absorbing material as described above. In an embodiment where an ultrasonic sensor (see <FIG> at <NUM>) is included in the respiratory apparatus <NUM> for detection of gas, the noise-damping member <NUM> is preferably positioned upstream of the ultrasonic sensor so as to absorb, reduce, or insulate most of, if not all, the undesirable high frequency noises for subsequent measurement performed downstream. This is particularly useful to improve the accuracy of detection conducted by the ultrasonic sensor.

As shown in <FIG>, an ultrasonic sensor <NUM> is arranged downstream of the flow sensor <NUM> and the noise-damping member <NUM> to determine the concentration of the pressurized gas in the mixed stream of gas, particularly oxygen content in the mixed gas passage <NUM>. The mixed gas later enters into the humidifying chamber <NUM> via the tube <NUM>. It is appreciated that in an embodiment where the respiratory apparatus does not include a flow sensor, the noise-damping member may be arranged anywhere along the flow path between the mixing chamber <NUM> and the humidifying chamber <NUM>, and upstream of the ultrasonic sensor <NUM>. It would also be appreciated that the noise-damping member <NUM> can be configured in any shape to be attached along the flow path.

Without intending to be limited by theory, it is believed that the presence of the noise-damping member <NUM> in the respiratory apparatus <NUM> of the present invention can improve the accuracy of gas detection and allow the operator to monitor the gas delivered to the user.

Furthermore, as shown in <FIG>, the respiratory apparatus <NUM> may further include a noise reduction device <NUM> mounted on the housing <NUM>, upstream of the mixing chamber, so as to further minimize noises created when supplying atmospheric air to the respiratory apparatus <NUM>. <FIG> show an embodiment of the noise reduction device <NUM> which has a cover <NUM> and a body <NUM>. The cover <NUM> and the body <NUM> are, preferably, separately manufactured and can be detachably engaged with each other through a locking means such as sliding or screwing.

In this embodiment, the cover <NUM> and the body <NUM> may be made of a plastic, such as a thermoset plastic, a resin, a polymeric material, etc. Such plastics are known in the art and typically include materials such as polycarbonate, polyethylene, polypropylene, polyvinyl chloride, acrylonitrile butadiene styrene, polymethyl methacrylate, phenolics, melamine formaldehyde, polysulfone, polyetherimide, polyethylene terephthalate, urea-formaldehyde, polyether ether ketone, and a combination thereof. Furthermore, the plastic may incorporate an anti-microbial compound by, for example, containing a coating, integrating the anti-microbial compound into the plastic, etc..

<FIG> shows an embodiment of the body <NUM> before engaging with the cover <NUM>. The body <NUM> has a noise reduction device gas outlet <NUM> and is mounted to the respiratory apparatus <NUM>. In this embodiment, the body <NUM> is configured with a cavity <NUM> surrounded by a side wall <NUM>. The side wall <NUM> extends perpendicularly from periphery of an inner surface <NUM> and includes a first end portion <NUM>. The cavity <NUM> may be open or closed depending on the configuration of the side wall <NUM>. In this embodiment, the cavity <NUM> is open with the side wall <NUM> configured as a C-shape, i.e. leaving an open portion <NUM>. At least part of the side wall <NUM> can be coupled to the cover <NUM> for forming a tight seal.

The cavity <NUM> may house a filter <NUM> (shown as a dotted line) therein. The filter <NUM> may be provided to filter dust, pollen, mold, bacteria, etc. from the gas, particularly atmospheric air, before the gas enters the respiratory apparatus. In an embodiment where the filter <NUM> is detachably arranged in the cavity <NUM> of the body <NUM>, the filter <NUM> can be replaced with a new one either randomly or regularly so as to keep the filtered gas free from, or at least with a reduced amount of, dust, pollen, mold, bacteria, etc. Without intending to be limited by theory, it is believed that this is particularly advantageous when the respiratory apparatus is used for clinical applications. It is also believed that the filter <NUM> can also act as a noise suppressor to reduce the noise generated in the cavity <NUM> when the gas passes through the noise reduction device <NUM>. The filter <NUM> may be, for example, a paper filter, a foam filter, a cotton filter, a high-efficiency particulate air filter, a HEPA filter, etc. as desired. One skilled in the art would appreciate that various suitable filters can be applied to the noise reduction device <NUM> of the present invention.

In this embodiment, the noise reduction device gas outlet <NUM> is radially offset and is supported by a supporting structure <NUM> which has a plurality of upright protrusions <NUM> on the inner surface <NUM> connecting to the noise reduction device gas outlet <NUM>. The noise reduction device gas outlet <NUM> may be aligned with the gas pathway in the respiratory apparatus, thereby reducing the formation of turbulence. One skilled in the art would appreciate that the noise reduction device gas outlet <NUM> may be positioned at the centre of the cavity <NUM> to achieve the similar purpose.

The cavity <NUM> may further include a converging portion <NUM> on the inner surface <NUM> which converges towards the noise reduction device gas outlet <NUM> so as to facilitate the gas flow. In addition to guiding the flow of the gas towards the noise reduction device gas outlet <NUM>, the supporting structure <NUM> may also help to hold the filter <NUM> in place. Without intending to be limited by theory, it is also believed that the upright protrusions <NUM> and supporting structure <NUM> may further enhance the structural integrity of the body <NUM> and/or the cover <NUM>. The upright protrusions <NUM> and the converging portion <NUM> support the filter <NUM> which may help to separate the filter <NUM> from the inner surface <NUM> to increase the effective surface area of the filter <NUM> and hence increase the amount of filtered gas flow. This may synergistically help to protect a blower <NUM> of the respiratory apparatus <NUM> by reducing its workload and thus further reducing the noise produced. In this embodiment, the upright protrusions <NUM> of the supporting structure <NUM> are configured as extending, continuously or discontinuously, radially from the noise reduction device gas outlet <NUM>.

In the embodiment of <FIG> and <FIG>, the body <NUM> is configured to detachably engage with the cover <NUM>. Preferably, the body <NUM> is enclosed by the cover <NUM> after engaging with the cover <NUM>. The body <NUM> may include two slots <NUM> (or tabs) respectively arranged on substantially diametrically opposite sides of the side wall <NUM> for complementary slide locking with corresponding tabs (or slots) on the cover <NUM>.

Turning to the cover <NUM>, with reference to <FIG> showing a rear view of it, the cover <NUM> has a side wall <NUM> and an inner surface <NUM> facing towards the inner surface (see <FIG> at <NUM>) of the body <NUM> when it is engaged with the body <NUM> to form the noise reduction device <NUM>. The side wall <NUM> extends perpendicularly from the periphery of the inner surface <NUM> and partially surrounds the cover <NUM> to form a cavity <NUM>. In this embodiment, the cavity <NUM> is open with the side wall <NUM> configured substantially as a C-shape to define a second end portion <NUM> and a third end portion <NUM> on the side wall <NUM> respectively, leaving an open portion <NUM>.

The cover <NUM> has a guiding member <NUM> being configured to extend substantially perpendicularly from the inner surface <NUM>. The guiding member <NUM> itself defines at least a part of a gas passage <NUM>, and is configured in a way to form the gas passage <NUM> between the body <NUM> and the cover <NUM> when they are engaged together. One skilled in the art would appreciate that possible configurations of the guiding member such as a spiral including Cotes's spiral, Archimedean spiral and golden spiral, may be used depending on the desired design and noise reduction requirements. Preferably, the area enclosed by the guiding member <NUM> is at least twice than area of the noise reduction device gas outlet <NUM> in order to increase the effective filtering area of the filter <NUM> and reduce gas resistance, thereby further reducing noise production.

In this embodiment, the guiding member <NUM> is substantially in form of a C-shape. The guiding member <NUM> has a fourth end portion <NUM> and a fifth end portion <NUM> defining an opening <NUM> aligning with the open portion <NUM> and to be closed by the side wall <NUM> of the body <NUM> when the body <NUM> and the cover <NUM> are engaged. The fourth end portion <NUM> includes a projection <NUM> for additional engagement and position fixing with the first end portion <NUM> of the body <NUM> when the body <NUM> and the cover <NUM> are engaged together.

The fourth end portion <NUM> and the second end portion <NUM> together define a flow deflecting portion <NUM> being a part of the gas passage <NUM> to provide an enlarged section for an increased level of gas entry, and facilitate a spiral flow of the gas into the gas passage. The flow deflecting portion <NUM> may also avoid transmission of noise from the blower inside the respiratory apparatus to the outside environment.

In this embodiment, the cover <NUM> is detachably engageable with the body <NUM> and preferably encloses the body <NUM> after engagement. Similar to the body <NUM>, two tabs <NUM> may be respectively arranged on substantially diametrically opposite sides of the side wall <NUM> for complementary slide locking with corresponding slots <NUM> on the body <NUM> to form a bayonet mount.

<FIG> shows the noise reduction device <NUM> when the body <NUM> and the cover <NUM> are slidably locked to one another. In this embodiment, the body <NUM> is oriented and inserted into the cavity (see <FIG> at <NUM>) of the cover <NUM> with the tabs (see <FIG> at <NUM>) being received in the slots (see <FIG> at <NUM>). A slight turning of either the body <NUM> or the cover <NUM> locks the two components with a bayonet lock as a locking mechanism <NUM> to hold them in place. In the present invention, the locking mechanism <NUM> includes at least one slot <NUM> arranged on the body <NUM>, and at least one corresponding tab (see<FIG> at <NUM>) arranged on the cover <NUM>. In another embodiment, the locking mechanism <NUM> may include a pair of magnetic members arranged on the cover <NUM> and the body <NUM> as the locking means. One skilled in the art would appreciate that other locking means, such as a push lock, a slide lock, a screw, a plug and/or a combination thereof, may be used herein.

In this figure, the outer surface <NUM> of the body <NUM> shows the noise reduction device gas outlet <NUM> which is to be mounted to the respiratory apparatus <NUM> for fluid communication with the blower <NUM> inside the respiratory apparatus <NUM>. The flow deflecting portion <NUM>, which is not covered by the body <NUM>, is shown adjacent to the second end portion <NUM> of the side wall <NUM>. Adjacent to the flow deflecting portion <NUM> is a noise reduction device gas inlet <NUM> arranged between the side wall (see <FIG> at <NUM>) and the side wall <NUM>. The first end portion <NUM> of the side wall <NUM> is arranged adjacent to the noise reduction device gas inlet <NUM>. Two tabs <NUM> (only one is shown) are disposed on substantially diametrically opposite ends of the outer surface <NUM> for detachable mounting on the respiratory apparatus <NUM> through sliding. One skilled in the art would appreciate that other locking means such as screwing may also be used depending on the configuration of the respiratory apparatus.

Referring to <FIG>, when the body <NUM> and the cover <NUM> are engaged, the side wall <NUM> of the body <NUM> is received in the gas passage <NUM> and the body <NUM> is enclosed by the cover <NUM>. The location of the first end portion <NUM> is shown as a dotted line forming a seal with the projection <NUM> and abutting the fourth end portion <NUM> of the guiding member <NUM> to define the planar spiral gas passage <NUM> between the side wall <NUM> and the guiding member <NUM>, wherein the fifth end portion <NUM> spaces apart from the side wall <NUM> to form a gap <NUM> and the noise reduction device gas inlet <NUM> is arranged to be perpendicularly to the noise reduction device gas outlet <NUM> in this embodiment. In an embodiment where a filter (see <FIG> at <NUM>) is placed in the body <NUM>, the guiding member <NUM> is in contact with the filter <NUM> when the body <NUM> and the cover <NUM> are engaged so as to keep the filter <NUM> in place by sandwiching the filter <NUM> between the guiding member <NUM> and the body <NUM>. This also helps to avoid oscillation of the filter <NUM> between the body <NUM> and the cover <NUM> when the gas passes the filter <NUM>.

During operation, the atmospheric air is drawn to the noise reduction device gas inlet <NUM> preferably by the blower <NUM> of the respiratory apparatus <NUM>, where the gas travels from the flow deflecting portion <NUM> of a wider cross section to the gas passage <NUM> of a narrower cross section for a smoother gas flow by maintaining or even reducing gas resistance. The gas then flows through the gas passage <NUM>, the gap <NUM>, and to the opening <NUM>. The gas then passes through the filter <NUM> which is in contact with the guiding member <NUM> when the body <NUM> and the cover <NUM> are engaged, and finally reaches the noise reduction device gas outlet <NUM> (shown by arrows). One skilled in the art would appreciate that with such configuration, the incoming gas is forced to travel an angular rotation β about a centre <NUM> of the noise reduction device gas outlet <NUM> of at least <NUM> degrees from the noise reduction device gas inlet <NUM> to the noise reduction device gas outlet <NUM>. In an alternative embodiment, the gas passage <NUM> formed may direct the gas flow to travel an angular rotation β about the centre <NUM> of the noise reduction device gas outlet <NUM> of at least <NUM> degrees, at least <NUM> degrees or at least <NUM> degrees, relative to the noise reduction device gas inlet <NUM> before discharging at the noise reduction device gas outlet <NUM>.

With reference to <FIG>, the noise reduction device <NUM> is mounted to the respiratory apparatus <NUM>. The body <NUM> is mounted to one side of the respiratory apparatus <NUM> by the tabs <NUM>. The tabs <NUM> on the cover <NUM> are oriented to be slidably locked with the corresponding slots <NUM>. A seal is to be formed by the first end portion <NUM> and the projection <NUM> of the guiding member <NUM> to define the gas passage <NUM>.

The noise reduction device <NUM> in the present invention can provide obvious noise reduction effect at the first gas inlet by decreasing the turbulence and resistance of gas flow to a larger extent and thus reducing the noise caused by the friction between the fluctuated gas flow and the noise reduction device gas inlet particularly before mixing the atmospheric air with the pressurized gas. Moreover, the configuration of the guiding member <NUM> being located on the cover <NUM> provides an easier and more convenient way to clean the gas passage <NUM>. The cover <NUM> can be disengaged from the body <NUM> and subject to common sterilization methods of medical equipment. Such arrangement also facilitates replacement of the cover <NUM> in case abrasion or damage is found on the guiding member <NUM> which may increase turbulent flow of the incoming gas and thus causes noise.

According to the above, it is believed that the respiratory apparatus of the present invention and that coupled with the noise reduction device as described above can generate less noise during operation and allow better measurement of gas content. The respiratory apparatus herein poses substantial improvements over the existing apparatus.

It should be understood that the above only illustrates and describes examples whereby the present invention may be carried out, and that modifications and/or alterations may be made thereto without departing away from of the invention.

Claim 1:
A respiratory apparatus (<NUM>), comprising: a first gas inlet (<NUM>) for supplying a first gas to the respiratory apparatus (<NUM>); a second gas inlet (<NUM>) connectable to a pressurized gas source to supply a pressurized gas; a mixing chamber (<NUM>) for mixing the first gas and the pressurized gas; and a noise-damping member (<NUM>) disposed downstream of the mixing chamber (<NUM>);
wherein the mixing chamber (<NUM>) further comprises a gas outlet (<NUM>) for discharging a mixed stream of gas towards a humidifying chamber (<NUM>);
characterized in that wherein the respiratory apparatus (<NUM>) further comprises a flow sensor (<NUM>) for determining a flow rate of the mixed stream of gas towards the humidifying chamber (<NUM>); and
wherein the noise-damping member (<NUM>) is cylindrical, and has a cylindrical body (217a) insertable into the flow sensor (<NUM>) and an end portion (217b) with a diameter greater than the diameter of the cylindrical body (217a).